Spinal Muscular Atrophy: Cell-based drug screens for treatment of axonal defects

描述（由申请人提供）：脊髓性肌萎缩症（SMA）是婴儿死亡的主要遗传原因。SMA是一种常染色体隐性神经肌肉疾病，其特征是脊髓前角运动神经元变性，导致对称性肌肉无力和萎缩。它是由编码存活运动神经元蛋白（SMN）的基因突变或缺失引起的，SMN是一种普遍存在的参与mRNA剪接的蛋白质。为什么运动神经元如此特别容易受到低水平SMN的影响，以及SMN缺乏如何选择性地导致运动神经元细胞死亡，目前仍不清楚。目前还没有治愈或治疗方法可以阻止其发展。我们和其他人已经证明，低水平的SMN会导致轴突生长缺陷，运动神经元生长锥中2-actin mRNA转运受损和2-actin蛋白水平降低。这些发现代表了SMN缺陷神经元中第一个已知的分子缺陷，并提示SMN具有轴突特异性功能。我们假设SMN可能是轴突生长锥中2-actin mRNA颗粒组装、运输和/或局部翻译的重要辅助因子。轴突mRNA定位和2-actin翻译的缺陷可能导致典型的SMA轴突功能障碍和神经变性。先前开发SMA治疗方法的努力并没有直接针对smn缺陷运动神经元的轴突缺陷。在这项向美国国立卫生研究院申请资助的转化研究中，我们建议对纠正smn缺陷运动神经元功能缺陷的药物进行基于细胞的高通量筛选。首先，我们将使用多能干细胞衍生的运动神经元来鉴定增强2-actin mRNA向轴突生长锥转运的药物。其次，我们将筛选提高生长锥中2-肌动蛋白水平的药物。在这些筛选中确定的新候选药物将通过培养的初级运动神经元和SMA小鼠模型的一系列渐进试验来验证其有效性。鉴于这种疾病对人类的伤害和缺乏有效的治疗方法，我们的目标是将运动神经元中SMN功能的最新进展转化为治疗SMA的有效药物的开发。

DESCRIPTION (provided by applicant): Spinal muscular atrophy (SMA) is the leading genetic cause of infant mortality. SMA is an autosomal recessive neuromuscular disorder characterized by degeneration of the anterior horn motor neurons in the spinal cord, leading to symmetrical muscle weakness and atrophy. It is caused by mutations or deletions in the gene encoding the survival motor neuron protein (SMN), a ubiquitous protein involved in mRNA splicing. It is still unknown why motor neurons are so specifically vulnerable to low levels of SMN and how SMN deficiency selectively causes motor neuron cell death. Currently there is no cure or treatment available to stop its progression. We and others have shown that low levels of SMN lead to axonal growth defects, impaired 2-actin mRNA transport and reduced 2-actin protein levels in growth cones of motor neurons. These findings represent the first known molecular defect in SMN-deficient neurons and suggest an axon-specific function for SMN. We hypothesizes that SMN may act as an important cofactor for the assembly, transport and/or local translation of 2-actin mRNA granules in axonal growth cones. Defects in axonal mRNA localization and translation of 2-actin may contribute to the axonal dysfunction and neurodegeneration typical of SMA. Previous efforts to develop treatments for SMA did not directly target axonal defects in SMN-deficient motor neurons. In this translational research application for funding to the NIH, we propose to perform cell-based high throughput screens for drugs that correct functional deficits in SMN-deficient motor neurons. Firstly, we will use pluripotent stem cell-derived motor neurons to identify drugs that enhance transport of 2-actin mRNA into axonal growth cones. Secondly, we will screen for drugs that raise 2-actin protein levels in growth cones. Novel drug candidates identified in these screens will be validated for effectiveness through a progressive series of tests in cultured primary motor neurons and SMA mouse models. Given the human toll of this disease and the lack of an effective therapy, it is our goal to translate recent progress in understanding the function of SMN in motor neurons into the development of effective drugs for the treatment of SMA. PUBLIC HEALTH RELEVANCE: We propose to use stem cell-derived motor neurons to screen for drugs for the treatment of axonal defects in spinal muscular atrophy. Molecules that raise 2-actin mRNA and protein levels in axons and growth cones have the potential to be used as drugs for the treatment of spinal muscular atrophy and possibly other neurodegenerative human diseases where axonal transport and synaptic defects are implicated.