PR001150 (Project)

Description:Apolipoprotein E e4 (APOE4) is the primary genetic risk factor for the late-onset form of Alzheimer's disease (AD). Although the reason for this association is not completely understood, researchers have uncovered numerous effects of APOE4 expression on AD-relevant brain processes, including amyloid beta (Aß) accumulation, lipid metabolism, endosomal-lysosomal processing and bioenergetics. In this study, we aimed to determine the effect of APOE4 allelic dosage on regional brain lipid composition in aged mice, as well as in cultured neurons. We performed a targeted lipidomic analysis on the entorhinal cortex (EC) and primary visual cortex (PVC) from 14–15 month-old APOE3/3, APOE3/4, and APOE4/4 targeted replacement mice, as well as on WT neurons cultured with conditioned media from APOE3/3 or APOE4/4 astrocytes. Our results reveal that the EC possesses increased susceptibility to APOE4-associated lipid alterations compared to the PVC. In the EC, APOE4 expression showed a dominant effect in decreasing diacylglycerol (DAG) levels, and a semi-dominant additive effect in the upregulation of multiple ceramide, glycosylated sphingolipid and bis(monoacylglycerol)phosphate (BMP) species, lipids known to accumulate as a result of endosomal-lysosomal dysfunction and defective lysosomal clearance. Neurons treated with conditioned media from APOE4 vs. APOE3 astrocytes also showed similar alterations of DAG and BMP species as those observed in the mouse EC. Our results suggest that APOE4 expression differentially modulates regional and neuronal lipid signatures, which may underlie the increased susceptibility of EC-localized neurons to AD pathology.