HUMAN EPIDERMIS RECONSTRUCTED ON SYNTHETIC MEMBRANE - INFLUENCE OF EXPERIMENTAL CONDITIONS ON TERMINAL DIFFERENTIATION

Cell suspensions of human keratinocytes seeded onto cell culture inser ts may undergo terminal differentiation in the absence of fibroblasts. Among the parameters that control these morphogenic events, exposure to air and the composition of the culture medium were investigated. In the latter case, three media were considered DMEM:Ham's F12, MCDB 153 , and keratinocyte SFM medium at equivalent calcium (1.5 mM) and fetal calf serum (5%) concentrations. Immunochemical methods and transmissi on electron microscopy show that cells cultured in DMEM:Ham's F12 medi um, and then raised at the air-liquid interface, form a basal layer pl us suprabasal cell layers corresponding to the stratum spinosum, strat um granulosum, and stratum corneum. The suprabasal keratinocyte layers show morphologies that resemble intact skin in which cells are connec ted by desmosomes and contain intermediate filaments and keratohyalin- filaggrin granules. When the cultures are kept submerged, the keratino cytes show occasional keratohyalin granules and are connected by fewer desmosomes. Additionally, no proper stratum corneum is formed. In ker atinocyte SFM medium and MCDB 153, cultures raised at the air-liquid i nterface are not able to form an epithelium of normal architecture ant i do not express terminal differentiation markers. Differentiation is initiated, however, since desmosomes and bundles of keratin filaments appear, on the other hand, filaggrin is not expressed even after 28 d in culture. Membrane-bound transglutaminase is expressed throughout th e entire suprabasal compartment in MCDB153 and DMEM:Ham's F12 media bu t never appears in keratinocyte SFM medium. These studies show the rel ative independence of epidermal differentiation program to the composi tion (including the calcium concentration) of the media contacting the dermis and filling the extracellular space. Conversely, differentiati on appears to depend on elements of basal medium and/or components syn thesized by keratinocytes under the influence of the culture medium.