The Impact of Methylglyoxal and SOD1 Mutation on TDP-43 Interaction in ALS Proteinopathy

Introduction: Proteinopathy is a key feature of amyotrophic lateral sclerosis (ALS) that causes the loss of motor neurons. Glycated SOD1 increases the levels of phospho-TDP-43, a form that aggregates in the cytosol of neurons experiencing neurodegeneration in most ALS cases. Objective: Here, we evaluated whether TDP-43 interacts with SOD1 and the impact of methylglyoxal (MGO) and G93A SOD1, found in patients, on this interaction. Methodology: TDP-43-SOD1 interaction was observed in H4 cells using the bimolecular fluorescence complementation (BiFC) system. Results: Exposure to MGO reduced SOD1 activity and the levels of phospho-TDP-43 only in cells expressing WT SOD1. Our results showed that both WT and G93A SOD1 interact with TDP-43 in the nucleus and cytosol, with a greater proportion of cells showing cytosolic interactions between TDP-43 and the SOD1 mutant. MGO did not affect the interaction between TDP-43 and WT SOD1; however, it did lead to an increase in cytosolic inclusions at 0.4 mM MGO, a stress that resulted in a 50% reduction in cell viability. These inclusions did not colocalize with stress granules. Treatment with Cyclosporin A, an inhibitor of calcineurin (a phosphatase that dephosphorylates TDP-43), reduced the number of cells containing TDP-43 and WT SOD1 inclusions, as well as the cells showing TDP-43 and G93A SOD1 interactions in the cytosol. Conclusion: Thus, we conclude that damaged SOD1, produced by MGO, or G93A mutation disrupts TDP-43 phosphorylation, altering its location within the cell and inducing its aggregation, which are important markers of ALS.