A Review of Mechanisms of Implantation

Fractalkine enhances endometrial receptivity and activates iron transport towards trophoblast cells in an in vitro co-culture system of HEC-1A and JEG-3 cells

Endometrium receptivity and successful implantation require a complex network of regulatory factors whom production is strictly controlled especially at the implantation window. Many regulators like steroid hormones, prostaglandins, cytokines, extracellular matrix proteins and downstream cell signalling pathways are involved in the process of embryo-endometrium interaction. Our work reveals the effect of fractalkine (FKN), a unique chemokine on progesterone receptor, SOX-17 and NRF2 expressions in HEC-1A endometrial cell line. FKN activates fractalkine receptor signalling and the expression of SOX-17 through progesterone receptor in HEC-1A endometrial cells, and as a consequence it increases endometrial receptivity. Fractalkine also activates the NRF2-Keap-1 signal transduction pathway regulating the IL-6 and IL-1β cytokine productions, which increase endometrial receptivity, as well. The NRF2 transcription factor increases the expression of the iron exporter ferroportin in HEC-1A cells activating iron release towards JEG-3 trophoblast cells. The iron measurements show that iron content of endometrial cells decreases while heme concentration increases at FKN treatment. At the same time, the trophoblast cells show increased iron uptake and total iron content. Based on our results it seems that FKN enhances the establishment of endometrial receptivity and meanwhile it regulates the iron homeostasis of endometrium contributing to the iron availability of the trophoblast cells and the embryo.

Cell Specific Expression of Vascular Endothelial Growth Factor Receptor-2 (Flk-1/KDR) in Developing Mice Embryo and Supporting Maternal Uterine Tissue during Early Gestation (D4-D7)

Background

Vascular endothelial growth factor (VEGF) and the corresponding receptors play key role in vasculogenesis and angiogenesis processes. VEGF is one of the prime candidates in regulating embryo implantation by increasing vascular permeability. VEGF receptor-2, also called Flk-1/KDR, is one of the prime receptor which is actively involved in the execution of various functions of VEGF. However, precise role of this receptor during early gestation period is yet to be addressed. In the present study, expression of Flk-1/KDR during peri-implantation mice uterus as well as fetal-maternal tissues from day 4-day 7 (D4-D7) of gestation was investigated.

Materials and Methods

In this experimental study, localization of Flk-1/KDR was investigated by immunohistochemistry and immunofluorescence techniques, in paraffin embedded tissue sections. Flk-1/KDR protein and mRNA expressions were investigated by western blotting and quantitative reverse transcription polymerase chain reaction (qRT-PCR), respectively. Effects of ovarian steroids on expression of Flk-1/KDR were also assessed by estrogen and progesterone antagonist treatment.

Results

Uterine tissue on D4 showed strong expression of Flk-1/KDR in luminal and uterine glandular epithelium. On D5 and D6, differential expression of Flk-1/KDR was evidenced in certain cell types of the embryo, maternal tissues and fetal-maternal interface with varied intensity. Flk-1/KDR was specifically expressed in the ectoplacental cone (EPC) and various cells of the embryo on D7. Flk-1/KDR expression was not evidenced in the estradiol-17β (E2) and progesterone (P4) antagonist treated uterus. Western blotting result revealed presence of Flk-1/KDR protein in the all gestation days, except antagonist treated uterus. qRT-PCR analysis showed significant increase of Flk-1/KDR mRNA transcript on D6 and D7.

Conclusion

Spatial-temporal expression of Flk-1/KDR during peri-implntation period in mice uterus especially in the feto-maternal interface was observed. This spatio-temporal specificity as well as increased expression of Flk-1/KDR could be one of the determinants for establishment of fetal-maternal cross talk during the critical period of development.

Genetic and epigenetic changes in the eutopic endometrium of women with endometriosis: association with decreased endometrial αvβ3 integrin expression

About 40% of women with infertility and 70% of women with pelvic pain suffer from endometriosis. The pregnancy rate in women undergoing IVF with low endometrial integrin αvβ3 (LEI) expression is significantly lower compared to the women with high endometrial integrin αvβ3 (HEI). Mid-secretory eutopic endometrial biopsies were obtained from healthy controls (C; n=3), and women with HEI (n=4) and LEI (n=4) and endometriosis. Changes in gene expression were assessed using human gene arrays and DNA methylation data were derived using 385 K Two-Array Promoter Arrays. Transcriptional analysis revealed that LEI and C groups clustered separately with 396 differentially expressed genes (DEGs) (P<0.01: 275 up and 121 down) demonstrating that transcriptional and epigenetic changes are distinct in the LEI eutopic endometrium compared to the C and HEI group. In contrast, HEI vs C and HEI vs LEI comparisons only identified 83 and 45 DEGs, respectively. The methylation promoter array identified 1304 differentially methylated regions in the LEI vs C comparison. The overlap of gene and methylation array data identified 14 epigenetically dysregulated genes and quantitative RT-PCR analysis validated the transcriptomic findings. The analysis also revealed that aryl hydrocarbon receptor (AHR) was hypomethylated and significantly overexpressed in LEI samples compared to C. Further analysis validated that AHR transcript and protein expression are significantly (P<0.05) increased in LEI women compared to C. The increase in AHR, together with the altered methylation status of the 14 additional genes, may provide a diagnostic tool to identify the subset of women who have endometriosis-associated infertility.

Mechanistic Drivers of Müllerian Duct Development and Differentiation Into the Oviduct

The conduits of life; the animal oviducts and human fallopian tubes are of paramount importance for reproduction in amniotes. They connect the ovary with the uterus and are essential for fertility. They provide the appropriate environment for gamete maintenance, fertilization and preimplantation embryonic development. However, serious pathologies, such as ectopic pregnancy, malignancy and severe infections, occur in the oviducts. They can have drastic effects on fertility, and some are life-threatening. Despite the crucial importance of the oviducts in life, relatively little is known about the molecular drivers underpinning the embryonic development of their precursor structures, the Müllerian ducts, and their successive differentiation and maturation. The Müllerian ducts are simple rudimentary tubes comprised of an epithelial lumen surrounded by a mesenchymal layer. They differentiate into most of the adult female reproductive tract (FRT). The earliest sign of Müllerian duct formation is the thickening of the anterior mesonephric coelomic epithelium to form a placode of two distinct progenitor cells. It is proposed that one subset of progenitor cells undergoes partial epithelial-mesenchymal transition (pEMT), differentiating into immature Müllerian luminal cells, and another subset undergoes complete EMT to become Müllerian mesenchymal cells. These cells invaginate and proliferate forming the Müllerian ducts. Subsequently, pEMT would be reversed to generate differentiated epithelial cells lining the fully formed Müllerian lumen. The anterior Müllerian epithelial cells further specialize into the oviduct epithelial subtypes. This review highlights the key established molecular and genetic determinants of the processes involved in Müllerian duct development and the differentiation of its upper segment into oviducts. Furthermore, an extensive genome-wide survey of mouse knockout lines displaying Müllerian or oviduct phenotypes was undertaken. In addition to widely established genetic determinants of Müllerian duct development, our search has identified surprising associations between loss-of-function of several genes and high-penetrance abnormalities in the Müllerian duct and/or oviducts. Remarkably, these associations have not been investigated in any detail. Finally, we discuss future directions for research on Müllerian duct development and oviducts.

Extracellular vesicles and female reproduction

Extracellular vesicles (EVs) are nano-sized membrane bound complexes that have been identified as a mean for intercellular communication between cells and tissues both in physiological and pathological conditions. These vesicles contain numerous molecules involved in signal transduction including microRNAs, mRNAs, DNA, proteins, lipids, and cytokines and can affect the behavior of recipient cells. Female reproduction is dependent on extremely fine-tuned endocrine regulation, and EVs may represent an added layer that contributes to this regulation. This narrative review article provides an update on the research of the role of EVs in female reproduction including folliculogenesis, fertilization, embryo quality, and implantation. We also highlight potential pitfalls in typical EV studies and discuss gaps in the current literature.

Expression of E-Cadherin in Pig-Tailed Monkey (Macaca nemestrina) Endometrium after Controlled Ovarian Hyperstimulation

An increase of steroid hormones in controlled ovarian hyperstimulation (COH) procedures is reducing the success rate in assisted reproductive technology (ART), and this includes the pregnancy rate and/or implantation rate. Research has found that the decrease in the success rate occurred due to the decreased expression of the protein that is needed to prepare the endometrium so that the embryo could attach. The aim of the study was to analyse the changes in E-chaderin expression due to COH and its relations with increased level of steroid hormones as one of the proteins in the endometrium. There were 13 samples of stored biological tissue from Macaca nemestrina endometrial tissue; came from one group of natural cycles as the control group (n = 4) and three groups of stimulated cycles. The first stimulated cycle group was injected by a 30 IU dose of rFSH (n = 2). The second stimulated cycle group was injected by a 50 IU dose of rFSH (n = 4). The third stimulated cycle group was injected by a 70 IU dose of rFSH (n = 3). The expression of E-cadherin was measured by the immunohistochemistry (IHC) technique. Estradiol (E2) and progesterone (P4) levels were assessed using ELISA and have already been done. The IHC staining expression of E-cadherin was found in the cytoplasm of glandular epithelium. Immunostaining measurement used the H_SCORE. We found that the expression of E-cadherin within the group was not significantly different (p value: 0.178). Similarly, both the correlation between the estradiol level with E-cadherin and the correlation between the progesterone level with E-cadherin were not significantly different (p value: 0.872 and p value: 0.836). The conclusion is that the level of E-Cadherin expression in the endometrium that were taken in themiddle secretion phase not affected by the dose regimen that given. In addition, the level of expression is not influenced by the increase of serum E2 and P4 levels.

Effect of Irisin on LIF and integrin αvβ3 in rats of implantation failure

OBJECTIVE

The aim of this study is to investigate the effect of irisin on leukemia inhibitory factor (LIF) and integrin αvβ3 in implantation failure uterus.

METHODS

Early pregnant rats were randomly divided into normal group (N), mifepristone treated group (M), irisin group (I) and progestin group (P). The implantation failure model was established using mifepristone. Second, we evaluated the average number of embryos and detected the expression of LIF and integrin αvβ3 protein and mRNA in endometrium.

RESULTS

Compared with group M, the average number of embryos was significantly higher in group N, P and I, the expression of LIF and integrin αvβ3 in endometrium was significantly higher in group N, P and I.

CONCLUSION

Irisin could improve the poor receptive state of endometrium by promoting LIF and integrin αvβ3 secretion to improve blastocyst implantation in rats of implantation failure.

Methods for Studying Endometrial Pathology and the Potential of Atomic Force Microscopy in the Research of Endometrium

The endometrium lines the uterine cavity, enables implantation of the embryo, and provides an environment for its development and growth. Numerous methods, including microscopic and immunoenzymatic techniques, have been used to study the properties of the cells and tissue of the endometrium to understand changes during, e.g., the menstrual cycle or implantation. Taking into account the existing state of knowledge on the endometrium and the research carried out using other tissues, it can be concluded that the mechanical properties of the tissue and its cells are crucial for their proper functioning. This review intends to emphasize the potential of atomic force microscopy (AFM) in the research of endometrium properties. AFM enables imaging of tissues or single cells, roughness analysis, and determination of the mechanical properties (Young’s modulus) of single cells or tissues, or their adhesion. AFM has been previously shown to be useful to derive force maps. Combining the information regarding cell mechanics with the alternations of cell morphology or gene/protein expression provides deeper insight into the uterine pathology. The determination of the elastic modulus of cells in pathological states, such as cancer, has been proved to be useful in diagnostics.

Maternal DNA Methylation During Pregnancy: a Review

Multiple environmental, behavioral, and hereditary factors affect pregnancy. Recent studies suggest that epigenetic modifications, such as DNA methylation (DNAm), affect both maternal and fetal health during the period of gestation. Some of the pregnancy-related risk factors can influence maternal DNAm, thus predisposing both the mother and the neonate to clinical adversities with long-lasting consequences. DNAm alterations in the promoter and enhancer regions modulate gene expression changes which play vital physiological role. In this review, we have discussed the recent advances in our understanding of maternal DNA methylation changes during pregnancy and its associated complications such as gestational diabetes and anemia, adverse pregnancy outcomes like preterm birth, and preeclampsia. We have also highlighted some major gaps and limitations in the area which if addressed might improve our understanding of pregnancy and its associated adverse clinical conditions, ultimately leading to healthy pregnancies and reduction of public health burden.

SWI/SNF inactivation in the endometrial epithelium leads to loss of epithelial integrity

Although ARID1A mutations are a hallmark feature, mutations in other SWI/SNF (SWItch/Sucrose Non-Fermentable) chromatin remodeling subunits are also observed in endometrial neoplasms. Here, we interrogated the roles of Brahma/SWI2-related gene 1 (BRG1, SMARCA4), the SWI/SNF catalytic subunit, in the endometrial epithelium. BRG1 loss affects more than one-third of all active genes and highly overlaps with the ARID1A gene regulatory network. Chromatin immunoprecipitation studies revealed widespread subunit-specific differences in transcriptional regulation, as BRG1 promoter interactions are associated with gene activation, while ARID1A binding is associated with gene repression. However, we identified a physiologically relevant subset of BRG1 and ARID1A co-regulated epithelial identity genes. Mice were genetically engineered to inactivate BRG1 specifically in the endometrial epithelium. Endometrial glands were observed embedded in uterine myometrium, indicating adenomyosis-like phenotypes. Molecular similarities were observed between BRG1 and ARID1A mutant endometrial cells in vivo, including loss of epithelial cell adhesion and junction genes. Collectively, these studies illustrate overlapping contributions of multiple SWI/SNF subunit mutations in the translocation of endometrium to distal sites, with loss of cell integrity being a common feature in SWI/SNF mutant endometrial epithelia.

Extracellular vesicles: Mediators of embryo-maternal crosstalk during pregnancy and a new weapon to fight against infertility

In modern-day life, infertility is one of the major issues that can affect an individual, both physically and psychologically. Several anatomical, physiological, and genetic factors might contribute to the infertility of an individual. Intercellular communication between trophectoderm and endometrial epithelium triggers successful embryo implantation and thereby establishes pregnancy. Recent studies demonstrate that Extracellular vesicles (EVs) are emerging as one of the crucial components that are involved in embryo-maternal communication and promote pregnancy. Membrane-bound EVs release several secreted factors within the uterine fluid, which mediates an intermolecular transfer of EVs' cargos between blastocysts and endometrium. Emerging evidences indicate that several events like imbalance in the release of endometrial or placenta-derived EVs (exosomes/MVs), uptake of their content, failure of embryo selection might lead to implantation failure. Here in this review, we have discussed the current knowledge of the involvement of EVs in maternal-fetal communications during implantation and also highlighted the EVs' rejuvenating ability to overcome infertility-related issues. We also discussed the alteration of the EVs' cargo in different pathological conditions that lead to infertility. Therefore, this review would give a better understanding of EVs' contribution in successful embryo implantation, which could help in the development of new diagnostic tools and cell-free biologics to improve the in vivo reproductive process and to treat infertility by restoring normal reproductive functions.

Role of neurotrophins in pregnancy and offspring brain development

Neurotrophins are a family of functionally and structurally related proteins which play a key role in the survival, development, and function of neurons in both the central and peripheral nervous systems. Brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4) are the family members of neurotrophins. Neurotrophins play a crucial role in influencing the development of the brain and learning and memory processes. Studies demonstrate that they also play crucial role in influencing reproductive and immune systems. Neurotrophins have been shown to influence various processes in the mother, placenta, and fetus during pregnancy. Development and maturation of feto-placental unit and the fetal growth trajectories are influenced by neurotrophins. In addition to neurotrophins, neuropeptides like neuropeptide Y also play a crucial role during various processes of pregnancy and during fetal brain development. Neurotrophins have also been shown to have a cross talk with various angiogenic factors and influence placental development. Alterations in the levels of neurotrophins and neuropeptides lead to placental pathologies resulting in various pregnancy complications like preeclampsia, intrauterine growth restriction and preterm births. Studies in animals have reported low levels of maternal micronutrients like folic acid, vitamin B₁₂ and omega-3 fatty acids influence brain neurotrophins resulting in impaired cognitive functioning in the offspring. Maternal nutrition is also known to affect the expression of neuropeptides. It is essential to understand the role of various neurotrophins across various stages of pregnancy and its relationship with neurodevelopmental outcomes in children. This will lead to early prediction of poor neurodevelopmental outcomes. The present review describes evidence describing the role of neurotrophins in determining pregnancy outcome and altered neurodevelopment in the offspring. The possible mechanism through which maternal nutrition influences neurotrophins and neuropeptides to regulate offspring brain development and function is also discussed.

Improving reproductive outcomes of intrauterine insemination: Does endometrial scratch injury help? A randomised controlled trial

OBJECTIVE(S)

Current evidence suggests that endometrial injury improves clinical pregnancy rate while having no effect on miscarriages in women undergoing IVF/ICSI. However, there is no substantial evidence to advocate the use of endometrial injury to benefit the outcomes of IUI treatment. Additionally, there is no clear consensus about the ideal timing, underlying mechanism and optimum intensity of endometrial injury required. The study examines the effect of intentional endometrial injury/scratch in the early proliferative phase of stimulated cycle on reproductive outcomes (clinical and ongoing pregnancy rates and miscarriage occurrence) of intra-uterine insemination treatment (IUI).

STUDY DESIGN, SIZE, DURATION

This prospective, randomized control interventional study was conducted in a tertiary level teaching institution from April 2018 to February 2020. 150 eligible couples requiring IUI treatment who agreed to participate were randomly allocated on 1:1 basis to either control or intervention group. The trial participants received up to 3 cycles ovulation induction with clomiphene citrate and intra-uterine insemination. In addition, women in intervention group were subjected to endometrial scratch injury on day 6-7 of their stimulated cycle. 154 cycles in control arm and 128 cycles in intervention group were analyzed for clinical pregnancy, miscarriages and pain experienced by the women during endometrial scratch injury using the statistical package SPSS (version 21).

RESULT

Similar cumulative clinical pregnancy rates (12.5% Vs 13.6%, RR 1.21, 95% CI 0.44-3.37, p = 0.713), biochemical pregnancy rates (17.1% vs 22.9%, RR 1.43, CI 0.59-3.47, p = 0.421) and ongoing pregnancy rates (10.93% Vs 11.47%, RR 1.05, CI 0.35-3.21, p = 924) were observed in control and intervention arms. Likewise, the relative risk of miscarriage occurrence in the intervention arm was 1.32 (95% CI 0.39-4.32, p = 1.000) which was not statistically different from control group. Mean pain score of 6.93 on numerical pain rating scale was experienced by women whilst having endometrial scratch injury.

CONCLUSIONS

There is insufficient evidence to defend the use of endometrial scratch injury in intra-uterine insemination treatment, as it is moderately painful and have uncertain beneficial influence on reproductive outcomes.

Chlorpyrifos effects on integrin alpha v and beta 3 in implantation window phase

Chlorpyrifos (CPF), as a worldwide pesticide, can effect on the integrins αv and β3 which play a main role in the implantation window. Therefore, the aim of this study was to consider CPF effects on integrin alpha v and beta 3 in implantation window phase. Thirty female NMRI mice were separated into groups of CPF, sham, and control. After 6 weeks, each group was mated, and on the 5th day of gestation, all mice were euthanized. Estradiol and progesterone levels were detected by the enzyme-linked immunosorbent assay (ELISA) test; two subunits of integrins (αv and β3) genes and proteins of endometrium were analyzed by real-time polymerase chain reaction (RT-PCR) and immunohistochemistry method, respectively. Fibrosis of the liver which evaluated by Masson's trichrome stain was increased in the CPF group compared with the others. But estradiol and progesterone levels were significantly decreased in CPF groups. Based on the findings, the proportion of genes' expressions of integrin subunits declined by the effect of CPF, while there was not any notable consequence on mice in the sham group. Alpha v and beta 3 integrin proteins expressed in all groups, but the concentration of these proteins in CPF groups was lower than in other groups. This study has shown that the decline of estradiol and progesterone downregulates the expression of αv and β3 integrins which were influenced by CPF exposure. Changing these patterns of proteins could have numerous influences on unsuccessful implantation. Therefore, this experimental study recommends that inclusive consideration of the effects of insecticides may be crucial to women's unrecognized cause of infertility.

Essential Role of Complement in Pregnancy: From Implantation to Parturition and Beyond

The complement cascade was identified over 100 years ago, yet investigation of its role in pregnancy remains an area of intense research. Complement inhibitors at the maternal-fetal interface prevent inappropriate complement activation to protect the fetus. However, this versatile proteolytic cascade also favorably influences numerous stages of pregnancy, including implantation, fetal development, and labor. Inappropriate complement activation in pregnancy can have adverse lifelong sequelae for both mother and child. This review summarizes the current understanding of complement activation during all stages of pregnancy. In addition, consequences of complement dysregulation during adverse pregnancy outcomes from miscarriage, preeclampsia, and pre-term birth are examined. Finally, future research directions into complement activation during pregnancy are considered.

Effect of single-dose depot leuprolide acetate on embryonal implantation: an experimental rat model

The objective of this article is to investigate the effect of single-dose depot leuprolide acetate in rat embryonal implantation and its association with glycodelin A, mucin-1 and leukemia inhibitory factor expression. Thirty-two pregnant Wistar Albino rats were divided into four equal groups: untreated control rats in group I (n = 8) and untreated pregnant rats in group II (n = 8) were injected intraperitoneally with single dose of normal saline, treated rats in group III (n = 8) and treated pregnant rats in group IV (n = 8) were given single 1 mg/kg subcutaneous injection of leuprolide acetate at day 8 of pregnancy. The dams were sacrificed on the 15th day of gestation, uterine horn samples were removed. Immunohistochemical examination of the tissue samples prepared from the control and experimental groups, a statistically significant difference was observed between the groups in the luminal-glandular-decidualized epithelium of the uterus with glycodelin A, mucin-1 and leukemia inhibitory factor. A statistically significant difference was observed between the groups for the concentration of glycodelin A but no statistically significant difference was found for the other two molecules. In light of our findings, leuprolide acetate adversely affected expression and concentration of all three molecules in embryonal implantation model.

Timing of exposure to gonadotropins has differential effects on the conceptus: evidence from a mouse model†

Superovulation with gonadotropins alters the hormonal milieu during early embryo development and placentation, and may be responsible for fetal and placental changes observed after in vitro fertilization (IVF). We hypothesized that superovulation has differential effects depending on timing of exposure. To test our hypothesis, we isolated the effect of superovulation on pre- and peri-implantation mouse embryos. Blastocysts were obtained from either natural mating or following superovulation and mating, and were transferred into naturally mated or superovulated pseudopregnant recipient mice. Fetal weight was significantly lower after peri-implantation exposure to superovulation, regardless of preimplantation exposure (p = 0.006). Placentas derived from blastocysts exposed to superovulation pre- and peri-implantation were larger than placentas derived from natural blastocysts that are transferred into a natural or superovulated environment (p < 0.05). Fetal-to-placental weight ratio decreased following superovulation during the pre- or peri-implantation period (p = 0.05, 0.01, respectively) and these effects were additive. Peg3 DNA methylation levels were decreased in placentas derived from exposure to superovulation both pre- and peri-implantation compared with unexposed embryos and exposure of the preimplantation embryo only. Through RNA sequencing on placental tissue, changes were identified in genes involved in immune system regulation, specifically interferon signaling, which has been previously implicated in implantation and maintenance of early pregnancy in mice. Overall, we found that the timing of exposure to gonadotropin stimulation can have differential effects on fetal and placental growth. These findings could impact clinical practice and underscores the importance of dissecting the role of procedures utilized during IVF on pregnancy complications.

Organoid technology in female reproductive biomedicine

Recent developments in organoid technology are revolutionizing our knowledge about the biology, physiology, and function of various organs. Female reproductive biology and medicine also benefit from this technology. Organoids recapitulate features of different reproductive organs including the uterus, fallopian tubes, and ovaries, as well as trophoblasts. The genetic stability of organoids and long-lasting commitment to their tissue of origin during long-term culture makes them attractive substitutes for animal and in vitro models. Despite current limitations, organoids offer a promising platform to address fundamental questions regarding the reproductive system's physiology and pathology. They provide a human source to harness stem cells for regenerative medicine, heal damaged epithelia in specific diseases, and study biological processes in healthy and pathological conditions. The combination of male and female reproductive organoids with other technologies, such as microfluidics technology, would enable scientists to create a multi-organoid-on-a-chip platform for the next step to human-on-a-chip platforms for clinical applications, drug discovery, and toxicology studies. The present review discusses recent advances in producing organoid models of reproductive organs and highlights their applications, as well as technical challenges and future directions.

Endometrial profilin 1: a key player in embryo-endometrial crosstalk

Objective

Despite extensive research on implantation failure, little is known about the molecular mechanisms underlying the crosstalk between the embryo and the maternal endometrium, which is critical for successful pregnancy. Profilin 1 (PFN1), which is expressed both in the embryo and in the endometrial epithelium, acts as a potent regulator of actin polymerization and the cytoskeletal network. In this study, we identified the specific role of endometrial PFN1 during embryo implantation.

Methods

Morphological alterations depending on the status of PFN1 expression were assessed in PFN1-depleted or control cells grown on Matrigel-coated cover glass. Day-5 mouse embryos were cocultured with Ishikawa cells. Comparisons of the rates of F-actin formation and embryo attachment were performed by measuring the stability of the attached embryo onto PFN1-depleted or control cells.

Results

Depletion of PFN1 in endometrial epithelial cells induced a significant reduction in cell-cell adhesion displaying less formation of colonies and a more circular cell shape. Mouse embryos co-cultured with PFN1-depleted cells failed to form actin cytoskeletal networks, whereas more F-actin formation in the direction of surrounding PFN1-intact endometrial epithelial cells was detected. Furthermore, significantly lower embryo attachment stability was observed in PFN1-depleted cells than in control cells. This may have been due to reduced endometrial receptivity caused by impaired actin cytoskeletal networks associated with PFN1 deficiency.

Conclusion

These observations definitively demonstrate an important role of PFN1 in mediating cell-cell adhesion during the initial stage of embryo implantation and suggest a potential therapeutic target or novel biomarker for patients suffering from implantation failure.

The Role of LIN28-let-7-ARID3B Pathway in Placental Development

Placental disorders are a major cause of pregnancy loss in humans, and 40–60% of embryos are lost between fertilization and birth. Successful embryo implantation and placental development requires rapid proliferation, invasion, and migration of trophoblast cells. In recent years, microRNAs (miRNAs) have emerged as key regulators of molecular pathways involved in trophoblast function. A miRNA binds its target mRNA in the 3ʹ-untranslated region (3ʹ-UTR), causing its degradation or translational repression. Lethal-7 (let-7) miRNAs induce cell differentiation and reduce cell proliferation by targeting proliferation-associated genes. The oncoprotein LIN28 represses the biogenesis of mature let-7 miRNAs. Proliferating cells have high LIN28 and low let-7 miRNAs, whereas differentiating cells have low LIN28 and high let-7 miRNAs. In placenta, low LIN28 and high let-7 miRNAs can lead to reduced proliferation of trophoblast cells, resulting in abnormal placental development. In trophoblast cells, let-7 miRNAs reduce the expression of proliferation factors either directly by binding their mRNA in 3ʹ-UTR or indirectly by targeting the AT-rich interaction domain (ARID)3B complex, a transcription-activating complex comprised of ARID3A, ARID3B, and histone demethylase 4C (KDM4C). In this review, we discuss regulation of trophoblast function by miRNAs, focusing on the role of LIN28-let-7-ARID3B pathway in placental development.

Annexin A1/Formyl Peptide Receptor Pathway Controls Uterine Receptivity to the Blastocyst

Embryo implantation into the uterine wall is a highly modulated, complex process. We previously demonstrated that Annexin A1 (AnxA1), which is a protein secreted by epithelial and inflammatory cells in the uterine microenvironment, controls embryo implantation in vivo. Here, we decipher the effects of recombinant AnxA1 in this phenomenon by using human trophoblast cell (BeWo) spheroids and uterine epithelial cells (Ishikawa; IK). AnxA1-treated IK cells demonstrated greater levels of spheroid adherence and upregulation of the tight junction molecules claudin-1 and zona occludens-1, as well as the glycoprotein mucin-1 (Muc-1). The latter effect of AnxA1 was not mediated through IL-6 secreted from IK cells, a known inducer of Muc-1 expression. Rather, these effects of AnxA1 involved activation of the formyl peptide receptors FPR1 and FPR2, as pharmacological blockade of FPR1 or FPR1/FPR2 abrogated such responses. The downstream actions of AnxA1 were mediated through the ERK1/2 phosphorylation pathway and F-actin polymerization in IK cells, as blockade of ERK1/2 phosphorylation reversed AnxA1-induced Muc-1 and claudin-1 expression. Moreover, FPR2 activation by AnxA1 induced vascular endothelial growth factor (VEGF) secretion by IK cells, and the supernatant of AnxA1-treated IK cells evoked angiogenesis in vitro. In conclusion, these data highlight the role of the AnxA1/FPR1/FPR2 pathway in uterine epithelial control of blastocyst implantation.

Vaginal versus intramuscular progesterone for luteal phase support in assisted reproductive techniques: a systematic review and meta-analysis of randomized controlled trials

We aimed to compare the efficacy of vaginal progesterone versus intramuscular progesterone (IMP) for luteal phase support in assisted reproductive techniques (ART). A comprehensive electronic search of four electronic databases (PubMed, Cochrane Library, Scopus, and ISI Web of Science) was performed from inception till August 2019 for randomized controlled trials (RCTs). We included studies performed different ART with the use of vaginal progesterone versus IMP for luteal phase support. Our primary outcome was clinical pregnancy rate. Our secondary outcomes were ongoing pregnancy, miscarriage, live birth rates, and satisfaction in both groups. 15 RCTs met our inclusion criteria with a total of 5656 patients. Our analysis indicated no significant differences between vaginal progesterone and IMP regarding clinical and ongoing pregnancies (RR = 0.90, 95% CI [0.80, 1.00], p = .06), (RR = 0.90, 95% CI [0.76, 1.06], p = .21), respectively. No significant differences were found between both routes of progesterone in miscarriage (p = .98) and live birth (p = .99). Subgroup analysis between fresh and frozen embryo transfer cycles in above outcomes showed no difference between progesterone routes. Vaginal progesterone was significantly associated with more satisfaction compared to IMP (p < .00001). In conclusion, vaginal progesterone can be used an alternative method for luteal phase support instead of IMP in ART.

Development of placental abnormalities in location and anatomy

Low‐lying placentas, placenta previa and abnormally invasive placentas are the most frequently occurring placental abnormalities in location and anatomy. These conditions can have serious consequences for mother and fetus mainly due to excessive blood loss before, during or after delivery. The incidence of such abnormalities is increasing, but treatment options and preventive strategies are limited. Therefore, it is crucial to understand the etiology of placental abnormalities in location and anatomy. Placental formation already starts at implantation and therefore disorders during implantation may cause these abnormalities. Understanding of the normal placental structure and development is essential to comprehend the etiology of placental abnormalities in location and anatomy, to diagnose the affected women and to guide future research for treatment and preventive strategies. We reviewed the literature on the structure and development of the normal placenta and the placental development resulting in low‐lying placentas, placenta previa and abnormally invasive placentas.

Smoke, alcohol and drug addiction and female fertility

BACKGROUND

Considerable interest has been gathered on the relevant impact of preventable factors, including incorrect lifestyle and unhealthy habits, on female fertility. Smoking, alcohol and addictive drugs consumption represent a major concern, given the broad range of diseases which might be favored or exacerbated by these dependable attitudes. Despite the well-characterized effects of prenatal exposure on pregnancy outcomes and fetus health, a substantial proportion of women of reproductive age is still concerned with these habits. At present, the impact of smoke, alcohol and addictive drugs on women fertility, and, particularly, the specific targets and underlying mechanisms, are still poorly understood or debated, mainly due to the scarcity of well-designed studies, and to numerous biases.

OBJECTIVE

The current review will provide a comprehensive overview of clinical and experimental studies in humans and animals addressing the impact of smoke, alcohol and addictive drugs on female fertility, by also embracing effects on ovary, oviduct, and uterus, with particular reference to primary endpoints such as ovarian reserve, steroidogenesis, ovulation and menstrual cycle, oviduct function and uterus receptivity and implantation. A brief focus on polycystic ovary syndrome and endometriosis will be also included.

METHODS

A Pubmed literature search was performed with selected keywords; articles were individually retrieved by each author. No limitation was set for publication date. Articles in languages other than English were excluded. Additional articles were retrieved from references list of selected manuscripts.

RESULTS AND CONCLUSIONS

Currently, the most consistent evidences of a detrimental effect of smoke, alcohol and addictive drugs on specific domains of the female reproductive function are provided by experimental studies in animals. Overall, clinical studies suggest that smoking is associated to decreased fertility, although causal inference should be further demonstrated. Studies addressing the effect of alcohol consumption on female fertility provide conflicting results, although the majority reported lack of a correlation. Extremely scarce studies investigated the effects of addictive drugs on female fertility, and the specific actions of selected drugs have been difficult to address, due to multidrug consumption.

Matrix Metalloproteinase 13 Activity is Required for Normal and Hypoxia-Induced Precocious Hatching in Zebrafish Embryos

Hypoxia induces precocious hatching in zebrafish, but we do not have a clear understanding of the molecular mechanisms regulating the activation of the hatching enzyme or how these mechanisms trigger precocious hatching under unfavorable environmental conditions. Using immunohistochemistry, pharmacological inhibition of matrix metalloproteinase 13 (Mmp13), and in vivo zymography, we show that Mmp13a is present in the hatching gland just as embryos become hatching competent and that Mmp13a activity is required for both normal hatching and hypoxia-induced precocious hatching. We conclude that Mmp13a likely functions in activating the hatching enzyme zymogen and that Mmp13a activity is necessary but not sufficient for hatching in zebrafish. This study highlights the broad nature of MMP function in development and provides a non-mammalian example of extra-embryonic processes mediated by MMP activity.

Development of A 3D Tissue Slice Culture Model for the Study of Human Endometrial Repair and Regeneration

The human endometrium undergoes sequential phases of shedding of the upper functionalis zone during menstruation, followed by regeneration of the functionalis zone from the remaining basalis zone cells, and secretory differentiation under the influence of the ovarian steroid hormones estradiol (E2) and progesterone (P4). This massive tissue regeneration after menstruation is believed to arise from endometrial stromal and epithelial stem cells residing in the basal layer of the endometrium. Although many endometrial pathologies are thought to be associated with defects in these stem cells, studies on their identification and regulation are limited, primarily due to lack of easily accessible animal models, as these processes are unique to primates. Here we describe a robust new method to study endometrial regeneration and differentiation processes using human endometrial tissue slice cultures incorporating an air-liquid interface into a 3D matrix scaffold of type I collagen gel, allowing sustained tissue viability over three weeks. The 3D collagen gel-embedded endometrial tissue slices in a double-dish culture system responded to ovarian steroid hormones, mimicking the endometrial changes that occur in vivo during the menstrual cycle. These changes included the E2-induced upregulation of Ki-67, estrogen receptor (ER), and progesterone receptor (PR) in all endometrial compartments and were markedly suppressed by both P4 and E2 plus P4 treatments. There were also distinct changes in endometrial morphology after E2 and P4 treatments, including subnuclear vacuolation and luminal secretions in glands as well as decidualization of stromal cells, typical characteristics of a progestational endometrium in vivo. This long-term slice culture method provides a unique in vivo-like microenvironment for the study of human endometrial functions and remodeling during early pregnancy and experiments on stem cell populations involved in endometrial regeneration and remodeling. Furthermore, this model has the potential to enable studies on several endometrial diseases, including endometrial cancers and pregnancy complications associated with defects in endometrial remodeling.

Molecular Signaling Regulating Endometrium-Blastocyst Crosstalk

Implantation of the embryo into the uterine endometrium is one of the most finely-regulated processes that leads to the establishment of a successful pregnancy. A plethora of factors are released in a time-specific fashion to synchronize the differentiation program of both the embryo and the endometrium. Indeed, blastocyst implantation in the uterus occurs in a limited time frame called the "window of implantation" (WOI), during which the maternal endometrium undergoes dramatic changes, collectively called "decidualization". Decidualization is guided not just by maternal factors (e.g., estrogen, progesterone, thyroid hormone), but also by molecules secreted by the embryo, such as chorionic gonadotropin (CG) and interleukin-1β (IL-1 β), just to cite few. Once reached the uterine cavity, the embryo orients correctly toward the uterine epithelium, interacts with specialized structures, called pinopodes, and begins the process of adhesion and invasion. All these events are guided by factors secreted by both the endometrium and the embryo, such as leukemia inhibitory factor (LIF), integrins and their ligands, adhesion molecules, Notch family members, and metalloproteinases and their inhibitors. The aim of this review is to give an overview of the factors and mechanisms regulating implantation, with a focus on those involved in the complex crosstalk between the blastocyst and the endometrium.

Human Chorionic Gonadotropin-Mediated Immune Responses That Facilitate Embryo Implantation and Placentation

Human chorionic gonadotropin (hCG) serves as one of the first signals provided by the embryo to the mother. Exactly at the time when the first step of the implantation process is initiated and the blastocyst adheres to the maternal endometrium, the embryonic tissue starts to actively secrete hCG. Shortly thereafter, the hormone can be detected in the maternal circulation where its concentration steadily increases throughout early pregnancy as it is continuously released by the forming placenta. Accumulating evidence underlines the critical function of hCG for embryo implantation and placentation. hCG not only regulates biological aspects of these early pregnancy events but also supports maternal immune cells in their function as helpers in the establishment of an adequate embryo-endometrial relationship. In view of its early presence in the maternal circulation, hCG has the potential to influence both local uterine immune cell populations as well as peripheral ones. The current review aims to summarize recent literature on the participation of innate and adaptive immune cells in embryo implantation and placentation with a specific focus on their regulation by hCG.

Hyperandrogenism and insulin resistance induce gravid uterine defects in association with mitochondrial dysfunction and aberrant reactive oxygen species production

Women with polycystic ovary syndrome (PCOS) are at increased risk of miscarriage, which often accompanies the hyperandrogenism and insulin resistance seen in these patients. However, neither the combinatorial interaction between these two PCOS-related etiological factors nor the mechanisms of their actions in the uterus during pregnancy are well understood. We hypothesized that hyperandrogensim and insulin resistance exert a causative role in miscarriage by inducing defects in uterine function that are accompanied by mitochondrial-mediated oxidative stress, inflammation, and perturbed gene expression. Here, we tested this hypothesis by studying the metabolic, endocrine, and uterine abnormalities in pregnant rats after exposure to daily injection of 5α-dihydrotestosterone (DHT; 1.66 mg·kg body wt^-1·day^-1) and/or insulin (6.0 IU/day) from gestational day 7.5 to 13.5. We showed that whereas DHT-exposed and insulin-exposed pregnant rats presented impaired insulin sensitivity, DHT + insulin-exposed pregnant rats exhibited hyperandrogenism and peripheral insulin resistance, which mirrors pregnant PCOS patients. Compared with controls, hyperandrogenism and insulin resistance in the dam were associated with alterations in uterine morphology and aberrant expression of genes responsible for decidualization (Prl8a2, Fxyd2, and Mt1g), placentation (Fcgr3 and Tpbpa), angiogenesis (Flt1, Angpt1, Angpt2, Ho1, Ccl2, Ccl5, Cxcl9, and Cxcl10) and insulin signaling (Akt, Gsk3, and Gluts). Moreover, we observed changes in uterine mitochondrial function and homeostasis (i.e., mitochondrial DNA copy number and the expression of genes responsible for mitochondrial fusion, fission, biogenesis, and mitophagy) and suppression of both oxidative and antioxidative defenses (i.e., reactive oxygen species, Nrf2 signaling, and interactive networks of antioxidative stress responses) in response to the hyperandrogenism and insulin resistance. These findings demonstrate that hyperandrogenism and insulin resistance induce mitochondria-mediated damage and a resulting imbalance between oxidative and antioxidative stress responses in the gravid uterus.

Electroacupuncture facilitates implantation by enhancing endometrial angiogenesis in a rat model of ovarian hyperstimulation

Controlled ovarian hyperstimulation (COH) impairs the synchronized development of endometrium and embryo, resulting in the failure of embryo implantation. Here, we investigated what effects electroacupuncture had on embryo implantation in COH rats. Female rats were randomly assigned to four groups: normal (N), model (M), electroacupuncture (EA), and electroacupuncture pretreatment (PEA). Rats in groups M, EA, PEA were injected with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin to establish the COH model. Rats in group EA received electroacupuncture treatment from the PMSG injection day to the 3rd day of pregnancy (D3), while those in group PEA received electroacupuncture treatment for 3 days before the PMSG day and continuing to D3. Furthermore, another 30 female rats who received the same treatment as the rats in group PEA were injected with siVEGFR2 into uterine lumen. The endometrial microvascular density (MVD) and the expression levels of vascular endothelial growth factor-A, angiopoietin-1, and fibroblast growth factor-2 were significantly lower in groups M than in groups N and PEA. The percentage of dolichos biflorus agglutinin positive uterine natural killer cells in groups N, EA and PEA was higher than that in group M. After the siVEGFR2 injection, the protein expression levels of vascular endothelial growth factor receptor 2 (VEGFR2), PI3K, p-AKT and p-ERK, the embryo number and the MVD were significantly reduced. In conclusion, electroacupuncture can facilitate embryo implantation in COH rats by activating the VEGFR2/PI3K/AKT and VEGFR2/ERK signaling pathways which have a positive relationship with endometrial angiogenesis.

Decidual cells from women with preeclampsia exhibit inadequate decidualization and reduced sFlt1 suppression

Uterine stromal cell decidualization of maternal tissue is essential for implantation of and local adaptation to the fetal allograft, as well as growth and maintenance of the placenta in healthy pregnancies. Maternal defects in decidualization have been suggested as a possible driver of preeclampsia. Preeclampsia (PE) pregnancies demonstrate shallow implantation, inadequate spiral artery remodeling, and elevated levels of the anti-angiogenic protein, sFlt1. To test whether stromal cells (DSCs) isolated from PE placentas exhibit inadequate re-decidualization and increased expression of sFlt1, DSCs from normotensive (NT-DSCs) and PE (PE-DSCs) placentas were treated for 8 days (D8) with cAMP to induce decidualization and levels of decidualization markers (PRL, IGFBP1, VEGF) and sFlt1 were measured at day 0 (D0), D8, and after reversal of treatment. NT-DSCs achieved statistically significant elevations in PRL and IFGBP1 expression (25.72 [5.78-50.04], p = 0.0008 and 92.09 [1.79-543.10], p = 0.005). PE-DSCs increased PRL and IFGBP1 expression to 6.15 [2.30-10.73] (p = 0.18) and 8.67 [1.64-376.10] (p = 0.04). NT-DSCs reduced sFlt1 expression at D8 to 0.25 [0.17-0.49] (p = 0.0021) compared to 0.31 [0.25-0.82] (p = 0.087) in PE-DSCs. These results show that, when induced to decidualize, PE-DSCs fail to increase expression of decidualization markers to levels achieved by NT-DSCs. sFlt1 expression is higher in PE-DSCs during decidualization, suggesting inadequate suppression during the crucial implantation period. These defects at the maternal fetal interface may lead to the failed spiral artery modification, decreased placental invasion of the uterus, and elevated circulating sFlt1 levels seen in PE pathology.

Inside the Endometrial Cell Signaling Subway: Mind the Gap(s)

Endometrial cells perceive and respond to their microenvironment forming the basis of endometrial homeostasis. Errors in endometrial cell signaling are responsible for a wide spectrum of endometrial pathologies ranging from infertility to cancer. Intensive research over the years has been decoding the sophisticated molecular means by which endometrial cells communicate to each other and with the embryo. The objective of this review is to provide the scientific community with the first overview of key endometrial cell signaling pathways operating throughout the menstrual cycle. On this basis, a comprehensive and critical assessment of the literature was performed to provide the tools for the authorship of this narrative review summarizing the pivotal components and signaling cascades operating during seven endometrial cell fate “routes”: proliferation, decidualization, implantation, migration, breakdown, regeneration, and angiogenesis. Albeit schematically presented as separate transit routes in a subway network and narrated in a distinct fashion, the majority of the time these routes overlap or occur simultaneously within endometrial cells. This review facilitates identification of novel trajectories of research in endometrial cellular communication and signaling. The meticulous study of endometrial signaling pathways potentiates both the discovery of novel therapeutic targets to tackle disease and vanguard fertility approaches.