Osteoprotegerin influences the bone resorption activity of osteoclasts

The aim of the present study was to determine whether osteoprotegerin (OPG) influences the bone resorption activity of osteoclasts. RAW264.7 cells were induced by macrophage colony-stimulating factor (M-CSF) + receptor activator of nuclear factor-κB ligand (RANKL) and 0, 10, 20, 50 and 100 ng/ml OPG were added into various groups in the presence of the two cytokines. The OPG treatment was continued for 24 h. Osteoclast differentiation and activation were estimated via TRAP staining assay, TRITC-conjugated phalloidin staining, resorption activity analysis. Furthermore, the expression levels of the osteoclastic bone resorption-related genes MMP-9, cathepsin K and carbonic anhydrase II (CA II) were examined using real-time polymerase chain reaction (PCR). The data demonstrated that high concentrations of OPG could inhibit the differentiation and activation of osteoclasts. Furthermore, real-time PCR analysis illustrated that OPG decreased the expression of MMP-9 and cathepsin K in different concentrations of OPG and it decreased the expression of CA II genes at 10 and 20 ng/ml concentrations of OPG. For the time gradient study, OPG decreased the expression of MMP-9 and CA II genes but not that of the cathepsin K gene. In summary, the resorption activity of osteoclasts was suppressed by high concentrations of OPG and, at the molecular level, OPG decreased the expression of osteoclastic bone resorption-related genes.