title: The suppressor of cytokine signaling 3 inhibits leptin activation of AMP-kinase in cultured skeletal muscle of obese humans.
abstract: BACKGROUND
  Leptin is thought to regulate whole-body adiposity and insulin sensitivity, at least in part, by stimulating fatty acid metabolism via activation of AMP-kinase (AMPK) in skeletal muscle. Human obesity is associated with leptin resistance, and recent studies have demonstrated that hypothalamic expression of the suppressors of cytokine signaling 3 (SOCS3) regulates leptin sensitivity in rodents.
  
  
  OBJECTIVE
  The objective of the study was to investigate the effects of leptin on fatty acid oxidation and AMPK signaling in primary myotubes derived from lean and obese skeletal muscle and evaluate the contribution of SOCS3 to leptin resistance and AMPK signaling in obese humans.
  
  
  RESULTS
  We demonstrate that leptin stimulates AMPK activity and increases AMPK Thr172 and acetyl-CoA carboxylase-beta Ser222 phosphorylation and fatty acid oxidation in lean myotubes but that in obese subjects leptin-dependent AMPK signaling and fatty acid oxidation are suppressed. Reduced activation of AMPK was associated with elevated expression of IL-6 ( approximately 3.5-fold) and SOCS3 mRNA ( approximately 2.5-fold) in myotubes of obese subjects. Overexpression of SOCS3 via adenovirus-mediated infection in lean myotubes to a similar degree as observed in obese myotubes prevented leptin but not AICAR (5-amino-imidazole-4-carboxamide-1-beta-d-ribofuranoside) activation of AMPK signaling.
  
  
  CONCLUSIONS
  These data demonstrate that SOCS3 inhibits leptin activation of AMPK. These data suggest that this impairment of leptin signaling in skeletal muscle may contribute to the aberrant regulation of fatty acid metabolism observed in obesity and that pharmacological activation of AMPK may be an effective therapy to bypass SOCS3-mediated skeletal muscle leptin resistance for the treatment of obesity-related disorders.
authors.affiliation: St. Vincent's Institute, 9 Princes Street, Fitzroy, Victoria 3065, Australia. gsteinberg@svi.edu.au
authors.forename: Gregory R
authors.initials: GR
authors.lastname: Steinberg
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: McAinch
authors.forename: Michael B
authors.initials: MB
authors.lastname: Chen
authors.forename: Paul E
authors.initials: PE
authors.lastname: O'Brien
authors.forename: John B
authors.initials: JB
authors.lastname: Dixon
authors.forename: David
authors.initials: D
authors.lastname: Cameron-Smith
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Kemp
mesh_terms: D000263:Adenylate Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000328:Adult; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D004789:Enzyme Activation; D005260:Female; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D020738:Leptin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008297:Male; D018485:Muscle Fibers, Skeletal; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism*; D009765:Obesity / Q000201:enzymology / Q000378:metabolism*; D010168:Palmitates / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012265:Ribonucleotides / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*
chemical_list: D007004:Hypoglycemic Agents; D020738:Leptin; D010168:Palmitates; D012333:RNA, Messenger; D012265:Ribonucleotides; C106644:SOCS3 protein, human; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D000620:Aminoimidazole Carboxamide; D000263:Adenylate Kinase; C031143:AICA ribonucleotide