Evaluating the Susceptibility of Mitochondrial DNA Germline Mutations in Chinese Cancer Patients

It has been suggested that impairment of mitochondrial oxidative phosphorylation (OXPHOS) is a common character in cancer cells, urging attention to variation on mitochondrial DNA (mtDNA) that encodes 13 units of the OXPHOS. However, most of mtDNA somatic mutations in cancer were suggested to result from the relaxed functional constrains and thus the byproducts of tumorigenesis. MtDNA germline mutations present not only in the cancer tissue but also in the normal tissue. However, it remains unclear whether the cancerous mtDNA germline mutations suffered similar selective constraints as the somatic mutations did. To address this question, we collected 153 whole mitochondrial genomes (including 20 newly obtained genomes in this study) from the normal tissues of cancer patients and compared with a number of 561 whole mtDNA sequences from the general population in China. Different from the observations on cancerous mtDNA somatic mutations, our results revealed that the germline mutations showed no significant difference between the cancer patients and the general population in either the sub-haplogroup composition, mutation pattern or the potential pathogenicity of the private mutations. It then seems that regulation on cellular OXPHOS level, triggered by mtDNA variation to some extent, exerts little influence on the susceptibility of cancer, which echoes the opinion that aerobic glycolysis, not mitochondrial respiration, plays the key role in generating energy in cancer cells, thus suggesting the role of most mtDNA mutations in cancer likely being overestimated.