Chronic hypoxia contributes to pulmonary hypertension through complex mechanisms that include enhanced NADPH oxidase expression and reactive oxygen species (ROS) generation in the lung. Stimulation of peroxisome proliferator-activated receptor g (PPARg) reduces the expression and activity of NADPH oxidase. Therefore, we hypothesized that activating PPARg with rosiglitazone would attenuate chronic hypoxia-induced pulmonary hypertension, in part, through suppressing NADPH oxidase-derived ROS that stimulate proliferative signaling pathways. Male C57Bl/6 mice were exposed to chronic hypoxia (CH, FI O 2 10%) or room air for 3 or 5 weeks. During the last 10 days of exposure, each animal was treated daily by gavage with either the PPARg ligand, rosiglitazone (10 mg/kg/d) or with an equal volume of vehicle. CH increased: (1) right ventricular systolic pressure (RVSP), (2) right ventricle weight, (3) thickness of the walls of small pulmonary vessels, (4) superoxide production and Nox4 expression in the lung, and (5) platelet-derived growth factor receptor b (PDGFRb) expression and activity and reduced phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression. Treatment with rosiglitazone prevented the development of pulmonary hypertension at 3 weeks; reversed established pulmonary hypertension at 5 weeks; and attenuated CH-stimulated Nox4 expression and superoxide production, PDGFRb activation, and reductions in PTEN expression. Rosiglitazone also attenuated hypoxia-induced increases in Nox4 expression in pulmonary endothelial cells in vitro despite hypoxia-induced reductions in PPARg expression. Collectively, these findings indicate that PPARg ligands attenuated hypoxia-induced pulmonary vascular remodeling and hypertension by suppressing oxidative and proliferative signals providing novel insights for mechanisms underlying therapeutic effects of PPARg activation in pulmonary hypertension.

Lu X, Murphy TC, Nanes MS, Hart CM. PPAR␥ regulates hypoxia-induced Nox4 expression in human pulmonary artery smooth muscle cells through NF-B. Am J Physiol Lung Cell Mol Physiol 299: L559 -L566, 2010. First published July 9, 2010; doi:10.1152/ajplung.00090.2010.-NADPH oxidases are a major source of superoxide production in the vasculature. The constitutively active Nox4 subunit, which is selectively upregulated in the lungs of human subjects and experimental animals with pulmonary hypertension, is highly expressed in vascular wall cells. We demonstrated that rosiglitazone, a synthetic agonist of the peroxisome proliferatoractivated receptor-␥ (PPAR␥), attenuated hypoxia-induced pulmonary hypertension, vascular remodeling, Nox4 induction, and reactive oxygen species generation in the mouse lung. The current study examined the molecular mechanisms involved in PPAR␥-regulated, hypoxia-induced Nox4 expression in human pulmonary artery smooth muscle cells (HPASMC). Exposing HPASMC to 1% oxygen for 72 h increased Nox4 gene expression and H 2O2 production, both of which were reduced by treatment with rosiglitazone during the last 24 h of hypoxia exposure or by treatment with small interfering RNA (siRNA) to Nox4. Hypoxia also increased HPASMC proliferation as well as the activity of a Nox4 promoter luciferase reporter, and these increases were attenuated by rosiglitazone. Chromatin immunoprecipitation assays demonstrated that hypoxia increased binding of the NF-B subunit, p65, to the Nox4 promoter and that binding was attenuated by rosiglitazone treatment. The role of NF-B in Nox4 regulation was further supported by demonstrating that overexpression of p65 stimulated Nox4 promoter activity, whereas siRNA to p50 or p65 attenuated hypoxic stimulation of Nox4 promoter activity. These results provide novel evidence for NF-B-mediated stimulation of Nox4 expression in HPASMC that can be negatively regulated by PPAR␥. These data provide new insights into potential mechanisms by which PPAR␥ activation inhibits Nox4 upregulation and the proliferation of cells in the pulmonary vascular wall to ameliorate pulmonary hypertension and vascular remodeling in response to hypoxia. nuclear factor-B; peroxisome proliferator-activated receptor-␥ NADPH OXIDASES ARE A MAJOR source of superoxide production in the vasculature that contributes to endothelial dysfunction and vascular cell proliferation (4,19). In nonphagocytic cells, the catalytic moiety of NADPH oxidases is composed of one or more gp91 phox (Nox2) homologs, Nox1, -3, -4, or -5, Duox1, or Duox2 (27). These Nox homologs associate with the membrane-bound p22 phox subunit to generate reactive oxygen species (ROS). Nox4 is highly expressed in vascular wall cells including smooth muscle and endothelial cells (47). In contrast to the other Nox homologs, current evidence indicates that Nox4 is constitutively active (1), and increases in Nox4 mRNA levels increase Nox4 activity (45). Nox4 expression is increased by diverse stimuli (4) including E2F transcription factors, serum starvati...

Recently, we demonstrated that the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligands, either 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) or ciglitazone, increased endothelial nitric oxide (.NO) release without altering endothelial nitric oxide synthase (eNOS) expression (4). However, the precise molecular mechanisms of PPAR-gamma-stimulated endothelial.NO release remain to be defined. Superoxide anion radical (O2-.) combines with .NO to decrease.NO bioavailability. NADPH oxidase, which produces O2-., and Cu/Zn-superoxide dismutase (Cu/Zn-SOD), which degrades O2-., thereby contribute to regulation of endothelial cell.NO metabolism. Therefore, we examined the ability of PPAR-gamma ligands to modulate endothelial O2-. metabolism through alterations in the expression and activity of NADPH oxidase or Cu/Zn-SOD. Treatment with 10 microM 15d-PGJ2 or ciglitazone for 24 h decreased human umbilical vein endothelial cell (HUVEC) membrane NADPH-dependent O2-. production detected with electron spin resonance spectroscopy. Treatment with 15d-PGJ2 or ciglitazone also reduced relative mRNA levels of the NADPH oxidase subunits, nox-1, gp91phox (nox-2), and nox-4, as measured using real-time PCR analysis. Concordantly, Western blot analysis demonstrated that 15d-PGJ2 or ciglitazone decreased nox-2 and nox-4 protein expression. PPAR-gamma ligands also stimulated both activity and expression of Cu/Zn-SOD in HUVEC. These data suggest that in addition to any direct effects on endothelial.NO production, PPAR-gamma ligands enhance endothelial.NO bioavailability, in part by altering endothelial O2-. metabolism through suppression of NADPH oxidase and induction of Cu/Zn-SOD. These findings further elucidate the molecular mechanisms by which PPAR-gamma ligands directly alter vascular endothelial function.

Objective-Peroxisome proliferator-activated receptor ␥ (PPAR␥) ligands reduce lesion formation in animal models of atherosclerosis by mechanisms that have not been defined completely. We hypothesized that PPAR␥ ligands stimulate endothelial-derived nitric oxide release (·NO) to protect the vascular wall. Methods and Results-The PPAR␥ ligands, 15-deoxy-⌬ 12,14 -prostaglandin J 2 (15d-PGJ 2 ) or ciglitazone, stimulated a PPAR response element-luciferase reporter construct in transfected porcine pulmonary artery endothelial cells (PAECs), demonstrating that PPAR␥ was transcriptionally functional. Treatment with 15d-PGJ 2 or ciglitazone significantly increased release of ·NO from PAECs or human aortic endothelial cells and augmented calcium ionophore-induced ·NO release from human umbilical vein endothelial cells measured by chemiluminescence analysis of culture media. Increases in ·NO release caused by treatment with 15d-PGJ 2 occurred at 24 hours, but not after 1 to 16 hours, and were abrogated by treatment with the transcriptional inhibitor ␣-amanitin. Overexpression of PPAR␥ or treatment with 9-cis retinoic acid also enhanced PAEC ·NO release. Neither 15d-PGJ 2 nor ciglitazone altered eNOS mRNA, whereas 15d-PGJ 2 , but not ciglitazone, decreased eNOS protein. Key Words: peroxisome proliferator-activated receptor ␥ Ⅲ endothelium Ⅲ nitric oxide Ⅲ nitric oxide synthase Ⅲ thiazolidinedione T he production of nitric oxide (·NO) by vascular endothelial cells is critical for maintenance of normal vascular physiology. 1 In endothelial cells (ECs), the type III endothelial nitric oxide synthase (eNOS) produces ·NO from the amino acid L-arginine. Our preliminary observations, 2 as well as reports by others, [3][4][5] indicate that exogenous fatty acids alter EC ·NO production. The molecular mechanism contributing to fatty acid-induced alterations in EC ·NO production remain unexplored. One potential mechanism for fatty acidinduced alterations in gene expression is the activation of peroxisome proliferator-activated receptors (PPARs). Originally described in 1990, PPARs belong to the nuclear hormone receptor superfamily of ligand-activated transcription factors including steroid, thyroid, and retinoid hormone receptors. 6 Structurally diverse ligands including long-chain fatty acids, eicosanoids, thiazolidinediones, and fibrates activate PPARs, which form obligate heterodimers with the 9-cis retinoic acid receptor, RXR. 7 On ligand binding, PPARs become transcriptionally active at PPAR response elements (PPRE) and alter the expression of target genes. Conclusions-TakenPPAR␥ is expressed in vascular endothelial cells 8 -11 and smooth muscle cells. 12 The expression of PPARs in vascular wall cells suggests their potential role in vascular disease. 8 -10 Some in vitro studies suggest potential atherogenic effects of PPAR␥ activation, 8,[13][14][15] whereas other studies associate PPAR␥ with potential vascular protective effects. 16 -21 Importantly, two independent in vivo studies using the LDL receptor knockout mouse demo...

Increased NADP reduced (NADPH) oxidase 4 (Nox4) and reduced expression of the nuclear hormone receptor peroxisome proliferator-activated receptor g (PPARg) contribute to hypoxiainduced pulmonary hypertension (PH). To examine the role of Nox4 activity in pulmonary vascular cell proliferation and PH, the current study used a novel Nox4 inhibitor, GKT137831, in hypoxiaexposed human pulmonary artery endothelial or smooth muscle cells (HPAECs or HPASMCs) in vitro and in hypoxia-treated mice in vivo. HPAECs or HPASMCs were exposed to normoxia or hypoxia (1% O 2 ) for 72 hours with or without GKT137831. Cell proliferation and Nox4, PPARg, and transforming growth factor (TGF)b1 expression were measured. C57Bl/6 mice were exposed to normoxia or hypoxia (10% O 2 ) for 3 weeks with or without GKT137831 treatment during the final 10 days of exposure. Lung PPARg and TGF-b1 expression, right ventricular hypertrophy (RVH), right ventricular systolic pressure (RVSP), and pulmonary vascular remodeling were measured. GKT137831 attenuated hypoxia-induced H 2 O 2 release, proliferation, and TGF-b1 expression and blunted reductions in PPARg in HPAECs and HPASMCs in vitro. In vivo GKT137831 inhibited hypoxia-induced increases in TGF-b1 and reductions in PPARg expression and attenuated RVH and pulmonary artery wall thickness but not increases in RVSP or muscularization of small arterioles. This study shows that Nox4 plays a critical role in modulating proliferative responses of pulmonary vascular wall cells. Targeting Nox4 with GKT137831 provides a novel strategy to attenuate hypoxiainduced alterations in pulmonary vascular wall cells that contribute to vascular remodeling and RVH, key features involved in PH pathogenesis.Keywords: rosiglitazone; PPARg; TGF-b; pulmonary hypertension Pulmonary hypertension (PH) is a progressive disorder associated with significant morbidity and mortality. Although recent therapeutic advances have improved survival for patients with PH, the prognosis remains poor (1). The pathobiology of PH is complex, and factors that contribute to endothelial dysfunction have been implicated in pathogenesis (2, 3). Among these factors, NADP reduced (NADPH) oxidase enzymes that produce reactive oxygen species (ROS) contribute to the development of a variety of vascular diseases, such as atherosclerosis (4) and systemic (5) and pulmonary hypertension (6). NADPH oxidases catalyze the reduction of molecular oxygen to generate superoxide (O 2 .2 ), hydrogen peroxide (H 2 O 2 ), or secondary oxidants (7). Seven isoforms of the catalytic moiety of the nonphagocytic NADPH oxidase enzyme have been described (Nox1-5, Duox1-2). These subunits are homologous to the catalytic moiety of the prototype phagocytic NADPH oxidase Nox2 (or gp91 phox ) but differ from each other regarding cellular localization, tissue distribution, regulation, activation, and expression (7,8). For example, although both Nox1 and Nox4 are expressed in vascular smooth muscle cells (VSMCs), they are targeted to discreet intracellular locations, are differe...