Decorin inhibits epithelial-to-mesenchymal transition and fibrogenesis in mesothelial cells through inhibition of MAPK phosphorylation

Abstract

INTRODUCTION AND AIMS: Peritoneal fibrosis is one of the most serious complications observed in patients on long-term peritoneal dialysis (PD) and is a major cause of technique failure. Mesothelial cells line the peritoneal cavity and contribute to peritoneal fibrosis through their synthesis of various growth factors and extracellular matrix components and their ability to undergo epithelial-to-mesenchymal transition (EMT). Mesothelial cells synthesize decorin, a dermatan sulfate proteoglycan with anti-fibrotic properties. In this study, we investigated the mechanisms through which decorin regulates EMT and fibrogenesis in mesothelial cells. METHODS: Confluent, growth arrested mesothelial cells were stimulated with exogenous TGF-β1, IL-1β and TNF-α - cytokines known to be increased in the peritoneal cavity during PD (10 ng/ml for both) in the presence or absence of specific inhibitors of ERK, p38 MAPK and JNK, or exogenous decorin (0-1000 ng/ml) for 24h. Cell morphology and expression of β-catenin, E-cadherin, snail and fibronectin, and phosphorylation of ERK, p38 MAPK and JNK was determined by phase contract microscopy and Western blot analysis respectively. RESULTS: Exogenous TGF-β1, IL-1β and TNF-α induced EMT in mesothelial cells. Phenotypic changes were accompanied by a decrease in E-cadherin, an increase in β-catenin, snail and fibronectin synthesis and phosphorylation of ERK, p38 MAPK and JNK. Incubation of mesothelial cells with PD98059, SB203580 and SP600125 - specific inhibitors to ERK, p38 MAPK and JNK respectively, demonstrated that all three signaling pathways contributed to induction of the EMT cascade and fibrogenesis in mesothelial cells. Incubation of cells with decorin inhibited EMT and fibronectin synthesis induced by TGF-β1, IL-1β and TNF-α (P<0.05, for all). The effect of decorin was mediated through the suppression of ERK, p38 MAPK and JNK phosphorylation. Gene silencing of decorin using RNAi resulted in the amplification of IL-1β induced fibronectin. CONCLUSIONS: Our data demonstrate that decorin can suppress EMT and fibrotic processes in mesothelial cells during PD through modulation of the MAPK signaling pathways.