Ropinirole improves the amyotrophic lateral sclerosis phenotype of TDP43-mutant iPSC-derived motor neurons via a D2R-independent mechanism

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by motor neuron (MN) degeneration. The dopamine D2 receptor (D2R, DRD2) agonist ropinirole hydrochloride (ROPI) constitutes a potential therapeutic candidate for ALS through phenotypic screening of disease models of MNs that use patient-derived induced pluripotent stem cells (iPSCs). The ROPALS trial, a phase I/II trial in patients with ALS, demonstrated the safety and efficacy of ROPI. However, the D2R antagonist and modulator only partially mitigated the suppressive effect of ROPI on the ALS phenotype, and the detailed mechanism of action of ROPI has not been fully elucidated. In this study, we investigated whether the therapeutic effects of ROPI in ALS depend on D2R. Using D2R-deficient iPSCs, we demonstrated that ROPI effectively mitigated neuronal cell death, reactive oxygen species (ROS) production, and neuronal hyperexcitation in a D2R-independent manner. Further analyses revealed that ROPI rescued aberrant RNA splicing and restored mRNA expression of mitochondrial proteins in a D2R-independent manner. Our data suggest that ROPI has not only a canonical D2R agonist effect, but also multifunctional effects that are mediated in a D2R-independent manner. Therefore, our findings may open new avenues for the development of more effective therapeutic approaches for ALS.