Involvement of placental peptidases associated with renin-angiotensin systems in preeclampsia

Second Trimester Amniotic Fluid Angiotensinogen Levels Linked to Increased Fetal Birth Weight and Shorter Gestational Age in Term Pregnancies

BACKGROUND

Despite the considerable progress made in recent years in fetal assessment, the etiology of fetal growth disturbances is not as yet well understood. In an effort to enhance our knowledge in this area, we investigated the associations of the amniotic fluid angiotensinogen of the renin-angiotensin system with fetal growth abnormalities.

METHODS

We collected amniotic fluid samples from 70 pregnant women who underwent amniocentesis during their early second trimester. Birth weight was documented upon delivery, after which the embryos corresponding to the respective amniotic fluid samples were categorized into three groups as follows: small for gestational age (SGA), appropriate for gestational age (AGA), and large for gestational age (LGA). Amniotic fluid angiotensinogen levels were determined by using ELISA kits.

RESULTS

Mean angiotensinogen values were 3885 ng/mL (range: 1625-5375 ng/mL), 4885 ng/mL (range: 1580-8460 ng/mL), and 4670 ng/mL (range: 1995-7250 ng/mL) in the SGA, LGA, and AGA fetuses, respectively. The concentrations in the three groups were not statistically significantly different. Although there were wide discrepancies between the mean values of the subgroups, the large confidence intervals in the three groups negatively affected the statistical analysis. However, multiple regression analysis revealed a statistically significant negative correlation between the angiotensinogen levels and gestational age and a statistically significant positive correlation between the birth weight and angiotensinogen levels.

DISCUSSION

Our findings suggest that fetal growth abnormalities did not correlate with differences in the amniotic fluid levels of angiotensinogen in early second trimester pregnancies. However, increased angiotensinogen levels were found to be consistent with a smaller gestational age at birth and increased BMI of neonates.

The rat placental renin-angiotensin system - a gestational gene expression study

BACKGROUND

The placenta is an essential organ that provides nutrients and oxygen to the developing fetus and removes toxic waste products from the fetal circulation. Maintaining placental blood osmotic pressure and blood flow is crucial for viable offspring. The renin-angiotensin system (RAS) in the placenta is a key player in the regulation of maternal-fetal blood flow during pregnancy. Therefore, the aim of this study was to determine if RAS genes are differentially expressed in mid to late gestation in rat placenta.

METHODS

Whole placental tissue samples from pregnant Sprague Dawley rats at embryonic (E) days 14.25, 15.25, 17.25 and 20 (n = 6 for each gestational age) were used for genome-wide gene expression by microarray. RAS genes with expression differences of >2 fold were further analyzed. Quantitative Real-Time PCR (qPCR) was performed on independent samples to confirm and validate microarray data. Immunohistochemisty and Western blotting were performed on a differentially expressed novel RAS pathway gene (ANPEP).

RESULTS

Six out of 17 genes of the RAS pathway were differentially expressed at different gestational ages. Gene expression of four genes (Angiotensin converting enzyme (Ace), angiotensin converting enzyme 2 (Ace2), membrane metalloendopeptidase (Mme) and angiotensin II receptor 1A (Agtr1a)) were significantly upregulated at E20 whereas two others (Thimet oligopeptidase 1 (Thop1) and Alanyl aminopeptidase (Anpep)) were downregulated at E20 prior to the onset of labour. These changes were confirmed by qPCR. Western blots revealed no overall differences in ANPEP protein expression in the placentae. Immunohistochemical studies, however, indicated that the localization of ANPEP differed at E17.25 and E20 as ANPEP localization in the giant trophoblast cell of the junctional zone was no longer detectable at E20.

CONCLUSIONS

The current study investigated the expression of members of the RAS pathway in rat placentae and observed significantly altered expression of 6 RAS genes at 4 gestational ages. These findings present the need for further comprehensive investigation of RAS genes in normal and complicated pregnancies.

The role of RAS in the pathogenesis of preeclampsia

Preeclampsia is a hypertensive disorder that is unique to pregnancy, with consistent involvement of the kidney. The renin-angiotensin system (RAS) has been implicated in the pathogenesis of preeclampsia. In the gravid state, in addition to the RAS in the kidney, there is a tissue-based RAS in the uteroplacental unit. Increased renin expression in human preeclampsia and in transgenic mouse models with a human preeclampsia-like syndrome shows that activation of the uteroplacental RAS, with angiotensin II entering the systemic circulation, may mediate the pathogenesis of preeclampsia. Vascular maladaptation in preeclampsia with increased vasomotor tone, endothelial dysfunction, and increased sensitivity to angiotensin II and norepinephrine in manifest preeclampsia may be explained on the basis of angiotensin II-mediated mechanisms through angiotensin receptor type I (AT1) activation. Recently, novel angiotensin II-related biomolecular mechanisms have been described in preeclampsia. These include AT1 and bradykinin B2 receptor heterodimerization and the production of autoantibody against AT1. Various organ systems with predilection for involvement in preeclampsia are sites of tissue-based RAS. Angiotensin II-mediated mechanisms may explain the primary clinicopathologic features of preeclampsia. In this review, these various aspects are critically examined and an integrated concept on the role of RAS in preeclampsia is presented.