Localization and differentiation of hair follicle stem cells

Objective: To identify the localization of hair follicles stem cell (HFSC) in different stages of hair and explore the differentiating capacity of HFSC into epidermis in vitro. Methods: HFSC were detected b y K19 immunostaining in normal human skin. Then, the isolated HFSC through enzyme digestion were seeded on dermal equivalent (DE) and cultured between the air-liquid interfaces for 14 days. Skin-equivalents was harvested and used for evaluation. Results: HFSC mainly located in outer root sheet in hair follicle and human anagen hair follicles containing two distinct reservoirs for K19-positive cells located in the bulge and bulb of the follicle. These two reservoirs fused in line of outer root sheets during the catagen-telogen transition phase and individualized again in the newly forming anagen hair follicle. Based on DE, growing HFSC built a multi-layered and confined epidermis. Conclusion: HFSC located in outer root sheets can promote hair cycle and differentiate into epidermis in vitro.