Abstract
Hypoxic adaptation mediated by HIF transcription factors has been shown to require mitochondria. Current models suggest that mitochondria regulate oxygen sensor (HIF prolyl hydroxylase) activity and HIF1α stability during hypoxia by either increasing mitochondrial peroxide as a second messenger or by serving as oxygen consumers that enhance the kinetics of cytoplasmic oxygen reduction. Here, we address the role of mitochondrial peroxide specifically in regulating HIF1α stability. We use state-of-the-art tools to evaluate the role of peroxide and other reactive oxygen species (ROS) in regulating HIF1α stability. We show that antioxidant enzymes are not homeostatically induced nor are peroxide levels increased in hypoxia. Forced expression of diverse antioxidant enzymes, all of which diminish peroxide, had disparate effects on HIF1α protein stability. Reduction of lipid peroxides by glutathione peroxidase-4 or superoxide by mitochondrial SOD failed to influence HIF1α protein stability. These data showed that mitochondrial, cytosolic and lipid ROS are dispensable for HIF1α stability and should affirm therapeutic efforts to activate the HIF pathway in disease states by HIF prolyl hydroxylase inhibition.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Kumar et al. leverage state-of-the art methods to address the role of reactive oxygen species in regulating hypoxia inducible factor 1α (HIF1α) stability in hypoxia. They use the ratiometric peroxide sensor, HyPer, to show that peroxide levels do not increase in hypoxia in a host of cell types. They manipulate peroxide using a cassette of peroxide scavenging enzymes in the cytosol, peroxisomes and mitochondria and show no effect on hypoxia-induced HIF stability. Finally, they also show that scavengers of oxidized lipids do not influence hypoxic-HIF stabilization. Together, these studies suggest that oxidants are dispensable for HIF mediated transcriptional adaptation.