Molecular pathways underlying amyloid precursor protein–mediated regulation of adult-born neurons

Cleavage of amyloid precursor protein (APP) produces toxic amyloid-beta peptides, which play a critical role in the pathogenesis of Alzheimer's disease. Neuronal loss is a key feature of Alzheimer's disease. Despite the importance of APP in the proliferation of neural progenitors and the survival of adult-born granule cells in the dentate gyrus, little is known about the effect of APP deficiency on neuronal electrophysiological activities and the survival of newly born neurons. Utilizing whole-cell patch-clamp recording in combination with retroviral labeling and immunofluorescent staining in Alzheimer's disease model mice with App knockout ( App-/- ), we show that APP deficiency increased the number of adult-born granule cells at 4 weeks post-injection, but did not affect their intrinsic excitability or miniature current activity. In contrast, at 10 weeks post-injection, adult-born granule cells showed increased abundance and intrinsic excitability that were associated with abnormal dendritic morphology, increased miniature excitatory- and inhibitory-synaptic transmission, and decreased potassium-chloride-cotransporter 2 expression. Compared with adult-born granule cells at 10 week post-injection, mature granule cells exhibited decreased intrinsic excitability and potassium-chloride-cotransporter 2 expression alongside increased apoptosis in App-/- mice. Additionally, although App-/- mice showed abnormal freezing behavior and elevated mature granule cell activation during contextual fear conditioning, adult-born granule cells were not recruited in either App-/- or wild-type control mice. Taken together, these findings suggest that APP is required for adult-born granule cell maturation and that APP deficiency induces excitotoxicity in adult-born granule cells at 10 weeks post-injection, promoting subsequent apoptosis of mature granule cells.