Geraniin Suppresses the Expression of Cathepsin K in Osteoclasts

Background: Cathepsin K (CatK) plays a critical role in osteoclast-induced bone degradation, and it may be a potential therapeutic target for osteoporosis treatment. In our previous experiments, geraniin was reported to have anti-osteoporotic effects against OVX-induced rat osteoporosis and inhibitory effects on bone resorption in vitro. However, it is not known whether geraniin exhibits an inhibitory effect on CatK expression in vitro. Method: In the present study, we investigated the effect of geraniin on the mRNA and protein expression of CatK in the primary osteoclasts isolated from rats. These cells were treated with different concentrations of geraniin, and the mRNA and proteins of CatK were quantified by in situ hybridization assay and immunocytochemical analysis. Results: : The results showed that different concentrations of geraniin (10-9 to 10-7 mol/L) significantly decreased the values of integral optical density and mean optical density of CatK mRNA and protein expression in positive cells in a concentration-dependent manner, as determined by in situ hybridization and immunocytochemistry. Moreover, similar results were observed between 10-7 mol/L geraniin and 10-6 mol/L E-64. Conclusion: These results demonstrated that geraniin can decrease the expression of CatK in osteoclasts. It may be a novel and potential CatK inhibitor came from natural plant. As a traditional Chinese herbal medicine, it may be used to treat osteoporosis in addition to its anti-inflammatory effect.