Effect of cyclic compressive force in rat gingival fibroblasts

Mechanical stress is known to be important for regulation of bone turnover, though the detailed mechanisms are not fully understood.We previously reported that osteoclastic bone resorption under the denture base has been influenced by mechanical force exerted through the denture base in histological and pathological studies.The present study was undertaken to examine the effect of mechanical stress on the production of cytokines using rat gingival fibroblasts isolated from the palate and to examine the indirect effect of mechanical stress on osteoclast differentiation using RAW 264.7 cells as osteoclast precursors.

Methods:

Rat gingival fibroblasts were exposed to cyclic compressive force (7.4%, 0.167Hz) for 2hr.The levels of cyclooxygenase-2 (COX-2), interleukin-6 (IL-6) and osteoprotegrin (OPG) mRNA and PGE₂production were measured at various time-points after applying the force.The effect of the cyclic force on osteoclast differentiation was also determined using tartrate-resistant acid phosphatase (TRAP) staining of RAW 264.7 cells cultured for 6 days with conditioned medium from the force-treated rat gingival fibroblasts and soluble receptor activator of NF-kB ligand (RANKL).

Results:

Cyclic compressive force stimulated the expression of COX-2 and IL-6. The mRNA levels of both cytokines were increased within 1 hr after the exposure of the force.PGE₂production was increased between 6 and 9 hrs after the exposure of the force.RAW264.7 cells demonstrated significantly increased TRAP activity when cocultured with conditioned medium.

Conclusions:

It was revealed that cyclic compressive force promoted production of PGE2 and induced osteoclast differentiation in rat gingival fibroblasts.