The Sigma-1 Receptor Mediates Pridopidine Rescue of Mitochondrial Function in Huntington Disease Models

Pridopidine is a selective Sigma-1 receptor (S1R) agonist in clinical development for Huntington disease (HD) and amyotrophic lateral sclerosis. S1R is a chaperone protein localized in mitochondria-associated endoplasmic reticulum (ER) membranes, a signaling platform that regulates Ca²⁺ signaling, reactive oxygen species (ROS) and mitochondrial fission. Here, we investigate the protective effects of pridopidine on various mitochondrial functions in human and mouse HD models. Pridopidine effects on mitochondrial dynamics were assessed in primary neurons from YAC128 HD mice expressing the mutant human HTT gene. We observe that pridopidine prevents the disruption of mitochondria-ER contact sites and improves the co-localization of inositol 1,4,5-trisphosphate receptor (IP₃R) and its chaperone S1R with mitochondria in YAC128 neurons, leading to increased mitochondrial activity, elongation, and motility. Increased mitochondrial respiration is also observed in YAC128 neurons and in pridopidine-treated HD human neural stem cells (hNSCs). ROS levels were assessed after oxidative insult or S1R knockdown in pridopidine-treated YAC128 neurons, HD hNSCs, and human HD lymphoblasts. All HD models show increased ROS levels and deficient antioxidant response, which are efficiently rescued with pridopidine. Importantly, pridopidine treatment before H₂O₂-induced mitochondrial dysfunction and S1R presence are required for HD cytoprotection. YAC128 mice treated at early/pre-symptomatic age with pridopidine show significant improvement in motor coordination, indicating a delay in symptom onset. Additionally, in vivo pridopidine treatment reduces mitochondrial ROS levels by normalizing mitochondrial complex activity. In conclusion, S1R-mediated enhancement of mitochondrial function contributes to the neuroprotective effects of pridopidine, providing insight into its mechanism of action and therapeutic potential.