Regulation of Bone Homeostasis by Osteocytes.

New data concerning the function of osteocytes as the central regulators of bone homeostasis are briefly outlined. It is established that osteocytes are the main target cells for parathormone. They are a rich source of sclerostin, the main inhibitor of osteoblast activity, and of the RANKL cytokine, the most important regulator of osteoclastogenesis. Under shear stress causing microinjury, osteocytes enter programmed cell death (apoptosis) and osteocyte apoptosis is a signal for nearby healthy osteocytes to activate osteoclasts to resorb bone.