MS-275, a benzamide histone deacetylase inhibitor, prevents osteoclastogenesis by down-regulating c-Fos expression and suppresses bone loss in mice.

Histone deacetylase (HDAC) enzymes play important roles in physiological and pathological processes by catalyzing the deacetylation of lysine residues in histone and non-histone proteins. Inhibition of HDACs has emerged as an attractive therapeutic strategy for various diseases including cancer and inflammatory diseases. We recently found that MS-275, a class I-specific HDAC inhibitor, exhibits an anabolic effect on bone through promoting expression of alkaline phosphatase in osteoblasts. MS-275 has also been suggested to inhibit inflammatory bone destruction, but the underlying mechanisms are still poorly understood. In this study, we investigated the effects and mechanism of action of MS-275 on osteoclast differentiation and activation. We found that MS-275 inhibits osteoclast differentiation in coculture of osteoblasts and bone marrow cells without affecting expression of receptor activator of NF-κB ligand (RANKL), a key cytokine for osteoclast differentiation, in osteoblasts. MS-275 inhibited RANKL-mediated osteoclast differentiation from its precursors by suppressing RANKL-induced expression of c-Fos, a crucial transcription factor for osteoclastogenesis. The inhibitory effect of MS-275 on osteoclast differentiation was blunted by ectopic overexpression of c-Fos. In addition to osteoclast differentiation, MS-275 decreased bone resorbing activity of mature osteoclasts. Consistent with the in vitro effects, MS-275 decreased osteoclast number and bone destruction in IL-1-induced mouse calvarial bone destruction model. Taken together, our results demonstrate that MS-275 suppresses bone destruction by inhibiting osteoclast differentiation and activation, suggesting a potential therapeutic value of MS-275 for bone disorders associated with increased bone resorption.

The potential of mouse skin-derived precursors to differentiate into mesenchymal and neural lineages and their application to osteogenic induction in vivo.

Although previous studies indicate that skin-derived precursors (SKPs) are multipotent dermal precursors that share similarities with neural crest stem cells (NCSCs), a shared ability for multilineage differentiation toward neural crest lineages between SKPs and NCSCs has not been fully demonstrated. Here, we report the derivation of SKPs from adult mouse skin and their directed multilineage differentiation toward neural crest lineages. Under controlled in vitro conditions, mouse SKPs were propagated and directed toward peripheral nervous system lineages such as peripheral neurons and Schwann cells, and mesenchymal lineages, such as osteogenic, chondrogenic, adipogenic, and smooth muscle cells. To ask if SKPs could generate these same lineages in vivo, a mixture of SKP-derived mesenchymal stem cells and hydroxyapatite/tricalcium phosphate was transplanted into the rat calvarial defects. Over the ensuing 4 weeks, we observed formation of osteogenic structure in the calvarial defect without any evidence of teratomas. These findings demonstrate the multipotency of adult mouse SKPs to differentiate into neural crest lineages. In addition, SKP-derived mesenchymal stem cells represent an accessible, potentially autologous source of precursor cells for tissue-engineered bone repair.

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.