Validation of primary epitheloid cell cultures isolated from bovine placental caruncles and cotyledons

Ultrastructural and Immunohistochemical Characterization of Maternal Myofibroblasts in the Bovine Placenta around Parturition

Myofibroblasts are contractile cells that exhibit features of both fibroblasts and smooth muscle cells. In the synepitheliochorial placenta of the cow myofibroblasts are found in the maternal stroma. However, a deeper understanding of the structure and function of the stromal myofibroblasts in the developed bovine placenta is still missing. Thus, immunohistochemical and ultrastructural analyses in bovine term placentomes, compared to non-pregnant caruncle samples, were conducted. To investigate functional aspects, contractility of placentomal caruncle slices was assessed in an in vitro contraction assay. Additionally, a three-dimensional reconstruction of a bovine placental myofibroblast was created. Immunofluorescent staining revealed a characteristic pattern, including cytoplasmic expression of α-smooth muscle actin, strong perinuclear signal for the intermediate filament vimentin and nuclear progesterone receptor staining. Ultrastructurally, stress fibers, extended cisternae of the rough endoplasmic reticulum and perinuclear intermediate filaments were observed. Moreover, in vitro stimulation with angiotensin-II, but not with prostaglandin F2α, induced contraction of placental caruncle tissue. Altogether, these results indicate that progesterone-responsive myofibroblasts represent a mesenchymal phenotype that is involved in the contractile properties of bovine placental stroma. Therefore, the present findings suggest a potential involvement of myofibroblasts in post-partum events of cattle, i.e., expulsion of fetal membranes and uterine involution.

A double deletion prevents replication of the pestivirus bovine viral diarrhea virus in the placenta of pregnant heifers

In contrast to wild type bovine viral diarhea virus (BVDV) specific double deletion mutants are not able to establish persistent infection upon infection of a pregnant heifer. Our data shows that this finding results from a defect in transfer of the virus from the mother animal to the fetus. Pregnant heifers were inoculated with such a double deletion mutant or the parental wild type virus and slaughtered pairwise on days 6, 9, 10 and 13 post infection. Viral RNA was detected via qRT-PCR and RNAscope analyses in maternal tissues for both viruses from day 6 p.i. on. However, the double deletion mutant was not detected in placenta and was only found in samples from animals infected with the wild type virus. Similarly, high levels of wild type viral RNA were present in fetal tissues whereas the genome of the double deletion mutant was not detected supporting the hypothesis of a specific inhibition of mutant virus replication in the placenta. We compared the induction of gene expression upon infection of placenta derived cell lines with wild type and mutant virus via gene array analysis. Genes important for the innate immune response were strongly upregulated by the mutant virus compared to the wild type in caruncle epithelial cells that establish the cell layer on the maternal side at the maternal–fetal interface in the placenta. Also, trophoblasts which can be found on the fetal side of the interface showed significant induction of gene expression upon infection with the mutant virus although with lower complexity. Growth curves recorded in both cell lines revealed a general reduction of virus replication in caruncular epithelial cells compared to the trophoblasts. Compared to the wild type virus this effect was dramtic for the mutant virus that reached only a TCID₅₀ of 1.0 at 72 hours post infection.

Here we report on animal studies elucidating mechanisms preventing the transfer of a double deletion mutant of a pestivirus to the fetus in pregnant heifers. This mutant lacks both known factors engaged in blocking the innate immune response to pestiviral infection. As shown also in earlier studies, this mutant was not detected in the fetuses at any of the tested time points in contrast to the wild-type (wt) virus. However, similar to the wt the mutant was detected in a large variety of different maternal tissues. The only exception was the placenta where only wt but not mutant virus was detected. Using gene array analyses we showed that infection of two cell lines derived either from the maternal or the fetal site of the maternal-fetal interface with the mutant virus induces a significant antiviral gene expression response. The reaction of cells from the maternal side was more complex and virus replication in these cells was reduced, almost completly blocking the mutant virus. These results support the hypothesis that replication of the mutant virus is blocked in the placenta due to a highly active innate immune response and the prevention of replication also blocks transfer of the virus to the fetus.

Exosomes derived from placental trophoblast cells regulate endometrial epithelial receptivity in dairy cows during pregnancy

Inadequate fetomaternal interactions could directly lead to pregnancy failure in dairy cows. Exosomes are widely involved in endometrial matrix remodeling, immune function changes, placental development, and other processes of embryo implantation and pregnancy in dairy cows. However, the role of exosomes derived from placental trophoblast cells in regulating the receptivity of endometrial cells and facilitating fetomaternal interaction remains unclear. In this study, bovine trophoblast cells (BTCs) were obtained from bovine placenta and immortalized by transfection with telomerase reverse transcriptase (TERT). Immortalized BTCs still possess the basic and key properties of primary BTCs without exhibiting any neoplastic transformation signs. Subsequently, the effect of trophoblast-derived exosomes (TDEs) on endometrial receptivity in endometrial epithelial cells (EECs) was determined, and the mechanism whereby TDEs and their proteins participate in the fetomaternal interaction during bovine pregnancy were explored. EECs were co-cultured with the exosomes derived from BTCs treated with progesterone (P4). Such treatment enhanced the expression of the endometrial receptivity factors, integrin αv, β3, Wnt7a, and MUC1 by changing the extracellular environment, metabolism, and redox balance in EECs via proteome alignment, compared with no treatment according to the DIA quantitation analysis. Our study demonstrated that trophoblast-derived exosome proteins are one of the most critical elements in fetomaternal interaction, and their changes may act as a key signal in altering endometrial receptivity and provide a potential target for improving fertility.

Effect of decorin and selected glycosylation inhibitors on the adhesion of caruncular epithelial cells of pregnant cows-part I

Adhesion process ensures the formation of the appropriate connection between mother and foetus during placentation and further placental development, which determines physiological pregnancy course. Extracellular matrix of foetal membranes are a rich source of biologically active proteins, the synthesis of which is regulated by hormones. Depending on the stage of pregnancy, the protein profile of the placenta changes, thanks to which its remodelling is possible. The aim of the study was to evaluate the effect of decorin, as well as selected glycosylation inhibitors on the adhesion of caruncular epithelial cells derived from cows during pregnancy. Placental cells were isolated from healthy, pregnant (2nd and 4th month) cows after slaughter, which allowed for the establishment of 4 primary cell cultures without visible cells of fibroblast morphology. The presence of decorin in cell monolayer and cell lysates was determined by the use of immunocytochemistry and Western blotting, respectively. The viability of cells was evaluated by MTT assay. The adhesion of cells to fibronectin was measured spectrophotometrically. Protein N-glycosylation and O-glycosylation have a modulating effect on the adhesion and viability of placental cells during early-mid pregnancy. Decorin and tunicamycin were shown to have anti-adhesive properties with respect to caruncular cells of the pregnant bovine uterus.

Modeling the Ruminant Placenta-Pathogen Interactions in Apicomplexan Parasites: Current and Future Perspectives

Neospora caninum and Toxoplasma gondii are one of the main concerns of the livestock sector as they cause important economic losses in ruminants due to the reproductive failure. It is well-known that the interaction of these parasites with the placenta determines the course of infection, leading to fetal death or parasite transmission to the offspring. However, to advance the development of effective vaccines and treatments, there are still important gaps on knowledge on the placental host-parasite interactions that need to be addressed. Ruminant animal models are still an indispensable tool for providing a global view of the pathogenesis, lesions, and immune responses, but their utilization embraces important economic and ethics restrictions. Alternative in vitro systems based on caruncular and trophoblast cells, the key cellular components of placentomes, have emerged in the last years, but their use can only offer a partial view of the processes triggered after infection as they cannot mimic the complex placental architecture and neglect the activity of resident immune cells. These drawbacks could be solved using placental explants, broadly employed in human medicine, and able to preserve its cellular architecture and function. Despite the availability of such materials is constrained by their short shelf-life, the development of adequate cryopreservation protocols could expand their use for research purposes. Herein, we review and discuss existing (and potential) in vivo, in vitro, and ex vivo ruminant placental models that have proven useful to unravel the pathogenic mechanisms and the host immune responses responsible for fetal death (or protection) caused by neosporosis and toxoplasmosis.

Proteomic Characterization of Host-Pathogen Interactions during Bovine Trophoblast Cell Line Infection by Neospora caninum

Despite the importance of bovine neosporosis, relevant knowledge gaps remain concerning the pathogenic mechanisms of Neospora caninum. Infection of the placenta is a crucial event in the pathogenesis of the disease; however, very little is known about the relation of the parasite with this target organ. Recent studies have shown that isolates with important variations in virulence also show different interactions with the bovine trophoblast cell line F3 in terms of proliferative capacity and transcriptome host cell modulation. Herein, we used the same model of infection to study the interaction of Neospora with these target cells at the proteomic level using LC-MS/MS over the course of the parasite lytic cycle. We also analysed the proteome differences between high- (Nc-Spain7) and low-virulence (Nc-Spain1H) isolates. The results showed that mitochondrial processes and metabolism were the main points of Neospora-host interactions. Interestingly, Nc-Spain1H infection showed a higher level of influence on the host cell proteome than Nc-Spain7 infection.

Characterisation of Listeria monocytogenes isolates from cattle using a bovine caruncular epithelial cell model

Listeria monocytogenes is an important foodborne pathogen in human and veterinary health, causing significant morbidity and mortality including abortion. It has a particular tropism for the gravid uterus, however, the route of infection in reproductive tissues of ruminants (i.e. placentome), is much less clear. In this study, we aimed to investigate a bovine caruncular epithelial cell (BCEC) line as a model for L. monocytogenes infection of the bovine reproductive tract. The BCEC infection model was used to assess the ability of 14 different L. monocytogenes isolates to infect these cells. Lysozyme sensitivity and bacterial survival in 580 μg lysozyme/ml correlated with attenuated ability to proliferate in BCEC (p = 0.004 and p = 0.02, respectively). Four isolates were significantly attenuated compared to the control strain 10403S. One of these strains (AR008) showed evidence of compromised cell wall leading to increased sensitivity to ß-lactam antibiotics, and another (7644) had compromised cell membrane integrity leading to increased sensitivity to cationic peptides. Whole genome sequencing followed by Multi Locus Sequence Type analysis identified that five invasive isolates had the same sequence type, ST59, despite originating from three different clinical conditions. Virulence gene analysis showed that the attenuated isolate LM4 was lacking two virulence genes (uhpT, virR) known to be involved in intracellular growth and virulence.

In conclusion, the BCEC model was able to differentiate between the infective potential of different isolates. Moreover, resistance to lysozyme correlated with the ability to invade and replicate within BCEC, suggesting co-selection for surviving challenging environments as the abomasum.

Effects of maternal nutrition on the expression of genomic imprinted genes in ovine fetuses

Genomic imprinting is an epigenetic phenomenon of differential allelic expression based on parental origin. To date, 263 imprinted genes have been identified among all investigated mammalian species. However, only 21 have been described in sheep, of which 11 are annotated in the current ovine genome. Here, we aim to i) use DNA/RNA high throughput sequencing to identify new monoallelically expressed and imprinted genes in day 135 ovine fetuses and ii) determine whether maternal diet (100%, 60%, or 140% of National Research Council Total Digestible Nutrients) influences expression of imprinted genes. We also reported strategies to solve technical challenges in the data analysis pipeline. We identified 80 monoallelically expressed, 13 new putative imprinted genes, and five known imprinted genes in sheep using the 263 genes stated above as a guide. Sanger sequencing confirmed allelic expression of seven genes, CASD1, COPG2, DIRAS3, INPP5F, PLAGL1, PPP1R9A, and SLC22A18. Among the 13 putative imprinted genes, five were localized in the known sheep imprinting domains of MEST on chromosome 4, DLK1/GTL2 on chromosome 18 and KCNQ1 on chromosome 21, and three were in a novel sheep imprinted cluster on chromosome 4, known in other species as PEG10/SGCE. The expression of DIRAS3, IGF2, PHLDA2, and SLC22A18 was altered by maternal diet, albeit without allelic expression reversal. Together, our results expanded the list of sheep imprinted genes to 34 and demonstrated that while the expression levels of four imprinted genes were changed by maternal diet, the allelic expression patterns were un-changed for all imprinted genes studied.

The newly established bovine endometrial gland cell line (BEGC) forms gland acini in vitro and is only IFNτ-responsive (MAPK42/44 activation) after E2 and P4-pre-incubation

INTRODUCTION

Uterine glands (UG) are crucial for the establishment of ruminant pregnancy and influenced (orchestrated manner) by estrogen (E₂), progesterone (P₄) and interferon tau (IFNτ). In the study we established a bovine endometrial glandular cell line (BGEC) and tested its functional reactivity (signaling) to IFNτ.

METHODS

BGEC was characterized by light microscopy (LM), epithelial markers (ezrin, CK18) [immunofluorescence (IF)/immunohistochemistry (IHC)] and ultrastructure (TEM/SEM) (apical microvilli). In vitro formation of gland acini and transepithelial-electric-resistance (TEER) measurements (EVOM) were done. The expression of mRNA-transcripts (RT-PCR) of steroid receptors (PR, PGRMC1/2, ESR1/2) and the IFNτ-system (IFNAR1/2, IRF1, 2, 9) was checked. BEGC was stimulated with IFNτ (10 ng/ml;1000 ng/ml) (15 min) after steroid pre-treatment [10 pg/ml E₂ (two days)/20 ng/ml P₄ (two days)]. Activation of MAPK42/44;STAT1 was evaluated (densitometrical Western Blot).

RESULTS

BGEC cells expressed epithelial markers and possessed apical microvilli. High TEER-values could be measured (2320-2620 ohm/cm²). The assembled BEGC acini (25 days) were similar to UG in vivo (markers/ultrastructure). All transcripts (steroid receptors/IFNτ-system) could be detected in BEGC (mRNA). MAPK42/44 were significantly activated after E₂/P₄ pre-treatment and IFNτ stimulation (10 ng/ml) (p < 0.05), whilst 1000 ng/ml IFNτ did not activate MAPK42/44. Neither a STAT1 (by IFNτ) nor an activation (MAPK42/44;STAT1) by IFNτ-only was observed.

DISCUSSION

BGEC retains its epithelial phenotype in culture and forms gland acini in vitro thereby confirming its glandular character. Cells were only reactive to (low) IFNτ concentrations when pre-treated with steroids thereby closely resembling implantation physiology in vivo. BEGC can be used as a bovine implantation model to study embryo-maternal communication during early pregnancy in cattle.

Differential susceptibility of bovine caruncular and trophoblast cell lines to infection with high and low virulence isolates of Neospora caninum

Background

Neospora caninum, one of the main causes of abortion in cattle, is very effective at crossing the placental barrier and placental damage is crucial in the pathogenesis of abortion. Bovine trophoblast and caruncular cell layers are key cellular components in the maternal-foetal interface in placentomes, playing a fundamental role in placental functionality.

Methods

We studied tachyzoite adhesion, invasion, proliferation and egress of high- (Nc-Spain7) and low- (Nc-Spain1H) virulence N. caninum isolates in established cultures of bovine caruncular epithelial (BCEC-1) and trophoblast (F3) cells. The parasite invasion rate (pInvR) and the cell infection rate (cInfR) were determined by immunostaining plaque assay at different time points and multiplicities of infection (MOIs), respectively. In addition, tachyzoite growth kinetics were investigated using real-time PCR (qPCR) analysis and immunostaining plaque assay at different times.

Results

Neospora caninum invaded and proliferated in both cell lines. The pInvR was higher in F3 compared to BCEC-1 cells for the Nc-Spain7 isolate (P < 0.05), and higher for the Nc-Spain7 than the Nc-Spain1H in F3 cells (P < 0.01). The cInfR was also higher in F3 cells than in BCEC-1 cells for both isolates (P < 0.0001), and the cInfR for the Nc-Spain7 isolate was higher than for the Nc-Spain1H isolate in both cell lines (P < 0.05). Tachyzoite growth kinetics showed tachyzoite exponential growth until egress at 58 hpi for both isolates in F3, whereas Nc-Spain1H showed a non-exponential growth pattern in BCEC-1. Asynchronous egress of both isolates was observed from 22 h post-infection onwards in BCEC-1. In addition, the tachyzoite yield (TY_58h) was higher in F3 than in BCEC-1 infected by both isolates (P < 0.0001), highlighting better replication abilities of both parasites in F3. Nc-Spain7 showed shorter doubling times and higher TY_58h compared to Nc-Spain1H in F3 cells; adhesion, invasion and proliferation mechanisms were very similar for both isolates in BCEC-1.

Conclusions

Our results indicate a highly similar behavior of high- and low-virulence isolates in their interactions with maternal caruncular cells and suggest an important role of foetal trophoblasts in the pathogenesis of N. caninum infection.

The bovine placenta in vivo and in vitro

The gross anatomic features (cotyledonary type) and histologic classification (synepitheliochorial) of the bovine placenta have been known for many years. Thorough ultrastructural analysis as well as a variety of descriptive studies dealing with the localization of cytoskeletal filaments, extracellular matrix, growth factor systems, steroid hormone receptors, and major histocompatibility complex have contributed further significant knowledge. However, this knowledge was not sufficient to solve clinical placenta-based problems, such as retained fetal membranes. Owing to the complexity of the fetomaternal interface in vitro, culture systems have been developed. As trophoblast giant cells (TGC) are thought to be key players in the cattle placenta, most cell culture models attempt to overcome the pitfall of losing the entire TGC population in vitro. Nevertheless, distinct cell line-based in vitro systems such as cell monolayers or 3-dimensional (co-culture) spheroids were generated for the fetal (trophoblast) and maternal (uterine epithelium) placental compartments. Monolayers have been used to study for example, growth factor or hormonal signaling and TGC formation, whereas spheroids served as models for, for example, trophoblast attachment, uterine epithelium depolarization, and also TGC formation. In the future, the use of more improved culture models might lead to better treatments of retained fetal membranes and increased prevention of embryonic loss. In addition, the in vitro models could shed more light on the mechanisms of the differentiation of uninucleate trophoblast into TGC.

Formation of bovine placental trophoblast spheroids

INTRODUCTION

In this study, we aimed to form spheroids with the bovine placental trophoblast cell line F3. Spheroids are 3-dimensional culture models which can be used to conduct versatile in vitro and in vivo experiments.

MATERIALS AND METHODS

The spheroids were generated using the hanging drop technique, 25% methocel and matrigel. The F3 spheroids were characterized morphologically by light microscopy and transmission (TEM) and scanning electron microscopy (SEM) and immunohistochemistry (ezrin, vimentin, cytokeratin, placental lactogen). The fluorescent dyes calcein and ethidium homodimer were used to determine the viability of the spheroidal F3 cells by immunofluorescence microscopy.

RESULTS

The cell line F3 only formed spheroids by the hanging drop technique when matrigel was added. The trophoblast spheroids were delimited and fully covered by extracellular matrix (light microscopy/TEM/SEM). Cells contributing to spheroids could not be discriminated from each other (light microscopy). The outer spheroidal layer consisted of cells which possessed an apical pole with microvilli that were directed to the outside (light microscopy/TEM). All of the spheroidal F3 cells expressed ezrin, vimentin and cytokeratin, but not placental lactogen. The spheroid core contained degenerating cells whilst the F3 cells of the outer rim were viable (TEM/immunofluorescence microscopy).

DISCUSSION

We have established a 3-dimensional spheroid model for the bovine placental trophoblast cell line F3. The developed culture model might prove valuable for future in vitro studies on the differentiation of bovine trophoblast cells.

Genetic reprogramming of transcription factor ap-2gamma in bovine somatic cell nuclear transfer preimplantation embryos and placentomes

Bovine somatic cell nuclear transfer (SCNT) efficiency remains very low despite a tremendous amount of research devoted to its improvement over the past decade. Frequent early and mid-gestational losses are commonly accompanied by placental abnormalities. A transcription factor, activating protein AP-2gamma, has been shown to be necessary for proper placental development in the mouse. We first evaluated the expression of the gene coding for AP-2gamma (Tfap2c) in several bovine fibroblast donor cell lines and found it was not expressed. Subsequently we determined the expression profile of Tfap2c in oocytes and various stages of preimplantation in vitro fertilized (IVF) embryos. Tfap2c was undetectable in oocytes and early embryos, and was detectable at relatively high levels in morula and blastocyst IVF embryos. The lack of expression in oocytes and donor cells means Tfap2c must be induced in the zygote at the morula stage in properly reprogrammed embryos. SCNT embryos expressed Tfap2c at the eight-cell stage, 2 days earlier than control embryos. Control embryos first expressed Tfap2c at the morula stage, and at this stage Tfap2c was significantly lower in the SCNT embryos. No differences in expression were detected at the blastocyst stage. To determine whether Tfap2c was properly reprogrammed in the placenta of SCNT pregnancies, we evaluated its expression in cotyledons and caruncles of SCNT and control pregnancies between days 55 and 90 gestation. Expression of Tfap2c in caruncles significantly increased between days 55 and 90, while expression in cotyledons was relatively consistent over that same period. Expression levels in SCNT tissues were not different from controls. This data indicates Tfap2c expression is altered in early preimplantation SCNT embryos, which may have developmental consequences resulting from genes influenced by Tfap2c, but expression was not different at the blastocyst stage and in placentomes.

Expression and localization of gap junctional connexins 26 and 43 in bovine periovulatory follicles and in corpus luteum during different functional stages of oestrous cycle and pregnancy

The aim of this study was to characterize the regulation of connexins (Cx26 and Cx43) in the bovine ovary (experiment 1-3). Experiment 1: ovaries containing preovulatory follicles or corpora lutea (CL) were collected at 0, 4, 10, 20, 25 (follicles) and 60 h (CL) relative to injection of GnRH. Experiment 2: CL were assigned to the following stages: days 1-2, 3-4, 5-7, 8-12, 13-16, >18 (after regression) of oestrous cycle and of early and late pregnancy (<4 and >4 months). Experiment 3: induced luteolysis, cows on days 8-12 were injected with PGF2alpha analogue (Cloprostenol), and CL were collected by transvaginal ovariectomy before and 0.5, 2, 4, 12, 24, 48 and 64 h after PGF2alpha injection. Real-time RT-PCR was applied to investigate mRNA expression and immunofluorescence was utilized for protein localization. Cx26 mRNA increased rapidly 4 h after GnRH injection (during LH surge) and decreased afterwards during the whole experimental period. Cx43 mRNA expression decreased continuously after GnRH application. Cx26 mRNA in CL increased significantly in the second part of oestrous cycle and after regression. In contrast, the highest mRNA expression for Cx43 in CL was detected during the early luteal phase. After induced luteolysis the mRNA expression of Cx26 increased significantly at 24 h. As shown by immunofluorescence, Cx26 was predominantly localized in the connective tissue and blood vessels of bovine CL, whereas Cx43 was present in the luteal cells and blood vessels. This resulted in a strong increase of Cx26 expression during the late luteal phase and after luteal regression. Subsequently, Cx43 expression was distinctly decreased after luteal regression. These data suggest that Cx26 and Cx43 are involved in the local cellular mechanisms participating in tissue remodelling during the critical time around periovulation as well as during CL formation (angiogenesis), function and regression in the bovine ovary.

Bovine caruncular epithelial cell line (BCEC-1) isolated from the placenta forms a functional epithelial barrier in a polarised cell culture model

In the bovine synepitheliochorial placenta key sites of fetal-maternal interaction are placentomes consisting of maternal caruncles interdigitating with fetal cotyledons. The aim of this study was to establish an epithelial cell line from caruncles of pregnant cows and to develop a model to study restricted trophoblast invasion, pathogenesis of pregnancy associated diseases and pathways of infection and transport. Primary epithelial cells were isolated, successfully subcultured for 32 passages and cryopreserved at various stages. The cultures were termed bovine caruncular epithelial cell line-1 (BCEC-1). Cytokeratin, zonula occludens-1 protein and vimentin but neither alpha-smooth muscle actin nor desmin were detected by immunofluorescence performed every 5 (+/-1) passages. These results were confirmed by Western blotting. BCEC-1 were then cultured either without matrix or on fibronectin or collagen coated Transwell polyester membrane inserts, respectively, enabling separate access to the basal or apical epithelial compartments. Transmission and scanning electron microscopy of BCEC-1 revealed ultrastructural features also observed in vivo, such as apical microvilli and junctional complexes. Transepithelial electrical resistance (TEER) was measured regularly and revealed an increase with advancing confluence in all cultures. Cultures on coated inserts reached confluence and corresponding TEER-levels at an earlier stage. In addition, the cells were tested negative for bovine virus diarrhoea (BVD) virus, but were permissive for the virus. In conclusion, the BCEC-1 cell line retained characteristics of maternal caruncular epithelial cells as observed in vivo and in primary cell cultures and thus will be a highly useful tool for future studies of pathways of invasion, fetal-maternal communication, transport and infection.