Abstract 18497: Attenuated Endothelial Cd39 Activity Mediates Vascular Remodeling in Pulmonary Arterial Hypertension

Occlusive intimal hyperplasia in pulmonary arterial hypertension (PAH) leads to devastating consequences in pulmonary circulation and increased mortality. A phenotypic switch in endothelial cells (EC) has been suggested to play a role in the pathobiology of occlusive vasculopathy. We hypothesized that alterations in extracellular purinergic signaling could play a role in regulating EC fate during PAH progression. Purine signaling is regulated by cell surface ecto-enzymes such as CD39 and CD73. These enzymes are powerful mediators of cellular signaling since their activity adjusts the level of extracellular purine nucleotides that are potent cell signaling molecules. By using our unique magnet bead-based ex vivo EC profiling strategy in the rat monocrotaline model of PAH we identified a major ~50% decrease (p<0.001) in adenosinetriphosphate (ATP) -hydrolyzing CD39 activity at early stages of the disease. The activity of AMP-hydrolyzing CD73 was not changed during the disease course. Similar ~50% (p<0.05) decrease in specific CD39 activity, leading to accumulation of ATP niche, was observed in cultured pulmonary ECs from end-stage human idiopathic PAH patients. This attenuated enzyme activity was, at least partly, mediated through down-regulation of CD39 expression on RNA (~70%, p<0.05) and protein level. Immunohistochemistry on human iPAH patient lung revealed that CD39 was significantly down-regulated in arteries with intimal disease compared to arteries with normal appearance. We then showed that suppression of CD39 through RNAi or excess 2 μM ATP niche initiates an EC phenotypic switch with apoptosis resistant and hyperproliferative phenotype, identical to iPAH ECs. We also show that increased ATP niche stimulates synthesis of extracellular matrix components associated with intimal disease, such as versican. In addition, increased 2 μM ATP concentration and co culture with CD39-deficient ECs induce pulmonary artery smooth muscle cell (PASMC) proliferation (~50%, p<0.005) and migration (~50%, p<0.05) and, thus, could contribute to SMC pathology in PAH. We show evidence, both in rat and human, that attenuation of CD39 activity is tightly linked to vascular remodeling, EC phenotypic switch and could represent a novel target for PAH therapy.