Expression of ENPP3 in human cyclic endometrium: a novel molecule involved in embryo implantation

The Sweet Relationship between the Endometrium and Protein Glycosylation

The endometrium is an important part of women's bodies for menstruation and pregnancy. Various proteins are widely expressed on the surface of endometrial cells, and glycosylation is an important post-translational modification of proteins. Glycosylation modification is closely related not only to endometrial receptivity but also to common diseases related to endometrial receptivity. Glycosylation can improve endometrial receptivity, promote embryo localization and trophoblast cell adhesion and invasion, and contribute to successful implantation. Two diseases related to endometrial receptivity include endometriosis and endometrial cancer. As a common benign disease in women, endometriosis is often accompanied by an increased menstrual volume, prolonged menstrual periods, progressive and aggravated dysmenorrhea, and may be accompanied by infertility. Protein glycosylation modification of the endometrial surface indicates the severity of the disease and may be an important pathogenesis of endometriosis. In cancer, glycosylation modifications on the surface of tumor cells can be a marker to distinguish the type and severity of endometrial cancer. This review highlights the role of protein glycosylation in embryo-maternal endometrial dialogue and explores its potential mechanisms in diseases related to endometrial receptivity, which could provide a new clinical approach for their diagnosis and treatment.

Endometrial Proliferative Phase-Centered View of Transcriptome Dynamics across the Menstrual Cycle

The endometrium, the inner mucosal lining of the uterus, undergoes complex molecular and cellular changes across the menstrual cycle in preparation for embryo implantation. Transcriptome-wide analyses have mainly been utilized to study endometrial receptivity, the prerequisite for successful implantation, with most studies, so far, comparing the endometrial transcriptomes between (i) secretory and proliferative endometrium or (ii) mid-secretory and early secretory endometrium. In the current study, we provide a complete transcriptome description of the endometrium across the entire menstrual cycle and, for the first time, comprehensively characterize the proliferative phase of the endometrium. Our temporal transcriptome analysis includes five time points including the mid-proliferative, late proliferative (peri-ovulatory phase), early secretory, mid-secretory, and late secretory phases. Thus, we unveil exhaustively the transitions between the consecutive proliferative and secretory phases, highlighting their unique gene expression profiles and possible distinct biological functions. The transcriptome analysis reveals many differentially expressed genes (DEGs) across the menstrual cycle, most of which are phase-specific. As an example of coordinated gene activity, the expression profile of histone-encoding genes within the HIST cluster on chromosome 6 shows an increase in cluster activity during the late proliferative and a decline during the mid-secretory phase. Moreover, numerous DEGs are shared among all phases. In conclusion, in the current study, we delineate the endometrial proliferative phase-centered view of transcriptome dynamics across the menstrual cycle. Our data analysis highlights significant transcriptomic and functional changes occurring during the late proliferative phase-an essential transition point from the proliferative phase to the secretory phase. Future studies should explore how the biology of the late proliferative phase endometrium impacts the achievement of mid-secretory endometrial receptivity or contributes to molecular aberrations leading to embryo implantation failure.

Basolateral secretions of human endometrial epithelial organoids impact stromal cell decidualization

Uterine glands and, by inference, their secretions impact uterine receptivity, blastocyst implantation, stromal cell decidualization, and placental development. Changes in gland function across the menstrual cycle are primarily governed by the steroid hormones estrogen (E2) and progesterone (P4) but can also be influenced by extrinsic factors from the stroma. Using a human endometrial epithelial organoid system, transcriptome and proteome analyses identified distinct responses of the organoids to steroid hormones and prostaglandin E2 (PGE2). Notably, P4 and PGE2 modulated the basolateral secretion of organoid proteins, particularly cystatin C (CST3), serpin family A member 3 (SERPINA3), and stanniocalcin 1 (STC1). CST3, but not SERPINA3 or STC1, attenuated the in vitro stromal decidualization response to steroid hormones and PGE2. These findings provide evidence that uterine gland-derived factors impact stromal cell decidualization, which has implications for pregnancy establishment and fertility in women.

β-Lactoglobulin affects the oxidative status and viability of equine endometrial progenitor cells via lncRNA-mRNA-miRNA regulatory associations

The β-lactoglobulin (β-LG) was previously characterized as a mild antioxidant modulating cell viability. However, its biological action regarding endometrial stromal cell cytophysiology and function has never been considered. In this study, we investigated the influence of β-LG on the cellular status of equine endometrial progenitor cells under oxidative stress. The study showed that β-LG decreased the intracellular accumulation of reactive oxygen species, simultaneously ameliorating cell viability and exerting an anti-apoptotic effect. However, at the transcriptional level, the reduced mRNA expression of pro-apoptotic factors (i.e. BAX and BAD) was accompanied by decreased expression of mRNA for anti-apoptotic BCL-2 and genes coding antioxidant enzymes (CAT, SOD-1, GPx). Still, we have also noted the positive effect of β-LG on the expression profile of transcripts involved in endometrial viability and receptivity, including ITGB1, ENPP3, TUNAR and miR-19b-3p. Finally, the expression of master factors of endometrial decidualization, namely prolactin and IGFBP1, was increased in response to β-LG, while non-coding RNAs (ncRNAs), that is lncRNA MALAT1 and miR-200b-3p, were upregulated. Our findings indicate a novel potential role of β-LG as a molecule regulating endometrial tissue functionality, promoting viability and normalizing the oxidative status of endometrial progenitor cells. The possible mechanism of β-LG action includes the activation of ncRNAs essential for tissue regeneration, such as lncRNA MALAT-1/TUNAR and miR-19b-3p/miR-200b-3p.

Development of Marine-Derived Compounds for Cancer Therapy

Cancer has always been a threat to human health with its high morbidity and mortality rates. Traditional therapy, including surgery, chemotherapy and radiotherapy, plays a key role in cancer treatment. However, it is not able to prevent tumor recurrence, drug resistance and treatment side effects, which makes it a very attractive challenge to search for new effective and specific anticancer drugs. Nature is a valuable source of multiple pharmaceuticals, and most of the anticancer drugs are natural products or derived from them. Marine-derived compounds, such as nucleotides, proteins, peptides and amides, have also shed light on cancer therapy, and they are receiving a fast-growing interest due to their bioactive properties. Their mechanisms contain anti-angiogenic, anti-proliferative and anti-metastasis activities; cell cycle arrest; and induction of apoptosis. This review provides an overview on the development of marine-derived compounds with anticancer properties, both their applications and mechanisms, and discovered technologies.

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.

Purinergic Signaling in Endometriosis-Associated Pain

Endometriosis is an estrogen-dependent gynecological disease, with an associated chronic inflammatory component, characterized by the presence of endometrial tissue outside the uterine cavity. Its predominant symptom is pain, a condition notably altering the quality of life of women with the disease. This review is intended to exhaustively gather current knowledge on purinergic signaling in endometriosis-associated pain. Altered extracellular ATP hydrolysis, due to changes in ectonucleotidase activity, has been reported in endometriosis; the resulting accumulation of ATP in the endometriotic microenvironment points to sustained activation of nucleotide receptors (P2 receptors) capable of generating a persistent pain message. P2X3 receptor, expressed in sensory neurons, mediates nociceptive, neuropathic, and inflammatory pain, and is enrolled in endometriosis-related pain. Pharmacological inhibition of P2X3 receptor is under evaluation as a pain relief treatment for women with endometriosis. The role of other ATP receptors is also discussed here, e.g., P2X4 and P2X7 receptors, which are involved in inflammatory cell-nerve and microglia-nerve crosstalk, and therefore in inflammatory and neuropathic pain. Adenosine receptors (P1 receptors), by contrast, mainly play antinociceptive and anti-inflammatory roles. Purinome-targeted drugs, including nucleotide receptors and metabolizing enzymes, are potential non-hormonal therapeutic tools for the pharmacological management of endometriosis-related pain.

The endometrial proteomic profile around the time of embryo implantation†

Embryo implantation is an intricate process which requires competent embryo and receptive endometrium. The failure of endometrium to achieve receptivity is a recognized cause of infertility. However, due to multiplicity of events involved, the molecular mechanisms governing endometrial receptivity are still not fully understood. Traditional one-by-one approaches, including western blotting and histochemistry, are insufficient to examine the extensive changes of endometrial proteome. Although genomics and transcriptomics studies have identified several significant genes, the underlying mechanism remains to be uncovered owing to post-transcriptional and post-translational modifications. Proteomic technologies are high throughput in protein identification, and they are now intensively used to identify diagnostic and prognostic markers in the field of reproductive medicine. There is a series of studies analyzing endometrial proteomic profile, which has provided a mechanistic insight into implantation failure. These published studies mainly focused on the difference between pre-receptive and receptive stages of endometrium, as well as on the alternation of endometrial proteomics in women with reproductive failure. Here, we review recent data from proteomic analyses regarding endometrium around the time of embryo implantation and propose possible future research directions.

Uterine Fluid Proteins for Minimally Invasive Assessment of Endometrial Receptivity

CONTEXT

Clinically used endometrial (EM) receptivity assays are based on transcriptomic patterning of biopsies at midsecretory endometrium (MSE) to identify the possible displacement or disruption of window of implantation (WOI) in patients with recurrent implantation failure (RIF). However, biopsies are invasive and cannot be performed in the same cycle with in vitro fertilization embryo transfer, while uterine fluid (UF) analysis is considered minimally invasive and can immediately precede embryo transfer.

OBJECTIVE

To determine whether UF proteome can be used for WOI monitoring and whether it would highlight the etiology of RIF.

PATIENTS

Paired early secretory endometrial (ESE) and MSE UF samples from six fertile control women for discovery, and an additional 11 paired ESE/MSE samples from controls and 29 MSE samples from RIF patients for validation.

RESULTS

Using discovery mass spectrometry (MS) proteomics we detected 3158 proteins from secretory phase UF of which 367 undergo significant (q < 0.05) proteomic changes while transitioning from ESE to MSE. Forty-five proteins were further validated with targeted MS, and 21 were found to display similar levels between control ESE and RIF MSE, indicating displacement of the WOI. A panel of PGR, NNMT, SLC26A2 and LCN2 demonstrated specificity and sensitivity of 91.7% for distinguishing MSE from ESE samples. The same panel distinguished control MSE samples from RIF MSE with a 91.7% specificity and 96.6% sensitivity.

CONCLUSION

UF proteins can be used for estimating uterine receptivity with minimal invasiveness. Women with RIF appear to have altered MSE UF profiles that may contribute to their low IVF success rate.

Impaired Expression of Ectonucleotidases in Ectopic and Eutopic Endometrial Tissue Is in Favor of ATP Accumulation in the Tissue Microenvironment in Endometriosis

Endometriosis is a prevalent disease defined by the presence of endometrial tissue outside the uterus. Adenosine triphosphate (ATP), as a proinflammatory molecule, promotes and helps maintain the inflammatory state of endometriosis. Moreover, ATP has a direct influence on the two main symptoms of endometriosis: infertility and pain. Purinergic signaling, the group of biological responses to extracellular nucleotides such as ATP and nucleosides such as adenosine, is involved in the biology of reproduction and is impaired in pathologies with an inflammatory component such as endometriosis. We have previously demonstrated that ectonucleotidases, the enzymes regulating extracellular ATP levels, are active in non-pathological endometria, with hormone-dependent changes in expression throughout the cycle. In the present study we have focused on the expression of ectonucleotidases by means of immunohistochemistry and in situ activity in eutopic and ectopic endometrial tissue of women with endometriosis, and we compared the results with endometria of women without the disease. We have demonstrated that the axis CD39-CD73 is altered in endometriosis, with loss of CD39 and CD73 expression in deep infiltrating endometriosis, the most severe, and most recurring, endometriosis subtype. Our results indicate that this altered expression of ectonucleotidases in endometriosis boosts ATP accumulation in the tissue microenvironment. An important finding is the identification of the nucleotide pyrophophatase/phosphodiesterase 3 (NPP3) as a new histopathological marker of the disease since we have demonstrated its expression in the stroma only in endometriosis, in both eutopic and ectopic tissue. Therefore, targeting the proteins directly involved in ATP breakdown could be an appropriate approach to consider in the treatment of endometriosis.