AbstractsBiology & Animal Science

Mechanical stress produced by orthodontic force is a factor in the remodeling of periodontal ligament (PDL) and alveolar bone, and consists of compressive and tensile forces. It has been reported that the expression of many cytokines associated with osteoclastogenesis, such as receptor activators of nuclear factor-κB ligand(RANKL) and macrophage colony-stimulating factor(M-CSF), are up-regulated when compressive forces act on osteoblasts and PDL cells. However, little is known about the direct effects of compressive forces on osteoclasts. Therefore, we investigated the effects of compressive force on osteoclasts in this study. Thenumbers of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated osteoclasts derived from RAW264.7 cells were counted. The gene expression of osteoclasts associated with differentiation and fusion changed in response to compressive force,and was evaluated by real-time PCR. Differentiation and fusion of osteoclasts increased rapidly on the 4th to 5th days. We then examined the effects of compressive force on osteoclasts using 3, 5, 7, 9 and 14-layered cover glass slips (slips) on the 4th day for 24 h. The number of large osteoclasts with more than 8 nuclei peaked with 7 slips. The force generated by 7 slips was regarded as the optimal compressive force. mRNA expression of osteoclast-associated genes, including nuclear factor of activated T cells c1(NFATc1), TRAP, matrix metalloproteinase-9 (MMP-9),dendritic cell specific trans membrane protein (DC-STAMP),osteoclast stimulatory trans membrane protein(OC-STAMP), cathepsin-K (cath-K), chloride channel 7 (ClC-7), ATPase H+ transporting vacuolar proton pump member I (ATP6i), Integrin-αv andβ3, increased significantly after 3 h of optimal compression. Thus, we were successful in directly applying compressive force to osteoclasts. These findings suggest that osteoclastogenesis acceleratesvia up-regulated and advanced mRNA expressions when applying optimal compressive force.