COMMENTARY
papilloma growth within 3 weeks. When transgenic mouse skin was transplanted to non-transgenic littermates, papillomas began to grow across the transplant surfaces (Figure 1). In contrast, no papillomas developed when the recipient mice were immunized successfully with an HPV8-E6DNA vaccine before transplantation. This is, at best, a long-term perspective for humans, but work in this area is worth every effort in view of the great skin cancer burden observed in allograft recipients who are immunosuppressed. CONFLICT OF INTEREST
The author states no conflict of interest.
See related article on pg 1303
Itch, Eosinophils, and Autoimmunity: A Novel Murine Model of Bullous Pemphigoid Kim B. Yancey1 Mice carrying a deletion in the NC14A domain of murine type XVII collagen begin scratching at age 2 months and then develop erosions, subepidermal vesicles, eosinophil-rich skin infiltrates, and autoantibodies directed against a 180 kDa skin protein that appears to be type XVII collagen. These mice represent a bullous pemphigoid animal model featuring pruritus in immunocompetent, mature, and largely unmanipulated animals. Journal of Investigative Dermatology (2015) 135, 1213–1215; doi:10.1038/jid.2014.537
REFERENCES Casabonne D, Michael KM, Waterboer T et al. (2007) A prospective pilot study of antibodies against human papillomaviruses and cutaneous squamous cell carcinoma nested in the Oxford component of the European Prospective Investigation into Cancer and Nutrition. Int J Cancer 121:1862–8 Euvrard S, Kanitakis J, Claudy A (2003) Skin cancers after organ transplantation. N Engl J Med 348:1681–91 Genders RE, Mazlom A, Michel A et al. (2015) The Presence of betapapillomavirus antibodies around transplantation predicts the development of keratinocyte carcinoma in organ transplant recipients: a cohort study. J Invest Dermatol 135:1275–82 Marcuzzi GP, Awerkiew S, Hufbauer M et al. (2014) Tumor prevention in HPV8 transgenic mice by HPV8-E6 DNA vaccination. Med Microbiol Immunol 203:155–63 Neale RE, Weissenborn S, Abeni D et al. (2013) Human papillomavirus load in eyebrow hair follicles and risk of cutaneous squamous cell carcinoma. Cancer Epidemiol Biomarkers Prev 22:719–27 Pfister H (2003) Human papillomavirus and skin cancer. J Natl Cancer Inst Monogr 31:52–6 Proby CM, Harwood CA, Neale RE et al. (2011) A case-control study of betapapillomavirus infection and cutaneous squamous cell carcinoma in organ transplant recipients. Am J Transplant 11:1498–508 Vajdic CM, McDonald SP, McCredie MRE et al. (2006) Cancer incidence before and after kidney transplantation. JAMA 296: 2823–31 Weissenborn S, Neale RE, Waterboer T et al. (2012) Beta-papillomavirus DNA loads in hair follicles of immunocompetent people and organ transplant recipients. Med Microbiol Immunol 201:117–25 Weissenborn SJ, De Koning MN, Wieland U et al. (2009) Intrafamilial transmission and familyspecific spectra of cutaneous betapapillomaviruses. J Virol 83:811–6
Type XVII collagen
Type XVII collagen (also called bullous pemphigoid antigen 2 ;BPAG2) is a type II transmembrane protein associated with hemidesmosome-anchoring filament complexes and plasma membranes in basal keratinocytes (Franzke et al., 2005). The cytoplasmic amino terminus of type XVII collagen consists of B500 amino acid residues, containing several potential phosphorylation sites within its central portion; by rotary shadowing, the intracytoplasmic domain of type XVII collagen appears as a globular head. The extracellular domain of type XVII collagen contains 15 interrupted collagenous segments (coll 1–15); by rotary shadowing, the extracellular domain of type XVII collagen appears as a central rod (corresponding to coll 15) with a flexible tail (corresponding to coll 1–14) (Hirako et al., 1996). Immunoelectron microscopy studies suggest that the rod portion of type XVII collagen’s ectodomain (i.e., coll 15) inserts into the lamina densa and that its carboxyterminal flexible tail then loops back through the lamina densa into the lamina lucida (Nonaka et al., 2000).
Type XVII collagen occurs in two forms, a 180 kDa full-length protein and a 120 kDa extracellular domain that is shed from plasma membranes of basal keratinocytes by proteolysis (Schacke et al., 1998). Proteolytic processing of type XVII collagen is mediated by ‘‘sheddases’’ of the disintegrin and metalloproteinase family. Phosphorylation of type XVII collagen by ecto-casein kinase 2 inhibits its proteolysis, a mechanism whereby the adhesion and motility of adjacent basal keratinocytes may be modulated (Zimina et al., 2007). In epidermal basement membranes (BMs), the extracellular domain of type XVII collagen is found as a homotrimer in which its collagenous domains form a cross-linked triple helix. The helix forms independently of amino acid sequences in its intracellular portion, apparently organized in a 50 to 30 orientation using the 16th non-collagenous portion of the protein (the 16th non- collagenous domain of BPAG2 (NC16)) as a nucleation site. The cytoplasmic domain of type XVII collagen associates with BPAG1, integrin b4, and plectin. The first extracellular segment of type XVII collagen (i.e.,
1
Department of Dermatology, University of Texas Southwestern Medical Center in Dallas, Dallas, Texas, USA Correspondence: Kim B. Yancey, Department of Dermatology NL8.116D, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9069, USA. E-mail: [email protected] Abbreviations: BPAG2, bullous pemphigoid antigen 2; BM, basement membrane; NC16, the 16th non collagenous domain of BPAG2; BP, bullous pemphigoid
www.jidonline.org 1213
COMMENTARY
Clinical Implications
At 2 to 3 months of age, mice carrying a deletion of the NC14A region of murine type XVII collagen (i.e., the murine homolog of human type XVII collagen’s NC16A (the 16th non-collagenous domain of BPAG2) domain) develop scratching, subepidermal vesicles, eosinophil-rich skin infiltrates, eosinophilia, elevated serum IgE levels, and IgG (and IgA) anti-basement membrane (BM) autoantibodies directed against a 180 kDa protein in wildtype skin that appears to be type XVII collagen.
DNC14A mice appear to represent a mouse model of bullous pemphigoid, featuring a primary, disease-related symptom (i.e., pruritus) in immunocompetent, mature animals that have not been subjected to passive transfer of large amounts of exogenous Ig or repeated bouts of immunization.
Future studies in DNC14A mice may elucidate the basis of this loss of selftolerance to an epidermal BM autoantigen, as well the development of pruritus, eosinophil-rich skin infiltrates, eosinophilia, and elevated serum IgE levels that resemble those seen in patients with bullous pemphigoid.
NC16) contains amino acid residues that bind integrin a6. Immunogold electron microscopy studies have suggested that the carboxy terminus of type XVII collagen interacts with laminin 332 at the interface of these two proteins near the junction of the lamina lucida and the lamina densa. Type XVII collagen is targeted by autoantibodies from patients with bullous pemphigoid (BP), pemphigoid gestationis (PG), mucous membrane pemphigoid (MMP), and linear IgA bullous dermatosis (LABD; Yancey and Egan, 2000). Autoantibodies from patients with BP, PG, and LABD typically target the NC16A domain of the protein, whereas those from patients with MMP tend to target its distal carboxy terminus, as well as NC16A. Patients with non-Herlitz junctional epidermolysis bullosa often possess null mutations in the gene encoding type XVII collagen (COL17A1). These individuals characteristically demonstrate a complete lack of type XVII collagen in their epidermal BM along with a tendency for skin fragility, subepidermal blister formation, alopecia, dystrophic nails, and dental enamel hypoplasia. Experimental animal models of bullous pemphigoid
BP is a polymorphic autoimmune subepidermal blistering disease that dominates in the elderly (Yancey and Egan, 2000). Although initial lesions may consist of urticarial plaques,
most patients eventually develop tense blisters on the trunk, groin, axillae, and flexor surfaces. Pruritus may be minimal or severe in patients with BP; it may precede the onset of blister formation by considerable periods of time. Biopsies of early lesional skin from patients with BP typically demonstrate subepidermal vesicles and/or bullae in association with an eosinophil-rich infiltrate within and adjacent to the epidermal BM. Direct immunofluorescence microscopy of normal-appearing perilesional skin from BP patients shows in situ deposits of IgG and C3 in the epidermal BM. Most BP patients are seropositive for IgG autoantibodies directed against two hemidesmosome-associated proteins in epidermal BM, BPAG1 and BPAG2 (i.e., type XVII collagen) (Yancey, 2005). Autoantibodies against type XVII collagen (and in particular its NC16A domain) are thought to have a key primary role in the pathophysiology of BP. Passive transfer of patient-derived or experimental IgG against human NC16A or its murine homolog elicits clinical, histologic, and immunopathologic alterations in neonatal humanized or neonatal BALB/c mice, respectively, that mimic those seen in patients with BP (Liu et al., 1993; Nishie et al., 2007). IgG-induced blister formation in these animal models is dependent upon complement activation, degranulation of dermal mast cells, and generation of neutrophil-rich infiltrates—the latter
1214 Journal of Investigative Dermatology (2015), Volume 135
providing sufficient amounts of unrestrained neutrophil elastase to degrade type XVII collagen and produce subepidermal blisters in vivo (Yancey, 2005). These and other thoroughly characterized experimental murine models are widely regarded to provide proof of concept that IgG anti-NC16A autoantibodies in patients with BP are pathogenic (reviewed extensively in Hurskainen et al. (2015)). To gain insight into the multiple functions of human type XVII collagen’s NC16A domain, Hurskainen et al. (2015) created genetically modified mice carrying a deletion of the corresponding NC14A region of murine type XVII collagen (DNC14A mice; Hurskainen et al., 2015). Interestingly, although these mice displayed no gross phenotypic changes at birth and grew normally, at 2 to 3 months of age they developed scratching, crusted erosions, subepidermal vesicles, eosinophil-rich skin infiltrates, eosinophilia, elevated serum IgE levels, and IgG (and IgA) anti-BM autoantibodies directed against a 180 kDa protein in wild-type (WT) skin that appears to be type XVII collagen. Hurskainen et al. (2015) suggest that DNC14A mice represent a BP-related mouse model featuring a primary, disease-related symptom (i.e., pruritus) in immunocompetent, mature animals that have not been subjected to passive transfer of large amounts of exogenous Ig or repeated bouts of immunization. Moreover, they point out that future studies in DNC14A mice may elucidate the basis for loss of self-tolerance to an epidermal BM autoantigen, as well the development of pruritus, eosinophil-rich skin infiltrates, eosinophilia, and elevated serum IgE levels like those seen in patients with BP. Additional considerations
Although the results by Hurskainen et al. (2015) are credible and exciting, several observations and questions about DNC14A mice are of additional interest. For example, 1. Why is the amount of type XVII collagen in DNC14A mice about half that seen in WT skin, and why does the relative amount differ so much in various mice?
COMMENTARY
2. Why is the shed ectodomain of type XVII collagen detectable in skin extracts of DNC14A mice? 3. Given that newborn DNC14A mice display subepidermal microblisters and rudimentary, malformed hemidesmosomes, why are levels of other adhesion proteins in the epidermal BM not notably reduced (especially when anchoring fibrils in DNC14A skin are short, disorganized, and abnormally clustered)? 4. What contributes to the onset of itch in DNC14A mice? Why does itch take several months to develop? Is itch related to humoral immunity (autoimmunity) and, if so, how? 5. Why do roughly 20% of DNC14A mice fail to develop scratching? Does this finding somehow relate to relative amounts of type XVII collagen in the skin? 6. What role does repeated injury (i.e., scratching) have in loss of self-tolerance to the skin? 7. What can be learned from the socalled healthy skin of adult DNC14A mice (i.e., the skin remote from sites scratched—the skin said not to differ from WT skin)? 8. About 70% of DNC14A ‘‘scratching mice’’ tested showed the presence of circulating IgG anti-BM autoantibodies against WT skin. Does the development and degree (i.e., titer) of seropositivity in this model correlate with the relative amounts of type XVII collagen in the skin, the degree of scratching displayed, or something else? 9. Why is murine type XVII collagen (rather than one or more other structural proteins in epidermal BM) the target of autoimmunity in this model? What epitopes within type XVII collagen are targeted? Why do such autoantibodies fail to elicit complement deposition in epidermal BM? 10. What mediators elicit elevated levels of eosinophils and IgE in the skin and sera of DNC14A ‘‘scratching mice’’?
in the epidermal BM (e.g., skin containing type XVII collagen that is not natively trimerized, processed, or appropriately bound to adjacent structural proteins). Indeed, one might suggest that the last thing imaginable is that deletion of the murine homolog of the immunodominant portion of type XVII collagen results in loss of tolerance to ‘‘modified self’’ and development of a novel murine model of BP. Such is the beauty of DNC14A mice and science itself—good questions about fundamental biological processes often yield unexpected insights and opportunities. CONFLICT OF INTEREST
The author states no conflict of interest.
REFERENCES Franzke CW, Bruckner P, Bruckner-Tuderman L (2005) Collagenous transmembrane proteins: recent insights into biology and pathology. J Biol Chem 280:4005–8 Hirako Y, Usukura J, Nishizawa Y et al. (1996) Demonstration of the molecular shape of BP180, a 180-kDa bullous pemphigoid antigen and its potential for trimer formation. J Biol Chem 271:13739–45
Hurskainen T, Kokkonen N, Sormunen R et al. (2015) Deletion of the major bullous pemphigoid epitope region of collagen XVII induces blistering, autoimmunization and itching in mice. J Invest Dermatol 135:1303–10 Liu Z, Diaz LA, Troy JL et al. (1993) A passive transfer model of the organ-specific autoimmune disease, bullous pemphigoid, using antibodies generated against the hemidesmosomal antigen, BP180. J Clin Invest 92:2480–8 Nishie W, Sawamura D, Goto M et al. (2007) Humanization of autoantigen. Nat Med 13:378–83 Nonaka S, Ishiko A, Masunaga T et al. (2000) The extracellular domain of BPAG2 has a loop structure in the carboxy terminal flexible tail in vivo. J Invest Dermatol 115:889–92 Schacke H, Schumann H, Hammami-Hauasli N et al. (1998) Two forms of collagen XVII in keratinocytes. A full-length transmembrane protein and a soluble ectodomain. J Biol Chem 273:25937–43 Yancey KB (2005) The pathophysiology of autoimmune blistering diseases. J Clin Invest 115:825–8 Yancey KB, Egan CA (2000) Pemphigoid: clinical, histologic, immunopathologic, and therapeutic considerations. JAMA 284:350–6 Zimina EP, Fritsch A, Schermer B et al. (2007) Extracellular phosphorylation of collagen XVII by ecto-casein kinase 2 inhibits ectodomain shedding. J Biol Chem 282:22737–46
See related article on pg 1348
Autophagy as a Melanocytic Self-Defense Mechanism Vijayasaradhi Setaluri1 Defects in autophagy have implications for melanocyte survival and manifestations of skin pigmentary disorders. Zhang et al. (2015) show that mouse melanocytes lacking the autophagy protein Atg7 undergo premature senescence in vitro and accumulate products of oxidative damage, despite activation of the redox response. Interestingly, contrary to previous findings, the melanocytespecific deficiency in autophagy did not cause major defects in melanosome biogenesis, nor did it produce visually striking changes in mouse coat color. Journal of Investigative Dermatology (2015) 135, 1215–1217; doi:10.1038/jid.2015.19
In this study, to test the role of autophagy in melanocytes, Zhang et al. (2015) deleted Atg7 specifically in
melanocytes using floxed- Atg7 and Tyr::Cre mice. Autophagy, often thought to be activated in response to cellular
Conclusion
Deletion of the NC14A domain of type XVII collagen would be predicted to yield mice with skin fragility as a consequence of impaired type XVII collagen
1
Department of Dermatology, University of Wisconsin-Madison, Madison, Wisconsin, USA
Correspondence: Vijayasaradhi Setaluri, Department of Dermatology, University of Wisconsin-Madison, Room 439, MSC, 1300 University Avenue, Madison, Wisconsin 53706, USA. E-mail: [email protected]
www.jidonline.org 1215
papilloma growth within 3 weeks. When transgenic mouse skin was transplanted to non-transgenic littermates, papillomas began to grow across the transplant surfaces (Figure 1). In contrast, no papillomas developed when the recipient mice were immunized successfully with an HPV8-E6DNA vaccine before transplantation. This is, at best, a long-term perspective for humans, but work in this area is worth every effort in view of the great skin cancer burden observed in allograft recipients who are immunosuppressed. CONFLICT OF INTEREST
The author states no conflict of interest.
See related article on pg 1303
Itch, Eosinophils, and Autoimmunity: A Novel Murine Model of Bullous Pemphigoid Kim B. Yancey1 Mice carrying a deletion in the NC14A domain of murine type XVII collagen begin scratching at age 2 months and then develop erosions, subepidermal vesicles, eosinophil-rich skin infiltrates, and autoantibodies directed against a 180 kDa skin protein that appears to be type XVII collagen. These mice represent a bullous pemphigoid animal model featuring pruritus in immunocompetent, mature, and largely unmanipulated animals. Journal of Investigative Dermatology (2015) 135, 1213–1215; doi:10.1038/jid.2014.537
REFERENCES Casabonne D, Michael KM, Waterboer T et al. (2007) A prospective pilot study of antibodies against human papillomaviruses and cutaneous squamous cell carcinoma nested in the Oxford component of the European Prospective Investigation into Cancer and Nutrition. Int J Cancer 121:1862–8 Euvrard S, Kanitakis J, Claudy A (2003) Skin cancers after organ transplantation. N Engl J Med 348:1681–91 Genders RE, Mazlom A, Michel A et al. (2015) The Presence of betapapillomavirus antibodies around transplantation predicts the development of keratinocyte carcinoma in organ transplant recipients: a cohort study. J Invest Dermatol 135:1275–82 Marcuzzi GP, Awerkiew S, Hufbauer M et al. (2014) Tumor prevention in HPV8 transgenic mice by HPV8-E6 DNA vaccination. Med Microbiol Immunol 203:155–63 Neale RE, Weissenborn S, Abeni D et al. (2013) Human papillomavirus load in eyebrow hair follicles and risk of cutaneous squamous cell carcinoma. Cancer Epidemiol Biomarkers Prev 22:719–27 Pfister H (2003) Human papillomavirus and skin cancer. J Natl Cancer Inst Monogr 31:52–6 Proby CM, Harwood CA, Neale RE et al. (2011) A case-control study of betapapillomavirus infection and cutaneous squamous cell carcinoma in organ transplant recipients. Am J Transplant 11:1498–508 Vajdic CM, McDonald SP, McCredie MRE et al. (2006) Cancer incidence before and after kidney transplantation. JAMA 296: 2823–31 Weissenborn S, Neale RE, Waterboer T et al. (2012) Beta-papillomavirus DNA loads in hair follicles of immunocompetent people and organ transplant recipients. Med Microbiol Immunol 201:117–25 Weissenborn SJ, De Koning MN, Wieland U et al. (2009) Intrafamilial transmission and familyspecific spectra of cutaneous betapapillomaviruses. J Virol 83:811–6
Type XVII collagen
Type XVII collagen (also called bullous pemphigoid antigen 2 ;BPAG2) is a type II transmembrane protein associated with hemidesmosome-anchoring filament complexes and plasma membranes in basal keratinocytes (Franzke et al., 2005). The cytoplasmic amino terminus of type XVII collagen consists of B500 amino acid residues, containing several potential phosphorylation sites within its central portion; by rotary shadowing, the intracytoplasmic domain of type XVII collagen appears as a globular head. The extracellular domain of type XVII collagen contains 15 interrupted collagenous segments (coll 1–15); by rotary shadowing, the extracellular domain of type XVII collagen appears as a central rod (corresponding to coll 15) with a flexible tail (corresponding to coll 1–14) (Hirako et al., 1996). Immunoelectron microscopy studies suggest that the rod portion of type XVII collagen’s ectodomain (i.e., coll 15) inserts into the lamina densa and that its carboxyterminal flexible tail then loops back through the lamina densa into the lamina lucida (Nonaka et al., 2000).
Type XVII collagen occurs in two forms, a 180 kDa full-length protein and a 120 kDa extracellular domain that is shed from plasma membranes of basal keratinocytes by proteolysis (Schacke et al., 1998). Proteolytic processing of type XVII collagen is mediated by ‘‘sheddases’’ of the disintegrin and metalloproteinase family. Phosphorylation of type XVII collagen by ecto-casein kinase 2 inhibits its proteolysis, a mechanism whereby the adhesion and motility of adjacent basal keratinocytes may be modulated (Zimina et al., 2007). In epidermal basement membranes (BMs), the extracellular domain of type XVII collagen is found as a homotrimer in which its collagenous domains form a cross-linked triple helix. The helix forms independently of amino acid sequences in its intracellular portion, apparently organized in a 50 to 30 orientation using the 16th non-collagenous portion of the protein (the 16th non- collagenous domain of BPAG2 (NC16)) as a nucleation site. The cytoplasmic domain of type XVII collagen associates with BPAG1, integrin b4, and plectin. The first extracellular segment of type XVII collagen (i.e.,
1
Department of Dermatology, University of Texas Southwestern Medical Center in Dallas, Dallas, Texas, USA Correspondence: Kim B. Yancey, Department of Dermatology NL8.116D, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9069, USA. E-mail: [email protected] Abbreviations: BPAG2, bullous pemphigoid antigen 2; BM, basement membrane; NC16, the 16th non collagenous domain of BPAG2; BP, bullous pemphigoid
www.jidonline.org 1213
COMMENTARY
Clinical Implications
At 2 to 3 months of age, mice carrying a deletion of the NC14A region of murine type XVII collagen (i.e., the murine homolog of human type XVII collagen’s NC16A (the 16th non-collagenous domain of BPAG2) domain) develop scratching, subepidermal vesicles, eosinophil-rich skin infiltrates, eosinophilia, elevated serum IgE levels, and IgG (and IgA) anti-basement membrane (BM) autoantibodies directed against a 180 kDa protein in wildtype skin that appears to be type XVII collagen.
DNC14A mice appear to represent a mouse model of bullous pemphigoid, featuring a primary, disease-related symptom (i.e., pruritus) in immunocompetent, mature animals that have not been subjected to passive transfer of large amounts of exogenous Ig or repeated bouts of immunization.
Future studies in DNC14A mice may elucidate the basis of this loss of selftolerance to an epidermal BM autoantigen, as well the development of pruritus, eosinophil-rich skin infiltrates, eosinophilia, and elevated serum IgE levels that resemble those seen in patients with bullous pemphigoid.
NC16) contains amino acid residues that bind integrin a6. Immunogold electron microscopy studies have suggested that the carboxy terminus of type XVII collagen interacts with laminin 332 at the interface of these two proteins near the junction of the lamina lucida and the lamina densa. Type XVII collagen is targeted by autoantibodies from patients with bullous pemphigoid (BP), pemphigoid gestationis (PG), mucous membrane pemphigoid (MMP), and linear IgA bullous dermatosis (LABD; Yancey and Egan, 2000). Autoantibodies from patients with BP, PG, and LABD typically target the NC16A domain of the protein, whereas those from patients with MMP tend to target its distal carboxy terminus, as well as NC16A. Patients with non-Herlitz junctional epidermolysis bullosa often possess null mutations in the gene encoding type XVII collagen (COL17A1). These individuals characteristically demonstrate a complete lack of type XVII collagen in their epidermal BM along with a tendency for skin fragility, subepidermal blister formation, alopecia, dystrophic nails, and dental enamel hypoplasia. Experimental animal models of bullous pemphigoid
BP is a polymorphic autoimmune subepidermal blistering disease that dominates in the elderly (Yancey and Egan, 2000). Although initial lesions may consist of urticarial plaques,
most patients eventually develop tense blisters on the trunk, groin, axillae, and flexor surfaces. Pruritus may be minimal or severe in patients with BP; it may precede the onset of blister formation by considerable periods of time. Biopsies of early lesional skin from patients with BP typically demonstrate subepidermal vesicles and/or bullae in association with an eosinophil-rich infiltrate within and adjacent to the epidermal BM. Direct immunofluorescence microscopy of normal-appearing perilesional skin from BP patients shows in situ deposits of IgG and C3 in the epidermal BM. Most BP patients are seropositive for IgG autoantibodies directed against two hemidesmosome-associated proteins in epidermal BM, BPAG1 and BPAG2 (i.e., type XVII collagen) (Yancey, 2005). Autoantibodies against type XVII collagen (and in particular its NC16A domain) are thought to have a key primary role in the pathophysiology of BP. Passive transfer of patient-derived or experimental IgG against human NC16A or its murine homolog elicits clinical, histologic, and immunopathologic alterations in neonatal humanized or neonatal BALB/c mice, respectively, that mimic those seen in patients with BP (Liu et al., 1993; Nishie et al., 2007). IgG-induced blister formation in these animal models is dependent upon complement activation, degranulation of dermal mast cells, and generation of neutrophil-rich infiltrates—the latter
1214 Journal of Investigative Dermatology (2015), Volume 135
providing sufficient amounts of unrestrained neutrophil elastase to degrade type XVII collagen and produce subepidermal blisters in vivo (Yancey, 2005). These and other thoroughly characterized experimental murine models are widely regarded to provide proof of concept that IgG anti-NC16A autoantibodies in patients with BP are pathogenic (reviewed extensively in Hurskainen et al. (2015)). To gain insight into the multiple functions of human type XVII collagen’s NC16A domain, Hurskainen et al. (2015) created genetically modified mice carrying a deletion of the corresponding NC14A region of murine type XVII collagen (DNC14A mice; Hurskainen et al., 2015). Interestingly, although these mice displayed no gross phenotypic changes at birth and grew normally, at 2 to 3 months of age they developed scratching, crusted erosions, subepidermal vesicles, eosinophil-rich skin infiltrates, eosinophilia, elevated serum IgE levels, and IgG (and IgA) anti-BM autoantibodies directed against a 180 kDa protein in wild-type (WT) skin that appears to be type XVII collagen. Hurskainen et al. (2015) suggest that DNC14A mice represent a BP-related mouse model featuring a primary, disease-related symptom (i.e., pruritus) in immunocompetent, mature animals that have not been subjected to passive transfer of large amounts of exogenous Ig or repeated bouts of immunization. Moreover, they point out that future studies in DNC14A mice may elucidate the basis for loss of self-tolerance to an epidermal BM autoantigen, as well the development of pruritus, eosinophil-rich skin infiltrates, eosinophilia, and elevated serum IgE levels like those seen in patients with BP. Additional considerations
Although the results by Hurskainen et al. (2015) are credible and exciting, several observations and questions about DNC14A mice are of additional interest. For example, 1. Why is the amount of type XVII collagen in DNC14A mice about half that seen in WT skin, and why does the relative amount differ so much in various mice?
COMMENTARY
2. Why is the shed ectodomain of type XVII collagen detectable in skin extracts of DNC14A mice? 3. Given that newborn DNC14A mice display subepidermal microblisters and rudimentary, malformed hemidesmosomes, why are levels of other adhesion proteins in the epidermal BM not notably reduced (especially when anchoring fibrils in DNC14A skin are short, disorganized, and abnormally clustered)? 4. What contributes to the onset of itch in DNC14A mice? Why does itch take several months to develop? Is itch related to humoral immunity (autoimmunity) and, if so, how? 5. Why do roughly 20% of DNC14A mice fail to develop scratching? Does this finding somehow relate to relative amounts of type XVII collagen in the skin? 6. What role does repeated injury (i.e., scratching) have in loss of self-tolerance to the skin? 7. What can be learned from the socalled healthy skin of adult DNC14A mice (i.e., the skin remote from sites scratched—the skin said not to differ from WT skin)? 8. About 70% of DNC14A ‘‘scratching mice’’ tested showed the presence of circulating IgG anti-BM autoantibodies against WT skin. Does the development and degree (i.e., titer) of seropositivity in this model correlate with the relative amounts of type XVII collagen in the skin, the degree of scratching displayed, or something else? 9. Why is murine type XVII collagen (rather than one or more other structural proteins in epidermal BM) the target of autoimmunity in this model? What epitopes within type XVII collagen are targeted? Why do such autoantibodies fail to elicit complement deposition in epidermal BM? 10. What mediators elicit elevated levels of eosinophils and IgE in the skin and sera of DNC14A ‘‘scratching mice’’?
in the epidermal BM (e.g., skin containing type XVII collagen that is not natively trimerized, processed, or appropriately bound to adjacent structural proteins). Indeed, one might suggest that the last thing imaginable is that deletion of the murine homolog of the immunodominant portion of type XVII collagen results in loss of tolerance to ‘‘modified self’’ and development of a novel murine model of BP. Such is the beauty of DNC14A mice and science itself—good questions about fundamental biological processes often yield unexpected insights and opportunities. CONFLICT OF INTEREST
The author states no conflict of interest.
REFERENCES Franzke CW, Bruckner P, Bruckner-Tuderman L (2005) Collagenous transmembrane proteins: recent insights into biology and pathology. J Biol Chem 280:4005–8 Hirako Y, Usukura J, Nishizawa Y et al. (1996) Demonstration of the molecular shape of BP180, a 180-kDa bullous pemphigoid antigen and its potential for trimer formation. J Biol Chem 271:13739–45
Hurskainen T, Kokkonen N, Sormunen R et al. (2015) Deletion of the major bullous pemphigoid epitope region of collagen XVII induces blistering, autoimmunization and itching in mice. J Invest Dermatol 135:1303–10 Liu Z, Diaz LA, Troy JL et al. (1993) A passive transfer model of the organ-specific autoimmune disease, bullous pemphigoid, using antibodies generated against the hemidesmosomal antigen, BP180. J Clin Invest 92:2480–8 Nishie W, Sawamura D, Goto M et al. (2007) Humanization of autoantigen. Nat Med 13:378–83 Nonaka S, Ishiko A, Masunaga T et al. (2000) The extracellular domain of BPAG2 has a loop structure in the carboxy terminal flexible tail in vivo. J Invest Dermatol 115:889–92 Schacke H, Schumann H, Hammami-Hauasli N et al. (1998) Two forms of collagen XVII in keratinocytes. A full-length transmembrane protein and a soluble ectodomain. J Biol Chem 273:25937–43 Yancey KB (2005) The pathophysiology of autoimmune blistering diseases. J Clin Invest 115:825–8 Yancey KB, Egan CA (2000) Pemphigoid: clinical, histologic, immunopathologic, and therapeutic considerations. JAMA 284:350–6 Zimina EP, Fritsch A, Schermer B et al. (2007) Extracellular phosphorylation of collagen XVII by ecto-casein kinase 2 inhibits ectodomain shedding. J Biol Chem 282:22737–46
See related article on pg 1348
Autophagy as a Melanocytic Self-Defense Mechanism Vijayasaradhi Setaluri1 Defects in autophagy have implications for melanocyte survival and manifestations of skin pigmentary disorders. Zhang et al. (2015) show that mouse melanocytes lacking the autophagy protein Atg7 undergo premature senescence in vitro and accumulate products of oxidative damage, despite activation of the redox response. Interestingly, contrary to previous findings, the melanocytespecific deficiency in autophagy did not cause major defects in melanosome biogenesis, nor did it produce visually striking changes in mouse coat color. Journal of Investigative Dermatology (2015) 135, 1215–1217; doi:10.1038/jid.2015.19
In this study, to test the role of autophagy in melanocytes, Zhang et al. (2015) deleted Atg7 specifically in
melanocytes using floxed- Atg7 and Tyr::Cre mice. Autophagy, often thought to be activated in response to cellular
Conclusion
Deletion of the NC14A domain of type XVII collagen would be predicted to yield mice with skin fragility as a consequence of impaired type XVII collagen
1
Department of Dermatology, University of Wisconsin-Madison, Madison, Wisconsin, USA
Correspondence: Vijayasaradhi Setaluri, Department of Dermatology, University of Wisconsin-Madison, Room 439, MSC, 1300 University Avenue, Madison, Wisconsin 53706, USA. E-mail: [email protected]
www.jidonline.org 1215
