title: Macrophage deletion of SOCS1 increases sensitivity to LPS and palmitic acid and results in systemic inflammation and hepatic insulin resistance.
abstract: OBJECTIVE
  Macrophage secretion of proinflammatory cytokines contributes to the pathogenesis of obesity-related insulin resistance. An important regulator of inflammation is the suppressor of cytokine signaling-1 (SOCS1), which inhibits the JAK-STAT and toll-like receptor-4 (TLR4) pathways. Despite the reported role of SOCS1 in inhibiting insulin signaling, it is surprising that a SOCS1 polymorphism that increases SOCS1 promoter activity is associated with enhanced insulin sensitivity despite obesity. In the current study, we investigated the physiological role of myeloid and lymphoid cell SOCS1 in regulating inflammation and insulin sensitivity.
  
  
  METHODS
  We used mice generated by crossing SOCS1 floxed mice with mice expressing Cre recombinase under the control of the LysM-Cre promoter (SOCS1 LysM-Cre). These mice have deletion of SOCS1 in macrophages and lymphocytes. We assessed macrophage inflammation using flow cytometry and serum cytokine levels using Bioplex assays. We then measured insulin sensitivity using glucose tolerance tests and the euglycemic-hyperinsulinemic clamp. Using bone marrow-derived macrophages, we tested the effects of SOCS1 deletion in regulating responses to the TLR4 ligands: lipopolysaccharide (LPS) and palmitic acid.
  
  
  RESULTS
  SOCS1 LysM-Cre mice had increased macrophage expression of CD11c, enhanced sensitivity to LPS, and palmitic acid and increased serum concentrations of tumor necrosis factor-α, interleukin-6, and monocyte chemoattractant protein. Increased inflammation was associated with impaired glucose tolerance and hyperinsulinemia as a result of reduced hepatic but not skeletal muscle insulin sensitivity.
  
  
  CONCLUSIONS
  The expression of SOCS1 in hematopoietic cells protects mice against systemic inflammation and hepatic insulin resistance potentially by inhibiting LPS and palmitate-induced TLR4 signaling in macrophages.
authors.affiliation: St. Vincent’s Institute of Medical Research and Department of Medicine, University of Melbourne, Fitzroy, Victoria, Australia.
authors.forename: Nirupa
authors.initials: N
authors.lastname: Sachithanandan
authors.forename: Kate L
authors.initials: KL
authors.lastname: Graham
authors.forename: Sandra
authors.initials: S
authors.lastname: Galic
authors.forename: Jane E
authors.initials: JE
authors.lastname: Honeyman
authors.forename: Stacey L
authors.initials: SL
authors.lastname: Fynch
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Hewitt
authors.forename: Gregory R
authors.initials: GR
authors.lastname: Steinberg
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Kay
mesh_terms: D000818:Animals; D007249:Inflammation / Q000276:immunology; D007328:Insulin; D007333:Insulin Resistance / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008099:Liver / Q000378:metabolism; D008264:Macrophages / Q000502:physiology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D019308:Palmitic Acid / Q000494:pharmacology; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics*; D051193:Toll-Like Receptors / Q000502:physiology
chemical_list: D007328:Insulin; D008070:Lipopolysaccharides; C491590:Socs1 protein, mouse; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D051193:Toll-Like Receptors; D019308:Palmitic Acid