Trichostatin A inhibits osteoclastogenesis and bone resorption by suppressing the induction of c-Fos by RANKL.

Histone deacetylases are enzymes involved in the remodeling of chromatin structure, in the regulation of transcriptional activity, and in epigenetic integrity. Histone deacetylase inhibitors such as trichostatin A (TSA) and suberoylanilide hydroxamic acid (SAHA) have emerged as potent anticancer drugs that have proved useful in preclinical and early clinical trials. The role of histone deacetylase inhibitors in regulating osteoclast differentiation, however, is not well established. In this study, we analyzed the effects of TSA on osteoclast differentiation induced by the differentiation factor RANKL (receptor activator of NF-kappaB ligand). TSA strongly inhibited osteoclast formation in coculture of bone marrow cells and osteoblasts without reducing RANKL expression in osteoblasts. Furthermore, TSA suppressed RANKL-induced osteoclast formation from primary bone marrow-derived macrophages. TSA was only effective when present during the early stage of osteoclast differentiation. This effect was accompanied by a significant decrease in the RANKL-stimulated induction of c-Fos and NFATc1, which are key transcription factors during early osteoclastogenesis. The ectopic introduction of c-Fos and a constitutively active form of NFATc1 reversed the TSA-induced antiosteoclastogenic effect. Consistent with the in vitro results, TSA inhibited lipopolysaccharide- and interleukin-1-induced bone resorption and osteoclast formation in an in vivo model. Taken together, our findings suggest a novel action of TSA: inhibiting RANKL-induced osteoclast formation by suppressing the induction of the osteoclastogenic transcription factor c-Fos. Also, the inhibitory effect of TSA on bone destruction in vivo suggests that histone deacetylase inhibitors may be novel therapeutics for treating typical bone diseases.

Trolox prevents osteoclastogenesis by suppressing RANKL expression and signaling.

Excessive receptor activator of NF-kappaB ligand (RANKL) signaling causes enhanced osteoclast formation and bone resorption. Thus, down-regulation of RANKL expression or its downstream signals may be a therapeutic approach to the treatment of pathological bone loss. In this study, we investigated the effects of Trolox, a water-soluble vitamin E analogue, on osteoclastogenesis and RANKL signaling. Trolox potently inhibited interleukin-1-induced osteoclast formation in bone marrow cell-osteoblast coculture by abrogating RANKL induction in osteoblasts. This RANKL reduction was attributed to the reduced production of prostaglandin E(2) via a down-regulation of cyclooxygenase-2 activity. We also found that Trolox inhibited osteoclast formation from bone marrow macrophages induced by macrophage colony-stimulating factor plus RANKL in a reversible manner. Trolox was effective only when present during the early stage of culture, which implies that it targets early osteoclast precursors. Pretreatment with Trolox did not affect RANKL-induced early signaling pathways, including MAPKs, NF-kappaB, and Akt. We found that Trolox down-regulated the induction by RANKL of c-Fos protein by suppressing its translation. Ectopic overexpression of c-Fos rescued the inhibition of osteoclastogenesis by Trolox in bone marrow macrophages. Trolox also suppressed interleukin-1-induced osteoclast formation and bone loss in mouse calvarial bone. Taken together, our findings indicate that Trolox prevents osteoclast formation and bone loss by inhibiting both RANKL induction in osteoblasts and c-Fos expression in osteoclast precursors.

Inhibition of osteoclast differentiation and bone resorption by sauchinone.

Osteoclasts are bone-specific multinucleated cells generated by differentiation of monocyte/macrophage lineage precursors. Regulation of osteoclast differentiation is considered an effective therapeutic approach to the treatment of bone-lytic diseases. In this study, we investigated effects of sauchinone, a lignan from Saururus chinensis, on osteoclastogenesis induced by the differentiation factor RANKL (receptor activator of nuclear factor kappa B ligand). Sauchinone strongly inhibited the osteoclastogenesis from primary bone marrow-derived macrophages (BMMs). This effect was accompanied by a significant decrease in the level of carbonic anhydrase II, calcitonin receptor, MMP9, and TRAP, which are normally upregulated during osteoclast differentiation. For the induction of osteoclastogenesis-associated genes, RANKL activates multiple transcription factors through mechanisms involving mitogen-activated protein kinases (MAPK) and reactive oxygen species (ROS). Sauchinone greatly attenuated the activation of ERK and, less prominently, that of p38 MAPKs by RANKL. The RANKL-stimulated induction of c-Fos and NFATc1 transcription factors was also abrogated by sauchinone. In addition, the activation of AP-1, NFAT, and NF-kappaB transcription factors was alleviated in sauchinone-treated cells. Sauchinone also diminished the RANKL-stimulated increase of ROS production in BMMs. Consistent with the in vitro anti-osteoclastogenic effect, sauchinone inhibited bone destruction and osteoclast formation caused by lipopolysaccharide in an animal model. Taken together, our data demonstrate that sauchinone inhibits RANKL-induced osteoclastogenesis by reducing ROS generation, which attenuates MAPK and NF-kappaB activation, ultimately leading to the suppression of c-Fos and NFATc1 induction. Also the in vivo effect of sauchinone on bone erosion strengthens the potential usefulness of this compound for diseases involving bone resorption.

Tanshinone IIA inhibits osteoclast differentiation through down-regulation of c-Fos and NFATc1.

Bone is a dynamic tissue that is regulated by the activity of bone-resorbing osteoclasts and bone-forming osteoblasts. Excessive osteoclast formation causes diseases such as osteoporosis and rheumatoid arthritis. Natural substances may be useful as therapeutic drugs to prevent many diseases in humans because they avoid the many side effects of treatment with chemical compounds. Here we show that tanshinone IIA isolated from Salvia miltiorrhiza Bunge inhibits the receptor activator of NF-kappaB ligand (RANKL)-mediated osteoclast differentiation of osteoclast precursors. Tanshinone IIA suppressed the expression levels of c-Fos and NFATc1 induced by RANKL. However, retrovirus-mediated overexpression of c-Fos induced the expression of NFATc1 despite the presence of tanshinone IIA and reversed the inhibitory effect of tanshinone IIA on osteoclast differentiation. Also, the introduction of osteoclast precursors with the NFATc1 retrovirus led to osteoclast differentiation in the presence of tanshinone IIA. Our results suggest that tanshinone IIA may have a role as a therapeutic drug in the treatment of bone disease such as osteoporosis.