Essential roles of plexin-B3+ oligodendrocyte precursor cells in the pathogenesis of Alzheimer's disease

The roles played by oligodendrocyte (OL) lineage cells, the largest glial population in the adult CNS, in the pathogenesis of Alzheimer9s disease (AD) remain elusive. Here, we show a newly developed culture method for adult OL progenitor cells (aOPCs) and identify novel plexin-B3-expressing (plexin-B3+) aOPCs as potential amyloid β peptides (Aβ)-secreting cells. Fibroblast growth factor 2 (FGF2) promotes the survival and proliferation of aOPCs in a serum-free defined medium. Although the whole expression profiles of the expanded aOPCs closely resemble those of in vivo OPCs, we found a subpopulation (up to 5%) of plexin-B3+/olig2+ aOPCs in the cultures growing in FGF2. FGF2 withdrawal decreased NG2+, but increased plexin-B3+ aOPCs with increased APP expression, Aβ1-40, -42 secretions and Aβ1-42/total Aβ ratios in association with cored senile plaque-like morphological changes. In vivo, plexin-B3+ aOPCs are distributed throughout the adult brain, although less densely so than NG2+ aOPCs. Spreading depolarization, a type of brain injury, induced unique delayed cortical plexin-B3+ aOPC gliosis in the ipsilateral, but not in the contralateral, remote cortex. In AD brains, virtually all senile plaques in the cortex were immunostained with plexin-B3 antibodies and the levels of cortical plexin-B3 expression increased significantly in the Salcosyl-soluble fractions. These findings suggest that plexin-B3+ aOPCs play important roles in the pathogenesis of AD most likely as a natural Aβ source.