Possible relationship between conditions associated with chronic hypoxia and brain mitochondrial DNA deletions

The brain relies heavily on aerobic metabolism which requires functional mitochondria. Mitochondria are subcellular organelles with their own genome which codes for 13 essential protein subunits. By employing PCR assays to examine brain tissue from 43 age-comparable individuals (between ages 34 and 73), we found a correlation between mitochondrial DNA deletion mutations, mtDNA(4977) deletions, and conditions associated with chronic hypoxia. In prior studies, utilizing only 6 to 12 clinical samples, mtDNA(4977) deletions were reported to increase in specific regions of the brain with aging. However, we found 12-fold and 5-fold higher levels of mtDNA(4977) deletions in the putamen and the superior frontal gyrus of the cortex, respectively, from individuals who had conditions associated with chronic hypoxia when compared with individuals without evidence of such conditions. These findings suggest that chronic hypoxia should be more closely examined in the pathophysiology of central nervous system diseases.