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，作为一种 结果，肌肉变弱，经常导致瘫痪和死亡。这种共性在罕见疾病之间是相同的，例如 脊髓性肌萎缩症、肌萎缩侧索硬化症和SMA合并I型呼吸窘迫(SMARD1)。 总体而言，“罕见”疾病非常常见，仅在美国就有约3000万人受到影响。理解 这些不同情况之间的共同点不仅利用了针对疾病的研究，而且还提供了 利用共同的生化途径进行治疗开发的机会。以此为背景，这个项目 重点关注IGHMBP2基因，当突变时会导致严重的运动神经元退行性疾病SMARD1； IGHMBP2突变也在CMT2(Charcot-Marie-Tooth Type2)患者的子集中发现。IGHMBP2是一种 普遍表达的具有解旋酶功能的蛋白质，并被认为在RNA调节或RNA代谢中发挥作用。 SMARD1是一种常染色体隐性遗传性运动神经元病，主要影响儿童，平均寿命为13岁 月份。在早发性SMA患者中，SMARD1的患病率约为1%。SMARD1最初的特征是远端 后肢肌肉萎缩，近端肌肉无力。首个主要的SMARD1临床症状，呼吸道 并发症，是由于横隔膜麻痹。我们最近制造了四种未发表的突变小鼠模型 在Ighmbp2中，这与SMARD1患者群体中的突变相关。这个项目的目标是描述 其中两个新模型具有Ighmbp2突变C495X和D564N。C495X与患者C496X突变相关 是在SMARD1中发现的最常见的IGHMBP2突变，也在一些CMT2患者中发现。发现C495X 在患者中表现为纯合子隐性突变和复合杂合突变，并表现为呼吸道症状 痛苦和运动神经元缺陷，早至数天，晚至数年。D564N与患者D565N突变和 仅被确认为一种复合杂合突变，临床症状早在几个月前就开始出现 年纪大了。D565N蛋白与核酸结合，具有ATPase活性，但缺乏解旋酶活性。 AIM I的实验旨在解决：疾病的发病、疾病的严重性以及 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。这些数据将与以下研究进行比较 我研究了NMD鼠标(目前唯一可用的SMARD1型号)以及SMA和ALS型号。AIM III将 解决翻译方法问题。这些研究应该为了解Ighmbp2在细胞中的作用提供重要信息。 流程和SMARD1开发。此外，这些研究应提供更多的知识基础，以便于 治疗进展和对相关神经疾病之间异同的更好理解 以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.