The role of axonal mRNA translation in Amyotrophic Lateral Sclerosis (resubmission)

肌萎缩侧索硬化症(ALS)是由运动神经元变性引起的一种破坏性疾病，通常在症状出现2-5年后导致瘫痪和死亡。目前还没有治愈或改变疾病的疗法，部分原因是我们仍然缺乏对疾病根本原因的基本了解。为了设计出更好的治疗策略，我们需要更多地了解导致这种选择性神经元变性的分子和细胞机制。绝大多数病例是散发性的，而5%-10%是遗传性的。在极少数情况下，研究导致这种疾病的基因突变为病因提供了重要线索。对导致这种疾病的突变的功能研究已经开始牵涉到许多机制。一个正在出现的关键机制是RNA生物学的失调。目前的证据表明，在疾病条件下，mRNA的形成和处理受到多个方面的影响，包括表达、成熟、稳定、亚细胞分布和翻译。现在的关键问题是，为什么mRNA处理的中断特别会导致运动神经的死亡，从而导致ALS。运动神经的一个独特特征是它们非常长；比大多数其他类型的神经长很多倍。近年来，很明显，mRNAs可以到达神经末梢，在那里它们提供局部翻译的模板，以支持基本的突触功能。将这些想法结合在一起，我们假设，对无数正常RNA调控过程的干扰导致运动神经末梢可供翻译的mRNAs数量发生变化，这是ALS启动的重要触发因素。为了探索这一观点，我们将确定哪些信使核糖核酸分子在体内的成年运动神经轴突中进行翻译。然后，我们将试图了解这种特征在衰老和疾病条件下是如何变化的。重要的是，这项工作将超越体外培养细胞的条件，通过对动物模型--黑腹果蝇进行分析。我们将使用与疾病相关的细胞类型(运动神经元)在其自然环境中，在完整的神经肌肉回路中解决这些基本问题。出于时间、成本和伦理方面的考虑，无脊椎动物模型提供了许多优势，但事实证明，它们在功能上与哺乳动物的运动神经相似。此外，使用遗传上容易处理的动物模型将使我们能够通过在生物水平上确定它们对疾病相关回路的功能影响来定义调控失调的mRNAs的病理相关性。这种类型的发现研究对于为更清楚地了解疾病原因、开发更有效的治疗方法奠定基础是必不可少的。

Amyotrophic lateral sclerosis (ALS) is a devastating disease caused by the degeneration of motor neurons leading to paralysis and death usually 2-5 years after onset of symptoms. Currently no cure or disease-modifying therapies exist, partly because we still lack basic understanding of the root-cause of the disease. To devise better therapeutic strategies, we need a greater understanding of the molecular and cellular mechanisms responsible for this selective neuronal degeneration. The vast majority of cases are sporadic while 5-10% are inherited. Studying the gene alterations that cause the disease in a rare few cases gives important clues into the causes. Functional studies of mutations that cause the disease have begun to implicate a number of mechanisms. One key mechanism that is emerging is the dysregulation of RNA biology. Current evidence indicates that multiple aspects of mRNA formation and handling are affected in disease conditions, including expression, maturation, stability, subcellular distribution and translation. The key question now is why disruption of mRNA handling leads specifically to the demise of motor nerves to cause ALS. A unique characteristic of motor nerves is their extraordinary length; many times longer than most other nerve types. In recent years, it has become clear that mRNAs can travel to the nerve extremities where they provide templates for local translation to support essential synaptic functions. Bringing these ideas together, we hypothesise that disruptions to the myriad of normal RNA regulatory processes leads to alterations in the population of mRNAs available for translation in motor nerve termini is an important trigger in how ALS starts. To explore this idea, we will determine which mRNA molecules are underdoing translation in adult motor nerve axons in vivo. We will then seek to understand how this profile changes during ageing and under disease conditions. Importantly, this work will go beyond the in vitro conditions of cultured cells by conducting our analysis in an animal model, Drosophila melanogaster. We will address these fundamental questions using the disease-relevant cell type (motor neurons) in their native environment, in an intact neuromuscular circuit. For time, cost and ethical considerations, invertebrate models provide many advantages yet have proven functional similarities to mammalian motor nerves. Moreover, using a genetically tractable animal model will allow us to define the pathological relevance of the mRNAs that are dysregulated by determining their functional impact on the disease-relevant circuits at an organismal level. This type of discovery research is essential to lay the foundations for a clearer understanding of the disease cause to develop more effective therapies.