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Angiotensin II type 1 receptor antibodies and increased angiotensin II sensitivity in pregnant rats.

ABSTRACT: Pregnant women who subsequently develop preeclampsia are highly sensitive to infused angiotensin (Ang) II; the sensitivity persists postpartum. Activating autoantibodies against the Ang II type 1 (AT(1)) receptor are present in preeclampsia. In vitro and in vivo data suggest that they could be involved in the disease process. We generated and purified activating antibodies against the AT(1) receptor (AT(1)-AB) by immunizing rabbits against the AFHYESQ epitope of the second extracellular loop, which is the binding epitope of endogenous activating autoantibodies against AT(1) from patients with preeclampsia. We then purified AT(1)-AB using affinity chromatography with the AFHYESQ peptide. We were able to detect AT(1)-AB both by ELISA and a functional bioassay. We then passively transferred AT(1)-AB into pregnant rats, alone or combined with Ang II. AT(1)-AB activated protein kinase C-? and extracellular-related kinase 1/2. Passive transfer of AT(1)-AB alone or Ang II (435 ng/kg per minute) infused alone did not induce a preeclampsia-like syndrome in pregnant rats. However, the combination (AT(1)-AB plus Ang II) induced hypertension, proteinuria, intrauterine growth retardation, and arteriolosclerosis in the uteroplacental unit. We next performed gene-array profiling of the uteroplacental unit and found that hypoxia-inducible factor 1? was upregulated by Ang II plus AT(1)-AB, which we then confirmed by Western blotting in villous explants. Furthermore, endothelin 1 was upregulated in endothelial cells by Ang II plus AT(1)-AB. We show that AT(1)-AB induces Ang II sensitivity. Our mechanistic study supports the existence of an "autoimmune-activating receptor" that could contribute to Ang II sensitivity and possible to preeclampsia.

SUBMITTER: Wenzel K

PROVIDER: S-EPMC3597080 | biostudies-literature | 2011 Jul

REPOSITORIES: biostudies-literature

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Angiotensin II type 1 receptor antibodies and increased angiotensin II sensitivity in pregnant rats.

Wenzel Katrin K Rajakumar Augustine A Haase Hannelore H Geusens Nele N Hubner Norbert N Schulz Herbert H Brewer Justin J Roberts Lyndsay L Hubel Carl A CA Herse Florian F Hering Lydia L Qadri Fatimunnisa F Lindschau Carsten C Wallukat Gerd G Pijnenborg Robert R Heidecke Harald H Riemekasten Gabriela G Luft Friedrich C FC Muller Dominik N DN Lamarca Babette B Dechend Ralf R

Hypertension (Dallas, Tex. : 1979) 20110516 1

Pregnant women who subsequently develop preeclampsia are highly sensitive to infused angiotensin (Ang) II; the sensitivity persists postpartum. Activating autoantibodies against the Ang II type 1 (AT(1)) receptor are present in preeclampsia. In vitro and in vivo data suggest that they could be involved in the disease process. We generated and purified activating antibodies against the AT(1) receptor (AT(1)-AB) by immunizing rabbits against the AFHYESQ epitope of the second extracellular loop, wh ...[more]

PMID: 21576625

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Project description:The angiotensin II (Ang II) type 1 receptor (AT1R) is involved in the regulation of blood pressure (through vasoconstriction) and water and ion homeostasis (mediated by interaction with the endogenous agonist). AT1R can also be activated by auto-antibodies (AT1R-Abs), which are associated with manifold diseases, such as obliterative vasculopathy, preeclampsia and systemic sclerosis. Knowledge of the molecular mechanisms related to AT1R-Abs binding and associated signaling cascade (dys-)regulation remains fragmentary. The goal of this study was, therefore, to investigate details of the effects of AT1R-Abs on G-protein signaling and subsequent cell proliferation, as well as the putative contribution of the three extracellular receptor loops (ELs) to Abs-AT1R signaling. AT1R-Abs induced nuclear factor of activated T-cells (NFAT) signaling, which reflects Gq/11 and Gi activation. The impact on cell proliferation was tested in different cell systems, as well as activation-triggered receptor internalization. Blockwise alanine substitutions were designed to potentially investigate the role of ELs in AT1R-Abs-mediated effects. First, we demonstrate that Ang II-mediated internalization of AT1R is impeded by binding of AT1R-Abs. Secondly, exclusive AT1R-Abs-induced Gq/11 activation is most significant for NFAT stimulation and mediates cell proliferation. Interestingly, our studies also reveal that ligand-independent, baseline AT1R activation of Gi signaling has, in turn, a negative effect on cell proliferation. Indeed, inhibition of Gi basal activity potentiates proliferation triggered by AT1R-Abs. Finally, although AT1R containing EL1 and EL3 blockwise alanine mutations were not expressed on the human embryonic kidney293T (HEK293T) cell surface, we at least confirmed that parts of EL2 are involved in interactions between AT1R and Abs. This current study thus provides extended insights into the molecular action of AT1R-Abs and associated mechanisms of interrelated pathogenesis.

Project description:Hypertensive disorders of pregnancy are the second leading cause of maternal deaths worldwide. Superimposed preeclampsia is an increasingly common problem and often associated with impaired placental perfusion. Understanding the underlying mechanisms and developing treatment options are crucial. The pregnant stroke-prone spontaneously hypertensive rat has impaired uteroplacental blood flow and abnormal uterine artery remodeling. We used Ang II (angiotensin II) infusion in pregnant stroke-prone spontaneously hypertensive rats to mimic the increased cardiovascular stress associated with superimposed preeclampsia and examine the impact on the maternal cardiovascular system and fetal development. Continuous infusion of Ang II at 500 or 1000 ng/kg per minute was administered from gestational day 10.5 until term. Radiotelemetry and echocardiography were used to monitor hemodynamic and cardiovascular changes, and urine was collected prepregnancy and throughout gestation. Uterine artery myography assessed uteroplacental vascular function and structure. Fetal measurements were made at gestational day 18.5, and placentas were collected for histological and gene expression analyses. The 1000 ng/kg per minute Ang II treatment significantly increased blood pressure (P<0.01), reduced cardiac output (P<0.05), and reduced diameter and increased stiffness of the uterine arteries (P<0.01) during pregnancy. The albumin:creatinine ratio was increased in both Ang II treatment groups (P<0.05; P<0.0001). The 1000 ng/kg per minute-treated fetuses were significantly smaller than vehicle treatment (P<0.001). Placental expression of Ang II receptors was increased in the junctional zone in 1000 ng/kg per minute Ang II-treated groups (P<0.05), with this zone showing depletion of glycogen content and structural abnormalities. Ang II infusion in pregnant stroke-prone spontaneously hypertensive rats mirrors hemodynamic, cardiac, and urinary profiles observed in preeclamptic women, with evidence of impaired fetal growth.

Project description:The renin-angiotensin system is involved in the development of hypertension and sarcopenia. Increased levels of angiotensin II (Ang II) lead to upregulation of Ang II type 1 receptor (AT1R), which results in increasing reactive oxygen species (ROS) by NAD(P)H oxidase (Nox). Increased ROS led to increased helper T17 (Th17) and decreased regulatory T (Treg) cells through HIF-1α. Increased Th17 secretes more IL-17, leading to increased NF-κB and muscle atrophy. We evaluated the effect of Ecklonia cava extracts (ECE) and dieckol (DK) on attenuating muscle atrophy by decreasing AT1R and NOX activity in spontaneous hypertensive rats (SHRs). The serum levels of Ang II and expression of AT1R in the muscle were higher in SHRs than in normotensive animals of Wistar-Kyoto rats (2.4 and 1.8 times higher than WKY, respectively). The expression of AT1R decreased by ECE or DK (0.62 and 0.84 times lower than SHR, respectively). In SHRs, the expression of Nox 1, 2, and 4 were increased (1.2-1.15 times higher than WKY) but were decreased by the administration of ECE (0.8-0.9 times lower than SHR) or DK (0.7-0.9 times lower than SHR). The Nox activity was increased in SHRs (2.3 times more than WKY) and it was decreased by ECE (0.9 times lower than SHRs) and DK (0.9 times lower than SHRs). The expression of HIF-1α, a marker of Th17 (RORγt), and cytokine secreted by Th17 (IL-17) was increased in SHRs and was decreased by ECE or DK. The marker of Treg (Foxp3) and cytokine secreted from Treg cells (IL-10) was decreased in SHRs and was increased by ECE or DK. The expression of NF-κB/IL-1β/TNF-α and MuRF-1/MAFbx/atrogin-1 was increased in SHRs and these were decreased by ECE or DK. The cross-sectional area of muscle fiber was decreased in SHRs (0.7 times lower than WKY) and was increased by ECE (1.3 times greater than SHR) or DK (1.5 times greater than SHR). In conclusion, ECE or DK leads to a decreased expression of AT1R and Nox activity which modulates Th17/Treg balance and consequently, decreased muscle atrophy.

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Angiotensin II type 1 receptor antibodies and increased angiotensin II sensitivity in pregnant rats.

Publications

Angiotensin II type 1 receptor antibodies and increased angiotensin II sensitivity in pregnant rats.

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