BACKGROUND: Rheumatoid arthritis (RA) is marked by joint pain, reduced functionality, and structural damage. The infiltration of immune cells, especially macrophages, is critical in the development of RA. Melatonin is a versatile hormone which possesses anti-inflammatory, antioxidant, and immunomodulatory properties. The efficacy of melatonin in treating diverse inflammatory autoimmune diseases has been well-documented, indicating its potential utility in the management and treatment of rheumatoid arthritis. Our study aimed to investigate whether melatonin could mitigate inflammation by orchestrating macrophage polarization in RA.
METHODS: Utilizing a collagen-induced arthritis (CIA) mouse model and the macrophage cell line RAW264.7 induced with lipopolysaccharide (LPS), we assessed melatonin's potential to counteract RA. The molecular mechanism of melatonin involved in mitophagy and macrophage polarization was investigated using transmission electron microscopy, RNA-seq, western blot, RT-qPCR and immunofluorescence in CIA mouse and RAW264.7 cells.
RESULTS: The findings revealed that melatonin markedly alleviated paw swelling, inhibited cartilage degeneration, and prevented bone erosion in CIA mice. Moreover, melatonin exhibited a dose-dependent inhibition of the M1 macrophage while concurrently enhancing the presence of the M2 macrophage. In addition, melatonin treatment promoted the expression of M2 macrophage-related cytokines and inhibited the expression of M1 macrophage-related cytokines in LPS-induced Raw264.7 cells. Melatonin treatment can also promote the mitophagy through the Src/Fundc1 signaling pathway. The effect of melatonin on regulating M1 macrophage polarization can be inhibited by blocking Fundc1 or using Mdivi-1 (mitophagy inhibitor).
CONCLUSION: Collectively, our data suggest that melatonin improves RA outcomes by recalibrating the balance of different macrophage phenotypes, facilitated by Fundc1-mediated mitophagy promotion. Overall, this study indicates that mitophagy may be a target for RA treatment. It also indicates that the potential of melatonin as a complementary therapy for RA patients warrants further exploration through clinical trials.
