Mechanism of action of androgen in human hair follicles

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In order to study the mechanism of action of androgen in human hair follicles, we examined the expressions of androgen receptor, 5alpha-reductase and in cultured human hair follicle cells. Androgen receptor mRNA was strongly expressed in axillary and beard DPC.While the expression of type I 5alpha-reductase is ubiquitous property of DPC,type II 5alpha-reductase gene expression is limited to beard and frontal scalp DPC.Female axillary DPC strongly expressed type III 17beta-hydroxysteroid dehydrogenase. In contrast, follicular epithelial cells do not have characteristics of the target cells. Although androgen itself did not have a proliferative effect on either type of cells when cultured alone, androgen significantly stimulated the proliferation of follicular epithelial cells which were cocultured with beard or axillary dermal papilla cells. We found that insulin-like growth factor-I (IGF-I) is one of the androgen dependent paracrine growth factors in DPC.Neutralizing antibody against IGF-I antagonized the stimulatory effect of androgen on the growth of outer root sheath cells cocultured with beard dermal papilla cells. The expression of IGF-I in beard and axillary DPC was stimulated by androgen. These findings suggest that IGF-I is a candidate for androgen induced hair growth factors. Recently we found that the expression of FGF8 which is an autocrine androgen-dependent growth factor in mouse mammary Sjionogi carcinoma cell line (SC-3) is also upregulated by androgen in beard DPC.FGF8 is another candidate for androgen dependent hair growth factor.