An interdisciplinary team of researchers from Technische Universität Dresden (TU Dresden) has just reported an intriguing finding: the human liver remains roughly three years old no matter the age of an average adult.
Their study, which appeared in the journal Cell Systems, showed that the age of your liver is around three years whether you are 20 or 84 years old.
The Liver
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The liver is a vital organ that helps in getting rid of toxins and harmful substances from the body. Due to the nature of its work, it could come to harm from the noxious substances that it fights. The organ, however, possesses an amazing ability to bounce back from injuries.
The human body typically loses its capacity to regenerate with age. Scientists wondered if the liver also loses its regenerative ability due to aging. Previous research did not fully unravel the nature of the organ’s renewal in humans.
“Some studies pointed to the possibility that liver cells are long-lived while others showed a constant turnover,” stated Dr. Olaf Bergmann, research group head at TU Dresden’s Center for Regenerative Therapies Dresden (CRTD). “It was clear to us that if we want to know what happens in humans, we need to find a way to directly assess the age of human liver cells.”
The research also showed that liver cells renew differently, depending on the amount of DNA.
Radiocarbon birth dating
Radiocarbon is a type of carbon, a pervasive chemical element that contributes to life on Earth. Naturally present in the atmosphere, this carbon isotope finds its way into plants via photosynthesis and passes from them into animals and humans.
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Radiocarbon is often employed in archeology to find out how old ancient samples are because of its unstable and weakly radioactive nature.
Dr. Bergmann specializes in using retrospective radiocarbon birth dating to establish the biological age of tissues in humans. Commonly used models in animal studies have not proved suitable when applied to humans.
Researchers in this study turned to the aboveground nuclear testing that took place in the 1950s to make their findings. Huge volumes of radiocarbon were released into the atmosphere following the tests. These found their way into plants and animals, making cells formed around this time to have higher radiocarbon levels in their DNA.
Atmospheric radiocarbon began to fall following the formal ban of aboveground nuclear tests in 1963. A similar dropping trend was also observed in the cells of living organisms.
“Even though these are negligible amounts that are not harmful, we can detect and measure them in tissue samples,” Dr. Bergmann said. “By comparing the values to the levels of atmospheric radiocarbon, we can retrospectively establish the age of the cells.”
The research team previously applied its retrospective radiocarbon birth dating know-how to the formation of brain and heart cells. It showed that the making of new cells continues all through life and is not restricted to prenatal time.
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A young organ
Dr. Bergmann’s group comprised biologists, physicists, clinicians, and mathematicians. In this study, the researchers examined the livers of people aged 20 to 84 years at their deaths. They found, to their surprise, that the liver cells of those subjects were about the same age.
“No matter if you are 20 or 84, your liver stays on average just under three years old,” stated Dr. Bergmann.
The findings reveal that regular replacement of liver cells helps to properly alter liver mass to meet the body’s needs and this continues as people get older. The continual cell replacement is pertinent for liver renewal and cancer formation.
All cells in the liver are not young, however. Researchers found that those cells having more DNA can continue living for up to a decade before renewing.
“Most of our cells have two sets of chromosomes, but some cells accumulate more DNA with age,” explained Dr. Bergmann. “In the end, such cells can carry four, eight, or even more sets of chromosomes.”
Researchers noted that the fraction of cells with more DNA increases gradually as people get older. This, they said, could be a way of protecting against a buildup of harmful mutations. The team expressed a need to find out whether similar mechanisms are involved in chronic liver disease, which can progress to cancer in certain cases.
Dr. Bergmann’s team is also currently probing whether new muscle cells can still be made in the hearts of people with chronic heart disease.
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References
Diploid hepatocytes drive physiological liver renewal in adult humans
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