Innate Immune Mechanisms of Motor Neuron Injury

描述（由申请人提供）：健康相关性：神经退行性疾病的一个中心问题是特定神经元群体如何经历细胞死亡。运动神经元的选择性变性发生在各种损伤的环境中，包括RNA病毒如HIV和西尼罗河病毒，以及广泛表达的基因如SOD 1的遗传突变。目前还不清楚为什么普遍表达的蛋白质，或者为什么不是特异性嗜神经的病毒，应该使运动神经元选择性地容易死亡。运动神经元的选择性脆弱性可能与其独特的代谢需求有关，或者，它们可能拥有一系列有利于细胞死亡途径的蛋白质。我们已经确定了TLR 3的表达，先天免疫模式识别受体的双链RNA，在多个神经元群体。虽然TLR 3在所有检查的神经元中表达，但皮质神经元或感觉神经元的激活对细胞存活没有影响。相反，TLR 3的激活导致原代分离脊髓培养物中运动神经元的选择性丧失。在新生小鼠中施用TLR 3激动剂导致腹角内胰岛-1阳性神经元的损失。选择性运动神经元死亡的原因可能是观察到TLR 3招募细胞死亡激活或抑制蛋白，并且我们发现其激活仅在运动神经元中诱导切割的caspase-3。长期目标：我们的长期目标是确定TLR 3在运动神经元疾病转化模型中作为运动神经元死亡的潜在介导者的功能。我们的假设是，TLR 3通路的激活诱导运动神经元的选择性死亡，作为其独特的脆弱性的结果。研究方法：在目标1中，我们将通过扩展我们现有的初步数据和研究所涉及的细胞机制，进一步研究运动神经元对TLR 3介导的死亡的选择性脆弱性。与运动神经元相比，将评估不同神经元群体在TLR 3活化后的细胞死亡。然后，我们将使用神经胶质-神经元共培养物确定TLR 3是否在运动神经元中自主地起作用以引起死亡，或者TLR 3是否在另外的神经胶质细胞类型中起作用以引起运动神经元死亡。我们还将通过比较TLR 3敲除与菌株匹配的对照来确定TLR 3在新生动物和成年动物中是否在体内起作用以诱导运动神经元的选择性死亡。在目标2中，我们将研究TLR 3介导运动神经元选择性死亡的分子基础。我们将使用细胞培养和体内模型确定近端衔接蛋白TRIF是否是TLR 3介导的运动神经元死亡所必需的。我们将研究TLR 3信号传导的基本分支点，以确定NF-κ B和caspase-8激活的平衡是否有利于运动神经元的细胞死亡和其他神经元类型的细胞存活。由于病毒和天然细胞配体都存在TLR 3，因此该途径代表了感染，细胞损伤和运动神经元疾病之间新的独特联系。公共卫生相关性：选择性运动损伤发生在许多神经退行性疾病中，例如原发性侧索硬化症、纯粹遗传性痉挛性截瘫、肯尼迪病、脊髓性肌萎缩症、进行性肌萎缩症和肌萎缩性侧索硬化症，以及病毒性疾病，例如脊髓灰质炎、艾滋病毒和西尼罗河。为什么特定的运动神经元群体选择性地易受与这些疾病相关的遗传和环境条件的影响，目前尚不清楚。我们已经确定了一种名为TLR 3的受体存在于所有神经元上，当激活时，只会导致运动神经元死亡。本申请继续研究，以确定这一发现与运动神经元疾病的相关性。

DESCRIPTION (provided by applicant): Health Relatedness: A central question in neurodegenerative diseases is how specific populations of neurons undergo cell death. Selective degeneration of motor neurons occurs in the setting of diverse insults including RNA viruses such as HIV and West Nile, and in heritable mutations of ubiquitously expressed genes such as SOD1. It is unclear why proteins that are ubiquitously expressed, or why viruses that are not specifically neurotropic, should render motor neurons selectively vulnerable to death. The selective vulnerability of motor neurons may relate to their unique metabolic demands or, alternatively, they may possess a repertoire of proteins that contextually favor cell-death pathways. We have identified expression of TLR3, an innate immune pattern recognition receptor for duplex RNA, on multiple neuronal populations. While TLR3 is expressed in all neurons examined, activation on cortical neurons or sensory neurons has no effect on cell survival. By contrast, activation of TLR3 results in selective loss of motor neurons in primary dissociated spinal cord cultures. Administration of a TLR3 agonist in neonatal mice results in a loss of islet-1 positive neurons within the ventral horns. A clue into the cause of selective motor neuron death may be the observation that TLR3 recruits either cell-death activating or repressing proteins and we found its activation induces cleaved caspase-3 in motor neurons exclusively. Long-term goals: Our long-term goal is to define the function of TLR3 as a potential mediator of motor neuron death in translational models of motor neuron disease. Our hypothesis is that activation of the TLR3 pathway induces selective death in motor neurons as a consequence of their unique vulnerability. Research Approach: In aim 1, we will further investigate the selective vulnerability of motor neurons to TLR3 mediated death by expanding on our existing preliminary data and studying the cellular mechanisms involved. Different neuronal populations will be assessed for cell death following TLR3 activation in comparison to motor neurons. We will then determine if TLR3 functions autonomously in motor neurons to cause death or if TLR3 functions in an additional glial cell type to cause motor neuron death using glial- neuronal co-cultures. We will also determine if TLR3 functions in vivo, in both neonatal and adult animals, to induce selective death of motor neurons by comparing TLR3 knock-outs with strain matched controls. In aim 2 we will study the molecular basis by which TLR3 mediates selective death of motor neurons. We will determine if the proximal adaptor protein TRIF is necessary for TLR3 mediated death of motor neurons using cell culture and in vivo models. We will examine the essential branch points of TLR3 signaling to determine if the balance of NF-kB and caspase-8 activation favors cell death in motor neurons and cell survival in other neuronal types. Since both viral and native cellular ligands exist for TLR3, this pathway represents a new and unique link between infection, cell injury, and motor neuron disease. PUBLIC HEALTH RELEVANCE: Selective motor injury occurs in a number of neurodegenerative diseases such as Primary Lateral Sclerosis, pure Hereditary Spastic Paraplegia, Kennedy's disease, Spinal Muscular Atrophy, Progressive Muscular Atrophy, and amyotrophic lateral sclerosis, as well as in viral diseases such as Polio, HIV, and West Nile. Why specific populations of motor neurons are selectively vulnerable to the genetic and environmental conditions associated with these diseases is unknown. We have identified a receptor termed TLR3 present on all neurons, that when activated, induces death to only motor neurons. This application pursues research to define the relevance of this finding to diseases of the motor neuron.