An imbalance in Akt/mTOR is involved in the apoptotic and acantholytic processes in a mouse model of pemphigus vulgaris

New insights into pyroptosis in pemphigus: from cellular structure to therapeutic targeting

BACKGROUND

Pemphigus is an autoimmune blistering disease where autoantibodies target desmoglein (Dsg) antigens on keratinocytes, triggering the p38 MAPK pathway, Dsg internalization, desmosomal dissolution, and keratinocyte apoptosis, are essential for blister formation. Recent research indicates keratinocyte pyroptosis may exacerbate acantholysis and delay wound healing. Current treatments, including corticosteroids and immunosuppressants, are effective but have significant side effects, such as prolonged wound healing and increased infection risk. Understanding these inflammatory processes is crucial for developing effective treatments for pemphigus.

METHODS

The authors conducted a comprehensive review of the literature, analyzing recent findings regarding the upregulation of pyroptosis-related proteins in pemphigus.

RESULTS

The present findings highlight a significant upregulation of pyroptosis-related proteins, which play a crucial role in the inflammatory response and blister formation characteristic of pemphigus. Key proteins such as cytokines IL-1β, IL-18, High Mobility Group Box-1 (HMGB1), and Parkin, along with NOD-like receptors and P2×7 receptors, were identified as pivotal in facilitating pyroptosis. The study also discusses potential therapeutic approaches targeting these proteins to modulate the disease pathway effectively.

STUDY LIMITATIONS

This study aimed to investigate the role of pyroptosis in the pathogenesis of pemphigus, focusing on its potential as a novel therapeutic target.

CONCLUSIONS

Pyroptosis significantly contributes to the pathogenesis of pemphigus and presents a promising target for therapy. Targeting specific molecules involved in the pyroptosis pathway offers the potential for developing more precise and less toxic treatments, allowing the shift from traditional therapies towards targeted therapeutic strategies.

EGFR Inhibition by Erlotinib Rescues Desmosome Ultrastructure and Keratin Anchorage and Protects against Pemphigus Vulgaris IgG-Induced Acantholysis in Human Epidermis

Pemphigus is a severe blistering disease caused by autoantibodies primarily against the desmosomal cadherins desmoglein (DSG)1 and DSG3, which impair desmosome integrity. Especially for the acute phase, additional treatment options allowing to reduce corticosteroids would fulfill an unmet medical need. In this study, we provide evidence that EGFR inhibition by erlotinib ameliorates pemphigus vulgaris IgG-induced acantholysis in intact human epidermis. Pemphigus vulgaris IgG caused phosphorylation of EGFR (Y845) and Rous sarcoma-related kinase in human epidermis. In line with this, a phosphotyrosine kinome analysis revealed a robust response associated with EGFR and Rous sarcoma-related kinase family kinase signaling in response to pemphigus vulgaris IgG but not to pemphigus foliaceus autoantibodies. Erlotinib inhibited pemphigus vulgaris IgG-induced epidermal blistering and EGFR phosphorylation, loss of desmosomes, as well as ultrastructural alterations of desmosome size, plaque symmetry, and keratin filament insertion and restored the desmosome midline considered as hallmark of mature desmosomes. Erlotinib enhanced both single-molecule DSG3-binding frequency and strength and delayed DSG3 fluorescence recovery, supporting that EGFR inhibition increases DSG3 availability and cytoskeletal anchorage. Our data indicate that EGFR is a promising target for pemphigus therapy owing to its link to several signaling pathways known to be involved in pemphigus pathogenesis.

What is novel in the clinical management of pemphigus vulgaris?

INTRODUCTION

Pemphigus, an uncommon autoimmune blistering disorder affecting the skin and mucous membranes, currently with mortality primarily attributed to adverse reactions resulting from treatment protocols. Additionally, the existing treatments exhibit a notable recurrence rate. The high incidence of relapse and the considerable adverse effects associated with treatment underscore the imperative to explore safer and more effective therapeutic approaches. Numerous potential therapeutic targets have demonstrated promising outcomes in trials or preliminary research stages. These encompass anti-CD-20 agents, anti-CD-25 agents, TNF-α inhibition, FAS Ligand Inhibition, FcRn inhibition, BAFF inhibition, Bruton's tyrosine kinase (BTK) inhibition, CAAR T Cells, JAK inhibition, mTOR inhibition, abatacept, IL-4 inhibition, IL-17 inhibition, IL-6 inhibition, polyclonal Regulatory T Cells, and autologous hematopoietic stem cell transplantation.

AREAS COVERED

The most significant studies regarding the impact and efficacy of the mentioned treatments on pemphigus were meticulously curated through a comprehensive search conducted on the PubMed database. Moreover, the investigations of interest cited in these studies were also integrated.

EXPERT OPINION

The efficacy and safety profiles of the other treatments under discussion do not exhibit the same level of robustness as anti-CD20 therapy, which is anticipated to endure as a critical element in pemphigus treatment well into the foreseeable future.

The PI3K-Akt-mTOR and Associated Signaling Pathways as Molecular Drivers of Immune-Mediated Inflammatory Skin Diseases: Update on Therapeutic Strategy Using Natural and Synthetic Compounds

The dysregulated phosphatidylinositol-3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) signaling pathway has been implicated in various immune-mediated inflammatory and hyperproliferative dermatoses such as acne, atopic dermatitis, alopecia, psoriasis, wounds, and vitiligo, and is associated with poor treatment outcomes. Improved comprehension of the consequences of the dysregulated PI3K/Akt/mTOR pathway in patients with inflammatory dermatoses has resulted in the development of novel therapeutic approaches. Nonetheless, more studies are necessary to validate the regulatory role of this pathway and to create more effective preventive and treatment methods for a wide range of inflammatory skin diseases. Several studies have revealed that certain natural products and synthetic compounds can obstruct the expression/activity of PI3K/Akt/mTOR, underscoring their potential in managing common and persistent skin inflammatory disorders. This review summarizes recent advances in understanding the role of the activated PI3K/Akt/mTOR pathway and associated components in immune-mediated inflammatory dermatoses and discusses the potential of bioactive natural products, synthetic scaffolds, and biologic agents in their prevention and treatment. However, further research is necessary to validate the regulatory role of this pathway and develop more effective therapies for inflammatory skin disorders.

Dsg3 epitope-specific signalling in pemphigus

Introduction

Pemphigus is an autoantibody driven disease that impairs the barrier function of the skin and mucosa by disrupting desmosomes and thereby impeding cellular cohesion. It is known that the different clinical phenotypes of pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are dependent on the autoantibody profile and target antigens that, amongst others, are primarily desmoglein (Dsg)1 and/or Dsg3 for PV and Dsg1 for PF. However, it was reported that autoantibodiesagainst different epitopes of Dsg1 and Dsg3 can be pathogenic or not. The underlying mechanisms are very complex and involve both direct inhibition of Dsg interactions and downstream signalling. The aim of this study was to find out whether there is target-epitope-specific Dsg3 signalling by comparing the effects of the two pathogenic murine IgGs, 2G4 and AK23.

Methods

Dispase-based dissociation assay, Western Blot analysis, Stimulated emission depletion microscopy, Fura-based Ca2+ flux measurements, Rho/Rac G-Protein-linked immunosorbent assay, Enzyme-linked immunosorbent assay.

Results

The IgGs are directed against the EC5 and EC1 domain of Dsg3, respectively. The data show that 2G4 was less effective in causing loss of cell adhesion, compared to AK23. STED imaging revealed that both autoantibodies had similar effects on keratin retraction and reduction of desmosome number whereas only AK23 induced Dsg3 depletion. Moreover, both antibodies induced phosphorylation of p38MAPK and Akt whereas Src was phosphorylated upon treatment with AK23 only. Interestingly, Src and Akt activation were p38MAPK-dependent. All pathogenic effects were rescued by p38MAPK inhibition and AK23-mediated effects were also ameliorated by Src inhibition.

Discussion

The results give first insights into pemphigus autoantibody-induced Dsg3 epitope-specific signalling which is involved in pathogenic events such as Dsg3 depletion.

Mouse models of pemphigus: valuable tools to investigate pathomechanisms and novel therapeutic interventions

Autoimmune blistering diseases (AIBD) are paradigms of autoantibody-mediated organ-specific autoimmune disorders that involve skin and/or mucous membranes. Compared to other autoimmune diseases, the pathogenicity of autoantibodies in AIBD is relatively well described. Pemphigus is a potentially lethal autoantibody driven autoimmune disorder with a strong HLA class II association. It is mainly characterized by IgG against the desmosomal adhesion molecules desmoglein 3 (Dsg3) and Dsg1. Several murine pemphigus models were developed subsequently, each allowing the analysis of a characteristic feature, such as pathogenic IgG or Dsg3-specific T or B cells. Thus, the models can be employed to preclinically evaluate potentially novel therapies. We here thoroughly summarize past and recent efforts in developing and utilizing pemphigus mouse models for pathomechanistic investigation and therapeutic interventions.

Mitochondrial Autoantibodies and the Role of Apoptosis in Pemphigus Vulgaris

Pemphigus vulgaris (PV) is an IgG autoantibody-mediated, potentially fatal mucocutaneous disease manifested by progressive non-healing erosions and blisters. Beyond acting to inhibit adhesion molecules, PVIgGs elicit a unique process of programmed cell death and detachment of epidermal keratinocytes termed apoptolysis. Mitochondrial damage by antimitochondrial antibodies (AMA) has proven to be a critical link in this process. AMA act synergistically with other autoantibodies in the pathogenesis of PV. Importantly, absorption of AMA inhibits the ability of PVIgGs to induce blisters. Pharmacologic agents that protect mitochondrial function offer a new targeted approach to treating this severe immunoblistering disease.

What protein kinases are crucial for acantholysis and blister formation in pemphigus vulgaris? A systematic review

Pemphigus vulgaris (PV) is a potentially fatal autoimmune blistering disease characterized by cell-cell detachment (or acantholysis) and blister formation. While the signaling mechanisms that associate with skin/mucosal blistering are being elucidated, specific treatment strategies targeting PV-specific pathomechanisms, particularly kinase signaling, have yet to be established. Hence, the aim of this review was to systematically evaluate molecules in the class of kinases that are essential for acantholysis and blister formation and are therefore candidates for targeted therapy. English articles from PubMed and Scopus databases were searched, and included in vitro, in vivo, and human studies that investigated the role of kinases in PV. We selected studies, extracted data and assessed risk of bias in duplicates and the results were reported according to the methodology outlined by the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). The risk of bias assessment was performed on in vivo studies utilizing SYRCLE's risk of bias tool. Thirty-five studies were included that satisfied the pathogenicity criterion of kinases in PV, the vast majority being experimental models that used PV sera (n = 13) and PV-IgG (n = 22). Inhibition of kinase activity (p38MAPK, PKC, TK, c-Src, EGFR, ERK, mTOR, BTK, and CDK2) was achieved mostly by pharmacological means. Overall, we found substantial evidence that kinase inhibition reduced PV-associated phosphorylation events and keratinocyte disassociation, prevented acantholysis, and blocked blister formation. However, the scarce adherence to standardized reporting systems and the experimental protocols/models used did limit the internal and external validity of these studies. In summary, this systematic review highlighted the pathogenic intracellular events mediated by kinases in PV acantholysis and presented kinase signaling as a promising avenue for translational research. In particular, the molecules identified and discussed in this study represent potential candidates for the development of mechanism-based interventions in PV.

Apoptolysis: a less understood concept in the pathogenesis of Pemphigus Vulgaris

Pemphigus Vulgaris (PV) is a severe autoimmune disease characterized by supra-basal blisters in the skin and mucous membranes of a wide range of mammals, including humans. It not only affects the skin but also has severe oral manifestations. It has been stated that auto-antibodies are produced, for unknown reasons, which are directed against desmogleins present on the epithelium and thus leads to acantholysis and intraepithelial blistering. But the exact mechanism is still not completely understood. Here we would like to shed light on a new pathologic mechanism i.e., apoptolysis, which emphasizes that apoptotic enzymes contribute to acantholysis development both in terms of molecular events and chronologic sequence. A possible role of apoptolysis has been discussed in purview of PV.

Marked to Die-Cell Death Mechanisms for Keratinocyte Acantholysis in Pemphigus Diseases

Pemphigus is a group of blistering autoimmune diseases causing painful skin lesions, characterized by acantholysis and by the production of autoantibodies against, mainly, adhesion proteins. We reviewed the literature for molecules and/ or features involved in the 12 cell death pathways described by Nomenclature Committee on Cell Death, taking place in pemphigus patients, cell lines, or human skin organ cultures treated with sera or IgG from pemphigus patients or in pemphigus mouse models, and found 61 studies mentioning 97 molecules involved in cell death pathways. Among the molecules, most investigated were pleiotropic molecules such as TNF and CASP3, followed by FASL and CASP8, and then by FAS, BAX, BCL2, and TP53, all involved in more than one pathway but interpreted to function only within apoptosis. Most of these previous investigations focused only on apoptosis, but four recent studies, using TUNEL assays and/or electron microscopy, disqualified this pathway as a previous event of acantholysis. For PV, apoptolysis was suggested as a cell death mechanism based on pathogenic autoantibodies diversity, mitochondrial dysfunction, and p38 MAPK signaling. To answer those many questions that remain on cell death and pemphigus, we propose well-controlled, statistically relevant investigations on pemphigus and cell death pathways besides apoptosis, to overcome the challenges of understanding the etiopathology of pemphigus diseases.

Caspase Inhibition as a Possible Therapeutic Strategy for Pemphigus Vulgaris: A Systematic Review of Current Evidence

Simple Summary

Pemphigus vulgaris is a potentially fatal disease characterised by blister formation affecting the skin and mouth. The mechanisms of blister formation may involve a biological process called apoptosis—a type of cell death—and some death-associated molecules known as caspases. Our review of the existing literature shows that caspase inhibitors exhibit an inhibitory effect on PV-induced apoptosis formation in vitro. In particular, activity of caspase 1 and caspase 3 is essential for the development of PV in vitro and in vivo. However, a majority of in vivo studies assessing caspase inhibition in PV models have a high risk of bias.

Abstract

Background: Pemphigus vulgaris (PV) is an IgG-mediated autoimmune disease characterised by epithelial cell–cell detachment (acantholysis) resulting in mucocutaneous blistering. The exact pathogenesis of blister formation is unknown and this has hampered the development of non-steroidal, mechanism-based treatments for this autoimmune disease. This systematic review aims to investigate the role of caspases in the pathogenesis of PV to inform the choice of more targeted therapeutic agents. Methods: A systematic search of MEDLINE/PubMed and Scopus databases was conducted to identify eligible studies. Multiple phases of inclusion and exclusion of the primary articles were conducted in pairs, and studies were recorded and analysed according to the latest version of the preferred reporting items for systematic reviews and meta-analyses (PRISMA). Risk of bias assessment was conducted for extracted in vivo animal intervention studies using SYRCLE’s risk of bias tool. Results: Eight articles from a total of 2338 in vitro, in vivo, and human studies met the inclusion criteria, with a high degree of inter-rater reliability. By and large, the results show that caspase activation was pathogenic in experimental PV because pan-caspase inhibitors could block or reduce PV acantholysis and blistering in vitro and in vivo, respectively. The pathogenic pathways identified involved caspase-1 and caspase-3. One study failed to show any improvement in the PV model with a caspase inhibitor. The majority of animal studies had high or unclear risk of bias. Conclusion: There are consistent data pointing towards a pathogenic role of caspase activation in PV acantholysis. However, high-quality evidence to confirm that caspase inhibition can prevent PV-induced blistering in vivo is limited. Therefore, further research is required to test the preclinical efficacy of caspase inhibitors in PV.

Mechanism-based therapeutic targets of pemphigus vulgaris: A scoping review of pathogenic molecular pathways

Pemphigus vulgaris (PV) is a potentially fatal autoimmune blistering disease characterised by cell-cell detachment or acantholysis. The mechanisms which follow antibody (Ab) binding and culminate in acantholytic changes and skin/mucosal blistering have not been fully clarified. Current treatment strategies are not specific to PV pathophysiology and although life-saving, harbour considerable side effects. We aimed to systematically assess the molecules amenable to targeted treatments that follow Ab binding and are associated with PV acantholysis. The resulting scoping review was conducted under PRISMA-ScR guidelines with clear inclusion and exclusion criteria and focused specifically on kinases, caspases, proteases, hydrolytic enzymes and other molecules of interest postulated to take part in the pathophysiology of PV. The review process resulted in the identification of 882 articles, of which 56 were eligible for qualitative synthesis. From the included articles, the majority (n = 42) used PV-IgG as the pathogenic agent, mainly via in vitro (n = 16) and in vivo (n = 10) models. Twenty-five molecules were found to play a pathogenic role in PV, including uPA, ADAM10, EGFR, Src, PKC, cdk2, ERK, PLC, calmodulin, NOS, p38MAPK and caspase-3. Selective inhibition of these molecules resulted in varying degrees of reduction in acantholysis and blistering. The pathogenic molecules identified in this review represent potential candidates for clinical translation.

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.

Critical appraisal of different triggering pathways for the pathobiology of pemphigus vulgaris-A review

Pemphigus vulgaris is an autoimmune blistering disease with an increased potential for mortality. The epithelium is key in understanding the pathobiology as it is specialized to perform functions like mechanical protection, immunological defense, and proprioception. In order to perform these array of functions, epithelial integrity is important. This integrity is maintained by a host of molecules which orchestrate the ability of the keratinocytes to function as a single unit. Desmoglein 3 antibodies formed in genetically susceptible individuals are known to cause the disruption of the intact oral mucosa leading to the formation of blisters in pemphigus vulgaris patients. However, there are underlying complex triggering pathways leading to the clinical disease. The aim of the review is to congregate and critically appraise the various triggering pathways which contribute toward the pathobiology of pemphigus vulgaris. Articles relevant to the pathobiology of pemphigus vulgaris were identified from various search databases till the year 2020. The pathogenesis of pemphigus vulgaris is complex, and it involves an in-depth understanding of the various predisposing factors, provoking factors, and progression mechanisms. Congregation of the various triggering pathways will open our minds to understand pemphigus vulgaris better and in turn develop a reliable treatment in the near future.

Role of PKC and ERK Signaling in Epidermal Blistering and Desmosome Regulation in Pemphigus

Desmosomes reinforce cohesion of epithelial cells at the interface between adjacent cells. They include the cadherin-type adhesion molecules desmoglein 1 (Dsg1) and Dsg3. Pemphigus vulgaris (PV) is an autoimmune disease in which circulating autoantibodies (PV-IgG) targeting Dsg1 and 3 cause characteristic epidermal blister formation. It has been shown that PV-IgG binding induced activation of kinases such as ERK and PKC, and inhibition of these signaling pathways prevented loss of cell cohesion in cell cultures. However, the role of Erk and PKC in blister formation and regulation of desmosome ultrastructure in human skin are unknown. Accordingly, we assessed the role of PKC and ERK signaling pathways in blister formation and regulation of desmosome ultrastructure in human epidermis. Here we performed electron microscopy analyses using human skin explants injected with PV-IgG together with inhibitors for PKC or ERK signaling. Inhibition of PKC was not effective to prevent suprabasal blister formation or ultrastructural alterations of desmosomes. In contrast, inhibition of ERK signaling significantly ameliorated blister formation and decrease in the number of desmosomes whereas shortening and splitting of desmosomes and keratin filament insertion were not different from samples treated with PV-IgG alone. However, apical desmosomes between basal and suprabasal cells remained unaltered when ERK signaling was inhibited. Therefore, our results show that inhibition of ERK but not PKC signaling appears to be effective to ameliorate blistering and alterations of desmosome ultrastructure triggered by PV-IgG in human skin.

The involvement of ADAM10 in acantholysis in mucocutaneous pemphigus vulgaris depends on the autoantibody profile of each patient

BACKGROUND

Acantholysis in pemphigus vulgaris (PV) may be triggered by desmoglein (Dsg) and non-Dsg autoantibodies. The autoantibody profile of each patient results in distinct intracellular signalling patterns.

OBJECTIVES

Based on our previous findings, we aimed to elucidate whether PV acantholysis in a mouse model may be mediated by activation of a disintegrin and metalloproteinase 10 (ADAM10).

METHODS

We used three PV-IgG fractions from different patients containing high or low levels of anti-Dsg1 and anti-Dsg3 antibodies, and the presence or not of anti-desmocollin (Dsc) antibodies, using a passive transfer mouse model of PV.

RESULTS

Although all of the PV-IgG fractions produced suprabasal acantholysis, only those containing anti-Dsg1/3, but not anti-Dsc2/3 antibodies, induced ADAM10 activation in a Src-dependent way, and an increase in the epidermal growth factor (EGF) receptor ligands EGF and betacellulin (BTC). In contrast, the presence of anti-Dsc2/3 antibodies, in addition to anti-Dsg1/3, triggered earlier and ADAM10-independent epidermal detachment, with no increase in EGF and BTC, which was associated with an earlier and more intense acantholysis.

CONCLUSIONS

All PV-IgG fractions produced suprabasal acantholysis, but our results reveal that depending on the levels of anti-Dsg antibodies or the presence of non-Dsg antibodies, such as anti-Dsc, more severe cell-cell epidermal detachment will occur at different times, and in an ADAM10-dependent manner or not. Acantholysis in these different groups of patients with PV may be a consequence of the activation of specific intracellular mechanisms downstream of Autoantibodies binding to Dsg or non-Dsg proteins, and therefore more specific therapeutic approaches in PV should be used. What's already known about this topic? Suprabasal acantholysis in pemphigus vulgaris (PV) may be triggered by both desmoglein (Dsg) and non-Dsg autoantibodies. The autoantibody profile of each patient is associated with a distinct intracellular signalling pattern. What does this study add? In patients with PV with anti-Dsg3 and anti-Dsg1, but not anti-desmocollin (Dsc)3 antibodies, ADAM10 activation is induced in an Src-dependent way, together with an increase in the epidermal growth factor receptor (EGFR) ligands EGF and betacellulin. The presence of anti-Dsc3 antibodies triggers an earlier and ADAM10-independent acantholysis, without increasing EGFR ligands, and is associated with more severe epidermal detachment. Lower levels of anti-Dsc3 antibodies are associated with less severe acantholysis. What is the translational message? In some patients with PV, the severity and the timing for cell-cell detachment seem to depend on the level of anti-Dsg1/3 antibodies, although other as yet uncharacterized antibodies may also participate. These patients with PV would exhibit inhibition of acantholysis by Src, ADAM10, EGF and EGFR inhibitors. In other patients, the presence of non-Dsg antibodies, such as anti-Dsc2/3, would produce an earlier and more severe ADAM10-independent suprabasal acantholysis.

Role of Dsg1- and Dsg3-Mediated Signaling in Pemphigus Autoantibody-Induced Loss of Keratinocyte Cohesion

Pemphigus is an autoimmune dermatosis in which mucocutaneous blisters are induced primarily by autoantibodies against Desmoglein (Dsg) 1 and 3. Pemphigus vulgaris (PV) usually is associated with autoantibodies against Dsg3 whereas pemphigus foliaceus (PF) patients present autoantibodies against Dsg1. Several signaling pathways were proposed to cause loss of keratinocyte adhesion. However, relevance of different signaling pathways and role of Dsg1 and 3 to trigger signaling are not fully understood. Here, we show that Ca²⁺ chelation reduced PV-IgG- and PF-IgG-mediated loss of HaCaT keratinocyte cohesion whereas EGFR inhibition did not inhibit effects of PF-IgG. PV-IgG activated EGFR in a Src-dependent manner whereas both PV-IgG and PF-IgG caused Ca²⁺ influx independent of EGFR. ERK activation was Src-dependent in response to PV-IgG but not PF-IgG. To delineate the roles of Dsg isoforms to trigger signaling pathways, Dsg3- and Dsg2-deficient HaCaT keratinocyte cell lines were generated using CRISPR/Cas9. Dsg3- but not Dsg2-deficient cells were protected against PV-IgG-induced loss of cell adhesion. Ca²⁺ influx and ERK activation in response to PF-IgG were preserved in both cell lines.

Cadherins: cellular adhesive molecules serving as signalling mediators

The single pass, transmembrane proteins of the cadherin family have been appreciated as important proteins that regulate intercellular adhesion. In addition to this critical function, cadherins contribute to important signalling events that control cellular homeostasis. Many examples exist of classical, desmosomal and atypical cadherins participating in the regulation of signalling events that control homeostatic functions in cells. Much of the work on cadherin mediated signalling focuses on classical cadherins or on specific disease states such as pemphigus vulgaris. Cadherin mediated signalling has been shown to play critical roles during development, in proliferation, apoptosis, disease pathobiology and beyond. It is becoming increasingly clear that cadherins operate through a range of molecular mechanisms. The diversity of pathways and cellular functions regulated by cadherins suggests that we have only scratched the surface in terms of the roles that these versatile proteins play in signalling and cellular function.

The Evolving Story of Autoantibodies in Pemphigus Vulgaris: Development of the "Super Compensation Hypothesis"

Emerging data and innovative technologies are re-shaping our understanding of the scope and specificity of the autoimmune response in Pemphigus vulgaris (PV), a prototypical humorally mediated autoimmune skin blistering disorder. Seminal studies identified the desmosomal proteins Desmoglein 3 and 1 (Dsg3 and Dsg1), cadherin family proteins which function to maintain cell adhesion, as the primary targets of pathogenic autoAbs. Consequently, pathogenesis in PV has primarily considered to be the result of anti-Dsg autoAbs alone. However, accumulating data suggesting that anti-Dsg autoAbs by themselves cannot adequately explain the loss of cell-cell adhesion seen in PV, nor account for the disease heterogeneity exhibited across PV patients has spurred the notion that additional autoAb specificities may contribute to disease. To investigate the role of non-Dsg autoAbs in PV, an increasing number of studies have attempted to characterize additional targets of PV autoAbs. The recent advent of protein microarray technology, which allows for the rapid, highly sensitive, and multiplexed assessment of autoAb specificity has facilitated the comprehensive classification of the scope and specificity of the autoAb response in PV. Such detailed deconstruction of the autoimmune response in PV, beyond simply tracking anti-Dsg autoAbs, has provided invaluable new insights concerning disease mechanisms and enhanced disease classification which could directly translate into superior tools for prognostics and clinical management, as well as the development of novel, disease specific treatments.

Autoantibody Signaling in Pemphigus Vulgaris: Development of an Integrated Model

Pemphigus vulgaris (PV) is an autoimmune skin blistering disease effecting both cutaneous and mucosal epithelia. Blister formation in PV is known to result from the binding of autoantibodies (autoAbs) to keratinocyte antigens. The primary antigenic targets of pathogenic autoAbs are known to be desmoglein 3, and to a lesser extent, desmoglein 1, cadherin family proteins that partially comprise the desmosome, a protein structure responsible for maintaining cell adhesion, although additional autoAbs, whose role in blister formation is still unclear, are also known to be present in PV patients. Nevertheless, there remain large gaps in knowledge concerning the precise mechanisms through which autoAb binding induces blister formation. Consequently, the primary therapeutic interventions for PV focus on systemic immunosuppression, whose side effects represent a significant health risk to patients. In an effort to identify novel, disease-specific therapeutic targets, a multitude of studies attempting to elucidate the pathogenic mechanisms downstream of autoAb binding, have led to significant advancements in the understanding of autoAb-mediated blister formation. Despite this enhanced characterization of disease processes, a satisfactory explanation of autoAb-induced acantholysis still does not exist. Here, we carefully review the literature investigating the pathogenic disease mechanisms in PV and, taking into account the full scope of results from these studies, provide a novel, comprehensive theory of blister formation in PV.

Monopathogenic vs multipathogenic explanations of pemphigus pathophysiology

This viewpoint highlights major, partly controversial concepts about the pathogenesis of pemphigus. The monopathogenic theory explains intra-epidermal blistering through the "desmoglein (Dsg) compensation" hypothesis, according to which an antibody-dependent disabling of Dsg 1- and/or Dsg 3-mediated cell-cell attachments of keratinocytes (KCs) is sufficient to disrupt epidermal integrity and cause blistering. The multipathogenic theory explains intra-epidermal blistering through the "multiple hit" hypothesis stating that a simultaneous and synchronized inactivation of the physiological mechanisms regulating and/or mediating intercellular adhesion of KCs is necessary to disrupt epidermal integrity. The major premise for a multipathogenic theory is that a single type of autoantibody induces only reversible changes, so that affected KCs can recover due to a self-repair. The damage, however, becomes irreversible when the salvage pathway and/or other cell functions are altered by a partnering autoantibody and/or other pathogenic factors. Future studies are needed to (i) corroborate these findings, (ii) characterize in detail patient populations with non-Dsg-specific autoantibodies, and (iii) determine the extent of the contribution of non-Dsg antibodies in disease pathophysiology.

Crosstalk between Signaling Pathways in Pemphigus: A Role for Endoplasmic Reticulum Stress in p38 Mitogen-Activated Protein Kinase Activation?

Pemphigus consists of a group of chronic blistering skin diseases mediated by autoantibodies (autoAbs). The dogma that pemphigus is caused by keratinocyte dissociation (acantholysis) as a distinctive and direct consequence of the presence of autoAb targeting two main proteins of the desmosome—desmoglein (DSG) 1 and/or DSG3—has been put to the test. Several outside-in signaling events elicited by pemphigus autoAb in keratinocytes have been described, among which stands out p38 mitogen-activated protein kinase (p38 MAPK) engagement and its apoptotic effect on keratinocytes. The role of apoptosis in the disease is, however, debatable, to an extent that it may not be a determinant event for the occurrence of acantholysis. Also, it has been verified that compromised DSG trans-interaction does not lead to keratinocyte dissociation when p38 MAPK is inhibited. These examples of conflicting results have been followed by recent work revealing an important role for endoplasmic reticulum (ER) stress in pemphigus’ pathogenesis. ER stress is known to activate the p38 MAPK pathway, and vice versa. However, this relationship has not yet been studied in the context of activated signaling pathways in pemphigus. Therefore, by reviewing and hypothetically connecting the role(s) of ER stress and p38 MAPK pathway in pemphigus, we highlight the importance of elucidating the crosstalk between all activated signaling pathways, which may in turn contribute for a better understanding of the role of apoptosis in the disease and a better management of this life-threatening condition.

Is Myc an Important Biomarker? Myc Expression in Immune Disorders and Cancer

The proto-oncogene Myc serves as a paradigm for understanding the dynamics of transcriptional regulation. Myc protein has been linked to immune dysfunction, cancer development and neoplastic transformation. We review recent research regarding functions of Myc as an important modulator in immune disorders, postallogeneic hematopoietic stem cell transplantation (HSCT) and several cancers. Myc overexpression has been repeatedly linked to immune disorders and specific cancers, such as myasthenia gravis, psoriasis, pemphigus vulgaris, atherosclerosis, long-term allogeneic survival among HSCT patients, (primary) inflammatory breast cancer, (primary) ovarian carcinoma and hematological malignancies: acute myeloid leukemia, chronic myelogenous leukemia, Hodgkin's lymphoma and diffuse large B-cell lymphoma. However, decreased expression of Myc has been observed in HSCT patients who did not survive. Understanding impaired or inappropriate expression of Myc may present a path for the discovery of new targets for therapeutic applications.

Different signaling patterns contribute to loss of keratinocyte cohesion dependent on autoantibody profile in pemphigus

Pemphigus is an autoimmune blistering skin disease caused primarily by autoantibodies against desmoglein (Dsg)1 and 3. Here, we characterized the mechanisms engaged by pemphigus IgG from patients with different clinical phenotypes and autoantibody profiles. All pemphigus vulgaris (PV) and pemphigus foliaceus (PF) IgG and AK23, a monoclonal mouse antibody against Dsg3, caused loss of cell cohesion, cytokeratin retraction and p38MAPK activation. Strong alterations in Dsg3 distribution were caused by mucosal (aDsg3 antibodies), mucocutaneous (aDsg1 + aDsg3) as well as atypical (aDsg3) PV-IgG. All PV-IgG fractions and AK23 compromised Dsg3 but not Dsg1 binding and enhanced Src activity. In contrast, rapid Ca²⁺ influx and Erk activation were induced by mucocutaneous PV-IgG and pemphigus foliaceus (PF) IgG (aDsg1) whereas cAMP was increased by mucosal and mucocutaneous PV-IgG only. Selective inhibition of p38MAPK, Src or PKC blocked loss of keratinocyte cohesion in response to all autoantibody fractions whereas Erk inhibition was protective against mucocutaneous PV-IgG and PF-IgG only. These results demonstrate that signaling patterns parallel the clinical phenotype as some mechanisms involved in loss of cell cohesion are caused by antibodies targeting Dsg3 whereas others correlate with autoantibodies against Dsg1. The concept of key desmosome regulators may explain observations from several experimental models of pemphigus.

Elucidation of the mTOR Pathway and Therapeutic Applications in Dermatology

The member of the phosphatidylinositol 3-kinase family, mammalian target of rapamycin, is involved in modulating inflammatory response and regulating cellular processes associated with growth, differentiation, and angiogenesis. Recent years have seen major advances in our understanding of the mammalian target of rapamycin signaling pathway and the implication of this pathway in multiple genetic and inflammatory diseases and tumors. The development of the mammalian target of rapamycin inhibitors has given rise to new treatment approaches that have led to substantially improved outcomes in many diseases. In this article, we review the role of the mammalian target of rapamycin signaling pathway in the different skin diseases with which it has been associated, examine the therapeutic applications of drugs targeting this pathway, and provide an overview of current trends and future directions in research.

E-cadherin and Src associate with extradesmosomal Dsg3 and modulate desmosome assembly and adhesion

Desmosomes provide strong intercellular cohesion essential for the integrity of cells and tissues exposed to continuous mechanical stress. For desmosome assembly, constitutively synthesized desmosomal cadherins translocate to the cell-cell border, cluster and mature in the presence of Ca(2+) to stable cell contacts. As adherens junctions precede the formation of desmosomes, we investigated in this study the relationship between the classical cadherin E-cadherin and the desmosomal cadherin Desmoglein 3 (Dsg3), the latter of which is indispensable for cell-cell adhesion in keratinocytes. By using autoantibodies from patients with the blistering skin disease pemphigus vulgaris (PV), we showed in loss of function studies that E-cadherin compensates for effects of desmosomal disassembly. Overexpression of E-cadherin reduced the loss of cell cohesion induced by PV autoantibodies and attenuated activation of p38 MAPK. Silencing of E-cadherin abolished the localization of Dsg3 at the membrane and resulted in a shift of Dsg3 from the cytoskeletal to the non-cytoskeletal protein pool which conforms to the notion that E-cadherin regulates desmosome assembly. Mechanistically, we identified a complex consisting of extradesmosomal Dsg3, E-cadherin, β-catenin and Src and that the stability of this complex is regulated by Src. Moreover, Dsg3 and E-cadherin are phosphorylated on tyrosine residues in a Src-dependent manner and Src activity is required for recruiting Dsg3 to the cytoskeletal pool as well as for desmosome maturation towards a Ca(2+)-insensitive state. Our data provide new insights into the role of E-cadherin and the contribution of Src signaling for formation and maintenance of desmosomal junctions.

Preclinical studies identify non-apoptotic low-level caspase-3 as therapeutic target in pemphigus vulgaris

The majority of pemphigus vulgaris (PV) patients suffer from a live-threatening loss of intercellular adhesion between keratinocytes (acantholysis). The disease is caused by auto-antibodies that bind to desmosomal cadherins desmoglein (Dsg) 3 or Dsg3 and Dsg1 in mucous membranes and skin. A currently unresolved controversy in PV is whether apoptosis is involved in the pathogenic process. The objective of this study was to perform preclinical studies to investigate apoptotic pathway activation in PV pathogenesis with the goal to assess its potential for clinical therapy. For this purpose, we investigated mouse and human skin keratinocyte cultures treated with PV antibodies (the experimental Dsg3 monospecific antibody AK23 or PV patients IgG), PV mouse models (passive transfer of AK23 or PVIgG into adult and neonatal mice) as well as PV patients' biopsies (n=6). A combination of TUNEL assay, analyses of membrane integrity, early apoptotic markers such as cleaved poly-ADP-ribose polymerase (PARP) and the collapse of actin cytoskeleton failed to provide evidence for apoptosis in PV pathogenesis. However, the in vitro and in vivo PV models, allowing to monitor progression of lesion formation, revealed an early, transient and low-level caspase-3 activation. Pharmacological inhibition confirmed the functional implication of caspase-3 in major events in PV such as shedding of Dsg3, keratin retraction, proliferation including c-Myc induction, p38MAPK activation and acantholysis. Together, these data identify low-level caspase-3 activation downstream of disrupted Dsg3 trans- or cis-adhesion as a major event in PV pathogenesis that is non-synonymous with apoptosis and represents, unlike apoptotic components, a promising target for clinical therapy. At a broader level, these results posit that an impairment of adhesive functions in concert with low-level, non-lethal caspase-3 activation can evoke profound cellular changes which may be of relevance for other diseases including cancer.

Signalling pathways in pemphigus vulgaris

Acantholysis in pemphigus vulgaris is induced by binding of autoantibodies to desmoglein 3 (Dsg3). The roles of signalling pathways on development of acantholysis have recently been extensively studied. In the study by Sayar et al., recently published in Exp Dermatol, epidermal growth factor receptor (EGFR) signalling was activated in both in vivo and in vitro pemphigus vulgaris experimental models. However, while EGFR inhibitors suppressed activity of p38 mitogen-activated protein kinase (p38MAPK) linearly, they suppressed activity of c-Myc and acantholysis in a non-linear, V-shaped relationship. These findings indicated complicated interactions among EGFR, p38MAPK and c-Myc in pemphigus vulgaris pathology.

EGFR inhibitors erlotinib and lapatinib ameliorate epidermal blistering in pemphigus vulgaris in a non-linear, V-shaped relationship

Novel insights into intra-cellular signalling involved in pemphigus vulgaris (PV), an autoimmune blistering disease of skin and mucous membranes, are now revealing new therapeutic approaches such as the chemical inhibition of PV-associated signals in conjunction with standard immunosuppressive therapy. However, extensive inhibition of signalling molecules that are required for normal tissue function and integrity may hamper this approach. Using a neonatal PV mouse model, we demonstrate that epidermal blistering can be prevented in a dose-dependent manner by clinically approved EGFR inhibitors erlotinib and lapatinib, but only up to approximately 50% of normal EGFR activity. At lower EGFR activity, blisters again aggravated and were highly exacerbated in mice with a conditional deletion of EGFR. Statistical analysis of the relation between EGFR activity and the extent of skin blistering revealed the best fit with a non-linear, V-shaped curve with a median break point at 52% EGFR activity (P = 0.0005). Moreover, lapatinib (a dual EGFR/ErbB2 inhibitor) but not erlotinib significantly reduced blistering in the oral cavity, suggesting that signalling mechanisms differ between PV predilection sites. Our results demonstrate that future clinical trials evaluating EGFR/ErbB2 inhibitors in PV patients must select treatment doses that retain a specific level of signal molecule activity. These findings may also be of relevance for cancer patients treated with EGFR inhibitors, for whom skin lesions due to extensive EGFR inhibition represent a major threat.

150(th) anniversary series: Desmosomes and autoimmune disease, perspective of dynamic desmosome remodeling and its impairments in pemphigus

Desmosomes are the most important intercellular adhering junctions that adhere two adjacent keratinocytes directly with desmosomal cadherins, that is, desmogleins (Dsgs) and desmocollins, forming an epidermal sheet. Recently, two cell-cell adhesion states of desmosomes, that is, "stable hyper-adhesion" and "dynamic weak-adhesion" conditions have been recognized. They are mutually reversible through cell signaling events involving protein kinase C (PKC), Src and epidermal growth factor receptor (EGFR) during Ca(2+)-switching and wound healing. This remodeling is impaired in pemphigus vulgaris (PV, an autoimmune blistering disease), caused by anti-Dsg3 antibodies. The antibody binding to Dsg3 activates PKC, Src and EGFR, linked to generation of dynamic weak-adhesion desmosomes, followed by p38MAPK-mediated endocytosis of Dsg3, resulting in the specific depletion of Dsg3 from desmosomes and acantholysis. A variety of pemphigus outside-in signaling may explain different clinical (non-inflammatory, inflammatory, and necrolytic) types of pemphigus. Pemphigus could be referred to a "desmosome-remodeling disease involving pemphigus IgG-activated outside-in signaling events".

Cell-cell adhesions and cell contractility are upregulated upon desmosome disruption

Desmosomes are perturbed in a number of disease states – including genetic disorders, autoimmune and bacterial diseases. Here, we report unexpected changes in other cell-cell adhesion structures upon loss of desmosome function. We found that perturbation of desmosomes by either loss of the core desmosomal protein desmoplakin or treatment with pathogenic anti-desmoglein 3 (Dsg3) antibodies resulted in changes in adherens junctions consistent with increased tension. The total amount of myosin IIA was increased in desmoplakin-null epidermis, and myosin IIA became highly localized to cell contacts in both desmoplakin-null and anti-Dsg3-treated mouse keratinocytes. Inhibition of myosin II activity reversed the changes to adherens junctions seen upon desmosome disruption. The increased cortical myosin IIA promoted epithelial sheet fragility, as myosin IIA-null cells were less susceptible to disruption by anti-Dsg3 antibodies. In addition to the changes in adherens junctions, we found a significant increase in the expression of a number of claudin genes, which encode for transmembrane components of the tight junction that provide barrier function. These data demonstrate that desmosome disruption results in extensive transcriptional and posttranslational changes that alter the activity of other cell adhesion structures.

Ribosomal protein s6-ps240 is expressed in lesional skin from patients with autoimmune skin blistering diseases

Background:

The in situ signaling transduction within skin biopsies from patients affected by autoimmune skin blistering diseases is not well-characterized.

Aim:

In autoimmune skin blistering diseases, autoantibodies seem to trigger several intracellular signaling pathways and we investigated the presence of the phosphorylated form of ribosomal protein S6-pS240 within autoimmune skin blistering diseases biopsies.

Materials and Methods:

We utilized immunohistochemistry to evaluate the presence of S6-pS240 in lesional skin biopsies of patients affected by autoimmune skin blistering diseases including patients with an endemic and nonendemic pemphigus foliaceus (non EPF), with bullous pemphigoid (BP), pemphigus vulgaris (PV), dermatitis herpetiformis (DH), and the respective controls.

Results:

Most autoimmune bullous skin diseases biopsies stained positive for S6-pS240 around lesional blisters, including adjacent areas of the epidermis; and within upper dermal inflammatory infiltrates, and/or mesenchymal-endothelial cell junctions within the dermis.

Conclusions:

We document that S6-pS240 is expressed in lesional areas of skin biopsies from patients with autoimmune skin blistering diseases, as well as on eccrine glands and piloerector muscles. Thus, the role of this molecule in autoimmune skin blistering diseases warrants further study.

Studying of the expression of PERP protein in the skin of patients with pemphigus

The authors disclosed the participation of apoptosis proteins in the development of acantholysis in patients with pemphigus. In this connection, studies of the PERP protein passing apoptosis signals and regulating desmosomal functions in keratinocytes are of interest. There is no information about any studies aimed at the PERP protein expression in patients with pemphigus in available literature. Goal. To assess the PERP protein expression in the skin of patients with pemphigus. Materials and methods. There was a study of 22 patients with pemphigus, a patient with bullous pemphigoid and ten healthy people. The PERP protein expression was studied in the biopsy materials obtained from lesion foci and apparently healthy skin of the patients as well as healthy people using the indirect immunofluorescence method. Results. The PERP protein expression was revealed in patients with pemphigus on areas of apparently intact skin, in lesion foci in the patient with bullous pemphigoid and skin of healthy volunteers in the membrane of keratinocytes from all epidermal layers.The PERP protein expression in the blister operculum in lesion foci in patients with pemphigus was absent. Conclusion. Substantial differences in the PERP protein expression in the blister operculum and apparently intact skin of patients with pemphigus were revealed.

Neural nitric oxide synthase participates in pemphigus vulgaris acantholysis through upregulation of Rous sarcoma, mammalian target of rapamycin and focal adhesion kinase

Pemphigus vulgaris (PV) is an autoimmune blistering skin disease characterized by suprabasal acantholysis produced as a consequence of desmoglein (Dsg) and non-Dsg autoantibodies binding to several targeting molecules localized on the membrane of keratinocytes. Nitric oxide (NO) may exert a pathogenic function in several immunological processes. We have previously demonstrated that neural nitric oxide synthase (nNOS) plays part in PV acantholysis. Also, our group has described a relevant role for HER [human epidermal growth factor receptor (EGFR) related] isoforms and several kinases such as Src (Rous sarcoma), mammalian target of rapamycin (mTOR) and focal adhesion kinase (FAK), as well as caspases in PV development. Using a passive transfer mouse model of PV, we aimed to investigate the relationship between the increase in nNOS and EGFR, Src, mTOR and FAK kinase upregulation observed in PV lesions. Our results revealed a new function for nNOS, which contributes to EGFR-mediated PV acantholysis through the upregulation of Src, mTOR and FAK. In addition, we found that nNOS participates actively in PV at least in part by increasing caspase-9 and caspase-3 activities. These findings underline the important issue that in PV acantholysis, caspase activation is a nNOS-linked process downstream of Src, mTOR and FAK kinase upregulation.

A pathophysiologic role for epidermal growth factor receptor in pemphigus acantholysis

The pemphigus family of autoimmune bullous disorders is characterized by autoantibody binding to desmoglein 1 and/or 3 (dsg1/dsg3). In this study we show that EGF receptor (EGFR) is activated following pemphigus vulgaris (PV) IgG treatment of primary human keratinocytes and that EGFR activation is downstream of p38 mitogen-activated protein kinase (p38). Inhibition of EGFR blocked PV IgG-triggered dsg3 endocytosis, keratin intermediate filament retraction, and loss of cell-cell adhesion in vitro. Significantly, inhibiting EGFR prevented PV IgG-induced blister formation in the passive transfer mouse model of pemphigus. These data demonstrate cross-talk between dsg3 and EGFR, that this cross-talk is regulated by p38, and that EGFR is a potential therapeutic target for pemphigus. Small-molecule inhibitors and monoclonal antibodies directed against EGFR are currently used to treat several types of solid tumors. This study provides the experimental rationale for investigating the use of EGFR inhibitors in pemphigus.

Exploiting PI3K/mTOR signaling to accelerate epithelial wound healing

The molecular circuitries controlling the process of skin wound healing have gained new significant insights in recent years. This knowledge is built on landmark studies on skin embryogenesis, maturation, and differentiation. Furthermore, the identification, characterization, and elucidation of the biological roles of adult skin epithelial stem cells and their influence in tissue homeostasis have provided the foundation for the overall understanding of the process of skin wound healing and tissue repair. Among numerous signaling pathways associated with epithelial functions, the PI3K/Akt/mTOR signaling route has gained substantial attention with the generation of animal models capable of dissecting individual components of the pathway, thereby providing a novel insight into the molecular framework underlying skin homeostasis and tissue regeneration. In this review, we focus on recent findings regarding the mechanisms involved in wound healing associated with the upregulation of the activity of the PI3K/Akt/mTOR circuitry. This review highlights critical findings on the molecular mechanisms controlling the activation of mTOR, a downstream component of the PI3K-PTEN pathway, which is directly involved in epithelial migration and proliferation. We discuss how this emerging information can be exploited for the development of novel pharmacological intervention strategies to accelerate the healing of critical size wounds.

Desmosomal adhesion and pemphigus vulgaris: the first half of the story

Pemphigus vulgaris (PV) is a paradigm of autoimmune disease affecting intercellular adhesion. The mechanisms that lead to cell-cell detachment (acantholysis) have crucial therapeutic implications and are currently undergoing major scrutiny. The first part of this review focuses on the classical view of the pathogenesis of PV, which is dominated by the cell adhesion molecules of the desmosome, namely desmogleins (Dsgs). Cloning of the DSG3 gene, generation DSG3 knock-out mice and isolation of monoclonal anti-Dsg3 IgG have aided to clarify the pathogenic mechanisms of PV, which are in part dependent on the fate of desmosomal molecules. These include perturbation of the desmosomal network at the transcriptional, translational, and interaction level, kinase activation, proteinase-mediated degradation, and hyper-adhesion. By the use of PV models, translational research has in turn helped shed light into the basic structure, function, and dynamics of assembly of desmosomal cadherins. The combined efforts of basic and applied research has resulted in tremendous advance into the understanding of epidermal adhesion and helped debunk old myths on the supposedly unique role of desmogleins in the mechanisms of cell-cell detachment in PV.

Methods for revealing therapeutic targets in case of true acantholytic pemphigus

The authors present a review of current approaches to studying the pathogenesis of true acantholytic pemphigus that may reveal new targets for therapeutic treatment. They discuss methods used for the first time to study this lethal dermatosis, and the development of previously used methods that are still important for studying true acantholytic pemphigus.

Urban legends: pemphigus vulgaris

Pemphigus vulgaris (PV) is the most common type of pemphigus. PV pathogenesis is still debated, and treatment remains challenging. We investigated five controversial topics: (1) What are the target antigens in PV? (2) Do desmogleins adequately address PV pathophysiology? (3) How does acantholysis occur in PV? (4) Is PV still a lethal disease? (5) What is the role of rituximab (RTX) in PV treatment? Results from extensive literature searches suggested the following: (1) Target antigens of PV include a variety of molecules and receptors that are not physically compartmentalized within the epidermis. (2) PV is caused by a variety of autoantibodies to keratinocyte self-antigens, which concur to cause blistering by acting synergistically. (3) The concept of apoptolysis distinguishes the unique mechanism of autoantibody-induced keratinocyte damage in PV from other known forms of cell death. (4) PV remains potentially life-threatening largely because of treatment side effects, but it is uncertain which therapies carry the highest likelihood of lethal risk. (5) RTX is a very promising treatment option in patients with widespread recalcitrant or life-threatening PV. RTX's cost is an issue, its long-term side effects are still unknown, and randomized controlled trials are needed to establish the optimal dosing regimen.