PPo9-1: Prion-like Propagation of SOD1 Misfolding in Amyotrophic Lateral Sclerosis

Neil R. Cashman

University of British Columbia; Vancouver, British Columbia Canada

Key words: protein misfolding, mechanisms of neurodegeneration, transmission

Prion-like propagation of protein misfolding has been implicated in Alzheimerís, Parkinsonís and Huntingtonís diseases, and the tauopathies. Amyotrophic lateral sclerosis (ALS) is a common and incurable adult motor neuron disease, in which mutation of the free-radical defense enzyme superoxide dismutase 1 (SOD1) is responsible for a subtype of familial ALS (fALS). We demonstrate that transfection of fALS SOD1 mutants G127X and G85R, as well as overexpression of non-mutant wild-type (wt) SOD1, can induce misfolding of natively-structured wild-type SOD1 in human mesenchymal and neural cell lines, as determined by molecular surface immunoreactivity with misfolding-specific monoclonal antibodies (mAbs), acquisition of protease sensitivity (suggesting structural loosening), generation of reactive oxygen species (ROS) and formation of non-native intermolecular disulfide bonds. Serial transmission of SOD1 misfolding was established by incubation in conditioned media from mtSOD1- or wtSOD1-transfected HEK cells, and knockdown of endogenous SOD1 expression in HEK cells by siRNA abrogated the transmission of SOD1 misfolding, consistent with endogenously expressed SOD1 being the substrate for conformational conversion. Pre-incubation of SOD1-transfected conditioned media with poly-specific SOD1 antibodies or misfolding-specific mAbs also blocked intercellular transducing activity, and passive administration of misfolding-specific mAbs extends survival in the G37R transgenic mouse model of ALS. We conclude that misfolded SOD1 participates in a template-directed misfolding cascade which provides a plausable molecular mechanism for progression of familial and sporadic ALS. Antibody-mediated neutralization of SOD1 misfolding propagation could prove beneficial in human ALS.


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