APP stimulates neural stem/progenitor cell proliferation by increasing cystatin C secretion. (Poster)

The amyloid precursor protein has been well studied for its role in Alzheimer’s disease. However, little is known about its normal function. In this study, we examined whether APP plays a role in neural stem or progenitor cell proliferation. Neural stem / progenitor cells (NSPCs) were cultured as neurospheres. We found that there was an increase in the proliferation of NSPCs derived from APP-overexpressing Tg2576 transgenic mice (P<0.05, n=7). However, NSPCs obtained from APP knockout mice (APP KO mice) had reduced proliferation rates (P<0.01, n=4). To examine if a secreted factor was responsible for the increased proliferation, the conditioned medium (CM) was collected from Tg2576, APP KO and wide-type neurosphere cultures and added into the neurosphere-derived cell cultures. CM from Tg2576 cultures stimulated neurosphere proliferation (P<0.05, n=5) compared to wild-type CM whereas CM from APP KO cultures had little effect on proliferation of neurosphere. To identify secreted molecules in the CM of Tg2576 cultures which can promote proliferation, the CM was analyzed for its effect on proliferation by immunoblotting and immunodepletion. Immunodepletion of APP from CM of Tg2576 did not reduce proliferation (P>0.05, n=4). Furthermore, recombinant APP did not stimulate proliferation. As cystatin C has been reported to stimulate neural stem cell proliferation, we examined the possibility that the secreted molecule may be cystatin C. Levels of cystatin C were higher in the CM of Tg2576 cells than in the CM of WT cells (P<0.05, n=5). Cystatin C was lower in the CM obtained from APP KO cultures (P<0.05, n=3). Immunodepletion of cystatin C from CM of Tg2576 culture decreased the effect on cell proliferation (P<0.05, n=4). The results demonstrate that APP stimulates NSPC proliferation, and that this effect is mediated via an increase in cystatin C secretion.