Germline mitochondrial DNA mutations aggravate ageing and can impair brain development.

Ageing is due to an accumulation of various types of damage1, 2, and mitochondrial dysfunction has long been considered to be important in this process3, 4, 5, 6, 7, 8. There is substantial sequence variation in mammalian mitochondrial DNA (mtDNA)9, and the high mutation rate is counteracted by different mechanisms that decrease maternal transmission of mutated mtDNA10, 11, 12, 13. Despite these protective mechanisms14, it is becoming increasingly clear that low-level mtDNA heteroplasmy is quite common and often inherited in humans15, 16. We designed a series of mouse mutants to investigate the extent to which inherited mtDNA mutations can contribute to ageing. Here we report that maternally transmitted mtDNA mutations can induce mild ageing phenotypes in mice with a wild-type nuclear genome. Furthermore, maternally transmitted mtDNA mutations lead to anticipation of reduced fertility in mice that are heterozygous for the mtDNA mutator allele (PolgAwt/mut) and aggravate premature ageing phenotypes in mtDNA mutator mice (PolgAmut/mut). Unexpectedly, a combination of maternally transmitted and somatic mtDNA mutations also leads to stochastic brain malformations. Our findings show that a pre-existing mutation load will not only allow somatic mutagenesis to create a critically high total mtDNA mutation load sooner but will also increase clonal expansion of mtDNA mutations17 to enhance the normally occurring mosaic respiratory chain deficiency in ageing tissues18, 19. Our findings suggest that maternally transmitted mtDNA mutations may have a similar role in aggravating aspects of normal human ageing.

From press release:

As we age, our cells change and become damaged. Now, researchers at Karolinska Institutet and the Max Planck Institute for Biology of Aging have shown that aging is determined not only by the accumulation of changes during our lifetime but also by the genes we acquire from our mothers. The results of the study are published in the journal Nature.



There are many causes of aging that are determined by an accumulation of various kinds of changes that impair the function of bodily organs. Of particular importance in aging, however, seems to be the changes that occur in the cell's power plant -- the mitochondrion. This structure is located in the cell and generates most of the cell's supply of ATP which is used as a source of chemical energy.

"The mitochondria contains their own DNA, which changes more than the DNA in the nucleus, and this has a significant impact on the aging process," said Nils-Göran Larsson, Ph.D., professor at the Karolinska Institutet and principal investigator at the Max Planck Institute for Biology of Aging, and leader of the current study alongside Lars Olson, Ph.D., professor in the Department of Neuroscience at the Karolinska Institutet. "Many mutations in the mitochondria gradually disable the cell's energy production," said Larsson.

For the first time, the researchers have shown that the aging process is influenced not only by the accumulation of mitochondrial DNA damage during a person's lifetime, but also by the inherited DNA from their mothers.

"Surprisingly, we also show that our mother's mitochondrial DNA seems to influence our own aging," said Larsson. "If we inherit mDNA with mutations from our mother, we age more quickly."

Normal and damaged DNA is passed down between generations. However, the question of whether it is possible to affect the degree of mDNA damage through lifestyle intervention is yet to be investigated. All that the researchers know now is that mild DNA damage transferred from the mother contributes to the aging process.

"The study also shows that low levels of mutated mDNA can have developmental effects and cause deformities of the brain," said lead author Jaime Ross, Ph.D., at the Karolinska Institutet.

"Our findings can shed more light on the aging process and prove that the mitochondria play a key part in aging; they also show that it's important to reduce the number of mutations," said Larsson.

"These findings also suggest that therapeutic interventions that target mitochondrial function may influence the time course of aging," said Barry Hoffer, M.D., Ph.D., a co-author of the study from the Department of Neurosurgery at University Hospitals Case Medical Center and Case Western Reserve University School of Medicine. He is also a visiting professor at the Karolinska Institutet. "There are various dietary manipulations and drugs that can up-regulate mitochondrial function and/or reduce mitochondrial toxicity. An example would be antioxidants. This mouse model would be a 'platform' to test these drugs/diets," said Dr. Hoffer.

The data published in the paper come from experiments on mice. The researchers now intend to continue their work on mice, and on fruit flies, to investigate whether reducing the number of mutations can extend their lifespan.