Ganglioside alterations in stimulated murine macrophages

Bis(monoacylglycero)phosphate as a Macrophage Enriched Phospholipid

Bis(monoacylglycero)phosphate (BMP) is a structural isomer of phosphatidylglycerol (PtdGro) with an unusual sn-1:sn-1' fatty acyl configuration and is found almost exclusively in late endosomes/lysosomes. BMP comprises only about 1-2% of the total phospholipids in most mammalian cells, but accumulates in tissues of humans and animals with lysosomal storage disorders including the gangliosidoses. Total BMP content was significantly greater in cells of macrophage/microglial origin than in cells of macroglial origin. BMP composition was similar in tumorigenic/metastatic macrophages and non-tumorigenic macrophages/microglia. Finally, BMP fatty acid composition differed between cells grown in culture and obtained in vivo suggesting an influence from growth environment.

Lack of lacto/neolacto-glycolipids enhances the formation of glycolipid-enriched microdomains, facilitating B cell activation

In a previous study, we demonstrated that beta1,3-N-acetylglucosaminyltransferase 5 (B3gnt5) is a lactotriaosylceramide (Lc(3)Cer) synthase that synthesizes a precursor structure for lacto/neolacto-series glycosphingolipids (GSLs) in in vitro experiments. Here, we generated B3gnt5-deficient (B3gnt5(-/-)) mice to investigate the in vivo biological functions of lacto/neolacto-series GSLs. In biochemical analyses, lacto/neolacto-series GSLs were confirmed to be absent and no Lc(3)Cer synthase activity was detected in the tissues of these mice. These results demonstrate that beta3GnT5 is the sole enzyme synthesizing Lc(3)Cer in vivo. Ganglioside GM1, known as a glycosphingolipid-enriched microdomain (GEM) marker, was found to be up-regulated in B3gnt5(-/-) B cells by flow cytometry and fluorescence microscopy. However, no difference in the amount of GM1 was observed by TLC-immunoblotting analysis. The GEM-stained puncta on the surface of B3gnt5(-/-) resting B cells were brighter and larger than those of WT cells. These results suggest that structural alteration of GEM occurs in B3gnt5(-/-) B cells. We next examined whether BCR signaling-related proteins, such as BCR, CD19, and the signaling molecule Lyn, had moved into or out of the GEM fraction. In B3gnt5(-/-) B cells, these molecules were enriched in the GEM fraction or adjacent fraction. Moreover, B3gnt5(-/-) B cells were more sensitive to the induction of intracellular phosphorylation signals on BCR stimulation and proliferated more vigorously than WT B cells. Together, these results suggest that lacto/neolacto-series GSLs play an important role in clustering of GEMs and tether-specific proteins, such as BCR, CD19, and related signaling molecules to the GEMs.

Gene-linked shift in ganglioside distribution influences growth and vascularity in a mouse astrocytoma

Brain tumor growth and progression is dependent upon vascularity, and is associated with altered ganglioside composition and distribution. In this study, we examined the influence of gangliosides on growth and vascularity in a malignant mouse astrocytoma, CT-2A. Ganglioside distribution was altered in CT-2A tumor cells using an antisense construct to beta-1,4-N-acetylgalactosaminyltransferase (GalNAc-T), a key enzyme that uses the simple ganglioside GM3 as a substrate for the synthesis of the more complex gangliosides, GM2, GM1 and GD1a. GalNAc-T gene expression was significantly lower in CT-2A cells stably transfected with the antisense GalNAc-T plasmid, pcDNA3.1/TNG (CT-2A/TNG) than in either non-transfected CT-2A or mock-transfected (CT-2A/V) control tumor cells. GM3 was elevated from 16% to 58% of the total ganglioside distribution, whereas GM1 and GD1a were reduced from 17% and 49% to 10% and 17%, respectively, in CT-2A/TNG tumor cells. Growth, vascularity (blood vessel density and Matrigel assay) and vascular endothelial growth factor (VEGF) expression was significantly less in CT-2A/TNG tumors than in control CT-2A brain tumors. In addition, the expression of VEGF, hypoxia-inducible factor 1alpha (HIF-1alpha) and neuropilin-1 (NP-1) was significantly lower in CT-2A/TNG tumor cells than in control CT-2A tumor cells. These data suggest that gene-linked changes in ganglioside composition influence the growth and angiogenic properties of the CT-2A astrocytoma.

Ganglioside composition of a mouse brain tumor grown in the severe combined immunodeficiency (SCID) mouse

The content and composition of gangliosides were examined in an experimental mouse brain tumor, EPEN, that was grown subcutaneously in the flank of the syngeneic C57BL/6J (B6) host and in the B6 severe combined immunodeficiency (SCID) host. SCID mice lack functional T- and B-lymphocytes, but have a normal complement of macrophages. The content and distribution of the brain tumor gangliosides were similar whether the tumor was grown in the immunocompetent B6 host or in the B6-SCID host. N-acetylneuraminic acid- (NeuAc) containing GM3 was the major ganglioside in the subcutaneous tumors and in the cultured EPEN cells. Significant amounts of N-glycolylneuraminic acid- (NeuGc) containing gangliosides were found in the tumor grown in both mouse hosts. NeuGc-containing gangliosides are not expressed in normal mouse brain, but are present in macrophages and serum. An extremely complex pattern of minor gangliosides was found in the subcutaneous tumors on two-dimensional, high-performance thin-layer chromatograms. Most of the minor gangliosides comigrated with those found in mouse macrophages. The results show that the absence of functional T- and B-lymphocytes does not markedly affect brain tumor ganglioside composition and suggest that NeuGc-containing gangliosides in the EPEN can be derived from tumor infiltrating host cells (mostly macrophages) and from the extracellular milieu (serum).

Modifications of cell surface sialic acids modulate cell adhesion mediated by sialoadhesin and CD22

An increasing number of mammalian cell adhesion molecules, including sialoadhesion, CD22 and the family of selectins, have been found to bind cell surface glycoconjugates containing sialic acids. Here we describe how the structural diversity of this sugar influences cell adhesion mediated by the related molecules sialoadhesin and CD22 in murine macrophages and B-cells respectively. We show that the 9-O-acetyl group of Neu5,9Ac2 and the N-glycoloyl residue of Neu5Gc interfere with sialoadhesin binding. In contrast, CD22 binds more strongly to Neu5Gc compared to Neu5Ac. Of two synthetic sialic acids tested, only CD22 bound the N-formyl derivative, whereas a N-trifluoroacetyl residue was accepted by sialoadhesin. The potential significance for the regulation of sialic acid dependent cell adhesion phenomena is discussed.

Influence of growth environment on the ganglioside composition of an experimental mouse brain tumor

Ganglioside composition was examined in an experimental mouse brain tumor growing as a solid tumor in vivo and as a cultured cell line in vitro. Gangliosides were also studied in the solid tumor rederived from the cultured tumor cell line. Although GM3-NeuAc was the major ganglioside in both the solid tumor and cultured tumor cells, several gangliosides expressed in the solid tumors (e.g., GM2-NeuGc, GM1, and GM1b) were not expressed in the cultured tumor cells. These gangliosides, however, are major components of mouse macrophages. Furthermore, significant amounts of gangliosides containing N-glycolylneuraminic acid (NeuGc) were found in the solid tumor growing in vivo, but only trace amounts were present in the cultured tumor cells. NeuGc is a common ganglioside sialic acid in mouse nonneural cells, whereas N-acetylneuraminic (NeuAc) is the predominant sialic acid in mouse brain. The trace amounts of NeuGc in the cultured cells are attributed to contamination from the fetal bovine serum. Radiolabeling of the cultured tumor cell gangliosides with [14C]galactose revealed that GM3-NeuAc was the only ganglioside synthesized by the tumor cells. The results suggest that nontumor-infiltrating cells, e.g., macrophages, lymphocytes, and endothelial cells, may contribute significantly to the total ganglioside composition of solid tumors growing in vivo.

The influence of ImuVert, a biological response modifier, on the growth and ganglioside composition of murine neural tumors

ImuVert is a biological response modifier (BRM) that has antitumor effects in humans and rats. The influence of ImuVert on the ganglioside composition of two experimental brain tumors, ependymoblastoma and CT-2A, was studied in C57BL/6J mice. Gangliosides are expressed on plasma membranes and can serve as markers to distinguish neural cells from nonneural cells in mouse brain tumors. N-acetylneuraminic (NeuAc) is the predominant sialic acid in mouse neural cells, whereas N-glycolylneuraminic (NeuGc) is a major sialic acid in nonneural cells, e.g., macrophages and lymphocytes. ImuVert treatment increased the NeuGc ganglioside concentration in the ependymoblastoma, but had no effect on the sialic acid concentration in the CT-2A brain tumor. ImuVert also had a slight inhibitory effect on the growth of both brain tumors.

Ganglioside alterations in YAC-1 cells cultivated in serum-supplemented and serum-free growth medium

Gangliosides of the 'GM1b-pathway' (GM1b and GalNAc-GM1b) have been found to be highly expressed by the mouse T lymphoma YAC-1 grown in serum-supplemented medium, whereas GM2 and GM1 ('GM1a-pathway') occurred only in low amounts [Müthing, J., Peter-Katalinić, J., Hanisch, F.-G., Neumann, U. (1991) Glycoconjugate J 8:414-23]. Considerable differences in the ganglioside composition of YAC-1 cells grown in serum-supplemented and in well defined serum-free medium were observed. After transfer of the cells from serum-supplemented medium (RPMI 1640 with 10% fetal calf serum) to serum-free medium (RPMI 1640 with well defined supplements), GM1b and GalNAc-GM1b decreased and only low amounts of these gangliosides could be detected in serum-free growing cells. The expression of GM1a was also diminished but not as strongly as that of GM1b and GalNAc-GM1b. These growth medium mediated ganglioside alterations were reversible, and the original ganglioside expression was achieved by readaptation of serum-free growing cells to the initial serum-supplemented medium. On the other hand, a 'new' ganglioside, supposed to represent GalNAc-GD1a and not expressed by serum-supplemented growing cells, was induced during serum-free cultivation, and increased strongly after readaptation. These observations reveal that the ganglioside composition of in vitro cultivated cells can be modified by the extracellular environment due to different supplementation of the basal growth medium.

Ganglioside distribution in murine neural tumors

The ganglioside composition of seven experimental brain tumors was examined in C57BL/6J mice. The tumors were produced from 20-methylcholanthrene (20-MC) implantation into either the cerebrum or cerebellum and were maintained in serial transplants through many generations. The tumors studied were grown subcutaneously as solid tumors, and cells from two of the tumors were also studied in culture. Histologically, all of the tumors were similar and could be broadly classified as highly malignant, poorly differentiated anaplastic astrocytomas. The total ganglioside sialic acid content of the solid tumors was markedly lower than that in adult mouse brain. In addition to N-acetylneuraminic acid (NeuAc), the gangliosides in the solid tumors contained significant amounts of N-glycolylneuraminic acid (NeuGc). The seven solid tumors fell into two general groups with respect to ganglioside composition. Furthermore, the differences in ganglioside composition between the two tumor groups were strongly associated with differences in tumor cell cohesion. The tumors in one group had high levels of GM3 hematosides, low levels of oligosialogangliosides, and grew as firm cohesive tissues. The tumors in the other group, however, had lower levels of GM3 hematosides, noticeable amounts of oligosialogangliosides and grew as soft noncohesive tissues. In culture, clonal cells from one of the tumors in the first group grew as clumps or islands and contained GM3 as the only major ganglioside, whereas clonal cells from a tumor in the second group grew as sheets or monolayers and contained little GM3, but expressed several gangliosides with complex structures. In marked contrast to the gangliosides in the solid tumors, the gangliosides in the cultured tumor cells contained trace amounts of NeuGc. Since NeuGc containing gangliosides are abundant in mouse nonneural tissues, the high content of NeuGc gangliosides in the solid tumors may arise from infiltration of nonneural tissue elements, e.g., macrophages, lymphocytes, and endothelial cells.

Detection of gangliosides with the fluorochrome NBD dihexadecylamine and its application for preparative high performance thin layer chromatography

A new method for the detection of gangliosides based on the lipophilic fluorescence agent 4-(N,N-dihexadecyl)amino-7-nitrobenz-2-oxa-1,3-diazole (NBD dihexadecylamine) and its application for preparative high performance thin layer chromatography is described. Brain gangliosides were chromatographed on silica gel coated thin layer plates and located with non-destructive fluorochrome under longwave ultraviolet light. The fluorescent zones were scraped off and the gangliosides were extracted with a mixture of chloroform/methanol/water (30/60/8; v/v/v). The gangliosides were separated from uncharged NBD dihexadecylamine by anion exchange chromatography and impurities were removed by Iatrobeads chromatography. The method described offers a simple and successful preparative thin layer chromatographic strategy to obtain pure gangliosides in microgram and milligram quantities.

Altered B-lymphocyte membrane architecture indicated by ganglioside accessibility in C3H/HeJ mice

We have analyzed both the total ganglioside composition and the surface accessibility of C3H/HeN B lymphocytes and C3H/HeJ B lymphocytes. Seventeen individual resorcinol-positive moieties were visualized by two-dimensional thin-layer chromatography of the purified gangliosides from both strains. Complete homology between strains was seen in the patterns of total gangliosides purified from the endotoxin-responsive and -hyporesponsive strains, with only minor differences in the relative concentrations of four gangliosides. In comparison, only 12 individual gangliosides were accessible to surface labeling following galactose oxidase treatment in these same strains, suggesting that some gangliosides are masked at the cell surface in both strains. However, labeling of the more polar components was greatly reduced in the endotoxin-hyporesponsive (C3H/HeJ) strain, suggesting that these gangliosides have decreased accessibility to galactose oxidase at the cell surface. Therefore, while the total ganglioside compositions of the two strains were nearly equivalent, there were dramatic differences in ganglioside surface accessibility. These findings indicate that an alteration in membrane structure that is associated with the endotoxin hyporesponsiveness observed in C3H/HeJ B lymphocytes exists.

Rapid detection of extended ganglio-series gangliosides with terminal GalNAc beta 1-4Gal sequence on high performance thin layer chromatography plates

The mouse monoclonal antibody 2D4, which recognizes the terminal GalNAc beta 1-4Gal-disaccharide of GgOse3Cer and GgOse5Cer, was used for the detection of ganglio-series gangliosides. The method involves separation of gangliosides on thin layer chromatography plates, followed by silica gel fixation, Arthrobacter ureafaciens neuraminidase treatment and final immunostaining of desialylated gangliosides with the monoclonal antibody 2D4. Both neuraminidase and the hybridoma 2D4 producing the specific monoclonal antibody are commercially available and therefore accessible to all researchers working in this field. Gangliosides from mouse T lymphocytes and the mouse T cell lymphoma YAC-1 have been used as examples. This technique may be used for fast screening of gangliosides with the GgOse5Cer core structure which have been described as T cell markers, antigens in human neuronal disease and receptors for certain pathogenic bacteria.

Detection of gangliosides of the GM1b type on high-performance thin-layer chromatography plates by immunostaining after neuraminidase treatment

A method for the detection of GM1b-type gangliosides in complex mixtures of gangliosides was developed. The procedure involves separation of gangliosides on high-performance thin-layer chromatography plates, fixation of the silica gel, treatment with neuraminidase from Vibrio cholerae in the absence of detergent, and incubation of the plates with GgOse4Cer-specific antibodies. Alkaline phosphatase-conjugated second antibodies are used to visualize bound first antibodies by generating a blue dye from 5-bromo-4-chloro-3-indolylphosphate. The procedure is capable of detecting as little as 30 ng of gangliosides. Gangliosides from murine T lymphocytes and from human brain served as examples. Besides GM1b, GD1 alpha is also detectable by this method, whereas the human brain gangliosides GM1a, GD1a, GD1b, and GT1b are not, because they are neuraminidase resistant. Since terminally sialylated gangliosides such as GM1b were described as virus receptors, and certain other terminally sialylated gangliosides are discussed as tumor markers, this method should be useful to screen gangliosides from different tissues or cell lines for the presence of such components, especially if only small amounts of material are available.

Bovine serum sialic acid: age-related changes in type and content

1. The sialic acid content of newborn calf serum (4.8 mumol/ml) is approx. 3-fold higher than that of mature animals (1.4 mumol/ml) and decreases to 2.4 mumol/ml at 20 days of age. Colostrum-fed and colostrum-deprived calves have similar levels of sialic acid from birth to 14 days of age. 2. The high level of sialic acid in newborn calf serum is due predominantly to N-acetylneuraminic acid, since this sialic acid accounts for 93% of the total and since less than 5% of the sialic acid is O-acetylated. 3. Comparison of day 0 and day 20 serum by gel filtration and by SDS polyacrylamide gel electrophoresis demonstrates that the increase in sialic acid is associated with increased production and/or sialylation of components with MW of 45-60 kDa. 4. A high percentage (64%) of the sialic acid in newborn calf serum is detected with the lipid-linked sialic acid assay, relative to 20 day old (25%) or mature (18%) animals. 5. This indicates that the glycoproteins of newborn calf serum are more efficiently extracted under the conditions of this assay than glycoproteins of mature serum.

Gangliosides block the inhibition of macrophage Fc-dependent phagocytosis by lipopolysaccharide

The mechanism whereby bacterial lipopolysaccharide (LPS) exerts its biologic effects on mammalian cells is unknown. Plasma membrane gangliosides bind bacterial toxins and have been implicated in modulating the effects of a variety of immunoregulatory substances. We investigated the possibility that gangliosides can inhibit the effect of lipopolysaccharide on Fc-dependent phagocytosis by murine peritoneal macrophages. Protein-free lipopolysaccharide preparations significantly inhibited Fc-mediated phagocytosis (less than 71% of control) at concentrations of 100 ng/ml or greater after 90 min of incubation. The inhibitory effect of LPS (1 micrograms/ml) was blocked when macrophages were incubated with mono-, di-, or trisialogangliosides (25-50 micrograms/ml). Neither asialoganglioside nor sialic acid alone were capable of blocking the effect of LPS. When chromatographed separately on a Sepharose 4B column, LPS and trisialoganglioside had different elution profiles. LPS and trisialoganglioside coeluted, however, when premixed at 37 degrees C for 60 min and then applied to the column. Therefore, abrogation of the effect of LPS on Fc-dependent phagocytosis may occur as a consequence of direct interaction between LPS and gangliosides. These data suggest that gangliosides may modulate the response of macrophages to bacterial lipopolysaccharide.