COMPLEX III AUGMENTS OXIDANTS DAMAGE IN ISCHEMIC AGED HEART

老化心脏缺血和再灌注后，心肌损伤会加重。衰老会降低 24 个月内氧化磷酸化的速率以及电子传递链的复合物 HI 和 IV 的活性。 Fischer 344 大鼠心脏，与 6 个月相比。成人控制。衰老损伤对心脏线粒体的纤维间群体具有选择性（0FM） 存在于肌原纤维中的线粒体，而位于质膜下方的肌膜下线粒体（SSM）则没有改变。复合物 III 包含 11 个肽亚基，包括三个催化中心：细胞色素 b、细胞色素 c1 和 Rieske 铁硫蛋白 (ISP)。衰老会改变 IFM 中底物氧化位点（即 Qo 位点）的细胞色素 b。 IFM 中复合物 III 的老化缺陷导致基线状态下活性氧 (ROS) 的产生增加。 成人和老年心脏缺血时会发生线粒体损伤。缺血会损害成人和老年心脏线粒体中复合物 III 的 ISP 并降低复合物 III 的活性。与成人心脏相比，衰老心脏在缺血期间对 SSM 和 IFM 都会造成额外的氧化损伤。心磷脂是一种关键的线粒体内膜磷脂，仅在衰老的心脏中发生修饰，产生一种新的心磷脂分子种类。细胞色素 c 位于心磷脂附近，仅在衰老的心脏中发生修饰。衰老心脏缺血后细胞色素氧化酶活性降低，并且与成人心脏不同，添加外源磷脂后细胞色素氧化酶活性无法恢复。在老年心脏中的这一观察结果表明，缺血导致细胞色素氧化酶肽亚基的持续损伤，而不是像成人心脏中那样对复合物的内膜环境造成可逆性损伤。因此，在缺血期间，电子传递链中的特定分子靶标（包括心磷脂）仅在 年迈的心。 线粒体是心肌缺血期间产生的ROS的主要来源。复合物 III 是成人心脏线粒体内 ROS 产生的主要部位。复合物 III 在衰老心脏缺血期间所遭受的氧化损伤中的作用尚不清楚。我们发现，通过在缺血前立即用鱼藤酮阻断复合物 I 来限制缺血期间进入复合物 III 的电子流，可以保持衰老心脏中通过复合物 III 和 IV 的氧化磷酸化速率。 我们提出，在缺血期间，复合物 III 是在衰老心脏中观察到的氧化损伤增强的关键机制，我们假设复合物 III 中的 ROS 会损害衰老心脏中的细胞色素氧化酶。 IFM 中复合物 III Qo 位点存在的老化缺陷加速了缺血期间的氧化损伤。我们假设细胞色素氧化酶的损伤进而导致细胞色素 c 和心磷脂的氧化修饰。我们假设，老化心脏线粒体缺血损伤后，ROS 的产生和释放增加，为再灌注期间的氧化损伤奠定了基础。 线粒体增强的 ROS 释放反过来会放大再灌注期间的心脏损伤和功能障碍，这可以通过在缺血期间可逆地限制电子流进入复合物 III 来减少。

Myocardial injury is increased following ischemia and reperfusion in the aged heart. Aging decreases the rate of oxidative phosphorylation and the activity of complexes HI and IV of the electron transport chain in the 24 mo. Fischer 344 rat heart, compared to 6 mo. adult controls. The aging impairment is selective to the interfibrillar population of cardiac mitochondria 0FM) that reside among the myofibrils, whereas subsarcolemmal mitochondria (SSM), located beneath the plasma membrane, are unaltered. Complex III contains 11 peptide subunits, including three catalytic centers: cytochrome b, cytochrome c1, and the Rieske iron-sulfur protein (ISP). Aging modifies cytochrome b at the site of substrate oxidation, the Qo site, in IFM. The aging defect in complex III in IFM leads to an increased production of reactive oxygen species (ROS) in the baseline state. Mitochondrial damage occurs during ischemia in the adult and aged heart. Ischemia damages the ISP of complex III and decreases complex III activity in both populations of mitochondria in adult and aged hearts. In contrast to the adult heart, the aged heart sustains additional oxidative damage to both SSM and IFM during ischemia. Cardiolipin, a key inner mitochondrial membrane phospholipid, is modified only in the aged heart, generating a new molecular species of cardiolipin. Cytochrome c, located in proximity to cardiolipin, is modified, again, only in the aged heart. Cytochrome oxidase activity decreases following ischemia in the aged heart, and, unlike in the adult heart, activity cannot be restored following the addition of exogenous phospholipid. This observation in the aged heart indicates that ischemia led to persistent damage to a peptide subunit of cytochrome oxidase, rather than reversible damage to the inner membrane environment of the complex as in the adult heart. Thus, during ischemia, specific molecular targets in the electron transport chain, including cardiolipin, sustain oxidative damage only in the aged heart. Mitochondria are the major source of the ROS generated during myocardial ischemia. Complex III is the major site of ROS production within mitochondria in the adult heart The role of complex III in the oxidative damage sustained by the aged heart during ischemia is unknown. We found that limitation of electron flow into complex III during ischemia achieved by blockade of complex I with rotenone immediately prior to ischemia preserves the rate of oxidative phosphorylation through complexes III and IV in the aged heart. We propose that during ischemia complex III is a key mechanism of the enhanced oxidative damage observed in the aged heart, We hypothesize that ROS from complex III damage cytochrome oxidase in the aged heart. Oxidative damage during ischemia is accelerated in IFM by the aging defect present at Qo site of complex III. We hypothesize that damage to cytochrome oxidase leads in turn to oxidative modification of cytochrome c and cardiolipin. We hypothesize that following ischemic damage to aged heart mitochondria, ROS production and release is increased, setting the stage for oxidative damage during reperfusion. Enhanced ROS release from mitochondria, in turn, amplifies cardiac damage and dysfunction during reperfusion that can be decreased by reversibly limiting electron flow into complex III during ischemia.