title: Loss-of-function mutation in myostatin reduces tumor necrosis factor alpha production and protects liver against obesity-induced insulin resistance.
abstract: OBJECTIVE
  Insulin resistance develops in tandem with obesity. Ablating myostatin (Mstn) prevents obesity, so we investigated if Mstn deficiency could improve insulin sensitivity. A loss-of-function mutation (Mstn(Ln)) in either one or both alleles of the Mstn gene shows how Mstn deficiency protects whole-body insulin sensitivity.
  
  
  METHODS
  Mstn(Ln/Ln) mice were weaned onto a high-fat diet (HFD) or standard diet. HFD-fed Mstn(Ln/Ln) mice exhibited high lean, low-fat body compositions compared with wild types. Wild-type and heterozygous and homozygous mutant mice were bled to determine basal levels of insulin, glucose, and homeostasis model assessment of insulin resistance. To evaluate postprandial insulin sensitivity between animals of a similar size, glucose and insulin tolerance tests and hyperinsulinemic-euglycemic clamp studies were performed with heterozygous and homozygous mutant mice. Quantitative RT-PCR quantified TNF proportional, variant, IL-6, IL-1beta, F4/80, GPR43, and CD36 expression in muscle, fat, and liver. Histological analysis measured hepatosteatosis.
  
  
  RESULTS
  Homozygous mutants were glucose tolerant and protected against overall insulin resistance compared with heterozygous mice. Hyperinsulinemic-euglycemic clamp studies revealed a dramatically improved glucose infusion rate, glucose disposal rate, and hepatic glucose production in 11-month-old Mstn(Ln/Ln) mice on an HFD. Improvements to muscle and liver insulin sensitivity (approximately 200-400%) correlated with 50-75% decreased tumor necrosis factor (TNF)alpha production and coincided with severe Mstn deficiency. Hepatosteatosis appeared to be ameliorated. Short-term treatment of Mstn(Ln/Ln) mice with recombinant Mstn led to increased plasma TNFalpha and insulin resistance.
  
  
  CONCLUSIONS
  We find that severe Mstn deficiency caused by Ln (lean) mutations in HFD-fed mice protects muscle and liver against obesity-induced insulin resistance.
authors.affiliation: Department of Cell Biology, Scripps Research Institute, La Jolla, California, USA.
authors.forename: Jason J
authors.initials: JJ
authors.lastname: Wilkes
authors.forename: David J
authors.initials: DJ
authors.lastname: Lloyd
authors.forename: Nick
authors.initials: N
authors.lastname: Gekakis
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D018955:CD36 Antigens / Q000235:genetics; D017931:DNA Primers; D004041:Dietary Fats / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism*; D015309:Glucose Clamp Technique; D006579:Heterozygote; D006720:Homozygote; D007333:Insulin Resistance / Q000235:genetics / Q000502:physiology*; D008099:Liver / Q000378:metabolism / Q000502:physiology*; D024821:Metabolic Syndrome / Q000517:prevention & control*; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D018482:Muscle, Skeletal / Q000502:physiology; D009154:Mutation; D055435:Myostatin / Q000235:genetics*; D009765:Obesity / Q000235:genetics / Q000503:physiopathology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D001786:Blood Glucose; D018955:CD36 Antigens; D017931:DNA Primers; D004041:Dietary Fats; D055435:Myostatin; D014409:Tumor Necrosis Factor-alpha; D005947:Glucose