SOD1-interacting proteins: Roles of aggregation cores and protein degradation systems.

Cu/Zn superoxide dismutase (SOD1) mutations are associated with amyotrophic lateral sclerosis (ALS). SOD1-positive aggregates in motor neurons, as well as proteins that interact with the aggregates are presumably involved in ALS neurotoxicity. We used a proteomics approach to compare differences in protein expression in spinal cord homogenates from non-transgenic (NTG) and ALS model mice. Using the homogenates, we identified proteins that interacted with SOD1 seeds in vitro. We assessed differences in SOD1-interacting proteins in cell cultures treated with proteasome or autophagy inhibitor. In the first experiment, intermediate filamentous and small heat shock proteins were upregulated in glial cells. We identified 26 protein types that interacted with aggregation cores in ALS model homogenates, and unexpectedly, 40 proteins in were detected in NTG mice. In cell cultures treated with proteasome and autophagy inhibitors, we identified 16 and 11 SOD1-interacting proteins, respectively, and seven proteins in untreated cells. These SOD1-interacting proteins were involved in multiple cellular functions such as protein quality control, cytoskeletal organization, and pathways involved in growth factor signaling and their downstream cascades. The complex interactions between pathways could cause further dysregulation, ultimately leading to fatal cellular dysfunction in ALS.