不同寡聚形式的Aβ42与细胞膜作用显示毒性差异

β-淀粉样蛋白（β-amyloid peptide, Aβ）与神经细胞膜的相互作用是阿尔茨海默症（Alzheimer’s disease, AD）发病的重要事件，但不同寡聚形式的Aβ与细胞膜相互作用的差异仍缺乏直接比较。本文通过膜天平、透射电子显微镜、Thioflavin T(ThT)和细胞毒性实验等方法，检测Aβ42单体、ADDL、原纤维等形式的β-淀粉样蛋白与磷脂膜的作用方式，分析不同形式淀粉样蛋白对细胞的毒性作用。结果显示，（1）单层膜的实验数据可以判断Aβ42单体和寡聚体插膜能力存在差异，Aβ42单体能插入磷脂单层膜内，而Aβ42 ADDL不具备插膜能力；（2）透射电镜和ThT荧光检测，定性定量地分析出不同聚集形式的Aβ42具有不同的纤维化能力，Aβ42单体纤维化能力最强，而Aβ42原纤维的纤维化能力次之，Aβ42ADDL很难形成纤维；（3）Aβ42单体细胞毒性较弱，而Aβ42 ADDL和原纤维的细胞毒性较强。由以上结果可以得出结论：在磷脂膜存在的条件下，Aβ42单体可以插入膜内并迅速形成无毒性的Aβ42纤维，因此，细胞毒性较弱。而ADDL及原纤维不能插入膜内，纤维化能力较弱，从而以寡聚体的形式发挥细胞毒性。将单体、ADDL及原纤维形式的Aβ42与细胞膜相互作用进行分析，将为Aβ42在AD中的毒性机制研究提供一定的参考。但各种寡聚体入胞的方式及毒性机制仍需要进一步研究。

Different Aggregation States of Aβ42 Lead to Varying Degrees of Toxicity through the Interaction with the Membranes

Interaction of Aβ42 with the cell membrane is an important event in the pathogenesis of Alzheimer disease (AD). However, very little work has been done to examine the interaction of different aggregation states of Aβ42 with the cell membranes in combination with their toxicity. Transmission electron microscopy (TEM), membrane balance, ThT assay and cytotoxicity test showed that: (1) Aβ42 monomers can be inserted into the phospholipid monolayer whereas ADDLs do not have the membrane insertion ability; (2) Transmission electron microscopy and ThT fluorescence analysis showed that different Aβ42 aggregation states have different abilities to form fibrils. The Aβ42 monomers had the strongest fibril formation propensity, whereas the Aβ42 protofibrils also had some propensity to form fibrils. Fibril formation from Aβ42 ADDLs was difficult. (3) Aβ42 monomer cytotoxicity was weak, and the cytotoxicity of Aβ42 ADDLs and protofibrils was very strong. This result suggests that the monomer rapidly inserts into the membrane to form fibrils, thus reducing its cytotoxicity. ADDLs and protofibrils do not have the ability to insert into the membranes therefore are cytotoxic. These toxic effects are probably caused by binding to the membrane receptors. These results will provide some reference for the study of the mechanism of Aβ42 toxicity in AD. However, the mechanism of endocytosis of various Aβ oligomers still needs further study.