Epithelial-to-mesenchymal transition of peritoneal mesothelial cells is regulated by an ERK/NF-kappaB/Snail1 pathway

Epithelial-to-mesenchymal transition (EMT) occurs in fibrotic diseases affecting the kidney, liver and lung, and in the peritoneum of patients undergoing peritoneal dialysis. EMT in the peritoneum is linked to peritoneal membrane dysfunction, and its establishment limits the effectiveness of peritoneal dialysis. The molecular regulation of EMT in the peritoneum is thus of interest from basic and clinical perspectives. Treatment of primary human mesothelial cells (MCs) with effluent from patients undergoing peritoneal dialysis induced a genuine EMT, characterized by downregulated E-cadherin and cytokeratin expression, cell scattering, and spindle-like morphology. This EMT was replicated by co-stimulation with transforming growth factor (TGF)-beta1 and interleukin (IL)-1beta. Retroviral overexpression of a mutant inhibitor of kappaB (IkappaB) demonstrated that NF-kappaB activation is required for E-cadherin and cytokeratin downregulation during EMT. Pre-treatment with the MAP kinase kinase (MEK)-1/2 inhibitor U0126 showed that cytokine-triggered NF-kappaB nuclear translocation and transcriptional activity are mediated by activation of extracellular regulated kinase (ERK). Cytokine-mediated induction of mRNA expression of the transcription factor Snail1, a repressor of E-cadherin expression and a potent inducer of EMT, was prevented by blockade of ERK or NF-kappaB. Finally, blockade of ERK/NF-kappaB signaling in ex vivo MCs that were cultured from peritoneal dialysis effluents reverted cells to an epithelioid morphology, upregulated E-cadherin and cytokeratin expression, and downregulated Snail1 expression. Modulation of the ERK/NF-kappaB/Snail1 pathway may provide a means of counteracting the progressive structural and functional deterioration of the peritoneal membrane during peritoneal dialysis.