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The human liver stays young throughout life

The liver is an essential organ which clears the toxins that accumulate in our bodies. Since it constantly deals with toxic substances, this organ is likely to be regularly injured. However, it has a unique capacity among all the other organs to quickly regenerate itself after damage. By using retrospective radiocarbon birth dating – an efficient method of assessing the biological age of human tissues – an international team of scientists has now found that the human liver stays young throughout life and is on average less than three years old.

Until recently, the nature of liver renewal in humans has remained a mystery. “Some studies pointed to the possibility that liver cells are long-lived while others showed a constant turnover,” said study senior author Olaf Bergmann, an expert in regenerative therapies at the Dresden University of Technology (TU Dresden). “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.”

By analyzing the livers of multiple individuals who died at ages between 20 and 84, Dr. Bergmann and his team made a surprising discovery: the liver cells of all subjects appeared to be approximately the same age. “No matter if you are 20 or 84, your liver stays on average just under three years old,” said Dr. Bergmann. These findings suggest that the adjustment of liver mass to the needs of an organisms is regulated through a constant replacement of liver cells – a process that is maintained even in older individuals.

However, a fraction of the liver cells can live up to 10 years before regenerating. These subpopulations carry more DNA than typical liver cells. “When we compared typical liver cells with the cells richer in DNA, we found fundamental differences in their renewal. Typical cells renew approximately once a year, while the cells richer in DNA can reside in the liver for up to a decade,” explained Dr. Bergmann. “As this fraction gradually increases with age, this could be a protective mechanism that safeguards us from accumulating harmful mutations. We need to find out if there are similar mechanisms in chronic liver disease, which in some cases can turn into cancer.” 

Further research is needed to shed more light on the cellular and molecular mechanisms of liver regeneration, in order to better understand how this amazing organ functions – or sometimes fails to function. Gaining more knowledge about the dynamics of liver regeneration could clarify the etiology of various liver diseases and help scientists devise better therapeutic pathways. 

The study is published in the journal Cell Systems

By Andrei Ionescu, Staff Writer

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