Intrauterine bacterial inoculation induces labor in the mouse by mechanisms other than progesterone withdrawal

Expression patterns and distribution of aquaporin water channels in cervix as a possible mechanism for cervical patency in bitches affected by pyometra

Pyometra is a life-threatening disease, the severity of which depends on cervical patency status. This study investigated cervical inflammation status as well as the expression patterns and localization of aquaporin (AQP1, AQP2, AQP3, AQP5, and AQP9), and hormone receptors in cervical tissue that influences canine pyometra. Of the 36 animals enrolled in the study, 24 were diagnosed with pyometra and separated into two groups: open cervix pyometra and close cervix pyometra, while 12 healthy animals presented for elective ovariohysterectomies were allocated into the control group. Surgical treatment was performed for treatment of pyometra. After each operation, cervix samples were collected and analyzed for AQP and hormone receptor expression patterns determined by qPCR and protein expression by means of immunohistochemistry. Blood samples were also collected to determine serum progesterone concentrations. AQP9 expression was downregulated approximately 3-fold while and PGR expression was downregulated more than 2 fold in both pyometra groups compared to the control group. AQP3 and AQP5 gene expression levels were upregulated more than 3 fold in the open-cervix pyometra group than the closed-cervix pyometra group (P < 0.05). This is the first study to describe the expression patterns and immunolocalization of AQPs in canine cervical tissue based on pyometra patency status and to report AQP3 and AQP5 expression in cervical tissue linked to cervical patency.

The hormonal control of parturition

Parturition is a complex physiological process that must occur in a reliable manner and at an appropriate gestation stage to ensure a healthy newborn and mother. To this end, hormones that affect the function of the gravid uterus, especially progesterone (P4), 17β-estradiol (E2), oxytocin (OT), and prostaglandins (PGs), play pivotal roles. P4 via the nuclear P4 receptor (PR) promotes uterine quiescence and for most of pregnancy exerts a dominant block to labor. Loss of the P4 block to parturition in association with a gain in prolabor actions of E2 are key transitions in the hormonal cascade leading to parturition. P4 withdrawal can occur through various mechanisms depending on species and physiological context. Parturition in most species involves inflammation within the uterine tissues and especially at the maternal-fetal interface. Local PGs and other inflammatory mediators may initiate parturition by inducing P4 withdrawal. Withdrawal of the P4 block is coordinated with increased E2 actions to enhance uterotonic signals mediated by OT and PGs to promote uterine contractions, cervix softening, and membrane rupture, i.e., labor. This review examines recent advances in research to understand the hormonal control of parturition, with focus on the roles of P4, E2, PGs, OT, inflammatory cytokines, and placental peptide hormones together with evolutionary biology of and implications for clinical management of human parturition.

Progesterone inactivation in decidual stromal cells: A mechanism for inflammation-induced parturition

The process of human parturition involves inflammation at the interface where fetal chorion trophoblast cells interact with maternal decidual stromal (DS) cells and maternal immune cells in the decidua (endometrium of pregnancy). This study tested the hypothesis that inflammation at the chorion-decidua interface (CDI) induces labor by negating the capacity for progesterone (P4) to block labor and that this is mediated by inactivation of P4 in DS cells by aldo-keto reductase family 1 member C1 (AKR1C1). In human, Rhesus macaque, and mouse CDI, AKR1C1 expression increased in association with term and preterm labor. In a human DS cell line and in explant cultures of term human fetal membranes containing the CDI, the prolabor inflammatory cytokine, interleukin-1ß (IL-1ß), and media conditioned by LPS-stimulated macrophages increased AKR1C1 expression and coordinately reduced nuclear P4 levels and P4 responsiveness. Loss of P4 responsiveness was overcome by inhibition of AKR1C1 activity, inhibition of AKR1C1 expression, and bypassing AKR1C1 activity with a P4 analog that is not metabolized by AKR1C1. Increased P4 activity in response to AKR1C1 inhibition was prevented by the P4 receptor antagonist RU486. Pharmacologic inhibition of AKR1C1 activity prevented parturition in a mouse model of inflammation-induced preterm parturition. The data suggest that inflammatory stimuli at the CDI drive labor by inducing AKR1C1-mediated P4 inactivation in DS cells and that inhibiting and/or bypassing of AKR1C1-mediated P4 inactivation is a plausible therapeutic strategy to mitigate the risk of inflammation-associated preterm birth.

The selective progesterone receptor modulator-promegestone-delays term parturition and prevents systemic inflammation-mediated preterm birth in mice

BACKGROUND

Progesterone, acting via its nuclear receptors called progesterone receptors, promotes myometrial relaxation during pregnancy, and suspension of this activity triggers labor. We previously found that 20α-hydroxysteroid dehydrogenase causes a local withdrawal of progesterone in the term and preterm myometrium by converting the progesterone into an inactive form before it accesses the progesterone receptors.

OBJECTIVE

We hypothesized that a selective progesterone receptor modulator called promegestone, which is not metabolized by 20α-hydroxysteroid dehydrogenase, would sustain progesterone receptor signaling and prevent/delay term labor and preterm labor in mice.

STUDY DESIGN

In the term labor mouse model, promegestone (0.2 mg/dam) or a vehicle were administered subcutaneously in timed-pregnant CD-1 mice at gestational days 15, 16, and 17 (term gestational days, 19.5). In the inflammation preterm labor model, pregnant mice received promegestone or a vehicle on gestational days 15, 16, and 17, which was 24 hours before, immediately before, and 24 hours after systemic bacterial endotoxin (50 μg intraperitoneal; lipopolysaccharide group) or vehicle (saline) administration. The maternal and fetal tissues were collected on gestational day 16 6 hours after lipopolysaccharide±promegestone injection and at term gestational day 18.75. The protein levels of 10 cytokines were measured by multiplex immunoassay in maternal plasma and amniotic fluid. Myometrial, decidual, and placental messenger RNA levels of multiple cytokines and procontractile proteins were evaluated by real-time polymerase chain reaction and confirmed by immunoblotting.

RESULTS

Promegestone prevented term labor and maintained mice pregnancy postterm >24 hours. The litter size and fetal weights were not different from the controls. Promegestone prevented systemic bacterial-endotoxin-induced preterm labor in 100% of the mice, blocked uterine contractions, significantly inhibited all systemic inflammation-induced myometrial cytokines, and partially inhibited decidual and placental inflammation. Promegestone did not prevent bacterial-endotoxin-induced fetal toxicity.

CONCLUSION

Promegestone a selective progesterone receptor modulator that binds progesterone receptors with high affinity and is not metabolized by 20α-hydroxysteroid dehydrogenase could completely suppress term parturition and systemic bacterial-endotoxin-induced preterm birth in mice. We suggest that such selective progesterone receptor modulators may represent a potential therapeutic approach to the prevention of preterm labor in women at high risk of preterm birth.

The alarmin interleukin-1α causes preterm birth through the NLRP3 inflammasome

Sterile intra-amniotic inflammation is a clinical condition frequently observed in women with preterm labor and birth, the leading cause of neonatal morbidity and mortality worldwide. Growing evidence suggests that alarmins found in amniotic fluid, such as interleukin (IL)-1α, are central initiators of sterile intra-amniotic inflammation. However, the causal link between elevated intra-amniotic concentrations of IL-1α and preterm birth has yet to be established. Herein, using an animal model of ultrasound-guided intra-amniotic injection of IL-1α, we show that elevated concentrations of IL-1α cause preterm birth and neonatal mortality. Additionally, using immunoblotting techniques and a specific immunoassay, we report that the intra-amniotic administration of IL-1α induces activation of the NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome in the fetal membranes, but not in the decidua, as evidenced by a concomitant increase in the protein levels of NLRP3, active caspase-1, and IL-1β. Lastly, using Nlrp3-/- mice, we demonstrate that the deficiency of this inflammasome sensor molecule reduces the rates of preterm birth and neonatal mortality caused by the intra-amniotic injection of IL-1α. Collectively, these results demonstrate a causal link between elevated IL-1α concentrations in the amniotic cavity and preterm birth as well as adverse neonatal outcomes, a pathological process that is mediated by the NLRP3 inflammasome. These findings shed light on the mechanisms underlying sterile intra-amniotic inflammation and provide further evidence that this clinical condition can potentially be treated by targeting the NLRP3 inflammasome.

Developing a theoretical evolutionary framework to solve the mystery of parturition initiation

Eutherian mammals have characteristic lengths of gestation that are key for reproductive success, but relatively little is known about the processes that determine the timing of parturition, the process of birth, and how they are coordinated with fetal developmental programs. This issue remains one of biology's great unsolved mysteries and has significant clinical relevance because preterm birth is the leading cause of infant and under 5 year old child mortality worldwide. Here, we consider the evolutionary influences and potential signaling mechanisms that maintain or end pregnancy in eutherian mammals and use this knowledge to formulate general theoretical evolutionary models. These models can be tested through evolutionary species comparisons, studies of experimental manipulation of gestation period and birth timing, and human clinical studies. Understanding how gestation time and parturition are determined will shed light on this fundamental biological process and improve human health through the development of therapies to prevent preterm birth.

Pathogenesis of preterm birth: bidirectional inflammation in mother and fetus

Preterm birth (PTB) complicates 5–18% of pregnancies globally and is a leading cause of maternal and fetal morbidity and mortality. Most PTB is spontaneous and idiopathic, with largely undefined causes. To increase understanding of PTB, much research in recent years has focused on using animal models to recapitulate the pathophysiology of PTB. Dysfunctions of maternal immune adaptations have been implicated in a range of pregnancy pathologies, including PTB. A wealth of evidence arising from mouse models as well as human studies is now available to support that PTB results from a breakdown in fetal-maternal tolerance, along with excessive, premature inflammation. In this review, we examine the current knowledge of the bidirectional communication between fetal and maternal systems and its role in the immunopathogenesis of PTB. These recent insights significantly advance our understanding of the pathogenesis of PTB, which is essential to ultimately designing more effective strategies for early prediction and subsequent prevention of PTB.

Preterm labor is characterized by a high abundance of amniotic fluid prostaglandins in patients with intra-amniotic infection or sterile intra-amniotic inflammation

Objective: To distinguish between prostaglandin and prostamide concentrations in the amniotic fluid of women who had an episode of preterm labor with intact membranes through the utilisation of liquid chromatography-tandem mass spectrometry.Study design: Liquid chromatography-tandem mass spectrometry analysis of amniotic fluid of women with preterm labor and (1) subsequent delivery at term (2) preterm delivery without intra-amniotic inflammation; (3) preterm delivery with sterile intra-amniotic inflammation (interleukin (IL)-6>2.6 ng/mL without detectable microorganisms); and (4) preterm delivery with intra-amniotic infection [IL-6>2.6 ng/mL with detectable microorganisms].Results: (1) amniotic fluid concentrations of PGE₂, PGF_2α, and PGFM were higher in patients with intra-amniotic infection than in those without intra-amniotic inflammation; (2) PGE₂ and PGF_2α concentrations were also greater in patients with intra-amniotic infection than in those with sterile intra-amniotic inflammation; (3) patients with sterile intra-amniotic inflammation had higher amniotic fluid concentrations of PGE₂ and PGFM than those without intra-amniotic inflammation who delivered at term; (4) PGFM concentrations were also greater in women with sterile intra-amniotic inflammation than in those without intra-amniotic inflammation who delivered preterm; (5) amniotic fluid concentrations of prostamides (PGE₂-EA and PGF_2α-EA) were not different among patients with preterm labor; (6) amniotic fluid concentrations of prostaglandins, but no prostamides, were higher in cases with intra-amniotic inflammation; and (7) the PGE₂:PGE₂-EA and PGF_2α:PGF_2α-EA ratios were higher in patients with intra-amniotic infection compared to those without inflammation.Conclusions: Mass spectrometric analysis of amniotic fluid indicated that amniotic fluid concentrations of prostaglandins, but no prostamides, were higher in women with preterm labor and intra-amniotic infection than in other patients with an episode of preterm labor. Yet, women with intra-amniotic infection had greater amniotic fluid concentrations of PGE₂ and PGF_2α than those with sterile intra-amniotic inflammation, suggesting that these two clinical conditions may be differentiated by using mass spectrometric analysis of amniotic fluid.

Cyclic-recombinase-reporter mouse model to determine exosome communication and function during pregnancy

BACKGROUND

During pregnancy, feto-maternal communication can be mediated through extracellular vesicles, specifically exosomes, 30- to 150-nm particles released from each cell. Exosomes carry cellular signals, and traffic between fetal and maternal tissues to produce functional changes in recipient cells. Exosomes may function as a biomarker indicative of the physiologic status of their tissue of origin. These properties of exosomes during pregnancy are not well studied.

OBJECTIVE

To test exosome trafficking and function, we used a transgenic mouse model containing membrane-targeted, red fluorescent protein tdTomato and enhanced green fluorescent protein cyclic recombinase-reporter construct expressed only in fetal tissues. This model allows fetal tissues and their exosomes to express tdTomato under normal conditions or green fluorescent protein if fetal tissues are exposed to cyclic recombinase that will excise tdTomato. As maternal tissue remains negative for this construct, tdTomato/green fluorescent protein expression and their switching can be used to determine fetal-specific cell and exosome trafficking.

MATERIALS AND METHODS

tdTomato/green fluorescent protein-homozygous male mice were mated with wild-type females to have all fetal tissues express the tdTomato/green fluorescent protein allele. Red fluorescence due to tdTomato expression of the tdTomato/green fluorescent protein allele in fetal tissues (placenta, fetal membranes) was confirmed by confocal microscopy on embryonic day 16. Localization of fetal exosomes in maternal uterine tissues were performed by immunostaining for exosome marker CD81 and tdTomato expression followed by confocal microscopy. Fetal exosomes (tdTomato-positive) in maternal plasma were immunoprecipitated using anti-red fluorescent protein tdTomato, followed by confirmation with flow cytometry. To further illustrate the fidelity of fetal exosomes in maternal samples, exosomes bioengineered to contain cyclic recombinase (1.0 × 1010 exosomes) were injected intraperitoneally on embryonic day 13. On embryonic day 16, fetal (placenta and fetal membranes) tissues were imaged to show tdTomato-to-green fluorescent protein transition. The green fluorescent protein-expressing exomes were localized in maternal tissues (confocal microscopy) and plasma (flow cytometry).

RESULTS

Mating between a male with the tdTomato/green fluorescent protein construct and a null female resulted in fetal tissues and their exosomes expressing tdTomato positivity. Total fetal exosomes in maternal plasma was about 35%. tdTomato-positive exosomes were isolated from maternal plasma and immunostaining localized tdTomato-positive exosomes in maternal uterine tissues. Maternal intraperitoneal injection of cyclic recombinase-enriched exosomes crossed placenta, excised tdTomato from the tdTomato/green fluorescent protein construct in the fetal tissues, and caused green fluorescent protein expression in fetal cells. Furthermore, green fluorescent protein-positive exosomes released from fetal cells were isolated from maternal blood.

CONCLUSION

In this pilot study, we report feto-maternal and maternal-fetal trafficking of exosomes indicative of paracrine signaling during pregnancy. Exosomes from the maternal side can produce functional changes in fetal tissues. Trafficking of exosomes suggests their potential role in pregnancy as biomarkers of fetal functions and usefulness as a carrier of drugs and other cargo to the fetal side during pregnancy. Isolation and characterization of fetal exosomes can advance fetal research without performing invasive procedures.

Gasdermin D: Evidence of pyroptosis in spontaneous preterm labor with sterile intra-amniotic inflammation or intra-amniotic infection

PROBLEM

Pyroptosis, inflammatory programmed cell death, is initiated through the inflammasome and relies on the pore-forming actions of the effector molecule gasdermin D. Herein, we investigated whether gasdermin D is detectable in women with spontaneous preterm labor and sterile intra-amniotic inflammation or intra-amniotic infection.

METHOD OF STUDY

Amniotic fluid samples (n = 124) from women with spontaneous preterm labor were subdivided into the following groups: (a) those who delivered at term (n = 32); and those who delivered preterm (b) without intra-amniotic inflammation (n = 41), (c) with sterile intra-amniotic inflammation (n = 32), or (d) with intra-amniotic infection (n = 19), based on amniotic fluid IL-6 concentrations and the microbiological status of amniotic fluid (culture and PCR/ESI-MS). Gasdermin D concentrations were measured using an ELISA kit. Multiplex immunofluorescence staining was also performed to determine the expression of gasdermin D, caspase-1, and interleukin-1β in the chorioamniotic membranes. Flow cytometry was used to detect pyroptosis (active caspase-1) in decidual cells from women with preterm labor and birth.

RESULTS

(a) Gasdermin D was detected in the amniotic fluid and chorioamniotic membranes from women who underwent spontaneous preterm labor/birth with either sterile intra-amniotic inflammation or intra-amniotic infection, but was rarely detected in those without intra-amniotic inflammation. (b) Amniotic fluid concentrations of gasdermin D were higher in women with intra-amniotic infection than in those with sterile intra-amniotic inflammation, and its expression in the chorioamniotic membranes was associated with caspase-1 and IL-1β (inflammasome mediators). (c) Decidual stromal cells and leukocytes isolated from women with preterm labor and birth are capable of undergoing pyroptosis given their expression of active caspase-1.

CONCLUSION

Pyroptosis can occur in the context of sterile intra-amniotic inflammation and intra-amniotic infection in patients with spontaneous preterm labor and birth.

Surfactant protein A suppresses preterm delivery induced by live Escherichia coli in mice

Preterm birth accounts for the majority of neonatal morbidity and mortality in the developed world. A significant proportion of cases of spontaneous preterm labor are attributable to infections within gestational tissues. Surfactant protein A (SP-A), a collectin produced in the fetal lung and other tissues, has been shown previously in mice to suppress preterm delivery due to intrauterine (IU) instillation of sterile proinflammatory substances. Here we report a powerful antilabor effect for SP-A after IU infection with live Escherichia coli. SP-A abolished preterm birth (rate reduced from 100% to 0%) when it was administered into the uterus simultaneously with bacterial infection, reducing it by 75% when administered intravenously at the same time as IU bacterial inoculation, and by 48% when administered intravenously 4 h after IU bacterial infection. This effect on preterm delivery was accompanied by a parallel benefit on fetal survival in utero. SP-A had no effect on bacterial growth but reversed several major consequences of infection, including increased production of inflammatory mediators and a shift in macrophage polarization to the M1 phenotype. These findings suggest that exogenous SP-A has potential use to counteract infection-induced labor by reversing its proinflammatory consequences.

Inflammatory Stimuli Increase Progesterone Receptor-A Stability and Transrepressive Activity in Myometrial Cells

The steroid hormone progesterone acting via the nuclear progesterone receptor (PR) isoforms, progesterone receptor A (PR-A) and progesterone receptor B (PR-B), is essential for the maintenance of uterine quiescence during pregnancy. Inhibition of PR signaling augments uterine contractility and induces labor. Human parturition is thought to be triggered by modulation of PR signaling in myometrial cells to induce a functional progesterone withdrawal. One mechanism for functional progesterone withdrawal is increased abundance of PR-A, which decreases progesterone responsiveness by inhibiting the transcriptional activity of PR-B. Human parturition also involves tissue-level inflammation within the myometrium. This study examined the control of PR-A abundance and transrepressive activity in myometrial cells and the role of the inflammatory stimuli in the form of interleukin-1β (IL-1β) and lipopolysaccharide (LPS) in these processes. We found that abundance of PR-A was markedly increased by progesterone and by exposure to IL-1β and LPS via posttranslational mechanisms involving increased PR-A protein stability. In contrast, progesterone decreased abundance of PR-B by increasing its rate of degradation. Together, progesterone and proinflammatory stimuli induced a PR-A-dominant state in myometrial cells similar to that observed in term laboring myometrium. IL-1β and LPS also increased the capacity for PR-A to inhibit the transcriptional activity of PR-B. Taken together, our data suggest that proinflammatory stimuli increase the steady-state levels of PR-A and its transrepressive activity in myometrial cells and support the hypothesis that tissue-level inflammation triggers parturition by inducing PR-A-mediated functional progesterone withdrawal.

Contributions to the dynamics of cervix remodeling prior to term and preterm birth

Major clinical challenges for obstetricians and neonatologists result from early cervix remodeling and preterm birth. Complications related to cervix remodeling or delivery account for significant morbidity in newborns and peripartum mothers. Understanding morphology and structure of the cervix in pregnant women is limited mostly to the period soon before and after birth. However, evidence in rodent models supports a working hypothesis that a convergence of factors promotes a physiological inflammatory process that degrades the extracellular collagen matrix and enhances biomechanical distensibility of the cervix well before the uterus develops the contractile capabilities for labor. Contributing factors to this remodeling process include innervation, mechanical stretch, hypoxia, and proinflammatory mediators. Importantly, the softening and shift to ripening occurs while progesterone is near peak concentrations in circulation across species. Since progesterone is required to maintain pregnancy, the premise of this review is that loss of responsiveness to progesterone constitutes a common final mechanism for remodeling the mammalian cervix in preparation for birth at term. Various inputs are suggested to promote signaling between stromal cells and resident macrophages to drive proinflammatory processes that advance the soft cervix into ripening. With infection, pathophysiological processes may prematurely drive components of this remodeling mechanism and lead to preterm birth. Identification of critical molecules and pathways from studies in various rodent models hold promise for novel endpoints to assess risk and provide innovative approaches to treat preterm birth or promote the progress of ripening at term.

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.

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.

Depletion of polymorphonuclear leukocytes has no effect on preterm delivery in a mouse model of Escherichia coli-induced labor

OBJECTIVE

The objective of the study was to investigate the role of polymorphonuclear leukocytes (PMNs) in a mouse model of Escherichia coli-induced labor.

STUDY DESIGN

Intraperitoneal injection of rabbit antimouse PMN antiserum or control was performed in CD-1 mice 29 hours and 5 hours prior to laparotomy and intrauterine injection of either killed E coli or phosphate-buffered saline on day 14.5 of pregnancy. Preterm delivery was defined as delivery of at least 1 pup within 48 hours. Circulating leukocyte counts were determined manually or by flow cytometry at the time of surgery and 8, 24, and 48 hours afterward. Maternal and fetal tissues were analyzed in a separate group of animals 8 hours after surgery.

RESULTS

Pretreatment with anti-PMN antiserum significantly decreased the numbers of circulating leukocytes and the proportion of neutrophils among all leukocytes by 70-80% at surgery and at least 8 hours thereafter. Neutrophil depletion significantly reduced 2 markers of neutrophil activation in the uterus and placenta (neutrophil elastase and myeloperoxidase activity) and neutrophil infiltration into gestational tissues in bacterially treated animals to baseline (control) levels but did not affect preterm birth rates. The large E coli-induced increases in uterine inflammatory markers (interleukin-1β, tumor necrosis factor, chemokine ligand-5, cyclooxygenase-2) were not affected or were only minimally affected by neutrophil depletion.

CONCLUSION

Although PMN antiserum reduces both neutrophil number and activity, it does not diminish sensitivity to bacterially induced delivery or meaningfully alter the expression of inflammatory markers in the mouse model. Preterm birth and inflammation in this model are not likely to depend on neutrophil function.

Mechanical signaling in reproductive tissues: mechanisms and importance

The organs of the female reproductive system are among the most dynamic tissues in the human body, undergoing repeated cycles of growth and involution from puberty through menopause. To achieve such impressive plasticity, reproductive tissues must respond not only to soluble signals (hormones, growth factors, and cytokines) but also to physical cues (mechanical forces and osmotic stress) as well. Here, we review the mechanisms underlying the process of mechanotransduction-how signals are conveyed from the extracellular matrix that surrounds the cells of reproductive tissues to the downstream molecules and signaling pathways that coordinate the cellular adaptive response to external forces. Our objective was to examine how mechanical forces contribute significantly to physiological functions and pathogenesis in reproductive tissues. We highlight how widespread diseases of the reproductive tract, from preterm labor to tumors of the uterus and breast, result from an impairment in mechanical signaling.

Probiotic Lactobacillus rhamnosus GR-1 supernatant prevents lipopolysaccharide-induced preterm birth and reduces inflammation in pregnant CD-1 mice

OBJECTIVE

The objective of this study was to determine the effect of probiotic Lactobacillus rhamnosus GR-1 supernatant (GR-1 SN) on lipopolysaccharide-induced preterm birth (PTB) and outputs of cytokines, chemokines, and progesterone in pregnant CD-1 mice.

STUDY DESIGN

We compared PTB rates after intrauterine injection of lipopolysaccharide with and without previous GR-1 SN treatment. Cytokines and chemokines in the maternal plasma, myometrium, placenta, and amniotic fluid were examined with multiplex assay, and circulating maternal progesterone was measured with enzyme-linked immunoassay. Statistical significance was assessed with 2-tailed 1-way analysis of variance or analysis of variance on ranks. Fetal sex ratios in mice that delivered preterm were compared with those that delivered at term after lipopolysaccharide and GR-1 SN treatments.

RESULTS

GR-1 SN reduced lipopolysaccharide-induced PTB by 43%. GR-1 SN significantly decreased the lipopolysaccharide-induced production of interleukin (IL)-1β, -6, and -12p40, tumor necrosis factor-α, CCL4, and CCL5 in maternal plasma; IL-6, -12p70, -17, and -13 and tumor necrosis factor-α in myometrium; IL-6, -12p70, and -17 in placenta; and IL-6, tumor necrosis factor-α, CCL3, and CCL4 in amniotic fluid. Maternal plasma progesterone was reduced significantly after lipopolysaccharide injection with and without GR-1 SN pretreatment. There was no difference in fetal sex ratios between mice that delivered preterm and those that did not after lipopolysaccharide and GR-1 SN treatments.

CONCLUSION

The supernatant of probiotic L rhamnosus GR-1 attenuated lipopolysaccharide-induced inflammation and PTB in vivo. GR-1 SN may confer therapeutic benefits in the prevention of infection-associated PTB by controlling systemic and intrauterine inflammation.

Hormonal influences on neuroimmune responses in the CNS of females

Particular reproductive stages such as lactation impose demands on the female. To cope with these demands, her physiology goes through numerous adaptations, for example, attenuation of immune and stress responses. Hormonal fluctuation during lactation exerts a strong influence, inducing neuroplasticity in the hypothalamus and extrahypothalamic regions, and diminishing the stress and inflammatory responses. Thus, hormones confer decreased vulnerability to the female brain. This mini-review focuses on the adaptations of the immune and stress response during maternity, and on the neuroprotective actions of progesterone and prolactin and their effects on inflammation. The importance of pregnancy and lactation as experimental models to study immune responses and disease is also highlighted.

Prostaglandins are essential for cervical ripening in LPS-mediated preterm birth but not term or antiprogestin-driven preterm ripening

Globally, an estimated 13 million preterm babies are born each year. These babies are at increased risk of infant mortality and life-long health complications. Interventions to prevent preterm birth (PTB) require an understanding of processes driving parturition. Prostaglandins (PGs) have diverse functions in parturition, including regulation of uterine contractility and tissue remodeling. Our studies on cervical remodeling in mice suggest that although local synthesis of PGs are not increased in term ripening, transcripts encoding PG-endoperoxide synthase 2 (Ptgs2) are induced in lipopolysaccharide (LPS)-mediated premature ripening. This study provides evidence for two distinct pathways of cervical ripening: one dependent on PGs derived from paracrine or endocrine sources and the other independent of PG actions. Cervical PG levels are increased in LPS-treated mice, a model of infection-mediated PTB, consistent with increases in PG synthesizing enzymes and reduction in PG-metabolizing enzymes. Administration of SC-236, a PTGS2 inhibitor, along with LPS attenuated cervical softening, consistent with the essential role of PGs in LPS-induced ripening. In contrast, during term and preterm ripening mediated by the antiprogestin, mifepristone, cervical PG levels, and expression of PG synthetic and catabolic enzymes did not change in a manner that supports a role for PGs. These findings in mice, supported by correlative studies in women, suggest PGs do not regulate all aspects of the parturition process. Additionally, it suggests a need to refocus current strategies toward developing therapies for the prevention of PTB that target early, pathway-specific processes rather than focusing on common late end point mediators of PTB.

Detection of anti-HLA antibodies in maternal blood in the second trimester to identify patients at risk of antibody-mediated maternal anti-fetal rejection and spontaneous preterm delivery

PROBLEM

Maternal anti-fetal rejection is a mechanism of disease in spontaneous preterm labor. The objective of this study was to determine whether the presence of human leukocyte antigen (HLA) panel-reactive antibodies (PRA) during the second trimester increases the risk of spontaneous preterm delivery.

METHODS OF STUDY

This longitudinal case-control study included pregnant women with spontaneous preterm deliveries (n = 310) and control patients with normal term pregnancies (n = 620), matched for maternal age and gravidity. Maternal plasma samples obtained at 14-16, 16-20, 20-24, and 24-28 weeks of gestation were analyzed for HLA class I and class II PRA positivity using flow cytometry. The fetal HLA genotype and maternal HLA alloantibody epitope were determined for a subset of patients with positive HLA PRA.

RESULTS

(i) Patients with spontaneous preterm delivery were more likely to exhibit HLA class I (adjusted OR = 2.54, P < 0.0001) and class II (adjusted OR = 1.98, P = 0.002) PRA positivity than those delivering at term; (ii) HLA class I PRA positivity for patients with spontaneous preterm delivery between 28 and 34 weeks (adjusted OR = 2.88; P = 0.001) and after 34 weeks of gestation (adjusted OR = 2.53; P < 0.0001) was higher than for those delivering at term; (iii) HLA class II PRA positivity for patients with spontaneous preterm delivery after 34 weeks of gestation was higher than for those delivering at term (adjusted OR = 2.04; P = 0.002); (iv) multiparous women were at a higher risk for HLA class I PRA positivity than nulliparous women (adjusted OR = 0.097, P < 0.0001 for nulliparity); (v) nulliparous women had a higher rate of HLA class I PRA positivity with advancing gestational age (P = 0.001); and (vi) 78% of women whose fetuses were genotyped had alloantibodies specific against fetal HLA class I antigens.

CONCLUSION

Pregnant women with positive HLA class I or class II PRA during the second trimester are at an increased risk of spontaneous preterm delivery due to antibody-mediated maternal anti-fetal rejection.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) enhances placental inflammation

Preterm birth is a leading cause of perinatal morbidity and mortality that is often associated with ascending infections from the lower genital tract. Recent studies with animal models have suggested that developmental exposure to the environmental toxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) can increase the risk of preterm birth in the offspring. How TCDD may modify placental immunity to ascending infections is unclear. Therefore, we studied the effects of TCDD treatment on basal and Escherichia coli-stimulated cytokine production by placental explants. Cultures of second-trimester placentas were treated with up to 40 nM TCDD for 72 h and then stimulated with 10(7)CFU/ml E. coli for an additional 24h. Concentrations of cytokines and PGE2 were measured in conditioned medium by immunoassay. TCDD exposure increased mRNA levels of IL-1β by unstimulated cultures, but no effects on protein levels of this cytokine were detected. TNF-α production was unaffected by TCDD for unstimulated cultures, but pre-treatment with 40 nM TCDD significantly increased E. coli-stimulated TNF-α production. Both basal and bacteria-stimulated PGE2 and COX-2 gene expression were enhanced by TCDD pretreatment. In contrast, production of the anti-inflammatory cytokine, IL-10, was reduced by TCDD pretreatment for both unstimulated and E. coli-stimulated cultures. No effect of TCDD on the viability of the cultures was detected. These results suggest that TCDD exposure may shift immunity to enhance a proinflammatory phenotype at the maternal-fetal interface that could increase the risk of infection-mediated preterm birth.

Progesterone is essential for protecting against LPS-induced pregnancy loss. LIF as a potential mediator of the anti-inflammatory effect of progesterone

Lipopolysaccharide (LPS) administration to mice on day 7 of gestation led to 100% embryonic resorption after 24 h. In this model, nitric oxide is fundamental for the resorption process. Progesterone may be responsible, at least in part, for a Th2 switch in the feto-maternal interface, inducing active immune tolerance against fetal antigens. Th2 cells promote the development of T cells, producing leukemia inhibitory factor (LIF), which seems to be important due to its immunomodulatory action during early pregnancy. Our aim was to evaluate the involvement of progesterone in the mechanism of LPS-induced embryonic resorption, and whether LIF can mediate hormonal action. Using in vivo and in vitro models, we provide evidence that circulating progesterone is an important component of the process by which infection causes embryonic resorption in mice. Also, LIF seems to be a mediator of the progesterone effect under inflammatory conditions. We found that serum progesterone fell to very low levels after 24 h of LPS exposure. Moreover, progesterone supplementation prevented embryonic resorption and LPS-induced increase of uterine nitric oxide levels in vivo. Results show that LPS diminished the expression of the nuclear progesterone receptor in the uterus after 6 and 12 h of treatment. We investigated the expression of LIF in uterine tissue from pregnant mice and found that progesterone up-regulates LIF mRNA expression in vitro. We observed that LIF was able to modulate the levels of nitric oxide induced by LPS in vitro, suggesting that it could be a potential mediator of the inflammatory action of progesterone. Our observations support the view that progesterone plays a critical role in a successful pregnancy as an anti-inflammatory agent, and that it could have possible therapeutic applications in the prevention of early reproductive failure associated with inflammatory disorders.

Cervical remodeling in term and preterm birth: insights from an animal model

Proper cervical function is essential for a normal pregnancy and birth to occur. Understanding the mechanisms that take place in normal pregnancy will allow a better comprehension of the complications involved in premature cervical remodeling and lead to better methods of diagnostics and prevention for preterm birth. Unfortunately, human samples are not easily available, and samples that are collected are often confounded by variations in timing and region of cervix from which sample is collected. Animal models, specifically the mouse, have facilitated a great deal of exploration into the mechanisms of cervical function and pathways of preterm birth. This review highlights some of the groundbreaking discoveries that have arisen from murine research including 1) the identification of early pregnancy changes in collagen fibril processing and assembly that result in progressive modifications to collagen architecture with subsequent loss of tissue stiffness during pregnancy, 2) the determination that immune cells are not key to cervical ripening at term but have diverse phenotypes and functions in postpartum repair, and 3) the finding that the process of preterm cervical ripening can differ from term ripening and is dependent on the etiology of prematurity. These findings, which are relevant to human cervical biology, provide new insights that will allow targeted studies on the human cervix as well as identify potential biomarkers for early detection of premature cervical ripening and development of improved therapies to prevent premature ripening of the cervix and subsequent preterm birth.

Expression of coagulation-related protein genes during LPS-induced preterm delivery in the pregnant mouse

Preterm delivery (PTD) has been associated with inflammation along with activation of the coagulation pathway. These studies sought to characterize the expression of several coagulation pathway genes including plasminogen activator inhibitor 1 (PAI-1), tissue factor (TF), protease-activated receptor 1 (Par1), protease-activated receptor 2 (Par2), fibrinogen-like protein 2 (Fgl2), and thrombomodulin (TM) during lipopolysaccharide (LPS)-induced PTD in day 15 pregnant CD-1 mice. Western blot studies confirmed protein expression for PAI-1, Par1, Par2, Fgl2, and TM in the mouse uterus. Quantitative reverse transcriptase polymerase chain reaction (RT-PCR) confirmed increased PAI-1 messenger RNA (mRNA) in the uteri, lung, kidney, and liver tissues at 2 to 6 hours after LPS injection. In contrast, TF expression significantly decreased by 12 hours in uterine tissue; whereas, its expression was unchanged in the other maternal tissues. The uterine mRNA for Par1, Par2, Fgl2, and TM remained stable. In summary, these studies have confirmed expression of coagulation pathway genes within the pregnant uterus; some of which are modulated during LPS-induced PTD.

The molecular mechanisms of cervical ripening differ between term and preterm birth

In the current study, the mechanisms of premature cervical ripening in murine models of preterm birth resulting from infection or early progesterone withdrawal were compared with the process of term cervical ripening. Tissue morphology, weight, gene expression, and collagen content along with immune cell populations were evaluated. Premature ripening induced by the progesterone receptor antagonist mifepristone results from an acceleration of processes in place during term ripening as well as partial activation of proinflammatory and immunosuppressive processes observed during postpartum repair. In contrast to term or mifepristone-induced preterm ripening, premature ripening induced in an infection model occurs by a distinct mechanism which is dominated by an influx of neutrophils into the cervix, a robust proinflammatory response and increased expression of prostaglandin-cyclooxygenase-endoperoxide synthase 2, important in prostaglandin biosynthesis. Key findings from this study confirm that cervical ripening can be initiated by more than one mechanism and is not necessarily an acceleration of the physiologic process at term. These results will influence current strategies for identifying specific etiologies of preterm birth and developing subsequent therapies.

Synergy between viral and bacterial toll-like receptors leads to amplification of inflammatory responses and preterm labor in the mouse

Toll-like receptors (TLRs) recognize molecular constituents of pathogens and activate host innate immune responses. TLR2 responds to Gram-positive organisms and components of their cell walls. TLR3 responds to double-stranded RNA (an intermediate in viral replication). A mouse macrophage cell line (RAW 264.7) and freshly obtained mouse peritoneal macrophages were treated in tissue culture for 5 or 10 h with either peptidoglycan (PGN; a TLR2 ligand, 1 μg/ml), polyinosinic:cytidylic acid (poly(I:C); a TLR3 ligand, 10 μg/ml), both PGN and poly(I:C), or neither. Total RNA was extracted, and RT-PCR was performed. A mouse model of preterm birth induced by intrauterine injection of TLR ligands was used to test in vivo effects. Compared to stimulation with either PGN or poly(I:C) alone, stimulation of macrophages with both ligands (whether simultaneously or sequentially) resulted in synergistic expression of inflammatory mediators, including inducible nitric oxide synthase, interleukin 1 beta, tumor necrosis factor alpha, and the chemokine CCL5 (RANTES). Using peritoneal macrophages obtained from mutant and control mice, this synergy was determined to be dependent upon TLR2 and the TLR-related intracellular adaptor proteins MYD88 and TICAM1 (TRIF). Simultaneous administration of both PGN and poly(I:C) to pregnant mice also produced dramatic synergy in the occurrence of preterm delivery. These results support a possible role for viral infection in preterm labor. Synergy in the mechanisms of parturition suggests the existence of a "two-hit" trigger mechanism that minimizes responses to stimuli of limited biological significance while providing an efficient amplification strategy for rapid activation of labor in response to multiple or more severe insults.

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.

Resistance to lipopolysaccharide-induced preterm delivery mediated by regulatory T cell function in mice

Intrauterine or intraperitoneal administration of lipopolysaccharide (LPS) into normal mice at midgestation induces preterm delivery (PTD) within 24 h through a mechanism dependent on Toll-like receptor signaling and expression of inflammatory cytokines. The exact participants in the cellular network involved in PTD are not known. Although the activities of innate immune cells are thought to be important, the extent to which this process depends on T and B cells has yet to be examined. Mice deficient in T and B cells due to genetic deficiency in the recombination activating gene 1 (Rag1(-/-)) were given LPS intraperitoneally on Day 15 of gestation and found to be susceptible to LPS-induced PTD. This was found to involve many of the inflammatory mediators reported as important in normal mice. Moreover, at a low dose (3 microg), pregnant Rag1(-/-) mice were found to be more susceptible to PTD than a cohort of normal mice on the same genetic background. This increased susceptibility was partially reversed by transfer, on Day 10 of gestation, of whole lymphocytes or purified CD4(+) T cells. Transfer of purified CD4(+) T cells to Rag1(-/-) mice resulted in a uterine draining node population of FOXP3(+) cells, suggesting that these cells may contribute to resistance to LPS-induced PTD. Overall, the data suggest that, although T and B lymphocytes are not critical positive regulators of LPS-induced PTD, CD4(+) T cells play a protective and regulatory role, and thus could be a target for preventive or therapeutic manipulation.

The genetics of birth timing: insights into a fundamental component of human development

The timing of birth necessitates the coupling of fetal maturation with the onset of parturition, and occurs at characteristic, but divergent gestations between mammals. Preterm birth in humans is an important but poorly understood outcome of pregnancy that uncouples fetal maturation and birth timing. The etiology of preterm birth is complex, involving environmental and genetic factors whose underlying molecular and cellular pathogenic mechanisms remain poorly understood. Animal models, although limited by differences with human physiology, have been crucial in exploring the role of various genetic pathways in mammalian birth timing. Studies in humans of both familial aggregation and racial disparities in preterm birth have contributed to the understanding that preterm birth is heritable. A significant portion of this heritability is due to polygenic causes with few true Mendelian disorders contributing to preterm birth. Thus far, studies of the human genetics of preterm birth using a candidate gene approach have met with limited success. Emerging research efforts using unbiased methods may yield promising results if concerns about study design can be adequately addressed. The findings from this frontier of research may have direct implications for the allocation of public health and clinical resources as well as spur the development of more effective therapeutics.

The adaptor protein MyD88 is essential for E coli-induced preterm delivery in mice

OBJECTIVE

We used a mouse model of infection-induced preterm delivery to examine the roles of 2 adaptor proteins with central functions in Toll-like receptor signaling: MyD88 (myeloid differentiation primary-response gene 88) and TRIF (Toll/IL-1 receptor (TIR)-domain-containing adaptor protein-inducing IFN-beta).

STUDY DESIGN

Mice deficient (KO) for MyD88, TRIF, both (DKO) or neither (WT) were inoculated into the uterus with killed Escherichia coli. Delivery outcomes, fetal status, serum progesterone, and nuclear translocation of the transcription factor nuclear factor kappa B (NFkappaB) were determined.

RESULTS

Preterm birth (delivery in less than 48 hours) occurred in WT and TRIF-KO animals in a dose-dependent fashion, reaching 100% with 5-10 x 10(9) bacteria, while MyD88-KO and DKO animals were completely protected from delivery. Intrauterine fetal survival, maintenance of circulating progesterone levels, and nuclear translocation of NFkappaB were also dependent upon MyD88 but not TRIF. In contrast, induction of uterine interleukin (IL)-1beta and tumor necrosis factor alpha (TNF-alpha) depends upon actions of both MyD88 and TRIF.

CONCLUSION

E coli-induced preterm delivery in the mouse is completely dependent upon MyD88 but not TRIF.

Insights into parturition biology from genetically altered mice

With the growing frequency of preterm birth, increased effort has been made to elucidate the physiology of normal and aberrant parturition. As with many developmental processes, the study of genetically altered mice has led to an increased understanding of mechanisms controlling the maintenance and resolution of pregnancy. Studies in genetically altered mice have implicated critical roles for both prostaglandin synthesis and degradation in luteolysis and the progression of labor. The importance of local modulation of progesterone activity to cervical ripening has also been demonstrated. Although a decline in levels of serum progesterone is a part of normal labor initiation in mice but not humans, murine labor without progesterone withdrawal has been reported in some cases. These findings emphasize the importance of other components of the parturition cascade that are shared in mice and humans and highlights the importance of an increased understanding of the physiology of mouse parturition.

Angiogenesis gene expression in mouse uterus during the common pathway of parturition

OBJECTIVE

The objective of the study was to investigate changes in the expression of angiogenesis-related genes during the common terminal pathway of parturition including spontaneous labor at term, as well as preterm labor (PTL), induced by either bacteria or ovariectomy.

STUDY DESIGN

Preterm pregnant mice (14.5 days of gestation) were treated with the following: (1) intrauterine injection of media; (2) intrauterine injection of heat-inactivated Escherichia coli; (3) ovariectomy; and (4) sham operation. Tissues from mice at term (19.5 days of gestation) were collected at term not in labor, term in labor, and 12 hours postpartum. Angiogenesis-related gene expression levels were quantitated by the measurement of specific mRNAs in uterine tissue by RT-qPCR and analyzed by repeated-measures analysis of variance.

RESULTS

The following results were found: (1) microarray analysis of the uterine transcriptome indicated an enrichment for the gene ontology category of angiogenesis in bacteria-induced PTL samples (P < or = .093); (2) several genes related to angiogenesis demonstrated significantly increased expression in samples in either term spontaneous labor or preterm labor; and (3) qRT-PCR measurements demonstrated that spontaneous term labor and preterm labor induced by either bacteria or ovariectomy all substantially increased the expression of multiple angiogenesis-related genes (P < or = .0003; Angpt2, Ctgf, Cyr61, Dscr1, Pgf, Serpine1, Thbs1, and Wisp 1).

CONCLUSION

Spontaneous labor at term, as well as pathologically induced preterm labor, all result in greatly increased expression of angiogenesis-related genes in the uterus.

PDE4 inhibition prevents preterm delivery induced by an intrauterine inflammation

The aim of this study was to explore the anti-inflammatory properties of phosphodiesterase-4 (PDE4) inhibitors in vivo and their potential ability to prevent inflammation-induced preterm delivery. Indeed, intrauterine inflammation is the major etiology of very preterm delivery, the leading cause of neonatal mortality and morbidity. Intrauterine injection of Escherichia coli LPS in 15-day-pregnant mice induced an increase of PDE4 activity and PDE4B expression at the maternofetal interface, a rise of amniotic fluid levels of TNF-alpha, IL-1beta, IL-6, and IL-10 and provoked massive preterm delivery and fetal demise. Selective PDE4 inhibition by rolipram prevented the rise in the proinflammatory cytokines. Following the nuclear translocation of the transcription factor NFkappaB, as a marker of cellular activation after the inflammatory challenge, showed a time-dependent sequential activation of the gestational tissues, from the uterine mesometrial to the fetal compartment, particularly in the glycogen-trophoblastic cells of the placenta. This activation was disrupted by PDE4 inhibition, and inflammation-induced preterm delivery and fetal demise were prevented. PDE4 selective inhibitors may thus represent a novel effective treatment to delay inflammation-induced preterm delivery and to prevent adverse outcomes in infants.

The preterm parturition syndrome

The implicit paradigm that has governed the study and clinical management of preterm labour is that term and preterm parturition are the same processes, except for the gestational age at which they occur. Indeed, both share a common pathway composed of uterine contractility, cervical dilatation and activation of the membranes/decidua. This review explores the concept that while term labour results from physiological activation of the components of the common pathway, preterm labour arises from pathological signalling and activation of one or more components of the common pathway of parturition. The term "great obstetrical syndromes" has been coined to reframe the concept of obstetrical disease. Such syndromes are characterised by: (1) multiple aetiology; (2) long preclinical stage; (3) frequent fetal involvement; (4) clinical manifestations that are often adaptive in nature; and (5) gene-environment interactions that may predispose to the syndromes. This article reviews the evidence indicating that the pathological processes implicated in the preterm parturition syndrome include: (1) intrauterine infection/inflammation; (2) uterine ischaemia; (3) uterine overdistension; (4) abnormal allograft reaction; (5) allergy; (6) cervical insufficiency; and (7) hormonal disorders (progesterone related and corticotrophin-releasing factor related). The implications of this conceptual framework for the prevention, diagnosis, and treatment of preterm labour are discussed.

Disruption of interleukin-18, but not interleukin-1, increases vulnerability to preterm delivery and fetal mortality after intrauterine inflammation

Preterm birth is a major contributor of adverse perinatal outcome. Clinical data suggest that an inflammatory response is important in the process leading to preterm labor. By using a recently introduced mouse model of localized intrauterine lipopolysaccharide-induced inflammation, the effect of interleukin (IL)-18 gene disruption and/or IL-18 neutralization as well as combined IL-1alpha/beta gene disruption on inflammation-induced fetal loss was investigated. The frequency of preterm fetal loss was significantly higher in IL-18 knockout mice (58.9%) and in mice administered IL-18-binding protein (59.7%) compared to wild-type controls (34.7%). The rate of fetal loss was not affected by IL-1alpha/beta gene deficiency (38.7%). Decreased IL-18 protein expression combined with elevated IL-12 protein expression in uterine tissue of IL-18 knockout mice and IL-18-binding protein-treated animals was noticed. These data demonstrate that preterm pregnancy loss in response to intrauterine inflammation was enhanced by disruption of the IL-18 gene and/or IL-18 neutralization, events that may relate to exaggerated Th1 responses because of an increased IL-12/IL-18 ratio.

Anti-inflammatory interventions in pregnancy: now and the future

A growing body of evidence implicates inflammatory pathways in adverse reproductive outcomes. This expanding evidence suggests that anti-inflammatory interventions may hold promise in reducing the maternal and neonatal morbidities and mortalities associated with these obstetrical complications. Preterm birth, preeclampsia, pregnancy loss and adverse neonatal outcomes have all been associated with the activation of inflammatory pathways during pregnancy. Because of the number of observational human studies, as well as animal models of preterm birth, the mechanisms by which inflammation may promote preterm parturition and adverse effects on the fetus are beginning to be elucidated. Although the future use of anti-inflammatory interventions in this context holds significant promise, much research is still warranted. Only when the pathogenesis of obstetrical complications is more fully understood can meaningful therapeutic interventions become a realistic goal.

Uterine transcriptomes of bacteria-induced and ovariectomy-induced preterm labor in mice are characterized by differential expression of arachidonate metabolism genes

OBJECTIVE

The purpose of this study was to identify changes in gene expression that are associated with preterm labor induced by either bacteria or ovariectomy.

STUDY DESIGN

Pregnant mice (14.5 days of gestation) were allocated to: (1) intrauterine injection of heat-inactivated Escherichia coli; (2) media alone; (3) ovariectomy; or (4) sham operation. The uterine transcriptome was studied with photolithographic, very short oligonucleotide-based microarrays, and arachidonate metabolism genes were assayed with quantitative reverse transcriptase-polymerase chain reaction. Significance was determined by analysis of variance.

RESULTS

Microarray-based gene expression changes in the arachidonate metabolism pathway are associated globally with bacteria-induced preterm labor (P < or = .0031) and ovariectomy-induced preterm labor (P < or = .00036). Quantitative real-time reverse transcriptase-polymerase chain reaction measurements demonstrated that bacteria-induced preterm labor substantially increased the expression of genes involved in prostaglandin synthesis. In contrast, ovariectomy-induced preterm labor increased the expression of genes involved in lipoxin, leukotriene, and hydroxyeicosatetraenoic acid synthesis.

CONCLUSION

Bacteria-induced and ovariectomy-induced preterm labor each express a different balance of genes that are required for the synthesis of prostaglandins, lipoxins, leukotrienes, and hydroxyeicosatetraenoic acids.

Utilization of different aquaporin water channels in the mouse cervix during pregnancy and parturition and in models of preterm and delayed cervical ripening

Biochemical changes of cervical connective tissue, including progressive disorganization of the collagen network and increased water content, occur during gestation to allow for cervical dilatation during labor, but the mechanisms that regulate cervical fluid balance are not fully understood. We examined whether aquaporins (AQPs), a family of membrane channel proteins that facilitate water transport, help mediate fluid balance in the mouse cervix during parturition. Of the 13 known murine AQPs, AQP0-2, 6, 7, 9, 11, and 12 were absent or at the limits of detection. By Northern blot and real-time PCR, AQP3 expression was low in nongravid and mid-pregnancy cervices with peak expression on d 19 and postpartum d 1 (PP1). AQP4 expression was generally low throughout pregnancy but showed a small upward trend at the time of parturition. AQP5 and AQP8 expression were significantly increased on d 12-15 but fell to nongravid/baseline by d 19 and PP1. By in situ hybridization and immunohistochemistry, AQP3 was preferentially expressed in basal cell layers of the cervical epithelium, whereas AQP4, 5, and 8 were primarily expressed in apical cell layers. Females with LPS-induced preterm labor had similar trends in AQP4, 5, and 8 expression to mice with natural labor at term gestation. Mice with delayed cervical remodeling due to deletion of the steroid 5alpha-reductase type 1 gene showed significant reduction in the levels of AQP3, 4, and 8 on d 19 or PP1. Together, these studies suggest that AQPs 3, 4, 5, and 8 regulate distinct aspects of cervical water balance during pregnancy and parturition.

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.

Animal models of preterm birth

Preterm birth continues to pose a significant clinical dilemma and contributes to both acute and long-term neonatal morbidity. Despite efforts, the incidence of preterm birth has not decreased, partly because of our lack of understanding of the mechanisms that trigger parturition. Animal models are essential research tools for investigating the pathways that promote preterm parturition and for testing therapeutic interventions. Growing evidence correlates infection or inflammation with preterm birth. Consequently, many investigators have created animal models that reflect these findings. Current models of preterm parturition include diverse species, varying means of inducing an inflammatory or infectious state, and different routes of administration. Although each of these models can advance our knowledge, it is important to understand their advantages, disadvantages and unique characteristics. An understanding of such models will hopefully promote continued research that will ultimately lead to a decrease in preterm birth and an improvement in neonatal outcome.

Medroxyprogesterone acetate, but not progesterone, protects against inflammation-induced parturition and intrauterine fetal demise

OBJECTIVE

This study was undertaken to determine whether progestational agents can prevent inflammation-induced preterm parturition and fetal demise.

STUDY DESIGN

The activation of contractile and inflammatory pathways in response to localized intrauterine inflammation was investigated by using quantitative polymerase chain reaction (PCR). Serum progesterone (P4) levels and alterations in progesterone receptor-B (PR-B) were determined with radioimmunoassay and quantitative PCR, respectively. With our in vivo model of intrauterine inflammation, animals were randomly assigned to pretreatment with P4 or medroxyprogesterone acetate (MPA) before intrauterine lipopolysaccharide (LPS). Animals were observed for preterm delivery. The number of live pups 48 hours after intrauterine LPS was recorded for each treatment group. The ability of MPA to alter signal transduction pathways leading to preterm parturition were investigated by quantitative PCR and histochemical studies.

RESULTS

Intrauterine inflammation is associated with decreased serum progesterone levels and decreased transcription of PR-B. Preterm delivery rates were 100% for LPS alone, 63% for LPS+P4, and 0% for LPS+MPA. No live pups remained at 48 hours in the LPS or LPS+P4 groups. Pretreatment with MPA significantly preserved fetal viability. MPA suppressed activation of contraction-associated genes and inflammatory mediators and prevented cervical ripening in response to intrauterine inflammation.

CONCLUSION

MPA, with its progestational and anti-inflammatory properties, prevented inflammation-induced preterm parturition and significantly preserved fetal viability.

Immunology of term and preterm labor

During pregnancy there is an alteration in maternal immunity within the uterus where innate, proinflammatory immune responses are tightly regulated to prevent immunological rejection of the fetal allograft. Disruption of the delicate balance of cytokines by bacteria or other factors increases the production of proinflammatory cytokines at the maternal-fetal interface and activates the parturition mechanism prematurely. Despite years of searching, there is still no broadly effective strategy for preventing preterm labor and most therapies are directed at inhibiting myometrial contractions and improving neonatal outcome. Recent studies with progestins and interleukin-10 (IL-10), however, are showing promise in randomized clinical trials and animal studies. Furthermore, the identification of the Toll-like receptors as upstream mediators of inflammation may offer alternative therapeutic targets for preventing this common pregnancy complication.