Abstract
Mechanical loading conditions result in alveolar bone resorption, which may be partly attributed to an imbalance in bone formation and resorption. To investigate the effects of mechanical loading on osteoblast and osteoclast differentiation, we used a stretch system for the cultured cells, simulating mechanical stress to culture MC3T3-E1 and RAW264.7 cells. Soluble RANKL (sRANKL) significantly enhanced the gene expressions of TRAP and cathepsin K mRNA, compared to that of controls (ANOVA,p<0.01). On the other hand, stretch system (5%) inhibited the enhanced expressions of TRAP and cathepsin K mRNA in RAW264.7 cells exposed to sRANKL (p < 0.05). The same phenomena were not observed in the presence of ionomycin, which is a calcium ionophore. Exposure of MC3T3-E1 cells to stretch in stretch system inhibited the expression of Osterix and ALPase, but enhanced that of RANKL and OPG genes. These results, taken together, demonstrate that 5% stretch loading inhibits the differentiation of MC3T3-E1 cells together with enhancement of RANKL and OPG gene expression, as well as the RANKL-dependent cellular fusion of RAW264.7 cells. Therefore, it is suggested that 5% stretch loading inhibits the differentiation of osteoclast and osteoblast cells.
