Novel SMARD1 Mouse Models: Characterization and Evaluation of Potential Therapeutic Targets

摘要 当运动神经元退化时，它们失去了与下游肌肉目标沟通的能力， 结果，肌肉变弱，常常导致瘫痪和死亡。这种共性在罕见疾病之间共享， 脊髓性肌萎缩、肌萎缩侧索硬化和SMA伴呼吸窘迫I型（SMARD 1）。 集体“罕见”疾病是惊人的普遍，仅在美国就有3000万人受到折磨。理解 这些不同疾病之间的共同点不仅有助于疾病特异性研究， 利用共享的生物化学途径进行治疗开发的机会。以此为背景，该项目 专注于IGHMBP2基因，当突变时会导致严重的运动神经元退行性疾病SMARD 1; IGHMBP2中的突变也在CMT2（Charcot-Marie-Tooth Type 2）患者的子集中发现。IGHMBP 2是一种 广泛表达的具有解旋酶功能的蛋白质，并在RNA调节或RNA代谢中发挥作用。 SMARD 1是一种常染色体隐性运动神经元疾病，主要影响儿童，预期寿命约为13岁。 个月SMARD 1的患病率约为早发SMA患者的1%。SMARD 1最初的特征是远端 下肢肌肉萎缩，随后出现近端肌无力。第一个主要的SMARD 1临床症状，呼吸道 并发症，是由于脑性瘫痪。我们最近生成了四个未发表的突变小鼠模型， 与SMARD 1患者人群中的突变相关的Ighmbp2。该项目的目标是描述 Ighmbp2突变C495X和D564N的两个新模型。C495X与患者C496X突变相关， 是在SMARD 1中鉴定的最普遍的IGHMBP2突变，并且也在一些CMT2患者中发现。C495X被发现 在患者中表现为纯合隐性突变和复合杂合突变， 痛苦和运动神经元缺陷，早至数天，晚至数年。D564N与患者D565N突变相关， 仅被鉴定为复合杂合突变，临床症状早在几个月就开始了 年龄。D565N蛋白结合核酸，具有ATP酶活性，但缺乏解旋酶活性。 AIM I中的实验旨在解决：疾病发作、疾病严重程度以及疾病类型之间的关系。 突变和SMARD1症状。在AIM II中，我们将检查分子和细胞表型，包括RNA和 蛋白质表达、运动神经元和肌肉分析以及呼吸功能。这些数据将与研究进行比较， 研究了nmd小鼠（目前唯一可用的SMARD 1模型）以及SMA和ALS模型。AIM III将 解决翻译方法。这些研究将为Ighmbp2在细胞凋亡中的作用提供重要信息。 智能制造1的发展。此外，这些研究应提供更大的知识基础， 治疗发展和更好地了解相关神经系统疾病之间的相似性和差异 更全面地解决治疗发展问题。

Abstract When motor neurons degenerate, they lose their ability to communicate with their downstream muscle targets and, as a result, muscles weaken, often leading to paralysis and death. This commonality is shared between rare diseases such as Spinal Muscular Atrophy, Amyotrophic Lateral Sclerosis, and SMA with Respiratory Distress Type I (SMARD1). Collectively “rare” disorders are strikingly common, afflicting ~30 million people in the United States alone. Understanding commonalties between these different conditions not only leverages disease-specific research but also provides opportunities to exploit shared biochemical pathways for therapeutic development. With this as a backdrop, this project focuses on the IGHMBP2 gene, that when mutated results in a severe motor neuron degenerative disease, SMARD1; mutations in IGHMBP2 are also found in a subset of CMT2 (Charcot-Marie-Tooth Type2) patients. IGHMBP2 is a ubiquitously expressed protein with helicase function and proposed roles in RNA regulation or RNA metabolism. SMARD1 is an autosomal recessive motor neuron disease that primarily affects children, with a life expectancy of ~13 months. The prevalence of SMARD1 is ~1 percent of early onset SMA patients. SMARD1 is initially characterized by distal lower limb muscle atrophy with proximal muscle weakness later. The first major SMARD1 clinical symptom, respiratory complication, is due to diaphragmatic paralysis. We have recently generated four unpublished mouse models with mutations in Ighmbp2 that correlate to mutations within the SMARD1 patient population. The objective of this project is to characterize two of the new models with Ighmbp2 mutations C495X and D564N. C495X correlates to the patient C496X mutation that is the most prevalent IGHMBP2 mutation identified in SMARD1 and is also found in some CMT2 patients. C495X is found as a homozygous recessive mutation and as a compound heterozygous mutation in patients and presents with respiratory distress and motor neuron defects as early as days and as late as years. D564N correlates to the patient D565N mutation and has only been identified as a compound heterozygous mutation with clinical symptoms initiating as early as several months of age. D565N protein binds nucleic acid, has ATPase activity, but lacks helicase activity. Experiments in AIM I are designed to address: disease onset, disease severity, and the relationship between the type of mutation and SMARD1 symptoms. In AIM II we will examine the molecular and cellular phenotypes, including RNA and protein expression, motor neuron and muscle analyses, and respiratory function. These data will be compared to studies that have examined the nmd mouse (the only SMARD1 model currently available) and SMA and ALS models. AIM III will address translational approaches. These studies should provide significant information into the role of Ighmbp2 in cellular processes and SMARD1 development. Additionally, these studies should provide a greater knowledge base to facilitate therapeutic development and a better understanding of the similarities and differences between related neurological diseases to more completely address therapeutic development.