Hypoxia induces downregulation of PPAR-γ in isolated pulmonary arterial smooth muscle cells and in rat lung via transforming growth factor-β signaling

Gong K, Xing D, Li P, Aksut B, Ambalavanan N, Yang Q, Nozell SE, Oparil S, Chen Y-F. Hypoxia induces downregulation of PPAR-gamma in isolated pulmonary arterial smooth muscle cells and in rat lung via transforming growth factor-beta signaling. Am J Physiol Lung Cell Mol Physiol 301: L899-L907, 2011. First published September 16, 2011; doi: 10.1152/ajplung.00062.2011.-Chronic hypoxia activates transforming growth factor-beta (TGF-beta) signaling and leads to pulmonary vascular remodeling. Pharmacological activation of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) has been shown to prevent hypoxia-induced pulmonary hypertension and vascular remodeling in rodent models, suggesting a vasoprotective effect of PPAR-gamma under chronic hypoxic stress. This study tested the hypothesis that there is a functional interaction between TGF-beta/Smad signaling pathway and PPAR-gamma in isolated pulmonary artery small muscle cells (PASMCs) under hypoxic stress. We observed that chronic hypoxia led to a dramatic decrease of PPAR-gamma protein expression in whole lung homogenates (rat and mouse) and hypertrophied pulmonary arteries and isolated PASMCs. Using a transgenic model of mouse with inducible overexpression of a dominant-negative mutant of TGF-beta receptor type II, we demonstrated that disruption of TGF-beta pathway significantly attenuated chronic hypoxia-induced downregulation of PPAR-gamma in lung. Similarly, in isolated rat PASMCs, antagonism of TGF-beta signaling with either a neutralizing antibody to TGF-beta or the selective TGF-beta receptor type I inhibitor SB431542 effectively attenuated hypoxia-induced PPAR-gamma downregulation. Furthermore, we have demonstrated that TGF-beta 1 treatment suppressed PPAR-gamma expression in PASMCs under normoxia condition. Chromatin immunoprecipitation analysis showed that TGF-beta 1 treatment significantly increased binding of Smad2/3, Smad4, and the transcriptional corepressor histone deacetylase 1 to the PPAR-gamma promoter in PASMCs. Conversely, treatment with the PPAR-gamma agonist rosiglitazone attenuated TGF-beta 1-induced extracellular matrix molecule expression and growth factor in PASMCs. These data provide strong evidence that activation of TGF-beta/Smad signaling, via transcriptional suppression of PAR-gamma expression, mediates chronic hypoxia-induced downregulation of PPAR-gamma expression in lung.