Aortic Single-Cell Transcriptome Analysis Reveals ApoE-Isoform-Specific Influences on Vascular Disease

The human APOE gene is polymorphic with three major alleles that encode apolipoprotein (apo) E2, apoE3, and apoE4. Both apoE2 and apoE4 are associated with increased atherosclerosis risk. This study utilized human APOE2, APOE3, and APOE4 gene replacement mice and single-cell RNA sequencing approach to delineate the mechanisms underlying this association. The human APOE2, APOE3, and APOE4 mice were fed a Western-type high fat-cholesterol diet for 16 weeks. Hyperlipidemia and significant atherosclerosis were observed in APOE2 mice but not in APOE3 or APOE4 mice. However, increased vascular inflammation was observed in both APOE2 and APOE4 mice. Single-cell RNA sequencing followed by cluster analysis identified 25 major cell types in the aorta that include various immune cell types, endothelial cells, and various vascular mural cell subsets. Results showed that cells from the APOE2 mice were enriched with genes associated with intracellular lipid accumulation and inflammation, whereas cells from the APOE4 mice displayed elevated oxidative- and/or endoplasmic reticulum-stress and inflammatory response. Thus, apoE2 accelerates atherosclerosis by inducing diet-induced hyperlipidemia and inflammation, while apoE4 does not induce hyperlipidemia but enhances inflammation that may prime the vasculature for atherosclerosis development. The distinct mechanisms by which apoE2 and apoE4 promote atherosclerosis underscore the importance of including apoE genotype information in the design of therapeutics for atherosclerosis intervention.