Regulation of haptoglobin gene expression in 3T3-L1 adipocytes by cytokines, catecholamines, and PPARγ

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Abstract

Factors which regulate expression of the haptoglobin (acute phase reactant) gene in adipocytes have been examined using 3T3-L1 cells. Haptoglobin expression was observed by Northern blotting in each of the major white adipose tissue depots of mice (epididymal, subcutaneous, mesenteric, and perirenal) and in interscapular brown fat. Expression occurred in mature adipocytes, but not in the stromal-vascular fraction. In 3T3-L1 cells, haptoglobin mRNA was detected from day 4 after the induction of differentiation into adipocytes. Lipopolysaccharide and the cytokines, TNFα and interleukin-6, resulted in substantial increases in haptoglobin mRNA in 3T3-L1 adipocytes; the increase (7-fold) was highest with TNFα. Increases in haptoglobin mRNA level were also induced by dexamethasone, noradrenaline, isoprenaline, and a β3-adrenoceptor agonist. In contrast, haptoglobin mRNA was reduced by nicotinic acid and the PPARγ agonist, rosiglitazone. RT-PCR showed that the haptoglobin gene was expressed in human adipose tissue (subcutaneous, omental). It is concluded that haptoglobin gene expression in adipocytes is stimulated by inflammatory cytokines, glucocorticoids, and the sympathetic system, while activation of the PPARγ nuclear receptor is strongly inhibitory.

Section snippets

Methods

Animals. Adult male CD-1 mice, aged 8 weeks, were obtained from Harlan Olac. On receipt, they were housed for 2 weeks at 21 °C with a 12 h light:12 h dark cycle and fed a commercial diet (CRM Diet, Labsure) containing 19.2% protein and 4.3% lipid (wt/wt). Both food and water were available ad libitum. The mice were killed by cervical dislocation and the following tissues were rapidly removed and frozen in liquid nitrogen: lung, small intestine, liver, kidney, brain, spleen, heart, skeletal muscle

Results

In initial experiments, a specific antisense oligonucleotide probe was used to examine the expression of the haptoglobin gene by Northern blotting in a range of mouse tissues. Strong expression was observed in the liver and the lung, and also in epididymal white adipose tissue (Fig. 1A). 3T3-L1 adipocytes, taken at day 8 after the induction of differentiation, were also probed and a signal was obtained (Fig. 1A). Expression was then examined in different white adipose tissue depots (epididymal,

Discussion

The present study demonstrates that the gene encoding the acute phase reactant haptoglobin is expressed in each of the main white adipose tissue depots of mice, both internal and subcutaneous, as well as in interscapular brown adipose tissue. This suggests that all adipose tissue depots could in principle contribute to the circulating pool of haptoglobin. Expression of the haptoglobin gene in white fat was originally observed for mouse epididymal tissue and in situ hybridisation was used to

Acknowledgements

Claudia Oller do Nascimento was a Visiting Scholar at the University of Liverpool and is grateful to CAPES (Brazil) for financial support. We thank Steve Wong (Liverpool) for the human adipose tissue samples. Our work is funded by the BBSRC and the European Union.

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    Permanent address: Department of Physiology, São Paulo Federal University, Rua Botucatu, 862 2o Andar, 04023—060 São Paulo–SP, Brazil.

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