JNK在棕榈酸致骨骼肌细胞胰岛素抵抗中的作用

目的:探讨棕榈酸造成L6GLUT4myc骨骼肌细胞胰岛素抵抗过程中c-JunN-末端激酶(JNK)所起的作用。方法:将L6GLUT4myc成肌细胞培养于24孔和6孔培养板中,随机分为溶剂组和棕榈酸组,分别用0.3mmol/L的棕榈酸盐和溶剂牛血清白蛋白(BSA)孵育16h,在棕榈酸组的后30min加入JNK的抑制剂,于胰岛素刺激前后用酶联免疫吸附测定(ELISA)细胞膜上GLUT4myc的含量,免疫印迹法测定蛋白激酶B(Akt)、JNK和胰岛素受体底物1(IRS1)的磷酸化。结果:与溶剂组相比,棕榈酸组中胰岛素增加的GLUT4myc水平的倍数和Akt的磷酸化降低(P<0.05);JNK和IRS1的丝氨酸位点S307的磷酸化水平变化差异无统计学意义(P>0.05)。结论:棕榈酸导致L6骨骼肌细胞胰岛素抵抗的机制可能不涉及JNK,或JNK的作用很小。     

脂联素影响骨骼肌胰岛素抵抗模型中葡萄糖转运蛋白4表达的研究

目的：通过建立骨骼肌L6细胞胰岛素抵抗模型,探讨骨骼肌L6细胞中脂联素（ APN）的分泌,以及脂联素对骨骼肌胰岛素抵抗模型中葡萄糖转运蛋白4（GLUT4）表达的影响。方法（1）体外培养大鼠L6成肌细胞,诱导分化后,给予不同浓度的棕榈酸（PA）,测定不同时间细胞培养上清液葡萄糖浓度,观察PA对L6细胞摄取葡萄糖的影响,建立胰岛素抵抗模型;（2）根据实验条件的不同分为三组：NC组（正常对照组,即骨骼肌L6细胞组）;IR组（胰岛素抵抗模型组）;IR＋PIO组（胰岛素抵抗模型＋吡格列酮组）。应用Western blot方法分别测定上述三组APN和GLUT4表达水平。结果（1）0．4 mmol· L^-1的棕榈酸在作用12、24、36 h以及0．6～0．8 mmol· L^-1棕榈酸作用8～36 h后,细胞培养上清液中葡萄糖含量,明显高于对照组。胰岛素抵抗模型建立;（2）Western blot结果显示：①与NC组比较,IR组APN和GLUT4表达均减少,差异有统计学意义;②与IR组比较,IR＋PIO组其APN和GLUT4表达均增加,差异有统计学意义。结论（1）大鼠L6成肌细胞培养并诱导分化后,经过一定条件下PA刺激,可以建立胰岛素抵抗模型;（2）大鼠L6细胞可分泌和表达脂联素,骨骼肌源性脂联素上调L6细胞GLUT4的表达;（3）吡格列酮作为PPAR-γ激动剂,可增加大鼠L6细胞脂联素的分泌,进而改善胰岛素敏感性。     

p38MAPK信号通路对骨骼肌胰岛素抵抗模型GLUT4表达的研究

目的通过建立棕榈酸(PA)诱导的大鼠L6肌细胞胰岛素抵抗模型,并探讨P38丝裂原活化蛋白激酶(p38MAPK)信号通路对胰岛素抵抗模型葡萄糖转运蛋白4(GLUT4)表达的影响。方法不同浓度的棕榈酸(PA)分别培养不同时间已分化的L6肌细胞,用葡萄糖氧化酶法分别检测各组培养液中剩余葡萄糖浓度,并以此判断胰岛素抵抗形成与否。L6肌细胞胰岛素抵抗模型建立后,给予不同条件干预,用Western blot方法检测胰岛素抵抗组(IR组)和吡格列酮干预组(IR+PIO组)中p-p38MAPK和GLUT4蛋白表达水平。结果通过葡萄糖氧化酶法检测培养皿上清液中葡萄糖含量发现,0.4 mmol·L-1的棕榈酸在作用24～36 h或0.6～0.8 mmol·L-1棕榈酸作用8～24 h后,其上清液中葡萄糖含量和对照组相比,明显高于对照组(P<0.05)。据此可以认为胰岛素抵抗模型建立。Western blot结果显示:和IR组相比I,R+PIO组p-p38MAPK和GLUT4水平明显增加,差异有统计学意义(P<0.05)。结论通过一定浓度和作用时间的PA的刺激可以建立大鼠L6成肌细胞胰岛素抵抗模型。p38MAPK信号通路可能是影响GLUT4表达的重要信号通路之一。吡格列酮作为PPARγ激动剂,其改善胰岛素敏感性的机制之一可能是通过激活p38MAPK信号通路。     

棕榈酸通过抑制IRS-1表达诱导大鼠骨骼肌细胞胰岛素抵抗

摘 要 目的：建立L6细胞胰岛素抵抗模型,筛选出最佳诱导条件,并探讨其作用机制。 方法: 用MTT法确定棕榈酸、胰岛素对L6细胞增殖的影响;用葡萄糖检测试剂盒检测葡萄糖含量,确定不同浓度的棕榈酸、胰岛素对L6细胞葡萄糖消耗的影响;通过Western Blot法检测IRS-1、PI3K、P-AKT、AKT、GLUT4的蛋白表达。结果: 0.4 mmol·L^-1棕榈酸诱导12 h、5×10^-7 mol·L^-1胰岛素诱导24 h以上,对L6细胞生长无影响且出现明显胰岛素抵抗,移除刺激后24 h内能够抑制胰岛素刺激状态下的糖转运;棕榈酸降低了IRS-1、PI3K、P-AKT、GLUT4在L6细胞上的表达。结论:高浓度棕榈酸能够通过抑制IRS-1等靶蛋白表达诱导L6细胞产生胰岛素抵抗。     

过表达KLF4对棕榈酸所致L6骨骼肌细胞胰岛素抵抗的影响

目的探讨Krtippel样因子4（KLF4）过表达对大鼠L6骨骼肌细胞胰岛素抵抗的影响。方法采用棕榈酸诱导法建立大鼠IJ6骨骼肌细胞的胰岛素抵抗模型,随机分为对照组和转染组。对照组转染腺病毒空载体（Ad）,转染组转染KLF4腺病毒表达载体（Ad—KLF4）。采用Real—timePCR和Western—blot检测两组KLF4、胰岛素受体（IR）和葡萄糖转运蛋白4（GLUT4）的表达水平,采用葡萄糖氧化酶法检测两组培养液中的葡萄糖浓度。结果与对照组比较,棕榈酸诱导组对葡萄糖的摄取量显著降低（P〈0．05）,KLF4、IR、GLUT4表达显著下调（P〈0．05）。KLF4过表达可显著提高细胞对胰岛素的敏感性,并上调IR、GLUT4表达。结论过表达KLF4可导致IR、GLUT4表达上调,并改善骨骼肌细胞的胰岛素抵抗。     

吡格列酮改善胰岛素抵抗状态下氧化应激水平及分子机制探讨

目的：探讨吡格列酮（Pio）对胰岛素抵抗状态下的氧化应激水平的影响,并初步探讨Pio改善胰岛素抵抗作用的分子机制。方法：用TNF-α（4ng／mL）刺激人肝癌细胞HepG2,建立胰岛素抵抗细胞模型。MTT法观察细胞毒性作用;氧化酶法检测细胞培养液中的葡萄糖浓度;用DCFH-DA荧光探针标记,流式细胞仪检测细胞内活性氧（ROS）的水平;Western blotting检测氨基末端激酶（JNK）、磷酸化氨基末端激酶（p-JNK）和胰岛素受体底物1（IRS1）的表达。结果：TNF-α刺激HepG2后,导致葡萄糖摄取障碍,细胞培养液上清中葡萄糖浓度显著升高,细胞内ROS的水平显著升高,JNK被激活,IRS1的表达降低。Pio可显著降低ROS的水平,抑制JNK的磷酸化,促进IRS1的表达,改善胰岛素抵抗。结论：Pio通过降低氧化应激水平,抑制JNK信号通路,改善胰岛素抵抗状态。     

CaMKⅡ在收缩促进骨骼肌细胞GLUT4转位中的作用

目的:探讨钙-钙调蛋白依赖性蛋白激酶Ⅱ(CaMKⅡ)在收缩促进骨骼肌细胞葡萄糖转运子4(GLUT4)转位机制中的作用。方法:将接种在培养板中的C2C12GLUT4myc小鼠肌管随机分为对照组和氨乙酰胆碱(Cch)组,各组分为抑制剂亚组和对照亚组。分别用10μmol/LCaMKⅡ的特异性抑制剂KN93或KN62预孵育,用酶联免疫吸附法(ELISA)测定细胞膜上GLUT4myc的含量(转位);用KN93预孵育后,免疫印迹法测定蛋白激酶CaMKⅡ的磷酸化。结果:氨乙酰胆碱使细胞膜上GLUT4myc的水平显著增加。KN93和KN62抑制氨乙酰胆碱刺激的GLUT4myc转位。氨乙酰胆碱可增加CaMKⅡ的磷酸化,KN93不影响对照组CaMKⅡ的磷酸化水平,但可以抑制Cch刺激的CaMKⅡ磷酸化。结论:CaMKⅡ位于Ca2+下游并有介导收缩促进骨骼肌细胞GLUT4myc转位的作用。     

巨噬细胞条件培养基对胰岛素调节骨骼肌细胞作用的影响

目的:探讨常氧和缺氧培养的巨噬细胞条件培养基对胰岛素调节骨骼肌葡萄糖转运子4(GLUT4)作用的影响。方法:常氧和缺氧培养巨噬细胞,提取条件培养基孵育C2C12GLUT4myc骨骼肌细胞,用偶联抗体的吸光度法测定细胞膜上GLUT4myc的含量,Real-timePCR法测定巨噬细胞TNF-αmRNA的表达,ELISA法测定巨噬细胞条件培基中TNF-α的含量。结果:常氧和缺氧培养的巨噬细胞条件培养基削弱胰岛素刺激的骨骼肌细胞GLUT4myc转位(P<0.01),但两种条件培养基对骨骼肌中胰岛素作用的影响差异无统计学意义;缺氧培养的巨噬细胞TNF-αmRNA和蛋白表达均高于常氧培养的巨噬细胞(P<0.05或P<0.01)。结论:常氧培养和缺氧培养的巨噬细胞条件培养基均直接造成骨骼肌细胞胰岛素抵抗,缺氧的巨噬细胞条件培养基并不能加重骨骼肌胰岛素抵抗。     

GDF11在棕榈酸诱导骨骼肌细胞胰岛素抵抗中的作用研究

目的探讨GDF11对棕榈酸诱导骨骼肌细胞胰岛素抵抗的影响。方法用棕榈酸构建骨骼肌细胞胰岛素抵抗模型,分为对照组、GDF11干预组、棕榈酸干预组和GDF11联合棕榈酸干预组。CCK-8检测细胞活力,2NBDG检测细胞葡萄糖摄取。实时荧光定量PCR检测肌管标志基因(desmin、myogenin),胰岛素介导葡萄糖摄取相关基因(GLUT-4、IRS-1)及PGC-1α的表达。Western blot检测PGC-1α蛋白水平的表达。结果不同浓度GDF11对骨骼肌细胞活力无明显影响。与对照组相比,棕榈酸干预组葡萄糖摄取及GLUT-4、IRS-1、PGC-1α的表达明显降低(P<0.05)。与棕榈酸干预组相比,GDF11联合棕榈酸干预组葡萄糖摄取及GLUT-4、IRS-1、PGC-1α的表达无明显变化。结论棕榈酸可成功诱导骨骼肌细胞胰岛素抵抗,而GDF11对骨骼肌细胞胰岛素抵抗没有明显改善作用。     

洋甘菊总黄酮改善IR-HepG2细胞的作用机制

目的:探究洋甘菊总黄酮对HepG2胰岛素抵抗细胞氧化应激损伤的保护作用。方法:用17.5 mmol·L^-1的葡萄糖胺诱导HepG2细胞24 h建立体外HepG2细胞胰岛素抵抗模型;通过CCK-8法测定不同浓度的洋甘菊总黄酮对HepG2细胞活力的影响;采用试剂盒测定葡萄糖(GLU)消耗量、细胞糖原含量和丙二醛(MDA)的含量,以及超氧化物歧化酶(SOD)和谷胱甘肽过氧化物酶(GSH-Px)的活性;Western blot法测定IRS1/PI3K/Akt通路关键信号分子蛋白的表达水平。结果:与模型组相比,洋甘菊总黄酮干预后细胞葡萄糖消耗量增加,细胞内糖原含量增多,MDA含量降低,SOD和GSH-Px酶活性升高,氧化应激损伤减轻;IRS1、PI3K和Akt等蛋白的磷酸化水平升高,葡萄糖转运蛋白4(GLUT4)表达上调(P<0.05)。结论:洋甘菊总黄酮可能通过调节IRS1/PI3K/Akt通路和GLUT4蛋白的表达来降低氧化应激损伤和抑制糖异生,从而改善细胞胰岛素抵抗。     

Carnosic acid as a component of rosemary extract stimulates skeletal muscle cell glucose uptake via AMPK activation

Compounds that increase the activity of the energy sensor AMP‐activated kinase (AMPK) have the potential to regulate blood glucose levels. Although rosemary extract (RE) has been reported to activate AMPK and reduce blood glucose levels in vivo, the chemical components responsible for these effects are not known. In the present study, we measured the levels of the polyphenol carnosic acid (CA) in RE and examined the effects and the mechanism of action of CA on glucose transport system in muscle cells. High performance liquid chromatography (HPLC) was used to measure the levels of CA in RE. Parental and GLUT4myc or GLUT1myc overexpressing L6 rat myotubes were used. Glucose uptake was assessed using [³H]‐2‐deoxy‐d ‐glucose. Total and phosphorylated levels of Akt and AMPK were measured by immunoblotting. Plasma membrane GLUT4myc and GLUT1myc levels were examined using a GLUT translocation assay. Statistics included analysis of variance (ANOVA) followed by Tukey's post‐hoc test. At concentrations found in rosemary extract, CA stimulated glucose uptake in L6 myotubes. At 2.0 μmol/L CA a response (226 ± 9.62% of control, P=.001), similar to maximum insulin (201 ± 7.86% of control, P=.001) and metformin (213 ± 10.74% of control, P=.001) was seen. Akt phosphorylation was not affected by CA while AMPK and ACC phosphorylation was increased and the CA‐stimulated glucose uptake was significantly reduced by the AMPK inhibitor compound C. Plasma membrane GLUT4 or GLUT1 glucose transporter levels were not affected by CA. Our study shows increased muscle cell glucose uptake and AMPK activation by low CA concentrations, found in rosemary extract, indicating that CA may be responsible for the antihyperglycemic properties of rosemary extract seen in vivo.     

Stimulation of glucose uptake by theasinensins through the AMP-activated protein kinase pathway in rat skeletal muscle cells

Theasinensins, dimeric catechins, have been reported to possess anti-hyperglycemic activity, but the underlying mechanism for this activity remains unknown. In this study, the effect of theasinensins A and B on glucose uptake into rat skeletal muscle cells (L6 myotubes) was investigated. A glucose uptake study using 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG) indicated that both theasinensins A and B stimulated glucose uptake in a concentration-dependent manner and translocation of glucose transporter 4 (GLUT4) to the plasma membrane. In addition, inhibition studies measuring 2-NBDG uptake in L6 cells revealed that compound C (AMP-activated protein kinase inhibitor) suppressed theasinensin-stimulated glucose uptake, whereas genistein (insulin receptor tyrosine kinase inhibitor) and wortmannin (phosphatidylinositol 3-kinase inhibitor) were inactive. Subsequent experiments on GLUT4-related signaling pathways in L6 cells demonstrated that theasinensins promoted the phosphorylation of AMPK, but not that of Akt, and that the theasinensin-promoted glucose uptake was blocked in the presence of a CaMKK inhibitor. The promotion of AMPK phosphorylation by theasinensins was not blocked in LKB1-knockdown cells. Consequently, it was concluded that theasinensins A and B did in fact promote GLUT4 translocation to the plasma membrane in L6 myotubes through the CaMKK/AMPK signaling pathway, but not through the PI3K/Akt pathway.     

Prolonged exposure to resistin inhibits glucose uptake in rat skeletal muscles

AIM: To assess the effects and mechanisms of the action of resistin on basal and insulin-stimulated glucose uptake in rat skeletal muscle cells. METHODS: Rat myoblasts (L6) were cultured and differentiated into myotubes followed by stimulation with single commercial resistin (130 ng/mL, 0-24 h) or cultured supernatant from 293-T cells transfected with resistin-expressing vectors (130 ng/mL, 0-24 h). Liquid scintillation counting was used to quantitate [3H] 2-deoxyglucose uptake. The translocation of insulin-sensitive glucose transporters GLUT4 and GLUT1, synaptosomal-associated protein 23 (SNAP23) and GLUT protein content, as well as the tyrosine phosphorylation status and protein content of insulin receptor substrate (IRS)-1, were assessed by Western blotting. RESULTS: Treatment of L6 myotubes with single resistin or cultured supernatant containing recombinant resistin reduced basal and insulin-stimulated 2-deoxyglucose uptake and impaired insulin-stimulated GLUT4 translocation. While SNAP23 protein content was decreased, no effects were noted in GLUT4 or GLUT1 protein content. Resistin also diminished insulin-stimulated IRS-1 tyrosine phosphorylation levels without affecting its protein content. The effects of recombinant resistin from 293-T cells transfected with resistin-expressing vectors were greater than that of single resistin treatment. CONCLUSION: Resistin regulated IRS-1 function and decreased GLUT4 translocation and glucose uptake in response to insulin. The downregulated expression of SNAP23 may have been partly attributed to the decrease of glucose uptake by resistin treatment. These observations highlight the potential role of resistin in the pathophysiology of type 2 diabetes related to obesity.     

Abrogation of hyperosmotic impairment of insulin signaling by a novel class of 1,2-dithiole-3-thiones through the inhibition of S6K1 activation

A previous study from this laboratory showed that oltipraz and synthetic dithiolethiones prevent tumor necrosis factor-alpha-induced hepatic insulin resistance via AMP-activated protein kinase-dependent p70S6 kinase (S6K) 1 inhibitory pathway. This study investigated whether oltipraz and a novel class of 1,2-dithiole-3-thiones were capable of preventing insulin resistance induced by hyperosmotic stress, thereby enhancing insulin-dependent signals, and, if so, whether the restoration of insulin signal was mediated with the inhibition of S6K1 activity stimulated by hyperosmotic stress. In HepG2 cells, oltipraz treatment inhibited insulin receptor substrate (IRS) 1 serine phosphorylation, a marker of insulin resistance, induced by sorbitol-, mannitol-, or sodium chloride-induced hyperosmotic stress. Consequently, this allowed cells to restore insulin signals, which was evidenced by decrease in the ratio of serine to tyrosine phosphorylations of IRS1 and increase in the phosphorylations of Akt and glycogen synthase kinase (GSK) 3beta. Hyperosmotic stress markedly activated S6K1; S6K1 activation was completely abolished by oltipraz pretreatment. An experiment using dominant-negative S6K1 supports the essential role of S6K1 in the hyperosmolarity-stimulated phosphorylation of IRS1. Transfection of constitutive active mutant S6K1 eliminated the protective effect of oltipraz on GSK3beta phosphorylation, indicating that oltipraz restores insulin signaling by inhibiting S6K1 activation. A variety of synthetic 1,2-dithiole-3-thione derivatives also inhibited S6K1 activity and insulin resistance induced by hyperosmotic stress in HepG2 cells. The results of this study demonstrate that a novel class of 1,2-dithiole-3-thiones improve insulin sensitivity under the condition of hyperosmotic stress, which results from the inhibition of S6K1 activation.     

Fargesin, a component of Flos Magnoliae, stimulates glucose uptake in L6 myotubes

Flos Magnoliae (FM) is a commonly used Chinese medicinal herb for symptomatic relief of allergic rhinitis, sinusitis and headache. Although several FM species have been used as substitutes or adulterants for clinical use, possible differences in their pharmacological actions have not been reported. To confirm the effects of FM on skeletal muscle glucose metabolism, we tested the effects of several compounds isolated from FM on glucose uptake by L6 myotubes. We found that fargesin, a component of FM, dose-dependently stimulated glucose consumption in L6 myotubes, which was accompanied by enhanced glucose transporter (GLUT)-4 translocation to the cell surface. Fargesin-stimulated glucose uptake was blocked by wortmannin, a phosphatidylinositol-3 kinase (PI3 K) inhibitor. Fargesin stimulated Akt phosphorylation, a key component in the insulin signaling pathway, which was completely inhibited by wortmannin. Here, we demonstrated that fargesin, a bioactive component of Flos Magnoliae, increases basal glucose uptake and GLUT4 translocation in L6 myotubes by activating the PI3 K–Akt pathway.     

HIV protease inhibitors induce metabolic dysfunction in part via increased JNK1/2 pro-inflammatory signaling in L6 cells

Protease inhibitors (PIs), such as atazanavir sulfate and ritonavir, are used clinically to prevent the progression of HIV and are known to induce insulin resistance. To determine whether PI-mediated insulin resistance is induced by activation of pro-inflammatory cascades, L6 skeletal muscle cells were treated ±atazanavir sulfate, ritonavir, or atazanavir sulfate + ritonavir, and ±insulin. Treatment with atazanavir sulfate, ritonavir, or atazanavir sulfate + ritonavir for 24 or 48 h significantly increased basal glucose uptake (P < 0.05) and atazanavir sulfate + ritonavir treatment increased basal glucose uptake significantly more than ritonavir or atazanavir sulfate treatment alone (P < 0.05). Atazanavir sulfate + ritonavir treatment for 48 h completely prevented insulin stimulation of glucose uptake (P > 0.05). When compared to untreated cells, basal palmitate uptake and oxidation was found to be significantly higher in cells treated with PIs alone or in combination (P < 0.05). Prior PI treatment alone or in combination prevented (P > 0.05) the insulin-mediated increase in palmitate uptake and the insulin-mediated decrease in palmitate oxidation observed in the control group. Atazanavir sulfate treatment alone or in combination with ritonavir significantly increased JNK1/2 phosphorylation when compared to the control or ritonavir group (P < 0.05) and this was accompanied by a rise (P < 0.05) in AKT^Ser473 phosphorylation in the basal state. Total JNK1/2 and p38 MAPK protein content and p38 MAPK phosphorylation state were not altered in any of the treatment groups (P > 0.05). Our data indicate that, in muscle cells, PIs induce metabolic dysfunction that is not limited to insulin-sensitive metabolism and that is potentially mediated by a rise in JNK1/2 pro-inflammatory signaling.     

Resistin induces insulin resistance, but does not affect glucose output in rat-derived hepatocytes

AIM: The aim of the present study was to observe the effects of resistin on insulin sensitivity and glucose output in rat-derived hepatocytes. METHODS: The rat hepatoma cell line H4IIE was cultured and stimulated with resistin; supernant glucose and glycogen content were detected. The insulin receptor substrate (IRS)-1 and IRS-2, protein kinase B/Akt, glycogen synthase kinase-3beta(GSK-3 beta), the suppressor of cytokine signaling 3 (SOCS-3) protein content, as well as the phosphorylation status were assessed by Western blotting. Specific antisense oligodeoxynucleotides directed against SOCS-3 were used to knockdown SOCS-3. RESULTS: Resistin induced insulin resistance, but did not affect glucose output in rat hepatoma cell line H4IIE. Resistin attenuated multiple effects of insulin, including insulin-stimulated glycogen synthesis and phosphorylation of IRS, protein kinase B/Akt, as well as GSK-3beta. Resistin treatment markedly induced the gene and protein expression of SOCS-3, a known inhibitor of insulin signaling. Furthermore, a specific antisense oligodeoxynucleotide directed against SOCS-3 treatment prevented resistin from antagonizing insulin action. CONCLUSION: The major function of resistin on liver is to induce insulin resistance. SOCS-3 induction may contribute to the resistin-mediated inhibition of insulin signaling in H4IIE hepatocytes.