The characterization of sphingolipids from neurons and astroglia of immature rat brain

Deciphering the Differential Effective and Toxic Responses of Bupleuri Radix following the Induction of Chronic Unpredictable Mild Stress and in Healthy Rats Based on Serum Metabolic Profiles

The petroleum ether fraction of Bupleuri Radix which is contained in the traditional Chinese medicine prescription of Xiaoyaosan (XYS) may have a therapeutic effect in depressed subjects based on the results of our previous study. It has been reported that Bupleuri Radix can cause liver toxicity following overdosing or long-term use. Therefore, this study aimed to decipher the differential effective and toxic responses of Bupleuri Radix in chronic unpredictable mild stress (CUMS) (with depression) and healthy rats based on serum metabolic profiles. Serum metabolic profiles were obtained using the UHPLC- Q Exactive Orbitrap-MS technique. Our results demonstrated that the petroleum ether fraction of Bupleuri Radix (PBR) produces an antidepressant effect through regulating glycometabolism, amino acid metabolism, sphingolipid metabolism, glycerophospholipid metabolism, and fatty acid metabolism. It also induces more severe toxic reactions in the liver or kidney in healthy rats than in CUMS rats, which exhibited a comparatively mild drug-induced toxic reaction. The altered lysine degradation, sphingolipid metabolism, glycerophospholipid metabolism, fatty acid metabolism, and bile acid metabolism could be at least partly responsible for the PBR toxic responses in healthy rats. The differential effective and toxic response of PBR in CUMS rats and healthy rats provide a new standard for the more rational and safer application of clinical drugs in the future.

Gangliosides of the Nervous System

This review begins by attempting to recount some of the pioneering discoveries that first identified the presence of gangliosides in the nervous system, their structures and topography. This is presented as prelude to the current emphasis on physiological function, about which much has been learned but still remains to be elucidated. These areas include ganglioside roles in nervous system development including stem cell biology, membranes and organelles within neurons and glia, ion transport mechanisms, receptor modulation including neurotrophic factor receptors, and importantly the pathophysiological role of ganglioside aberrations in neurodegenerative disorders. This relates to their potential as therapeutic agents, especially in those conditions characterized by deficiency of one or more specific gangliosides. Finally we attempt to speculate on future directions ganglioside research is likely to take so as to capitalize on the impressive progress to date.

Ceramides and depression: A systematic review

BACKGROUND

Major depressive disorder is a significant contributor to global disability and mortality. The mechanisms of depression are vast and not fully understood, and as a result current treatment of depression is suboptimal. Aberrant sphingolipid metabolism has been observed in some cases of depression, specifically alterations in ceramide concentrations. The role of ceramides and other sphingolipids in depression is a novel concept. This review summarizes and evaluates the current state of evidence for a role of ceramides in depression pathophysiology and the potential for novel depression pharmacotherapies targeting ceramide metabolism.

METHODS

Medline, Embase, and PsycINFO databases were searched through October 2016 for English-language studies using combinations of the search terms: ceramide, depression, sphingolipid, and depressive symptoms.

RESULTS

Of the 489 articles screened, 14 were included in the qualitative synthesis of this review article. Pre-clinical and clinical evidence suggest that ceramide species may contribute to depression pathophysiology. In human studies, ceramides C18:0 and C20:0 are the species most strongly linked to depression. Evidence for altered ceramide metabolism in depression is present, but data for a causal role of ceramides in depression are lacking.

LIMITATIONS

This review was limited by potential reporting bias. Furthermore, a lack of specificity of which ceramides were altered in depression was common.

CONCLUSIONS

Pharmacotherapy targeting ceramide metabolism may be a novel treatment option for depression. A number of pharmacological targets exists for ceramide reduction and a number of currently approved medications inhibit ceramide production. More evidence, pre-clinical and clinical, is warranted to determine the extent and consistency of the role of ceramides in depression.

Multi-dimensional mass spectrometry-based shotgun lipidomics and novel strategies for lipidomic analyses

Since our last comprehensive review on multi-dimensional mass spectrometry-based shotgun lipidomics (Mass Spectrom. Rev. 24 (2005), 367), many new developments in the field of lipidomics have occurred. These developments include new strategies and refinements for shotgun lipidomic approaches that use direct infusion, including novel fragmentation strategies, identification of multiple new informative dimensions for mass spectrometric interrogation, and the development of new bioinformatic approaches for enhanced identification and quantitation of the individual molecular constituents that comprise each cell's lipidome. Concurrently, advances in liquid chromatography-based platforms and novel strategies for quantitative matrix-assisted laser desorption/ionization mass spectrometry for lipidomic analyses have been developed. Through the synergistic use of this repertoire of new mass spectrometric approaches, the power and scope of lipidomics has been greatly expanded to accelerate progress toward the comprehensive understanding of the pleiotropic roles of lipids in biological systems.

Sulfatases and human disease

Sulfatases are a highly conserved family of proteins that cleave sulfate esters from a wide range of substrates. The importance of sulfatases in human metabolism is underscored by the presence of at least eight human monogenic diseases caused by the deficiency of individual sulfatases. Sulfatase activity requires a unique posttranslational modification, which is impaired in patients with multiple sulfatase deficiency (MSD) due to a mutation of the sulfatase modifying factor 1 (SUMF1). Here we review current knowledge and future perspectives on the evolution of the sulfatase gene family, on the role of these enzymes in human metabolism, and on new developments in the therapy of sulfatase deficiencies.

Developmental expression of the type I diabetes related antigen sulfatide and sulfated lactosylceramide in mammalian pancreas

Previous studies have shown that sulfatide is present and functionally involved in beta cells, and that anti-sulfatide antibodies (ASA) exist during development of type I diabetes mellitus. To further explore the possible role of sulfatide in type I diabetes, developmental expression was examined in human pancreas and in pancreas of the type I diabetes models BB rat and NOD mouse compared to Lewis rat and BALB/c mouse, respectively. Sulfatide was not only expressed in adult pancreas, but also in human fetal and rodent neonatal pancreas, i.e., during the growing period of the immunological self. Sulfatide had a different expression pattern in human beings and rodents, concerning both the amounts of sulfatide and expression during development. There was no change in the sulfatide fatty acid isoform expression during development. The pancreatic expression of another sulfated glycosphingolipid, sulfated lactosylceramide, indicated that this molecule is a potential fetal/neonatal marker, which was further expressed in the type I diabetic models. In conclusion, these findings give further support to the possibility that sulfatide is a relevant autoantigen in type I diabetes and that sulfated lactosylceramide might function as a potential risk factor for disease development, at least in the animal models.

Sulfatide and GM1 ganglioside modulate the high-affinity dopamine uptake in rat striatal synaptosomes: evidence for the involvement of their ionic charges

The present study was undertaken to examine the effects of the anionic glycolipids GM1 ganglioside and sulfatide on the high-affinity dopamine (DA) uptake in rat striatal synaptosomes. After 1h of incubation, GM1 stably bound to synaptosomes and modified the activity of the neuronal dopamine transporter (DAT). With 1.2 and 12 microM GM1, V(max) decreased by 13 and 23%, respectively, reflecting a slight reduction of the number of functional uptake sites and K(m) was lowered by 21 and 33%, thus showing an increase of the affinity. Treatment of synaptosomes with 1.2 microM of sulfatide, which possesses an anionic sulfated group, led to a similar decrease of V(max) (19%) than GM1, but to a significantly higher reduction of K(m) (35%). In fact, sulfatide associated to synaptosomes in a 3.5-fold higher extent than GM1. Conversely, when GM1 and sulfatide were replaced by GM1 alcohol and galactosylceramide, respectively, no modification of the DA uptake occurred, although these neutral glycolipids incorporated into the synaptosomes to the same extent as the related anionic compounds.Altogether, these results demonstrate the key role of negative charges linked to the oligosaccharide chains of glycolipids in the modulation of DA transport across the synaptosomal membrane.

Expression of the myelin and oligodendrocyte progenitor marker sulfatide in neurons and astrocytes of adult rat brain

Sulfatide is a myelin component of the central (CNS) and peripheral nervous system (PNS) and is used extensively to identify oligodendrocyte progenitor cells. We have explored sulfatide expression in CNS gray matter (cerebellum, cerebral cortex, and hippocampus) and the PNS in adult rats using an anti-sulfatide antibody (Sulph I) and confocal microscopy. Biochemical analyses revealed two Sulph I antigens, sulfatide and seminolipid; sulfatide was present at about five times higher concentration, and the affinity of Sulph I for sulfatide was 2.5 times higher than that for seminolipid. Thus sulfatide was considered the dominant antigen. We found Sulph I immunostaining, in addition to that in myelinated areas in subpopulations of astrocytes and neurons. Astrocyte Sulph I staining was localized to the cell bodies and in some cases also to the processes. In the cerebellum, some Sulph I-positive astrocytes corresponded to Golgi epithelial cell bodies. We also found Sulph I staining in neuronal cell bodies, which in some neurons was clearly localized to the cytoplasm and in others to the nuclear membrane. Sulph I immunostaining in the PNS was located in the myelin sheath and paranodal end segments. These results demonstrate the expression of sulfatide in cell types other than oligodendrocytes and Schwann cells, showing that sulfatide is not a selective marker for adult oligodendrocyte progenitor cells. Moreover, these findings show that sulfatide is localized also to intracellular compartments and indicate that other roles of sulfatide in astrocytes and neurons, compared to myelin, might be considered.

Schwann cells are removed from the spinal cord after effecting recovery from paraplegia

Remyelination of the CNS is necessary to restore neural function in a number of demyelinating conditions. Schwann cells, the myelinating cells of the periphery, are candidates for this purpose because they have more robust regenerative properties than their central homologs, the oligodendrocytes. Although the ability of Schwann cells to remyelinate the CNS has been demonstrated, their capacity to enter the adult spinal cord in large numbers and effect functional recovery remains uncertain. We used cholera toxin B-subunit conjugated to saporin to demyelinate the rat lumbar spinal cord, remove macroglia, and produce paraplegia. After the removal of oligodendrocyte and astrocyte debris by invading macrophages, there was a spontaneous entry of Schwann cells into the spinal cord, along with axonal remyelination and concomitant functional recovery from paraplegia occurring within 75 d. The Schwann cells appeared to enter the dorsal funiculi via the dorsal root entry zone and the lateral funiculi via rootlets that had become adherent to the lateral spinal cord after the inflammation. In the following weeks, Schwann cell myelin surrounding central axons was progressively replaced by oligodendrocyte myelin without lapse in motor function. Our results show that endogenous Schwann cells can reverse a severe neurological deficit caused by CNS demyelination and enable later oligodendrocyte remyelination.

Parameters related to lipid metabolism as markers of myelination in mouse brain

Myelination, during both normal development and with respect to disorders of myelination, is commonly studied by morphological and/or biochemical techniques that assay as their end-points the extent of myelination. The rate of myelination is potentially a more useful parameter, but it is difficult and time-consuming to establish, requiring a complete developmental study with labor-intensive methodology. We report herein development of methodology to assay the absolute rate of myelination at any desired time during development. This involves intraperitoneal injection of (3)H(2)O to label body water pools, followed by determination of label in the myelin-specific lipid, cerebroside. The absolute amount of cerebroside synthesized can then be calculated from the specific radioactivity of body water and knowledge of the number of hydrogens from water incorporated into cerebroside. During development, the rate of cerebroside synthesis correlated well with the rate of accumulation of the myelin-specific components, myelin basic protein and cerebroside. For purposes of control, we also tested other putative, albeit less quantitative, indices of the rate of myelination. Levels of mRNA for ceramide galactosyltransferase (rate-limiting enzyme in cerebroside synthesis) and for myelin basic protein did not closely correlate with myelination at all times. Cholesterol synthesis closely matched the rate of cholesterol accumulation but did not track well with myelination. Synthesis of fatty acids did not correlate well with accumulation of either fatty acids (phospholipids) or myelin markers. We conclude that measurement of cerebroside synthesis rates provides a good measure of the rate of myelination. This approach may be useful as an additional parameter for examining the effects of environmental or genetic alterations on the rate of myelination.

Inhibition of human platelet function by sulfatides

Sulfatides are glycolipid constituents of human platelet cell membranes and have been shown to interact with platelet-binding proteins involved in hemostasis. Because little is known about the physiological role of sulfatides in platelet function, the effect of sulfatide on platelet adhesion, aggregation, release, and ristocetin-induced platelet agglutination (RIPA) was studied. These processes are inhibited when exogenous sulfatide is present in vitro. Inhibition of aggregation induced by collagen, thrombin, and ristocetin by sulfatide was dose dependent. Adenosine diphosphate-mediated adhesion and aggregation were not significantly affected by sulfatide, nor was serotonin- and epinephrine-mediated aggregation. Collagen mediate release of serotonin was reduced sulfatide. RIPA demonstrated dose-dependent inhibition in response to sulfatide. These results suggest that sulfatide may play a role in modulating platelet activation.

Immunohistochemically visualized localisation of gangliosides Glac2 (GD3) and Gtri2 (GD2) in cells of human intracranial tumors

Antibodies against two major gangliosides detected in human brain and brain tumors--Glac2 (GD3) and Gtri2 (GD2)--were tested by immunohistochemistry in an unselected sample of intracranial tumors during the years 1986 through 1991. Two groups emerged as evaluable samples, namely gliomas of different grades and meningiomas. In a pilot series, it was shown that these gangliosides could be visualized in frozen sections of cells of gliomas and meningiomas (as well as neurinomas) and in some structures of the normal brain. It was however not possible in frozen sections to further analyze the cellular or subcellular expression pattern of the mentioned components and paraffin sections with conventional processing were only weakly and diffusely stained. A modified protocol therefore was created that replaced alcohol processing by acetone. With this protocol, interpretable results in paraffin sections were obtained. With this method, 133 single intracranial tumors were investigated as to their immunohistologically detectable ganglioside expression. The most consistent result was that the whole cytoplasm of highly fibrillary (gemistocytic) astrocytes in all grades of gliomas was stained by Gtri2 (GD2) and Glac2 (GD3) with high preponderance of Gtri2 (GD2) expression. In all meningiomas, Glac2 (GD3) had a higher expression than Gtri2. No constant pattern in the other entities emerged. By comparison with GFAP expression in gliomas and vimentin in meningiomas, the colocalisation of gangliosides and intermediary filament proteins is supposed.

Purification and characterization of a glucuronyltransferase involved in the biosynthesis of the HNK-1 epitope on glycoproteins from rat brain

The glucuronyltransferase involved in the biosynthesis of the HNK-1 epitope on glycoproteins was purified to an apparent homogeneity from the Nonidet P-40 extract of 2-week postnatal rat forebrain by sequential chromatographies on CM-Sepharose CL-6B, UDP-GlcA-Sepharose 4B, asialo-orosomucoid-Sepharose 4B, Matrex gel Blue A, Mono Q, HiTrap chelating, and HiTrap heparin columns. The purified enzyme migrated as a 45-kDa protein upon SDS-polyacrylamide gel electrophoresis under reducing conditions, but eluted as a 90-kDa protein upon Superose gel filtration in the presence of Nonidet P-40, suggesting that the enzyme forms homodimers under non-denatured conditions. The enzyme transferred glucuronic acid to various glycoprotein acceptors bearing terminal N-acetyllactosamine structure such as asialo-orosomucoid, asialo-fetuin, and asialo-neural cell adhesion molecule, whereas little activity was detected to paragloboside, a precursor glycolipid of the HNK-1 epitope on glycolipids. These results suggested that the enzyme is specifically associated with the biosynthesis of the HNK-1 epitope on glycoproteins. Sphingomyelin was specifically required for expression of the enzyme activity. Stearoyl-sphingomyelin (18:0) was the most effective, followed by palmitoyl-sphingomyelin (16:0) and lignoceroyl-sphingomyelin (24:0). Interestingly, activity was demonstrated only for sphingomyelin with a saturated fatty acid, i.e. not for that with an unsaturated fatty acid, regardless of the length of the acyl group.

Characterization of a novel brain neutral glycosphingolipid composition in house musk shrew (Suncus murinus)

Glycosphingolipids were extracted from the brain of house musk shrew (Suncus murinus). Neutral glycosphingolipids were purified by QAE-Sephadex column chromatography followed by high-performance liquid chromatography using an Iatrobeads column. Purified glycosphingolipids were identified by high-performance thin-layer chromatography, carbohydrate analysis, fast-atom bombardment mass spectrometry and TLC immunostaining. The ganglioside pattern was almost the same as the pattern obtained for rat brain gangliosides. The brain of S. murinus, however, was unique in its neutral glycosphingolipid composition; it contained gangliotriaosylceramide and gangliotetraosylceramide as the major neutral glycosphingolipids in addition to monohexosylceramides. Mass spectroscopy analysis showed that C18:1 sphingosine and C24:0 normal fatty acids were the major ceramide constituents in the glycosphingolipis, except in the case where a slower-migrating monohexosylceramide that contained C24 h:0 hydroxy fatty acids was observed. A day after birth, monohexosylceramide contained only normal fatty acids. The amounts of hydroxy-fatty-acid-containing monohexosylceramide increased rapidly as the age of the animals increased, and the ratio of these two kinds of monohexosylceramides was reversed within five weeks. Monohexosylceramide, ganglioside, and sulfatide contents in bulbus olfactorius were almost equal in amount in contrast to the glycolipids in the cerebrum and cerebellum that contained monohexosylceramide as the major constituent. The amount of monohexosylceramide in the bulbus olfactorius was 0.3-0.4 times the values obtained for the cerebrum and cerebellum.

Pattern of nervous tissue immunostaining by human anti-glycolipid antibodies

Immunostaining of human, bovine and rodent unfixed nervous tissue sections was performed in order to characterize the structures recognized by anti-glycolipid antibodies. Four human sera from patients, two with M-IgM and motor neuron syndrome or motor neuropathy and two with motor neuropathy and polyclonal IgG antibody activity against gangliosides (GL; i.e. GM1, GD1b, GD1a), were utilized. Serum from a patient with sensory neuropathy and M-IgM immunoglobulins with antibody activity against sulfatide (SUL) was included in this series. This study shows that polyclonal and monoclonal anti-glycolipid antibodies give three different patterns of staining. The first is cholera toxin-like showing a more restricted neuronal pattern of staining. The second is peanut agglutinin-like, which includes the carbohydrate epitope shared by a group of glycoproteins in the gray and white matter. The third (anti-SUL) gives a preferential myelin staining. However, sera with anti-GM1 and anti-SUL antibodies recognize a number of closely situated determinants in the gray matter of the spinal cord and in the granule cells, while in peripheral nerves or in neuronal cells in culture their binding produces a different pattern (nodes of Ranvier for anti-GL; myelin for anti-SUL). These findings indicate that immunohistochemistry with anti-GL and anti-SUL antibodies may provide information regarding the glycolipid-bearing anatomical structures as target antigens and further substantiate the role of these molecules in the pathogenesis of autoimmune neurological disorders.

Isolated bovine spinal motoneurons have specific ganglioside antigens recognized by sera from patients with motor neuron disease and motor neuropathy

The gangliosides GM1 and GD1b have recently been reported to be potential target antigens in human motor neuron disease (MND) or motor neuropathy. The mechanism for selective motoneuron and motor nerve impairment by the antibodies directed against these gangliosides, however, is not fully understood. We recently investigated the ganglioside composition of isolated bovine spinal motoneurons and found that the ganglioside pattern of the isolated motoneurons was extremely complex. GM1, GD1a, GD1b, and GT1b, which are major ganglioside components of CNS tissues, were only minor species in motoneurons. Among the various ganglioside species in motoneurons, several were immunoreactive to sera from patients with MND and motor neuropathy. One of these gangliosides was purified from bovine spinal cord and characterized as N-glycolylneuraminic acid-containing GM1 [GM1(NeuGc)] by compositional analysis, fast atom bombardment mass spectra, and the use of specific antibodies. Among seven sera with anti-GM1 antibody activities, five sera reacted with GM1(NeuGc) and two did not. Two other gangliosides, which were recognized by another patient's serum, appeared to be specific for motoneurons. We conclude that motoneurons contained, in addition to the known ganglioside antigens GM1 and GD1b, other specific ganglioside antigens that could be recognized by sera from patients with MND and motor neuropathy.

Anti-ganglioside antibodies reveal subsets of cultured rat dorsal root ganglion neurons

Subsets of cultured dorsal root ganglion neurons were identified by using the anti-ganglioside monoclonal antibodies A2B5, D1.1, R24 and JONES. A2B5 and D1.1 labelled a population of cells that was relatively stable between 2 and 20 days in vitro, while the population of cells labeled with both R24 and JONES decreased with time, suggesting that the gangliosides recognized by Jones and R24 are developmentally regulated. Given the observation that the relative proportions of ganglioside species changes with time in culture, it is very important to carefully define the stability of ganglioside antigens before using them as cell markers.

Cell membrane changes in brains manifesting senile plaques: an immunohistochemical study of GM1 membranous ganglioside

To investigate structural changes in cell membranes of the Alzheimer-type dementia (ATD) brain, we immunostained for GM1 ganglioside which is a major component of the cell membrane. Our results have shown that astrocytic membranes and senile plaques (SPs) have the same immunoreactivity against the monoclonal anti-ganglioside GM1 antibody. Moreover, the astrocytic processes within the SPs were altered and their abnormal membranes seemed to contribute to the formation of SPs.

Effect of differentiation and cell density on glycosphingolipid class and molecular species composition of mouse neuroblastoma NB2a cells

The effects of cell density and retinoic acid-induced differentiation on the class and molecular species composition of mouse neuroblastoma NB2a cell glycosphingolipids were examined under conditions where the period of culture was controlled. The total amount of neutral glycosphingolipids per cell decreased both with differentiation and as the cells became confluent. The relative amount of the neutral glycosphingolipid classes was not affected by differentiation, whereas there were small but significant changes in the relative amount of the neutral glycosphingolipid classes as the cells became confluent. The total amount of the gangliosides was unaffected by either differentiation or cell density, but there were significant changes in the ganglioside class composition as a result of both cell density and differentiation, and the effects were additive. The molecular species of all the major neutral glycosphingolipid and ganglioside classes were essentially identical, and were altered only slightly by either differentiation or cell density.

Coexpression of lactosyl and gangliotetraosyl gangliosides in rat cerebellar radial glial cells in culture

The expression of gangliosides of the lactosylceramide (LC) and of the gangliotetraosylceramide (GTC) series on the surface of cells from rat embryonic cerebellar tissue was investigated by double-color indirect immunofluorescence. GD3 was assumed to be representative of LC and was detected using a specific monoclonal antibody. GM1 was assumed to be representative of GTC and was detected using the binding of cholera toxin followed by the binding of cholera toxin antibodies. The expression of polysialosylated GTC (polysialosyl-GTC) was detected using the cholera toxin-cholera toxin antibody experimental approach after conversion of polysialosyl-GTC to GM1 by treatment of the cells with neuraminidase. To distinguish the major neural cell types present in the cultures the expression of the following cell type-specific markers was investigated: neuron-specific enolase and microtubule-associated protein-2 (MAP-2) as probes for neuronal cells and the intermediate filament protein glial fibrillar acidic protein (GFAP) as a probe for astroglial cells. More than 80% of cells dissociated from cerebellar tissue of 15-day-old rat embryos (E15) are positive for the expression of GD3 and about 50% for the expression of GM1 and polysialosyl-GTC, but most are negative for the expression of neuron-specific enolase, MAP-2, and GFAP. After culturing for 4 days (E15 + 4) most cells that show characteristics of neuronal cells are positive for the expression of polysialosyl-GTC and "inactivate" the expression of GD3. Most cells with characteristics of radial and stellate glial cells are also positive for the expression of polysialosyl-GTC, but unlike neuron-like cells, they do not "inactivate" the expression of GD3.

In vivo labeling of myelin lipids and proteolipid protein with [3H]myristate, [14C]linoleate, and [14C]linolenate

To investigate the incorporation of essential fatty acids into myelin components, 24-day-old rabbits were injected intracerebrally with [14C]linoleate, [14C]linolenate, or [3H]myristate for comparison. Animals were killed 22 hr later and myelin was isolated. [3H]myristate labeled all myelin lipids including monogalactosyl diglyceride, with the exception of sulfatides. With 14C-essential fatty acids, only glycerophospholipids were efficiently labeled and their specific activities were in the following decreasing orders: PC greater than PI greater than PE greater than PS with [14C]linoleate, and PE greater than PC greater than PI = PS with [14C]linolenate. Among myelin proteins, PLP and DM-20 were labeled with all 3 precursors. PLP was purified from myelin labeled with 14C-essential fatty acids. The label was then cleaved from the protein by alkaline methanolysis and was identified as a dienoic [( 14C]linoleate) or a tetraenoic [( 14C]linolenate) fatty acid. MBP was not labeled with [3H]myristate, but was slightly labeled with both 14C-essential fatty acids. The signification of the latter result is discussed.

Gangliosides of cultured astroglia

Cultured astrocytes prepared from newborn rat brain and 13-day-old chick embryonic brain were analyzed qualitatively and quantitatively for ganglioside content. All preparations contained approximately the same total level: 2.4-3.4 micrograms N-acetylneuraminic acid (NeuAc)/mg protein. In contrast, the value for primary cultures of neurons from chick embryonic brain was 5.9. The non-hexosamine-containing species, GM3 and GD3, comprised 75-85% of the total in astroglial cultures, the remainder consisting mainly of structural types other than the gangliotetraose series; choleragenoid assay revealed the latter to be virtually absent or to comprise at most a few percent. Deficiency of gangliotetraose synthesizing ability was indicated by the very low level of UDP-GalNac:GM3 N-acetylgalactosaminyltransferase detected in the cells. Treatment of cultured astrocytes with astroglial growth factor 2 or dibutyryl cyclic AMP caused little if any change in quantity or pattern of gangliosides. The large majority of cells stained in a manner characteristic of astrocytes: positive for glial fibrillary acidic protein, negative for galactosyl ceramides. Staining with cholera toxin and anti-GM1 antibody was essentially negative, as was that with tetanus toxin, A2B5 monoclonal antibody, and antibody to GD3. All evidence thus points to cultured astrocytes of rat and chick brain containing appreciable gangliosides, most of which are GM3 and GD3 with the majority of the remainder comprising structures other than the gangliotetraose type.

Ganglioside content of astroglia and neurons isolated from maturing rat brain: consideration of the source of astroglial gangliosides

Previous biochemical and histochemical studies have failed to clarify the nature or quantity of gangliosides in CNS astrocytes. Using improved methodologies for bulk isolation of both neurons and astrocytes as well as for ganglioside purification, we find significantly higher ganglioside concentration in astrocytes and very similar thin-layer chromatography (TLC) patterns for the two cell types. However, in vivo labeling of glycoconjugates via intracerebral injection of [3H]glucosamine prior to cell isolation revealed a different picture: whereas glycoproteins were well-labeled in both cell types after labeling periods of 1-2 h, gangliosides were appreciably labeled only in neurons. With longer time periods (8-48 h) between injection and sacrifice, there was convergence of specific radioactivity of gangliosides from the two isolated cell preparations. These changes are compared to those observed in synaptosomes and microsomes that were isolated simultaneously. The results suggest limited ganglioside synthetic ability in astrocytes as compared to neurons, a conclusion supported by assay of UDP-galNAc:GM3 N-acetylgalactosaminyltransferase in the isolated cells. Nevertheless, the presence of ganglioside GM1 in a substantial portion of bulk-isolated astrocytes was demonstrated by indirect immunofluorescent detection of cholera toxin binding. Ideas on the reconciliation of these apparently contradictory phenomena, including the possibility of intercellular transfer and/or phagocytosis are discussed.

Expression of GD3 ganglioside by developing rat cerebellar Purkinje cells in situ

GD3 is a major ganglioside of the immature vertebrate CNS, and its expression is suggested to be characteristic of immature neuroectodermal cells. Using immunocytochemistry on cryostat sections of developing rat cerebellum with a monoclonal antibody specific for GD3, we have found that GD3 begins to be expressed on the plasma membrane of Purkinje cell bodies and dendrites beginning at postnatal day 7. Staining became brighter as the dendritic tree of the cells enlarged. As the Purkinje cells began to mature in different folia, they became GD3+, until by 15 days postnatal all Purkinje cells were GD3+. Positive staining of the dendritic tree was still present in the adult cerebellum. Using a monoclonal antibody 7-8D2, which recognizes cerebellar granule cells and their axons (the parallel fibres), and polyclonal antibodies against a synaptic vesicle component synaptophysin, double-immunofluorescence staining together with anti-GD3 antibodies suggested that the appearance of GD3 immunoreactivity did not correlate either with the ingrowth of parallel fibres or the presence of their synapses on Purkinje cell dendrites. However, comparison with earlier morphological studies showed that the appearance of GD3 immunoreactivity correlated well with the formation of climbing fibre synapses on Purkinje cell dendrites and the onset of the rapid expansion of the dendritic tree. These results are in keeping with the idea that elevated GD3 concentrations are found in certain cell types during periods of rapid growth or high metabolic activity but also show that this is not only restricted to immature cells.

Gangliosides and other lipids of the growth cone membrane

Growth cone membranes, derived from growth cone particles isolated from 16- to 18-day-old fetal rat brain, were found to be rich in overall lipid content with a lipid-to-protein ratio of 3.5. The phospholipid-to-cholesterol ratio indicated considerably less cholesterol than plasma membranes from mature neurons. All major classes of phospholipid were present in the usual proportions except sphingomyelin, which could not be detected. Gangliosides expressed in relation to protein were present at somewhat higher levels compared to previously reported values for synaptic plasma membranes (73 versus 44 micrograms/mg protein), but when related to phospholipid their level was well below that of the latter (26 versus 62 micrograms/mg phospholipid). The ganglioside pattern was generally similar to that of mature synaptic membranes except for the presence of relatively more GD3 and less GD1a, a phenomenon also observed in whole fetal brain of the same age. Several neutral glycosphingolipids were detected, glucosylceramide being the major one of this group. Their total level in growth cone membranes was roughly comparable to that of gangliosides, but unlike the latter their concentration in whole brain decreased with development. For comparison we analyzed the ganglioside composition of mixed membrane fractions from the same fetal brains and found no significant differences between these and growth cone membranes, suggesting that these glycoconjugates are not localized specifically in the growth cones. Neutral glycosphingolipids, on the other hand, appeared somewhat more concentrated in growth cones than in the mixed membranes.

Biosynthesis of neutral glucocerebroside homologues in the absence of myelin assembly after nerve transection

The biosynthesis of myelin-associated glycolipids during various stages of myelination was studied by in vitro incorporation of [3H]Gal, [3H]Glc, or [35S]sulfate into the endoneurium of rat sciatic nerve. In the normal adult nerve, where the level of myelin assembly is substantially reduced and Schwann cells are principally involved in maintaining the existing myelin membrane, [3H]Gal was primarily incorporated into monogalactosyl diacylglycerol (MGDG) and the galactocerebrosides (GalCe) with lower levels of incorporation into the sulfatides. Such incorporation was enhanced 35 days after crush injury of the adult rat sciatic nerve, which is characterized by active myelin assembly. In contrast, at 35 days after permanent nerve transection where there is no axonal regeneration or myelin assembly, the incorporation of [3H]Gal or [3H]Glc into GalCe was nearly undetected whereas the incorporation of [3H]Gal into MGDG was completely inhibited. Instead, the 3H-labeled glycolipids in transected nerve were identified as the glucocerebrosides (GlcCe) and oligohexosylceramide derivatives with tetrahexosylceramide being a major product. In contrast, [35S]sulfate was incorporated into endoneurial sulfatides in the transected nerve, which suggests that endogenous GalCe rather than newly synthesized GalCe served as the substrate for the sulfotransferase reaction. The GlcCe homologues are not considered as constituents of the myelin membrane but are likely plasma membrane components synthesized in the absence of myelin assembly. It is likely that the cells responsible for GlcCe biosynthesis are Schwann cells, since they comprise 90% of the total endoneurial cell area in the distal nerve segment at 35 days after transection.(ABSTRACT TRUNCATED AT 250 WORDS)

Ganglioside GM1, a molecular target for immunological and toxic attacks: similarity of neuropathological lesions induced by ganglioside-antiserum and cholera toxin

Ganglioside-antisera, the ganglioside GM1-ligands, cholera toxin (CT), and CT subunit B, respectively, were injected into the lumbosacral subarachnoid space of normal rats. The cytotoxic effects of the injected compounds on the peripheral and central nervous system were investigated by light and electron microscopy; the severity of CNS lesions was evaluated by quantitation of macrophages containing debris. In contrast to control sera and GM2-antiserum, antisera against a mixture of the major brain gangliosides GM1, GD1a, GD1b, and GT1b (MaBG) or against GM1 induced demyelination in spinal roots and spinal cord, as well as alterations of astroglia. CT induced the same cytotoxic effects as MaBG- and GM1-antisera, whereas CT subunit B was without effect. The ineffectiveness of GM2-antiserum is obviously due to the very low concentration of the specific binding target, GM2, on cell surfaces; that of CT subunit B to the lack of the cytotoxic operator, subunit A. Our results indicate that a similar pattern of neuropathological lesions may be effected by different cytotoxic mechanisms through attachment of the cytotoxic agent onto the cell surface via a common target molecule, and further substantiate the role of GM1-antibodies in the pathogenesis of demyelination.

Neuroimmunology of gangliosides in human neurons and glial cells in culture

Gangliosides (sialic-acid-bearing glycolipids) have received attention in recent years because of their role in cell recognition phenomena, synaptic transmission, memory generation, and nerve regeneration in the fields of neurosciences. It is suggested that each brain region or each neural cell type may contain a specific and characteristic set of gangliosides. We have investigated the immunocytochemical localization of several classes of gangliosides that include GM1, GM4, GD3, and GQ gangliosides on the cell surface of various cell types found in human neural cell cultures with antibodies specific for these gangliosides. Cell cultures were obtained from adult human brains and fetal human dorsal root ganglia and spinal cord and cultured in vitro for the period up to 6 months and utilized for the ganglioside immunocytochemistry. It was demonstrated that GM1 ganglioside was present in all galactocerebroside-positive oligodendrocytes and most of glial fibrillary acid protein (GFAP)-positive astrocytes (80%), most of neurofilament-positive neurons (80%), 50-70% of Schwann cells, and 5-10% of fibronectin-positive fibroblasts; GM4 ganglioside could be detected in all oligodendrocytes, 80% of astrocytes, and 50% of Schwann cells, while no staining was found in neurons or fibroblasts; GD3 ganglioside was present in all oligodendrocytes and 5-10% of astrocytes but not in neurons, Schwann cells, or fibroblasts; and all of fetal CNS neurons and approximately 80-90% of fetal dorsal root ganglia (DRG) neurons and a small percentage of astrocytes (10-20% in fetal and less than 1% in adult astrocytes) was labeled by A2B5 antibody which is specific for GQ ganglioside, while this antibody did not stain cell surface of oligodendrocytes, Schwann cells, or fibroblasts. Three classes of gangliosides, GM1, GM4, and GD3 were found to be definite components of fetal and adult human oligodendroglial plasma membrane, while GM1 and GM4 gangliosides were detected on the surface of most astrocytes. Only a minor population of astrocytes from both fetal and adult human CNS contained GD3 and GQ gangliosides. Two classes of gangliosides, GM1 and GQ, were detected on the surface of fetal human neurons. More than half of fetal Schwann cells reacted to GM1 and GM4 antibodies but did not to GD3 or GQ antibodies. We recognized the presence of a specific and characteristic set of gangliosides on the cell surface of different human neural cell types and these findings should facilitate further investigation of the precise biological activity of these gangliosides.

Myelin-associated galactolipids in primary cultures from dissociated fetal rat brain: biosynthesis, accumulation, and cell surface expression

Galactolipid metabolism was investigated as a function of development in primary cultures initiated from 19-21-day-old dissociated fetal rat brain. Significant amounts of galactocerebrosides, sulfatides, and monogalactosylglycerides were synthesized and accumulated by 8 days in culture. Thereafter the synthetic rates and levels of these galactolipids increased rapidly, reaching maximal values approximately 22-29 days in culture. Galactolipids containing nonhydroxy or 2-hydroxy fatty acid were both synthesized at approximately equal rates. The initial rates of synthesis, investigated at 15, 29, and 50 days in culture, were three- to fivefold higher for galactocerebrosides than for sulfatides and two- to threefold higher than for monogalactosylglycerides. The total number of cells staining with antisera against galactocerebroside of sulfatide also increased very rapidly between 8 and 22 days in culture, reaching levels of 4-5 million cells per seeded fetal brain. The amount of galactocerebroside or sulfatide per cell stained with the corresponding antiserum increased severalfold from 10 to 27 days in culture and remained high until at least 36 days in culture (the latest time point examined). Thus, the temporal expression of galactolipid accumulation in the cell cultures was comparable to that occurring in rat brain, but some important quantitative reductions in the levels of accumulation per cell in culture were noted. In addition, in contrast to normal brain in which galactolipid synthetic rates are reduced after the period of most active myelination, in culture both synthesis and turnover of these galactolipids remained high, suggestive of a partial arrest in myelin maturation.

Ganglioside GD3: structure, cellular distribution, and possible function

Insight on the function of gangliosides can emerge from knowledge of their cellular distribution. In this paper we review the structure of ganglioside GD3 and recent information on its cellular distribution. GD3 appears to be enriched in a variety of neural cell types including: reactive glia, gliomas, undifferentiated neurons, Muller glia, and oligodendroglia. Because each of these cell types share an enhanced permeability to ions and metabolites or possess properties associated with enhanced permeability, we suggest that GD3 is associated with enhanced membrane permeability. A possible function for GD3 in membrane permeability has implications for other cellular events such as metabolism, growth and interactions.

Spinal ganglia and peripheral nerves from a patent with Tay-Sachs disease. Morphological and ganglioside studies

We examined the spinal ganglia and peripheral nerves from a patient with Tay-Sachs disease, comparing the other nervous tissues morphologically and lipid-biochemically. The spinal ganglia and peripheral nerves showed numerous membranous cytoplasmic inclusion bodies (MCBs), which are characteristic of GM2-ganglioside storage in the neuronal cell bodies of the patient brains. In spinal ganglia, all neurons and satellite cells around the neurons contained membrane-bound lipid materials. In peripheral nerves, Schwann cells and myelinated axons except for enlarged axons were devoid of MCBs. Major ganglioside stored in both spinal ganglia and peripheral nerve was also GM2-ganglioside. The contents of ganglioside in the spinal ganglia and peripheral nerves were 50 and 10 times more than those from normal tissues, respectively. The spinal cord contained a slightly higher amount of gangliosides than the normal control. The cerebral white matter totally demyelinated in this patient accumulated a much higher amount of gangliosides than the cerebral gray matter. The retinal tissue showed GM2-ganglioside as the major one also.

Lipids of nervous tissue: composition and metabolism

As indicated in the Introduction, the many significant developments in the recent past in our knowledge of the lipids of the nervous system have been collated in this article. That there is a sustained interest in this field is evident from the rather long bibliography which is itself selective. Obviously, it is not possible to summarize a review in which the chemistry, distribution and metabolism of a great variety of lipids have been discussed. However, from the progress of research, some general conclusions may be drawn. The period of discovery of new lipids in the nervous system appears to be over. All the major lipid components have been discovered and a great deal is now known about their structure and metabolism. Analytical data on the lipid composition of the CNS are available for a number of species and such data on the major areas of the brain are also at hand but information on the various subregions is meagre. Such investigations may yet provide clues to the role of lipids in brain function. Compared to CNS, information on PNS is less adequate. Further research on PNS would be worthwhile as it is amenable for experimental manipulation and complex mechanisms such as myelination can be investigated in this tissue. There are reports correlating lipid constituents with the increased complexity in the organization of the nervous system during evolution. This line of investigation may prove useful. The basic aim of research on the lipids of the nervous tissue is to unravel their functional significance. Most of the hydrophobic moieties of the nervous tissue lipids are comprised of very long chain, highly unsaturated and in some cases hydroxylated residues, and recent studies have shown that each lipid class contains characteristic molecular species. Their contribution to the properties of neural membranes such as excitability remains to be elucidated. Similarly, a large proportion of the phospholipid molecules in the myelin membrane are ethanolamine plasmalogens and their importance in this membrane is not known. It is firmly established that phosphatidylinositol and possibly polyphosphoinositides are involved with events at the synapse during impulse propagation, but their precise role in molecular terms is not clear. Gangliosides, with their structural complexity and amphipathic nature, have been implicated in a number of biological events which include cellular recognition and acting as adjuncts at receptor sites. More recently, growth promoting and neuritogenic functions have been ascribed to gangliosides. These interesting properties of gangliosides wIll undoubtedly attract greater attention in the future.(ABSTRACT TRUNCATED AT 400 WORDS)

GD3 ganglioside is a glycolipid characteristic of immature neuroectodermal cells

Biochemical studies have indicated that the disialoganglioside, GD3, is a major glycolipid component of the immature vertebrate CNS, but a minor element within the mature CNS. We have investigated its cellular localization in rat CNS by immunofluorescence using a mouse monoclonal antibody that recognizes GD3. In tissue sections of postnatal CNS, the antibody bound to cells in several areas known to contain immature neuroectodermal populations: the subventricular zone beneath the lateral ventricle, the external germinative layer of the cerebellar cortex, and the dentate gyrus of the hippocampus. GD3-containing cells were also found in developing white matter of the forebrain and cerebellar folia. Using a double-label immunofluorescence method, we found that the GD3-positive white matter cells did not express the astrocytic marker, glial fibrillary acidic protein. In adult rat CNS, we could not detect antibody binding to neurons or glia. Scattered GD3-positive cells were apparent in the adult subventricular zone. Our results indicate that GD3 ganglioside is a membrane component characteristically expressed in the rat CNS by neuroectodermal stem cells, both neuronal and glial precursors.

Absence of ganglioside GM1 in astroglial cells from 21-day old rat brain: immunohistochemical, histochemical, and biochemical studies

A procedure was developed for the cultivation of cells derived from the cerebral hemispheres of the 21-day old rat. Approximately 98 percent of the cells in a 10 day culture are astrocytes that contain glial fibrillary acidic protein. Analysis of the extracted gangliosides by thin layer chromatography revealed that ganglioside GM1 was absent and that the predominant ganglioside was GM3. Very small amounts of the polysialogangliosides GD1a, GD1b, and GT1b were detected. The concentration of gangliosidic NeuNAc per mg protein in these astrocytes was only 3 percent that observed in the 5 day culture of a mixed cell preparation from newborn rat brain. Immunohistochemical and histochemical studies were performed on the mixed cell population of the minced tissue of 21-day old rat brain prior to cultivation. Astrocytes did not stain for hyaluronectin. These cells also did not provide a positive staining reaction for ganglioside GM1 utilizing the antiganglioside GM1 peroxidase-antiperoxidase procedure and the biotinylated choleragen-avidin-peroxidase procedure. These two histochemical methods for ganglioside GM1 also did not stain astrocytes that had been cultured for 5 days. Oligodendroglial cells, which were also present in the uncultured 21-day-old minced brain tissue, stained positively for ganglioside GM1 and hyaluronectin. Hyaluronectin had previously been shown to be a marker for oligodendroglia. Oligodendroglial cells which were present in the 5 day cultures of 21-day old brain tissue also provided a positive reaction for ganglioside GM1. It is concluded that ganglioside GM1 is absent in astroglia. The presence of small amounts of polysialogangliosides in the "pure" astrocyte preparation is discussed.

Cholesterol esters in rat brain infected with acute measles encephalitis: concentration and fatty acid composition

The present study deals with the concentration and fatty acid composition of cholesterol esters in rat brains infected experimentally with measles virus to induce acute encephalitis. The left side of the cerebrum, as well as other portions of the brain, when inoculated percutaneously contained a large amount of cholesterol esters. The major fatty acids from the esters in the brain were C16:0, C16:1, C18:0, and C18:1; those from the serum were C18:1, C18:2, and C20:4. This result indicates that cholesterol esters may not come from serum but can be synthesized in situ, even in the brain with acute viral infection.

Carbon monoxide-induced brain injury: neurochemical studies after single and repeated exposures

Biochemical effects of a single and once-repeated exposure to carbon monoxide (0.2% CO, 30 min) were studied in mouse brain. The effect of the severity of the first exposure on the brain reaction to the second exposure (0.2% CO, 30 min) was also studied after exposure to four different CO doses (0.2% CO for 0, 2 or 5 h, and 0.3% CO for 2 h). 1. The DNA content of brain decreased after single and once-repeated CO exposures. The effect of the second exposure was greater than that of the first. 2. The changes in the glycosphingolipid synthesis of brain were measured as the specific rate of precursor incorporation into the two isolated galactolipid fractions, i.e., cerebrosides and gangliosides following a 2-h pulse-labelling with 3H-galactose in vivo. The synthesis of cerebrosides was substantially inhibited for a short period after the first and the second exposures. A late compensatory over-recovery of synthesis was found only after the second exposure. The rate of galactose incorporation into gangliosides was not immediately depressed after CO exposure, but otherwise the changes were similar to those of cerebrosides. 3. The protein, phospholipid and cerebroside contents of brain were also affected in parallel fashion with the changes of DNA content. The content of gangliosides was increased after the first, but not after the second exposure. The enhanced reaction of brain to the second CO poisoning suggests the existence of sublethal brain cell injury which is produced by the first CO exposure and manifested by altered reactions to the second exposure.

High-performance liquid chromatographic resolution of p-nitrobenzyloxyamine derivatives of brain gangliosides

A new quantitative procedure for the high-performance liquid chromatographic (HPLC) resolution of human brain gangliosides employing reversed-phase chromatography is described. To provide a derivative which can be determined by UV absorption techniques, p-nitrobenzyloxyamine was coupled to the gangliosides. Derivatization involves ozonation and cleavage of the ceramide double bond followed by oxime formation to the nascent aldehyde. Individual gangliosides, as they were resolved by HPLC, were collected. These fractions were then identified by thin-layer chromatography (TLC) and by gas chromatography of their monosaccharides. Quantitative results were obtained along with a marked increase in sensitivity over conventional resorcinol-hydrochloric acid quantitation of TLC-resolved gangliosides.

Effects of cell density on the neutral glycolipid composition of cultured human brain and glioma cells

Density dependent chain elongation of neutral glycosphingolipids (NGSL) is associated with contact inhibition of mitosis in several normal cultured cell lines. Transformed non-neural cell lines which have impaired contact inhibition frequently lose this biochemical response. To determine if either of these phenomena occur in human neural cells we determined NGSL compositions of cultured glioblastoma multiforme and normal fetal brain cells. Fetal cells generally had more total NGSL than the tumor cells. As a percentage of total NGSL, both cell lines at higher cell densities had larger proportions of ceramide trihexoside and globoside, but smaller proportions of cerebroside. This decrease was mainly in non-hydroxy fatty acid cerebroside of glioma cells, but in hydroxy fatty acid cerebroside of normal fetal brain cells. These results demonstrate that although glioblastoma multiforme cells have markedly impaired growth control, they still preserve density dependent chain elongation of NGSL. A role for this phenomenon in normal cellular growth control has yet to be established.