Fetal membranes and placenta of the African green monkey (Cercopithecus aethiops)

Organ-On-Chip Technology: The Future of Feto-Maternal Interface Research?

The placenta and fetal membrane act as a protective barrier throughout pregnancy while maintaining communication and nutrient exchange between the baby and the mother. Disruption of this barrier leads to various pregnancy complications, including preterm birth, which can have lasting negative consequences. Thus, understanding the role of the feto-maternal interface during pregnancy and parturition is vital to advancing basic and clinical research in the field of obstetrics. However, human subject studies are inherently difficult, and appropriate animal models are lacking. Due to these challenges, in vitro cell culture-based studies are most commonly utilized. However, the structure and functions of conventionally used in vitro 2D and 3D models are vastly different from the in vivo environment, making it difficult to fully understand the various factors affecting pregnancy as well as pathways and mechanisms contributing to term and preterm births. This limitation also makes it difficult to develop new therapeutics. The emergence of in vivo-like in vitro models such as organ-on-chip (OOC) platforms can better recapitulate in vivo functions and responses and has the potential to move this field forward significantly. OOC technology brings together two distinct fields, microfluidic engineering and cell/tissue biology, through which diverse human organ structures and functionalities can be built into a laboratory model that better mimics functions and responses of in vivo tissues and organs. In this review, we first provide an overview of the OOC technology, highlight two major designs commonly used in achieving multi-layer co-cultivation of cells, and introduce recently developed OOC models of the feto-maternal interface. As a vital component of this review, we aim to outline progress on the practicality and effectiveness of feto-maternal interface OOC (FM-OOC) models currently used and the advances they have fostered in obstetrics research. Lastly, we provide a perspective on the future basic research and clinical applications of FM-OOC models, and even those that integrate multiple organ systems into a single OOC system that may recreate intrauterine architecture in its entirety, which will accelerate our understanding of feto-maternal communication, induction of preterm labor, drug or toxicant permeability at this vital interface, and development of new therapeutic strategies.

The role of invasive trophoblast in implantation and placentation of primates

We here review the evolution of invasive placentation in primates towards the deep penetration of the endometrium and its arteries in hominoids. The strepsirrhine primates (lemurs and lorises) have non-invasive, epitheliochorial placentation, although this is thought to be derived from a more invasive type. In haplorhine primates, there is differentiation of trophoblast at the blastocyst stage into syncytial and cellular trophoblast. Implantation involves syncytiotrophoblast that first removes the uterine epithelium then consolidates at the basal lamina before continuing into the stroma. In later stages of pregnancy, especially in Old World monkeys and apes, cytotrophoblast plays a greater role in the invasive process. Columns of trophoblast cells advance to the base of the implantation site where they spread out to form a cytotrophoblastic shell. In addition, cytotrophoblasts advance into the lumen of the spiral arteries. They are responsible for remodelling these vessels to form wide, low-resistance conduits. In human and great apes, there is additional invasion of the endometrium and its vessels by trophoblasts originating from the base of the anchoring villi. Deep trophoblast invasion that extends remodelling of the spiral arteries to segments in the inner myometrium evolved in the common ancestor of gorilla, chimp and human.

Phylogenetic evidence for early hemochorial placentation in eutheria

The eutherian placenta is remarkable for its structural and functional variability. In order to construct and test comparative hypotheses relating ecological, behavioral and physiological traits to placental characteristics it is first necessary to reconstruct the historical course of placental evolution. Previous attempts to do so have yielded inconsistent results, particularly with respect to the early evolution of structural relationships between fetal and maternal circulatory systems. Here, we bring a battery of phylogenetic methods - including parsimony, likelihood and Bayesian approaches - to bear on the question of placental evolution. All of these approaches are consistent in indicating that highly invasive hemochorial placentation, as found in human beings and numerous other taxa, was an early evolutionary innovation present in the most ancient ancestors of the living placental mammals.

Amniotic membranes as prosthetic material: experimental utilization data of a rat model

BACKGROUND/PURPOSE

Prosthetic materials are applied for closing big tissue defects, the repair of traumatized organs, or hernias. Because nonabsorbable synthetic materials are rigid, possess a defined and unchangeable size, and foreign body reaction (FBR) may occur, biological materials may be an alternative.

METHODS

In experimental studies in rats the authors implanted the fetal parts of the human amniotic membranes and examined the utilization and FBR induced in a standardized model. In addition amnion (AM) was combined with vicryl-net (VN) for higher implant stability. Fifteen, 30 and 90 days after implantation, macroscopic appearance was examined, and light microscopy and immunohistology testing of the specimens were performed.

RESULTS

Adhesions to parenchymal organs and omentum were present irrespective of the side facing the abdominal cavity. AM induced a rapid FBR, which diminished with time. Chorion (CH) and parts of the AM were resorbed within the examined period after infiltration with recipient cells and neovascularisation. The combined implant, AM, and VN showed best results because disadvantages of one material could be compensated for by the advantages of the other.

CONCLUSION

The studies show that AM, in its anatomic definition, combined with VN proves to be a safe and reliable prosthetic material for the use in tissue defects.

Ovine amniotic and allantoic epithelia across gestation

BACKGROUND

Extensive studies on the regulation of the volume and composition of amniotic and allantoic fluid in the sheep have suggested that the amniotic and allantoic membranes must play an active role in these processes. Little is known of the functional morphology of the sheep amnion and allantois beyond the presence of an epithelium overlying connective tissue.

METHODS

The ovine amnion and allantois were characterized at a range of gestational ages (27-140 days of gestation, where term is 145-150 days) by electron microscopy (SEM and TEM) and the presence of transporting ATPases examined by use of immunohistochemistry (Ca++-ATPase) and in situ hybridization (Na,K-ATPase).

RESULTS

With increasing gestational age, the cell height of epithelium of the membranes increased, as did the number of apical microvilli and the length of zonulae occludentes. Epithelial cell cytoplasm increased in complexity, and cell shape changed from flattened to cuboidal. Proliferation of cells occurred until close to term. Immunoreactivity to Ca++-ATPase was present in the basolateral membranes at all stages of gestation examined, but hybridization with the alpha and beta subunits of Na,K-ATPase was present only at or after 100 days of gestation.

CONCLUSIONS

The epithelia of the sheep amnion and allantois display characteristics typical of transporting epithelia. As the epithelia mature, changes related to increased capacity for solute and fluid transport regulation occur.

Amnion as a prosthetic material in congenital defects

In pediatric surgery, amniotic membranes taken from autologous placenta are occasionally used as an implant in cases of large ventral abdominal clefts. The questions arise, which part of this organ should be used and how to use it in the recipient organism. Amniotic membranes consist anatomically of amnion and chorion, which are of fetal origin, and maternal decidua. In our experimental studies, we used the fetal parts of the amniotic membrane as an implant in a standardized rat model and investigated the utilization and possible foreign-body reaction (FBR) induced. Fifteen, 30, and 90 days after implantation the macroscopic appearance, light microscopy, and immunohistology of the specimens were examined. Adhesions to parenchymal organs and omentum were present irrespective of the side facing the abdominal cavity. Amnion induced a rapid FBR that diminished with time. Chorion and parts of the amnion were resorbed within the examined period after infiltration with recipient cells and neovascularization. Our studies have shown that for best results, only amnion in its anatomical definition and parts of the chorion should be prefered as an implant.

Development and structure of the placenta and fetal membranes of nonhuman primates

This survey examines placental and fetal membrane structure, function, and development in nonhuman primates. It will focus on these aspects of fetal membranes in species exemplifying the two main types of primate placentation. The chorioallantoic placentas of most strepsirhine primates (e.g., lorises and lemurs), are diffuse, villous and epitheliochorial in structure. Villi are stout, usually unbranched and interdigitate with indentations in the uterine lining. Early in gestation trophoblast cells are columnar but with advancing gestational age considerable thinning of the interhemal membrane occurs. The villous tips have indented regions that appear to be involved in absorption of histotroph. Accessory placental structures known as areolae or chorionic vesicles occur in many strepsirhines. These are cup-shaped specializations that develop opposite the mouths of uterine glands and appear active in absorption of glandular secretions. In addition, most strepsirhines are characterized by a large yolk sac early in gestation, a transient choriovitelline placenta, and most have a large allantoic sac. In strepsirhines, amniogenesis occurs by folding. In contrast, the chorioallantoic placentas of most haplorhines are discoidal, villous, and hemochorial. The species emphasized in the review are macaque monkeys. The placental villi are covered by a layer of syncytiotrophoblast; the latter is active in maternal-fetal transport and hormone synthesis. In some haplorhines, extravillous trophoblast invades deeply into the endometrium and also into spiral arteries supplying the placenta. Other fetal membranes include 1) nonvillous chorion (chorion laeve); there is evidence supporting both an absorptive and synthetic role for trophoblast of the chorion laeve; 2) yolk sac, which is unusual in that a secondary yolk sac is formed. The yolk sac has both synthetic and absorptive functions in early gestation; and 3) amnion; amniogenesis in haplorhines occurs by cavitation.