Polymorphic ApoE at the crossroad of lipid metabolism and inflammation in atherosclerosis

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ABSTRACT Additional novel therapeutic strategies based on better understanding of how specific genetic risk factors participate in the pathogenesis and pathophysiology of cardiovascular disease are necessary to further reduce the burden associated with this major cause of death. A major genetic risk factor of cardiovascular disease is polymorphisms in the APOE gene. ApoE is synthesized in many cell types and the importance of liver-derived apoE in maintaining plasma lipid homeostasis is well documented. How does apoE (dys)function in other cell type influences atherosclerosis has not been delineated completely. The goal of this project is to ascertain how each apoE variant expressed in myeloid cells and adipocytes influences atherosclerosis. Preliminary results showed that: (i) bone marrow cells from human APOE2 and APOE4 gene replacement mice were less effective than APOE3 cells to reduce atherosclerosis in ApoE-/- mice; (ii) apoE2 and apoE4 enhance myeloid cell inflammatory response via distinct mechanisms; and (iii) APOE2 but not APOE3 or APOE4 adipocytes are dysfunctional with elevated intracellular cholesterol content to accelerate inflammation and atherogenesis. Our premise is that apoE2 and apoE4 augment inflammation and metabolic dysfunctions through distinct mechanisms, and in a cell type-specific manner, to accelerate atherosclerosis. Our hypothesis is that apoE2 causes cellular dysfunction through impaired intracellular cholesterol efflux, whereas apoE4 causes myeloid cell dysfunction by inducing oxidative and ER stress. Aim 1 will test the hypothesis that myeloid apoE2 expression increases myelopoiesis and promote early stages of atherogenesis, whereas myeloid apoE4 accelerates atherosclerosis advancement to later stages due to its impairment of efferocytosis and metabolic stress. Single- cell RNA-seq will be performed on lesion smooth muscle and immune cells at 3 stages of atherosclerosis to delineate how each apoE variant expressed in myeloid cells influences smooth muscle cell plasticity and lesion immune cell repertoire to alter lesion composition and enhance atherosclerosis. Follow-up studies will test the effectiveness of reducing intracellular cholesterol levels in APOE2 bone marrow cells and reducing ER stress in APOE4 bone marrow cells in atherosclerosis protection. Aim 2 will transplant macrophage-depleted perivascular adipose tissues (PVAT) from APOE2 and APOE3 mice to the carotid arteries of Ldlr-/- mice to test the hypothesis that the dysfunctional APOE2 adipocytes recruit inflammatory cells to the PVAT tissue to promote inflammation, which in turn signals to the vasculature to enhance inflammatory cell recruitment to the lesion area to exacerbate atherosclerosis. Single-nucleus RNA-seq will be performed to compare how adipocyte-derived apoE2 and apoE3 influences adipocyte plasticity and elicit different immune cell repertoires to the PVAT and vasculature to modulate atherosclerosis. We will also test the hypothesis that increasing cholesterol efflux in APOE2 adipocytes will reduce inflammation and atherossclerosis. Novel mechanistic information gained from these studies can be harnessed to design personalized intervention strategies based on APOE genotype to reduce vascular diseases.