A new in vitro culture system to produce a fully differentiated epidermis from human hair follicle outer root sheath cells

Abstract

During wound healing, interfollicular epidermis can be regenerated from the outer root sheath of hair follicles, showing that the cells of this structure can shift toward an interfollicular epidermal phenotype. Similarly, it has been shown that a multilayered epithelium originating from outer sheath cells can be obtained in vitro by culturing hair follicles. However, in the culture systems developed so far, the phenotypical shift was incomplete since the cells retained some of their original characteristics and did not acquire several key markers of terminally differentiated epidermis. In this paper we describe a new tissue culture method for obtaining a multilayered epithelium from outer sheath cells. This is performed by implanting human hair follicles vertically into dermal equivalents and then raising the culture to the air-liquid interface. The morphological, immunological and biochemical features of the in vitro reconstructed tissue are very similar to those observed in normal interfollicular epidermis, including those specific for terminally differentiated keratinocytes. In particular, the basic 67 kDa keratin (normally absent in conventional cultures and in freshly isolated hair follicles) is present and detectable from the first suprabasal layers, as in normal skin. Thus, under appropriate in vitro conditions, outer root sheath cell differentiation can be modulated so as to express an interfollicular epidermal phenotype as occurs in vivo during wound healing.