Abstract
Hair follicle is composed primarily of epithelial and dermal components that develop from embryonic ectoderm and mesoderm respectively. Hair growth cycle is coordinated and complex processes that are dependent on the interactions of epithelial and dermal components. Beard and frontal scalp dermal papilla cells (DPCs) were recently shown to possess the characteristics of androgen target cells. These DPCs expressed androgen receptor and type II 5α-reductase mRNA. To know the mode of androgen action in human hair follicles, we developed an in vitro coculture system using DPCs and follicular keratinocytes. Androgen significantly stimulated the proliferation of keratinocytes cocultured with beard DPCs, suggesting that these DPCs produce androgen-dependent diffusible growth factors. Insulin-like growth factor-I (IGF-I) was identified as one of the androgen dependent paracrine growth factors from beard DPCs. On the contrary, we could identify inhibitory roles of androgen on the growth of keratinocytes cocultured with DPCs from human balding frontal scalp, when DPCs were transfected with the AR expression vector. The inhibitory effect was mediated by TGF-β1 from the DPCs. Minoxidil and Finasteride were recently introduced for the treatment of androgenetic alopecia, and TGF-β1 is a next target for the innovative treatment.
