The Abeta protein of Alzheimer's Disease is an antimicrobial peptide

描述（由申请人提供）：这份新的研究者申请详细介绍了一项鉴定阿尔茨海默病（AD）主要病理因子A ²正常功能的提案。A？最常被描述为淀粉样前体蛋白（APP）的偶然分解代谢副产物，没有功能作用。然而，A？和典型的人类抗菌肽（AMP）LL-37的详细比较揭示了在生理化学和生物活性方面惊人的相似性。被引用为A？的异常病理行为的性质和作用介导LL-37的正常功能。我们提出，A？的生理化学和生物学活性与作为先天免疫系统的抗菌肽的主要功能一致。与我们的假设一致，初步实验表明A？抑制八种临床重要微生物的生长，包括白色念珠菌、大肠杆菌、表皮葡萄球菌、肺炎链球菌、金黄色葡萄球菌、单核细胞增生李斯特菌、粪肠球菌和无乳链球菌。对于这些微生物中的至少两种，A？是比LL-37更有效的抗菌剂。此外，实验确定了抗A免疫耗竭减弱的AD脑匀浆中的抗微生物活性。从已知的A？的生理化学外推，我们还确定了LL-37的新型金属介导的寡聚化活性。寡聚化是AMP作用的关键步骤，初步实验表明A？寡聚体具有增强的抗微生物活性。与寡聚体在A？抗菌作用中的关键作用一致，我们的初步数据表明，将肽与细菌细胞孵育也会促进寡聚化。发现不同的细菌物种产生不同的A？寡聚体，包括高度神经毒性的SDS稳定的二聚体和三聚体。拟议的研究将使用临床微生物学和分子生物学的既定方法来表征A？的体外抗菌活性。此外，实验将研究寡聚体在A的抗菌作用中的作用，以及肽与微生物细胞的相互作用是否产生具有高神经毒性的物种。在我们提出的研究实验的最后阶段，将测试APP基因敲除小鼠对细菌性脑膜炎的抵抗力是否降低。相反，将测试在CNS中过表达A？的转基因小鼠对细菌性脑膜炎的抗性增加。 我们的项目是一个新的方法，长期以来，在很大程度上被忽视的方面的生物学。我们认为，这条调查路线很有可能产生真实的和新颖的见解，这将有助于改善A的病理行为的更好策略。 公共卫生相关性：拟议研究的关键推断是，与AD病理学（A？）最相关的生物分子通常作为抗微生物剂发挥作用，并且是先天免疫系统的组成部分。 如果得到验证，A？作为抗菌剂的鉴定提高了预防淀粉样变性的可能性，即通过先发制人地靶向刺激大脑先天免疫系统的病原体/损伤。其次，它确定了先天免疫系统的炎症途径作为调节A？生成的靶点。

DESCRIPTION (provided by applicant): This new investigator application details a proposal to identify the normal function of A¿, the leading pathological agent in Alzheimer's disease (AD). A¿ is most often characterized as an incidental catabolic byproduct of the amyloid precursor protein (APP) with no functional role. However, a detailed comparison of A¿ and the archetypical human antimicrobial peptide (AMP) LL-37 reveals striking similarities in physiochemical and biological activities. Properties and actions cited as abnormal pathological behavior for A¿ mediate normal functions of LL-37. We propose that the physiochemical and biological activities of A¿ are consistent with a primary function as an antimicrobial peptide of the innate immune system. Consistent with our hypothesis preliminary experiments show A¿ inhibits the growth of eight clinically important microorganisms, including Candida albicans, Escherichia coli, Staphylococcus epidermidis, Streptococcus pneumoniae, Staphylococcus aureus, Listeria monocytogenes, Enterococcus faecalis, and Streptococcus agalactiae. A¿ is a more potent antimicrobial agent than LL-37 for at least two of these microorganisms. Furthermore, experiments identified an antimicrobial activity in AD brain homogenates attenuated by anti-A¿ immunodepletion. Extrapolating from the known physiochemistry of A¿ we have also identified novel metal-mediated oligomerization activities for LL-37. Oligomerization is a key step in AMP action and preliminary experiments suggest A¿ oligomers have potentiated antimicrobial activity. Consistent with a key role for oligomers in A¿s antimicrobial action our preliminary data suggest incubation of the peptide with bacterial cells also promotes oligomerization. Different bacteria species were found to generate distinct A¿ oligomers, including highly neurotoxic SDS-stable dimers and trimers. The proposed study will use established methods from clinical microbiology and molecular biology to characterize the in vitro antimicrobial activity of A¿. In addition, experiments will investigate the role of oligomers in A¿s antimicrobial action and if interaction of the peptide with microbial cells generates species with high neurotoxicity. In the final phase of our proposed study experiments will test if APP knockout mice have reduced resistance to bacterial meningitis. Conversely, transgenic mice over-expressing A¿ in the CNS will be tested for increased resistance to bacterial meningitis. Our project is a fresh approach to a long standing and largely ignored aspect of A¿ biology. We feel this line of enquiry has a high probability of yielding real and novel insights that will facilitate better strategies for ameliorating the pathological actions of A¿. PUBLIC HEALTH RELEVANCE: The key inference of the proposed study is that the biomolecule most associated with AD pathology (A¿) normally functions as an antimicrobial agent and is a component of the innate immune system. If validated the identification of A¿ as an antimicrobial agent raises the possibility of preventing amyloidosis from starting by preemptive targeting of pathogens/insults that stimulate the brain's innate immune system. Secondly, it identifies the inflammatory pathways of the innate immune system as targets for modulating A¿ generation.