Vascular Endothelial (VEGF) and Epithelial Growth Factor (EGF) as Well as Platelet-Activating Factor (PAF) and Receptors are Expressed in the Early Pregnant Canine Uterus

The effect of folic acid supplementation and folate deficiency on embryo implantation

Implantation is a critical stage of pregnancy, which occurs in a short period of interaction between the receptive endometrium and the embryo. Folic acid (FA) is a synthetic derivative of folate and is recommended as a pre-conceptional supplement. However, the impact of different doses of FA supplementation and folate deficiency during the early stages of pregnancy requires further investigation. The aim of this study was to investigate the possible effects of FA supplementation and folate deficiency on expression of Estrogen Receptor Alpha (ER-α), Vascular Endothelial Growth Factor-A (VEGFA), and Integrin alpha V and beta3 (Integrin αVβ3). A total of 32, 6-8-week old Wistar albino rats were divided into four groups of control, folate-deficiency, low-dose, and high-dose FA supplement groups. After five weeks of FA supplementation and folate deficiency model formation, mated rats were sacrificed on the 5th gestational day (GD), and implantation sites were collected. The expression of ER- α, VEGFA, and Integrin αVβ3 in the implantation sites were examined with immunohistochemistry and real-time PCR. The results revealed that the mRNA levels of ESR1, VEGFA, and Integrin αV and β3 were significantly increased in the high-dose FA group and significantly decreased in the folate deficiency group compared to the control group (p < 0.05). Based on these results, it can be concluded that FA supplementation before pregnancy has positive effects on the maintenance of pregnancy, and folate deficiency may lead to implantation disorders.

Selected Uterine Immune Events Associated With the Establishment of Pregnancy in the Dog

In the dog, implantation takes place at approximately 17 days of embryonal life and, while exposed to relatively high circulating progesterone concentrations, embryos presence is required for the formation of decidua. Furthermore, a balance between pro- and anti-inflammatory responses in conceptus-maternal communication is crucial for the onset of pregnancy. Strikingly, the understanding of such immune mechanisms in canine reproduction is still elusive. Here, canine uterine samples from pre-implantation (day 10-12, E+) and corresponding non-pregnant controls (E-), implantation (day 17, Imp) and post-implantation (day 18-25, Post-Imp) stages of pregnancy were used to investigate the expression and localization of several immune-related factors. The most important findings indicate increased availability of CD4, MHCII, NCR1, IDO1, AIF1, CD25, CCR7, and IL6 in response to embryo presence (E+), while FoxP3 and CCL3 were more abundant in E- samples. Implantation was characterized by upregulated levels of FoxP3, IL12a, ENG, and CDH1, whereas CD4, CCR7, IL8, and -10 were less represented. Following implantation, decreased transcript levels of TNFR1, MHCII, NCR1, TLR4, CD206, FoxP3, and IL12a were observed concomitantly with the highest expression of IL6 and IL1β. MHCII, CD86, CD206, CD163, TNFα, IDO1, and AIF1 were immunolocalized in macrophages, CD4 and Nkp46 in lymphocytes, and some signals of IDO1, AIF1, and TNF-receptors could also be identified in endothelial cells and/or uterine glands. Cumulatively, new insights regarding uterine immunity in the peri-implantation period are provided, with apparent moderated pro-inflammatory signals prevailing during pre-implantation, while implantation and early trophoblast invasion appear to be associated with immunomodulatory and rather anti-inflammatory conditions.

Endometrial receptivity and embryo implantation in carnivores-commonalities and differences with other mammalian species

Endometrial receptivity and embryo implantation processes are a major point of pregnancy failure in many mammalian species, including humans. Although reproductive biology in many carnivore species remains enigmatic, the few that have been studied so far are invaluable comparative models. The goals of this review are to (1) summarize current data on the mechanisms involved in uterine receptivity and embryo implantation in carnivores, including commonalities and differences with other mammalian species and (2) identify research priorities to better understand a key phenomenon in a critical group of mammals. Besides unique reproductive traits in some carnivores (induced vs. spontaneous ovulation in cats, ovulation at the germinal vesicle stage in dogs), preimplantation embryo development is comparable with other orders. However, the timing of implantation varies, especially in species having an embryonic diapause. Mechanisms involved in endometrial receptivity and decidualization still remain to be fully understood, but specific markers have already been identified. Importantly, the use of endogenous hormones to control the ovarian activity may impact endometrial receptivity and subsequent embryo implantation. Next, research efforts should take advantage of advanced technologies to further study embryo implantation in carnivores and to provide more relevant models to reproductive medicine or for the conservation of rare and endangered species.

Canine conceptus-maternal communication during maintenance and termination of pregnancy, including the role of species-specific decidualization

Among domestic animal species, the reproductive biology of the dog belongs to the most peculiar. This includes the conceptus-maternal communication and endocrine mechanisms involved in maintenance of pregnancy. Dogs fully depend on luteal progesterone (P4) throughout pregnancy, with similar steroid secretion patterns in pregnant and non-pregnant bitches until prepartum luteolysis. Thus, dogs lack the classical recognition of pregnancy. The luteal P4 is the most important hormone regulating the onset and maintenance of pregnancy in previously estrogenized bitches. Although the canine uterus is exposed to high P4 levels, decidualization is not spontaneous but induced by the presence of embryos. Following implantation, decidualization continues, associated with development of the invasive endotheliochorial placenta, leading to establishment of maternal decidual cells expressing the nuclear P4 receptor (PGR). Consequently, although not producing steroids, the canine placenta remains highly sensitive to circulating ovarian steroids. The placental conceptus-maternal communication is responsible for the maintenance of pregnancy, with functional withdrawal of PGR evoking a luteolytic cascade with prepartum PGF2α release. The fetal trophoblast is the major source of prepartum placental prostaglandins. This conceptus-maternal communication is unique to the dog and has clinical implications. Due to luteal steroids, there is no prepartum estradiol increase. Elevated cortisol levels are observed irregularly. This emphasizes the unique character of canine reproductive physiology and the challenges in transferring translational research to the dog. Further research is needed for better understanding of canine reproduction and improving clinical protocols, including the latest results obtained from applying modern laboratory technologies such as the transcriptomic approach.

The Female Response to Seminal Fluid

Seminal fluid is often assumed to have just one function in mammalian reproduction, delivering sperm to fertilize oocytes. But seminal fluid also transmits signaling agents that interact with female reproductive tissues to facilitate conception and .pregnancy. Upon seminal fluid contact, female tissues initiate a controlled inflammatory response that affects several aspects of reproductive function to ultimately maximize the chances of a male producing healthy offspring. This effect is best characterized in mice, where the female response involves several steps. Initially, seminal fluid factors cause leukocytes to infiltrate the female reproductive tract, and to selectively target and eliminate excess sperm. Other signals stimulate ovulation, induce an altered transcriptional program in female tract tissues that modulates embryo developmental programming, and initiate immune adaptations to promote receptivity to implantation and placental development. A key result is expansion of the pool of regulatory T cells that assist implantation by suppressing inflammation, mediating tolerance to male transplantation antigens, and promoting uterine vascular adaptation and placental development. Principal signaling agents in seminal fluid include prostaglandins and transforming growth factor-β. The balance of male signals affects the nature of the female response, providing a mechanism of ‟cryptic female choiceˮ that influences female reproductive investment. Male-female seminal fluid signaling is evident in all mammalian species investigated including human, and effects of seminal fluid in invertebrates indicate evolutionarily conserved mechanisms. Understanding the female response to seminal fluid will shed new light on infertility and pregnancy disorders and is critical to defining how events at conception influence offspring health.

Morphological, histological and molecular investigations on canine uterine tissue after ovariectomy

In the present study, we investigated the course of atrophy in canine uterine tissue and the expression of estrogen receptors (ER) and progesterone receptors (PR) within 6 months after ovariectomy (OE). In nine primipar bitches of different breeds, bilateral OE and removal of one horn was performed. Six months after surgery, the remaining uterine tissue was removed. The tissue was examined for signs of inflammation and proliferation, and for expression of ER, PR and Ki67 by means of immunohistochemistry (IHC); furthermore transcription of vascular endothelial growth factor (VEGF), transforming growth factor-ß (TGF-ß), epithelial growth factor (EGF), platelet activating factor (PAF), tumor necrosis factor α (TNFα), and their specific receptors was determined by means of RT-qPCR. Serum concentrations of estrogen and progesterone were measured immediately before the first and second operation. Six month after OE, no inflammation was seen in any uterine tissue, the thickness of the stump was decreased in most bitches. Protein expression of Ki67 revealed high individual differences after the second operation. Concentration of both hormones was not significantly changed, the estrogen concentration always revealed high individual differences. The expression of ER was significantly decreased in stromal and smooth muscle cells of the uterine tissue (p < 0.01), and the expression of PR in stromal cells only (p < 0.05). The gene expression of growth factors did not change significantly between first and second operation. We conclude that complete atrophy did not occur within 6 months after OE, instead, a high percentage of uterine cells still expressed ER and PR, rendering the stump susceptible to hormone treatments.

Decidualization of the canine uterus: From early until late gestational in vivo morphological observations, and functional characterization of immortalized canine uterine stromal cell lines

The apparent lack of classical mechanisms for maternal recognition of pregnancy is one of the most intriguing features of canine reproduction. Consequently, similar levels of circulating luteal steroids are observed in pregnant and non-pregnant dogs. However, the early pre-implantation canine embryo locally modulates uterine responses to its presence, facilitating the successful onset of pregnancy. As a part of this interaction, the canine uterus undergoes a species-specific decidualization. Maternal stroma-derived decidual cells develop, the only cells of the canine placenta expressing progesterone receptor (PGR). There exists an acute need for an in vitro stable cell line model for canine decidualization. Therefore, herein our goal was to establish, immortalize and characterize such a cell line. We immortalized three monolayer dog uterine stromal (DUS) cell lines by stably transfecting them with SV40Tag oncogene. Cells retained their mesenchymal character for over 30 passages, as evidenced by VIMENTIN staining. Genomic incorporation of the SV40Tag protein was confirmed by immunofluorescence and Western blot analyses. Cells submitted to a classical in vitro decidualization protocol (N6,2'-O-dibutyryladenosine-3',5'-cyclic monophosphate) revealed upregulated gene levels of selected major decidualization markers (e.g. PRLR, PGR, IGF1, PTGES). Additionally, the basic decidualization capability of PGE2 was demonstrated, revealing increased levels of, for example, PGR and PRLR gene expression, thereby implying its involvement in the progesterone-dependent decidualization in the canine uterus. In summary, our in vitro model with immortalized DUS cell line could serve as an ideal and unique model to study the underlying molecular and endocrine mechanisms of canine decidualization.

Differential Spatiotemporal Patterns of Galectin Expression are a Hallmark of Endotheliochorial Placentation

PROBLEM

Galectins influence the progress of pregnancy by regulating key processes associated with embryo-maternal cross talk, including angiogenesis and placentation. Galectin family members exert multiple roles in the context of hemochorial and epitheliochorial placentation; however, the galectin prolife in endotheliochorial placenta remains to be investigated.

METHOD OF STUDY

Here, we used immunohistochemistry to analyze galectin (gal)-1, gal-3 and gal-9 expression during early and late endotheliochorial placentation in two different species (dogs and cats).

RESULTS

We found that during early feline gestation, all three galectin members were more strongly expressed on trophoblast and maternal vessels compared to the decidua. This was accompanied by an overall decrease of gal-1, gal-3 and gal-9 expressions in late feline gestation. In canine early pregnancy, we observed that gal-1 and gal-9 were expressed strongly in cytotrophoblast (CTB) cells compared to gal-3, and no galectin expression was observed in syncytiotrophoblast (STB) cells. Progression of canine gestation was accompanied by increased gal-1 and gal-3 expressions on STB cells, whereas gal-9 expression remained similar in CTB and STB.

CONCLUSION

These data suggest that both the maternal and fetal compartments are characterized by a spatiotemporal regulation of galectin expression during endotheliochorial placentation. This strongly suggests the involvement of the galectin family in important developmental processes during gestation including immunemodulation, trophoblast invasion and angiogenesis. A conserved functional role for galectins during mammalian placental development emerges from these studies.

Expression and localization of vascular endothelial growth factor A (VEGFA) and its two receptors (VEGFR1/FLT1 and VEGFR2/FLK1/KDR) in the canine corpus luteum and utero-placental compartments during pregnancy and at normal and induced parturition

VEGFA is one of the most potent known inducers of angiogenesis. However, the function of angiogenic factors in the canine corpus luteum (CL) of pregnancy and in the pregnant uterus and placenta has not yet been elucidated. Therefore, here we investigated the expression and localization of VEGFA and its receptors (VEGFR1/FLT1 and VEGFR2/FLK1/KDR) in the canine CL and utero-placental compartments (ut-pl) throughout pregnancy until prepartum luteolysis. Antigestagen-mediated effects on expression of VEGF system in ut-pl were elucidated in mid-pregnant dogs. While displaying high individual variation, the luteal VEGFA was elevated during pre-implantation and post-implantation, followed by a decrease during mid-gestation, which was more pronounced at the mRNA level, and showed constant expression afterwards. Within the uterus, it increased following implantation and during mid-gestation in ut-pl compartments, but was downregulated at prepartum luteolysis. Luteal VEGFR1 expression resembled that of VEGFA; VEGFR2 remained unaffected throughout pregnancy. In ut-pl compartments, both receptors increased gradually towards mid-gestation; a prepartum decrease was observed for VEGFR1. Antigestagen-treatment resulted in decreased expression of ut-pl VEGFR1. In the CL, VEGFA stained in luteal cells. Uterine signals of VEGFA and its two receptors were observed in epithelial and vascular compartments, and in myometrium. In placental labyrinth, additionally, trophoblast stained positively. Luteal VEGFR1 was localized to the luteal cells and tunica media of blood vessels, whereas VEGFR2 stained only in capillary endothelial cells. The upregulation of luteal and the ut-pl VEGF system during early gestational stages supports the increased vascularization rate during this time. The diminishing effects of the prepartum endocrine milieu on VEGFA function seem to be more pronounced in the ut-pl units.

Expression of hypoxia-inducible factors and vascular endothelial growth factor during pregnancy in the feline uterus

Hypoxia-inducible factors (HIFs) and vascular endothelial growth factor (VEGF) have critical roles during the development of the fetomaternal unit. The HIFs regulate placentation and vascularization by stimulation of VEGF gene expression. This study aimed to investigate the expression profiles of HIF gene family and VEGF in the cat uterus during pregnancy. Tissue samples of the whole uterine wall were collected after ovariohysterectomy and allocated to the following groups: embryo positive (group 1 [G1], n = 7, 7 days after mating), early pregnancy (group 2 [G2], n = 7, 20 days after mating), mid-pregnancy (group 3 [G3], n = 7, 24 days after mating), late pregnancy (group 4 [G4], n = 7, 30-45 days after mating), and oocyte positive groups (group 5 [G5], n = 7, 7 days after induction of ovulation with GnRH analog). Relative mRNA levels were determined by real-time polymerase chain reaction. As housekeeping gene, glyceraldehyde-3-phosphate dehydrogenase was used. The relative gene expression of HIF1A in G5 was found to be significantly higher than that of other groups (G1, G2, G3, and G4) (P < 0.05). In addition, the expression of HIF2A in G5 was higher than that of G1 and HIF2A gene expression at placentation sites of G4 was higher than in G1, G2, and G3 (P < 0.05). Immunohistochemistry indicated that HIF1A, HIF2A, and VEGF expressions were observed in different cell types of uterine and placental tissues in late pregnancy and oocyte groups. The expression of HIF3A did not change significantly in any group investigated. These observations suggest that HIFs and VEGF may play a role in the establishment and development of pregnancy.

The Dog: Nonconformist, Not Only in Maternal Recognition Signaling

Although similar at the molecular and cellular levels, endocrine mechanisms governing reproductive function in the domestic dog (Canis familiaris) differ markedly at the regulatory level from those known in other domestic animal species. Some of the events, e.g., the lack of luteolysis in the absence of pregnancy, resulting in similar luteal function and, therefore, hormonal profiles in early pregnant and nonpregnant animals, are species-specific. Consequently, no early gestation marker has so far been identified for the dog. Following implantation, relaxin of fetal placental origin can be detected and used for pregnancy diagnosis. Characterized by the lack of an active luteolytic principle from intra- or extra-luteal sources, the canine reproductive cycle appears to represent a "basic" form of mammalian reproductive function with apparently reduced opportunities for facilitating fecundity and hastening reproduction. Nevertheless, in the dog some kind of mechanism for synchronization between blastocyst development and uterine preparation for pregnancy must have evolved in order to support gestation. Driven by this assumption, studies including our recent investigations have been initiated aimed at characterizing some of the embryo-mediated effects of the preimplantation embryo on the canine uterus. Moreover, the lack of a uterine luteolysin and consequently the absence of a need to develop an antiluteolytic strategy make the dog an interesting model for investigating early evolutionary mechanisms involved in the preparation for implantation and ensuring embryo survival. These mechanisms result in an inverse relationship between the duration of pregnancy and of the nonpregnant cycle in the dog, compared with all other domestic animal species.

Temporal changes in neutral endopeptidase/CD10 immunoexpression in the cyclic and early pregnant canine endometrium

CD10 is a multifunctional transmembrane neutral endopeptidase (NEP) that is considered to be a reliable marker of ectopic human endometrial stroma. Available information on NEP/CD10 protein expression in animal endometria is scarce. This study focused on the immunolocalization of NEP/CD10 in the canine uterus and on its temporal changes during the estrous cycle and early pregnancy (Days 11 to 23 post-LH surge) in healthy females. NEP/CD10 expression was found in the canine endometrial stroma in all stages of the estrous cycle, showing cyclic differences both in intensity and in distribution pattern. A small population of negative stromal cells in subsurface position was also observed. This population shared some morphological characteristics with the human predecidual cells, which became positive in progesterone-associated stages of the cycle. In addition, positive immunolabeling was also observed in canine myometrial stroma. In early pregnancy, the basal glandular epithelia and the syncytium cords remained negative to this marker contrasting with the trophoblast and the lacunar epithelium. A weak to moderate intensity of immunolabeling was observed in the decidual cells, whereas stromal immunolabeling was more intense at the delimitation of the syncytium cords. In conclusion, CD10 is consistently expressed in the canine endometrial stroma and myometrium but not in the endometrial epithelia. The characteristic pattern seen in early pregnancy also suggests a role for this molecule in the process of embryo invasion at implantation.

Early canine pregnancy--a battle for successful growth and angiogenesis

Currently, no early pregnancy marker has been identified in the bitch. However, significantly decreased concentrations of heat-shock protein (HSP) 70 and increased activity of matrix metalloproteinases (MMP) 2,9 were detected in serum from bitches during the pre-implantation period between days 5 and 13 after mating, that is, 2-3 days after ovulation as determined by the measurement of progesterone and vaginal cytology. Especially during the implantation period and thereafter (days 15-55), high serum concentrations of antibodies against desmin are present, which is believed to indicate or regulate decidualization. Pre-implantation embryos express mRNA for enzymes and cytokines, known to promote and regulate trophoblast growth, and some intrauterine changings like the increased activity of MMP 2,9 in maternal endometrium are dependant on the presence of embryos. Some mechanisms that protect canine embryos from attack by the maternal immune system can also be identified. The embryos express CD4, a receptor known to interact with immune cells. They, furthermore, do not express MHC I and II, which might prevent them from being recognized as foreign antigen. Pre-implantation embryos express FasL, which probably renders them able to destroy Fas-bearing cytotoxic T cells. Furthermore, the uterus during pre-implantation and implantation expresses cytokines that modulate the intrauterine milieu towards a predominance of Th2 cells. During pre-implantation and implantation, an increased uterine expression of platelet activating factor (PAF) and PAFR, vascular endothelial growth factor (VEGF) and EGFR2 as well as epithelial growth factor (EGF) is characteristic. Towards placentation, the upregulation of leukaemia inhibiting factor (LIF) and at placentation the expression of insulin-like growth factor(IGF)2 and granulocyte-macrophage colony-stimulating factor (GM-CSF) are striking. Progesterone receptor (PR) appears to be downregulated inside the uterus except at placentation sites, presumably where it is essential for maintenance of pregnancy. In addition, receptor-bound P4 regulates the activity of MMP 2,9. Apoptosis seems to be a further regulatory mechanism. Expression of Fas and FasL mRNA in uterine tissue is maximum until implantation, both factors then decreased significantly. These changings might indicate increased endometrial apoptosis and defence against maternal cytotoxic T cells, probably promoting trophoblast invasion. In human decidual stromal cells, GnRH is involved in the regulation of apoptosis, which is proposed to be similar in pregnant bitches, as GnRH-R is expressed at canine implantation sites. Our work investigating immunological changes in pregnant bitches has elucidated aspects of the complex physiology of implantation but raises important questions about the mechanisms involved.