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

Evolution of biotechnological advances and regenerative therapies for endometrial disorders: a systematic review

BACKGROUND

The establishment and maintenance of pregnancy depend on endometrial competence. Asherman syndrome (AS) and intrauterine adhesions (IUA), or endometrial atrophy (EA) and thin endometrium (TE), can either originate autonomously or arise as a result from conditions (i.e. endometritis or congenital hypoplasia), or medical interventions (e.g. surgeries, hormonal therapies, uterine curettage or radiotherapy). Affected patients may present an altered or inadequate endometrial lining that hinders embryo implantation and increases the risk of poor pregnancy outcomes and miscarriage. In humans, AS/IUA and EA/TE are mainly treated with surgeries or pharmacotherapy, however the reported efficacy of these therapeutic approaches remains unclear. Thus, novel regenerative techniques utilizing stem cells, growth factors, or tissue engineering have emerged to improve reproductive outcomes.

OBJECTIVE AND RATIONALE

This review comprehensively summarizes the methodologies and outcomes of emerging biotechnologies (cellular, acellular, and bioengineering approaches) to treat human endometrial pathologies. Regenerative therapies derived from human tissues or blood which were studied in preclinical models (in vitro and in vivo) and clinical trials are discussed.

SEARCH METHODS

A systematic search of full-text articles available in PubMed and Embase was conducted to identify original peer-reviewed studies published in English between January 2000 and September 2023. The search terms included: human, uterus, endometrium, Asherman syndrome, intrauterine adhesions, endometrial atrophy, thin endometrium, endometritis, congenital hypoplasia, curettage, radiotherapy, regenerative therapy, bioengineering, stem cells, vesicles, platelet-rich plasma, biomaterials, microfluidic, bioprinting, organoids, hydrogel, scaffold, sheet, miRNA, sildenafil, nitroglycerine, aspirin, growth hormone, progesterone, and estrogen. Preclinical and clinical studies on cellular, acellular, and bioengineering strategies to repair or regenerate the human endometrium were included. Additional studies were identified through manual searches.

OUTCOMES

From a total of 4366 records identified, 164 studies (3.8%) were included for systematic review. Due to heterogeneity in the study design and measured outcome parameters in both preclinical and clinical studies, the findings were evaluated qualitatively and quantitatively without meta-analysis. Groups using stem cell-based treatments for endometrial pathologies commonly employed mesenchymal stem cells (MSCs) derived from the human bone marrow or umbilical cord. Alternatively, acellular therapies based on platelet-rich plasma (PRP) or extracellular vesicles are gaining popularity. These are accompanied by the emergence of bioengineering strategies based on extracellular matrix (ECM)-derived hydrogels or synthetic biosimilars that sustain local delivery of cells and growth factors, reporting promising results. Combined therapies that target multiple aspects of tissue repair and regeneration remain in preclinical testing but have shown translational value. This review highlights the myriad of therapeutic material sources, administration methods, and carriers that have been tested.

WIDER IMPLICATIONS

Therapies that promote endometrial proliferation, vascular development, and tissue repair may help restore endometrial function and, ultimately, fertility. Based on the existing evidence, cost, accessibility, and availability of the therapies, we propose the development of triple-hit regenerative strategies, potentially combining high-yield MSCs (e.g. from bone marrow or umbilical cord) with acellular treatments (PRP), possibly integrated in ECM hydrogels. Advances in biotechnologies together with insights from preclinical models will pave the way for developing personalized treatment regimens for patients with infertility-causing endometrial disorders such as AS/IUA, EA/TE, and endometritis.

REGISTRATION NUMBER

https://osf.io/th8yf/.

Novel therapeutic targets, including IGFBP3, of umbilical cord mesenchymal stem-cell-conditioned medium in intrauterine adhesion

Mesenchymal stem cells play important roles in repairing injured endometrium. However, the molecular targets and potential mechanism of the endometrial recipient cells for stem cell therapy in intrauterine adhesion (IUA) are poorly understood. In this study, umbilical cord mesenchymal stem-cell-conditioned medium (UCMSCs-CM) produced positive effects on a Transforming growth factor beta (TGF-β) induced IUA cell model. RNA-sequencing was performed on clinical IUA tissues, and the top 40 upregulated and top 20 downregulated mRNAs were selected and verified using high-throughput (HT) qPCR in both tissues and cell models. Based on a bioinformatic analysis of RNA-sequencing and HT-qPCR results, 11 mRNAs were uncovered to be the intervention targets of UCMSCs-CM on IUA endometrium cell models. Among them, IGFBP3 was striking as a key pathogenic gene and a potential diagnostic marker of IUA, which exhibited the area under the curve (AUC), sensitivity, specificity were 0.924, 93.1% and 80.6%, respectively in 60 endometrial tissues. The silencing of IGFBP3 exerted positive effects on the IUA cell model through partially upregulating MMP1 and KLF2. In conclusion, RNA-sequencing combined with HT qPCR based on clinical tissues and IUA cell models were used in IUA research and our results may provide some scientific ideas for the diagnosis and treatment of IUA.

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.

Impaired receptivity of thin endometrium: therapeutic potential of mesenchymal stem cells

The endometrium is a resilient and highly dynamic tissue, undergoing cyclic renewal in preparation for embryo implantation. Cyclic endometrial regeneration depends on the intact function of several cell types, including parenchymal, endothelial, and immune cells, as well as adult stem cells that can arise from endometrial or extrauterine sources. The ability of the endometrium to undergo rapid, repeated regeneration without scarring is unique to this tissue. However, if this tissue renewal process is disrupted or dysfunctional, women may present clinically with infertility due to endometrial scarring or persistent atrophic/thin endometrium. Such disorders are rate-limiting in the treatment of female infertility and in the success of in vitro fertilization because of a dearth of treatment options specifically targeting the endometrium. A growing number of studies have explored the potential of adult stem cells, including mesenchymal stem cells (MSCs), to treat women with disorders of endometrial regeneration. MSCs are multipotent adult stem cells with capacity to differentiate into cells such as adipocytes, chondrocytes, and osteoblasts. In addition to their differentiation capacity, MSCs migrate toward injured sites where they secrete bioactive factors (e.g. cytokines, chemokines, growth factors, proteins and extracellular vesicles) to aid in tissue repair. These factors modulate biological processes critical for tissue regeneration, such as angiogenesis, cell migration and immunomodulation. The MSC secretome has therefore attracted significant attention for its therapeutic potential. In the uterus, studies utilizing rodent models and limited human trials have shown a potential benefit of MSCs and the MSC secretome in treatment of endometrial infertility. This review will explore the potential of MSCs to treat women with impaired endometrial receptivity due to a thin endometrium or endometrial scarring. We will provide context supporting leveraging MSCs for this purpose by including a review of mechanisms by which the MSC secretome promotes regeneration and repair of nonreproductive tissues.

MicroRNA-122-5p alleviates endometrial fibrosis via inhibiting the TGF-β/SMAD pathway in Asherman's syndrome

RESEARCH QUESTION

What is the effect of miR-122 on the progression and recovery of fibrosis in Asherman's syndrome?

DESIGN

Endometrial tissue was collected from 21 patients, 11 with intrauterine adhesion (IUA) and 10 without IUA. Quantitative real-time polymerase chain reaction, immunofluorescence and Western blot were applied to observe the expression of mRNAs/miRNAs and protein, respectively. The endometrial physical injury was carried out in C57BL/6 mice to create an endometrial fibrosis model, with intrauterine injection of adenovirus to compare the antifibrosis and repair function of miR-122 on endometrium. The morphology of the uterus was observed using haematoxylin and eosin staining, and fibrosis markers were detected by immunohistochemistry.

RESULTS

miR-122 expression was reduced in patients with IUAs, accompanied by fibrosis. MiR-122 overexpression reduced the degree of fibrosis in endometrial stromal cells. Further molecular analyses demonstrated that miR-122 inhibited fibrosis through the TGF-β/SMAD pathway by directly targeting the 3' untranslated region of SMAD family member 3, suppressing its expression. Notably, miR-122 promoted endometrial regeneration and recovery of pregnancy capacity in a mouse endometrial injury model.

CONCLUSIONS

miR-122 is a critical regulator for repair of endometrial fibrosis and provided new insight for the clinical treatment of intrauterine adhesions.

Mechanisms of Regeneration and Fibrosis in the Endometrium

The uterine lining (endometrium) regenerates repeatedly over the life span as part of its normal physiology. Substantial portions of the endometrium are shed during childbirth (parturition) and, in some species, menstruation, but the tissue is rapidly rebuilt without scarring, rendering it a powerful model of regeneration in mammals. Nonetheless, following some assaults, including medical procedures and infections, the endometrium fails to regenerate and instead forms scars that may interfere with normal endometrial function and contribute to infertility. Thus, the endometrium provides an exceptional platform to answer a central question of regenerative medicine: Why do some systems regenerate while others scar? Here, we review our current understanding of diverse endometrial disruption events in humans, nonhuman primates, and rodents, and the associated mechanisms of regenerative success and failure. Elucidating the determinants of these disparate repair processes promises insights into fundamental mechanisms of mammalian regeneration with substantial implications for reproductive health.

Etiology, Risk Factors, and Management of Asherman Syndrome

Asherman syndrome is characterized by a triad of symptoms including pain, menstrual abnormalities, and infertility and is a result of intrauterine scar tissue after instrumentation of a gravid uterus. Saline sonohysterogram is typically the most sensitive diagnostic tool; however, hysteroscopy is the criterion standard for diagnosis. Treatment includes hysteroscopic-guided lysis of adhesion, with restoration of the anatomy of the uterine cavity. Several modalities are used in an attempt to reduce the reformation of scar tissue after surgery; however, there is no consensus on the ideal method. Stem cells and platelet-rich plasma are being explored as means of regenerative therapy for the endometrium, but data remain limited. At present, most individuals can have restoration of menstrual function; however, lower pregnancy rates and obstetric complications are not uncommon. These complications are worse for patients with a higher grade of disease. Efforts are needed in standardizing classification, reducing uterine instrumentation of the gravid uterus, and referring patients to health care professionals with clinical expertise in this area.

Dulaglutide Ameliorates Intrauterine Adhesion by Suppressing Inflammation and Epithelial-Mesenchymal Transition via Inhibiting the TGF-β/Smad2 Signaling Pathway

Intrauterine adhesion (IUA) is a common gynecological disease with limited therapeutic options. Dulaglutide is a long-acting glucagon-like peptide-1 (GLP-1) analog with some anti-fibrotic and anti-inflammatory properties; however, its action on IUA remains uncertain. The purpose of the experiments in this study was to explore the effect of dulaglutide on IUA and to elucidate its mechanism to provide new ideas for the clinical treatment of IUA. An IUA mouse model was established via mechanical curettage and inflammation induction; mice received subcutaneous injection with three doses of dulaglutide once a day for two weeks (treatment) or equal amounts of sterile ddH₂O (control), and sham-operated mice were treated similarly to the control mice. Mice were sacrificed, and uterine tissues were subjected to hematoxylin and eosin (H&E) and Masson's trichrome staining for histomorphological and pathological analyses and real-time quantitative polymerase chain reaction (RT-qPCR) and Western blotting (WB) for gene and protein expression analyses. Dulaglutide improved the shape of the uterine cavity, increased endometrial thickness and the number of glands, and significantly reduced the area of collagen fiber deposition in the endometrium. It significantly reduced collagen type I A 1 (COL1A1), interleukin-1beta (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), C-C motif chemokine ligand 2 (CCL2), F4/80 (macrophage), vimentin and transforming growth factor-beta (TGF-β) mRNA levels and COL1A1, IL-1β, IL-6, TNF-α, F4/80, vimentin, E-cadherin, TGF-β, and p-Smad2 protein expression levels. This study demonstrates that dulaglutide reduces inflammatory responses by inhibiting M1 macrophage polarization and inflammatory factor release and may ameliorate fibrosis by inhibiting epithelial-mesenchymal transition (EMT) via TGF-β/Smad2 signaling.

The Therapeutic Potential of Multipotent Mesenchymal Stromal Cell-Derived Extracellular Vesicles in Endometrial Regeneration

Disruption of endometrial regeneration, fibrosis formation, and intrauterine adhesions underlie the development of "thin" endometrium and/or Asherman's syndrome (AS) and are a common cause of infertility and a high risk for adverse obstetric outcomes. The methods used (surgical adhesiolysis, anti-adhesive agents, and hormonal therapy) do not allow restoration of the regenerative properties of the endometrium. The experience gained today with cell therapy using multipotent mesenchymal stromal cells (MMSCs) proves their high regenerative and proliferative properties in tissue damage. Their contribution to regenerative processes is still poorly understood. One of these mechanisms is based on the paracrine effects of MMSCs associated with the stimulation of cells of the microenvironment by secreting extracellular vesicles (EVs) into the extracellular space. EVs, whose source is MMSCs, are able to stimulate progenitor cells and stem cells in damaged tissues and exert cytoprotective, antiapoptotic, and angiogenic effects. This review described the regulatory mechanisms of endometrial regeneration, pathological conditions associated with a decrease in endometrial regeneration, and it presented the available data from studies on the effect of MMSCs and their EVs on endometrial repair processes, and the involvement of EVs in human reproductive processes at the level of implantation and embryogenesis.

Therapeutic restoration of female reproductive and endocrine dysfunction using stem cells

Millions of women worldwide suffer from infertility associated with gynecologic disorders such as premature ovarian insufficiency, polycystic ovary syndrome, Asherman syndrome, endometriosis, preeclampsia, and fallopian tube obstruction. These disorders can lead to infertility and thereby affect the quality of life of the infertile couple because of their psychological impact and significant costs. In recent years, stem cell therapy has emerged as a therapeutic approach to repair or replace damaged tissues or organs. This review describes the recent development as well as the underlying mechanisms of stem cell therapy for a variety of female reproductive diseases, offering us new therapeutic options for the treatment of female reproductive and endocrine dysfunction.

Homogenous subpopulation of human mesenchymal stem cells and their extracellular vesicles restore function of endometrium in an experimental rat model of Asherman syndrome

BACKGROUND

Asherman syndrome (AS), or intrauterine adhesions, is a main cause of infertility in reproductive age women after endometrial injury. Mesenchymal stem cells (MSCs) and their extracellular vesicles (EVs) are promising candidates for therapies that repair damaged endometria. However, concerns about their efficacy are attributed to heterogeneity of the cell populations and EVs. A homogenous population of MSCs and effective EV subpopulation are needed to develop potentially promising therapeutic options in regenerative medicine.

METHODS

AS model was induced by mechanical injury in adult rat uteri. Then, the animals were treated immediately with homogeneous population of human bone marrow-derived clonal MSCs (cMSCs), heterogenous parental MSCs (hMSCs), or cMSCs-derived EV subpopulations (EV20K and EV110K). The animals were sacrificed two weeks post-treatment and uterine horns were collected. The sections were taken, and hematoxylin-eosin was used to examine the repair of endometrial structure. Fibrosis was measured by Masson's trichrome staining and α-SMA and cell proliferation by Ki67 immunostaining. The function of the uteri was explored by the result of mating trial test. Expression changes of TNFα, IL-10, VEGF, and LIF were assayed by ELISA.

RESULTS

Histological analysis indicated fewer glands, thinner endometria, increased fibrotic areas, and decreased proliferation of epithelial and stroma of the uteri in the treated compared with intact and sham-operated animals. However, these parameters improved after transplantation of both types of cMSCs and hMSCs and/or both cryopreserved EVs subpopulations. The cMSCs demonstrated more successful implantation of the embryos in comparison with hMSCs. The tracing of the transplanted cMSCs and EVs showed that they migrated and localized in the uteri. Protein expression analysis results demonstrated downregulation of proinflammatory factor TNFα and upregulation of anti-inflammatory cytokine IL-10, and endometrial receptivity cytokines VEGF and LIF in cMSC- and EV20K-treated animals.

CONCLUSION

Transplantation of MSCs and EVs contributed to endometrial repair and restoration of reproductive function, likely by inhibition of excessive fibrosis and inflammation, enhancement of endometrial cell proliferation, and regulation of molecular markers related to endometrial receptivity. Compared to classical hMSCs, cMSCs were more efficient than hMSCs in restoration of reproductive function. Moreover, EV20K is more cost-effective and feasible for prevention of AS in comparison with conventional EVs (EV110K).

Potential Therapeutic Effects of Human Amniotic Epithelial Cells on Gynecological Disorders Leading to Infertility or Abortion

The induction of feto-maternal tolerance, fetal non-immunogenicity, and the regulation of mother's immune system are essential variables in a successful pregnancy. Fetal membranes have been used as a source of stem cells and biological components in recent decades. Human amniotic epithelial cells (hAEC) have stem/progenitor characteristics like those found in the amniotic membrane. Based on their immunomodulatory capabilities, recent studies have focused on the experimental and therapeutic applications of hAECs in allograft transplantation, autoimmune disorders, and gynecological problems such as recurrent spontaneous abortion (RSA), recurrent implantation failure (RIF), and premature ovarian failure (POF). This review discusses some of the immunomodulatory features and therapeutic potential of hAECs in preventing infertility, miscarriage, and implantation failure by controlling the maternal immune system.

Amniotic stem cells as a source of regenerative medicine to treat female infertility

Impaired reproductive health is a worldwide problem that affects the psychological well-being of a society. Despite the technological developments to treat infertility, the global infertility rate is increasing significantly. Many infertility conditions are currently treated using various advanced clinical approaches such as intrauterine semination (IUI), in vitro fertilization (IVF), and intracytoplasmic injection (ICSI). Nonetheless, clinical management of some conditions such as dysfunctional endometrium, premature ovarian failure, and ovarian physiological aging still pose significant challenges. Stem cells based therapeutic strategies have a long-standing history to treat many infertility conditions, but ethical restrictions do not allow the broad-scale utilization of adult mesenchymal stromal/stem cells (MSCs). Easily accessible, placental derived or amniotic stem cells present an invaluable alternative source of non-immunogenic and non-tumorigenic stem cells that possess multilineage potential. Given these characteristics, placental or amniotic stem cells (ASCs) have been investigated for therapeutic purposes to address infertility in the last decade. This study aims to summarize the current standing and progress of human amniotic epithelial stem cells (hAECs), amniotic mesenchymal stem cells (hAMSCs), and amniotic fluid stem cells (hAFSCs) in the field of reproductive medicine. The therapeutic potential of these cells to restore or enhance normal ovarian function and pregnancy outcomes are highlighted in this study.

Human amniotic mesenchymal stem cells promote endometrium regeneration in a rat model of intrauterine adhesion

Human amniotic transplantation has been proposed to improve the therapeutic efficacy of intrauterine adhesions (IUAs). Human amniotic mesenchymal stem stromal cells (hAMSCs) can differentiate into multiple tissue types. This study aimed to investigate the mechanism by which hAMSCs transplantation promotes endometrial regeneration. The rat models with IUA were established through mechanical and infective methods, and PKH26-labeled hAMSCs were transplanted through the tail vein (combined with/without estrogen). Under three different conditions, hAMSCs differentiated into endometrium-like cells. HE and Mason staining assays, and immunohistochemistry were used to compare the changes in rat models treated with hAMSCs and/or estrogen transplantation. To define the induction of hAMSCs to endometrium-like cells in vitro, an induction medium (cytokines, estrogen) was used to investigate the differentiation of hAMSCs into endometrium-like cells. qRT-polymerase chain reaction (PCR) and western blotting were performed to detect the differentiation of hAMSCs into endometrium-like cells. A greater number of glands, fewer endometrial fibrotic areas, and stronger expression of vascular endothelial growth factor and cytokeratin in the combined group (hAMSCs transplantation combined with estrogen) than in the other treatment groups were observed. hAMSCs could be induced into endometrium-like cells by cytokine treatment (TGF-β1, EGF, and PDGF-BB). Transplantation of hAMSCs is an effective alternative for endometrial regeneration after injury in rats. The differentiation protocol for hAMSCs will be useful for further studies on human endometrial regeneration.

Functional acellular matrix for tissue repair

In view of their low immunogenicity, biomimetic internal environment, tissue- and organ-like physicochemical properties, and functionalization potential, decellularized extracellular matrix (dECM) materials attract considerable attention and are widely used in tissue engineering. This review describes the composition of extracellular matrices and their role in stem-cell differentiation, discusses the advantages and disadvantages of existing decellularization techniques, and presents methods for the functionalization and characterization of decellularized scaffolds. In addition, we discuss progress in the use of dECMs for cartilage, skin, nerve, and muscle repair and the transplantation or regeneration of different whole organs (e.g., kidneys, liver, uterus, lungs, and heart), summarize the shortcomings of using dECMs for tissue and organ repair after refunctionalization, and examine the corresponding future prospects. Thus, the present review helps to further systematize the application of functionalized dECMs in tissue/organ transplantation and keep researchers up to date on recent progress in dECM usage.

Cell therapy for the treatment of reproductive diseases and infertility: an overview from the mechanism to the clinic alongside diagnostic methods

Infertility is experienced by 8%-12% of adults in their reproductive period globally and has become a prevalent concern. Besides routine therapeutic methods, stem cells are rapidly being examined as viable alternative therapies in regenerative medicine and translational investigation. Remarkable progress has been made in understanding the biology and purpose of stem cells. The affected pluripotent stem cells (iPSCs) and mesenchymal stem cells (MSCs) are further studied for their possible use in reproductive medicine, particularly for infertility induced by premature ovarian insufficiency and azoospermia. Accordingly, this study discusses current developments in the use of some kinds of MSCs such as adipose-derived stem cells, bone marrow stromal cells, umbilical cord MSCs, and menstrual blood MSCs. These methods have been used to manage ovarian and uterine disorders, and each technique presents a novel method for the therapy of infertility.

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.

Recent progress of Bioinspired Hydrogel-based delivery system for endometrial repair

Endometrial injury is the main fact leading to infertility. Current treatments of endometrial injury present many problems, such as unable to achieve desired effects due to low retention and the inherent potential risk of injury. Besides, it is important to the development of bioinspired material that can mimic the natural tissue and possess native tissue topography. Hydrogel is a kind of bioinspired superhydrophilic materials with unique characteristics, such as excellent biocompatibility, biodegradability, porosity, swelling, and cross-linkage. These unique physiochemical properties of bioinspired hydrogels enable their promising application as novel delivery platform and alternative therapies for endometrial injury. In this mini review, we summarize the recent advances in bioinispred hydrogel-based delivery system for endometrial repair, including as a post-operative physical barrier and therapeutic delivery system. In addition, present status, limitations, and future perspectives are also discussed.

UC-MSCs seeded on small intestinal submucosa to repair the uterine wall injuries

OBJECTIVE

The effectiveness of tissue engineering materials combining porcine small intestine submucosa (SIS) and umbilical cord mesenchymal stem cells (UC-MSCs) on uterine injury in female rat after full-thickness uterine resection was evaluated as a basis for clinical treatment of postoperative uterine injury.

METHODS

After complex culture with SIS and UC-MSCs, cell adhesion, growth and proliferation were assessed . Before the implantation, a surgical procedure of bilateral full-thickness uterine resection (0.5 ~ 2.0 cm long and 0.3 cm wide) was performed to obtain the rat uterine injury model, while the sham-operated rats were used as controls. H&E staining results and fertility of female rats in each group were assessed to determine the critical resection length of the full-thickness uterine resection. Then SIS or UC-MSCs-SIS were implanted into the female rats from the uterine injury group, followed by assessments of H&E staining, the expressions of ki67, α-SMA and LIF, and fertility to determine the effectiveness of SIS and UC-MSCs-SIS on uterine injury in female rat.

RESULTS

At 24, 48 and 72 h, the cells grew progressively on the SIS material. In the 1.5 cm and 2.0 cm groups, the pregnancy rate, proportion of the uterus supporting live embryo growth, number of live embryos, and proportion of live embryos were all significantly less than those in the 0.5 cm and sham-operated groups. In the 2.0 cm group, there was little tissue regeneration at the center of the injury and not conducive to subsequent assessment. The UC-MSCs-SIS and SIS groups were better on morphological development, cell proliferation, LIF expression and fertility than the control group.

CONCLUSION

UC-MSCs show good adhesion, growth, and proliferation on the SIS scaffold material. The optimal resection length in full-thickness uterine resection on female rat is 1.5 cm. UC-MSCs-SIS is the effective treatment for repairing a injury after the full-thickness resection of the uterus in this research.

Bone marrow mesenchymal stem cells combined with estrogen synergistically promote endometrial regeneration and reverse EMT via Wnt/β-catenin signaling pathway

BACKGROUND

Intrauterine adhesion (IUA) is a clinical disease characterized by the uterine cavity occlusion caused by the damage of the endometrial basal layer. Bone marrow mesenchymal stem cells (BMSCs) transplantation have the potential to promote endometrial regeneration mainly through paracrine ability. Estrogen is an indispensable and important factor in the repair of endometrial damage, which has been reported as a promising and adjunctive therapeutic application for stem cell transplantation therapy. This study aims to investigate the synergistic effect of BMSCs and estrogen on improving the endometrial regeneration and restoring the endometrium morphology in a dual damage model of IUA in rabbits and the underlying molecular mechanisms.

METHODS

BMSCs were isolated and identified by adipogenic and osteogenic differentiation and flow cytometry assays. The rabbit IUA animal model was established by a dual damage method of mechanical curettage and lipopolysaccharide infection. Additionally, we investigated the therapeutic impact of both BMSCs and estrogen either separately or in combination in a rabbit model. The retention of PKH26-labeled BMSCs was observed by vivo fluorescence imaging.The number of endometrial glands and the degree of fibrosis were observed by H&E and Masson staining respectively. Western blotting, Immunohistochemistry and immunofluorescence staining were performed to detect biomarkers related to endometrial epithelium, endometrial fibrosis and EMT. Finally, the protein expression of core molecules of Wnt/β-catenin pathway was detected by Western blotting.

RESULTS

PKH26-labeled fluorescence results revealed that BMSCs appeared and located in the endometrial glands and extracellular matrix area when orthotopic transplanted into the uterine cavity. Histological assays showed that remarkably increasing the number of endometrial glands and decreasing the area of endometrial fibrosis in the BMSCs combined with estrogen treatment group. Moreover, downregulated expression of fibrosis markers (fibronectin, CollagenI, a-SMA) and interstitial markers (ZEB1, Vimentin, N-cadherin), as well as upregulated E-cadherin expression were found in the combined group. Further study of in vivo staining revealed that fluorescence intensity of CK7 was stronger in the combined group than that of direct BMSCs intrauterine transplantation, while vimentin showed the opposite results. Moreover, the protein levels of β-catenin, Axin2, C-myc, CycinE of Wnt/β-catenin signaling pathway increased in the BMSCs combined with estrogen group than in the other treatment groups.

CONCLUSION

BMSCs combined with estrogen can promote the differentiation of stem cells into endometrial epithelial cells to facilitate the regeneration of damaged endometrium. The potential mechanism of the synergistic effect may inhibit the occurrence of EMT by activating the Wnt/β-catenin signaling pathway.

Human umbilical cord blood-derived MSCs trans-differentiate into endometrial cells and regulate Th17/Treg balance through NF-κB signaling in rabbit intrauterine adhesions endometrium

Purpose

The fundamental cause of intrauterine adhesions (IUAs) is the destruction and reduction in stem cells in endometrial basal layer, resulting in endometrial reconstruction very difficult. The purpose of this study was to investigate the effects and underlying mechanism of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) on the endometrial reconstruction after transplantation.

Methods

hUCB-MSCs were isolated and identified by flow cytometry, osteogenic, adipogenic and chondrogenic differentiation assays. The rabbit IUA models were established and set five groups (control, 14/28th day after surgery, estrogen and hUCB-MSCs treatment). The number of endometrial glands and the fibrosis rate were evaluated using HE and Masson staining, respectively. Endometrial proliferation, angiogenesis and inflammation were evaluated by immunohistochemical staining of ER, Ki-67and TGF-β1, respectively. Single-cell RNA sequencing (scRNA-seq) was applied to explore the cell differentiation trajectory after hUCB-MSCs transplanted into IUA endometrium. Finally, molecular mechanism of hUCB-MSCs repairing damaged endometrium was investigated by RNA sequencing, qRT-PCR and Western blot assays.

Results

After transplantation of the hUCB-MSCs, the increase in endometrial gland number, estrogen receptor (ER) and Ki-67 expression, and the decrease in fibrosis rate and TGF-β expression (P < 0.05), suggested the endometrial repair, angiogenesis and inflammatory suppression. The therapeutic effect of hUCB-MSCs was significantly improved compared with 28th day after surgery and estrogen group. ScRNA-seq demonstrated that the transplanted hUCB-MSCs can trans-differentiate into endometrial cells: epithelial, fibroblast and macrophage. RNA sequencing of six IUA samples combined with qRT-PCR and Western blot assays further revealed that hUCB-MSCs may regulate Th17/Treg balance through NF-κB signaling, thus inhibiting the immune response of damaged endometrium.

Conclusions

Our study demonstrated that hUCB-MSCs can repair damaged endometrium through trans-differentiation, immunomodulatory capacities and NF-κB signaling, suggesting the treatment value of hUCB-MSCs in IUA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02990-1.

The Role of Endometrial Stem/Progenitor Cells in Recurrent Reproductive Failure

Recurrent implantation failure (RIF) and recurrent pregnancy loss (RPL), collectively referred to as recurrent reproductive failure (RRF), are both challenging conditions with many unanswered questions relating to causes and management options. Both conditions are proposed to be related to an aberrant endometrial microenvironment, with different proposed aetiologies related to a restrictive or permissive endometrium for an invading embryo. The impressive regenerative capacity of the human endometrium has been well-established and has led to the isolation and characterisation of several subtypes of endometrial stem/progenitor cells (eSPCs). eSPCs are known to be involved in the pathogenesis of endometrium-related disorders (such as endometriosis) and have been proposed to be implicated in the pathogenesis of RRF. This review appraises the current knowledge of eSPCs, and their involvement in RRF, highlighting the considerable unknown aspects in this field, and providing avenues for future research to facilitate much-needed advances in the diagnosis and management of millions of women suffering with RRF.

Therapeutic Effects and Repair Mechanism of HGF Gene-Transfected Mesenchymal Stem Cells on Injured Endometrium

There are many studies on the advantages of using mesenchymal stem cells (MSCs) that secrete various paracrine factors for repairing endometrial injury. However, the stability and effectiveness of MSCs require improvement to become a viable therapy. Hepatocyte growth factor (HGF), one of the cytokines secreted by MSCs, promotes vascular repair and mesenchymal to epithelial transformation (MET). Therefore, HGF likely promotes the repair process of the endometrium. We prepared MSCs transfected with the HGF gene to explore its repair effects and mechanism using a damaged endometrium mouse model. HGF gene-transfected MSCs were prepared by electroporation. The transfected MSCs retained their cellular characteristics and significantly increased the expression of HGF ( $P<0.01$ ). HGF gene-transfected MSCs helped damaged endometrium to recover its morphological characteristics, improved proliferation and decreased apoptosis of endometrial cells, increased the expression of endometrial vascular growth-related factors, and activated phosphorylated c-Met and AKT in the mouse endometrial damage model ( $P<0.05$ ). Compared with normal MSCs, HGF gene-transfected MSCs produced a more significant effect on damaged endometrial epithelium repair by activating the HGF/c-Met and downstream signaling pathways. Our results indicate that HGF gene-transfected MSCs provide an effective and promising tool for injured endometrium therapy.

Extracorporeal Shock Wave Therapy Combined with Platelet-Rich Plasma during Preventive and Therapeutic Stages of Intrauterine Adhesion in a Rat Model

Intrauterine adhesion (IUA) is caused by artificial endometrial damage during intrauterine cavity surgery. The typical phenotype involves loss of spontaneous endometrium recovery and angiogenesis. Undesirable symptoms include abnormal menstruation and infertility; therefore, prevention and early treatment of IUA remain crucial issues. Extracorporeal shockwave therapy (ESWT) major proposed therapeutic mechanisms include neovascularization, tissue regeneration, and fibrosis. We examined the effects of ESWT and/or platelet-rich plasma (PRP) during preventive and therapeutic stages of IUA by inducing intrauterine mechanical injury in rats. PRP alone, or combined with ESWT, were detected an increased number of endometrial glands, elevated vascular endothelial growth factor protein expression (hematoxylin-eosin staining and immunohistochemistry), and reduced fibrosis rate (Masson trichrome staining). mRNA expression levels of nuclear factor-kappa B, tumor necrosis factor-α, transforming growth factor-β, interleukin (IL)-6, collagen type I alpha 1, and fibronectin were reduced during two stages. However, PRP alone, or ESWT combined with PRP transplantation, not only increased the mRNA levels of vascular endothelial growth factor (VEGF) and progesterone receptor (PR) during the preventive stage but also increased PR, insulin-like growth factor 1 (IGF-1), and IL-4 during the therapeutic stage. These findings revealed that these two treatments inhibited endometrial fibrosis and inflammatory markers, thereby inhibiting the occurrence and development of intrauterine adhesions.

Efficacy of Freeze-Dried Amnion Grafts on Cytokines in Uterine Exudates Following Hysteroscopic Adhesiolysis of Severe Intrauterine Adhesions

Background

Intrauterine adhesions (IUAs) are a benign uterine disorder that results in intrauterine adhesions and scarring. This study was conducted to assess the effects of freeze-dried amnion grafts on the concentrations of adhesion-related cytokines in uterine exudates following hysteroscopic adhesiolysis of IUAs.

Materials and Methods

This study was a prospective randomized controlled trial. Thirty patients who underwent hysteroscopic adhesiolysis for severe IUAs were enrolled. They were randomly divided into a study group (with freeze-dried amnion graft treatment after surgery, N = 15) and a control group (without a graft, N = 15). After complete separation of adhesions, a Foley balloon containing a freeze-dried amnion graft was inserted into the uterine cavity in the study group, while a Foley balloon with no graft was placed in the control group. Enzyme-linked immunosorbent assays were performed to test adhesion-related cytokine concentrations in uterine exudates, including IL-1β, TNF-α, and VEGF, at different time intervals after surgery. Second-look hysteroscopy was conducted three months after the surgery. On the basis of the American Fertility Society (AFS) scoring system, the level of adhesions was evaluated during hysteroscopy.

Results

The postoperative volume of the uterine exudates in the study group was significantly lower than that of the control group (P < 0.05). The adhesion-related cytokine concentrations of TNF-α, VEGF, and IL-1β significantly increased after surgery in both groups. Their concentrations were significantly lower in the study group than in the control group (P < 0.05). Moreover, IL-1β exhibited a long-lasting effect in the study group. AFS scores and readhesion rates were significantly lower in the study group than in the control group after hysteroscopic adhesiolysis of severe IUAs.

Conclusion

The application of freeze-dried amnion grafts is beneficial to the postoperative recovery of patients with severe IUAs and may reduce the readhesion rate after hysteroscopic adhesiolysis by lowering adhesion-related cytokines, including TNF-α, VEGF, and IL-1β.

Cell-based therapy in thin endometrium and Asherman syndrome

Numerous treatment strategies have so far been proposed for treating refractory thin endometrium either without or with the Asherman syndrome. Inconsistency in the improvement of endometrial thickness is a common limitation of such therapies including tamoxifen citrate as an ovulation induction agent, acupuncture, long-term pentoxifylline and tocopherol or tocopherol only, low-dose human chorionic gonadotropin during endometrial preparation, aspirin, luteal gonadotropin-releasing hormone agonist supplementation, and extended estrogen therapy. Recently, cell therapy has been proposed as an ideal alternative for endometrium regeneration, including the employment of stem cells, platelet-rich plasma, and growth factors as therapeutic agents. The mechanisms of action of cell therapy include the cytokine induction, growth factor production, natural killer cell activity reduction, Th17 and Th1 decrease, and Treg cell and Th2 increase. Since cell therapy is personalized, dynamic, interactive, and specific and could be an effective strategy. Despite its promising nature, further research is required for improving the procedure and the safety of this strategy. These methods and their results are discussed in this article.

Human amniotic mesenchymal stem cells combined with PPCNg facilitate injured endometrial regeneration

BACKGROUND

Caused by the injury to the endometrial basal layer, intrauterine adhesions (IUA) are characterized by uterine cavity obliteration, leading to impaired fertility. Human amniotic mesenchymal stem cells (hAMSCs) have the potential to promote endometrial regeneration mainly through paracrine ability. PPCNg is a thermoresponsive biomaterial consisted of Poly (polyethylene glycol citrate-co-N-isopropylacrylamide) (PPCN) mixed with gelatin, which has been reported as a scaffold for stem cell transplantation. This study aims to investigate the therapeutic effect of hAMSCs combined with PPCNg transplantation in promoting the regeneration of injured endometrium.

METHODS

hAMSCs were cultured in different concentrates of PPCNg in vitro, and their proliferation, apoptosis and cell cycle were examined by CCK-8 assay and flow cytometry. Immunofluorescence was used to determine the MSCs specific surface markers. The expression of pluripotent genes was analyzed by qRT-PCR. The multiple-lineage differentiation potential was further evaluated by detecting the differentiation-related genes using qRT-PCR and specific staining. The Sprague-Dawley (SD) rat IUA model was established with 95% ethanol. hAMSCs combined with PPCNg were transplanted through intrauterine injection. The retention of DiR-labeled hAMSCs was observed by vivo fluorescence imaging. The endometrium morphology was assessed using hematoxylin and eosin (H&E) and Masson staining. Immunohistochemistry staining was performed to detect biomarkers related to endometrial proliferation, re-epithelialization, angiogenesis and endometrial receptivity. The function of regenerated endometrium was evaluated by pregnancy tests.

RESULTS

hAMSCs maintained normal cell proliferation, apoptosis and cell cycle in PPCNg. Immunofluorescence and qRT-PCR showed that hAMSCs cultured in PPCNg and hAMSCs cultured alone expressed the same surface markers and pluripotent genes. hAMSCs exhibited normal multilineage differentiation potential in PPCNg. Vivo fluorescence imaging results revealed that the fluorescence intensity of hAMSCs combined with PPCNg intrauterine transplantation was stronger than that of direct hAMSCs intrauterine transplantation. Histological assays showed the increase in the thickness of endometrial and the number of endometrial glands, and the remarkably decrease in the fibrosis area in the PPCNg/hAMSCs group. The expressions of Ki-67, CK7, CK19, VEGF, ER and PR were significantly increased in the PPCNg/hAMSCs group. Moreover, the number of implanted embryos and pregnancy rate were significantly higher in the PPCNg/hAMSCs group than in the hAMSCs group.

CONCLUSIONS

PPCNg is suitable for growth, phenotype maintenance and multilineage differentiation of hAMSCs. hAMSCs combined with PPCNg intrauterine transplantation can facilitate the regeneration of injured endometrium by improving utilization rates of hAMSCs, and eventually restore reproductive capacity.

Making More Womb: Clinical Perspectives Supporting the Development and Utilization of Mesenchymal Stem Cell Therapy for Endometrial Regeneration and Infertility

The uterus is a homeostatic organ, unwavering in the setting of monthly endometrial turnover, placental invasion, and parturition. In response to ovarian steroid hormones, the endometrium autologously prepares for embryo implantation and in its absence will shed and regenerate. Dysfunctional endometrial repair and regeneration may present clinically with infertility and abnormal menses. Asherman's syndrome is characterized by intrauterine adhesions and atrophic endometrium, which often impacts fertility. Clinical management of infertility associated with abnormal endometrium represents a significant challenge. Endometrial mesenchymal stem cells (MSC) occupy a perivascular niche and contain regenerative and immunomodulatory properties. Given these characteristics, mesenchymal stem cells of endometrial and non-endometrial origin (bone marrow, adipose, placental) have been investigated for therapeutic purposes. Local administration of human MSC in animal models of endometrial injury reduces collagen deposition, improves angiogenesis, decreases inflammation, and improves fertility. Small clinical studies of autologous MSC administration in infertile women with Asherman's Syndrome suggested their potential to restore endometrial function as evidenced by increased endometrial thickness, decreased adhesions, and fertility. The objective of this review is to highlight translational and clinical studies investigating the use of MSC for endometrial dysfunction and infertility and to summarize the current state of the art in this promising area.

Management of intrauterine adhesions using human amniotic mesenchymal stromal cells to promote endometrial regeneration and repair through Notch signalling

Intrauterine adhesions (IUAs) severely hamper women's reproductive functions. Human amniotic mesenchymal stromal cell (hAMSC) transplantation is effective in treating IUAs. Here, we examined the function of Notch signalling in IUA treatment with hAMSC transplantation. Forty-five Sprague-Dawley female rats were randomly divided into the sham operation, IUA, IUA + E2, IUA + hAMSCs and IUA + hAMSCs + E2 groups. After IUA induction in the rats, hAMSCs promoted endometrial regeneration and repair via differentiation into endometrial epithelial cells. In all groups, the expression of key proteins in Notch signalling was detected in the uterus by immunohistochemistry. The results indicated Notch signalling activation in the hAMSCs and hAMSCs + E2 groups. We could also induce hAMSC differentiation to generate endometrial epithelial cells in vitro. Furthermore, the inhibition of Notch signalling using the AdR-dnNotch1 vector suppressed hAMSC differentiation (assessed by epithelial and mesenchymal marker levels), whereas its activation using the AdR-Jagged1 vector increased differentiation. The above findings indicate Notch signalling mediates the differentiation of hAMSCs into endometrial epithelial cells, thus promoting endometrial regeneration and repair; Notch signalling could have an important function in IUA treatment.

Bioengineered endometrial hydrogels with growth factors promote tissue regeneration and restore fertility in murine models

Extracellular matrix (ECM) hydrogels obtained from decellularized tissues are promising biocompatible materials for tissue regeneration. These biomaterials may provide important options for endometrial pathologies such as Asherman's syndrome and endometrial atrophy, which lack effective therapies thus far. First, we performed a proteomic analysis of a decellularized endometrial porcine hydrogel (EndoECM) to describe the specific role of ECM proteins related to regenerative processes. Furthermore, we investigated the ability of a bioengineered system-EndoECM alone or supplemented with growth factors (GFs)-to repair the endometrium in a murine model of endometrial damage. For this model, the uterine horns of female C57BL/6 mice were first injected with 70% ethanol, then four days later, they were treated with: saline (negative control); biotin-labeled EndoECM; or biotin-labeled EndoECM plus platelet-derived GF, basic fibroblast GF, and insulin-like GF 1 (EndoECM+GF). Endometrial regeneration and fertility restoration were evaluated by assessing the number of glands, endometrial area, cell proliferation, neaoangiogenesis, reduction of collagen deposition, and fertility restoration. Interestingly, regenerative effects such as an increased number of endometrial glands, increased area, high cell proliferative index, development of new blood vessels, reduction of collagen deposition, and higher pregnancy rate occurred in mice treated with EndoECM+GF. Thus, a bioengineered system based on EndoECM hydrogel supplemented with GFs may be promising for the clinical treatment of endometrial conditions such as Asherman's syndrome and endometrial atrophy. STATEMENT OF SIGNIFICANCE: In the last years, the bioengineering field has developed new and promising approaches to regenerate tissues or replace damaged and diseased tissues. Bioengineered hydrogels offer an ideal option because these materials can be used not only as treatments but also as carriers of drugs and other therapeutics. The present work demonstrates for the first time how hydrogels derived from pig endometrium loaded with growth factors could treat uterine pathologies in a mouse model of endometrial damage. These findings provide scientific evidence about bioengineered hydrogels based on tissue-specific extracellular matrix offering new options to treat human infertility from endometrial causes such as Asherman's syndrome or endometrial atrophy.

Stem cell-based therapy for ameliorating intrauterine adhesion and endometrium injury

Intrauterine adhesion refers to endometrial repair disorders which are usually caused by uterine injury and may lead to a series of complications such as abnormal menstrual bleeding, recurrent abortion and secondary infertility. At present, therapeutic approaches to intrauterine adhesion are limited due to the lack of effective methods to promote regeneration following severe endometrial injury. Therefore, to develop new methods to prevent endometrial injury and intrauterine adhesion has become an urgent need. For severely damaged endometrium, the loss of stem cells in the endometrium may affect its regeneration. This article aimed to discuss the characteristics of various stem cells and their applications for uterine tissue regeneration.

Bioprinting of a Blue Light-Cross-Linked Biodegradable Hydrogel Encapsulating Amniotic Mesenchymal Stem Cells for Intrauterine Adhesion Prevention

Intrauterine adhesion (IUA) is a common and prevailing complication after uterine surgery, which can lead to clinical symptoms such as a low menstrual volume, amenorrhea, periodic lower abdominal pain, infertility, and so on. Placing a three-dimensional printing hydrogel between the injured site and the adjacent tissue is considered to be a physical barrier to prevent adhesion, which can isolate the damaged area during the healing process. In this work, a tissue hydrogel with various proportions of a methacrylated gelatin (GelMA) and methacrylated collagen (ColMA) composite hydrogel loaded with amniotic mesenchymal stem cells (AMSCs) was constructed by using three-dimensional biological printing technology. Compared with the single GelMA hydrogel, the composite antiadhesion hydrogel (GelMA/ColMA) showed an appropriate swelling ratio, enhanced mechanical properties, and impressive stability. Meanwhile, the microstructure of the GelMA/ColMA composite hydrogel showed a denser and interconnected microporous structure. In addition, the cytotoxicity study indicated that the GelMA/ColMA hydrogel has a cytocompatibility nature toward AMSCs. Finally, the fabrication of stem cell encapsulation hydrogels was studied, and the cells could be released continuously for more than 7 days with the normal cell function. The results of in vivo experiments indicated that the GelMA/ColMA/hAMSC (human amnion mesenchymal stem cell) hydrogel can prevent cavity adhesion in a rat IUA model. Therefore, bioprinting a biodegradable hydrogel cross-linked by blue light has satisfactory anticavity adhesion effects with excellent physical properties and biocompatibility, which could be used as a preventive barrier for intrauterine adhesion.

Strategies for managing asherman's syndrome and endometrial atrophy: Since the classical experimental models to the new bioengineering approach

Endometrial function is essential for embryo implantation and pregnancy, but managing endometrial thickness that is too thin to support pregnancy or an endometrium of compromised functionality due to intrauterine adhesions is an ongoing challenge in reproductive medicine. Here, we review current and emerging therapeutic and experimental options for endometrial regeneration with a focus on animal models used to study solutions for Asherman's syndrome and endometrial atrophy, which both involve a damaged endometrium. A review of existing literature was performed that confirmed the lack of consensus on endometrial therapeutic options, though promising new alternatives have emerged in recent years (platelet-rich plasma, exosomes derived from stem cells, bioengineering-based techniques, endometrial organoids, among others). In the future, basic research using established experimental models of endometrial pathologies (combined with new high-tech solutions) and human clinical trials with large population sizes are needed to evaluate these emerging and new endometrial therapies.

Unresponsive thin endometrium caused by Asherman syndrome treated with umbilical cord mesenchymal stem cells on collagen scaffolds: a pilot study

Background

Unresponsive thin endometrium caused by Asherman syndrome (AS) is the major cause of uterine infertility. However, current therapies are ineffective. This study is to evaluate the effect of transplantation with collagen scaffold/umbilical cord mesenchymal stem cells (CS/UC-MSCs) on this refractory disease.

Methods

Eighteen infertile women with unresponsive thin endometrium, whose frozen–thawed embryo transfers (FETs) were cancelled due to reduced endometrial thickness (ET ≤ 5.5 mm), were enrolled in this before and after self-control prospective study. Hysteroscopic examination was performed to confirm no intrauterine adhesions, then twenty million UC-MSCs loaded onto a CS were transplanted into the uterine cavity in two consecutive menstrual cycles. Then uterine cavity was assessed through hysteroscopy after two transplants. FETs were performed in the following cycle. Pregnancy outcomes were followed up. Endometrial thickness, uterine receptivity and endometrial angiogenesis, proliferation and hormone response were compared before and after treatment.

Results

Sixteen patients completed the study. No treatment-related serious adverse events occurred. Three months after transplantation, the average ET increased from 4.08 ± 0.26 mm to 5.87 ± 0.77 mm (P < 0.001). Three of 15 patients after FET got pregnant, of whom 2 gave birth successfully and 1 had a miscarriage at 25 weeks’ gestation. One of 2 patients without FET had a natural pregnancy and gave birth normally after transplantation. Immunohistochemical analysis showed increased micro-vessel density, upregulated expression of Ki67, estrogen receptor alpha, and progesterone receptor, indicating an improvement in endometrial angiogenesis, proliferation, and response to hormones.

Conclusion

CS/UC-MSCs is a promising and potential approach for treating women with unresponsive thin endometrium caused by AS.

Trial registration

ClinicalTrials.gov NCT03724617. Registered on 26 October 2018—prospectively registered, https://register.clinicaltrials.gov/

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02499-z.

Application of Stem Cell Therapy for Infertility

Infertility creates an immense impact on the psychosocial wellbeing of affected couples, leading to poor quality of life. Infertility is now considered to be a global health issue affecting approximately 15% of couples worldwide. It may arise from factors related to the male (30%), including varicocele, undescended testes, testicular cancer, and azoospermia; the female (30%), including premature ovarian failure and uterine disorders; or both partners (30%). With the recent advancement in assisted reproduction technology (ART), many affected couples (80%) could find a solution. However, a substantial number of couples cannot conceive even after ART. Stem cells are now increasingly being investigated as promising alternative therapeutics in translational research of regenerative medicine. Tremendous headway has been made to understand the biology and function of stem cells. Considering the minimum ethical concern and easily available abundant resources, extensive research is being conducted on induced pluripotent stem cells (iPSCs) and mesenchymal stem cells (MSC) for their potential application in reproductive medicine, especially in cases of infertility resulting from azoospermia and premature ovarian insufficiency. However, most of these investigations have been carried out in animal models. Evolutionary divergence observed in pluripotency among animals and humans requires caution when extrapolating the data obtained from murine models to safely apply them to clinical applications in humans. Hence, more clinical trials based on larger populations need to be carried out to investigate the relevance of stem cell therapy, including its safety and efficacy, in translational infertility medicine.

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 in Preclinical Infertility Cytotherapy: A Retrospective Review

Infertility is a global reproductive disorder which is caused by a variety of complex diseases. Infertility affects the individual, family, and community through physical, psychological, social and economic consequences. The results from recent preclinical studies regarding stem cell-based therapies are promising. Stem cell-based therapies cast a new hope for infertility treatment as a replacement or regeneration strategy. The main features and application prospects of mesenchymal stem cells in the future of infertility should be understood by clinicians. Mesenchymal stem cells (MSCs) are multipotent stem cells with abundant source, active proliferation, and multidirectional differentiation potential. MSCs play a role through cell homing, secretion of active factors, and participation in immune regulation. Another advantage is that, compared with embryonic stem cells, there are fewer ethical factors involved in the application of MSCs. However, a number of questions remain to be answered prior to safe and effective clinical application. In this review, we summarized the recent status of MSCs in the application of the diseases related to or may cause to infertility and suggest a possible direction for future cytotherapy to infertility.

Expression and potential role of CXCL5 in the pathogenesis of intrauterine adhesions

Objective

C-X-C motif chemokine ligand 5 (CXCL5), a member of the chemokine family, is associated with remodeling of connective tissues. However, its role in formation of intrauterine adhesions (IUA) remains unclear. We aimed to investigate the expression and mechanism underlying the role of CXCL5 in IUA.

Methods

Expression of CXCL5 in IUA was detected by immunohistochemistry in a rat model of IUA and by real-time PCR and western blotting in patients with IUA. The protein levels of matrix metalloproteinase 9 (MMP9) and transcription factor p65 in human endometrial cells were assessed by western blotting after CXCL5 overexpression.

Results

Protein expression of CXCL5 was significantly decreased in the endometria of IUA rats compared with that of control and sham-operated rats. Real-time PCR and western blotting in patients with IUA showed similar results to those from the rat model. After overexpression, CXCL5 significantly upregulated expression of MMP9 and slightly upregulated expression of p65 in human endometrial cells.

Conclusions

CXCL5 plays an important role in IUA formation after endometrial injury. We propose a molecular mechanism to explain formation of IUA, including downregulation of MMP9 by low CXCL5 expression. These findings provide valuable information for the prevention and targeted therapy of IUA.

Hierarchical cluster analysis in the study of the effect of cytokine expression patterns on endometrial repair and receptivity after hysteroscopic adhesiolysis

Background

In a previous study, we reported that amnion promotes endometrial cell growth by regulating cytokines. In this study, hierarchical cluster analysis enabled the evaluation of cytokine expression changes after amnion treatment to be explored by cluster patterns. The role of IL1B on endometrial repair and receptivity was revealed.

Methods

A total of 30 patients were recruited in this clinical trial (NCT02496052) of hysteroscopic adhesiolysis. They were randomly allocated into an amnion grafts group (amnion group) and a control group. After hysteroscopic adhesiolysis, a Foley catheter covered with a sterilized freeze-dried amnion graft was inserted into the uterine cavity of the participants in the amnion group, whereas for the control group, a Foley catheter without amnion graft was inserted. After surgery, patient follow-up was done for a year. Uterine exudates were collected every day for seven days after surgery, and analyzed by enzyme-linked immunosorbent assays. Hierarchical cluster analysis was performed to compare expression patterns of each cytokine. Single-gene gene set enrichment analysis and differentially expressed genes enrichment analysis of IL1B were performed using NCBI GEO (N=151) to evaluate its potential mechanisms and impact on endometrial receptivity.

Results

Compared to the control group, cytokine expression patterns of the amnion group revealed significant stratifications, which were highly correlated with the expression levels of IL1B on the sixth to seventh day after surgery, improving the pregnant rate. Wilcoxon test revealed significantly low expression levels of IL1B in the reduced endometrial receptivity group compared to the normal group. Moreover, gene set enrichment analysis showed that lysosomes, cell cycle, and calcium signaling pathways were associated with the biological processes in which IL1B plays a role. Screening and enrichment analyses of differentially expressed genes further verified the mechanisms of action of IL1B on endometrial repair and receptivity recovery.

Conclusions

Amnion promotes endometrial repair and receptivity by altering the expression levels and patterns of IL1B. Furthermore, by affecting lysosomal, cell cycle, and calcium signaling pathways, IL1B may be one of the factors involved in endometrial repair and receptivity recovery.

Cell-based endometrial regeneration: current status and future perspectives

Endometrial-related disorders including Asherman's syndrome, thin endometrium, pelvic organ prolapse, and cesarean scar pregnancies can be accompanied by different symptoms such as amenorrhea, infertility, abnormal placental implantation and recurrent miscarriage. Different methods have been introduced to overcome these problems such as surgery and hormonal therapy but none of them has shown promising outcomes. On the other hand, the development of novel regenerative therapeutic strategies has opened new avenues for the treatment of endometrial-related deficiencies. In this regard, different types of scaffolds, acellular matrices and also cell therapy with adult or stem cells have been investigated for the treatment of endometrial-related deficiencies. In this paper, we review the current status of cell-based endometrium regeneration using scaffold dependent and scaffold-free methods and future perspectives in this field. Moreover, we discuss the endometrial diseases that can be candidates for cell-based treatments. Also, the cells with the potential for endometrial regeneration are explained.

The efficacy of amniotic membrane-mediated sequential double-barrier therapy for the treatment of postoperative intrauterine adhesions

To study the efficacy of using amniotic membrane, balloon and intrauterine device (IUD) as barrier therapy to prevent re-adhesion after hysteroscopic adhesiolysis.A total of 45 patients diagnosed with intrauterine adhesions in Changzhou Maternal and Child Health Hospital from June 2014 to December 2017 were included in this retrospective case control study. According to different postoperative isolation barrier methods, the patients were divided into group A (Foley balloon + fresh amniotic membrane Day1 + IUD Day7) (22 cases) and group B (Foley balloon Day1 + IUD Day7) (23 cases). Three months after the surgery, the second hysteroscopy was performed to observe the condition of the uterine cavity and the improvement of menstruation, and to monitor the thickness of the endometrium.The efficacy of hysteroscopic procedure in group A was significantly higher than that of group B (P < .05). After 3 months of treatment, the improvement rate of menstruation was significantly higher in group A than in group B (P < .05). Endometrial thickness in both group A and B was significantly increased compared with that before the surgery (P < .05). The postoperative endometrium of group A was significantly thicker than that of group B (P < .05).Amniotic membrane-mediated sequential double-barrier method is clinically feasible for preventing recurrent intrauterine adhesions.

Stem Cells and the Endometrium: From the Discovery of Adult Stem Cells to Pre-Clinical Models

Adult stem cells (ASCs) were long suspected to exist in the endometrium. Indeed, several types of endometrial ASCs were identified in rodents and humans through diverse isolation and characterization techniques. Putative stromal and epithelial stem cell niches were identified in murine models using label-retention techniques. In humans, functional methods (clonogenicity, long-term culture, and multi-lineage differentiation assays) and stem cell markers (CD146, SUSD2/W5C5, LGR5, NTPDase2, SSEA-1, or N-cadherin) facilitated the identification of three main types of endogenous endometrial ASCs: stromal, epithelial progenitor, and endothelial stem cells. Further, exogenous populations of stem cells derived from bone marrow may act as key effectors of the endometrial ASC niche. These findings are promoting the development of stem cell therapies for endometrial pathologies, with an evolution towards paracrine approaches. At the same time, promising therapeutic alternatives based on bioengineering have been proposed.

The glucagon-like peptide-1 (GLP-1) analog exenatide ameliorates intrauterine adhesions in mice

OBJECTIVE

The purpose of the experiments in this study was to explore the effect of exenatide on intrauterine adhesions (IUAs) and to elucidate its mechanism to provide new ideas for the clinical treatment of IUAs.

METHODS

In this study, an animal model of IUAs was established by double stimulation using mechanical curettage and inflammation. After modeling, the treatment group was injected subcutaneously with three doses of exenatide for two weeks. The model group was injected with sterile ultrapure water, and the sham operation group was treated the same as the normal group, except for the observation of abdominal wound changes. Two weeks later, all mice were sacrificed by cervical dysfunction. The obtained mouse uterine tissue was used for subsequent experimental detection, using HE and Masson staining for histomorphological and pathological analysis; qRT-PCR for the detection of TGF-β1, α-SMA, and MMP-9 gene expression in uterine tissue; and western blotting analysis of TGF-β1, α-SMA, and collagen 1 protein expression to verify whether exenatide has a therapeutic effect on IUAs in mice.

RESULTS

In the high-dose exenatide treatment group, the endometrial glands significantly increased in size, and the deposition area of collagen fibers in the endometrial tissue was significantly reduced. We observed that the mRNA expression of TGF-β1 and α-SMA in the endometrial tissue of IUAs mice in this group was significantly reduced, while the expression of MMP-9 was significantly increased. In addition, we found that the protein expression of TGF-β1, α-SMA, and collagen 1 remarkably decreased after treatment with exenatide.

CONCLUSION

Exenatide may reduce the deposition of collagen fibers in the uterus of IUAs mice and promote the proliferation of endometrial glands in mice.

Recent developments in bio-scaffold materials as delivery strategies for therapeutics for endometrium regeneration

Intrauterine adhesions (IUAs) refer to the repair disorder after endometrial injury and may lead to uterine infertility, recurrent miscarriage, abnormal menstrual bleeding, and other obstetric complications. It is a pressing public health issue among women of childbearing age. Presently, there are limited clinical treatments for IUA, and there is no sufficient evidence that these treatment modalities can effectively promote regeneration after severe endometrial injury or improve pregnancy outcome. The inhibitory pathological micro-environment is the main factor hindering the repair of endometrial damaged tissues. To address this, tissue engineering and regenerative medicine have been achieving promising developments. Particularly, biomaterials have been used to load stem cells or therapeutic factors or construct an in situ delivery system as a treatment strategy for endometrial injury repair. This article comprehensively discusses the characteristics of various bio-scaffold materials and their application as stem cell or therapeutic factor delivery systems constructed for uterine tissue regeneration.

Characteristics and Therapeutic Potential of Human Amnion-Derived Stem Cells

Stem cells including embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs) and adult stem cells (ASCs) are able to repair/replace damaged or degenerative tissues and improve functional recovery in experimental model and clinical trials. However, there are still many limitations and unresolved problems regarding stem cell therapy in terms of ethical barriers, immune rejection, tumorigenicity, and cell sources. By reviewing recent literatures and our related works, human amnion-derived stem cells (hADSCs) including human amniotic mesenchymal stem cells (hAMSCs) and human amniotic epithelial stem cells (hAESCs) have shown considerable advantages over other stem cells. In this review, we first described the biological characteristics and advantages of hADSCs, especially for their high pluripotency and immunomodulatory effects. Then, we summarized the therapeutic applications and recent progresses of hADSCs in treating various diseases for preclinical research and clinical trials. In addition, the possible mechanisms and the challenges of hADSCs applications have been also discussed. Finally, we highlighted the properties of hADSCs as a promising source of stem cells for cell therapy and regenerative medicine and pointed out the perspectives for the directions of hADSCs applications clinically.

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.

Effectiveness of Stem Cell Therapy in the Treatment of Ovarian Disorders and Female Infertility: A Systematic Review

BACKGROUND

Infertility is a major problem worldwide. Various strategies are being used to develop better treatments for infertility and The most trending strategy is the stem cell therapy. In this study, the literature on stem cell therapy for ovarian disorders is summarized with analysis of current developments.

OBJECTIVE

Different published studies on stem cell-based therapy for the treatment of various types of ovarian insufficiency and disorders such as Premature Ovarian Insufficiency (POI) in the affected female population in animal or human clinical studies are systematically reviewed.

METHODS

We monitored five databases, including PubMed, Cochrane, Embase, Scopus, and ProQuest. A comprehensive online search was done using the criteria targeting the application of stem cells in animal models for menopause. Two independent reviewers carefully evaluated titles and abstracts of studies. The stem cell type, source, dosage, route of administration were highlighted in various POI animals models. Non-relevant and review articles were excluded.

OUTCOMES

648 published studies were identified during the initial comprehensive search process from which 41 were selected according to designed criteria. Based on our analysis, stem cells could accelerate ovarian tissues rejuvenation, regulate systemic sex-related hormones levels and eventually increase fertility rate.

CONCLUSION

The evidence suggests that stem cell-based therapies could be considered as an alternative modality to deal with women undergoing POI.

Application of Hydrogel-Based Delivery System in Endometrial Repair

A receptive endometrium with proper thickness is essential for successful embryo implantation. However, endometrial injury caused by intrauterine procedures often leads to pathophysiological changes in its environment, resulting in subsequent female infertility. Among diverse treatment methods of endometrial injury, hydrogels are a class of hydrophilic three-dimensional polymeric network with biocompatibility as well as the capability of absorbing water and encapsulation, which have potential applications as a promising intrauterine controlled-release delivery system. This review summarizes recent advances in the approaches of endometrial repair and further focuses on the application of a hydrogel-based delivery system in endometrial repair, including its preparation, therapeutic loading considerations, clinical applications, as well as working mechanisms.