The mechanisms underlying hypoxia-induced Nox4 expression in the lung and its contribution to the pathogenesis of pulmonary hypertension have not Dorsomorphin been defined. Previous reports have demonstrated that Nox4-derived ROS mediate hypoxic-induced pulmonary artery smooth muscle cell proliferation (49), and hypoxia-induced increases in smooth muscle cells surrounding small pulmonary vessels characterize hypoxia-induced pulmonary vascular alterations in the mouse (39). The current study reveals that hypoxia stimulates Nox4 expression, ROS production, and HPASMC proliferation and that rosiglitazone-mediated PPAR�� activation attenuates hypoxia-induced Nox4 expression, H2O2 production, and HPASMC proliferation.

siRNA to Nox4 only partially inhibited hypoxia-induced H2O2 production, suggesting less than complete Nox4 knockdown by siRNA as well as potential contribution of additional sources of ROS to hypoxia-induced H2O2 production. Nevertheless, Nox4 siRNA more fully inhibited hypoxia-induced HPASMC proliferation, suggesting that Nox4 may specifically contribute to HPASMC proliferation. Several recent studies suggested that the transcription factor, NF-��B, was actively involved in hypoxic signaling (5, 46). NF-��B constitutes a family of transcription factors that is classically activated following stimulation with proinflammatory ligands, including cytokines, antigens, and bacteria. This complex signaling mechanism involves activation of the IKK complex, leading to I��B phosphorylation and proteasomal degradation.

Hypoxic activation of NF-��B is in part due to decreased prolyl hydroxylase-dependent hydroxylation of I��B kinase B in the canonical pathway but may also involve other mechanisms including tyrosine phosphorylation of I��B�� (50). In addition, I��B��, through direct interaction with NF-��B and hypoxia-inducible factor-1�� (HIF-1��), may play a pivotal role in the cross talk between the molecular events that underlie hypoxic and inflammatory responses (46). Previous studies have AV-951 also implicated NF-��B in the regulation of other NADPH oxidase subunits, including gp91phox, p47phox, and p22phox (3, 16, 33, 37). Collectively, these reports suggest that NF-��B activation occurs during hypoxia and may contribute to enhanced NADPH oxidase expression. Previous reports have demonstrated that NF-��B stimulates NADPH oxidases in human phagocytes and vascular smooth muscle cells (3, 5, 44). However, little is known about the role of NF-��B in regulation of the Nox4 promoter under normal or hypoxic conditions. To our knowledge, the present study is the first to report that there are NF-��B binding elements on the Nox4 promoter and that PPAR�� regulates Nox4 expression through these binding elements.