Mechanisms of neuronal injury during virus infection of the CNS

描述（由申请人提供）：食源性和水传播的小核糖核酸病毒，如肠道病毒71是一个全球性的健康问题。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。不幸的是，小核糖核酸病毒对中枢神经系统（CNS）损伤的机制尚不清楚。我们认为先天免疫反应是急性感染中神经元死亡的重要原因。这与普遍认为神经元损失仅由病毒介导的假设相反。虽然我们不怀疑一些神经元直接因病毒感染而死亡，但我们的初步发现表明，某些群体，如海马中的CA1锥体神经元，是被先天免疫反应杀死的，而不是被病毒杀死的。我们利用Theiler氏小鼠脑脊髓炎病毒建立了小核糖核酸病毒感染中枢神经系统的小鼠模型，直接检测中性粒细胞在神经元凋亡启动中的作用。我们的初步证据表明，在急性小核糖核酸病毒感染中枢神经系统时，许多未感染的CA1锥体神经元发生与氧化损伤、calpain活性和caspase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表现。我们进一步观察到中性粒细胞在感染后数小时内浸润海马。中性粒细胞浸润减少对神经有保护作用，而将活化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引起海马损伤。最后，用钙蛋白酶抑制剂治疗可以保护海马神经元免于死亡，保持认知功能，而不限制介导宿主防御和病毒清除所必需的炎症反应。在这些观察的基础上，我们假设在中枢神经系统急性小核糖核酸病毒感染期间，中性粒细胞通过calpain依赖机制杀死海马神经元。我们打算解决以下实验问题：1)中性粒细胞是否足以杀死海马神经元？2)在急性中枢神经系统感染引起的中性粒细胞反应引起的死亡过程中，calpain是否是海马神经元的关键刽子手？我们提出了一些创新，包括使用活体动物成像和中性粒细胞过继转移，以解决这些问题。我们提出的关键概念是，虽然炎症介导宿主对病毒感染的防御，但炎症反应可能间接杀死神经元，因此旨在防止神经元死亡而不阻碍病毒的炎症控制的治疗干预可能保留宿主功能。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。虽然成人易受感染，但儿童尤其容易受到这种神经毒性感染。我们从小鼠模型中得到证据，认知功能随着海马神经元的死亡而丧失。我们也有证据表明，这种神经元死亡是由一种叫做中性粒细胞的特定免疫细胞群引起的，它们试图从大脑中清除病毒。重要的是，我们发现用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清除大脑病毒的能力。

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.