Histochemical characterization of the surface mucoprotein of normal and abnormal human trophoblast

Low Soluble Syndecan-1 Precedes Preeclampsia

INTRODUCTION

Syndecan-1 (Sdc1; CD138) is a major transmembrane heparan sulfate proteoglycan expressed on the extracellular, luminal surface of epithelial cells and syncytiotrophoblast, thus comprising a major component of the glycocalyx of these cells. The "soluble" (shed) form of Sdc1 has paracrine and autocrine functions and is normally produced in a regulated fashion. We compared plasma soluble Sdc1 concentrations, in relation to placental Sdc1 expression, in uncomplicated (control) and preeclamptic pregnancies.

METHODS

We evaluated soluble Sdc1 across uncomplicated pregnancy, and between preeclamptic, gestational hypertensive and control patients at mid-pregnancy (20 weeks) and 3rd trimester by ELISA. Placental expression level of Sdc1 was compared between groups in relation to pre-delivery plasma soluble Sdc1. Participants were recruited from Magee-Womens Hospital.

RESULTS

In uncomplicated pregnancy, plasma soluble Sdc1 rose significantly in the 1st trimester, and reached an approximate 50-fold increase at term compared to post pregnancy levels. Soluble Sdc1 was lower at mid-pregnancy in women who later developed preeclampsia (P<0.05), but not gestational hypertension, compared to controls, and remained lower at late pregnancy in preeclampsia (P<0.01) compared to controls. Sdc1 was prominently expressed on syncytiotrophoblast of microvilli. Syncytiotrophoblast Sdc1 immunostaining intensities, and mRNA content in villous homogenates, were lower in preeclampsia vs. controls (P<0.05). Soluble Sdc1 and Sdc1 immunostaining scores were inversely associated with systolic blood pressures, and positively correlated with infant birth weight percentile.

CONCLUSION

Soluble Sdc1 is significantly lower before the clinical onset of preeclampsia, with reduced expression of Sdc1 in the delivered placenta, suggesting a role for glycocalyx disturbance in preeclampsia pathophysiology.

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.

Ultrastructural localization of glycosaminoglycans in human term placenta

Sulfated glycoconjugates were stained in normal human term placentas using Spicer's high-iron diamine (HID) method with thiocarbohydrazide and silver proteinate (TCH-SP) enhancement. Specific identification of glycosaminoglycans (GAG) was accomplished by digestion of the stained material with chondroitinase ABC or AC for removal of chondroitin sulfates and nitrous acid for removal of N-sulfated GAGs. The syncytiotrophoblast apical surface demonstrated moderate to intense staining with HID-TCH-SP, which was removed by prior digestion with the chondroitinases, but not by nitrous acid. The syncytiotrophoblast basal surface and endothelial cell surfaces lacked sulfate staining. A few cytoplasmic granules in syncytiotrophoblast cells demonstrated staining similar to the apical surface. Three layers of the basal lamina were identified in these preparations. The lamina lucida immediately beneath the syncytiotrophoblast and the majority of the lamina densa stained weakly or not at all, whereas the underlying lamina diffusa and stroma demonstrated moderate to intense staining. The majority of lamina diffusa staining was removed by chondroitinase ABC or AC; the remaining material was removed by nitrous acid digestion. Thus the syncytiotrophoblast surface contains a chondroitin sulfate and the basal lamina contains a mixture of intensely stained chondroitin sulfate and a weakly stained N-sulfated GAG.

Colloidal iron hydroxide staining of surface carbohydrates after glycerol treatment of uterine epithelial cells

The structural relationships between intramembraneous particles (IMPs) and surface carbohydrates has been studied in uterine epithelial cells with a colloidal iron hydroxide (CIH) technique. To aggregate IMPs, glycerol treatment of unfixed cells was used and this treatment also caused some patching of CIH deposits on the cell surface. We conclude that some of the CIH receptors may be the surface expression of the IMPs.

Histochemical localization of acidic glycosaminoglycans in normal human placentae

First-trimester and term placentae were studied histochemically with alcian blue stain before and after specific enzyme treatments. A specific deposition of glycosaminoglycans was detected in the villous stroma, fetal blood vessels and on the surface of the syncytiotrophoblast, the latter being discontinuous and of variable thickness. Treatments of sections with hyaluronidases from Streptomyces and from bovine testes and with chondroitinase ABC indicated the presence of (1) chondroitin sulphates and hyaluronic acid mainly in the stroma; (2) heparan sulphate and dermatan sulphate associated with villous fetal blood vessels and the intervillous surface of the syncytiotrophoblast. It is suggested that the location of individual glycosaminoglycans could be related to their functions with regard to the maintenance of the structural integrity of the placenta by preventing its compression and to their involvement in blood anticoagulation and in lipid metabolism.

Lysis of placental syncytiotrophoblast by allogenic leukocytes in vitro: effects of neuraminidase and chorionic gonadotropin

51chromium-labeled syncytiotrophoblasts purified from human placentae were lysed by allogenic leukocytes in vitro. The extent of syncytiotrophoblast lysis was dependent upon the dose of the leukocytes, occurred after a lag period of 42 h, and was inhibited by excess of unlabeled syncytiotrophoblasts. Autologous leukocytes failed to lyse syncytiotrophoblasts. Neuraminidase pretreatment of the syncytiotrophoblasts significantly enhanced their lysis by leukocytes. HCG failed to influence the extent of lysis of untreated syncytiotrophoblasts but significantly reduced the lysis of neuraminidase-treated targets. The significance of these observations in relation to the "immunologic privilege" of the trophoblast in vivo is discussed. (Am J Reprod Immunol. 1982; 204-207.)

The distribution and mobility of anionic sites on the surface of human placental syncytial trophoblast

The purpose of this study was to examine the distribution and mobility of anionic sites on the surface of fetal trophoblast in contact with maternal blood using polycationic ferritin (PCF) as a probe. Pieces of human placental villi were washed to remove maternal blood, and fresh, unfixed tissue was exposed to PCF for varying times, concentrations, and temperatures to determine the effects on labeling patterns. The major findings were: 1) anionic sites were localized almost exclusively on the microvillous portion of the trophoblast surface; inter-microvillous regions of the surface, including the coated pits, were generally not labeled with PCF; 2) PCF binding present as small clusters on the microvilli. This pattern was observed in tissue incubated 5-10 sec at 4 degrees C and 23 degrees C. The size of the clusters was increased with increased incubation time, suggesting some aggregation or patching can occur; 3) following the formation of patches, the anionic sites showed no evidence of being cleared from the membrane by endocytosis during incubation subsequent to labeling; 4) the binding of PCF to the surface was reduced by pretreatment of the tissue with neuraminidase. Tissue fixed in glutaraldehyde prior to PCF exposure showed both clustered and more dispersed labeling. The results indicate that anionic sites on human trophoblast surface have a non-random distribution and have restricted mobility on the surface. This may be indicative of a segregation of different membrane proteins and functions within different structural regions of the placental cell surface.

Trophoblast transferrin and transferrin receptors in the host--parasite relationship of human pregnancy

Transferrin and specific transferrin receptors are demonstrated on the microvillous surface of syncytiotrophoblast in human immature and term placentae by immuno histological techniques with the use of light and electron microscopy. That the distribution of transferrin is limited to the materno-foetal interface supports the hypothesis that binding of maternal transferrin to trophoblast receptors is involved in the process of iron transport to the foetus. Parallel studies with baboon placentae demonstrate the presence of trophoblast receptors which bind both baboon and human transferrin, thereby putting forward an experimental model which might be used to test the biological significance of placental transferrin receptors in primates. In addition, investigation of a large number of human cell lines shows that many transformed cells, but no normal cells (such as blood lymphocytes) or cells from primary culture (such as neonatal foreskin fibroblasts), possess the ability to bind transferrin to their membranes. These findings suggest that transferrin receptors may play important biological roles in addition to that of iron transport from mother to foetus. One such role could be the limitation of iron in intervillous spaces, thus depriving iron-requiring microorganisms of iron, hence serving as a non-specific factor of resistance for placentae. Another role for foetal transferrin receptors on trophoblasts could be to bind maternal transferrin at the materno-foetal interface, thus frustrating maternal immunosurveillance. This is similar to a mechahism used by schistosomes in the host-parasite relation where host proteins are bound by the parasite to escape immunological recognition. The presence of transferrin receptors on transformed cells suggests that this mechanism might also be employed by tumour cells. Finally, in view of previous studies which show that transferrin is required by stimulated lymphocytes to pass from the G1 to the S phase of cellular replication, it is proposed that trophoblast transferrin receptors could limit the amount of transferrin in intervillous spaces and thus impede the proliferation and possible cytotoxicity of maternal activated lymphocytes at the materno-foetal interface.

Saccharide distribution in human trophoblast demonstrated using fluorescein-labelled lectins

The reaction of six Flourescein-conjugated lectins with human trophoblast and foetal limb are described. The trophoblast had marked membrane fluorescence after treatment with wheatgerm and Lotus tetragonolobus lectins. Concanavalin A reacted strongly with the trophoblastic cytoplasm but did not react with the nuclei. Most of the lectins had only weak reactions with foetal tissue, apart from the cartilage matrix which fluoresced strongly after treatment with several of the lectins. In addition, concanavalin A reacted with amylase-labile material, probably glycogen, in the skin epidermis and chondrocyte cytoplasm. Various substances were tested in order to determine the nature of the wheatgerm lectin receptor of trophoblast. Several secretory and binding proteins were found not to be responsible, and the identity of the receptor remains unknown.

Mucin histochemistry of human cholangiocarcinoma

Histochemical studies of mucins were carried out on 17 autopsy specimens of cholangiocarcinomas associated with clonorchiasis. All tumours produced epithelial mucins which were mixtures of neutral and acid mucopolysaccharides without any histochemically demonstrable components of sialic and uronic acids. The mucins were qualitatively similar to that secreted by normal and Clonorchis-infested bile ducts. However carboxymucins were reduced and sulphomucins were absent or present only in trace amounts in the neoplastic epithelium; in the hyperplastic epithelium in clonorchiasis sulphomucins were abundant. The HID-AB technique for sulphomucins is valuable in differentiating hyperplastic bile ducts and cholangiocarcinoma.

The nonuniform distribution of acidic components on the human placental syncytial trophoblast surface membrane: a cytochemical and analytical study

The surface coat of syncytial trophoblast from term human placentas was studied using cytochemical methods (colloidal iron, alcian blue-lanthanum nitrate, dialyzed iron) in coordination with tissue enzyme digestions (trypsin, neuraminidase) and sialic acid analyses. The presence of at least two highly acidic anionic components that contribute significantly to the surface negativity of trophoblast has been demonstrated. The first of these, sialic acid, was removed with neuraminidase. Tissue digestion with this glycosidase was accompanied by a decrease in trophoblast surface staining with colloidal iron, a decrease in tissue sialic acid, and an increase in the concentration of sialic acid in the incubating medium. Results from methylation experiments were consistent with the presence of sialic acid. The second anionic component(s) was identified by removal with trypsin of a glycocalyx constituent that stained with both colloidal iron and lanthanum. After trypsinization, tissue sialic acid levels were not significantly different from control values, and no detectable sialic acid was present in the incubating medium. The identity of this anionic component has not been established. Both sialic acid and nonsialic acid acidic components are distributed in higher density on membrane of microvilli than on intermicrovillous surface membrane. In addition, the sialic acid moieties appear to be clustered in the glycocalyx.

Preliminary observations on the histochemistry of the cell surface of carcinoma of the cervix

Histochemical studies on the cell surface and intercellular matrix of normal cervical epithelium, and squamous cell carcinomata have shown the mucosubstances present may be symbolized by the descriptive formula:C(G) mucosubstance; B 3.5; A 2.5 (0.6m MgCl(2)); T; S.This indicates that sulphate groups are absent and that the intercellular matrix and cell coat are rich in hyaluronic and sialic acids or closely related compounds. These may be important in masking the antigenic expression of the tumour cells.We have not been able to detect any alteration in the mucosubstances at 7 days following radium treatment.