PPARγ regulates hypoxia‐induced Nox4 expression in human pulmonary artery smooth muscle cells through NF‐κB

Abstract

The Nox4 NADPH oxidase, which is highly expressed in vascular wall cells, is selectively upregulated in the lungs of human subjects and experimental animals with pulmonary hypertension. We demonstrated that rosiglitazone, a synthetic PPARγ agonist, attenuated hypoxia‐induced pulmonary hypertension, vascular remodeling, Nox4 induction and reactive oxygen species generation in the mouse lung. The current study examined PPARγ‐regulated, hypoxia‐induced Nox4 expression in human pulmonary artery smooth muscle cells (HPASMC). Exposure to 1% oxygen for 72 hours increased Nox4 gene expression and HPASMC H2O2 production, both of which were reduced by treatment with rosiglitazone or with siRNA to Nox4. Rosiglitazone also attenuated hypoxia‐induced HPASMC proliferation and the activity of a Nox4 promoter luciferase reporter. Chromatin immunoprecipitation assays demonstrated that hypoxic‐induced binding of the NF‐κB subunits, p65 and C‐rel, to the Nox4 promoter was attenuated by rosiglitazone. The role of NF‐κB in Nox4 regulation was further supported by demonstrating that overexpression of p65 stimulated Nox4 promoter activity whereas siRNA to p50 or p65 attenuated hypoxic‐stimulated Nox4 promoter activity. These results provide novel evidence for NF‐κB‐mediated stimulation of Nox4 expression in HPASMC that can be negatively regulated by PPARγ.