Castano E M, Prelli F, Wisniewski T, Golabek A, Kumar R A, Soto C, Frangione B
Department of Pathology, New York University Medical Center, NY 10016.
Biochem J. 1995 Mar 1;306 ( Pt 2)(Pt 2):599-604. doi: 10.1042/bj3060599.
A central event in Alzheimer's disease is the conformational change from normally circulating soluble amyloid beta peptides (A beta) and tau proteins into amyloid fibrils, in the form of senile plaques and neurofibrillary tangles respectively. The apolipoprotein E (apoE) gene locus has recently been associated with late-onset Alzheimer's disease. It is not know whether apoE plays a direct role in the pathogenesis of the disease. In the present work we have investigated whether apoE can affect the known spontaneous in vitro formation of amyloid-like fibrils by synthetic A beta analogues using a thioflavine-T assay for fibril formation, electron microscopy and Congo Red staining. Our results show that, under the conditions used, apoE directly promotes amyloid fibril formation, increasing both the rate of fibrillogenesis and the total amount of amyloid formed. ApoE accelerated fibril formation of both wild-type A beta-(1-40) and A beta-(1-40A), an analogue created by the replacement of valine with alanine at residue 18, which alone produces few amyloid-like fibrils. However, apoE produced only a minimal effect on A beta-(1-40Q), found in the Dutch variant of Alzheimer's disease. When recombinant apoE isoforms were used, apoE4 was more efficient than apoE3 at enhancing amyloid formation. These in vitro observations support the hypothesis that apoE acts as a pathological chaperone, promoting the beta-pleated-sheet conformation of soluble A beta into amyloid fibres, and provide a possible explanation for the association of the apoE4 genetic isoform with Alzheimer's disease.
阿尔茨海默病的一个核心事件是正常循环的可溶性淀粉样β肽（Aβ）和tau蛋白分别转变为淀粉样纤维，形成老年斑和神经原纤维缠结。载脂蛋白E（apoE）基因位点最近与晚发性阿尔茨海默病相关。目前尚不清楚apoE是否在该疾病的发病机制中起直接作用。在本研究中，我们使用硫黄素-T检测法检测纤维形成、电子显微镜和刚果红染色，研究了apoE是否能影响合成Aβ类似物在体外已知的自发形成淀粉样纤维的过程。我们的结果表明，在所使用的条件下，apoE直接促进淀粉样纤维的形成，提高了纤维形成的速率和形成的淀粉样物质的总量。apoE加速了野生型Aβ-(1-40)和Aβ-(1-40A)（一种在第18位残基处用丙氨酸替代缬氨酸产生的类似物，其单独形成的淀粉样纤维很少）的纤维形成。然而，apoE对在荷兰型阿尔茨海默病变体中发现的Aβ-(1-40Q)的影响很小。当使用重组apoE异构体时，apoE4在增强淀粉样物质形成方面比apoE3更有效。这些体外观察结果支持了apoE作为一种病理性伴侣蛋白发挥作用的假说，即促进可溶性Aβ的β折叠构象转变为淀粉样纤维，并为apoE4基因异构体与阿尔茨海默病的关联提供了一种可能的解释。
