PROJECT SUMMARY/ABSTRACT Cardiovascular disease (CVD) is the leading cause of death in the United States. Atherosclerosis, a major cause of CVD, is an inflammatory disease resulting from the build-up of cholesterol in plaque along the artery walls. These plaques are formed by accumulation of macrophage foam cells as an inflammatory response to oxidized low-density lipoprotein (oxLDL) in damaged endothelial cells. Free fatty acid receptor 4 (FFAR4), also known as G-protein coupled receptor 120 (GPR120), is a long-chain unsaturated fatty acid receptor expressed in adipocytes, endothelial cells, and macrophages. Activation of FFAR4 helps maintain metabolic homeostasis by regulating adipogenesis, insulin sensitivity, and inflammation. While FFAR4 is best known for its protective role in preventing obesity and diabetes, recent studies have demonstrated that FFAR4 may also play an important role in the prevention of atherosclerosis and CVD. Given FFAR4’s importance in anti-inflammatory signaling and high expression levels in macrophages, we designed experiments to test the hypothesis that FFAR4 plays a cardioprotective role by preventing pathways that lead to atherosclerosis. These experiments will require macrophages harvested from wild-type and FFAR4-knockout mice, and in some cases, macrophages treated with FFAR4 agonists. In Aim 1, we will investigate the effects of FFAR4 deficiency on macrophage foam cell formation. Specifically, we will determine whether FFAR4 deficiency increases oxLDL uptake (Aim 1.1), decreases cholesterol efflux (Aim 1.2), and decreases macrophage migration (Aim 1.3). In Aim 2, we will investigate the signaling mechanisms utilized by FFAR4 to protects against foam cell formation and test the hypothesis that canonical Gaq/11 FFAR4 signaling reduces cholesterol uptake and promotes cholesterol efflux by inhibiting the transcription factor PPARg. In Aim 3, we will investigate the physiological role of FFAR4 in atherosclerosis. Aim 3.1 will examine how FFAR4 deficiency in vivo impacts lipid levels and circulating inflammatory cytokines. Aim 3.2 will assess atherosclerotic lesion size differences and immune cell activation status in the aorta of LDLR-/- mice following transplantation of bone marrow from FFAR4+/+ or FFAR4-/- mice. The outcomes of these proposed studies will uncover the biological functions of FFAR4 and mechanisms that underlie how FFAR4 protects against macrophage foam cell formation, a hallmark of atherosclerosis. Ultimately, our combined current and future studies may identify FFAR4 as a novel therapeutic target for atherosclerosis.