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.     

Rottlerin inhibits multiple steps involved in insulin-induced glucose uptake in 3T3-L1 adipocytes

Recently, it was shown that rottlerin inhibits insulin-stimulated glucose uptake and reduces intracellular adenosine triphosphate (ATP) levels in 3T3-L1 adipocytes, suggesting that these two events are causally linked. However, several other reports show that ATP-depletion induces glucose uptake in both muscle cells and adipocytes. In the present study, the mechanism of inhibition by rottlerin was studied in detail, in order to resolve this apparent discrepancy. It was found that rottlerin strongly reduces insulin-stimulated 2-deoxyglucose (2-DOG) uptake in 3T3-L1 adipocytes by a partial inhibition of the translocation of the insulin-responsive GLUT4 glucose transporter towards the plasma membrane (PM). Whereas the insulin-induced phosphatidyl-inositol-3' (PI-3') kinase signaling pathway is unaffected by rottlerin, Cbl tyrosine phosphorylation, which provides an essential, PI-3' kinase-independent signal towards GLUT4 translocation, is markedly attenuated. Furthermore, we also observed a direct inhibitory effect of rottlerin on insulin-induced glucose uptake in 3T3-L1 adipocytes. The direct inhibition of insulin-stimulated 2-DOG uptake by rottlerin displayed characteristics of uncompetitive inhibition: with the K(m(app)) of glucose uptake reduced from 1.6 to 0.9 mM and the V(max(app)) reduced from 5.2 to 1.0 nmol/minmg in the presence of rottlerin. In conclusion, rottlerin inhibits multiple steps involved in insulin-stimulated 2-DOG uptake in 3T3-L1 adipocytes. The observed reduction in GLUT4 translocation towards the PM and the uncompetitive inhibition of the glucose transport process provide alternative explanations for the inhibitory effects of rottlerin aside from the effects of rottlerin on intracellular levels of ATP.     

Karanjin from Pongamia pinnata induces GLUT4 translocation in skeletal muscle cells in a phosphatidylinositol-3-kinase-independent manner

Insulin-stimulated glucose uptake in skeletal muscle is decreased in type 2 diabetes due to impaired translocation of insulin-sensitive glucose transporter 4 (GLUT4) from intracellular pool to plasma membrane. Augmenting glucose uptake into this tissue may help in management of type 2 diabetes. Here, the effects of an identified antihyperglycemic molecule, karanjin, isolated from the fruits of Pongamia pinnata were investigated on glucose uptake and GLUT4 translocation in skeletal muscle cells. Treatment of L6-GLUT4myc myotubes with karanjin caused a substantial increase in the glucose uptake and GLUT4 translocation to the cell surface, in a concentration-dependent fashion, without changing the total amount of GLUT4 protein and GLUT4 mRNA. This effect was associated with increased activity of AMP-activated protein kinase (AMPK). Cycloheximide treatment inhibited the effect of karanjin on GLUT4 translocation suggesting the requirement of de novo synthesis of protein. Karanjin-induced GLUT4 translocation was further enhanced with insulin and the effect is completely protected in the presence of wortmannin. Moreover, karanjin did not affect the phosphorylation of AKT (Ser-473) and did not alter the expression of the key molecules of insulin signaling cascade. We conclude that karanjin-induced increase in glucose uptake in L6 myotubes is the result of an increased translocation of GLUT4 to plasma membrane associated with activation of AMPK pathway, in a PI-3-K/AKT-independent manner.     

Rubiscolin-6 activates opioid receptors to enhance glucose uptake in skeletal muscle

Rubiscolin-6 is an opioid peptide derived from plant ribulose bisphosphate carboxylase/oxygenase (Rubisco). It has been demonstrated that opioid receptors could control glucose homeostasis in skeletal muscle independent of insulin action. Therefore, Rubiscolin-6 may be involved in the control of glucose metabolism. In the present study, we investigated the effect of rubiscolin-6 on glucose uptake in skeletal muscle. Rubiscolin-6-induced glucose uptake was measured using the fluorescent indicator 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxyglucose (2-NBDG) in L6 and C2C12 cell lines. The protein expressions of glucose transporter 4 (GLUT4) and AMP-activated protein kinase (AMPK) in L6 cells were observed by Western blotting. The in vivo effects of rubiscolin-6 were characterized in streptozotocin (STZ)-induced diabetic rats. Rubiscolin-6 induced a concentration-dependent increase in glucose uptake levels. The increase of phospho-AMPK (pAMPK) and GLUT4 expressions were also observed in L6 and C2C12 cells. Effects of rubiscolin-6 were blocked by opioid receptor antagonists and/or associated signals inhibitors. Moreover, Rubiscolin-6 produced a dose-dependent reduction of blood glucose and increased GLUT4 expression in STZ-induced diabetic rats. In conclusion, rubiscolin-6 increases glucose uptake, potentially via an activation of AMPK to enhance GLUT4 translocation after binding to opioid receptors in skeletal muscle.     

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。     

JNK在棕榈酸造成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的机制中,c-Jun N-末端激酶(JNK)的作用。方法:第一部分将细胞分两组,分别用0.3 mmol／L的棕榈酸盐或用溶剂牛血清白蛋白（BSA）孵育16 h;第二部分在如上处理的后30 min加入JNK的抑制剂,用或不用胰岛素刺激后,检测细胞膜上GLUT4myc的含量以及蛋白激酶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,棕榈酸组中胰岛素刺激的GLUT4myc转位和Akt的磷酸化降低(P<0.05);JNK和IRS1Ser307的磷酸化水平则没有变化。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。     

二甲双胍与罗格列酮对2型糖尿病大鼠GLUT4表达的比较

目的比较二甲双胍与罗格列酮对2型糖尿病大鼠骨骼肌葡萄糖转运蛋白4(GLUT4)mRNA表达的影响.方法以低剂量链脲佐菌素(STZ)加高热量饲料喂养制作模型,灌胃给药4周,检测糖耐量、空腹血清胰岛素(Ins)及骨骼肌GLUT4 mRNA表达量的变化.结果造模后大鼠注射葡葡糖后30,60,120min血糖显著升高,空腹Ins无明显变化,骨骼肌GLUT4 mRNA表达量显著降低.两药均可使注糖后120min血糖下降;罗格列酮尚可降低空腹血糖.二甲双胍可使骨骼肌GLUT4 mRNA表达量明显升高,但罗格列酮对骨骼肌GLUT4 mRNA表达的降低无影响.结论本造模方法可导致大鼠产生类似2型糖尿病的变化,两药均可改善此模型糖耐量异常,二甲双胍的作用与增强骨骼肌GLUT4基因表达有关,而罗格列酮的作用可能与其它环节有关.     

Tissue- and time-dependent effects of endothelin-1 on insulin-stimulated glucose uptake.

Hyperendothelinaemia is associated with various insulin-resistant states, e.g., diabetes, obesity and heart failure, but whether endothelin-1 (ET-1) has a direct effect on insulin-mediated glucose uptake is unclear because the interpretation of in vivo metabolic studies is complicated by ET-1 effects on muscle blood flow and insulin secretion. This study investigated the effects of ET-1 (1-10 nM) on basal and insulin-stimulated 2-deoxy-D-[3H]glucose (2-DOG) uptake in cultured L6 myoblasts and 3T3-adipocytes. RT-PCR analysis showed that both cell types express ET(A) but not ET(B) receptors. ET-1 had no effect on basal (non-insulin-mediated) glucose transport, but there was evidence of a tissue- and time-dependent inhibitory effect of ET-1 on insulin-stimulated glucose uptake. Specifically, ET-1 10 nM had a transient (0.5 h) inhibitory effect on glucose uptake in 3T3 cells (C(I-150) [dose of insulin required to increase glucose uptake by 50%, relative to control 100%] increased from 89 +/- 14 nM to 270 +/- 12 nM at 30 mins, P < 0.05) but no effect on insulin sensitivity in L6 myoblasts (C(I-150) was 56 +/- 14 nM [control], 43 +/- 14 [30 mins] and 26 +/- 16 [2 h]). In conclusion, the inhibitory effect of ET-1 on insulin-stimulated glucose uptake is transient and occurs in 3T3-L1 adipocytes but not skeletal muscle-derived cells, perhaps reflecting tissue differences in ET(A)-receptor signaling. It is therefore unlikely that chronic hyperendothelinaemia has a direct insulin-antagonist effect contributing to peripheral (ie muscle/fat) insulin resistance in vivo.     

Role of SNARE's in the GLUT4 translocation response to insulin in adipose cells and muscle

Insulin stimulates glucose transport in skeletal muscle, heart, and adipose tissue by promoting the appearance of GLUT4, the major glucose transporter isoform present in these tissues, on the cell surface. This is achieved by differentially modulating GLUT4 exocytosis and endocytosis, between a specialized intracellular compartment and the plasma membrane. Ligands which activate the heterotrimeric GTP-binding proteins Gs and Gi appear to modulate insulin-stimulated glucose transport through effects on the fusion of docked GLUT4-containing vesicles with the plasma membrane. In insulin resistance states, reduced cellular GLUT4 levels in adipose cells fully account for the decreased glucose transport response to insulin in these cells. In contrast, although insulin-stimulated GLUT4 translocation is also impaired in muscle, total cellular levels of GLUT4 are not altered. The defect in muscle has been attributed to a GLUT4 trafficking problem and thus studies of this mechanism could provide clues as to the nature of the impairment. The movement of GLUT4-containing vesicles from an intracellular storage site to the plasma membrane and the fusion of docked GLUT4-containing vesicles with the plasma membrane are conceptually similar to some secretory processes. A general hypothesis called the SNARE hypothesis (soluble NSF attachment protein receptors where NSF stands for N-ethylmaleimide-sensitive fusion protein) postulates that the specificity of secretory vesicle targeting is generated by complexes that form between membrane proteins on the transport vesicle (v-SNARE's) and membrane proteins located on the target membrane (t-SNARE's). Several v- and t-SNARE's have been identified in adipose cells and muscle. VAMP2 and VAMP3/cellubrevin (v-SNARE's) have been shown to interact with the t-SNARE's syntaxin 4 and SNAP-23. The cytosolic protein NSF has the characteristic of binding to the v-/t-SNARE complex through its interaction with alpha-SNAP, another soluble factor. Furthermore, recent studies have demonstrated that VAMP2/3, syntaxin 4, SNAP-23, and NSF are functionally involved in insulin-stimulated GLUT4 translocation in adipose cells and thus are likely to be involved in the Gs- and Gi-mediated modulation of the glucose transport response to insulin as well. This review summarizes recent advances on the normal mechanism of GLUT4 translocation and discusses how this process could be affected in insulin resistant states such as type II diabetes.     

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。     

小檗碱改善2型糖尿病大鼠胰岛素抵抗与PI-3K、GLUT4蛋白相关性的研究

目的观察小檗碱对2型糖尿病大鼠骨骼肌组织磷脂酰肌醇3激酶(phosphatidylinositol-3-kinase,PI-3K)之p85亚基、葡萄糖转运子4(glucose transporter4,GLUT4)蛋白表达的影响,以探讨小檗碱改善胰岛素抵抗,防治2型糖尿病的分子机制。方法采用尾静脉注射小剂量链脲佐菌素(streptozotocin,STZ,30mg.kg-1)加高脂高热量饲料喂养的方法建立2型糖尿病大鼠模型,以小檗碱干预10wk,检测血糖和血清胰岛素,用Western blot方法检测小檗碱干预后2型糖尿病大鼠骨骼肌组织PI-3K之p85亚基、GLUT4蛋白表达水平。结果小檗碱干预的2型糖尿病大鼠骨骼肌组织PI-3K之p85亚基、GLUT4蛋白表达水平均较模型组显著增加。结论小檗碱对2型糖尿病的治疗效应可能与提高骨骼肌组织中PI-3K之p85亚基、GLUT4蛋白表达水平有关。     

Inhibitory mechanisms of flavonoids on insulin-stimulated glucose uptake in MC3T3-G2/PA6 adipose cells

We assessed the effects of different classes of flavonoids on insulin-stimulated 2-deoxy-D-[1-(3)H]glucose uptake by mouse MC3T3-G2/PA6 cells differentiated into mature adipose cells. Among the flavonoids examined, the flavones, apigenin and luteolin, the flavonols, kaempferol, quercetin and fisetin, an isoflavone, genistein, a flavanonol, silybin, and the flavanols, (-)-epigallocatechin gallate (EGCG) and theaflavins, significantly inhibited insulin-stimulated glucose uptake. Key structural features of flavonoids for inhibition of insulin-stimulated glucose uptake are the B-ring 4'- or 3',4'-OH group and the C-ring C2-C3 double bond of the flavones and flavonols, the A-ring 5-OH of isoflavones, and the galloyl group of EGCG and theaflavins. Luteolin significantly inhibits insulin-stimulated phosphorylation of insulin receptor-beta subunit (IR-beta), and apigenin, kaempferol, quercetin and fisetin, also tended to inhibit the IR-beta phosphorylation. On the other hand, isoflavones, flavanols or flavanonols did not affect insulin-stimulated IR-beta phosphorylation. Apigenin, luteolin, kaempferol, quercetin and fisetin also appeared to inhibit insulin-stimulated activation of Akt, a pivotal downstream effector of phosphatidylinositol 3-kinase (PI3K), and suppressed insulin-dependent translocation of a glucose transporter, (GLUT)4, into the plasma membrane. Although genistein, silybin, EGCG and theaflavins had no effect on the insulin-stimulated activation of Akt, they blocked insulin-dependent GLUT4 translocation. These results provide novel insights into the modulation by flavonoids of insulin's actions, including glucose uptake in adipocytes.     

Inhibition of insulin-dependent glucose uptake by trivalent arsenicals: possible mechanism of arsenic-induced diabetes

Chronic exposures to inorganic arsenic (iAs) have been associated with increased incidence of noninsulin (type-2)-dependent diabetes mellitus. Although mechanisms by which iAs induces diabetes have not been identified, the clinical symptoms of the disease indicate that iAs or its metabolites interfere with insulin-stimulated signal transduction pathway or with critical steps in glucose metabolism. We have examined effects of iAs and methylated arsenicals that contain trivalent or pentavalent arsenic on glucose uptake by 3T3-L1 adipocytes. Treatment with inorganic and methylated pentavalent arsenicals (up to 1 mM) had little or no effect on either basal or insulin-stimulated glucose uptake. In contrast, trivalent arsenicals, arsenite (iAs(III)), methylarsine oxide (MAs(III)O), and iododimethylarsine (DMAs(III)O) inhibited insulin-stimulated glucose uptake in a concentration-dependent manner. Subtoxic concentrations of iAs(III) (20 microM), MAs(III)O (1 microM), or DMAs(III)I (2 microM) decreased insulin-stimulated glucose uptake by 35-45%. Basal glucose uptake was significantly inhibited only by cytotoxic concentrations of iAs(III) or MAs(III)O. Examination of the components of the insulin-stimulated signal transduction pathway showed that all trivalent arsenicals suppressed expression and possibly phosphorylation of protein kinase B (PKB/Akt). The concentration of an insulin-responsive glucose transporter (GLUT4) was significantly lower in the membrane region of 3T3-L1 adipocytes treated with trivalent arsenicals as compared with untreated cells. These results suggest that trivalent arsenicals inhibit insulin-stimulated glucose uptake by interfering with the PKB/Akt-dependent mobilization of GLUT4 transporters in adipocytes. This mechanism may be, in part, responsible for the development of type-2 diabetes in individuals chronically exposed to iAs.     

Metformin enhances insulin signalling in insulin-dependent and-independent pathways in insulin resistant muscle cells

1 Metformin lowers blood glucose levels in type 2 diabetic patients. To evaluate the insulin sensitizing action of metformin on skeletal muscle cells, we have used C2C12 skeletal muscle cells differentiated in chronic presence or absence of insulin. 2 Metformin was added during the last 24 h of differentiation of the C2C12 myotubes. Insulin-stimulated tyrosine phosphorylation of insulin receptor (IR) and insulin receptor substrate-1 (IRS-1) was determined. 3 Chronic insulin treatment resulted in 60 and 40% reduction in insulin-stimulated tyrosine phosphorylation of IR and IRS-1, respectively. Treatment with metformin was able to increase the tyrosine phosphorylation of IR and IRS-1 by 100 and 90% respectively. 4 Chronic insulin treatment drastically reduced (45%) insulin-stimulated phosphatidyl inositol 3-kinase (PI 3-kinase) activity. Metformin treatment restored PI 3-kinase activity in insulin-resistant myotubes. 5 Insulin-stimulated glucose uptake was impaired in chronically insulin-treated myotubes. Metformin increased basal glucose uptake to significant levels (P<0.05), but metformin did not increase insulin-stimulated glucose transport. 6 All the three mitogen-activated protein kinases (MAPK) were activated by insulin in sensitive myotubes. The activation of p38 MAPK was impaired in resistant myotubes, while ERK and JNK were unaffected. Treatment with metformin enhanced the basal activation levels of p38 in both sensitive and resistant myotubes, but insulin did not further stimulate p38 activation in metformin treated cells. 7 Treatment of cells with p38 inhibitor, SB203580, blocked insulin- and metformin-stimulated glucose uptake as well as p38 activation. 8 Since the effect of metformin on glucose uptake corresponded to p38 MAPK activation, this suggests the potential role p38 in glucose uptake. 9 These data demonstrate the direct insulin sensitizing action of metformin on skeletal muscle cells.     

2型糖尿病大鼠模型GLUT4 mRNA表达的研究

目的：研究葡萄糖转运体4（GLUT4）mRNA表达在2型糖尿病胰岛素抵抗中的分子机制。方法：采用高脂高糖饲养，一次性腹腔注射链脲佐菌素（STZ）制备2型糖尿病大鼠模型。逆转录聚合酶链反应（RT-PCR）分析大鼠骨骼肌、心肌和脂肪组织中GLUT4 mRNA的表达量变化与差别。结果：正常对照组和2型糖尿病大鼠模型组GLUT4 mRNA在骨骼肌中有相对较高表达，在心肌中表达次之，在脂肪组织中表达相对偏低。2型糖尿病大鼠模型组骨骼肌中GLUT4 mRNA表达量只有对照组骨骼肌的48％、心肌的44％、脂肪组织的38％。结论：GLUT4 mRNA表达量下降导致骨骼肌、心肌和脂肪组织对葡萄糖摄取利用减少是胰岛素抵抗的重要分子基础，是诱发2型糖尿病原因之一。     

Adipocyte-derived exosomal miR-27a induces insulin resistance in skeletal muscle through repression of PPARγ

OBJECTIVE To explore increasingly exosomal serum miR-27 a derived from adipocytes could be taken up by skeletal muscle tissue and induce insulin resistance in skeletal muscle in obese state. METHODS The association between miR-27 a and insulin resistance in skeletal muscle was determined in obese children,high-fat diet-induced miR-27 a knockdown obese mice,db/db mice and C2C12 cells overexpressing miR-27 a.The crosstalk mediated by exosomal miR-27 a between adipose tissue and skeletal muscle was determined in C2C12 cel s incubated with conditioned medium prepared from palmitate-treated 3 T3-L1 adipocytes. RESULTS After knockdown miR-27 a in obese insulin resistance mice,impaired insulin resistance, glucose intolerance and insulin resistance of skeletal muscle were partly restored. In high-fat diet group, the expressions of IRS-1 and GLUT4 in glucose uptake signal pathway of skeletal muscle were significantly decreased, while the expression of IRS-1 and GLUT4 was restored after miR-27 a knockdown. The content of FABP4, a marker specific for exosomes from adipocytes, was detected in sera, skeletal muscle, supernatant of adipocytes and co-cultured C2C12 cells; furthermore,exosomal miR-27 a in serum and adipocyte supernatants were detect, and fluorescence co-localization experiments were conducted to detect whether the exosomal miR-27 a in serum is mainly derived from adipocyte; finally,we used the supernatant of adipose tissue to construct conditioned media to treat with C2C12 cells, and detected whether adipocytes derived exosomal miR-27 a could impaired glucose uptake signaling pathway of skeletal muscle. the expressions of PPARγ silencing high-fat diet induced C57 BL/6 J obese mouse model and adenovirus intervention miR-27 a knockdown model were examined,and a C2C12 cell model overexpressing miR-27 a in the absence or presence with rosiglitazone(PPARγ activator)were established to test glucose consumption, glucose uptake, and glucose uptake signaling pathways of skeletal muscle cells. CONCLUSION These results identify a novel crosstalk signaling pathway between adipose tissue and skeletal muscle in the development of insulin resistance, and indicate that adipose tissue-derived miR-27 a may play a key role in the development of obesity-triggered insulin resistance in skeletal muscle.     

小牛血清去蛋白注射液对2型糖尿病胰岛素抵抗大鼠模型骨骼肌GLUT4 mRNA表达的影响

目的观察小牛血清去蛋白注射液(DECB)对2型糖尿病胰岛素抵抗模型大鼠骨骼肌中葡萄糖转运因子4(GLUT4)的mRNA表达的影响。方法以高脂高糖饮食加链脲佐菌素制作2型糖尿病胰岛素抵抗大鼠模型,观察DECB对大鼠葡萄糖耐量(OGTT),运用RT-PCR方法检测大鼠模型骨骼肌中GLUT-4的mRNA表达。结果 DECB可改善OGTT,增加大鼠模型骨骼肌中GLUT4的mRNA表达。结论 DECB具有较好的降血糖、改善胰岛素抵抗、防治糖尿病并发症的作用。     

Regulation of hippocampal long-term potentiation by p21-activated protein kinase 1 (PAK1)

The Rho family small GTPases are critically involved in the regulation of spine and synaptic properties, but the underlying mechanisms are poorly defined. We took genetic approaches to create and analyze knockout mice deficient in the expression of the protein kinase PAK1 that is directly associated with and activated by the Rho GTPases. We demonstrated that while these knockout mice were normal in both basal and presynaptic function, they were selectively impaired in long-term potentiation (LTP) at hippocampal CA1 synapses. Consistent with the electrophysiological deficits, the PAK1 knockout mice showed changes in the actin cytoskeleton and the actin binding protein cofilin. These results indicate that PAK1 is critical in hippocampal synaptic plasticity via regulating cofilin activity and the actin cytoskeleton.     

胰岛素与硒对链脲佐菌素诱导的糖尿病大鼠心肌胰岛素信号转导的联合作用

为阐明小剂量胰岛素(1u.kg-1)与硒(180μg.kg-1)对糖尿病大鼠糖脂代谢及其对心肌细胞胰岛素信号分子表达的联合作用,采用One TouchⅡ血糖仪和血糖试纸测定血糖水平;微柱法测定糖化血红蛋白浓度;酶学法测定甘油三酯(TG)和总胆固醇(TC)含量;免疫印迹和免疫组化法检测心肌细胞中PI3K和GLUT4表达的变化。结果表明,联合用药组血糖和血脂明显下降(P<0.01);同时联合用药明显增加糖尿病大鼠心肌细胞上PI3K和GLUT4的表达(P<0.01)。整体动物实验结果表明:胰岛素和硒联合应用在降低血糖和血脂方面发挥了协同作用;胰岛素与硒联合应用通过改善糖尿病大鼠心肌细胞胰岛素信号转导通路中PI3K的表达,从而改善了GLUT4的移位障碍,最终改善心肌的能量代谢。