Project description:APOE, a well-established genetic risk factor for Alzheimer’s disease, is also closely associated with the aging process. Previous studies have demonstrated age-related declines in APOE expression within astrocytes. To investigate the mechanisms underlying this reduction, in this study, we performed small RNA sequencing on extracellular vesicles (EVs) derived from human fetal brain astrocytes. Our findings reveal miR-let-7b, enriched in astrocyte-derived EVs, as a key mediator of age-related APOE downregulation. Furthermore, we uncover a novel role for APOE in regulating astrocyte senescence, providing new insights into the molecular interplay between aging and neurodegenerative disorders.
Project description:To determine how APOE genotypes impact the gene signature of microglia and astrocytes during aging at single cell level, we isolated brain cells from young (3 month of age) and aged (24 month of age) APOE2 and APOE3 and APOE4 mice, and conducted single cell RNA sequencing (scRNAseq) (4 mice/age/genotype). We annotated all the cells based on their gene markers and then focused on microglia and astrocytes for further downstream analysis. We functionally annotated each subcluster with microglia and astrocytes, based on the expression pattern of the widely accepted typical maker genes from multiple publications. Further, we identified the differentially expressed genes (DEG) in the comparison between young and aged mice for each subcluster in each APOE genotype and characterized the pathways related to these DEGs. Taken together, our dataset provided comprehensive resources to understand the APOE-regulated microglial and astrocytic responses to aging.
Project description:The excitatory amino acid transporter 2 (EAAT2) is the major glutamate transporter in the brain expressed predominantly in astrocytes and at low levels in neurons and axonal terminals. EAAT2 expression is reduced in aging and sporadic Alzheimer’s disease (AD) patients’ brains. The role EAAT2 plays in cognitive aging and its associated mechanisms remains largely unknown. Here, we show that conditional deletion of astrocytic and neuronal EAAT2 results in age-related cognitive deficits. Astrocytic, but not neuronal EAAT2, deletion leads to early deficits in short-term memory and in spatial reference learning and long-term memory. Neuronal EAAT2 loss results in late-onset spatial reference long-term memory deficit. Neuronal EAAT2 deletion leads to dysregulation of the kynurenine pathway, and astrocytic EAAT2 deficiency results in dysfunction of innate and adaptive immune pathways, which correlate with cognitive decline. Astrocytic EAAT2 deficiency also shows transcriptomic overlaps with human aging and AD. Overall, the present study shows that in addition to the widely recognized astrocytic EAAT2, neuronal EAAT2 plays a role in hippocampus-dependent memory. Furthermore, the gene expression profiles associated with astrocytic and neuronal EAAT2 deletion are substantially different, with the former associated with inflammation and synaptic function similar to changes observed in human AD and gene expression changes associated with inflammation similar to the aging human brain.
Project description:The e4 allele of the apolipoprotein E (APOE) gene is the strongest genetic risk factor for late-onset Alzheimer's disease and has been shown to increase amyloid pathology relative to the presence of the e2 and e3 alleles. In the brain, apoE is primarily produced by astrocytes and under pathological conditions also by microglia. The cell-type-specific role of apoE in amyloid pathology, especially after amyloid plaque deposition, has not been fully elucidated. We generated APPPS1-21/Aldh1l1-Cre/ERT2/apoE4flox/flox and APPPS1-21/apoE4flox/flox mice. At 3.8-months-of-age, during the phase of rapid plaque growth, we administered tamoxifen to reduce astrocytic APOE4 and assessed mice at 6-months-of-age. One day before tamoxifen treatment, mice were injected with methoxy-X04, a blood-brain-barrier permeant fluorescent marker that labeled the pre-existing fibrillar amyloid plaques. By using this strategy, we were able to characterize pre-existing plaques prior to the loss of astrocytic APOE4 and to also analyze newly-formed amyloid plaques after the loss of astrocytic APOE4. Interestingly, astrocytic APOE4 deletion strongly reduced pre-existing plaques. It also prevented new plaque formation and decreased glial reactivity. Importantly, the removal of astrocytic APOE4 resulted in enhanced microglial and astrocytic phagocytic ability, which may contribute to the reduction of the amyloid pathology.