Regulation of Hepatic Lipogenesis by a Mitochondrial Pyruvate Carrier-Citrate Carrier Axis

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Project Summary Aberrant hepatic de novo synthesis of fatty acids and cholesterol is a major contributor to serum hyperlipidemia in obesity and type 2 diabetes. Carbohydrates are a major carbon source for lipogenesis. Citrate, generated in the mitochondrial matrix, occupies a key node linking carbohydrate availability to lipogenesis. The mitochondrial pyruvate carrier (MPC) gates matrix entry of pyruvate for citrate synthesis and the mitochondrial citrate carrier (CIC) controls its export to the cytosol for lipogenesis. Here we propose that a novel MPC-CIC axis that controls the flux of glucose derived carbons to lipogenesis through modulation and cellular distribution of citrate. Our preliminary data indicate that liver specific loss of the MPC have decreased pyruvate flux into citrate and improved serum lipids. In addition, we have generated novel CIC liver specific knockout mice. Initial characterization reveal that these mice have decreased serum cholesterol, consistent with its pro-lipogenic role. The overall goal of this application is to delineate mechanisms through which the MPC-CIC axis controls hepatic lipogenesis in T2D. This goal will be addressed by pursuing two specific aims: (1) To determine the contribution of the MPC-CIC axis to hepatic lipogenesis in T2D and (2) To determine the regulation of the MPC-CIC axis by nutritional-hormonal status. The studies in Aim 1 will test the hypothesis that the MPC-CIC drives excess lipogenesis and contributes to serum dyslipidemia in T2D. The studies in Aim 2 will test the hypothesis that (1) the activity of the CIC is modulated by glucose and insulin, and (2) that alternative substrates can bypass regulatory nodes of the MPC-CIC axis to partially sustain lipogenesis. This research is significant because successful completion will provide critical information on the role of the mitochondrial carrier system in obesity associated dyslipidemia. This research is innovative because the it will be the first study to examine CIC in vivo and investigate a role of the MPC-CIC axis in hepatic lipogenesis. We expect that these studies will describe a new paradigm to understand the dyslipidemic effects of obesity.