Parkinson's disease (PD) is a prevalent neurodegenerative disorder characterized by dopaminergic neuronal death of unclear etiology. While levodopa remains the gold standard for managing PD motor symptoms, it lacks disease-modifying efficacy, necessitating new neuroprotective therapies. Mitochondrial dysfunction and impaired autophagy are key hallmarks of PD. This study utilized 1-methyl-4-phenylpyridinium (MPP+)-treated SH-SY5Y cells to investigate the neuroprotective mechanisms of catalpol, an iridoid glycoside derived from Rehmannia glutinosa. We found that catalpol attenuated MPP+-induced neurotoxicity, mitochondrial membrane depolarization, and ATP depletion. This protection was critically dependent on autophagy; it was enhanced by the activator rapamycin but abolished by the inhibitor wortmannin and the autophagosome-lysosome fusion inhibitor bafilomycin A1. Catalpol activated autophagy by increasing autophagosome formation, elevating Beclin 1 and LC3-II levels, and promoting p62 degradation. Furthermore, catalpol reversed MPP+-induced mitophagy suppression and restored the regulatory protein PINK1 and DJ-1 expression. Given that Akt/BDNF/Bcl-2 and TrkB/BDNF pathways promote neuronal survival, we investigated their involvement. We found that the TrkB agonist 7,8-DHF mimicked catalpol's neuroprotection against MPP+-induced neurotoxicity, whereas the pan-Trk inhibitor GNF-5837 abolished it. Western blotting demonstrated that catalpol reversed MPP+-mediated suppression of TrkB and Akt phosphorylation, as well as BDNF and Bcl-2 expression. Molecular docking indicated that catalpol may interact with the TrkB ligand-binding domain with higher affinity than 7,8-DHF, and shares key binding residues. Our findings suggest that catalpol exerts neuroprotection via a dual mechanism: preserving mitochondrial function through PINK1/DJ-1-mediated mitophagy and activating the TrkB/Akt/BDNF/Bcl-2 survival pathway, potentially by interacting with the TrkB receptor, highlighting its therapeutic potential for PD.
