Semaphorin 4D induces vaginal epithelial cell apoptosis to control mouse postnatal vaginal tissue remodeling

Abstract

The opening of the mouse vaginal cavity to the skin is a postnatal tissue remodeling process that occurs at approximately five weeks of age for the completion of female genital tract maturation at puberty. The tissue remodeling process is primarily composed of a hormonally triggered apoptotic process predominantly occurring in the epithelium of the distal section of the vaginal cavity. However, the detailed mechanism underlying the apoptotic induction remains to be elucidated. In the present study, it was observed that the majority of BALB/c mice lacking the class 4 semaphorin, semaphorin 4D (Sema4D), developed imperforate vagina and hydrometrocolpos resulting in a perpetually unopened vaginal cavity regardless of a normal estrogen level comparable with that in wildtype (WT) mice. Administration of βstradiol to infant Sema4Ddeficient (Sema4D/) mice did not induce precocious vaginal opening, which was observed in WT mice subjected to the same βestradiol administration, excluding the possibility that the closed vaginal phenotype was due to insufficient estrogen secretion at the time of vaginal opening. In order to assess the role of Sema4D in the postnatal vaginal tissue remodeling process, the expression of Sema4D and its receptor, plexinB1, was examined as well as the level of apoptosis in the vaginal epithelia of fiveweekold WT and Sema4D/mice. Immunohistochemical analyses confirmed the localization of Sema4D and plexinB1 in the mouse vaginal epithelia. Terminal deoxynucleotidyl transferase dUTP nick end labeling assay and immunohistochemistry detecting activated caspase3 revealed significantly fewer apoptotic cells in situ in the vaginal mucosa of fiveweekold Sema4D/mice compared with WT mice. The addition of recombinant Sema4D to Sema4D/vaginal epithelial cells in culture significantly enhanced apoptosis of the vaginal epithelial cells, demonstrating the apoptosisinducing activity of Sema4D. The experimental reduction of plexinB1 expression in vaginal epithelial cells demonstrated the integral role of plexinB1 in Sema4Dinduced apoptotic cell death. These results suggest a nonredundant role of Sema4D in the postnatal tissue remodeling process in fiveweekold BALB/c mice, which involves the induction of vaginal epithelial cell apoptosis through Sema4D binding to plexinB1.