title: IGFBP-2 inhibits adipogenesis and lipogenesis in human visceral, but not subcutaneous, adipocytes.
abstract: OBJECTIVE
  IGF-binding protein (IGFBP)-2 is the principal IGFBP produced by white adipocytes during adipogenesis, and circulating levels are reduced in obesity. Overexpression of IGFBP-2 in transgenic mice prevents obesity, but depot-specific effects of IGFBP-2 on adipo/lipogenesis are unknown. The present study aimed to investigate whether IGFBP-2 affects adipo/lipogenesis in a depot-specific manner and explore potential mechanisms.
  
  
  METHODS
  Following adipocyte characterisation, IGFBP-2 levels were measured from human subcutaneous and visceral preadipocytes, and IGFBP-2 dose-responses were then undertaken with exogenous IGFBP-2 in an in vitro IGF-I-free system to examine adipo/lipogenesis. Following this, both types of adipocytes were transfected with human siRNA IGFBP-2 to assess auto-/para-/intra-crine effects, with and without additional add-back IGFBP-2. To elucidate the potential mechanisms, visceral preadipocytes were treated with either wild-type or Heparin Binding Domain (HBD)-mutant IGFBP-2 (which is unable to bind to cell-surface components), and experiments were also undertaken using Echistatin (an integrin receptor blocker). Outcomes included gene expression profiles, protein levels and phosphorylation and lipid staining.
  
  
  RESULTS
  Human visceral adipocytes produced significantly more IGFBP-2 than subcutaneous adipocytes. Subsequent dose-responses to IGFBP-2 demonstrated significant reductions in adipo/lipogenesis in visceral, but not subcutaneous, adipocytes in response to increasing IGFBP-2. Silencing IGFBP-2 resulted in exaggerated adipo/lipogenesis in visceral, but not subcutaneous, adipocytes, an effect completely inhibited by add-back IGFBP-2. These effects occurred in the absence of changes in IGF-I levels. HBD-mutant IGFBP-2 had reduced effects compared with wild-type IGFBP-2. Wild-type IGFBP-2 increased phosphorylation of focal adhesion kinase (FAK) and decreased phosphatase and tensin homolog (PTEN) levels, suggestive of integrin-mediated signalling. Blockade of this signalling, using Echistatin, completely negated the effects of IGFBP-2 on visceral adipo/lipogenesis.
  
  
  CONCLUSIONS
  IGFBP-2 inhibits both adipogenesis and lipogenesis in visceral, but not subcutaneous, adipocytes. This depot-specific impairment appears to be independent of IGF-I and involves cell-surface association of IGFBP-2 and activation of integrin signalling pathways.
authors.affiliation: 1] Centre for Hormone Research, Murdoch Childrens Research Institute and Royal Children's Hospital, Melbourne, Victoria, Australia [2] Department of Paediatrics, University of Melbourne, Melbourne, Victoria, Australia [3] Department of Physiology, Monash University, Melbourne, Victoria, Australia.
authors.forename: S W
authors.initials: SW
authors.lastname: Yau
authors.affiliation: 1] Centre for Hormone Research, Murdoch Childrens Research Institute and Royal Children's Hospital, Melbourne, Victoria, Australia [2] Department of Paediatrics, University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: V C
authors.initials: VC
authors.lastname: Russo
authors.affiliation: Department of Physiology, Monash University, Melbourne, Victoria, Australia.
authors.forename: I J
authors.initials: IJ
authors.lastname: Clarke
authors.affiliation: Faculty of Veterinary and Agricultural Sciences, University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: F R
authors.initials: FR
authors.lastname: Dunshea
authors.affiliation: 1] Centre for Hormone Research, Murdoch Childrens Research Institute and Royal Children's Hospital, Melbourne, Victoria, Australia [2] Department of Paediatrics, University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: G A
authors.initials: GA
authors.lastname: Werther
authors.affiliation: 1] Centre for Hormone Research, Murdoch Childrens Research Institute and Royal Children's Hospital, Melbourne, Victoria, Australia [2] Department of Paediatrics, University of Melbourne, Melbourne, Victoria, Australia [3] Department of Physiology, Monash University, Melbourne, Victoria, Australia.
authors.forename: M A
authors.initials: MA
authors.lastname: Sabin
mesh_terms: D017667:Adipocytes / Q000378:metabolism; D050156:Adipogenesis / Q000187:drug effects*; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D006801:Humans; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins; D050152:Intra-Abdominal Fat / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D050155:Lipogenesis / Q000187:drug effects; D051379:Mice; D008822:Mice, Transgenic; D010455:Peptides / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*
chemical_list: D018971:Insulin-Like Growth Factor Binding Protein 2; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D010975:Platelet Aggregation Inhibitors; C057986:echistatin; D007334:Insulin-Like Growth Factor I