Effects of epithelial-to-mesenchymal transition on acute stress response in human peritoneal mesothelial cells.

BACKGROUND During peritoneal dialysis, mesothelial cells undergo epithelial-to-mesenchymal transition (EMT), resulting in markedly altered protein expression. This potentially includes heat-shock proteins (HSP), the main effectors of cellular repair. Thus, chronic cellular processes, such as EMT, may influence acute stress responses and thus survival of mesothelial cells following non-lethal injury upon exposure to peritoneal dialysis fluid (PDF). METHODS In this study, we investigated the effects of EMT on acute stress responses and cytoresistance in human peritoneal mesothelial cells. In vivo EMT was defined as a fibroblast-like growth pattern in mesothelial cells grown from peritoneal effluents, and in vitro EMT was induced by TGF-beta1 in mesothelial cells grown from omental tissue. Morphologic EMT was validated by western blot analysis of EMT marker proteins (ezrin, alpha-SMA). Expression of HSP and cellular survival was evaluated in a simple in vitro PDF exposure model. RESULTS In vivo and in vitro EMT resulted in marked effects on phenotypes of mesothelial cells, associated with differential HSP expression. In vivo 'chronic' EMT resulted in lower expression of HSP-27 and HSP-72, whereas in vitro 'acute' EMT was associated with increased HSP-27 and decreased HSP-72 expression. Following PDF exposure, there were no effects of in vivo EMT on the stress induction of HSP, and survival of epithelial versus fibroblast-like phenotypes was comparable. The non-stressful induction of HSP-27 following TGF-beta1 pretreatment resulted in the attenuated stress induction of HSP, and in improved survival in following PDF exposure. CONCLUSIONS Taken together, this study confirms that mesothelial cells are not 'unchanged' or 'static targets' during the clinical course of PD treatment. The cellular processes during EMT play a complex role in acute cellular stress response and cytoresistance of mesothelial cells. Sequential analysis at different stages of EMT will be essential to provide more insights on cytoprotective cellular processes in in vitro and in vivo models of PD.