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. 2007 Jun;56(6):1600-7.
doi: 10.2337/db06-1016. Epub 2007 Feb 28.

The Mammalian _target of rapamycin pathway regulates nutrient-sensitive glucose uptake in man

Michael Krebs  1 , Barbara Brunmair, Attila Brehm, Michaela Artwohl, Julia Szendroedi, Peter Nowotny, Erich Roth, Clemens Fürnsinn, Miriam Promintzer, Christian Anderwald, Martin Bischof, Michael Roden
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The Mammalian _target of rapamycin pathway regulates nutrient-sensitive glucose uptake in man

Michael Krebs et al. Diabetes. 2007 Jun.

Abstract

The nutrient-sensitive kinase mammalian _target of rapamycin (mTOR) and its downstream _target S6 kinase (S6K) are involved in amino acid-induced insulin resistance. Whether the mTOR/S6K pathway directly modulates glucose metabolism in humans is unknown. We studied 11 healthy men (29 years old, BMI 23 kg/m(2)) twice in random order after oral administration of 6 mg rapamycin, a specific mTOR inhibitor, or placebo. An amino acid mixture was infused to activate mTOR, and somatostatin-insulin-glucose clamps created conditions of low peripheral hyperinsulinemia (approximately 100 pmol/l, 0-180 min) and prandial-like peripheral hyperinsulinemia (approximately 450 pmol/l, 180-360 min). Glucose turnover was assessed using d-[6,6-(2)H(2)]glucose infusion (n = 8). Skeletal muscle biopsies were performed at baseline and during prandial-like peripheral hyperinsulinemia (n = 3). At low peripheral hyperinsulinemia, whole-body glucose uptake was not affected by rapamycin. During prandial-like peripheral hyperinsulinemia, rapamycin increased glucose uptake compared with placebo by 17% (R(d 300-360 min), 75 +/- 5 vs. 64 +/- 5 micromol x kg(-1) x min(-1), P = 0.0008). Rapamycin affected endogenous glucose production neither at baseline nor during low or prandial-like peripheral hyperinsulinemia. Combined hyperaminoacidemia and prandial-like hyperinsulinemia increased S6K phosphorylation and inhibitory insulin receptor substrate-1 (IRS-1) phosphorylation at Ser312 and Ser636 in the placebo group. Rapamycin partially inhibited this increase in mTOR-mediated S6K phosphorylation and IRS-1 Ser312 and Ser636 phosphorylation. In conclusion, rapamycin stimulates insulin-mediated glucose uptake in man under conditions known to activate the mTOR/S6K pathway.

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