Hyperoside protects against poly-GR-mediated neurodegeneration via regulation of mitochondrial fission and oxidative stress in C9orf72-associated ALS

Background Arginine-rich poly-glycine-arginine (poly-GR), a toxic dipeptide repeat protein generated from C9orf72 hexanucleotide repeat expansion, drives mitochondrial dysfunction, oxidative stress, and neuronal loss in amyotrophic lateral sclerosis (ALS). Hyperoside, a bioactive flavonoid, exhibits antioxidant and cytoprotective properties, but its therapeutic relevance to C9orf72 -associated ALS remains unclear. Purpose To determine whether hyperoside attenuates poly-GR-induced mitochondrial and oxidative injury and improves neuronal survival in cellular and animal models of C9orf72 -ALS. Methods A combined in vitro and in vivo experimental study using motor neuron-like cells and an AAV-mediated neonatal mouse model of poly-GR toxicity. NSC34 cells expressing EGFP-GR 50 were analyzed for mitochondrial morphology, membrane potential, ROS generation, antioxidant signaling, and apoptosis using confocal microscopy, CellROX/MitoTracker assays, Western blot analysis, and viability testing. For in vivo assessment, neonatal mice received intracerebroventricular AAV9-EGFP-GR50 followed by intraperitoneal hyperoside (10 mg/kg). Survival, cerebral hemisphere length, and cortical NeuN⁺ neuron numbers were quantified. Results Poly-GR expression induced pronounced mitochondrial fragmentation, reduced membrane potential, elevated ROS, and suppressed Nrf2/HO-1/GPx4 signaling, accompanied by increased Drp1 and reduced Opa1 expression. Hyperoside reversed these abnormalities by restoring mitochondrial integrity, normalizing the Drp1/Opa1 balance, enhancing Nrf2 nuclear accumulation, and increasing the expression of HO-1 and GPx4. Hyperoside also reduced cleaved caspase-3 and corrected the Bax/Bcl-2 ratio, improving cell viability under basal and oxidative stress conditions. In vivo, hyperoside modestly prolonged survival, increased cerebral hemisphere length, and significantly preserved cortical neuronal numbers in AAV9-EGFP-GR 50 mice. Conclusion Hyperoside mitigates poly-GR-induced neurotoxicity by alleviating excessive mitochondrial fission, strengthening Nrf2-dependent antioxidant defenses, and suppressing apoptosis. These findings support hyperoside as a promising multi-target therapeutic candidate for C9orf72 -associated ALS.