Characterization of the role for cadherin 6 in the regulation of human endometrial receptivity

Prediction of genomic biomarkers for endometriosis using the transcriptomic dataset

BACKGROUND

Endometriosis is a clinical condition characterized by the presence of endometrial glands outside the uterine cavity. While its incidence remains mostly uncertain, endometriosis impacts around 180 million women worldwide. Despite the presentation of several epidemiological and clinical explanations, the precise mechanism underlying the disease remains ambiguous. In recent years, researchers have examined the hereditary dimension of the disease. Genetic research has aimed to discover the gene or genes responsible for the disease through association or linkage studies involving candidate genes or DNA mapping techniques.

AIM

To identify genetic biomarkers linked to endometriosis by the application of machine learning (ML) approaches.

METHODS

This case-control study accounted for the open-access transcriptomic data set of endometriosis and the control group. We included data from 22 controls and 16 endometriosis patients for this purpose. We used AdaBoost, XGBoost, Stochasting Gradient Boosting, Bagged Classification and Regression Trees (CART) for classification using five-fold cross validation. We evaluated the performance of the models using the performance measures of accuracy, balanced accuracy, sensitivity, specificity, positive predictive value, negative predictive value and F1 score.

RESULTS

Bagged CART gave the best classification metrics. The metrics obtained from this model are 85.7%, 85.7%, 100%, 75%, 75%, 100% and 85.7% for accuracy, balanced accuracy, sensitivity, specificity, positive predictive value, negative predictive value and F1 score, respectively. Based on the variable importance of modeling, we can use the genes CUX2, CLMP, CEP131, EHD4, CDH24, ILRUN, LINC01709, HOTAIR, SLC30A2 and NKG7 and other transcripts with inaccessible gene names as potential biomarkers for endometriosis.

CONCLUSION

This study determined possible genomic biomarkers for endometriosis using transcriptomic data from patients with/without endometriosis. The applied ML model successfully classified endometriosis and created a highly accurate diagnostic prediction model. Future genomic studies could explain the underlying pathology of endometriosis, and a non-invasive diagnostic method could replace the invasive ones.

Evaluation of GFM1 mutations pathogenicity through in silico tools, RNA sequencing and mitophagy pahtway in GFM1 knockout cells

GFM1 is a nuclear gene that plays a role in mitochondrial function. In recent decades, various homozygous and compound heterozygous mutations have been identified, leading to significant health issues in patients and often resulting in early death. There is a few experimental research on this gene, particularly regarding its pathogenicity through in silico methods and RNA sequencing and experimental validation in GFM1 knockout cells. This study aims to explore how high-risk pathogenic variants affect protein stability and function using a comprehensive bioinformatics approach. Analyses with Align-GVGD, PolyPhen-2, MupRo, and SIFT indicated that most variants are likely to be highly pathogenic and destabilize the protein structure. The variants were consistently classified as high-risk by Align-GVGD and were deemed "probably damaging" or "possibly damaging" by PolyPhen-2. MupRo analysis suggested a reduction in protein stability, while SIFT indicated functional impacts for all variants. Further analysis with MetaRNN and structural assessments showed that these variants affect protein size, charge, and hydrophobicity, which may disrupt inter-domain interactions and hinder protein function. Differential gene expression analysis in GFM1 knockout HK2 and 293 T cells revealed significant changes in gene expression, particularly in areas related to translation, mitochondrial function, and cellular responses. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses indicated that the affected genes are linked to neurodegenerative diseases, cancer, and various signaling pathways. GFM1 knockout cells displayed notable pathway changes, including those related to oxidative phosphorylation and neurodegenerative diseases (e.g., Parkinson's, Alzheimer's, Huntington's). Upregulation of mitochondrial electron transport chain components (COX17, NDUFB1, ATP5MC1) suggests a compensatory mechanism in response to impaired mitochondrial function. Disruptions in proteostasis and protein synthesis were highlighted by dysregulated proteasome and ribosomal pathways. Markers of mitophagy, such as increased HSP90 and decreased TOMM20 levels, along with changes in PINK1 protein, emphasize GFM1's involvement in mitophagy. Protein-protein interaction analysis connected GFM1 to key mitophagy proteins (e.g., OPTN, Park2/Parkin). Functional experiments confirmed increased mitophagy, indicating a protective response. These results highlight the negative impact of high-risk pathogenic variants on protein stability and cellular function, shedding light on their potential roles in disease progression. This study offers valuable insights into the pathogenic mechanisms linked to GFM1 mutations, underscoring its critical role in mitochondrial function and cellular balance. The findings highlight the gene's involvement in mitophagy, oxidative phosphorylation, and neurodegenerative pathways, laying the groundwork for future research into therapeutic approaches targeting GFM1-related dysfunctions.

Non-coding RNAs in Recurrent implantation failure

Recurrent implantation failure (RIF), defined as the inability to achieve conception following multiple consecutive in-vitro fertilization (IVF) attempts, represents a complex and multifaceted challenge in reproductive medicine. The emerging role of non-coding RNAs in RIF etiopathogenesis has only gained prominence over the last decade, illustrating a new dimension to our understanding of the intricate network underlying RIF. Successful embryo implantation demands a harmonious synchronization between an adequately decidualized endometrium, a competent blastocyst, and effective maternal-embryonic interactions. Emerging evidence has clarified the involvement of a sophisticated network of non-coding RNAs, including microRNAs, circular RNAs, and long non-coding RNAs, in orchestrating these pivotal processes. Disconcerted expression of these molecules can disrupt the delicate equilibrium required for implantation, amplifying the risk of RIF. This comprehensive review presents an in-depth investigation of the complex role played by non-coding RNAs in the pathogenesis of RIF. Furthermore, it underscores the vast potential of non-coding RNAs as diagnostic biomarkers and therapeutic targets, with the ultimate goal of enhancing implantation success rates in IVF cycles. As ongoing research continues to unravel the intercalated web of molecular interactions, exploiting the power of non-coding RNAs may offer promising avenues for mitigating the challenges posed by RIF and improving the outcomes of assisted reproduction.

Recombinant human granulocyte colony stimulating factor (rhG-CSF) participates in the progression of implantation via the hsa_circ_0001550-miRNA-mRNA interaction network

Inadequate endometrial receptivity is a key factor affecting the successful implantation of embryos. Recombinant human granulocyte colony stimulating factor (rhG-CSF) can increase endometrial thickness and improve the outcomes of assisted reproductive technologies (ARTs). In this preliminary study, the function and possible molecular mechanisms of recombinant human granulocyte colony stimulating factor (rhG-CSF) which affects endometrial receptivity and implantation in human Embryonic Stem Cells (hESCs) were investigated. The cell viability of endometrial stromal cells treated with rhG-CSF 0.5 ng/ml for 24 h was significantly increased. Moreover, the expression of hsa_circ_0001550 was downregulated in endometrial stromal cells treated with rhG-CSF. Furthermore, the hsa_circ_0001550-miRNA-mRNA network was constructed and the downstream target genes (including 4 miRNAs and 117 mRNAs) of hsa_circ_0001550 were mainly involved in the cAMP and calcium signalling pathways, which play important roles in regulating endometrial receptivity and embryo implantation. We conclude that rhG-CSF participates in the regulation of embryo implantation by regulating the hsa_circ_0001550-miRNA-mRNA interaction network.

Current knowledge on the role of extracellular vesicles in endometrial receptivity

Endometrial receptivity has been widely understood as the capacity of the endometrium to receive implantable embryos. The establishment of endometrial receptivity involves multiple biological processes including decidualization, tissue remodeling, angiogenesis, immune regulation, and oxidative metabolism. Extracellular vesicles (EVs) are lipid-bilayer-membrane nanosized vesicles mediating cell-to-cell communication. Recently, EVs and their cargo have been proven as functional factors in the establishment of endometrial receptivity. In this review, we comprehensively summarized the alteration of endometrium/embryo-derived EVs during the receptive phase and retrospected the current findings which revealed the pivotal role and potential mechanism of EVs to promote successful implantation. Furthermore, we highlight the potentiality and limitations of EVs being translated into clinical applications such as biomarkers of endometrial receptivity or reproductive therapeutic mediators, and point out the direction for further research.

The Effect of Metformin and Carbohydrate-Controlled Diet on DNA Methylation and Gene Expression in the Endometrium of Women with Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is an endocrine disease associated with infertility and metabolic disorders in reproductive-aged women. In this study, we evaluated the expression of eight genes related to endometrial function and their DNA methylation levels in the endometrium of PCOS patients and women without the disease (control group). In addition, eight of the PCOS patients underwent intervention with metformin (1500 mg/day) and a carbohydrate-controlled diet (type and quantity) for three months. Clinical and metabolic parameters were determined, and RT-qPCR and MeDIP-qPCR were used to evaluate gene expression and DNA methylation levels, respectively. Decreased expression levels of HOXA10, GAB1, and SLC2A4 genes and increased DNA methylation levels of the HOXA10 promoter were found in the endometrium of PCOS patients compared to controls. After metformin and nutritional intervention, some metabolic and clinical variables improved in PCOS patients. This intervention was associated with increased expression of HOXA10, ESR1, GAB1, and SLC2A4 genes and reduced DNA methylation levels of the HOXA10 promoter in the endometrium of PCOS women. Our preliminary findings suggest that metformin and a carbohydrate-controlled diet improve endometrial function in PCOS patients, partly by modulating DNA methylation of the HOXA10 gene promoter and the expression of genes implicated in endometrial receptivity and insulin signaling.

The Extracellular Vesicles Proteome of Endometrial Cells Simulating the Receptive Menstrual Phase Differs from That of Endometrial Cells Simulating the Non-Receptive Menstrual Phase

Successful embryo implantation into a receptive endometrium requires mutual endometrial-embryo communication. Recently, the function of extracellular vehicles (EVs) in cell-to-cell interaction in embryo-maternal interactions has been investigated. We explored isolated endometrial-derived EVs, using RL95-2 cells as a model of a receptive endometrium, influenced by the menstrual cycle hormones estrogen (E2; proliferative phase), progesterone (P4; secretory phase), and estrogen plus progesterone (E2P4; the receptive phase). EV sized particles were isolated by differential centrifugation and size exclusion chromatography. Nanoparticle tracking analysis was used to examine the different concentrations and sizes of particles and EV proteomic analysis was performed using shotgun label-free mass spectrometry. Our results showed that although endometrial derived EVs were secreted in numbers independent of hormonal stimulation, EV sizes were statistically modified by it. Proteomics analysis showed that hormone treatment changes affect the endometrial EV's proteome, with proteins enhanced within the EV E2P4 group shown to be involved in different processes, such as embryo implantation, endometrial receptivity, and embryo development, supporting the concept of a communication system between the embryo and the maternal endometrium via EVs.

The Role of Cadherin 12 (CDH12) in the Peritoneal Fluid among Patients with Endometriosis and Endometriosis-Related Infertility

Cadherin 12 (CDH 12) can play a role in the pathogenesis of endometriosis. The aim of this study was to compare the levels of cadherin 12 in the peritoneal fluid between women with and without endometriosis. This was a multicenter cross-sectional study. Eighty-two patients undergoing laparoscopic procedures were enrolled in the study. Cadherin 12 concentrations were determined using the enzyme-linked immunosorbent assay. The level of statistical significance was set at p < 0.05. No differences in cadherin 12 concentrations between patients with and without endometriosis were observed (p = 0.4). Subgroup analyses showed that CDH 12 concentrations were significantly higher in patients with infertility or primary infertility and endometriosis in comparison with patients without endometriosis and without infertility or primary infertility (p = 0.02) and also higher in patients with stage I or II endometriosis and infertility or primary infertility than in patients without endometriosis and infertility or primary infertility (p = 0.03, p = 0.048, respectively). In total, CDH 12 levels were significantly higher in patients diagnosed with infertility or primary infertility (p = 0.0092, p = 0.009, respectively) than in fertile women. Cadherin 12 can possibly play a role in the pathogenesis of infertility, both in women with and without endometriosis.

Dinitramine induces implantation failure by cell cycle arrest and mitochondrial dysfunction in porcine trophectoderm and luminal epithelial cells

The herbicide market is growing rapidly, as weed control is a significant challenge in agriculture. Many studies have reported the toxicity of herbicides to non-target organisms. Dinitramine is a dinitroaniline herbicide that is particularly toxic to aquatic organisms. However, little is known about the effects of dinitramine on the female reproductive system. Therefore, in the present study, we utilized porcine trophectoderm (pTr) cells and porcine endometrial luminal epithelial (pLE) cells to verify the reproductive toxicity of dinitramine. Dinitramine reduced the viability of both cell types, by triggering cell cycle arrest, especially at the sub-G1 phase, and increasing apoptosis, inhibiting DNA replication. Dinitramine disrupted intracellular calcium homeostasis and induced oxidative stress by producing reactive oxygen species, leading to the loss of mitochondrial membrane potential and alteration of mitochondrial respiration. Mitogen-activated protein kinase pathways were altered, and migration decreased in pTr and pLE cells after dinitramine treatment; the expression of pregnancy-related genes in these cells was decreased. Thus, dinitramine reduced the viability and migratory capacity of both cell types, and this could interrupt the early stages of pregnancy.

Genome-Wide Association Studies, Runs of Homozygosity Analysis, and Copy Number Variation Detection to Identify Reproduction-Related Genes in Bama Xiang Pigs

Litter size and teat number are economically important traits in the porcine industry. However, the genetic mechanisms influencing these traits remain unknown. In this study, we analyzed the genetic basis of litter size and teat number in Bama Xiang pigs and evaluated the genomic inbreeding coefficients of this breed. We conducted a genome-wide association study to identify runs of homozygosity (ROH), and copy number variation (CNV) using the novel Illumina PorcineSNP50 BeadChip array in Bama Xiang pigs and annotated the related genes in significant single nucleotide polymorphisms and common copy number variation region (CCNVR). We calculated the ROH-based genomic inbreeding coefficients (FROH) and the Spearman coefficient between FROH and reproduction traits. We completed a mixed linear model association analysis to identify the effect of high-frequency copy number variation (HCNVR; over 5%) on Bama Xiang pig reproductive traits using TASSEL software. Across eight chromosomes, we identified 29 significant single nucleotide polymorphisms, and 12 genes were considered important candidates for litter-size traits based on their vital roles in sperm structure, spermatogenesis, sperm function, ovarian or follicular function, and male/female infertility. We identified 9,322 ROHs; the litter-size traits had a significant negative correlation to FROH. A total of 3,317 CNVs, 24 CCNVR, and 50 HCNVR were identified using cnvPartition and PennCNV. Eleven genes related to reproduction were identified in CCNVRs, including seven genes related to the testis and sperm function in CCNVR1 (chr1 from 311585283 to 315307620). Two candidate genes (NEURL1 and SH3PXD2A) related to reproduction traits were identified in HCNVR34. The result suggests that these genes may improve the litter size of Bama Xiang by marker-assisted selection. However, attention should be paid to deter inbreeding in Bama Xiang pigs to conserve their genetic diversity.

Towards an Improved Understanding of the Effects of Elevated Progesterone Levels on Human Endometrial Receptivity and Oocyte/Embryo Quality during Assisted Reproductive Technologies

Ovarian stimulation is an indispensable part of IVF and is employed to produce multiple ovarian follicles. In women who undergo ovarian stimulation with gonadotropins, supraphysiological levels of estradiol, as well as a premature rise in progesterone levels, can be seen on the day of hCG administration. These alterations in hormone levels are associated with reduced embryo implantation and pregnancy rates in IVF cycles with a fresh embryo transfer. This article aims to improve the reader’s understanding of the effects of elevated progesterone levels on human endometrial receptivity and oocyte/embryo quality. Based on current clinical data, it appears that the premature rise in progesterone levels exerts minimal or no effects on oocyte/embryo quality, while advancing the histological development of the secretory endometrium and displacing the window of implantation. These clinical findings strongly suggest that reduced implantation and pregnancy rates are the result of a negatively affected endometrium rather than poor oocyte/embryo quality. Understanding the potential negative impact of elevated progesterone levels on the endometrium is crucial to improving implantation rates following a fresh embryo transfer. Clinical studies conducted over the past three decades, many of which have been reviewed here, have greatly advanced our knowledge in this important area.

A microphysiological model of human trophoblast invasion during implantation

Successful establishment of pregnancy requires adhesion of an embryo to the endometrium and subsequent invasion into the maternal tissue. Abnormalities in this critical process of implantation and placentation lead to many pregnancy complications. Here we present a microenigneered system to model a complex sequence of orchestrated multicellular events that plays an essential role in early pregnancy. Our implantation-on-a-chip is capable of reconstructing the three-dimensional structural organization of the maternal-fetal interface to model the invasion of specialized fetal extravillous trophoblasts into the maternal uterus. Using primary human cells isolated from clinical specimens, we demonstrate in vivo-like directional migration of extravillous trophoblasts towards a microengineered maternal vessel and their interactions with the endothelium necessary for vascular remodeling. Through parametric variation of the cellular microenvironment and proteomic analysis of microengineered tissues, we show the important role of decidualized stromal cells as a regulator of extravillous trophoblast migration. Furthermore, our study reveals previously unknown effects of pre-implantation maternal immune cells on extravillous trophoblast invasion. This work represents a significant advance in our ability to model early human pregnancy, and may enable the development of advanced in vitro platforms for basic and clinical research of human reproduction.

Chronic Venous Disease in Pregnant Women Causes an Increase in ILK in the Placental Villi Associated with a Decrease in E-Cadherin

Chronic venous disease (CVD) is a multifactorial vascular disorder frequently manifested in lower limbs in the form of varicose veins (VVs). Women are a vulnerable population for suffering from CVD, especially during pregnancy, when a plethora of changes occur in their cardiovascular system. Previous studies have indicated a worrisome association between CVD in pregnancy with the placental structure and function. Findings include an altered cellular behavior and extracellular matrix (ECM) composition. Integrin-linked kinase (ILK) is a critical molecule involved in multiple physiological and pathological conditions, and together with cadherins, is essential to mediate cell to ECM and cell to cell interplay, respectively. Thus, the aim of this study was to evaluate the implication of ILK and a set of cadherins (e-cadherin, cadherin-6 and cadherin-17) in placentas of women with CVD in order to unravel the possible pathophysiological role of these components. Gene expression (RT-qPCR) and protein expression (immunohistochemistry) studies were performed. Our results show a significant increase in the gene and protein expression of ILK, cadherin-6 and cadherin-17 and a decrease of e-cadherin in the placenta of women with CVD. Overall, this work shows that an abnormal expression of ILK, e-cadherin, cadherin-6 and cadherin-17 may be implicated in the pathological changes occurring in the placental tissue. Further studies should be conducted to determine the possible associations of these changes with maternal and fetal well-being.

Increased expression of HMGB1 in the implantation phase endometrium is related to recurrent implantation failure

BACKGROUND

Impaired endometrial receptivity was the main cause of recurrent implantation failure (RIF); however, its underlying mechanisms had not been elucidated. This study aimed to determine the expression level of high-mobility group box protein 1 (HMGB1) in the endometrium with RIF and its effect on endometrial receptivity.

METHODS AND RESULTS

Genome-wide expression profiling, real-time reverse transcription PCR, immunohistochemical staining, western blot, and in vitro assays were performed in this study. We found that HMGB1 expression was significantly decreased in the implantation phase endometrium in the control group (patients with tubal infertility and successfully achieve conception after the first embryo transfer) (P = 0.006). However, the expression levels of HMGB1 mRNA and protein were significantly upregulated during the implantation phase in endometrial tissues obtained from patients with RIF compared to that in the control group (P = 0.001), consistent with the results of the genome-wide expression profiling. Moreover, in vitro assays showed that increased expression of HMGB1 in human endometrial epithelial cells dramatically displayed a marked deficiency in supporting blastocysts and human embryonic JAR cells adhesion, which mimic the process of embryo adhesion.

CONCLUSION

These findings strongly indicated that increased HMGB1 levels suppressed the epithelial cell adhesion capability, therefore contributing to impaired endometrial receptivity in patients with recurrent implantation failure, which can be used as a target for the recognition and treatment of recurrent implantation failure in clinical practice.

Jagged1 regulates endometrial receptivity in both humans and mice

The human endometrium undergoes cycle-dependent changes and is only receptive to an implanting blastocyst within a narrow window of 2-4 days in the mid-secretory phase. Such functional changes require delicate interplay between a diversity of factors including cytokines and signaling pathways. The Notch signaling pathway members are expressed in human endometrium. We have previously demonstrated that Notch ligand Jagged1 (JAG1) localizes in the endometrial luminal epithelium (LE) and is abnormally reduced in infertile women during receptivity. However, the functional consequences of reduced JAG1 production on endometrial receptivity to implantation of the blastocyst are unknown. This study aimed to determine the role of JAG1 in regulating endometrial receptivity in humans and mice. Knockdown of JAG1 in both primary human endometrial epithelial cells and Ishikawa cells significantly reduced their adhesive capacity to HTR8/SVneo (trophoblast cell line) spheroids. We confirmed that in human endometrial epithelial cells, JAG1 interacted with Notch Receptor 3 (NOTCH3) and knockdown of JAG1 significantly reduced the expression of Notch signaling downstream target HEY1 and classical receptivity markers. Knockdown of Jag1 in mouse LE significantly impaired blastocyst implantation. We identified ten genes (related to tight junction, infertility, and cell adhesion) that were differentially expressed by Jag1 knockdown in LE in mice. Further analysis of the tight junction family members in both species revealed that JAG1 altered the expression of tight junction components only in mice. Together, our data demonstrated that JAG1 altered endometrial epithelial cell adhesive capacity and regulated endometrial receptivity in both humans and mice likely via different mechanisms.

MAML1: a coregulator that alters endometrial epithelial cell adhesive capacity

BACKGROUND

Abnormalities in endometrial receptivity has been identified as a major barrier to successful embryo implantation. Endometrial receptivity refers to the conformational and biochemical changes occurring in the endometrial epithelial layer which make it adhesive and receptive to blastocyst attachment. This takes place during the mid-secretory phase of woman's menstrual cycle and is a result of a delicate interplay between numerous hormones, cytokines and other factors. Outside of this window, the endometrium is refractory to an implanting blastocyst. It has been shown that Notch ligands and receptors are dysregulated in the endometrium of infertile women. Mastermind Like Transcriptional Coactivator 1 (MAML1) is a known coactivator of the Notch signaling pathway. This study aimed to determine the role of MAML1 in regulating endometrial receptivity.

METHODS

The expression and localization of MAML1 in the fertile human endometrium (non-receptive proliferative phase versus receptive mid-secretory phase) were determined by immunohistochemistry. Ishikawa cells were used as an endometrial epithelial model to investigate the functional consequences of MAML1 knockdown on endometrial adhesive capacity to HTR8/SVneo (trophoblast cell line) spheroids. After MAML1 knockdown in Ishikawa cells, the expression of endometrial receptivity markers and Notch dependent and independent pathway members were assessed by qPCR. Two-tailed unpaired or paired student's t-test were used for statistical analysis with a significance threshold of P < 0.05.

RESULTS

MAML1 was localized in the luminal epithelium, glandular epithelium and stroma of human endometrium and the increased expression identified in the mid-secretory phase was restricted only to the luminal epithelium (P < 0.05). Functional analysis using Ishikawa cells demonstrated that knockdown of MAML1 significantly reduced epithelial adhesive capacity (P < 0.01) to HTR8/SVneo (trophoblast cell line) spheroids compared to control. MAML1 knockdown significantly affected the expression of classical receptivity markers (SPP1, DPP4) and this response was not directly via hormone receptors. The expression level of Hippo pathway target Ankyrin repeat domain-containing protein 1 (ANKRD1) was also affected after MAML1 knockdown in Ishikawa cells.

CONCLUSION

Our data strongly suggest that MAML1 is involved in regulating the endometrial adhesive capacity and may facilitate embryo attachment, either directly or indirectly through the Notch signaling pathway.

Tripeptidyl peptidase I promotes human endometrial epithelial cell adhesive capacity implying a role in receptivity

The endometrium undergoes cyclic remodelling throughout the menstrual cycle in preparation for embryo implantation which occurs in a short window during the mid-secretory phase. It is during this short 'receptive window' that the endometrial luminal epithelium acquires adhesive capacity permitting blastocysts firm adhesion to the endometrium to establish pregnancy. Dysregulation in any of these steps can compromise embryo implantation resulting in implantation failure and infertility. Many factors contribute to these processes including TGF-β, LIF, IL-11 and proteases. Tripeptidyl peptidase 1 (TPP1) is a is a lysosomal serine-type protease however the contribution of the TPP1 to receptivity is unknown. We aimed to investigate the role of TPP1 in receptivity in humans.In the current study, TPP1 was expressed in both epithelial and stromal compartments of the endometrium across the menstrual cycle. Expression was confined to the cytoplasm of luminal and glandular epithelial cells and stromal cells. Staining of mid-secretory endometrial tissues of women with normal fertility and primary unexplained infertility showed reduced immunostaining intensity of TPP1 in luminal epithelial cells of infertile tissues compared to fertile tissues. By contrast, TPP1 levels in glandular epithelial and stromal cells were comparable in both groups in the mid-secretory phase. Inhibition of TPP1 using siRNA compromised HTR8/SVneo (trophoblast cell line) spheroid adhesion on siRNA-transfected Ishikawa cells (endometrial epithelial cell line) in vitro. This impairment was associated with decreased sirtuin 1 (SIRT1), BCL2 and p53 mRNA and unaltered, CD44, CDH1, CDH2, ITGB3, VEGF A, OSTEOPONTIN, MDM2, CASP4, MCL1, MMP2, ARF6, SGK1, HOXA-10, LIF, and LIF receptor gene expression between treatment groups. siRNA knockdown of TPP1 in primary human endometrial stromal cells did not affect decidualization nor the expression of decidualization markers prolactin (PRL) and insulin-like growth factor-binding protein 1 (IGFBP1). Taken together, our data strongly suggests a role for TPP1 in endometrial receptivity via its effects on epithelial cell adhesion and suggests reduced levels associated with unexplained infertility may contribute to implantation failure.

Chloride intracellular channel 4 is dysregulated in endometrium of women with infertility and alters receptivity

The endometrium remodels in each menstrual cycle to become receptive in preparation for embryo implantation which occurs in the mid-secretory phase of the cycle. Failure of blastocyst adhesion and implantation cause infertility. We compared chloride intracellular channel 4 (CLIC4) expression in human endometrium from women with normal fertility and primary unexplained infertility in the mid-secretory/receptive phase of the menstrual cycle. CLIC4 localised to both the epithelial and stromal regions of the endometrium of fertile tissues across the cycle. CLIC4 expression was significantly reduced in the luminal and glandular epithelium and remained unchanged in the stromal region of mid-secretory infertile endometrium compared to fertile endometrium. siRNA knockdown of CLIC4 significantly compromised adhesive capacity of Ishikawa cells (endometrial epithelial cell line). This reduced adhesion and CLIC4 expression was associated with elevated SGK1, p53, SIRT1, BCL2 and MCL1 gene expression in the Ishikawa cells. CLIC4 expression was increased in primary human endometrial stromal cells during decidualization, however, siRNA knockdown of CLIC4 did not affect decidualization. Our data provide evidence that CLIC4 may regulate receptivity and facilitate blastocyst attachment initiating implantation. Reduced CLIC4 levels may be causative of implantation failure in women.