Isolation and characterization of the major glycosphingolipids from the liver of the rainbow trout (Oncorhynchus mykiss): identification of an abundant source of 9-O-acetyl GD3

9-O Acetylated Gangliosides in Health and Disease

Glycosphingolipids comprise a lipid class characterized by the presence of sugar moieties attached to a ceramide backbone. The role of glycosphingolipids in pathophysiology has gained relevance in recent years in parallel with the development of analytical technologies. Within this vast family of molecules, gangliosides modified by acetylation represent a minority. Described for the first time in the 1980s, their relation to pathologies has resulted in increased interest in their function in normal and diseased cells. This review presents the state of the art on 9-O acetylated gangliosides and their link to cellular disorders.

Aeromonas salmonicida binds α2-6 linked sialic acid, which is absent among the glycosphingolipid repertoires from skin, gill, stomach, pyloric caecum, and intestine

Carbohydrates can both protect against infection and act as targets promoting infection. Mucins are major components of the slimy mucus layer covering the fish epithelia. Mucins can act as decoys for intimate pathogen interaction with the host afforded by binding to glycosphingolipids in the host cell membrane. We isolated and characterized glycosphingolipids from Atlantic salmon skin, gill, stomach, pyloric caeca, and intestine. We characterized the glycosphingolipids using liquid chromatography – mass spectrometry and tandem mass spectrometry and the glycan repertoire was compared with the glycan repertoire of mucins from the same epithelia. We also investigated Aeromonas salmonicida binding using chromatogram and microtiter well based binding assays. We identified 29 glycosphingolipids. All detected acid glycans were of the ganglio-series (unless shorter) and showed a high degree of polysialylation. The non-acid glycans were mostly composed of the neolacto, globo, and ganglio core structures. The glycosphingolipid repertoire differed between epithelia and the proportion of the terminal moieties of the glycosphingolipids did not reflect the terminal moieties on the mucins from the same epithelia. A. salmonicida did not bind the Atlantic salmon glycosphingolipids. Instead, we identified that A. salmonicida binding to sialic acid occurred to α2–6 Neu5Ac but not to α2–3 Neu5Ac. α2–6 Neu5Ac was present on mucins whereas mainly α2–3 Neu5Ac was found on the glycosphingolipids, explaining the difference in A. salmonicida binding ability between these host glycoconjugates. A. salmonicida´s ability to bind to Atlantic salmon mucins, but not the glycosphingolipids, is likely part of the host defence against this pathogen.

Regulation of triglyceride metabolism in medaka (Oryzias latipes) hepatocytes by Neu3a sialidase

Fish store triglycerides (TGs) in the liver, muscle, and adipose tissue and TGs constitute an energy source upon metabolic demand. The liver generally plays important roles in lipid metabolism. Recent studies have suggested the possibility of hepatic lipid metabolic regulation by ganglioside in mammals; however, ganglioside-mediated regulation of lipid metabolism is unclear in fish. This study aimed to clarify the role of ganglioside in fish TG metabolism, with particular reference to Neu3a, a ganglioside-specific sialidase expressed in the fish liver. Under fasting conditions, there was a decrease in hepatic TG contents, and neu3a mRNA level was significantly up-regulated in the medaka liver. To determine the role of Neu3a in hepatic lipid metabolism, Neu3a stable transfectants were generated using fish liver Hepa-T1 cells. After treating Neu3a cells with oleic acid, reduction of TG was detected in comparison with the mock cells. Furthermore, lipase activity was greater in Neu3a cells than in mock cells. To examine which ganglioside regulates these events, alterations of ganglioside composition in Neu3a cells were analyzed. Neu3a cells exhibited increased level of lactosylceramide (LacCer), a Neu3 enzymatic product originating from GM3. In addition, exposure of LacCer toward Hepa-T1 cells resulted in an increase of neutral lipase activity. The present results suggest that Neu3a up-regulation in medaka under fasting condition accelerates hepatic TG degradation for energy production via GM3 desialylation.

Targeting O-Acetyl-GD2 Ganglioside for Cancer Immunotherapy

Target selection is a key feature in cancer immunotherapy, a promising field in cancer research. In this respect, gangliosides, a broad family of structurally related glycolipids, were suggested as potential targets for cancer immunotherapy based on their higher abundance in tumors when compared with the matched normal tissues. GD2 is the first ganglioside proven to be an effective target antigen for cancer immunotherapy with the regulatory approval of dinutuximab, a chimeric anti-GD2 therapeutic antibody. Although the therapeutic efficacy of anti-GD2 monoclonal antibodies is well documented, neuropathic pain may limit its application. O-Acetyl-GD2, the O-acetylated-derivative of GD2, has recently received attention as novel antigen to target GD2-positive cancers. The present paper examines the role of O-acetyl-GD2 in tumor biology as well as the available preclinical data of anti-O-acetyl-GD2 monoclonal antibodies. A discussion on the relevance of O-acetyl-GD2 in chimeric antigen receptor T cell therapy development is also included.

GD3- and O-acetylated GD3-gangliosides in the GM2 synthase-deficient mouse brain and their immunohistochemical localization

Gangliosides in the brain of the knockout mouse deficient in the activity of β1,4 N-acetylgalactosaminyl transferase (β1,4 GalNAc-T)(GM2 synthase) consisted of nearly exclusively of GM3- and GD3-gangliosides as expected from the known substrate specificity of the enzyme and in confirmation of the initial reports from two laboratories that generated the mutant mouse experimentally. The total molar amount of gangliosides was approximately 30% higher in the mutant mouse brain than that in the wild-type brain. However, contrary to the initial reports, one-fourth of total GD3-ganglioside was O-acetylated. It reacted positively with an anti-O-acetylated GD3 monoclonal antibody and disappeared with a corresponding increase in GD3-ganglioside after mild alkaline treatment. The absence of O-acetylated GD3 in the initial reports can be explained by the saponification step included in their analytical procedures. Although quantitatively much less and identification tentative, we also detected GT3 and O-acetylated GT3. Anti-GD3 and anti-O-acetylated GD3 monoclonal antibodies gave positive reactions in the brain of mutant mouse as expected from the analytical results. Either antibody barely stained wild-type brain except for immunoreactivity of GD3 in the cerebellar Purkinje cells. The distributions of GD3 and O-acetylated GD3 in the brain of mutant mouse were similar but differential localization was noted in the cerebellar Purkinje cells and cerebral cortex.

Liver gangliosides of various animals ranging from fish to mammalian species

Liver gangliosides of different animal species were analyzed. Bony fish liver contained a major ganglioside that migrated faster than GM3 on thin-layer chromatography (TLC). This ganglioside was identified to be GM4 (NeuAc) by methods including product analysis after sialidase treatment and negative-ion electrospray ionization (ESI)-mass spectrometry (MS). The presence of GM4 (NeuGc) in fish liver was also demonstrated. The main ganglioside band of bovine liver consisted of two different molecular species, i.e. GD1a (NeuAc/NeuAc) and GD1a (NeuAc/NeuGc). Major gangliosides of liver tissue exhibited a distinct phylogenetic profile; GM4 was expressed mainly in lower animals such as bony fish and frog liver, whereas mammalian liver showed ganglioside patterns with smaller proportions of monosialo ganglioside species. While c-series gangliosides were consistently expressed in lower animals, they were found only in mammalian liver of particular species. No apparent trend was observed between the concentration of liver gangliosides and the phylogenetic stage of animals. The present study demonstrates the species-specific expression of liver gangliosides.

Very low density lipoproteins and interleukin 2 enhance the immunogenicity of 9-O-acetyl-GD3 ganglioside in BALB/c mice

Gangliosides expressed by tumor cells constitute potential targets for immunotherapy. A major limitation of protocols aiming to immunize patients against tumor gangliosides is the weak immunogenicity of these molecules. We have previously shown that exogenous gangliosides are essentially bound to serum lipoproteins. In this study we have analyzed the influence of human serum lipoproteins on the immunogenicity of purified human ganglioside 9-O-acetyl-GD3 in BALB/c mice. Although expressed at very low levels in mice, this ganglioside was not immunogenic when administered in the form of micelles. However 9-O-acetyl-GD3 adsorbed onto Very Low Density Lipoproteins (VLDL) was strongly and reproducibly immunogenic, inducing both an IgM and an IgG response, with higher titers than those obtained with total serum. The IgM antibody response appeared after a single injection whereas the IgG response was observed after 3 weeks but was stronger and more durable. The antibody response to 9-O-acetyl-GD3 bound to other serum fractions was weak or absent. The addition of recombinant interleukin 2 (IL-2) enhanced weak antibody responses to 9-O-acetyl-GD3 thereby facilitating responses to ganglioside in micelles and in protein-free Very Low Density Particles. Using in vitro assays, we demonstrated that VLDL-bound ganglioside 14C-GM3 was more sensitive to the effect of neuraminidase than gangliosides bound to other lipoprotein fractions, suggesting greater accessibility of VLDL-bound gangliosides. These results indicate that VLDL-bound gangliosides are the most immunologically active fraction of serum gangliosides. VLDL or similar particles and recombinant IL-2 may be useful adjuvants for immunization with gangliosides.

Isolation and characterization of biliary epithelial cells from rainbow trout liver

Lectin binding and density gradient centrifugation were explored for isolating epithelial cells from trout liver. Hepatocytes exhibited preferential attachment of coverslips coated with Phaseolus vulgaris erythroagglutinin. Biliary epithelial cells attached with glycine max agglutinin; however, significant attachment of cellular debris limited the use of glycine max agglutinin. Percoll-density gradient centrifugation separated liver cells into two distinct populations with biliary cells and hepatocytes banding at densities of 1.04 and 1.09, respectively. A discontinuous gradient composed of 13% Ficoll (wt/wt) separated biliary cells from hepatocytes. The recovery of highly enriched biliary epithelial cells from trout liver using Ficoll gradients yielded approximately 8 million cells (0.1 ml packed cells) from 10 g liver. Western blot analysis demonstrated that the cytokeratin profile for extracts from biliary epithelial cell-enriched populations differ significantly from those seen with whole liver extracts or with extracts with hepatocyte-enriched populations. Ficoll-gradient purified biliary cells and hepatocytes attached to culture plates coated with trout skin extract and carried out linear incorporation of leucine into protein and thymidine into DNA for 24 h. A mixture of growth hormones (insulin, epidermal growth factor, and dexamethasone) stimulated thymidine incorporation into DNA; however, long-term culture of dividing biliary epithelial cells was not achieved. Chemical analysis of neutral and acidic glycolipids indicated that hepatocytes and biliary cells have similar glycolipid profiles with an exception in the region of GM3 mobility, which is attributed to differences in the ceramide moiety. These studies provide a starting point for further characterization of unique cell types of the trout liver that may be important in their responses to toxic and carcinogenic agents.

Ganglioside GM3 inhibits the proliferation of cultured keratinocytes

Ganglioside GM3 is the predominant ganglioside of keratinocyte membranes. It has been proposed in other cell types that GM3 may participate in the regulation of cell proliferation. To examine the role of GM3 in keratinocyte proliferation, purified GM3 was added to cultured keratinocytes from normal foreskin, from lesional skin of patients with psoriasis and ichthyosis, and to cutaneous squamous carcinoma cell lines. Supplemental GM3 inhibited the growth of all cultured keratinocytes in a dose-dependent manner at concentrations of 10-100 microM. Keratinocytes from patients with psoriasis and ichthyosis were most sensitive to the inhibitory effects of GM3, and confluent undifferentiated keratinocytes were least sensitive. No change in differentiation was noted after addition of GM3. GD3, 9-0-acetyl-GD3, and GD1b also inhibited keratinocyte proliferation. Gangliosides GM1 and GD1a and sialic acid had little effect. Addition of 50 microM 3H-GM3 to cultured keratinocytes resulted in 1.7 times the amount of cellular GM3. These data suggest that hematoside (GM3) and "b" pathway gangliosides (GD3, GD1b), generated by the preferential activation of sialyltransferase II versus N-acetylgalactosaminyltransferase, may be involved in control of keratinocyte growth but not of differentiation.

Partial purification and characterization of cytidine-5'-monophosphosialate synthase from rainbow trout liver

Trout liver is a rich source of sialate cytidylyltransferase activity. Three procedures are described by which the enzyme was enriched between 67- and 647-fold with high specific activities varying between 0.67 and 1.88 U/mg protein. In the simplest procedure studied, 100,000 x g supernatant of liver homogenate was chromatographed on Q-Sepharose and beta-[3-(2-aminoethylthio)propyl]-N- acetylneuraminic acid as affinity matrix, leading to an enzyme preparation (0.67 U/mg protein) well suited for the synthesis of CMP-N-acetylneuraminic acid. The synthase has a molecular mass of 160 kDa, a temperature optimum of 28 degrees C, a pH-optimum of 9.3 and exhibits Km-values for CTP, N-acetylneuraminic acid and N-glycoloylneuraminic acid of 1.7 mM, 2.1 mM and 2.9 mM, respectively. It is inactive with N-acetyl-9-O-acetylneuraminic acid. The enzyme is inhibited by CMP, CDP and 2'-deoxy-CTP. The sialic acid fraction of trout liver after hydrolysis is composed by N-acetylneuraminic acid (86%), N-acetyl-9-O-acetylneuraminic acid (12%) and N-acetyl-9-O-lactoylneuraminic acid (2%).

Characterization of a CMPNeuAc: lactosylceramide alpha 2----3sialyltransferase from rainbow trout hepatoma (RTH-149) cells

1. The rainbow trout (Oncorhynchus mykiss) CMPNeuAc:lactosylceramide alpha 2----3sialytransferase enzyme from RTH-149 cells has been characterized. 2. Transfer of sialic acid to lactosylceramide was optimal at a pH of 5.9, temperature of 25 degrees C, and in the pressure of 0.3% CF-54, 10 mM Mn2+, 0.1 M sodium cacodylate, and 2 mM ATP. 3. Golgi-rich membrane fractions of RTH-149 cells were found to be enriched in sialidase activity and as such the addition of 40 microM 2,3-dehydro-2-deoxy-N-acetylneuraminic acid was necessary to assay alpha 2----3sialyltransferase activity optimally. 4. Apparent Km for donor (CMPNeuAc) and acceptor (lactosylceramide) were found to be 243 microM and 34 microM, respectively. 5. The alpha 2----3sialyltransferase characterized was found to be primarily specific for lactosylceramide though minor activity with other glycolipid acceptors was observed. 6. The presence of another sialyltransferase with differing substrate specificity was noted. 7. Properties of this enzyme, compared to analogous mammalian enzymes, are discussed.