Granulocyte macrophage-colony stimulating factor and keratinocyte growth factor control of early stages of differentiation of oral epithelium

Abstract

Oral epithelial differentiation is known to be directed by underlying fibroblasts,but the responsible factor(s) have not been identified. We aimed here to identifyfibroblast-derived factors responsible for oral epithelial differentiation. Primary nor-mal human oral keratinocytes and fibroblasts were isolated from healthy volunteersafter informed consent (n=5) and 3D-organotypic (3D-OT) cultures were con-structed. Various growth factors were added at a range of 0.1-100 ng/ml. 3D-OTswere harvested after ten days and assessed histologically, by immunohistochemistryand the TUNEL method. Epithelium developed in 3D-OT without fibroblasts showedan undifferentiated phenotype. Addition of granulocyte macrophage-colony stim-ulating factor (GM-CSF) induced expression of cytokeratin 13 in suprabasal celllayers. Admixture of GM-CSF and keratinocyte growth factor (KGF) induced, inaddition, polarization of epidermal growth factor (EGF) receptor andβ1-integrin tobasal cell layer and collagen IV deposition. Terminal differentiation with polariza-tion of TUNEL-positive cells to superficial layers occurred only in the presence of fibroblasts in collagen gels either in direct contact or at distance from normal oralkeratinocytes. Taken together, these results show that major aspects of oral epithelialdifferentiation are regulated by the synergic combination of GM-CSF and KGF. How-ever, the terminal stage seems to be controlled by other yet unidentified fibroblast-derived diffusible factor(s).