Exosomes derived from human dermal papilla cells promote hair growth in cultured human hair follicles and augment the hair‐inductive capacity of cultured dermal papilla spheres

Dermal papillae (DP) play key roles in hair growth and regeneration by regulating follicular cell activity. Owing to the established roles of exosomes (Exos) in the regulation of cell functions, we investigated whether DP-derived Exos, especially those from three-dimensional (3D)-cultured DP cells, affect hair growth, cycling and regeneration. Exos derived from 3D DP (3D DP-Exos) promoted the proliferation of DP cells and outer root sheath (ORS) cells and increased the expression of growth factors (IGF-1, KGF and HGF) in DP cells. 3D DP-Exo treatment also increased hair shaft elongation in cultured human hair follicles. In addition, local injections of 3D DP-Exos induced anagen from telogen and also prolonged anagen in mice. Moreover, Exo treatment in human DP spheres augmented hair follicle neogenesis when the DP spheres were implanted with mouse epidermal cells. Similar results were obtained using Exos derived from 2D-cultured DP cells (2D DP-Exo). Collectively, our data strongly suggest that Exos derived from DP cells promote hair growth and hair regeneration by regulating the activity of follicular dermal and epidermal cells; accordingly, these findings have implications for the development of therapeutic strategies for hair loss.