Innate immunity in Alzheimer's disease: Role of toll-like receptor signaling

描述（由申请人提供）：阿尔茨海默病（AD）患者的大脑中出现聚集的淀粉样蛋白（A）沉积。蓄积被认为是AD病因学中的因果事件。AD脑中的原纤维A2沉积伴随着先天性免疫应答，例如活化的小胶质细胞和增加的细胞因子水平。越来越多的证据支持这一假设，即激活的小胶质细胞，中枢神经系统中的先天免疫细胞，在AD进展中发挥关键作用：通过吞噬活性清除A？沉积物或释放细胞毒性物质。Toll样受体（TLR）是先天免疫系统中的一类模式识别受体。TLR的重要作用之一是激活吞噬细胞/小胶质细胞以响应包括病原体和受损宿主细胞的损伤，导致病原体、受损组织和累积废物的清除。我们假设这些保护功能是由MyD 88依赖性通路介导的，并且大脑中的A？负荷可以通过TLR 4信号转导来调节。我们将通过完成特定目标1和2来确定MyD 88依赖性通路和TLR 4信号传导在A？清除中的作用。我们进一步假设，脑中的负荷和认知功能由TLR 4效应细胞因子/趋化因子调节，这将通过进行Aim 3来测试。在目标4中，我们将检验以下假设：大脑中A ²的积累会诱导小胶质细胞中TLR 4信号传导功能障碍，导致AD患者和AD小鼠模型中A ²沉积的加剧。具体目的是（目的1）确定在MyD 88缺陷遗传背景下AD小鼠模型的脑A？负荷、炎症和行为缺陷，（目的2）确定脑A？负荷、炎症和行为缺陷，（目的3）确定MyD 88缺陷遗传背景下AD小鼠模型的脑A？负荷、炎症和行为缺陷，（目的4）确定MyD 88缺陷遗传背景下AD小鼠模型的脑A？负荷、炎症和行为缺陷。过表达TLR 4的AD小鼠模型中的负荷、炎症和行为缺陷，（目的3a）比较TLR 4野生型和突变型AD小鼠模型之间的脑细胞因子和趋化因子表达谱，（目的3b）通过腺相关病毒基因递送在脑中过表达TLR 4效应细胞因子和/或趋化因子，并确定AD小鼠模型中的脑A？负荷、炎症和行为缺陷，和（目的4）使用培养的小胶质细胞、AD小鼠模型和来自AD患者的组织样品，确定A？是否诱导TLR信号传导的功能障碍。本研究的长期目标是确定TLR信号传导及其效应细胞因子/趋化因子在AD进展中的作用。公共卫生相关性：阿尔茨海默病（AD）是老年痴呆症最常见的原因。然而，迄今为止，没有令人满意的治疗AD。AD患者在大脑中形成聚集的淀粉样蛋白2（A？）沉积。蓄积被认为是AD病因学中的因果事件。这项研究将阐明A？沉积物被清除的机制，并作为证明我们的新型细胞因子/趋化因子基因治疗方式是否有效治疗AD动物模型的原理证明。

DESCRIPTION (provided by applicant): Patients with Alzheimer's disease (AD) develop deposits of aggregated amyloid ¿-protein (A¿) in the brain. A¿ accumulation is thought to be a causal event in the etiology of AD. Fibrillar A2 deposits in AD brain are accompanied by innate immune responses such as activated microglia and increased levels of cytokines. Accumulating evidence supports the hypothesis that activated microglia, innate immune cells in the central nervous system, play a pivotal role in the AD progression: either clearing A¿ deposits by phagocytic activity or releasing cytotoxic substances. Toll-like receptors (TLRs) are a class of pattern-recognition receptors in the innate immune system. One of the important roles of TLRs is to activate phagocytes/microglia to respond to insults including pathogens and damaged host cells, leading to clearance of pathogens, damaged tissues and accumulated wastes. We hypothesize that these protective functions are mediated by MyD88-dependent pathways and that A¿ load in the brain can be modulated by TLR4 signaling. We will determine the roles of MyD88-dependent pathways and TLR4 signaling in A¿ clearance by completing the Specific Aim 1 and 2. We further hypothesize that A¿ load in the brain and cognitive functions are modulated by TLR4 effector cytokines/chemokines, which will be tested by performing Aim 3. In Aim 4, we will test the hypothesis that accumulation of A¿ in the brain induces dysfunction of TLR4 signaling in microglia resulting in exacerbation of A¿ deposition in AD patients and AD mouse models. Specific Aims are (Aim 1) to determine cerebral A¿ load, inflammation and behavioral deficits in AD mouse models on a MyD88-deficient genetic background, (Aim 2) to determine cerebral A¿ load, inflammation and behavioral deficits in AD mouse models that overexpress TLR4, (Aim 3a) to compare cerebral cytokine and chemokine expression profiles between TLR4 wild-type and mutant AD mouse models, (Aim 3b) to overexpress TLR4 effector cytokines and/or chemokines in the brain via adeno-associated virus gene delivery and determine cerebral A¿ load, inflammation and behavioral deficits in the AD mouse models, and (Aim 4) to determine whether A¿ induces dysfunction of TLR signaling, using cultured microglia, AD mouse models and tissue samples from AD patients. The long term goal of this research is to determine the roles of TLR signaling and its effector cytokines/chemokines in the AD progression. PUBLIC HEALTH RELEVANCE: Alzheimer's disease (AD) is the most common cause of dementia in the elderly. To date, however, no satisfactory treatments are available for AD. Patients with AD develop deposits of aggregated amyloid 2 protein (A¿) in the brain. A¿ accumulation is thought to be a causal event in the etiology of AD. This study will elucidate the mechanisms by which A¿ deposits are cleared and serve as a proof of principle to demonstrate if our novel cytokine/chemokine gene therapy modality is effective in treating an animal model of AD.