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

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-beta signaling"were down-regulated in the WAT of Fsp27-/- mice. Most importantly, regulatory factors that determine BAT identity such as CEBPalpha/beta, 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. 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 micrograms). Duplicate experiments were carried out.背景：棕色脂肪组织（BAT，Brown Adipose Tissue）与白色脂肪组织（WAT，White Adipose Tissue）在调控能量稳态以及肥胖与糖尿病的发生发展中发挥关键作用。Fsp27在BAT与WAT中均有表达，可促进脂质储存以及肥胖与糖尿病的发生发展。此外，Fsp27缺陷的白色脂肪细胞会获得部分BAT样特性，包括脂滴尺寸减小与线粒体活性增强。本研究通过微阵列（microarray）与半定量实时PCR（semi-quantitative real-time PCR）分析，系统分析了Fsp27缺陷的WAT与BAT中的基因表达谱。结果：我们观察到，在Fsp27敲除（Fsp27-/-）小鼠的WAT中，BAT选择性基因显著上调，而WAT选择性基因则出现下调。在瘦素与Fsp27双缺陷小鼠的WAT中，BAT选择性基因的表达水平同样显著上调。此外，我们发现，Fsp27-/-小鼠WAT中多条代谢通路相关基因的表达水平均有所升高，包括氧化磷酸化、三羧酸（TCA）循环以及脂肪酸合成与氧化通路。与之相反，Fsp27-/-小鼠WAT中细胞外基质重塑、经典补体通路以及转化生长因子-β（TGF-β）信号通路相关基因的表达水平出现下调。最为关键的是，决定BAT特性的调控因子，如CEBPα/β、PRDM16以及cAMP通路的主要组成成分，在Fsp27-/-小鼠的WAT中均显著上调。值得注意的是，我们在Fsp27-/-小鼠的BAT中观察到了截然不同的基因表达谱。结论：本研究数据表明，Fsp27作为上游调控因子控制多条通路的基因表达，尤其是调控决定BAT与WAT特性的关键调控因子的表达。因此，Fsp27是决定WAT特性的重要分子调控因子，Fsp27的缺失会导致WAT向BAT样组织转化。我们从5对3月龄野生型与Fsp27完全缺陷（Fsp27-null）雄性小鼠的性腺周WAT中提取总RNA。将每一种基因型的5对小鼠的RNA等量混合，制备得到RNA混合样本（总质量为45微克）。实验设置重复组。