[Localization and differentiation of hair follicle stem cells]

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.HFSC were detected by 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.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 multilayered and confined epidermis.HFSC located in outer root sheets can promote hair cycle and differentiate into epidermis in vitro.