Endometrial stem cells and reproduction

NOTCH1- and CD117-positive stem cells in human endometrium and their implications for successful implantation

OBJECTIVE

To investigate the quantity of 2 stem cell types in the endometrial stroma of women undergoing in vitro fertilization and their association with steroid hormone signaling and implantation success after embryo transfer.

DESIGN

Prospective cohort study.

SETTING

Private hospital.

PATIENT(S)

A total of 109 patients undergoing in vitro fertilization.

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

Immunohistochemistry staining of endometrial biopsies taken during the midluteal phase using antibodies against NOTCH1 and CD117 was performed. The percentage of endometrial stromal cells positive for these markers was determined. The link of these stem cell percentages with the serum progesterone and estradiol levels and the endometrial expression of their respective receptors were assessed. After embryo transfer, the quantity of stained cells for each marker was also compared according to implantation outcome.

RESULT(S)

The percentage of NOTCH1+ stromal cells ranged from 0.003%-2.112% (median, 0.062%) and was significantly higher than that of CD117+ cells, which ranged from 0.000%-0.210% (median, 0.020%) (Z = -7.035). The percentage of NOTCH1+ stem cells showed no difference between the studied serum hormone level groups and no relationship with the expression of their receptors in the endometrium. In contrast, the number of CD117+ cells significantly differed between patients with high and low levels of serum progesterone (cutoff, 14.9 ng/mL) and estradiol (cutoff, 135.6 pg/mL). Furthermore, the quantity of CD117+ stem cells was positively correlated with the progesterone receptor (R = 0.277) and estradiol receptor (R= 0.318) expression levels in the endometrium. Although the quantity of NOTCH1+ cells did not differ between the 2 implantation groups, the median percentage of CD117+ cells was significantly higher in patients with successful implantation than in those with unsuccessful implantation (0.03% vs. 0.01%, respectively). The cutoff value for the percentage of CD117+ cells predicting successful implantation was 0.018% (area under the curve, 0.66; 95% confidence interval, 0.56-0.77; sensitivity, 63.1%; specificity, 61.4%).

CONCLUSION(S)

This study indicates that the quantity of certain stem cell types (CD117+), but not others (NOTCH1+), in the functional endometrium is associated with implantation success and sex hormone signaling during the midluteal phase. These findings highlight the role of CD117+ cells in preparing the endometrium for embryo implantation, and their quantity may be an indirect indicator of endometrial receptivity.

Research progress of stem cell therapy for endometrial injury

Endometrial damage is an important factor leading to infertility and traditional conventional treatments have limited efficacy. As an emerging technology in recent years, stem cell therapy has provided new hope for the treatment of this disease. By comparing the advantages of stem cells from different sources, it is believed that menstrual blood endometrial stem cells have a good application prospect as a new source of stem cells. However, the clinical utility of stem cells is still limited by issues such as colonization rates, long-term efficacy, tumor formation, and storage and transportation. This paper summarizes the mechanism by which stem cells repair endometrial damage and clarifies the material basis of their effects from four aspects: replacement of damaged sites, paracrine effects, interaction with growth factors, and other new targets. According to the pathological characteristics and treatment requirements of intrauterine adhesion (IUA), the research work to solve the above problems from the aspects of functional bioscaffold preparation and multi-functional platform construction is also summarized. From the perspective of scaffold materials and component functions, this review will provide a reference for comprehensively optimizing the clinical application of stem cells.

Effects of smoking on the tissue regeneration-associated functions of human endometrial stem cells via a novel target gene SERPINB2

BACKGROUND

Smokers directly inhale mainstream cigarette smoke, which contains numerous known and potential toxic substances, and thus, smoking is expected to have broad harmful effects that cause tissue injury and dysfunction. Interestingly, many studies have suggested that the recent decline in female fertility and increased rate of spontaneous abortion could be associated with increased smoking rates. Indeed, women that smoked for 10 years or more were reported to have a ~ 20% higher infertility rate than women that had never smoked. However, the reasons for the underlying harmful aspects of smoking on female fertility remain a matter of debate. Importantly, a previous study revealed that resident endometrial stem cell deficiency significantly limits the cyclic regeneration potential of endometrium, which, in turn, decreases successful pregnancy outcomes. In this context, we postulated that exposure to mainstream cigarette smoke extracts might decrease female fertility by inhibiting the functions of resident endometrial stem cells.

METHODS

We investigated whether cigarette mainstream smoke exposure directly inhibits various tissue regeneration-associated functions of endometrial stem cells, such as self-renewal, migration, pluripotency, and differentiation capacity in vitro. Next, we determined whether SERPINB2 mediates cigarette smoke-induced suppressive effects on various tissue regeneration-associated functions by depleting SERPINB2 expression with specific shRNA targeting SERPINB2. Mice were injected intraperitoneally with low (0.5 mg/kg) or high (1 mg/kg) doses of cigarette smoke extract (10 times for two weeks), and endometrial stem cells were then isolated from mice uterine tissues.

RESULTS

We found that exposure to cigarette smoke extracts remarkably suppressed various tissue regeneration-associated functions of endometrial stem cells, such as self-renewal, migration, multilineage differentiation ability, and pluripotency in vitro and in vivo by activating the SERPINB2 gene. Indeed, cigarette smoke-induced inhibitory effects on various endometrial stem cell functions were significantly abolished by SERPINB2 knockdown.

CONCLUSIONS

These findings provide valuable information on the harmful effects of cigarette smoking on resident endometrial stem cells and hopefully will facilitate the developments of promising therapeutic strategies for subfertile or infertile women that smoke cigarettes.

Effect of MiR-100-5p on proliferation and apoptosis of goat endometrial stromal cell in vitro and embryo implantation in vivo

The growth of endometrial stromal cells (ESCs) at implantation sites may be a potential factor affecting the success rate of embryo implantation. Incremental proofs demonstrated that ncRNAs (e.g. miRNAs, lncRNAs and circRNAs) were involved in various biological procedures, including proliferation and apoptosis. In this study, the role of miR‐100‐5p on proliferation and apoptosis of goat ESCs in vitro and embryo implantation in vivo was determined. The mRNA expression of miR‐100‐5p was significantly inhibited in the receptive phase (RE) rather than in the pre‐receptive phase (PE). Overexpression of miR‐100‐5p suppressed ESCs proliferation and induced apoptosis. The molecular target of MiR‐100‐5p, HOXA1, was confirmed by 3′‐UTR assays. Meanwhile, the product of HOXA1 mRNA RT‐PCR increased in the RE more than that in the PE. The HOXA1‐siRNA exerted significant negative effects on growth arrest. Instead, incubation of ESCs with miR‐100‐5p inhibitor or overexpressed HOXA1 promoted the cell proliferation. In addition, Circ‐9110 which acted as a sponge for miR‐100‐5p reversed the relevant biological effects of miR‐100‐5p. The intrinsic apoptosis pathway was suppressed in ESCs, revealing a crosstalk between Circ‐9110/miR‐100‐5p/HOXA1 axis, PI3K/AKT/mTOR, and ERK1/2 pathways. To further evaluate the progress in study on embryo implantation regulating mechanism of miR‐100‐5p in vivo, the pinopodes of two phases were observed and analysed, suggesting that, as similar as in situ, miR‐100‐5p was involved in significantly regulating embryo implantation in vivo. Mechanistically, miR‐100‐5p performed its embryo implantation function through regulation of PI3K/AKT/mTOR and ERK1/2 pathways by targeting Circ‐9110/miR‐100‐5p/HOXA1 axis in vivo.

The impact of fine particulate matter (PM) on various beneficial functions of human endometrial stem cells through its key regulator SERPINB2

Fine particulate matter (PM) has a small diameter but a large surface area; thus, it may have broad toxic effects that subsequently damage many tissues of the human body. Interestingly, many studies have suggested that the recent decline in female fertility could be associated with increased PM exposure. However, the precise mechanisms underlying the negative effects of PM exposure on female fertility are still a matter of debate. A previous study demonstrated that resident stem cell deficiency limits the cyclic regenerative capacity of the endometrium and subsequently increases the pregnancy failure rate. Therefore, we hypothesized that PM exposure induces endometrial tissue damage and subsequently reduces the pregnancy rate by inhibiting various beneficial functions of local endometrial stem cells. Consistent with our hypothesis, we showed for the first time that PM exposure significantly inhibits various beneficial functions of endometrial stem cells, such as their self-renewal, transdifferentiation, and migratory capacities, in vitro and in vivo through the PM target gene SERPINB2, which has recently been shown to be involved in multiple stem cell functions. In addition, the PM-induced inhibitory effects on the beneficial functions of endometrial stem cells were significantly diminished by SERPINB2 depletion. Our findings may facilitate the development of promising therapeutic strategies for improving reproductive outcomes in infertile women.

Airborne pollutants may reduce female fertility through their debilitating effects on the stem cells that maintain the endometrium, the interior lining of the uterus. Recent evidence suggests that toxic byproducts from fossil fuels known as ‘particulate matter’ represent a danger to women’s reproductive health. South Korean researchers led by Ji-Won Jung, Korea Centers for Disease Control and Prevention, and In-Sun Hong, Gachon University, Incheon, have investigated this risk by exposing cultured human endometrial stem cells to diesel-derived particulate matter. These stem cells normally maintain the endometrium, allowing embryonic implantation to take place, but exposure to particulate matter greatly impaired the cells’ regenerative function. Mice exposed to particulate matter exhibited similar impairments of endometrial maintenance. The researchers identified a molecular pathway associated with this response that could guide development of fertility-restoring treatments.

Noncanonical functions of glucocorticoids: A novel role for glucocorticoids in performing multiple beneficial functions in endometrial stem cells

Chronic stress has a negative impact on many fertility-related functions; thus, the recent decline in female fertility seems to be at least partially associated with increased stress. The secretion of glucocorticoids is a typical endocrine response to chronic stress and indirectly reduces uterine receptivity through the hypothalamus-pituitary-gonadal (HPG) axis. However, in addition to its well-known canonical role, the direct effects of chronic stress-induced glucocorticoids on various uterine functions and their underlying molecular mechanisms are complex and have not yet been revealed. Recent studies have found that resident stem cell deficiency is responsible for the limited regenerative potential of the endometrium (the innermost lining of the uterine cavity) during each menstrual cycle, which subsequently increases infertility rates. In this context, we hypothesized that stress-induced glucocorticoids directly damage endometrial stem cells and consequently negatively affect endometrial reconstruction, which is important for uterine receptivity. In addition to its well-known canonical roles, we identified for the first time that cortisol, the most abundant and potent glucocorticoid in humans, directly suppresses the multiple beneficial functions (self-renewal, transdifferentiation, and migratory potential) of human endometrial stem cells through its functional receptor, glucocorticoid receptor (GR). Glucocorticoids inhibit well-known survival signals, such as the PI3K/Akt and FAK/ERK1/2 pathways. More importantly, we also found that immobilization of stress-induced glucocorticoids suppresses the various beneficial functions of tissue resident stem cells in vivo. To the best of our knowledge, this is the first study to investigate the direct effects of glucocorticoids on the regenerative capacity of endometrial stem cells, and the findings will facilitate the development of more promising therapeutic approaches to increase female fertility.

Gonadotropin-releasing hormone analogs: Mechanisms of action and clinical applications in female reproduction

Extra-hypothalamic GnRH and extra-pituitary GnRH receptors exist in multiple human reproductive tissues, including the ovary, endometrium and myometrium. Recently, new analogs (agonists and antagonists) and modes of GnRH have been developed for clinical application during controlled ovarian hyperstimulation for assisted reproductive technology (ART). Additionally, the analogs and upstream regulators of GnRH suppress gonadotropin secretion and regulate the functions of the reproductive axis. GnRH signaling is primarily involved in the direct control of female reproduction. The cellular mechanisms and action of the GnRH/GnRH receptor system have been clinically applied for the treatment of reproductive disorders and have widely been introduced in ART. New GnRH analogs, such as long-acting GnRH analogs and oral nonpeptide GnRH antagonists, are being continuously developed for clinical application. The identification of the upstream regulators of GnRH, such as kisspeptin and neurokinin B, provides promising potential to develop these upstream regulator-related analogs to control the hypothalamus-pituitary-ovarian axis.

Preventive Effects of Intrauterine Injection of Bone Marrow-Derived Mesenchymal Stromal Cell-Conditioned Media on Uterine Fibrosis Immediately after Endometrial Curettage in Rabbit

Uterine fibrosis is an acquired disorder leading to menstrual irregularities, implantation impairment, and abortion. Mesenchymal stromal cells (MSCs) have antifibrotic properties through chemokine secretion. MSC-conditioned media (MSC-CM) contain paracrine components-exosomes-with a great potential for repairing damaged tissue or preventing fibrosis. The main goal of this study was to evaluate the preventive effects of bone marrow-derived MSC-CM (BM-MSC-CM) on uterine fibrosis after uterine curettage in rabbits. This study included 12 female rabbits (24 uterine horns in total). Excised uteri of each of the 12 female rabbits were randomly divided into four groups of intact negative control, curettage positive control, BM-MSC injection, and BM-MSC-CM injection in the way that two corresponding uteri from a rabbit were allocated to different groups. The MSC-CM were collected from cultivated BM-MSCs 48 hours after having been washed three times and replaced in serum-free media. Through a surgical approach, the caudal parts of the uteri were submitted to traumatic endometrial curettage, except for the intact negative uteri. After suturing the uterine walls, BM-MSCs or BM-MSC-CM were injected in the curettage site. Endometrial regeneration was histologically evaluated 30 days after treatment. Based on the evaluation of histomorphometric indices, curettage with or without preventive injections increased the growth of endometrial layers. However, the amount of fibrotic tissue in the CM and the BM-MSC injection groups was the same as the normal control groups, and all were less than the curettage group. A single injection of CM of MSCs after 30 days prevented the fibrotic tissue formation induced by curettage in endometrial layers of rabbits. Injecting BM-MSC-CM immediately after curettage prevented and reduced the uterine fibrosis similar to BM-MSCs in a rabbit model.

CD34+KLF4+ Stromal Stem Cells Contribute to Endometrial Regeneration and Repair

The regenerative capacity of the human endometrium requires a population of local stem cells. However, the phenotypes, locations, and origin of these cells are still unknown. In a mouse menstruation model, uterine stromal SM22α⁺-derived CD34⁺KLF4⁺ stem cells are activated and integrate into the regeneration area, where they differentiate and incorporate into the endometrial epithelium; this process is correlated with enhanced protein SUMOylation in CD34⁺KLF4⁺ cells. Mice with a stromal SM22α-specific SENP1 deletion (SENP1smKO) exhibit accelerated endometrial repair in the regeneration model and develop spontaneous uterine hyperplasia. Mechanistic studies suggest that SENP1 deletion induces SUMOylation of ERα, which augments ERα transcriptional activity and proliferative signaling in SM22α⁺CD34⁺KLF4⁺ cells. These cells then transdifferentiate to the endometrial epithelium. Our study reveals that CD34⁺KLF4⁺ stromal-resident stem cells directly contribute to endometrial regeneration, which is regulated through SENP1-mediated ERα suppression.

The regenerative capacity of the human endometrium requires a population of local stem cells. Here, Yin et al. show that uterine stromal SM22α⁺CD34⁺KLF4⁺ stem cells are activated by ERα SUMOylation and integrate into the regeneration area, where they differentiate and incorporate into the endometrial epithelium.

Regenerative Potential of Menstrual Blood-Derived Stem Cells and Platelet-Derived Growth Factor in Endometrial Injury

Background

Endometrial regeneration is essential for normal endometrial function; however, it is unclear whether and how menstrual blood-derived stem cells (MenSCs) and platelet-derived growth factor (PGDF) are associated with this phenomenon. The present study explored this topic.

Material/Methods

EM-E6/E7/hTERT cells were divided into 5 groups: control group, NC group, PDGF group, MenSCs group, and PDGF+MenSCs group. The effects of MenSCs and PDGF on cell proliferation, invasion, and microvascular formation of endometrial epithelium were investigated by CCK-8, Transwell, and tube formation assays, respectively. Mouse endometrial injury models were established and mice were randomly divided into control, model, PDGF, MenSCs, and PDGF+MenSCs groups. Pathological change was examined with hematoxylin and eosin (H&E) staining. Microvessel formation of endometrial epithelium was estimated by detecting the expression of CD34 protein with immunohistochemical (IHC) staining. Western blot analysis was used to detect the activation of Akt and Bad proteins in endometrial tissue.

Results

MenSCs, PDGF, and the combination treatments significantly promoted the proliferation, migration, and tube formation of endometrial epithelium compared to the control and NC group. The combination of MenSCs and PDGF remarkably promoted re-epithelialization and endometrial repair. IHC staining analysis showed significant increases in CD34 expression of the endometrial tissue following treatment with PDGF and MenSCs. The combination treatments also markedly enhanced the phosphorylation of Akt and Bad in endometrial tissue.

Conclusions

These results suggest that MenSCs and PDGF may be candidate substances for endometrial injury repair.

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

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

Double-edged sword of gonadotropin-releasing hormone (GnRH): A novel role of GnRH in the multiple beneficial functions of endometrial stem cells

Gonadotropin-releasing hormone (GnRH) stimulates the synthesis and release of gonadotropins, which induce estrogen production and subsequent ovulation. Therefore, long-term GnRH exposure to regulate ovarian hyperstimulation is recognized as the gold standard for most in vitro fertilization (IVF) strategies. However, one of the most disappointing aspects of current IVF technology is relatively low rate (between 35 and 50%) of positive pregnancy outcomes, and the major reason for this high cancellation rate has not yet been revealed. Previous studies have demonstrated that resident stem cell deficiency limits the cyclic regenerative capacity of the endometrium and subsequently increases pregnancy failure rates. Therefore, we hypothesized that long-term GnRH exposure directly damages endometrial stem cells and consequently negatively affects pregnancy outcomes in GnRH-based IVF. In addition to their well-known roles in regulating the hypothalamus-pituitary-gonadal axis, GnRH and its receptors also localize in the extra-hypothalamic endometrium, suggesting a possible non-canonical role in endometrial stem cells. Consistent with our hypothesis, we show for the first time that GnRH suppresses the multiple beneficial functions of endometrial stem cells via the PI3K/Akt signaling pathway in vitro and in vivo. To the best of our knowledge, this is the first study to focus on the direct effects of GnRH on the regenerative potential of stem cells, and the findings will facilitate the development of more promising IVF strategies.

Mesenchymal stem cells: a promising tool for targeted gene therapy of endometriosis

Endometriosis is a leading, benign gynecological disorder around the world. Last few years have witnessed tremendous growth in the field of endometriosis and endometrial stem-cell research. Despite advancements in the biology and pathology of endometriosis, disease recurrence is still an enigma. Gene therapy holds promise in treating many pathologic conditions including endometriosis. Mesenchymal stem cells (MSCs) serve as ideal candidates for regenerative medicine and cell-based therapies. Owing to their specificity to the endometrium, residing endometrial MSC populations could be utilized as ideal candidates for targeting endometrial disorders. Recently, we demonstrated their flexibility for gene transduction using adenoviral vectors. The review highlights the potential of endometrial MSCs in devising targeted gene therapies for endometriosis.

Endometriosis: a role for stem cells

Endometriosis is a complex gynecologic condition affecting 6-10% of reproductive aged women and is a major cause of chronic pain and infertility. Mechanisms of disease pathogenesis are poorly understood. Considerable evidence supports the existence of a stem cell population in the endometrium which provides a physiologic source of regenerative endometrial cells, and multiple lines of evidence now support a key role for stem cells in the pathogenesis of endometriosis. In addition, new blood vessel formation is critical for the establishment and maintenance of endometriotic implants, a process in which endothelial progenitor cells may play an integral role. These new insights into disease pathogenesis present exciting opportunities to develop targeted and more effective therapeutic options in the management of this common and challenging disease.

Constitutive activation of transforming growth factor Beta receptor 1 in the mouse uterus impairs uterine morphology and function

Despite increasing evidence pointing to the essential involvement of the transforming growth factor beta (TGFB) superfamily in reproduction, a definitive role of TGFB signaling in the uterus remains to be unveiled. In this study, we generated a gain-of-function mouse model harboring a constitutively active (CA) TGFB receptor 1 (TGFBR1), the expression of which was conditionally induced by the progesterone receptor (Pgr)-Cre recombinase. Overactivation of TGFB signaling was verified by enhanced phosphorylation of SMAD2 and increased expression of TGFB target genes in the uterus. TGFBR1 Pgr-Cre CA mice were sterile. Histological, cellular, and molecular analyses demonstrated that constitutive activation of TGFBR1 in the mouse uterus promoted formation of hypermuscled uteri. Accompanying this phenotype was the upregulation of a battery of smooth muscle genes in the uterus. Furthermore, TGFB ligands activated SMAD2/3 and stimulated the expression of a smooth muscle maker gene, alpha smooth muscle actin (ACTA2), in human uterine smooth muscle cells. Immunofluorescence microscopy identified a marked reduction of uterine glands in TGFBR1 Pgr-Cre CA mice within the endometrial compartment that contained myofibroblast-like cells. Thus, constitutive activation of TGFBR1 in the mouse uterus caused defects in uterine morphology and function, as evidenced by abnormal myometrial structure, dramatically reduced uterine glands, and impaired uterine decidualization. These results underscore the importance of a precisely controlled TGFB signaling system in establishing a uterine microenvironment conducive to normal development and function.

Prospective biomarkers of stem cells of human endometrium and fallopian tube compared with bone marrow

The applicability of stem cells from the human endometrium and fallopian tube for regeneration is a fascinating area of research because of the role of these cells in dynamic tissue remodelling and their cyclical regenerative property during the menstrual cycle and pregnancy. Nevertheless, studies on the identity of biomarkers of these stem cells are limited and need to be extended. The present study has aimed at exploring the tissue-specific biomarkers of stem cells derived from the human endometrium and fallopian tube compared with those from bone marrow. Cells were isolated from human endometrium and fallopian tubes and characterized for biomarkers, including CD34, CD133, CD117, CD90, CD105, CD73, nestin, CD29, CD44, CD31, CD54, CD166, CD106, CD49d, CD45, ABCG2, SSEA4, OCT4, SOX2, CD140b and CD146, by flowcytometry. Both endometrium and fallopian tube sources exhibited positivity over a wide range of markers, as did bone marrow. In particular, they exhibited pluripotency, perivascular and mesenchymal stem cell markers and cell adhesion molecules, thereby suggesting their relevance in tissue repair and regeneration. Overall, the results of this study provide evidence for the presence of stem cells in the human endometrium and fallopian tube, which could thus represent additional stem cell sources for regenerative medicine.

Reproductive stem cell differentiation: extracellular matrix, tissue microenvironment, and growth factors direct the mesenchymal stem cell lineage commitment

The mesenchymal stem cells (MSCs) have awakened interest in regenerative medicine due to its high capability to proliferate and differentiate in multiple specialized lineages under defined conditions. The reproductive system is considered a valuable source of MSCs, which needs further investigations. Many factors have been reported as critical for these cell lineage specification and determination. In this review, we discuss the main effects of extracellular matrix or tissue environment and growth factors in the cell lineage commitment, including the reproductive stem cells. The MSCs responses to culture medium stimuli or to soluble factors probably occur through several intracellular activation pathways. However, the molecular mechanisms in which the cells respond to these mechanical or chemical perturbations remain elusive. Recent findings suggest a synergic effect of microenvironment and soluble cell culture factors affecting cell differentiation. For future applications in cell therapy, protocols of reproductive MSCs differentiation must be established.