Investigating the strain-specific role of Bacteroides in the etiology of Alzheimer's disease

项目摘要 虽然已提出感染性病因学参与阿尔茨海默氏症的起始和进展， 疾病（AD），需要更多的证据来支持特定感染因子的作用，并确定 他们采取行动的机制。鉴于AD的慢性性质以及我们在动物模型中的发现， 我们推测，慢性和亚急性感染的特定拟杆菌菌株有助于AD 通过影响Ab和tau的磷酸化、聚集和清除，并导致神经元毒性。在 为了支持我们的假设，我们是第一个证明拟杆菌不仅与抗体相关的小组。 在大脑中的水平，但实际上增加了淀粉样斑块时，给药的动物模型的AD。引人注目的是， 拟杆菌在AD中升高，与Ab42和磷酸化tau的CSF水平相关，并且与AD相关。 AD患者的肠道炎症标志物，表明与人类疾病直接相关。在我们的初步调查中 数据，我们发现，B。fragilis影响参与APP和tau磷酸化的基因的皮质表达， 促进它们的聚集，以及与记忆和神经元死亡相关的基因。我们还发现 拟杆菌下调小胶质细胞基因的抗体清除的重要性。类杆菌的消耗， 甲硝哒唑减少淀粉样斑块，增加皮质胰岛素降解酶的表达，从而 可以降解Ab，并影响参与多种蛋白质降解途径的基因。我们发现 类杆菌在体内外均能损害巨噬细胞Ab的吞噬功能。重要的是我们发现 从AD患者到小鼠的人类肠道微生物群影响了与蛋白质相关的类似小胶质细胞基因， 降解和清除，以及与神经元细胞死亡相关的途径，表明AD肠道 微生物群可能隐藏有助于疾病过程的感染因子。因为拟杆菌 在人类中高度流行，并且在菌株之间表现出高度的功能变异， 所有拟杆菌都与AD有关。在这个建议中，我们将修改科赫的假设，以检测拟杆菌菌株 与AD相关联，与健康对照和非AD痴呆对照相比，在纯培养物中分离这些菌株， 使用体外试验优化体内研究的菌株选择。然后，我们将AD衍生菌株转移至WT 小鼠和AD动物模型，测量AD病理学，并重新分离我们的AD衍生菌株，以确定 它们是否起着因果作用。为了研究潜在的机制，我们还将研究AD菌株是否 可能影响APP和tau蛋白的聚集和清除，神经元毒性，或破坏转录网络， 小胶质细胞和神经元。通过研究AD中拟杆菌的分子和功能多样性， 有潜力在拟杆菌中鉴定新的致病因子， AD的治疗。

PROJECT SUMMARY While an infectious etiology has been proposed to be involved in the initiation and progression of Alzheimer’s disease (AD), more evidence is needed to support the roles of specific infectious agents and to identify mechanisms by which they act. Given the chronic nature of AD and based on our discoveries in animal models of AD, we hypothesize that a chronic and sub-acute infection with specific Bacteroides strains contributes to AD by affecting Ab and tau phosphorylation, aggregation, and clearance, and contributing to neuronal toxicity. In support of our hypothesis, we were the first group to demonstrate that Bacteroides not only correlated with Ab levels in the brain, but actually increased amyloid plaques when administered to animal models of AD. Strikingly, Bacteroides is elevated in AD, correlates with CSF levels of Ab42 and phospho-tau, and is associated with markers of gut inflammation in AD patients, suggesting a direct relevance to human disease. In our preliminary data, we found that B. fragilis affected cortical expression of genes involved in APP and tau phosphorylation that promote their aggregation, as well as genes related to memory and neuronal death. We also found that Bacteroides downregulated microglial genes important for the clearance of Ab. Depletion of Bacteroides with metronidazole decreased amyloid plaques, increased cortical expression of insulin degrading enzyme, which can degrade Ab, and affected genes involved in multiple protein degradation pathways. We found that Bacteroides could impair macrophage Ab phagocytosis in vitro and in vivo. Importantly, we found that transfer of human gut microbiota from AD patients into mice affected similar microglia genes involved in protein degradation and clearance, as well as pathways related to neuronal cell death, suggesting that the AD gut microbiota may harbor infectious agents that contribute to the disease process. Because Bacteroides species are highly prevalent in humans and exhibit a high degree of functional variation among strains, it is not likely that all Bacteroides contribute to AD. In this proposal, we will modify Koch’s postulates to detect Bacteroides strains associated with AD vs. healthy controls and non-AD dementia controls, isolate these strains in pure culture, and use in vitro assays to optimize strain selection for in vivo studies. We will then transfer AD-derived strains to WT mice and animal models of AD, measure AD pathology, and re-isolate our AD-derived strains to determine whether they play a causal role. To investigate potential mechanisms, we will also investigate whether AD strains can affect APP and tau aggregation and clearance, neuronal toxicity, or disrupt transcriptional networks in microglia and neurons. By investigating the molecular and functional diversity in Bacteroides in AD, our studies have the potential to identify novel pathogenicity factors in Bacteroides that could be used both for the diagnosis and treatment of AD.