ADA Junior Faculty Award: Regulation of Adipose Lipolysis by a Novel Inhibitor

50-70% of the energy for myocardial contraction derives from fatty acid (FA) oxidation. Adipose triglyceride lipase (ATGL) and hormone sensitive lipase (HSL) are responsible for hydrolyzing triacylglycerol (TAG) stored in lipid droplets and providing FAs for oxidation. Recent work from our laboratory demonstrates G0S2, a novel protein highly expressed in heart, liver and adipose tissue, as a selective inhibitor of ATGL. G0S2 is a lipid droplet-associated protein capable of direct interaction with ATGL but not HSL. Coexpression of G0S2 with ATGL in HeLa cells dramatically inhibited the ATGL-mediated lipid droplet degradation and the TAG lipase activity of ATGL. Moreover, adenoviral-mediated expression and siRNA-mediated knockdown both demonstrate that G0S2 negatively regulates TAG lipolysis in adipocytes. The overall GOAL of this proposed study is to elucidate the mechanisms whereby G0S2 regulates ATGL, and to evaluate the role of G0S2 in cardiac energy metabolism. The goal will be accomplished by determining (1) the structural components responsible for G0S2 interaction with ATGL and its inhibitory effect on ATGL activity; (2) the role of G0S2 in the control of TAG lipolysis, fatty acid oxidation and glucose utilization in mouse cardiomyocytes. The strategy for aim 1 is to generate a series of deletion mutants and test their ability to influence protein interaction and ATGL activity in vitro, and lipid droplet degradation and TAG accumulation in HeLa cells. Aim 2 will be accomplished by using mouse HL-1 cardiomyocyte cell line and isolated neonatal cardiomyocytes. We will attempt to manipulate relative intracellular levels of G0S2 and ATGL by adenovirus-mediated overexpression and siRNA-mediated knockdown. We will then conduct functional studies to evaluate the effects on ATGL-mediated lipolysis and β-oxidation of FAs. We will also examine the impact on insulin-regulated glucose metabolism and the susceptibility of cells to lipotoxicity.