Early pregnancy loss: the default outcome for fertilized human oocytes

Endometrial Glucose Metabolism During Early Pregnancy

Approximately 50% of human pregnancies humans fail, most before or during implantation. One factor contributing to pregnancy loss is abnormal glucose metabolism in the endometrium. Glucose contributes to preimplantation embryo development, uterine receptivity, and attachment of the embryo. Across multiple species, the epithelium stores glucose as the macromolecule glycogen at estrus. This reserve is mobilized during the preimplantation period. Glucose from circulation or glycogenolysis can be secreted into the uterine lumen for use by the embryo or metabolized via glycolysis, producing ATP for the cell. The resulting pyruvate could be converted to lactate, another important nutrient for the embryo. Fructose is an important nutrient for early embryos, and the epithelium and placenta can convert glucose to fructose via the polyol pathway. The epithelium also uses glucose to glycosylate proteins, which regulates embryo attachment. In some species, decidualization of the stroma is critical to successful implantation. Formation of the decidua requires increased glucose metabolism via the pentose phosphate pathway and glycolysis. After decidualization, the cells switch to aerobic glycolysis to produce ATP. Paradoxically, the decidua also stores large amounts of glucose as glycogen. Too little glucose or an inability to take up glucose impairs embryo development and decidualization. Conversely, too much glucose inhibits these same processes. This likely contributes to the reduced pregnancy rates associated with conditions like obesity and diabetes. Collectively, precise control of glucose metabolism is important for several endometrial processes required to establish a successful pregnancy. The factors regulating these metabolic processes remain poorly understood.

Events Leading to the Establishment of Pregnancy and Placental Formation: The Need to Fine-Tune the Nomenclature on Pregnancy and Gestation

Today, there is strong and diversified evidence that in humans at least 50% of early embryos do not proceed beyond the pre-implantation period. This evidence comes from clinical investigations, demography, epidemiology, embryology, immunology, and molecular biology. The purpose of this article is to highlight the steps leading to the establishment of pregnancy and placenta formation. These early events document the existence of a clear distinction between embryonic losses during the first two weeks after conception and those occurring during the subsequent months. This review attempts to highlight the nature of the maternal-embryonic dialogue and the major mechanisms active during the pre-implantation period aimed at "selecting" embryos with the ability to proceed to the formation of the placenta and therefore to the completion of pregnancy. This intense molecular cross-talk between the early embryo and the endometrium starts even before the blastocyst reaches the uterine cavity, substantially initiating and conditioning the process of implantation and the formation of the placenta. Today, several factors involved in this dialogue have been identified, although the best-known and overall, the most important, still remains Chorionic Gonadotrophin, indispensable during the first 8 to 10 weeks after fertilization. In addition, there are other substances acting during the first days following fertilization, the Early Pregnancy Factor, believed to be involved in the suppression of the maternal response, thereby allowing the continued viability of the early embryo. The Pre-Implantation Factor, secreted between 2 and 4 days after fertilization. This linear peptide molecule exhibits a self-protective and antitoxic action, is present in maternal blood as early as 7 days after conception, and is absent in the presence of non-viable embryos. The Embryo-Derived Platelet-activating Factor, produced and released by embryos of all mammalian species studied seems to have a role in the ligand-mediated trophic support of the early embryo. The implantation process is also guided by signals from cells in the decidualized endometrium. Various types of cells are involved, among them epithelial, stromal, and trophoblastic, producing a number of cellular molecules, such as cytokines, chemokines, growth factors, and adhesion molecules. Immune cells are also involved, mainly uterine natural killer cells, macrophages, and T cells. In conclusion, events taking place during the first two weeks after fertilization determine whether pregnancy can proceed and therefore whether placenta's formation can proceed. These events represent the scientific basis for a clear distinction between the first two weeks following fertilization and the rest of gestation. For this reason, we propose that a new nomenclature be adopted specifically separating the two periods. In other words, the period from fertilization and birth should be named "gestation", whereas that from the completion of the process of implantation leading to the formation of the placenta, and birth should be named "pregnancy".

ELF1/PRR11/ARP2/3 promoted trophoblast cells proliferation and motility in early pregnancy

BACKGROUND/OBJECTIVE

Early pregnancy loss (EPL) is a common adverse pregnancy outcome with an incidence of approximately 10-30%. There are many factors that cause EPL, among which the lack of proliferation and invasive properties of trophoblast cells can lead to embryonic development. Therefore, in this study, the molecular biology of trophoblast cells was investigated.

METHODS

Placental villous tissues from EPL patients were collected to explore ELF1 and PRR11 gene expression. The proliferation and migration of trophoblast cells were assessed by MTT, crystalline violet staining, and traswell assays, respectively. Western blotting and RT-qPCR were performed to investigate the relationship between ELF1, PRR11, and ARP2/3. F-actin polymerization and FAK activation were evaluated by immunofluorescence and western blotting. Ultimately, ELF1/PRR11/ARP2/3 expression was verified in the EPL mice model RESULTS: ELF1 and PRR11 were lowly expressed in placental villous tissues from EPL. The overexpression of ELF1 and PRR11 promoted proliferation and migration of trophoblast cells. Moreover, while ELF1 bound to the PRR11 promoter and promoted transcriptional activation. Finally, ELF1/PRR11/ARP2/3 showed low expression in the placental tissue of EPL mice.

CONCLUSION

Our study suggested that PRR11 promoted the motility of trophoblast cells by binding to the ARP2/3 complex to promote F-actin polymerization and FAK activation. In addition, ELF1 bound to the initiation site of PRR11 to promote its transcription. ELF1/PRR11/ARP2/3 may play an important role in EPL.

Endometrial glycogen metabolism during early pregnancy in mice

Glucose is critical during early pregnancy. The uterus can store glucose as glycogen but uterine glycogen metabolism is poorly understood. This study analyzed glycogen storage and localization of glycogen metabolizing enzymes from proestrus until implantation in the murine uterus. Quantification of diastase-labile periodic acid-Schiff (PAS) staining showed glycogen in the glandular epithelium decreased 71.4% at 1.5 days postcoitum (DPC) and 62.13% at DPC 3.5 compared to proestrus. In the luminal epithelium, glycogen was the highest at proestrus, decreased 46.2% at DPC 1.5 and 63.2% at DPC 3.5. Immunostaining showed that before implantation, glycogen metabolizing enzymes were primarily localized to the glandular and luminal epithelium. Stromal glycogen was low from proestrus to DPC 3.5. However, at the DPC 5.5 implantation sites, stromal glycogen levels increased sevenfold. Similarly, artificial decidualization resulted in a fivefold increase in glycogen levels. In both models, decidualization increased expression of glycogen synthase as determine by immunohistochemistry and western blot. In conclusion, glycogen levels decreased in the uterine epithelium before implantation, indicating that it could be used to support preimplantation embryos. Decidualization resulted in a dramatic increase in stromal glycogen levels, suggesting it may have an important, but yet undefined, role in pregnancy.

Infertility and subsequent recurrent miscarriage: Current state of the literature and future considerations for practice and research

Background: Recurrent miscarriage (RM) and infertility are independently associated with adverse pregnancy outcomes, in addition to psychological sequelae. Experiencing pregnancy loss alongside infertility is particularly difficult. International guidance regarding RM is conflicting, and applicability to women with infertility is undetermined. The aim of this study was to: (i) establish if women/couples with a history of infertility are recognised in the literature on the investigation and management of RM, and (ii) determine if the specific needs of women/couples experiencing RM and infertility are ascertained and incorporated into clinical management strategies. Methods: We examined the wide-ranging literature to ascertain what gaps existed. Studies were retrieved through searches of PubMed and Google Scholar up to 21 January 2021 using appropriate controlled vocabulary and combinations of key words. No language or study design restrictions were applied. Results: While women/couples experiencing RM after infertility appear in studies evaluating investigations and proposed treatments, high-quality studies are lacking. Furthermore, they are largely excluded from international clinical guidance and qualitative research. Conclusions: The experiences of women/couples with RM and infertility and their specific care needs within maternity and fertility services are underexplored. It is unclear from current RM guidelines how best to manage and support this complex cohort. Women/couples with infertility and RM are underserved in the literature and in clinical guidance. Further robust studies are warranted to examine pregnancy outcomes, investigations and treatments currently used. Qualitative research is also required to identify their medical and psychological needs to better support this vulnerable group.