缺血预处理减轻肥厚心肌缺血再灌注损伤及其信号途径

目的探讨缺血预处理(IPC)对肥厚心肌体外缺血再灌注(IR)损伤的影响及其信号机制。方法48只心肌肥厚大鼠随机分为4组:IR对照组I、PC组I、PC加磷脂酰肌醇-3激酶(PI3K)抑制剂Wortmannin处理组、Wortmannin处理对照组,观察IPC对心肌肥厚大鼠体外IR心脏左心室收缩压、冠状动脉流量、肌酸磷酸激酶(CPK)和乳酸脱氢酶(LDH)释放、心肌梗死范围以及心肌蛋白激酶B(Akt)、糖原合成酶激酶-3β(GSK-3β)磷酸化的影响。结果与IR对照组比较,IPC组心脏左心室收缩压、冠状动脉流量显著提高,CPK、LDH释放减少,心肌梗死范围减小,心肌Akt、GSK-3β磷酸化水平增高,Wortmannin能够抑制IPC所致的Akt、GSK-3β磷酸化,但只能部分消除IPC的心脏保护效应。结论IPC能够减轻心肌肥厚大鼠体外心脏IR损伤,PI3K、Akt、GSK-3β信号途径参与介导IPC对体外IR肥厚心肌的保护作用。     

Aβ1~42对阿尔茨海默病小鼠PI3K/PKB信号通路的影响

目的探讨Aβ_1~42对阿尔茨海默病(AD)小鼠磷脂酰肌醇3激酶/蛋白激酶B(PI3K/PKB)信号通路的影响。方法雄性小鼠侧脑室注射链脲佐菌素制备AD模型,随机分为:假手术组、模型组、Aβ_1~42低剂量(0.015 mg/kg)组、Aβ_1~42中剂量(0.050 mg/kg)组、Aβ_1~42高剂量(0.150 mg/kg)组、胰岛素组。跳台实验检测小鼠认知功能;酶联免疫吸附试验(ELISA)检测各组小鼠海马胰岛素受体(InR)的含量;Western印迹法检测小鼠磷酸化蛋白激酶B(p-PKB)、磷酸化糖原合成酶激酶(p-GSK)-3β和磷酸化Tau蛋白(p-Tau)的表达量。结果与假手术组比较,模型组练习错误和记忆错误次数增多、潜伏期缩短(P<0.05);与模型组比较,Aβ_1~42不同剂量组练习和记忆错误次数增加、潜伏期缩短(P<0.05),胰岛素组练习和记忆错误次数减少、潜伏期增加(P<0.05)。与假手术组比较,模型组InR表达量降低(P<0.05)。与模型组比较,Aβ_1~42不同剂量组InR表达量降低(P<0.05);胰岛素组InR表达量升高(P<0.05)。与假手术组比较,模型组p-PKB、p-GSK-3β蛋白表达量降低,p-Tau表达量升高(P<0.05)。与模型组比较,Aβ_1~42不同剂量组p-PKB、p-GSK-3β蛋白表达量降低,p-Tau表达量升高(P<0.05);胰岛素组p-PKB、p-GSK-3β的表达量升高,p-Tau表达水平降低(P<0.05)。结论Aβ_1~42能够产生神经毒性,诱导小鼠认知功能障碍,其机制可能为干扰PI3K/PKB信号通路传导,下调InR表达,抑制PKB和GSK-3β磷酸化,使AD小鼠Tau蛋白磷酸化水平增加,导致认知功能障碍。     

归脾汤对沉默LncRNA MALAT1大鼠下丘脑胰岛素信号通路的影响

目的 探讨沉默肺腺癌转移相关转录本(MALAT)1配合应用归脾汤对胰岛素信号通路中磷脂酰肌醇-3激酶(PI3K)、蛋白激酶B(PKB)和糖原合成酶激酶(GSK)-3β表达的影响及对胰岛素抵抗的改善情况。方法 长期给予高脂饲料，后期注射链脲佐菌素(STZ)建立并筛选出糖尿病脑病(DE)大鼠模型；除对照组外，将筛选出的DE模型大鼠随机分为模型组、沉默LncRNA MALAT1配合归脾汤治疗(M归脾汤)组、归脾汤组、西药组。以氧化酶法测其血糖水平，以酶联免疫吸附试验(ELISA)测其胰岛素水平，计算胰岛素敏感指数，以实时荧光聚合酶链反应(RT-PCR)法测其下丘脑中GSK-3β mRNA的相对表达；应用Western印迹测下丘脑中PI3K、PKB和GSK-3β蛋白的相对表达。结果 与模型组比较，归脾汤组和西药组胰岛素水平显著升高，M归脾汤组和西药组胰岛素敏感指数(ISI)显著升高(P<0.05),归脾汤组中GSK-3β mRNA和蛋白的相对表达显著降低(P<0.05),归脾汤组中PI3K蛋白的相对表达显著提高(P<0.05)。与归脾汤组比较，M归脾汤组GSK-3β mRNA...     

中药肝复康对四氯化碳诱导的肝纤维化大鼠肝组织PI3K/PKB信号通路和PDGFR-β表达的影响

目的探讨中药肝复康对大鼠肝纤维化组织PI3K/PKB信号通路和血小板衍生生长因子受体-β(PDGFR-β)表达的影响。方法制备大鼠四氯化碳诱导的肝纤维化模型,给予肝复康干预。采用免疫组织化学法检测肝组织PDGFR-β蛋白的表达,采用半定量RT-PCR法测定肝组织PI3K和PKB1mRNA水平的变化。结果与对照组比,模型组肝组织PDGFR-β蛋白的表达上调,而肝复康治疗组其表达被显著抑制;模型组肝组织PI3K和PKB1 mRNA水平的相对光密度值分别为2.08±0.09和2.54±0.10,较对照组均显著上升(0.86±0.04和0.36±0.03,P<0.01),但肝复康治疗组其水平均被显著抑制(分别为0.88±0.05和0.41±0.03,与模型组比,P<0.01)。结论肝复康对肝纤维化的治疗作用可能与其作用于PI3K/PKB信号转导途径和抑制PDGFR-β表达有关。     

茶多酚对代谢综合征大鼠过氧化物酶体增殖物激活受体及胰岛素信号传导通路的作用研究

目的研究茶多酚(TP)对MS大鼠糖脂代谢的改善作用及其分子作用机制。方法高糖高脂饮食诱导方案建立大鼠MS模型,30只雄性SD大鼠随机分成TP(n=10)组、MS对照(MS,n=10)组和常规喂养的正常对照(NC,n=10)组。干预16周后测定各组血糖、血脂、胰岛素、FFA水平。RTPCR及Western blot分别检测各组脂肪组织过氧化物酶体增殖物激活受体(PPAR-γ)、下游基因胰岛素受体底物(IRS-1、IRS-2)、磷脂酰肌醇3-激酶(PI3K)、蛋白激酶B(PKB)、葡萄糖转运蛋白(GLUT-1、GLUT-4)的mRNA及蛋白表达水平。结果 TP组FPG、TG、TC、LDL-C、FFA水平均较MS组下降(P0.05)。TP组脂肪组织PPAR-γ、IRS-1、IRS-2、PI3K、PKB、GLUT-4的mRNA及蛋白表达水平较MS组上调(P0.05),GLUT-1的mRNA表达及蛋白表达水平比较,差异无统计学意义(P0.05)。结论 TP可改善MS大鼠的糖脂代谢,减轻IR,其作用机制可能是通过上调MS大鼠PPAR-γ的表达,进而影响其下游基因IRS-1、IRS-2、PI3K、PKB、GKUT-4的表达来发挥改善IR的作用。     

nesfatin-1在胰岛素抵抗骨骼肌细胞中对PI3K/AKT信号通路的影响

目的探讨过表达新型饱食分子蛋白(nesfatin-1)对L6骨骼肌胰岛素抵抗及磷脂酰肌醇3-激酶/蛋白激酶B(PI3K/AKT)信号通路和下游糖原合成酶激酶(GSK)-3β、葡萄糖转运蛋白(GLUT)-4表达的影响。方法建立L6细胞胰岛素抵抗模型后,用过表达nesfatin-1的腺相关病毒(AAV)和空载对照腺相关病毒(PC)感染L6细胞,将细胞分为四组,分别为空载对照腺相关病毒组(PC组),PC+棕榈酸(PA)组,过表达nesfatin-1组,nesfatin-1+PA组,四组均加入100 nmol/L重组人胰岛素(Insulin),PC+PA组和nesfatin-1+PA组再加入250μmol/L PA处理24 h后收集培养基上清,用葡萄糖过氧化物酶方法测定上清液中葡萄糖含量,用Western印迹检测PI3K、AKT及其下游信号分子GSK-3β、GLUT-4的蛋白表达变化。结果与PC组比较,过表达nesfatin-1组p-AKT、GSK-3β、GLUT-4蛋白表达水平明显增高(P<0.05);与PC+PA组相比,nesfatin-1+PA组p-AKT、GSK-3β、GLUT-4蛋白表达水平明显增高(P<0.05);与nesfatin-1组相比,nesfatin-1+PA组p-AKT、GSK-3β、GLUT-4蛋白表达水平明显下降(P<0.05)。结论过表达nesfatin-1可显著增加骨骼肌细胞对葡萄糖的摄取,减轻胰岛素抵抗,并经PI3K-AKT通路上调下游GSK-3β、GLUT-4的表达。     

急性脑缺血再灌注大鼠海马CA1区细胞凋亡与β-catenin、GSK-3β蛋白表达的关系

目的探讨急性脑缺血再灌注(IR)大鼠海马CA1区细胞凋亡与Wnt信号通路β-连环蛋白(β-catenin)、糖原合成酶激酶3β(GSK-3β)蛋白表达的关系。方法选择雄性SD大鼠36只,随机分为假手术组6只、脑IR组30只,脑IR组又分为IR后3、6、24、48、72 h各6只,采用线栓法制作大鼠大脑中动脉缺血再灌注模型。应用原位末端标记法检测各组细胞凋亡情况,免疫组化法及Western blotting蛋白印记法分别检测β-catenin、GSK-3β蛋白表达;并对IR组的β-catenin、GSK-3β蛋白表达与细胞凋亡进行相关性分析。结果与假手术组比较,IR组各时间点细胞凋亡数、GSK-3β蛋白阳性数及β-catenin蛋白表达量明显增加(P均<0.01),β-catenin蛋白阳性数、GSK-3β蛋白表达量增加,但无统计学意义(P均>0.05)。脑IR后不同时间点的细胞凋亡数与GSK-3β蛋白阳性数呈正相关(P<0.05),与β-catenin蛋白阳性数无相关性(P>0.05)。结论 Wnt信号通路在脑IR组损伤中可能发挥重要作用,GSK-3β蛋白对缺血性脑损伤的细胞凋亡起促进作用。     

神经肌肉电刺激对脑血管病大鼠模型神经元tau蛋白表达和氧化应激水平的影响

目的探讨神经肌肉电刺激(NMES)对脑血管病大鼠模型神经元tau蛋白表达和氧化应激水平的影响。方法选取30只清洁级SD雄性大鼠,随机分为三组。分别设置空白对照组(B组),脑血管病模型组(C组)和NMES组(N组),每组10只。造模后,使用免疫组化方法对各组大鼠海马Tau蛋白磷酸化程度进行检测;通过实时荧光定量(RT)-PCR方法对磷脂酰肌醇3-激酶/蛋白激酶B(PI3K/Akt)的相关基因表达进行检测;对各组大鼠进行丙二醛(MDA)、超氧化物歧化酶(SOD)含量进行检测。结果 C、N组大鼠由于存在脑血管病,表现为过度磷酸化。NMES后,N组大鼠Tau蛋白磷酸化程度与C组相比,蛋白含量明显减少(P0.01),磷酸化程度明显改善(P0.01);与N组相比,B组和C组的基因表达受到抑制,基因呈现下调,NMES后N组大鼠受到抑制的Akt基因被激活不在为失活状态,差异均具有统计学意义(P0.01);离心取得的大鼠血清中,经检测,与B组相比,C组中大鼠MDA明显升高,SOD活性明显下降。随着NMES程度的增加,可显著提高大鼠SOD活性,降低MDA含量,减少磷酸化程度。结论 NMES对脑血管病大鼠磷酸化程度有所缓解,可有效降低tau蛋白表达,同时,对体内抗氧化有显著的治疗效果。其作用机制可能与抑制PI3K/Akt通路的表达有关。     

血管紧张素（1-7）对糖尿病大鼠胰岛素抵抗的影响及机制研究

目的探讨血管紧张素(1-7)[Ang-(1-7)]对DM大鼠IR的影响及可能机制。方法随机选取Wistar大鼠10只为正常对照组(NC),另取24只予高脂饮食喂养联合STZ注射构建DM模型,造模成功的20只大鼠随机分为糖尿病组(DM)、Ang-(1-7)组[Ang-(1-7)300μg/(kg.d)皮下注射],每组各10只。干预8周后检测FPG、FIns及血管紧张素II(Ang II)水平,计算稳态模型胰岛素抵抗指数(HOMA-IR)及敏感指数(HOMA-ISI),观察肝脏病理改变,检测肝脏炎症通路及Ins信号转导通路相关因子的mRNA及蛋白表达。结果与NC组比较,DM、Ang-(1-7)组体重、FIns、HOMA-ISI、IRS-2 mRNA、磷脂酰肌醇3激酶(PI3K)mRNA和蛋白、丝氨酸/苏氨酸蛋白激酶2(Akt-2)mRNA和蛋白表达降低(P0.05),FPG、Ang II、HOMA-IR、肝脏指数、IκB激酶β(IKKβ)mRNA和蛋白、核因子κB(NF-κB)mRNA和蛋白、TNF-αmRNA、IL-6 mRNA、糖原合成酶激酶3α(GSK-3α)mRNA和蛋白表达升高(P0.05)。与DM组比较,Ang-(1-7)组FPG、Ang II、HOMA-IR、肝脏指数、IKKβmRNA和蛋白、NF-κB mRNA和蛋白、TNF-αmRNA、IL-6 mRNA、GSK-3αmRNA和蛋白表达降低,FIns、HOMA-ISI、IRS-2 mRNA、PI3K m RNA和蛋白、Akt-2 mRNA和蛋白表达升高(P0.05)。结论 Ang-(1-7)可能通过抑制肝脏IKKβ/NF-κB炎症通路及上调IRS-2/PI3K/Akt-2胰岛素信号通路,改善IR。     

白藜芦醇通过PI3K/Akt/GSK-3β通路对6-OHDA致帕金森病小鼠神经退行性病变改善的作用研究

目的探讨白藜芦醇通过磷脂酰肌醇3-激酶(PI3K)/蛋白激酶(Akt)/糖原合成酶激酶3β(GSK-3β)通路改善6-羟基多巴胺(6-OHDA)所致帕金森病小鼠神经退行性病变。方法将30只SPF级C57BL/6小鼠随机分为3组,其中6-OHDA致病组和白藜芦醇治疗组(Res治疗组)脑内分别注射6-OHDA诱导帕金森病模型,正常组注射等量生理盐水,造模后Res治疗组给予Res灌胃治疗(20 mg/kg),6-OHDA致病组和正常组给予等量生理盐水灌胃,14 d后腹腔注射吗啡,观察小鼠行为学变化,TUNEL染色观察脑黑质内多巴胺神经元凋亡,逆转录-聚合酶链反应(RT-PCR)检测小鼠脑黑质内Caspase-3表达,蛋白印迹法(Western Blot)检测实验小鼠脑黑质内PI3K、磷酸化蛋白激酶B(p-Akt)、磷酸化糖原合酶激酶3(p-GSK-3β)蛋白含量。结果 Res治疗组小鼠30 min内向右旋转圈数低于6-OHDA致病组;6-OHDA致病组小鼠脑黑质内多巴胺神经元凋亡率高于正常组(P0.05),Res治疗组小鼠脑黑质内多巴胺神经元凋亡率低于6-OHDA致病组(P0.05);6-OHDA致病组小鼠脑黑质内Caspase-3较正常组增加,Res治疗组小鼠脑黑质内Caspase-3含量较6-OHDA致病组降低(P0.05)。6-OHDA致病组小鼠脑黑质内PI3K、p-Akt、p-GSK-3β蛋白含量均低于正常组(P0.05),且Res治疗组PI3K、p-Akt、p-GSK-3β蛋白含量较6-OHDA致病组升高(P0.05)。结论白藜芦醇可有效改善由6-OHDA诱导的帕金森病小鼠运动功能障碍,并降低脑黑质内多巴胺神经元凋亡,这种抑制作用可能通过激活PI3K/Akt/GSK-3β信号通路,抑制GSK-3β活性实现。     

胰岛素样生长因子1降低tau蛋白磷酸化作用机制的研究

目的探讨胰岛素样生长因子1(IGF-1)对6样淀粉蛋白(A6)导致大鼠PC1 2细胞tau蛋白磷酸化的保护作用及其机制。方法实验分为预处理1组、2组、3组、模型组、对照组、保护组和氯化锂组。MTT法观察不同浓度IGF-1对PC12细胞存活率的影响。Western blot法检测Aβ_(1-40)处理后PC12细胞tau蛋白磷酸化、总tau蛋白和糖原合成激酶3β(GSK-36)及GSK-3β Ser~9的表达情况。结果 tau蛋白Ser~(396)、Ser~(199/202)位点磷酸化水平在Aβ_(1-40)诱导3 h开始增高,1 2 h达高峰。与对照组比较,模型组GSK-3β明显升高,GSK-3β Ser~9明显降低(P0.05);与模型组比较,氯化锂组及保护组tau蛋白Ser~(396)、Ser~(199/202)位点磷酸化水平和总tau蛋白明显降低(P0.05);GSK 36明显降低,GSK-3β Ser~9明显升高(P0.05,P0.01)。结论 Aβ_(1-40)主要通过激活GSK-3β使tau蛋白的磷酸化水平增高。IGF-1有抑制GSK-3β的活性,降低Aβ_(1-40)所诱导的PC12细胞tau蛋白过度磷酸化的作用。     

Roles of phospho-GSK-3β in myocardial protection afforded by activation of the mitochondrial KATP channel

The aim of this study was to determine the roles of glycogen synthase kinase-3β (GSK-3β) in cardioprotection by activation of the mitochondrial ATP-sensitive K⁺ channel (mK_ATP channel). In isolated rat hearts, an mK_ATP activator, diazoxide, and a GSK-3β inhibitor, SB216763, similarly limited infarct size and the combination of these agents did not afford further protection. The protection by pre-ischemic treatment with diazoxide was abolished by inhibition of protein kinase C-ε (PKC-ε) or phosphatidylinositol-3-kinase (PI3K) upon reperfusion. Infusion of a GSK-3β inhibitor (LiCl), but not diazoxide, during reperfusion limited infarct size. Inhibition of PKC-ε or PI3K did not affect the protection by LiCl. Diazoxide infusion alone did not induce GSK-3β phosphorylation. However, diazoxide infusion before ischemia increased mitochondrial phospho-GSK-3β level and reduced cyclophilin-D (CypD) binding to adenine nucleotide translocase (ANT) at 10 min after reperfusion. This diazoxide-induced GSK-3β phosphorylation was inhibited by blockade of the mK_ATP channel before ischemia and by blockade of PKC-ε, PI3K or the adenosine A2b receptor at the time of reperfusion. Inhibition of GSK-3β by LiCl during reperfusion increased phospho-GSK-3β but had no significant effect on CypD-ANT binding. These results suggest that GSK-3β phosphorylation at the time of reperfusion by a PKC-ε, PI3K- and A2b receptor-dependent mechanism contributes to prevention of myocardial necrosis by pre-ischemic activation of the mK_ATP channel. Inhibition of CypD-ANT interaction may contribute to mK_ATP-induced myocardial protection, though it is not the sole mechanism of phospho-GSK-3β-mediated cytoprotection.     

Short-term in vitro inhibition of glycogen synthase kinase 3 potentiates insulin signaling in type I skeletal muscle of Zucker Diabetic Fatty rats

Overactivity of glycogen synthase kinase 3 (GSK-3) is associated with insulin resistance of skeletal muscle glucose transport in prediabetic and type 2 diabetic rodent models. However, limited information is available concerning the potential molecular mechanisms underlying the role GSK-3 plays in the etiology of insulin resistance in the male Zucker Diabetic Fatty (ZDF) rat, a model of type 2 diabetes mellitus. Therefore, we assessed the functionality of proximal and distal insulin signaling elements in isolated type I (slow-twitch oxidative) soleus muscles of ZDF rats after in vitro exposure to a selective GSK-3 inhibitor (1 micromol/L CT98014, K(i) <10 nmol/L for GSK-3alpha and GSK-3beta). Moreover, Ser307 phosphorylation of insulin receptor substrate 1 (IRS-1), which has been implicated in the development of insulin resistance, was also determined in the absence or presence of this GSK-3 inhibitor. Maximally insulin-stimulated (5 mU/mL) GSK-3beta serine phosphorylation was significantly less (35%, P < .05) in soleus muscle of ZDF rats compared with insulin-sensitive lean Zucker rats, indicating GSK-3 overactivity. In the absence of insulin, no effects of GSK-3 inhibition were detected. GSK-3 inhibition led to significant enhancement (28%) of insulin-stimulated glucose transport activity that was associated with significant up-regulation of tyrosine phosphorylation of IR (52%) and IRS-1 (50%), and with enhanced Akt Ser473 phosphorylation (48%) and GSK-3beta Ser9 phosphorylation (36%). Moreover, the selective GSK-3 inhibitor induced a significant reduction in the phosphorylation of IRS-1 Ser307 (26%) and c-jun N-terminal kinases 1 and 2 (31%), a mediator of IRS-1 Ser307 phosphorylation. These results indicate that selective inhibition of GSK-3 activity in type I skeletal muscle from overtly diabetic ZDF rats enhances IRS-1-dependent insulin signaling, possibly by a decrease in c-jun N-terminal kinase activation and a diminution of the deleterious effects of IRS-1 Ser307 phosphorylation.     

Acute elevation of circulating fatty acids impairs downstream insulin signalling in rat skeletal muscle in vivo independent of effects on stress signalling

The aim of this study was to examine the effect of an acute, physiological increase in plasma free fatty acid (FFA) on initial signalling events in rat red quadriceps muscle (RQ). Male Wistar rats received a 7% glycerol (GLYC) or 7% Intralipid/heparin (LIP) infusion for 3 h, after which they were either killed or infused with insulin at a rate of 0.5 U/kg per h for 5 min, before RQ collection. Plasma FFAs were elevated to approximately 2 mM in the LIP rats only. Insulin-stimulated insulin receptor (IR) Tyr1162/Tyr1163 phosphorylation and IR substrate (IRS)-1 Tyr612 phosphorylation were increased at least twofold over basal in GLYC rats with insulin and this increase was not significantly impaired in the LIP rats. However, there was no insulin-stimulated protein kinase B (PKB) Ser473 or glycogen synthase kinase (GSK)-3beta Ser9 phosphorylation in the LIP rats, compared with at least a twofold increase over basal in GLYC rats for both proteins. c-Jun N-terminal kinase, inhibitor of kappa kinase beta and inhibitor of nuclear factor-kappaB phosphorylation and total protein expression, as well as Ser307-IRS-1 phosphorylation, were not altered by lipid infusion compared with GLYC infusion. These data indicate that acute, physiological elevation in FFA has a greater impact on insulin signalling downstream of IR and IRS-1, at the level of PKB and GSK-3beta, and that under these conditions stress signalling pathways are not significantly stimulated. Decreased PKB and GSK-3beta phosphorylation in RQ may therefore be primary determinants of the reduced insulin action observed in situations of acute FFA oversupply.     

Shaggy/glycogen synthase kinase 3β and phosphorylation of Sarah/regulator of calcineurin are essential for completion of Drosophila female meiosis

The Ca(2+)/Calmodulin-dependent phosphatase calcineurin is essential for exit from meiotic arrest at metaphases I and II in Drosophila and Xenopus oocytes. We previously found that Sarah, the Drosophila homolog of regulator of calcineurin, acts as a positive regulator of calcineurin and is required to complete anaphase I of female meiosis. Here, we undertook biochemical approaches, including MS and posttranslational modification analyses, to better understand the mechanism by which Sarah regulates calcineurin. A search for phosphorylated residues revealed that Sarah is highly phosphorylated at Ser100, Thr102, and Ser219 in both ovaries and activated eggs and that Ser215 is phosphorylated only in activated eggs. Functional analyses using mutant forms of Sarah showed that phosphorylation at Ser215, a consensus phosphorylation site for glycogen synthase kinase 3β (GSK-3β) and its priming kinase site Ser219, are essential for Sarah function. Furthermore, germ-line clones homozygous for a null allele of shaggy (Drosophila GSK-3β) both fail to complete meiosis and lack phosphorylation of Sarah at Ser215, suggesting that the phosphorylation of Sarah by Shaggy/GSK-3β is required to complete meiosis. Our findings suggest a mechanism in which Shaggy/GSK-3β activates calcineurin through Sarah phosphorylation on egg activation in Drosophila.     

Modulation of the mitochondrial permeability transition pore complex in GSK-3beta-mediated myocardial protection

Recently we found that the level of anti-infarct tolerance afforded by ischemic preconditioning (IPC) and erythropoietin (EPO) infusion was closely correlated with the level of Ser9-phospho-GSK-3beta upon reperfusion in the heart. To get an insight into the mechanism by which phospho-GSK-3beta protects the myocardium from ischemia/reperfusion injury, we examined the effects of IPC and EPO on interactions between GSK-3beta and subunits of the mitochondrial permeability transition pore (mPTP) in this study. Rat hearts were subjected to 25-min global ischemia and 5-min reperfusion in vitro with or without IPC plus EPO infusion (5 units/ml) before ischemia. Ventricular tissues were sampled before or after ischemia/reperfusion to separate subcellular fractions for immunoblotting and immunoprecipitation. Reperfusion increased mitochondrial GSK-3beta by 2-fold and increased phospho-GSK-3beta level in all fractions examined. Major subunits of mPTP, adenine nucleotide translocase (ANT) and voltage-dependent anion channel (VDAC), were co-immunoprecipitated with GSK-3beta after reperfusion. Phospho-GSK-3beta was co-immunoprecipitated with ANT but not with VDAC. IPC+EPO significantly increased the levels of GSK-3beta and phospho-GSK-3beta that were co-immunoprecipitated with ANT to 145+/-8% and 143+/-16%, respectively, of baseline but did not induce phospho-GSK-3beta-VDAC binding. A PKC inhibitor and a PI3 kinase inhibitor suppressed the IPC+EPO-induced increase in the level of phospho-GSK-3beta-ANT complex. The level of cyclophilin D co-immunoprecipitated with ANT after reperfusion was significantly reduced to 39+/-10% of the control by IPC+EPO. These results suggest that reduction in affinity of ANT to cyclophilin D by increased phospho-GSK-3beta binding to ANT may be responsible for suppression of mPTP opening and myocardial protection afforded by IPC+EPO.     

Protective Effect of Morphine Against the Oxidant-Induced Injury in H9c2 Cells

There are some indications that morphine may exert myocardial protective effects under certain conditions. The aim of the present study was to investigate the effect of morphine on viability and oxidative state of H9c2 cells (rat cardiomyoblasts) influenced by oxidative stress that was elicited by exposure to tert-butyl hydroperoxide (t-BHP). Our experiments showed that pretreatment with morphine before the addition of t-BHP markedly improved cell viability. Morphine was able to increase total antioxidant capacity of H9c2 cells and to reduce the production of reactive oxygen species, protein carbonylation, and lipid peroxidation. Cellular damage caused by t-BHP was associated with low levels of p38 MAPK and GSK-3β phosphorylation. Pretreatment with morphine augmented p38 phosphorylation, and the increased phospho-p38/p38 ratio was preserved even in the presence of t-BHP. Morphine did not change the level of GSK-3β phosphorylation, but interestingly, the phospho-GSK-3β/GSK-3β ratio significantly increased after subsequent incubation with t-BHP. Furthermore, morphine exposure resulted in upregulation of the antioxidant enzyme catalase. The protective effect of morphine was abrogated by the addition of the PI3K inhibitor wortmannin and/or p38 MAPK inhibitor SB203580. It can be concluded that morphine may protect H9c2 cells against oxidative stress and that this protection is at least partially mediated through activation of the p38 MAPK and PI3K/GSK-3β pathways.     

Increased in vivo phosphorylation of insulin receptor at serine 994 in the liver of obese insulin-resistant Zucker rats

Serine phosphorylation of the insulin receptor (IR) has been proposed to exert an inhibitory influence on its tyrosine kinase activity. Previous works using site-directed mutagenesis suggested that serine 994 of the IR (IR Ser 994) might be part of an inhibitory domain of the receptor. In this study we examined whether this residue is subjected to phosphorylation in vivo. We used a site-phosphospecific antibody to determine the extent of phosphorylation of IR Ser 994 in insulin target tissues from two animal models of insulin resistance with different IR kinase (IRK) activity: obese (fa/fa) Zucker rats and transgenic mice overexpressing bovine growth hormone (PEPCK-bGH mice).Phosphorylation at IR Ser 994 was markedly increased in liver of obese rats. This alteration appeared to be tissue-selective since no phosphorylation on Ser 994 was detected in IRs isolated from skeletal muscle of these animals. On the other hand, the phosphorylation level of IR Ser 994 was very low in liver of PEPCK-bGH mice and did not differ from that of the control group. We have also demonstrated that protein kinase (PK) C isoforms alpha, betaI and zeta are able to promote the in vitro phosphorylation of the IR on Ser 994. Differential findings in these two models of insulin resistance might thus reflect increased PKC activity resulting from increased lipid availability in obese Zucker rats. Our results suggest that Ser 994 is a novel in vivo IR phosphorylation site that might be involved in the regulation of the IRK in some states of insulin resistance.     

Phosphorylation of insulin receptor substrate 1 by glycogen synthase kinase 3 impairs insulin action

The phosphorylation of insulin receptor substrate 1 (IRS-1) on tyrosine residues by the insulin receptor (IR) tyrosine kinase is involved in most of the biological responses of insulin. IRS-1 mediates insulin signaling by recruiting SH2 proteins through its multiple tyrosine phosphorylation sites. The phosphorylation of IRS-1 on serine/threonine residues also occurs in cells; however, the particular protein kinase(s) promoting this type of phosphorylation are unknown. Here we report that glycogen synthase kinase 3 (GSK-3) is capable of phosphorylating IRS-1 and that this modification converts IRS-1 into an inhibitor of IR tyrosine kinase activity in vitro. Expression of wild-type GSK-3 or an “unregulated” mutant of the kinase (S9A) in CHO cells overexpressing IRS-1 and IR, resulted in increased serine phosphorylation levels of IRS-1, suggesting that IRS-1 is a cellular target of GSK-3. Furthermore, insulin-induced tyrosine phosphorylation of IRS-1 and IR was markedly suppressed in cells expressing wild-type or the S9A mutant, indicating that expression of GSK-3 impairs IR tyrosine kinase activity. Taken together, our studies suggest a new role for GSK-3 in attenuating insulin signaling via its phosphorylation of IRS-1 and may provide new insight into mechanisms important in insulin resistance.