Villous trophoblast: morphometric perspectives on growth, differentiation, turnover and deposition of fibrin-type fibrinoid during gestation

Characterizing Histopathologic Features in Pregnancies With Chronic Histiocytic Intervillositis Using Computerized Image Analysis

CONTEXT.—

Chronic histiocytic intervillositis (CHI) is a rare condition characterized by maternal immune cell infiltration into the human placenta. CHI is strongly associated with fetal growth restriction, miscarriage, and stillbirth, and knowledge of its etiology, and consequently effective treatment, is limited. Currently, diagnosis is largely subjective and varies between centers, making comparison between studies challenging.

OBJECTIVE.—

To objectively quantify and interrelate inflammatory cells and fibrin in placentas with CHI compared with controls and determine how pathology may be altered in subsequent pregnancies following diagnosis. Macrophage phenotype was also investigated in untreated cases of CHI.

DESIGN.—

Computerized analysis was applied to immunohistochemically stained untreated (index) cases of CHI, subsequent pregnancies, and controls. Index placentas were additionally stained by immunofluorescence for M1 (CD80 and CD86) and M2 macrophage markers (CD163 and CD206).

RESULTS.—

Quantification revealed a median 32-fold increase in macrophage infiltration in index cases versus controls, with CHI recurring in 2 of 11 (18.2%) subsequent pregnancies. A total of 4 of 14 placentas (28.6%) with a diagnosis of CHI did not exhibit infiltration above controls. Macrophages in index pregnancies strongly expressed CD163. There was no significant difference in fibrin deposition between index cases and controls, although subsequent pregnancies displayed a 2-fold decrease compared with index pregnancies. CD3+ T cells were significantly elevated in index pregnancies; however, they returned to normal levels in subsequent pregnancies.

CONCLUSIONS.—

In CHI, intervillous macrophages expressed CD163, possibly representing an attempt to resolve inflammation. Computerized analysis of inflammation in CHI may be useful in determining how treatment affects recurrence, and alongside pathologist expertise in grading lesion severity.

Assessment of the Integrity and Function of Human Term Placental Explants in Short-Term Culture

Human placental explants (HPEs) culture has generated significant interest as a valuable in vitro model for studying tissue functions in response to adverse conditions, such as fluctuations in oxygen levels, nutrient availability, exposure to pathogenic microorganisms, and toxic compounds. HPEs offers the advantage of replicating the intricate microenvironment and cell-to-cell communication involved in this critical and transient organ. Although HPEs culture conditions have been extensively discussed, a protocol for assessing the viability and function of HPEs during short-term culture has not been previously outlined. In this study, we have developed a short-term HPEs culture protocol, specifically up to 72 h, and have employed quantitative, semi-quantitative, and qualitative analyses to evaluate tissue viability and function over time. Under our standardized conditions, placental villi explants began to regain their structural properties (the integrity of the trophoblast and villous stroma) and the functionality of the HPEs (production of angiogenic, endocrine, and immunological factors) starting from 48 h of culture. This restoration ensures a suitable environment for several applications. The data presented here can be highly valuable for laboratories aiming to implement an HPEs model, whether in the process of standardization or seeking to enhance and optimize working conditions and timing with placental tissue.

The application of epiphenotyping approaches to DNA methylation array studies of the human placenta

BACKGROUND

Genome-wide DNA methylation (DNAme) profiling of the placenta with Illumina Infinium Methylation bead arrays is often used to explore the connections between in utero exposures, placental pathology, and fetal development. However, many technical and biological factors can lead to signals of DNAme variation between samples and between cohorts, and understanding and accounting for these factors is essential to ensure meaningful and replicable data analysis. Recently, "epiphenotyping" approaches have been developed whereby DNAme data can be used to impute information about phenotypic variables such as gestational age, sex, cell composition, and ancestry. These epiphenotypes offer avenues to compare phenotypic data across cohorts, and to understand how phenotypic variables relate to DNAme variability. However, the relationships between placental epiphenotyping variables and other technical and biological variables, and their application to downstream epigenome analyses, have not been well studied.

RESULTS

Using DNAme data from 204 placentas across three cohorts, we applied the PlaNET R package to estimate epiphenotypes gestational age, ancestry, and cell composition in these samples. PlaNET ancestry estimates were highly correlated with independent polymorphic ancestry-informative markers, and epigenetic gestational age, on average, was estimated within 4 days of reported gestational age, underscoring the accuracy of these tools. Cell composition estimates varied both within and between cohorts, as well as over very long placental processing times. Interestingly, the ratio of cytotrophoblast to syncytiotrophoblast proportion decreased with increasing gestational age, and differed slightly by both maternal ethnicity (lower in white vs. non-white) and genetic ancestry (lower in higher probability European ancestry). The cohort of origin and cytotrophoblast proportion were the largest drivers of DNAme variation in this dataset, based on their associations with the first principal component.

CONCLUSIONS

This work confirms that cohort, array (technical) batch, cell type proportion, self-reported ethnicity, genetic ancestry, and biological sex are important variables to consider in any analyses of Illumina DNAme data. We further demonstrate the specific utility of epiphenotyping tools developed for use with placental DNAme data, and show that these variables (i) provide an independent check of clinically obtained data and (ii) provide a robust approach to compare variables across different datasets. Finally, we present a general framework for the processing and analysis of placental DNAme data, integrating the epiphenotype variables discussed here.

The application of epiphenotyping approaches to DNA methylation array studies of the human placenta

Background : Genome-wide DNA methylation (DNAme) profiling of the placenta with Illumina Infinium Methylation bead arrays is often used to explore the connections between in utero exposures, placental pathology, and fetal development. However, many technical and biological factors can lead to signals of DNAme variation between samples and between cohorts, and understanding and accounting for these factors is essential to ensure meaningful and replicable data analysis. Recently, "epiphenotyping" approaches have been developed whereby DNAme data can be used to impute information about phenotypic variables such as gestational age, sex, cell composition, and ancestry. These epiphenotypes offer avenues to compare phenotypic data across cohorts, and to understand how phenotypic variables relate to DNAme variability. However, the relationships between placental epiphenotyping variables and other technical and biological variables, and their application to downstream epigenome analyses, have not been well studied. Results : Using DNAme data from 204 placentas across three cohorts, we applied the PlaNET R package to estimate epiphenotypes gestational age, ancestry, and cell composition in these samples. PlaNET ancestry estimates were highly correlated with independent polymorphic ancestry informative markers, and epigenetic gestational age, on average, was estimated within 4 days of reported gestational age, underscoring the accuracy of these tools. Cell composition estimates varied both within and between cohorts, but reassuringly were robust to placental processing time. Interestingly, the ratio of cytotrophoblast to syncytiotrophoblast proportion decreased with increasing gestational age, and differed slightly by both maternal ethnicity (lower in white vs. non-white) and genetic ancestry (lower in higher probability European ancestry). The cohort of origin and cytotrophoblast proportion were the largest drivers of DNAme variation in this dataset, based on their associations with the first principal component. Conclusions : This work confirms that cohort, array (technical) batch, cell type proportion, self-reported ethnicity, genetic ancestry, and biological sex are important variables to consider in any analyses of Illumina DNAme data. Further, we demonstrate that estimating epiphenotype variables from the DNAme data itself, when possible, provides both an independent check of clinically-obtained data and can provide a robust approach to compare variables across different datasets.

Potentially causal associations between placental DNA methylation and schizophrenia and other neuropsychiatric disorders

Increasing evidence supports the role of placenta in neurodevelopment and potentially, in the later onset of neuropsychiatric disorders. Recently, methylation quantitative trait loci (mQTL) and interaction QTL (iQTL) maps have proven useful to understand SNP-genome wide association study (GWAS) relationships, otherwise missed by conventional expression QTLs. In this context, we propose that part of the genetic predisposition to complex neuropsychiatric disorders acts through placental DNA methylation (DNAm). We constructed the first public placental cis-mQTL database including nearly eight million mQTLs calculated in 368 fetal placenta DNA samples from the INMA project, ran cell type- and gestational age-imQTL models and combined those data with the summary statistics of the largest GWAS on 10 neuropsychiatric disorders using Summary-based Mendelian Randomization (SMR) and colocalization. Finally, we evaluated the influence of the DNAm sites identified on placental gene expression in the RICHS cohort. We found that placental cis-mQTLs are highly enriched in placenta-specific active chromatin regions, and useful to map the etiology of neuropsychiatric disorders at prenatal stages. Specifically, part of the genetic burden for schizophrenia, bipolar disorder and major depressive disorder confers risk through placental DNAm. The potential causality of several of the observed associations is reinforced by secondary association signals identified in conditional analyses, regional pleiotropic methylation signals associated to the same disorder, and cell type-imQTLs, additionally associated to the expression levels of relevant immune genes in placenta. In conclusion, the genetic risk of several neuropsychiatric disorders could operate, at least in part, through DNAm and associated gene expression in placenta.

Human placental proteomics and exon variant studies link AAT/SERPINA1 with spontaneous preterm birth

BACKGROUND

Preterm birth is defined as live birth before 37 completed weeks of pregnancy, and it is a major problem worldwide. The molecular mechanisms that lead to onset of spontaneous preterm birth are incompletely understood. Prediction and evaluation of the risk of preterm birth is challenging as there is a lack of accurate biomarkers. In this study, our aim was to identify placental proteins that associate with spontaneous preterm birth.

METHODS

We analyzed the proteomes from placentas to identify proteins that associate with both gestational age and spontaneous labor. Next, rare and potentially damaging gene variants of the identified protein candidates were sought for from our whole exome sequencing data. Further experiments we performed on placental samples and placenta-associated cells to explore the location and function of the spontaneous preterm labor-associated proteins in placentas.

RESULTS

Exome sequencing data revealed rare damaging variants in SERPINA1 in families with recurrent spontaneous preterm deliveries. Protein and mRNA levels of alpha-1 antitrypsin/SERPINA1 from the maternal side of the placenta were downregulated in spontaneous preterm births. Alpha-1 antitrypsin was expressed by villous trophoblasts in the placenta, and immunoelectron microscopy showed localization in decidual fibrinoid deposits in association with specific extracellular proteins. siRNA knockdown in trophoblast-derived HTR8/SVneo cells revealed that SERPINA1 had a marked effect on regulation of the actin cytoskeleton pathway, Slit-Robo signaling, and extracellular matrix organization.

CONCLUSIONS

Alpha-1 antitrypsin is a protease inhibitor. We propose that loss of the protease inhibition effects of alpha-1 antitrypsin renders structures critical to maintaining pregnancy susceptible to proteases and inflammatory activation. This may lead to spontaneous premature birth.

The etiology of preeclampsia

Preeclampsia is one of the "great obstetrical syndromes" in which multiple and sometimes overlapping pathologic processes activate a common pathway consisting of endothelial cell activation, intravascular inflammation, and syncytiotrophoblast stress. This article reviews the potential etiologies of preeclampsia. The role of uteroplacental ischemia is well-established on the basis of a solid body of clinical and experimental evidence. A causal role for microorganisms has gained recognition through the realization that periodontal disease and maternal gut dysbiosis are linked to atherosclerosis, thus possibly to a subset of patients with preeclampsia. The recent reports indicating that SARS-CoV-2 infection might be causally linked to preeclampsia are reviewed along with the potential mechanisms involved. Particular etiologic factors, such as the breakdown of maternal-fetal immune tolerance (thought to account for the excess of preeclampsia in primipaternity and egg donation), may operate, in part, through uteroplacental ischemia, whereas other factors such as placental aging may operate largely through syncytiotrophoblast stress. This article also examines the association between gestational diabetes mellitus and maternal obesity with preeclampsia. The role of autoimmunity, fetal diseases, and endocrine disorders is discussed. A greater understanding of the etiologic factors of preeclampsia is essential to improve treatment and prevention.

Omics Approaches to Study Formation and Function of Human Placental Syncytiotrophoblast

Proper development of the placenta is vital for pregnancy success. The placenta regulates exchange of nutrients and gases between maternal and fetal blood and produces hormones essential to maintain pregnancy. The placental cell lineage primarily responsible for performing these functions is a multinucleated entity called syncytiotrophoblast. Syncytiotrophoblast is continuously replenished throughout pregnancy by fusion of underlying progenitor cells called cytotrophoblasts. Dysregulated syncytiotrophoblast formation disrupts the integrity of the placental exchange surface, which can be detrimental to maternal and fetal health. Moreover, various factors produced by syncytiotrophoblast enter into maternal circulation, where they profoundly impact maternal physiology and are promising diagnostic indicators of pregnancy health. Despite the multifunctional importance of syncytiotrophoblast for pregnancy success, there is still much to learn about how its formation is regulated in normal and diseased states. ‘Omics’ approaches are gaining traction in many fields to provide a more holistic perspective of cell, tissue, and organ function. Herein, we review human syncytiotrophoblast development and current model systems used for its study, discuss how ‘omics’ strategies have been used to provide multidimensional insights into its formation and function, and highlight limitations of current platforms as well as consider future avenues for exploration.

Cell dynamics in human villous trophoblast

BACKGROUND

Villous cytotrophoblast (vCTB) is a precursor cell population that supports the development of syncytiotrophoblast (vSTB), the high surface area barrier epithelium of the placental villus, and the primary interface between maternal and fetal tissue. In light of increasing evidence that the placenta can adapt to changing maternal environments or, under stress, can trigger maternal disease, we consider what properties of these cells empower them to exert a controlling influence on pregnancy progression and outcome.

OBJECTIVE AND RATIONALE

How are cytotrophoblast proliferation and differentiation regulated in the human placental villus to allow for the increasing demands of the fetal and environmental challenges and stresses that may arise during pregnancy?

SEARCH METHODS

PubMed was interrogated using relevant keywords and word roots combining trophoblast, villus/villous, syncytio/syncytium, placenta, stem, transcription factor (and the individual genes), signalling, apoptosis, autophagy (and the respective genes) from 1960 to the present. Since removal of trophoblast from its tissue environment is known to fundamentally change cell growth and differentiation kinetics, research that relied exclusively on cell culture has not been the main focus of this review, though it is mentioned where appropriate. Work on non-human placenta is not systematically covered, though mention is made where relevant hypotheses have emerged.

OUTCOMES

The synthesis of data from the literature has led to a new hypothesis for vCTB dynamics. We propose that a reversible transition can occur from a reserve population in G0 to a mitotically active state. Cells from the in-cycle population can then differentiate irreversibly to intermediate cells that leave the cycle and turn on genes that confer the capacity to fuse with the overlying vSTB as well as other functions associated with syncytial barrier and transport function. We speculate that alterations in the rate of entry to the cell cycle, or return of cells in the mitotic fraction to G0, can occur in response to environmental challenge. We also review evidence on the life cycle of trophoblast from the time that fusion occurs, and point to gaps in knowledge of how large quantities of fetal DNA arrive in maternal circulation. We critique historical methodology and make a case for research to re-address questions about trophoblast lifecycle and dynamics in normal pregnancy and the common diseases of pre-eclampsia and fetal growth restriction, where altered trophoblast kinetics have long been postulated.

WIDER IMPLICATIONS

The hypothesis requires experimental testing, moving research away from currently accepted methodology towards a new standard that includes representative cell and tissue sampling, assessment of cell cycle and differentiation parameters, and robust classification of cell subpopulations in villous trophoblast, with due attention to gestational age, maternal and fetal phenotype, disease and outcome.

Disorders of placental villous maturation are present in one-third of cases with spontaneous preterm labor

OBJECTIVES

Spontaneous preterm labor is an obstetrical syndrome accounting for approximately 65-70% of preterm births, the latter being the most frequent cause of neonatal death and the second most frequent cause of death in children less than five years of age worldwide. The purpose of this study was to determine and compare to uncomplicated pregnancies (1) the frequency of placental disorders of villous maturation in spontaneous preterm labor; (2) the frequency of other placental morphologic characteristics associated with the preterm labor syndrome; and (3) the distribution of these lesions according to gestational age at delivery and their severity.

METHODS

A case-control study of singleton pregnant women was conducted that included (1) uncomplicated pregnancies (controls, n=944) and (2) pregnancies with spontaneous preterm labor (cases, n=438). All placentas underwent histopathologic examination. Patients with chronic maternal diseases (e.g., chronic hypertension, diabetes mellitus, renal disease, thyroid disease, asthma, autoimmune disease, and coagulopathies), fetal malformations, chromosomal abnormalities, multifetal gestation, preeclampsia, eclampsia, preterm prelabor rupture of the fetal membranes, gestational hypertension, gestational diabetes mellitus, and HELLP (hemolysis, elevated liver enzymes and low platelet count) syndrome were excluded from the study.

RESULTS

Compared to the controls, the most prevalent placental lesions among the cases were the disorders of villous maturation (31.8% [106/333] including delayed villous maturation 18.6% [62/333] vs. 1.4% [6/442], q<0.0001, prevalence ratio 13.7; and accelerated villous maturation 13.2% [44/333] vs. 0% [0/442], q<0.001). Other lesions in decreasing order of prevalence included hypercapillarized villi (15.6% [68/435] vs. 3.5% [33/938], q<0.001, prevalence ratio 4.4); nucleated red blood cells (1.1% [5/437] vs. 0% [0/938], q<0.01); chronic inflammatory lesions (47.9% [210/438] vs. 29.9% [282/944], q<0.0001, prevalence ratio 1.6); fetal inflammatory response (30.1% [132/438] vs. 23.2% [219/944], q<0.05, prevalence ratio 1.3); maternal inflammatory response (45.5% [195/438] vs. 36.1% [341/944], q<0.01, prevalence ratio 1.2); and maternal vascular malperfusion (44.5% [195/438] vs. 35.7% [337/944], q<0.01, prevalence ratio 1.2). Accelerated villous maturation did not show gestational age-dependent association with any other placental lesion while delayed villous maturation showed a gestational age-dependent association with acute placental inflammation (q-value=0.005).

CONCLUSIONS

Disorders of villous maturation are present in nearly one-third of the cases of spontaneous preterm labor.

Cell-specific characterization of the placental methylome

BACKGROUND

DNA methylation (DNAm) profiling has emerged as a powerful tool for characterizing the placental methylome. However, previous studies have focused primarily on whole placental tissue, which is a mixture of epigenetically distinct cell populations. Here, we present the first methylome-wide analysis of first trimester (n = 9) and term (n = 19) human placental samples of four cell populations: trophoblasts, Hofbauer cells, endothelial cells, and stromal cells, using the Illumina EPIC methylation array, which quantifies DNAm at > 850,000 CpGs.

RESULTS

The most distinct DNAm profiles were those of placental trophoblasts, which are central to many pregnancy-essential functions, and Hofbauer cells, which are a rare fetal-derived macrophage population. Cell-specific DNAm occurs at functionally-relevant genes, including genes associated with placental development and preeclampsia. Known placental-specific methylation marks, such as those associated with genomic imprinting, repetitive element hypomethylation, and placental partially methylated domains, were found to be more pronounced in trophoblasts and often absent in Hofbauer cells. Lastly, we characterize the cell composition and cell-specific DNAm dynamics across gestation.

CONCLUSIONS

Our results provide a comprehensive analysis of DNAm in human placental cell types from first trimester and term pregnancies. This data will serve as a useful DNAm reference for future placental studies, and we provide access to this data via download from GEO (GSE159526), through interactive exploration from the web browser ( https://robinsonlab.shinyapps.io/Placental_Methylome_Browser/ ), and through the R package planet, which allows estimation of cell composition directly from placental DNAm data.

The placenta in fetal growth restriction: What is going wrong?

The placenta is essential for the efficient delivery of nutrients and oxygen from mother to fetus to maintain normal fetal growth. Dysfunctional placental development underpins many pregnancy complications, including fetal growth restriction (FGR) a condition in which the fetus does not reach its growth potential. The FGR placenta is smaller than normal placentae throughout gestation and displays maldevelopment of both the placental villi and the fetal vasculature within these villi. Specialized epithelial cells called trophoblasts exhibit abnormal function and development in FGR placentae. This includes an altered balance between proliferation and apoptotic death, premature cellular senescence, and reduced colonisation of the maternal decidual tissue. Thus, the placenta undergoes aberrant changes at the macroscopic to cellular level in FGR, which can limit exchange capacity and downstream fetal growth. This review aims to compile stereological, in vitro, and imaging data to create a holistic overview of the FGR placenta and its pathophysiology, with a focus on the contribution of trophoblasts.

Disorders of placental villous maturation in fetal death

Objective The aims of this study were to ascertain the frequency of disorders of villous maturation in fetal death and to also delineate other placental histopathologic lesions in fetal death. Methods This was a retrospective observational cohort study of fetal deaths occurring among women between January 2004 and January 2016 at Hutzel Women's Hospital, Detroit, MI, USA. Cases comprised fetuses with death beyond 20 weeks' gestation. Fetal deaths with congenital anomalies and multiple gestations were excluded. Controls included pregnant women without medical/obstetrical complications and delivered singleton, term (37-42 weeks) neonate with 5-min Apgar score ≥7 and birthweight between the 10th and 90th percentiles. Results Ninety-two percent (132/143) of placentas with fetal death showed placental histologic lesions. Fetal deaths were associated with (1) higher frequency of disorders of villous maturation [44.0% (64/143) vs. 1.0% (4/405), P < 0.0001, prevalence ratio, 44.6; delayed villous maturation, 22% (31/143); accelerated villous maturation, 20% (28/143); and maturation arrest, 4% (5/143)]; (2) higher frequency of maternal vascular malperfusion lesions [75.5% (108/143) vs. 35.7% (337/944), P < 0.0001, prevalence ratio, 2.1] and fetal vascular malperfusion lesions [88.1% (126/143) vs. 19.7% (186/944), P < 0.0001, prevalence ratio, 4.5]; (3) higher frequency of placental histologic patterns suggestive of hypoxia [59.0% (85/143) vs. 9.3% (82/942), P < 0.0001, prevalence ratio, 6.8]; and (4) higher frequency of chronic inflammatory lesions [53.1% (76/143) vs. 29.9% (282/944), P < 0.001, prevalence ratio 1.8]. Conclusion This study demonstrates that placentas of women with fetal death were 44 times more likely to present disorders of villous maturation compared to placentas of those with normal pregnancy. This suggests that the burden of placental disorders of villous maturation lesions is substantial.

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.

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 immunology of the macaque placenta: A detailed analysis and critical comparison with the human placenta

The cynomolgus monkey is increasingly considered in toxicological research as the most appropriate model for humans due to the species' close physiological contiguity, including reproductive physiology. Here, literature on the cynomolgus monkey placenta is reviewed in regards to its similarity to the human placenta and particularly for its immunological role, which is not entirely mirrored in humans. Pertinent original data are included in this article. The cynomolgus monkey placenta is evaluated based on three aspects: first, morphological development; second, the spatial and temporal appearance of maternal and fetal immune cells and certain immune cell products of the innate and adaptive immune systems; and third, the expression of relevant immune tolerance-related molecules including the homologs of anti-human leucocyte antigen, indoleamine 2,3-dioxygenase, FAS/FAS-L, annexin II, and progesterone. Parameters relevant to the immunological role of the placenta are evaluated from the immunologically immature stage of gestational day (GD) 50 until more mature stages close to birth. Selected comparisons are drawn with human and other laboratory animal placentas. In conclusion, the cynomolgus monkey placenta has a high degree of morphological and physiological similarity to the human placenta. However, there are differences in the topographical distribution of cell types and immune tolerance-related molecules. Three basic features are recognized: (1) the immunological capacity of the placenta changes throughout the lifetime of the organ; (2) these immunological changes include multiple parameters such as morphological adaptations, cell type involvement, and changes in immune-relevant molecule expression; and (3) the immune systems of two genetically disparate individuals (mother and child) are functionally intertwined at the maternal-fetal interface.

Placental Lesions in Meconium Aspiration Syndrome

Background

Meconium aspiration syndrome (MAS) is defined by respiratory distress requiring supplemental oxygen in a meconium-stained neonate. MAS is clinically subclassified as mild, moderate, and severe according to the oxygen requirement. The aims of this study were to compare the histological findings in the placentas of MAS neonates with those of meconium-stained but non-MAS neonates and to analyze the correlation between the severity of MAS and the grade of its histological parameters.

Methods

We collected 160 singleton term placentas from neonates with meconium staining at birth from a tertiary medical center, Seoul, Republic of Korea. We reviewed hematoxylin and eosin sections of tissue samples (full-thickness placental disc, chorioamniotic membranes, and umbilical cord).

Results

Funisitis was present more frequently in MAS than in non-MAS (p < .01), of which the stage was correlated with the severity of MAS (p < .001). The histological findings consistent with maternal underperfusion and chronic deciduitis were more frequent in MAS than in non-MAS (p < .05). There was a correlation between the degree of chorionic vascular muscle necrosis and the severity of MAS (p < .05).

Conclusions

Our results suggest that fetal inflammatory response evidenced by funisitis occurs prenatally in MAS and that the stage of funisitis and of chorionic vascular muscle necrosis may be a predictive marker of the severity of MAS.

Working Towards a Reproducible Method for Quantifying Placental Syncytial Knots

Prominent syncytial knots (SK) in placentas signal advanced gestation or placental malperfusion, reflecting exposures that adversely affect placental development and pregnancy outcomes. Molecular-level interrogations of syncytiotrophoblast have altered perceptions of and raised questions about the function and disposition of SK. Quantifying SK and achieving acceptable levels of interrater reliability have been challenging. Our objective was to develop a simple, reproducible protocol for counting SK and demonstrate interrater reliability overall and within 3 parameters, ie, preterm vs term delivery, presence vs absence of diffuse prominent SK (DPSK), and SK relationship with a lesion, all of which could influence measurement reproducibility and interpretation. Criteria for defining SK and a grid system drawn on glass slides were developed for counting percentage of villi with SK. One disc section each from 151 placentas, sampled from 8 groups defined by the 3 parameters, was assessed by 2 pretrained pathologists. The resulting weighted kappa statistic for overall interrater agreement was 0.60 (very good) and Spearman correlation coefficient for ranking quartiles was >0.70. Agreement was best for preterm placentas, kappa  =  0.61, and those only showing DPSK associated with a lesion, kappa  =  0.67. Agreement was low in the absence of DPSK, kappa  =  0.22, or when DPSK was present in a placenta not associated with a lesion, kappa  =  0.32. The proposed method offers a potentially reliable approach for categorizing SK counts as normal vs abnormal or providing continuous measure counts. More extensive pretraining, focused on placentas with few SK and those without an associated lesion, is recommended to improve agreement.

The Influence of Oxygen and Tumor Necrosis Factor-α on the Cellular Kinetics of Term Placental Villous Explants in Culture

Explanted placental fragments may provide a more physiological in vitro model of component cell function than single cell isolates. We have characterized these fragments for cell turnover and have monitored responses from 14 normal placentas under conditions of exogenous TNFα and atypical oxygen concentrations (3% and 17%), conditions associated with abnormal pregnancy and an aberrant in utero environment. Explants were assessed for apoptotic morphology, immunolocalization of Mib-1 (a proliferation marker), caspase 3 activity (an apoptosis promoter), lactate dehydrogenase (a necrosis marker), and human chorionic gonadotrophin [hCG, a marker of cytotrophoblast (CT) differentiation]. Consistent with a reduction in hCG, explants under 17% O2 (with and without TNFα) showed a progressive degeneration of syncytiotrophoblast (ST) (days 0–2) followed by a restoration of hCG (days 4–8) localized to newly differentiated but not syncytialized CTs. In 3% O2, hCG showed the same initial decline but failed to recover thereafter. Proliferation dropped significantly in 17% O2 but was restored and exaggerated sixfold in 3% O2. All reductions in hCG were associated with cell death and caspase-3. Early apoptosis was linked with syncytial loss; later apoptosis (days 8–11) was localized to the non-ST. Prolonged exposure to TNFα (days 4–11) increased ST apoptosis and necrosis but 3% O2 had no significant effect. These findings show that placental explants can accommodate many aspects of CT proliferation, differentiation, and ST apoptosis in culture. TNFα enhanced ST decline but 3% oxygen (compared with 17%) was associated with reduced CT differentiation and a strong shift towards proliferation. These outcomes may reflect previous morphological changes in compromised pregnancies and confirm a possible role for oxygen and TNFα in aberrant trophoblast turnover.

PreImplantation Factor (PIF*) endogenously prevents preeclampsia: Promotes trophoblast invasion and reduces oxidative stress

Preeclampsia is a unique pregnancy disorder whose patho-physiology is initiated early in gestation, while clinical manifestations typically occur in mid-to-late pregnancy. Thus, prevention should optimally be initiated in early gestation. The intimate interaction between PIF, secreted early by viable embryos, and its host-mother provides insight into putative mechanisms of preeclampsia prevention. PIF is instrumental at the two critical events underlying preeclampsia. At first, shallow implantation leads to impaired placentation, oxidative stress, protein misfolding, and endothelial dysfunction. Later in gestation, hyper-oxygenation due to overflow of maternally derived oxygenated blood compromises the placenta. The first is likely involved in early preeclampsia occurrence due to reduced effectiveness of trophoblast/uterus interaction. The latter is observed with later-onset preeclampsia, caused by a breakdown in placental blood flow regulation. We reported that 1. PIF promotes implantation, endometrium receptivity, trophoblast invasion and increases pro-tolerance trophoblastic HLA-G expression and, 2. PIF protects against oxidative stress and protein misfolding, interacting with specific targets in embryo, 3. PIF regulates systemic immunity to reduce oxidative stress. Using PIF as an early preventative preeclampsia intervention could ameliorate or even prevent the disease, whose current main solution is early delivery.

Turnover of human villous trophoblast in normal pregnancy: what do we know and what do we need to know?

How the turnover of villous trophoblast is regulated is important for understanding normal and complicated pregnancies. There is considerable accord that syncytiotrophoblast (STB) grows and is refreshed by recruiting post-mitotic cells from the deeper cytotrophoblast (CTB). Nuclei in STB exhibit a spectrum of morphologies and packing densities and, until recently, there seemed to be a consensus that this variation reflected a transition from an early undifferentiated CTB-like phenotype to a long pre-apoptotic and brief apoptotic phase. In these later phases, nuclei are sequestered in clusters (syncytial knots) prior to extrusion as part of normal epithelial turnover. Early in gestation, nuclear clustering and formation of protrusions (syncytial sprouts) also occurs as a preliminary to villous sprouting. Nuclei in these clusters have a CTB-like phenotype and some sprouts may also detach from STB and pass into the uteroplacental circulation. However, this apparent consensus has been challenged and new interpretations of events in the proliferative (CTB), terminal differentiation (STB) and deportation compartments have emerged. Several different types of STB fragment are deported in normal pregnancy: larger multinucleate STB fragments, smaller uninucleate elements with CTB-like morphology, anucleate cytoplasmic fragments, microparticles and nanovesicles. This review identifies points of agreement and disagreement and offers possible avenues of future research. An obvious need is to standardise best practice in several areas including choosing appropriate references for cell cycle phase labelling indices and combining immunolabeling of cell cycle and apoptosis markers (at LM or TEM levels) with design-based stereological estimates of absolute numbers of cells and nuclei in different compartments throughout normal gestation. This would also provide a surer foundation for interpreting results from different research groups and changes in normal and complicated pregnancies.

Placental villous hypermaturation is associated with idiopathic preterm birth

OBJECTIVE

Pregnancy complications such as intra-amniotic infection, preeclampsia, and fetal intrauterine growth restriction (IUGR) account for most cases of preterm birth (PTB), but many spontaneous PTB cases do not have a clear etiology. We hypothesize that placental insufficiency may be a potential cause of idiopathic PTB.

METHODS

Secondary analysis of 82 placental samples from women with PTB obtained from a multicenter trial of repeat versus single antenatal corticosteroids. Samples were centrally reviewed by a single placental pathologist masked to clinical outcomes. The histopathologic criterion for infection was the presence of acute chorioamnionitis defined as neutrophils marginating into the chorionic plate. Placental villous hypermaturation (PVH) was defined as a predominance of terminal villi (similar to term placenta) with extensive syncytial knotting. Idiopathic PTB comprised a group without another known etiology such as preeclampsia, IUGR or infection.

RESULTS

Acute chorioamnionitis was observed in 33/82 (40%) cases. Other known causes of PTB were reported in 18/82 (22%). The remaining 31/82 (38%) were idiopathic. The frequency of PVH in idiopathic PTB (26/31 = 84%) was similar to cases with IUGR or preeclampsia (16/18 = 89%), but significantly more common than PVH in the group with acute chorioamnionitis (10/33 = 30%) (p < 0.001).

CONCLUSIONS

PVH, which is a histologic marker of relative placental insufficiency, is a common finding in idiopathic PTB.

Magnetic resonance imaging relaxation time measurements of the placenta at 1.5 T

Placental insufficiency is a major cause of fetal growth restriction (FGR) and accumulating evidence indicates several aspects of placental morphology are altered in this condition. MRI provides quantitative indices that may be used in non-invasive assessment of the human placenta, such as relaxation time measurements, T1 and T2. We hypothesised that placental relaxation times relate to alterations in placental tissue morphology and hence may be useful in identifying the changes associated with FGR. We report on the first phase of testing this hypothesis, in a study of women in normal pregnancy.

AIMS

To assess relaxation time measurements in the placenta in normal pregnancy and correlate these with gestational age and stereological analyses of placental morphology following delivery.

METHODS

30 women underwent MRI examination (1.5 T) between 20 and 41 weeks gestation. Placental T1 and T2 measurements were acquired from a mid-depth placental region, co-localised to a structural scan. Fixed, wax-embedded sections of these placentas collected at delivery were stained with hematoxylin/eosin and subjected to stereological analysis.

RESULTS

Placental T1 and T2 show a significant negative correlation with gestation, (Pearson correlation p=0.01, 0.03 respectively). 17 placentas were analysed stereologically. In the group as a whole there was no significant correlation between T1 and T2 and morphological features. However, in a subset of 7 pregnancies scanned within a week of delivery, a significant positive correlation was observed between the fibrin volume density and the ratio of fibrin: villous volume densities and T2 (Spearman correlation p=0.02, 0.03 respectively).

DISCUSSION

The correlations between placental T1 and T2 and gestation show that these variables are clearly influenced by changes in placental structure. Fibrin might be a key component but further work is needed to fully elucidate the major structural influences on placental T1 and T2.

Thrombophilic-type placental pathologies and skeletal growth delay following maternal administration of angiostatin4.5 in mice

During placentation, the concentration of fibrinous deposits on the surfaces of maternal vasculature plays a role in villous development and has been strongly implicated in the pathophysiology of human fetal growth restriction (FGR). Fibrinous deposits are conspicuous sites of platelet aggregation where there is local activation of the hemostatic cascade. During activation of the hemostatic cascade, a number of pro- and antiangiogenic agents may be generated at the cell surface, and an imbalance in these factors may contribute to the placental pathology characteristic of FGR. We tested the hypothesis that angiostatin(4.5) (AS(4.5)), a cleavage fragment of plasminogen liberated at the cell surface, is capable of causing FGR in mice. Increased maternal levels of AS(4.5) in vivo result in reproducible placental pathology, including an altered vascular compartment (both in decidual and labyrinthine layers) and increased apoptosis throughout the placenta. In addition, there is significant skeletal growth delay and conspicuous edema in fetuses from mothers that received AS(4.5). Maternally generated AS(4.5), therefore, can access maternal placental vasculature and have a severe effect on placental architecture and inhibit fetal development in vivo. These findings strongly support the hypothesis that maternal AS(4.5) levels can influence placental development, possibly by directly influencing trophoblast turnover in the placenta, and contribute to fetal growth delay in mice.

Syncytial knots as a reflection of placental maturity: reference values for 20 to 40 weeks' gestational age

Syncytiotrophoblastic knots or syncytial knots are aggregates of syncytial nuclei at the surface of terminal villi. In the term placenta, most syncytial knots are thought to be artifacts from tangential sectioning while the minority are syncytial sprouts, bridges, or apoptotic knots. Syncytial knots are consistently present, increasing with increasing gestational age, and can be used to evaluate villous maturity. Increased syncytial knots are associated with conditions of uteroplacental malperfusion and are important in placental examination. Although 30% of terminal villi with syncytial knots at term are often reported, no reference values have been developed for the percentage of villi with syncytial knots at different gestational ages. We counted the percentage of chorionic villi with syncytial knots at different gestational ages from 20 to 40 weeks using cases with no history of malperfusion or clinical conditions known to be associated with malperfusion. We provide normal reference data for the average percentage of syncytial knots for gestational ages ranging from 20 to 40 weeks. There was a significant positive correlation of gestational age with percentage of villi with syncytial knots. Term placentas (37-40 weeks) showed an average of 28% syncytial knots. A drop-off to a mean of 22.5% was noted at 36 weeks; at 26 to 33 weeks, syncytial knots varied from 10.8% to 14.7%; between 20 and 25 weeks, syncytial knots ranged between 5.2% and 9.l%. These reference data can facilitate histologic assessment of normal placental maturation as well as evaluation of placental morphology in placental malperfusion.

Regulation of trophoblast migration and survival by a novel neural regeneration peptide

Although placental trophoblast migration is tightly controlled in an autocrine/paracrine manner, the nature of chemoattractive factors facilitating and directing this biological activity remains largely elusive. Neural regeneration peptides (NRP), a recently discovered peptide family, stimulate neuronal migration, differentiation and survival of post-natal neurons within the murine central nervous system. Based on the neural-repair related activities of these peptides and parallels between neuronal and placental cell behaviour patterns, this study postulated that they play a role in placental development, in particular trophoblast migration and survival and investigated the role of a newly discovered NRP motif (NNZ-4920), which exhibits about 70% homology to the mouse NRP motif sequence and is homologous to a 13-mer fragment within the N-terminus of human CAPS2, in trophoblast migration and survival regulation. NNZ-4920 significantly enhanced trophoblast migration by 51% (P<0.01) compared with controls and protected against stress induced by serum withdrawal and tumour necrosis factor-alpha/interferon-gamma treatment, at femtomolar concentrations, with efficacy similar to epidermal growth factor. CAPS2 expression was detected in purified term trophoblast and decidual cells. In conclusion, the placenta may be a source of NRP-related gene expression. Its encoded peptide products exert biological effects on term trophoblast migration and survival in vitro.

Placental dysferlin expression is reduced in severe preeclampsia

Dysferlin (DYSF) and myoferlin (MYOF), members of the ferlin family of membrane proteins, are co-expressed in human placental syncytiotrophoblast (STB). Although the role of these ferlin proteins in the placenta has yet to be established, it has been suggested that DYSF and MYOF may contribute to the stability of the apical STB plasma membrane. The release of STB-derived cellular debris increases in the setting of preeclampsia (PE), suggesting relative destabilization of the hemochorial interface. To test whether PE was associated with alterations in placental expression of DYSF and/or MYOF, a cross-sectional study was performed using specimens of villous placenta collected form women with severe PE (n=10) and normotensive controls (n=10). DYSF and MYOF expression were examined using quantitative real-time RT-PCR, immunoblotting, and immunofluorescence labeling of tissue specimens. Placental DYSF expression was 57% lower at the mRNA level (p=0.03) and 38% lower at the protein level (p=0.026) in severe PE as compared to normotensive subjects. There were no differences in placental MYOF protein or mRNA expression between these groups. No appreciable changes in the distribution of DYSF or MYOF within placental villi was observed in PE relative to control specimens. We conclude that DYSF expression is reduced in severe PE relative to gestational age-matched controls. As DYSF has a role in membrane repair, these data suggest a role for DYSF in the stability of the apical STB plasma membrane and may account, at least in part, for the increased shedding of microparticles from this membrane in PE.

The C5b-9 membrane attack complex of complement activation localizes to villous trophoblast injury in vivo and modulates human trophoblast function in vitro

The complement system plays an important role in normal human pregnancy. Uncontrolled activation of this system has been associated with many disease states. We tested the hypothesis that the C5b-9 membrane attack complex (MAC) localizes to sites of villous injury and modulates trophoblast function. Placental sections from pregnancies with no complications, intrauterine growth restriction, or preeclampsia were immunostained and the surface density for MAC and fibrin was determined by morphometric analysis. Primary cytotrophoblasts from term placentas were cultured in a FiO(2) of <1%, 8% and 20% with 10% human serum containing active MAC or heat-inactivated control serum. Immunofluorescent MAC binding to trophoblast was quantified, and the neoepitopes formed in cytokeratin 18 filaments and poly-ADP-ribose polymerase during apoptosis were used to measure cell death. Trophoblast differentiation was assessed by HCG secretion, formation of syncytia, and expression of syncytin. MAC localized to fibrin deposits in normal placentas, and especially in placentas from IUGR and preeclampsia. MAC binding to cytotrophoblasts was inversely proportional to FiO(2) and enhanced apoptosis. MAC increased markers of differentiation in cultures at 72h (medium HCG, syncytia and syncytin expression). Our findings demonstrate that MAC associates with fibrin deposits at sites of villous injury in vivo. Hypoxia also enhances MAC deposition in cultured trophoblasts and MAC alters trophoblast function in a phenotype specific manner.

A stereological perspective on placental morphology in normal and complicated pregnancies

Stereology applied to randomly-generated thin sections allows minimally-biased and economical quantitation of the 3D structure of the placenta from molecular to whole-organ levels. With these sampling and estimation tools, it is possible to derive global quantities (tissue volumes, interface surface areas, tubule lengths and particle numbers), average values (e.g. mean cell size or membrane thickness), spatial relationships (e.g. between compartments and immunoprobes) and functional potential (e.g. diffusive conductance). This review indicates ways in which stereology has been used to interpret the morphology of human and murine placentas including the processes of villous growth, trophoblast differentiation, vascular morphogenesis and diffusive transport. In human placenta, global quantities have shown that villous maturation involves differential growth of fetal capillaries and increases in endothelial cell number. Villous trophoblast is a continuously renewing epithelium and, through much of gestation, exhibits a steady state between increasing numbers of nuclei in cytotrophoblast (CT) and syncytiotrophoblast (ST). The epithelium gradually becomes thinner because its surface expands at a faster rate than its volume. These changes help to ensure that placental diffusing capacity matches the growth in fetal mass. Comparable events occur in the murine placenta. Some of these processes are perturbed in complicated pregnancies: 1) fetoplacental vascular growth is compromised in pregnancies accompanied by maternal asthma, 2) changes in trophoblast turnover occur in pre-eclampsia and intrauterine growth restriction, and 3) uteroplacental vascular development is impoverished, but diffusive transport increases, in pregnant mice exposed to particulate urban air pollution. Finally, quantitative immunoelectron microscopy now permits more rigorous analysis of the spatial distributions of interesting molecules between subcellular compartments or shifts in distributions following experimental manipulation.

Fibrin Enhances Differentiation, but not Apoptosis, and Limits Hypoxic Injury of Cultured Term Human Trophoblasts

We hypothesized that fibrin enhances apoptosis and modulates differentiation of trophoblast in vitro. Cytotrophoblasts isolated from normal term human placentas were cultured < or =72 h in DMEM-10%-FBS on a fibrin matrix in standard or hypoxic conditions. Trophoblasts were cultured on plastic (control), type I collagen (matrix control), or dishes with fibrinogen, fibrin degradation products (FDP), thrombin, plasma fibronectin or cellular fibronectin. Apoptosis was determined by western analysis of the cleavage products of poly-ADP-ribose polymerase and cytokeratin 18 and caspase 3 activity. Cell cycle regulation was quantified by expression of proliferating cell nuclear antigen (PCNA) and p27 protein. Differentiation was determined by media level of hCG and hPL. Compared to the two controls, fibrin matrix had no effect on trophoblast apoptosis or total cell death in standard conditions. Neither fibrin nor collagen altered expression of PCNA or p27. In contrast, fibrin significantly increased the secretion of both hCG and hPL. Fibrin, but not FDP, thrombin or fibronectins, promoted hormonal differentiation. Fibrin limited the impact of a < or =8h of hypoxia on trophoblast hormone release but did not avert the effects of 24h of low oxygen and did not alter apoptosis in hypoxic trophoblast. We conclude that fibrin provides an environment conducive for trophoblast re-epithelialization of the surface of villi, where injury is marked by fibrin deposition.

Maternal smoking, intrauterine growth restriction, and placental apoptosis

Pregnant women who smoke are at greater risk of delivering a growth-restricted infant than nonsmoking mothers. We wanted to see if apoptosis could be involved in the mechanisms behind smoke-induced growth restriction, and our aim was to compare apoptosis in the placenta of smoking mothers giving birth to growth-restricted infants and nonsmoking mothers with infants of appropriate weight. The project was conducted at the Magee--Womens Hospital and Magee--Womens Research Institute, University of Pittsburgh, PA. Histological sections from 20 placentas were selected from smoking mothers who had given birth to small-for-gestational-age infants (birth weight < or = 2 SD). The controls were gestational-age matched nonsmoking mothers with infants having appropriate-for-gestational-age weight. The TUNEL method was used to demonstrate DNA fragmentation in nuclei, and a monoclonal antibody M30, specific for a neo-epitope on cytokeratin 18, was used to identify apoptotic epithelial cells. The positive nuclei (TUNEL) and positive cells (M30-positive cytoplasm) were counted blindly both in villous tissue and in decidual/basal plate tissue. M30-positive cells in villous tissues were significantly increased in placentas from smoking mothers compared to nonsmoking mothers. When evaluated by the TUNEL method, the difference between the two groups of women was not significant. Our study shows that apoptosis was increased in the placentas of smoking mothers with growth-restricted infants. The difference between the two groups was mainly in the syncytiotrophoblast layer and in connection with perivillous fibrin deposition. Cigarette smoke with reduction in blood flow has previously been shown to increase apoptosis, and it is possible that this could be one of the mechanisms playing a role in the growth restriction.

Maternal vascular underperfusion: nosology and reproducibility of placental reaction patterns

Placental examination can be a useful tool for specifying the etiology, prognosis, and recurrence risk of pregnancy disorders. The purpose of this study was to test the reliability of a predetermined set of placental reaction patterns seen with maternal vascular underperfusion in the hope that this might provide a useful diagnostic framework for practicing pathologists. Study cases (14 with clinical and pathologic evidence of maternal underperfusion plus 6 controls) were evaluated for the presence or absence of 11 lesions by eight perinatal pathologists. After analysis of initial results, diagnostic criteria were refined and a second, overlapping set of cases was reviewed. The collective sensitivity, specificity, and efficiency of individual assessments for the 11 lesions relative to the group consensus ranged from 74-93% (22/33 > 90%). Reproducibility was measured by unweighted kappa-values and interpreted as follows: < 0.2 poor, 0.2-0.6 fair/moderate, > 0.6 substantial. Kappa values for lesions affecting villi and the intervillous space were increased syncytial knots (any -0.42, severe -0.50), villous agglutination (0.42), increased intervillous fibrin (0.25), and distal villous hypoplasia (0.57). Individual estimates of percent involvement for syncytial knots, intervillous fibrin, and distal villous hypoplasia were correlated with placental and fetal weight for gestational age. Extent of increased intervillous fibrin showed the strongest correlation with both placental weight ( R = -0.64) and fetal weight ( R = -0.45). Kappa values for lesions affecting maternal vessels and the implantation site were acute atherosis (0.50), mural hypertrophy of membrane arterioles (0.43), muscularized basal plate arteries (0.48), increased placental site giant cells (0.54), and immature intermediate trophoblast (0.36). Correlation of maternal vessel and implantation site lesions with the clinical diagnosis of preeclampsia showed that excessive placental site giant cells and immature intermediate trophoblast were more sensitive and efficient predictors, whereas atherosis and muscularized basal plate arteries were more specific. Kappa value for a thin umbilical cord, a possible indicator of fetal volume depletion, was 0.61. Reproducibility for a global impression of maternal vascular underperfusion, taking into account all of the above lesions, was moderate (kappa 0.54) and improved after inclusion of additional pathologic and clinical data (kappa 0.68). Adoption of this clearly defined, clinically relevant, and pathologically reproducible terminology could enhance clinicopathologic correlation and provide a more objective framework for future clinical research.

Large Variability of Trophoblast Gene Expression Within and Between Human Normal Term Placentae

Human placenta extracts are widely used in clinical and fundamental research, particularly to study the hormonal and exchange functions of the placenta. However, very little is known about the distribution of the main hormone mRNAs in the placenta as a whole. Total placenta extracts are heterogeneous in their cellular components, as they contain material of both fetal and maternal origin, and in their structure. Results vary greatly depending upon the location of the biopsy and the number of biopsies performed. We used real-time quantitative RT-PCR to determine whether transcripts corresponding to the main hormones secreted by the human placenta (e.g. hCG, HPL and PGH) are equally distributed within and between term placentae. We also measured cytokeratin 7 transcripts, which are specifically expressed in the trophoblast, and transcripts corresponding to nuclear receptors PPARgamma and RXRalpha. A comparison of the results obtained with 12 different samples from each of four normal term placentae revealed that the amounts of transcripts differ considerably within and between each placenta. This emphasizes the need to study large numbers of samples when looking for significant differences in gene expression.

Syncytiotrophoblast Degradation and the Pathophysiology of the Malaria-infected Placenta

Malaria is associated with excessive parasitic infection of the placenta and a reduction in neonatal birthweight. This study has investigated placental cell death in women with active and past malarial infection. Term placentae, with and without malarial pathology, were obtained from women in The Gambia. Active and past malaria infections were identified in placental sections and histological examination was used to determine the number of villi, the incidence of apoptosis, syncytial degradation, fibrinoid deposition and the frequency of syncytial knots. Placentae with active malaria infection showed erythrocyte adhesion of infected cells to syncytiotrophoblast, syncytial degradation, increased syncytial knotting and, in rare cases, localized destruction of the villi. Past malarial infection was characterized by syncytiotrophoblast disruption and fibrin-type fibrinoid (FTF) deposition. Perivillous FTF deposition was consistent with increased syncytial lesions and both increased lesions and syncytial knots were associated with birthweight reductions. Active malaria infection produced no alteration in placental apoptosis. The numbers of chorionic villi remained unchanged and infiltration of inflammatory cells, although not measured directly, appeared to be non-pervasive within the infected tissue. These observations establish a direct link between malaria parasitic infection and syncytiotrophoblast damage. The placental rejection of parasite-affected syncytia may invoke structural changes to compensate for inadequate placental exchange. Syncytial destruction could have serious implications; impairing fetal growth and in some rare cases, providing a previously unrecognized pathway to congenital infection.

Urokinase receptor is up-regulated in endothelial cells and macrophages associated with fibrinoid deposits in the human placenta

Clearance of fibrin deposits within the human placenta is an ongoing process during normal placental development. Plasminogen is a circulating fibrinolytic protease zymogen activated in situ by plasminogen activators. We have previously reported that the receptor for urokinase plasminogen activator (uPAR) is expressed by cells either covering or enmeshed within the perivillous fibrinoid deposits. Whereas these cells seemed likely to be trophoblasts, a definitive identification was lacking, and this question is central to the understanding of the cellular mechanisms directing fibrinolysis in the placenta. In this study we have performed immunohistochemical co-localization studies and found that the uPAR-positive cells covering fibrinoid deposits are immunoreactive for CD31 and vWF, indicating that they are actually endothelial cells. In addition, we found that perivillous fibrinoid deposits not covered with uPAR-positive endothelial cells were covered with platelets identified by integrin alpha(IIb)beta(3)-immunoreactivity. Also surprisingly, the uPAR-positive cells enmeshed within fibrinoid deposits express a cell specific marker indicating that they are macrophages. Both uPAR-positive cell populations also express uPA immunoreactivity. Taken together, the data suggest that both fibrinoid-covering endothelial cells and fibrinoid-enmeshed macrophages can participate in the clearance process of perivillous fibrinoid deposits formed in the human placenta.

Haemostatic mechanisms in human placenta

The placenta is a unique organ with dual blood circulation functioning throughout fetal development. The architecture and functions of the placenta, where maternal blood flows into the intervillous space, present haemostatic problems, mainly the risk of haemorrhage. Placental trophoblasts express and produce coagulation components, participating not only in haemostasis but also in placental vascular development and differentiation. The expression of tissue factor, membrane phosphatidylserine and fibrin render the trophoblasts pro-coagulant, thus compromising the risk of bleeding while exposing the placenta to pro-thrombotic risks. Local inhibitory mechanisms-TFPI-1 and TFPI-2, thrombomodulin, annexin V and the fibrinolytic system-limit coagulation activation and fibrin deposition. Pregnancy complications have been associated with abnormalities in the functions of these inhibitors. Haemostatic processes in placental cells change throughout gestation and are affected by the changing requirements of the organ.

Maternal diabetes mellitus is associated with altered deposition of fibrin-type fibrinoid at the villous surface in term placentae

Placentae from control and diabetic patients were used to test three null hypothesis: (1) there are no significant group differences in the volumes of villous syncytiotrophoblast compartments or intervillous fibrin-type fibrinoid, (2) perivillous fibrin-type fibrinoid is deposited randomly at the surface of trophoblast, and (3) amounts and deposition patterns of perivillous fibrin-type fibrinoid do not vary between groups. Term placentae were collected from non-diabetic subjects and five groups of diabetic women classified according to duration, severity and insulin dependence. Tissue specimens and sections were obtained by uniform random sampling. Volumes and surface areas of fibrin-type fibrinoid and trophoblast compartments (thin, syncytial knot, syncytial bridge and denuded regions) were estimated stereologically and compared using variance, chi-squared and contingency table analyses. As to null hypothesis (1), no group differences in volumes of trophoblast compartments were found but volumes of intervillous fibrin-type fibrinoid were greater in the non-insulin-dependent diabetic group. As to null hypothesis (2), regardless of group, fibrin-type fibrinoid was deposited preferentially at sites of denudation in every placenta examined. As to null hypothesis (3), villous surface areas occupied by perivillous fibrin-type fibrinoid were greater in type 1 (insulin-dependent) diabetics with complications (diabetic nephropathy or retinopathy). The surfaces of trophoblast occupied by fibrin-type fibrinoid were also notably larger in non-insulin-dependent diabetics and type 1 diabetics with complications. Except for the surface of denudation sites (which also increased in diabetes), there were no differences in the surfaces of trophoblast regions. These results confirm that the haemostatic steady state is perturbed in the diabetic placenta, that perivillous fibrin-type fibrinoid is deposited preferentially at sites of epithelial loss/damage, and that some diabetic groups are affected differentially.

Fibrin-type fibrinoid in placentae from pregnancies associated with maternal smoking: association with villous trophoblast and impact on intervillous porosity

Smoking during pregnancy perturbs maternal haemostasis via activated coagulation which could include greater coagulation (fibrin-type fibrinoid deposition) in the placental intervillous space. This might affect intervillous haemodynamics and transport of oxygen and nutrients to the fetus. Fibrin deposits could influence the sizes and numbers of intervillous spaces ('pores') and perivillous fibrin could reflect changes in the nature or activity of trophoblast. Here, we test whether or not smoking is associated with differences in the composition of villous trophoblast, the amounts and patterns of fibrin and, hence, the dimensions and numbers of intervillous pores. Random samples of placentae were taken from pregnancies classified according to smoking status (non-smokers, light smokers, heavy smokers). Stereology was used to estimate volumes of intervillous space and fibrin, test for differences in trophoblast composition and patterns of fibrin deposition at the villous surface, and determine the impact of deposits on the mean volumes and theoretical numbers of intervillous pores. No group differences were found in total volumes or surfaces of trophoblast or total volume of intervillous fibrin. However, the total surfaces of syncytial knots declined in smokers and the surfaces of syncytial bridges increased. Particularly in heavy smokers, this was associated with reduced deposits of perivillous fibrin at syncytial knots. In all placentae, the greatest deposits occurred where there was trophoblast denudation. Little fibrin was seen on thin regions of syncytium. Regardless of smoking status, intervillous fibrin reduced intervillous pore size and increased pore number. However, heavy smokers had larger pores. Reductions in syncytial knots are consistent with reports that smoking reduces the incidence of trophoblast apoptosis whilst increases in syncytial bridges are consistent with enhanced branching angiogenesis. Results confirm that perivillous fibrin accumulates preferentially at denudation sites. They also suggest that smoking perturbs the normal pattern of fibrin deposition, that the impact is greater in heavy smokers and that the placental site is privileged or active in terms of fibrinolytic or anti-coagulatory activity. This activity seems to reside in thin regions of syncytium.

The 'reference trap' revisited: examples of the dangers in using ratios to describe fetoplacental angiogenesis and trophoblast turnover

Examples of the use of relative or ratio data are to be found throughout biomedical sciences and include such variables as stereological component densities per cell volume (morphology), transport rates per tissue volume or membrane surface (physiology), gold labelling frequencies (immunocytochemistry) and amounts of DNA relative to protein (biochemistry). This report emphasizes the potential pifalls associated with drawing biological conclusions and interpretations from relative data when there has been no attempt to monitor the absolute size of the reference space. This is know as the 'reference trap'. The dangers to interpretation inherent in confining results to such data are illustrated using the sorts of data found in current placental studies on fetoplacental angiogenesis and villous trophoblast turnover but are pertinent to many other areas. Where it is possible to do so, these dangers can be avoided by the simple expedient of estimating the size of the pertinent reference space and using this to calculate absolute values. Sometimes (e.g. when relying on biopsy samples), the size of the reference cannot be determined. In such cases, ratio data must be interpreted with due caution.

Hypobaric hypoxia and villous trophoblast: evidence that human pregnancy at high altitude (3600 m) perturbs epithelial turnover and coagulation-fibrinolysis in the intervillous space

Spatial relationships between fibrin-type fibrinoid and regions of villous trophoblast were examined in order to address two main questions: [1] is high-altitude pregnancy accompanied by changes in the sizes of trophoblast compartments (cytotrophoblast, syncytiotrophoblast, denudation sites)?, and [2] do highland placentae differ in the amounts and distribution patterns of perivillous fibrin-type fibrinoid? Placentae were collected from two ethnic groups completing term pregnancies at low (400 m above sea level; n=25) and high (3600 m; n=45) altitude in Bolivia. Masson trichrome-stained sections were sampled randomly and analysed stereologically to estimate compartment volumes and surfaces. Comparisons were drawn using variance, Chi-squared and contingency table analyses. At high altitude, birthweights were 265 g lower and placentas had a larger intervillous space (270 cf 181 cm(3)), less fibrin-type fibrinoid (4.1 cf 8.4 cm(3) by volume; 2570 cf 4430 cm(2) by surface area), less villous trophoblast (50 cf 73 cm(3)) and a smaller villous surface (5.6 cf 7.0 m(2)). Volumes were reduced in all syncytiotrophoblast compartments (with and without nuclear aggregations). Cytotrophoblast was maintained and its relative volume increased significantly (from 2.7 to 3.6 per cent of trophoblast volume). Decreases in villous surface area affected primarily thinner (nuclear aggregate-free) regions of syncytium. Regardless of altitude, fibrin-type fibrinoid was deposited non-randomly: it was preferentially located at sites of trophoblast denudation. Although no altitudinal differences in fibrin-type fibrinoid patterns were detected, absolute surfaces were diminished on denuded and thinner regions of trophoblast but not on syncytial knots or bridges. Ethnic differences at low altitude (relatively greater deposits on denudations in Amerindians) were minimized at high altitude. We conclude that pregnancy at high altitude alters the epithelial steady state (towards cytotrophoblast and away from syncytiotrophoblast) and the coagulation-fibrinolysis steady state in the intervillous space (to favour fibrinolysis over coagulation). Thinner regions of syncytiotrophoblast may be the main sites of greater fibrinolytic or anticoagulatory activity. The findings are partly consistent with results from in vitro studies which indicate that hypoxia stimulates proliferation of cytotrophoblast but impairs fusion into syncytium.