Cryogenic and low temperature preservation of human placental villous explants – A new way to explore drugs in pregnancy disorders

Ovine placental explants: A new ex vivo model to study host‒pathogen interactions in reproductive pathogens

Reproductive failure is one of the main performance constraints in ruminant livestock. Transmissible agents such as Toxoplasma gondii and Neospora caninum are commonly involved in the occurrence of abortion in ruminants, but little is known about the mechanisms involved. While in vivo models are optimal for the study of abortion pathogenesis, they have a high economic cost and come with ethical concerns. Unfortunately, alternative in vitro models fail to replicate the complex in vivo placental structure. To overcome the limitations of currently available models, we developed an ex vivo model based on the cultivation of fresh and cryopreserved sheep placental explants, enabling the biobanking of tissues. Reproducible and simple markers of tissue integrity (histology, RNA concentrations), viability (resazurin reduction), and functionality (synthesis of steroid hormones) were also investigated, allowing a clear quality assessment of the model. This work shows that, similar to fresh explants, tissues cryopreserved in ethylene glycol using slow freezing rates maintain not only their structure and function but also their receptivity to T. gondii and N. caninum infection. In addition, the findings demonstrate that explant lifespan is mainly limited by the culture method, with protocols requiring improvements to extend it beyond 2 days. These findings suggest that cryopreserved tissues can be exploited to study the initial host‒pathogen interactions taking place in the placenta, thus deepening the knowledge of the specific mechanisms that trigger reproductive failure in sheep. Importantly, this work paves the way for the development of similar models in related species and contributes to the reduction of experimental animal use in the future.

Human Maternal-Fetal Interface Cellular Models to Assess Antiviral Drug Toxicity during Pregnancy

Pregnancy is a period of elevated risk for viral disease severity, resulting in serious health consequences for both the mother and the fetus; yet antiviral drugs lack comprehensive safety and efficacy data for use among pregnant women. In fact, pregnant women are systematically excluded from therapeutic clinical trials to prevent potential fetal harm. Current FDA-recommended reproductive toxicity assessments are studied using small animals which often do not accurately predict the human toxicological profiles of drug candidates. Here, we review the potential of human maternal-fetal interface cellular models in reproductive toxicity assessment of antiviral drugs. We specifically focus on the 2- and 3-dimensional maternal placental models of different gestational stages and those of fetal embryogenesis and organ development. Screening of drug candidates in physiologically relevant human maternal-fetal cellular models will be beneficial to prioritize selection of safe antiviral therapeutics for clinical trials in pregnant women.

Information on dysregulation of microRNA in placenta linked to preeclampsia

MicroRNAs are single-stranded, non-coding RNA molecules, regulate gene expression at the post-transcriptional level. They are expressed in the human body and have a significant impact on the different processes of pathological illness. A developing placenta undergoes a series of stages after successful fertilization, such as cell division, migration, adhesion, apoptosis, and angiogenesis. MicroRNAs dysregulation in placenta has been linked to pregnancy-related complications such as preeclampsia. Therefore, it is of interest to document known information (list of microRNA) on this issue in the development of biological tools for diagnosis, treatment and prevention of the disease.

Modeling the Ruminant Placenta-Pathogen Interactions in Apicomplexan Parasites: Current and Future Perspectives

Neospora caninum and Toxoplasma gondii are one of the main concerns of the livestock sector as they cause important economic losses in ruminants due to the reproductive failure. It is well-known that the interaction of these parasites with the placenta determines the course of infection, leading to fetal death or parasite transmission to the offspring. However, to advance the development of effective vaccines and treatments, there are still important gaps on knowledge on the placental host-parasite interactions that need to be addressed. Ruminant animal models are still an indispensable tool for providing a global view of the pathogenesis, lesions, and immune responses, but their utilization embraces important economic and ethics restrictions. Alternative in vitro systems based on caruncular and trophoblast cells, the key cellular components of placentomes, have emerged in the last years, but their use can only offer a partial view of the processes triggered after infection as they cannot mimic the complex placental architecture and neglect the activity of resident immune cells. These drawbacks could be solved using placental explants, broadly employed in human medicine, and able to preserve its cellular architecture and function. Despite the availability of such materials is constrained by their short shelf-life, the development of adequate cryopreservation protocols could expand their use for research purposes. Herein, we review and discuss existing (and potential) in vivo, in vitro, and ex vivo ruminant placental models that have proven useful to unravel the pathogenic mechanisms and the host immune responses responsible for fetal death (or protection) caused by neosporosis and toxoplasmosis.

Towards biobanking technologies for natural and bioengineered multicellular placental constructs

Clinical application of a large variety of biomaterials is limited by the imperfections in storage technology. Perspective approaches utilizing low-temperature storage are especially challenging for multicellular structures, such as tissues, organs, and bioengineered constructs. Placenta, as a temporary organ, is a widely available unique biological material, being among the most promising sources of various cells and tissues for clinical and experimental use in regenerative medicine and tissue engineering. The aim of this study was to analyse the mechanisms of cryoinjuries in different placental tissues and bioengineered constructs as well as to support the viability after low temperature storage, which would contribute to development of efficient biobanking technologies. This study shows that specificity of cryodamage depends on the structure of the studied object, intercellular bonds, as well as interaction of its components with cryoprotective agents. Remarkably, it was possible to efficiently isolate cells after thawing from all of the studied tissues. While the outcome was lower in comparison to the native non-frozen samples, the phenotype and expression levels of pluripotency genes remained unaffected. Further progress in eliminating of recrystallization processes during thawing would significantly improve biobanking technologies for multicellular constructs and tissues.

Placenta and Placental Derivatives in Regenerative Therapies: Experimental Studies, History, and Prospects

Placental structures, capable to persist in a genetically foreign organism, are a natural model of allogeneic engraftment carrying a number of distinctive properties. In this review, the main features of the placenta and its derivatives such as structure, cellular composition, immunological and endocrine aspects, and the ability to invasion and deportation are discussed. These features are considered from a perspective that determines the placental material as a unique source for regenerative cell therapies and a lesson for immunological tolerance. A historical overview of clinical applications of placental extracts, cells, and tissue components is described. Empirically accumulated data are summarized and compared with modern research. Furthermore, we define scopes and outlooks of application of placental cells and tissues in the rapidly progressing field of regenerative medicine.

Cell- and Tissue-Based Models for Study of Placental Development

Decades of research into the molecular mechanisms by which the placenta forms and functions have sought to improve prevention, diagnosis, and management of disorders of this vital tissue. This research has included development of experimental models intended to replicate behavior of the native placenta in both health and disease. Animal models devised in rodents, sheep, cattle, or other domestic animal species have the advantage of being biologically "complete," but all differ to some degree in developmental timing and anatomical details compared to the human, suggesting subtle differences in molecular mechanism. Consequently, investigators have resorted to simplified systems, characterizing the mechanisms of placental development by using explants of maternal and fetal tissue, primary cell cultures, and immortalized or choriocarcinoma-derived cell lines. Such studies have advanced our understanding of mechanisms by which trophoblasts and associated tissues invade the endometrium, produce chorionic gonadotropin, manage immune tolerance of the fetus, or elaborate proteins that may contribute to placental dysfunction. More recently, use of three-dimensional spheroid cultures, computational modeling of placental tissue dynamics and blood flow, and bioengineering of tissue constructs have been undertaken, aimed to recapitulate the types of interactions that occur among diverse uterine and placental cell types in utero. New technologies and biological paradigms, stemming in part from the ongoing Human Placenta Project, promise to expand the array of available tools, increasing the likelihood that the years ahead will see significant improvements in the ability to prevent, diagnose, and treat life-threatening disorders of placental formation and function.

Biological Tools to Study the Effects of Environmental Contaminants at the Feto-Maternal Interface

The identification of reproductive toxicants is a major scientific challenge for human health. Prenatal life is the most vulnerable and important time span of human development. For obvious ethical reasons, in vivo models cannot be used in human pregnancy, and animal models do not perfectly reflect human physiology. This review describes the in vitro test models representative of the human feto-maternal interface and the effects of environmental chemicals with estrogen-like activity, mainly bisphenol A and para-nonylphenol, with a particular emphasis on the effects at low, nontoxic doses similar to concentrations commonly detected in the population.

Safety of placental, umbilical cord and fetal membrane explants after cryopreservation

There have been studied morphological safety and functional state of the explants of human placenta, umbilical cord and fetal membranes by vital staining techniques using the MTT and resazurin reduction tests, level of glucose in incubation medium, activity of lactate dehydrogenase and alkaline phosphatase before and after cryopreservation. It has been found that proposed program of cryopreservation allows keeping a high level of viability of the explants of placenta, umbilical cord and fetal membranes, the most informative methods of assessing the safety of these biological objects before and after cryopreservation are method of vital staining, determination of glucose content in incubation medium, MTT-test and resazurin reduction test.

Cellular characteristics of cultured canine trophoblasts

CONTENTS

Shallow trophoblast invasion is detrimental in human pregnancies, but represents normal endotheliochorial placentation in dogs. Factors regulating shallow trophoblast invasion into the canine decidua are not well described, but it is known that matrix metalloproteinases (MMPs) play a crucial role in trophoblast invasion in many species. Following the methods previously described for isolating human trophoblasts, canine trophoblasts were isolated using collagenase and trypsin digestions with Percoll density gradient centrifugation. In addition, placental pieces were cryopreserved prior to primary culture following methods previously described for human tissue. Expression of cytokeratin-7, MMP2 and MMP9 was confirmed using fluorescent immunocytochemistry. Cellular morphology was similar to that reported for trophoblasts. More than 97% of the cells cultured expressed cytokeratin-7. More cultured canine trophoblasts expressed MMP9 (54.7 ± 3.4%) compared with MMP2 (40.3 ± 1.8%) (p = 0.02). Although both MMPs were immunolocalized to the cytoplasm, MMP2 was found in large, coalescing granules, whereas MMP9 was more diffusely expressed throughout the cell. Cryogenic freezing of placental tissue prior to primary cell culture had no effect on cell proliferation (p = 0.37). This research has established a baseline for future studies investigating the canine placenta as a model for disorders of shallow trophoblast invasion in humans.