ADAMTS18 regulates vaginal opening through influencing the fusion of Mullerian duct and apoptosis of vaginal epithelial cells in mice

The ADAMTS (A Disintegrin and Metalloproteinase with Thrombospondin Motifs) enzymes are secreted metalloproteinases with major roles in development, morphogenesis, and tissue repair via the assembly and degradation of extracellular matrix (ECM). In this study, we investigated the role of ADAMTS18 in the development of the reproductive tract in female mice by phenotyping Adamts18 knockout (Adamts18⁻/⁻) mice. The results showed that Adamst18 mRNAs were abundantly expressed in vaginal epithelial cells and muscularis cells of the developing vagina. At the time of vaginal opening (5 weeks of age), about 41 % of Adamts18⁻/⁻ females showed enlarged protrusions in the upper and middle parts of the vagina, reduced vaginal length, and simultaneously exhibited vaginal atresia. 6% Adamts18⁻/⁻ females exhibited vaginal septum. Histological analyses revealed that the paired Mullerian ducts in ∼33 % female Adamts18⁻/⁻ embryos failed to fuse at embryonic day 15.5 (E15.5) resulting in the formation of two vaginal cavities. Results of TUNEL assay and immunohistochemistry for caspase-3 showed that the number of apoptotic cells in the terminal portion of the vagina of 5-week-old Adamts18⁻/⁻ females with vaginal atresia was significantly decreased. Adamts18⁻/⁻ females also showed a significant decrease in serum estradiol E2 compared to age-matched Adamts18⁺/⁺ females. Results of qRT-PCR showed that the expression level of the anti-apoptosis gene Bcl-2 was significantly increased and that of the apoptosis-related gene Epha1 was decreased in the vagina of 5-week-old Adamts18⁻/⁻ females. These results suggest that ADAMTS18 regulates vaginal opening through influencing the fusion of Mullerian ducts and apoptosis of vaginal cells in mice.