Role of purine-converting ecto-enzymes in angiogenic phenotype of pulmonary artery adventitial vasa vasorum endothelial cells of chronically hypoxic calves

Abstract

Our previous studies demonstrated that angiogenic expansion of the vasa vasorum network can be observed in the pulmonary artery adventitia of chronically hypoxic calves. Because extracellular ATP and ADP are important regulators of vascular cell function, we hypothesized that these nucleotides may contribute to vasa vasorum neovascularization induced by chronic hypoxia. Treatment of pulmonary artery adventitial vasa vasorum endothelial cells (VVEC) with exogenous ATP or non-hydrolysable nucleotide analogs dramatically increased DNA synthesis and migration. Similar mitogenic responses have been observed in lung microvascular endothelial cells (MVEC), but not in endothelial cell isolated from large blood vessels of the same animals, such as aorta (AOEC) and main pulmonary artery (MPAEC). By using thin-layer chromatography assay, we also found that cultured VVEC displayed substantially lower ecto-ADPase/NTPDase and ecto-5′-nucleotidase activities compared to MPAEC and MVEC. In addition, VVEC are characterized by higher activities of ATP-regenerating ecto-enzymes, adenylate kinase and nucleotide diphosphokinase, consistent with a potent mitogenic effect of exogenous nucleotides in VVEC versus MPA and MVEC. Together, these studies indicate that VVEC, isolated from the sites of active neovascularization, may represent a unique pro-angiogenic phenotype with an augmented reliance to extracellular ATP and ADP. Our studies also demonstrated important role of endothelial purine-converting ecto-enzymes in the control of angiogenesis via directional regulation of local nucleotide levels. © Springer Science+Business Media B.V. 2010.