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

神经细胞使用电信号相互通信，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，大脑使用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年老的亲戚记忆力不佳的经历。通过使用大量的氧气来产生能量，大脑也产生了一种副产品，当允许积累时，它会变得有毒。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，大脑可以科普低水平的ROS，这是正常代谢的副产品，因为它有一套保护机制来中和ROS。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，因此ROS水平变得过高，ROS引起的损伤的迹象更加明显。ROS与细胞的结构单元发生化学反应并破坏细胞的结构单元。随着废物材料的积累，它还可以产生第二个ROS源，由积累的废物材料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开始了。由于这种周期性的性质，目前还不清楚ROS如何影响神经系统的第一个例子，而不是二级或三级连锁反应。我们以前发现，当ROS过量时，神经细胞之间的连接（称为突触）会过度生长。我们知道突触会根据神经元的活动来调整自己的大小，尽管神经细胞如何感知活动水平还不完全清楚。首先，我们正在研究一个假设，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，告知它们的活动水平。接下来，我们将研究ROS调节突触大小和功能的分子机制。最后，我们将测试的假设，ROS信号是进化保守的，我们将研究如何在果蝇的遗传模型系统的发现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保守性意味着在果蝇中发现的大多数发现，包括学习和记忆的基础机制，都与我们对人类大脑的理解直接相关。重要的是，果蝇是最强大的遗传实验生物之一，可以前所未有地精确地遗传操纵已识别的神经元及其连接伙伴。在我们的实验系统中，当我们在神经元中诱导活性，但同时减少ROS时，我们防止了我们在单独诱导活性或ROS时看到的突触过度生长。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。我们已经发现了一种蛋白质的功能，DJ 1（又名帕金森病蛋白7）对于感知ROS水平，然后激活已知的细胞生长促进途径以扩大突触非常重要。我们观察到的这些DJ1介导的过程对于我们理解随着年龄的增长大脑功能的下降非常重要，这项提议旨在进一步研究DJ1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，并最终导致衰老大脑中神经细胞功能的失败。这项工作的结果很有可能有助于发现药物和治疗方法，以减轻老龄化的不利影响，从而最终造福于整个社会。

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.