Uterine Excitability and Ion Channels and Their Changes with Gestation and Hormonal Environment

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.

Mapping uterine calcium dynamics during the ovulatory cycle in live mice

Uterine contraction patterns vary during the ovulatory cycle and throughout pregnancy but prior measurements have produced limited and conflicting information on these patterns. We combined a virally delivered genetically encoded calcium reporter (GCaMP8m) and ultra-widefield imaging in live nonpregnant mice to characterize uterine calcium dynamics at organ scale throughout the estrous cycle. Prior to ovulation (proestrus and estrus) uterine excitations primarily initiated in a region near the oviduct, but after ovulation (metestrus and diestrus), excitations initiated at loci homogeneously distributed throughout the organ. The frequency of excitation events was lowest in proestrus and estrus, higher in metestrus and highest in diestrus. These results establish a platform for mapping uterine activity, and show that the question of whether there is an anatomically localized trigger for uterine excitations depends on the estrous cycle phase.

Phenanthroline relaxes uterine contractions induced by diverse contractile agents by decreasing cytosolic calcium concentration

Uterine contractions during labor and preterm labor are influenced by a complex interplay of factors, including hormones and inflammatory mediators. This complexity may contribute to the limited efficacy of current tocolytics for preterm labor, a significant challenge in obstetrics with 15 million cases annually and approximately 1 million resulting deaths worldwide. We have previously shown that the myometrium expresses bitter taste receptors (TAS2Rs) and that their activation leads to uterine relaxation. Here, we investigated whether the selective TAS2R5 agonist phenanthroline can induce relaxation across a spectrum of human uterine contractions and whether the underlying mechanism involves changes in intracellular Ca2+ signaling. We performed experiments using samples from pregnant women undergoing scheduled cesarean delivery, assessing responses to various inflammatory mediators and oxytocin with and without phenanthroline. Our results showed that phenanthroline concentration-dependently inhibited contractions induced by PGF2α, U46619, 5-HT, endothelin-1 and oxytocin. Furthermore, in hTERT-infected human myometrial cells exposed to uterotonics, phenanthroline effectively suppressed the increase in intracellular Ca2+ concentration induced by PGF2α, U46619, oxytocin, and endothelin-1. These results suggest that the selective TAS2R5 agonist may not only significantly reduce uterine contractions but also decrease intracellular Ca2+ levels. This study highlights the potential development of TAS2R5 agonists as a new class of uterine relaxants, providing a novel avenue for improving the management of preterm labor.

Investigating the role of CFTR in human and mouse myometrium

Background

Abnormal cystic fibrosis transmembrane conductance regulator (CFTR) function in cystic fibrosis (CF) has been linked to airway smooth muscle abnormalities including bronchial hyperresponsiveness. However, a role for CFTR in other types of smooth muscle, including myometrium, remains largely unexplored. As CF life expectancy and the number of pregnancies increases, there is a need for an understanding of the potential role of CFTR in myometrial function.

Methods

We investigated the role of CFTR in human and mouse myometrium. We used immunofluorescence to identify CFTR expression, and carried out contractility studies on spontaneously contracting term pregnant and non-pregnant mouse myometrium and term pregnant human myometrial biopsies from caesarean sections.

Results

CFTR was found to be expressed in term pregnant mouse myometrium. Inhibition of CFTR, with the selective inhibitor CFTRinh-172, significantly reduced contractility in pregnant mouse and human myometrium in a concentration-dependent manner (44.89 ± 11.02 term pregnant mouse, 9.23 ± 4.75 term-pregnant human; maximal effect at 60 μM expressed as a percentage of the pre-treatment control period). However, there was no effect of CFTRinh-172 in non-pregnant myometrium.

Conclusion

These results demonstrate decreased myometrial function when CFTR is inhibited, which may have implications on pregnancy and labour outcome and therapeutic decisions for labour in CF patients.

The physiological basis with uterine myometrium contractions from electro-mechanical/hormonal myofibril function to the term and preterm labor

Background

Most labor-related problems can be attributed to the uterine myometrium muscle, as this irritable tissue must suppress its irritability potential during pregnancy. Unfortunately, fewer studies have investigated the causes of this lack of suppression in preterm labor.

Methods

We conducted a scoping narrative review using three online databases (PubMed, Scopus, and Science Direct).

Results

The review focused on ion channel functions in the myometrium, including sodium channels [Na K-ATPase, Na-activated K channels (Slo2), voltage-gated (SCN) Na+, Na+ leaky channels, nonselective (NALCN) channels], potassium channels [KATP (Kir6) channels, voltage-dependent K channels (Kv4, Kv7, and Kv11), twin-pore domain K channels (TASK, TREK), inward rectifier Kir7.1, Ca2+-activated K+ channels with large (KCNMA1, Slo1), small (KCNN1-3), intermediate (KCNN4) conductance], and calcium channels [L-Type and T-type Ca2+ channels, calcium-activated chloride channels (CaCC)], as well as hyperpolarization-activated cation channels. These channels' functions are associated with hormonal effects such as oxytocin, estrogen/progesterone, and local prostaglandins.

Conclusion

Electromechanical/hormonal activity and environmental autocrine factors can serve as the primary practical basis for premature uterine contractions in term/preterm labor. Our findings highlight the significance of.1.the amplitude rate of hyperpolarization and the frequency of contractions,2.changes in the estrogen/progesterone ratio,3.Prostaglandins E/F involvement in initiating potential spikes and the increase of intracytoplasmic Ca2+.This narrative study highlights the range of hyperpolarization and the frequency of myometrium contractions as crucial factors. The synchronized complex progress of estrogen to progesterone ratio and prostaglandins plays a significant role in initiating potential spikes and increasing intracytoplasmic Ca2+, which further influences the contraction process during labor. Insights into myometrium physiology gained from this study may pave the way for much-needed new treatments to reduce problems associated with normal and preterm labor.

Multiple pregnancies, the myometrium and the role of mechanical factors in the timing of labour

Multiple pregnancy remains a relatively common occurrence, but it is associated with increased risks of adverse outcomes for the mother and her babies and presents unique challenges to healthcare providers. This review will briefly discuss multiple pregnancies, their aetiology and their problems, including preterm birth, before reviewing the processes leading to normal labour onset and how they may be different in a multiple pregnancy. The mechanisms by which mechanical factors i.e., uterine distension or 'stretch' contribute to uterine excitability and the timing of labour onset will be the major focus, and how over distention may pre-dispose multiple pregnancies to preterm birth. This includes current thinking around the role of mechano (stretch) sensitive ion channels in the myometrium and changes to other important regulators of excitability and contraction which have been identified from studies using in vitro and in vivo models of uterine stretch. Physiological stimuli arising from the fetus(es) and placenta(s) will also be discussed. In reviewing what we know about the myometrium in multiple pregnancy in humans, the focus will be on twin pregnancy as it is the most common type of multiple pregnancy and has been the most studied.

Close encounters with oxytocin

The purpose of this narrative review is to use a personal perspective to describe unanticipated and pivotal findings that drew the author into the study oxytocin. Oxytocin was originally described as a "female reproductive hormone." However, supporting reproduction is only one of a myriad of functions now attributed to oxytocin. Oxytocin promotes survival and resilience in both sexes and across the lifespan, especially in the context of stress or trauma and helps to explain the health benefits of relationships. Oxytocin works in the context of individual histories and in conjunction with other molecules, as well as the autonomic nervous system and immune factors. The chemical properties of oxytocin make it biologically active, but difficult to measure. As a deeper understanding of the biology of oxytocin is emerging, we may use knowledge of the properties of oxytocin to uncover adaptive strategies that protect and heal in the face of stress and adversity in both males and females.

Associations of Prenatal Agricultural Farm Work with Fetal Overgrowth and Pregnancy Complications in State of Arizona Birth Records

OBJECTIVE

The purpose of this study is to examine fetal growth outcomes from agricultural worker households.

METHODS

Using Arizona 2006 to 2013 birth certificates with parental occupation, we identified N = 623,185 live births by agricultural household status. Logistic regression models estimated adjusted odds ratios (aORs) for macrosomia (>4000 g), postterm birth (>41 weeks), low birth weight (<2500 g), preterm birth (<37 weeks), large for GA, small for GA, and 5-minute APGAR (<7).

RESULTS

Newborns of agricultural households (n = 6371) had a higher risk of macrosomia (aOR, 1.15; 95% CI, 1.05-1.26), large for GA (aOR, 1.12; 95% CI, 1.03-1.22), postterm birth (aOR, 1.20; 95% CI, 1.09-1.33), and low 5-minute APGAR (aOR, 1.39; 95% CI, 1.07-1.81), whereas low birth weight (aOR, 0.85; 95% CI, 0.76-0.96) and preterm birth (aOR, 0.82; 95% CI, 0.74-0.92) were inversely related.

CONCLUSIONS

Having an agriculture working parent increased the likelihood of fetal overgrowth and low APGAR.

The Pathophysiology of Labor Dystocia: Theme with Variations

Abnormally prolonged labor, or labor dystocia, is a common complication of parturition. It is the indication for about half of unplanned cesarean deliveries in low-risk nulliparous women. Reducing the rate of unplanned cesarean birth in the USA has been a public health priority over the last two decades with limited success. Labor dystocia is a complex disorder due to multiple causes with a common clinical outcome of slow cervical dilation and fetal descent. A better understanding of the pathophysiologic mechanisms of labor dystocia could lead to new clinical opportunities to increase the rate of normal vaginal delivery, reduce cesarean birth rates, and improve maternal and neonatal health. We conducted a literature review of the causes and pathophysiologic mechanisms of labor dystocia. We summarize known mechanisms supported by clinical and experimental data and newer hypotheses with less supporting evidence. We review recent data on uterine preparation for labor, uterine contractility, cervical preparation for labor, maternal obesity, cephalopelvic disproportion, fetal malposition, intrauterine infection, and maternal stress. We also describe current clinical approaches to preventing and managing labor dystocia. The variation in pathophysiologic causes of labor dystocia probably limits the utility of current general treatment options. However, treatments targeting specific underlying etiologies could be more effective. We found that the pathophysiologic basis of labor dystocia is under-researched, offering wide opportunities for translational investigation of individualized labor management, particularly regarding uterine metabolism and fetal position. More precise diagnostic tools and individualized therapies for labor dystocia might lead to better outcomes. We conclude that additional knowledge of parturition physiology coupled with rigorous clinical evaluation of novel biologically directed treatments could improve obstetric quality of care.

Pharmacological Interventions in Labor and Delivery

While there is not a wide range of pregnancy-specific drugs, there are some very specific high-risk areas of obstetric care for which unique pharmacological approaches have been established. In preterm birth, labor induction and augmentation, and the management of postpartum hemorrhage, these pharmacological approaches have become the bedrock in managing some of the most common and problematic areas of antenatal and intrapartum care. In this review, we summarize the existing established and emerging evidence that supports and broadens these pharmacological approaches to obstetric management and its impact on clinical practice. It is clear that existing therapeutics are limited. They have largely been developed from our knowledge of the physiology of the myometrium and act on hormonal receptors and their signaling pathways or on ion channels influencing excitability. Newer drugs in development are mostly refinements of these two approaches, but novel agents from plants and improved formulations are also discussed.

Effectiveness of Scutellaria baicalensis Georgi root in pregnancy-related diseases: A review

The root of Scutellaria baicalensis Georgi, also called Huangqin, is frequently used in traditional Chinese medicine. In ancient China, S. baicalensis root was used to clear heat, protect the fetus, and avoid a miscarriage for thousands of years. In modern times, pregnancy-related diseases can seriously affect maternal and fetal health, but few systematic studies have explored the mechanisms and potential targets of S. baicalensis root in the treatment of pregnancy-related diseases. Flavonoids (baicalein, wogonin and oroxylin A) and flavonoid glycosides (baicalin and wogonoside) are the main chemical components in the root of S. baicalensis. This study presents the current understanding of the major chemical components in the root of S. baicalensis, focusing on their traditional uses, potential therapeutic effects and ethnopharmacological relevance to pregnancy-related disorders. The mechanisms, potential targets and experimental models of S. baicalensis root for ameliorating pregnancy-related diseases, such as recurrent spontaneous abortion, preeclampsia, preterm birth, fetal growth restriction and gestational diabetes mellitus, are highlighted.

Modeling and experimental approaches for elucidating multi-scale uterine smooth muscle electro- and mechano-physiology: A review

The uterus provides protection and nourishment (via its blood supply) to a developing fetus, and contracts to deliver the baby at an appropriate time, thereby having a critical contribution to the life of every human. However, despite this vital role, it is an under-investigated organ, and gaps remain in our understanding of how contractions are initiated or coordinated. The uterus is a smooth muscle organ that undergoes variations in its contractile function in response to hormonal fluctuations, the extreme instance of this being during pregnancy and labor. Researchers typically use various approaches to studying this organ, such as experiments on uterine muscle cells, tissue samples, or the intact organ, or the employment of mathematical models to simulate the electrical, mechanical and ionic activity. The complexity exhibited in the coordinated contractions of the uterus remains a challenge to understand, requiring coordinated solutions from different research fields. This review investigates differences in the underlying physiology between human and common animal models utilized in experiments, and the experimental interventions and computational models used to assess uterine function. We look to a future of hybrid experimental interventions and modeling techniques that could be employed to improve the understanding of the mechanisms enabling the healthy function of the uterus.

HIF-1α is essential for the augmentation of myometrial contractility during labor†

Uterine contraction is crucial for a successful labor and the prevention of postpartum hemorrhage. It is enhanced by hypoxia; however, its underlying mechanisms are yet to be elucidated. In this study, transcriptomes revealed that hypoxia-inducible factor-1alpha was upregulated in laboring myometrial biopsies, while blockade of hypoxia-inducible factor-1alpha decreased the contractility of the myometrium and myocytes in vitro via small interfering RNA and the inhibitor, 2-methoxyestradiol. Chromatin immunoprecipitation sequencing revealed that hypoxia-inducible factor-1alpha directly binds to the genome of contraction-associated proteins: the promoter of Gja1 and Ptgs2, and the intron of Oxtr. Silencing the hypoxia-inducible factor-1alpha reduced the expression of Ptgs2, Gja1, and Oxtr. Furthermore, blockade of Gja1 or Ptgs2 led to a significant decrease in myometrial contractions in the hypoxic tissue model, whereas atosiban did not remarkably influence contractility. Our study demonstrates that hypoxia-inducible factor-1alpha is essential for promoting myometrial contractility under hypoxia by directly targeting Gja1 and Ptgs2, but not Oxtr. These findings help us to better understand the regulation of myometrial contractions under hypoxia and provide a promising strategy for labor management and postpartum hemorrhage treatment.

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.

Uterine slow wave: directionality and changes with imminent delivery

OBJECTIVE

The slow wave (SW) of the electrohysterogram (EHG) may contain relevant information on the electrophysiological condition of the uterus throughout pregnancy and labor. Our aim was to assess differences in the SW as regards the imminence of labor and the directionality of uterine myoelectrical activity.

APPROACH

The SW of the EHG was extracted from the signals of the Icelandic 16-electrode EHG database in the bandwidth [5, 30] mHz and its power, spectral content, complexity and synchronization between the horizontal (X) and vertical (Y) directions were characterized by the root mean square (RMS), dominant frequency (domF), sample entropy (SampEn) and maximum cross-correlation (CCmax) of the signals, respectively. Significant differences between parameters at time-to-delivery (TTD) ≤7 vs. >7 days and between the horizontal vs. vertical directions were assessed.

MAIN RESULTS

The SW power significantly increased in both directions as labor approached (TTD≤7d vs. >7d (mean±SD): x= 0.12±0.10 vs. 0.08±0.06mV; y= 0.12±0.09 vs. 0.08±0.05mV), as well as the dominant frequency in the horizontal direction (= 9.1±1.3 vs. 8.5±1.2mHz) and the synchronization between both directions (= 0.44±0.16 vs. 0.36±0.14). Furthermore, its complexity decreased in the vertical direction (= 6.13·10-2±8.7·10-3 vs. 6.50·10-2±8.3·10-3), suggesting a higher cell-to-cell electrical coupling. Whereas there were no differences between the SW features in both directions in the general population, statistically significant differences were obtained between them in individuals in many cases.

SIGNIFICANCE

Our results suggest that the SW of the EHG is related to bioelectrical events in the uterus and could provide objective information to clinicians in challenging obstetric scenarios.

In vivo multi-channel measurement of electrical activity of the non-pregnant rat uterus

In the uterus, the characteristics of smooth muscle contraction and the electrical activity that drives this contraction depends on hormonal cycles, and pregnancy status. Smooth muscle contraction is initiated by a change in membrane electrical potential, due to the flux of ions in and out of the intracellular space. Chains of action potentials throughout a section of muscle can result in coordinated contraction events. In this study, flexible printed circuit electrode arrays were applied to measure the bioelectric signals on the surface of a rat uterus in vivo. Variations in the electrical activity were quantified, including intermittent periods of activity and inactivity, which contain both slow-wave type activity (0.039 Hz ±0.017 Hz) and faster, spike-like activity (3.26 Hz ±0.27 Hz). The spike activity initiated at the ovarian end of the uterine horn, spreading towards the cervical end with a propagation velocity of 5.34 ± 2.32 mm [Formula: see text]. In conclusion, this pilot study outlines a new method of in vivo measurement of uterine electrical activity in rats. Clinical Relevance- Measurement of bioelectrical data using in vivo techniques provides insight into the electromechanical function of uterine smooth muscle, which could provide insights into what drives coordinated contraction in the uterus.

Oxytocin and love: Myths, metaphors and mysteries

Oxytocin is a peptide molecule with a multitude of physiological and behavioral functions. Based on its association with reproduction - including social bonding, sexual behavior, birth and maternal behavior - oxytocin also has been called “the love hormone.” This essay specifically examines association and parallels between oxytocin and love. However, many myths and gaps in knowledge remain concerning both. A few of these are described here and we hypothesize that the potential benefits of both love and oxytocin may be better understood in light of interactions with more ancient systems, including specifically vasopressin and the immune system. Oxytocin is anti-inflammatory and is associated with recently evolved, social solutions to a variety of challenges necessary for mammalian survival and reproduction. The shared functions of oxytocin and love have profound implications for health and longevity, including the prevention and treatment of excess inflammation and related disorders, especially those occurring in early life and during periods of chronic threat or disease.

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Oxytocin is a peptide molecule with functions that support a sense of safety, sociality, as well as survival and reproduction.

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Oxytocin is associated with social and neuroimmune solutions to chronic stress.

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The related, but more primitive, peptide vasopressin supports more individualistic survival strategies.

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Controversies and myths surround the properties of oxytocin and love.

Calcium-Activated Chloride Channels in Myometrial and Vascular Smooth Muscle

In smooth muscle tissues, calcium-activated chloride channels (CaCC) provide the major anionic channel. Opening of these channels leads to chloride efflux and depolarization of the myocyte membrane. In this way, activation of the channels by a rise of intracellular [Ca²⁺], from a variety of sources, produces increased excitability and can initiate action potentials and contraction or increased tone. We now have a good mechanistic understanding of how the channels are activated and regulated, due to identification of TMEM16A (ANO1) as the molecular entity of the channel, but key questions remain. In reviewing these channels and comparing two distinct smooth muscles, myometrial and vascular, we expose the differences that occur in their activation mechanisms, properties, and control. We find that the myometrium only expresses “classical,” Ca²⁺-activated, and voltage sensitive channels, whereas both tonic and phasic blood vessels express classical, and non-classical, cGMP-regulated CaCC, which are voltage insensitive. This translates to more complex activation and regulation in vascular smooth muscles, irrespective of whether they are tonic or phasic. We therefore tentatively conclude that although these channels are expressed and functionally important in all smooth muscles, they are probably not part of the mechanisms governing phasic activity. Recent knockdown studies have produced unexpected functional results, e.g. no effects on labour and delivery, and tone increasing in some but decreasing in other vascular beds, strongly suggesting that there is still much to be explored concerning CaCC in smooth muscle.

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.