线粒体通透性转换孔在心肌缺血/再灌注损伤中的作用

线粒体在生理情况下是细胞的能量转化器,支持细胞的存活,在缺血/再灌注损伤(IR I)中可介导细胞的凋亡和坏死。线粒体通透性转换孔(mPTP)是细胞内外信息交换的中心枢纽。目前认为,mPTP是IR I后细胞发生坏死或凋亡的共同通路,已成为研究心肌保护机制的重要靶点。     

线粒体通透性转换孔与心脏病

线粒体是细胞能量加工器,对维持细胞的正常能量代谢和存活有重要作用。线粒体功能紊乱可引起心肌细胞的凋亡和坏死。线粒体通透性转换孔(mitochon-drial permeability transition pore,mPTP)大量开放是导致线粒体功能紊乱的关键,它与多种心脏病的发生、发展密切相关。该文对mPTP的构成、调控、功能及与心脏病关系的进展作一综述。     

线粒体通透性转换孔与老年心肌的研究进展

随着人体的衰老进程，心肌细胞的结构、功能均会发生变化，这就使得老年心肌细胞对缺血缺氧等应激事件较年轻心肌细胞更为敏感，且耐受性差，因此，心血管疾病已经成为老年人群中最致命的杀手。线粒体通透性转换孔（mPTP）是一种非选择性的线粒体膜通道，mPTP的启闭在心肌细胞的保护中具有重要作用。在老年心肌中，对于mPTP开放的调节存在着一定的特殊性：一些抑制其开放的药物对年轻心肌具有保护作用，而对老年心肌保护作用却不明显。另外，mPTP的开放反过来也影响着细胞的衰老进程。因此，研究老年心肌的mPTP的结构和功能对提高老年人心血管疾病治疗水平有重要意义。     

sRAGE对缺氧/复氧大鼠心肌细胞线粒体膜电位的影响

目的观察可溶性糖基化终产物受体(sRAGE)对缺氧/复氧(H/R)大鼠心肌细胞线粒体凋亡途径的影响。方法取大鼠心肌细胞培养72 h,以缺氧3 h、复氧2 h复制H/R模型,实验分为4组:对照组、对照+sRAGE组、H/R组、H/R+sRAGE组。以荧光探针JC-1方法检测线粒体膜电位,酯化钙黄绿素和氯化钴共孵育测定线粒体通透性转换孔(mPTP)开放,Western blot方法检测心肌细胞凋亡。结果与对照组比较,H/R组mPTP开放增多,线粒体膜电位去极化程度增加,凋亡率升高(P均<0.05);与H/R组比较,H/R+sRAGE组mPTP开放减少,线粒体膜电位去极化程度减轻,凋亡率下降(P均<0.05)。结论 sRAGE可通过抑制线粒体凋亡途径,拮抗心肌H/R损伤。     

环孢素A在心肌缺血再灌注损伤中的心脏保护作用研究进展

越来越多的证据显示线粒体通透性转换孔（mPTP）的开放在心肌缺血再灌注损伤中发挥着关键作用。尽管其结构仍不明确,但亲环素D却是其主要的组成成分之一。环孢素A是一种有效的免疫抑制剂,可结合于线粒体亲环素D,从而抑制mPTP的开放。许多动物实验及部分小规模临床研究表明,其可以通过抑制mPTP而减少心肌梗死面积。然而,也有研究提示环孢素A并没有心脏保护作用。现就环孢素A在心肌缺血再灌注损伤中可能的心脏保护作用机制、相关的动物实验模型及临床研究、可能的影响因素及进一步研究方向进行综述。     

线粒体通透性转换孔与心肌缺血再灌注损伤

线粒体在细胞的存活和死亡中起着重要的作用。线粒体通透性转换孔（MPTP）是线粒体内外信息交流的中心枢纽其功能的发挥依赖于其自身的开放状态。大量研究表明，MPTP在照血再灌注损伤中扮演着重要角色MPTP开放是照血再灌注后细胞坏死和凋亡的共同通路。     

线粒体通透性转换孔与心肌保护

线粒体在生理情况下是细胞的能量转换器,支持细胞存活;在缺血再灌注损伤时则中介细胞凋亡和坏死,线粒体通透性转换孔（mitochondrial permeability transition pore,MPTP）在此过程扮演了关键角色.抑制MPTP的开放是心肌保护最有前途的药物作用靶点之一,该文综述其研究进展.     

钙离子调节改变与心肌缺血再灌注损伤

心肌细胞钙离子失去稳态调节是多种心脏病变的基础，与缺血/再罐注（I/R）损伤关系密切。I/R引起细胞内外钙离子调节方式发生变化，导致胞浆及线粒体基质钙超载；通过能量依赖性肌纤维过度收缩、钙蛋白酶介导的细胞蛋白水解、线粒体渗透性转换孔的开放、诱导细胞凋亡，以及关闭缝隙连接通道使细胞活动失同步等途径致使心肌结构破坏、功能下降或电生理紊乱。干预细胞钙离子调节不同的环节，纠正或维持钙离子稳态则被证实有助于防止或减轻心肌I/R损伤。     

线粒体通透性转换与非酒精性脂肪性肝病

线粒体通透性转换孔（MPTP）是由位于线粒体内、外膜,多蛋白成分组成的小分子通道,由其介导线粒体与胞浆间蛋白及离子转运。线粒体通透性转换（MPT）引起的质子转运导致线粒体膜电势崩塌,是引起ATP合成减少、能量失衡的重要原因;MPT的开放引起线粒体水肿及膜间隙促凋亡蛋白细胞色素c（cytochromec）等释放,一方面使线粒体呼吸链的完整性受损,加重细胞氧化应激损伤;另一方面则激活了细胞死亡机制。     

细胞外信号调节激酶通路在七氟醚后处理对抗大鼠离体心脏缺血再灌注损伤中的作用

目的研究活性氧（ROS）、细胞外信号调节激酶（ERK1/2）及线粒体通透性转换孔（mPTP）在七氟醚缺血后处理减轻离体大鼠心脏缺血-再灌注损伤中的作用。方法以K-H缓冲液灌注离体大鼠心脏,全心缺血30min后复灌60min建立缺血-再灌注损伤模型。七氟醚缺血后处理的心脏于缺血后复灌最初15min以3%七氟醚饱和的K-H缓冲液灌注。分别单独给予或与七氟醚同时给予ROS清除剂NAC（4mM）或ERK1/2阻断剂PD98059（20μM）,用以评价ROS及ERK1/2在七氟醚缺血后处理中的作用。比较各组间血流动力学、心肌梗死面积、冠脉流出液中乳酸脱氢酶（LDH）及肌酸肌酶-MB（CK-MB）水平。同时,测定各组缺血30min复灌60min后心肌丙二醛（MDA）含量以反映氧化应激损伤程度。Western blotting测定ERK1/2的磷酸化情况。测定心肌烟酰胺腺嘌呤二核苷酸（NAD＋）含量以反映mPTP的开放情况。结果与对照组相比,复灌之初给予3%七氟醚可显著改善心功能（增加左室发展压力、左室最大收缩/舒张速率、冠脉流量、心率,并降低左室舒张末期压力）、降低心肌梗死面积及减少LDH及CK-MB释放（P〈0.05）。七氟醚的心肌保护作用同样表现在降低缺血-再灌注损伤后心肌的MDA含量（P〈0.05）。然而,给予NAC或PD98059不仅可消除上述保护作用,而且可以抑制七氟醚增强ERK1/2磷酸化及抑制mPTP开放的保护作用（P〈0.05）。结论 3%七氟醚缺血后处理通过ROS-ERK1/2-mPTP信号通路可为健康大鼠离体心脏的缺血-再灌注损伤提供保护。     

Bax regulates primary necrosis through mitochondrial dynamics

The defining event in apoptosis is mitochondrial outer membrane permeabilization (MOMP), allowing apoptogen release. In contrast, the triggering event in primary necrosis is early opening of the inner membrane mitochondrial permeability transition pore (mPTP), precipitating mitochondrial dysfunction and cessation of ATP synthesis. Bcl-2 proteins Bax and Bak are the principal activators of MOMP and apoptosis. Unexpectedly, we find that deletion of Bax and Bak dramatically reduces necrotic injury during myocardial infarction in vivo. Triple knockout mice lacking Bax/Bak and cyclophilin D, a key regulator of necrosis, fail to show further reduction in infarct size over those deficient in Bax/Bak. Absence of Bax/Bak renders cells resistant to mPTP opening and necrosis, effects confirmed in isolated mitochondria. Reconstitution of these cells or mitochondria with wild-type Bax, or an oligomerization-deficient mutant that cannot support MOMP and apoptosis, restores mPTP opening and necrosis, implicating distinct mechanisms for Bax-regulated necrosis and apoptosis. Both forms of Bax restore mitochondrial fusion in Bax/Bak-null cells, which otherwise exhibit fragmented mitochondria. Cells lacking mitofusin 2 (Mfn2), which exhibit similar fusion defects, are protected to the same extent as Bax/Bak-null cells. Conversely, restoration of fused mitochondria through inhibition of fission potentiates mPTP opening in the absence of Bax/Bak or Mfn2, indicating that the fused state itself is critical. These data demonstrate that Bax-driven fusion lowers the threshold for mPTP opening and necrosis. Thus, Bax and Bak play wider roles in cell death than previously appreciated and may be optimal therapeutic targets for diseases that involve both forms of cell death.     

Mitochondrial permeability transition pore and postconditioning

Postconditioning has recently been described as a powerful cardioprotection that prevents lethal reperfusion injury. Growing evidence suggests that mitochondrial permeability transition may be a key event in postconditioning. This proposition arises from the complementary observations that: (1) conditions for the mitochondrial permeability transition pore (mPTP) opening are built up during early reperfusion, (2) mPTP opens at the time of reperfusion, (3) transgenic structural alteration of mPTP modifies its opening probability following ischemia-reperfusion, (4) mPTP plays a role in preconditioning, and (5) postconditioning attenuates lethal reperfusion injury. We review in this article current evidence for an important role of the mitochondrial transition pore in postconditioning.     

Ischemia/reperfusion injury and cardioprotective mechanisms: Role of mitochondria and reactive oxygen species

Reperfusion therapy must be applied as soon as possible to attenuate the ischemic insult of acute myocardial infarction(AMI).However reperfusion is responsible for additional myocardial damage,which likely involves opening of the mitochondrial permeability transition pore(mPTP).In reperfusion injury,mitochondrial damage is a determining factor in causing loss of cardiomyocyte function and viability.Major mechanisms of mitochondrial dysfunction include the long lasting opening of mPTPs and the oxidative stress resulting from formation of reactive oxygen species(ROS).Several signaling cardioprotective pathways are activated by stimuli such as preconditioning and postconditioning,obtained with brief intermittent ischemia or with pharmacological agents.These pathways converge on a common target,the mitochondria,to preserve their function after ischemia/reperfusion.The present review discusses the role of mitochondria in cardioprotection,especially the involvement of adenosine triphosphate-dependent potassium channels,ROS signaling,and the mPTP.Ischemic postconditioning has emerged as a new way to target the mitochondria,and to drastically reduce lethal reperfusion injury.Several clinical studies using ischemic postconditioning during angioplasty now support its protective effects,and an interesting alternative is pharmacological postconditioning.In fact ischemic postconditioning and the mPTP desensitizer,cyclosporine A,have been shown to induce comparable protection in AMI patients.     

Trimetazidine inhibits mitochondrial permeability transition pore opening and prevents lethal ischemia-reperfusion injury

Trimetazidine (TMZ) affects mitochondrial function during ischemia. Mitochondrial permeability transition is a pivotal event in cardiomyocyte death following acute ischemia. The aim of the present study was to determine whether the anti-ischemic agent TMZ might modulate mitochondrial permeability transition pore (mPTP) opening and limit lethal ischemia-reperfusion injury. Anesthetized NZW rabbits underwent 30 min of coronary artery occlusion followed by 4 hours of reperfusion. Prior to this, they underwent either no intervention (control, C), ischemic preconditioning (PC), or an IV injection of 5 mg kg(-1) TMZ 10 min before ischemia (TMZ). Additional rabbits (Sham group) underwent no ischemia/reperfusion throughout the experiment. Infarct size was assessed by triphenyltetrazolium staining, and apoptosis via measurement of caspase 3 activity. Ca(2+)-induced mPTP opening was assessed in mitochondria isolated from ischemic myocardium. TMZ and PC significantly reduced infarct size that averaged 34 +/- 4% and 21 +/- 4% of the risk region respectively, versus 63 +/- 6% in controls (P<0.005). Caspase 3 activity was reduced in both TMZ and PC groups: 37 +/- 11 and 29 +/- 7 respectively, versus 68 +/- 9 nmol min(-1) mg(-1) mitochondrial protein in controls (P=0.01 versus TMZ and PC). In controls, Ca(2+) load required for mPTP opening averaged 11 +/- 4 microM mg(-1) mitochondrial protein versus 116 +/- 6 in shams (P<0.0001). Pre-treatment by TMZ or PC attenuated this, with Ca(2+) loads averaging 45 +/- 4 and 46 +/- 4 microM mg(-1) mitochondrial proteins, respectively (P<0.005 versus C). These data suggest that TMZ inhibits mPTP opening and protects the rabbit heart from prolonged ischemia-reperfusion injury.     

The mitochondrial permeability transition pore as a target for preconditioning and postconditioning

The experimental evidence supporting the mitochondrial permeability transition pore (mPTP) as a major mediator of lethal myocardial reperfusion injury and therefore a critical target for cardioprotection is persuasive. Although, its molecular identity eludes investigators, it is generally accepted that mitochondrial cyclophilin-D, the target for the inhibitory effects of cyclosporine-A on the mPTP, is a regulatory component of the mPTP. Animal myocardial infarction studies and a recent clinical proof-of-concept study have demonstrated that pharmacologically inhibiting its opening at the onset of myocardial reperfusion reduces myocardial infarct size in the region of 30–50%. Interestingly, the inhibition of mPTP opening at this time appears to underpin the infarct-limiting effects of the endogenous cardioprotective strategies of ischemic preconditioning (IPC) and postconditioning (IPost). However, the mechanism underlying this inhibitory action of IPC and IPost on mPTP opening is unclear. The objectve of this review article will be to explore the potential mechanisms which link IPC and IPost to mPTP inhibition in the reperfused heart.     

Mitochondrial Involvement in Cardiac Apoptosis During Ischemia and Reperfusion: Can We Close the Box?

Myocardial ischemia is the main cause of death in the Western societies. Therapeutic strategies aimed to protect the ischemic myocardium have been extensively studied. Reperfusion is the definitive treatment for acute coronary syndromes, especially acute myocardial infarction; however, reperfusion has the potential to exacerbate tissue injury, a process termed reperfusion injury. Ischemia/reperfusion (I/R) injury may lead to cardiac arrhythmias and contractile dysfunction that involve apoptosis and necrosis in the heart. The present review describes the mitochondrial role on cardiomyocyte death and some potential pharmacological strategies aimed at preventing the opening of the box, i.e., mitochondrial dysfunction and membrane permeabilization that result into cell death. Data in the literature suggest that mitochondrial disruption during I/R can be avoided, although uncertainties still exist, including the fact that the optimal windows of treatment are still fairly unknown. Despite this, the protection of cardiac mitochondrial function should be critical for the patient survival, and new strategies to avoid mitochondrial alterations should be designed to avoid cardiomyocyte loss.     

Inhibiting mitochondrial permeability transition pore opening at reperfusion protects against ischaemia-reperfusion injury

OBJECTIVE: The opening of the mitochondrial permeability transition pore (mPTP) in the first few minutes of post-ischaemic reperfusion is a critical determinant of reperfusion-induced cell death. We hypothesised that the novel immunosuppressant, sanglifehrin-A (SFA), given at the time of reperfusion, protects the myocardium from ischaemia-reperfusion injury, by suppressing mPTP opening. METHODS: Isolated perfused rat hearts were subjected to 35 min ischaemia/120 min reperfusion, and were treated with (1) SFA (1.0 microM) or (2) DMSO vehicle for the first 15 min of reperfusion or (3) SFA (1.0 microM) after the first 15 min of reperfusion. We examined the effect of SFA on mPTP opening directly, using a myocyte model of oxidative stress. Laser illumination of adult rat myocytes loaded with the fluorophore, TMRM, generates oxidative stress, which induces mPTP opening (represented by mitochondrial membrane depolarisation) followed by rigour contracture. RESULTS: In the isolated perfused heart model, SFA, given during the first 15 min of post-ischaemic reperfusion, reduced the infarct-risk volume ratio from 43.9+/-2.5% in the control group to 23.8+/-4.2% with SFA (p=0.001). However, when SFA was given after the first 15 min of reperfusion, there was no change in infarct size (43.8+/-5.7% with SFA vs. 43.9+/-2.5% in control; p=NS), suggesting that SFA has to be present during the first 15 min of reperfusion to induce protection. In the isolated adult myocyte model, SFA was shown to inhibit mPTP opening in the setting of oxidative stress, represented by an increase in the ROS threshold required to induce: mitochondrial membrane depolarisation (from 269+/-21 to 777+/-100 s; p<0.001) and rigour contracture (from 613+/-14 to 1329+/-129 s; p<0.001). CONCLUSIONS: Inhibiting mPTP opening during the first few minutes of reperfusion, using sanglifehrin-A, limits infarct size and protects myocytes from oxidative stress.