Tryptophan residues in TDP-43 and SOD1 modulate the cross-seeding and toxicity of SOD1
Edward Pokrishevsky, Michèle G. DuVal, Luke McAlary, Sarah Louadi, Silvia Pozzi, Andrei Roman, Steven S. Plotkin, Anke A. Dijkstra, Jean‐Pierre Julien, W. Ted Allison, Neil R. Cashman
Abstract
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of motor neurons. Neuronal superoxide dismutase-1 (SOD1) inclusion bodies are characteristic of familial ALS with SOD1 mutations, while a hallmark of sporadic ALS is inclusions containing aggregated wild-type TAR DNA-binding protein 43 (TDP-43). We show here that co-expression of mutant or wild-type TDP-43 with SOD1 leads to misfolding of endogenous SOD1 and aggregation of SOD1 reporter protein SOD1 G85R -GFP in human cell cultures, and promotes synergistic axonopathy in zebrafish. Intriguingly, this pathological interaction is modulated by natively solvent-exposed tryptophans in SOD1 (tryptophan-32) and TDP-43 RNA-recognition motif RRM1 (tryptophan-172), in concert with natively sequestered TDP-43 N-terminal domain tryptophan-68. TDP-43 RRM1 intrabodies reduce wild-type SOD1 misfolding in human cell cultures, via blocking tryptophan-172. Tryptophan-68 becomes antibody-accessible in aggregated TDP-43 in sporadic ALS motor neurons and cell culture. 5-fluorouridine inhibits TDP-43-induced G85R-GFP SOD1 aggregation in human cell cultures, and ameliorates axonopathy in zebrafish, via its interaction with SOD1 tryptophan-32. Collectively, our results establish a novel and potentially druggable tryptophan-mediated mechanism whereby two principal ALS disease effector proteins might directly interact in disease.