Project Summary / Abstract Obesity-related metabolic disorders, including insulin resistance, type 2 diabetes, and non-alcoholic fatty liver disease, are thought to be caused by low-grade non-infectious inflammation as a result of lipid-mediated immune cell activation, particularly macrophages. However, it has become clear that focusing on macrophage inflammatory signaling is overly simplistic and fails to explain the complex relationship between increased immune cell recruitment to metabolic tissues and disease pathogenesis. Phenotyping of macrophages in adipose tissue and liver demonstrates induction of a lysosomal lipid metabolism program in diet-induced obesity, suggesting that macrophage recruitment to lipid-overloaded tissues might be compensatory in nature. If so, then enhancing a cell-intrinsic program of lipid hydrolysis and metabolism in macrophages should have beneficial metabolic effects. In preliminary work, we show that overexpression of macrophage TFEB, a master transcriptional regulator of lysosomal and fatty acid oxidation genes, enhances the ability of macrophages to metabolize lipids in vitro and ameliorates diet-induced metabolic dysfunction in vivo, presumably because of reduced fatty acid release from adipose tissue. In this proposal, we will investigate the consequences and mechanisms by which activating macrophage lysosomal lipid metabolism in distinct macrophage subsets impacts obesity-induced metabolic dysfunction and fatty liver disease. In Aim-1, we will explore the role of TFEB in adipose tissue macrophages (ATM) in regulating adipose tissue and systemic metabolic function in obesity. This includes assessing TFEB’s effects on the metabolic handling of lipid-rich exosomes and dying adipocytes found in crown-like structures. Our findings in mice will also be confirmed in a human population where we will determine if increased lysosomal lipid metabolism in ATM associates with metabolically normal or metabolically abnormal obesity. In Aim-2, we will utilize unique genetic models to determine the impact of TFEB in liver resident Kupffer cells vs. recruited monocyte-derived macrophages on diet-induced steatosis and fibrosis. Taken together, this proposal will test the hypothesis that induction of a macrophage lysosomal lipid degradation- mitochondrial fatty acid oxidation gene network via TFEB will enhance macrophage lipid handling and could be leveraged to treat obesity-associated insulin resistance and fatty liver disease.