The synthesis, secretion and uptake of prorenin in human amnion

Megalin, Proton Pump Inhibitors and the Renin-Angiotensin System in Healthy and Pre-Eclamptic Placentas

Soluble Fms-like tyrosine kinase-1 (sFlt-1) is increased in pre-eclampsia. The proton pump inhibitor (PPI) lowers sFlt-1, while angiotensin increases it. To investigate whether PPIs lower sFlt-1 by suppressing placental renin–angiotensin system (RAS) activity, we studied gene expression and protein abundance of RAS components, including megalin, a novel endocytic receptor for prorenin and renin, in placental tissue obtained from healthy pregnant women and women with early-onset pre-eclampsia. Renin, ACE, ACE2, and the angiotensin receptors were expressed at identical levels in healthy and pre-eclamptic placentas, while both the (pro)renin receptor and megalin were increased in the latter. Placental prorenin levels were upregulated in pre-eclamptic pregnancies. Angiotensinogen protein, but not mRNA, was detectable in placental tissue, implying that it originates from maternal blood. Ex vivo placental perfusion revealed a complete washout of angiotensinogen, while prorenin release remained constant. The PPI esomeprazole dose-dependently reduced megalin/(pro)renin receptor-mediated renin uptake in Brown Norway yolk sac epithelial cells and decreased sFlt-1 secretion from placental villous explants. Megalin inhibition blocked angiotensinogen uptake in epithelial cells. In conclusion, our data suggest that placental RAS activity depends on angiotensinogen taken up from the maternal systemic circulation. PPIs might interfere with placental (pro)renin-AGT uptake/transport, thereby reducing angiotensin formation as well as angiotensin-induced sFlt-1 synthesis.

The role of oxygen in regulating microRNAs in control of the placental renin-angiotensin system

Human placental renin-angiotensin system (RAS) expression is highest in early gestation, at a time when placental oxygen tension is at its lowest (1-3%), and promotes placental development. Some miRNAs predicted to target RAS mRNAs are downregulated in early gestation. We tested the hypothesis that low oxygen suppresses expression of miRNAs that target placental RAS mRNAs, thus increasing concentrations of RAS mRNAs. HTR-8/SVneo cells were cultured in 1, 5 and 20% oxygen for 48 h. Differences in miRNA expression were measured on an Affymetrix miRNA microarray (n = 3/group). Those predicted to target RAS mRNAs, or that were decreased in early gestation, were confirmed by qPCR (n = 9/group). RAS protein levels were assessed by ELISAs or immuno-blotting. Microarray analysis identified four miRNAs predicted to target RAS mRNAs that were differentially expressed between 1 and 5% oxygen. Using qPCR, 15 miRNAs that target the RAS were measured in HTR-8/SVneo cells. Five miRNAs were downregulated in 1% compared with 5% oxygen. Expression of a number of RAS mRNAs (ATP6AP2, AGT, ACE and AGTR1) were increased in either, or both, 1 and 5% oxygen compared with 20% oxygen. AGT protein levels were increased in 1% oxygen compared with 5%. Further validation is needed to confirm that these miRNAs target RAS mRNAs directly and that placental development is partly regulated by oxygen-sensitive miRNAs that target RAS mRNAs. Since placental oxygen tension changes across gestation, changes in expression of these miRNAs may contribute to the transgestational changes in placental RAS expression and the resulting effects on placental development.