Epithelial-mesenchymal interactions in normal and neoplastic human oral mucosa. A study on in vitro organotypic models

Abstract

Epithelial-mesenchymal interactions are necessary for the development of oral epithelium during embryogenesis, but adult oral epithelium is also under the influence of mesenchymal tissue in both normal and neoplastic conditions. The aim of this study was to investigate the role of fibroblasts on morphogenesis of normal and neoplastic human oral epithelium. In vitro organotypic models of normal, early neoplastic and neoplastic human oral mucosa have been developed (Papers I and III). The cultured tissues obtained in the laboratory were assessed by morphometry, immunohistochemistry and the TUNEL method. Our data showed that fibroblasts had a crucial effect on cell growth and differentiation of the reconstituted normal human oral epithelium. Epithelial growth, but not differentiation could be restored by keratinocyte growth factor (KGF), one of the soluble factors synthesised by them. A novel finding was that fibroblasts were essential for restoring the normal pattern of cell death in reconstituted normal human oral epithelium (Paper II). The studies done on step-wise models of oral carcinogenesis showed that the role of fibroblasts on epithelial growth was maintained during in vitro tumour progression (Papers III and IV). In contrast, the tight control exerted by fibroblasts on epithelial differentiation and cell death of in vitro reconstituted normal human oral epithelium was gradually lost during in vitro neoplastic progression (Paper III). Furthermore, our results pointed to an important role for the keratinocyte-fibroblast cross talk and fibroblast-derived diffusible factors in triggering local invasiveness of early neoplastic oral keratinocytes. An interesting finding was the species-specificity of fibroblasts required for the invasive growth of early neoplastic keratinocytes to occur (Paper IV). This finding brings some concerns on the sensitivity of the in vivo xenotransplantation method as single test system for identifying putative malignant human neoplastic cells. In conclusion, this study brings in vitro evidence for the role of fibroblasts in coordinating the major biological processes of the suprajacent epithelium in both normal and neoplastic human oral mucosa.