Biphasic activation of p38MAPK suggests that apoptosis is a downstream event in pemphigus acantholysis

In pemphigus vulgaris and pemphigus foliaceus (PF), autoantibodies against desmoglein-3 and desmoglein-1 induce epidermal cell detachment (acantholysis) and blistering. Activation of keratinocyte intracellular signaling pathways is emerging as an important component of pemphigus IgG-mediated acantholysis. We previously reported activation of p38 mitogen-activated protein kinase (MAPK) in response to pathogenic pemphigus vulgaris and PF IgG. Inhibition of p38MAPK blocked pemphigus IgG-induced cytoskeletal reorganization in tissue culture and blistering in pemphigus mouse models. We now extend these observations by demonstrating two peaks of p38MAPK activation in pemphigus tissue culture and mouse models. Administration of the p38MAPK inhibitor SB202190 before PF IgG injection blocked both peaks of p38MAPK phosphorylation and blister formation, consistent with our previous findings; however, administration of the inhibitor 4 h after PF IgG injection blocked only the later peak of p38MAPK activation but failed to block blistering. Examination of the temporal relationship of p38MAPK phosphorylation and apoptosis showed that apoptosis occurs at or after the second peak of p38MAPK activation. The time course of p38MAPK activation and apoptotic markers, as well as the ability of inhibitors of p38MAPK to block activation of the proapoptotic proteinase caspase-3, suggest that activation of apoptosis is downstream to, and a consequence of, p38MAPK activation in pemphigus acantholysis. Furthermore, these observations suggest that the earlier peak of p38MAPK activation is part of the mechanism leading to acantholysis, whereas the later peak of p38MAPK and apoptosis may not be essential for acantholysis.

Focal adhesion kinase is expressed in acantholytic keratinocytes associated with pemphigus vulgaris and pemphigus foliaceus

Focal adhesion kinase is a protein-tyrosine kinase that is found in cellular contact sites and is phosphorylated in response to cell attachment. It is possible that the immunohistochemical detection of this enzyme might be increased in keratinocytes involved in an acantholytic process. Normal skin, pemphigus vulgaris and foliaceus, Darier's disease, Hailey--Hailey disease, warty dyskeratoma, Grover's disease and spongiotic dermatitis were assayed for the immunohistochemical expression of focal adhesion kinase. Focal adhesion kinase was not observed in normal epidermis. This antigen was observed in keratinocytes adjacent to acantholytic spaces and in acantholytic cells in pemphigus vulgaris and foliaceus. Focal adhesion kinase was not detected in keratinocytes involved in focal acantholytic dyskeratoses such as Darier's disease, Grover's disease and warty dyskeratoma but was weakly detected in Hailey--Hailey disease. One consequence of immunologically mediated acantholysis is the upregulation of focal adhesion kinase possibly as a component of biochemical pathways that reconstruct the process of adhesion or respond to the process of acantholysis.

Immunolocalization of human gelatinase (type IV collagenase, MMP-9) and tissue inhibitor of metalloproteinase 1 in Hailey-Hailey and Darier's diseases

BACKGROUND

The formation of lacunae and acantholysis as well as dyskeratosis are characteristic features of Hailey-Hailey disease (HHD) and Darier's disease (DD). Matrix metalloproteinases (MMPs) and their inhibitors like tissue inhibitors of metalloproteinases (TIMPs) have been thought to play major roles in the tissue metabolism.

OBJECTIVE

The aim of this study was to investigate the role of MMP-9 and TIMP-1 in HHD and DD.

METHODS

We examined localizations of these two molecules by immunostaining using specific monoclonal antibodies.

RESULTS

MMP-9 was positively stained in dyskeratotic or detaching cells around lacunae in HHD and DD. TIMP-1 showed a positive staining pattern throughout the epidermis.

CONCLUSION

MMP-9 might be involved in the pathophysiological process of HHD and DD in the presence of TIMP-1.

Imbalance between plasminogen activator and its inhibitors in thiol-induced acantholysis

Pemphigus may be an idiopathic disease or a syndrome induced by drugs, mainly thiol drugs. Autoantibodies, always present in the idiopathic form but often lacking in the drug-induced one, may cause acantholysis by activating endogenous proteolytic enzymes. Pathogenesis of drug-induced pemphigus when antibodies are absent has not been elucidated yet. Extracts of skin tissues cultured for 4 days with penicillamine, captopril or thiopronine were assayed for the presence of plasminogen activator (PA) and plasminogen activator inhibitors (PAI) on agar fibrin plates. Moreover, uPA, tPA, and PAI-1 were identified in the extracts by immunoenzymatic assay. The results have shown progressively decreasing amounts of PAI-1 in penicillamine, thiopronine and captopril-cultured tissue extracts, respectively. This suggests that the acantholytic potential of thiol drugs is directly correlated to their capability of reducing PAI-1 in the epidermal cells leading to increased PA activity. This PA-PAI imbalance may be itself the cause of intraepidermal splitting.

Cantharide acantholysis: endogenous protease activation leading to desmosomal plaque dissolution

Using a method which allowed us to study the morphological consequences of the expression and the inhibition of proteases in living tissues, we demonstrated that the primary detectable cellular event in cantharide acantholysis is the dissolution of the dense plaque, leading to the detachment of tonofilaments from desmosomes. This process is inhibited by neutral serine protease inhibitors. This suggests that the desmosome-tonofilament complex, more precisely the desmosomal dense plaque, is the primary target of activated proteases during cantharide acantholysis, and can be disrupted by a specific epidermal protease-anti protease system. Cantharide acantholysis may be useful model for studying desmosomal turnover.