Icariin regulates RANKL-induced osteoclast differentiation via the ER α / c -Src/RANK signaling.

Osteoporosis (OP) is a common metabolic bone disease. Excessive osteoclastic activity significantly contributes to the development of OP. Icariin (ICA) is a flavonol glycoside derived from herbal plants and possesses curative effects on postmenopausal OP and bone fracture. This study aimed to investigate the effects of ICA on osteoclast differentiation induced by receptor activator of nuclear factor kappa B (RANK) ligand (RANKL) and the involvement of estrogen receptor α (ER α ) and RANK signaling cascade in this process. RANKL was used to induce the differentiation of RAW264.7 cells to into osteoclasts. Small interfering RNA technique was used to knockdown ER α in cells. Cell counting kit-8 assay was performed to determine the cytotoxicity of ICA. The number of tartrate-resistant acid phosphatase (TRAP)-positive cells was quantified by TRAP staining. RANKL induced the differentiation of RAW264.7 cells into osteoclasts, while ICA abolished the pro-osteoporotic effect of RANKL. Moreover, ER α knockdown abolished the effects of ICA on RANKL-induced osteoclastogenesis. Further exploration revealed that ICA inhibited the phosphorylation of c -Src in osteoclasts via regulating ER α , while inactivation of c -Src reversed ER α knockdown-promoted osteoclastogenesis. Lastly, ICA inhibited the activation of the mitogen-activated protein kinase signaling pathway and downregulated the expressions of target osteoclastogenic proteins in RANKL-treated RAW 264.7 cells, while ER α knockdown almost completely diminished the effects of ICA. ICA inhibited RANKL-induced osteoclast differentiation via regulating the ER α / c -Src/RANK signaling. These findings elucidated a novel mechanism by which ICA exerts an anti-osteoporotic effect.