The effects of epithelial rests of Malassez cells on periodontal ligament fibroblasts: A co-culture investigation for epithelialmesenchymal interactions

Abstract

=Background: The major function of epithelial rests of Malassez (ERM) cells is to maintain the homeostasis of the periodontal ligament (PDL). The purpose of this study was to characterize the effects of ERM cells on PDL fibroblasts in vitro using a co-culture system. Methods: PDL fibroblasts and ERM cells derived from porcine tissues were used. PDL fibroblasts were seeded in 6-welldishes. ERM cells plated in a chamber with a 0.4 μm pore membrane, were placed into the wells for 5 days. Osteocalcin (OCN), bone sialoprotein (BSP), osteoprotegerin (OPG) and receptor activator of NF-k B ligand (RANKL) mRNA levels in the PDL fibroblasts were then analyzed using real time RT-PCR. Alkaline phosphatase (ALP) activity was also measured. PDL fibroblasts cultured without ERM cells were used as a control. Results: OCN, BSP and OPG mRNA levels in PDL fibroblasts co-cultured with ERM cells were lower than the levels in the control group. Meanwhile, the RANKL mRNA level in PDL fibroblasts co-cultured with ERM cells was significantly higher than that of the controls (P<0.01). ALP activity of PDL fibroblasts co-cultured with ERM cells was significantly lower than in the controls (P<0.01). Conclusion: This study shows that ERM cells affect the functions of PDL fibroblasts, which decrease hard tissue formation and increase bone resorption. Therefore, ERM cells prevent dento-alveolar ankylosis of the PDL.