Impaired nucleocytoplasmic transport in SOD1-mediated ALS

Impaired nucleocytoplasmic transport (NCT) has emerged as a shared pathogenic mechanism in various neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS). Although mutations in the gene encoding superoxide dismutase 1 (SOD1) account for approximately 20% of familial ALS cases, the impact of mutant SOD1 accumulation on the NCT remains unclear. Utilizing in vitro and in vivo models, patient-derived fibroblasts, and postmortem spinal cord tissues from ALS patients with SOD1 mutations, we determined the effects of mutant SOD1 on NCT dynamics, nuclear morphology and cellular localization of transport receptors and nuclear pore components. Mutant SOD1 disrupts nuclear import and export trafficking, causing cytosolic accumulation of key transport regulators such as RanGAP1 and exportin 1 (XPO1). Mutant SOD1 also lowers the abundance of FG-Nups at the nuclear pore without altering nuclear circularity. Abnormal accumulation of NCT components was identified in Iba1-positive microglia, indicating a previously overlooked, non-cell-autonomous contribution to disease pathogenesis. Importantly, AAV-mediated reduction of mutant SOD1 in transgenic mice restored nuclear XPO1 localization, underscoring the causal role of mutant SOD1 in NCT abnormalities. Finally, comparable NCT perturbations were observed in patient-derived fibroblasts and in post-mortem spinal cord tissues from individuals with SOD1-ALS. Our results implicate NCT disruption as a shared disease mechanism between SOD1-mediated ALS and other familial and sporadic forms of ALS, adding support for targeting this pathway as an attractive therapeutic strategy in this fatal disease.