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。运动神经元被一种精确调节的突触活动模式激活， 感觉神经元、局部脊髓中间神经元和来自大脑的下行通路。在早期发育过程中， 由运动神经元接收的突触活动形成它们的功能特性。相反， 在运动神经元接收神经元布线或突触驱动中引起的扰动通常导致运动神经元 系统紊乱这种情况的一个突出的例子是脊髓性肌萎缩症（SMA）-一种遗传性 由运动神经元存活蛋白（SMN）普遍缺乏引起的神经肌肉疾病。SMA 发病机制涉及运动回路的多个组成部分的改变，导致脊髓损伤的异常。 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。我们之前的工作使我们发现了 导致突触丢失的分子机制，部分涉及经典的补体级联反应。 兴奋-抑制性神经传递的失衡使运动神经元在紧张性抑制下变得脆弱。 重要的是，SMA运动神经元通过涉及p53通路、Mdm 2和Mdm 3的细胞自主机制死亡。 Mdm 4以及SMN的下游靶标Stasimon。然而，分子和细胞机制 导致SMA小鼠姿势和运动缺陷的原因尚不清楚。因此解开了分子 负责这两种表型的机制将提供对疾病机制的关键见解。在 目的1、研究多巴胺能突触功能障碍是否是姿势障碍的原因 SMA小鼠。为了解决这个问题，我们将采用小鼠遗传学与形态和功能测定。 在目标2中，我们将研究腹侧脊髓小脑束神经元引起步态和运动缺陷的作用 SMA小鼠。我们还将使用小鼠遗传学，病毒介导的Cre表达，结合形态学， 生理和行为分析来完成这部分项目。在目标3中，我们将探讨分子 与CD 47和SIRPα相关的突触丢失机制以及与CD 47和SIRPα的潜在协同作用 C1 q，经典补体途径的起始蛋白，在小鼠普遍存在的SMN缺陷下 疾病的模型。

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 has led us in uncovering part of the molecular mechanisms responsible for synaptic loss, implicating in part the classical complement cascade. Imbalance of excitatory-inhibitory neurotransmission renders vulnerable motor neurons under tonic inhibition. Importantly, SMA motor neurons die through cell-autonomous mechanisms implicating p53 pathway, Mdm2 & Mdm4 as well as Stasimon, a downstream target of SMN. However, the molecular and cellular mechanisms responsible for postural and locomotor deficits in SMA mice are not known. Unraveling therefore the molecular mechanisms responsible for these two phenotypes would provide key insights into the disease mechanisms. In Aim 1, we will study whether dysfunction of dopaminergic synapses is responsible for the postural impairments in SMA mice. To address this, we will employ mouse genetics together with morphological and functional assays. In Aim 2, we will investigate the role of ventral spinocerebellar tract neurons causing gait and locomotor deficits in SMA mice. We will also use mouse genetics, viral-mediated Cre expression, combined with morphological, physiological and behavioral assays to complete this part of the project. In Aim 3, we will probe into the molecular mechanisms that are responsible for synaptic loss involving CD47 and SIRPα as well as potential synergy with C1q, the initiating protein in the classical complement pathway, under ubiquitous SMN deficiency in mouse models of the disease.