Mitochondrial mutations in mammalian aging: An over-hasty about-turn?

The very low abundance of mitochondrial DNA (mtDNA) mutations in nearly all mammalian tissues even in old age has led most mitochondriologists to reject the idea that such mutations might have a causal role in aging, despite (1) the strong circumstantial (e.g., interspecies) evidence that they do have such a role, (2) the promulgation since 1998 of two detailed mechanisms whereby low levels of mtDNA mutations could be harmful, and (3) the report of a transgenic mouse with cardiomyopathy apparently caused by artificially high levels of mtDNA mutations in the heart. A recent report of a mouse with ubiquitously accelerated accumulation of mtDNA mutations and an array of phenotypes reminiscent of aging has abruptly overturned this consensus, with not only the authors but also many other expert commentators suggesting that the mtDNA mutation theory of aging has risen from the ashes. However, there are compelling reasons to doubt the relevance of this mouse to normal mammalian aging, and thus to seek further testing of specific mechanistic hypotheses for how mtDNA mutations could cause age-related dysfunction.