Abstract / Summary
Abstract The apolipoprotein E ( APOE ) gene is the strongest genetic risk factor for Alzheimer’s disease (AD), influencing amyloid-β (Aβ) aggregation, clearance, and glial function. While APOE4 promotes Aβ pathology and APOE2 is protective, how these opposing alleles interact in the heterozygous APOE2/4 state remains unknown. Here, using littermate-controlled heterozygous APOE mice ( APOE2/3 , APOE3/4 , and APOE2/4 ) alongside APOE3/3 controls crossed with 5xFAD mice, we show that APOE3/4 mice exhibit increased Aβ deposition, maladaptive microglial activation, and reduced microglial interactions with plaques. These changes were attenuated in APOE2/4 mice, accompanied by a brain proteomic profile more similar to those of APOE3/3 and APOE2/3 mice. Increased myelin basic protein (MBP) abundance was observed in APOE2/3 but not APOE2/4 mice. Plasma lipidomics revealed shared alterations in APOE3/4 and APOE2/4 mice, with distinct signatures in APOE2/3 mice. These findings define allele interaction-dependent effects of APOE on brain and systemic phenotypes and provide a framework for understanding the biological consequences of the APOE2/4 genotype.