Targeting axonal transport regulation by neurotrophic factors to treat peripheral nerve degeneration

Charcot-Marie-Tooth病(CMT)是一种遗传性神经系统疾病，每2500人中就有一人患病，这使其成为影响神经和肌肉的最常见疾病之一。CMT的症状通常在青少年时期开始，但这种疾病不会影响生存，因此它会导致终生残疾，仅在英国，估计每年的社会成本约为5亿GB。患有CMT的人有行动不便和感觉困难，因为两种不同类型的神经细胞，即运动神经元和感觉神经元，会出现故障并逐渐恶化。目前尚不清楚这些周围神经受到影响的原因，这使得开发治疗CMT的方法变得困难。100多个不同基因的突变导致CMT，而与大多数CMT亚型相连的基因集合都产生被称为氨基酰tRNA合成酶(ARS)的酶。ARS酶是所有细胞制造蛋白质所必需的。为了更好地了解CMT是如何引起的，我们研究了两个ARS基因-GARS1和YARS1。GARS1产生GlyRS蛋白，与CMT 2D(CMT2D)连锁，YARS1产生TyrRS蛋白，与DI-CMTC亚型连锁。使用细胞和小鼠模型，我们研究CMT2D和DI-CMTC，以了解为什么运动神经元和感觉神经元退化，因为这将使我们能够设计更好的治疗方法来对抗这种疾病。GARS1和YARS1中CMT导致的突变影响它们产生的蛋白质的结构。我的实验室发现，这会导致突变的GlyRS和突变的TyrRS与一系列名为Trk受体的重要蛋白质错误相互作用，Trk受体存在于神经细胞表面，通常与称为神经营养素的生存分子结合。最近，我们发现突变的ARS蛋白和Trk受体之间的异常关联损害了神经细胞中一个关键的、持续活跃的过程，称为轴突运输。神经细胞有一个细长的管状结构，称为轴突，它有助于在很长的距离内传递电信号和细胞组件。为了让神经正常运作并存活下来，它们需要通过轴突运输过程中的轴突上下输送许多物质。特别是，运动神经元和感觉神经元依靠这一过程将神经营养因子从肌肉输送到大脑。因此，我们提高了CMT小鼠肌肉中这些关键神经营养因子之一BDNF的水平，并表明它可以治疗轴突运输中断，并改善疾病的其他特征。我们现在建议详细研究神经营养因子和其他类似的神经营养因子(NTF)在调节运动神经和感觉神经的轴突运输过程中所起的作用。这样做，不仅可以让我们更好地了解CMT中这些周围神经恶化的原因，而且它将使我们能够实现我们的主要目标，即开发一种多管齐下的方法来治疗CMT的症状，并提高患者的生活质量。我们将通过四个主要目标来实现这一点：1)我们将评估ARS和Trk受体蛋白的结构，准确地识别它们是如何错误相互作用的，以便我们可以设计专门阻断这些异常联系的治疗方法。2)确定NTF以外的关键蛋白可以靶向治疗轴突运输缺陷，3)通过测试一系列神经营养因子，我们将确定是否可以向肌肉供应BDNF以外的分子，以缓解人类神经元和小鼠的轴突运输障碍。4)我们将调整我们的治疗策略，使BDNF和目标3中确认的其他神经营养因子持续、长期地输送到使用无害病毒的所有肌肉，然后在几种不同亚型CMT的小鼠模型中测试这些治疗方法的有效性。

Charcot-Marie-Tooth disease (CMT) is an inherited nervous system disease that affects 1 in about 2,500 people, which makes it one of the most common diseases to affect both nerves and muscles. The symptoms of CMT usually begin during teenage years, but the disease does not affect survival, therefore it causes life-long disability, for which the estimated societal cost is approximately £0.5 billion per year in the UK alone. People with CMT have mobility issues and difficulties with sensation, because two different types of nerve cell, known as motor neurons and sensory neurons, malfunction and progressively deteriorate. It is unknown why these peripheral nerves are affected, which has made it difficult to develop treatments for CMT.Mutations in more than 100 different genes cause CMT, and the collection of genes linked to the most CMT subtypes all produce enzymes known as aminoacyl tRNA-synthetases (ARSs). The ARS enzymes are essential to all cells for making protein. To better understand how CMT is caused, we study two ARS genes - GARS1, which produces GlyRS protein and is linked to CMT type 2D (CMT2D) and YARS1, which produces TyrRS protein and is linked to a subtype known as DI-CMTC. Using cell and mouse models, we study CMT2D and DI-CMTC to understand why motor and sensory neurons deteriorate, because this will enable us to design better treatments to combat the disease.CMT-causing mutations in GARS1 and YARS1 affect the structure of the proteins they produce. My laboratory discovered that this causes mutant GlyRS and mutant TyrRS to mis-interact with a series of important proteins called Trk receptors, which are found on the surface of nerve cells and normally bind to survival molecules called neurotrophins.Recently, we have shown that the aberrant association between mutant ARS proteins and Trk receptors impairs a critical and continually active process in nerve cells known as axonal transport. Nerve cells have a long, thin pipe-like structure called an axon, which helps to deliver electrical signals and cellular components over large distances. For nerves to function correctly and survive, they require many substances to be delivered up and down axons by the process of axonal transport. In particular, motor and sensory neurons rely on this process to deliver neurotrophins from muscles towards the brain. We therefore boosted the levels of one of these key neurotrophins, BDNF, in muscles of CMT mice and showed that it can treat the disruption in axonal transport and improve other features of the disease. We now propose to examine in detail the role that neurotrophins and other similar neurotrophic factors (NTFs) play in regulating the process of axonal transport in motor and sensory nerves. Doing so, will not only allow us to better understand why these peripheral nerves deteriorate in CMT, but it will enable us to achieve our main goal, which is to develop a multi-pronged approach to treat the symptoms of CMT and improve patient quality of life.We will accomplish this through four main objectives:1) We will assess the structures of ARS and Trk receptor proteins, identifying exactly how they mis-interact, so that we can design treatments blocking specifically these aberrant associations.2) To identify key proteins other than NTFs that can be targeted to treat defects in axonal transport, we will generate and study new models of CMT2D and DI-CMTC using human motor neurons.3) By testing a collection of NTFs, we will identify whether molecules other than BDNF can be supplied to muscle to alleviate the axonal transport impairment in both human neurons and mice.4) We will adapt our treatment strategy to enable the continual and long-term delivery of BDNF, and other NTFs identified in Aim 3, to all muscles using harmless viruses and then test the effectiveness of these therapies in mouse models of several different subtypes of CMT.