Abstract 14517: apoE Receptor-2-R952Q Variant in Macrophages Potentiates Hyperlipidemia and Atherosclerosis in LDL Receptor-Knockout Mice via Increased Secretion of Soluble LDL Receptor-Related Protein-1

Abstract

Introduction and objective: Apolipoprotein E Receptor-2 (apoER2) is a type I transmembrane receptor in the LDLR family expressed in vascular smooth muscle cells (VSMC), endothelium, and macrophages. An apoER2 mutation referred to as apoER2-R952Q (R952Q) is associated with elevated plasma triglyceride levels and increased risk of premature coronary artery disease and myocardial infarction in humans. This study investigated the role of the R952Q mutation of apoER2 in modulating disease development. Methods and Results: We generated R952Q-expressing mice using a CRISPR-directed approach. This mouse line was crossed with the LDLR knockout mouse line and the progenies were fed a high cholesterol diet for 16 or 24 weeks. Results showed that unlike apoER2 knockout, the accelerated atherosclerosis R952Q variant mice exhibited was linked to increased plasma lipid levels. Considering apoER2's expression, which is notably absent in hepatocytes, we investigated the impact of R952Q myeloid cells on disease progression via bone marrow transplant. Results showed that wildtype apoER2 mouse recipients of R952Q bone marrow recapitulated the elevated plasma lipid level phenotype while R952Q mouse recipients of wildtype apoER2 bone marrow did not. Due to the absence of LDLR in our model, we investigated LRP1’s role in the context of myeloid-specific R952Q and found an increase in the production of hypercholesterolemia-associated soluble LRP1 (sLRP1) in the plasma of high cholesterol diet-fed mice with myeloid-specific R952Q. sLRP1 may compete with cell-surface LRP1 in lipoprotein clearance, suggesting a novel mechanism by which the R952Q mutation in macrophages may increase plasma lipid levels, thereby accelerating atherosclerosis. Conclusion: The R952Q mutation in apoER2 accelerates atherosclerosis via overproduction of soluble LRP1, a gain-of-function mechanism in macrophages resulting in hypercholesterolemia.