Viera Spustová, Kornélia Štefíková
Bone remodeling is a continual process of bone resorption and formation which runs through the whole life. The bone remodeling cycle consists of series of highly regulated processes in which hormones, cytokines, prostaglandins and growth factors take place. The control of bone turnover is provided by the RANK/RANKL and osteoprotegerin (OPG) system. RANK (receptor activator of nuclear factor κB) is a receptor expressed on preosteoclasts. RANKL (receptor activator of nuclear factor κB ligand) and OPG are synthesised in osteoblasts. RANKL is ligand for RANK and OPG has high afinity to RANKL. The interaction between RANKL and RANK stimulates differentiation and maturation of osteoclasts. The effect of RANKL is blocked by OPG which acts as soluble receptor for RANKL, by that it hinders binding of RANKL to RANK; it leads to a decrease in osteoclast maturation and subsequently to decreasing of bone resorption. The ratio RANKL/OPG determines the rate of bone remodeling. The system RANK/RANKL/OPG is a newly discovered physiological mechanism which has an important role in bone metabolism, immune system and vascular biology. Imbalance in this system participates to the development of several bone, inflammatory, and genetic diseases which were defined on the basis of this knowledge. Postmenopausal osteoporosis, glucocorticoid- induced osteoporosis, hyperparathyreoidism, Paget’s disease, rheumatoid arthritis and bone tumors belong to the most important. At present, antibody against RANKL is used as a treatment for osteoporosis.