Effect of epithelial rests of Malassez’ cells on RANKL mRNA expression and ALP activity by periodontal ligament fibroblasts stimulated with sonicated Porphyromonas gingivalis in vitro

ObjectivesThe purpose of this study was to investigate the effects of epithelial rests of Malassez’ (ERM) cells on RANKL expression and alkaline phosphatase (ALP) activity by periodontal ligament (PDL) fibroblasts in the presence of lipopolysaccharides (LPS) in vitro using a co-culture technique.Materials and methodsPorcine PDL fibroblasts and ERM cells were used. PDL fibroblasts were seeded in 6-well dishes. ERM cells plated in a chamber with a 0.4 μm pore membrane were placed in the wells for 5 days, and then were stimulated with sonicated Porphyromonas gingivalis (P.g.) for 6 h. PDL cells were then evaluated for mRNA and protein expression of RANKL and mRNA expression of bone sialoprotein (BSP) and ALP activity was also analyzed.ResultsRANKL mRNA expression by PDL cells co-cultured with ERM cells and sonicated P.g. was higher than when co-cultured with ERM cells without P.g. and when cultured without ERM cells. RANKL protein levels in the cytoplasm of PDL fibroblasts co-cultured with ERM cells were stronger than in PDL fibroblasts cultured without ERM cells. BSP mRNA expression and ALP activity of PDL fibroblasts co-cultured with ERM cells was significantly lower than in PDL fibroblasts cultured without ERM cells.ConclusionsIn the presence of sonicated P.g., ERM cells increase RANKL expression by PDL cells, but decrease BSP mRNA and ALP activity by PDL cells. Therefore, ERM cells secreted more RANKL to stimulate more osteoclasts differentiation to resorb the alveolar bone under the condition of co-culture in the environment of the presence of sonicated P.g.