Activation of local chorionic villi angiotensin II levels but not angiotensin (1-7) in preeclampsia

Abstract

The chorionic villi in the placenta are responsible for the regulation of fetal oxygen and nutrient transport. Although the peripheral renin-angiotensin system is activated during normal pregnancy, the regulation of the local chorionic villi renin-angiotensin system remains unknown. Therefore, placental chorionic villous tissue was collected from nulliparous third-trimester normotensive or preeclamptic subjects and was analyzed for angiotensin peptide content, angiotensinogen, renin, angiotensin-converting enzyme (ACE), ACE2, neprilysin, angiotensin II type 1 (AT(1)), angiotensin II type 2, Mas receptor mRNAs, and angiotensin receptor density and subtype. Angiotensin II in chorionic villi was significantly higher in preeclamptic subjects, whereas angiotensin (1-7) was not different. Angiotensinogen and AT(1) receptor gene expression was significantly higher in preeclamptic subjects. No differences were observed in renin, ACE, ACE2, or neprilysin gene expression. Mas receptor mRNA in preeclamptic subjects was decreased. The AT(1) receptor was the predominant receptor subtype in normal and preeclamptic chorionic villi. There was no difference in the density of the AT(1,) angiotensin II type 2, and angiotensin (1-7) receptors. These results indicate that enhanced chorionic villous expression of angiotensin II may result from increased angiotensinogen. Elevated angiotensin II, acting through the AT(1) receptor, may favor vasoconstriction in placental chorionic villi and contribute to impaired fetal blood flow and decreased fetal nutrition observed during preeclampsia.

Figure 1

Angiotensin peptide levels in normal pregnant and preeclamptic chorionic villi. Angiotensin peptide levels were measured by radioimmunoassay of Ang I (A), Ang II (B), and Ang-(1–7) (C) in normal and preeclamptic placental chorionic villi. There was a significant increase in Ang II (P<0.05) but no change in Ang I or Ang-(1–7) peptide levels in preeclamptic vs normal chorionic villi. Ang II is the predominant peptide in the chorionic villi (P<0.001). Data are expressed as the means±SEMs. *P<0.05 preeclamptic vs normal chorionic villi.

Figure 2

Gene expression of RAS components in normal pregnant and preeclamptic chorionic villi. Relative gene expression as determined by reverse transcription, real-time PCR of angiotensinogen and renin (A); NEP, ACE, and ACE2 (B); AT₁ receptor (C); and Mas receptor (D) in normal and preeclamptic placental chorionic villi. Angiotensinogen (P<0.01) and AT₁ receptor (P<0.01) mRNA were upregulated in preeclamptic chorionic villi when compared with normal subjects. The Mas receptor was down-regulated in preeclamptic chorionic villi when compared with normal subjects (P<0.01). There was no change in renin, NEP, ACE, or ACE2 mRNA. Data are expressed as the means±SEMs. P<0.01 preeclamptic vs normal chorionic villi.

Figure 3

Angiotensin receptor binding in normal pregnant and preeclamptic chorionic villi. Receptor density of AT₁, AT₂, and AT_1–7 was measured by receptor autoradiography in normal and preeclamptic placental chorionic villi and was assessed by the displacement of ¹²⁵I-[sarcosine¹, threonine⁸]-Ang II binding by the AT₁ receptor antagonist losartan (3 µmol/L), the AT₂ receptor antagonist PD123319 (3 µmol/L), and the AT_1–7 receptor antagonist A779 (3 µmol/L). Quantification of receptor density showed no changes between normal and preeclamptic subjects for AT₁, AT₂, or AT_1–7 receptors. The AT₁ receptor was found to be the predominant receptor in the chorionic villi of both normal and preeclamptic placentas (P<0.001). In addition, the AT₂ and AT_1–7 receptors made up <15% of the RAS receptors in the chorionic villi of both groups. Data are expressed as the means±SEMs. *P<0.001 AT₁ vs AT₂ and AT_1–7 receptor density in the normal chorionic villi, #P<0.001 AT₁ vs AT₂ and AT_1–7 receptor density in the preeclamptic chorionic villi.