A negative correlation was found between the life span of an animal and the size of hepatocytes - its liver cells.
Humans are one of the longest-living mammals: we are able to live up to 70 or 90 years - a period unimaginable to almost anyone else. And it's not even the size. Rhinos weighing 20-30 times our size usually live for 40 years, as do the noticeably smaller chimpanzees. But the lifespan negatively correlates with the size of liver cells, hepatocytes, as described in a new article published in the journal Developmental Cell.
Yuval Dor and his colleagues are studying diabetes to find new ways to combat this difficult and difficult to treat disease. Hepatocytes play a special role here: a violation of their ability to produce insulin can be one of the causes of the disease. Examining these cells in newborn mice, the authors noted their striking miniature size: hepatocytes were not even easy to distinguish using a conventional microscope.
There are no such problems with hepatocytes of adult mice, which means that with age, these cells should grow not only in number, but also in size. Curious, the researchers searched for previous work describing the size of hepatocytes in other mammalian species. Data were collected for a total of 23 species, from cows and rhinos to bats. Indeed, it has been found that in adults, liver cells can be of a wide variety of sizes.
Volumes of hepatocytes ranged from 4288 cubic meters. microns (in the pygmy shrew) up to 457 cubic meters. μm (in rhinos); for a person, they amounted to about 1031 cubic meters. microns. The authors noted that for animals of similar sizes, the rule is observed: the smaller and more numerous their liver cells, the longer the lifespan.
Scientists believe that the large size of hepatocytes is associated with accelerated puberty. For us it takes about fifteen years, for most other animals - much less. In turn, late maturation requires a long life for reproduction (animals rarely survive their fertile years: in fact, besides humans, only a couple of whale species live much longer than their reproductive age).
Puberty in mammals is associated with the active production of mTOR, a target protein for rapamycin. It plays an important role in the control of cell growth, and its increased synthesis leads to an increase in cell size. So in animals with fast maturation and short lifespan, hepatocytes grow earlier - and vice versa. Those mammals that live longer do not experience the early and powerful effects of the mTOR protein, as indicated by their small liver cells.