New regulation mechanisms of osteoclast differentiation.

Osteoclasts play a crucial role in both physiological and pathological bone resorption. It is, thus, of compelling importance to understand the molecular mechanisms of osteoclast regulation. Because receptor activator of nuclear factor-κB ligand (RANKL) is the key cytokine that induces osteoclast differentiation, we have focused on the investigation of RANKL signaling and RANKL-expressing cells. Here, we summarize the recent advances in the understanding of osteoclastogenic signaling and the cells that express RANKL in the context of osteoimmunology. The scope of osteoimmunology has been extended to now encompass a wide range of molecular and cellular interactions, and its framework provides a scientific basis for future therapeutic approaches to diseases related to the bone and/or immune systems.