Mechanisms of neuronal injury during virus infection of the CNS

描述(申请人提供)：食源性和水源性微小核糖核酸病毒，如肠道病毒71型，是一个全球卫生问题。与神经毒性非脊髓灰质炎小核糖核酸病毒感染相关的神经系统并发症是一个严重的持续健康问题，特别是在儿童中。遗憾的是，小核糖核酸病毒对中枢神经系统(CNS)的损伤机制尚不清楚。我们认为先天免疫反应是急性感染时神经元死亡的重要原因。这与流行的假设相反，即神经元损失完全由病毒介导。虽然我们不怀疑一些神经元直接死于病毒感染，但我们的初步发现表明，某些群体，如海马区的CA1锥体神经元，是由先天免疫反应而不是病毒杀死的。我们用泰勒氏小鼠脑脊髓炎病毒建立了小鼠中枢神经系统微小核糖核酸病毒感染的模型，以直接测试中性粒细胞在启动神经细胞凋亡中的作用。我们的初步证据表明，在急性微小核糖核酸病毒感染中枢神经系统期间，许多未感染的CA1区锥体神经元经历了与氧化损伤、钙蛋白酶活性和半胱氨酸天冬氨酸酶活性相关的凋亡性死亡；这种损伤严重降低了空间记忆测试中的认知能力。我们进一步观察到，中性粒细胞在感染后数小时内渗入海马体。减少中性粒细胞的渗透具有神经保护作用，而将激活的中性粒细胞过继转移到中性粒细胞反应缺陷的小鼠体内会导致海马区损伤。最后，使用钙蛋白酶抑制剂治疗可以保护海马神经元免于死亡，并在不抑制炎症反应的情况下保留认知功能，而炎症反应是介导宿主防御和病毒清除所必需的。在这些观察的基础上，我们假设中性粒细胞在中枢神经系统的急性微小病毒感染期间通过钙蛋白酶依赖的机制杀死海马神经元。我们打算解决以下实验问题：1)中性粒细胞是杀死海马神经元的必要条件和充分条件吗？2)在中性粒细胞对急性中枢神经系统感染的反应诱导的海马神经元死亡过程中，Calain是关键的执行者吗？我们提出了几项创新，包括使用活体动物成像和中性粒细胞领养转移，以解决这些问题。我们建议的关键概念是，虽然炎症是宿主对病毒感染的关键防御措施，但炎症反应可能会间接杀死神经元，因此旨在防止神经元死亡而不阻碍对病毒的炎症控制的治疗性干预可能会保护宿主的功能。公共卫生相关性：某些食源性和水源性病毒具有感染大脑的能力。尽管成年人很容易感染，但儿童特别容易患上这种神经毒性感染。我们有来自小鼠模型的证据表明，认知功能的丧失伴随着海马神经元的死亡。我们也有证据表明，这种神经元死亡是由一种名为中性粒细胞的特定免疫细胞引起的，这些细胞试图从大脑中清除病毒。重要的是，我们发现，使用FDA批准的药物治疗可以保护神经元和认知功能，而不会改变免疫系统从大脑中清除病毒的能力。

DESCRIPTION (provided by applicant): Foodborne and waterborne picornaviruses such as enterovirus 71 are a global health issue. Neurologic complications associated with neurovirulent non-polio picornavirus infection are a serious ongoing health problem, especially in children. Unfortunately, the mechanisms of picornavirus-induced injury to the central nervous system (CNS) are unclear. We propose that the innate immune response is an important cause of neuron death during acute infection. This is in contrast to the prevailing hypothesis that neuron loss is mediated solely by virus. While we do not doubt that some neurons die directly as the result of viral infection, our preliminary findings suggest that certain populations, such as CA1 pyramidal neurons in the hippocampus, are killed by the innate immune response rather than by the virus. We have established a mouse model of picornavirus infection of the CNS using the Theiler's murine encephalomyelitis virus to directly test the role of neutrophils in the initiation of neuronal apoptosis. Our preliminary evidence indicates that during acute picornaviral infection of the CNS, many uninfected CA1 pyramidal neurons undergo apoptotic death associated with oxidative injury, calpain activity, and caspase activity; this injury severely reduces cognitive performance in a spatial memory test. We have further observed that neutrophils infiltrate the hippocampus within hours of infection. Reduced neutrophil infiltration is neuroprotective, while adoptive transfer of activated neutrophils into mice with a defective neutrophil response induces hippocampal injury. Finally, treatment with calpain inhibitors protects hippocampal neurons from death and preserves cognitive function without constraining the inflammatory response that is necessary to mediating host defense and viral clearance. On the basis of these observations we hypothesize that neutrophils kill hippocampal neurons via a calpain-dependent mechanism during acute picornaviral infections of the CNS. We intend to address the following experimental questions: 1) are neutrophils necessary and sufficient to kill hippocampal neurons?; 2) is calpain the key executioner of hippocampal neurons during death induced by the neutrophil response to acute CNS infection? We propose several innovations, including the use of live animal imaging and adoptive transfer of neutrophils, to address these questions. The key concept of our proposal is that while inflammation critically mediates host defense to virus infection, the inflammatory response may indirectly kill neurons, and therefore therapeutic interventions aimed at preventing neuronal death without thwarting inflammatory control of virus may preserve host function. PUBLIC HEALTH RELEVANCE: Certain foodborne and waterborne viruses have the ability to infect the brain. Although adults are susceptible, children are at particular risk for such neurovirulent infections. We have evidence from a mouse model that cognitive function is lost concomitantly with the death of hippocampal neurons. We also have evidence that this neuronal death is caused by a specific population of immune cells called neutrophils that are trying to clear the virus from the brain. Importantly, we have found that treatment with an FDA-approved drug protects neurons and cognitive function without altering the ability of the immune system to clear the virus from the brain.