DNA oxidation in regulatory D‐loop region of the mitochondrial genome is important for hypoxia‐induced mitochondrial biogenesis in rat pulmonary artery endothelial cells (PAECs)

Emerging evidence suggests that hypoxia‐induced transcription of nuclear genes requires controlled DNA damage and repair (Al‐ Mehdi et al, Sci Signaling, 2012). Whether such a mechanism operates in mitochondria is unknown. Here we explored the hypothesis that hypoxia‐induced mitochondrial (mt) DNA replication requires sequence‐specific oxidative DNA modifications in the mitochondrial genome. Using slot blot and quantitative Southern blot analyses, respectively, we found that increased mtDNA copy number in hypoxic PAECs was accompanied by oxidative modifications in the D‐loop region of the mitochondrial genome. Transfection of rat PAECs with a mitochondria‐targeted DNA repair enzyme OGG1 suppressed hypoxia‐induced DNA oxidation in the D‐loop region and reduced binding of mitochondrial transcription factor TFAM to both regulatory and coding regions of the mitochondrial genome, as assessed by ChIP analysis. OGG1 over‐expression also attenuated hypoxia‐induced mtDNA replication. Interestingly, hypoxia increased number of hyperpolarized mitochondria in wild‐type PAECs, as evidenced by JC‐1 fluorescence. Mitochondria in OGG1‐transfected cells were hyperpolarized under normal conditions and less affected by hypoxia. These observations support the concept that oxidative DNA modifications in the D‐loop region are important for hypoxia‐induced mitochondrial biogenesis. Supported by NIH.