PPAR gamma and Nox4 in pulmonary hypertension

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DESCRIPTION (provided by applicant): Pulmonary hypertension (PH) is a complex disorder that causes significant morbidity and mortality. Mounting evidence suggests that metabolic derangements account for the pathophysiology underlying PH. This proposal focuses peroxisome proliferator-activated receptor gamma (PPARγ), a major metabolic regulator that is decreased PH. Hypoxia and other causes of PH decrease PPARγ expression which increases NADPH oxidase 4 (Nox4) expression and activity. Nox4 generates reactive oxygen species (ROS) that contribute to pulmonary vascular cell proliferation and PH pathogenesis. On the other hand, stimulating PPARγ reduces the expression and activity of Nox4 and attenuates hypoxia-induced vascular remodeling, right ventricular hypertrophy, and PH. The mechanisms by which PPARγ modulates PH continue to be defined. Preliminary data suggest that reductions in PPARγ reduce the expression of PPARγ coactivator 1 alpha (PGC1α) and uncoupling protein 2 (UCP2), proteins that regulate mitochondrial (MT) biogenesis and reactive oxygen species (ROS) generation, respectively. The proposed studies will test the hypothesis that PPARγ depletion reduces pulmonary artery smooth muscle cell (PASMC) PGC1α and UCP2 and stimulates MT dysfunction and ROS production. The investigators further postulate that MT ROS activate the ERK 1/2-NF-κB axis to increase Nox4 expression and H2O2 generation which promote PASMC proliferation, pulmonary vascular remodeling, and PH. To test this hypothesis, Specific Aim 1 will explore the role of reduced PPARγ activity in MT dysfunction, Nox4 induction, and PASMC proliferation using complementary in vitro and in vivo models. Genetic or pharmacological reductions in PPARγ activity will be used in human PASMC in vitro, and inducible, smooth muscle-targeted PPARγ knockout mice (smPPARγKO) will be employed in vivo. Specific Aim 2 will examine the role of reductions in PPARγ in hypoxia-induced alterations in PGC1α and UCP2, MT dysfunction, Nox4 induction, and PASMC proliferation. In vitro and in vivo gain and loss of PPARγ function models will be exposed to well characterized control or hypoxic conditions, and MT function, ROS production, and PASMC proliferation will be determined. Hypoxia-induced PH will be assessed with measures of right ventricular systolic pressure, right ventricular hypertrophy, and ventricular function (echocardiography). PASMC proliferation will be examined with immunohistochemistry for proliferating cellular nuclear antigen and morphometric analysis of lung sections stained for α-smooth muscle actin. The ability of full and partial (10- nitro-oleic acid) PPARγ ligands to attenuate hypoxic proliferatin and PH will be tested. Critical observations will be confirmed in PASMC isolated from patients with idiopathic pulmonary arterial hypertension. The proposed studies, conducted by a productive and collaborative research team, will advance understanding of the role of PPARγ in regulating PASMC phenotype during health and disease and identify novel strategies by which targeting PPARγ can interrupt PH pathogenesis.