Characterization of the living skin equivalent as a model of cutaneous re-epithelialization

The living skin equivalent, a three-dimensional organotypic model, has been widely used to investigate many aspects of cutaneous biology. However, there are relatively few studies assessing how faithfully the skin equivalent reproduces normal skin biology. The skin equivalent was fabricated by seeding human epidermal keratinocytes onto the upper surface of a hydrated collagen lattice populated with human dermal fibroblasts and subsequently raised to the air-liquid interface where keratinocyte stratification and differentiation led to the formation of a tissue which showed many common morphological features to that of normal skin. Histology and immunohistochemical detection of keratinocyte integrins and matrix metalloproteinases (MMPs) were used as cytological markers to assess the accuracy of the model during cutaneous re-epithelialization. Analysis of expression of keratinocyte integrins revealed that whilst there were a number of similarities to normal skin, skin equivalent keratinocytes appeared to be 'activated' and hyper-proliferating. Wounding of the skin equivalent, by complete bisection, induced re-epithelialization from both wound edges within 8-12 h, which completely restored the epidermis within 4 days. This migration, like that in vivo, was associated with nascent expression of MMPs and upregulation of certain integrins. However, whilst integrin expression, was similar to in vivo re-epithelialization, there were subtle differences in the level of expression and distribution of certain integrins.