Characterization of epithelial cells derived from periodontal ligament by gene expression patterns of bone-related and enamel proteins

The cells of epithelial rests of Malassez (ERM) are thought to play a number of roles, such as protection against root resorption and cementoblast differentiation. However, little is known about characteristics of these cells. In the present study, we compared the expression patterns of the bone-related proteins osteopontin (OPN), osteonectin/secreted protein, acidic and rich in cysteine (SPARC), osteoprotegerin (OPG), bone morphogenetic proteins (BMP-2 and BMP-4) and the enamel matrix proteins amelogenin and tuftelin in epithelial cells derived from human periodontal ligament (ECHPL) with those of human gingival epithelial cells (HGEC) and oral mesenchymal cells (human gingival fibroblasts, human periodontal ligament fibroblasts and human pulp cells). The mRNA expression patterns were determined by the reverse-transcription polymerase chain reaction (RT-PCR). Cytokeratin 8 mRNA was expressed by oral epithelial cells but not oral mesenchymal cells. The OPN mRNA levels in ECHPL were by far the highest in the five cell types investigated. ECHPL and oral mesenchymal cells expressed OPG mRNA, whereas HGEC did not. BMP-2, SPARC and tuftelin mRNAs were detected in ECHPL and the other cells examined. The oral mesenchymal cells expressed BMP-4 mRNA much more strongly than did the oral epithelial cells. Amelogenin mRNA expression could not be detected in any of the cells. These findings suggest that cultured ERM cells are characterized by expression of the cytokeratin 8, OPG and OPN genes.