Arrest of mouse preterm labor until term delivery by combination therapy with atosiban and mundulone, a natural product with tocolytic efficacy

There is a lack of FDA-approved tocolytics for the management of preterm labor (PL). In prior drug discovery efforts, we identified mundulone and mundulone acetate (MA) as inhibitors of in vitro intracellular Ca2+-regulated myometrial contractility. In this study, we probed the tocolytic potential of these compounds using human myometrial samples and a mouse model of preterm birth. In a phenotypic assay, mundulone displayed greater efficacy, while MA showed greater potency and uterine-selectivity in the inhibition of intracellular-Ca2+ mobilization. Cell viability assays revealed that MA was significantly less cytotoxic. Organ bath and vessel myography studies showed that only mundulone exerted inhibition of myometrial contractions and that neither compounds affected vasoreactivity of ductus arteriosus. A high-throughput combination screen identified that mundulone exhibits synergism with two clinical-tocolytics (atosiban and nifedipine), and MA displayed synergistic efficacy with nifedipine. Of these combinations, mundulone+atosiban demonstrated a significant improvement in the in vitro therapeutic index compared to mundulone alone. The ex vivo and in vivo synergism of mundulone+atosiban was substantiated, yielding greater tocolytic efficacy and potency on myometrial tissue and reduced preterm birth rates in a mouse model of PL compared to each single agent. Treatment with mundulone after mifepristone administration dose-dependently delayed the timing of delivery. Importantly, mundulone+atosiban permitted long-term management of PL, allowing 71% dams to deliver viable pups at term (>day 19, 4-5 days post-mifepristone exposure) without visible maternal and fetal consequences. Collectively, these studies provide a strong foundation for the development of mundulone as a single or combination tocolytic for management of PL.

Arrest of mouse preterm labor until term delivery by combination therapy with atosiban and mundulone, a natural product with tocolytic efficacy

Currently, there is a lack of FDA-approved tocolytics for the management of preterm labor (PL). In prior drug discovery efforts, we identified mundulone and its analog mundulone acetate (MA) as inhibitors of in vitro intracellular Ca 2+ -regulated myometrial contractility. In this study, we probed the tocolytic and therapeutic potential of these small molecules using myometrial cells and tissues obtained from patients receiving cesarean deliveries, as well as a mouse model of PL resulting in preterm birth. In a phenotypic assay, mundulone displayed greater efficacy in the inhibition of intracellular-Ca 2+ from myometrial cells; however, MA showed greater potency and uterine-selectivity, based IC 50 and E max values between myometrial cells compared to aorta vascular smooth muscle cells, a major maternal off-target site of current tocolytics. Cell viability assays revealed that MA was significantly less cytotoxic. Organ bath and vessel myography studies showed that only mundulone exerted concentration-dependent inhibition of ex vivo myometrial contractions and that neither mundulone or MA affected vasoreactivity of ductus arteriosus, a major fetal off-target of current tocolytics. A high-throughput combination screen of in vitro intracellular Ca 2+ -mobilization identified that mundulone exhibits synergism with two clinical-tocolytics (atosiban and nifedipine), and MA displayed synergistic efficacy with nifedipine. Of these synergistic combinations, mundulone + atosiban demonstrated a favorable in vitro therapeutic index (TI)=10, a substantial improvement compared to TI=0.8 for mundulone alone. The ex vivo and in vivo synergism of mundulone and atosiban was substantiated, yielding greater tocolytic efficacy and potency on isolated mouse and human myometrial tissue and reduced preterm birth rates in a mouse model of PL compared to each single agent. Treatment with mundulone 5hrs after mifepristone administration (and PL induction) dose-dependently delayed the timing of delivery. Importantly, mundulone in combination with atosiban (FR 3.7:1, 6.5mg/kg + 1.75mg/kg) permitted long-term management of PL after induction with 30 μg mifepristone, allowing 71% dams to deliver viable pups at term (> day 19, 4-5 days post-mifepristone exposure) without any visible maternal and fetal consequences. Collectively, these studies provide a strong foundation for the future development of mundulone as a stand-alone single- and/or combination-tocolytic therapy for management of PL.

Development of the Mouse Placenta

Placenta forms as a momentary organ inside the uterus with a slew of activities only when the woman is pregnant. It is a discoid-shaped hybrid structure consisting of maternal and embryonic components. It develops in the mesometrial side of the uterus following blastocyst implantation to keep the two genetically different entities, the mother and embryo, separated but connected. The beginning and progression of placental formation and development following blastocyst implantation coincides with the chronological developmental stages of the embryo. It gradually acquires the ability to perform the vascular, respiratory, hepatic, renal, endocrine, gastrointestinal, immune, and physical barrier functions synchronously that are vital for fetal development, growth, and safety inside the maternal environment. The uterus ejects the placenta when its embryonic growth and survival supportive roles are finished; that is usually the birth of the baby. Despite its irreplaceable role in fetal development and survival over the post-implantation progression of pregnancy, it still remains unclear how it forms, matures, performs all of its activities, and starts to fail functioning. Thus, a detailed understanding about normal developmental, structural, and functional aspects of the placenta may lead to avoid pregnancy problems that arise with the placenta.

Comparative analysis of myometrial and vascular smooth muscle cells to determine optimal cells for use in drug discovery

Novel therapeutic regulators of uterine contractility are needed to manage preterm labor, induce labor and control postpartum hemorrhage. Therefore, we previously developed a high-throughput assay for large-scale screening of small molecular compounds to regulate calcium-mobilization in primary mouse uterine myometrial cells. The goal of this study was to select the optimal myometrial cells for our high-throughput drug discovery assay, as well as determine the similarity or differences of myometrial cells to vascular smooth muscle cells (VSMCs)-the most common off-target of current myometrial therapeutics. Molecular and pharmacological assays were used to compare myometrial cells from four sources: primary cells isolated from term pregnant human and murine myometrium, immortalized pregnant human myometrial (PHM-1) cells and immortalized non-pregnant human myometrial (hTERT-HM) cells. In addition, myometrial cells were compared to vascular SMCs. We found that the transcriptome profiles of hTERT-HM and PHM1 cells were most similar (r = 0.93 and 0.90, respectively) to human primary myometrial cells. Comparative transcriptome profiling of primary human myometrial transcriptome and VSMCs revealed 498 upregulated (p ≤ 0.01, log2FC≥1) genes, of which 142 can serve as uterine-selective druggable targets. In the high-throughput Ca²⁺-assay, PHM1 cells had the most similar response to primary human myometrial cells in OT-induced Ca²⁺-release (E_max = 195% and 143%, EC₅₀ = 30 nM and 120 nM, respectively), while all sources of myometrial cells showed excellent and similar robustness and reproducibility (Z' = 0.52 to 0.77). After testing a panel of 61 compounds, we found that the stimulatory and inhibitory responses of hTERT-HM cells were highly-correlated (r = 0.94 and 0.95, respectively) to human primary cells. Moreover, ten compounds were identified that displayed uterine-selectivity (≥5-fold E_max or EC₅₀ compared to VSMCs). Collectively, this study found that hTERT-HM cells exhibited the most similarity to primary human myometrial cells and, therefore, is an optimal substitute for large-scale screening to identify novel therapeutic regulators of myometrial contractility. Moreover, VSMCs can serve as an important counter-screening tool to assess uterine-selectivity of targets and drugs given the similarity observed in the transcriptome and response to compounds.

Monitoring uterine contractility in mice using a transcervical intrauterine pressure catheter

In mouse models used to study parturition or pre-clinical therapeutic testing, measurement of uterine contractions is limited to either ex vivo isometric tension or operative intrauterine pressure (IUP). The goal of this study was to: (1) develop a method for transcervical insertion of a pressure catheter to measure in vivo intrauterine contractile pressure during mouse pregnancy, (2) determine whether this method can be utilized numerous times in a single mouse pregnancy without affecting the timing of delivery or fetal outcome and (3) compare the in vivo contractile activity between mouse models of term and preterm labor (PTL). Visualization of the cervix allowed intrauterine pressure catheter (IUPC) placement into anesthetized pregnant mice (plug = day 1, delivery = day 19.5). The amplitude, frequency, duration and area under the curve (AUC) of IUP was lowest on days 16-18, increased significantly (P < 0.05) on the morning of day 19 and reached maximal levels during by the afternoon of day 19 and into the intrapartum period. An AUC threshold of 2.77 mmHg discriminated between inactive labor (day 19 am) and active labor (day 19 pm and intrapartum period). Mice examined on a single vs every experimental timepoint did not have significantly different IUP, timing of delivery, offspring number or fetal/neonatal weight. The IUP was significantly greater in LPS-treated and RU486-treated mouse models of PTL compared to time-matched vehicle control mice. Intrapartum IUP was not significantly different between term and preterm mice. We conclude that utilization of a transcervical IUPC allows sensitive assessment of in vivo uterine contractile activity and labor progression in mouse models without the need for operative approaches.

Development of a modular fluorescence overlay tissue imaging system for wide-field intraoperative surgical guidance

Fluorescence imaging is a well-established optical modality that has been used to localize and track fluorophores in vivo and has demonstrated great potential for surgical guidance. Despite the variety of fluorophores currently being researched, many existing intraoperative fluorescence imaging systems are specifically designed for a limited number of applications. We present a modular wide-field fluorescence overlay tissue imaging system for intraoperative surgical guidance that is comprised of commercially available standardized components. Its modular layout allows for the accommodation of a broad range of fluorophores, fields of view (FOV), and spatial resolutions while maintaining an integrated portable design for intraoperative use. Measurements are automatic and feature a real-time projection overlay technique that intuitively displays fluorescence maps directly onto a [Formula: see text] FOV from a working distance of 35 cm. At a 20-ms exposure time, [Formula: see text] samples of indocyanine green could be measured with high signal-to-noise ratio and was later tested in an in vivo mouse model before finally being demonstrated for intraoperative autofluorescence imaging of human soft tissue sarcoma margins. The system's modular design and ability to enable naked-eye visualization of wide-field fluorescence allow for the flexibility to adapt to numerous clinical applications and can potentially extend the adoption of fluorescence imaging for intraoperative use.

Prostaglandin-Endoperoxide Synthase 1 Mediates the Timing of Parturition in Mice Despite Unhindered Uterine Contractility

Cyclooxygenase (COX)-derived prostaglandins stimulate uterine contractions and prepare the cervix for parturition. Prior reports suggest Cox-1 knockout (KO) mice exhibit delayed parturition due to impaired luteolysis, yet the mechanism for late-onset delivery remains unclear. Here, we examined key factors for normal onset of parturition to determine whether any could account for the delayed parturition phenotype. Pregnant Cox-1KO mice did not display altered timing of embryo implantation or postimplantation growth. Although messenger RNAs of contraction-associated proteins (CAPs) were differentially expressed between Cox-1KO and wild-type (WT) myometrium, there were no differences in CAP agonist-induced intracellular calcium release, spontaneous or oxytocin (OT)-induced ex vivo uterine contractility, or in vivo uterine contractile pressure. Delayed parturition in Cox-1KO mice persisted despite exogenous OT treatment. Progesterone (P4) withdrawal, by ovariectomy or administration of the P4-antagonist RU486, diminished the delayed parturition phenotype of Cox-1KO mice. Because antepartum P4 levels do not decline in Cox-1KO females, P4-treated WT mice were examined for the effect of this hormone on in vivo uterine contractility and ex vivo cervical dilation. P4-treated WT mice had delayed parturition but normal uterine contractility. Cervical distensibility was decreased in Cox-1KO mice on the day of expected delivery and reduced in WT mice with long-term P4 treatment. Collectively, these findings show that delayed parturition in Cox-1KO mice is the result of impaired luteolysis and cervical dilation, despite the presence of strong uterine contractions.

In vivo Raman spectral analysis of impaired cervical remodeling in a mouse model of delayed parturition

Monitoring cervical structure and composition during pregnancy has high potential for prediction of preterm birth (PTB), a problem affecting 15 million newborns annually. We use in vivo Raman spectroscopy, a label-free, light-based method that provides a molecular fingerprint to non-invasively investigate normal and impaired cervical remodeling. Prostaglandins stimulate uterine contractions and are clinically used for cervical ripening during pregnancy. Deletion of cyclooxygenase-1 (Cox-1), an enzyme involved in production of these prostaglandins, results in delayed parturition in mice. Contrary to expectation, Cox-1 null mice displayed normal uterine contractility; therefore, this study sought to determine whether cervical changes could explain the parturition differences in Cox-1 null mice and gestation-matched wild type (WT) controls. Raman spectral changes related to extracellular matrix proteins, lipids, and nucleic acids were tracked over pregnancy and found to be significantly delayed in Cox-1 null mice at term. A cervical basis for the parturition delay was confirmed by other ex vivo tests including decreased tissue distensibility, hydration, and elevated progesterone levels in the Cox-1 null mice at term. In conclusion, in vivo Raman spectroscopy non-invasively detected abnormal remodeling in the Cox-1 null mouse, and clearly demonstrated that the cervix plays a key role in their delayed parturition.

Embryo implantation triggers dynamic spatiotemporal expression of the basement membrane toolkit during uterine reprogramming

Basement membranes (BMs) are specialized extracellular scaffolds that influence behaviors of cells in epithelial, endothelial, muscle, nervous, and fat tissues. Throughout development and in response to injury or disease, BMs are fine-tuned with specific protein compositions, ultrastructure, and localization. These features are modulated through implements of the BM toolkit that is comprised of collagen IV, laminin, perlecan, and nidogen. Two additional proteins, peroxidasin and Goodpasture antigen-binding protein (GPBP), have recently emerged as potential members of the toolkit. In the present study, we sought to determine whether peroxidasin and GPBP undergo dynamic regulation in the assembly of uterine tissue BMs in early pregnancy as a tractable model for dynamic adult BMs. We explored these proteins in the context of collagen IV and laminin that are known to extensively change for decidualization. Electron microscopic analyses revealed: 1) a smooth continuous layer of BM in between the epithelial and stromal layers of the preimplantation endometrium; and 2) interrupted, uneven, and progressively thickened BM within the pericellular space of the postimplantation decidua. Quantification of mRNA levels by qPCR showed changes in expression levels that were complemented by immunofluorescence localization of peroxidasin, GPBP, collagen IV, and laminin. Novel BM-associated and subcellular spatiotemporal localization patterns of the four components suggest both collective pericellular functions and distinct functions in the uterus during reprogramming for embryo implantation.

Gene profiling the window of implantation: Microarray analyses from human and rodent models

Poor uterine receptivity leads to implantation defects or failure. Identification of uterine molecules crucial to uterine receptivity and/or embryo implantation provides the opportunity to design a diagnostic screening toolkit for uterine receptivity or targeted drug discovery for treating implantation-based infertility. In this regard, gene-profiling studies performed in humans and rodents have identified numerous genes involved in the transcriptional regulation of uterine receptivity and embryo implantation. In this article, we compared available uterine microarray datasets collected during the time of uterine receptivity and implantation in humans, mice and hamsters to uncover conserved gene sets. We also compared the transcriptome signature of women with unexplained infertility (UIF) and recurrent implantation failure (RIF) to gain insight into genes potentially dysregulated during endometrial receptivity or embryo implantation. Among numerous differentially expressed genes, few were revealed that might have molecular diagnostic screening potential for identifying the uterine receptive state during the time of implantation. Finally, functional annotation of gene sets uncovered altered uterine apoptosis or cell adhesion pathways in women with UIF and RIF, respectively. These conserved or divergent gene sets provide insights into the uterine receptive state for supporting blastocyst implantation.

Basement membrane ultrastructure and component localization data from uterine tissues during early mouse pregnancy

Basement membranes (BMs) are specialized extracellular scaffolds that provide architecture and modulate cell behaviors in tissues, such as fat, muscle, endothelium, endometrium, and decidua. Properties of BMs are maintained in homeostasis for most adult tissues. However, BM ultrastructure, composition, and localization are rapidly altered in select uterine tissues that are reprogrammed during pregnancy to enable early maternal-embryo interactions. Here, our data exhibit both static and dynamic BMs that were tracked in mouse uterine tissues during pre-, peri-, and postimplantation periods of pregnancy. The data exhibit spatial-temporal patterns of BM property regulation that coincide with the progression of adapted physiology. Further interpretation and discussion of these data in this article are described in the associated research article titled, "Embryo implantation triggers dynamic spatiotemporal expression of the basement membrane toolkit during uterine reprogramming" (C.R. Jones-Paris, S. Paria, T. Berg, J. Saus, G. Bhave, B.C. Paria, B.G. Hudson, 2016) [1].

High-Throughput Screening of Myometrial Calcium-Mobilization to Identify Modulators of Uterine Contractility

The uterine myometrium (UT-myo) is a therapeutic target for preterm labor, labor induction, and postpartum hemorrhage. Stimulation of intracellular Ca²⁺-release in UT-myo cells by oxytocin is a final pathway controlling myometrial contractions. The goal of this study was to develop a dual-addition assay for high-throughput screening of small molecular compounds, which could regulate Ca²⁺-mobilization in UT-myo cells, and hence, myometrial contractions. Primary murine UT-myo cells in 384-well plates were loaded with a Ca²⁺-sensitive fluorescent probe, and then screened for inducers of Ca²⁺-mobilization and inhibitors of oxytocin-induced Ca²⁺-mobilization. The assay exhibited robust screening statistics (Z´ = 0.73), DMSO-tolerance, and was validated for high-throughput screening against 2,727 small molecules from the Spectrum, NIH Clinical I and II collections of well-annotated compounds. The screen revealed a hit-rate of 1.80% for agonist and 1.39% for antagonist compounds. Concentration-dependent responses of hit-compounds demonstrated an EC₅₀ less than 10μM for 21 hit-antagonist compounds, compared to only 7 hit-agonist compounds. Subsequent studies focused on hit-antagonist compounds. Based on the percent inhibition and functional annotation analyses, we selected 4 confirmed hit-antagonist compounds (benzbromarone, dipyridamole, fenoterol hydrobromide and nisoldipine) for further analysis. Using an ex vivo isometric contractility assay, each compound significantly inhibited uterine contractility, at different potencies (IC₅₀). Overall, these results demonstrate for the first time that high-throughput small-molecules screening of myometrial Ca²⁺-mobilization is an ideal primary approach for discovering modulators of uterine contractility.

Alkaline phosphatase protects lipopolysaccharide-induced early pregnancy defects in mice

Excessive cytokine inflammatory response due to chronic or superphysiological level of microbial infection during pregnancy leads to pregnancy complications such as early pregnancy defects/loss and preterm birth. Bacterial toxin lipopolysaccharide (LPS), long recognized as a potent proinflammatory mediator, has been identified as a risk factor for pregnancy complications. Alkaline phosphatase (AP) isozymes have been shown to detoxify LPS by dephosphorylation. In this study, we examined the role of alkaline phosphatase (AP) in mitigating LPS-induced early pregnancy complications in mice. We found that 1) the uterus prior to implantation and implantation sites following embryo implantation produce LPS recognition and dephosphorylation molecules TLR4 and tissue non-specific AP (TNAP) isozyme, respectively; 2) uterine TNAP isozyme dephosphorylates LPS at its sites of production; 3) while LPS administration following embryo implantation elicits proinflammatory cytokine mRNA levels at the embryo implantation sites (EISs) and causes early pregnancy loss, dephosphorylated LPS neither triggers proinflammatory cytokine mRNA levels at the EISs nor induces pregnancy complications; 4) AP isozyme supplementation to accelerate LPS detoxification attenuates LPS-induced pregnancy complications following embryo implantation. These findings suggest that a LPS dephosphorylation strategy using AP isozyme may have a unique therapeutic potential to mitigate LPS- or Gram-negative bacteria-induced pregnancy complications in at-risk women.

Cross-species transcriptomic approach reveals genes in hamster implantation sites

The mouse model has greatly contributed to understanding molecular mechanisms involved in the regulation of progesterone (P4) plus estrogen (E)-dependent blastocyst implantation process. However, little is known about contributory molecular mechanisms of the P4-only-dependent blastocyst implantation process that occurs in species such as hamsters, guineapigs, rabbits, pigs, rhesus monkeys, and perhaps humans. We used the hamster as a model of P4-only-dependent blastocyst implantation and carried out cross-species microarray (CSM) analyses to reveal differentially expressed genes at the blastocyst implantation site (BIS), in order to advance the understanding of molecular mechanisms of implantation. Upregulation of 112 genes and downregulation of 77 genes at the BIS were identified using a mouse microarray platform, while use of the human microarray revealed 62 up- and 38 down-regulated genes at the BIS. Excitingly, a sizable number of genes (30 up- and 11 down-regulated genes) were identified as a shared pool by both CSMs. Real-time RT-PCR and in situ hybridization validated the expression patterns of several up- and down-regulated genes identified by both CSMs at the hamster and mouse BIS to demonstrate the merit of CSM findings across species, in addition to revealing genes specific to hamsters. Functional annotation analysis found that genes involved in the spliceosome, proteasome, and ubiquination pathways are enriched at the hamster BIS, while genes associated with tight junction, SAPK/JNK signaling, and PPARα/RXRα signalings are repressed at the BIS. Overall, this study provides a pool of genes and evidence of their participation in up- and down-regulated cellular functions/pathways at the hamster BIS.

Aminoglycoside-mediated relaxation of the ductus arteriosus in sepsis-associated PDA

Sepsis is strongly associated with patency of the ductus arteriosus (PDA) in critically ill newborns. Inflammation and the aminoglycoside antibiotics used to treat neonatal sepsis cause smooth muscle relaxation, but their contribution to PDA is unknown. We examined whether: 1) lipopolysaccharide (LPS) or inflammatory cytokines cause relaxation of the ex vivo mouse DA; 2) the aminoglycosides gentamicin, tobramycin, or amikacin causes DA relaxation; and 3) newborn infants treated with aminoglycosides have an increased risk of symptomatic PDA (sPDA). Changes in fetal mouse DA tone were measured by pressure myography in response to LPS, TNF-α, IFN-γ, macrophage-inflammatory protein 2, IL-15, IL-13, CXC chemokine ligand 12, or three aminoglycosides. A clinical database of inborn patients of all gestations was analyzed for association between sPDA and aminoglycoside treatment. Contrary to expectation, neither LPS nor any of the inflammatory mediators caused DA relaxation. However, each of the aminoglycosides caused concentration-dependent vasodilation in term and preterm mouse DAs. Pretreatment with indomethacin and N-(G)-nitro-L-arginine methyl ester did not prevent gentamicin-induced DA relaxation. Gentamicin-exposed DAs developed less oxygen-induced constriction than unexposed DAs. Among 488,349 infants who met the study criteria, 40,472 (8.3%) had sPDA. Confounder-adjusted odds of sPDA were higher in gentamicin-exposed infants, <25 wk and >32 wk. Together, these findings suggest that factors other than inflammation contribute to PDA. Aminoglycoside-induced vasorelaxation and inhibition of oxygen-induced DA constriction support the paradox that antibiotic treatment of sepsis may contribute to DA relaxation. This association was also found in newborn infants, suggesting that antibiotic selection may be an important consideration in efforts to reduce sepsis-associated PDA.

Raman spectroscopy provides a noninvasive approach for determining biochemical composition of the pregnant cervix in vivo

The molecular changes that occur with cervical remodelling during pregnancy are not completely understood. This study reviews Raman spectroscopy, an optical technique for detecting changes in the pregnant cervix, and reports preliminary studies on cervical remodelling in mice that suggest that the technique provides advantages over other methods.

CONCLUSION

Raman spectroscopy is sensitive to biochemical changes in the pregnant cervix and has high potential as a tool for detecting premature cervical remodelling in pregnant women.

Transcriptional profiling reveals ductus arteriosus-specific genes that regulate vascular tone

Failure of the ductus arteriosus (DA) to close at birth can lead to serious complications. Conversely, certain profound congenital cardiac malformations require the DA to be patent until corrective surgery can be performed. In each instance, clinicians have a very limited repertoire of therapeutic options at their disposal - indomethacin or ibuprofen to close a patent DA (PDA) and prostaglandin E1 to maintain patency of the DA. Neither treatment is specific to the DA and both may have deleterious off-target effects. Therefore, more therapeutic options specifically targeted to the DA should be considered. We hypothesized the DA possesses a unique genetic signature that would set it apart from other vessels. A microarray was used to compare the genetic profiles of the murine DA and ascending aorta (AO). Over 4,000 genes were differentially expressed between these vessels including a subset of ion channel-related genes. Specifically, the alpha and beta subunits of large-conductance calcium-activated potassium (BKCa) channels are enriched in the DA. Gain- and loss-of-function studies showed inhibition of BKCa channels caused the DA to constrict, while activation caused DA relaxation even in the presence of O2. This study identifies subsets of genes that are enriched in the DA that may be used to develop DA-specific drugs. Ion channels that regulate DA tone, including BKCa channels, are promising targets. Specifically, BKCa channel agonists like NS1619 maintain DA patency even in the presence of O2 and may be clinically useful.

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.

Alkaline phosphatases contribute to uterine receptivity, implantation, decidualization, and defense against bacterial endotoxin in hamsters

Alkaline phosphatase (AP) activity has been demonstrated in the uterus of several species, but its importance in the uterus, in general and during pregnancy, is yet to be revealed. In this study, we focused on identifying AP isozyme types and their hormonal regulation, cell type, and event-specific expression and possible functions in the hamster uterus during the cycle and early pregnancy. Our RT-PCR and in situ hybridization studies demonstrated that among the known Akp2, Akp3, Akp5, and Akp6 murine AP isozyme genes, hamster uteri express only Akp2 and Akp6; both genes are co-expressed in luminal epithelial cells. Studies in cyclic and ovariectomized hamsters established that while progesterone (P₄) is the major uterine Akp2 inducer, both P₄ and estrogen are strong Akp6 regulators. Studies in preimplantation uteri showed induction of both genes and the activity of their encoded isozymes in luminal epithelial cells during uterine receptivity. However, at the beginning of implantation, Akp2 showed reduced expression in luminal epithelial cells surrounding the implanted embryo. By contrast, expression of Akp6 and its isozyme was maintained in luminal epithelial cells adjacent to, but not away from, the implanted embryo. Following implantation, stromal transformation to decidua was associated with induced expressions of only Akp2 and its isozyme. We next demonstrated that uterine APs dephosphorylate and detoxify endotoxin lipopolysaccharide at their sites of production and activity. Taken together, our findings suggest that uterine APs contribute to uterine receptivity, implantation, and decidualization in addition to their role in protection of the uterus and pregnancy against bacterial infection.

Cimetidine-associated patent ductus arteriosus is mediated via a cytochrome P450 mechanism independent of H2 receptor antagonism

Persistent patency of the ductus arteriosus (PDA) is a common problem in preterm infants. The antacid cimetidine is a potent antagonist of the H2 histamine receptor but it also inhibits certain cytochrome P450 enzymes (CYPs), which may affect DA patency. We examined whether cimetidine contributes to PDA and is mediated by CYP inhibition rather than H2 blockade. Analysis of a clinical trial to prevent lung injury in premature infants revealed a significant association between cimetidine treatment and PDA. Cimetidine and ranitidine, both CYP inhibitors as well as H2 blockers, caused relaxation of the term and preterm mouse DA. CYP enzymes that are inhibited by cimetidine were expressed in DA subendothelial smooth muscle. The selective CYP3A inhibitor ketoconazole induced greater DA relaxation than cimetidine, whereas famotidine and other H2 antagonists with less CYP inhibitory effects caused less dilation. Histamine receptors were developmentally regulated and localized in DA smooth muscle. However, cimetidine caused DA relaxation in histamine-deficient mice, consistent with CYP inhibition, not H2 antagonism, as the mechanism for PDA. Oxygen-induced DA constriction was inhibited by both cimetidine and famotidine. These studies show that antacids and other compounds with CYP inhibitory properties pose a significant and previously unrecognized risk for PDA in critically ill newborn infants.

Isoprostanes as physiological mediators of transition to newborn life: novel mechanisms regulating patency of the term and preterm ductus arteriosus

BACKGROUND

Increased oxygen tension at birth regulates physiologic events that are essential to postnatal survival, but the accompanying oxidative stress may also generate isoprostanes. We hypothesized that isoprostanes regulate ductus arteriosus (DA) function during postnatal vascular transition.

METHODS

Isoprostanes were measured by gas chromatography-mass spectrometry. DA tone was assessed by pressure myography. Gene expression was measured by quantitative PCR.

RESULTS

Oxygen exposure was associated with increased 8-iso-prostaglandin (PG)F2α in newborn mouse lungs. Both 8-iso-PGE2 and 8-iso-PGF2α induced concentration-dependent constriction of the isolated term DA, which was reversed by the thromboxane A2 (TxA2) receptor antagonist SQ29548. SQ29548 pretreatment unmasked an isoprostane-induced DA dilation mediated by the EP4 PG receptor. Exposure of the preterm DA to 8-iso-PGE2 caused unexpected DA relaxation that was reversed by EP4 antagonism. In contrast, exposure to 8-iso-PGF2α caused preterm DA constriction via TxA2 receptor activation. Further investigation revealed the predominance of the TxA2 receptor at term, whereas the EP4 receptor was expressed and functionally active from mid-gestation onward.

CONCLUSION

This study identifies a novel physiological role for isoprostanes during postnatal vascular transition and provide evidence that oxidative stress may act on membrane lipids to produce vasoactive mediators that stimulate physiological DA closure at birth or induce pathological patency of the preterm DA.

Adherens junction proteins in the hamster uterus: their contributions to the success of implantation

The adherens junction (AJ) is important for maintaining uterine structural integrity, composition of the luminal environment, and initiation of implantation by virtue of its properties of cell-cell recognition, adhesion, and establishment of cell polarity and permeability barriers. In this study, we investigated the uterine changes of AJ components E-cadherin, beta-catenin, and alpha-catenin at their mRNA and protein levels, together with the cellular distribution of meprinbeta, phospho-beta-catenin, and active beta-catenin proteins, in hamsters that show only ovarian progesterone-dependent uterine receptivity and implantation. By in situ hybridization and immunofluorescence, we have demonstrated that uterine epithelial cells expressed three of these AJ proteins and their mRNAs prior to and during the initial phase of implantation. Immunofluorescence study showed no change in epithelial expression patterns of uterine AJ proteins from Days 1 to 5 of pregnancy. With advancement of the implantation process, AJ components were primarily expressed in cells of the secondary decidual zone (SDZ), but not in the primary decidual zone (PDZ). In contrast, we noted strong expression of beta-catenin and alpha-catenin proteins in the PDZ, but not in the SDZ, of mice. Taken together, these results suggest that AJ proteins contribute to uterine barrier functions by cell-cell adhesion to ensure protection of the embryo. In addition, cleavage of E-cadherin by meprinbeta might contribute to weakening uterine epithelial cell-cell contact for blastocyst implantation. We also report that the nuclear localization of active beta-catenin from Day 4 onward in hamsters implies that beta-catenin/Wnt-signal transduction is activated in the uterus during implantation and decidualization.

Dynamics of zonula occludens-2 expression during preimplantation embryonic development in the hamster

The objective was to study the expression of zonula occludens-2, a tight junction protein, during preimplantation hamster embryonic development, to predict its possible localization, source, and roles in trophectoderm differentiation and blastocyst formation in this species. Comparison of zonula occludens-2 expression pattern between the hamster and mouse preimplantation embryos from the zygote up to the blastocyst stage was also an objective of this study. Zonula occludens-2 localization was noted in nuclei of blastomeres in all stages of hamster and mouse embryonic development. Compared to mice, where zonula occludens-2 was first localized in the interblastomere membrane at the morula stage, hamster embryos had membranous zonula occludens-2 localization from the 2-cell stage onwards. Based on combined results of immunolocalization study in parthenogenic embryos and ovarian and epididymal sections, and quantitative PCR done in oocytes and all developmental stages of preimplantation embryos, perhaps there was a carry-over of zonula occludens-2 proteins or mRNA from the dam to the embryo. Based on these findings, we inferred that maternally derived zonula occludens-2 was involved in nuclear functions, as well as differentiation of blastomeres and blastocoel formation during preimplantation embryonic development in the hamster.

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.

Leukemia inhibitory factor ligand-receptor signaling is important for uterine receptivity and implantation in golden hamsters (Mesocricetus auratus)

Blastocyst implantation occurs in the progesterone-primed uterus of hamsters, but not in mice where the progesterone-primed uterus requires estrogen influence. Leukemia inhibitory factor (Lif), an estrogen-regulated gene in mice, is an absolutely needed cytokine for uterine receptivity and implantation in this species. This study aimed to evaluate the importance of Lif ligand-receptor signaling during uterine receptivity and implantation in hamsters. We investigated whether or not the uterine expression patterns of Lif and its receptors, Lif-r and gp130, during the periimplantation period of pregnancy and its hormonal regulation in the ovariectomized hamster correlate with some of the vital phases of uterine changes during early pregnancy. Uterine Lif, Lif-r, and gp130 mRNA expressions were examined by Northern and in situ hybridization. During the uterine preparatory phase for implantation, Lif, Lif-r, and gp130 were expressed either in the gland, luminal epithelium or both. As the implantation process began, Lif expression was minimal, but Lif-r and gp130 extended to the decidual areas. This decidual expression of Lif-r and gp130 was not dependent on the presence of the embryo since these genes were expressed in the suture-induced deciduomata. We also observed that, while the uterine Lif was induced by estrogen, Lif-r and gp130 were induced by progesterone in ovariectomized hamsters. Additionally, we show that a Lif antibody when instilled intraluminally on day 3 of pregnancy reduced the number of implantation sites. Taken together, these data suggest that Lif signaling is important for uterine receptivity and implantation in hamsters.

The hamster as a model for embryo implantation: insights into a multifaceted process

Defects in preimplantation embryonic development, uterine receptivity, and implantation are the leading cause of infertility, pregnancy problems and birth defects. Significant progress has been made in our basic understanding of these processes using the mouse model, where implantation is ovarian estrogen-dependent in the presence of progesterone. However, an animal model where implantation is progesterone-dependent must also be studied to gain a full understanding of the embryo and uterine events that are required for implantation. In this regard, the hamster is a useful model and this review summarizes the information currently available regarding mechanisms involved in synchronous preimplantation embryo and uterine development for implantation in this species.

The Bysl gene product, bystin, is essential for survival of mouse embryos

Human bystin is a cytoplasmic protein directly binding to trophinin, a cell adhesion molecule potentially involved in human embryo implantation. The present study shows that bystin is expressed in luminal and glandular epithelia in the mouse uterus at peri-implantation stages. In fertilized embryos, bystin was not seen until blastocyst stage. Bystin expression started during hatching and increased in expanded blastocyst. However, bystin apparently disappeared from the blastocyst during implantation. After implantation bystin re-appeared in the epiblast. Targeted disruption of the mouse bystin gene, Bysl, resulted in embryonic lethality shortly after implantation, indicating that bystin is essential for survival of mouse embryos.

Indian hedgehog, but not histidine decarboxylase or amphiregulin, is a progesterone-regulated uterine gene in hamsters

Implantation occurs only in the progesterone (P4)-primed uterus in the majority of species, but little effort has been given to identify P4-mediated molecules in these species. Using hamsters as a model for P4-dependent implantation and three well-known uterine receptivity-associated P4-regulated genes, Indian hedgehog (Ihh), histidine decarboxylase (Hdc), and amphiregulin (Areg), in mice that require ovarian estrogen for uterine receptivity and implantation, our strategy aimed to determine whether P4 regulates uterine expression of these genes in hamsters and whether the event- and cell-specific uterine expression patterns of these genes during the periimplantation period in hamsters follow similarly with their patterns in mice. We report here that P4-mediated Ihh signaling is important for uterine receptivity and implantation in hamsters because uterine epithelial Ihh expression was regulated by P4 and its expression patterns during the periimplantation period of hamsters closely follow its pattern in mice. In contrast, we noted no hormonal regulation of Hdc and Areg in the hamster uterus. However, this did not diminish their importance in hamsters because their expression patterns and functions are event and cell specific during the periimplantation period: whereas Hdc was expressed exclusively in d 4 uterine glands and regulated by the blastocyst, Areg was expressed on the decidual area adjacent to the embryo from d 5 onward and involved in stromal cell proliferation. We conclude that similarities and dissimilarities exist in uterine expression pattern of implantation-related genes, including hormonal regulation and their event-specific importance.

Importance of uterine cell death, renewal, and their hormonal regulation in hamsters that show progesterone-dependent implantation

This study was initiated to investigate the significance of uterine cell death and proliferation during the estrous cycle and early pregnancy and their correlation with sex steroids in hamsters where blastocyst implantation occurs in only progesterone-primed uteri. The results obtained in hamsters were also compared with mice where blastocyst implantation occurs in progesterone-primed uteri if estrogen is provided. Apoptotic cells in the uterus were detected by using terminal deoxynucleotide transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) technique. Uterine cell proliferation was determined by 5-bromo-2'-deoxyuridine labeling followed by immunohistochemistry and methyl-tritiated [(3)H]thymidine labeling. Active caspase-3, an executor protein of cell death, expression was assayed by immunohistochemistry/immunofluorescence. Our results demonstrate that epithelial proliferation on the second day after mating marks the initiation of pregnancy-related uterine changes in both species despite their differences in hormonal requirements. Hamsters and mice showed subtle differences in uterine proliferative and apoptotic patterns during early pregnancy and in response to steroids. There existed almost a direct correlation between apoptosis and caspase-3 expression, suggesting uterine cell death mostly involves the caspase pathway. Consistent with these findings, we showed, for the first time, that execution of uterine epithelial cell apoptosis by caspase-3 is important for blastocyst implantation because a caspsase-3 inhibitor N-acetyl-DEVD-CHO when instilled inside the uterine lumen on d 3 of pregnancy inhibits implantation in hamsters and mice. The overall results indicate that uterine cell apoptosis and proliferation patterns are highly ordered cell-specific phenomena that play an important role in maintaining the sexual cycle and pregnancy-associated uterine changes.

Methodologies to study implantation in mice

Pregnancy begins with fertilization of the ovulated oocyte by the sperm. After fertilization, the egg undergoes time-dependent mitotic division while trying to reach the blastocyst stage and the uterus for implantation. Uterine preparation for implantation is regulated by coordinated secretions and functions of ovarian sex steroids. The first sign of contact between the blastocyst and the uterus can be detected experimentally by an intravenous blue dye injection as early as the end of day 4 or the beginning of day 5 of pregnancy. This blastocyst-uterine attachment reaction leads to stromal decidual reaction only at sites of implantation. The process of implantation can be postponed and reinstated experimentally by manipulating ovarian estrogen secretion. Stromal decidualization can also be induced experimentally in the hormonally prepared uterus in response to stimuli other than the embryo. Fundamental biological questions surrounding these essential features of early pregnancy can be addressed through the application of various techniques and manipulation of this period of early pregnancy. This chapter describes the routine laboratory methodologies to study the events of early pregnancy, with special emphasis on the implantation process in mice.

Histamine enhances cytotrophoblast invasion by inducing intracellular calcium transients through the histamine type-1 receptor

Blastocyst implantation and placentation require molecular and cellular interactions between the uterine endometrium and blastocyst trophectoderm. Previous studies showed that histamine produced in the mouse uterine luminal epithelium interacts with trophoblast histamine type-2 receptors (H2) to initiate blastocyst implantation. However, it is unknown whether similar histamine activity is operative in humans. Using a human cell line (HTR-8/SVneo) derived from first-trimester cytotrophoblasts that expresses both histamine type-1 receptor (H1) and H2, we found that histamine promotes cytotrophoblast invasiveness specifically through activation of H1. Stimulation of H1 in human cytotrophoblasts by histamine induced intracellular Ca2+ (Ca(2+)i) transients by activating phospholipase C and the inositol trisphosphate pathway. The enhanced invasion induced by histamine was blocked by pretreatment with H1 antagonist or by chelation of Ca(2+)i. These findings suggest possible differences between rodents and humans in histamine signaling to the trophoblast.

Embryo-uterine interactions via the neuregulin family of growth factors during implantation in the mouse

Neuregulins (NRGs) are cell-signaling molecules with recognized roles in cancer and development, but little is known about their role in embryo implantation. Among representative NRG-1 isoforms, neu differentiation factor (NDF, type I) is expressed in the female reproductive tract and is localized to the implantation site. Here, we show that sensory and motor neuron-derived factor (SMDF, type III) is expressed in the uterine subepithelial stroma around the blastocyst and is only upregulated at the time of implantation. The cellular distribution of SMDF is similar to that of NDF and requires an implantation-competent blastocyst. The glial growth factor (GGF, type II) isoform of NRG-1 and the NRG-2 and NRG-3 genes were not expressed in the peri-implantation uterus, as determined by reverse transcription-polymerase chain reaction or in situ hybridization. In contrast to the cellular expression pattern of NDF and SMDF, NRG-4 was present in the luminal and glandular epithelium throughout the uterus during the preimplantation period. Expression of NRG-4 declined in the uterine luminal epithelium during implantation but persisted in the glandular epithelium through Day 8 of pregnancy. Studies in ovariectomized mice showed that NRG-4 is a progesterone-regulated gene, with partial augmentation by estrogen. We also observed upregulation of the erbB2 and erbB3 receptors at the blastocyst stage of embryo development. Together, these findings suggest that a distinct subset of NRGs participates in the signaling network that directs embryo implantation. Upregulation of embryonic erbB2/ erbB3 in the blastocyst trophectoderm and induction of certain NRG-1 isoforms with blastocyst activation help to define additional aspects of the embryo-uterine cross-talk that underlies the implantation process.

Prostaglandin E2 Is a Product of Induced Prostaglandin-endoperoxide Synthase 2 and Microsomal-type Prostaglandin E Synthase at the Implantation Site of the Hamster

Certain uterine prostaglandins (PGs) are elevated at implantation sites and are needed to trigger the events of blastocyst implantation that include blastocyst-uterine attachment and stromal decidualization with vascular permeability changes. Several decades of investigations showed that treatment with PG synthesis inhibitors, prior to or during the time of implantation, resulted in either complete inhibition or a delay in implantation or reduction in the number of implantation sites with diminished decidual tissue. Consistent with these findings, we observed that whereas a selective PG endoperoxide synthase (Ptgs) 1 inhibitor SC-560 failed to inhibit implantation, a selective Ptgs2 inhibitor SC-236 showed significantly reduced number and size of implantation sites in progesterone-treated ovariectomized pregnant hamsters. It is known that Ptgs2 expression and Ptgs2-derived prostacyclin (PGI2) synthesis at implantation sites are needed for implantation in the mouse (a rodent that needs ovarian estrogen for implantation). However, it is unknown which Ptgs and PG synthases produce which PGs at implantation sites of the hamster (a rodent that does not need ovarian estrogen for implantation). Here we demonstrate that as blastocyst implantation proceeds, a reduction in Ptgs1 expression from uterine luminal epithelial cells and a gradual induction in Ptgs2 expression exclusively in luminal epithelial and adjacent decidual cells occurred at implantation sites of hamsters. Results also reveal that PGE2, but not PGI2, is the major PG at implantation sites where Ptgs2 and microsomal type PGE synthases but not PGI synthases are co-expressed. This elevated uterine PGE2 at implantation sites may serve to initiate or amplify physiological signals required for specific aspects of the implantation process in hamsters.

Molecular cues to implantation

Successful implantation is the result of reciprocal interactions between the implantation-competent blastocyst and receptive uterus. Although various cellular aspects and molecular pathways of this dialogue have been identified, a comprehensive understanding of the implantation process is still missing. The receptive state of the uterus, which lasts for a limited period, is defined as the time when the uterine environment is conducive to blastocyst acceptance and implantation. A better understanding of the molecular signals that regulate uterine receptivity and implantation competency of the blastocyst is of clinical relevance because unraveling the nature of these signals may lead to strategies to correct implantation failure and improve pregnancy rates. Gene expression studies and genetically engineered mouse models have provided valuable clues to the implantation process with respect to specific growth factors, cytokines, lipid mediators, adhesion molecules, and transcription factors. However, a staggering amount of information from microarray experiments is also being generated at a rapid pace. If properly annotated and explored, this information will expand our knowledge regarding yet-to-be-identified unique, complementary, and/or redundant molecular pathways in implantation. It is hoped that the forthcoming information will generate new ideas and concepts for a process that is essential for maintaining procreation and solving major reproductive health issues in women.

α5β1, αVβ3 and the platelet-associated integrin αIIbβ3 coordinately regulate adhesion and migration of differentiating mouse trophoblast cells

During blastocyst implantation, interaction between integrins on the apical surface of the trophoblast and extracellular matrix (ECM) in the endometrium anchors the embryo to the uterine wall. Strong adhesion of the blastocyst to fibronectin (FN) requires integrin signaling initiated by exogenous fibronectin. However, it is not known how integrin signaling enhances blastocyst adhesion. We present new evidence that the integrin, alphaIIbbeta3, plays a key role in trophoblast adhesion to fibronectin during mouse peri-implantation development. Trafficking of alphaIIb to the apical surface of the trophoblast increased dramatically after blastocysts were exposed to fibronectin, whereas other fibronectin-binding integrins, alpha5beta1 and alphaVbeta3, were resident at the apical surface before ligand exposure. Functional comparisons among the three integrins revealed that ligation of alpha5beta1 most efficiently strengthened blastocyst fibronectin-binding activity, while subsequent trophoblast cell migration was dependent primarily on the beta3-class integrins. In vivo, alphaIIb was highly expressed by invasive trophoblast cells in the ectoplacental cone and trophoblast giant cells of the parietal yolk sac. These data demonstrate that trafficking of alphaIIb regulates adhesion between trophoblast cells and fibronectin as invasion of the endometrium commences.

HB-EGF directs stromal cell polyploidy and decidualization via cyclin D3 during implantation

Stromal cell polyploidy is a unique phenomenon that occurs during uterine decidualization following embryo implantation, although the developmental mechanism still remains elusive. The general consensus is that the aberrant expression and altered functional activity of cell cycle regulatory molecules at two particular checkpoints G1 to S and G2 to M in the cell cycle play an important role in the development of cellular polyploidy. Despite the compelling evidence of intrinsic cell cycle alteration, it has been implicated that the development of cellular polyploidy may be controlled by specific actions of extracellular growth regulators. Here we show a novel role for heparin-binding EGF-like growth factor (HB-EGF) in the developmental process of stromal cell polyploidy in mice. HB-EGF, which is one of the earliest known molecular mediators of implantation in mice and humans, promotes stromal cell polyploidy via upregulation of cyclin D3. Adenoviral delivery of antisense cyclin D3 attenuates cyclin D3 expression and abrogates HB-EGF-induced stromal cell polyploidy in vitro and in vivo. Collectively, the results demonstrate that the regulation of stromal cell polyploidy and decidualization induced by HB-EGF depend on cyclin D3 induction.

Differential G protein-coupled cannabinoid receptor signaling by anandamide directs blastocyst activation for implantation

Mammalian fertility absolutely depends on synchronized development of the blastocyst to the stage when it is competent to implant, and the uterus to the stage when it is receptive to implantation. However, the molecular basis for the reciprocal interaction between the embryo and the uterus remains largely unexplored. One potentially important mechanism involves signaling between an evolutionarily conserved G protein-coupled protein cannabinoid receptor, CB1, that is expressed at high levels on the surface of the trophectoderm and anandamide (N-arachi-donoylethanolamine), an endocannabinoid ligand found to be produced at higher levels by the uterus before implantation and then down-regulated at the time of implantation. Using genetic, pharmacological, and physiological approaches, we show here that anandamide within a very narrow range regulates blastocyst function and implantation by differentially modulating mitogen-activated protein kinase signaling and Ca2+ channel activity via CB1 receptors. Anandamide at a low concentration (7 nM) induces extracellular regulated kinase phosphorylation and nuclear translocation in trophectoderm cells without influencing Ca2+ channels, and renders the blastocyst competent for implantation in the receptive uterus. In contrast, anandamide at a higher concentration (28 nM) inhibits Ca2+ channel activity and blastocyst competency for implantation without influencing mitogen-activated protein kinase signaling. Besides uncovering a potentially important regulatory mechanism for synchronizing blastocyst and uterine competency to implantation, this observation has high clinical relevance, because elevated levels of anandamide induce spontaneous pregnancy loss in women.

Embryonic signals direct the formation of tight junctional permeability barrier in the decidualizing stroma during embryo implantation

The protection of the embryo from the maternal adverse environment during early pregnancy is considered to be achieved by the establishment of a transitory permeability barrier created by decidual cells immediately surrounding the implanting embryo. Normally, the polarized epithelium acts as a barrier by regulating paracellular passage of substances through tight junctions. The expression of tight junction proteins in the uterine luminal epithelium prior to implantation is consistent with this idea. However, limited information is available regarding the nature and regulation of the permeability barrier that is created by decidualizing stromal cells during implantation. We show here that the tight junction proteins, occludin, claudin-1, zonula occludens-1 and zonula occludens-2, are all expressed and physically associated in decidualizing stromal cells of the primary decidual zone forming a barrier surrounding the embryo with the loss of adjacent luminal epithelium. The blastocyst trophectoderm appears to be the stimulus for the creation of this barrier, since isolated inner cell mass or artificial stimuli failed to induce such a barrier. Furthermore, the primary decidual zone induced by the normal blastocyst is impermeable to immunoglobulin molecules. These findings suggest that trophoblast-induced expression of tight junctions forms a temporary barrier in cells of the primary decidual zone that restricts the passage of injurious stimuli such as maternal immunoglobulins to the embryo.

Estrogen is a critical determinant that specifies the duration of the window of uterine receptivity for implantation

Many underlying causes of human infertility have been overcome by using in vitro fertilization (IVF) and embryo transfer (ET) techniques. Nevertheless, implantation rates in IVF programs remain low despite the transfer of apparently healthy embryos. This suggests that there are problems with the differentiation of the uterus to the receptive state in response to the ovarian hormones estrogen and progesterone. The molecular basis of this receptive state when the uterine environment is conducive to blastocyst acceptance and implantation remains poorly understood. Normally, the "window" of uterine receptivity lasts for a limited time. Using ETs and the progesterone-treated delayed-implantation model in mice, we demonstrate here that levels of estrogen within a very narrow range determine the duration of the window of uterine receptivity. Although estrogen at different physiological concentrations can initiate implantation, we find that the window of uterine receptivity remains open for an extended period at lower estrogen levels but rapidly closes at higher levels. The uterine refractoriness that follows the receptive state at high estrogen levels is accompanied by aberrant uterine expression of implantation-related genes. These results suggest that careful regulation of estrogen levels is one of the important factors for improvement of female fertility in IVFET programs.

Endocannabinoid signaling in synchronizing embryo development and uterine receptivity for implantation

There are reports of adverse effects of cannabinoids on pregnancy outcome including retarded embryo development and pregnancy failure. Thus, discoveries of endogenous cannabinoid-like lipid mediators and cannabinoid receptors raise questions about their pathophysiological roles during normal pregnancy. We previously reported that anandamide, an endogenously produced arachidonate derivative (endocannabinoid), is synthesized in the female reproductive tracts, and it acts on cannabinoid receptors expressed on the cell surface of the embryo to regulate the preimplantation embryo development and implantation in mice. This review presents genetic, molecular, physiological and pharmacological evidence that the levels of uterine anandamide and blastocyst CB1 cannabinoid receptors are coordinately regulated to synchronize preimplantation development and uterine receptivity for implantation in mice.

Inhibition of improgan antinociception by the cannabinoid (CB)(1) antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716A): lack of obligatory role for endocannabinoids acting at CB(1) receptors

Improgan, a nonopioid antinociceptive agent, activates descending, pain-relieving mechanisms in the brain stem, but the receptor for this compound has not been identified. Because cannabinoids also activate nonopioid analgesia by a brain stem action, experiments were performed to assess the significance of cannabinoid mechanisms in improgan antinociception. The cannabinoid CB(1) antagonist N-(piperidin-1-yl)-5-(4-chloro phenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716A) induced dose-dependent inhibition of improgan antinociception on the tail-flick test after i.c.v. administration in rats. The same treatments yielded comparable inhibition of cannabinoid [R-(+)-(2,3-dihydro-5-methyl-3-[(4-mor pholinyl)methyl]pyrol[1,2,3-de]-1,4-benzoxazin-6-yl)(1-naphthalenyl)methanone monomethanesulfonate, WIN 55,212-2] analgesia. Inhibition of improgan and WIN 55,212-2 antinociception by SR141716A was also observed in Swiss-Webster mice. Radioligand binding studies showed no appreciable affinity of improgan on rat brain, mouse brain, and human recombinant CB(1) receptors, ruling out a direct action at these sites. To test the hypothesis that CB(1) receptors indirectly participate in improgan signaling, the effects of improgan were assessed in mice with a null mutation of the CB(1) gene with and without SR141716A pretreatment. Surprisingly, improgan induced complete antinociception in both CB(1) (-/-) and wild-type control [CB(1) (+/+)] mice. Furthermore, SR141716A inhibited improgan antinociception in CB(1) (+/+) mice, but not in CB(1) (-/-) mice. Taken together, the results show that SR141716A reduces improgan antinociception, but neither cannabinoids nor CB(1) receptors seem to play an obligatory role in improgan signaling. Present and previous studies suggest that Delta(9)-tetrahydrocannabinol may act at both CB(1) and other receptors to relieve pain, but no evidence was found indicating that improgan uses either of these mechanisms. SR141716A will facilitate the study of improgan-like analgesics.

Dual source and target of heparin-binding EGF-like growth factor during the onset of implantation in the hamster

Heparin binding EGF-like growth factor (HB-EGF), encoded by the Hegfl gene, is considered as an important mediator of embryo-uterine interactions during implantation in mice. However, it is unknown whether HB-EGF is important for implantation in species with different steroid hormonal requirements. In mice and rats, maternal ovarian estrogen and progesterone (P4) are essential to implantation. In contrast, blastocyst implantation can occur in hamsters in the presence of P4 alone. To ascertain whether HB-EGF plays any role in implantation in hamsters, we examined the expression, regulation and signaling of HB-EGF in the hamster embryo and uterus during the periimplantation period. We demonstrate that both the blastocyst and uterus express HB-EGF during implantation. Hegfl is expressed solely in the uterine luminal epithelium surrounding the blastocyst prior to and during the initiation of implantation. Hypophysectomized P4-treated pregnant hamsters also showed a similar pattern of implantation-specific Hegfl expression. These results suggest that uterine Hegfl expression at the implantation site is driven by either signals emanating from the blastocyst or maternal P4, but not by maternal estrogen. However, in ovariectomized hamsters, uterine induction of Hegfl requires the presence of estrogen and activation of its nuclear receptor (ER), but not P4. This observation suggests an intriguing possibility that an estrogenic or unidentified signal from the blastocyst is the trigger for uterine HB-EGF expression. An auto-induction of Hegfl in the uterus by blastocyst-derived HB-EGF is also a possibility. We further observed that HB-EGF induces autophosphorylation of ErbB1 and ErbB4 in the uterus and blastocyst. Taken together, we propose that HB-EGF production and signaling by the blastocyst and uterus orchestrate the ‘two-way’ molecular signaling to initiate the process of implantation in hamsters.

Cyclooxygenase-2 differentially directs uterine angiogenesis during implantation in mice

Increased vascular permeability and angiogenesis at the site of blastocyst apposition in the uterus are two hallmarks of the implantation process. The present investigation shows that although the proangiogenic vascular endothelial growth factor (VEGF) and its receptor, Flk-1, are primarily important for uterine vascular permeability and angiogenesis prior to and during the attachment phase of the implantation process, VEGF in complementation with the angiopoietins and their receptor, Tie-2, directs angiogenesis during decidualization following implantation. Mice with null mutation for the gene encoding cyclooxygenase-2 (COX-2), a rate-limiting enzyme in prostaglandin (PG) biosynthesis, show implantation and decidualization failure. Using reporter and mutant mice, we show here that COX-2-derived prostaglandins (PGs) are important for uterine vascular permeability and angiogenesis during implantation and decidualization, suggesting that one cause of the failure of these latter processes in Cox-2-/- mice is the deregulated vascular events in the absence of COX-2. The attenuation of uterine angiogenesis in these mice is primarily due to defective VEGF signaling and not due to the defective angiopoietin system.

Deciphering the cross-talk of implantation: advances and challenges

Implantation involves a series of steps leading to an effective reciprocal signaling between the blastocyst and the uterus. Except for a restricted period when ovarian hormones induce a uterine receptive phase, the uterus is an unfavorable environment for blastocyst implantation. Because species-specific variations in implantation strategies exist, these differences preclude the formulation of a unifying theme for the molecular basis of this event. However, an increased understanding of mammalian implantation has been gained through the use of the mouse model. This review summarizes recognized signaling cascades and new research in mammalian implantation, based primarily on available genetic and molecular evidence from implantation studies in the mouse. Although the identification of new molecules associated with implantation in various species provides valuable insight, important questions remain regarding the common molecular mechanisms that govern this process. Understanding the mechanisms of implantation promises to help alleviate infertility, enhance fetal health, and improve contraceptive design. The success of any species depends on its reproductive efficiency. For sexual reproduction, an egg and sperm must overcome many obstacles to fuse and co-mingle their genetic material at fertilization. The zygote develops into a blastocyst with two cell lineages (the inner cell mass and the trophectoderm), migrates within the reproductive tract, and ultimately implants into a transiently permissive host tissue, the uterus. However, the molecular basis of the road map connecting the blastocyst with the endometrium across species is diverse (1) and not fully understood. Recent advances have identified numerous molecules involved in implantation (1-4), yet new discoveries have not yielded a unifying scheme for the mechanisms of implantation.

Cytosolic phospholipase A2α is crucial for ‘on-time’ embryo implantation that directs subsequent development

Cytosolic phospholipase A2α (cPLA2α) is a major provider of arachidonic acid (AA) for the cyclooxygenase (COX) system for the biosynthesis of prostaglandins (PGs). Female mice with the null mutation for Pla2g4a (cPLA2α) produce small litters and often exhibit pregnancy failures, although the cause(s) of these defects remains elusive. We show that the initiation of implantation is temporarily deferred in Pla2g4a–/– mice, shifting the normal ‘window’ of implantation and leading to retarded feto-placental development without apparent defects in decidual growth. Furthermore, cPLA2α deficiency results in aberrant uterine spacing of embryos. The deferred implantation and deranged gestational development in Pla2g4a–/– mice were significantly improved by exogenous PG administration. The results provide evidence that cPLA2α-derived AA is important for PG synthesis required for on-time implantation. This study in Pla2g4a–/– mice, together with the results of differential blastocyst transfers in wild-type mice provides the first evidence for a novel concept that a short delay in the initial attachment reaction creates a ripple effect propagating developmental anomalies during the subsequent course of pregnancy.

Molecules in blastocyst implantation: uterine and embryonic perspectives

Synchronized development of the embryo to the active stage of the blastocyst, differentiation of the uterus to the receptive state, and a "cross talk" between the blastocyst and uterine luminal epithelium are essential to the process of implantation. In spite of considerable accumulation of information and the present state of the knowledge, our understanding of the definitive mechanisms that regulate these events remains elusive. Although there are species variations in the process of implantation, many basic similarities do exist among various species. This review focuses on specific aspects of the implantation process in mice with the hope that many of the findings will be relevant to the process in humans. To establish signaling mechanisms of embryo-uterine interactions during implantation, studies on both embryonic and uterine consequences are required to generate more meaningful information. Due to ethical restriction and experimental limitation, it is difficult to generate such information in humans. This review has attempted to provide a comprehensive, but not complete, narration of a number of embryonic and uterine factors that are involved in the process of implantation in autocrine, paracrine, and/or juxtacrine manners in mice at the physiological, cellular, molecular, and genetic levels.