The immune environment in human endometrium during the window of implantation

IFNT-induced IRF1 enhances bovine endometrial receptivity by transactivating LIFR

Interferon-τ (IFN-τ) participates in the establishment of endometrial receptivity in ruminants. However, the precise mechanisms by which IFN-τ establishes bovine endometrial receptivity remain largely unknown. Interferon regulatory factor 1 (IRF1) is a classical interferon-stimulated gene (ISG) induced by type I interferon, including IFN-τ. Leukemia inhibitory factor receptor (LIFR) is a transmembrane receptor for leukemia inhibitory factor (LIF), which is a key factor in regulating embryo implantation in mammals. This study aimed to investigate the roles of IRF1 and LIFR in the regulation of bovine endometrial receptivity by IFN-τ. In vivo, we found IRF1 and LIFR were upregulated in the bovine endometrial luminal epithelium on Day 18 of pregnancy compared to Day 18 of the estrous cycle. In vitro, IFN-τ could upregulate IRF1, LIFR, and endometrial receptivity markers (LIF, HOXA10, ITGAV, and ITGB3) expression, downregulate E-cadherin expression and reduce the quantity of microvilli of bovine endometrial epithelial cells (bEECs). Overexpression of IRF1 had similar effects to IFN-τ on endometrial receptivity, and interference of LIFR could block these effects, suggesting the positive effects of IRF1 on endometrial receptivity were mediated by LIFR. Dual luciferase reporter assay verified that IRF1 could transactivate LIFR transcription by binding to its promoter. In conclusion, IFN-τ can induce IRF1 expression in bovine endometrial epithelial cells, and IRF1 upregulates LIFR expression by binding to LIFR promoter, contributing to the enhancement of bovine endometrial receptivity.

Endometrial Proliferative Phase-Centered View of Transcriptome Dynamics across the Menstrual Cycle

The endometrium, the inner mucosal lining of the uterus, undergoes complex molecular and cellular changes across the menstrual cycle in preparation for embryo implantation. Transcriptome-wide analyses have mainly been utilized to study endometrial receptivity, the prerequisite for successful implantation, with most studies, so far, comparing the endometrial transcriptomes between (i) secretory and proliferative endometrium or (ii) mid-secretory and early secretory endometrium. In the current study, we provide a complete transcriptome description of the endometrium across the entire menstrual cycle and, for the first time, comprehensively characterize the proliferative phase of the endometrium. Our temporal transcriptome analysis includes five time points including the mid-proliferative, late proliferative (peri-ovulatory phase), early secretory, mid-secretory, and late secretory phases. Thus, we unveil exhaustively the transitions between the consecutive proliferative and secretory phases, highlighting their unique gene expression profiles and possible distinct biological functions. The transcriptome analysis reveals many differentially expressed genes (DEGs) across the menstrual cycle, most of which are phase-specific. As an example of coordinated gene activity, the expression profile of histone-encoding genes within the HIST cluster on chromosome 6 shows an increase in cluster activity during the late proliferative and a decline during the mid-secretory phase. Moreover, numerous DEGs are shared among all phases. In conclusion, in the current study, we delineate the endometrial proliferative phase-centered view of transcriptome dynamics across the menstrual cycle. Our data analysis highlights significant transcriptomic and functional changes occurring during the late proliferative phase-an essential transition point from the proliferative phase to the secretory phase. Future studies should explore how the biology of the late proliferative phase endometrium impacts the achievement of mid-secretory endometrial receptivity or contributes to molecular aberrations leading to embryo implantation failure.

NK cell receptor profiling of endometrial and decidual NK cells reveals pregnancy-induced adaptations

Natural killer (NK) cells, with a unique NK cell receptor phenotype, are abundantly present in the non-pregnant (endometrium) and pregnant (decidua) humanuterine mucosa. It is hypothesized that NK cells in the endometrium are precursors for decidual NK cells present during pregnancy. Microenvironmental changes can alter the phenotype of NK cells, but it is unclear whether decidual NK cell precursors in the endometrium alter their NK cell receptor repertoire under the influence of pregnancy. To examine whether decidual NK cell precursors reveal phenotypic modifications upon pregnancy, we immunophenotyped the NK cell receptor repertoire of both endometrial and early-pregnancy decidual NK cells using flow cytometry. We showed that NK cells in pre-pregnancy endometrium have a different phenotypic composition compared to NK cells in early-pregnancy decidua. The frequency of killer-immunoglobulin-like receptor (KIR expressing NK cells, especially KIR2DS1, KIR2DL2L3S2, and KIR2DL2S2 was significantly lower in decidua, while the frequency of NK cells expressing activating receptors NKG2D, NKp30, NKp46, and CD244 was significantly higher compared to endometrium. Furthermore, co-expression patterns showed a lower frequency of NK cells co-expressing KIR3DL1S1 and KIR2DL2L3S2 in decidua. Our results provide new insights into the adaptations in NK cell receptor repertoire composition that NK cells in the uterine mucosa undergo upon pregnancy.

Identifying a causal link between prolactin signaling pathways and COVID-19 vaccine-induced menstrual changes

COVID-19 vaccines have been instrumental tools in the fight against SARS-CoV-2 helping to reduce disease severity and mortality. At the same time, just like any other therapeutic, COVID-19 vaccines were associated with adverse events. Women have reported menstrual cycle irregularity after receiving COVID-19 vaccines, and this led to renewed fears concerning COVID-19 vaccines and their effects on fertility. Herein we devised an informatics workflow to explore the causal drivers of menstrual cycle irregularity in response to vaccination with mRNA COVID-19 vaccine BNT162b2. Our methods relied on gene expression analysis in response to vaccination, followed by network biology analysis to derive testable hypotheses regarding the causal links between BNT162b2 and menstrual cycle irregularity. Five high-confidence transcription factors were identified as causal drivers of BNT162b2-induced menstrual irregularity, namely: IRF1, STAT1, RelA (p65 NF-kB subunit), STAT2 and IRF3. Furthermore, some biomarkers of menstrual irregularity, including TNF, IL6R, IL6ST, LIF, BIRC3, FGF2, ARHGDIB, RPS3, RHOU, MIF, were identified as topological genes and predicted as causal drivers of menstrual irregularity. Our network-based mechanism reconstruction results indicated that BNT162b2 exerted biological effects similar to those resulting from prolactin signaling. However, these effects were short-lived and didn't raise concerns about long-term infertility issues. This approach can be applied to interrogate the functional links between drugs/vaccines and other side effects.

Natural killer cell subsets in endometrial fluid: a pilot study of their association with the endometrial cycle and reproductive parameters

PURPOSE

To investigate if there are natural killer (NK) cells in endometrial fluid (EF) and their relationship with the endometrial cycle and reproductive parameters.

METHODS

The population under study consisted of 43 women aged 18-40 undergoing infertility workup at our University Hospital in 2021-2022. The EF samples were obtained at the first visit to our unit, on occasion of the mock embryo transfer. The day of the cycle was considered only in cycles of 27-29 days. An immunophenotype study of NK in EF was performed by flow cytometry analysis. In a subgroup of women, on the same day, NK was studied in EF and peripheral blood.

RESULTS

Our study is the first to evidence NK cells in EF. None of the NK cells observed corresponded to a mature peripheral blood NK cell population (stages 4-5), and neither endometrial nor decidual uNK cells were detected. Nevertheless, we found 2 patient groups with an NK cell subset with a higher expression of CD16+, which could belong to an intermediate or transient stage between the uNK and pbNK NK cell population in the EF. We found that CD16 was significantly increased in the mid-late luteal phase and its correlation with the day of the cycle. The NK immunophenotype was different in EF and peripheral blood.

CONCLUSION

We described a new component of the EF, the NK cells, whose CD16 activity is closely correlated with the day of the cycle. These cells could play a role in implantation/implantation failure.

The Role of Interleukins in Recurrent Implantation Failure: A Comprehensive Review of the Literature

Recurrent implantation failure (RIF) is a multifactorial condition affecting 10-15% of in vitro fertilization (IVF) couples. Data suggest that functional dysregulation of the endometrial immune system constitutes one of the main pathophysiological mechanisms leading to RIF. The aim of this article is to provide a thorough presentation and evaluation of the role of interleukins (ILs) in the pathogenesis of RIF. A comprehensive literature screening was performed summarizing current evidence. During implantation, several classes of ILs are secreted by epithelial and stromal endometrial cells, including IL-6, IL-10, IL-12, IL-15, IL-18, and the leukemia inhibitory factor. These ILs create a perplexing network that orchestrates both proliferation and maturation of uterine natural killer cells, controls the function of regulatory T and B cells inhibiting the secretion of antifetal antibodies, and supports trophoblast invasion and decidua formation. The existing data indicate associations between ILs and RIF. The extensive analysis performed herein concludes that the dysregulation of the ILs network indeed jeopardizes implantation leading to RIF. This review further proposes a mapping of future research on how to move forward from mere associations to robust molecular data that will allow an accurate profiling of ILs in turn enabling evidence-based consultancy and decision making when addressing RIF patients.

Down-regulation of PBK inhibits proliferation of human endometrial stromal cells in thin endometrium

BACKGROUND

Thin endometrium (TE) is a challenging clinical issue in the reproductive medicine characterized by inadequate endometrial thickness, poor response to estrogen and no effective treatments currently. At present, the precise pathogenesis of thin endometria remains to be elucidated. We aimed to explore the related molecular mechanism of TE by comparing the transcriptome profiles of late-proliferative phase endometria between TE and matched controls.

METHODS

We performed a bulk RNA-Seq (RNA-sequencing) of endometrial tissues in the late-proliferative phase in 7 TE and 7 matched controls for the first time. Differential gene expression analysis, gene ontology enrichment analysis and protein-protein interactions (PPIs) network analysis were performed. Immunohistochemistry was used for molecular expression and localization in endometria. Human endometrial stromal cells (HESCs) were isolated and cultured for verifying the functions of hub gene.

RESULTS

Integrative data mining of our RNA-seq data in endometria revealed that most genes related to cell division and cell cycle were significantly inhibited, while inflammation activation, immune response and reactive oxygen species associated genes were upregulated in TE. PBK was identified as a hub of PPIs network, and its expression level was decreased by 2.43-fold in endometria of TE patients, particularly reduced in the stromal cells, which was paralleled by the decreased expression of Ki67. In vitro experiments showed that the depletion of PBK reduced the proliferation of HESCs by 50% and increased the apoptosis of HESCs by 1 time, meanwhile PBK expression was inhibited by oxidative stress (reduced by 76.2%), hypoxia (reduced by 51.9%) and inflammatory factors (reduced by approximately 50%). These results suggested that the insufficient expression of PBK was involved in the poor endometrial thickness in TE.

CONCLUSIONS

The endometrial transcriptome in late-proliferative phase showed suppressed cell proliferation in women with thin endometria and decreased expression of PBK in human endometrial stromal cells (HESCs), to which inflammation and reactive oxygen species contributed.

The Role of Uterine Natural Killer Cells on Recurrent Miscarriage and Recurrent Implantation Failure: From Pathophysiology to Treatment

Uterine natural killer (uNK) cells constitute a unique uterine leucocyte subpopulation facilitating implantation and maintaining pregnancy. Herein, we critically analyze current evidence regarding the role of uNK cells in the events entailed in recurrent implantation failure (RIF) and recurrent miscarriages (RM). Data suggest an association between RIF and RM with abnormally elevated uNK cells’ numbers, as well as with a defective biological activity leading to cytotoxicity. However, other studies do not concur on these associations. Robust data suggesting a definitive causative relationship between uNK cells and RIF and RM is missing. Considering the possibility of uNK cells involvement on RIF and RM pathophysiology, possible treatments including glucocorticoids, intralipids, and intravenous immunoglobulin administration have been proposed towards addressing uNK related RIF and RM. When considering clinical routine practice, this study indicated that solid evidence is required to report on efficiency and safety of these treatments as there are recommendations that clearly advise against their employment. In conclusion, defining a causative relationship between uNK and RIF–RM pathologies certainly merits investigation. Future studies should serve as a prerequisite prior to proposing the use of uNK as a biomarker or prior to targeting uNK cells for therapeutic purposes addressing RIF and RM.

Uterine natural killer cell biology and role in early pregnancy establishment and outcomes

Objective

While immune cells were originally thought to only play a role in maternal tolerance of the semiallogenic fetus, an active role in pregnancy establishment is becoming increasingly apparent. Uterine natural killer (uNK) cells are of specific interest because of their cyclic increase in number during the window of implantation. As a distinct entity from their peripheral blood counterparts, understanding the biology and function of uNK cells will provide the framework for understanding their role in early pregnancy establishment and adverse pregnancy outcomes.

Evidence Review

This review discusses unique uNK cell characteristics and presents clinical implications resulting from their dysfunction. We also systematically present existing knowledge about uNK cell function in three processes critical for successful human embryo implantation and placentation: stromal cell decidualization, spiral artery remodeling, and extravillous trophoblast invasion. Finally, we review the features of uNK cells that could help guide future investigations.

Results

It is clear the uNK cells are intimately involved in multiple facets of early pregnancy. This is accomplished directly, through the secretion of factors that regulate stromal cells and trophoblast function; and indirectly, via interaction with other maternal cell types present at the maternal-fetal interface. Current work also suggests that uNK cells are a heterogenous population, with subsets that potentially accomplish different functions.

Conclusion

Establishment of pregnancy through successful embryo implantation and placentation requires crosstalk between multiple maternal cell types and invading fetal trophoblast cells. Defects in this process have been associated with multiple adverse perinatal outcomes including hypertensive disorders of pregnancy, placenta accreta, and recurrent miscarriage though the mechanism underlying development of these defects remain unclear. Abnormalities in NK cell number and function which would disrupt physiological maternal-fetal crosstalk, could play a critical role in abnormal implantation and placentation. It is therefore imperative to dissect the unique physiological role of uNK cells in pregnancy and use this knowledge to inform clinical practice by determining how uNK cell dysfunction could lead to reproductive failure.

Murine endometrial-derived mesenchymal stem cells suppress experimental autoimmune encephalomyelitis depending on indoleamine-2,3-dioxygenase expression

Cellular therapy with mesenchymal stem cells (MSCs) is a huge challenge for scientists, as little translational relevance has been achieved. However, many studies using MSCs have proved their suppressive and regenerative capacity. Thus, there is still a need for a better understanding of MSCs biology and the establishment of newer protocols, or to test unexplored tissue sources. Here, we demonstrate that murine endometrial-derived MSCs (meMSCs) suppress Experimental Autoimmune Encephalomyelitis (EAE). MSC-treated animals had milder disease, with a significant reduction in Th1 and Th17 lymphocytes in the lymph nodes and in the central nervous system (CNS). This was associated with increased Il27 and Cyp1a1 expression, and presence of IL-10-secreting T CD4+ cells. At EAE peak, animals had reduced CNS infiltrating cells, histopathology and demyelination. qPCR analysis evidenced the down-regulation of several pro-inflammatory genes and up-regulation of indoleamine-2,3-dioxygenase (IDO). Consistently, co-culturing of WT and IDO-/- meMSCs with T CD4+ cells evidenced the necessity of IDO on the suppression of encephalitogenic lymphocytes, and IDO-/- meMSCs were not able to suppress EAE. In addition, WT meMSCs stimulated with IL-17A and IFN-γ increased IDO expression and secretion of kynurenines in vitro, indicating a negative feedback loop. Pathogenic cytokines were increased when CD4+ T cells from AhR-/- mice were co-cultured with WT meMSC. In summary, our research evidences the suppressive activity of the unexplored meMSCs population, and shows the mechanism depends on IDO-kynurenines-Aryl hydrocarbon receptor (AhR) axis. To our knowledge this is the first report evidencing that the therapeutic potential of meMSCs relying on IDO expression.

Uterine Insulin Sensitivity Defects Induced Embryo Implantation Loss Associated with Mitochondrial Dysfunction-Triggered Oxidative Stress

Methods and Results

Herein, a comprehensive proteomic analysis was conducted on proliferative endometria from sows with low and normal reproductive performance (LRP and NRP, respectively). Enrichment analysis of differentially expressed proteins revealed alterations in endometrial remodeling, substance metabolism (mainly lipid, nitrogen, and retinol metabolism), immunological modulation, and insulin signaling in LRP sows. Importantly, aberrant lipid metabolite accumulation and dysregulation of insulin signaling were coincidently confirmed in endometria of LPR sows, proving an impaired insulin sensitivity. Furthermore, established high-fat diet- (HFD-) induced insulin-resistant mouse models revealed that uterine insulin resistance beginning before pregnancy deteriorated uterine receptivity and decreased implantation sites and fetal numbers. Mitochondrial biogenesis and fusion were decreased, and reactive oxygen species was overproduced in uteri from the HFD group during the implantation period. Ishikawa and JAR cells directly demonstrated that oxidative stress compromised implantation in vitro.

Conclusions

This study demonstrated that uterine insulin sensitivity impairment beginning before pregnancy resulted in implantation and fetal loss associated with oxidative stress induced by mitochondrial dysfunction.

ALK3-SMAD1/5 Signaling Mediates the BMP2-Induced Decrease in PGE2 Production in Human Endometrial Stromal Cells and Decidual Stromal Cells

BMP2 is a critical factor that is involved in the processes of embryo implantation and uterine decidualization. The expression of cyclooxygenase (COX) and subsequent prostaglandin E2 (PGE2) production are critical for successful pregnancy. However, it is not clear whether BMP2 can regulate the production of PG during endometrial decidualization. The aim of this study was to investigate the effects of BMP2 on COX-1 expression and PGE2 production as well as the underlying molecular mechanisms in the human endometrium. Immortalized human endometrial stromal cells (HESCs) and human decidual stromal cells (HDSCs) were used as the study model to investigate the effects of BMP2-induced cellular activities. Our results showed that BMP2 treatment significantly decreased PGE2 production by downregulating COX-1 expression in both human endometrial stromal and decidual stromal cells. Additionally, BMP2 induced an increase in the levels of phosphorylated SMAD1/5/8, and this effect was completely abolished by the addition of the inhibitors DMH-1 and dorsomorphin, but not by SB431542. Knocking down ALK3 completely reversed the BMP2-induced downregulation of COX-1. Moreover, concomitantly knocking down SMAD1 and SMAD5 completely reversed the BMP2-induced downregulation of COX-1. Our results indicated that BMP2 decreased PGE2 production by downregulating COX-1 expression, most likely through the ALK3/SMAD1-SMAD5 signaling pathway in human endometrial stromal and human decidual stromal cells. These findings deepen our understanding of the functional role of BMP2 in the regulation of endometrial decidualization in humans.

Human chorionic gonadotropin-mediated modulation of pregnancy-compatible peripheral blood natural killer cells in frozen embryo transfer cycles

PROBLEM

To evaluate pregnancy-compatible phenotypic and functional changes in peripheral blood natural killer (pNK) cells during frozen embryo transfer (FET) cycles.

METHOD OF STUDY

Peripheral blood was collected from patients undergoing frozen embryo transfer cycles at three separate time points in the cycle. pNK cell phenotype was analyzed by flow cytometry. Impact of pregnancy status on pNK cell cytotoxicity was characterized by two methods: (1) a three-dimensional endovascular tube formation approach and (2) a NK cell-specific K562 cell kill assay.

RESULTS

A total of 35 patients were enrolled, 15 with clinical pregnancies and 20 with negative serum β-hCG levels. Overall percentage of CD45⁺ CD3^- CD56⁺ pNK cell did not change during the FET cycle. Pregnancy resulted in an increase in CD45⁺ CD3^- CD56⁺ pNK cell population on the day of serum β-hCG. pNK cells from non-pregnant patients caused significant tube disruption when compared to pregnant patients. Addition of serum from pregnant women reduced the tube disruption by pNK cells from non-pregnant patients. pNK cells from pregnant patients showed significantly lower cytotoxicity toward K562 cells in serum-free conditions. The addition of pregnancy serum decreased non-pregnant pNK cell cytotoxicity. Pregnancy status had no impact on VEGF-A and VEGF-C serum levels. Recombinant hCG added to non-pregnant serum resulted in a significant reduction in non-pregnant pNK cell-mediated K562 cell kill.

CONCLUSION

There was no difference in pNK cell populations based on timing of the FET cycle. However, pregnancy increased the percentage of CD45⁺ CD3^- CD56⁺ pNK cells. Additionally, pNK cells from pregnant women have reduced cytotoxicity and this is possibly mediated by hCG.

Oestrogen-induced expression of decay accelerating factor is spatiotemporally antagonised by progesterone-progesterone receptor signalling in mouse uterus

Decay accelerating factor (DAF) is upregulated in the fetoplacental trophoblast, which protects the fetus from maternal complement injury. DAF was found to be downregulated in the endometrium of patients with repeated implantation failure. Thus, we examined the molecular mechanisms of DAF expression regulation by ovarian steroid hormones in the mouse uterus. Immunofluorescence staining demonstrated its exclusive localisation in the apical region of the epithelium in the uterus. Oestrogen (E2) significantly induced Daf mRNA in a time-dependent manner. Progesterone (P4) did not have any significant effect on Daf expression; however, it negatively modulated E2-induced DAF expression and RU486 effectively interfered with the inhibitory action of P4 in the uterus. During early pregnancy DAF was higher on Day 1 of pregnancy, but significantly decreased from Day 3, which is consistent with its E2-dependent regulation. Interestingly, DAF expression seemed to be influenced by the implanting blastocyst on Day 5 and it was gradually increased during preimplantation embryo development with peak levels at blastocyst stages. We demonstrated that E2-dependent DAF expression is antagonised by P4-progesterone receptor signalling in the uterine epithelium. Spatiotemporal regulation of DAF in the uterus and preimplantation embryos suggest that DAF functions as an immune modulator for embryo implantation and early pregnancy in mice.

Biomarkers in Fetomaternal Tolerance

Multiple mechanisms of tolerance operate in the immune cross-talk at the fetomaternal interface, contributing to successful pregnancy outcome. The cross-talk includes interaction between various cell subsets and between cytokines and molecules of the endocrine system. A depiction of how all these components interact with each other and contribute to tolerance of the fetus is not clearly understood. Dysregulation in one or more of these mechanisms leads to fetal loss. Few effective biomarkers are available that can safely predict fetal loss. This review discusses some potential biomarkers that can predict failure of tolerance at the fetomaternal interface.

Lectin histochemical analysis of uterine natural killer cells in normal, hydatidiform molar and invasive molar pregnancy

Uterine natural killer (uNK) cells have been hypothesized to serve a role in controlling trophoblast invasion and proliferation. The aim of the present study was to identify the distribution and number of uNK cells in normal pregnancy (NP), partial mole (PM), complete mole (CM) and invasive mole (IM). uNK cells were detected using dolichos biflorus agglutinin lectin immunohistochemistry in decidual and villous tissues from early NP (n=15), late NP (n=15), PM (n=22), CM (n=20) and IM (n=10). A scaled eye piece was used for cell counting to obtain semi-quantitative results. It was revealed that uNK cells were mainly located in the uterine deciduas of early NP. As pregnancy progressed, the number of decidual uNK cells significantly decreased. Decidual uNK cells of PM, CM and IM were located near blood vessel endothelial cells. No significant differences were detected with respect to the numbers of decidual uNK between early NP and PM. However, the number of decidual uNK cells was significantly reduced in CM and IM compared with early NP. The populations of decidual uNK cells were not significantly different between CM and IM. No uNK cells were detected in the villi of PM, CM or IM. The decrease of decidual uNK cells in late NP, CP and IM, compared with early NP, suggested that uNK cells served an important role in controlling trophoblast invasion and proliferation.

Potential Marker Pathways in the Endometrium That May Cause Recurrent Implantation Failure

The aim of this prospective cohort study was to identify altered biologic processes in the endometrium that may be potential markers of receptive endometrium in patients with repeated implantation failure (RIF) as compared with fertile controls. The study was conducted in a university-affiliated in vitro fertilization (IVF) gynecology clinic and molecular biology and genetics laboratory. Healthy fertile controls (n = 24) and patients with RIF (n = 24) were recruited. Window of implantation gene profiling associated with RIF was performed. Six hundred forty-one differentially expressed genes were identified, and 44 pathways were found enriched. Upon clustering of the enriched pathways, 9 representative pathways were established. The important pathways that were identified included circadian rhythm, pathways in cancer, proteasome, complement and coagulation cascades, citrate cycle, adherens junction, immune system and inflammation, cell cycle, and renin-angiotensin system. The involvement of the circadian rhythm pathway and other related pathways may alter the endometrium's functioning to ultimately cause RIF. Furthermore, we found that the pathogenesis of RIF was multifaceted and that numerous processes were involved. We believe that a better understanding of the underlying mechanisms of RIF will ultimately give rise to better treatment opportunities and to better outcomes in IVF.

Implications of uterine NK cells and regulatory T cells in the endometrium of infertile women

A range of studies have shown that the complex process of implantation and an establishment of a pregnancy also involves immune factors. Disturbances in these underlying immune mechanisms might lead to implantation and pregnancy failure and may be involved in the pathogenesis of unexplained infertility. Several studies have reported that imbalances in uterine NK (uNK) cell abundance are associated with infertility; however, controversies exist. An increased amount of CD56⁺ uNK cells along with a decrease in CD16⁺ uNK cells have been associated with normal fertility in some studies. Very few studies of FoxP3⁺ regulatory T cells (Tregs) in the pre-implantation endometrium have been performed. Results are sparse and controversial, studies reporting both increased and decreased numbers of Tregs, respectively, in women suffering from infertility. In conclusion, studies imply that uNK cells, Tregs and HLA-G carry pivotal roles regarding the establishment of a healthy pregnancy, and that abnormal immune mechanisms involving these parameters may be associated with infertility. However, more research in early phases of the reproductive cycle, such as investigating the conditions in the endometrium before implantation, is needed to further clarify the underlying mechanisms.

Decidualization of the human endometrium

BACKGROUND

Decidualization of the human endometrium, which involves a dramatic morphological and functional differentiation of human endometrial stromal cells (ESCs), is essential for the establishment of a successful pregnancy. Decidualization results from a complex interplay of transcription factors, morphogens, cytokines, cell cycle regulators, and signaling pathways.

METHODS

Based on a literature review, the regulation of, and the molecular mechanisms involved in, the decidualization of the endometrium are described.

MAIN FINDINGS

Progesterone, together with proteins that are regulated by progesterone and/or cyclic adenosine monophosphate, including homeobox A10, forkhead box O1, signal transducers and activators of transcription, and heart and neural crest derivatives expressed transcript 2, forms a critical network for ESC decidualization and is a prerequisite to successful implantation. Decidualized ESCs contribute to the microenvironment at the feto-maternal interface and its direct or indirect influence on extracellular matrix remodeling, regulation of the local immune response, anti-oxidative stress, and angiogenesis (vascular maturation). Impairment of this process is associated with a variety of pregnancy disorders, including infertility, recurrent miscarriages, and uteroplacental disorders.

CONCLUSION

A deeper understanding of the process of decidualization is expected to provide new insights into the fields of reproductive biology and reproductive medicine.

Uterine responses to early pre-attachment embryos in the domestic dog and comparisons with other domestic animal species

In the dog, there is no luteolysis in the absence of pregnancy. Thus, this species lacks any anti-luteolytic endocrine signal as found in other species that modulate uterine function during the critical period of pregnancy establishment. Nevertheless, in the dog an embryo-maternal communication must occur in order to prevent rejection of embryos. Based on this hypothesis, we performed microarray analysis of canine uterine samples collected during pre-attachment phase (days 10-12) and in corresponding non-pregnant controls, in order to elucidate the embryo attachment signal. An additional goal was to identify differences in uterine responses to pre-attachment embryos between dogs and other mammalian species exhibiting different reproductive patterns with regard to luteolysis, implantation, and preparation for placentation. Therefore, the canine microarray data were compared with gene sets from pigs, cattle, horses, and humans. We found 412 genes differentially regulated between the two experimental groups. The functional terms most strongly enriched in response to pre-attachment embryos related to extracellular matrix function and remodeling, and to immune and inflammatory responses. Several candidate genes were validated by semi-quantitative PCR. When compared with other species, best matches were found with human and equine counterparts. Especially for the pig, the majority of overlapping genes showed opposite expression patterns. Interestingly, 1926 genes did not pair with any of the other gene sets. Using a microarray approach, we report the uterine changes in the dog driven by the presence of embryos and compare these results with datasets from other mammalian species, finding common-, contrary-, and exclusively canine-regulated genes.

Expression of indoleamine 2,3-dioxygenase 1 as transcript and protein in the healthy and diseased equine endometrium

The enzyme indoleamine 2,3-dioxygenase 1 (IDO1) acts immunomodulatory and restricts bacterial growth. In the uterus of women and mice, it likely contributes to tissue homeostasis and disease pathogenesis. Pregnancy failure in mares is often caused by endometritis and endometrosis. The pathogenesis of nonsuppurative endometritis and endometrosis is still uncertain. To the authors' knowledge, no information on IDO1 expression in the equine endometrium is published. Aim of this study was to examine the presence of IDO1 as transcripts and proteins in the healthy and diseased endometrium of 25 mares and to determine its cellular expression. By PCR, IDO1 transcripts were detected in healthy (3 mares) and diseased endometria (22 mares). Western blot on 15 samples showed the concurrent presence of IDO1 proteins. Immunohistochemistry revealed its expression in macrophages and epithelial cells. Endometria of 21 mares showed an intense staining of glandular epithelia, whereas glands of the remaining 4 mares were negative or contained only few positive cells. Tissue samples of all mares showed a minimal to mild IDO1 expression in the surface epithelium and glandular ducts. Quantification of immunohistochemistry on biopsies of 6 mares collected at different stages of the same endometrial cycle indicated that the IDO1 expression is not influenced by the endometrial cycle. This study confirmed IDO1 expression also in the equine endometrium and suggests an immunomodulatory role of uterine macrophages and epithelial cells. A markedly reduced glandular IDO1 expression as detected in 4 mares may be associated with alterations of uterine immune defenses.

Lower inflammatory markers in women with antenatal depression brings the M1/M2 balance into focus from a new direction

BACKGROUND

Antenatal depression and use of serotonin reuptake inhibitors (SSRI) in pregnancy have both been associated with an increased risk of poor pregnancy outcomes, such as preterm birth and impaired fetal growth. While the underlying biological pathways for these complications are poorly understood, it has been hypothesized that inflammation may be a common physiological pathway. The aim of the present study was to assess peripheral inflammatory markers in healthy women, women with antenatal depression, and in women using SSRI during pregnancy.

METHODS

160 healthy pregnant controls, 59 women with antenatal depression and 39 women on treatment with SSRIs were included. The relative levels of 92 inflammatory proteins were analyzed by proximity extension assay technology.

RESULTS

Overall, 23 of the inflammatory markers were significantly lower in women with antenatal depression and in women on treatment with SSRIs in comparison with the healthy controls. No difference in any of the inflammatory markers was observed between women with antenatal depression and those who were using SSRI. Top three inflammatory markers that were down-regulated in women with antenatal depression were TNF-related apoptosis-inducing ligand (TRAIL), p=0.000001, macrophage colony-stimulating factor 1 (CSF-1), p=0.000004, and fractalkine (CX3CL1), p=0.000005. Corresponding inflammatory markers in SSRI users were CSF-1, p=0.000011, vascular endothelial growth factor A (VEGF-A), p=0.000016, and IL-15 receptor subunit alpha (IL-15RA), p=0.000027. The inflammatory markers were negatively correlated with cortisone serum concentrations in controls, but not in the cases. Differential DNA methylation of was found for seven of these inflammatory markers in an independent epigenetics cohort.

CONCLUSION

Women with antenatal depression or on SSRI treatment have lower levels of a number of peripheral inflammatory markers than healthy pregnant controls. Hypothetically, this could be due to dysregulated switch to the pro-M2 milieu that characterizes normal third trimester pregnancy. However, longitudinal blood sampling is needed to elucidate whether the presumably dysregulated M2 shift is driving the development of antenatal depression or is a result of the depression.

Evaluation of endometrial natural killer cell expression of CD4, CD103, and CD16 cells in women with unexplained infertility

OBJECTIVE

To determine whether natural killer cell (NK) concentrations in the mid-secretory endometrial tissue of women with unexplained infertility differ from those in the mid-secretory endometrial tissue of fertile women.

METHODS

This study was conducted with 22 patients with unexplained infertility caused by unsuccessful ovulation induced with gonadotrophins and 12 healthy fertile women, who formed a control group. Mid-secretory endometrial tissue samples were obtained with a Pipelle catheter, and the endometrial NK cell phenotypes were determined by flow cytometry.

RESULTS

The median number of CD4+ cells in the endometrium was significantly lower in women with unexplained infertility compared with in the fertile controls (3.31 vs. 5.81; p=0.02). The CD4(+)/CD8(+) cell ratio in the unexplained-infertility group was significantly lower than that in the control group (0.42 vs. 0.76, p=0.01). The median number of CD103(+) cells in the endometrium of the infertile group was significantly lower than that in the endometrium of the control group (4.40 vs. 6.73, p=0.02). The median number of CD16(+) cells was significantly higher in infertile women than in control women (0.12 vs. 0.001, p=0.01).

CONCLUSIONS

Significant reductions in the numbers of CD4(+) and CD103(+) cells as well as in the CD4(+)/CD8(+) ratio but an increased number of CD16(+) cells in the endometrium of infertile women suggest that disordered NK cell activity may be a contributor to the etiology of unexplained infertility.

The effect of a high progesterone concentration before oocyte retrieval on the peri-implantation endometrium

In this single-centre, prospective cohort study, the effect of high progesterone level before oocyte retrieval on endometrial morphology and uterine natural killer cell (uKN) count in the peri-implantation period was investigated. A total of 106 women undergoing IVF treatment who did not proceed to fresh embryo transfer were included. Endometrial samples were obtained 7 days after HCG administration. Multiple regression analysis was used to identify factors affecting the results of histological staging and uNK cell count. Progesterone level on the day after HCG administration was the only significant variable associated with the results of histological staging (P = 0.004). Endometrial development in women with high progesterone level was significantly (P < 0.001) more advanced than that of women with normal progesterone; progesterone level on the day of HCG administration was the only significant variable associated with uNK cell count. The median (range) of uNK cell count of 9.6% (2.3-21.6%) in women with high progesterone was significantly (P < 0.001) higher than the median (range) of uNK cell count of 5.7% (1.4-18.7%) in women with normal progesterone. High progesterone level before oocyte retrieval was correlated with advancement in endometrial development as well as increased uNK cell count.

Transcriptome of early embryonic invasion at implantation sites in a murine model

Successful implantation relies on the interaction between a competent embryo and a receptive endometrium. The aim of the present study was to investigate genes differentially expressed in early invasive embryonic tissue versus decidual tissue in mice. Samples were obtained from the ectoplacental cone, the immediately surrounding deciduas and from deciduas from interimplantation sites. Microarray analysis showed that 817 genes were differentially expressed between extra-embryonic tissue and the surrounding decidua and that 360 genes were differentially expressed between the different deciduas, with a high representation of developmental processes. Genes differentially expressed in the maternal compartment included chemokines, lipoproteins, growth factors and transcription factors, whereas the embryonic invasive tissue expressed genes commonly observed in invasive tumour-like processes. These results provide information about genes involved in early embryonic invasion and the control exerted by the surrounding decidua. This information may be useful to find targets involved in pathologies associated with implantation failure and early pregnancy loss.

Natural killer cell in the developing life

\Natural killer (NK) cells that provide first-line innate immune reactions against virus-infected and tumor cells have different roles in different body sites and in different stages. From the beginning of life, NK cells participate in many aspects of development, especially in a successful pregnancy and a healthy neonatal stage. This article reviews recent advances regarding the role of NK cells in implantation, placentation and immune tolerance during pregnancy as well as in the neonatal immune defense. The interactions between NK cells and other immune cells in each developmental stage are discussed.

Ovarian stimulation affects the population of mouse uterine NK cells at early pregnancy

The aim of this study was to determine the influence of ovarian stimulation on endometrial mouse NK cell population. For superovulation, the female adult NMRI mice were injected i.p. with 10 IU of the pregnant mare serum gonadotropin followed 48 h later by an i.p. injection of 10 IU human chorionic gonadotropin hormone. Ovarian stimulated and nonstimulated mice were mated with fertile male. The presence of vaginal plug proved natural pregnancy, and this day was considered as day one of pregnancy. Tissue samples were prepared from the uterine horn and spleen of both groups of study on 7th day of pregnancy. Serum estradiol-17β and progesterone were measured at the same time. The tissue cryosections were prepared and double stained for CD 161 and CD3 markers, and NK cells population was analyzed. Relative frequency of NK cells was significantly lower in stroma and myometrium in hyperstimulated mice compared with the control group. However, no difference was seen in percentage of NK cells in spleen. The ovarian stimulation influences the proportion of uterine NK cells and may affect the embryo implantation.

The association of trefoil factor 3 gene polymorphisms and haplotypes with unexplained female infertility: molecular insights into TFF3 regulation in receptive phase endometrium

Abstract This study examined the genetic variation within the gene trefoil factor 3 (TFF3) in relation to unexplained female infertility in a group of women where aberrant endometrial maturation was suspected. The study consisted of 113 women with a diagnosis of unexplained infertility and 289 healthy fertile volunteers. Five single nucleotide polymorphisms rs225439, rs533093, rs225361, rs11701143, and rs77436142 within TFF3 gene were analyzed using real-time PCR. The formed haplotype pattern within the TFF3 gene in relation to infertility was also assessed. TFF3 protein localization and expression in receptive stage endometrium at the time of implantation was measured in a subset of fertile (n = 7) and infertile (n = 12) women. Allele and genotype frequencies did not differ significantly between fertile and infertile women, nor did the formed haplotypes. TFF3 protein was expressed in all cell types in receptive stage endometria in fertile and infertile women. No significant association was observed between protein expression and analyzed genotypes. A significantly higher TFF3 expression in luminal epithelial cells was detected in women with unexplained infertility (p = 0.003).

Maternal decidual macrophages inhibit NK cell killing of invasive cytotrophoblasts during human pregnancy

Human pregnancy is an immunological paradox. Semiallogeneic (fetal) placental cells (extravillous cytotrophoblasts [CTBs]) invade the uterine lining (decidua), which contains a unique decidual natural killer (dNK) cell population, identified by the cell surface phenotype CD56(bright) CD16(-) CD3(-) and CD14(+) CD206(+) macrophages (dMac). Previous reports suggested that human dNK cells are not a threat to the fetoplacental unit because they are anergic. In contrast, here we showed that purified and exogenously stimulated dNK cells are capable killers of cellular targets, including semiallogeneic CTBs. However, dMacs in the decidual leukocyte (DL) population restrained dNK killing through a transforming growth factor beta1 (TGF-beta1)-dependent mechanism. Our findings support a new model whereby dNK cells, capable of killing CTBs, are prevented from doing so by neighboring macrophages, thus protecting the fetal cells from NK cell attack. We speculate that this mechanism would inhibit dNK cell-mediated killing, even under conditions where high levels of cytokines may stimulate dNK cells, which could pose a threat to the developing placenta.

Complement C3 and decay-accelerating factor expression levels are modulated by human chorionic gonadotropin in endometrial compartments during the implantation window

The control of complement activation in the embryo-maternal environment has been demonstrated to be critical for embryo survival. Complement proteins are expressed in the human endometrium; however, the modulation of this expression by embryo signals has not been explored. To assess the expression of complement proteins in response to human chorionic gonadotropin (hCG), we designed an experimental study using in vivo and in vitro models. Twelve fertile women were treated with hCG or left untreated during the mid-luteal phase, and an endometrial biopsy was performed 24 hours later. The localizations of C3, membrane cofactor protein (MCP; CD46), decay-accelerating factor (DAF; CD55), and protectin (CD59) were assessed by immunohistochemistry, and the messenger RNA (mRNA) levels of these proteins were quantified by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) in cells harvested from endometrial compartments using laser capture microdissection. Endometrial explants were cultured with or without hCG for 24 hours, and the C3 and DAF protein levels were measured by Western blotting. Elevated C3 mRNA levels in stromal cells and elevated DAF levels in epithelial luminal cells were detected after hCG treatment. In the endometrial explant model, the progesterone receptor antagonist RU486 inhibited the increases in the levels of C3 and DAF in response to hCG. The findings of this study indicate that hCG plays a role in embryo-endometrium communication and affects the expression of complement proteins in endometrial compartments during the implantation window.

Modulation of the expression of the transcription factors T-bet and GATA-3 in immortalized human endometrial stromal cells (HESCs) by sex steroid hormones and cAMP

T-bet and GATA-3 are known to regulate cytokine expression in T lymphocytes, and cytokines have been implicated in endometrial regulation and implantation. Previous work showed that female steroid hormones modulate the expression of T-bet in endometrial epithelial cells, suggesting a mechanism for local immune regulation in the human endometrium. We hypothesized that stromal cells are involved in immune regulation, as they have been shown to exert paracrine effects on other endometrial cells and compartments and also secrete cytokines. The objective of this study was to examine the modulation of the gene expression of T-bet and GATA-3, and of the cytokines interferon γ (IFN-γ) and interleukin 4 (IL-4), by female steroid hormones, in human endometrial stromal cells (HESC) in long-term cultures (30 days) mimicking the normal menstrual cycle. T-bet and GATA-3 messenger RNA (mRNA) expression was detected by real-time polymerase chain reaction, and intracellular protein production was demonstrated by immunoblotting. In addition, secretion of IL-4 and IL-15 was measured by enzyme-linked immunosorbent assay. T-bet and IL-4 mRNA expression increased and GATA-3 decreased under decidualization conditions; IFN-γ was not detected. Secretion of IL-15 increased during decidualization, and IL-15 upregulated T-bet gene expression. In conclusion, gene expression of T-bet and GATA-3 by endometrial stromal cells is under hormonal conditions mimicking decidualization, and the results are consistent with an autocrine regulatory mechanism of IL-15 secretion and T-bet expression.

Effects of lactation and pregnancy on gene expression of endometrium of Holstein cows at day 17 of the estrous cycle or pregnancy

Objectives were to determine effects of lactation and pregnancy on endometrial gene expression on d 17 of the estrous cycle and pregnancy. Heifers (n = 33) were assigned randomly after parturition to lactating (L, n = 17) or nonlactating (NL, n = 16) groups. Cows were subjected to an ovulation synchronization program for a timed artificial insemination (TAI); 10 cows in L and 12 in NL were inseminated. Slaughter occurred 17 d after the day equivalent to TAI, and intercaruncular endometrial tissues were collected. Gene expression was determined by DNA microarray analysis for pregnant (L, n = 8; NL, n = 6) and noninseminated cyclic (L, n = 7; NL, n = 4) cows. Differentially expressed genes were selected with a P-value <0.01 and absolute expression >40. In addition, a fold effect >1.5 was used as a criterion for genes affected by pregnancy. In total, 210 genes were differentially regulated by lactation (136 downregulated and 74 upregulated), and 702 genes were differentially regulated by pregnancy (407 downregulated and 295 upregulated). The interaction effect of pregnancy and lactation affected 61 genes. Genes up- and downregulated in pregnant cows were associated with several gene ontology terms, such as defense response and interferon regulatory factor, cell adhesion, and extracellular matrix. The gene ontology analyses of up- and downregulated genes of lactating cows revealed terms related to immunoglobulin-like fold, immune response, COMM domain, and non-membrane-bounded organelle. Several genes upregulated by lactation, such as IGHG1, IGLL1, IGK, and TRD, were related to immune function, particularly for B cells and γδ T cells. Developmental genes related to limb and neural development and glucose homeostasis (e.g., DKK1, RELN, PDK4) were downregulated by lactation, whereas an interaction was also detected for RELN. The stated genes associated with immune function and developmental genes expressed in the endometrium affected by lactational state are possible candidate genes for interventions to improve fertility of lactating dairy cows.

The endocrine and paracrine control of menstruation

During the reproductive life, the human endometrium undergoes cycles of substantial remodeling including, at menstruation, a massive but delimited tissue breakdown immediately followed by scarless repair. The present review aims at summarizing the current knowledge on the endocrine and paracrine control of menstruation in the light of recent observations that undermine obsolete dogmas. Menstruation can be globally considered as a response to falling progesterone concentration. However, tissue breakdown is heterogeneous and tightly controlled in space and time by a complex network of regulators and effectors, including cytokines, chemokines, proteases and various components of an inflammatory response. Moreover, menstruation must be regarded as part of a complex and integrated mechanism of tissue remodeling including features that precede and follow tissue lysis, i.e. decidualization and immediate post-menstrual regeneration. The understanding of the regulation of menstruation is of major basic and clinical interest. Indeed, these mechanisms largely overlap with those controlling other histopathological occurrences of tissue remodeling, such as development and cancer, and inappropriate control of menstrual features is a major potential cause of two frequent endometrial pathologies (i.e. abnormal uterine bleeding and endometriosis).

Global gene expression profiling of proliferative phase endometrium reveals distinct functional subdivisions

The human endometrium follows a predictable pattern of development during the proliferative phase. Endometrial thickness increases after day 3 and then plateaus at days 9 to 10 of the menstrual cycle despite continued high serum levels of estrogen. We hypothesized that proliferative phase endometrium undergoes more than simple estrogen responsive growth, rather it is characterized by complex time-dependent functional activities reflected in differential gene expression. Nine endometrial RNA samples from healthy participants were subjected to microarray analysis and 15 samples were used for quantitative real-time polymerase chain reaction. The samples were divided into early, mid, or late proliferative phase. The early proliferative phase showed higher expression of genes including transforming growth factor β2, chemokine (C-C motif) ligand 18 (CCL18), and metallothionein 2A. The mid-proliferative phase was characterized by higher expression of heat shock proteins and implantation-associated genes including Indian hedgehog, secreted frizzled protein 4, and progesterone receptor. In the late proliferative phase, we identified increased angiotensin II receptor, type 2 and large decrease in expression of genes related to natural killer (NK) cell function. We demonstrate a unique gene expression signature at distinct time points within the proliferative phase. The early proliferative phase is characterized by tissue remodeling, angiogenesis, and modulation of inflammation; the mid-proliferative phase is characterized not only by proliferation in response to estrogens but also marks the onset of expression of genes required for endometrial receptivity and a dampening of estrogen responsiveness. In the late proliferative phase, changes in immune function and NK cells predominate. The proliferative phase is not simply a uniform period of estrogen responsive endometrial growth that can be considered as a single experimental time point when evaluating endometrial development; rather the proliferative phase is complex with differing functions and patterns of gene expression.

Cell death mechanisms at the maternal-fetal interface: insights into the role of granulysin

During mammal pregnancy, a sensitive balance between hormones, cytokines, humoral factors, and local cellular interactions must be established. Cytotoxic cells infiltrating the decidua are heavily equipped with cytolytic molecules, in particular perforin and granulysin. Granulysin is especially abundant in NK cells which are able to spontaneously secrete high quantities of granulysin. Besides being a potent bactericidal and tumoricidal molecule, granulysin is also found to be a chemoattractant and a proinflammatory molecule. The precise role(s) of granulysin at the maternal-fetal interface has not been elucidated yet. It is possible that it behaves as a double-edged sword simultaneously acting as an immunomodulatory and a host defense molecule protecting both the mother and the fetus from a wide spectrum of pathogens, and on the other hand, in case of an NK cell activation, acting as an effector molecule causing the apoptosis of semiallograft trophoblast cells and consequently leading to various pregnancy disorders or pregnancy loss.

The distribution of immune cells and macrophages in the endometrium of women with recurrent reproductive failure I: Techniques

Recurrent miscarriage affects approximately 1% of the population and in half of these cases no cause is found. Abnormally functioning immunocompetent cells, including natural killer (NK) cells, in the endometrium, are thought to be responsible for many such cases and treatment trials including oral prednisolone and intravenous immunoglobulins are now underway. Despite these encouraging developments, there is neither adequate standardization of counting uterine NK cells nor consensus as to what constitutes an abnormal level. To address this issue, immunohistochemistry was used to examine the presence and distribution of selected immune cells and macrophages in the endometrium from 222 women who had a routine endometrial biopsy for investigation of recurrent miscarriage or IVF failure, at various stages of the menstrual cycle, and accessioned prospectively over a 7-month period. Biopsies were examined by H+E and immunostained for CD8(+) T-cells, CD163(+) macrophages, CD56(+) NK cells, and CD57(+) cells. Cell numbers (expressed as immunopositive cells per mm(2)) were determined in the stroma of the functional layer of endometrium and the relative concentrations of some cell types (CD163(+) macrophages, CD56(+) NK cells) were expressed as a percentage of all stromal cells. Routine H+E sections revealed 12 patients with focal "endometritis" without plasma cells. CD8(+) T-cells showed focal perivascular aggregates in most instances, and non-random but scattered cells in all cases, with a twofold increase in the luteal phase. CD163(+) cells were distributed evenly throughout the superficial endometrial stroma and also present as single or clustered macrophages within the lumens of superficial glands, mostly in the luteal phase. CD56(+) NK cells showed "diffuse" but variable distribution throughout the functional layer and perivascular aggregates of various sizes in two thirds of cases. Raw cell counts were low and relatively stable in the proliferative phase, but increased somewhat during the first half of the secretory phase, while in the second half of secretory phase they increased six to tenfold. Percentage counts rose from approximately 5% of stromal cells in the early part of the secretory phase of the cycle to over 35% in premenstrual endometrium. CD57(+) cells were present in very low numbers in most cases. The study illustrates the complexity and variability of immune cell infiltration of endometrium. We stress the need for strict counting protocols and attention to histological criteria if any immunological perturbations potentially responsible for recurrent reproductive failure are to be identified. Reference ranges for individual cell types are only valid for individual "days" of a normalized menstrual cycle.

Does metformin influence the insulin-, IGF I- and IGF II-receptor gene expression and Akt phosphorylation in human decidualized endometrial stromal cells?

OBJECTIVE

To assess the effects of metformin on insulin-, IGF I-, and IGF II-receptor gene expression and Akt phosphorylation in decidualized human endometrial stromal cells (ESC) after stimulation with insulin, IGF I and II.

STUDY DESIGN

ESC were isolated from healthy, regularly cycling women and after two passages decidualized with estrogen/progesterone±metformin. Cells were incubated with insulin, IGF I or IGF II for 1, 5, and 10 min to assess Akt phosphorylation by Western blot. To investigate the insulin-, IGF I- and IGF II-receptor gene expression ESC were incubated with insulin, IGF I or IGF II for 6 and 24h.

RESULTS

Insulin- and IGF I-receptor gene expression in ESC changed significantly after incubation with insulin, IGF I or IGF II. This was further augmented in metformin pretreated cells, while IGF II-receptor gene expression changed particularly after pretreatment with metformin. Akt phosphorylation peaked after 5 min insulin, IGF I and IGF II stimulation in ESC in both control (control 0.08 ± 0.03 vs. insulin 0.74 ± 0.19, IGF I 0.68 ± 0.22, IGF II 0.53 ± 0.13, p<0.05) and metformin pretreated cells (control 0.03 ± 0.01 vs. insulin 0.75 ± 0.11, IGF I 0.74 ± 0.15, IGF II 0.67 ± 0.09, p<0.005). However, there was no significant difference between the control and metformin pretreated group.

CONCLUSION

Insulin, IGF I and IGF II lead to changes in their receptor gene expression and induced Akt phosphorylation in ESC. These effects were further highlighted in the presence of metformin.

Expression and regulation of DNA methyltransferases in human endometrium

The messenger RNA of the DNA methyltransferases DNMT3a and DNMT3b are expressed temporally in the endometrium across the menstrual cycle, as is the steroid hormone regulation of DNMT1, DNMT3a, and DNMT3b. This suggests that DNA methylation in endometrium is changeable during the menstrual cycle and potentially alters gene expression.

Inflammatory pathways in endometrial disorders

Complex interactions between the endocrine and immune systems govern the key endometrial events of implantation and menstruation. In contrast to other tissue sites, cyclical endometrial inflammation is physiological. However, dysregulation of this inflammatory response can lead to endometrial disorders. This review examines the inflammatory processes occurring in the normal endometrium during menstruation and implantation, highlighting recent advances in our understanding and gaps in current knowledge. Subsequently, the role of inflammatory pathways in the pathology of various common endometrial conditions is discussed, including heavy menstrual bleeding, dysmenorrhoea (painful periods), uterine fibroids, endometriosis and recurrent miscarriage.

NK cells, autoantibodies, and immunologic infertility: a complex interplay

Infertility and recurrent spontaneous abortion (RSA) are heterogeneous conditions that have been frequently explained with an immunological pathomechanism. A deeper insight into apparently unexplained infertility and RSA shows increasing evidences supporting both alloimmune and autoimmune mechanisms, in which natural killer (NK) cells and autoantibodies seem to play a relevant role. Successful pregnancy is considered as Th1-Th2 cooperation phenomenon, with a predominantly Th2-type lymphocytes response, together with the emerging role of interleukin (IL)-12, IL-15, and IL-18 and of other unidentified soluble factors dependent on NK cells. Uterine NK cells comprise the largest population at implantation site, and their activity, characteristics, and abundance suggest that they participate at the "decidualization" process that, vice versa, induces NK activation and recruitment in each menstrual cycle. However, NK cell alteration may be associated with impaired pregnancy, and the modulation in the number of circulating NK cells is most likely to be a primary event rather than an active inflammation/drug administration consequence during an inflammatory/autoimmune process, thus playing an important role in the pathogenesis of immunological infertility. Relationships within immunological infertility, recurrent spontaneous abortion, autoantibodies, and NK cells will be reviewed herein.

Bioinformatic detection of E47, E2F1 and SREBP1 transcription factors as potential regulators of genes associated to acquisition of endometrial receptivity

BACKGROUND

The endometrium is a dynamic tissue whose changes are driven by the ovarian steroidal hormones. Its main function is to provide an adequate substrate for embryo implantation. Using microarray technology, several reports have provided the gene expression patterns of human endometrial tissue during the window of implantation. However it is required that biological connections be made across these genomic datasets to take full advantage of them. The objective of this work was to perform a research synthesis of available gene expression profiles related to acquisition of endometrial receptivity for embryo implantation, in order to gain insights into its molecular basis and regulation.

METHODS

Gene expression datasets were intersected to determine a consensus endometrial receptivity transcript list (CERTL). For this cluster of genes we determined their functional annotations using available web-based databases. In addition, promoter sequences were analyzed to identify putative transcription factor binding sites using bioinformatics tools and determined over-represented features.

RESULTS

We found 40 up- and 21 down-regulated transcripts in the CERTL. Those more consistently increased were C4BPA, SPP1, APOD, CD55, CFD, CLDN4, DKK1, ID4, IL15 and MAP3K5 whereas the more consistently decreased were OLFM1, CCNB1, CRABP2, EDN3, FGFR1, MSX1 and MSX2. Functional annotation of CERTL showed it was enriched with transcripts related to the immune response, complement activation and cell cycle regulation. Promoter sequence analysis of genes revealed that DNA binding sites for E47, E2F1 and SREBP1 transcription factors were the most consistently over-represented and in both up- and down-regulated genes during the window of implantation.

CONCLUSIONS

Our research synthesis allowed organizing and mining high throughput data to explore endometrial receptivity and focus future research efforts on specific genes and pathways. The discovery of possible new transcription factors orchestrating the CERTL opens new alternatives for understanding gene expression regulation in uterine function.

Modulation of the maternal immune system by the pre-implantation embryo

Background

A large proportion of pregnancy losses occur during the pre-implantation period, when the developing embryo is elongating rapidly and signalling its presence to the maternal system. The molecular mechanisms that prevent luteolysis and support embryo survival within the maternal environment are not well understood. To gain a more complete picture of these molecular events, genome-wide transcriptional profiles of reproductive day 17 endometrial tissue were determined in pregnant and cyclic Holstein-Friesian dairy cattle.

Results

Microarray analyses revealed 1,839 and 1,189 differentially expressed transcripts between pregnant and cyclic animals (with ≥ 1.5 fold change in expression; P-value < 0.05, MTC Benjamini-Hochberg) in caruncular and intercaruncular endometrium respectively. Gene ontology and biological pathway analysis of differentially expressed genes revealed enrichment for genes involved in interferon signalling and modulation of the immune response in pregnant animals.

Conclusion

The maternal immune system actively surveys the uterine environment during early pregnancy. The embryo modulates this response inducing the expression of endometrial molecules that suppress the immune response and promote maternal tolerance to the embryo. During this period of local immune suppression, genes of the innate immune response (in particular, antimicrobial genes) may function to protect the uterus against infection.

Oestrogen and progesterone regulation of inflammatory processes in the human endometrium

The human endometrium is a unique tissue that has to undergo cycles of proliferation, differentiation, destruction and repair. This ensures that the endometrium is optimally prepared for potential embryo implantation but in the absence of an embryo, menstruation occurs to allow endometrial regeneration. These cycles of tissue remodelling occur under the sequential influence of the sex steroid hormones, oestrogen and progesterone. The physiological events of implantation and menstruation display features of inflammation, tightly regulated by oestrogen and progesterone. After menstruation cellular proliferation and blood vessel growth is modulated by oestrogen while after ovulation progesterone is the dominant hormone. In preparation for implantation, progesterone regulates decidualization of the endometrium, uterine natural killer cell numbers within the endometrium and chemokine and cytokine expression. Menstruation, in contrast, is preceded by progesterone withdrawal, which results in an influx of leukocytes into the endometrium and increased production of chemokines and matrix metalloproteinases allowing tissue degradation. The aim of this article is to review the current knowledge on the regulation of inflammatory events within the endometrium by oestrogen and progesterone, in relation to two pivotal events for human reproduction, implantation and menstruation.

Research on Blastocyst Implantation Essential Factors (BIEFs)

Blastocyst implantation is a process of interaction between embryo and the uterus. To understand this process, this review tries to summarize what blastocyst implantation essential factors (BIEFs) play what roles, as well as where in the uterus and at what stage of implantation process. Addition of more new data to this kind of compilation of information will help the development of diagnosis and treatment of infertility caused by implantation failure. The major, important cells of the endometrial cells that interact with invading blastocyst (trophoblast) are luminal epithelial cells, stromal cells (decidual cells) and resident immune cells. BIEFs regulate these cells to successfully maintain pregnancy.

The embryo's cystatin C and F expression functions as a protective mechanism against the maternal proteinase cathepsin S in mice

A successful implantation of a mammalian embryo into the maternal endometrium depends on a highly synchronized fetal–maternal dialogue involving chemokines, growth factors, and matrix-modifying enzymes. A growing body of evidence suggests an important role for proteinases playing a role in matrix degeneration and enhancing the embryo's invasive capacity and influencing the mother's immunological status in favor of the conceptus. This study focused on the expression of cathepsin S (CTSS) and its inhibitors in the murine fetal–maternal interface as well as the detection of the cellular sources of either proteinase and inhibitors. Nested RT-PCR for detection of embryonic mRNAs, immunohistochemistry of maternal and fetal tissues in B6C3F1 mice, and FACS analysis for determination of immunocompetent cell population were applied. This study shows that the cysteine proteinase CTSS is upregulated in the stroma of the implantation site, and that pregnancy induces an influx of CTSS-positive uterine natural killer cells. Compared to maternal tissues, the CTSS inhibitors cystatin F and C, but not the proteinase itself, are expressed in blastocysts. In conclusion, CTSS underlies a hormonal regulation in the maternal tissue and therewith most likely supports the embryonic implantation. The invading embryo regulates the depth of its own invasion through the expression of the cathepsin inhibitors and furthermore, interleukin-6 to activate CTSS in maternal tissues. Additionally, the observed decrease in CD3+ cells leads to the hypothesis that cells of the cytotoxic T-cell group are down-regulated in the decidua to support the implantation and ensure the survival of the embryo.