B5.2 INTERACTIONS BETWEEN THE EPIDERMIS AND DERMAL PAPILLA IN VITRO

Amici A W¹, Yamato M², Okano T², Kobayashi K³

¹Graduate School of Science and Technology, Chiba University, Chiba, Japan ²Institute of Biomedical Engineering, Tokyo Women’s Medical University, Tokyo, Japan ³Department of Biology, Faculty of Science, Chiba University, Chiba, Japan

Objectives: Hair follicles develop as a result of a series of epithelial-mesenchymal interactions between epidermal keratinocytes and a cluster of dermal fibroblasts that later form the dermal papilla (DP). The DP plays an important role in the cyclic activity of hair follicles during postnatal life and has also hair follicle inductive ability; when it is combined with glabrous sole skin and transplanted subcutaneously, hair follicle formation is induced between 5 to 10 days. Although this characteristic is widely known, the mechanism is still unclear. In this study, we aimed to establish a new culture model, which makes possible the analysis and comprehension of hair follicle induction.

Methods: Recombinants of rat sole skin and DPs isolated from rat vibrissa follicles were cultured on polyethylene terephthalate membranes with 8µm pores in standard keratinocyte medium, and harvested after 7 days of incubation. In order to verify whether the DP and the epidermis still maintain hair follicle induction capacity and response ability, respectively, cultured recombinants were transplanted subcutaneously in the rat dorsal skin and harvested after 1 and 2 weeks. Recently, a novel technology for harvesting transplantable cultured epithelium without dispase treatment was reported. Multilayered keratinocyte sheets can be detached from surfaces grafted with a temperature responsive polymer (N-isopropylacrylamide) only by reducing the temperature. It was also demonstrated that the cell sheet harvested by this method retained cell adhesion molecules and deposited extracellular matrix. In this study, we applied this technology to prepare sole skin and bulge keratinocyte sheets and investigated their capacity to respond to dermal papilla signals in vitro and in vivo.

Results: In some cultured recombinants, the epidermal cells surrounding the DP were in mitosis and stained basophilic, while the basal cells were cuboidal and well organized, showing a follicle bulb-like structure. In most of the grafts, however, interactions were not observed. In recombinants transplanted after culture, hair bulb formation was observed in all grafts and inner root sheeth and hair shaft were also differentiated in some cases.

Conclusions: The epidermis-DP recombinants maintain their inductive and response abilities during culture.