Submitted to: Obesity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2007
Publication Date: 6/16/2008
Citation: Cao, H., Urban Jr, J.F., Anderson, R.A. 2008. Insulin increases tristetraprolin and decreases VEGF gene expression in mouse 3T3-L1 adipocytes. Obesity. 16:1208-1218. Interpretive Summary: Obesity, one of the most pervasive public health problems, is increasing in both developed and developing countries, and affecting both adults and children. According to the World Health Organization report in 2002, more than 1 billion adults worldwide were overweight and about 300 million people were clinically obese. Each year, obesity causes at least 300,000 excess deaths in the U.S. and healthcare costs of American adults with obesity amount to approximately $100 billion. Furthermore, obesity increases risks of developing type 2 diabetes, cardiovascular diseases, and other diseases. Obesity is a disease of appetite regulation and energy metabolism, resulting in excess fat accumulation in adipocytes (fat cells). Obesity is associated with chronic inflammation, but the mechanisms of how inflammation relates to obesity are not completely understood. Tristetraprolin (TTP), an anti-inflammatory protein, binds and helps to destroy clinically important molecules. The objectives of this study were to analyze the relative abundance of the TTP family of mRNAs in mouse fat cells and macrophage (a type of white blood cells) and to investigate the effects of insulin on TTP family and vascular endothelial growth factor (VEGF) gene expression in adipocytes. We selected a cell model for the study of obesity and demonstrated that TTP gene expression was induced by insulin in mouse fat cells, resulting in decreases in VEGF gene expression. This study established a foundation for the investigation of the role of TTP family and VEGF genes in the regulation of appetite and energy regulation.
Technical Abstract: Tristetraprolin (TTP/ZFP36) family proteins bind and destabilize AU-rich element-containing mRNAs encoding cytokines such as vascular endothelial growth factor (VEGF). Little is known about the expression and insulin-regulation of TTP family and related genes in adipocytes. We analyzed the relative abundance of TTP family mRNAs and investigated the effects of insulin on the expression of 42 genes including TTP family, VEGF, adiponectin, leptin, pro-inflammatory cytokines, and insulin signaling pathway components in mouse 3T3-L1 adipocytes. Relative abundance of mRNA levels was determined by quantitative real-time PCR. TTP and ZFP36L1 proteins were detected by immunoblotting. Zfp36l1 and Zfp36l2 genes were expressed at 8 to 10-fold higher than Ttp in adipocytes. Zfp36l3 mRNA was detected at approximately 1% of Ttp mRNA levels in adipocytes and its low level expression was confirmed in RAW cells. Insulin at 10 and 100 nM increased Ttp mRNA levels by 5 to 7-fold, but decreased those of Zfp36l3 by 40% in adipocytes after a 30-min treatment. Immunoblotting showed that insulin induced TTP but did not affect ZFP36L1 protein levels in adipocytes. Insulin decreased mRNA levels of Vegf and a number of other genes in adipocytes. Insulin induced Ttp mRNA and protein expression and decreased Vegf mRNA levels in adipocytes. Zfp36l3 mRNA was detected, for the first time, in cells other than mouse placenta and extra-embryonic tissues. This study established a basis for the investigation of TTP family and VEGF genes in the regulation of obesity and suggested that Vegf mRNA may be a target for TTP in fat cells.