HIF-1α protects against oxidative stress by directly targeting mitochondria

The transcription factor hypoxia inducible factor-1 alpha (HIF-1 alpha) mediates adaptive responses to oxidative stress by nuclear translocation and regulation of gene expression. Mitochondrial changes are critical for the adaptive response to oxidative stress. However, the transcriptional and non-transcriptional mechanisms by which HIF-1 alpha regulates mitochondria in response to oxidative stress are poorly understood. Here, we examined the subcellular localization of HIF-1 alpha in human cells and identified a small fraction of HIF-1 alpha that translocated to the mitochondria after exposure to hypoxia or H2O2 treatment. Moreover, the livers of mice with CCl4-induced fibrosis showed a progressive increase in HIF-1 alpha association with the mitochondria, indicating the clinical relevance of this finding. To probe the function of this HIF-1 alpha population, we ectopically expressed a mitochondrial-targeted form of HIF-1 alpha (mito-HIF-1 alpha). Expression of mito-HIF-1 alpha was sufficient to attenuate apoptosis induced by exposure to hypoxia or H2O2-induced oxidative stress. Moreover, mito-HIF-1 alpha expression reduced the production of reactive oxygen species, the collapse of mitochondrial membrane potential, and the expression of mitochondrial DNA-encoded mRNA in response to hypoxia or H2O2 treatment independently of nuclear pathways. These data suggested that mitochondrial HIF-1 alpha protects against oxidative stress induced-apoptosis independently of its well-known role as a transcription factor.