Proteomic Analysis Reveals Oxidative Phosphorylation and JAK-STAT Pathways Mediated Pathogenesis of Pemphigus Vulgaris.

Pemphigus vulgaris (PV) stands as a rare autoimmune bullous disease, while the precise underlying mechanism remains incompletely elucidated. High-throughput proteomic methodologies, such as LC-MS/MS, have facilitated the quantification and characterisation of proteomes from clinical skin samples, enhancing our comprehension of PV pathogenesis. The objective of this study is to elucidate the signalling mechanisms underlying PV through proteomic analysis. Proteins and cell suspension were extracted from skin biopsies obtained from both PV patients and healthy volunteers and subsequently analysed using LC-MS/MS and scRNA-seq. Cultured keratinocytes were treated with PV serum, followed by an assessment of protein expression levels using immunofluorescence and western blotting. A total of 880, 605, and 586 differentially expressed proteins (DEPs) were identified between the lesion vs. control, non-lesion vs. control, and lesion vs. non-lesion groups, respectively. The oxidative phosphorylation (OXPHOS) pathway showed activation in PV. Keratinocytes are the major cell population in the epidermis and highly expressed ATP5PF, ATP6V1G1, COX6B1, COX6A1, and NDUFA9. In the cellular model, there was a notable increase in the expression levels of OXPHOS-related proteins (V-ATP5A, III-UQCRC2, II-SDHB, I-NDUFB8), along with STAT1, p-STAT1, and p-JAK1. Furthermore, both the OXPHOS inhibitor metformin and the JAK1 inhibitor tofacitinib demonstrated therapeutic effects on PV serum-induced cell separation, attenuating cell detachment. Metformin notably reduced the expression of V-ATP5A, III-UQCRC2, II-SDHB, I-NDUFB8, p-STAT1, p-JAK1, whereas tofacitinib decreased the expression of p-STAT1 and p-JAK1, with minimal impact on the expression of V-ATP5A, III-UQCRC2, II-SDHB, and I-NDUFB8. Our results indicate a potential involvement of the OXPHOS and JAK-STAT1 pathways in the pathogenesis of PV.

Binding to the neonatal Fc receptor enhances the pathogenicity of anti-desmoglein-3 antibodies in keratinocytes.

The neonatal Fc receptor (FcRn) is important for numerous cellular processes that involve antibody recycling and trafficking. A major function of FcRn is IgG recycling and half-life prolongation, and FcRn blockade results in a reduction of autoantibodies in IgG-mediated autoimmune diseases. In epithelial cells, FcRn functions in processes different from IgG recycling, such as antibody transcytosis in intestinal cells. In pemphigus vulgaris, an autoimmune disease of the epidermis, IgG autoantibodies directed against desmosomal adhesion proteins, especially desmoglein-3 and -1, cause loss of keratinocyte adhesion. We have previously demonstrated that FcRn blockade with efgartigimod, a human Fc fragment with enhanced FcRn binding, significantly reduces the keratinocyte monolayer fragmentation caused by anti-desmoglein-3 antibodies. This points to a direct function of FcRn in keratinocytes, beyond IgG recycling, but the mechanisms have not yet been elucidated in detail. Here, we show that FcRn binding is required for the full pathogenicity of recombinant anti-desmoglein-3 antibodies in keratinocytes, and that antibodies that exhibit enhanced or reduced FcRn affinity due to targeted substitutions in their Fc region, as well as F(ab')2 fragments not binding to FcRn display different degrees of pathogenicity. Blockade of FcRn by efgartigimod only shows a protective effect on keratinocyte adhesion against antibodies capable of binding to FcRn. Furthermore, antibody-induced degradation of desmoglein-3 in keratinocytes does not depend on FcRn, demonstrating that desmoglein-3 degradation and acantholysis are functionally disconnected processes. Our data suggest that the role of FcRn in autoimmune diseases is likely to be versatile and cell-type dependent, thus stressing the importance of further studies on FcRn function in autoimmune diseases.

Unbiased screening identifies regulators of cell-cell adhesion and treatment options in pemphigus.

Cell-cell junctions, and specifically desmosomes, are crucial for robust intercellular adhesion. Desmosomal function is compromised in the autoimmune blistering skin disease pemphigus vulgaris. We combine whole-genome knockout screening and a promotor screen of the desmosomal gene desmoglein 3 in human keratinocytes to identify novel regulators of intercellular adhesion. Kruppel-like-factor 5 (KLF5) directly binds to the desmoglein 3 regulatory region and promotes adhesion. Reduced levels of KLF5 in patient tissue indicate a role in pemphigus vulgaris. Autoantibody fractions from patients impair intercellular adhesion and reduce KLF5 levels in in vitro and in vivo disease models. These effects were dependent on increased activity of histone deacetylase 3, leading to transcriptional repression of KLF5. Inhibiting histone deacetylase 3 increases KLF5 levels and protects against the deleterious effects of autoantibodies in murine and human pemphigus vulgaris models. Together, KLF5 and histone deacetylase 3 are regulators of desmoglein 3 gene expression and intercellular adhesion and represent potential therapeutic targets in pemphigus vulgaris.

Distorted frequency and functionality of natural killer cells in pemphigus vulgaris: A potential therapeutic target.

Pemphigus vulgaris (PV) is a rare autoimmune disorder where autoantibodies target the desmosomal proteins resulting in blistering of oral mucosa and skin. While the pathogenesis of PV is mainly mediated by the adaptive immune system, key players of innate immunity are also emerging. This study outlines the phenotypic as well as functional attributes of NK cells in PV. Through in-depth analysis using flow cytometry we identified an increase in the frequency of CD56+ CD3- NK cells and their subtypes in periphery. Along with this there is an increased frequency of IFNγ+ CD56bright CD16dim NK cells. mRNA expression of sorted NK cells for differentially expressed genes, particularly key transcription factors such as T-bet and EOMES, as well as surface receptors like NKG2D and KIR2D, and the cytokine IFNγ, displayed significant upregulation. A significant activation of NK cells was seen in the disease state. The levels of perforin and IFNγ were significantly elevated in the culture supernatants of patients. Additionally, a significantly higher cytotoxicity of NK cells in PV was observed. In lesioned tissues of PV, NK related markers were significantly increased. Lastly, we observed NK cells using confocal microscopy in the tissue biopsies of patients which showed significant infiltration of CD56+ CD3- NK cells at the lesional sites. This study aimed to shed light on the pivotal role of NK cells in the immunopathology of PV, offering a thorough understanding of their behaviour and changes in expression which might help in contributing to the development of novel therapeutics.

Alteration of reactive oxygen species master transcription factor Nrf2 in keratinocytes exposed to monoclonal pathogenic antibody AK23 against desmoglein-3 in pemphigus vulgaris.

Keratinocytes in mucosal and skin tissues maintain tissue integrity via desmosomes and desmoglein-3 (Dsg3). Pemphigus Vulgaris (PV) is a life-threatening autoimmune blistering disease characterized by autoantibodies against Dsg3, disrupting desmosomes. Nuclear factor erythroid 2-related factor 2 (Nrf2) regulates oxidative stress responses crucial for skin tissue protection. Although the pathogenesis of PV is known, the detailed molecular events remain unclear. This study investigates changes in Nrf2 expression in keratinocytes following pathogenic anti-Dsg3 antibody AK23 exposure, using dose- and time-dependent studies employing immunofluorescence analysis. N/TERT keratinocytes were cultured in keratinocytes serum-free medium and treated with AK23 at varying doses (5 µg/mL,40µg/mL,75µg/mL) and durations (2, 6, 24 h). Immunofluorescence staining was performed to assess the expression of Nrf2 and Dsg3. All fluorescent images were analyzed using ImageJ software. A dose-dependent increase in Dsg3 was noted following AK23 treatment, while Nrf2 expression and subcellular localization varied. Time-course analyses showed decreased Nrf2 at 24 h and increased Dsg3 levels. Early time-point (2 and 6 h) variations were evident in Nrf2 levels. This study highlights the impact of AK23 on Nrf2 expression, potentially disrupting Nrf2-mediated cytoprotection and implicating oxidative stress (ROS generation) in PV pathogenesis. Further investigation is necessary to validate the findings.

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.

C3d Immunohistochemical Staining on Paraffin-Embedded Tissue for Diagnosis of Pemphigus.

CONTEXT.­: Pemphigus is an autoimmune blister disease that causes blisters on the skin and mucosal surfaces. Direct immunofluorescence (DIF) testing is critical for the clinical diagnosis of pemphigus. However, it is limited to fresh tissue specimens and fluorescence microscopy. OBJECTIVE.­: To assess the value of C3d immunohistochemistry (IHC) on paraffin-embedded skin tissue for the diagnosis of pemphigus by comparing C3d-IHC results to DIF and enzyme-linked immunosorbent assay testing in pemphigus and other blister-related skin diseases. DESIGN.­: C3d-IHC assays were retrospectively performed on paraffin-embedded skin tissue sections from 115 patients (63 with pemphigus and 52 controls). Both the case group and the control group underwent the same protocol, and cases with C3d position in the peripheral spinous layer were considered as positive samples. RESULTS.­: C3d-IHC and DIF testing had similar performance for pemphigus diagnosis, with a sensitivity of 71.0% (95% CI, 51.8%-85.1%) and 77.4% (95% CI, 58.5%-89.7%), specificity of 96.4% (95% CI, 79.8%-99.8%) and 100% (95% CI, 85.0%-100%), positive predictive value of 95.7% (95% CI, 76.0%-99.8%) and 100% (95% CI, 82.8%-100%), and a negative predictive value of 75.0% (95% CI, 57.5%-87.3%) and 80.0% (95% CI, 62.5%-90.9%), respectively. CONCLUSIONS.­: Our study indicated that C3d-IHC results for paraffin-fixed tissues were not significantly different from DIF results for the diagnosis of pemphigus. The C3d-IHC assay has the potential for routine diagnosis of pemphigus, especially in the absence of fresh-frozen tissue.

Tacrolimus reverses pemphigus vulgaris serum-induced depletion of desmoglein in HaCaT cells via inhibition of heat shock protein 27 phosphorylation.

BACKGROUND: Glucocorticoids are the first-line treatment for Pemphigus vulgaris (PV), but its serious side effects can be life-threatening for PV patients. Tacrolimus (FK506) has been reported to have an adjuvant treatment effect against PV. However, the mechanism underlying the inhibitory effect of FK506 on PV-IgG-induced acantholysis is unclear. OBJECTIVE: The objective of this study was to explore the effect of FK506 on desmoglein (Dsg) expression and cell adhesion in an immortalized human keratinocyte cell line (HaCaT cells) stimulated with PV sera. METHODS: A cell culture model of PV was established by stimulating HaCaT cells with 5% PV sera with or without FK506 and clobetasol propionate (CP) treatment. The effects of PV sera on intercellular junctions and protein levels of p38 mitogen-activated protein kinase (p38MAPK), heat shock protein 27 (HSP27), and Dsg were assayed using western blot analysis, immunofluorescence staining, and a keratinocyte dissociation assay. RESULTS: PV sera-induced downregulation of Dsg3 was observed in HaCaT cells and was blocked by FK506 and/or CP. Immunofluorescence staining revealed that linear deposits of Dsg3 on the surface of HaCaT cells in the PV sera group disappeared and were replaced by granular and agglomerated fluorescent particles on the cell surface; however, this effect was reversed by FK506 and/or CP treatment. Furthermore, cell dissociation assays showed that FK506 alone or in combination with CP increased cell adhesion in HaCaT cells and ameliorated loss of cell adhesion induced by PV sera. Additionally, FK506 noticeably decreased the PV serum-induced phosphorylation of HSP 27, but had no effect on p38MAPK phosphorylation. CONCLUSION: FK506 reverses PV-IgG induced-Dsg depletion and desmosomal dissociation in HaCaT cells, and this effect may be obtained by inhibiting HSP27 phosphorylation.

The Role of T Follicular Helper Cells in Clinical Remission and Relapse in Patients with Pemphigus Treated with Rituximab.

BACKGROUND: Pemphigus is a rare chronic autoimmune disease. Recent studies have found that T follicular helper (Tfh) cells may play a role in autoimmune diseases. In this study, Tfh cells frequency, BCL6 gene expression, IL-21, and IL-6 cytokines levels were examined, with the aim of understanding the effect of RTX on these cells in the onset of clinical remission or relapse in patients with pemphigus. METHODS: 20 patients with pemphigus vulgaris and 20 healthy controls without any autoimmune diseases that were admitted to the Dermatology and Venereology Clinic of the Akdeniz University Hospital were included. Peripheral blood sample was taken from all individuals and studied to analyze Tfh cell distribution, IL-21 and IL-6 distribution in CD3+CD4+CXCR5+ lymphocytes with flow cytometry, plasma IL-21 levels with ELISA, and mRNA levels that refer to BCL6 expression with PCR. RESULTS: Circulating Tfh cell distribution and IL-21 and IL-6 distribution in CD3+CD4+CXCR5+ lymphocytes and mRNA levels that refer to BCL6 expression showed no difference between patient and control groups. However, in patients who had received rituximab treatment there was a significant reduction in Tfh cells compared with other groups. Plasma IL-21 levels were significantly higher in the patient group. CONCLUSIONS: We found that plasma concentrations of the cytokine IL-21 were greatly increased in the pemphigus compared with the control group. There were no significant differences in Tfh cell percentages between the patient and control groups. Tfh cells were decreased in patients who received rituximab treatment. Our findings show that the response to RTX in pemphigus causes a reduction in circulating T follicular helper cells, but not in the plasma IL-21 level. Further studies are required to clarify the role of Tfh cells in pemphigus vulgaris.

cAMP: A master regulator of cadherin-mediated binding in endothelium, epithelium and myocardium.

Regulation of cadherin-mediated cell adhesion is crucial not only for maintaining tissue integrity and barrier function in the endothelium and epithelium but also for electromechanical coupling within the myocardium. Therefore, loss of cadherin-mediated adhesion causes various disorders, including vascular inflammation and desmosome-related diseases such as the autoimmune blistering skin dermatosis pemphigus and arrhythmogenic cardiomyopathy. Mechanisms regulating cadherin-mediated binding contribute to the pathogenesis of diseases and may also be used as therapeutic targets. Over the last 30 years, cyclic adenosine 3',5'-monophosphate (cAMP) has emerged as one of the master regulators of cell adhesion in endothelium and, more recently, also in epithelial cells as well as in cardiomyocytes. A broad spectrum of experimental models from vascular physiology and cell biology applied by different generations of researchers provided evidence that not only cadherins of endothelial adherens junctions (AJ) but also desmosomal contacts in keratinocytes and the cardiomyocyte intercalated discs are central targets in this scenario. The molecular mechanisms involve protein kinase A- and exchange protein directly activated by cAMP-mediated regulation of Rho family GTPases and S665 phosphorylation of the AJ and desmosome adaptor protein plakoglobin. In line with this, phosphodiesterase 4 inhibitors such as apremilast have been proposed as a therapeutic strategy to stabilize cadherin-mediated adhesion in pemphigus and may also be effective to treat other disorders where cadherin-mediated binding is compromised.

Deregulated phenotype of autoreactive Th17 and Treg clone cells in pemphigus vulgaris after in-vitro treatment with desmoglein antigen (Dsg-3).

The loss of balance between regulatory T (Treg) and T helper 17 (Th17) causes loss of tolerance against desmoglein (Dsg)-3 leading to pemphigus vulgaris (PV), an autoimmune bullous skin disorder associated with autoantibodies against Dsg-3. We aimed to elucidate the complex relationship of Th17 and Treg cells, their molecules, and the underlying mechanism in the development of PV disease. Using cytokine secretion assays, Th17 and Treg cells were sorted by FACS Aria-III within Dsg-3-responsive PBMC population and homogeneous T cell clones were generated in-vitro. Different cell surface molecules like CD25, GITR, CD122, CD152, CD45RO, IL-23R, STAT3, STAT5, CD127, HLA-DR, CCR4, CCR5, CCR6 and CCR7 were studied. The functional response of Th17 and Treg cells were elucidated by measuring the levels of various cytokines released by IL-10 and IL-17 T cells. The mRNA expression of transcription factors (FoxP3 and RORγt) was also analyzed. IL-17 secreting (Th17) cells with phenotype CD4+IL-17+ were greatly increased and IL-10 secreting (Treg) cells with phenotype CD4+IL-10+ were reduced in PV cases than healthy controls. The qPCR analysis showing high expression of retinoic acid receptor-related orphan receptor gamma (RORγt) mRNA in comparison to forkhead box P3 (FoxP3) mRNA confirmed the development of pro-inflammatory Th17 response in PV. Further, the cytokine profile of pro-inflammatory and anti-inflammatory cytokines suggested defective suppressive functions in Treg cells with high inflammatory response. Our findings indicate that autoantigen Dsg-3 specifically allows the proliferation of IL-17 secreting T cells though has a negative effect on IL-10 secreting T cells leading to dysregulation of immunity in PV patients. This antagonistic relationship between Dsg-3-specific Th17 and Treg cells may be critical for the onset and persistence of inflammation in PV cases.

Cytoskeletal anchorage of different Dsg3 pools revealed by combination of hybrid STED/SMFS-AFM.

Desmoglein 3 (Dsg3) is a desmosomal cadherin mediating cell adhesion within desmosomes and is the antigen of the autoimmune blistering skin disease pemphigus vulgaris. Therefore, understanding of the complex desmosome turnover process is of high biomedical relevance. Recently, super resolution microscopy was used to characterize desmosome composition and turnover. However, studies were limited because adhesion measurements on living cells were not possible in parallel. Before desmosomal cadherins are incorporated into nascent desmosomes, they are not bound to intermediate filaments but were suggested to be associated with the actin cytoskeleton. However, direct proof that adhesion of a pool of desmosomal cadherins is dependent on actin is missing. Here, we applied single-molecule force spectroscopy measurements with the novel single molecule hybrid-technique STED/SMFS-AFM to investigate the cytoskeletal anchorage of Dsg3 on living keratinocytes for the first time. By application of pharmacological agents we discriminated two different Dsg3 pools, only one of which is anchored to actin filaments. We applied the actin polymerization inhibitor Latrunculin B to modify the actin cytoskeleton and the PKCα activator PMA to modulate intermediate filament anchorage. On the cellular surface Dsg3 adhesion was actin-dependent. In contrast, at cell-cell contacts, Dsg3 adhesion was independent from actin but rather is regulated by PKC which is well established to control desmosome turn-over via intermediate filament anchorage. Taken together, using the novel STED/SMFS-AFM technique, we demonstrated the existence of two Dsg3 pools with different cytoskeletal anchorage mechanisms.

Transcriptomic profiling of pemphigus lesion infiltrating mononuclear cells reveals a distinct local immune microenvironment and novel lncRNA regulators.

Pemphigus is an autoimmune skin disease. Ectopic lymphoid-like structures (ELSs) were found to be commonly present in the pemphigus lesions, presumably supporting in situ desmoglein (Dsg)-specific antibody production. Yet functional phenotypes and the regulators of Lymphoid aggregates in pemphigus lesions remain largely unknown. Herein, we used microarray technology to profile the gene expression in skin lesion infiltrating mononuclear cells (SIMC) from pemphigus patients. On top of that, we compared SIMC dataset to peripheral blood mononuclear cells (PBMC) dataset to characterize the unique role of SIMC. Functional enrichment results showed that mononuclear cells in skin lesions and peripheral blood both had over-represented IL-17 signaling pathways while neither was characterized by an activation of type I Interferon signaling pathways. Cell-type identification with relative subsets of known RNA transcripts (CIBERSORT) results showed that naïve natural killer cells (NK cells) were significantly more abundant in pemphigus lesions, and their relative abundance positively correlated with B cells abundance. Meanwhile, plasma cells population highly correlated with type 1 macrophages (M1) abundance. In addition, we also identified a lncRNA LINC01588 which might epigenetically regulate T helper 17 cells (Th17)/regulatory T cells (Treg) balance via the peroxisome proliferator-activated receptor (PPAR) signaling pathway. Here, we provide the first transcriptomic characterization of lesion infiltrating immune cells which illustrates a distinct interplay network between adaptive and innate immune cells. It helps discover new regulators of local immune response, which potentially will provide a novel path forward to further uncover pemphigus pathological mechanisms and develop targeted therapy.

Up-regulation of ST18 in pemphigus vulgaris drives a self-amplifying p53-dependent pathomechanism resulting in decreased desmoglein 3 expression.

Pemphigus vulgaris (PV) is a life-threatening autoimmune mucocutaneous blistering disease which is to a large extent genetically determined, and results, at least in part, from the deleterious activity of autoantibodies directed against desmoglein (DSG)3, a prominent intra-epidermal adhesion molecule. Those autoantibodies lead to decreased membranal DSG3 expression in keratinocytes (KCs), thereby destabilizing cell-cell adhesion within the epidermis and leading to blister formation. We previously showed that rs17315309, a strong risk variant for PV within the promoter of the ST18 transcription factor gene, promotes epidermal ST18 up-regulation in a p53/p63-dependent manner. Accordingly, ST18 was found to be overexpressed in the skin of PV patients. Increased ST18 expression was then shown to markedly augment PV autoantibodies-mediated loss of KCs cohesion. Here, we demonstrate that ST18 overexpression significantly increases autoantibody-mediated DSG3 down-regulation in keratinocytes. In addition, DSG3 decreased expression boosts p53 function through p38 mitogen-activated protein kinase (p38MAPK) activation and dramatically augments p53-dependent ST18 promoter activity. Finally, the PV risk variant rs17315309 is associated with increased p53 expression in PV skin. Taken collectively, these observations reveal a novel self-amplifying pathomechanism involving ST18, DSG3, p38 and p53, capable of perpetuating disease activity, and therefore indicative of novel actionable molecular targets in PV.

Downregulation of aquaporin 3 in patients with pemphigus vulgaris.

Pemphigus vulgaris (PV) is an autoimmune bullous skin disease. Aquaporin 3 (AQP3) is a glycerol/water channel involved in several physiological functions. Evaluation of the tissue expression and localization of AQP3 in the skin of PV patients. Twenty-seven PV patients and 30 controls were included. The patients were subjected to history taking, clinical evaluation, Autoimmune Bullous Skin Disorder Intensity Score and 4-mm punch biopsy. The biopsies were stained using anti-human AQP3 antibody and the immunofluorescence pattern and intensity were evaluated using a scoring system and ImageJ software analysis. AQP3 was expressed in the basal epidermis in 27 (100%) and in the suprabasal epidermis in 19 PV patients (70.4%). It was expressed in all controls in basal and suprabasal layers. Intensity of AQP3 immunofluorescence was strong in 2 (7.4%), moderate in 19 (70.4%) and weak in 6 patients (22.2%) while it was strong in 18 (60%) and moderate in 12 controls (40%). AQP3 expression was significantly lower in patients than controls in the suprabasal epidermis (p = 0.001). Patients with extensive disease had significantly weaker AQP3 intensity than those with marked disease (p = 0.005) Downregulation of AQP3 in patients with PV, especially in the suprabasal layers and in extensive clinical disease, suggests a potential role of AQP3 in the pathogenesis of PV.

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.

Electron microscopy reveals that phospholipase C and Ca2+ signaling regulate keratin filament uncoupling from desmosomes in Pemphigus.

Pemphigus vulgaris (PV) is a severe autoimmune blistering skin disease caused primarily by autoantibodies (PV-IgG) against the desmosomal cadherins desmoglein (Dsg) 1 and Dsg 3. Pemphigus is a model disease to study desmosome regulation because patient lesions are characterized by ultrastructural hallmarks including loss, shrinkage and splitting of desmosomes as well as by retraction of keratin filaments. The mechanisms underlying the disease are not completely understood but involve several intracellular signaling pathways triggered by autoantibody binding. Recently, we demonstrated that Phosphoinositid-Phospholipase C (PLC) and Ca2+ signaling are required for acantholysis in human epidermis. Here, we used transmission electron microscopy to characterize the role of PLC and Ca2+ signaling with regard to the pathogenic effects of PV-IgG on desmosome ultrastructure in human ex vivo skin model. First, we observed that the PV-IgG used in this study significantly reduced desmosome length and caused uncoupling of desmosomes from keratin filaments. Moreover, PV-IgG enhanced the number of split desmosomes but did not cause a significant loss of desmosomes. We found that inhibition of PLC and Ca2+ signaling significantly blocked keratin filament uncoupling but not shrinkage of desmosomes. Blocking Ca2+ flux prevented desmosome splitting. The ultrastructural analysis revealed that for preventing skin blistering it is sufficient to enhance keratin filament insertion, which is regulated by PLC/ Ca2+. Here, we underscore the unique role of electron microscopy to investigate the underlying mechanisms by which a signaling pathway regulates desmosome ultrastructure in pemphigus.

Bruton's tyrosine kinase inhibition-An emerging therapeutic strategy in immune-mediated dermatological conditions.

Bruton's tyrosine kinase (BTK), a member of the Tec kinase family, is critically involved in a range of immunological pathways. The clinical application of BTK inhibitors for B-cell malignancies has proven successful, and there is strong rationale for the potential benefits of BTK inhibitors in some autoimmune and allergic conditions, including immune-mediated dermatological diseases. However, the established risk-to-benefit profile of "first-generation" BTK inhibitors cannot be extrapolated to these emerging, non-oncological, indications. "Next-generation" BTK inhibitors such as remibrutinib and fenebrutinib entered clinical development for chronic spontaneous urticaria (CSU); rilzabrutinib and tirabrutinib are being studied as potential treatments for pemphigus. Promising data from early-phase clinical trials in CSU suggest potential for these agents to achieve strong pathway inhibition, which may translate into measurable clinical benefits, as well as other effects such as the disruption of autoantibody production. BTK inhibitors may help to overcome some of the shortcomings of monoclonal antibody treatments for immune-mediated dermatological conditions such as CSU, pemphigus, and systemic lupus erythematosus. In addition, the use of BTK inhibitors may improve understanding of the pathophysiological roles of mast cells, basophils, and B cells in such conditions.

Immunohistochemical expression of regulatory T cells (CD4 + CD25 + bright FOXP3 + ) in pemphigus patients.

BACKGROUND: Pemphigus is a series of autoimmune skin disorders caused by IgG. Regulatory T cells (Tregs) are a subset of CD4+ T cells that mostly block pathogenic immune responses mediated by self-reactive cells; therefore, a lack of Tregs or a malfunction in their activity could lead to a loss of tolerance and the development of autoimmunity. AIMS: To evaluate the expression of lesional and perilesional Treg markers (CD4 + CD25 + bright FOXP3 + ) in pemphigus patients. PATIENTS AND METHODS: Twenty-three pemphigus patients and 20 healthy controls were included in this study. The expression of CD4 , CD25, and Foxp3 was evaluated by immunohistochemistry. RESULTS: There was statistically significant increase in CD4+ T lymphocytes in lesional skin of pemphigus compared to perilesional skin and control group (p-value: 0.001). There was statistically significant decrease in CD25+ and Foxp3+ cells in lesional skin compared to perilesional and control group (p-value: <0.001, 0.025, respectively). CONCLUSION: The reduction of lesional skin Tregs may play an important role in the pemphigus pathogenesis.

Chronic exposure to the anti-M3 muscarinic acetylcholine receptor autoantibody in pemphigus vulgaris contributes to disease pathophysiology.

Pemphigus vulgaris (PV) is a potentially lethal autoimmune mucocutaneous blistering disease characterized by binding of IgG autoantibodies (AuAbs) to keratinocytes (KCs). In addition to AuAbs against adhesion molecules desmogleins 1 and 3, PV patients also produce an AuAb against the M3 muscarinic acetylcholine (ACh) receptor (M3AR) that plays an important role in regulation of vital functions of KCs upon binding endogenous ACh. This anti-M3AR AuAb is pathogenic because its adsorption eliminates the acantholytic activity of PV IgG; however, the molecular mechanism of its action is unclear. In the present study, we sought to elucidate the mode of immunopharmacologic action of the anti-M3AR AuAb in PV. Short-term exposures of cultured KCs to PV IgG or the muscarinic agonist muscarine both induced changes in the expression of keratins 5 and 10, consistent with the inhibition of proliferation and upregulated differentiation and in keeping with the biological function of M3AR. In contrast, long-term incubations induced a keratin expression pattern consistent with upregulated proliferation and decreased differentiation, in keeping with the hyperproliferative state of KCs in PV. This change could result from desensitization of the M3AR, representing the net antagonist-like effect of the AuAb. Therefore, chronic exposure of KCs to the anti-M3AR AuAb interrupts the physiological regulation of KCs by endogenous ACh, contributing to the onset of acantholysis. Since cholinergic agents have already demonstrated antiacantholytic activity in a mouse model of PV and in PV patients, our results have translational significance and can guide future development of therapies for PV patients employing cholinergic drugs.