Exploring the Functions of tRNA Synthetases in the Nucleus and their Relationship to CMT

摘要 Charcot-Marie-Tooth(CMT)病，又称遗传性运动和感觉神经病(HMSN)，是 最常见的遗传性周围神经病，估计患病率为每2500人中有1人， 相当于美国大约12.5万人。CMT在一定程度上影响周围神经- 依赖方式，其特征是四肢远端肌肉无力和消瘦，导致 进行性运动障碍、感觉丧失和骨骼畸形。CMT患者没有可用的治疗方法。 CMT中涉及的最大基因家族编码氨基酰-tRNA合成酶(AARs)，这是必不可少的 催化蛋白质生物合成中的第一反应的酶，即转移RNA(TRNAs)的荷电 以及它们的同源氨基酸。然而，理解CMT和AARS之间的联系是一个挑战。 由于AARs是蛋白质合成的重要参与者，人们认为引起cmt的trna突变 合成酶一定会以某种方式影响蛋白质的合成。奇怪的是，引起CMT的突变并不一定 影响酶的氨酰化功能；几乎所有的tRNA合成酶突变都是CMT- 相关的有常染色体显性遗传，提示一种功能获得性疾病机制。最后，AS 蛋白质合成对所有组织类型都是必不可少的，这是与CMT相关的极端组织特异性 表型使生物学上对AARS在CMT疾病中的作用的理解复杂化。有趣的是， 胞浆AARs也存在于真核细胞的细胞核中。虽然最初的假设是AARS 在校对新合成的tRNAs中起作用，后来的发现表明，核定位的AARs 参与调节广泛的生物过程，包括血管发育、炎症、 而压力反应主要是由于它们与转录机制相互作用的独特能力。 然而，核TyrRs的生物学功能在哺乳动物体内从未被研究过。 本项目的目标是探索核内AARs的生理功能及其与 CMT。我们的主要关注点是TyrRS，因为已经建立了探索所需的试剂和知识 在哺乳动物系统中，因为最近来自果蝇模型的证据表明， CMT中的核酪氨酸受体。虽然主要关注的是TyrRS，但我们将探索与其他子类型的共性 周围神经病以及其他神经退行性疾病，如阿尔茨海默病、帕金森氏症 疾病、亨廷顿氏病和肌萎缩侧索硬化症。这是因为TyrRS的核功能 很可能与氧化应激以及其他重要的途径和基因调节因子有关 与独立于CMT突变的神经退变过程相关。

Abstract Charcot-Marie-Tooth (CMT) disease, also known as hereditary motor and sensory neuropathy (HMSN), is the most common form of inherited peripheral neuropathy, with an estimated prevalence of 1 in 2500 people, equating to approximately 125,000 people in the United States. CMT affects peripheral nerves in a length- dependent manner and is characterized by weakness and wasting of the distal limb muscles leading to progressive motor impairment, sensory loss, and skeletal deformities. No therapy is available for CMT patients. The largest gene family implicated in CMT encodes aminoacyl-tRNA synthetases (aaRSs), which are essential enzymes that catalyze the first reaction in protein biosynthesis, namely, the charging of transfer RNAs (tRNAs) with their cognate amino acids. However, understanding the connection between CMT and aaRSs is a challenge. Because aaRSs are essential players in protein synthesis, it is believed that the CMT-causing mutations in tRNA synthetases must affect protein synthesis in some way. Curiously, CMT-causing mutations do not necessarily affect the aminoacylation function of the enzyme; and almost all tRNA synthetase mutations that are CMT- associated have autosomal dominant inheritance, suggesting a gain-of-function disease mechanism. Lastly, as protein synthesis is essential for all tissue types, the extreme tissue specificity associated with the CMT phenotypes has complicated the biological understanding of the role of aaRSs in CMT disease. Intriguingly, cytosolic aaRSs are also detected in the nucleus of eukaryotic cells. While the initial hypothesis was that aaRSs function here in proofreading newly-synthesized tRNAs, later findings suggest that the nuclear-localized aaRSs are involved in regulating a wide range of biological processes including vascular development, inflammation, and stress responses mainly due to their distinctive abilities to interact with the transcriptional machinery. However, the biological function of nuclear TyrRS has never been investigated in vivo in a mammalian system. The goal of this project is to explore the physiological functions of aaRSs in the nucleus and their relationship to CMT. Our main focus is on TyrRS, because of the established reagents and knowledge necessary for exploration in a mammalian system and because of the recent evidence from a Drosophila model for the involvement of nuclear TyrRS in CMT. Although the main focus is on TyrRS, we will probe commonality with other subtypes of peripheral neuropathy as well as other neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, and amyotrophic lateral sclerosis. This is because the nuclear function of TyrRS is likely to be generally related to oxidative stress and to other important pathways and gene regulators that are relevant to the neurodegenerative process independent of CMT mutations.