Kinesin-1 and ARL8B-Dependent Targeting of a Prion Mutant into Axonal Pre-lysosomal Compartments Promotes Prion Aggregation in Neurons

Abstract

A characteristic of prion pathology is the presence of axonal swellings containing PrP aggregates and accumulations of abnormal amounts of microtubule-associated molecular motor proteins, vesicles, and organelles. Here, we report a novel mechanism by which aggregation in neurons of a pathogenic mutant PrP is a direct consequence of the direct targeting of these prions to pre-lysosomal compartments by Kinesin-1 and Arl8b. We show that upon expression in neurons, mutant PrP turns on ER stress and in response is constitutively exported into the axon in Golgi-derived vesicles by interactions with the small GTPase Arl8b, which in turn recruits molecular motors to move PrP vesicles towards the termini. Mutant PrP transiently accesses the cell surface along the axon before immediate internalization into late endosomal/pre-lysosomal compartments. We further show that internalized mutant PrP is poorly degraded in lysosomes, leading to the progressive accumulation and aggregation of mutant PrP in axons. Our data a direct relationship between intracellular transport and misfolded protein aggregate formation and demonstrate that formation of prion aggregates in axons is a late event strictly dependent on Kinesin-1 motor activity and in delivery to- and endocytosis from the plasma membrane, suggesting that post-Golgi re-routing of abnormal PrP is deleterious for neurons.