Chronic hypoxia inhibits pregnancy-induced upregulation of SKCa channel expression and function in uterine arteries

Endothelial cell vasodilator dysfunction mediates progressive pregnancy-induced hypertension in endothelial cell tetrahydrobiopterin deficient mice

BACKGROUND AND PURPOSE

Pregnancy-associated vascular remodelling is essential for both maternal and fetal health. We have previously shown that maternal endothelial cell tetrahydrobiopterin (BH4) deficiency causes poor pregnancy outcomes. Here, we investigated the role and mechanisms of endothelial cell-mediated vasorelaxation function in these outcomes.

EXPERIMENTAL APPROACH

The vascular reactivity of mouse aortas and uterine arteries from non-pregnant and pregnant endothelial cell-specific BH4 deficient mice (Gch1^fl/flTie2cre mice) was assessed by wire myography. Systolic blood pressure was assessed by tail cuff plethysmography.

KEY RESULTS

In late pregnancy, systolic blood pressure was significantly higher (∼24 mmHg) in Gch1^fl/flTie2cre mice compared with wild-type littermates. This was accompanied by enhanced vasoconstriction and reduced endothelial-dependent vasodilation in both aorta and uterine arteries from pregnant Gch1^fl/flTie2cre mice. In uterine arteries loss of eNOS-derived vasodilators was partially compensated by upregulation of intermediate and large-conductance Ca²⁺-activated K⁺ channels. In rescue experiments, oral BH4 supplementation alone did not rescue vascular dysfunction and pregnancy-induced hypertension in Gch1^fl/flTie2cre mice. However, combination with the fully reduced folate, 5-methyltetrahydrofolate (5-MTHF), restored endothelial cell vasodilator function and blood pressure.

CONCLUSIONS AND IMPLICATIONS

We identify a critical requirement for maternal endothelial cell Gch1/BH4 biosynthesis in endothelial cell vasodilator function in pregnancy. Targeting vascular Gch1 and BH4 biosynthesis with reduced folates may provide a novel therapeutic target for the prevention and treatment of pregnancy-related hypertension.

Ca2+-Activated K+ Channels and the Regulation of the Uteroplacental Circulation

Adequate uteroplacental blood supply is essential for the development and growth of the placenta and fetus during pregnancy. Aberrant uteroplacental perfusion is associated with pregnancy complications such as preeclampsia, fetal growth restriction (FGR), and gestational diabetes. The regulation of uteroplacental blood flow is thus vital to the well-being of the mother and fetus. Ca²⁺-activated K⁺ (K_Ca) channels of small, intermediate, and large conductance participate in setting and regulating the resting membrane potential of vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) and play a critical role in controlling vascular tone and blood pressure. K_Ca channels are important mediators of estrogen/pregnancy-induced adaptive changes in the uteroplacental circulation. Activation of the channels hyperpolarizes uteroplacental VSMCs/ECs, leading to attenuated vascular tone, blunted vasopressor responses, and increased uteroplacental blood flow. However, the regulation of uteroplacental vascular function by K_Ca channels is compromised in pregnancy complications. This review intends to provide a comprehensive overview of roles of K_Ca channels in the regulation of the uteroplacental circulation under physiological and pathophysiological conditions.

Potassium Channels in the Uterine Vasculature: Role in Healthy and Complicated Pregnancies

A progressive increase in maternal uterine and placental blood flow must occur during pregnancy to sustain the development of the fetus. Changes in maternal vasculature enable an increased uterine blood flow, placental nutrient and oxygen exchange, and subsequent fetal development. K⁺ channels are important modulators of vascular function, promoting vasodilation, inducing cell proliferation, and regulating cell signaling. Different types of K⁺ channels, such as Ca²⁺-activated, ATP-sensitive, and voltage-gated, have been implicated in the adaptation of maternal vasculature during pregnancy. Conversely, K⁺ channel dysfunction has been associated with vascular-related complications of pregnancy, including intrauterine growth restriction and pre-eclampsia. In this article, we provide an updated and comprehensive literature review that highlights the relevance of K⁺ channels as regulators of uterine vascular reactivity and their potential as therapeutic targets.

Placental protein 13 dilation of pregnant rat uterine vein is endothelium dependent and involves nitric oxide/calcium activated potassium channels signals

INTRODUCTION

Accumulating evidence demonstrates the importance of the galectin protein Placental Protein 13 (PP13) in predicting Preeclampsia (PE), a gestational disorder that has no cure and is associated with a compromised uterine vascular adaptation to pregnancy. Uterine vasculature undergoes significant remodeling (growth in length and in circumference) during normal pregnancy to accommodate the increased blood volume to the feto-placental unit. The aim of this study was to demonstrate the role of PP13 on the uterine veins (UVs).

METHODS

PP13 was tested on UVs isolated from rat by using a pressurized myograph. The PP13 investigation was carried out in the presence of: a) nitric oxide synthases inhibitors (l-NAME + L-NNA, 2 x 10^-4 M); b) small conductance Ca²⁺-activated K⁺ channels (SK_ca) inhibitor (Apamin, 10^-7 M); c) intermediate conductance Ca²⁺-activated K⁺ channels (IK_ca) inhibitor (TRAM-34, 10^-5 M); d) big conductance Ca²⁺-activated K⁺ channels (BK_ca) inhibitor (Paxilline, 10^-5 M) and in the absence of endothelium.

RESULTS

Our results showed that in late pregnancy, PP13 induced a significant dilation of UVs that is endothelium dependent. Further, PP13-dilation is mediated by the SKca - NO - BKca pathway.

DISCUSSION

For the first time, this study provides evidence that in pregnancy, the UVs are dilated by PP13 and suggests SK_Ca as a potential target for treatments aimed at restoring pregnancy complication associated with deficiency in uterine adaptation.

Hypoxic Regulation of the Large-Conductance, Calcium and Voltage-Activated Potassium Channel, BK

Hypoxia is a condition characterized by a reduction of cellular oxygen levels derived from alterations in oxygen balance. Hypoxic events trigger changes in cell-signaling cascades, oxidative stress, activation of pro-inflammatory molecules, and growth factors, influencing the activity of various ion channel families and leading to diverse cardiovascular diseases such as myocardial infarction, ischemic stroke, and hypertension. The large-conductance, calcium and voltage-activated potassium channel (BK) has a central role in the mechanism of oxygen (O₂) sensing and its activity has been related to the hypoxic response. BK channels are ubiquitously expressed, and they are composed by the pore-forming α subunit and the regulatory subunits β (β1–β4), γ (γ1–γ4), and LINGO1. The modification of biophysical properties of BK channels by β subunits underly a myriad of physiological function of these proteins. Hypoxia induces tissue-specific modifications of BK channel α and β subunits expression. Moreover, hypoxia modifies channel activation kinetics and voltage and/or calcium dependence. The reported effects on the BK channel properties are associated with events such as the increase of reactive oxygen species (ROS) production, increases of intracellular Calcium ([Ca²⁺]_i), the regulation by Hypoxia-inducible factor 1α (HIF-1α), and the interaction with hemeproteins. Bronchial asthma, chronic obstructive pulmonary diseases (COPD), and obstructive sleep apnea (OSA), among others, can provoke hypoxia. Untreated OSA patients showed a decrease in BK-β1 subunit mRNA levels and high arterial tension. Treatment with continuous positive airway pressure (CPAP) upregulated β1 subunit mRNA level, decreased arterial pressures, and improved endothelial function coupled with a reduction in morbidity and mortality associated with OSA. These reports suggest that the BK channel has a role in the response involved in hypoxia-associated hypertension derived from OSA. Thus, this review aims to describe the mechanisms involved in the BK channel activation after a hypoxic stimulus and their relationship with disorders like OSA. A deep understanding of the molecular mechanism involved in hypoxic response may help in the therapeutic approaches to treat the pathological processes associated with diseases involving cellular hypoxia.

Uteroplacental Circulation in Normal Pregnancy and Preeclampsia: Functional Adaptation and Maladaptation

Uteroplacental blood flow increases as pregnancy advances. Adequate supply of nutrients and oxygen carried by uteroplacental blood flow is essential for the well-being of the mother and growth/development of the fetus. The uteroplacental hemodynamic change is accomplished primarily through uterine vascular adaptation, involving hormonal regulation of myogenic tone, vasoreactivity, release of vasoactive factors and others, in addition to the remodeling of spiral arteries. In preeclampsia, hormonal and angiogenic imbalance, proinflammatory cytokines and autoantibodies cause dysfunction of both endothelium and vascular smooth muscle cells of the uteroplacental vasculature. Consequently, the vascular dysfunction leads to increased vascular resistance and reduced blood flow in the uteroplacental circulation. In this article, the (mal)adaptation of uteroplacental vascular function in normal pregnancy and preeclampsia and underlying mechanisms are reviewed.

Role of potassium channels in female reproductive system

Potassium channels are widely expressed in most types of cells in living organisms and regulate the functions of a variety of organs, including kidneys, neurons, cardiovascular organs, and pancreas among others. However, the functional roles of potassium channels in the reproductive system is less understood. This mini-review provides information about the localization and functions of potassium channels in the female reproductive system. Five types of potassium channels, which include inward-rectifying (Kir), voltage-gated (Kv), calcium-activated (K_Ca), 2-pore domain (K_2P), and rapidly-gating sodium-activated (Slo) potassium channels are expressed in the hypothalamus, ovaries, and uterus. Their functions include the regulation of hormone release and feedback by Kir6.1 and Kir6.2, which are expressed in the luteal granulosa cells and gonadotropin-releasing hormone neurons respectively, and regulate the functioning of the hypothalamus–pituitary–ovarian axis and the production of progesterone. Both channels are regulated by subtypes of the sulfonylurea receptor (SUR), Kir6.1/SUR2B and Kir6.2/SUR1. K_v and Slo2.1 affect the transition from uterine quiescence in late pregnancy to the state of strong myometrial contractions in labor. Intermediate- and small-conductance K_Ca modulate the vasodilatation of the placental chorionic plate resistance arteries via the secretion of nitric oxide and endothelium-derived hyperpolarizing factors. Treatment with specific channel activators and inhibitors provides information relevant for clinical use that could help alter the functions of the female reproductive system.

The endometrium histopathology and cell ultrastructure in bitches with pyometra induced using progesterone and Escherichia coli

BACKGROUND

We investigated uterine histopathological and ultrastructural changes in female dogs with pyometra induced by Escherichia coli (E. coli) inoculation using progesterone and/or estradiol.

METHODS

Dogs were ovariectomized and classified into six groups: Groups 1-6 corresponding to estradiol treatment followed by progesterone supplementation, progesterone supplementation only, estradiol supplementation only, simultaneous treatment using estradiol and progesterone, similar to Group 1 but with a double dose, and control group, respectively.

RESULTS

Pyometra was successfully induced in Groups 1, 2, 4, and 5, but not in Group 3. An uneven endometrial surface was observed, along with a purulent discharge, bleeding, inflammatory lesions, cystic endometrial hyperplasia (CEH) or cystic endometrial atrophy. Endometrial thickness percentage, uterine wall thickness, and the percentage of endometrial cyst area increased. Endometrial epithelial mushroom-like hyperplasia and the honeycomb-like structure exposed under the epithelium after flaky exfoliation were found, and the glandular epithelial villi became longer or shorter. Mitochondria expansion and increased lysosome were observed. Endoplasmic reticulum dilation and swelling and many inflammatory cells, especially plasma cell infiltration in the stroma, were found.

CONCLUSIONS

Endometrial histopathology and ultrastructural changes in affected dogs were accompanied by induction of pyometra, and they were affected by different hormonal patterns and E. coli.

AMP-activated protein kinase activator AICAR attenuates hypoxia-induced murine fetal growth restriction in part by improving uterine artery blood flow

KEY POINTS

Pregnancy at high altitude is associated with a greater incidence of fetal growth restriction due, in part, to lesser uterine artery blood flow. AMP-activated protein kinase (AMPK) activation vasodilates arteries and may increase uterine artery blood flow. In this study, pharmacological activation of AMPK by the drug AICAR improved fetal growth and elevated uterine artery blood flow. These results suggest that AMPK activation is a potential strategy for improving fetal growth and raising uterine artery blood flow in pregnancy, which may be important in pregnancy disorders characterized by uteroplacental ischaemia and/or fetal hypoxia.

ABSTRACT

Uteroplacental hypoxia is associated with pregnancy disorders such as intrauterine growth restriction and preeclampsia, which are characterized by uteroplacental ischaemia and/or fetal hypoxia. Activation of AMP-activated protein kinase (AMPK) results in vasodilatation and is therefore a potential therapeutic strategy for restoring uteroplacental perfusion in pregnancy disorders. In this study, C57Bl/6 mice were treated with subcutaneous pellets containing vehicle, the AMPK activator AICAR (200 mg kg^-1 day^-1 ), or the AMPK inhibitor Compound C (20 mg kg^-1 day^-1 ) beginning on gestational day 13.5, and were exposed to hypoxia starting on gestational day 14.5 that induced intrauterine growth restriction. Pharmacological AMPK activation by AICAR partially prevented hypoxia-induced fetal growth restriction (P < 0.01), due in part to increased uterine artery blood flow (P < 0.0001). The proportion of total cardiac output flowing through the uterine artery was increased with AICAR in hypoxic mice (P < 0.001), suggesting that the vasodilator effect of AICAR was selective for the uterine circulation. Further, pharmacological inhibition of AMPK with Compound C reduced uterine artery diameter and increased uterine artery contractility in normoxic mice, providing evidence that physiological levels of AMPK activation are necessary for vasodilatation in healthy pregnancy. Two-way ANOVA analyses indicated that hypoxia reduced AMPK activation in the uterine artery and placenta, and AICAR increased AMPK activation in these tissues compared to vehicle. These findings provide support for further investigation into the utility of pharmacological AMPK activation for treatment of fetal growth restriction.

Plasticity of the Maternal Vasculature During Pregnancy

Maternal cardiovascular changes during pregnancy include an expansion of plasma volume, increased cardiac output, decreased peripheral resistance, and increased uteroplacental blood flow. These adaptations facilitate the progressive increase in uteroplacental perfusion that is required for normal fetal growth and development, prevent the development of hypertension, and provide a reserve of blood in anticipation of the significant blood loss associated with parturition. Each woman's genotype and phenotype determine her ability to adapt in response to molecular signals that emanate from the fetoplacental unit. Here, we provide an overview of the major hemodynamic and cardiac changes and then consider regional changes in the splanchnic, renal, cerebral, and uterine circulations in terms of endothelial and vascular smooth muscle cell plasticity. Although consideration of gestational disease is beyond the scope of this review, aberrant signaling and/or maternal responsiveness contribute to the etiology of several common gestational diseases such as preeclampsia, intrauterine growth restriction, and gestational diabetes.

Influence of Estrogens on Uterine Vascular Adaptation in Normal and Preeclamptic Pregnancies

During pregnancy, the maternal cardiovascular system undergoes significant changes, including increased heart rate, cardiac output, plasma volume, and uteroplacental blood flow (UPBF) that are required for a successful pregnancy outcome. The increased UPBF is secondary to profound circumferential growth that extends from the downstream small spiral arteries to the upstream conduit main uterine artery. Although some of the mechanisms underlying uterine vascular remodeling are, in part, known, the factors that drive the remodeling are less clear. That higher circulating levels of estrogens are positively correlated with gestational uterine vascular remodeling suggests their involvement in this process. Estrogens binding to the estrogen receptors expressed in cytotrophoblast cells and in the uterine artery wall stimulate an outward hypertrophic remodeling of uterine vasculature. In preeclampsia, generally lower concentrations of estrogens limit the proper uterine remodeling, thereby reducing UPBF increases and restricting the growth of the fetus. This review aims to report estrogenic regulation of the maternal uterine circulatory adaptation in physiological and pathological pregnancy that favors vasodilation, and to consider the underlying molecular mechanisms by which estrogens regulate uteroplacental hemodynamics.

High Altitude Reduces NO-Dependent Myometrial Artery Vasodilator Response During Pregnancy

The chronic hypoxia of high-altitude (HA) residence reduces uterine artery blood flow during pregnancy, likely contributing to an increased frequency of preeclampsia and intrauterine growth restriction. We hypothesized that this lesser pregnancy blood flow rise was due, in part, to reduced vasodilation of myometrial arteries (MAs). Here, we assessed MA vasoreactivity in healthy residents of high (2902±39 m) or low altitude (LA; 1669±10 m). MA contractile responses to potassium chloride, phenylephrine, or the thromboxane A2 agonist U46619 did not differ between LA and HA women. Acetylcholine vasodilated phenylephrine or U466119 preconstricted MAs at LA, yet had no effect on HA MAs. In contrast, another vasodilator, bradykinin, relaxed MAs from both altitudes similarly. At LA, the NO synthase inhibitor L-N^G-nitroarginine methyl ester decreased both acetylcholine and bradykinin vasodilation by 56% and 33%, respectively. L-N^G-nitroarginine methyl ester plus the COX (cyclooxygenase) inhibitor indomethacin had similar effects on acetylcholine and bradykinin vasodilation (68% and 42% reduction, respectively) as did removing the endothelium (78% and 50% decrease, respectively), suggesting a predominantly NO-dependent vasodilation at LA. However, at HA, L-N^G-nitroarginine methyl ester did not change bradykinin vasodilation, whereas indomethacin or endothelium removal decreased it by 28% and 72%, respectively, indicating impaired NO signaling at HA. Suggesting that the impairment was downstream of eNOS (endothelial NO synthase), HA attenuated the vasodilation elicited by the NO donor sodium nitroprusside. We concluded that reduced NO-dependent MA vasodilation likely contributes to diminished uteroplacental perfusion in HA pregnancies.

Effect of Oxidative Stress on the Estrogen-NOS-NO-KCa Channel Pathway in Uteroplacental Dysfunction: Its Implication in Pregnancy Complications

During pregnancy, the adaptive changes in uterine circulation and the formation of the placenta are essential for the growth of the fetus and the well-being of the mother. The steroid hormone estrogen plays a pivotal role in this adaptive process. An insufficient blood supply to the placenta due to uteroplacental dysfunction has been associated with pregnancy complications including preeclampsia and intrauterine fetal growth restriction (IUGR). Oxidative stress is caused by an imbalance between free radical formation and antioxidant defense. Pregnancy itself presents a mild oxidative stress, which is exaggerated in pregnancy complications. Increasing evidence indicates that oxidative stress plays an important role in the maladaptation of uteroplacental circulation partly by impairing estrogen signaling pathways. This review is aimed at providing both an overview of our current understanding of regulation of the estrogen-NOS-NO-K_Ca pathway by reactive oxygen species (ROS) in uteroplacental tissues and a link between oxidative stress and uteroplacental dysfunction in pregnancy complications. A better understanding of the mechanisms will facilitate the development of novel and effective therapeutic interventions.

Targeting the vascular dysfunction: Potential treatments for preeclampsia

Preeclampsia is a pregnancy-specific disorder, primarily characterized by new-onset hypertension in combination with a variety of other maternal or fetal signs. The pathophysiological mechanisms underlying the disease are still not entirely clear. Systemic maternal vascular dysfunction underlies the clinical features of preeclampsia. It is a result of oxidative stress and the actions of excessive anti-angiogenic factors, such as soluble fms-like tyrosine kinase, soluble endoglin, and activin A, released by a dysfunctional placenta. The vascular dysfunction then leads to impaired regulation and secretion of relaxation factors and an increase in sensitivity/production of constrictors. This results in a more constricted vasculature rather than the relaxed vasodilated state associated with normal pregnancy. Currently, the only effective "treatment" for preeclampsia is delivery of the placenta and therefore the baby. Often, this means a preterm delivery to save the life of the mother, with all the attendant risks and burdens associated with fetal prematurity. To lessen this burden, there is a pressing need for more effective treatments that target the maternal vascular dysfunction that underlies the hypertension. This review details the vascular effects of key drugs undergoing clinical assessment as potential treatments for women with preeclampsia.

Gestational Hypoxia and Developmental Plasticity

Hypoxia is one of the most common and severe challenges to the maintenance of homeostasis. Oxygen sensing is a property of all tissues, and the response to hypoxia is multidimensional involving complicated intracellular networks concerned with the transduction of hypoxia-induced responses. Of all the stresses to which the fetus and newborn infant are subjected, perhaps the most important and clinically relevant is that of hypoxia. Hypoxia during gestation impacts both the mother and fetal development through interactions with an individual's genetic traits acquired over multiple generations by natural selection and changes in gene expression patterns by altering the epigenetic code. Changes in the epigenome determine "genomic plasticity," i.e., the ability of genes to be differentially expressed according to environmental cues. The genomic plasticity defined by epigenomic mechanisms including DNA methylation, histone modifications, and noncoding RNAs during development is the mechanistic substrate for phenotypic programming that determines physiological response and risk for healthy or deleterious outcomes. This review explores the impact of gestational hypoxia on maternal health and fetal development, and epigenetic mechanisms of developmental plasticity with emphasis on the uteroplacental circulation, heart development, cerebral circulation, pulmonary development, and the hypothalamic-pituitary-adrenal axis and adipose tissue. The complex molecular and epigenetic interactions that may impact an individual's physiology and developmental programming of health and disease later in life are discussed.

Chronic hypoxia upregulates DNA methyltransferase and represses large conductance Ca2+-activated K+ channel function in ovine uterine arteries

Chronic hypoxia during gestation suppresses large-conductance Ca2+-activated K+ (BKCa) channel function and impedes uterine arterial adaptation to pregnancy. This study tested the hypothesis that chronic hypoxia has a direct effect in upregulating DNA methyltransferase (DNMT) and epigenetically repressing BKCa channel beta-1 subunit (KCNMB1) expression in uterine arteries. Resistance-sized uterine arteries were isolated from near-term pregnant sheep maintained at ∼300 m above sea level or animals acclimatized to high-altitude (3,801 m) hypoxia for 110 days during gestation. For ex vivo hypoxia treatment, uterine arteries from normoxic animals were treated with 21.0% O2 or 10.5% O2 for 48 h. High-altitude hypoxia significantly upregulated DNMT3b expression and enzyme activity in uterine arteries. Similarly, ex vivo hypoxia treatment upregulated DNMT3b expression and enzyme activity that was blocked by a DNMT inhibitor 5-aza-2'-deoxycytidine (5-Aza). Of importance, 5-Aza inhibited hypoxia-induced hypermethylation of specificity protein (SP) 1 binding site at the KCNMB1 promoter and restored transcription factor binding to the KCNMB1 promoter, resulting in the recovery of KCNMB1 gene expression in uterine arteries. Furthermore, 5-Aza blocked the effect of hypoxia and rescued BKCa channel activity and reversed hypoxia-induced decrease in BKCa channel-mediated relaxations and increase in myogenic tone of uterine arteries. Collectively, these results suggest that chronic hypoxia during gestation upregulates DNMT expression and activity, resulting in hypermethylation and repression of KCNMB1 gene and BKCa channel function, impeding uterine arterial adaptation to pregnancy.

Involvement of dysregulated IKCa and SKCa channels in preeclampsia

INTRODUCTION

Excessive constriction of placental chorionic plate arteries (CPAs) may be associated with preeclampsia (PE). Nitric oxide (NO) as well as intermediate and small Ca²⁺-activated K⁺ channels (IK_Ca and SK_Ca) plays vital roles in vasodilation of CPAs. We hypothesized that dysregulated IK_Ca and SK_Ca channels may be involved in the pathogenesis of PE mediated by the impaired NO system on CPAs.

METHODS

The location of IK_Ca and SK_Ca channels, activities of NO synthases (NOS), and expression levels of these molecules were studied on CPAs from 30 normal pregnancies and 30 PE. The vasodilating function of CPAs was measured under openers or blockers of IK_Ca/SK_Ca channels in the presence or absence of NO donor or inhibitor.

RESULTS

IK_Ca and SK_Ca channels were located both on endothelium and on smooth muscles of CPAs and the expressions of them were downregulated in PE women comparing to those in normal pregnant women. The protein expressions of endothelial NOS (eNOS) and inducible NOS (iNOS) were downregulated on CPAs in PE accompanied by decreased activity of eNOS. Notably, the vasodilatory functions mediated by IK_Ca/SK_Ca channels and by NO were aberrant on preeclamptic CPAs. In addition, IK_Ca and SK_Ca channels were responsible for nitric oxide (NO)-attributable vasorelaxation and activity modulation of NO synthases.

CONCLUSIONS

This study provides evidence that dysregulated IK_Ca and SK_Ca channels might contribute to fetal pathogenesis of PE through direct promotion of vascular constriction of CPAs and through affecting functions of NO and activities of NOS.

MicroRNA-210 Targets Ten-Eleven Translocation Methylcytosine Dioxygenase 1 and Suppresses Pregnancy-Mediated Adaptation of Large Conductance Ca2+-Activated K+ Channel Expression and Function in Ovine Uterine Arteries

Gestational hypoxia inhibits large conductance Ca2+-activated K+ (BKCa) channel expression and function in uterine arterial adaptation to pregnancy. Given the findings that microRNA-210 (miR-210) is increased in hypoxia during gestation and preeclampsia, the present study sought to investigate the role of miR-210 in the regulation of BKCa channel adaptation in the uterine artery. Gestational hypoxia significantly increased uterine vascular resistance and blood pressure in pregnant sheep and upregulated miR-210 in uterine arteries. MiR-210 bound to ovine ten-eleven translocation methylcytosine dioxygenase 1 mRNA 3' untranslated region and decreased ten-eleven translocation methylcytosine dioxygenase 1 mRNA and protein abundance in uterine arteries of pregnant sheep, as well as abrogated steroid hormone-induced upregulation of ten-eleven translocation methylcytosine dioxygenase 1 expression in uterine arteries of nonpregnant animals. In accordance, miR-210 blocked pregnancy- and steroid hormone-induced upregulation of BKCa channel β1 subunit expression in uterine arteries. Functionally, miR-210 suppressed BKCa channel current density in uterine arterial myocytes of pregnant sheep and inhibited steroid hormone-induced increases in BKCa channel currents in uterine arteries of nonpregnant animals. Blockade of endogenous miR-210 inhibited hypoxia-induced suppression of BKCa channel activity. In addition, miR-210 decreased BKCa channel-mediated relaxations and increased pressure-dependent myogenic tone of uterine arteries. Together, the results demonstrate that miR-210 plays an important role in the downregulation of ten-eleven translocation methylcytosine dioxygenase 1 and repression of BKCa channel function in uterine arteries, revealing a novel mechanism of epigenetic regulation in the maladaptation of uterine hemodynamics in gestational hypoxia and preeclampsia.

Direct effect of chronic hypoxia in suppressing large conductance Ca(2+)-activated K(+) channel activity in ovine uterine arteries via increasing oxidative stress

KEY POINTS

Chronic hypoxia has a direct effect in down-regulating the BKCa channel β1 subunit and inhibiting the BKCa channel activity in uterine arteries of pregnant sheep. Oxidative stress plays a causal role in hypoxia-mediated suppression of BKCa channel function. The steroid hormone-induced effect on BKCa channels is a target of hypoxia-mediated oxidative stress. Inhibition of oxidative stress ameliorates the adverse effect of hypoxia both ex vivo and in vivo in pregnant sheep exposed to long-term high-altitude hypoxia. Our findings provide novel evidence of a causative role of oxidative stress in hypoxia-mediated inhibition of the BKCa channel activity in uterine arteries and new insights in understanding and alleviating pregnancy complications associated with gestational hypoxia such as pre-eclampsia and fetal growth restriction.

ABSTRACT

Uterine arteries of pregnant sheep acclimatized to long-term high-altitude hypoxia were associated with a decrease in large-conductance Ca(2+)-activated K(+) (BKCa) channel activity. The present study tested the hypothesis that prolonged hypoxia has a direct effect in suppressing BKCa channel activity by increasing oxidative stress. Uterine arteries were isolated from non-pregnant and near-term (∼142 days) pregnant sheep, and were treated ex vivo with 21.0 or 10.5% O2 for 48 h. The hypoxia treatment significantly increased the production of reactive oxygen species in uterine arteries, which was blocked by N-acetylcysteine. In uterine arteries of pregnant sheep, hypoxia significantly inhibited BKCa channel current density, decreased NS1619-induced relaxations and increased pressure-dependent tone, which were annulled by N-acetylcysteine. In accordance, hypoxia resulted in down-regulation of BKCa channel β1 subunit, which was restored in the presence of N-acetylcysteine. In addition, the N-acetylcysteine treatment significantly increased BKCa channel β1 subunit abundance and BKCa channel current density in uterine arteries from pregnant sheep exposed to high-altitude hypoxia (3801 m, PaO2: 60 mmHg) for 110 days. In uterine arteries of non-pregnant animals, hypoxia inhibited steroid hormone-induced up-regulation of BKCa channel current density and NS1619-mediated relaxations, which were reversed by N-acetylcysteine. Furthermore, the synthetic superoxide dismutase and catalase mimetic EUK-134 also ablated the effects of hypoxia on BKCa channel currents in uterine arteries. The results demonstrate a direct effect of hypoxia in inhibiting the BKCa channel activity in uterine arteries via increased oxidative stress.

Impairment of IKCa channels contributes to uteroplacental endothelial dysfunction in rat diabetic pregnancy

Diabetes in rat pregnancy is associated with impaired vasodilation of the maternal uteroplacental vasculature. In the present study, we explored the role of endothelial cell (EC) Ca(2+)-activated K(+) channels of small conductance (SKCa channels) and intermediate conductance (IKCa channels) in diabetes-induced uterine vascular dysfunction. Diabetes was induced by injection of streptozotocin to second-day pregnant rats and confirmed by the development of maternal hyperglycemia. Control rats were injected with citrate buffer. Changes in smooth muscle cell intracellular Ca(2+) concentration, membrane potential, and vasodilation induced by SKCa/IKCa channel activators were studied in uteroplacental arteries of control and diabetic rats. The impact of diabetes on SKCa- and IKCa-mediated currents was explored in freshly dissociated ECs. NS309 evoked a potent vasodilation that was effectively inhibited by TRAM-34 but not by apamin. NS309-induced smooth muscle cell intracellular Ca(2+) concentration, membrane potential, and dilator responses were significantly diminished by diabetes; N-cyclohexyl-N-2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-4-pyrimidinamine (CyPPA)-evoked responses were not affected. Ca(2+)-activated ion currents in ECs were insensitive to paxilline, markedly inhibited by charybdotoxin (ChTX), and diminished by apamin. NS309-induced EC currents were generated mostly due to activation of ChTX-sensitive channels. Maternal diabetes resulted in a significant reduction in ChTX-sensitive currents with no effect on apamin-sensitive or CyPPA-induced currents. We concluded that IKCa channels play a prevalent role over SKCa channels in the generation of endothelial K(+) currents and vasodilation of uteroplacental arteries. Impaired function of IKCa channels importantly contributes to diabetes-induced uterine endothelial dysfunction. Therapeutic restoration of IKCa channel function may be a novel strategy for improvement of maternal uteroplacental blood flow in pregnancies complicated by diabetes.

Molecular mechanisms of maternal vascular dysfunction in preeclampsia

In preeclampsia, as a heterogeneous syndrome, multiple pathways have been proposed for both the causal as well as the perpetuating factors leading to maternal vascular dysfunction. Postulated mechanisms include imbalance in the bioavailability and activity of endothelium-derived contracting and relaxing factors and oxidative stress. Studies have shown that placenta-derived factors [antiangiogenic factors, microparticles (MPs), cell-free nucleic acids] are released into the maternal circulation and act on the vascular wall to modify the secretory capacity of endothelial cells and alter the responsiveness of vascular smooth muscle cells to constricting and relaxing stimuli. These molecules signal their deleterious effects on the maternal vascular wall via pathways that provide the molecular basis for novel and effective therapeutic interventions.

The SK3 channel promotes placental vascularization by enhancing secretion of angiogenic factors

Proper placental perfusion is essential for fetal exchange of oxygen, nutrients, and waste with the maternal circulation. Impairment of uteroplacental vascular function can lead to pregnancy complications, including preeclampsia and intrauterine growth restriction (IUGR). Potassium channels have been recognized as regulators of vascular proliferation, angiogenesis, and secretion of vasoactive factors, and their dysfunction may underlie pregnancy-related vascular diseases. Overexpression of one channel in particular, the small-conductance calcium-activated potassium channel 3 (SK3), is known to increase vascularization in mice, and mice overexpressing the SK3 channel (SK3(T/T) mice) have a high rate of fetal demise and IUGR. Here, we show that overexpression of SK3 causes fetal loss through abnormal placental vascularization. We previously reported that, at pregnancy day 14, placentas isolated from SK3(T/T) mice are smaller than those obtained from wild-type mice. In this study, histological analysis reveals that SK3(T/-) placentas at this stage have abnormal placental morphology, and microcomputed tomography shows that these placentas have significantly larger and more blood vessels than those from wild-type mice. To identify the mechanism by which these vascularization defects occur, we measured levels of vascular endothelial growth factor (VEGF), placental growth factor, and the soluble form of VEGF receptor 1 (sFlt-1), which must be tightly regulated to ensure proper placental development. Our data reveal that overexpression of SK3 alters systemic and placental ratios of the angiogenic factor VEGF to antiangiogenic factor sFlt-1 throughout pregnancy. Additionally, we observe increased expression of hypoxia-inducing factor 2α in SK3(T/-) placentas. We conclude that the SK3 channel modulates placental vascular development and fetal health by altering VEGF signaling.

Gestational hypoxia increases reactive oxygen species and inhibits steroid hormone-mediated upregulation of Ca(2+)-activated K(+) channel function in uterine arteries

Gestational hypoxia inhibits steroid hormone-induced upregulation of Ca(2+)-activated K(+) (KCa) channel activities in uterine arteries. We tested the hypothesis that increased reactive oxygen species play an important role in hypoxia-mediated inhibition of KCa channel activities. Uterine arteries were isolated from nonpregnant (nonpregnant uterine artery) and near-term (≈142-145 day) pregnant (pregnant uterine artery) sheep maintained at either sea level or high altitude (3820 m, Pao2: 60 mm Hg) for 110 days. In pregnant uterine arteries, hypoxia significantly decreased large conductance channel opener NS1619- and small conductance channel opener NS309-induced relaxations, which were partially restored by reactive oxygen species inhibitor N-acetylcysteine (NAC). NAC significantly increased large conductance KCa but not small conductance KCa current densities in uterine arterial smooth muscle cells in pregnant animals acclimatized to high altitude. The NAC-sensitive component of small conductance KCa-induced relaxations was diminished in endothelium-denuded arteries. In nonpregnant uterine arteries, NS1619- and NS309-induced relaxations were diminished compared with those in pregnant uterine arteries. Treatment of nonpregnant uterine arteries with 17β-estradiol and progesterone for 48 hours increased small conductance KCa type 3 protein abundance and NS1619- and NS309-induced relaxations, which were inhibited by hypoxia. This hypoxia-mediated inhibition was reversed by NAC. Consistently, steroid hormone treatment had no significant effects on large conductance KCa current density in nonpregnant uterine arteries of hypoxic animals in the absence of NAC but significantly increased it in the presence of NAC. These results suggest an important role of hypoxia-mediated reactive oxygen species in negatively regulating steroid hormone-mediated upregulation of KCa channel activity and adaptation of uterine vascular reactivity in pregnancy, which may contribute to the increased incidence of preeclampsia and fetal intrauterine growth restriction associated with gestational hypoxia.

Gestational hypoxia up-regulates protein kinase C and inhibits calcium-activated potassium channels in ovine uterine arteries

OBJECTIVE

The present study tested the hypothesis that gestational hypoxia up-regulates protein kinase C (PKC) and inhibits calcium-activated potassium channels (KCa)-mediated relaxations of uterine arteries in pregnancy.

STUDY DESIGN

Uterine arteries were isolated from nonpregnant (NPUA) and pregnant (PUA) (~140 day gestation) sheep maintained at either sea level or high altitude (3,820 m for 110 days, PaO2: 60 mmHg). Contractions of uterine arteries were determined.

KEY FINDINGS

In normoxic PUA, selective inhibition of large-conductance KCa (BK) channels significantly enhanced PKC activator phorbol 12, 13-dibutyrate (PDBu)-induced contractions. This effect was abrogated by chronic hypoxia in gestation. Unlike BK channels, inhibition of small-conductance KCa (SK) channels had no significant effect on PDBu-mediated contractions. In normoxic PUA, activation of both BK with NS1619 or SK with NS309 produced concentration-dependent relaxations, which were not altered by the addition of PDBu. However, in uterine arteries treated with chronic hypoxia (10.5% O2 for 48 h), both NS1619- and NS309-induced relaxations were significantly attenuated by PDBu. In NPUAs, inhibition of BK channels significantly enhanced PDBu-induced contractions in both normoxic and hypoxic animals.

CONCLUSION

The results suggest that in the normoxic condition BK inhibits PKC activity and uterine vascular contractility, which is selectively attenuated by chronic hypoxia during gestation. In addition, hypoxia induces PKC-mediated inhibition of BK and SK activities and relaxations of uterine arteries in pregnancy.