Proteome analysis of a plasma membrane-enriched fraction at the placental feto-maternal barrier

Purpose : We want to identify proteins that are part of or associated with the plasma membrane of the human feto‐maternal barrier, which is crucially important for nutrient, gas, and waste exchange between the mother and the fetus. All transfer processes occur through one specialized endothelial cell layer, the multinuclear syncytiotrophoblast (STB). Specifically, the apical plasma membrane of the STB interacts with the maternal blood and is the site of initial transport processes across the placenta. Experimental design : We used a proteomic approach that employed the enrichment of apical STB membranes isolated from healthy placentae by ultracentrifugation and saccharose gradient centrifugation steps in combination with 1‐D SDS‐PAGE and ESI‐MS analysis. Results : We identified 296 different proteins, 175 of which were integral and peripheral membrane proteins, partially containing 1–12 transmembrane domains or lipid anchors. One hundred and sixty‐one proteins (54%) were allocated to the plasma membrane. Conclusions and clinical relevance : A high number of transporters, receptors, and proteins involved in signal transduction processes and vesicular trafficking were identified for the first time at the feto‐maternal barrier. Our results are valuable sources for further studies of the cell physiology of the healthy placenta at the time of birth or the pathophysiology of several pregnancy disorders.     

Reduced Placental CD24 in Preterm Preeclampsia Is an Indicator for a Failure of Immune Tolerance

Introduction: CD24 is a mucin-like glycoprotein expressed at the surface of hematopoietic and tumor cells and was recently shown to be expressed in the first trimester placenta. As it was postulated as an immune suppressor, CD24 may contribute to maternal immune tolerance to the growing fetus. Preeclampsia (PE), a major pregnancy complication, is linked to reduced immune tolerance. Here, we explored the expression of CD24 in PE placenta in preterm and term cases. Methods: Placentas were derived from first and early second trimester social terminations (N = 43), and third trimester normal term delivery (N = 67), preterm PE (N = 18), and preterm delivery (PTD) (N = 6). CD24 expression was determined by quantitative polymerase chain reaction (qPCR) and Western blotting. A smaller cohort included 3–5 subjects each of term and early PE, and term and preterm delivery controls analyzed by immunohistochemistry. Results: A higher expression (2.27-fold) of CD24 mRNA was determined in the normal term delivery compared to first and early second trimester cases. The mRNA of preterm PE cases was only higher by 1.31-fold compared to first and early second trimester, while in the age-matched PTD group had a fold increase of 5.72, four times higher compared to preterm PE. The delta cycle threshold (ΔCt) of CD24 mRNA expression in the preterm PE group was inversely correlated with gestational age (r = 0.737) and fetal size (r = 0.623), while correlation of any other group with these parameters was negligible. Western blot analysis revealed that the presence of CD24 protein in placental lysate of preterm PE was significantly reduced compared to term delivery controls (p = 0.026). In immunohistochemistry, there was a reduction of CD24 staining in villous trophoblast in preterm PE cases compared to gestational age-matched PTD cases (p = 0.042). Staining of PE cases at term was approximately twice higher compared to preterm PE cases (p = 0.025) but not different from normal term delivery controls. Conclusion: While higher CD24 mRNA expression levels were determined for normal term delivery compared to earlier pregnancy stages, this expression level was found to be lower in preterm PE cases, and could be said to be linked to reduced immune tolerance in preeclampsia.     

Differences in Glycolysis and Mitochondrial Respiration between Cytotrophoblast and Syncytiotrophoblast In-Vitro: Evidence for Sexual Dimorphism

In the placenta the proliferative cytotrophoblast cells fuse into the terminally differentiated syncytiotrophoblast layer which undertakes several energy-intensive functions including nutrient uptake and transfer and hormone synthesis. We used Seahorse glycolytic and mitochondrial stress tests on trophoblast cells isolated at term from women of healthy weight to evaluate if cytotrophoblast (CT) and syncytiotrophoblast (ST) have different bioenergetic strategies, given their different functions. Whereas there are no differences in basal glycolysis, CT have significantly greater glycolytic capacity and reserve than ST. In contrast, ST have significantly higher basal, ATP-coupled and maximal mitochondrial respiration and spare capacity than CT. Consequently, under stress conditions CT can increase energy generation via its higher glycolytic capacity whereas ST can use its higher and more efficient mitochondrial respiration capacity. We have previously shown that with adverse in utero conditions of diabetes and obesity trophoblast respiration is sexually dimorphic. We found no differences in glycolytic parameters between sexes and no difference in mitochondrial respiration parameters other than increases seen upon syncytialization appear to be greater in females. There were differences in metabolic flexibility, i.e., the ability to use glucose, glutamine, or fatty acids, seen upon syncytialization between the sexes with increased flexibility in female trophoblast suggesting a better ability to adapt to changes in nutrient supply.     

Ultrastructural study on human placenta from intrauterine growth retardation cases

A morphological study was performed on 27 human placentas from normal gestations (Group 1) and compared with those from eight cases of intrauterine growth restriction (IUGR) (Group 2). Semithin section light microscopy, transmission, and scanning electron microscopy were carried out on trophoblastic terminal villi, carefully identified under the stereomicroscope. In growth retardation cases, villi appear longer, thinner, and less vascularized, compared to the normal condition. Fibrinoid, an extracellular material of hematic origin, frequently fills villar stroma. The density of apical microvilli appears considerably reduced and occasional microvilli-free areas are observed in growth retardation cases. Moreover, the underlying basal membrane appears significantly thicker than that of normal syncytiotrophoblast. Recently, particular attention has been paid to apoptosis as a possible cell deletion mechanism in growth restriction. In our study, a majority of typical apoptotic features appear indifferently in both IUGR and normal pregnancy. Our data hints that growth retardation might be correlated with a complex of structural changes, suggestive of maternofetal traffic downregulation, but further studies are required to understand the underlying functional mechanisms.