Polarised bovine endometrial epithelial cells vectorially secrete prostaglandins and chemotactic factors under physiological and pathological conditions

Evaluation of the effect of an amniotic membrane derived bio-nano product (LifeCell) on human endometrial cells proliferation and gene expression: An in-vitro study

OBJECTIVE

Successful assisted reproductive technology (ART) requires a receptive endometrium with appropriate thickness and the presence of specific cytokines, chemokines, and growth factors. Despite advancements in ART, the success rates remain suboptimal, particularly in individuals with thin endometrium resistant to treatment. In this study, we evaluated the potential effects of LifeCell, a product of BioNano Technology, on the growth, development, and acceptance of endometrial cells.

STUDY DESIGN

We cultured endometrial cells in a defined medium with different concentrations of LifeCell and examined cell growth, development, and the expression of genes involved in endometrial receptivity.

RESULTS

Co-culture of primary human endometrial cells with 5 % Life cell solution significantly stimulated the endometrial cell growth, development and receptivity genes expression. The expression levels of FGF2 and CSF in the 72 h co-cultured were significantly increased compared with other groups (P < 0.01). HOXA10 and LIF significantly increased in the 72 h co-cultured compared with 24 h co-cultured and control groups but had no significant level compared with 48 h cocultured. HOXA10 significantly increased in the 48 h cocultured compared with control group. IL-6 and Hb-EGF increased in the 48 h co-cultured compared to other groups but had no significant level. VEGF increased in the treated groups compared to control but had no significant level. The expression of OPN, unlike the other genes, decreased in the treated group compared to the control, which was not significant.

CONCLUSIONS

These findings suggest that LifeCell may be a potential option for patients with treatment-resistant thin endometrium in cases of infertility.

Understanding conceptus-maternal interactions: what tools do we need to develop?

Communication between the maternal endometrium and developing embryo/conceptus is critical to support successful pregnancy to term. Studying the peri-implantation period of pregnancy is critical as this is when most pregnancy loss occurs in cattle. Our current understanding of these interactions is limited, due to the lack of appropriate in vitro models to assess these interactions. The endometrium is a complex and heterogeneous tissue that is regulated in a transcriptional and translational manner throughout the oestrous cycle. While there are in vitro models to study endometrial function, they are static and 2D in nature or explant models and are limited in how well they recapitulate the in vivo endometrium. Recent developments in organoid systems, microfluidic approaches, extracellular matrix biology, and in silico approaches provide a new opportunity to develop in vitro systems that better model the in vivo scenario. This will allow us to investigate in a more high-throughput manner the fundamental molecular interactions that are required for successful pregnancy in cattle.

Generation of a novel three-dimensional scaffold-based model of the bovine endometrium

Bovine in vitro endometrial models that resemble tissue function in vivo are needed to study infertility, long-term uterine alterations induced by pathogens and impact of endocrine disruptor chemicals on reproductive function and other reproductive system complications that cause high economic losses in livestock species. The present study aimed to generate an innovative, reproducible, and functional 3D scaffold-based model of the bovine endometrium structurally robust for long term-culture. We developed a multicellular model containing both endometrial epithelial and stromal cells. Epithelial cells organized to form a luminal-like epithelial layer on the surface of the scaffold. Stromal cells produced their own extracellular matrix forming a stable subepithelial compartment that physiologically resembles the normal endometrium. Both cell types released prostaglandin E2 and prostaglandin F2α following a treatment with oxytocin and arachidonic acid. Additionally signal pathways mediating oxytocin and arachidonic acid stimulation of prostaglandin synthesis were analyzed by real time PCR (RT-PCR). Oxytocin receptor (OXTR), prostaglandin E2 receptor 2 (EP2), prostaglandin E2 receptor 4 (EP4), prostaglandin F receptor (PTGFR), prostaglandin E synthase (PTGES), PGF-synthase (PGFS) and prostaglandin-endoperoxide synthase 2 (COX-2) expression was detected in both control and treatment groups, however, only significant changes in abundance of OXTR mRNA transcripts were found. The results obtained by this study are a step forward in bovine in vitro culture technology. This 3D scaffold-based model provides a platform to study regulatory mechanisms involved in endometrial physiology and can set the basis for a broader tool for designing and testing novel therapeutic strategies for recurrent uterine pathologies.

ATP Induces Interleukin-8, Intracellular Calcium Release, and ERK1/2 Phosphorylation in Bovine Endometrial Cells, Partially through P2Y Receptors

The bovine endometrium has an important defensive role in the postpartum period that acts when an inflammatory process associated with tissue damage or infection by bacteria is produced. Endometrial cells release cytokines and chemokines that recruit inflammatory cells, which release danger-associated molecular patterns (DAMPs), such as adenosine triphosphate (ATP), and initiate and regulate the inflammatory response. However, the role of ATP in bovine endometrial cells is unclear. The aim of this study was to determine the effect of ATP on interleukin-8 (IL-8) release, intracellular calcium mobilization, ERK1/2 phosphorylation, and the role of P2Y receptors, in bovine endometrial cells. Bovine endometrial (BEND) cells were incubated with ATP and the IL-8 release was determined by the ELISA assay. ATP of 50 and 100 μM significantly increased IL-8 released in BEND cells (50 μM: 23.16 ± 3.82 pg/mL, p = 0.0018; 100 μM: 30.14 ± 7.43 pg/mL, p = 0.0004). ATP (50 μM) also induced rapid intracellular calcium mobilization in Fura-2AM-loaded BEND cells, as well as ERK1/2 phosphorylation (ratio 1.1 ± 0.04, p = 0.0049). Suramin (50 μM), a pan-antagonist of P2Y receptors, partially reduced the intracellular calcium mobilization, ERK1/2 phosphorylation (ratio 0.83 ± 0.08, p = 0.045), and IL-8 release (9.67 ± 0.02 pg/mL, p = 0.014) induced by ATP. Finally, BEND cells expressed higher mRNA levels of P2Y1 and P2Y2 purinergic subtype receptors, and lower levels of P2Y11 and P2Y12 receptors, as determined by RT-qPCR. In conclusion, these results showed that ATP activates pro-inflammatory responses in BEND cells, which are partially mediated via P2Y receptors, and BEND cells express the mRNA of subtypes of P2Y receptors, which could have a key role in bovine endometrial inflammation.

MSX1 Regulates Goat Endometrial Function by Altering the Plasma Membrane Transformation of Endometrial Epithelium Cells during Early Pregnancy

MSX1 is an important member of the muscle segment homeobox gene (Msh) family and acts as a transcription factor to regulate tissue plasticity, yet its role in goat endometrium remodeling remains elusive. In this study, an immunohistochemical analysis showed that MSX1 was mainly expressed in the luminal and glandular epithelium of goat uterus, and the MSX1 expression was upregulated in pregnancy at days 15 and 18 compared with pregnancy at day 5. In order to explore its function, goat endometrial epithelial cells (gEECs) were treated with 17 β-estrogen (E₂), progesterone (P₄), and/or interferon-tau (IFNτ), which were used to mimic the physiological environment of early pregnancy. The results showed that MSX1 was significantly upregulated with E₂- and P₄-alone treatment, or their combined treatment, and IFNτ further enhanced its expression. The spheroid attachment and PGE2/PGF2α ratio were downregulated by the suppression of MSX1. The combination of E₂, P₄, and IFNτ treatment induced the plasma membrane transformation (PMT) of gEECs, which mainly showed the upregulation of N-cadherin (CDH2) and concomitant downregulation of the polarity-related genes (ZO-1, α-PKC, Par3, Lgl2, and SCRIB). The knockdown of MSX1 partly hindered the PMT induced by E₂, P₄, and IFNτ treatment, while the upregulation of CDH2 and the downregulation of the partly polarity-related genes were significantly enhanced when MSX1 was overexpressed. Moreover, MSX1 regulated the CDH2 expression by activating the endoplasmic reticulum (ER) stress-mediated unfolded protein response (UPR) pathway. Collectively, these results suggest that MSX1 was involved in the PMT of the gEECs through the ER stress-mediated UPR pathway, which affects endometrial adhesion and secretion function.

Hyperthermia alters interleukin-6 production in response to lipopolysaccharide via endoplasmic reticulum stress in bovine endometrial cells

In the postpartum period, cows experience the uterine bacterial infection and develop the endometritis. To eliminate bacteria and recover from endometritis, endometrial epithelial and stromal cells secrete the cytokine and chemokine, such as interleukin 6 (IL-6), IL-8, and monocyte chemotactic protein 1 (MCP1), to recruit immune cells. Moreover, the symptom of endometritis is prolonged in summer and we have recently indicated that hyperthermia suppresses and enhances the IL-6 production in response to lipopolysaccharide (LPS) challenge in endometrial epithelial and stromal cells, respectively. However, the mechanisms for the opposite reaction of IL-6 secretion in response to LPS challenge in both types of endometrial cells under hyperthermia conditions were still unclear. To reveal these mechanisms, both types of endometrial cells were cultured with LPS under the control (38.5°C) or hyperthermia (40.5°C) conditions and comprehensively analyzed differential gene expressions of them by RNA-seq. In addition, based on these results, we examined the effect of endoplasmic reticulum (ER) stress on the IL-6 production in both types of endometrial cells cultured with LPS under hyperthermia conditions. In comprehensive analysis, hyperthermia induced the ER stress in the endometrial stromal cells but not in the endometrial epithelial cells. Actually, we confirmed that hyperthermia increased the gene expression of BiP, ATF4, and sXBP1 and protein expression of BiP and phosphorylated inositol requiring 1, ER stress marker, in the endometrial stromal cells but not in the endometrial epithelial cells. Moreover, in the endometrial stromal cells exposed to LPS, activation and inhibition of ER stress enhanced the IL-6 production under control conditions and suppressed it under hyperthermia conditions, respectively. In this study, we could uncover the one of causes for the disruption of IL-6 production in response to LPS challenge in the endometrial cells under hyperthermia conditions. This finding might be a clue for the improvement of the symptom of endometritis in cows during summer.

Endometrial glycogen metabolism on days 1 and 11 of the reproductive cycle in dairy cows

Embryos need glucose or fructose to remain viable; however, it is not well understood how secretion of these carbohydrates is regulated. This study was conducted to evaluate endometrial glycogen and associated enzymes on Days 1 and 11 of the estrous cycle (Day 0 = behavioral estrus) in cattle. Diastase-liable periodic acid-Schiff (PAS) staining of luminal epithelia decreased 81 % between Days 1 and 11. Similarly, glycogen content of glandular epithelia was 66 % less on Day 11 than Day 1. There was dense PAS staining in the lumen of some glands, and this staining was removed when there was pretreatment with diastase. Based on western blot results, there was no difference in glycogen metabolizing enzymes between Days 1 and 11. Results from conducting immunohistochemistry procedures indicated hexokinase 1 was more abundant in the epithelial cells than stroma, but immunostaining was not different between Day 1 and 11. In contrast, phospho-glycogen synthase was undetectable on Day 1 but was present in glandular epithelia on Day 11. Glycogen synthase was localized to the epithelia, and was in larger abundance on Day 1. The abundance of glycogen phosphorylase was greater in the epithelium than stroma and on Day 11 than 1. Furthermore, glucose-6-phosphatase 3 was more abundant in the epithelium on both Days 1 and 11. In conclusion, in the uterus of cattle glycogen is stored in a reproductive cycle-dependent manner. Glucose released from endometrial glycogen stores could potentially be utilized by the endometrium or secreted into the uterine lumen.

Chlorogenic acid ameliorates mice clinical endometritis by activating Keap1/Nrf2 and inhibiting NFκB signalling pathway

OBJECTIVES

Clinical endometritis is a common reproductive disorder in mammals that seriously endangers animal health and causes economic losses worldwide. This study aims to use lipopolysaccharide and Trueperella pyogenes exotoxin as modelling reagents (LC) to perfuse the mouse uterus in order to establish a model of clinical endometritis and to investigate the anti-inflammatory and antioxidant effects of chlorogenic acid (CGA).

METHODS

In this study, five LC uterine perfusions were selected to model clinical endometritis. The anti-inflammatory and antioxidant effects of CGA were clarified. Through HE staining, proinflammatory cytokines, blood testing, NFκB and Keap1/Nrf2 signalling pathways and other index changes to explore the protection mechanism of CGA.

KEY FINDINGS

After CGA treatment, the appearance, inflammatory damage and blood indicators of the mouse uterus returned to normal. Simultaneously, CGA could inhibit the activation of NFκB and reduce the release of inflammatory cytokines; CGA could also activate Keap1/Nrf2, promote the dissociation of Keap1 and Nrf2 and significantly increase the expression of the downstream genes HO-1 and NQO1.

CONCLUSIONS

The above results together explain that five LC uterine perfusions can be used to establish a mouse model of clinical endometritis. CGA can treat clinical endometritis by activating Keap1/Nrf2 and inhibiting the NFκB signalling pathway.

Conceptus-induced, interferon tau-dependent gene expression in bovine endometrial epithelial and stromal cells†

Bovine endometrium consists of epithelial and stromal cells that respond to conceptus interferon tau (IFNT), the maternal recognition of pregnancy (MRP) signal, by increasing expression of IFN-stimulated genes (ISGs). Endometrial epithelial and stromal-cell-specific ISGs are largely unknown but hypothesized to have essential functions during pregnancy establishment. Bovine endometrial epithelial cells were cultured in inserts above stromal fibroblast (SF) cells for 6 h in medium alone or with IFNT. The epithelial and SF transcriptomic response was analyzed separately using RNA sequencing and compared to a list of 369 DEGs recently identified in intact bovine endometrium in response to elongating bovine conceptuses and IFNT. Bovine endometrial epithelial and SF shared 223 and 70 DEGs in common with the list of 369 endometrial DEGs. Well-known ISGs identified in the epithelial and SF were ISG15, MX1, MX2, and OAS2. DEGs identified in the epithelial but not SF included a number of IRF molecules (IRF1, IRF2, IRF3, and IRF8), mitochondria SLC transporters (SLC25A19, SLC25A28, and SLC25A30), and a ghrelin receptor. Expression of ZC3HAV1, an anti-retroviral gene, increased specifically within the SF. Gene ontology analysis identified the type I IFN signaling pathway and activation of nuclear factor kappa B transcription factors as biological processes associated with the epithelial cell DEGs. This study has identified biologically relevant IFNT-stimulated genes within specific endometrial cell types. The findings provide critical information regarding the effects of conceptus IFNT on specific endometrial compartments during early developmental processes in cattle.

Alteration of chemokine production in bovine endometrial epithelial and stromal cells under heat stress conditions

After parturition, cows frequently develop uterine bacterial infections, resulting in the onset of endometritis. To eliminate the bacteria, bovine endometrial cells secrete chemokines, such as IL-6 and MCP1, which attract macrophages (MΦs) to the subepithelial stroma. These attracted MΦs are not only involved in bacterial elimination but also the orchestration of inflammation and tissue repair. These immune responses aid in the recovery from endometritis; however, the recovery from endometritis takes longer in summer than in any other season. Based on these findings, we hypothesized that heat stress (HS) affects the chemokine production in endometrial cells. To confirm this hypothesis, we compared IL-6 and MCP1 production induced by lipopolysaccharide (LPS) in bovine endometrial epithelial and stromal cells under normal (38.5°C) and HS conditions (40.5°C). In the endometrial epithelial cells, IL-6 production stimulated by LPS was significantly (p < .05) suppressed under HS conditions. MCP1 production in endometrial epithelial cells was not detected under both the control and HS conditions regardless of the presence of LPS. Moreover, LPS significantly (p < .05) stimulated IL-6 and MCP1 production in endometrial stromal cells. Moreover, HS significantly (p < .05) enhanced their production compared to that under the control conditions. In addition, HS did not affect the migration ability of MΦs; however, the supernatant of the endometrial stromal cells cultured under the HS condition significantly (p < .05) attracted the MΦs when compared to the control condition. These results suggest that HS disrupts chemokine production in two types of endometrial cells and alters the distribution of MΦs in the endometrium during the summer.

Improved filtration method to isolate pure populations of primary bovine endometrial epithelial and stromal cells for immunological studies

Objectives

Isolation and culture of distinct primary endometrial cells are key to reliable in-vitro models to investigate the uterine immune response and optimse new disease interventions. Details on the isolation method and purity of distinct cell populations is lacking in currently available protocols leading to inconsistent results across laboratories.

Methods

Bovine endometrial tissue from non-pregnant bovine uteri were collected immediately post-mortem and separated using differential size filtering. Isolations (n = 15) yielded an average of 3.1 × 10⁵ ± 0.7 × 10⁵ epithelial cells and 1.88 × 10⁶ ± 5.44 × 10⁵ stromal fibroblasts per uterine horn. Following expansion in culture, the purity of cell populations was confirmed using morphology and positive staining for cytokeratin and vimentin which identifies epithelial and stromal fibroblast populations, respectively. Using PCR, cDNA from both cell populations was negative for CD45, a marker of immune cells.

Results

On challenge with a bacterial PAMP (LPS), epithelial and stromal fibroblasts showed a marked increase in the expression of the inflammatory mediators IL8, IL6, S100A8 and S100A9, with both cell populations displaying distinct expression profiles. Here we provide a detailed methodology on the culture of primary bovine endometrial epithelial and stromal cells and demonstrate these cells provide a physiologically relevant model for studies of endometrial inflammation and its regulation.

Electronic supplementary material

The online version of this article (10.1007/s11259-020-09770-3) contains supplementary material, which is available to authorized users.

Ssc-novel-miR-106-5p reduces lipopolysaccharide-induced inflammatory response in porcine endometrial epithelial cells by inhibiting the expression of the target gene mitogen-activated protein kinase kinase kinase 14 (MAP3K14)

As an important gram-negative bacterial outer membrane component, lipopolysaccharide (LPS) plays an important role in bacterial-induced endometritis in sows. However, how LPS induces endometritis is unclear. We stimulated sow endometrial epithelial cells (EECs) with LPS and detected cell viability and tumour necrosis factor-α (TNF-α) and interleukin-1 (IL-1) secretion. LPS affected EEC viability and TNF-α and IL-1 secretion in a dose-dependent manner. LPS induced differential expression in 10 of 393 miRNAs in the EECs (downregulated, nine; upregulated, one). MicroRNA (miRNA) high-throughput sequencing of the LPS-induced EECs plus bioinformatics analysis and the dual-luciferase reporter system revealed a novel miRNA target gene: mitogen-activated protein kinase kinase kinase 14 (MAP3K14). Ssc-novel-miR-106-5p mimic, inhibitor and the nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα) phosphorylation inhibitor Bay11-7085 were used to detect EEC nuclear factor-κB phosphorylation levels (p-NF-κB) and TNF-α and IL-1 secretion. MiR-106-5p mimic downregulated MAP3K14 mRNA and protein expression levels, inhibited p-NF-κB levels and decreased IL-1 and TNF-α secretion, whereas miR-106-5p inhibitor had the opposite effect. Bay11-7085 inhibited p-NF-κB expression and TNF-α and IL-1 secretion. These results suggest that LPS downregulates ssc-novel-miR-106-5p expression in sow EECs to increase MAP3K14 expression, which increases p-NF-κB to promote IL-1 and TNF-α secretion.

Functional expression of the free fatty acids receptor-1 and -4 (FFA1/GPR40 and FFA4/GPR120) in bovine endometrial cells

Endometrial epithelial cells play a key defensive role as part of the innate immune response of cow uterus. An association between risk of acquiring infectious diseases and increased levels of free fatty acids postpartum has been suggested, and the use of omega-3 fatty acids such as docosahexaenoic acid (DHA) has been proposed as a beneficial strategy to improve immunity and fertility. The goal of our study was to demonstrate the presence of free fatty acid (FFA)-1 and 4 receptors in endometrial cells and to investigate their role on DHA interference in lipopolysaccharide (LPS)-induced inflammatory endometrial activation. We demonstrated that the bovine endometrial (BEND) cells line and bovine endometrium express both FFA1 and FFA4 receptors. FFA1 and FFA4 receptors were localized in the epithelium lining the endometrial cavity and in endometrial glands whereas in BEND cells a characteristic cell membrane localization of both receptors was observed. DHA, a FFA4 natural agonist, increased intracellular calcium mobilization in BEND cells, but the FFA1 agonists oleic and linoleic acids did not increase this response. DHA-induced intracellular calcium mobilization was inhibited by the FFA4 and FFA1 antagonists AH7614 and GW1100, respectively. DHA significantly reduced LPS-induced prostaglandin E2 (PGE2) production, but none of the antagonists reduced the effect produced by DHA. On the contrary, linoleic acid increased LPS-induced PGE2 production. In conclusion, endometrial cells express FFA4 and FFA1 receptors, and DHA induces intracellular calcium release via FFA4 and FFA1 receptors. DHA reduces PGE2, but this response was not mediated by FFA4 or FFA1 receptors.

Non-canonical Inflammasome-Mediated IL-1β Production by Primary Endometrial Epithelial and Stromal Fibroblast Cells Is NLRP3 and Caspase-4 Dependent

Inflammation of the post-partum uterus is a normal physiological event, crucial for tissue involution and repair. However, in the bovine, some cows fail to resolve this inflammation, resulting in endometritis, which compromises fertility. Earlier work has identified upregulated expression of the potent inflammatory cytokine IL-1β early post-partum, in cows which subsequently develop endometritis. As a result, targeting IL-1β expression holds potential as a novel treatment for this disease, yet the regulatory mechanisms contributing to IL-1β expression in the bovine endometrium remain unknown. To investigate this, endometrial tissue samples were obtained 7 and 21 days post-partum (DPP) from cows that were diagnosed with endometritis at 21 DPP and cows that experienced a physiological level of inflammation throughout involution. IL-1β was measured by qPCR, ELISA, and immunohistochemistry. Seven DPP, endometrial IL-1β protein levels were significantly higher in animals that proceeded to develop endometritis at 21 DPP. IL-1β production could be detected in luminal and glandular epithelium, in underlying stromal fibroblasts as well as infiltrating immune cells. To investigate the mechanisms regulating IL-1β expression, primary endometrial epithelial cells, stromal fibroblasts and PBMCs were stimulated with LPS and the inflammasome activator nigericin. Stromal fibroblast cells were particularly potent producers of IL-1β. Basolateral LPS stimulation of polarized epithelial cells induced IL1B mRNA and a previously undescribed IL-1β protein isoform, with preferential protein secretion into the apical compartment. Key inflammasome components [nod-like receptor protein 3 (NLRP3), nima-related kinase-7 (NEK7), apoptosis speck like protein containing a CARD (ASC), and gasdermin-D] were expressed by endometrial cells following stimulation. Endometrial cell stimulation in the presence of NLRP3 receptor (MCC950) and pan-caspase (Z-VAD-FMK) inhibitors blocked IL-1β production, demonstrating its dependence on the NLRP3 inflammasome and on caspase activity. Furthermore, caspase-4 specific siRNA prevented IL-1β production, confirming that inflammasome activation in endometrial cells is caspase-4 but not caspase-1 dependent, as shown in other species. Identifying the tissue- and species-specificity of inflammasome assembly and activation has critical relevance for our understanding of inflammation and suggests new therapeutic targets to enhance the resolution of inflammatory pathologies including endometritis in cattle.

Tolerance and Innate Immunity Shape the Development of Postpartum Uterine Disease and the Impact of Endometritis in Dairy Cattle

Bacteria are ubiquitous in the bovine uterus after parturition, but 50 years ago, cows tolerated these bacteria and few animals developed uterine disease. Now, up to 40% of dairy cattle develop postpartum uterine disease. Uterine disease causes infertility by compromising the function of not only the endometrium but also the ovary. Animals defend themselves against pathogens using tolerance and resistance mechanisms. Tolerance is the ability to limit the disease severity induced by a given pathogen burden. Resistance is the ability to limit the pathogen burden and is usually the function of immunity. Endometrial cells contribute to tolerance and have roles in innate immunity and the inflammatory response to pathogens. However, failures in endometrial tolerance and the character of the inflammatory response shape postpartum uterine disease. We propose that uterine health is more dependent on the ability of the endometrium to tolerate pathogens than the ability to resist invading bacteria.

In vitro cultured bovine endometrial cells recognize embryonic sex

Endometrial cell co-culture (ECC) with single embryo may reflect endometrium responses in vivo. Bovine Day-6 in vitro-produced morulae were cultured until Day-8 in modified synthetic oviductal fluid (mSOF), or on the epithelial side of ECC. Expression of epithelial- and stromal-cell transcripts was analyzed by RT-PCR in ECC with one male (ME) or female embryo (FE). Concentrations of ARTEMIN (ARTN) and total protein were determined in epithelial cell-conditioned medium. ECCs yielded embryos with more cells in the inner cell mass than embryos cultured in mSOF. Embryos altered transcript expression only in epithelial cells, not in stromal ones. Thus, ME induced larger reductions than FE and controls (i.e., no embryos cultured) in hexose transporter solute carrier family 2 member 1 (SLC2A1) and member 5 (SLC2A5), connective tissue growth factor (CTGF), artemin (ARTN), and interferon alpha and beta receptors subunit IFNAR1 and IFNAR2. FE reduced SLC2A1 and SLC2A5, and increased ARTN expression with respect to controls. ME tended to reduce total protein concentration (P < 0.082) in ECC-conditioned medium, while ARTN protein and gene expressions strongly correlated (R > 0.90; P < 0.05) in the group of ME or FE, but not in controls (without embryo). Isolated male and female embryos may differentially release signaling factors that induce sexually dimorphic responses in endometrial cells.

Effects of preimplantation factor on interleukin-6 and prostaglandin F2α and E2 in the bovine endometrium

Preimplantation factor (PIF) is a pregnancy specific peptide with immune modulatory properties exerted on the human endometrium. Viable bovine embryos secrete PIF, but its effect on the bovine endometrial immune response is unknown, both in native and inflammatory stimulated endometrial tissue. An ex vivo bovine endometrial tissue culture model was used with lipopolysaccharide (LPS) as an inflammatory stimulant. The effect of synthetic PIF (sPIF) was assessed, in three separate experiments, on the secretion or mRNA expression of essential prostaglandins and cytokines. Radioimmunoassays were used to assess prostaglandin secretion and ELISA for IL-6 secretion from endometrial explants. mRNA expression of IL6 and IL8 was analysed from endometrial explants with real-time PCR. Synthetic PIF reduced native IL-6 secretion from explants when pre-treated for 24 h. There was no effect of sPIF on IL-6 secretion from LPS challenged explants; however, sPIF increased IL6 mRNA expression when challenged with 500 ng/mL LPS. There was no effect of sPIF on prostaglandin secretion or mRNA expression of IL8. Therefore, sPIF is able to modulate the native IL-6 production pathway in the bovine endometrium, yet demonstrates no effect on prostaglandin secretion or IL8 expression. Unlike in human studies, effects of sPIF were minimal, thus sPIF is not an effective modulator of the immune targets investigated in the bovine endometrium.

Bovine Endometrial Epithelial Cells Scale Their Pro-inflammatory Response In vitro to Pathogenic Trueperella pyogenes Isolated from the Bovine Uterus in a Strain-Specific Manner

Among different bacteria colonizing the bovine uterus, Trueperella pyogenes is found to be associated with clinical endometritis (CE). The ability of cows to defend against T. pyogenes infections depends on the virulence of invading bacteria and on the host's innate immunity. Therefore, to gain insights into bacterial factors contributing to the interplay of this host pathogen, two strains of T. pyogenes were included in this study: one strain (TP2) was isolated from the uterus of a postpartum dairy cow developing CE and a second strain (TP5) was isolated from a uterus of a healthy cow. The two strains were compared in terms of their metabolic fingerprints, growth rate, virulence gene transcription, and effect on bovine endometrial epithelial cells in vitro. In addition, the effect of the presence of peripheral blood mononuclear cells (PBMCs) on the response of endometrial epithelial cells was evaluated. TP2, the strain isolated from the diseased cow, showed a higher growth rate, expressed more virulence factors (cbpA, nanH, fimE, and fimG), and elicited a higher mRNA expression of pro-inflammatory factors (PTGS2, CXCL3, and IL8) in bovine endometrial epithelial cells compared with TP5, the strain isolated from the healthy cow. The presence of PBMCs amplified the mRNA expression of pro-inflammatory factors (PTGS2, CXCL3, IL1A, IL6, and IL8) in bovine endometrial epithelial cells co-cultured with live TP2 compared with untreated cells, especially as early as after 4 h. In conclusion, particular strain characteristics of T. pyogenes were found to be important for the development of CE. Furthermore, immune cells attracted to the site of infection might also play an important role in up-regulation of the pro-inflammatory response in the bovine uterus and thus significantly contribute to the host-pathogen interaction.

Lactobacillus rhamnosus GR-1 Limits Escherichia coli-Induced Inflammatory Responses via Attenuating MyD88-Dependent and MyD88-Independent Pathway Activation in Bovine Endometrial Epithelial Cells

Intrauterine Escherichia coli infection after calving reduces fertility and causes major economic losses in the dairy industry. We investigated the protective effect of the probiotic Lactobacillus rhamnosus GR-1 on E. coli-induced cell damage and inflammation in primary bovine endometrial epithelial cells (BEECs). L. rhamnosus GR-1 reduced ultrastructure alterations and the percentage of BEECs apoptosis after E. coli challenge. Increased messenger RNA (mRNA) expression of immune response indicators, including pattern recognition receptors (toll-like receptor [TLR]2, TLR4, nucleotide-binding oligomerization domain [NOD]1, and NOD2), inflammasome proteins (NOD-like receptor family member pyrin domain-containing protein 3, apoptosis-associated speck-like protein, and caspase-1), TLR4 downstream adaptor molecules (myeloid differentiation antigen 88 [MyD88], toll-like receptor adaptor molecule 2 [TICAM2]), nuclear transcription factor kB (NF-kB), and the inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-8, IL-10, IL-18, and interferon (IFN)-β, was observed following E. coli challenge. However, these increases were attenuated by L. rhamnosus GR-1 pretreatment. Our data indicate that L. rhamnosus GR-1 ameliorates the E. coli-induced disruption of cellular ultrastructure, subsequently reducing the percentage of BEECs apoptosis and limiting inflammatory responses, partly via attenuation of MyD88-dependent and MyD88-independent pathway activation. Certain probiotics could potentially prevent postpartum uterine diseases in dairy cows, ultimately reducing the use of antibiotics.

Signal transducer and activator of transcription-3 licenses Toll-like receptor 4-dependent interleukin (IL)-6 and IL-8 production via IL-6 receptor-positive feedback in endometrial cells

Interleukin 6 (IL-6), acting via the IL-6 receptor (IL6R) and signal transducer and activator of transcription-3 (STAT3), limits neutrophil recruitment once bacterial infections are resolved. Bovine endometritis is an exemplar mucosal disease, characterized by sustained neutrophil infiltration and elevated IL-6 and IL-8, a neutrophil chemoattractant, following postpartum Gram-negative bacterial infection. The present study examined the impact of the IL6R/STAT3 signaling pathway on IL-8 production by primary endometrial cells in response to short- or long-term exposure to lipopolysaccharide (LPS) from Gram-negative bacteria. Tyrosine phosphorylation of STAT3 is required for DNA binding and expression of specific targets genes. Immunoblotting indicated constitutive tyrosine phosphorylation of STAT3 in endometrial cells was impeded by acute exposure to LPS. After 24 h exposure to LPS, STAT3 returned to a tyrosine phosphorylated state, indicating cross-talk between the Toll-like receptor 4 (TLR4) and the IL6R/STAT3 signaling pathways. This was confirmed by short interfering RNA targeting the IL6R, which abrogated the accumulation of IL-6 and IL-8, induced by LPS. Furthermore, there was a differential endometrial cell response, as the accumulation of IL-6 and IL-8 was dependent on STAT3, suppressor of cytokine signaling 3, and Src kinase signaling in stromal cells, but not epithelial cells. In conclusion, positive feedback through the IL6R amplifies LPS-induced IL-6 and IL-8 production in the endometrium. These findings provide a mechanistic insight into how elevated IL-6 concentrations in the postpartum endometrium during bacterial infection leads to marked and sustained neutrophil infiltration.

Cellular Barriers after Extravasation: Leukocyte Interactions with Polarized Epithelia in the Inflamed Tissue

During the inflammatory response, immune cells egress from the circulation and follow a chemotactic and haptotactic gradient within the tissue, interacting with matrix components in the stroma and with parenchymal cells, which guide them towards the sites of inflammation. Polarized epithelial cells compartmentalize tissue cavities and are often exposed to inflammatory challenges such as toxics or infections in non-lymphoid tissues. Apicobasal polarity is critical to the specialized functions of these epithelia. Indeed, a common feature of epithelial dysfunction is the loss of polarity. Here we review evidence showing that apicobasal polarity regulates the inflammatory response: various polarized epithelia asymmetrically secrete chemotactic mediators and polarize adhesion receptors that dictate the route of leukocyte migration within the parenchyma. We also discuss recent findings showing that the loss of apicobasal polarity increases leukocyte adhesion to epithelial cells and the consequences that this could have for the inflammatory response towards damaged, infected or transformed epithelial cells.

A three-dimensional model of primary bovine endometrium using an electrospun scaffold

Endometrial stromal and epithelial cell function is typically studied in vitro using standard two-dimensional monocultures, but these cultures fail to reflect the complex three-dimensional (3D) architecture of tissue. A 3D model of bovine endometrium that reflects the architectural arrangement of in vivo tissue would beneficially assist the study of tissue function. An electrospun polyglycolide (PGA) scaffold was selected to grow a 3D model of primary bovine endometrial epithelial and stromal cells, that reflects the architecture of the endometrium for the study of pathophysiology. Electrospun scaffolds were seeded with stromal and epithelial cells, and growth was assessed using histological techniques. Prostaglandin E2 and prostaglandin F2α responsiveness of endometrial scaffold constructs was tested using oxytocin plus arachidonic acid (OT + AA) or lipopolysaccharide (LPS). Stromal and epithelial cells growing on the electrospun scaffold had an architectural arrangement that mimicked whole tissue, deposited fibronectin, had appropriate expression of vimentin and cytokeratin and were responsive to OT + AA and LPS, as measured by prostaglandin accumulation. In conclusion, a functional 3D model of stromal and epithelial cells was developed using a PGA electrospun scaffold which may be used to study endometrial pathophysiology.

Sodium houttuyfonate inhibits inflammation by blocking the MAPKs/NF-κB signaling pathways in bovine endometrial epithelial cells

Sodium houttuyfonate (SH) has traditionally been used for the therapy of inflammatory diseases. In this research, we tried to assess the anti-inflammatory effects of SH on LPS-induced bovine endometrial epithelial cell (bEEC) inflammation. SH cell toxicity was measured using the MTT and LDH assays, and inflammatory cytokine expression was assessed by ELISA, qRT-PCR and Western blotting. We demonstrated that SH was not cytotoxic to bEECs, and that it significantly decreased the LPS-induced mRNA and protein expression of tumor necrosis factor (TNF) α, interleukin (IL)-1β, IL-6 and IL-8. Furthermore, in LPS-induced bEECs, SH inhibited IκBα degradation and NF-κB p65 phosphorylation, and suppressed the phosphorylation of the mitogen-activated protein kinases (MAPKs), p38, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK). In conclusion, we found that SH could effectively block the NF-κB-mediated signaling pathway and reduce the inflammatory process, thereby exerting a protective effect on bEECs.

Polarized Epithelial Cells Secrete Interleukin 6 Apically in the Bovine Endometrium

Endometrial epithelial cells are the first line of defense against pathogenic bacteria infecting the uterus. Innate immune responses by these polarized epithelial cells to bacteria and tissue damage are characterized by release of the chemokine (C-X-C motif) ligand 8 (CXCL8) to attract immune cells from the circulation to the site of infection, where they are regulated by the cytokine interleukin (IL) 6. The present study tested the hypothesis that IL6 is predominantly secreted apically from polarized bovine endometrial epithelial cells in response to stimuli associated with bacterial infection and tissue damage. In postpartum animals, concentrations of IL6, but not of CXCL8, were higher in uterine mucus than in peripheral blood. In vitro, polarized endometrial epithelial cells only secreted IL6 apically when treated with bacteria, the pathogen-associated molecule lipopolysaccharide, or the damage-associated molecule IL1alpha, whereas CXCL8 accumulated apically and basolaterally. Furthermore, IL6 accumulated apically irrespective of whether lipopolysaccharide was applied to the apical or basolateral surface of epithelial cells. Secretion of IL6 from epithelial cells was dependent on the trans-Golgi network but was not affected by exogenous ovarian steroids or by coculture with stromal cells. However, a confluent epithelium was essential to protect underlying stromal cells against noxious challenges, including bacteria, lipopolysaccharide, IL1alpha, and a cytolysin. In summary, when a confluent endometrial epithelial cell barrier is faced with infection and damage, chemokines attract immune cells to the uterine lumen, but IL6 is solely secreted apically to ensure immune cells are only exposed to IL6 once they reach the lumen.

Pathogenic Escherichia coli and lipopolysaccharide enhance the expression of IL-8, CXCL5, and CXCL10 in canine endometrial stromal cells

Chemokines play a central role in cellular communication in response to bacterial infection. However, the knowledge of the chemokine responses to bacterial infections in dogs remains limited. Uterine bacterial infection (pyometra) is one of the most common bacterial diseases in dogs and causes sepsis in most of the cases. We have shown previously that dogs with pyometra have higher messenger RNA (mRNA) levels of chemokines in uterus. To assess whether the stromal part of the endometrium expresses chemokines in response to bacterial infection, we cultured endometrial stromal cells isolated from healthy dogs and exposed them to either live pathogenic Escherichia coli, isolated from the uterus of a dog with pyometra, or lipopolysaccharide. Changes in the mRNA expression of ELR(+) CXC chemokines, IL-8, CXCL5, CXCL7, and ELR(-) CXC chemokine, CXCL10, were measured after 24 hours using quantitative real-time polymerase chain reaction. Levels of IL-8, CXCL5, and CXCL10 were upregulated in endometrial stromal cells exposed to E coli and lipopolysaccharide, whereas the level of CXCL7 was decreased or unaffected. In addition, levels of IL-8 and CXCL5, but not CXCL7 or CXCL10, were significantly higher in dogs with pyometra than those in healthy dogs. Our findings show that pathogenic uterine-derived E coli induces a CXC chemokine response both in cultured endometrial stromal cells within 24 hours and in pyometra-affected uteri from dogs. Stromal cells could therefore play an important role in early neutrophil and T cell recruitment to the site of inflammation during gram-negative bacterial infection of the uterus. Further studies are needed to clarify the role of chemokines in host response to bacterial infection in dogs and the possibility of using chemokines as diagnostic parameters for bacterial infection in this species.

Effects of differentn-6:n-3 fatty acid ratios and of enterolactone on gene expression and PG secretion in bovine endometrial cells

Feeding flaxseed to dairy cows can modulate gene expression and PG synthesis in the uterus at the time of peri-implantation. The objectives of the present study were to determine which flaxseed components are responsible for these effects and how different endometrial cell types are affected. We evaluated the effects of six different linoleic acid (n-6):α-linolenic acid (n-3) ratios and three concentrations of the lignan enterolactone (ENL) on endometrial stromal cells (SC) and epithelial cells (EC). The mRNA abundance of genes with known or suspected roles in embryo survival or PG synthesis was evaluated, along with PGE2and PGF2αconcentrations in culture media. The mRNA abundance of several genes was modulated by different fatty acid (FA) ratios and/or ENL, and this modulation differed between cell types. The FA4 (FA at ann-6:n-3 ratio of 4) treatment (rich inn-3 FA) increased the mRNA abundance of genes that have positive effects on uterine receptivity and implantation when compared with the FA25 (FA at ann-6:n-3 ratio of 25) treatment (rich inn-6 FA). ENL decreased PGE2and PGF2αconcentrations in both cell types, and this reduction was associated with lower mRNA abundance of the PG synthase genesAKR1B1andPTGESin SC. The combination of ENL with FA (FA4 treatment) resulted in the greatest reduction in PGF2αconcentrations when compared with the addition of FA (FA4) or ENL alone. Because of the known luteolytic properties of PGF2α, a reduction in endometrial PGF2αsecretion would favour the establishment and maintenance of pregnancy.

Innate immunity and inflammation of the bovine female reproductive tract in health and disease

Mammalian reproductive physiology and the development of viviparity co-evolved with inflammation and immunity over millennia. Many inflammatory mediators contribute to paracrine and endocrine signalling, and the maintenance of tissue homeostasis in the female reproductive tract. However, inflammation is also a feature of microbial infections of the reproductive tract. Bacteria and viruses commonly cause endometritis, perturb ovarian follicle development and suppress the endocrine activity of the hypothalamus and pituitary in cattle. Innate immunity is an evolutionary ancient system that orchestrates host cell inflammatory responses aimed at eliminating pathogens and repairing damaged tissue. Pattern recognition receptors on host cells bind pathogen-associated molecular patterns and damage-associated molecular patterns, leading to the activation of intracellular MAPK and NFκB signalling pathways and the release of inflammatory mediators. Inflammatory mediators typically include the interleukin cytokines IL1β and IL6, chemokines such as IL8, interferons and prostaglandins. This review outlines the mechanisms of inflammation and innate immunity in the bovine female reproductive tract during health and disease condition.