Mechanisms of Central Synaptic Dysfunction in SMA

项目摘要 运动回路控制基本行为，如吞咽、呼吸和运动。脊髓运动 神经元是将中枢神经系统内产生的运动指令翻译成 外周肌肉目标。运动神经元是由精确调节的突触活动模式激活的 从感觉神经元、局部脊髓中间神经元和来自大脑的下行通路。早期 在发育过程中，运动神经元接受的突触活动塑造了它们的功能特性。相比之下， 在运动神经元接受的神经元布线或突触驱动中引起扰动的突变通常 导致运动系统障碍。这种情况的一个突出的例子是脊髓性肌萎缩症（SMA）-一种 由运动神经元存活蛋白（SMN）普遍缺乏引起的遗传性神经肌肉疾病。 SMA发病机制涉及运动回路的多个组成部分的改变，导致运动神经元的异常。 脊髓反射、运动神经元丧失和骨骼肌萎缩。然而，分子，细胞和电路 SMA的潜在机制在很大程度上仍然难以捉摸。我们之前的工作让我们发现了 分子扰动涉及“延迟整流”钾通道Kv2.1的下调， 运动神经元放电调节中的重要决定因素。此外，SMA运动神经元在 增强的紧张性抑制源自运动前抑制性中间神经元。最后，我们确定了 神经营养因子3（NT 3）的减少是运动回路选择性脆弱性的候选者， 激活与远端肌肉相比更脆弱的近端肌肉。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，非细胞自主地起作用，是否负责 SMA小鼠的运动回路功能障碍。我们将采用小鼠遗传学与形态学和 功能测定在目标2中，我们将研究钾离子的动态下调是否“延迟”， 通过异常去磷酸化的“整流”通道Kv2.1表达是减少细胞凋亡的主要原因。 在MN中，SMA中重复发射。我们将使用ES分化的运动神经元与中间神经元共培养， 已经被设计成在抗生素暴露后下调SMN蛋白水平。此外，我们将 使用小鼠模型来确定报道的调节Kv2.1的主要三种酶的贡献。 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，这些研究已经确定减少 NT 3在SMA脊髓中在疾病发作早期，以确定其在选择性脊髓损伤中的相对贡献。 SMA小鼠运动回路的脆弱性。NT 3在运动神经元中的特异性和选择性上调， 肌肉将提供对NT 3损伤来源的进一步了解。

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.