Calpain system regulates the differentiation of adult primitive mesenchymal ST-13 adipocytes

The activity of calpain, a calcium-activated protease, is required during the mitotic clonal expansion phase of 3T3-L1 embryonic preadipocyte differentiation. Here we examined the role of calpain in the adipogenesis of ST-13 preadipocytes established from adult primitive mesenchymal cells, which do not require mitotic clonal expansion. After exposure to the calpain inhibitor, N-benzyloxycarbonyl-L-leucyl-L-leucinal or overexpression of calpastatin, a specific endogenous inhibitor of calpain, ST-13 preadipocytes acquired the adipocyte phenotype. Overexpression of calpastatin in ST-13 adipocytes stimulated the expression of adipocyte-specific CCAAT/enhancer-binding protein-alpha (C/EBPalpha), peroxisome proliferator-activated receptor (PPAR)-gamma, sterol regulatory element-binding protein 1, and the insulin signaling molecules, insulin receptor alpha, insulin-receptor substrates, and GLUT4. However, insulin-stimulated glucose uptake was reduced by approximately 52%. The addition of calpain to the nuclear fraction of ST-13 adipocytes resulted in the Ca(2+)-dependent degradation of PPARgamma and C/EBPalpha but not sterol regulatory element-binding protein 1. Exposing ST-13 adipocytes to A23187 also led to losses of endogenous PPARgamma and C/EBPalpha. Under both conditions, calpain inhibitors almost completely prevented C/EBPalpha cleavage but partially blocked the decrease of PPARgamma. Two ubiquitous forms of calpain, mu- and m-calpain, localized to the cytosol and the nucleus, whereas the activated form of mu- but not m-calpain was found in the nucleus. Finally, stable dominant-negative mu-calpain transfectants showed accelerated adipogenesis and increase in the levels of PPARgamma and C/EBPalpha during adipocyte program. These results support evidence that the calpain system is involved in regulating the differentiation of adult primitive mesenchymal ST-13 preadipocytes.     

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.     

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.     

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.     

Grape-seed derived procyanidins interfere with adipogenesis of 3T3-L1 cells at the onset of differentiation

OBJECTIVE: Our group's previous results on the effects of a grape seed procyanidin extract (GSPE) on adipose metabolism showed that peroxisome proliferator-activated receptor-gamma (PPARgamma) plays a central role in the lipolytic effects of GSPE on adipocytes. Since PPARgamma2 is a main regulator of the differentiation process of adipocytes, we investigated whether GSPE affects the adipogenesis of 3T3-L1 cells. DESIGN: We performed a time point screening by treating 3T3-L1 cells with GSPE during the differentiation process for 24 h. MEASUREMENTS: Differentiation markers and differential gene expression due to GSPE treatment (using the microarray technique). RESULTS: Twenty four hour-GSPE treatment at the onset of differentiation reduces adipose-specific markers and maintains the expression of preadipocyte marker preadipocyte factor-1 (Pref-1) significantly elevated. These effects were not found in other time points. Microarray analysis of gene expression after GSPE treatment at the early stage of differentiation showed a modified gene expression profile in which cell cycle and growth-related genes were downregulated by GSPE. CONCLUSION: These results suggest that GSPE affects adipogenesis, mainly at the induction of differentiation, and that procyanidins may have a new role in which they impede the formation of adipose cells.     

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。     

抵抗素在3T3-L1前脂细胞分化前后表达量的变化

目的检测3T3-L1前脂细胞诱导分化为脂肪细胞前后抵抗素基因表达量的变化情况，为阐明抵抗素在细胞分化过程中所起作用并为研究其与胰岛素抵抗（珉）及2型糖尿病的相关性奠定基础。方法用地塞米松、甲基异丁基黄嘌呤与胰岛素联合诱导法抽提诱导分化前后细胞总RNA，半定量RT-PCR检测抵抗素基因表达量。结果抵抗素在3T3-L1细胞诱导前后表达量明显上升。结论抵抗素在3T3-L1细胞分化过程中表达量的提高，提示其很有可能在鼠脂肪细胞产生珉的过程中发挥积极作用。     

3T3-L1前脂肪细胞分化过程中chemerin基因表达水平的变化

目的 探讨体外培养3T3-L1前脂肪细胞诱导分化过程中chemerin基因表达水平的变化与脂肪细胞分化、脂质积聚之间的关系.方法 应用3-异丁基-1-甲基黄嘌呤、胰岛紊、地塞米松联合方案诱导其分化为成熟的脂肪细胞,采用油红0染色观察脂肪细胞分化及脂质聚集情况,并应用RT-PCR和Western印迹技术检测chemerin基因表达的变化.结果 3T3 -L1脂肪细胞分化过程中,chemerin mRNA表达水平逐渐升高,分化至第6天达到较高水平且逐渐趋于稳定.利用Western印迹可观察到,随着脂肪细胞分化成熟.chemerin基因的蛋白表达水平逐渐增高.结论 chemerin mRNA及蛋白质在脂肪细胞分化成熟过程中表达水平升高,提示其很有可能参与了脂肪细胞分化和脂质聚集.     

Apoptosis of human abdominal preadipocytes before and after differentiation into adipocytes in culture

Differentiation of murine 3T3-L1 preadipocytes into adipocytes is associated with the acquisition of apoptotic resistance accompanied by the upregulation of cell survival genes. We have now examined the effect of adipogenesis on apoptotic susceptibility of human abdominal preadipocytes in primary culture. To induce apoptosis, human preadipocytes, or their differentiated counterparts, were serum-deprived for 24 or 48 hours. When indicated, ceramide was also used as an apoptotic trigger. Cell death was assessed by enumeration of adherent viable cells, and its apoptotic nature was verified by Hoechst staining and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). After 48 hours of serum withdrawal, cell death was 26% +/- 4% in preadipocytes and was increased to 41% +/- 4% in differentiated adipocytes (mean +/- SE; n = 7 patients; P <.002). Under serum-free conditions for 24 hours, ceramide-induced cell death was 40% +/- 6% in preadipocytes and increased to 68% +/- 8% in adipocytes (mean +/- SE; P <.01; n = 8 patients). Neuronal apoptosis inhibitor protein (NAIP), an antiapoptotic protein cell survival that increases upon 3T3-L1 adipogenesis, was reduced in human preadipocytes undergoing differentiation (n = 6 patients). Preadipocytes derived from omental versus subcutaneous abdominal fat were more susceptible to apoptosis induced by serum deprivation, 16% +/- 4% versus 31% +/- 3% cell death, respectively (mean +/- SE; P <.02; n = 7 patients). Although the murine 3T3-L1 preadipocyte cell line is a useful model that approximates primary preadipocyte cell biology, our data derived from human preadipocyte studies suggest important differences with respect to the regulation of apoptosis.     

Thiazolidinedione- and tumor necrosis factor alpha-induced downregulation of peroxisome proliferator-activated receptor gamma mRNA in differentiated 3T3-L1 adipocytes

Thiazolidinediones (TZDs) are antidiabetic insulin-sensitizing agents that bind to peroxisome proliferator-activated receptor gamma (PPARgamma) and have potent adipogenic effects on 3T3-L1 preadipocytes. In fully differentiated 3T3-L1 adipocytes, TZDs markedly decreased PPARgamma mRNA levels without reducing the expression of genes that are positively regulated by PPARgamma, such as adipocyte lipid-binding protein 2 (aP2) or lipoprotein lipase-(LPL). PPARgamma mRNA levels were also downregulated by tumor necrosis factor alpha (TNFalpha), an antiadipogenic cytokine. We propose that the downregulation of PPARgamma is not the common denominator of the metabolic effects of TZDs and TNFalpha on mature adipocytes.     

Growth hormone induces c-fos and c-jun expression in cells with varying requirements for differentiation.

GH is one of the major factors required for the differentiation of 3T3-F442A preadipocyte fibroblasts into adipocytes. An early event following the addition of GH to 3T3-F442A preadipocytes is induction of the expression of c-fos and c-jun. Although c-fos and c-jun expression has been observed in conjunction with growth factor-stimulated differentiation in several cell types, it is not clear whether protooncogene expression and differentiation are necessarily related. In this study the relationship between the induction of these protooncogenes and differentiation was evaluated by taking advantage of several cell lines that are related to 3T3-F442A cells but have varying GH requirements for differentiation. Adipose differentiation in the adipogenic cell lines 3T3-L1 and 3T3-GI-16 is known to be GH independent, requiring insulin or insulin-like growth factor-I. In both 3T3-L1 and 3T3-GI-16 preadipocytes, GH, nevertheless, induced the expression of mRNA for both protooncogenes. GH (2.2 nM) was more effective than insulin (1 microM) in inducing c-fos expression in these two adipogenic cell lines, suggesting that induction of the protooncogenes is not sufficient to induce adipogenesis. 3T3-C2 fibroblasts do not differentiate in response to any of the stimuli that convert 3T3-F442A fibroblasts to adipocytes. However, GH (2.2 nM) as well as calf serum induced the expression of c-fos and c-jun in 3T3-C2 cells. NIH-3T3 fibroblasts, which do not undergo differentiation, also showed induction of c-fos by GH. Thus, GH-induced expression of c-fos and c-jun occurs in nondifferentiating cells. Furthermore, in differentiated 3T3-F442A adipocytes, GH stimulated the expression of c-fos and c-jun as it does in the preadipocytes. Since GH elicits a variety of metabolic responses in 3T3-F442A adipocytes, the present findings raise the possibility that induction of c-fos and c-jun expression might be associated with multiple events in GH-stimulated 3T3-F442A adipocytes. The lack of requirement for GH in GH-independent and nondifferentiating cells compared to 3T3-F442A cells does not appear to reflect the lack of GH receptors, since expression of mRNA for the GH receptor was evident in all of the cell types tested and, thus, corresponds with the ability of GH to induce protooncogene expression. Although GH-induced c-fos expression was relatively invariant, since it was evident in all of the cell types studied, this response could clearly be regulated, since it was attenuated by prior exposure to GH or serum in 3T3-F442A preadipocytes.(ABSTRACT TRUNCATED AT 400 WORDS)