2012 Volume 55 Issue 2 Pages 141-150
Objective: Enamel molecules are believed to regulate cementoblast differentiation and to initiate the formation of acellular extrinsic fiber cementum. However, their precise spatial expression patterns and molecular roles are not clearly understood. Epithelial-mesenchymal interactions are responsible for morphogenesis and cell differentiation during periodontal regeneration. The current study was undertaken to examine the expression of amelogenins, ameloblastin, MMP-20, and KLK4 with respect to interactions between the cells of the epithelial rests of Malassez and fibroblasts from human periodontal ligament. Methods: Explants of human periodontal ligament tissues produced outgrowths containing both epithelial rests of Malassez cells and periodontal ligament fibroblasts after incubation in a modified serum-free medium. The distribution and expression of amelogenin, ameloblastin, MMP-20, and KLK4 were analyzed by in situ hybridization and RT-PCR. Epithelial rests of Malassez cells were cultured separately and used as a control. Results: RT-PCR analysis showed that amelogenin mRNA was expressed when epithelial rests of Malassez cells and periodontal ligament fibroblasts were cultured together. The expression levels of ameloblastin and KLK4 mRNAs were significantly higher when epithelial rests of Malassez cells and periodontal ligament fibroblasts were cultured together than when epithelial rests of Malassez cells were cultured alone. In situ hybridization analysis revealed that epithelial rests of Malassez cells expressed amelogenin mRNA, ameloblastin mRNA, and KLK4 mRNA at the interface between epithelial rests of Malassez cells and periodontal ligament fibroblasts. MMP-20 mRNA was not seen. Conclusion: These findings indicate that the interactions between epithelial rests of Malassez cells and periodontal ligament fibroblasts induce the expression of mRNAs for amelogenin, ameloblastin, and KLK4, suggesting that epithelial-mesenchymal interactions play an important role in maintaining the periodontal ligament space.
