Regeneration of uterine horns in rats using collagen scaffolds loaded with human embryonic stem cell-derived endometrium-like cells

Endometrial Regeneration in Asherman's Syndrome: Clinical and Translational evidence of Stem Cell Therapies

Asherman's Syndrome or Intrauterine adhesions is an acquired uterine condition where fibrous scarring forms within the uterine cavity, resulting in reduced menstrual flow, pelvic pain and infertility. Until recently, the molecular mechanisms leading to the formation of fibrosis were poorly understood, and the treatment of Asherman's syndrome has largely focused on hysteroscopic resection of adhesions, hormonal therapy, and physical barriers. Numerous studies have begun exploring the molecular mechanisms behind the fibrotic process underlying Asherman's Syndrome as well as the role of stem cells in the regeneration of the endometrium as a treatment modality. The present review offers a summary of available stem cell-based regeneration studies, as well as highlighting current gaps in research.

Effect of Autologous Adipose-Derived Stromal Vascular Fraction Transplantation on Endometrial Regeneration in Patients of Asherman's Syndrome: a Pilot Study

This study aimed to investigate the efficacy of the transplantation of autologous adipose-derived stromal vascular fraction (AD-SVF) containing adipose stem cells (ASCs) in regenerating functional endometrium in patients with severe Asherman's syndrome (AS). This was a prospective clinical study involving six infertile women aged 20-44 years who were diagnosed with severe AS by hysteroscopy. Autologous AD-SVF were isolated from patient's adipose tissue obtained by liposuction and then transplanted into uterus by transcervical instillation using an embryo transfer catheter followed by estrogen hormone therapy. Endometrial growth and pregnancy outcomes were assessed after fresh or frozen embryo transfer. Of the five patients who remained in the study, two women who had amenorrhea resumed their menstruation with irregular scant bleeding. Three women with oligomenorrhea had increased menstrual amount. Before therapy, the maximum EMT measured ultrasonographically was 3.0 ± 1.0 mm (range: 1.7 to 4.4 mm), which significantly increased to 6.9 ± 2.9 mm (range: 5.2 to 12.0 mm, p = 0.043) after cell transplantation and hormone therapy. Five women had embryo transfer after therapy: one fresh and four frozen-thawed. One woman conceived but aborted spontaneously at 9-week gestation. AD-SVF is a safe and easily available cell product containing adipose-derived stem cells. Autologous transplantation of AD-SVF may regenerate damaged human endometrium and increase endometrial receptivity. Our study showed the feasibility of AD-SVF in restoring endometrial function and increasing endometrial thickness. This cell therapy may become a promising treatment for infertile women with endometrial dysfunction and needs further investigation.

Urinary bladder matrix scaffolds improve endometrial regeneration in a rat model of intrauterine adhesions

Intrauterine adhesions caused by damage to the basal layer of the endometrium have a serious impact on women's fertility. Currently, there is no effective treatment to promote the regeneration of the endometrium. Urinary bladder matrix (UBM) is a derivative extracellular matrix biomaterial that has a complete basement membrane and provides a basis for the body to achieve complete self-functional repair. In this study, UBM was transplanted into the uterine horns of intrauterine adhesions in Sprague-Dawley rats to test whether UBM could improve endometrial regeneration in rats with intrauterine adhesions. Thicker endometria, increased numbers of glands, fewer fibrotic areas and increased proliferation of cells and blood vessels were found in the UBM group compared to the injury group. Transplantation of UBM reduced the mRNA levels of proinflammatory cytokines (tumor necrosis factor α) and increased those of anti-inflammatory cytokines (basic fibroblast growth factor) compared to the injury group. In the UBM group, the mRNA expression of endometrial receptivity factors (leukemia inhibitory factor and integrin αVβ₃) was higher than that in the injury group, but it was lower than that in the normal group and the sham-operated group. More embryos were seen in the UBM group than in the injury group, although the UBM group had fewer embryos than the normal and sham-operated groups. Therefore, UBM may contribute to endometrial regeneration and may improve endometrial receptivity and fertility.

A collagen scaffold loaded with human umbilical cord-derived mesenchymal stem cells facilitates endometrial regeneration and restores fertility

In women of reproductive age, severe injuries to the endometrium are often accompanied by endometrial scar formation or intrauterine adhesions (IUAs), which can result in infertility or miscarriage. Although many approaches have been used to treat severe IUAs, high recurrence rates and endometrial thinning have limited therapeutic efficiency. In this study, a collagen scaffold (CS) loaded with human umbilical cord-derived mesenchymal stem cells (UC-MSCs) was fabricated and applied for endometrial regeneration. The CS/UC-MSCs promoted human endometrial stromal cell proliferation and inhibited apoptosis in vitro through paracrine effects. In a model of endometrial damage, transplantation with the CS/UC-MSCs maintained normal luminal structure, promoted endometrial regeneration and collagen remodeling, induced intrinsic endometrial cell proliferation and epithelium recovery, and enhanced the expression of estrogen receptor α and progesterone receptor. An improved ability of the regenerated endometrium to receive embryos was confirmed. Together, our results indicate that the CS/UC-MSCs promoted endometrial structural reconstruction and functional recovery. Topical administration of the CS/UC-MSCs after trans-cervical resection of adhesions might prevent re-adhesion, promote endometrium regeneration and improve pregnancy outcomes for patients with severe IUAs. STATEMENT OF SIGNIFICANCE: Intrauterine adhesions due to severe endometrium injuries happen frequently in clinic and become one of the crucial reasons for women's infertility or miscarriage. Therefore, how to regenerate the damaged endometrium is a big challenge. In this study, a collagen scaffold (CS) loaded with human umbilical cord-derived mesenchymal stem cells (UC-MSCs) was fabricated and applied for endometrium regeneration. Herein, UC-MSCs, known for low immunogenicity and high proliferative potential, exhibit promising potential for endometrium regeneration; and collagen scaffolds provide suitable physical support. It was proved that transplantation with CS/UC-MSCs promoted endometrial regeneration and fertility restoration. It suggested that topical administration of CS/UC-MSCs in uterus could be a promising strategy for patients suffering severe intrauterine adhesion and infertility.

Synergistic regenerative effects of functionalized endometrial stromal cells with hyaluronic acid hydrogel in a murine model of uterine damage

Clinically intractable infertility and recurrent miscarriage due to irreversible endometrial damage need to be treated with biomaterial- and cell-based therapies. Some previous studies have reported on the efficacy of a collagen scaffold and/or bone marrow-derived mesenchymal stem cells. However, the functional differentiation of grafted cells was uncertain, and the time required for regeneration was long in these studies. Here, we show the synergistic regenerative effects of hyaluronic acid (HA) hydrogel with in vitro decidualized endometrial stromal cells (EMSCs) in a murine uterine infertility (synechiae) model. Decidualized EMSCs (dEMSCs) were encapsulated with HA hydrogel, combined with three different doses of fibrinogen/thrombin (5, 50, and 500 mIU/mL). The HA/fibrin gel showed biocompatibility when mixed with dEMSCs. The addition of thrombin enhanced gel formation (5 and 50 mIU/mL) and engraftment and enabled the effective release of adhesion molecules. Within two weeks, which is a short duration, treatment with hydrogel decreased the fibrous tissue and increased the thickness of the endometrium. The regenerated endometrium demonstrated functional recovery, as evidenced by the expression and secretion of molecules essential for embryonic implantation, such as Desmin, CD44, PECAM, and IGF-1. Transferred embryos successfully implanted and the normal development of implanted embryos (n = 37) were evaluated by co-localization of distinct markers of the three germ layers (Sox2, Nestin, Brachyury, AFP, and HNF4α). Live birth of offspring was achieved in the regenerated endometrium by HA hydrogel. Therefore, HA hydrogel-mixed dEMSCs can be an innovative treatment strategy with rapid recovery of endometrial damage and may also have therapeutic potential in intractable infertility or recurrent miscarriage. STATEMENT OF SIGNIFICANCE: Decidualized EMSCs (dEMSCs) encapsulated with HA hydrogel combined with fibrinogen/thrombin (50 mIU/mL) showed injectability and biocompatibility when mixed with dEMSCs. Hydrogel-encapsulated dEMSCs can be a useful treatment for damaged endometrium in short duration, with successful implantation and normal development in a murine model.

Efficient Production of Murine Uterine Damage Model

BACKGROUND

Thin or damaged endometrium causes uterine factor-derived infertility resulting in a failure of embryonic implantation. Regeneration of endometrium is a major issue in gynecology and reproductive medicine. Various types of cells and scaffolds were studied to establish an effective therapeutic strategy. For this type of investigations, production of optimal animal models is indispensable. In this study, we tried to establish various murine uterine damage models and compared their features.

METHODS

Three to ten-week-old C57BL/6 female mice were anesthetized using isoflurane. Chemical and mechanical methods using ethanol (EtOH) at 70 or 100% and copper scraper were compared to determine the most efficient condition. Damage of uterine tissue was induced either by vaginal or dorsal surgical approach. After 7-10 days, gross and microscopic morphology, safety and efficiency were compared among the groups.

RESULTS

Both chemical and mechanical methods resulted in thinner endometrium and reduced number of glands. Gross morphology assessment revealed that the damaged regions of uteri showed various shapes including shrinkage or cystic dilatation of uterine horns. The duration of anesthesia significantly affected recovery after procedure. Uterine damage was most effectively induced by dorsal approach using 100% EtOH treatment compared to mechanical methods.

CONCLUSION

Taken together, murine uterine damage models were most successfully established by chemical treatment. This production protocols could be applied further to larger animals such as non-human primate.

Current status of uterine regenerative medicine for absolute uterine factor infertility

Though assisted reproduction technology has been developed, a treatment for absolute uterine factor infertility (AUFI), such as defects in the uterus, has not yet been established. Regenerative medicine has been developed and applied clinically over recent years; however, whole solid organs still cannot be produced. Though uterine regeneration has the potential to be a treatment for AUFI, there have been only a few studies on uterine regeneration involving the myometrium in vivo. In the present report, those relevant articles are reviewed. A literature search was conducted in PubMed with a combination of key words, and 10 articles were found, including nine in rat models and one in a mouse model. Of these studies, eight used scaffolds and two were performed without scaffolds. In four of these studies, scaffolds were re-cellularized with various cells. In the remaining four studies, scaffolds were transplanted alone, or other structures were used. Though the methods differed, the injured uterus recovered well, morphologically and functionally, in every study. Only 10 articles were relevant to our investigation, but the results were favorable, if limited to partial regeneration. Recently, uterus transplantation (UTx) has been investigated as a treatment for AUFI. However, UTx has many problems in the medical, ethical and social fields. Though the artificial uterus was also researched and some improvements in this technology were reported, it will take long time for this to reach a clinically applicable stage. Though the results of uterine regeneration studies were promising, these studies were conducted using animal models, so further human studies and trials are needed.

Effects of menstrual blood‑derived stem cells on endometrial injury repair

The present study aimed to investigate the effects of menstrual blood-derived stem cells (MenSCs) on endometrial injury repair. MenSCs were isolated from human menstrual blood and were cultured in vitro. Flow cytometric analysis of cells in the third generation demonstrated that MenSCs exhibited higher expression levels of cluster of differentiation (CD)90 and lower expression levels of CD146, which suggested that the MenSCs were cultured successfully. A mechanical damage model of unilateral (right) endometrium was established in BALB/c nude mice, which were divided into four groups, Normal, negative control (NC), Model and MenSC. MenSCs transfected with adenovirus-enhanced green fluorescent protein were transplanted into the right uterine cavity of mice in the MenSC and NC groups. The protein expression levels of keratin, vimentin, and vascular endothelial growth factor (VEGF) and the average endometrial thickness were measured by immunohistochemistry; the average optical density of vimentin, VEGF and keratin in the MenSC-treated group was significantly higher compared with the untreated Model group. Fertility tests were performed to determine the pregnancy rate of each group; following endometrial damage in BALB/c nude mice, endometrial thickness was decreased in the Model group, whereas model mice treated with MenSC exhibited increased endometrial thickness and increased the pregnancy rates. Therefore, MenSCs may promote the repair of endometrial lesions in mice by promoting the expression of vimentin, VEGF and keratin.

Generation of Progesterone-Responsive Endometrial Stromal Fibroblasts from Human Induced Pluripotent Stem Cells: Role of the WNT/CTNNB1 Pathway

Defective endometrial stromal fibroblasts (EMSFs) contribute to uterine factor infertility, endometriosis, and endometrial cancer. Induced pluripotent stem cells (iPSCs) derived from skin or bone marrow biopsies provide a patient-specific source that can be differentiated to various cells types. Replacement of abnormal EMSFs is a potential novel therapeutic approach for endometrial disease; however, the methodology or mechanism for differentiating iPSCs to EMSFs is unknown. The uterus differentiates from the intermediate mesoderm (IM) to form coelomic epithelium (CE) followed by the Müllerian duct (MD). Here, we successfully directed the differentiation of human iPSCs (hiPSCs) through IM, CE, and MD to EMSFs under molecularly defined embryoid body culture conditions using specific hormonal treatments. Activation of CTNNB1 was essential for expression of progesterone receptor that mediated the final differentiation step of EMSFs before implantation. These hiPSC-derived tissues illustrate the potential for iPSC-based endometrial regeneration for future cell-based treatments.

•

We developed a molecularly defined system for differentiating hiPSCs to EMSFs

•

hiPSC-derived EMSFs undergo decidualization in response to hormonal stimulation

•

D14 embryoid bodies recapitulate the molecular signature of primary EMSFs

•

The WNT/CTNNB1 pathway is required for induction of EMSF from hiPSCs

The role of resveratrol on full - Thickness uterine wound healing in rats

OBJECTIVE

Healing of the uterus after cesarean section and myomectomy operation is clinically important. In this study, we aimed to investigate the effects of resveratrol (3,5,4'-o-trihydroxystilbene) on the wound healing process of the uterus in rats treated with resveratrol following full thickness injury of the uterus.

MATERIALS AND METHODS

Twenty-one female wistar albino rats were divided randomly into three groups (1) control group with no intervention (2) injury group with uterine full thickness injury (3) resveratrol group with uterine full thickness injury and treated with resveratrol. Resveratrol was injected by oral gavage at the doses of 0.5 mg/kg/day for 30 days following uterine full thickness injury. Vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) distributions were assessed using the immunohistochemical methods in tissue and ELISA methods in the tissue homogenate. Glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities were evaluated with colorimetric method and malondialdehyde (MDA) levels also were measured using high performance liquid chromatography in the tissue homogenate. The effects of resveratrol on the uterine histology also were evaluated histologically with the light microscopy.

RESULTS

Histological evaluation and immunohistochemical evaluations showed that treatment with a resveratrol significantly increased the thickness of the uterine wall and VEGF expression and decreased expression PDGF during wound healing. Biochemically, GPx and SOD activities were increased significantly after treatment with resveratrol. Additionally, resveratrol administration decreased MDA levels.

CONCLUSION

These results showed that the antioxidant effects of resveratrol has been shown to have a positive influence on wound healing of the uterus.

Stem cell therapy in Asherman syndrome and thin endometrium: Stem cell- based therapy

The endometrium is one of the essential components of the uterus. The endometrium of human is a complex and dynamic tissue, which undergoes periods of growth and turn over during any menstrual cycle. Stem cells are initially undifferentiated cells that display a wide range of differentiation potential with no distinct morphological features. Stem cell therapy method recently has become a novel procedure for treatment of tissue injury and fibrosis in response to damage. Currently, there is massive interest in stem cells as a novel treatment method for regenerative medicine and more specifically for the regeneration of human endometrium disorder like Asherman syndrome (AS) and thin endometrium. AS also known as intrauterine adhesion (IUA) is a uterine disorder with the aberrant creation of adhesions within the uterus and/or cervix. Patients with IUA are significantly associated with menstrual abnormalities and suffer from pelvic pain. In addition, IUA might prevent implantation of the blastocyst, impair the blood supply to the uterus and early fetus, and finally result in the recurrent miscarriage or infertility in the AS patients. It has been evidenced that the transplantation of different stem cells with a diverse source in the endometrial zone had effects on endometrium such as declined the fibrotic area, an elevated number of glands, stimulated angiogenesis, the enhanced thickness of the endometrium, better formed tissue construction, protected gestation, and improved pregnancy rate. This study presents a summary of the investigations that indicate the key role of stem cell therapy in regeneration and renovation of defective parts.

Differentiating mouse embryonic stem cells express markers of human endometrium

BACKGROUND

Modeling early endometrial differentiation is a crucial step towards understanding the divergent pathways between normal and ectopic endometrial development as seen in endometriosis.

METHODS

To investigate these pathways, mouse embryonic stem cells (mESCs) and embryoid bodies (EBs) were differentiated in standard EB medium (EBM). Immunofluorescence (IF) staining and reverse-transcription polymerase chain reaction (RT-PCR) were used to detect expression of human endometrial cell markers on differentiating cells, which were sorted into distinct populations using fluorescence-activated cell sorting (FACS).

RESULTS

A subpopulation (50%) of early differentiating mESCs expressed both glandular (CD9) and stromal (CD13) markers of human endometrium, suggestive of a novel endometrial precursor cell population. We further isolated a small population of endometrial mesenchymal stem cells, CD45-/CD146+/PDGFR-β+, from differentiating EBs, representing 0.7% of total cells. Finally, quantitative PCR demonstrated significantly amplified expression of transcription factors Hoxa10 and Foxa2 in CD13+ EBs isolated by FACS (p = 0.03).

CONCLUSIONS

These findings demonstrate that mESCs have the capacity to express human endometrial cell markers and demonstrate potential differentiation pathways of endometrial precursor and mesenchymal stem cells, providing an in vitro system to model early endometrial tissue development. This model represents a key step in elucidating the mechanisms of ectopic endometrial tissue growth. Such a system could enable the development of strategies to prevent endometriosis and identify approaches for non-invasive monitoring of disease progression.

Bioengineering Strategies to Treat Female Infertility

Bioengineering strategies have demonstrated enormous potential to treat female infertility as a result of chemotherapy, uterine injuries, fallopian tube occlusion, massive intrauterine adhesions, congenital uterine malformations, and hysterectomy. These strategies can be classified into two broad categories as follows: (i) Transplantation of fresh or cryopreserved organs into the host and (ii) tissue engineering approaches that utilize a combination of cells, growth factors, and biomaterials that leverages the body's inherent ability to regenerate/repair reproductive organs. While whole organ transplant has demonstrated success, the source of the organ and the immunogenic effects of allografts remain challenging. Even though tissue engineering strategies can avoid these issues, their feasibilities of creating whole organ constructs are yet to be demonstrated. In this article we summarize the recent advancements in the applications of bioengineering to treat female infertility.

Human amniotic mesenchymal stromal cell transplantation improves endometrial regeneration in rodent models of intrauterine adhesions

BACKGROUND AIMS

Intrauterine adhesion (IUA) is a common uterine cavity disease characterized by the unsatisfactory regeneration of damaged endometria. Recently, stem cell transplantation has been proposed to promote the recovery process. Here we investigated whether human amniotic mesenchymal stromal cells (hAMSCs), a valuable resource for transplantation therapy, could improve endometrial regeneration in rodent IUA models.

METHODS

Forty female Sprague-Dawley rats were randomly assigned to five groups: normal, sham-operated, mechanical injury, hAMSC transplantation, and negative control group. One week after intervention and transplantation, histological analyses were performed, and immunofluorescent and immunohistochemical expression of cell-specific markers and messenger RNA expression of cytokines were measured.

RESULTS

Thicker endometria, increased gland numbers and fewer fibrotic areas were found in the hAMSC transplantation group compared with the mechanical injury group. Engraftment of hAMSCs was detected by the presence of anti-human nuclear antigen-positive cells in the endometrial glands of the transplantation uteri. Transplantation of hAMSCs significantly decreased messenger RNA levels of pro-inflammatory cytokines (tumor necrosis factor-α and interleukin-1β), and increased those of anti-inflammatory cytokines (basic fibroblast growth factor, and interleukin-6) compared with the injured uterine horns. Immunohistochemical expression of endometrial epithelial cells was revealed in specimens after hAMSC transplantation, whereas it was absent in the mechanically injured uteri.

CONCLUSIONS

hAMSC transplantation promotes endometrial regeneration after injury in IUA rat models, possibly due to immunomodulatory properties. These cells provide a more easily accessible source of stem cells for future research into the impact of cell transplantation on damaged endometria.

Bioengineering the Uterus: An Overview of Recent Advances and Future Perspectives in Reproductive Medicine

Since the initial in vitro attempts to more complex models, research on uterine regeneration is moving towards the creation of a functional bioengineered uterus with possible clinical applications. We describe here the most relevant advances in bioengineering of the uterus published in the last decades considering the use of stem cells and biomaterials as well as future developing techniques in Regenerative Medicine.

Use of nonhuman primates for the development of bioengineered female reproductive organs

Nonhuman primates (NHPs) have been widely used in reproductive biology, neuroscience, and drug development since a number of primate species are phylogenetically close to humans. In this review, we summarize the use of NHPs for nonclinical application in the reproductive system disorders including the loss or failure of an organ or tissue. Causes of infertility include congenital aplasia and acquired disorders of the reproductive organs. In addition, anti-cancer treatments can deplete ovarian follicles, leading to premature ovarian failure, infertility and long-term health risks. Along with a limited supply of human reproductive organs, anatomic/physiologic similarities to humans support the need for NHP models (New-World monkeys such as the common marmoset and Old-World monkeys such as cynomolgus and rhesus monkeys) to promote the advances in female infertility studies. For maintaining and executing animal studies using NHP, special protocols including animal care, anesthetic protocol, surgical technique, and immunosuppressive protocol are necessary. With a growing interest in the potential therapies such as endometrial tissue engineering, and ovary/follicle cryopreservation and grafting in Korea, this review can be useful in selecting appropriate animal models and can bridge between nonclinical studies and clinical applications by providing detailed information on the use of NHPs in the field of reproductive organ disorders.

Endometrial stem/progenitor cells: the first 10 years

BACKGROUND

The existence of stem/progenitor cells in the endometrium was postulated many years ago, but the first functional evidence was only published in 2004. The identification of rare epithelial and stromal populations of clonogenic cells in human endometrium has opened an active area of research on endometrial stem/progenitor cells in the subsequent 10 years.

METHODS

The published literature was searched using the PubMed database with the search terms ‘endometrial stem cells and menstrual blood stem cells' until December 2014.

RESULTS

Endometrial epithelial stem/progenitor cells have been identified as clonogenic cells in human and as label-retaining or CD44⁺ cells in mouse endometrium, but their characterization has been modest. In contrast, endometrial mesenchymal stem/stromal cells (MSCs) have been well characterized and show similar properties to bone marrow MSCs. Specific markers for their enrichment have been identified, CD146⁺PDGFRβ⁺ (platelet-derived growth factor receptor beta) and SUSD2⁺ (sushi domain containing-2), which detected their perivascular location and likely pericyte identity in endometrial basalis and functionalis vessels. Transcriptomics and secretomics of SUSD2⁺ cells confirm their perivascular phenotype. Stromal fibroblasts cultured from endometrial tissue or menstrual blood also have some MSC characteristics and demonstrate broad multilineage differentiation potential for mesodermal, endodermal and ectodermal lineages, indicating their plasticity. Side population (SP) cells are a mixed population, although predominantly vascular cells, which exhibit adult stem cell properties, including tissue reconstitution. There is some evidence that bone marrow cells contribute a small population of endometrial epithelial and stromal cells. The discovery of specific markers for endometrial stem/progenitor cells has enabled the examination of their role in endometrial proliferative disorders, including endometriosis, adenomyosis and Asherman's syndrome. Endometrial MSCs (eMSCs) and menstrual blood stromal fibroblasts are an attractive source of MSCs for regenerative medicine because of their relative ease of acquisition with minimal morbidity. Their homologous and non-homologous use as autologous and allogeneic cells for therapeutic purposes is currently being assessed in preclinical animal models of pelvic organ prolapse and phase I/II clinical trials for cardiac failure. eMSCs and stromal fibroblasts also exhibit non-stem cell-associated immunomodulatory and anti-inflammatory properties, further emphasizing their desirable properties for cell-based therapies.

CONCLUSIONS

Much has been learnt about endometrial stem/progenitor cells in the 10 years since their discovery, although several unresolved issues remain. These include rationalizing the terminology and diagnostic characteristics used for distinguishing perivascular stem/progenitor cells from stromal fibroblasts, which also have considerable differentiation potential. The hierarchical relationship between clonogenic epithelial progenitor cells, endometrial and decidual SP cells, CD146⁺PDGFR-β⁺ and SUSD2⁺ cells and menstrual blood stromal fibroblasts still needs to be resolved. Developing more genetic animal models for investigating the role of endometrial stem/progenitor cells in endometrial disorders is required, as well as elucidating which bone marrow cells contribute to endometrial tissue. Deep sequencing and epigenetic profiling of enriched populations of endometrial stem/progenitor cells and their differentiated progeny at the population and single-cell level will shed new light on the regulation and function of endometrial stem/progenitor cells.