Zhang J, Suh Y, Choi Y M, Ahn J, Davis M E, Lee K
1 Department of Animal Sciences, The Ohio State University, Columbus, OH 43210, USA.
Animal. 2014 May;8(5):800-9. doi: 10.1017/S1751731114000469.
Increase of fat cells (FCs) in adipose tissue is attributed to proliferation of preadipocytes or immature adipocytes in the early stage, as well as adipogenic differentiation in the later stage of adipose development. Although both events are involved in the FC increase, they are contrary to each other, because the former requires cell cycle activity, whereas the latter requires cell cycle withdrawal. Therefore, appropriate regulation of cell cycle inhibition is critical to adipogenesis. In order to explore the important cell cycle inhibitors and study their expression in adipogenesis, we adopted a strategy combining the Gene Expression Omnibus (GEO) database available on the NCBI website and the results of quantitative real-time PCR (qPCR) data in porcine adipose tissue. Three cell cycle inhibitors - cyclin G2 (CCNG2), cyclin-dependent kinase inhibitor 2C (CDKN2C) and peripheral myelin protein (PMP22) - were selected for study because they are relatively highly expressed in adipose tissue compared with muscle, heart, lung, liver and kidney in humans and mice based on two GEO DataSets (GDS596 and GDS3142). In the latter analysis, they were found to be more highly expressed in differentiating/ed preadipocytes than in undifferentiated preadipocytes in human and mice as shown respectively by GDS2366 and GDS2743. In addition, GDS2659 also suggested increasing expression of the three cell cycle inhibitors during differentiation of 3T3-L1 cells. Further study with qPCR in Landrace pigs did not confirm the high expression of these genes in adipose tissue compared with other tissues in market-age pigs, but confirmed higher expression of these genes in FCs than in the stromal vascular fraction, as well as increasing expression of these genes during in vitro adipogenic differentiation and in vivo development of adipose tissue. Moreover, the relatively high expression of CCNG2 in adipose tissue of market-age pigs and increasing expression during development of adipose tissue was also confirmed at the protein level by western blot analysis. Based on the analysis of the GEO DataSets and results of qPCR and Western blotting we conclude that all three cell cycle inhibitors may inhibit adipocyte proliferation, but promote adipocyte differentiation and hold a differentiated state by inducing and maintaining cell cycle inhibition. Therefore, their expression in adipose tissue is positively correlated with age and mature FC number. By regulating the expression of these genes, we may be able to control FC number, and, thus, reduce excessive fat tissue in animals and humans.
脂肪组织中脂肪细胞（FCs）数量的增加，在早期归因于前脂肪细胞或未成熟脂肪细胞的增殖，而在脂肪发育后期则归因于脂肪生成分化。虽然这两个过程都与脂肪细胞数量增加有关，但它们是相互矛盾的，因为前者需要细胞周期活性，而后者需要退出细胞周期。因此，适当调节细胞周期抑制对脂肪生成至关重要。为了探索重要的细胞周期抑制剂并研究它们在脂肪生成中的表达，我们采用了一种策略，将NCBI网站上可用的基因表达综合数据库（GEO）与猪脂肪组织中的定量实时PCR（qPCR）数据结果相结合。选择了三种细胞周期抑制剂——细胞周期蛋白G2（CCNG2）、细胞周期蛋白依赖性激酶抑制剂2C（CDKN2C）和外周髓磷脂蛋白（PMP22）进行研究，因为基于两个GEO数据集（GDS596和GDS3142），在人类和小鼠中，与肌肉、心脏、肺、肝脏和肾脏相比，它们在脂肪组织中的表达相对较高。在后续分析中，如分别由GDS2366和GDS2743所示，发现它们在人类和小鼠的分化/已分化前脂肪细胞中的表达高于未分化前脂肪细胞。此外，GDS2659也表明在3T3-L1细胞分化过程中这三种细胞周期抑制剂的表达增加。在长白猪中进行的qPCR进一步研究未证实这些基因在上市猪的脂肪组织中比在其他组织中高表达，但证实了这些基因在脂肪细胞中的表达高于基质血管部分，以及在体外脂肪生成分化和体内脂肪组织发育过程中这些基因的表达增加。此外，通过蛋白质印迹分析在蛋白质水平上也证实了上市猪脂肪组织中CCNG2的相对高表达以及在脂肪组织发育过程中的表达增加。基于对GEO数据集的分析以及qPCR和蛋白质印迹的结果，我们得出结论，所有这三种细胞周期抑制剂可能抑制脂肪细胞增殖，但促进脂肪细胞分化并通过诱导和维持细胞周期抑制来保持分化状态。因此，它们在脂肪组织中的表达与年龄和成熟脂肪细胞数量呈正相关。通过调节这些基因的表达，我们或许能够控制脂肪细胞数量，从而减少动物和人类体内过多的脂肪组织。
