Decidual GM-CSF is a critical common intermediate necessary for thrombin and TNF induced in-vitro fetal membrane weakening

The role of placental insufficiency in spontaneous preterm birth: A literature review

Preterm Birth (delivery before 37 weeks of gestation) is the leading cause of childhood mortality and is also associated with significant morbidity both in the neonatal period and beyond. The aetiology of spontaneous preterm birth is unclear and likely multifactorial incorporating factors such as infection/inflammation and cervical injury. Placental insufficiency is emerging as an additional contributor to spontaneous preterm delivery; however, the mechanisms by which this occurs are not fully understood. Serum biomarkers and imaging techniques have been investigated as potential predictors of placental insufficiency, however none have yet been found to have a sufficient predictive value. This review examines the evidence for the role of the placenta in preterm birth, preterm prelabour rupture of the membranes and abruption as well as highlighting areas where further research is required.

Matrix metalloproteinases in preterm prelabor rupture of membranes in the setting of chorioamnionitis: A scoping review

Fetal or gestational membranes extend from the placenta to enclose the fetus and amniotic fluid. While the membranes spontaneously rupture at term in normal pregnancies, they can rupture prematurely before the onset of labor, termed preterm prelabor rupture of membranes (PPROM). PPROM can be triggered by bacterial infection or sterile inflammation in the membranes, known as chorioamnionitis (CAM). The membranes derive their tensile strength from a collagen-rich extracellular matrix (ECM); as such, understanding the enzymes and processes that can degrade the membrane ECM are of paramount importance. Matrix metalloproteinases (MMPs) are a class of enzymes capable of degrading collagen and other components of the ECM, and can be induced by inflammation. We used a scoping review to address the question of how MMP activity is associated with PPROM, particularly their induction due to sterile or nonsterile CAM. We have found that the most studied MMPs in PPROM were MMPs 2, 8, and 9. Additionally, some MMPs are constitutively active, while others are induced by inflammation. Mechanistic studies of the pathways that induce MMP activation are sparse, and this area is ripe for future studies. Targeting MMP activation could be a future strategy to delay or prevent PPROM.

Single Nucleotide Polymorphisms from CSF2, FLT1, TFPI and TLR9 Genes Are Associated with Prelabor Rupture of Membranes

A prelabor rupture of membranes (PROM) and its subtypes, preterm PROM (pPROM) and term PROM (tPROM), are associated with disturbances in the hemostatic system and angiogenesis. This study was designed to demonstrate the role of single nucleotide polymorphisms (SNPs), localized in CSF2 (rs25881), FLT1 (rs722503), TFPI (C-399T) and TLR9 (rs352140) genes, in PROM. A population of 360 women with singleton pregnancy consisted of 180 PROM cases and 180 healthy controls. A single-SNP analysis showed a similar distribution of genotypes in the studied polymorphisms between the PROM or the pPROM women and the healthy controls. Double-SNP TT variants for CSF2 and FLT1 polymorphisms, CC variants for TLR9 and TFPI SNPs, TTC for CSF2, FLT1 and TLR9 polymorphisms, TTT for FLT1, TLR9 and TFPI SNPs and CCCC and TTTC complex variants for all tested SNPs correlated with an increased risk of PROM after adjusting for APTT, PLT parameters and/or pregnancy disorders. The TCT variants for the CSF2, FLT1 and TLR9 SNPs and the CCTC for the CSF2, FLT1, TLR9 and TFPI polymorphisms correlated with a reduced risk of PROM when corrected by PLT and APTT, respectively. We concluded that the polymorphisms of genes, involved in hemostasis and angiogenesis, contributed to PROM.

Cross talk: Trafficking and functional impact of maternal exosomes at the Feto-maternal Interface under normal and pathologic states

Fetal cell-derived exosomes promote inflammation in uterine and cervical cells to promote labor and delivery. However, the effect of maternal exosomes on fetal cells is still not known. We tested the hypothesis that cervical cells exposed to infectious and oxidative stress (OS) signals produce exosomes that can induce inflammation at the feto-maternal interface (FMi). Exosomes isolated from medium samples from human ectocervical epithelial cells (Ecto), endocervical epithelial cells (Endo), and cervical stromal cells (Stroma) in normal cell culture (control) or exposed to infection or OS conditions were characterized based on morphology, size, quantity, expression of tetraspanin markers, and cargo proteins. Human decidual, chorion trophoblast (CTC), chorion mesenchymal (CMC), amnion mesenchymal (AMC), and amnion epithelial cells (AEC) were treated with control, LPS-, or OS-treated cervical exosomes. ELISA for pro-inflammatory cytokines and progesterone was done to determine the recipient cells' inflammatory status. Ecto, endo, and stroma released ∼110 nm, cup-shaped exosomes. LPS and OS treatments did not affect exosome size; however, OS significantly increased the number of exosomes released by all cervical cells. Cervical exosomes were detected by fluorescence microscopy in each target cell after treatment. Exosomes from LPS- and CSE-treated cervical cells increased the inflammatory cytokine levels in the decidual cells, CMC, AMC, and AEC. LPS-treated stromal cell exosomes increased IL-6, IL-8, and progesterone in CTC. In conclusion, infection and OS can produce inflammatory cargo-enriched cervical exosomes that can destabilize FMi cells. However, the refractoriness of CTC to exosome treatments suggests a barrier function of the chorion at the FMi.

Why Do the Fetal Membranes Rupture Early after Fetoscopy? A Review

Iatrogenic preterm premature rupture of the fetal membranes (iPPROM) remains the Achilles' heel of keyhole fetal surgery (fetoscopy) despite significant efforts in preclinical models to develop new therapies. This limited success is partially due to incomplete understanding why the fetal membranes rupture early after fetoscopy and notable differences in membrane physiology between humans and domestic species. In this review, we summarize aspects of fetoscopy that may contribute to iPPROM, the previous efforts to develop new therapies, and limitations of preclinical models commonly used in fetal membrane research.

Molecular Changes on Maternal-Fetal Interface in Placental Abruption-A Systematic Review

Placental abruption is the separation of the placenta from the lining of the uterus before childbirth. It is an infrequent perinatal complication with serious after-effects and a marked risk of maternal and fetal mortality. Despite the fact that numerous placental abruption risk factors are known, the pathophysiology of this issue is multifactorial and not entirely clear. The aim of this review was to examine the current state of knowledge concerning the molecular changes on the maternal–fetal interface occurring in placental abruption. Only original research articles describing studies published in English until the 15 March 2021 were considered eligible. Reviews, book chapters, case studies, conference papers and opinions were excluded. The systematic literature search of PubMed/MEDLINE and Scopus databases identified 708 articles, 22 of which were analyzed. The available evidence indicates that the disruption of the immunological processes on the maternal–fetal interface plays a crucial role in the pathophysiology of placental abruption. The features of chronic non-infectious inflammation and augmented immunological cytotoxic response were found to be present in placental abruption samples in the reviewed studies. Various molecules participate in this process, with only a few being examined. More advanced research is needed to fully explain this complicated process.

Granulocyte-macrophage colony-stimulating factor initiates amniotic membrane rupture and preterm birth in a mouse model

OBJECTIVE

Preterm premature rupture of membranes is associated with 30% of all preterm births. The weakening of amniotic membranes is associated with an increase in matrix metallopeptidases (MMPs) along with a decrease in their inhibitors, tissue inhibitor metallopeptidases (TIMPs). Additionally, granulocyte-macrophage colony-stimulating factor (GM-CSF) has been shown to weaken fetal membranes in-vitro. We hypothesize pregnant mice treated with GM-CSF lead to increased MMPs:TIMPs resulting in membrane rupture and preterm birth.

STUDY DESIGN

Pregnant CD-1 mice on gestational day 17 received either an intrauterine injection of GM-CSF or vehicle control. A second series of mice were administered an intrauterine injection of Lipopolysaccharide along with either anti-mouse GM-CSF or control antibody. Mice were evaluated for rupture of membranes and/or preterm birth and the uterus, amniotic fluid, and serum were collected for analysis.

RESULTS

87.5% of GM-CSF mice exhibited evidence of membrane rupture or preterm birth, compared with 0% in control mice (p < .001). Treatment with GM-CSF decreased the expression of TNFα (p < .05) while increasing the ratio of MMP2:TIMP1 (p < .05), MMP2:TIMP2 (p < .05), MMP2:TIMP3 (p < .001), MMP9:TIMP1 (p < .01), MMP9:TIMP2 (p < .05), MMP9:TIMP3 (p < .001), and MMP10:TIMP1 (p < .05). Mice treated with LPS and the GM-CSF antibody resulted in a decrease in the ratio of MMP2:TIMP1 (p < .0001) compared with controls.

CONCLUSION

These studies demonstrate GM-CSF will result in membrane rupture and preterm birth by increasing the ratio MMPs:TIMPs in our animal model. By increasing our understanding of the molecular pathways associated with GM-CSF, we may be able to develop future therapies to prevent preterm birth and reduce neonatal morbidity.

Mechanism of Human Fetal Membrane Biomechanical Weakening, Rupture and Potential Targets for Therapeutic Intervention

Using a novel in vitro model system combining biochemical/histologic with bioengineering approaches has provided significant insights into the physiology of fetal membrane weakening and rupture along with potential mechanistic reasons for lack of efficacy of currently clinically used agents to prevent preterm premature rupture of the membranes (pPROM) and preterm births. Likewise, the model has also facilitated screening of agents with potential for preventing pPROM and preterm birth.

α-Lipoic acid blocks the GMCSF induced protease/protease inhibitor spectrum associated with fetal membrane weakening in-vitro

INTRODUCTION

We use an in-vitro human fetal membrane (FM) explant-based model to study inflammation-induced FM weakening, a prerequisite for PPROM. In this system, GMCSF is a critical intermediate, both necessary and sufficient for TNFα and thrombin induced FM weakening. α-Lipoic-acid (LA) blocks TNFα and thrombin, as well as GMCSF-induced weakening. Recently, we reported LA concomitantly blocks GMCSF-induction of MMPs 2, 9 and 10 and inhibition of TIMPs 1-3. The aim of this study was to show that LA blocks GMCSF-induced increases in additional proteases and reductions in additional protease inhibitors.

METHODS

FM fragments were cultured±LA and then±GMCSF. In other experiments, weak versus strong, fresh FM were cultured without additions. Fragments were strength tested and media analyzed by multiplex protein ELISA for proteases and protease inhibitors.

RESULTS

GMCSF induced FM weakening and concomitantly increased several Proteases (Cathepsin-S, Proteinase-3, Elastase-2) and decreased several protease inhibitors (NGAL, Cystatin-C, HE4 and Thrombospondin1). LA inhibited GMCSF-induced FM weakening and all enzymatic changes. Untreated weaker versus stronger regions of fresh FM showed comparable differences in proteases and protease inhibitor patterns to GMCSF-stimulated versus controls.

CONCLUSION

LA blocks GMCSF-induced human FM weakening and associated protease increases and inhibitor decreases. The GMCSF-induced spectrum of protease/protease-inhibitor changes is similar to that in the natural weak FM fragments. In concert with previously reported GMCSF-induced changes in MMPs & TIMPs, these other protease and protease-inhibitor changes presumably facilitate FM weakening and rupture. LA blocks these GMCSF effects and therefore may be a useful agent to prevent PPROM.

Occurrence of a RAGE-Mediated Inflammatory Response in Human Fetal Membranes

Context:

Sterile inflammation has been shown to play a key role in the rupture of the fetal membranes (FMs). Moreover, an early and exacerbated runaway inflammation can evolve into a preterm premature rupture of membranes and lead to potential preterm birth. In this context, we investigated the receptor for advanced glycation end products (RAGE), an axis implied in physiological sterile inflammation, in conjunction with two major ligands: AGEs and High-Mobility Group Box 1 (HMGB1). Our first objective was to determine the spatiotemporal expression profiles of the different actors of the RAGE-signaling axis in human FMs, including its intracellular adaptors Diaphanous-1 and Myd88. Our second goal was to evaluate the functionality of RAGE signaling in terms of FMs inflammation.

Methods

The presence of the actors (RAGE, HMGB1, Myd88, and Diaphanous-1) at the mRNA level was investigated by reverse transcription quantitative polymerase chain reaction (RT-qPCR) in the human amnion and choriodecidua at the three trimesters and at term. Measurements were conducted at two distinct zones: the zone of intact morphology (ZIM) and the zone of altered morphology (ZAM). Then, proteins were quantified using Western blot analysis, and their localization was evaluated by immunofluorescence in term tissues. In addition, pro-inflammatory cytokine secretion was quantified using a Multiplex assay after the treatment of amnion and choriodecidua explants with two RAGE ligands (AGEs and HMGB1) in the absence or presence of a RAGE inhibitor (SAGEs).

Results

The FMs expressed the RAGE-signaling actors throughout pregnancy. At term, RNA and protein overexpression of the RAGE, HMGB1, and Diaphanous-1 were found in the amnion when compared to the choriodecidua, and the RAGE was overexpressed in the ZAM when compared to the ZIM. The two RAGE ligands (AGEs and HMGB1) induced differential cytokine production (IL1β and TNFα) in the amnion and choriodecidua.

Conclusion

Considered together, these results indicate that RAGE signaling is present and functional in human FMs. Our work opens the way to a better understanding of FMs weakening dependent on a RAGE-based sterile inflammation.

IRAK1 Is a Critical Mediator of Inflammation-Induced Preterm Birth

Preterm birth (PTB) is a major cause of neonatal mortality and morbidity, often triggered by chorioamnionitis or intrauterine inflammation (IUI) with or without infection. Recently, there has been a strong association of IL-1 with PTB. We hypothesized that IL-1R-associated kinase 1 (IRAK1), a key signaling mediator in the TLR/IL-1 pathway, plays a critical role in PTB. In human fetal membranes (FM) collected immediately after birth from women delivering preterm, p-IRAK1 was significantly increased in all the layers of FM with chorioamnionitis, compared with no-chorioamnionitis subjects. In a preterm rhesus macaque model of IUI given intra-amniotic LPS, induction of p-IRAK1 and downstream proinflammatory signaling mediators were seen in the FM. In a C57BL/6J wild-type PTB mouse model of IUI given intrauterine LPS, an IRAK1 inhibitor significantly decreased PTB and increased live birth in a dose-dependent manner. Furthermore, IRAK1 knockout mice were protected from LPS-induced PTB, which was seen in wild-type controls. Activation of IRAK1 was maintained by K63-mediated ubiquitination in preterm FM of humans with chorioamnionitis and rhesus and mouse IUI models. Mechanistically, IRAK1 induced PTB in the mouse model of IUI by upregulating expression of COX-2. Thus, our data from human, rhesus, and mouse demonstrates a critical role IRAK1 in IUI and inflammation-associated PTB and suggest it as potential therapeutic target in IUI-induced PTB.

Thrombin-Induced Decidual Colony-Stimulating Factor-2 Promotes Abruption-Related Preterm Birth by Weakening Fetal Membranes

Preterm premature rupture of membranes (PPROM) and thrombin generation by decidual cell-expressed tissue factor often accompany abruptions. Underlying mechanisms remain unclear. We hypothesized that thrombin-induced colony-stimulating factor-2 (CSF-2) in decidual cells triggers paracrine signaling via its receptor (CSF2R) in trophoblasts, promoting fetal membrane weakening and abruption-associated PPROM. Decidua basalis sections from term (n = 10), idiopathic preterm birth (PTB; n = 8), and abruption-complicated pregnancies (n = 8) were immunostained for CSF-2. Real-time quantitative PCR measured CSF2 and CSF2R mRNA levels. Term decidual cell (TDC) monolayers were treated with 10^-8 mol/L estradiol ± 10^-7 mol/L medroxyprogesterone acetate (MPA) ± 1 IU/mL thrombin pretreatment for 4 hours, washed, and then incubated in control medium with estradiol ± MPA. TDC-derived conditioned media supernatant effects on fetal membrane weakening were analyzed. Immunostaining localized CSF-2 primarily to decidual cell cytoplasm and cytotrophoblast cell membranes. CSF-2 immunoreactivity was higher in abruption-complicated or idiopathic PTB specimens versus normal term specimens (P < 0.001). CSF2 mRNA was higher in TDCs versus cytotrophoblasts (P < 0.05), whereas CSF2R mRNA was 1.3 × 10⁴-fold higher in cytotrophoblasts versus TDCs (P < 0.001). Thrombin enhanced CSF-2 secretion in TDC cultures fourfold (P < 0.05); MPA reduced this effect. Thrombin-pretreated TDC-derived conditioned media supernatant weakened fetal membranes (P < 0.05), which MPA inhibited. TDC-derived CSF-2, acting via trophoblast-expressed CSFR2, contributes to thrombin-induced fetal membrane weakening, eliciting abruption-related PPROM and PTB.

Fetal Membranes, Not a Mere Appendage of the Placenta, but a Critical Part of the Fetal-Maternal Interface Controlling Parturition

Fetal membranes (FMs) play a role in pregnancy maintenance and promoting parturition at term. The FMs are not just part of the placenta, structurally or functionally. Although attached to the placenta, the amnion has a separate embryologic origin, and the chorion deviates from the placenta by the first month of pregnancy. Other than immune protection, these FM functions are not those of the placenta. FM dysfunction is associated with and may cause adverse pregnancy outcomes. Ongoing research may identify biomarkers for pending preterm premature rupture of the FMs as well as therapeutic agents, to prevent it and resulting preterm birth.

Influence of osmolarity and hydration on the tear resistance of the human amniotic membrane

The amnion is considered to be the load-bearing part of the fetal membranes. We investigated the influence of osmolarity of the testing medium and hydration on its fracture toughness. Mode I fracture tests revealed that physiological variations in the bath osmolarity do not influence the tear resistance of amnion, while larger changes, i.e. from physiological saline solution to distilled water, lead to a significant reduction of the fracture toughness. Uniaxial tensile tests on collagen hydrogels confirmed the reduction in toughness, suggesting that lower bath osmolarity triggers changes in the failure properties of single collagen fibers. Prenatal surgeries, in particular fetoscopic procedures with partial amniotic carbon dioxide insufflation, might result in dehydration of the amnion. Dehydration induced a brittle behavior; however, subsequent rehydration for 15 min resulted in a similar tear resistance as for the fresh tissue.

Granulocyte macrophage colony stimulating factor (GM-CSF), the critical intermediate of inflammation-induced fetal membrane weakening, primarily exerts its weakening effect on the choriodecidua rather than the amnion

INTRODUCTION

We have previously demonstrated two associations of PPROM, (1) inflammation/infection (modeled by tumor necrosis factor (TNF)) and (2) decidual bleeding (modeled by thrombin), both decrease fetal membrane (FM) rupture strength in-vitro. Furthermore, Granulocyte-Macrophage-Colony-Stimulating-Factor (GM-CSF) induced by both TNF and thrombin is a critical intermediate, necessary and sufficient for weakening by either agent. The amnion is the strength component of FM and must weaken for FM to rupture. It is unclear whether GM-CSF weakens amnion (AM) directly, or initially targets choriodecidua (CD) which secondarily releases agents to act on amnion.

METHODS

Full thickness FM fragments were treated with/without GM-CSF. Some were preincubated with alpha-lipoic acid (LA), a known inhibitor of FM weakening. The FM fragments were then strength-tested. Separately, FM fragments were initially separated to AM and CD. AM fragments were cultured with Medium ± GM-CSF and then strength-tested. In other experiments, CD fragments were cultured with Medium, GM-CSF, LA, or LA + GM-CSF. Conditioned medium from each group was then incubated with AM. AM was then strength-tested. Matrix Metalloproteinases (MMPs) and Tissue Inhibitors of Matrix Metalloproteinases (TIMPs) were analyzed by Mutiplex Elisa.

RESULTS

GM-CSF weakened intact FM which was blocked by LA. GM-CSF did not weaken isolated AM. However, GM-CSF conditioned CD media weakened AM and this weakening was inhibited by LA. GM-CSF treatment of CD increased MMPs 2, 9, and 10, and decreased TIMPs 1-3. LA reversed these effects.

CONCLUSIONS

GM-CSF does not weaken amnion directly; GM-CSF acts on CD to increase proteases and decrease anti-proteases which secondarily weaken the amnion.

Targeting mechanotransduction mechanisms and tissue weakening signals in the human amniotic membrane

Mechanical and inflammatory signals in the fetal membrane play an important role in extracellular matrix (ECM) remodelling in order to dictate the timing of birth. We developed a mechanical model that mimics repetitive stretching of the amniotic membrane (AM) isolated from regions over the placenta (PAM) or cervix (CAM) and examined the effect of cyclic tensile strain (CTS) on mediators involved in mechanotransduction (Cx43, AKT), tissue remodelling (GAGs, elastin, collagen) and inflammation (PGE₂, MMPs). In CAM and PAM specimens, the application of CTS increased GAG synthesis, PGE₂ release and MMP activity, with concomitant reduction in collagen and elastin content. Co-stimulation with CTS and pharmacological agents that inhibit either Cx43 or AKT, differentially influenced collagen, GAG and elastin in a tissue-dependent manner. SHG confocal imaging of collagen fibres revealed a reduction in SHG intensity after CTS, with regions of disorganisation dependent on tissue location. CTS increased Cx43 and AKT protein and gene expression and the response could be reversed with either CTS, the Cx43 antisense or AKT inhibitor. We demonstrate that targeting Cx43 and AKT prevents strain-induced ECM damage and promotes tissue remodelling mechanisms in the AM. We speculate that a combination of inflammatory and mechanical factors could perturb typical mechanotransduction processes mediated by Cx43 signalling. Cx43 could therefore be a potential therapeutic target to prevent inflammation and preterm premature rupture of the fetal membranes.

Physiological effects of partial amniotic carbon dioxide insufflation with cold, dry vs heated, humidified gas in a sheep model

OBJECTIVE

Partial amniotic carbon dioxide (CO₂ ) insufflation (PACI) is used to improve visualization and facilitate complex fetoscopic surgery. However, there are concerns about fetal hypercapnic acidosis and postoperative fetal membrane inflammation. We assessed whether using heated and humidified, rather than cold and dry, CO₂ might reduce the impact of PACI on the fetus and fetal membranes in sheep.

METHODS

Twelve fetal lambs of 105 days' gestational age (term = 145 days) were exteriorized partially, via a midline laparotomy and hysterotomy, and arterial catheters and flow probes were inserted surgically. The 10 surviving fetuses were returned to the uterus, which was then closed and insufflated with cold, dry (22 °C at 0-5% humidity, n = 5) or heated, humidified (40 °C at 100% humidity, n = 5) CO₂ at 15 mmHg for 180 min. Fetal membranes were collected immediately after insufflation for histological analysis. Physiological data and membrane leukocyte counts, suggestive of membrane inflammation, were compared between the two groups.

RESULTS

After 180 min of insufflation, fetal survival was 0% in the group which underwent PACI with cold, dry CO₂ , and 60% (n = 3) in the group which received heated, humidified gas. While all insufflated fetuses became progressively hypercapnic (PaCO₂  > 68 mmHg), this was considerably less pronounced in those in which heated, humidified gas was used: after 120 min of insufflation, compared with those receiving cold, dry gas (n = 3), fetuses undergoing heated, humidified PACI (n = 5) had lower arterial partial pressure of CO₂ (mean ± standard error of the mean, 82.7 ± 9.1 mmHg for heated, humidified CO₂ vs 170.5 ± 28.5 for cold, dry CO₂ during PACI, P < 0.01), lower lactate levels (1.4 ± 0.4 vs 8.5 ± 0.9 mmol/L, P < 0.01) and higher pH (pH, 7.10 ± 0.04 vs 6.75 ± 0.04, P < 0.01). There was also a non-significant trend for fetal carotid artery pressure to be higher following PACI with heated, humidified compared with cold, dry CO₂ (30.5 ± 1.3 vs 8.7 ± 5.5 mmHg, P = 0.22). Additionally, the median (interquartile range) number of leukocytes in the chorion was significantly lower in the group undergoing PACI with heated, humidified CO₂ compared with the group receiving cold, dry CO₂ (0.7 × 10^-5 (0.5 × 10^-5 ) vs 3.2 × 10^-5 (1.8 × 10^-5 ) cells per square micron, P = 0.02).

CONCLUSIONS

PACI with cold, dry CO₂ causes hypercapnia, acidosis, hypotension and fetal membrane inflammation in fetal sheep, raising potential concerns for its use in humans. It seems that using heated, humidified CO₂ for insufflation partially mitigates these effects and this may be a suitable alternative for reducing the risk of fetal acid-base disturbances during, and fetal membrane inflammation following, complex fetoscopic surgery. © 2018 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.

Heated humidified carbon dioxide for partial uterine insufflation in fetoscopic myelomeningocele repair: insights from animal model

Linked Comment: Ultrasound Obstet Gynecol 2018; 53: 340-347.

The effects of partial amniotic carbon dioxide insufflation in an ovine model

OBJECTIVE

We aim to assess the effect of partial amniotic carbon dioxide insufflation (PACI) at increasing pressures on fetal acid-base, fetal-placental perfusion, and fetal membrane morphology in an ovine model.

METHOD

Pregnant ewes and fetuses were instrumented under isoflurane anesthesia at 105 days gestation (term 145 days) to monitor utero-placental blood flow, fetal and maternal blood pressure, heart rate, and blood gas status. One group (n = 6) was exposed to PACI (unheated dry CO₂ ), involving 10 mm Hg stepwise increases in insufflation pressure (5 to 25 mm Hg), for 80 minutes followed by 20 minutes of desufflation. Un-insufflated controls (n = 5) were monitored for 100 minutes. At postmortem, fetal membranes were collected for histological analysis.

RESULTS

PACI at 25 mm Hg caused severe fetal hypercapnia (PaCO₂  = 143 ± 5 vs 54 ± 5 mm Hg, P < 0.001), acidosis (pH = 6.85 ± 0.02 vs 7.25 ± 0.02, P < 0.001), hypoxia (SaO₂  = 31 ± 4% vs 57 ± 4%, P = 0.01), and reduced uterine artery flow (50 ± 15 vs 196 ± 13 mL/min/kg, P = 0.005) compared with controls. These effects were greater at higher PACI pressures. PACI resulted in leukocyte infiltration in the amnion (1.77 × 10^-5  ± 0.61 × 10^-5 vs 0.38 × 10^-5  ± 0.19 × 10^-5  cells/μm² , P = 0.04) and chorionic membranes (2.94 × 10^-5  ± 0.67 × 10^-5 vs 0.84 × 10^-5  ± 0.42 × 10^-5  cells/μm² , P = 0.01).

CONCLUSION

Higher PACI pressures results in larger disturbances in fetal acid-base, uterine blood flow, and fetal membrane inflammation in sheep. Differences between human and sheep utero-placental structure should be considered.

In an in-vitro model using human fetal membranes, α-lipoic acid inhibits inflammation induced fetal membrane weakening

INTRODUCTION

We established an in-vitro model for the study of human fetal membrane (FM) weakening leading to pPROM. In this model, granulocyte-macrophage colony-stimulating factor (GM-CSF) is a critical intermediate for both tumor necrosis factor-α (TNF; modeling infection/inflammation) and thrombin (modeling decidual bleeding/abruption)-induced weakening. Thus, inhibitors of FM weakening can be categorized as targeting GM-CSF production, GM-CSF downstream action, or both. Most progestogens inhibit both, except 17-α hydroxyprogesterone caproate which inhibits FM weakening at only one point, GM-CSF production. α-lipoic acid (LA), an over-the-counter dietary supplement, has also been previously shown to inhibit TNF and thrombin induced FM weakening.

OBJECTIVE

To determine the point of action of LA inhibition of FM weakening.

METHODS

FM fragments were mounted in Transwell inserts and preincubated with/without LA/24 h, then with/without addition of TNF, thrombin or GM-CSF. After 48 h, medium was assayed for GM-CSF, and FM fragments were rupture-strength tested.

RESULTS

TNF and thrombin both weakened FM and increased GM-CSF levels. GM-CSF also weakened FM. LA inhibited both TNF and thrombin induced FM weakening and concomitantly inhibited the increase in GM-CSF in a concentration-dependent manner. In addition, LA inhibited GM-CSF induced FM weakening in a concentration dependent manner.

CONCLUSIONS

LA blocks TNF and thrombin induced FM weakening at two points, inhibiting both GM-CSF production and downstream action. Thus, we speculate that LA may be a potential standalone therapeutic agent, or supplement to current therapy for prevention of pPROM related spontaneous preterm birth, if preclinical studies to examine feasibility and safety during pregnancy are successfully accomplished.

In an in-vitro model using human fetal membranes, 17-α hydroxyprogesterone caproate is not an optimal progestogen for inhibition of fetal membrane weakening

BACKGROUND

The progestogen 17-α hydroxyprogesterone caproate (17-OHPC) is 1 of only 2 agents recommended for clinical use in the prevention of spontaneous preterm delivery, and studies of its efficacy have been conflicting. We have developed an in-vitro model to study the fetal membrane weakening process that leads to rupture in preterm premature rupture of the fetal membranes (pPROM). Inflammation/infection associated with tumor necrosis factor-α (TNF-α) induction and decidual bleeding/abruption associated thrombin release are leading causes of preterm premature rupture of the fetal membranes. Both agents (TNF-α and thrombin) cause fetal membrane weakening in the model system. Furthermore, granulocyte-macrophage colony-stimulating factor (GM-CSF) is a critical intermediate for both TNF-α and thrombin-induced fetal membrane weakening. In a previous report, we demonstrated that 3 progestogens, progesterone, 17-alpha hydroxyprogesterone (17-OHP), and medroxyprogesterone acetate (MPA), each inhibit both TNF-α- and thrombin-induced fetal membrane weakening at 2 distinct points of the fetal membrane weakening pathway. Each block both the production of and the downstream action of the critical intermediate granulocyte-macrophage colony-stimulating factor.

OBJECTIVE

The objective of the study was to characterize the inhibitory effects of 17-OHPC on TNF-α- and thrombin-induced fetal membrane weakening in vitro.

STUDY DESIGN

Full-thickness human fetal membrane fragments from uncomplicated term repeat cesarean deliveries were mounted in 2.5 cm Transwell inserts and cultured with/without 17-alpha hydroxyprogesterone caproate (10^-9 to 10^-7 M). After 24 hours, medium (supernatant) was removed and replaced with/without the addition of tumor necrosis factor-alpha (20 ng/mL) or thrombin (10 U/mL) or granulocyte-macrophage colony-stimulating factor (200 ng/mL). After 48 hours of culture, medium from the maternal side compartment of the model was assayed for granulocyte-macrophage colony-stimulating factor and the fetal membrane fragments were rupture strength tested.

RESULTS

Tumor necrosis factor-alpha and thrombin both weakened fetal membranes (43% and 62%, respectively) and increased granulocyte-macrophage colony-stimulating factor levels (3.7- and 5.9-fold, respectively). Pretreatment with 17-alpha hydroxyprogesterone caproate inhibited both tumor necrosis factor-alpha- and thrombin-induced fetal membrane weakening and concomitantly inhibited the induced increase in granulocyte-macrophage colony-stimulating factor in a concentration-dependent manner. However, contrary to our prior reports regarding progesterone and other progestogens, 17-alpha hydroxyprogesterone caproate did not also inhibit granulocyte-macrophage colony-stimulating factor-induced fetal membrane weakening.

CONCLUSION

17-Alpha hydroxyprogesterone caproate blocks tumor necrosis factor-alpha- and thrombin-induced fetal membrane weakening by inhibiting the production of granulocyte-macrophage colony-stimulating factor. However, 17-alpha hydroxyprogesterone caproate did not also inhibit granulocyte-macrophage colony-stimulating factor-induced weakening. We speculate that progestogens other than 17-alpha hydroxyprogesterone caproate may be more efficacious in preventing preterm premature rupture of the fetal membranes-related spontaneous preterm birth.

N,N-Dimethylacetamide Significantly Attenuates LPS- and TNFα-Induced Proinflammatory Responses Via Inhibition of the Nuclear Factor Kappa B Pathway

Previously, we have shown that N,N-dimethylacetamide (DMA) prevents inflammation-induced preterm birth in a murine model, inhibits LPS-induced increases in placental pro-inflammatory cytokines and up-regulates the anti-inflammatory cytokine Interleukin-10 (IL-10). However, DMA's mechanism of action remains to be elucidated. In the current study we investigate how DMA produces its anti-inflammatory effect. Using in vitro and ex vivo models, we show that DMA suppresses secretion of pro-inflammatory cytokines in lipopolysaccharide (LPS)-induced RAW 264.7 cells, TNFα-challenged JEG-3 cells and LPS-stimulated human placental explants. DMA significantly attenuated the secretion of TNFα, IL-6, IL-10, and granulocyte macrophage colony stimulating factor (GM-CSF) from LPS-stimulated RAW 264.7 cells, IL-6 secretion from TNFα-stimulated JEG-3 cells and TNFα, IL-6, IL-10, GM-CSF and Interleukin-8 (IL-8) from LPS-stimulated human placental explants. We further investigated if DMA's effect on cytokine expression involves the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and mitogen-activated protein kinase (MAPK) pathways. DMA (10 mM) significantly inhibited nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα) degradation in LPS-stimulated RAW 264.7 cells, but there was no significant change in the expression of phosphorylated or native forms of downstream proteins in the MAPK pathway. In addition, DMA significantly attenuated luciferase activity in cells co-transfected with NF-κB-Luc reporter plasmid, but not with AP-1-Luc or CEBP-Luc reporters. Overall, our findings suggest that the anti-inflammatory activity of DMA is mediated by inhibition of the NF-κB pathway via decreased IκBα degradation.

Human amnion mesenchymal cells are pro-inflammatory when activated by the Toll-like receptor 2/6 ligand, macrophage-activating lipoprotein-2

INTRODUCTION

Infection accounts for over 40% of preterm premature rupture of the fetal membranes (PPROM), a major cause of preterm birth. Toll-like receptors (TLR) play key roles in pathogen surveillance but their expression and function in amnion mesenchymal cells (AMC) is unclear. The aims of this study were to determine the expression of all TLR isoforms and the effect of macrophage-activating lipoprotein-2 (MALP-2), derived from a common pathogen involved in PPROM, on human AMC.

METHODS

AMC were isolated from normal, term amnion from repeat cesarean section. Semi-quantitative RT-PCR, immunocytochemistry, immunohistochemistry and western blotting were used to detect TLR isoform expression. Immunocytochemistry of NF-κB p65, pro-inflammatory cytokine secretion (ELISA), MTT assay, LDH assay, immunoblotting of cytosolic cytochrome c and cleaved caspase-3, and expression of 84 microRNAs by Qiagen miRNA PCR array were used to determine the functional effect of MALP-2 on AMC.

RESULTS

TLR1-10 was detected in AMC, and protein expression of TLR2, 4, and 6 were confirmed. MALP-2 induced nuclear translocation of p65, reaching significance after 45 min (ANOVA, P < 0.05). MALP-2 did not cause apoptosis but did lead to significant secretion of IL-4, IL-6, and IL-8 (P < 0.05, 0.01, 0.001, respectively) and significant changes in miRNA-320a and miRNA-18a (P < 0.05).

DISCUSSION

These results suggest that AMC elicit a pro-inflammatory response following stimulation with the known TLR2/6 ligand MALP-2. This data supports the idea that AMC express the innate immune system receptors that could help with immune surveillance during infection and contribute to inflammatory responses that lead to PPROM.

Novel concepts on pregnancy clocks and alarms: redundancy and synergy in human parturition

The signals and mechanisms that synchronize the timing of human parturition remain a mystery and a better understanding of these processes is essential to avert adverse pregnancy outcomes. Although our insights into human labor initiation have been informed by studies in animal models, the timing of parturition relative to fetal maturation varies among viviparous species, indicative of phylogenetically different clocks and alarms; but what is clear is that important common pathways must converge to control the birth process. For example, in all species, parturition involves the transition of the myometrium from a relaxed to a highly excitable state, where the muscle rhythmically and forcefully contracts, softening the cervical extracellular matrix to allow distensibility and dilatation and thus a shearing of the fetal membranes to facilitate their rupture. We review a number of theories promulgated to explain how a variety of different timing mechanisms, including fetal membrane cell senescence, circadian endocrine clocks, and inflammatory and mechanical factors, are coordinated as initiators and effectors of parturition. Many of these factors have been independently described with a focus on specific tissue compartments.In this review, we put forth the core hypothesis that fetal membrane (amnion and chorion) senescence is the initiator of a coordinated, redundant signal cascade leading to parturition. Whether modified by oxidative stress or other factors, this process constitutes a counting device, i.e. a clock, that measures maturation of the fetal organ systems and the production of hormones and other soluble mediators (including alarmins) and that promotes inflammation and orchestrates an immune cascade to propagate signals across different uterine compartments. This mechanism in turn sensitizes decidual responsiveness and eventually promotes functional progesterone withdrawal in the myometrium, leading to increased myometrial cell contraction and the triggering of parturition. Linkage of these processes allows convergence and integration of the gestational clocks and alarms, prompting a timely and safe birth. In summary, we provide a comprehensive synthesis of the mediators that contribute to the timing of human labor. Integrating these concepts will provide a better understanding of human parturition and ultimately improve pregnancy outcomes.

Human fetal membranes at term: Dead tissue or signalers of parturition?

Various endocrine, immune, and mechanical factors produced by feto-maternal compartments at term increase intrauterine inflammatory loads to induce labor. The role of fetal (placental) membranes (amniochorion) as providers of parturition signals has not been well investigated. Fetal membranes line the intrauterine cavity and grow with and protect the fetus. Fetal membranes exist as an entity between the mother and fetus and perform unique functions during pregnancy. Membranes undergo a telomere-dependent p38 MAPK-induced senescence and demonstrate a decline in functional and mechanical abilities at term, showing signs of aging. Fetal membrane senescence is also allied with completion of fetal maturation at term as the fetus readies for delivery, which may also indicate the end of independent life and longevity of fetal membranes as their functional role concludes. Fetal membrane senescence is accelerated at term because of oxidative stress and increased stretching. Senescent fetal membranes cells produce senescence-associated secretory phenotype (SASP-inflammation) and also release proinflammatory damage-associated molecular patterns (DAMPs), namely HMGB1 and cell-free fetal telomere fragments. In a feedback loop, SASP and DAMPs increase senescence and enhance the inflammatory load to promote labor. Membranes increase the inflammatory load to disrupt homeostatic balance to transition quiescent uterine tissues toward a labor phenotype. Therefore, along with other well-described labor-promoting signals, senescent fetal membranes may also contribute to human term parturition.

The physiology of fetal membrane weakening and rupture: Insights gained from the determination of physical properties revisited

Rupture of the fetal membranes (FM) is precipitated by stretch forces acting upon biochemically mediated, pre-weakened tissue. Term FM develop a para-cervical weak zone, characterized by collagen remodeling and apoptosis, within which FM rupture is thought to initiate. Preterm FM also have a weak region but are stronger overall than term FM. Inflammation/infection and decidual bleeding/abruption are strongly associated with preterm premature FM rupture (pPROM), but the specific mechanisms causing FM weakening-rupture in pPROM are unknown. There are no animal models for study of FM weakening and rupture. Over a decade ago we developed equipment and methodology to test human FM strength and incorporated it into a FM explant system to create an in-vitro human FM weakening model system. Within this model TNF (modeling inflammation) and Thrombin (modeling bleeding) both weaken human FM with concomitant up regulation of MMP9 and cellular apoptosis, mimicking the characteristics of the spontaneous FM rupture site. The model has been enhanced so that test agents can be applied directionally to the choriodecidual side of the FM explant consistent with the in-vivo situation. With this enhanced system we have demonstrated that the pathways involving inflammation/TNF and bleeding/Thrombin induced FM weakening overlap. Furthermore GM-CSF production was demonstrated to be a critical common intermediate step in both the TNF and the Thrombin induced FM weakening pathways. This model system has also been used to test potential inhibitors of FM weakening and therefore pPROM. The dietary supplement α-lipoic acid and progestogens (P4, MPA and 17α-hydroxyprogesterone) have been shown to inhibit both TNF and Thrombin induced FM weakening. The progestogens act at multiple points by inhibiting both GM-CSF production and GM-CSF action. The use of a combined biomechanical/biochemical in-vitro human FM weakening model system has allowed the pathways of fetal membrane weakening to be delineated, and agents that may be of clinical use in inhibiting these pathways to be tested.

Inflammatory Response of Human Gestational Membranes to Ureaplasma parvum Using a Novel Dual-Chamber Tissue Explant System

Preterm premature rupture of membranes (PPROM) is often associated with intra-amniotic inflammation and infection. Current understanding of the pathogenesis of PPROM includes activation of pro-inflammatory cytokines and proteolytic enzymes leading to compromise of membrane integrity. The impact of exposure to bacterial pathogens, including Ureaplasma parvum, on gestational membranes is poorly understood. Our objective was to develop a dual-chamber system to characterize the inflammatory response of gestational membranes to U. parvum in a directional nature. Full-thickness human gestational membrane explants, with either choriodecidua or amnion oriented superiorly, were suspended between two washers in a cylindrical device, creating two distinct compartments. Brilliant green dye was introduced into the top chamber to assess the integrity of the system. Tissue viability was evaluated after 72 h using a colorimetric cell proliferation assay. Choriodecidua or amnion was exposed to three doses of U. parvum and incubated for 24 h. Following treatment, media from each compartment were used for quantification of U. parvum (quantitative PCR), interleukin (IL)-8 (enzyme-linked immunosorbent assay), and matrix metalloproteinase (MMP)-2 and MMP-9 activity (zymography). We observed that system integrity and explant viability were maintained over 72 h. Dose-dependent increases in recovered U. parvum, IL-8 concentration, and MMP-2 activity were detected in both compartments. Significant differences in IL-8 concentration and MMP-9 activity were found between the choriodecidua and amnion. This tissue explant system can be used to investigate the inflammatory consequences of directional bacterial exposure for gestational membranes and provides insight into the pathogenesis of PPROM and infectious complications of pregnancy.

The role of decidual cells in uterine hemostasis, menstruation, inflammation, adverse pregnancy outcomes and abnormal uterine bleeding

BACKGROUND

Human pregnancy requires robust hemostasis to prevent hemorrhage during extravillous trophoblast (EVT) invasion of the decidualized endometrium, modification of spiral arteries and post-partum processes. However, decidual hemorrhage (abruption) can occur throughout pregnancy from poorly transformed spiral arteries, causing fetal death or spontaneous preterm birth (PTB), or it can promote the aberrant placentation observed in intrauterine growth restriction (IUGR) and pre-eclampsia; all leading causes of perinatal or maternal morbidity and mortality. In non-fertile cycles, the decidua undergoes controlled menstrual bleeding. Abnormal uterine bleeding (AUB) accompanying progestin-only, long-acting, reversible contraception (pLARC) accounts for most discontinuations of these safe and highly effective agents, thereby contributing to unwanted pregnancies and abortion. The aim of this study was to investigate the role of decidual cells in uterine hemostasis, menstruation, inflammation, adverse pregnancy outcomes and abnormal uterine bleeding.

METHODS

We conducted a critical review of the literature arising from PubMed searches up to December 2015, regarding in situ and in vitro expression and regulation of several specific proteins involved in uterine hemostasis in decidua and cycling endometrium. In addition, we discussed clinical and molecular mechanisms associated with pLARC-induced AUB and pregnancy complications with abruptions, chorioamnionitis or pre-eclampsia.

RESULTS

Progestin-induced decidualization of estradiol-primed human endometrial stromal cells (HESCs) increases in vivo and in vitro expression of tissue factor (TF) and type-1 plasminogen activator inhibitor (PAI-1) while inhibiting plasminogen activators (PAs), matrix metalloproteinases (MMPs), and the vasoconstrictor, endothelin-1 (ET-1). These changes in decidual cell-derived regulators of hemostasis, fibrinolysis, extracellular matrix (ECM) turnover, and vascular tone prevent hemorrhage during EVT invasion and vascular remodeling. In non-fertile cycles, progesterone withdrawal reduces TF and PAI-1 while increasing PA, MMPs and ET-1, causing menstrual-associated bleeding, fibrinolysis, ECM degradation and ischemia. First trimester decidual hemorrhage elicits later adverse outcomes including pregnancy loss, pre-eclampsia, abruption, IUGR and PTB. Decidual hemorrhage generates excess thrombin that binds to decidual cell-expressed protease-activated receptors (PARs) to induce chemokines promoting shallow placentation; such bleeding later in pregnancy generates thrombin to down-regulate decidual cell progesterone receptors and up-regulate cytokines and MMPs linked to PTB. Endometria of pLARC users display ischemia-induced excess vasculogenesis and progestin inhibition of spiral artery vascular smooth muscle cell proliferation and migration leading to dilated fragile vessels prone to bleeding. Moreover, aberrant TF-derived thrombin signaling also contributes to the pathogenesis of endometriosis via induction of angiogenesis, inflammation and cell survival.

CONCLUSION

Perivascular decidualized HESCs promote endometrial hemostasis during placentation yet facilitate menstruation through progestational regulation of hemostatic, proteolytic, and vasoactive proteins. Pathological endometrial hemorrhage elicits excess local thrombin generation, which contributes to pLARC associated AUB, endometriosis and adverse pregnancy outcomes through several biochemical mechanisms.

In-vivo stretch of term human fetal membranes

INTRODUCTION

Fetal membranes (FM) usually fail prior to delivery during term labor, but occasionally fail at preterm gestation, precipitating preterm birth. To understand the FM biomechanical properties underlying these events, study of the baseline in-vivo stretch experienced by the FM is required. This study's objective was to utilize high resolution MRI imaging to determine in-vivo FM stretch.

METHODS

Eight pregnant women (38.4 ± 0.4wks) underwent abdominal-pelvic MRI prior to (2.88 ± 0.83d) caesarean delivery. Software was utilized to determine the total FM in-vivo surface area (SA) and that of its components: placental disc and reflected FM. At delivery, the SA of the disc and FM in the relaxed state were measured. In-vivo (stretched) to delivered SA ratios were calculated. FM fragments were then biaxially stretched to determine the force required to re-stretch the FM back to in-vivo SA.

RESULTS

Total FM SA, in-vivo vs delivered, was 2135.51 ± 108.47 cm(2) vs 842.59 ± 35.86 cm(2); reflected FM was 1778.42 ± 107.39 cm(2) vs 545.41 ± 22.90 cm(2), and disc was 357.10 ± 28.08 cm(2) vs 297.18 ± 22.14 cm(2). The ratio (in-vivo to in-vitro SA) of reflected FM was 3.26 ± 0.11 and disc was 1.22 ± 0.10. Reflected FM re-stretched to in-vivo SA generated a tension of 72.26 N/m, corresponding to approximate pressure of 15.4 mmHg. FM rupture occurred at 295.08 ± 31.73 N/m corresponding to approximate pressure of 34 mmHg. Physiological SA was 70% of that at rupture.

DISCUSSION

FM are significantly distended in-vivo. FM collagen fibers were rapidly recruited once loaded and functioned near the failure state during in-vitro testing, suggesting that, in-vivo, minimal additional (beyond physiological) stretch may facilitate rapid, catastrophic failure.

Progesterone inhibits in vitro fetal membrane weakening

OBJECTIVE

Inflammation/infection and abruption are leading causes of preterm premature rupture of the membranes. Recently, we identified granulocyte-macrophage colony-stimulating factor (GM-CSF) as a critical mediator of both tumor necrosis factor-α- (TNF; modeling inflammation) and thrombin-induced (modeling abruption) weakening of the fetal membranes. We found that (1) TNF and thrombin both induced GM-CSF in the choriodecidua, (2) blockade of GM-CSF action with neutralizing antibodies inhibited both TNF- and thrombin-induced fetal membrane weakening, and (3) GM-CSF alone induced fetal membrane weakening. GM-CSF is thus part of an overlap of the inflammation and abruption-induced fetal membrane weakening pathways. The effects of progesterone analogs on the pathways by which fetal membranes are weakened have not been investigated. We examined the effects of progesterone, medroxyprogesterone acetate (MPA) and 17α-hydroxyprogesterone (HP) on TNF- and thrombin-induced fetal membrane weakening.

STUDY DESIGN

Full-thickness fetal membranes from uncomplicated term repeat cesarean deliveries were mounted in Transwell inserts in Minimum Essential Medium alpha and incubated at 37°C in 5% CO2. The choriodecidua side of the fetal membrane fragments were preincubated with progesterone, MPA, HP, or vehicle for 24 hours. Fetal membranes were then exposed to TNF, thrombin, or GM-CSF on the choriodecidua side for an additional 48 hours. The fetal membrane tissues were then strength tested, and medium from the choriodecidua and amnion compartments was assayed for GM-CSF content.

RESULTS

TNF and thrombin both weakened fetal membranes and elevated media GM-CSF levels on the choriodecidua side of the fetal membrane. Pretreatment with progesterone, MPA, or HP inhibited both TNF- and thrombin-induced fetal membrane weakening and also inhibited the induced increase in GM-CSF. GM-CSF decreased fetal membrane rupture strength by 68%, which was inhibited by progestogen pretreatment with a potency order: progesterone <MPA <HP.

CONCLUSION

Progestogen pretreatment blocks TNF- and thrombin-induced fetal membrane weakening by inhibiting both the production and action of GM-CSF. These findings are consistent with the administration of progestogens in the prevention of preterm premature rupture of the membranes.