Osteoprotegerin (OPG) is a glycoprotein belonging to the tumor necrosis factor receptor superfamily. Its key function is regulating bone metabolism: it acts as a decoy receptor for receptor activator of nuclear factor-κB ligand (RANKL), blocking RANKL's binding to RANK on osteoclasts. This inhibition prevents osteoclast differentiation and activation, thereby reducing bone resorption and maintaining bone homeostasis. It has been demonstrated that treatment with OPG can induce a significant increase in cells. To test the effect of OPG on cell proliferation, U2OS cells were seeded into triplicate wells of 96-well plates and allowed to attach, replaced with various concentrations of recombinant human OPG. After incubated for 72h, cells were observed by inverted microscope and cell proliferation was measured by Cell Counting Kit-8 (CCK-8). Briefly, 10 µl of CCK-8 solution was added to each well of the plate, then the absorbance at 450 nm was measured using a microplate reader after incubating the plate for 1-4 hours at 37 ℃. Cell viability was assessed by CCK-8 assay after incubation with recombinant human OPG for 72h. The result was shown in Figure 1. It was obvious that OPG significantly increased cell viability of U2OS cells. The ED50 of recombinant human OPG is 0.945 μg/ml.