Hair follicle development and cycle are regulated by the reciprocal interactions between epithelial and mesenchymal cells. Mechanisms responsible for the regulation have mainly been studied using experimental animals such as rodent fetuses. The purpose of this study is to understand such communications by using in vitro cell culture models of human hair follicle-derived cells. Human dermal papilla cells (DPCs) were cultured using 2-dimensional (2D), spheroid (3D), and spheroid microwell array cultures in an oxygen-permeable substrate (3D-oxy). Exosomes secreted in the culture media were collected and purified. All three types of exosomes moderately promoted proliferation of human hair follicle stem cells (HFSCs). Exosomes from the 3D-oxy culture most efficiently upregulated the expression of CD200, CD34, and K15 in HFSCs compared to those from the other two culture methods. To investigate the effects of exosomes on in vitro hair follicle formation, mouse embryonic epithelial and mesenchymal cells were used to prepare hair follicle organoids. The expression analysis of trichogenic and HFSC marker genes revealed that exosomes from the 3D-oxy culture were the most effective in maintaining stem cells and stimulating hair follicle sprouting in vitro. Exosomes from human DPCs may have substantial potential for treating patients with hair loss.

Hair follicle morphogenesis is triggered by reciprocal interactions between epithelial and mesenchymal layers in the hair follicle germ. Techniques to create follicle germ-like structures in vitro may be useful for understanding hair follicle morphogenesis and for creating transplantable tissue for hair regenerative medicine. Microwell arrays with oxygen-permeable materials have been proposed as a promising tool for in vitro fabrication of hair follicle germ. In this study, we investigated the effects of microwell morphology and culture process on the formation and function of hair follicle germ. Microwell geometries (flat, round-bottom, pen, and cone) significantly affected the formation of hair follicle germ and the expression of hair growth-related genes. Specifically, pen-type microwells enhanced the rate of follicle germ formation by promoting cell assembly. Even in typical round-bottom wells, centrifugal filling of cells into the microwells enhanced cell assembly and follicular germ formation rates. The higher the efficiency of two cell types to form two separate follicular germ, the higher the expression of hair growth-associated gene, versican. The highest expression of versican was observed when cells were centrifugally packed in round-bottom wells. Aside from hair follicle formation, these microwell array with various shapes may be useful for producing various other organoids and tissues.