FIBROBLAST GROWTH-FACTOR AND EPIDERMAL GROWTH-FACTOR IN HAIR DEVELOPMENT

Hair follicles arise in developing skin as a result of a complex of in teractions that are likely to be mediated by diffusible, cell- and mat rix-bound factors. Growth factors such as fibroblast growth factor (FG F) and epidermal growth factor (EGF) have been implicated in the contr ol of epidermal and mesenchymal cell function, and it is likely that t hey also affect proliferation and differentiation of the cells of the cutaneous appendages during development. Immunolocalization of basic F GF adjacent to areas of proliferation in developing and in mature foll icles suggests that this factor may regulate the mitotic activity of e pithelially-derived cells; acidic FGF, on the other hand, appears in t he differentiating cells of the follicle bulb and may therefore partic ipate in the formation of structural components of the follicle or of the fiber. EGF has been identified as a potent modulator of cellular g rowth and is also present during follicle differentiation. These facto rs may act through autocrine and paracrine mechanisms because their re ceptors are also found on epidermally derived and mesenchymal structur es in the skin. We have studied the effects of these growth factors on hair follicle development in the newborn mouse. Daily injections for 1 week after birth resulted in significant changes in the morphogenesi s of the hair follicle population. Histologic examination of skin of F GF-treated mice suggested that the growth factor had affected hair fol licle initiation and development, which resulted in a significant dela y in the first and subsequent hair cycles when compared to control ani mals. Because aFGF and bFGF are not readily diffusible, these effects remained confined to the area of treatment. In contrast, EGF affected the whole body coat of the treated animals, induced hyperkeratinizatio n of the skin, and caused a significant delay in hair follicle develop ment.