A new study from Cold Spring Harbor Laboratory (CSHL) has shed light on why our brains produce fewer and fewer neurons with age, a phenomenon thought to underlie age-related cognitive decline.
The study suggested that this drop in production is due to the shrinking cache of adult stem cells in our brains.
The new neurons are critical for some facets of memory—for instance, when similar events need to be memorized as separate episodes—and for the response to anti-depressant therapies and repair after brain injury.
“That the production of new neurons declines with age has been well established, but why this happens has been a matter of debate,” said Associate Professor Grigori Enikolopov, who led the CSHL team.
Between one month and two years of age—a mouse”s normal life span—the scientists observed a 100-fold decrease in the number of brain stem cells.
The rate of this decrease slowed with age, but the output per cell—measured as the number of progeny each cell gives rise to—increased, which Enikolopov said might be a strategy to cope with the loss of stem cells.
Enikolopov”s group found that the adult stem cells in the brain remain quiescent for a prolonged time until they are activated. They then undergo a series of rapid divisions that give rise to progeny that differentiate into neurons.
After that, the stem cells abandon their “stemness” by differentiating into astrocytes, a type of non-neural “helper” cells.
“This implies that each adult brain stem cell is used only once and hence is disposable, as opposed to stem cells in the blood or gut that self-renew many times during the lifespan,” said Enikolopov.
The study was published in the May 6 issue of Cell Stem Cell.