Expression of AT1R, AT2R and AT4R and their roles in extravillous trophoblast invasion in the human

The effects of cyclic AMP, sex steroids and global hypomethylation on the expression of genes controlling the activity of the renin-angiotensin system in placental cell lines

The placental renin-angiotensin system (RAS) is involved in placentation. We have shown that prorenin mRNA (REN) is expressed in a first trimester trophoblast cell line (HTR-8/SVneo) but not in a choriocarcinoma cell line (BeWo). We attempted to stimulate RAS expression in these cells by cAMP, 5'-aza-2'-deoxycytidine (AZA; an inhibitor of methylation), cAMP and AZA combined, and the sex steroids medroxyprogesterone acetate (MPA) and estradiol-17β (E(2)) with and without cAMP. RAS mRNAs were measured by qPCR and prorenin concentration in supernatants measured by an ELISA. In HTR-8/SVneo cells, all treatments increased REN expression compared to controls and cAMP + AZA combined was more effective than either treatment alone. Prorenin levels in supernatants were similarly upregulated. In HTR-8/SVneo cells, angiotensinogen (AGT) mRNA expression was increased by MPA + E(2) either with or without cAMP. AGT expression was also significantly increased by AZA. BeWo cells did not express REN or prorenin and it was not inducible with any treatment. AGT expression was significantly increased with AZA, the combination of cAMP + AZA, and MPA + E(2) + cAMP treatments. Since cAMP, AZA, cAMP and AZA combined, or MPA and E(2) with and without cAMP in HTR-8/SVneo cells, a cell line most similar in its RAS expression to the in vivo placenta, these factors may affect placental RAS activity. Surprisingly, these treatments also induced AGT expression in BeWo cells. Whether they are involved in regulating AGT in choriocarcinomas in vivo remains to be determined.

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

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.

The placental renin-angiotensin system and oxidative stress in pre-eclampsia

There is an inverse correlation between human birthweight and umbilical venous angiotensin II (AngII) concentrations. Oxidative stress and increased pro-renin receptor (PRR) both enhance the cleavage of angiotensin I from angiotensinogen (AGT). Pre-eclampsia, a hypertensive disorder of pregnancy, manifests as high blood pressure and proteinuria, and is a state of increased oxidative stress.

OBJECTIVES, STUDY DESIGN AND MAIN OUTCOME MEASURES

HYPOTHESIS

Pre-eclampsia will be associated with increased placental expression of components of the renin-angiotensin system, which could result in reduced infant birthweight. Biopsies were taken 1 cm from the placental edge from 27 normotensive controls and 23 pre-eclamptic White European women. Immunohistochemistry was performed for AGT, PRR, glutathione peroxidase 3 (GPx3) and the AT1R and AT2R AngII receptors. Protein expression was semi-quantitatively assessed (H-score).

RESULTS

AT1R expression was significantly increased in pre-eclamptic placentae, and negatively correlated with birthweight (r = -0.529, P = 0.009). AT1R expression was also negatively correlated with GPx3 expression overall (r = -0.647; P = 0.005). AT2R expression positively correlated with AGT (r = 0.615, P = 0.002) in the pre-eclamptic placentae only.

CONCLUSIONS

The raised AT1R expression in pre-eclampsia, together with inadequate antioxidant protection, possibly through lower GPx activity, might enhance the vasoconstrictor effect of locally-generated AngII, contributing to the restricted fetal growth characteristic of pre-eclampsia. Conversely, the AT2R:AGT association within the pre-eclamptic placenta may provide a compensatory mechanism.

Expression of renin-angiotensin system components in the early bovine embryo

The renin-angiotensin system (RAS), mainly associated with the regulation of blood pressure, has been recently investigated in female reproductive organs and the developing foetus. Angiotensin II (Ang II) influences oviductal gamete movements and foetal development, but there is no information about RAS in the early embryo. The aim of this study was to determine whether RAS components are present in the pre-implantation embryo, to determine how early they are expressed and to investigate their putative role at this stage of development. Bovine embryos produced in vitro were used for analysis of RAS transcripts (RT-PCR) and localisation of the receptors AGTR1 and AGTR2 (immunofluorescent labelling). We also investigated the effects of Ang II, Olmesartan (AGTR1 antagonist) and PD123319 (AGTR2 antagonist) on oocyte cleavage, embryo expansion and hatching. Pre-implanted embryos possessed AGTR1 and AGTR2 but not the other RAS components. Both receptors were present in the trophectoderm and in the inner cell mass of the blastocyst. AGTR1 was mainly localised in granular-like structures in the cytoplasm, suggesting its internalisation into clathrin-coated vesicles, and AGTR2 was found mainly in the nuclear membrane and in the mitotic spindle of dividing trophoblastic cells. Treating embryos with PD123319 increased the proportion of hatched embryos compared with the control. These results, the first on RAS in the early embryo, suggest that the pre-implanted embryo responds to Ang II from the mother rather than from the embryo itself. This may be a route by which the maternal RAS influences blastocyst hatching and early embryonic development.

Altered placental expression of kisspeptin and its receptor in pre-eclampsia

Kisspeptin, originally identified as metastatin, important in preventing cancer metastasis, has more recently been shown to be important in pregnancy. Roles indicated for kisspeptin in pregnancy include regulating trophoblast invasion and migration during placentation. The pregnancy-specific disorder pre-eclampsia (PE) is now accepted to begin with inadequate trophoblast invasion and the current study therefore sets out to characterise placental expression of both kisspeptin (KISS1) and its receptor (KISS1R) throughout pregnancy and in PE. Placental tissue was obtained from women undergoing elective surgical termination of early pregnancy (n=10) and from women following Caesarean section at term in normal pregnancy (n=10) and with PE (n=10). Immunohistochemistry of paraffin embedded sections and western immunoblotting were performed to assess protein localisation and expression. Quantitative real-time PCR was carried out to evaluate mRNA expression of both KISS1 and KISS1R. Protein and mRNA expression was found to mirror each other with KISS1 expression found to be reduced in PE compared with that in normal term pregnancy. Interestingly, KISS1R expression at both the mRNA and protein levels was found to be increased in PE compared with that in normal term pregnancy. The current findings of increased KISS1R expression may represent a mechanism by which functional activity of KISS1 is higher in PE than in normal pregnancy. Higher levels of activity of KISS1R may be involved in inhibition of trophoblast invasion and angiogenesis, which are associated with PE.

Regulation of the renin-angiotensin system (RAS) in BeWo and HTR-8/SVneo trophoblast cell lines

OBJECTIVES

The renin-angiotensin system (RAS) is implicated in placentation. We determined which RAS pathways are present in two trophoblast cell lines (HTR-8/SVneo and BeWo cells) and the effects of cAMP, which stimulates renal renin.

STUDY DESIGN

The effect of cAMP on RAS gene expression and on prorenin and angiotensin peptides in HTR-8/SVneo and BeWo cells were investigated.

RESULTS

In HTR-8/SVneo cells, prorenin mRNA (REN) and protein, (pro)renin receptor (ATP6AP2) and angiotensin II type 1 receptor (AGTR1) were stimulated by cAMP (P < 0.05, P < 0.05, P < 0.001 and P < 0.05, respectively). HTR-8/SVneo cells also expressed angiotensinogen (AGT) and angiotensin converting enzyme 1 (ACE1), but did not express AGTR2 or ACE2 nor the Ang 1-7 receptor (MAS1). BeWo cells did not express REN, and REN was not inducible by cAMP, but cAMP increased ACE2 and MAS1 (both P < 0.05) and decreased AGT (P < 0.05). BeWo cells expressed AGT, ACE1, ACE2 and MAS1 but not ATP6AP2, AGTR1 nor AGTR2. There was net destruction of Ang II in media from HTR-8/SVneo and BeWo incubations and net production of Ang 1-7 by BeWo and untreated HTR-8/SVneo cells.

CONCLUSION

HTR-8/SVneo cells express REN and produce prorenin as well as expressing other RAS genes likely to regulate Ang II/AT(1)R interactions and respond to cAMP, like renal renin-secreting cells. They are more similar to early gestation placentae and are therefore useful for studying effects of renin/ACE/Ang II/AT₁R on cell function. BeWo cells express the ACE2/Ang 1-7/Mas pathway, which is sensitive to cAMP and therefore are useful for studying the effects of ACE2/Ang 1-7/Mas on trophoblast function.

Down-regulation of the transcription factor snail in the placentas of patients with preeclampsia and in a rat model of preeclampsia

BACKGROUND

Placental malfunction in preeclampsia is believed to be a consequence of aberrant differentiation of trophoblast lineages and changes in utero-placental oxygenation. The transcription factor Snail, a master regulator molecule of epithelial-mesenchymal transition in embryonic development and in cancer, is shown to be involved in trophoblast differentiation as well. Moreover, Snail can be controlled by oxidative stress and hypoxia. Therefore, we examined the expression of Snail and its downstream target, e-cadherin, in human normal term, preterm and preeclamptic placentas, and in pregnant rats that developed preeclampsia-like symptoms in the response to a 20-fold increase in sodium intake.

METHODS

Western blotting analysis was used for comparative expression of Snail and e- cadherin in total protein extracts. Placental cells expressing Snail and e-cadherin were identified by immunohistochemical double-labeling technique.

RESULTS

The levels of Snail protein were decreased in human preeclamptic placentas by 30% (p < 0.01) compared to normal term, and in the rat model by 40% (p < 0.001) compared to control placentas. In preterm placentas, the levels of Snail expression varied, yet there was a strong trend toward statistical significance between preterm and preeclamptic placentas. In humans, e-cadherin protein level was 30% higher in preeclamptic (p < 0.05) placentas and similarly, but not significantly (p = 0.1), high in the preterm placentas compared to normal term. In the rat model of preeclampsia, e-cadherin was increased by 60% (p < 0.01). Immunohistochemical examination of human placentas demonstrated Snail-positive staining in the nuclei of the villous trophoblasts and mesenchymal cells and in the invasive trophoblasts of the decidua. In the rat placenta, the majority of Snail positive cells were spongiotrophoblasts of the junctional zone, while in the labyrinth, Snail-positive sinusoidal giant trophoblasts cells were found in some focal areas located close to the junctional zone.

CONCLUSION

We demonstrated that human preeclampsia and the salt-induced rat model of preeclampsia are associated with the reduced levels of Snail protein in placenta. Down-regulation of the transcription factor Snail in placental progenitor cell lineages, either by intrinsic defects and/or by extrinsic and maternal factors, may affect normal placenta development and function and thus contribute to the pathology of preeclampsia.

Folate transporter expression decreases in the human placenta throughout pregnancy and in pre-eclampsia

The transport of folate across the placenta involves a number of different receptors including folate receptor-alpha (FR-α), reduced folate carrier (RFC) and proton coupled folate transporter (PCFT). In addition there are a number of ATP-dependent transporters which have also recently been shown to be involved in folate transport; these include ABCB1, ABCC2 and BCRP (ABCG2). The aim of the current study was to characterise the placental mRNA and protein expression of these folate transporters throughout gestation and also to see if expression is altered in pre-eclampsia. Placental tissue was collected from women undergoing termination of pregnancy (TOP) and from women undergoing elective Caesarean section. To investigate mRNA expression quantitative real time PCR was used with gene specific oligonucleotide primers to FR-α, RFC, PCFT, ABCB1, ABCC2, BCRP and the reference gene YWHAZ. Protein expression was also characterised using immunohistochemistry of paraffin embedded placental tissue. Both protein and mRNA expression of all transporters examined decreased as the gestation progressed. Expression of FR-α and PCFT mRNA and protein were decreased in pre-eclampsia compared with normal term pregnancy. The higher levels of expression of FR-α, RFC, PCFT, ABCB1, ABCC2 and BCRP in early pregnancy indicate that these transporters may have an important role in the establishment and development of the placenta, with expression reducing in preparation for parturition. Reductions in FR-α and PCFT in pre-eclampsia may be a mechanism involved in the pathogenesis of pre-eclampsia by limiting placental folate uptake resulting in reduced levels of angiogenesis, cell proliferation and antioxidant protection.

Angiotensin IV protects against angiotensin II-induced cardiac injury via AT4 receptor

Angiotensin II (Ang II) is an important regulator of cardiac function and injury in hypertension. The novel Ang IV peptide/AT4 receptor system has been implicated in several physiological functions and has some effects opposite to those of Ang II. However, little is known about the role of this system in Ang II-induced cardiac injury. Here we studied the effect of Ang IV on Ang II-induced cardiac dysfunction and injury using isolated rat hearts, neonatal cardiomyocytes and cardiac fibroblasts. We found that Ang IV significantly improved Ang II-induced cardiac dysfunction and injury in the isolated heart in response to ischemia/reperfusion (I/R). Moreover, Ang IV inhibited Ang II-induced cardiac cell apoptosis, cardiomyocyte hypertrophy, and proliferation and collagen synthesis of cardiac fibroblasts; these effects were mediated through the AT4 receptor as confirmed by siRNA knockdown. These findings suggest that Ang IV may have a protective effect on Ang II-induced cardiac injury and dysfunction and may be a novel therapeutic target for hypertensive heart disease.

Challenges posed to the maternal circulation by pregnancy

In primates, adequate growth of the fetus depends on the development of the uteroplacental unit. On the fetal side, this is achieved by the creation of the vascular network of the placenta. On the maternal side, the transformation of the spiral arteries into saccular nonreactive vessels by the trophoblast provides high blood flow to the intervillous space. Apart from the changes in the uterine arteries, the mother expands her plasma volume – at the expense of stimulating the renin-angiotensin-aldosterone system – and her cardiac output. In the maintaining of normotension in the face of an increased cardiac output and plasma volume, the renin-angiotensin-aldosterone system requires an enhanced vasodilator synthesis. Finally, in the late stages of pregnancy, a normal endothelial function is required to provide an ample margin to the activation provoked by deportation of syncytiotrophoblast fragments/factors to the maternal circulation. These four adaptative processes require various interrelated vasodilator systems. Deficient adaptations cause isolated or proteinuric arterial hypertension, intrauterine growth restriction, preterm delivery, and stillbirths, among others. Moreover, a normal or a defective adaptation to pregnancy influences maternal cardiovascular health in later life, as evidenced by various studies, most of them epidemiological; thus, pregnancy is now considered a stress test to the maternal cardiovascular system. Because of this, women planning to become pregnant should be screened for clinical and biochemical cardiovascular risks. Inversely, women presenting with hypertension in pregnancy should be thoroughly studied to detect and correct cardiovascular risks. The incorporation of the predictive value of a hypertensive pregnancy should help reduce cardiovascular disease in women.

Novel expression and regulation of voltage-dependent potassium channels in placentas from women with preeclampsia

Preeclampsia is associated with structural/functional alterations in placental and maternal vasculature. Voltage-dependant potassium channels encoded by KCNQ1-5 genes have been detected in several types of blood vessels where they promote vascular relaxation. Voltage-dependant potassium channel function can be modulated by KCNE1-5-encoded accessory proteins. The aim of this study was to determine whether KCNQ and KCNE genes are differentially expressed in placentas from women with preeclampsia compared with normotensive controls and to examine any differences in those who delivered preterm (<37 weeks) or term. Placental biopsies (from midway between the cord and periphery) were obtained, with consent, from white European control (n=24; term) and preeclamptic (n=22; of whom 8 delivered before 37 weeks' gestation) women. KCNQ/KCNE and GAPDH mRNA expressions were determined by quantitative RT-PCR. Protein expression/localization was assessed using immunohistochemistry. KCNQ3 and KCNE5 mRNA expressions were significantly upregulated in preeclampsia (median [interquartile range]: 1.942 [0.905 to 3.379]) versus controls (0.159 [0.088 to 0.288]; P=0.001) and exhibited a strong positive correlation with each other (P<0.001), suggesting a novel heterodimer. Enhanced protein expression of KCNQ3 and KCNE5 in preeclampsia was confirmed with localization mainly restricted to the syncytiotrophoblast. KCNQ4 and KCNE1 isoforms were suppressed in placentas from term preeclamptic women versus controls (P≤0.05). KCNQ1 mRNA expression was increased and KCNQ5 decreased in the preterm preeclamptic group versus controls (P<0.05). In summary, voltage-dependant potassium channels are expressed and markedly modulated in placentas from preeclamptic women. Differential expression of isoforms may lead to altered cell proliferation. The correlation between KCNQ3 and KCNE5 expression is indicative of a novel channel complex and warrants further investigation.

Differential expression of angiotensin II type 1 and type 2 receptors at the maternal–fetal interface: potential roles in early placental development

Angiotensin II (Ang II) is locally generated in the placenta and regulates syncytial transport, vascular contractility and trophoblast invasion. It acts through two receptor subtypes, AGTR1 and AGTR2 (AT1 and AT2), which typically mediate antagonising actions. The objectives of this study are to characterise the cellular distribution of AGTR1 and AGTR2 at the maternal–fetal interface and explore the effects on cytotrophoblast turnover. Low levels ofAGTR2mRNA were detected in first trimester placental homogenates using real-time PCR. Immunohistochemistry using polyclonal antibodies against AGTR1 and AGTR2 detected the receptors in first trimester placenta, decidua basalis and villous tip outgrowths in culture. Serial staining with cytokeratin-7 was used to identify extravillous trophoblasts (EVTs). AGTR1 was found in the syncytiotrophoblast microvillous membrane, in a subpopulation of villous cytotrophoblasts, and in Hofbauer cells. AGTR1 was strongly upregulated in cytotrophoblasts in cell columns and villous tip outgrowths, but was absent in interstitial and endovascular EVTs within the decidua. AGTR2 immunostaining was present in Hofbauer cells and villous cytotrophoblasts, but was absent from syncytiotrophoblast. Faint staining was detected in cell column cytotrophoblasts and villous outgrowths, but not in EVTs within the decidua. Both receptors were detected in placental homogenates by western blotting. Ang II significantly increased proliferation of cytotrophoblasts in both villous explants and villous tip outgrowths, but did not affect apoptosis. Blockade of AGTR1 and AGTR2 together abrogated this effect. This study shows specific expression patterns for AGTR1 and AGTR2 in distinct trophoblast populations at the maternal–fetal interface and suggests that Ang II plays a role in placental development and generation of EVTs.