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

描述(申请人提供)：脊髓性肌萎缩症(SMA)是导致婴儿死亡的主要遗传原因。SMA是一种常染色体隐性遗传性神经肌肉疾病，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是一种参与mRNA剪接的普遍蛋白质。目前尚不清楚为什么运动神经元对低水平的SMN如此敏感，以及SMN缺乏是如何选择性地导致运动神经元细胞死亡的。目前还没有治愈或治疗方法来阻止它的发展。我们和其他人已经证明，低水平的SMN会导致轴突生长缺陷，损害2-肌动蛋白mRNA的运输，并降低运动神经元生长锥体中2-肌动蛋白的蛋白水平。这些发现代表了第一个已知的SMN缺陷神经元的分子缺陷，并提示了SMN的轴突特异性功能。我们推测SMN可能是轴突生长锥内2-肌动蛋白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-肌动蛋白翻译缺陷可能是SMA典型的轴突功能障碍和神经变性的原因之一。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。在这项为美国国立卫生研究院提供资金的转译研究申请中，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来源的运动神经元来鉴定能够促进2-肌动蛋白mRNA转运到轴突生长锥体的药物。其次，我们将筛选提高生长锥体中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在培养的初级运动神经元和SMA小鼠模型中进行的一系列渐进测试来验证有效性。鉴于这种疾病造成的人员伤亡和缺乏有效的治疗方法，我们的目标是将最近在了解SMN在运动神经元中的功能方面的进展转化为治疗SMA的有效药物的开发。 公共卫生相关性：我们建议使用干细胞来源的运动神经元来筛选治疗脊髓性肌萎缩症轴突缺陷的药物。提高轴突和生长锥体中2-肌动蛋白mRNA和蛋白水平的分子有可能被用作治疗脊髓性肌萎缩症和可能涉及轴突运输和突触缺陷的其他神经退行性人类疾病的药物。

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.