The liver does not age
Scientists have found out the age of liver cells of young and elderly people
Maria Azarova, Naked Science
A team of biologists, physicists, mathematicians and clinicians, led by the Center for Regenerative Therapy at the Dresden Technical University (Germany), applied the method of retrospective radiocarbon dating to determine the age of the human liver, because this organ has the ability to regenerate due to updated hepatocytes — parenchymal cells. According to the study, the results of which are presented in the journal Cell Systems (Heinke et al., Diploid hepatocytes drive physiological liver renewal in adult humans), age does not affect the process of liver renewal: cells are equally well replaced in both young and elderly.
Although it is known that hepatocytes can be renewed in adulthood, until now there was no clear picture of their behavior: scientists did not know whether hepatocytes exchange throughout life or whether they are physiologically long-lived cells, like cardiomyocytes and neurons.
The authors of the new work examined the liver of 33 people who died between the ages of 20 and 84: DNA was extracted from cell nuclei to obtain a comprehensive model of hepatocyte renewal and their age distribution.
As a result, with the help of retrospective radiocarbon dating and computer modeling, it was possible to find out that liver cells in all people are almost the same age — a little younger than three years. According to the researchers, their discovery for the first time indicates that this organ remains young to the end.
"Since the liver consists of different types of cells, we additionally separated the nuclei from hepatocytes and non-hepatocytes. Genomic concentrations of carbon-14 (14C) suggest that hepatocytes are renewed throughout life at the level of 19% per year and are 2.7 years old for young people. In adulthood and older age, they are updated by 17% per year, the average age of hepatocytes is 2.9 years. Non-hepatocytes make up only a small part of liver cells, but they are a very diverse group with different functions. <...> There is no real characteristic of their unique update dynamics. We only got a general idea: they are updated at the level of 16% per year for a 25-year—old person and 13% per year for a 75-year—old," the paper says.
However, it turned out that not all liver cells are so young: the researchers found a lower rate of renewal in polyploid cells, whose age was estimated on average at ten years, and their number increased during human aging. Unlike diploid cells that have two sets of chromosomes, these accumulate more DNA, can carry four, eight or more sets of chromosomes, are gigantic in size and are often found in tumor tissues or exposed to penetrating radiation.
In the picture from the press release Your liver is just under three years old, a white arrow indicates a cell with two sets of chromosomes, yellow - polyploid cells – VM.
"Whether long—lived polyploid cells make the liver more susceptible to age—related diseases or they act as a resistance factor to cope with cellular stress, thereby preventing the loss of organ function and the development of cancer, remains an important question that needs to be addressed," the scientists concluded.
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