Peroxisome proliferator-activated receptor gamma (PPAR<inf>γ</inf>) regulates thrombospondin-1 and Nox4 expression in hypoxia-induced human pulmonary artery smooth muscle cell proliferation

• Type of Material: Article
• Authors: David Green, Emory University; Bum-Yong Kang, Emory University; Tamara C. Murphy, Emory University; Charles Hart, Emory University
• Language: English
• Date: 2012-10
• Publisher: University of Chicago Press: No Paid Open Access
• Publication Version: Final Published Version
• Copyright Statement: © 2012, Taylor and Francis Inc. All rights reserved.
• License: Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported
• Final Published Version (URL): http://dx.doi.org/10.4103/2045-8932.105037
• Title of Journal or Parent Work: Pulmonary Circulation
• ISSN: 2045-8932
• Volume: 2
• Issue: 4
• Start Page: 483
• End Page: 491
• Grant/Funding Information: Source of Support: Research Service of the Atlanta Veterans Affairs Medical Center and the National Institutes of Health (R01 DK 074518). NHLBI T32 training grant (HL076118-06).
• Keywords: hypoxia; Nox4; PPARγ; rosiglitazone; thrombospondin-1
• Research Categories: Biology, Cell; Biology, Genetics

Abstract

Transforming growth factor-β1 (TGF-β1) and thrombospondin-1 (TSP-1) are hypoxia-responsive mitogens that promote vascular smooth muscle cell (SMC) proliferation, a critical event in the pathogenesis of pulmonary hypertension (PH). We previously demonstrated that hypoxia-induced human pulmonary artery smooth muscle (HPASMC) cell proliferation and expression of the NADPH oxidase subunit, Nox4, were attenuated by the peroxisome proliferator-activated receptor γ (PPARγ) agonist, rosiglitazone. The current study examines the hypothesis that rosiglitazone regulates Nox4 expression and HPASMC proliferation by attenuating TSP-1 signaling. Selected HPASMC were exposed to normoxic or hypoxic (1% O 2 ) environments or TSP-1 (0-1 μg/ ml) for 72 hours ± administration of rosiglitazone (10 μM). Cellular proliferation, Nox4, TSP-1, and TGF-β1 expression and reactive oxygen species generation were measured. Mice exposed to hypoxia (10% O 2 ) for three weeks were treated with rosiglitazone (10 mg/kg/day) for the final 10 days, and lung TSP-1 expression was examined. Hypoxia increased TSP-1 and TGF-β1 expression and HPASMC proliferation, and neutralizing antibodies to TSP-1 or TGF-β1 attenuated proliferation. Rosiglitazone attenuated hypoxia-induced HPASMC proliferation and increases in mouse lung and HPASMC TSP-1 expression, but failed to reduce increases in TGF-β1 expression or Nox4 expression and activity caused by direct TSP-1 stimulation. Transfecting HPASMC with siRNA to Nox4 attenuated hypoxia-or TSP-1-stimulated HPASMC proliferation. These findings provide novel evidence that TSP-1-mediated Nox4 expression plays a critical role in hypoxia-induced HPASMC proliferation. PPARγ activation with exogenous ligands attenuates TSP-1 expression to reduce Nox4 expression. These results clarify mechanisms of hypoxia-induced SMC proliferation and suggest additional pathways by which PPARγ agonists may regulate critical steps in the pathobiology of PH.