Gap junctional connexin messenger RNA expression in the ovine uterus and placenta: effects of estradiol-17β-treatment, early pregnancy stages, and embryo origin

Genetic loss of Uchl1 leads to female infertility by affecting oocyte quality and follicular development

RESEARCH QUESTION

Ubiquitin C-terminal hydrolase L1 (UCHL1) is a deubiquitinating enzyme specifically highly expressed in the brain and gonads. Inhibition of UCHL1 hydrolase activity impairs oocyte maturation. Uchl1 knockout mice exhibit reproductive dysfunction, but the underlying pathogenesis remains unclear.

DESIGN

Uchl1 knockout mice were used to explore the role of UCHL1 in oocyte maturation and follicle development. Oocyte development potential and mitochondrial membrane potential were also assessed to determine UCHL1 function on early embryo development. Transcriptome and proteomic analyses were conducted to elucidate molecular changes associated with Uchl1 knockout.

RESULTS

Uchl1-/- mice exhibited ovarian dysfunction and infertility, with decreased serum estrogen, reduced antral follicle number, and diminished oocyte developmental potential compared to wild types. Histological examination revealed compromised follicle development and disrupted granulosa cell function in Uchl1-/- ovaries. In vitro, Uchl1-/- follicles had impaired preantral follicle development and poor FSH response. Loss of UCHL1 not only leads to mitochondrial dysfunction in oocytes, but also negatively affected estrogen biosynthesis with downregulation of steroidogenic acute regulatory protein (STAR) and estrogen receptor alpha (ER-α) in granulosa cells. Additionally, downregulated expression of connexin 37 (CX37), which is known to impair gap junction intercellular communication between oocyte and granulosa cells, transmitted the Uchl1 gene damage from oocyte to granulosa cells, which in turn affected functions of follicles and even the whole ovary.

CONCLUSIONS

Loss of UCHL1 leads to significant disruptions in follicular development and oocyte quality, resulting in infertility. UCHL1 in oocytes influences not only the quality and quantity of the oocytes themselves, but also the follicles and the ovaries as a whole. This disruption ultimately manifests in symptoms similar to diminished ovarian reserve (DOR).

Associations between mycoestrogen exposure and sex steroid hormone concentrations in maternal serum and cord blood in the UPSIDE pregnancy cohort

Zearalenone (ZEN) is a fungal-derived toxin found in global food supplies including cereal grains and processed foods, impacting populations worldwide through diet. Because the chemical structure of ZEN and metabolites closely resembles 17β-estradiol (E2), they interact with estrogen receptors α/β earning their designation as 'mycoestrogens'. In animal models, gestational exposure to mycoestrogens disrupts estrogen activity and impairs fetal growth. Here, our objective was to evaluate relationships between mycoestrogen exposure and sex steroid hormone concentrations in maternal circulation and cord blood for the first time in humans. In each trimester, pregnant participants in the UPSIDE study (n = 297) provided urine for mycoestrogen analysis and serum for hormone analysis. At birth, placental mycoestrogens and cord steroids were measured. We fitted longitudinal models examining log-transformed mycoestrogen concentrations in relation to log-transformed hormones, adjusting for covariates. Secondarily, multivariable linear models examined associations at each time point (1st, 2nd, 3rd trimesters, delivery). We additionally considered effect modification by fetal sex. ZEN and its metabolite, α-zearalenol (α-ZOL), were detected in >93% and >75% of urine samples; >80% of placentas had detectable mycoestrogens. Longitudinal models from the full cohort exhibited few significant associations. In sex-stratified analyses, in pregnancies with male fetuses, estrone (E1) and free testosterone (fT) were inversely associated with ZEN (E1 %Δ: -6.68 95%CI: -12.34, -0.65; fT %Δ: -3.22 95%CI: -5.68, -0.70); while α-ZOL was positively associated with E2 (%Δ: 5.61 95%CI: -1.54, 9.85) in pregnancies with female fetuses. In analysis with cord hormones, urinary mycoestrogens were inversely associated with androstenedione (%Δ: 9.15 95%CI: 14.64, -3.30) in both sexes, and placental mycoestrogens were positively associated with cord fT (%Δ: 37.13, 95%CI: 4.86, 79.34) amongst male offspring. Findings support the hypothesis that mycoestrogens act as endocrine disruptors in humans, as in animal models and livestock. Additional work is needed to understand impacts on maternal and child health.

The vasodilator effect of Eugenol on uterine artery - potential therapeutic applications in pregnancy-associated hypertension

Preeclampsia, a gestational associated hypertension, has been reported in 6-8% of pregnant women worldwide leading to premature delivery and low birth weight of newborn due to reduced blood flow to placenta. Although several vasodilators (Methyl dopa, hydralazine, β-blockers and diuretics) are currently in use to treat preeclampsia, still there is a search for safer drugs with better efficacy. Lately, antihypertensive vasodilators from natural sources are gaining importance in treating preeclampsia. Eugenol (Eug), a natural essential oil, has been traditionally used in health and food products without any risk. In the present study, ex vivo experiments were designed to examine the vasorelaxation effect of Eug and its signaling pathways in a middle uterine artery (MUA) of pregnant Capra hircus (Ch). In presence of different blockers (L-NAME, indomethacin, ODQ, Ouabain, glibenclamide, 4-AP, Ba2, Carbenoxolone and 18β Glycyrrhetinic acid), Eug-induced concentration-dependent vasorelaxation response was elicited. The results showed that Eug caused a greater vasorelaxation effect in the MU of pregnant animals, which is mediated by potential activation of eNOS, KATP channels, and Kir channels with moderate activation of Na+- K+- ATPase and sGC and MEGJ. These findings provide a strong basis for developing Eug as a therapeutic candidate in the treatment of pregnancy-associated hypertension.

Nutritional Regulation of Embryonic Survival, Growth, and Development

Maternal nutritional status affects conceptus development and, therefore, embryonic survival, growth, and development. These effects are apparent very early in pregnancy, which is when most embryonic losses occur. Maternal nutritional status has been shown to affect conceptus growth and gene expression throughout the periconceptual period of pregnancy (the period immediately before and after conception). Thus, the periconceptual period may be an important "window" during which the structure and function of the fetus and the placenta are "programmed" by stressors such as maternal malnutrition, which can have long-term consequences for the health and well-being of the offspring, a concept often referred to as Developmental Origins of Health and Disease (DOHaD) or simply developmental programming. In this review, we focus on recent studies, using primarily animal models, to examine the effects of various maternal "stressors," but especially maternal malnutrition and Assisted Reproductive Techniques (ART, including in vitro fertilization, cloning, and embryo transfer), during the periconceptual period of pregnancy on conceptus survival, growth, and development. We also examine the underlying mechanisms that have been uncovered in these recent studies, such as effects on the development of both the placenta and fetal organs. We conclude with our view of future research directions in this critical area of investigation.

Programming of Embryonic Development

Assisted reproductive techniques (ART) and parental nutritional status have profound effects on embryonic/fetal and placental development, which are probably mediated via "programming" of gene expression, as reflected by changes in their epigenetic landscape. Such epigenetic changes may underlie programming of growth, development, and function of fetal organs later in pregnancy and the offspring postnatally, and potentially lead to long-term changes in organ structure and function in the offspring as adults. This latter concept has been termed developmental origins of health and disease (DOHaD), or simply developmental programming, which has emerged as a major health issue in animals and humans because it is associated with an increased risk of non-communicable diseases in the offspring, including metabolic, behavioral, and reproductive dysfunction. In this review, we will briefly introduce the concept of developmental programming and its relationship to epigenetics. We will then discuss evidence that ART and periconceptual maternal and paternal nutrition may lead to epigenetic alterations very early in pregnancy, and how each pregnancy experiences developmental programming based on signals received by and from the dam. Lastly, we will discuss current research on strategies designed to overcome or minimize the negative consequences or, conversely, to maximize the positive aspects of developmental programming.

Gene and protein expression of connexins 37 and 43 in cumulus-oocytes complexes throughout the canine oestrous cycle

The aim of this study was to evaluate the expression of connexin (Cx) 37 and Cx43 in canine cumulus-oocyte complexes (COCs) during the oestrous cycle. Cx localisation was analysed by immunohistochemistry and immunofluorescence, whereas protein and gene expression was evaluated by western blotting and quantitative polymerase chain reaction respectively; comparisons were made using analysis of variance. Both Cx37 and Cx43 were expressed in all follicular stages; Cx43 was identified in cumulus cells and Cx37 was identified in cumulus cells, zonae pellucida and oocytes. Immunofluorescence analyses showed that Cx37 remained unchanged during the preovulatory stage but decreased after ovulation, whereas Cx43 remained unchanged before and after ovulation. Cx43 transcripts increased (P<0.05) during anoestrus and dioestrus in medium-sized follicles but remained unaltered during the pro-oestrus and antral stages during oestrus, before and after ovulation. Cx37 mRNA levels decreased in ovulated COCs (P<0.05). The highest levels of Cx37 protein (P<0.05) were detected in the preantral stage during anoestrus. In contrast, strong Cx43 signals were detected in oestrus and in medium-sized antral follicles in dioestrus (P<0.05). Overall, we demonstrated that Cx37 and Cx43 exhibit different expression patterns, suggesting specific roles throughout growth. Maintenance of Cx expression before ovulation indicates the involvement of Cx37 and Cx43 in the prolonged meiotic arrest.

Expression of Selected Connexin and Aquaporin Genes and Real-Time Proliferation of Porcine Endometrial Luminal Epithelial Cells in Primary Culture Model

Luminal epithelial cells are the first embryonic-maternal contact site undergoing very specific changes associated with reproductive processes. Cells prepare for embryo development by increasing their volume, with the help of aquaporins that provide a transcellular path of rapid water movement during the secretion and absorption of fluids, as well as connexins enabling the flow of inorganic ions and small molecules. In this work, we have examined how AQPs and Cx's behave in luminal epithelium primary cell culture. Cells obtained from porcine specimen during slaughter were primarily in vitro cultured for 7 days. Their proliferation patterns were then analyzed using RTCA, with the expression of genes of interest evaluated with the use of immunofluorescence and RT-qPCR. The results of these changes of gene of interest expression were analyzed on each of the seven days of the porcine luminal primary cell culture. Our study showed that the significant changes were noted in the case of Cx43, whose level of protein expression and distribution increases after 120 hours of culture, when the cells enter the lag phase, and maintains an upward trend until the end of the culture. We noted an increase in AQP4, AQP7, AQP8, and AQP11 levels throughout the entire culture period, while the largest differences in expression were found in AQP3, AQP4, and AQP10. The obtained results could become a point of reference for further in vivo and clinical research. Experiments conducted with these proteins showed that they influence the endometrial fluid content during the oestrous cycle and participate in the process of angiogenesis, which intensifies during endometrial development.

Placental development during early pregnancy in sheep: nuclear estrogen and progesterone receptor mRNA expression in the utero-placental compartments

Sex steroid hormones are major regulators of uterine and placental growth and functions, as well as many other biological processes. To examine the mRNA expression of nuclear estrogen (ESR1 and 2) and progesterone (PGRAB and B) receptors in different compartments of the uterus and placenta, tissues were collected in experiment 1 on days 16, 20, and 28 after natural mating (NAT) and on day 10 after estrus (nonpregnant controls [NP]); and in experiment 2 on day 22 of NAT, and pregnancies established after transfer of embryos generated through mating of FSH-treated ewes (NAT-ET), in vitro fertilization (IVF), or in vitro activation (parthenotes). In experiment 1, ESR1 expression in endometrial stroma (ES), endometrial glands (EGs), and myometrial blood vessels (MBVs), ESR2 in endometrial blood vessels (EBV), PGRAB in ES, and PGRB in ES, EG, and MBV was greater in pregnant than NP ewes depending on the day of pregnancy. The day of pregnancy affected the expression of ESR1 in MBV, ESR2 in EBV and MBV, and PGRAB in ES. In experiment 2, ESR1, PGRAB, and PGRB in EG, but not in other compartments, was greater in NAT-ET than NAT, and PGRB was greater for NAT-ET than IVF. These data demonstrate that ESR and PGR expression differ in pregnant versus NP ewes in selected compartments and was affected by pregnancy stage or embryo origin in selected utero-placental compartments. Thus, sex steroid hormone mRNA expression is differentially regulated in a spatiotemporal manner in the uterus and placenta and is affected by the application of assisted reproductive technology in sheep.

Uterine and placental distribution of selected extracellular matrix (ECM) components in the dog

For many years, modifications of the uterine extracellular matrix (ECM) during gestation have not been considered as critical for successful canine (Canis lupus familiaris) pregnancy. However, previous reports indicated an effect of free-floating blastocysts on the composition of the uterine ECM. Here, the expression of selected genes involved in structural functions, cell-to-cell communication and inhibition of matrix metalloproteinases were targeted utilizing qPCR and immunohistochemistry. We found that canine free-floating embryos affect gene expression of FN1, ECM1 and TIMP4 This seems to be associated with modulation of trophoblast invasion, and proliferative and adhesive functions of the uterus. Although not modulated at the beginning of pregnancy, the decrease of structural ECM components (i.e. COL1, -3, -4 and LAMA2) from pre-implantation toward post-implantation at placentation sites appears to be associated with softening of the tissue in preparation for trophoblast invasion. The further decrease of these components at placentation sites at the time of prepartum luteolysis seems to be associated with preparation for the release of fetal membranes. Reflecting a high degree of communication, intercellular cell adhesion molecules are induced following placentation (Cx26) or increase gradually toward prepartum luteolysis (Cx43). The spatio-temporal expression of TIMPs suggests their active involvement in modulating fetal invasiveness, and together with ECM1, they appear to protect deeper endometrial structures from trophoblast invasion. With this, the dog appears to be an interesting model for investigating placental functions in other species, e.g. in humans in which Placenta accreta appears to share several similarities with canine subinvolution of placental sites (SIPS). In summary, the canine uterine ECM is only moderately modified in early pregnancy, but undergoes vigorous reorganization processes in the uterus and placenta following implantation.

Inhibition of estrogen receptor reduces connexin 43 expression in breast cancers

Connexins are widely supported as tumor suppressors due to their downregulation in cancers, nevertheless, more recent evidence suggests roles for connexins in facilitating tumor progression in later stages, including metastasis. One of the key factors regulating the expression, modification, stability, and localization of connexins is hormone receptors in hormone-dependent cancers. It is reasonable to consider that hormones/hormone receptors may modulate connexins expression and play critical roles in the cellular control of connexins during breast cancer progression. In estrogen receptor (ER)-positive breast cancers, tamoxifen and fulvestrant are widely used therapeutic agents and are considered to alter ER signaling. In this present study, we investigated the effects of fulvestrant and tamoxifen in Cx43 expression, and we also explored the role of Cx43 in ER-positive breast cancer migration and the relationship between Cx43 and ER. The involvement of estrogen/ER in Cx43 modulation was further verified by administering tyrosine kinase inhibitors and chemotherapeutic agents. We found that inhibition of ER promoted the binding of E3 ligase Nedd4 to Cx43, leading to Cx43 ubiquitination. Furthermore, inhibition of ER by fulvestrant and tamoxifen phosphorylated p38 MAPK, and inhibition of Rac, MKK3/6, and p38 reversed fulvestrant-reduced Cx43 expression. These findings suggest that Cx43 expression which may positively regulate cell migration is ER-dependent in ER-positive breast cancer cells.

Gap junction proteins are key drivers of endocrine function

It has long been known that the main secretory cells of exocrine and endocrine glands are connected by gap junctions, made by a variety of connexin species that ensure their electrical and metabolic coupling. Experiments in culture systems and animal models have since provided increasing evidence that connexin signaling contributes to control the biosynthesis and release of secretory products, as well as to the life and death of secretory cells. More recently, genetic studies have further provided the first lines of evidence that connexins also control the function of human glands, which are central to the pathogenesis of major endocrine diseases. Here, we summarize the recent information gathered on connexin signaling in these systems, since the last reviews on the topic, with particular regard to the pancreatic beta cells which produce insulin, and the renal cells which produce renin. These cells are keys to the development of various forms of diabetes and hypertension, respectively, and combine to account for the exploding, worldwide prevalence of the metabolic syndrome. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.