Nitric oxide and reactive oxygen species exert opposing effects on the stability of hypoxia inducible factor‐1α (HIF‐ 1α) in explants of human pial arteries

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Abstract
Hypoxia induces angiogenesis, partly through stabilization of hypoxia-inducible factor-1 alpha (HIF-1 alpha), leading to transcription of pro-angiogenic factors. Here we examined the regulation of HIF-1 alpha by hypoxia and nitric oxide (NO) in explants of human cerebrovascular smooth muscle cells. Cells were treated with NO donors under normoxic or hypoxic (2% O-2) conditions, followed by analysis of HIF-1 alpha protein levels. Treatment with the NO donor sodium nitroprusside reduced levels of HIF-1 alpha, whereas NO donors, NOC-18 and S-nitrosoglutathione, increased HIF-1 alpha levels. SIN-1, which releases both NO and superoxide (O-2 center dot(-)), reduced HIF-1 alpha levels, suggesting that inhibitory NO donors may elicit effects through peroxynitrite (ONOO center dot(-)). O2 center dot(-) generation by xanthine/xanthine oxidase also reduced HIF-1 alpha levels, confirming an inhibitory role for reactive oxygen species (ROS). Furthermore, superoxide dismutase increased HIF-1 alpha levels, and the NO scavenger carboxy-PTIO reversed HIF-1 alpha stabilization by NO donors. Effects on HIF-1 alpha levels correlated with vascular endothelial growth factor transcription but did not affect HIF-1a transcription, as measured by RT-PCR and luciferase-reporter assays. The results indicate that HIF-1 alpha is stabilized by agents that produce NO and reduce ROS but destabilized by agents that increase ROS, including O2 center dot(-) and ONOO center dot(-). Thus we propose that the effect of NO on HIF-1 alpha signaling is critically dependent on the form of NO and the physiological environment of the responding cell.
Funding Information
  • American Heart Association (9930218N)
  • National Institutes of Health (1R01 HL‐67351)