Regulation of haptoglobin gene expression in 3T3-L1 adipocytes by cytokines, catecholamines, and PPARgamma

Factors which regulate expression of the haptoglobin (acute phase reactant) gene in adipocytes have been examined using 3T3-L1 cells. Haptoglobin expression was observed by Northern blotting in each of the major white adipose tissue depots of mice (epididymal, subcutaneous, mesenteric, and perirenal) and in interscapular brown fat. Expression occurred in mature adipocytes, but not in the stromal-vascular fraction. In 3T3-L1 cells, haptoglobin mRNA was detected from day 4 after the induction of differentiation into adipocytes. Lipopolysaccharide and the cytokines, TNFalpha and interleukin-6, resulted in substantial increases in haptoglobin mRNA in 3T3-L1 adipocytes; the increase (7-fold) was highest with TNFalpha. Increases in haptoglobin mRNA level were also induced by dexamethasone, noradrenaline, isoprenaline, and a beta3-adrenoceptor agonist. In contrast, haptoglobin mRNA was reduced by nicotinic acid and the PPARgamma agonist, rosiglitazone. RT-PCR showed that the haptoglobin gene was expressed in human adipose tissue (subcutaneous, omental). It is concluded that haptoglobin gene expression in adipocytes is stimulated by inflammatory cytokines, glucocorticoids, and the sympathetic system, while activation of the PPARgamma nuclear receptor is strongly inhibitory.     

FGF21 attenuates lipolysis in human adipocytes - a possible link to improved insulin sensitivity

Fibroblast growth factor 21 (FGF21) is active in murine adipocytes and has beneficial metabolic effects in animal models of type 2 diabetes mellitus. We assessed whether FGF21 influences lipolysis in human adipocytes and 3T3-L1 cells. FGF21 had no short-time effect (h) while a 3-day incubation with FGF21 attenuated hormone-stimulated lipolysis. FGF21 did not influence the mRNA expression of genes involved in regulating lipolysis, but significantly reduced the expression of the lipid droplet-associated phosphoprotein perilipin without affecting differentiation. Via reduced release of fatty acids into the circulation, the anti-lipolytic effect could be a mechanism through which FGF21 promotes insulin sensitivity in man.     

The effect of chronic fatty acid treatment on lipolysis in 3T3-L1 adipocytes.

Various saturated and unsaturated fatty acids were included in the culture medium to test their effects on lipolysis in 3T3-L1 adipocytes. Following prolonged incubation, only oleate was found to exert enhancing effect on basal and isoproterenol-stimulated lipolysis. The effect of oleate was concentration-dependent and was accompanied with increased intracellular cAMP content. Furthermore, the lipolytic response induced by isobutyl-methylxanthine, forskolin or dibutyryl cAMP was also increased in adipocytes treated with oleate. Thus, it appears that in addition to an increased cAMP accumulation, a step distal to cAMP production in the cells may be involved in inducing enhanced lipolysis in 3T3-L1 adipocytes by prolonged exposure to oleate.     

Development of a human adipocyte model derived from human mesenchymal stem cells (hMSC) as a tool for toxicological studies on the action of TCDD

Abstract Efforts were made to develop a human adipocyte model that is useful for toxicological studies in vitro. For this purpose, a stem cell line derived from human bone marrow cells, originally from an adult, was induced to differentiate towards adipocytes by treating them with insulin, dexamethasone, indomethacin and 3-isobutyl-1-methylxanthine for 3 d, followed by additional incubation for 3 d in Dulbecco's modified Eagle's medium supplemented with insulin only. In most cases, thus differentiated cells through such one cycle of differentiation treatment were further subjected to the second cycle of differentiation. The resulting 2-cycle differentiated cells were found to exhibit many characteristics of typical adipocytes. Dioxin (TCDD), when added at the beginning of their treatment with differentiation-inducing hormone cocktail, clearly prevented them from becoming adipocytes, as in the case of TCDD-treated 3T3-L1 cells. Furthermore, TCDD, even when administered to previously differentiated human mesenchymal stem cells (hMSC) adipocytes, consistently induced the sign of inflammatory responses during the early period of TCDD action (24 h), which was followed by gradual loss of adipocyte-specific markers during the 5-d incubation period. In conclusion, hMSC-derived adipocytes appear to offer a promising human cell model suited for future toxicological studies.     

下调Fsp27基因表达联合杨梅素干预对3T3-L1细胞脂解的影响

目的:下调脂肪特异性蛋白27(Fsp27)基因表达联合杨梅素干预,观察对3T3-L1细胞中脂质代谢的影响,并探究脂滴发生、发展变化的调控机制。方法:常规培养3T3-L1前脂肪细胞,采用"鸡尾酒"法诱导其分化为成熟脂肪细胞。脂质体法转染sh-Fsp27干扰载体,以杨梅素浓度为100μmol/L的完全培养基干预成熟脂肪细胞72h。油红O染色,观察脂滴形态及大小的变化;酶法测定细胞内甘油及甘油三酯的含量,观察细胞脂质代谢的变化。Western blot检测Fsp27、激素敏感性甘油三酯脂肪酶(HSL)、甘油三酯脂肪酶(ATGL)以及丝裂原活化蛋白激酶(MAPK)信号通路蛋白的表达。结果:1. 3T3-L1细胞诱导分化后,形态由纤维样变成圆形,并伴随有细胞体积的增大。2.与对照组相比,杨梅素组和转染组细胞中甘油三酯含量下降,甘油含量升高(P 0. 05)。与其他三组相比,联合干预组细胞中甘油三酯含量减少,甘油含量增加(P 0. 05)。3.与对照组相比,其余三组细胞内Fsp27蛋白的表达量均降低,ATGL和PPARγ的表达量升高(P 0. 05)。另外,联合干预组和杨梅素组细胞内HSL的表达量和p-p38MAPK/p38MAPK的比值均大于sh-Fsp27组和对照组(P 0. 05)。结论:1. Fsp27基因沉默与杨梅素联合干预可以更大程度地促进脂肪分解代谢。2.杨梅素可通过激活MAPK信号通路,上调HSL和ATGL的蛋白表达来发挥其促脂解的作用; sh-Fsp27干扰载体通过调节PPARγ和Fsp27蛋白的表达,增加ATGL含量来加速脂肪分解。     

Gene expression of isoformic enzymes in arachidonate cyclooxygenase pathway and the regulation by tumor necrosis factor alpha during life cycle of adipocytes

Adipocytes serve not only as a storage depot of fats but also as endocrine cells secreting adipocytokines including tumor necrosis factor alpha (TNFalpha). Using preadipogenic 3T3-L1 cells, we attempt to determine the response of adipocytes at different stages of the life cycle to TNFalpha with respect to the gene expression of the arachidonate cyclooxygenase (COX) pathway and the role of endogenous prostaglandins (PGs). The gene expression analysis of the COX pathway revealed the marked increase in mRNA and protein levels of COX-2 in response to TNFalpha in preadipocytes, whereas COX-1 was expressed constitutively. Moreover, the cells at different cycle stages exhibited the specific gene expression of isoformic enzymes of prostaglandin (PG) synthases for PGs of the D(2), E(2), and F(2alpha) series upon exposure to TNFalpha. The treatment of preadipocytes with TNFalpha along with calcium ionophore A23187 resulted in the stimulated formation of PGE(2) and PGF(2alpha), attenuating the apoptotic cell death induced by TNFalpha alone. The response of adipocytes to synthesize these PGs declined during the differentiation and maturation phases. The cells during the differentiation phase were the most sensitive to TNFalpha in terms of the decrease in adipogenesis without the mediation of endogenous PGs. TNFalpha was also effective in suppressing adipogenesis during the maturation process. Taken together, TNFalpha can control cell number of preadipocytes as well as the size of fat storage in mature adipocytes. The action of TNFalpha on preadipocytes can be modulated by the production of endogenous PGs through the induction of COX-2.     

TNF-alpha induction of lipolysis is mediated through activation of the extracellular signal related kinase pathway in 3T3-L1 adipocytes

Tumor necrosis factor-alpha (TNF-alpha) increases adipocyte lipolysis after 6-12 h of incubation. TNF-alpha has been demonstrated to activate mitogen-activated protein (MAP) kinases including extracellular signal-related kinase (ERK) and N-terminal-c-Jun-kinase (JNK) in different cell types. To determine if the MAP kinases have a role in TNF-alpha-induced lipolysis, 3T3-L1 adipocytes were treated with the cytokine (10 ng/ml), in the presence or absence of PD98059 or U0126 (100 micromoles), specific inhibitors of ERK activity. We demonstrated that U0126 or PD98059 blocked TNF-alpha-induced ERK activity and decreased TNF-alpha-induced lipolysis by 65 or 76% respectively. The peroxisome-proliferator-activated receptor gamma (PPARgamma) agonists, rosiglitazone (ros), and 15-deoxy-Delta-(12,14)- prostaglandin J(2) (PGJ2) have been demonstrated to block TNF-alpha-induced lipolysis. Pretreatment of adipocytes with these agents almost totally blocked TNF-alpha-induced ERK activation and reduced lipolysis by greater than 90%. TNF-alpha also stimulated JNK activity, which was not affected by PD98059 or PPARgamma agonist treatment. The expression of perilipin, previously proposed to contribute to the mechanism of lipolysis, is diminished in response to TNF-alpha treatment. Pretreatment of adipocytes with PD98059 or ros significantly blocked the TNF-alpha-induced reduction of perilipin A protein level as determined by Western analysis. These data suggest that activation of the ERK pathway is an early event in the mechanism of TNF-alpha-induced lipolysis.     

2,3,7,8-tetrachlorodibenzo-p-dioxin mechanism of action to reduce lipoprotein lipase activity in the 3T3-L1 preadipocyte cell line

Lipoprotein lipase (LPL) is important in the process of triglyceride storage in adipose tissue. Depression of LPL activity in adipose tissue is associated with 2,3,7,8-tetrachlorodibenzo-p -dioxin (TCDD)-induced wasting syndrome and may have a role in the associated serum hyperlipidemia produced by TCDD. The 3T3-L1 cell line was used as an in vitro model, independent of hormonal, nutritional, or other interfering factors associated with in vivo studies, in order to systematically examine the mechanism of action of TCDD. TCDD produced a statistically significant (P < 0.05) time- and dose-dependent decrease in LPL activity. Results of experiments with Ah-receptor blockers and structure activity studies with different polychlorinated biphenyl (PCB) and dioxin congeners were consistent with reduction of LPL activity being mediated by the Ah receptor. Culturing of 3T3-L1 cells without glucose or with cytochalasin B, a blocker of facilitative glucose transporters (GLUT), was effective in reducing LPL activity (P < 0.05). TCDD did not further reduce LPL activity in cytochalasin B pretreated 3T3-L1 cells or in 3T3-L1 cells cultured in glucose-free media. Dexamethasone pretreatment, which is known to increase GLUT expression in 3T3-L1 cells, prevented the reduction of LPL activity by TCDD. Protein tyrosine kinase activities, assayed using γ-³²P-ATP and RR-SRC, a src specific peptide substrate, were significantly increased (P < 0.05) over control levels by both TCDD and glucose deprivation. Furthermore, results of experiments treating 3T3-L1 cells with either insulin, EGF, 8-Br-cAMP, TPA, or genistein, alone or in combination with TCDD, were generally consistent with the hypothesis that lowered intracellular glucose and altered cellular kinase activities may be involved in reduction of LPL activities by TCDD. Further work is needed to confirm and better understand the role protein phosphorylation plays in TCDD-mediated alteration of glucose disposition and LPL activity. In summary, TCDD reduced LPL activity in 3T3-L1 cells as seen in vivo. Manipulation of glucose transport through a number of experimental approaches produced changes in 3T3-L1 LPL activity consistent with results of previous investigators showing glucose to be a positive regulator of LPL activity and consistent with our hypothesis that TCDD-mediated reduction of glucose transport is an important factor in the down regulation of LPL activity by TCDD. © 1997 John Wiley & Sons, Inc. J Biochem Toxicol 12: 29–39, 1998     

Induction of SOCS-3 is insufficient to confer IRS-1 protein degradation in 3T3-L1 adipocytes

Insulin receptor substrate (IRS)-1 is a key protein in insulin signaling. Several studies have shown that the expression of IRS-1 can be modulated by protein degradation via the proteasome and the degradation of IRS-1 can be related to insulin-resistant states. The degradation of IRS-1 has been shown to be induced by SOCS-1 and SOCS-3 via the ubiquitin pathway. The goal of our study was to determine if the induction of SOCS-3 correlated with increased IRS-1 degradation in cultured 3T3-L1 adipocytes. Interestingly, our studies have shown that there is little correlation between the induction in SOCS-3 expression and the degradation of IRS-1 in mature 3T3-L1 adipocytes. Our results clearly demonstrate that treatment with leukemia inhibitory factor (LIF) or cardiotrophin (CT)-1 strongly induces the expression of SOCS-3 in mature 3T3-L1 adipocytes, but does not affect the degradation of IRS-1. On the contrary, tumor necrosis factor (TNF) alpha and insulin, which very weakly induce SOCS-3 expression, have profound effects on IRS-1 degradation. In summary, our results indicate that the expression of SOCS-3 does not correlate with the degradation of IRS-1 proteins in fat cells.     

α-Mangostin induces apoptosis and suppresses differentiation of 3T3-L1 cells via inhibiting fatty acid synthase

α-Mangostin, isolated from the hulls of Garcinia mangostana L., was found to have in vitro cytotoxicity against 3T3-L1 cells as well as inhibiting fatty acid synthase (FAS, EC 2.3.1.85). Our studies showed that the cytotoxicity of α-mangostin with IC(50) value of 20 μM was incomplicated in apoptotic events including increase of cell membrane permeability, nuclear chromatin condensation and mitochondrial membrane potential (ΔΨm) loss. This cytotoxicity was accompanied by the reduction of FAS activity in cells and could be rescued by 50 μM or 100 μM exogenous palmitic acids, which suggested that the apoptosis of 3T3-L1 preadipocytes induced by α-mangostin was via inhibition of FAS. Futhermore, α-mangostin could suppress intracellular lipid accumulation in the differentiating adipocytes and stimulated lipolysis in mature adipocytes, which was also related to its inhibition of FAS. In addition, 3T3-L1 preadipocytes were more susceptible to the cytotoxic effect of α-mangostin than mature adipocytes. Further studies showed that α-mangostin inhibited FAS probably by stronger action on the ketoacyl synthase domain and weaker action on the acetyl/malonyl transferase domain. These findings suggested that α-mangostin might be useful for preventing or treating obesity.     

Tumor necrosis factor receptor-1 can function through a G alpha q/11-beta-arrestin-1 signaling complex

Tumor necrosis factor-alpha (TNFalpha) is a proinflammatory cytokine secreted from macrophages and adipocytes. It is well known that chronic TNFalpha exposure can lead to insulin resistance both in vitro and in vivo and that elevated blood levels of TNFalpha are observed in obese and/or diabetic individuals. TNFalpha has many acute biologic effects, mediated by a complex intracellular signaling pathway. In these studies we have identified new G-protein signaling components to this pathway in 3T3-L1 adipocytes. We found that beta-arrestin-1 is associated with TRAF2 (TNF receptor-associated factor 2), an adaptor protein of TNF receptors, and that TNFalpha acutely stimulates tyrosine phosphorylation of G alpha(q/11) with an increase in G alpha(q/11) activity. Small interfering RNA-mediated knockdown of beta-arrestin-1 inhibits TNFalpha-induced tyrosine phosphorylation of G alpha(q/11) by interruption of Src kinase activation. TNFalpha stimulates lipolysis in 3T3-L1 adipocytes, and beta-arrestin-1 knockdown blocks the effects of TNFalpha to stimulate ERK activation and glycerol release. TNFalpha also led to activation of JNK with increased expression of the proinflammatory gene, monocyte chemoattractant protein-1 and matrix metalloproteinase 3, and beta-arrestin-1 knockdown inhibited both of these effects. Taken together these results reveal novel elements of TNFalpha action; 1) the trimeric G-protein component G alpha(q/11) and the adapter protein beta-arrestin-1 can function as signaling molecules in the TNFalpha action cascade; 2) beta-arrestin-1 can couple TNFalpha stimulation to ERK activation and lipolysis; 3) beta-arrestin-1 and G alpha(q/11) can mediate TNFalpha-induced phosphatidylinositol 3-kinase activation and inflammatory gene expression.     

槟榔碱对3T3-L1脂肪细胞脂代谢的影响

目的：观察槟榔碱对3T3-L1脂肪细胞脂代谢的影响并探讨其可能机制。方法：采用经典的"鸡尾酒"法诱导3T3-L1前脂肪细胞分化成熟,随后用不同浓度的槟榔碱（0、25、50、100 μmol/L）处理成熟脂肪细胞72 h。72 h后,四甲基偶氮唑盐（MTT）法检测细胞的活性;油红O染色观察胞浆内脂滴情况;Western blot检测脂肪酸合成酶（FAS）、甘油三酯脂肪酶（ATGL）、激素敏感性脂肪酶（HSL）蛋白表达。结果：诱导分化成熟的脂肪细胞胞浆内可见大量脂滴;MTT显示：0~100 μmol/L槟榔碱对脂肪细胞活力无显著影响;油红O染色后脂质含量测定结果表明槟榔碱能减少成熟脂肪细胞中脂质含量;Western blot结果显示：与0 μmol/L组（对照组）相比,槟榔碱可显著降低脂肪细胞内FAS的蛋白表达,增加ATGL和HSL的蛋白表达;其中以50 μmol/L组最为显著。结论：槟榔碱使脂肪细胞脂解增强,可能与降低脂质合成关键酶FAS的表达,增加脂质分解代谢关键酶ATGL和HSL的表达有关。     

The role of cyclic nucleotide phosphodiesterases in the regulation of adipocyte lipolysis

This study assessed the effects of selective inhibitors of 3',5'-cyclic nucleotide phosphodiesterases (PDEs) on adipocyte lipolysis. IC224, a selective inhibitor of type 1 phosphodiesterase (PDE1), suppressed lipolysis in murine 3T3-L1 adipocytes (69.6 +/- 5.4% of vehicle control) but had no effect in human adipocytes. IC933, a selective inhibitor of PDE2, had no effect on lipolysis in either cultured murine 3T3-L1 adipocytes or human adipocytes. Inhibition of PDE3 with cilostamide moderately stimulated lipolysis in murine 3T3-L1 and rat adipocytes (397 +/- 25% and 235 +/- 26% of control, respectively) and markedly stimulated lipolysis in human adipocytes (932 +/- 7.6% of control). Inhibition of PDE4 with rolipram moderately stimulated lipolysis in murine 3T3-L1 adipocytes (291 +/- 13% of control) and weakly stimulated lipolysis in rat adipocytes (149 +/- 7.0% of control) but had no effect on lipolysis in human adipocytes. Cultured adipocytes also responded differently to a combination of PDE3 and PDE4 inhibitors. Simultaneous exposure to cilostamide and rolipram had a synergistic effect on lipolysis in murine 3T3-L1 and rat adipocytes but not in human adipocytes. Hence, the relative importance of PDE3 and PDE4 in regulating lipolysis differed in cultured murine, rat, and human adipocytes.     

Endothelin-1 induces lipolysis through activation of the GC/cGMP/Ca2+/ERK/CaMKIII pathway in 3T3-L1 adipocytes

Endothelin-1 (ET-1) is a potent vasoconstrictive peptide produced and secreted mainly by endothelial cells. Recent studies indicate that ET-1 can regulate lipid metabolism, which may increase the risk of insulin resistance. Our previous studies revealed that ET-1 induced lipolysis in adipocytes, but the underlying mechanisms were unclear. 3T3-L1 adipocytes were used to investigate the effect of ET-1 on lipolysis and the underlying mechanisms. Glycerol levels in the incubation medium and hormone-sensitive lipase (HSL) phosphorylation were used as indices for lipolysis. ET-1 significantly increased HSL phosphorylation and lipolysis, which were completely inhibited by ERK inhibitor (PD98059) and guanylyl cyclase (GC) inhibitor (LY83583). LY83583 reduced ET-1-induced ERK phosphorylation. A Ca²⁺-free medium and PLC inhibitor caused significant decreases in ET-1-induced lipolysis as well as ERK and HSL phosphorylation, and IP₃ receptor activator (D-IP₃) increased lipolysis. ET-1 increased cGMP production, which was not affected by depletion of extracellular Ca²⁺. On the other hand, LY83583 diminished the ET-1-induced Ca²⁺ influx. Transient receptor potential vanilloid-1 (TRPV-1) antagonist and shRNA partially inhibited ET-1-induced lipolysis. ET-1-induced lipolysis was completely suppressed by CaMKIII inhibitor (NH-125). These results indicate that ET-1 stimulates extracellular Ca²⁺ entry and activates the intracellular PLC/IP₃/Ca²⁺ pathway through a cGMP-dependent pathway. The increased cytosolic Ca²⁺ that results from ET-1 treatment stimulates ERK and HSL phosphorylation, which subsequently induces lipolysis. ET-1 induces HSL phosphorylation and lipolysis via the GC/cGMP/Ca²⁺/ERK/CaMKIII signaling pathway in 3T3-L1 adipocytes.     

Correlation between the high expression of C/EBPbeta protein in F442A cells and their relative resistance to antiadipogenic action of TCDD in comparison to 3T3-L1 cells

We compared the ability of two clonally derived murine preadipocyte cell lines, 3T3-L1(L1) and 3T3-F442A (F442A), to differentiate after treatment by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and found that the former cell line was clearly suppressed by TCDD but the latter was not. It was initially postulated that the easiest way to explain the lack of response to TCDD in F442A cells could be an alteration in aryl hydrocarbon receptor (AhR) functionality. This hypothesis was tested first, but no differences were found in the levels or functions of AhR. To find an alternate explanation for such a differential effect of TCDD, we tested the action of several diagnostic agents on the process of adipocyte differentiation of these two cells. No differences were found between these two lines of cells in the susceptibility to the antiadipogenic action of 12-0-tetradecanoylphorbol-13-acetate (TPA), or to TNFalpha, indicating that the basic biochemical components engaged in the antiadipogenic actions of these agents in these two cell lines are similar. In contrast, F442A cells were found to be more resistant to the antiadipogenic action of EGF or TGFbeta than L1 cells which were tested side by side. Based on the knowledge that TNFalpha preferentially affects C/EBPalpha and that TGFbeta specifically controls C/EBPbeta and delta in their antiadipogenic action, we hypothesized that the major cause for the differential response of these two similar cell lines could be the insensitivity of C/EBPbeta and/or delta of F442A cells to the action of TCDD. We could obtain supporting data for this hypothesis, showing that in F442A cells, the level of C/EBPbeta is already high even before the addition of adipocyte differentiation factors and that TCDD did not cause any significant changes in the titer of C/EBPbeta.     

Fucoxanthin exerts differing effects on 3T3-L1 cells according to differentiation stage and inhibits glucose uptake in mature adipocytes

Progression of 3T3-L1 preadipocyte differentiation is divided into early (days 0–2, D0–D2), intermediate (days 2–4, D2–D4), and late stages (day 4 onwards, D4-). In this study, we investigated the effects of fucoxanthin, isolated from the edible brown seaweed Petalonia binghamiae, on adipogenesis during the three differentiation stages of 3T3-L1 preadipocytes. When fucoxanthin was applied during the early stage of differentiation (D0–D2), it promoted 3T3-L1 adipocyte differentiation, as evidenced by increased triglyceride accumulation. At the molecular level, fucoxanthin increased protein expression of peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer-binding protein α (C/EBPα), sterol regulatory element-binding protein 1c (SREBP1c), and aP2, and adiponectin mRNA expression, in a dose-dependent manner. However, it reduced the expression of PPARγ, C/EBPα, and SREBP1c during the intermediate (D2–D4) and late stages (D4–D7) of differentiation. It also inhibited the uptake of glucose in mature 3T3-L1 adipocytes by reducing the phosphorylation of insulin receptor substrate 1 (IRS-1). These results suggest that fucoxanthin exerts differing effects on 3T3-L1 cells of different differentiation stages and inhibits glucose uptake in mature adipocytes.     

胰岛素对3T3-L1脂肪细胞中极低密度脂蛋白受体基因表达的影响

体外培养3T3-L1细胞分化模型,研究不同浓度胰岛素及慢性胰岛素刺激对3T3-L1脂肪细胞中极低密度脂蛋白受体（VLDLR）基因表达的影响.在不同浓度胰岛素及胰岛素慢性刺激的干预下,用半定量RT-PCR检测细胞VLDLR mRNA水平的变化.微量化GOD-PAP法检测培养基中残存的葡萄糖.在细胞诱导分化过程中,胰岛素浓度的增高促进VLDLR的表达;胰岛素慢性刺激下,VLDLR表达因浓度差异呈现不同变化.研究结果表明,胰岛素的浓度及慢性刺激对3T3-L1脂肪细胞的成熟和VLDLR基因的表达有显著作用,而胰岛素抵抗明显减低成熟脂肪细胞VLDLR的表达.     

Fat-specific protein 27, a novel lipid droplet protein that enhances triglyceride storage

Fat-specific protein (FSP)27/Cidec is most highly expressed in white and brown adipose tissues and increases in abundance by over 50-fold during adipogenesis. However, its function in adipocytes has remained elusive since its discovery over 15 years ago. Here we demonstrate that FSP27/Cidec localizes to lipid droplets in cultured adipocytes and functions to promote lipid accumulation. Ectopically expressed FSP27-GFP surrounds lipid droplets in 3T3-L1 adipocytes and colocalizes with the known lipid droplet protein perilipin. Immunostaining of endogenous FSP27 in 3T3-L1 adipocytes also confirmed its presence on lipid droplets. FSP27-GFP expression also markedly increases lipid droplet size and enhances accumulation of total neutral lipids in 3T3-L1 preadipocytes as well as other cell types such as COS cells. Conversely, RNA interference-based FSP27/Cidec depletion in mature adipocytes significantly stimulates lipolysis and reduces the size of lipid droplets. These data reveal FSP27/Cidec as a novel adipocyte lipid droplet protein that negatively regulates lipolysis and promotes triglyceride accumulation.     

Spexin: A novel regulator of adipogenesis and fat tissue metabolism

Spexin (SPX, NPQ) is a novel peptide involved in the regulation of energy metabolism. SPX inhibits food intake and reduces body weight. In obese humans, SPX is the most down-regulated gene in fat. Therefore, SPX might be involved in the regulation of lipid metabolism. Here, we study the effects of SPX on lipolysis, lipogenesis, glucose uptake, adipogenesis, cell proliferation and survival in isolated human adipocytes or murine 3T3-L1 cells. SPX and its receptors, GALR2 and GALR3, are present at mRNA and protein levels in murine 3T3-L1 cells and human adipocytes. SPX inhibits adipogenesis and down-regulates mRNA expression of proadipogenic genes such as Pparγ, C/ebpα, C/ebpβ and Fabp4. SPX stimulates lipolysis by increasing the phosphorylation of hormone sensitive lipase (HSL). Simultaneously, SPX inhibits lipogenesis and glucose uptake in human adipocytes and murine 3T3-L1 cells. SPX has no effect on murine 3T3-L1 cell proliferation and viability. Moreover, our research showed that the SPX effect on adipocytes metabolism is mediated via GALR2 and GALR3 receptors. SPX is a novel regulator of lipid metabolism in murine 3T3-L1 and human adipocytes.