Impaired axon development in SMA

项目摘要 运动神经元疾病脊髓性肌萎缩症（SMA）是婴儿期死亡的主要遗传原因 还有童年它是由运动神经元生存基因1（SMN 1）的隐性突变引起的。所有患者 保留一个或多个拷贝的同源SMN 2基因，但产生的SMN蛋白水平不足 这是由于选择性剪接事件。旨在调节SMN 2剪接的新型治疗剂，包括反义 寡核苷酸和小分子最近被FDA批准或目前在SMA患者中进行临床试验。 虽然这是一个成功，但仍不清楚为什么许多患者的治疗反应不足。 定义SMN诱导的最佳时机和组织靶向受到以下因素的限制： 患者的早期疾病病理学。为了解决这一知识差距，在初步研究中，我们检查了 腹根轴突的严重SMA患者和模型小鼠，发现运动轴突的显着损害 分选和放射状生长，开始于产前，随后是未成熟轴突的退化 围产期的该项目旨在确定这些病理是否可能是疾病早期发作的基础， 典型的虚弱模式和重度SMA患者的急剧下降。具体目标1： 在重度和轻度SMA小鼠中表征该病理学的时间和地形图模式 模型和人体样本。在具体目标2中，我们将定义这种病理的细胞贡献者 利用一系列条件性SMA小鼠系，其特异性地在两种运动中表达增加的SMN， 神经元、雪旺氏细胞或肌肉。我们还将评估神经调节蛋白1 III型（NRG 1-III），一个关键的 外周轴突发育的调节因子，在SMA中失调，并探讨是否过度表达 NRG 1-III可以改善SMA轴突病理。最后，在具体目标3中，我们将确定何时SMN- 诱导药物，包括SMN 2剪接转换反义寡核苷酸和小分子SMN-C3， 必须递送以恢复轴突成熟，防止运动单位退化，并提供最佳的 表型拯救总之，这些研究将描述一个新认识的和突出的病理学， 重度SMA患者，并确定最佳治疗时机。这些调查的结果将 提供关于目前参加临床试验的患者结局的重要见解，影响 设计未来的试验，并可能发现新的SMA治疗靶点。

PROJECT SUMMARY The motor neuron disease spinal muscular atrophy (SMA) is the leading inherited cause of death in infancy and childhood. It is caused by recessive mutations of the survival motor neuron 1 gene (SMN1). All patients retain one or more copies of the homologous SMN2 gene, but it produces inadequate levels of SMN protein due to an alternative splice event. Novel therapeutics aiming to modulate SMN2 splicing including antisense oligonucleotides and small molecules are recently FDA-approved or currently in clinical trials in SMA patients. While this is a success, it remains unknown why many patients have inadequate therapeutic responses. Defining the optimal timing and tissue targeting of SMN induction has been limited by poor understanding of early disease pathology in patients. To address this knowledge gap, in preliminary studies we examined ventral root axons in severe SMA patients and model mice and discovered marked impairments of motor axon sorting and radial growth, which begin prenatally and are followed by degeneration of immature axons perinatally. This project aims to determine if these pathologies may underlie the early disease onset, stereotypical pattern of weakness, and precipitous decline of severe SMA patients. In Specific Aim 1, we will characterize the temporal and topographic patterns of this pathology in both a severe and milder SMA mouse model and in human samples. In Specific Aim 2, we will define the cellular contributors to this pathology utilizing a series of conditional SMA mouse lines expressing increased SMN specifically in either motor neurons, Schwann cells, or muscle. We will also evaluate whether neuregulin 1 type III (NRG1-III), a key regulator of peripheral axon development, is dysregulated in SMA and explore whether overexpression of NRG1-III can ameliorate SMA axonal pathologies. Finally, in Specific Aim 3, we will establish when SMN- inducing drugs, including SMN2 splice-switching antisense oligonucleotides and the small molecule SMN-C3, must be delivered to restore axonal maturation, prevent motor unit degeneration, and provide optimal phenotypic rescue. Together, these studies will characterize a newly recognized and prominent pathology of severe SMA patients and define the optimal timing of therapeutics. The results of these investigations will provide important insights regarding the outcomes of patients currently enrolled in clinical trials, influence the design of future trials, and potentially uncover novel SMA therapeutic targets.