Examining the role of Nucleoredoxin (NRX) in Amyotrophic Lateral Sclerosis (ALS)

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disorder that progresses rapidly and affects motor neurons in the brain, brainstem and spinal cord. Pathological forms of TAR DNA-binding protein-43 (TDP-43) are recognized as the major hallmarks of ALS. Inclusion formation, cytoplasmic aggregation of nuclear TDP-43, dysregulated nucleocytoplasmic transport and oxidative stress are all implicated as important pathogenic mechanisms. However, there is no effective treatment for ALS, so there is an urgent need to find new therapeutic targets. As a redox-regulated chaperone, nucleoredoxin (NRX) is known to inhibit protein misfolding and oxidative stress. Furthermore, it is normally present in the nucleus, but it shuttles to the cytoplasm, similar to TDP-43 and other proteins associated with ALS. It is therefore conceivable that NRX may be a possible therapeutic target for ALS given its major role in guarding the nucleus against redox dysregulation. However, a role for NRX has not been investigated previously in ALS.  In this study, NRX was found to be protective against the mislocalization of TDP-43, inclusion formation, nuclear morphology, and nucleocytoplasmic transport dysfunction in neuronal cells. Mutant TDP-43 induces irregular, invaginated morphological changes to the nucleus in neurons, and here we examined nuclear morphology by immunocytochemistry using antibodies against components of the nuclear pore complexes (NPCs). NES-tdTomato-NLS, a fluorescent reporter, was used to study abnormalities in nucleocytoplasmic transport caused by mutant TDP-43 M337V. This is frequently used to study nucleocytoplasmic transport because when the nuclear import mechanism is dysregulated, it accumulates in the cytoplasm. Quantitative analysis revealed that NRX reduced the nuclear-to-cytoplasmic (N/C) localization of the fluorescent reporter in cells expressing mutant TDP-43 M337V. Similarly, we also examined RanGAP1, a significant regulator of nucleocytoplasmic transport that is mislocalized to the cytoplasm in ALS, and found that overexpressing NRX prevented this mislocalization. This study, therefore, demonstrates that NRX is protective against important pathological features associated with ALS. In addition, a preliminary study was performed to optimize the detection of FoxO proteins using immunocytochemistry. These transcription factors play a significant role in protein misfolding, oxidative stress, and aging, but have been poorly studied in ALS.