Rapid demethylation of the genome is a harbinger of early death
There's not much left:
researchers have learned to predict life expectancy by DNAIrina Yakutenko, Mednovosti
People have always dreamed of finding out how long they have left to live.
Fortune-tellers and other psychics exploit a person's desire to look into the future with might and main. Although the reliability of their predictions is zero, people persistently bring money to the "visionaries". It seems that fans of fortune-telling on coffee grounds have a much more reliable source of information: researchers have learned to predict the approximate life expectancy of a person by his DNA.
Unlike "magicians" and "sorcerers", scientists do not name the exact date of death. Their assessment is extremely probabilistic: experts from the University of Edinburgh noticed that the less modified a person's DNA is, the higher the probability that he will die earlier (Marioni et al., DNA methylation age of blood predicts all-cause mortality in later life // Genome Biology, 2015). Scientists were interested in a very specific modification with the complex name DNA methylation.
It was this modification that cost the life of Dolly the sheep – more precisely, it was because of her that the cloned beast died seven years after birth, much earlier than time. Methylation is the addition to DNA strands of a small group of four atoms, one carbon and three hydrogens (chemists call it a methyl group, and the formula looks like CH 3). This "appendage", which is attached to DNA by special proteins, signals to cellular enzymes that the labeled DNA is special. Most often, the addition of CH 3 "turns off" DNA, "forbidding" enzymes to read the information embedded in it.
Methyl groups and other labels do not change the DNA sequence itself, but affect how exactly the information embedded in it is reproduced. The impact turned out to be so serious that a special term "epigenetics" was coined for such changes, that is, supra-genomic regulation of the genome. If we imagine that our body with all its physiological features and personality traits is a state, then genetics and epigenetics are at least its president and prime minister. And it is not clear to the end which of them is more important.
Different epigenetic markers have different effects on DNA, but the CH 3 group is almost always a "silencing" label. For a long time, scientists were sure that as living beings age, there are more and more methyl groups in their DNA. However, recent studies have shown that this is not the case. "In general, the methylation of the genome decreases with aging," says Alexey Gavrilov, senior researcher at the Institute of Gene Biology of the Russian Academy of Sciences, PhD. – The key point is that over the years, the methyl tags "move" to other parts of the DNA. The human genome is full of so–called mobile elements - fragments that can "jump" from place to place and disrupt the work of genes. In young people, such elements are "blocked" by CH 3 groups, in older people this blockage is removed, and the genome becomes unstable."
Regrouping and changing the number of CH 3-groups lead to other age-related changes. While we are young, protective proteins work in our cells that prevent the development of tumors. Over the years, the genes encoding such proteins "turn off" due to the fact that methyl residues are attached to them. As a result, the body remains unarmed and cannot resist cancer.
"With age, there are more CH 3-groups on the genes of ribosomal RNAs, from which ribosomes are assembled – cellular "machines" that synthesize proteins. The fewer ribosomes, the worse protein synthesis goes, and this is directly related to aging, because our body is actually built from proteins," explains Gavrilov.
Biological clockDespite the fact that all the mechanisms by which methylation regulates the work of genes are still unclear, the total number of CH3 groups in the genome can be used to predict life expectancy.
Edinburgh scientists analyzed data from four long-term studies, the authors of which over the years followed a total of five thousand elderly people. At the beginning of the observations, blood samples were taken from all participants, from which DNA can be isolated.
Scottish specialists carried out sad work: they looked at how many people did not live to the end of the research, and determined how strongly their DNA was methylated compared to other participants. Previously, scientists have determined the average number of CH 3-groups in the genome for each age. It turned out that too rapid demethylation of the genome is a harbinger of early death. Moreover, the risk of people with non-methylated (relative to the age norm) The risk of dying too early did not depend on how healthy a lifestyle they lead, whether they have diabetes or heart and vascular problems and other factors that affect life expectancy.
"We can say that DNA methylation is such a kind of biological clock. In the body of people whose clocks are running ahead of time, probably some important processes occur faster than the average. Including the aging process," explains Alexey Gavrilov. – At the same time, methylation may not be the actual cause of aging, but only reflect the processes that lead to it. However, it cannot be ruled out that artificially changing the methylation status can reverse some of these processes."
While scientists do not understand what exactly makes our bodies decrepit. But the work of Scottish researchers provides a convenient diagnostic tool to determine exactly when unpleasant things will begin. However, the big question is whether this knowledge will make our life easier.
Portal "Eternal youth" http://vechnayamolodost.ru09.02.2015