Ikeda Daisuke, Sakaue Shinji, Kamigaki Mitsunori, Ohira Hiroshi, Itoh Naofumi, Ohtsuka Yoshinori, Tsujino Ichizo, Nishimura Masaharu
First Department of Medicine, Graduate School of Medicine, Hokkaido University, Sapporo 060-8638, Japan.
Endocrinology. 2008 Dec;149(12):6037-42. doi: 10.1210/en.2008-0158. Epub 2008 Aug 14.
Obesity is a condition in which adipose tissue mass is expanded. Increases in both adipocyte size and number contribute to enlargement of adipose tissue. The increase in cell number is thought to be caused by proliferation and differentiation of preadipocytes. Macrophage migration inhibitory factor (MIF) is expressed in adipocytes, and intracellular MIF content is increased during adipogenesis. Therefore, we hypothesized that MIF is associated with adipocyte biology during adipogenesis and focused on the influence of MIF on adipogenesis. To examine the effects of MIF on adipocytes, MIF expression in 3T3-L1 preadipocytes was inhibited by RNA interference, and cell differentiation was induced by standard procedures. The triglyceride content of MIF small interfering RNA (siRNA)-transfected 3T3-L1 cells was smaller than that of nonspecific siRNA-transfected cells. In addition, MIF knockdown apparently abrogated increases in adiponectin mRNA levels during differentiation. Gene expression of peroxisome proliferator-activated receptor (PPAR)gamma, CCAAT/enhancer binding protein (C/EBP)alpha, and C/EBPdelta decreased with MIF siRNA transfection, but C/EBPbeta expression increased. Cell number and incorporation of 5-bromo-2-deoxyuridine into cells decreased from 1-3 d and from 14-20 h, respectively, after induction of differentiation in MIF siRNA-transfected cells, thus suggesting that MIF siRNA inhibits mitotic clonal expansion. Taken together, these results indicated that MIF regulates differentiation of 3T3-L1 preadipocytes, at least partially, through inhibition of mitotic clonal expansion and/or C/EBPdelta expression.
肥胖是一种脂肪组织量增加的状态。脂肪细胞大小和数量的增加都有助于脂肪组织的增大。细胞数量的增加被认为是由前脂肪细胞的增殖和分化引起的。巨噬细胞移动抑制因子(MIF)在脂肪细胞中表达,并且在脂肪生成过程中细胞内MIF含量增加。因此,我们推测MIF在脂肪生成过程中与脂肪细胞生物学相关,并着重研究了MIF对脂肪生成的影响。为了检测MIF对脂肪细胞的作用,通过RNA干扰抑制3T3-L1前脂肪细胞中的MIF表达,并采用标准程序诱导细胞分化。转染MIF小干扰RNA(siRNA)的3T3-L1细胞的甘油三酯含量低于转染非特异性siRNA的细胞。此外,MIF基因敲低明显消除了分化过程中脂联素mRNA水平的升高。过氧化物酶体增殖物激活受体(PPAR)γ、CCAAT/增强子结合蛋白(C/EBP)α和C/EBPδ的基因表达随着MIF siRNA转染而降低,但C/EBPβ表达增加。在诱导MIF siRNA转染的细胞分化后,细胞数量和5-溴-2-脱氧尿苷掺入细胞的量分别在1至3天和14至20小时后减少,这表明MIF siRNA抑制有丝分裂克隆扩增。综上所述,这些结果表明MIF至少部分地通过抑制有丝分裂克隆扩增和/或C/EBPδ表达来调节3T3-L1前脂肪细胞的分化。