Interleukin-6 is an essential determinant of on-time parturition in the mouse

IL-6 abundance in amniotic fluid and uterine tissues increases in late gestation or with infection-associated preterm labor. A role in regulation of labor onset is suggested by observations that IL-6 increases expression of genes controlling prostaglandin synthesis and signaling in isolated uterine cells, but whether IL-6 is essential for normal parturition is unknown. To evaluate the physiological role of IL-6 in parturition in mice, we investigated the effect of Il6 null mutation on the timing of parturition and expression of genes associated with uterine activation. Il6 null mutant mice delivered 24 h later than wild-type mice, although circulating progesterone fell similarly in both genotypes during the prepartal period. Il6 null mutant mice were also refractory to low doses of lipopolysaccharide sufficient to induce preterm delivery in wild-type mice. The characteristic late-gestation elevation in uterine expression of Oxtr mRNA encoding oxytocin receptor, and peripartal increases in Ptgfr and Ptgs2 mRNAs regulating prostaglandin synthesis and signaling were delayed by 24 h in Il6 null mutant mice. Conversely, Ptger4 mRNA encoding the prostaglandin E receptor-4 was abnormally elevated in late-gestation in Il6 null mutant mice. Administration of recombinant IL-6 from d 11.5 postcoitum until term restored the normal timing of delivery and normalized Ptger4 mRNA expression in late gestation. We conclude that IL-6 has a key role in controlling the progression of events culminating in parturition and that it acts downstream of luteolysis in the uterus to regulate genes involved in the prostaglandin-mediated uterine activation cascade.

Identifying genetic networks underlying myometrial transition to labor

BACKGROUND

Early transition to labor remains a major cause of infant mortality, yet the causes are largely unknown. Although several marker genes have been identified, little is known about the underlying global gene expression patterns and pathways that orchestrate these striking changes.

RESULTS

We performed a detailed time-course study of over 9,000 genes in mouse myometrium at defined physiological states: non-pregnant, mid-gestation, late gestation, and postpartum. This dataset allowed us to identify distinct patterns of gene expression that correspond to phases of myometrial 'quiescence', 'term activation', and 'postpartum involution'. Using recently developed functional mapping tools (HOPACH (hierarchical ordered partitioning and collapsing hybrid) and GenMAPP 2.0), we have identified new potential transcriptional regulatory gene networks mediating the transition from quiescence to term activation.

CONCLUSIONS

These results implicate the myometrium as an essential regulator of endocrine hormone (cortisol and progesterone synthesis) and signaling pathways (cyclic AMP and cyclic GMP stimulation) that direct quiescence via the transcriptional upregulation of both novel and previously associated regulators. With term activation, we observe the upregulation of cytoskeletal remodeling mediators (intermediate filaments), cell junctions, transcriptional regulators, and the coordinate downregulation of negative control checkpoints of smooth muscle contractile signaling. This analysis provides new evidence of multiple parallel mechanisms of uterine contractile regulation and presents new putative targets for regulating myometrial transformation and contraction.

Mechanical stretch of human uterine smooth muscle cells increases IL-8 mRNA expression and peptide synthesis

Labour is associated with increased synthesis of interleukin-8 (IL-8) by the fetal membranes and myometrium, which leads to an inflammatory infiltrate. Stretch has been shown to increase the expression of contraction-associated proteins in animal models of labour and in human myocytes in vitro. In this study, we tested the hypothesis that mechanical stretch of human myometrial cells increases IL-8 messenger ribonucleic acid (mRNA) expression. We isolated myocytes from non-pregnant women undergoing hysterectomy and pregnant women undergoing Caesarean section before and after the onset of labour. Myocytes in culture were subjected to stretch of varying intensity (6-16%) and duration (1 or 6 h) using the Flexercell system. IL-8 mRNA expression was lowest in myocytes from pregnant women not in labour, intermediate in those from non-pregnant women and greatest in those from pregnant women in labour. Stretch increased IL-8 mRNA expression independent of reproductive state. The stretch-induced increase in IL-8 mRNA expression was associated with higher IL-8 levels in the culture supernatant and enhanced promoter activity. These data suggest that stretch contributes to the increase in myometrial IL-8 synthesis associated with the onset of labour in humans.

G-1-activated membrane estrogen receptors mediate increased contractility of the human myometrium

Estrogens are key mediators of increased uterine contractility at labor. We sought to determine whether membrane-associated estrogen receptors, such as the recently described seven-transmembrane receptor G protein-coupled receptor 30 (GPR30), mediated some of this effect. Using human myometrium obtained at term cesarean section before or after the onset of labor, we demonstrated the presence of GPR30 mRNA and protein using quantitative RT-PCR and Western blotting. GPR30 receptor was localized to the cell membrane and often colocalized with calveolin-1. Using the specific estrogen membrane receptor agonist G-1 and myometrial explants, we showed that membrane receptor activation led to phosphorylation of MAPK and the actin-modifying small heat shock protein 27. Using myometrial strips incubated with G-1 or vehicle we demonstrated that estrogen membrane receptor activation increased the myometrial contractile response to oxytocin. These data suggest that activation of the plasma membrane estrogen receptor GPR30 likely participates in the physiology of the human myometrium during pregnancy and identifies it as a potential target to modify uterine activity.

Human effector/initiator gene sets that regulate myometrial contractility during term and preterm labor

OBJECTIVE

Distinct processes govern transition from quiescence to activation during term (TL) and preterm labor (PTL). We sought gene sets that are responsible for TL and PTL, along with the effector genes that are necessary for labor independent of gestation and underlying trigger.

STUDY DESIGN

Expression was analyzed in term and preterm with or without labor (n=6 subjects/group). Gene sets were generated with logic operations.

RESULTS

Thirty-four genes were expressed similarly in PTL/TL but were absent from nonlabor samples (effector set); 49 genes were specific to PTL (preterm initiator set), and 174 genes were specific to TL (term initiator set). The gene ontogeny processes that comprise term initiator and effector sets were diverse, although inflammation was represented in 4 of the top 10; inflammation dominated the preterm initiator set.

CONCLUSION

TL and PTL differ dramatically in initiator profiles. Although inflammation is part of the term initiator and the effector sets, it is an overwhelming part of PTL that is associated with intraamniotic inflammation.

Effects of progesterone treatment on expression of genes involved in uterine quiescence

An important action of progesterone during pregnancy is to maintain the uterus in a quiescent state and thereby prevent preterm labor. The causes of preterm labor are not well understood, so progesterone action on the myometrium can provide clues about the processes that keep the uterus from contracting prematurely. Accordingly, we have carried out Affymetrix GeneChip analysis of progesterone effects on gene expression in immortalized human myometrial cells cultured from a patient near the end of pregnancy. Progesterone appears to inhibit uterine excitability by a number of mechanisms, including increased expression of calcium and voltage-operated K(+) channels, which dampens the electrical activity of the myometrial cell, downregulation of agents, and receptors involved in myometrial contraction, reduction in cell signal components that lead to increased intracellular Ca(2+) concentrations in response to contractile stimuli, and downregulation of proteins involved in the cross-linking of actin and myosin filaments to produce uterine contractions.

The roles of prostaglandin EP 1 and 3 receptors in the control of human myometrial contractility

CONTEXT

Prostaglandins are central to the processes of human labor. Prostaglandin E(2) (PGE(2)) synthesized within the uterus mediates cervical ripening and uterine contractions. PGE receptors, EP1 and EP3, may each mediate contractions, and represent potential therapeutic targets in the management of preterm labor. Studies of the expression and function of EP1 and EP3 in pregnant myometrium are inconsistent.

OBJECTIVE

The objective of the study was to determine the relative importance of EP1 and EP3 in human myometrial contractility.

DESIGN

We studied the expression of EP1 and EP3 in upper- and lower-segment myometrium at term in vivo and the effects of specific inhibitors on contractions in vitro.

PATIENTS

Myometrial biopsies for both in vivo and in vitro studies were taken at cesarean section at term before or in labor in uncomplicated pregnancies.

RESULTS

We found no differences in the expression of EP1 or EP3 at mRNA or protein level between the upper and lower segment myometrium and no overall changes associated with the onset of labor. Upon labor, EP1, but not EP3, was found to relocalize to the nucleus. In studies of contractility, we found no differences in spontaneous or PGE(2)-induced contractility between the upper- and lower-segment samples. Spontaneous contractions were inhibited by acetylsalicylic acid and were rescued by PGE(2). Although an EP1 antagonist, ZD6416, had no effect, an EP3 antagonist, L798106, inhibited both spontaneous and PGE(2)-induced contractions.

CONCLUSIONS

EP3 is the primary receptor subtype that mediates PGE(2) induced contractility in human pregnant myometrium at term and represents a possible therapeutic target.

Transgene Insertion on Mouse Chromosome 6 Impairs Function of the Uterine Cervix and Causes Failure of Parturition1

The molecular mechanisms controlling the initiation of parturition remain largely undefined. We report a new animal model in which parturition does not occur. A line of mice expressing a human apolipoprotein B (APOB) gene fail to deliver their young if the transgene is present in homozygous (Tg/Tg), but not in heterozygous (Tg/Wt), form. Cloning and mapping of the transgene insertion locus indicate that 10 copies of the 80-kilobase APOB genomic fragment inserted into mouse chromosome 6 result in a small, 390-base pair deletion of mouse genomic DNA. Nine other lines expressing the transgene have normal labor, suggesting that transgene insertion in this mutant line disrupted a mouse gene crucial for successful parturition. The pathophysiology of parturition failure in these animals was defined using physiological, endocrinological, and morphological techniques. Results indicate that luteolysis occurs in Tg/Tg mice but is delayed by 1 day. Delivery did not occur in mutant mice at term after spontaneous luteolysis or even after removal of progesterone action by ovariectomy or antiprogestin treatment. Biomechanical and functional studies of the uterus and cervix revealed that the primary cause of failed parturition in Tg/Tg mice was not inadequate uterine contractions of labor but, rather, a rigid, inelastic cervix at term that was abnormally rich in neutrophils and tissue monocytes. Characterization of the transgene insertional mutant, Tg/Tg, indicates that progesterone withdrawal is insufficient to complete parturition in the presence of inadequate cervical ripening at term.

Overexpression of SK3 channels dampens uterine contractility to prevent preterm labor in mice

The mechanisms that control the timing of labor have yet to be fully characterized. In a previous study, the overexpression of small conductance calcium-activated K(+) channel isoform 3 in transgenic mice, Kcnn3(tm1Jpad)/Kcnn3(tm1Jpad) (also known as SK3(T/T)), led to compromised parturition, which indicates that KCNN3 (also known as SK3) plays an important role in the delivery process. Based on these findings, we hypothesized that SK3 channel expression must be downregulated late in pregnancy to enable the uterus to produce the forceful contractions required for parturition. Thus, we investigated the effects of SK3 channel expression on gestation and parturition, comparing SK3(T/T) mice to wild type (WT) mice. Here, we show in WT mice that SK3 transcript and protein are significantly reduced during pregnancy. We also found the force produced by uterine strips from Pregnancy Day 19 (P19) SK3(T/T) mice was significantly less than that measured in WT or SK3 knockout control (SK3(DOX)) uterine strips, and this effect was reversed by application of the SK3 channel inhibitor apamin. Moreover, two treatments that induce labor in mice failed to result in complete delivery in SK3(T/T) mice within 48 h after injection. Thus, stimuli that initiate parturition under normal circumstances are insufficient to coordinate the uterine contractions needed for the completion of delivery when SK3 channel activity is in excess. Our data indicate that SK3 channels must be downregulated for the gravid uterus to generate labor contractions sufficient for delivery in both term and preterm mice.

Estrogen receptor alpha isoform ERdelta7 in myometrium modulates uterine quiescence during pregnancy

BACKGROUND

Circulating estrogen (E2) levels are high throughout pregnancy and increase towards term, however its local tissue specific actions vary across gestation. For example, myometrial E2 regulated uterotonic action is disabled until term, whereas it's proliferative function is maintained in the breast. We have identified gestationally regulated splicing events, mediated by hnRNPG and modulated by E2 that generate alternatively spliced estrogen receptor alpha (ERα) variants (ERΔ7 and ERα46) in the myometrium. These variants allow for differential, gestationally regulated, modulation of the uterotonic action of E2.

METHODS

Human myometrium isolated from preterm and term non-laboring and laboring pregnant women were analyzed for ERα isoforms and splice factor levels. Lentiviral mediated shRNA knockdown of hnRNPG and overexpression of ERΔ7 were performed in human myometrial (hTERT-HM) cells. Functional 3D collagen contraction assays were executed.

FINDINGS

ERΔ7 acts as a dominant negative repressor of the uterotonic action of ERα66 and ERα46 isoforms through the regulation of the myometrial gap junction protein GJA1. Elimination of hnRNPG inhibits the generation of ERΔ7 while overexpression of ERΔ7 inhibited GJA1 expression. Moreover in vivo human myometrial hnRNPG levels decline at term in an E2 dependent manner resulting in a withdrawal of ERΔ7 levels and its tocolytic action at term.

INTERPRETATION

Our findings implicate the unique role of ERΔ7 as a modulator of myometrial quiescence and define the mechanism of ERΔ7 generation, through hormonally regulated splicing events. FUND: This study was supported by NIH OPRU U01 supplement (HD047905), University of Pittsburgh and Wayne State University Perinatal Research Initiative (USA).

Functional and molecular characterization of tachykinins and tachykinin receptors in the mouse uterus

The aim of this study was to analyze the function and expression of tachykinins, tachykinin receptors, and neprilysin (NEP) in the mouse uterus. A previous study showed that the uterotonic effects of substance P (SP), neurokinin A (NKA), and neurokinin B (NKB) in estrogen-treated mice were mainly mediated by the tachykinin NK1 receptor. In the present work, further contractility studies were undertaken to determine the nature of the receptors mediating responses to tachykinins in uteri of late pregnant mice. Endpoint and real-time quantitative RT-PCR were used to analyze the expression of the genes that encode the tachykinins SP/NKA, NKB, and hemokinin-1 (HK-1) (Tac1, Tac2, and Tac4); and the genes that encode tachykinin NK1 (Tacr1), NK2 (Tacr2), and NK3 (Tacr3) receptors in uteri from pregnant and nonpregnant mice. The data show that the mRNAs of tachykinins (particularly NKB and HK-1), tachykinin receptors, and NEP are locally expressed in the mouse uterus, and their expression changes during the estrous cycle and during pregnancy. The tachykinin NK1 receptor is the predominant tachykinin receptor in the nonpregnant and early pregnant mouse and may mediate tachykinin-induced uterine contractions in the nonpregnant mouse. The tachykinin NK2 receptor is predominant in the late pregnant mouse and is the main receptor mediating uterotonic responses to tachykinins at late pregnancy. The tachykinin NK3 receptor is expressed in considerable amounts only in uteri from nonpregnant diestrous animals, and its physiological significance remains to be clarified.

Epigenetics of human myometrium: DNA methylation of genes encoding contraction-associated proteins in term and preterm labor

Preterm birth involves the interaction of societal and environmental factors potentially modulating the length of gestation via the epigenome. An established form of epigenetic regulation is DNA methylation where promoter hypermethylation is associated with gene repression. We hypothesized we would find differences in DNA methylation in the myometrium of women with preterm labor of different phenotypes versus normal term labor. Myometrial tissue was obtained at cesarean section at term with or without labor, preterm without labor, idiopathic preterm labor, and twin gestations with labor. Genomic DNA was isolated, and samples in each group were combined and analyzed on a NimbleGen 2.1M human DNA methylation array. Differences in methylation from -8 to +3 kb of transcription start sites of 22 contraction-associated genes were determined. Cytosine methylation was not present in CpG islands of any gene but was present outside of CpG islands in shores and shelves in 19 genes. No differential methylation was found across the tissue groups for six genes (PTGES3L, PTGER2, PTGER4, PTGFRN, ESR2, and GJA1). For 13 genes, differential methylation occurred in several patterns between tissue groups. We find a correlation between hypomethylation and increased mRNA expression of PTGES/mPGES-1, indicating potential functional relevance of methylation, but no such correlation for PTGS2/COX-2, suggesting other regulatory mechanisms for PTGS2 at labor. The majority of differential DNA methylation of myometrial contraction-associated genes with different labor phenotypes occurs outside of CpG islands in gene promoters, suggesting that the entirety of DNA methylation across the genome should be considered.

Insights into the physiology of childbirth using transcriptomics

Romero and colleagues discuss a study in PLoS Medicine that used microarrays to determine labor-associated gene expression profiles in the human uterus.

Mechanical and signaling mechanisms that guide pre-implantation embryo movement

How a mammalian embryo determines and arrives at its attachment site has been studied for decades, but our understanding of this process is far from complete. Using confocal imaging and image analysis, we evaluate embryo location along the longitudinal oviductal-cervical axis of murine uteri. Our analysis reveals three distinct pre-implantation phases: embryo entry, unidirectional movement of embryo clusters and bidirectional scattering and spacing of embryos. We show that unidirectional clustered movement is facilitated by a mechanical stimulus of the embryo and is regulated by adrenergic uterine smooth muscle contractions. Embryo scattering, on the other hand, depends on embryo-uterine communication reliant on the LPAR3 signaling pathway and is independent of adrenergic muscle contractions. Finally, we demonstrate that uterine implantation sites in mice are neither random nor predetermined but are guided by the number of embryos entering the uterine lumen. These studies have implications for understanding how embryo-uterine communication is key to determining an optimal implantation site necessary for the success of a pregnancy.

The pregnant myometrium is epigenetically activated at contractility-driving gene loci prior to the onset of labor in mice

During gestation, uterine smooth muscle cells transition from a state of quiescence to one of contractility, but the molecular mechanisms underlying this transition at a genomic level are not well-known. To better understand these events, we evaluated the epigenetic landscape of the mouse myometrium during the pregnant, laboring, and postpartum stages. We generated gestational time point–specific enrichment profiles for histone H3 acetylation on lysine residue 27 (H3K27ac), histone H3 trimethylation of lysine residue 4 (H3K4me3), and RNA polymerase II (RNAPII) occupancy by chromatin immunoprecipitation with massively parallel sequencing (ChIP-seq), as well as gene expression profiles by total RNA-sequencing (RNA-seq). Our findings reveal that 533 genes, including known contractility-driving genes (Gap junction alpha 1 [Gja1], FBJ osteosarcoma oncogene [Fos], Fos-like antigen 2 [Fosl2], Oxytocin receptor [Oxtr], and Prostaglandin G/H synthase 2 (Ptgs2), for example), are up-regulated at day 19 during active labor because of an increase in transcription at gene bodies. Labor-associated promoters and putative intergenic enhancers, however, are epigenetically activated as early as day 15, by which point the majority of genome-wide H3K27ac or H3K4me3 peaks present in term laboring tissue is already established. Despite this early exhibited histone signature, increased noncoding enhancer RNA (eRNA) production at putative intergenic enhancers and recruitment of RNAPII to the gene bodies of labor-associated loci were detected only during labor. Our findings indicate that epigenetic activation of the myometrial genome precedes active labor by at least 4 days in the mouse model, suggesting that the myometrium is poised for rapid activation of contraction-associated genes in order to exit the state of quiescence.

A study of the epigenomic and transcriptomic basis of pregnancy and labor onset in a mouse model identifies genes that are epigenetically poised for activation four days before labour onset, and implicates AP-1 transcription factors in the up-regulation of genes during labor.

HoxA13 Regulates Phenotype Regionalization of Human Pregnant Myometrium

CONTEXT

Bipedalism separates humans from most other animal species, but results in significant physiologic challenges, particularly with respect to the maintenance of pregnancy and induction of parturition. A contracted lower uterine segment (LUS) and a relaxed uterine fundal myometrium (FUN) during pregnancy are required to prevent pressure on the cervix from the fetal head due to gravity. With the onset of labor, this regionalization of myometrial function must be reversed, allowing descent of the fetus, dilation of the cervix, and expulsion of the fetus through the birth canal. However, the molecular mechanisms remain unclear.

OBJECTIVE AND DESIGN

This study sought to identify phenotypic regionalization of LUS and FUN during pregnancy, RNA sequencing was performed to analyze the human myometrial transcriptome. Real-time PCR and immunoblotting were applied to validate sequencing results. Cell contraction/adhesion assays and gene microarrays were used to study the cellular functions of the identified genes.

RESULTS

Homeobox A13 (HoxA13), prostacyclin synthase (PTGIS), and periostin (POSTN) genes are more highly expressed in LUS than FUN of nonlaboring, but not laboring, myometrial cells at term. HoxA13 up-regulates transcription of PTGIS and POSTN genes. Elevated HoxA13 expression enhances myometrial cell contractility and cell-cell adhesion. Gene microarray studies show that HoxA13-regulated genes are associated with immune response, gap junction/cell adhesion, and pregnancy.

CONCLUSION

The LUS expresses higher levels of HoxA13, PTGIS, and POSTN, and is more contractile than the FUN at term prior to labor. This pregnancy-maintaining regionalization of myometrial function may be mediated by HoxA13.

Stimulation of contractions in pregnant human myometrium is associated with 5-HT3 receptors

BACKGROUND

Serotonin (5-HT) is known to play an important role in regulating uterine contractions. However, the specific receptors involved have not been well characterized. We evaluated whether 5-HT3 receptors exist in human myometrium, and their effects on myometrial contractility when stimulated by a 5-HT3 agonist.

METHODS

Four tissue samples taken from patients undergoing hysterectomy (n=2) and elective cesarean delivery (n=2) were used to detect expression of 5-HT3 receptors on the myometrium using western blotting. For isometric tension measurement, another 12 myometrial strips obtained from patients undergoing elective cesarean delivery were randomly divided into a control group (Group CON) and an RS56812 group (Group RG). In increasing doses from 10-7M to 10-4M, RS56812, a 5-HT3 receptor agonist, was used to investigate the contractile effects after bonding to the 5-HT3 receptor, following which the effects of granisetron were assessed. Amplitude, interval and duration of myometrial contractions were recorded.

RESULTS

Proteins with a molecular mass of 55kDa, consistent with 5-HT3 receptors, were detected both on non-pregnant and late-pregnant human uteri. RS56812 increased the contractile amplitude at concentrations of 10-6M, 10-5M and 10-4M, achieving maximum effect at 10-5M. A prolonged contractile interval was detected at the concentration of 10-4M. However, RS56812 showed no significant effect on contraction duration. Granisetron did not reverse the contractile effects induced by RS56812.

CONCLUSION

5-HT3 receptors are expressed on non-pregnant and pregnant uteri. RS56812 enhanced myometrial contractions, but this was not affected by granisetron, the mechanism of which requires further investigation.

Intermedin in rat uterus: changes in gene expression and peptide levels across the estrous cycle and its effects on uterine contraction

BACKGROUND

The present study demonstrates the expression of intermedin (IMD) and its receptor components in the uterus of the female rat during the estrous cycle and its effect on uterine contraction.

METHODS

The gene expression level of intermedin and its receptor components and the peptide level of intermedin were studied by real-time RT-PCR and enzyme immunoassay (EIA) respectively. The separation of precursor and mature IMD was studied by gel filtration chromatography and EIA. The localization of IMD in the uterus was investigated by immunohistochemistry. The effect of IMD on in vitro uterine contraction was studied by organ bath technique.

RESULTS

Uterine mRNAs of Imd and its receptor components and IMD levels displayed cyclic changes across the estrous cycle. Imd mRNA level was the highest at proestrus while the IMD level was the highest at diestrus. IMD was found in the luminal and glandular epithelia and IMD treatment significantly reduced the amplitude and frequency of uterine contraction but not the basal tone. Both calcitonin gene-related peptide (CGRP) receptor antagonist hCGRP8-37 and adrenomedullin (ADM) receptor antagonist hADM22-52 partially abolished the inhibitory effect of IMD on uterine contraction while the specific IMD receptor antagonist hIMD17-47 completely blocked the actions. The enzyme inhibitors of NO (L-NAME) and PI3K (Wortmannin) pathways diminished the IMD effects on uterine contraction while the cAMP/PKA blocker, KT5720, had no effect, indicating an involvement of NO and PI3K/Akt but not PKA.

CONCLUSIONS

IMD and the gene expression of its receptor components are differentially regulated in the uterus during the estrous cycle and IMD inhibits uterine contraction by decreasing the amplitude and frequency.

Contraction-associated proteins expression by human uterine smooth muscle cells depends on maternal serum and progranulin associated with gestational weight gain

Pregnant women with obesity are at increased risk of parturition dysfunction; however, the biological mechanism has remained unknown. We hypothesized that molecules circulating in the serum of pregnant women with obesity may induce the aberrant expression of contraction-associated proteins (CAPs), leading to insufficient uterine contractions. This study aimed to investigate the effects of maternal serum on CAPs expression by human uterine smooth muscle cells (UtSMCs) and elucidate the influence of maternal obesity. Blood samples were collected from singleton pregnant women at 36-41 weeks of gestation before the onset of labor. UtSMCs were incubated in the serum, and the mRNA expressions of PTGFR, OXTR, GJA1, and PTGS2 were examined by RT-PCR. Progranulin (PGRN) is a circulating glycoprotein associated with insulin resistance characterized by the accumulation of visceral fat. The serum PGRN levels of the samples were measured by ELISA. After incubated with PGRN (100-1,000 ng/mL), mRNA expression of PTGFR, OXTR, and GJA1 and protein expression of CX43 were examined by RT-PCR and western blotting, respectively. The mRNA expressions of PTGFR, OXTR, and GJA1 showed significantly negative correlations with gestational weight gain (GWG). Serum PGRN levels showed a significantly positive correlation with GWG. High levels of PGRN suppressed the mRNA expression of GJA1 and the protein expression of CX43. The change in maternal serum induced by GWG suppressed the CAPs expression by UtSMCs. PGRN is one of the factors in the serum responsible for inhibiting the expression of CX43.

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.

LncRNA GAS5 Regulates Myometrial Cell Contractions in an m6A-Dependent Manner

LncRNAs are engaged in signaling pathways in human physiological and pathological states. However, LncRNAs mediate the onset of human labor still remains unknown. RNA sequencing of lower segment myometrium (in labor vs. not in labor) was analyzed. N6-Methyladenosine (m6A) complexes were detected by RIP and meRIP in human myometrial cells. Plasmid and siRNA transfection was performed, and contraction ability was assessed. RNA pulldown, silver staining, protein mass spectrometry, and RIP were used to identify binding proteins. FISH and immunofluorescence costaining were applied to assess the coexpression. GAS5 was upregulated in human myometrium after labor onset. METTL3 and IGF2BP1 maintained GAS5 RNA stability based on actinomycin assay, thus strengthening the contraction of myometrial cells. RIP and meRIP revealed the binding sites of GAS5 with METTL3 and IGF2BP1, respectively. Furthermore, GAS5 binds TPM4 in cytoplasm of myometrium cells and transports TPM4 to the contraction filaments. m6A RNA modifications were also noted in the mouse myometrium after labor onset. These findings highlighted the critical role of m6A modification in GAS5, providing a new method to explore RNA epigenetic regulatory patterns in human parturition.

Etiology behind canine uterine inertia: Role of uterine expression of MLCK4, MYH2, and PKC genes

Dystocia is an obstetrical emergency, and primary uterine inertia (PUI) is the major etiological reason among the more prevalent maternal causes in dogs. The present study involved the relative expression analysis of genes associated with myometrial contraction in medium-sized dog breeds with uterine inertia. Dogs without any progress in the parturition process even after four hours of the onset of labor and the absence of uterine contractions were considered to have complete primary uterine inertia (CPUI, n = 9). Dogs that had expelled at least one fetus and made no further progress in parturition in the absence of active uterine contraction were considered to be experiencing partial primary uterine inertia (PPUI, n = 6). Dogs with the fetal cause of dystocia (FCD), i.e., obstructive dystocia, were taken as the third (n = 7) group. Uterine tissue samples were collected during cesarean section in each group, RNA was isolated, and the relative expression of myometrial ACTA2, ACTG2, MLCK4, MYH2, and PKC genes was analyzed. The MLCK4 gene expression was downregulated in CPUI (P ≤ 0.05) and PPUI (P ≤ 0.01) when compared to FCD. The MYH2 gene expression was downregulated in PPUI in comparison to CPUI (P ≤ 0.01) and FCD (P ≤ 0.05). The PKC gene expression was upregulated in PPUI in comparison to FCD and CPUI (P ≤ 0.05). The downregulation of MLCK4 and MYH2 gene expressions recorded in PPUI indicated the possibility of myometrial defects. The possibility of myometrial defects was also observed in CPUI, but to a lesser degree, suggesting other etiologies.

BKCa channels are involved in spontaneous and lipopolysaccharide-stimulated uterine contraction in late gestation mice†

The large-conductance, voltage-gated, calcium (Ca2+)-activated potassium channel (BKCa) is one of the most abundant potassium channels in the myometrium. Previous work conducted by our group has identified a link between inflammation, BKCa channels and excitability of myometrial smooth muscle cells. Here, we investigate the role of BKCa channels in spontaneous and lipopolysaccharide (LPS)-stimulated uterine contraction to gain a better understanding of the relationship between the BKCa channel and uterine contraction in basal and inflammatory states. Uteri of C57BL/6 J mice on gestational day 18.5 (GD18.5) were obtained and either fixed in formalin or used immediately for tension recording or isolation of primary myocytes for patch-clamp. Paraffin sections were used for immunofluorescenctdetection of BKCa and Toll-like receptor (TLR4). For tension recordings, LPS was administered to determine its effect on uterine contractions. Paxilline, a BKCa inhibitor, was used to dissect the role of BKCa in uterine contraction in basal and inflammatory states. Finally, patch-clamp recordings were performed to investigate the relationship between LPS, the BKCa channel and membrane currents in mouse myometrial smooth muscle cells (mMSMCs). We confirmed the expression of BKCa and TLR4 in the myometrium of GD18.5 mice and found that inhibiting BKCa channels with paxilline suppressed both spontaneous and LPS-stimulated uterine contractions. Furthermore, application of BKCa inhibitors (paxilline or iberiotoxin) after LPS inhibited BKCa channel activity in mMSMCs. Moreover, pretreatment with BKCa inhibitor or the TLR4 inhibitor suppressed LPS-activated BKCa currents. Our study demonstrates that BKCa channels are involved in both basal and LPS-stimulated uterine contraction in pregnant mice.

Decline in corepressor CNOT1 in the pregnant myometrium near term impairs progesterone receptor function and increases contractile gene expression

Progesterone (P4), acting via its nuclear receptor (PR), is critical for pregnancy maintenance by suppressing proinflammatory and contraction-associated protein (CAP)/contractile genes in the myometrium. P4/PR partially exerts these effects by tethering to NF-κB bound to their promot-ers, thereby decreasing NF-κB transcriptional activity. However, the underlying mechanisms whereby P4/PR interaction blocks proinflammatory and CAP gene expression are not fully understood. Herein, we characterized CCR-NOT transcription complex subunit 1 (CNOT1) as a corepressor that also interacts within the same chromatin complex as PR-B. In mouse myome-trium increased expression of CAP genes Oxtr and Cx43 at term coincided with a marked decline in expression and binding of CNOT1 to NF-κB-response elements within the Oxtr and Cx43 promoters. Increased CAP gene expression was accompanied by a pronounced decrease in enrichment of repressive histone marks and increase in enrichment of active histone marks to this genomic region. These changes in histone modification were associated with changes in expression of corresponding histone modifying enzymes. Myometrial tissues from P4-treated 18.5 dpc pregnant mice manifested increased Cnot1 expression at 18.5 dpc, compared to vehicle-treated controls. P4 treatment of PR-expressing hTERT-HM cells enhanced CNOT1 expression and its recruitment to PR bound NF-κB-response elements within the CX43 and OXTR promoters. Furthermore, knockdown of CNOT1 significantly increased expression of contractile genes. These novel findings suggest that decreased expression and DNA-binding of the P4/PR-regulated transcriptional corepressor CNOT1 near term and associated changes in histone modifications at the OXTR and CX43 promoters contribute to the induction of myometrial contractility leading to parturition.

HIF1A facilitates hypoxia-induced changes in H3K27ac modification to promote myometrial contractility

Prior studies have established that myometrial hypoxia during labor is pivotal in intensifying contractions, the alterations in gene expression and histone modifications in myometrial cells under hypoxia have yet to be documented. Here, hypoxia's enhancement of cellular contractility was confirmed, and RNA-seq identified 2,262 differentially expressed genes in human myometrial smooth muscle cells (hMSMCs) under hypoxia. Chromatin immunoprecipitation (ChIP), high-throughput chromosome conformation capture followed by ChIP (Hi-ChIP) were employed to investigate the epigenetic changes, specifically histone modifications (H3K27ac, H3K4me1, H3K27me3, and H3K4me3), in hMSMCs under hypoxia. We identified the enhancer and super-enhancer regions in hMSMCs and found HIF1A as the key mediator of these H3K27ac changes under hypoxia. Labor-associated genes regulated by HIF1A have been identified. Validation experiments on these genes such as CXCL8, RUNX1, IL-6, and PTGES3 demonstrated that HIF1A knockdown reduces their expression and associated H3K27ac modifications in peak regions of their promoters or enhancers. These findings indicate that HIF1A probably mediate changes in histone H3K27ac modifications to regulate myometrial cell contractions under hypoxia, providing potential therapeutic and intervention targets for disorders related to parturition.