Targeting Mitochondrial Fission Produces Both Neuroprotective and Detrimental Effects in the SOD1 Mouse Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neuromuscular disease characterized by progressive motor neuron (MN) degeneration and severe skeletal muscle atrophy. Despite extensive research, the mechanisms driving disease onset and progression remain incompletely understood. While MN loss is a defining feature of ALS, increasing evidence indicates that mitochondrial dysfunction contributes to disease pathogenesis. Here, we investigated the hypothesis that Mdivi-1, a pharmacological inhibitor of mitochondrial fission protein Drp-1, may exert neuroprotective properties in the SOD1G93A mouse model of ALS. Treatment was initiated prior to symptomatic onset to assess its potential disease-modifying effects. Mdivi-1 administration resulted in partial preservation of spinal MNs, however, this benefit did not translate into functional improvement. Moreover, treated animals exhibited exacerbated muscle atrophy, increased cytoplasmic localization of TDP-43 in MNs and compromised synaptic plasticity. Drp-1 expression was reduced in SOD1 mice and further decreased following Mdivi-1 treatment, suggesting that mitochondrial dynamics may already be compromised in this model. Overall, our results also highlight possible off-target effects of Mdivi-1 and point to a context-dependent role of mitochondrial dynamics in ALS.