Glycosphingolipids in congenital disorders of glycosylation (CDG)

Congenital disorders of glycosylation (CDG) are a large family of rare disorders affecting the different glycosylation pathways. Defective glycosylation can affect any organ, with varying symptoms among the different CDG. Even between individuals with the same CDG there is quite variable severity. Associating specific symptoms to deficiencies of certain glycoproteins or glycolipids is thus a challenging task. In this review, we focus on the glycosphingolipid (GSL) synthesis pathway, which is still rather unexplored in the context of CDG, and outline the functions of the main GSLs, including gangliosides, and their role in the central nervous system. We provide an overview of GSL studies that have been performed in CDG and show that abnormal GSL levels are not only observed in CDG directly affecting GSL synthesis, but also in better known CDG, such as PMM2-CDG. We highlight the importance of studying GSLs in CDG in order to better understand the pathophysiology of these disorders.

Coordinated existence of multiple gangliosides is required for cartilage metabolism

OBJECTIVE

Gangliosides, ubiquitously existing membrane components that modulate transmembrane signaling and mediate cell-to-cell and cell-to-matrix interactions, are key molecules of inflammatory and neurological disorders. However, the functions of gangliosides in the cartilage degradation process remain unclear. We investigated the functional role of gangliosides in cartilage metabolism related to osteoarthritis (OA) pathogenesis.

DESIGN

We generated knockout (KO) mice by targeting the β1, 4-N-acetylgalactosaminyltransferase (GalNAcT) gene, which encodes an enzyme of major gangliosides synthesis, and the GD3 synthase (GD3S) gene, which encodes an enzyme of partial gangliosides synthesis. In vivo OA and in vitro cartilage degradation models were used to evaluate the effect of gangliosides on the cartilage degradation process.

RESULTS

The GalNAcT and GD3S KO mice developed and grew normally; nevertheless, OA changes in these mice were enhanced with aging. The GalNAcT KO mice showed significantly enhanced OA progression compared to GD3S mice in vivo. Both GalNAcT and GD3S KO mice showed severe IL-1α-induced cartilage degradation ex vivo. Phosphorylation of MAPKs was enhanced in both GalNAcT and GD3S KOs after IL-1α stimulation. Gangliosides modulated by GalNAcT or GD3S rescued an increase of MMP-13 induced by IL-1α in mice lacking GalNAcT or GD3S after exogenous replenishment in vitro.

CONCLUSION

These data show that the deletion of gangliosides in mice enhanced OA development. Moreover, the gangliosides modulated by GalNAcT are important for cartilage metabolism, suggesting that GalNAcT is a potential target molecule for the development of novel OA treatments.

Neuronal expression of GalNAc transferase is sufficient to prevent the age-related neurodegenerative phenotype of complex ganglioside-deficient mice

Gangliosides are widely expressed sialylated glycosphingolipids with multifunctional properties in different cell types and organs. In the nervous system, they are highly enriched in both glial and neuronal membranes. Mice lacking complex gangliosides attributable to targeted ablation of the B4galnt1 gene that encodes β-1,4-N-acetylegalactosaminyltransferase 1 (GalNAc-transferase; GalNAcT(-/-)) develop normally before exhibiting an age-dependent neurodegenerative phenotype characterized by marked behavioral abnormalities, central and peripheral axonal degeneration, reduced myelin volume, and loss of axo-glial junction integrity. The cell biological substrates underlying this neurodegeneration and the relative contribution of either glial or neuronal gangliosides to the process are unknown. To address this, we generated neuron-specific and glial-specific GalNAcT rescue mice crossed on the global GalNAcT(-/-) background [GalNAcT(-/-)-Tg(neuronal) and GalNAcT(-/-)-Tg(glial)] and analyzed their behavioral, morphological, and electrophysiological phenotype. Complex gangliosides, as assessed by thin-layer chromatography, mass spectrometry, GalNAcT enzyme activity, and anti-ganglioside antibody (AgAb) immunohistology, were restored in both neuronal and glial GalNAcT rescue mice. Behaviorally, GalNAcT(-/-)-Tg(neuronal) retained a normal "wild-type" (WT) phenotype throughout life, whereas GalNAcT(-/-)-Tg(glial) resembled GalNAcT(-/-) mice, exhibiting progressive tremor, weakness, and ataxia with aging. Quantitative electron microscopy demonstrated that GalNAcT(-/-) and GalNAcT(-/-)-Tg(glial) nerves had significantly increased rates of axon degeneration and reduced myelin volume, whereas GalNAcT(-/-)-Tg(neuronal) and WT appeared normal. The increased invasion of the paranode with juxtaparanodal Kv1.1, characteristically seen in GalNAcT(-/-) and attributed to a breakdown of the axo-glial junction, was normalized in GalNAcT(-/-)-Tg(neuronal) but remained present in GalNAcT(-/-)-Tg(glial) mice. These results indicate that neuronal rather than glial gangliosides are critical to the age-related maintenance of nervous system integrity.

Gangliosides play an important role in the organization of CD82-enriched microdomains

Four-transmembrane-domain proteins of the tetraspanin superfamily are the organizers of specific microdomains at the membrane [TERMs (tetraspanin-enriched microdomains)] that incorporate various transmembrane receptors and modulate their activities. The structural aspects of the organization of TERM are poorly understood. In the present study, we investigated the role of gangliosides in the assembly and stability of TERM. We demonstrated that inhibition of the glycosphingolipid biosynthetic pathway with specific inhibitors of glucosylceramide synthase [NB-DGJ (N-butyldeoxygalactonojirimycin) and PPMP (D-threo-1-phenyl-2-hexadecanoylamino-3-morpholino-1-propanol.HCl)] resulted in specific weakening of the interactions involving tetraspanin CD82. Furthermore, ectopic expression of the plasma-membrane-bound sialidase Neu3 in mammary epithelial cells also affected stability of the complexes containing CD82: its association with tetraspanin CD151 was decreased, but the association with EGFR [EGF (epidermal growth factor) receptor] was enhanced. The destabilization of the CD82-containing complexes upon ganglioside depletion correlated with the re-distribution of the proteins within plasma membrane. Importantly, depletion of gangliosides affected EGF-induced signalling only in the presence of CD82. Taken together, our results provide strong evidence that gangliosides play an important role in supporting the integrity of CD82-enriched microdomains. Furthermore, these results demonstrate that the association between different tetraspanins in TERM is controlled by distinct mechanisms and identify Neu3 as a first physiological regulator of the integrity of these microdomains.

Gangliosides potentially inhibit extracellular nucleotide metabolism

Gangliosides are glycolipids that contain sialic acid and they are mainly located on the outer leaflet of the cellular plasma membrane of most vertebrate and some invertebrate cells. Because they have structurally diverse, bulky and negatively charged oligosaccharide moieties, gangliosides endow cell membranes with unique molecular characteristics. Although they are abundant in the central nervous system (CNS), the complete loss of gangliosides in mice does not result in gross morphological abnormalities of the CNS. However, mutant mice develop neurodegenerative diseases and die soon after birth, suggesting that gangliosides are required for the maintenance and development of a stable CNS and are crucial to sustain life. At the cellular level, gangliosides influence cell growth and death, probably because they are involved in the lipid-mediated assembly of signaling molecules such as growth factor receptors or integrins on the membranes. This article addresses the structural similarity between the tandem sialic acid residues of gangliosides and nicotinamide adenine dinucleotide (NAD(+)) determined from biochemical data showing that gangliosides inhibit NAD(+) glycohydrolase activity and theoretical considerations. An essential feature of the structural similarity resides in a negative charge cluster formed by the two carboxyl groups in the tandem sialic acid residues and the diphosphate moiety of NAD(+). The potential physiological role(s) of gangliosides on the regulation of extracellular nucleotide metabolism are discussed.

Enhanced susceptibility to kainate-induced seizures, neuronal apoptosis, and death in mice lacking gangliotetraose gangliosides: protection with LIGA 20, a membrane-permeant analog of GM1

Knock-out (KO) mice lacking gangliotetraose gangliosides attributable to disruption of the gene for GM2/GD2 synthase [GalNAcT (UDP-N-acetylgalactosamine:GM3/GD3 beta-1,4-N-acetylgalactosaminyltransferase; EC 2.4.1.92 [EC])] are revealing key neural functions for the complex gangliosides of brain. This study has found such animals to be highly susceptible to kainic acid (KA)-induced seizures in terms of both seizure severity and duration. Intraperitoneal injection of 25 mg/kg KA produced status epilepticus for approximately 200 min in normal mice or heterozygotes and more than four times longer in the KO mice. The latter group suffered approximately 30% mortality, which increased to approximately 75% at dosage of 30 mg/kg KA, compared with 10-14% for the other two genotypes at the latter dosage. Nissl staining and terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling assay revealed substantial deterioration of pyramidal neurons attributable to apoptosis in the KO hippocampus, especially the CA3 region. Seizure activity in the KO mouse was only moderately diminished by intraperitoneal injection of GM1 ganglioside, whereas LIGA 20, a semisynthetic analog of GM1, substantially reduced both seizure severity and cell damage. The potency of LIGA 20 was correlated with its enhanced membrane permeability (compared with GM1), as seen in the increased uptake of [3H]LIGA 20 into the subcellular fractions of brain including cell nuclei. The latter finding is consonant with LIGA 20-induced restoration of the Na+/Ca2+ exchanger located at the inner membrane of the nuclear envelope in KO mice, an exchanger dependent on tight association with GM1 or its analog for optimal activity. These results point to a neuroprotective role for GM1 and its associated exchanger in the nucleus, based on regulation of Ca2+ flux between nucleoplasm and nuclear envelope.

Sensory nerve-dominant nerve degeneration and remodeling in the mutant mice lacking complex gangliosides

Gangliosides, sialic acid-containing glycosphingo-lipids, are enriched in the mammalian nervous system. Since mutant mice with disrupted beta1,4-N-acetylgalactosaminyl-transferase (GM2/GD2 synthase) were generated, there have been several studies on the pathology of the mutant mice, i.e. mild functional disorders and Wallerian degeneration in the peripheral nervous system. To further analyze the chronological alteration in the mutant mice, we examined the peripheral and CNS mainly with morphological approaches, such as electron microscopy and immunohistochemistry. Accordingly with the sensory dysfunction, neural degeneration, glial proliferation and synaptic remodeling in the dorsal horn of the spinal cord were found in adult mice. Thick astrocytic processes with densely packed glial filaments were extended among the neuropils and around blood vessels. Morphological changes in the synaptic vesicles and modes of synaptic contacts with central terminals were detected, suggesting synaptic remodeling following the degeneration. These results suggest that complex gangliosides are essential in the maintenance of integrity in architecture and function of the nervous system, lack of which results in neural degeneration in a sensory nerve-dominant manner.

Myelin-associated glycoprotein and complementary axonal ligands, gangliosides, mediate axon stability in the CNS and PNS: neuropathology and behavioral deficits in single- and double-null mice

Complementary interacting molecules on myelin and axons are required for long-term axon-myelin stability. Their disruption results in axon degeneration, contributing to the pathogenesis of demyelinating diseases. Myelin-associated glycoprotein (MAG), a minor constituent of central and peripheral nervous system myelin, is a member of the Siglec family of sialic acid-binding lectins and binds to gangliosides GD1a and GT1b, prominent molecules on the axon surface. Mice lacking the ganglioside biosynthetic gene Galgt1 fail to express complex gangliosides, including GD1a and GT1b. In the current studies, CNS and PNS histopathology and behavior of Mag-null, Galgt1-null, and double-null mice were compared on the same mouse strain background. When back-crossed to >99% C57BL/6 strain purity, Mag-null mice demonstrated marked CNS, as well as PNS, axon degeneration, in contrast to prior findings using mice of mixed strain background. On the same background, Mag- and Galgt1-null mice exhibited quantitatively and qualitatively similar CNS and PNS axon degeneration and nearly identical decreases in axon diameter and neurofilament spacing. Double-null mice had qualitatively similar changes. Consistent with these findings, Mag- and Galgt1-null mice had similar motor behavioral deficits, with double-null mice only modestly more impaired. Despite their motor deficits, Mag- and Galgt1-null mice demonstrated hyperactivity, with spontaneous locomotor activity significantly above that of wild type mice. These data demonstrate that MAG and complex gangliosides contribute to axon stability in both the CNS and PNS. Similar neuropathological and behavioral deficits in Galgt1-, Mag-, and double-null mice support the hypothesis that MAG binding to gangliosides contributes to long-term axon-myelin stability.

Different response of the knockout mice lacking b-series gangliosides against botulinum and tetanus toxins

We assessed the response in knockout mice lacking the b-series (G(D2), G(D1b), G(T1b) and G(Q1b)) gangliosides against Clostridium botulinum (types A, B and E) and tetani toxins. We found that botulinum toxins were fully toxic, while tetanus toxin was much less toxic in the knockout mice. Combining the present results with our previous finding that tetanus toxin and botulinum types A and B toxins showed essentially no toxic activity in the knockout mice lacking both the a-series and b-series gangliosides (complex gangliosides), we concluded that the b-series gangliosides is the major essential substance for tetanus toxin, while b-series gangliosides may be not the essential substance for botulinum toxins, at the initial step during the intoxication process in mouse.

A cellular deficiency of gangliosides causes hypersensitivity to Clostridium perfringens phospholipase C

Clostridium perfringens phospholipase C (Cp-PLC), also called alpha-toxin, is the major virulence factor in the pathogenesis of gas gangrene. Previously, a cellular UDP-Glc deficiency was related with a hypersensitivity to the cytotoxic effect of Cp-PLC. Because UDP-Glc is required in the synthesis of proteoglycans, N-linked glycoproteins, and glycosphingolipids, the role of these gly-coconjugates in the cellular sensitivity to Cp-PLC was studied. The cellular sensitivity to Cp-PLC was significantly enhanced by glycosphingolipid synthesis inhibitors, and a mutant cell line deficient in gangliosides was found to be hypersensitive to Cp-PLC. Gangliosides protected hypersensitive cells from the cytotoxic effect of Cp-PLC and prevented its membrane-disrupting effect on artificial membranes. Removal of sialic acids by C. perfringens sialidase increases the sensitivity of cultured cells to Cp-PLC and intramuscular co-injection of C. perfringens sialidase, and Cp-PLC in mice potentiates the myotoxic effect of the latter. This work demonstrated that a reduction in gangliosides renders cells more susceptible to the membrane damage caused by Cp-PLC and revealed a previously unrecognized synergism between Cp-PLC and C. perfringens sialidase, providing new insights toward understanding the pathogenesis of clostridial myonecrosis.

Ganglioside-dependent cell attachment and endocytosis of murine polyomavirus-like particles

For murine polyomavirus (Py), previous studies suggest the cellular target is a terminal alpha2,3-linked sialic acid. Here, we investigate the binding and uptake of mouse polyomavirus-like particles (PyVLP) derived from bacterially expressed VP1. We find that in fibroblast 3T6 cells, binding of PyVLP was substantially reduced by sialidase treatment, but only moderately affected by protease treatment, suggesting glycolipids such as the sialic acid-containing gangliosides mediate cell attachment. We further tested the entry requirement of PyVLP using the ganglioside-deficient GM95 murine cell line, and find PyVLP binding and entry were reduced in these cells. Finally, we find that addition of gangliosides G(M1), G(D1a), and G(T1b) to GM95 cells restored cellular PyVLP binding and uptake. Taken together, results indicate that gangliosides function in PyVLP cell attachment and endocytosis.

b-series Ganglioside deficiency exhibits no definite changes in the neurogenesis and the sensitivity to Fas-mediated apoptosis but impairs regeneration of the lesioned hypoglossal nerve

The polymorphic carbohydrate structures of gangliosides play regulatory roles. In particular, b-series gangliosides, all of which contain alpha-2,8 sialic acids, have been considered to be critical in various biological events such as adhesion, toxin binding, neurite extension, cell growth, and apoptosis. To clarify the physiological functions of b-series gangliosides in vivo, we have established a gene knockout mouse of GD3 synthase. Although all b-series structures were deleted in the mutant mice, they showed an almost complete nervous tissue morphology with no apparent abnormal behavior. Moreover, no differences in Fas-mediated apoptotic reaction of lymphocytes between wild type and the mutant mice were detected. However, the mutant mice exhibited clearly reduced regeneration of axotomized hypoglossal nerves compared with the wild type, suggesting that b-series gangliosides are more important in the repair rather than in the differentiation of the nervous system and apoptotic process induced via Fas.

Cerebellar neurons lacking complex gangliosides degenerate in the presence of depolarizing levels of potassium

Mice engineered to lack GM2/GD2 synthase (GalNAc-T), with resultant deficit of GM2, GD2, and all gangliotetraose gangliosides, were originally described as showing a relatively normal phenotype with only a slight reduction in nerve conduction. However, a subsequent study showed that similar animals suffer axonal degeneration, myelination defects, and impaired motor coordination. We have examined the behavior of cerebellar granule neurons from these neonatal knockouts in culture and have found evidence of impaired capacity for Ca2+ regulation. These cells showed relatively normal behavior when grown in the presence of physiological or moderately elevated K+ but gradually degenerated in the presence of high K+. This degeneration in depolarizing medium was accompanied by progressive elevation of intracellular calcium and onset of apoptosis, phenomena not observed with normal cells. No differences were detected in cells from normal vs. heterozygous mice. These findings suggest that neurons from GalNAc-T knockout mice are lacking a calcium regulatory mechanism that is modulated by one or more of the deleted gangliosides, and they support the hypothesis that maintenance of calcium homeostasis is one function of complex gangliosides during, and perhaps subsequent to, neuronal development.

Neutrophils are cytotoxic and growth-inhibiting for neuroblastoma cells with an anti-GD2 antibody but, without cytotoxicity, can be growth-stimulating

Neutrophils and mononuclear cells (MNC) can mediate antibody-dependent cellular cytotoxicity (ADCC) against cancer cells. To study cytotoxicity and growth inhibition of neuroblastoma cells by neutrophils and MNC with chimeric anti-disialoganglioside (GD2) monoclonal antibody (mAb) ch14.18, we developed digital image microscopy scanning (DIMSCAN) assays that measure fluorescence of target cells in 96-well plates after 6-18 h (cytotoxicity assay) or 7 days (growth assay). Neuroblastoma cell lines (GD2-positive: SMS-KCN, SMS-LHN, LA-N-1; GD2-negative: SK-N-SH) were preloaded with calcein acetoxymethyl ester for the cytotoxicity assay or labeled in situ after 7 days of culture with fluorescein diacetate in the growth assay. Fluorescence, as quantified by DIMSCAN, was correlated with neuroblastoma cell number in both assays (100-2000 cells/well). In the cytotoxicity test, both neutrophils and MNC effectively mediated ADCC of GD2-positive but not GD2-negative neuroblastoma cell lines. Cytotoxicity of both neutrophils and MNC increased with effector to target cell (E:T) ratio (5-50:1) and mAb ch.14.18 dose (0.1-10 microg/ml). ADCC of neutrophils, but not MNC, increased with addition of GM-CSF. Neutrophils, especially with rhGM-CSF, significantly suppressed growth of GD2-positive cell lines at a high E:T ratio (50:1) and mAb dose (10 microg/ml). Without antibody, neutrophils inhibited growth of one cell line (LA-N-1) but stimulated growth of two others (SMS-KCN, SMS-LHN). If neuroblastoma cells did not express GD2 (SK-N-SH), neutrophils stimulated growth whether or not antibody was present. Neutrophil culture supernatants increased growth of SK-N-SH, LA-N-1, and SMS-KCN cells, and MNC culture supernatants increased growth of SK-N-SH. In conclusion, neutrophils can mediate cytotoxicity and growth inhibition with a chimeric anti-GD2 antibody but also can promote tumor cell growth if antibody is not present or if GD2 is not expressed.

The gangliosides as a possible molecular coupling factor between the proportion of radiosensitive cells in vitro and the metastatic potential in vivo within a human melanoma cell line

With an experimental model of spontaneous lung metastases in immunosuppressed newborn rats, seven clones and variants with different metastatic potential and gangliosides expression were derived from a single parental human melanoma cell line M4Be. The cellular radiosensitivity of M4Be and its seven sublines was estimated using an in vitro colony assay. The total amount of gangliosides in M4Be and its seven sublines was determined by cell extraction and thin-layer chromatography, while the expression of GD3 gangliosides was estimated by flow cytometry with a monoclonal antibody. The radiation-cell survival curves of most clones and variants derived from M4Be showed a zero dose extrapolation clearly lower than 100%, suggesting that two populations of cells of very different radiosensitivity coexist within each of these clones and variants. Although the proportion of radiosensitive cells could be estimated from the shape of the survival curve, its radiosensitivity is too high to be properly evaluated by the colony assay. The eight survival curves differ essentially in the proportion of radiosensitive cells--which varied from 0% to 40% among M4Be and its seven sublines--whereas the cellular radiosensitivity of the radioresistant population was similar among them. The metastatic potential in vivo of M4Be and its seven sublines was not significantly related to the cellular radiosensitivity of their corresponding radioresistant population, but significantly increased with the fraction of radiosensitive cells. This relationship is valid only when the highly metastatic cells are cultured for no more than five passages in vitro as the fraction of radiosensitive cells is rapidly lost during subcultures. The relationship remains valid in vivo as metastatic melanoma-bearing newborn rats whole body irradiated with 20 cGy show no lung metastasis compared with controls. The radiosensitive cell fraction is inversely correlated with both the total ganglioside content (r = 0.84, P < 0.02) and the number of cells positively labelled with the monoclonal antibody directed to GD3 (r = 0.92, P < 0.001). The incubation of a radiosensitive clone with the exogenous bovine brain ganglioside GM1 significantly increases the proportion of radioresistant cells and suppresses its metastatic potential, while the inhibition of the endogenous gangliosides synthesis in the radioresistant cell line M4Be increases the proportion of radiosensitive cells. This study provides a possible explanation for the correlation between the metastatic potential and the proportion of radiosensitive cells within the seven sublines derived from a single parental human melanoma cell line.

Human melanoma cell lines deficient in GD3 ganglioside expression exhibit altered growth and tumorigenic characteristics

We have selected GD3-deficient human melanoma cell lines, in order to investigate the function of GD3 ganglioside. This was done by treating SK-MEL-28 cells with anti-GD3 antibody (R24) and rabbit complement and subsequent subcloning of the surviving cells, resulting in the derivation of two cell lines deficient in the cell surface expression of GD3. Neither cell line (designated SK-MEL-28-N1 and SK-MEL-28-N2) had detectable cell surface expression of GD3 as analyzed with monoclonal antibody R24, and no GD3 was detectable in either cell line by glycolipid isolation, thin-layer chromatography, or resorcinol-HC1 spray, but thin-layer chromatography immunostaining with monoclonal antibody R24 showed the presence of low amounts of GD3 in both N1 and N2 (1/40 of the amount in the parent cell line in N1 and 1/500 in N2). In SK-MEL-28-N1, the residual GD3 was shown by immunofluorescence assays on permeabilized cells to be present in discrete intracellular organelles, suggesting that these cells have a defect in the transport of GD3 as well as in its synthesis. Both SK-MEL-28-N1 and -N2 had an increase in detectable GM3 expression. The mutant cell lines had altered cell morphology in comparison to the parent cell line and both had slower growth rates in vitro and lower tumorgenicity in nu/nu mice. These results indicate that GD3 ganglioside plays an important role in proliferation and growth of melanoma cells.

Expression of gangliosides as receptors at the cell surface controls infection of NCTC 2071 cells by Sendai virus

The involvement of gangliosides as receptors for Sendai virus was established previously using experimentally produced receptor-deficient cells. In the search for a naturally occurring counterpart, NCTC 2071 cells emerged as a likely candidate. These cells in their native state were not agglutinated nor infected by Sendai virus, but were infected by the virus when the gangliosides GD1a, GT1b, or GQ1b were supplied in the culturing medium. Preliminary analysis indicated that NCTC 2071 cells contained an unusually high ratio of sialoglycoproteins to gangliosides. A brief treatment of the cell surface with the protease trypsin made greater than 99% of the native monolayer susceptible to infection by the wild-type virus which contains the viral attachment protein HN. (Incubation of the trypsin-treated cells with a temperature-sensitive mutant missing HN produced no detectable infection.) The increased binding of cholera toxin, a ganglioside-specific probe, after incubation of the cells with trypsin and sialidase, was consistent with the hypothesis that gangliosides more complex than GM1 are on the surface of NCTC 2071 cells and that trypsin treatment increases their accessibility. The presence of receptor gangliosides in lipid extracts of NCTC 2071 cells was confirmed by thin-layer chromatography of the ganglioside fraction and by the binding of cholera toxin. These results demonstrate that cells containing receptor gangliosides may still be resistant to infection because these are not expressed properly at the cell surface as receptors for interaction with the HN protein of Sendai virus.

Fluorescent gangliosides as probes for the retention and organization of fibronectin by ganglioside-deficient mouse cells

Ganglioside-deficient transformed mouse fibroblasts (NCTC 2071A cells), which grow in serum-free medium, synthesize fibronectin but do not retain it on the cell surface. When fluorescent derivatives of gangliosides, containing either rhodamine or Lucifer yellow CH attached to the sialic acid residues, were added to the culture medium, the cells incorporated the derivatives and their surfaces became highly fluorescent. When the cells were stained with anti-fibronectin antibodies and a fluorescent second antibody, fibrillar strands of fibronectin were observed to be attached to the cell surface, with partial coincidence of the patterns of direct ganglioside fluorescence and indirect fibronectin immunofluorescence at the cell surface. When the cells were exposed to bacterial neuraminidase during the time of ganglioside insertion, similar patterns of fluorescence were observed. Because the fluorescent gangliosides are resistant to the enzyme, these results suggest that neuraminidase-sensitive endogenous glycoconjugates were not involved in the ganglioside-mediated retention and organization of endogenous fibronectin. After cells were exposed to exogenous chicken fibronectin, most of the fibronectin was attached to the substratum and only a few fibrils were attached to the cells. When exogenous gangliosides were included in the incubation, there was a striking increase in cell-associated exogenous fibronectin, which was highly organized into a fibrillar network. Conversely, cells incubated for 18 h with exogenous unmodified gangliosides exhibited a highly organized network of endogenously derived fibronectin. Upon further incubation of the cells for 2 h with fluorescent gangliosides, there was considerable co-distribution of the fluorescent gangliosides with the fibronectin network as revealed by immunofluorescence. Our results support the concept that gangliosides can mediate the attachment of fibronectin to the cell surface and its organization into a fibrillar network.

Alterations in brain gangliosides and other lipids of patients with Creutzfeldt-Jakob disease and subacute sclerosing panencephalitis (SSPE)

Lipid composition was examined with cerebral cortices of three cases of Creutzfeldt-Jakob (C-J) disease and one case of subacute sclerosing panencephalitis (SSPE). Phosphatidylethanolamine decreased in both C-J and SSPE brains. Sphingomyelin increased in CJ. The levels of cholesterol esters which occurred in a trace amount in normal control were elevated in C-J and more severely in SSPE. The total amounts of gangliosides were reduced in C-J and SSPE. Gangliosides GD1b, GT1b and GQ1b in the biosynthetic pathway B [23] specifically decreased in C-J, while GM1 and GD3 increased. An increased content of GD3 may be related to the proliferation of reactive astrocytes. A decrease of 22:6 (n-3) accompanied with an increase of oleic acid in the fatty acid composition of the acidic phospholipid fraction was observed. This might be a cause for alterations in membrane function.

Deficient Ganglioside Biosynthesis: a novel human sphingolipidosis

An unusual lipid storage disese is chracterized by the accumulation of hematoside (Gms3) in the patient's liver and brain. In contrast to the other sphingoliidoses, the accumulation of Gm3 is not the result of a defective catabolic reaction, but is the first disorder caused by deficiency in ganglioside biosynthesis to be described in man.