title: The adipokine lipocalin 2 is regulated by obesity and promotes insulin resistance.
abstract: OBJECTIVE
  We identified lipocalin 2 (Lcn2) as a gene induced by dexamethasone and tumor necrosis factor-alpha in cultured adipocytes. The purpose of this study was to determine how expression of Lcn2 is regulated in fat cells and to ascertain whether Lcn2 could be involved in metabolic dysregulation associated with obesity.
  
  
  METHODS
  We examined Lcn2 expression in murine tissues and in 3T3-L1 adipocytes in the presence and absence of various stimuli. We used quantitative Western blotting to observe Lcn2 serum levels in lean and obese mouse models. To assess effects on insulin action, we used retroviral delivery of short hairpin RNA to reduce Lcn2 levels in 3T3-L1 adipocytes.
  
  
  RESULTS
  Lcn2 is highly expressed by fat cells in vivo and in vitro. Expression of Lcn2 is elevated by agents that promote insulin resistance and is reduced by thiazolidinediones. The expression of Lcn2 is induced during 3T3-L1 adipogenesis in a CCAAT/enhancer-binding protein-dependent manner. Lcn2 serum levels are elevated in multiple rodent models of obesity, and forced reduction of Lcn2 in 3T3-L1 adipocytes improves insulin action. Exogenous Lcn2 promotes insulin resistance in cultured hepatocytes.
  
  
  CONCLUSIONS
  Lcn2 is an adipokine with potential importance in insulin resistance associated with obesity.
authors.affiliation: Division of Endocrinology, Diabetes, and Metabolism, Beth Israel Deaconess Medical Center, Boston, MA 02115, USA.
authors.forename: Qing-Wu
authors.initials: QW
authors.lastname: Yan
authors.forename: Qin
authors.initials: Q
authors.lastname: Yang
authors.forename: Nimesh
authors.initials: N
authors.lastname: Mody
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Graham
authors.forename: Chung-Hsin
authors.initials: CH
authors.lastname: Hsu
authors.forename: Zhao
authors.initials: Z
authors.lastname: Xu
authors.forename: Nicholas E
authors.initials: NE
authors.lastname: Houstis
authors.forename: Barbara B
authors.initials: BB
authors.lastname: Kahn
authors.forename: Evan D
authors.initials: ED
authors.lastname: Rosen
mesh_terms: D016475:3T3 Cells; D000209:Acute-Phase Proteins / Q000235:genetics / Q000502:physiology*; D017667:Adipocytes / Q000187:drug effects / Q000502:physiology; D000273:Adipose Tissue / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002454:Cell Differentiation; D005786:Gene Expression Regulation; D007333:Insulin Resistance / Q000502:physiology; D008055:Lipids / Q000235:genetics; D000071068:Lipocalin-2; D054834:Lipocalins; D008264:Macrophages / Q000187:drug effects / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D009765:Obesity / Q000235:genetics / Q000503:physiopathology; D015513:Oncogene Proteins / Q000097:blood / Q000235:genetics / Q000502:physiology*; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000494:pharmacology; D017154:Stromal Cells / Q000187:drug effects / Q000502:physiology; D014162:Transfection
chemical_list: D000209:Acute-Phase Proteins; D008055:Lipids; D000071068:Lipocalin-2; D054834:Lipocalins; C086724:Lipofectamine; D015513:Oncogene Proteins; D011994:Recombinant Proteins; C071332:Lcn2 protein, mouse