Stress and CRF Signaling in Alzheimer?s Disease Pathogenesis

描述（由申请人提供）：压力被认为是与年龄相关的神经退行性疾病的一个促成因素，如阿尔茨海默病（AD），其定义为由-淀粉样蛋白(a)组成的斑块积累和由细胞骨架蛋白tau的过度磷酸化形式组成的神经原纤维缠结。压力对这些AD特征的作用方式仍有待阐明。我们发现，急性暴露于情绪压力源（身体约束）会导致小鼠海马体中tau磷酸化（tau- p）的显著增加，海马体是学习和记忆的关键结构。我们未能将应激诱导的糖皮质激素分泌与这方面联系起来，但发现通过1型促肾上腺皮质激素释放因子受体（CRFR1）的信号被破坏而消除，并在crfr2缺陷小鼠中被夸大。此外，虽然急性抑制诱导的海马tau-P的增加是短暂的，但每天重复的应激过程（14天）导致tau-P的累积增加及其以不溶性、致病性前形式的封存。为了进一步探讨应激和CRF信号系统在AD发病机制中的作用，我们提出了五个目标，包括生化、组织化学/神经解剖学和行为分析。首先，我们将确定急性抑制诱导的tau-P是否会推广到阿尔茨海默病的其他大脑区域，以及其他在效力和种类上不同的应激源，并探讨这种反应的生化机制。其次，为了确定潜在的电路，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）位点，使用联合逆行追踪和组织化学方法来确定含有CRF配体的海马输入来源，然后通过实验测试相关神经通路的参与。第三，我们将描述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依赖性。免疫电子显微镜将用于寻找反复应激导致致病性前tau聚集体形成的初步证据。第四，我们将评估应激暴露在很大一部分生命周期内对AD小鼠模型以及正常衰老中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对crfr的依赖性。最后，我们将利用来自人类AD患者的独特脑材料库，在应激敏感性和认知障碍指标上全面表征死前特征，以确定AD中CRF信号分子的表达如何改变，以及这种改变与行为措施的关联程度。这些结果有望阐明(1)情绪应激暴露对AD相关tau和A¿发病机制的影响，(2)这些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，这可能证明有理由考虑作为AD治疗干预的目标。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，目前大约有500万美国人患有这种疾病。这个项目建立在我们最近发现的基础上，即阿尔茨海默病的一个关键生化过程可以被日常生活中遇到的那种压力单次或多次刺激，并且阻断大脑中特定的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脑回路和机制的理解，拟议的实验将评估一个合法的候选靶标，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.