PROJECT SUMMARY/ABSTRACT Despite novel treatments, pulmonary hypertension (PH) represents a progressive, highly morbid, and often fatal condition. Recent studies suggest that metabolic derangements such as the glycolytic switch, ROS production, and mitochondrial dysfunction play a key role in the pathogenesis of PH. Disruptions of ROS homeostasis, primarily regulated by the superoxide (SOD) family, have been associated with PH. Extracellular superoxide dismutase (EC-SOD) is the most prevalent isoform of SOD in the vasculature and has been previously associated with PH in mouse models. In humans, the R213G EC-SOD SNP leads to a reduced matrix binding affinity of EC-SOD, leading to low vascular concentration but higher plasma levels and normal activity. In mice, this SNP has been associated with higher right ventricular pressures at baseline that worsen with hypoxia. Interestingly, these same mice are protected against PH in the Sugen-hypoxia model. We hypothesize that the redistribution of R213G variant of EC-SOD due to its reduced binding affinity will have discrepant effects depending on the model of PH and this effect will be due to distinct model-dependent activation of AMPK and mitochondrial dysfunction in endothelial cells (PAEC) vs. smooth muscle cells (PASMC). Preliminary data demonstrated that at baseline, mice with the R213G EC-SOD variant have significant differences in lung and right ventricular (RV) fatty acid oxidation and electron transport chain activity. To test the effects of loss of vascular EC-SOD in PH, mice with the R213G EC-SOD SNP will be exposed to chronic hypoxia or Sugen-hypoxia to develop pulmonary hypertension, confirmed via invasive hemodynamic and histologic measures (Aim 1). Mitochondrial respiration and ROS production will be measured by high- resolution respirometry and electron paramagnetic resonance, respectively, in whole lung and RV homogenates as well as human pulmonary artery endothelial and smooth muscle cells (Aim 2).