Molecular biology of calcific aortic valve disease: towards new pharmacological therapies.

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Molecular biology of calcific aortic valve disease: towards new pharmacological therapies Expert Rev. Cardiovasc. Ther. 12(7), 851–862 (2014)

Patrick Mathieu*1,2, Marie-Chloe´ Boulanger1 and Rihab Bouchareb1 1 Department of Surgery, Laboratoire d’E´tudes Mole´culaires des Valvulopathies (LEMV), Groupe de Recherche en Valvulopathies (GRV), Quebec Heart and Lung Institute/ Research Center, Laval University, Quebec, Canada 2 Institut de Cardiologie et de Pneumologie de Que´bec/Quebec Heart and Lung Institute, 2725 Chemin Ste-Foy, Quebec, G1V-4G5, Canada *Author for correspondence: Tel.: +41 865 647 17 Fax: +41 865 647 07 [email protected]

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Calcific aortic valve disease (CAVD) is a chronic process leading to fibrosis and mineralization of the aortic valve. Investigations in the last several years have emphasized that key underlying molecular processes are involved in the pathogenesis of CAVD. In this regard, the processing of lipids and their retention has been underlined as an important mechanism that triggers inflammation. In turn, inflammation promotes/enhances the mineralization of valve interstitial cells, the main cellular component of the aortic valve. On the other hand, transformation of valve interstitial cells into myofibroblasts and osteoblast-like cells is determined by several signaling pathways having reciprocal cross-talks. In addition, the mineralization of the aortic valve has been shown to rely on ectonucleotidase and purinergic signaling. In this review, the authors have highlighted key molecular underpinnings of CAVD that may have significant relevance for the development of novel pharmaceutical therapies. KEYWORDS: aortic stenosis • bone morphogenetic protein • calcific aortic stenosis • calcific aortic valve disease • calcification • ectonucleotidase • lipid • Lp-PLA2 • notch • ox-LDL • TGF-b • Wnt

Calcific aortic valve disease (CAVD) is the most frequent heart valve disease, and there is so far no medical treatment to stop or alter the natural course of the disorder [1]. Progressive and pathological mineralization of leaflets are the root cause of CAVD [1]. Risk factors associated with CAVD are age, diabetes, metabolic syndrome (MetS), hypertension and dyslipidemia [2,3]. By far, the strongest risk factor for CAVD is age. In this regard, the prevalence of CAVD is 15–25% in subjects over 65 years [2]. Early in its course, the disease process starts with the mineralization of valvular tissue, which is not associated with hemodynamic consequences and is often referred at this stage as aortic sclerosis. When the mineralizing process is sufficiently severe to restrict the opening of the aortic valve, it is then referred to as aortic stenosis. However, we should highlight that aortic sclerosis and stenosis represent a continuum. In the last several years, important advances have been made and have contributed to shed light on the molecular mechanisms that drive ectopic valve mineralization. Studies have highlighted that mineralization 10.1586/14779072.2014.923756

of the aortic valve shares, to some extent, similarities with bone ossification. In explanted human aortic valves, the expression of osteogenic transcription factors and bone morphogenetic proteins (BMPs) is increased [4]. Herein, we are reviewing the latest discoveries about the pathobiology of CAVD. A special emphasis is put on signaling pathways promoting aortic valve mineralization. We have also underlined potential therapeutic implications of these novel findings. The role of lipids in CAVD Lipid infiltration of valvular tissues: role of small, dense LDL

Analyses of explanted CAVD tissues revealed that lipoproteins and oxidized lipid species are present often in the vicinity of mineralized areas [5]. In this regard, ApoB, Lp(a) and ApoA1 are found in stenotic aortic valves. Cote et al. documented that the level of oxidized LDL (ox-LDL) in mineralized aortic valves is related to inflammation [6]. Specifically, valves with higher ox-LDL content had higher densities of leukocytes and macrophages,

2014 Informa UK Ltd

ISSN 1477-9072

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Mathieu, Boulanger & Bouchareb

Lp(a)

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• Fibrocalcific remodeling • Osteogenic transition of VICs

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Figure 1. Retention of lipids and inflammation. Lp(a) and LDL infiltrate the aortic valve. A high expression of BGN and decorin forming a complex with LPL helped to retain lipoproteins, which become oxidized LDL. BGN stimulates the TLR2, expressed by VICs, and promotes the expression of phospholipid transfer protein, which binds to ApoA1 of HDL and may thus prevent the reverse cholesterol transport. Hence, ox-LDL accumulates in the aortic valve and triggers the recruitment of macrophages and the production of Lp-PLA2. Lp-PLA2 uses ox-LDL to produce the highly reactive lysophosphatidylcholine, which promotes the expression of ectonucleotidases ENPP1 and ALP. Also, the presence of ACE and chymase promotes the production of angiotensin II, which increases the fibrocalcific remodeling of the aortic valve. ACE: Angiotensin-converting enzyme; ALP: Alkaline phosphatase; BGN: Biglycan; BMP: Bone morphogenetic proteins; ENPP: Ectonucleotide pyrophosphatase/phosphodiesterase; LDL: Low-density lipoprotein; LPC: Lysophosphatidylcholine; LPL: Lipoprotein lipase; RCT: Reverse cholesterol transport; TLR: Toll-like receptor; VIC: Valve interstitial cells.

as well as increased expression of TNF-a. Moreover, circulating levels of ox-LDL are related to the remodeling score of aortic valves [6]. It is suspected that endothelial dysfunction, induced by oxidized lipid species, may promote the recruitment of inflammatory cells. On the other hand, the production of cytokines by inflammatory cells as well as by valve interstitial cells (VICs) promotes the mineralization of the aortic valve. In LDLR-/- and ApoE-/- mice, the administration of a lipid-rich diet promotes aortic valve thickening and mineralization [7,8] Hence, these data suggested that lipid-derived factors play a role in the development of CAVD (FIGURE 1). This has led to the hypothesis that lowering LDL levels with statins could prevent the progression of stenosis. However, in three successive randomized control trials, statins failed to prevent stenosis progression and to reduce valve-related events [9]. Hence, why lipid-lowering therapies did not prevent the progression of CAVD? The answer is possibly multifactorial. It has been suggested that statins were given too late in the disease process and 852

therefore could not impact the mineralizing process that was too advanced. However, a post hoc analysis of the SEAS trial, a double-blinded randomized study evaluating rosuvastatin combined with ezetimibe in CAVD, showed that regardless of the aortic stenosis severity at the entry of participants in the trial, the lipid-lowering strategy was ineffective to reduce both the progression of stenosis and valve-related events [10]. Of note, an in vitro study using porcine VICs has recently documented that simvastatin increased the expression of osteogenic markers in cells already committed to an osteoblast-like phenotype [11]. To this effect, it is worth to emphasize that VICs are a heterogeneous cell population with a high phenotypic plasticity [12]. Hence, in valves with a high content of VICs with an osteoblast phenotype, it is possible that statins enhance and sustain the osteogenic transdifferentiation of cells. Also, it should be pointed out that though statins reduce the LDL cholesterol quite remarkably, they have at best a modest effect on the size of LDL particles [13]. Patients with visceral obesity and insulin Expert Rev. Cardiovasc. Ther. 12(7), (2014)


Molecular biology of CAVD

resistance often have normal or near-normal LDL cholesterol values but have a very high proportion of small, dense LDLs, which are prone to oxidation. Mohty et al. previously documented that a high proportion of circulating small, dense LDL was associated with aortic valve accumulation of ox-LDL, inflammation and a faster hemodynamic progression rate of stenosis [14]. An often underappreciated observation is that statins may worsen insulin sensitivity. A recent post hoc analysis of the ASTRONOMER study, a randomized trial comparing rosuvastatin with a placebo in aortic stenosis, has underscored that in patients with the metabolic syndrome statins were associated with a higher resistance to insulin and a faster progression rate of stenosis [15]. Hence, though lipids play a role in CAVD, the key underlying mechanisms linking lipid-derived factors with ectopic mineralization of the aortic valve remains to be clearly determined. Lipid retention: role of PGs

In vitro, ox-LDLs promote the mineralization of VIC cultures and expression of several osteogenic markers [16]. Immunostaining studies of stenotic aortic valve have shown that ox-LDL colocalized with proteoglycans (PGs), which are interacting with lipoproteins and promote their retention [17]. Biglycan is highly expressed in CAVD, and it is thus contributing to retain lipoproteins within the aortic valve. Moreover, biglycan binds to the toll-like receptor 2 (TLR2) and triggers the expression of phospholipid transfer protein (PLTP) by VICs [17]. In turn, PLTP increases HDL binding to biglycan [18]. As such, PLTP promotes the retention and modification of HDL and may prevent its function, namely the reverse cholesterol transport. A recent work has also underlined that stimulation of TLR2 by biglycan promotes and exacerbates the mineralization of VICs [19]. Hence, a high expression of biglycan in CAVD entrains the retention of lipids while also promoting the mineralization process. Recently, Osman et al. showed that TGF-b1, which is overexpressed in CAVD, promoted the incorporation of sulfate into PGs and resulted in higher affinity of PGs for lipids [20]. Lipoprotein lipase (LPL) is also expressed in stenotic aortic valves where it colocalized with ox-LDL and decorin [21]. It has been documented that LPL interacts with decorin and LDL in promoting lipid retention [22]. Therefore, several mechanisms are in place in the aortic valve in order to promote the retention of different lipid species. In the last several years, compounds derived from xylose analogs have been shown to inhibit biosynthesis of PGs [23]. However, whether these derivatives have in vivo biological activities and could be used as a preventive mean to reduce lipid retention process has not been explored. Further research in this direction could provide important novel insights. Interaction between Lp(a) & lipoprotein-associated phospholipase A2: a novel target for CAVD?

CAVD is a complex trait disorder in which genotype–environment interactions play a crucial role. The genetic component informahealthcare.com

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involved in CAVD is still poorly understood. However, recently an important genome-wide association study has documented that a gene variant of LPA (rs10455872) encoding for Lp(a) was significantly associated with CAVD [24]. In the EPIC-Norfolk study population, the LPA gene variant rs10455872 was also significantly associated with CAVD [25]. Using data from the Copenhagen City Heart Study and the Copenhagen Population Study, Kamstrup et al. showed that in a Mandelian randomization study design including 77,680 subjects followed over 20 years, carriers of the genetic LPA variants rs10455872 and rs3798220 had elevated blood plasma levels of Lp(a), which was independently associated with the risk of developing CAVD [26]. Publishing at the same time, Mahmut et al. demonstrated that in CAVD, lipoprotein-associated phospholipase A2 (Lp-PLA2) is overexpressed in stenotic aortic valves and its level correlated with several indices of tissue remodeling [16]. Lp-PLA2 uses oxidized phospholipids, which are transported in the aortic valve by Lp(a) and LDL as a substrate and produces the highly reactive lysophosphatidylcholine (LPC). Of interest, in the latter work, the authors documented that LPC is found in mineralized aortic valves and that it promoted the mineralization of VICs through a cAMP/protein kinase A pathway. LPC induced the expression of ectonucleotidases, enzymes playing a crucial role in the control of calcification, and promoted apoptosis-mediated mineralization of VICs. During programmed cell death, membrane remnants are produced and act as nidus of nucleation for calcium and phosphate [27]. Taken together, these findings suggest that Lp(a) and Lp-PLA2 could be linked in a chain of event leading to the development of CAVD [28]. Though not yet fully investigated, it is possible that a high level of Lp(a) promotes the accumulation of ox-PLs in the aortic valves, which triggers an inflammatory response and secretion of Lp-PLA2 by macrophages. In turn, LPC generated from Lp-PLA2 could promote the mineralization of VICs. In this scheme of things, it could be relevant in future studies to evaluate strategies to lower Lp(a) and/or inhibit Lp-PLA2. Darapladib is an inhibitor of Lp-PLA2 [29]. In a recent randomized trial in patients with coronary artery disease, darapladib did not modify the cardiovascular outcomes [30]. However, it is worth to point out that, as exemplified with the statin story, we should not infer results of drugs tested in atherosclerosis to CAVD. Proper clinical randomized trials should possibly be conducted in CAVD to test Lp-PLA2 inhibitor. Also, though until recently, few drugs existed to lower Lp(a), novel therapeutic strategies are now emerging and may hold promise in the treatment of CAVD. Antisense oligonucleotides have been developed for Lp(a) and have been shown in an animal model to reduce substantially the level of Lp (a) [31]. On the other hand, novel inhibitors of proprotein convertase subtilisin/kexin type 9 have been shown to reduce Lp(a) by 25–30% [32]. Hence, further preclinical studies as well as randomized clinical trials could be conducted to 853

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evaluate different strategies targeting the Lp(a)–Lp-PLA2 axis in CAVD [28].


Is HDL playing a role in CAVD?

HDLs have anti-inflammatory properties and play a major role in allowing the reverse cholesterol transport to the liver. There is a well-known association between a low level of HDL and the cardiovascular risk [33]. However, Mendelian randomized studies suggested that HDLs may not be causally related to atherosclerosis [34]. More recently, it has been shown that HDLs are trapped in atherosclerotic aortas and are oxidized, which hamper their biological functions [35]. In CAVD, it has been demonstrated that small, dense, HDLs were associated with a higher accumulation of ox-LDL in the aortic valve [21]. In this regard, studies have documented that small, dense HDLs are less efficient and may even be proinflammatory. Also, a study showed that ApoA1 is modified into amyloid substance in mineralized aortic valves and has promineralizing activities by still an elusive mechanism [36]. But, it is suspected that amyloid depots derived from CAVD may induce mineralization of VICs by an apoptotic mechanism. A recent study has found that in patients with CAVD, cholesterol efflux mediated by ABCA1 and SR-B1 were not modified compared with control subjects [37]. However, it should be underlined that cholesterol efflux studies were performed with circulating HDLs. One important question is whether HDLs from mineralized aortic valves have similar efficacy in cholesterol efflux assay than their circulating counterparts? Although not yet thoroughly studied, it is possible that HDLs are transformed in the aortic valve and may even have a detrimental effect. In mice, the administration of an ApoA1 mimetic peptide has been shown to prevent the development of aortic valve thickening [38]. Also, in the hypercholesterolemic rabbit, a treatment with recombinant ApoA1 reversed inflammation/thickening of the aortic valve [39,40]. Hence, the role of HDL in CAVD is far from being elucidated, and further work is necessary to decipher the role of this lipoprotein in the pathogenesis of aortic valve mineralization.

shown to induce eccentric hypertrophy, which was related to the activation of the mTOR pathway [43]. It should be pointed out that TZDs have been shown to increase the retention of fluid, which could explain that in patients with compromised left ventricular function, TZDs may precipitate heart failure [44]. These side effects are of concern since patients with aortic stenosis often have concomitant left ventricular hypertrophy and left ventricular dysfunction. Hence, further preclinical work is necessary to investigate the role of PPAR-g agonists in CAVD. Oxidative stress

In stenotic aortic valves, Miller et al. showed that oxidative stress is increased, particularly in mineralized areas [45]. It was documented that in calcified regions, the expression of antioxidant enzymes such as superoxide dismutase was decreased. Moreover, the authors found that the production of superoxide anion (O2–) and hydrogen peroxide was largely the result of nitric oxide synthase (NOS) uncoupling. In physiological conditions, endothelial NOS prevents the fibrocalcific response of the aortic valve [46,47]. Uncoupling of NOS occurs when there is a deficiency of the NOS cofactor tetrahydrobiopterin or of Larginine, the enzyme substrate. Also, the presence of endogenous NOS inhibitor, such as asymmetric dimethylarginine, may participate to NOS uncoupling [48]. However, the exact mechanism by which NOS is uncoupled in mineralized aortic valves remains to be determined. A high production of reactive oxygen species in the stenotic aortic valve may contribute to the oxidative transformation of different lipid species, which in turn may promote inflammation and mineralization. Of note, a new compound that is an enhancer of endothelial NOS, Ave3085, has been shown to prevent NOS uncoupling by, among other things, increasing tetrahydrobiopterin levels. Ave3085 restored endothelial dysfunction and lowered blood pressure in spontaneously hypertensive rats [49]. Whether it would be possible to pharmacologically manipulate NOS uncoupling in CAVD remains to be investigated. Is inflammation the missing link in mediating mineralization of the aortic valve?

Peroxisome proliferator-activated receptor-g & CAVD

TNF & TNF-related apoptosis-inducing ligand

Peroxisome proliferator-activated receptor-g (PPAR-g) is a nuclear transcription factor, which regulates the expression of genes involved in glucoregulation and lipid metabolism. PPAR-g is stimulated by free fatty acids, eicosanoids and oxidized LDL [41]. Pharmacological agents, the thiazolidinedione (TZD), which include rosiglitazone and pioglitazone, are used in the treatment of Type 2 diabetes. Recently, Chu et al. showed that in LDLR-/-/ApoB100/100 mice under a western type diet, pioglitazone (20 mg/kg/day) administered for 6 months significantly reduced the lipid and mineral contents in the aortic valve [42]. Mice treated with pioglitazone had lower level of valvular apoptosis and lower expression of cytokines such as TNF-a and IL-6. However, mice treated with pioglitazone had increased left ventricular systolic and diastolic volumes, as well as a decreased ejection fraction. In rats, rosiglitazone has been

Lipid-derived factors such as ox-PLs are potent promoter of inflammation. Cote et al. showed that in 285 patients, the presence of dense inflammatory infiltrates in the aortic valve of patients operated for CAVD was associated with a higher remodeling score of the aortic valve and with a greater density of neovascularization [50]. The aortic valve is normally avascular, the presence of blood vessels in the aortic valve during CAVD may help to recruit inflammatory cells. Mice that are deficient for chondromodulin-I, an antiangiogenic factor, have increased expression of VEGF-A in aortic cusps along with neovascularization and mineralization of the aortic valve [51]. Inflammatory infiltrates predominantly comprise macrophages and a few scattered T cells. Oxidized lipid species induce the production of TNF-a by macrophages, which in turn stimulate the mineralization process. Immunohistochemistry studies in human

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stenotic aortic valves revealed that TNF-a is colocalized with matrix metalloproteinase-1 [52]. Inflammation and mechanical stress contribute to increase the expression of matrix metalloproteinase in CAVD, which in turn promote the remodeling process [53–56]. Recently, a member of the TNF superfamily, TNF-related apoptosis-inducing ligand, was found to promote the mineralization of VIC cultures [57]. TNF-related apoptosis-inducing ligand binds to the death receptor 4, which is incidentally overexpressed in stenotic aortic valves. It then follows that a downstream cascade is triggered, and apoptosis of VICs is promoted through a caspase-8 pathway. In turn, a high-level apoptosis promoted mineralization of cell cultures. Noteworthy, the IL-1 receptor antagonist knockout mice have elevated circulating levels of TNF-a and developed a thickening of the aortic valve [58]. Taken together, these findings suggest that dysregulation of TNF pathway is involved in CAVD. IL-6: a master regulator of mineralization in CAVD

One study has highlighted that IL-6, a cytokine overexpressed in CAVD, promoted endothelial to mesenchymal transition (EMT) of cells and may thus participate into the recruitment of novel mesenchymal cells in the aortic valve [59]. Whether the mesenchymal cells derived from EMT may participate in the mineralization of the aortic valve is presently unknown. It should be pointed out that the role of IL-6 into the pathobiology of CAVD was relatively unknown until recently. El Husseini et al. documented that in stenotic aortic valves, there is an activation of the nuclear factor-kB (NF-kB) pathway as exemplified by high level of phosphorylated IkB in mineralized tissues [60]. In vitro, during the mineralization of VICs phosphorylated IKK contributed to the activation of IkB, which resulted in the nuclear translocation of p65 subunit of NF-kB. As a result, mineralization of VICs, induced by phosphate, was associated with a high production of IL-6, a downstream target of p65-NF-kB. In turn, it was found that IL-6 secreted by VICs acted by auto/paracrine effect in mediating the osteogenic transition of VICs through a BMP2 pathway. In recent years, new therapeutic strategies have been developed to target cytokines by using the administration of monoclonal antibodies. As such, monoclonal antibodies targeting IL-6 have been developed for the treatment of inflammatory disorders. However, whether such a strategy would provide benefit has not yet been tested in preclinical animal models. However, the potential benefit of such an approach should be cautiously weighted against the potential side effects of these therapies. For instance, anti-IL-6 therapy is associated with a worsening of the lipid blood profile and may increase the incidence of infectious complications [61]. The renin angiotensin system

The prevalence of hypertension is elevated in patients with CAVD (~70%) and may contribute to the pathogenesis of this disorder through the renin angiotensin system (RAS) [62]. In prehypertensive patients, the blood plasma levels of informahealthcare.com

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angiotensinogen and angiotensin II are associated with the expression of IL-6 in the aortic valves [63]. In VIC cultures, angiotensin II has been shown to promote the production of TGF-b1 [64]. On the other hand, the expression of BMP2 is increased in human umbilical vein endothelial cells following a treatment with angiotensin II [65]. Taken together, these findings underline that angiotensin II could promote the fibrocalcific remodeling of the aortic valve (FIGURE 1). Observational studies conducted a decade ago suggested that inhibition of the RAS may decrease the progression of stenosis [66]. More recently, Capoulade et al. showed that in an observational prospective study, angiotensin type 1 receptor blockers (ARBs) but not angiotensin-converting enzyme (ACE) inhibitors were associated with a decrease progression rate of aortic stenosis [67]. Of interest, stenotic aortic valves of patients taking ARBs have a lower expression of IL-6 and are less remodeled [68]. In mice, the administration of angiotensin II, at a dosage that did not affect blood pressure, resulted in thickening of the aortic valve [69]. In human explanted stenotic aortic valves, immunostaining studies have documented that ACE and chymase are expressed in the aortic valve [70]. It is worth to highlight that chymase represents another pathway by which angiotensin II is produced locally in the aortic valve. Hence, considering that ACE inhibitors do not impact on chymase activity, it is possible that ARBs may be more potent to inhibit the RAS in CAVD. In the hypercholesterolemic rabbit, the administration of olmesartan, an ARB, decreased the expression of smooth muscle a-actin in the aortic valve and lowered the thickening of cusps [71]. Therefore, there is accumulating data that support the role of the RAS in CAVD. Further work evaluating the role of the RAS and its signaling cascade in CAVD is certainly needed. Moreover, considering that safety issues for ACEi and ARBs are no more of concern in patients with aortic stenosis, clinical trials are needed to address the role of these drugs in CAVD [72]. Notch, Wnt & BMP2

Garg et al. were the first to report on the importance of the Notch signaling pathway in CAVD [73]. They identified a mutation of Notch1 receptor in families with a clustering of bicuspid aortic valve (BAV) and left ventricular outflow tract malformations. The Notch pathway plays a crucial role in cell fate and is involved in the transdifferentiation of VICs into osteogenic cells. Following the binding of Notch receptors to their agonists, jagged and delta-like proteins, the g-secretase complex is activated and releases the Notch intracellular domain (NICD) that translocates to the nucleus. The NICD binds to the recombining binding protein suppressor of hairless (RBPjk), which in turn leads to the expression of the Hairy family of repressors [74]. In VICs, the Hairy repressors prevent the production of BMP2, a powerful osteogenic factor [75]. Hence, dysfunction of the Notch pathway in CAVD is conducive to osteogenic differentiation of VICs. The Notch 1-/+ and RBPjk+/- mice have trileaflets aortic valve and under a high-fat diet, it developed a thickening and mineralization of the aortic 855

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Figure 2. The role Notch and Wnt signaling in calcific aortic valve disease. The binding of Notch receptor by its agonists, jagged and DLL proteins, activates the g-secretase and liberates the NICD, which translocates to the nucleus where it controls the expression of BMP2 and Runx2. Elevated level of Wnt3a in CAVD stimulates the LRP5/6/frizzled receptor, which is next followed by the recruitment of Dsh and a complex formed by APC, Axin and GSK3B, which help to stabilize b-catenin. The transport of b-catenin to the nucleus amplifies the expression of osteoblastic genes. Crosstalk between Notch and Wnt may help to reduce the nuclear translocation of b-catenin (dotted line). Hence, a lower Notch signaling and a concomitant stimulation of Wnt pathway are conducive to the osteogenic transdifferentiation of VICs. APC: Adenomatous polyposis coli; BMP: Bone morphogenetic; CAVD: Calcific aortic valve disease; DLL: Delta-like ligand; Dsh: Dishevelled; NICD: Notch intracellular domain; VIC: Valve interstitial cells.

valve [76]. Hence, it suggests that the dysfunction of the Notch pathway is not only involved in BAV mineralization but may also play a significant role in the calcification of tricuspid aortic valves (TAV). Supporting this view, a study reported that Notch1 mutations were also associated with CAVD in patients with TAV [77]. Mineralization of the aortic valve is associated with the expression of bone-related gene markers and activation of the Lrp5/Wnt/b-catenin pathway [78,79]. The Wnt pathway is also involved in cell fate/tissue patterning and has crosstalk with the Notch signaling cascade (FIGURE 2) [80]. In mineralized aortic 856

valves, the level of Wnt3a is elevated [81]. In the canonical Wnt signaling pathway, the agonist binds to the receptor formed by Lrp5/6 and frizzled. Activation of the receptor leads to inactivation of a complex formed by adenomatous polyposis coli, Axin and glycogen synthase kinase 3. In the absence of Wnt, the adenomatous polyposis coli/Axin/glycogen synthase kinase 3 complex phosphorylates b-catenin which is next degraded by the proteasome [80]. Hence, elevated Wnt agonists promote the nuclear transclocation of b-catenin and expression of its target genes such as BMP2 [82]. In the hypercholesterolemic rabbit, mineralization of the aortic valve is associated with an elevated Expert Rev. Cardiovasc. Ther. 12(7), (2014)



expression of LRP5 and b-catenin [79]. Of interest, the ApoE-/Lrp5-/- mice on a cholesterol-rich diet developed less mineralization of the aortic valve compared with the ApoE-/- mice under the same diet [83]. Although the exact molecular mechanism remains to be determined, studies have also shown that the NICD interferes with the translocation of b-catenin and therefore may represent a significant regulator of the Wnt pathway [84]. The Notch and Wnt pathways may thus converge to promote osteoblastic transition of VICs by elevating the production of BMP2 as well as the expression of Runx2, a bone transcription factor. miRNAs & the expression of BMP2

In the last several years, noncoding RNAs such as miRNAs have emerged as important regulators of cell function. The miRNA-30b prevents BMP-2-induced expression of Runx2 and in doing so is a negative regulator of osteogenic transition in VICs [85]. Of interest, the level of miRNA-30b is decreased in mineralized aortic valves. Also, one study reported that in stenotic aortic valves the level of miRNA141 was lower in BAV tissues compared with TAV cusps [86]. Of interest, miRNA-141 has been shown to negatively regulate TGF-binduced expression of BMP2. Other noncoding RNAs act as positive regulator of BMP2 signaling. As such, miRNA-378 enhances BMP2-induced differentiation of osteoblast with a higher activity of alkaline phosphatase (ALP) [87]. However, whether miRNA-378 is involved in CAVD remains to be investigated. Hence, further research in this field is clearly needed and may identify crucial miRNAs, which could be targeted with antisense oligonucleotides. TGF-b & calcific aortic valve disease

Ectopic valve mineralization is intricately linked to fibrosis. Moreover, increasing evidence suggest that in addition to mineralization, fibrosis is playing an important role in driving aortic valve thickening. The expression of TGF-b1 is increased in mineralized aortic valves [88]. Furthermore, the downstream Smad cascade is also activated in explanted stenotic aortic valves [89]. Treatment of porcine VICs with TGF-b1 induces the activation of cells with the expression of myofibroblast markers and formation of nodules. TGF-b1-induced formation of nodule is dependent on cadherin 11, which is incidentally overexpressed in stenotic aortic valves [90]. Moreover, Chen et al. showed that TGF-b1 helps to stabilize b-catenin and may thus participate in osteogenic transdifferentiation of VICs [91]. This effect of TGF-b1 on the nuclear translocation of b-catenin was observed only on a stiffer matrix, which mimicked the biomechanical properties of the fibrosa. This finding is of interest and may explain that the mineralization of the aortic valve starts in the fibrosa layer. Recently, it has been shown that the noncanonical TGF-b1 signaling via Src and p38MAPK is promoting the activation of VICs into myofibroblast [92]. Noteworthy, in this study, the authors reported that serotonergic receptor 5-HT2B had important crosstalk with noncanonical TGF-b1 signaling. To this effect, informahealthcare.com

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antagonism of 5-HT2B led to the sequestration of phosphorylated Src and prevented TGF-b1-induced activation of VICs into myofibroblast. Hence, further work is necessary in order to determine the relationships between the serotonergic system and TGF-b1. Phosphate signaling: role of ectonucleotidases & P2Y2 receptor

Phosphate is a powerful signaling molecule and plays a crucial role in the mineralization process [93]. Blood plasma level of phosphate has been shown to be a strong and independent predictor of aortic valve mineralization [94]. Membrane-bound enzymes, the ectonucleotidases, are powerful regulator of mineralization by metabolizing secreted nucleotides into phosphate and pyrophosphate [95]. It then follows that ectonucleotidases regulate Pi/PPi levels while also controlling purinergic signaling. To this effect, a study reported that ALP, an ectonucleotidase with a wide range of substrate, is promoting the mineralization of VICs [96]. Recently, singlenucleotide polymorphisms for ectonucleotide pyrophosphatase/ phosphodiesterase 1 (ENPP1) were significantly associated with CAVD [97]. Moreover, patients with the gene variant rs9402349 had elevated levels of ENPP1 in the aortic valves. ENPP1 is using ATP as a substrate and generates PPi, a negative regulator of mineralization opposing the effect of Pi. Hence, ENPP1-/- mice developed calcification of soft tissues and tendons [98]. On the other hand, the overexpression of ENPP1 in both VICs and chondrocytes promotes a robust mineralization of cell culture [97]. ENPP1, when overexpressed may increase mineralization of the aortic valve by three mechanisms (FIGURE 3). First, PPi generated by ENPP1 is rapidly metabolized into Pi by ALP increasing the Pi/PPi ratio, which is then driving positively the mineralization of the aortic valve. In turn, Pi enters VICs by using the NaPi cotransporter Pit1, whereby Pi mediates the expression of several osteoblastic genes. It is worth to point out that the expression of Pit1 is elevated in stenotic aortic valves [99]. Second, a high level of ectonucleotidases depletes the extracellular levels of ATP, which in turn lower P2Y2 receptor (P2Y2R) signaling. P2Y2R delivers crucial survival signal in VICs through a PI3K/Akt pathway. In this regard, a transfection of Akt rescued and prevented apoptosis-mediated mineralization of VICs [99]. Thus, a low level of extracellular ATP contributes to promote apoptosis-mediated mineralization. Third, a recent report showed that Akt, which is activated in VICs through the P2Y2 receptor, acts as an important negative regulator of IKK phosphorylation upstream in the NF-kB cascade [60]. Hence, cells with a high level of ectonucleotidase had elevated secretion of IL-6, which is an important promoter of osteogenic transition through a BMP2 pathway. In a rat model, the inhibition of ectonucleotidases prevented warfarin-induced mineralization of the aortic valve [100]. Hence, further work on ectonucleotidases/purinergic signaling may help to develop novel strategies to prevent the mineralization of the aortic valve. 857

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IL-6

BMP2


Figure 3. The ectonucleotidase/purinergic receptor signaling. A high expression of ENPP1 and ALP promotes the production of phosphate and lowers the bioavailability of ATP. Pi is channeled within the cell by the sodium phosphate cotransporter Pit1/SLC20A1. Also, a decreased signaling through the P2Y2 receptor will lower PI3K/Akt signaling, which increases apoptosis and inflammation of VICs through a NF-kB pathway. ALP: Alkaline phosphatase; BMP: Bone morphogenetic proteins; ENPP: Ectonucleotide pyrophosphatase/phosphodiesterase; P2Y2R: P2Y2 receptor; VIC: Valve interstitial cell.

Conclusion

CAVD is a highly prevalent disorder in our aging societies. In the last decade, our knowledge about the mechanisms involved in aortic valve mineralization has expanded considerably. It then follows that potential novel targets have been identified. Further work on these promising targets may in a near future lead to the development of novel pharmaceutical treatment for CAVD. Meanwhile, basic and translational studies are urgently needed in order to develop new therapeutic strategies. Expert commentary

In the last decade, our knowledge of the basic mechanisms involved in CAVD has expanded considerably. New potential targets have been identified, which may open novel research avenues and therapeutic opportunities. In this regard, studies have emphasized that lipid retention and inflammation play a determinant role in triggering the mineralization of the aortic valve. Also, several works have underscored that mineralization of the aortic valve involves the ectonucleotidases and an 858

osteoblastic transdifferentiation of VICs. Hence, it is possible that by blocking key pathways involved in the control of ectopic valve mineralization, it will be possible to prevent the progression of CAVD. Five-year view

A turning point in clinical research in CAVD will be to increase the number of clinical trial for this condition. For instance, randomized trials evaluating ARBs/ACE inhibitors should be prompted by the identification of the RAS as a potential target in CAVD. Also, the recent discovery that Lp(a) and Lp-PLA2 play a role in the pathogenesis of CAVD should spur further investigations. Meanwhile, further basic and translational research are needed to identify key processes involved in the pathogenesis of CAVD. Also, the development of novel pharmaceutical compounds to target the ectonucleotidases/ purinergic receptors may hold promise, while more investigation in the field of noncoding RNAs may open novel and unsuspected therapeutic opportunities. Expert Rev. Cardiovasc. Ther. 12(7), (2014)


Financial & competing interests disclosure

The authors are supported by HSFC grant, CIHR grants MOP245048, MOP114893 and the Quebec Heart and Lung Institute Fund. P Mathieu is a research scholar from the Fonds de Recherche en Sante´ du Que´bec, Montreal, Que´bec, Canada and holds a patent application for the use of ectonucleotidases and Lp-PLA2 inhibitors in the treatment of

Review

CAVD. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. No writing assistance was utilized in the production of this manuscript.

Key issues Expert Review of Cardiovascular Therapy Downloaded from informahealthcare.com by Nyu Medical Center on 01/07/15 For personal use only.

• Calcific aortic valve disease (CAVD) is the most common heart valve disorder with a high prevalence in our aging societies. • The development of novel pharmaceutical therapies for CAVD would represent a major breakthrough. • The retention and modification of different lipid species during CAVD play an important role in promoting inflammation/mineralization of the aortic valve. • Inflammation and the production of cytokines play a role in enhancing mineralization of the aortic valve. • The renin angiotensin system promotes the remodeling of the aortic valve. • TGF-b and serotonergic system have interrelationships in promoting activation of valve interstitial cells and in triggering a profibrotic response in CAVD. • Osteogenic transdifferentiation of valve interstitial cells and the modulation of ectonucleotidases/purinergic receptors are important mechanisms involved in the mineralization of the aortic valve.

nonrheumatic stenotic aortic valves. Arterioscler Thromb Vasc Biol 1999;19(5): 1218-22

References Papers of special note have been highlighted as: • of interest •• of considerable interest 1.

Rajamannan NM, Evans FJ, Aikawa E, et al. Calcific aortic valve disease: not simply a degenerative process: a review and agenda for research from the National Heart and Lung and Blood Institute Aortic Stenosis Working Group. Executive summary: calcific aortic valve disease-2011 update. Circulation 2011; 124(16):1783-91

2.

Stewart BF, Siscovick D, Lind BK, et al. Clinical factors associated with calcific aortic valve disease. Cardiovascular Health Study. J Am Coll Cardiol 1997;29(3):630-4

3.

Mathieu P, Despres JP, Pibarot P. The ’valvulo-metabolic’ risk in calcific aortic valve disease. Can J Cardiol 2007; 23(Suppl B):32B-9B

4.

Bosse Y, Miqdad A, Fournier D, et al. Refining molecular pathways leading to calcific aortic valve stenosis by studying gene expression profile of normal and calcified stenotic human aortic valves. Circ Cardiovasc Genet 2009;2(5):489-98

•

5.

Genome-wide expression array of calcific aortic valve disease (CAVD), which highlighted the complex interactions between genes of different pathways during the mineralization of the aortic valve. Olsson M, Thyberg J, Nilsson J. Presence of oxidized low density lipoprotein in


6.

Cote C, Pibarot P, Despres JP, et al. Association between circulating oxidised low-density lipoprotein and fibrocalcific remodelling of the aortic valve in aortic stenosis. Heart 2008;94(9):1175-80

pathobiology. Am J Pathol 2007;171(5): 1407-18 13.

Mathieu P, Pibarot P, Larose E, et al. Visceral obesity and the heart. Int J Biochem Cell Biol 2008;40(5):821-36

14.

Mohty D, Pibarot P, Despres JP, et al. Association between plasma LDL particle size, valvular accumulation of oxidized LDL, and inflammation in patients with aortic stenosis. Arterioscler Thromb Vasc Biol 2008;28(1):187-93

7.

Weiss RM, Ohashi M, Miller JD, et al. Calcific aortic valve stenosis in old hypercholesterolemic mice. Circulation 2006;114(19):2065-9

15.

8.

Aikawa E, Aikawa M, Libby P, et al. Arterial and aortic valve calcification abolished by elastolytic cathepsin S deficiency in chronic renal disease. Circulation 2009;119(13):1785-94

Capoulade R, Clavel MA, Dumesnil JG, et al. Impact of metabolic syndrome on progression of aortic stenosis: influence of age and statin therapy. J Am Coll Cardiol 2012;60(3):216-23

16.

9.

Teo KK, Corsi DJ, Tam JW, et al. Lipid lowering on progression of mild to moderate aortic stenosis: meta-analysis of the randomized placebo-controlled clinical trials on 2344 patients. Can J Cardiol 2011; 27(6):800-8

Mahmut A, Boulanger MC, El HD, et al. Elevated expression of lipoprotein-associated phospholipase A2 in calcific aortic valve disease: implications for valve mineralization. J Am Coll Cardiol 2014; 63(5):460-9

••

10.

Gerdts E, Rossebo AB, Pedersen TR, et al. Impact of baseline severity of aortic valve stenosis on effect of intensive lipid lowering therapy (from the SEAS study). Am J Cardiol 2010;106(11):1634-9

This study showed that lipoprotein-associated phospholipase A2 is highly expressed in the aortic valve and contributes to the mineralization process.

17.

11.

Monzack EL, Masters KS. A time course investigation of the statin paradox among valvular interstitial cell phenotypes. Am J Physiol Heart Circ Physiol 2012;303(7): H903-9

Derbali H, Bosse Y, Cote N, et al. Increased biglycan in aortic valve stenosis leads to the overexpression of phospholipid transfer protein via Toll-like receptor 2. Am J Pathol 2010;176(6):2638-45

18.

12.

Liu AC, Joag VR, Gotlieb AI. The emerging role of valve interstitial cell phenotypes in regulating heart valve

O’Brien KD, Vuletic S, McDonald TO, et al. Cell-associated and extracellular phospholipid transfer protein in human

859

Review


coronary atherosclerosis. Circulation 2003; 108(3):270-4 19.


20.

21.

22.

Song R, Zeng Q, Ao L, et al. Biglycan induces the expression of osteogenic factors in human aortic valve interstitial cells via Toll-like receptor-2. Arterioscler Thromb Vasc Biol 2012;32(11):2711-20 Osman N, Grande-Allen KJ, Ballinger ML, et al. Smad2-dependent glycosaminoglycan elongation in aortic valve interstitial cells enhances binding of LDL to proteoglycans. Cardiovasc Pathol 2013;22(2):146-55 Mahmut A, Boulanger MC, Fournier D, et al. Lipoprotein lipase in aortic valve stenosis is associated with lipid retention and remodelling. Eur J Clin Invest 2013; 43(6):570-8 Edwards IJ, Goldberg IJ, Parks JS, et al. Lipoprotein lipase enhances the interaction of low density lipoproteins with artery-derived extracellular matrix proteoglycans. J Lipid Res 1993;34(7): 1155-63

23.

Tsuzuki Y, Nguyen TK, Garud DR, et al. 4-deoxy-4-fluoro-xyloside derivatives as inhibitors of glycosaminoglycan biosynthesis. Bioorg Med Chem Lett 2010;20(24): 7269-73

24.

Thanassoulis G, Campbell CY, Owens DS, et al. Genetic associations with valvular calcification and aortic stenosis. N Engl J Med 2013;368(6):503-12

••

First genome-wide association study on CAVD, which showed the association with the LPA gene encoding for Lp(a).

25.

Arsenault BJ, Boekholdt SM, Dube MP, et al. Lipoprotein(a) levels, genotype and incident aortic valve stenosis: a prospective mendelian randomization study and replication in a case-control cohort. Circ Cardiovasc Genet 2014. [Epub ahead of print]

26.

29.

Wilensky RL, Macphee CH. Lipoprotein-associated phospholipase A2. and atherosclerosis. Curr Opin Lipidol 2009;20(5):415-20

30.

White HD, Held C, Stewart R, et al. Darapladib for preventing ischemic events in stable coronary heart disease. N Engl J Med 2014;370:1702-11

41.

Nagy L, Tontonoz P, Alvarez JG, et al. Oxidized LDL regulates macrophage gene expression through ligand activation of PPARgamma. Cell 1998;93(2):229-40

31.

Merki E, Graham M, Taleb A, et al. Antisense oligonucleotide lowers plasma levels of apolipoprotein (a) and lipoprotein (a) in transgenic mice. J Am Coll Cardiol 2011;57(15):1611-21

42.

Chu Y, Lund DD, Weiss RM, et al. Pioglitazone attenuates valvular calcification induced by hypercholesterolemia. Arterioscler Thromb Vasc Biol 2013;33(3): 523-32

32.

McKenney JM, Koren MJ, Kereiakes DJ, et al. Safety and efficacy of a monoclonal antibody to proprotein convertase subtilisin/ kexin type 9 serine protease, SAR236553/ REGN727, in patients with primary hypercholesterolemia receiving ongoing stable atorvastatin therapy. J Am Coll Cardiol 2012;59(25):2344-53

43.

Festuccia WT, Laplante M, Brule S, et al. Rosiglitazone-induced heart remodelling is associated with enhanced turnover of myofibrillar protein and mTOR activation. J Mol Cell Cardiol 2009;47(1):85-95

44.

Nissen SE, Wolski K. Effect of rosiglitazone on the risk of myocardial infarction and death from cardiovascular causes. N Engl J Med 2007;356(24):2457-71

45.

Miller JD, Chu Y, Brooks RM, et al. Dysregulation of antioxidant mechanisms contributes to increased oxidative stress in calcific aortic valvular stenosis in humans. J Am Coll Cardiol 2008;52(10): 843-50

••

This study described the uncoupling of nitric oxide synthase as one important mechanism that promotes the oxidative stress in CAVD.

46.

El Accaoui RN, Gould ST, Hajj GP, et al. Aortic valve sclerosis in mice deficient in endothelial nitric oxide synthase. Am J Physiol Heart Circ Physiol 2014;306: H1302-H13

47.

Rajamannan NM, Subramaniam M, Stock SR, et al. Atorvastatin inhibits calcification and enhances nitric oxide synthase production in the hypercholesterolaemic aortic valve. Heart 2005;91(6):806-10

48.

Li H, Forstermann U. Uncoupling of endothelial NO synthase in atherosclerosis and vascular disease. Curr Opin Pharmacol 2013;13(2):161-7

49.

Forstermann U, Li H. Therapeutic effect of enhancing endothelial nitric oxide synthase (eNOS) expression and preventing eNOS uncoupling. Br J Pharmacol 2011;164(2): 213-23

50.

Cote N, Mahmut A, Bosse Y, et al. Inflammation is associated with the remodeling of calcific aortic valve disease. Inflammation 2013;36(3):573-81

51.

Yoshioka M, Yuasa S, Matsumura K, et al. Chondromodulin-I maintains cardiac

33.

34.

35.

Arsenault BJ, Lemieux I, Despres JP, et al. HDL particle size and the risk of coronary heart disease in apparently healthy men and women: the EPIC-Norfolk prospective population study. Atherosclerosis 2009; 206(1):276-81 Holmes MV, Asselbergs FW, Palmer TM, et al. Mendelian randomization of blood lipids for coronary heart disease. Eur Heart J 2014. [Epub ahead of print] Didonato JA, Aulak K, Huang Y, et al. Site-specific nitration of apolipoprotein A-I at tyrosine 166 is both abundant within human atherosclerotic plaque and dysfunctional. J Biol Chem 2014;289(15): 10276-92

36.

Audet A, Cote N, Couture C, et al. Amyloid substance within stenotic aortic valves promotes mineralization. Histopathology 2012;61(4):610-19

37.

Arsenault BJ, Dube MP, Brodeur MR, et al. Evaluation of links between high-density lipoprotein genetics, functionality, and aortic valve stenosis risk in humans. Arterioscler Thromb Vasc Biol 2014;34(2):457-62

Kamstrup PR, Tybjaerg-Hansen A, Nordestgaard BG. Elevated lipoprotein(a) and risk of aortic valve stenosis in the general population. J Am Coll Cardiol 2014;63(5):470-7

27.

Bouchareb R, Boulanger MC, Fournier D, et al. Mechanical strain induces the production of spheroid mineralized microparticles in the aortic valve through a RhoA/ROCK-dependent mechanism. J Mol Cell Cardiol 2014;67:49-59

38.

Trapeaux J, Busseuil D, Shi Y, et al. Improvement of aortic valve stenosis by ApoA-I mimetic therapy is associated with decreased aortic root and valve remodelling in mice. Br J Pharmacol 2013;169(7): 1587-99

28.

Hung MY, Witztum JL, Tsimikas S. New Therapeutic Targets for Calcific Aortic Valve Stenosis: the Lipoprotein(a)Lipoprotein-Associated Phospholipase A2-Oxidized Phospholipid Axis. J Am Coll Cardiol 2014;63(5):478-80

39.

Busseuil D, Shi Y, Mecteau M, et al. Regression of aortic valve stenosis by ApoA-I mimetic peptide infusions in rabbits. Br J Pharmacol 2008;154(4):765-73

40.

Speidl WS, Cimmino G, Ibanez B, et al. Recombinant apolipoprotein A-I Milano

860

rapidly reverses aortic valve stenosis and decreases leaflet inflammation in an experimental rabbit model. Eur Heart J 2010;31(16):2049-57




valvular function by preventing angiogenesis. Nat Med 2006;12(10): 1151-9

63.

Cote N, Pibarot P, Pepin A, et al. Oxidized low-density lipoprotein, angiotensin II and increased waist cirumference are associated with valve inflammation in prehypertensive patients with aortic stenosis. Int J Cardiol 2010;145(3):444-9

73.

Garg V, Muth AN, Ransom JF, et al. Mutations in NOTCH1 cause aortic valve disease. Nature 2005;437(7056):270-4

••

First study to underline the role of Notch in bicuspid aortic valve and aortic valve mineralization.

74.

Guruharsha KG, Kankel MW, Artavanis-Tsakonas S. The Notch signalling system: recent insights into the complexity of a conserved pathway. Nat Rev Genet 2012;13(9):654-66

75.

Nigam V, Srivastava D. Notch1 represses osteogenic pathways in aortic valve cells. J Mol Cell Cardiol 2009;47(6):828-34

76.

O’Brien KD, Probstfield JL, Caulfield MT, et al. Angiotensin-converting enzyme inhibitors and change in aortic valve calcium. Arch Intern Med 2005;165(8): 858-62

Nus M, MacGrogan D, Martinez-Poveda B, et al. Diet-induced aortic valve disease in mice haploinsufficient for the Notch pathway effector RBPJK/CSL. Arterioscler Thromb Vasc Biol 2011;31(7):1580-8

77.

Capoulade R, Clavel MA, Mathieu P, et al. Impact of hypertension and reninangiotensin system inhibitors in aortic stenosis. Eur J Clin Invest 2013;43(12): 1262-72

Ducharme V, Guauque-Olarte S, Gaudreault N, et al. NOTCH1 genetic variants in patients with tricuspid calcific aortic valve stenosis. J Heart Valve Dis 2013;22(2):142-9

78.

Cote N, Mahmut A, Fournier D, et al. Angiotensin receptor blockers are associated with reduced fibrosis and interleukin-6 expression in calcific aortic valve disease. Pathobiology 2014;81(1):15-24

Rajamannan NM, Subramaniam M, Rickard D, et al. Human aortic valve calcification is associated with an osteoblast phenotype. Circulation 2003;107(17): 2181-4

79.

Fujisaka T, Hoshiga M, Hotchi J, et al. Angiotensin II promotes aortic valve thickening independent of elevated blood pressure in apolipoprotein-E deficient mice. Atherosclerosis 2013;226(1): 82-7

Rajamannan NM, Subramaniam M, Caira F, et al. Atorvastatin inhibits hypercholesterolemia-induced calcification in the aortic valves via the Lrp5 receptor pathway. Circulation 2005;112(9 Suppl): I229-34

80.

Komiya Y, Habas R. Wnt signal transduction pathways. Organogenesis 2008; 4(2):68-75

81.

Caira FC, Stock SR, Gleason TG, et al. Human degenerative valve disease is associated with up-regulation of low-density lipoprotein receptor-related protein 5 receptor-mediated bone formation. J Am Coll Cardiol 2006;47(8):1707-12

••

This study identified the role of LRP5/ Wnt/bcatenin in CAVD.

82.

Zhang R, Oyajobi BO, Harris SE, et al. Wnt/beta-catenin signaling activates bone morphogenetic protein 2 expression in osteoblasts. Bone 2013;52(1):145-56

83.

Rajamannan NM. The role of Lrp5/6 in cardiac valve disease: experimental hypercholesterolemia in the ApoE-/-/Lrp5-/mice. J Cell Biochem 2011;112(10): 2987-91

84.

Deregowski V, Gazzerro E, Priest L, et al. Notch 1 overexpression inhibits osteoblastogenesis by suppressing Wnt/beta-

•

This work highlighted the role of chondromulin-1 and angiogenesis in the pathobiology of CAVD.

52.

Kaden JJ, Dempfle CE, Grobholz R, et al. Inflammatory regulation of extracellular matrix remodeling in calcific aortic valve stenosis. Cardiovasc Pathol 2005;14(2): 80-7

64.

Campbell SE, Katwa LC. Angiotensin II stimulated expression of transforming growth factor-beta1 in cardiac fibroblasts and myofibroblasts. J Mol Cell Cardiol 1997;29(7):1947-58

53.

Edep ME, Shirani J, Wolf P, et al. Matrix metalloproteinase expression in nonrheumatic aortic stenosis. Cardiovasc Pathol 2000;9(5):281-6

65.

54.

Sun L, Rajamannan NM, Sucosky P. Defining the role of fluid shear stress in the expression of early signaling markers for calcific aortic valve disease. PLoS One 2013; 8(12):e84433

Zhang M, Wang J, Liu JH, et al. Effects of probucol on angiotensin II-induced BMP2 expression in human umbilical vein endothelial cells. Mol Med Rep 2013;7(1): 177-82

55.

Sun L, Chandra S, Sucosky P. Ex vivo evidence for the contribution of hemodynamic shear stress abnormalities to the early pathogenesis of calcific bicuspid aortic valve disease. PLoS One 2012;7(10): e48843

56.

Charest A, Pepin A, Shetty R, et al. Distribution of SPARC during neovascularisation of degenerative aortic stenosis. Heart 2006;92(12):1844-9

57.

Galeone A, Brunetti G, Oranger A, et al. Aortic valvular interstitial cells apoptosis and calcification are mediated by TNF-related apoptosis-inducing ligand. Int J Cardiol 2013;169(4):296-304

58.

Isoda K, Matsuki T, Kondo H, et al. Deficiency of interleukin-1 receptor antagonist induces aortic valve disease in BALB/c mice. Arterioscler Thromb Vasc Biol 2010;30(4):708-15

59.

Mahler GJ, Farrar EJ, Butcher JT. Inflammatory cytokines promote mesenchymal transformation in embryonic and adult valve endothelial cells. Arterioscler Thromb Vasc Biol 2013;33(1):121-30

60.

El Husseini D, Boulanger MC, Mahmut A, et al. P2Y2 receptor represses IL-6 expression by valve interstitial cells through Akt: implication for calcific aortic valve disease. J Mol Cell Cardiol 2014;72:146-56

61.

62.

Tanaka T, Ogata A, Narazaki M. Tocilizumab for the treatment of rheumatoid arthritis. Expert Rev Clin Immunol 2010;6(6):843-54 Cote N, Couture C, Pibarot P, et al. Angiotensin receptor blockers are associated with a lower remodelling score of stenotic aortic valves. Eur J Clin Invest 2011;41(11): 1172-9


66.

67.

68.

69.

70.

••

Review

Helske S, Lindstedt KA, Laine M, et al. Induction of local angiotensin II-producing systems in stenotic aortic valves. J Am Coll Cardiol 2004;44(9):1859-66 This study underlined that both chymase and angiotensin-converting enzyme are expressed in CAVD and promoted in the aortic valve the production of angiotensin II.

71.

Arishiro K, Hoshiga M, Negoro N, et al. Angiotensin receptor-1 blocker inhibits atherosclerotic changes and endothelial disruption of the aortic valve in hypercholesterolemic rabbits. J Am Coll Cardiol 2007;49(13):1482-9

72.

O’Brien KD, Zhao XQ, Shavelle DM, et al. Hemodynamic effects of the angiotensin-converting enzyme inhibitor, ramipril, in patients with mild to moderate aortic stenosis and preserved left ventricular function. J Investig Med 2004;52(3): 185-91

861

Review


catenin but not bone morphogenetic protein signaling. J Biol Chem 2006;281(10): 6203-10 85.


86.

87.

88.

89.

Zhang M, Liu X, Zhang X, et al. MicroRNA-30b is a multifunctional regulator of aortic valve interstitial cells. J Thorac Cardiovasc Surg 2014;147(3): 1073-80 Yanagawa B, Lovren F, Pan Y, et al. miRNA-141 is a novel regulator of BMP-2-mediated calcification in aortic stenosis. J Thorac Cardiovasc Surg 2012; 144(1):256-62 Hupkes M, Sotoca AM, Hendriks JM, et al. MicroRNA miR-378 promotes BMP2-induced osteogenic differentiation of mesenchymal progenitor cells. BMC Mol Biol 2014;15:1-15 Jian B, Narula N, Li QY, et al. Progression of aortic valve stenosis: TGF-beta1 is present in calcified aortic valve cusps and promotes aortic valve interstitial cell calcification via apoptosis. Ann Thorac Surg 2003;75(2):457-65 Ankeny RF, Thourani VH, Weiss D, et al. Preferential activation of SMAD1/5/8 on the fibrosa endothelium in calcified human aortic valves-association with low BMP antagonists and SMAD6. PLoS One 2011; 6(6):e20969

862

90.

Hutcheson JD, Chen J, Sewell-Loftin MK, et al. Cadherin-11 regulates cell-cell tension necessary for calcific nodule formation by valvular myofibroblasts. Arterioscler Thromb Vasc Biol 2013;33(1):114-20

96.

Mathieu P, Voisine P, Pepin A, et al. Calcification of human valve interstitial cells is dependent on alkaline phosphatase activity. J Heart Valve Dis 2005;14(3): 353-7

91.

Chen JH, Chen WL, Sider KL, et al. beta-catenin mediates mechanically regulated, transforming growth factor-beta1-induced myofibroblast differentiation of aortic valve interstitial cells. Arterioscler Thromb Vasc Biol 2011; 31(3):590-7

97.

Cote N, El HD, Pepin A, et al. ATP acts as a survival signal and prevents the mineralization of aortic valve. J Mol Cell Cardiol 2012;52(5):1191-202

98.

Okawa A, Nakamura I, Goto S, et al. Mutation in Npps in a mouse model of ossification of the posterior longitudinal ligament of the spine. Nat Genet 1998; 19(3):271-3

99.

El Husseini D, Boulanger MC, Fournier D, et al. High expression of the Pi-transporter SLC20A1/Pit1 in calcific aortic valve disease promotes mineralization through regulation of Akt-1. PLoS One 2013;8(1):e53393

100.

Cote N, El Husseini D, Pepin A, et al. Inhibition of ectonucleotidase with ARL67156 prevents the development of calcific aortic valve disease in warfarin-treated rats. Eur J Pharmacol 2012; 689(1-3):139-46

92.

93.

Hutcheson JD, Ryzhova LM, Setola V, et al. 5-HT(2B) antagonism arrests non-canonical TGF-beta1-induced valvular myofibroblast differentiation. J Mol Cell Cardiol 2012;53(5):707-14 Lau WL, Pai A, Moe SM, Giachelli CM. Direct effects of phosphate on vascular cell function. Adv Chronic Kidney Dis 2011; 18(2):105-12

94.

Linefsky JP, O’Brien KD, Sachs M, et al. Serum phosphate is associated with aortic valve calcification in the Multi-ethnic Study of Atherosclerosis (MESA). Atherosclerosis 2014;233(2):331-7

95.

Mathieu P. Pharmacology of ectonucleotidases: relevance for the treatment of cardiovascular disorders. Eur J Pharmacol 2012;696(1-3):1-4


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