Journal Article

Downregulation of AMPK Accompanies Leucine- and Glucose-Induced Increases in Protein Synthesis and Insulin Resistance in Rat Skeletal Muscle

Deoliveira, Rosangela, Brandon, Amanda E., Saha, Asish K., Kraegen, Edward W., Xu, X. Julia, Lawson, Ebony, Ruderman, Neil B.

2010

Overview

Branched-chain amino acids, such as leucine and glucose, stimulate protein synthesis and increase the phosphorylation and activity of the mammalian target of rapamycin (mTOR) and its downstream target p70S6 kinase (p70S6K). We examined in skeletal muscle whether the effects of leucine and glucose on these parameters and on insulin resistance are mediated by the fuel-sensing enzyme AMP-activated protein kinase (AMPK). Rat extensor digitorum longus (EDL) muscle was incubated with different concentrations of leucine and glucose with or without AMPK activators. Muscle obtained from glucose-infused rats was also used as a model. In the EDL, incubation with 100 or 200 μmol/l leucine versus no added leucine suppressed the activity of the α2 isoform of AMPK by 50 and 70%, respectively, and caused concentration-dependent increases in protein synthesis and mTOR and p70S6K phosphorylation. Very similar changes were observed in EDL incubated with 5.5 or 25 mmol/l versus no added glucose and in muscle of rats infused with glucose in vivo. Incubation of the EDL with the higher concentrations of both leucine and glucose also caused insulin resistance, reflected by a decrease in insulin-stimulated Akt phosphorylation. Coincubation with the AMPK activators AICAR and α-lipoic acid substantially prevented all of those changes and increased the phosphorylation of specific sites of mTOR inhibitors raptor and tuberous sclerosis complex 2 (TSC2). In contrast, decreases in AMPK activity induced by leucine and glucose were not associated with a decrease in raptor or TSC2 phosphorylation. The results indicate that both leucine and glucose modulate protein synthesis and mTOR/p70S6 and insulin signaling in skeletal muscle by a common mechanism. They also suggest that the effects of both molecules are associated with a decrease in AMPK activity and that AMPK activation prevents them.

• Publisher: American Diabetes Association
• Subject: Adenylate Kinase - metabolism / Aminoimidazole Carboxamide - analogs & derivatives / Aminoimidazole Carboxamide - metabolism / AMP-Activated Protein Kinases - metabolism / Animals / Antibodies / Biological and medical sciences / Biotechnology / Carrier Proteins - drug effects / Carrier Proteins - metabolism / Diabetes. Impaired glucose tolerance / Dose-Response Relationship, Drug / Down-Regulation - drug effects / Endocrine pancreas. Apud cells (diseases) / Endocrinopathies / Enzymes / Etiopathogenesis. Screening. Investigations. Target tissue resistance / Fluorides / Fundamental and applied biological sciences. Psychology / Glucose / Glucose - pharmacology / Insulin resistance / Insulin Resistance - physiology / Intracellular Signaling Peptides and Proteins - drug effects / Intracellular Signaling Peptides and Proteins - metabolism / Kinases / Kinetics / Lactates - metabolism / Leucine - pharmacology / Medical sciences / Metabolism / Muscle, Skeletal - drug effects / Muscle, Skeletal - enzymology / Musculoskeletal system / Peptides / Phosphoproteins - drug effects / Phosphoproteins - metabolism / Phosphorylation / Protein Serine-Threonine Kinases - drug effects / Protein Serine-Threonine Kinases - metabolism / Protein synthesis / Proteins / Pyruvates - metabolism / Rats / Research design / Ribonucleotides - metabolism / Ribosomal Protein S6 Kinases, 70-kDa - drug effects / Ribosomal Protein S6 Kinases, 70-kDa - metabolism / Striated muscle. Tendons / TOR Serine-Threonine Kinases / Vertebrates: osteoarticular system, musculoskeletal system