Mechanisms of Central Synaptic Dysfunction in SMA

描述(申请人提供)：脊髓性肌萎缩症(SMA)是一种遗传性神经退行性疾病，以运动神经元丢失和骨骼肌萎缩为特征。SMA是导致婴儿死亡的最常见的遗传原因，但目前还没有有效的治疗方法。虽然人们对这种疾病的遗传原因知道得很多，但关于解释受影响个体表现出的运动症状严重程度的生理变化的信息却很少。特定的、脆弱的神经元群体的功能障碍可能会加速神经回路的继发性变化，从而可能加剧神经元功能障碍。在脊髓，运动神经元接受来自局部中间神经元、来自大脑的下行通路和感觉神经元的直接突触输入。在以前的研究中，我们报道了SMA小鼠感觉初级传入和运动神经元之间的单突触联系的强度在疾病早期大大降低，然后才能检测到实质性的运动神经元细胞丢失。这种功能的丧失部分是由SMA小鼠运动神经元上初级传入神经元的丧失所介导的。这项研究的目的是确定哪些输入或运动回路的部分特别受到疾病的影响，以及这是由于运动神经元功能障碍还是这些神经元回路中SMN缺陷所固有的。在目标1中，我们将分析产生直接突触的神经元群体对SMA小鼠脊髓运动神经元的胞体和树突的功能影响。此外，我们将通过对SMA小鼠运动神经元上的突触密度进行定位和量化，将功能缺陷和结构缺陷联系起来。这些研究将纵向扩展，以确定疾病过程中缺陷的时间进程。在目标2中，我们将利用Cre-lox技术的新小鼠来研究SMN蛋白的调节在逆转疾病严重表型中的作用。我们将使用行为、生理和形态分析来确定这些方法的有效性。激光捕获显微切割也将被用来从对照组和SMA小鼠中分离出选定的与疾病相关的神经元类型，用于RNA分析。这些将包括腰椎脊髓腹角的运动神经元以及其他几个神经元和非神经元群体。在目标3中，我们将研究SMA中受影响的运动回路中涉及突触丢失的机制。我们将使用免疫组织化学标记物通过比较SMA和野生型脊髓来识别疾病不同阶段受影响的突触的来源。总的来说，这些实验有可能阐明突触缺陷在SMA小鼠疾病进展中的重要性。

DESCRIPTION (provided by applicant): Spinal muscular atrophy (SMA) is an inherited neurodegenerative disease characterized by motor neuron loss and skeletal muscle atrophy. SMA is the most common genetic cause of death in infancy, but no effective treatment is currently available. While much is known about the genetic causes of the disease, less information is available on the physiological alterations that explain the severity of motor symptoms displayed by affected individuals. Dysfunction of specific, vulnerable neuronal populations may precipitate secondary changes in neural circuits that could exacerbate neuronal dysfunction. In the spinal cord, motor neurons receive direct synaptic inputs from local interneurons, descending pathways from the brain, and sensory neurons. In a previous study we reported that the strength of monosynaptic connections between sensory primary afferents and motor neurons in SMA mice is greatly reduced early in the course of the disease, before substantial motor neuron cell loss can be detected. This loss of function is mediated in part by the loss of primary afferent boutons on motor neurons in SMA mice. The goals of this study is to identify which inputs or parts of the motor circuit are particularly affected by the disease and whether this is due to motor neuron dysfunction or intrinsic to SMN deficiency in these neuronal circuits. In Aim 1, we will analyze the functional effects of a neuronal population that makes direct synapses on the somata and dendrites of spinal motor neurons in SMA mice. In addition we will correlate functional and structural defects by mapping and quantifying the synaptic density on motor neurons in SMA mice. These studies will extend longitudinally to determine the time course of the defects in the course of the disease. In Aim 2, we will use novel mice taking advantage of the Cre-lox technology to study the effects of regulation of SMN protein in reversing the severe phenotype of the disease. We will employ behavioral, physiological and morphological assays to determine efficacy of these approaches. Laser capture microdissection will also be employed to isolate selected, disease-relevant neuronal types from control and SMA mice for RNA analysis. These will include motor neurons in the ventral horns of the lumbar spinal cord and several other neuronal and non-neuronal populations. In Aim 3, we will investigate mechanisms involved in synaptic loss in the motor circuits affected in SMA. We will employ immunohistochemical markers to identify the origin of the synapses affected at different stages of the disease by comparing SMA and wild type spinal cords. Collectively, these experiments have the potential to elucidate the importance of synaptic defects in the progression of the disease in SMA mice.