A\u03b2 accumulation causes MVB enlargement and is modelled by dominant negative VPS4A

Katarina Willén,Gunnar K Gouras,Clare E Futter,Takafumi Hasegawa,Nobuyuki Tanaka,James R Edgar

doi:10.1186/s13024-017-0203-y

Abstract

BackgroundAlzheimer’s disease (AD)-linked β-amyloid (Aβ) accumulates in multivesicular bodies (MVBs) with the onset of AD pathogenesis. Alterations in endosomes are among the earliest changes associated with AD but the mechanism(s) that cause endosome enlargement and the effects of MVB dysfunction on Aβ accumulation and tau pathology are incompletely understood.MethodsMVB size and Aβ fibrils in primary neurons were visualized by electron microscopy and confocal fluorescent microscopy. MVB-dysfunction, modelled by expression of dominant negative VPS4A (dnVPS4A), was analysed by biochemical methods and exosome isolation.ResultsHere we show that AD transgenic neurons have enlarged MVBs compared to wild type neurons. Uptake of exogenous Aβ also leads to enlarged MVBs in wild type neurons and generates fibril-like structures in endocytic vesicles. With time fibrillar oligomers/fibrils can extend out of the endocytic vesicles and are eventually detectable extracellularly. Further, endosomal sorting complexes required for transport (ESCRT) components were found associated with amyloid plaques in AD transgenic mice. The phenotypes previously reported in AD transgenic neurons, with net increased intracellular levels and reduced secretion of Aβ, were mimicked by blocking recycling of ESCRT-III by dnVPS4A. DnVPS4A further resembled AD pathology by increasing tau phosphorylation at serine 396 and increasing markers of autophagy.ConclusionsWe demonstrate that Aβ leads to MVB enlargement and that amyloid fibres can form within the endocytic pathway of neurons. These results are consistent with the scenario of the endosome-lysosome system representing the site of initiation of Aβ aggregation. In turn, a dominant negative form of the CHMP2B-interacting protein VPS4A, which alters MVBs, leads to accumulation and aggregation of Aβ as well as tau phosphorylation, mimicking the cellular changes in AD.

Highlights

Alzheimer’s disease (AD)-linked β-amyloid (Aβ) accumulates in multivesicular bodies (MVBs) with the onset of AD pathogenesis
In order to examine whether increased levels of Aβ can lead to the enlarged endosomal phenotype seen in AD, MVB size was compared between Amyloid precursor protein (APP)/Presenilin 1 (PS1) transgenic and wt primary mouse neurons
Electron micrographs showed a significantly greater MVB diameter (52% increase; p < 0.001) in APP/PS1 transgenic compared to wt neurons at 12 days in vitro (DIV) (Fig. 1a and b) consistent with the larger diameter of endosomes described in human AD

Summary

Introduction

Alzheimer’s disease (AD)-linked β-amyloid (Aβ) accumulates in multivesicular bodies (MVBs) with the onset of AD pathogenesis. Alzheimer’s disease (AD) is characterized by progressive decline in cognitive function, anatomical selective loss of synapses and neurons, and aggregation of the β-amyloid peptide (Aβ) in amyloid plaques and hyperphosphorylated tau in neurofibrillary tangles (NFTs). In AD transgenic mice, cognitive, physiological and structural impairments appear prior to plaques [7,8,9] and are accompanied by intraneuronal Aβ peptide accumulation, supporting that accumulation of intraneuronal Aβ peptides is one of the earliest events in AD pathogenesis [10]. Sorting of EGFR via the MVB pathway was impaired by endosomal Aβ accumulation in cultured AD transgenic neurons [21]. Translocation into MVBs appeared affected, suggesting Aβ dependent dysfunction of the late endosomal sorting complexes required for transport (ESCRT) pathway in AD

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