Neural stem cells get plenty of good press, and understandably so. They're the matriarchal cells of the brain, from which spring all except one type of cell populating our most highly regarded (at least by itself) organ. They can remain in their primordial state for decades, languidly dividing just enough to replace their own numbers. Alternatively, they can spawn daughter cells that depart from the primordial state.
It's the matriarchs' daughters - so-called neural progenitor cells - that embark on committed differentiation pathways giving rise to nerve cells and other key brain cells. Given that lofty ambition, it's not surprising that neural progenitor cells divide much more rapidly than their parents do, outnumbering neural stem cells probably by 1,000 to 1 or more.
It turns out that neural progenitors can do more than breed. They're excellent managers, too. In a new Nature Neuroscience study that I describe in this news release, Stanford neuroscientist Tony Wyss-Coray, PhD, and his colleagues demonstrated that neural progenitor cells squirt out substances regulating the behavior of the one type of brain cell that doesn't call them grandma.
Microglia, which trace their lineage to the immune system, are a combination police force, clean-up crew, and nursing team. They can migrate toward the sites of brain injury, put out chemical signals, and gobble up detritus, microbes, or dead or dying cells. As I note in my release:
Microglia normally are distributed throughout the brain - rather small, quiescent cells sprouting long, skinny projections that meekly but efficiently survey large areas that, taken together, cover the entire brain. But if this surveillance reveals signs of a disturbance, such as injury or infection, the microglia whirl into action. They begin proliferating and their puny bodies puff up, metamorphosing from mild-mannered Clark Kent-like reporters to buffed Supermen who fly to the scene of trouble, where they secrete substances that can throttle bad actors or call in reinforcements. Within these activated cells, internal garbage disposals called lysosomes form in large numbers and start whirring, ready to make mincemeat out of pathogens or cellular debris.
Wyss-Coray's group showed, in rodents, that specific factors secreted by neural progenitor cells get microglia pumped. The discovery is significant considering that in the two places in the adult mammalian brain (including the human variety) where neural stem and progenitor cells reside, they're typically closely associated with an entourage of microglia.
Now we know who's boss. And we may have a clue about why stem-cell transplants seem to improve brain function, even though the stem cells don't actually engraft very well.
Previously: Old blood + young brain = old brain, Could stem cells help brain-cancer patients regains cognitive abilities? and Unsung brain-cell population implicated in variety of autism
Photo by minijack3