Characterization of the human syncytiotrophoblast plasma membrane associated components

Simultaneous differentiation of endothelial and trophoblastic cells derived from human embryonic stem cells

Here we present a simple two-step in vitro model of vascularized trophoblastic tissue derived from human embryonic stem (hES) cells. The first step is the formation of cystic embryoid bodies (EBs) in suspension in a semisolid methyl cellulose medium, within which an endothelial platelet/endothelial cell adhesion molecule-1 (PECAM-1(+)) cell network develops. In a second step, deposition of these EBs on the bottom of nontreated, polystyrene tissue culture plates, leads by centrifugal outgrowth of the EB to the emergence of an adherent cell layer, with which a PECAM-1(+) network is associated. Cells of this adherent layer expressed VE-cadherin (CD144), PECAM-1 (CD31), and alpha-fetoprotein (alpha-FP). Trophoblastic differentiation was strongly suggested by the secretion of beta-human chorionic gonadotropin (beta-hCG) and by the presence of the cytotrophoblast and syncytiotrophoblast marker GB25. The INSL4 gene, a cyto and syncytio-trophoblast marker, was also highly expressed in the adherent layer, as well as other trophoblast genes such as CGA, CDX1, CDX2, and HAND1, compared to hES cell gene expression taken as reference. In contrast, expression of self-renewal genes, such as TERT, POU5F1, ZFP42, GDF3, and NODAL were decreased. No ectodermal or endodermal genes were expressed, but the mesodermal genes PECAM-1 and GATA2 were. The possibility of removing the EBs during the second step would permit analysis of their relative contribution to angiogenesis or possible hemangioblast formation, compared to that of the trophoblastic adherent layer. This primitive vascularized trophoblastic model could also provide a tool to study early steps of normal and pathological placental development.

Normal and atypical butyrylcholinesterases in placental development, function, and malfunction

1. In utero exposure to poisons and drugs (e.g., anticholinesterases, cocaine) is frequently associated with spontaneous absorption and placental malfunction. The major protein interacting with these compounds is butyrylcholinesterase (BuChE), which attenuates the effects of such xenobiotics by their hydrolysis or sequestration. Therefore, we studied BuChE expression during placental development. 2. RT-PCR revealed both BuChEmRNA and acetylcholinesterase (AChE) mRNA throughout gestation. However, cytochemical staining detected primarily BuChE activity in first-trimester placenta but AChE activity in term placenta. 3. As the atypical variant of BuChE has a narrower specificity for substrates and inhibitors than the normal enzyme, we investigated its interactions with alpha-solanine and cocaine, and sought a correlation between the occurrence of this variant and placental malfunction. 4. Atypical BuChE of serum or recombinant origin presented > 10-fold weaker affinities than normal BuChE for cocaine and alpha-solanine. However, BuChE in the serum of the heterozygote and a homozygous normal were similar in their drug affinities. Therefore, heterozygous serum or placenta can protect the fetus from drug or poison exposure, unlike homozygous atypical serum or placenta. 5. Genotype analyses revealed that heterozygous carriers of atypical BuChE were threefold less frequent among 49 patients with placental malfunction than among 76 controls of the entire Israeli population. These observations exclude heterozygote carriers of atypical BuChE from being at high risk for placental malfunction under exposure to anticholinesterases.

Inhibition of induced lymphocyte proliferation by lipid and protein components of the syncytiotrophoblast plasma membrane

PROBLEM

The aim of this work was to define the respective responsibilities of the lipid and protein components of syncytiotrophoblast plasma membranes on the inhibition of lymphocyte proliferation induced in vitro.

METHOD

A fractionation method using octyl-beta-D-glucopyranoside enabled lipoprotein, lipid, and protein fractions to be isolated from the membrane.

RESULTS

The lipid fraction was shown nonspecifically to inhibit lymphocyte proliferation, to a lower extent compared with the native membrane. Alternatively, the protein fraction used as a proteoliposome contained the totality of the cytostatic effect of the native fraction.

CONCLUSION

These results are discussed generally in the context of the immunoregulatory role of membrane lipids and proteins and in relation to the local properties of syncytiotrophoblast plasma membrane components in fetal graft tolerance.

Inhibitory effect of human syncytiotrophoblast plasma membrane vesicles on Jurkat cells activated by phorbol ester and calcium ionophore

The effects of syncytiotrophoblast plasma membrane vesicles (STPM) on stimulated Jurkat leukemic T cells have been investigated. STPM inhibited IL-2 production and the expression of protein P55 of the IL-2 receptor (IL-2R P55), when Jurkat cells were stimulated by a combination of calcium ionophore A23187 (CaI) + phorbol 12-myristate 13-acetate (PMA). STPM also inhibited IL-2R P55 when cells were stimulated by PMA alone, a situation in which IL-2 production is negligible. On the other hand, STPM had no effect on the sustained mobilization of intracellular Ca2+ induced by CaI nor on the PKC-dependent CD3 down regulation induced by PMA. Finally STPM had no effect on intracellular cAMP levels. These results show that (i) the inhibitory effect of STPM on IL-2R P55 expression is independent of the inhibition of IL-2 production, and (ii) the inhibitory effects of STPM are at least partially independent of phosphatidylinositol 4,5-bisphosphate hydrolysis. They suggest that STPM affect a signaling pathway activated by PMA but possibly PKC independent.

The inhibitory effect of human syncytiotrophoblast plasma membrane vesicles on in vitro lymphocyte proliferation is associated with reduced interleukin 2 receptor expression

The mechanisms by which vesicles of syncytiotrophoblast plasma membranes (STPM) prepared from full-term human placentas inhibit lymphocyte proliferation have been investigated. In the presence of STPM, IL-2 secretion and the expression of protein P55 (IL-2R P55) from its receptor were examined in two models of PBMC proliferation: induced by PHA in 3-day-old cultures, and induced by IL-2 in 6-day-old cultures. In the case of PHA stimulation, STPM strongly inhibited IL-2 (but not IL-1) secretion and IL-2R P55 expression at a concentration where lymphocyte proliferation was also blocked. In these conditions, the addition of excess recombinant IL-2 (rIL-2) only partially restored proliferation and IL-2R P55 expression. In addition, STPM inhibited proliferation and IL-2R P55 expression when resting PBMC were stimulated by a high concentration of rIL-2. These results suggest that STPM inhibit lymphocyte proliferation by affecting one or several events occurring in the synthesis and/or expression of IL-2R P55 by a mechanism which is at least partially independent of its inhibitory effect on IL-2 secretion. The significance of these results is discussed in the context of the survival of the fetal allograft.

Syncytiotrophoblast membrane protein glycosylation patterns in normal human pregnancy and changes with gestational age and parturition

The fetally derived syncytiotrophoblast in the placenta form the major interface with the maternal circulation. Cell surface N-linked oligosaccharides are known to influence cell-cell interactions in a variety of ways. The N-linked oligosaccharide component of the human syncytiotrophoblast membrane has been purified from term placentae, and its biochemical structure analysed. Ninety-five per cent of structures were complex N-linked oligosaccharides, with the remaining 5 per cent being of the oligomannose type. Seventy-two per cent of oligosaccharides were sialylated; 50 per cent having two or more sialic acid residues. Such a population of N-linked oligosaccharides would be expected to provide a surface which inhibits interactions between trophoblast and maternal leukocytes. The temporal changes in syncytiotrophoblast N-linked oligosaccharides from the end of the second, and through the third trimester (25-41 weeks) were analysed, as were the changes which occur during parturition. There was no change in the degree of sialylation of these structures. The only significant change was a 37 per cent decrease in core fucosylation of complex N-linked sugars during gestation (P less than 0.005). Women delivered by caesarean section at term, had significantly higher levels of fucosylation (equivalent to women with a gestational age of 31-36 weeks), than those who laboured at term. Present knowledge of core fucosylation of N-linked oligosaccharides is discussed in relation to trophoblast functioning.

Ultrastructure of the normal human placenta

In this review, the ultrastructure of the normal human chorionic villus is examined and illustrated. The outer covering of trophoblast, comprising the generative cytotrophoblast and the multinucleated syncytiotrophoblast which is derived from it, is described, including such features as the microvillous surface, vesicles and vacuoles, endoplasmic reticulum and secretory droplets. The structure, composition, development and inclusions of the trophoblastic basement membrane are discussed, and the ultrastructure of the various components of the stroma, including reticulum cells, fibroblasts, Hofbauer cells, capillaries and the non-cellular matrix are illustrated and described, with special reference to their inter-relationships and function.

Long-term study of serum glycosyl-transferase levels in pregnant women and their newborn infants

1. The authors have studied changes of glucosyl-, galactosyl- and sialyl-transferase activities in the sera of women during pregnancy and the early post-partum period, and in neonates from birth to 1 yr of age. 2. Galactosyl- and glucosyl-transferase activities throughout pregnancy were high in comparison to control values, and increased with advancing gestation. In the early post-partum period, the activities of these enzymes decreased markedly, reaching values similar to those of control subjects. 3. There were no variations, however, in serum sialyl-transferase activity at any stage of pregnancy or the post-partum period. In newborn infants, serum glucosyl- and sialyl-transferase activities were identical to control values. 4. Galactosyl-transferase activity was high at birth, decreased progressively and returned to the normal range only after 1 yr. 5. The physiological significance of these glycosyl-transferases in the sera of pregnant women and newborn infants is discussed.

In vitro inhibitory effect of human syncytiotrophoblast plasma membranes on the cytolytic activities of CTL and NK cells

We have previously described the purification procedure for syncytiotrophoblast plasma membranes (STPM) and have now studied their immunomodulatory properties on the in vitro cytotoxic assays of generated cytotoxic T-lymphocytes (CTL) and natural killer cells (NK). STPM inhibited the cytolytic activities of CTL and NK against their target cells, whereas RBC ghosts, even at the highest protein concentration used, were ineffective. This inhibitory effect was dose-dependent upon the STPM-protein concentration and appeared to be particularly distinct at low effector/target ratios. It is hypothesized that the inhibitory activity of STPM may be exerted by blocking the effector cells or by masking their targets. Regardless of the mode of action, since cytotoxic cell activities are known to play an important role in the allograft rejection process, this suppressive inhibitory effect of STPM might be a crucial mechanism in the tolerance of the semiallogenic fetal graft.