In a surprise breakthrough, researchers at the UC Davis MIND Institute and their colleagues have found that microglia remove healthy neural progenitor cells (NPCs) through phagocytosis to control neuron production during brain development. This newly discovered mechanism keeps neuron numbers in check, preventing brain overgrowth.
The discovery could open up new avenues for brain research and lead to therapies for a variety of neurological conditions.
The study was published online in the The Journal of Neuroscience.
Microglia are the immune component cell of the central nervous system. Similar to macrophages, microglia provide the brain’s primary defense against pathogens and foreign bodies, clear away dying cells and help repair neural damage. When inactive, they act as sentinels. When a problem is located, they activate and eliminate it. However, until recently, no one had realized the important roles they play in brain development.
"We have known for some time that neurons can undergo apoptosis, a form of cell death, and ultimately be removed by microglia," said Stephen Noctor, assistant professor in the Department of Psychiatry and Behavioral Sciences and the study’s lead author. "But this is new. Microglia are actually eating healthy progenitor cells, thereby regulating the number of neurons produced in the developing brain."
During development, NPCs produce neurons in the brain’s proliferative zones. However, creating too many or too few neurons can have dire consequences.
"If you have too many cells, there’s only so much trophic support (brain infrastructure for cell growth and survival) to keep neurons alive," Noctor said. "All these cells competing for resources could easily throw off connectional properties, altering the way surviving neurons interact. Likewise, having too few cortical cells would have profoundly negative consequences."
(Image: Antoine Triller, Alain Bessis & Serge Marty - Département de Biologie, ENS)