Endothelin-dependent vasoconstriction in human uterine artery: application to preeclampsia

Connecting G protein-coupled estrogen receptor biomolecular mechanisms with the pathophysiology of preeclampsia: a review

BACKGROUND

Throughout the course of pregnancy, small maternal spiral arteries that are in contact with fetal tissue undergo structural remodeling, lose smooth muscle cells, and become less responsive to vasoconstrictors. Additionally, placental extravillous trophoblasts invade the maternal decidua to establish an interaction between the fetal placental villi with the maternal blood supply. When successful, this process enables the transport of oxygen, nutrients, and signaling molecules but an insufficiency leads to placental ischemia. In response, the placenta releases vasoactive factors that enter the maternal circulation and promote maternal cardiorenal dysfunction, a hallmark of preeclampsia (PE), the leading cause of maternal and fetal death. An underexplored mechanism in the development of PE is the impact of membrane-initiated estrogen signaling via the G protein-coupled estrogen receptor (GPER). Recent evidence indicates that GPER activation is associated with normal trophoblast invasion, placental angiogenesis/hypoxia, and regulation of uteroplacental vasodilation, and these mechanisms could explain part of the estrogen-induced control of uterine remodeling and placental development in pregnancy.

CONCLUSION

Although the relevance of GPER in PE remains speculative, this review provides a summary of our current understanding on how GPER stimulation regulates some of the features of normal pregnancy and a potential link between its signaling network and uteroplacental dysfunction in PE. Synthesis of this information will facilitate the development of innovative treatment options.

Vascular Dysfunction in Preeclampsia

Preeclampsia is a life-threatening pregnancy-associated cardiovascular disorder characterized by hypertension and proteinuria at 20 weeks of gestation. Though its exact underlying cause is not precisely defined and likely heterogenous, a plethora of research indicates that in some women with preeclampsia, both maternal and placental vascular dysfunction plays a role in the pathogenesis and can persist into the postpartum period. Potential abnormalities include impaired placentation, incomplete spiral artery remodeling, and endothelial damage, which are further propagated by immune factors, mitochondrial stress, and an imbalance of pro- and antiangiogenic substances. While the field has progressed, current gaps in knowledge include detailed initial molecular mechanisms and effective treatment options. Newfound evidence indicates that vasopressin is an early mediator and biomarker of the disorder, and promising future therapeutic avenues include mitigating mitochondrial dysfunction, excess oxidative stress, and the resulting inflammatory state. In this review, we provide a detailed overview of vascular defects present during preeclampsia and connect well-established notions to newer discoveries at the molecular, cellular, and whole-organism levels.

Hypoxic Conditions Promote Rhythmic Contractile Oscillations Mediated by Voltage-Gated Sodium Channels Activation in Human Arteries

Arterial smooth muscle exhibits rhythmic oscillatory contractions called vasomotion and believed to be a protective mechanism against tissue hypoperfusion or hypoxia. Oscillations of vascular tone depend on voltage and follow oscillations of the membrane potential. Voltage-gated sodium channels (Na_v), responsible for the initiation and propagation of action potentials in excitable cells, have also been evidenced both in animal and human vascular smooth muscle cells (SMCs). For example, they contribute to arterial contraction in rats, but their physiopathological relevance has not been established in human vessels. In the present study, we investigated the functional role of Na_v in the human artery. Experiments were performed on human uterine arteries obtained after hysterectomy and on SMCs dissociated from these arteries. In SMCs, we recorded a tetrodotoxin (TTX)-sensitive and fast inactivating voltage-dependent I_Na current. Various Na_v genes, encoding α-subunit isoforms sensitive (Na_v 1.2; 1.3; 1.7) and resistant (Na_v 1.5) to TTX, were detected both in arterial tissue and in SMCs. Na_v channels immunostaining showed uniform distribution in SMCs and endothelial cells. On arterial tissue, we recorded variations of isometric tension, ex vivo, in response to various agonists and antagonists. In arterial rings placed under hypoxic conditions, the depolarizing agent KCl and veratridine, a specific Na_v channels agonist, both induced a sustained contraction overlaid with rhythmic oscillations of tension. After suppression of sympathetic control either by blocking the release of catecholamine or by antagonizing the target adrenergic response, rhythmic activity persisted while the sustained contraction was abolished. This rhythmic activity of the arteries was suppressed by TTX but, in contrast, only attenuated by antagonists of calcium channels, Na⁺/Ca²⁺ exchanger, Na⁺/K⁺-ATPase and the cardiac Na_v channel. These results highlight the role of Na_v as a novel key element in the vasomotion of human arteries. Hypoxia promotes activation of Na_v channels involved in the initiation of rhythmic oscillatory contractile activity.

Acute intravenous exposure to silver nanoparticles during pregnancy induces particle size and vehicle dependent changes in vascular tissue contractility in Sprague Dawley rats

The use of silver nanoparticles (AgNP) raises safety concerns during susceptible life stages such as pregnancy. We hypothesized that acute intravenous exposure to AgNP during late stages of pregnancy will increase vascular tissue contractility, potentially contributing to alterations in fetal growth. Sprague Dawley rats were exposed to a single dose of PVP or Citrate stabilized 20 or 110nm AgNP (700μg/kg). Differential vascular responses and EC50 values were observed in myographic studies in uterine, mesenteric arteries and thoracic aortic segments, 24h post-exposure. Reciprocal responses were observed in aortic and uterine vessels following PVP stabilized AgNP with an increased force of contraction in uterine artery and increased relaxation responses in aorta. Citrate stabilized AgNP exposure increased contractile force in both uterine and aortic vessels. Intravenous AgNP exposure during pregnancy displayed particle size and vehicle dependent moderate changes in vascular tissue contractility, potentially influencing fetal blood supply.

Preeclampsia serum-induced collagen I expression and intracellular calcium levels in arterial smooth muscle cells are mediated by the PLC-γ1 pathway

In women with preeclampsia (PE), endothelial cell (EC) dysfunction can lead to altered secretion of paracrine factors that induce peripheral vasoconstriction and proteinuria. This study examined the hypothesis that PE sera may directly or indirectly, through human umbilical vein ECs (HUVECs), stimulate phospholipase C-γ1-1,4,5-trisphosphate (PLC-γ1-IP₃) signaling, thereby increasing protein kinase C-α (PKC-α) activity, collagen I expression and intracellular Ca²⁺ concentrations ([Ca²⁺]_i) in human umbilical artery smooth muscle cells (HUASMCs). HUASMCs and HUVECs were cocultured with normal or PE sera before PLC-γ1 silencing. Increased PLC-γ1 and IP₃ receptor (IP₃R) phosphorylation was observed in cocultured HUASMCs stimulated with PE sera (P<0.05). In addition, PE serum significantly increased HUASMC viability and reduced their apoptosis (P<0.05); these effects were abrogated with PLC-γ1 silencing. Compared with normal sera, PE sera increased [Ca²⁺]_i in cocultured HUASMCs (P<0.05), which was inhibited by PLC-γ1 and IP₃R silencing. Finally, PE sera-induced PKC-α activity and collagen I expression was inhibited by PLC-γ1 small interfering RNA (siRNA) (P<0.05). These results suggest that vasoactive substances in the PE serum may induce deposition in the extracellular matrix through the activation of PLC-γ1, which may in turn result in thickening and hardening of the placental vascular wall, placental blood supply shortage, fetal hypoxia–ischemia and intrauterine growth retardation or intrauterine fetal death. PE sera increased [Ca²⁺]_i and induced PKC-α activation and collagen I expression in cocultured HUASMCs via the PLC-γ1 pathway.

Role of endothelin in uteroplacental circulation and fetal vascular function

Endothelins are 21-amino acid peptides involved in vascular homeostasis. Three types of peptide have been identified, with endothelin-1 (ET-1) being the most potent vasoconstrictor currently known. Two endothelin receptor subtypes are found in various tissues, including the brain, heart, blood vessel, lung, and placenta. The ETA-receptor is associated with vasoconstriction in vascular smooth muscle. Conversely, the ETB-receptor can elicit a vasoconstrictor effect in vascular smooth muscle and a vasodilator effect via its action in endothelial cells. Both receptors play a key role in maintaining circulatory homeostasis and vascular function. Changes in ET-1 expression are found in various disease states, and overexpression of ET-1 is observed in hypertension and preeclampsia in pregnancy. Placental localization of ET-1 implies a key role in regulating the uteroplacental circulation. Additionally, ET-1 is important in the fetal circulation and is involved in the pulmonary circulation and closure of the ductus arteriosus after birth, as well as fetal growth constriction in utero. ET receptor antagonists and nitric oxide donors may provide therapeutic potential in treating conditions associated with overexpression of ET and hypertension.

Endothelin(A)-endothelin(B) receptor cross talk in endothelin-1-induced contraction of smooth muscle

The efficacy of selective endothelin (ET) receptor antagonists may be limited by a functional interaction between the ET(A) and ET(B) receptors. This interaction, also termed "cross talk", is characterized by the dependency of the inhibition of an ET-1 response due to antagonism of one ET receptor subtype upon concomitant antagonism of the other ET receptor subtype. Although a reduction in ET(A)-ET(B) receptor cross talk would presumably increase the efficacy of selective ET receptor antagonists, an approach that accomplishes this aim is largely absent due to a lack of mechanistic understanding. Toward this goal, we evaluated the characteristics and potential dependencies of cross talk in smooth muscle. Smooth muscle was adopted as an exemplar not only because cross talk is widely reported in this tissue type, thereby allowing numerous comparisons, but also significant controversy surrounds the use of selective versus nonselective ET receptor antagonists in ET-1-related pathophysiologies involving smooth muscle. Based on this evaluation, we suggest that ET(A)-ET(B) receptor cross talk is a dynamic process directed by either or both ET receptor subtypes and expressed to varying magnitudes depending on the ET-1 and selective ET receptor antagonist concentrations, tone due to intraluminal pressure/stretch, agonists acting at receptors other than the ET(A)/ET(B) receptors, and endothelial/epithelial function. It is speculated that ET(A)-ET(B) receptor cross talk occurs through signal transduction pathways along with changes at the receptor level. Pharmacologic intervention of the signaling pathways could increase the therapeutic efficacy of ET receptor antagonists.