The effect of pemphigus sera on apoptosis of keratinocytes

Background: Pemphigus is an autoimmune blistering disease of skin and mucous membrane characterized by loss of adhesion between keratinocytes, a process known as acantholysis. The target molecules of autoantibodies are desmogleins which belong to cadherin family proteins of desmosome. Independently from the autoantibodies involved, the question whether apoptosis plays a role in the pathogenesis of pemphigus has not been addressed. Objectives: The purpose of this study was to determine if pemphigus sera induce apoptosis in HaCaT cells and to elucidate the mechanism of apoptosis induced by pemphigus sera. Methods: We treated pemphigus sera on HaCaT cells for 48 h and investigated whether apoptosis was induced or not through FACS analysis and TUNEL staining. In addition, we performed western blot analysis to detect cleavage of PARP, cytosolic cytochrome c and activation of caspase-8, 3, which play a major role in apoptosis. Soluble Fas ligand protein level in pemphigus sera was compared with the level in normal sera by ELISA. Pemphigus sera from which IgG was eliminated, were treated on HaCaT cells to elucidate the role of IgG in pemphigus sera-induced apoptosis. Results: Using FACS analysis with Annexin-V and PI staining, we have shown that pemphigus sera induced apoptosis in HaCaT cells. TUNEL staining assay also confirmed the apoptosis were induced in HaCaT cells after treatment of pemphigus sera. Western blot analysis showed activation of caspase-3, release of cytochrome c, cleavage of PARP and decrease of procaspase-8 which is proform of active caspase-8 in HaCaT cells treated with pemphigus sera. We could not detect increased Fas ligand protein level in pemphigus sera compared with the level in normal sera. Moreover, since the removal of IgG obliterated the apoptosis inducing effects of pemphigus sera in HaCaT cells, IgG might be involved in the activation of caspase-8 and caspase-3. Conclusion: We concluded that treatment of pemphigus serum induces the apoptosis of HaCaT cells through, at least in part, activation of caspase-8, caspase-3 and cytochrome c related mechanism, and that IgG in the pemphigus serum rather than Fas ligand is involved in the apoptosis. These results suggest that apoptosis may play an important role in the pathomechanism of pemphigus lesion.