Expression of myometrial activation and stimulation genes in a mouse model of preterm labor: myometrial activation, stimulation, and preterm labor

Preventing Preterm Birth: Exploring Innovative Solutions

This review examines the complexities of preterm birth (PTB), emphasizes the pivotal role of inflammation in the pathogenesis of preterm labor, and assesses current available interventions. Antibiotics, progesterone analogs, mechanical approaches, nonsteroidal anti-inflammatory drugs, and nutritional supplementation demonstrate a limited efficacy. Tocolytic agents, targeting uterine activity and contractility, inadequately prevent PTB by neglecting to act on uteroplacental inflammation. Emerging therapies targeting toll-like receptors, chemokines, and interleukin receptors exhibit promise in mitigating inflammation and preventing PTB.

Preterm Labor and Preterm-PROM at a Lower Gestational Age Are Associated with a Longer Latency-to-Delivery Even in Patients with the Same Intensity of Intra-Amniotic Inflammation: "Carroll-Model" Revisited

A previous study by Carroll et al. demonstrated that the time from preterm-PROM to delivery was longer at a lower gestational age (GA) when the membranes rupture, although the presence or absence of intra-amniotic inflammation (IAI) was not examined in that study. However, patients with either preterm labor (PTL) or preterm-PROM at a lower GA had more frequent IAI, which was associated with a shorter amniocentesis-to-delivery (ATD) interval as compared with inflammation-free amniotic fluid (AF). Up to now, there is no information about whether PTL and preterm-PROM at a lower GA are associated with a shorter or longer latency to delivery in cases with the same intensity of IAI. The objective of the study is to examine this issue. AF MMP-8 was measured in 476 singleton early preterm-gestations (21.5 < GA at amniocentesis < 34 wks) with PTL (n = 253) and preterm-PROM (n = 223). Patients were divided into three groups according to GA at amniocentesis (i.e., group-1: <26 wks; group-2: 26−30 wks; group-3: 30−34 wks). IAI was defined as an elevated AF MMP-8 (≥23 ng/mL), and IAI was classified into either mild IAI (AF MMP-8: 23−350 ng/mL) or severe IAI (AF MMP-8 ≥ 350 ng/mL). ATD interval was examined according to GA at amniocentesis in the context of the same intensity of IAI (i.e., inflammation-free AF, mild IAI, and severe IAI) among pregnant women with either PTL or preterm-PROM. IAI was more frequent at a lower GA in cases with PTL (group-1 vs. group-2 vs. group-3; 59.5% vs. 47.4% vs. 25.1%; X2test, p = 0.000034 and linear by linear association [LBLA], p = 0.000008) and in those with preterm-PROM (group-1 vs. group-2 vs. group-3; 69.2% vs. 50.0% vs. 32.0%; X2test, p = 0.000104, and LBLA, p = 0.000019). Of note, cases without IAI at a lower GA had a longer ATD interval in both PTL (Spearman’s rank correlation test, γ = −0.360, p = 0.000003) and preterm-PROM (γ = −0.570, p = 0.000001) groups. Moreover, the lower the GA, the longer the ATD interval, even among patients with mild and severe IAI in both PTL (Spearman’s rank correlation test; mild IAI, γ = −0.290, p = 0.039; severe IAI, γ = −0.299, p = 0.048) and preterm-PROM (mild IAI, γ = −0.565, p = 0.000013; severe IAI, γ = −0.363, p = 0.015) groups. In conclusion, PTL and preterm-PROM at a lower GA are associated with a longer latency to delivery, even in patients with the same intensity of IAI. This finding suggests that a more intense IAI may be needed for spontaneous preterm birth at a lower GA.

Clarithromycin prevents preterm birth and neonatal mortality by dampening alarmin-induced maternal–fetal inflammation in mice

Background

One of every four preterm neonates is born to a woman with sterile intra-amniotic inflammation (inflammatory process induced by alarmins); yet, this clinical condition still lacks treatment. Herein, we utilized an established murine model of sterile intra-amniotic inflammation induced by the alarmin high-mobility group box-1 (HMGB1) to evaluate whether treatment with clarithromycin prevents preterm birth and adverse neonatal outcomes by dampening maternal and fetal inflammatory responses.

Methods

Pregnant mice were intra-amniotically injected with HMGB1 under ultrasound guidance and treated with clarithromycin or vehicle control, and pregnancy and neonatal outcomes were recorded (n = 15 dams each). Additionally, amniotic fluid, placenta, uterine decidua, cervix, and fetal tissues were collected prior to preterm birth for determination of the inflammatory status (n = 7–8 dams each).

Results

Clarithromycin extended the gestational length, reduced the rate of preterm birth, and improved neonatal mortality induced by HMGB1. Clarithromycin prevented preterm birth by interfering with the common cascade of parturition as evidenced by dysregulated expression of contractility-associated proteins and inflammatory mediators in the intra-uterine tissues. Notably, clarithromycin improved neonatal survival by dampening inflammation in the placenta as well as in the fetal lung, intestine, liver, and spleen.

Conclusions

Clarithromycin prevents preterm birth and improves neonatal survival in an animal model of sterile intra-amniotic inflammation, demonstrating the potential utility of this macrolide for treating women with this clinical condition, which currently lacks a therapeutic intervention.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-022-04764-2.

A single-cell atlas of the myometrium in human parturition

Parturition is a well-orchestrated process characterized by increased uterine contractility, cervical ripening, and activation of the chorioamniotic membranes; yet, the transition from a quiescent to a contractile myometrium heralds the onset of labor. However, the cellular underpinnings of human parturition in the uterine tissues are still poorly understood. Herein, we performed a comprehensive study of the human myometrium during spontaneous term labor using single-cell RNA sequencing (scRNA-Seq). First, we established a single-cell atlas of the human myometrium and unraveled the cell type–specific transcriptomic activity modulated during labor. Major cell types included distinct subsets of smooth muscle cells, monocytes/macrophages, stromal cells, and endothelial cells, all of which communicated and participated in immune (e.g., inflammation) and nonimmune (e.g., contraction) processes associated with labor. Furthermore, integrating scRNA-Seq and microarray data with deconvolution of bulk gene expression highlighted the contribution of smooth muscle cells to labor-associated contractility and inflammatory processes. Last, myometrium-derived single-cell signatures can be quantified in the maternal whole-blood transcriptome throughout pregnancy and are enriched in women in labor, providing a potential means of noninvasively monitoring pregnancy and its complications. Together, our findings provide insights into the contributions of specific myometrial cell types to the biological processes that take place during term parturition.

Inflammatory Amplification: A Central Tenet of Uterine Transition for Labor

In preparation for delivery, the uterus transitions from actively maintaining quiescence during pregnancy to an active parturient state. This transition occurs as a result of the accumulation of pro-inflammatory signals which are amplified by positive feedback interactions involving paracrine and autocrine signaling at the level of each intrauterine cell and tissue. The amplification events occur in parallel until they reach a certain threshold, ‘tipping the scale’ and contributing to processes of uterine activation and functional progesterone withdrawal. The described signaling interactions all occur upstream from the presentation of clinical labor symptoms. In this review, we will: 1) describe the different physiological processes involved in uterine transition for each intrauterine tissue; 2) compare and contrast the current models of labor initiation; 3) introduce innovative models for measuring paracrine inflammatory interactions; and 4) discuss the therapeutic value in identifying and targeting key players in this crucial event for preterm birth.

In vitro selenium supplementation suppresses key mediators involved in myometrial activation and rupture of fetal membranes

Spontaneous preterm birth, which can affect up to 20% of all pregnancies, is the greatest contributor to perinatal morbidity and mortality. Infection is the leading pathological cause of spontaneous preterm birth. Infection activates the maternal immune system, resulting in the upregulation of pro-inflammatory and pro-labor mediators that activate myometrial contractions and rupture of fetal membranes. Anti-inflammatory agents therefore have the potential for the prevention of spontaneous preterm birth. Selenium, an essential micronutrient, has been shown to be a potent anti-inflammatory regulator. Notably, clinical and epidemiological studies have suggested a link between selenium and preterm birth. Thus, the aim of this study was to assess the effect of selenite (an inorganic form of selenium) on the expression of pro-inflammatory and pro-labor mediators in human gestational tissues. Human fetal membranes and myometrium were pre-incubated with or without selenite before incubation with the bacterial product lipopolysaccharide (LPS) to stimulate inflammation associated with preterm birth. Selenite blocked LPS-induced expression of pro-inflammatory cytokines and chemokines and enzymes involved in remodelling of myometrium and degradation of fetal membranes. Of note, selenite also suppressed myometrial activation induced by inflammation as evidenced by a decrease in LPS-induced prostaglandin signalling and myometrial cell contractility. These effects of selenite were mediated by the MAPK protein ERK as selenite blunted LPS induced activation of ERK. In conclusion, selenite suppresses key mediators involved in inflammation induced activation of mediators involved in active labor in human fetal membranes and myometrium. These findings support recent clinical studies demonstrating selenium supplementation is associated with decreased incidence of spontaneous preterm birth.

Do uterine PTGS2, PGFS, and PTGFR expression play a role in canine uterine inertia?

The aetiology of primary uterine inertia (PUI), which is the most common cause of canine dystocia, is still not elucidated. Prostaglandins (PGs) play a crucial role in parturition. We hypothesized that the expression of prostaglandin endoperoxidase synthase 2 (PTGS2), PGF2α synthase (PGFS), and corresponding receptor (PTGFR) is altered in PUI. We investigated PTGS2, PGFS, and PTGFR mRNA expression, and PTGS2 and PGFS protein expression in interplacental (IP) and uteroplacental sites (UP) in bitches with PUI, obstructive dystocia (OD), and prepartum (PC). PTGS2, PGFS, and PTGFR mRNA expression did not differ significantly between PUI and OD (IP/UP). PTGFR ratio in UP was higher in PC than in OD (p = 0.014). PTGS2 immunopositivity was noted in foetal trophoblasts, luminal and superficial glandular epithelial cells, smooth muscle cells of both myometrial layers, and weakly and sporadically in deep uterine glands. PGFS was localized in luminal epithelial cells and in the epithelium of superficial uterine glands. PTGS2 and PGFS staining was similar between PUI and OD, while PGFS protein expression differed between OD and PC (p = 0.0215). For PTGS2, the longitudinal myometrial layer of IP stained significantly stronger than the circular layer, independent of groups. These results do not support a role for PTGS2, PGFS, and PTGFR in PUI. Reduced PGFS expression in IP during parturition compared with PC and the overall lack of placental PGFS expression confirm that PGFS is not the main source of prepartal PGF2alpha increase. The difference in PTGS2 expression between IP myometrial layers warrants further investigation into its physiological relevance.

Anisotropic Mechanical Properties of the Human Uterus Measured by Spherical Indentation

The mechanical function of the uterus is critical for a successful pregnancy. During gestation, uterine tissue grows and stretches to many times its size to accommodate the growing fetus, and it is hypothesized the magnitude of uterine tissue stretch triggers the onset of contractions. To establish rigorous mechanical testing protocols for the human uterus in hopes of predicting tissue stretch during pregnancy, this study measures the anisotropic mechanical properties of the human uterus using optical coherence tomography (OCT), instrumented spherical indentation, and video extensometry. In this work, we perform spherical indentation and digital image correlation to obtain the tissue's force and deformation response to a ramp-hold loading regimen. We translate previously reported fiber architecture, measured via optical coherence tomography, into a constitutive fiber composite material model to describe the equilibrium material behavior during indentation. We use an inverse finite element method integrated with a genetic algorithm (GA) to fit the material model to our experimental data. We report the mechanical properties of human uterine specimens taken across different anatomical locations and layers from one non-pregnant (NP) and one pregnant (PG) patient; both patients had pathological uterine tissue. Compared to NP uterine tissue, PG tissue has a more dispersed fiber distribution and equivalent stiffness material parameters. In both PG and NP uterine tissue, the mechanical properties differ significantly between anatomical locations.

Contraction-associated proteins expression by human uterine smooth muscle cells depends on maternal serum and progranulin associated with gestational weight gain

Pregnant women with obesity are at increased risk of parturition dysfunction; however, the biological mechanism has remained unknown. We hypothesized that molecules circulating in the serum of pregnant women with obesity may induce the aberrant expression of contraction-associated proteins (CAPs), leading to insufficient uterine contractions. This study aimed to investigate the effects of maternal serum on CAPs expression by human uterine smooth muscle cells (UtSMCs) and elucidate the influence of maternal obesity. Blood samples were collected from singleton pregnant women at 36-41 weeks of gestation before the onset of labor. UtSMCs were incubated in the serum, and the mRNA expressions of PTGFR, OXTR, GJA1, and PTGS2 were examined by RT-PCR. Progranulin (PGRN) is a circulating glycoprotein associated with insulin resistance characterized by the accumulation of visceral fat. The serum PGRN levels of the samples were measured by ELISA. After incubated with PGRN (100-1,000 ng/mL), mRNA expression of PTGFR, OXTR, and GJA1 and protein expression of CX43 were examined by RT-PCR and western blotting, respectively. The mRNA expressions of PTGFR, OXTR, and GJA1 showed significantly negative correlations with gestational weight gain (GWG). Serum PGRN levels showed a significantly positive correlation with GWG. High levels of PGRN suppressed the mRNA expression of GJA1 and the protein expression of CX43. The change in maternal serum induced by GWG suppressed the CAPs expression by UtSMCs. PGRN is one of the factors in the serum responsible for inhibiting the expression of CX43.

Cooperative effects of sequential PGF2α and IL-1β on IL-6 and COX-2 expression in human myometrial cells†

The change from the state of pregnancy to the state of parturition, which we call uterine transitioning, requires the actions of inflammatory mediators and results in an activated uterus capable of performing the physiology of labor. Interleukin (IL)-1β and prostaglandin (PG)F2α are two key mediators implicated in preparing the uterus for labor by regulating the expression of uterine activation proteins (UAPs) and proinflammatory cytokines and chemokines. To investigate this process, primary human myometrial smooth muscle cells (HMSMC) isolated from the lower segment of women undergoing elective cesarean sections at term (not in labor) were used to test the inflammatory cytokine and UAP outputs induced by PGF2α and IL-1β alone or in sequential combinations. PGF2α and IL-1β regulate mRNA abundance of the PGF2α receptor FP, the IL-1 receptor system, interleukin 6, and other UAPs (OXTR, COX2), driving positive feedback interactions to further amplify their own proinflammatory effects. Sequential stimulation of HMSMC by PGF2α and IL-1β in either order results in amplified upregulation of IL-6 and COX-2 mRNA and protein, compared to their effects individually. These profound increases were unique to myometrium and not observed with stimulation of human fetal membrane explants. These results suggest that PGF2α and IL-1β act cooperatively upstream in the birth cascade to maximize amplification of IL-6 and COX-2, to build inflammatory load and thereby promote uterine transition. Targeting PGF2α or IL-1β, their actions, or intermediates (e.g. IL-6) would be an effective therapeutic intervention for preterm birth prevention or delay.

Does early weaning shape future endocrine and metabolic disorders? Lessons from animal models

Obesity and its complications occur at alarming rates worldwide. Epidemiological data have associated perinatal conditions, such as malnutrition, with the development of some disorders, such as obesity, dyslipidemia, diabetes, and cardiovascular diseases, in childhood and adulthood. Exclusive breastfeeding has been associated with protection against long-term chronic diseases. However, in humans, the interruption of breastfeeding before the recommended period of 6 months is a common practice and can increase the risk of several metabolic disturbances. Nutritional and environmental changes within a critical window of development, such as pregnancy and breastfeeding, can induce permanent changes in metabolism through epigenetic mechanisms, leading to diseases later in life via a phenomenon known as programming or developmental plasticity. However, little is known regarding the underlying mechanisms by which precocious weaning can result in adipose tissue dysfunction and endocrine profile alterations. Here, the authors give a comprehensive report of the different animal models of early weaning and programming that can result in the development of metabolic syndrome. In rats, for example, pharmacological and nonpharmacological early weaning models are associated with the development of overweight and visceral fat accumulation, leptin and insulin resistance, and neuroendocrine and hepatic changes in adult progeny. Sex-related differences seem to influence this phenotype. Therefore, precocious weaning seems to be obesogenic for offspring. A better understanding of this condition seems essential to reducing the risk for diseases. Additionally, this knowledge can generate new insights into therapeutic strategies for obesity management, improving health outcomes.

Maternal and fetal intrauterine tissue crosstalk promotes proinflammatory amplification and uterine transition†

Birth is a complex biological event requiring genetic, cellular, and physiological changes to the uterus, resulting in a uterus activated for completing the physiological processes of labor. We define the change from the state of pregnancy to the state of parturition as uterine transitioning, which requires the actions of inflammatory mediators and localized paracrine interactions between intrauterine tissues. Few studies have examined the in vitro interactions between fetal and maternal gestational tissues within this proinflammatory environment. Thus, we designed a co-culture model to address this gap, incorporating primary term human myometrium smooth muscle cells (HMSMCs) with human fetal membrane (hFM) explants to study interactions between the tissues. We hypothesized that crosstalk between tissues at term promotes proinflammatory expression and uterine transitioning for parturition. Outputs of 40 cytokines and chemokines encompassing a variety of proinflammatory roles were measured; all but one increased significantly with co-culture. Eighteen of the 39 cytokines increased to a higher abundance than the sum of the effect of each tissue cultured separately. In addition, COX2 and IL6 but not FP and OXTR mRNA abundance significantly increased in both HMSMCs and hFM in response to co-culture. These data suggest that synergistic proinflammatory upregulation within intrauterine tissues is involved with uterine transitioning.

Pimpinella anisum extract attenuates spontaneous and agonist-induced uterine contraction in term-pregnant rats

ETHNOPHARMACOLOGY RELEVANCE

Pimpinella anisum is a well-known traditional medicinal herb which has been used in folk medicine as an antiulcer, anticancer, antibacterial and as a muscle relaxant.

AIM OF THE STUDY

This study was performed to explore the modulatory effects of Pimpinella anisum on term-pregnant rat uterine contractility and to investigate its possible underlying mechanisms.

MATERIAL AND METHODS

Intact uterine strips without endometrial layer were isolated from female term-pregnant Wistar rats (22 days of gestation) and mounted in a tissue bath apparatus for in vitro isometric force recording. The effects of different concentrations of Pimpinella anisum extract (PAE) (1, 3, 5, and 7 mg/mL) were examined on uterine contractions generated spontaneously or induced with oxytocin (5 nmol/L), Bay K8644 (1 μmol/L), and carbachol (10 μmol/L). In some experiments, PAE was applied on depolarized myometrium in the presence of high-KCl solution (60 mmol/L). The effect on Ca²⁺ release was also examined.

RESULTS

Application of PAE significantly reduced uterine contractions generated spontaneously or induced with oxytocin, Bay K8644, and carbachol in a concentration-dependent manner (n = 7; P < 0.01). In depolarized myometrium, PAE significantly reduced the tonic force induced by high-KCl solution (n = 7; P < 0.01). PAE prevented oxytocin-induced transient contraction in the entire absence of external calcium (n = 7; P < 0.01).

CONCLUSION

The present findings demonstrate the potentials of PAE to relax pregnant uterine contractions possibly by blocking Ca²⁺ entry via L-type calcium channels and inhibiting Ca²⁺ release from the internal store. The tocolytic effects of PAE may be a potential adjuvant against strong premature uterine contractions which threaten early pregnancy although clinical studies are required.

Immunobiology of Cervix Ripening

The cervix is the essential gatekeeper for birth. Incomplete cervix remodeling contributes to problems with delivery at or post-term while preterm birth is a major factor in perinatal morbidity and mortality in newborns. Lack of cervix biopsies from women during the period preceding term or preterm birth have led to use of rodent models to advanced understanding of the mechanism for prepartum cervix remodeling. The critical transition from a soft cervix to a compliant prepartum lower uterine segment has only recently been recognized to occur in various mammalian species when progesterone in circulation is at or near the peak of pregnancy in preparation for birth. In rodents, characterization of ripening resembles an inflammatory process with a temporal coincidence of decreased density of cell nuclei, decline in cross-linked extracellular collagen, and increased presence of macrophages in the cervix. Although a role for inflammation in parturition and cervix remodeling is not a new concept, a comprehensive examination of literature in this review reveals that many conclusions are drawn from comparisons before and after ripening has occurred, not during the process. The present review focuses on essential phenotypes and functions of resident myeloid and possibly other immune cells to bridge the gap with evidence that specific biomarkers may assess the progress of ripening both at term and with preterm birth. Moreover, use of endpoints to determine the effectiveness of various therapeutic approaches to forestall remodeling and reduce risks for preterm birth, or facilitate ripening to promote parturition will improve the postpartum well-being of mothers and newborns.

Mouse models of preterm birth: suggested assessment and reporting guidelines

Preterm birth affects approximately 1 out of every 10 births in the United States, leading to high rates of mortality and long-term negative health consequences. To investigate the mechanisms leading to preterm birth so as to develop prevention strategies, researchers have developed numerous mouse models of preterm birth. However, the lack of standard definitions for preterm birth in mice limits our field's ability to compare models and make inferences about preterm birth in humans. In this review, we discuss numerous mouse preterm birth models, propose guidelines for experiments and reporting, and suggest markers that can be used to assess whether pups are premature or mature. We argue that adoption of these recommendations will enhance the utility of mice as models for preterm birth.

Toll-like receptor 4 contributes to uterine activation by upregulating pro-inflammatory cytokine and CAP expression via the NF-κB/P38MAPK signaling pathway during pregnancy

Evidence indicates that inflammatory response is significant during the physiological process of human parturition; however, the specific signaling pathway that triggers inflammation is undefined. Toll-like receptors (TLRs) are key upstream gatekeepers that control inflammatory activation before preterm delivery. Our previous study showed that TLR4 expression was significantly increased in human pregnancy tissue during preterm and term labor. Therefore, we explore whether TLR4 plays a role in term labor by initiating inflammatory responses, therefore promoting uterine activation. The results showed that expression of TLR4, interleukin-1β (IL-1β), IL-6, tumor necrosis factor-α (TNF-α), CC chemokine ligand 2 (CCL-2), and uterine contraction-associated proteins (CAPs) was upregulated in the human and mice term labor (TL) group compared with the not-in-labor (TNL) group, and the TLR4 level positively correlated with CAP expression. In pregnant TLR4-knockout (TLR4^-/- ) mice, gestation length was extended by 8 hr compared with the wild-type group, and the expression of IL-1β, IL-6, TNF-α, CCL-2, and CAPs was decreased in TLR4^-/- mice. Furthermore, nuclear factor-κB (NF-κB) and P38MAPK activation is involved in the initiation of labor but was inhibited in TLR4^-/- mice. In uterine smooth muscle cells, the expression of inflammatory cytokines and CAPs decreased when the NF-κB and P38MAPK pathway was inhibited. Our data suggest that TLR4 is a key factor in regulating the inflammatory response that drives uterine activation and delivery initiation via activating the NF-κB/P38MAPK pathway.

Effector and Activated T Cells Induce Preterm Labor and Birth That Is Prevented by Treatment with Progesterone

Preterm labor commonly precedes preterm birth, the leading cause of perinatal morbidity and mortality worldwide. Most research has focused on establishing a causal link between innate immune activation and pathological inflammation leading to preterm labor and birth. However, the role of maternal effector/activated T cells in the pathogenesis of preterm labor/birth is poorly understood. In this study, we first demonstrated that effector memory and activated maternal T cells expressing granzyme B and perforin are enriched at the maternal-fetal interface (decidua) of women with spontaneous preterm labor. Next, using a murine model, we reported that prior to inducing preterm birth, in vivo T cell activation caused maternal hypothermia, bradycardia, systemic inflammation, cervical dilation, intra-amniotic inflammation, and fetal growth restriction, all of which are clinical signs associated with preterm labor. In vivo T cell activation also induced B cell cytokine responses, a proinflammatory macrophage polarization, and other inflammatory responses at the maternal-fetal interface and myometrium in the absence of an increased influx of neutrophils. Finally, we showed that treatment with progesterone can serve as a strategy to prevent preterm labor/birth and adverse neonatal outcomes by attenuating the proinflammatory responses at the maternal-fetal interface and cervix induced by T cell activation. Collectively, these findings provide mechanistic evidence showing that effector and activated T cells cause pathological inflammation at the maternal-fetal interface, in the mother, and in the fetus, inducing preterm labor and birth and adverse neonatal outcomes. Such adverse effects can be prevented by treatment with progesterone, a clinically approved strategy.

Oxytocin can regulate myometrial smooth muscle excitability by inhibiting the Na+ -activated K+ channel, Slo2.1

KEY POINTS

At the end of pregnancy, the uterus transitions from a quiescent state to a highly contractile state. This transition requires that the uterine (myometrial) smooth muscle cells increase their excitability, although how this occurs is not fully understood. We identified SLO2.1, a potassium channel previously unknown in uterine smooth muscle, as a potential significant contributor to the electrical excitability of myometrial smooth muscle cells. We found that activity of the SLO2.1 channel is negatively regulated by oxytocin via Gαq-protein-coupled receptor activation of protein kinase C. This results in depolarization of the uterine smooth muscle cells and calcium entry, which may contribute to uterine contraction. These findings provide novel insights into a previously unknown mechanism by which oxytocin may act to modulate myometrial smooth muscle cell excitability. Our findings also reveal a new potential pharmacological target for modulating uterine excitability.

ABSTRACT

During pregnancy, the uterus transitions from a quiescent state to a more excitable contractile state. This is considered to be at least partly a result of changes in the myometrial smooth muscle cell (MSMC) resting membrane potential. However, the ion channels controlling the myometrial resting membrane potential and the mechanism of transition to a more excitable state have not been fully clarified. In the present study, we show that the sodium-activated, high-conductance, potassium leak channel, SLO2.1, is expressed and active at the resting membrane potential in MSMCs. Additionally, we report that SLO2.1 is inhibited by oxytocin binding to the oxytocin receptor. Inhibition of SLO2.1 leads to membrane depolarization and activation of voltage-dependent calcium channels, resulting in calcium influx. The results of the present study reveal that oxytocin may modulate MSMC electrical activity by inhibiting SLO2.1 potassium channels.

Effect of molecular hydrogen on uterine inflammation during preterm labour

Intrauterine inflammation causes preterm birth and is associated with complications in preterm neonates. Thus, strategies aimed at suppressing inflammation are expected to be effective for reducing the risk of preterm birth and associated complications. Our previous studies demonstrated that molecular hydrogen (H₂), an anti-inflammatory agent, prevented inflammation-induced impairment in foetal brain and lung tissues in lipopolysaccharide (LPS)-induced rodent models. However, it remains unclear whether H₂ is capable of inhibiting preterm labour. The aim of the current study was therefore to investigate the effect of H₂ on inflammation-induced preterm labour. Pregnant ICR (CD-1) mice were divided into three groups: Control, LPS and H₂ water (HW) + LPS. In the control and LPS groups, vehicle and LPS, respectively, were intraperitoneally injected on embryonic day 15.5. In the HW + LPS group, HW was administered 24 h prior to LPS injection. The time from LPS administration to parturition was compared between the LPS and HW + LPS groups. Maternal uterus was collected 6 h after LPS injection and the transcript levels of pro-inflammatory cytokines, contractile-associated proteins (CAPs), matrix metalloproteinase-3 (Mmp3) and endothelin-1 (Et1) were assessed by reverse transcription-quantitative polymerase chain reaction. The protein levels of cyclooxygenase-2 (Cox2) were also evaluated by immunohistochemistry. The time from LPS administration to parturition in the HW + LPS group was significantly increased compared with that in the LPS group (33.5±3.4 vs. 18.3±8.8 h, respectively, P=0.020). H₂ administration also resulted in significantly higher progesterone levels compared with LPS treatment alone (P=0.002). The transcript levels of pro-inflammatory cytokines, CAPs, Mmp3 and Et1 in the uteri of the LPS group were significantly higher than those in the control group (all P<0.05). In turn, all these levels with the exception of interleukin-8 and Mmp3 were significantly lower in the HW + LPS group compared with those in the LPS group (all P<0.05). The protein levels of Cox2 in the LPS group were also significantly increased compared with those in the control (P<0.001) and HW + LPS (P=0.003) groups. These results suggest that inflammation-induced changes in the uterus may be ameliorated through maternal H₂ administration. Preventive H₂ administration may therefore represent an effective strategy for the suppression of inflammation during preterm labour.

Proteomics study reveals that the dysregulation of focal adhesion and ribosome contribute to early pregnancy loss

Purpose

Early pregnancy loss (EPL) affects 50–70% pregnant women in first trimester. The precise molecular mechanisms underlying EPL are far from being fully understood. Therefore, we aim to identify the molecular signaling pathways relating to EPL.

Experimental design

We performed proteomics and bioinformatics analysis of the placental villi in women who have undergone EPL and in normal pregnant women. The proteomics data were validated by Western blot analysis.

Results

We identified a total of 5952 proteins in placental villi, of which 588 proteins were differentially expressed in the EPL women. Bioinformatics analysis revealed that these differentially expressed proteins participated in a variety of signaling pathways, including the focal adhesion pathway and ribosome pathway. Moreover, results of the Western blot confirmed that Desmin, Lamin A/C, MMP‐9, and histone H4 were upregulated in EPL and the Lamin C/ Lamin A ratio decreased obviously in EPL. These proteins could be associated with the pathophysiology of EPL. The data have been deposited to the ProteomeXchange with identifier PXD002391.

Conclusion and clinical relevance

Our study demonstrated that the focal adhesion pathway and ribosome pathway are involved in EPL, and these findings might contribute to unveil the pathophysiology of EPL.

Characterization of Contractile Activity and Intracellular Ca2+ Signalling in Mouse Myometrium

OBJECTIVE

To characterize the contractile responses of mouse myometrium, the associated calcium (Ca2+) changes and the role of the sarcoplasmic reticulum (SR), and to better understand excitation contraction coupling in this tissue.

METHODS

Strips of longitudinal myometrium were used, and Ca2+ was measured after loading with Indo-1.

RESULTS

Intracellular Ca2+ transients, produced by Ca2+ entry, preceded phasic spontaneous contractions. Depolarization with high potassium concentration significantly increased the amplitude of the contractions and transformed the pattern of activity from phasic to tonic, with accompanying changes in intracellular Ca2+ concentration ([Ca2+]i). Oxytocin significantly stimulated contractile activity and [Ca2+]i above the level occurring spontaneously. Thus all forms of contractile activity were closely correlated with Ca2+. When the SR was emptied using a blocker of the SR calcium-adenosinetriphosphatase, cyclopiazonic acid, spontaneous Ca2+ and force transients increased greatly in frequency and amplitude. Ryanodine, a blocker of Ca(2+)-induced Ca2+ release (CICR), did not impair activity. In the absence of external Ca2+, oxytocin was able to release Ca2+ from the SR through IP3 but produced only a small increase in force, demonstrating a requirement for Ca2+ entry as part of the mechanism of agonist action.

CONCLUSION

Mouse myometrium, (1) produces contractile activity reflecting changes in [Ca2+]i irrespective of the stimulus, (2) has a significant SR Ca2+ content releasable by agonists but not CICR, (3) has an SR acting to inhibit spontaneous activity, and (4) behaves qualitatively similarly to human and rat myometrium in major aspects of excitation contraction coupling and is therefore a useful model tissue.

Modeling hormonal and inflammatory contributions to preterm and term labor using uterine temporal transcriptomics

BACKGROUND

Preterm birth is now recognized as the primary cause of infant mortality worldwide. Interplay between hormonal and inflammatory signaling in the uterus modulates the onset of contractions; however, the relative contribution of each remains unclear. In this study we aimed to characterize temporal transcriptome changes in the uterus preceding term labor and preterm labor (PTL) induced by progesterone withdrawal or inflammation in the mouse and compare these findings with human data.

METHODS

Myometrium was collected at multiple time points during gestation and labor from three murine models of parturition: (1) term gestation; (2) PTL induced by RU486; and (3) PTL induced by lipopolysaccharide (LPS). RNA was extracted and cDNA libraries were prepared and sequenced using the Illumina HiSeq 2000 system. Resulting RNA-Seq data were analyzed using multivariate modeling approaches as well as pathway and causal network analyses and compared against human myometrial transcriptome data.

RESULTS

We identified a core set of temporal myometrial gene changes associated with term labor and PTL in the mouse induced by either inflammation or progesterone withdrawal. Progesterone withdrawal initiated labor without inflammatory gene activation, yet LPS activation of uterine inflammation was sufficient to override the repressive effects of progesterone and induce a laboring phenotype. Comparison of human and mouse uterine transcriptomic datasets revealed that human labor more closely resembles inflammation-induced PTL in the mouse.

CONCLUSIONS

Labor in the mouse can be achieved through inflammatory gene activation yet these changes are not a requisite for labor itself. Human labor more closely resembles LPS-induced PTL in the mouse, supporting an essential role for inflammatory mediators in human "functional progesterone withdrawal." This improved understanding of inflammatory and progesterone influence on the uterine transcriptome has important implications for the development of PTL prevention strategies.

Molecular evidence of functional progesterone withdrawal in human myometrium

Progesterone suppresses uterine contractility acting through its receptors (PRA/B). The mechanism by which human labour is initiated in the presence of elevated circulating progesterone has remained an enigma since Csapo first theorized of a functional withdrawal of progesterone in 1965. Here we report that in vitro progesterone-liganded nuclear PRB forms a complex including JUN/JUN homodimers and P54(nrb)/Sin3A/HDAC to repress transcription of the key labour gene, Cx43. In contrast, unliganded PRA paradoxically activates Cx43 transcription by interacting with FRA2/JUND heterodimers. Furthermore, we find that while nuclear progesterone receptor (PR) is liganded during human pregnancy, it becomes unliganded during both term and preterm labour as a result of increased expression of the progesterone-metabolizing enzyme 20α HSD and reduced nuclear progesterone levels. Our data provide a mechanism by which human labour can occur in the presence of elevated circulating progesterone and suggests non-metabolizable progestogen might represent an alternative new therapeutic approach to preterm birth prevention.

Maternal and fetal roles in bacterially induced preterm labor in the mouse

BACKGROUND

The relative roles of the mother and fetus in signaling for labor remain poorly understood.

OBJECTIVE

We previously demonstrated using gene knockout (KO) mice that Escherichia coli-induced preterm delivery is completely dependent on MyD88, a toll-like receptor adaptor protein. Here we leveraged this finding to conduct a genetic experiment testing whether the mother, the fetus, or both signal for parturition in bacterially induced labor.

STUDY DESIGN

Six different maternal/fetal genotype combinations for MyD88 were studied: wild-type (WT) dams carrying one of the following: (1) WT or (2) MyD88 heterozygous (het) fetuses (generated by mating WT females with WT or MyD88-knockout [KO] males, respectively); (3) WT dams carrying MyD88-KO fetuses (generated by replacing the ovaries of WT females with MyD88-KO ovaries, followed by mating with MyD88-KO males); a similar strategy was used to generate MyD88-KO dams carrying (4) MyD88-KO, (5) MyD88 het, or (6) WT fetuses. On day 14.5 of gestation, mice received intrauterine injections of either 1 × 10(9) killed E coli or sterile medium. Delivery of ≥ 1 fetus within 48 hours was considered preterm. A separate group of similarly treated pregnant mice was euthanized 5 hours after surgery for gene expression and tissue analysis.

RESULTS

E coli-induced preterm delivery is dependent on maternal and not fetal genotype: > 95% of WT and < 5% of MyD88-KO dams deliver prematurely, regardless of fetal genotype (P = .0001). In contrast, fetal survival in utero is influenced by fetal genotype: in MyD88-KO dams, in which premature birth rarely occurs, only 81% of WT and 86% of MyD88-heterozygous fetuses were alive 48 hours after surgery compared with 100% of MyD88-KO fetuses (P < .01). Messenger ribonucleic acids for the inflammatory mediators interleukin-1β, tumor necrosis factor, interleukin-6, and cyclooxygenase-2 were elevated in uterine tissues only in WT mothers treated with E coli and were low or undetectable in the uteri of KO mothers or in animals treated with saline. Serum progesterone levels were lower in KO mothers with WT ovaries than in WT mothers with KO ovaries, but bacterial exposure did not have an impact on these levels.

CONCLUSION

In the murine E coli-induced labor model, preterm delivery and uterine expression of inflammatory mediators is determined by the mother and not the fetus and is not attributable to a decline in serum progesterone.

Toll-Like Receptor 4 Is an Essential Upstream Regulator of On-Time Parturition and Perinatal Viability in Mice

An inflammatory response is instrumental in the physiological process of parturition but the upstream signals initiating inflammation are undefined. Because endogenous ligands for Toll-like receptor 4 (TLR4) are released in late gestation, we hypothesized that on-time labor requires TLR4 signaling, to trigger a cytokine and leukocyte response and accelerate the parturition cascade. In pregnant TLR4-deficient (Tlr4-/-) mice, average gestation length was extended by 13 hours and increased perinatal mortality was seen compared with wild-type controls. Quantification of cytokine and uterine activation gene expression showed that late gestation induction of Il1b, Il6, Il12b, and Tnf expression seen in control placenta and fetal membranes was disrupted in Tlr4-/- mice, and accompanied by a transient delay in expression of uterine activation genes, including prostaglandin F receptor, oxytocin receptor, and connexin-43. Leukocyte populations were altered before birth in TLR4-deficient females, with fewer neutrophils and macrophages in the placenta, and fewer dendritic cells and more regulatory T cells in the myometrium. Administration of TLR4 ligand lipopolysaccharide to pregnant wild-type mice induced cytokine expression and fetal loss, whereas Tlr4-/- pregnancies were protected. The small molecule TLR4 antagonist (+)-naloxone increased mean duration of gestation by 16 hours in wild-type mice. Collectively, these data demonstrate that TLR4 is a key upstream regulator of the inflammatory response acting to drive uterine activation and control the timing of labor. Because causal pathways for term and preterm labor converge with TLR4, interventions to manipulate TLR4 signaling may have therapeutic utility for women at risk of preterm labor, or in postterm pregnancy.

Physiological roles of connexins in labour and lactation

The connexin family of proteins are best known as oligomerizing to form intercellular membrane channels (gap junctions) that metabolically and ionically couple cells to allow for coordinated cellular function. Nowhere in the body is this role better illustrated than in the uterine smooth muscle during parturition, where gap junctions conduct the contraction wave throughout the tissue to deliver the baby. Parturition is followed by the onset of lactation with connexins contributing to both the dramatic reorganization of mammary gland tissue leading up to lactation and the smooth muscle contraction of the myoepithelial cells which extrudes the milk. This review summarizes what is known about the expression and roles of individual connexin family members in the uterus during labour and in the mammary glands during development and lactation. Connexin loss or malfunction in mammary glands and the uterus can have serious implications for the health of both the mother and the newborn baby.

Prevalence and clinical significance of sterile intra-amniotic inflammation in patients with preterm labor and intact membranes

PROBLEM

Inflammation and infection play a major role in preterm birth. The purpose of this study was to (i) determine the prevalence and clinical significance of sterile intra-amniotic inflammation and (ii) examine the relationship between amniotic fluid (AF) concentrations of high mobility group box-1 (HMGB1) and the interval from amniocentesis to delivery in patients with sterile intra-amniotic inflammation.

METHOD OF STUDY

AF samples obtained from 135 women with preterm labor and intact membranes were analyzed using cultivation techniques as well as broad-range PCR and mass spectrometry (PCR/ESI-MS). Sterile intra-amniotic inflammation was defined when patients with negative AF cultures and without evidence of microbial footprints had intra-amniotic inflammation (AF interleukin-6 ≥ 2.6 ng/mL).

RESULTS

(i) The frequency of sterile intra-amniotic inflammation was significantly greater than that of microbial-associated intra-amniotic inflammation [26% (35/135) versus 11% (15/135); (P = 0.005)], (ii) patients with sterile intra-amniotic inflammation delivered at comparable gestational ages had similar rates of acute placental inflammation and adverse neonatal outcomes as patients with microbial-associated intra-amniotic inflammation, and (iii) patients with sterile intra-amniotic inflammation and high AF concentrations of HMGB1 (≥8.55 ng/mL) delivered earlier than those with low AF concentrations of HMGB1 (P = 0.02).

CONCLUSION

(i) Sterile intra-amniotic inflammation is more frequent than microbial-associated intra-amniotic inflammation, and (ii) we propose that danger signals participate in sterile intra-amniotic inflammation in the setting of preterm labor.

The CRTH2 agonist Pyl A prevents lipopolysaccharide-induced fetal death but induces preterm labour

We have previously demonstrated that the anti-inflammatory prostaglandin 15-deoxy-Δ 12,14-prostaglandin J(2) (15dPGJ(2)) delays inflammation-induced preterm labour in the mouse and improves pup survival through the inhibition of nuclear factor-κB (NF-κB) by a mechanism yet to be elucidated. 15dPGJ(2) is an agonist of the second prostaglandin D(2) receptor, chemoattractant receptor homologous to the T helper 2 cell (CRTH2). In human T helper cells CRTH2 agonists induce the production of the anti-inflammatory interleukins IL-10 and IL-4. We hypothesized that CRTH2 is involved in the protective effect of 15dPGJ(2) in inflammation-induced preterm labour in the murine model. We therefore studied the effects of a specific small molecule CRTH2 agonist on preterm labour and pup survival. An intrauterine injection of lipopolysaccharide (LPS) was administered to CD1 mice at embryonic day 16, ± CRTH2 agonist/vehicle controls. Mice were killed at 4.5 hr to assess fetal wellbeing and to harvest myometrium and pup brain for analysis of NF-κB, and T helper type 1/2 interleukins. To examine the effects of the CRTH2 agonist on LPS-induced preterm labour, mice were allowed to labour spontaneously. Direct effects of the CRTH2 agonist on uterine contractility were examined ex vivo on contracting myometrial strips. The CRTH2 agonist increased fetal survival from 20 to 100% in LPS-treated mice, and inhibited circular muscle contractility ex vivo. However, it augmented LPS-induced labour and significantly increased myometrial NF-κB, IL-1β, KC-GRO, interferon-γ and tumour necrosis factor-α. This suggests that the action of 15dPGJ(2) is not via CRTH2 and therefore small molecule CRTH2 agonists are not likely to be beneficial for the prevention of inflammation-induced preterm labour.

Integrin upregulation and localization to focal adhesion sites in pregnant human myometrium

Focal adhesions are integrin-rich microdomains that structurally link the cytoskeleton to the extracellular matrix and transmit mechanical signals. In the pregnant uterus, increases in integrin expression and activation are thought to be critical for the formation of the mechanical syncytium required for labor. The aim of this study was to determine which integrins are upregulated and localized to focal adhesions in pregnant human myometrium. We used quantitative polymerase chain reaction, Western blotting, and confocal microscopy to determine the expression levels and colocalization with focal adhesion proteins. We observed increases in several integrin transcripts in pregnant myometrium. At the protein level, integrins such as α5-integrin (ITGA5), ITGA7, ITGAV, and ITGB3 were significantly increased during pregnancy. The integrins ITGA3, ITGA5, ITGA7, and ITGB1 colocalized with focal adhesion proteins in term human myometrium. These data suggest that integrins α3β1, α5β1, and α7β1 are the most likely candidates to transmit mechanical signals from the extracellular matrix through focal adhesions in pregnant human myometrium.

Re-establishment of gap junctional intercellular communication (GJIC) between human endometrial carcinomas by prostaglandin E(2)

Reduced intercellular communication via gap junctions is correlated with carcinogenesis. Gap junctional intercellular communication (GJIC), between normal human endometrial epithelial cells is enhanced when endometrial stromal cells were present in culture. This enhancement of GJIC between normal epithelial cells also occurs when they are cultured in medium conditioned by stromal cells. This observation indicated that a soluble compound (or compounds) produced and secreted by stromal cells mediates GJIC in epithelial cells. Previous studies have shown that endometrial stromal cells release prostaglandin E(2) (PGE(2)) and prostaglandin F(2α) (PGF(2α)) under physiological conditions. When we evaluated the response of normal endometrial epithelial cells to various concentrations of PGE(2,) we found enhanced GJIC with 1nM PGE(2). This is a smaller increase in GJIC than that induced by medium conditioned by stromal cells. When the extracellular concentration of PGE(2) was measured after incubation with stromal cells, it was found to be similar to the concentrations showing maximal GJIC between the normal epithelial cells. When indomethacin was used to inhibit prostaglandin synthesis by stromal cells, GJIC was reduced but not eliminated between normal endometrial epithelial cells. These observations suggest that although PGE(2) secreted by stromal cells is an important mediator of GJIC between the epithelial cells, it is not the sole mediator. Transformed endometrial epithelial cells did not demonstrate GJIC even in the presence of stromal cells. However, we were able to re-establish GJIC in transformed epithelial cells when we added PGE(2) to the cells. Our findings show that PGE(2) may serve as an intercellular mediator between stromal and epithelial cells that regulates GJIC in normal and malignant epithelial cells. This suggests that maintenance of GJIC by preserving or replacing PGE(2) secretion by endometrial stromal cells may have the potential to suppress carcinogenesis in endometrial epithelial cells.

A molecular signature of an arrest of descent in human parturition

OBJECTIVE

This study was undertaken to identify the molecular basis of an arrest of descent.

STUDY DESIGN

Human myometrium was obtained from women in term labor (TL; n = 29) and arrest of descent (AODes; n = 21). Gene expression was characterized using Illumina HumanHT-12 microarrays. A moderated Student t test and false discovery rate adjustment were applied for analysis. Confirmatory quantitative reverse transcription-polymerase chain reaction and immunoblot were performed in an independent sample set.

RESULTS

Four hundred genes were differentially expressed between women with an AODes compared with those with TL. Gene Ontology analysis indicated enrichment of biological processes and molecular functions related to inflammation and muscle function. Impacted pathways included inflammation and the actin cytoskeleton. Overexpression of hypoxia inducible factor-1a, interleukin -6, and prostaglandin-endoperoxide synthase 2 in AODes was confirmed.

CONCLUSION

We have identified a stereotypic pattern of gene expression in the myometrium of women with an arrest of descent. This represents the first study examining the molecular basis of an arrest of descent using a genome-wide approach.

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.

Preventing preterm birth: the past limitations and new potential of animal models

The high rate of preterm birth in the USA and many other countries is a potential target for improving children’s immediate health and reducing the medical problems they face as adults. The acute complications for infants born prematurely often require intensive care management and are followed by long-lasting cognitive, sensory, motor, and cardiovascular deficits that substantially limit adult capabilities and survival. The inability to effectively reduce preterm birth stems from the failure to understand normal mechanisms of parturition in humans. Although studies from several model organisms help define the physiology of maintenance and termination of pregnancy, there are fundamental differences between species. For example, species regulate their production of progesterone, the crucial hormone in sustaining pregnancy, differently. This limits the extent to which models can provide meaningful information about the physiological mechanisms of human gestation. The growing wealth of sequenced mammalian genomes, computational comparative genomic tools and systems biology approaches provides new potential to utilize the divergence of DNA sequences and physiology between species to understand the genetic underpinnings of preterm birth.

Restoration of on-time embryo implantation corrects the timing of parturition in cytosolic phospholipase A2 group IVA deficient mice

Cytosolic phospholipase A2 (cPLA2, PLA2G4A) catalyzes the release of arachidonic acid for prostaglandin synthesis by cyclooxygenase 1 (PTGS1) and cyclooxygenase 2 (PTGS2). Mice with Pla2g4a deficiency have parturition delay and other reproductive deficits, including deferred onset of implantation, crowding of implantation sites, and small litters. In this study, we examined the contribution of PLA2G4A to parturition in mice. Pla2g4a mRNA and protein expression were discretely localized in the term and preterm uterine luminal epithelium and colocalized with Ptgs1, but not Ptgs2, expression. The levels of PGE2, PGF2alpha, 6-keto-PGF1alpha, and TxB2 were significantly decreased in Pla2g4a-null uterine tissues, similar to Ptgs1-null uteri, consistent with predominance of PLA2G4A-PTGS1-mediated prostaglandin synthesis in preparation for murine parturition. Litter size was strongly associated with the timing of parturition in Pla2g4a-null mice but could not fully account for the parturition delay. Pla2g4a-null females that received PGE2 + carbaprostacyclin at the time of implantation delivered earlier (20.5 +/- 0.2 days vs. 21.6 +/- 0.2 days, P < 0.01), although litter size was not improved (4.6 vs. 4.4 pups per litter, P = 0.6). After correction for small litter size, multivariate analysis indicated that Pla2g4a-null mice given prostaglandin treatment to improve implantation timing had gestational length that was similar to wild-type and Pla2g4a heterozygous mice. These results indicate that, despite specific Pla2g4a expression and function in term gestation uteri, the delayed parturition phenotype in Pla2g4a-null mice is primarily due to deferral of implantation. The role of PLA2G4A in timely parturition appears to be critically related to its actions in early pregnancy.

Myometrial oxytocin receptor mRNA concentrations at preterm and term delivery - the influence of external oxytocin

The hormonal system for induction of term and preterm labour is not fully understood. Therefore, we investigated myometrial gene expressions for neurohypophyseal hormones and their receptors, prostaglandin F(2alpha) and ovarian steroid receptors in women delivered by Caesarean section. Myometrial tissue for real time PCR was collected from 39 women delivered at term before and after the onset of labour and preterm. Women delivered electively at term had significantly higher oxytocin receptor mRNA expressions (2.52 +/- 0.37 oxytocin receptor/actin; median +/- SEM) than those delivered with ongoing labour at term (1.01 +/- 0.34; p = 0.015) and those at preterm (1.08 +/- 0.25; p = 0.004). Sub-analyses revealed that the difference at term pregnancies solely was related to patients receiving oxytocin during labour (p = 0.007). These patients had higher oxytocin peptide mRNA levels than those without labour at term (p = 0.009). PGF(2alpha) receptor mRNA concentrations were 27.80 +/- 3.55, 11.46 +/- 2.87 and 19.54 +/- 5.52 PGF receptor/actin, respectively, for the groups. Women without labour at term had higher concentration than those with labour (p = 0.005). Our results suggest that oxytocin, its receptor and the PGF(2alpha) receptor are involved in the regulation of labour through a paracrine mechanism.

Identification of 9 uterine genes that are regulated during mouse pregnancy and exhibit abnormal levels in the cyclooxygenase-1 knockout mouse

BACKGROUND

Preterm birth is the leading cause of all infant mortality. In 2004, 12.5% of all births were preterm. In order to understand preterm labor, we must first understand normal labor. Since many of the myometrial changes that occur during pregnancy are similar in mice and humans and mouse gestation is short, we have studied the uterine genes that change in the mouse during pregnancy. Here, we used microarray analysis to identify uterine genes in the gravid mouse that are differentially regulated in the cyclooxygenase-1 knockout mouse model of delayed parturition.

METHODS

Gestational d18.0 uteri (n = 4) were collected from pregnant wild-type and cyclooxygenase-1 knockout mice. Part of the uterus was used for frozen sections and RNA was isolated from the remainder. Microarray analysis was performed at the Indiana University School of Medicine Genomic Core and analyzed using the Microarray Data Portal. Northern analysis was performed to confirm microarray data and the genes localized in the gravid uterus by in situ hybridization.

RESULTS

We identified 277 genes that are abnormally expressed in the gravid d18.0 cyclooxygenase-1 knockout mouse. Nine of these genes are also regulated in the normal murine uterus during the last half of gestation. Many of these genes are involved in the immune response, consistent with an important role of the immune system in parturition. Expression of 4 of these genes; arginase I, IgJ, Tnfrsf9 and troponin; was confirmed by Northern analysis to be mis-regulated during pregnancy in the knockout mouse. In situ hybridization of these genes demonstrated a similar location in the gravid wild-type and Cox-1 knockout mouse uteri.

CONCLUSION

To our knowledge, this is the first work to demonstrate the uterine location of these 4 genes in the mouse during late pregnancy. There are several putative transcription factor binding sites that are shared by many of the 9 genes identified here including; estrogen and progesterone response elements and Ets binding sites. In summary, this work identifies 9 uterine murine genes that may play a role in parturition. The function of these genes is consistent with an important role of the immune system in parturition.

The Interleukin 1beta-Induced Expression of Human Prostaglandin F2alpha Receptor Messenger RNA in Human Myometrial-Derived ULTR Cells Requires the Transcription Factor, NFkappaB1

The molecular mechanisms that regulate the expression of genes involved in parturition are poorly understood. The mRNA expression of the prostaglandin F(2alpha) receptor (PTGFR), a uterine activating gene, is increased at labor and is required for uterine contractile activity in numerous animal models, although the signaling pathways responsible for this increased expression have not been identified. Proinflammatory cytokines have been proposed to regulate the expression of the uterine activating genes via activation of the nuclear transcription factor, NFkappaB, and initiate labor. However, it is uncertain whether uterine PTGFR is regulated this way. In this report, we demonstrate for the first time that treatment of immortalized human myometrial-derived ULTR cells with the proinflammatory cytokine IL1beta causes an increase in PTGFR mRNA levels. Furthermore, IL1beta treatment increased the nuclear levels of the RELA subunit of NFkappaB and increased binding of RELA to the NFkappaB DNA-binding site. Inhibition of NFkappaB activation with either the proteasome inhibitor MG132 or phenethyl caffeiate reduced PTGFR mRNA levels, which indicates that this transcription factor is important for basal transcription. Furthermore, this inhibition prevented IL1beta induction ofPTGFRmRNA, which confirms that NFkappaB is required for the IL1beta-induced increase inPTGFR. These results are consistent with the proposal that proinflammatory cytokines directly regulate uterine activation genes and that the transcription factor NFkappaB is involved in both basal and IL1beta-stimulated transcription of the PTGFR gene.

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.

Proteomics, Part II: The Emerging Role of Proteomics Over Genomics in Spontaneous Preterm Labor/Birth

Conventional wisdom holds that complications of immature organ systems such as respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, and bronchopulmonary dysplasia are the primary causes of the high neonatal morbidity and mortality attendant preterm delivery. However, recent evidence suggests that a major cause of prematurity-associated neonatal pathology is the fetal and neonatal response to inflammation/infection. Although functional genomics offered the promise of providing answers to many of these questions, the identification of the genes intrinsic to human parturition proved to be a difficult task. Proteomic profiling of the amniotic fluid (AF) provides a precise means for detection of inflammation by revealing the presence of 4 biomarkers (defensins-2 and -1, calgranulin-C, and calgranulin-A) that are highly predictive of intrauterine inflammation (MR score). The MR score is especially useful as it presents a gradient of disease activity progressing from "absent" to "mild" to "severe" inflammation. Thus, it provides the ability to identify patients who may benefit from interventions in utero in a modern diagnostic-therapeutic framework.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader should be able to explain that the cause or causes of preterm delivery are still unknown, recall that functional genomics has not given the answer to these causes, and state that proteomic profiling of amniotic fluid, through mass-restricted (MR) scoring, may be predictive of intrauterine inflammation and allow for potential diagnosis and potential therapy.

Ablation of connexin43 in uterine smooth muscle cells of the mouse causes delayed parturition

Gap junctions are characteristically increased in the myometrium during term and preterm delivery and are thought to be essential for the development of uterine contractions during labour. Expression of connexin43 (Cx43), the major myometrial gap junction protein, is increased during delivery. We have generated a mouse mutant (Cx43fl/fl:SM-CreERT2), in which the coding region of Cx43 can be specifically deleted in smooth muscle cells at any given time point by application of tamoxifen. By this approach, we were able to study long-term effects on myometrial functions that are necessary for parturition as well as gap junction intercellular communication in primary myometrial cell cultures. We found a prolongation of the pregnancy in 82% of tamoxifen-treated Cx43fl/fl:SM-CreERT2 mice as well as decreased dye coupling in cultured primary myocytes of these animals. Other parturition-specific parameters such as the regulation of oxytocin receptor, prostaglandin F receptor or progesterone remained unchanged. Our results indicate the important function of Cx43 during parturition in the living animal and suggest further strategies to investigate the role of connexins in uterine contractility in transgenic mice.

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.

The molecular pathophysiology of bacterially induced preterm labor: insights from the murine model

Premature delivery, the most important problem in obstetrics in developed countries, continues to vex clinicians and researchers. Despite decades of investigation, the pathophysiology of premature labor is incompletely understood, and therapies or preventive strategies tailored to each of the many potential causes do not exist. The present review addresses one cause of prematurity, namely, intrauterine bacterial infection. Given the vastness of the literature for even this single etiology, we focus on the mouse as a model organism from which much can be learned about mammalian parturition. The underpinnings of bacterially induced labor are believed to involve a signaling cascade that begins with recognition of offending pathogens by cell-surface receptors (toll-like receptors). This cascade then operates through multiple branching and redundant pathways to bring about the changes within the gestational compartment that produce cervical ripening, labor, and ultimately delivery. The major challenge facing researchers is to understand the levels of complexity in the host response, so that prevention and treatment strategies may be sufficiently focused to minimize unwanted side effects, yet sufficiently broad to be effective. Given the complexity of the problem, this understanding can be aided by efficient model systems, of which one in vivo example is the mouse, an organism that shares with humans many similarities in the biochemical and molecular aspects of inflammation-induced preterm labor. We propose that tools with the power to assess simultaneously the myriad elements of the hypothesized signaling cascade (ie, genomic and proteomic technologies) are important components of the solution to the puzzle of parturition.

Delay of preterm birth in sheep by THG113.31, a prostaglandin F2alpha receptor antagonist

OBJECTIVE

A novel prostaglandin F2alpha receptor antagonist, THG113.31, was tested for the suppression of uterine contractility and delay of preterm labor in sheep.

STUDY DESIGN

We determined the tocolytic effectiveness of THG113.31 on contractions that were stimulated in vitro by prostaglandin F2alpha and E2 in longitudinal and circular myometrial strips. We also tested the ability of THG113.31 in vivo to lower uterine electromyographic activity that was induced by the progesterone receptor blocker, RU486, and to delay preterm birth.

RESULTS

THG113.31 suppressed the amplitude of prostaglandin F2alpha, but not prostaglandin E2-induced contractions of both circular and longitudinal myometrium (P<.01). The times to delivery after RU486 were 34.8+/-1.1 hours (saline solution) and 41.9+/-0.5 hours (THG113.31; P<.001) or an average delay of 7.1 hours. There were no changes in fetal blood gases (PaO2 , PaCO2 , pH, or SaO2) because of THG113.31. Fetal cortisol levels rose in each group, and fetal and maternal prostaglandin E2 and F2alpha metabolite concentrations rose similarly in both groups.

CONCLUSION

THG113.31 specifically suppresses prostaglandin F2alpha-induced myometrial contractility and delays delivery.

TGF-beta1 regulation in hepatocyte-NIH3T3 co-culture is important for the enhanced hepatocyte function in 3D microenvironment

Co-culture of hepatocytes or hepatocyte spheroids with the supporting NIH3T3 in a 3D microcapsule formed with a hybrid natural/synthetic matrix has led to enhanced hepatocyte functions. We investigated the mechanism of the functional enhancement in co-culture with respect to the contributions of soluble factors and direct cell-cell interactions. The conditioned media from the co-culture induced higher P450 cytochrome oxidase activity (indicated by EROD assay) in the microencapsulated hepatocytes than the conditioned media from the NIH3T3- or the hepatocytes-alone controls. Conditioned media from physically separated co-culture of hepatocytes-NIH3T3 by a membrane insert reduced the functional enhancement. Among the known stimulators of hepatocyte functions, TGF(beta)1 is primarily responsible for the stimulation of hepatocyte functions in this 3D co-culture since the removal of TGF(beta)1 by antibody depletion eliminated the functional enhancement and the reconstitution of TGF(beta)1 restored the functional enhancement. Activation of latent TGF(beta)1 in an extracellular environment were upregulated in co-culture with no observable increase in the TGF(beta)1 expression at transcriptional and translational levels. Our data led to an improved understanding of how co-culture enhances hepatocyte functions in vitro and pave the way for further innovations in liver tissue engineering, drug metabolism studies, and other applications that require functional hepatocytes cultured in vitro.

Effect of Proteasome Pathway on Initiation of Mouse Labor Induced by Antiprogesterone

PROBLEM

Various kinds of contraction-associated molecules are up-regulated at the initiation of labor. However, expression profiling has revealed that many molecules are also down-regulated. The effect of down-regulation of molecules by protein degradation on parturition is not known.

METHODS OF STUDY

We administered lactacystin, a specific proteasome inhibitor, to mouse preterm birth model induced by antiprogesterone RU486 on day 16.0 post-coitus. NF-kappaB activity, and the levels of transcripts for oxytocin receptor, prostaglandin F(2alpha) receptor (FP), cyclooxygenase-1, -2, and interleukin-1beta in the uterus were examined by electrophoretic mobility shift assay and semi-quantitative reverse transcriptase-polymerase chain reaction, respectively.

RESULTS

Administration of lactacystin significantly prolonged the time until the delivery of the first pup. FP mRNA level was solely elevated by RU486 treatment, and lactacystin significantly suppressed this up-regulation.

CONCLUSIONS

Proteolysis by proteasomes in the uterus regulates the initiation of labor, at least in part, via control of contraction-associated molecules such as FP.