Melatonin promotes osteoblastic differentiation through the BMP/ERK/Wnt signaling pathways

Although melatonin has a variety of biological actions such as antitumor, antiangiogenic, and antioxidant activities, the osteogenic mechanism of melatonin still remains unclear. Thus, in the present study, the molecular mechanism of melatonin was elucidated in the differentiation of mouse osteoblastic MC3T3-E1 cells. Melatonin enhanced osteoblastic differentiation and mineralization compared to untreated controls in preosteoblastic MC3T3-E1 cells. Also, melatonin increased wound healing and dose-dependently activated osteogenesis markers such as runt-related transcription factor 2 (Runx2), osteocalcin (OCN), bone morphogenic protein (BMP)-2 and -4 in MC3T3-E1 cells. Of note, melatonin activated Wnt 5 alpha/beta, beta-catenin and the phosphorylation of c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) in a time-dependent manner while it attenuated phosphorylation of glycogen synthase kinase 3 beta (GSK-3 beta) in MC3T3-E1 cells. Consistently, confocal microscope observation revealed that BMP inhibitor Noggin blocked melatonin-induced nuclear localization of beta-catenin. Furthermore, Western blotting showed that Noggin reversed activation of beta-catenin and Wnt5 alpha/beta and suppression of GSK-3 beta induced by melatonin in MC3T3-E1 cells, which was similarly induced by ERK inhibitor PD98059. Overall, these findings demonstrate that melatonin promotes osteoblastic differentiation and mineralization in MC3T3-E1 cells via the BMP/ERK/Wnt pathways.