Bone marrow-derived stem cells contribute to regeneration of the endometrium

New advances in the treatment of thin endometrium

Thin endometrium (TE) is defined as a mid-luteal endometrial thickness ≤7mm. TE can affect endometrial tolerance, leading to lower embryo implantation rates and clinical pregnancy rates, and is also associated with impaired outcomes from assisted reproductive treatment. Herein, we systematically review TE causes, mechanisms, and treatments. TE pathogenesis has multiple causes, with the endometrium becoming thinner with age under hormonal influence. In addition, uterine cavity factors are important, as the inflammatory environment may affect expressions of certain genes thereby inhibiting endometrial stromal cell proliferation and promoting apoptosis. Long-term oral contraceptive use or the use of ovulation-promoting drugs are also definite factors contributing to endometrial thinning. Other patients have primary factors, for which the clinical etiology remains unknown. The main therapeutic strategies available for TE are pharmacological (including hormonal and vasoactive drugs), regenerative medicine, intrauterine infusion of growth factor-granulocyte colony-stimulating factor, autologous platelet-rich plasma, and complementary alternative therapies (including traditional Chinese herbal medicine and acupuncture). However, the associated mechanisms of action are currently unclear. Clinical scholars have proposed various approaches to improve treatment outcomes in patients with TE, and are exploring the principles of efficacy, offering potentials for novel treatments. It is hoped that this will improve TE tolerance, increase embryo implantation rates, and help more couples with infertility with effective treatments.

Endometrial mesenchymal stromal/stem cells improve regeneration of injured endometrium in mice

BACKGROUND

The monthly regeneration of human endometrial tissue is maintained by the presence of human endometrial mesenchymal stromal/stem cells (eMSC), a cell population co-expressing the perivascular markers CD140b and CD146. Endometrial regeneration is impaired in the presence of intrauterine adhesions, leading to infertility, recurrent pregnancy loss and placental abnormalities. Several types of somatic stem cells have been used to repair the damaged endometrium in animal models, reporting successful pregnancy. However, the ability of endometrial stem cells to repair the damaged endometrium remains unknown.

METHODS

Electrocoagulation was applied to the left uterine horn of NOD/SCID mice causing endometrial injury. Human eMSC or PBS was then injected into the left injured horn while the right normal horn served as controls. Mice were sacrificed at different timepoints (Day 3, 7 and 14) and the endometrial morphological changes as well as the degree of endometrial injury and repair were observed by histological staining. Gene expression of various inflammatory markers was assessed using qPCR. The functionality of the repaired endometrium was evaluated by fertility test.

RESULTS

Human eMSC successfully incorporated into the injured uterine horn, which displayed significant morphological restoration. Also, endometrium in the eMSC group showed better cell proliferation and glands formation than the PBS group. Although the number of blood vessels were similar between the two groups, gene expression of VEGF-α significantly increased in the eMSC group. Moreover, eMSC had a positive impact on the regeneration of both stromal and epithelial components of the mouse endometrium, indicated by significantly higher vimentin and CK19 protein expression. Reduced endometrial fibrosis and down-regulation of fibrosis markers were also observed in the eMSC group. The eMSC group had a significantly higher gene expression of anti-inflammatory factor Il-10 and lower mRNA level of pro-inflammatory factors Ifng and Il-2, indicating the role of eMSC in regulation of inflammatory reactions. The eMSC group showed higher implantation sites than the PBS group, suggesting better endometrial receptivity with the presence of newly emerged endometrial lining.

CONCLUSIONS

Our findings suggest eMSC improves regeneration of injured endometrium in mice.

Strategies for modelling endometrial diseases

Each month during a woman's reproductive years, the endometrium undergoes vast changes to prepare for a potential pregnancy. Diseases of the endometrium arise for numerous reasons, many of which remain unknown. These endometrial diseases, including endometriosis, adenomyosis, endometrial cancer and Asherman syndrome, affect many women, with an overall lack of efficient or permanent treatment solutions. The challenge lies in understanding the complexity of the endometrium and the extensive changes, orchestrated by ovarian hormones, that occur in multiple cell types over the period of the menstrual cycle. Appropriate model systems that closely mimic the architecture and function of the endometrium and its diseases are needed. The emergence of organoid technology using human cells is enabling a revolution in modelling the endometrium in vitro. The goal of this Review is to provide a focused reference for new models to study the diseases of the endometrium. We provide perspectives on the power of new and emerging models, from organoids to microfluidics, which have opened up a new frontier for studying endometrial diseases.

Surgical and nutritional interventions for endometrial receptivity: A case report and review of literature

BACKGROUND

Polycystic ovary syndrome (PCOS) is an endocrine disease that combines metabolic, reproductive, and psychological dysfunctions. Ovulation disorders and impaired endometrial receptivity in PCOS can cause infertility. Insulin resistance (IR) is a pathological state of inadequate response to insulin that affects reproduction in PCOS, as damage caused by IR at the endometrial level becomes an obstacle for embryo implantation. Reversing IR resulted in spontaneous pregnancies in PCOS patients, indicating that metabolic corrections improve endometrial dysfunctions. Mesenchymal stem-cell treatment has also corrected endometrial quality and lead to pregnancies in patients with Asherman’s syndrome. We propose a combination of nutritional intervention with the surgical placement of stem cells to improve endometrial quality to achieve pregnancy in a PCOS patient undergoing in vitro fertilization (IVF) treatment.

CASE SUMMARY

After two failed IVF cycles, a metabolic intervention, consisting of a ketogenic diet with daily consumption of 50 g of carbohydrates (CH), was indicated until pregnancy. Metabolic Syndrome was assessed using the Harmonizing Definition (3 of 5 pathologies: Central obesity, hypertension, hyperglycemia, hypertriglyceridemia, and dyslipidemia), and the Homeostatic Model Assessment of IR (HOMA-IR) was used to measure the level of IR. Once IR improved, endometrial quality improved. However, two day 5-thawed embryos (euploid, donated oocyte–partner's sperm) failed to implant, suggesting endometrial quality improvement was insufficient. Therefore, transmyometrial implantation of mesenchymal stem cells from the stromal vascular fraction of adipose tissue was performed to enrich the endometrial stem cell niche. Minimal endometrial mean thickness for embryo transfer (6.9 mm) was achieved three months after stem cell treatment and continuous dietary control of IR. Two euploid-day 5-thawed embryos (donated oocyte–partner's sperm) were transferred, and embryo implantation was confirmed on day 14 by β-hCG serum levels. Currently, a 37 wk baby girl is born.

CONCLUSION

In PCOS, endometrial quality can be improved by combining nutrient-based metabolic correction with endometrial stem cell niche enrichment.

Stem Cells and Organs-on-chips: New Promising Technologies for Human Infertility Treatment

Having biological children remains an unattainable dream for most couples with reproductive failure or gonadal dysgenesis. The combination of stem cells with gene editing technology and organ-on-a-chip models provides a unique opportunity for infertile patients with impaired gametogenesis caused by congenital disorders in sex development or cancer survivors. But how will these technologies overcome human infertility? This review discusses the regenerative mechanisms, applications, and advantages of different types of stem cells for restoring gametogenesis in infertile patients, as well as major challenges that must be overcome before clinical application. The importance and limitations of in vitro generation of gametes from patient-specific human-induced pluripotent stem cells (hiPSCs) will be discussed in the context of human reproduction. The potential role of organ-on-a-chip models that can direct differentiation of hiPSC-derived primordial germ cell-like cells to gametes and other reproductive organoids is also explored. These rapidly evolving technologies provide prospects for improving fertility to individuals and couples who experience reproductive failure.

Uterus: A Unique Stem Cell Reservoir Able to Support Cardiac Repair via Crosstalk among Uterus, Heart, and Bone Marrow

Clinical evidence suggests that the prevalence of cardiac disease is lower in premenopausal women compared to postmenopausal women and men. Although multiple factors contribute to this difference, uterine stem cells may be a major factor, as a high abundance of these cells are present in the uterus. Uterine-derived stem cells have been reported in several studies as being able to contribute to cardiac neovascularization after injury. However, our studies uniquely show the presence of an “utero-cardiac axis”, in which uterine stem cells are able to home to cardiac tissue to promote tissue repair. Additionally, we raise the possibility of a triangular relationship among the bone marrow, uterus, and heart. In this review, we discuss the exchange of stem cells across different organs, focusing on the relationship that exists between the heart, uterus, and bone marrow. We present increasing evidence for the existence of an utero-cardiac axis, in which the uterus serves as a reservoir for cardiac reparative stem cells, similar to the bone marrow. These cells, in turn, are able to migrate to the heart in response to injury to promote healing.

The Double Engines and Single Checkpoint Theory of Endometriosis

Endometriosis is a chronic disease characterized by the ectopic localization of the endometrial tissue in the peritoneal cavity. Consequently, it causes local pathological changes and systemic symptoms, affecting at least one in every ten women. This disease is difficult to diagnose early, it is prone to dissemination, is difficult to eradicate, tends to recur, and is regarded as “a cancer of no kill”. Indeed, the development of endometriosis closely resembles that of cancer in the way of mutagenesis, pelvic spreading, and immunological adaptation. While retrograde menstruation has been regarded as the primary cause of endometriosis, the role of ovulation and menstrual stimuli in the development of endometriosis has long been overlooked. The development of ovarian and peritoneal endometrioses, similar to the development of high-grade serous carcinoma in the fallopian tube fimbriae with intraperitoneal metastasis, depends highly on the carcinogens released during ovulation. Moreover, endometriosis carries an extremely hypermutated genome, which is non-inferior to the ultra-mutated endometrial cancer. The hypermutation would lead to an overproduction of new proteins or neoantigens. Because of this, the developing endometriosis may have to turn on the PD-1/PDL-1 “self-tolerance” checkpoint to evade immune surveillance, leaving an Achilles tendon for an immune checkpoint blockade. In this review, we present the double engines and single checkpoint theory of the genesis of endometriosis, provide the current pieces of evidence supporting the hypothesis, and discuss the new directions of prevention and treatment.

Bone Marrow-Derived Cells in Endometrial Cancer Pathogenesis: Insights from Breast Cancer

Endometrial cancer is the most common gynecological cancer, representing 3.5% of all new cancer cases in the United States. Abnormal stem cell-like cells, referred to as cancer stem cells (CSCs), reside in the endometrium and possess the capacity to self-renew and differentiate into cancer progenitors, leading to tumor progression. Herein we review the role of the endometrial microenvironment and sex hormone signaling in sustaining EC progenitors and potentially promoting dormancy, a cellular state characterized by cell cycle quiescence and resistance to conventional treatments. We offer perspective on mechanisms by which bone marrow-derived cells (BMDCs) within the endometrial microenvironment could promote endometrial CSC (eCSC) survival and/or dormancy. Our perspective relies on the well-established example of another sex hormone-driven cancer, breast cancer, in which the BM microenvironment plays a crucial role in acquisition of CSC phenotype and dormancy. Our previous studies demonstrate that BMDCs migrate to the endometrium and express sex hormone (estrogen and progesterone) receptors. Whether the BM is a source of eCSCs is unknown; alternatively, crosstalk between BMDCs and CSCs within the endometrial microenvironment could be an additional mechanism supporting eCSCs and tumorigenesis. Elucidating these mechanisms will provide avenues to develop novel therapeutic interventions for EC.

Birth of a healthy infant after bone marrow-derived cell therapy

Bone marrow-derived cell (BMDC) therapy has numerous applications as potential biological cells for use in regenerative medicine. Here, we present an original case of endometrial atrophy associated with genital tuberculosis in a woman who achieved a live birth with BMDC. This 27-year-old woman came to our center with endometrial atrophy and primary infertility. She had a past history of genital tuberculosis and amenorrhea. Her husband’s semen quality was normal. The patient was counseled for hysteroscopy due to thin endometrium and advised in vitro fertilization (IVF) with donor eggs in lieu of poor ovarian reserve. Several attempts of IVF with hormone replacement therapy (HRT) were made, but the desired thickness of the endometrium was not achieved. Uterine artery injection of BMDC through interventional radiology was given, followed by HRT for three months, which resulted in improved endometrium. This was subsequently followed by IVF with donor egg. The treatment resulted in the conception and delivery of a 3.1-kg baby boy through lower segment caesarean section with no antenatal, intranatal or postnatal complications. Recently, there has been massive interest in stem cells as a novel treatment method for regenerative medicine, and more specifically for the regeneration of human endometrium disorders like Asherman syndrome and thin endometrium, which was the reason behind using this strategy for treatment.

Transplantation of Human Adipose Stem Cells Using Acellular Human Amniotic Membrane Improves Angiogenesis in Injured Endometrial Tissue in a Rat Intrauterine Adhesion Model

Endometrial injury resulting in intrauterine adhesion is associated with extensive damage to the regenerative basal layer of the endometrium and represents a major therapeutic challenge. Human adipose stem cells (hASCs) hold promise for future clinical use in the individualized therapy of injured endometrial tissue. Here, we observed that the use of the acellular human amniotic membrane (AHAM) significantly increased the expression of angiogenic factors, including angiogenin (ANG) and vascular endothelial growth factor (VEGF), in hASCs in vitro. The three-dimensional engineered hASC-AHAM grafts significantly increased the endometrial receptivity, as increased endometrial thickness, greater numbers of endometrial glands, and higher protein levels of leukemia inhibitory factor were observed in injured endometrial tissue that was treated with these grafts compared to those detected in injured endometrial tissue that was treated with AHAM alone. In addition, the hASC-AHAM grafts significantly increased the vascular density in the injured endometrial tissue in rats, when transplanted into an injured uterine cavity. Using the EGFP⁺-hASC-AHAM grafts for transplantation, we confirmed that the hASCs maintained higher protein levels of ANG and VEGF in the injured uterine cavity in vivo. The results of this study suggest that the ability of the engineered hASC-AHAM grafts to repair injured endometrial tissue may be associated with their ability to promote angiogenesis through the upregulated expression of angiogenic factors in hASCs. These findings may support individualized stem cell–based therapy for endometrial disease using bioartificial grafts.

Stem Cell-Based Therapy for Asherman Syndrome: Promises and Challenges

Asherman syndrome (AS) has an adverse effect on reproductive health and fertility by affecting endometrial regeneration. Stem cell-based therapies hold promise for future use in activating non-functional endometrium and reconstructing the endometrium in vivo. It has been postulated that various endometrial stem cells (EnSCs) are responsible for endometrial regeneration. Numerous studies have focused on bone marrow-derived stem cells (BMDSCs), which may provide new ideas for repairing endometrial lesions and reconstructing the endometrium. Other sources of stem cells, such as menstrual blood, umbilical cord, and amniotic membrane, have also attracted much attention as candidates for transplantation in AS. This review discusses the features and specific biomarkers among four types of resident endometrial stem cells, applications of four different sources of exogenous stem cells in AS, and development of stem cell therapy using biomaterials and exosomes.

Mesenchymal stem cells for restoring endometrial function: An infertility perspective

BACKGROUND

Mesenchymal stem cells (MSCs) can be derived from several tissues such as bone marrow, placenta, adipose tissue, or endometrial tissue. MSCs gain a lot of attention for cell-based therapy due to their characteristics including differentiation ability and immunomodulatory effect. Preclinical and clinical studies demonstrated that MSCs can be applied to treat female infertility by improving of the functions of ovary and uterus. This mini- review focuses on the current study of treatment of endometrial infertility by using MSCs.

METHODS

The present study performed a literature review focusing on the effect of MSCs for treatment of women infertility caused by endometrial dysfunction.

RESULTS

Bone marrow-, umbilical cord-, adipose-, amniotic-, and menstruation-derived MSCs enhance endometrial cell proliferation, injury repairs as well as reducing scar formation. The beneficial mechanism probably via immunomodulatory, cell differentiation, stimulates endometrial cell proliferation and down-regulation of fibrosis genes. The major advantage of using MSCs is to improve endometrial functions resulting in increased implantation and pregnancy.

CONCLUSIONS

MSCs exhibit a potential for endometrial infertility treatment. Adipose- and menstruation-derived stem cells show advantages over other sources because the cells can be derived easily and do not causes graft rejection after autologous transplantation.

Intrauterine transplantation of autologous menstrual blood stem cells increases endometrial thickness and pregnancy potential in patients with refractory intrauterine adhesion

AIM

This study was designed to evaluate the effects of intrauterine transplantation of menstrual blood stem cells (MenSCs) on endometrial thickness and pregnancy outcomes in patients with refractory intrauterine adhesion (IUA).

METHODS

This study included a group of infertile women (n = 12, age 22-40 years), with refractory IUA. Autologous MenSCs isolated from the women's menstrual blood were expanded in vitro and transplanted into their uteruses, followed by hormone replacement therapy. Transvaginal ultrasound examination was performed to assess the endometrial thickness. Transabdominal ultrasound was conducted to detect pregnancy outcome.

RESULTS

Autologous MenSCs were successfully isolated and expanded from menstrual blood and transplanted into the uterus of each patient. A significant improvement of the endometrial thickness was observed from 3.9 ± 0.9 to 7.5 ± 0.6 mm (P < 0.001). No adverse reaction was observed. The duration of menstruation was increased from 2.4 ± 0.7 to 5.3 ± 0.6 days (P < 0.001). Five out of 12 patients achieved clinical pregnancy and the pregnancy rate was 41.7%.

CONCLUSIONS

Intrauterine transplantation of autologous MenSCs results in regeneration of endometrium, a prolongation of menstrual duration and an increase rate of pregnancy in patients with refractory IUA.

Organoid technology in female reproductive biomedicine

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