The effect of aging on functions of Malassez's epithelial rest

Objectives: The function of Malassez's epithelial rest (MER) has been revealed in vivo and in vitro. The major function of MER might help maintain homeostasis of the periodontal ligament, including cementogenesis. In contrast, inflammatory stimulation induces proliferation and differentiation of cells of the MER into the lining epithelium of jaw cysts or the pocket epithelium of periodontitis. Recently, it has been reported that MER has the capacity to synthesize either BMP2, which is related to osteogenesis and cementogenesis, or beta-defensin 1, which is known as an antibacterial protein. However, no studies have addressed the changing of these functions with aging. The purpose of this study was to investigate the effect of aging on functions of MER in vitro.

Methods: MER cells were obtained from porcine periodontal ligament according to the method of Brunette (1977), and cultured in a 35-mm dish. Subcultured cells were used, 3^rd-, 11^th-, and 17^th-passage MER cells were analyzed by microarray for evaluation of gene expression profiles. Quantified real-time polymerase chain-reaction analysis was performed to confirm the microarray data for selected genes, and cellular enzyme-linked immunosorbent assay (CELISA) was also performed to confirm the expression at the protein level.

Results: Analysis of the microarray data revealed that approximately 4300 of 21,123 genes were expressed with significant differences. Among them, 230 genes including BMP2 showed significant decrease (over two-fold) between the 3rd and 11th passages. Moreover, 23 genes including beta-defensin 1 were down-regulated through the 3rd to 17th passages. The expression of mRNA and protein levels also showed significant differences (p < 0.01).

Conclusions: These results suggest that cementogenesis and the antibacterial functions of MER cells might be decreased by aging. This study was partially supported by HRC7 of Tokyo Dental College.