By Erin Blakemore
When it comes to the human body, age is just a number. Thanks to the regenerative powers of human cells, our bodies constantly create new cells - to the tune of about 330 billion a day.
But until now, researchers haven’t known much about how long the cells of one of the most important organs, the liver, live. Research in the journal Cell Systems reveals that humans’ livers are forever young, clocking in at less than three years old despite their hosts’ biological age.
German researchers studied the livers of 33 adults who were between ages 20 and 84 when they died. They isolated the nuclei of liver cells called hepatocytes - the workhorses of the human liver. Hepatocytes make up the bulk of the human liver and perform a dizzying variety of tasks, from aiding with metabolism to taking part in the body’s immune response.
The researchers wanted to know whether hepatocytes are long-lived, like neurons or the heart’s muscle cells, or whether they’re more transient. Previous studies had focused mainly on rodent livers, leaving unanswered questions on the life cycle of human liver cells.
When the scientists dated the cells, they found an average age of about three years regardless of the age of the person who generated the cells. The hepatocytes “show continuous and lifelong turnover, allowing the liver to remain a young organ”, they write.
The turnover depended on the type of liver cell. Ninety-five percent of the cells with two complete sets of chromosomes turned over within a year, but up to 12% of a cell subtype that have more than one pair of chromosomes can survive up to a decade.
“As this fraction gradually increases with age, this could be a protective mechanism that safeguards us from accumulating harmful mutations,” Olaf Bergmann, a research group leader at the Dresden University of Technology’s Center for Regenerative Therapies, said in a news release. “We need to find out if there are similar mechanisms in chronic liver disease, which in some cases can turn into cancer.”
The older the subject, the older the hepatocytes, although the researchers say most are short-lived.
All in all, the researchers project, our bodies produce about 700 million hepatocytes each day - not bad for a 1.4kg organ.