Angiotensin-converting enzyme 2 deficiency is associated with impaired gestational weight gain and fetal growth restriction

Abstract

Angiotensin-converting enzyme 2 (ACE2) is a key enzyme of the renin-angiotensin system that influences the relative expression of angiotensin II (Ang II) and Ang-(1-7). Although ACE2 expression increases in normal pregnancy, the impact of ACE2 deficiency in pregnancy has not been elucidated. We determined the influence of ACE2 deficiency on circulating and tissue renin-angiotensin system components, fetal and maternal growth characteristics, and maternal hemodynamics (mean blood pressure and cardiac output) at day 18 of gestation. Gestational body weight gain was lower in the ACE2 knockout (KO) versus C57BL/6 (wild-type) mice (30.3±4.7 versus 38.2±1.0 g; P<0.001). Fetal weight (0.94±0.1 versus 1.24±0.01 g; P<0.01) and length (19.6±0.2 versus 22.2±0.2 mm; P<0.001) were less in KO. Mean blood pressure was significantly reduced in C57BL/6 with pregnancy; it was elevated (P<0.05) in the KO virgin and pregnant mice, and this was associated with an increased cardiac output in both C57BL/6 and KO pregnant mice (P<0.05). Plasma Ang-(1-7) was reduced in pregnant KO mice (P<0.05). Placenta Ang II levels were higher in KO mice (52.9±6.0 versus 22.0±3.3 fmol/mg of protein; P<0.001). Renal Ang II levels were greater in KO virgin mice (30.0±1.7 versus 23.7±1.1 fmol/mg of protein; P<0.001). There was no change in the Ang-(1-7) levels in the KO placenta and virgin kidney. These results suggest that ACE2 deficiency and associated elevated placenta Ang II levels impact pregnancy by impairing gestational weight gain and restricting fetal growth.

Figure 1

Maternal characteristics of virgin and pregnant C57BL/6 and ACE2KO females. Panel A. Pregnant ACE2KO body weight was significantly reduced compared to C57BL/6 pregnant females(n = 7). Panel B. ACE2KO maternal weight - total pup weight/pregnancy was significantly reduced compared to C57BL/6 females (n = 7). Panel C. Mean blood pressure was significantly higher for virgin and pregnant ACE2KO (n = 5, 4) females compared to the respective C57BL/6 females (n = 7, 5). Values are mean ± SEM. * p<0.05 vs virgin; # p<0.01; ## p<0.001 vs C57BL/6.

Figure 2

18 day gestation fetal characteristics in C57BL/6 and ACE2KO. Pup weight (Panel A) (n = 64, 48), pup length (Panel B), and total pup weight/pregnancy (Panel C) (n = 8, 7) were significantly reduced in ACE2KO. The number of resorption sites (Panel D) was significantly higher in ACE2KO mice (n = 8, 7). Values are mean ± SEM. #p<0.05; ##p<0.01 vs C57BL/6.

Figure 3

Panel A. Angiotensin peptide levels in the plasma of virgin and pregnant C57BL/6 and ACE2KO mice (n = 9, 6, 6, 6). No significant differences were seen among the groups for Ang I or Ang II. Ang-(1–7) was reduced in pregnant ACE2KO vs virgin ACE2KO. Panel B. Serum ACE and ACE2 activity. Panel Bi. Serum ACE activity measured using an ALPCO diagnostic Kit (n = 10, 4, 6, 3). ACE activity was significantly reduced in pregnant C57BL/6 and ACE2KO. Panel Bii. Serum ACE activity using ¹²⁵I labeled Ang I (n = 4). ACE activity was significantly reduced in pregnant ACE2KO females compared to virgin ACE2KO females. Panel Biii. Serum ACE2 activity using ¹²⁵I labeled Ang II (n = 4). ACE2 activity was significantly increased in pregnant C57BL/6 mice. Values are mean ± SEM. *p<0.05; **p<0.001 vs virgin of the same background.

Figure 4

Panel A. Angiotensin peptide levels in the kidney of virgin and pregnant C57BL/6 and ACE2KO mice (n = 20, 12, 8, 7). Ang II levels were significantly increased in virgin ACE2KO females. Ang I and Ang-(1–7) were significantly increased in pregnant C57BL/6 mice. Panel B. ACE and NEP activity in the kidney (n = 5, 5, 4, 5). NEP was significantly increased in virgin and pregnant ACE2KO mice. Values are mean ± SEM. **p<0.01; ***p<0.001 vs virgin of the same background; #p<0.05; ##p<0.01, ###p<0.001 vs C57BL/6.

Figure 5

Panel A. Angiotensin peptide levels in the placenta of pregnant C57BL/6 and ACE2KO mice. Ang II levels were increased in ACE2KO females compared to C57BL/6 (n = 6, 7). Panel B. ACE and NEP activity in the placenta (n = 6, 4). ACE was decreased in ACE2KO, whereas NEP was unchanged as compared to C57BL/6. Values are mean ± SEM. ##p<0.01 vs C57BL/6.