Rosiglitazone inhibits angiotensin II-induced CTGF expression in vascular smooth muscle cells--Role of PPAR-γ in vascular fibrosis

Angiotensin (Ang) II plays a pivotal role in vascular fibrosis, which leads to serious complications in hypertension and diabetes. Connective tissue growth factor (CTGF) is a potent profibrotic factor implicated in the Ang II-induced pathologic fibrosis process. PPAR-γ activators thiazolidinediones have been recently reported to have beneficial vascular effects. However, their effects and related molecular mechanisms on extracellular matrix (ECM) turnover in vascular smooth muscle cells (VSMCs) are unknown. The present study evaluated the regulation of Ang II-induced CTGF, ECM production and cell growth by rosiglitazone in VSMCs. In aorta of Ang II-infused rats, CTGF expression was markedly increased, and type III collagen and fibronectin overexpression was observed. Cotreatment with rosiglitazone diminished these changes, whereas increased nuclear PPAR-γ expression in VSMCs. In growth-arrested VSMCs, rosiglitazone attenuated the proliferation and apoptosis, increased PPAR-γ production and activation, and reduced CTGF and ECM production in response to Ang II in a dose-dependent fashion. These inhibitory effects were attenuated by the pretreatment of cells with PPAR-γ antagonist GW9662 or bisphenol A diglycidyl ether (BADGE). Furthermore, rosiglitazone inhibited Ang II-induced Smad2 production and phosphorylation but had no effect on transforming growth factor-β₁ (TGF-β₁) expression. These results suggest that in Ang II-stimulated VSMCs, rosiglitazone caused an antiproliferative, antiapototic effect and reduces ECM production through mechanisms that include reducing CTGF expression, and a crosstalk between PPAR-γ and Smad may be involved in the inhibitory effects of rosiglitazone. This novel finding suggests a role of PPAR-γ activators in preventing Ang II-induced vascular fibrosis.