Melittin inhibits MPP⁺-induced HT22 cell death by suppressing Bax activation and improving mitochondrial function

Melittin (MEL) is the main bioactive component of bee venom and has been reported to have various pharmacological effects. This study investigates the protective effect of MEL on MPP⁺-injured HT22 cells and the possible mechanisms involved. We treated the cells with 4 mM MPP⁺ for 24 h to induce a cellular injury model. HT22 cells were pretreated with 0.1 μM MEL for 6 h and then exposed to 4 mM MPP⁺ for 24 h. We measured cell viability, the expression of Bax, the indicators and protein levels associated with apoptosis and parthanatos, and the co-localisation of MEL and mitochondria, and mitochondrial function-related indices such as the mitochondrial membrane potential (MMP) and mito-SOX. We show that PAR protein expression was significantly increased in the MPP⁺-treated cell model and that the parthanatos inhibitor DPQ significantly reduced MPP⁺-induced cell death, suggesting that MPP⁺ can cause PARP1-dependent cell death. MEL significantly inhibited cell death, increased cell viability as well as NAD+ and ATP levels, increased the expression of Bcl-2 and suppressed the activation of Bax, cleaved-caspase3, and cleaved-PARP1. Moreover, MEL was found to be localised on the mitochondria of HT22 cells and to improve mitochondrial functions including increased MMP and decreased mitochondrial reactive oxygen species. We speculate that MEL may protect neurons against MPP⁺-induced HT22 cell injury by inhibiting Bax activation, suppressing changes in mitochondrial permeability, and improving mitochondrial function, thereby preventing cell parthanatos and apoptosis.