[Osteoprotegerin/RANKL/RANK system and postmenopausal osteoporosis. The possible therapeutic aspects]

The osteoprotegerin/RANKL/RANK system seems to be an essential signalling pathway by which osteoblasts control the pool size of active osteoclasts. According to the convergence hypothesis, numerous osteotropic hormones and cytokines act by increasing or decreasing the osteoprotegerin (OPG) or receptor activator of NF-kappa B ligand (RANKL) expression in osteoblasts. The role of OPG as the decoy receptor is to bind RANKL that prevents RANKL from activating its receptor RANK in osteoclast lineage cells. The effects are inhibition of osteoclasts differentiation and activation as well as induction of osteoclasts apoptosis. Estrogen and bisphosphonates stimulate the production of OPG that may, at least partly be responsible for their antirsorptive effect on bone. The results of reported experiments suggest that OPG could be a useful agent in therapy of excessive bone resorption diseases.