Sephin1 directly targets PHB2 to activate PINK1-PRKN-dependent mitophagy and alleviate α-synuclein neurotoxicity in Parkinson's disease models.

Parkinson's disease (PD) is a prevalent age-related neurodegenerative disorder characterized by pathological α-synuclein aggregation, mitochondrial dysfunction, and progressive loss of dopaminergic neurons, with no effective disease-modifying treatment available. Sephin1 has been proven to exert protective effects in multiple models of proteostasis diseases. However, its therapeutic potential and the underlying mechanisms in PD remain largely uncharacterized. To investigate the neuroprotective effects and mechanisms of Sephin1 in PD models, we used α-synuclein pre-formed fibrils (PFFs)-stimulated SH-SY5Y cells and primary midbrain neurons for in vitro assays, and A53T transgenic mice for in vivo evaluation. Neurotoxicity, mitochondrial function, mitophagy flux, and α-synuclein pathology were assessed. Limited proteolysis mass spectrometry (Lip-MS), surface plasmon resonance (SPR) assays, cellular thermal shift assay (CETSA), and molecular docking were applied to identify and validate direct targets. In vitro experiments revealed that Sephin1 alleviated PFFs-induced α-synuclein neurotoxicity in a dose-dependent manner. It restored mitochondrial homeostasis and inhibited oxidative stress through PINK1-PRKN-mediated mitophagy, independent of the canonical GADD34 pathway. Mechanistically, Sephin1 directly bound Prohibitin-2 (PHB2), strengthened the PHB2-LC3B interaction, and activated the PARL-PGAM5-PINK1 signaling axis. In vivo, Sephin1 mitigated motor dysfunction, rescued defective mitophagy, and attenuated α-synuclein pathology in A53T mice. Collectively, our findings establish the protective effect of Sephin1 in PD and uncover a previously unrecognized mechanism by which Sephin1 directly targets PHB2 to activate mitophagy.