Peroxisome proliferator-activated receptor-γ agonists attenuate the profibrotic response induced by TGF-β1 in renal interstitial fibroblasts

Background. Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a ligand-dependent transcription factor that plays an important role in the regulation of insulin sensitivity and lipid metabolism. Studies have shown that PPAR-gamma agonists also ameliorated renal fibrotic lesions in both diabetic nephropathy and nondiabetic chronic kidney diseases. In order to elucidate the antifibrotic mechanism of PPAR-gamma agonists, we investigated the effects of PPAR-gamma activation on TGF-beta 1-induced renal interstitial fibroblasts activation. Methods. In rat renal interstitial fibroblasts cell (NRK/49F cells), the effects of PPAR-gamma ligand 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2) and its agonists troglitazone and ciglitazone on mRNA expression of TGF-beta 1-induced alpha-smooth muscle actin (alpha-SMA), connective tissue growth factor (CTGF), fibronectin (FN), and Collagen type III (Col III) were observed by reverse transcriptase-polymerase chain reaction (RT-PCR). The effects of PPAR-gamma agonists on the protein expression of FN, and Smads induced by TGF-beta 1 were observed by Western blot. Results. In NRK/49F cells, TGF-beta 1 enhanced CTGF, FN, and Col III mRNA expression in a dose- and time-dependent manner. The level of a-SMA, CTGF, FN, and Col III mRNA and also FN protein expression in 15d-PGJ2-, troglitazone- and ciglitazone-pretreated groups, respectively, were significantly decreased compared with the TGF-beta 1-stimulated group. TGF-beta 1 (5 ng/mL) enhanced p-Smad2/3 protein expression in a time-dependent manner, with the optimal time course at 1 hour. The level of p-Smad2/3 protein expression was significantly increased in the 5 ng/mL TGF-beta 1 stimulated group compared with 2 ng/mL TGF-beta 1. Compared with the TGF-beta 1-stimulated group, the level of p-Smad2/3 protein expression induced by TGF-beta 1 in PPAR-gamma agonists-pretreated groups decreased significantly with no statistical difference amongst drug-pretreated groups. The level of Smad2 and Smad3 protein expression was unchanged in all groups. Conclusion. PPAR-gamma agonists could inhibit TGF-beta 1-induced renal fibroblast transdifferentiation, CTGF expression, and ECM synthesis through abrogating the TGF-beta 1/Smads signaling pathway. Our results suggest PPAR-gamma agonists may potentially play a role in preventing tubulointerstitial fibrosis, which may represent a novel approach to preventing ESRD progression. Copyright (C) 2007.