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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.

Motivation: Spatio-temporal regulation of gene expression is an indispensable characteristic in the development processes of all animals. ‘Master switches’, a central set of regulatory genes whose states (on/off or activated/deactivated) determine specific developmental fate or cell-fate specification, play a pivotal role for whole developmental processes. In this study on genome-wide integrative network analysis the underlying design principles of developmental gene regulatory networks are examined. Results: We have found an intriguing design principle of developmental networks: hub nodes, genes with high connectivity, equipped with positive feedback loops are prone to function as master switches. This raises the important question of why the positive feedback loops are frequently found in these contexts. The master switches with positive feedback make the developmental signals more decisive and robust such that the overall developmental processes become more stable. This finding provides a new evolutionary insight: developmental networks might have been gradually evolved such that the master switches generate digital-like bistable signals by adopting neighboring positive feedback loops. We therefore propose that the combined presence of positive feedback loops and hub genes in regulatory networks can be used to predict plausible master switches. Contact: ckh@kaist.ac.kr Supplementary information: Supplementary data are available at Bioinformatics online.