Who Let the Dogs In: A Canine Trophoblast Invasion Model for Pre-eclampsia

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.

Comparative matrix metalloproteinase-2 and -9 expression and activity during endotheliochorial and hemochorial trophoblastic invasiveness

To establish a functional placenta, its development needs adequate trophoblastic invasiveness. The intricate and complex morphological and molecular aspects regulating trophoblastic invasion during endotheliochorial placentation of domestic carnivores and their similarities and differences with the hemochorial placenta are still poorly understood. During placentation processes, from the time of implantation, trophoblast cells invade the uterine endometrium where they achieve extensive degradation and remodeling of extracellular matrix components; in this process, matrix metalloproteinases (MMPs), particularly MMP-2 and 9, have an essential role in rebuilding, cell migration, and invasiveness. This review provides an overview of comparative trophoblast invasive events and the expression and activity of MMP-2 and 9 during endotheliochorial and hemochorial placentation, emphasizing dog and mouse placental models. Understanding of trophoblastic invasiveness in two models of placentation, the intermediately invasive domestic carnivore endotheliochorial placenta, and the more highly invasive mouse hemochorial placenta, contributes to deepen knowledge of the trophoblast invasive processes and their diverse and complex human placental alterations, such as preeclampsia.

Canine Endotheliochorial Placenta: Morpho-Functional Aspects

In the domestic dog, placentation arises from central implantation, passing through a transitional, yet important stage of choriovitelline placenta (yolk sac placenta), on the way to the formation of the definite, deciduate, zonary (girdle) allantochorionic endotheliochorial placenta.Sharing some similarities with other invasive types of placentation, e.g., by revealing decidualization, it is characterized by restricted (shallow) invasion of trophoblast not affecting maternal capillaries and maternal decidual cells. Thus, being structurally and functionally placed between noninvasive epitheliochorial placentation and the more invasive hemochorial type, it presents an interesting and important model for understanding the evolutionarily determined aspects of mammalian placentation. More profound insights into the biological mechanisms underlying the restricted invasion of the fetal trophoblast into maternal uterine structures and the role of decidual cells in that process could provide better understanding of some adverse conditions occurring in humans, like preeclampsia or placenta accreta. As an important endocrine organ actively responding to ovarian steroids and producing its own hormones, e.g., serving as the source of gestational relaxin or prepartum prostaglandins, the canine placenta has become an attractive research target, both in basic and clinical research. In particular, the placental feto-maternal communication between maternal stroma-derived decidual cells and fetal trophoblast cells (i.e., an interplay between placenta materna and placenta fetalis) during the maintenance and termination of canine pregnancy serves as an interesting model for induction of parturition in mammals and is an attractive subject for translational and comparative research. Here, an updated view on morpho-functional aspects associated with canine placentation is presented.

Abundance of insulin-like growth factors 1 and 2, and type 1 insulin-like growth factor receptor in placentas of dogs

Insulin-like growth factors (IGFs) are among the primary compounds regulating placental development. In bitches, relative abundance of IGF1, IGF2 and IGFR1 mRNA transcripts have been studied in the pre-implantation uterus and early endotheliochorial placentas. The IGF2 and IGFR1 distribution has also been previously described in the uterus before embryo implantation. The aim of this study was to detect, characterize, and localize the presence of IGF1, IGF2, and IGFR1 in early-developing and mature placentas of dogs. Placentas of 15 bitches were analyzed using immunohistochemistry. The IGFs were located in endometrial epithelium and glands, with the staining pattern and intensity being less in mature placentas. Cytotrophoblast cells (CTB) and syncytiotrophoblast (STB) cells contained both IGFs; the labeling was greater in CTB of the early-developing than mature placentas. The maternal endothelium was positively stained for both IGFs, while the vascular endothelium of the chorioallantoic membrane were only stained for IGF2. The IGFR1 was detected in all cell populations evaluated. Results regarding trophoblastic IGF are quite consistent with those reported in human placentas. Spatiotemporal IGFs/IGFR1 pattern might reflect the occurrence of autocrine and paracrine signaling during placentation in bitches, and the involvement in early placental developmental processes. Furthermore, it is hypothesized that, besides hemotrophic actions of plasma IGFs, endometrial secreted IGFs may promote early placental development through histotrophic signaling.

Differential expression and activity of matrix metalloproteinases 2 and 9 in canine early placenta

The zonary and endotheliochorial dog placenta is the most invasive placenta of carnivores. The importance of matrix metalloproteinases (MMP) in placenta invasiveness has been determined in several mammals including species with haemochorial, epitheliochorial and endotheliochorial placentation. Regarding the latter, the expression of MMP enzymes has been studied in the cat and the mature canine placenta. The aim of this study was to analyse the expression and activity of MMP-2 and MMP-9 in the early dog placenta. Placentae from 18 to 30 days of pregnancy were collected from four bitches. Two placentae from each bitch were analysed. Placental tissue from one uterine horn was fixed in formaldehyde for immunohistochemistry, while marginal haematoma, labyrinth, non-implantative and implantative endometrium from the contralateral horn were immediately frozen in dry ice for the analysis of MMP expression (Western blot [WB]) and activity (zymography). MMP-2 and MMP-9 were evidenced in the labyrinth, maternal glands and marginal haematoma; this finding was directly correlated with levels of MMP expression by WB, and with the activity of MMP-2, mainly in the haematoma (the area of major remodelling of tissues). Thus, although MMP-9 is well expressed in the early canine placenta, it is not active. Given the important role of MMPs for invasiveness, maternal-foetal angiogenesis and the establishment of a correct foetal nutrition, the results are consistent with the findings in other species in which the MMP-2 activation precedes the MMP-9 one in early placentation.

Placental Evolution within the Supraordinal Clades of Eutheria with the Perspective of Alternative Animal Models for Human Placentation

Here a survey of placental evolution is conducted. Placentation is a key factor for the evolution of placental mammals that had evolved an astonishing diversity. As a temporary organ that does not allow easy access, it is still not well understood. The lack of data also is a restriction for better understanding of placental development, structure, and function in the human. Animal models are essential, because experimental access to the human placenta is naturally restricted. However, there is not a single ideal model that is entirely similar to humans. It is particularly important to establish other models than the mouse, which is characterised by a short gestation period and poorly developed neonates that may provide insights only for early human pregnancy. In conclusion, current evolutionary studies have contributed essentially to providing a pool of experimental models for recent and future approaches that may also meet the requirements of a long gestation period and advanced developmental status of the newborn in the human. Suitability and limitations of taxa as alternative animal models are discussed. However, further investigations especially in wildlife taxa should be conducted in order to learn more about the full evolutionary plasticity of the placenta system.