The secret of their longevity
Japanese longevity explained by breaks in DNA
They proved to be a barrier to harmful cell mutations in old age
Ivan Ortega, "The Attic"
Russian biologists together with foreign colleagues studied the mitochondrial genomes of Japanese centenarians and established what their features affect the long life of carriers. Scientists have come to the conclusion that biologically life expectancy is not fixed rigidly and varies markedly depending on the set of genes of an organism.
For a long time, scientists believed that all multicellular organisms are susceptible to aging and death. In the XX century, it turned out that the situation is not so unambiguous: a number of species show the so-called negligible senescence. Individual species, such as the shooting genus Turritopsis, are potentially biologically immortal. Of course, this thesis should be taken with caution, because in order to be convinced of the "immortality" of an organism, it is necessary to observe such a creature for an infinite number of years, which science cannot do. Now we can only say that scientists have not recorded deaths from old age in representatives of this species.
After scientists discovered negligible aging in naked diggers, it became clear that the situation with aging can be ambiguous for mammals as well. This potentially indicates that with certain combinations of genes, a person's life expectancy may differ from the standard one. There are hypotheses that the death and aging of multicellular organisms are not their original features. It is as if multicellular animals acquired all this in the course of evolution, since the death of older individuals allowed the species to change faster in a rapidly changing environment.
The authors of the new work (Mikhailova et al., Deleterious in late life mitochondrial alleles and aging: secrets of Japanese centenarians) turned to data on Japanese famous for their longevity. They studied the carriers of the mitochondrial haplogroup D4a, which are unusually numerous among those Japanese who are older than 105 years old. The mitochondrial genome is inherited only through the female line, and specifically D4a is distributed mainly in Japan, Thailand and Laos.
The researchers focused on how the mitochondrial genome of carriers of this haplogroup affects the accumulation of mutations in somatic (non-sexual) cells. The accumulation of such mutations after cell division is one of the main factors of aging. The frequency of such mutations is higher, the more direct repeats of individual segments in the DNA, so researchers consider such repeats as alleles (different forms of the same gene are called alleles), potentially harmful in old age.
Scientists were looking for such alleles in the mitochondrial genome of carriers of haplogroup D4a. The researchers found that there are point "breaks" in the common direct repeats of these alleles– the longest repeats in the mitochondrial genome. They are mutations in the form of genes, the appearance of which is changed by random processes. These genes do not repeat from one common direct repeat to another.
From this, the researchers conclude that such breaks in DNA at least partially explain the extraordinary longevity among Japanese carriers of haplogroup D4a. At the same time, the authors could not find any signs that such a feature of mitochondrial DNA somehow helps its carriers transmit their genes as part of selection. When they tried to find in 700 mammalian species a similar relationship between a small number of direct common repeats in mitochondrial DNA and success in sexual selection, they also found no such connection.
Apparently, this feature manifests itself only at such an old age that reproduction is almost not going on (it does not go completely for women because of menopause and is unlikely for men because of the age and reproductive status of their sexual partners). If the chances of reproducing from a particular DNA feature do not increase, then such a feature of the genome does not experience any positive selection.
However, such a trait does not prevent its carriers from undergoing natural selection, that is, to reproduce or succeed at a young and middle age. The absence of "minuses" in such a feature of mitochondrial DNA makes it a positive feature. Scientists note that the detection of such a selection-neutral trait that promotes healthy and long-term old age is important both for the creation of future geroprotectors and in order to better understand the evolutionary processes that led to aging.
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