BBAMCB-57548; No. of pages: 19; 4C: 3, 5, 6, 7, 8, 12, 14 Biochimica et Biophysica Acta xxx (2013) xxx–xxx

Contents lists available at ScienceDirect

Biochimica et Biophysica Acta journal homepage: www.elsevier.com/locate/bbalip

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J. van Smeden 1, M. Janssens 1, G.S. Gooris, J.A. Bouwstra ⁎

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Department of Drug Delivery Technology, Leiden Academic Centre for Drug Research, Leiden University, Leiden, The Netherlands

a r t i c l e

i n f o

a b s t r a c t

Article history: Received 20 August 2013 Received in revised form 8 November 2013 Accepted 10 November 2013 Available online xxxx

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The skin protects the body from unwanted influences from the environment as well as excessive water loss. The barrier function of the skin is located in the stratum corneum (SC). The SC consists of corneocytes embedded in a lipid matrix. This lipid matrix is crucial for the lipid skin barrier function. This paper provides an overview of the reported SC lipid composition and organization mainly focusing on healthy and diseased human skin. In addition, an overview is provided on the data describing the relation between lipid modulations and the impaired skin barrier function. Finally, the use of in vitro lipid models for a better understanding of the relation between the lipid composition, lipid organization and skin lipid barrier is discussed. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. © 2013 Published by Elsevier B.V.

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1. Introduction

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Two main functions of the skin are to act as an effective barrier against unwanted environmental influences as well as to prevent excessive water loss from the body. The skin consists of the epidermis and

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Abbreviations: AD, atopic dermatitis; CD, Chanarin–Dorfman; CEMOVIS, cryo-electron microscopy of vitreous skin section; CER, ceramide; CHOL, cholesterol; ED, electron diffraction; ELA, elastase; ELOVL, elongation of very long chain fatty acids; FFA, free fatty acid; FLG, filaggrin gene; FTIR, Fourier transform infrared spectroscopy; FTS, full thickness skin; GC, gas chromatography; GLC, gas/liquid chromatography; GlcCER, glucosylceramide; HSE, human skin equivalent; IV, ichthyosis vulgaris; LB, lamellar body; LC, liquid chromatography; LI, lamellar ichthyosis; LPP, long periodicity phase; MS, mass spectrometry; MUFA, mono-unsaturated fatty acid; NTS, Netherton; PUFA, poly-unsaturated fatty acid; PPAR, peroxisome proliferator-activated receptor; SAXD, small angle X-ray diffraction; SB, stratum basale; SC, stratum corneum; SCD, stearoyl CoA desaturase; SCS, stratum corneum substitute; SG, stratum granulosum; SPP, short periodicity phase; SS, stratum spinosum; TAG, triacylglycerides; TEWL, transepidermal water loss; TLC, thin layer chromatography; WAXD, wide angle X-ray diffraction ☆ This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. ⁎ Corresponding author at: P.O. Box 9502, Einsteinweg 55, 2333 CC Leiden, The Netherlands. Tel.: +31 71 5274219; fax: +31 71 5274565. E-mail address: [email protected] (J.A. Bouwstra). 1 These authors contributed equally.

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Keywords: Stratum corneum Barrier lipids Lipid composition Lipid organization Skin barrier function Ceramides Free fatty acids Cholesterol Lipid lamellae Lamellar ichthyosis Atopic dermatitis Netherton disease Chanarin–Dorfman Psoriasis

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The important role of stratum corneum lipids for the cutaneous barrier function☆

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dermis as well as the subcutaneous fat tissue [1]. The epidermis is the outermost layer of the skin and consists of four distinctive layers. Each layer displays one of the sequential differentiation stages of the keratinocytes, the major cell type in the epidermis. The layers include the superficial stratum corneum (SC), stratum granulosum (SG), stratum spinosum (SS), and the inner most stratum basale (SB). The SG, SS and SB are part of the viable epidermis (thickness: 50–100 μm), whereas the SC (thickness: 10–20 μm) is part of the non-viable epidermis and the final differentiation product. The SB contains the proliferating keratinocytes. After the keratinocytes escape from the SB, they transiently migrate towards the SC, after which they are finally released from the skin surface, a process called desquamation. During this migration the keratinocytes differentiate: They flatten out and finally adopt the dimensions which are characteristic for the dead cells of the SC, the corneocytes. The keratinocytes in the SG contain a high number of membrane-coating granules referred to as the lamellar bodies (LBs) in which lipids are stored, such as glucosylceramides (GlcCERs), sphingomyelin and phospholipids. These are precursors of the SC lipids, and are enzymatically processed into their final constituents: ceramides (CERs) and free fatty acids (FFAs). CERs and FFAs are, together with cholesterol (CHOL), the main lipid classes in the SC. By means of exocytose, the lipid content of the LBs is released together with hydrolytic enzymes

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Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

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Human SC lipids consist of FFAs, CERs and CHOL in an approximately equimolar ratio [14]. FFAs and CERs contain respectively 1 and 2 carbon chains that differ in their molecular structure: FFAs are predominantly saturated whereas CERs consist of a sphingoid base and a fatty acid (acyl) chain. Both FFAs and CERs show a wide distribution in their carbon chain lengths. Research on the SC lipid composition goes back as early as 1962, when Reinertson and Wheatley [15] published the chemical composition of human epidermal lipids. He demonstrated the presence of fatty acids and CHOL as well as other (non-specified) lipids that would later on be referred to as sphingolipids [16] and CERs [17]. The level of detail on this lipid composition has improved rapidly. Regarding the FFAs, in 1970 Ansari et al. reported on the composition of human epidermis by means of gas/liquid chromatography (GLC). For the first time, information on the variation in chain lengths (12–30 carbon atom range) and degree of unsaturation was provided. Besides saturated FFAs, they demonstrated the presence of monounsaturated fatty acids (MUFAs), poly-unsaturated fatty acids (PUFAs) and hydroxyl-FFAs [18]. Although at that time they were already able to detect wide distribution in FFA chain length, the level of very long chain FFAs (≥24 carbon atoms) was underestimated. For example, the level of FFA with 24 carbon atoms long was estimated around 13%, whereas current reports indicate values around 30% [19,20]. Also Lampe et al. describe the FFA composition of human SC and shows regional differences in FFA chain length. However, they also overestimate the short chain length FFAs and did not identify FFAs with chains longer than 22 carbon atoms. The overestimation of the level of shorter chain fatty acids may be one of the reasons that other groups select lipid mixtures with short chain FFAs for studying the physical interaction between the main lipid classes [21,22]. This is surprising, as Wertz et al. already reported in 1987 that the FFA composition in human epidermal cysts are mainly 22 and 24 carbon atoms long [23,24], a very important observation. It is not before 1998 that Norlèn et al. extended the knowledge on the FFA composition by introducing a novel gas chromatography coupled to mass spectrometry (GC/MS) method, illustrating that human SC FFAs contain chain lengths as long as 36 carbon atoms, with C18, C24 and C26 being the most prominent FFAs [20]. This FFA composition has been confirmed by Ponec et al. using GC [25] (2002), and recently by our lab using liquid chromatography coupled to MS (LC/MS) [19]. In the latter study it was observed that in healthy human SC the fraction of hydroxy FFAs and MUFAs are low (both around 20%) compared with the saturated FFA, which is in agreement to the first report on the FFAs by Ansari mentioned above [18].

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Knowledge on the CER composition in human SC has also rapidly progressed. In 1978 a very important publication of Gray and White demonstrated, by using quantitative thin layer chromatography (TLC) in combination with GLC, that human SC contains several CER subclasses. They reported that the sphingoid base can be a sphingosine or dihydrosphingosine (also referred to as sphingenine and sphinganine, respectively) and the acyl chain can be non-hydroxylated or hydroxylated [26]. In these early days it was already shown that the chain length of in particular the acyl chain varied between 14 and 30 carbon atoms, whereas the sphingoid base was mainly 16–20 carbon atoms long. Wertz et al. extended this knowledge and demonstrated that there are a total of 6 different CER subclasses, mentioning for the first time an ω-hydroxy esterified CER (CER [EOS]) [27], again a crucial observation as CER [EOS] plays an important role in the characteristic properties of the SC lipid matrix. Hereafter, the CER subclass diversity expanded, and a new nomenclature based on the structure of the individual CER chains was introduced by Motta et al. [28], illustrated in Fig. 1, which is also used in this review. Robson et al. and Stewart et al. introduced a 7th and 8th CER subclass, respectively, using TLC in conjunction with NMR to elucidate the newly identified 6-hydroxy-4-sphingenine base structure, linked to either an α-hydroxy acyl chain (CER [AH]) or non-hydroxy acyl chain (CER [NH]) [29,30]. It took several years until Ponec et al. reported in 2003 the discovery of a 9th subclass, CER [EOP], using a combination of TLC and NMR [25]. The introduction of LC/MS led to the (re) introduction of 3 additional subclasses by Masukawa et al. (CER [NdS], CER [AdS]) [31], and van Smeden et al. (CER [EOdS]) [32]. Note that the former two have been mentioned by Gray and White in 1978 as sphingenine-CERs, but never considered as subclasses and were usually excluded in later papers. These advancements have led to the discovery of a total of 12 CER subclasses that are present in the human SC lipid matrix. As can be observed in Fig. 1, the [EO] subclasses (from here on referred to as acyl-CERs subclasses) possesses a unique structure; these CERs consist of an ω-hydroxy fatty acid chain to which linoleic acid is esterified. The introduction of LC/MS has led to several improvements. First, its unmatched sensitivity led to the discovery of additional lipid subclasses as well as much smaller sample sizes necessary for lipid quantification, especially important for clinical studies. Second, without cumbersome sample preparation techniques, it is possible to quantify the sample and also obtain structural information thanks to the possibility of fragmentation (MS/MS), all within a very small time frame. Although the analysis of multiple lipid classes at once has been performed using TLC back in the early 80s, the amount of structural information obtained using this technique is limited, and additional NMR or GC studies were necessary to identify the molecular structure (lipid chain lengths and head group architecture). The frequency that LC/MS is used for SC lipid analysis has increased over the last decade, which led to multiple different applicable methods [32–35], greatly enhancing the knowledge on the SC lipid composition. Also in terms of quantification (usually one of the main difficulties of MS) several improvements have been made. Masukawa et al. report on a fully quantitative LC/MS method for CER analysis and demonstrate its similarity to quantification by TLC in two Asian subjects [34] (Table 1). Additionally, lipid profiling of 15 healthy Caucasian subjects using a totally different LC/MS method displayed comparable results [19]. In general, CER [NP] is the most abundant subclass whereas the ultra-long acyl-CER subclasses ([EOdS], [EOS], [EOP], and [EOH]) contribute to a total of around 8–13% of the CERs. By means of fragmentation MS (MS/MS), Masukawa et al. performed a comprehensive analysis on the individual chain lengths (i.e. sphingoid base and acyl chain) of each CER subclass, although they were not able to include MS/MS on the very short chain CERs (b 40 carbon atoms) [34]. They reported that the acyl chain of the CERs varies between C14 and C32, whereas the sphingoid base varies in carbon chain length between C14 and C28. The very long sphingoid bases with C24–C28 are mainly detected in CER [NS] and CER [NdS], whereas the very long

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into the intercellular space at the SG/SC interface. Human SC contains 10 to 25 corneocyte layers that are oriented approximately parallel to the skin surface and are embedded in a lipid matrix [2–4]. The structure of the SC is often referred to as a “bricks in mortar” structure, in which the corneocytes are the bricks and the lipids are the mortar [2]. The corneocytes are filled with water and microfibrillar keratin that is surrounded by a cornified envelope which consists of a densely crosslinked layer of proteins such as filaggrin, loricrin and involucrin (see articles by Elias, Rabionet and Radner, elsewhere in this issue). A monolayer of non-polar lipids (ω-hydroxylated CERs and FFAs) referred to as the lipid envelope is esterified to the cornified envelope, mainly to glutamate residues of involucrin [3–6]. This so-called lipid envelope is suggested to form a template for the formation of the intercellular lipid layers [7–9] (see article by Breiden in this issue). The cornified envelope, together with the lipid envelope, minimizes the uptake of most substances into the corneocytes and allows proper formation of the lipid matrix. Indeed, a deficient lipid envelope results in a defective skin permeability function and an irregular lipid matrix [10–13]. This lipid matrix acts as the main barrier for diffusion of substances through the skin.

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Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

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Polar head group

O HN

Fatty acid chain with variable chain length

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Sphingosine chain with variable chain length

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Fig. 1. Explanation of CER subclasses and CER chain length. CERs are composed of a fatty acid chain linked to a sphingosine base. Both chains show a wide distribution in their carbon chain length (indicated by the arrows). This results in a wide range of the total carbon chain length of CERs. In addition, CERs can have an additional functional group, which results in the presence of 12 subclasses, denoted as: [NdS], [AdS], [EOdS], [NS], [AS], [EOS], [NP], [AP], [EOP], [NH], [AH], and [EOH]. This image was adapted from Journal of Lipid Research [116].

acyl chains (C28–C32) are mainly detected in the acyl-CERs, but also CER [NS] and [NP] exhibit some very long acyl chains.

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2.2. Lipid organization in healthy human skin

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2.2.1. Lamellar lipid organization The intercellular lipid matrix in human SC shows a unique lamellar arrangement. In the seventies it was demonstrated for the first time using freeze fracture electron microscopy that the lipids were organized in lipid sheets [36–38]. The visualization of the lipid stacks using

t1:1 t1:2 t1:3

Table 1 CER composition in healthy human SC determined by thin layer chromatography (TLC) and liquid chromatography/mass spectrometry (LC/MS).

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Analysis by TLC

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Analysis by LC/MS

(n = 2, Asian)

(n = 2, Asian)

(n = 15, Caucasian)

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6.1 6.4 22.1 22.5 3.4 0.8 15.7 15.3 ND 4.3 0.9 2.6

8.6 6.7 25.8 12.4 3.8 1.9 13.4 12.4 1.3 5.4 2.7 5.4

NP NH AS⁎ AdS⁎

25.4 21.0 5.6⁎

AP AH EOdS EOS EOP EOH

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ND means not detected. Data obtained from Masukawa et al. [34] and van Smeden et al. [19]. ⁎ These subclasses are not separated on TLC and therefore share a common value.

embedded tissue appeared to be very difficult, and no lamellar stacks could be visualized by using OsO4, which was often used for fixation of lipids. It was not until 1987 with the introduction of RuO4 postfixation that the lipid stacks were visualized in embedded SC tissue. RuO4 was required as hardly any unsaturated lipids are present in SC, which is necessary for fixation by OsO4. This was a big step forward in understanding the lipid organization in the SC as it was shown that the lipids were organized in lamellar sheets regularly stacked on top of each other. Furthermore, the lipids appeared to be organized in a so called broad–narrow–broad arrangement showing the exceptional arrangement of SC lipids [39–41] (Fig. 2). The overall width of this broad–narrow–broad sequence is approximately 12 nm [39]. In addition, it was shown that the lipid layers within the intercellular spaces were repeated either 3, 6, 9 or 12 times, indicating a trilayer arrangement. Small angle X-ray diffraction (SAXD) revealed the presence of a 13 nm lamellar phase in mice skin, later on referred to as the long periodicity phase in mice skin (LPP, see Fig. 3). The presence of acyl-CERs is crucial for the formation of this LPP [42–44]. Besides a 13 nm lamellar phase, a second lamellar phase has also been detected first in human SC. The periodicity of this phase is approximately 6 nm and is therefore indicated as the short periodicity phase (SPP) [45,46]. Fig. 4 illustrates the principle of SAXD and shows SAXD curves of isolated human SC, SC from cultured human skin (referred to as human skin equivalents, HSEs), and full thickness skin (FTS). It can be observed that in human SC that both the LPP and SPP are present. No significant changes in the q-value (indicative for the repeating distance) of the peak positions are observed between FTS and HSC. This indicates that, processing of fresh skin by trypsin digestion to obtain SC does not influence the lamellar lipid organization. In contrast to the SPP, the LPP is very unique for the SC lipid organization, which suggests that this

Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

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2.2.2. Lateral lipid organization The organization of the lipids within the lamellae is referred to as the lateral organization, explained in Fig. 3. In healthy human SC lipids are mainly present in a very dense – orthorhombic – organization, although a subpopulation is packed in a less dense – hexagonal – organization or even in the lower density, disordered, liquid phase [53,54]. Several analytical techniques have been used to investigate the lateral packing, such as Fourier transform infrared spectroscopy (FTIR), electron diffraction (ED) and wide angle X-ray diffraction (WAXD). The first WAXD measurements on SC lipids were performed on mice SC [55].

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Several years later, studies were performed on mice and human SC sheets, confirming the existence of an orthorhombic lateral packing [46,56]. However, with WAXD it is not possible to determine whether a hexagonal lipid organization coexists, as one of the reflections in the X-ray pattern of the orthorhombic lateral packing (at 0.41 and 0.37 nm) obscures the reflection in the X-ray pattern of the hexagonal packing (at 0.41 nm). In the same period as the first WAXD studies were reported, FTIR measurements using isolated human SC and extracted lipids from SC showed that the lipids form mainly an orthorhombic organization at skin temperature [57,58]. It was in 1996 that in vitro studies using lipid mixtures demonstrated the importance of long chain FFAs for the presence of this orthorhombic lipid organization [59]. However, also domains with a hexagonal or liquid organization coexist [42–44]. In agreement to the in vitro and ex vivo results on human SC, FTIR studies of in vivo human SC revealed the presence of mainly an orthorhombic lateral organization [54,60]. In the latter publications the bandwidth of the CH2 scissoring modes in the FTIR spectrum are a proper measure for the frequency and size of orthorhombic lipid domains: a large bandwidth is indicative for large orthorhombic domains (Fig. 5). For the first time it was shown that the lateral packing is important for the cutaneous barrier as monitored by TEWL in healthy human skin in vivo. Approximately 8 years after the first FTIR studies, ED studies were performed. In contrast to WAXD, ED allows one to distinguish between

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phase plays an important role in the cutaneous barrier function [47]. The LPP has also been detected in HSEs [48,49]. Using X-ray diffraction similar results were obtained by Hatta et al. [50] and the observed repeat distance was comparable to that observed in the trilayered structures using RuO4 [51]. A recent study of Iwai et al. uses cryo-electron microscopy of vitreous skin section (CEMOVIS) in order to determine the lamellar lipid organization [52] (Fig. 2b). They examined five Caucasian subjects and observed a pattern that is characterized by an asymmetric ~ 11 nm repeating unit, which is shorter than those observed using X-ray diffraction. More studies are required to clarify whether these differences are related to methodological variation, biological variation, or may be caused by another yet unknown factor.

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Fig. 2. a) Electron micrograph of SC showing dense and lucent bands in the lamellar lipid layers [39]. b) The lipid matrix of the SC, visualized using high-magnification cryo-electron microscopy of vitreous skin section (CEMOVIS) [52]. The pictures were used with permission from the Journal of Investigative Dermatology and the respective authors.

Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

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Lateral organization

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Human epidermis

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Human stratum corneum: Bricks (corneocytes) and Mortar (lipid matrix) model

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LI was as one of the first skin diseases in which detailed information on both the lipid composition and organization in SC was obtained. Studies by Ghadially et al. and Fartasch et al. indicated that besides the absence of the enzyme transglutaminase 1 (responsible for crosslinking of the cornified envelope), changes in the SC lipids may also play a role in the impaired skin barrier of patients with LI [64,65]. By means of RuO4-stained SC sections, they showed irregularly distributed intercellular lipid lamellae and reported regions in SC containing excessive numbers of lipid bilayers. Studies by Lavrijsen et al. provided more numerical data on the lipid composition and organization of 3 LI patients that were obtained by means of TLC and SAXD, respectively [66]. These patients showed an impaired skin barrier function as TEWL was significantly increased. As far as the lipids are concerned, a decrease in the FFA/CHOL and FFA/CER ratios were reported, whereas the CER/CHOL ratio was similar as in control skin. These data therefore suggest a strong reduction in the FFA level in the SC lipid matrix. Paige et al. quantitatively determined the CER subclasses in LI and observed a reduction in CER [EOS] and [NP] in these patients [67]. In addition to these changes in lipid composition, these LI patients also showed changes in their lamellar lipid organization as examined by SAXD (Fig. 6a) [66]: The SAXD patterns demonstrate that the main

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Diseased skin often shows an impaired barrier function. In order to examine whether the changes in lipid properties in SC contribute to this impaired skin barrier, information on the lipid composition and organization is crucial. Even if the lipid properties are not causative for the disease, such studies can provide additional information on the mechanisms underlying the changes in lipid composition and thus lipid organization. This may provide indications on how the lipid properties are associated with changes in e.g. skin barrier protein expression, changes in proliferation and differentiation of keratinocytes and/or inflammation. Because variations in the SC lipid properties are expected to be much larger in SC of diseased skin (with a reduced skin barrier function) than in SC of healthy skin, correlations between lipid composition, lipid organization, and skin barrier function are easier to draw. However, for the fundamental information about the role of certain lipid species for the lipid organization and skin barrier function additional information should be provided. This can be achieved from either in vivo studies or lipid model systems, discussed in Section 4. Here we report on the current status of some of the skin diseases focusing on a reduced

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3.1. Lamellar ichthyosis (LI)

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cutaneous barrier function that might be related to changes in the SC lipid properties. Table 2 summarizes the findings on the lipid composition and organization in the different diseases, which are mentioned below.

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the hexagonal and orthorhombic lipid organization and to examine the lipid organization in vivo in humans even as a function of depth [61]. ED studies revealed that patterns in which only the hexagonal lateral packing is observed were mainly present in the outer SC layers. It was also shown that this is probably due to the sebum on top of the skin, interacting with the skin barrier lipids [62]. This is in agreement with findings in literature using FTIR [57,63].

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Lipid layers (lamellae) in between corneocytes

Orthorhombic (ordered, densely packed)

Hexagonal (ordered, less densely packed)

Liquid (disordered)

Lamellar organization

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Fig. 3. Lipid organization in human stratum corneum. (1) The outermost layer of the epidermis, the stratum corneum (SC), consists of dead cells (corneocytes) embedded in a lipid matrix, also referred to as the brick (corneocytes) and mortar (lipids) structure (2). The intercellular lipids are arranged in layers (lamellae) (3), with either a long or short repeat distance (d), referred to as the LPP (~13 nm) or SPP (~6 nm), respectively. The lateral organization is the plane perpendicular to the direction of the lamellar organization. There are three possible arrangements of the lipids: a very dense, ordered orthorhombic organization, a less dense, ordered hexagonal organization, or a disordered liquid organization. This image was originally published in the Journal of Lipid Research [116].

Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

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a)

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d ≈13 nm

n=3 n 3 n=2 n=1

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N

336 337

single diffraction peak is located at a significantly higher q-value compared with controls corresponding to smaller repeat distances of the lamellar phases. Freeze fracture electron microscopic studies illustrated that the lamellae were less ordered and more undulating compared with the lamellae of control skin [68]. The same study provided information on the lateral lipid organization in these 3 patients by means of ED. Fig. 7a–c shows the principle behind the technique and illustrates the differences in scattering profile obtained with control SC and SC from patients with LI. A strong increase was observed of lipids organized in a hexagonal packing at the expense of lipids adopting an orthorhombic packing. The origin of a different SC lipid composition may (partially) be related to certain lipid transporters involved during lipid synthesis. For example the ABCA12 transporter, being involved in the transport of lipids from the Golgi apparatus to the LBs. Changes in the ABCA12 genotype can therefore attribute to the changes observed in

U

335

Orthorhombic

Hexagonal / Liquid

Intensity

334

E

C

T

Fig. 4. a) Principle of small angle X-ray diffraction. The X-ray beam is scattered at a certain angle (θ) by the SC sheet, resulting in a 2D-image indicative for the lamellar lipid organization. b) The scattering intensity is usually plotted as a function of q, which is defined by q = 4πsin θ / λ, in which λ is the wavelength of the X-rays and θ the angle of the scattered X-rays. A schematic drawing of the X-ray curves of the keratin, LPP and SPP is also shown on the left. The 1st, 2nd, 3rd, 4th, 5th and 6th orders of the LPP (indicated by 1l–6l) and 1st and 2nd orders of the SPP (indicated by 1s and 2s). From the positions of the peaks (q) the repeat distance of the LPP and SPP can be calculated using the equation d = n · 2π / qn (n = order of diffraction peak). The right graph shows a typical SAXD profile of human SC. This curve is composed of mainly 3 components, one with high intensity at low q-values due to keratin in the corneocytes and a series of peaks. The peaks indicated by 1 (weak peak), 2 (strong peak) and 3 (weak peak) are attributed to the LPP. Peak II is also attributed to the SPP. The peak indicated by # is due to phase separated CHOL. Higher order reflections cannot be detected due to the low intensities of these peaks. c) SAXD profiles of human SC (HSC), full thickness skin (FTS) and human skin equivalents (HSE).

~8 cm-1

1460

cm-1

~11 cm-1

1480

1460

cm-1

1480

Fig. 5. CH2 scissoring vibrations (1460–1480 cm−1): an orthorhombic organization results in splitting of the scissoring vibrations, whereas a hexagonal packing results in a single vibration.

the SC CER composition and lipid organization (see article by Akiyama, elsewhere in this issue). It is known that mutations in the ABCA12 gene are related to LI type 2 as well as Harlequin ichthyosis [69–71]. However, it is not known whether this transporter is also related to the LI type 1 patients examined in the abovementioned study.

349

3.2. Psoriasis

354

Another disease in which the role of the lipids has been studied in relation to the skin barrier function is psoriasis. It is a chronically inflammatory skin disease affecting about 2% of the population of Western countries. Studies on the genetics of psoriasis demonstrate that epidermal immunology plays a role [72,73]. However, the disease may also be due to primary abnormalities in skin barrier aspects, as Zhang et al. (and others) report on polymorphisms in genes encoding for cornified envelope proteins [74,75]. The disease is characterized by abnormal epidermal proliferation leading to an incomplete differentiation. Motta et al. were the first to analyze the lipid composition in lesional psoriatic SC and demonstrated a relative decrease for CER subclasses [EOS], [NP], and [AP] (about 40%, 65%, and 25%, respectively), whereas CERs [AS] and [NS] were increased (about 33% and 65%, respectively) [28]. Moreover, they demonstrated that the skin barrier function was significantly decreased: Increased TEWL values were observed on psoriatic plaques and fissured plaques, whereas the increase in TEWL was not significant in uninvolved skin [76]. They suggest that the reduction in CER [EOS] may (partly) attribute to the decreased skin barrier function in lesional skin of psoriasis patients. Additional information on non-lesional psoriatic skin is reported

355

Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

350 351 352 353

356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374

J. van Smeden et al. / Biochimica et Biophysica Acta xxx (2013) xxx–xxx t2:1 t2:2

7

Table 2 Overview of skin diseases and alterations in lipid properties. Disease

Lipid composition⁎

Lipid organization⁎

Main references

Lamellar ichthyosis Psoriasis

Altered LPP, shorter lamellar periodicities, orthorhombicity ↓ Altered LPP, shorter lamellar periodicities

[66–68] [28,76,77] and unpublished data

t2:6

Netherton

Altered LPP, shorter lamellar periodicities, orthorhombicity ↓

[84]

t2:7

Atopic dermatitis

Altered LPP, shorter lamellar periodicities, orthorhombicity ↓

[68,77,91,92,108,110–113,115,116,120,121,124,172]

t2:8

Chanarin–Dorfman

CER [NP] [EOS] ↓ CER [EOP] [NP] [AP] ↓ CER [AS] and [NS] ↑ CER [EOS], [EOP], [EOH], [EOdS] [NP] ↓ short chain lipids ↑, unsaturated lipids ↑ CER [EOS], [EOP], [EOH], [EOdS] ↓ CER [AS], [AH], [AP], [AdS] ↑ Short chain lipids ↑ unsaturated FFAs ↑ Acyl-CERs↓ TAG ↑

Presence of non-lamellar lipid domains

[147,148]

t2:9

⁎ Among all the different studies, the general consensus is listed over here.

O

R O

a)

D

Intensity

Intensity

1

LI 1

E

LI 2

1 2

1

2

3

C

q (nm-1)

b)

T

1

E

1

2

q (nm-1)

R

P1 P2

2

3

#

P3 P4 2

3

Atopic eczema

1

Intensity

R

Intensity

3

(non-lesional)

0

3

q (nm-1)

c)

NTS 2 Control NTS 3

3

e)

(non-lesional)

1

NTS 1

2

0

Psoriasis

0

3

2

Control LI 3 0

Netherton

P

d)

Lamellar ichthyosis

N C O

379

collaboration with the Department of Dermatology at the Radboud Hospital in Nijmegen the lamellar lipid organization of SC isolated from lesional and non-lesional psoriatic skin of 4 patients using SAXD (Fig. 6b,c). These studies demonstrate no differences in the lamellar lipid organization between non-lesional psoriatic SC

1

q (nm-1)

2

Control AE AE 3

Psoriasis (lesional)

Intensity

377 378

by Farwanah et al., using a newly developed LC/MS method which demonstrated that CER composition in SC of psoriasis patients are comparable to those of healthy skin [77]. No data are currently reported regarding the SC lipid organization in psoriasis patients. However, our lab recently analyzed in

U

375 376

F

t2:3 t2:4 t2:5

0

1

q (nm-1)

2

3

P1 P2 P3 P4

Fig. 6. SAXD diffraction curves of a) LI patients (LI 1, LI 2 and LI 3) and of a control subject [66]. The diffraction patterns of the patients show a shifted and broader peak. Note that due to the sampling method (scraping), no details on the SAXD profiles are observed. b) Non-lesional psoriatic SC and c) lesional psoriatic SC (unpublished results). Non-lesional psoriatic SC has a lamellar lipid organization that is comparable with that of healthy SC. In lesional psoriatic SC, the peak shape is altered and shifted. d) Three NTS patients and one control SC [84]. NTS patients 2 and 3 show acyl-CERs present in their SC, whereas NTS patient 1 has no detectable acyl-CERs in the SC. e) Two patients with AD (non-lesional skin) and one control subject [116,124]. The middle curve of the AD patient shows a similar pattern to that of the control subject, indicating the presence of both the LPP and SPP. In the lower curve there is an altered diffraction pattern, with a clear shift of the peak. Peaks labeled 1, 2, and 3 are indicative for the first, second and third orders of the LPP. The SPP also contributes to peak 2. # indicates phase separated CHOL. The changes in SAXD profiles of all diseases shown in this figure are indicative for an altered lamellar lipid organization, e.g. shorter periodicities and/or a reduced presence of the LPP.

Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

380 381 382 383 384

408

F

O

R O

406 407

D

404 405

a)

E

402 403

T

400 401

410 411

C

398 399

NTS is a severe skin disease in which the SC lipids have sporadically been investigated. It is a rare skin disorder with a fatality rate of around 20% in the first year. The disease is characterized by erythroderma, hair shaft defects (bamboo hair), and severe atopic manifestations [78]. In addition, NTS patients show a drastically reduced cutaneous barrier function [79–81]. There is hardly any information on the SC lipid properties in NTS patients. In a study using transgenic mice overexpressing elastase 2 (ELA2) as a model for NTS, Bonnart et al. reported a threefold increase in TEWL demonstrating a decreased skin barrier function [82]. They were the first to analyze the lipids in the total epidermis and observed an increased level of total GlcCERs and reduction of sphingomyelin, and significant decrease in FFA levels. Studies in human subjects also report on irregular loose stacks of lipid lamellae [80,82,83]. Recently, the SC lipid composition and organization of NTS patients was studied, examining both the CER and FFA subclasses and the chain length of these lipids. The lateral and lamellar organization was also examined [84]. Despite the fact that a large variation in lipid composition was observed among the various patients, dramatic differences were observed compared with the control group. Concerning FFAs, a decreased FFA chain length and an increased level of MUFAs was observed in SC of NTS patients compared with controls. Furthermore, the level of short-chain CERs, especially those with a chain length between 32 and

E

396 397

hexagonal

b)

R

394 395

R

392 393

409

orthorhombic

c)

O

391

3.3. Netherton syndrome (NTS)

C

389 390

N

387 388

compared with control SC, which corresponds to the aforementioned results of Farwanah et al. concerning the lipid composition. On the contrary, lesional skin shows clearly distinguishable SAXD curves in all 4 of the psoriatic patients. In three out of four patients, a shift to higher q-values of the peak 2 position in the diffraction patterns was observed. This is indicative for shorter repeat distances of the lamellar lipid phases and/or a reduced presence of the LPP. Lesional skin of the fourth patient showed no diffraction peaks at all, which indicates the absence of a repetitive lamellar structure in the SC of lesional skin. The studies in SC of psoriatic skin show that at lesional skin sites the SC lipid organization changed dramatically. The changes in lipid organization may partly be caused by a change in the levels of CER [EOS], as reported by the studies of Motta et al. [28], but also a reduced chain length may contribute to the change in lipid organization. It would be of interest to study in detail the SC lipid composition in lesional skin of these patients. When focusing on the diffraction profiles of SC in lesional skin, several features (such as the absence of a peak position at 0.5 nm−1 and the shift of the peak at 1.0 nm− 1 to higher q-values) indicate a reduced presence of the LPP and/or a reduction in the chain length of the CERs and FFAs. The fact that lipid changes are most affected at lesional spots implies that factors like inflammation or changes in the differentiation process play a role in the observed changes in SC lipid properties.

U

385 386

J. van Smeden et al. / Biochimica et Biophysica Acta xxx (2013) xxx–xxx

P

8

Control SC

d)

AE - hexagonal

Lamellar ichthyosis

e)

f)

AE - hexagonal (+orth)

AE - orthorhombic (+hex)

Fig. 7. ED patterns showing: a) a schematic illustration demonstrating the principle of ED patterns. Hexagonally organized lipids consist of three pairs of reflections with interplanar angles of 60°. On the contrary, orthorhombic organized lipids show reflections with interplanar angles of 56° and 68°, and two out of the 6 reflections (yellow) are located at a larger distance from the primary beam. b) Control human SC, showing an orthorhombic lipid organization. c) Patient with lamellar ichthyosis, indicative for a hexagonal lipid organization [68]. d–f) demonstrate the variety of different ED profiles possible in AD patients (unpublished results and [68]): d) Typical example of a ED profile indicative for a hexagonal lipid organization. e) This pattern (consisting of one ring and very frequently observed for AD patients) is indicative for a hexagonal lipid organization, but the presence of an orthorhombic lipid organization cannot be excluded. f) ED pattern of a patient with AD, indicative for mainly an orthorhombic lipid organization. However, the presence of a hexagonal lipid organization cannot be excluded.

Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

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453 454 455 456 457 458

462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494

C

451 452

E

449 450

R

F

447 448

R

445 446

N C O

443 444

U

441 442

O

With respect to the lipid composition and organization, AD is by far the most intensively studied disease. It is a chronic relapsing inflammatory skin disease characterized by a broad spectrum of clinical manifestations such as erythema, dryness and intense pruritus [85,86]. AD affects over 15% of Caucasian children and 2–10% of adults, and its prevalence is increasing rapidly, especially in developed countries [87–91]. Patients have a decreased skin barrier function in lesional and nonlesional skin [92–96]. Although mutations in the filaggrin gene (FLG) are currently the highest known genetic risk factor for the development of AD [97–102], other aspects like immunological factors and environmental factors also play a role in this multi-factorial skin disease [85,103–105]. Back in 1988, Werner et al. reported (by means of electron microscopy) disturbed lamellar body maturation in dry skin of patients with AD, and that it may be related to the skin barrier function [106]. Fartasch et al. demonstrated by electron microscopic analysis from biopsies of AD patients using ruthenium tetroxide (RuO4) postfixation a delayed and probably incomplete extrusion of lamellar bodies [64,107]. They suggested that retention of lipids at their synthesis site occurs which makes them unavailable to the extracellular lipid matrix of the SC. They hypothesized that this could partially explain the impaired barrier function in AD patients. From the numerous additional studies that have been performed until now, it became apparent that extracellular SC lipids play a role in the impaired cutaneous barrier in AD. Most research started with analysis of the total lipids and the ratio of the SC lipid classes (CERs, FFAs and CHOL) as explained below.

439 440

R O

461

438

P

3.4. Atopic dermatitis (AD)

436 437

3.4.1. Lipid composition in AD The total level of SC lipids was found to be decreased in non-lesional as well as lesional skin [108,109]. There is contradicting evidence about the lipid ratios in literature: Melnik et al. reported a decrease in CER levels (wt.%) compared with CER levels of control subjects, when analyzing all SC lipids from both sole and lumbar SC. [108]. Others report no decrease in CER content in non-lesional AD skin [77,110,111]. Also

a recent study by Angelova-Fischer et al. demonstrates no difference in the level of total lipids nor in the relative (%) FFA and CER levels in lesional and non-lesional skin compared with controls [112]. In contrast Di Nardo et al. have reported a reduced CER/CHOL ratio in non-lesional AD skin [92]. Besides the studies that examine the SC lipid classes, others report on lipid classes and subclasses in a more extensive manner. In 1991 Imokawa et al. demonstrated that both the level of total lipids and CERs were decreased in SC of AD. [108]. More specifically, the level of CER [EOS] was most drastically reduced, both in non-lesional as well as in lesional skin, whereas CER [NS], [AS], and [AP] showed a relative increase in AD SC. Additional studies on the lipid composition were performed by Yamamoto, Bleck and Di Nardo, reporting a similar reduction in CER [EOS] as observed by Imokawa et al. [92,111,113]. The latter two also report a significant decrease in CER [NP] (in both lesional and non-lesional skin), which correlated with a decrease in skin barrier function. These studies were all performed before 2006, and therefore no correlation was examined with FLG mutations, an important predisposing factor for AD [97,114]. Jungersted et al. reported for the first time the SC lipid composition in AD including the effect of FLG mutations on the SC barrier lipids [115]. They also observed a significant decrease in acyl-CERs, which was not related to FLG mutations. They suggested that the observed changes in CER composition is related to AD-effects other than FLG mutations. In another study, small but significant differences were observed regarding the level of CHOL, CER⁄CHOL ratio and triglycerides in non-lesional skin of AD patients with FLG mutations compared with AD patients without FLG mutations [112]. In a recent study we have observed changes in lipid composition compared with controls, but the modulation in lipid composition is not associated with FLG mutations [116]. However, the lipid composition may also be affected by other features, such as inflammation and/or microbial activity: It is known that in AD patients the antimicrobial activity is related with decreased levels of sphingosine, a natural antimicrobial agent and also precursor for the sphingoid backbone of the CERs [117]. It would therefore be of great interest to study a related disease, ichthyosis vulgaris (IV). FLG null mutations are the origin of IV and no inflammation is involved. These patients show abnormalities in the extracellular lipid organization [118], but the lipid composition has not yet been studied. This modulated lipid organization may contribute to the permeability barrier impairment in this disease, besides loss-of-function mutations in the FLG gene [118]. However, the elevation in TEWL in IV patients is in general less drastic than in AD patients and only significant when patients are either homozygote or compound heterozygote [118,119]. All these studies suggest that factors other than FLG mutations also play a role in the skin barrier function. Until now, most papers report on the CER subclass composition. With the introduction of LC/MS, the possibility to study the lipid chain lengths arose, and two studies have reported on the CER lipid chain length distribution in AD patients. In 2010, Ishikawa et al. performed a study in 8 AD patients and observed an increased level of CERs with very short chains (with a total chain length of 34 carbon atoms, referred to as C34 CERs) in the CER [NS] subclass in lesional AD skin [110]. The increased level in CER [NS] C34 correlated significantly with the skin barrier function monitored by TEWL: a higher level of short chain CER [NS] C34 correlated with a higher TEWL. The same study reported a correlation between reduced levels of long chain acyl-CERs and increased TEWL values. These findings suggested for the first time that not only CER subclasses but also the lipid chain length may play an important role in the skin barrier function in AD patients. Recently, the full CER profile of AD patients was studied, examining all CER subclasses, the CER chain length distribution of all these subclasses as well as the effect of FLG mutations and skin barrier function assessed by TEWL [116]. In non-lesional skin an increased level of C34 CERs was observed and a reduced level of acyl-CERs. These two parameters together correlate in an

D

460

434 435

T

459

38 carbon atoms, was increased dramatically in NTS patients and also unsaturated CERs were observed. In a subgroup of patients we detected a strong reduction in acyl-CER levels. Interestingly, the precursors of these acyl-CERs, the glucosyl-acyl-CERs, were increased in these patients, suggesting abnormalities in the lipid processing enzymes. Indeed, β-glucocerebrosidase (the enzyme responsible for conversion of glucosyl-CERs into CERs, more detail below) was one of the key enzymes related to SC lipid processing which showed a clearly distinguishable expression profile in NTS patients compared with that in control subjects [84]. The changes in lipid composition were related with changes in the lipid organization: an increased disordering of the lipids in SC of NTS patients and an indication of an increased presence of a hexagonal packing were observed. In addition, SAXD patterns indicated that in a subgroup of patients no lamellar ordering was present, whereas in the other group of patients the LPP was observed with a reduced repeat distance (Fig. 6d). All patients that showed a dramatic reduction in the acyl-CER level in the SC also showed an absence of the lamellar lipid ordering. This is the third disease we report on (besides from LI and psoriasis) in which the reduction of acyl-CERs has a detrimental effect on the lamellar lipid organization. Furthermore, the dramatic changes in lipid composition in SC of NTS patients are expected to contribute to the barrier dysfunction in NTS. NTS is an inflammatory disease that has several similarities in skin phenotype compared with AD. Moreover, the pathogenesis overlaps with that of AD patients via increased serine proteases. Therefore, the question arises whether in AD skin changes in lipid composition and organization are similar to those in NTS skin. This will be explained below.

E

432 433

9

Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560

a)

3.4.2. Lipid organization in AD Besides studies that describe the SC lipid composition in AD, there are some reports describing the lipid organization in AD patients. The first study regarding the lateral packing was performed by Pilgram et al. [68]. They used ED to examine the lateral lipid organization in SC of 3 controls and non-lesional SC of 3 AD patients (Fig. 7d–f) and report an increased percentage of hexagonal organized lipids in non-lesional AD SC compared with SC of control subjects. Recently, similar studies

592 593

O

F

581 582

b) 30

r = 0.77

25

10

5

0

5

10

15

20

c) r = 0.73

22

20

15

10

5

0 25

0

0.35

20

15

25

r = 0.75

0.30

0.25

0.20

18

0.15

17

0.10 6.0

10

d)

19

4.0

5

Lipid organization (SAXD Peak II position (lamellar organization) and FTIR scissoring bandwidth (lateral organization))

CER composition (Total CER [EO] and total C34 CER content)

21

20

E T

15

23

D

TEWL (g/m2/h)

25

20

0

r = 0.76

P

30

Lipid/Protein ratio

580

with non-lesional skin and the MUFA-levels were significantly increased indicating that inflammation or antimicrobial activity may play a role in modulating the SC lipid composition. A remarkable relation was observed between the composition of the FFAs and CERs: the chain length of the FFAs parallels the composition of the CERs. This is in line with the current hypothesis that human SC CERs and FFAs share a common synthetic pathway [122,123]. As FFAs are building blocks for the CERs, the correlation between the two lipid classes suggests that a reduced CER chain length observed in AD originates from a reduced FFA chain length. However, to fully establish this relationship, further studies need to be performed.

C

578 579

E

576 577

R

574 575

R

572 573

O

570 571

C

568 569

N

567

U

565 566

TEWL (g/m2/h)

563 564

excellent way with TEWL values, as depicted in Fig. 8a. In a second study the CER composition of lesional skin was also examined and compared with non-lesional skin and control skin [120]. It was obvious that all changes noticed in non-lesional skin were also detected in lesional skin, but to a higher degree. For example, a reduction of almost 50% was observed for the long chain acyl‐CERs in SC of lesional AD and a ~threefold increase in C34 CERs was observed when comparing lesional with non-lesional skin. Together, this results in a further reduction of the average CER chain length in lesional skin compared with nonlesional AD SC and control SC. Compared with the composition of CERs, there is less information available about the FFA composition in AD skin. It was reported that the level of very long chain fatty acids (more than 24 carbon atoms) was reduced in non-lesional as well as lesional skin of AD patients [121]. Recently it was shown that very long chain FFAs (≥ 24 carbon atoms) were strongly reduced whereas shorter FFAs – in particular C16:0 and C18:0 – were increased already in non-lesional AD SC [120]. These changes in FFA profiles were much stronger in lesional skin, similarly as observed for the CER chain lengths. Within a patient the reduction in chain length was stronger in lesional skin compared

Mean FFA chain length (carbon atoms)

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J. van Smeden et al. / Biochimica et Biophysica Acta xxx (2013) xxx–xxx

R O

10

8.0

10.0

12.0

14.0

Scissoring bandwidth (FTIR bandwith, cm-1)

43

44

45

46

47

48

49

Mean lipid chain length (carbon atoms)

Fig. 8. Correlation plots illustrating the relation between a) The CER composition and the skin barrier function as measured by TEWL. The univariate analysis plot is composed of two parameters: the total acyl-CER level (CER [EO] level) and the total C34 CER level [116]; b) The scissoring bandwidth versus TEWL [116]. The univariate analysis plot is composed of two parameters: the SAXD peak 2 position and the FTIR scissoring bandwidth; c) The mean FFA chain length and bandwidth of the CH2 scissoring modes of the FTIR spectrum, indicative for the orthorhombicity of the lipids [120]; and d) The lipid/protein ratio and mean lipid chain length [127]. Symbols ■, ♦,○ correspond to data points of lesional AD skin, non-lesional AD skin, and skin from control subjects, respectively. All correlation plots were reproduced with permission.

Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

583 584 585 586 587 588 589 590 591

594 595 596 597 598 599

J. van Smeden et al. / Biochimica et Biophysica Acta xxx (2013) xxx–xxx

621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664

690 691

O

F

3.4.4. Origin of the altered SC lipids in AD As the knowledge on the changes in SC lipid composition and organization evolves and becomes more detailed, the observed changes signify altered biological pathways that underlie these changes. Although these pathways are still not fully elucidated, some particular enzymes are suggested to be involved that are related to the changes in lipid composition and lipid organization (Fig. 9a). Regarding the differences in CER subclasses, deficiencies in βglucosylcerebrosidase and sphingomyelinase are often reported in relation to AD. The former enzyme cleaves the glycosidic bond of the GlcCER (resulting in the removal of a glucose group), whereas the latter cleaves the phosphocholine group (Fig. 9b). For both enzymatic reactions, the end product is a CER molecule, but CER [NS] and [AS] are known to be converted not only by β-glucocerebrosidase, but also by sphingomyelinase [128–130]. These CER subclasses show an increased abundance in AD patients whereas several other CER subclasses are decreased (like CER [NP] and [EOS], which are converted via βglucosylcerebrosidase). These enzymes may therefore be affected in AD. Indeed, several studies in AD patients show changes in both expression levels and activity of sphingomyelinase and β-glucocerebrosidase [131–135]. Also with respect to other diseases, deficiencies in βglucosylcerebrosidase and sphingomyelinase are known to be the origin for other skin (related) diseases, like Gaucher disease [136,137] and Niemann–Pick disease [138]. In addition to sphingomyelinase and β-glucocerebrosidase, Hara et al. published in 2000 the involvement of different enzymes in AD: sphingomyelin deacylase and GlcCER deacylase [139]. These enzymes cleave the fatty acid from respectively sphingomyelin and GlcCERs, resulting in either a glucosyl sphingoid base or a sphingoid base phosphorylcholine (Fig. 9b). The mechanism of these enzymes and their relation to AD is extended by Imokawa et al., who stated that deacylase enzymes are involved in SC of AD patients rather than β-glucocerebrosidase and sphingomyelinase [140,141]. However, these enzymes have never been identified in the epidermis and these could be of bacterial origin. Thus, although this alternative pathway could definitely be involved in AD it is probable that other enzymes are involved. Also, the number of lipids that are converted by this synthetic route is relatively small compared with the changes in CER levels observed in AD. An overview of the role of CERs and their related enzymes with respect to skin diseases is reviewed by Choi et al. [142].

R O

619 620 Q5

P

617 618

665 666

D

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ratio plays a role in the skin barrier function. Therefore, not only the lipid composition but also the lipid to protein ratio has been examined [127]. In that study it was demonstrated that changes in the lipid/protein ratio are in line with changes in the skin barrier function as measured by TEWL. Primarily the level of lipids was reduced in non-lesional and lesional AD SC whereas the dry SC mass was only slightly decreased in lesional SC. Although the reason for this reduced lipid/protein ratio was not investigated, a correlation was observed between the lipid/protein ratio and the composition of the lipids, i.e. the mean lipid chain length (Fig. 8d). This correlation illustrates that a change in the lipid/protein ratio is associated with changes in lipid composition, indicating that enzymes or transporter proteins involved in lipid synthesis and lipid transport are simultaneously affected together with the LB extrusion process. The reduced level of lipids could be the result of an incomplete lamellar body extrusion process, which may be present in AD skin, also in noneczematous skin [41]. This is probably related to serine proteases that bind to the PAR2 receptor, thereby inhibiting the lamellar body extrusion process (see article by Elias in this issue). The analyzed SC lipid composition may then be deceptive because the lipids inside the lamellar bodies do not contribute to the SC lipid matrix. However, they are taken into account when lipids are extracted and subsequently analyzed. It is unlikely that incomplete lamellar body extrusion distorts the SC lipid composition to a major extent, as there is still a very high correlation between the SC lipid composition and the skin barrier function (assessed by TEWL), both in non-lesional and lesional skin [110,116,120].

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were performed in a larger group of AD patients, but in this study the correlation was examined between the degree of hexagonal lateral packing and both TEWL values and the presence of filaggrin mutations. An increased presence of the lipids adopting a hexagonal lipid organization was observed in non-lesional SC of AD patients, indicating a less dense lipid organization. These changes were associated with reduced TEWL values, but did not correlate with the presence of FLG mutations [116]. Recently, the FTIR method (explained in Fig. 5) was also used to determine the level of orthorhombic domains in non-lesional AD skin [116,120]. A smaller bandwidth in CH2 scissoring vibrations and an increase in the stretching vibrations were observed in the FTIR spectra of non-lesional AD skin (Fig. 8b and c). Both changes in the molecular vibrations correlated with increased TEWL values. This indicates that the subpopulations of lipids in a highly ordered orthorhombic phase are less dominantly present in lesional AD skin compared with control subjects, which confirms the results obtained by ED. Very recently the CH2 scissoring vibrations of lesional SC were also examined [120]. All changes in lipid organization noticed in non-lesional skin were also detected in lesional skin, but more drastically present. As mentioned earlier and also explained in Section 3.4.2, the lateral lipid organization is thought to be primarily related to the FFA composition. We therefore studied the link between the lateral lipid organization and the FFA chain length in these AD patients and observed a positive relation between the chain length and the lateral lipid organization, as measured by the CH2 scissoring bandwidth in the FTIR spectra (Fig. 8c): A reduced scissoring bandwidth value corresponds to a less orthorhombic lipid organization, which is related to a shorter FFA chain length distribution. Regarding the lamellar lipid organization, previous studies indicate that this organization is altered in non-lesional SC of AD patients [116,124]. A shift in the peak position marked by a 2 in Fig. 6e (indicative for the LPP and SPP) of the SAXD curves of a subgroup of AD patients was observed. This indicates a reduced value of the repeat distances of the lamellar phases and/or a reduced formation of the LPP [45]. This corresponds excellently to the findings in lipid composition, as a reduced chain length of the lipids will result in a reduced repeat distance of the lamellar phases. However, there is another important observation. In the diffraction pattern of a subgroup of patients no 3rd order peak was observed. When the 3rd order reflection was absent, also the 1st order peak was not observed. These two reflections are solely attributed to the LPP, and the disappearance of both reflections suggests a reduced formation of the LPP. Remarkably, the CER [EOH] and total acyl-CER levels in AD patients having a SAXD pattern without peak ‘3’ (attributed to the third order of the LPP, explained in Fig. 5) was significantly lower compared with subjects with peak ‘3’ in the SAXD pattern (5.4 ± 1.8% versus, 9.6 ± 2.6%, respectively). A significant difference in these two groups of patients was not found for other CER subclasses that were altered in non-lesional skin compared with control SC (i.e. CERs [NS], [NP], [NH], [AS] and [AH]). This indicates again the importance of the acyl-CERs in the formation of the LPP. In previous studies such a relationship was also examined in dry skin. In these studies a significant reduction in CER [EOS] in the SC coincided with the absence of the 3rd order diffraction peak in the corresponding SAXD curves [125], suggesting a reduced formation of the LPP. Finally, when focusing on SC of HSEs, high values of acyl-CERs are observed. In SC of HSEs only a LPP has been detected and not the SPP [126]. This link between levels of acyl-CERs and the formation of the LPP being observed in SC of diseased skin, dry skin and HSEs is very consistent throughout all these measurements. The importance of the LLP for the skin barrier will be further discussed in Section 4.

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3.4.3. Lipid protein ratio in AD As not only lipid composition and lipid organization in the SC play a role in the cutaneous barrier function but also the level of lipids, it is relevant to study whether the amount of protein in SC or the lipid/protein

Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

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Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

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In addition to the skin diseases mentioned above, it is known that several disorders primarily related to the (hepatic) metabolism have secondary effects on the epidermis, hence the SC lipids may be affected. As an example, we will briefly discuss one metabolic lipid disease from which additional data on the SC lipids were recently provided: Chanarin–Dorfman. An excellent overview of skin lipid abnormalities in inherited disorders of lipid metabolism is provided elsewhere by Elias et al. [145]. CD is a neutral lipid storage disorder with ichthyosis in human skin. Loss of function mutations in the ABHD5 gene/CGI-58 in humans are

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Because several reviews in this special issue will include mice skin, we briefly mention some results obtained from mice studies focusing on the enzymes involved in the lipid synthesis. Mice studies contribute to the understanding of mechanisms involved in lipid synthesis and can therefore be very relevant for certain aspects of a disease. However, the differences and similarities in lipid composition between human and mice SC need to be pointed out: Until now, in mice SC there are only 9 CER subclasses identified: The CER subclasses containing a sphingoid base of [S], [H] and [P] with an acyl chain that is either [N], [A] or [EO] are detected. However, no CERs containing the sphingoid base [dS] have been identified [149], which is different from human skin. Liou et al. reported levels of CER [EOS] around 70% of the total CER fraction, which is very high compared with other reported values and not comparable to that in human SC [150,151]. As far as the lipid organization is concerned, RuO4 post fixation combined with transmission electron microscopy revealed the broad–broad–narrow pattern of the lipid lamellae. Besides, White et al. were the first to perform studies using SAXD and reported the LPP together with an orthorhombic lateral packing [46]. In additional studies the presence of this phase was confirmed and the SPP was also detected, although less abundantly present than the LPP [152]. These studies show that the lipid composition and organization is comparable, although differences are also observed. Furthermore, in contrast to human skin, a very high level of sebum is reported at the skin surface of mice [153]. Focusing on CER synthesis and FFA synthesis, the precursors of the CER subclasses are sphingomyelin and GlcCERs. Whereas GlcCERs are precursors of all CER subclasses, sphingomyelin seems only a precursor of CER [AS] and CER [NS] [129,130]. As the phosphorylcholine and glucosyl group are cleaved at the interface between the viable epidermis and the SC, the activity of these enzymes as function of pH are relevant to study. Numerous studies showed that the activity of these enzymes are indeed pH dependent and that a change in pH gradient over the SC may trigger a change in lipid composition [154,155]. In a more recent study it was shown that acidification leads to increased barrier repair in mice skin, contributed by increased β-glucocerebrosidase and sphingomyelinase activity [156]. As reported above, the CERs and FFAs have very long hydrocarbon chains, which are synthesized by ELOVLs 1–7. The importance of elongases in several skin diseases has been suggested. In an AD mice model, a reduction in CER chain length was reported [157]. In the same model the expression of ELOVL 1, 4 and 6 on RNA level and

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causative for the disease. This results in inhibited breakdown of triacylglycerides (TAGs) to diglycerides and FFAs, causing them to accumulate in the cytosol. Regarding the lipids, this disease is associated with a deficiency in acyl-CERs and bound omega-hydroxy FFAs [146]. As these are crucial for a normal permeability barrier function of the skin, this is likely to contribute to SC barrier abnormalities and also the observed lamellar/nonlamellar phase separation due to accumulated TAGs within the extracellular SC lipid domains: Demerjian et al. demonstrated the presence of non-lamellar lipid domains in the SC of patients that contribute to the skin barrier dysfunction (assessed by TEWL) in CD [147]. Goto-Inoue et al. visualizes the distribution of CERs in CD syndrome with imaging MS in a human subject. Using MALDI-MS, they demonstrated an accumulation of TAGs in the SC, whereas acyl-CERs were depleted in SC of CD mice [148] (Fig. 10).

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Concerning the reduced FFA chain length in AD patients, the underlying mechanism may be related to two contrary enzyme pathways: the elongation of very long chain fatty acids (ELOVL) and stearoyl CoA desaturase (SCD) families. ELOVL are responsible for proper elongation of long and very long FFA chains. ELOVL4 (and ELOVL1) for example, elongates FFAs with a chain length of 24 carbon atoms and higher. As these FFAs are the ones that are decreased in AD, a reduced ELOVL4 expression or activity may result in this change in lipid composition. Indeed, Vasireddy et al. performed a study in which inactivated ELOVL4 in murine skin showed decreased FFA chain length, supporting this hypothesis, (see also next paragraph) [143]. In addition, they demonstrate a reduced level of very long chain CERs (acyl CERs), establishing a link between the importance of ELOVL4 for the synthesis of ω-hydroxy CERs and subsequently ultra-long acyl-CERs. Uchida et al. reviewed the relation between ELOVL and acyl-CERs [123]. If elongation of FFAs is reduced, an alternative pathway that involves SCD may be of increased importance. This enzyme inserts one degree of unsaturation in the FFA molecule, which is thought to be a practically irreversible process. A higher level of unsaturated lipids is thought to be a destabilizing factor for a proper orthorhombic lipid organization (see Section 5). The fact that long chain fatty acids are crucial for the orthorhombic packing as has recently been demonstrated from in vivo data (Fig. 8c) [120]: a lower level of orthorhombic lipid domains correlates to a high extent with a decreased FFA chain length. Although the enzymatic activity or expression has not been studied to date, results on HSEs show similar changes in their FFA profile compared with human SC. These HSEs also show an increased expression of SCD in the epidermis. Thus, besides lipid subclass and lipid chain length, the degree of unsaturation is likely to be another important factor for a proper lipid organization and skin barrier function. This is supported by in vitro studies and will be discussed in more detail in Section 5: “Relation between in vivo findings and in vitro observations”. In addition to the enzymes discussed above, several other enzymes are involved in lipid processing and therefore may play a role in the pathogenesis of AD [96]. Most of the changes in enzymes described above are considered secondary abnormalities. However, the pathogenesis of AD is also linked to primary abnormalities in the stratum corneum, of which mutations in the FLG gene are without doubt the most eminent ones described in literature. A review by Elias and Schmuth elaborate in much more detail on this matter [144]. We also refer to articles elsewhere in this issue (by Elias, Radner Breiden and Rabionet), which describe these enzymes involved in epidermal lipid processing, as well as articles that elaborate on lipid transporter enzymes (like ABCA12 mentioned above) that are related to SC lipid abnormalities (see articles by Akiyama and Lin, in this issue).

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Fig. 9. a) Schematic overview of main enzymatic processes involved in the formation of SC lipid lamellae. Arrows indicate the transport or conversion of lipids that are catalyzed by enzymes of which the most important ones are denoted by the abbreviations in blue. FAS = fatty acid synthase; ELOVL = elongation of very long chain fatty acids family (1 to 7); SCD = stearoylCoA desaturase; SPT = serine palmitoyltransferase; KSR = 3-ketosphinganine reductase; (A)GPAT = (acyl)glycerol-3-phosphate acyltransferase; CERS = ceramide synthase family (1 to 6); DES = dihydroceramide desaturase (1 and 2); GCS = glucosylceramide synthase; SMS = sphingomyelin synthase; SULT = cholesterol sulfotransferase type 2B isoform 1b; CSase = cholesterol sulfatase; PLA-2 = phospholipase; β-GCase = β-glucocerebrosidase; aSMASe = acid sphingomyelinase. b) Catabolic pathways for SC CER precursors. In healthy human SC, most CER precursors (viz. glucosylceramides and sphingomyelin) are converted to ceramides via β-glucocerebrosidase and (acid) sphingomyelinase. In AD, these enzymatic pathways may be affected, although studies by Hara et al. and Imokawa et al. demonstrate that different pathways involving glucosylceramide deacylase and sphingomyelin deacylase may be upregulated as well, leading to accumulation of glucosyl sphingosine and sphingosyl phosphorylcholine [139–141].

Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

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In several skin diseases a modulation in lipid composition and/or organization has been reported and in a few cases the relation between modulation in lipid properties and skin barrier function (as monitored by TEWL) has been described. However, compared with control skin,

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a depletion in SC CERs with ω-hydroxy very long chain fatty acids (≥ C28) and accumulation of CERs with non ω-hydroxy fatty acids of C26, demonstrating C26 FFAs as possible substrates of ELOVL 4 [143]. Very recently, Loiseau et al. demonstrate in AD model mice abnormalities in the sphingoid base, the precursors and catabolites of CERs [160]. They show that changes in the sphingoid base may change the thermotropic behavior of the lipid lamellae and affect the permeability.

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ELOVL 1 and 4 also on a protein level was reduced, indicating a relation between ELOVL expression and the chain length of CERs. There are other noteworthy studies directly related to the expression of the elongases and the enzyme CER synthase 3. The latter is responsible for linkage of the very long chain fatty acids to the sphingoid backbone [158]. Very recently it has been reported that mice deficient in the ELOVL 1 gene show a reduced acyl chain length in CERs [159]: Whereas the level of CERs with a C16 to C24 acyl chain were increased or equal, the levels of CERs with longer acyl chains were reduced. This clearly demonstrates the effect of ELOVL 1 deficiency on the elongation of the FFAs and the acyl chains in CERs. The same study also demonstrated that CER synthase 2 and 3 affect the ability of ELOVL 1 to synthesize either FFAs with chain length of up to C24 chain length or increase the activity toward C26 FFA synthesis. The latter is enhanced by a higher expression of the abovementioned CER synthase 3. Finally, the absence of ELOVL 4 has been studied as well, and showed

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Fig. 10. Imaging mass spectrometry of skin sections demonstrating the depletion of acyl-CERs in the SC layers of CD patient compared with a healthy control (upper picture), as well as accumulation of TAG in the SC of CD patient (lower picture). Gray dotted line highlights the SC layer. *: the MS signal with a mass (m/z) of 1048.7 amu corresponds to an acyl-CER d18:1/C34:1. **: the MS signal with a mass (m/z) of 895.7 amu corresponds to a C16:0/C18:1/C18:2 TAGs. The image is adapted from Goto-Inoue et al. in PlosOne 2012 [148].

Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

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In AD, LI, and NTS the hexagonal lateral packing is more prominently present than observed in SC of healthy human skin. When focusing on the three lipid classes, mixtures prepared with isolated CERs and CHOL form a hexagonal lateral packing over a wide range of CER/CHOL molar ratios [53,162]. When adding low levels of FFAs, the formation of an orthorhombic packing was induced and a further gradual increase in the FFA level enhanced the formation of the orthorhombic lateral packing. When increasing the FFA levels to an equimolar CER/CHOL/FFA ratio a dominant presence of the orthorhombic lateral packing was detected [59]. Extrapolating these results to diseased skin, it is obvious that reduced levels of FFAs contribute to a more prominent presence of a hexagonal packing. Therefore the low levels of FFA in SC of LI patients are probably responsible for the hexagonal lateral packing in these patients [66]. As the presence of FFAs are crucial for the formation of the orthorhombic packing, the chain length of FFAs may also affect the lateral packing. Indeed, a drastic reduction in chain length from mainly 22–24 carbon atoms to approximately 16 carbon atoms resulted in a hexagonal lateral packing [163]. Concerning LI, no information is currently present on the chain length distribution of FFAs and CERs. For AD and NTS, a significant shortening of FFA chain length has been observed probably being an important factor for the observed increased hexagonal packing in SC of these skin diseases. In addition, similarly as for the FFAs, the CER chain length is also shortened in AD and NTS skin which may contribute also to an increased level of hexagonal packing. Besides a reduced level of FFAs and a modulation in chain length, the level of unsaturated FFAs may also affect the lipid phase behavior, in particular the lateral packing. Very recently we performed studies by replacing several subclasses of FFAs by their mono-unsaturated counterparts. An increase in the hexagonal packing was noticed (Mojumdar et al., unpublished results). As an increased level of unsaturated FFAs in SC of AD and NTS is observed, this may also contribute to the higher level of hexagonal packing. The effect of modulation in CER subclass composition on the lateral packing has also been reported. Studies focused on acyl-CERs revealed that these subclasses may enhance the stability of the orthorhombic packing [164]. A reduction in the level of acyl-CERs may therefore also contribute to an increased hexagonal lateral packing as observed in AD and NTS patients. In conclusion, as far as the lateral packing is concerned, in LI the drastic reduction in FFA levels is expected to cause this reduced level of orthorhombic packing. When focusing on AD and NTS patients, most probably a concerted effect of a reduced FFA chain

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length, a reduced level of acyl-CER and an increased level of unsaturated FFAs (and CERs in case of NTS) all contribute to a reduced formation of the orthorhombic lateral packing. Focusing on the lamellar phases, lipid mixtures containing isolated human CERs mixed with CHOL show the prominent presence of the LPP, whereas a small fraction of lipids forms the SPP. These data show that FFAs are not required for the formation of the lamellar phases present in human SC. Interestingly, the formation of the lamellar phases is not sensitive to the CHOL/CER ratio either: an increase in CHOL/CER molar ratio from 0.2 to 1.0 does not affect lamellar phase behavior [53]. In LI, AD, psoriasis and NTS, a shift of the main diffraction peak to higher q-values and thus shorter spacings are observed. As explained in Fig. 4, this main diffraction peak is based on both the SPP and the LPP. Such a shift to shorter spacing can be caused by both a shorter repeat distance of the LPP and SPP and/or a reduction in the formation of the LPP. If the latter occurs, the intensity of the 3rd peak in Fig. 4 should also be reduced. With respect to the chain length of CERs and FFAs, it has been reported that a reduced FFAs chain length results in shorter repeat distances and this is expected to be the case also for the CERs [162]. The alternative, a reduced presence of the LPP, can be achieved by modulating the CER subclasses: when acyl-CERs are excluded from CER mixtures, the formation of the LPP is drastically reduced or even absent [42,162]. Therefore, besides the presence of CHOL and CER classes, especially the presence of acyl-CERs is critical for the formation of the LPP. When extrapolating these results to those observed with AD patients, a shift in peak position may be due to both a shorter chain length of CERs and FFAs and a reduction in acyl-CERs. Several patients in the cohort of AD show no 3rd peak in the X-ray diffraction patterns. This confirms a reduced presence of the LPP in SC of these patients and was associated with a reduced acyl-CER level in this group. When combining the in vitro and in vivo results, it becomes clear that the acyl-CERs are a determining factor for the formation of the LPP and changes in (the level) of acyl-CERs contribute to a shift in the diffraction patterns of SC of some AD patients. Not only in AD, but in dry skin and HSEs the relationship between acyl-CER levels and the presence of the LPP has been reported [125]. The absence of lamellar ordering in SC of the NTS patients is only observed when the acyl-CER levels are extremely low. As the reduction in acyl-CER simultaneously occurs with increased level of MUFAs and the reduced chain length of CERs and FFAs in these patients, this concerted change in lipid composition may result in reduced van der Waals interactions between the hydrocarbon chains, possibly leading to the absence of long-range ordering.

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studying diseased skin usually results in the observation of multiple changes in lipid composition and protein expression. This makes it difficult to select the critical modulation in lipid composition underlying the change in lipid organization and subsequently the impaired skin barrier function. For this reason, additional information is often required. Lipid model systems are attractive candidates to study this as it is possible to systematically change their lipid composition. An important requirement for these models is that they should mimic the lipid organization in SC of control subjects as closely as possible. This depends on both the selected lipids and the thermal history of the sample. Here, we will first discuss the results we obtained with mixtures prepared with the SC lipid classes focusing on the relation between lipid composition and lipid organization. Subsequently, we will discuss the relation between lipid composition, organization, and skin barrier function using oriented lipid membrane systems casted on a porous membrane. We like to stress that concerning lipid model systems, there are many interesting studies focusing on the fundamental interactions between CERs, CHOL and FFAs. As these mixtures are often two, three, or four component systems and thus very simplified compared with the situation in SC, these studies will not be covered here but have been reviewed elsewhere [161].

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5.3. Changes in lipid composition and organization induce an impaired 978 lipid barrier 979 In order to relate lipid composition and organization with lipid barrier function, permeability studies have been performed using lipid membranes sprayed on a porous support [165]. This membrane system is referred to as the SC substitute (SCS) and mimics the barrier properties of human SC very closely [166]. The SCS has been prepared with synthetic CERs that mimic closely the CER composition in porcine SC, in which predominantly one acyl-CER is present, namely CER [EOS]. Using this SCS, the role of CER [EOS] on the barrier properties was investigated and showed that in the absence of CER [EOS] – and thus an absence of the LPP – a two-fold increase in transport was observed [166]. This demonstrates that the importance of CER [EOS] not only relates to the formation of the LPP, but also to the cutaneous barrier function. This signifies that in AD, NTS, and psoriasis, a reduction in the level of acyl-CERs may be one of the causes for the impaired skin barrier function. Concerning the presence of the orthorhombic lateral packing, the relation to the cutaneous barrier function is not that obvious. In a first series of studies the permeability of the SCS was examined in a temperature range at which the orthorhombic to hexagonal phase transition occurs. These studies revealed that the lipid barrier was insensitive

Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

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Summarizing, in the skin diseases that have been studied until now and reviewed in this paper, changes in lipid composition are observed. Among those diseases in which also the lipid organization has been examined, the lipid organization is also altered (see Table 2 for an overview). However, whether these changes in lipid properties correlate to an impaired skin barrier function has only been studied in detail in AD skin. In fact, the information on the SC lipid properties in diseased skin is still very limited. Nevertheless, some very interesting general trends are observed in those skin diseases that show an altered lipid composition and organization, especially for those in which inflammation plays a role. The SC lipid composition and organization in LI, psoriasis, NTS, and AD have been studied and the results obtained with these patients demonstrate: i) a disturbed lamellar body extrusion process; ii) changes in the lamellar lipid organization: there is a shift in peak position to higher q-values corresponding to shorter repeat distances of the lipid layers, as assessed by several SAXD studies; iii) a more prominent presence of a less dense hexagonal lateral packing; and iv) changes in the lipid composition: more specifically, the level of acyl-CERs are reduced in several skin diseases whereas the chain length of all lipids (CERs and FFAs) are reduced as well. In addition, an increased level of MUFAs has been detected. Our lipid model studies show that all these changes are expected to contribute to an impaired skin barrier function. Then the question arises, is there an underlying common factor for these changes in lipid composition and thus lipid organization in SC in these skin diseases? Possibly a pH of the skin surface may change the protease activity of the enzymes involved in the degradation of the desmosomes. This may affect the activity of acid β-glucocerebrosidase and acid sphingomyelinase involved in the final step of CER processing [167,168]. This may contribute to the changes in the level of CER subclasses, such as a reduced CER [NP] as noticed in AD as well as in NTS and LI. However, in AD SC another explanation is provided by Imokawa et al. suggesting that deacylases are responsible for the hydrolysis of sphingomyelin and GlcCERs, although these enzymes could be of bacterial origin. As reported before, the enzymes involved in the elongation of the CERs and FFAs are the ELOVL1–7, especially ELOVL1 and 4. A reduction in activity or protein level may reduce the chain length of these fatty acids, as is found in murine AD models [12,122,123,143,169]. Then the question arises whether this may also be induced by a change in pH at the skin surface? This may only be possible if a change in pH induces a cascade of changes that finally results in a change of the activity of these enzymes, located mainly in the SG. Another denominator of these skin diseases is inflammation. Almost no information is available on the effect of inflammation on the lipid synthesis in the epidermis, although it is known that peroxisome proliferator-activated receptors (PPARs) play an important role here [170]. In ex vivo studies using HSEs, we recently noticed that cytokine supplementation indeed affects the lipid synthesis [171]. Therefore, inflammation may result in lower acyl-CER levels. This will in turn alter the lipid organization and is in agreement with the lowered levels of acyl-CERs observed in AD, NTS, and psoriasis. When combining the data of all the above mentioned diseases, it becomes clear that there is increasing evidence that lipids play an important role in several skin diseases, also in those where the primary cause

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We like to thank Dr. Ellen van den Bogaard and Dr. J. Bergboer from the Department of Dermatology of the Radboud University Nijmegen for the excellent collaboration and for providing the biopsies for the SAXD studies focusing on psoriasis. We also like to thank the Dutch Technology Foundation STW for their nearly continuous financial support and thank the personal at the DUBBLE beam line at the ESRF (France), as well as Daresbury (UK) for their excellent support regarding the X-ray measurements for a period of already more than 20 years.

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is not a reduced skin barrier. The data discussed above suggest that in case of an increased disease severity the deviation in lipid composition and subsequent organization is often increased too. However, to really establish this relation between SC lipids and disease severity, additional studies are required. In conclusion, as time progressed the information on the lipids advanced and more specific details on the role of the individual lipid classes are elucidated. The increased understanding in how the SC lipids are affected in skin diseases provides new insights on possible treatments of skin diseases as well as fundamental knowledge on the cause of the disease. It is therefore not surprising that current research focuses on why these lipids are altered in these skin diseases and which enzymatic pathways are involved.

[1] H. Schaefer, T.E. Redelmeier, Skin Barrier: Principles of Percutaneous Absorption, Karger, Basel, 1996. (u.a.). [2] P.M. Elias, Epidermal lipids, barrier function, and desquamation, J. Invest. Dermatol. 80 (1983) 44s–49s. [3] N.D. Lazo, J.G. Meine, D.T. Downing, Lipids are covalently attached to rigid corneocyte protein envelopes existing predominantly as beta-sheets — a solid-state nuclear-magnetic-resonance study, J. Investig. Dermatol. 105 (1995) 296–300. [4] D.C. Swartzendruber, P.W. Wertz, K.C. Madison, D.T. Downing, Evidence that the corneocyte has a chemically bound lipid envelope, J. Invest. Dermatol. 88 (1987) 709–713. [5] P.W. Wertz, D.T. Downing, Covalently bound omega-hydroxyacylsphingosine in the stratum-corneum, Biochim. Biophys. Acta 917 (1987) 108–111. [6] L.N. Marekov, P.M. Steinert, Ceramides are bound to structural proteins of the human foreskin epidermal cornified cell envelope, J. Biol. Chem. 273 (1998) 17763–17770. [7] R. Sandhoff, Very long chain sphingolipids: tissue expression, function and synthesis, FEBS Lett. 584 (2010) 1907–1913. [8] C.G. Schuette, T. Doering, T. Kolter, K. Sandhoff, The glycosphingolipidoses — from disease to basic principles of metabolism, Biol. Chem. 380 (1999) 759–766. [9] P.W. Wertz, D.C. Swartzendruber, D.J. Kitko, K.C. Madison, D.T. Downing, The role of the corneocyte lipid envelopes in cohesion of the stratum corneum, J. Invest. Dermatol. 93 (1989) 169–172. [10] S. Meguro, Y. Arai, Y. Masukawa, K. Uie, I. Tokimitsu, Relationship between covalently bound ceramides and transepidermal water loss (TEWL), Arch. Dermatol. Res. 292 (2000) 463–468. [11] M. Behne, Y. Uchida, T. Seki, P.O. de Montellano, P.M. Elias, W.M. Holleran, Omega-hydroxyceramides are required for corneocyte lipid envelope (CLE) formation and normal epidermal permeability barrier function, J. Investig. Dermatol. 114 (2000) 185–192. [12] W.M. Li, R. Sandhoff, M. Kono, P. Zerfas, V. Hoffmann, B.C.H. Ding, R.L. Proia, C.X. Deng, Depletion of ceramides with very long chain fatty acids causes defective skin permeability barrier function, and neonatal lethality in ELOVL4 deficient mice, Int. J. Biol. Sci. 3 (2007) 120–128. [13] D.T. Downing, Lipid and protein structures in the permeability barrier of mammalian epidermis, J. Lipid Res. 33 (1992) 301–313. [14] A. Weerheim, M. Ponec, Determination of stratum corneum lipid profile by tape stripping in combination with high-performance thin-layer chromatography, Arch. Dermatol. Res. 293 (2001) 191–199. [15] R.P. Reinertson, V.R. Wheatley, Studies on the chemical composition of human epidermal lipids, J. Invest. Dermatol. 32 (1959) 49–59. [16] N. Nicolaid, Skin lipids — their biochemical uniqueness, Science 186 (1974) 19–26. [17] G.M. Gray, H.J. Yardley, Lipid compositions of cells isolated from pig, human, and rat epidermis, J. Lipid Res. 16 (1975) 434–440. [18] M.N. Ansari, N. Nicolaides, H.C. Fu, Fatty acid composition of the living layer and stratum corneum lipids of human sole skin epidermis, Lipids 5 (1970) 838–845. [19] J. van Smeden, W.A. Boiten, T. Hankemeier, R. Rissmann, J.A. Bouwstra, R.J. Vreeken, Combined LC/MS-platform for analysis of all major stratum corneum lipids, and the profiling of skin substitutes, Biochim. Biophys. Acta 1841 (2013) 70–79.

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towards the lateral packing for this particular model drug (benzoic acid) [163]. However, in more recent studies (in which hydrocortisone was used as model drug) a more prominent presence of the hexagonal lateral packing reduced the lipid barrier. Therefore, the increased presence of the hexagonal lateral packing in patients with AD, LI and NeS may also contribute to the impaired skin barrier function. Finally, an increase in the level of MUFAs resulted also in an increased level of the hexagonal organization and an increased transport of hydrocortison through the membranes.

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[52] I. Iwai, H.M. Han, L. den Hollander, S. Svensson, L.G. Ofverstedt, J. Anwar, J. Brewer, M. Bloksgaard, A. Laloeuf, D. Nosek, S. Masich, L.A. Bagatolli, U. Skoglund, L. Norlen, The human skin barrier is organized as stacked bilayers of fully extended ceramides with cholesterol molecules associated with the ceramide sphingoid moiety, J. Investig. Dermatol. 132 (2012) 2215–2225. [53] J.A. Bouwstra, G.S. Gooris, F.E. Dubbelaar, M. Ponec, Phase behavior of lipid mixtures based on human ceramides: coexistence of crystalline and liquid phases, J. Lipid Res. 42 (2001) 1759–1770. [54] F. Damien, M. Boncheva, The extent of orthorhombic lipid phases in the stratum corneum determines the barrier efficiency of human skin in vivo, J. Invest. Dermatol. 130 (2010) 611–614. [55] P.M. Elias, L. Bonar, S. Grayson, H.P. Baden, X-ray diffraction analysis of stratum corneum membrane couplets, J. Invest. Dermatol. 80 (1983) 213–214. [56] J.A. Bouwstra, G.S. Gooris, M.A. Salomonsdevries, J.A. Vanderspek, W. Bras, Structure of human stratum-corneum as a function of temperature and hydration — a wide-angle X-ray-diffraction study, Int. J. Pharm. 84 (1992) 205–216. [57] D. Bommannan, R.O. Potts, R.H. Guy, Examination of stratum corneum barrier function in vivo by infrared spectroscopy, J. Invest. Dermatol. 95 (1990) 403–408. [58] C.L. Gay, R.H. Guy, G.M. Golden, V.H. Mak, M.L. Francoeur, Characterization of low-temperature (i.e., b65 degrees C) lipid transitions in human stratum corneum, J. Invest. Dermatol. 103 (1994) 233–239. [59] G.S. Gooris, J.A. Bouwstra, Infrared spectroscopic study of stratum corneum model membranes prepared from human ceramides, cholesterol, and fatty acids, Biophys. J. 92 (2007) 2785–2795. [60] M. Boncheva, F. Damien, V. Normand, Molecular organization of the lipid matrix in intact stratum corneum using ATR-FTIR spectroscopy, Biochim. Biophys. Acta 1778 (2008) 1344–1355. [61] G.S. Pilgram, A.M. Engelsma-van Pelt, J.A. Bouwstra, H.K. Koerten, Electron diffraction provides new information on human stratum corneum lipid organization studied in relation to depth and temperature, J. Invest. Dermatol. 113 (1999) 403–409. [62] G.S. Pilgram, J. van der Meulen, G.S. Gooris, H.K. Koerten, J.A. Bouwstra, The influence of two azones and sebaceous lipids on the lateral organization of lipids isolated from human stratum corneum, Biochim. Biophys. Acta 1511 (2001) 244–254. [63] L. Brancaleon, M.P. Bamberg, N. Kollias, Spectral differences between stratum corneum and sebaceous molecular components in the mid-IR, Appl. Spectrosc. 54 (2000) 1175–1182. [64] M. Fartasch, Epidermal barrier in disorders of the skin, Microsc. Res. Tech. 38 (1997) 361–372. [65] R. Ghadially, M.L. Williams, S.Y. Hou, P.M. Elias, Membrane structural abnormalities in the stratum corneum of the autosomal recessive ichthyoses, J. Invest. Dermatol. 99 (1992) 755–763. [66] A.P. Lavrijsen, J.A. Bouwstra, G.S. Gooris, A. Weerheim, H.E. Bodde, M. Ponec, Reduced skin barrier function parallels abnormal stratum corneum lipid organization in patients with lamellar ichthyosis, J. Invest. Dermatol. 105 (1995) 619–624. [67] D.G. Paige, N. Morsefisher, J.I. Harper, Quantification of stratum-corneum ceramides and lipid envelope ceramides in the hereditary ichthyoses, Br. J. Dermatol. 131 (1994) 23–27. [68] G.S. Pilgram, D.C. Vissers, H. van der Meulen, S. Pavel, S.P. Lavrijsen, J.A. Bouwstra, H.K. Koerten, Aberrant lipid organization in stratum corneum of patients with atopic dermatitis and lamellar ichthyosis, J. Invest. Dermatol. 117 (2001) 710–717. [69] C. Lefevre, S. Audebert, F. Jobard, B. Bouadjar, H. Lakhdar, O. Boughdene-Stambouli, C. Blanchet-Bardon, R. Heilig, M. Foglio, J. Weissenbach, M. Lathrop, J.F. Prud'homme, J. Fischer, Mutations in the transporter ABCA12 are associated with lamellar ichthyosis type 2, Hum. Mol. Genet. 12 (2003) 2369–2378. [70] T. Annilo, S. Shulenin, Z.Q. Chen, I. Arnould, C. Prades, C. Lemoine, C. Maintoux-Larois, C. Devaud, M. Dean, P. Denefle, M. Rosier, Identification and characterization of a novel ABCA subfamily member, ABCA12, located in the lamellar ichthyosis region on 2q34, Cytogenet. Genome Res. 98 (2002) 169–176. [71] M. Akiyama, The roles of ABCA12 in keratinocyte differentiation and lipid barrier formation in the epidermis, Dermato-Endocrinology 3 (2011) 107–112. [72] C.T. Jordan, L. Cao, E.D.O. Roberson, S.H. Duan, C.A. Helms, R.P. Nair, K.C. Duffin, P.E. Stuart, D. Goldgar, G. Hayashi, E.H. Olfson, B.J. Feng, C.R. Pullinger, J.P. Kane, C.A. Wise, R. Goldbach-Mansky, M.A. Lowes, L. Peddle, V. Chandran, W. Liao, P. Rahman, G.G. Krueger, D. Gladman, J.T. Elder, A. Menter, A.M. Bowcock, Rare and common variants in CARD14, encoding an epidermal regulator of NF-kappaB, in psoriasis, Am. J. Hum. Genet. 90 (2012) 796–808. [73] L.C. Tsoi, S.L. Spain, J. Knight, E. Ellinghaus, P.E. Stuart, F. Capon, J. Ding, Y.M. Li, T. Tejasvi, J.E. Gudjonsson, H.M. Kang, M.H. Allen, R. McManus, G. Novelli, L. Samuelsson, J. Schalkwijk, M. Stahle, A.D. Burden, C.H. Smith, M.J. Cork, X. Estivill, A.M. Bowcock, G.G. Krueger, W. Weger, J. Worthington, R. Tazi-Ahnini, F.O. Nestle, A. Hayday, P. Hoffmann, J. Winkelmann, C. Wijmenga, C. Langford, S. Edkins, R. Andrews, H. Blackburn, A. Strange, G. Band, R.D. Pearson, D. Vukcevic, C.C.A. Spencer, P. Deloukas, U. Mrowietz, S. Schreiber, S. Weidinger, S. Koks, K. Kingo, T. Esko, A. Metspalu, H.W. Lim, J.J. Voorhees, M. Weichenthal, H.E. Wichmann, V. Chandran, C.F. Rosen, P. Rahman, D.D. Gladman, C.E.M. Griffiths, A. Reis, J. Kere, R.P. Nair, A. Franke, J.N.W.N. Barker, G.R. Abecasis, J.T. Elder, R.C. Trembath, K.C. Duffin, C. Helms, D. Goldgar, Y. Li, J. Paschall, M.J. Malloy, C.R. Pullinger, J.P. Kane, J. Gardner, A. Perlmutter, A. Miner, B.J. Feng, R. Hiremagalore, R.W. Ike, E. Christophers, T. Henseler, A. Ruether, S.J. Schrodi, S. Prahalad, S.L. Guthery, J. Fischer, W. Liao, P. Kwok, A. Menter, G.M. Lathrop, C. Wise, A.B. Begovich, A. Onoufriadis, M.E. Weale, A. Hofer, W. Salmhofer, P. Wolf, K. Kainu, U. Saarialho-Kere, S. Suomela, P. Badorf, U. Huffmeier, W. Kurrat, W. Kuster, J. Lascorz, R. Mossner, F. Schurmeier-Horst, M. Stander, H. Traupe, J.G.M. Bergboer, M. den Heijer, P.C.V. van de Kerkhof, P.L.J.M. Zeeuwen, L. Barnes, L.E. Campbell, C. Cusack, C. Coleman, J. Conroy, S. Ennis, O. Fitzgerald, P. Gallagher, A.D. Irvine, B. Kirby, T. Markham,

E

T

[20] L. Norlen, I. Nicander, A. Lundsjo, T. Cronholm, B. Forslind, A new HPLC-based method for the quantitative analysis of inner stratum corneum lipids with special reference to the free fatty acid fraction, Arch. Dermatol. Res. 290 (1998) 508–516. [21] D.B. Fenske, J.L. Thewalt, M. Bloom, N. Kitson, Models of stratum corneum intercellular membranes: 2H NMR of macroscopically oriented multilayers, Biophys. J. 67 (1994) 1562–1573. [22] A. Percot, M. Lafleur, Direct observation of domains in model stratum corneum lipid mixtures by Raman microspectroscopy, Biophys. J. 81 (2001) 2144–2153. [23] P.W. Wertz, D.T. Downing, Epidermal lipids, in: L.A. Goldsmith (Ed.), Physiology, Biochemistry and Molecular Biology of the Skin, Oxford University Press, New York, 1991, pp. 205–238. [24] P.W. Wertz, D.C. Swartzendruber, K.C. Madison, D.T. Downing, Composition and morphology of epidermal cyst lipids, J. Investig. Dermatol. 89 (1987) 419–425. [25] M. Ponec, A. Weerheim, P. Lankhorst, P. Wertz, New acylceramide in native and reconstructed epidermis, J. Invest. Dermatol. 120 (2003) 581–588. [26] G.M. Gray, R.J. White, Glycosphingolipids and ceramides in human and pig epidermis, J. Invest. Dermatol. 70 (1978) 336–341. [27] P.W. Wertz, M.C. Miethke, S.A. Long, J.S. Strauss, D.T. Downing, The composition of the ceramides from human stratum corneum and from comedones, J. Invest. Dermatol. 84 (1985) 410–412. [28] S. Motta, M. Monti, S. Sesana, R. Caputo, S. Carelli, R. Ghidoni, Ceramide composition of the psoriatic scale, Biochim. Biophys. Acta 1182 (1993) 147–151. [29] K.J. Robson, M.E. Stewart, S. Michelsen, N.D. Lazo, D.T. Downing, 6-Hydroxy4-sphingenine in human epidermal ceramides, J. Lipid Res. 35 (1994) 2060–2068. [30] M.E. Stewart, D.T. Downing, A new 6-hydroxy-4-sphingenine-containing ceramide in human skin, J. Lipid Res. 40 (1999) 1434–1439. [31] Y. Masukawa, H. Narita, E. Shimizu, N. Kondo, Y. Sugai, T. Oba, R. Homma, J. Ishikawa, Y. Takagi, T. Kitahara, Y. Takema, K. Kita, Characterization of overall ceramide species in human stratum corneum, J. Lipid Res. 49 (2008) 1466–1476. [32] J. van Smeden, L. Hoppel, R. van der Heijden, T. Hankemeier, R.J. Vreeken, J.A. Bouwstra, LC/MS analysis of stratum corneum lipids: ceramide profiling and discovery, J. Lipid Res. 52 (2011) 1211–1221. [33] H. Farwanah, J. Wohlrab, R.H. Neubert, K. Raith, Profiling of human stratum corneum ceramides by means of normal phase LC/APCI-MS, Anal. Bioanal. Chem. 383 (2005) 632–637. [34] Y. Masukawa, H. Narita, H. Sato, A. Naoe, N. Kondo, Y. Sugai, T. Oba, R. Homma, J. Ishikawa, Y. Takagi, T. Kitahara, Comprehensive quantification of ceramide species in human stratum corneum, J. Lipid Res. 50 (2009) 1708–1719. [35] R. t'Kindt, L. Jorge, E. Dumont, P. Couturon, F. David, P. Sandra, K. Sandra, Profiling and characterizing skin ceramides using reversed-phase liquid chromatographyquadrupole time-of-flight mass spectrometry, Anal. Chem. 84 (2012) 403–411. [36] A.S. Breathnach, T. Goodman, C. Stolinski, M. Gross, Freeze-fracture replication of cells of stratum corneum of human epidermis, J. Anat. 114 (1973) 65–81. [37] A.S. Breathnach, Aspects of epidermal ultrastructure, J. Invest. Dermatol. 65 (1975) 2–15. [38] S. Grayson, P.M. Elias, Isolation and lipid biochemical characterization of stratum corneum membrane complexes: implications for the cutaneous permeability barrier, J. Invest. Dermatol. 78 (1982) 128–135. [39] K.C. Madison, D.C. Swartzendruber, P.W. Wertz, D.T. Downing, Presence of intact intercellular lipid lamellae in the upper layers of the stratum corneum, J. Invest. Dermatol. 88 (1987) 714–718. [40] S.Y. Hou, A.K. Mitra, S.H. White, G.K. Menon, R. Ghadially, P.M. Elias, Membrane structures in normal and essential fatty acid-deficient stratum corneum: characterization by ruthenium tetroxide staining and x-ray diffraction, J. Invest. Dermatol. 96 (1991) 215–223. [41] M. Fartasch, I.D. Bassukas, T.L. Diepgen, Disturbed extruding mechanism of lamellar bodies in dry non-eczematous skin of atopics, Br. J. Dermatol. 127 (1992) 221–227. [42] M.W. de Jager, G.S. Gooris, M. Ponec, J.A. Bouwstra, Lipid mixtures prepared with well-defined synthetic ceramides closely mimic the unique stratum corneum lipid phase behavior, J. Lipid Res. 46 (2005) 2649–2656. [43] T.J. McIntosh, M.E. Stewart, D.T. Downing, X-ray diffraction analysis of isolated skin lipids: reconstitution of intercellular lipid domains, Biochemistry 35 (1996) 3649–3653. [44] J.A. Bouwstra, G.S. Gooris, F.E. Dubbelaar, A.M. Weerheim, A.P. Ijzerman, M. Ponec, Role of ceramide 1 in the molecular organization of the stratum corneum lipids, J. Lipid Res. 39 (1998) 186–196. [45] J.A. Bouwstra, G.S. Gooris, J.A. van der Spek, W. Bras, Structural investigations of human stratum corneum by small-angle X-ray scattering, J. Invest. Dermatol. 97 (1991) 1005–1012. [46] S.H. White, D. Mirejovsky, G.I. King, Structure of lamellar lipid domains and corneocyte envelopes of murine stratum corneum. An X-ray diffraction study, Biochemistry 27 (1988) 3725–3732. [47] J.A. Bouwstra, F.E.R. Dubbelaar, G.S. Gooris, M. Ponec, The lipid organisation in the skin barrier, Acta Derm. Venereol. (2000) 23–30. [48] M. Ponec, S. Gibbs, G. Pilgram, E. Boelsma, H. Koerten, J. Bouwstra, M. Mommaas, Barrier function in reconstructed epidermis and its resemblance to native human skin, Skin Pharmacol. Appl. Skin Physiol. 14 (Suppl. 1) (2001) 63–71. [49] V.S. Thakoersing, G.S. Gooris, A. Mulder, M. Rietveld, A. El Ghalbzouri, J.A. Bouwstra, Unraveling barrier properties of three different in-house human skin equivalents, Tissue Eng. Part C Methods 18 (2012) 1–11. [50] I. Hatta, N. Ohta, K. Inoue, N. Yagi, Coexistence of two domains in intercellular lipid matrix of stratum corneum, Biochim. Biophys. Acta 1758 (2006) 1830–1836. [51] D.C. Swartzendruber, P.W. Wertz, D.J. Kitko, K.C. Madison, D.T. Downing, Molecular models of the intercellular lipid lamellae in mammalian stratum corneum, J. Invest. Dermatol. 92 (1989) 251–257.

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[86] [87]

[88]

[89]

[90]

[91] [92]

[93]

[94]

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O

[85]

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[95] S. Seidenari, G. Giusti, Objective assessment of the skin of children affected by atopic dermatitis: a study of pH, capacitance and TEWL in eczematous and clinically uninvolved skin, Acta Derm. Venereol. 75 (1995) 429–433. [96] P.M. Elias, M. Schmuth, Abnormal skin barrier in the etiopathogenesis of atopic dermatitis, Curr. Opin. Allergy Clin. Immunol. 9 (2009) 437–446. [97] C.N. Palmer, A.D. Irvine, A. Terron-Kwiatkowski, Y. Zhao, H. Liao, S.P. Lee, D.R. Goudie, A. Sandilands, L.E. Campbell, F.J. Smith, G.M. O'Regan, R.M. Watson, J.E. Cecil, S.J. Bale, J.G. Compton, J.J. DiGiovanna, P. Fleckman, S. Lewis-Jones, G. Arseculeratne, A. Sergeant, C.S. Munro, B. El Houate, K. McElreavey, L.B. Halkjaer, H. Bisgaard, S. Mukhopadhyay, W.H. McLean, Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis, Nat. Genet. 38 (2006) 441–446. [98] S.J. Brown, W.H. McLean, One remarkable molecule: filaggrin, J. Invest. Dermatol. 132 (2012) 751–762. [99] G.M. O'Regan, A.D. Irvine, The role of filaggrin loss-of-function mutations in atopic dermatitis, Curr. Opin. Allergy Clin. Immunol. 8 (2008) 406–410. [100] A.D. Irvine, W.H.I. McLean, D.Y.M. Leung, Mechanisms of disease: filaggrin mutations associated with skin and allergic diseases, N. Engl. J. Med. 365 (2011) 1315–1327. [101] I. Jakasa, E.S. Koster, F. Calkoen, W.H. McLean, L.E. Campbell, J.D. Bos, M.M. Verberk, S. Kezic, Skin barrier function in healthy subjects and patients with atopic dermatitis in relation to filaggrin loss-of-function mutations, J. Invest. Dermatol. 131 (2011) 540–542. [102] M. Akiyama, FLG mutations in ichthyosis vulgaris and atopic eczema: spectrum of mutations and population genetics, Br. J. Dermatol. 162 (2010) 472–477. [103] T. Bieber, Atopic dermatitis, N. Engl. J. Med. 358 (2008) 1483–1494. [104] A.D. Irvine, Fleshing out filaggrin phenotypes, J. Invest. Dermatol. 127 (2007) 504–507. [105] M.K. Oyoshi, R. He, L. Kumar, J. Yoon, R.S. Geha, Cellular and molecular mechanisms in atopic dermatitis, Adv. Immunol. 102 (2009) 135–226. [106] Y. Werner, M. Lindberg, B. Forslind, Membrane-coating granules in “dry” non-eczematous skin of patients with atopic dermatitis. A quantitative electron microscopic study, Acta Derm. Venereol. 67 (1987) 385–390. [107] M. Fartasch, T.L. Diepgen, The barrier function in atopic dry skin. Disturbance of membrane-coating granule exocytosis and formation of epidermal lipids? Acta Derm. Venereol. Suppl. (Stockh) 176 (1992) 26–31. [108] G. Imokawa, A. Abe, K. Jin, Y. Higaki, M. Kawashima, A. Hidano, Decreased level of ceramides in stratum corneum of atopic dermatitis: an etiologic factor in atopic dry skin? J. Invest. Dermatol. 96 (1991) 523–526. [109] M. Janssens, J. van Smeden, G. Puppels, A. Lavrijsen, P. Caspers, J.A. Bouwstra, Lipid to Protein Ratio Plays an Important Role in the Skin Barrier Function of Atopic Eczema Patients, 2013. (submitted for publication). [110] J. Ishikawa, H. Narita, N. Kondo, M. Hotta, Y. Takagi, Y. Masukawa, T. Kitahara, Y. Takema, S. Koyano, S. Yamazaki, A. Hatamochi, Changes in the ceramide profile of atopic dermatitis patients, J. Invest. Dermatol. 130 (2010) 2511–2514. [111] A. Yamamoto, S. Serizawa, M. Ito, Y. Sato, Stratum corneum lipid abnormalities in atopic dermatitis, Arch. Dermatol. Res. 283 (1991) 219–223. [112] I. Angelova-Fischer, A.C. Mannheimer, A. Hinder, A. Ruether, A. Franke, R.H. Neubert, T.W. Fischer, D. Zillikens, Distinct barrier integrity phenotypes in filaggrin-related atopic eczema following sequential tape stripping and lipid profiling, Exp. Dermatol. 20 (2011) 351–356. [113] O. Bleck, D. Abeck, J. Ring, U. Hoppe, J.P. Vietzke, R. Wolber, O. Brandt, V. Schreiner, Two ceramide subfractions detectable in Cer(AS) position by HPTLC in skin surface lipids of non-lesional skin of atopic eczema, J. Invest. Dermatol. 113 (1999) 894–900. [114] A. Sandilands, A. Terron-Kwiatkowski, P.R. Hull, G.M. O'Regan, T.H. Clayton, R.M. Watson, T. Carrick, A.T. Evans, H. Liao, Y. Zhao, L.E. Campbell, M. Schmuth, R. Gruber, A.R. Janecke, P.M. Elias, M.A. van Steensel, I. Nagtzaam, M. van Geel, P.M. Steijlen, C.S. Munro, D.G. Bradley, C.N. Palmer, F.J. Smith, W.H. McLean, A.D. Irvine, Comprehensive analysis of the gene encoding filaggrin uncovers prevalent and rare mutations in ichthyosis vulgaris and atopic eczema, Nat. Genet. 39 (2007) 650–654. [115] J.M. Jungersted, H. Scheer, M. Mempel, H. Baurecht, L. Cifuentes, J.K. Hogh, L.I. Hellgren, G.B. Jemec, T. Agner, S. Weidinger, Stratum corneum lipids, skin barrier function and filaggrin mutations in patients with atopic eczema, Allergy 65 (2010) 911–918. [116] M. Janssens, J. van Smeden, G.S. Gooris, W. Bras, G. Portale, P.J. Caspers, R.J. Vreeken, T. Hankemeier, S. Kezic, R. Wolterbeek, A.P. Lavrijsen, J.A. Bouwstra, Increase in short-chain ceramides correlates with an altered lipid organization and decreased barrier function in atopic eczema patients, J. Lipid Res. 53 (2012) 2755–2766. [117] J. Arikawa, M. Ishibashi, M. Kawashima, Y. Takagi, Y. Ichikawa, G. Imokawa, Decreased levels of sphingosine, a natural antimicrobial agent, may be associated with vulnerability of the stratum corneum from patients with atopic dermatitis to colonization by Staphylococcus aureus, J. Invest. Dermatol. 119 (2002) 433–439. [118] R. Gruber, P.M. Elias, D. Crumrine, T.K. Lin, J.M. Brandner, J.P. Hachem, R.B. Presland, P. Fleckman, A.R. Janecke, A. Sandilands, W.H. McLean, P.O. Fritsch, M. Mildner, E. Tschachler, M. Schmuth, Filaggrin genotype in ichthyosis vulgaris predicts abnormalities in epidermal structure and function, Am. J. Pathol. 178 (2011) 2252–2263. [119] A.M. Perusquia-Ortiz, V. Oji, M.C. Sauerland, T. Tarinski, I. Zaraeva, N. Seller, D. Metze, K. Aufenvenne, I. Hausser, H. Traupe, Complete filaggrin deficiency in ichthyosis vulgaris is associated with only moderate changes in epidermal permeability barrier function profile, J. Eur. Acad. Dermatol. Venereol. (2013). [120] J. van Smeden, M. Janssens, E. Kaye, P. Caspers, A. Lavrijsen, R. Vreeken, J. Bouwstra, The Importance of Free Fatty Acid Chain Length for the Skin Barrier Function in Atopic Eczema Patients, 2013. (submitted for publication).

T

[75]

C

[74]

W.H.I. McLean, J. McPartlin, S.F. Rogers, A.W. Ryan, A. Zawirska, E. Giardina, T. Lepre, C. Perricone, G. Martin-Ezquerra, R.M. Pujol, E. Riveira-Munoz, A. Inerot, A.T. Naluai, L. Mallbris, K. Wolk, J. Leman, A. Barton, R.B. Warren, H.S. Young, I. Ricano-Ponce, G. Trynka, F.J. Pellett, A. Henschel, M. Aurand, B. Bebo, C. Gieger, T. Illig, S. Moebus, K.H. Jockel, R. Erbe, P. Donnelly, L. Peltonen, J.M. Blackwell, E. Bramon, M.A. Brown, J.P. Casas, A. Corvin, N. Craddock, A. Duncanson, J. Jankowski, H.S. Markus, C.G. Mathew, M.I. McCarthy, C.N.A. Palmer, R. Plomin, A. Rautanen, S.J. Sawcer, N. Samani, A.C. Viswanathan, N.W. Wood, C. Bellenguez, C. Freeman, G. Hellenthal, E. Giannoulatou, M. Pirinen, Z. Su, S.E. Hunt, R. Gwilliam, S.J. Bumpstead, S. Dronov, M. Gillman, E. Gray, N. Hammond, A. Jayakumar, O.T. McCann, J. Liddle, M.L. Perez, S.C. Potter, R. Ravindrarajah, M. Ricketts, M. Waller, P. Weston, S. Widaa, P. Whittaker, C.A.S. Psoriasi, G.A.P. Consortium, P.A.G. Extension, W.T.C.C. Consor, Identification of 15 new psoriasis susceptibility loci highlights the role of innate immunity, Nat. Genet. 44 (2012) 1341–1348. X.J. Zhang, W. Huang, S. Yang, L.D. Sun, F.Y. Zhang, Q.X. Zhu, F.R. Zhang, C. Zhang, W.H. Du, X.M. Pu, H. Li, F.L. Xiao, Z.X. Wang, Y. Cui, F. Hao, J. Zheng, X.Q. Yang, H. Cheng, C.D. He, X.M. Liu, L.M. Xu, H.F. Zheng, S.M. Zhang, J.Z. Zhang, H.Y. Wang, Y.L. Cheng, B.H. Ji, Q.Y. Fang, Y.Z. Li, F.S. Zhou, J.W. Han, C. Quan, B. Chen, J.L. Liu, D. Li, L. Fan, A.P. Zhang, S.X. Liu, C.J. Yang, P.G. Wang, W.M. Zhou, G.S. Lin, W.D. Wu, X. Fan, M. Gao, B.Q. Yang, W.S. Lu, Z. Zhang, K.J. Zhu, S.K. Shen, M. Li, X.Y. Zhang, T.T. Cao, W. Ren, X. Zhang, J. He, X.F. Tang, S. Lu, J.Q. Yang, L. Zhang, D.N. Wang, F. Yuan, X.Y. Yin, H.J. Huang, H.F. Wang, X.Y. Lin, J.J. Liu, Psoriasis genome-wide association study identifies susceptibility variants within LCE gene cluster at 1q21, Nat. Genet. 41 (2009) 205–210. L. Puig, A. Julia, S. Marsal, The pathogenesis and genetics of psoriasis, Actas Dermosifiliogr. (2013). S. Motta, M. Monti, S. Sesana, L. Mellesi, R. Ghidoni, R. Caputo, Abnormality of water barrier function in psoriasis. Role of ceramide fractions, Arch. Dermatol. 130 (1994) 452–456. H. Farwanah, K. Raith, R.H. Neubert, J. Wohlrab, Ceramide profiles of the uninvolved skin in atopic dermatitis and psoriasis are comparable to those of healthy skin, Arch. Dermatol. Res. 296 (2005) 514–521. S.L. Greene, S.A. Muller, Netherton's syndrome. Report of a case and review of the literature, J. Am. Acad. Dermatol. 13 (1985) 329–337. E. Bitoun, S. Chavanas, A.D. Irvine, L. Lonie, C. Bodemer, M. Paradisi, D. Hamel-Teillac, S. Ansai, Y. Mitsuhashi, A. Taieb, Y. de Prost, G. Zambruno, J.I. Harper, A. Hovnanian, Netherton syndrome: disease expression and spectrum of SPINK5 mutations in 21 families, J. Invest. Dermatol. 118 (2002) 352–361. M. Fartasch, M.L. Williams, P.M. Elias, Altered lamellar body secretion and stratum corneum membrane structure in Netherton syndrome: differentiation from other infantile erythrodermas and pathogenic implications, Arch. Dermatol. 135 (1999) 823–832. J.P. Hachem, F. Wagberg, M. Schmuth, D. Crumrine, W. Lissens, A. Jayakumar, E. Houben, T.M. Mauro, G. Leonardsson, M. Brattsand, T. Egelrud, D. Roseeuw, G.L. Clayman, K.R. Feingold, M.L. Williams, P.M. Elias, Serine protease activity and residual LEKTI expression determine phenotype in Netherton syndrome, J. Invest. Dermatol. 126 (2006) 1609–1621. C. Bonnart, C. Deraison, M. Lacroix, Y. Uchida, C. Besson, A. Robin, A. Briot, M. Gonthier, L. Lamant, P. Dubus, B. Monsarrat, A. Hovnanian, Elastase 2 is expressed in human and mouse epidermis and impairs skin barrier function in Netherton syndrome through filaggrin and lipid misprocessing, J. Clin. Invest. 120 (2010) 871–882. I. Hausser, I. Anton-Lamprecht, Severe congenital generalized exfoliative erythroderma in newborns and infants: a possible sign of Netherton syndrome, Pediatr. Dermatol. 13 (1996) 183–199. J. van Smeden, M. Janssens, W. Boiten, R. Vreeken, S. Hovnanian, J. Bouwstra, Skin Barrier Lipid Composition and Organization in Netherton Syndrome Patients, 2013. (accepted for publication). M.J. Cork, D.A. Robinson, Y. Vasilopoulos, A. Ferguson, M. Moustafa, A. MacGowan, G.W. Duff, S.J. Ward, R. Tazi-Ahnini, New perspectives on epidermal barrier dysfunction in atopic dermatitis: gene-environment interactions, J. Allergy Clin. Immunol. 118 (2006) 3–21(quiz 22–23). D.Y. Leung, T. Bieber, Atopic dermatitis, Lancet 361 (2003) 151–160. S. Alanne, M. Nermes, R. Soderlund, K. Laitinen, Quality of life in infants with atopic dermatitis and healthy infants: a follow-up from birth to 24 months, Acta Paediatr. 100 (2011) e65–70. H. Mozaffari, Z. Pourpak, S. Pourseyed, A. Farhoodi, A. Aghamohammadi, M. Movahadi, M. Gharaghozloo, M. Moin, Quality of life in atopic dermatitis patients, J. Microbiol. Immunol. Infect. 40 (2007) 260–264. M.J. Slattery, M.J. Essex, E.M. Paletz, E.R. Vanness, M. Infante, G.M. Rogers, J.E. Gern, Depression, anxiety, and dermatologic quality of life in adolescents with atopic dermatitis, J. Allergy Clin. Immunol. 128 (2011) 668–671(e663). R.W. van Valburg, M.G. Willemsen, P.C. Dirven-Meijer, A.P. Oranje, J.C. van der Wouden, H. Moed, Quality of life measurement and its relationship to disease severity in children with atopic dermatitis in general practice, Acta Derm. Venereol. 91 (2011) 147–151. H. Williams, C. Flohr, How epidemiology has challenged 3 prevailing concepts about atopic dermatitis, J. Allergy Clin. Immunol. 118 (2006) 209–213. A. Di Nardo, P. Wertz, A. Giannetti, S. Seidenari, Ceramide and cholesterol composition of the skin of patients with atopic dermatitis, Acta Derm. Venereol. 78 (1998) 27–30. T. Yoshiike, Y. Aikawa, J. Sindhvananda, H. Suto, K. Nishimura, T. Kawamoto, H. Ogawa, Skin barrier defect in atopic dermatitis: increased permeability of the stratum corneum using dimethyl sulfoxide and theophylline, J. Dermatol. Sci. 5 (1993) 92–96. Y. Werner, M. Lindberg, Transepidermal water loss in dry and clinically normal skin in patients with atopic dermatitis, Acta Derm. Venereol. 65 (1985) 102–105.

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[147] M. Demerjian, D.A. Crumrine, L.M. Milstone, M.L. Williams, P.M. Elias, Barrier dysfunction and pathogenesis of neutral lipid storage disease with ichthyosis (Chanarin–Dorfman syndrome), J. Invest. Dermatol. 126 (2006) 2032–2038. [148] N. Goto-Inoue, T. Hayasaka, N. Zaima, K. Nakajima, W.M. Holleran, S. Sano, Y. Uchida, M. Setou, Imaging mass spectrometry visualizes ceramides and the pathogenesis of Dorfman–Chanarin syndrome due to ceramide metabolic abnormality in the skin, PLoS One 7 (2012) e49519. [149] Y.B. Liou, M.T. Sheu, D.Z. Liu, S.Y. Lin, H.O. Ho, Quantitation of ceramides in nude mouse skin by normal-phase liquid chromatography and atmospheric pressure chemical ionization mass spectrometry, Anal. Biochem. 401 (2010) 107–113. [150] T. Doering, H. Brade, K. Sandhoff, Sphingolipid metabolism during epidermal barrier development in mice, J. Lipid Res. 43 (2002) 1727–1733. [151] J. Reichelt, T. Doering, E. Schnetz, M. Fartasch, K. Sandhoff, A.M. Magin, Normal ultrastructure, but altered stratum corneum lipid and protein composition in a mouse model for epidermolytic hyperkeratosis, J. Invest. Dermatol. 113 (1999) 329–334. [152] J.A. Bouwstra, G.S. Gooris, J.A. van der Spek, S. Lavrijsen, W. Bras, The lipid and protein structure of mouse stratum corneum: a wide and small angle diffraction study, Biochim. Biophys. Acta 1212 (1994) 183–192. [153] B.A. van den Bergh, J.A. Bouwstra, H.E. Junginger, P.W. Wertz, Elasticity of vesicles affects hairless mouse skin structure and permeability, J. Control. Release 62 (1999) 367–379. [154] J.P. Hachem, M.Q. Man, D. Crumrine, Y. Uchida, B.E. Brown, V. Rogiers, D. Roseeuw, K.R. Feingold, P.M. Elias, Sustained serine proteases activity by prolonged increase in pH leads to degradation of lipid processing enzymes and profound alterations of barrier function and stratum corneum integrity, J. Invest. Dermatol. 125 (2005) 510–520. [155] J.P. Hachem, D. Crumrine, J. Fluhr, B.E. Brown, K.R. Feingold, P.M. Elias, pH directly regulates epidermal permeability barrier homeostasis, and stratum corneum integrity/cohesion, J. Invest. Dermatol. 121 (2003) 345–353. [156] J.P. Hachem, T. Roelandt, N. Schurer, X. Pu, J. Fluhr, C. Giddelo, M.Q. Man, D. Crumrine, D. Roseeuw, K.R. Feingold, T. Mauro, P.M. Elias, Acute acidification of stratum corneum membrane domains using polyhydroxyl acids improves lipid processing and inhibits degradation of corneodesmosomes, J. Invest. Dermatol. 130 (2010) 500–510. [157] Y.H. Park, W.H. Jang, J.A. Seo, M. Park, T.R. Lee, D.K. Kim, K.M. Lim, Decrease of ceramides with very long-chain fatty acids and downregulation of elongases in a murine atopic dermatitis model, J. Invest. Dermatol. 132 (2012) 476–479. [158] R. Jennemann, M. Rabionet, K. Gorgas, S. Epstein, A. Dalpke, U. Rothermel, A. Bayerle, F. van der Hoeven, S. Imgrund, J. Kirsch, W. Nickel, K. Willecke, H. Riezman, H.J. Grone, R. Sandhoff, Loss of ceramide synthase 3 causes lethal skin barrier disruption, Hum. Mol. Genet. 21 (2012) 586–608. [159] T. Sassa, Y. Ohno, S. Suzuki, T. Nomura, C. Nishioka, T. Kashiwagi, T. Hirayama, M. Akiyama, R. Taguchi, H. Shimizu, S. Itohara, A. Kihara, Impaired epidermal permeability barrier in mice lacking elovl1, the gene responsible for very-long-chain fatty acid production, Mol. Cell. Biol. 33 (2013) 2787–2796. [160] N. Loiseau, Y. Obata, S. Moradian, H. Sano, S. Yoshino, K. Aburai, K. Takayama, K. Sakamoto, W.M. Holleran, P.M. Elias, Y. Uchida, Altered sphingoid base profiles predict compromised membrane structure and permeability in atopic dermatitis, J. Dermatol. Sci. (2013). [161] D. Kessner, A. Ruettinger, M.A. Kiselev, S. Wartewig, R.H.H. Neubert, Properties of ceramides and their impact on the stratum corneum structure: a review — part 2: stratum corneum lipid model systems, Skin Pharmacol. Physiol. 21 (2008) 58–74. [162] J.A. Bouwstra, G.S. Gooris, K. Cheng, A. Weerheim, W. Bras, M. Ponec, Phase behavior of isolated skin lipids, J. Lipid Res. 37 (1996) 999–1011. [163] D. Groen, D.S. Poole, G.S. Gooris, J.A. Bouwstra, Is an orthorhombic lateral packing and a proper lamellar organization important for the skin barrier function? Biochim. Biophys. Acta 1808 (2011) 1529–1537. [164] D. de Sousa Neto, G. Gooris, J. Bouwstra, Effect of the omega-acylceramides on the lipid organization of stratum corneum model membranes evaluated by X-ray diffraction and FTIR studies (Part I), Chem. Phys. Lipids 164 (2011) 184–195. [165] M. de Jager, W. Groenink, J. van der Spek, C. Janmaat, G. Gooris, M. Ponec, J. Bouwstra, Preparation and characterization of a stratum corneum substitute for in vitro percutaneous penetration studies, Biochim. Biophys. Acta 1758 (2006) 636–644. [166] M. de Jager, W. Groenink, R. Bielsa i Guivernau, E. Andersson, N. Angelova, M. Ponec, J. Bouwstra, A novel in vitro percutaneous penetration model: evaluation of barrier properties with p-aminobenzoic acid and two of its derivatives, Pharm. Res. 23 (2006) 951–960. [167] T. Mauro, in: P.M. Elias, K.R. Feingold (Eds.), Skin barrier, Taylor & Francis, New York, 2006, pp. 223–229. [168] K.R. Feingold, The outer frontier: the importance of lipid metabolism in the skin, J. Lipid Res. 50 (2009) S417–S422(Suppl.). [169] A. Kihara, Very long-chain fatty acids: elongation, physiology and related disorders, J. Biochem. 152 (2012) 387–395. [170] D. Staumont-Salle, G. Abboud, C. Brenuchon, A. Kanda, T. Roumier, C. Lavogiez, S. Fleury, P. Remy, J.P. Papin, J. Bertrand-Michel, F. Terce, B. Staels, E. Delaporte, M. Capron, D. Dombrowicz, Peroxisome proliferator-activated receptor alpha regulates skin inflammation and humoral response in atopic dermatitis, J. Allergy Clin. Immunol. 121 (2008) 962–968(e966). [171] M.O. Danso, V. van Drongelen, M. A.A., J. van Esch, H. Scott, J. van Smeden, A. El Ghalbzouri, J.A. Bouwstra, TNF-alpha and TH-2 cytokines Induce Atopic Dermatitis Like Features on Protein and Lipid Level in Human Skin Equivalents, 2013. (submitted for publication). [172] B. Melnik, J. Hollmann, U. Hofmann, M.S. Yuh, G. Plewig, Lipid composition of outer stratum corneum and nails in atopic and control subjects, Arch. Dermatol. Res. 282 (1990) 549–551.

E

T

[121] O. Macheleidt, H.W. Kaiser, K. Sandhoff, Deficiency of epidermal protein-bound omega-hydroxyceramides in atopic dermatitis, J. Invest. Dermatol. 119 (2002) 166–173. [122] Y. Ohno, S. Suto, M. Yamanaka, Y. Mizutani, S. Mitsutake, Y. Igarashi, T. Sassa, A. Kihara, ELOVL1 production of C24 acyl-CoAs is linked to C24 sphingolipid synthesis, Proc. Natl. Acad. Sci. U. S. A. 107 (2010) 18439–18444. [123] Y. Uchida, The role of fatty acid elongation in epidermal structure and function, Dermato-Endocrinology 3 (2011) 65–69. [124] M. Janssens, J. van Smeden, G.S. Gooris, W. Bras, G. Portale, P.J. Caspers, R.J. Vreeken, S. Kezic, A.P. Lavrijsen, J.A. Bouwstra, Lamellar lipid organization and ceramide composition in the stratum corneum of patients with atopic eczema, J. Invest. Dermatol. 131 (2011) 2136–2138. [125] V. Schreiner, G.S. Gooris, S. Pfeiffer, G. Lanzendorfer, H. Wenck, W. Diembeck, E. Proksch, J. Bouwstra, Barrier characteristics of different human skin types investigated with X-ray diffraction, lipid analysis, and electron microscopy imaging, J. Invest. Dermatol. 114 (2000) 654–660. [126] V.S. Thakoersing, J. van Smeden, A.A. Mulder, R.J. Vreeken, A. El Ghalbzouri, J.A. Bouwstra, Increased presence of monounsaturated fatty acids in the stratum corneum of human skin equivalents, J. Invest. Dermatol. 133 (2013) 59–67. [127] M. Janssens, J. van Smeden, G. Puppels, A. Lavrijsen, P. Caspers, J. Bouwstra, Lipid to Protein Ratio Plays an Important Role in the Skin Barrier Function of Patients With Atopic Eczema, 2013. (submitted for publication). [128] W.M. Holleran, Y. Takagi, G.K. Menon, G. Legler, K.R. Feingold, P.M. Elias, Processing of epidermal glucosylceramides is required for optimal mammalian cutaneous permeability barrier function, J. Clin. Invest. 91 (1993) 1656–1664. [129] Y. Uchida, M. Hara, H. Nishio, E. Sidransky, S. Inoue, F. Otsuka, A. Suzuki, P.M. Elias, W.M. Holleran, S. Hamanaka, Epidermal sphingomyelins are precursors for selected stratum corneum ceramides, J. Lipid Res. 41 (2000) 2071–2082. [130] S. Hamanaka, M. Hara, H. Nishio, F. Otsuka, A. Suzuki, Y. Uchida, Human epidermal glucosylceramides are major precursors of stratum corneum ceramides, J. Invest. Dermatol. 119 (2002) 416–423. [131] J.M. Jensen, R. Folster-Holst, A. Baranowsky, M. Schunck, S. Winoto-Morbach, C. Neumann, S. Schutze, E. Proksch, Impaired sphingomyelinase activity and epidermal differentiation in atopic dermatitis, J. Invest. Dermatol. 122 (2004) 1423–1431. [132] M. Ishibashi, J. Arikawa, R. Okamoto, M. Kawashima, Y. Takagi, K. Ohguchi, G. Imokawa, Abnormal expression of the novel epidermal enzyme, glucosylceramide deacylase, and the accumulation of its enzymatic reaction product, glucosylsphingosine, in the skin of patients with atopic dermatitis, Lab. Invest. 83 (2003) 397–408. [133] K. Jin, Y. Higaki, Y. Takagi, K. Higuchi, Y. Yada, M. Kawashima, G. Imokawa, Analysis of beta-glucocerebrosidase and ceramidase activities in atopic and aged dry skin, Acta Derm. Venereol. 74 (1994) 337–340. [134] S. Kusuda, M. Takahashi, K. Ahisu, T. T., Human epidermal sphingomyelinase is decreased in the skin of the aged and atopic dermatitis patients, J. Investig. Dermatol. 101 (1993) 431. [135] Y. Murata, J. Ogata, Y. Higaki, M. Kawashima, Y. Yada, K. Higuchi, T. Tsuchiya, S. Kawainami, G. Imokawa, Abnormal expression of sphingomyelin acylase in atopic dermatitis: an etiologic factor for ceramide deficiency? J. Invest. Dermatol. 106 (1996) 1242–1249. [136] W.M. Holleran, E.I. Ginns, G.K. Menon, J.U. Grundmann, M. Fartasch, C.E. McKinney, P.M. Elias, E. Sidransky, Consequences of beta-glucocerebrosidase deficiency in epidermis. Ultrastructure and permeability barrier alterations in Gaucher disease, J. Clin. Invest. 93 (1994) 1756–1764. [137] B.E. Rosenbloom, N.J. Weinreb, Gaucher disease: a comprehensive review, Crit. Rev. Oncog. 18 (2013) 163–175. [138] M. Schmuth, M.Q. Man, F. Weber, W. Gao, K.R. Feingold, P. Fritsch, P.M. Elias, W.M. Holleran, Permeability barrier disorder in Niemann–Pick disease: sphingomyelinceramide processing required for normal barrier homeostasis, J. Invest. Dermatol. 115 (2000) 459–466. [139] J. Hara, K. Higuchi, R. Okamoto, M. Kawashima, G. Imokawa, High-expression of sphingomyelin deacylase is an important determinant of ceramide deficiency leading to barrier disruption in atopic dermatitis, J. Investig. Dermatol. 115 (2000) 8. [140] R. Okamoto, J. Arikawa, M. Ishibashi, M. Kawashima, Y. Takagi, G. Imokawa, Sphingosylphosphorylcholine is upregulated in the stratum corneum of patients with atopic dermatitis, J. Lipid Res. 44 (2003) 93–102. [141] G. Imokawa, A possible mechanism underlying the ceramide deficiency in atopic dermatitis: expression of a deacylase enzyme that cleaves the N-acyl linkage of sphingomyelin and glucosylceramide, J. Dermatol. Sci. 55 (2009) 1–9. [142] M.J. Choi, H.I. Maibach, Role of ceramides in barrier function of healthy and diseased skin, Am. J. Clin. Dermatol. 6 (2005) 215–223. [143] V. Vasireddy, Y. Uchida, N. Salem, S.Y. Kim, M.N.A. Mandal, G.B. Reddy, R. Bodepudi, N.L. Alderson, J.C. Brown, H. Hama, A. Dlugosz, P.M. Elias, W.M. Holleran, R. Ayyagari, Loss of functional ELOVL4 depletes very long-chain fatty acids (N= C28) and the unique omega-O-acylceramides in skin leading to neonatal death, Hum. Mol. Genet. 16 (2007) 471–482. [144] P.M. Elias, M. Schmuth, Abnormal skin barrier in the etiopathogenesis of atopic dermatitis, Curr. Opin. Allergy Clin. Immunol. 9 (2009) 437–446. [145] P.M. Elias, M.L. Williams, W.M. Holleran, Y.J. Jiang, M. Schmuth, Pathogenesis of permeability barrier abnormalities in the ichthyoses: inherited disorders of lipid metabolism, J. Lipid Res. 49 (2008) 697–714. [146] Y. Uchida, Y. Cho, S. Moradian, J. Kim, K. Nakajima, D. Crumrine, K. Park, M. Ujihara, M. Akiyama, H. Shimizu, W.M. Holleran, S. Sano, P.M. Elias, Neutral lipid storage leads to acylceramide deficiency, likely contributing to the pathogenesis of Dorfman–Chanarin syndrome, J. Invest. Dermatol. 130 (2010) 2497–2499.

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Please cite this article as: J. van Smeden, et al., The important role of stratum corneum lipids for the cutaneous barrier function, Biochim. Biophys. Acta (2013), http://dx.doi.org/10.1016/j.bbalip.2013.11.006

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