Desmosomal Adhesion Research Articles

034 Impaired frequency and function of transitional B cells in patients with pemphigus vulgaris

Pemphigus vulgaris (PV) is an autoimmune disease clinically characterized by blisters on the skin and/or mucosa. Pathophysiologically, PV is mediated by close interaction of B cells and autoreactive T cells, inducing proliferation, differentiation, and production of autoantibodies targeting desmosomal adhesion proteins, namely desmoglein 3 and/or 1. To elucidate B cell changes at different stages of PV, canonical B cell populations, like naïve, memory, transitional, non-switched, switched B cells, and plasmablasts were monitored in peripheral blood.

Defective Desmosomal Adhesion Causes Arrhythmogenic Cardiomyopathy by Involving an Integrin-αVβ6/TGF-β Signaling Cascade.

Arrhythmogenic cardiomyopathy (ACM) is characterized by progressive loss of cardiomyocytes with fibrofatty tissue replacement, systolic dysfunction, and life-threatening arrhythmias. A substantial proportion of ACM is caused by mutations in genes of the desmosomal cell-cell adhesion complex, but the underlying mechanisms are not well understood. In the current study, we investigated the relevance of defective desmosomal adhesion for ACM development and progression. We mutated the binding site of DSG2 (desmoglein-2), a crucial desmosomal adhesion molecule in cardiomyocytes. This DSG2-W2A mutation abrogates the tryptophan swap, a central interaction mechanism of DSG2 on the basis of structural data. Impaired adhesive function of DSG2-W2A was confirmed by cell-cell dissociation assays and force spectroscopy measurements by atomic force microscopy. The DSG2-W2A knock-in mouse model was analyzed by echocardiography, ECG, and histologic and biomolecular techniques including RNA sequencing and transmission electron and superresolution microscopy. The results were compared with ACM patient samples, and their relevance was confirmed in vivo and in cardiac slice cultures by inhibitor studies applying the small molecule EMD527040 or an inhibitory integrin-αVβ6 antibody. The DSG2-W2A mutation impaired binding on molecular level and compromised intercellular adhesive function. Mice bearing this mutation develop a severe cardiac phenotype recalling the characteristics of ACM, including cardiac fibrosis, impaired systolic function, and arrhythmia. A comparison of the transcriptome of mutant mice with ACM patient data suggested deregulated integrin-αVβ6 and subsequent transforming growth factor-β signaling as driver of cardiac fibrosis. Blocking integrin-αVβ6 led to reduced expression of profibrotic markers and reduced fibrosis formation in mutant animals in vivo. We show that disruption of desmosomal adhesion is sufficient to induce a phenotype that fulfils the clinical criteria to establish the diagnosis of ACM, confirming the dysfunctional adhesion hypothesis. Deregulation of integrin-αVβ6 and transforming growth factor-β signaling was identified as a central step toward fibrosis. A pilot in vivo drug test revealed this pathway as a promising target to ameliorate fibrosis. This highlights the value of this model to discern mechanisms of cardiac fibrosis and to identify and test novel treatment options for ACM.

Defining domain-specific orientational order in the desmosomal cadherins

Desmosomes are large, macromolecular protein assemblies that mechanically couple the intermediate filament cytoskeleton to sites of cadherin-mediated cell adhesion, thereby providing structural integrity to tissues that routinely experience large forces. Proper desmosomal adhesion is necessary for the normal development and maintenance of vertebrate tissues, such as epithelia and cardiac muscle, while dysfunction can lead to severe disease of the heart and skin. Therefore, it is important to understand the relationship between desmosomal adhesion and the architecture of the molecules that form the adhesive interface, the desmosomal cadherins (DCs). However, desmosomes are embedded in two plasma membranes and are linked to the cytoskeletal networks of two cells, imposing extreme difficulty on traditional structural studies of DC architecture, which have yielded conflicting results. Consequently, the relationship between DC architecture and adhesive function remains unclear. To overcome these challenges, we utilized excitation-resolved fluorescence polarization microscopy to quantify the orientational order of the extracellular and intracellular domains of three DC isoforms: desmoglein 2, desmocollin 2, and desmoglein 3. We found that DC ectodomains were significantly more ordered than their cytoplasmic counterparts, indicating a drastic difference in DC architecture between opposing sides of the plasma membrane. This difference was conserved among all DCs tested, suggesting that it may be an important feature of desmosomal architecture. Moreover, our findings suggest that the organization of DC ectodomains is predominantly the result of extracellular adhesive interactions. We employed azimuthal orientation mapping to show that DC ectodomains are arranged with rotational symmetry about the membrane normal. Finally, we performed a series of mathematical simulations to test the feasibility of a recently proposed antiparallel arrangement of DC ectodomains, finding that it is supported by our experimental data. Importantly, the strategies employed here have the potential to elucidate molecular mechanisms for diseases that result from defective desmosome architecture.

IgG against the Membrane-Proximal Portion of the Desmoglein 3 Ectodomain Induces Loss of Keratinocyte Adhesion, a Hallmark in Pemphigus Vulgaris

Pemphigus vulgaris is a severe autoimmune blistering disease characterized by IgG autoantibodies (auto-abs) against the desmosomal adhesion molecules desmoglein (DSG) 3 and DSG1. Underlying mechanisms leading to blister formation upon binding of DSG-specific IgG auto-abs are not fully understood. Numerous studies showed the pathogenicity of IgG auto-ab binding to the aminoterminal region 1 (EC1) of the DSG3 ectodomain. However, auto-abs in pemphigus vulgaris are polyclonal, including IgG against both aminoterminal- and membrane-proximal epitopes of the DSG3 ectodomain. In this study, the pathogenicity of a previously uncharacterized murine monoclonal IgG antibody, 2G4, directed against the membrane-proximal region (EC5) of the DSG3 ectodomain was characterized and tested in various specificity and functionality assays. The results clearly show that 2G4 is capable of inhibiting intercellular keratinocyte adhesion and of inducing cellular DSG3 redistribution by activation of the p38MAPK signal transduction pathway. In this study, we provide evidence that an IgG auto-abs directed against the membrane-proximal region EC5 of DSG3 induces acantholysis, the hallmark in pemphigus vulgaris. These findings challenge the current concept that IgG auto-abs targeting the NH2-terminal portion of the DSG3 ectodomain are pathogenic only. Our study provides further aspects for a deeper understanding of desmosomal keratinocyte adhesion and improves our insight into the complex auto-ab‒induced blister formation in pemphigus vulgaris.

TROP2 Down-regulated DSG2 to Promote Gastric Cancer Cell Invasion and Migration by EGFR/AKT and DSG2/PG/β-Catenin Pathways.

Gastric cancer (GC) is the fourth most commonly found cancer and the second- highest cause of cancer-related death worldwide. TROP2 overexpression is closely related to many cancers, including gastrointestinal tumors. DSG2 is an important protein in cell adhesion, and its loss affects cell migration. This study aimed to explore the specific mechanism of TROP2 in promoting gastric cancer and provide a basis for the prevention and treatment of gastric cancer. DSG2 was identified as an interacting protein of TROP2 in GC cells by coimmunoprecipitation and mass spectrometry. The regulated behavior of TROP2 on DSG2 expression was investigated with TROP2 over-expressure or knockdown. Cell-cell adhesion capacity mediated by DSG2 was evaluated by adhesion-related assays. Electron microscope observation was made for accessing GC tumor desmosome assembly. Proteins in EGFR/AKT and DSG2/PG/β-catenin pathways were evaluated by western blotting. This study suggests that abundant expression of TROP2 in GC cells lessened DSG2 levels as well as desmosome adhesion, increased cell invasion and migration, and promoted malignant progression through EGFR/AKT and DSG2/PG/β-catenin pathways. TROP2 promotes cell invasion and migration in gastric cancer by decreasing DSG2 expression through EGFR/AKT and DSG2/PG/β-catenin pathways.

An observational study to determine the role of indirect immunofluorescence and ELISA for desmogleins in the diagnosis and monitoring of autoimmune bullous disorders

BackgroundAutoimmune bullous disorder (AIBD) is a diverse group of blistering dermatoses that affects the skin and mucous membrane, characterized by the formation of autoantibodies against the desmosomal glycoproteins and adhesion molecular components of the basement membrane zone. Various immunoassay techniques for serological diagnosis are Direct Immunofluorescence (DIF), Indirect Immunofluorescence (IIF), Enzyme Linked Immunosorbent Assay (ELISA) and immunoblotting. Quantitative ELISA titer can also be used to monitor the disease activity and response to treatment. The aim of this study was to evaluate the role of IIF in diagnosing various AIBDs and the role of ELISA for desmogleins in monitoring disease activity in the pemphigus group of disorders. MethodsA total of 45 patients with freshly diagnosed AIBD were included in the study. Skin biopsies were done to establish the diagnosis by histopathology and DIF. BIOCHIP-based IIF assay was performed on the sera of the patient. The sensitivity and specificity of the IIF assay were then calculated based on the established diagnosis by Histopathological examination (HPE) and DIF. Quantitative ELISA titer was performed to measure the antibody (anti desmoglein (Dsg) 1 and 3) titre in serum samples of patients with pemphigus at baseline, 1 and 3 months follow-up after initiation of appropriate treatment therapy and results were then compared with disease activity scoring system. ResultsSensitivity and specificity of IIF for Dsg 1 for the pemphigus group were derived to be 85.7% and 98.2% respectively, while that for Dsg 3 were 100% and 98.7%, respectively. Sensitivity (90–100%) of IIF for Bullous pemphigoid was higher than specificity (85–96%). The ELISA titers of anti Dsg1 and 3 were also observed to fall sequentially so was the disease activity score during the follow-up visits at 1 and 3 months. ConclusionBiochip IIF assay can be used as a screening tool for the serological diagnosis of AIBD and quantitative ELISA for monitoring the disease activity and response to treatment.

143 Structure of a novel endoplasmic reticulum-desmosome complex and its role in skin disease

Desmosomes are adhesive intercellular junctions that provide strength and integrity to the epidermis and other epithelia. Dysfunction of the endoplasmic reticulum (ER) resident calcium pump, SERCA2, causes Darier’s disease (DD), an epidermal disorder characterized by compromised desmosomal adhesion and abnormal keratinocyte differentiation. However, the mechanism by which ER dysfunction impairs desmosome formation is unclear. Using electron microscopy and live-cell fluorescence imaging, we found that peripheral ER tubules are in close proximity to desmosomes and form mirror image arrangements at desmosomes.

DESMOSOMES IN ORAL DISEASES – A REVIEW

Desmosomes are the adhesion proteins that function both as an adhesive complex and as a cell surface attachment site for keratin intermediate filaments of the cytoskeleton. Desmosomes are more widely distributed along the lateral membranes. Desmosomes contain two types of transmembrane proteins desmogleins and desmocollins which belong to cadherin family. These desmosomal cadherins are linked to the keratin cytoskeleton via several cytoplasmic proteins such as desmoplakin and plakoglobin. Desmosomes play a critical role in the maintenance of normal tissue architecture. They are frequently mutated and desmosomal adhesion is compromised by antibodies in autoimmune diseases and result in blistering disorders in epithelium. Inherited mutations in genes in desmosomal constituents can also affect the skin and the heart. Desmosomes may have a tumour suppressor function and desmosomal cadherins have the capacity to suppress the invasiveness of cells in culture.

In Vitro, Ex Vivo, and In Vivo Models for the Study of Pemphigus.

Pemphigus is a life-threatening autoimmune disease. Several phenotypic variants are part of this family of bullous disorders. The disease is mainly mediated by pathogenic autoantibodies, but is also directed against two desmosomal adhesion proteins, desmoglein 1 (DSG1) and 3 (DSG3), which are expressed in the skin and mucosae. By binding to their antigens, autoantibodies induce the separation of keratinocytes, in a process known as acantholysis. The two main Pemphigus variants are Pemphigus vulgaris and foliaceus. Several models of Pemphigus have been described: in vitro, ex vivo and in vivo, passive or active mouse models. Although no model is ideal, different models display specific characteristics that are useful for testing different hypotheses regarding the initiation of Pemphigus, or to evaluate the efficacy of experimental therapies. Different disease models also allow us to evaluate the pathogenicity of specific Pemphigus autoantibodies, or to investigate the role of previously not described autoantigens. The aim of this review is to provide an overview of Pemphigus disease models, with the main focus being on active models and their potential to reproduce different disease subgroups, based on the involvement of different autoantigens.

Mechanisms Causing Acantholysis in Pemphigus-Lessons from Human Skin.

Pemphigus vulgaris (PV) is an autoimmune bullous skin disease caused primarily by autoantibodies (PV-IgG) against the desmosomal adhesion proteins desmoglein (Dsg)1 and Dsg3. PV patient lesions are characterized by flaccid blisters and ultrastructurally by defined hallmarks including a reduction in desmosome number and size, formation of split desmosomes, as well as uncoupling of keratin filaments from desmosomes. The pathophysiology underlying the disease is known to involve several intracellular signaling pathways downstream of PV-IgG binding. Here, we summarize our studies in which we used transmission electron microscopy to characterize the roles of signaling pathways in the pathogenic effects of PV-IgG on desmosome ultrastructure in a human ex vivo skin model. Blister scores revealed inhibition of p38MAPK, ERK and PLC/Ca2+ to be protective in human epidermis. In contrast, inhibition of Src and PKC, which were shown to be protective in cell cultures and murine models, was not effective for human skin explants. The ultrastructural analysis revealed that for preventing skin blistering at least desmosome number (as modulated by ERK) or keratin filament insertion (as modulated by PLC/Ca2+) need to be ameliorated. Other pathways such as p38MAPK regulate desmosome number, size, and keratin insertion indicating that they control desmosome assembly and disassembly on different levels. Taken together, studies in human skin delineate target mechanisms for the treatment of pemphigus patients. In addition, ultrastructural analysis supports defining the specific role of a given signaling molecule in desmosome turnover at ultrastructural level.

Rituximab - Progress but Still Not a Final Resolution for Pemphigus Patients: Clinical Report From a Single Center Study.

Pemphigus is a rare autoimmune disease characterized by the production of pathogenic autoantibodies against desmosomal adhesion proteins, desmoglein 1 and 3. The pathophysiological process leads to the development of blisters and erosions on mucosal and/or skin surfaces as the main clinical manifestation of the disease. Rituximab emerged as the first-line therapeutic option for pemphigus due to its ability to induce remission by depleting peripheral B lymphocytes. Our aim was to assess the efficacy of rituximab in the treatment of patients in Croatia. A single-center, retrospective study was conducted on 19 patients treated with rituximab following a rheumatoid arthritis dosing protocol between October 2015 and March 2021, with a mean follow-up of 24.1 months. After the first rituximab cycle, two patients achieved complete remission off therapy (10.5%), and six patients achieved complete remission on minimal therapy (31.6%). Partial remission was observed among ten patients (52.6%). Eight patients (44.4%) relapsed after the first rituximab cycle. The mean relapse time was 21 months. Seven patients received two rituximab cycles, and three patients received three cycles. Overall, 13 out of 19 patients experienced complete remission at some point during the study, while there were no non-responders after the rituximab treatment. No statistically significant associations were observed between age, sex, type of disease involvement and clinical remission, either on or off therapy. A steady decrease in anti-desmoglein 1 and anti-desmoglein 3 levels was measured among all patients following rituximab treatment. One patient experienced a treatment-related adverse event of infectious etiology (cellulitis). One patient died following the first rituximab cycle, with the cause of death likely not to be associated with the treatment. Rituximab is an effective disease-modifying agent in the treatment of pemphigus with the main benefit of reducing corticosteroid exposure and steroid-related side effects among pemphigus patients. However, a feature of rituximab therapy is high relapse rates and the need for repeated treatment cycles to achieve complete remission. Developing an optimal protocol for rituximab treatment and finding suitable markers for predicting relapse will improve the management of pemphigus patients.

Stabilization of Keratinocyte Monolayer Integrity in the Presence of Anti-Desmoglein-3 Antibodies through FcRn Blockade with Efgartigimod: Novel Treatment Paradigm for Pemphigus?

Pemphigus vulgaris is an autoimmune blistering disease of the epidermis, caused by autoantibodies against desmosomal proteins, mainly desmogleins 1 and 3, which induce an impairment of desmosomal adhesion and blister formation. Recent findings have shown that inhibition of immunoglobulin G binding on the neonatal Fc receptor, FcRn, results in reduced autoantibody recycling and shortens their half-life, providing a valid treatment option for PV. We have here analyzed the role of FcRn in human keratinocytes treated with antibodies isolated from pemphigus vulgaris patient or with recombinant anti-desmoglein-3 antibodies that induce pathogenic changes in desmosomes, such as loss of monolayer integrity, aberrant desmoglein-3 localization and degradation of desmoglein-3. We show that blocking IgG binding on FcRn by efgartigimod, a recombinant Fc fragment undergoing clinical studies for pemphigus, stabilizes the keratinocyte monolayer, whereas the loss of desmoglein-3 is not prevented by efgartigimod. Our data show that FcRn may play a direct role in the pathogenesis of pemphigus at the level of the autoantibody target cells, the epidermal keratinocytes. Our data suggest that in keratinocytes, FcRn may have functions different from its known function in IgG recycling. Therefore, stabilization of keratinocyte adhesion by FcRn blocking entities may provide a novel treatment paradigm for pemphigus.

Autoimmune Pemphigus: Latest Advances and Emerging Therapies.

Pemphigus represents a group of rare and severe autoimmune intra-epidermal blistering diseases affecting the skin and mucous membranes. These painful and debilitating diseases are driven by the production of autoantibodies that are mainly directed against the desmosomal adhesion proteins, desmoglein 3 (Dsg3) and desmoglein 1 (Dsg1). The search to define underlying triggers for anti-Dsg-antibody production has revealed genetic, environmental, and possible vaccine-driven factors, but our knowledge of the processes underlying disease initiation and pathology remains incomplete. Recent studies point to an important role of T cells in supporting auto-antibody production; yet the involvement of the myeloid compartment remains unexplored. Clinical management of pemphigus is beginning to move away from broad-spectrum immunosuppression and towards B-cell-targeted therapies, which reduce many patients’ symptoms but can have significant side effects. Here, we review the latest developments in our understanding of the predisposing factors/conditions of pemphigus, the underlying pathogenic mechanisms, and new and emerging therapies to treat these devastating diseases.

Evaluation of the Role of Oral Mucosal Direct Immunofluorescence and Salivary Desmoglein 1 and 3 Enzyme-Linked Immunosorbent Assay in Patients With Oral Mucosal Pemphigus.

Background:Pemphigus vulgaris (PV) is characterized by antibodies against desmosomal adhesion proteins desmoglein (Dsg) 1 and 3 which can be detected by direct immunofluorescence (DIF) or enzyme-linked immunosorbent assay (ELISA). Oral lesions usually precede cutaneous lesions and an early diagnosis can prevent mortality and morbidity. Dsg antibodies can be detected by ELISA in saliva of patients with oral mucosal pemphigus. This study compares oral mucosal DIF with the salivary Dsg1 and 3 ELISA.Materials and Methods:A total of 26 biopsy and/or DIF-proven PV patients with oral erosions without cutaneous lesions were included in the study. Biopsy of oral mucosa was taken for DIF by standard method. Saliva sample was obtained and processed for ELISA. The results were then compared.Results:Out of 26 patients, 22 (84.6%) had a positive oral mucosal DIF and four patients (15.4%) had negative DIF. Nine patients (34%) had positive salivary Dsg3 ELISA. Seven patients (27%) had positive salivary Dsg1 ELISA. Taking oral DIF as the gold standard, the sensitivity of salivary Dsg1 ELISA was 31.8% and of salivary Dsg3 ELISA was 40.9%.Conclusion:Although DIF is the gold standard for the diagnosis of PV, salivary Dsg1 and 3 ELISA can also be used in the diagnosis of oral pemphigus.

High-Pacing-Induced Heart Failure Strengthens Desmosomal Adhesion in Dogs via Sympathetic Activation

High-Pacing-Induced Heart Failure Strengthens Desmosomal Adhesion in Dogs via Sympathetic Activation

Desmoglein 2 regulates cardiogenesis by restricting hematopoiesis in the developing murine heart

Cardiac morphogenesis relies on intricate intercellular signaling. Altered signaling impacts cardiac function and is detrimental to embryonic survival. Here we report an unexpected regulatory role of the desmosomal cell adhesion molecule desmoglein 2 (Dsg2) on murine heart development. A large percentage of Dsg2-mutant embryos develop pericardial hemorrhage. Lethal myocardial rupture is occasionally observed, which is not associated with loss of cardiomyocyte contact but with expansion of abnormal, non-myocyte cell clusters within the myocardial wall. Two types of abnormal cell clusters can be distinguished: Type A clusters involve endocard-associated, round-shaped CD31+ cells, which proliferate and invade the myocardium. They acquire Runx1- and CD44-positivity indicating a shift towards a hematopoietic phenotype. Type B clusters expand subepicardially and next to type A clusters. They consist primarily of Ter119+ erythroid cells with interspersed Runx1+/CD44+ cells suggesting that they originate from type A cell clusters. The observed pericardial hemorrhage is caused by migration of erythrocytes from type B clusters through the epicardium and rupture of the altered cardiac wall. Finally, evidence is presented that structural defects of Dsg2-depleted cardiomyocytes are primary to the observed pathogenesis. We propose that cardiomyocyte-driven paracrine signaling, which likely involves Notch1, directs subsequent trans-differentiation of endo- and epicardial cells. Together, our observations uncover a hitherto unknown regulatory role of Dsg2 in cardiogenesis.

Pemphigus Vulgaris Combination Adjuvant Therapy of Systemic Corticosteroid with Sparing Agent Sodium Mycophenolate

Pemphigus Vulgaris(PV) is an autoimmune disease characterized by vesicles and bullae on the skin and mucosa resulting from an autoantibody reaction to desmosomal adhesion molecules desmoglein (Dsg) 1 and 3, which function as strong adhesions between keratinocytes. Pemphigus Vulgarisis more common in the fifth and sixth decades of age. The lesions are fragile blisters on the mucosa and skin. Diagnosing PV requires anamnesis, physical examination,and investigations such as histopathologic examination and direct immunofluorescence. Therapy generally uses steroids. Adjuvant treatmentis given to reduce the side effects of corticosteroids. We reported a male, 59 years old, was treated with blisters that break easily into blisters on the head, face, chest, back, groin and buttocks accompanied by burning and itching. In the scalp, facial, anterior et posteriortrunk, inguinal,and gluteal regions, multiple erythematous maculeswere found with lenticular-plaqueshape; it waspartially confluentwith thick brown crustswhich werechallengingto remove. The histopathologicexamination found the presence of suprabasal bullae with lymphocyte inflammation cells. The patient was diagnosed with PV and treated with corticosteroids with the sparing agent mycophenolate sodium andshowed clinical improvement. The first-linetreatment for pemphigus Vulgarisis systemic corticosteroids. Adjuvant sparing agent therapy is given to reduce the side effects of corticosteroids. Sodium mycophenolate sparing agent was selected because ofitsminimum side effects. In systemic management, the dose of corticosteroid and sparing agent mycophenolate sodium was gradually decreased. The patient experienced initial remission after treatment

Autoantibody-Specific Signalling in Pemphigus.

Pemphigus is a severe autoimmune disease impairing barrier functions of epidermis and mucosa. Autoantibodies primarily target the desmosomal adhesion molecules desmoglein (Dsg) 1 and Dsg 3 and induce loss of desmosomal adhesion. Strikingly, autoantibody profiles in pemphigus correlate with clinical phenotypes. Mucosal-dominant pemphigus vulgaris (PV) is characterised by autoantibodies (PV-IgG) against Dsg3 whereas epidermal blistering in PV and pemphigus foliaceus (PF) is associated with autoantibodies against Dsg1. Therapy in pemphigus is evolving towards specific suppression of autoantibody formation and autoantibody depletion. Nevertheless, during the acute phase and relapses of the disease additional treatment options to stabilise desmosomes and thereby rescue keratinocyte adhesion would be beneficial. Therefore, the mechanisms by which autoantibodies interfere with adhesion of desmosomes need to be characterised in detail. Besides direct inhibition of Dsg adhesion, autoantibodies engage signalling pathways interfering with different steps of desmosome turn-over. With this respect, recent data indicate that autoantibodies induce separate signalling responses in keratinocytes via specific signalling complexes organised by Dsg1 and Dsg3 which transfer the signal of autoantibody binding into the cell. This hypothesis may also explain the different clinical pemphigus phenotypes.

Evolving Mechanisms in the Pathophysiology of Pemphigus Vulgaris: A Review Emphasizing the Role of Desmoglein 3 in Regulating p53 and the Yes-Associated Protein

The immunobullous condition Pemphigus Vulgaris (PV) is caused by autoantibodies targeting the adhesion proteins of desmosomes, leading to blistering in the skin and mucosal membrane. There is still no cure to the disease apart from the use of corticosteroids and immunosuppressive agents. Despite numerous investigations, the pathological mechanisms of PV are still incompletely understood, though the etiology is thought to be multifactorial. Thus, further understanding of the molecular basis underlying this disease process is vital to develop targeted therapies. Ample studies have highlighted the role of Desmoglein-3 (DSG3) in the initiation of disease as DSG3 serves as a primary target of PV autoantibodies. DSG3 is a pivotal player in mediating outside-in signaling involved in cell junction remodeling, cell proliferation, differentiation, migration or apoptosis, thus validating its biological function in tissue integrity and homeostasis beyond desmosome adhesion. Recent studies have uncovered new activities of DSG3 in regulating p53 and the yes-associated protein (YAP), with the evidence of dysregulation of these pathways demonstrated in PV. The purpose of this review is to summarize the earlier and recent advances highlighting our recent findings related to PV pathogenesis that may pave the way for future research to develop novel specific therapies in curing this disease.

Disruption of the desmoglein adhesive interface causes Arrhythmogenic Cardiomyopathy

Arrhythmogenic Cardiomyopathy (ACM) in the majority of cases is caused by mutations in genes of the desmosomal cell-cell adhesion complex. ACM is characterized by progressive loss of cardiomyocytes with fibrosis, ventricular systolic dysfunction and life-threatening arrhythmias. Even though the pathological phenotype is well known, the underlying mechanisms are controversial and not well understood. Here, we tested the hypothesis that impaired adhesive function of desmosomes is central for disease development and progression. We generated a CRISPR/Cas9-based knock-in mouse model with exchange of tryptophan 2 to alanin in desmoglein-2 (Dsg2-W2A), which is a crucial desmosomal adhesion molecule in cardiomyocytes. This mutation, based on structural data, aims to abrogate the so-called tryptophan swap, a suggested central binding mechanism of Dsg2. In line with the dysfunctional adhesion hypothesis, mutant mice develop a severe cardiac phenotype recalling the characteristics of ACM including cardiac fibrosis, impaired systolic function and arrhythmia after adrenergic stimulation. While protein levels and localization of intercalated disc molecules were unchanged, structurally altered and even disrupted configurations of cardiomyocyte interfaces were evident on the ultrastructural level. Cell-cell dissociation assays and force spectroscopy measurements by atomic force microscopy confirmed the suspected adhesion defect of Dsg2-W2A molecules on cellular and molecular level. In summary, the adhesion-deficient Dsg2-W2A mouse model fulfils the criteria required to establish an ACM diagnosis. This shows that disruption of desmosomal adhesion is sufficient for ACM development with induction of the described phenotype. Further, the Dsg2-W2A mouse line represents a valuable model to study mechanisms of the disease and to identify novel treatments for ACM in vivo.