Mechanism of action of androgen in hair follicles

The study investigated testosterone's (T) action on human hair follicles by examining T metabolism and androgen receptor localization in outer root sheath cells (ORSC) and dermal papilla cells (DPC) from various body sites. Testosterone was mainly metabolized to androstenedione in both beard ORSC and epidermal keratinocytes, with no significant difference in the ratio of 5 alpha-reductase (5 alpha-R) to 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) between these cells. Beard DPC showed three times higher 5 alpha-R activity compared to DPC from the occipital scalp and axillary regions, with an optimum pH of 5.5, indicating the presence of type 2 5 alpha-R enzyme. In contrast, DPC from axillary and occipital scalp hair had a broader optimum pH range (6.5-9.0), suggesting type 1 5 alpha-R. Androgen receptors were found in beard and axillary hair follicles' DPC but not in occipital scalp follicles, as shown by immunohistochemical staining. Cultured beard and axillary DPC also displayed nuclear androgen receptors, whereas occipital scalp DPC showed little staining. Testosterone did not promote proliferation in cultured ORSC and DPC when they were cultured alone.