Activation of xanthine oxidase mediates intermittent hypoxia‐induced HIF‐2 degradation

Abstract

We previously showed that IH leads to increased degradation of HIF‐2α via [Ca2+]i activated calpains, which contributes to IH‐induced oxidative stress via insufficient transcription of antioxidant enzymes (J. Nanduri et al. PNAS, 2009). In this study, we examined the mechanisms associated with activation of calpains by IH in PC12 cell cultures. In IH treated PC12 cells, ROS levels as well as calpain activity increased and anti‐oxidant treatment prevented these effects suggesting the involvement of ROS signaling. Pharmacological or genetic blockade of NADPH oxidase 2 (Nox2) had no effect on IH‐evoked calpain activation and HIF‐2α degradation. However, IH markedly increased xanthine oxidase (XO) activity. Allopurinol, a XO inhibitor or silencing of XO by siRNA prevented IH induced HIF‐2α degradation, increased intracellular calcium levels and calpain activity. Systemic adminsitration of allopurinol to rats during the IH exposure prevented the oxidative stress, rescued HIF‐2α degradation in the adrenal medulla and prevented hypertension. These results demonstrate that ROS generated by XO activation mediates IH‐induced HIF‐2α down regulation and suggest that ROS‐induced ROS as a potential mechanism contributing to IH‐induced cardiovascular morbidity.