Gene Expression Profiling of 3t3-L1 Adipocytes Expressing the Mitochondrial Uncoupling Protein 1
Fatih Senocak1, Yaguang Si2, Kyongbum Lee2, and Arul Jayaraman3. (1) Chemical Engineering, Texas A&M University, 3122 TAMU, College Station, TX 77843, (2) Biology, Tufts University, 4 Colby Street, Medford, MA 02155, (3) Department of Chemical Engineering,, Texas A& M University, College Station, TX 77843-3122
Obesity is a chronic condition that primarily develops from an increase in body fat in the form of white adipose tissue (WAT) mass. The resulting adiposity is a risk factor for many diseases, including type-2 diabetes (T2D), cardiovascular diseases, and some forms of cancer. In particular, obesity-induced insulin resistance is a major contributor to T2D pathogenesis. Reducing WAT mass by targeted modulation of metabolic enzymes in fat cell metabolism is an attractive molecular therapeutic alternative to dietary approaches. Increasing molecular evidence points to a family of uncoupling proteins (UCPs) playing an important role in adipocyte fat metabolism. Of specific interest is UCP1, which mediates energy dissipation as heat in brown adipocytes by de-coupling respiration and ATP synthesis. However, UCP1 is not expressed in white adipocytes. The aim of this study was to determine the effects of exogenous UCP1 expression in white adipocytes on global changes in energy metabolism. A regulatable vector system (Tet-Off; Clontech, CA) was used to stably insert the UCP1 cDNA in preadipocytes. Upon differentiation using a standard hormone cocktail, UCP1 was stably expressed in mature 3T3-L1 white adipocytes. Codelink microarrays (n = 3) were used to characterize the changes in adipocyte gene expression upon UCP1 expression. The gene expression data was filtered based on reproducibility and statistical significance (p < 0.05 relative to controls). The data indicate that 552 and 851 were significantly up- or down-regulated, respectively, in UCP1 expressing adipocytes as compared to control adipocytes. Genes involved in oxidative phosphorylation were observed to be significantly down-regulated, as expected with UCP1 expression. In addition, a majority of the metabolic pathways, including those involved in glycolysis, lipid catabolism, lipid biosynthesis, were all down regulated at the transcriptional level in UCP1 expressing adipocytes. It is likely that the dramatic down-regulation in metabolism transcripts arises from the need to minimize ATP consumption upon unabated uncoupling of ATP synthesis and oxidative phosphorylation. We postulate that adipocytes increase the stability and half-lives of key metabolic enzymes (i.e., post-transcriptional regulation) to minimize the energy required for synthesizing these transcripts, thereby, conserving energy under ATP limiting conditions. Evidence to this hypothesis is seen in the microarray data, as genes involved in the ubiquitin-proteasome degradation pathway are also significantly down-regulated in UCP1 expressing cells. These results suggest UCP1 and other metabolic enzymes as potential targets for development of pharmacological agents for the treatment of obesity and related disorders.