title: Glucagon like peptide-1-induced glucose metabolism in differentiated human muscle satellite cells is attenuated by hyperglycemia.
abstract: BACKGROUND
  Glucagon like peptide-1 (GLP-1) stimulates insulin secretion from the pancreas but also has extra-pancreatic effects. GLP-1 may stimulate glucose uptake in cultured muscle cells but the mechanism is not clearly defined. Furthermore, while the pancreatic effects of GLP-1 are glucose-dependent, the glucose-dependency of its extra-pancreatic effects has not been examined.
  
  
  METHODS
  Skeletal muscle satellite cells isolated from young (22.5 ± 0.97 yr), lean (BMI 22.5 ± 0.6 kg/m(2)), healthy males were differentiated in media containing either 22.5 mM (high) or 5 mM (normal) glucose for 7 days in the absence or presence of insulin and/or various GLP-1 concentrations. Myocellular effects of GLP-1, insulin and glucose were assessed by western-blot, glucose uptake and glycogen synthesis.
  
  
  RESULTS
  We firstly show that the GLP-1 receptor protein is expressed in differentiated human muscle satellite cells (myocytes). Secondly, we show that in 5 mM glucose media, exposure of myocytes to GLP-1 results in a dose dependent increase in glucose uptake, GLUT4 amount and subsequently glycogen synthesis in a PI3K dependent manner, independent of the insulin signaling cascade. Importantly, we provide evidence that differentiation of human satellite cells in hyperglycemic (22.5 mM glucose) conditions increases GLUT1 expression, and renders the cells insulin resistant and interestingly GLP-1 resistant in terms of glucose uptake and glycogen synthesis. Hyperglycemic conditions did not affect the ability of insulin to phosphorylate downstream targets, PKB or GSK3. Interestingly we show that at 5 mM glucose, GLP-1 increases GLUT4 protein levels and that this effect is abolished by hyperglycemia.
  
  
  CONCLUSIONS
  GLP-1 increases glucose uptake and glycogen synthesis into fully-differentiated human satellite cells in a PI3-K dependent mechanism potentially through increased GLUT4 protein levels. The latter occurs independently of the insulin signaling pathway. Attenuation of both GLP-1 and insulin-induced glucose metabolism by hyperglycemia is likely to occur downstream of PI3K.
authors.affiliation: The Centre of Inflammation and Metabolism at Department of Infectious Diseases and Copenhagen Muscle Research Centre, Rigshospitalet, The Faculty of Health Sciences, University of Copenhagen, Denmark. cgreen@inflammation-metabolism.dk
authors.forename: Charlotte J
authors.initials: CJ
authors.lastname: Green
authors.forename: Tora I
authors.initials: TI
authors.lastname: Henriksen
authors.forename: Bente K
authors.initials: BK
authors.lastname: Pedersen
authors.forename: Thomas P J
authors.initials: TP
authors.lastname: Solomon
mesh_terms: D002454:Cell Differentiation / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D052216:Glucagon-Like Peptide 1 / Q000494:pharmacology*; D000067757:Glucagon-Like Peptide-1 Receptor; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D006943:Hyperglycemia / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D018027:Receptors, Glucagon / Q000378:metabolism; D032496:Satellite Cells, Skeletal Muscle / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D055815:Young Adult
chemical_list: C000593833:GLP1R protein, human; D000067757:Glucagon-Like Peptide-1 Receptor; D007328:Insulin; D018027:Receptors, Glucagon; D052216:Glucagon-Like Peptide 1; D006003:Glycogen; D005947:Glucose