What is a human epidermal skin model?

Reconstructed human Epidermis (RhE) models are three dimensional human epidermis equivalents which can be used as in vitro methods for different applications. They are derived from normal human keratinocytes and form a multilayered, highly differentiated model of the human epidermis that mimics biochemical and physiological properties of the epidermis. During cultivation the tissue cultures are lifted to the air-liquid interphase to induce differentiation, epithelial stratification and cornification. The cellular structure of RhE closely resembles the human epidermis including a basement membrane, proliferating keratinocytes and a stratum corneum with intact barrier function.
Due to the skin barrier function of the epidermis, liquid, creamy and solid substances can be applied topically -onto the stratum corneum - to closely mimic the in vivo situation. Substances can also be applied systemically by adding to the cell culture medium.

How can the epidermal skin model be characterised?

The morphology and architecture of epiCS shows a high comparability to human native epidermis. It comprises of a stratified squamous epithelium. Proliferating cells of the basal layer undergo a series of morphological and biochemical changes that culminate in the production of dead, flattened, enucleated squames. Several markers of differentiation prove the functionality of the reconstructed epidermis:

Fig. 1
The presence of a properly formed basal lamina at the border to the insert membrane was shown using a specific antibody against collagen IV (Collagen IV is produced by the keratinocytes only) (Fig. 1a). The increase in differentiation was observed by staining against cytokeratin 14 and 10. The cells of the basal layer stain positive for cytokeratin 14 whereas the upper layers do not (Fig. 1b).On the other hand cytokeratin 10 is expressed only in the suprabasal layers (Fig. 1c). Additionally, staining of markers for late differentiation stages, like involucrin, filaggrin (both not shown) and transglutaminase (Fig. 1d) is restricted to the upper cell layers and -to a lesser extent- to the cornified envelope. As expected staining of those markers map clearly the cell membranes. The epidermal permeability layer is maintained by extracellular lipid membranes within the interstices of the stratum corneum. Separation of the extracted lipids from epiCS shows the same pattern as in native epidermis. The presence of an intact barrier function is demonstrated by reproducible ET50 values of > 2h after treatment with TX-100 (1%).

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