Amazing regeneration: Our liver renews itself amazingly quickly. Regardless of our age, the liver cells are on average no older than three years, as a study reveals.
Researchers discovered this using special radiocarbon dating, which reveals the age of tissue down to the individual cell. They also came across special cells in the liver with an unusual amount of DNA: they carry four, eight or even more sets of chromosomes.
The liver is a vital organ. It breaks down fats from food, stores minerals and produces bile, which is important for digestion. In addition, the liver ensures that our blood is constantly detoxified.
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Because of their great importance for our metabolism and their frequent contact with toxins, the liver tissue can regenerate particularly well. In the event of injuries or tissue damage, new liver cells are reproduced – this has been known for some time. However, it was unclear how long liver cells survive under normal circumstances and how much the ability to regenerate decreases with age.
Now it turns out that our liver remains surprisingly young throughout life. This was discovered by Paula Heinke from the Technical University of Dresden and her colleagues when they dated the age of human liver tissue using a new method.
To do this, they took cell samples from the livers of 33 people who had died between the ages of 20 and 84 and isolated the DNA from the cell nuclei. They then subjected the genetic material molecules to radiocarbon dating.
This dating, which is otherwise used primarily in archaeology, determines how high the proportion of the unstable carbon isotope C14 is in the sample. “Even if the amounts are tiny, we can detect and measure them in tissue samples,” explains Heinke’s colleague Olaf Bergmann. “By comparing the values with atmospheric radiocarbon, we can retrospectively determine the age of the cells.”
The surprising result: the liver cells renew themselves at high speed and are constantly replaced throughout life. “The liver stays on average less than three years old – regardless of whether you are 20 or 84 years old,” says Bergmann.
In young people, hepatocytes divide at a rate of 19 percent per year, in older people it is still around 17 percent. Age therefore has little influence on the renewal of liver cells.
“This suggests that our liver is a highly regenerative organ in which most of the cells are constantly being renewed over the course of human life,” the researchers state. “The liver remains a young organ throughout life.”
However, there is another change in the liver with age. It affects a subset of liver cells that carry more genetic material than normal.
“Most of our cells have two sets of chromosomes, but some cells accumulate more DNA as they age. In the end, such cells can carry four, eight or even more sets of chromosomes,” explains Bergmann. The team found that the proportion of these polyploid liver cells increases with age, while that of normal diploid liver cells decreases. In old age, the DNA-rich liver cells can account for up to 40 percent.
The interesting thing about it: “When we compared typical liver cells with the DNA-rich cells, we found fundamental differences in their renewal,” says Bergmann. “Typical cells renew themselves about once a year, while the DNA-rich cells can remain in the liver for up to a decade.”
As a result, the age distribution of the liver cells shifts over the course of life: in a 25-year-old person, 84 percent of the hepatocytes are less than two years old, in a 75-year-old the proportion of these young cells drops to 67 percent.
However, even in old people, the liver remains predominantly young and capable of regeneration: “Although polyploid liver cells live significantly longer than diploid ones, the majority of all hepatocytes are young – regardless of age, more than half of our liver cells were only born in the last six months.” , the researchers report.
However, this raises the question of why liver diseases such as liver cirrhosis and liver cancer still occur and why these are more common in older people.
So far this is still unclear. However, Heinke and her colleagues suspect that this could be related to the DNA-rich cells. “Polyploid cells are often associated with chromosomal errors and genomic instability,” explains the team.
As these cells increase with age, this could increase the liver’s susceptibility to disease. On the other hand, the polyploid liver cells divide less often, which in turn reduces the risk of copying errors and harmful mutations. Therefore, what is behind age-related liver diseases needs further research.
At the same time, the researchers are already using their dating method to determine the cell age in the heart. Among other things, they want to find out whether new heart muscle cells can still be formed in people with chronic heart disease.
They had previously discovered that new neurons are still being formed in our adult brain.
“Our research shows that directly studying cell renewal in humans is technically very challenging, but can provide unparalleled insights into the underlying cellular and molecular mechanisms of human organ regeneration,” says Bergmann.
Source: Technical University of Dresden
This article was written by Nadja Podbregar
The original to this post “A young, regenerative liver can still get sick” comes from scinexx.
