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SIRT1 is a NAD+-dependent deacetylase thought to regulate cellular metabolic pathways in response to alterations in nutrient flux. In the current study we investigated whether acute changes in SIRT1 expression affect markers of muscle mitochondrial content and also determined whether SIRT1 influenced muscle insulin resistance induced by acute glucose oversupply. In male Wistar rats either SIRT1 or a deacetylase inactive mutant form (H363Y) was electroprated into the tibialis cranialis (TC) muscle. The other leg was electroporated with an empty control vector. One week later, glucose was infused and hyperglycaemia was maintained at ~11mM. After 5 hours, 11mM glucose induced significant insulin resistance in skeletal muscle. Interestingly, overexpression of either SIRT1 or SIRT1 (H363Y) for 1 week did not change markers of mitochondrial content or function. SIRT1 or SIRT1 (H363Y) overexpression had no effect on the reduction in glucose uptake and glycogen synthesis in muscle in response to hyperglycemia. Therefore we conclude that acute increases in SIRT1 protein have little impact on mitochondrial content and that overexpressing SIRT1 does not prevent the development of insulin resistance during hyperglycaemia. [ABSTRACT FROM AUTHOR]

Abstract: Glucose infusion into rats causes skeletal muscle insulin resistance that initially occurs without changes in insulin signaling. The aim of the current study was to prolong glucose infusion and evaluate other events associated with the transition to muscle insulin resistance. Hyperglycemia was produced in rats by glucose infusion for 3, 5 and 8h. The rate of infusion required to maintain hyperglycemia was reduced at 5 and 8h. Glucose uptake into red quadriceps (RQ) and its incorporation into glycogen decreased between 3 and 5h, further decreasing at 8h. The earliest observed change in RQ was decreased AMPKα2 activity associated with large increases in muscle glycogen content at 3h. Activation of the mTOR pathway occurred at 5h. Akt phosphorylation (Ser473) was decreased at 8h compared to 3 and 5, although no decrease in phosphorylation of downstream GSK-3β (Ser9) and AS160 (Thr642) was observed. White quadriceps showed a similar but delayed pattern, with insulin resistance developing by 8h and decreased AMPKα2 activity at 5h. These results indicate that, in the presence of a nutrient overload, alterations in muscle insulin signaling occur, but after insulin resistance develops and appropriate changes in energy/nutrient sensing pathways occur. [Copyright &y& Elsevier]