Pridopidine Protects ALS Patient-Derived Neural Progenitor Cells via Sigma-1 Receptor Activation

The sigma-1 receptor (S1R) is an endoplasmic reticulum (ER)-resident protein enriched at the mitochondria-associated ER membranes (MAMs) that supports ER homeostasis, preserves mitochondrial function, and enhances cell survival under stress. Disruptions of MAM integrity and prolonged ER stress are well-recognized pathological features of amyotrophic lateral sclerosis (ALS), contributing to motor neuron dysfunction and degeneration. In this study, we evaluated the protective effects of pridopidine, a highly selective and potent S1R agonist currently in clinical development for Huntington's disease (HD) and ALS, using neural progenitor cells (NPCs) derived from induced pluripotent stem cells (iPSCs) from a patient with sporadic ALS. Exposure of ALS NPCs to the ER stressor tunicamycin increased the ER stress markers binding immunoglobulin protein (BiP) and C/EBP homologous protein (CHOP), disrupted mitochondrial membrane potential, upregulated expression of the mitochondrial apoptotic marker, BAX, increased caspase-3 activation, and reduced cell viability. Pridopidine significantly attenuated tunicamycin-induced BiP and CHOP expression in a biphasic, dose-dependent manner (with maximal efficacy at 1 µM), consistent with the typical pharmacology of S1R agonists. Pridopidine restored mitochondrial membrane potential, reduced mitochondrial apoptotic signaling, shown by decreased BAX expression and caspase-3 activation, and improved survival of ALS-NPCs under ER stress. Co-treatment with the selective S1R antagonist, NE-100, attenuated these effects, supporting an S1R-mediated mechanism of action for pridopidine. Together, these results demonstrate that S1R activation by pridopidine mitigates ER-stress-induced mitochondrial dysfunction and cell loss in ALS-NPCs, resulting in enhanced survival of NPCs supporting the therapeutic potential of pridopidine in ALS.