Expression of the vascular endothelial growth factor-receptor system in the porcine endometrium throughout the estrous cycle and early pregnancy

Differential expression of angiogenesis-related genes in goat uterus and corpus luteum during pregnancy

Vascularization and the control of luteal and endometrial development are regulated by hypoxia-inducible factors (HIFs) and vascular endothelial growth factor (VEGF) during pregnancy. In this study, the mRNA and protein expression levels of HIFs (HIF1A, HIF2A and HIF3A) and VEGF in goat uterine and ovarian tissues during various stages of pregnancy were evaluated. A total of 42 Hair goats were used and were allocated into six groups, namely embryo-positive (G1), early pregnancy (G2), mid-term pregnancy (G3), late pregnancy (G4), oocyte-positive group (G5) and diestrus group (G6). The mRNA expression of the examined genes was evaluated by RT-qPCR, and protein expression was evaluated by immunohistochemistry (IHC). In caruncles, HIF1A mRNA expression was greater in G1, G2 and G4 than in G3 (p < .05). HIF1A and HIF2A expression was greater in G1 than in G5 (p < .05). In cotyledons, HIF1A, HIF2A and HIF3A mRNA expression was greater in G2 and G3 compared to G4 (p < .05). In luteal tissue, HIF1A mRNA expression was greater in G1 and G2 than in G3 and G4 (p < .05). In the immunohistochemical examination, HIF1A, HIF2A, HIF3A and VEGF immunoreactions were detected in uterine and luteal tissues. Findings suggest that HIFs and VEGF are involved in the regulation of ovarian functions as well as the processes of implantation and placentation.

Novel insights into conceptus-maternal signaling during pregnancy establishment in pigs

Pregnancy establishment in mammals, including pigs, requires coordinated communication between developing conceptuses (embryos with associated membranes) and the maternal organism. Porcine conceptuses signalize their presence by secreting multiple factors, of which estradiol-17β (E2) is considered the major embryonic signal initiating the maternal recognition of pregnancy. During this time, a limited supply of prostaglandin (PGF2α) to the corpora lutea and an increased secretion of luteoprotective factors (e.g., E2 and prostaglandin E2 [PGE2]) lead to the corpus luteum's maintained function of secreting progesterone, which in turn primes the uterus for implantation. Further, embryo implantation is related to establishing an appropriate proinflammatory environment coordinated by the secretion of proinflammatory mediators including cytokines, growth factors, and lipid mediators of both endometrial and conceptus origin. The novel, dual role of PGF2α has been underlined. Recent studies involving high-throughput technologies and sophisticated experimental models identified a number of novel factors and revealed complex relationships between these factors and those already established. Hence, it seems that early pregnancy should be regarded as a sequence of processes orchestrated by pleiotropic factors that are involved in redundancy and compensatory mechanisms that preserve the essential functions critical for implantation and placenta formation. Therefore, establishing the hierarchy between all molecules present at the embryo-maternal interface is now even more challenging.

Extracellular vesicles: Focus on peri-implantation period of pregnancy in pigs

The establishment of cell-to-cell communication between the endometrium and the developing embryo is the most important step in successful mammalian pregnancy. Close interaction between the uterine luminal epithelium and trophoblast cells requires triggering timely molecular dialog for successful maternal recognition of pregnancy, embryo implantation, and placenta development. Quite recently, extracellular vesicles (EVs) carrying unique molecular cargo emerged as evolutionarily conserved mediators of cell-to-cell communication during early pregnancy. To date, the presence of EVs at the embryo-maternal interface has been demonstrated in numerous mammals, including domestic livestock, such as pigs. However, few studies have focused on revealing the mechanism of EV-mediated crosstalk between developing early embryos and receptive endometrium. Over the past years, it has appeared that understanding the role of EVs in mammalian reproduction can substantially improve our understanding of the biological challenges of successful reproductive performance. This review describes current knowledge of EVs, specifically in relation to the peri-implantation period in pigs, characterized by common features of embryo implantation and high embryonic mortality in mammals.

Expression and localization of vascular endothelial growth factor and its receptors in the pig uterus during peri-implantation and determination of the in vitro effect of the angiogenesis inhibitor SU5416 on VEGF system expression

The aim of this work was to determine endometrial mRNA expression and uterine protein localization of vascular endothelial growth factor (VEGF) and its receptors VEGFR1 and VEGFR2 during the estrous cycle and peri-implantation period in sows. Uterine tissues were collected from pregnant sows on days 12, 14, 16, and 18 after artificial insemination and from non-pregnant animals on days 2 and 12 of the estrous cycle (day 0 = day of estrus). Using immunohistochemistry, a positive signal for VEGF and its receptor VEGFR2 was found in uterine luminal epithelial cells, endometrial glands, stroma, blood vessels, and myometrium. A VEGFR1 signal was only found in endometrial and myometrial blood vessels and stroma. By day 18 of gestation, the mRNA expression levels of VEGF, VEGFR1, and VEGFR2 were higher than those observed on days 2 and 12 of the estrous cycle and on days 12, 14, and 16 of gestation. Then, a primary culture of sow endometrial epithelial cells was established to define the potential of the selective inhibition of VEGFR2 after treatment with inhibitor SU5416 and determine its effects on the expression pattern of the VEGF system. The endometrial epithelial cells treated with SU5416 showed a dose-dependent decrease in VEGFR1 and VEGFR2 mRNA expression. The present study provides additional evidence on the importance of the VEGF system during peri-implantation, as well as on the specific inhibitory activity of SU5416 in epithelial cells, which, as demonstrated, express the protein and mRNA of VEGF and its receptors VEGFR1 and VEGFR2.

Expression profile of genes related to pregnancy maintenance in Dromedary Camel during the first trimester

So far, few signals involved in embryo-maternal dialogue have been identified in pregnant she-camel. Our objective was to investigate expression profiles of genes relevant to uterine extracellular matrix remodeling (ITGB4, SLCO2A1, FOS, and JUN), uterine tissue vascularization, and placental formation (VEGFA, PGF, and PDGFA), embryonic growth and development (IGF1 and PTEN), plus cell death of uterine tissue (BCL2) in early pregnant versus non-pregnant she-camels. Forty genital tracts (20 pregnant and 20 non-pregnant) and blood samples were collected from abattoirs. Total RNA was extracted from uterine tissues and qRT-PCR was conducted for candidate genes. Serum concentrations of progesterone (P4) and estradiol17-β (E2) were measured. Expression of ITGB4, FOS, and PGF genes increased (P < 0.001) in the right uterine horn of pregnant versus non-pregnant she-camels. Moreover, JUN, SLCO2A1, VEGFA, and PTEN mRNAs were up-regulated (P < 0.001) in various segments of uterine tissues in pregnant groups. The PDGFA transcript was over-expressed (P < 0.001) in both uterine horns of pregnant groups. Additionally, IGF1 was higher (P < 0.001) in the right horn and the uterine body of pregnant groups, and expression of BCL2 was increased (P < 0.001) in the pregnant uterine body. Moreover, serum concentrations of P4 were higher (P < 0.001) and E2 lower (P < 0.05) in pregnant she-camels. Taken together, the fine-tuning of genes related to implantation, matrix formation, vascularization, and placental formation is highly required for successful pregnancy in she-camels.

Acupuncture Improves Endometrial Angiogenesis by Activating PI3K/AKT Pathway in a Rat Model with PCOS

Background. Acupuncture, a treatment derived from traditional Chinese medicine, can effectively relieve the symptoms and improve pregnancy outcome in patients with polycystic ovary syndrome (PCOS); however, its mechanism remains unclear. This study aimed at investigating whether acupuncture could improve endometrial angiogenesis and thus endometrial receptivity via activating PI3K/AKT pathway in PCOS rats. Methods. We established a rat model with PCOS, which was induced by DHEA. Acupuncture was performed every other day for 15 days, and the PI3K inhibitor (LY294002) was intraperitoneal injected 30 mins before acupuncture treatment. Females rats were mated with male SPF SD rats in a ratio of 2 : 1 after treatment and sacrificed on the 5th day when the vaginal plug was identified. The number of implantation sites was observed, followed by ovarian and endometrial morphology detected with hematoxylin-eosin staining and a scanning electron microscope, estrous cycle detected with vaginal smear analysis, and sex hormones and angiogenesis-related PI3K/AKT gene/protein expression detected with enzyme-linked immunosorbent assay, western blotting, immune histochemistry, and quantitative real-time PCR. Results. Acupuncture notably improved implantation sites’ number, endometrial receptivity factors including endometrial morphology, pinopodes, HOX-10, and LIF protein expression, as well as angiogenesis and PI3K/AKT pathway factors such as VEGF, VEGFR2, Ang-1, PI3K, AKT, and P-AKT gene/protein expression and the level of eNOS and NO in the endometrium of rats with PCOS; PCOS-like symptoms were alleviated as well. The efficacy of acupuncture on a rat model with PCOS was counteracted by the combination with the PI3K inhibitor. Conclusion. Acupuncture improves endometrial angiogenesis by activating the PI3K/AKT pathway, thus promoting endometrial receptivity and the number of implantation sites in rats with PCOS.

Effects of P4 Antagonist RU486 on VEGF and Its Receptors' Signaling during the In Vivo Transition from the Preovulatory to Periovulatory Phase of Ovarian Follicles

The development of an adequate blood vessel network is crucial for the accomplishment of ovarian follicle growth and ovulation, which is necessary to support the proliferative and endocrine functions of the follicular cells. Although the Vascular Endothelial Growth Factor (VEGF) through gonadotropins guides ovarian angiogenesis, the role exerted by the switch on of Progesterone (P4) during the periovulatory phase remains to be clarified. The present research aimed to investigate in vivo VEGF-mediated mechanisms by inducing the development of periovulatory follicles using a pharmacologically validated synchronization treatment carried out in presence or absence of P4 receptor antagonist RU486. Spatio-temporal expression profiles of VEGF, FLT1, and FLK1 receptors and the two major MAPK/ERKs and PI3K/AKT downstream pathways were analyzed on granulosa and on theca compartment. For the first time, the results demonstrated that in vivo administration of P4 antagonist RU486 inhibits follicular VEGF receptors' signaling mainly acting on the theca layer by downregulating the activation of ERKs and AKTs. Under the effect of RU486, periovulatory follicles' microarchitecture did not move towards the periovulatory stage. The present evidence provides new insights on P4 in vivo biological effects in driving vascular and tissue remodeling during the periovulatory phase.

Application of Ligilactobacillus salivarius CECT5713 to Achieve Term Pregnancies in Women with Repetitive Abortion or Infertility of Unknown Origin by Microbiological and Immunological Modulation of the Vaginal Ecosystem

In this study, the cervicovaginal environment of women with reproductive failure (repetitive abortion, infertility of unknown origin) was assessed and compared to that of healthy fertile women. Subsequently, the ability of Ligilactobacillus salivarius CECT5713 to increase pregnancy rates in women with reproductive failure was evaluated. Vaginal pH and Nugent score were higher in women with reproductive failure than in fertile women. The opposite was observed regarding the immune factors TGF-β 1, TFG-β 2, and VEFG. Lactobacilli were detected at a higher frequency and concentration in fertile women than in women with repetitive abortion or infertility. The metataxonomic study revealed that vaginal samples from fertile women were characterized by the high abundance of Lactobacillus sequences, while DNA from this genus was practically absent in one third of samples from women with reproductive failure. Daily oral administration of L. salivarius CECT5713 (~9 log₁₀ CFU/day) to women with reproductive failure for a maximum of 6 months resulted in an overall successful pregnancy rate of 56%. The probiotic intervention modified key microbiological, biochemical, and immunological parameters in women who got pregnant. In conclusion, L. salivarius CECT5713 has proved to be a good candidate to improve reproductive success in women with reproductive failure.

Prokineticin 1-prokineticin receptor 1 signaling promotes angiogenesis in the porcine endometrium during pregnancy†

Pregnancy establishment in mammals, including pigs, requires proper communication between embryos and the maternal reproductive tract. Prokineticin 1 (PROK1) has been described as a secretory protein with pleiotropic functions and as a novel tissue-specific angiogenic factor. However, despite the studies performed mainly on human cell lines and in mice, the function of PROK1 in the endometrium during early pregnancy is still not fully elucidated. We hypothesized that PROK1 contributes to pregnancy establishment in pigs. The present study is the first to report that the expression of PROK1 and its receptor (PROKR1) is elevated in the porcine endometrium during the implantation and early placentation period. PROK1 protein was detected mainly in luminal epithelial cells, glandular epithelial cells, and blood vessels in the endometrium. Using the porcine in vivo model of unilateral pregnancy, we revealed that conceptuses induced the endometrial expression of PROK1 and PROKR1. Moreover, the embryonic signal, estradiol-17β, as well as progesterone, stimulated the endometrial expression of PROK1 and PROKR1. We also evidenced that PROK1-PROKR1 signaling supports endometrial angiogenesis in pigs. The PROK1-stimulated proliferation of primary porcine endometrial endothelial (PEE) cells involved PI3K/AKT/mTOR, MAPK, cAMP, and NFKB signaling pathways. Furthermore, PROK1 via PROKR1 promoted the formation of capillary-like structures by PEE cells. PROK1 also stimulated VEGFA and PGF2α secretion, which in turn may indirectly support angiogenic changes within endometrial tissue. In summary, our study suggests that PROK1 acts as an embryonic signal mediator that regulates endometrial angiogenesis and secretory function during the implantation and early placentation period in pigs.

Vascular Endothelial Growth Factor A and VEGFR-1 Change during Preimplantation in Heifers

Vascular endothelial growth factor A (VEGFA) plays a critical angiogenic role in the endometrium of placentalia during preimplantation. The role of VEGFA and its receptors is not fully characterised in bovine reproduction. We analysed the mRNA expression of VEGFA isoforms 121, 165 and 189, and VEGF receptors 1 and 2 in three experimental settings (A, B and C). We compared intercaruncular endometrium of cyclic to pregnant heifers at Days 12, 15 and 18 post insemination (Day 0), and between Day 15 and Day 18 conceptuses (A). We further compared caruncular versus intercaruncular endometrium at Day 15 (B), and endometrium of heifers carrying embryos originating from somatic cell nuclear transfer (SCNT) versus in vitro fertilisation (IVF) at Day 18 (C). Endometrial VEGFA protein was localised and quantified. Pregnant heifers displayed lower intercaruncular endometrial mRNA expression of VEGFA-121 (p = 0.045) and VEGFA-189 (p = 0.009) as well as lower VEGFA protein abundance (p < 0.001) at Day 15. The VEGFA protein was localised in intercaruncular luminal, glandular epithelium and in tunica muscularis of blood vessels. At Day 15, caruncular endometrium displayed higher VEGFA mRNA expression than intercaruncular endometrium (p < 0.05). Intercaruncular endometrial VEGFA protein at Day 18 was higher in abundance in SCNT than in IVF (p = 0.038). Therefore, during preimplantation in cattle, there may be a need for timely physiological reduction in intercaruncular endometrial VEGFA expression in favour of the caruncular area to facilitate a gradient towards the implantation sites. A higher expression of VEGFA in SCNT may predispose for later placentation abnormalities frequently observed following SCNT.

Prostaglandin F2α stimulates angiogenesis at the embryo-maternal interface during early pregnancy in the pig

Blood vessel formation is a critical process for successful pregnancy establishment and placenta formation. Angiogenic factors such as vascular endothelial growth factor (VEGF), angiopoietins (ANGPTs) or fibroblast growth factor 2 (FGF2) are known to be involved in angiogenesis. However, the mechanism regulating their expression in the porcine endometrium and trophoblast has not been described during early pregnancy establishment. Recently, we reported an important role for prostaglandin F2α (PGF2α) in supporting processes accompanying the peri-implantation period in the pig. The aim of the present study was to determine the effect of PGF2α on angiogenic factor gene and protein expression at the embryo-maternal interface and on capillary-like structure formation by endometrial endothelial cells. In the present study, we used various in vitro models involving endometrial tissue explants, primary porcine trophoblast and endometrial endothelial cells, as well as a swine umbilical vein endothelial cell line (G1410). ANGPT1, ANGPT2 and FGF2 gene expression was analyzed in porcine endometrial explants and in primary trophoblast cells incubated with PGF2α (100 nM, 1 μM). VEGFA gene expression and protein secretion by porcine primary trophoblast cells were studied in vitro using primary trophoblast cells. A network formation assay using the G1410 cell line and primary endothelial cells of endometrial origin was performed to assess the effect of PGF2α on capillary-like structure formation. We found that PGF2α stimulated VEGFA gene expression (1 μM) and secretion of this protein (100 nM) by porcine trophoblast cells (P < 0.05). In endometrial explants, PGF2α increased the expression of the ANGPT1, ANGPT2 and FGF2 genes (P < 0.05). PGF2α stimulated the formation of capillary-like structures acting on porcine endometrial endothelial cells on days 15 and 20 of pregnancy and in the G1410 cell line (P < 0.05). PGF2α-stimulated endothelial cell network formation was diminished by using a MEK kinase inhibitor in G1410 cells. Our results indicate an important role for PGF2α in the regulation of angiogenesis at the embryo-maternal interface. PGF2α promotes angiogenesis in the porcine endometrium by activating the MAPK signaling pathway. The stimulating effect of PGF2α on the formation of capillary-like structures by endothelial cells, together with our previous findings, supports the hypothesis that PGF2α is an important factor promoting the development of the placenta during early pregnancy in the pig.

Temporal expression and localization of vascular endothelial growth factor family members in the bovine uterus during peri-implantation period

The aim of this study was to determine endometrial mRNA expression patterns and uterine protein localizations of vascular endothelial growth factor (VEGF) ligands (VEGFA, VEGFB, VEGFC, and VEGFD) and their receptors (VEGFR1, soluble VEGFR1 (sVEGFR1), VEGFR2, and VEGFR3) during the peri-implantation period in cows. The number of blood and lymphatic vessels in the bovine uterus was also investigated. Bovine uterine tissues were collected from pregnant animals on days 15, 18, and 27 after artificial insemination and from non-pregnant animals on days 15 and 18 of the estrous cycle (day 0 = day of estrus). The mRNA expression level of VEGFA, VEGFR1, sVEGFR1, and VEGFR3 were higher on day 18 than on day 15 in the non-pregnant group. On day 18, the levels of mRNA expression of these genes were higher in the non-pregnant group than in the pregnant group. VEGFB mRNA expression levels was higher on day 15 than on days 18 and 27 of gestation and was higher in the pregnant group than in the non-pregnant group on day 15. Using immunohistochemistry, VEGF ligands and their receptors were found in luminal epithelium, glandular epithelium, stroma, and blood vessels of the endometrium. In addition, VEGFA, VEGFD, and VEGFR3 were also detected in the uterine myometrium. In the pregnant group, the number of blood vessels in the endometrium increased from day 15 to 18 and was greater than that of the non-pregnant group on day 18. Our results demonstrate that the VEGF family is expressed and regulated in the bovine uterus during the peri-implantation period, which may be associated with uterine functions, including vascular remodeling in maternal recognition of pregnancy and implantation.

Variable chemokine expression in porcine trophoblasts and endometrium during the peri-implantation period

Successful embryo implantation and its further development depends on appropriate endometrial remodelling. Porcine early pregnancy is associated with intensive endometrial angiogenesis and establishment of an immunotolerant environment for the embryo. An increasing number of factors are believed to participate in endometrial remodelling. The aim of this study was to elucidate the involvement of selected chemokines at the porcine maternal-foetal interface during the peri-implantation period. Real-time PCR analysis revealed several upregulated chemokines during the time of implantation, and Western blot/ELISA analyses and immunohistochemical staining confirmed their presence at the protein level. The gene expression of several chemokines and receptors was also confirmed in early porcine trophoblasts. The results indicated that IFNG, a porcine trophoblast signal, positively influenced the expression of some chemokines in endometrial cells. In conclusion, we suggest that some of the examined chemokines may be involved in endometrial communication with the trophoblast (CCL2, CCL5, CCL11, CXCL12), whereas others are implicated in the recruitment of immune cells and establishment of an immunotolerant environment for the embryo (CXCL9, CXCL10).

Presence of trophoblast in the uterine lumen affects VEGF-C expression in porcine endometrium

Early pregnancy is associated with morphological and functional changes within the uterus, accompanied by angiogenesis, increased vascular permeability and activation of immune tolerance. Intensive angiogenesis leads to accelerated vascular leakage and accumulation of interstitial fluid in endometrium. To protect the trophoblast from the harmful effect of extracellular fluid, process known as lymphangiogenesis is crucial. These studies are focused on VEGF-C, factor responsible of lymphatic vessels creating, and its receptors: Flk1 (VEGFR2) and Flt4 (VEGFR3) during the time of implantation as well as the effect of trophoblast signals (IFNG and E2) on VEGF-C production. Endometrial samples were collected from mature gilts from days 8, 10, 12, 14 of estrous cycle and pregnancy. Real-Time PCR analysis revealed increased mRNA expression of VEGF-C on days 10, 12, 14 of pregnancy compared to corresponding days of estrous cycle. The highest VEGF-C mRNA expression was observed on 14 day of pregnancy (p < 0.05). Increased mRNA expression of Flk1 and Flt4 was noticed on day 14 of pregnancy in comparison to day 10. Enhanced Flk1 mRNA expression during 14 day of pregnancy was observed compared to corresponding day of estrous cycle (p < 0.05). No significant difference on the protein level was revealed. VEGF-C and its receptors were localized mainly in luminal and glandular epithelial cells, but their presence were confirmed also in endothelial cells of blood and lymphatic vessels and 14 d trophoblasts. In vitro studies revealed positive effect of IFNG on VEGF-C mRNA expression in stromal cells and protein content in medium after stromal cells culture (p < 0.05). Our studies demonstrated the presence of VEGF-C system in porcine endometrium and indicated its possible important role during the time of implantation.

Endometrial response to conceptus-derived estrogen and interleukin-1β at the time of implantation in pigs

The establishment of pregnancy is a complex process that requires a well-coordinated interaction between the implanting conceptus and the maternal uterus. In pigs, the conceptus undergoes dramatic morphological and functional changes at the time of implantation and introduces various factors, including estrogens and cytokines, interleukin-1β2 (IL1B2), interferon-γ (IFNG), and IFN-δ (IFND), into the uterine lumen. In response to ovarian steroid hormones and conceptus-derived factors, the uterine endometrium becomes receptive to the implanting conceptus by changing its expression of cell adhesion molecules, secretory activity, and immune response. Conceptus-derived estrogens act as a signal for maternal recognition of pregnancy by changing the direction of prostaglandin (PG) F_2α from the uterine vasculature to the uterine lumen. Estrogens also induce the expression of many endometrial genes, including genes related to growth factors, the synthesis and transport of PGs, and immunity. IL1B2, a pro-inflammatory cytokine, is produced by the elongating conceptus. The direct effect of IL1B2 on endometrial function is not fully understood. IL1B activates the expression of endometrial genes, including the genes involved in IL1B signaling and PG synthesis and transport. In addition, estrogen or IL1B stimulates endometrial expression of IFN signaling molecules, suggesting that estrogen and IL1B act cooperatively in priming the endometrial function of conceptus-produced IFNG and IFND that, in turn, modulate endometrial immune response during early pregnancy. This review addresses information about maternal-conceptus interactions with respect to endometrial gene expression in response to conceptus-derived factors, focusing on the roles of estrogen and IL1B during early pregnancy in pigs.

Pregnancy and spontaneous fetal loss: A pig perspective

Pigs have a unique, non-invasive epitheliochorial placenta where maternal and fetal layers lay in apposition. Indentation of fetal capillaries into the trophoblasts and maternal capillaries into the uterine epithelium reduce the distance between the fetal and maternal blood, ensuring nutrient transfer for proper conceptus development. Another unique feature of pig pregnancy is conceptus-mediated immune cell enrichment during the early stages of conceptus attachment (around gestation Day 15). This period coincides with the development of vasculature networks at the maternal-fetal interface, which is critical for successful conceptus growth. Specific chemokines, their receptors, and chemokine decoy receptor networks coordinate this immune cell enrichment and the positioning at the maternal-fetal interface. The recruited immune cells, in turn, adopt a specialized phenotype to support key processes of maternal-fetal adaptations, including tolerance to the semi-allogeneic fetus and supporting vascularization. Disturbance in coordinated cross talk between the conceptus and maternal endometrium is an important mechanism associated with spontaneous fetal loss. The exact mechanism of fetal loss is still not yet identified, although research in the last two decades point to various factors including genetics, nutrition, uterine capacity, placental efficiency, and imbalanced immune factors at the maternal-fetal interface. In this review, we summarize some of the recent advances in endometrial immune cell functions and their regulation. We also provide insights into endometrial/placental transcriptome, microRNA biology, and extravesicular transport across the maternal-fetal interface, as well as their potential implications in porcine pregnancy success or failure.

Development of In Vitro Embryo Production System Using Collagen Matrix Gel Attached with Vascular Endothelial Growth Factor Derived from Interleukin-1 Beta-Treated Porcine Endometrial Tissue

The aim of this study was to establish an embryo culture system using collagen gel attached with vascular endothelial growth factor (VEGF) derived from interleukin-1 beta (IL-1β)-treated endometrial tissues from pigs. Endometria were separated from the porcine uterus at the follicular phase of the estrous cycle and were cultured with IL-1β. The collagen gels coincubated with IL-1β-treated endometria (C, without endometrial tissue; CE, with endometrial tissue; and CEI, IL-1β-treated endometrial tissue) were used for embryo culture. We found that, compared with the comparable figures in the control group, prostaglandin synthase-2 (PTGS-2) mRNA was increased in IL-1β-treated endometrial tissue (p < 0.05). The VEGF protein was not observed in collagen gel coincubated without endometrial tissue (C); however, it was detected in collagen gels coincubated with endometrial tissue (CE and CEI). The embryo cleavage rates and blastocyst formation did not differ among the treatment groups. The proportion of blastocysts did not differ among the groups. However, the number of blastocyst cells was significantly (p < 0.05) higher in the CEI group than in the other groups. These results clarify the effects of the intrauterine environment on preimplantation embryos and may be useful in research on the effects of extracellular matrix- and cytokine-treated endometrial tissue on embryo development.

Prostaglandin F2α promotes angiogenesis and embryo-maternal interactions during implantation

Implantation in humans and other mammals is a critical period during which high embryonic mortality rates occur. Prostaglandins (PGs) are key mediators regulating interactions between the reproductive tract and the conceptus (embryo with extraembryonic membranes). Although the significance of PGF2α as a regulator of corpus luteum regression is well established, the role of its high amounts in the uterine lumen in most mammals, regardless of placentation type, during the implantation period remains unresolved. We hypothesized that PGF2α acting as an embryonic signal mediator contributes to pregnancy establishment. Using a porcine model, we demonstrated that the conceptus and its signal (estradiol-17β) elevated endometrial expression of PGF2α receptor (PTGFR) in vivo and in vitro PTGFR protein was expressed mainly in luminal epithelial (LE) and glandular epithelial cells and blood vessels in the endometrium. PGF2α stimulated the MAPK1/3 pathway in endometrial LE cells that coincided with elevated gene expression and secretion of endometrial vascular endothelial growth factor A (VEGFA) protein. PGF2α-PTGFR and adenylyl cyclase signaling were involved in this process. PGF2α-induced VEGFA acting through its receptors stimulated proliferation of endometrial endothelial cells. Moreover, PGF2α elevated gene expression of biglycan, matrix metalloproteinase 9, transforming growth factor β3, and interleukin 1α in the endometrium. In summary, our study indicates that PGF2α participates in pregnancy establishment by promoting angiogenesis and expression of genes involved in tissue remodeling and conceptus-maternal interactions in porcine endometrium during early pregnancy.

Expression of microRNAs and isomiRs in the porcine endometrium: implications for gene regulation at the maternal-conceptus interface

Background

Embryo implantation is a complex, synchronized process that requires establishment of a reciprocal dialogue between a receptive endometrium and developing blastocysts. Recently, microRNAs (miRNAs), known to modulate gene expression through post-transcriptional mechanisms, were implicated in regulation of early pregnancy events including maternal recognition of pregnancy and implantation. To characterize complex transcriptomic changes, expression of miRNAs in pregnant and cyclic endometria collected on days 12, 16 and 20 was analyzed using Illumina deep sequencing and analyzed with bioinformatic pipeline. Moreover, expression profiles of ten genes related to miRNA synthesis and transport such as DROSHA, DGCR8, XPO5, DICER, TARBP2, TNRC6A, and AGO1-4 were determined.

Results

Among genes involved in miRNA transport and synthesis DROSHA, XPO5, DICER1, TARBP, and AGO1 expression was affected by the reproductive status. Moreover, DICER1 and AGO2 proteins were localized in luminal and glandular epithelium with immunofluorescence staining. Several hundred mature, canonical and non-canonical miRNAs were found to be expressed in the endometrial samples. Detailed analysis revealed that miRNA length variants, isomiRs, accounted for the vast majority of defined sequences. Both miRNA and isomiR of miR-140-3p were shown to affect expression of putative targets in endometrial stromal cells in vitro. Computational analysis of putative target genes for miRNAs differentially expressed (DE) between pregnant and cyclic animals resulted in lists of biological processes and regulatory pathways indicating their role in cellular development, cell cycle, immunological response and organismal development. Among predicted target genes for DE miRNAs, vascular endothelial growth factor (VEGF), progesterone and estradiol receptors (PGR, ESR1) and leukemia inhibitory factor (LIF) were found.

Conclusions

This research revealed a repertoire of pregnancy-related miRNAs in porcine endometrium during initial stages of conceptus implantation and during the estrous cycle, and sheds light on mechanisms regulating miRNA-mediated gene expression at the maternal-conceptus interface.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2172-2) contains supplementary material, which is available to authorized users.

MicroRNAome of porcine conceptuses and trophoblasts: expression profile of micrornas and their potential to regulate genes crucial for establishment of pregnancy

Tightly coordinated, reciprocal embryo-maternal interactions affect gene expression during early pregnancy. Recently, microRNAs (miRNAs) have emerged as new players in the fine tuning of embryo development and implantation in mammals via posttranscriptional gene regulation mechanisms. Here, we integrated transcriptomic and computational approaches to profile miRNAs and miRNA synthesis and transport-related genes at different developmental stages of porcine conceptuses and trophoblast during early pregnancy in the pig. Using semiquantitative RT-PCR, we examined mRNA levels of 10 genes encoding proteins involved in miRNA synthesis and transport: DROSHA, DGCR8, XPO5, DICER1, TARBP2, TNRC6A, AGO1, AGO2, AGO3, and AGO4. Custom, multispecies microarrays were used to profile miRNAs. Prediction algorithms of miRNA-mRNA interactions allowed identification of target transcripts for the analyzed miRNAs. These included VEGF, LIF, PTGS2, and IL-6R, known to be crucial components of embryo-maternal interactions in the pig. Two selected miRNAs, miR-26a and miR-125b, were tested for the presence in the extracellular vesicles isolated from uterine luminal flushings during pregnancy. Results of in vitro study demonstrated that miRNAs, such as miR-125b, can regulate expression of genes crucial for embryo development and implantation in porcine endometrial luminal epithelial cells. For the first time, expression profiles of miRNAs and related genes in porcine conceptuses and trophoblast during maternal recognition of pregnancy and embryo implantation in the pig were described. Altogether, our results indicate potential roles of these small, noncoding RNAs in the early development of embryos and embryo-maternal cross-talk during early pregnancy in the pig.

Vascular endothelial growth factor A improves quality of matured porcine oocytes and developing parthenotes

Vascular endothelial growth factor is a multipotent angiogenic factor implicated in cell survival and proliferation. The objective was to determine effects of exogenous recombinant human VEGFA (or VEGFA165) in culture media on porcine oocyte maturation and parthenote development. Adding 5 ng/mL VEGFA to the culture medium improved the maturation rate of denuded oocytes (P < 0.05), although 5, 50, or 500 ng/mL did not significantly affect nuclear maturation of oocytes. Parthenotes from oocytes cultured either in in vitro maturation or in vitro culture medium supplemented with 5 or 50 ng/mL VEGFA had an improved blastocyst rate and increased total numbers of cells (P < 0.05). Moreover, those treated with 5 ng/mL of VEGFA had a higher hatched blastocyst rate (average of 121 cells per blastocyst). All VEGFA-treated oocytes had reduced apoptotic indices (P < 0.05), except for those with a higher dose (500 ng/mL) of VEGFA which had more apoptotic cells (P < 0.05). Adding 5 ng/mL VEGFA to oocytes during the last 22 h of in vitro maturation improved (P < 0.05) blastocyst rates and total numbers of cells, with reduced apoptosis indices similar to that of long-term (44 h) culture. Furthermore, Axitinib (VEGFR inhibitor) reversed the effects of VEGFA on parthenote development (P < 0.05). Follicular fluids from medium (2-6 mm) to large (>6 mm) follicles contained 5.3 and 7.0 ng/mL vascular endothelial growth factor protein, respectively, higher (P < 0.05) than concentrations in small (<2 mm) follicles (0.4 ng/mL). Also, VEGFA and its receptor (VEGFR-2) were detected (immunohistochemistry) in growing follicles and developing blastocysts. In addition, VEGFA inhibited caspase-3 activation in matured oocytes (P < 0.05). In conclusion, this is apparently the first report that VEGFA has proliferative and cytoprotective roles in maturing porcine oocytes and parthenotes. Furthermore, an optimal VEGFA concentration promoted porcine oocyte maturation and subsequent development.

Relationship between macrophages in mouse uteri and angiogenesis in endometrium during the peri-implantation period

The objective of this study is to examine the change in macrophage numbers, inducible form of NO synthase (iNOS), and vascular endothelial growth factor (VEGF) expression both before and after embryo implantation in the uterine tissue of mice. In order to explore the mechanism of macrophages in endometrial angiogenesis, 8-week-old female mice were divided into three groups: pregnant group, pseudopregnant group (mated to male mice that had been vasectomized), and estrous group (unmated). Individuals from these three groups were sacrificed at time intervals D1.5 to D6.5. Formalin-fixed paraffin-embedded tissue was used for immunocytochemical localization of Mφ, iNOS, and VEGF utilizing standard methodology. The proportion of macrophages in the peripheral blood was determined by flow cytometry, and the relationship between macrophage, iNOS, and VEGF expression was analyzed. The proportion of peripheral blood macrophages in the pregnancy group was significantly higher than that in the other groups. The results of immunohistochemistry determined that the macrophages exhibited changes in both numbers and distribution. The number of macrophages in the endometrium of the pregnancy and pseudopregnancy groups was significantly higher than that in the control (estrous) group. In the pregnancy group, macrophage numbers dramatically decreased and gradually transferred to the perimetrium on D4.5. Immunostaining revealed strong staining in the pregnancy group and weaker staining in the pseudopregnant and control groups for both iNOS and VEGF. There was strong, dense immunostaining at the implantation site for both iNOS and VEGF, whereas light immunostaining was seen in interimplantation tissues on D5.5 to D6.5. In the pregnant group, peripheral blood and uterine macrophage proportions were negatively correlated, whereas the amount of macrophages, iNOS, and VEGF expression in the endometrium were positively correlated. The expression of iNOS and VEGF in the endometrium also displayed a strong positive correlation. In conclusion, during embryo implantation, macrophages levels decreased in the uterus, whereas the number of peripheral macrophages increased, suggesting that macrophages may migrate into the peripheral blood and uterus to adapt for pregnancy. Additionally, an increase in the expression of iNOS and VEGF was observed during the implantation window, implying that iNOS and VEGF may play an important role in promoting embryo implantation. The positive correlation between macrophages, iNOS, and VEGF in the implanting uterus implied that macrophages might regulate iNOS and VEGF during the implantation process.

Effect of antiprogesterone RU486 on VEGF expression and blood vessel remodeling on ovarian follicles before ovulation

Background

The success of ovarian follicle growth and ovulation is strictly related to the development of an adequate blood vessel network required to sustain the proliferative and endocrine functions of the follicular cells. Even if the Vascular Endothelial Growth Factor (VEGF) drives angiogenesis before ovulation, the local role exerted by Progesterone (P₄) remains to be clarified, in particular when its concentration rapidly increases before ovulation.

Aim

This in vivo study was designed to clarify the effect promoted by a P₄ receptor antagonist, RU486, on VEGF expression and follicular angiogenesis before ovulation, in particular, during the transition from pre to periovulatory follicles induced by human Chorionic Gonadotropins (hCG) administration.

Material and Methods

Preovulatory follicle growth and ovulation were pharmacologically induced in prepubertal gilts by combining equine Chorionic Gonadotropins (eCG) and hCG used in the presence or absence of RU486. The effects on VEGF expression were analyzed using biochemical and immunohistochemical studies, either on granulosa or on theca layers of follicles isolated few hours before ovulation. This angiogenic factor was also correlated to follicular morphology and to blood vessels architecture.

Results and Conclusions

VEGF production, blood vessel network and follicle remodeling were impaired by RU486 treatment, even if the cause-effect correlation remains to be clarified. The P₄ antagonist strongly down-regulated theca VEGF expression, thus, preventing most of the angiogenic follicle response induced by hCG. RU486-treated follicles displayed a reduced vascular area, a lower rate of endothelial cell proliferation and a reduced recruitment of perivascular mural cells. These data provide important insights on the biological role of RU486 and, indirectly, on steroid hormones during periovulatory follicular phase. In addition, an in vivo model is proposed to evaluate how periovulatory follicular angiogenesis may affect the functionality of the corpus luteum (CL) and the success of pregnancy.

Stimulatory Effect of Vascular Endothelial Growth Factor on Proliferation and Migration of Porcine Trophectoderm Cells and Their Regulation by the Phosphatidylinositol-3-Kinase-AKT and Mitogen-Activated Protein Kinase Cell Signaling Pathways

Vascular endothelial growth factor (VEGF), a potent stimulator for angiogenesis, is likely to regulate implantation by stimulating endometrial angiogenesis and vascular permeability. In addition to known angiogenetic effects, VEGF has been suggested to participate in development of the early embryo as a mediator of fetal-maternal dialogue. Current studies have determined VEGF in terms of its role in endometrial vascular events, but VEGF-induced effects on the peri-implantation conceptus (embryo and extraembryonic membranes) remains unknown. In the present study, endometrial VEGF, VEGF receptor-1 (VEGFR-1), and VEGF receptor-2 (VEGFR-2) mRNAs increased significantly during the peri-implantation period of pregnancy as compared to the estrous cycle. Expression of VEGF, VEGFR-1, and VEGFR-2 mRNAs was abundant in endometrial luminal and glandular epithelia, endothelial blood vessels, and scattered cells in the stroma and conceptus trophectoderm. In addition, porcine trophectoderm (pTr) cells treated with VEGF exhibited increased abundance of phosphorylated (p)-AKT1, p-ERK1/2, p-p70RSK, p-RPS6, and p-4EBP1 in a time-dependent manner. The addition of U0126, an inhibitor of ERK1/2, inhibited VEGF-induced ERK1/2 phosphorylation, but AKT1 phosphorylation was not affected. The addition of LY294002, a PI3K inhibitor, decreased VEGF-induced phosphorylation of ERK1/2 and AKT1. Furthermore, VEGF significantly stimulated proliferation and migration of pTr cells, but these effects were blocked by SB203580, U0126, rapamycin, and LY294002, which inhibit p38 MAPK, ERK1/2, mTOR, and PI3K, respectively. These results suggest that VEGF is critical to successful growth and development of pTr during early pregnancy and that VEGF-induced stimulatory effect is coordinately regulated by multiple cell signaling pathways, including PI3K-AKT1 and MAPK signaling pathways.

The novel effect of hCG administration on luteal function maintenance during the estrous cycle/pregnancy and early embryo development in the pig

Two independent experiments were performed on cyclic (Experiment I) and pregnant (Experiment II) gilts to examine the effect of human Chorionic Gonadotropin (hCG) administration on day 12 of the estrous cycle/pregnancy on ovarian and endometrial secretory function. Animals were divided into hCG Group (injection of 750 IU hCG) and Control Group (injection of saline). In Experiment I, the prolonged lifespan of the corpus luteum (CL), extended progesterone (P4) production (P < 0.05) and delayed luteolysis were found. In hCG Group increased ratio of PGE2:PGFM during 12 hrs period on day 15 (P < 0.05) of the estrous cycle was observed. In both experiments, higher concentrations of E2 in hCG treated gilts (P < 0.05) on days 14-15 of the estrous cycle/pregnancy were found. In Experiment II, hCG injection did not affect P4, PGE2 and PGFM concentrations in blood plasma, but reduced the number of resorbed embryos on day 30 of pregnancy. In the pregnant hCG treated gilts the immunostaining against von Willebrand Factor (vWF) demonstrated an enhanced (P < 0.05) angiogenesis in CLs and endometrium. Furthermore, the flow cytometry revealed an increased (P < 0.05) viability of cells in CLs of hCG Group. An augmented expression of Steroidogenic Acute Regulatory Protein (STAR; P < 0.05) and LH/hCG receptor mRNA (P < 0.05) in CLs of hCG Group were observed, but an elevated concentration of protein was confirmed only for STAR (P < 0.05). Our studies revealed, for the first time, that administration of hCG affects PGE2:PGFM ratio during the estrous cycle as well as the development of conceptuses through enhanced angiogenesis and decreased luteal apoptosis in early pregnant pigs.

The Akt/mTor signaling cascade is modified during placentation in the porcine uterine tissue

Recently we showed that essential components for the initiation of protein synthesis, namely the eukaryotic initiation factor 4E (eIF4E, mRNA-cap-binding protein) and its repressors 4E-BP1 as well as 4E-BP2, are proteolytically processed in the porcine endometrium during implantation. Here, the situation during placentation was compared with ovariectomized (OVX) animals and animals on pregnancy day 1 (PD1). Furthermore, the research was extended to factors which phosphorylate eIF4E and 4E-BPs and regulate their activities. These are the protein kinase B/mammalian target of rapamycin kinase (Akt/mTor) with the regulators Raptor and Rictor as well as the mitogen activated protein kinases (MAPKs): extra cellular-signal regulated kinase 1 and 2 (ERK1 and ERK2). Striking differences in the placentation site (PS) and the areas aside from PS (peri-PS) were observed. EIF4E and 4E-BP2 truncation as well as 4E-BP1 degradation took place in the endometrium of the peri-PS on PD24. Accompanied by a fragmentation of Akt/mTor, no expression of Rictor was observed, whereas the abundance of Raptor was not altered. On the contrary, MAPKs expression and phosphorylation remained almost stable in the peri-PS. In conclusion, the results indicated that on PD24 the translational regulation was shifted to 4E-BP2 control. Furthermore, the Akt/mTor signaling cascade seemed to be down regulated which suggest reduced phosphorylation of 4E-BP2. Whereas Akt was proteolyzed, the observed mTor fragments represented most likely splicing variants. The results indicate that translational control of gene expression is an important feature in the porcine endometrium during early pregnancy.

Effect of conceptus on expression of prostaglandin F2α receptor in the porcine endometrium

Increased synthesis of prostaglandin F(2α) (PGF(2α)) in the endometrium and conceptus during the implantation period results in elevated concentration of PGF(2α) in the uterine lumen in pregnant gilts. PGF(2α) exerts its effects through PGF(2α) receptor (PTGFR), a G-protein-coupled receptor. However, besides studies concerning the function of PTGFR in endometrial abnormalities, the role of PTGFR in the endometrium during early pregnancy has not been elucidated. Therefore, the aim of this study was: (1) to evaluate the profile of PTGFR gene and protein expression in the porcine endometrium during early pregnancy and the estrous cycle; (2) to determine if the effect of conceptus on PTGFR expression is dependent on type of endometrial cells-luminal epithelial (LE) or stromal (ST) cells; and (3) to elucidate if the putative effect of conceptus on endometrial PTGFR expression is mediated by estrogen receptor. We evaluated the expression pattern of PTGFR gene and protein in the endometrium during day 9, 11, 12, 15, and 18 of the estrous cycle and pregnancy (N = 4-6 per group). The expression of PTGFR mRNA was greater on day 18 of pregnancy and the estrous cycle (vs. days 9-15 of the estrous cycle and pregnancy, P < 0.05). Expression of PTGFR protein was approximately 10-fold upregulated in the endometrium on day 15 of pregnancy when compared with day 15 of the estrous cycle (P < 0.01). Endometrial expression of PTGFR protein increased from day 12 to 18 of pregnancy (P < 0.05). PTGFR mRNA was expressed in LE and ST cells. In a subsequent experiment, we used a coculture model in which LE cells were cultured on collagen-coated inserts placed in wells plated with ST cells. Day 11 or 15 conceptus-exposed medium (CEM) elevated expression of PTGFR mRNA (2- and 1.5-fold, respectively, P < 0.05) in LE cells cocultured with ST cells. CEM did not have an effect on PTGFR mRNA expression in ST cells. The 11-day CEM-induced increase of PTGFR mRNA was abolished by incubation of LE cells in the presence of the estrogen receptor antagonist (ICI-182,780; P < 0.01). Summarizing, the conceptus upregulated expression of PTGFR in the endometrium during the implantation period. Moreover, this study indicates that expression of PTGFR gene was elevated in LE cells of endometrium by embryonic signal of estradiol. Our results suggest para- and autocrine effects of PGF(2α) through its receptor PTGFR in the porcine endometrium, especially in luminal epithelium which is in direct contact with the conceptus during the implantation period.

Does seminal plasma affect angiogenesis in the porcine oviduct?

In the present study we examined the effect of seminal plasma (SP) on angiogenesis in the porcine oviduct. Gene expressions of vascular endothelial growth factor (VEGF) and its two receptors (Flt-1: fms-like tyrosine kinase and Flk-1/KDR: fetal liver kinase-1/kinase insert domain-containing receptor) as well as fibroblast growth factors (FGF-1 and 2) and von Willenbrand factor (VWF) were determined in the oviduct of SP-treated and control (PBS-treated) gilts. Moreover, vascular density (VD) indicated by endothelial cell area immunolocalized by VWF staining, was assessed in the oviducts. Real-time PCR revealed significantly higher expression of FGF-2 and VWF on day 1 (p<0.05) after SP administration in comparison to control animals. In contrast, Flt-1 mRNA level on day 1 was lower in SP-treated gilts compared to controls (p<0.05). In the examined oviductal sections, VD did not differ between control and SP-treated animals. However, in SP-treated animals VD was higher on day 5 than on day 1 (p<0.05) or 3 (p<0.01). SP had no significant effect on VEGF, Flk-1/KDR and FGF-1 mRNA expression. In conclusion, our results suggest that SP affects the vascular network by changing the expression of factors contributing to angiogenesis.

Conceptus-mediated endometrial vascular changes during early pregnancy in mares: an anatomic, histomorphometric, and vascular endothelial growth factor receptor system immunolocalization and gene expression study

This work examined how the conceptus modulates endometrial tissue remodeling and vascular development prior to implantation in mares. A macroscopic uterine examination was completed at day 21 of pregnancy.In situmorphology revealed that the endometrium involved in encroachment is restricted to the dorsal endometrium immediately overlying the yolk sac. The amount of stromal area occupied by blood vessels and the number of endometrial glands were increased during early pregnancy. Endometrial histomorphometry as well as the endometrial mRNA abundance and immunolocalization of VEGF, VEGFR1, VEGFR2, and Ki-67 was completed at days 14 and 21 of pregnancy, at day 10 of the estrous cycle, and during estrus. No obvious differences in VEGF and VEGFR1 protein localization were detected between pregnant and cycling mares but differential staining pattern for VEGFR2 and Ki-67 was observed. VEGFR2 localized to luminal and glandular epithelium of pregnant mares, while luminal epithelium was negative in cycling mares. Ki-67 staining was weak during the luteal phase but exhibited prominent luminal epithelium staining during estrus. In pregnant mares, all endometrial layers were Ki-67 positive. Quantitative RT-PCR revealed a greater abundance ofVEGFmRNA during pregnancy.VEGFR2transcript abundance was greatest in pregnant mares on day 21. This study supports the concept that the conceptus plays an active role in directing vasculogenesis within the uterus and thereby establishing hemotrophic nutrition that supports pregnancy after implantation.

The expression of vascular endothelial growth factor and its receptors (flt1/fms, flk1/KDR, flt4) and vascular endothelial growth inhibitor in the bovine uterus during the sexual cycle and their correlation with serum sex steroids

The present study was conducted to demonstrate of the immunohistochemical localization of vascular endothelial growth factor (VEGF) and its receptors (flt1/fms, flk1/KDR and flt4) as well as vascular endothelial growth inhibitor (VEGI) and to determine the correlation of VEGF and its receptors and VEGI with serum sex steroids (estrogen and progesterone) in the bovine uterus during the sexual cycle. The stage of the estrous cycle in 30 Holstein cattle was assessed based on the gross and histological appearance of the ovaries and uterus and on blood steroid hormone levels. Tissue samples obtained from the uterus were fixed in 10% formaldehyde for routine histological processing. During both follicular and luteal phases, positive cytoplasmic and membrane staining was achieved for VEGF and its receptors (flt1/fms, flk1/KDR and flt4) as well as VEGI in the luminal and glandular epithelial cells, the connective tissue and smooth muscle cells, and the vascular endothelial cells and smooth muscle cells in the uterus. The intensity, proportional and total scores determined for VEGF and its receptors (flt1/fms and flt4) as well as VEGI were greater in the luminal and glandular epithelial cells compared to the connective tissue and smooth muscle cells (P < 0.05). Furthermore, the number and intensity of the flk1/KDR positive cells were greater among the connective tissue cells compared to the luminal and glandular epithelial cells (P < 0.05). As a result, it was determined that the expression of VEGF and its receptors as well as VEGI in the bovine uterus during the follicular and luteal phases varied with different cell types. This suggests that depending on the stage of the sexual cycle, these factors may mediate the establishment of an appropriate environment for the nutritional supply and implantation of the embryo primarily due to the stimulation of angiogenesis but also through the increase in the secretory activity of the epithelial cells in the uterus. Furthermore, this indicates that ovarian steroid hormones play a significant role in regulating the expression of VEGF and its receptors as well as VEGI.

Expression of the vascular endothelial growth factor (VEGF-A) and its receptors in the umbilical cord in the course of pregnancy in the pig

The umbilical cord (UC) and the placenta are important organs through which respiratory gases, nutrients, wastes and biologically active substances are exchanged between the maternal and the foetal system. A rapid placental vascularization observed in the second half of pig pregnancy is positively correlated with the mRNA expression of the vascular endothelial growth factor (VEGF). Based on these findings, we hypothesized that VEGF may have a stimulatory effect in the dynamically growing UC. To further understand the role of the VEGF-VEGFR system during UC development, mRNA and protein expression as well as the cellular localization of VEGF-A, VEGFR-1 and VEGFR-2 in UC were examined on days 40, 60, 75 and 90 of pregnancy and after physiological delivery in the pig (day 114 of pregnancy). Real Time RT-PCR analysis showed an increase in the mRNA levels of VEGF120 and VEGF164 from day 90 of pregnancy. VEGFR-1 mRNA expression was significantly increased on day 75 of pregnancy. No significant changes in VEGFR-2 mRNA expression were detected. In turn, western blot analysis revealed an increase in VEGF-A protein expression on day 40, compared to the later days of pregnancy. A rapid increase in the VEGFR-1 protein level was noted on day 75 and 90 of gestation. No significant changes in VEGFR-2 protein expression were detected on any of the analysed days of pregnancy. Immunohistochemical staining enabled detection of VEGF-VEGFR system, in endothelial and tunica media cells of the umbilical vessels and in allantoic duct and amniotic epithelium on all analysed days of pregnancy. Positive reactions for VEGF-A and VEGFR-1, but not VEGFR-2, were also observed in myofibroblasts. In conclusion, this data shows that members of the VEGF-VEGFR system are temporally and spatially well localized for playing key roles during umbilical cord formation and its intensive growth observed after day 75 of pregnancy.

Seminal plasma affects prostaglandin synthesis in the porcine oviduct

Seminal fluids introduced to the female reproductive tract at mating can affect subsequent events, such as ovulation, fertilization, conception, and pregnancy. Bioactive molecules present in seminal plasma can modify the cellular composition, structure, and function of local tissues and of tissues distal to the tract. The oviduct plays a decisive role in reproduction providing a beneficial milieu for gamete maturation, fertilization, and early embryonic development. Therefore we have investigated whether intrauterine infusion of seminal plasma can modulate prostaglandin (PG) synthesis in the porcine oviduct through regulation of gene and protein expression of enzymes of prostaglandin synthesis pathway. Among several enzymes involved in the prostaglandin synthesis pathway tested in the present study PGF(2α) synthase (PTGFS) and prostaglandin 9-ketoreductase (CBR1), which convert PGE(2) to PGF(2α), expression were significantly down-regulated in the oviducts on Day 1 after seminal plasma infusion into the uterine horns. The effects of the treatment were transient and by Day 5 levels of PTGFS and CBR1 were comparable in seminal plasma-treated and control animals. Additionally, increased PGE(2) to PGF(2α) and PGFM to PGF(2α) ratios in the oviductal tissues were indicated. Our results clearly demonstrate that seminal plasma affects prostaglandin synthesis in the porcine oviduct. Altered PTGFS and CBR1 expression in consequence changed PGE(2) to PGF(2α) and PGFM to PGF(2α) ratios in the porcine oviduct.

Vasculogenesis and angiogenesis in the endometrium during menstrual cycle and implantation

Blood vessels develop via two subsequent processes, vasculogenesis and angiogenesis, both being of crucial importance during menstrual cycle and implantation. These processes are also involved in the development of the fetal and placental vasculatures. During vasculogenesis, formation of the earliest primitive capillaries is achieved by in situ differentiation of hemangiogenic stem cells that are derived from pluripotent mesenchymal cells. The subsequent process, angiogenesis, is characterized by development of new vessels from already existing vessels, and is a well coordinated process initiated by stimulation of various growth factors. Vasculogenesis and angiogenesis are important and complex processes involving extensive interplay between cells and growth factors. The development, maturation and maintenance of the vascular network are necessary for successful hemochorial placentation as well as normal embryonic development and growth. In this review, we outline the basic mechanisms of vasculogenesis and angiogenesis in the endometrium during the menstrual cycle and different stages of implantation, and consider how this data can be applied to human pregnancy. Recent studies have shown that during the initiation steps of implantation, angiogenic factors trigger vasculogenesis and angiogenesis. Different inducers and stimulators affect angiogenesis and vasculogenesis by directly or indirectly stimulating proliferation, differentiation and migration of endothelial or respective precursor cells. As a conclusion, understanding the mechanisms of angiogenesis and the roles of angiogenic factors during the menstrual cycle and implantation may provide new insights and possible approaches for embryo implantation and healthy pregnancy.

Bibliography. Current world literature

This bibliography is compiled by clinicians from the journals listed at the end of this publication. It is based on literature entered into our database between 1 February 2008 and 31 January 2009 (articles are generally added to the database about two and a half months after publication). In addition, the bibliography contains every paper annotated by reviewers; these references were obtained from a variety of bibliographic databases and published between the beginning of the review period and the time of going to press. The bibliography has been grouped into topics that relate to the reviews in this issue.

Expression of VEGF-receptor system in conceptus during peri-implantation period and endometrial and luteal expression of soluble VEGFR-1 in the pig

In view of the importance of vascular events observed during gestation, it was hypothesized that the VEGF-receptor system plays a critical role during early pregnancy and maternal recognition of pregnancy in pigs. This hypothesis was tested by examining the expression of the VEGF-receptor system in the porcine conceptus. Additionally, the endometrium, corpus luteum (CL) and embryos were studied for the expression of soluble VEGF receptor 1 (sVEGFR-1), the strong endogenous antagonist of VEGF. The expression patterns show that VEGF164 mRNA levels increase gradually in line with conceptus development, whereas VEGF120 and VEGFR-2 remain unchanged during the peri-implantation period. Interestingly, elevated VEGFR-1 expression was observed in conceptuses on days 15-16 of gestation (P<0.05). Comparison of the endometrial sVEGFR-1 mRNA expression revealed up-regulation on days 12 and 15-16 of pregnancy (P<0.01 and P<0.05, respectively). Furthermore, increased sVEGFR-1 levels were observed on day 12 of the estrous cycle in the CL (P<0.05). Concluding, it seems that conceptus-derived VEGF164 plays crucial role in peri-implantation vascular events in pigs. These results support a potential role of VEGFR-1 in the proper growth and development of porcine conceptus during pregnancy. Moreover, expression patterns of sVEGFR-1 in the endometrium of pregnant pigs suggest that it may participate in vascular remodeling important for successful implantation. Finally, luteal sVEGFR-1 may be involved in the maintenance of CL function whenever pregnancy occurs in pigs.

Assessment of VEGF-receptor system expression in the porcine endometrial stromal cells in response to insulin-like growth factor-I, relaxin, oxytocin and prostaglandin E2

Several factors participate in regulation of growth and development as well as angiogenesis of the uterus during pregnancy, and hence little is known about the role of hormonal regulation of vascular endothelial growth factor (VEGF)-receptor system expression. This study has examined the effect of insulin-like growth factor-I (IGF-I), relaxin (RLX), oxytocin (OT) and prostaglandin (PG) E(2), on VEGF secretion and VEGF-receptor system mRNA expression in the porcine endometrial stromal cells. IGF-I and RLX were identified as the most effective inducers of VEGF secretion and mRNA expression. Although PGE(2) stimulated VEGF secretion and VEGF164 mRNA expression, OT inhibited both secretion and mRNA expression of VEGF. When tested for VEGF receptors (R), all factors failed to affect their mRNA expression. Media conditioned by stromal cells collected after IGF-I and RLX treatment significantly increased endothelial cell proliferation and this effect was blocked by soluble VEGFR-1. These data suggest that during early pregnancy IGF-I, RLX and PGE(2) can affect VEGF expression in the endometrium and therefore may support uterine and embryo development, implantation and pregnancy.