Abstract: Objective To explore the effect of melatonin (MT) on 2,2',4,4'-tetrabromodiphenylether (PBDE-47)-induced abnormal autophagy and apoptosis in rat adrenal medullary pheochromocytoma PC12 cells. Methods PC12 cells were pretreated with a concentration gradient (12.5, 25, 50, 100, and 200 μmol/L) of melatonin for 2 h before exposure to 20 μmol/L PBDE-47 for 24 h to determine the optimal concentration of melatonin for cell treatment. In subsequent experiments, PC12 cells were treated with 0.5‰ DMSO (control group), 20 μmol/L PBDE-47, 25 μmol/L melatonin, or both PBDE-47 and melatonin. Immuno-fluorescence assay was used to detect the positive staining of microtubule associated protein 1 light chain 3 (LC3; a marker protein of autophagy); Western blotting was performed to determine the expression levels of the key autophagic proteins including autophagy-related protein 7 (ATG7), LC3-II and autophagy substrate p62, and the key apoptotic proteins including active cysteine-containing aspartate specific protease-3 (active caspase-3) and cleaved poly(ADP ribose) polymerase (cleaved PARP). Results PBDE-47 treatment significantly reduced the viability of PC12 cells (P=0.001), but pretreatment with 25 μmol/L melatonin maintained a cell viability over 80% following exposure to PBDE-47 (P=0.023). PBDE-47-treated PC12 cells showed obviously enhanced immunofluorescent staining of LC3 protein, a significantly decreased expression of ATG7 and increased expression levels of p62, LC3-II, active caspase-3 and cleaved PARP (P<0.001). The cells treated with both PBDE-47 and melatonin showed obviously reduced staining of LC3 protein with a signficantly increased expression level of ATG7 (P=0.034) and decreased expressions of p62 (P=0.048), LC3-II (P=0.018), active caspase-3 (P<0.001) and cleaved PARP (P=0.032). Conclusion PBDE-47 exposure impairs autophagy to cause autophagosome accumulation and promote apoptosis of PC12 cells. Melatonin can improve PBDE-47-induced abnormal autophagy and apoptosis and thus promote the survival of PC12 cells

Key words: melatonin; 2,2',4,4'-tetrabromodiphenylether; neurotoxicity; autophagy; apoptosis