Resistin messenger-RNA expression is increased by proinflammatory cytokines in vitro☆

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Abstract

Resistin is a recently discovered polypeptide that induces insulin resistance in rodents. While in rodents resistin is predominantly expressed in adipocytes, in humans peripheral blood mononuclear cells (PBMC) seem to a be a major source of resistin. In the present study, we show that in human PBMC resistin mRNA expression—determined by fluorescence-based real-time polymerase chain reaction—is strongly increased by the proinflammatory cytokines interleukin (IL)-1, IL-6, tumor necrosis factor α (TNF-α), and also by lipopolysaccharides (LPS), respectively, while no effect was found by interferon-γ (IFN-γ) or leptin. Our results suggest that in humans resistin may be a link in the well-known association between inflammation and insulin resistance.

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Materials and methods

Cell culture. PBMC were isolated from heparinized blood of healthy volunteers by density gradient centrifugation through Ficoll–Hypaque (Sigma, St. Louis, MO). Cells were washed three times in RPMI 1640 (Gibco Life Technologies, Lofer, Austria) and subsequently used for experiments. About 4 × 106 cells were resuspended in 4 ml RPMI 1640 (Sigma) in polypropylene round bottom tubes (Falcon, Franklin Lakes, NJ). PBMC were exposed to IL-1β (PeproTech EC, London, UK), IL-6 (PeproTech), TNF-α

Results

PBMC were either unstimulated or were exposed to IL-1β for 6, 12, and 24 h at concentrations of 1, 10, and 100 ng/ml, respectively. Resistin/GAPDH cDNA ratios were significantly increased up to 4-fold in a dose-dependent manner at concentrations of 10 and 100 ng/ml after 6 h exposure and at all tested concentrations after 12 and 24 h exposure (Fig. 1A).

When PBMC were exposed to IL-6, resistin/GAPDH cDNA ratio significantly increased 2.5-fold at a concentration of 500 pg/ml after a 6 h exposure period.

Discussion

It has been speculated that obesity might be associated with low-grade systemic inflammatory condition. Mediators of inflammation including IL-6, TNF-α, and leptin are elevated in overweight children and adults [13], [14]. Obesity is frequently associated with insulin resistance or manifest diabetes mellitus. Several substances including leptin, TNF-α, adiponectin, IL-6, and the recently discovered protein resistin [2], [3] are thought to contribute to insulin resistance in obesity [1]. In

Acknowledgements

The authors thank Karin Salzmann and Barbara Enrich for experimental assistance. This work was supported by Grant No. 53 of the Medizinischer Forschungsfonds (MFF) Tirol (to S.K.).

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    Abbreviations: IL, interleukin; LPS, lipopolysaccharides; PBMC, peripheral blood mononuclear cells; TNF, tumor necrosis factor; mRNA, messenger RNA; PPARγ, peroxisome proliferator-activated receptor γ.

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