Progesterone-induced miR-152 interferes with embryonic implantation by downregulating GLUT3 in endometrial epithelium

Expression of aldose reductase in mouse endometrial epithelial cells and its role in sperm capacitation

The survival, motility and capacitation of sperm in the female reproductive tract are important prerequisites for fertilization. The uterus is the main location for sperm capacitation. One of the most important physiological functions of the endometrial epithelium is to create a suitable uterine environment under the regulation of ovarian hormones, to ensure sperm capacitation. The composition of uterine fluid directly affects sperm capacitation. Fructose is an important component of semen that supports sperm viability and motility. Aldose reductase, a rate-limiting enzyme in the polyol pathway, metabolizes sorbitol and fructose, thereby supplying cells with necessary energy for functional activities. Existing studies have reported the presence aldose reductase in the endometrium, leading us to hypothesize that its expression in endometrial epithelium might promote sperm capacitation by maintaining the uterine environment. Yet, the mechanism of regulation has not been clarified. In this study, we investigated the expression of aldose reductase in mouse endometrial epithelium and its potential role in sperm capacitation. We initially investigated the periodic characteristics of glucose, fructose and sorbitol in uterine fluid. We then studied the temporal and spatial characteristics of aldose reductase in the endometrial epithelium. Next, we examined the effect of aldose reductase on glucose, fructose and sorbitol in uterine fluid. Finally, we explored the effect of aldose reductase on sperm capacitation and fertilization. The results showed that glucose and fructose content in uterine fluid and the expression of aldose reductase fluctuated periodically during physiological periods. Inhibition of aldose reductase in the endometrial epithelium interfered with sperm capacitation and fertilization by reducing the fructose levels in the uterine fluid. To conclude, the aldose reductase-mediated polyol pathway in endometrial epithelial cells is essential to maintain an appropriate fructose environment in the uterine fluid for sperm capacitation and fertilization.

Endometrial Glucose Transporters in Health and Disease

Pregnancy loss is a frequent occurrence during the peri-implantation period, when there is high glucose demand for embryonic development and endometrial decidualization. Glucose is among the most essential uterine fluid components required for those processes. Numerous studies associate abnormal glucose metabolism in the endometrium with a higher risk of adverse pregnancy outcomes. The endometrium is incapable of synthesizing glucose, which thus must be delivered into the uterine lumen by glucose transporters (GLUTs) and/or the sodium-dependent glucose transporter 1 (SGLT1). Among the 26 glucose transporters (14 GLUTs and 12 SGLTs) described, 10 (9 GLUTs and SGLT1) are expressed in rodents and 8 (7 GLUTs and SGLT1) in the human uterus. This review summarizes present knowledge on the most studied glucose transporters in the uterine endometrium (GLUT1, GLUT3, GLUT4, and GLUT8), whose data regarding function and regulation are still lacking. We present the recently discovered SGLT1 in the mouse and human endometrium, responsible for controlling glycogen accumulation essential for embryo implantation. Moreover, we describe the epigenetic regulation of endometrial GLUTs, as well as signaling pathways included in uterine GLUT’s expression. Further investigation of the GLUTs function in different endometrial cells is of high importance, as numerous glucose transporters are associated with infertility, polycystic ovary syndrome, and gestational diabetes.

Expression of SGLT1 in the Mouse Endometrial Epithelium and its Role in Early Embryonic Development and Implantation

Many functional activities of endometrium epithelium are energy consuming which are very important for maintaining intrauterine environment needed by early embryonic development and establishment of implantation window. Glucose is a main energy supplier and one of the main components of intrauterine fluid. Obviously, glucose transports in endometrium epithelium involve in for these activities but their functions have not been elucidated. In this research, we observed a spatiotemporal pattern of sodium glucose transporter 1 (SGLT1) expression in the mouse endometrium. We also determined that progesterone can promote the expression of SGLT1 in the mouse endometrial epithelium in response to the action of oestrogen. Treatment with the SGLT1 inhibitor phlorizin or small interfering RNA specific for SGLT1 (SGLT1-siRNA) altered glucose uptake in primary cultured endometrial epithelial cells, which exhibited reduced ATP levels and AMPK activation. The injection of phlorizin or SGLT1-siRNA into one uterine horn of each mouse on day 2 of pregnancy led to an increased glucose concentration in the uterine fluid and decreased number of harvested normal blastocysts and decreased expression of integrin αVβ3 in endometrial epithelium and increased expression of mucin 1 and lactoferrin in endometrial epithelium and the uterine homogenates exhibited activated AMPK, a decreased ATP level on day 4, and a decreased number of implantation sites on day 5. In embryo transfer experiments, pre-treatment of the uterine horn with phlorizin or SGLT1-siRNA during the implantation window led to a decreased embryo implantation rate on day 5 of pregnancy, even when embryos from normal donor mice were used. In conclusion, SGLT1, which participates in glucose transport in the mouse endometrial epithelium, inhibition and/or reduced expression of SGLT1 affects early embryo development by altering the glucose concentration in the uterine fluid. Inhibition and/or reduced expression of SGLT1 also affects embryo implantation by influencing energy metabolism in epithelial cells, which consequently influences implantation-related functional activities.

Role of miRNAs in Normal Endometrium and in Endometrial Disorders: Comprehensive Review

The molecular responses to hormonal stimuli in the endometrium are modulated at the transcriptional and post-transcriptional stages. Any imbalance in cellular and molecular endometrial homeostasis may lead to gynecological disorders. MicroRNAs (miRNAs) are involved in a wide variety of physiological mechanisms and their expression patterns in the endometrium are currently attracting a lot of interest. miRNA regulation could be hormone dependent. Conversely, miRNAs could regulate the action of sexual hormones. Modifications to miRNA expression in pathological situations could either be a cause or a result of the existing pathology. The complexity of miRNA actions and the diversity of signaling pathways controlled by numerous miRNAs require rigorous analysis and findings need to be interpreted with caution. Alteration of miRNA expression in women with endometriosis has been reported. Thus, a potential diagnostic test supported by a specific miRNA signature could contribute to early diagnosis and a change in the therapeutic paradigm. Similarly, specific miRNA profile signatures are expected for RIF and endometrial cancer, with direct implications for associated therapies for RIF and adjuvant therapies for endometrial cancer. Advances in targeted therapies based on the regulation of miRNA expression are under evaluation.

An Update on the Progress of Endometrial Receptivity in Women with Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a significant public health issue with diverse presentations, including reproductive, metabolic, and psychological disorders. Although problems with ovulation, metabolism, and hormonal imbalance can be pharmacologically improved, even the excellent quality of transferred embryos does not necessarily increase the pregnancy rate. Poor endometrial receptivity in women with PCOS perturbs endometrial decidualization and blastocyst implantation, increasing adverse pregnancy outcomes, such as miscarriage and poor embryonic development. The etiological and pathophysiological mechanisms involved in defective endometrial receptivity in women with PCOS have not been fully elucidated to date. Various contributing factors have been reported as primary causes of defective endometrial receptivity in women with PCOS, including metabolic alterations, inflammatory events, and some abnormally expressed endometrial molecular markers. However, few studies to date have investigated in depth the complex mechanisms underlying the compromised endometrial receptivity in women with PCOS. This article reviews recent reports mainly on metabolic alterations and some new endometrial molecular markers in order to collate the existing data and improve our understanding in this field. The aim was to discuss current novel insights on defective endometrial receptivity in women with PCOS in order to provide a theoretical basis for reducing adverse pregnancy outcomes and improving the live birth rate in PCOS.

Micro-RNA miR-542-3p suppresses decidualization by targeting ILK pathways in human endometrial stromal cells

Decidualization of human endometrial stromal cells (HESCs) is a vital step for successful pregnancy. However, the process by which micro-RNAs (miRNAs) regulate decidualization remains elusive. Our current study was designed to identify the mechanism of miRNA miR-542-3p and its potential targets in regulating decidualization. The results showed that miR-542-3p was down-regulated in HESCs. Luciferase assay confirmed that integrin-linked kinase (ILK) is a direct target of miR-542-3p. Overexpression of miR-542-3p resulted in decreased ILK and downstream transforming growth factor β1 (TGF-β1) and SMAD family member 2 (SMAD2) expression. Additional expression of ILK attenuates the miR542-3p-induced down-regulation of TGF-β1 and SMAD2, changes properties such as suppression of proliferation and invasion, and induction of apoptosis, thereby affecting the differentiation of HESCs. Moreover, miR-542-3p overexpression caused down-regulation of the angiogenic factors vascular endothelial growth factor (VEGF), cyclooxygenase-2 (COX-2) and matrix metalloproteinase-9 (MMP-9), and the supernatant of HESCs overexpressing miR-542-3p inhibited the formation of tubular structures in human umbilical vein endothelial cells (HUVECs), suggesting that miR-542-3p inhibits angiogenesis of HUVECs. Furthermore, in our mouse model, following injection of miR-542-3p mimic into the endometrium of mice at pregnancy day 8 (D8), we found decreased miR-542-3p expression and loss of embryo implantation sites. In conclusion, miR-542-3p can affect the process of endometrial decidualization by down-regulating ILK. The present study adds further understanding of the process and regulation of decidualization.

Inhibition of miR-152 during In Vitro Maturation Enhances the Developmental Potential of Porcine Embryos

Simple Summary

MiR-152 is a highly conserved miRNA across different species and plays a role in the regulation of cell differentiation, proliferation, and survival. However, the exact role of miR-152 in oocyte and embryo development is not yet known. In this study, we specifically manipulated the expression level of miR-152 in porcine cumulus-oocyte complexes (COCs) and monitored their developmental competence until the blastocyst stage. We mainly found that a suppressed expression of miR-152 during oocyte maturation significantly improved the blastocyst rate. Our results indicate that this negative correlation between miR-152 during oocyte maturation and the blastocyst rate in pigs could be through targeting IGF system components during oocyte development. These results provide more insights into the role of miRNAs during oocyte and embryonic development that could improve the in vitro production system for mammalian embryos.

Abstract

Oocyte developmental competence is regulated by various mechanisms and molecules including microRNAs (miRNAs). However, the functions of many of these miRNAs in oocyte and embryo development are still unclear. In this study, we managed to manipulate the expression level of miR-152 during oocyte maturation to figure out its potential role in determining the developmental competence of porcine oocytes. The inhibition (Inh) of miR-152 during oocyte maturation does not affect the MII and cleavage rates, however it significantly enhances the blastocyst rate compared to the overexpression (OvExp) and control groups. Pathway analysis identified several signaling pathways (including PI3K/AKT, TGFβ, Hippo, FoxO, and Wnt signaling) that are enriched in the predicted target genes of miR-152. Gene expression analysis revealed that IGF1 was significantly up-regulated in the Inh group and downregulated in the OvExp group of oocytes. Moreover, IGF1R was significantly upregulated in the Inh oocyte group compared to the control one and IGFBP6 was downregulated in the Inh oocyte group compared to the other groups. Blastocysts developed from the OvExp oocytes exhibited an increase in miR-152 expression, dysregulation in some quality-related genes, and the lowest rate of blastocyst formation. In conclusion, our results demonstrate a negative correlation between miR-152 expression level and blastocyst rate in pigs. This correlation could be through targeting IGF system components during oocyte development.

Sex steroids influence organizational but not functional decidualization of feline endometrial cells in a 3D culture system†

Successful implantation requires complex signaling between the uterine endometrium and the blastocyst. Prior to the blastocyst reaching the uterus, the endometrium is remodeled by sex steroids and other signals to render the endometrium receptive. In vitro models have facilitated major advances in our understanding of endometrium preparation and endometrial-blastocyst communication in mice and humans, but these systems have not been widely adapted for use in other models which might generate a deeper understanding of these processes. The objective of our study was to use a recently developed, three-dimensional culture system to identify specific roles of female sex steroids in remodeling the organization and function of feline endometrial cells. We treated endometrial cells with physiologically relevant concentrations of estradiol and progesterone, either in isolation or in combination, for 1 week. We then examined size and density of three-dimensional structures, and quantified expression of candidate genes known to vary in response to sex steroid treatments and that have functional relevance to the decidualization process. Combined sex steroid treatments recapitulated organizational patterns seen in vivo; however, sex steroid manipulations did not induce expected changes to expression of decidualization-related genes. Our results demonstrate that sex steroids may not be sufficient for complete decidualization and preparation of the feline endometrium, thereby highlighting key areas of opportunity for further study and suggesting some unique functions of felid uterine tissues.

Ovarian stimulation and exogenous progesterone affect the endometrial miR-16-5p, VEGF protein expression, and angiogenesis

Angiogenesis, where vascular endothelial growth factor (VEGF) is critically involved, is an important factor in endometrial receptivity. Angio-miRNAs form a special class of microRNAs (miRNAs) that target angiogenic genes and regulate angiogenesis. Various studies have shown that ovarian stimulation and exogenous progesterone affect endometrial vascular density. The present research aimed to assess the impact of HMG/HCG and progesterone on miR-16-5p, VEGF protein expression, and angiogenesis in the mouse endometrium during the preimplantation period. Forty adult female mice were divided into four groups: 1) control, 2) ovarian stimulation (HMG and 48 h after HCG IP), 3) progesterone (progesterone IP for 3 days), 4) ovarian stimulation + progesterone (HMG and 48 h after HCG IP) + (progesterone IP for 3 days) groups.The mice were sacrificed 96 h following HCG administration. miR-16-5p, VEGF protein expression, and CD31-positive cell (Endothelial cell) density were specified.The results showed that endothelial cell density,VEGF protein, and miR-16-5p expression increased in all treatment groups, with the maximum increase belonging to the ovarian stimulation + progesterone group. This study provides evidence that ovarian stimulation and progesterone administration enhance endometrial angiogenesis through VEGF protein upregulation. Furthermore, except for miR-16-5p, other miRNAs and molecules appear to be involved in angiogenic pathways, thereby requiring further studies.