Reduced Placental Regulator of G‐Protein Signaling‐2 (RGS2) and Preeclampsia

Abstract

Though mid‐ and late‐gestational mechanisms of the late‐pregnancy cardiovascular disorder preeclampsia (PreE) are relatively well characterized, genetic risk factors and mechanisms driving the early gestational pathogenesis of PreE remain largely unclear. Various hormone activators of Gαq second‐messenger signaling pathways (eg ‐ vasopressin, endothelin, and angiotensin) have been implicated in preeclampsia. Regulator of G‐protein Signaling 2 (RGS2) acts as an endogenous terminator of Gαq signaling, and previous association studies have identified an increased risk for PreE and its sequelae in women carrying a single nucleotide polymorphism that results in reduced RGS2. We hypothesized that RGS2 is expressed in placental trophoblasts, and that reduced expression of RGS2 in placental tissue may represent a risk factor for the development of PreE due to disinhibited Gαq signaling. Placental tissue samples from PreE and clinically‐matched control pregnancies were obtained from the University of Iowa Maternal‐Fetal Tissue Bank and examined for mRNA of the B/R4 family of RGS proteins, including RGS2. Of the members examined (RGS2, ‐3, ‐4.2, ‐4.3, ‐4.4, ‐4.5, and ‐ 5) in control placentas (n=9), only RGS2 (Ct 28.8±0.7 vs 18S Ct 12.1±0.4) and RGS4.3 (Ct 23.0±0.4 vs 18S Ct 13.3±0.3) transcripts were detected above background levels. In PreE placenta (n=11), RGS2 mRNA may be suppressed (1.0±0.4 vs 0.2±0.3‐fold, p=0.1) while RGS4.3 remains unchanged (1.0±0.4 vs 1.1±0.4 fold, p=0.8). Immunohistochemical (IHC) detection similarly confirms cytoplasmic localization of RGS2 protein in trophoblasts of placentas from control and PreE human pregnancies. RGS2 positive trophoblasts are found in the junctional zone and labyrinth of placentas from wildtype C57BL/6J mice. We next examined the cardiovascular consequences of reducing feto‐placental RGS2 within a wildtype mother (wildtype C57BL/6J dam bred with either an RGS2‐knockout (KO) or littermate control sire). Reduced RGS2 in the feto‐placental unit caused increased HIF1α binding to chromatin (control 0.144±0.004 vs RGS2‐KO 0.155±0.004 AU, p=0.05, n=5 each), supporting placental hypoxia. Further, dams exhibited isolated diastolic hypertension by telemetry (24 hr mean: pre‐pregnancy control n=3, 92±2 vs RGS2‐KO n=5, 92±2; late‐pregnancy control 92±2 vs RGS2‐KO 98.2±2 mmHg; p<0.05 vs pre‐pregnancy RGS2‐KO, and pregnant control), consistent with microvascular dysfunction. We conclude that RGS2 is present in the cytoplasm of trophoblasts, that placental RGS2 is suppressed in PreE, and that loss of feto‐placental RGS2 is sufficient to cause placental hypoxia and maternal diastolic hypertension. Collectively these studies provide evidence supporting the novel concepts that disinhibited Gαq signaling in the placenta may contribute to PreE, and that a father's genetics may contribute to the risk for PreE.