From the VIB Center for the Biology of Disease, the Center for Human Genetics and Leuven Institute for Neurodegenerative Diseases, University of Leuven.
the VIB Switch Laboratory, the Switch Laboratory, Department of Cellular and Molecular Medicine.
J Biol Chem. 2014 Nov 7;289(45):30977-89. doi: 10.1074/jbc.M114.599027. Epub 2014 Sep 24.
Missense mutations in alanine 673 of the amyloid precursor protein (APP), which corresponds to the second alanine of the amyloid β (Aβ) sequence, have dramatic impact on the risk for Alzheimer disease; A2V is causative, and A2T is protective. Assuming a crucial role of amyloid-Aβ in neurodegeneration, we hypothesized that both A2V and A2T mutations cause distinct changes in Aβ properties that may at least partially explain these completely different phenotypes. Using human APP-overexpressing primary neurons, we observed significantly decreased Aβ production in the A2T mutant along with an enhanced Aβ generation in the A2V mutant confirming earlier data from non-neuronal cell lines. More importantly, thioflavin T fluorescence assays revealed that the mutations, while having little effect on Aβ42 peptide aggregation, dramatically change the properties of the Aβ40 pool with A2V accelerating and A2T delaying aggregation of the Aβ peptides. In line with the kinetic data, Aβ A2T demonstrated an increase in the solubility at equilibrium, an effect that was also observed in all mixtures of the A2T mutant with the wild type Aβ40. We propose that in addition to the reduced β-secretase cleavage of APP, the impaired propensity to aggregate may be part of the protective effect conferred by A2T substitution. The interpretation of the protective effect of this mutation is thus much more complicated than proposed previously.
淀粉样前体蛋白（APP）中丙氨酸 673 的错义突变，与淀粉样 β（Aβ）序列的第二个丙氨酸相对应，对阿尔茨海默病的风险有巨大影响；A2V 是致病的，而 A2T 是保护性的。鉴于淀粉样蛋白-Aβ 在神经退行性变中的关键作用，我们假设 A2V 和 A2T 突变会导致 Aβ 性质的明显变化，这至少可以部分解释这两种完全不同的表型。使用人 APP 过表达原代神经元，我们观察到 A2T 突变体中 Aβ 生成显著减少，而 A2V 突变体中 Aβ 生成增强，这证实了先前来自非神经元细胞系的数据。更重要的是，硫黄素 T 荧光测定显示，这些突变对 Aβ42 肽聚集几乎没有影响，但极大地改变了 Aβ40 池的性质，A2V 加速了 Aβ 肽的聚集，而 A2T 则延缓了聚集。与动力学数据一致，Aβ A2T 在平衡时的溶解度增加，这种效应也在 A2T 突变体与野生型 Aβ40 的所有混合物中观察到。我们提出，除了 APP 的β-分泌酶切割减少之外，聚集倾向受损可能是 A2T 取代赋予保护作用的一部分。因此，对该突变的保护作用的解释比之前提出的要复杂得多。
