Mitochondrial ROS level was measured by the fluorometric assay, as previously described [26 (link)]. Prepared PC12 cells seeded in 96-well microplates (106 cells/well) were incubated with MitoSOX red reagent (Invitrogen, M36008, USA) at a concentration of 4 μM in the dark at 37°C for 10 min. Cells were then washed twice with warm PBS. The ROS level was identified using a SpectraMax M5e Multi-Mode microplate reader (Molecular Devices, USA).