Oncostatin M stimulates prostaglandin D 2 -induced osteoprotegerin and interleukin- 6 synthesis in osteoblasts

Abstract

Abstract Oncostatin M produced by osteal macrophages has important roles in fracture healing. Osteoprotegerin (OPG) secreted by osteoblasts, binds to RANK ligand (RANKL) as a decoy receptor, and prevents RANKL from binding to RANK, resulting in the suppression of bone resorption. IL-6 is a pro-inflammatory cytokine and generally regulates bone resorption. However, accumulating evidence suggests that IL-6 plays pivotal roles in bone formation. We previously showed that prostaglandin D2 (PGD2) induces OPG synthesis by activating p38 mitogen-activated protein (MAP) kinase, stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), and p44/p42 MAP kinase in osteoblast-like MC3T3-E1 cells. We also demonstrated that PGD2 stimulates IL-6 synthesis by activating p38 MAP kinase and p44/p42 MAP kinase in MC3T3-E1 cells. In the present study, we investigated whether oncostatin M affects PGD2-stimulated OPG and IL-6 synthesis in MC3T3-E1 cells through the MAP kinase activation. The osteoblast-like MC3T3-E1 cells were treated with oncostatin M and then stimulated with PGD2. OPG and IL-6 synthesis were measured using an OPG and IL-6 enzyme-linked immunosorbent assay kit. OPG and IL-6 mRNA expression levels were evaluated by real-time RT-PCR. The phosphorylation of p38 MAP kinase, SAPK/JNK, and p44/p42 MAP kinase were evaluated by Western blotting. As a result, oncostatin M significantly increased the PGD2-stimulated OPG and IL-6 release. Oncostatin M significantly enhanced mRNA expression levels of OPG and IL-6 induced by PGD2. Regarding the signaling mechanism, oncostatin M did not affect the phosphorylation of p38 MAP kinase, SAPK/JNK, and p44/p42 MAP kinase. Our results suggest that oncostatin M upregulates the PGD2-stimulated OPG and IL-6 synthesis in osteoblasts and therefore affect bone remodeling. However, OPG and IL-6 synthesis are not mediated through p38 MAP kinase, p44/p42 MAP kinase, or SAPK/JNK pathways.