Investigation and manipulation of SOD1 mutant misfolding, aggregation and seeding

The presence of ubiquitylated protein aggregates in neurons and surrounding cells is considered one of the hallmarks of neurodegenerative disorders, such as amyotrophic lateral sclerosis (ALS). Since the identification of SOD1 as the first causative gene in 1993, extensive research has been carried out to investigate the role Cu/Zn superoxide dismutase-1 (SOD1) aggregation plays in ALS pathogenesis. Recently, it has been reported that SOD1 inclusions could propagate in a prion-like manner, by seeding the aggregation of soluble functional proteins and transmitting aggregation to neighbouring cells. HSJ1 (DnaJB2) is a chaperone that can reduce protein aggregation in several neurodegenerative disease models; such as, Huntington’s disease and Parkinson’s disease. HSJ1a overexpression has also been shown to improve motor neuron survival in an animal model of SOD1-ALS. In this study, I tested the hypothesis that HSJ1 could alter SOD1-aggregation and seeding in vitro and in cell models. I developed an in vitro system with purified proteins to explore the tendency of SOD1 wild type (SOD1WT) and mutants (SOD1MT) to aggregate and seed further aggregation. The results showed that SOD1WT is resistant to seeding unless the protein is destabilized and partially unfolded. Purified HSJ1 could reduce SOD1 aggregation. I then developed transient and inducible cell models to investigate the effects of HSJ1 on SOD1 aggregate formation and expansion. In cells, HSJ1 interacted preferentially with SOD1MT, and could reduce SOD1 inclusion formation, and disassembled pre-existing SOD1 inclusions. Using an inducible stable cell line expressing HSJ1a, unfolded protein response (UPR) markers were modestly reduced after ER stress, suggesting HSJ1a expression could potentially reduce disease-related intracellular stress. Collectively, these findings shed light on HSJ1 as a potential candidate targeting misfolded and aggregated SOD1 for future investigation