Cytoplasmic TDP-43 aggregation promotes oxidative stress and neurotoxicity through Trx1 mRNA sequestration and translational suppression

Transactive response (TAR) DNA-binding protein 43 (TDP-43) is a multifunctional DNA/RNA binding protein. Cytoplasmic TDP-43 aggregation is a pathological hallmark of diverse neurodegenerative diseases collectively termed TDP-43 proteinopathy. Oxidative stress is closely associated with TDP-43 aggregation and neurotoxicity in TDP-43 proteinopathy, yet the underlying molecular mechanisms remain elusive. To delineate molecular basis of TDP-43 proteinopathy, we conducted deep quantitative proteomic profiling using Neuro-2a (N2a) neuronal cell model of TDP-43 proteinopathy overexpressing human wild-type TDP-43 (N2a-hTDP-43). We identified thioredoxin-1 (Trx1) as a central node linking mitochondrial dysfunction and redox dysregulation to TDP-43 proteinopathy. Consistent with this, TDP-43 overexpression markedly reduced Trx1 protein levels. Moreover, inhibiting Trx1 exacerbates, whereas overexpressing Trx1 alleviates, cytoplasmic TDP-43 aggregation and neurotoxicity in N2a-hTDP-43 cells. Furthermore, overexpressing Trx1 alleviates TDP-43-associated pathologies in mouse primary neurons. Notably, we identified that cytoplasmic TDP-43 proteins sequester Trx1 mRNAs into insoluble inclusions, leading to its translational suppression. We also demonstrated that suppression of Trx1 is a core mechanism eliciting oxidative stress and mitochondrial dysfunction in TDP-43 proteinopathy. Importantly, in human induced pluripotent stem cell (iPSC)-derived motor neurons (MN) harboring the pathogenic TDP-43 M337V mutation (TDP-43M337V iPSC-MNs), Trx1 expression is downregulated, concomitant with increased oxidative stress, compared to the isogenic TDP-43WT iPSC-MN control. Furthermore, inducing Trx1 expression markedly reduces oxidative stress and cytoplasmic TDP-43 aggregation in TDP-43M337V iPSC-MNs, suggesting conserved neuroprotective role of Trx1 in TDP-43 proteinopathy in human. Collectively, we identified Trx1 as a pivotal regulator of TDP-43 proteinopathy, highlighting therapeutic potential of Trx1 for TDP-43 proteinopathies.