Motor axon development in a zebrafish model of Charcot-Marie-Tooth disease

描述（由申请人提供）：腓骨肌萎缩症（CMT）是最常见的遗传性神经肌肉疾病，是一种进行性疾病，其特征为长运动和感觉轴突变性，导致肌肉萎缩和长期残疾。远端遗传性运动神经病（dHMN）是一种非常密切相关的疾病，其特征是运动，但不是感觉，轴突变性。这些疾病通常表现为显性遗传，症状首先出现在生命的第二或第三个十年。已知几种基因中的任何一种突变都会导致其中一种或两种疾病。例如，小热休克蛋白（sHSP）HSP 27或HSPB 8的突变可以导致CMT或dHMN。众所周知，sHSP在保护细胞免受环境应激因素影响以及调节肌动蛋白和中间丝动力学方面发挥作用。在培养的细胞中错误表达HSP 27的致病变体导致中间丝蛋白的聚集，这表明CMT和dHMN的轴突变性特征可能是由于中间丝的隔离和随后未能适当地建立或维持轴突结构，或蛋白聚集体的毒性。了解这些疾病的病因是复杂的家庭内的异质性-至少两个同卵双胞胎之间-这表明环境和/或多种遗传因素可能有助于疾病的进展。最后，虽然假设突变在神经元内自主作用，但HSP 27在发育中的肌肉中表达，并且在成人肌肉中响应于生理应激而上调。以斑马鱼为模型系统，我们提出确定（1）HSP 27疾病突变如何影响运动轴突的发育和维持，（2）突变是否使轴突对环境应激的影响敏感，以及（3）神经元、肌肉或两者是否需要HSP 27。为了实现这些目标，我们将在斑马鱼中错误表达HSP 27疾病变体的斑马鱼版本（所有这些变体都占主导地位），无论是普遍存在还是在神经元或肌肉中，并测定对运动轴突结构和蛋白质聚集的发育和维持的影响。这些研究结果将有助于我们更好地了解导致CMT和dHMN轴突变性的细胞生物学事件。此外，由于CMT和dHMN的进展和严重程度可能至少部分由环境因素决定，因此这些研究的结果可能对这些疾病的预防和管理具有直接影响。本提案中概述的这项研究旨在解决小热休克蛋白Hsp 27突变如何导致两种神经退行性疾病，Charcot-Marie-Tooth病和远端遗传性运动神经病，并测试环境压力是否有助于其发展或进展。这些研究的结果可能会显著影响我们预防或减缓疾病进展的能力，从而提高这些患者的生活质量，并降低与治疗其症状相关的医疗保健成本。

DESCRIPTION (provided by applicant): Charcot-Marie-Tooth disease (CMT), the most common inherited neuromuscular disorder, is a progressive disease characterized by degeneration of long motor and sensory axons, resulting in muscle atrophy and long-term disability. Distal hereditary motor neuropathy (dHMN) is a very closely-related disease characterized by motor, but not sensory, axon degeneration. These diseases usually show dominant inheritance, with symptoms first appearing during the second or third decade of life. Mutations in any one of several genes are known to cause either or both diseases. For example, mutations in the small heat shock proteins (sHSPs) HSP27 or HSPB8 can cause either CMT or dHMN. sHSPs are well known for their roles in protecting cells from the effects of environmental stressors and for regulating actin and intermediate filament dynamics. Misexpressing the disease-causing variants of HSP27 in cultured cells results in aggregation of intermediate filament proteins, suggesting that the axonal degeneration characteristic of CMT and dHMN may be due to either the sequestration of intermediate filaments and subsequent failure to appropriately establish or maintain axon architecture, or toxicity of protein aggregates. Understanding the etiology of these diseases is complicated by the large degree of heterogeneity within families -- and between at least two identical twins -- suggesting that environmental and/or multiple genetic factors may contribute to disease progression. Finally, while the mutations are assumed to act autonomously within neurons, HSP27 is expressed in developing muscle and it is upregulated in adult muscle in response to physiologic stress. Using zebrafish as a model system, we propose to determine (1) how HSP27 disease mutations affect the development and maintenance of motor axons, (2) whether the mutations sensitize axons to the effects of environmental stress, and (3) whether HSP27 is required in neurons, muscle, or both. In order to accomplish these objectives, we will misexpress zebrafish versions of the HSP27 disease variants (all of which act dominantly) in the zebrafish, either ubiquitously or in neurons or muscle and assay the effects on the development and maintenance of motor axon architecture and protein aggregation. The results of these studies will help us to better understand the cell biological events leading to axon degeneration in CMT and dHMN. Furthermore, since the progression and severity of CMT and dHMN are likely determined, at least in part, by environmental factors, the results of these studies could have direct implications for the prevention and management of these diseases. PUBLIC HEALTH RELEVANCE This research outlined in this proposal is designed to address how mutations in the small heat shock protein Hsp27 cause two neurodegenerative diseases, Charcot-Marie-Tooth Disease and Distal Hereditary Motor Neuropathy and to test whether environmental stress contributes to their development or progression. The results of these studies could significantly impact our ability to prevent or slow progression of the diseases, thus improving the quality of life of these patients as well as reducing health care costs associated with treating their symptoms.