Expression of αVβ3 integrin in rat endometrial epithelial cells and its functional role during implantation

The αVβ3 integrin as a marker of endometrial receptivity has been well established in human and other mammalian species; however, its expression is still not known in rats. Our objective was to establish the expression of αVβ3 integrin as a marker of endometrial receptivity in rat and to further prove its role in implantation by function-blocking studies in this species. Immunocytochemical, immunohistochemical and flow-cytometric studies were performed in rat endometrial epithelial cells (EEC) to demonstrate the expression of αVβ3 integrin during non-receptive, pre-receptive and receptive phases of the uterus. Results revealed positive immunocytochemical staining for αv and β3 subunits on the surface of EEC of days 4 and 5 p.c. (post-coitum), but the intensity was higher in cells of day 5 p.c. Flow-cytometric study revealed higher level of αVβ3 on day 5 p.c. as compared to day 4 p.c. and non-pregnant animals. Immunohistochemical analysis of uterine tissue also revealed that the αVβ3 expression in LE was higher on day 5 p.c. morning as compared to that observed on day 4 p.c. In addition, the expression of β3 subunit was not evident in rats receiving ormeloxifene, an agent known to inhibit the uterine receptivity. Immunoblotting experiments also revealed higher expression of uterine β3 on day 5 p.c. On day 6, expression of β3 was high in implantation sites than on inter-implantation sites. In immature ovariectomized rats, αVβ3 was up-regulated by progesterone and by a combination of estrogen and progesterone. The expression of αVβ3 was also up-regulated in EEC co-cultured with blastocysts. All the agents used for function-blocking studies showed significant reduction in the number of implantation sites in treated horn as compared to sham control horn. The present study has successfully demonstrated the expression of αVβ3 in rat EEC as a marker of endometrial receptivity and showed that this molecule is indispensable for the process of implantation in this species.