Propagating prion-like amyloid proteins invade target cells through endocytic vesicle rupture

Abstract

Numerous pathologic amyloid proteins spread from cell to cell during neurodegenerative disease, facilitating the propagation of cellular pathology and disease progression in a prion-like fashion. Understanding the mechanism by which amyloid assemblies enter target cells and induce dysfunction is therefore key to understanding the progressive nature of diseases like Alzheimer's, Parkinson's, Huntington's, and chronic traumatic encephalopathy. In this study, we utilized an imaging-based assay to monitor the ability of amyloid assemblies to induce the rupture of intracellular vesicles following endocytosis, as well as to elucidate the cellular consequences of this damaging mechanism of invasion. We observe that induction of vesicle rupture is a conserved ability of fibrillar amyloid assemblies of alpha-synuclein, tau, and polyglutamine-rich huntingtin. Endocytic vesicle rupture potency is strongly influenced by strain conformation and is increased by assembly phosphorylation. Vesicles ruptured by alpha-synuclein can accumulate and fuse into large, intracellular structures resembling Lewy bodies in vitro, and the same markers of vesicle rupture surround Lewy bodies in brain sections from Parkinson's patients. Finally, ruptured vesicles containing alpha-synuclein can be observed in the extracellular environment and can be seen trafficking from cell to cell. These data underscore the importance of endocytic vesicle rupture as a conserved mechanism of cellular invasion by multiple disease-associated amyloid protein assemblies, implicate this process in the formation of proteinaceous inclusions such as Lewy bodies, and suggest that this form of cellular damage can serve as both a driving force and a vector for amyloid protein release and subsequent transmission to neighboring cells.