Melatonin enhances autophagy and decreases apoptosis induced by nanosilica in RAW264.7 cells

Melatonin is one of the main hormones that regulate biological rhythms and have immunomodulation, anti-inflammatory, and antioxidation functions. In this study, we aimed to explore the effect of melatonin on the autophagy, apoptosis, and inflammatory reaction of macrophages (RAW264.7 cells) stimulated by nanosilica. SiO2 (100 mg/mL, 10-20 nm) was used to stimulate RAW264.7 cells at different time points (0, 2, 4, 8, 12, and 24 hr). Melatonin (200 mu M) was added to SiO2-stimulated macrophages at 12 hr. Beclin-1, LC3, Bax, Bcl-2, and Caspase-3 were examined with western blotting. Flow cytometry was used to detect apoptosis. The levels of TNF-alpha, IL-1 beta, and IL-18 were detected by ELISA. The level of TNF-alpha in the supernatant of SiO2-stimulated cells gradually increased with time but decreased following melatonin administration. In contrast, the expression of IL-1 beta and IL-18 increased after melatonin treatment. LC3 and Bax signaling pathways were activated in SiO2-stimulated RAW264.7 cells, showing elevated expression of LC3 and reduced expression of Bax in the melatonin-treated cells. GFP-LC3 puncta were significantly increased in SiO2-stimulated RAW264.7 cells and decreased in melatonin-treated cells. The apoptotic rate in SiO2-stimulated RAW264.7 cells increased with time and decreased after melatonin treatment, and the number of phagosomes increased with the stimulation of nanosilica and the treatment of melatonin. Melatonin might promote autophagy and inhibit apoptosis as well as inflammatory responses of RAW264.7 cells stimulated by nanosilica. (c) 2019 IUBMB Life, 2019