Roles of ANGPTL3 and ANGPTL8 in Lipid and Energy Metabolism

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Plasma levels of lipoproteins are major risk factors for coronary heart disease (CHD). Our laboratory has used human genetics to elucidate the physiology and pathophysiology of circulating lipoproteins, and identify new targets for therapeutic intervention. Here we focus on the angiopoietin-like proteins 3 and 8 (ANGPTL3 and ANGPTL8), which exert powerful effects on lipoprotein metabolism. Humans lacking ANGPTL3 have striking panhypolipidemia, with marked reductions in plasma levels of LDL-cholesterol and triglycerides (TG). In the last funding period we showed that ANGPTL8 (A8) is a paralog of ANGPTL3 (A3)) that acts together with its progenitor to direct trafficking of circulating TG to peripheral tissues. Deficiency of ANGPTL8 reduces plasma levels of TG in both humans and mice. More recently, our group demonstrated that A3 and A8 both play a critical role in energy metabolism. Mice lacking the two genes are hypermetabolic, with increased body temperatures, increased VO2 and impaired fat accumulation. In contrast to the extensive literature on the effect of genetic differences in A3 and A8 on circulating lipoproteins, virtually nothing is known about the roles of these two proteins in energy metabolism. In this proposal, we will address 3 questions: 1) What are the roles of A3 and A8 in lipid and energy metabolism? 2) What is the potential therapeutic utility of inactivating A3 and/or A8? 3) How does variation in plasma A3 or A8 levels impact on other metabolic pathways humans? In Aim 1, genetically-modified mice will be used to investigate the actions of A3 and A8 on TG trafficking and energy metabolism. Unlike A3, A8 is expressed in adipose tissue as well as liver; therefore, we will use tissue-specific A8 KO mice to determine the function of A8 in the two tissues. We will then investigate the metabolic and molecular basis for the remarkable and unexpected increases in body temperature and basal metabolic rate observed in mice lacking both A3 and A8. In Aim 2 we will use monoclonal antibodies (mAbs) to assess the therapeutic potential of singly and jointly inactivating circulating A3 and A8. In Aim 3 we will use newly developed anti-A8 antibodies (Ab) to establish a sensitive and specific ELISA to quantify A8 in plasma. For these studies we will take advantage of a well-characterized population-based study that we established in Dallas, the Dallas Heart Study, to determine how plasma levels of A8 are related to metabolic and cardiovascular disease in humans. The reagents and expertise required for the studies outlined in this grant are already established in our laboratory. Successful completion of these studies will elucidate an important metabolic pathway and could provide the impetus for development of a new generation of lipid-lowering drugs that reduce plasma lipid levels and promote energy utilization. C/PPG 2015 – RP4 – 30-line Summary