Activin A‐induced signalling controls hair follicle neogenesis

Acquisition of potent human dermal papilla (DP) cells that can induce hair follicle neogenesis is an overarching concern, and various approaches have been tried. In an attempt to solve the problem, we previously introduced the three-dimensional (3D) culture of human DP cells and observed de novo formation of hair follicles when conducting a patch hair reconstitution assay using 3D cultured DP spheres with mouse epidermal cells. In this study, we have subsequently focused our attention on activin A, one of the notably upregulated proteins in DP spheres compared with 2D cultured DP cells. We then adopted a small interfering RNA-mediated gene knock-down approach and hair reconstitution assay to investigate the role of activin A. We observed that human DP spheres with activin A knock-down are severely impaired in hair follicle neogenesis when combined with mouse epidermal cells. In addition, activin receptor 2B (ActvR2B) knock-down mouse epidermal cells showed severe impairment of hair follicle neogenesis when combined with human DP spheres. Moreover, recombinant activin A treatment of mouse epidermal cells increased the expression of downstream genes of the activin pathway. Taken together, our data strongly suggest that activin A-induced signalling plays a critical role in hair follicle neogenesis, which has not been previously reported.