Plasmin plays a role in the in vitro generation of the linear IgA dermatosis antigen LADB97

Matrikines in the skin: Origin, effects, and therapeutic potential

The extracellular matrix (ECM) represents a complex multi-component environment that has a decisive influence on the biomechanical properties of tissues and organs. Depending on the tissue, ECM components are subject to a homeostasis of synthesis and degradation, a subtle interplay that is influenced by external factors and the intrinsic aging process and is often disturbed in pathologies. Upon proteolytic cleavage of ECM proteins, small bioactive peptides termed matrikines can be formed. These bioactive peptides play a crucial role in cell signaling and contribute to the dynamic regulation of both physiological and pathological processes such as tissue remodeling and repair as well as inflammatory responses. In the skin, matrikines exert an influence for instance on cell adhesion, migration, and proliferation as well as vasodilation, angiogenesis and protein expression. Due to their manifold functions, matrikines represent promising leads for developing new therapeutic options for the treatment of skin diseases. This review article gives a comprehensive overview on matrikines in the skin, including their origin in the dermal ECM, their biological effects and therapeutic potential for the treatment of skin pathologies such as melanoma, chronic wounds and inflammatory skin diseases or for their use in anti-aging cosmeceuticals.

S2k guidelines on diagnosis and treatment of linear IgA dermatosis initiated by the European Academy of Dermatology and Venereology

INTRODUCTION

Linear IgA dermatosis (LAD) is a rare subepidermal autoimmune bullous disease (AIBD) defined by predominant or exclusive immune deposits of immunoglobulin A at the basement membrane zone of skin or mucous membranes. This disorder is a rare, clinically and immunologically heterogeneous disease occurring both in children and in adults. The aim of this project is to present the main clinical features of LAD, to propose a diagnostic algorithm and provide management guidelines based primarily on experts' opinion because of the lack of large methodologically sound clinical studies.

METHODS

These guidelines were initiated by the European Academy of Dermatology and Venereology (EADV) Task Force Autoimmune Bullous Diseases (AIBD). To achieve a broad consensus for these S2k consensus-based guidelines, a total of 29 experts from different countries, both European and non-European, including dermatologists, paediatric dermatologists and paediatricians were invited. All members of the guidelines committee agreed to develop consensus-based (S2k) guidelines. Prior to a first virtual consensus meeting, each of the invited authors elaborated a section of the present guidelines focusing on a selected topic, based on the relevant literature. All drafts were circulated among members of the writing group, and recommendations were discussed and voted during two hybrid consensus meetings.

RESULTS

The guidelines summarizes evidence-based and expert opinion-based recommendations (S2 level) on the diagnosis and treatment of LAD.

CONCLUSION

These guidelines will support dermatologists to improve their knowledge on the diagnosis and management of LAD.

From Molecular Insights to Clinical Perspectives in Drug-Associated Bullous Pemphigoid

Bullous pemphigoid (BP), the most common autoimmune blistering disease, is characterized by the presence of autoantibodies targeting BP180 and BP230 in the basement membrane zone. This leads to the activation of complement-dependent and independent pathways, resulting in proteolytic cleavage at the dermoepidermal junction and an eosinophilic inflammatory response. While numerous drugs have been associated with BP in the literature, causality and pathogenic mechanisms remain elusive in most cases. Dipeptidyl peptidase 4 inhibitors (DPP4i), in particular, are the most frequently reported drugs related to BP and, therefore, have been extensively investigated. They can potentially trigger BP through the impaired proteolytic degradation of BP180, combined with immune dysregulation. DPP4i-associated BP can be categorized into true drug-induced BP and drug-triggered BP, with the latter resembling classic BP. Antineoplastic immunotherapy is increasingly associated with BP, with both B and T cells involved. Other drugs, including biologics, diuretics and cardiovascular and neuropsychiatric agents, present weaker evidence and poorly understood pathogenic mechanisms. Further research is needed due to the growing incidence of BP and the increasing identification of new potential triggers.

Levels of type XVII collagen (BP180) ectodomain are elevated in circulation from patients with multiple cancer types and is prognostic for patients with metastatic colorectal cancer

BACKGROUND

Collagens are the major components of the extracellular matrix (ECM) and are known to contribute to tumor progression and metastasis. There are 28 different types of collagens each with unique functions in maintaining tissue structure and function. Type XVII collagen (BP180) is a type II transmembrane protein that provides stable adhesion between epithelial cells and the underlying basement membrane. Aberrant expression and ectodomain shedding of type XVII collagen have been associated with epithelial damage, tumor invasiveness, and metastasis in multiple tumor types and may consequently be used as a potential (non-invasive) biomarker in cancer and treatment target.

METHOD

An ELISA targeting the type XVII collagen ectodomain (PRO-C17) was developed for use in serum. PRO-C17 was measured in a cohort of patients with 11 different cancer types (n = 214) and compared to healthy controls (n = 23) (cohort 1). Based on the findings from cohort 1, PRO-C17 and its association with survival was explored in patients with metastatic colorectal cancer (mCRC) treated with bevacizumab in combination with chemotherapy (n = 212) (cohort 2).

RESULTS

PRO-C17 was robust and specific towards the ectodomain of type XVII collagen. In cohort 1, PRO-C17 levels were elevated (p < 0.05) in serum from patients with CRC, kidney, ovarian, bladder, breast, and head and neck cancer compared to healthy controls. PRO-C17 was especially good at discriminating between CRC patients and healthy controls with an AUROC of 0.904. In cohort 2, patients with mCRC and high levels (tertile 3) of PRO-C17 had shorter overall survival (OS) with a median OS of 390 days compared to 539 days for patients with low levels of PRO-C17. When evaluated by multivariate Cox regression analysis, high PRO-C17 was predictive for poor OS independent of risk factors and the tumor fibrosis biomarker PRO-C3.

CONCLUSION

PRO-C17 measures the ectodomain of type XVII collagen in serum and is a promising non-invasive biomarker that can aid in understanding tumor heterogeneity as well as elaborate on the role of collagen XVII in tumor progression. Moreover, the findings in the study proposes PRO-C17 as novel biomarker of epithelial damage in specific cancer types including CRC.

Bullous Pemphigoid Associated With Dipeptidyl Peptidase-4 Inhibitors: A Case Report and Review of Current Evidence

Dipeptidyl peptidase-4 inhibitors (DPP-4i), or gliptins, are a widely used glucose-lowering agents. A growing amount of evidence pointed to a possible role of DPP-4i in the induction of bullous pemphigoid (BP), which is an auto-immune skin blistering disease that mainly affects the elderly. In this article we discuss a case of DPP-4i associated BP and we provide an updated review of the current knowledge regarding this emerging entity. Use of DPP-4i, particularly vildagliptin, was found to significantly increase the risk of BP. BP180 would be in the center of the aberrant immune response. DPP-4i induced BP is thought to be associated with male gender, mucosal involvement, and milder inflammatory phenotype especially in Asian population. Generally, patients may not remit fully after DPP-4i withdrawal only and require either topical or systemic glucocorticoid courses.

Native autoantigen complex detects pemphigoid autoantibodies

Pemphigoid diseases are a group of autoimmune disorders characterized by subepidermal blistering in the skin and mucosa. Among them, mucous membrane pemphigoid (MMP) autoantibodies are characterized by targeting multiple molecules in the hemidesmosomes, including collagen XVII, laminin-332, and integrin a6/β4. Traditionally, recombinant proteins of the autoantigens have been employed to identify circulating autoantibodies by immune assays. However, developing an efficient detection system for MMP autoantibodies has been challenging because the autoantibodies have heterogeneous profiles and the antibody titers are typically low. In this study, we introduce an ELISA that takes advantage of a native autoantigen complex rather than simple recombinant proteins. We generated HaCaT keratinocytes with a DDDDK-tag knocked in at the COL17A1 locus by CRISPR/Cas9-mediated gene editing. Immunoprecipitation using the DDDDK-tag isolated a native complex that contained full-length and processed collagen XVII and integrin α6/β4. Then, we used the complex proteins to prepare an ELISA system and enrolled 55 MMP cases to validate its diagnostic performance. The sensitivity and specificity of the ELISA for detecting MMP autoantibodies were 70.9% and 86.7%, respectively, far superior to those of conventional assays. In autoimmune diseases such as MMP, in which autoantibodies target various molecules, isolating the antigen-protein complexes can help establish a diagnostic system.

BP180/Collagen XVII: A Molecular View

BP180 is a type II collagenous transmembrane protein and is best known as the major autoantigen in the blistering skin disease bullous pemphigoid (BP). The BP180 trimer is a central component in type I hemidesmosomes (HD), which cause the adhesion between epidermal keratinocytes and the basal lamina, but BP180 is also expressed in several non-HD locations, where its functions are poorly characterized. The immunological roles of intact and proteolytically processed BP180, relevant in BP, have been subject to intensive research, but novel functions in cell proliferation, differentiation, and aging have also recently been described. To better understand the multiple physiological functions of BP180, the focus should return to the protein itself. Here, we comprehensively review the properties of the BP180 molecule, present new data on the biochemical features of its intracellular domain, and discuss their significance with regard to BP180 folding and protein-protein interactions.

EGFR-mediated epidermal stem cell motility drives skin regeneration through COL17A1 proteolysis

Skin regenerative capacity declines with age, but the underlying mechanisms are largely unknown. Here we demonstrate a functional link between epidermal growth factor receptor (EGFR) signaling and type XVII collagen (COL17A1) proteolysis on age-associated alteration of keratinocyte stem cell dynamics in skin regeneration. Live-imaging and computer simulation experiments predicted that human keratinocyte stem cell motility is coupled with self-renewal and epidermal regeneration. Receptor tyrosine kinase array identified the age-associated decline of EGFR signaling in mouse skin wound healing. Culture experiments proved that EGFR activation drives human keratinocyte stem cell motility with increase of COL17A1 by inhibiting its proteolysis through the secretion of tissue inhibitor of metalloproteinases 1 (TIMP1). Intriguingly, COL17A1 directly regulated keratinocyte stem cell motility and collective cell migration by coordinating actin and keratin filament networks. We conclude that EGFR-COL17A1 axis-mediated keratinocyte stem cell motility drives epidermal regeneration, which provides a novel therapeutic approach for age-associated impaired skin regeneration.

Antigen Processing, Presentation, and Tolerance: Role in Autoimmune Skin Diseases

Autoreactive T cells pose a constant risk for the emergence of autoimmune skin diseases in genetically predisposed individuals carrying certain HLA risk alleles. Immune tolerance mechanisms are opposed by broad HLA-presented self-immunopeptidomes, a predefined repertoire of polyspecific TCRs, the continuous generation of new antibody specificities by somatic recombination of Ig genes in B cells, and heightened proinflammatory reactivity. Increased autoantigen presentation by HLA molecules, cross-activation of pathogen-induced T cells against autologous structures, altered metabolism of self-proteins, and excessive production of proinflammatory signals may all contribute to the breakdown of immune tolerance and the development of autoimmune skin diseases.

Risk Factors for Mucosal Involvement in Bullous Pemphigoid and the Possible Mechanism: A Review

Bullous pemphigoid (BP) is the most common type of autoimmune bullous disease and is characterized by the presence of circulating anti-BP180 and/or anti-BP230 autoantibodies. Patients with BP often present with tense blisters and erythema, mainly on the trunk and limbs, but a few patients also have mucosal involvement. In this article, we discuss the fact that BP patients with mucosal involvement tend to have more serious conditions and their disease is more difficult to control. Potential risk factors for mucous involvement include earlier age at onset, drugs such as dipeptidyl peptidase-4 inhibitors, cancer, and blood/serum biomarkers, including lower eosinophil count, higher erythrocyte sedimentation rate, IgG autoantibodies against both the NH₂- and COOH-termini of BP180, and the absence of anti-BP230 antibodies. IgA and C3 deposition at the dermo-epidermal junction may also be present. Understanding these risk factors may benefit earlier diagnosis of these patients and promote the development of novel treatments. What's more, it's helpful in deeper understanding of BP development and the relationship between BP and mucous membrane pemphigoid (MMP).

Clinical, Laboratory and Histological Features of Dipeptidyl Peptidase-4 Inhibitor Related Noninflammatory Bullous Pemphigoid

Bullous pemphigoid (BP) is an autoimmune blistering disease of elderly patients that has shown increasing incidence in the last decades. Higher prevalence of BP may be due to more frequent use of provoking agents, such as antidiabetic dipeptidyl peptidase-4 inhibitor (DPP4i) drugs. Our aim was to assess DPP4i-induced bullous pemphigoid among our BP patients and characterize the clinical, laboratory and histological features of this drug-induced disease form. In our patient cohort, out of 127 BP patients (79 females (62.2%), 48 males (37.7%)), 14 (9 females and 5 males) were treated with DPP4i at the time of BP diagnosis. The Bullous Pemphigoid Disease Area Index (BPDAI) urticaria/erythema score was significantly lower, and the BPDAI damage score was significantly higher in DPP4i-BP patients compared to the nonDPP4i group. Both the mean absolute eosinophil number and the mean periblister eosinophil number was significantly lower in DPP4i-BP patients than in nonDPP4i cases (317.7 ± 0.204 vs. 894.0 ± 1.171 cells/μL, p < 0.0001; 6.75 ± 1.72 vs. 19.09 ± 3.1, p = 0.0012, respectively). Our results provide further evidence that DPP4i-associated BP differs significantly from classical BP, and presents with less distributed skin symptoms, mild erythema, normal or slightly elevated peripheral eosinophil count, and lower titers of BP180 autoantibodies. To our knowledge, this is the first case series of DPP4i-related BP with a non-inflammatory phenotype in European patients.

Association between dipeptidyl peptidase-4 inhibitors and risk of bullous pemphigoid in patients with type 2 diabetes: A population-based cohort study

AIMS

Higher bullous pemphigoid (BP) risk has been reported to be associated with dipeptidyl peptidase 4 inhibitor (DPP4i). The aim of this study is to examine the association between BP risk and DPP4i treatment.

METHODS

We conducted a nationwide cohort study based on the Taiwan National Health Insurance Database between 2000 and 2015. 124,619 diabetic patients who were receiving DPP4i therapy were matched 1: 1 with diabetic patients who had never received DPP4i by age, sex, duration of diabetes, insulin usage, and propensity score-matching of comorbidities.

RESULTS

The 6-year cumulative incidence of BP in the DPP4i-treated cohort was significantly higher than that in the non-DPP4i group (0.74 per 1000 vs 0.38 per 1000, P = 0.001). Modified Cox regression analysis revealed that DPP4i treatment (HR: 2.15, 95% CI: 1.18-3.91, P = 0.01), age (HR: 1.06, P < 0.001), renal disease (HR: 2.32, P < 0.001), and metformin user (HR: 1.93, P = 0.006) were associated with increased BP risk.

CONCLUSIONS

DPP4i users had a 2.2-fold increase in the risk of BP, and the risk was the highest in those with concomitant use of DPP4i and insulin.

Autoantibodies Against the Immunodominant Bullous Pemphigoid Epitopes Are Rare in Patients With Dermatitis Herpetiformis and Coeliac Disease

Dermatitis herpetiformis (DH) is an extraintestinal manifestation of coeliac disease (CD). Patients with DH have an elevated risk of development of another autoimmune blistering skin disease, bullous pemphigoid (BP). In this study we investigated whether patients with DH and CD (mean age for both 49 years) have circulating autoantibodies against BP180, the major BP autoantigen. ELISA tests showed that only a few DH (3/46) and CD (2/43) patients had BP180-NC16A IgG autoantibodies. Immunoblotting found that more than half of the DH samples contained IgG autoantibodies against full-length BP180. Epitope mapping with 13 fusion proteins covering the BP180 polypeptide revealed that in DH and CD patients, IgG autoantibodies did not target the NC16A or other epitopes typical of BP but recognized other intracellular and mid-extracellular regions of BP180. None of the analyzed DH and CD patients with either ELISA or immunoblotting positivity had IgG or IgA reactivity against the cutaneous basement membrane in indirect immunofluorescence analysis or skin symptoms characteristic of BP. Although only a minority of middle-aged DH patients had IgG autoantibodies against the immunodominant epitopes of BP180, our results do not exclude the possibility that intermolecular epitope spreading could explain the switch from DH to BP in elderly patients.

Transmembrane collagens-Unexplored mediators of epidermal-dermal communication and tissue homeostasis

Tissue homeostasis is maintained through constant, dynamic and heterogeneous communication between cells and their microenvironment. Proteins that are at the same time active at the intracellular, cell periphery and deeper extracellular levels possess the ability to, on the individual molecular level, influence the cells and their microenvironment in a bidirectional manner. The transmembrane collagens are a family of such proteins, which are of notable interest for tissue development and homeostasis. In skin, expression of all transmembrane collagens has been reported and deficiency of transmembrane collagen XVII manifests with distinct skin phenotypes. Nevertheless, transmembrane collagens in skin remain understudied despite the association of them with epidermal wound healing and dermal fibrotic processes. Here, we present an overview of transmembrane collagens and put a spotlight on them as regulators of epidermal-dermal communication and as potential players in fibrinogenesis.

Dipeptidyl peptidase 4 inhibitors and their potential immune modulatory functions

Dipeptidyl peptidase 4 (DPP4) inhibitors (DPP4is) are oral anti-diabetic drugs (OADs) for the treatment of type 2 diabetes mellitus (T2DM) through inhibiting the degradation of incretin peptides. Numerous investigations have been focused on the effects of DPP4is on glucose homeostasis. However, there are limited evidences demonstrating their Potential modulatory functions in the immune system. DPP4, originally known as the lymphocyte cell surface protein CD26, is widely expressed in many types of immune cells including CD4(+) and CD8(+) T cells, B cells, NK cells, dendritic cells, and macrophages; and regulate the functions of these cells. In addition, DPP4 is capable of modulating plenty of cytokines, chemokines and peptide hormones. Accordingly, DPP4/CD26 is speculated to be involved in various immune/inflammatory diseases and DPP4is may become a new drug class applied in these diseases. This review focuses on the regulatory effects of DPP4is on immune functions and their possible underlying mechanisms. Further clinical studies will be necessitated to fully evaluate the administration of DPP4is in diabetic patients with or without immune diseases.

O-glycan initiation directs distinct biological pathways and controls epithelial differentiation

Post-translational modifications (PTMs) greatly expand the function and potential for regulation of protein activity, and O-glycosylation is among the most abundant and diverse PTMs. Initiation of O-GalNAc glycosylation is regulated by 20 distinct GalNAc-transferases (GalNAc-Ts), and deficiencies in individual GalNAc-Ts are associated with human disease, causing subtle but distinct phenotypes in model organisms. Here, we generate a set of isogenic keratinocyte cell lines lacking either of the three dominant and differentially expressed GalNAc-Ts. Through the ability of keratinocytes to form epithelia, we investigate the phenotypic consequences of the loss of individual GalNAc-Ts. Moreover, we probe the cellular responses through global transcriptomic, differential glycoproteomic, and differential phosphoproteomic analyses. We demonstrate that loss of individual GalNAc-T isoforms causes distinct epithelial phenotypes through their effect on specific biological pathways; GalNAc-T1 targets are associated with components of the endomembrane system, GalNAc-T2 targets with cell-ECM adhesion, and GalNAc-T3 targets with epithelial differentiation. Thus, GalNAc-T isoforms serve specific roles during human epithelial tissue formation.

The Role of Collagen XVII in Cancer: Squamous Cell Carcinoma and Beyond

Alterations in the extracellular matrix (ECM) likely facilitate the first steps of cancer cell metastasis and supports tumor progression. Recent data has demonstrated that alterations in collagen XVII (BP180), a transmembrane protein and structural component of the ECM, can have profound effects on cancer invasiveness. Collagen XVII is a homotrimer of three α1 (XVII) chains. Its intracellular domain contains binding sites for plectin, integrin β4, and BP230, while the extracellular domain facilitates interactions between the cell and the ECM. Collagen XVII and its shed ectodomain have been implicated in cell motility and adhesion and are believed to promote tumor development and invasion. A strong association of collagen XVII ectodomain shedding and tumor invasiveness occurs in squamous cell carcinoma (SCC). Aberrant expression of collagen XVII has been reported in many epithelial cancers, ranging from squamous cell carcinoma to colon, pancreatic, mammary, and ovarian carcinoma. Thus, in this review, we focus on collagen XVII's role in neoplasia and tumorigenesis. Lastly, we discuss the importance of targeting collagen XVII and its ectodomain shedding as a novel strategy to curb tumor growth and reduce metastatic potential.

Life before and beyond blistering: The role of collagen XVII in epidermal physiology

Type XVII collagen (COL17) is a transmembranous protein that is mainly expressed in the epidermal basal keratinocytes. Epidermal-dermal attachment requires COL17 expression at the hemidesmosomes of the epidermal basement membrane zone because congenital COL17 deficiency leads to junctional epidermolysis bullosa and acquired autoimmunity to COL17 induces bullous pemphigoid. Recently, in addition to facilitating epidermal-dermal attachment, COL17 has been reported to serve as a niche for hair follicle stem cells, to regulate proliferation in the interfollicular epidermis and to be present along the non-hemidesmosomal plasma membrane of epidermal basal keratinocytes. This review focuses on the physiological properties of COL17 in the epidermis, its role in maintaining stem cells and its association with signalling pathways. We propose possible solutions to unanswered questions in this field.

Association of Bullous Pemphigoid With Dipeptidyl-Peptidase 4 Inhibitors in Patients With Diabetes: Estimating the Risk of the New Agents and Characterizing the Patients

Importance

The association of bullous pemphigoid (BP) with the use of dipeptidyl-peptidase 4 (DPP-4) inhibitors among patients with diabetes has recently emerged. The risk of developing BP during treatment with new DPP-4 inhibitor agents like linagliptin is yet to be established. The clinical features and the prognostic outcomes of patients with DPP-4 inhibitor-associated BP are yet to be established.

Objectives

Primarily to estimate the association between DPP-4 inhibitor exposure and the development of BP, and secondarily to characterize the clinical features and history of patients with DPP-4 inhibitor-associated BP.

Design, Setting, and Participants

A retrospective case-control study of the intake of different DPP-4 inhibitor agents and metformin and occurrence of BP among patients with diabetes in a tertiary care referral center for autoimmune bullous diseases in northern Israel. Included were 82 consecutive patients with diabetes and immunopathologically validated BP diagnosed between January 1, 2011, and December 31, 2017, and 328 age-, sex-, and ethnicity-matched control participants with diabetes but without BP.

Main Outcomes and Measures

Patients with diabetes and BP and exposure to DPP-4 inhibitors were followed up for a median of 2.0 years and compared with other patients with diabetes and BP who were not exposed to DPP-4 inhibitors regarding clinical and immunological features, laboratory analyses, treatments, and clinical outcomes.

Results

Eighty-two patients with BP and 328 age- and sex-matched control participants were enrolled; mean (SD) age, 79.1 (9.1) years; and 44 patients were female (53.7%). Overall, DPP-4 inhibitor intake was associated with a 3-fold increased risk for BP (adjusted odds ratio [OR], 3.2; 95% CI, 1.9-5.4). The adjusted ORs for vildagliptin and linagliptin were 10.7 (95% CI, 5.1-22.4) and 6.7 (95% CI, 2.2-19.7), respectively. The association of DPP-4 inhibitor use with BP was independent of the use of metformin and was stronger among male (OR, 4.46; 95% CI, 2.11-9.40) than female (OR, 1.88; 95%, CI 0.92-3.86) patients and strongest in patients younger than 70 years (OR, 5.59; 95% CI, 1.73-18.01). Patients with DPP-4 inhibitor-associated BP presented with higher mucosal involvement (22.2% vs 6.5%; P = .04) and lower mean (SD) peripheral eosinophil counts (399.8 [508.0] vs 1117.6 [1847.6] cells/μL; P = .01) than those with BP who had not been exposed to DPP-4 inhibitor. Discontinuation of DPP-4 inhibitor treatment was followed by improved clinical outcomes.

Conclusions and Relevance

Vildagliptin and, to a lesser extent, linagliptin are associated with an increased risk of BP. This may partly explain the increasing incidence of BP in Israel. Discontinuation of DPP-4 inhibitor treatment in patients with diabetes should be considered when BP is diagnosed.

Proteases in Pemphigoid Diseases

Pemphigoid diseases are a subgroup of autoimmune skin diseases characterized by widespread tense blisters. Standard of care typically involves immunosuppressive treatments, which may be insufficient and are often associated with significant adverse events. As such, a deeper understanding of the pathomechanism(s) of pemphigoid diseases is necessary in order to identify improved therapeutic approaches. A major initiator of pemphigoid diseases is the accumulation of autoantibodies against proteins at the dermal-epidermal junction (DEJ), followed by protease activation at the lesion. The contribution of proteases to pemphigoid disease pathogenesis has been investigated using a combination of in vitro and in vivo models. These studies suggest proteolytic degradation of anchoring proteins proximal to the DEJ is crucial for dermal-epidermal separation and blister formation. In addition, proteases can also augment inflammation, expose autoantigenic cryptic epitopes, and/or provoke autoantigen spreading, which are all important in pemphigoid disease pathology. The present review summarizes and critically evaluates the current understanding with respect to the role of proteases in pemphigoid diseases.

Dipeptidyl Peptidase-4 Inhibitor-Associated Bullous Pemphigoid

Bullous pemphigoid (BP) is an organ-specific autoantibody-mediated blistering skin disease that mainly affects the elderly. Typical clinical features include the widespread blisters, often preceded by and/or associated with itchy urticarial or eczema-like lesions. BP patients have circulating autoantibodies against BP180 and/or the plakin family protein BP230 both of which are components of hemidesmosomes in basal keratinocytes. Most BP autoantibodies particularly target the epitopes within the non-collagenous NC16A domain of BP180. Clinical findings and murine models of BP have provided evidence of a pathogenic role of anti-NC16A autoantibodies. However, it is largely unknown what triggers the breakage of immunotolerance against BP180 in elderly individuals. The incidence of BP has been increased over the past two decades in several countries. Aside from aging populations, the factors behind this phenomenon are still not fully understood. Neurodegenerative diseases such as multiple sclerosis, Parkinson's disease, and certain dementias are independent risk factors for BP. Recently several case reports have described BP in patients with diabetes mellitus (DM) patients who have been treated with dipeptidyl peptidase-4 inhibitors (DPP-4i or gliptins), which are a widely used class of anti-DM drugs. The association between the use of DPP-4is, particularly vildagliptin, and BP risk has been confirmed by several epidemiological studies. Evidence suggests that cases of gliptin-associated BP in Japan display certain features that set them apart from cases of “regular” BP. These include a “non-inflammatory” phenotype, targeting by antibodies of different immunodominant BP180 epitopes, and a specific association with the human leukocyte antigen (HLA) types. However, recent studies in European populations have found no major differences between the clinical and immunological characteristics of gliptin-associated BP and “regular” BP. The DPP-4 protein (also known as CD26) is ubiquitously expressed and has multiple functions in various cell types. The different effects of the inhibition of DPP-4/CD26 activity include, for example, tissue modeling and regulation of inflammatory cells such as T lymphocytes. Although the pathomechanism of gliptin-associated BP is currently largely unknown, investigation of the unique effect of gliptins in the induction of BP may provide a novel route to better understanding of how immunotolerance against BP180 breaks down in BP.

Preferential Reactivity of Dipeptidyl Peptidase-IV Inhibitor-Associated Bullous Pemphigoid Autoantibodies to the Processed Extracellular Domains of BP180

Bullous pemphigoid (BP) is a common autoimmune blistering disease in which autoantibodies target the hemidesmosomal components BP180 and/or BP230 in basal keratinocytes. In BP, 80 to 90% of autoantibodies target the juxtamembranous extracellular non-collagenous 16th A (NC16A) domain of BP180. Recently, the administration of dipeptidyl peptidase-IV inhibitors (DPP4i), which are widely used as antihyperglycemic drugs, has been recognized to be a causative factor for BP. DPP4i-associated BP (DPP4i-BP) autoantibodies tend to target epitopes on non-NC16A regions of BP180, and the pathomechanism for the development of the unique autoantibodies remains unknown. To address the characteristics of DPP4i-BP autoantibodies in detail, we performed epitope analysis of 18 DPP4i-BP autoantibodies targeting the non-NC16A domains of BP180 using various domain-specific as well as plasmin-digested polypeptides derived from recombinant BP180. Firstly, Western blotting showed that only one DPP4i-BP serum reacted with the epitopes on the intracellular domain of BP180, and no sera reacted with the C-terminal domain of the molecule. In addition, only 2 DPP4i-BP sera reacted with BP230 as determined by enzyme-linked immunosorbent assay. Thus, DPP4i-BP autoantibodies were found to mainly target the non-NC16A mid-portion of the extracellular domain of BP. Interestingly, Western blotting using plasmin-digested BP180 as a substrate revealed that all of the DPP4i-BP sera reacted more intensively with the 97-kDa processed extracellular domain of BP180, which is known as the LABD97 autoantigen, than full-length BP180 did. All of the DPP4i-BP autoantibodies targeting the LABD97 autoantigen were IgG1, and IgG4 was observed to react with the molecule in only 7 cases (38.9%). In summary, the present study suggests that IgG1-class autoantibodies targeting epitopes on the processed extracellular domain of BP180, i.e., LABD97, are the major autoantibodies in DPP4i-BP.

Dipeptidyl peptidase IV inhibitor-associated bullous pemphigoid: a recently recognized autoimmune blistering disease with unique clinical, immunological and genetic characteristics

Bullous pemphigoid (BP) is an organ-specific autoantibody-mediated autoimmune blistering skin disorder that tends to affect the elderly. Tense blister formation associated with itchy urticarial erythema is clinically observed in BP, and subepidermal blister formation with eosinophilic infiltration is a histopathological characteristic. BP autoantibodies target two hemidesmosomal components in basal keratinocytes: BP180 and BP230. Anti-BP180 autoantibodies play major roles in blister formation. Although the autoantibody-mediated pathomechanism of blister formation has been extensively studied, little is known about how and why immune tolerance to BP180 may be broken in certain elderly individuals. Recently, BP has been increasingly reported in diabetes mellites (DM) patients receiving dipeptidyl peptidase-IV inhibitors (DPP4is), which are widely used anti-DM drugs. Pharmacovigilance and cohort studies have revealed that DPP4is, especially vildagliptin, teneligliptin, and linagliptin, are a potential risk factor for BP onset. Interestingly, it has been revealed that Japanese DPP4i-BP tends to show a non-inflammatory phenotype, with less erythema than normal BP, and that DPP4i-BP autoantibodies target distinct epitopes on BP180. In addition, human leukocyte antigen-DQB1*03:01 was identified as the major haplotype in Japanese DPP4i-BP. This review summarizes the latest understanding of the pathogenesis of BP, with a special focus on the recently recognized DPP4i-BP.

Epidermolysis bullosa: Molecular pathology of connective tissue components in the cutaneous basement membrane zone

Epidermolysis bullosa (EB), a group of heritable skin fragility disorders, is characterized by blistering, erosions and chronic ulcers in the skin and mucous membranes. In some forms, the blistering phenotype is associated with extensive mutilating scarring and development of aggressive squamous cell carcinomas. The skin findings can be associated with extracutaneous manifestations in the ocular as well as gastrointestinal and vesico-urinary tracts. The phenotypic heterogeneity reflects the presence of mutations in as many as 20 different genes expressed in the cutaneous basement membrane zone, and the types and combinations of the mutations and their consequences at the mRNA and protein levels contribute to the spectrum of severity encountered in different subtypes of EB. This overview highlights the molecular genetics of EB based on mutations in the genes encoding type VII and XVII collagens as well as laminin-332. The mutations identified in these protein components of the extracellular matrix attest to their critical importance in providing stability to the cutaneous basement membrane zone, with implications for heritable and acquired diseases.

The Growing Incidence of Bullous Pemphigoid: Overview and Potential Explanations

Bullous pemphigoid (BP) is the most common type of subepidermal autoimmune bullous diseases. BP characteristically affects the elderly and is seen mainly in patients older than 70 years. While the annual incidence of BP has been estimated to be between 2.4 and 23 cases per million in the general population, it rises exponentially to 190-312 cases per million in individuals older than 80 years. In addition, a growing body of evidence reports a remarkable trend of increased incidence of BP, showing a 1.9- to 4.3-fold rise over the past two decades. This demonstrable increase warrants a higher awareness of the increased risk to develop BP. This review summarizes the current understanding of the epidemiological features of BP and sheds light on the putative explanations for its growing incidence.

Granzyme B is elevated in autoimmune blistering diseases and cleaves key anchoring proteins of the dermal-epidermal junction

In healthy skin, epidermis and dermis are anchored together at the dermal-epidermal junction (DEJ), a specialized basement membrane pivotal for skin integrity and function. However, increased inflammation in the DEJ is associated with the disruption and separation of this junction and sub-epidermal blistering. Granzyme B (GzmB) is a serine protease secreted by immune cells. Dysregulated inflammation may lead to increased GzmB accumulation and proteolysis in the extracellular milieu. Although elevated GzmB is observed at the level of the DEJ in inflammatory and blistering skin conditions, the present study is the first to explore GzmB in the context of DEJ degradation in autoimmune sub-epidermal blistering. In the present study, GzmB induced separation of the DEJ in healthy human skin. Subsequently, α6/β4 integrin, collagen VII, and collagen XVII were identified as extracellular substrates for GzmB through western blot, and specific cleavage sites were identified by mass spectrometry. In human bullous pemphigoid, dermatitis herpetiformis, and epidermolysis bullosa acquisita, GzmB was elevated at the DEJ when compared to healthy samples, while α6/β4 integrin, collagen VII, and collagen XVII were reduced or absent in the area of blistering. In summary, our results suggest that regardless of the initial causation of sub-epidermal blistering, GzmB activity is a common final pathway that could be amenable to a single targeted treatment approach.

Gliptin Accountability in Mucous Membrane Pemphigoid Induction in 24 Out of 313 Patients

Mucous membrane pemphigoids (MMPs) and bullous pemphigoid (BP) are autoimmune bullous diseases that share physiopathological features: both can result from autoantibodies directed against BP180 or BP230 antigens. An association has been reported between BP and intake of gliptins, which are dipeptidyl peptidase-IV inhibitors used to treat type 2 diabetes mellitus. Clinical and immunological differences have been reported between gliptin-induced BPs and classical BPs: mucosal involvement, non-inflammatory lesions, and target BP180 epitopes other than the NC16A domain. Those findings accorded gliptins extrinsic accountability in triggering MMP onset. Therefore, we examined gliptin intrinsic accountability in a cohort of 313 MMP patients. To do so, we (1) identified MMP patients with gliptin-treated (challenge) diabetes; (2) selected those whose interval between starting gliptin and MMP onset was suggestive or compatible with gliptin-induced MMP; (3) compared the follow-ups of patients who did not stop (no dechallenge), stopped (dechallenge) or repeated gliptin intake (rechallenge); (4) compared the clinical and immunological characteristics of suggestive-or-compatible-challenge patients to 121 never-gliptin-treated MMP patients serving as controls; and (5) individually scored gliptin accountability as the trigger of each patient's MMP using the World Health Organization-Uppsala Monitoring Center, Naranjo- and Begaud-scoring systems. 17 out of 24 gliptin-treated diabetic MMP patients had suggestive (≤12 weeks) or compatible challenges. Complete remission at 1 year of follow-up was more frequent in the 11 dechallenged patients. One rechallenged patient's MMP relapsed. These 17 gliptin-treated diabetic MMP patients differed significantly from the MMP controls by more cutaneous, less buccal, and less severe involvements and no direct immunofluorescence IgA labeling of the basement membrane zone. Multiple autoantibody-target antigens/epitopes (BP180-NC16A, BP180 mid- and C-terminal parts, integrin α6β4) could be detected, but not laminin 332. Last, among the 24 gliptin-treated diabetic MMP patients, five had high (I4-I3), 12 had low (I2-I1) and 7 had I0 Begaud intrinsic accountability scores. These results strongly suggest that gliptins are probably responsible for some MMPs. Consequently, gliptins should immediately be discontinued for patients with a positive accountability score. Moreover, pharmacovigilance centers should be notified of these events.

Targeting of Cell Surface Proteolysis of Collagen XVII Impedes Squamous Cell Carcinoma Progression

Squamous cell carcinoma (SCC) is one of the most common skin cancers and causes significant morbidity. Although the expression of the epithelial adhesion molecule collagen XVII (ColXVII) has been linked to SCC invasion, only little is known about its mechanistic contribution. Here, we demonstrate that ColXVII expression is essential for SCC cell proliferation and motility. Moreover, it revealed that particularly the post-translational modification of ColXVII by ectodomain shedding is the major driver of SCC progression, because ectodomain-selective immunostaining was mainly localized at the invasive front of human cutaneous SCCs, and exclusive expression of a non-sheddable ColXVII mutant in SCC-25 cells inhibits their matrix-independent growth and invasiveness. This cell surface proteolysis, which is strongly elevated during SCC invasion and metastasis, releases soluble ectodomains and membrane-anchored endodomains. Both released ColXVII domains play distinct roles in tumor progression: the endodomain induces proliferation and survival, whereas the ectodomain accelerates invasiveness. Furthermore, specific blockage of shedding by monoclonal ColXVII antibodies repressed matrix-independent growth and invasion of SCC cells in organotypic co-cultures. Thus, selective inhibition of ColXVII shedding may offer a promising therapeutic strategy to prevent SCC progression.

C-Terminal Processing of Collagen XVII Induces Neoepitopes for Linear IgA Dermatosis Autoantibodies

Transmembrane collagen XVII (COL17) is a hemidesmosomal component of basal keratinocytes that can be targeted by autoantibodies in autoimmune blistering disorders, including linear IgA dermatosis (LAD). COL17 can be physiologically cleaved within the juxtamembranous extracellular NC16A domain, and LAD autoantibodies preferentially react with the processed ectodomains, indicating that the processing induces neoepitopes. However, the details of how neoepitopes develop have not been elucidated. In this study, we show that C-terminal processing of COL17 also plays a role in inducing neoepitopes for LAD autoantibodies. First, the mAb hC17-ect15 targeting the 15th collagenous domain of COL17 was produced, which showed characteristics similar to LAD autoantibodies. The mAbs preferentially reacted with C-terminally deleted (up to 682 amino acids) recombinant COL17, suggesting that C-terminal processing shows neoepitopes on the 15th collagenous domain. The LAD autoantibodies also react with C-terminal deleted COL17. Therefore, neoepitopes for LAD autoantibodies also develop after C-terminal processing. Finally, the passive transfer of the mAb hC17-ect15 into human COL17-expressing transgenic mice failed to induce blistering disease, suggesting that neoepitope-targeting antibodies are not always pathogenic. In summary, this study shows that C-terminal processing induces dynamic structural changes and neoepitopes for LAD autoantibodies on COL17.

Idiopathic linear IgA bullous dermatosis: prognostic factors based on a case series of 72 adults

BACKGROUND

Linear IgA bullous dermatosis (LABD) is a clinically and immunologically heterogeneous, subepidermal, autoimmune bullous disease (AIBD), for which the long-term evolution is poorly described.

OBJECTIVES

To investigate the clinical and immunological characteristics, follow-up and prognostic factors of adult idiopathic LABD.

METHODS

This retrospective study, conducted in our AIBD referral centre, included adults, diagnosed between 1995 and 2012, with idiopathic LABD, defined as pure or predominant IgA deposits by direct immunofluorescence. Clinical, histological and immunological findings were collected from charts. Standard histology was systematically reviewed, and indirect immunofluorescence (IIF) on salt-split skin (SSS) and immunoblots (IBs) on amniotic membrane extracts using anti-IgA secondary antibodies were performed, when biopsies and sera obtained at diagnosis were available. Prognostic factors for complete remission (CR) were identified using univariate and multivariate analyses.

RESULTS

Of the 72 patients included (median age 54 years), 60% had mucous membrane (MM) involvement. IgA IIF on SSS was positive for 21 of 35 patients tested; 15 had epidermal and dermal labellings. Immunoelectron microscopy performed on the biopsies of 31 patients labelled lamina lucida (LL) (26%), lamina densa (23%), anchoring-fibril zone (AFz) (19%) and LL+AFz (23%). Of the 34 IgA IBs, 22 were positive, mostly for LAD-1/LABD97 (44%) and full-length BP180 (33%). The median follow-up was 39 months. Overall, 24 patients (36%) achieved sustained CR, 19 (29%) relapsed and 35% had chronic disease. CR was significantly associated with age > 70 years or no MM involvement. No prognostic immunological factor was identified.

CONCLUSIONS

Patients with LABD who are < 70 years old and have MM involvement are at risk for chronic evolution.

Amino acid duplication in the coiled-coil structure of collagen XVII alters its maturation and trimerization causing mild junctional epidermolysis bullosa

The function and stability of collagens depend on the accurate triple helix formation of three distinct polypeptide chains. Disruption of this triple-helical structure can result in connective-tissue disorders. Triple helix formation is thought to depend on three-stranded coiled-coil oligomerization sites within non-collagenous domains. However, only little is known about the physiological relevance of these coiled-coil structures. Transmembrane collagen XVII, also known as 180 kDa bullous pemphigoid antigen provides mechanical stability through the anchorage of epithelial cells to the basement membrane. Mutations in the collagen XVII gene, COL17A1, cause junctional epidermolysis bullosa (JEB), characterized by chronic trauma-induced skin blistering. Here we exploited a novel naturally occurring COL17A1 mutation, leading to an in-frame lysine duplication within the coiled-coil structure of the juxtamembranous NC16A domain of collagen XVII, which resulted in a mild phenotype of JEB due to reduced membrane-anchored collagen XVII molecules. This mutation causes structural changes in the mutant molecule and interferes with its maturation. The destabilized coiled-coil structure of the mutant collagen XVII unmasks a furin cleavage site that results in excessive and non-physiological ectodomain shedding during its maturation. Furthermore, it decreases its triple-helical stability due to defective coiled-coil oligomerization, which makes it highly susceptible to proteolytic degradation. As a consequence of altered maturation and decreased stability of collagen XVII trimers, reduced collagen XVII is incorporated into the cell membrane, resulting in compromised dermal-epidermal adhesion. Taken together, using this genetic model, we provide the first proof that alteration of the coiled-coil structure destabilizes oligomerization and impairs physiological shedding of collagen XVII in vivo.

Autoantibody Profile Differentiates between Inflammatory and Noninflammatory Bullous Pemphigoid

Bullous pemphigoid (BP) is a major autoimmune blistering skin disorder, in which a majority of the autoantibodies (autoAbs) target the juxtamembranous extracellular noncollagenous 16A domain (NC16A) domain of hemidesmosomal collagen XVII. BP-autoAbs may target regions of collagen XVII other than the NC16A domain; however, correlations between epitopes of BP-autoAbs and clinical features have not been fully elucidated. To address correlations between the clinical features and specific epitopes of BP-autoAbs, we evaluated the epitope profiles of BP-autoAbs in 121 patients. A total of 87 patients showed a typical inflammatory phenotype with erythema and autoAbs targeting the anti-NC16A domain, whereas 14 patients showed a distinct noninflammatory phenotype, in which autoAbs specifically targeted the midportion of collagen XVII, but not NC16A. Interestingly, this group clinically showed significantly reduced erythema associated with scant lesional infiltration of eosinophils. Surprisingly, 7 of the 14 cases (50.0%) received dipeptidyl peptidase-IV inhibitors for the treatment of diabetes. Dipeptidyl peptidase-IV inhibitors were used in 3 of 76 (3.9%) typical cases of BP with autoAbs targeting NC16A; thus, dipeptidyl peptidase-IV inhibitors are thought to be involved in the development of atypical noninflammatory BP. This study shows that the autoAb profile differentiates between inflammatory and noninflammatory BP, and that noninflammatory BP may be associated with dipeptidyl peptidase-IV inhibitors.

Collagen XVII Shedding Suppresses Re-Epithelialization by Directing Keratinocyte Migration and Dampening mTOR Signaling

Transmembrane collagen XVII is traditionally viewed as an important hemidesmosomal attachment component that promotes stable dermal-epidermal adhesion in the skin. However, its expression is highly elevated at the leading edges of cutaneous wounds or invasive carcinomas, suggesting alternative functions in cell migration. The collagenous ectodomain of collagen XVII is constitutively shed from the cell surface by a disintegrin and metalloproteinases, and this shedding is strongly induced during wound healing. Recently, we investigated the physiological relevance of collagen XVII shedding by generating knock-in mice, which exclusively express a functional non-sheddable collagen XVII mutant. Prevention of ectodomain shedding in these mice caused no spontaneous phenotype in resting skin, but accelerated re-epithelialization on skin wounding. Here, we investigated the mechanistic function of shedding during wound healing. Using the non-shedding collagen XVII mice as a model, we uncovered ectodomain shedding as a highly dynamic modulator of in vivo proliferation and motility of activated keratinocytes through tight coordination of α6β4 integrin-laminin-332 interactions and dampening of mechanistic target of rapamycin signaling at the wound edges. Thus, our studies identify ectodomain shedding of collagen XVII as an interactive platform that translates shedding into a signal for directed cell growth and motility during skin regeneration.

Extracellular cleavage of collagen XVII is essential for correct cutaneous basement membrane formation

In skin, basal keratinocytes in the epidermis are tightly attached to the underlying dermis by the basement membrane (BM). The correct expression of hemidesmosomal and extracellular matrix (ECM) proteins is essential for BM formation, and the null-expression of one molecule may induce blistering diseases associated with immature BM formation in humans. However, little is known about the significance of post-translational processing of hemidesmosomal or ECM proteins in BM formation. Here we show that the C-terminal cleavage of hemidesmosomal transmembrane collagen XVII (COL17) is essential for correct BM formation. The homozygous p.R1303Q mutation in COL17 induces BM duplication and blistering in humans. Although laminin 332, a major ECM protein, interacts with COL17 around p.R1303, the mutation leaves the binding of both molecules unchanged. Instead, the mutation hampers the physiological C-terminal cleavage of COL17 in the ECM. Consequently, non-cleaved COL17 ectodomain remnants induce the aberrant deposition of laminin 332 in the ECM, which is thought to be the major pathogenesis of the BM duplication that results from this mutation. As an example of impaired cleavage of COL17, this study shows that regulated processing of hemidesmosomal proteins is essential for correct BM organization in skin.

Epidermal Basement Membrane in Health and Disease

Skin, as the organ protecting the individual from environmental aggressions, constantly meets external insults and is dependent on mechanical toughness for its preserved function. Accordingly, the epidermal basement membrane (BM) zone has adapted to enforce tissue integrity. It harbors anchoring structures created through unique organization of common BM components and expression of proteins exclusive to the epidermal BM zone. Evidence for the importance of its correct assembly and the nonredundancy of its components for skin integrity is apparent from the multiple skin blistering disorders caused by mutations in genes coding for proteins associated with the epidermal BM and from autoimmune disorders in which autoantibodies target these molecules. However, it has become clear that these proteins not only provide mechanical support but are also critically involved in tissue homeostasis, repair, and regeneration. In this chapter, we provide an overview of the unique organization and components of the epidermal BM. A special focus will be given to its function during regeneration, and in inherited and acquired diseases.

Context-Dependent Regulation of Collagen XVII Ectodomain Shedding in Skin

Pemphigoid is a common autoimmune blistering disorder in which autoantibodies target transmembrane collagen XVII (COL17), a component of hemidesmosomes in basal keratinocytes. The ectodomain of COL17 can be cleaved from the cell surface within the juxtamembranous extracellular NC16A domain, and, interestingly, certain autoantibodies of pemphigoid patients preferentially react with the shed ectodomain. These findings suggest that COL17 ectodomain shedding generates neoepitopes on the shed form; however, the regulatory mechanism of the shedding in in vivo skin and the pathogenicity of the neoepitope-targeting antibodies still are uncertain. To address these issues, we produced rabbit antibodies specifically reacting with N-terminal cleavage sites of the shed COL17 ectodomain. The antibodies showed that certain amounts of the human COL17 ectodomain are cleaved physiologically at Gln(525) in in vivo skin. In contrast, migrating human keratinocytes cleave COL17 at Leu(524) but not at Gln(525). The passive transfer of antibodies reacting with an N-terminal cleavage site of the mouse COL17 ectodomain into neonatal wild-type mice failed to induce blister formation, even though the antibodies bound to the dermal-epidermal junctions, indicating that cleavage site-specific antibodies have reduced or absent pathogenicity for blister formation. This study shows the ectodomain shedding of COL17 to be a physiological event in in vivo human skin that probably generates nonpathologic epitopes on the cleavage sites.

Bullous pemphigoid autoantibodies directly induce blister formation without complement activation

Complement activation and subsequent recruitment of inflammatory cells at the dermal/epidermal junction are thought to be essential for blister formation in bullous pemphigoid (BP), an autoimmune blistering disease induced by autoantibodies against type XVII collagen (COL17); however, this theory does not fully explain the pathological features of BP. Recently, the involvement of complement-independent pathways has been proposed. To directly address the question of the necessity of the complement activation in blister formation, we generated C3-deficient COL17-humanized mice. First, we show that passive transfer of autoantibodies from BP patients induced blister formation in neonatal C3-deficient COL17-humanized mice without complement activation. By using newly generated human and murine mAbs against the pathogenic noncollagenous 16A domain of COL17 with high (human IgG1, murine IgG2), low (murine IgG1), or no (human IgG4) complement activation abilities, we demonstrate that the deposition of Abs, and not complements, is relevant to the induction of blister formation in neonatal and adult mice. Notably, passive transfer of BP autoantibodies reduced the amount of COL17 in lesional mice skin, as observed in cultured normal human keratinocytes treated with the same Abs. Moreover, the COL17 depletion was associated with a ubiquitin/proteasome pathway. In conclusion, the COL17 depletion induced by BP autoantibodies, and not complement activation, is essential for the blister formation under our experimental system.

Major cleavage-dependent epitopes for linear IgA bullous dermatosis are formed at the boundary between the non-collagenous 16A and collagenous 15 domains of BP180

BACKGROUND

The autoantigen for the major type of linear IgA bullous dermatosis (LAD, lamina lucida type) is the shed ectodomain of BP180. However, it is unknown why most LAD sera react with the shed ectodomain but not with the intact BP180/type XVII collagen.

OBJECTIVE

The aim of this study was to characterize the unique cleavage-dependent epitope(s) in the shed ectodomain.

METHODS

We used a monoclonal antibody (MAb-1337) and six LAD sera, which reacted preferentially with the shed ectodomain of BP180. The location and characteristics of the epitopes for these antibodies were analyzed mainly by immunoblotting using chimeric bovine-human BP180 mammalian recombinant proteins and variously truncated bacterial recombinant proteins.

RESULTS

LAD sera and MAb-1337 reacted with the plasmin-digested products of full-length BP180. Four of the six LAD sera reacted to a bacterial recombinant protein consisting of the human non-collagenous 16th A (NC16A) and the collagenous 15th (C15) domains, while these sera were negative or only faintly reactive with the NC16A and C15 recombinants. The epitope for MAb-1337 was localized to the COOH-terminal 21 amino acid region within the NC16A domain.

CONCLUSION

The results in this study indicate that the major epitopes for LAD sera are formed or exposed by a cleavage-induced conformational change, but not by a post-translational modification that occurs only in the shed ectodomain, and are located at the boundary between the NC16A and C15 domains.

Update on the pathogenesis of bullous pemphigoid: an autoantibody-mediated blistering disease targeting collagen XVII

Bullous pemphigoid (BP) is a common autoimmune blistering skin disorder that tends to affect the elderly. Autoantibodies (autoAbs) from BP patients react with two hemidesmosomal components: transmembrane collagen XVII (BP180 or BPAG2) and plakin family protein BP230 (BPAG1). Of these, collagen XVII (COL17) is thought to be a major autoantigen. The binding of autoAbs to COL17 following the activation of complements and inflammatory pathways eventually leads to the degradation of COL17, and this has been regarded as the main pathogenesis of BP. However, recent investigations have suggested other pathways, including a complement-independent pathway and a pathway involving IgE-autoAbs. BP-autoAbs can directly deplete COL17, leading to fragility of the dermal-epidermal junction. In addition, IgE-autoAbs to COL17 may be involved in the formation of itchy urticarial erythema associated with eosinophilic infiltration. This article summarizes the update on pathogenesis of BP, with a special focus on blister formation by autoAbs to COL17.

Collagen XVII is expressed in malignant but not in benign melanocytic tumors and it can mediate antibody induced melanoma apoptosis

The 180 kDa transmembrane collagen XVII is known to anchor undifferentiated keratinocytes to the basement membrane in hemidesmosomes while constitutively shedding a 120 kDa ectodomain. Inherited mutations or auto-antibodies targeting collagen XVII cause blistering skin disease. Collagen XVII is down-regulated in mature keratinocytes but re-expressed in skin cancer. By recently detecting collagen XVII in melanocyte hyperplasia, here we tested its expression in benign and malignant melanocytic tumors using endodomain and ectodomain selective antibodies. We found the full-length collagen XVII protein in proliferating tissue melanocytes, basal keratinocytes and squamous cell carcinoma whereas resting melanocytes were negative. Furthermore, the cell-residual 60 kDa endodomain was exclusively detected in 62/79 primary and 15/18 metastatic melanomas, 8/9 melanoma cell lines, HT199 metastatic melanoma xenografts and atypical nests in 8/63 dysplastic nevi. The rest of 19 nevi including common, blue and Spitz subtypes were also negative. In line with the defective ectodomain, sequencing of COL17A1 gene revealed aberrations in the ectodomain coding region including point mutations. Collagen XVII immunoreaction-stained spindle cell melanomas, showed partly overlapping profiles with those of S100B, Melan A and HMB45. It was concentrated at vertical melanoma fronts and statistically associated with invasive phenotype. Antibody targeting the extracellular aa507-529 terminus of collagen XVII endodomain promoted apoptosis and cell adhesion, while inhibiting proliferation in HT199 cells. These results suggest that the accumulation of collagen XVII endodomain in melanocytic tumors is associated with malignant transformation to be a potential marker of malignancy and a target for antibody-induced melanoma apoptosis.

Coiled coils ensure the physiological ectodomain shedding of collagen XVII

α-Helical coiled coils, frequent protein oligomerization motifs, are commonly observed in vital proteins. Here, using collagen XVII as an example, we provide evidence for a novel function of coiled coils in the regulation of ectodomain shedding. Transmembrane collagen XVII, an epithelial cell surface receptor, mediates dermal-epidermal adhesion in the skin, and its dysfunction is linked to human skin blistering diseases. The ectodomain of this collagen is constitutively shed from the cell surface by proteinases of a disintegrin and metalloprotease family; however, the mechanisms regulating shedding remain elusive. Here, we used site-specific mutagenesis to target the coiled-coil heptad repeats within the juxtamembranous, extracellular noncollagenous 16th A (NC16A) domain of collagen XVII. This resulted in a substantial increase of ectodomain shedding, which was not mediated by disintegrin and metalloproteases. Instead, conformational changes induced by the mutation(s) unmasked a furin recognition sequence that was used for cleavage. This study shows that apart from their functions in protein oligomerization, coiled coils can also act as regulators of ectodomain shedding depending on the biological context.

Pathogenesis of bullous pemphigoid

Bullous pemphigoid, the most common autoimmune blistering disease, is induced by autoantibodies against type XVII collagen. Passive transfer of IgG or IgE antibodies against type XVII collagen into animals has revealed not only the pathogenicity of these antibodies but also the subsequent immune responses, including complement activation, mast cell degranulation, and infiltration of neutrophils and/or eosinophils. In vitro studies on ectodomain shedding of type XVII collagen have also provided basic knowledge on the development of bullous pemphigoid. The pathogenic role of autoreactive CD4+ T lymphocytes in the development of the pathogenic autoantibodies to type XVII collagen should also be noted.

Linear immunoglobulin A bullous dermatosis

Linear immunoglobulin A (IgA) bullous dermatosis, also known as linear IgA disease, is an autoimmune mucocutaneous disorder characterized by subepithelial bullae, with IgA autoantibodies directed against several different antigens in the basement membrane zone. Its immunopathologic characteristic resides in the presence of a continuous linear IgA deposit along the basement membrane zone, which is clearly visible on direct immunofluorescence. This disorder shows different clinical features and distribution when adult-onset of linear IgA disease is compared with childhood-onset. Diagnosis is achieved via clinical, histopathologic, and immunopathologic examinations. Two common therapies are dapsone and sulfapyridine, which reduce the inflammatory response and achieve disease remission in a variable period of time.

Kindler syndrome: extension of FERMT1 mutational spectrum and natural history

Mutations in the FERMT1 gene (also known as KIND1), encoding the focal adhesion protein kindlin-1, underlie the Kindler syndrome (KS), an autosomal recessive skin disorder with an intriguing progressive phenotype comprising skin blistering, photosensitivity, progressive poikiloderma with extensive skin atrophy, and propensity to skin cancer. Herein we review the clinical and genetic data of 62 patients, and delineate the natural history of the disorder, for example, age at onset of symptoms, or risk of malignancy. Although most mutations are predicted to lead to premature termination of translation, and to loss of kindlin-1 function, significant clinical variability is observed among patients. There is an association of FERMT1 missense and in-frame deletion mutations with milder disease phenotypes, and later onset of complications. Nevertheless, the clinical variability is not fully explained by genotype-phenotype correlations. Environmental factors and yet unidentified modifiers may play a role. Better understanding of the molecular pathogenesis of KS should enable the development of prevention strategies for disease complications.

Key role of heparan sulfate chains in assembly of anchoring complex at the dermal-epidermal junction

Epidermal basement membrane forms anchoring complex composed of hemidesmosomes, anchoring filaments, lamina densa and anchoring fibrils to link epidermis to dermis. However, the anchoring complex is rarely formed in skin equivalent models, probably because of degradation of extracellular matrix (ECM) proteins and heparan sulfate chains by matrix metalloproteinases (MMPs) and heparanase, respectively. To explore the roles of ECM proteins and heparan sulfate in anchoring complex assembly, we used specific inhibitors of MMPs and heparanase, and the formation of anchoring complex was analysed in terms of polarized deposition of collagen VII, BP180 and β4 integrin at the dermal-epidermal junction (DEJ) by means of immunohistochemistry and transmission electron microscopy (TEM). The deposition of collagen VII was polarized to the basal side by the addition of MMP inhibitor, and the staining intensity was increased by combined treatment with MMP inhibitor and heparanase inhibitor, which enhanced anchoring fibril formation as observed by TEM. BP180 was polarized to the basal side by heparanase inhibitor, which protects HS chains, but not by MMP inhibitor. MMP inhibitor improved the polarization of β4 integrin. Hemidesmosomes were formed in the presence of each inhibitor, as observed by TEM, and formation was greatly enhanced by the combined treatment. These findings suggest that heparan sulfate chains, in addition to ECM proteins at the DEJ, play an important role in the assembly of anchoring complex, especially hemidesmosomes and anchoring fibrils.