Expression and localization of vascular endothelial growth factor and its receptors in the pig uterus during peri-implantation and determination of the in vitro effect of the angiogenesis inhibitor SU5416 on VEGF system expression

Abstract

The aim of this work was to determine endometrial mRNA expression and uterine protein localization of vascular endothelial growth factor (VEGF) and its receptors VEGFR1 and VEGFR2 during the estrous cycle and peri-implantation period in sows. Uterine tissues were collected from pregnant sows on days 12, 14, 16, and 18 after artificial insemination and from non-pregnant animals on days 2 and 12 of the estrous cycle (day 0 = day of estrus). Using immunohistochemistry, a positive signal for VEGF and its receptor VEGFR2 was found in uterine luminal epithelial cells, endometrial glands, stroma, blood vessels, and myometrium. A VEGFR1 signal was only found in endometrial and myometrial blood vessels and stroma. By day 18 of gestation, the mRNA expression levels of VEGF, VEGFR1, and VEGFR2 were higher than those observed on days 2 and 12 of the estrous cycle and on days 12, 14, and 16 of gestation. Then, a primary culture of sow endometrial epithelial cells was established to define the potential of the selective inhibition of VEGFR2 after treatment with inhibitor SU5416 and determine its effects on the expression pattern of the VEGF system. The endometrial epithelial cells treated with SU5416 showed a dose-dependent decrease in VEGFR1 and VEGFR2 mRNA expression. The present study provides additional evidence on the importance of the VEGF system during peri-implantation, as well as on the specific inhibitory activity of SU5416 in epithelial cells, which, as demonstrated, express the protein and mRNA of VEGF and its receptors VEGFR1 and VEGFR2.