266-LB: Evidence for a Hexosamine Biosynthesis Pathway-Mediated Sp1 Cholesterolgenic Response Being an Early Etiological Factor of Insulin Resistance

Excess plasma membrane cholesterol-mediated cellular insulin resistance has been shown to result from increased hexosamine biosynthesis pathway (HBP) O-GlcNAcylation of the transcription factor Sp1 in 3T3-L1 adipocytes and L6 skeletal muscle myotubes. Here we tested the causal relationship between excess skeletal muscle membrane (SMM) cholesterol and insulin resistance, as well as probed the potential HBP/Sp1 link, in mice fed a Western-style high-fat diet for one week or in mice with targeted skeletal muscle overexpression of glucosamine-fructose aminotransferase (GFAT, the rate-limiting enzyme of the HBP). HF feeding increased SMM cholesterol and impaired GLUT4 regulation, glucose tolerance and insulin sensitivity within one week. These early skeletal muscle and systemic metabolic abnormalities were fully prevented in HF-fed mice treated during the one-week diet challenge with two subcutaneous injections of the cholesterol-depleting agent methyl-β-cyclodextrin. Consistent with in vitro data, an HBP-mediated Sp1 cholesterolgenic response contributing to SMM cholesterol accumulation, the transcription of HMG-CoA reductase, the rate-limiting enzyme in cholesterol biosynthesis, was increased in skeletal muscle from HF-fed mice. Furthermore, treating HF-fed mice during the one-week HF-feeding challenge with mithramycin, an agent that blocks Sp1 binding to DNA, prevented the SMM cholesterol buildup, glucose intolerance, and insulin resistance. Skeletal muscle GFAT overexpression also caused accumulation of SMM cholesterol, glucose intolerance, and insulin resistance.These data suggest that early skeletal muscle insulin resistance in the setting of HF feeding are a consequence of a HBP-mediated Sp1 cholesterolgenic transcriptional response and that targeting this pathway has therapeutic potential for preventing insulin resistance and the development of T2D. Disclosure B.A. Grice: None. J.D. Covert: None. A.M. Kreilach: None. M. Thornburg: None. L. Tackett: None. D. McClain: None. J.S. Elmendorf: None. Funding American Diabetes Association (1-15-BS-053 to J.S.E.); National Institutes of Health (R01DK114222-01A1, UL1TR001108T32, DK064466, T32GM077229, P30DK097512); Indiana University-Purdue University; Indianapolis Research Support Funds