Role of a Novel Hormone Complex, Fabkin, in Dyslipidemia and Inflammation in Atherosclerosis

Project Summary: Despite effective strategies for lowering cholesterol, atherosclerosis, and related cardiovascular diseases remain the leading cause of death worldwide, even in the COVID era. Recent clinical data highlights a key benefit of targeting inflammatory processes in atherosclerosis. Thus, the discovery of novel therapeutics that can modulate both dyslipidemia and inflammation would represent a major breakthrough for atherosclerosis treatment. This proposal is focused on the fatty acid-binding protein 4 (FABP4) hormone complex we discovered, called Fabkin, as a key mediator of dyslipidemia and inflammation that contributes to atherosclerosis. In Fabkin, FABP4, adenosine kinase, and nucleoside diphosphate kinase interact to regulate extracellular ATP and ADP levels, which signal through purinergic receptors. Our long-term goal is to understand Fabkin's roles and mechanisms in physiology and cardio-metabolic pathophysiology and elucidate translational opportunities. Our objective in this proposal is to elucidate the roles and mechanisms of Fabkin in lipid metabolism and inflammation and assess its potential as a therapeutic target for atherosclerosis. We hypothesize that Fabkin is a key regulator of hepatic lipid metabolism and a pro-inflammatory factor, contributing to dyslipidemia and macrophage inflammation via purinergic signaling to promote atherosclerosis. This is based on available evidence of a role of purinergic signaling in atherosclerosis, our compelling preliminary data showing that mice lacking adipocyte FABP4 hormone, or treated with Fabkin-targeting monoclonal antibody, are protected from dyslipidemia and atherosclerosis, and our experiments supporting a role of Fabkin to induce de novo lipogenesis (DNL) and very low-density lipoprotein (VLDL) secretion in hepatocytes, and inflammation in macrophages. We will test our hypothesis in the following three specific aims: 1) Determine the effect of in vivo Fabkin deficiency on dyslipidemia and atherosclerosis. 2) Elucidate the roles and signaling mechanisms of Fabkin in hepatocyte DNL and VLDL secretion, 3) Identify the roles and signaling mechanisms of Fabkin in macrophage responses to cholesterol stress. In Aim 1 we will treat ApoE-/- mice with Fabkin-targeting antibody and employ ApoE-/-Ndpk-/- mice to examine the effects of in vivo Fabkin deficiency on atherosclerosis, dyslipidemia, and hepatic DNL and VLDL secretion. In Aim 2 we will characterize Fabkin's direct effects on hepatocyte DNL and VLDL secretion in vitro, test the efficacy of Fabkin-targeting antibody, and identify the purinergic signaling pathways induced by Fabkin. In Aim 3 we will determine Fabkin's direct effects on macrophage responses to cholesterol stress in vitro, including foam cell formation, inflammation, ER stress, and cell death. We will also test the efficacy of Fabkin-targeting antibody and identify the underlying purinergic signaling pathways. The expected outcome of these studies will be a clear understanding of the functions and mechanisms of action of Fabkin in lipid metabolism and inflammation, and its potential as a novel therapeutic target for treating atherosclerosis.