Reactive Oxygen Species, metabolic by-products of mitochondrial respiration, as conserved regulators of synapse growth and neuronal homeostasis.

神经细胞通过电信号相互交流，这需要大量的能量，使大脑成为身体中最需要燃料的结构。因此，大脑需要大量的氧气来产生处理信息、控制行为和认知所需的能量。大脑对衰老也非常敏感，我们大多数人都有过这样的经历：上了年纪的亲戚记忆力不好。通过使用大量的氧气来产生能量，大脑也会产生一种副产品，当它积累起来时就会变得有毒。这种副产物是有毒形式的氧，被称为“活性氧”，简称ROS。正常情况下，大脑可以应对低水平的活性氧，这是正常代谢的副产品，因为大脑有一系列的保护机制来中和活性氧。但随着大脑年龄的增长，这些自我修复机制变得不那么有效，结果ROS水平变得过高，ROS引起的损伤迹象更加明显。活性氧与细胞发生化学反应并破坏细胞的组成部分。随着废物的积累，它还可以产生第二个ROS来源，即积累的废物中的金属与氧气反应产生更多的ROS。因此，一个自我延续的损害循环随之而来。由于这种周期性，目前尚不清楚活性氧是如何首先影响神经系统的，而不是继发或第三次连锁反应。我们之前发现，当活性氧过多时，神经细胞之间的连接，即突触，会过度生长。众所周知，突触会根据神经元的活动来调整它们的大小，尽管神经细胞是如何感知活动水平的还不完全清楚。通过这项提议，我们正在解决这些基本问题。首先，我们正在研究一种假设，即在正常的神经系统发育和功能过程中，细胞使用ROS作为信号来告知它们的活动水平。接下来，我们将研究ROS调控突触大小和功能的分子机制。最后，我们将测试ROS信号是进化保守的假设，我们将研究果蝇遗传模型系统中的发现如何也适用于脊椎动物神经细胞。我们使用果蝇作为实验系统，因为基本细胞过程的高度进化守恒意味着，在果蝇身上取得的大多数发现，包括学习和记忆的基础机制，与我们对人类大脑的理解直接相关。重要的是，果蝇是最强大的基因实验生物之一，可以前所未有地精确地对已识别的神经元及其连接伙伴进行基因操作。在我们的实验系统中，当我们在诱导神经元活动的同时减少ROS时，我们就能防止突触过度生长，这是我们单独诱导活动或ROS时看到的。这表明神经元使用能量制造过程中产生的ROS作为其活动的读数，并且ROS信号突触生长。我们已经发现一种蛋白质DJ1（又名帕金森病蛋白7）的功能对于感知ROS水平，然后激活已知的细胞生长促进途径来扩大突触非常重要。我们观察到的这些DJ1介导的过程很可能对我们理解随着年龄的增长大脑功能的下降至关重要，本研究旨在进一步研究DJ1的功能。总之，这项工作将帮助我们了解导致变化的机制、事件和分子，并最终导致老化的大脑中神经细胞功能的失败。这项工作的结果完全有可能帮助发现减轻衰老不利影响的药物和治疗方法，从而最终使整个社会受益。

Nerve cells communicate with each other using electrical signals, which require large amounts of energy, making the brain the most fuel-demanding structure in the body. Brains therefore use a great deal of oxygen to generate the energy required for processing information, controlling behavior and for cognition. Brains are also very sensitive to ageing and most of us have experience of ageing relatives with faulty memories. By using a lot of oxygen to generate energy, the brain also produces a by-product, which becomes toxic when allowed to accumulate. This by-product is toxic forms of oxygen and is termed 'Reactive Oxygen Species', or ROS for short. Normally, the brain can cope with low levels of ROS that are a by-product of normal metabolism, because it has a battery of protective mechanisms to neutralise ROS. But as the brain ages, these self-repair mechanisms become less efficient, and as a consequence ROS levels become excessive and signs of ROS-caused damage more evident. ROS chemically react with and damage the building blocks of cells. As waste material accumulates, it can also generate a second source of ROS, generated by metals within the accumulated waste material reacting with oxygen to produce more ROS. Thus, a self-perpetuating cycle of damage ensues. Because of this cyclical nature, it has remained unclear precisely how ROS affect the nervous system in the first instance, as opposed to secondary or tertiary knock-on effects. We previously found that the connections between nerve cells, called synapses, grow excessively when ROS are excessive. Synapses are known to adjust their size in response to neuronal activity, though how nerve cells sense activity levels is incompletely understood.With this proposal we are tackling these fundamental questions. First, we are investigating the hypothesis that during normal nervous system development and function, cells use ROS as signals that inform them about their activity levels. Next, we will study the molecular mechanisms by which ROS regulate the size and function of synapses. Last, we will test the hypothesis that ROS signaling is evolutionary conserved and we will examine how discoveries made in the genetic model system of the fruitfly also apply to vertebrate nerve cells. We use the fruitfly, Drosophila, as an experimental system, because the high evolutionary conservation of basic cellular processes has meant that most discoveries made in the fly, including mechanisms that underlie learning and memory, are directly pertinent to our understanding of the human brain. Importantly, the fruitfly is one of the most powerful genetic experimental organisms and allows unprecedented precision for genetically manipulating identified neurons and their connecting partners. In our experimental system, when we induce activity in neurons, but reduce ROS at the same time, we prevent the synapse overgrowth that we see when we induce activity or ROS alone. This suggests that neurons use ROS generated during energy manufacturing as a readout for their activity and that ROS signal synapse growth. We have discovered the function of one protein, DJ1 (aka Parkinson Disease Protein 7) as important for sensing ROS levels and then activating a known cell growth promoting pathway to enlarge synapses. These DJ1 mediated processes that we have observed are very likely of critical importance to our understanding of the decline in brain function as we age, and this proposal aims to investigate DJ1 function further. In summary, this work will help us to understand the mechanisms, events and molecules that cause change and, ultimately, failure in nerve cell function in the ageing brain. The results of this work have every potential to aid the discovery of drugs and treatments to alleviate adverse effects of ageing and will thus, in time, benefit society as a whole.