Differential expression of pro- and anti-angiogenic factors in the endometrium between repeat breeder and normally fertile cows

Abstract

In cattle, the establishment of appropriate endometrial vasculature during the estrous cycle is required for preparing a receptive endometrium. This study aimed to investigate 1) mRNA expression of potent pro- and anti-angiogenic factors, 2) protein localization of the anti-angiogenic factor thrombospondin (TSP), and 3) vascularity in the endometrium of repeat breeder (RB) and normally fertile (non-RB) cows. Caruncular and intercaruncular endometrium was collected from RB and non-RB cows during the luteal phase of the estrous cycle. RB cows had greater mRNA expression levels of TSP ligands (TSP1 and TSP2) and receptors (CD36 and CD47) than non-RB cows. Although the mRNA expression levels of most angiogenic factors did not change by repeat breeding, RB cows had greater mRNA expression of fibroblast growth factor receptor 1 (FGFR1), angiopoietin 1 (ANGPT1), and ANGPT2 and a less mRNA expression of vascular endothelial growth factor B (VEGFB) than non-RB cows. By immunohistochemistry, TSP1, TSP2, CD36, and CD47 were detected in the luminal epithelium, glandular epithelium, stromal cells, and blood vessels of the endometrium. Two indexes of vascularity, the number of blood vessels and the percentage of area stained positive for the von Willebrand factor, were lower in the endometrium of RB than in that of non-RB cows. These results demonstrate that RB cows have a greater expression of both ligands and receptors for the anti-angiogenic factor TSP and a reduced vascular distribution in the endometrium compared with non-RB cows, suggesting suppressed endometrial angiogenesis.