Resistin Knockout Mice Exhibit Impaired Adipocyte Glucose-Dependent Insulinotropic Polypeptide Receptor (GIPR) Expression

  1. Christopher H.S. McIntosh
  1. Department of Cellular & Physiological Sciences and the Diabetes Research Group, Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada
  1. Corresponding author: Christopher H.S. McIntosh, mcintoch{at}mail.ubc.ca

Abstract

Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone that also plays a regulatory role in fat metabolism. In 3T3-L1 cells, resistin was demonstrated to be a key mediator of GIP stimulation of lipoprotein lipase (LPL) activity, involving activation of protein kinase B (PKB) and reduced phosphorylation of liver kinase B1 (LKB1) and AMP-activated protein kinase (AMPK). The current study was initiated to determine whether resistin has additional roles in GIP-regulated adipocyte functions. Analysis of primary adipocytes isolated from Retn−/−, Retn+/−, and Retn+/+ mice found that GIP stimulated the PKB/LKB1/AMPK/LPL pathway and fatty acid uptake only in Retn+/+ adipocytes, suggesting that GIP signaling and/or GIP responsiveness were compromised in Retn+/− and Retn−/− adipocytes. GIP receptor (GIPR) protein and mRNA were decreased in Retn+/− and Retn−/− adipocytes, but resistin treatment rescued LPL responsiveness to GIP. In addition, genes encoding tumor necrosis factor (TNF), TNF receptor 2 (TNFR2), and the signaling proteins stress-activated protein kinase (SAPK)/Jun NH2-terminal kinase (JNK), were downregulated, and phosphorylated levels of SAPK/JNK/c-Jun were decreased in Retn−/− mice. Chromatin immunoprecipitation assays were used to identify a 12-O-tetradecanoylphorbol-13-acetate (TPA)-response element (TRE-III) responsible for c-Jun–mediated transcriptional activation of Gipr. Blunted GIP responsiveness in Retn+/− and Retn−/− adipocytes was therefore largely due to the greatly reduced GIPR expression associated with decreased c-Jun–mediated transcriptional activation of Gipr.

Footnotes

  • Received February 28, 2012.
  • Accepted July 26, 2012.

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  1. Diabetes vol. 62 no. 2 471-477
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