Androgen Regulation of the Human Hair Follicle: The Type I Hair Keratin hHa7 Is a Direct Target Gene in Trichocytes

The study identified the type I hair keratin hHa7 as a direct target gene regulated by androgens in human hair follicles, specifically in trichocytes of sexual hairs like beard, axillary, and pubic hairs. Unlike other hair keratins, hHa7 was not found in terminal scalp hairs but was constitutively expressed in medullary cells of sexual hairs, which develop from vellus hairs during puberty under androgen influence. The presence of androgen receptors (AR) and androgen receptor-binding elements (AREs) in the hHa7 promoter confirmed its androgen-dependent regulation, with ARE-3 showing the strongest transactivating capacity. This discovery suggested that hHa7 could serve as a marker for androgen action in hair follicles and might be useful for studying androgen-dependent hair disorders, including androgenetic alopecia. The study highlighted the complex interactions between AR and specific DNA sequences in androgen-mediated gene regulation, influencing hair growth and differentiation.