Does oxygen concentration affect shedding of trophoblastic debris or production of inflammatory mediators from first trimester human placenta?

Upregulation of pannexin-1 hemichannels explains the apparent death of the syncytiotrophoblast during human placental explant culture

BACKGROUND

It has been reported that during the culture of human placental explants, the syncytiotrophoblast dies between 3 and 24 h and is then replaced within 48 h by a new syncytiotrophoblast layer formed by the fusion of underlying cytotrophoblasts. Most frequently the death of the syncytiotrophoblast is indicated by the uptake of nuclear stains such as propidium iodide (PI). This process is reportedly similar in both early and late gestation placental explants.

METHODS

We cultured first trimester placental explants for up to 48 h and tested membrane intactness by exposure to PI. Connexin and pannexin mRNAs were quantified by RT-PCR and protein levels determined by immunofluorescence. The syncytiotrophoblast membrane leak was determined by culturing explants in the presence of hemichannel blockers. Extrusion of extracellular vesicles from the syncytiotrophoblast was quantified.

RESULTS

Nuclei of the syncytiotrophoblast were stained with PI following approximately 4 h of culture and this was prevented by culturing the explants with pannexin-1 blockers. Expression of pannexin-1 hemichannels increased during explant culture (p = 0.0027). Extracellular vesicles were most abundantly extruded from the explants during the first 3 h of culture and the temporal pattern of extrusion was unaltered by blocking hemichannels.

DISCUSSION

We show the mechanism of uptake of nuclear non-viability stains into the syncytiotrophoblast during explant culture is via upregulation of pannexin 1 hemichannels. Contrary to suggestions by some, the production of extracellular vesicles from cultured placental explants is not an in vitro artefact resulting from the apparent death of the syncytiotrophoblast in explant cultures.

Suppressyn localization and dynamic expression patterns in primary human tissues support a physiologic role in human placentation

We previously identified suppressyn (SUPYN), a placental protein that negatively regulates the cell fusion essential for trophoblast syncytialization via binding to the trophoblast receptor for syncytin-1, ASCT2, and hypothesized that SUPYN may thereby regulate cell-cell fusion in the placenta. Here, we redefine in vivo SUPYN localization using specific monoclonal antibodies in a rare early placental sample, showing SUPYN localization in villous and extravillous trophoblast subtypes, the decidua and even in placental debris in the maternal vasculature. In human trophoblast cell lines, we show SUPYN alters ASCT2 glycosylation within the secretory pathway and that this binding is associated with inhibition of cell fusion. Using newly-optimized trophoblast isolation protocols that allow tracking of ex vivo cell fusion, we present transcription and translation dynamics of fusion-related proteins over 96 hours in culture and the effects of changes in ambient oxygen levels on these processes. We report converse syncytin-1 and SUPYN transcriptional and translational responses to surrounding oxygen concentrations that suggest both are important in the effects of hypoxia and hyperoxia on placental syncytialization. Our results suggest that SUPYN’s anti-fusogenic properties may be exerted at several sites in the maternal body and its dysregulation may be associated with diseases of abnormal placentation.

Estimation of the burden of human placental micro- and nano-vesicles extruded into the maternal blood from 8 to 12 weeks of gestation

BACKGROUND

The human placenta extrudes a variety of extracellular vesicles (EVs) into the maternal blood daily. These vesicles may be crucial to the adaptation of the maternal cardiovascular and immune systems to pregnancy. Quantifying the EVs that are released in early gestation is important to our understanding of how placental EVs may contribute to the regulation of maternal physiology.

METHODS

EVs were isolated from first trimester placental explants and separated into micro- and nano-vesicles by differential centrifugation. The numbers of each type of EVs extruded from each milligram of placentae between gestational weeks 8 and 12 was determined by Nanoparticle Tracking Analysis. The total protein or DNA content of the vesicles was determined by BCA assay or Qubit^® 2.0.

RESULTS

Neither the number of micro- nor nano-EVs/mg explant (n = 49), nor the total protein (n = 19) and DNA content (n = 29) of these EVs changed significantly between 8 and 12 weeks of gestation. When the increasing placental weight with gestation was accounted for, the daily number of placental EVs extruded into the maternal blood increased by more than 100 fold between 8 and 12 weeks (micro-EVs 6.23 X 10¹⁴ and nano-EVs 1.84 X 10¹⁴ at 12 weeks, p = 0.0003).

DISCUSSION

Constant production of micro- and nano-EVs per-milligram placenta, regardless of gestational age, and the increased daily burden of EVs across gestational age indicate these EVs have the potential to regulate maternal physiology from early pregnancy. Since total EV protein content, like EV numbers was, constant, this is a potentially reliable surrogate for quantifying EVs.

Extravillous Trophoblast and Endothelial Cell Crosstalk Mediates Leukocyte Infiltration to the Early Remodeling Decidual Spiral Arteriole Wall

Decidual spiral arteriole (SpA) remodeling is essential to ensure optimal uteroplacental blood flow during human pregnancy, yet very little is known about the regulatory mechanisms. Uterine decidual NK (dNK) cells and macrophages infiltrate the SpAs and are proposed to initiate remodeling before colonization by extravillous trophoblasts (EVTs); however, the trigger for their infiltration is unknown. Using human first trimester placenta, decidua, primary dNK cells, and macrophages, we tested the hypothesis that EVTs activate SpA endothelial cells to secrete chemokines that have the potential to recruit maternal immune cells into SpAs. Gene array, real-time PCR, and ELISA analyses showed that treatment of endothelial cells with EVT conditioned medium significantly increased production of two chemokines, CCL14 and CXCL6. CCL14 induced chemotaxis of both dNK cells and decidual macrophages, whereas CXCL6 also induced dNK cell migration. Analysis of the decidua basalis from early pregnancy demonstrated expression of CCL14 and CXCL6 by endothelial cells in remodeling SpAs, and their cognate receptors are present in both dNK cells and macrophages. Neutralization studies identified IL-6 and CXCL8 as factors secreted by EVTs that induce endothelial cell CCL14 and CXCL6 expression. This study has identified intricate crosstalk between EVTs, SpA cells, and decidual immune cells that governs their recruitment to SpAs in the early stages of remodeling and has identified potential key candidate factors involved. This provides a new understanding of the interactions between maternal and fetal cells during early placentation and highlights novel avenues for research to understand defective SpA remodeling and consequent pregnancy pathology.

Trophoblastic debris extruded from hydatidiform molar placentae activates endothelial cells: Possible relevance to the pathogenesis of preeclampsia

INTRODUCTION

Preeclampsia is currently thought to be induced by a placental factor that triggers maternal endothelial activation. It is now well known that trophoblastic debris shed from the placenta into the maternal blood is associated with this disease. Hydatidiform mole is a pathological pregnancy characterised by hyperplastic trophoblast with little or no fetal development. Women with molar pregnancies may exhibit symptoms resembling preeclampsia. Deportation of trophoblastic debris occurs in molar pregnancies but, whether trophoblastic debris from molar pregnancies expresses pathogenic signals or activates endothelial cells is unknown.

METHODS

Trophoblastic debris were collected from either hydatidiform molar or normal first trimester placental explants and then exposed to monolayers of endothelial cell for 24 h. Endothelial cell activation was measured by quantifying cell-surface ICAM-1using ELISA. In addition, the expressions of High mobility group box 1(HMGB1) and heat shock protein 70 (HSP70) on molar placenta were examined by immunohistochemistry and western blotting. Circulating levels of sEndoglin in molar pregnancy was also measured.

RESULTS

Exposing trophoblastic debris from molar placentae increased endothelial cell surface ICAM-1 expression compared to endothelial cells exposed to trophoblastic debris from controls. Expression of HSP70 but not HMGB1 was significantly increased in hydatidiform molar placentae. The circulating levels of sEndoglin in hydatidiform molar pregnancy were not increased compared to controls.

DISCUSSION

Our results suggest that trophoblastic debris from molar pregnancies induces endothelial cell activation. HSP70 but not HMGB1 expressed on hydatidiform molar placenta may be a pathogenic signal to endothelial cells.

Proteomic characterization of macro-, micro- and nano-extracellular vesicles derived from the same first trimester placenta: relevance for feto-maternal communication

STUDY QUESTION

What proteins are carried by extracellular vesicles (EVs) released from normal first trimester placentae?

SUMMARY ANSWER

One thousand five hundred and eighty-five, 1656 and 1476 proteins were characterized in macro-, micro- and nano-vesicles, respectively, from first trimester placentae, with all EV fractions being enriched for proteins involved in vesicle transport and inflammation.

WHAT IS KNOWN ALREADY

Placental EVs are being increasingly recognized as important mediators of both healthy and pathological pregnancies. However, current research has focused on detecting changes in specific proteins in particular fractions of vesicles during disease. This is the first study to investigate the full proteome of different-sized fractions of EVs from the same first trimester placenta and highlights the differences/similarities between the vesicle fractions.

STUDY DESIGN, SIZE, DURATION

A well-established ex vivo placental explant culture model was used to generate macro-, micro- and nano-vesicles from 56 first trimester placentae. Vesicle fractions were collected by differential ultracentrifugation, quantified and characterized.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Placental macro-, micro- and nano-vesicles were characterized by microscopy, dynamic light scattering and nanoparticle tracking analysis. The proteome of each EV fraction was interrogated using liquid chromatography-coupled tandem mass spectrometry. Results were validated by semi-quantitative western blotting.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 1585, 1656 and 1476 proteins were identified in macro-, micro- and nano-vesicles, respectively. One thousand one hundred and twenty-five proteins were shared between all three fractions while up to 223 proteins were unique to each fraction. Gene Ontology pathway analysis showed an enrichment of proteins involved in vesicle transport and inflammation in all three fractions of EVs. The expression levels of proteins involved in internalization of vesicles (annexin V, calreticulin, CD31, CD47), the complement pathway [C3, decay-accelerating factor (DAF), membrane cofactor protein (MCP), protectin] and minor histocompatibility antigens [ATP-dependent RNA helicase (DDX3), ribosomal protein S4 (RPS4)] were different between different-sized EVs.

LIMITATIONS, REASONS FOR CAUTION

This study is largely hypothesis-generating in nature. It is important to validate these findings using EVs isolated from maternal plasma and the function of the different EV fractions would need further investigation.

WIDER IMPLICATIONS OF THE FINDINGS

Our results support the concept that various EV factions can interact with different maternal cells and have unique effects to mediate feto-maternal communication during early pregnancy. This study also provides a list of candidate proteins, which may inform the identification of robust markers that can be used to isolate placental vesicles from the maternal blood in the future.

STUDY FUNDING/COMPETING INTERESTS

M.T. is a recipient of the University of Auckland Health Research Doctoral Scholarship and the Freemasons Postgraduate Scholarship. This project was supported by a School of Medicine Performance-based research fund (PBRF) grant awarded to L.W.C. No authors have any conflicts of interest to disclose.

Validation of murine and human placental explant cultures for use in sex steroid and phase II conjugation toxicology studies

Human primary placental explant culture is well established for cytokine signaling and toxicity, but has not been validated for steroidogenic or metabolic toxicology. The technique has never been investigated in the mouse. We characterized human and mouse placental explants for up to 96 h in culture. Explant viability (Lactate dehydrogenase) and sex steroid levels were measured in media using spectrophotometry and ELISA, respectively. Expression and activities of the steroidogenic (3β-hydroxysteroid dehydrogenase, Cytochrome P45017A1, Cytochrome P45019), conjugation (UDP-glucuronosyltransferase, sulfotransferase (SULT)), and regeneration (β-glucuronidase, arylsulfatase C (ASC)) enzymes were determined biochemically in tissues with fluorimetric and spectrophotometric assays, and western blot. Explants were viable up to 96 h, but progesterone, estrone, and 17β-estradiol secretion decreased. Steroidogenic enzyme expression and activities were stable in mouse explants and similar to levels in freshly isolated tissues, but were lower in human explants than in fresh tissue (P<0.01). Human and mouse explants exhibited significantly less conjugation after 96 h, SULT was not detected in the mouse, and neither explants had active ASC, although proteins were expressed. Mouse explants may be useful for steroid biochemistry and endocrine disruption studies, but not metabolic conjugation. In contrast, human explants may be useful for studying conjugation for <48 h, but not for steroid/endocrine studies.

Trophoblast debris extruded from preeclamptic placentae activates endothelial cells: a mechanism by which the placenta communicates with the maternal endothelium

INTRODUCTION

Preeclampsia is characterized by maternal endothelial dysfunction. While the mechanisms leading to preeclampsia are unclear, a factor(s) from the placenta is responsible for triggering the disease. One placental factor implicated in triggering preeclampsia is trophoblast debris which may transmit pathogenic signals from the placenta to endothelial cells. In this study, we investigated whether trophoblast debris from preeclamptic placentae triggered endothelial cell activation.

METHODS

Trophoblast debris from preeclamptic or normotensive placentae, or trophoblast debris from normal placental explants that had been cultured with preeclamptic (n = 14) or normotensive sera (n = 14) was exposed to endothelial cells. Activation of the endothelial cells was quantified by cell surface ICAM-1 and U937 adhesion to endothelial cells. The levels of IL-1β, pro-caspase-1 and active caspase-1 in the trophoblast debris were measured.

RESULTS

Compared to controls, the levels of ICAM-1 and U937 adhesion to endothelial cells were significantly increased following exposure of the endothelial cells to trophoblast debris from preeclamptic placentae or placentae treated with preeclamptic sera. The levels IL-1β, pro-caspase-1 and active caspase-1 were significantly increased in both trophoblast debris from preeclamptic placentae and placentae treated with preeclamptic sera.

DISCUSSION

These results provide the first direct evidence that trophoblast debris produced from preeclamptic placentae or placentae treated with preeclamptic sera can activate the endothelium.

CONCLUSIONS

Trophoblast debris from preeclamptic but not normotensive placentae can induce endothelial cell activation. This may be one mechanism by which the preeclamptic placenta communicates with the maternal endothelium to induce activation of the endothelium.