Distribution of the glycoconjugate oligosaccharides in the human placenta from pregnancies complicated by altered glycemia: lectin histochemistry

Sialylation status in placentas from anti-Ro/SSA- and anti-La/SSB-positive pregnant women

Women affected by different autoimmune diseases and displaying positivity for anti-Ro/SSA and anti-La/SSB autoantibodies are at high risk of adverse pregnancies in which placental dysfunction seems to play a determinant role. Sialylation is known to have important implications in the maintenance of the normal morpho-functional features of the placenta. Hence, the present study aimed to investigate possible changes in the distribution and content of sialic acids (Sias) with different glycosidic linkages (i.e., α2,3 and α2,6 Galactose- or N-acetyl-Galactosamine-linked Sias, and polysialic acid) in placentas from anti-Ro/SSA- and anti-La/SSB-positive pregnant women with autoimmune diseases by using lectin histochemistry and polysialic acid immunohistochemistry. Our findings revealed lower levels of α2,3-linked Sias in the trophoblast and basement membrane and/or basal plasma membrane of the pathological cases respect to control placentas. Some vessels of the pathological cases displayed α2,3-linked Sias. α2,6-linked Sias positivity was detected in the trophoblast and in some vessels of the pathological cases, while in control samples it was present only in the vessels. Lower levels of polysialic acid were observed in the trophoblast of pathological cases compared to controls. Collectively, our findings suggest that multiple changes in the sialylation status of placenta might affect placental morpho-functional features in anti-Ro/SSA- and anti-La/SSB-positive pregnancies.

Sialylation status in placentas from pregnancies with SARS-CoV-2 infection

INTRODUCTION

Recent investigations suggest the potential negative impact of SARS-CoV-2 infection on pregnant women and pregnancy outcome. In addition, some studies have described pathological changes in the placental tissue of SARS-CoV-2-positive mothers, which are related or not to the infection severity and/or infection trimester. Among the various molecules involved in the normal structure and functionality of the placenta, sialic acids (Sias) seem to play an important role. Hence, we aimed to investigate possible changes in the distribution and content of Sias with different glycosidic linkages, namely α2,3 and α2,6 Galactose- or N-acetyl-Galactosamine-linked Sias and polymeric Sia (PolySia), in placentas from pregnant women infected by SARS-CoV-2 during the three different pregnancy trimesters.

METHODS

α2,3 and α2,6 Galactose-linked Sias were evaluated by lectin histochemistry (Maackia amurensis agglutinin (MAA) and Sambucus nigra agglutinin (SNA), respectively), while immunohistochemistry was used for PolySia detection.

RESULTS

Data showed lower levels of α2,3 Galactose-linked Sias in the trophoblast and underlying basement membrane/basal plasma membrane in placentas from women infected during the second and third infection trimester compared with uninfected cases and those infected during first trimester. On the other hand, higher levels of PolySia were detected in the trophoblast during the second and third infection trimester.

CONCLUSIONS

Our findings suggest that changes in the sialylation status of trophoblast and its basement membrane/basal plasma membrane, together with other concomitant factors, could be at the basis of the most common placental histopathological alterations and gestational complications found especially in pregnancies with SARS-CoV-2 infection during the second and third trimester.

Placental colonization by Fusobacterium nucleatum is mediated by binding of the Fap2 lectin to placentally displayed Gal-GalNAc

While the existence of an indigenous placental microbiota remains controversial, several pathogens are known to be involved in adverse pregnancy outcomes. Fusobacterium nucleatum is an oral bacterium that is one of several bacteria associated with preterm birth. Oral fusobacteria translocate to the placenta hematogenously; however, the mechanisms localizing them to the placenta remain unclear. Here, using peanut agglutinin, we demonstrate that the level of Gal-GalNAc (Galβ1-3GalNAc; Thomsen Friedenreich antigen) found on trophoblasts facing entering maternal blood rises during gestation and is recognized by the fusobacterial Fap2 Gal-GalNAc lectin. F. nucleatum binding to human and mouse placenta correlates with Gal-GalNAc levels and is reduced upon O-glycanase treatment or with soluble Gal-GalNAc. Fap2-inactivated F. nucleatum shows reduced binding to Gal-GalNAc-displaying placental sections. In a mouse model, intravenously injected Fap2-expressing F. nucleatum, but not a Fap2 mutant, reduces mouse fetal survival by 70%.

Development and Applications of Lectins as Biological Tools in Biomedical Research

As a new and burgeoning area following genomics and proteomics, glycomics has become a hot issue due to its pivotal roles in many physiological and pathological processes. Glycans are much more complicated than genes or proteins since glycans are highly branched and dynamic. Antibodies and lectins are the two major molecular tools applied for glycan profiling. Though the study of antibodies and lectins started at almost the same time in 1880s, lectins gained much less attention than the antibodies until recent decades when the importance and difficulties of glycomics were realized. The present review summarizes the discovery history of lectins and their biological functions with a special emphasis on their various applications as biological tools. Both older techniques that had been developed in the last century and new technologies developed in recent years, especially lectin microarrays and lectin-based biosensors, are included in this account.

Glycosylation pattern and axin expression in normal and IUGR placentae

OBJECTIVE

The aim of this study was to investigate the protein glycosylation pattern and AXIN1 protein expression in human placentae of normal pregnancies and compare them with placentae of pregnancies complicated with intrauterine growth restriction (IUGR).

METHODS

A total of 38 placentae (17 placentae of IUGR fetuses from singleton pregnancies and gestational age-matched 21 control placentae from normal singleton pregnancies) were collected from the Clinical Hospital Sveti Duh, Department of Gynecology and Obstetrics, Zagreb, Croatia. Gestational age was determined according to the last menstrual period (LMP) and by ultrasound measurements. Expression of glycoproteins was measured by Western blotting with SNA, UEA-I, PHA-E and DBA lectins as probes whereas expression of AXIN1 was determined by immunohistochemistry.

RESULTS

Comparison of detected sugars revealed differences in protein glycosylation between normal and IUGR placentae. Higher expression of AXIN1 protein located mostly in the cytoplasm of syncytiotrophoblast and to a lesser extent in its nuclei was found in IUGR placentae.

CONCLUSION

Results of our study suggest that changes in glycoprotein content may contribute to restricted placenta growth and development. Higher expression of AXIN1 protein in IUGR placentae indicates a role of Wnt/β-catenin signaling pathway in pathology of placental development.

Intermediate filament proteins expression and carbohydrate moieties in trophoblast and decidual cells of mature cat placenta

The aim of this study was to characterize cytoskeletal intermediate filament proteins and glycoconjugates of syncytiotrophoblast, cytotrophoblast and decidual cells of feline endotheliochorial placenta. Samples from 12 normal pregnant female cats, after 45 ± 5 days of gestation, were obtained removing the uterine horns by hysterectomy. Sections were processed for routine observation and for immunohistochemistry using anticytokeratin, antivimentin and antidesmin antibodies. In addition, lectin histochemistry was performed using a panel of several biotinylated lectins to characterize glycosides expression profile. Cytotrophoblast and syncytiotrophoblast showed immunoreactivity only with acidic and basic cytokeratins. Decidual cells were only positive to vimentin, consistent with their origin from endometrial fibroblasts. Trophoblast expressed a broad population of glycans, highly exposing terminal N-acetyl glucosamine residues and non-sialylated galactose and N-acetyl galactosamine oligomers. Oligosaccharides bound by Phaseolus vulgaris erythroagglutinin were the only highly branched N-linked residues evidenced in cats, and they were restricted to the syncytium. Unlike results reported on humans, mice and rats on lectin affinity of decidual cells, sialid acids and complex N-linked oligosaccharides were not demonstrated in cats. Glycosylation of proteins determines many of their final properties, thus becoming essential for the embryo-maternal dialogue during implantation and placentation. Changes in glycosylation pattern have been related to pathological pregnancies in other species. Hence, the knowledge about glycosylation profile of the normal cat placenta may lead to a better understanding of both normal and pathological reproductive events.

Detection of sugar chain expression in hydatidiform mole using lectin histochemistry

Background

Hydatidiform moles carry a significant risk for developing persistent gestational trophoblastic disease. Lectins are useful tools to identify cellular glycosylation pattern and changes in glycosylation that occur during growth, development, differentiation and also, during disease states.

Objectives

Considering the changes in glycosylation that occur during cell proliferation, differentiation and transformation, the aim of the present study was to evaluate the sugar chain expression in hydatidiform mole by using HRP-conjugated lectins.

Materials and Methods

Lectin histochemistry with a panel of HRP-conjugated lectins comprising SBA, PNA, VVA, UEA-1, LTA, GS-І (B4) and WGA were performed in 20 molar (partial & complete moles) formalin-fixed, paraffin-embedded tissue samples.

Results

The partial and complete moles generally showed similar reactivity with all used lectins. None of lectins reacted with villous cytotrophoblasts, whereas 4 of 7 lectins comprising WGA, LTA, UEA-І and PNA (after pretreatment with neuraminidase) showed a moderate to strong reactivity with villous syncytiotrophoblasts in both partial and complete hydatidiform moles. The villous stroma reacted with all used lectins except VVA.

Conclusions

Our histochemical findings showed a relatively heavy glycosylation of syncytiotrophoblasts of both partial and complete molar tissues, which was prominent in apical portion. This may play a role in their capacity to increase trophoblastic proliferation.

N-Glycosylation Pattern of Human Placental Insulin-Like Growth Factor and Insulin Receptors in Well-Controlled Pregestational Diabetes Mellitus

Diabetes mellitus is a complex disease that leads to alterations in the glycosylation of proteins. Insulin-like growth factor and insulin receptors are involved in the regulation of fetal and placental growth and development. In this work the N-glycans of these receptors, originating from placentas obtained from pregnancies complicated by pregestational insulin dependent diabetes mellitus, were studied. Diabetic mothers were under regular insulin therapy. Solubilised membrane samples from healthy and diabetic placentas were analysed using lectin-affinity chromatography. N-glycans bound to insulin-like growth factor and insulin receptors were studied in terms of their interaction with eleven agarose-immobilised lectins: wheat germ agglutinin, succinylated wheat germ agglutinin,Ricinus communisagglutinin I,Sambucus nigraagglutinin,Erythrina cristagallilectin,Ulex europaeusagglutinin,Lens culinarisagglutinin,Canavalia ensiformislectin,Phaseolus vulgariserythro- and leukoagglutinin andMaackia amurensisagglutinin. A very similar type of N-glycans and content of the terminal saccharide residues were found in both groups of placentas. The results of this work suggest that the tight glycemic control may prevent alterations in the glycosylation of insulin-like growth factor and insulin receptors, thus maintaining physiological homeostasis during pregnancy and fetal growth.

Distribution of sugar residues in human placentas from pregnancies complicated by hypertensive disorders

The aim of the study was to investigate the content and distribution of sugar residues in placentas from pregnancies complicated by hypertensive disorders. Placentas from women with uncomplicated pregnancies (group 1), pregnancies complicated by gestational hypertension (group 2), pregnancies complicated by pre-eclampsia (group 3), pregnancies complicated by pre-eclampsia with HELLP syndrome (hemolysis, elevated liver enzymes and low platelets) (group 4) were collected. Lectins: ConA, WGA, PNA, SBA, DBA, UEA I, GNA, DSA, MAA, SNA, in combination with chemical and enzymatic treatments, were used. Data showed a decrease and/or lack of α-d-mannose, α-d-glucose and d-galactose-(β1-4)-N-acetyl-d-glucosamine in placentas from pre-eclampsia and pre-eclampsia with HELLP syndrome compared with control and hypertension cases. N-acetyl-d-galactosamine appeared and/or increased in placentas from hypertensive disorders. A different distribution of various types of sialic acid was observed in placentas from hypertensive disorders compared with the controls. In particular, placentas from pre-eclampsia, with and without HELLP syndrome, lacked the acetylated sialic acid side-chain. These findings demonstrate various alterations of the carbohydrate metabolism in the placentas from pregnancies complicated by different types of hypertensive disorders. This indicates correlation with the placental morpho-functional changes characteristic of these complications and with the degree of clinical severity.

Influence of placental mannose/n-acetyl glucosamine-binding proteins on the interaction of insulin and insulin-like growth factors with their receptors

Placenta is a source of carbohydrate-binding proteins that function as molecular scavengers, but they could also be involved in interactions that assist in metabolic control. Mannose/N-acetyl-glucosamine (Man/GlcNAc)-binding proteins from placenta were isolated and their reactivity towards placental insulin and insulin-like growth factor receptors (IR and IGF-Rs) was analyzed. The lectins reduced the binding of insulin and IGF-I in a dose-dependent manner, while almost no effect was observed on the binding of IGF-II. The shape of the inhibition curves changed, suggesting altered binding specificity. The presence of sugar could not reverse completely the effect of the lectins, implicating both lectin-sugar and protein-protein conformational recognition. Since biological molecules in our experimental system were those that are in close relation in vivo, placental Man/GlcNAc-specific lectins may be regarded as potential allosteric modulators of ligand-receptor interactions in a system of homologous ligands, selectively affecting only binding to tyrosine kinase type receptors (IR and IGF-1R).

Lectin binding in normal, keratoconus and cross-linked human corneas

In this study the characterization of various types of sugar residues in normal, keratoconus and cross-linked human corneas was performed using immunohistochemical localization with lectins. Corneal samples were collected and divided into three groups: (1) normal corneas from cadavers; (2) keratoconic corneal buttons; (3) keratoconic corneal buttons treated with cross-linking. A series of lectins including: DBA, SBA, PNA, ConA, WGA, UEA I, GNA, DSA, MAA, SNA, were used in combination with chemical and enzymatic treatments. Compared with the normal corneas, N-acetyl-D-glucosamine increased in the keratoconus corneas. L-fucose increased and/or appeared in the keratoconus and the cross-linked corneas. N-acetyl-D-galactosamine was more abundant in the epithelium of keratoconus corneas, but was lacking in the keratoconus and cross-linked endothelium. D-galactose-(β1-4)-N-acetyl-D-glucosamine was absent in the whole stroma of the keratoconus corneas and in the deep layers of the cross-linked ones. Sialic acids increased in the keratoconus corneas and decreased in the cross-linked ones. These results showed altered glycosylation in the keratoconic corneas and partially similar glycosylation in the cross-linked corneas, compared to the normal ones. This suggests a role played by sugar residues in maintaining the corneal structure. The changes could be related to structural alterations in keratoconus. The present findings contribute to our understanding of the effect of cross-linking treatment of keratoconic corneas in therapeutic attempts to re-establish the normal corneal structure.

Effect of impaired glucose tolerance during pregnancy on the expression of VEGF receptors in human placenta

The aim of the present study was to determine the expression of vascular endothelial growth factor (VEGF) receptors VEGFR-1, VEGFR-2 and VEGFR-3 in placentas from pregnancies complicated by altered glycaemia. Placentas from women with physiological pregnancies (Group 1), pregnancies complicated by minor degree of glucose intolerance (MDGI, Group 2) and by gestational diabetes mellitus (GDM) treated with insulin (Group 3) were collected. Immunohistochemistry, RT-PCR and western blot were employed to evaluate receptor expression. In the three study groups, VEGFR-1 immunoreactivity was detected in all the placental components. VEGFR-2 immunoreactivity was observed in the vessels of all the placentas from Groups 1 and 2, but only in some placentas of Group 3. VEGFR-3 reactivity was observed in all the components of Group 1; in Groups 2 and 3 reactivity was observed in some portions of the trophoblast or the whole trophoblast, and in the stroma. VEGFR-1 and VEGFR-2 mRNA levels in Groups 2 and 3 were significantly higher compared with Group 1, whereas those of VEGFR-3 were significantly lower. Receptor protein levels were significantly lower in Groups 2 and 3 compared with Group 1. These findings demonstrated dysregulation of expression of the three placental receptors, both in GDM and in MDGI.

State-of-the-art technologies, current opinions and developments, and novel findings: news from the field of histochemistry and cell biology

Investigations of cell and tissue structure and function using innovative methods and approaches have again yielded numerous exciting findings in recent months and have added important data to current knowledge, inspiring new ideas and hypotheses in various fields of modern life sciences. Topics and contents of comprehensive expert reviews covering different aspects in methodological advances, cell biology, tissue function and morphology, and novel findings reported in original papers are summarized in the present review.

Recent progress in histochemistry

The progress in discerning the structure and function of cells and tissues in health and disease has been achieved to a large extent by the continued development of new reagents for histochemistry, the improvement of existing techniques and new imaging techniques. This review will highlight some advancements made in these fields.