Patients with preeclampsia develop agonistic autoantibodies against the angiotensin AT1 receptor

Abstract

Preeclampsia usually occurs after week 20 of gestation and features hypertension and an increased peripheral vascular resistance. The mechanisms are unknown (1). Several lines of evidence implicate angiotensin II (Ang II) and its binding site, the AT 1 receptor. Preeclamptic patients manifest exaggerated pressor responses to Ang II. Gant et al. (2) infused Ang II into pregnant patients from week 10 of pregnancy onward and observed that those who later developed sustained hypertension required diminishing amounts of Ang II to obtain a similar pressor response. One possible explanation for this phenomenon might be increased expression of the AT 1 receptor. Baker et al. (3) also performed Ang II infusion experiments in pregnant patients and identified five patients who subsequently developed hypertension after week 20. These women were compared with seven who did not develop hypertension. The platelets of the preeclamptic women exhibited increased calcium signaling and increased binding sites for Ang II. The authors suggested increased stimulus-effect coupling in terms of Ang II responses in preeclamptic patients. We also observed increased cytosolic calcium responses in the platelets of preeclamptic patients in response to Ang II (4). However, circulating levels of Ang II are not increased in preeclampsia (5-7). In an earlier study of patients with essential hypertension, we observed a remarkably high incidence of circulating antibodies that cross-reacted with the α1-adrenoceptor and stimulated its signaling mechanism (8). In the present study, we tested the hypothesis that circulating antibodies to a vascular receptor might be responsible for the hypertension observed in preeclampsia. We employed a bioassay of beating neonatal rat cardiomyocytes, as well as Western blotting and confocal microscopy. We found that immunoglobulin from preeclamptic women contains a factor that binds to, and stimulates, the AT 1 receptor. MethodsCell culture. Isolation and cultivation of neonatal heart cells were performed as described previously (9). Briefly, single cells were dissociated from the minced ventricles of Wistar rats (1-2 days old) with a 0.25% solution of crude trypsin and were cultured as monolayers with a density of 800 cells/mm 2 in Halle SM 20-I medium equilibrated with humidified air. The medium contained 10% heat-inactivated FCS and 2 µmol/l fluorodeoxyuridine (Serva, Heidelberg, Germany) the latter to prevent proliferation of nonmuscle cells. On the third or fourth days, the cells were incubated for 2 h in 2 ml fresh serum-containing medium. Seven to 10 selected cells or synchronously contracting cell clusters per flask were counted for 15 s. This procedure was Immune mechanisms and the renin-angiotensin system are implicated in preeclampsia. We investigated 25 preeclamptic patients and compared them with 12 normotensive pregnant women and 10 pregnant patients with essential hypertension. Antibodies were detected by the chronotropic responses to AT 1 receptor-mediated stimulation of cultured neonatal rat cardio...

Agonistic AT1 Receptor Autoantibody Increases in Serum of Patients with Refractory Hypertension and Improves Ca2+ Mobilization in Cultured Rat Vascular Smooth Muscle Cells

“…There were several speculations on the origin of AT 1 -AAs in previous works. In preeclampia, diminished placental perfusion could alter the AT 1 receptor expression in an aberrant fashion, thereby permitting autoantibody production (6). And in allograft renal-rejection subjects, posttransplantation reperfusion injury may alter the intragraft expression of AT 1 receptor, change its density, or cause conformational changes; a permissive environmental phenomenon might enhance local intragraft immunoreactivity owing to an activated innate immune response (33).…”

“…P1 corresponding to the second extracelluar loop of the human AT 1 receptor was used in the ELISA assay and preparation of the immunoglobulin (Ig) fractions. P2 corresponding to portion of the second extracelluar loop of the human AT 1 receptor was an epitope recognized by AT 1 -AAs from preeclamptic individuals (6), and was used in antibody neutralization experiment.…”

“…Preparation of the Ig fractions was outlined in detail earlier (6). Briefly, the Ig fractions in the sera were isolated by ammonium sulfate precipitation at a saturation of 40%.…”

“…Agonistic AT 1 receptor autoantibodies (AT 1 -AAs) were first described by Wallukat et al (6). The patients with preeclampsia developed the autoantibodies capable of activating the angiotensin II receptor type 1 (AT 1 receptor).…”

New Aspects in the Pathophysiology of Preeclampsia

“…AT-1AA were purified and identified as belonging to a fraction of IgG antibodies. Wallukat et al (67) showed that AT1-AA bound to a certain seven amino acid sequence on the second extracellular loop of AT1-AA. They documented specificity by means of Western blotting and co-localization studies.…”