Mechanisms of Central Synaptic Dysfunction in SMA

项目摘要 马达电路控制吞咽、呼吸和运动等基本行为。脊椎运动 神经元是将中枢神经系统内产生的运动指令转换为 外周肌肉靶标。运动神经元由突触活动的精确调节模式激活 来自感觉神经元、局部脊髓中间神经元和来自大脑的下行通路。在早期 在发育过程中，运动神经元接收到的突触活动塑造了它们的功能特性。相比之下，基因 导致运动神经元接收到的神经元连接或突触驱动的扰动的突变通常 导致运动系统紊乱。这种情况的一个突出例子是脊髓性肌萎缩症(SMA)-AN 遗传性神经肌肉疾病，由存活运动神经元(SMN)蛋白普遍缺乏引起。 SMA的发病机制涉及到运动回路的多个成分的改变，导致 脊椎反射、运动神经元丧失和骨骼肌萎缩。然而，分子、细胞和电路 SMA背后的机制在很大程度上仍然难以捉摸。我们以前的工作使我们发现了小说 涉及“延迟整流”钾通道Kv2.1下调的分子微扰 在运动神经元放电调节中的重要决定因素。此外，SMA运动神经元 紧张性抑制增强起源于运动前抑制中间神经元。最后，我们确定了 神经营养素3(NT3)的减少是导致运动回路选择性易损性的候选因素 激活近端肌肉，与远端肌肉相比，近端肌肉更脆弱。在目标1中，我们将研究 运动神经元上抑制性突触驱动的增加是否是导致非细胞自主行为的原因 SMA小鼠的运动回路功能障碍。我们将利用小鼠遗传学和形态学和 功能分析。在目标2中，我们将调查钾离子的动态下调是否延迟 Kv2.1通道Kv2.1通过异常脱氧短链途径表达是导致Kv2.1表达下降的主要原因 在MN中，在SMA中重复发射。我们将使用胚胎干细胞分化的运动神经元与中间神经元共同培养 已经被设计成在抗生素暴露后下调SMN蛋白水平。此外，我们还将 利用小鼠模型确定报道的调节Kv2.1的三种主要酶的作用 在神经元中的表达。在目标3中，我们将扩大我们的初步研究，初步研究已确定减少 NT3在脊髓SMA发病早期，确定其在选择性脊髓损伤中的相对贡献 SMA小鼠运动回路的易损性。NT3在运动神经元中的特异性和选择性上调 肌肉将为NT3损伤的来源提供进一步的见解。

Project Summary Motor circuits control fundamental behaviors such as swallowing, breathing and locomotion. Spinal motor neurons are the key mediators translating motor commands generated within the central nervous system to peripheral muscle targets. Motor neurons are activated by a precisely regulated pattern of synaptic activity from sensory neurons, local spinal interneurons and descending pathways from the brain. During early development, synaptic activity received by motor neurons shapes their functional properties. In contrast, gene mutations that induce perturbations in either neuronal wiring or synaptic drive received by motor neurons often result in motor system disorders. A prominent example of this situation is spinal muscular atrophy (SMA)—an inherited neuromuscular disease caused by ubiquitous deficiency in the survival motor neuron (SMN) protein. SMA pathogenesis involves alterations of multiple components of the motor circuit leading to abnormalities in spinal reflexes, motor neuron loss and skeletal muscle atrophy. However, the molecular, cellular and circuit mechanisms underlying SMA remain largely elusive. Our previous work have led us in uncovering novel molecular perturbations involving the downregulation of the "delayed rectifier" potassium channel Kv2.1 as an important determinant in the regulation of motor neuron firing. In addition, SMA motor neurons are under increased tonic inhibitory originating from pre-motor inhibitory interneurons. Finally, we have identified reduction of neurotrophin 3 (NT3) as a candidate for the selective vulnerability of motor circuits responsible for activating proximal muscles which are more vulnerable compared to distal muscles. In Aim 1, we will study whether increased inhibitory synaptic drive on motor neurons, acting non-cell autonomously, is responsible for motor circuit dysfunction in SMA mice. We will employ mouse genetics together with morphological and functional assays. In Aim 2, we will investigate whether the dynamic downregulation of the potassium "delayed rectifier" channel Kv2.1 expression through abnormal dephopshorylation is a major contributor for the reduction in MN repetitive firing in SMA. We will use ES-differentiated motor neurons co-cultured with interneurons that have been engineered to downregulate SMN protein levels following antibiotic exposure. In addition, we will use mouse models to determine the contribution of the main three enzymes reported to regulate Kv2.1 expression in neurons. In Aim 3, we will expand on our preliminary studies, which has identified reduction of NT3 in SMA spinal cords early in the disease onset, to determine its relative contribution in the selective vulnerability of motor circuits in SMA mice. Specific and selective upregulation of NT3 in motor neurons or muscles will provide further insights into the source of NT3 impairment.