Fibroblast growth factor and epidermal growth factor in hair development

Hair follicles arise in developing skin as a result of a complex of interactions that are likely to be mediated by diffusible, cell- and matrix-bound factors. Growth factors such as fibroblast growth factor (FGF) and epidermal growth factor (EGF) have been implicated in the control of epidermal and mesenchymal cell function, and it is likely that they also affect proliferation and differentiation of the cells of the cutaneous appendages during development. Immunolocalization of basic FGF adjacent to areas of proliferation in developing and in mature follicles suggests that this factor may regulate the mitotic activity of epithelially-derived cells; acidic FGF, on the other hand, appears in the differentiating cells of the follicle bulb and may therefore participate in the formation of structural components of the follicle or of the fiber. EGF has been identified as a potent modulator of cellular growth and is also present during follicle differentiation. These factors may act through autocrine and paracrine mechanisms because their receptors are also found on epidermally derived and mesenchymal structures 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 morphogenesis of the hair follicle population. Histologic examination of skin of FGF-treated mice suggested that the growth factor had affected hair follicle initiation and development, which resulted in a significant delay in the first and subsequent hair cycles when compared to control animals. 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 hyperkeratinization of the skin, and caused a significant delay in hair follicle development.