title: Liver X receptor agonists ameliorate TNFalpha-induced insulin resistance in murine brown adipocytes by downregulating protein tyrosine phosphatase-1B gene expression.
abstract: OBJECTIVE
  The nuclear receptors, including nuclear receptor subfamily 1, group H, member 3 (NR1HR, also known as liver X receptor [LXR]), are sensors of cholesterol metabolism and lipid biosynthesis that have recently been proposed as insulin sensitisers. TNFalpha has been described as a link between obesity and the development of insulin resistance, an important contributor to the pathogenesis of type 2 diabetes. Therefore, we decided to investigate the ability of NR1HR agonists to ameliorate TNFalpha-induced insulin resistance in brown adipocytes.
  
  
  METHODS
  Primary brown adipocytes from rat fetuses, and from wild-type neonate mice and neonate mice deficient in the gene encoding protein tyrosine phosphatase-1B (Ptpn1, also known as Ptp1b) were cultured in the absence or presence of TNFalpha and different nuclear receptor agonists. Among them, the unrelated NR1HR ligands T0901317, GW3965 and (22R)-hydroxycholesterol were tested. After insulin stimulation, glucose uptake and solute carrier family 2 (facilitated glucose transporter), member 4 (SLC2A4, formerly known as GLUT4) translocation were measured. Next the insulin signalling cascade was determined by submitting cells to lysis, immunoprecipitation and immunoblotting.
  
  
  RESULTS
  NR1HR agonists ameliorate TNFalpha-induced insulin resistance restoring completely insulin-stimulated glucose uptake and SLC2A4 translocation to plasma membrane. This effect is parallel to the recovery of the insulin cascade insulin receptor/IRS-2/phosphatidylinositol 3-kinase/protein kinase B, and could be due to the fact that T0901317 prevents the increase of PTPN1 production and phosphatase activity produced by TNFalpha. In this regard, Ptpn1-deficient brown adipocytes showed protection against insulin resistance by TNFalpha. Moreover, we observed that T0901317 produced in itself a significant increase over basal glucose uptake consistent with an increase of SLC2A4 protein content in plasma membrane, attributable to the activation of protein kinase zeta and/or the increase of Slc2a4 expression.
  
  
  CONCLUSIONS
  Nuclear receptors NR1HR are interesting potential targets for drug treatment of insulin resistance.
authors.affiliation: Department of Biochemistry and Molecular Biology II, Faculty of Pharmacy, Complutense University, Madrid, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Fernández-Veledo
authors.forename: I
authors.initials: I
authors.lastname: Nieto-Vazquez
authors.forename: C M
authors.initials: CM
authors.lastname: Rondinone
authors.forename: M
authors.initials: M
authors.lastname: Lorenzo
mesh_terms: D017667:Adipocytes / Q000187:drug effects / Q000502:physiology*; D002001:Adipose Tissue, Brown / Q000187:drug effects / Q000196:embryology / Q000201:enzymology / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D001692:Biological Transport / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000819:agonists* / Q000502:physiology; D005333:Fetus; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D005947:Glucose / Q000378:metabolism; D007333:Insulin Resistance / Q000502:physiology*; D000071518:Liver X Receptors; D051379:Mice; D018345:Mice, Knockout; D057093:Orphan Nuclear Receptors; D017027:Protein Tyrosine Phosphatases / Q000172:deficiency / Q000235:genetics*; D051381:Rats; D017208:Rats, Wistar; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists* / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D004268:DNA-Binding Proteins; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D014409:Tumor Necrosis Factor-alpha; D017027:Protein Tyrosine Phosphatases; D005947:Glucose