Role of epithelial-mesenchymal transition regulated by twist basic helix-loop-helix transcription factor 2 (Twist2) in embryo implantation in mice

In a previous study we found the expression of epithelial-mesenchymal transition (EMT) biomarkers, including E-cadherin and N-cadherin, was significantly altered in uterine endometrium during embryo implantation via regulation by microRNA (miRNA)-429 and protocadherin-8 (Pcdh8). As a natural continuation of the previous study, the aim of the present study was to explore the role of EMT during embryo implantation and the potential activity of twist basic helix-loop-helix transcription factor 2 (Twist2) in regulating embryo implantation. A pregnancy model was established by naturally mating adult female ICR mice with fertile males. A pseudopregnancy model was established by mating fertile female ICR mice with vasectomised males. An invitro model of embryo implantation was established by the coculture of Ishikawa and JAR spheroids. Endometrial tissue during the peri-implantation period was collected, as were Ishikawa cells, JAR cells and cocultured cells. The expression of EMT markers (E-cadherin, N-cadherin, vimentin and cytokeratin) and Twist2 was detected invivo and invitro using the western blot analysis during embryo implantation. The expression of N-cadherin and vimentin (mesenchymal markers) was upregulated in the invitro implantation model, with downregulation of E-cadherin and cytokeratin (epithelial markers) expression. The expression of N-cadherin, vimentin and Twist2 increased significantly at the implantation sites at the time of implantation (Day 5), whereas the expression of E-cadherin and cytokeratin decreased. Location of Twist2 during embryo implantation was detected by immunohistochemistry (IHC), which revealed that it was extensively expressed in endometrial glandular epithelium and luminal epithelium at implantation sites on Day 5. The effect of the expression of Twist2 on embryo implantation was evaluated by suppressing Twist2 using Twist2-short interference (si) RNA in invivo and invitro models. The numbers of implanted embryos and the implantation rate were compared invivo and invitro. Western blot analysis showed that suppression of Twist2 led to upregulation of E-cadherin and cytokeratin, accompanied by downregulation of N-cadherin and vimentin (P<0.05). The number of implanted embryos after Twist2-siRNA interference was lower than in normal pregnancy (mean (+/- s.d.) 2.4 +/- 0.5 vs 6.8 +/- 1.3 respectively; P<0.05). These findings suggest the involvement of EMT in embryo implantation. The suppression of Twist2 could suppress embryo implantation by regulating EMT.