Inhibitory effects of PPAR gamma ligands on TGF-beta 1-induced CTGF expression in cat corneal fibroblasts

摘要

Ligands of Peroxisome Proliferator Activated Receptor gamma (PPAR gamma) possess strong anti-fibrotic properties in the cornea and several other body tissues. In the cornea, we recently showed this class of molecules to prevent stromal myofibroblast differentiation partially by blocking the actions of p38 mitogen-activated protein kinase (MAPK). However, given the important role assigned to connective tissue growth factor (CTGF) in mediating corneal fibrosis, here we asked whether PPAR gamma ligands also act by affecting transforming growth factor-beta (TGF-beta) 1-induced expression of CTGF in cultured corneal fibroblasts. Corneal keratocytes were isolated from young, adult cats and early passage cells were exposed to TGF-beta 1 with or without the PPAR gamma ligands Rosiglitazone, Troglitazone and 15d-PGJ2. Western blots were used to assay levels of CTGF and alpha smooth muscle actin (alpha SMA), a marker of myofibroblast differentiation. CTGF siRNA demonstrated a critical role for CTGF in TGF-beta 1-mediated myofibroblast differentiation, while exogenously applied CTGF potentiated the pro-fibrogenic effects of TGF-beta 1. TGF-beta 1-mediated increases in CTGF and aSMA expression were strongly inhibited by all three PPAR gamma ligands tested, and by a c-jun N-terminal kinase (INK) inhibitor. However, while extracellular signal-regulated kinase (ERR) 1/2, protein kinase B (ART) and p38 MAPK inhibitors also blocked TGF-beta 1-induced alpha SMA induction, they did not dampen TGF-beta 1-induced increases in levels of CTGF. Thus, we conclude that PPAR gamma ligands block TGF-beta 1-induced increases in CTGF levels in cat corneal fibroblasts. They appear to do this in addition to their anti-fibrotic effect on p38 MAPK, providing a second intracellular pathway by which PPAR gamma ligands block alpha SMA induction. (C) 2015 Elsevier Ltd. All rights reserved.