Characterization of adult hippocampal neurogenesis in the novel App ^SAA Knock-in Alzheimer’s disease mouse model

Adult hippocampal neurogenesis (AHN) declines with age and is thought to be severely exacerbated in neurodegenerative disorders like Alzheimer’s disease (AD). Despite numerous efforts to understand how AHN is altered in AD mouse models, results have been inconsistent, largely due to limitations of first-generation transgenic AD mouse models. The newly developed App Knock-in models address many of these limitations. Here, we provide the first in-depth characterization of hippocampal cell populations and AHN across different ages in the novel App ^SAA Knock-in (AppKI) mouse model. Our findings reveal that AppKI mice show no early deficits in excitatory dentate granule cells or inhibitory interneurons at 2 and 4 months, but significant loss of both populations emerges by 6 months of age. We also identified a progressive decline in AHN with the survival of newborn neurons being impaired first at 4 months, followed by a deficit in proliferation at 6 months. Furthermore, we demonstrate that exposure to enriched environment, a form of hippocampus-engaged exploration, robustly enhances AHN in AppKI mice, primarily by promoting survival. In conclusion, our study provides a foundational characterization of the AppKI model, establishing a timeline for cellular and AHN deficits.