Yes / Male sex hormones-androgens-regulate male physique development. Without androgen signaling, genetic males appear female. During puberty, increasing androgens harness the hair follicle's unique regenerative ability to replace many tiny vellus hairs with larger, darker terminal hairs (e.g., beard). Follicle response is epigenetically varied: some remain unaffected (e.g., eyelashes) or are inhibited, causing balding. How sex steroid hormones alter such developmental processes is unclear, despite high incidences of hormone-driven cancer, hirsutism, and alopecia. Unfortunately, existing development models are not androgen sensitive. Here, we use hair follicles to establish an androgen-responsive human organ culture model. We show that women's intermediate facial follicles respond to men's higher androgen levels by synthesizing more hair over several days, unlike donor-matched, androgen-insensitive, terminal follicles. We demonstrate that androgen receptors-androgen-activated gene transcription regulators-are required and are present in vivo within these follicles. This is the first human organ that involves multiple cell types that responds appropriately to hormones in prolonged culture, in a way which mirrors its natural behavior. Thus, intermediate hair follicles offer a hormone-switchable human model with exceptional, unique availability of genetically identical, but epigenetically hormone-insensitive, terminal follicles. This should enable advances in understanding sex steroid hormone signaling, gene regulation, and developmental and regenerative systems and facilitate better therapies for hormone-dependent disorders.

Lack of hair due to alopecia or skin grafting procedures causes significant distress due to hair's role in social and sexual communication. Only limited pharmacological agents are currently available to stimulate hair growth; their development is hampered by inappropriate model systems. Most research involves large terminal scalp follicles rather than the clinical targets of tiny vellus or intermediate follicles. The overall aim of this thesis was to develop a novel model system based on intermediate hair follicles. Initially, intermediate follicles from female pre-auricular skin were characterised and compared to matched terminal follicles. Intermediate follicles were smaller, less pigmented, shorter and possessed a more 'tubular' bulb morphology than their more 'bulbous' terminal counterparts. Significant correlations were demonstrated between various hair follicle measurements and corresponding dermal papilla diameters. Isolated terminal follicles grew significantly more than intermediate hair follicles in organ culture for 9 days. Testosterone (10nM), the major regulator of human hair growth, increased only intermediate follicle growth; the anti-androgen, cyproterone acetate (1¿M), prevented this stimulation, unlike the 5¿-reductase type 2 inhibitor finasteride (40ng/ml). Immunohistochemistry demonstrated androgen receptor and 5¿-reductase type 2 proteins in both follicle types, while quantitative real-time PCR and gene microarray analysis detected their increased gene expression in intermediate follicles. Thus, smaller intermediate follicles showed major morphological and gene expression differences to terminal follicles in vivo and retained significant, biologically-relevant differences in vitro in organ culture including androgen-responsiveness. Therefore, intermediate hair follicles offer a novel, exciting, more clinically relevant, albeit technically difficult, model for future investigations into hair growth.

Lack of hair due to alopecia or skin grafting procedures causes significant distress due to hair's role in social and sexual communication. Only limited pharmacological agents are currently available to stimulate hair growth; their development is hampered by inappropriate model systems. Most research involves large terminal scalp follicles rather than the clinical targets of tiny vellus or intermediate follicles. The overall aim of this thesis was to develop a novel model system based on intermediate hair follicles. Initially, intermediate follicles from female pre-auricular skin were characterised and compared to matched terminal follicles. Intermediate follicles were smaller, less pigmented, shorter and possessed a more 'tubular' bulb morphology than their more 'bulbous' terminal counterparts. Significant correlations were demonstrated between various hair follicle measurements and corresponding dermal papilla diameters. Isolated terminal follicles grew significantly more than intermediate hair follicles in organ culture for 9 days. Testosterone (10nM), the major regulator of human hair growth, increased only intermediate follicle growth; the anti-androgen, cyproterone acetate (1μM), prevented this stimulation, unlike the 5α-reductase type 2 inhibitor finasteride (40ng/ml). Immunohistochemistry demonstrated androgen receptor and 5α-reductase type 2 proteins in both follicle types, while quantitative real-time PCR and gene microarray analysis detected their increased gene expression in intermediate follicles. Thus, smaller intermediate follicles showed major morphological and gene expression differences to terminal follicles in vivo and retained significant, biologically-relevant differences in vitro in organ culture including androgen-responsiveness. Therefore, intermediate hair follicles offer a novel, exciting, more clinically relevant, albeit technically difficult, model for future investigations into hair growth.