GPER Stimulation Attenuates Cardiac Dysfunction in a Rat Model of Preeclampsia

Abstract

Background: Preeclampsia poses a substantial clinical challenge, characterized by maternal hypertension, cardiac dysfunction, and persistent cardiovascular risks for both the mother and offspring. Despite the known roles of the estrogen receptor (GPER [G protein-coupled estrogen receptor]) in placental development, its impact on cardiovascular aspects within a preeclampsia animal model remains unexplored. We propose that G-1, a GPER agonist, could have the potential to regulate not only hypertension but also cardiac dysfunction in rats with preeclampsia.

Methods: To explore the influence of G-1 on preeclampsia, we used the reduced uterine perfusion pressure (RUPP) model. RUPP rats were administered either G-1 (100 µg/kg per day) or hydralazine (25 mg/kg per day). We conducted echocardiography to probe the intricate cardiac effects of G-1.

Results: The RUPP rat model revealed signs of hypertension and cardiac dysfunction and alterations in gene and protein expression within placental and heart tissues. G-1 treatment reduced blood pressure and reversed cardiac dysfunction in rats with preeclampsia. In contrast, administration of the vasodilator hydralazine reduced blood pressure without an improvement in cardiac function. In addition, while G-1 treatment restored the levels of sFLT-1 (soluble fms-like tyrosine kinase-1) in RUPP rats, hydralazine did not normalize this antiangiogenic factor.

Conclusions: The therapeutic intervention of G-1 significantly mitigated the cardiovascular dysfunction observed in the RUPP rat model of preeclampsia. This discovery underscores the broader significance of understanding GPER's role in the context of preeclampsia-related cardiovascular complications.

Keywords: estrogen; heart diseases; hypertension; hypoxia; placenta; preeclampsia; pregnancy-induced.

Figure 1:

G-1 administration significantly mitigates cardiac dyssynchrony, as assessed using speckle tracking echocardiography. (A) Global longitudinal strain, (B) strain rate in the long axis, (C) global radial strain, and (D) strain rate in long axis were all significantly altered following the RUPP procedure. Hydralazine treatment in preeclamptic animals significantly restored radial strain in the long axis and partially normalized the radial strain rate. However, it did not affect the longitudinal strain and strain rate in the long axis. G-1 resulted in an enhancement of cardiac synchrony, as demonstrated by the restoration of global longitudinal and radial strain and strain rates compared to untreated RUPP rats. Data is presented as mean ± SEM, with 6 experiments for the SHAM group, 7 for the RUPP group, 6 for the RUPP + hydralazine group, and 7 for the RUPP + G-1 group. Statistical analysis involved one-way ANOVA, followed by Dunnett’s multiple comparisons test for post-hoc analysis. A statistically significant difference relative to the SHAM group is denoted as (*p < 0.05), a statistically significant difference relative to the RUPP group is denoted as (#p < 0.05), and a statistically significant difference relative to the RUPP + hydralazine group is denoted as (†p < 0.05).

Figure 2:

GPER activation by G-1 improved conventional echocardiographic systolic and diastolic metrics in rats with experimentally induced preeclampsia. To evaluate left ventricular systolic function: (A) Representative images of the pulse wave Doppler echocardiography of left ventricle in four chamber view. Mitral valve Doppler was performed to record mitral annular velocities and mitral inflow curves. (B) Ejection fraction was measured. Rats challenged with RUPP exhibited a significant reduction in this conventional index of left ventricular systolic function compared to the SHAM group. While hydralazine treatment did not change LV EF in RUPP hearts, G-1 restored systolic function to normal levels in preeclamptic rats. (C) The E/A filling ratio was significantly decreased in RUPP rats compared to SHAM counterparts. Only G-1 administration led to a normalization of diastolic function, as evidenced by a higher E/A ratio compared to untreated RUPP rats. (D) Cardiac output was significantly reduced four days after RUPP surgery compared to SHAM controls. Hydralazine administration did not improve cardiac output, whereas treatment of RUPP rats with G-1 significantly increased it. Data is presented as mean ± SEM, with 6 experiments for the SHAM group, 7 for the RUPP group, 6 for the RUPP + hydralazine group, and 7 for the RUPP + G-1 group. Statistical analysis involved one-way ANOVA, followed by Dunnett’s multiple comparisons test for post-hoc analysis. A statistically significant difference relative to the SHAM group is denoted as (*p < 0.05), a statistically significant difference relative to the RUPP group is denoted as (#p < 0.05), and a statistically significant difference relative to the RUPP + hydralazine group is denoted as (†p < 0.05).Emax (early transmitral filling velocity), Amax (late transmitral filling velocity), E/A (early-to-late filling ratio); HDZ, hydralazine.

Figure 3:

GPER stimulation normalizes molecular changes in placental and blood from RUPP rats. (A) Western blot showing the expression and (B) quantification analysis of expression levels of placental HIF-1α. (C) Western blot showing the expression and (D) quantification analysis of expression levels of placental CD31. RUPP surgery significantly increased placental expression of HIF-1α while reducing CD31 levels. Hydralazine treatment normalized HIF-1α levels but did not affect CD31 in RUPP placentas. In contrast, G-1 treatment normalized the placental expression of these molecules. (E) Circulating levels of sFLT-1 were significantly higher in RUPP animals compared to the SHAM group. Only G-1 treatment, not hydralazine, was able to restore sFLT-1 levels in the serum of preeclamptic animals to normal levels. Data is presented as mean ± SEM, with 4–6 experiments for the SHAM group, 4–7 for the RUPP group, 4–6 for the RUPP + hydralazine group, and 4–7 for the RUPP + G-1 group. Statistical analysis involved one-way ANOVA, followed by Dunnett’s multiple comparisons test for post-hoc analysis. A statistically significant difference relative to the SHAM group is denoted as (*p < 0.05), a statistically significant difference relative to the RUPP group is denoted as (#p < 0.05), and a statistically significant difference relative to the RUPP + hydralazine group is denoted as (†p < 0.05). HIF-1α, hypoxia-inducible factor 1 alpha; HDZ, hydralazine; CD31, platelet endothelial cell adhesion molecule-1; sFLT-1, fms-like tyrosine kinase-1.

Figure 4:

Selective activation of GPER mitigates molecular changes in the hearts of rats with preeclampsia. On gestational day 19, we evaluated myocardial expression levels of CD31 and VEGF (A) Western blot showing the expression and (B) quantification analysis of expression levels of cardiac CD31. (C) mRNA expression levels of cardiac CD31. (D) Western blot showing the expression and (E) quantification analysis of expression levels of cardiac VEGF. (F) mRNA expression levels of cardiac VEGF. Treatment with G-1, not hydralazine, normalized the cardiac expression of these molecules. Data is presented as mean ± SEM, with 4–6 experiments for the SHAM group, 4–7 for the RUPP group, 4–6 for the RUPP + hydralazine group, and 4–7 for the RUPP + G-1 group. Statistical analysis involved one-way ANOVA, followed by Dunnett’s multiple comparisons test for post-hoc analysis. A statistically significant difference relative to the SHAM group is denoted as (*p < 0.05), a statistically significant difference relative to the RUPP group is denoted as (#p < 0.05), and a statistically significant difference relative to the RUPP + hydralazine group is denoted as (†p < 0.05).CD31, platelet endothelial cell adhesion molecule-1; HDZ, hydralazine; VEGF, vascular endothelial growth factor.

Figure 5:

Activation of GPER with G-1 ameliorates maternal symptoms of preeclampsia in rats. (A) Depicted are representative tracings of systemic arterial blood pressure at gestational day 19 of the study. (B) MAP, (C) SBP, and (D) DBP were significantly elevated in RUPP-induced preeclampsia rats compared to SHAM controls. Treatment with both hydralazine and G-1 significantly lowered MAP, SBP, and DBP in preeclamptic rats. Data is presented as mean ± SEM, with 6 experiments for the SHAM group, 7 for the RUPP group, 6 for the RUPP + hydralazine group, and 7 for the RUPP + G-1 group. Statistical analysis involved one-way ANOVA, followed by Dunnett’s multiple comparisons test for post-hoc analysis. A statistically significant difference relative to the SHAM group is denoted as (*p < 0.05), a statistically significant difference relative to the RUPP group is denoted as (#p < 0.05), and a statistically significant difference relative to the RUPP + hydralazine group is denoted as (†p < 0.05). MAP, mean arterial pressure; SBP, systolic blood pressure; DBP, diastolic blood pressure.