Diarylheptanoid Hirsutenone Attenuates Osteoclastogenesis by Suppressing IFNγ and NF-κB Signaling in Th1 and Preosteoclastic Cells.

The aim of the present study was to examine the inhibitory roles and mechanisms of hirsutenone (HTN) in the regulation of osteoclastogenesis. Gene levels were compared to assure the effects of HTN on osteoclastogenesis in mouse splenocytes/CD4(+) T cells, mouse macrophage-like cell line RAW264.7 (preosteoclast), MG63 (osteoblast), and RPMI1788 (B cell) cells. The mechanism by which HTN regulates the degradation of tumor necrosis factor receptor-associated factor 6 (TRAF6) and inhibits inhibitor of kappaB (I kappa B) and nuclear factor-kappaB (NF-kappa B) signaling was examined by Western blotting and luciferase reporter assays. Our results demonstrated that HTN effectively downregulated the expression of interferon gamma (IFN gamma), interleukin-22 (IL-22), IL-1 beta, and tartrate-resistant acid phosphatase (TRAP) in splenocyte-/CD4(+) -RAW264.7 co-culture system. Moreover, receptor activator of nuclear factor-kappa B ligand (RANKL) and CD25 expression were also significantly inhibited in MG63 and CD4(+) single culture system, suggesting an additional independent effect of HTN on osteoclastogenesis. Notably, TRAF6 was markedly degraded along with a decrease in nuclear factor of activated T-cells (NFATc) and NF-kappa B activities in RAW264.7 cells. Finally, we concluded that HTN directly or indirectly inhibits osteoclastogenesis via the inhibition of NF-kappa B signaling by promoting TRAF6 degradation, and plays a crucial role in suppressing the expression of RANKL and cytokines expressed in IFN gamma-producing T-helper 1 (Th1) cells. These findings suggest that HTN may be a promising therapeutic candidate for diseases resulting from bone loss.