Interplay of transcriptional signaling by progesterone, cyclic AMP, and inflammation in myometrial cells: implications for the control of human parturition

The hormonal control of parturition

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

Integrative analysis of noncoding mutations identifies the druggable genome in preterm birth

Preterm birth affects ~10% of pregnancies in the US. Despite familial associations, identifying at-risk genetic loci has been challenging. We built deep learning and graphical models to score mutational effects at base resolution via integrating the pregnant myometrial epigenome and large-scale patient genomes with spontaneous preterm birth (sPTB) from European and African American cohorts. We uncovered previously unidentified sPTB genes that are involved in myometrial muscle relaxation and inflammatory responses and that are regulated by the progesterone receptor near labor onset. We studied genomic variants in these genes in our recruited pregnant women administered progestin prophylaxis. We observed that mutation burden in these genes was predictive of responses to progestin treatment for preterm birth. To advance therapeutic development, we screened ~4000 compounds, identified candidate molecules that affect our identified genes, and experimentally validated their therapeutic effects on regulating labor. Together, our integrative approach revealed the druggable genome in preterm birth and provided a generalizable framework for studying complex diseases.

Exploring myometrial microenvironment changes at the single-cell level from nonpregnant to term pregnant states

The microenvironment and cell populations within the myometrium play crucial roles in maintaining uterine structural integrity and protecting the fetus during pregnancy. However, the specific changes occurring at the single-cell level in the human myometrium between nonpregnant (NP) and term pregnant (TP) states remain unexplored. In this study, we used single-cell RNA sequencing (scRNA-Seq) and spatial transcriptomics (ST) to construct a transcriptomic atlas of individual cells in the myometrium of NP and TP women. Integrated analysis of scRNA-Seq and ST data revealed spatially distinct transcriptional characteristics and examined cell-to-cell communication patterns based on ligand-receptor interactions. We identified and categorized 87,845 high-quality individual cells into 12 populations from scRNA-Seq data of 12 human myometrium tissues. Our findings demonstrated alterations in the proportions of five subpopulations of smooth muscle cells in TP. Moreover, an increase in monocytic cells, particularly M2 macrophages, was observed in TP myometrium samples, suggesting their involvement in the anti-inflammatory response. This study provides unprecedented single-cell resolution of the NP and TP myometrium, offering new insights into myometrial remodeling during pregnancy.NEW & NOTEWORTHY Using single-cell RNA sequencing and spatial transcriptomics, the myometrium was examined at the single-cell level during pregnancy. We identified spatially distinct cell populations and observed alterations in smooth muscle cells and increased M2 macrophages in term pregnant women. These findings offer unprecedented insights into myometrial remodeling and the anti-inflammatory response during pregnancy. The study advances our understanding of pregnancy-related myometrial changes.

Maternal Infection and Preterm Birth: From Molecular Basis to Clinical Implications

As the leading cause of neonatal morbidity and mortality, preterm birth is recognized as a major public health concern around the world. The purpose of this review is to analyze the connection between infections and premature birth. Spontaneous preterm birth is commonly associated with intrauterine infection/inflammation. The overproduction of prostaglandins caused by the inflammation associated with an infection could lead to uterine contractions, contributing to preterm delivery. Many pathogens, particularly Chlamydia trachomatis, Neisseria gonorrhoeae, Trichomonas vaginalis, Gardnerella vaginalis, Ureaplasma urealyticum, Mycoplasma hominis, Actinomyces, Candida spp., and Streptococcus spp. have been related with premature delivery, chorioamnionitis, and sepsis of the neonate. Further research regarding the prevention of preterm delivery is required in order to develop effective preventive methods with the aim of reducing neonatal morbidity.

Molecular Mechanism of Mouse Uterine Smooth Muscle Regulation on Embryo Implantation

Myometrium plays critical roles in multiple processes such as embryo spacing through peristalsis during mouse implantation, indicating vital roles of smooth muscle in the successful establishment and quality of implantation. Actin, a key element of cytoskeleton structure, plays an important role in the movement and contraction of smooth muscle cells (SMCs). However, the function of peri-implantation uterine smooth muscle and the regulation mechanism of muscle tension are still unclear. This study focused on the molecular mechanism of actin assembly regulation on implantation in smooth muscle. Phalloidin is a highly selective bicyclic peptide used for staining actin filaments (also known as F-actin). Phalloidin staining showed that F-actin gradually weakened in the CD-1 mouse myometrium from day 1 to day 4 of early pregnancy. More than 3 mice were studied for each group. Jasplakinolide (Jasp) used to inhibit F-actin depolymerization promotes F-actin polymerization in SMCs during implantation window and consequently compromises embryo implantation quality. Transcriptome analysis following Jasp treatment in mouse uterine SMCs reveals significant molecular changes associated with actin assembly. Tagln is involved in the regulation of the cell cytoskeleton and promotes the polymerization of G-actin to F-actin. Our results show that Tagln expression is gradually reduced in mouse uterine myometrium from day 1 to 4 of pregnancy. Furthermore, progesterone inhibits the expression of Tagln through the progesterone receptor. Using siRNA to knock down Tagln in day 3 SMCs, we found that phalloidin staining is decreased, which confirms the critical role of Tagln in F-actin polymerization. In conclusion, our data suggested that decreases in actin assembly in uterine smooth muscle during early pregnancy is critical to optimal embryo implantation. Tagln, a key molecule involved in actin assembly, regulates embryo implantation by controlling F-actin aggregation before implantation, suggesting moderate uterine contractility is conducive to embryo implantation. This study provides new insights into how the mouse uterus increases its flexibility to accommodate implanting embryos in the early stage of pregnancy.

Reproductive Functions of the Mitochondrial Progesterone Receptor (PR-M)

Classic transcriptional regulation by progesterone via the nuclear progesterone receptors A and B (PR-A, PR-B) has been recognized for decades. Less attention has been given to a mitochondrial progesterone receptor (PR-M) responsible for non-nuclear activities. PR-M is derived from the progesterone receptor (PR) gene from an alternate promoter with the cDNA encoding a unique 5' membrane binding domain followed by the same hinge and hormone-binding domain of the nPR. The protein binds to the mitochondrial outer membrane and functions to increase cellular respiration via increased beta-oxidation and oxidative phosphorylation with resulting adenosine triphosphate (ATP) production. Physiologic activities of PR-M have been studied in cardiac function, spermatozoa activation, and myometrial growth, all known to respond to progesterone. Progesterone via PR-M increases cardiomyocyte cellular respiration to meet the metabolic demands of pregnancy with increased contractility. Consequential gene changes associated with PR-M activation include production of proteins for sarcomere development and for fatty acid oxidation. Regarding spermatozoa function, progesterone via PR-M increases cellular energy production necessary for progesterone-dependent hyperactivation. A role of progesterone in myometrial and leiomyomata growth may also be explained by the increase in necessary cellular energy for proliferation. Lastly, the multi-organ increase in cellular respiration may contribute to the progesterone-dependent increase in metabolic rate reflected by an increase in body temperature through compensatory non-shivering thermogenesis. An evolutionary comparison shows PR-M expressed in humans, apes, and Old World monkeys, but the necessary gene sequence is absent in New World monkeys and lower species. The evolutionary advantage to PR-M remains to be defined, but its presence may enhance catabolism to support the extended gestation and brain development found in these primates.

Myometrial progesterone receptor determines a transcription program for uterine remodeling and contractions during pregnancy

The uterine myometrium expands and maintains contractile quiescence before parturition. While the steroid hormone progesterone blocks labor, the role of progesterone signaling in myometrial expansion remains elusive. This study investigated the myometrial functions of the progesterone receptor, PGR. Pgr ablation in mouse smooth muscle leads to subfertility, oviductal embryo retention, and impaired myometrial adaptation to pregnancy. While gross morphology between mutant and control uteri are comparable, mutant uteri manifest a decrease of 76.6% oxytocin-stimulated contractility in a pseudopregnant context with a reduced expression of intracellular calcium homeostasis genes including Pde5a and Plcb4. At mid-pregnancy, the mutant myometrium exhibits discontinuous myofibers and disarrayed extracellular matrix at the conceptus site. Transcriptome of the mutant mid-pregnant uterine wall manifests altered muscle and extracellular matrix profiles and resembles that of late-pregnancy control tissues. A survey of PGR occupancy, H3K27ac histone marks, and chromatin looping annotates cis-acting elements that may direct gene expression of mid-pregnancy uteri for uterine remodeling. Further analyses suggest that major muscle and matrix regulators Myocd and Ccn2 and smooth muscle building block genes are PGR direct downstream targets. Cataloging enhancers that are topologically associated with progesterone downstream genes reveals distinctive patterns of transcription factor binding motifs in groups of enhancers and identifies potential regulatory partners of PGR outside its occupying sites. Finally, conserved correlations are found between estimated PGR activities and RNA abundance of downstream muscle and matrix genes in human myometrial tissues. In summary, PGR is pivotal to direct the molecular program for the uterus to remodel and support pregnancy.

The Bradykinin System Contributes to the Regulation of Prostaglandin-Endoperoxide Synthase 2 Expression in Human Amnion Fibroblasts: Implications for Term and Preterm Birth

BACKGROUND

Bradykinin (BK) and its biologically active metabolite des-Arg9 bradykinin (DABK) play a pivotal role in inflammation. Since chorioamnionitis is the leading cause of preterm birth and prostaglandin E2 (PGE2) derived from the amnion is key to labor initiation, we investigated if bradykinin peptides are part of the regulatory network of PGE2 synthesis in human amnion at parturition.

METHODS

Human amnion tissue was obtained from term and preterm birth for the study of the changes of the bradykinin system at parturition. Cultured primary human amnion fibroblasts, the major source of PGE2, were used to study the effects of bradykinin peptides on PTGS2 expression and PGE2 production as well as the effects of infection mediators on bradykinin receptors.

RESULTS

Bradykinin peptides and their receptors BDKRB1 and BDKRB2 were present in human amnion, and their abundance increased in term and preterm labor. However, transcripts of the genes encoding the bradykinin precursor and its proteolytic cleavage enzymes were hardly detectable in human amnion despite the increased abundance of bradykinin peptides in term and preterm labor, suggesting that there is an alternative source of bradykinin peptides for human amnion and their actions are enhanced in human amnion at parturition. In-vitro studies in cultured human amnion fibroblasts showed that both BK and DABK increased the expression of prostaglandin-endoperoxide synthase 2 (PTGS2), the rate-limiting enzyme in prostaglandin synthesis, and subsequent PGE2 production. These effects of BK and DABK were mediated through BDKRB2 and BDKRB1 receptors, respectively, with subsequent activation of the p38 and ERK1/2 pathways. Moreover, lipopolysaccharide (LPS) and serum amyloid A1 (SAA1), the important mediators of infectious inflammation, induced the expression of both BDKRB1 and BDKRB2 through toll-like receptor 4 (TLR4). Induction of BDKRB1 and BDKRB2 expression by LPS and SAA1 enhanced BK- or DABK-induced PTGS2 expression and PGE2 production in human amnion fibroblasts.

CONCLUSIONS

This study demonstrated for the first time that the human amnion is a target tissue of bradykinin peptides and the bradykinin system may be part of the regulatory network of PTGS2 expression and PGE2 production in human amnion fibroblasts at both term and preterm birth, which may be enhanced by infection.

Transcriptome changes in maternal peripheral blood during term parturition mimic perturbations preceding spontaneous Preterm birth†

The complex physiologic process of parturition includes the onset of labor, which requires the orchestrated stimulation of a common pathway involving uterine contractility, cervical ripening, and chorioamniotic membrane activation. However, the labor-specific processes taking place in these tissues have limited use as predictive biomarkers unless they can be probed in non-invasive samples, such as the peripheral blood. Herein, we utilized a transcriptomic dataset to assess labor-specific changes in the peripheral blood of women who delivered at term. We identified a set of genes that were differentially expressed with labor and enriched for immunological processes, and these gene expression changes were strongly correlated with results from prior studies, providing in silico validation of our findings. We then identified significant correlations between labor-specific transcriptomic changes in the maternal circulation and those reported in the chorioamniotic membranes, myometrium, and cervix of women at term, demonstrating that tissue-specific labor signatures are partly mirrored in the peripheral blood. Last, we demonstrated a significant overlap between the peripheral blood transcriptomic changes in term parturition and those observed in asymptomatic women prior to the diagnosis of preterm prelabor rupture of membranes who delivered preterm. Collectively, we provide evidence that the normal process of labor at term is characterized by a unique immunological expression signature, which may serve as a useful tool for assessing labor status and potentially identifying women at risk for preterm birth.

The Role of Formyl Peptide Receptor 1 in Uterine Contraction During Parturition

Parturition involves the transformation of the quiescent myometrium into a highly excitable and contractile state, a process that is driven by changes in myometrial gene expression. This study aimed to identify myometrial transcriptomic signatures and potential novel hub genes in parturition, which have great significance for understanding the underlying mechanisms of successful parturition and treating labor-associated pathologies such as preterm birth. In our study, comparative transcriptome analysis was carried out on human myometrial tissues collected from women undergoing caesarean section at term in the presence (TL = 8) and absence of labor (TNL = 8). A total of 582 differentially expressed genes (DEGs) between TL and TNL tissues were identified. Gene ontology (GO), Kyoto encyclopedia of genes and genomes (KEGG) and gene set enrichment analysis (GSEA) revealed that the DEGs were enriched in signal transduction, regulation of signaling receptor activity, inflammatory response, cytokine-cytokine receptor interaction, IL-17 signaling pathway, TNF signaling pathway, among others. Thus, transcriptome analysis of the myometrium during term labor revealed that labor onset was associated with an inflammatory response. Moreover, protein-protein interactions network analysis identified FPR1, CXCL8, CXCL1, BDKRB2, BDKRB1, and CXCL2 as the hub genes associated with onset of labor. Formyl peptide receptor 1 (FPR1) was highly expressed in laboring myometrial tissues, with the activation of FPR1 in vitro experiments resulting in increased myometrial contraction. Our findings demonstrate the novel role of FPR1 as a modulator of myometrial contraction.

TBX2, a Novel Regulator of Labour

Background and Objectives: Therapeutic interventions targeting molecular factors involved in the transition from uterine quiescence to overt labour are not substantially reducing the rate of spontaneous preterm labour. The identification of novel rational therapeutic targets are essential to prevent the most common cause of neonatal mortality. Based on our previous work showing that Tbx2 (T-Box transcription factor 2) is a putative upstream regulator preceding progesterone withdrawal in mouse myometrium, we now investigate the role of TBX2 in human myometrium. Materials and Methods: RNA microarray analysis of (A) preterm human myometrium samples and (B) myometrial cells overexpressing TBX2 in vitro, combined with subsequent analysis of the two publicly available datasets of (C) Chan et al. and (D) Sharp et al. The effect of TBX2 overexpression on cytokines/chemokines secreted to the myometrium cell culture medium were determined by Luminex assay. Results: Analysis shows that overexpression of TBX2 in myometrial cells results in downregulation of TNFα- and interferon signalling. This downregulation is consistent with the decreased expression of cytokines and chemokines of which a subset has been previously associated with the inflammatory pathways relevant for human labour. In contrast, CXCL5 (C-X-C motif chemokine ligand 5), CCL21 and IL-6 (Interleukin 6), previously reported in relation to parturition, do not seem to be under TBX2 control. The combined bioinformatical analysis of the four mRNA datasets identifies a subset of upstream regulators common to both preterm and term labour under control of TBX2. Surprisingly, TBX2 mRNA levels are increased in preterm contractile myometrium. Conclusions: We identified a subset of upstream regulators common to both preterm and term labour that are activated in labour and repressed by TBX2. The increased TBX2 mRNA expression in myometrium collected during a preterm caesarean section while in spontaneous preterm labour compared to tissue harvested during iatrogenic preterm delivery does not fit the bioinformatical model. We can only explain this by speculating that the in vivo activity of TBX2 in human myometrium depends not only on the TBX2 expression levels but also on levels of the accessory proteins necessary for TBX2 activity.

Transcription factors regulated by cAMP in smooth muscle of the myometrium at human parturition

Cyclic adenosine monophosphate (cAMP) contributes to maintenance of a quiescent (relaxed) state in the myometrium (i.e. uterine smooth muscle) during pregnancy, which most commonly has been attributed to activation of protein kinase A (PKA). PKA-mediated phosphorylation of cytosolic contractile apparatus components in myometrial smooth muscle cells (mSMCs) are known to promote relaxation. Additionally, PKA also regulates nuclear transcription factor (TF) activity to control expression of genes important to the labour process; these are mostly involved in actin-myosin interactions, cell-to-cell connectivity and inflammation, all of which influence mSMC transition from a quiescent to a contractile (pro-labour) phenotype. This review focuses on the evidence that cAMP modulates the activity of TFs linked to pro-labour gene expression, predominantly cAMP response element (CRE) binding TFs, nuclear factor κB (NF-κB), activator protein 1 (AP-1) family and progesterone receptors (PRs). This review also considers the more recently described exchange protein directly activated by cAMP (EPAC) that may oppose the pro-quiescent effects of PKA, as well as explores findings from other cell types that have the potential to be of novel relevance to cAMP action on TF function in the myometrium.

Obesity as a contributor to immunopathology in pregnant and non-pregnant adults with COVID-19

The ongoing coronavirus disease 2019 (COVID‐19) pandemic has led to a global public health emergency with the need to identify vulnerable populations who may benefit from increased screening and healthcare resources. Initial data suggest that overall, pregnancy is not a significant risk factor for severe coronavirus disease 2019 (COVID‐19). However, case series have suggested that maternal obesity is one of the most important comorbidities associated with more severe disease. In obese individuals, suppressors of cytokine signaling are upregulated and type I and III interferon responses are delayed and blunted leading to ineffective viral clearance. Obesity is also associated with changes in systemic immunity involving a wide range of immune cells and mechanisms that lead to low‐grade chronic inflammation, which can compromise antiviral immunity. Macrophage activation in adipose tissue can produce low levels of pro‐inflammatory cytokines (TNF‐α, IL‐1β, IL‐6). Further, adipocyte secretion of leptin is pro‐inflammatory and high circulating levels of leptin have been associated with mortality in patients with acute respiratory distress syndrome. The synergistic effects of obesity‐associated delays in immune control of COVID‐19 with mechanical stress of increased adipose tissue may contribute to a greater risk of pulmonary compromise in obese pregnant women. In this review, we bring together data regarding obesity as a key co‐morbidity for COVID‐19 in pregnancy with known changes in the antiviral immune response associated with obesity. We also describe how the global burden of obesity among reproductive age women has serious public health implications for COVID‐19.

Prevention of preterm birth: Proactive and reactive clinical practice-are we on the right track?

Preterm birth remains the major cause of death and disability among children under the age of five. In developing countries antenatal preterm birth prevention clinics are set up to provide cervical length surveillance and/or treatment modalities such as cerclage or progesterone for those women with identified risk factors such as previous cervical treatment or preterm birth. However, 85% of women have no risk factors for PTB and currently there is no biomarker to screen women early in pregnancy. Women will present unexpectedly in threatened preterm labour and we have no choice but to adopt a re-active approach to their care by using predication and preparation strategies such as fetal fibronectin, tocolytic therapy and steroids. Despite these strategies approximately 15-20% of these women will give birth preterm before 34 weeks. There is a urgent need to re-design primary, secondary and tertiary prevention strategies for spontaneous preterm labour (sPTL) in singleton pregnancies aimed at identifying and addressing key gaps in clinical practice and research.

Dynamic transcriptome, accessible genome, and PGR cistrome profiles in the human myometrium

The myometrium undergoes structural and functional remodeling during pregnancy. We hypothesize that myometrial genomic elements alter correspondingly in preparation for parturition. Human myometrial tissues from nonpregnant (NP) and term pregnant (TP) human subjects were examined by RNAseq, ATACseq, and PGR ChIPseq assays to profile transcriptome, assessible genome, and PGR occupancy. NP and TP specimens exhibit 2890 differentially expressed genes, reflecting an increase of metabolic, inflammatory, and PDGF signaling, among others, in adaptation to pregnancy. At the epigenome level, patterns of accessible genome change between NP and TP myometrium, leading to the altered enrichment of binding motifs for hormone and muscle regulators such as the progesterone receptor (PGR), Krüppel-like factors, and MEF2A transcription factors. PGR genome occupancy exhibits a significant difference between the two stages of the myometrium, concomitant with distinct transcriptomic profiles including genes such as ENO1, LHDA, and PLCL1 in the glycolytic and calcium signaling pathways. Over-representation of SRF, MYOD, and STAT binding motifs in PGR occupying sites further suggests interactions between PGR and major muscle regulators for myometrial gene expression. In conclusion, changes in accessible genome and PGR occupancy are part of the myometrial remodeling process and may serve as mechanisms to formulate the state-specific transcriptome profiles.