Water-soluble Abeta and its role in Alzheimer's disease

描述（由申请人提供）：阿尔茨海默病（AD）代表了个人和社会的悲剧，需要加速努力开发有效的治疗方法。强有力的遗传证据表明淀粉样蛋白前体蛋白（APP）及其蛋白水解衍生物与AD有关。一种主要的假设认为，APP的一个小的两亲性片段，即淀粉样蛋白b (Ab)，自我结合形成被松散地称为“寡聚物”的组装体，并引发一系列复杂的致病事件，最终导致痴呆。然而，Ab在人脑中的毒性形式及其与疾病的关系尚未得到严格的研究。鉴于阿尔茨海默病给全球医疗保健系统带来的不可持续的负担，有必要直接和迅速地解决有关Ab的作用以及如何最好地靶向Ab的科学疑问。十多年前，我们和其他人提出，某些非单体、非纤维形式的Ab是强效的神经毒素，可能是AD的沉淀剂。然而，这些“有毒低聚物”的确切生化特性仍不清楚。此外，虽然大量的Ab结构和活性研究都使用了人工合成的Ab肽，但现在很明显，脑源性Ab制剂对神经元的损害更大，而且比体外形成的Ab组装体更容易形成淀粉样蛋白。我们假设脑源性低聚物毒性活性的增强与不同Ab序列混合物的存在、翻译后修饰和/或共价交联的形成有关，所有这些都有助于增加毒性组合的稳定性。这在朊病毒疾病中似乎是正确的，我们预测Ab组装体的大小、构象和稳定性强烈影响它们的毒性活性。使用AD脑的水提取物，并基于大量的初步数据，我们建议严格调查：(i)组装大小，（ii）构象和（iii）有毒Ab物种的动态性质。在此基础上，提出了将其纯化为均匀的方法，并阐明了其组成。在整个实验过程中，我们将不断地将我们的物理分析与与AD直接相关的神经生物学活动的测量联系起来。此后，我们将分析死后组织，比较痴呆受试者与高斑块负担认知正常人群大脑中有毒低聚物的数量和质量。使用相同的人体组织，我们还将测量其他APP片段的水平，看看这些片段是否比Ab与疾病有更好的关系。然后，我们将检查接受AN1792疫苗接种的AD患者的脑组织和血浆。这个特殊实验的目的是确定疫苗接种如何影响人类大脑中Ab的水平和形式，以及是否一些免疫的患者产生能够靶向有毒低聚物的抗体。最后，从20个候选抗体中，我们将确定一个

DESCRIPTION (provided by applicant): Alzheimer's disease (AD) represents a personal and societal tragedy that demands an accelerated effort to develop effective therapies. Strong genetic evidence links the amyloid precursor protein (APP) and its proteolytic derivatives to AD. A leading hypothesis proposes that a small amphipathic fragment of APP, amyloid b-protein (Ab), self-associates to form assemblies loosely referred to as "oligomers", and that these trigger a complex pathogenic sequence of events that culminate in dementia. However, the toxic forms of Ab in human brain, and their relationship to disease have not been rigorously studied. Given the unsustainable burden that AD is placing on healthcare systems worldwide, it is essential that scientific doubts about the role of Ab and how it is best targeted are dealt with directly and swiftly. More than a decade ago, we and others proposed that certain non-monomeric, non-fibrillar forms of Ab are potent neurotoxins and may be the precipitating agent in AD. Yet the precise biochemical identity of these "toxic oligomers" remains unclear. Moreover, while the vast bulk of studies of Ab structure and activity have used synthetic Ab peptides, it is now apparent that brain-derived Ab preparations are much more damaging to neurons and much better seeds for amyloidogenesis than are Ab assemblies formed in vitro. We hypothesize that the enhanced toxic activity of brain-derived oligomers is related to the presence of mixtures of different Ab sequences, post-translational modifications and/or formation of covalent cross-links, all of which act to increase the stability of toxic assemblies. s appears to be true in prion diseases, we predict that the size, conformation and stability of Ab assemblies strongly influence their toxic activity. Using aqueous extracts of AD brains, and based on substantial preliminary data, we propose to investigate rigorously: (i) the assembly size, (ii) conformations and (iii) dynamic nature of toxic Ab species. Then we propose to purify them to homogeneity and to elucidate their composition. Throughout our experiments, we will constantly link our physical analyses with measures of neurobiological activity directly relevant to AD. Thereafter, we will analyze postmortem tissue to compare the quantity and quality of toxic oligomers in brains of demented subjects vs. cognitively normal humans with high plaque burdens. Using the same human tissues, we will also measure the levels of other APP fragments to see if any of these better relate to disease than does Ab. Then we will examine brain tissue and plasma from AD patients that received the AN1792 vaccination. The goal of this particular experiment is to ascertain how vaccination affects the levels and forms of Ab in the human brain and whether some immunized patients develop antibodies capable of targeting the toxic oligomers. Finally, from a selection of 20 candidate antibodies in hand, we will identify one that preferentially recognizes toxic oligomers. Then we expect to learn whether it can protect against Ab species in AD mouse models better than does the current lead therapeutic antibody, mAb266.