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

描述(申请人提供)：阿尔茨海默病(AD)患者在大脑中形成聚集的淀粉样蛋白(A？)沉积。在阿尔茨海默病的病因中，积聚被认为是一种因果事件。阿尔茨海默病脑内纤维状A2沉积伴随着先天免疫反应，如激活的小胶质细胞和升高的细胞因子水平。越来越多的证据支持这样的假设，即激活的小胶质细胞，即中枢神经系统中的先天免疫细胞，在AD的进展中发挥关键作用：要么通过吞噬活动清除沉积的A？，要么释放细胞毒性物质。Toll样受体是天然免疫系统中的一类模式识别受体。TLRs的重要作用之一是激活吞噬细胞/小胶质细胞对包括病原体和受损宿主细胞在内的伤害做出反应，从而清除病原体、受损组织和堆积的废物。我们假设这些保护功能是由MyD88依赖的通路介导的，大脑中的A？负荷可以通过TLR4信号来调节。我们将通过完成特定的目标1和2来确定MyD88依赖的通路和TLR4信号在A？清除中的作用。我们进一步假设A？在大脑中的负荷和认知功能受到TLR4效应细胞因子/趋化因子的调节，这将通过执行目标3来验证。在目标4中，我们将检验A？在大脑中的积累导致小胶质细胞中TLR4信号的功能障碍，从而加剧AD患者和AD小鼠模型中A？的沉积。具体目标是(目标1)确定MyD88缺乏遗传背景的AD小鼠模型的脑A负荷、炎症和行为缺陷，(目标2)确定过度表达TLR4的AD小鼠模型的脑A负荷、炎症和行为缺陷，(目标3a)比较TLR4野生型和突变型AD小鼠模型的脑细胞因子和趋化因子表达谱，(目标3b)通过腺相关病毒基因传递在脑内过表达TLR4效应细胞因子和/或趋化因子，并确定AD模型中的脑A负荷、炎症和行为缺陷，以及(目的4)利用培养的小胶质细胞、AD小鼠模型和AD患者的组织样本，确定A是否导致TLR信号转导功能障碍。本研究的长期目标是确定TLR信号及其效应细胞因子/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)是导致老年人痴呆症的最常见原因。然而，到目前为止，还没有令人满意的治疗AD的方法。阿尔茨海默病患者会在大脑中形成聚集的淀粉样蛋白2(A？)。在阿尔茨海默病的病因中，积聚被认为是一种因果事件。这项研究将阐明A？沉积被清除的机制，并作为原则证明，证明我们新的细胞因子/趋化因子基因治疗方式在治疗AD动物模型中是否有效。

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.