title: Effect of TNF-Alpha on Caveolin-1  Expression and Insulin Signaling During  Adipocyte Differentiation and in Mature  Adipocytes.
abstract: OBJECTIVE
  Tumor necrosis factor-α (TNF-α)-mediated chronic low-grade inflammation of adipose tissue is associated with obesity and insulin resistance. Caveolin-1 (Cav-1) is the central component of adipocyte caveolae and has an essential role in the regulation of insulin signaling. The effects of TNF-α on Cav-1 expression and insulin signaling during adipocyte differentiation and in mature adipocytes were studied.
  
  
  METHODS
  3T3-L1 cells were differentiated (21 days) in the presence TNF-α (10 ng/mL) and mature adipocytes were also treated with TNF-α for 48 hours. Cav-1 and insulin receptor (IR) gene methylation were determined as well as Cav-1, IR, PKB/AKT-2 and Glut-4 expression and activation by real time RT-PCR and western blot. Baseline and insulin-induced glucose uptake was measured by the 2-[C14]-deoxyglucose uptake assay.
  
  
  RESULTS
  TNF-α slowed down the differentiation program, hindering the expression of some insulin signaling intermediates without fully eliminating insulin-mediated glucose uptake. In mature adipocytes, TNF-α did not compromise lipid-storage capacity, but downregulated the expression of the insulin signaling intermediates, totally blocking insulin-mediated glucose uptake. Insulin sensitivity correlated with the level of activated phospho-Cav-1 in both situations, strongly suggesting the direct contribution of Cav-1 to the maintenance of this physiological response.
  
  
  CONCLUSIONS
  Cav-1 activation by phosphorylation seems to be essential for the maintenance of an active and insulin-sensitive glucose uptake.
authors.forename: Sara
authors.initials: S
authors.lastname: Palacios-Ortega
authors.forename: Maider
authors.initials: M
authors.lastname: Varela-Guruceaga
authors.forename: Miriam
authors.initials: M
authors.lastname: Algarabel
authors.forename: Fermín
authors.initials: F
authors.lastname: Ignacio Milagro
authors.forename: J
authors.initials: J
authors.lastname: Alfredo Martínez
authors.forename: Carlos
authors.initials: C
authors.lastname: de Miguel
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology* / Q000378:metabolism; D050156:Adipogenesis; D054392:Adipokines / Q000378:metabolism; D000818:Animals; D051242:Caveolin 1 / Q000235:genetics* / Q000378:metabolism; D002470:Cell Survival; D019175:DNA Methylation; D005786:Gene Expression Regulation; D005947:Glucose / Q000378:metabolism; D007328:Insulin / Q000378:metabolism*; D007333:Insulin Resistance; D050356:Lipid Metabolism; D051379:Mice; D010766:Phosphorylation; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D054392:Adipokines; D051242:Caveolin 1; D007328:Insulin; D014409:Tumor Necrosis Factor-alpha; D005947:Glucose