The liver is a wondrous and essential organ, capable of regenerating itself to recover from the regular battering it takes as the body’s way of clearing toxins. Workplace injuries for such an organ are therefore common and so repairing itself is all part of the job, but for a long time it was assumed this regeneration lost its vigor as we age as much of the body’s bouncebackability fades.
Comparing the livers of deceased people, young and old, however, yielded surprising results, as new research published in Cell Systems demonstrates that the “age” of the liver stays young even when we are old. While there are some long-lived cells that linger for around 10 years, the study reports an average liver cell age of less than three years.
“No matter if you are 20 or 84, your liver stays on average just under three years old,” said Dr Olaf Bergmann, research group leader at the Center for Regenerative Therapies Dresden (CRTD) at TU Dresden, in a statement.
In order to directly assess the age of human liver cells, the researchers analyzed the livers of a group of humans who had died somewhere between 20 and 84 years old. While radiocarbon dating is often used to age ancient artifacts, it is not applicable to human tissue but the research was able to take advantage of humans' history with aboveground nuclear testing.
Nuclear testing aboveground was banned in 1963, but in the 1950s it released enormous amounts of radiocarbon into the atmosphere which trickled down into the DNA of animals. While Bergmann says these “negligible amounts are not harmful,” they can be detected and measured in human tissue.
“By comparing the values to the levels of atmospheric radiocarbon, we can retrospectively establish the age of the cells,” he said.
Aging the liver cells revealed that on average they were younger than three years old regardless of the age of the human they came from, demonstrating that in most cases the liver continues regenerating and stays young throughout our lives. However, this isn’t to say that damage can’t accumulate as not all cells regenerate at the same rate with some staying put for up to a decade.
“Some studies pointed to the possibility that liver cells are long-lived while others showed a constant turnover,” said Bergmann. “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.”
“Our research shows that studying cell renewal directly in humans is technically very challenging, but it can provide unparalleled insights into the underlying cellular and molecular mechanisms of human organ regeneration.”