Endogenous carbohydrate-binding proteins in oligodendrogliomas. A histochemical study

Galectins are differentially expressed in supratentorial pilocytic astrocytomas, astrocytomas, anaplastic astrocytomas and glioblastomas, and significantly modulate tumor astrocyte migration

Galectins, a family of mammalian lectins with specificity to beta-galactosides, are involved in growth-regulatory mechanisms and cell adhesion. A relationship is assumed to exist between the levels of expression of galectins and the level of malignancy in human gliomas. A comparative study of this aspect in the same series of clinical samples is required to prove this hypothesis. Using computer-assisted microscopy, we quantitatively characterized by immunohistochemistry the levels of expression of galectins-1, -3 and -8 in 116 human astrocytic tumors of grades I to IV. Extent of transcription of galectins-1, -3, and -8 genes was investigated in 8 human glioblastoma cell lines by means of RT-PCR techniques. Three of these cell lines were grafted into the brains of nude mice in order to characterize in vivo the galectins-1, -3 and -8 expression in relation to the patterns of the tumor invasion of the brain. The role of galectin-1, -3 and -8 in tumor astrocyte migration was quantitatively determined in vitro by means of computer-assisted phase-contrast videomicroscopy. The data indicate that the levels of galectin-1 and galectin-3 expression significantly change during the progression of malignancy in human astrocytic tumors, while that of galectin-8 remains unchanged. These three galectins are involved in tumor astrocyte invasion of the brain parenchyma since their levels of expression are higher in the invasive parts of xenografted glioblastomas than in their less invasive parts. Galectin-3, galectin-1, and to a lesser extent galectin-8, markedly stimulate glioblastoma cell migration in vitro. Since bands for the transcripts of human galectins-2, -4 and -9 were apparently less frequent and intense in the 8 human glioblastoma cell lines, this system provides an excellent model to assign defined roles to individual galectins and delineate overlapping and distinct functional aspects.

Galectin-1 is highly expressed in human gliomas with relevance for modulation of invasion of tumor astrocytes into the brain parenchyma

Protein (lectin)-carbohydrate interaction is supposed to be relevant for tumor cell behavior. The aims of the present work are to investigate whether galectin-1 modulates migration/invasion features in human gliomas in vitro, whether it can be detected in human gliomas immunohistochemically, and whether its expression is attributable to certain glioma subgroups with respect to invasion and prognosis. For this purpose, we quantitatively determined (by computer-assisted microscopy) the immunohistochemical expression of galectin-1 in 220 gliomas, including 151 astrocytic, 38 oligodendroglial, and 31 ependymal tumors obtained from surgical resection. We also xenografted three human glioblastoma cell lines (the H4, U87, and U373 models) into the brains of nude mice in order to characterize the in vivo galectin-1 expression pattern in relation to tumor invasion of the normal brain parenchyma. In addition, we characterized the role in vitro of galectin-1 in U373 tumor astrocyte migration and kinetics. Our data reveal expression of galectin-1 in all human glioma types with no striking differences between astrocytic, oligodendroglial, and ependymal tumors. The level of galectin-1 expression correlated with the grade in the group of astrocytic tumors only. Furthermore, immunopositivity of high-grade astrocytic tumors from patients with short-term survival periods was stronger than that of tumors from patients with long-term survivals. In human glioblastoma xenografts, galectin-1 was preferentially expressed in the more invasive parts of these xenografts. In vitro experiments revealed that galectin-1 stimulates migration of U373 astrocytes.

Distinct differences in binding capacity to saccharide epitopes in supratentorial pilocytic astrocytomas, astrocytomas, anaplastic astrocytomas, and glioblastomas

We monitored the expression of glycan-binding sites on a panel of 10 biotinylated neoglycoconjugates by means of quantitative computer-assisted microscopy to further study the molecular mechanisms in the extensive infiltration of the surrounding brain parenchyma by most astrocytic tumors. Three distinct histological compartments were analyzed for each of the 108 astrocytic tumors (15 pilocytic astrocytomas (WHO grade I), 25 astrocytomas (WHO grade II), 30 anaplastic astrocytomas (WHO grade III), and 38 glioblastomas (WHO grade IV) included in our series. These compartments were tumors (nonperivascular tumor astrocytes), perivascular tumor astrocytes, and blood vessel walls. Clear differences were observed between the pilocytic and the diffuse astrocytic tumors. Furthermore, malignant progression in the latter category was paralleled by a decrease in cells' ability to bind distinct sugar epitopes, especially the D-GalNAc(alpha1-3)-D-GalNAc-beta1-R determinant of the Forssman pentasaccharide in tumors, the alpha-L-fucose in perivascular tumor areas, and the beta-D-glucose in tumor vessel walls. Markedly, the level of binding site expression for alpha-D-mannose decreased in the tumors, the perivascular tumor areas, and the vessel walls. These glycohistochemical results imply the functional relevance of protein-carbohydrate interactions in this tumor system.

Oligodendrogliomas: a clinical, histological, immunocytochemical and lectin-binding study

We have studied 27 oligodendrogliomas with a panel of antibodies (vimentin, GFAP, S-100 protein, myelin basic protein, CAM 5.2) and of lectins (WGA, Con A, PNA, RCA, DBA, SBA) to different glycoproteins. There were 16 well-differentiated tumours, including one gliofibrillary and 11 anaplastic oligodendrogliomas, three of which were gliofibrillary. Four cases showed positivity for vimentin, three of which were anaplastic tumours. Fifteen cases were positive for S-100 protein (nine well-differentiated and six anaplastic tumours) and 13 contained GFAP-positive cells (three well-differentiated and 10 anaplastic tumours). WGA binding was positive in 75% of well-differentiated and 63% of anaplastic oligodendrogliomas, the corresponding figures were 50% and 45% for PNA, 37% and 81% for Con-A and 25% and 54% for RCA. On the basis of the results with lectin binding, we believe that there are changes in the spectrum of tumour cell-associated lectin-like proteins during malignant transformation. Our observations also suggest that the pattern of lectin expression can undergo substantial changes in the course of differentiation.

Spatial differences of endogenous lectin expression within the cellular organization of the human heart: a glycohistochemical, immunohistochemical, and glycobiochemical study

Protein-carbohydrate recognition may be involved in an array of molecular interactions on the cellular and subcellular levels. To gain insight into the role of proteins in this type of interaction, surgically removed specimens of human endomyocardial tissue were processed for histochemical and biochemical analysis. The inherent capacity of these sections to bind individual sugar moieties, which are constituents of the carbohydrate part of cellular glycoconjugates, was assessed using a panel of biotinylated neoglycoproteins according to a standardized procedure. Together with appropriate controls, it primarily allowed localization of endogenous lectins. Differences in lectin expression were observed between layers of endocardial tissue, myocardial cell constituents, connective-tissue elements, and vascular structures. The endocardium proved to be positive with beta-galactoside-bearing probes; with neoglycoproteins carrying beta-xylosides, alpha-fucosides, and galactose-6-phosphate moieties; and with probes containing a carboxyl group within the carbohydrate structure, namely sialic acid and glucuronic acid. In contrast, only fucose-and maltose-specific receptors were apparent in the elastic layers of the endocardium. Aside from ascertaining the specificity of the protein-carbohydrate interaction by controls, i.e., lack of binding of the probe in the presence of the unlabelled neoglycoprotein and lack of binding of the labelled sugar-free carrier protein, respective sugar receptors were isolated from heart extracts by using histochemically effective carbohydrates as immobilized affinity ligand. Moreover, affinity chromatography using immobilized lactose as affinity ligand as well as the use of polyclonal antibodies against the predominant beta-galactoside-specific lectin of heart demonstrated that the lactose-specific neoglycoprotein binding was due to this lectin. Remarkably, the labelled endogenous lectin, preferred to plant lectins for detecting ligands of the endogenous lectin, localized ligands in tissue parts where the lectin itself was detected glycohistochemically as well as immunohistologically. This demonstration of receptor-ligand presence in the same system is a further step toward functional assignment of the recorded protein-carbohydrate interaction. Overall, the observed patterns of lectin expression may serve as a guideline to elucidate the precise physiological relevance of lectins and to analyze pathological conditions comparatively.

Reduced expression of mannose-specific receptors on murine peripheral blood polymorphonuclear leukocytes following prolonged anaesthesia with different inhalation agents

Inhalation anaesthetic agents are known to depress phagocytic functions such as mobilization, attachment, chemotactic motility, engulfment and intracellular killing. Mannose-specific sugar receptors on the surface of leukocytes are involved in a series of phagocytosis-related activities. To investigate the effect of anaesthesia on the expression of this type of sugar receptor, mice were anaesthetized with halothane, enflurane and isoflurane. The presence of mannose-binding receptors on peripheral blood polymorphonuclear leukocytes was examined glycocytochemically using the biotinylated neoglycoprotein mannosylated bovine serum albumin. Prolonged administration of inhalation anaesthetic agents, especially halothane, markedly depressed expression of mannose-specific receptors. This reduction may possibly contribute to postoperative immunodepression, resulting from the impaired cellular interaction which is involved in the phagocytic function of granulocytes.

Mapping of receptors for carbohydrate constituents of glycoconjugates in well-differentiated and malignant ependymomas: a glycohistochemical study

Recognitive interactions between the carbohydrate part of cellular glycoconjugates and endogenous receptors supposedly govern important biological processes. Consequently, their elucidation can be of considerable value in tumour diagnosis. The histochemical patterns of expression of endogenous sugar receptors (e.g. endogenous lectin-like proteins) of 10 cases of well-differentiated ependymoma and 10 cases of malignant ependymoma were analysed, using a panel of 18 biotinylated (neo)glycoproteins and a standardized staining protocol. Within this panel, differences in the extent of staining for intracellular sugar receptors in well-differentiated and malignant ependymomas were histochemically detectable. In comparison to the well-differentiated ependymomas, the anaplastic form of the tumour exhibited a generally higher capacity to specifically bind labelled (neo)glycoproteins, containing alpha- or beta-glucosides and a disaccharide, characteristic for one type of beta-galactoside-terminated chain structure of glycoproteins. A significantly reduced binding was seen for tumours of the anaplastic type with labelled markers, carrying histochemically indispensable glucuronic acid residues. These findings suggest that labelled neoglycoproteins are a valuable tool for assessing the endogenous sugar-binding capacity in diagnostic histopathology. Our descriptive analysis of endogenous sugar receptors may also be a rational basis for studies on the functional significance of changes in the expression of their endogenous ligands and the cellular glycoconjugates. Further investigations are also possible on the correlation between the degree of differentiation and expression of both parts of a recognitive system, based on protein (receptor)-carbohydrate (ligand) interactions, in tumours of the central nervous system, especially ependymomas.

Is part of the molecular basis of the perineurial barrier function the lack of endogenous carbohydrate-binding proteins?

The sugar part of cellular glycoconjugates and specific endogenous sugar receptors, i.e., lectins, can establish a system of biological recognition based on protein-carbohydrate interactions. An assortment of labelled (neo)glycoproteins, carrying different types of sugar moieties, is synthesized to localize respective sugar receptors. With these tools, the histochemical patterns of endogenous carbohydrate-binding receptors of the epi-, peri-, and endoneurium were analyzed in human sural and accessory nerves and in swine sciatic nerve. This approach is complementary to the application of plant lectins, focusing on endogenous carbohydrate-binding proteins (lectins). In contrast to the epi- and endoneurium, which bound certain types of carbohydrates, such endogenous sugar receptors were histochemically not detectable in the perineurial cells. Moreover, no histochemical reaction was present in the "connective tissue septa" localized in the endoneurium in which the endoneurial vessels were embedded. This common property supplies evidence that these septa are composed of perineurial cells. They may represent a barrier in addition to the capillary endothelium. Our observations suggest histogenetical differences between the cell populations of epi- and endoneurium vs. perineurium. This significant difference in the ability to bind carbohydrate residues, conjugated to a carrier protein, is contradictory to the assumption that perineurial cells and fibroblasts are functional variants of the same cell type. The histochemical patterns of endogenous carbohydrate-binding receptors found in human and swine nerves were similar but not identical, with exception of the perineurium, reflecting phylogenetic differences in the expression of sugar-binding proteins. The absence of specific sugar receptors in perineurial cells, however, seems to be a more general phenomenon.(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous sugar receptor pattern in human glioblastomas and gangliocytomas studied by histochemical application of biotinylated (neo)glycoproteins and affinity chromatography

Biotinylation of chemically glycosylated bovine serum albumin, yielding a panel of neoglycoproteins, and of desialylated, naturally occurring glycoproteins allowed to systematically evaluate presence and distribution of various types of endogenous sugar receptors in the sections of human glioblastomas and gangliocytomas by a routine histochemical procedure. Pronounced cytoplasmic staining with markers, carrying constituents of natural glycoconjugates, e.g. for beta-galactoside-specific receptors, contrasted with the different intensities, noticed for alpha- and beta-glucoside-specific receptors. Significant qualitative differences between the two tumor types were detected with N-acetyl-D-galactosamine- and sialic acid-carrying probes. Nuclear staining with only a part of the applied panel underscored the specificity of the protein-carbohydrate interaction. Fine structural features of the synthetic neoglycoproteins, e.g. the mode of coupling of the carbohydrate moiety to the protein, were found to exert a significant influence on their suitability as histochemical markers. On the basis of the histochemical results, exemplary biochemical analysis of certain classes of endogenous sugar receptors by affinity chromatography and subsequent gel electrophoresis, namely of beta-galactoside-, alpha-fucoside-, alpha-mannoside- and alpha-glucoside-specific proteins, revealed presence and characteristics of respective sugar receptors that can contribute to the histochemical staining. Similar extent of histochemical staining with the respective probes notwithstanding, the different tumor types exhibited qualitative differences in the expression of individual endogenous sugar receptors. The combined histochemical and biochemical analysis is supposed to be of conspicuous value for biological and clinical investigations on endogenous sugar receptors.

(Neo)glycoproteins as tools in neuropathology: histochemical patterns of the extent of expression of endogenous carbohydrate-binding receptors, like lectins, in meningiomas

Biotinylated (neo)glycoproteins were used to specifically detect endogenous sugar receptors such as lectins in sections of formaldehydefixed, paraffin-embedded tissue from meningiomas. The histochemical methods used consisted of the application of a carrier protein and various covalently linked sugar moieties, available mainly through chemical synthesis, in an optimized standard protocol. They proved valuable in elucidating differential binding patterns within the various meningioma subtypes. alpha-Fucoside-, beta-galactoside-, alpha-mannoside- and beta-xyloside-specific carbohydrate-binding receptors were detected in all the tumor subclasses examined, although the levels of expression exhibited pronounced quantitative differences. In addition, differences in the extent of histochemical staining were observed, using a labelled carrier protein, derived from N-acetylglucosamine and mannose-6-phosphate moieties, respectively. Quantitative differences in the reaction intensity were also measured in the respective subtypes. Receptors for N-acetyl-D-galactosamine were detected only in the analplastic forms, while glucuronic acid-specific receptors were only present in the meningotheliomatous meningioma. In contrast to the other types, malignant meningiomas failed to show cytoplasmic staining with the alpha-glucoside-specific maltose-(BSA-biotin). Distinct differences in the pattern of expression of endogenous sugar receptors, evaluated by a standard protocol, provided further evidence for a possible additional subtype of meningioma, the submalignant meningioma. Our results suggest that labelled (neo)glycoproteins could be used routinely as tools for assessing the expression of endogenous sugar receptors in diagnostic neuro-oncology.