ORGANOTYPIC COCULTURES AS MODELS TO STUDY CELL-CELL AND CELL-MATRIX INTERACTIONS OF HUMAN HAIR FOLLICLE CELLS

In the hair follicle complex interactions of specialized epithelial an d mesenchymal cells as well as extracellular components are crucial fo r regulation of proliferation and differentiation. In order to mimic t his situation in vitro, techniques to cultivate follicular cells such as outer root sheath (ORS) cells, hair matrix cells (HMC) and hair pap illa cells (HPC) were developed. Human dermal fibroblasts (HDF) and HP C markedly enhanced proliferation of ORS cells when cocultured spatial ly separated in a two-chamber system, which was more pronounced with p ostmitotic than with mitotic mesenchymal cells. In organotypic cocultu res of ORS cells on HDF- or HPC-populated collagen gels lifted at the air-medium interface, stratified epithelia developed largely reminisce nt of the epidermis. The morphology was well structured and differenti ation markers were expressed (e.g. suprabasal keratins, filaggrin, inv olucrin, basement membrane components). Both proliferation and differe ntiation were dependent on the presence of HDF or HPC. When grown embe dded in extracellular matrix (Matrigel) without HDF, ORS cells formed large spheroids with inward directed differentiation. Also herein HDF or HPC sustained both cell growth and balanced, epidermis-type differe ntiation. While in organotypic cocultures with HDF, HMC also organized into stratified epithelia, epidermis-type stratification was prevente d by HPC. Similarly, in the presence of HDF, HMC in Matrigel formed ke ratinizing spheroids, whereas this was largely suppressed in the prese nce of HPC. However, hair-type differentiation was not observed, sugge sting a crucial role of other yet unknown components or of the surroun ding matrix.