EXPRESSION OF RANKL AND OPG mRNAs IN RAT PERIODONTAL LIGAMENT CELLS FOLLOWING MECHANICAL STRESS AND CO-CULTURE WITH RAT DENTAL PULP CELLS in vitro

Background and Aim: The aim of this study was to investigate the responses of periodontal ligament (PDL) cells following application of mechanical stress, co-cultured with dental pulp (DP) cells on the expression of receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) mRNAs in vitro. Materials and Methods: PDL cells were subjected to 4800 rpm / 20 min of centrifugal force as mechanical stress. The experimental group was PDL cells subjected to mechanical stress and co-cultured with DP cells (EXP). PDL cells without mechanical stress (CONTI), PDL cells without mechanical stress that were co-cultured with DP cells (CONTII) and PDL cells treated with mechanical stress but without co-culture (CONTIII) were control groups. mRNA levels of RANKL and OPG were analyzed at 1 and 3 days of co-culture. Furthermore, RANKL expression levels were analyzed at day 3. Results: Expression of RANKL mRNA in the EXP group was significantly higher than those in the 3 control groups. The CONTII group showed significantly higher expression of RANKL mRNA compared to the other 2 control groups at day 3. The expression of OPG mRNA in the CONTI and CONTIII groups was significantly higher than CONTII and EXP at day 1. RANKL immunoreacted more positive than the control groups and expressed diffusely in the cellular membranes of PDL cells in the EXP group. Conclusion: Mechanical stress may increase the capability of PDL cells to react to soluble factors emitted from DP cells, which may accelerate osteoclastogenesis.