RNAseq of isolated astrocytes and microglia from APPPS1E4fl/fl mice following astroycte APOE removal

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. Overall design: Microglia or astrocytes were sorted from APPPS1::APOE4fl/fl::ALDH1L1-CreERT (n=4), APPPS1::APOE4fl/fl (n=4), APOE4fl/fl (n=2), and APOE4::ALDH1L1-CreERT (n=2) All mice were treated with tamoxifen at 3.8 months of age and cells isolated by FACS 10 days later using using anti-Cd11b-Cy7 antibodies for microglia and anti-ACSA-2-PE antibodies for astrocytes.