间歇有氧运动训练上调SIRT3改善衰老心肌线粒体功能

目的 探讨间歇有氧运动训练（AIT）对调节SIRT3介导的抗氧化酶系统改善老年小鼠心肌线粒体功能的影响。方法 采用C57小鼠（20月龄）20只,随机分为AIT组和非运动组,每组10只。以成年野生型C57小鼠非运动组(4月龄,10只)为对照组。建立间歇有氧运动训练12周小鼠模型,跑台训练由3部分构成:10 min热身运动,7 min间歇训练（4 min高强度和3 min低强度训练）及1 min冷却。每日训练1 h,每周训练5 d,训练时间为12周。应用蛋白免疫印迹法(Western blot)检测心肌线粒体抗氧化酶相关蛋白的表达。结果 AIT显著上调衰老心肌中线粒体去乙酰化酶sirtuin-3（SIRT3）表达水平,提高AMP依赖的蛋白激酶(AMPK)的磷酸化水平(P<0.05);AIT可改善老年组小鼠心肌线粒体抗氧化酶(MnSOD、Catalase)的活性,有效减少衰老心肌脂质过氧化损伤(P<0.05);AIT训练显著提高衰老心肌线粒体生物合成能力改善了线粒体的功能(均P<0.05)。结论 有氧间歇运动训练可有效地上调衰老小鼠心肌细胞SIRT3水平,有效提高衰老小鼠心肌线粒体功能,其机制可能与激活心肌SIRT3所介导的抗氧化酶系统有关。     

有氧运动对衰老模型大鼠心肌细胞凋亡及Bcl-2和Bax蛋白表达的影响

目的 探讨有氧运动对衰老模型大鼠心肌细胞凋亡及Bcl-2和Bax蛋白表达的影响.方法 建立衰老大鼠模型,随机分为对照组和两组运动组,运动组分别给予6次/w、 3次(隔日)/w游泳训练,每次持续90 min,训练12 w,于末次训练48 h后处死动物,TUNEL法检测心肌细胞凋亡,免疫印迹法检测心肌Bcl-2、Bax的表达,并计算Bax/Bcl-2的比值.结果 与对照组相比,两组运动组心肌细胞凋亡指数(AI)均显著降低(P＜0.01),Bcl-2蛋白表达显著升高(P＜0.01),Bax蛋白表达降低(P＜0.05),Bcl-2/Bax显著升高(P＜0.01);与6次/w运动组相比较,3次/w运动组心肌AI降低(P＜0.05),Bcl-2升高(P＜0.05),Bax降低(P＜0.05),Bcl-2/Bax升高(P＜0.05).结论 长期有氧运动使 Bcl-2/Bax比值优化,降低心肌细胞AI,促进心肌细胞存活,延缓心肌衰老;隔日有氧运动效果更佳.     

衰老心肌自噬减退的新机制-转录因子EB的关键作用

目的 探讨转录因子EB（TFEB）在衰老心肌自噬减退中的作用。方法 采用老年（22月龄）雄性C57BL/6小鼠为实验对象,以成年（4月龄）雄性C57BL/6小鼠为对照,分析心肌自噬水平、心肌TFEB表达水平。结果 与成年心肌相比,衰老心肌自噬水平显著降低（P<0.05）。衰老心肌中自噬体标志物Atg5、LC3和Beclin-1,溶酶体标志物LAMP1在蛋白和mRNA水平上均出现降低。与成年心肌相比,衰老心肌TFEB蛋白水平显著降低（P<0.05）,衰老心肌细胞核内的TFEB水平下降更为显著（P<0.05）,提示衰老心肌TFEB转录能力减退。给予小剂量雷帕霉素处理,可提高衰老心肌细胞核内TFEB水平,并且改善LC3及LAMP1的mRNA和蛋白水平,提高衰老心肌自噬水平。结论 本研究发现衰老导致的心肌TFEB水平降低严重影响心肌自噬能力,提示TFEB是心肌自噬增龄性减退机制中的关键调节因子。     

内源性二氧化硫抑制血管紧张素Ⅱ致心肌肥厚小鼠心肌细胞自噬的研究

目的探讨内源性二氧化硫(SO_2)对血管紧张素Ⅱ(AngⅡ)致心肌肥厚小鼠心肌细胞自噬的抑制作用。方法 9周龄健康C57BL小鼠16只,按随机数字表法随机分为野生型对照组(WT Con组)、野生型+AngⅡ组(WT AngⅡ组);心肌特异性天冬氨酸氨基转移酶2(AAT2)转基因小鼠16只,按随机数字表法随机分为AAT2对照组(AAT2 Con组)、AAT2+AngⅡ组(AAT2 AngⅡ组)。每组8只。每只小鼠在背部皮下植入预装生理盐水或AngⅡ的胶囊渗透压泵,连续给药4周。检测4组小鼠全心重/体重(HW/BW)比值;HE染色观察心肌细胞结构变化;免疫组织化学染色检测心肌标志分子α重链肌球蛋白(α-MHC)的表达;高效液相色谱检测心肌组织SO_2含量;Western blot检测内源性SO_2生成酶AAT1和AAT2、心肌表型标志分子α-MHC和β-MHC以及心肌自噬标志分子Beclin-1、LC3、Atg4B以及p62蛋白表达变化。结果与WT Con组相比,WT AngⅡ组心肌组织SO_2含量显著降低(P0.01),AAT1蛋白表达无明显变化(P0.05),AAT2蛋白表达显著减少(P0.05),HW/BW明显增加(P0.01),心肌纤维明显增粗,免疫组织化学法显示心肌细胞浆中α-MHC蛋白表达明显减弱,Western blot结果显示心肌细胞α-MHC蛋白表达显著降低(P0.01),β-MHC蛋白表达显著升高(P0.01),心肌组织LC3Ⅱ/LC3Ⅰ比值显著升高,Beclin-1和Atg4B蛋白表达显著升高,p62蛋白表达显著降低(均P0.01)。与WT Con组相比,AAT2 AngⅡ组小鼠心肌组织SO_2含量和AAT2蛋白表达显著升高(P0.01),AAT1的蛋白表达无显著变化(P0.05),HW/BW显著降低(P0.05),心肌纤维的增粗显著减轻,α-MHC蛋白向β-MHC蛋白的转化显著降低(P0.01),心肌细胞自噬水平显著降低。结论内源性SO_2/AAT2体系可抑制AngⅡ致小鼠心肌肥厚及心肌细胞自噬。     

大鼠心肌梗死后心脏线粒体及自噬小体的变化与Parkin蛋白活性的相关性

目的:本实验通过研究心肌梗死(心梗)后心肌组织内线粒体自噬功能以及帕金(Parkin)蛋白的变化,进而揭示Parkin蛋白在调节心脏线粒体自噬功能中的作用。方法:采用随机分组原则,将大鼠分为正常组,伪手术组和心梗组。心梗大鼠模型建立4周后,超声测量各组大鼠左室收缩末期内径(LVESD)、左室舒张末期内径(LVEDD)、左室射血分数(EF)、左室短轴缩短率(FS)和左室舒张期和收缩期容量。取心肌组织,在电镜下观察各组的线粒体和自噬小体的形态、大小和数量变化。采用Western Blot技术分析心肌组织内自噬相关蛋白LC3及Parkin蛋白的活性。结果:心梗4周后,心梗组大鼠与正常组相比,心功能降低,LVESD和LVEDD均增大(P0.05),左室EF降低,慢性心梗模型制备成功。大鼠心梗后心肌内线粒体及自噬小体数量增多(P0.05),且线粒体正常形态破坏。氯喹(CQ)能增强正常组大鼠心肌自噬流(P0.05),然而CQ对心梗组大鼠心肌自噬小体的变化无明显影响(P0.05)。此外,心梗组心肌内自噬相关蛋白LC3II表达水平相比正常组增加(P0.05)并且Parkin蛋白活性显著降低(P0.05)。结论:慢性心梗的过程中,心肌细胞线粒功能的破坏以及自噬小体清除能力的损害与Parkin蛋白密切相关。     

线粒体自噬相关蛋白在阿霉素诱导的心脏毒性中的表达及意义

目的探讨线粒体自噬相关蛋白在阿霉素诱导的急性心肌损伤中的表达及意义。方法将40只8～10周龄的雄性野生型C57小鼠随机分为对照组和阿霉素组,每组各20只,阿霉素组小鼠腹腔注射大剂量阿霉素(15mg/kg)诱导急性心肌损伤模型,对照组小鼠给予腹腔注射等量生理盐水。各组于第6天进行心功能检测并取材。分别采用RT-PCR和免疫印迹法检测PTEN诱导性激酶蛋白1(PINK1)、Parkin、自噬标记轻链3(LC3)、Bax、Bcl-2、半胱氨酸天冬氨酸特异性蛋白酶3(C-caspase3)mRNA和蛋白表达水平。苏木精-伊红染色检测各组心肌损伤,TUNEL染色检测各组凋亡心肌细胞数量。结果与对照组比较,阿霉素组左心室舒张末期内径[(4.32±0.50)mmvs (3.85±0.30)mm]、左心室收缩末期内径[(3.34±0.40)mmvs (2.56±0.19)mm]和舒张末期室间隔厚度增加[(0.76±0.12)mmvs (0.48±0.09)mm,P0.05],左心室短轴缩短率降低[(26.0±2.7)%vs (37.0±4.0)%,P0.05]。阿霉素组小鼠心肌PINK1、LC3、Bax和C-caspase3mRNA和蛋白表达水平均增加(P0.05),Parkin和Bcl-2mRNA和蛋白表达水平均降低(P0.05)。苏木精-伊红染色显示,阿霉素组心肌细胞排列紊乱,并出现细胞质空泡化现象。TUNEL染色显示,阿霉素组细胞核呈致密浓染、凋亡心肌细胞较对照组明显增多(P0.05)。结论线粒体自噬介导细胞凋亡参与阿霉素诱导的急性心肌损伤的过程。     

羟基红花黄素A对缺血性心力衰竭大鼠心肌自噬及ERK1/2通路的影响

目的:探讨羟基红花黄素A(HSYA)对缺血性心力衰竭(IHF)大鼠心肌自噬及细胞外调节蛋白激酶(ERK1/2)通路的影响。方法:将72只大鼠随机分为假手术组、模型组、阳性对照组(卡托普利组)、低剂量HSYA组(L-HSYA)、中剂量HSYA组(M-HSYA)、高剂量HSYA组(H-HSYA),每组12只。采用冠脉结扎法建立缺血性心力衰竭大鼠模型。超声仪检测大鼠左心室心功能水平,酶联免疫吸附法(ELISA)检测血清N-末端脑钠肽前体(NTpro BNP)和超敏肌钙蛋白(hs-TnT)水平,透射电镜观察心肌细胞自噬,Western blot法检测心肌组织自噬相关因子微管相关蛋白1(Beclin1)、微管相关蛋白轻链3(LC3)、泛素和LC3结合蛋白p62(p62)、ERK1/2蛋白表达。结果:与模型组比较,阳性对照组、M-HSYA和H-HSYA组大鼠左室收缩末期室间隔厚度(LVSs)、左室舒张末期室间隔厚度(LVSd)、收缩末期左心室后壁厚度(LVPWs)、舒张末期左心室后壁厚度(LVPWd)、左心室射血分数(LVEF)及LHSYA组LVSd显著升高(均P 0. 05);心电图T波幅度和ST段抬高幅度显著降低,QT间期显著缩短(均P 0. 05);大鼠血清NT-proBNP和hs-TnT水平显著降低(均P 0. 05),心肌细胞自噬小体数量减少,自噬率显著降低(P 0. 05);心肌组织Beclin-1、LC3Ⅰ、LC3Ⅱ蛋白表达显著降低(均P 0. 05),p62和p-ERK1/2蛋白表达显著升高(均P 0. 05)。结论:IHF大鼠心肌损伤与自噬关系密切,HSYA可能通过激活ERK1/2信号通路抑制IHF大鼠心肌细胞自噬。     

外源性生长激素释放肽通过调节腺苷酸活化蛋白

目的 探索生长激素释放肽(Ghrelin)的心脏保护效应机制,明确外源性Ghrelin是否通过调节腺苷酸活化蛋白激酶(AMPKα2)及葡萄糖转运蛋白4(Glut4)表达而改善自发性糖尿病大鼠(GK)心脏功能.方法 GK大鼠编号随机分为3组:GK组、二甲双胍组(二甲双胍灌胃4周)和Ghrelin组(外源性Ghrelin腹腔注射4周),另选Wistar大鼠为对照.通过透射电镜观察大鼠心肌超微结构;应用多道生理记录仪观察大鼠心脏功能;留取大鼠动脉血液计算胰岛素抵抗指数(HOMA-IR);采用RT-PCR法测量AMPKα2及Glut4基因表达.结果 实验4周后,与Wistar组及GK组比较,Ghrelin组心率降低,舒张、收缩功能改善(P＜0.05);Ghrelin组大鼠的HOMA-IR指数低于GK组(P＜0.05);Ghrelin组大鼠心肌内线粒体及心肌间微血管接近Wistar组;Ghrelin及二甲双胍干预后大鼠心肌AMPKα2和Glut4 mRNA表达量有明显增加(P＜0.05).结论 Ghrelin腹腔注射可减轻自发性糖尿病大鼠胰岛素抵抗,提高自发性糖尿病大鼠心脏左心室舒张和收缩功能,其机制可能与较长期在体上调心肌细胞AMPK表达而促进葡萄糖转运有关.     

辛二酰苯胺异羟肟酸通过抑制组蛋白去乙酰化酶改善小鼠心肌肥厚的研究

目的:探讨组蛋白去乙酰化酶(HDAC)抑制剂辛二酰苯胺异羟肟酸(SAHA)改善小鼠心肌肥厚的作用,为防治心肌肥厚提供新思路。方法:选取60只昆明小鼠,随机分为正常组、假手术组、心肌肥厚组、心肌肥厚+SAHA组,通过部分结扎小鼠胸主动脉建立心肌肥厚模型,最终每组纳入6只。采用苏木素伊红(HE)染色观察小鼠心肌细胞,超声心动图检测小鼠心功能,比色法检测HDAC活性,小鼠心肌组织中HDAC亚型HDAC5和β-肌球蛋白重链(β-MHC)信使核糖核酸(mRNA)和蛋白表达水平分别运用逆转录-聚合酶链反应(RT-PCR)和蛋白免疫印迹(Western blot)检测。结果:HE染色结果表明心肌肥厚组小鼠心肌细胞肥大、排列紊乱、细胞核深染。心肌肥厚组小鼠左心室舒张末期直径、左心室舒张末期容积均显著低于假手术组(P0.05),而室间隔明显较假手术组增厚(P0.05)。心肌肥厚组小鼠HDACs活性显著高于假手术组(P0.05);心肌肥厚组HDAC5和β-MHC的mRNA及蛋白表达水平均显著高于假手术组(P0.05)。SAHA能够显著降低HDAC5表达水平,显著下调心脏肥厚相关基因β-MHC的表达并改善小鼠心功能和心肌肥厚(P均0.05)。结论:HDAC参与了心肌肥厚的发生,HDAC抑制剂SAHA通过抑制HDAC5的表达从而改善小鼠心肌肥厚。     

Pyr1-apelin-13对大鼠心肌成纤维细胞AMPK/mTOR自噬信号和氧化应激损伤的影响

目的探讨Pyr¹-apelin-13对于大鼠心肌成纤维细胞自噬和氧化应激的影响及其作用机制。方法提取新生大鼠心肌成纤维细胞(CFs),给与血管紧张素Ⅱ(AngⅡ),Pyr¹-apelin-13,雷帕霉素干预,使用Western blot法和免疫荧光技术检测自噬信号分子,使用DHE法检测氧自由基生成,观察Pyr¹-apelin-13在AMPK/mTOR通路中的作用。结果在体外培养的CFs细胞中,AngⅡ刺激通过上调P62和磷酸化mTOR抑制自噬水平,伴有LC3II、Beclin-1和磷酸化AMPK降低及氧化应激水平增高;而Pyr¹-apelin-13或雷帕霉素干预后逆转AngⅡ介导的自噬下调,表现为LC3II/I、Beclin-1和磷酸化AMPK水平上升,P62表达和磷酸化mTOR下降,细胞氧化应激损伤减轻。结论Pyr¹-apelin-13可通过调控大鼠心肌成纤维细胞AMPK/mTOR自噬信号发挥其抗氧化和促自噬的细胞保护功效。     

Cardiac overexpression of metallothionein rescues cardiac contractile dysfunction and endoplasmic reticulum stress but not autophagy in sepsis

Sepsis is characterized by systematic inflammation where oxidative damage plays a key role in organ failure. This study was designed to examine the impact of the antioxidant metallothionein (MT) on lipopolysaccharide (LPS)-induced cardiac contractile and intracellular Ca²⁺ dysfunction, oxidative stress, endoplasmic reticulum (ER) stress and autophagy. Mechanical and intracellular Ca²⁺ properties were examined in hearts from FVB and cardiac-specific MT overexpression mice treated with LPS. Oxidative stress, activation of mitogen-activated protein kinase pathways (ERK, JNK and p38), ER stress, autophagy and inflammatory markers iNOS and TNFα were evaluated. Our data revealed enlarged end systolic diameter, decreased fractional shortening, myocyte peak shortening and maximal velocity of shortening/relengthening as well as prolonged duration of relengthening in LPS-treated FVB mice associated with reduced intracellular Ca²⁺ release and decay. LPS treatment promoted oxidative stress (reduced glutathione/glutathione disulfide ratio and ROS generation). Western blot analysis revealed greater iNOS and TNFα, activation of ERK, JNK and p38, upregulation of ER stress markers GRP78, Gadd153, PERK and IRE1α, as well as the autophagy markers Beclin-1, LCB3 and Atg7 in LPS-treated mouse hearts without any change in total ERK, JNK and p38. Interestingly, these LPS-induced changes in echocardiographic, cardiomyocyte mechanical and intracellular Ca²⁺ properties, ROS, stress signaling and ER stress (but not autophagy, iNOS and TNFα) were ablated by MT. Antioxidant N-acetylcysteine and the ER stress inhibitor tauroursodeoxycholic acid reversed LPS-elicited depression in cardiomyocyte contractile function. LPS activated AMPK and its downstream signaling ACC in conjunction with an elevated AMP/ATP ratio, which was unaffected by MT. Taken together, our data favor a beneficial effect of MT in the management of cardiac dysfunction in sepsis.     

Macrophage migration inhibitory factor deficiency augments cardiac dysfunction in Type 1 diabetic murine cardiomyocytes

Background: It has become evident that macrophage migration inhibitory factor (MIF) is associated with the development of Type 1 diabetes mellitus. The aim of the present study was to determine whether MIF plays a role in cardiac contractile dysfunction in T1DM mice. Methods: Mechanical and intracellular Ca²⁺ properties were measured in cardiomyocytes isolated from wild‐type (WT) and MIF‐knockout (MIF‐KO) mice administrated or not streptozotocin (200 mg/kg, i.p.). Relative stress signaling was evaluated using western blot analysis. Results: Peak shortening (PS) and maximal velocity of shortening/relengthening (±dL/dt) were reduced and the duration of relengthening (TR90) was prolonged in both WT and MIF‐KO cardiomyocytes treated with STZ (P < 0.01 vs control), which may be associated with reduced intracellular Ca²⁺ decay in both groups. However, STZ‐treated WT cardiomyocytes demonstrated significantly better contractile function and intracellular Ca²⁺ properties compared with STZ‐treated MIF‐KO cardiomyocytes (all P < 0.05). Interestingly, the physiological data clearly showed that blood glucose levels were significantly higher in STZ‐treated MIF‐KO mice than STZ‐treated WT mice (P < 0.01). Moreover, phosphorylation of AMP‐activated protein kinase (AMPK) and its direct downstream target acetyl‐CoA carboxylase (ACC) was markedly lower in hearts from STZ‐treated MIF‐KO mice than STZ‐treated WT mice (P < 0.05). There were no significant differences between untreated WT and MIF‐KO control groups. Conclusions: There is a beneficial action of MIF in the management of cardiac dysfunction in T1DM. The cardioprotective effect of MIF may be associated with AMPK signaling.     

Chronic akt activation accentuates aging-induced cardiac hypertrophy and myocardial contractile dysfunction: role of autophagy

Aging is often accompanied with geometric and functional changes in the heart, although the underlying mechanisms remain unclear. Recent evidence has described a potential role of Akt and autophagy in aging-associated organ deterioration. This study was to examine the impact of cardiac-specific Akt activation on aging-induced cardiac geometric and functional changes and underlying mechanisms involved. Cardiac geometry, contractile and intracellular Ca²⁺ properties were evaluated using echocardiography, edge-detection and fura-2 techniques. Level of insulin signaling and autophagy was evaluated by western blot. Our results revealed cardiac hypertrophy (enlarged chamber size, wall thickness, myocyte cross-sectional area), fibrosis, decreased cardiac contractility, prolonged relengthening along with compromised intracellular Ca²⁺ release and clearance in aged (24–26 month-old) mice compared with young (3–4 month-old) mice, the effects of which were accentuated by chronic Akt activation. Aging enhanced Akt and mTOR phosphorylation while reducing that of PTEN, AMPK and ACC with a more pronounced response in Akt transgenic mice. GSK3β phosphorylation and eNOS levels were unaffected by aging or Akt overexpression. Levels of beclin-1, Atg5 and LC3-II-to-LC3-I ratio were decreased in aged hearts, the effect of which with the exception of Atg 5 was exacerbated by Akt overactivation. Levels of p62 were significantly enhanced in aged mice with a more pronounced increase in Akt mice. Neither aging nor Akt altered β-glucuronidase activity and cathepsin B although aging reduced LAMP1 level. In addition, rapamycin reduced aging-induced cardiomyocyte contractile and intracellular Ca²⁺ dysfunction while Akt activation suppressed autophagy in young but not aged cardiomyocytes. In conclusion, our data suggest that Akt may accentuate aging-induced cardiac geometric and contractile defects through a loss of autophagic regulation.     

Cardiac contractile function is enhanced in isolated ventricular myocytes from growth hormone transgenic mice

Growth hormone (GH) plays a key role in cardiac growth and function. However, excessive levels of GH often result in cardiac dysfunction, which is the major cause of death in acromegalic patients. Transgenic mice with GH over-expression serve as useful models for acromegaly and exhibit impaired cardiac functions using echocardiography, similar to those of human acromegaly. However, the mechanism underscoring the impaired ventricular function has not been well defined. This study was designed to evaluate the cardiac excitation-contraction coupling in GH over-expressing transgenic mice at the single ventricular myocyte level. Myocytes were isolated from GH and age-matched wild-type mouse hearts. Mechanical properties were evaluated using an IonOptix MyoCam system. The contractile properties analyzed included peak shortening (PS), time-to-peak shortening (TPS) and time-to-90% relengthening (TR(90)), and maximal velocities of shortening/relengthening (+/-dL/dt). Intracellular Ca2+ properties were evaluated by fura-2. GH transgenic mice exhibited significantly increased body weights and enlarged heart and myocyte size. Myocytes from GH transgenic mice displayed significantly enhanced PS and+/-dL/dt associated with similar TPS and TR(90) compared with the wild-type littermates. Myocytes from GH transgenic mice displayed a similar resting intracellular Ca2+ level and Ca2+ removal rate but exhibited an elevated peak intracellular Ca2+ level compared with the wild-type group. Myocytes from both groups were equally responsive to increases in extracellular Ca2+ concentration and stimulating frequency. These results suggest that GH over-expression is associated with enhanced contractile function in isolated myocytes and that the impaired cardiac function observed in whole hearts may not be due to defects at the myocyte level.     

Impaired cardiac excitation-contraction coupling in ventricular myocytes from Ames dwarf mice with IGF-I deficiency.

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) are involved in the regulation of cardiovascular function. GH/IGF-I deficiency is associated with impaired cardiac performance manifested as reduced left ventricular ejection fraction and diastolic filling. This study was to determine the impact of IGF-I deficiency on single cardiac myocyte excitation-contraction (E-C) coupling. Ventricular myocytes were isolated from adult Ames dwarf mice and age-matched wild-type siblings. Dwarf mice are characterized by severe IGF-I deficiency. Mechanical properties were evaluated using a video edge detection system. Myocytes were electrically stimulated at 0.5 Hz. The contractile properties analysed included peak shortening (PS), time to peak shortening (TPS) and time to 90% relengthening (TR(90)), and maximal velocities of shortening/relengthening (+/-d L/d t). Intracellular Ca(2+) transients were evaluated by fura-2 fluorescence microscopy. Dwarf mice exhibited significantly reduced body and heart weights and severely deficient plasma IGF-I. Myocytes from dwarf mice displayed significantly smaller cell lengths (CLs), prolonged TPS/TR(90) and reduced +/-d L/d t compared with the wild-type littermates. The absolute PS was similar although PS/CL was enhanced in the dwarf group. Myocytes from dwarf animals displayed reduced peak intracellular Ca(2+) levels and slowed intracellular Ca(2+) clearing associated with a comparable resting intracellular Ca(2+). Furthermore, myocytes from the dwarf hearts were equally responsive to an elevation in extracellular Ca(2+) and exhibited an augmented stepwise decrease in response to minimal increase in stimulating frequencies compared with those from the wild-type group. These results suggest that deficiency in IGF-I may be directly associated with cardiac E-C coupling dysfunction at the ventricular myocyte level.     

Cardiac overexpression of alcohol dehydrogenase exacerbates cardiac contractile dysfunction,lipid peroxidation,and protein damage after chronic ethanol ingestion

BACKGROUND: Alcoholic cardiomyopathy is manifested as ventricular dysfunction, although its specific toxic mechanism remains obscure. This study was designed to examine the impact of enhanced acetaldehyde exposure on cardiac function via cardiac-specific overexpression of alcohol dehydrogenase (ADH) after alcohol intake. METHODS: ADH transgenic and wild-type FVB mice were placed on a 4% alcohol or control diet for 8 weeks. Mechanical and intracellular Ca2+ properties were evaluated in cardiac myocytes. Levels of acetaldehyde, lipid peroxidation, and protein carbonyl formation were determined. RESULTS: FVB and ADH mice consuming ethanol exhibited elevated blood ethanol/acetaldehyde, cardiac acetaldehyde, and cardiac hypertrophy compared with non-ethanol-consuming mice. However, the levels of cardiac acetaldehyde and hypertrophy were significantly greater in ADH ethanol-fed mice than FVB ethanol-fed mice. ADH transgene itself did not affect mechanical and intracellular Ca2+ properties with the exception of reduced resting intracellular Ca2+ and Ca2+ re-sequestration at low pace frequency. Myocytes from ethanol-fed mice showed significantly depressed peak shortening, velocity of shortening/relengthening, rise of intracellular Ca2+ transients, and sarco(endo)plasmic reticulum Ca2+ load associated with similar duration of shortening/relengthening compared with myocytes from control mice. Strikingly, the ethanol-induced mechanical and intracellular Ca2+ defects were exacerbated in ADH myocytes compared with the FVB group except velocity of shortening/relengthening. The lipid peroxidation end products malondialdehyde and protein carbonyl formation were significantly elevated in both livers and hearts after chronic ethanol consumption, with the cardiac lipid and protein damage being exaggerated by ADH transgene. CONCLUSION: These data suggest that increased cardiac acetaldehyde exposure due to ADH transgene may play an important role in cardiac contractile dysfunctions associated with lipid and protein damage after alcohol intake.     

Transgenic overexpression of insulin-like growth factor I prevents streptozotocin-induced cardiac contractile dysfunction and beta-adrenergic response in ventricular myocytes

Diabetic cardiomyopathy is characterized by cardiac dysfunction and altered level/function of insulin-like growth factor I (IGF-I). Both endogenous and exogenous IGF-I have been shown to effectively alleviate diabetes-induced cardiac dysfunction and oxidative stress. This study was designed to examine the effect of cardiac overexpression of IGF-I on streptozotocin (STZ)-induced cardiac contractile dysfunction in mouse myocytes. Both IGF-I heterozygous transgenic mice and their wild-type FVB littermates were made diabetic with a single injection of STZ (200 mg/kg, i.p.) and maintained for 2 weeks. The following mechanical indices were evaluated in ventricular myocytes: peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR90) and maximal velocity of shortening/relengthening (+/- dL/dt). Intracellular Ca2+ was evaluated as resting and peak intracellular Ca2+ levels, Ca2+-induced Ca2+ release and intracellular Ca2+ decay rate (tau). STZ led to hyperglycemia in FVB and IGF-I mice. STZ treatment prolonged TPS and TR90, reduced Ca2+-induced Ca2+ release, increased resting intracellular Ca2+ levels and slowed tau associated with normal PS and +/- dL/dt. All of which, except the elevated resting intracellular Ca2+, were prevented by the IGF-I transgene. In addition, myocytes from STZ-treated FVB mice displayed an attenuated contractile response to the beta-adrenergic agonist isoproterenol, which was restored by the IGF-I transgene. Contractile response to the alpha-adrenergic agonist phenylephrine and angiotensin II was not affected by either STZ treatment or IGF-I. These results validate the beneficial role of IGF-I in diabetic cardiomyopathy, possibly due to an improved beta-adrenergic response.     

Insulin resistance induces hyperleptinemia, cardiac contractile dysfunction but not cardiac leptin resistance in ventricular myocytes

Insulin resistance is a metabolic syndrome commonly seen in obesity. Leptin, the obese gene product, plays a role in the regulation of cardiac function. Elevated leptin levels have been demonstrated under insulin-resistant states such as obesity and hypertension, although their role in cardiac dysfunction is unknown. This study was designed to determine the impact of prediabetic insulin resistance on leptin levels and leptin-induced cardiac contractile response. Whole-body insulin resistance was generated with a 10-week dietary sucrose feeding. Contractile and intracellular Ca(2+) properties were evaluated in ventricular myocytes using an IonOptix system. The contractile indices analyzed included peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR(90)), maximal velocity of shortening/relengthening (+/-dL/dt), fura-fluorescence intensity change (deltaFFI) and decay rate (tau). Sucrose-fed rats displayed significantly elevated body weight and plasma leptin levels, depressed PS, +/-dL/dt, shortened TPS, prolonged TR(90) and tau, as well as reduced deltaFFI compared to the starch-fed control group. Leptin (1-1000 nM) elicited a concentration-dependent depression of PS and deltaFFI in myocytes from both starch and sucrose groups. Leptin-induced contractile depression was abolished by the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyle ester, elevation of the extracellular Ca(2+) concentration, the Janus activated kinase 2 inhibitor AG-490 or the mitogen activated protein kinase inhibitor SB203580 in myocytes from both sucrose and starch groups. Moreover, AG-490 and SB203580 unmasked a positive response of PS in myocytes from both groups. These data indicate that insulin resistance directly induces hyperleptinemia and cardiac contractile dysfunction, without affecting leptin-mediated cardiac contractile function at the myocyte level.