Lipid-Mediated Control of Acetyl-CoA Metabolism in the Pathogenesis of NAFLD

PROJECT SUMMARY/ABSTRACT Altered lipid and glucose homeostasis in response to overnutrition is central to the pathogenesis of non- alcoholic fatty liver disease (NAFLD). Because current management options remain limited, the discovery of new metabolic pathways will serve to identify novel opportunities for intervention. This research proposal addresses the unanswered question of how membrane lipids regulate nutrient homeostasis. Our long-term goal is to understand the relationships between membranes and metabolic regulation and to leverage these for therapeutic purposes. The objective of this research is to elucidate lipid-mediated regulation of acetyl- CoA metabolism in health and overnutrition. Acyl-CoA thioesterase 12 (Acot12), which is highly expressed in liver and intestine, is the enzyme responsible for the cytosolic conversion of acetyl-CoA to acetate plus CoA. Acot12 comprises tandem N-terminal enzymatic domains and a C-terminal lipid-binding domain. The central hypothesis is that Acot12 activity controls lipid and glucose homeostasis by limiting utilization of acetyl-CoA for lipogenesis and for transcription factor acetylation. The rationale is that identifying the molecular mechanisms that underlie this novel lipid-regulated pathway should reveal distinct new insights into the pathogenesis of NAFLD. Guided by extensive preliminary data, the central hypothesis will be tested in three specific aims: 1) To define mechanisms whereby Acot12 controls lipid and glucose metabolism in liver; 2) To demonstrate key roles for Acot12 in intestinal lipid absorption and barrier function; and 3) To elucidate the cellular and molecular determinants of Acot12 activity. Aim 1 will test the hypothesis that Acot12-mediated hydrolysis of acetyl-CoA limits substrate availability for lipogenesis and reduces transcriptional expression of glycerolipid biosynthetic and gluconeogenic genes through acetylation of transcriptional regulators. We will further examine whether reduced production of lysophosphatidic acid functions to preserve Hippo signaling, thereby inhibiting hepatocarcinogenesis. Aim 2 will test the hypothesis that upregulation of intestinal Acot12 in response to overnutrition promotes glycerolipid trafficking with enterocytes, as well as the assembly and assimilation of chylomicrons. We will further investigate whether Acot12 maintains the barrier function of the intestinal epithelium in the setting of overnutrition by reducing inflammation and necroptotic cell death, thereby preventing hepatic injury in the setting of diet-induced steatosis. Aim 3 will test the hypothesis that Acot12 localizes preferentially to the cytoplasm or nucleus depending on metabolic conditions. We will define the lipid ligand(s) of Acot12 and demonstrate how lipid binding regulates both cellular localization and enzymatic activity. Overall, this proposal will elucidate new mechanisms of lipid-mediated metabolic regulation, which is significant because membrane lipid composition varies in health and disease. These studies are expected to inform new therapeutic strategies for the management of NAFLD.