The ?2 allele in the APOE gene, encoding the apolipoprotein E2 (apoE2) isoform is a risk factor, independent of cholesterol levels, for peripheral vascular diseases including carotid atherosclerosis, cerebrovascular disease and ischemia of lower extremity arteries in humans. The ?2 allele is also associated with higher body mass index and type 2 diabetes. This project integrates these gene association studies with the goal of identifying the mechanisms by which apoE2 promotes obesity and related peripheral vascular diseases. The overall hypothesis is that apoE2 increases the risk of peripheral vascular diseases by two distinct but synergistic mechanisms: First, defective hepatic clearance of apoE2-containing triglyceride-rich lipoproteins increases lipid partitioning to extrahepatic tissue, most notably the adipose tissues to increase adiposity; and second, apoE2 expression in adipocytes and macrophages each contribute uniquely through different mechanisms to cause robust adipose tissue inflammation that synergizes with hyperlipidemia to promote atherosclerosis. Our recent studies revealed that, in comparison to human APOE3 gene replacement mice, the APOE2 mice are more susceptible to diet- induced obesity and their adipose tissues are more inflamed with increased number of dead adipocytes. The apoE2-expressing adipocytes and macrophages are also dysfunctional with impairments suggestive of a contributory role toward inflammation and atherosclerosis.
Aim 1 will test the hypothesis that defective hepatic clearance of apoE2-containing triglyceride-rich lipoproteins favors plasma lipid re-distribution to other tissues including adipose tissue, thereby increasing obesity and accelerating adipose tissue remodeling that leads to tissue dysfunction and inflammation.
In Aim 2, adipose tissues from APOE2 and APOE3 mice containing the isoforms only in adipocytes will be reciprocally transplanted into recipient mice to test the hypothesis that apoE2 expression in adipocytes destabilizes lipid droplets and favors lipolysis, thereby synergizing with hyperlipidemia to promote lipotoxicity that leads to adipocyte death and adipose tissue inflammation.
In Aim 3, reciprocal bone marrow transplants will be performed between APOE2 and APOE3 mice to test the hypothesis that macrophage- specific apoE2 oligomerization impairs macrophage functions, which also synergizes with hyperlipidemia in contributing to the robust adipose tissue inflammation observed in obese APOE2 mice.
Aim 4 represents the culmination of the three mechanistic studies by performing perivascular adipose tissue (PVAT) transplants to carotid arteries of APOE2 and APOE3 mice to test the hypothesis that apoE2-induced PVAT dysfunction and inflammation provides periadventitial outside-in signals that act synergistically with elevated apoE2-induced hyperlipidemia to promote carotid atherosclerosis. Insights gained from these studies will allow for translation to human patients with direct impact on intervention strategies for ~10% of the population that are ?2 carriers. Since peripheral vascular disease is a common manifestation of atherosclerosis affecting ~30 million individuals, understanding how increased PVAT inflammation impacts atherosclerosis will also be valuable.

Public Health Relevance

Genetic association studies have identified the epsilon2 allele of the APOE gene with increased risk and severity of peripheral vascular disease and obesity-related diabetes. This proposal will delineate the mechanism(s) by which the epsilon2 encoded apoE2 protein promotes these metabolic diseases and increases atherosclerosis progression. The clinical implication of this mechanism-based study is that information obtained will optimize dietary and therapeutic intervention strategies to minimize metabolic diseases in epsilon2 carriers representing >10% of the population.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Special Emphasis Panel (ZRG1)
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Liu, Lijuan
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University of Cincinnati
Schools of Medicine
United States
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Reardon, Catherine A; Lingaraju, Amulya; Schoenfelt, Kelly Q et al. (2018) Obesity and Insulin Resistance Promote Atherosclerosis through an IFN?-Regulated Macrophage Protein Network. Cell Rep 23:3021-3030
Getz, Godfrey S; Reardon, Catherine A (2018) Diet, Microbes, and Murine Atherosclerosis. Arterioscler Thromb Vasc Biol 38:2269-2271
Getz, Godfrey S; Reardon, Catherine A (2016) ApoE knockout and knockin mice: the history of their contribution to the understanding of atherogenesis. J Lipid Res 57:758-66
Hui, David Y (2016) Intestinal phospholipid and lysophospholipid metabolism in cardiometabolic disease. Curr Opin Lipidol 27:507-12
Getz, Godfrey S; Reardon, Catherine A (2016) Do the Apoe-/- and Ldlr-/- Mice Yield the Same Insight on Atherogenesis? Arterioscler Thromb Vasc Biol 36:1734-41