Regulation of gene expression program by Fsp27 in white and brown adipose tissue. Mus musculus

Background: Brown and white adipose tissues (BAT and WAT) play critical roles in controlling energy homeostasis and in the development of obesity and diabetes. Fsp27 is expressed in both BAT and WAT and promotes lipid storage and the development of obesity and diabetes. In addition, Fsp27-deficient white adipocytes acquired certain BAT-like properties including reduced lipid droplet size and increased mitochondrial activity. Using microarray and semi-quantitative real-time PCR analyses, we systematically analyzed the gene expression profile in Fsp27-deficient WAT and BAT. Results: We observed that BAT-selective genes were significantly up-regulated, whereas WAT-selective genes were down-regulated in the WAT of Fsp27-/- mice. Expression levels of BAT-selective genes were also dramatically up-regulated in the WAT of leptin and Fsp27 double deficient mice. Furthermore, we observed that expression levels of genes in multiple metabolic pathways including oxidative phosphorylation, the TCA cycle and fatty acid synthesis and oxidation were increased in the Fsp27-/- WAT. In contrast, expression levels for extracellular matrix remodeling, the classic complement pathway and TGF-β signaling"were down-regulated in the WAT of Fsp27-/- mice. Most importantly, regulatory factors that determine BAT identity such as CEBPα/β, PRDM16 and major components in the cAMP pathway were markedly up-regulated in the WAT of Fsp27-/- mice. Interestingly, we observed distinct gene expression profiles in the BAT of Fsp27-/- mice. Conclusion: Our data suggest that Fsp27 acts at upstream to control gene expression of diverse pathways, in particular the expression of regulatory factors that determine the identity of BAT and WAT. Therefore, Fsp27 is an important molecular determinant for the identity of WAT, and loss of Fsp27 leads to the conversion of WAT to a BAT-like tissue. Overall design: Total RNAs were extracted from individual gonadal WAT of five pairs of 3-month-old wild-type and Fsp27-null male mice. Equal amounts of RNA from five pairs of mice with each genotype were pooled to form RNA pools (total 45 μg). Duplicate experiments were carried out.