Acyl-CoA synthetase-mediated regulation of lipid homeostasis

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PROJECT SUMMARY / ABSTRACT Systemic lipid homeostasis is controlled by the liver via complex but precisely regulated biochemical, signaling, and cellular pathways. In obesity, hepatic lipid metabolism is altered, commonly leading to the pathogenic accumulation of triacylglycerol and to a spectrum of liver disorders known as non-alcoholic fatty liver disease (NAFLD). NAFLD is considered the hepatic manifestation of metabolic syndrome; as such, it often occurs in a setting of insulin resistance and is associated with type 2 diabetes, dyslipidemia, and cardiovascular disease. It is the most prevalent chronic liver disease worldwide, for which there is no approved pharmacotherapy. The etiology of NAFLD is still unclear and advances in understanding the molecular mechanisms leading to hepatic triacylglycerol accumulation are critical to the development of targeted therapies. Within the hepatocyte, free fatty acid molecules experience one of several metabolic fates, including synthesis of complex lipids and oxidation. An obligatory step in the metabolism of long-chain fatty acids is its activation by thioesterification to CoA to form acyl-CoA. This reaction is catalyzed by the acyl-CoA synthetase (ACSL) enzymes. The specific tissue distributions, subcellular locations, and substrate preferences suggest that individual ACSL isoforms have distinct metabolic functions in partitioning acyl-CoAs into specific metabolic pathways. ACSL3 and ACSL5 isoforms are highly expressed in human and murine livers and studies in cell systems suggest that these enzymes promote lipogenesis. However, to date, the metabolic roles of ACSL3 and ACSL5 in the liver in vivo remain unresolved. We hypothesize that ACSL3 and ACSL5 function in the liver to direct acyl-CoA towards lipid synthesis and away from oxidative pathways, thereby promoting hepatic triacylglycerol accumulation and VLDL secretion. In Aim 1, we will use AAV-CRISPR/Cas9 technology to generate the first liver-specific knockout mice for Acsl3 and Acsl5 to test the hypothesis that ACSL3 and ACSL5 activities in the liver contribute to the synthesis of triacylglycerol, which in turn leads to hepatic steatosis and hypertriglyceridemia. In Aim 2, we will establish the roles of ACSL3 and ACSL5 in human NAFLD pathogenesis by using AAV-CRISPR/Cas9 to achieve liver-specific knockout of ACSL3 and ACSL5 in human liver chimeric mice. The proposed research delineates hepatocellular basis contributing to the progression of metabolic diseases, which is clinically important as it provides new targets for the management of obesity-related disorders such as NAFLD and dyslipidemia. In addition, this project provides an intensive research career development training opportunity under the guidance of experienced mentors in an outstanding scientific environment. This will allow me to consolidate and launch my independent research program dedicated to the understanding of the molecular basis for human metabolic disorders. The successful completion of these studies will: (i) provide me with knowledge and skills in liver-targeted genome engineering and its application to clinically relevant human liver disorders; and (ii) inform an NIH R01 application for the study of pathophysiological mechanisms that regulate hepatic lipid homeostasis.