NADPH oxidase is critical for up‐regulation of HIF‐1[alpha] by intermittent hypoxia

Intermittent hypoxia (IH) increases HIF‐1α expression and HRE activation in PC12 cells ( Yuan et al. J. Biol. Chem. 2005). Reactive oxygen species (ROS)‐mediated signaling plays a critical for IH‐evoked cellular and systemic responses. In the present study we examined whether ROS play a role in HIF‐1α accumulation by IH, and if so to assess the source of ROS generation. Experiments were performed on PC12 cells exposed to either 20% O 2 (normoxic control) or 60 cycles of IH (30 sec at 1.5% O 2 followed by 5 min at 20% O 2 ). ROS scavengers, MnTMPyP, and PEG‐catalase prevented IH‐induced HIF‐1α accumulation. IH increased ROS generation as evidenced by decreases in aconitase enzyme activity in both cytosolic and mitochondrial fractions. Apocynin, an inhibitor of NADPH oxidase prevented IH‐induced HIF‐1α accumulation and ROS generation. IH upregulated NADPH oxidase subunits including gp91phox, p47phox, p22phox, and p67phox and increased NADPH oxidase enzyme activity. These observations suggest that ROS generated by NADPH oxidase plays an important role in IH‐induced up‐regulation of HIF‐1α. (Supported by NIH‐HL‐25830).