Enhanced HOXA10 sumoylation inhibits embryo implantation in women with recurrent implantation failure

EHD1 impaired decidualization of endometrial stromal cells in recurrent implantation failure: role of SENP1 in modulating progesterone receptor signalling†

Recurrent implantation failure (RIF) patients exhibit poor endometrial receptivity and abnormal decidualization with reduced effectiveness and exposure to progesterone, which is an intractable clinical problem. However, the associated molecular mechanisms remain elusive. We found that EH domain containing 1 (EHD1) expression was abnormally elevated in RIF and linked to aberrant endometrial decidualization. Here we show that EHD1 overexpressed in human endometrial stromal cells significantly inhibited progesterone receptor (PGR) transcriptional activity and the responsiveness to progesterone. No significant changes were observed in PGR mRNA levels, while a significant decrease in progesterone receptor B (PRB) protein level. Indeed, EHD1 binds to the PRB protein, with the K388 site crucial for this interaction. Overexpression of EHD1 promotes the SUMOylation and ubiquitination of PRB, leading to the degradation of the PRB protein. Supplementation with the de-SUMOylated protease SENP1 ameliorated EHD1-repressed PRB transcriptional activity. To establish a functional link between EHD1 and the PGR signalling pathway, sg-EHD1 were utilized to suppress EHD1 expression in HESCs from RIF patients. A significant increase in the expression of prolactin and insulin-like growth factor-binding protein 1 was detected by interfering with the EHD1. In conclusion, we demonstrated that abnormally high expression of EHD1 in endometrial stromal cells attenuated the activity of PRB associated with progesterone resistance in a subset of women with RIF.

GM-CSF improves endometrial receptivity in a thin endometrium rat model by upregulating HOXA10

Endometrial receptivity is a prerequisite for the success of assisted reproduction. Patients with a consistently thin endometrium frequently fail to conceive, owing to low endometrial receptivity, and there are currently very few therapeutic options available. Our previous study demonstrated that intrauterine granulocyte-macrophage colony-stimulating factor (GM-CSF) administration resulted in a significant improvement in clinical pregnancy and implantation rates and was an effective means of increasing endometrial thickness on the day of embryo transfer in patients with thin endometrium. In order to explore the underlying process, an animal model with a thin endometrium was constructed, the homeobox A10 gene (HOXA10) was downregulated, and an inhibitor of the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway (MAPK/ERK) was employed. Our findings strongly suggest a marked decrease in GM-CSF levels in the thin endometrial rat model, and the suppression of HOXA10 impeded the therapeutic efficacy of GM-CSF in this model. Moreover, we showed that GM-CSF significantly increases endometrial receptivity in the rat model and upregulates HOXA10 via the MAPK/ERK pathway. Our data provide new molecular insights into the mechanisms underlying formation of a thin endometrium and highlight a novel, potential clinical treatment strategy as well as directions for further research.

Expression of HOXA10 Gene in Women with Endometriosis: A Systematic Review

The homeobox A10 (HOXA10) gene is known to be related to endometriosis; however, due to a lack of knowledge/evidence in the pathogenesis of endometriosis, the mechanisms that link HOXA10 to endometriosis still need to be clarified. This review addresses the difference in the expression of the HOXA10 gene in endometriotic women versus non-endometriotic women across populations by country and discusses its influences on women's fertility. An organized search of electronic databases was conducted in Scopus, ScienceDirect, PubMed, and Web of Science. The keywords used were (HOXA10 OR "homeobox A10" OR PL OR HOX1 OR HOX1H OR HOX1.8) AND ("gene expression") AND (endometriosis). The initial search resulted in 623 articles, 10 of which were included in this review. All ten papers included in this study were rated fair in terms of the quality of the studies conducted. The expression of the HOXA10 gene was found to be downregulated in most studies. However, one study provided evidence of the downregulation and upregulation of HOXA10 gene expression due to the localization of endometriotic lesions. Measuring the expression of the HOXA10 gene in women is clinically essential to predicting endometriosis, endometrial receptivity, and the development of pinopodes in the endometrium during the luteal phase.

An ultrasound-based deep learning radiomic model combined with clinical data to predict clinical pregnancy after frozen embryo transfer: a pilot cohort study

RESEARCH QUESTION

Can a multi-modal fusion model based on ultrasound-based deep learning radiomics combined with clinical parameters provide personalized evaluation of endometrial receptivity and predict the occurrence of clinical pregnancy after frozen embryo transfer (FET)?

DESIGN

Prospective cohort study of women (n = 326) who underwent FET between August 2019 and December 2021. Input quantitative variables and input image data for radiomic feature extraction were collected to establish a multi-modal fusion prediction model. An additional independent dataset of 453 ultrasound endometrial images was used to establish the segmentation model to determine the endometrial region on ultrasound images for analysis. The performance of different algorithms and different input data for prediction of FET outcome were compared.

RESULTS

A total of 240 patients with complete data were included in the final cohort. The proposed multi-modal fusion model performed significantly better than the use of either image or quantitative variables alone to predict the occurrence of clinical pregnancy after FET (P ≤ 0.034). Its area under the curve, accuracy, sensitivity, specificity, positive predictive value and negative predictive value of the proposed model were 0.825, 72.5%, 96.2%, 58.3%, 72.3% and 89.5%, respectively. The Dice coefficient of the multi-task endometrial ultrasound segmentation model was 0.89. Use of endometrial segmentation features significantly improved the prediction performance of the model (P = 0.041).

CONCLUSIONS

The multi-modal fusion model based on ultrasound-based deep learning radiomics combined with clinical quantitative variables offers a favourable and rapid non-invasive approach for personalized prediction of FET outcome.

Mst1-mediated phosphorylation of Nur77 improves the endometrial receptivity in human and mice

BACKGROUND

Successful embryo implantation requires the attachment of a blastocyst to the receptive endometrial epithelium, which was disturbed in the women with recurrent implantation failure (RIF). Endometrial β3-integrin was the most important adhesion molecule contributing to endometrial receptivity in both humans and mice. Nur77 has been proven indispensable for fertility in mice, here we explore the role of Nur77 on embryo-epithelial adhesion and potential treatment to embryo implantation failure.

METHODS

The expression and location of Mst1 and Nur77 in endometrium from fertile women and RIF patients were examined by IHC, qRT-PCR and Western blotting. In vitro kinase assay following with LC-MS/MS were used to identify the phosphorylation site of Nur77 activated by Mst1. The phosphorylated Nur77 was detected by phos-tag SDS-PAGE assay and specific antibody against phospho-Nur77-Thr366. The effect of embryo-epithelium interaction was determined in the BeWo spheroid or mouse embryo adhesion assay, and delayed implantation mouse model. RNA-seq was used to explore the mechanism by which Nur77 derived peptide promotes endometrial receptivity.

FINDINGS

Endometrial Mammalian sterile 20 (STE20)-like kinase 1 (Mst1) expression level was decreased in the women with RIF than that in the fertile control group, while Mst1 activation in the epithelial cells promoted trophoblast-uterine epithelium adhesion. The effect of Nur77 mediated trophoblast-uterine epithelium adhesion was facilitated by active Mst1. Mechanistically, mst1 promotes the transcription activity of Nur77 by phosphorylating Nur77 at threonine 366 (T366), and consequently increased downstream target β3-integrin expression. Furthermore, a Nur77-derived peptide containing phosphorylated T366 markedly promoted mouse embryo attachment to Ishikawa cells ([4 (2-4)] vs [3 (2-4)]) and increased the embryo implantation rate (4 vs 1.4) in a delayed implantation mouse model by regulating integrin signalling. Finally, it is observed that the endometrial phospho-Nur77 (T366) level is decreased by 80% in the women with RIF.

INTERPRETATION

In addition to uncovering a potential regulatory mechanism of Mst1/Nur77/β3-integrin signal axis involved in the regulation of embryo-epithelium interaction, our finding provides a novel marker of endometrial receptivity and a potential therapeutic agent for embryo implantation failure.

FUNDING

National Key Research and Development Program of China (2018YFC1004400), the National Natural Science Foundation of China (82171653, 82271698, 82030040, 81971387 and 30900727), and National Institutes of Health grants (R01HL103869).

Endometriosis Stem Cells as a Possible Main Target for Carcinogenesis of Endometriosis-Associated Ovarian Cancer (EAOC)

Endometriosis is a serious recurrent disease impairing the quality of life and fertility, and being a risk for some histologic types of ovarian cancer defined as endometriosis-associated ovarian cancers (EAOC). The presence of stem cells in the endometriotic foci could account for the proliferative, migrative and angiogenic activity of the lesions. Their phenotype and sources have been described. The similarly disturbed expression of several genes, miRNAs, galectins and chaperones has been observed both in endometriotic lesions and in ovarian or endometrial cancer. The importance of stem cells for nascence and sustain of malignant tumors is commonly appreciated. Although the proposed mechanisms promoting carcinogenesis leading from endometriosis into the EAOC are not completely known, they have been discussed in several articles. However, the role of endometriosis stem cells (ESCs) has not been discussed in this context. Here, we postulate that ESCs may be a main target for the carcinogenesis of EAOC and present the possible sequence of events resulting finally in the development of EAOC.

FHL1 mediates HOXA10 deacetylation via SIRT2 to enhance blastocyst-epithelial adhesion

Recurrent implantation failure (RIF) is a rather thorny problem in the clinical practice of assisted reproductive technology. Due to the complex aetiology of RIF, its pathogenesis is far from fully understood, and there is no effective treatment available. Here, We explored the regulatory mechanism of the four half-domains of LIM domain 1 (FHL1), which is significantly downregulated in the endometrium of RIF patients, in blastocyst-epithelial adhesion. Indeed, FHL1 expression was dramatically increased in normal female mid-secretory endometrial epithelial cells and was abnormally reduced in RIF patients. Furthermore, FHL1 overexpression promoted blastocyst-epithelial adhesion, and interfering with FHL1 expression in the mouse uterus significantly inhibited embryo implantation. Mechanistically, FHL1 did not regulate HOXA10 mRNA expression but increased HOXA10 protein stability and activated HOXA10, thereby promoting its regulation of downstream gene expression and the β3 integrin/FAK pathway. Meanwhile, FHL1 regulates HOXA10 function by increasing HOXA10 deacetylation through enhanced binding of HOXA10 and SIRT2. SIRT2-specific inhibitors can significantly inhibit this effect. In the endometrial epithelial cells of RIF patients, the correlation between FHL1 and HOXA10 and its downstream target genes has also been verified. Finally, our data indicated FHL1 is a regulatory molecule that promotes blastocyst-epithelial adhesion. Altogether, downstream dysfunction due to aberrant FHL1 expression is an important molecular basis for embryo implantation failure in patients with RIF and to provide new potential therapeutic targets.

Progress of oxidative stress in endometrium decidualization

The difficulty in maintaining the balance between oxides and antioxidants causes a phenomenon named oxidative stress. Oxidative stress often leads to tissue damage and participates in the pathogenesis of a series of diseases. Decidua provides the 'soil' for embryo implantation, and the normal decidualization shows the characteristics of strong antioxidation. Once the mechanism of antioxidant stress goes awry, it will lead to a series of pregnancy-related diseases. In recent years, more and more studies have shown that oxidative stress is involved in pregnancy-related diseases caused by abnormal decidualization of the endometrium. In order to have a more comprehensive understanding of the role of oxidative stress in decidual defect diseases, this paper reviews the common decidual defect diseases in conjunction with relevant regulatory molecules, in order to arouse thinking about the importance of oxidative stress, and to provide more theoretical basis for the aetiology of decidual defects.

MEKK4-mediated Phosphorylation of HOXA10 at Threonine 362 facilitates embryo adhesion to the endometrial epithelium

Embryo adhesion is a very important step in the embryo implantation process. Homeobox A10 (HOXA10), a key transcriptional factor of endometrial receptivity, is indispensable for embryo adhesion. However, how to control the activation status of HOXA10 remains elusive. Here, we found that Mitogen-activated protein kinase kinase kinase 4 (MEKK4) was associated with HOXA10 and directly phosphorylated HOXA10 at threonine 362. This MEKK4-mediated phosphorylation enhanced HOXA10-mediated transcriptional responses and adhesion between the embryo and endometrial epithelium. Specific deletion or kinase inactivation of MEKK4 in endometrial epithelial cells attenuates adhesion between embryo and epithelium. Therefore, the identification of MEKK4 as a novel physiological positive regulator of HOXA10 activation provides mechanistic insights to improve embryo implantation success. Moreover, when Thr362 was mutated to alanine (T362A) to mimic its dephosphorylation, the protein stability and transcriptional regulation of HOXA10 were decreased. In addition, HOXA10 -promoted embryo adhesion was weakened after the mutation of Thr362, suggesting that the phosphorylation of HOXA10 at this site may be a new indicator for evaluating endometrial receptivity and judging the ‘implantation window’.

CDC42 governs normal oviduct multiciliogenesis through activating AKT to ensure timely embryo transport

Ciliated and secretory cells are two major cell types that comprise the oviduct epithelia. Accumulating evidences support a role of oviductal multiciliated epithelia for embryo transport, however the mechanisms underlying this specialized cell type differentiation remain elusive. Here, we report that CDC42 depletion in oviduct epithelia hampers the morphogenesis of multiciliated cell, and results in embryo retention, leading to early pregnancy failure. Utilizing the oviduct organoid model, we further observed that CDC42 guides secretory cells transition into multiciliated cells independent of its GTPase activity and the well-known Notch pathway. Further exploration uncovered the AKT as a novel indispensable regulator for multiciliated cells differentiation, whose activity was maintained by CDC42 through interacting with the p110β. Consistently, re-activating AKT partially incites multiciliated cells differentiation in Cdc42 knockout oviductal organoids. Finally, low levels of CDC42 and phospho-AKT with reduced multiciliated cells in the oviduct are observed in women with ectopic pregnancy. Collectively, we provide previously unappreciated evidence that CDC42-AKT signaling is a critical determinant for morphogenesis of oviduct multiciliated cell, which possesses the clinical application in understanding the pathology of ectopic pregnancy and facilitating the development of prevention strategies.

Increased METTL3-mediated m6A methylation inhibits embryo implantation by repressing HOXA10 expression in recurrent implantation failure

BACKGROUND

Recurrent implantation failure (RIF) is a major limitation of assisted reproductive technology, which is associated with impaired endometrial receptivity. Although N⁶-methyladenosine (m⁶A) has been demonstrated to be involved in various biological processes, its potential role in the endometrium of women with RIF has been poorly studied.

METHODS

Global m⁶A levels and major m⁶A methyltransferases/demethylases mRNA levels in mid-secretory endometrium from normal and RIF women were examined by colorimetric m⁶A quantification strategy and quantitative real-time PCR, respectively. The effects of METTL3-mediated m⁶A modification on embryo attachment were evaluated by an vitro model of a confluent monolayer of Ishikawa cells co-cultured with BeWo spheroids, and the expression levels of homeo box A10 (HOXA10, a well-characterized marker of endometrial receptivity) and its downstream targets were evaluated by quantitative real-time PCR and Western blotting in METTL3-overexpressing Ishikawa cells. The molecular mechanism for METTL3 regulating HOXA10 expression was determined by methylated RNA immunoprecipitation assay and transcription inhibition assay.

RESULTS

Global m⁶A methylation and METTL3 expression were significantly increased in the endometrial tissues from women with RIF compared with the controls. Overexpression of METTL3 in Ishikawa cells significantly decreased the ration of BeWo spheroid attachment, and inhibited HOXA10 expression with downstream decreased β3-integrin and increased empty spiracles homeobox 2 expression. METTL3 catalyzed the m⁶A methylation of HOXA10 mRNA and contributed to its decay with shortened half-life. Enforced expression of HOXA10 in Ishikawa cells effectively rescued the impairment of METTL3 on the embryo attachment in vitro.

CONCLUSION

Increased METTL3-mediated m⁶A modification represents an adverse impact on embryo implantation by inhibiting HOXA10 expression, contributing to the pathogenesis of RIF.

SUMO Modification of OsFKBP20-1b Is Integral to Proper Pre-mRNA Splicing upon Heat Stress in Rice

OsFKBP20-1b, a plant-specific cyclophilin protein, has been implicated to regulate pre-mRNA splicing under stress conditions in rice. Here, we demonstrated that OsFKBP20-1b is SUMOylated in a reconstituted SUMOylation system in E.coli and in planta, and that the SUMOylation-coupled regulation was associated with enhanced protein stability using a less SUMOylated OsFKBP20-1b mutant (5KR_OsFKBP20-1b). Furthermore, OsFKBP20-1b directly interacted with OsSUMO1 and OsSUMO2 in the nucleus and cytoplasm, whereas the less SUMOylated 5KR_OsFKBP20-1b mutant had an impaired interaction with OsSUMO1 and 2 in the cytoplasm but not in the nucleus. Under heat stress, the abundance of an OsFKBP20-1b-GFP fusion protein was substantially increased in the nuclear speckles and cytoplasmic foci, whereas the heat-responsiveness was remarkably diminished in the presence of the less SUMOylated 5KR_OsFKBP20-1b-GFP mutant. The accumulation of endogenous SUMOylated OsFKBP20-1b was enhanced by heat stress in planta. Moreover, 5KR_OsFKBP20-1b was not sufficiently associated with the U snRNAs in the nucleus as a spliceosome component. A protoplast transfection assay indicated that the low SUMOylation level of 5KR_OsFKBP20-1b led to inaccurate alternative splicing and transcription under heat stress. Thus, our results suggest that OsFKBP20-1b is post-translationally regulated by SUMOylation, and the modification is crucial for proper RNA processing in response to heat stress in rice.

Downregulation of decidual SKP2 is associated with human recurrent miscarriage

BACKGROUND

Recurrent miscarriage (RM) is a very frustrating problem for both couples and clinicians. To date, the etiology of RM remains poorly understood. Decidualization plays a critical role in implantation and the maintenance of pregnancy, and its deficiency is closely correlated with RM. The F-box protein S-phase kinase associated protein 2 (SKP2) is a key component of the SCF-type E3 ubiquitin ligase complex, which is critically involved in ErbB family-induced Akt ubiquitination, aerobic glycolysis and tumorigenesis. SKP2 is pivotal for reproduction, and SKP2-deficient mice show impaired ovarian development and reduced fertility.

METHODS

Here, we investigated the expression and function of SKP2 in human decidualization and its relation with RM. A total of 40 decidual samples were collected. Quantitative PCR analysis, western blot analysis and immunohistochemistry analysis were performed to analyze the differential expression of SKP2 between RM and control cells. For in vitro induction of decidualization, both HESCs (human endometrial stromal cells) cell line and primary ESCs (endometrial stromal cells) were used to analyze the effects of SKP2 on decidualization via siRNA transfection.

RESULTS

Compared to normal pregnant women, the expression of SKP2 was reduced in the decidual tissues from individuals with RM. After in vitro induction of decidualization, knockdown of SKP2 apparently attenuated the decidualization of HESCs and resulted in the downregulation of HOXA10 and FOXM1, which are essential for normal human decidualization. Moreover, our experiments demonstrated that SKP2 silencing reduced the expression of its downstream target GLUT1.

CONCLUSIONS

Our study indicates a functional role of SKP2 in RM: downregulation of SKP2 in RM leads to impaired decidualization and downregulation of GLUT1 and consequently predisposes individuals to RM.

Global Protease Activity Profiling Identifies HER2-Driven Proteolysis in Breast Cancer

Differential expression of extracellular proteases and endogenous protease inhibitors has been associated with distinct molecular subtypes of breast cancer. However, due to the tight post-translational regulation of protease activity, protease expression-level data alone are not sufficient to understand the role of proteases in malignant transformation. Therefore, we hypothesized that global profiles of extracellular protease activity could more completely reflect differences observed at the transcriptional level in breast cancer and that subtype-associated protease activity may be leveraged to identify specific proteases that play a functional role in cancer signaling. Here, we used a global peptide library-based approach to profile the activities of proteases within distinct breast cancer subtypes. Analysis of 3651 total peptide cleavages from a panel of well-characterized breast cancer cell lines demonstrated differences in proteolytic signatures between cell lines. Cell line clustering based on protease cleavages within the peptide library expanded upon the expected classification derived from transcriptional profiling. An isogenic cell line model developed to further interrogate proteolysis in the HER2 subtype revealed a proteolytic signature consistent with activation of TGF-β signaling. Specifically, we determined that a metalloprotease involved in TGF-β signaling, BMP1, was upregulated at both the protein (2-fold, P = 0.001) and activity (P = 0.0599) levels. Inhibition of BMP1 and HER2 suppressed invasion of HER2-expressing cells by 35% (P < 0.0001), compared to 15% (P = 0.0086) observed in cells where only HER2 was inhibited. In summary, through global identification of extracellular proteolysis in breast cancer cell lines, we demonstrate subtype-specific differences in protease activity and elucidate proteolysis associated with HER2-mediated signaling.

MicroRNA‑378d inhibits Glut4 by targeting Rsbn1 in vitamin D deficient ovarian granulosa cells

Vitamin D (VD) is not only associated with bone growth and development, but is also closely associated with numerous other pathological conditions. The present study aimed to investigate the effect of microRNA (miRNA/miR)-378d on ovarian granulosa cells by regulating the round spermatid basic protein 1 (Rsbn1) in the absence of VD. The abnormal expression of miRNAs in ovarian tissues of the VD-deficient mouse was analyzed using transcriptome sequencing. miR-378d, glucose transporter 4 (Glut4) and aromatase (Cyp19a) expression levels were examined via reverse transcription-quantitative (RT-q)PCR and western blotting. The expression levels of Rsbn1, Glut4 and Cyp19a were detected in transfected mouse ovarian granulosa cells. The targeting regulation between miR-378d and Rsbn1 was verified using double reporter gene assay and functional rescue experiments. Among the 672 miRNAs that were differentially expressed, cluster analysis revealed that 17 were significantly upregulated and 16 were significantly downregulated. Moreover, miR-378d showed significant upregulation, which was further verified via RT-qPCR. It was identified that the protein expression level of Rsbn1 was significantly downregulated. Furthermore, Glut4 mRNA expression was significantly decreased in the mimic group but markedly increased in the inhibitor group. By contrast, the mRNA expression levels of Rsbn1 and Cyp19a did not demonstrate any significant difference. The western blotting results indicated that the protein expression levels of Rsbn1 and Glut4 were decreased and increased, respectively, while Cyp19a did not show any significant change. In addition, the double reporter gene experiments confirmed that Rsbn1 was the target gene of miR-378d. Collectively, the present results demonstrated that miR-378d was abnormally overexpressed in the ovarian tissues of the VD-deficient mice, and that miR-378d could inhibit Glut4 production by targeting Rsbn1, which may lead to insulin resistance.

Increased SUMOylation of TCF21 improves its stability and function in human endometriotic stromal cells†

Endometriosis is an estrogen-dependent disease. Our previous study demonstrated that elevated levels of transcription factor 21 (TCF21) in endometriotic tissues enhanced steroidogenic factor-1 (SF-1) and estrogen receptor β (ERβ) expression by forming a heterodimer with upstream stimulatory factor 2 (USF2), allowing these TCF21/USF2 complexes to bind to the promoters of SF-1 and ERβ. Furthermore, TCF21 contributed to the increased proliferation of endometriotic stromal cells (ESCs), suggesting that TCF21 may play a vital role in the pathogenesis of endometriosis. SUMOylation is a posttranslational modification that has emerged as a crucial molecular regulatory mechanism. However, the mechanism regulating TCF21 SUMOylation in endometriosis is incompletely characterized. Thus, this study aimed to explore the effect of TCF21 SUMOylation on its expression and regulation in ovarian endometriosis. We found that the levels of SUMOylated TCF21 were increased in endometriotic tissues and stromal cells compared with eutopic endometrial tissues and stromal cells and enhanced by estrogen. Treatment with the SUMOylation inhibitor ginkgolic acid and the results of a protein half-life assay demonstrated that SUMOylation can stabilize the TCF21 protein. A coimmunoprecipitation assay showed that SUMOylation probably increased its interaction with USF2. Further analyses elucidated that SUMOylation of TCF21 significantly increased the binding activity of USF2 to the SF-1 and ERβ promoters. Moreover, the SUMOylation motifs in TCF21 affected the proliferation ability of ESCs. The results of this study suggest that SUMOylation plays a critical role in mediating the high expression of TCF21 in ESCs and may participate in the development of endometriosis.

Embryo implantation in the laboratory: an update on current techniques

BACKGROUND

The embryo implantation process is crucial for the correct establishment and progress of pregnancy. During implantation, the blastocyst trophectoderm cells attach to the epithelium of the endometrium, triggering intense cell-to-cell crosstalk that leads to trophoblast outgrowth, invasion of the endometrial tissue, and formation of the placenta. However, this process, which is vital for embryo and foetal development in utero, is still elusive to experimentation because of its inaccessibility. Experimental implantation is cumbersome and impractical in adult animal models and is inconceivable in humans.

OBJECTIVE AND RATIONALE

A number of custom experimental solutions have been proposed to recreate different stages of the implantation process in vitro, by combining a human embryo (or a human embryo surrogate) and endometrial cells (or a surrogate for the endometrial tissue). In vitro models allow rapid high-throughput interrogation of embryos and cells, and efficient screening of molecules, such as cytokines, drugs, or transcription factors, that control embryo implantation and the receptivity of the endometrium. However, the broad selection of available in vitro systems makes it complicated to decide which system best fits the needs of a specific experiment or scientific question. To orient the reader, this review will explore the experimental options proposed in the literature, and classify them into amenable categories based on the embryo/cell pairs employed.The goal is to give an overview of the tools available to study the complex process of human embryo implantation, and explain the differences between them, including the advantages and disadvantages of each system.

SEARCH METHODS

We performed a comprehensive review of the literature to come up with different categories that mimic the different stages of embryo implantation in vitro, ranging from initial blastocyst apposition to later stages of trophoblast invasion or gastrulation. We will also review recent breakthrough advances on stem cells and organoids, assembling embryo-like structures and endometrial tissues.

OUTCOMES

We highlight the most relevant systems and describe the most significant experiments. We focus on in vitro systems that have contributed to the study of human reproduction by discovering molecules that control implantation, including hormones, signalling molecules, transcription factors and cytokines.

WIDER IMPLICATIONS

The momentum of this field is growing thanks to the use of stem cells to build embryo-like structures and endometrial tissues, and the use of bioengineering to extend the life of embryos in culture. We propose to merge bioengineering methods derived from the fields of stem cells and reproduction to develop new systems covering a wider window of the implantation process.

Skp2 Deteriorates the Uterine Receptivity by Interacting with HOXA10 and Promoting its Degradation

Receptive endometrium plays a core role in successful embryo implantation, and about one-third of repeated embryo implantation failures are attributed to endometrial receptive defects. S-phase kinase-associated protein 2 (SKP2), a member of the F-box protein family, plays an important role in many cellular processes, including cell proliferation and apoptosis. However, its role in endometrial receptivity is still unclear. Here, we identified SKP2 was obviously upregulated in the patients with infertility. Functional study showed that SKP2 overexpression inhibited endometrial epithelial cell (EEC) proliferation, whereas SKP2 knockdown promoted the proliferation of EECs. In addition, the overexpression of SKP2 also repressed adhesion rate of embryonic cells to EECs. In vivo studies further suggested that the upregulation of SKP2 obviously suppressed endometrium receptivity formation and embryo implantation potential. Mechanistical study clarified that SKP2 directly interacted with HOXA10 and decreased protein stability through promoting the ubiquitin-mediated proteasome degradation of HOXA10. In conclusion, the current study documented that the high expression of SKP2 deteriorates endometrial receptivity formation by decreasing the HOXA10 expression and suggested that SKP2 may be defined as a marker of endometrial receptivity, and as a target for the diagnosis and treatment of infertility.

Anti-phospholipid antibody may reduce endometrial receptivity during the window of embryo implantation

BACKGROUND

Anti-phospholipid antibodies (aPL) have been reported to be associated with repeated implantation failure (RIF), but the mechanism remains controversial. Endometrial receptivity is well known to be crucial for embryo implantation. This study aims to investigate the effect of aPL on endometrial receptivity in RIF women with positive aPL.

METHODS

Sixty-four infertile women with normal menstrual cycles were enrolled. The control group comprised 32 pregnant women with negative aPL who conceived successfully after their first in vitro fertilization-embryo transfer (IVF-ET) cycle, and the RIF group comprised 32 women with positive aPL. Endometrial biopsy samples were collected seven days after the luteinizing hormone surge (LH + 7). The expression of LIF and HOXA10 was evaluated by immunohistochemistry, qRT-PCR and Western blot. Endometrial pinopode development was examined by scanning electron microscopy.

RESULTS

The mRNA expression of LIF and HOXA10 in the RIF group was significantly decreased compared with that in the control group during the implantation window. The immunohistochemistry and Western blot results confirmed these findings. Then, ultrastructural analyses of endometrial cells showed fewer pinopode processes, a more atypical morphology and increased atrophy in the RIF group compared with the control group, and these results were statistically significant.

CONCLUSION

aPL positivity may inhibit the expression of LIF and HOXA10 in the endometrium and influence pinopode development. Our findings suggest that positivity for aPL is associated with impaired endometrial receptivity, which results in the development of RIF.

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.

Bisphenol a affects endometrial stromal cells decidualization, involvement of epigenetic regulation

Bisphenol A(BPA) is one of the most widespread endocrine disruptors in the environment and is associated with reproductive diseases. In this study, we focused on the correlation between environmentally relevant levels of BPA exposure and histone modification during endometrial stromal cells decidualization. BPA exposure changed the morphology of decidualized endometrial stromal cells, with inhibition of mixed-lineage leukemia 1(MLL1) and induction of enhancer of zeste homolog2 (EZH2) during in vitro decidualization. The expression of HOXA10, PRL and IGFBP-1 was down-regulated upon BPA treatment. Furthermore, chromatin immunoprecipitation quantitative PCR(ChIP-qPCR) was performed to evaluate the recruitment of histone-3, lysine-4 trimethylation (H3K4me3) and histone-3, lysine-27 trimethylation (H3K27me3) at the gene promoters. The decreased H3K4me3 and the increased H3K27me3 at HOXA10, PRL and IGFBP-1 promoter regions were consistent with the expression of MLL1 and EZH2 respectively. The effect of BPA on MLL1 and EZH2 could be abrogated by ICI 182,780. Our study provides the first indication that environmentally relevant levels of BPA exposure can regulate the expression of decidualization-related genes by affecting histone modification, impairing endometrial decidualization.

Evidence from three cohort studies on the expression of MUC16 around the time of implantation suggests it is an inhibitor of implantation

PURPOSE

To examine the expression of MUC16 in the endometrium peri-implantation period in three different cohort studies.

METHODS

This was a retrospective observational cohort study. A total of 245 participants were recruited in three separate cohort studies: (1) women with recurrent miscarriage (n = 50) and fertile controls (n = 29); (2) women who had high (n = 20) or normal (n = 20) progesterone on the day of hCG trigger in ovarian stimulation cycle for IVF; and (3) women who did (n = 95) or did not (n = 31) conceive following frozen embryo transfer in HRT cycles. All subjects had archived endometrial samples precisely taken on LH+7 in natural cycles, or hCG+6 in ovarian stimulation cycles, or P+5 in HRT cycles. The H-score (median, range) of MUC16 in the luminal epithelium and glandular epithelium was determined by using immunohistochemistry.

RESULTS

The median (range) of H-score of MUC16 in the luminal epithelium (1) in women with recurrent pregnancy loss was 23.7 (0-300), which was significantly (P < 0.05) lower than that of 118.4 (7.7-300) in fertile controls; (2) in women with elevated progesterone on the day of hCG administration (147.8, 18.0-230.1), significantly (P < 0.05) higher than that of women with normal progesterone (61.0, 2.3-205.3); (3) in women who conceived (23.1, 0-250.3), significantly (P < 0.001) lower than that in women who did not conceive (58.4, 0-300).

CONCLUSION

The expression of MUC16 in all three cohort studies is consistent with it being an inhibitor of implantation.

Regulatory mechanisms of endometrial decidualization and pregnancy-related diseases

Endometrial decidualization is one of the earliest changes by which the uterus adapts to pregnancy. During this period, the endometrium undergoes complex changes in its biochemistry, physiology, and function at various levels, providing a suitable microenvironment for embryo implantation and development. Favorable decidualization lays an essential foundation for subsequent gestation, without which pregnancy failure or pregnancy complications may occur. The interaction between pregnancy-related hormones and cytokines produced by embryonic and uterine cells is known to be essential for decidualization, in which some transcription factors also play pivotal roles. Increasing evidence has revealed the importance of metabolism in regulating decidualization. Here, we summarize and discuss these crucial elements in decidualization and the relationship between decidualization and pregnancy complications. A better comprehension of these issues should help to improve the prediction of pregnancy outcomes and the use of appropriate intervention.

HOXA2 activity regulation by cytoplasmic relocation, protein stabilization and post-translational modification

HOX proteins are homeodomain transcription factors critically involved in patterning animal embryos and controlling organogenesis. While the functions of HOX proteins and the processes under their control begin to be well documented, the modalities of HOX protein activity regulation remain poorly understood. Here we show that HOXA2 interacts with PPP1CB, a catalytic subunit of the Ser/Thr PP1 phosphatase complex. This interaction co-localizes in the cytoplasm with a previously described HOXA2 interactor, KPC2, which belongs to the KPC E3 ubiquitin ligase complex. We provide evidence that HOXA2, PPP1CB and KPC2 define a molecularly and functionally interacting complex. Collectively, our experiments support that PPP1CB and KPC2 together inhibit the activity of HOXA2 by activating its nuclear export, but favored HOXA2 de-ubiquitination and stabilization thereby establishing a store of HOXA2 in the cytoplasm.

Homeobox A10 promotes the proliferation and invasion of bladder cancer cells via regulation of matrix metalloproteinase-3

Homeobox A10 (HOXA10) belongs to the family of HOX genes, which are closely connected with embryonic development and serve important roles in various tumors. However, the role of HOXA10 in bladder cancer (BC) remains unclear. In the present study, the role of HOXA10 in BC and the underlying mechanisms by which it promotes the disease progression were investigated. Immunohistochemical analysis demonstrated that the expression of the HOXA10 protein was significantly higher in BC tissues as compared with that in adjacent normal tissues. Subsequent statistical analysis revealed that upregulation of HOXA10 was significantly associated with the pathological grade and clinical stage of BC patients. In the BC cell lines T24 and 5637, silencing of HOXA10 by small interfering RNA transfection suppressed the proliferation, migration and invasion of BC cells, and led to decreased matrix metalloproteinase-3 expression. Taken together, overexpression of HOXA10 may be associated with poor prognosis in BC, and may serve as a novel antitumor therapy target for the treatment of this disease.

Homeobox genes for embryo implantation: From mouse to human

The proper development of uterus to a state of receptivity and the attainment of implantation competency for blastocyst are 2 indispensable aspects for implantation, which is considered to be a critical event for successful pregnancy. Like many developmental processes, a large number of transcription factors, such as homeobox genes, have been shown to orchestrate this complicated but highly organized physiological process during implantation. In this review, we focus on progress in studies of the role of homeobox genes, especially the Hox and Msx gene families, during implantation, together with subsequent development of post-implantation uterus and related reproductive defects in both mouse models and humans, that have led to better understanding of how implantation is precisely regulated and provide new insights into infertility.