Intercellular propagated misfolding of wild-type Cu/Zn superoxide dismutase occurs via exosome-dependent and -independent mechanisms

Authors

Leslie I. Grad, University of British Columbia
Justin J. Yerbury, University of WollongongFollow
Bradley J. Turner, University of Melbourne
William C. Guest, University of British Columbia
Edward Pokrishevsky, University of British Columbia
Megan A. O'Neill, University of British Columbia
Anat Yanai, University of British Columbia
Judith M. Silverman, University of British Columbia
Rafaa Zeineddine, University of WollongongFollow
Lisa Corcoran, University of WollongongFollow
Janet Kumita, University of Cambridge
Leila Luheshi, University of Cambridge
Masoud Yousefi, University of British Columbia
Bradley M. Coleman, University of Melbourne
Andrew Hill, University of Melbourne
Steven S. Plotkin, University of British Columbia
Ian R. Mackenzie, University of British Columbia
Neil R. Cashman, University of British Columbia

RIS ID

87876

Publication Details

Grad, L. I., Yerbury, J., Turner, B. J., Guest, W. C., Pokrishevsky, E., O'Neill, M. A., Yanai, A., Silverman, J. M., Zeineddine, R., Corcoran, L., Kumita, J. R., Luheshi, L. M., Yousefi, M., Coleman, B. M., Hill, A. F., Plotkin, S. S., Mackenzie, I. R. & Cashman, N. R. (2014). Intercellular propagated misfolding of wild-type Cu/Zn superoxide dismutase occurs via exosome-dependent and -independent mechanisms. Proceedings of the National Academy of Sciences of USA, 111 (9), 3620-3625.

Abstract

Amyotrophic lateral sclerosis (ALS) is predominantly sporadic, but associated with heritable genetic mutations in 5-10% of cases, including those in Cu/Zn superoxide dismutase (SOD1). We previously showed that misfolding of SOD1 can be transmitted to endogenous human wild-type SOD1 (HuWtSOD1) in an intracellular compartment. Using NSC-34 motor neuron-like cells, we now demonstrate that misfolded mutant and HuWtSOD1 can traverse between cells via two nonexclusive mechanisms: protein aggregates released from dying cells and taken up by macropinocytosis, and exosomes secreted from living cells. Furthermore, once HuWtSOD1 propagation has been established, misfolding of HuWtSOD1 can be efficiently and repeatedly propagated between HEK293 cell cultures via conditioned media over multiple passages, and to cultured mouse primary spinal cord cells transgenically expressing HuWtSOD1, but not to cells derived from nontransgenic littermates. Conditioned media transmission of HuWtSOD1 misfolding in HEK293 cells is blocked by HuWtSOD1 siRNA knockdown, consistent with human SOD1 being a substrate for conversion, and attenuated by ultracentrifugation or incubation with SOD1 misfolding-specific antibodies, indicating a relatively massive transmission particle which possesses antibody-accessible SOD1. Finally, misfolded and protease-sensitive HuWtSOD1 comprises up to 4% of total SOD1 in spinal cords of patients with sporadic ALS (SALS). Propagation of HuWtSOD1 misfolding, and its subsequent cell-to-cell transmission, is thus a candidate process for the molecular pathogenesis of SALS, which may provide novel treatment and biomarker targets for this devastating disease.