Endosomal-autophagic-lysosomal (EAL) dysfunction is an early and prominent neuropathological feature of Alzheimers's disease, yet the exact molecular mechanisms contributing to this pathology remain undefined. By combined biochemical, immunohistochemical and ultrastructural approaches, we demonstrate a link between EAL pathology and the intraneuronal accumulation of the β-secretase-derived βAPP fragment (C99) in two in vivo models, 3xTgAD mice and adeno-associated viral-mediated C99-infected mice. We present a pathological loop in which the accumulation of C99 is both the effect and causality of impaired lysosomal-autophagic function. The deleterious effect of C99 was found to be linked to its aggregation within EAL-vesicle membranes leading to disrupted lysosomal proteolysis and autophagic impairment. This effect was Aβ independent and was even exacerbated when γ-secretase was pharmacologically inhibited. No effect was observed in inhibitor-treated wild-type animals suggesting that lysosomal dysfunction was indeed directly linked to C99 accumulation. In some brain areas, strong C99 expression also led to inflammatory responses and synaptic dysfunction. Taken together, this work demonstrates a toxic effect of C99 which could underlie some of the early-stage anatomical hallmarks of Alzheimer's disease pathology. Our work also proposes molecular mechanisms likely explaining some of the unfavorable side-effects associated with γ-secretase inhibitor-directed therapies.

中文翻译：

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APP (C99) 的 β-CTF 片段在神经元内聚集可诱导 Aβ 独立的溶酶体自噬病理。

内体自噬溶酶体（EAL）功能障碍是阿尔茨海默病的一个早期且显着的神经病理学特征，但导致这种病理学的确切分子机制仍不清楚。通过结合生化、免疫组织化学和超微结构方法，我们在两个体内模型（3xTgAD 小鼠和腺相关病毒介导的 C99 感染小鼠）中证明了 EAL 病理学与 β-分泌酶衍生的 βAPP 片段 (C99) 的神经元内积累之间的联系。老鼠。我们提出了一个病理循环，其中 C99 的积累既是溶酶体自噬功能受损的结果，也是其因果关系。研究发现 C99 的有害作用与其在 EAL 囊泡膜内的聚集有关，导致溶酶体蛋白水解破坏和自噬损伤。这种作用与 Aβ 无关，并且当 γ-分泌酶受到药理学抑制时甚至会加剧。在抑制剂处理的野生型动物中没有观察到效果，这表明溶酶体功能障碍确实与 C99 积累直接相关。在某些大脑区域，C99 的强烈表达还会导致炎症反应和突触功能障碍。总而言之，这项工作证明了 C99 的毒性作用，这可能是阿尔茨海默病病理学的一些早期解剖学特征的基础。我们的工作还提出了可能解释与 γ-分泌酶抑制剂导向疗法相关的一些不利副作用的分子机制。