Dissociated skin cells regenerate hair follicles in a microwound, "The Punch Assay".

The purpose of this study was to develop a new, easily executed hair follicle regeneration system and assay, which could be further developed for clinical or cosmetic applications. Dissociated epidermal and dermal progenitor cells, isolated either from neonatal C57BL/6 mice or human foetal scalp tissues, were suspended in (10 μL) F12 medium and pipetted into a 1 or 2 mm-diameter punch biopsy wounds on the back skin of immunodeficient mice. At 3 weeks after transplantation, although pigmented mouse hairs could efficiently form at the injection sites with delivery of mouse cells, none hair formed on the host mouse skin at 3 months after delivery of human cells. Under the same conditions, human follicles could be regenerated when the human skin cells were delivered onto a 2 mm size punch created on a reconstituted human skin (hRSK), which previously generated on the back of an immunodeficient mouse, but the efficiency of hair formation was low. We demonstrated that both mouse and human regenerated follicles showed normal histology and differentiation markers; moreover, the cell chasing experiment confirmed that the regenerated hair follicles were formed from transplanted cells. Compared to other current hair reconstituted assays, the Punch Assay is relatively simple and generates normal hair follicles within a smaller wound. We suggest that the punch assay is a better in vivo assay of cell trichogenicity.