Gq Signaling in the Placental Syncytiotrophoblast Layer During Preeclampsia

Preeclampsia is a pregnancy-associated cardiovascular disorder characterized by hypertension and proteinuria after 20 weeks of gestation. Generalized cellular 'stress' (oxidative, mitochondrial, etc.) within the syncytiotrophoblast (STB) layer of placenta is theorized to drive its pathogenesis. Hormones implicated in preeclampsia such as angiotensin, endothelin, and vasopressin signal via receptors that typically couple to the Gq second-messenger cascade, and Regulator of G protein Signaling-2 (RGS2) buffers this signaling. We have published that RGS2 expression is decreased in human preeclamptic placenta, and reducing RGS2 expression in placenta is sufficient to cause development of key features of this disorder in mice. Unpublished in situ hybridization data indicate that in both humans and mice, RGS2 is present in the STB layer - and that RGS2 expression in the STB layer is reduced during preeclampsia in humans. Collectively, these findings lead us to generally hypothesize that excess Gq signaling specifically within the STB layer, whether due to excessive hormonal activation or loss of RGS2-mediated buffering, causes STB-Stress and thereby contributes to the pathogenesis of preeclampsia. Therefore, the objective of this study was to test whether artificial, exogenous activation of Gq signaling only within STB cells is sufficient to induce placental and maternal phenotypes of preeclampsia in mice.CAG-FLEX-hM3Dq (Gαq DREADD, Jax 026943) or C57BL/6J dams were bred with Gcm1-Cre sires (Jax 026625) or non-transgenic littermates to elicit STB-restricted hM3Dqexpression in ≍50% or 0% of placentas. The synthetic DREADD ligand clozapine N-oxide (CNO) or saline vehicle was administered (2 mg/kg/d, ip) mid-gestation (GD 12.5-14.5). Placental and maternal phenotypes were compared between Cre and Cre placentas within a dam, CNO- vs saline-injected double-transgenic dams, and double- vs single/non-transgenic dams treated with CNO. Activation of Gq in the STB layer caused maternal proteinuria (n=4-9, 49±6 mg/day vs 28±4 mg/day; p=0.01). Labyrinth vascularization, assessed by percentage of CD31 area, was reduced with Gq activation (n=5, Cre 21±1%, Cre 27±2%; p=0.01), while other regions remained unaffected (Decidua: Cre 14±4%, Cre 14±3%; Junctional Zone: Cre 11±4%, Cre 12±3%). Possible reductions in placental mass (n=5 Cre 0.12±0.01g, Cre 0.15±0.01g; p=0.06), and placental vascular endothelial growth factor protein levels (n=6-7 117±67 ng/g vs 151±12 ng/g; p=0.06) were noted, but no obvious trend in fetal growth restriction was observed (n=5 Cre 0.21±0.06g, Cre 0.29±0.04g). These data support the pathological significance of excess Gq signaling specifically within the STB layer. Ongoing studies are aimed at further characterizing maternal phenotypes (blood pressure, circulating factors) in these models, and the synergistic effects of simultaneous STB-specific deletion of RGS2 upon sensitivity to Gq stimulation in this cell type.