HIF2α-arginase axis is essential for the development of pulmonary hypertension

Hypoxic pulmonary vasoconstriction is correlated with pulmonary vascular remodeling. The hypoxia-inducible transcription factors (HIFs) HIF-1 alpha and HIF-2 alpha are known to contribute to the process of hypoxic pulmonary vascular remodeling; however, the specific role of pulmonary endothelial HIF expression in this process, and in the physiological process of vasoconstriction in response to hypoxia, remains unclear. Here we show that pulmonary endothelial HIF-2 alpha is a critical regulator of hypoxia-induced pulmonary arterial hypertension. The rise in right ventricular systolic pressure (RVSP) normally observed following chronic hypoxic exposure was absent in mice with pulmonary endothelial HIF-2 alpha deletion. The RVSP of mice lacking HIF-2 alpha in pulmonary endothelium after exposure to hypoxia was not significantly different from normoxic WT mice and much lower than the RVSP values seen in WT littermate controls and mice with pulmonary endothelial deletion of HIF-1 alpha exposed to hypoxia. Endothelial HIF-2 alpha deletion also protected mice from hypoxia remodeling. Pulmonary endothelial deletion of arginase-1, a downstream target of HIF-2 alpha, likewise attenuated many of the pathophysiological symptoms associated with hypoxic pulmonary hypertension. We propose a mechanism whereby chronic hypoxia enhances HIF-2 alpha stability, which causes increased arginase expression and dysregulates normal vascular NO homeostasis. These data offer new insight into the role of pulmonary endothelial HIF-2 alpha in regulating the pulmonary vascular response to hypoxia.