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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, TNFalpha and interleukin-6, resulted in substantial increases in haptoglobin mRNA in 3T3-L1 adipocytes; the increase (7-fold) was highest with TNFalpha. Increases in haptoglobin mRNA level were also induced by dexamethasone, noradrenaline, isoprenaline, and a beta3-adrenoceptor agonist. In contrast, haptoglobin mRNA was reduced by nicotinic acid and the PPARgamma 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 PPARgamma nuclear receptor is strongly inhibitory.

We have examined whether GLUT-10 and GLUT-12, members of the Class III group of the recently expanded family of facilitative glucose transporters, are expressed in adipose tissues. The mouse GLUT-12 gene, located on chromosome 10, comprises at least five exons and encodes a 622 amino acid protein exhibiting 83% sequence identity and 91% sequence similarity to human GLUT-12. Expression of the GLUT-12 gene was evident in all the major mouse adipose tissue depots (epididymal, perirenal, mesenteric, omental, and subcutaneous white; interscapular brown). The GLUT-10 gene is also expressed in mouse adipose tissues and as with GLUT-12 expression occurred in the mature adipocytes as well as the stromal vascular cells. 3T3-L1 adipocytes express GLUT-10, but not GLUT-12, and expression of GLUT-12 was not induced by insulin or glucose. Both GLUT-10 and GLUT-12 expression was also found in human adipose tissue (subcutaneous and omental) and SGBS adipocytes. It is concluded that white fat expresses a wide range of facilitative glucose transporters.