Cysteine String Protein Controls Two Routes of Export for Misfolded Huntingtin.

Desmond Pink,John D Lewis,Julien Donnelier,Janice E A Braun

doi:10.3389/fnins.2021.762439

Abstract

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 several routes. We have previously identified a cellular pathway that is responsible for the export of mutant huntingtin via extracellular vesicles. Identifying the EV sub-populations that carry misfolded huntingtin cargo is critical to understanding disease progression. In this work we expressed a form of polyglutamine expanded huntingtin (GFP-tagged 72Qhuntingtinexon1) in cells to assess the EVs involved in cellular export. We demonstrate that the molecular chaperone, cysteine string protein (CSPα; DnaJC5), facilitates export of disease-causing-polyglutamine-expanded huntingtin cargo in 180–240 nm vesicles as well as larger 10–30 μm vesicles.

Highlights

The cell-to-cell transfer of extracellular vesicles (EVs) is a conserved process
We have found that CSPα mediates export of mutant huntingtin through two subpopulations of EVs, sized at 180–240 nm and 10–30 μm and that resveratrol reduces export of mutant huntingtin through both EV routes
The large EVs contain multiple mutant huntingtin aggregates which are pliable and sensitive to proteinase K degradation, yet stable when applied to recipient cells

Summary

Introduction

The continuous exchange among different cells generates a dynamic and heterogeneous pool of EVs (Pegtel and Gould, 2019). EVs come in different sizes and carry different cargoes that exert profound effects in recipient cells following uptake. The physiological roles of EVs include exchanging information between cells as well as removing unwanted proteins from cells (Vella et al, 2016; Hill, 2019; Pegtel and Gould, 2019). How EVs facilitate the spread of disease in cancer and neurodegenerative disease and what distinguishes physiological from pathological EVs is a current focus of investigation (Hill, 2019; Pegtel and Gould, 2019). The most widely studied EVs are exosomes, which originate from fusion of multivesicular bodies

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Conclusion