Roles of BMAL1 in adipocytes

脂肪分化受多种转录因子的调控，如C/EBP家族和PPARγ-2。在3T3-L1细胞脂肪分化过程中，BMAL mRNA水平开始升高，在分化细胞中高表达。在分离自C57BL/6J小鼠的白色脂肪组织中，BMALI主要在脂肪细胞部分表达，而间质-血管部分则主要表达。通过RNAi技术下调3T3-L1细胞中BMAL1mRNA的表达，使细胞能够在细胞中积累最少量的脂滴。分化7d后，对照组细胞中脂肪细胞相关基因的表达明显增强。与形态学观察一致的是，在BMAL-1基因敲除细胞中诱导了最少量的脂肪细胞相关基因。腺病毒介导的BMAL1在成熟脂肪细胞中的表达诱导了几个脂代谢所需的基因。这些结果表明，BMAL1在3T3-L1细胞的成脂过程中起作用。然后。我们希望研究BMALI是否有能力促进NIH3T3细胞的脂肪生成，NIH3T3细胞是一种相对不成脂的细胞系。将高表达全长BMALI mRNA的载体或对照载体稳定地导入NIH3T3细胞。为了评估克隆的分化潜能，将细胞培养成融合细胞，然后用含有PPARγ2配体(曲格列酮或ETYA)的标准分化诱导培养基处理细胞。在NIH3T3细胞中过表达BMAL1后，与对照细胞相比，BMAL1诱导了大量的脂质聚集。通过测量脂肪细胞相关基因的表达，也证实了这一结果。这些结果表明，BMAL1在脂肪分化的调控中起着重要作用。

Adipose differentiation is regulated by several transcription factors, such as a C/EBP family and PPARγ2. In this study, we have studied the roles of the BMAL1 in adipogenesis. During adipose differentiation in 3T3-L1 cells, the level of the BMAL mRNA began to increase is highly expressed in differentiated cells. In white adipose tissues isolated from C57BL/6J mice, BMALI is predominantly expressed in adipocytes fraction compared with stromal-vascular fraction. Knock down of BMAL1 mRNA expression in 3T3-L1 cells by RNAi technique allowed the cells to accumulate minimum amounts of lipid droplets in the cells. Expression of adipocytes-related genes was greatly induced in the control cells after 7 days of differentiation. Consistent with the morphological observations, a minimum amount of adipocytes-related genes was induced in the BMAL 1 knock down cells. Adenovirus-mediated expression of BMAL1 in mature adipocytes induced several genes required for lipid metabolism. These results indicated that BMAL1 play roles in adipogenesis in 3T3-L1 cells. Then. we wished to examine if BMALI has the ability to promote adipogenesis in NIH 3T3 cells, a relatively nonadipogenic cell line. NIH 3T3 cells were stably transfected with a vector expressing high levels of full length BMALI mRNA, or a control vector. To evaluate the differentiation potency of the clones, the cells were cultured to confluence and then treated with a standard differentiation-induction medium containing and PPAR γ2 ligands (troglitazone or ETYA). Overexpression of BMAL1 in NIH 3T3 cells induced significant amounts of lipids accumulation compared with the control cells. The results were also confirmed by measuring the expression of adipocyte-related genes. These results suggest that BMAL1 plays important role in the regulation of adipose differentiation.