Physiology and Pathophysiology of the Epithelial Barrier of the Female Reproductive Tract

Bioinformatic analysis of endometrial miRNA expression profile at day 26-28 of pregnancy in the mare

The establishment of the fetomaternal interface depends on precisely regulated communication between the conceptus and the uterine environment. Recent evidence suggests that microRNAs (miRNAs) may play an important role in embryo-maternal dialogue. This study aimed to determine the expression profile of endometrial miRNAs during days 26-28 of equine pregnancy. Additionally, the study aimed to predict target genes for differentially expressed miRNAs (DEmiRs) and their potential role in embryo attachment, adhesion, and implantation. Using next-generation sequencing, we identified 81 DEmiRs between equine endometrium during the pre-attachment period of pregnancy (day 26-28) and endometrium during the mid-luteal phase of the estrous cycle (day 10-12). The identified DEmiRs appear to have a significant role in regulating the expression of genes that influence cell fate and properties, as well as endometrial receptivity formation. These miRNAs include eca-miR-21, eca-miR-126-3p, eca-miR-145, eca-miR-451, eca-miR-491-5p, members of the miR-200 family, and the miRNA-17-92 cluster. The target genes predicted for the identified DEmiRs are associated with ion channel activity and sphingolipid metabolism. Furthermore, it was noted that the expression of mucin 1 and leukemia inhibitory factor, genes potentially regulated by the identified DEmiRs, was up-regulated at day 26-28 of pregnancy. This suggests that miRNAs may play a role in regulating specific genes to create a favorable uterine environment that is necessary for proper attachment, adhesion, and implantation of the embryo in mares.

Ovarian follicular fluid levels of phthalates and benzophenones in relation to fertility outcomes

BACKGROUND

Many endocrine disrupting chemicals (EDCs), for instance phthalates and benzophenones, are associated with adverse fertility outcomes and semen quality parameters.

OBJECTIVE

To evaluate if concentrations of selected phthalate metabolites and benzophenones measured in follicular fluid are associated with fertility outcomes (i.e., reproductive hormones, antral follicle count, detected heartbeat at gestational week 7, and live birth) and, in a supplementary study, if measured concentrations of chemicals in follicular fluid can exert biological effects on human spermatozoa.

METHODS

Overall, 111 couples from a fertility clinic in Denmark contributed with 155 follicular fluid samples. Concentrations of 43 metabolites from 19 phthalates and phthalate substitutes and six benzophenones were measured in follicular fluid using liquid chromatography-tandem mass spectrometry. Multiple linear and logistic regression with an applied generalized estimating equation model allowing more than one measurement per woman assessed the association between follicular EDC levels and fertility outcomes. The assessment of biological effects of individual and mixtures of EDCs on human spermatozoa was conducted through a human sperm cell based Ca2+-fluorimetric assay.

RESULTS

Benzophenone-3 (BP-3) and seven metabolites of five phthalates were detectable in follicular fluid. Women with metabolites of dibutyl phthalate isomers in the highest tertiles had lower antral follicle count (MiBP: β = -5.35 [95 % CI: -9.06; -2.00], MnBP: β = -5.25 [95 % CI: -9.00; -2.00]) and lower odds for detecting a heartbeat at gestational week 7 (MiBP: OR = 0.35 [95 % CI: 0.14; 0.91], MnBP: OR = 0.39 [95 % CI: 0.13; 1.15]). Mixtures of the measured concentrations of BP-3 and the seven phthalate metabolites induced a small significant increase in the intracellular calcium ion concentration in human spermatozoa from healthy donors (n = 3).

DISCUSSION

Phthalate metabolites and BP-3 were detectable in follicular fluid and high concentrations of some phthalate metabolites were linked with lower chance of successful fertility treatment outcomes. Chemical mixture concentrations in follicular fluid induced a calcium response in human spermatozoa highlighting possible biological effects at physiologically relevant concentrations.

CFTR Modulates Hypothalamic Neuron Excitability to Maintain Female Cycle

Cystic fibrosis transmembrane conductance regulator (CFTR), known as an epithelial Cl- channel, is increasingly noted to be expressed in the nervous system, although whether and how it plays a role in neuronal excitability is unclear. Given the association of CFTR with fertility, we tested here possible involvement of CFTR in regulating hypothalamic neuron excitability. Patch-clamp and Ca2+ imaging showed that pharmacological inhibition of CFTR evoked electrical pulses and Ca2+ spikes in primary rat hypothalamic neurons, which was dependent on extracellular Cl-. Hypothalamic neurons in brain-slice preparations from adult female mice with CFTR mutation (DF508) exhibited significantly reduced electrical pulses as compared to the wild-type controls. Removal of extracellular Cl- eliminated hypothalamic electrical pulses in the wild-type brain slices, which was reversible by subsequent addition of Cl-. In adult female mice, Ca2+ indicator (GCaMP6s)-based fiber-photometry showed that hypothalamic Ca2+ activities in vivo were enhanced at the proestrus/estrus phase as compared to the diestrus phase of the female cycle. Such estrus-associated hypothalamic activities were largely diminished in DF508 female mice, together with delayed puberty and disturbed female cycles. Therefore, these findings suggest a critical role of CFTR in modulating hypothalamic neuron excitability, which may account for the disturbed female cycles and reduced female fertility associated with CFTR mutations.

Biphasic regulation of CFTR expression by ENaC in epithelial cells: The involvement of Ca2+-modulated cAMP production

The regulatory interaction between two typical epithelial ion channels, cystic fibrosis transmembrane conductance regulator (CFTR) and the epithelial sodium channel (ENaC), for epithelial homeostasis has been noted, although the underlying mechanisms remain unclear. Here, we report that in a human endometrial epithelial cell line (ISK), shRNA-based stable knockdown of ENaC produced a biphasic effect: a low (∼23%) degree of ENaC knockdown resulted in significant increases in CFTR mRNA and protein levels, CFTR-mediated Cl⁻ transport activity as well as intracellular cAMP concentration, while a higher degree (∼50%) of ENaC knockdown did not further increase but restored CFTR expression and cAMP levels. The basal intracellular Ca²⁺ level of ISK cells was lowered by ENaC knockdown or inhibition in a degree-dependent manner. BAPTA-AM, an intracellular Ca²⁺ chelator that lowers free Ca²⁺ concentration, elevated cAMP level and CFTR mRNA expression at a low (5 µM) but not a high (50 µM) dose, mimicking the biphasic effect of ENaC knockdown. Moreover, KH-7, a selective inhibitor of soluble adenylyl cyclase (sAC), abolished the CFTR upregulation induced by low-degree ENaC knockdown or Ca²⁺ chelation, suggesting the involvement of sAC-driven cAMP production in the positive regulation. A luciferase reporter to indicate CFTR transcription revealed that all tested degrees of ENaC knockdown/inhibition stimulated CFTR transcription in ISK cells, suggesting that the negative regulation on CFTR expression by the high-degree ENaC deficiency might occur at post-transcription stages. Additionally, similar biphasic effect of ENaC knockdown on CFTR expression was observed in a human bronchial epithelial cell line. Taken together, these results have revealed a previously unidentified biphasic regulatory role of ENaC in tuning CFTR expression involving Ca²⁺-modulated cAMP production, which may provide an efficient mechanism for dynamics and plasticity of the epithelial tissues in various physiological or pathological contexts.

Rictor/mTORC2 is involved in endometrial receptivity by regulating epithelial remodeling

Successful embryo implantation requires well-functioning endometrial luminal epithelial cells to establish uterine receptivity. Inadequate uterine receptivity is responsible for approximately two thirds of implantation failures in humans. However, the regulatory mechanism governing this functional process remains largely unexplored. A previous study revealed that the expression of Rictor, the main member of mTORC2, in mouse epithelial cells is increased on the fourth day of gestation (D4). Here, we provide the first report of the involvement of Rictor in the regulation of endometrial receptivity. Rictor was conditionally ablated in the mouse endometrium using a progesterone receptor cre (PRcre ) mouse model. Loss of Rictor altered polarity remodeling and the Na+ channel protein of endometrial cells by mediating Rac-1/PAK1(pPAK1)/ERM(pERM) and Sgk1/pSgk1 signaling, respectively, ultimately resulting in impaired fertility. In the endometrium of women with infertility, the expression of Rictor was changed, along with the morphological transformation and Na+ channel protein of epithelial cells. Our findings demonstrate that Rictor is crucial for the establishment of uterine receptivity in both mice and humans. The present study may help improve the molecular regulatory network of endometrial receptivity and provide new diagnostic and treatment strategies for infertility.

GLUT4 in Mouse Endometrial Epithelium: Roles in Embryonic Development and Implantation

GLUT4 is involved in rapid glucose uptake among various kinds of cells to contribute to glucose homeostasis. Prior data have reported that aberrant glucose metabolism by GLUT4 dysfunction in the uterus could be responsible for infertility and increased miscarriage. However, the expression and precise functions of GLUT4 in the endometrium under physiological conditions remain unknown or controversial. In this study, we observed that GLUT4 exhibits a spatiotemporal expression in mouse uterus on pregnant days 1–4; its expression especially increased on pregnant day 4 during the window of implantation. We also determined that estrogen, in conjunction with progesterone, promotes the expression of GLUT4 in the endometrial epithelium in vivo or in vitro. GLUT4 is an important transporter that mediates glucose transport in endometrial epithelial cells (EECs) in vitro or in vivo. In vitro, glucose uptake decreased in mouse EECs when the cells were treated with GLUT4 small interfering RNA (siRNA). In vivo, the injection of GLUT4-siRNA into one side of the mouse uterine horns resulted in an increased glucose concentration in the uterine fluid on pregnant day 4, although it was still lower than in blood, and impaired endometrial receptivity by inhibiting pinopode formation and the expressions of leukemia inhibitory factor (LIF) and integrin ανβ3, finally affecting embryonic development and implantation. Overall, the obtained results indicate that GLUT4 in the endometrial epithelium affects embryo development by altering glucose concentration in the uterine fluid. It can also affect implantation by impairing endometrial receptivity due to dysfunction of GLUT4.

Cystic ovary disease impairs transport speed, smooth muscle contraction, and epithelial ion transport in the bovine oviduct

Cystic ovary disease (COD) is a common cause of bovine infertility but the impact of this disease on the oviduct is unknown. The aim of this study was to analyze the effects of COD on particle transport speed (PTS), ciliary beat frequency, myosalpinx contraction, and epithelial ion transport. Oviducts were obtained from cows affected by COD and compared with those of healthy, mid-diestrus cows. PTS and CBF were examined using live-cell imaging. Smooth muscle contraction and epithelial ion transport were investigated using organ baths and Ussing chambers. Our results showed that muscarinic receptors are involved in cholinergic signaling in the oviduct and that forskolin-induced cyclic AMP production is involved in active ion transport in the oviductal epithelium. Oviducts from cows with luteal cysts revealed significantly decreased PTS (p = 0.02). Further to that, in the oviducts of COD cows, the cholinergic regulation of smooth muscle contractions and active epithelial ion transport were significantly diminished (p < 0.0001). These results imply that in COD cows, oviductal transport is compromised by decreased fluid flow speed and reduced cholinergic regulation of smooth muscle contraction and ion transport. This knowledge contributes to a more comprehensive understanding of COD supporting the development of novel therapeutic concepts for infertility treatment.

Trichomonas vaginalis infection impairs anion secretion in vaginal epithelium

Trichomonas vaginalis is a common protozoan parasite, which causes trichomoniasis associated with severe adverse reproductive outcomes. However, the underlying pathogenesis has not been fully understood. As the first line of defense against invading pathogens, the vaginal epithelial cells are highly responsive to environmental stimuli and contribute to the formation of the optimal luminal fluid microenvironment. The cystic fibrosis transmembrane conductance regulator (CFTR), an anion channel widely distributed at the apical membrane of epithelial cells, plays a crucial role in mediating the secretion of Cl⁻ and HCO₃⁻. In this study, we investigated the effect of T. vaginalis on vaginal epithelial ion transport elicited by prostaglandin E₂ (PGE₂), a major prostaglandin in the semen. Luminal administration of PGE₂ triggered a remarkable and sustained increase of short-circuit current (I_SC) in rat vaginal epithelium, which was mainly due to Cl⁻ and HCO₃⁻ secretion mediated by the cAMP-activated CFTR. However, T. vaginalis infection significantly abrogated the I_SC response evoked by PGE₂, indicating impaired transepithelial anion transport via CFTR. Using a primary cell culture system of rat vaginal epithelium and a human vaginal epithelial cell line, we demonstrated that the expression of CFTR was significantly down-regulated after T. vaginalis infection. In addition, defective Cl⁻ transport function of CFTR was observed in T. vaginalis-infected cells by measuring intracellular Cl⁻ signals. Conclusively, T. vaginalis restrained exogenous PGE₂-induced anion secretion through down-regulation of CFTR in vaginal epithelium. These results provide novel insights into the intervention of reproductive complications associated with T. vaginalis infection such as infertility and disequilibrium in vaginal fluid microenvironment.

Trichomonas vaginalis is a common sexually transmitted parasite that colonized the urogenital mucosa and causes trichomoniasis, a neglected sexually transmitted infection associated with multiple adverse reproductive outcomes in humans. However, the underlying mechanisms remain largely unknown. The epithelial cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel conducting both Cl⁻ and HCO₃⁻, which participates in the regulation of luminal fluid microenvironment conducive to the success of reproductive events. Prostaglandin E₂ (PGE₂), a bioactive molecule abundant in human seminal fluid, has been demonstrated to exhibit a robust pro-secretory action by activating CFTR in the female genital tract epithelial cells such as endometrial epithelium. These discoveries motivated the authors to investigate the effect of T. vaginalis infection on exogenous PGE₂-induced transepithelial transport of electrolytes in vagina. Here, we found that in rat vaginal epithelium, luminal administration of PGE₂ elicited a response of Cl⁻ and HCO₃⁻ secretion mediated by cAMP-activated CFTR. However, T. vaginalis infection impaired transepithelial anion transport evoked by PGE₂, which is probably related to the defective expression and function of CFTR. These outcomes may complement and expand our knowledge of the complex interaction between T. vaginalis and the infected host, providing a novel therapeutic strategy for disequilibrium in vaginal fluid microenvironment and infertility induced by T. vaginalis infection.

Changes in fluid composition and expression of ion channels in rat cervix during different phases of the estrus cycle

We investigated changes in the composition of cervical fluid at different phases of the female rat reproductive cycle. Fluid was collected from the cervix of rats by direct cervical flushing and analyzed for changes in Na⁺ and Cl^- content and osmolarity. Following sacrifice, the cervix was harvested and expressions of mRNA and protein for ENaCs, CFTR and AQPs were measured using qPCR and immunohistochemistry, respectively. Cervical fluid Na⁺ and Cl^- content was high during estrus, but osmolarity was high during metestrus and diestrus. Expressions of CFTR, AQP-1 and AQP-2 in the cervix were high during estrus, but low during diestrus. Expression of ENaC (α, β, γ), AQP-5 and AQP-7 was high during metestrus and diestrus and low during estrus. Changes in expression of ion channels in the cervix could explain changes in cervical fluid composition during the estrus cycle phases that could affect female fertility.

In vivo measurement of pH and CO2 levels in the uterus of sows through the estrous cycle and after insemination

The pH-CO₂-HCO₃^- system is a ubiquitous biological regulator with important functional implications for reproduction. Knowledge of the physiological values of its components is relevant for reproductive biology and the optimization of Assisted Reproductive Technologies (ARTs). However, in situ measurements of these parameters in the uterus are scarce or null. This study describes a non-invasive method for in situ time-lapse recording of pH and CO₂ within the uterus of non-anesthetized sows. Animals were at three different reproductive conditions, estrous with no insemination and two hours after insemination, and diestrous. From pH and CO₂ data, HCO₃^- concentration was estimated. The non-invasive approach to the porcine uterus with novel optical probes allowed the obtaining of in situ physiological values of pH, CO₂, and HCO₃^-. Variable oscillatory patterns of pH, CO₂ and HCO₃^- were found independently of the estrous condition. Insemination did not immediately change the levels of uterine pH, CO₂ (%) and HCO₃^- concentration, but all the values were affected by the estrous cycle decreasing significantly at diestrous condition. This study contributes to a better understanding of the in vivo regulation of the pH-CO₂-HCO₃^- system in the uterus and may help to optimize the protocols of sperm treatment for in vitro fertilization.

Intestinal Transcriptome Analysis Reveals Soy Derivative-Linked Changes in Atlantic Salmon

Intestinal inflammation in farmed fish is a non-infectious disease that deserves attention because it is a major issue linked to carnivorous fishes. The current norm is to formulate feeds based on plant-derived substances, and the ingredients that have antinutritional factors are known to cause intestinal inflammation in fishes such as Atlantic salmon. Hence, we studied inflammatory responses in the distal intestine of Atlantic salmon that received a feed rich in soybean derivatives, employing histology, transcriptomic and flow cytometry techniques. The fish fed on soy products had altered intestinal morphology as well as upregulated inflammation-associated genes and aberrated ion transport-linked genes. The enriched pathways for the upregulated genes were among others taurine and hypotaurine metabolism, drug metabolism-cytochrome P450 and steroid biosynthesis. The enriched gene ontology terms belonged to transmembrane transporter- and channel-activities. Furthermore, soybean products altered the immune cell counts; lymphocyte-like cell populations were significantly higher in the whole blood of fish fed soy products than those of control fish. Interestingly, the transcriptome of the head kidney did not reveal any differential gene expression, unlike the observations in the distal intestine. The present study demonstrated that soybean derivatives could evoke marked changes in intestinal transport mechanisms and metabolic pathways, and these responses are likely to have a significant impact on the intestine of Atlantic salmon. Hence, soybean-induced enteritis in Atlantic salmon is an ideal model to investigate the inflammatory responses at the cellular and molecular levels.

Single nucleotide polymorphisms in Renalase and KCNQ1 genes and female infertility: A cross-sectional study in Pakistan

A global increase in the incidence of subfertility is observed, and research suggests strong genetic influences that might restrict fertility directly or indirectly. It therefore becomes important to rule out the existence of genetic causes and counsel infertile couples before offering "Advanced Infertility Treatment Techniques." This cross-sectional study aimed to explore the association of KCNQ1 (rs2237895) and Renalase (rs2576178 and rs10887800) single nucleotide polymorphisms with different causes of infertility by analysing 508 fertile and 164 infertile women. Gene variant (AC/CC) of KCNQ1 rs2237895 showed a slight difference in the endometriosis group compared to the fertile group (p = .049), with the C allele showing a significant association with infertility overall (OR = 1.42 [1.100-1.833]; p < .0069). The variant AG/GG of Renalase rs2576178 was significantly associated with overall infertility (OR = 2.266; p < .001), with a strong G allele association with unexplained infertility OR = 2.796 (p = .002) that remained significant after adjusting for age and body mass index. Similarly, Renalase rs10887800 AG/GG and G allele showed significant association with both infertility due to polycystic ovarian syndrome and unexplained infertility. Expression of single nucleotide polymorphism rs2237895 and rs2576178 in both KCNQ1 and Renalase genes might be responsible for altering reproductive potential, hence leading to infertility in women.

Increased intracellular Cl- concentration mediates Trichomonas vaginalis-induced inflammation in the human vaginal epithelium

Trichomonas vaginalis is a primary urogenital parasite that causes trichomoniasis, a common sexually transmitted disease. As the first line of host defense, vaginal epithelial cells play critical roles in orchestrating vaginal innate immunity and modulate intracellular Cl^- homeostasis via the cystic fibrosis transmembrane conductance regulator (CFTR), an anion channel that plays positive roles in regulating nuclear factor-κB (NF-κB) signalling. However, the association between T. vaginalis infection and intracellular Cl^- disequilibrium remains elusive. This study showed that after T. vaginalis infection, CFTR was markedly down-regulated by cysteine proteases in vaginal epithelial cells. The intracellular Cl^- concentration ([Cl^-]_i) was consequently elevated, leading to NF-κB signalling activation via serum- and glucocorticoid-inducible kinase-1. Moreover, heightened [Cl^-]_i and activated NF-κB signalling could be sustained in a positive feedback regulatory manner resulting from decreased intracellular cAMP through NF-κB-mediated up-regulation of phosphodiesterase 4. The results conclusively revealed that the intracellular Cl^- of the human vaginal epithelium could be dynamically modulated by T. vaginalis, which contributed to mediation of epithelial inflammation in the human vagina.

Deficient LRRC8A-dependent volume-regulated anion channel activity is associated with male infertility in mice

Ion channel-controlled cell volume regulation is of fundamental significance to the physiological function of sperm. In addition to volume regulation, LRRC8A-dependent volume-regulated anion channel (VRAC) activity is involved in cell cycle progression, insulin signaling, and cisplatin resistance. Nevertheless, the contribution of LRRC8A and its dependent VRAC activity in the germ cell lineage remain unknown. By utilizing a spontaneous Lrrc8a mouse mutation (c.1325delTG, p.F443*) and genetically engineered mouse models, we demonstrate that LRRC8A-dependent VRAC activity is essential for male germ cell development and fertility. Lrrc8a-null male germ cells undergo progressive degeneration independent of the apoptotic pathway during postnatal testicular development. Lrrc8a-deficient mouse sperm exhibit multiple morphological abnormalities of the flagella (MMAF), a feature commonly observed in the sperm of infertile human patients. Importantly, we identified a human patient with a rare LRRC8A hypomorphic mutation (c.1634G>A, p.Arg545His) possibly linked to Sertoli cell-only syndrome (SCOS), a male sterility disorder characterized by the loss of germ cells. Thus, LRRC8A is a critical factor required for germ cell development and volume regulation in the mouse, and it might serve as a novel diagnostic and therapeutic target for SCOS patients.

LEFTY2 inhibits endometrial receptivity by downregulating Orai1 expression and store-operated Ca2+ entry

Abstract

Early embryo development and endometrial differentiation are initially independent processes, and synchronization, imposed by a limited window of implantation, is critical for reproductive success. A putative negative regulator of endometrial receptivity is LEFTY2, a member of the transforming growth factor (TGF)-β family. LEFTY2 is highly expressed in decidualizing human endometrial stromal cells (HESCs) during the late luteal phase of the menstrual cycle, coinciding with the closure of the window of implantation. Here, we show that flushing of the uterine lumen in mice with recombinant LEFTY2 inhibits the expression of key receptivity genes, including Cox2, Bmp2, and Wnt4, and blocks embryo implantation. In Ishikawa cells, a human endometrial epithelial cell line, LEFTY2 downregulated the expression of calcium release-activated calcium channel protein 1, encoded by ORAI1, and inhibited store-operated Ca²⁺ entry (SOCE). Furthermore, LEFTY2 and the Orai1 blockers 2-APB, MRS-1845, as well as YM-58483, inhibited, whereas the Ca²⁺ ionophore, ionomycin, strongly upregulated COX2, BMP2 and WNT4 expression in decidualizing HESCs. These findings suggest that LEFTY2 closes the implantation window, at least in part, by downregulating Orai1, which in turn limits SOCE and antagonizes expression of Ca²⁺-sensitive receptivity genes.

Key messages

•Endometrial receptivity is negatively regulated by LEFTY2.

•LEFTY2 inhibits the expression of key murine receptivity genes, including Cox2, Bmp2and Wnt4, and blocks embryo implantation.

•LEFTY2 downregulates the expression of Orai1 and inhibits SOCE.

•LEFTY2 and the Orai1 blockers 2-APB, MRS-1845, and YM-58483 inhibit COX2, BMP2, and WNT4 expression in endometrial cells.

•Targeting LEFTY2 and Orai1 may represent a novel approach for treating unexplained infertility.

Electronic supplementary material

The online version of this article (10.1007/s00109-017-1610-9) contains supplementary material, which is available to authorized users.

Upregulation of CFTR in patients with endometriosis and its involvement in NFκB-uPAR dependent cell migration

Endometriotic tissues exhibit high migration ability with the underlying mechanisms remain elusive. Our previous studies have demonstrated that cystic fibrosis transmembrane conductance regulator (CFTR) acts as a tumor suppressor regulating cell migration. In the present study, we explored whether CFTR plays a role in the development of human endometriosis. We found that both mRNA and protein expression levels of CFTR and urokinase-type plasminogen activator receptor (uPAR) were significantly increased in ectopic endometrial tissues from patients with endometriosis compared to normal endometrial tissues from women without endometriosis and positively correlated. In human endometrial Ishikawa (ISK) cells, overexpression of CFTR stimulated cell migration with upregulated NFκB p65 and uPAR. Knockdown of CFTR inhibited cell migration. Furthermore, inhibition of NFκB with its inhibitors (curcumin or Bay) significantly reduced the expression of uPAR and cell migration in the CFTR-overexpressing ISK cells. Collectively, the present results suggest that the CFTR-NFκB-uPAR signaling may contribute to the progression of human endometriosis, and indicate potential targets for diagnosis and treatment.

Chemical UV Filters Mimic the Effect of Progesterone on Ca2+ Signaling in Human Sperm Cells

Progesterone released by cumulus cells surrounding the egg induces a Ca²⁺ influx into human sperm cells via the cationic channel of sperm (CatSper) Ca²⁺ channel and controls multiple Ca²⁺-dependent responses essential for fertilization. We hypothesized that chemical UV filters may mimic the physiological action of progesterone on CatSper, thus affecting Ca²⁺ signaling in human sperm cells. We examined 29 UV filters allowed in sunscreens in the United States and/or the European Union for their ability to induce Ca²⁺ signals in human sperm by applying measurements of the intracellular free Ca²⁺ concentration. We found that 13 UV filters induced a significant Ca²⁺ signal at 10 μM. Nine UV filters induced Ca²⁺ signals primarily by activating the CatSper channel. The UV filters 3-benzylidene camphor (3-BC) and benzylidene camphor sulfonic acid competitively inhibited progesterone-induced Ca²⁺ signals. Dose-response relations for the UV filters showed that the Ca²⁺ signal-inducing effects began in the nanomolar-micromolar range. Single-cell Ca²⁺ measurements showed a Ca²⁺ signal-inducing effect of the most potent UV filter, 3-BC, at 10 nM. Finally, we demonstrated that the 13 UV filters acted additively in low-dose mixtures to induce Ca²⁺ signals. In conclusion, 13 of 29 examined UV filters (44%) induced Ca²⁺ signals in human sperm. Nine UV filters primarily activated CatSper and thereby mimicked the effect of progesterone. The UV filters 3-BC and benzylidene camphor sulfonic acid competitively inhibited progesterone-induced Ca²⁺ signals. In vivo exposure studies are needed to investigate whether UV filter exposure affects human fertility.

Hypothyroidism affects differentially the cell size of epithelial cells among oviductal regions of rabbits

Oviductal regions show particular histological characteristics and functions. Tubal pathologies and hypothyroidism are related to primary and secondary infertility. The impact of hypothyroidism on the histological characteristics of oviductal regions has been scarcely studied. Our aim was to analyse the histological characteristics of oviductal regions in control and hypothyroid rabbits. Hypothyroidism was induced by oral administration of methimazole (MMI) for 30 days. For both groups, serum concentrations of thyroid and gonadal hormones were determined. Sections of oviductal regions were stained with the Masson's trichrome technique to analyse both epithelial and smooth muscle layers. The percentage of proliferative epithelial cells (anti-Ki67) in diverse oviductal regions was also quantified. Data were compared with Student t-test, Mann-Whitney U-test, or Fischer's test. In comparison with the control group, the hypothyroid group showed: (i) a low concentration of T3 and T4, but a high level of TSH; (ii) similar values of serum estradiol, progesterone and testosterone; (iii) a large size of ciliated cells in the ampulla (AMP), isthmus (IST) and utero-tubal junction (UTJ); (iv) a large size of secretory cells in the IST region; (v) a low percentage of proliferative secretory cells in the fimbria-infundibulum (FIM-INF) region; and (vi) a similar thickness of the smooth muscle layer and the cross-sectional area in the AMP and IST regions. Modifications in the size of the oviductal epithelium in hypothyroid rabbits could be related to changes in the cell metabolism that may impact on the reproductive functions achieved by oviduct.

Ion channels in the endometrium: regulation of endometrial receptivity and embryo implantation

BACKGROUND

Although embryo implantation is a prerequisite for human reproduction, it remains a poorly understood process. The molecular mechanisms regulating endometrial receptivity and/or embryo implantation are still largely unclear.

METHODS

Pubmed and Medline literature databases were searched for articles in English published up to December 2013 with relevant keywords including 'endometrium', 'Na(+), Cl(-), K(+), or Ca(2+) channels', 'ion channels', 'endometrial receptivity', 'blastocyst implantation' and 'embryo implantation'.

RESULTS

At the time of writing, more than 14 types of ion channels, including the cystic fibrosis transmembrane conductance regulator, epithelial sodium channel and various Ca(2+) and K(+) channels, had been reported to be expressed in the endometrium or cells of endometrial origin. In vitro and/or in vivo studies conducted on different species, including rodents, pigs and humans, demonstrated the involvement of various ion channels in the process of embryo implantation by regulating: (i) uterine luminal fluid volume; (ii) decidualization; and (iii) the expression of the genes associated with implantation. Importantly, abnormal ion channel expression was found to be associated with implantation failure in IVF patients.

CONCLUSIONS

Ion channels in the endometrium are emerging as important players in regulating endometrial receptivity and embryo implantation. Abnormal expression or function of ion channels in the endometrium may lead to impaired endometrial receptivity and/or implantation failure. Further investigation into the roles of endometrial ion channels may provide a better understanding of the complex process of embryo implantation and thus reveal novel targets for diagnosis and treatment of implantation failure.

Genistein induces increase in fluid pH, Na+ and HCO3(-) concentration, SLC26A6 and SLC4A4 (NBCe1)-B expression in the uteri of ovariectomized rats

Genistein has been reported to stimulate luminal HCO₃⁻ secretion. We hypothesized that genistein mediates this effect via SLC26A6 and SLC4A4 (NBCe1) transporters. Our study aimed to: investigate changes in uterine fluid pH, Na⁺ and HCO₃⁻ concentration and expression of uterine SLC26A6 and NBCe1 under genistein effect. Ovariectomized adult female rats received 25, 50 and 100 mg/kg/day genistein for a week with and without ICI 182780. A day after the last injection, in vivo uterine perfusion was performed to collect uterine fluid for Na⁺, HCO₃⁻ and pH determination. The animals were then sacrificed and uteri were removed for mRNA and protein expression analyses. SLC26A6 and NBCe1-A and NBCe1-B distribution were visualized by immunohistochemistry (IHC). Genistein at 50 and 100 mg/kg/day stimulates uterine fluid pH, Na⁺ and HCO₃⁻ concentration increase. Genistein at 100 mg/kg/day up-regulates the expression of SLC26A6 and SLC4A4 mRNA, which were reduced following concomitant ICI 182780 administration. In parallel, SLC26A6 and NBCe1-B protein expression were also increased following high dose genistein treatment and were localized mainly at the apical membrane of the luminal epithelia. SLC26A6 and NBCe1-B up-regulation by genistein could be responsible for the observed increase in the uterine fluid pH, Na⁺ and HCO₃⁻ concentration under this condition.

Modulation of sodium-bicarbonate co-transporter (SLC4A4/NBCe1) protein and mRNA expression in rat's uteri by sex-steroids and at different phases of the oestrous cycle

Oestrogen-induced uterine fluid sodium (Na(+)) and bicarbonate (HCO3(-)) secretion may involve SLC4A4. We hypothesized that uterine SLC4A4 expression changes under different sex-steroid influence, therefore may account for the fluctuation in uterine fluid Na(+) and HCO3(-) content throughout the oestrous cycle. The aim of this study is to investigate the differential effects of sex-steroids and oestrous cycle phases on uterine SLC4A4 expression.

METHODS

Adult female WKY rats were ovariectomised and treated with different doses of 17β-oestradiol (E2) (0.2, 2, 20 and 50 μg/ml/day) or progesterone (P4) (4 mg/ml/day) for three consecutive days and 3 days treatment with 0.2 μg/ml/day E2 followed by another 3 days with P4 to mimic the hormonal changes in early pregnancy. Oestrous cycle phases in intact, non-ovariectomised rats were determined by vaginal smear. The animals were then sacrificed and uteri were removed for protein and mRNA expression analyses by Western blotting and Real Time PCR, respectively. SLC4A4 distribution was observed by immunohistochemistry.

RESULTS

Treatment with increasing E2 doses resulted in a dose-dependent increase in SLC4A4 protein expression. High SLC4A4 protein and mRNA expression can be seen at estrus. SLC4A4 is distributed mainly at the apical as well as basolateral membranes of the luminal and glandular epithelia following E2 treatment and at Es. Meanwhile, SLC4A4 expression was reduced following P4 treatment and was low at diestrus.

CONCLUSION

High SLC4A4 expression under estrogen dominance may contribute to the increase in uterine fluid Na(+) and HCO3(-) content, while its low expression under P4 dominance may result in vice versa.

SLC26 anion exchangers in uterine epithelial cells and spermatozoa: clues from the past and hints to the future

The solute carrier 26 (SLC26) family emerges as a distinct class of anion transporters with its members SLC26A3 (Slc26a3) and SLC26A6 (Slc26a6) reported to be electrogenic Cl(-)/HCO3(-) exchangers. While it is known that uterine fluid has high HCO3(-) content and that HCO3(-) is essential for sperm capacitation, the molecular mechanisms underlying the transport of HCO3(-) across uterine epithelial cells and sperm have not been fully investigated. The present review re-examines the results from early reports studying anion transport, finding clues for the involvement of Cl(-)/HCO3(-) anion exchangers in electrogenic HCO3(-) transport across endometrial epithelium. We also summarise recent work on Slc26a3 and Slc26a6 in uterine epithelial cells and sperm, revealing their functional role in working closely with the cystic fibrosis transmembrane conductance regulator (CFTR) for HCO3(-) transport in these cells. The possible involvement of these anion exchangers in other HCO3(-) dependent reproductive processes and their implications for infertility are also discussed.

In-vivo functional study on the involvement of CFTR, SLC26A6, NHE-1 and CA isoenzymes II and XII in uterine fluid pH, volume and electrolyte regulation in rats under different sex-steroid influence

Precise control of uterine fluid pH, volume and electrolytes is important for the reproductive processes. In this study, we examined the functional involvement of multiple proteins including Cystic Fibrosis Transmembrane Regulator (CFTR), Cl(-)/HCO3 (-) exchanger (SLC26A6), sodium-hydrogen exchanger-1 (NHE-1) and carbonic anhydrase (CA) in the regulation of these uterine fluid parameters.

METHODS

Adult female WKY rats were divided into intact, non-ovariectomised at different oestrous cycle phases and ovariectomised treated with sex-steroids. Following oestrous phase identification or sex-steroid treatment, in-vivo uterine perfusion was performed with and without the presence of these inhibitors: glibenclamide, DIDS, ACTZ and EIPA. The pH, volume, Cl(-), HCO3 (-) and Na(+) concentrations of the perfusate from different groups were then analyzed. Meanwhile, the expression of CFTR, SLC26A6, NHE-1, CAII and CAXII was visualized by immunohistochemistry (IHC).

RESULTS

Parallel increase in the pH, volume, Cl(-), HCO3 (-) and Na(+) concentrations was observed at estrus (Es), proestrus (Ps) and following 17β-oestradiol (E) treatment, which was inhibited by glibenclamide, DIDS and ACTZ while parallel reduction in these parameters was observed at diestrus (Ds) and following progesterone (P) treatment which was inhibited by ACTZ and EIPA. CFTR and SLC26A6 expression were up-regulated under E dominance, while NHE-1 expression was up-regulated under P dominance. Meanwhile, CA isoenzymes were expressed under both E and P influence.

CONCLUSION

CFTR, SLC26A6 and CA were involved in mediating parallel increase in the uterine fluid volume, pH and electrolyte concentration under E while NHE and CA were involved in mediating the reduction of these parameters under P.