Functional significance of amyloid dynamics and deposition in the AD brain

描述（申请人提供）：阿尔茨海默病的典型特征是淀粉样蛋白- β (Abeta)肽在大脑内的积累和沉积，这些过程是疾病发病机制的核心。一个关键的尚未解决的问题是，β肽如何相互作用形成多聚体，分布到不同的池中，并沉积成弥漫性和致密性斑块。最重要的是，不同的β蛋白如何干扰大脑功能仍然存在争议。人们普遍认为，可溶性多聚物种对突触功能的干扰是认知和记忆损伤的基础。也许最长久的争论围绕着淀粉样斑块的功能意义以及这些结构是否真的重要。该应用程序建议部署新发现的工具和生物分析来探索这些问题。阿尔茨海默病与大脑对β的清除受损有关，这一过程通常由载脂蛋白E （ApoE）促进。ApoE的表达是通过核受体过氧化物酶体增殖物激活受体（ppar β）和肝脏X受体（LXR）与类视黄醛X受体（RXR）的相互作用而转录诱导的。口服RXR激动剂bexarotene对阿尔茨海默病小鼠模型可在数小时内以载脂蛋白e依赖的方式增强可溶性β的清除。通过小胶质细胞介导的吞噬作用，斑块面积在72小时内减少了60%。此外，贝沙罗汀刺激了认知、社交和嗅觉缺陷的快速逆转，并改善了神经回路功能。RXR激动剂通过不同的机制促进可溶性和沉积形式的Abeta清除的能力的发现，为确定这些库如何作为年龄和疾病进展的函数相互关联提供了前所未有的机会。重要的是，这些研究具有治疗意义，因为它们将为贝沙罗汀治疗AD及其前驱状态的初始临床试验设计提供信息。此应用程序的目标是：目标1。建立脑内β池的动态及其功能意义。我们将在实验环境中探索间质液、“可溶性”β水平和斑块负担之间的关系，在实验环境中刺激可溶性β或斑块清除，并确定这些与神经网络活动和行为缺陷之间的关系。目标2。确定年龄和斑块负荷是否影响淀粉样斑块溶解和重组的动力学。我们将确定年龄和总体斑块负荷是否影响淀粉样斑块对小胶质细胞介导的清除的易感性。我们还将在不同年龄和初始斑块负荷的小鼠中确定斑块清除后的斑块重组率。目标3。确定β水平的降低是否会预防或延缓淀粉样蛋白沉积和行为损害。我们将测试长期增强Abeta清除是否会防止行为缺陷和淀粉样蛋白沉积的出现。目标4。目的：确定RXR激活是否刺激小胶质细胞向M2“替代”激活状态转化，并恢复其吞噬能力。我们拟在体外测试贝沙罗汀对小胶质细胞表型极化和吞噬活性的影响。这些研究将会

DESCRIPTION (provided by applicant): Alzheimer's disease is typified by the accumulation and deposition of amyloid-beta (Abeta) peptides within the brain and these processes are central to disease pathogenesis. A critical unresolved issue is how the Abeta peptides interact to form multimers, distribute into various pools and are deposited into both diffuse and compact plaques. Most importantly, it remains controversial how the diverse Abeta species act to perturb brain function. There is general agreement that soluble multimeric species subserve perturbation of synaptic function that underlies the impairment of cognition and memory. Perhaps the longest lived controversy revolves around the functional significance of amyloid plaques and whether these structures really matter. This application proposes to deploy newly discovered tools and biological assays to explore these questions. Alzheimer's disease is associated with impaired clearance of Abeta from the brain, a process normally facilitated by apolipoprotein E (ApoE). ApoE expression is transcriptionally induced through the action of the nuclear receptors peroxisome proliferator activated receptor (PPARbeta) and liver X receptors (LXR) through their interaction with retinoid X receptors (RXR). Oral administration of the RXR agonist, bexarotene, to a murine model of Alzheimer's disease resulted in enhanced clearance of soluble Abeta within hours in an apoE-dependent manner. Abeta plaque area was reduced >60% within just 72 hours through microglial-mediated phagocytosis. Furthermore, bexarotene stimulated the rapid reversal of cognitive, social, and olfactory deficits and improved neural circuit function. The discovery of the ability of RXR agonists to promote the clearance of soluble and deposited forms of Abeta through distinct mechanisms allows an unprecedented opportunity to determine how these pools are related to one another as a function of age and disease progression. Importantly, these studies are of therapeutic significance as they will inform the design of the initial clinical trials of bexarotene in AD and its prodromal states. The aims of this application are: Aim 1. To establish the dynamics of Abeta pools in the brain and their functional significance. We will explore the relationships between interstitial fluid, 'solube' Abeta levels and plaque burden in an experimental setting where either soluble Abeta or plaque clearance is stimulated and determine how these are related to deficits in neural network activity and behavior. Aim 2. To determine if age and plaque burden affect the kinetics of amyloid plaque dissolution and reformation. We will determine if age and overall plaque burden affects the susceptibility of amyloid plaques to microglial- mediated clearance. We will also determine the rate of plaque reformation following their clearance in mice of different ages and initial plaque burden. Aim 3. Determination of whether reduction in Abeta levels will prevent or delay amyloid deposition and behavioral impairment. We will test if long term enhancement of Abeta clearance will prevent the appearance of behavioral deficits and amyloid deposition. Aim 4. To ascertain if RXR activation provokes the conversion of microglia into M2 "alternative" activation states and restores their phagocytic competence. We propose to test the effects of bexarotene on the phenotypic polarization and phagocytic activity of microglia in vitro. These studies will be extended to the analysis APP/PS1 mice treated with bexarotene.