Maslinic acid suppresses osteoclastogenesis and prevents ovariectomy-induced bone loss by regulating RANKL-mediated NF-κB and MAPK signaling pathways.

Activation of NF-κB and MAPK/activator protein 1 (AP-1) signaling pathways by receptor activator NF-κB ligand (RANKL) is essential for osteoclast activity. Targeting NF-κB and MAPK/AP-1 signaling to modulate osteoclast activity has been a promising strategy for osteoclast-related diseases. In this study we examined the effects of maslinic acid (MA), a pentacyclic triterpene acid that is widely present in dietary plants, on RANKL-induced osteoclastogenesis, osteoclast function, and signaling pathways by in vitro and in vivo assay systems. In mouse bone marrow monocytes (BMMs) and RAW264.7 cells, MA inhibited RANKL-induced osteoclastogenesis in a dose-dependent manner within nongrowth inhibitory concentration, and MA decreased osteoclastogenesis-related marker gene expression, including TRACP, MMP9, c-Src, CTR, and cathepsin K. Specifically, MA suppressed osteoclastogenesis and actin ring formation at early stage. In ovariectomized mice, administration of MA prevented ovariectomy-induced bone loss by inhibiting osteoclast activity. At molecular levels, MA abrogated the phosphorylation of MAPKs and AP-1 activity, inhibited the IκBα phosphorylation and degradation, blocked NF-κB/p65 phosphorylation, nuclear translocation, and DNA-binding activity by downregulating RANK expression and blocking RANK interaction with TRAF6. Together our data demonstrate that MA suppresses RANKL-induced osteoclastogenesis through NF-κB and MAPK/AP-1 signaling pathways and that MA is a promising agent in the treatment of osteoclast-related diseases such as osteoporosis.

Li C ，Yang Z ，Li Z ，Ma Y ，Zhang L ，Zheng C ，Qiu W ，Wu X ，Wang X ，Li H ，Tang J ，Qian M ，Li D ，Wang P ，Luo J ，Liu M ... -  《-》

Caffeic acid 3,4-dihydroxy-phenethyl ester suppresses receptor activator of NF-κB ligand–induced osteoclastogenesis and prevents ovariectomy-induced bone loss through inhibition of mitogen-activated protein kinase/activator protein 1 and Ca2+–nuclear fact

Receptor activator of NF-κB ligand (RANKL) stimulation leads to the activation of mitogen-activated protein kinase (MAPK)/AP-1 and Ca2+–nuclear factor of activated T-cells cytoplasmic 1 (NFATc1) signaling pathways in osteoclastogenesis. Targeting these pathways has been an encouraging strategy for bone-related diseases, such as postmenopausal osteoporosis. In this study, we examined the effects of caffeic acid 3,4-dihydroxy-phenethyl ester (CADPE) on osteoclastogenesis. In mouse bone marrow monocytes (BMMs) and RAW264.7 cells, CADPE suppressed RANKL-induced osteoclast differentiation and actin-ring formation in a dose-dependent manner within non–growth inhibitory concentrations at the early stage, while CADPE had no effect on macrophage colony-stimulating factor (M-CSF)-induced proliferation and differentiation. At the molecular level, CADPE inhibited RANKL-induced phosphorylation of MAPKs, including extracellular signal-regulated kinases 1/2 (ERK1/2), p38, and c-Jun N-terminal kinase (JNK), without significantly affecting the NF-κB signaling pathway. CADPE abrogated RANKL-induced activator protein 1 (AP-1)/FBJ murine osteosarcoma viral oncogene homolog (c-Fos) nuclear translocation and activation. Overexpression of c-Fos prevented the inhibition by CADPE of osteoclast differentiation. Furthermore, CADPE suppressed RANKL-induced the tumor necrosis factor receptor associated factor 6 (TRAF6) interaction with c-src tyrosine kinase (c-Src), blocked RANKL-induced the phosphorylation of protein kinase B (AKT), and inhibited RANKL-induced Ca2+ oscillation. As a result, CADPE decreased osteoclastogenesis-related marker gene expression, including NFATc1, TRAP, cathepsin K, and c-Src. To test the effects of CADPE on osteoclast activity in vivo, we showed that CADPE prevented ovariectomy-induced bone loss by inhibiting osteoclast activity. Together, our data demonstrate that CADPE suppresses osteoclastogenesis and bone loss through inhibiting RANKL-induced MAPKs and Ca2+-NFATc1 signaling pathways. CADPE is a novel agent in the treatment of osteoclast-related diseases, such as osteoporosis.

Wu X ，Li Z ，Yang Z ，Zheng C ，Jing J ，Chen Y ，Ye X ，Lian X ，Qiu W ，Yang F ，Tang J ，Xiao J ，Liu M ，Luo J ... -  《-》

12-O-tetradecanoylphorbol-13-acetate (TPA) inhibits osteoclastogenesis by suppressing RANKL-induced NF-kappaB activation.

Wang C ，Steer JH ，Joyce DA ，Yip KH ，Zheng MH ，Xu J ... -  《JOURNAL OF BONE AND MINERAL RESEARCH》

Licorice isoliquiritigenin suppresses RANKL-induced osteoclastogenesis in vitro and prevents inflammatory bone loss in vivo.

Osteoclasts, bone-specialized multinucleated cells, are responsible for bone destructive diseases such as osteoporosis, periodontitis, and rheumatoid arthritis. Natural plant-derived products have received substantial attention given their potential therapeutic and preventive activities against human diseases. In the present study, we investigated the effects of isoliquiritigenin (ISL), a natural flavonoid isolated from licorice, on receptor activator of nuclear factor-κB ligand (RANKL)-induced in vitro osteoclastogenesis and inflammation-mediated bone destruction in vivo. We observed that ISL dose-dependently inhibited RANKL-induced osteoclast formation from RAW 264.7 and primary mouse bone marrow-derived macrophages (BMMs), as well as decreased the extent of lacunar resorption. Specifically, ISL targeted RANKL-induced osteoclastogenesis and F-actin rings formation at an early stage. The RANKL-stimulated mRNA expression of osteoclast-related genes and transcription factors were also diminished by ISL. Mechanistically, ISL blocked the RANKL-triggered RANK-TRAF6 association, phosphorylation of mitogen-activated protein kinases (MAPKs), inhibitor of κBα (IκBα) phosphorylation and degradation, nuclear factor-κB (NF-κB) p65 nuclear translocation, as well as activator protein (AP)-1 activation. ISL almost abrogated the nuclear factor of activated T cells (NFATc1) expression and inhibited its nuclear translocation specifically in pre-osteoclasts. Furthermore, the ectopic introduction of NFATc1 into osteoclast precursors almost reversed the ISL-elicited anti-osteoclastogenic effects. Consistent with the in vitro results, administration of ISL prevented inflammatory bone loss in mice by attenuating osteoclast activity. Taken together, our results demonstrated that ISL suppresses RANKL-induced osteoclastogenesis and inflammatory bone loss via RANK-TRAF6, MAPK, IκBα/NF-κB, and AP-1 signaling pathways. Therefore, ISL may be considered as a novel therapeutic and/or preventive strategy against lytic bone diseases.

Zhu L ，Wei H ，Wu Y ，Yang S ，Xiao L ，Zhang J ，Peng B ... -  《-》

Inhibition of RANKL-induced osteoclastogenesis by (-)-DHMEQ, a novel NF-kappaB inhibitor, through downregulation of NFATc1.

Takatsuna H ，Asagiri M ，Kubota T ，Oka K ，Osada T ，Sugiyama C ，Saito H ，Aoki K ，Ohya K ，Takayanagi H ，Umezawa K ... -  《JOURNAL OF BONE AND MINERAL RESEARCH》