Department of Biophysics, University of Michigan, Ann Arbor, MI, USA.
Biophys J. 2013 Feb 19;104(4):894-903. doi: 10.1016/j.bpj.2012.12.051.
Soluble oligomers of the amyloid-β peptide have been implicated as proximal neurotoxins in Alzheimer's disease. However, the identity of the neurotoxic aggregate(s) and the mechanisms by which these species induce neuronal dysfunction remain uncertain. Physiologically relevant experimentation is hindered by the low endogenous concentrations of the peptide, the metastability of Aβ oligomers, and the wide range of observed interactions between Aβ and biological membranes. Single-molecule microscopy represents one avenue for overcoming these challenges. Using this technique, we find that Aβ binds to primary rat hippocampal neurons at physiological concentrations. Although amyloid-β(1-40) as well as amyloid-β(1-42) initially form larger oligomers on neurites than on glass slides, a 1:1 mix of the two peptides result in smaller neurite-bound oligomers than those detected on-slide or for either peptide alone. With 1 nM peptide in solution, Aβ40 oligomers do not grow over the course of 48 h, Aβ42 oligomers grow slightly, and oligomers of a 1:1 mix grow substantially. Evidently, small Aβ oligomers are capable of binding to neurons at physiological concentrations and grow at rates dependent on local Aβ42:Aβ40 ratios. These results are intriguing in light of the increased Aβ42:Aβ40 ratios shown to correlate with familial Alzheimer's disease mutations.
淀粉样蛋白-β肽的可溶性低聚物已被认为是阿尔茨海默病的近端神经毒素。然而，神经毒性聚集物的身份以及这些物质诱导神经元功能障碍的机制仍不确定。生理相关的实验受到肽的内源性浓度低、Aβ 低聚物的亚稳性以及 Aβ与生物膜之间广泛存在的相互作用的阻碍。单分子显微镜代表了克服这些挑战的一种途径。使用这种技术，我们发现 Aβ在生理浓度下与原代大鼠海马神经元结合。尽管淀粉样蛋白-β（1-40）和淀粉样蛋白-β（1-42）最初在神经突上形成比在载玻片上更大的低聚物，但两种肽的 1:1 混合物导致与神经突结合的低聚物比在载玻片上或单独使用任何一种肽检测到的低聚物都小。在溶液中含有 1 nM 肽的情况下，Aβ40 低聚物在 48 小时内不会生长，Aβ42 低聚物略有生长，而 1:1 混合物的低聚物则大量生长。显然，小的 Aβ 低聚物能够以生理浓度与神经元结合，并且其生长速度取决于局部 Aβ42:Aβ40 比值。鉴于与家族性阿尔茨海默病突变相关的 Aβ42:Aβ40 比值增加，这些结果令人着迷。
