Journal
ACTA NEUROPATHOLOGICA COMMUNICATIONS
Volume 8, Issue 1, Pages -Publisher
BMC
DOI: 10.1186/s40478-020-00956-z
Keywords
Down syndrome; Alzheimer's disease; Early endosomes; Endocytosis; Electron microscopy; Super-resolution microscopy
Categories
Funding
- Fondation Vaincre Alzheimer
- Fondation Jerome Lejeune
- Agence Nationale de la Recherche [ANR-10-IAIHU-06]
- Wellcome Trust [098330/Z/12/Z]
- National Research Foundation Singapore [NMRC/CS-IRG/1438/2015]
- Wellcome Trust Collaborative Award in Science [217199/Z/19/Z]
- Research Cooperability Programme of the Croatian Science Foundation [PZS-2019-024277]
- French National Research Agency [ANR-10-INBS-04]
- Wellcome Trust [217199/Z/19/Z] Funding Source: Wellcome Trust
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Enlarged early endosomes have been visualized in Alzheimer's disease (AD) and Down syndrome (DS) using conventional confocal microscopy at a resolution corresponding to endosomal size (hundreds of nm). In order to overtake the diffraction limit, we used super-resolution structured illumination microscopy (SR-SIM) and transmission electron microscopies (TEM) to analyze the early endosomal compartment in DS. By immunofluorescence and confocal microscopy, we confirmed that the volume of Early Endosome Antigen 1 (EEA1)-positive puncta was 13-19% larger in fibroblasts and iPSC-derived neurons from individuals with DS, and in basal forebrain cholinergic neurons (BFCN) of the Ts65Dn mice modelling DS. However, EEA1-positive structures imaged by TEM or SR-SIM after chemical fixation had a normal size but appeared clustered. In order to disentangle these discrepancies, we imaged optimally preserved High Pressure Freezing (HPF)-vitrified DS fibroblasts by TEM and found that early endosomes were 75% denser but remained normal-sized. RNA sequencing of DS and euploid fibroblasts revealed a subgroup of differentially-expressed genes related to cargo sorting at multivesicular bodies (MVBs). We thus studied the dynamics of endocytosis, recycling and MVB-dependent degradation in DS fibroblasts. We found no change in endocytosis, increased recycling and delayed degradation, suggesting a traffic jam in the endosomal compartment. Finally, we show that the phosphoinositide PI (3) P, involved in early endosome fusion, is decreased in DS fibroblasts, unveiling a new mechanism for endosomal dysfunctions in DS and a target for pharmacotherapy.
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