Alzheimer's-Type amyloidosis in transgenic mice impairs survival of newborn neurons derived from adult hippocampal neurogenesis

Alzheimer's disease ( AD) is characterized by severe neuronal loss in several brain regions important for learning and memory. Of the structures affected by AD, the hippocampus is unique in continuing to produce new neurons throughout life. Mounting evidence indicates that hippocampal neurogenesis contributes to the processing and storage of new information and that deficits in the production of new neurons may impair learning and memory. Here, we examine whether the overproduction of amyloid-beta( A beta) peptide in a mouse model for AD might be detrimental to newborn neurons in the hippocampus. We used transgenic mice overexpressing familial AD variants of amyloid precursor protein ( APP) and/ or presenilin- 1 to test how the level ( moderate or high) and the aggregation state ( soluble or deposited) of A beta impacts the proliferation and survival of new hippocampal neurons. Although proliferation and short- term survival of neural progenitors in the hippocampus was unaffected by APP/A beta overproduction, survival of newborn cells 4 weeks later was dramatically diminished in transgenic mice with Alzheimer's-type amyloid pathology. Phenotypic analysis of the surviving population revealed a specific reduction in newborn neurons. Our data indicate that overproduction of A beta and the consequent appearance of amyloid plaques cause an overall reduction in the number of adult- generated hippocampal neurons. Diminished capacity for hippocampal neuron replacement may contribute to the cognitive decline observed in these mice.