Cyclic tensile force up-regulates BMP-2 expression through MAP kinase and COX-2/PGE₂ signaling pathways in human periodontal ligament cells

Periodontal ligament cells play important roles in the homeostasis of periodontal tissue by mechanical stress derived from mastication, such as tension, compression, fluid shear, and hydrostatic force. In the present study, we showed that cyclic tensile force increased the gene expression level of bone morphogenetic protein (BMP)-2, a crucial regulator of mineralization, in human periodontal ligament cells using real-time PCR. Signaling inhibitors, PD98059/U0126 (extracellular signal-regulated kinase (ERK) inhibitors) and SB203580/SB202190 (p38 inhibitors), revealed that tensile force-mediated BMP-2 expression was dependent on activation of the ERK1/2 and p38 mitogen-activated protein (MAP) kinase pathways. Cyclic tensile force also induced cyclooxygenase-2 (COX-2) gene expression in a manner dependent on ERK1/2 and p38 MAP kinase pathways, and induced prostaglandin E₂ (PGE₂) biosynthesis. NS-398, a COX-2 inhibitor, significantly reduced tensile force-mediated BMP-2 expression, indicating that PGE₂ synthesized by COX-2 may be involved in the BMP-2 induction. The inhibitory effect of NS-398 was completely restored by the addition of exogenous PGE₂. However, stimulation with PGE₂ alone in the absence of tensile force had no effect on the BMP-2 induction, indicating that some critical molecule(s) other than COX-2/PGE₂ may be required for cyclic tensile force-mediated BMP-2 induction. Collectively, the results indicate that cyclic tensile force activates ERK1/2 and p38 MAP kinase signaling pathways, and induces COX-2 expression, which is responsible for the sequential PGE₂ biosynthesis and release, and furthermore, mediates the increase in BMP-2 expression at the transcriptional level.