Localization of rat FGF-5 protein in skin macrophage-like cells and FGF-5Sprotein in hair follicle: Possible involvement of two Fgf-5 gene products in hair growth cycle regulation

It has been reported that the gene for murine fibroblast growth factor-5 (F gf-5) is expressed in the rat hair follicle and that this expression may be associated with catagen induction (Hebert et al, 1994). In this study, we analyzed the Fgf-5 gene product in skin because the gene generates two mRNA that translate into the FGF-5 protein and a short form of the FGF-5 protei n (FGF-5S) as a result of an alternative splicing (Hattori et al, 1996; Oza wa et al, 1996). Indeed, we detected both types of FGF-5 mRNA in rat skin s amples. Two monoclonal anti-FGF-5 antibodies, one (E723) being specific for FGF-5 long-form protein and the other (B2B6) being reactive with both FGF- 5 and FGF-5S proteins, were used to locate these proteins by immunohistoche mistry. Staining of the rat skin revealed that only the B2B6 antibody react ed with hair follicles and that both antibodies reacted with macrophage-lik e round cells, suggesting that the product of the Fgf-5 gene in the hair fo llicle is FGF-5S. The immunoreactivity of the FGF-5S protein increased duri ng early anagen VI and decreased rapidly during catagen. The density of FGF -5-positive macrophage-like cells in the dermis increased during anagen and decreased during catagen and telogen, whereas the density of these cells i n the panniculus adiposus did not change during anagen and increased during catagen and telogen, There was no apparent association between the density of FGF-5-positive macrophage-like cells and that of FGF-5-negative, dendri tic macrophage-like cells. Thus, the results suggest the possible involveme nt of FGF-5S in the hair follicle in anagen VI and catagen development and that the density of FGF-5-positive macrophage-like cells may also be associ ated with the hair growth cycle.