Decorin suppresses fibrotic processes in human peritoneal mesothelial cells through inhibition of PKC-alpha phosphorylation

Abstract

OBJECTIVES: Mesothelial cell dysfunction contributes to peritoneal fibrosis during long-term peritoneal dialysis (PD). We previously reported that mesothelial cells synthesize decorin, a dermatan sulfate proteoglycan with anti-fibrotic properties. In this study, we investigated the mechanisms through which decorin regulates fibrogenesis in mesothelial cells in the setting of PD. METHODS: All experiments were conducted with human peritoneal mesothelial cells (HPMC), isolated from omental specimens by enzymatic digestion, at the second passage and growth arrested for 72 h. HPMC were stimulated with spent PD fluid, exogenous TGF-1 or IL-1 (10 ng/ml), in the presence or absence of TGF-1 neutralizing antibody (1 g/ml), IL-1 receptor antagonist (1 g/ml) or decorin (500 ng/ml) for 24 h. Cell morphology, its expression of fibronectin and -smooth muscle actin, and PKC-a activation was assessed. The role of decorin in fibrotic processes in HPMC was further investigated following gene silencing of decorin. RESULTS: Noninfected PDF induced epithelial-to-mesenchymal transition (EMT) and cell detachment in HPMC, and these phenotypic changes were exacerbated in cells exposed to infected PD fluid. Pre-incubation of HPMC with TGF-1 neutralizing antibody or IL-1 receptor antagonist inhibited PD fluid-induced EMT. Incubation of HPMC with exogenous decorin inhibited EMT induced by PD fluid, TGF-1 or IL-1. This was accompanied by decreased fibronectin synthesis and -smooth muscle actin expression. The effect of decorin was mediated through the suppression of PKC- phosphorylation. Knockdown of decorin expression in HPMC resulted in amplification of TGF-1-and IL-1-induced fibronectin synthesis and -smooth muscle actin expression. CONCLUSION: The data demonstrate that decorin ameliorates fibrotic processes in HPMC during PD through the suppression of PKC- signaling pathway.