Background: During the first trimester of pregnancy, normal placental development occurs in a low oxygen environment. A low oxygen environment can stimulate angiogenesis via upregulation of vascular endothelial growth factor (VEGF). High levels of expression of genes that control the activity of the placental renin-angiotensin system (RAS) occur in early pregnancy. While the RAS and oxygen can both stimulate angiogenesis, how they interact within the placenta is unknown. We postulated that low oxygen increases expression of the pro-angiogenic RAS pathway and this is associated with increased VEGF in a first trimester human trophoblast cell line (HTR-8/SVneo).
Method: HTR-8/SVneo cells were cultured in one of three oxygentensions (1%, 5% and 20%). RAS and VEGF mRNA expression were determined by qPCR. Prorenin, angiotensin converting enzyme (ACE) and VEGF protein levels in the supernatant as well as prorenin and ACE in cell lysates were measured using ELISAs.
Results: Low oxygen significantly increased the expression of both angiotensin II type 1 receptor (AGTR1)and VEGF (both P<0.05). There was a positive correlation between AGTR1 and VEGF expression at low oxygen (r=0.64, P<0.005). Corresponding increases in VEGF protein were observed with low oxygen (P<0.05). Despite no change in ACE1 expression, ACE levels in the supernatant increased with low oxygen (1 and 5%, P<0.05). Expression of other RAS components did not change.
Conclusions: Low oxygen increased AGTR1 and VEGF expression as well as ACE and VEGF protein levels suggesting that it activates the pro-angiogenic RAS pathway. This highlights a potential role for the placental RAS in mediating the pro-angiogenic effects of low oxygen in placental development.