The inhibitory effects of MIF on accumulation of canine degenerative myelopathy-associated mutant SOD1 aggregation.

Abstract

Canine degenerative myelopathy (DM) is a progressive neurodegenerative disorder, which is commonly associated with c.118G > A (p. E40K) missense mutation in the superoxide dismutase 1 (SOD1) gene. Mutant SOD1 protein (SOD1) is likely to be misfolded, acquire insolubility, aggregate in the cytoplasm of neural cells, and lead to degeneration of the nervous tissues. Along with a chaperone activity, macrophage migration inhibitory factor (MIF) is a multifunctional protein that has been shown to directly inhibit human mutant SOD1 misfolding and enhance survival of mutant SOD1-expressing motor neurons. The purpose of this study was to determine whether MIF also inhibits DM-related SOD1misfolding and accumulation of SOD1 aggregates. Human embryonic kidney 293A cells were transfected SOD1or SOD1with or without MIF. The percentages of cells containing transfected SOD1 aggregates were measured by immunocytochemistry, and the amount of SOD1in the insoluble fraction was evaluated by immunoblotting. The percentage of cells with SOD1aggregates and the amount of insoluble SOD1protein decreased in the presence of MIF. Because the chaperone activity of MIF assists in SOD1folding and enhances the refolding and degradation of misfolded SOD1, the results of this study suggests that MIF regulates the accumulation of SOD1 aggregates by its chaperone activity. We propose that enhancing intracellular MIF chaperone activity could be an effective therapeutic strategy for DM.