Abstract | BACKGROUND/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. CONCLUSION:
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.
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Authors | S W Yau, V C Russo, I J Clarke, F R Dunshea, G A Werther, M A Sabin |
Journal | International journal of obesity (2005)
(Int J Obes (Lond))
Vol. 39
Issue 5
Pg. 770-81
(May 2015)
ISSN: 1476-5497 [Electronic] England |
PMID | 25370576
(Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
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Chemical References |
- Insulin-Like Growth Factor Binding Protein 2
- Intercellular Signaling Peptides and Proteins
- Peptides
- Platelet Aggregation Inhibitors
- echistatin
- Insulin-Like Growth Factor I
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Topics |
- Adipocytes
(metabolism)
- Adipogenesis
(drug effects)
- Animals
- Cell Differentiation
(drug effects)
- Cells, Cultured
- Gene Expression Regulation
- Humans
- Insulin-Like Growth Factor Binding Protein 2
(pharmacology)
- Insulin-Like Growth Factor I
(metabolism)
- Intercellular Signaling Peptides and Proteins
- Intra-Abdominal Fat
(drug effects, metabolism, physiopathology)
- Lipogenesis
(drug effects)
- Mice
- Mice, Transgenic
- Peptides
(pharmacology)
- Phosphorylation
(drug effects)
- Platelet Aggregation Inhibitors
(pharmacology)
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