Impaired desquamation in the in vitro reconstructed human epidermis

A fully differentiated epidermis generated in vitro by culturing normal human keratinocytes at the air-liquid interface shares many similarities with native tissue. However, in contrast to native epidermis, its stratum corneum consists of a larger number of compactly packed corneocyte layers, indicating that the processes involved in corneocyte desquamation are disturbed. Although the tri-lamellar appearance of desmosomes in viable cell layers of both types of epidermis is similar, abnormalities in the transformation of desmosomes into the corneosomal plug in the stratum corneum of reconstructed epidermis have been observed. In the native epidermis, desmosomes are transformed into corneosomes at the stratum granulosum/stratum corneum interface. This process is retarded in vitro, since desmosomal structures with preserved lamellar appearance are present in the lower parts of the stratum corneum. Moreover, the corneosome frequency in reconstructed epidermis is significantly higher than in native human skin. A comparison of reconstructed epidermis with hyperproliferative epidermis, such as UV-irradiated epidermis, psoriatic epidermis and recently healed burn-wounds treated with cultured epidermal autografts, has revealed that only the structure of the stratum corneum derived from psoriatic skin is similar to that of reconstructed epidermis. The stratum corneum organization in the UV-treated epidermis and in recently healed burn-wound is, however, close to that seen in native skin.