Exposure of mice to estrogen or keratinocyte growth factor (KGF) in vivo during the neonatal period results in estrogen-independent persistent proliferation and cornification of the vaginal epithelium when the animals become adults. Here, whether and how KGF-signaling is involved in the effects of estrogen on the neonatal mouse vagina were studied with an in vitro method. Newborn mouse vaginae were cultured for 3 days in serum-free medium containing various combinations of estradiol-17β (E2), KGF, anti-KGF antibody, KGFR inhibitory peptide and heparin, and then transplanted into ovariectomized host mice for 35 days. The vaginae cultured with 5 μg/ml E2 or 5 μg/ml KGF had a cornified thick epithelium, while the epithelium of the vehicle-treated controls stayed thin. The E2 effect was blocked by concurrent treatment with anti-KGF antibody or KGFR inhibitory peptide. KGF treatment alone at doses less than 500 ng/ml did not induce permanent vaginal changes but such changes did occur in vaginae treated with heparin plus as little as 10 ng/ml KGF. On the other hand, heparin inhibited the permanent vaginal changes induced by estrogen. These results suggest that irreversible vaginal changes are induced by the direct action of KGF on the developing vagina and that the developmental estrogenization syndrome of mouse vagina is caused by intensification of endogenous KGF/KGFR signaling by exogenous estrogen.
