Compressive-force promotes osteoblastic differentiation via MAPK of undifferentiated mesenchymal cells

Objective: Orthodontic tooth movement occurs during the sequential bone remodering induced by therapeutic mechanical stress. It is well known that periodontal ligament cells that are composed of heterogeneous cell populations, including undifferentiated puluripotent mesenchymal cells play an essential role in orthodontic tooth movement. However, relatively little information is available regarding the particular effect of mechanical stress on the differentiation of pluripotent masenchymal cells. So we examined the effect of different magnitudes of mechanical stress on the terminal differentiation of C2C12 cells by examining the expression levels of specific mRNAs and proteins and elucidating the mechanism by which specific kinases, such as p38 MAPK, respond to mechanical stress-induced signaling.

Methods: C2C12 cells were cultured continuously under compressive force (0.25-2.0 g/cm²). After mechanical stress loading, the levels of expression of mRNAs and proteins for phenotype-specific markers of osteoblasts (Runx2, Msx2, Dlx5, Osterix, AJ18), chondroblasts (Sox5, Sox9), myoblasts (MyoD), and adipocytes (PPARγ) were measured by real-time PCR and Western blot analysis. The expression of activated p38 mitogen-activated protein kinase (p38 MAPK) was measured by Western blotting and ELISA.

Results: Loading 0.5 g/cm² of compressive force significantly increased the expression levels of Runx2, Msx2, Dlx5, Osterix, Sox5, and Sox9. In contrast, the expression levels of AJ18, MyoD and PPARγ were decreased by exposure to 0.5 g/cm² of compressive force. Loading 0.5 g/cm² of compressive force also induced the phosphorylation of p38 MAPK. The specific inibitor of p38 MAPK (SB203580) inhibited the compressive force-induced phosphorylation of p38 MAPK and partially blocked compressive force-induced Runx2 mRNA expression.

Conclusion: These results demonstrated that our compressive force stimulation could direct the differentiation pathway of C2C12 cells into the osteoblast and chondroblast lineage via activated phosphorylation of p38 MAPK.