Endosomal trafficking and amyloidogenic cleavage of amyloid precursor protein (APP) is believed to play a role in the neurodegeneration observed in Alzheimer’s disease (AD). Recent evidence has suggested that packaging and secretion of APP and its amyloidogenic cleaved products into small extracellular vesicles (EVs) may facilitate uptake of these neurotoxic factors during disease progression. However, the molecular mechanisms underlying trafficking of APP into EVs are poorly understood. In this study, the mechanism and impact of APP trafficking into extracellular vesicles (EVs) were assessed by a series of inducible gene knockdowns. We demonstrate that vesicle-associated proteins Alix and Syntenin-1 are essential for proper subcellular localization and efficient EV secretion of APP via an endosomal sorting complexes required for transport (ESCRT)-independent pathway. The neurotoxic C-terminal fragment (CTFβ) of APP is similarly secreted in association with small vesicles. These mechanisms are conserved in terminally differentiated neuron-like cells. Furthermore, knockdown of Alix and Syntenin-1 alters the subcellular localization of APP, sequestering the precursor protein to endoplasmic reticulum and endolysosomal compartments, respectively. Finally, transfer of small EVs containing mutant APP confers an increase in reactive oxygen species production and neurotoxicity to human induced pluripotent stem cell-derived cortical neurons and naïve primary neurons, an effect that is ameliorated by Alix and Syntenin-1 depletion. Altogether these findings elucidate a novel mechanism for understanding the intracellular trafficking of APP and CTFβ into secreted extracellular vesicles, and the resultant potential impact on neurotoxicity in the context of Alzheimer’s disease amyloidopathy.

中文翻译：

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Alix 和 Syntenin-1 直接将淀粉样前体蛋白运输到细胞外囊泡中。


淀粉样前体蛋白 (APP) 的内体运输和淀粉样蛋白生成裂解被认为在阿尔茨海默病 (AD) 中观察到的神经变性中发挥作用。最近的证据表明，将 APP 及其淀粉样蛋白裂解产物包装和分泌到小细胞外囊泡 (EV) 中可能会促进疾病进展过程中这些神经毒性因子的摄取。然而，人们对将 APP 贩运到 EV 中的分子机制知之甚少。在这项研究中，通过一系列诱导基因敲低评估了 APP 运输到细胞外囊泡 (EV) 的机制和影响。我们证明，囊泡相关蛋白 Alix 和 Syntenin-1 对于正确的亚细胞定位和通过运输 (ESCRT) 独立途径所需的内体分选复合物有效 EV 分泌 APP 至关重要。 APP 的神经毒性 C 末端片段 (CTFβ) 类似地与小囊泡相关分泌。这些机制在终末分化的神经元样细胞中是保守的。此外，Alix 和 Syntenin-1 的敲低会改变 APP 的亚细胞定位，分别将前体蛋白隔离在内质网和内溶酶体区室中。最后，含有突变 APP 的小型 EV 的转移会增加活性氧的产生，并增加人类诱导的多能干细胞衍生的皮质神经元和幼稚初级神经元的神经毒性，这种效应可以通过 Alix 和 Syntenin-1 的消耗得到改善。 总而言之，这些发现阐明了一种新机制，可用于了解 APP 和 CTFβ 在细胞内运输到分泌的细胞外囊泡中，以及由此产生的对阿尔茨海默病淀粉样变性中神经毒性的潜在影响。