The biological function of BMAL1 in skeleton development and disorders.

BMAL1 is a core component of the circadian clock loop, which directs the sophisticated circadian expression of clock-controlled genes. Skeletal Bone development is a complex biological process involving intramembranous ossification, endochondral ossification and bone remodeling, as well as specific cells, such as mesenchymal cells, osteoblasts, osteoclasts, chondrocytes, etc. Growing evidences suggest that BMAL1 is indispensable for hard tissue development, including bone, cartilage and teeth. Loss of BMAL1 in animals can inhibit bone and cartilage development, and result in abnormal bone mass. In mesenchymal cells, BMAL1 defect inhibits osteoblastic and chondrocytic differentiation. Inactivation of BMAL1 also can promote the differentiation and formation of osteoclasts and increase bone resorption. Specifically, preclinical data demonstrate that the abnormity of BMAL1 expression is associated with skeletal disorders such as skeletal mandibular hypoplasia, osteoarthritis, osteoporosis, etc. In this review, we systemically describe the impact of BMAL1 in skeletal development and homeostasis, and devote to searching new therapy strategies for bone disorders.