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全球死亡和衰弱的主要原因。然而，冠状动脉血流恢复到看似可行的心肌组织通常伴随着心脏功能的丧失，并且从长远来看，心力衰竭的发展。这种矛盾的现象，广泛地称为缺血/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/再灌注损伤中发挥核心作用。线粒体对维持心脏能量状态和功能至关重要，在缺血期间线粒体表现出呼吸和氧化磷酸化速率的下降，在再灌注时进一步出现明显的年龄依赖性缺陷。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定义这种功能丧失的机制：Ca 2+过载和促氧化剂产生。心肌缺血导致细胞色素c从线粒体内膜脱离，这是导致电子传递速率下降的事件。在再灌注期间，氧化还原敏感酶复合物I、α-酮戊二酸脱氢酶和乌头酸酶表现出活性下降。分离的线粒体暴露于模拟从缺血到再灌注的过渡的pH和Ca 2+浓度的改变导致细胞色素c解离和这些氧化还原敏感酶的氧化抑制。根据氧化应激的程度和持续时间，可逆抑制可发展为不可逆失活。假设：心肌缺血/再灌注期间线粒体Ca 2+浓度增加导致细胞色素c从线粒体内膜解离，导致自由基产生增加和氧化还原敏感酶的氧化抑制。这会暂时降低线粒体呼吸速率、自由基产生和对不可逆氧化损伤的易感性。衰老增加线粒体Ca 2+超载，增加了线粒体功能从可逆调节进展到不可逆失活的可能性。利用体内大鼠模型，将使用不同年龄的动物改变心脏缺血和再灌注的持续时间，以鉴定导致线粒体促氧化剂产生增加的分子事件（Aim 1）、氧化还原依赖性修饰的特异性靶点和机制（Aim 2）、氧化修饰的生物化学后果（Aim 2），以及在心脏缺血/再灌注期间促进线粒体功能不可修复的损失的年龄依赖性因素（目的1和2）。阐明负责缺血/再灌注损伤的分子事件是优化策略以有利地影响结果所必需的，特别是在老年人群中。通俗描述：心脏病是衰弱和死亡的主要原因，特别是在老龄化人口中。我们的研究旨在确定与年龄相关的因素，这些因素会增加心脏病的严重程度，以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.