Effects of all-trans retinoic acid and Ca++ on human skin in organ culture.

In this study, we have established an organ culture model of human skin and examined the effects of both all-trans retinoic acid (RA) and extracellular Ca++ on the epidermal and dermal components of the organ-cultured skin. Our data show that while organ cultures maintained in serum-free, growth factor-free culture medium containing 0.15 mM Ca++ degenerated rapidly, those treated with concentrations of RA that have been shown previously to stimulate fibroblast and keratinocyte proliferation in monolayer culture (J Invest Dermatol 1989, 93:449; 1990, 94:717; Am J Pathol 1990, 136:1275) demonstrated a healthy appearance for up to 12 days. Degeneration of the control cultures was characterized by separation of the epidermis from the underlying dermis, progressive cell necrosis leading to a complete absence of viable cells from both the dermal and epidermal compartments, disintegration and fibrillation of the dermal connective tissue, and a cessation of protein synthesis. RA-treated organ cultures contained large numbers of healthy-appearing cells in both the epidermal and dermal compartments. One or several layers of viable basal cells in the epidermis could be seen at least through day 12. However, the upper layers of the epidermis frequently separated from the cells in the basal layer. The dermal connective tissue was histologically well-preserved. Furthermore, the level of protein synthesis was higher in the RA-treated cultures than in the control cultures. In addition to treating organ cultures with RA, other cultures were exposed to serum-free, growth factor-free culture medium containing 1.4 mM Ca++. The presence of the elevated Ca++ concentration also preserved cellular and connective tissue structures in the dermal and epidermal compartments. In comparison to RA there was better preservation of the overall epidermal structure. The upper layers of epidermal cells did not separate from the basal cells, and the various stages of epithelial differentiation could be seen. Histologically, the dermis was well-preserved in the presence of elevated extracellular Ca++. Specimens treated with a combination of Ca++ and RA demonstrated features consistent with the features induced by each treatment separately. This included an expanded basal layer of epithelial cells and a prominent keratotic layer with a fairly orderly pattern of differentiation. The tendency of the upper epidermis to separate from the basal cells was partially mitigated. Taken together, these data indicate that both RA and extracellular Ca++ act to prevent the degeneration of human skin in organ culture but probably do so through different mechanisms.