Amelioration of Tau and ApoE4-linked glial lipid accumulation and neurodegeneration with an LXR agonist
Apolipoprotein E (APOE) is a strong genetic risk factor for late-onset Alzheimer's disease (AD) with APOE4 increasing and APOE2 decreasing risk relative to APOE3. In the P301S mouse model of tauopathy, ApoE4 increases tau pathology and neurodegeneration when compared to ApoE3 or the absence of ApoE. However, the role of ApoE isoforms in regulating lipid metabolism in the setting of tauopathy is unknown. Here, by using targeted lipidomics coupled with histological analysis, we demonstrate that in P301S tau mice, ApoE4 strongly promotes glial lipid accumulation along with significant perturbations in cholesterol metabolism and lysosomal function. Increasing lipid efflux in glia via administration of the LXR agonist GW3965 reduces lipid droplet accumulation in primary E4 microglia in vitro and GW3965 or Abca1 overexpression strongly attenuates tau pathology, neurodegeneration, and synapse loss in P301S/ApoE4 mice. By immunostaining, bulk and snRNA sequencing, we demonstrate reductions in reactive astrocytes and microglia as well as significant changes in cholesterol biosynthesis and metabolism in glia of tauopathy mice in response to LXR activation. These data suggest that promoting efflux of glial lipids via Abca1 could serve as a therapeutic approach to ameliorate tau and ApoE4-linked neurodegeneration. Overall design: RNAseq was performed on hippocampal tissue of 9.5 month old APOE4-KI mice or PS19/APOE4-KI mice treated with control or GW3965 diet from 6-9.5.months