The roles of signaling pathways in bone repair and regeneration.

Regenerative medicine has sparked interest in potential strategies for bone repair. Bone defects are widespread and could be caused by trauma, congenital malformations, infections, and surgery. Although bone has a large self-healing capacity, some defects or fractures are too big to regenerate. To regenerate bone structures which can be used for treatment of patients, bone growth must be induced by a number of bioactive implantable materials, cell types and intracellular, and extracellular molecular signaling pathways. Since mesenchymal stem cells (MSCs) and their differentiation during remodeling processes have important roles in bone regeneration, it is believed that understanding molecular signaling pathways involved is crucial to the development of bone implants, bone substitute materials, and cell-based scaffolds for bone regeneration. In this review, we briefly introduce concepts in fracture repair and regeneration following bone injuries, and then discuss the current clinical methods in bone regeneration. In the next section, we review the involvement of the various key signaling pathways in bone regeneration.