Ethanol disordering of GM1-enriched short-sleep synaptosomal plasma membranes

The Long-Sleep (LS) and Short-Sleep (SS) mouse synaptosomal plasma membranes differ in ethanol sensitivity at superficial membrane regions, which corresponds with the behavioral response of the mice to ethanol hypnosis. The only significant difference between these synaptosomal plasma membranes is the synaptosomal monosialoganglioside (GM1) content, LS > SS. Here, GM1 was examined as a parameter for increasing membrane sensitivity to ethanol effects in the ethanol-resistant SS membranes. Synaptosomal plasma membranes from SS mice were allowed to incorporate exogenous GM1. Membrane order was then studied at the surface, intermediate, and interior regions of the membranes by delayed Fourier transform proton NMR in the presence and absence of perdeuterated ethanol. Differences in membrane order were observed in all three membrane regions with increasing perdeuterated ethanol concentrations depending on the synaptosomal GM1 content.     

Molecular cloning and characterization of a plasma membrane-associated sialidase specific for gangliosides

Gangliosides are plasma membrane components thought to play important roles in cell surface interactions, cell differentiation, and transmembrane signaling. A mammalian sialidase located in plasma membranes is unique in specifically hydrolyzing gangliosides, suggesting crucial roles in regulation of cell surface functions. Here we describe the cloning and expression of a cDNA for the ganglioside sialidase, isolated from a bovine brain cDNA library based on the amino acid sequence of the purified enzyme from bovine brain. This cDNA encodes a 428-amino acid protein containing a putative transmembrane domain and the three Asp boxes characteristic of sialidases and sharing 19-38% sequence identity with other sialidases. Northern blot and polymerase chain reaction analyses revealed a general distribution of the gene in mammalian species, including man, and the mouse. In COS-7 cells transiently expressing the sialidase, the activity was found to be 40-fold that of the control level with ganglioside substrates in the presence of Triton X-100, and the hydrolysis was almost specific to gangliosides other than GM1 and GM2, both alpha2-->3 and alpha2-->8 sialyl linkages being susceptible. The major subcellular localization of the expressed sialidase was assessed to be plasma membrane by Percoll density gradient centrifugation of cell homogenates and by immunofluorescence staining of the transfected COS-7 cells. Analysis of the membrane topology by protease protection assay suggested that this sialidase has a type I membrane orientation with its amino terminus facing to the extracytoplasmic side and lacking a signal sequence.     

Clinical, ultrastructural and biochemical study of a case of GM1 type 2 gangliosidosis

Clinical, histological, ultrastructural and biochemical studies have been performed in a living 20-month-old infant with GM1-gangliosidosis type 2. Rectum, brain and liver biopsies were done. The histological and ultrastructural examination revealed the presence of cytoplasmic membranous bodies in the nervous system and a vacuolisation of the visceral parenchymatous cells, particularly histiocytes. The diagnosis was established by the finding of a generalized beta-galactosidase deficiency and an accumulation of GM1-ganglioside in brain. In leukocytes, the activity of p-nitrophenyl-beta-galactosidase was below 5%, and that of GM1-ganglioside beta-galactosidase below 1% of values obtained in controls. In cerebral tissue, GM1 ganglioside constituted 80% of total gangliosides; its concentration was 15 times that in age-matched controls. No accumulation of GM1 could be evidence in liver. Enzymatic examination of leukocytes obtained from the consanguineous parents revealed heterozygote values.     

The GM2-1 ganglioside islet autoantigen in insulin-dependent diabetes mellitus is expressed in secretory granules and is not beta-cell specific

The pancreatic islet monosialo-ganglioside (GM2-1), an autoantigen in insulin-dependent diabetes mellitus (IDDM) recently shown to be the target of autoantibodies associated with diabetes development in relatives of IDDM patients, is islet specific within the pancreas, and its expression is metabolically regulatable. In the present study we sought to establish 1) whether GM2-1 is beta-cell specific, and 2) its intracellular localization. To this end, we analyzed the pattern of ganglioside expression in highly purified beta- and non-beta-cells isolated from rat islets. In addition, ganglioside levels were determined in subcellular fractions of a rat beta-cell line (INS). No qualitative or quantitative difference was found in the pattern of ganglioside expression between beta and non-beta rat islet cells, with GM3, GM2-1, and GD3 gangliosides expressed in both cell populations. Within INS cells, GM2-1 ganglioside was expressed in the fraction containing secretory granules and, to a lesser extent, in plasma membranes; GM3 was expressed in secretory granules, whereas GD3 was found only in plasma membranes. These data indicate that the GM2-1 autoantigen is not beta-cell specific within the islets, in accordance with the observation that this molecule is a target of islet cell autoantibodies that bind to the whole pancreatic islet. Interestingly, this autoantigen is present in secretory granules similarly to other autoantigens in IDDM (insulin, carboxypeptidase H, 38-kDa protein, etc.), suggesting that the autoimmunity to the components of this organelle may be central to the pathogenesis of the disease.     

Ganglioside GM1 activates the mitogen-activated protein kinase Erk2 and p70 S6 kinase in U-1242 MG human glioma cells

Gangliosides are implicated in the regulation of cellular proliferation as evidenced by differences in ganglioside composition associated with malignant transformation and density of cells in culture, as well as their inhibitory effects when added to cells growing in culture. Exogenously added gangliosides have a bimodal effect on proliferation in U-1242 MG glioma cells, inhibiting DNA synthesis in growing cells and stimulating it in quiescent cells. We investigated the mechanisms involved in stimulation of DNA synthesis using [3H]thymidine incorporation and immune complex kinase assays to identify responsible signal transduction pathways. Treatment of quiescent U-1242 MG cells with GM1 caused activation of the mitogen-activated protein (MAP) kinase isoform Erk2. Pretreatment with the specific MAP kinase kinase inhibitor PD98059 prevented the GM1-stimulated Erk2 activation and GM1-stimulated DNA synthesis. GM1 treatment stimulated another distinct signaling pathway leading to activation of p70 S6 kinase (p70s6k), and this was prevented by pretreatment with rapamycin. Rapamycin also inhibited GM1-stimulated DNA synthesis. Activation of both pathways and stimulation of DNA synthesis were inhibited by forskolin treatment; however, GM1 had no effect on cyclic AMP levels. Platelet-derived growth factor also activated both Erk2 and p70s6k but did not cause DNA synthesis, suggesting that GM1 may stimulate additional cascades, which also contribute to GM1-mediated DNA synthesis.     

Complex gangliosides affect GD3 accessibility to antibody in developing neuronal cells

Ganglioside expression of embryonic chick retina cells developed in vitro was analyzed by indirect immunofluorescence. Immature neurons were GD3 positive cells and the labeling was chiefly distributed all over their cell membrane. Mature neurons became GD3 negative and expressed complex gangliosides of the a- and b-pathways; nevertheless, the content of GD3 accounted for approximately 40% of the total gangliosides in these cells. Neuraminidase hydrolysis pointed out that GD3 was located in membrane of differentiated cells. The frequency of cells with the GD3 immunostain localized in restricted area of membrane of undifferentiated neurons increased significantly after adding a mixture of bovine brain gangliosides (largely complex gangliosides). Antibody binding to immobilized GD3 showed a dose-dependent inhibition by adding a mixture of bovine brain gangliosides, GM1, GD1a or asialo-GM1. Glycosphingolipids with shorter oligosaccharide chains, as cerebrosides or sulfatides, did not affect this binding. These results suggest that, concomitant with the accretion of content of complex gangliosides, a rearrangement in the membrane would occur, which progressively masks GD3 to its antibody. This rearrangement might affect putative ganglioside functions involved in neuronal differentiation.     

Membrane fluidity increases during apoptosis of sheep ileal Peyer's patch B cells

To investigate specific plasma membrane structural changes associated with apoptosis, whole cells and purified plasma membranes of apoptotic B cells from the ileal Peyer's patch of sheep were analyzed for their "membrane fluidity." The ileal Peyer's patch of sheep provided a large number of B cells required for plasma membrane isolation (> 5 x 10(9)). As the incidence of apoptosis increased with time of culture, the fluidity of purified plasma membranes, as measured with the fluorophore DPH (diphenylhexatriene), increased. To evaluate this phenomenon with intact cells, B cells at different apoptotic stages were fractionated on discontinuous Percoll gradients. Similar results were obtained using the fluorophore TMA-DPH (trimethylammoniumdiphenylhexatriene), which has been shown to localize specifically to the plasma membrane. Functionally, the increase in plasma membrane fluidity associated with apoptosis may represent either a mechanism to cycle phosphatidylserine to the outer leaflet, mediating phagocytic recognition of apoptotic cells, or a consequence of this event.     

Colocalization and complex formation between prosaposin and monosialoganglioside GM3 in neural cells

Prosaposin, the precursor of saposins A, B, C, and D, was recently identified as a neurotrophic factor in vitro as well as in vivo. Its neurotrophic activity has been localized to a linear 12-amino acid sequence located in the NH2-terminal portion of the saposin C domain. In this study, we show the colocalization of prosaposin and ganglioside GM3 on NS20Y cell plasma membrane by scanning confocal microscopy. Also, TLC and western blot analyses showed that GM3 was specifically associated with prosaposin in immunoprecipitates; this binding was Ca2+-independent and not disassociated during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The association of prosaposin-GM3 complexes on the cell surface appeared to be functionally important, as determined by differentiation assays. Neurite sprouting, induced by GM3, was inhibited by antibodies raised against a 22-mer peptide, prosaptide 769, containing the neurotrophic sequence of prosaposin. In addition, pertussis toxin inhibited prosaptide-induced neurite outgrowth, as well as prosaptide-enhanced ganglioside concentrations in NS20Y cells, suggesting that prosaposin acted via a G protein-mediated pathway, affecting both ganglioside content and neuronal differentiation. Our findings revealed a direct and tight GM3-prosaposin association on NS20Y plasma membranes. We suggest that ganglioside-protein complexes are structural components of the prosaposin receptor involved in cell differentiation.     

Further characterization of equine brain gangliosides: the presence of GM3 having N-glycolyl neuraminic acid in the central nervous system

Equine brain gangliosides were isolated and their structures were characterized, to examine whether equine brain has N-glycolyl neuraminic acid in gangliosides, since other mammals predominantly possess N-acetyl neuraminic acid in brain gangliosides, and equine erythrocytes and organs except the brain have gangliosides exclusively containing N-glycolyl neuraminic acid. The gangliosides purified from the brain were identified by proton NMR spectroscopy and mass spectrometry, as well as GLC, resulting in their identification as GM4, GM3, GM2, GM1, GD1a, GD1b, and GT1b. Of these gangliosides, GM3 possessed N-glycolyl neuraminic acid as a minor component (18% of the total GM3), whereas other gangliosides exclusively contained N-acetyl neuraminic acid. The N-glycolyl neuraminic acid residue of the GM3 was confirmed by TLC immunostaining. The possibility of contamination of the GM3 by erythrocytes was eliminated based on the finding that the lipid compositions were characteristic of brain gangliosides. The presence, even as a minor component, of the N-glycolyl neuraminic acid in equine brain gangliosides is exceptional among the sialic acid species in mammalian central nervous system.     

The effects of reactive centre loop length upon serpin polymerisation

Our rapid method of microwave-mediated saponification for preparing lysoglycosphingolipids from their parent glycosphingolipids was also able to prepare lysogangliosides or modified lysogangliosides, which were identified by delayed extraction matrix-assisted laser desorption ionization time-of-flight mass spectrometric (DE MALDI-TOF MS) analysis. When GM3, GM2, and GM1 isolated from adult human brain gangliosides were subjected to the saponification, GM3 was found to give rise to only lyso-GM3 containing de-N-acetylneuraminic acid (de-N-acetyl lyso-GM3), whereas the GM2 produced both lyso-GM2 and the de-N-acetyl compound, and GM1 also gave both lyso-GM1 and the de-N-acetyl compound. In the saponification of GM1 and GDla, isolated from rat brain gangliosides, GM1 similarly produced both lyso-GM1 and the de-N-acetyl compound, but GDla was found to give rise to both dehydrated de-N-monoacetyl and dehydrated de-N-diacetyl lyso-GDla. However, the saponification of the GM1 fraction isolated from porcine brain gangliosides gave rise not only to both lyso-GM1 and the de-N-acetyl compound, but also unexpectedly to both lyso-fucosyl GM1 and its de-N-acetyl compound. The untreated GM1 fraction was examined by TLC and DE MALDI-TOF mass spectrometry, and proved to contain fucosyl-GM1. The DE MALDI-TOF MS analysis of the prepared lyso-gangliosides showed that their long chain bases consisted of d18:1 and d20:1 sphingosines in various ratios reflecting those of the different mammalian brain gangliosides.     

Strontium causes osteomalacia in chronic renal failure rats

The galanin neuropeptide system is widely distributed throughout the brain and periphery and is thought to play a role in feeding, pain and reproduction. To evaluate the human galanin receptor 1 as a potential therapeutic target, we fully characterized its interaction with several galanin-like peptides. The human galanin receptor 1 receptor was stably expressed using an episomal system in human embryonic kidney 293E cells. Saturation isotherms using 125I-human galanin revealed two distinct populations of receptor affinity states in membranes and whole cells with picomolar and nanomolar affinities at the high- and low affinity states, respectively. A scintillation proximity assay revealed that 125I-human galanin binding in membranes reached steady-state within 2 to 2.5 hr; however, only 50% of galanin radiolabel dissociated from the receptors by excess galanin or guanosine 5'-O-3-thiotriphosphate even after 20 hr. In contrast, galanin binding in whole cells was completely reversible within 1 hr. Competition binding assays showed that galanin-like peptides bound with picomolar affinities in membranes and whole cells. These peptides behaved as full agonists as determined by the inhibition of forskolin-stimulated cyclic 3'5'-adenosine monophosphate production and the stimulation of guanosine 5'-O-(3-[35S]thiotriphosphate binding. The agonist profile of M40, a representative chimeric peptide, was found not to be the result of receptor reserve because receptor inactivation by partial alkylation experiments confirmed its full intrinsic efficacy under conditions of a "zero" reserve state. These observations suggest that the antagonist effects in vivo of M40, and perhaps other chimeric peptides, are not mediated via direct interactions with the galanin receptor 1 receptor.     

Left ventricular function during exercise in athletes and in sedentary men

Galactose-1-phosphate uridyltransferase (GALT) is a key enzyme in the metabolism of galactose. GALT activates the galactose-glucose interconversion and enables the synthesis of glucose-1-phosphate and UDP-galactose (UDP-Gal). UDP-Gal is the galactosyl donor for the incorporation of galactose into complex oligosaccharides, glycoproteins and glycolipids. The expression of GALT was characterized both in vivo and in vitro during late embryonic and postnatal development of the brain and peripheral nerve of the rat. Assays of GALT mRNA and protein showed that it is weakly expressed during late embryonic development with a second peak of expression concomitant with myelinogenesis. GALT was prominently expressed in myelinating Schwann cells in a rat dorsal root ganglia culture system. GALT deficiency in humans results in galactosemia, a disease characterized by long-term intellectual impairment, and probably dysmyelination. The developmentally regulated pattern of GALT expression during maturation of the nervous system may provide a molecular basis for these neurological complications which seriously compromise the outcome of many galactosemic patients.     

Electron microscopic detection of glycoconjugates in the chicken lens

The cytochemical localization of glycoconjugates in the 14-day old embryonic chick lens was analysed by lectin-gold labelling. Con A/HRP gold particles, specific for D-mannose labelled the interior of the rough endoplasmic reticulum, membranes of the Golgi complex, secretory vesicles and the plasma membranes of the lens epithelial cell. The lens capsule was heavily labelled. Lens fiber cell membranes were also labelled. In contrast LFA, specific for neuraminic acid, did not bind to the endoplasmic reticulum or nuclear membrane. Labelling of the Golgi complex, secretory vesicles and capsule was observed. The plasma membranes of epithelial and fiber cells were extensively labelled, and probably reflects the presence of glycolipids such as gangliosides.     

Margatoxin binds to a homomultimer of K(V)1.3 channels in Jurkat cells. Comparison with K(V)1.3 expressed in CHO cells

Voltage-gated potassium (K(V)) channels play key roles in setting the resting potential and in the activation cascade of human peripheral T lymphocytes. Margatoxin (MgTX), a 39-amino acid peptide from Centruroides margaritatus, is a potent inhibitor of lymphocyte K(V) channels. The binding of monoiodotyrosinyl margatoxin ([125I]MgTX) to plasma membranes prepared from either Jurkat cells, a human leukemic T cell line, or CHO cells stably transfected with the Shaker-type voltage-gated K+ channel, K(V)1.3, has been used to investigate the properties of lymphocyte K(V) channels. These data were compared with [125I]MgTX binding to heterotetrameric K(V) channels in rat brain synaptic plasma membranes [Knaus, H. G., et al. (1995) Biochemistry 34, 13627-13634]. The affinity for [125I]MgTX is 100-200 fM in either Jurkat or CHO/K(V)1.3 membranes, and the receptor density is 20-120 fmol/mg in Jurkat membranes or 1000 fmol/mg in CHO/K(V)1.3 membranes. In contrast to rat brain, [125I]MgTX binding to Jurkat and CHO/K(V)1.3 membranes exhibits an absolute requirement for K+, with no potentiation of binding by Na+. K(V)1.3 was the only K(V)1 series channel present in either CHO/K(V)1.3 or Jurkat plasma membranes as determined by immunoprecipitation of [125I]MgTX binding or by Western blot analyses using sequence-specific antibodies prepared against members of the K(V)1 family. The relative potencies of a series of peptidyl K(V) channel inhibitors was essentially the same for inhibition of [125I]MgTX binding to Jurkat, CHO, or rat brain membranes and for blocking 86Rb+ efflux from the CHO/K(V)1.3 cells, except that alpha-dendrotoxin was more potent at blocking binding to rat brain membranes than in the other assays. The characteristics of [125I]MgTX binding, the antibody profiles, and the effects of the peptidyl K(V) inhibitors all indicate that the [125I]MgTX receptor in Jurkat lymphocytes is comprised of a homomultimer of K(V)1.3, unlike the heteromultimeric arrangement of the receptor in rat brain.     

Ganglioside structure dictates signal transduction by cholera toxin and association with caveolae-like membrane domains in polarized epithelia

In polarized cells, signal transduction by cholera toxin (CT) requires apical endocytosis and retrograde transport into Golgi cisternae and perhaps ER (Lencer, W.I., C. Constable, S. Moe, M. Jobling, H.M. Webb, S. Ruston, J.L. Madara, T. Hirst, and R. Holmes. 1995. J. Cell Biol. 131:951-962). In this study, we tested whether CT's apical membrane receptor ganglioside GM1 acts specifically in toxin action. To do so, we used CT and the related Escherichia coli heat-labile type II enterotoxin LTIIb. CT and LTIIb distinguish between gangliosides GM1 and GD1a at the cell surface by virtue of their dissimilar receptor-binding B subunits. The enzymatically active A subunits, however, are homologous. While both toxins bound specifically to human intestinal T84 cells (Kd approximately 5 nM), only CT elicited a cAMP-dependent Cl- secretory response. LTIIb, however, was more potent than CT in eliciting a cAMP-dependent response from mouse Y1 adrenal cells (toxic dose 10 vs. 300 pg/well). In T84 cells, CT fractionated with caveolae-like detergent-insoluble membranes, but LTIIb did not. To investigate further the relationship between the specificity of ganglioside binding and partitioning into detergent-insoluble membranes and signal transduction, CT and LTIIb chimeric toxins were prepared. Analysis of these chimeric toxins confirmed that toxin-induced signal transduction depended critically on the specificity of ganglioside structure. The mechanism(s) by which ganglioside GM1 functions in signal transduction likely depends on coupling CT with caveolae or caveolae-related membrane domains.     

Evoked acetylcholine release expressed in neuroblastoma cells by transfection of mediatophore cDNA

Transmitter release was elicited in two ways from cultured cells filled with acetylcholine: (a) in a biochemical assay by successive addition of a calcium ionophore and calcium and (b) electrophysiologically, by electrical stimulation of individual cells and real-time recording with an embryonic Xenopus myocyte. Glioma C6-Bu-1 cells were found to be competent for Ca(2+)-dependent and quantal release. In contrast, no release could be elicited from mouse neuroblastoma N18TG-2 cells. However, acetylcholine release could be restored when N18TG-2 cells were transfected with a plasmid coding for mediatophore. Mediatophore is a protein of nerve terminal membranes purified from the Torpedo electric organ on the basis of its acetylcholine-releasing capacity. The transfected N18TG-2 cells expressed Torpedo mediatophore in their plasma membrane. In response to an electrical stimulus, they generated in the myocyte evoked currents that were curare sensitive and calcium dependent and displayed, discrete amplitude levels, like in naturally occurring synapses.     

Fertility impairment in granulocyte-macrophage colony-stimulating factor-deficient mice

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been identified as a potentially important mediator of intercellular communication in the female reproductive tract, with principal target cells being the large populations of myeloid leukocytes in the cycling and pregnant uterus, the preimplantation embryo, and trophoblast cells of the developing placenta. To determine the physiological significance of this cytokine in reproduction, the fertility of genetically GM-CSF-deficient (GM-/-) mice was examined. Implantation rates were normal in GM-/- mice, and viable pups were produced. However, the mean litter sizes of GM-/- x GM-/- breeding pairs were 25% smaller at weaning than those of GM+/- x GM+/- pairs, due to fetal death late in gestation and early in postnatal life, with a disproportionate loss of male pups. On Day 17 of pregnancy, the mean number of resorbing and malformed fetuses was twice as high in pregnant GM-/- females (21%, vs. 11% in GM+/- females); the mean fetal weight and the mean fetal:placental ratio in surviving conceptuses were diminished by 7% and 6%, respectively; and the number of very small fetuses (< 500 mg) was 9-times as high (23% vs. 2.5%). Mortality during the first 3 wk of life was 4.5-times as high in pups born to GM-/- mothers (9%, vs. 2% in GM+/- females), and diminished size persisted in GM-/- pups, particularly males, into adulthood. The detrimental effect of maternal GM-CSF deficiency was less apparent when GM-/- females were mated with GM+/+ males; litter sizes at birth and at weaning were not significantly smaller than in GM+/- matings, and fetal weights and fetal:placental ratios were also comparable. When polymerase chain reaction was used to genotype embryonic tissue in heterozygote matings, GM-/- fetuses from GM-/- females were found to be smaller than their GM+/- littermates and smaller than GM-/- fetuses gestated in GM+/- females. The size and distribution of uterine granulocyte and macrophage populations were normal during the estrous cycle, during early pregnancy, and in midgestation. Analysis of placental structure revealed that the ratio of labyrinthine to spongiotrophoblast areas was reduced by approximately 28% in GM-/- placentae, and the proportion of vacuolated trophoblast "glycogen cells" in the spongiotrophoblast layer was diminished. Compromised placental function as a result of subtle developmental aberrations may therefore partially account for embryonic growth retardation in GM-CSF-deficient mice. Collectively, these studies show that fetal growth and viability are jeopardized in the absence of maternal GM-CSF. The detrimental effects are most clearly evident when the conceptus is also GM-CSF deficient, suggesting that GM-CSF of either maternal or fetal origin is required for optimal growth and survival of the fetus in mice.