Role of Mitochondrial Reactive Oxygen Species in Stress Adaptation during Ageing

如今，衰老是现代生物学需要回答的主要问题之一。我们需要了解我们是如何衰老的，尤其是为什么衰老，才能完全理解进化的过程。此外，不断增长的老龄化人口是英国的主要问题之一。减轻与年龄相关的退行性疾病（如阿尔茨海默病、帕金森病、癌症或糖尿病）造成的痛苦的唯一方法是充分了解驱动衰老的潜在进化力量，并设计延缓衰老过程的策略。线粒体是细胞的发电站，产生生存所需的大部分能量。这些小细胞工厂在衰老过程中会退化，无法提供细胞维持所需的能量。线粒体失效的原因目前尚不清楚，但可能与它们产生能量的方式有关。线粒体利用氧作为最终的电子受体来运作。正常情况下，这些氧气是由线粒体安全管理的，它们被完全还原成含有四个电子和两个质子的水。然而，在极少数情况下，氧被不完全还原（少于四个电子），产生所谓的活性氧（ROS），可以破坏所有细胞成分。线粒体自由基老化理论（MFRTA）是近一个世纪以来流行的一种解释衰老的理论。MFRTA提出，ROS是呼吸的副产物，会引起氧化损伤，积累并导致衰老。MFRTA主要由相关数据支持。氧化损伤随着年龄的增长而积累，mtROS水平在与衰老相关的退行性疾病中发生改变。然而，直接的实验证据不能支持MFRTA。增加mtROS并不会缩短寿命，而且补充抗氧化剂对健康的影响很差。研究表明，mtROS在细胞分化、免疫反应和应激适应中起着重要作用。总之，mtROS对老龄化的贡献尚不清楚。由于活性氧在病理和非病理情况下的重要性，有必要了解它们在体内发挥的生理作用。在本提案中，我们的目标是详细了解ROS在正常生理和应激适应中的作用，特别是在衰老过程中。根据我们的初步结果，我们假设存在两种不同类型的ROS群体。一个种群是好的，它的产生与清理细胞的机制的激活有关。当这些活性氧被抑制时，质量控制机制就不能正常工作，细胞稳态就会丧失。这可以解释与补充或过度表达抗氧化剂相关的负面后果。另一种种群是有害的，只有当线粒体质量控制机制失效时才会产生。这些活性氧的特点是由高水平的游离铁和羟基自由基引起的非常具有攻击性的化学反应。利用果蝇遗传学的力量，我们将产生新的转基因模型，这将允许在体内精确操纵这两个ROS种群。我们将使用这项新技术来表征活性氧激活的下游生理反应。我们的目标是找到可能被特定药物或基因干预靶向的确切途径和基因。这些干预措施应该有助于延长健康寿命。由于基本的代谢途径在进化过程中是高度保守的，预计类似的策略可能在人类中实施，以延缓衰老和预防与年龄有关的疾病的发生。

Nowadays, ageing is one of the main questions that modern biology needs to answer. We need to understand how and especially why we age to fully understand the process of evolution. In addition, a growing ageing population is one of the main problems in United Kingdom. The only way to alleviate the suffering caused by age-related degenerative disease (e.g. Alzheimer, Parkinson, cancer or diabetes) is to fully understand the underlying evolutionary forces, which drive ageing and design strategies to delay the ageing process. Mitochondria are the powerhouses of the cell generating most of the energy required for survival. These small cell factories deteriorate during ageing, failing to deliver the energy required for cellular maintenance. The reason why mitochondria fail is currently unknown, but it could be related with the way they produce energy. To operate, mitochondria use oxygen as final electron acceptor. Normally, this oxygen is safely managed by mitochondria being completely reduced to water with four electrons and two protons. However, in a minimal number of occasions oxygen is incompletely reduced (with less than four electrons) producing the so-called Reactive Oxygen Species (ROS) that can damage all cellular components.The Mitochondrial Free Radical Theory of Ageing (MFRTA) was a popular theory to explain ageing in the past century. MFRTA proposes that ROS, produced as by-products of respiration, cause oxidative damage that accumulates and causes ageing. MFRTA is mainly supported by correlative data. Oxidative damage accumulates with age, and mtROS levels are altered in degenerative disease associated with ageing. However, direct experimental evidence fails to support MFRTA. Increasing mtROS does not shorten lifespan, and antioxidant supplementation has poor effects on health. It has been shown that mtROS are instrumental for cell differentiation, the immune response and stress adaptation. In conclusion, the contribution of mtROS to ageing is unclear. Because of the importance ROS have in pathological and non-pathological situations it is imperative to understand the physiological role they play in vivo.In this proposal, we aim to understand in detail the role ROS play in normal physiology and in stress adaptation, particularly during ageing. Based on our preliminary results, we hypothesize that there are two different types of ROS populations. One population is good, and its generation is associated with the activation of mechanisms that clean up the cells. When these ROS are suppressed quality control mechanisms do not work properly and cellular homeostasis is lost. This would explain the negative consequences associated with supplementation or overexpression of antioxidants. The other population is deleterious, and it is produced only when mechanisms of mitochondrial quality control fail. These ROS are characterized by a very aggressive chemistry led by high levels of free iron and hydroxyl radicals. Using the power of fruit fly genetics we will generate new transgenic models that will allow a precise manipulation of these two ROS populations in vivo. We will use this new technology to characterize the downstream physiological responses activated by ROS. We aim to find the exact pathways and genes that may be targeted by specific drugs or genetic interventions. These interventions should help to extend healthy lifespan. Since essential metabolic pathways are highly conserved during evolution, it is expected that similar strategies may be implemented in humans to delay ageing and prevent the onset of age-related diseases.