Differentiating the Stem Cell Pool of Human Hair Follicle Outer Root Sheath into Functional Melanocytes

Abstract

Bench-to-Bedside concepts for regenerative therapy place significant weight on noninvasive approaches, with harvesting of the starting material as a header. This is particularly important in autologous treatments, which use one’s bodily constituents for therapy. Precisely the stretch between obtaining therapeutic elements invasively and noninvasively places non-intrusive “sampling” rather than “biopsy” in the center of the road map of developing an autologous regenerative therapy. We focus on such a noninvasively available source of adult stem cells that we carry with us throughout our life, available at our fingertips—or shall we say hair roots, by a simple plucking of hair: the human hair follicle. This chapter describes an explant procedure for cultivating melanocytes differentiated from the stem cell pool of the hair follicle O uter R oot S heath (ORS). In vivo, the most abundant derivatives of the heterogeneous ORS stem cell pool are epidermal cells—melanocytes and keratinocytes which complete their differentiation—either spontaneously or upon picking up regenerative cues from damaged skin—and migrate from the ORS towards the adjacent regenerating area of the epidermis. We have taken advantage of the ORS developmental potential by optimizing explant primary culture, expansion and melanogenic differentiation of resident ORS stem cells towards end-stage melanocytes in order to obtain functional melanocytes noninvasively for the purposes of transplantation and use them for the treatment of depigmentation disorders. Our protocol specifies sampling of hair with their ORS, follicle medium-air interface primary culture, stimulation of cell outgrowth, adherent culture and differentiation of ORS stem cells and precursors towards fully functional melanocytes. Along with cultivation, we describe selection techniques for establishing and maintaining a pure melanocyte population and methods suitable for determining melanocyte identity.