MitoBOX: The mitochondrial basis of hypoxia tolerance in marine mollusks

氧(O2)在生物能量传递中起着关键作用，而氧缺乏(缺氧)对生物体的健康和生存具有严重的后果。低氧引起细胞应激、能量储备耗竭和代谢废物的积累，而复氧则由于氧化应激引起细胞损伤。不同动物对缺氧的敏感度有很大不同。在哺乳动物等对缺氧敏感的生物中，线粒体是缺氧/复氧损伤的中枢，导致ATP合成能力丧失、氧化损伤和细胞死亡。相比之下，一些耐缺氧的生物(如潮间带软体动物)每天经历缺氧-复氧循环，没有任何明显的不良影响。线粒体对O2波动的适应性机制尚不清楚。在这项研究中，我们将通过确定线粒体对O2水平波动的适应机制并确定这些机制如何与整个生物体的生物能量相结合来扩展当前动物耐缺氧的概念。作为一个模型系统，我们将使用三种海洋双壳类(扇贝、牡蛎和Quahog)，它们涵盖了广泛的耐缺氧能力，在缺氧中的生存时间从几个小时到几个月不等。我们将使用代谢控制分析(MCA)来确定低氧-复氧(H/R)应激对线粒体关键子系统能力的影响及其对呼吸、ATP合成和ROS产生的控制。线粒体对H/R应激反应的分子机制将通过测定线粒体关键酶的活性和H/R应激过程中可逆蛋白磷酸化的调节作用来评估。将使用整体呼吸测量和磁共振成像(MRI)和核磁共振波谱来确定缺氧后恢复过程中的有氧代谢是否受到线粒体或全身机制的限制。这项拟议的研究将揭示参与适应氧气水平波动的新的线粒体机制，建立缺氧和恢复期间代谢控制的分层(线粒体到生物体)模型，并确定导致线粒体对H/R应激敏感的代谢“薄弱环节”。结合之前发表的对哺乳动物模型的广泛研究，关于耐缺氧软体动物的新数据可能会发现经过进化测试的解决方案，以克服线粒体对H/R应激的敏感性，并有助于产生新的假说，以缓解心力衰竭或中风期间发生的脆弱组织中的线粒体应激。该项目还将为博士生提供线粒体生理学、整体生物能量学和最先进的生理学研究技术(如核磁共振)方面的跨学科培训。

Oxygen (O2) plays a key role in biological energy transductions, and O2 deficiency (hypoxia) has severe consequences for fitness and survival of an organism. Hypoxia induces cellular stress due to the low rates of ATP production, depletion of energy reserves and accumulation of metabolic wastes, whereas reoxygenation causes cellular injury due to the oxidative stress. Sensitivity to hypoxia greatly varies among animals. In hypoxia-sensitive organisms such as mammals, mitochondria are the hub of hypoxia/reoxygenation-induced damage leading to the loss of ATP synthesis capacity, oxidative damage and cell death. In contrast, some hypoxia-tolerant organisms (such as intertidal mollusks) endure daily hypoxia-reoxygenation cycles without any apparent ill effects. The mechanisms responsible for such exceptional mitochondrial resilience to O2 fluctuations are not known.In this study, we will expand the current concept of hypoxia tolerance in animals by identifying the mitochondrial mechanisms involved in adaptation to fluctuating O2 levels and determining how these mechanisms are integrated with the whole-organism bioenergetics.As a model system, we will use three species of marine bivalves (scallops, oysters and quahogs) that encompass a broad range of hypoxia tolerance with survival times ranging from hours to months in hypoxia. We will use the metabolic control analysis (MCA) to determine the effects of the hypoxia-reoxygenation (H/R) stress on the capacity of key mitochondrial subsystems and their control over respiration, ATP synthesis and ROS production. The molecular mechanisms underlying the mitochondrial resilience to H/R will be assessed by determining the activity of key mitochondrial enzymes and the regulatory role of the reversible protein phosphorylation during H/R stress. Whole-organism respirometry and magnetic resonance imaging (MRI) and NMR spectroscopy will be used to determine whether aerobic metabolism during post-hypoxic recovery is limited by the mitochondrial or systemic mechanisms. The proposed study will reveal novel mitochondrial mechanisms involved in adaptation to fluctuating O2 levels, produce a hierarchical (mitochondria-to-organism) model of metabolic control during hypoxia and recovery, and identify the metabolic ‘weak links’ that contribute to the susceptibility to H/R stress in mitochondria. Together with the previously published extensive research on mammalian models, the novel data on hypoxia-tolerant mollusks could discover the evolutionarily tested solutions to overcome the mitochondrial susceptibility to H/R stress and help generate new hypotheses to mitigate mitochondrial stress in vulnerable tissues such as occurs during cardiac failure or stroke. This project will also provide cross-disciplinary training in mitochondrial physiology, whole-organism bioenergetics and in state-of-the-art techniques for physiology research such as MRI to a Ph.D. student.