Journal
ACTA NEUROPATHOLOGICA
Volume 132, Issue 2, Pages 257-276Publisher
SPRINGER
DOI: 10.1007/s00401-016-1577-6
Keywords
Alzheimer; C99; Lysosomes; Autophagy; Aggregation; Triple-transgenic mouse; gamma-Secretase inhibition
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Funding
- LABEX (excellence laboratory, program investment for the future) DISTALZ (Development of Innovative Strategies for a Transdisciplinary approach to ALZheimer's disease
- Conseil Departemantal des Alpes Maritimes
- University hospital Federation (FHU) OncoAge
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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 beta-secretase-derived beta APP 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 A beta independent and was even exacerbated when gamma-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 gamma-secretase inhibitor-directed therapies.
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