Roles and regulation of the matrix metalloproteinase system in parturition

Upregulated TIMP1 facilitates and coordinates myometrial contraction by decreasing collagens and cell adhesive capacity during human labor

Myometrial contraction is one of the key events involved in parturition. Increasing evidence suggests the importance of the extracellular matrix (ECM) in this process, in addition to the functional role of myometrial smooth muscle cells, and our previous study identified an upregulated tissue inhibitor of metalloproteinase 1 (TIMP1) in human laboring myometrium compared to nonlabor samples. This study aimed to further explore the potential role of TIMP1 in myometrial contraction. First, we confirmed increased myometrial TIMP1 levels in labor and during labor with cervical dilation using transcriptomic and proteomic analyses, followed by real-time PCR, western blotting, and immunohistochemistry. Then, a cell contraction assay was performed to verify the decreased contractility after TIMP1 knockdown in vitro. To further understand the underlying mechanism, we used RNA-sequencing analysis to reveal the upregulated genes after TIMP1 knockdown; these genes were enriched in collagen fibril organization, cell adhesion, and ECM organization. Subsequently, a human matrix metalloproteinase (MMP) array and collagen staining were performed to determine the TIMPs, MMPs and collagens in laboring and nonlabor myometrium. A real-time cell adhesion assay was used to detect cell adhesive capacity. The results showed upregulated MMP8 and MMP9, downregulated collagens, and attenuated cell adhesive capacity in laboring myometrium, while lower MMP levels and higher collagen levels and cell adhesive capacity were observed in nonlabor. Moreover, TIMP1 knockdown led to restoration of cell adhesive capacity. Together, these results indicate that upregulated TIMP1 during labor facilitates and coordinates myometrial contraction by decreasing collagen and cell adhesive capacity, which may provide effective strategies for the regulation of myometrial contraction.

Adverse birth outcomes are associated with circulating matrix metalloproteinases among pregnant women in Puerto Rico

Matrix metalloproteinases (MMPs) are major extracellular matrix (ECM) remodeling proteinases and regulate uterine remodeling, which is a critical process for healthy pregnancies. The goal of this study was to investigate associations between maternal blood MMPs during pregnancy and birth outcomes among 898 pregnant women in the Puerto Rico PROTECT birth cohort. MMPs (MMP1, MMP2, and MMP9) were quantified using a customized Luminex assay in blood samples collected at two gestational study visits (around 18 and 26 weeks gestation). Linear and logistic regression models were used to regress continuous and binary birth outcomes, respectively, on MMPs at each study visit separately. Sensitivity analyses were conducted to test for effect modification by fetal sex on associations between MMPs and birth outcomes. We observed significant associations between MMP2 at visit 1 and newborn length that were in the opposite direction from the associations between MMP9 at visit 3 and newborn length. MMPs were associated with increased odds of preeclampsia and gestational diabetes mellitus, though case numbers were low. We also observed significant inverse associations with gestational age for MMP9 and MMP2 at visit 1 and visit 3, respectively, and these associations were observed only in mothers carrying male fetuses. Further, MMP2 was associated with heavier female fetuses, whereas MMP9 was associated with lighter female fetuses. We observed significant associations between birth outcomes and MMPs, and the majority of these associations differed by fetal sex. This study highlighted significant MMPs-birth outcomes associations that may provide a basis to explore the impact of MMPs on endometrium health and physiology.

Stress of Prematurity in the Experience of the COVID-19 Pandemic-Current State of Knowledge

Stress is a process that triggers various physiological, hormonal and psychological mechanisms in response to a threat, which significantly affects the health of an individual. The COVID-19 pandemic introduced a lot of social changes that required constant adaptation to unfavorable conditions. The aim of the study was to assess the impact of stress related to this pandemic on pregnant women, mothers of premature infants and their families, and on obstetric complications, particularly preterm birth. A comprehensive literature review was performed using electronic databases such as Pubmed, Science Direct and Google Scholar. Keywords such as: "prematurity"; "pregnancy"; "stress"; "COVID-19" and various combinations of the above were used. Maternal stress and anxiety increase the levels of corticotropin-releasing hormone (CRH) in the placenta, which in turn affects the incidence of preterm birth and many other related maternal and neonatal complications. In addition, it was found that SARS-CoV-2 infection may increase the risk of this phenomenon. The COVID-19 pandemic has adversely affected preterm birth rates and the mental health of mothers of preterm infants, exacerbating their negative experience of having a premature baby. More research is needed to demonstrate the long-term effects of COVID-19 stress on prematurity.

Preterm Birth Therapies to Target Inflammation

Preterm birth (PTB; defined as delivery before 37 weeks of pregnancy) is the leading cause of morbidity and mortality in infants and children aged <5 years, conferring potentially devastating short‐ and long‐term complications. Despite extensive research in the field, there is currently a paucity of medications available for PTB prevention and treatment. Over the past few decades, inflammation in gestational tissues has emerged at the forefront of PTB pathophysiology. Even in the absence of infection, inflammation alone can prematurely activate the main components of parturition resulting in uterine contractions, cervical ripening and dilatation, membrane rupture, and subsequent PTB. Mechanistic studies have identified critical elements of the complex inflammatory molecular pathways involved in PTB. Here, we discuss therapeutic options that target such key mediators with an aim to prevent, postpone, or treat PTB. We provide an overview of more traditional therapies that are currently used or being tested in humans, and we highlight recent advances in preclinical studies introducing novel approaches with therapeutic potential. We conclude that urgent collaborative action is required to address the unmet need of developing effective strategies to tackle the challenge of PTB and its complications.

Matrix metalloproteinase-induced cervical extracellular matrix remodelling in pregnancy and cervical cancer

Abstract

The phenomenal extracellular matrix (ECM) remodelling of the cervix that precedes the myometrial contraction of labour at term or preterm appears to share some common mechanisms with the occurrence, growth, invasion and metastasis of cervical carcinoma. Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that are pivotal to the complex extracellular tissue modulation that includes degradation, remodelling and exchange of ECM components, which contribute to homeostasis under normal physiological conditions such as cervical remodelling during pregnancy and puerperium. However, in cancer such as that of the uterine cervix, this extensive network of extracellular tissue modulation is altered leading to disrupted cell-cell and cell-basement membrane adhesion, abnormal tissue growth, neovascularization and metastasis that disrupt homeostasis. Cervical ECM remodelling during pregnancy and puerperium could be a physiological albeit benign neoplasm. In this review, we examined the pathophysiologic differences and similarities in the role of MMPs in cervical remodelling and cervical carcinoma.

Lay summary

During pregnancy and childbirth, the cervix, which is the barrel-shaped lower portion of the womb that connects to the vagina, gradually softens, shortens and opens to allow birth of the baby. This process requires structural and biochemical changes in the cervix that are stimulated by enzymes known as matrix metalloproteinases. Interestingly, these enzymes also affect the structural and biochemical framework of the cervix during cervical cancer, although cervical cancers usually occur after infection by human papillomavirus. This review is intended to identify and explain the similarities and differences between the structural and chemical changes in the cervix during pregnancy and childbirth and the changes seen in cervical cancer.

Low CLOCK and CRY2 in 2nd trimester human maternal blood and risk of preterm birth: A nested case-control study

Previous studies have observed an association between maternal circadian rhythm disruption and preterm birth (PTB). However, the underlying molecular mechanisms and the potential of circadian clock genes to serve as predictors of PTB remain unexplored. We examined the association of 10 core circadian transcripts in maternal blood with spontaneous PTB (sPTB) vs term births using a nested case-control study design. We used a public gene expression dataset (GSE59491), which was nested within the All Our Babies (AOB) study cohort in Canada. Maternal blood was sampled in trimesters 2-3 from women with sPTB (n = 51) and term births (n = 106), matched for 5 demographic variables. In 2nd trimester maternal blood, only CLOCK and CRY2 transcripts were significantly lower in sPTB vs term (p = 0.02 ~ 0.03, FDR < 0.20). A change of PER3 mRNA from trimesters 2 to 3 was significantly associated with sPTB (decline in sPTB, p = 0.02, FDR < 0.20). When CLOCK and CRY2 were modeled together in 2nd trimester blood, the odds ratio of being in the low level of both circadian gene transcripts was greater in sPTB vs term (OR = 4.86, 95%CI = (1.75,13.51), p < 0.01). Using GSVA and Pearson correlation, we identified 98 common pathways that were negatively or positively correlated with CLOCK and CRY2 expression (all p < 0.05, FDR < 0.10). The top three identified pathways were amyotrophic lateral sclerosis, degradation of extracellular matrix, and inwardly rectifying potassium channels. These three processes have previously been shown to be involved in neuron death, parturition, and uterine excitability during pregnancy, respectively.

Changes in gene expression of cervical collagens, metalloproteinases, and tissue inhibitors of metalloproteinases after partial cervical excision-induced preterm labor in mice

We investigated changes in gene expression of cervical collagens, matrix metalloproteinases (MMPs), and tissue inhibitors of metalloproteinases (TIMPs) during pre-gestational uterine cervical excision and/or inflammation-induced preterm labor in mice. Forty sexually mature female mice were uniformly divided into four groups: sham, cervical excision, lipopolysaccharide (LPS) injection, and cervical excision plus LPS injection. Partial cervical tissue excision was performed at five weeks of age before mating. LPS was injected into the lower right uterine horn near the cervix on gestational day 16. Mice were sacrificed immediately postpartum. Uterine cervices were collected and subjected to quantitative real-time PCR. Col4α1 and Col5α1 expression increased significantly in the cervical excision plus LPS injection group compared to the sham group (p < 0.01 and p = 0.024, respectively). MMP-14 expression levels increased in the cervical excision plus LPS injection group compared to the sham group (p < 0.01). TIMP-1 expression was not significantly decreased in this group. Increased expression levels of Col4α1, Col5α1, and MMP-14 were associated with cervical excision plus inflammation-induced preterm labor. Thus, pre-gestational cervical remodeling through specific collagen metabolism and MMP activation may involve the pathogenesis of spontaneous preterm labor.

Transcriptome Profiling of the Retained Fetal Membranes-An Insight in the Possible Pathogenesis of the Disease

Simple Summary

Retained fetal membranes (RFM) in mares is a disease of a multifactorial etiology with not fully understood pathogenesis. Profound analysis of genes expressed in the placenta may reveal pathways and processes which might be comprised in mares with this disease and hence help to explain the pathogenesis of RFM. This work employed RNA sequencing to identify and compare genes differentially expressed (DEGs) in the placenta of mares that retained fetal membranes and those that released them physiologically. Results showed that within DEGs genes important for apoptosis, inflammatory-related processes, and metabolism of extracellular matrix were identified.

Abstract

Retained fetal membranes (RFM) is one of the most common post-partum diseases of a complex etiology. Moreover, its pathogenesis is still not elucidated. Detailed transcriptomic analysis of physiological and retained placenta may bring profound insight in the pathogenesis of the disease. The aim of the study was to compare the transcriptome of the retained and physiologically released placenta as well as biological pathways and processes in order to determine the possible pathogenesis of the disease. Samples of the endometrium and the allantochorion were taken within 2 h after parturition from control mares (n = 3) and mares with RFM (n = 3). RNA sequencing was performed with the use of all samples and mRNA expression of chosen genes was validated with Real Time PCR. Analysis of RNA-seq identified 487 differentially expressed genes in the allantochorion and 261 in the endometrium of control and RFM mares (p < 0.0001). Within genes that may be important in the release of fetal membranes and were differentially expressed, our report pinpointed BGN, TIMP1, DRB, CD3E, C3, FCN3, CASP3, BCL2L1. Gene ontology analysis showed possible processes which were altered in RFM that are apoptosis, inflammatory-related processes, and extracellular matrix metabolism and might be involved in the pathogenesis of RFM. This is the first report on the transcriptome of RFM and physiologically released placenta in mares.

Evidence for anti-inflammatory effects of firocoxib administered to mares with experimentally induced placentitis

PROBLEM

Minimal evidence exists supporting therapeutic selections for equine placentitis. The goal of this study was to characterize the anti-inflammatory effects of firocoxib when administered to mares with placentitis.

METHODS

Mares (gestation D270-300) were assigned to: INFECT (n = 6; placentitis, no treatment), FIRO (n = 6; placentitis, firocoxib, 0.1 mg/kg, PO, daily), and NORM (n = 6; no infection/treatment). Allantoic fluid (8 hours, 24 hours, birth) and amniotic fluid (birth) were collected from mares after infection. Concentrations of IL-1β, IL-6, TNF-α, IL-10, PGF_2α , and PGE₂ in fluids were measured by ELISA. mRNA expression of IL-1β, IL-6, TNF-α, IL-8, IL-10, matrix metalloproteinases (MMPs) -1, 3, and 9 in fetal membranes/fetuses was quantified using real-time PCR.

RESULTS

Allantoic TNF-α concentrations were lowest in FIRO at 8 hours and 24 hours post-infection; IL-6 concentrations were lower in FIRO than NORM at 8 hours, lower in FIRO than INFECT at 24 hours post-inoculation, and lower in NORM than FIRO or INFECT at birth. Marginal mean allantoic IL-β and IL-10 concentrations were lower in FIRO and NORM than INFECT. Amniotic fluid cytokines were lowest in NORM with all measurements in that group being below the limit of detection. Allantoic PGF_2α concentrations were lower in FIRO and INFECT than NORM at 8 hours post-inoculation, and lower in FIRO than INFECT or NORM at 24 hours post-inoculation. Allantoic PGE₂ concentrations were lower in FIRO than INFECT. Amniotic PGF_2α and PGE₂ concentrations were lower in NORM than INFECT. In fetal membranes, group differences with respect to IL-1β, IL-6, IL-8, and MMP1 were dependent on tissue type.

CONCLUSIONS

Data suggest a suppressive effect of firocoxib administration on cytokine and prostaglandin production in mares with placentitis.

Activated Neutrophils Propagate Fetal Membrane Inflammation and Weakening through ERK and Neutrophil Extracellular Trap-Induced TLR-9 Signaling

Preterm birth is associated with significant neonatal mortality and morbidity worldwide. Chorioamnionitis, inflammation of the fetal membranes (FMs), is a major risk factor and is characterized by neutrophil infiltration. However, the role of neutrophils at the FMs remains unclear. We recently reported that FMs exposed to bacterial LPS recruited more neutrophils compared with resting FMs and activated them to degranulate and release reactive oxygen species, chemokines/cytokines, and neutrophil extracellular traps. We posit that under resting conditions, neutrophils play a protective surveillance role, whereas during infection/inflammation, they induce FM tissue injury. To test this, human FM explants were exposed to neutrophil conditioned media (CM). We demonstrate that CM from neutrophils exposed to resting FM-CM did not affect FM viability or function. Conversely, CM from neutrophils activated by LPS-stimulated FM-CM significantly increased FM secretion of inflammatory IL-6, IL-8, GRO-α, and the markers of membrane weakening, MMP-9 and PGE₂ This FM response was partially mediated by ERK signaling and neutrophil extracellular traps through the activation of the DNA sensor, TLR-9. Thus, neutrophils recruited by FMs during infection can propagate FM inflammation and weakening, acting in a feed-forward mechanism to propagate tissue injury at the maternal-fetal interface, increasing the risk of premature FM rupture and preterm birth in women with intrauterine infection.

Hyaluronidase Impairs Neutrophil Function and Promotes Group B Streptococcus Invasion and Preterm Labor in Nonhuman Primates

Invasive bacterial infections during pregnancy are a major risk factor for preterm birth, stillbirth, and fetal injury. Group B streptococci (GBS) are Gram-positive bacteria that asymptomatically colonize the lower genital tract but infect the amniotic fluid and induce preterm birth or stillbirth. Experimental models that closely emulate human pregnancy are pivotal for the development of successful strategies to prevent these adverse pregnancy outcomes. Using a unique nonhuman primate model that mimics human pregnancy and informs temporal events surrounding amniotic cavity invasion and preterm labor, we show that the animals inoculated with hyaluronidase (HylB)-expressing GBS consistently exhibited microbial invasion into the amniotic cavity, fetal bacteremia, and preterm labor. Although delayed cytokine responses were observed at the maternal-fetal interface, increased prostaglandin and matrix metalloproteinase levels in these animals likely mediated preterm labor. HylB-proficient GBS dampened reactive oxygen species production and exhibited increased resistance to neutrophils compared to an isogenic mutant. Together, these findings demonstrate how a bacterial enzyme promotes GBS amniotic cavity invasion and preterm labor in a model that closely resembles human pregnancy.

Matrix metalloproteinases 2 and 9 are elevated in human preterm laboring uterine myometrium and exacerbate uterine contractility†

Matrix metalloproteinases 2 and 9 (MMP2/9) have previously been shown to be elevated in serum and amniotic fluid from women undergoing preterm birth. We performed experiments to determine the effects of MMP2/9 on uterine contraction and birth timing. Pregnant mice were injected daily with 50 mg/kg of SB-3CT or vehicle control beginning on gestational day 14-18 to determine if MMP2/9 inhibition would affect parturition timing. MMP2/9 expression in human myometrial tissue was determined by Simple Western (Wes) and semiquantitative western blot. Purified MMP2/9 and SB-3CT inhibitor were added to human myometrial strips to determine the effects of MMP2/9 on oxytocin-induced uterine contraction. Parturition was delayed in mice treated with MMP2/9 inhibitor SB-3CT. MMP2/9 protein levels were elevated in preterm laboring uterine myometrium. Gelatinase activity was confirmed in cell extracts and supernatants from immortalized and primary human uterine myometrial cells in culture. Addition of purified MMP2/9 increased the oxytocin-induced contractile response in myometrial tissue strips from pregnant women. In contrast, addition of the MMP2/9 inhibitor SB-3CT decreased the contractile response to oxytocin in a dose-dependent manner. These results suggest abnormal MMP2/9 expression affects the contractile state of the uterine myometrium to promote parturition and that MMP2/9 inhibition attenuates this effect.

Cervical epithelial damage promotes Ureaplasma parvum ascending infection, intrauterine inflammation and preterm birth induction in mice

Around 40% of preterm births are attributed to ascending intrauterine infection, and Ureaplasma parvum (UP) is commonly isolated in these cases. Here we present a mouse model of ascending UP infection that resembles human disease, using vaginal inoculation combined with mild cervical injury induced by a common spermicide (Nonoxynol-9, as a surrogate for any mechanism of cervical epithelial damage). We measure bacterial load in a non-invasive manner using a luciferase-expressing UP strain, and post-mortem by qPCR and bacterial titration. Cervical exposure to Nonoxynol-9, 24 h pre-inoculation, facilitates intrauterine UP infection, upregulates pro-inflammatory cytokines, and increases preterm birth rates from 13 to 28%. Our results highlight the crucial role of the cervical epithelium as a barrier against ascending infection. In addition, we expect the mouse model will facilitate further research on the potential links between UP infection and preterm birth.

Cervicovaginal Fluid Protein Microarray for Detection of Microbial Invasion of the Amniotic Cavity in Preterm Labor

We aimed to identify cervicovaginal fluid (CVF) biomarkers that can detect microbial invasion of the amniotic cavity (MIAC) in women with preterm labor (PTL) with an antibody microarray and to develop the best combined model for detection of MIAC using these biomarkers in combination with conventional clinical variables. This retrospective cohort study included 168 singleton pregnant women with PTL (23-34 weeks) who underwent amniocentesis. AF was cultured, and CVF samples were obtained at the time of amniocentesis. An antibody microarray was used to analyze the CVF proteome (n = 40). The validation of four candidate biomarkers of interest was performed by enzyme-linked immunosorbent assay (ELISA) in the final cohort (n = 168). For comparison with candidate markers, CVF IL-6 concentration was also measured. Twenty-seven molecules studied exhibited intergroup differences. Validation by ELISA confirmed significantly higher levels of CVF DKK3, M-CSF, and TIMP-1, but not of IGFBP-2, independent of gestational age, in CVF of women with MIAC. The area under the curve (AUC) of DKK3, M-CSF, and TIMP-1 from CVF was not significantly different from the AUC of IL-6 from CVF for detecting MIAC in women with PTL. By using a stepwise regression analysis, a combined detection model was developed, which included the CVF M-CSF, TIMP-1, and gestational age at sampling (AUC = 0.823). An antibody microarray identified useful biomarkers (DKK3, M-CSF, and TIMP-1) in CVF for detection of MIAC, and a combined model including these biomarkers and gestational age can accurately detect MIAC in women with PTL.

Peptidomics analysis of myometrium tissues in term labor compared with term nonlabor

Preterm birth (PTB) is a major cause of neonatal mortality, with a poorly understood etiology. The regular contraction of the myometrium was considered as contributing to the etiology of the onset of labor, especially PTB. Thus, studying the mechanism of myometrium contraction is very important for understanding the initiation of labor and also for preventing PTB. Using liquid chromatography-mass spectrometry, we found 322 significantly differential peptides in myometrium tissues between term nonlabor and term labor groups (absolute fold change ≥ 2 and P < .05). We next analyzed length, molecular weights, isoelectric point, and cleavage site of all the different peptides. We, next, analyzed the functions of different peptides through their precursor proteins by Gene Ontology, enrichment and canonical pathway analysis. The results indicated that the extracellular matrix (ECM) played a major role in biological process, the cellular component, and molecular function categories, and revealed that ECM remodeling played a vital role in myometrial contraction. In addition, some known signaling, such as corticotropin-releasing hormone signaling and calcium signaling were proven to be involved in this process. Ingenuity Pathways Analysis upstream regulator analysis suggested that some of the known molecules, which reportedly were very important in labor onset, were included, for example, nuclear factor κB, tubulin, and phosphoinositide 3-kinase. We also identified 23 peptides derived from the precursor protein TITIN, of which 21 peptides sequences from TITIN were located in functional domains. These results suggested that peptides play an important role in labor onset and provide further insight into PTB therapy.

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.

Urinary phthalate metabolite concentrations in relation to levels of circulating matrix metalloproteinases in pregnant women

Phthalate exposure has been shown to be associated with adverse pregnancy outcomes. However, human studies informing relevant mechanistic pathways are lacking. Experimental studies have reported that matrix metalloproteinases (MMPs), which are responsible for extracellular protein degradation, may be upregulated in response to phthalate exposure. In this exploratory study we measured urinary phthalate metabolite concentrations, plasma MMP levels, and relevant covariates among 134 pregnant women. There were statistically significant or suggestive positive relationships between several phthalates, particularly between metabolites of di-(2-ethylhexyl) phthalate, with MMP-1 and MMP-9 levels. Further research is needed to confirm these results and how they may inform the mechanisms involved between phthalate exposure and adverse pregnancy outcomes.

Expression of Matrix Metalloproteinases in the Mouse Uterus and Human Myometrium During Pregnancy, Labor, and Preterm Labor

BACKGROUND

Uterine extracellular matrix (ECM) remodeling occurs throughout pregnancy and at parturition. Imbalanced availability of key mediators in ECM degradation, namely, matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs), is implicated in the pathogenesis of preterm labor (PTL).

OBJECTIVES

Examine the expression of MMPs and their inhibitors TIMPs in (a) the mouse uterus throughout normal gestation, at labor, and during inflammation-induced PTL and (b) the human term and preterm myometrium.

METHODS

The expression of Mmp-2/9/3/10 and Timp-1/2 was determined in the uterus of C57BL/6 mice (n = 6/group) during pregnancy (on days (d) 5, 8, 12, 15, 17, and 18), at normal labor, and during lipopolysaccharide-induced PTL (n = 6/group). The expression of MMP-10 and TIMP-1 was determined in human term and preterm myometrium before the onset of labor (TNL, n = 7; PTNL, n = 7) and during active labor (TL, n = 8; PTL, n = 8). Gene expression and tissue localization were assessed by quantitative polymerase chain reaction and immunohistochemistry, respectively.

RESULTS

Mmp-10 was higher during murine labor (53-fold vs early pregnancy) in contrast to Mmp-2/3/9 and Timp-1, the expression of which reached a nadir at labor ( P < .001 vs d5 [ Mmp-2/ 9] or P < .05 vs d8 [ Mmp-3 and Timp-1]). The Mmp-3/10 and Timp-1 were localized to the uterine epithelium and stroma/myometrium. In the human myometrium, TIMP-1 messenger RNA was higher and MMP-10 was lower in TL versus TNL ( P < .05), PTL ( P < .001), and PTNL ( P < .001). MMP-10 and TIMP-1 were localized to the myometrial smooth muscle cells, interstitial fibroblasts, and inflammatory cells.

CONCLUSIONS

These data implicate MMP-3, TIMP-1, and MMP-10 in the uterine ECM remodeling during physiological and pathological parturition.

Time-Variant Genetic Effects as a Cause for Preterm Birth: Insights from a Population of Maternal Cousins in Sweden

Preterm delivery (PTD) is the leading cause of neonatal mortality worldwide, yet its etiology remains largely unexplained. We propose that the genetic factors controlling this trait could act in a nonuniform manner during pregnancy, with each factor having a unique “window of sensitivity.” We test this hypothesis by modeling the distribution of gestational ages (GAs) observed in maternal cousins from the Swedish Medical Birth Register (MBR) (n = 35,541 pairs). The models were built using a time-to-event framework, with simulated genetic factors that increase the hazard of birth either uniformly across the pregnancy (constant effect) or only in particular windows (varying effect). By including various combinations of these factors, we obtained four models that were then optimized and compared. Best fit to the clinical data was observed when most of the factors had time-variant effects, independently of the number of loci simulated. Finally, power simulations were performed to assess the ability to discover varying-effect loci by usual methods for genome-wide association testing. We believe that the tools and concepts presented here should prove useful for the design of future studies of PTD and provide new insights into the genetic architecture determining human GA.

Regulation of Matrix Metalloproteinases-2 and -9 Gene Expression in Cultured Human Fetal Membrane Cells by Influenza Virus Infection

In order to understand a possible etiology of adverse pregnancy outcomes associated with intrauterine influenza virus infection, we examined the effect of influenza virus infection on gene expression of matrix metalloproteinases (MMPs) in cultured amnion epithelial, amnion mesenchymal and chorion trophoblast cells prepared from human fetal membrane tissues by gelatin zymography, Western blotting and reverse transcriptase-PCR. The cells were infected with influenza A (H1N1) virus. The levels of pro-MMP-9 activity in culture supernatants of three types of cells were increased during the period of 24-48 h after the virus infection as compared to those of mock infection. Chorion trophoblast cells spontaneously released a much greater level of pro-MMP-2 activity than amnion epithelial and amnion mesenchymal cells. The cleavage of pro-MMP-2 into an active intermediate form was enhanced in chorion trophoblast cells by the virus infection. The activity levels of MMP-2 and MMP-9 in culture supernatants were consistent with their protein levels. The virus infection induced the mRNA expression of MMP-9, but not MMP-2, in three types of cells. These results suggest that influenza virus infection induces the gene expression of MMP-9 and the cleavage of pro-MMP-2 into an active intermediate form in human fetal membrane cells, resulting in weakening of the membranes through extracellular matrix degradation. Therefore, it is possible that the regulation of MMPs gene expression in fetal membrane cells by influenza virus infection is implicated in a part of the etiology of adverse pregnancy outcomes associated with intrauterine infection with the virus.