Morfología, remodelación tisular y angiogénesis en placentas de yeguas mestizas

Abstract

The placenta forms the interface between the embryo/fetus and the mother, being a determining factor and a source of signaling molecules to maintain a favorable environment and achieve a successful pregnancy. These functions are possible through the formation of an extensive vascular network from endometrium to placenta, term angiogenesis. The equine placenta is classified histologically as diffuse and adeciduate microcotyledonary epitheliochorial. The aim of this study was to describe the placental morphology, tissue development and expression of angiogenic factors in mares. 15 healthy crossbreed mares from the central Argentina region were used and the pregnant uterus were obtained. Pregnancy thirds were determined as first third (0 to 120 days of gestation), second third (120 to 240 days) and third third (240 days to delivery). The samples from the maternal-fetal interface and endometrial cups were used for structural and ultrastructural analysis, immunohistochemical study of the main angiogenic factors and equine chorionic gonadotrophin hormone (eCG), evaluation of placental cell remodeling, and histomorphometric study of blood vessels. In early gestation, the luminal epithelium of the endometrium was found to be formed by cuboidal cells with the formation of shallow endometrial folds and glands on the apical surface of the maternal endometrium. As the pregnacy progresses, deeper endometrial sulci form that physically correspond to the developed chorionic projections on the fetal side. From day 60, the folding process in secondary and tertiary villi continues until the formation of organized microcotyledons (primary unit of hemotrophic exchange) from day 100 to day 240 of gestation. From the second third of pregnancy, the chorionic cell layer of the villi was found to be thinner, allowing the recognition of abundant capillaries immersed in the scarce connective tissue that supports them, immediately below the chorionic and endometrial epithelia, confirmed by MOAR and by TEM. The results of cell apoptosis together with an important mitotic activity during the early period of pregnancy, show an active tissue remodeling, an essential process in equine gestation, since before implantation and prior to the formation of microcotyledons, the nutrition of the embryo it is histotrophic. The presence in this organ of angiogenic factors such as VEGF, Ang-2 and their Flk-1 and Tie-2 receptors indicate that they would act complementary in vascular development, would exert their action in synergy and they would be an essential part of the paracrine and autocrine cell signaling pathways on the endothelial cells of the capillaries, favoring their growth and close location towards the epithelial surface, reducing the interhemal distance. The histomorphometric study allowed us to identify that the increase in the vascular area and perimeter of the placenta, added to the absence of immunostaining of the VEGF/Ang system and its receptors in the endothelium at the end of gestation, shows that there is no new formation of vessels during this period and added to a maintenance of the moderate immunostaining of the angiogenic factors in the endometrial glands, affirms the protagonism of the same in assuming dominance in the conduction of both fetal and maternal capillary development and growth, which would occur in the final stages of gestation. It was determined that there is death by apoptosis in the specialized trophoblastic cells of the endometrial cups throughout their development and it should be noted that this is the first study to describe and deepen angiogenesis in equine placentas.