Renin-angiotensin system (RAS) enzymes and placental trophoblast syncytialisation

Placental renin-angiotensin system (RAS) components; prorenin, angiotensinogen, and angiotensin (Ang) II type 1 receptor (AT₁R) are upregulated during syncytialisation. This study examined whether angiotensin-converting enzyme (ACE), ACE2 and neprilysin (NEP) are also altered during syncytialisation. Two in vitro models of syncytialisation were used: forskolin-treated BeWo cells and spontaneously syncytialising primary human trophoblast cells. Term placentae and primary trophoblasts had the highest levels of ACE, ACE2 and NEP mRNA. In primary trophoblasts, ACE mRNA levels significantly increased with syncytialisation, ACE2 and NEP mRNA levels decreased. ACE, ACE2 and NEP protein levels and ACE2 activity did not change. Syncytialisation of primary trophoblasts decreased soluble (s)ACE and sNEP but not sACE2 levels. In primary trophoblasts, the balance between the enzymes controlling the two opposing pathways of the RAS was maintained. These findings were unable to be reproduced in BeWo cells. Future studies exploring placental levels of these enzymes in pregnancies complicated by placental insufficiency are warranted.

The (pro)renin receptor (ATP6AP2) does not play a role in syncytialisation of term human primary trophoblast cells

INTRODUCTION

In the placenta, the (pro)renin receptor (ATP6AP2) is localised to the syncytiotrophoblast. ATP6AP2 can activate the placental renin-angiotensin system (RAS), producing Angiotensin II (Ang II) which, acting via the angiotensin II type 1 receptor (AGTR1), is important for placental development and function. ATP6AP2 can also independently stimulate intracellular signalling pathways known to regulate trophoblast syncytialisation. We proposed that ATP6AP2 plays a role in trophoblast syncytialisation.

METHODS

Primary trophoblast cells were isolated from human placentae and transfected with an ATP6AP2 siRNA, a negative control siRNA or vehicle and allowed to spontaneously syncytialise. Syncytialisation was determined by secretion of human chorionic gonadotrophin (hCG) and by decreased CDH1 (E-cadherin) levels. Expression of RAS mRNAs and proteins were measured by qPCR and immunoblotting, respectively.

RESULTS

Primary trophoblast cells spontaneously syncytialised in culture. Syncytialisation did not affect ATP6AP2 mRNA or protein levels. However, the expression of REN, AGT and AGTR1 mRNAs were increased (P = 0.02, P = 0.01 and P = 0.03, respectively). ATP6AP2 siRNA had no effect on syncytialisation.

DISCUSSION

In primary trophoblasts, syncytialisation was associated with increased expression of the RAS. hCG was increased during syncytialisation and is known to stimulate REN and possibly AGT, however further experiments are needed to confirm that this was the mechanism via which the RAS was activated. Therefore, syncytialisation of primary trophoblasts may involve hCG-induced RAS activation and downstream activation of signalling pathways and growth factors, which can be stimulated via the interaction of Ang II with AGTR1. Nevertheless, it appears that the (pro)renin receptor is not involved.