Mutant presenilin 1 expression in excitatory neurons impairs enrichment-mediated phenotypes of adult hippocampal progenitor cells.

Inheritance of mutant presenilin 1 genes (PSEN1) encoding presenilin 1 (PS1)variants causes autosomal dominant forms of familial Alzheimer's disease (FAD). We previously reported that ubiquitous expression of FAD-linked PS1 variants in mice impairs environmental enrichment (EE)-induced proliferation and neuronal commitment of adult hippocampal neural progenitor cells (AHNPCs). Notably, the self-renewal and differentiation properties of cultured AHNPCs expressing either human PS1 wild-type or PS1 variants were identical, suggesting that accessory cells within the hippocampal niche expressing PS1 variants may modulate AHNPC phenotypes in vivo. We now report that nontransgenic mouse AHNPCs transduced with retroviruses harboring cDNAs that encode either human PS1 wild-type or FAD-linked PS1 variants show no differences in EE-mediated proliferation and neuronal differentiation. Moreover, conditional inactivation of a mutant PS1 transgene in type-1 primary progenitor cells failed to rescue impairments of EE-induced proliferation, survival, or neurogenesis. In contrast, conditional inactivation of the mutant PS1 transgene in excitatory neurons of the mouse forebrain largely rescued the deficits in EE-induced proliferation and survival of AHNPCs, but not their differentiation into mature neuronal phenotypes. These results persuasively argue for a noncell autonomous effect of FAD-linked PS1 mutants on EE-mediated adult hippocampal neurogenesis.