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

描述(由申请人提供)：这一新的研究人员申请详细说明了一项关于确定阿尔茨海默病(AD)的主要病原体A？的正常功能的建议。最常见的特征是淀粉样前体蛋白(APP)附带的分解代谢副产物，没有任何功能作用。然而，将A？与典型的人类抗菌肽(AMP)LL-37进行详细比较，发现其在物理化学和生物活性上具有惊人的相似之处。被引用为异常病理行为的性质和行为介导了LL-37的正常功能。我们认为Aβ的理化和生物活性与其作为天然免疫系统的抗菌肽的主要功能是一致的。与我们的假设一致，初步实验表明，A？抑制了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、单核细胞增生性李斯特菌、粪肠球菌和无乳链球菌。对于这些微生物中的至少两种，A？是一种比LL-37更有效的抗菌剂。此外，实验还证实了AD脑匀浆中的一种抗微生物活性，该活性可通过抗A免疫耗竭而减弱。从已知的A的物理化学推断，我们还发现了LL-37的新的金属介导的齐聚活性。齐聚是AMP作用的关键步骤，初步实验表明，A？齐聚物具有增强抗菌活性的作用。与低聚物在S抗菌作用中的关键作用相一致，我们的初步数据表明，该肽与细菌细胞孵育也促进了寡聚化。不同的细菌种类被发现产生不同的A？寡聚体，包括高度神经毒性的十二烷基硫酸钠稳定的二聚体和三聚体。这项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，实验还将调查低聚物在S抗菌作用中的作用，以及该肽与微生物细胞的相互作用是否会产生具有高神经毒性的物种。在我们提议的研究的最后阶段，实验将测试APP基因敲除小鼠是否降低了对细菌性脑膜炎的抵抗力。相反，在中枢神经系统中过度表达A？的转基因小鼠将被测试增强对细菌性脑膜炎的抵抗力。我们的项目是对生物学中一个长期存在且基本上被忽视的方面的一种新的方法。我们认为，这条研究路线很有可能产生真实和新颖的见解，这将促进更好的策略来改善A？的病理行为。 公共卫生相关性：拟议研究的关键推论是，与AD病理(A？)最相关的生物分子通常作为抗菌剂发挥作用，是先天免疫系统的组成部分。如果被证实是一种抗菌剂，那么通过先发制人地瞄准刺激大脑固有免疫系统的病原体/侮辱来预防淀粉样变性的可能性增加了。其次，它将先天免疫系统的炎症途径确定为调节A？代的目标。

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.