Synapse Loss in Spinal Muscular Atrophy

描述（由申请人提供）：近端脊髓性肌萎缩症（SMA）是婴儿死亡的主要遗传原因，是一种常染色体隐性疾病，其特征是脊髓运动神经元丧失、肌肉萎缩和运动障碍，具有不同的发病和严重程度（I型为严重，II型为中度，III型为轻度）。目前，这种毁灭性的神经系统疾病还没有治愈的方法，而且SMA的发病机制也不清楚。在这项应用中，II型SMA样小鼠模型（smn7 SMA和SMN- hung SMA）将被用来测试一个新的概念，即脊髓运动神经元突触输入的减少，而不是神经肌肉连接的退化，是导致运动损伤的关键事件。目的1将验证神经肌肉连接处不是II型SMA小鼠缺陷的主要部位的假设。与年龄和性别匹配的非SMA幼崽相比，将应用光镜和电子显微镜以及电生理分析来检查不同年龄的II型SMA小鼠的神经肌肉连接是否有神经支配和功能正常。目的2将验证II型SMA小鼠脊髓运动神经元突触输入减少的假设。形态学和生化分析将用于比较II型SMA与年龄和性别匹配的非SMA幼崽脊髓运动神经元突触点的数量和脊髓突触囊泡蛋白的表达。突触丢失是否涉及小胶质细胞剥离突触也将被检查。此外，突触缺陷是否归因于背根神经节本体感觉神经元突触输入的减少或退化将被研究。该研究的发现将提供一个新的概念，即SMA是脊髓运动神经元突触丧失的疾病，而不是像主流观点所认为的神经肌肉连接变性。因此，拟议的研究与开发针对脊髓突触缺陷的SMA新疗法有关。这一新的治疗理念可用于治疗其他类型的运动神经元疾病。公共卫生相关性：拟议的研究与脊髓性肌萎缩症（SMA）高度相关，这是婴儿死亡的主要遗传原因，其特征是运动障碍和脊髓运动神经元的丧失。我们将使用模拟II型（中度）SMA的小鼠模型来验证一个新概念，即脊髓运动神经元的突触丧失是导致运动损伤的关键事件。这项拟议的研究将通过针对脊髓突触缺陷来开发新的SMA治疗方法。

DESCRIPTION (provided by applicant): Proximal Spinal Muscular Atrophy (SMA), a leading genetic cause of infant mortality, is an autosomal recessive disease characterized by the loss of spinal motoneurons, muscle atrophy, and motor impairments with varying disease onset and severity (type I is severe; type II, moderate; type III, mild). Currently, there is no cure for this devastating neurological disease, and the mechanisms of the pathogenesis of SMA are not well understood. In this application, type II SMA-like mouse models (SMN 7 SMA and SMN-Hung SMA) will be used to test a novel concept that reduction of synaptic inputs to motoneurons in the spinal cord, instead of degeneration of neuromuscular junctions, is the key event contributing to motor impairments. Aim 1 will test the hypothesis that the neuromuscular junction is not the major site of defects in type II SMA mice. Light and electron microscopy, as well as electrophysiological analyses, will be applied to examine whether neuromuscular junctions in type II SMA mice at various ages are innervated and function normally, as compared with age- and gender-matched non-SMA littermates. Aim 2 will test the hypothesis that synaptic inputs onto spinal motoneurons are reduced in type II SMA mice. Morphological and biochemical analyses will be used to compare numbers of synaptic puncta on spinal motoneurons and the expression of synaptic vesicle proteins in the spinal cord in type II SMA with those in age- and gender-matched non-SMA littermates. Whether the synapse loss involves synaptic stripping by microglia also will be examined. In addition, whether the synaptic defects are attributed to a decrease or degeneration of synaptic inputs from proprioceptive sensory neurons in the dorsal root ganglion will be investigated. The findings of the proposed research will provide a new concept that SMA is a disease of synapse loss in the spinal motoneurons, rather than degeneration of neuromuscular junctions, as suggested by the prevailing thinking. The proposed research is thus relevant to the development of novel therapies for SMA by targeting synaptic defects in the spinal cord. The new therapeutic concept could be applied to treat other types of motoneuron diseases. PUBLIC HEALTH RELEVANCE: The proposed research is highly relevant to Spinal Muscular Atrophy (SMA), a leading genetic cause of infant death characterized by motor impairments and the loss of motor neurons in the spinal cord. We will use mouse models mimicking type II (moderate) SMA to test a novel concept that synapse loss in spinal motoneurons is a key event contributing to motor impairments. The proposed research would lead to future development of novel therapies for SMA by targeting synaptic defects in the spinal cord.