[Bone remodelling and its regulators].

Both cortical and trabecular bones continuously renew themselves to maintain their mechanical strength and bone volume. The sequence of cellular events at the site of bone remodeling is as follows: (1) Activation; osteoclast precursors are activated and differentiated. (2) Resorption; osteoclasts resorb a certain volume of bone by removing mineral and matrix. (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 such as estrogen, PTH, calcitonin, or vitamin D, but also by local factors such as TGF-beta, BMP, IGF-I, IGF-II, prostaglandins, IL-1, IL-4, IL-6, or TNF-alpha. We explain here the mechanism of bone remodeling and review the various regulators for bone remodeling.