Rosiglitazone Inhibits Transforming Growth Factor-β1 Mediated Fibrogenesis in ADPKD Cyst-Lining Epithelial Cells

Background: Interstitial fibrosis plays an important role in progressive renal dysfunction in autosomal dominant polycystic kidney disease (ADPKD). In our previous studies, we confirmed that PPAR-gamma agonist, rosiglitazone could protect renal function and prolong the survival of a slowly progressive ADPKD animal model by reducing renal fibrosis. However, the mechanism remains unknown. Methods: Primary culture epithelial cells pretreated with TGF-beta 1 were incubated with rosiglitazone. Extracellular matrix proteins were detected using real-time PCR and Western blotting. MAPK and Smad2 phosphorylation were measured with western blot. ERK1/2 pathway and P38 pathway were inhibited with the specific inhibitors PD98059 and SB203580. The Smad2 pathway was blocked with the siRNA. To address whether PPAR-gamma agonist-mediated inhibition of TGF-beta 1-induced collagen type I expression was mediated through a PPAR-gamma dependent mechanism, genetic and pharmaceutical approaches were used to block the activity of endogenous PPAR gamma. Results: TGF-beta 1-stimulated collagen type I and fibronectin expression of ADPKD cyst-lining epithelia were inhibited by rosiglitazone in a dosage-dependent manner. Smad2, ERK1/2 and P38 pathways were activated in response to TGF-beta 1; however, TGF-beta 1 had little effect on JNK pathway. Rosiglitazone suppressed TGF-beta 1 induced Smad2 activation, while ERK1/2 and P38MAPK signals remained unaffected. Rosiglitazone could also attenuate TGF-beta 1-stimulated collagen type I and fibronectin expression in primary renal tubular epithelial cells, but had no effect on TGF-beta 1-induced activation of Smad2, ERK1/2 and P38 pathways. There was no crosstalk between the Smad2 and MAPK pathways in ADPKD cyst-lining epithelial cells. These inhibitory effects of rosiglitazone were reversed by the PPAR gamma specific antagonist GW9662 and PPAR gamma siRNA. Conclusion: ADPKD cyst-lining epithelial cells participate in TGF-beta 1 mediated fibrogenesis. Rosiglitazone could suppress TGF-beta 1-induced collagen type I and fibronectin expression in ADPKD cyst-lining epithelia through modulation of the Smad2 pathway. Our study may provide therapeutic basis for clinical applications of rosiglitazone in retarding the progression of ADPKD.