Increased Phosphorylation of Skeletal Muscle Glycogen Synthase at NH2-Terminal Sites During Physiological Hyperinsulinemia in Type 2 Diabetes

• Published in: Diabetes (New York, N.Y.) Vol. 52; no. 6; pp. 1393 - 1402
• Main Authors: Højlund, Kurt, Staehr, Peter, Hansen, Bo Falck, Green, Kevin A, Hardie, D Grahame, Richter, Erik A, Beck-Nielsen, Henning, Wojtaszewski, Jørgen F P
• Format: Journal Article
• Language: English
• Published: Alexandria, VA American Diabetes Association 01.06.2003
• Subjects: Adipose Tissue - anatomy & histology; Binding Sites; Biological and medical sciences; Blood Glucose - metabolism; Body Mass Index; Diabetes Mellitus, Type 2 - blood; Diabetes Mellitus, Type 2 - physiopathology; Fundamental and applied biological sciences. Psychology; Glycated Hemoglobin A - analysis; Glycogen Synthase - chemistry; Glycogen Synthase - drug effects; Glycogen Synthase - metabolism; Humans; Hyperinsulinism - chemically induced; Hyperinsulinism - physiopathology; Infusions, Intravenous; Insulin - administration & dosage; Insulin - pharmacology; Insulin Receptor Substrate Proteins; Lipids - blood; Male; Middle Aged; Muscle, Skeletal - drug effects; Muscle, Skeletal - enzymology; Phosphatidylinositol 3-Kinases - metabolism; Phosphoproteins - metabolism; Phosphorylation; Reference Values
• ISSN: 0012-1797; 1939-327X
• DOI: 10.2337/diabetes.52.6.1393

Increased Phosphorylation of Skeletal Muscle Glycogen Synthase at NH 2 -Terminal Sites During Physiological Hyperinsulinemia in Type 2 Diabetes Kurt Højlund 1 , Peter Stæhr 1 , Bo Falck Hansen 2 , Kevin A. Green 3 , D. Grahame Hardie 3 , Erik A. Richter 4 , Henning Beck-Nielsen 1 and Jørgen F.P. Wojtaszewski 4 1 Diabetes Research Centre, University of Southern Denmark and Department of Endocrinology, Odense University Hospital, Odense, Denmark 2 Diabetes Biology, Novo Nordisk, Bagsvaerd, Denmark 3 Wellcome Trust Biocentre, Division of Molecular Physiology, School of Life Sciences, Dundee University, Dundee, Scotland, U.K 4 Copenhagen Muscle Research Centre, Institute of Exercise and Sport Sciences, Department of Human Physiology, University of Copenhagen, Copenhagen, Denmark Abstract In type 2 diabetes, insulin activation of muscle glycogen synthase (GS) is impaired. This defect plays a major role for the development of insulin resistance and hyperglycemia. In animal muscle, insulin activates GS by reducing phosphorylation at both NH 2 - and COOH-terminal sites, but the mechanism involved in human muscle and the defect in type 2 diabetes remain unclear. We studied the effect of insulin at physiological concentrations on glucose metabolism, insulin signaling and phosphorylation of GS in skeletal muscle from type 2 diabetic and well-matched control subjects during euglycemic-hyperinsulinemic clamps. Analysis using phospho-specific antibodies revealed that insulin decreases phosphorylation of sites 3a + 3b in human muscle, and this was accompanied by activation of Akt and inhibition of glycogen synthase kinase-3α. In type 2 diabetic subjects these effects of insulin were fully intact. Despite that, insulin-mediated glucose disposal and storage were reduced and activation of GS was virtually absent in type 2 diabetic subjects. Insulin did not decrease phosphorylation of sites 2 + 2a in healthy human muscle, whereas in diabetic muscle insulin infusion in fact caused a marked increase in the phosphorylation of sites 2 + 2a. This phosphorylation abnormality likely caused the impaired GS activation and glucose storage, thereby contributing to skeletal muscle insulin resistance, and may therefore play a pathophysiological role in type 2 diabetes. Footnotes Address correspondence and reprint requests to Kurt Højlund, MD, Department of Endocrinology, Odense University Hospital, Kloevervaenget 6, DK-5000, Odense C, Denmark. E-mail: k.hojlund{at}dadlnet.dk . Received for publication 16 May 2002 and accepted in revised form 10 March 2003. AMPK, AMP-activated protein kinase; ECL, enhanced chemiluminescence; FFA, free fatty acid; G6P, glucose-6-phosphate; GDR, glucose disposal rate; GS, glycogen synthase; GSK-3, glycogen synthase kinase-3; PI 3-kinase; phosphatidylinositol 3-kinase; PKC, protein kinase C; PP2A C , catalytic subunit of protein phosphatase 2A; TBST, Tris-buffered saline with Tween. DIABETES