| Summary: | 博士 === 國防醫學院 === 生命科學研究所 === 106 === Alzheimer’s disease (AD) has been discovered about one hundred years ago. Currently, it has become the most prevalent neurodegenerative disease in the elder population over age of 65. However, there is no cure within the elusive underlying pathogenic mechanisms, which leads to failure of large amount of clinical trials. So, it’s required to gain more insight from the basic mechanism of the AD. Here, we focused on characterizing the interaction of zinc (Zn) with the pathological hallmark, amyloid-β (Aβ), which are enriched in the senile plaques of brain of AD patients. To understand the characters of ZnAβ, we systematically mixed equal molar ratio of Zn2+ with Aβ and found both ZnAβ40 and ZnAβ42 form spherical species with diameter of 12~14 nm under this preparation and represent reduced of β-sheet content. A series of biophysical approached were applied to analyze the assembly, hydrophobic exposure, immunoreactivity of ZnAβ, which reveals distinct properties with Aβ-derived diffusible ligand (ADDLs). We further elucidate the β-sheet structure of ZnAβ40 and compared with Aβ40 fibrils by 13C site-specific labeled solid-state nuclear magnetic resonance (NMR). Removal of Zn2+ by EDTA also shifted ZnAβ oligomers back to fibrillization pathway within a faster conformational transition. In the cell model, ZnAβ oligomers were more toxic than ADDLs in the toxicity and viability assay. We also found that ZnAβ oligomers potently inhibited long-term potentiation (LTP) in the hippocampal slice of wild-type mice ex vivo. Besides characterizing the effect of Zn2+ on Aβ fibrillization, we also examined the fibrillar structures of various Aβ fibrils. We previously produced homo-fibrils of wild-type and three E22 variants of (E22G, E22K, and E22Q), and hetero-fibrils composed of equal molar of the wild type and each E22 mutant fibrils. Based on the previous result, we found E22K fibrils are most thermostable within maintain β-sheets at high temperature. We further performed seeding experiment to compare the seeding effect of seeds generated from WT and E22K fibrils after heated at high temperature. Interestingly, E22K fibril seeds maintain more seeding ability and immunoreactivity of anti-fibril antibody after heated at high temperature. Overall, we demonstrated that ZnAβ form toxic and off- pathway oligomers, and E22K mutation increases stability of Aβ fibril structure against high temperature. These findings provide more insights for future AD therapeutic development.
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