Genome-wide association analyses have linked variants of the LRP8 gene, including the R952Q LRP8 variant, with premature atherosclerosis and acute myocardial infarction in humans, indicating that its encoded protein apoE receptor-2 (apoER2) has a major impact on cardiovascular health and disease. How apoER2 influences cardiovascular biology is entirely unknown. We recently discovered that apoER2 deletion in LDL receptor-null mice causes marked acceleration of atherogenesis and promotes lesion necrosis without influencing plasma lipoprotein metabolism. The overall goal of this multiple-PI project is to determine how apoER2 in endothelium and macrophages contributes to cardiovascular protection. This will be accomplished by two currently collaborating laboratories with complementary expertise in the study of lipoproteins, lipoprotein receptors and vascular biology. Our recent cell culture work has revealed that through apoER2, apolipoprotein E3 (apoE3) activates endothelial NO synthase (eNOS) and thereby promotes endothelial cell migration, and also blunts endothelial cell-monocyte adhesion. In contrast, apoER2-R952Q has dominant-negative effect on eNOS activation by wild-type receptor. It has further been found that Lrp8-/- mice have impaired reendothelialization.
In Aim 1, an apoER2 cytoplasmic domain mutant incapable of adaptor protein interaction and candidate adaptor protein knockdown will be employed to determine the biochemical basis for apoER2 action in endothelium. The underpinnings of apoER2-R952Q dysfunction will also be discerned, and the rescue of cardioprotective behaviors by apoER2-R952Q- expressing endothelial cells will be attempted with NO donor. Using a recently-created floxed Lrp8 mouse, endothelial apoER2 regulation of endothelial cell-leukocyte adhesion will also be studied in vivo by intravital microscopy. Preliminary work has additionally shown that in macrophages apoER2 deficiency causes exaggerated oxLDL-induced neutral lipid accumulation and cell death/apoptosis. Lack of apoER2 in macrophages also results in increases in PPAR and PPAR-responsive gene expression. With a focus on PPAR-mediated processes, in Aim 2 the mechanism(s) by which apoER2 modulates intracellular signaling in macrophages and thereby governs their function and fate will be discerned.
In Aim 3, studies will be done using the Lrp8 floxed mouse or bone marrow reconstitution on LDL receptor-null background to determine the contributions of endothelial versus macrophage apoER2 to protection from atherosclerosis progression and plaque necrosis. The planned studies will provide critical new understanding of the basis by which apoER2 and its major ligand apoE influence cardiovascular health. The new information gained promises to improve as well as personalize therapies to combat cardiovascular disease in a large number of individuals with LRP8 variants (~1%) and/or apoE polymorphisms (~15%). The general population may also benefit by the development of novel therapies that harness these processes to optimize cardiovascular protection.
Genome wide linkage scans have identified variants of LRP8, the gene encoding apolipoprotein E receptor-2 (apoER2), contribute to premature coronary artery disease and acute myocardial infarction. This proposal addresses the cellular and molecular mechanisms by which apoER2 dysfunction promotes macrophage- and endothelial cell-dysfunctions in accelerating vascular occlusive diseases. The clinical implication of this mechanism-based study is that results will contribute valuable information to improve and personalize treatment strategies to suppress myocardial infarction in millions of people with atherosclerotic plaque buildup in the vessel wall.
