Expression of alkaline phosphatase in differentiated rat labyrinthine trophoblast tissue

Evaluation of Molecular Interactions and Cellular Dynamics at the Maternal-Fetal Interface During Placental Morphogenesis

Molecular events at the maternal-fetal interface establish successful pregnancies. Identifying and characterizing the heterogeneous cell population and their cross-talk at the cellular and molecular levels are essential to expand our knowledge on the progression and maintenance of pregnancy. In this chapter, we briefly discuss the organization of maternal-fetal interface in mice/rats and humans. We illustrate methods for studying the cell composition using flow cytometry, immunocytochemical and biochemical studies, intercellular interaction using co-culture system and spheroid assay, and function of trophoblast cells using ELISA, RNA sequencing, mass spectrometry (MS) to analyze the proteome, invasion assay, and scratch wound assay.

Activation of Proneuronal Transcription Factor Ascl1 in Maternal Liver Ensures a Healthy Pregnancy

BACKGROUND & AIMS

Maternal liver shows robust adaptations to pregnancy to accommodate the metabolic needs of the developing and growing placenta and fetus by largely unknown mechanisms. We found that Ascl1, a gene encoding a basic helix-loop-helix transcription factor essential for neuronal development, is highly activated in maternal hepatocytes during the second half of gestation in mice.

METHODS

To investigate whether and how Ascl1 plays a pregnancy-dependent role, we deleted the Ascl1 gene specifically in maternal hepatocytes from midgestation until term.

RESULTS

As a result, we identified multiple Ascl1-dependent phenotypes. Maternal livers lacking Ascl1 showed aberrant hepatocyte structure, increased hepatocyte proliferation, enlarged hepatocyte size, reduced albumin production, and increased release of liver enzymes, indicating maternal liver dysfunction. Simultaneously, maternal pancreas and spleen and the placenta showed marked overgrowth; and the maternal ceca microbiome showed alterations in relative abundance of several bacterial subpopulations. Moreover, litters born from maternal hepatic Ascl1-deficient dams experienced abnormal postnatal growth after weaning, implying an adverse pregnancy outcome. Mechanistically, we found that maternal hepatocytes deficient for Ascl1 showed robust activation of insulin-like growth factor 2 expression, which may contribute to the Ascl1-dependent phenotypes widespread in maternal and uteroplacental compartments.

CONCLUSIONS

In summary, we show that maternal liver, via activating Ascl1 expression, modulates the adaptations of maternal organs and the growth of the placenta to maintain a healthy pregnancy. Our studies show that Ascl1 is a novel and critical regulator of the physiology of pregnancy.

The promise of placental extracellular vesicles: models and challenges for diagnosing placental dysfunction in utero†

Monitoring the health of a pregnancy is of utmost importance to both the fetus and the mother. The diagnosis of pregnancy complications typically occurs after the manifestation of symptoms, and limited preventative measures or effective treatments are available. Traditionally, pregnancy health is evaluated by analyzing maternal serum hormone levels, genetic testing, ultrasonographic imaging, and monitoring maternal symptoms. However, researchers have reported a difference in extracellular vesicle (EV) quantity and cargo between healthy and at-risk pregnancies. Thus, placental EVs (PEVs) may help to understand normal and aberrant placental development, monitor pregnancy health in terms of developing placental pathologies, and assess the impact of environmental influences, such as infection, on pregnancy. The diagnostic potential of PEVs could allow for earlier detection of pregnancy complications via noninvasive sampling and frequent monitoring. Understanding how PEVs serve as a means of communication with maternal cells and recognizing their potential utility as a readout of placental health have sparked a growing interest in basic and translational research. However, to date, PEV research with animal models lags behind human studies. The strength of animal pregnancy models is that they can be used to assess placental pathologies in conjunction with isolation of PEVs from fluid samples at different time points throughout gestation. Assessing PEV cargo in animals within normal and complicated pregnancies will accelerate the translation of PEV analysis into the clinic for potential use in prognostics. We propose that appropriate animal models of human pregnancy complications must be established in the PEV field.

Transforming growth factor-beta induces differentiation of the labyrinthine trophoblast stem cell line SM10

The mammalian placenta consists of different trophoblast cell types that assist in the variety of functions required for the maintenance of pregnancy. In rodents, labyrinthine trophoblasts of the placenta are especially important, because they are capable of differentiating into fused labyrinthine cells, which form the feto-maternal exchange surface. Even though the molecular signals triggering labyrinthine trophoblast differentiation are poorly understood, transforming growth factor-beta (TGF-beta) has been shown to be present in the placental environment and alter trophoblast development. In this study, we investigated the effects of TGF-beta on the differentiation of the labyrinthine trophoblast stem cell lines SM10 and HRP-1. RT-PCR analyses demonstrated that while the molecular expression of labyrinthine-specific lineage markers (Esx1, Tfeb, and Tec) was maintained in TGF-beta-treated SM10 and HRP-1 cells, TGF-beta induced the down-regulation of trophoblast stem cell markers Id2 and Cdx2. In contrast, TGF-beta induced the expression of a marker of differentiated labyrinthine trophoblasts, Gcm1, only in the SM10 cell line. Furthermore, we demonstrated an increased glucose uptake in the TGF-beta-treated SM10 cells, indicative of functional differentiation. Finally, cell fusion in TGF-beta-treated SM10 and HRP-1 cells was investigated by western blotting analysis of placental alkaline phosphatase and cadherin-11 and by microscopic analyses of cell morphology using green fluorescent protein (GFP) and rhodamine phalloidin staining. The western blotting and morphological analyses indicate TGF-beta-induced cell fusion and morphological differentiation in the SM10 cell line. The SM10 cell line will provide a new and unique model for detailed analysis of TGF-beta-induced molecular events associated with labyrinthine trophoblast differentiation and function.

SNAT expression in rat placenta

Amino acid transport System A (SysA) activity is present within the rodent and human placentas. Inhibition of this transport system is associated with fetal growth retardation. Several cDNAs encoding SysA transport proteins have been discovered, and their presence documented within the human placenta. We have demonstrated the presence of mRNA encoding three of these transporters, SNAT1, 2, and 4 within the rat placenta over the final third of gestation. Abundance of these mRNA species increases from day 14 to day 20 of gestation. Immunohistochemistry demonstrates the presence of SNAT1 and 2 within the placental labyrinth at both days 14 and 20. Transport proteins are also present within marginal giant cells and, for SNAT1, within fetal endothelium. In conclusion, several proteins capable of SysA transport activity are present within the rodent placenta. mRNA expression increases over the final third of gestation, coincident with the period of greatest need for fetal amino acid delivery.

Potent differentiation-inducing properties of the antiretroviral agent 9-(2-phosphonylmethoxyethyl) adenine (PMEA) in the rat choriocarcinoma (RCHO) tumor cell model

9-(2-phosphonylmethoxyethyl)adenine (PMEA) and its closely related structural analogue (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) are potent inhibitors of retroviruses and hepatitis B virus. In its oral prodrug form (adefovir dipivoxil), PMEA is currently the subject of advanced phase II/III clinical trials for the treatment of HIV infections. PMEA has also been shown to be a potent differentiation-inducing agent. In the present study, PMEA was found to have a strong differentiation-inducing effect on rat choriocarcinoma (RCHO) cells, comparable to that of methotrexate, which is the drug of choice for the chemotherapy of choriocarcinoma in humans. PMEA induced differentiation of choriocarcinoma trophoblast cells in a concentration-dependent manner within the 2- to 50-microM concentration range, as ascertained by giant cell formation, alkaline phosphatase induction, progesterone secretion, and the disappearance of a cytotrophoblast-specific surface antigen. PMEA had to be exposed to the rat choriocarcinoma cell cultures for at least 2-3 days to achieve optimal growth inhibition and differentiation of the tumor cells. Unlike PMEA, (R)-9-(2-phosphonylmethoxypropyl)adenine failed to induce differentiation of proliferating cytotrophoblasts into nonproliferating, hormonally active giant cells. This points to the specificity of PMEA as an inducer of choriocarcinoma cell differentiation.

In vitro and in vivo inhibitory activity of the differentiation-inducing agent 9-(2-phosphonylmethoxyethyl)adenine (PMEA) against rat choriocarcinoma

The acyclic nucleoside phosphonate 9-(2-phosphonylmethoxyethyl)adenine (PMEA) has previously been shown to be a strong inducer of differentiation in several tumor cell lines. We have now investigated the in vitro differentiation-inducing and the in vivo antitumor, properties of PMEA in a rat choriocarcinoma tumor cell model. PMEA at 2 to 50 microM induced choriocarcinoma RCHO cell differentiation in vitro in a concentration-dependent manner, as monitored by morphological changes, induction of alkaline phosphatase and production and secretion of progesterone. Likewise, a clear dose-response relationship was established for the in vivo antitumor activity of PMEA in choriocarcinoma-bearing rats. (R)-PMPA, a structural analogue of PMEA which is much less effective than PMEA in inducing differentiation in vitro did not demonstrate any in vivo antitumor activity. This observation points to the specificity of the differentiation-inducing potential of PMEA.

Analysis of rat placental plasma membrane proteins by two-dimensional gel electrophoresis

The placenta plays an essential role in fetal growth and the maintenance of pregnancy and its functions are strictly controlled in a stage-specific manner. To gain an insight into placental functions and their regulation, we analyzed the plasma membrane proteins of rat placenta by two-dimensional polyacrylamide gel electrophoresis (2D/E). Plasma membrane fractions of the placenta obtained on days 12, 14, 16, 18 and 20 of pregnancy were purified by Percoll gradient centrifugation, and subjected to 2D/E analysis. After the proteins on the 2D/E gels had been visualized by silver staining, the patterns on the gels at different stages of pregnancy were compared using image analysis software. Proteins within an isoelectric point (pI) range of 4.0 to 7.0 and a molecular weight (Mw) range of 20-100 kDa were analyzed in detail, and about 800 proteins on average were recognized on each gel. Of these, the expression of 150 proteins was found to change dramatically according to the stage of pregnancy. According to their expression patterns, these proteins were categorized into two groups, Group I and Group II. The proteins belonging to Group I showed a higher intensity of expression on day 12 and disappeared on day 20. They included 119 plasma membrane proteins and were divided into five subgroups. Group II, which consisted of three subgroups, included 31 proteins showing a low or negligible expression on day 12 and higher expression on day 20. Most of the other membrane proteins (about 600) were expressed constantly during pregnancy. On the basis of our data, we constructed a database for plasma membrane proteins of the rat placenta.

The human immunodeficiency virus(HIV) inhibitor 9-(2-phosphonylmethoxyethyl)adenine (PMEA) is a strong inducer of differentiation of several tumor cell lines

9-(2-phosphonylmethoxyethyl)adenine (PMEA) is the prototype compound of a series of acyclic nucleoside phosphonate derivatives endowed with potent and selective anti-retroviral activity in vitro and in vivo. We have now found that PMEA is also a potent inducer of differentiation of a number of tumor cells, including human erythroleukemia K562 cells, rat choriocarcinoma RCHO cells and human acute promyelocytic leukemic HL-60 cells. At 10 microM PMEA, rat RCHO cell cultures could be almost fully differentiated, and at 50 microM PMEA, approximately 50% of the K562 cells could be triggered to produce hemoglobin. The differentiating activity of butyric acid was at least partially additive to that of PMEA when both drugs were combined in K562 cell cultures. PMEA needs to be present for at least 2 or 3 days in the K562 cell cultures to achieve optimal differentiating activity. This suggests that either a PMEA metabolite and/or its anti-metabolic effects may be responsible for differentiation of the tumor cells.

Changes in the pattern of expression of alkaline phosphatase in the mouse uterus and placenta during gestation

The development of the rodent chorio-allantoic placenta is a complicated process that results in the formation of a transport system capable of sustaining embryonic and fetal growth and development. Intimately linked to this process is alkaline phosphatase (AP), a cell-surface glycoprotein that possibly functions as a transport protein. In the present study, we have mapped the location of AP-expressing cells in the mouse utero-placental unit during the development of the chorio-allantoic placenta by use of enzyme histochemistry and in situ hybridization histochemistry. We found that at implantation the expression of the tissue non-specific AP (TNAP) gene is located exclusively in the decidua and that most of this decidual expression ceases as the placenta starts to form. One exception is a mesometrially located marginal zone of the decidua, which continues to express the TNAP gene until day 12 and the active protein until at least day 16. Trophoblasts of the chorion already express AP before the time of fusion with the ectoplacental cone, after which AP is expressed by trophoblasts of the resulting ectoplacental plate. AP expression in the mature chorio-allantoic placenta is localized in the placental labyrinth and spongy zones. In the latter zone, expression ceases on about day 14. Giant trophoblasts start to express AP on about day 10, with some cells still positive for AP at day 16. The yolk sac does not express AP at any developmental stage. The results show that AP expression during placental development is neither restricted to cells known to be involved in transport, nor expressed in all cells thought to be involved in this transport. This may indicate that AP is not merely a transport protein but has additional functions.

Trophoblast cell differentiation and organization: role of fetal and ovarian signals

The rat chorioallantoic placenta is organized into two distinct zones (junctional and labyrinth) and expresses six members of the placental prolactin (PRL) family: placental lactogen-I (PL-I), PL-I variant (PL-Iv), PL-II, PRL-like protein-A (PLP-A), PLP-B, and PLP-C. These placental hormones are expressed in distinct cell- and temporal-specific patterns and can be used to monitor the state of differentiation of rat trophoblast cells. This study was initiated to examine the role of the fetus and maternal ovaries in the regulation of trophoblast cell differentiation and organization. Expression of the placental PRL family was monitored by Northern and Western blotting and immunocytochemical analysis. The roles of the fetus and maternal ovaries were examined by chemically induced fetal death (DFX, induced by intraamniotic injection of digoxin) and surgical removal of the ovaries (OVX), respectively. The endocrine differentiation of the placenta was assessed on day 19 of gestation (sperm positive = day 0, parturition = day 21). Day 10 of gestation was the earliest day that DFX could be reliably performed. Day 10 is a time point during pregnancy preceding the onset of expression of all members of the placental PRL family except PL-I. DFX on day 10 of gestation did not affect the endocrine differentiation of the trophoblast cells but did alter the organization of the chorioallantoic placenta. PL-II, PL-Iv, and the PLPs were all expressed in their appropriate molecular forms and cell types in placentas developing in the absence of fetal influence. The maternal ovaries, in the absence of the fetus, had two distinct actions on the placenta: ovarian signals were essential during a period at midgestation for the maintenance of the placenta and exposure of the developing placenta to ovarian signals during the second half of gestation, in the absence of the fetus, arrested labyrinth zone development. The active ovarian signals were progesterone and estrogen. We conclude that trophoblast cell differentiation occurs independent of the fetus and maternal ovaries. However, signals from both the fetus and maternal ovaries are required for normal organization of the chorioallantoic placenta.