Glutathione monoethyl ester prevents TDP-43 pathology in motor neuronal NSC-34 cells

Oxidative stress is recognised as central in a range of neurological diseases including Amyotrophic lateral sclerosis (ALS), a disease characterised by fast progressing death of motor neurons in the brain and spinal cord. Cellular pathology includes cytosolic protein aggregates in motor neurons and glia of which potentially cytotoxic hyper-phosphorylated fragments of the Transactive response DNA Binding Protein 43 kDa (TDP-43) constitute a major component. This is closely associated with an additional loss of nuclear TDP-43 expression indicating a "loss of function" mechanism, accelerating motor neuron (MN) loss. Furthermore, mutations in TDP-43 cause familial ALS and ALS-like disease in animal models. In this study, we investigated the role of glutathione (GSH) in modulating oxidative stress responses in TDP-43 pathology in motor neuron NSC-34 cells. Results demonstrate that depletion of GSH produces pathology similar to that of mutant TDP-43, including occurrence of cytosolic aggregates, TDP-43 phosphorylation and nuclear clearing of endogenous TDP-43. We also demonstrate that introduction of mutant TDP-43^A315T and silencing of endogenous TDP-43, but not overexpression of wild-type TDP-43, result in similar pathology, including depletion of intracellular GSH, possibly resulting from a decreased expression of a regulatory subunit of ɣ-glutamylcysteine ligase (GCLM), a rate limiting enzyme in GSH synthesis. Importantly, treatment of mutant cells with GSH monoethyl ester (GSHe) that directly increases intracellular GSH and bypasses the need for GSH synthesis, protected against mutant-induced TDP-43 pathology, including reducing aggregate formation, nuclear clearance, reactive oxygen species (ROS) production and cell death. Our data strongly suggest that oxidative stress is central to TDP-43 pathology and may result from a loss of function affecting GSH synthesis and that treatments directly aimed at restoring cellular GSH content may be beneficial in preventing cell death in TDP-43-mediated ALS.