- Title
- The role of angiotensin converting enzyme 2 (ACE2) in pregnancy: preeclampsia and small for gestational age
- Creator
- Tamanna, Sonia
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Angiotensin converting enzyme 2 (ACE2) is a component of the renin-angiotensin system (RAS). ACE2 determines the relative amount of angiotensin (Ang) II and Ang-(1-7). ACE2, therefore, plays a key role in maintaining the balance between the vasoconstrictor (Ang II/ACE/AT1R) and vasodilatory (Ang-(1-7)/ACE2/MasR) pathways. The maternal circulatory RAS regulates blood pressure, electrolyte, and fluid homeostasis and alterations in components of the circulating RAS are seen in women with preeclampsia (PE) and fetal growth restriction (FGR). Similarly, the placental tissue RAS, which has roles in regulating trophoblast proliferation, angiogenesis, migration, and invasion, is also dysregulated in pregnancies associated with placental insufficiency. Furthermore, it has been shown that components of the RAS (prorenin, angiotensinogen, and Ang II type 1 receptor (AT1R)) are stimulated during placental trophoblast syncytialisation. This syncytialisation is particularly essential, as the placental syncytiotrophoblast, which is formed via the process of syncytialisation, is responsible for providing nutrients to the baby and exchange of gases and waste between the mother and fetus. Therefore, impaired, or aberrant syncytialisation, and a dysfunctional placental RAS could cause pregnancy complications such as PE and FGR. This thesis aimed to investigate the potential role of circulating and placental ACE2 in pregnancy complications such as PE and small for gestational age (SGA). I firstly measured circulating levels of RAS enzymes (angiotensin converting enzymes (ACE, ACE2) and neprilysin (NEP) and angiotensin peptides in non-pregnant women (NP), healthy pregnant women, women with PE and in women giving birth to SGA babies. I have shown for the first time that the maternal plasma levels of ACE, ACE2 and ACE2 activity are enhanced during normal pregnancy, and these higher levels are maintained throughout gestations. I also found that Ang-(1-7) peptide levels were higher in normal pregnancy compared to non-pregnant women. In SGA pregnancies, maternal plasma ACE2 levels were higher at 13, 18 and 30 weeks of gestation compared with normal pregnancies. I also showed that plasma ACE levels were higher at 18 weeks of gestation compared with those found in women with normal pregnancies. The increase in ACE2 in early to mid-gestation could counteract the high ACE levels, thus preventing the activity of Ang II (causes vasoconstriction) via the AT1R. These studies could be beneficial to future studies to determine if ACE and ACE2 are early biomarkers for SGA or fetal growth restriction. I have also shown that maternal plasma ACE, ACE2 and NEP levels and ACE2 activity and Ang-(1-7) were significantly decreased in women with PE compared with normal pregnant women. These findings suggest that in PE, decreased levels of angiotensin processing enzymes could cause the reduction in Ang peptide levels that are seen in women with PE. The second part of this thesis focussed on the placental RAS using two well described models of trophoblast syncytialisation, BeWo cells and primary human trophoblasts. I found that placental tissue had significantly increased levels of ACE mRNA compared with primary trophoblast cells and human BeWo choriocarcinoma cells. Furthermore, there were significant differences between forskolin induced syncytialisation of BeWo choriocarcinoma cells and spontaneously syncytialised trophoblast cells in terms of changes in expression of RAS enzymes during syncytialisation. The mRNA expression of ACE increased in primary trophoblasts with syncytialisation, whereas ACE2 and NEP mRNA were decreased. However, the protein levels of ACE, ACE2 and NEP in primary trophoblast cells remained unchanged with syncytialisation. Thus, in primary trophoblasts, the balance between the two pathways of the RAS is likely to have been maintained during syncytialisation. In contrast, ACE mRNA and protein expression was decreased, and ACE2 mRNA, protein and activity were increased during syncytialisation in BeWo cells. The expression of NEP was unchanged. Thus, in BeWo cells the Ang-(1-7)/ACE2/Mas receptor pathway, which is vasodilatory, is activated during syncytialisation, whereas, in primary trophoblast cells the balance between the two opposing RAS pathways is likely to be maintained and thus contribute to a successful pregnancy. As BeWo cells fail to mimic the findings of trophoblast cells, this study also suggests BeWo cells should be reconsidered as a model of syncytialisation, particularly when investigating the RAS. I then went on to investigate the secretion of soluble RAS enzymes in the two in vitro models. I found that both BeWo and primary trophoblast cells secrete soluble RAS enzymes. Forskolin-induced syncytialisation did not influence the secretion of these enzymes in BeWo cells. In spontaneously syncytialising primary trophoblasts however, sACE and sNEP levels were significantly reduced with syncytialisation though sACE2 levels remain unchanged. Finally, I examined the expression of RAS enzymes in placentae from pregnancies classified as: preterm control (PTC); early-onset PE (EOPE); term control (TC); or late-onset PE (LOPE). I found that the mRNA expression of ACE, ACE2 and NEP and protein levels of ACE and ACE2 were not significantly different between PTC and EOPE and between TC and LOPE. However, NEP protein levels were higher in EOPE placentae compared with PTC placentae. The higher protein, but not mRNA levels in the EOPE placental tissue might mean that the expression of NEP is regulated through post transcriptional or posttranslational mechanisms. Overall, this thesis provided new insights into the role of ACE2 in pregnancy complications including PE and SGA. This thesis also described the levels of RAS enzymes during trophoblast syncytialisation and their contribution in maintaining the balance between two major RAS pathways in the placenta. This thesis also demonstrated that placental RAS enzymes levels might be interrupted in women with PE. This work will also serve as an imperative resource for future functional and clinical investigations to uncover the role of ACE2 and the RAS in pregnancy to better understand and treat IUGR and PE.
- Subject
- angiotensin converting enzyme 2; pregnancy; preeclampsia; small for gestational age; syncytialisation; placenta
- Identifier
- http://hdl.handle.net/1959.13/1504974
- Identifier
- uon:55606
- Rights
- Copyright 2022 Sonia Tamanna
- Language
- eng
- Full Text
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