Electrophilic PPARγ ligands inhibit corneal fibroblast to myofibroblast differentiation in vitro: A potentially novel therapy for corneal scarring

A critical component of corneal scarring is the TGF beta-induced differentiation of corneal keratocytes into myofibroblasts. Inhibitors of this differentiation are potentially therapeutic for corneal scarring. In this study, we tested the relative effectiveness and mechanisms of action of two electrophilic peroxisome proliferator-activated receptor gamma (PPAR gamma) ligands: cyano-3,12-dioxolean-1,9-dien-28-oic acid-methyl ester (CDDO-Me) and 15-deoxy-Delta(-12,14)-prostaglandin J(2) (15d-PGJ(2)) for inhibiting TGF beta-induced myofibroblast differentiation in vitro. TGF beta was used to induce myofibroblast differentiation in cultured, primary human corneal fibroblasts. CDDO-Me and 15d-PGJ(2) were added to cultures to test their ability to inhibit this process. Myofibroblast differentiation was assessed by measuring the expression of myofibroblast-specific proteins (alpha SMA, collagen 1, and fibronectin) and mRNA (alpha SMA and collagen III). The role of PPAR gamma in the inhibition of myofibroblast differentiation by these agents was tested in genetically and pharmacologically manipulated cells. Finally, we assayed the importance of electrophilicity in the actions of these agents on TGF beta-induced alpha SMA expression via Western blotting and immunofluorescence. Both electrophilic PPAR gamma ligands (CDDO-Me and 15d-PGJ2) potently inhibited TGF beta-induced myofibroblast differentiation, but PPAR gamma was only partially required for inhibition of myofibroblast differentiation by either agent. Electrophilic PPAR gamma ligands were able to inhibit myofibroblast differentiation more potently than non-electrophilic PPAR gamma ligands, suggesting an important role of electrophilicity in this process. CDDO-Me and 15d-PGJ(2) are strong inhibitors of TGF beta-induced corneal fibroblast to myofibroblast differentiation in vitro, suggesting this class of agents as potential novel therapies for corneal scarring warranting further study in pre-clinical animal models. CI 2011 Elsevier Ltd. All rights reserved.