Immunohistological and flow cytometric analysis of glycosphingolipid expression in mouse lymphoid tissues

Emerging concepts of ganglioside metabolism

Gangliosides (GGs) are sialic acid-containing glycosphingolipids (GSLs) and major membrane components enriched on cellular surfaces. Biosynthesis of mammalian GGs starts at the cytosolic leaflet of endoplasmic reticulum (ER) membranes with the formation of their hydrophobic ceramide anchors. After intracellular ceramide transfer to Golgi and trans-Golgi network (TGN) membranes, anabolism of GGs, as well as of other GSLs, is catalyzed by membrane-spanning glycosyltransferases (GTs) along the secretory pathway. Combined activity of only a few promiscuous GTs allows for the formation of cell-type-specific glycolipid patterns. Following an exocytotic vesicle flow to the cellular plasma membranes, GGs can be modified by metabolic reactions at or near the cellular surface. For degradation, GGs are endocytosed to reach late endosomes and lysosomes. Whereas membrane-spanning enzymes of the secretory pathway catalyze GSL and GG formation, a cooperation of soluble glycosidases, lipases and lipid-binding cofactors, namely the sphingolipid activator proteins (SAPs), act as the main players of GG and GSL catabolism at intralysosomal luminal vesicles (ILVs).

A Fluorescence-based Lymphocyte Assay Suitable for High-throughput Screening of Small Molecules

High-throughput screening (HTS) is currently the mainstay for the identification of chemical entities capable of modulating biochemical reactions or cellular processes. With the advancement of biotechnologies and the high translational potential of small molecules, a number of innovative approaches in drug discovery have evolved, which explains the resurgent interest in the use of HTS. The oncology field is currently the most active research area for drug screening, with no major breakthrough made for the identification of new immunomodulatory compounds targeting transplantation-related complications or autoimmune ailments. Here, we present a novel in vitro murine fluorescent-based lymphocyte assay easily adapted for the identification of new immunomodulatory compounds. This assay uses T or B cells derived from a transgenic mouse, in which the Nur77 promoter drives GFP expression upon T- or B-cell receptor stimulation. As the GFP intensity reflects the activation/transcriptional activity of the target cell, our assay defines a novel tool to study the effect of given compound(s) on cellular/biological responses. For instance, a primary screening was performed using 4,398 compounds in the absence of a "target hypothesis", which led to the identification of 160 potential hits displaying immunomodulatory activities. Thus, the use of this assay is suitable for drug discovery programs exploring large chemical libraries prior to further in vitro/in vivo validation studies.

Activation of ganglioside GM3 biosynthesis in human blood mononuclear cells in atherosclerosis

Using blood monocytes and lymphocytes from atherosclerotic patients and healthy subjects we have investigated activity of GM3 synthase, cellular levels of ganglioside GM3 and its role in monocyte adhesion to cultured human umbilical vein endothelial cells (HUVEC). The results showed that activity of GM3 synthase and cellular levels of ganglioside GM3 in blood mononuclear cells from atherosclerotic patients were several-fold higher than those from healthy subjects. In monocytes the activity of GM3 synthase was one an order of magnitude higher than in lymphocytes from both groups studied; this suggests the major contribution of monocytes to enhanced biosynthesis and levels of GM3 in mononuclear cells in atherosclerosis. Enrichment of monocytes from healthy subjects with ganglioside GM3 by incubation in medium containing this ganglioside increased adherence of these monocytes to HUVEC up to the values typical for monocytes from atherosclerotic patients. In addition, an increase in CD11b integrin expression was observed that was comparable to that seen in lipopolysaccharide-activated monocytes. It is suggested that in atherosclerosis the enhanced cellular levels of GM3 in monocytes and lymphocytes may be an important element of cell activation that facilitates their adhesion to endothelial cells and penetration into intima.

Cancer vaccines and carbohydrate epitopes

Tumor-associated carbohydrate antigens (TACA) result from the aberrant glycosylation that is seen with transformation to a tumor cell. The carbohydrate antigens that have been found to be tumor-associated include the mucin related Tn, Sialyl Tn, and Thomsen-Friedenreich antigens, the blood group Lewis related Lewis(Y), Sialyl Lewis(X) and Sialyl Lewis(A), and Lewis(X) (also known as stage-specific embryonic antigen-1, SSEA-1), the glycosphingolipids Globo H and stage-specific embryonic antigen-3 (SSEA-3), the sialic acid containing glycosphingolipids, the gangliosides GD2, GD3, GM2, fucosyl GM1, and Neu5GcGM3, and polysialic acid. Recent developments have furthered our understanding of the T-independent type II response that is seen in response to carbohydrate antigens. The selection of a vaccine target antigen is based on not only the presence of the antigen in a variety of tumor tissues but also on the role this antigen plays in tumor growth and metastasis. These roles for TACAs are being elucidated. Newly acquired knowledge in understanding the T-independent immune response and in understanding the key roles that carbohydrates play in metastasis are being applied in attempts to develop an effective vaccine response to TACAs. The role of each of the above mentioned carbohydrate antigens in cancer growth and metastasis and vaccine attempts using these antigens will be described.

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.

Expression of Neutral Glycosphingolipids in the Brain and Spleen of Mice Lacking TNF Receptor 1

We investigated the expression of neutral glycosphingolipids (GSLs) in the brain and spleen of mice lacking the gene for the tumor necrosis factor-alpha receptor p55 (TNFR1). Neutral GSLs of the ganglio-, globo-, and neolacto-series were determined in the tissues of homozygous (TNFR1-/-) and control heterozygous (TNFR1+/-) animals by high performance thin layer chromatography (HPTLC) overlay immunostaining with specific antibodies. The spleen of homozygous TNFR1 knockout mice lacked glucosylceramide substituted with palmitic acid, GlcCer(C16), and showed severe reduction in the expression of GlcCer(C24). In addition, gangliotetraosylceramide substituted with palmitic acid, Gg4Cer(C16), and globotetraosylceramide, Gb4Cer, were down-regulated in the TNFR1-/- spleen in comparison with the heterozygous control. The brain of both groups of animals (TNFR1-/- and TNFR1+/-) did not express detectable levels of Gg4Cer, Gb5Cer and Gb4Cer, but the brain of TNFR1 knockout mice expressed abundant globotriaosylceramide, Gb3Cer, compared to no expression in control heterozygous mice. nLcCer(C24) had slightly higher (1.4 fold) expression in the brain of TNFR1-/- mice compared with the control animals. This study provides in vivo evidence that TNF signaling via the TNFR1 is involved in the acquisition of a divergent GSL assembly in the brain, an immunologically privileged organ, and the spleen, typical secondary lymphoid organ.

Jaa-f11: extending the life of mice with breast cancer

JAA-F11 antibody (Ab) is a monoclonal Ab that is specific for the Thomsen-Friedenreich antigen, Galbeta1-3GalNAcalpha (TF-Ag). TF-Ag, discovered in the late 1920s, is a tumor-associated carbohydrate Ag of many clinically widespread carcinomas. In a mouse model, JAA-F11 Ab significantly extended median survival time of animals with metastatic 4T1 breast tumors and caused > 50% inhibition of lung metastasis. (124)Iodine labeled JAA-F11 Ab in in vivo micro positron emission tomography showed tumor specificity in a mouse breast tumor model, with no preferential uptake by any other organ. Human cancer cell adhesion to vascular endothelium was also blocked by JAA-F11. Structural specificity of the Ab was shown with glycan array analysis and indicated that this Ab, unlike many other Abs to TF-Ag, will not bind to a related glycolipid on natural killer cells, kidney or spleen. Patients with higher levels of naturally occurring anti-TF-Ag Ab appear to have a better prognosis, indicating that passive transfer of JAA-F11 or active immunization, resulting in production of anti-TF-Ag Ab, would clinically be beneficial for the patient.

The galactophilic lectin (PA-IL, gene LecA) from Pseudomonas aeruginosa. Its binding requirements and the localization of lectin receptors in various mouse tissues

The opportunistic pathogen Pseudomonas aeruginosa contains lectins of which one of them, PA-IL (gene lecA), shows preference for alpha-galactosylated glycans. The bacterial lectin is probably important in the carbohydrate-mediated adhesion of the microorganism to endothelia and epithelia and thereby the lectin facilitates entering and damaging of the cells. The requirements for the interaction between PA-IL and the carbohydrate epitopes to which the bacterial lectin may bind were here studied using alpha-galactosylated neoglycoproteins that were immobilized on Microtiter plates. It is concluded that the carbohydrate recognizing site of the lectin can have a binding requirement of only one saccharide. Lectin histochemistry was performed on sections from wild type mice and from knock-out mice, which lack function of the alpha1,3-galactosyltransferase gene. All assays with the P. aeruginosa lectin were compared with the results obtained using an isolectin from the legume shrub Griffonia simplicifolia: the GSI-B4 isolectin, which is highly specific for glycans terminating in Galalpha1-R. In the wild-type mice, lectin histochemistry showed a strong capillary reaction in heart, kidney and adrenal gland while none of the two lectins were able to detect capillaries in the pancreas. This could indicate a differential glycosylation with respect to endothelial cell Galalpha epitopes among different organs. Further, since no PA-IL binding to the endothelial cells in the KO mouse was observed, it seems that, in the mouse, the Pseudomonas lectin adheres to the Galalpha1-3Galbeta1-4GlcNAc carbohydrate on endothelial cells in most organs and tissues. Finally, lectin staining of the basement membrane of the acini in the exocrine pancreas suggests the presence of Galalpha1-3Gal epitopes in WT mice basement membranes that are not detected by the P. aeruginosa lectin.

Murine glycosyltransferases responsible for the expression of globo-series glycolipids: cDNA structures, mRNA expression, and distribution of their products

Biological functions of globo-series glycosphingolipids are not well understood. In this study, murine cDNAs of two glycosyltransferases responsible for the synthesis of globo-series glycolipids and mRNA expression of those genes were analyzed. Distribution of their products was also analyzed. Murine cDNAs for Gb3/CD77 synthase and Gb4 synthase predicted that both of them are type II membrane proteins with 348 and 331 amino acids, respectively. In northern blotting, Gb3/CD77 synthase gene was mainly expressed in kidney and lung but also detected in many other tissues. Gb4 synthase was expressed in brain, heart, kidney, liver, skin, and testis. In the immunohistological analysis, Gb3/CD77 was mainly expressed in the proximal tubules as revealed with coincidental expression with angiotensin-converting enzyme (ACE). In spleen, it was detected in pre-B cells in the peripheral region of the white pulp, as suggested with coincidental expression with CD10. It was also expressed on the endothelia of the alveolar capillaries in lung and on the sebaceous ducts aside of the hair follicles. Gb4 was also detected mainly on the proximal tubules in kidney and on the endothelia of the alveolar capillaries in lung as Gb3/CD77. But it was also detected on the epithelium of the bronchus, seminiferous tubules and tails of spermatozoa in testis, blood vessels of choroids plexus and endothelial cells in brain, and central and hepatoportal veins in liver. The expression patterns of two genes and their products almost corresponded with some exception. The results would provide essential information for the functional studies of globo-series glycolipids.

Carbohydrate profiling reveals a distinctive role for the C-type lectin MGL in the recognition of helminth parasites and tumor antigens by dendritic cells

Dendritic cells (DCs) are key to the maintenance of peripheral tolerance to self-antigens and the orchestration of an immune reaction to foreign antigens. C-type lectins, expressed by DCs, recognize carbohydrate moieties on antigens that can be internalized for processing and presentation. Little is known about the exact glycan structures on self-antigens and pathogens that are specifically recognized by the different C-type lectins and how this interaction influences DC function. We have analyzed the carbohydrate specificity of the human C-type lectin macrophage galactose-type lectin (MGL) using glycan microarray profiling and identified an exclusive specificity for terminal alpha- and beta-linked GalNAc residues that naturally occur as parts of glycoproteins or glycosphingolipids. Specific glycan structures containing terminal GalNAc moieties, expressed by the human helminth parasite Schistosoma mansoni as well as tumor antigens and a subset of gangliosides, were identified as ligands for MGL. Our results indicate an endogenous function for DC-expressed MGL in the clearance and tolerance to self-gangliosides, and in the pattern recognition of tumor antigens and foreign glycoproteins derived from helminth parasites.

Expression of glycosphingolipids in lymph nodes of mice lacking TNF receptor 1: biochemical and flow cytometry analysis

The expression of gangliosides and neutral glycosphingolipids (GSLs) in the lymph nodes of mice lacking the gene for the tumour necrosis factor-alpha receptor p55 (TNFR1) has been investigated. GSL expression in the tissues of mice homozygous (TNFR1-/-) or heterozygous (TNFR1+/-) for the gene deletion was analysed by flow cytometry and high-performance thin-layer chromatography (HPTLC) followed by immunostaining with specific antibodies. HPTLC immunostaining revealed that lymph nodes from TNFR1-/- mice had reduced expression of ganglioside GM1b and GalNAc-GM1b, neolacto-series gangliosides, as well as the globo- (Gb3, Gb4 and Gb5) and ganglio-series (Gg3 and Gg4) neutral GSLs. Flow cytometry of freshly isolated lymph node cells showed no significant differences in GSL expression, except for the GalNAc-GM1b ganglioside, which was less abundant on T lymphocytes from TNFR1-/- lymph nodes. In TNFR1-/- mice, GalNAc-GM1b+/CD4+ T cells were twofold less abundant (3.8% vs 7.6% in the control mice), whereas GalNAc-GM1b+/CD8+ T cells were fourfold less abundant (5.0% vs 20.2% in the control mice). This study provides in vivo evidence that TNF signalling via the TNFR1 is important for the activation of GM1b-type ganglioside biosynthetic pathway in CD8 T lymphocytes, suggesting its possible role in the effector T lymphocyte function.

Increased bone mass is a part of the generalized lymphoproliferative disorder phenotype in the mouse

We investigated the bone phenotype of mice with generalized lymphoproliferative disorder (gld) due to a defect in the Fas ligand-mediated apoptotic pathway. C57BL/6-gld mice had greater whole body bone mineral density and greater trabecular bone volume than their wild-type controls. gld mice lost 5-fold less trabecular bone and had less osteoclasts on bone surfaces after ovariectomy-induced bone resorption. They also formed more bone in a model of osteogenic regeneration after bone marrow ablation, had less osteoclasts on bone surfaces and less apoptotic osteoblasts. gld and wild-type mice had similar numbers of osteoclasts in bone marrow cultures, but marrow stromal fibroblasts from gld mice formed more alkaline phosphatase-positive colonies. Bone diaphyseal shafts and bone marrow stromal fibroblasts produced more osteoprotegerin mRNA and protein than wild-type mice. These findings provide evidence that the disturbance of the bone system is a part of generalized lymphoproliferative syndrome and indicates the possible role of osteoprotegerin as a regulatory link between the bone and immune system.

Ganglioside expression in tissues of mice lacking beta2-microglobulin

This study presents a comparative analysis of gangliosides from lymphoid (spleen and thymus) and other (brain, liver, lungs and muscle) tissues of C57BL/6 mice lacking the gene for beta2-microglobulin (beta2M), a constitutive component of the MHC class I molecule. Ganglioside fractions in the tissues of mice homozygous (beta2M-/-) and heterozygous (beta2M-/+) for the gene deletion were determined by high performance thin-layer chromatography (HPTLC), followed by immunostaining with specific polyclonal antibodies. Ubiquitous gangliosides GM3(Neu5Ac) and GM3(Neu5Gc) were the dominant gangliosides in the lungs of the control beta2M-/+ mice, whereas the homozygous knockout mice had substantially decreased expression of these structures. The lungs of the beta2M-/- mice also had reduced expression of T-lymphocyte-specific GM1b-type gangliosides (GM1b and GalNAc-GM1b). beta2M-deficient mice also had more GM1a and GD1a gangliosides in the liver, and several neolacto-series gangliosides were increased in the brain and lungs. This study provides in vivo evidence that the beta2M molecule can influence the acquisition of a distinct ganglioside assembly in different mouse organs, implicating its non-immunological functions.

Modelling the human immune response: can mice be trusted? Commentary

The mouse is now the animal of choice for laboratory-based medical research. Although its contribution to advancing understanding of our inner workings is indisputable, we should acknowledge that mice and humans are tangibly different. This article highlights, and attempts some rationale for, discrepancies between the two species' immune systems.