Arginine vasopressin acts directly upon human placental trophoblasts to elicit calcium responses

Previously we demonstrated that preeclampsia, a hypertensive disorder of pregnancy, is associated with elevated secretion of arginine vasopressin (AVP) as early as the sixth week of gestation. In addition, chronic low‐dose infusion of AVP into pregnant wildtype C57BL/6J is sufficient to initiate all of the cardinal phenotypes of preeclampsia including gestational‐dependent de novo hypertension, renal glomerular endotheliosis, placental hypoxia and intrauterine growth restriction. We hypothesize that AVP acts directly upon placental trophoblasts to cause placental dysfunction, and that this mechanism contributes to placental dysfunction during preeclampsia. First, we performed in silico re‐analyses of a published microarray dataset (GSE75010). In this dataset (n=77 controls, n=80 preeclampsia), all five types of AVP receptors were abundantly expressed at the mRNA level in placental tissue. Interestingly, placentas from human pregnancies complicated by preeclampsia exhibited increases in expression of the AVPR1A (p=0.03) and OXTR (p<0.01) receptors, but no significant changes in the other AVP‐sensitive receptors including AVPR1B (p=0.14), AVPR2 (p=0.98), or CUL5 (p=0.09). Second, we confirmed that all five receptor subtypes are expressed at the mRNA level in cultured immortalized human first‐trimester trophoblasts (HTR8/SVneo cells). Third, we examined second‐messenger signaling mechanisms, focusing on intracellular Ca 2+ release, as the Gαq‐calcium pathway is commonly activated by AVPR1A, AVPR1B, and OXTR. Increases in intracellular Ca 2+ concentration ([Ca 2+ ] i ) with graded doses of AVP were examined in HTR8/SVneo cells pre‐loaded with the fluorescent Ca 2+ ‐sensitive indicator FURA‐2. AVP evoked [Ca 2+ ] i responses of increasing amplitude at 10, 100 and 1000 nM. Fourth, we examined AVPR1A receptor‐dependence of these [Ca 2+ ] i responses. Pre‐treatment of the HTR8/SVneo cells with the AVPR1A‐selective antagonist relcovaptan (1 uM) abolished [Ca 2+ ] i responses to AVP (100 nM), and subsequent washout of the antagonist restored responsiveness. These findings lead us to conclude that human placental trophoblasts express AVP receptors which functionally couple to Gαq‐calcium signaling. Together, the findings that (i) AVP secretion is elevated during preeclampsia, (ii) AVP is sufficient to initiate preeclampsia phenotypes in mice, (iii) AVPR1A appears to be increased in placenta from preeclamptic pregnancies, and (iv) AVPR1A activation functionally couples to Ca 2+ signaling in trophoblasts supports the overall concept that AVP‐AVPR1A‐Ca 2+ signaling in the trophoblast may contribute to placental dysfunctions in preeclampsia.