Impaired axon development in SMA

项目总结 运动神经元疾病脊髓性肌萎缩症(SMA)是婴儿期主要的遗传性死亡原因。 和童年。它是由存活运动神经元1基因(SMN1)的隐性突变引起的。所有患者 保留同源SMN2基因的一个或多个拷贝，但它产生不充分的SMN蛋白水平 由于另一个拼接事件。包括反义在内的旨在调节SMN2剪接的新疗法 寡核苷酸和小分子最近获得了FDA的批准，或目前正在对SMA患者进行临床试验。 虽然这是成功的，但仍不清楚为什么许多患者的治疗反应不充分。 定义SMN诱导的最佳时机和组织靶向一直受到以下方面的限制 患者的早期疾病病理。为了解决这一知识差距，在初步研究中，我们检查了 重症SMA患者和模型小鼠的腹根轴突和运动性轴突明显受损 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早期疾病发病的基础， 严重的SMA患者的刻板印象是虚弱和急剧下降。在具体目标1中，我们将 描述重度和轻度SMA小鼠这种病理的时间和地形图特征 在模型和人体样本中。在特定的目标2中，我们将定义导致这种病理的细胞因素。 利用一系列有条件的SMA小鼠系，在任一种运动中特异性表达增加的SMN 神经元、雪旺细胞或肌肉。我们还将评估中性调节蛋白1型III型(NRG1-III)，一种关键的 外周轴突发育的调节因子，在SMA中调节失调，并探讨是否过度表达 NRG1-III可改善SMA轴突病变。最后，在具体目标3中，我们将确定何时SMN-- 诱导药物，包括SMN2剪接开关反义寡核苷酸和小分子SMN-C3， 必须交付以恢复轴突成熟，防止运动单位退化，并提供最佳 表型救援。总而言之，这些研究将描述一种新发现的突出的 严重的SMA患者并确定最佳治疗时机。这些调查的结果将 提供有关目前参与临床试验的患者的结果的重要见解，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.