膜内成骨和软骨内成骨是骨发生的两种方式。申请者研究发现褪黑素促进骨髓间充质干细胞（MSCs）向成骨细胞分化而促进膜内成骨（Zhang L et al, J Pineal Res. 2010; Zhang L et al, J Pineal Res. 2012），但是褪黑素在软骨内成骨中的作用仍有待研究。申请者初步研究发现褪黑素促进MSCs软骨分化-肥大，其作用与BMPs和Ihh信号通路有关，这提示褪黑素可能加速软骨内成骨过程。本研究拟深入研究褪黑素在MSCs向软骨分化、肥大中的作用，并探讨其作用是否通过膜受体和核受体介导；研究褪黑素与BMPs信号通路和Ihh-PTHrP负反馈循环的关系，探讨褪黑素促进软骨细胞肥大分化的分子机制；最后在小鼠体内考察褪黑素与软骨内成骨的关系。从而阐明褪黑素在MSCs向软骨分化、肥大及软骨内成骨过程中的作用机制，揭示褪黑素在软骨内成骨中的重要意义。

There are two types of ossification in the human body: endochondral and intramembranous ossification. Applicants have demonstrated that melatonin enhanced intramembranous ossification by stimulating osteogenic differentiation of MSCs (Zhang L et al, J Pineal Res 2010; Zhang L et al, J Pineal Res 2012). However, further study remains to be done on whether melatonin affects endochondral ossification. We preliminary study found that melatonin promoted MSCs chondrogenesis, which might be related to BMPs and Ihh signaling pathway, suggesting that melatonin may play an important role in endochondral bone formation. In this study, we will (i) study the role of melatonin on chondrogenic differentiate and hypertrophic differentiation of chondrocytes, and then investigate whether its role mediated by membrane receptors or nuclear receptors; (ii) reveal the molecular mechanism of melatonin by studying how melatonin enhances endochondral ossification through BMPs signaling pathway and Ihh-PTHrP negative feedback loop; (iii) finally apply melatonin to endochondral bone formation in vivo to investigate whether melatonin stimulate endochondral bone formation in mice. The result of this project should reveal the effect of melatonin on endochondral bone formation and provide further insight into role of melatonin on the process of bone formation.