Effects of subepithelial fibroblasts on epithelial differentiation in human skin and oral mucosa: heterotypically recombined organotypic culture model

The stratified squamous epithelia differ regionally in their patterns of morphogenesis and differentiation. Although some reports suggested that the adult epithelial phenotype is an intrinsic property of the epithelium, there is increasing evidence that subepithelial connective tissue can modify the phenotypic expression of the epithelium. The aim of this study was to elucidate whether the differentiation of cutaneous and oral epithelia is influenced by underlying mesenchymal tissues. Three normal skin samples and three normal buccal mucosa samples were used for the experiments. Skin equivalents were constructed in four ways, depending on the combinations of keratinocytes (cutaneous or mucosal keratinocytes) and fibroblasts (dermal or mucosal fibroblasts), and the effects of subepithelial fibroblasts on the differentiation of oral and cutaneous keratinocytes were studied with histological examinations and immunohistochemical analyses with anti-cytokeratin (keratins 10 and 13) antibodies. For each experiment, three paired skin equivalents were constructed by using single parent keratinocyte and fibroblast sources for each group; consequently, nine (3 x 3) organotypic cultures per group were constructed and studied. The oral and cutaneous epithelial cells maintained their intrinsic keratin expression. The keratin expression patterns in oral and cutaneous epithelia of skin equivalents were generally similar to their original patterns but were partly modified exogenously by the topologically different fibroblasts. The mucosal keratinocytes were more differentiated and expressed keratin 10 when cocultured with dermal fibroblasts, and the expression patterns of keratin 13 in cutaneous keratinocytes cocultured with mucosal fibroblasts were different from those in keratinocytes cocultured with cutaneous fibroblasts. The results suggested that the epithelial phenotype and keratin expression could be extrinsically modified by mesenchymal fibroblasts. In epithelial differentiation, however, the intrinsic control by epithelial cells may still be stronger than extrinsic regulation by mesenchymal fibroblasts.