Gp130-SHP2-ERK Pathway Has Negative Regulatory Role for the Osteoblast Differentiation

Objectives: IL-6 family cytokines are known to act on osteoblasts and induce differentiation. However, their effects on osteoblasts are still unclear because the results are conflicting depending on the study models employed. IL-6 family cytokines share the common receptor subunit, gp130, which generates two major signaling pathways; SHP2-ERK pathway and STAT3 pathway. To clarify the function of two pathways in the regulation of osteoblast differentiation, we used the gp130 knock-in mouse lines, gp130^F759/F759 and gp130^FXXQ/FXXQ having selective defect of signaling pathway for SHP2 and STAT3, repectively. Methods: Osteoblastic cells prepared from calvarium were cultured with or without IL-6. The proliferation of osteoblastic cells was measured by MTT assay. The differentiation of osteoblastic cells was measured by alkaline phosphatase activity. Histomorphomeric analyses of bone were practiced by double-labeling technique. Results: When osteoblastic cells prepared from wild-type mice were cultured with IL-6, IL-6 promoted alkaline phosphatase activity and suppressed the proliferation. In the case of osteoblastic cells prepared from gp130^FXXQ/FXXQ mice, although the proliferation of gp130^FXXQ/FXXQ osteoblastic cells was similar to wild-type osteoblastic cells, alkaline phosphatase activity was scarcely detected. On the other hand, gp130^F759/F759 osteoblastic cells showed lower proliferation and higher alkaline phosphatase activity compared to wild-type osteoblastic cells. Histomorphomeric analyses revealed that gp130^F759/F759 mice showed the increase of total bone volume, in vivo. Conclusion: Gp130-STAT3 pathway of osteoblasts was essential for the osteoblast differentiation in vitro. On the other hand, gp130-SHP2-ERK pathway has negative regulatory role for the osteoblast differentiation, in vitro and in vivo. This study was supported by Grant-in-Aid for Scientific Resaerch (16791155) from the Japan Society for the Promotion of Science.