Striking changes in the structure and organization of rat fetal membranes precede parturition

Micronuclei and nuclear buds in amniotic tissue of rats treated with cyclophosphamide

Fetal development can be altered by DNA damage caused by maternal exposure to chemical, physical, or biological agents during gestation. One method of assessing genotoxicity is to detect micronuclei (MNs) and/or nuclear abnormalities. This can be performed in vivo and requires only frequently dividing tissues, such as amniotic tissue (AT), which is in contact with the fetal environment and is composed of very thin layers of cells. This study evaluated the presence of MNs, nucleoplasmic bridges, and nuclear buds (NBs) in the fetal AT following maternal exposure to cyclophosphamide (CP) during pregnancy. Pregnant Wistar rats were divided into a negative control group and an experimental group that was orally administered CP (10 mg/kg). Daily blood smears were obtained from pregnant rats on days 14-19 of gestation. The rats were dissected, and fetal ATs were obtained on the 19th day of gestation. The MN and NB frequencies in AT cells were analyzed using a fluorescence microscope (100 ×). Micronucleated erythrocytes in the peripheral blood of the control rats were also assessed. Micronucleated polychromatic erythrocyte frequencies were significantly higher than those in the controls. Polychromatic erythrocyte frequencies were lower in CP-treated rats than in controls at 48-120 h. Fetuses in the CP-treated group also showed a significant increase in MNs and NBs in AT cells. In conclusion, AT could be used for analyzing MNs and NBs in rats following maternal exposure to a genotoxic agent and as a viable alternative for analyzing the integrity of fetal DNA during gestation.

The comparative aspects of hystricomorph subplacenta: potential endocrine organ

Background

The placenta of hystricomorph rodents, lagomorphs and some primates includes an unusual structure, termed a subplacenta, which essentially consists of trophoblastic cells located deep to the central implantation site within the area of decidualization. It has been suggested that the subplacenta is functionally important, although considerable controversy remains on the issue. In this context, our objective was to compare the architecture and structure of the subplacentas of different hystricomorph species, to investigate the possibility that it is active in hormone synthesis.

Methods

In total, the placentas of 3 capybaras (Hydrochaeris hydrochaeris), 2 pacas (Agouti paca), 5 agoutis (Dasyprocta leporina), 5 rock cavies (Kerodon rupestris) and 3 guinea pigs (Cavia porcellus) at different stages of pregnancy (early, middle and near term) were used for gross and microscopic examination. This included the preparation of latex injection casts, immunohistochemistry for steroidogenic enzymes, scanning and transmission electron microscopy. Tissue steroid concentrations were also determined.

Results

The gross morphology and microvascular arrangement of the subplacentas were similar among the hystricomorphs studied including ultra-structural verification of cytotrophoblast and syncytiotrophoblast in all species. In guinea pigs, trophoblast cells exhibited characteristics consistent with intense metabolic and secretory activity in general. However, immuno-histochemical evidence also indicated that subplacental trophoblast expressed key steroidogenic enzymes, mainly in the chorionic villus region, consistent with tissue steroid concentrations.

Conclusions

The subplacentas within placentas of hystricomorph rodent species are structurally similar and, in guinea pigs, have potential for steroid hormone secretion from, at least the early stages of pregnancy.

Cell-Free DNA Release by Mouse Fetal Membranes

INTRODUCTION

Cell-free "fetal" DNA is released from the placenta. Because the fetal membranes also arise from the trophectoderm layer of the blastocyst, these studies sought to test the hypothesis that the membranes also release cell-free DNA (cfDNA).

METHODS

Fetal membranes were harvested from pregnant CD-1 mice and cultured in 12-well plates containing media alone or with staurosporine and thapsigargin (apoptosis stimulators), Q-VD-OPh (caspase inhibitor), Trolox (vitamin E analog), and lipopolysaccharide and tumor necrosis factor α (TNFα; inflammatory mediators). The cfDNA in the media was extracted, quantified, and normalized for tissue weight. Media was used for a lactate dehydrogenase (LDH) assay. Membrane homogenates were used to assess activated caspase levels and the expression of DNA fragmentation factor B (DFFB) and BAX proteins. 5-Methylcytosine was assessed using a 5-mC DNA enzyme-linked immunosorbent assay. The cfDNA was used to stimulate interleukin 6 (IL6) release by J774A.1 mouse macrophage cells.

RESULTS

Increased cfDNA release at 6 and 21 hours occurred in parallel with increasing LDH levels. The cfDNA concentrations were significantly suppressed by Q-VD-OPh and Trolox and increased by thapsigargin and TNFα. Increased caspase activity was suppressed by Q-VD-OPh and increased by TNFα, thapsigargin, and staurosporine. The expression of BAX and DFFB proteins significantly increased by 21 hours. 5-Methylcytosine levels were significantly lower in fetal membranes and placentas and below detectable in the cfDNA released by the explants. The cfDNA-stimulated IL6 release by macrophage cells was suppressed by chloroquine, a Toll-like receptor 9 (TLR9) inhibitor.

CONCLUSIONS

These studies have confirmed cfDNA release by the mouse fetal membranes; cfDNA was markedly hypomethylated and a robust stimulator of TLR9.

Characteristic Changes in Decidual Gene Expression Signature in Spontaneous Term Parturition

Background

The decidua has been implicated in the “terminal pathway” of human term parturition, which is characterized by the activation of pro-inflammatory pathways in gestational tissues. However, the transcriptomic changes in the decidua leading to terminal pathway activation have not been systematically explored. This study aimed to compare the decidual expression of developmental signaling and inflammation-related genes before and after spontaneous term labor in order to reveal their involvement in this process.

Methods

Chorioamniotic membranes were obtained from normal pregnant women who delivered at term with spontaneous labor (TIL, n = 14) or without labor (TNL, n = 15). Decidual cells were isolated from snap-frozen chorioamniotic membranes with laser microdissection. The expression of 46 genes involved in decidual development, sex steroid and prostaglandin signaling, as well as pro- and anti-inflammatory pathways, was analyzed using high-throughput quantitative real-time polymerase chain reaction (qRT-PCR). Chorioamniotic membrane sections were immunostained and then semi-quantified for five proteins, and immunoassays for three chemokines were performed on maternal plasma samples.

Results

The genes with the highest expression in the decidua at term gestation included insulin-like growth factor-binding protein 1 (IGFBP1), galectin-1 (LGALS1), and progestogen-associated endometrial protein (PAEP); the expression of estrogen receptor 1 (ESR1), homeobox A11 (HOXA11), interleukin 1β (IL1B), IL8, progesterone receptor membrane component 2 (PGRMC2), and prostaglandin E synthase (PTGES) was higher in TIL than in TNL cases; the expression of chemokine C-C motif ligand 2 (CCL2), CCL5, LGALS1, LGALS3, and PAEP was lower in TIL than in TNL cases; immunostaining confirmed qRT-PCR data for IL-8, CCL2, galectin-1, galectin-3, and PAEP; and no correlations between the decidual gene expression and the maternal plasma protein concentrations of CCL2, CCL5, and IL-8 were found.

Conclusions

Our data suggests that with the initiation of parturition, the decidual expression of anti-inflammatory mediators decreases, while the expression of pro-inflammatory mediators and steroid receptors increases. This shift may affect downstream signaling pathways that can lead to parturition.

Differential Secretion of Matrix Metalloproteinase-2 and -9 After Selective Infection With Group B Streptococci in Human Fetal Membranes

OBJECTIVE

This study evaluated the secretions of zymogen and active forms of matrix metalloproteinase (MMP)-9 and MMP-2 and their specific inhibitors, TIMP-1 and TIMP-2 by fetal membranes stimulated with group B Streptoccocci (GBS).

METHODS

We used an in vitro experimental model that allowed us to estimate the individual contribution of the amnion (AM) and the choriodecidua (CHD) to the microbial insult. Membranes were obtained after delivery by elective cesarean delivery from women at 37 to 40 weeks of gestation without evidence of either active labor or intrauterine infection. Membranes were mounted in Transwell devices (Costar, New York, NY), physically separating the upper and lower chambers; 1 x 10(6) CFU of GBS was added to either AM or CHD and the secretions and gelatinolytic activity of MMP-2 and MMP-9 were measured in both compartments by enzyme-linked immunosorbent assay (ELISA) and zymography. TIMPs secretion was measured by ELISA. Both MMPs were immunolocalized in tissue sections.

RESULTS

The simultaneous stimulation at both sides was followed by increases of proMMP-9 (85.0 +/- 18.63 pg/mL) and proMMP-2 (4.10 +/- 1.90 ng/mL) in the CHD (P <.05). When only one side of the membrane was stimulated, the secretion level of proMMP-2 increased 2.3-fold and that of proMMP-9 2.5-fold in the CHD. The active forms of both enzymes did not change with any modality of stimulation. The secretion level of both TIMPs remained without significant changes. CHD and AM were positive for immunoreactive MMP-2 and MMP-9.

CONCLUSION

We propose that infection of fetal membranes with GBS is followed by active secretion of MMP and the CHD is the principal source of these mediators of extracellular matrix degradation.

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.

Cell-Free Fetal DNA, Telomeres, and the Spontaneous Onset of Parturition

Multiple previous reports have provided compelling support for the premise that spontaneous parturition is mediated by activation of inflammation-related signaling pathways leading to increased secretion of cytokines and chemokines, the influx of neutrophils and macrophages into the pregnant uterus, increased production of uterine activation proteins (eg, connexin-43, cyclo-oxygenase-2, oxytocin receptors, etc), activation of matrix metalloproteinases, and the release of uterotonins leading to cervical ripening, membrane rupture, and myometrial contractions. The missing link has been the fetal/placental signal that triggers these proinflammatory events in the absence of microbial invasion and intrauterine infection. This article reviews the biomedical literature regarding the increase in cell-free fetal DNA (cffDNA), which is released during apoptosis in the placenta and fetal membranes at term, the ability of apoptosis modified vertebrate DNA to stimulate toll-like receptor-9 (TLR9) leading to increased release of cytokines and chemokines, and the potential "fail-safe" role for the anti-inflammatory cytokine IL-10. This article also reviews the literature supporting the key role that telomere loss plays in regard to increasing the ability of vertebrate (including placental) DNA to stimulate TLR9, and in regard to signaling the onset of apoptosis in the placenta and fetal membranes, thereby providing a biologic clock that determines the length of gestation and the timing for the onset of parturition. In summary, this literature review provides a strong rationale for future research to test the hypothesis that telomere loss and increased cffDNA levels trigger the proinflammatory events leading to the spontaneous onset of parturition in mammals: the "cffDNA/telomere hypothesis."

Synergy and interactions among biological pathways leading to preterm premature rupture of membranes

Preterm premature rupture of membranes (PPROM) occurs in 1% to 2% of births. Impact of PPROM is greatest in low- and middle-income countries where prematurity-related deaths are most common. Recent investigations identify cytokine and matrix metalloproteinase activation, oxidative stress, and apoptosis as primary pathways to PPROM. These biological processes are initiated by heterogeneous etiologies including infection/inflammation, placental bleeding, uterine overdistention, and genetic polymorphisms. We hypothesize that pathways to PPROM overlap and act synergistically to weaken membranes. We focus our discussion on membrane composition and strength, pathways linking risk factors to membrane weakening, and future research directions to reduce the global burden of PPROM.

Characterization of the myometrial transcriptome in women with an arrest of dilatation during labor

OBJECTIVE

The molecular basis of failure to progress in labor is poorly understood. This study was undertaken to characterize the myometrial transcriptome of patients with an arrest of dilatation (AODIL).

STUDY DESIGN

Human myometrium was prospectively collected from women in the following groups: (1) spontaneous term labor (TL; n=29) and (2) arrest of dilatation (AODIL; n=14). Gene expression was characterized using Illumina® HumanHT-12 microarrays. A moderated Student's t-test and false discovery rate adjustment were used for analysis. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) of selected genes was performed in an independent sample set. Pathway analysis was performed on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database using Pathway Analysis with Down-weighting of Overlapping Genes (PADOG). The MetaCore knowledge base was also searched for pathway analysis.

RESULTS

(1) Forty-two differentially expressed genes were identified in women with an AODIL; (2) gene ontology analysis indicated enrichment of biological processes, which included regulation of angiogenesis, response to hypoxia, inflammatory response, and chemokine-mediated signaling pathway. Enriched molecular functions included transcription repressor activity, heat shock protein (Hsp) 90 binding, and nitric oxide synthase (NOS) activity; (3) MetaCore analysis identified immune response chemokine (C-C motif) ligand 2 (CCL2) signaling, muscle contraction regulation of endothelial nitric oxide synthase (eNOS) activity in endothelial cells, and triiodothyronine and thyroxine signaling as significantly overrepresented (false discovery rate <0.05); (4) qRT-PCR confirmed the overexpression of Nitric oxide synthase 3 (NOS3); hypoxic ischemic factor 1A (HIF1A); Chemokine (C-C motif) ligand 2 (CCL2); angiopoietin-like 4 (ANGPTL4); ADAM metallopeptidase with thrombospondin type 1, motif 9 (ADAMTS9); G protein-coupled receptor 4 (GPR4); metallothionein 1A (MT1A); MT2A; and selectin E (SELE) in an AODIL.

CONCLUSION

The myometrium of women with AODIL has a stereotypic transcriptome profile. This disorder has been associated with a pattern of gene expression involved in muscle contraction, an inflammatory response, and hypoxia. This is the first comprehensive and unbiased examination of the molecular basis of an AODIL.

The chorion layer of fetal membranes is prematurely destroyed in women with preterm premature rupture of the membranes

Preterm premature rupture of the membranes (PPROM) is an important etiology of preterm birth and source of significant neonatal morbidity. We propose that PPROM occurs in the setting of long-standing altered tissue remodeling, which creates a vulnerable environment for the fetal membranes and pregnancy. We tested the hypothesis that PPROM is the result of tissue remodeling in the fetal membranes, specifically the chorion, and this weakening of the chorion compromises the protection provided to the amnion. The purpose of this study was to quantify thickness and apoptosis in the choriodecidua of fetal membranes in patients with PPROM, preterm labor (PTL), preterm no labor (PTNL), and women with term labor (TERM). We conducted a retrospective evaluation of fetal membrane samples from 86 placentas. Immunohistochemistry was performed using a cytokeratin antibody, and mean chorion cellular thickness was compared between each clinical group. To evaluate chorion apoptosis, fetal membranes from patients with PPROM, PTL, and TERM were stained with the M30 antibody, and the degree of cellular apoptosis was determined. Statistical analysis was performed using analysis of variance with corrections for multiple comparisons. The chorion cellular layer was thinner in patients with PPROM compared to patients with PTNL and TERM (62, 140, and 169 µm, respectively, P < .0001), though not significantly different from PTL (95 µm, P > .05). The percentage of apoptotic cells within the chorion among the patients with PPROM was greater compared to PTL and TERM (24.2%, 13.1%, and 8.4%, respectively, P < .001). The chorion cellular layer is thinner and demonstrates increased apoptosis in PPROM compared to patients with PTL, PTNL, and TERM, suggesting differential remodeling between clinical phenotypes.

Optical coherence tomography: A potential tool to predict premature rupture of fetal membranes

A fundamental question addressed in this study was the feasibility of preterm birth prediction based on a noncontact investigation of fetal membranes in situ. Although the phenomena of preterm birth and the premature rupture of the fetal membrane are well known, currently, there are no diagnostic tools for their prediction. The aim of this study was to assess whether optical coherence tomography could be used for clinical investigations of high-risk pregnancies. The thickness of fetal membranes was measured in parallel by optical coherence tomography and histological techniques for the following types of birth: normal births, preterm births without premature ruptures and births at full term with premature rupture of membrane. Our study revealed that the membrane thickness correlates with the birth type. Normal births membranes were statistically significantly thicker than those belonging to the other two groups. Thus, in spite of almost equal duration of gestation of the normal births and the births at full term with premature rupture, the corresponding membrane thicknesses differed. This difference is possibly related to previously reported water accumulation in the membranes. The optical coherence tomography results were encouraging, suggesting that this technology could be used in future to predict and distinguish between different kinds of births.

A molecular signature of an arrest of descent in human parturition

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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

Dynamics of activities of matrix metalloproteinases-9 and -2, and the tissue inhibitors of MMPs in fetal fluid compartments during gestation and at parturition in the mare

During late gestation in the mare, rapid fetal growth is accompanied by considerable placental growth and further invasion of the endometrium by microvilli. This growth requires extensive remodeling of the extracellular matrix (ECM). In early pregnancy, we know that matrix metalloproteinase (MMP)-9 and -2 are involved in the endometrial invasion during endometrial cup formation. The present study investigated whether MMPs are found in fetal fluids later in gestation and during parturition, and if there was a difference in their activities between normal and preterm delivery. Amniotic fluids were collected from pony mares during the latter half of gestation, and amniotic and allantoic fluids from pony and thoroughbred mares at foaling. The fluids were analysed for the activity of MMP-9 and -2, and TIMPs using zymography techniques. There was an increase (P = 0.002) in activity of latent MMP-9 when approaching normal foaling, and a decrease (P < 0.001) during foaling. MMP-2 activity did not change through gestation, or during foaling. When comparing samples from pregnancies resulting in preterm deliveries with samples from foaling mares, the activity of MMP-9 was lower (P < 0.001) and MMP-2 activity was higher (P = 0.004) during foaling than preceding preterm delivery. The activity of MMP-9 was lower (P = 0.002) prior to preterm delivery than before delivery of a live foal at term, whereas no difference (P = 0.07) was demonstrated for latent MMP-2 activity when comparing the same groups. The activity of TIMP-2 was higher (P < 0.001) in the pre-parturient period before normal foaling than preceding preterm delivery. These results suggest that MMPs may have a role as markers for high risk pregnancy in the mare.

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Characterization of the transcriptome of chorioamniotic membranes at the site of rupture in spontaneous labor at term

OBJECTIVE

The purpose of this study was to compare the transcriptome between the site of membrane rupture and the chorioamniotic membranes away from the site of rupture.

STUDY DESIGN

The transcriptome of amnion and chorion (n=20 each) from and distal to the site of rupture from women with spontaneous labor and vaginal delivery at term after spontaneous rupture of membranes was profiled with Illumina HumanHT-12 microarrays. Selected genes were validated with the use of quantitative reverse transcription-polymerase chain reaction.

RESULTS

Six hundred seventy-seven genes were differentially expressed in the chorion between the rupture and nonrupture sites (false discovery rate<0.1; fold change>1.5). Quantitative reverse transcription-polymerase chain reaction confirmed the differential expression in 10 of 14 genes. Enriched biological processes included anatomic structure development, cell adhesion and signal transduction. Extracellular matrix-receptor interaction was the most impacted signaling pathway.

CONCLUSION

The transcriptome of fetal membranes after spontaneous rupture of membranes in term labor is characterized by region- and tissue-specific differential expression of genes that are involved in signature pathways, which include extracellular matrix-receptor interactions.

Biomechanics of the fetal membrane prior to mechanical failure: review and implications

Annually, premature birth is a major public health problem accounting for over 13,000 deaths and 30,000 surviving infants with life-long morbidity. Preterm premature rupture of the membranes is the initiating event leading to preterm birth of 40% of these premature infants. Fetal membrane (FM) rupture is a catastrophic tissue failure, a unique event in normal physiology; other tissue failures (bone breaks, aneurism ruptures) are pathological processes. The mechanisms which cause FM failure and thereby rupture are not understood. A full understanding of FM failure process requires a complete characterization of structural and biomechanical behavior at near/full term under sub-failure (forces well below that which induce rupture) and failure conditions as well as elucidating the biological factors which modulate its failure. The relatively, highly loaded state of the FM in vivo may also facilitate its susceptibility to enzymatic degradation, which was shown to be augmented with increased load in collagenous tissues. Indeed, this last observation may help to provide the link between biomechanical degradation and premature mechanical failure in the FM. This integrated approach will further the understanding of this unique physiological event and thereby provide insight into how to anticipate and when appropriate, intervene to prevent preterm FM rupture.

Chronic stretching of amniotic epithelial cells increases pre-B cell colony-enhancing factor (PBEF/visfatin) expression and protects them from apoptosis

In normal pregnancy, the fetal membranes become increasingly distended towards term and in multifetal gestations they become over-distended. Apoptosis of the amniotic epithelium increases with advancing gestation and may contribute to fetal membrane weakening and rupture. The effects of chronic static stretching for 36h have been investigated using primary amniotic epithelial cells. Pre-B cell colony-enhancing factor (PBEF) is a stretch-responsive cytokine and expression of its gene, intracellular and secreted protein were all significantly increased by 4h and its secretion sustained over 36h, contrasting with the rapid increase and decline in expression of IL-8. Increased expression of SIRT1 and decreased p53 paralleled the changes in PBEF, are known to be responsive to PBEF, and contribute to cell survival. Distension had no effects on proliferation or necrosis but protected the cells from apoptosis, knocking-down PBEF with antisense probes abrogated this protective effect. There was increased immunostaining of PBEF in the compact layer of the amnion in multifetal tissues and significantly fewer apoptotic amniotic epithelial cells. These results show that chronic stretching of the amniotic epithelial cells increases PBEF expression, which protects them from apoptosis.

The biomechanics of amnion rupture: an X-ray diffraction study

Pre-term birth is the leading cause of perinatal and neonatal mortality, 40% of which are attributed to the pre-term premature rupture of amnion. Rupture of amnion is thought to be associated with a corresponding decrease in the extracellular collagen content and/or increase in collagenase activity. However, there is very little information concerning the detailed organisation of fibrillar collagen in amnion and how this might influence rupture. Here we identify a loss of lattice like arrangement in collagen organisation from areas near to the rupture site, and present a 9% increase in fibril spacing and a 50% decrease in fibrillar organisation using quantitative measurements gained by transmission electron microscopy and the novel application of synchrotron X-ray diffraction. These data provide an accurate insight into the biomechanical process of amnion rupture and highlight X-ray diffraction as a new and powerful tool in our understanding of this process.

Identification of a calcium-dependent matrix metalloproteinase complex in rat chorioallantoid membranes during labour

The induction of the expression of matrix metalloproteinases (MMPs) and their extracellular activation are key processes in connective tissue degradation in the chorioallantoid membrane during rat labour. However, the regulatory mechanisms remain largely unknown. Here, we report the identification of a calcium-dependent high molecular weight complex composed of MMP-9, MMP-3, MMP-2, tissue inhibitor of metalloproteinase 1 (TIMP-1) and TIMP-2, identified by zymography and western blotting. Molecular sieve chromatography confirmed the presence of a complex of MMPs and TIMPs with an exclusion volume >670 kDa. Differential scanning calorimetry of the complex confirmed the existence of a macromolecular complex that unfolds with a broad transition; it is denatured over a wide range of temperatures and has a T(m) of 72 degrees C in the presence of Ca(2+). When denatured in the absence of Ca(2+), there were at least eight transitions with T(m)s that corresponded to pro-MMP-9, MMP-9, pro-MMP-3, MMP-3, pro-MMP-2, MMP-2, TIMP-1 and TIMP-2. Co-localization of the same molecular components was demonstrated by confocal microscopy using cell-depleted chorioallantoid membranes. The assembly and disassembly of the complex can be reproduced at physiological concentrations of Ca(2+). This complex provides a potential mechanism for the enzymatic regulation of MMPs, which may participate in connective tissue degradation leading to the rupture of the fetal membranes during labour.

Fetal membranes from term vaginal deliveries have a zone of weakness exhibiting characteristics of apoptosis and remodeling

BACKGROUND

Recently we identified a weak zone in term, pre-labor (repeat Cesarean section) human fetal membranes (FM) overlying the cervix with biochemical characteristics suggestive of apoptosis and collagen remodeling. We suggested that this weak zone is the FM rupture initiation site. Vaginally delivered patients have a weak zone in their FM overlying the cervix; a comparable weak zone lies adjacent to the tear line in FM after spontaneous rupture (SROM).

METHODS

FM from vaginally delivered patients with artificial rupture (AROM) and SROM were collected. FM of AROM patients were marked per vagina to identify the FM zone overlying the cervix. Postpartum FM were cut, strength tested, and piece strengths were remapped to their former location on a three-dimensional model. A 10-cm diameter zone centered on the marked area (AROM), or defined weak zone (SROM) was compared with the remaining FM.

RESULTS

AROM FM exhibit a para-cervical weak zone. SROM FM exhibit a comparable zone on the tear line. The mean rupture strength within weak zones was 60% of the remaining membranes (P <.001). AROM and SROM FM weak zones both exhibit increased matrix metalloproteinase 9, increased poly (ADP-ribose) polymerase I cleavage, decreased tissue inhibitor of metalloproteinase 3 protein, and histology consistent with remodeling and apoptosis.

CONCLUSION

Vaginally delivered AROM FM contain a weak zone overlying the cervix. Vaginally delivered SROM FM contain a weak zone adjacent to the tear line that exhibits biochemical and mechanical characteristics suggestive of collagen remodeling and apoptosis comparable to those of the AR FM weak zone.

Separation of amnion from choriodecidua is an integral event to the rupture of normal term fetal membranes and constitutes a significant component of the work required

OBJECTIVE

This study was undertaken to determine the sequence of events that occur during fetal membrane (FM) rupture and to compare the biophysical properties of intact FM with its separated individual components (amnion and choriodecidua).

STUDY DESIGN

FM physical properties were determined with computerized, specially adapted, industrial, strength testing equipment and the rupture sequence (in vitro) video documented. Separated individual FM component properties were compared with those of reapproximated components, and of intact FMs.

RESULTS

The sequence of FM rupture was (1) FM components stretch together under load; (2) amnion separates from choriodecidua; (3) choriodecidua ruptures; (4) amnion distends further, nonelastically; and (5) amnion ruptures. In all FMs tested, amnion was stronger, stiffer, and more ductile than choriodecidua. The sum of work required to rupture separated FM components (amnion + choriodecidua), or reapproximated components, was significantly less than that of intact FMs.

CONCLUSION

Separation of amnion from choriodecidua occurs as part of normal term FM rupture. FMs become significantly weaker as a result of this separation.

Term Human Fetal Membranes Have a Weak Zone Overlying the Lower Uterine Pole and Cervix Before Onset of Labor1

The etiology of fetal membrane (FM) rupture is unknown. A hypothesis that the FM weakens by a process of collagen remodeling and apoptosis to facilitate rupture has been proposed. Human FMs reportedly exhibit a zone of altered histology, postulated to be the FM rupture site, but concomitant FM weakness has not been demonstrated. We hypothesized that a discrete zone of FM with marked weakness, histological change, and evidence of remodeling and apoptosis, develops in late gestation in the FM overlying the cervix. FM tissue from women undergoing prelabor cesarean delivery were perioperatively marked to identify the FM overlying the cervix, cut with a procedure that facilitates remapping the rupture strength of FM pieces to their former location and orientation on a three-dimensional model, and tested for strength. A 10-cm FM zone centered at the cervical mark was compared with the remaining FM. Mean rupture strength within the cervical zone was 55% of the remaining FM. The cervical zone also exhibited increased MMP-9 protein, decreased tissue inhibitor of metalloproteinases-3 (TIMP-3) protein, and increased PARP cleavage coincident with the previously reported zone of altered histology. A discrete zone of weakness is present in term prelabor FMs overlying the cervix and has biochemical characteristics consistent with tissue remodeling and apoptosis.

Expression analysis of the entire MMP and TIMP gene families during mouse tissue development

Matrix metalloproteinases (MMPs) and adamalysins (ADAMs) cleave many extracellular proteins, including matrix, growth factors, and receptors. We profiled the RNA levels of every MMP, several ADAMs, and inhibitors of metalloproteinases (TIMPs and RECK) in numerous mouse tissues during development and in the uterus during pregnancy. Observations include: most secreted MMPs are expressed at low to undetectable levels in tissues, whereas membrane-bound MMPs, ADAMs and inhibitors are abundant; almost every proteinase and inhibitor is present in the uterus or placenta at some time during gestation; the mouse collagenases mColA and mColB are found exclusively in the uterus and testis; and each tissue has its unique signature of proteinase and inhibitor expression.

Physiological apoptotic agents have different effects upon human amnion epithelial and mesenchymal cells

Foetal membrane rupture is thought to follow from gene-controlled tissue remodelling and apoptosis. We reported previously that staurosporine, cycloheximide, actinomycin D, as well as more physiological apoptotic agents (lactosylceramide, 15d-PGJ(2)) increase prostaglandin release in parallel with induction of apoptosis in WISH and amnion epithelial cells. Also, inhibition of prostaglandin release by cyclooxygenase inhibitors or PKA activators is accompanied by a parallel decrease in apoptosis. We hypothesize that amnion prostaglandin metabolism is linked with apoptosis in amnion epithelial cells and thus to membrane rupture. Amnion mesenchymal cells are also critical for membrane integrity. Their susceptibility to apoptotic agents is unknown and is the subject of this report. In amnion epithelial cells, lactosylceramide (125 microM) induced 6.5-fold, 20-fold increases in PGE(2) and NMP production (apoptosis), respectively. Conversely, in mesenchymal cells, lactosylceramide doses up to 200 microM had no effect on PGE(2) or NMP release. In both cell types, incubation with 15d-PGJ(2) (5-100 microM) demonstrated dose and time dependent increases in PGE(2) and NMP. PKA activators inhibited 15d-PGJ(2) induced PGE(2) release and apoptotis in epithelial cells, but not in mesenchymal cells, however. Major amnion cell types have different sensitivities to physiological apoptotic agents. Prostaglandin release occurs coincident with apoptosis in both amnion epithelial and mesenchymal cells.

Apoptosis in the normal human amnion at term, independent of Bcl-2 regulation and onset of labour

This study was designed to detect apoptosis in the human amnion and to elucidate the signalling pathway involved in its regulation. Samples of human amnion were obtained from 34 women (weeks 11-42 of gestation) and studied using the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL) method with light microscopy (LM) and transmission electron microscopy (TEM). Apoptotic regulators in the samples were studied by immunohistochemistry and caspase activity assay. The TUNEL method with LM demonstrated that the percentage of TUNEL-positive cells in the amniotic epithelium was the highest in weeks 40-41 of gestation (P < 0.05) independent of the onset of labour, and the cells were often detached from the epithelium into the amniotic cavity at term. The TUNEL method with TEM clearly showed the characteristic features of apoptosis such as the nuclear condensed chromatin with abundant free 3'-OH DNA ends, cell shrinkage and a decrease in the number of desmosomes, except for the presence of apoptotic bodies. Fas and Fas ligand (FasL) were constantly expressed on apical membranes of amniotic epithelial cells from weeks 16-27 through to 40-41 of gestation, while no Bcl-2 expression was observed throughout the gestational periods. Activities of caspase-3 and caspase-8, but not of caspase-9, were higher in weeks 40-41 than those from weeks 16-27 of gestation (P < 0.01). We conclude that apoptosis in term amniotic epithelium is independent of Bcl-2 regulation and onset of labour, and may play an important role in the fragility and rupture of human fetal membranes at term.

Matrix metalloproteinases-9 in preterm and term human parturition

OBJECTIVE

Spontaneous rupture of the fetal membranes occurs after the commencement of labor in 90% of cases. Recent evidence indicates that the process of parturition requires not only an increase in myometrial contractility and cervical ripening, but also degradation of extracellular matrix in fetal membranes (i.e., leakage of fibronectin into cervico-vaginal secretions). This study was undertaken to determine if parturition is associated with in vivo evidence of increased bioavailability of matrix metalloproteinases-9 (MMP-9) and its inhibitor, tissue inhibitor of metalloproteinases-1(TIMP-1).

METHODS

A cross-sectional study was conducted with women in the following categories: 1) midtrimester (n = 25); 2) preterm labor and intact membranes in the absence of intraamniotic infection (n = 78); 3) term not in labor (n = 25); and 4) term with intact membranes in labor (n = 25). MMP-9, and TIMP-1 were measured using sensitive and specific immunoassays.

RESULTS

1) Spontaneous labor at term was associated with a significant increase in MMP-9 but not in TIMP-1.2) Women with preterm labor who delivered prematurely had significantly higher concentrations of MMP-9 but not TIMP-1 in amniotic fluid than those with preterm labor who delivered at term. 3) The concentrations of TIMP-1 decreased with advancing gestational age. In contrast, MMP-9 concentrations did not change with advancing gestational age.

CONCLUSIONS

Spontaneous human parturition is associated with specific changes in the enzymatic machinery responsible for extracellular matrix degradation.

Rat amnion type IV collagen composition and metabolism: implications for membrane breakdown

We report here that rat amnion type IV collagens are composed primarily of alpha1(IV) and alpha2(IV) chains. Amnion basement membrane collagens were more sensitive to degradation by collagenases than were adult rat kidney basement membrane collagens, which are enriched in alpha3(IV), alpha4(IV), and alpha6(IV) chains. Amnion type IV collagen content per unit of protein was markedly reduced by Day 21 of pregnancy, the day of delivery. Increased amnion levels of matrix metalloproteinase (MMP)-2 and MMP-9, gelatinases that degrade type IV collagen, were found by Day 21, suggesting that collagen breakdown was responsible, in part, for the decline in amnion type IV collagen. Infection of organ cultures of Day 18 rat amnions with a recombinant adenovirus expressing MMP-9 (AdMMP-9) caused release of collagen fragments detected as hydroxyproline in the culture fluid, amnion cell detachment, and apoptosis. The AdMMP-9-induced apoptosis was prevented by the MMP inhibitor batimastat. These findings suggest that MMPs are implicated in anoikis and apoptotic death of amnion cells, and may be part of a complex program of fetal membrane remodeling that occurs before delivery.

Induction of matrix metalloproteinases and collagenolysis in chick embryonic membranes before hatching

The membranes surrounding the chick embryo undergo striking morphological changes before hatching, which include structural degradation of the allantoic membrane. The fibrillar collagen content of the membranes declined by embryonic day (ED) 20 (the day of hatching). By ED 19, a 55-kDa matrix metalloproteinase (MMP) activity appeared in the extraembryonic fluid, and by ED 20 there was substantial 55-kDa MMP activity in embryonic membrane extracts. Reverse transcription-polymerase chain reaction was employed to clone a partial cDNA representing the chicken homologue of MMP-13, a 55- to 57-kDa enzyme. MMP-13 mRNA dramatically increased in abundance in embryonic membranes by ED 19, reaching a peak on ED 20. Introduction of the MMP inhibitor batimastat into the extraembryonic fluid prevented the structural changes in the embryonic membranes before hatching. We conclude that, like mammalian fetal membranes, chick embryonic membranes undergo terminal remodeling before hatching, in part as a result of increased MMP activity. The chicken egg system represents a novel in vivo model for exploring biochemical events leading to embryonic membrane remodeling prior to birth and to test inhibitors of MMPs for their ability to prevent collagenolysis and fetal membrane rupture.

A role for matrix metalloproteinase-9 in spontaneous rupture of the fetal membranes

OBJECTIVES

Preterm premature rupture of fetal membranes is responsible for 30% to 40% of preterm deliveries. Fetal membranes are composed primarily of collagen. Matrix metalloproteinases are enzymes capable of degrading extracellular matrix macromolecules, including collagens. Expression of matrix metalloproteinase-9 (gelatinase B, 92 kd) and its tissue inhibitor (tissue inhibitor of metalloproteinase-1) has been localized in amnion and chorion. The objective of this study was to determine whether rupture of fetal membranes and intrauterine infection are associated with changes in the expression of matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-1.

STUDY DESIGN

Two hundred one women in the following categories had amniotic fluid retrieved: (1) preterm labor and intact membranes in the presence (n = 42) or absence (n = 21) of microbial invasion of the amniotic cavity, (2) preterm premature rupture of the membranes with (n = 29) or without (n = 23) microbial invasion of the amniotic cavity, and (3) term gestation with intact membranes (n = 50) or with premature rupture of the membranes (n = 40). Women in groups 1 and 2 were matched for gestational age at amniocentesis. Microbial invasion of the amniotic cavity was defined by a positive amniotic fluid culture for micro-organisms. Matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-1 were measured with use of sensitive and specific immunoassays that were validated for amniotic fluid.

RESULTS

Spontaneous rupture of membranes at term is associated with a significant increase in the amniotic fluid concentrations of matrix metalloproteinase-9 (premature rupture of membranes, no labor: median 3.9 ng/mL, range 2. 7 to 11.1 ng/mL vs no premature rupture of membranes, no labor: median <0.4 ng/mL, range <0.4 to 22.4 ng/mL; P <.001). Patients with preterm premature rupture of the membranes had higher median matrix metalloproteinase-9 concentrations than those with preterm labor and intact membranes who were delivered at term (7.6 ng/mL, range <0.4 to 230.81 ng/mL vs <0.4 ng/mL, range <0.4 to 1650 ng/mL; P =.06). Women with microbial invasion of the amniotic cavity had higher median matrix metalloproteinase-9 concentrations than did those without microbial invasion regardless of membrane status (preterm labor: 54.5 ng/mL, range <0.4 to 3910 ng/mL vs <0.4 ng/mL, range <0. 4 to 1650 ng/mL; P <.01; preterm premature rupture of membranes: 179. 8 ng/mL, range <0.4 to 611 ng/mL vs 7.6 ng/mL, range <0.4 to 230.81; P <.001).

CONCLUSION

Our data support a role for matrix metalloproteinase-9 in the mechanisms responsible for membrane rupture in term and preterm gestations.

Keratinocyte growth factor expression in the mesenchymal cells of human amnion

Amnion epithelial and mesenchymal cells were separated by differential protease treatment, and the separated cells were maintained in monolayer culture. Keratinocyte growth factor (KGF) messenger RNA (mRNA) was readily detected by Northern analysis of amnion mesenchymal cell total RNA (10 micrograms) but not in amnion epithelial cells. Treatment of the amnion mesenchymal cells in serum-free medium with tetradecanoyl phorbol acetate (1 nM) caused an increase in the level of KGF mRNA. Forskolin treatment also caused an increase in KGF mRNA but not to the levels attained with tetradecanoyl phorbol acetate treatment. Dexamethasone (1 nM) treatment of these cells effected a reduction in the level of KGF mRNA. Prolonged maintenance of mesenchymal cells in serum-free medium also was associated with an increase in the level of KGF mRNA. Treatment with a variety of other agents, viz., interleukin (IL)-1, IL-6 plus or minus IL-6 soluble receptor, IL-11, oncostatin M, epidermal growth factor (EGF), and transforming growth factor-beta and not modify the level of KGF mRNA. Treatment of amnion epithelial cells with KGF caused an increase in the rate of [3H]thymidine incorporation, but the rate of cell replication induced by KGF was less than that induced by treatment with EGF. Transforming growth factor-beta treatment inhibited basal and EGF- and KGF-stimulated amnion epithelial cell replication. The findings of this study are indicative the KGF is expressed in human amnion mesenchymal cells, and that KGF may act on the epithelial cells of this tissue.

Tissue inhibitor of metalloproteinase-1 and tissue inhibitor of metalloproteinase-2 expression in human amnion mesenchymal and epithelial cells

OBJECTIVE

This study was conducted to define the cellular site of expression of tissue inhibitor of metalloproteinase-1 and tissue inhibitor of metalloproteinase-2 in human amnion by an evaluation of the levels of messenger ribonucleic acids in separated amnion epithelial and mesenchymal cells and to ascertain whether amnion epithelial and mesenchymal cells maintained in culture continue to express tissue inhibitor of metalloproteinase messenger ribonucleic acids.

STUDY DESIGN

Human placentas and fetal membranes were obtained immediately after delivery. Amnion tissue was separated from chorion laeve and either frozen immediately (-80 degrees C) or processed by differential enzymatic treatment to separate the epithelial and mesenchymal cells, which were frozen (-80 degrees C) or else plated and maintained in monolayer culture. The levels of tissue inhibitor of metalloproteinase types 1 and 2 messenger ribonucleic acid were evaluated by Northern analyses of total ribonucleic acid extracted from amnion tissue, freshly separated epithelial and mesenchymal cells, and epithelial and mesenchymal cells in monolayer culture.

RESULTS

Tissue inhibitor of metalloproteinase types 1 and 2 messenger ribonucleic acids were detected by Northern analysis in freshly isolated amnion tissues from midtrimester and term pregnancies. The major species of tissue inhibitor of metalloproteinase-1 messenger ribonucleic acid was 0.9 kb in length; a minor species of approximately 3.5 kb also was present. Tissue inhibitor of metalloproteinase-2 messenger ribonucleic acids of 3.5 and 1.0 kb and of similar intensity were also detected. The levels of type 1 messenger ribonucleic acid were not different in amnion tissues obtained at term or during the midtrimester of pregnancy. The levels of tissue inhibitor of metalloproteinase type 2 messenger ribonucleic acids in amnion tissue most commonly were greater at term than in tissues obtained during the midtrimester. The level of type 1 messenger ribonucleic acid in mesenchymal cells was appreciably greater than that in epithelial cells, and this difference was maintained during culture of these cells. The level of type 2 messenger ribonucleic acid was similar in both cell types and was maintained during culture. The levels of type 1 or 2 messenger ribonucleic acids were not affected by treatment of amnion epithelial or mesenchymal cells in culture with a variety of test agents, including steroid hormones, cytokines, and growth factors.

CONCLUSION

The amnion mesenchymal cells are the primary source of tissue inhibitor of metalloproteinase-1 in human amnion, whereas both cell types have the potential to produce tissue inhibitor of metalloproteinase-2.

A program of cell death and extracellular matrix degradation is activated in the amnion before the onset of labor

Fetal membranes usually rupture during the process of labor. Premature fetal membrane rupture occurs not infrequently and is associated with significant fetal and maternal morbidity. The mechanisms of normal and pathologic fetal membrane rupture are not well understood. We have examined structural and biochemical changes in the rat amnion as labor approaches in order to characterize this process in normal pregnancy. Here we report that before the onset of active labor the amnion epithelial cells undergo apoptotic cell death which encompasses degradation of 28S ribosomal subunit RNA and associated P proteins and fragmentation of nuclear DNA. Concurrent with these cellular changes, the amnion type I collagen matrix is degraded with the accumulation of three-quarter length type I collagen fragments in extraembryonic fluid, characteristic of the cleavage of fibrillar collagen by interstitial collagenase. Western blot and immunohistochemical analyses confirmed that interstitial collagenase protein appears in association with the loss of amnion type I collagen. We conclude that amnion epithelial cells undergo a process of programmed cell death associated with orchestrated extracellular matrix degradation which begins before the onset of active labor. Thus, fetal membrane rupture is likely to be the result of biochemical changes as well as physical forces.

The pathobiology of premature rupture of membranes

Premature rupture of membranes arises from what are likely multifaceted and multistep pathogenic pathways. Pathophysiological processes may involve both endogenous and exogenous fetal and maternal factors. This article reviews and analyzes information regarding, first, the form and function of fetal membranes; second, how membranes physically fail (rupture) at term and preterm gestations; and third, evaluates if we can reduce risks of rupture using physiological understanding and evidence-based clinical studies.