Expression of prostanoid receptors in human lower segment pregnant myometrium

Progesterone control of myometrial contractility

During pregnancy, the primary function of the uterus is to be quiescent and not contract, which allows the growing fetus to develop and mature. A uterine muscle layer, myometrium, is composed of smooth muscle cells (SMCs). Before the onset of labor contractions, the uterine SMCs experience a complex biochemical and molecular transformation involving the expression of contraction-associated proteins. Labor is initiated when genes in SMCs are activated in response to a combination of hormonal, inflammatory and mechanical signals. In this review, we provide an overview of molecular mechanisms regulating the process of parturition in humans, focusing on the hormonal control of the myometrium, particularly the steroid hormone progesterone. The primary reason for discussing the regulation of myometrial contractility by progesterone is the importance of the clinical problem of preterm birth. It is thought that the hormonal mechanisms regulating premature uterine contractions represent an untimely triggering of the normal events occurring during term parturition. Yet, our knowledge of the complex and redundant hormonal pathways controlling uterine contractile activity leading to delivery of the neonate remains incomplete. Finally, we introduce recent animal studies using a novel class of drugs, Selective Progesterone Receptor Modulators, targeting progesterone signaling to prevent premature myometrial contractions.

Immune regulation by activation markers at feto-maternal interface in infection-associated spontaneous preterm birth

BACKGROUND

Spontaneous preterm birth (sPTB) is a global health concern. Studies reveal infections are majorly responsible for sPTB and immune activation markers play a role in regulation of maternal immune responses against pathogens during sPTB.

AIM

To study the mRNA expression and correlation of activation markers (CD66a, ICAM1, ITGB1, TIM3, CD25, CD95) and associated cytokines (IL-1β and IL-17)/prostaglandin receptors (EP2 and IP) in the placenta of Chlamydia trachomatis, Mycoplasma hominis, Ureaplasma urealyticum-infected sPTB women.

METHODS

Placental samples were collected from 160 sPTB and 160 term birth women. PCR was used for the detection of C. trachomatis, M. hominis, U. urealyticum. The mRNA expression of activation markers, cytokines and prostaglandin receptors was evaluated by real-time qPCR.

RESULTS

The fold-change expression of CD66a, ICAM1, TIM3, CD25 and CD95 was 2.89, 5.5, 4.95, 6.44 and 6.95-fold (p < 0.001), respectively; while for cytokines- IL-1β and IL-17 was 5.41 and 4.71-fold (p < 0.001), respectively and for prostaglandin receptors- EP2 and IP was 5.5 and 5-fold (p < 0.001) upregulated, respectively in infected sPTB women. Significant positive correlation was obtained among ICAM-1 and IL-1β/EP2/IL-17, TIM3 and IP/IL-17. Significant negative correlation was obtained between CD66a and EP2/IL-17, CD25 and IL-1β/EP2, CD95 and IL-1β/EP2 in infected sPTB women.

CONCLUSIONS

CD66a, ICAM1 and TIM3 may play role in inflammation and have potential for the clinical beginning of preterm labour during infection while CD25 and CD95 are possibly involved in immunotolerance at feto-maternal interface during C. trachomatis, M. hominis and U. urealyticum infection.

Prostacyclin Synthesis and Prostacyclin Receptor Expression in the Porcine Myometrium: Prostacyclin Potential to Regulate Fatty Acid Transporters, Cytokines and Contractility-Related Factors

Simple Summary

Prostacyclin (prostaglandin I2; PGI2) is an important modulator of vascular functions and is involved in various reproductive processes. PGI2 was also described as a modulator of uterine contractility in several species, including the pig. However, its synthesis and role in the myometrium of the porcine uterus are still not fully described. The objective of this study was to evaluate profiles of PGI2 synthesis and PGI2 receptor expression in the myometrium of gilts throughout the estrous cycle and during early pregnancy and to investigate the in vitro effect of PGI2 on the mRNA expression of factors engaged in smooth muscle contraction, nutrient transport, prostaglandin synthesis and action, and inflammatory response. The obtained results showed that the synthesis of PGI2 changes in the myometrium of pigs during both the estrous cycle and early pregnancy, resulting in much greater concentrations of PGI2 in cyclic than in pregnant gilts. Moreover, PGI2 stimulated the expression of fatty acid transporters and contractility-related calponin 1 and caldesmon 1, whereas it decreased cytokine expression. This study indicates that PGI2 may participate in the regulation of myometrial functions modulating the availability of factors involved in smooth muscle activity and inflammatory reaction in the uterus of pigs.

Abstract

Although prostacyclin (PGI2) has been well described as a regulator of smooth muscle activity, limited data are available concerning its role in the myometrium of pigs. The present research aimed to examine profiles of PGI2 synthase (PTGIS) and PGI2 receptor (PTGIR) expression and 6-keto PGF1α (a PGI2 metabolite) concentrations in the myometrium of gilts throughout the estrous cycle and during early pregnancy using qPCR, Western blot, and/or ELISA methods. Furthermore, myometrial explants were exposed to iloprost (a stable PGI2 analog) to investigate the effect of PGI2 on the mRNA expression of factors engaged in smooth muscle contraction, nutrient transport, prostaglandin synthesis and action, and inflammatory response. PTGIS mRNA expression was greater in cyclic than in pregnant gilts on days 11–12 after estrus and was accompanied by greater concentrations of 6-keto PGF1α detected in cyclic than in pregnant animals on days 11–20. Iloprost stimulated fatty acid transporters and contractility-related calponin 1 and caldesmon 1 mRNA expression and decreased interleukin 1β and tumor necrosis factor transcript abundance. The obtained results indicate a physiologically relevant role of PGI2 during the estrous cycle in the porcine myometrium with its importance for regulating the expression of contractility-, nutrient transport- and inflammatory response-related factors.

Expression and functional maintenance of volume-regulated anion channels in myometrial smooth muscles of pregnant mice

Pregnancy causes changes in the uterus, such as increased cell volume and altered water content. However, the mechanisms that protect the structure and maintain the function of uterine smooth muscle cells against these changes during pregnancy have not been clarified. This study focused on the volume-regulated anion channel (VRAC), which opens with cell swelling under low osmotic pressure and releases Cl- ions and various organic osmolytes to resist cell swelling and regulates a wide range of biological processes such as cell death. In this study, myometrial smooth muscle (MSM) tissues and cells (MSMCs) were collected from non-pregnant and pregnant mice. Using western blotting and immunocytochemistry, leucine-rich repeat containing protein 8A (LRRC8A), an essential membrane protein that constitutes part of the VRAC, was determined to be diffused throughout MSMCs including in the cell membrane. Patch-clamp experiments were performed to investigate the electrophysiology of swelling-induced Cl- currents (ICl, swell) mediated by the VRAC. No significant changes between non-pregnancy and pregnancy groups were observed in either the expression density of LRRC8A or the current density of ICl, swell, however the presence of LRRC8A on the cell membrane was significantly increased in the third trimester of pregnancy compared to the non-pregnancy. This study suggests that the VRAC may play a role, such as maintaining cellular homeostasis in the pregnant MSM.

PGE2 vs PGF2α in human parturition

Prostaglandin E2 (PGE2) and F2α (PGF2α) are the two most prominent prostanoids in parturition. They are involved in cervical ripening, membrane rupture, myometrial contraction and inflammation in gestational tissues. Because multiple receptor subtypes for PGE2 and PGF2α exist, coupled with diverse signaling pathways, the effects of PGE2 and PGF2α depend largely on the spatial and temporal expression of these receptors in intrauterine tissues. It appears that PGE2 and PGF2α play different roles in parturition. PGE2 is probably more important for labor onset, while PGF2α may play a more important role in labor accomplishment, which may be attributed to the differential effects of PGE2 and PGF2α in gestational tissues. PGE2 is more powerful than PGF2α in the induction of cervical ripening. In terms of myometrial contraction, PGE2 produces a biphasic effect with an initial contraction and a following relaxation, while PGF2α consistently stimulates myometrial contraction. In the fetal membranes, both PGE2 and PGF2α appear to be involved in the process of membrane rupture. In addition, PGE2 and PGF2α may also participate in the inflammatory process of intrauterine tissues at parturition by stimulating not only neutrophil influx and cytokine production but also cyclooxygenase-2 expression thereby intensifying their own production. This review summarizes the differential roles of PGE2 and PGF2α in parturition with respect to their production and expression of receptor subtypes in gestational tissues. Dissecting the specific mechanisms underlying the effects of PGE2 and PGF2α in parturition may assist in developing specific therapeutic targets for preterm and post-term birth.

Distribution and Function of Prostaglandin E2 Receptors in Mouse Uterus: Translational Value for Human Reproduction

Prostaglandin (PG) E analogs are used clinically to ripen the cervix and induce labor. However, selective receptor agonists may have potential to improve induction response rates or manage unwanted uterine hypercontractility in conditions such as dysmenorrhea and preterm labor. To characterize their therapeutic value, PGE₂ analogs were used to investigate the functional E-type prostanoid (EP) receptor population in isolated human uterus. Responsiveness in mouse tissues was also examined to validate its use as a preclinical model. Uterine samples were obtained from mice at dioestrus (n = 12), term gestation (n = 14), and labor (n = 12) and from the lower uterus of women undergoing hysterectomy (n = 12) or Caesarean section (n = 18). Vehicle and agonist effects were assessed using superfusion and immersion techniques. PGE₂ evoked predominant excitatory responses in mouse and relaxation in human tissues. Selective EP₄ agonists inhibited tissue activity in both nonpregnant species, while the EP₂ mimetic CP533536 also attenuated uterine contractions throughout gestation. The uterotonic effects of the EP_3/1 agonist sulprostone were more pronounced than the EP₁ agonist ONO-D1-004, corresponding to abundant EP₃ receptor expression in all samples. The contractile phenotype in mouse compared with human uteri may relate to regional differences as well as high expression of EP₃ receptor transcripts. Similarities in nonpregnant and gestational tissues across species suggest that EP₃ may represent a valuable translational drug target for preventing uterine hypercontractility by employing a selective antagonist. SIGNIFICANCE STATEMENT: This research validates the use of nonpregnant mice for preclinical drug discovery of uterine EP receptor targets. To determine the utility of novel drugs and delivery systems at term pregnancy and labor, pharmacological agents interacting with EP₃ receptors have clear translational value.

Pharmacokinetics, safety and tolerability of OBE022, a selective prostaglandin F2α receptor antagonist tocolytic: A first-in-human trial in healthy postmenopausal women

AIMS

Preterm birth remains a significant risk for later disability. The selective inhibition of the prostaglandin F_2α receptor has significant advantages for a tocolytic. The prodrug OBE022 and its metabolite OBE002 are novel prostaglandin F_2α receptor antagonists under development for treating preterm labour.

METHODS

We performed a prospective, first in human, Phase I, dose escalation, placebo-controlled, randomized trial at a clinical trial site in the UK. Placebo, single ascending doses of 10, 30, 100, 300, 1000 or 1300 mg, and multiple ascending doses over 7 days of 100, 300 or 1000 mg day^-1 ; were administered to postmenopausal female volunteers. Food interaction was additionally evaluated.

RESULTS

Subjects tolerated OBE022 well at all single and multiple doses. No clinically relevant changes in safety parameters were shown and there were no serious adverse events. Observations showed that prodrug OBE022 was readily absorbed and rapidly converted into its equally active stable metabolite OBE002. The plasma level of OBE002 rose with increasing doses, reaching exposure levels that were anticipated to be clinically relevant within 1 h following administration. There was no clinically significant food interaction, with peak exposures reduced to 80% and area under the curve staying bioequivalent. The mean half-life of OBE002 ranged between 8 and 11 h following administration of a single dose and 22-29 h after multiple doses.

CONCLUSIONS

Administration of OBE022 was safe and had favourable pharmacokinetic characteristics and no clinically relevant interaction with food. Our results allow further investigation of OBE022 in preterm labour patients.

OBE022, an Oral and Selective Prostaglandin F2α Receptor Antagonist as an Effective and Safe Modality for the Treatment of Preterm Labor

Preterm birth is the major challenge in obstetrics, affecting ∼10% of pregnancies. Pan-prostaglandin synthesis inhibitors [nonsteroidal anti-inflammatory drugs (NSAIDs)] prevent preterm labor and prolong pregnancy but raise concerns about fetal renal and cardiovascular safety. We conducted preclinical studies examining the tocolytic effect and fetal safety of the oral prodrug candidate OBE022 [(S)-2-amino-3-methyl-butyric acid (S)-3-{[(S)-3-(biphenyl-4-sulfonyl)-thiazolidine-2-carbonyl]-amino}-3-(4-fluoro-phenyl)-propyl ester] and its parent OBE002 [(S)-3-(biphenyl-4-sulfonyl)-thiazolidine-2-carboxylic acid [(S)-1-(4-fluoro-phenyl)-3-hydroxy-propyl]-amide], both potent and highly selective antagonist of the contractile prostaglandin F_2α (PGF_2α ) receptor (FP). Efficacy of OBE022 and OBE002, alone and in combination with other tocolytics, was assessed in human tissues and pregnant animal models for inhibition of uterine contraction and delay of parturition. Selective safety of OBE022 and/or OBE002, compared with NSAID indomethacin, was assessed on renal function, closure of the ductus arteriosus, and inhibition of platelet aggregation. In in vitro studies, OBE002 inhibited spontaneous, oxytocin- and PGF_2α -induced human myometrial contractions alone and was more effective in combination with atosiban or nifedipine. In in vivo studies, OBE022 and OBE002 reduced spontaneous contractions in near-term pregnant rats. In pregnant mice, OBE022 delayed RU486 [(8S,11R,13S,14S,17S)-11-[4-(dimethylamino)phenyl]-17-hydroxy-13-methyl-17-prop-1-ynyl-1,2,6,7,8,11,12,14,15,16-decahydrocyclopenta[a]phenanthren-3-one] -induced parturition and exerted synergistic effects in combination with nifedipine. OBE022 and/or OBE002 did not show the fetal side effects of ductus arteriosus constriction, impairment of kidney function, or inhibition of platelet aggregation observed with indomethacin. Orally active OBE022 and OBE002 exhibits potent tocolytic effects on human tissues ex vivo and animal models in vivo without causing the adverse fetal side effects seen with indomethacin. Selectively targeting the FP receptor in combination with existing tocolytics may be an effective strategy for preventing or delaying preterm delivery.

Expression of prostaglandin receptors in Chlamydia trachomatis-infected recurrent spontaneous aborters

A study was undertaken to quantify the expression of prostaglandin (PG) receptors and find the effect of gestational age on expression of PG receptor genes in Chlamydia trachomatis-infected recurrent spontaneous aborters (RSA). Endometrial curettage tissue (ECT) was collected from 130 RSA (Group I) and 100 age-matched controls (Group II) at the Department of Obstetrics and Gynecology, Safdarjung Hospital, New Delhi (India). PCR was performed for diagnosis of C. trachomatis cryptic plasmid; mRNA expression of PG receptor genes was assessed by real-time PCR (q-PCR), while serum progesterone/estrogen levels were determined by respective commercial kits. Data were evaluated statistically. A total of 15.4 % RSA (GroupI) were diagnosed as C. trachomatis-positive (200 bp), whereas controls were uninfected. q-PCR showed significant upregulation (P<0.0001) of PGE2 (EP-1, EP-2, EP-3, EP-4), PGF2α (FP) and PGI2 (IP) receptors in Group I versus Group II. The expression of PG receptors increased significantly with advanced gestational age (P<0.002); however, only contractile receptors, EP-1, EP-3 and FP, were positively correlated with gestational age in Group-I. In infected RSA, mean serum progesterone level was significantly low (P<0.0001) while serum oestrogen was high (P<0.0001). Overall, the data suggest that increased expression of PG receptors, particularly contractile gene receptors (EP-1, EP-3, FP), with advanced gestational age and altered steroid levels could be a possible risk factor for abortion in Chlamydia-infected RSA.

EP2 receptor activates dual G protein signaling pathways that mediate contrasting proinflammatory and relaxatory responses in term pregnant human myometrium

Prostaglandin (PG) E2 (PGE(2)) plays a central role in the regulation of smooth muscle contractions. Classically, PGE(2) stimulates contractions via EP1 and EP3 receptors, whereas EP2 and EP4 maintain quiescence. Labor involves a change from myometrial quiescence to contractions with a shift from anti- to proinflammatory pathways. EP2, a Gαs-coupled receptor, is known to mediate its actions via cAMP signaling. However, we have recently shown that EP2 also activates the proinflammatory PG G/H synthase-2 (PGHS-2). Here, we identify the mechanism underlying the ability of EP2 to maintain uterine quiescence and activate a proinflammatory/prolabor response in term-pregnant human myometrium. Human myometrial biopsies for in vivo and in vitro studies were taken at cesarean section at term, before or after the onset of labor. Activation of EP2 increased intracellular levels of cAMP and reduced contractility. Contrastingly, EP2 stimulation increased levels of PGHS-2, membrane-associated PGE synthase-1, and PGE(2). This was entirely dependent on EP2-mediated activation of calcium signaling. Both calcium signaling and up-regulation of PGHS-2 were insensitive to the Gαi inhibitor pertussis toxin but inhibited by small interfering RNA knockdown of Gαq/11. There were no differences in EP2 mRNA or protein levels between upper or lower segment myometrium or between pre- and postlabor myometrium. However, in myocytes taken after the onset of labor, cAMP signaling was markedly attenuated, whereas activation of calcium and PGHS-2 was preserved. Overall, the dual coupling of EP2 to Gαs-cAMP and Gαq/11-calcium pathways underlies its ability to mediate contrasting functions in term pregnancy and the "switching" to a prolabor receptor.

Association of a common genetic factor, PTGER3, with outcome of periodontal therapy and preterm birth

BACKGROUND

Clinical evidence suggests an association between preterm birth and periodontal disease. This study explores whether specific genetic polymorphisms are associated with success of periodontal therapy in pregnant women with periodontal disease and, further, whether any of these same polymorphisms are also associated with spontaneous preterm birth (sPTB).

METHODS

One hundred sixty high-risk pregnant women (6 to 20 weeks of gestation) with periodontal disease (≥ 3 sites with attachment loss ≥ 4 mm) were studied. All women received scaling and root planing plus oral hygiene instruction. Periodontal examinations were performed before treatment and 20 weeks later. Participants were classified according to two study outcomes: 1) success or failure of periodontal treatment; and 2) presence or absence of sPTB. Maternal DNA samples from mucosal swabs were characterized using a 1536-SNP (single-nucleotide polymorphism) custom polymerase chain reaction chip. A probabilistic model of each dichotomous outcome, derived using a stepwise Bayesian procedure, was compared to respective null hypotheses on the basis of Monte Carlo simulations and significance estimates obtained using three measures (z-test, Welch t-test, and probability convolution). The models were further confirmed by logistic regression analyses.

RESULTS

The models revealed a significant relation between a specific polymorphism of prostaglandin E receptor 3 (a gene associated with inflammatory response) and both periodontal treatment failure (odds ratio 11.09, P <0.0002) and sPTB (odds ratio 6.89, P < 0.0032).

CONCLUSIONS

These results demonstrate that the risk of unsuccessful periodontal treatment is associated with tag SNPs in specific genes that regulate the inflammatory response, one of which is also associated with sPTB.

Prostaglandin E2 represses interleukin 1 beta-induced inflammatory mediator output from pregnant human myometrial cells through the EP2 and EP4 receptors

Inflammatory mediators, including prostaglandins, cytokines, and chemokines, are strongly implicated in the mechanism of human labor, though their precise roles remain unknown. Here we demonstrate that interleukin 1 beta (IL-1beta) significantly increased the expression and release of interleukin-8 (CXCL8), monocyte chemotactic protein-1 (CCL2), and granulocyte macrophage colony-stimulating factor (CSF2) by primary human myometrial cells. However, this effect was repressed by prostaglandin E(2) (PGE(2)). As PGE(2) can activate four distinct PGE(2) receptors (EP(1), EP(2), EP(3), and EP(4)) to elicit various responses, we sought to define the EP receptor(s) responsible for this repression. Using selective EP receptor agonists and a selective EP(4) antagonist, we show that PGE(2) mediates the repression of IL-1beta-induced release of CXCL8, CCL2, and CSF2 via activation of the EP(2) and EP(4) receptors. The use of siRNA gene-specific knockdown further confirmed a role for both receptors. Real-time RT-PCR demonstrated that EP(2) was the most highly expressed of all four EP receptors at the mRNA level in human myometrial cells, and immunocytochemistry showed that EP(2) protein is abundantly present throughout the cells. Interestingly, PGE(2) does not appear to reduce mRNA expression of CXCL8, CCL2, and CSF2. Our results demonstrate that PGE(2) can elicit anti-inflammatory responses via activation of the EP(2) and EP(4) receptors in lower segment term pregnant human myometrial cells. Further elucidation of the EP receptor-mediated signaling pathways in the pregnant human uterus may be beneficial for optimizing the maintenance of pregnancy, induction of labor or indeed treatment of preterm labor.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Role of prostaglandin E and its receptors in the process of ductus arteriosus maturation and functional closure in the rabbit

1. Patent ductus arteriosus (PDA) is a common congenital heart defect in premature infants. The present study was designed to determine the role of the prostaglandin (PG) E(2) pathway in the process of ductus arteriosus (DA) maturation and functional closure. 2. Changes in PGE(2) pathway-related enzymes and receptors in DA in preterm and term rabbits were examined at both the mRNA and protein levels. In addition, responses of DA rings to Po(2) and PGE(2) were determined. 3. Circulating PGE(2) levels remained high until 2 h after birth. High levels of the EP(4) receptor were found in preterm DA. These tissues were sensitive to PGE(2), which caused vessel dilation, but were insensitive to increased Po(2). In contrast, DA tissues from term rabbits exhibited an immediate contractile response to increased Po(2) and PGE(2) treatment resulted in vasoconstriction, which was associated with increased EP(3) and decreased EP(4) receptor expression in term DA. 4. In conclusion, the preterm PDA is maintained by high levels of PGE(2), which mainly binds to the EP(4) receptor under conditions of hypoxia. In contrast, in the term DA, in which levels of the EP(3) receptor are higher than in preterm DA, exposure to PGE(2) resulted in vasoconstriction under normoxic conditions. These findings suggest that blocking the EP(4) receptor may represent a more selective treatment for the preterm PDA, whereas activating the EP(3) receptor may be more suitable for the treatment of the term PDA.

Effect of PGE2 on DA tone by EP4 modulating Kv channels with different oxygen tension between preterm and term

OBJECTIVE

To investigate common downstream mechanism of PGE2 and O2-sensitive voltage-dependent potassium (Kv) channels in preterm and term DA tone regulations, for suggesting respective prescriptions for preterm and term PDA.

STUDY DESIGN

The expressions of Kv1.2, 1.5 and 2.1 were compared between preterm and term in rabbit and human DAs at mRNA and protein levels; DA contracting responses caused by O2, Kv channels blocker 4-AP, EP4 antagonist GW627368X, and PGE2 reduce using vessels rings and Whole-Cell Patch-Clamp were explored.

RESULTS

Kv 1.2 and 2.1 expressions were developed with pregnant age in preterm DA and decreased after birth with oxygen stimulation in term DA. GW627368X led significant DA constriction and DASMC IK current decrease in preterm, which was slimier to 4-AP effects, but just slightly influenced on DA tension and DASMC IK current at term. In addition, PGE2 led great DA dilation and IK current increase of DASMC in preterm but not in term. These DA tension and IK current changes were in line with Kv channel expressions.

CONCLUSION

Higher levels of PGE2 binds with GPCR EP4, which activates G-protein to couple with O2-sensitive Kv channels and to open them, leading to DA vasorelaxation in the fetus. It indicates that EP4 inhibitors, instead of PGE2 or its analogue PGE1, may be a selectable strategy for preterm PDA.

Quantitative detection of EP3-II, III and VI messenger RNA in gravid and non-gravid human myometrium using real-time RT-PCR

OBJECTIVE

To examine mRNA expression of prostaglandin E2 receptor isoforms EP3-II, III and VI in lower uterine segment myometrium in the non-pregnant and pregnant state using quantitative real-time RT-PCR.

METHODS

Myometrial samples were obtained at the time of cesarean delivery or hysterectomy. Pregnant subjects were categorised based on the presence or absence of labour. Labour was defined as regular uterine contractions resulting in cervical change. Quantification for EP3 isoforms II, III and VI mRNA was performed using real-time RT-PCR.

RESULTS

There were no differences between non-pregnant and non-labouring pregnant subjects in mRNA expression of EP3-II, III and VI. However, when compared to pregnant subjects not in labour, labouring subjects had a 3.8-fold reduction in EP3-II expression (p < 0.001) and 5.3-fold reduction in EP3-VI expression (p = 0.022).

CONCLUSIONS

In human parturition, there is decreased mRNA expression of lower-uterine segment EP3 receptor isoforms II and VI during labour. This may reflect differential relaxation of the lower segment of the uterus allowing dilatation and descent of the fetus.

Prostacyclin primes pregnant human myometrium for an enhanced contractile response in parturition

An incomplete understanding of the molecular events that regulate the myometrial transition from the quiescent pregnant state to the active contractile state during labor has hindered the development of improved therapies for preterm labor. During myometrial activation, proteins that prime the smooth muscle for contraction are upregulated, allowing maximal responsiveness to contractile agonists and thereby producing strong phasic contractions. Upregulation of one such protein, COX-2, generates PGs that induce contractions. Intriguingly, the predominant myometrial PG produced just prior to labor is prostacyclin (PGI2), a smooth muscle relaxant. However, here we have shown that activation of PGI2 receptor (IP) upregulated the expression of several contractile proteins and the gap junction protein connexin 43 through cAMP/PKA signaling in human myometrial tissue in organ and cell culture. Functionally, these IP-dependent changes in gene expression promoted an enhanced contractile response to oxytocin in pregnant human myometrial tissue strips, which was inhibited by the IP antagonist RO3244794. Furthermore, contractile protein induction was dependent on the concentration and time of exposure to the PGI2 analog iloprost and was blocked by both RO3244794 and PKA knockdown. We therefore propose that PGI2-mediated upregulation of contractile proteins and connexin 43 is a critical step in myometrial activation, allowing for a maximal contractile response. Our observations have important implications regarding activation of the myometrium prior to the onset of labor.

Vasorelaxation induced by prostaglandin E2 in human pulmonary vein: role of the EP4 receptor subtype

BACKGROUND AND PURPOSE

PGE2 has been shown to induce relaxations in precontracted human pulmonary venous preparations, while in pulmonary arteries this response was not observed. We investigated and characterized the prostanoid receptors which are activated by PGE2 in the human pulmonary veins.

EXPERIMENTAL APPROACH

Human pulmonary arteries and veins were cut as rings and set up in organ baths in presence of a TP antagonist. A pharmacological study was performed using selective EP1-4 ligands. The cellular localization of the EP4 receptors by immunohistochemistry and their corresponding transcripts were also investigated in these vessels.

KEY RESULTS

PGE2 and the EP4 agonists (L-902688, ONO-AE1-329) induced potent vasodilatation of the human pulmonary vein, pEC50 values: <7.22+/-0.20, 8.06+/-0.12 and 7.80+/-0.09, respectively. These relaxations were inhibited by the EP(4) antagonist GW627368X and not modified in presence of the DP antagonist L-877499. Higher concentrations (>or=1 microM) of the EP2 agonist ONO-AE1-259 induced relaxations of the veins. The EP4 agonists had no effect on the precontracted arteries. Finally, the EP(1) antagonists ONO-8713 and SC-51322 potentiated the relaxation of the veins induced by PGE2. EP4 and EP1 receptors were detected by immunohistochemistry in the veins but not in the arteries. EP4 mRNA accumulation was also greater in the veins when compared with the arterial preparations.

CONCLUSIONS AND IMPLICATIONS

Of the 4 EP receptor subtypes, smooth muscle cells in the human pulmonary vein express the EP4 and EP1 receptor subtypes. The relaxations induced by PGE2 in this vessel result from the activation of the EP4 receptor.

Effects of lubiprostone on human uterine smooth muscle cells

Lubiprostone, a bicyclic fatty acid derivative and member of a new class of compounds called prostones, locally activates ClC-2 Cl(-) channels without activation of prostaglandin receptors. The present study was specifically designed to test and compare lubiprostone and prostaglandin effects at the cellular level using human uterine smooth muscle cells. Effects on [Ca(2+)](i), membrane potential and [cAMP](i) in human uterine smooth muscle cells were measured. 10 nM lubiprostone significantly decreased [Ca(2+)](i) from 188 to 27 nM, which was unaffected by 100 nM SC-51322, a prostaglandin EP receptor antagonist. In contrast 10nM PGE(2) and PGE(1) both increased [Ca(2+)](i) 3-5-fold which was blocked by SC-51322. Similarly, lubiprostone and prostaglandins had opposite/different effects on membrane potential and [cAMP](i). Lubiprostone caused SC-51322-insensitive membrane hyperpolarization and no effect on [cAMP](i). PGE(2) and PGE(1) both caused SC-51322-sensitive membrane depolarization and increased [cAMP](i). Lubiprostone has fundamentally different cellular effects from prostaglandins that are not mediated by EP receptors.

Arrest of preterm labor in rat and mouse by an oral and selective nonprostanoid antagonist of the prostaglandin F2alpha receptor (FP)

OBJECTIVE

The purpose of this study was to assess the tocolytic effect of AS604872, an orally active, potent, and selective prostanoid prostaglandin F2alpha receptor (FP) antagonist.

STUDY DESIGN

Compound AS604872 was characterized and tested for its ability to block uterine contraction and delay preterm parturition in rodent models.

RESULTS

AS604872 inhibited spontaneous uterine contractions in pregnant rat near term. In pregnant mouse, AS604872 delayed parturition induced by either the antiprogesterone RU-486 or the endotoxin lipopolysaccharide. Pups from treated mothers were delivered alive. The efficacy of AS604872 was superior to the beta-mimetic drug ritodrine. Combination of AS604872 and ritodrine showed an additive inhibitory effect on spontaneous uterine contractions in rat.

CONCLUSION

A selective antagonist of the FP receptor suppresses uterine contractility and delays labor. Our findings identify a new potential modality for the pharmacological management of preterm labor.

Tocolytic effect of a selective FP receptor antagonist in rodent models reveals an innovative approach to the treatment of preterm labor

Background

Management of preterm labor by tocolysis remains an unmet medical need. Prostaglandins play a major role in regulation of uterine activity and in molecular mechanisms of human labor and parturition. There is some circumstantial evidence that prostaglandin F2α by action through the prostaglandin receptor subtype FP is effective in key events during labor uterine contraction, rupture of membranes and cervical dilation. This role of FP is briefly reviewed. In this study, we tested the hypothesis that an orally active and selective FP antagonist may arrest labor and delay parturition in animal models.

Methods

We examined the effects of a small molecule selective antagonist of the FP receptor (AS604872) in inhibition of spontaneous uterine contraction in pregnant rat near term. We tested AS604872 for its ability to delay preterm birth in a mouse model in which the anti-progestin agent RU486 triggered parturition.

Results

By oral or intravenous dosing AS604872 reduced markedly and dose-dependently the spontaneous uterine contractions in late-term pregnant rats at gestational days 19–21. In pregnant mice, AS604872 delayed the preterm birth caused by RU486 administration. The effect was dose-dependent with a significant increase in the mean delivery time of 16 and 33 hours at oral doses of 30 mg/kg and 100 mg/kg, respectively, in the case of labor triggered at gestational day 14. In both models AS604872 appeared more effective than the β-agonist ritodrine.

Conclusion

The tocolytic activity displayed by a selective FP receptor antagonist supports a key role for the FP receptor in the pathophysiology of premature birth and demonstrates the therapeutic potential of an FP antagonist for the treatment of preterm labor cases in which uterine hyperactivity plays a dominant role.

Preterm labour. Myometrial function in prematurity

The primary function of the uterus during gestation is to harbour the growing conceptus in a largely quiescent environment. Upon maturation of the fetus to a point sufficient for extrauterine survival, the uterus must remodel itself sufficiently to generate forceful contractions during labour. During preterm delivery, the process of remodelling of the myometrium occurs early due to a number of different causes, although the underlying basis for myometrial contraction remains the same. This review summarises the anatomical, physiological and molecular basis for contraction. We describe the fibre structure of the human uterus and how this relates to the spread of electrical excitation during a contraction. The process of excitation within a single myometrial cell is described, as well as how this relates to contraction. We then focus on how excitation-contraction coupling is modulated by intercellular communication, pharmacomechanical-coupling and hormonal milieu. Lastly, we consider the actions of the commonly accepted uterine agonists oxytocin, prostaglandin F(2alpha), and prostaglandin E(2), and the tocolytic ritodrine.

Expression and regulation of prostaglandin E synthase isoforms in human myometrium with labour

Since the controversies regarding the use of non-steroidal anti-inflammatory drugs (NSAIDs) and selective cyclo-oxygenase (COX)-2 antagonists for the treatment of preterm labour (PTL), more emphasis has been placed on investigating the terminal synthases involved in the production of prostaglandins (PGs) to allow more targeted therapy in PTL. Prostaglandin E(2) (PGE(2)) is synthesized by one of three enzymes, cytosolic prostaglandin E synthase (cPGES), microsomal PGES-1 (mPGES-1) and microsomal PGES-2 (mPGES-2). We have determined (i) the immuno-localization of all three PGES enzymes in lower segment pregnant human myometrium, (ii) the expression of PGES and COX-2 mRNA expression at term and preterm gestation with and without labour and (iii) the effect of interleukin (IL)-1beta on COX-2 and PGES mRNA and protein expression in human myometrial smooth muscle (HMSM) cell cultures. We show mPGES-1 protein located predominantly in myometrial and vascular smooth muscle cells (SMCs), whilst mPGES-2 protein is largely in stromal cells surrounding the SMC and cPGES is diffusely located throughout the myometrium. Expression of mPGES-2 mRNA increased with term labour and PTL and expression of COX-2 and mPGES-1 mRNA with term labour, whereas cPGES expression did not change. IL-1beta stimulated release of PGE(2) by HMSM cells and increased COX-2 and mPGES-1 mRNA and protein expression. Thus, COX-2 expression and mPGES-1 expression are co-ordinately up-regulated in lower segment myometrium with term labour and with IL-1beta treatment in HMSM cells.

Regional Expression of Prostaglandin E2 and F2alpha Receptors in Human Myometrium, Amnion, and Choriodecidua with Advancing Gestation and Labor1

The change from uterine quiescence to enhanced contractile activity may be due to the differential expression of prostaglandin receptors within the myometrium and fetal membranes, in a temporal and topographically distinct manner. To address this question, we determined the localization and expression of the PGE2 receptor subtypes (PTGER1-4) and the PGF2alpha receptor (PTGFR) in paired upper and lower segment myometrium, amnion, and choriodecidual samples throughout human pregnancy, with and without labor. All receptor subtypes were found throughout the muscle layers in both the upper and lower uterine segments, colocalizing with alpha smooth muscle actin. A change in intracellular localization was observed at term labor, where PTGER1 and PTGER4 were predominately associated with the nucleus. Minimal changes in the expression of the PGE2 and PGF2alpha receptor subtypes were observed with gestational age, labor, or between the upper and lower myometrial segments. Receptor expression in maternal and fetal tissues differed between the receptor subtypes; PTGER1 and PTGER4 were predominately expressed in the fetal membranes, PTGER2 was greatest in the myometrium, whereas PTGER3 and PTGFR were similarly expressed in the myometrium and fetal membranes. Myometrial activation through the prostaglandin receptors is perhaps more subtle and may be mediated by a balance between one or several of the prostaglandin receptor subtypes together with other known contraction associated proteins. Lack of coordination in receptor expression between the myometrium and fetal membranes may indicate different regulatory mechanisms between these tissues, or it may suggest a function for these receptors in the amnion and choriodecidua that is independent of that seen in the myometrium.

Anti-inflammatory and relaxatory effects of prostaglandin E2 in myometrial smooth muscle

The onset of human labour is complex and involves multiple mediators, prostaglandins, cytokines and chemokines. However, whilst prostaglandins are routinely used for labour induction and inhibitors of prostaglandin synthesis are used to prevent pre-term labour, these practices are not invariably successful, and the rationale for their use is equivocal. As COX-2 and prostaglandin E(2) (PGE(2)) production is increased towards term, we have investigated the effect of PGE(2) and other cAMP-elevating agents on events associated with labour induction. Time-dependent increases in granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-8 (IL-8) release were observed following treatment of primary human myometrial smooth muscle (HMSM) cells with IL-1beta, via mechanisms that required de novo transcription and translation. Prior treatment with PGE(2) (1 microM) produced 86 and 80% decreases in GM-CSF and IL-8 release, respectively. Similarly, the cAMP analogue, 8-bromo-cAMP (8Br-cAMP) and the phosphodiesterase-4 (PDE(4)) inhibitor, rolipram, also repressed GM-CSF and IL-8 release. In addition, PGE(2), 8Br-cAMP, rolipram and salbutamol all had a dose-dependent inhibitory effect on spontaneous myometrial contractions in vitro. In this study, PGE(2) reduced the release of factors associated with cervical ripening and attenuated force development in myometrial smooth muscle, raising the possibility that in myometrium, PGE(2) may act to down-regulate some of the processes that contribute to the onset of human labour and may be beneficial in helping to maintain pregnancy towards term.

Prostanoid receptors in human uterine myocytes: the effect of reproductive state and stretch

In the human, prostanoids are known to be important mediators of uterine relaxation and contraction during pregnancy and parturition. We have previously shown that stretch of uterine smooth muscle cells increased prostaglandin H synthase 2 (PGHS-2) mRNA expression, PGHS-2 peptide synthesis and activity, however, the net effect on uterine contractility of this increase in prostaglandin synthesis would be determined by the expression of the different prostanoid receptors. Therefore, the aims of this study were to establish the expression of prostanoid receptor mRNA in uterine myocytes obtained from women in different reproductive states and to test the hypothesis that stretch of uterine myocytes alters prostanoid receptor mRNA expression to promote uterine contractility. Myocytes were isolated from women undergoing hysterectomy (NP) and pregnant women undergoing LSCS either before (NL) or after the onset of labour (L) and were subjected to 11% stretch for 1 h (n = 6 in all cases). Copy numbers of the individual receptors varied widely with reproductive state but followed the pattern: FP > IP = DP = EP-4 > TP = EP-3 = EP-2 > EP-1. FP mRNA expression was significantly lower in the NL group compared to the NP group and EP-3, EP-4 and TP mRNA expression was significantly lower in both NL and L groups compared to NP group levels. The level of mRNA expression of EP-1, EP-2, DP and IP did not differ between NP, NL and L groups. Stretch of cells derived from the NP group resulted in a significant decrease in EP-4 mRNA expression alone and of the NL group a significant decrease in EP-2 mRNA expression alone. Stretch had no effect on cells derived from the L group. These data show that pregnancy is associated with a significant reduction in 3 of 4 pro-contraction associated prostanoid receptor mRNA expression and 1 of 4 pro-relaxant. Stretch elicited no consistent change in prostanoid receptor mRNA expression.

Identification and localization of prostaglandin E2 receptors in upper and lower segment human myometrium during pregnancy

Prostaglandin E2 (PGE2) plays a key role in the maintenance of human pregnancy and labour onset. PGE2 can elicit diverse actions within the uterus depending on the PGE2 receptors (EP1, EP2, EP3 and EP4) expressed. By signalling through different intracellular pathways the EP receptors may inhibit or promote smooth muscle contractility. Nine different EP3 receptor splice variants have been identified with divergent signalling pathways. RT-PCR and immunohistochemistry were utilized to identify and localize EP receptor isoforms within the upper segment (US) and lower segment (LS) myometrium. EP1 was significantly increased in the LS myometrium with term labour. EP3 (and EP3 splice variants EP3I(1b), EP3II, EP3III and EP3IV) was down-regulated in pregnancy (US and/or LS) with a further decrease at term labour in the LS. Overall, expression of EP2 was significantly higher in the LS while EP3 was significantly higher in the US. No significant EP4 changes were observed. Consistent with the RT-PCR results, immunohistochemistry confirmed the presence and, interestingly, showed nuclear localization of EP receptors in the myometrium with higher EP1 expression and lower expression of EP3. The differential regulation of EP receptors within the myometrium indicates that they may play a role in controlling the onset and maintenance of human labour.