Adaptability and potential for treatment of placental functions to improve embryonic development and postnatal health

Placental Models for Evaluation of Nanocarriers as Drug Delivery Systems for Pregnancy Associated Disorders

Pregnancy-associated disorders affect around 20% of pregnancies each year around the world. The risk associated with pregnancy therapeutic management categorizes pregnant women as "drug orphan" patients. In the last few decades, nanocarriers have demonstrated relevant properties for controlled drug delivery, which have been studied for pregnancy-associated disorders. To develop new drug dosage forms it is mandatory to have access to the right evaluation models to ensure their usage safety and efficacy. This review exposes the various placental-based models suitable for nanocarrier evaluation for pregnancy-associated therapies. We first review the current knowledge about nanocarriers as drug delivery systems and how placenta can be used as an evaluation model. Models are divided into three categories: in vivo, in vitro, and ex vivo placental models. We then examine the recent studies using those models to evaluate nanocarriers behavior towards the placental barrier and which information can be gathered from these results. Finally, we propose a flow chart on the usage and the combination of models regarding the nanocarriers and nanoparticles studied and the intended therapeutic strategy.

Complex patterns of cell growth in the placenta in normal pregnancy and as adaptations to maternal diet restriction

The major milestones in mouse placental development are well described, but our understanding is limited to how the placenta can adapt to damage or changes in the environment. By using stereology and expression of cell cycle markers, we found that the placenta grows under normal conditions not just by hyperplasia of trophoblast cells but also through extensive polyploidy and cell hypertrophy. In response to feeding a low protein diet to mothers prior to and during pregnancy, to mimic chronic malnutrition, we found that this normal program was altered and that it was influenced by the sex of the conceptus. Male fetuses showed intrauterine growth restriction (IUGR) by embryonic day (E) 18.5, just before term, whereas female fetuses showed IUGR as early as E16.5. This difference was correlated with differences in the size of the labyrinth layer of the placenta, the site of nutrient and gas exchange. Functional changes were implied based on up-regulation of nutrient transporter genes. The junctional zone was also affected, with a reduction in both glycogen trophoblast and spongiotrophoblast cells. These changes were associated with increased expression of Phlda2 and reduced expression of Egfr. Polyploidy, which results from endoreduplication, is a normal feature of trophoblast giant cells (TGC) but also spongiotrophoblast cells. Ploidy was increased in sinusoidal-TGCs and spongiotrophoblast cells, but not parietal-TGCs, in low protein placentas. These results indicate that the placenta undergoes a range of changes in development and function in response to poor maternal diet, many of which we interpret are aimed at mitigating the impacts on fetal and maternal health.

The Placental Atlas Tool (PAT): A collaborative research and discovery platform for the placental research community

INTRODUCTION

The placenta is one of the least understood, yet arguably one of the most important organs for human health and development. While there have been numerous research efforts dedicated to understanding the placenta's critical role, these studies and the data they produced remain separated and largely disparate. In order to facilitate placental research, the Eunice Kennedy Shriver National Institute of Child and Human Development (NICHD) released in October 2018 the Placental Atlas Tool (PAT) (https://pat.nichd.nih.gov/), an internet-based platform offering users a centralized placental database of molecular datasets, analytic tools, and images.

METHODS

PAT is a cloud-based system developed by the business requirements defined by NICHD leadership and extramural placental researchers. PAT employs a metadata-driven web interface to provide curated placental datasets and images, enriched with structured, descriptive metadata to enhance data discoverability. PAT also incorporates open source molecular data analytical tools to provide a flexible analytics workflow for placental researchers.

RESULTS

PAT launched with 426 analyzable molecular placental datasets consisting of over 12,500 samples from 10 distinct species, all systematically annotated and processed for enhanced research utility. 828 placental images, consisting of 7 imaging modalities across 47 species, and nearly 300 annotated linked publications supplement the datasets to facilitate knowledge integration and hypothesis generation across disparate molecular studies.

DISCUSSION

PAT will maximize the NICHD's investment in placental research by reinforcing open scientific inquiry, facilitating reuse of datasets, promoting novel research and testing of new hypotheses and analytic methods, and facilitating education of new researchers.

The platelet-derived growth factor receptor alpha promoter-directed expression of cre recombinase in mouse placenta

Background

Numerous pathologies of pregnancy originate from placental dysfunction. It is essential to understand the functions of key genes in the placenta in order to discern the etiology of placental pathologies. A paucity of animal models that allow conditional and inducible expression of a target gene in the placenta is a major limitation for studying placental development and function.

Results

To study the platelet‐derived growth factor receptor alpha (PDGFRα)‐directed and tamoxifen‐induced Cre recombinase expression in the placenta, PDGFRα‐CreER mice were crossed with mT/mG dual‐fluorescent reporter mice. The expression of endogenous membrane‐localized enhanced green fluorescent protein (mEGFP) and/or dTomato in the placenta was examined to identify PDGFRα promoter‐directed Cre expression. Pregnant PDGFRα‐CreER;mT/mG mice were treated with tamoxifen at various gestational ages. Upon tamoxifen treatment, reporter protein mEGFP was observed in the junctional zone (JZ) and chorionic plate (CP). Furthermore, a single dose of tamoxifen was sufficient to induce the recombination.

Conclusions

PDGFRα‐CreER expression is restricted to the JZ and CP of mouse placentas. PDGFRα‐CreER mice provide a useful tool to conditionally knock out or overexpress a target gene in these regions of the mouse placenta.

Inducible PDGFRα‐directed Cre expression trophoblasts cells.

A single tamoxifen treatment is sufficient to induce the recombination.

Valuable tool to temporary knockout or over‐express a target gene in the placenta.

Do not require sophisticated system and suitable for ordinary laboratory setting.

Effects of maternal nutrient restriction followed by realimentation during early and mid-gestation in beef cows. II. Placental development, umbilical blood flow, and uterine blood flow responses to diet alterations

The objectives were to examine the effects of maternal nutrient restriction followed by realimentation during early to mid-gestation on placental development and uterine and umbilical hemodynamics in the beef cow. On day 30 of pregnancy, multiparous, non-lactating beef cows (620.5 ± 11.3 kg) were assigned to 1 of 2 dietary treatments: control (C; 100% National Research Council [NRC] recommendations; n = 18) and restricted (R; 60% NRC; n = 30). On day 85, cows were slaughtered (C, n = 6; R, n = 6), remained on control (CC; n = 12) and restricted (RR; n = 12), or were realimented to control (RC; n = 11). On day 140, cows were slaughtered (CC, n = 6; RR, n = 6; RC, n = 5), remained on control (CCC, n = 6; RCC, n = 5), or were realimented to control (RRC, n = 6). On day 254, all remaining cows were slaughtered. Heart rate and umbilical and uterine hemodynamics [blood flow, resistance index (RI), and pulsatility index (PI)] were determined via Doppler ultrasonography. As expected umbilical blood flow increased and fetal heart rate decreased as gestation advanced. Umbilical PI in RRC cows was less (P = 0.01) compared to RCC and CCC. During late gestation, RCC cows had greater (P = 0.02) ipsilateral and total uterine blood flow vs. CCC and RRC. There was an increase in the number and weight of placentomes from R cows (P ≤ 0.02) compared to C cows (i.e. day 85). There were more placentomes (P = 0.03) in RR vs. CC and RC cows, but placentome weight was not affected (P = 0.18) by maternal dietary treatment at day 140. Maternal nutrient restriction during early to mid-gestation increased the weight (by day 85) and number (day 85 and 140) of placentomes, and did not reduce fetal weight compared to control cows. A longer realimentation period may enhance uterine blood flow and individual placentome size during later gestation, which may compensate for reduced nutrients experienced early in gestation.

Placentation in different mammalian species

The placenta is a complex, transient organ associated with viviparity, which is located at the interface of the dam and fetus during pregnancy. It is formed after attachment, or implantation, of the blastocyst on the uterine lining and derives from complex cellular and molecular interactions between uterine and embryonic tissues. In mammals, there are many forms of placentation but this organ has the same function in all species: it is responsible for orchestrating materno-fetal exchanges, together with endocrine and immunological functions.