Modulation of Mitochondrial Function by Pro-Oxidants

描述(由申请人提供)：心脏供血减少引起的并发症是世界范围内死亡和虚弱的主要原因。然而，冠脉血流恢复到看似可存活的心肌组织往往伴随着心功能的丧失，并在长期内发展为心力衰竭。这种矛盾的现象，广义地称为缺血/再灌注损伤，在老年人中表现得更严重。线粒体可能在心肌缺血/再灌注损伤中起中心作用。线粒体是维持心脏能量状态和功能的关键，在缺血期间，线粒体的呼吸和氧化磷酸化速率下降，再灌流时，进一步的年龄依赖性缺陷明显。拟议的研究试图通过统一与缺血/再灌注相关的两个事件来确定导致这种功能丧失的机制：钙超载和促氧化剂产生。心肌缺血导致细胞色素c从线粒体膜内脱离，这是导致电子传递速率下降的一个事件。在再灌流过程中，氧化还原敏感酶复合体I、α-酮戊二酸脱氢酶和乌头酸酶活性下降。将分离的线粒体暴露于模拟从缺血到再灌注的pH值和钙离子浓度的变化中，导致细胞色素c解离和这些氧化还原敏感酶的氧化抑制。根据氧化应激的大小和持续时间，可逆抑制可以进展到不可逆转的失活。推测：心肌缺血/再灌流过程中线粒体钙离子浓度升高，导致细胞色素c从线粒体膜上解离，导致自由基生成增加，氧化还原敏感酶受到氧化抑制。这短暂地降低了线粒体呼吸、自由基产生的速率，以及对不可逆转的氧化损伤的敏感性。衰老增加了线粒体钙超载，增加了线粒体功能从可逆调节发展为不可逆失活的可能性。利用在体大鼠模型，利用不同年龄的动物，心脏缺血和再灌注的持续时间将有所不同，以确定导致线粒体促氧化剂产生增加的分子事件(目标1)、氧化还原依赖修饰的特定靶点和机制(目标2)、氧化修饰的生化后果(目标2)以及促进心肌缺血/再灌注期间线粒体功能不可修复的丧失的年龄依赖因素(目标1和2)。尤其是在老年人群中，需要阐明导致缺血/再灌注损伤的分子事件，以优化有利影响预后的策略。外行描述：心脏病是导致衰弱和死亡的主要原因，特别是在老龄化人口中。我们的研究试图定义与年龄相关的因素，这些因素会增加心脏病的严重性，以努力设计改善结果的策略。

DESCRIPTION (provided by applicant): Complications arising from reduction of blood supply to the heart are a leading cause of death and debilitation worldwide. Nevertheless, restoration of coronary blood flow to seemingly viable myocardial tissue is often accompanied by loss of cardiac function and, in the long term, development of heart failure. This paradoxical phenomenon, broadly termed ischemia/reperfusion injury, is manifested more severely in the elderly. Mitochondria likely play a central role in myocardial ischemia/reperfusion injury. Critical for the maintenance of cardiac energy status and function, mitochondria exhibit declines in the rate of respiration and oxidative phosphorylation during ischemia, with further age-dependent deficits evident upon reperfusion. The proposed studies seek to define mechanisms responsible for this loss in function by unifying two events associated with ischemia/reperfusion: Ca2+ overload and pro-oxidant production. Cardiac ischemia results in detachment of cytochrome c from the inner mitochondrial membrane, an event responsible for declines in the rate of electron transport. During reperfusion, the redox sensitive enzymes complex I, a-ketoglutarate dehydrogenase, and aconitase exhibit declines in activity. Exposure of isolated mitochondria to alterations in pH and Ca2+ concentration that mimic the transition from ischemia to reperfusion results in cytochrome c dissociation and oxidative inhibition of these redox sensitive enzymes. Depending on the magnitude and duration of oxidative stress, reversible inhibition can progress to irreversible inactivation. It is hypothesized that: Increases in mitochondrial Ca2+ concentration during myocardial ischemia/reperfusion lead to dissociation of cytochrome c from the inner mitochondrial membrane resulting in an increase in free radical production and oxidative inhibition of redox sensitive enzymes. This transiently reduces the rates of mitochondrial respiration, free radical production, and susceptibility to irreversible oxidative damage. Aging augments mitochondrial Ca2+ overload, increasing the likelihood of progression from reversible modulation to irreversible inactivation of mitochondrial function. Utilizing an in vivo rat model, durations of cardiac ischemia and reperfusion will be varied using animals of different ages to identify molecular events that result in increased mitochondrial pro-oxidant production (Aim 1), specific targets and mechanisms of redox- dependent modification (Aim 2), biochemical consequences of oxidative modification (Aim 2), and age- dependent factors that promote irreparable loss in mitochondrial function during cardiac ischemia/reperfusion (Aims 1 and 2). Elucidation of molecular events responsible for ischemia/reperfusion injury is required for optimization of strategies for favorably influencing the outcome particularly in the elderly population. Lay Description: Heart disease is a leading cause of debilitation and death, particularly in the aging population. Our studies seek to define age-related factors that enhance the severity of heart disease in an effort to design strategies to improve the outcome.