Avaliação de sistemas vasoativos: papel dos autoanticorpos na preeclâmpsia

Abstract

Preeclampsia (PE) is a leading cause of maternal death and a major contributor to maternal and perinatal morbitidy. However, the mechanisms implicated in this disease are still poorly understood. Recent studies have shown that PE is associated with a mismatch between the vasoconstrictor peptide angiotensin II (Ang II), and thevasodilator peptide angiotensin-(1-7)/receptor Mas (Ang-(1-7)/Mas) axis. Moreover, Ang-(1-7), is decreased while endothelin, a potent vasoconstrictor peptide, is elevated in preeclamptic women (PEW). Furthermore, maternal autoantibodies (AABs), capable of binding to and activating the Ang II receptor type 1 (AT1), have also been implicatedin this disease. The aims of this study were both to evaluate placental vasoactive systems and to investigate the frequency and the targets of AABs in PE. Women at third trimester of gestation were divided into two groups: preeclamptic (32 cases); normotensive healthy (29 cases). All women underwent Doppler examination of uterine arteries resistence index (uterine RI), bilateral notches, umbilical artery index (U/PI)and cerebralumbilical artery pulsatility index (C/U). Protein expression (fetal placental tissues) for the Ang-(1-7) receptor Mas, angiotensin converting enzyme 2 (ACE2), angiotensin converting enzyme (ACE), Ang II receptor AT1, endothelial oxid nitric sintase (eNOS) and endothelin receptor ETA were analysed by western blotting. In PEW there was a decreased expression of Mas and eNOS while ETA receptor wasupregulated (p= 0.0016; p= 0.004; p= 0.002, respectively). No significant changes were observed for AT1 receptor, ACE, ACE2 expression in preeclamptic ones when compared to controls. Furthermore, immunoglobulins were prepared from serum samples. The presence of AABs were assessed on cultured neonatal spontaneously beating rat cardiomyocytes. In preeclamptic patients (97%) presented AABs directedagainst the Ang II receptor AT1. The agonistic effect of the the AABs was blocked by AT1 antagonist Irbesartan and neutralized by a peptide corresponding to the second extracelular loop of this receptor. Strikingly, we discovered that 53% of the PEWs serum contained additionally to the AT1 receptor AABs, a novel agonistic-like autoantibody, directed against the endothelin ETA receptor (ETA AABs). It was selectively blocked by the antagonist BQ123 and also neutralized by peptidescorresponding to the second extracelular loop of ETA receptor. In normotensive pregnant women no AABs were detected.Moreover, these PEW showed increased U/PI (p= 0.003) compared to controls. In this study, we described for the first time, the presence of ETA-AABs in PE. Our results suggest that an imbalance of Mas/ETA receptors and eNOS associated to the presence of both agonistic AABs, against AT1 and ETA receptors, may be involved in the pathogenesis of PE. Furthermore, there were also evaluated the chronotropic effects of both Ang-(1-7) and endothelin (ET-1) on cultured neonatal spontaneously beating rat cardiomyocytes. At last, it was assessed the modulation of RAS by ET-1 on ACE2 and Mas receptor protein expression in these myocytes. Our data showed that, Ang-(1-7) evoked a negative chronotropic effect, which was abolished by the addition of A779, and thisblockage elicited an increased positive chronotropic effect evoked by Ang II (p<0.001). Similarly, the positive chronotropic effects elicited by agonistic AABs against AT1 receptor were increased by the blockage of Mas receptor with A779 (p<0.001). Our last results demonstrated, for the first time, that ET-1 dowregulated both ACE2 and Mas receptor protein expression (p<0.001) in cardiomyocytes. At last, the incubation of themyocytes with ET-1 increased the positive chronotropic effects elicited by Ang II and reduced the negative chronotropic effects evoked by Ang-(1-7) (p< 0.001). Therefore, these results suggest that there is an intrinsic modulation between the antagonic axis: Ang II/ ACE/AT1 and Ang-(1-7)/ACE2/ Mas. Moreover, ET-1 modulates RAS, deviatingthe system to the vasoconstrictor axis. In conclusion, the balance between these antagonic axis can determinate the direction of RAS forward to either physiological or pathological conditions.