Brain injury activates microglia that induce neural stem cell proliferation ex vivo and promote differentiation of neurosphere-derived cells into neurons and oligodendrocytes

Brain damage, such as ischemic stroke, enhances proliferation of neural stem/progenitor cells (NSPCs) in the subventricular zone (SVZ) To date, no reliable in vitro systems, which can be used to unravel the potential mechanisms underlying this lesion induced effect, have been established Here we developed an ex vivo method to investigate how the proliferation of NSPCs changes over time after experimental stroke or excitotoxic striatal lesion in the adult rat brain by studying the effects of microglial cells derived from an in jured brain on NSPCs We isolated NSPCs from the SVZ of brains with lesions and analyzed their growth and differentiation when cultured as neurospheres We found that NSPCs isolated from the brains 1-2 weeks following injury consistently generated more and larger neurospheres than those harvested from naive brains We attributed these effects to the presence of microglial cells in NSPC cultures that originated from injured brains We suggest that the effects are due to released factors because we observed increased proliferation of NSPCs isolated from non-injured brains when they were exposed to conditioned medium from cultures containing microglial cells derived from injured brains Furthermore, we found that NSPCs derived from injured brains were more likely to differentiate into neurons and oligodendrocytes than astrocytes Our ex vivo system reliably mimics what is ob served in vivo following brain injury It constitutes a powerful tool that could be used to identify factors that promote NSPC proliferation and differentiation in response to injury induced activation of microglial cells, by using tools such as proteomics and gene array technology (C) 2010 IBRO Published by Elsevier Ltd All rights reserve