Osteoclasts are multinucleated cells that have a unique role in bone degradation. Modulation of osteoclast formation and/or its activity is an important approach for the treatment of bone-destructive diseases such as osteoporosis and rheumatoid arthritis. In this study, Gymnasterkoreayne F (GK-F), a natural compound isolated from Gymnaster koraiensis, was found to inhibit osteoclast differentiation from primary bone marrow-derived macrophages (BMMs) in a dose-dependent manner. The inhibition occurred through the suppression of nuclear factor of activated T cells c1 (NFATc1) expression, which then led to the decreased levels of osteoclastogenic markers, including Cathepsin K and tartrate-resistant acid phosphatase (TRAP). In addition, GK-F abolished pre-osteoclast fusion induced by the receptor activator of nuclear factor kappa B ligand (RANKL), lipopolysaccharide (LPS) and TNF-α. Reflecting its inhibitory effects on cell-cell fusion, GK-F attenuated the gene expression of an essential molecule of osteoclast fusion, the dendritic cell-specific transmembrane protein (DC-STAMP). Furthermore, GK-F inhibited the bone resorptive activity of differentiated osteoclasts through its ability to block RANKL-induced actin ring formation. The effect was associated with a significant decrease in the induction of β3 integrin expression, which is an essential regulator of osteoclast cytoskeletal function. Taken together, these results suggest that GK-F might be useful as a therapeutic agent for bone resorption-related diseases.
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