Neural stem and progenitor cells in the aged subependyma are activated by the young niche.

Previous studies have demonstrated an age related decline in the size of the neural stem cell (NSC) pool and a decrease in neural progenitor cell proliferation, however, the mechanisms underlying these changes are unclear. In contrast to previous reports, we report that the numbers of NSCs is unchanged in the old age subependyma and the apparent loss is because of reduced proliferative potential in the aged stem cell niche. Transplantation studies reveal that the proliferation kinetics and migratory behavior of neural precursor cells are dependent on the age of the host animal and independent of the age of the donor cells suggesting that young and old age neural precursors are not intrinsically different. Factors from the young stem cell niche rescue the numbers of NSC colonies derived from old age subependyma and enhance progenitor cell proliferation in vivo in old age mice. Finally, we report a loss of Wnt signaling in the old age stem cell niche that underlies the lack of expansion of the NSC pool after stroke.