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Bone fracture is an important trauma frequently encountered into emergency medicine as well as orthopedics reflecting an aging society. Oncostatin M, an inflammatory cytokine produced by osteal macrophages, has been considered to play a crucial role in fracture healing. Macrophage colony-stimulating factor (M-CSF) secreted from osteoblasts is essential in osteoclastgenesis, and the secretion is stimulated by transforming growth factor-β (TGF-β). The aim of this study is to elucidate the effects of oncostatin M on the TGF-β-induced M-CSF synthesis in osteoblast-like MC3T3-E1 cells and the underlying mechanisms. Oncostatin M attenuated the TGF-β-stimulated M-CSF release and the mRNA expressions. SMAD3 inhibitor SIS3, p38 MAP kinase inhibitor SB203580, MEK1/2 inhibitor PD98059, and SAPK/JNK inhibitor SP600125 significantly suppressed the M-CSF release. Oncostatin M suppressed the TGF-β-induced phosphorylation of p44/p42 MAP kinase and SAPK/JNK, but failed to affect the phosphorylation of SMAD3 and p38 MAP kinase. Oncostatin M attenuated the TGF-β-stimulated vascular endothelial growth factor (VEGF) release and the TGF-β-induced mRNA expressions of VEGF. These results strongly suggest that oncostatin M downregulates TGF-β signaling upstream of p44/p42 MAP kinase and SAPK/JNK, but not SMAD 2/3 and p38 MAP kinase, in osteoblasts, leading to the attenuation of M-CSF synthesis. Our findings might provide a new therapeutic strategy for the acceleration of fracture healing process.

Selective estrogen receptor modulator (SERM) binds to estrogen receptors (ERs) and acts as both an agonist or an antagonist, depending on the target tissue. Raloxifene and bazedoxifene as SERMs are currently used hormone replacement medicines for postmenopausal osteoporosis. Macrophage colony-stimulating factor (M-CSF) secreted from osteoblasts promotes osteoclastogenesis. We have previously demonstrated that transforming growth factor (TGF)-β induces the synthesis of M-CSF via SMAD2/3, p38 mitogen-activated protein kinase (MAPK), p44/p42 MAPK and c-Jun N-terminal kinase (JNK) in osteoblast-like MC3T3-E1 cells. In the present study, we investigated whether SERM affects the M-CSF synthesis by TGF-β in MC3T3-E1 cells. Raloxifene and bazedoxifene significantly suppressed the synthesis of M-CSF. PPT, an ERα agonist, but not ERB041, an ERβ agonist, inhibited the release of M-CSF. MPP, an ERα antagonist, reversed the suppression by raloxifene of the M-CSF release. Raloxifene attenuated the TGF-β-induced phosphorylation of JNK but not SMAD3, p42 MAPK and p38 MAPK. Bazedoxifene and PPT also inhibited the phosphorylation of JNK. Furthermore, MPP, an ERα antagonist, reversed the suppression by both raloxifene and bazedoxifene of the phosphorylation of JNK. Our results strongly indicate that raloxifene and bazedoxifene, SERMs, suppress the TGF-β-induced synthesis of M-CSF through ERα-mediated inhibition of JNK pathway in osteoblasts.

Acetaminophen is one of the most widely used analgesic and antipyretic medicines, whose long-period use has reportedly been associated with an increased risk of bone fracture. However, the mechanism underlying this undesired effect remains to be investigated. The homeostatic control of bone tissue depends on the interaction between osteoblasts and osteoclasts. Osteoprotegerin produced by osteoblasts is known to play an essential role in suppressing osteoclast induction. We have previously reported that prostaglandin (PG) E 2 and PGF 2α induce osteoprotegerin synthesis through p38 mitogen-activated protein kinase (MAPK), p44/p42 MAPK and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in osteoblast-like MC3T3-E1 cells. In the present study, we investigated the effects of acetaminophen on the osteoprotegerin synthesis induced by PGE 2 and PGF 2α in MC3T3-E1 cells. Acetaminophen significantly suppressed the osteoprotegerin release stimulated by PGE 2 and PGF 2α . The PGE 2 -induced expression of osteoprotegerin mRNA was also reduced by acetaminophen. Acetaminophen markedly downregulated the phosphorylation of SAPK/JNK stimulated by PGE 2 and PGF 2α , but not those of p38 MAPK or p44/p42 MAPK. SP600125, an inhibitor of SAPK/JNK, suppressed the levels of PGE 2 - and PGF 2α -upregulated osteoprotegerin mRNA expression. Taken together, these results strongly suggest that acetaminophen reduces the PGE 2 - and PGF 2α -stimulated synthesis of osteoprotegerin in osteoblasts, and that the suppressive effect is exerted via attenuation of SAPK/JNK. These findings provide a molecular basis for the possible effect of acetaminophen on bone tissue metabolism.

Migration of osteoblasts to the sites resorbed by osteoclasts is an essential step in bone remodeling. However, the exact mechanism of osteoblast migration is still not known. We have shown that platelet-derived growth factor (PDGF)-BB induces the migration of osteoblast-like MC3T3-E1 cells through the activation of p38 mitogen-activated protein (MAP) kinase, c-Jun N-terminal kinase (JNK) and p44/p42 MAP kinase. Evidence is accumulating that heat shock protein 90 (HSP90) acts as a central regulator of proteostasis under stress conditions and physiological cell functions. In the present study, using transwell cell migration assay and wound-healing assay, we investigated the involvement of HSP90 in the PDGF-BB-stimulated migration of MC3T3-E1 cells, and the underlying signaling mechanism estimated by Western blot analyses. Onalespib, an HSP90 inhibitor, significantly reduced the PDGF-BB-stimulated migration evaluated by the two types of migration assays. The cell migration was also suppressed by geldanamycin, another type of HSP90 inhibitor. Onalespib markedly attenuated the PDGF-BB-elicited phosphorylation of p44/p42 MAP kinase without affecting that of p38 MAP kinase or JNK. In addition, the phosphorylation of p44/p42 MAP kinase by PDGF-BB was reduced by geldanamycin. Taken together, these results strongly suggest that HSP90 inhibitors suppress the PDGF-BB-induced osteoblast migration through the attenuation of p44/p42 MAP kinase activity.