Alterations in neural stem cell quiescence and activation in the 3xTG-AD model of Alzheimer's Disease

Abstract: Alzheimer′s Disease (AD) is the most common form of dementia with progressive cognitive deficits and mood disorders (Knopman et al., 2021). Recent studies have associated AD pathology with the impairment of adult neurogenesis, as indicated by impaired neural stem cell (NSCs) homeostasis (Bond et al., 2015). Recent work has further associated AD progression with a decline in the number and maturation of adult-born neurons in the SGZ, distinct from typical age-related decline (Moreno-Jiménez et al., 2019). In 3xTG-AD mice, a well-established mouse model of AD, our and other groups have demonstrated impairments to NSC pool and neural progenitor proliferation, as well as adult-born neurons, before the onset of Aβ plaques and NFTs (Hamilton et al., 2010, 2015; Rodrĺguez; et al., 2008, 2009). However, the regulatory mechanisms underlying the functional impairment of adult NSCs remain to be resolved. Here, we employ single-cell RNA-Seq to establish population-specific defects in the 3xTG-AD mouse model during adult SGZ neurogenesis. Relative to control mice, we observe a dramatic AD-induced decrease in the primed and activated NSC population, which results in a progressive loss of cells committed to neurogenesis. Transcriptome measurements suggest that 3xTG-AD NSCs and their progeny represent enhanced ribosomal and mitochondrial biogenesis, and disturbed Notch signaling pathway. RNA velocity analysis reveals reduced NSC activation as evidenced by a large fraction of Ascl1-postive cells, instead of entering cell cycle, returning to the primed and quiescent state. This is further supported by reduced numbers of Lpar1-expressing cells, a marker of neural progenitor cells, in the SGZ. Our work explores, at a stage-specific resolution, changes in the regulatory networks guiding adult neurogenesis, and identifies niche disturbances in the regulation of NSC quiescence and activation. These NSC deficits underlying impaired neurogenesis identified in AD mice, may be key contributors underlying the compromised hippocampal function in AD.