Utero-placental expression of angiotensin-(1-7) and ACE2 in the pregnant guinea-pig

Abstract

Background: In humans, trophoblast invasion, vascular remodeling and placental development are critical to determine the fate of pregnancy. Since guinea-pigs (GP) and humans share common pregnancy features including extensive trophoblast invasion, transformation of the uterine spiral arteries and a haemomonochorial placenta, the GP animal model was deemed suitable to extend our knowledge on the spatio-temporal immunoreactive expression of the vasodilator arpeptide of the renin-angiotensin system, angiotensin-(1-7) [Ang-(1-7)] and its main generating enzyme, angiotensin converting enzyme 2 (ACE2).

Methods: Utero-placental units were collected in days 15, 20, 40 and 60 of a 64-67 day long pregnancy in 25 Pirbright GP. Ang-(1-7) and ACE2 expression in utero-placental units were evaluated by immunohistochemistry.

Results: Ang-(1-7) and ACE2 were detected in the endothelium and syncytiotrophoblast of the labyrinthine placenta, interlobium, subplacenta, giant cells, syncytial sprouts, syncytial streamers, and myometrium throughout pregnancy. In late pregnancy, perivascular or intramural trophoblasts in spiral and mesometrial arteries expressed both factors. Immunoreactive Ang-(1-7) and ACE2 were present in decidua and in the vascular smooth muscle of spiral, myometrial and mesometrial arteries, which also express kallikrein (Kal), the bradykinin receptor 2 (B2R), vascular endothelial growth factor (VEGF) and its type 2 receptor (KDR), but no endothelial nitric oxide synthase (eNOS). In addition, the signal of Ang-(1-7) and ACE2 was especially remarkable in giant cells, which also show Kal, B2R. eNOS, VEGF and KDR.

Conclusions: The spatio-temporal expression of Ang-(1-7) and ACE2 in GP, similar to that of humans, supports a relevant evolutionary conserved function of Ang-(1-7) and ACE2 in decidualization, trophoblast invasion, vascular remodeling and placental flow regulation, as well as the validity of the GP model to understand the local adaptations of pregnancy. It also integrates Ang-(1-7) to the utero-placental vasodilatory network. However, its antiangiogenic effect may counterbalance the proangiogenic activity of some of the other vasodilator components.

Figure 1

Ang-(1–7) immunoreactivity in different stages and structures of the utero-placental unit. This expression (orange-brown) is depicted in giant cells (GC), syncytial streamers (S), labyrinth (LAB) and vascular smooth muscle (VSM) in myometrial artery of gestational days (G) 14, 20, 40 and 60 of the pregnant guinea-pig. (B) ACE2 immunoreactivity in different stages and structures of the utero-placental unit. This expression (orange-brown) is depicted in giant cells, syncytial streamers and vascular smooth muscle of myometrial artery of gestational days (G) 15, 20, 40 and 60 of the pregnant guinea-pig. (x400).

Figure 2

Immunoreactive expression of Ang-(1–7) and ACE2 in giant cells (GC) and labyrinth (LAB), from a gestational day 60 pregnant guinea-pig. Sections were preincubated with and without the immunizing peptide. (x400).

Figure 3

Sequential sections of the myometrial artery in gestational day 40, which in Figure1A and B displays immunoreactivity for Ang-(1–7) and ACE2. These show a moderate signal for kallikrein (Kal), a faint and scanty one for bradykinin R2 (B2R), vascular endothelial growth factor (VEGF) and its type 2 receptor (KDR), and no endothelial nitric oxide synthase (eNOS), in vascular smooth muscle (VSM) characterized by α-smooth muscle actin. These vasodilators are present in endothelial cells characterized by von Willebrand factor (vWF). Absence of cytokeratin (CK) positive cells demonstrates no intraarterial extravillous trophoblasts. (x200).

Figure 4

Giant cell (GC) expression of vasodilator factors. The signal is intense for vascular endothelial growth factor (VEGF), moderate for its type 2 receptor (KDR), kallikrein (Kal), the bradykinin B2 receptor (B2R) and endothelial nitric oxide synthase (eNOS) in two different sets of sequential sections (upper and lower panels). Asterisks indicate the same cell in each panel. Visceral yolk sac=VYS, interlobium=IL. (x400).