Knockdown of macrophage migration inhibitory factor disrupts adipogenesis in 3T3-L1 cells

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.     

Mechanism of adult primitive mesenchymal ST-13 preadipocyte differentiation

Convincing evidence supports the idea that adipogenesis occurs throughout the life of organisms. However, little is known about the adipogenesis program for adult adipocytes. We examine this issue using mouse adult primitive mesenchymal ST-13 preadipocytes that express the peroxisome proliferator-activated receptor-gamma (PPARgamma) gene while in a predifferentiated state. The gene expression of PPARgamma was sustained throughout differentiation when ST-13 preadipocytes were induced to become adipocytes by a PPARgamma ligand. However, the differentiation of pluripotent C3H10T1/2 stem cells and 3T3-L1 embryonic fibroblastic cells was associated with enhanced expression of the PPARgamma gene. Immunoblotting analysis revealed that C3H10T1/2 and 3T3-L1 cells expressed low levels of PPARgamma1 from the early stage, and the amount increased during differentiation, whereas PPARgamma2 appeared at the late stage. In contrast, ST-13 preadipocytes expressed an appreciable amount of PPARgamma1 that significantly decreased on differentiation, and a small amount of PPARgamma2 appeared late in the differentiation process. Furthermore, the standard hormone cocktail containing dexamethasone, methylisobutylxanthine, and insulin induced an increase in PPARgamma1 protein only at the early stage, and a low level of PPARgamma2 protein appeared late in ST-13 cells. However, levels of both PPARgamma1 and PPARgamma2 proteins were significantly induced within 2 d in 3T3-L1 cells in this hormonal adipogenesis. Moreover, exposing ST-13 preadipocytes to dexamethasone and insulin induced differentiation, but failed to induce adipogenesis in 3T3-L1. Adipogenesis in adult rat primary preadipocytes was also induced in a similar manner to that of ST-13. Our results indicate that ST-13 cells and primary preadipocytes derived from adults possess an adipogenesis program distinct from that of 3T3-L1 and C3H10T1/2 cells, and that it may represent the adipogenesis program for adult-specific adipocytes.     

CCAAT/enhancer binding protein alpha is sufficient to initiate the 3T3-L1 adipocyte differentiation program.

Previous studies showed that CCAAT/enhancer binding protein alpha (C/EBP alpha) is required for differentiation of 3T3-L1 preadipocytes induced by exogenous hormonal agents. It was not possible to ascertain, however, whether C/EBP alpha alone is sufficient to induce differentiation because its antimitogenic activity precluded propagating 3T3-L1 cell lines that constitutively express C/EBP alpha at high levels. This problem was circumvented by using 3T3-L1 preadipocytes stably transfected with an isopropyl beta-D-thiogalactoside (IPTG)-inducible p42 C/EBP alpha expression vector system. IPTG-induced expression of the 42-kDa isoform of C/EBP alpha in preadipocytes caused expression of several endogenous adipocyte-specific genes (genes encoding the 422 adipose P2 protein, glucose transporter 4, and C/EBP alpha) and the accumulation of cytoplasmic triglyceride. Thus, C/EBP alpha is not only necessary but also is sufficient to trigger differentiation of growth-arrested 3T3-L1 preadipocytes without use of exogenous hormonal agents.     

分泌型卷曲相关蛋白/β-联蛋白信号通路对脂肪形成的影响

目的:探讨分泌型卷曲相关蛋白(sFRP5)和经典Wnt信号通路在脂肪细胞形成中的作用及机制。方法:诱导3T3-L1前体脂肪细胞分化,用过表达sFRP5的携带绿色荧光蛋白基因的重组腺病毒(Ad-sFRP5-GFP)感染3T3-L1细胞并诱导成熟,利用实时荧光定量PCR检测经典Wnt下游靶基因和脂肪分化相关基因mRNA水平的变化。3T3-L1细胞分化成熟后,进行油红染色,观察过表达sFRP5对脂滴形成的影响;提取核浆蛋白,用蛋白质印迹法检测sFRP5对β-联蛋白核转位的影响。结果:3T3-L1细胞分化成熟后期,sFRP5、CCAAT增强子结合蛋白α(C/EBPα)、过氧化物酶体增殖物活化受体γ2(PPARγ2)表达均显著增加,同时,细胞周期蛋白D1表达显著下调。而诱导分化成熟后,过表达sFRP5的3T3-L1细胞周期蛋白D1无显著改变。与空载对照组相比,过表达sFRP5的3T3-L1细胞脂滴形成无明显变化。给予3T3-L1细胞重组小鼠sFRP5直接刺激或感染Ad-sFRP5-GFP,均未明显改变β-联蛋白核转位。结论:sFRP5的表达随着脂肪细胞分化而显著增加,但不影响体外脂肪细胞分化,sFRP5在体外不直接通过拮抗Wnt/β-联信号通路的方式发挥作用。     

Effect of collagen I and aortic carboxypeptidase-like protein on 3T3-L1 adipocyte differentiation

Aortic carboxypeptidase-like protein (ACLP) is a secreted protein expressed in preadipocytes and down-regulated during adipogenesis. Results from previous studies on the influence of ACLP overexpression on adipogenesis vary from no effect to complete inhibition. We hypothesized that ACLP may modulate adipogenesis in the presence of collagen I, a protein to which it binds. We compared control (pLXSN) 3T3-L1 preadipocytes with 3T3-L1 preadipocytes stably overexpressing ACLP (pLXSN-ACLP) that were grown in standard vs collagen I-coated dishes. Aortic carboxypeptidase-like protein overexpression, via retroviral transduction, resulted in a 3.2-fold increase in ACLP cellular levels and a 2.1-fold increase in ACLP levels released into medium. Aortic carboxypeptidase-like protein overexpression did not inhibit differentiation in standard dishes. In collagen I-coated dishes compared with standard dishes, control preadipocytes, when induced to differentiate, exhibited the same increase in triacylglycerol accumulation, but showed a significantly higher induction of fatty acid synthase (1.6-fold more), peroxisome proliferator-activated receptor γ (1.4-fold more), and CCAAT/enhancer-binding protein α (1.4-fold more). Aortic carboxypeptidase-like protein overexpression significantly reduced this enhanced induction of fatty acid synthase, peroxisome proliferator-activated receptor γ, and CCAAT/enhancer-binding protein α by 65%, 59%, and 66%, respectively, but had no effect on the accumulation of triacylglycerol during differentiation. Finally, studies on proadipogenic insulin signaling in ACLP-overexpressing preadipocytes demonstrated that insulin-stimulated Akt phosphorylation was significantly decreased by 27% in cells cultured in collagen I-coated dishes vs standard dishes. Our data suggest that ACLP inhibits certain aspects of 3T3-L1 adipogenesis in a collagen I-rich environment.     

microRNA-200c对3T3-L1前体脂肪细胞向脂肪细胞分化的调控作用

目的 探讨microRNA(miRNA)-200c对3T3-L1前体脂肪细胞分化的影响.方法 利用实时PCR检测miRNA-200c在小鼠骨髓间充质干细胞(MSCs)向脂肪细胞分化过程及向骨细胞分化过程中的表达.通过将miRNA-200c类似物、miRNA-200c抑制剂转染至3T3-L1前体脂肪细胞,从而在细胞中增强或抑制miRNA-200c的表达,油红O染色检测转染后3T3-L1前体脂肪细胞诱导成熟后的脂滴形成情况.实时PCR检测转染后脂肪细胞特异性转录因子过氧化物酶体增殖物活化受体γ(PPARγ)和表征基因aP2在成脂过程中的表达变化.结果 实时PCR结果显示,在小鼠骨髓MSCs诱导成脂后miRNA-200c表达升高(t=24.709,P＜0.01),而诱导成骨后,miRNA-200c表达下降(t=8.783,P＜0.01).转染miRNA-200c类似物后,3T3-L1前体脂肪细胞中脂滴明显增多,PPARγ和aP2表达显著升高(t=7.674、9.657,P均＜0.01);转染miRNA-200c抑制剂后,3T3-L1前体脂肪细胞中脂滴明显减少,PPARγ、aP2表达显著降低(t=9.483、6.419,P均＜0.01).结论 miRNA-200c能够促进3T3-L1前体脂肪细胞向脂肪细胞分化.     

S100A16基因促进3T3-L1前脂肪细胞分化

目的 研究S100A16基因在3T3-L1前脂肪细胞分化过程中的作用及机制.方法 构建过表达S100A16的慢病毒载体(PLJMI-S100A16-GFP),转染3T3-L1细胞.以Western印迹法检测S100A16正常3T3-L1细胞分化过程中S100A16的表达;采用油红O观察脂滴堆积情况;采用Western印迹和实时定量PCR方法检测前体脂肪细胞分化过程中相关基因的表达变化.免疫共沉淀方法检测S100A16是否与p53相互作用.结果 成功构建S100A16过表达3T3-L1细胞株;随着3T3-L1前脂肪细胞的分化,S100A16蛋白表达水平逐渐升高;高表达S100A16能够促进3T3-L1前脂肪细胞分化,促进甘油三酯在脂肪细胞内聚集(P＜0.01),同时上调脂肪细胞分化标志基因PPARy、CCAAT增强子结合蛋白α(C/EBP-α)、脂蛋白脂酶、脂肪细胞脂肪酸结合蛋白(aP2)及脂肪酸合成酶的表达(P＜0.05或P＜0.01);免疫共沉淀结果提示,S100A16蛋白与p53相互作用.结论 S100A16通过抑制p53活性进而促进3T3-L1前脂肪细胞的分化.     

C-terminal Src kinase (CSK) modulates insulin-like growth factor-I signaling through Src in 3T3-L1 differentiation

IGF-I stimulates both proliferation and differentiation of adipocyte-precursor cells, preadipocytes in vivo and in vitro. We have previously shown that IGF-I stimulates proliferation of 3T3-L1 preadipocytes through activation of MAPK and MAPK activation by IGF-I is mediated through the Src family of nonreceptor tyrosine kinases. In addition, we have shown that when 3T3-L1 cells reach growth arrest and are stimulated to differentiate, IGF-I can no longer activate the MAPK pathway. We hypothesized that the loss of IGF-I signaling to MAPK in differentiating 3T3-L1 cells is due to loss of IGF-I activation of Src family kinases. We measured c-Src kinase activity in cell lysates from proliferating, growth-arrested and differentiating 3T3-L1 cells. Src activity increased 2- to 4-fold in IGF-I-stimulated proliferating cells; however, IGF-I had a marginal affect on Src activity in growth-arrested cells and inhibited Src activity localized at the membrane in differentiating cells. C-terminal Src kinase (CSK), a ubiquitously expressed nonreceptor tyrosine kinase, negatively regulates the Src family kinases by phosphorylation of the Src C-terminal tyrosine. IGF-I decreased phosphorylation of the Src C-terminal tyrosine in proliferating cells and increased phosphorylation of this site in differentiating cells. IGF-I stimulated CSK kinase activity 2-fold in differentiating 3T3-L1 cells. An association between CSK and c-Src was detected by immunoprecipitation following IGF-I stimulation of differentiating but not proliferating 3T3-L1 cells. These results suggest that the loss of IGF-I downstream mitogenic signaling in differentiating 3T3-L1 cells is due to a change in IGF-I activation of c-Src and CSK may mediate the inactivation of c-Src by IGF-I in 3T3-L1 adipogenesis.     

Macrophage-conditioned medium inhibits the differentiation of 3T3-L1 and human abdominal preadipocytes

Aims/hypothesis In obesity, a limited adipogenic capacity may promote adipocyte hypertrophy and increase the risk of insulin resistance and type 2 diabetes. Recent data indicate that macrophages reside within adipose tissue in obese rodents and humans. We hypothesised that secreted macrophage factors may inhibit adipogenesis.Materials and methods Conditioned media from cultured murine J774 or human THP-1 macrophages were collected, and added to either murine 3T3-L1 preadipocytes or human abdominal stromal preadipocytes from subcutaneous or omental fat depots.Results Macrophage-conditioned medium (MacCM) strongly inhibited 3T3-L1 adipogenesis. Dose–response studies with J774-MacCM revealed that 80 and 100% of J774-MacCM completely suppressed triacylglycerol accumulation as well as the induction of fatty acid synthase, peroxisome proliferator-activated receptor γ, CCAAT/enhancer binding protein α, and adiponectin. Similar inhibitory effects on 3T3-L1 preadipocytes were observed with THP-1-MacCM. Differentiation of human abdominal subcutaneous stromal preadipocytes was moderately reduced (subcutaneous>omental) by J744-MacCM. In contrast, the differentiation of both subcutaneous and omental stromal preadipocytes was completely inhibited by THP-1-MacCM, as determined on the basis of morphology and triacylglycerol accumulation, as well as fatty acid synthase and adiponectin protein expression.Conclusions/interpretation Secreted macrophage products inhibit the differentiation of 3T3-L1 preadipocytes as well as human abdominal stromal preadipocytes.     

基因重组融合蛋白hNPY对小鼠前脂肪细胞增殖和分化影响的实验研究

目的：前脂肪细胞是一类具有增殖和向脂肪细胞分化潜力的特异化的前体细胞,如能找到可促进前脂肪细胞增殖和分化的因子或药物,并在脂肪组织移植的同时使用,则有希望提高脂肪组织的移植效果,本实验探索一种新的人体肥胖关联基因和外周脂肪细胞激动剂一基因重组融合蛋白hNPY对小鼠3T3-L1前脂肪细胞增殖和分化的影响及其分子调控机制。方法：采用基因工程技术设计hNPY基因上下游序列,经过PCR反应合成hNPY的cDNA后与pET28a＋载体重组,再将已构建好、并经测序确认无误的重组质粒pET28a—NPY转导至大肠杆菌BL21（DE3）,再由IPTG诱导表达hNPY融合蛋白、并进行纯化;然后,将体外培养的小鼠3T3-L1前脂肪细胞经由3-异丁基-1-甲基黄嘌呤、胰岛素和地塞米松进行联合诱导;诱导2d后,再将此细胞分为三组,即空白对照组（未加任何诱导剂组）、经典诱导组（胰岛素诱导）和实验干预组（hNPY融合蛋白干预）,其中,实验干预组再按照hNPY融合蛋白浓度不同又分为高、中、低三个浓度组（10^-8mol／L、10^-19mol／L和10^-9 mol／L）。分别于细胞培养的第7d和第12d用相差显微镜观察各组细胞的形态学变化,再于细胞培养的第12d用油红O染色观察脂肪细胞的分化程度;同时,采用MTT法检测该细胞的增殖状况;采用Westernblot法检测脂肪细胞分化相关基因过氧化物体增殖剂活化受体-γ（PPAR-γ）、CAAT／增强子结合蛋白-a（C／EBP-a）蛋白的表达水平。结果：低浓度（10^-10 mol／L）的hNPY融合蛋白,无明显促进小鼠3T3-L1前脂肪细胞增殖和分化的作用效果;中浓度（10^-9 mol／L）的hNPY融合蛋白,可有效促进小鼠3T3-L1前脂肪细胞增殖及细胞数量增多;而高浓度（10^-8 mol／L）的hNPY融合蛋白,不仅能明显促进小鼠3T3-L1前脂肪细胞的细胞增殖和分化,且能显著提高该细胞C／EBPa和PPARγ的表达水平、而明显降低INSIG-2的表达。结论：高浓度（10^-8mol／L）的基因重组融合蛋白hNPY能够明显促进小鼠3T3-L1前脂肪细胞的增殖和分化,其促进3T3-L1细胞增殖和分化的分子调控机制很可能与上调PPARγ、C／EBPa表达和降低INSIG-2表达水平有关,这提示：hNPY作为脂肪细胞膜上受体NPYR的有效促进剂或激动剂,未来很可能成为人体外周脂肪细胞一个新的作用靶点。     

Exendin-4对脂肪细胞分化及糖脂代谢相关基因mRNA表达的影响

目的探讨Exendin-4对3T3-L1前脂肪细胞的分化及糖脂代谢相关基因mRNA表达的影响。方法体外培养3T3-L1前脂肪细胞,在脂肪细胞分化成熟过程中的不同时期分别用Exendin-4等干预,采用油红O染色,观察脂肪细胞分化及脂质积聚情况;采用荧光定量PCR检测脂肪细胞糖脂代谢标志基因GLUT-4、PPARγ、HSLmRNA表达水平。酶法测定脂肪细胞的甘油三酯含量。结果分化成熟的脂肪细胞经油红O染色可见细胞质内大片脂滴呈亮红色,而未分化细胞不被油红O染色。在脂肪细胞分化第0天和第6天用Exendin-4干预,脂肪细胞内TG的含量较空白组增加（P〈0．01）,GLUT-4、HSL、PPARγ mRNA的表达上调（P〈0．01）;在脂肪细胞分化的第12天干预,Exendin-4对肪细胞分化及相关基因mRNA的表达与空白组无明显差异。结论Exendin-4促进脂肪细胞的分化并上调糖脂代谢相关基因GLUT-4、PPARγ、HSL mRNA表达,可能为Exendin-4抗糖尿病的部分作用机制。     

Resistin promotes 3T3-L1 preadipocyte differentiation

OBJECTIVE: To investigate the relationship between resistin (a potential link between obesity and type 2 diabetes) and preadipocyte differentiation. DESIGN: A rat resistin expression vector was transfected into 3T3-L1 preadipocytes and differentiation was compared between normal 3T3-L1 cells, rat resistin-transfected cells and non-transfected cells grown in conditioned medium taken from resistin-expressing cultures. METHODS: The rat resistin gene was inserted into the pDual GC and pEFGP-N2 expression vectors for examination of the effects of resistin overexpression in 3T3-L1 cells before and after differentiation was stimulated with 3-isobutyl-1-methyxanthine (MIX), insulin and dexamethasone (DEX). Smaller conserved fragments were inserted into short interference RNA (siRNA) expression vectors, for examination of the effect of targeted resistin inhibition on differentiation of resistin-overexpressing 3T3-L1 cells. RESULTS: Prior to stimulation, the resistin-transfected 3T3-L1 cells contained many more small lipid droplets than did non-transfected 3T3-L1 cells. Following stimulation, differentiation in the resistin-transfected 3T3-L1 cells was dramatically promoted, especially in the early stages. Stimulation of differentiation was also observed in non-transfected 3T3-L1 cells grown in resistin protein-containing conditioned medium. The expression of adipocyte differentiation-associated markers such as CCAAT enhancer binding protein (C/EBPalpha), retinoid X receptor (RXRalpha) and lipoprotein lipase (LPL) was upregulated in resistin-overexpressing cells, whereas expression of preadipocyte factor-1 (Pref-1), an inhibitor of preadipocyte differentiation, was downregulated. In addition, expression of two of the three tested siRNAs inhibited the adipoconversion process, providing further evidence that resistin promotes the differentiation of preadipocytes to adipocytes. CONCLUSION: Resistin can promote preadipocyte differentiation. Based on this, we propose that resistin may be an important candidate mediator of obesity-induced insulin resistance.     

Lipopolysaccharides Reduce Adipogenesis in 3T3-L1 Adipocytes Through Activation of NF-κB Pathway and Downregulation of AMPK Expression

Lipopolysaccharides (LPS) from the outer membrane of Gram-negative bacteria serve as endotoxin to exert potent immune responses. However, the effect of LPS on adipogenesis has not been elucidated. The present study was designed to examine the effect of LPS on adipogenesis in 3T3-L1 preadipocytes and possible mechanism(s) of action involved. Our results revealed that LPS challenge significantly suppressed adipogenesis in 3T3-L1 preadipocytes mainly through downregulated expression of the late adipogenic markers PPARγ and aP2 as well as AMP-activated protein kinase (AMPK) expression and activity. As an inflammatory factor, LPS was found to lead to an overt reduction in IκBα levels compared with the time-matched controls, consolidating its pro-inflammatory property in 3T3-L1 preadipocytes. Our data also revealed that LPS retarded adipogenesis, the effect of which was partially reversed by the selective inhibitor of IKKβ. IκBα was found to be involved in the anti-adipogenic effect of LPS. In conclusion, LPS is capable of inhibiting adipogenesis in 3T3-L1 adipocytes possibly through activation of NF-κB and inhibition of AMPK. With the activation of NF-κB pathway and inhibition of AMPK, LPS suppresses C/EBP α DNA-binding activity and the expression of late adipogenic markers PPARγ and aP2.