Hu William, Gray Noah W, Brimijoin Stephen
Int J Physiol Pathophysiol Pharmacol. 2009 Jan 1;1(1):15-24.
Amyloid-beta (Aβ), the main peptide constituent of senile plaques, is a suspected pathogenic mediator in Alzheimer's Disease (AD). Plaques also contain acetylcholinesterase (AChE), which may promote Aβ toxicity. We previously found that Aβ increased AChE levels in neuron-like N1E.115 neuroblastoma cells by reducing AChE degradation and surface shedding. Here we show that Aβ also alters the intracellular fate of surface AChE. When surface AChE was tagged with FITC-conjugated Fasciculin II (FasII), fluorescence gradually accumulated in intracellular particles. In the presence of extracellular Aβ this accumulation increased and shifted from the juxtanuclear zone to more peripheral cytoplasm. The cytoplasmic FasII-positive structures were positive for Lysosomal-Associated Membrane Protein 1, identifying them as late endosomes and early lysosomes. Thus, surface AChE trafficked into the lysosomal compartment, but further transport was impaired. Aβ also affected the transport or disposition of fluorescent dextran, an index of pinocytosis, and caused a 60% increase in intracellular accumulation similar to the lysosomotropic effects of chloroquine. On the other hand, Aβ caused no apparent changes in clathrin- and caveolae-mediated endocytosis. Overall it appears that selective alteration of endocytic mechanisms and an accumulation of organelles containing improperly processed substrates might contribute to the neuronal damage associated with age and disease-related accumulation of neurotoxic Aβ in the human brain.
β淀粉样蛋白（Aβ）是老年斑的主要肽成分，被怀疑是阿尔茨海默病（AD）的致病介质。斑块中还含有乙酰胆碱酯酶（AChE），它可能会促进Aβ的毒性。我们之前发现，Aβ通过减少AChE的降解和表面脱落来增加神经元样N1E.115神经母细胞瘤细胞中的AChE水平。在此我们表明，Aβ还会改变表面AChE的细胞内命运。当表面AChE用异硫氰酸荧光素（FITC）偶联的束状肌动蛋白II（FasII）标记时，荧光逐渐在细胞内颗粒中积累。在细胞外Aβ存在的情况下，这种积累增加，并从近核区转移到更多的外周细胞质。细胞质中FasII阳性结构对溶酶体相关膜蛋白1呈阳性，将它们鉴定为晚期内体和早期溶酶体。因此，表面AChE被转运到溶酶体区室，但进一步的转运受到损害。Aβ还影响了作为胞饮作用指标的荧光葡聚糖的转运或处置，并导致细胞内积累增加60%，类似于氯喹的溶酶体亲和效应。另一方面，Aβ对网格蛋白和小窝介导的内吞作用没有明显影响。总体而言，似乎内吞机制的选择性改变以及含有加工不当底物的细胞器的积累可能导致与人类大脑中与年龄和疾病相关的神经毒性Aβ积累相关的神经元损伤。
