Our data demonstrate that blistering can be prevented by inhibition of p38MAPK in the human epidermis. Moreover, typical morphological alterations induced by mcPV-IgG such as interdesmosomal widening and the reduction of desmosome size at least in part require p38MAPK signalling.

Autoantibodies against desmoglein (Dsg) 1 and Dsg3 primarily cause blister formation in the autoimmune disease pemphigus vulgaris (PV). Src was proposed to contribute to loss of keratinocyte cohesion. However, the role and underlying mechanisms are unclear. In keratinocytes, cell cohesion in response to autoantibodies was reduced in a Src‐dependent manner by two patient‐derived PV‐IgG fractions as well as by AK23, but not by a third PV‐IgG fraction, although Src was activated by all autoantibodies. Loss of cell cohesion was progredient and AK23 similar to PV‐IgG interfered with reconstitution of cell cohesion after Ca2+‐switch, indicating that the autoantibodies also interfered with desmosome assembly. Dsg3 co‐localized along cell contacts and interacted with the Src substrate cortactin. Concomitantly, cell adhesion was impaired in keratinocytes isolated from cortactin‐deficient mice in comparison to keratinocytes isolated from wildtype (wt). AK23‐induced loss of cell cohesion was Src‐dependent only when cortactin was expressed. Similarly, AK23 impaired reconstitution of desmosomal adhesion in Src‐dependent fashion only in the presence of cortactin and AK23‐induced skin blistering was abolished by Src inhibition in wt but not cortactin‐deficient mice. However, in human epidermis, PV‐IgG‐induced skin blistering and ultrastructural alterations of desmosomes were not affected by Src inhibition. Our data suggest that Src and cortactin are involved in pemphigus skin blistering but the contribution of Src is variable. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Intercalated discs (ICDs), which connect adjacent cardiomyocytes, are composed of desmosomes, adherens junctions (AJs) and gap junctions (GJs). Previous data demonstrated that adrenergic signaling enhances cardiac myocyte cohesion, referred to as positive adhesiotropy, via PKA-mediated phosphorylation of plakoglobin (PG). However, it was unclear whether positive adhesiotropy caused ultrastructural modifications of ICDs. Therefore, we further investigated the role of PG in adrenergic signaling-mediated ultrastructural changes in the ICD of cardiomyocytes. Quantitative transmission electron microscopy (TEM) analysis of ICD demonstrated that cAMP elevation caused significant elongation of area composita and thickening of the ICD plaque, paralleled by enhanced cardiomyocyte cohesion, in WT but not PG-deficient cardiomyocytes. STED microscopy analysis supported that cAMP elevation ex vivo enhanced overlap of desmoglein-2 (Dsg2) and N-cadherin (N-cad) staining in ICDs of WT but not PG-deficient cardiomyocytes. For dynamic analyses, we utilized HL-1 cardiomyocytes, in which cAMP elevation induced translocation of Dsg2 and PG but not of N-cad to cell junctions. Nevertheless, depletion of N-cad but not of Dsg2 resulted in a decrease in basal cell cohesion whereas positive adhesiotropy was abrogated in monolayers depleted for either Dsg2 or N-cad. In the WT mice, ultrastrutural changes observed after cAMP elevation were paralleled by phosphorylation of PG at serine 665. Our data demonstrate that in murine hearts adrenergic signaling enhanced N-cad and Dsg2 in the ICD paralleled by ultrastrutural strengthening of ICDs and that effects induced by positive adhesiotropy were strictly dependent on Pg.

Background Pemphigus is a severe bullous autoimmune skin disease. Pemphigus foliaceus (PF) is characterized by antidesmoglein (Dsg) 1 IgG causing epidermal blistering; mucosal pemphigus vulgaris (mPV) by anti-Dsg3 IgG inducing erosions in the mucosa; and mucocutaneous pemphigus vulgaris (PV) by affecting both, with autoantibodies targeting Dsg1 and Dsg3. Objectives To characterize the Ca 2+ flux pathway and delineate its importance in pemphigus pathogenesis and clinical phenotypes caused by different antibody profiles. Methods Immunoprecipitation, Ca 2+ flux analysis, Western blotting, immunofluorescence staining, dissociation assays and a human skin ex vivo model were used. Results PV IgG and PF IgG, but neither Dsg3-specific monoclonal antibody (AK23) nor mPV IgG, caused Ca 2+ influx in primary human keratinocytes. Phosphatidylinositol 4-kinase a interacts with Dsg1 but not with Dsg3. Its downstream targetphospholipase-C-c1 (PLC)was activated by PV IgG and PF IgG but not AK23 or mPV IgG. PLC releases inositol 1,4,5-trisphosphate (IP3) causing IP3 receptor (IP3R) activation and Ca 2+ flux from the endoplasmic reticulum into the cytosol, which stimulates Ca 2+ release-activated channels (CRAC)-mediated Ca 2+ influx. Inhibitors against PLC, IP3R and CRAC effectively blocked PV IgG and PF IgG-induced Ca 2+ influx; ameliorated alterations of Dsg1 and Dsg3 localization, and reorganization of keratin and actin filaments; and inhibited loss of cell adhesion in vitro. Finally, inhibiting PLC or IP3R was protective against PV IgG-induced blister formation and redistribution of Dsg1 and Dsg3 in human skin ex vivo. Conclusions Ca 2+ -mediated signalling is important for epidermal blistering and dependent on the autoantibody profile, which indicates different roles for signalling complexes organized by Dsg1 and Dsg3. Interfering with PLC and Ca 2+ signalling may be a promising approach to treat epidermal manifestations of pemphigus.What is already known about this topic?• Autoantibody-induced Ca 2+ signalling and activation of phospholipase C in keratinocytes has been reported as the first signalling pathway in pemphigus.• Ca 2+ influx correlates with the presence of autoantibodies targeting desmoglein (Dsg) 1.

Summary Background Pemphigus vulgaris (PV) is an autoimmune disease characterized by blister formation in the epidermis and oral mucosa due to loss of keratinocyte cohesion. Autoantibodies present in patients with PV (PV‐IgG) are known to primarily target desmoglein (Dsg)1 and Dsg3 in desmosomes. The mucosal‐dominant subtype of PV (mdPV) is caused by PV‐IgG autoantibodies against the cadherin‐type adhesion molecule Dsg3. p38 mitogen‐activated protein kinase (p38MAPK) signalling has been characterized as an important pathway downstream of PV‐IgG binding and its inhibition is protective in ex vivo human skin. However, the role of p38MAPK signalling in mdPV is unknown as no experimental model has been available. Objectives To establish a human ex vivo oral mucosa culture, and evaluate the p38MAPK dependency of blister formation and of ultrastructural alterations of desmosomes induced by mdPV‐IgG. Methods Human labial mucosa was injected with mdPV‐IgG as well as AK23, a pathogenic mouse monoclonal Dsg3 antibody, in the presence or absence of p38MAPK inhibitors. Viability was evaluated by 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay and apoptosis by terminal deoxynucleotidyl transferase dUTP nick‐end labelling assay. Blister score was determined following haematoxylin and eosin staining and Dsg3 distribution by immunostaining. Samples were processed for transmission electron microscopy to analyse desmosome ultrastructure. Results Both AK23 and mdPV‐IgG induced blisters and caused reduction in desmosome size and number in labial mucosa. Inhibition of p38MAPK was not effective in preventing these alterations. Conclusions In contrast with human epidermis, PV‐IgG and AK23 induce blisters and desmosome ultrastructural changes in labial mucosa via a mechanism not dependent on p38MAPK. What's already known about this topic? Pemphigus vulgaris IgG (PV‐IgG) induces blistering as well as a reduction in desmosome number and size mediated by p38 mitogen‐activated protein kinase (p38MAPK) signalling in ex vivo human skin. What does this study add? This study establishes a new human ex vivo mucosa model to test pathomechanisms mediated by PV‐IgG. The study demonstrates that both AK23 and mucosal‐dominant PV induce blisters and associated ultrastructural changes in labial mucosa via a mechanism not dependent on p38MAPK signalling. What is the translational message? This study highlights the respective tissue‐specific responses of oral mucosa and skin related to PV pathogenesis, similar to the patient situation.