Ion channels in the endometrium: regulation of endometrial receptivity and embryo implantation

Establishing life is a calcium-dependent TRiP: Transient receptor potential channels in reproduction

Calcium plays a key role in many different steps of the reproduction process, from germ cell maturation to placental development. However, the exact function and regulation of calcium throughout subsequent reproductive events remains rather enigmatic. Successful pregnancy requires the establishment of a complex dialogue between the implanting embryo and the endometrium. On the one hand, endometrial cell will undergo massive changes to support an implanting embryo, including stromal cell decidualization. On the other hand, trophoblast cells from the trophectoderm surrounding the inner cell mass will differentiate and acquire new functions such as hormone secretion, invasion and migration. The need for calcium in the different gestational processes implicates the presence of specialized ion channels to regulate calcium homeostasis. The superfamily of transient receptor potential (TRP) channels is a class of calcium permeable ion channels that is involved in the transformation of extracellular stimuli into the influx of calcium, inducing and coordinating underlying signaling pathways. Although the necessity of calcium throughout reproduction cannot be negated, the expression and functionality of TRP channels throughout gestation remains elusive. This review provides an overview of the current evidence regarding the expression and function of TRP channels in reproduction.

Role of the Na+/K+-ATPase ion pump in male reproduction and embryo development

Na⁺/K⁺-ATPase was one of the first ion pumps studied because of its importance in maintaining osmotic and ionic balances between intracellular and extracellular environments, through the exchange of three Na⁺ ions out and two K⁺ ions into a cell. This enzyme, which comprises two main subunits (α and β), with or without an auxiliary polypeptide (γ), can have specific biochemical properties depending on the expression of associated isoforms (α1β1 and/or α2β1) in the cell. In addition to the importance of Na⁺/K⁺-ATPase in ensuring the function of many tissues (e.g. brain, heart and kidney), in the reproductive tract this protein is essential for embryo development because of its roles in blastocoel formation and embryo hatching. In the context of male reproduction, the discovery of a very specific subunit (α4), apparently restricted to male germ cells, only expressed after puberty and able to influence sperm function (e.g. motility and capacitation), opened a remarkable field for further investigations regarding sperm biology. Therefore, the present review focuses on the importance of Na⁺/K⁺-ATPase on male reproduction and embryo development.

Adamts 1, 4, 5, 8, and 9 in Early Pregnancies

INTRODUCTION

The aim of this study was to immunohistochemically investigate the presence and localization of ADAMTS 1, 4, 5, 8 and 9 in decidual and chorionic tissues in first trimester pregnancy losses.

MATERIALS AND METHODS

This study was conducted with early pregnancy failure decidual and chorionic tissue samples from 36 pregnant women in the first trimester of pregnancy (ongoing pregnancies, missed miscarriages, anembryonic pregnancies) Results: It was observed that the decidual and chorionic tissue levels of ADAMTS 1, 4, 5, and 8 in ongoing pregnancies were more intensely expressed when compared with miscarriages. ADAMTS 1 expression was not observed in the anembryonic pregnancies, ADAMTS 4, 5, and 8 were less intensely expressed. ADAMTS 9 showed no staining in any group.

CONCLUSION

ADAMTS 1 may be necessary during the decidualization and implantation stages of early normal pregnancy.

MRP4 regulates ENaC-dependent CREB/COX-2/PGE2 signaling during embryo implantation

Multi-drug resistance protein 4 (MRP4), a potential chemotherapeutic target as well as a transporter for endogenous signaling molecules (e.g. prostaglandins), is known to be expressed in the endometrium, although its possible role(s) in the physiology of the endometrium remains unknown. Here, we show that MRP4 is upregulated at implantation window and localized to the basolateral membrane of the endometrial epithelium, the interface between the epithelium and stroma in mice. In human endometrial epithelial cells, MRP4 expression is upregulated by ENaC activation and the inhibition of MRP4 blocks ENaC-dependent PGE₂ release as well as phosphorylation of CREB. Intrauterine injection of MRP4 inhibitor in mice prior to implantation significantly downregulated implantation markers COX-2, Claudin4 and Lif, and reduced implantation rate. These results in together have revealed a previously undefined role of MRP4 in mediating ENaC-dependent CREB/COX-2/PGE₂ signaling essential to embryo implantation with implication in cancer progression as well.

A comparison of transcriptomic profiles in endometrium during window of implantation between women with unexplained recurrent implantation failure and recurrent miscarriage

The endometrium becomes receptive to the embryo only in the mid-luteal phase, but not in the other stages of the menstrual cycle. Endometrial factors play an important role in implantation. Women with recurrent miscarriage and recurrent implantation failure have both been reported to have altered expression of receptivity markers during the window of implantation. We aimed to compare the gene expression profiles of the endometrium in the window of implantation among women with unexplained recurrent implantation failures (RIF) and unexplained recurrent miscarriages (RM) by RNA sequencing (RNA-Seq). In total 20 patients (9 RIF and 11 RM) were recruited. In addition 4 fertile subjects were included as reference. Endometrium samples were precisely timed on the 7th day after luteal hormone surge (LH + 7). All the 24 endometrium samples were extracted for total RNA. The transcriptome was determined by RNA-Seq in the first 14 RNA samples (5 RIF, 6 RM and 3 fertile). Differentially expressed genes between RM and RIF were validated by quantitative real-time PCR (qPCR) in all 24 RNA samples (9 RIF, 11 RM and 4 fertile). Transcriptomic profiles of RM and RIF, but not control samples, were separated from each other by principle component analysis (PCA) and support vector machine (SVM). Complementary and coagulation cascades pathway was significantly up-regulated in RIF while down-regulated in RM. Differentially expressed genes C3, C4, C4BP, DAF, DF and SERPING1 in complement and coagulation cascade pathway between RM and RIF were further validated by qPCR. This study compared endometrial transcriptome among patients with RIF and RM in the window of implantation; it identified differential molecular pathways in endometrium between RIF and RM, which potentially affect the implantation process.

Upregulation of CFTR in patients with endometriosis and its involvement in NFκB-uPAR dependent cell migration

Endometriotic tissues exhibit high migration ability with the underlying mechanisms remain elusive. Our previous studies have demonstrated that cystic fibrosis transmembrane conductance regulator (CFTR) acts as a tumor suppressor regulating cell migration. In the present study, we explored whether CFTR plays a role in the development of human endometriosis. We found that both mRNA and protein expression levels of CFTR and urokinase-type plasminogen activator receptor (uPAR) were significantly increased in ectopic endometrial tissues from patients with endometriosis compared to normal endometrial tissues from women without endometriosis and positively correlated. In human endometrial Ishikawa (ISK) cells, overexpression of CFTR stimulated cell migration with upregulated NFκB p65 and uPAR. Knockdown of CFTR inhibited cell migration. Furthermore, inhibition of NFκB with its inhibitors (curcumin or Bay) significantly reduced the expression of uPAR and cell migration in the CFTR-overexpressing ISK cells. Collectively, the present results suggest that the CFTR-NFκB-uPAR signaling may contribute to the progression of human endometriosis, and indicate potential targets for diagnosis and treatment.

Survival and growth of C57BL/6J mice lacking the BK channel, Kcnma1: lower adult body weight occurs together with higher body fat

Big conductance potassium (BK) channels contribute to K⁺ flow and electrical behavior in many cell types. Mice made null for the gene (Kcnma1) producing the BK channel (BK^KO) exhibit numerous deficits in physiological functions. Breeding mice lacking a single allele of Kcnma1 (C57BL/6J background) had litter sizes of approximately eight pups. For the period of maternal care (P0–P21), pup deaths peaked at P1 with a second less severe interval of death peaking near P13. Early deaths were twice as likely during a 20‐month period of building construction compared with the quiescent period after cessation of construction. Births during construction were not consistent with Mendelian predictions indicating the likelihood of a specific disadvantage induced by this environmental stressor. Later BK^KO pup deaths (~P13) also were more numerous than Mendelian expectations. After weaning, weight gain was slower for BK^KO mice compared with wild‐type littermates: 5 g less for male BK^KO mice and 4 g less for female BK^KO mice. Body composition determined by quantitative magnetic resonance indicated a higher fat proportion for wild‐type female mice compared with males, as well as a higher hydration ratio. Both male and female BK^KO mice showed higher fat proportions than wild‐type, with female BK^KO mice exhibiting greater variation. Together, these results indicate that BK^KO mice suffered disadvantages that lead to prenatal and perinatal death. A metabolic difference likely related to glucose handling led to the smaller body size and distinct composition for BK^KO mice, suggesting a diversion of energy supplies from growth to fat storage.

Involvement of serum glucocorticoid-regulated kinase 1 in reproductive success

Reproductive processes, in particular events that concern pregnancy, are fine-tuned to produce offspring. Reproductive success is of prime importance for the survival of every species. The highly conserved and ubiquitously expressed serum glucocorticoid-regulated kinase 1 (SGK1) was first implicated in infertility as a regulator of a Na⁺ channel. In this review, we emphasize the prominent role of SGK1 during early pregnancy: 1) balancing uterine luminal fluid secretion and reabsorption to aid blastocyst adhesion and to import nutrients and energy; 2) transducing signals from the blastocyst to the receptive endometrium; 3) inducing multiple genes that are involved in uterine receptivity and trophoblast invasion; 4) regulating cell differentiation and antioxidant defenses at the fetomaternal interface; and 5) contributing to the proliferation and survival of decidual stromal cells. Accordingly, SGK1 coordinates many cellular processes that are crucial to reproductive activities. Aberrant expression or function of SGK1 results in implantation failure and early pregnancy loss. Further investigation of the molecular mechanisms of the function of SGK1 might provide novel diagnostic tools and interventions for reproductive complications.-Lou, Y., Hu, M., Mao, L., Zheng, Y., Jin, F. Involvement of serum glucocorticoid-regulated kinase 1 in reproductive success.

The Calcium-Sensing Receptor and the Reproductive System

Active placental transport of maternal serum calcium (Ca²⁺) to the offspring is pivotal for proper development of the fetal skeleton as well as various organ systems. Moreover, extracellular Ca²⁺ levels impact on distinct processes in mammalian reproduction. The calcium-sensing receptor (CaSR) translates changes in extracellular Ca²⁺-concentrations into cellular reactions. This review summarizes current knowledge on the expression of CaSR and its putative functions in reproductive organs. CaSR was detected in placental cells mediating materno-fetal Ca²⁺-transport such as the murine intraplacental yolk sac (IPYS) and the human syncytiotrophoblast. As shown in casr knock-out mice, ablation of CaSR downregulates transplacental Ca²⁺-transport. Receptor expression was reported in human and rat ovarian surface epithelial (ROSE) cells, where CaSR activation stimulates cell proliferation. In follicles of various species a role of CaSR activation in oocyte maturation was suggested. Based on studies in avian follicles, the activation of CaSR expressed in granulosa cells may support the survival of follicles after their selection. CaSR in rat and equine sperms was functionally linked to sperm motility and sperm capacitation. Implantation involves complex interactions between the blastocyst and the uterine epithelium. During early pregnancy, CaSR expression at the implantation site as well as in decidual cells indicates that CaSR is important for blastocyst implantation and decidualization in the rat uterus. Localization of CaSR in human extravillous cytotrophoblasts suggests a role of CaSR in placentation. Overall, evidence for functional involvement of CaSR in physiologic mammalian reproductive processes exists. Moreover, several studies reported altered expression of CaSR in cells of reproductive tissues under pathologic conditions. However, in many tissues we still lack knowledge on physiological ligands activating CaSR, CaSR-linked G-proteins, activated intracellular signaling pathway, and functional relevance of CaSR activation. Clearly, more work is required in the future to decode the complex physiologic and pathophysiologic relationship of CaSR and the mammalian reproductive system.

Epithelial sodium channel (ENaC) family: Phylogeny, structure-function, tissue distribution, and associated inherited diseases

The epithelial sodium channel (ENaC) is composed of three homologous subunits and allows the flow of Na(+) ions across high resistance epithelia, maintaining body salt and water homeostasis. ENaC dependent reabsorption of Na(+) in the kidney tubules regulates extracellular fluid (ECF) volume and blood pressure by modulating osmolarity. In multi-ciliated cells, ENaC is located in cilia and plays an essential role in the regulation of epithelial surface liquid volume necessary for cilial transport of mucus and gametes in the respiratory and reproductive tracts respectively. The subunits that form ENaC (named as alpha, beta, gamma and delta, encoded by genes SCNN1A, SCNN1B, SCNN1G, and SCNN1D) are members of the ENaC/Degenerin superfamily. The earliest appearance of ENaC orthologs is in the genomes of the most ancient vertebrate taxon, Cyclostomata (jawless vertebrates) including lampreys, followed by earliest representatives of Gnathostomata (jawed vertebrates) including cartilaginous sharks. Among Euteleostomi (bony vertebrates), Actinopterygii (ray finned-fishes) branch has lost ENaC genes. Yet, most animals in the Sarcopterygii (lobe-finned fish) branch including Tetrapoda, amphibians and amniotes (lizards, crocodiles, birds, and mammals), have four ENaC paralogs. We compared the sequences of ENaC orthologs from 20 species and established criteria for the identification of ENaC orthologs and paralogs, and their distinction from other members of the ENaC/Degenerin superfamily, especially ASIC family. Differences between ENaCs and ASICs are summarized in view of their physiological functions and tissue distributions. Structural motifs that are conserved throughout vertebrate ENaCs are highlighted. We also present a comparative overview of the genotype-phenotype relationships in inherited diseases associated with ENaC mutations, including multisystem pseudohypoaldosteronism (PHA1B), Liddle syndrome, cystic fibrosis-like disease and essential hypertension.

Expression and function of transient receptor potential channels in the female bovine reproductive tract

The epithelium lining the oviduct is critical for early reproductive events, many of which are mediated via intracellular calcium ions. Despite this, little is known about the regulation of calcium homeostasis in the oviductal epithelium. Epithelial transient receptor potential channels (TRPCs) modulate calcium flux in other tissues, and their expression and functional regulation have therefore been examined using the bovine oviduct as a model for the human. The effects of FSH, LH, 17β-estradiol, and progesterone on TRPCs expression and intracellular calcium flux were determined. Transient receptor potential channels 1, 2, 3, 4, and 6 were expressed in the bovine reproductive tract, and their gene expression varied throughout the estrous cycle. In more detailed studies undertaken on TRPC1 and 6, we show that protein expression varied through the estrus cycle; specifically, 17β-estradiol, FSH, and LH individually and in combination upregulated TRPC1 and 6 expression in cultured bovine oviduct epithelial cells although progesterone antagonized these effects. Functional studies showed changes in calcium mobilization in bovine oviduct epithelial cells were dependent on TRPCs. In conclusion, TRPC1, 2, 3, 4, and 6 are present in the epithelium lining the bovine oviduct, and TRPC1 and 6 vary through the estrous cycle suggesting an important role in early reproductive function.

Estrogen-dependent up-regulation of TRPA1 and TRPV1 receptor proteins in the rat endometrium

Transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1) receptors expressed predominantly in sensory nerves are activated by inflammatory stimuli and mediate inflammation and pain. Although they have been shown in the human endometrium, their regulation and function are unknown. Therefore, we investigated their estrogen- and progesterone-dependent alterations in the rat endometrium in comparison with the estrogen-regulated inflammatory cytokine macrophage migration inhibitory factor (MIF). Four-week-old (sexually immature) and four-month-old (sexually mature) female rats were treated with the non-selective estrogen receptor (ER) agonist diethylstilboestrol (DES), progesterone and their combination, or ovariectomized. RT-PCR and immunohistochemistry were performed to determine mRNA and protein expression levels respectively. Channel function was investigated with ratiometric [Ca(2+)]i measurement in cultured primary rat endometrial cells. Both TRP receptors and MIF were detected in the endometrium at mRNA and protein levels, and their localizations were similar. Immunostaining was observed in the immature epithelium, while stromal, glandular and epithelial positivity were observed in adults. Functionally active TRP receptor proteins were shown in endometrial cells by activation-induced calcium influx. In adults, Trpa1 and Trpv1 mRNA levels were significantly up-regulated after DES treatment. TRPA1 increased after every treatment, but TRPV1 remained unchanged following the combined treatment and ovariectomy. In immature rats, DES treatment resulted in increased mRNA expression of both channels and elevated TRPV1 immunopositivity. MIF expression changed in parallel with TRPA1/TRPV1 in most cases. DES up-regulated Trpa1, Trpv1 and Mif mRNA levels in endometrial cell cultures, but 17β-oestradiol having ERα-selective potency increased only the expression of Trpv1. We provide the first evidence for TRPA1/TRPV1 expression and their estrogen-induced up-regulation in the rat endometrium in correlation with the MIF.

Cytokines and Blastocyst Hatching

Blastocyst implantation into the uterine endometrium establishes early pregnancy. This event is regulated by blastocyst- and/or endometrium-derived molecular factors which include hormones, growth factors, cell adhesion molecules, cytokines and proteases. Their coordinated expression and function are critical for a viable pregnancy. A rate-limiting event that immediately precedes implantation is the hatching of blastocyst. Ironically, blastocyst hatching is tacitly linked to peri-implantation events, although it is a distinct developmental phenomenon. The exact molecular network regulating hatching is still unclear. A number of implantation-associated molecular factors are expressed in the pre-implanting blastocyst. Among others, cytokines, expressed by peri-implantation blastocysts, are thought to be important for hatching, making blastocysts implantation competent. Pro-inflammatory (IL-6, LIF, GM-CSF) and anti-inflammatory (IL-11, CSF-1) cytokines improve hatching rates; they modulate proteases (MMPs, tPAs, cathepsins and ISP1). However, functional involvement of cytokines and their specific mediation of hatching-associated proteases are unclear. There is a need to understand mechanistic roles of cytokines and proteases in blastocyst hatching. This review will assess the available knowledge on blastocyst-derived pro-inflammatory and anti-inflammatory cytokines and their role in potentially regulating blastocyst hatching. They have implications in our understanding of early embryonic loss and infertility in mammals, including humans.

Perinatal outcomes after fresh versus vitrified-warmed blastocyst transfer: retrospective analysis

OBJECTIVE

To investigate the possible effect of controlled ovarian stimulation on the perinatal outcomes of assisted reproductive technology pregnancies, by comparing the outcomes from fresh ET with frozen ET (FET) with blastocysts of similar quality.

DESIGN

Retrospective observational study.

SETTING

Private fertility center.

PATIENT(S)

Seven hundred eighty-four fresh transfers and 382 vitrified-warmed double blastocyst transfers.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Miscarriage, perinatal mortality, preterm delivery, live birth, live-birth weights, and gestational age of live births.

RESULT(S)

FET resulted in higher implantation rates (51.5% vs. 40.6%), higher live-birth rates per transfer (56.8% vs. 44.3%), and lower ectopic pregnancy rates (0.32% vs. 1.80%). FET pregnancies also had higher day 14 βhCG levels per implantation (148.2 vs. 176.2 IU/L) and higher infant birth weights (singletons Δ109.4 g, twins Δ124 g). Female infants benefitted the most in terms of birth weight. Miscarriage, premature delivery, perinatal morbidity, and live birth per pregnancy were all nonsignificantly different between fresh ET and FET.

CONCLUSION(S)

Clinically significant differences between the peri-implantation and perinatal outcomes of fresh ET and FET suggest better endometrial receptivity and placentation in FET cycles.

Functional expression of transient receptor potential channels in human endometrial stromal cells during the luteal phase of the menstrual cycle

STUDY QUESTION

Are members of the transient receptor potential (TRP) channel superfamily functionally expressed in the human endometrial stroma?

SUMMARY ANSWER

The Ca(2+)-permeable ion channels TRPV2, TRPV4, TRPC6 and TRPM7 are functionally expressed in primary endometrial stromal cells.

WHAT IS KNOWN ALREADY

Intercellular communication between epithelial and stromal endometrial cells is required to initiate decidualization, a prerequisite for successful implantation. TRP channels are possible candidates as signal transducers involved in cell-cell communication, but no fingerprint is available of the functional distribution of TRP channels in the human endometrium during the luteal phase of the menstrual cycle.

STUDY DESIGN, SIZE, DURATION

Endometrial biopsy samples (previously frozen) from patients of reproductive age with regular menstrual cycles, who were undergoing diagnostic laparoscopic surgery for pain and/or infertility, were analysed. Samples were obtained from the menstrual (Days 1-5, n = 3), follicular (Days 6-14, n = 6), early luteal (Days 15-20, n = 5) and late luteal (Days 21-28, n = 5) phases. In addition, a total of 13 patient samples taken during the luteal phase were used to set up primary cell cultures for further experiments.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Quantitative real-time PCR (qRT-PCR), immunocytochemistry, Fura2-based Ca(2+)-microfluorimetry and whole-cell patch clamp experiments were performed to study the functional expression pattern of TRP channels. Specific pharmacological agents, such as Δ(9)-tetrahydrocannabinol, GSK1016790A and 1-oleoyl-2-acetyl-glycerol, were used to functionally assess the expression of TRPV2, TRPV4 and TRPC6, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

Expression of TRPV2, TRPV4, TRPC1, TRPC4, TRPC6, TRPM4 and TRPM7 was detected at the mRNA level in endometrial biopsies (n = 19) and in primary endometrial stromal cell cultures obtained from patients during the luteal phase (n = 5) of the menstrual cycle. Messenger RNA levels of TRPV2, TRPC4 and TRPC6 were significantly increased (P < 0.01) in the late luteal phase compared with the early luteal phase. Immunocytochemistry experiments showed a positive staining for TRPV2, TRPV4, TRPC6 and TRPM7 in the plasma membrane and in the cytoplasm of primary endometrial stromal cells. Ca(2+)-microfluorimetry revealed significant increases (P < 0.001) in intracellular Ca(2+) levels when stromal cells were incubated with specific activators of TRPV2, TRPV4 and TRPC6. Further functional characterization was performed using whole-cell patch clamp experiments. Taken together, these data provide evidence for the functional activity of TRPV2, TRPV4, TRPC6 and TRPM7 channels in primary stromal cell cultures.

LIMITATIONS, REASONS FOR CAUTION

Although mRNA levels are detected for TRPV6, TRPC1, TRPC4 and TRPM4, the limited supply of specific antibodies and lack of selective pharmacological agents restricted any additional analysis of these ion channels.

WIDER IMPLICATIONS OF THE FINDINGS

Embryo implantation is a dynamic developmental process that integrates many signalling molecules into a precisely orchestrated programme. Our findings identified certain members of the TRP superfamily as candidate sensors in the epithelial-stromal crosstalk. These results are very helpful to unravel the signalling cascade required for successful embryo implantation. In addition, this knowledge could lead to new strategies to correct implantation failure and facilitate the development of novel non-hormonal contraceptives.

STUDY FUNDING/ COMPETING INTERESTS

This work was supported by grants from the Research Foundation-Flanders (G.0856.13N to J.V.), the Research Council of the KU Leuven (OT/13/113 to J.V. and T.D. and PF-TRPLe to T.V.) and by the Planckaert-De Waele fund (to J.V.). K.D.C. and K.H. are funded by the FWO Belgium. None of the authors have a conflict of interest.

Neurodevelopment and phenotype-modulating functions of S100B protein: a pilot study

The importance of certain neurotrophic proteins found in maternal blood and milk for breastfed infants has remained ambiguous. This study was conducted to present evidence of the impact of an induced deficit of active S100B protein on neonate development. Newborn mice from two groups of mothers, immunized or sham-immunized against S100B, were subjected to various behavioral tests, and the development of their morphological characteristics was recorded from birth until weaning. Morphological problems, including weight gain and fur coating, a delay in the maturation of neurobehavioral systems and a deficit in neuromotor functions, including visual abilities, somato-sensory and posture reactions, muscular strength, locomotion, and fear/orienting processes, were observed in pups of immunized mothers. The S100B protein of external or internal origin in infants may be considered to be a specific factor that determines neuro- and morphological development and a risk-avoidance ('homeward-bent' or fearful) phenotype. The suppression of activity of the S100B protein results in a slower neonatal development and the formation of a risk-tolerant (fearless) phenotype of the offspring. This study thus considers the mechanism of neuroplastic regulation on the extent of sensation-seeking or risk-taking (homeless-like or fearless) and sensation- or risk-avoidance (home-bound or fearful) features in individual phenotypes.

Regulation of miR-101/miR-199a-3p by the epithelial sodium channel during embryo implantation: involvement of CREB phosphorylation

In our previous study, we have demonstrated that the epithelial sodium channel (ENaC) mediates the embryo-derived signals leading to the activation of CREB and upregulation of cyclooxygenase type 2 (COX2) required for embryo implantation. This study aims to investigate whether microRNAs (miRNAs) are involved in the ENaC-induced upregulation of COX2 during embryo implantation. The results show that the levels of miR-101 and miR-199a-3p, two COX2 targeting miRNAs, are reduced by ENaC activation, and increased by ENaC inhibition or knock-down of ENaC subunit (ENaCα) in human endometrial surface epithelial (HES) cells or in mouse uteri during implantation. Phosphorylation of CREB is induced by the activation of ENaC, and blocked by ENaC inhibition or knockdown in HES cells. Knockdown of ENaCα or CREB in HES cells or in mouse uterus in vivo results in increases in miR-101 and miR-199a-3p, accompanied with decreases in COX2 protein levels and reduction in implantation rate. The downregulation of COX2 caused by knockdown of ENaC or CREB can be recovered by the inhibitors of miR-101 or miR-199a-3p in HES cells. These results reveal a novel molecular mechanism modulating COX2 expression during embryo implantation via ENaC-dependent CREB activation and COX2-targeting miRNAs.