Deficiency in clonogenic endometrial mesenchymal stem cells in obese women with reproductive failure--a pilot study

Endometrial and placental stem cells in successful and pathological pregnancies

The endometrium is a dynamic tissue that undergoes extensive remodeling during the menstrual cycle and further gets modified during pregnancy. Different kinds of stem cells are reported in the endometrium. These include epithelial stem cells, endometrial mesenchymal stem cells, side population stem cells, and very small embryonic-like stem cells. Stem cells are also reported in the placenta which includes trophoblast stem cells, side population trophoblast stem cells, and placental mesenchymal stem cells. The endometrial and placental stem cells play a pivotal role in endometrial remodeling and placental vasculogenesis during pregnancy. The dysregulation of stem cell function is reported in various pregnancy complications like preeclampsia, fetal growth restriction, and preterm birth. However, the mechanisms by which it does so are yet elusive. Herein, we review the current knowledge of the different type of stem cells involved in pregnancy initiation and also highlight how their improper functionality leads to pathological pregnancy.

Subtle changes in perivascular endometrial mesenchymal stem cells after local endometrial injury in recurrent implantation failure

Improvements in reproductive techniques have resulted in the live birth rates from IVF procedures increasing from 5% to approximately 30% in recent decades but has plateaued since. Emerging preclinical and clinical data implicates endometrial receptivity deficiencies in patients with recurrent implantation failure (RIF) as the predominant factor hindering successful implantation. Mechanisms on how local endometrial injury (LEI) improves implantation rates in patients with RIF are currently unknown. We hypothesized that LEI may influence perivascular endometrial mesenchymal stem/progenitor cells (eMSCs) which are thought to regenerate the stromal vascular component of the functional layer every month. Here, we assessed the effect of LEI on the proportion and function of eMSCs present in consecutive LEI biopsies. Consecutive paired mid-luteal phase endometrial biopsies obtained from patients with RIF were digested to single cells and the proportion of SUSD2-expressing cells determined. Growth kinetics and decidualization were compared between the consecutive LEI samples. A mid-luteal LEI altered the decidualization capacity of SUSD2⁺ eMSCs in women with RIF, but not their proportion or clonogenicity. With the potential of LEI to improve IVF outcomes in women with RIF, additional investigations are needed to understand the impact of the altered decidualization response in eMSCs.

Miscarriage syndrome: Linking early pregnancy loss to obstetric and age-related disorders

Upon embryo implantation, the uterine mucosa - the endometrium - transforms into a robust decidual matrix that accommodates the fetal placenta throughout pregnancy. This transition is driven by the differentiation of endometrial fibroblasts into specialised decidual cells. A synchronised influx of circulating natural killer (NK) cells and bone marrow-derived mesenchymal stem/progenitor cells (BM-MSC) is pivotal for decidual homeostasis and expansion in early pregnancy. We hypothesise that pathological signals interfering with the recruitment or activity of extrauterine cells at the maternal-fetal interface link miscarriage to subsequent adverse pregnancy outcomes, including further pregnancy losses and preterm labour. NK cells and BM-MSC are key homeostatic regulators in multiple tissues, pointing towards a shared aetiology between recurrent miscarriage and age-related disorders, including cardiometabolic disease. We propose the term ‘miscarriage syndrome’ to capture the health risks associated with miscarriage and discuss how this paradigm can inform clinical practice and accelerate the development of preventative strategies.

Obesity Affects the Proliferative Potential of Equine Endometrial Progenitor Cells and Modulates Their Molecular Phenotype Associated with Mitochondrial Metabolism

The study aimed to investigate the influence of obesity on cellular features of equine endometrial progenitor cells (Eca EPCs), including viability, proliferation capacity, mitochondrial metabolism, and oxidative homeostasis. Eca EPCs derived from non-obese (non-OB) and obese (OB) mares were characterized by cellular phenotype and multipotency. Obesity-induced changes in the activity of Eca EPCs include the decline of their proliferative activity, clonogenic potential, mitochondrial metabolism, and enhanced oxidative stress. Eca EPCs isolated from obese mares were characterized by an increased occurrence of early apoptosis, loss of mitochondrial dynamics, and senescence-associated phenotype. Attenuated metabolism of Eca EPCs OB was related to increased expression of pro-apoptotic markers (CASP9, BAX, P53, P21), enhanced expression of OPN, PI3K, and AKT, simultaneously with decreased signaling stabilizing cellular homeostasis (including mitofusin, SIRT1, FOXP3). Obesity alters functional features and the self-renewal potential of endometrial progenitor cells. The impaired cytophysiology of progenitor cells from obese endometrium predicts lower regenerative capacity if used as autologous transplants.

The Role of Decidual Subpopulations in Implantation, Menstruation and Miscarriage

In each menstrual cycle, the endometrium becomes receptive to embryo implantation while preparing for tissue breakdown and repair. Both pregnancy and menstruation are dependent on spontaneous decidualization of endometrial stromal cells, a progesterone-dependent process that follows rapid, oestrogen-dependent proliferation. During the implantation window, stromal cells mount an acute stress response, which leads to the emergence of functionally distinct decidual subsets, reflecting the level of replication stress incurred during the preceding proliferative phase. Progesterone-dependent, anti-inflammatory decidual cells (DeC) form a robust matrix that accommodates the conceptus whereas pro-inflammatory, progesterone-resistant stressed and senescent decidual cells (senDeC) control tissue remodelling and breakdown. To execute these functions, each decidual subset engages innate immune cells: DeC partner with uterine natural killer (uNK) cells to eliminate senDeC, while senDeC co-opt neutrophils and macrophages to assist with tissue breakdown and repair. Thus, successful transformation of cycling endometrium into the decidua of pregnancy not only requires continuous progesterone signalling but dominance of DeC over senDeC, aided by recruitment and differentiation of circulating NK cells and bone marrow-derived decidual progenitors. We discuss how the frequency of cycles resulting in imbalanced decidual subpopulations may determine the recurrence risk of miscarriage and highlight emerging therapeutic strategies.

Endometrial stem/progenitor cells and their roles in immunity, clinical application, and endometriosis

Endometrial stem/progenitor cells have been proved to exist in periodically regenerated female endometrium and can be divided into three categories: endometrial epithelial stem/progenitor cells, CD140b+CD146+ or SUSD2+ endometrial mesenchymal stem cells (eMSCs), and side population cells (SPs). Endometrial stem/progenitor cells in the menstruation blood are defined as menstrual stem cells (MenSCs). Due to their abundant sources, excellent proliferation, and autotransplantation capabilities, MenSCs are ideal candidates for cell-based therapy in regenerative medicine, inflammation, and immune-related diseases. Endometrial stem/progenitor cells also participate in the occurrence and development of endometriosis by entering the pelvic cavity from retrograde menstruation and becoming overreactive under certain conditions to form new glands and stroma through clonal expansion. Additionally, the limited bone marrow mesenchymal stem cells (BMDSCs) in blood circulation can be recruited and infiltrated into the lesion sites, leading to the establishment of deep invasive endometriosis. On the other hand, cell derived from endometriosis may also enter the blood circulation to form circulating endometrial cells (CECs) with stem cell-like properties, and to migrate and implant into distant tissues. In this manuscript, by reviewing the available literature, we outlined the characteristics of endometrial stem/progenitor cells and summarized their roles in immunoregulation, regenerative medicine, and endometriosis, through which to provide some novel therapeutic strategies for reproductive and cancerous diseases.

Endometrial stem cells: origin, biological function, and therapeutic applications for reproductive disorders

PURPOSE OF REVIEW

Endometrial stem cells (ESCs) are multipotent cells that are thought to originate locally in the endometrium as well as in the bone marrow (BM). They have remarkable plasticity and hold promise as an autologous source for regenerative medicine. This review focuses on recent studies that have advanced our understanding of the biology and function of ESCs and BM-derived stem cells (BMDSCs) as related to physiological reproductive processes and pathologies. Moreover, it reviews recent data on potential therapeutic applications of stem cells to endometrial disorders that lead to reproductive failure.

RECENT FINDINGS

Growing evidence from basic and preclinical studies suggests that ESCs participate in endometrial tissue regeneration and repair. Recent evidence also suggests that ESCs and BMDSCs play important roles in physiological reproductive functions including decidualization, implantation, pregnancy maintenance, and postpartum uterine remodeling. Initial preclinical and clinical studies with ESCs and BMDSCs suggest they have the potential to provide new therapies for various endometrial disorders associated with reproductive failure.

SUMMARY

Uterine ESCs and BMDSCs appear to play an important biological role in reproductive success and failure, and have the potential to become treatment targets for reproductive diseases including recurrent implantation failure, thin endometrium, Asherman, and recurrent pregnancy loss.

Uterine contractile activity and fetal outcome in rats treated with vitamin C during late gestational variable stress exposure

OBJECTIVES

Stress responses vary throughout pregnancy and impact of late gestational variable stress (LGVS) with vitamin C supplementation on uterine contractility is barely explored. This study investigates fetal weight outcome and in-vitro uterine contractile responses to pharmacological agents during LGVS exposure.

METHODS

Twenty four nulliparous pregnant rats were divided into four groups of six. During gestation days 10-19, groups 1 & 2 received normal saline and vitamin C (10 mg/kg) respectively. Groups 3 and 4 were exposed to stress (sleep deprivation, predator exposure, immobility, rapid cage changes, noise, and foreign object) with group 4 concurrently supplemented with vitamin C (10 mg/kg). Serum cortisol, oxidative bio-markers, fetal weights and in-vitro contractile responses of excised uterine tissue to acetylcholine (Ach), oxytocin, calcium chloride (CaCl₂), potassium chloride (KCl), diclofenac, and magnesium ions were determined.

RESULTS

Malondialdehyde activity and cortisol were significantly increased in variable stress only exposed group when compared with control and vitamin C supplemented groups. Fetal body weights, superoxide dismutase and catalase activity were significantly reduced in variable stress only exposed group. Significantly impaired contractile responses to Ach, CaCl₂ & KCl in variable stress only exposed group were modulated in vitamin C supplemented groups. Impaired contractile response to oxytocin was however not reversed. Relaxation responses to diclofenac and magnesium ions were statistically unaltered across groups.

CONCLUSIONS

Impaired fetal weights and uterine contractile activity to Ach, CaCl₂ and KCl during LGVS was modulated by vitamin C supplementation. Impaired oxytocin contractile activity was however unreversed.

Characterization of highly proliferative decidual precursor cells during the window of implantation in human endometrium

Pregnancy depends on the wholesale transformation of the endometrium, a process driven by differentiation of endometrial stromal cells (EnSC) into specialist decidual cells. Upon embryo implantation, decidual cells impart the tissue plasticity needed to accommodate a rapidly growing conceptus and invading placenta, although the underlying mechanisms are unclear. Here we characterize a discrete population of highly proliferative mesenchymal cells (hPMC) in midluteal human endometrium, coinciding with the window of embryo implantation. Single-cell transcriptomics demonstrated that hPMC express genes involved in chemotaxis and vascular transmigration. Although distinct from resident EnSC, hPMC also express genes encoding pivotal decidual transcription factors and markers, most prominently prolactin. We further show that hPMC are enriched around spiral arterioles, scattered throughout the stroma, and occasionally present in glandular and luminal epithelium. The abundance of hPMC correlated with the in vitro colony-forming unit activity of midluteal endometrium and, conversely, clonogenic cells in culture express a gene signature partially conserved in hPMC. Cross-referencing of single-cell RNA-sequencing data sets indicated that hPMC differentiate into a recently discovered decidual subpopulation in early pregnancy. Finally, we demonstrate that recurrent pregnancy loss is associated with hPMC depletion. Collectively, our findings characterize midluteal hPMC as novel decidual precursors that are likely derived from circulating bone marrow-derived mesenchymal stem/stromal cells and integral to decidual plasticity in pregnancy.

Vascular Adhesion Protein-1 Determines the Cellular Properties of Endometrial Pericytes

Vascular adhesion protein-1 (VAP-1) is an inflammation-inducible adhesion molecule and a primary amine oxidase involved in immune cell trafficking. Leukocyte extravasation into tissues is mediated by adhesion molecules expressed on endothelial cells and pericytes. Pericytes play a major role in the angiogenesis and vascularization of cycling endometrium. However, the functional properties of pericytes in the human endometrium are not known. Here we show that pericytes surrounding the spiral arterioles in midluteal human endometrium constitutively express VAP-1. We first characterize these pericytes and demonstrate that knockdown of VAP-1 perturbed their biophysical properties and compromised their contractile, migratory, adhesive and clonogenic capacities. Furthermore, we show that loss of VAP-1 disrupts pericyte-uterine natural killer cell interactions in vitro. Taken together, the data not only reveal that endometrial pericytes represent a cell population with distinct biophysical and functional properties but also suggest a pivotal role for VAP-1 in regulating the recruitment of innate immune cells in human endometrium. We posit that VAP-1 could serve as a potential biomarker for pregnancy pathologies caused by a compromised perivascular environment prior to conception.

Tracking placental development in health and disease

Pre-eclampsia and fetal growth restriction arise from disorders of placental development and have some shared mechanistic features. Initiation is often rooted in the maldevelopment of a maternal-placental blood supply capable of providing for the growth requirements of the fetus in later pregnancy, without exerting undue stress on maternal body systems. Here, we review normal development of a placental bed with a safe and adequate blood supply and a villous placenta-blood interface from which nutrients and oxygen can be extracted for the growing fetus. We consider disease mechanisms that are intrinsic to the maternal environment, the placenta or the interaction between the two. Systemic signalling from the endocrine placenta targets the maternal endothelium and multiple organs to adjust metabolism for an optimal pregnancy and later lactation. This signalling capacity is skewed when placental damage occurs and can deliver a dangerous pathogenic stimulus. We discuss the placental secretome including glycoproteins, microRNAs and extracellular vesicles as potential biomarkers of disease. Angiomodulatory mediators, currently the only effective biomarkers, are discussed alongside non-invasive imaging approaches to the prediction of disease risk. Identifying the signs of impending pathology early enough to intervene and ameliorate disease in later pregnancy remains a complex and challenging objective.

Impact of Sustained Transforming Growth Factor-β Receptor Inhibition on Chromatin Accessibility and Gene Expression in Cultured Human Endometrial MSC

Endometrial mesenchymal stem cells (eMSC) drive the extraordinary regenerative capacity of the human endometrium. Clinical application of eMSC for therapeutic purposes is hampered by spontaneous differentiation and cellular senescence upon large-scale expansion in vitro. A83-01, a selective transforming growth factor-β receptor (TGFβ-R) inhibitor, promotes expansion of eMSC in culture by blocking differentiation and senescence, but the underlying mechanisms are incompletely understood. In this study, we combined RNA-seq and ATAC-seq to study the impact of sustained TGFβ-R inhibition on gene expression and chromatin architecture of eMSC. Treatment of primary eMSC with A83-01 for 5 weeks resulted in differential expression of 1,463 genes. Gene ontology analysis showed enrichment of genes implicated in cell growth whereas extracellular matrix genes and genes involved in cell fate commitment were downregulated. ATAC-seq analysis demonstrated that sustained TGFβ-R inhibition results in opening and closure of 3,555 and 2,412 chromatin loci, respectively. Motif analysis revealed marked enrichment of retinoic acid receptor (RAR) binding sites, which was paralleled by the induction of RARB, encoding retinoic acid receptor beta (RARβ). Selective RARβ inhibition attenuated proliferation and clonogenicity of A83-01 treated eMSC. Taken together, our study provides new insights into the gene networks and genome-wide chromatin changes that underpin maintenance of an undifferentiated phenotype of eMSC in prolonged culture.

Impact of sitagliptin on endometrial mesenchymal stem-like progenitor cells: A randomised, double-blind placebo-controlled feasibility trial

BACKGROUND

Recurrent pregnancy loss (RPL) is associated with the loss of endometrial mesenchymal stem-like progenitor cells (eMSC). DPP4 inhibitors may increase homing and engraftment of bone marrow-derived cells to sites of tissue injury. Here, we evaluated the effect of the DPP4 inhibitor sitagliptin on eMSC in women with RPL, determined the impact on endometrial decidualization, and assessed the feasibility of a full-scale clinical trial.

METHODS

A double-blind, randomised, placebo-controlled feasibility trial on women aged 18 to 42 years with a history of 3 or more miscarriages, regular menstrual cycles, and no contraindications to sitagliptin. Thirty-eight subjects were randomised to either 100 mg sitagliptin daily for 3 consecutive cycles or identical placebo capsules. Computer generated, permuted block randomisation was used to allocate treatment packs. Colony forming unit (CFU) assays were used to quantify eMSC in midluteal endometrial biopsies. The primary outcome measure was CFU counts. Secondary outcome measures were endometrial thickness, study acceptability, and first pregnancy outcome within 12 months following the study. Tissue samples were subjected to explorative investigations.

FINDINGS

CFU counts following sitagliptin were higher compared to placebo only when adjusted for baseline CFU counts and age (RR: 1.52, 95% CI: 1.32-1.75, P<0.01). The change in CFU count was 1.68 in the sitagliptin group and 1.08 in the placebo group. Trial recruitment, acceptability, and drug compliance were high. There were no serious adverse events. Explorative investigations showed that sitagliptin inhibits the expression of DIO2, a marker gene of senescent decidual cells.

INTERPRETATION

Sitagliptin increases eMSCs and decreases decidual senescence. A large-scale clinical trial evaluating the impact of preconception sitagliptin treatment on pregnancy outcome in RPL is feasible and warranted.

FUNDING

Tommy's Baby Charity.

CLINICAL TRIAL REGISTRATION

EU Clinical Trials Register no. 2016-001120-54.

Adult bone marrow progenitors become decidual cells and contribute to embryo implantation and pregnancy

Decidua is a transient uterine tissue shared by mammals with hemochorial placenta and is essential for pregnancy. The decidua is infiltrated by many immune cells promoting pregnancy. Adult bone marrow (BM)-derived cells (BMDCs) differentiate into rare populations of nonhematopoietic endometrial cells in the uterus. However, whether adult BMDCs become nonhematopoietic decidual cells and contribute functionally to pregnancy is unknown. Here, we show that pregnancy mobilizes mesenchymal stem cells (MSCs) to the circulation and that pregnancy induces considerable adult BMDCs recruitment to decidua, where some differentiate into nonhematopoietic prolactin-expressing decidual cells. To explore the functional importance of nonhematopoietic BMDCs to pregnancy, we used Homeobox a11 (Hoxa11)-deficient mice, having endometrial stromal-specific defects precluding decidualization and successful pregnancy. Hoxa11 expression in BM is restricted to nonhematopoietic cells. BM transplant (BMT) from wild-type (WT) to Hoxa11-/- mice results in stromal expansion, gland formation, and marked decidualization otherwise absent in Hoxa11-/- mice. Moreover, in Hoxa11+/- mice, which have increased pregnancy losses, BMT from WT donors leads to normalized uterine expression of numerous decidualization-related genes and rescue of pregnancy loss. Collectively, these findings reveal that adult BMDCs have a previously unrecognized nonhematopoietic physiologic contribution to decidual stroma, thereby playing important roles in decidualization and pregnancy.

An Endogenous Anti-aging Factor, Sonic Hedgehog, Suppresses Endometrial Stem Cell Aging through SERPINB2

Endometrial stem cells are located in the basal layer of the endometrium, and they are responsible for the cyclic regeneration of the uterus during the menstrual cycle. Recent studies have revealed that recurrent pregnancy loss is associated with an age-related stem cell deficiency in the endometrium. Therefore, intensive study of endometrial stem cell aging may provide new insights for preventing recurrent pregnancy loss. Sonic hedgehog (SHH) signaling has been identified as a morphogen during the embryonic development processes. In addition to this canonical function, we found that the age-associated decline in regenerative potential in the endometrium may be due to decreased SHH-signaling integrity in local stem cells with aging. Importantly, the current study also showed that SHH activity clearly declines with aging both in vitro and in vivo, and exogenous SHH treatment significantly alleviates various aging-associated declines in multiple endometrial stem cell functions, suggesting that SHH may act as an endogenous anti-aging factor in human endometrial stem cells. Moreover, we found that stem cell senescence may enhance SERPINB2 expression, which in turn mediates the effect of SHH on alleviating senescence-induced endometrial stem cell dysfunctions, suggesting that SERPINB2 is a master regulator of SHH signaling during the aging process.

Uterine stem cells: from basic research to advanced cell therapies

BACKGROUND

Stem cell research in the endometrium and myometrium from animal models and humans has led to the identification of endometrial/myometrial stem cells and their niches. This basic knowledge is beginning to be translated to clinical use for incurable uterine pathologies. Additionally, the implication of bone marrow-derived stem cells (BMDSCs) in uterine physiology has opened the field for the exploration of an exogenous and autologous source of stem cells.

OBJECTIVE AND RATIONALE

In this review, we outline the progress of endometrial and myometrial stem/progenitor cells in both human and mouse models from their characterization to their clinical application, indicating roles in Asherman syndrome, atrophic endometrium and tissue engineering, among others.

SEARCH METHODS

A comprehensive search of PubMed and Google Scholar up to December 2017 was conducted to identify peer-reviewed literature related to the contribution of bone marrow, endometrial and myometrial stem cells to potential physiological regeneration as well as their implications in pathologies of the human uterus.

OUTCOMES

The discovery and main characteristics of stem cells in the murine and human endometrium and myometrium are presented together with the relevance of their niches and cross-regulation. The current state of advanced stem cell therapy using BMDSCs in the treatment of Asherman syndrome and atrophic endometrium is analyzed. In the myometrium, the understanding of genetic and epigenetic defects that result in the development of tumor-initiating cells in the myometrial stem niche and thus contribute to the growth of uterine leiomyoma is also presented. Finally, recent advances in tissue engineering based on the creation of novel three-dimensional scaffolds or decellularisation open up new perspectives for the field of uterine transplantation.

WIDER IMPLICATIONS

More than a decade after their discovery, the knowledge of uterine stem cells and their niches is crystalising into novel therapeutic approaches aiming to treat with cells those conditions that cannot be cured with drugs, particularly the currently incurable uterine pathologies. Additional work and improvements are needed, but the basis has been formed for this therapeutic application of uterine cells.

Antioxidants and Oxidative Stress: Focus in Obese Pregnancies

The prevalence of obesity in women of childbearing age around the globe has dramatically increased in the last decades. Obesity is characterized by a low-state chronic inflammation, metabolism impairment and oxidative stress, among other pathological changes. Getting pregnant in this situation involves that gestation will occur in an unhealthy environment, that can potentially jeopardize both maternal and fetal health. In this review, we analyze the role of maternal obesity-induced oxidative stress as a risk factor to develop adverse outcomes during gestation, including reduced fertility, spontaneous abortion, teratogenesis, preeclampsia, and intrauterine growth restriction. Evidences of macromolecule oxidation increase in reactive oxygen species generation and antioxidant defense alterations are commonly described in maternal and fetal tissues. Thus, antioxidant supplementation become an interesting prophylactic and therapeutic tool, that yields positive results in cellular, and animal models. However, the results from most meta-analysis studying the effect of these therapies in complicated gestations in humans are not really encouraging. It is still to be analyzed whether these therapies could work if applied to cohorts of patients at a high risk, such as those with low concentration of antioxidants or obese pregnant women.

Deregulation of the endometrial stromal cell secretome precedes embryo implantation failure

STUDY QUESTION

Is implantation failure following ART associated with a perturbed decidual response in endometrial stromal cells (EnSCs)?

SUMMARY ANSWER

Dynamic changes in the secretome of decidualizing EnSCs underpin the transition of a hostile to a supportive endometrial microenvironment for embryo implantation; perturbation in this transitional pathway prior to ART is associated with implantation failure.

WHAT IS KNOWN ALREADY

Implantation is the rate-limiting step in ART, although the contribution of an aberrant endometrial microenvironment in IVF failure remains ill defined.

STUDY DESIGN, SIZE, DURATION

In vitro characterization of the temporal changes in the decidual response of primary EnSCs isolated prior to a successful or failed ART cycle. An analysis of embryo responses to secreted cues from undifferentiated and decidualizing EnSCs was performed. The primary clinical outcome of the study was a positive urinary pregnancy test 14 days after embryo transfer.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Primary EnSCs were isolated from endometrial biopsies obtained prior to IVF treatment and cryopreserved. EnSCs from 10 pregnant and 10 non-pregnant patients were then thawed, expanded in culture, subjected to clonogenic assays, and decidualized for either 2 or 8 days. Transcript levels of decidual marker gene [prolactin (PRL), insulin-like growth factor binding protein 1 (IGFBP1) and 11β-hydroxysteroid dehydrogenase (HSD11B1)] were analysed using real-time quantitative PCR and temporal secretome changes of 45 cytokines, chemokines and growth factors were measured by multiplex suspension bead immunoassay. The impact of the EnSC secretome on human blastocyst development was scored morphologically; and embryo secretions in response to EnSC cues analyzed by multiplex suspension bead immunoassay.

MAIN RESULTS AND THE ROLE OF CHANCE

Clonogenicity and induction of decidual marker genes were comparable between EnSC cultures from pregnant and non-pregnant group groups (P > 0.05). Analysis of 23 secreted factors revealed that successful implantation was associated with co-ordinated secretome changes in decidualizing EnSCs, which were most pronounced on Day 2 of differentiation: 17 differentially secreted proteins on Day 2 of decidualization relative to undifferentiated (Day 0) EnSCs (P < 0.05); 11 differentially secreted proteins on Day 8 relative to Day 2 (P < 0.05); and eight differentially secreted proteins on Day 8 relative to Day 0 (P < 0.05). By contrast, failed implantation was associated with a disordered secretome response. Blastocyst development was compromised when cultured for 24 h in medium conditioned by undifferentiated EnSCs when compared to decidualizing EnSCs. Analysis of the embryo microdroplets revealed that human blastocysts mount a secretory cytokine response to soluble decidual factors produced during the early (Day 2) but not late phase (Day 8) of differentiation. The embryo responses to secreted factors from decidualizing EnSCs were comparable between the pregnant and non-pregnant group (P > 0.05).

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

Although this study uses primary EnSCs and human embryos, caution is warranted when extrapolating the results to the in vivo situation because of the correlative nature of the study and limited sample size.

WIDER IMPLICATIONS OF THE FINDINGS

Our finding raises the prospect that endometrial analysis prior to ART could minimize the risk of treatment failure.

STUDY FUNDING AND COMPETING INTEREST(S)

This work was supported by funds from the Biomedical Research Unit in Reproductive Health, a joint initiative of the University Hospitals Coventry & Warwickshire NHS Trust and Warwick Medical School, the University of Nottingham and Nurture Fertility, and the National Medical Research Council, Singapore (NMRC/BNIG14NOV023), the "Instituut voor Innovatie door Wetenschap en Technologie" (IWT, Flanders, Belgium), the "Fonds voor Wetenschappelijk Onderzoek" (FWO, Flanders, Belgium) and the "Wetenschappelijk Fonds Willy Gepts" (WFWG, UZ Brussel). The authors have declared that no conflict of interest exists.

Endometrial mesenchymal stem stromal cells in mature and immature sheep: An in vitro study

BACKGROUND

Endometrial mesenchymal stem stromal cells (EnMSCs) are critical for uterine function, repair, and regeneration.

OBJECTIVE

This study introduced isolation technique of EnMSCs and compared the characteristics of EnMSCs in mature and immature ewes.

MATERIALS AND METHODS

Endometrial tissue samples from the uterus of 10 ewes were collected from the slaughterhouse. Endometrial cells were isolated from tissue using cold incubation and then chopping and treating was performed with collagenase type I. Isolated cells were cultured in cell culture medium and then attached cells to flasks were harvested as EnMSCs and subcultured. To enumerate the cells, the population doubling time (PDT) was determined and 2.2×10⁴ cells in passage 4 were seeded into 24-well culture plates to compare the growth curves of isolated cells. Reverse transcription polymerase chain reaction (RT-PCR) was performed for detection of CD34 and CD73 markers. The osteogenic and adipogenic potential of isolated cells were determined using differentiation tests.

RESULTS

EnMSCs adhered to the flasks and displayed spindle-shape. Based on findings of the cell count and the growth curves, the EnMSCs growth was significantly more prominent in immature ewes in comparison to mature sheep. The PDT of EnMSCs in immature ewes was about 21 hr whereas this time period was two times higher (45 hr) in mature sheep. RT-PCR analyses of EnMSCs were positive for CD73 and negative for CD34. EnMSCs were differentiated into osteoblasts and adipocytes.

CONCLUSION

Based on mesenchymal stem cells characters confirmed in EnMSCs, they can be a candidate for cell therapy and regenerative medicine.

Clearance of senescent decidual cells by uterine natural killer cells in cycling human endometrium

In cycling human endometrium, menstruation is followed by rapid estrogen-dependent growth. Upon ovulation, progesterone and rising cellular cAMP levels activate the transcription factor Forkhead box O1 (FOXO1) in endometrial stromal cells (EnSCs), leading to cell cycle exit and differentiation into decidual cells that control embryo implantation. Here we show that FOXO1 also causes acute senescence of a subpopulation of decidualizing EnSCs in an IL-8 dependent manner. Selective depletion or enrichment of this subpopulation revealed that decidual senescence drives the transient inflammatory response associated with endometrial receptivity. Further, senescent cells prevent differentiation of endometrial mesenchymal stem cells in decidualizing cultures. As the cycle progresses, IL-15 activated uterine natural killer (uNK) cells selectively target and clear senescent decidual cells through granule exocytosis. Our findings reveal that acute decidual senescence governs endometrial rejuvenation and remodeling at embryo implantation, and suggest a critical role for uNK cells in maintaining homeostasis in cycling endometrium.

The impact of uterine immaturity on obstetrical syndromes during adolescence

Pregnant nulliparous adolescents are at increased risk, inversely proportional to their age, of major obstetric syndromes, including preeclampsia, fetal growth restriction, and preterm birth. Emerging evidence indicates that biological immaturity of the uterus accounts for the increased incidence of obstetrical disorders in very young mothers, possibly compounded by sociodemographic factors associated with teenage pregnancy. The endometrium in most newborns is intrinsically resistant to progesterone signaling, and the rate of transition to a fully responsive tissue likely determines pregnancy outcome during adolescence. In addition to ontogenetic progesterone resistance, other factors appear important for the transition of the immature uterus to a functional organ, including estrogen-dependent growth and tissue-specific conditioning of uterine natural killer cells, which plays a critical role in vascular adaptation during pregnancy. The perivascular space around the spiral arteries is rich in endometrial mesenchymal stem-like cells, and dynamic changes in this niche are essential to accommodate endovascular trophoblast invasion and deep placentation. Here we evaluate the intrinsic (uterine-specific) mechanisms that predispose adolescent mothers to the great obstetrical syndromes and discuss the convergence of extrinsic risk factors that may be amenable to intervention.

Advances in improving fertility in women through stem cell-based clinical platforms

INTRODUCTION

Due to their regenerative ability, stem cells are looked at as a promising tool for improving infertility treatments in women. As the main limiting factor in female fertility is represented by the decrease of ovarian reserve, the main goals of stem cell-based clinical platforms would be to obtain in vitro or in vivo neo-oogenesis. Refractory endometrial factor infertility also represents an obstacle for female reproduction for which stem cells might provide novel treatment strategies. Areas covered: A systematic search of the literature was performed on MEDLINE/PubMed database to identify relevant articles using stem-cell based clinical or research platforms in the field of female infertility. Expert opinion: In vitro oogenesis has not so far developed beyond the stage of oocyte-like cells whose normal progression to mature oocytes and ability to be fertilized was not proved. Extensive epigenetic programming of gamete precursors and the complex interactions between somatic and germ cells required for human oogenesis likely represent the main obstacles in stem-cell-based neo-oogenesis. Also resuming oogenesis in vivo in adulthood still appears a distant hypothesis, as there is still a lack of consensus about the existence and functionality of adult ovarian stem cells.

Success after failure: the role of endometrial stem cells in recurrent miscarriage

Endometrial stem-like cells, including mesenchymal stem cells (MSCs) and epithelial progenitor cells, are essential for cyclic regeneration of the endometrium following menstrual shedding. Emerging evidence indicates that endometrial MSCs (eMSCs) constitute a dynamic population of cells that enables the endometrium to adapt in response to a failed pregnancy. Recurrent miscarriage is associated with relative depletion of endometrial eMSCs, which not only curtails the intrinsic ability of the endometrium to adapt to reproductive failure but also compromises endometrial decidualization, an obligatory transformation process for embryo implantation. These novel findings should pave the way for more effective screening of women at risk of pregnancy failure before conception.

The potential perinatal origin of placentation disorders in the young primigravida

The fetus is exposed to high plasma concentrations of unbound estrogens and progesterone throughout pregnancy. However, secretory or decidual changes in the fetal uterus occur relatively infrequently before birth, suggesting a variable endometrial progesterone response at the time of birth. Arguably, partial progesterone resistance that persists into adolescent years may compromise the physiological transformation of the spiral arteries and predispose for defective placentation in the case of pregnancy. Decidualization of the endometrial stromal compartment and junctional zone myometrium precedes trophoblast invasion. It represents the first step in the process of spiral artery remodeling needed to establish effective uteroplacental blood flow by midpregnancy. The major obstetric syndromes caused by impaired placental bed spiral artery remodeling are prevalent in teenage pregnancies, including preeclampsia, fetal growth restriction, and spontaneous preterm labor. Preconditioning of the uterus in response to cyclic menstruation during adolescence may be critical to achieve full uterine responsiveness to hormonal cues. Understanding the mechanisms of functional maturation of the uterus during the early reproductive years may yield novel insights into the major obstetric syndromes.

Regenerative potential of endometrial stem cells: a mini review

Recent findings in stem cell biology have opened a new window in regenerative medicine. The endometrium possesses mesenchymal stem cells (MSCs) called endometrial stem cells (EnSCs) having specific regenerative properties linked to adult stem cells. They contribute in tissue remodeling and engineering and were shown to have immuno-modulating effects. Many clinical trials were undertaken to ascertain the therapeutic potential of EnSCS. In this mini review, we showed that EnSCs are readily available sources of adult stem cells in the uterus that can be highlighted for their renewable multipotent and differentiation properties. This cell population may be a practical solution of choice in reproductive biology, regenerative medicine and autologous stem cell therapy.

Cyclic decidualization of the human endometrium in reproductive health and failure

Decidualization denotes the transformation of endometrial stromal fibroblasts into specialized secretory decidual cells that provide a nutritive and immunoprivileged matrix essential for embryo implantation and placental development. In contrast to most mammals, decidualization of the human endometrium does not require embryo implantation. Instead, this process is driven by the postovulatory rise in progesterone levels and increasing local cAMP production. In response to falling progesterone levels, spontaneous decidualization causes menstrual shedding and cyclic regeneration of the endometrium. A growing body of evidence indicates that the shift from embryonic to maternal control of the decidual process represents a pivotal evolutionary adaptation to the challenge posed by invasive and chromosomally diverse human embryos. This concept is predicated on the ability of decidualizing stromal cells to respond to individual embryos in a manner that either promotes implantation and further development or facilitates early rejection. Furthermore, menstruation and cyclic regeneration involves stem cell recruitment and renders the endometrium intrinsically capable of adapting its decidual response to maximize reproductive success. Here we review the endocrine, paracrine, and autocrine cues that tightly govern this differentiation process. In response to activation of various signaling pathways and genome-wide chromatin remodeling, evolutionarily conserved transcriptional factors gain access to the decidua-specific regulatory circuitry. Once initiated, the decidual process is poised to transit through distinct phenotypic phases that underpin endometrial receptivity, embryo selection, and, ultimately, resolution of pregnancy. We discuss how disorders that subvert the programming, initiation, or progression of decidualization compromise reproductive health and predispose for pregnancy failure.

Decidualization induces a secretome switch in perivascular niche cells of the human endometrium

The endometrial perivascular microenvironment is rich in mesenchymal stem-like cells that express type 1 integral membrane protein Sushi domain containing 2 (SUSD2) but the role of these cells in the decidual transformation of this tissue in pregnancy is unknown. We used an antibody directed against SUSD2 (W5C5) to isolate perivascular (W5C5(+)) and nonperivascular (W5C5(-)) fibroblasts from mid-luteal biopsies. We show that SUSD2 expression, and hence the ratio of W5C5(+):W5C5(-) cells, changes in culture depending on cell-cell contact and activation of the Notch signaling pathway. RNA sequencing revealed that cultures derived from W5C5(+) progenitor cells remain phenotypically distinct by the enrichment of novel and established endometrial perivascular signature genes. In an undifferentiated state, W5C5(+)-derived cells produced lower levels of various chemokines and inflammatory modulators when compared with their W5C5(-) counterparts. This divergence in secretomes was switched and became more pronounced upon decidualization, which transformed perivascular W5C5(+) cells into the dominant source of a range of chemokines and cytokines, including leukemia inhibitory factor and chemokine (C-C motif) ligand 7. Our findings suggest that the decidual response is spatially organized at the embryo-maternal interface with differentiating perivascular cells establishing distinct cytokine and chemokine profiles that could potentially direct trophoblast toward maternal vessels and govern local immune responses in pregnancy.