Endocrine Abstracts

Preadipocytes differentiate into mature adipocytes when treated with insulin, T3, isobutylmethylxanthine and dexamethasone but the role of their autocrine factors in their survival and function has only recently been appreciated. We have examined the expression and role of autocrine FGF-2 during preadipocyte differentiation. Using human preadipocytes isolated from subcutaneous fat, we induced differentiation in differentiation medium with and without the insulin-sensitising drug, rosiglitazone. Western blotting of cells showed strong expression of 24 kDa FGF-2 but the 18 kDa form was not expressed. FGF-2 was not detected in the conditioned medium. Six-nine days following induction of differentiation, autocrine FGF-2 expression markedly decreased. This was coincident with the first appearance of visible lipid droplets within the cells. FGF receptor 1 (FGFR1) was detected as a single band of 125 kDa and its expression, like that of FGF-2, declined as differentiation progressed. To inhibit FGFR1 signalling in preadipocytes, recombinant adenovirus expressing dominant negative FGFR1 (RAdDN-FGFR1) was transduced into preadipocytes. Data were corrected against control infections with adenovirus expressing beta-galactosidase used at the same multiplicity of infection. The truncated DN-FGFR1 (90kDa) was expressed in the cells two days post infection. Protein content in the cell layer was reduced to 64 plus/minus 6 % SEM (without rosiglitazone) and 51.8 plus/minus 7.5% SEM (with rosiglitazone) of control incubations following 14 day treatment with RAdDN-FGFR1. Preadipocyte differentiation was measured by the incorporation of 14C glucose into lipid and corrected for protein content. Differentiation was inhibited by 70-80% in RAdDN-FGFR1 infected cells compared with control. Rosiglitazone increased both the rate and level of preadipocyte differentiation but the autocrine expression of FGF-2 and the inhibitory effects of RAdDN-FGFR1 on lipogenesis were not changed. We conclude that autocrine FGF-2 is expressed by human preadipocytes and is required for preadipocyte survival and the commitment to differentiation.