[Regulatory mechanisms of bone remodeling]

Bone tissues continuously renew themselves to maintain their bone volume and mechanical strength. Sequence of the cellular events at the site of bone remodeling is as follows: (1) Activation; osteoclast progenitors are activated and differentiated. (2) Resorption; osteoclasts resorb a certain volume of bone by removing bone matrix and mineral. (3) Formation; osteoblasts differentiate and form new bone. The cellular coupling in space and time between osteoclastic resorption and osteoblastic formation is regulated not only by systemic hormones (estrogen, PTH, calcitonin, or vitamin D etc.) and local factors (TGF-beta, BMPs, IGFs, prostaglandins, interleukins, or TNF-alpha, etc.), but also by mechanical stress. We review the various regulators for bone remodeling and comment on the regulatory mechanism of bone remodeling.