Amyloid-β42 Aggregation on Cellular Membranes Facilitates its Cellular Uptake

Abstract

One of the pathological hallmarks of Alzheimer's disease (AD) are extracellular plaques with 42aa Amyloid beta peptide (Aβ1-42) as the main component. Although the Aβ1-42 peptide accumulates extracellularly, neurons internalize the Aβ peptide which could contribute to disease progression and which might be the first step to both cytotoxicity and propagation of misfolded Aβ1-42 between cells. However, the mechanistic details of this process are still under debate.We studied the relation between the aggregation state of extracellular Aβ1-42 and the efficiency of its neuronal uptake to determine, whether aggregate formation is a prerequisite of cellular uptake or its consequence. We used fluorescently labelled Aβ1-42 to detect the formation of intracellular Aβ1-42 aggregates in cultured neuroblastoma cells (Sh-EP) after treatment with different Aβ1-42 aggregate species; and to monitor the aggregation of Aβ1-42 in the extracellular space and on the cell membrane by fluorescence energy transfer (FRET).Our observation shows that extracellular Aβ1-42 monomer bound rapidly to plasma membranes, and, once a critical concentration was reached, aggregated spontaneously. Small Aβ1-42 aggregates were then internalized via a non-clathrin mediated endocytosis pathway. Cellular uptake efficiency increased in the course of aggregation. It was accelerated by a pre-aggregation of Aβ1-42 in vitro.Our results indicate that Aβ1-42 can be internalized following an accumulation and aggregation on plasma membrane, confirm the oligomer hypothesis of amyloid toxicity by suggesting that Aβ1-42 oligomers are central to the uptake process which may initiate toxicity in AD. Targeting the binding and aggregation of Aβ1-42 on plasma membrane, and small aggregates could yield an early effective treatment of AD.