Do androgens influence hair growth by altering the paracrine factors secreted by dermal papilla cells?

Androgens regulate many aspects of human hair growth in both sexes. After p uberty they transform tiny vellus follicles in many areas, e.g. the face, t o terminal ones producing long, thick, pigmented hairs. In genetically pred isposed individuals, androgens also cause the reverse transformation of ter minal scalp follicles into vellus ones, causing balding. In the current hyp othesis for androgen action, androgens control most follicular cells indire ctly acting via the mesenchyme-derived dermal papilla which regulates many aspects of follicular activity. In this model androgens binding to androgen receptors in dermal papilla cells alter their production of regulatory mol ecules which influence other follicular components; these molecules may be soluble paracrine factors and/or extracellular matrix proteins. This hypothesis is supported by immunohistochemical localisation of androge n receptors in dermal papilla cell nuclei and the demonstrations that andro gen receptor content and testosterone metabolism patterns of cultured derma l papilla cells from various body sites reflect hair growth in androgen-ins ensitivity syndromes. The next question is whether androgens alter the para crine factors secreted by dermal papilla cells, Cultured dermal papilla cel ls do release soluble, proteinaceous factors into their media which stimula te the growth of keratinocytes and other dermal papilla cells. This mitogen ic potential can cross species from humans to rodents. Importantly, testost erone in vitro stimulates the mitogenic potential of beard cells, but in co ntrast inhibits production by balding scalp cells reflecting their in vivo androgenic responses. Since androgen in vitro do alter the secretion of paracrine factors the cur rent focus lies in identifying specific factors produced, e.g. IGF-I and st em cell factor (SCF), using ELISA and RT-PCR, and comparing their expressio n in cells from follicles with varying responses to androgens in vivo or un der androgen stimulation in vitro. This should lead to greater understandin g of androgen action and enable the development of better treatment for adr ogen-potentiated disorders.