Arginase inhibition enhances angiogenesis in endothelial cells exposed to hypoxia

• We investigated the role of arginase in hypoxia-mediated angiogenesis.
• Endothelial cell (EC) arginase expression and activity are elevated by hypoxia.
• Inhibition of arginase enhances EC network formation and NO levels.
• Arginase inhibition also limits ROS formation and elevates VEGF levels.
• Arginase plays a fundamental role in angiogenesis

Hypoxia-induced arginase elevation plays an essential role in several vascular diseases but influence of arginase on hypoxia-mediated angiogenesis is completely unknown. In this study, in vitro network formation in bovine aortic endothelial cells (BAEC) was examined after exposure to hypoxia for 24 h with or without arginase inhibition. Arginase activity, protein levels of the two arginase isoforms, eNOS, and VEGF as well as production of NO and ROS were examined to determine the involvement of arginase in hypoxia-mediated angiogenesis. Hypoxia elevated arginase activity and arginase 2 expression but reduced active p-eNOSSer1177 and NO levels in BAEC. In addition, both VEGF protein levels and endothelial elongation and network formation were reduced with continued hypoxia, whereas ROS levels increased and NO levels decreased. Arginase inhibition limited ROS, restored NO formation and VEGF expression, and prevented the reduction of angiogenesis. These results suggest a fundamental role of arginase activity in regulating angiogenic function.