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Role of p38MAPK in ultrastructural alterations of desmosomes in human ex vivo pemphigus model
Role of p38MAPK in ultrastructural alterations of desmosomes in human ex vivo pemphigus model
Desmosomes interconnect epithelial cells together and are abundant in tissues constantly challenged by shear forces. They are composed of different isoforms of intercellular adhesion proteins which include desmogleins (Dsg) and desmocollins (Dsc). These proteins of apposing cells interact in homophilic and heterophilic manner thereby conferring integrity to the tissue. When this crucial role of desmosomes is compromised, several desmosome-associated diseases such as pemphigus may occur. Pemphigus is a blistering disease of the skin and oral mucosa. It is caused by anti-Dg3 and anti-Dsg1 autoantibodies that bind to the extracellular domains of the desmogleins and perturb their interaction. There are different phenotypes of the disease depending on the autoantibody profiles. Pemphigus vulgaris (PV) is caused by autoantibodies (PV-IgG) targeting Dsg1 and Dsg3 whereas pemphigus foliaceus (PF) is associated with autoantibodies against Dsg1 only. Pemphigus vulgaris is recognized as two sub-types; i.e, the mucosal-dominant form (mdPV) caused by anti-Dsg3 autoantibodies and the mucocutaneus (mcPV) variant caused by both anti-Dsg1 and anti-Dsg3 autoantibodies. Several lines of evidence demonstrated that pemphigus is caused by disruption of Dsg interaction when the autoantibodies are interposed between the interacting Dsg (steric hindrance) and signaling triggered by autoantibody binding. It has been widely accepted that different signaling pathways work in concert in the modulation of desmosome structure and dynamics. p38 mitogen activated protein kinase (p38MAPK) has been extensively studied and its phosphorylation was detected in cell cultures in response to PV-IgG binding as well as in skin lesions of pemphigus patients. Pharmacological inactivation of this pathway attenuated cell dissociation in cultures and blister formation in murine models. However, no data was available with respect to the role of p38MAPK in blister formation in human skin and mucosa. Therefore, we tested the dependency of blister formation and desmosome ultrastructural alteration on p38MAPK signaling induced by PV-IgG in human skin and mucosa explant cultures. Accordingly, we adapted the existing ex vivo skin model and also established a novel ex vivo mucosa model, and employed histological, immune-histochemical as well as electron microscopy analyses to determine the role of p38MAPK signaling in PV pathogenesis. Human skin biopsies were treated with the mouse monoclonal Dsg3-specific antibodyAK23, in comparison to antibody fractions from patients with mucocutaneous PV (mcPV-IgG) or mucosal PV (mdPV-IgG). mcPV-IgG only were sufficient to induce blisters as well as alterations in desmosome ultrastructure. In contrast, in human labial mucosa explants both AK23 and mdPV-IgG were sufficient to induce blisters as well as alterations in desmosome ultrastructure. Moreover, inhibition of p38MAPK using the specific inhibitor SB202190 was effective to avert blister formation, rescue desmosome size and number as well as preserved keratin filament association with desmosomal plaques in human skin. However, in the newly established human ex vivo mucosa model, inhibition of p38MAPK with specific inhibitors SB202190 and SB203580 was not effective to prevent these alterations. Taken together, our data demonstrate that p38MAPK plays a key role in blister formation through modulation of desmosome ultrastructure in human skin. In contrast, blister formation and associated ultrastructural changes of desmosomes in mucosa may depend on steric hindrance and other signaling pathways independent of p38MAPK.
Pemphigus, Desmosomes, Desmoglein, Keratin, Skin blistering, ultrastructure, Electon microscopy
Egu, Desalegn Tadesse
2020
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Egu, Desalegn Tadesse (2020): Role of p38MAPK in ultrastructural alterations of desmosomes in human ex vivo pemphigus model. Dissertation, LMU München: Faculty of Medicine
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Abstract

Desmosomes interconnect epithelial cells together and are abundant in tissues constantly challenged by shear forces. They are composed of different isoforms of intercellular adhesion proteins which include desmogleins (Dsg) and desmocollins (Dsc). These proteins of apposing cells interact in homophilic and heterophilic manner thereby conferring integrity to the tissue. When this crucial role of desmosomes is compromised, several desmosome-associated diseases such as pemphigus may occur. Pemphigus is a blistering disease of the skin and oral mucosa. It is caused by anti-Dg3 and anti-Dsg1 autoantibodies that bind to the extracellular domains of the desmogleins and perturb their interaction. There are different phenotypes of the disease depending on the autoantibody profiles. Pemphigus vulgaris (PV) is caused by autoantibodies (PV-IgG) targeting Dsg1 and Dsg3 whereas pemphigus foliaceus (PF) is associated with autoantibodies against Dsg1 only. Pemphigus vulgaris is recognized as two sub-types; i.e, the mucosal-dominant form (mdPV) caused by anti-Dsg3 autoantibodies and the mucocutaneus (mcPV) variant caused by both anti-Dsg1 and anti-Dsg3 autoantibodies. Several lines of evidence demonstrated that pemphigus is caused by disruption of Dsg interaction when the autoantibodies are interposed between the interacting Dsg (steric hindrance) and signaling triggered by autoantibody binding. It has been widely accepted that different signaling pathways work in concert in the modulation of desmosome structure and dynamics. p38 mitogen activated protein kinase (p38MAPK) has been extensively studied and its phosphorylation was detected in cell cultures in response to PV-IgG binding as well as in skin lesions of pemphigus patients. Pharmacological inactivation of this pathway attenuated cell dissociation in cultures and blister formation in murine models. However, no data was available with respect to the role of p38MAPK in blister formation in human skin and mucosa. Therefore, we tested the dependency of blister formation and desmosome ultrastructural alteration on p38MAPK signaling induced by PV-IgG in human skin and mucosa explant cultures. Accordingly, we adapted the existing ex vivo skin model and also established a novel ex vivo mucosa model, and employed histological, immune-histochemical as well as electron microscopy analyses to determine the role of p38MAPK signaling in PV pathogenesis. Human skin biopsies were treated with the mouse monoclonal Dsg3-specific antibodyAK23, in comparison to antibody fractions from patients with mucocutaneous PV (mcPV-IgG) or mucosal PV (mdPV-IgG). mcPV-IgG only were sufficient to induce blisters as well as alterations in desmosome ultrastructure. In contrast, in human labial mucosa explants both AK23 and mdPV-IgG were sufficient to induce blisters as well as alterations in desmosome ultrastructure. Moreover, inhibition of p38MAPK using the specific inhibitor SB202190 was effective to avert blister formation, rescue desmosome size and number as well as preserved keratin filament association with desmosomal plaques in human skin. However, in the newly established human ex vivo mucosa model, inhibition of p38MAPK with specific inhibitors SB202190 and SB203580 was not effective to prevent these alterations. Taken together, our data demonstrate that p38MAPK plays a key role in blister formation through modulation of desmosome ultrastructure in human skin. In contrast, blister formation and associated ultrastructural changes of desmosomes in mucosa may depend on steric hindrance and other signaling pathways independent of p38MAPK.