Colorado PROFILES, The Colorado Clinical and Translational Sciences Institute (CCTSI)
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Lipoprotein lipase in myocyte fuel partitioning

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Obesity and insulin resistance are reaching epidemic proportions in the United States.lntracellular accumulation of fatty acid-derived lipids is felt to be an important process in the pathogenesis of these disorders. Fatty acids are delivered to cells as either free fatty acids bound to albumin (FFA) or esterified in triglycerides (TG) carried by lipoproteins. Lipoprotein lipase (LPL) hydrolyzes lipoprotein TG, making lipoprotein-derived fatty acids (LPFA) available for uptake. It is not known whether LPFA and FFA are taken up and partitioned within cells by similar mechanisms, or whether their uptake and partitioning is separate. The following hypotheses will be investigated: 1) LPFA and FFA are taken up into separate intracellular pools, with LPFA initially committed to TG storage; 2) Enzymatic activity and physical Iocationof LPL specifically mediate the uptake/partitioning of LPFA independent of FFA uptake; an 3) Overexpression of LPL and lipoprotein TG hydrolysis both increase GLUT-1 mediated basal glucose uptake and/or phosphorylation to provide glucose for intracellular TG synthesis. Experiments will be carried out in an vitro model of LPFA and FFA delivery to cultured c2c12 and primary myocytes. Time courses of cell lipid accumulation and oxidation of these fatty acid types will be compared in control and LPL-overexpressing cells, before and after inhibition of LPL enzymatic activity or release of LPL from the cell surface. The role of CD36/FAT in the uptake and partitioning of LPFA and FFA will be assessed via inhibition. Glucose transport/phosphorylation mechanisms, and intracellular fate of glucose, will also be examined in the presence and absence of TG substrate in the culture medium. Results of these experiments will contribute to the understanding of intramyocellular lipid trafficking and how it relates to changes in glucose utilization in muscle. These studies have important implications for understanding the development of obesity, the metabolic syndrome and type 2 diabetes mellitus.

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