Regulation of axonal transport by neurotrophic factors in health and disease

Charcot-Marie-Tooth病(CMT)是一种衰弱的遗传性神经肌肉疾病，其特征是肌肉无力和感觉障碍，主要发生在手和脚。将基因改变(突变)与这种神经退行性变联系起来的机制仍未解决，目前还没有有效的治疗方法。为了更好地了解CMT并开发治疗方法，我研究了由GARS基因突变引起的2D亚型(CMT2D)，GARS产生甘氨酰-tRNA合成酶(GlyRS)蛋白。GlyRS几乎存在于身体的所有细胞中，但受这种疾病影响的是负责运动(运动神经元)和感觉(感觉神经元)的神经。通过准确地了解这些周围神经退化的原因，我们将能够更好地设计有针对性的分子疗法。以前已经表明，GARS中CMT2D连锁的突变会影响所产生的GlyRS蛋白的结构。我最近发现，这种构象变化导致突变的GlyRS与神经细胞表面发现的称为原肌球蛋白受体激酶(Trk)受体的特定蛋白质异常相互作用。Trk受体对生命至关重要，因为它们与称为神经营养素的生存分子结合，因此它们也被称为神经营养素受体。我已经证明了突变的GlyRS与Trk蛋白结合扰乱了通常对神经营养因子的神经反应，损害了CMT2D小鼠的感觉神经系统发育。此外，这种非生理性的相互作用导致了轴突运输过程中的缺陷，轴突运输对神经细胞的功能和生存也是必不可少的。我已经成功地治疗了CMT2D小鼠的这些缺陷，方法是注射纯化的神经营养因子，以克服突变的GlyRS结合的有害影响。这项工作不仅发现了一种治疗CMT2D的可能方法，而且揭示了神经营养因子在调节轴突运输动力学中以前未被认识到的作用。我现在提议揭开神经营养因子对健康神经中轴突运输的调节的分子机制，并在此过程中准确地确定突变的GlyRS与Trk受体结合如何降低CMT2D中的神经存活。我将首先测试各种神经营养因子对健康和CMT2D小鼠轴突运输的影响，以确定与这一基本细胞过程最相关的信号节点。作为补充，我将评估神经营养因子受体在肌肉中的位置，并确定受体的位置和水平是否与CMT2D小鼠不同肌肉对虚弱和退化的易感性有关。然后，我将在组织培养中培养神经细胞，并用它们来准确确定神经营养因子调节的通路中的损伤是如何扰乱轴突运输的。最后，我将设计由无害的病毒提供的基因疗法，以提高CMT2D小鼠肌肉中特定神经营养因子的水平，并测试这一策略作为一种潜在的疾病疗法。这一建议不仅将增强我们对神经营养因子如何调节健康神经中的轴突运输的理解，而且它具有为CMT产生创新基因疗法的非常真实的潜力。

Charcot-Marie-Tooth disease (CMT) is a debilitating, inherited neuromuscular condition that is characterised by muscle weakness and sensation deficiencies mainly in the hands and feet. The mechanisms linking gene alterations (mutations) to this neurodegeneration remain unresolved, and there are currently no effective treatments for the disease. To better understand CMT and develop therapies, I study the 2D subtype (CMT2D) caused by mutations in the gene GARS, which produces glycyl-tRNA synthetase (GlyRS) protein. GlyRS is found in almost all cells of the body, yet it is the nerves responsible for movement (motor neurons) and sensation (sensory neurons) that are affected by the disease. By understanding exactly why these peripheral nerves deteriorate, we will be better able to engineer targeted, molecular therapies.It has previously been shown that CMT2D-linked mutations in GARS affect the structure of the resulting GlyRS protein. I recently discovered that this conformational change causes mutant GlyRS to aberrantly interact with specific proteins called tropomyosin receptor kinase (Trk) receptors found on the surface of nerve cells. Trk receptors are crucial to life because they bind to survival molecules called neurotrophins, hence they are also known as neurotrophin receptors. I have shown that mutant GlyRS binding to Trk proteins disturbs the usual nerve response to neurotrophins, impairing sensory nervous system development in CMT2D mice. In addition, this non-physiological interaction leads to defects in a process called axonal transport, which is also essential for nerve cell function and survival. I have successfully treated these defects in CMT2D mice by injecting purified neurotrophic factors to overcome the detrimental impact of mutant GlyRS binding. This work has not only identified a possible way to treat CMT2D, but it has uncovered a previously unappreciated role for neurotrophic factors in regulating the dynamics of axonal transport.I now propose to unravel the molecular mechanism responsible for the modulation performed by neurotrophic factors on axonal transport in healthy nerves and, in the process, determine exactly how mutant GlyRS binding to Trk receptors reduces nerve survival in CMT2D.I will begin by testing the effects of a variety of neurotrophic factors on axonal transport in healthy and CMT2D mice in order to identify the signalling nodes most relevant to this essential cellular process. Complementing this, I will assess where the neurotrophic factor receptors are found in the muscle, and determine whether receptor localisation and levels are linked with the susceptibility of different muscles to weakness and degeneration in CMT2D mice. I will then grow nerve cells in tissue culture and use them to determine exactly how impairments in neurotrophic factor-regulated pathways disrupt axonal transport. Finally, I will design gene therapies, which will be delivered by harmless viruses, to boost levels of specific neurotrophic factors in CMT2D mice muscles and test this strategy as a potential therapy for the disease.This proposal will not only enhance our understanding of how neurotrophic factors regulate axonal transport in healthy nerves, but it has the very real potential of generating innovative gene therapies for CMT.