Cargo-Loading of Misfolded Proteins into Extracellular Vesicles: The CSPα-EV Export Pathway

Extracellular vesicles (EVs) are secreted vesicles of diverse size and cargo that are implicated in the cell-to-cell transmission of disease-causing-proteins in several neurodegenerative diseases. Mutant huntingtin, the disease-causing entity in Huntington’s disease, has an expanded polyglutamine track at the N terminus that causes the protein to misfold and form toxic intracellular aggregates. In Huntington’s disease, mutant huntingtin aggregates are transferred between cells by an unknown route. We have previously identified a cellular pathway that is responsible for the export of mutant huntingtin via extracellular vesicles, given the heterogeneity of EVs, here we examine the specific EVs involved. In this work we expressed a form of polyglutamine expanded huntingtin (GFP-tagged 72Qhuntingtin exon1 ) in cells to assess the EVs involved in cellular export. We demonstrate that the molecular chaperone, cysteine string protein (CSPα; DnaJC5), mediates export of disease-causing-polyglutamine-expanded huntingtin cargo via two distinct vesicle populations of 180-240nm and 15-30μm. In doing so, our data links the molecular chaperone, CSPα, and the packaging of pathogenic misfolded huntingtin into two separate extracellular vesicles pathways.