Canine Endotheliochorial Placenta: Morpho-Functional Aspects

Canine and feline foetal fluids: Volume, hormonal and biochemical characterization during pregnancy

BACKGROUND AND OBJECTIVES

This study aimed to evaluate the volume, the concentration of steroid hormones, and biochemical composition of the foetal fluids at different gestational ages in dogs and cats.

METHODS

Following the ovariohysterectomy, the allantoic and amniotic fluid samples were collected from pregnant bitches and queens and were assigned to different groups according to their gestational age.

RESULTS

The canine and feline allantoic fluid volume increased during pregnancy, reached its maximum values on days 40-49 and then decreased. The canine and feline amniotic fluid volume increased steadily by the last days of pregnancy. In spite of significant changes of sex hormones in the foetal fluids, their concentration and ratios were not significantly different between male and female fetuses. The canine amniotic cortisol concentration increased until days 40-49 and decreased significantly afterwards. The maximum cortisol concentrations in the feline allantoic and amniotic fluids were observed on days 50-60 and 40-49, respectively. During the canine pregnancy, the concentrations of calcium, phosphorus, chloride, sodium, triglyceride, cholesterol, total protein, albumin and the activities of aminotransferase (AST), alkaline phosphatase (ALP), amylase and gamma-glutamyl transferase (GGT) in the amniotic fluid were higher than the allantoic fluid. The magnesium, potassium, lactate dehydrogenase (LDH) activity, creatine and lipase were higher in the allantoic fluid. In the feline allantoic fluid, potassium, magnesium, phosphorus, creatinine, albumin and glucose concentrations and the activities of creatine kinase (CK), GGT, LDH and lipase were higher. The ALP, AST activities, sodium and calcium concentrations were higher in the amniotic fluid (p < 0.05).

CONCLUSION

Volume of foetal fluids was determined in dogs and cats. Concentration of sex hormones did not different between male and female fetuses.

Applying a novel kinomics approach to study decidualization and the effects of antigestagens using a canine model†

Maternal decidual cells are crucial for the maintenance of canine pregnancy as they are the only cells expressing the nuclear progesterone (P4) receptor (PGR) in the placenta. Interfering with P4/PGR signaling adversely affects decidual cells and terminates pregnancy. Although immortalized dog uterine stromal (DUS) cells can be decidualized in vitro using cAMP, the involvement of cAMP-dependent kinases in canine decidualization had not been investigated. Therefore, the present project investigated changes in the kinome of DUS cells following in vitro decidualization, using the serine/threonine kinase (STK) PamChip assay (PamGene). Decidualization led to a predicted activation of 85 STKs in DUS cells, including protein kinase (PK) A, PKC, extracellular signal-regulated kinase (ERK)1/2 and other mitogen-activated protein kinases (MAPKs), calcium/calmodulin-dependent protein kinases (CAMKs), and Akt1/2. In addition, blocking PGR with type 2 antigestagens (aglepristone or mifepristone) decreased the activity of virtually all kinases modulated by decidualization. The underlying transcriptional effects were inferred from comparison with available transcriptomic data on antigestagen-mediated effects in DUS cells. In targeted studies, interfering with PKA or MAPK kinase (MEK)1/2 resulted in downregulation of important decidualization markers (e.g., insulin-like growth factor 1 (IGF1), prostaglandin E2 synthase (PTGES), prolactin receptor (PRLR), PGR, and prostaglandin-endoperoxide synthase 2 (PTGS2/COX2)). Conversely, blocking of PKC decreased the mRNA availability of IGF1, PGR, and PTGS2, but not of PTGES and PRLR. Moreover, suppressing PKA decreased the phosphorylation of the transcription factors cJUN and CREB, whereas blocking of PKC affected only cJUN. This first kinomics analysis to target decidualization showed an increased activity of a wide range of STKs, which could be hindered by disrupting P4/PGR signaling. Decidualization appears to be regulated in a kinase-dependent manner, with PKA and PKC evoking different effects.

Emergency cesarean section in dogs: Usefulness of amniotic fluid biochemical parameters and placental morphology as indicators of neonatal viability

In recent years, special attention has been paid to the analysis of fetal fluids and placental histopathology to identify parameters that can be used as indicators of maternal reproductive quality, embryonic viability, and fetal and neonatal health. Newborn health reflects the functioning of the fetal adnexa and its relationship with maternal tissues. Therefore, evaluating these components is promising for the early detection of newborns at risk. This study aimed to detect the biochemical characteristics of the amniotic fluid (AF) and histopathological characteristics of the placenta for comparison between canine neonates born by elective (EL) and emergency (EM) cesarean sections (CSs) and associate the results with neonatal viability in the first 24 h. A total of 38 neonates born by ELCS (n = 19) and EMCS (n = 19) were selected. AF was collected to analyze the concentration of its biochemical components [alanine aminotransferase (ALT), alkaline phosphatase (ALP), creatinine, urea, total protein, albumin, total and direct bilirubin, lactate, glucose, potassium, chloride, calcium, and sodium]. Histopathological processing of the placenta was used to describe the lesions and identify the arrangement of collagen fibers using hematoxylin-eosin and picrosirius staining. There was an increase in ALP activity (P = 0.035) and the concentrations of lactate (P < 0.001) and potassium (P = 0.031), and a decrease in chlorides (P < 0.001) in the AF of neonates in the EMCS group. The comparisons between the groups did not show differences between the presence and extent of lesions in the placenta; however, a difference was observed in the arrangement of collagen fibers in the placental structure. A comparison between AF and histopathological findings showed a negative correlation (r = -0.609, P = 0.003) between glucose concentration and the presence of necrosis in the placental labyrinth. It was observed that the composition of the AF changed owing to the influence of the type of cesarean, possibly caused by prolonged hypoxia in cases of dystocia. ALP activity and lactate, potassium, and chloride concentrations in the AF might be explored as markers of neonatal health in EMCS. Under the conditions of this study, no correlations were found between the placenta's histopathological characteristics and the neonates' viability.

Membrane-bound progesterone receptors in the canine uterus and placenta; possible targets in the maintenance of pregnancy

To date, the biological functions of P4 within the canine placenta have been attributed to maternal stroma-derived decidual cells as the only placental cells expressing the nuclear P4 receptor (PGR). However, P4 can also exert its effects via membrane-bound receptors. To test the hypothesis that membrane-bound P4 receptors are involved in regulating placental function in the dog, the expression of mPRα, -β, -γ, PGRMC1 and -2 was investigated in the uterine and placental compartments derived from different stages of pregnancy and from prepartum luteolysis. Further, to assess the PGR signaling-mediated effects upon membrane P4 receptors in canine decidual cells, in vitro decidualized dog uterine stromal (DUS) cells were treated with type II antigestagens (aglepristone or mifepristone). The expression of all membrane P4 receptors was detectable in reproductive tissues and in DUS cells. The main findings indicate their distinguishable placental spatio-temporal distribution; PGRMC2 was predominantly found in decidual cells, PGRMC1 was strong in maternal endothelial compartments, and syncytiotrophoblast showed abundant levels of mPRα and mPRβ. In vitro decidualization was associated with increased expression of PGRMC1 and -2, while their protein levels were diminished by antigestagen treatment. The involvement of membrane-bound P4 signaling in the regulation of canine placental function is implied, with P4 effects being directly exerted through maternal and fetal cellular compartments. The indirect effects of PGR might involve the modulation of membrane-bound receptors availability in decidual cells, implying a self-regulatory loop of P4 in regulating the availability of its own receptors in the canine placenta.

Tobacco Smoke Exposure in Pregnant Dogs: Maternal and Newborn Cotinine Levels: A Pilot Study

Active and passive smoking in pregnant women is associated with perinatal morbidity and mortality risk, including abortion, preterm birth, low birthweight, and malformations. No data are available on intrauterine exposure to smoking during pregnancy in dogs. This study aimed to fill this gap by exploring the detectability and quantity of cotinine, the major metabolite of nicotine, in maternal (serum and hair) and newborn (amniotic fluid and hair) biospecimens collected at birth in dogs. For this purpose, twelve pregnant bitches, six exposed to the owner's smoke and six unexposed, were enrolled. A further six non-pregnant bitches exposed to passive smoke were included to investigate the role of pregnancy status on cotinine uptake. Exposed dogs, dams, and puppies had greater cotinine concentrations than unexposed ones. Although without statistical significance, serum and hair cotinine concentrations were higher in pregnant compared to non-pregnant bitches, suggesting a different sensitivity to tobacco smoke exposure during gestation. The present results provide evidence for cotinine transplacental passage in the dog. It is conceivable that fragile patients such as pregnant, lactating, and neonate dogs may be more susceptible to the harmful effects of second-hand smoke exposure. Owners should be sensitized to the risk of smoke exposure for their pets.

Decidual cells and decidualization in the carnivoran endotheliochorial placenta

Decidualization is considered a distinctive feature of eutherian pregnancy, and has appeared during evolution along with the development of invasive forms of placentation, as the endotheliochorial placenta. Although decidualization is not massive in carnivores, as it is in most species developing hemochorial placentas, isolated or grouped cells regarded as decidual have been documented and characterized, mainly in bitches and queens. For the majority of the remaining species of the order, data in the bibliography are fragmentary. In this article, general morphological aspects of decidual stromal cells (DSCs), their time of appearance and lasting, data about the expression of cytoskeletal proteins and molecules considered as markers of decidualization were reviewed. From the data reviewed, it follows that carnivoran DSCs take part either in the secretion of progesterone, prostaglandins, relaxin, among other substances, or at least in the signaling pathways triggered by them. Beyond their physiological roles, some of those molecules are already being used, or are yet under study, for the non-invasive endocrine monitoring and reproductive control of domestic and wild carnivores. Only insulin-like growth factor binding protein 1, among the main decidual markers, has been undoubtedly demonstrated in both species. Laminin, on the contrary, was found only in feline DSCs, and prolactin was preliminary reported in dogs and cats. Prolactin receptor, on the other hand, was found in both species. While canine DSCs are the only placental cell type expressing the nuclear progesterone receptor (PGR), that receptor has not been demonstrated neither in feline DSCs, nor in any other cell in the queen placenta, although the use of PGR blockers leads to abortion. Against this background, and from the data gathered so far, it is unquestionable that DSCs in carnivorans do play a pivotal role in placental development and health. The knowledge about placental physiology is critical for medical care and breeding management, primarily in domestic carnivores; it is also absolutely crucial for a conservation approach in the management of endangered carnivore species.

Endometrial extracellular matrix components do not change over the course of embryonic diapause and reactivation in the roe deer (Capreolus capreolus)

The modification of the endometrial extracellular matrix (ECM) is a crucial step for embryo implantation in many mammalian species. The embryo of the European roe deer (Capreolus capreolus) displays a 4-5 months long temporary reduction of developmental pace termed embryonic diapause. A reduction of epithelial cell height during diapause has previously been described. Co-occurring ECM modifications may contribute to the changes of the intra-uterine milieu during reactivation at which the embryo regains developmental velocity. We assessed the localization of five ECM proteins (collagen I and IV, fibronectin, laminin, and extracellular matrix protein 1) using immunohistochemistry in animals with early, late, and post-diapause (elongating) embryos. While our results confirmed the reduction of epithelial height during diapause, we only detected marginal differences in localization and staining intensities of the selected ECM proteins. Major ECM remodelling events in the roe deer endometrium are thus likely to occur only at implantation.

Transcriptomic profiling of canine decidualization and effects of antigestagens on decidualized dog uterine stromal cells

Maternal-stroma derived decidual cells, the only cell population in the canine placenta expressing the nuclear progesterone (P4) receptor (PGR), are crucial for the maintenance of canine pregnancy. Decreased circulating progesterone (P4) levels, or blockage of PGR function with antigestagens, terminate canine pregnancy. As an in vitro model for canine decidualization, dog uterine stromal (DUS) cells can be decidualized in vitro with cAMP. The antigestagens aglepristone and mifepristone ablate the expression of decidualization markers in DUS cells (e.g., PGR, PRLR, IGF1 or PTGES). Here, the transcriptome profile of DUS cells was investigated to acquire deeper insights into decidualization-associated changes. Additionally, effects mediated by antigestagens (competitive PGR blockers) in decidualized cells were assessed. Decidualization led to the upregulation of 1841 differentially expressed genes (DEGs, P and FDR < 0.01) involved in cellular proliferation and adhesion, mesenchymal-epithelial transition, extracellular matrix organization, and vaso- and immunomodulation. The 1475 DEGs downregulated after decidualization were mostly associated with apoptosis and cell migration. In decidualized DUS cells, aglepristone modulated 1400 DEGs and mifepristone 1558 DEGs. Interestingly, around half of the identified DEGs were modulated by only one of the antigestagens. In all cases, however, PGR-blockage was mainly associated with an inversion of several decidualization-induced effects. Comparison between antigestagen-mediated effects and transcriptional changes in the canine placenta at term allowed the identification of 191 DEGs associated with diminished cell proliferation and adhesion, and vascular and immune modulation. This study emphasizes the importance of P4/PGR signaling for decidual cell function, providing new insights into the maintenance of canine pregnancy.

Antigestagens Mediate the Expression of Decidualization Markers, Extracellular Matrix Factors and Connexin 43 in Decidualized Dog Uterine Stromal (DUS) Cells

Simple Summary

Adequate embryo-maternal communication is essential for a successful pregnancy. In the dog, this interaction is intimately associated with maternal stroma-derived decidual cells, the only cell population in the canine placenta expressing the nuclear progesterone receptor (PGR) and, therefore, sensitive to the circulating progesterone levels. Prepartum decrease of progesterone or clinical application of PGR blockers (antigestagens, e.g., aglepristone and mifepristone) induce placental release of luteolytic factors and terminate pregnancy. However, the importance of progesterone for decidual cells functionality has not been fully elucidated. Therefore, we investigated the effects of PGR blockers on the expression of markers of decidualization and cellular viability, as well as on epithelial and mesenchymal factors in in vitro decidualized dog uterine stromal (DUS) cells. Decidualization increased the expression of the respective markers, including factors involved in cell growth and prostaglandin synthesis. Their expression was suppressed by the application of antigestagens. Additionally, the expression of factors involved in tissue remodeling and cell-cell communication was increased, and antiproliferative and proapoptotic effects were induced in decidualized cells. Altogether, progesterone signaling appears to be crucial for modulating decidual cells physiology and biological activity, and thus for the maintenance of pregnancy.

Abstract

Feto-maternal communication in the dog involves the differentiation of stromal cells into decidual cells. As the only placental cells expressing the nuclear progesterone (P4) receptor (PGR), decidual cells play crucial roles in the maintenance and termination of pregnancy. Accordingly, to investigate possible PGR-mediated mechanisms in canine decidual cells, in vitro decidualized dog uterine stromal (DUS) cells were treated with functional PGR-blockers, mifepristone and aglepristone. Effects on decidualization markers, epithelial and mesenchymal factors, and markers of cellular viability were assessed. Decidualization increased the expression of PTGES, PGR, IGF1, and PRLR, along with ECM1, COL4 and CX43, but downregulated IGF2. DUS cells retained their mesenchymal character, and the expression of COL4 indicated the mesenchymal-epithelial transformation. Antigestagen treatment decreased the availability of PTGES, PRLR, IGF1 and PGR. Furthermore, antigestagens decreased the mRNA and protein expression of CX43, and transcriptional levels of ECM1 and COL4. Additionally, antigestagens increased levels of activated-CASP3 (a proapoptotic factor), associated with lowered levels of PCNA (a proliferation marker). These data reveal important aspects of the functional involvement of PGR in canine decidual cells, regarding the expression of decidualization markers and acquisition of epithelial-like characteristics. Some of these mechanisms may be crucial for the maintenance and/or termination of canine pregnancy.