Stress and CRF Signaling in Alzheimer?s Disease Pathogenesis

描述(申请人提供)：压力是老年性神经退行性疾病的一个促成因素，如阿尔茨海默病(AD)，阿尔茨海默病(AD)的定义是由β-淀粉样蛋白(A？)组成的斑块的积累和由细胞骨架蛋白tau的过度磷酸化形式组成的神经纤维缠结。应激导致这些AD特征的方式仍有待阐明。我们发现，急性暴露在情绪应激源(身体束缚)下会引起小鼠海马区tau磷酸化(tau-P)的显著增加，tau-P是学习和记忆中的关键结构。我们未能在这方面涉及应激诱导的糖皮质激素分泌，但发现这种反应被通过1型促肾上腺皮质激素释放因子受体(CRFR1)的信号中断而取消，并在CRFR2缺陷的小鼠中被夸大。此外，虽然急性束缚诱导的海马tau-P的增加是短暂的，但重复的每日应激(14天)会导致tau-P的累积增加，并以不溶于致病前的形式储存。通过生化、组织化学、神经解剖学和行为学分析，提出了五个目标，以进一步探讨应激和CRF信号系统在AD发病机制中的作用。首先，我们将确定急性束缚诱导的tau-P是否推广到AD患者的其他脑区，以及效力和种类不同的其他应激源，并探索反应背后的生化机制。其次，为了确定潜在的回路，我们将使用报告CRFR表达的转基因小鼠来表征应激诱导的tau-P(和细胞激活)的位置，使用逆行追踪和组织化学相结合的方法来确定含有CRF配体的海马区输入的来源，然后实验测试涉及的神经通路。第三，我们将表征反复暴露于情绪应激对tau-P和A？产生的影响，并探讨其机制和CRFR依赖。免疫电子显微镜将被用来寻找重复应激导致致病前tau聚集体形成的初步证据。第四，我们将评估在AD小鼠模型中以及在正常衰老中，在很大一部分生命周期内应激暴露对tau和A？发病机制的组织化学、生化和行为指标的调节能力，并确定观察到的影响的CRFR依赖性。最后，我们将利用一个独特的大脑材料储存库，该库来自人类AD患者，在生前对应激敏感性和认知障碍指数进行了彻底的表征，以确定CRF信号分子在AD中的表达是如何改变的，以及这种改变可能在多大程度上与行为指标相关。这些结果有望阐明(1)情绪应激暴露揭示AD相关tau和A？发病机制的能力，(2)这种影响背后的神经回路和生化机制，以及(3)它们通过CRFR信号介导/调节的程度，这很可能被证明是值得考虑的AD治疗干预的靶点。与公共卫生相关阿尔茨海默病是一种进行性的、与年龄相关的神经退行性疾病，影响记忆和其他高级大脑功能，目前约有500万美国人受到这种疾病的困扰。这个项目建立在我们最近的发现基础上，即阿尔茨海默病中涉及的一个关键生化过程可以通过单次或重复暴露于日常生活中遇到的那种压力来刺激，并且阻断大脑中的特定神经递质系统可以消除压力的这种潜在有害影响。为了加深对这些影响背后的大脑电路和机制的理解，拟议的实验将评估一个合法的候选靶点，用于开发可能减缓或预防阿尔茨海默病进展的药物。

DESCRIPTION (provided by applicant): Stress is implicated as a contributing factor in age-related neurodegenerative disorders such as Alzheimer's Disease (AD), which is defined by the accumulation of plaques composed of ¿-amyloid (A¿) and neurofibrillary tangles consisting of hyperphosphorylated forms of the cytoskeletal protein, tau. The means by which stress contributes to these AD hallmarks remain to be elucidated. We have found that acute exposure to an emotional stressor (physical restraint) elicits robust increases in tau phosphorylation (tau-P) in mouse hippocampus, a pivotal structure in learning and memory. We fail to implicate stress-induced glucocorticoid secretion in this respect, but find the response is abolished by disruption of signaling via the type 1 corticotropin-releasing factor receptor (CRFR1) and exaggerated in CRFR2-deficient mice. Moreover, while acute restraint-induced increments in hippocampal tau-P were short-lived, repeated daily stress sessions (14 days) led to cumulative increases in tau-P and its sequestration in insoluble, pre-pathogenic form. Five aims employing a range of biochemical, histochemical/neuroanatomical and behavioral assays are proposed to further explore the role of stress and the CRF signaling system in mechanisms of AD pathogenesis. First, we will determine whether acute restraint-induced tau-P generalizes to other brain regions afflicted in AD, other stressors that differ in potency and kind, and probe the biochemical mechanisms underlying the response. Second, to define the underlying circuitry, we will characterize sites of stress-induced tau-P (and cellular activation) using transgenic mice that report CRFR expression, use combined retrograde tracing and histochemical methods to identify sources of CRF ligand-containing inputs to hippocampus, and then test experimentally the involvement of implicated neural pathways. Third, we will characterize the effects of repeated exposure to emotional stress on tau-P and A¿ production, and explore their mechanisms and CRFR-dependence. Immunoelectron microscopy will be used to pursue preliminary evidence that repeated stress results in the formation of pre-pathogenic tau aggregates. Fourth, we will assess the ability of stress exposure over a significant portion of lifespan to modulate histochemical, biochemical and behavioral indices of tau and A¿ pathogenesis in a murine model of AD, as well as in normal aging, and determine the CRFR-dependence of observed effects. Finally, we will take advantage of a unique repository of brain material from human AD patients thoroughly characterized antemortem on indices of stress sensitivity and cognitive impairment to determine how the expression of CRF signaling molecules is altered in AD, and the extent to which such alterations may correlate with behavioral measures. The results are expected to clarify (1) the capacity of emotional stress exposure to promulgate AD- related tau and A¿ pathogenesis, (2) the neural circuitry and biochemical mechanisms underlying such effects, and (3) the extent to which they are mediated/modulated by signaling through CRFRs, which may well prove to warrant consideration as targets for therapeutic intervention in AD. PUBLIC HEALTH RELEVANCE Alzheimer's Disease is a progressive, age-related neurodegenerative disorder affecting memory and other higher brain functions, which currently afflicts roughly five million Americans. This project builds on our recent finding that a key biochemical process involved in Alzheimer's Disease can be stimulated by single or repeated exposures to stresses of the kind encountered in everyday life, and that blocking a particular neurotransmitter system in the brain can eliminate this potentially deleterious effect of stress. In deepening understanding of the brain circuits and mechanisms underlying these effects, the proposed experiments will evaluate a legitimate candidate target for the development of drugs that may slow or prevent the progression of Alzheimer's Disease.