Surface proteins modulate extracellular vesicle mediated inhibition of Aβ(1-42) aggregation

Aggregation of the amyloid-β (Aβ) peptide into amyloid oligomers and fibrils is a central pathogenic feature and therapeutic target in Alzheimer's disease (AD). Understanding the aggregation reaction and how it is modulated by the biological environment is therefore important. Cell-secreted extracellular vesicles (EVs) are emerging as modulators of Aβ aggregation, transport and toxicity. Here, we show that EVs from a variety of human and non-human cells have highly similar retarding effects on the rate of Aβ(1-42) fibril formation, suggesting that aggregation inhibition is a common EV feature. Furthermore, we examine how different EV biomolecular classes contribute to shape this effect. We show that enzymatic removal of surface-associated EV proteins significantly enhances their ability to inhibit aggregation. Similar, albeit considerably smaller, alterations were observed upon removal of cell surface protein-associated glycans. This suggests that EV-mediated inhibition of Aβ(1-42) aggregation may primarily be regulated by lipids and that surface proteins function to modulate this effect, through steric hindrance and/or direct interactions with Aβ(1-42) species. We further observed a minor but statistically robust enhancement of EV-mediated Aβ(1-42) aggregation inhibition upon removal of proteoglycans, suggesting that carbohydrates on the EV-surface also contribute to modulate their inhibitory effect. Altogether, these observations contribute mechanistic insight into the role of EVs as modulators of Aβ aggregation and highlight their possible contributions to maintenance of extracellular protein homeostasis.