Oxytocin signaling in human myometrium is impaired by prolonged exposure to interleukin-1

Maternal plasma cytokines and the subsequent risk of uterine atony and postpartum hemorrhage

OBJECTIVES

To determine whether the maternal plasma concentrations of cytokines are higher in pregnant women with postpartum hemorrhage (PPH) compared to pregnant women without PPH.

METHODS

A retrospective case-control study included 36 women with PPH and 72 matched controls. Cases and controls were matched for gestational age at delivery, labor status, delivery route, parity, and year of sample collection. Maternal plasma samples were collected up to 3 days prior to delivery. Comparison of the plasma concentrations of 29 cytokines was performed by using linear mixed-effects models and included adjustment for covariates and multiple testing. A false discovery rate adjusted p-value <0.1 was used to infer significance. Random forest models with evaluation by leave-one-out and 9-fold cross-validation were used to assess the combined value of the proteins in predicting PPH.

RESULTS

Concentrations of interleukin (IL)-16, IL-6, IL-12/IL-23p40, monocyte chemotactic protein 1 (MCP-1), and IL-1β were significantly higher in PPH than in the control group. This difference remained significant after adjustment for maternal age, clinical chorioamnionitis, and preeclampsia. Multi-protein random forest proteomics models had moderate cross-validated accuracy for prediction of PPH [area under the ROC curve, 0.69 (0.58-0.81) by leave-one-out cross validation and 0.73 (0.65-0.81) by 9-fold cross-validation], and the inclusion of clinical and demographic information did not increase the prediction performance.

CONCLUSIONS

Pregnant women with severe PPH had higher median maternal plasma concentrations of IL-16, IL-6, IL-12/IL-23p40, MCP-1, and IL-1β than patients without PPH. These cytokines could serve as biomarkers or their pathways may be therapeutic targets.

Is there a relationship between plasma, cytokine concentrations, and the subsequent risk of postpartum hemorrhage?

BACKGROUND

Postpartum hemorrhage remains the leading cause of maternal mortality. However, there is an insufficient understanding of atonic postpartum hemorrhage. Uterine atony is the most common cause of postpartum hemorrhage. Although an association between myometrium inflammatory cytokines and atonic postpartum hemorrhage has been demonstrated preliminarily, it is not clinically useful in predicting postpartum hemorrhage. Plasma is more readily available, and the assessment of its inflammatory status is more relevant to biological markers of postpartum hemorrhage and might explain the pathophysiology of atonic postpartum hemorrhage.

OBJECTIVE

Our objective was to examine changes in maternal plasma cytokines in women with atonic postpartum hemorrhage.

STUDY DESIGN

This was a retrospective longitudinal case-control study of pregnant women with singleton gestations at term undergoing vaginal delivery. Cases were women with atonic postpartum hemorrhage, and 1:1 propensity-score matching was used to match the control group. Maternal plasma was collected in the first trimester, early third trimester, and late third trimester, and multiplex Luminex assay was used to determine the cytokine concentrations. Multivariate logistic regressions were used to determine the association between maternal cytokines at different stages of pregnancy and atonic postpartum hemorrhage.

RESULTS

A total of 36 pregnant women met the clinical diagnostic criteria for atonic postpartum hemorrhage, and 36 patients without postpartum hemorrhage were matched as the control group. Concentrations were lower for most cytokines in the atonic postpartum hemorrhage group in the first and early third trimester. However, in the late third trimester, higher plasma concentrations of basic fibroblast growth factor, interleukin-1 alpha, interleukin-1 beta, interleukin-1 receptor antagonist, interleukin-2 receptor alpha, interleukin-16, interleukin-18, macrophage colony stimulating factor, macrophage inflammatory protein-1 alpha, beta-nerve growth factor, tumor necrosis factor-related apoptosis-induced ligand, and stem cell factor were significantly associated with increased risk of atonic postpartum hemorrhage. Multiple testing correction showed that basic fibroblast growth factor (P<.001; fold change [FC]=1.16), macrophage inflammatory protein-1 alpha (P<.001; FC=1.15), and stem cell factor (P=.001; FC=1.25) had the most significant difference (P<.001). The prediction model of atonic postpartum hemorrhage constructed by these significantly changed cytokines had a high predictive efficiency (area under the curve, 0.84; sensitivity, 0.78; specificity, 0.83; +likelihood ratio, 4.66; -likelihood ratio, 0.27).

CONCLUSION

Higher concentrations of maternal plasma cytokines in the late third trimester are associated with high risk of subsequent atonic postpartum hemorrhage. These indicators may be potential biomarkers for predicting atonic postpartum hemorrhage.

Myometrial cytokines and their role in the onset of labour

Human labour is an inflammatory event, physiologically driven by an interaction between hormonal and mechanical factors and pathologically associated with infection, bleeding and excessive uterine stretch. The initiation and communicators of inflammation is still not completely understood; however, a key role for cytokines has been implicated. We summarise the current understanding of the nature and role of cytokines, chemokines and hormones and their involvement in signalling within the myometrium particularly during labour.

Maternal inflammatory markers and term labor performance

OBJECTIVE

We sought to examine the relationship between maternal markers of inflammation and labor performance.

STUDY DESIGN

A nested cohort study was performed utilizing an established cohort of term nulliparous patients. Maternal blood was collected at the onset of regular, painful contractions in patients undergoing labor induction or at admission in patients with spontaneous labor. Levels of cytokines including interleukin (IL)-1, IL-6, and tumor necrosis factor-α were determined using standard multiplex methodology. Maternal demographic data were collected prospectively. Detailed retrospective chart review was performed to extract data on cervical dilation, effacement, and station during labor. Subjects were excluded if they failed to achieve complete dilation. Mixed effects modeling was used to examine the association between serum cytokine quartiles and labor progress in the latent and active phases.

RESULTS

In all, 334 women were included in our analysis. The lowest quartile of IL-6 was associated with slower latent labor (P = .001). In contrast, the highest quartiles of IL-1 and tumor necrosis factor-α were associated with slower active labor (P = .03 and .0002, respectively).

CONCLUSION

Proinflammatory activation is important in labor initiation. However, once active labor is established, excess inflammation can be detrimental to efficient labor progress. These data may explain, in part, the known associations among clinical chorioamnionitis, cesarean delivery, and postpartum hemorrhage.

Characterization of the myometrial transcriptome and biological pathways of spontaneous human labor at term

AIMS

to characterize the transcriptome of human myometrium during spontaneous labor at term.

METHODS

myometrium was obtained from women with (n=19) and without labor (n=20). Illumina HumanHT-12 microarrays were utilized. Moderated t-tests and false discovery rate adjustment of P-values were applied. Real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) was performed for a select set of differentially expressed genes in a separate set of samples. Enzyme-linked immunosorbent assay and Western blot were utilized to confirm differential protein production in a third sample set.

RESULTS

1) Four hundred and seventy-one genes were differentially expressed; 2) gene ontology analysis indicated enrichment of 103 biological processes and 18 molecular functions including: a) inflammatory response; b) cytokine activity; and c) chemokine activity; 3) systems biology pathway analysis using signaling pathway impact analysis indicated six significant pathways: a) cytokine-cytokine receptor interaction; b) Jak-STAT signaling; and c) complement and coagulation cascades; d) NOD-like receptor signaling pathway; e) systemic lupus erythematosus; and f) chemokine signaling pathway; 4) qRT-PCR confirmed over-expression of prostaglandin-endoperoxide synthase-2, heparin binding epidermal growth factor (EGF)-like growth factor, chemokine C-C motif ligand 2 (CCL2/MCP1), leukocyte immunoglobulin-like receptor, subfamily A member 5, interleukin (IL)-8, IL-6, chemokine C-X-C motif ligand 6 (CXCL6/GCP2), nuclear factor of kappa light chain gene enhancer in B-cells inhibitor zeta, suppressor of cytokine signaling 3 (SOCS3) and decreased expression of FK506 binding-protein 5 and aldehyde dehydrogenase in labor; 5) IL-6, CXCL6, CCL2 and SOCS3 protein expression was significantly higher in the term labor group compared to the term not in labor group.

CONCLUSIONS

myometrium of women in spontaneous labor at term is characterized by a stereotypic gene expression pattern consistent with over-expression of the inflammatory response and leukocyte chemotaxis. Differential gene expression identified with microarray was confirmed with qRT-PCR using an independent set of samples. This study represents an unbiased description of the biological processes involved in spontaneous labor at term based on transcriptomics.

Are animal models relevant to key aspects of human parturition?

Preterm birth remains the most serious complication of pregnancy and is associated with increased rates of infant death or permanent neurodevelopmental disability. Our understanding of the regulation of parturition remains inadequate. The scientific literature, largely derived from rodent animal models, suggests two major mechanisms regulating the timing of parturition: the withdrawal of the steroid hormone progesterone and a proinflammatory response by the immune system. However, available evidence strongly suggests that parturition in the human has significantly different regulators and mediators from those in most of the animal models. Our objectives are to critically review the data and concepts that have arisen from use of animal models for parturition and to rationalize the use of a new model. Many animal models have contributed to advances in our understanding of the regulation of parturition. However, we suggest that those animals dependent on progesterone withdrawal to initiate parturition clearly have a limitation to their translation to the human. In such models, a linear sequence of events (e.g., luteolysis, progesterone withdrawal, uterine activation, parturition) gives rise to the concept of a "trigger" mechanism. Conversely, we propose that human parturition may arise from the concomitant maturation of several systems in parallel. We have termed this novel concept "modular accumulation of physiological systems" (MAPS). We also emphasize the urgency to determine the precise role of the immune system in the process of parturition in situations other than intrauterine infection. Finally, we accentuate the need to develop a nonprimate animal model whose physiology is more relevant to human parturition. We suggest that the guinea pig displays several key physiological characteristics of gestation that more closely resemble human pregnancy than do currently favored animal models. We conclude that the application of novel concepts and new models are required to advance translational research in parturition.

Cytokine networks and the regulation of uterine function in pregnancy and parturition

Complex cytokine networks play an important role in a wide range of reproductive and pregnancy related processes. Here, we review the current knowledge concerning the impact of cytokines on uterine physiology and pathophysiology. Cytokines influence a range of uterine functions during the menstrual cycle, implantation, pregnancy and labour. The synergistic interactions between individual cytokines are intricate and dynamic, and modulated by pregnancy hormones. It is not surprising therefore, that perturbations to cytokine signalling are associated with adverse pregnancy outcomes, such as miscarriage, pre-eclampsia, preterm labour and foetal brain injury. Further insight into the complexity of cytokine networks will be required to develop novel therapeutic strategies for the treatment of cytokine imbalances in pregnancy.

Molecular cloning and initial characterization of African green monkey (Cercopithecus aethiops) corticotropin releasing factor receptor type 1 (CRF1) from COS-7 cells

We report the expression of endogenous CRF1 in COS-7 cells (African green monkey origin). Cloning of the coding region of CRF1 gene identified three alternatively spliced isoforms with nucleotide and predicted amino acid sequences corresponding to the membrane bound alpha and c and soluble e isoforms. DNA sequencing of the main isoform CRF1alpha showed homologies of 99%, 97% and 91% with the rhesus monkey, human and rodent genes, respectively; the deduced protein sequence differed in only one amino acid with rhesus monkey and human. Western blot analysis with antibodies against human CRF1 demonstrated immunoreactive proteins with MW of 37, 52, 70 and 80-85 in crude membrane or cytoplasm preparation; two additional species of 40 and 60 kDa were detected only in the cytoplasmic fraction. On immunocytochemistry CRF1 was localized to both the cell surface and intracellularly. The receptor was functional, e.g., addition of CRF to COS-7 cells inhibited cell proliferation and stimulated release of arachidonic acid; nevertheless, it was poorly coupled to cAMP production (its stimulation was minimal in native cells). In conclusion, COS cells that are routinely used for the study of transfected CRF receptors do express endogenous CRF1 mRNA with splicing behavior similar to that reported in human and rodent cells, and translated into functional CRF1 receptors.

Regulation of the endothelin/endothelin receptor system by interleukin-1{beta} in human myometrial cells

Proinflammatory cytokines produced at the fetomaternal interface, such as IL-1beta, have been implicated in preterm and term labor. The present study was performed to evaluate the influence of IL-1beta on the endothelin (ET)/ET receptor system in human myometrial cells. We report that myometrial cells under basal conditions not only respond to but also secrete ET-1, one of the main regulators of uterine contractions. Prolonged exposure of the cells to IL-1beta led to a decrease in prepro-ET-1 and ET-3 mRNA correlated with a decrease in immunoreactive ET-1 and ET-3 levels in the culture medium. Whereas ETA receptor expression at both protein and mRNA levels was not affected by IL-1beta treatment, we demonstrated an unexpected predominance of the ETB receptor subtype under this inflammatory condition. Whereas the physiological function of ETB remains unclear, we confirmed that only ETA receptors mediate ET-1-induced myometrial cell contractions under basal conditions. By contrast, prolonged exposure of the cells to IL-1beta abolished the contractile effect induced by ET-1. Such a regulation of IL-1beta on the ET release and the balance of ETA to ETB receptors leading to a loss of ET-1-induced myometrial cell contractions suggest that complex regulatory mechanisms take place to constraint the onset of infection-induced premature contractions.

Intraperitoneal infusion of proinflammatory cytokines does not cause activation of the rat uterus during late gestation

Increased concentrations of IL-1beta and TNF-alpha have been associated with parturition. However, the role of these cytokines is unknown. Before parturition, the uterus undergoes a process of activation, during which there are significant changes in expression of genes associated with increased uterine contractility, including the receptors for oxytocin (OT) and prostaglandin (PG)F(2alpha) (FP), PGH(2) synthase isoform 2 (PGHS2), the gap junction protein connexin-43 (Cx-43), and the inducible isoform of nitric oxide synthase (iNOS). To determine whether IL-1beta or TNF-alpha was part of the causal mechanism for increased uterine contractions, we placed osmotic pumps infusing IL-1beta or TNF-alpha into the peritoneal cavity of late pregnant rats (gestation day 19) and measured the effects on uterine contractility and on the uterine concentrations of mRNA for the contraction-associated genes 24 h later. Maternal serum concentrations of IL-1beta and TNF-alpha were increased significantly. By day 21, the control animals had significant increases (P < or = 0.05) in mRNA for OT, FP, PGHS2, and Cx-43, a decrease (P < or = 0.05) in iNOS, and an increase (P < or = 0.05) in uterine sensitivity and responsiveness to OT. Infusion of IL-1beta or TNF-alpha had no effect on uterine contractility or on expression of the activation-associated genes. We conclude that intraperitoneal infusion of IL-1beta or TNF-alpha resulting in significantly increased maternal serum cytokine levels does not cause uterine activation. The role of proinflammatory cytokines in the mechanism of parturition remains unclear.

Chorioamnionitis and labor

Chorioamnionitis is a puerperal infection that exists in histologic, clinical, and subclinical forms. This entity is believed to play a causative role in many cases of spontaneous preterm delivery. It also is associated with an increased risk of dysfunctional labor. This article focuses on the effects of chorioamnionitis on the progress of labor and the appropriate treatment of patients with clinical chorioamnionitis. The epidemiology, pathogenesis, and associated maternal and neonatal outcomes also are reviewed.

Uterine motor alterations and estrous cycle disturbances associated with colonic inflammation in the rat

The impact of colitis on uterine contractility and estrous cycle was investigated after intracolonic administration of 2,4,6-trinitrobenzenesulfonic acid (TNBS) in rats. Colitis severity was assessed by macroscopic damage scoring (MDS) 4 days after TNBS, and myeloperoxidase (MPO) activity was measured in both colon and uterus of control and colitic rats. Estrous cycle stages were determined by vaginal smears and histology, and uterine contractility was assessed in vitro on longitudinal and circular strips. In control rats, uterine MPO activity varied markedly during the cycle and peaked around estrus. In rats with moderate colitis [MDS < 5, 3.1 ± 0.2 (mean ± SE)], uterine MPO decreased by 61% compared with estrus control, without disruption of the cycle. Frequency of spontaneous contractions was reduced by 32% in circular muscle. Contractile responses to KCl and carbachol were not affected, whereas maximal response to oxytocin decreased by 47% in the longitudinal muscle. In rats with severe colitis (MDS > 5, 6.0 ± 0.2), uterine MPO was reduced by 96% and estrous cycle was disrupted. Spontaneous contractility was impaired in circular strips, and a 39% decrease in the contraction frequency occurred in the longitudinal strips. Circular strips did not contract to KCl or carbachol; however, longitudinal strips had maximal responses to KCl, carbachol, and oxytocin reduced by 36%, 27%, and 46%, respectively. Estrogen replacement protected the uterine responses to carbachol in colitic rats, whereas oxytocin responses remained depressed. These data indicate that colonic inflammation can influence both spontaneous and evoked uterine contractility, in relation to estrous cycle disturbances, impaired estradiol production, and functional alterations of myometrial cells.

Interleukin-1beta induces calcium transients and enhances basal and store operated calcium entry in human myometrial smooth muscle

We have previously reported increased protein expression of sarcoplasmic reticulum calcium ATPase (SERCA) 2b in myometrium from women in labor at term, but the stimulus for this change is unknown. Proinflammatory cytokines have been implicated in the cascade of events leading to preterm and term labor, and we hypothesize that interleukin (IL)-1beta may induce changes in key calcium homeostatic mechanisms and, in turn, augment myometrial contractility before labor. The aim of the present study was to investigate the long-term effects of IL-1beta on SERCA 2b protein expression, calcium mobilization from intracellular stores, and store-operated calcium entry. Myometrial biopsies were obtained, with consent, from women undergoing elective cesarean section at term. Primary-cultured human myometrial smooth muscle (HMSM) cells were exposed to IL-1beta (10 ng/ml) for 24 h or to culture medium alone (control). Cells were subsequently used in Western blot studies or loaded with fura-2 to assess calcium dynamics using fluorescent digital imaging. The present study clearly demonstrated that IL-1beta significantly increased SERCA 2b protein expression in HMSM cells. Cyclopiazonic acid-induced calcium transients were also augmented, predominantly by activation of lanthanum-sensitive, store-operated calcium entry. HMSM cell excitability was enhanced, as evidenced by increased basal calcium entry and the initiation of spontaneous calcium transients in 37% of IL-1beta-treated cells. IL-1beta modulation of calcium mobilization may be an important mechanism in the cascade of events preparing the pregnant uterus for labor.

Transcriptional regulation of oxytocin receptor by interleukin-1beta and interleukin-6

The up-regulation of oxytocin (OT) receptors in late pregnancy results principally from increased synthesis of messenger RNA. The 5'-flanking region of the human OT receptor gene contains several putative binding sites for nuclear factor-interleukin-6 (NF-IL6), also known as CAAT/enhancer binding protein-beta. This trans-acting factor modulates the expression of genes involved in acute inflammatory responses. Proinflammatory cytokines, such as IL-1beta or IL-6, have been implicated as mediators in both preterm and term labor, particularly in association with intrauterine infection. We hypothesized that IL-1beta and IL-6 induce OT receptor gene expression in human myometrial cells, and this is mediated by NF-IL6 and cognate response elements in the 5'-flanking region of the OT receptor gene. Contrary to the hypothesis, both IL-1beta and IL-6 treatment resulted in a significant decrease in OT receptor messenger RNA measured by ribonuclease protection analysis. Using electrophoretic mobility shift assay, we have shown that NF-IL6 is present at low levels that appear to be increased after treatment with either IL-1beta or IL-6. Using deletion analysis and functional transfection studies in HeLa cells, we demonstrated that the OT receptor gene promoter displays constitutive basal activity and is negatively regulated by both IL-1beta and IL-6. This suppressive ability of IL-1beta and IL-6 depends on the -1203/-722 region of the OT receptor promoter, which contains binding sites for NF-IL6, acute phase response element, and NF-kappaB. Our findings suggest a role for IL-1beta and IL-6 in the transcriptional regulation of the human OT receptor gene.