Let's check the biological clock
Breasts age first
Scientists have developed a new method for determining the biological age of human tissuesPolina Rozentsvet, <url>
According to this method, cancer cells are older than healthy ones, and breast tissue ages faster than the rest of the body.
DNA methylation (attachment of the methyl group CH3 to the nitrogenous base cytosine) is a natural chemical modification of a molecule that does not lead to a change in its sequence, that is, not a mutation. Nevertheless, methylation affects the work of many genes, this is one of the most important ways to regulate it. Methylation keeps in check those genes that should not be working in a given cell at a given time.
With age, the degree of methylation decreases. This fact was first discovered by Soviet scientists under the leadership of Academician Andrei Belozersky in 1973. Later, researchers from different laboratories found that similar changes (decrease in methylation) occur in tumor cells. Hence, the hypothesis arose that demethylation provokes aging and causes a predisposition to tumor transformation. Now American scientists have released a remake of this version. Steve Horvath, professor of genetics and biostatistics at the University of California at Los Angeles (UCLA), assessed the degree of DNA methylation in different tissues of people of different ages.
In his work published in the journal Genome Biology (DNA methylation age of human tissues and cell types, in the open access – VM), the scientist claims that he has developed a method to estimate the age of most tissues and cell types by the level of DNA methylation.
Steve Horvath analyzed DNA sequences from almost 8000 samples of 51 types of tissues and cells collected by other scientists who studied methylation in healthy and cancerous human tissues (the researcher thanks colleagues for the data provided). He determined the degree of methylation at 353 DNA points and the dependence of this indicator on age – the sample included people from newborns to centenarians (101 years old).
Having calibrated the "clock" in this way, Horvath checked its accuracy by comparing the biological age of different tissues with the chronological one.
In the brain, heart, lungs, liver, kidneys and cartilage, the biological clock showed the time very accurately, but the breast tissue turned out to be 2-3 years older than other body tissues.
If a woman suffered from breast cancer, then her breasts were even older. The healthy tissue adjacent to the tumor was on average 12 years older, and the tumor itself was about 36 years older than other tissues. These results, according to Horvath, explain why the risk of developing cancer increases with age and why breast cancer is the most common cancer in women.
It turned out that the speed of the clock is not constant. In a newborn and a child, they go very fast, gradually slowing down, and by the age of 20 they acquire a constant speed.
The result was unexpected, according to which the cells of children suffering from progeria, a genetic disease that causes premature aging, look normal and methylated in accordance with their true, chronological age. However, Horvath notes that he had too little data to say for sure.
According to Horvath's biological clock, embryonic stem cells have zero age, they are newborns. In the course of development, their methylation level changes. But if you take an adult cell and reverse its development – stimulate its transformation into a pluripotent one (that is, one from which cells of different tissues can be obtained), this manipulation again turns the biological clock to zero.
In principle, methylation can be influenced, the question is whether this will help control the aging process.
There are many questions in connection with the biological clock, it is convenient to have an experimental model for studying them, in which the dependence of DNA methylation on age would be similar to a human one. Studies have shown that the state of DNA in the tissues of the heart, liver and kidneys, as well as in blood cells, is similar in chimpanzees and humans. Gorillas are more different from humans.
The researcher hopes that by the level of DNA methylation from easily accessible sources (saliva, epithelial cells of the inner surface of the cheek, blood, skin), it will be possible to judge the condition of hard-to-reach tissues, such as the brain, liver or kidneys. In this case, the level of DNA methylation can become a convenient marker of a person's age, development and health status, as well as an indirect indicator of the effect of anti-aging therapy. In addition, the ability to compare the age of different tissues in one person will allow you to identify tissues whose accelerated aging indicates a disease.
Portal "Eternal youth" http://vechnayamolodost.ru21.10.2013