Project Summary: ACE2 shows tremendous promise in the treatment of pulmonary arterial hypertension (PAH). It corrects many of the molecular defects caused by the most common heritable cause of disease, BMPR2 mutation. It has reversed disease in a variety of animal models of PAH, including heritable, hypoxic, and inflammatory models. We have tested it acutely in human idiopathic PAH patients, and shown a variety of hemodynamic and molecular improvements, including a 40% improvement in cardiac output with associated reduction in pulmonary vascular resistance. Unfortunately, because of difficulties with both synthesis and delivery, it will be difficult to translate to common use. Understanding key mediators of its effect is thus the primary barrier to effective translation of this extraordinarily promising intervention. The proposed studies will identify the key molecular mechanisms of downstream effect of ACE2 in the context of PAH, in regulation of the cytoskeleton (aim 1), metabolism (aim 2), and improvements in right ventricle function in the heart (aim 3). The unifying hypothesis to these aims is that ACE2’s therapeutic effect is primarily through MAS1- mediated correction of cytoskeletal defects caused by suppressed BMPR2. These defects include cell-cell junctions, mitochondrial dynamics, and regulation of eNOS. The project makes use of genetic mouse models, including a new far-red reporter mouse which allows non-invasive imaging of heart stress, patient-derived endothelial precursor cells, our new artificial arteriole system which accurately reproduces pulse pressure, stiffness, flow, and shear in a cell culture system, thus combining human, mouse, and new cell culture systems to answer these questions.