灵芝多糖对3T3-L1胰岛素抵抗细胞模型PI-3K p85和GLUT4蛋白表达的影响

目的 研究灵芝多糖对3T3-L1胰岛素抵抗细胞模型PI-3K p85和GLUT4蛋白表达的影响,探讨灵芝多糖改善胰岛素抵抗的分子机制.方法 3T3-L1前脂肪细胞经1-甲基-3-异丁基-黄嘌呤、地塞米松、胰岛素诱导分化成3T3-L1脂肪细胞,以葡萄糖氧化酶法测定培养液中残余的葡萄糖含量.比较二甲双胍组,检测培养液中葡萄糖含量及PI-3K p85和GLUT4蛋白表达变化.结果 地塞米松联合胰岛素诱导3T3-L1脂肪细胞产生胰岛素抵抗,细胞对葡萄糖的摄取量减少.灵芝多糖可改善3T3-L1脂肪细胞胰岛素抵抗.胰岛素抵抗细胞的PI-3K p85和GLUT4蛋白表达明显减少;应用灵芝多糖后,相关蛋白表达增加.结论 灵芝多糖通过提高PI-3K p85和GLUT4蛋白的表达,参与胰岛素抵抗状态下3T3-L1细胞的葡萄糖代谢.     

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.     

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。     

Rheb过表达在前体脂肪细胞株3T3-L1分化中的作用

目的:利用前体脂肪细胞株3T3-L1细胞观察mTOR(mammalian target of rapamycin)信号通路中上游调控因子Rheb(Ras homolog enriched in brain)对其分化的影响。方法:利用高表达Rheb的基因重组质粒转染前体脂肪细胞株,3T3-L1。通过蛋白质免疫印迹实验鉴定质粒成功转染细胞后,诱导该细胞脂肪分化。予以分化第8天的3T3-L1细胞油红染色,并检测细胞内甘油三酯的含量。另外,我们用Western blot方法检测脂肪细胞特异性转录因子PPAR-γ(Peroxisome proliferator-activated receptor-γ)和C/EBP-α(CCAAT-enhancer-binding protein-α)的表达情况来研究Rheb在脂肪细胞分化过程中的作用。结果:我们成功构建了高表达Rheb的3T3-L1细胞株,发现高表达Rheb后可以促进脂滴的生成,油红O染色有显著区别,与对照组相比Rheb高表达组的三酰甘油含量明显升高(P0.05);C/EBP-α和PPAR-γ等脂肪细胞特异性的转录因子蛋白表达量与对照组相比也均有升高(P0.05)。结论:Rheb基因作为mTOR通路上游调控因子,可以促进脂肪细胞的分化。     

水通道蛋白7对蛋白激酶B的影响

该文旨在探讨水通道蛋白7(AQP7)在3T3-L1脂肪细胞不同分化阶段的表达以及其对胰岛素信号通路中蛋白激酶B(PKB)的影响。通过培养3T3-L1前体脂肪细胞,诱导分化为成熟的脂肪细胞,用荧光定量PCR、Western blot、酶学方法分析显示,随3T3-L1脂肪细胞分化过程,AQP7与PKB磷酸化水平同步上升,同时培养基中释放的甘油浓度伴随AQP7的表达平行增加。以TNF-α处理分化成熟的脂肪细胞构建胰岛素抵抗模型,AQP7与PKB磷酸化水平均下降,转染高表达AQP7基因的重组腺病毒载体(Ad-AQP7)之后,随着AQP7表达上调,胰岛素刺激下的PKB磷酸化水平提高,并且葡萄糖代谢能力增强。由此可见,AQP7水平随3T3-L1脂肪细胞分化过程逐渐上升,其高表达可能通过增加PKB磷酸化水平改善胰岛素敏感性,提示AQP7可能成为治疗肥胖的一个重要作用靶点。     

辣椒碱对3T3-L1 前脂肪细胞葡萄糖摄取的影响

目的:探讨辣椒碱对3T3-L1前脂肪细胞葡萄糖摄取的影响。方法:不同浓度的辣椒碱作用于3T3-L1前脂肪细胞,采用MTT测定细胞活性,GLU Test试剂盒法测定葡萄糖摄取,Western Blot法检测葡萄糖转运蛋白1(GLUT-1)表达的变化。结果:25μM辣椒碱作用72 h和50μM、100μM辣椒碱作用48 h、72 h,可显著抑制3T3-L1细胞增殖,6.25、12.5、25μM辣椒碱作用可显著促进3T3-L1细胞的葡萄糖摄入,Western Blot结果显示辣椒碱能够显著增加GLUT1蛋白表达量,差异均具有统计学意义(P0.05)。结论:低剂量辣椒碱具有降糖作用,其作用机制可能与增加GLUT-1蛋白表达有关。     

促酰化蛋白对脂肪细胞分化中脂滴相关蛋白TIP47表达的影响

研究促酰化蛋白（acylation stimulating protein, ASP）在3T3-L1脂肪细胞分化中对脂滴相关蛋白TIP47(tail-interacting protein 47 kD)表达的影响,从而探讨ASP在成脂方面的重要意义．用免疫荧光染色法观察3T3-L1前脂肪细胞中TIP47的表达定位;采用经典激素鸡尾酒法诱导分化3T3-L1前脂肪细胞,用RT-PCR和Western 印迹方法检测诱导分化的3T3-L1脂肪细胞中TIP47 mRNA和蛋白表达;在分化过程中不同时点,对诱导分化中的3T3-L1脂肪细胞分别给予胰岛素和ASP处理,并设立相应空白对照,用RT-PCR和Western印迹方法检测TIP47 mRNA和蛋白表达． 结果显示,3T3-L1前脂肪细胞中TIP47主要在胞浆内表达;诱导分化过程中的3T3-L1脂肪细胞TIP47 mRNA和蛋白的表达水平呈时间依赖性降低;ASP对诱导分化的3T3-L1脂肪细胞中TIP47 mRNA和蛋白表达有显著的上调作用,但随着分化至48 h,其上调作用已不明显;胰岛素仅在分化的0 d对脂肪细胞中TIP47 mRNA和蛋白表达有上调作用,之后基本无影响．结果提示,ASP促成脂作用可能与其调节脂滴相关蛋白TIP47的表达密切相关,从而为认识及防治肥胖症开拓新的思路．     

舒林酸调节IKK通路对3T3-L1细胞IRS-1酪氨酸磷酸化的影响

目的探讨舒林酸通过调节IKK通路对分化成熟3T3-L1细胞胰岛素受体后信号转导蛋白胰岛素受体底物1（IRS-1）蛋白酪氨酸/丝氨酸（Tyr/Ser）残基磷酸化表达的影响。 方法用地塞米松、IBMX和胰岛素三联培养诱导3T3-L1前脂肪细胞分化为成熟脂肪细胞,油红O染色观察脂肪细胞形态。诱导分化成熟的脂肪细胞如下分组干预,实时荧光定量PCR检测不同浓度炎症因子IL-1 β（0,1,10,100 ng/ml）和（或）不同浓度IKK特异阻断剂舒林酸（0,0.1,1,10 mmol/L）对诱导分化成熟的脂肪细胞IKK通路激活状态的影响。Western Blot检测IL-1β和（或）舒林酸对诱导分化成熟的脂肪细胞IRS-1酪氨酸/丝氨酸残基磷酸化状态的影响。采用单因素方差分析进行统计学分析。 结果实时荧光定量PCR和Western Blot结果显示,IL-1β 10 ng/ml组诱导成熟脂肪细胞IKKβ mRNA较对照组相对表达水平增加,分别为[（2.85±0.16）﹪,（1.00±0.12）﹪,P < 0.01];而IRS-1酪氨酸的磷酸化相对表达量较对照组下降,分别为[（0.72±0.26）﹪,（1.00±0.24）﹪,P < 0.01]。进一步予舒林酸（1?mmol/?L、10?mmol/L）干预后较对照组显著逆转IL-1β诱导脂肪细胞IRS-1酪氨酸磷酸化的表达水平,分别为[（1.72±0.16）﹪,（1.90±0.08）﹪,（1.00±0.13）﹪,P < 0.01],同时下调IRS-1丝氨酸磷酸化的表达水平[（0.79±0.16）﹪,（0.66±0.08）﹪,（1.00±0.10）﹪,P < 0.05]。 结?论IL-1β通过促进诱导分化成熟脂肪细胞IKKβ的表达,激活脂肪细胞IKK炎症通路,抑制脂肪细胞IRS-1酪氨酸残基磷酸化的表达,舒林酸通过调节脂肪细胞IRS-1酪氨酸/丝氨酸残基磷酸化的表达,改善脂肪细胞胰岛素受体后信号转导。     

脂肪细胞在肝细胞胰岛素耐受过程中的作用

目的研究脂肪细胞在不同分化阶段对肝细胞胰岛素抵抗的影响。方法体外诱导3T3-L1脂肪前体细胞分化,细胞内脂滴增加,逐步分化成脂肪细胞。采用不同分化阶段脂肪细胞（未分化0 d、中期分化4d、接近完全分化8d）与原代肝细胞共培养。Western印迹法检测共培养后肝细胞内胰岛素信号通路的反应性;葡萄糖同位素标记方法检测肝细胞糖原合成能力。结果以未共培养的肝细胞为对照组,共培养后肝细胞内胰岛素受体底物-2酪氨酸磷酸化（Tyr^612）（pIRS-2）水平及Akt磷酸化（Ser^473）（pAkt）水平均显著下调;肝糖原合成能力明显降低;与较成熟脂肪细胞共培养后,肝细胞pIRS-2及pAkt水平与其他分化阶段组共培养比较下调明显,肝糖原合成能力随着脂肪细胞的成熟而明显降低。结论脂肪细胞可能诱导肝细胞发生胰岛素抵抗,肝细胞胰岛素信号通路的阻滞程度与脂肪细胞的分化程度呈正相关。     

促酰化蛋白(ASP)诱导3T3-L1前脂肪细胞分化

促酰化蛋白 (ASP)代替经典激素“鸡尾酒”诱导法中胰岛素 ,通过形态学观察、油红染色分化百分比测定、脂肪细胞甘油三酯合成率和甘油三酯总量测定 ,并与经典激素“鸡尾酒”法诱导前脂肪细胞分化情况比较 ,探讨ASP是否具有诱导 3T3 L1前脂肪细胞分化作用 .ASP组诱导分化第 6d ,3T3 L1前脂肪细胞变大、变圆 ,出现大量脂肪滴 ,形态由前脂肪细胞向成熟脂肪细胞转变 ;随着诱导分化时间延长 ,胞浆中脂滴进一步积累 .分化 9d时 ,3T3 L1前脂肪细胞分化完全 .油红染色结果显示 ,ASP组分化率很高 (85 % ) ,与胰岛素组分化率 (90 % )相似 ,明显高于IBMX +DEX组 (4 0 % ) .ASP不仅促进 3T3 L1前脂肪细胞形态向成熟脂肪细胞转化 ,同时促进细胞中甘油三酯的合成和积累 .ASP组诱导分化第 3d时 ,脂肪细胞甘油三酯合成率明显高于对照组和IBMX +DEX组 ,但仍低于胰岛素组 ;在分化第 6d和第 9d时 ,ASP组甘油三酯合成率进一步升高 ,与对照组和IBMX +DEX组相比差异有极显著性 ,与胰岛素组相比无显著性差异 .ASP组诱导分化 3d时 ,脂肪细胞中甘油三酯总量明显高于对照组和IBMX +DEX组 ;分化 6d和 9d时 ,甘油三酯总量进一步升高 ,与对照组和IBMX +DEX组相比差异有极显著性 ,而与胰岛素组相比无显著性差异 .结果表明 ,新型脂源性激     

Induction of cell death by photodynamic therapy with a new synthetic photosensitizer DH-I-180-3 in undifferentiated and differentiated 3T3-L1 cells

To examine the photodynamic therapy (PDT) effect on adipocytes, we investigated whether PDT using DH-I-180-3, a new synthetic lipophilic photosensitizer, induced cell death of both undifferentiated and differentiated 3T3-L1. 3T3-L1 pre-adipocytes were differentiated into adipocytes in the culture medium containing pantothenate, insulin, dexamethasone, isobutylmethylxanthine, and troglitazone. PDT was applied to both undifferentiated and differentiated 3T3-L1. Photosensitizer uptake in fat cells was determined by measuring its mean fluorescence intensity. DH-I-180-3 mediated effectively PDT-induced cell death of both pre-adipocytes and adipocytes. And the photosensitizer was accumulated more rapidly in 3T3-L1 adipocytes, compared with other cancer cell lines. These results demonstrate that PDT is a potent cell death inducer in pre-adipocytes and adipocytes. Thus, PDT with DH-I-180-3 may be applied for a new therapeutic modality for obesity treatment.     

人源FGF-21在脂肪细胞糖代谢中的作用

近年来研究发现,成纤维细胞生长因子(FGF)-21是一种新的代谢调节因子.为了深入研究人源FGF-21（hFGF-21）的生物活性,本实验利用SUMO高效表达载体,高效表达成熟的hFGF-21,并利用小鼠3T3-L1脂肪细胞检测hFGF-21的糖代谢活性．实验结果表明,hFGF-21可促进脂肪细胞的葡萄糖吸收,且葡萄糖吸收效率呈剂量依赖性．hFGF-21作用4 h即可促进脂肪细胞糖吸收,其活性可持续24 h以上．hFGF-21与胰岛素共同作用的葡萄糖吸收效果,明显优于它们的单独作用结果,说明hFGF-21与胰岛素发挥协同作用．脂肪细胞经hFGF-21预处理后,显著增加了胰岛素促进脂肪细胞吸收葡萄糖的效率,说明hFGF-21可以增加胰岛素的敏感性．本实验为临床应用hFGF-21治疗糖尿病,增加胰岛素敏感性提供了依据．     

脂联素siRNA对3T3-L1细胞基础葡萄糖转运的影响(英文)

目的:构建携带小鼠脂联素(Acrp30)siRNA腺病毒载体,并检测其对小鼠脂肪细胞Acrp30表达以及对3T3-L1脂肪细胞基础葡萄糖转运的影响。方法:设计并化学合成小鼠脂肪细胞Acrp30 siRNA片断,将其亚克隆入AdEaxy XL腺病毒载体系统,在293细胞内包装扩增为重组腺病毒。用此重组腺病毒感染3T3-L1脂肪细胞,用RT-PCR和ELISA检测其Acrp30 mRNA和蛋白表达。采用2 Deoxy-[3H]D-glucose掺入法测定脂肪细胞葡萄糖转运。结果:设计并构建了小鼠Acrp30基因特异性siRNA腺病毒载体,该载体感染脂肪细胞后,能显著抑制Acrp30 mRNA和蛋白表达,影响3T3-L1脂肪细胞基础葡萄糖的转运,与对照组相比,差异有显著性意义(P<0.05)。结论:构建的Acrp30基因特异性siRNA腺病毒载体能有效的抑制脂联素在3T3-L1脂肪细胞中的表达,从而影响3T3-L1脂肪细胞基础葡萄糖转运。     

Efficient adenovirus transduction of 3T3-L1 adipocytes stably expressing coxsackie-adenovirus receptor

3T3-L1 adipocytes have proven difficult to transfect with plasmid-encoded cDNAs or even infect with virally-derived cDNAs. We have developed and characterized a 3T3-L1 adipocyte cell line stably expressing the truncated receptor for coxsackievirus and adenovirus receptor (CAR) for its ability to be infected with adenoviruses at a low multiplicity of infection (m.o.i.). Using green fluorescent protein driven by the cytomegalovirus promoter in adenovirus fiber type 5 we compared infection efficiencies of CAR adipocytes versus the parental 3T3-L1 adipocytes. As assessed by immunofluorescence, CAR adipocytes were infected at approximately 100-fold greater efficiency than regular 3T3-L1 adipocytes. The efficiency of transduction for the CAR adipocytes was >90% at multiplicities of infection of 50 whereas standard adipocytes were poorly transduced even at an m.o.i. of 2000. Since many investigators studying insulin action use 3T3-L1 adipocytes, we compared CAR adipocytes versus regular adipocytes and showed that the two cell lines were similar with respect to insulin stimulation of insulin receptor, MAPK, and Akt phosphorylation and basal- and insulin-stimulated glucose transport. In addition, CAR adipocytes accumulated GLUT4 and SCD1 proteins during the adipogenesis program with the same time course as regular 3T3-L1 adipocytes. Lastly, CAR adipocytes produced and secreted the adipose-specific hormone Acrp30. These data suggest 3T3-L1CARDelta1 adipocytes are virtually indistinguishable from their parental cells, but demonstrate a significant advantage with improved efficiency of adenoviral transduction for gain or deletion of function studies.     

R-alpha-lipoic acid action on cell redox status, the insulin receptor, and glucose uptake in 3T3-L1 adipocytes.

The insulin signaling pathway has been reported to mediate R-alpha-lipoic acid- (R-LA-)-stimulated glucose uptake into 3T3-L1 adipocytes and L6 myotubes. We investigated the role of the thiol antioxidant dihydrolipoic acid (DHLA) and intracellular glutathione (GSH) in R-LA-stimulated glucose transport and explored the hypothesis that R-LA could increase glucose uptake into 3T3-L1 adipocytes in an oxidant-mimetic manner. R-LA pretreatment of 3T3-L1 cells stimulated glucose transport at early time points (30 min - 6 h), whereas it inhibited glucose uptake at later time points. Analysis of the oxidized and reduced content of LA in cells and medium showed that >90% of lipoic acid present was in its oxidized form. Furthermore, all oxidized forms of LA (S-, R-, and racemic LA) stimulated glucose uptake, whereas the reduced form, dihydrolipoic acid, was ineffective. Intracellular GSH levels were not changed at the early time points (before 12 h), while longer preincubation (24 - 48 h) of cells with R-LA significantly increased intracellular GSH. Pretreatment of adipocytes with R-LA increased intracellular peroxide levels at early time points (30 min - 6 h), after which it was decreased (12 - 48 h). R-LA also increased tyrosine phosphorylation of immunoprecipitated insulin receptors from 3T3-L1 adipocytes. These results indicate that (i) 3T3-L1 adipocytes have a low capacity to reduce R-LA and the oxidized form of lipoic acid is responsible for stimulating glucose uptake, (ii) R-LA modulates glucose uptake by changing the intracellular redox status, and (iii) the insulin receptor is a potential cellular target for R-LA action.     

Somatotropin antagonism of insulin-stimulated glucose utilization in 3T3-L1 adipocytes

It is well established that somatotropin (GH) antagonizes insulin action in vivo and that supraphysiologic concentrations of GH frequently result in insulin resistance and glucose intolerance. However, the demonstration of an anti-insulin activity by GH in vitro has been difficult. This study, therefore, set out to determine whether cultures of 3T3-L1 adipocytes could be used to examine the anti-insulin activity of GH. The ability of insulin to stimulate glucose utilization by 3T3-L1 adipocytes increases approximately five-fold during the first 4 days following treatment of the cells with a differentiation medium. It was found that glucose utilization in 3T3-L1 adipocytes is regulated in a reciprocal fashion by insulin and GH. Bovine or human GH directly inhibit up to 50% of insulin-stimulated [14C]-glucose incorporation into lipids in a concentration-dependent manner. The 3T3-L1 sensitivity to GH appears to be at the maximum (50% inhibition of an insulin response) immediately following removal of the cells from the differentiation medium and remains essentially constant during the subsequent 4 days. The GH inhibition of insulin action does not appear to be due GH enhancement of cellular degradation of insulin, competitive binding of GH to the insulin receptor, or GH-induced decrease in cell number. The 3T3-L1 adipocyte system appears to be a sensitive and reliable in vitro model with which to study the molecular mechanisms involved in both GH antagonism of insulin action and development of hormone responsiveness during cellular differentiation into adipocytes.     

Emodin with PPARgamma ligand-binding activity promotes adipocyte differentiation and increases glucose uptake in 3T3-Ll cells

Emodin, one of the main active components in the root and rhizome of Rheum palmatum L, promoted the conversion of 3T3-L1 fibroblasts to adipocytes, as evidenced by increased glycerol-3-phosphate dehydrogenase (GPDH) activity and the expression of adipocyte aP2 mRNA, as well as accelerated triacylglycerol (TG) accumulation, which was associated with increased mRNA expression levels of both C/EBPalpha and PPARgamma2. By using surface plasmon resonance (SPR) experiment, it was showed that emodin exhibited a very high binding affinity to PPARgamma. In differentiated 3T3-L1 adipocytes, emodin induced a time- and dose-dependent increase in glucose uptake as well as GLUT1 and GLUT4 mRNA expression, and the rate of uptake was partly abrogated by wortmannin (phosphoinositide 3-kinase inhibitor). Meanwhile, insulin-stimulated glucose uptake was increased significantly after treatment with low doses of emodin, and the degree of potentiation was decreased thereafter in response to increasing concentrations. Furthermore, 50 microM emodin profoundly inhibited insulin-stimulated glucose uptake by 25%. These data suggest a new role for emodin as a PPARgamma agonist in 3T3-L1 cells. Besides, it is possible that emodin may also possess other properties contribute to glucose utilization in the adipocytes.     

Differential effects of palmitate on glucose uptake in rat-1 fibroblasts and 3T3-L1 adipocytes.

Non-esterified fatty acids are thought to be one of the causes for insulin resistance. However, the molecular mechanism of fatty acid-induced insulin resistance is not clearly known. In this study, we first examined the effect of palmitate on insulin signaling in 3T3-L1 adipocytes. We found that 1h treatment with 1 mmol/l palmitate had no effect on insulin binding, tyrosine phosphorylation of insulin receptors, 185 kDa proteins and Shc, and PI3 kinase activity in 3T3-L1 adipocytes. Then, the effects of palmitate on MAP kinase activity and glucose uptake in fully differentiated 3T3-L1 adipocytes were compared with those in poorly differentiated 3T3-L1 cells and in HIRc-B cells. Palmitate treatment had no effect on MAP kinase activity in fully differentiated 3T3-L1 adipocytes, while it inhibited MAP kinase in poorly differentiated 3T3-L1 cells and HIRc-B cells. Glucose transport in 3T3-L1 adipocytes treated with palmitate for 1 h, 4 h and 16 h was higher than that in control cells, but palmitate treatment caused a rightward shift of the insulin-dose responsive curve for glucose uptake in HIRc-B cells. Palmitate treatment did not significantly affect basal and insulin-stimulated GLUT4 translocation. When the cells were treated with PD98059, a specific MEK inhibitor, insulin-stimulated glucose uptake was not affected in 3T3-L1 adipocytes, while it was almost completely inhibited in HIRc-B cells. These results suggest the primary effect of palmitate on adipocytes may not involve insulin resistance of adipocytes themselves.