A reappraisal of ganglioside GD3 expression in the CNS

Gangliosidome of a Human Hippocampus in Temporal Lobe Epilepsy Resolved by High-Resolution Tandem Mass Spectrometry

In this study, we developed a high-resolution tandem mass spectrometry (HR MS) approach to assess presumed changes in gangliosidome of a human hippocampus affected by temporal lobe epilepsy (TLE) in comparison with a normal hippocampus. Gangliosides, membrane glycolipids, are particularly diverse and abundant in the human brain, and participate in ion transport and modulation of neuronal excitability. Changes in structural ganglioside pattern potentially linked to TLE molecular pathogenesis have not been explored in detail. Aiming to characterize TLE-specific gangliosidome, we analyzed the native gangliosides purified from a human hippocampal tissue sample affected by TLE and a control hippocampus using HR MS. Marked differences of ganglioside expression were shown in TLE vs. control, particularly with respect to the sialylation degree of components, discovered as a characteristic feature of TLE. Another major finding is the occurrence of tetrasialofucogangliosides in TLE and species modified by either O-acetylation or CH3COO−. Structural analysis by higher-energy collisional dissociation (HCD) MS/MS gave rise to fragmentation patterns implying that the GQ1b (d18:1/18:0) isomer is specifically associated with TLE. Further investigation in a larger sample is needed in order to confirm the discovery of ganglioside structures specifically expressed in human TLE and to provide information on the probable role of gangliosides in the molecular events underlying seizures.

Ganglioside GD3 is up-regulated in microglia and regulates phagocytosis following global cerebral ischemia

Gangliosides, the major sialic-acid containing glycosphingolipids in the mammalian brain, play important roles in brain development and neural functions. Here, we show that the b-series ganglioside GD3 and its biosynthetic enzyme, GD3-synthase (GD3S), were up-regulated predominantly in the microglia of mouse hippocampus from 2 to 7 days following global cerebral ischemia (GCI). Interestingly, GD3S knockout (GD3S-KO) mice exhibited decreased hippocampal neuronal loss following GCI, as compared to wild-type (WT) mice. While comparable levels of astrogliosis and microglial proliferation were observed between WT and GD3S-KO mice, the phagocytic capacity of the GD3S-KO microglia was significantly compromised after GCI. At 2 and 4 days following GCI, the GD3S-KO microglia demonstrated decreased amoebic morphology, reduced neuronal material engulfment, and lower expression of the phagolysosome marker CD68, as compared to the WT microglia. Finally, by using a microglia-primary neuron co-culture model, we demonstrated that the GD3S-KO microglia isolated from mouse brains at 2 days after GCI are less neurotoxic to co-cultured hippocampal neurons than the WT-GCI microglia. Moreover, the percentage of microglia with engulfed neuronal elements in the co-cultured wells was also significantly decreased in the GD3S-KO mice after GCI. Interestingly, the impaired phagocytic capacity of GD3S-KO microglia could be partially restored by pre-treatment with exogenous ganglioside GD3. Altogether, this study provides functional evidence that ganglioside GD3 regulates phagocytosis by microglia in an ischemic stroke model. Our data also suggest that the GD3-linked microglial phagocytosis may contribute to the mechanism of delayed neuronal death following ischemic brain injury.

O-acetylated Gangliosides as Targets for Cancer Immunotherapy

O-acetylation of sialic acid residues is one of the main modifications of gangliosides, and modulates ganglioside functions. O-acetylation of gangliosides is dependent on sialyl-O-acetyltransferases and sialyl-O-acetyl-esterase activities. CAS1 Domain-Containing Protein 1 (CASD1) is the only human sialyl-O-acetyltransferases (SOAT) described until now. O-acetylated ganglioside species are mainly expressed during embryonic development and in the central nervous system in healthy adults, but are re-expressed during cancer development and are considered as markers of cancers of neuroectodermal origin. However, the specific biological roles of O-acetylated gangliosides in developing and malignant tissues have not been extensively studied, mostly because of the requirement of specific approaches and tools for sample preparation and analysis. In this review, we summarize our current knowledge of ganglioside biosynthesis and expression in normal and pathological conditions, of ganglioside O-acetylation analysis and expression in cancers, and of the possible use of O-acetylated gangliosides as targets for cancer immunotherapy.

Sex-Related Abnormalities in Substantia Nigra Lipids in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative movement disorder involving the selective loss of dopamine-producing neurons in the substantia nigra (SN). Differences in disease presentation, prevalence, and age of onset have been reported between males and females with PD. The content and composition of the major glycosphingolipids, phospholipids, and cholesterol were evaluated in the SN from 12 PD subjects and in 18 age-matched, neurologically normal controls. Total SN ganglioside sialic acid content and water content (%) were significantly lower in the male PD subjects than in the male controls. The content of all major gangliosides were reduced in the male PD subjects to some degree, but the neuronal-enriched gangliosides, GD1a and GT1b, were most significantly reduced. The distribution of phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol was also significantly lower in the male PD subjects than in the male controls. However, the distribution of myelin-enriched cerebrosides and sulfatides was significantly higher in the male PD subjects than in the male controls suggesting myelin sparing in the male PD subjects. No elevation was detected for astrocytosis-linked GD3. These neurochemical changes provide evidence of selective neuronal loss in SN of the males with PD without robust astrocytosis. In contrast to the SN lipid abnormalities found in the male PD subjects, no significant abnormalities were found in the female PD subjects for SN water content or for any major SN lipids. These data indicate sex-related differences in SN lipid abnormalities in PD.

Prevalence of IgG Autoantibodies against GD3 Ganglioside in Acute Zika Virus Infection

Zika virus (ZIKV) disease has become a global health emergency with devastating effects on public health. Recent evidences implicate the virus as an emergent neuropathological agent promoting serious pathologies of the human nervous system, that include destructive and malformation consequences such as development of ocular and fetal brain lesions, microcephaly in neonates, and Guillain–Barré syndrome (GBS) in adults. These neurological disorders of both central and peripheral nervous systems are thought to be associated to the neurotropic properties of the virus that has ability to infect neural stem cells as well as peripheral neurons, a hallmark of its pathogenicity. The presence of autoantibodies against gangliosides plays a pivotal role in the etiogenesis of GBS and a variety of neurological disorders. Gangliosides are a class of galactose-containing cerebrosides mainly expressed in nervous system tissues playing a critical role in the physiology of neural cells and neurogenesis. Herein, our findings indicate that patients at acute phase of ZIKV infection without any neurological signs show increased levels of IgG autoantibody against GD3 gangliosides, a class of glycolipid found to be highly expressed in neural stem cell acting in the maintenance of their self-renewal cellular capacity. It is possible that a pathological threshold of these antibodies is only acquired in secondary or subsequent infections. In the light of these evidences, we propose that the target of GD3 by autoimmune responses may possibly has an effect in the neuropathy and neurogenesis disorder seen during ZIKV infection.

Progenitor/Stem Cell Markers in Brain Adjacent to Glioblastoma: GD3 Ganglioside and NG2 Proteoglycan Expression

Characterization of tissue surrounding glioblastoma (GBM) is a focus for translational research because tumor recurrence invariably occurs in this area. We investigated the expression of the progenitor/stem cell markers GD3 ganglioside and NG2 proteoglycan in GBM, peritumor tissue (brain adjacent to tumor, BAT) and cancer stem-like cells (CSCs) isolated from GBM (GCSCs) and BAT (PCSCs). GD3 and NG2 immunohistochemistry was performed in paired GBM and BAT specimens from 40 patients. Double-immunofluorescence was carried out to characterize NG2-positive cells of vessel walls. GD3 and NG2 expression was investigated in GCSCs and PCSCs whose tumorigenicity was also evaluated in Scid/bg mice. GD3 and NG2 expression was higher in tumor tissue than in BAT. NG2 decreased as the distance from tumor margin increased, regardless of the tumor cell presence, whereas GD3 correlated with neoplastic infiltration. In BAT, NG2 was coexpressed with a-smooth muscle actin (a-SMA) in pericytes and with nestin in the endothelium. Higher levels of NG2 mRNA and protein were found in GCSCs while GD3 synthase was expressed at similar levels in the 2 CSC populations. PCSCs had lower tumorigenicity than GCSCs. These data suggest the possible involvement of GD3 and NG2 in pre/pro-tumorigenic events occurring in the complex microenvironment of the tissue surrounding GBM.

The changing phenotype of microglia from homeostasis to disease

It has been nearly a century since the early description of microglia by Rio-Hortega; since then many more biological and pathological features of microglia have been recognized. Today, microglia are generally considered to be beneficial to homeostasis at the resting state through their abilities to survey the environment and phagocytose debris. However, when activated microglia assume diverse phenotypes ranging from fully inflamed, which involves the release of many pro-inflammatory cytokines, to alternatively activated, releasing anti-inflammatory cytokines or neurotrophins, the consequences to neurons can range from detrimental to supportive. Due to the different experimental sets and conditions, contradictory results have been obtained regarding the controversial question of whether microglia are “good” or “bad.” While it is well understood that the dual roles of activated microglia depend on specific situations, the underlying mechanisms have remained largely unclear, and the interpretation of certain findings related to diverse microglial phenotypes continues to be problematic. In this review we discuss the functions of microglia in neuronal survival and neurogenesis, the crosstalk between microglia and surrounding cells, and the potential factors that could influence the eventual manifestation of microglia.

Regulation by GD3 of the proinflammatory response of microglia mediated by interleukin-15

The interleukin (IL)-15-dependent immune responses of murine microglia were strongly affected by low concentrations of the ganglioside GD3. The ganglioside binding to IL-15 inhibited the proinflammatory effects of the cytokine, reducing IL-15-dependent T-cell proliferation as well as mRNA expression for IL-15Ralpha, p65, and NFATc2 in the N13 murine microglial cell line. Treatment of primary murine microglial cultures with GD3 abolished IL-15 production, without affecting cellular viability, but decreased the production of nitric oxide, a direct sensor of inflammation and nuclear factor-kappaB activity. We conclude that low doses of GD3 could inhibit specific proinflammatory mechanisms and modulate the inflammatory environment, leading to a less reactive scene. Microglial cells are one of the main actors in the inflammatory events that follow CNS trauma or an autoimmune disease episode, modulating the internal production of cytokines, growth factors, and other homeostatic molecules that may determine the evolution and outcome of tissue damage. Proinflammatory cytokines have a relevant role in the initial events, and modulation of their activity by gangliosides could cut down their harmful effects and interfere with invasion of the CNS by peripheral immune cells. The antiinflammatory properties of GD3 could be significant in the treatment of pain subsequent to CNS damage.

Expression of gangliosides on glial and neuronal cells in normal and pathological adult human brain

Few studies have assessed the glycolipid phenotype of glial cells in the human central nervous system (CNS) in situ. We investigated by immunohistochemistry the expression and cellular distribution of a panel of gangliosides (GM1, GM2, acetyl-GM3, GD1a, GD1b, GD2, GD3, GT1b, GQ1b and the A2B5 antibody) in adult, human normal and pathological brain, namely multiple sclerosis (MS) and other neurological diseases (OND). In normal conditions, we found diffuse expression in the white matter of most gangliosides tested, with the exception of acetyl-GM3, GT1b and GQ1b. By double immunofluorescence with phenotypic markers, GM1 and GD1b were preferentially expressed on GFAP+ astrocytes, GD1a on NG2+ oligodendrocyte precursors, A2B5 immunostained both populations, while GD2 was selectively present on mature oligodendrocytes. In the gray matter, only GM1, GD2 and A2B5 were present on neuronal cells. Interestingly, those gangliosides present on astrocytes in normal conditions were preferentially expressed on NG2+ cells in chronic MS lesions and in OND. Selective expression of GT1b upon astrocytes and NG2+ cells was instead observed in MS lesions, but not in OND. The definition of the glycolipid phenotype of CNS glial cells may be useful to identify distinct biological glial subsets and provide insights on the potential autoantigenic role of gangliosides in CNS autoimmune diseases.

Substrate reduction reduces gangliosides in postnatal cerebrum-brainstem and cerebellum in GM1 gangliosidosis mice

II3NeuAc-GgOse4Cer (GM1) gangliosidosis is an incurable lysosomal storage disease caused by a deficiency in acid beta-galactosidase (beta-gal), resulting in the accumulation of ganglioside GM1 and its asialo derivative GgOse4Cer (GA1) in the central nervous system, primarily in the brain. In this study, we investigated the effects of N-butyldeoxygalacto-nojirimycin (N B-DGJ), an imino sugar that inhibits ganglioside biosynthesis, in normal C57BL/6J mice and in beta-gal knockout (beta-gal-/-) mice from postnatal day 9 (p-9) to p-15. This is a period of active cerebellar development and central nervous system (CNS) myelinogenesis in the mouse and would be comparable to late-stage embryonic and early neonatal development in humans. N B-DGJ significantly reduced total ganglioside and GM1 content in cerebrum-brainstem (C-BS) and in cerebellum of normal and beta-gal-/- mice. N B-DGJ had no adverse effects on body weight or C-BS/cerebellar weight, water content, or thickness of the external cerebellar granule cell layer. Sphingomyelin was increased in C-BS and cerebellum, but no changes were found for cerebroside (a myelin-enriched glycosphingolipid), neutral phospholipids, or GA1 in the treated mice. Our findings indicate that the effects of N B-DGJ in the postnatal CNS are largely specific to gangliosides and suggest that N B-DGJ may be an effective early intervention therapy for GM1 gangliosidosis and other ganglioside storage disorders.

Activation of Fas receptor is required for the increased formation of the disialoganglioside GD3 in cultured cerebellar granule cells committed to apoptotic death

Apoptosis was induced in cultured cerebellar granule cells by lowering extracellular K+ concentrations (usually from 25 to 10 mM). The apoptotic phenotype was preceded by an early and transient increase in the intracellular levels of the disialoganglioside, GD3, which behaves as a putative pro-apoptotic factor. We examined whether activation of Fas receptor mediates the increase in GD3 formation in granule cells committed to die. Degenerating granule cells showed increased expression of both Fas receptor and its ligand (Fas-L), at times that coincided with the increase in GD3 levels and the induction of GD3 synthase mRNA. Addition of neutralizing anti-Fas-L antibodies reduced the extent of 'low-K+'-induced apoptosis and abolished the increase in GD3 levels and GD3 synthase mRNA. Similar reductions were observed in cultures prepared from gld or lpr mice, which harbor loss-of-function mutations of Fas-L and Fas receptor, respectively. In addition, exogenous application of soluble Fas-L further enhanced both the increase in GD3 formation and cell death in cultured granule cells switched from 25 into 10 mM K+. We conclude that activation of Fas receptor is entirely responsible for the increase in GD3 levels and contributes to the development of apoptosis by trophic deprivation in cultured cerebellar granule cells.

Preferential vulnerability of astroglia and glial precursors to combined opioid and HIV-1 Tat exposure in vitro

Human immunodeficiency virus (HIV)-1 infection can cause characteristic neural defects such as progressive motor dysfunction, striatal pathology and gliosis. Recent evidence suggests that HIV-induced pathogenesis is exacerbated by heroin abuse and that the synergistic neurotoxicity is a direct effect of heroin on the CNS, an alarming observation considering the high incidence of HIV infection with injection drug abuse. Although HIV infection results in neurodegeneration, neurons themselves are not directly infected. Instead, HIV affects microglia and astroglia, which subsequently contributes to the neurodegenerative changes. Opioid receptors are widely expressed by macroglia and macroglial precursors, and the activation of mu-opioid receptors can modulate programmed cell death, as well as the response of neural cells to cytotoxic insults. For this reason, we questioned whether opioid drugs might modify the vulnerability of macroglia and macroglial precursors to HIV-1 Tat protein. To address this problem, the effects of morphine and/or HIV Tat(1-72) on the viability of macroglia and macroglial precursors were assessed in mixed-glial cultures derived from mouse striatum. Our findings indicate that sustained exposure to morphine and Tat(1-72) viral protein induces the preferential death of glial precursors and some astrocytes. Moreover, the increased cell death is mediated by mu-opioid receptors and accompanied by the activation of caspase-3. Our results imply that opiates can enhance the cytotoxicity of HIV-1 Tat through direct actions on glial precursors and/or astroglia, suggesting novel cellular targets for HIV-opiate interactions.

GD3 ganglioside and apoptosis

Lipid and glycolipid mediators are important messengers of the adaptive responses to stress, including apoptosis. In mammalian cells, the intracellular accumulation of ganglioside GD3, an acidic glycosphingolipid, contributes to mitochondrial damage, a crucial event during the apoptopic program. GD3 is a minor ganglioside in most normal tissues. Its expression increases during development and in pathological conditions such as cancer and neurodegenerative disorders. Intriguingly, GD3 can mediate additional biological events such as cell proliferation and differentiation. These diverse and opposing effects indicate that tightly regulated mechanisms, including 9-O-acetylation, control GD3 function, by affecting intracellular levels, localization and structure of GD3, and eventually dictate biological outcomes and cell fate decisions.

Progenitors in the postnatal cerebellar white matter are antigenically heterogeneous

Progenitors that migrate through the white matter of the postnatal cerebellum give rise to cortical interneurons, astroglia, and oligodendroglia. To determine whether this progenitor population is heterogeneous with respect to specific lineage markers, we infected progenitors in vivo with a retrovirus encoding the green fluorescent protein on postnatal day 4/5 and labeled them in situ with various antibodies 2 days postviral injection: the neuronal marker was the transcription factor SOX1; early oligodendroglial markers were chondroitin sulfate proteoglycan antigen and platelet-derived growth factor receptor-alpha. Markers for astroglial progenitors were vimentin, nestin, zebrin II, and the astroglial-specific glutamate transporter subtype GLAST. None of the progenitors was doubly labeled with any combination of markers characteristic for different cell lineages. Most progenitors were not labeled with any of the various combinations of antibodies used. Progenitors did not express markers characteristic for mature astroglia (GFAP), oligodendroglia (CNPase), or neurons (MAP2). Thus, although these progenitors are morphologically indistinguishable, a minority expresses markers of early neuronal or glial lineages, suggesting that they begin to differentiate during migration.

The glial precursor proteoglycan, NG2, is expressed on tumour neovasculature by vascular pericytes in human malignant brain tumours

Glial precursor cells express NG2 and GD3 in the developing brain. These antigens are both over-expressed during neoplasia, which suggests they may have specific functions in the malignant progression of human brain tumours. This study describes the expression of NG2 and GD3 in 28 paediatric and adult brain tumours. Glioblastoma biopsy spheroids were also implanted into nude rats to assess the regional distribution of the molecules within the tumour. These xenografts showed extensive infiltration and growth that mimicked the growth patterns of human gliomas in situ. NG2 was identified in 20 out of 28 brain tumours, where the expression was confined to the main mass of the tumour, and was reduced towards the tumour periphery. NG2 was mainly associated with blood vessels on both the pericyte and basement membrane components of the tumour vasculature. Ki67 (MIB-1) labelling indicated that NG2 expression was associated with areas of high cellular proliferation. Conversely, all the tumours expressed GD3, which was present both in the tumour main mass and throughout the periphery. Thus, the expression of NG2 may be indicative of tumour progression and might be an amenable target for future therapeutic interventions.

An early increase in the disialoganglioside GD3 contributes to the development of neuronal apoptosis in culture

We induced apoptosis in primary cultures of cerebellar granule neurons by switching the growing medium into a medium containing lower concentrations of K(+) (5 or 10 mM instead of 25 mM) or, alternatively, by addition of staurosporine. The apoptotic phenotype was always preceded by an early increase in the intracellular levels of the disialoganglioside GD3, which peaked at 2-6 h and returned back to normal at 12 h. GD3 synthase, the enzyme that forms GD3 from the monosialoganglioside GM3, was also induced at early times after the induction of apoptosis in granule cells. Immunofluorescent staining showed that GD3 increased in neuronal cell bodies and neurites, but was never localized in cell nuclei. In cultures switched into a low K(+)-containing medium, exogenously applied GD3, but not the disialoganglioside GD1a, accelerated the development of neuronal apoptosis. In contrast, the antisense-induced knock-down of GD3 synthase was protective against granule cell death induced by lowering extracellular K(+) from 25 to 10 - but not 5 - mM. These results demonstrate that an early and transient increase in GD3 synthesis is one of the factors that contribute to the induction of neuronal apoptosis in culture.

Beta-amyloid-induced synthesis of the ganglioside GD3 is a requisite for cell cycle reactivation and apoptosis in neurons

We have shown that cortical neurons challenged with toxic concentrations of beta-amyloid peptide (betaAP) enter the S phase of the cell cycle before apoptotic death. Searching for a signaling molecule that lies at the border between cell proliferation and apoptotic death, we focused on the disialoganglioside GD3. Exposure of rat cultured cortical neurons to 25 microm betaAP(25-35) induced a substantial increase in the intracellular levels of GD3 after 4 hr, a time that precedes neuronal entry into S phase. GD3 levels decreased but still remained higher than in the control cultures after 16 hr of exposure to betaAP(25-35). Confocal microscopy analysis showed that the GD3 synthesized in response to betaAP colocalized with nuclear chromatin. The increase in GD3 was associated with a reduction of sphingomyelin (the main source of the ganglioside precursor ceramide) and with the induction of alpha-2,8-sialyltransferase (GD3 synthase), the enzyme that forms GD3 from the monosialoganglioside GM3. A causal relationship between GD3, cell-cycle activation, and apoptosis was demonstrated by treating the cultures with antisense oligonucleotides directed against GD3 synthase. This treatment, which reduced betaAP(25-35)-stimulated GD3 formation by approximately 50%, abolished the neuronal entry into the S phase and was protective against betaAP(25-35)-induced apoptosis.

Analysis of fractal dimension of O2A glial cells differentiating in vitro

Fractal dimension is a quantitative measure of morphological complexity. Glial cells of the oligodendrocyte-type 2 astrocyte (O2A) lineage exhibit increasing morphological complexity as they differentiate in vitro. Enriched populations of O2A progenitor cells isolated from neonatal rat cerebral hemispheres or optic nerves were allowed to differentiate in vitro, and their fractal dimensions were measured over time. The fractal dimensions of the maturing cells correlated with perceived complexity; cells with elaborate process branching had larger fractal dimensions than cells with a simpler morphology. An analysis of changes in fractal dimension revealed distinct rates of growth for both oligodendrocytes and type 2 astrocytes. The fractal dimension remained constant over a 10-fold range in optical magnification, demonstrating that cultured O2A glial cells exhibit self-similarity, a defining characteristic of fractal objects. These results illustrate that fractal dimension analysis of maturing cell populations is a useful method for quantitatively describing the process of cell differentiation.

Biology of oligodendrocyte and myelin in the mammalian central nervous system

Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), and astrocytes constitute macroglia. This review deals with the recent progress related to the origin and differentiation of the oligodendrocytes, their relationships to other neural cells, and functional neuroglial interactions under physiological conditions and in demyelinating diseases. One of the problems in studies of the CNS is to find components, i.e., markers, for the identification of the different cells, in intact tissues or cultures. In recent years, specific biochemical, immunological, and molecular markers have been identified. Many components specific to differentiating oligodendrocytes and to myelin are now available to aid their study. Transgenic mice and spontaneous mutants have led to a better understanding of the targets of specific dys- or demyelinating diseases. The best examples are the studies concerning the effects of the mutations affecting the most abundant protein in the central nervous myelin, the proteolipid protein, which lead to dysmyelinating diseases in animals and human (jimpy mutation and Pelizaeus-Merzbacher disease or spastic paraplegia, respectively). Oligodendrocytes, as astrocytes, are able to respond to changes in the cellular and extracellular environment, possibly in relation to a glial network. There is also a remarkable plasticity of the oligodendrocyte lineage, even in the adult with a certain potentiality for myelin repair after experimental demyelination or human diseases.

Re-evaluation of nestin as a marker of oligodendrocyte lineage cells

Maturation of oligodendrocyte progenitors (O2A) is characterized by morphological changes and the sequential expression of specific antigens leading to the formation of myelin membrane. Monoclonal antibodies A2B5, A007, anti-vimentin, and anti-galactocerebroside, recognize oligodendroglia at different stages of development. The neuroepithelial precursor marker nestin is also expressed by the oligodendroglial lineage; we have used enriched populations of progenitors isolated from neonatal rat brain cultures to further examine the cellular distribution of this intermediate filament protein. The phenotypic distribution of nestin positive cells among the oligodendrocyte lineage showed that 65% reacted with A2B5, whereas only 5% were A007(+), and 4% galactocerebroside(+). The remaining 25% of the cells were not labeled and had small cellular bodies devoid of processes, characteristic of the pre-O2A progenitor. Further analysis of the nestin(+) population showed that the majority of the cells were also vimentin(+). Antibody-dependent complement mediated cytolysis of A2B5(+) (O2A cells) and galactocerebroside(+) (mature oligodendrocytes) cells left a population of nestin(+) cells that were induced to proliferate in the presence of growth factors and to differentiate into A2B5(+) and galactocerebroside(+) cells. Proliferating cells maintained in the presence of platelet-derived growth factor or basic fibroblast growth factor retained nestin expression along with A2B5. By contrast, in serum-free medium nestin expression decreased while postmitotic cells acquired A007 and galactocerebroside. Our results suggest that nestin expression is a marker of pre-O2A cells that is maintained in proliferating glial progenitors, but is quickly down-regulated in postmitotic oligodendrocytes (A007(+)/galacto-cerebroside(+)) along with A2B5 and vimentin. However, other glial cells including type 2 astrocytes and some amoeboid microglia also share nestin expression.

Anencephaly: structural characterization of gangliosides in defined brain regions

Gangliosides from histopathologically-defined human cerebrum-resembling remnant and cerebellum from 37 and 30 gestational week-old anencephaluses were identified using mass spectrometry and high performance thin layer chromatography combined with immunochemical analysis in comparison to respective normal newborn/fetal and adult brain regions. A novel strategy of nano-electrospray ionization quadrupole time-of-flight tandem MS has been developed for identification of ganglioside components in complex mixtures. By morphoanatomical and histological investigation the anencephalic cerebral remnant was found to be aberrant, while the anencephalic cerebellum was defined as normal. Total ganglioside concentrations in the anencephalic cerebral remnant and the cerebellum were 34% and 13% lower in relation to the age-matched controls. In the cerebral remnant, GD3, GM2 and GT1b were elevated, while GD1a was decreased in the anencephalic cerebral remnant, but enriched in anencephalic cerebellum. GQ1b was reduced in both anencephalic regions. Gg4Cer, GM1b and GD1alpha, members of the alpha-series biosynthetic pathway, and neolacto-series gangliosides were found to be present in anencephalic, as well as in normal, fetal and adult brain tissues, indicating the occurrence of these biosynthetic pathways in human brain. In both cerebral and cerebellar anencephalic tissues, GM1b, GD1alpha, nLM1 and nLD1 were expressed at a higher rate in relation to normal tissue. It can be demonstrated that the anencephalic cerebral remnant, as a primitive brain structure, represents a naturally-occurring model to study the ganglioside involvement in induction of aberrant brain development.

Disialoganglioside GD3 is selectively expressed by developing and mature human mast cells

BACKGROUND

Disialoganglioside GD3 is expressed on the surface of selected cell types. Anti-GD3 mAb administered to human subjects with malignant melanoma produces signs and symptoms of immediate hypersensitivity reactions.

OBJECTIVE

The expression of GD3 by human mast cells was assessed during mast cell development in vitro and in samples of lung and skin.

METHODS

GD3 on tissue- and in vitro-derived mast cells was analyzed after double labeling of cells for tryptase (G3 mAb) or Kit (YB5.B8 mAb) and GD3 (R24 mAb). Glycolipids in extracts of fetal liver-derived mast cells were examined by using high-performance thin-layer chromatography.

RESULTS

Flow cytometry showed that the percentage of GD3+ cells increased in parallel to Kit+ cells during the recombinant human stem cell factor-dependent development of fetal liver-derived mast cells. Double-labeling experiments showed that GD3+ cells were also surface Kit+ and granule tryptase positive, identifying them as mast cells in preparations of lung-, skin-, fetal liver-, and cord blood-derived cells. The major acidic glycolipid detected was NeuAcalpha2-8NeuAcalpha2-3Galbeta1-4Glcbeta1-1'Cer (GD3). Among peripheral blood leukocytes, only basophils and about 10% of the T cells were labeled with anti-GD3 mAb. Anti-GD3 mAb-conjugated magnetic beads were used to purify mast cells to greater than 90% purity from dispersed skin cells enriched to approximately 12% purity by means of density-dependent sedimentation but were less proficient for dispersed human lung mast cells, most likely because of other cell types that express GD3.

CONCLUSION

GD3 is expressed on the surface of developing human mast cells in parallel to tryptase in secretory granules and, like Kit, can serve as a target for their enrichment by immunoaffinity techniques.

Immunostaining of ganglioside GD1b, GD3 and GM1 in rat cerebellum: cellular layer and cell type specific associations

We have studied the cellular distribution of gangliosides GD1b, GD3 and GM1 in rat cerebellum by immunostaining, using monoclonal antibodies and confocal microscopy. Antibodies against astroglial, neuronal and synaptic vesicle associated molecules were used for colocalization analyses. In the gray matter, the anti-GD1b antibody stained thin strands in the molecular layer (ML), interpreted as Bergman glia fibers based on colocalized staining with anti-glial fibrillary acidic protein (GFAP). The neuropil in the granule (GL) and Purkinje (PL) cell layers was also anti-GD1b positive. The anti-GD3 antibody stained the ML, the neuropil in the GL and PL and also the granule and Purkinje cell bodies, appearing intracytoplasmically and vesicle associated. Anti-GD1b and anti-GD3 staining in the GL glomeruli were colocalized with anti-synaptophysin staining. The anti-GM1 antibody stained cell bodies in the ML but they could not be characterized in colocalization experiments. The GL and PL were not stained with the anti-GM1 antibody. In the white matter, different staining patterns were seen for the gangliosides, the anti-GM1 staining being the most intense. This study shows cellular layer and cell type specific associations of the investigated gangliosides and localization of GD1b and GD3 at synaptic sites, warranting further studies on their role in synaptic mechanisms.

Cell reactions following acute brain injury: a review

The proliferative behavior of glia following a cerebral stab wound in adult rats is reviewed. Proliferation was determined by both PCNA and [3H]thymidine labeling. Microglia were the first cells to divide and constituted the bulk of dividing cells. Both ramified and ameboid microglia divided. A smaller number of astrocytes entered the cell cycle a day later and were shown to derive from differentiated reactive cells. No differentiated oligodendroglia were labeled by thymidine, although a small number of dividing immature oligodendroglia could be detected in cultures of cells labeled in vivo. Recent studies of the properties of oligodendroglial precursors in brain repair mechanisms are discussed. The results so far support our conclusion that differentiated oligodendrocytes do not divide.

A new procedure for determining ganglioside GD3 a potential glial cell activation marker in cerebrospinal fluid

Increased amounts of ganglioside GD3 [II3 (NeuAc)2-LacCer], associated with reactive gliosis, have been documented in a variety of neurodegenerative disorders. GD3 expression has also been reported in microglial cells, not only during development but also in reactive states, where the glial activation is considered to be part of the repair process. It is important to find markers in cerebrospinal fluid that will enable us to identify damage and register changes in pathological processes within the brain. A sensitive and practically applicable method for determination of GD3 ganglioside in cerebrospinal fluid has been developed. The procedure, which includes extraction, purification on silica gel and thin-layer enzyme-linked immunostaining, also allows determination of sulphatide, a marker of demyelinating processes, in the same portion of CSF. The method has been applied to CSF samples from 101 normal individuals aged 2-83 years. The GD3 concentration was found to be significantly correlated to age and reflecting the concentrations within the brain. GD3 ganglioside analysis by means of this method might be useful for studying glial changes during brain maturation as well as in brain disorders.

A role for glutamate and its receptors in the regulation of oligodendrocyte development in cerebellar tissue slices

We tested the hypothesis that the neurotransmitter glutamate would influence glial proliferation and differentiation in a cytoarchitecturally intact system. Postnatal day 6 cerebellar slices were maintained in organotypic culture and treated with glutamate receptor agonists or antagonists. After dissociation, cells were stained with antibodies for different oligodendrocyte developmentally regulated antigens. Treatment of the slices with the glutamate receptor agonists kainate or alpha -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid significantly decreased the percentage of LB1(+), NG2(+) and O4(+) cells, and their bromodeoxyuridine labeling index. The non-N-methyl-D-aspartate glutamate receptor antagonist 6,7-dinitroquinoxaline-2,3-dione increased the percentage and bromodeoxyuridine labeling of LB1(+), NG2(+) and O4(+) cells. In intact slices, RNA levels of the oligodendrocyte gene for 2′,3′-cyclic nucleotide 3′-phosphodiesterase were decreased by kainate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, and increased by 6,7-dinitroquinoxaline-2,3-dione. The percentage of astrocytes was not modified by kainate, alpha -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid or 6, 7-dinitroquinoxaline-2,3-dione. Treatment with the N-methyl-D-aspartate receptor antagonist 2-amino-5-phosphonopentanoic acid did not alter the percentage of O4(+) cells, nor their proliferation. Incubation with the gamma-aminobutyric acid receptor antagonist bicuculline did not modify the percentage of LB1(+), A2B5(+) and O4(+) cells. In purified cerebellar oligodendrocyte progenitor cells, glutamate receptor agonists blocked K+ currents, and inhibited cell proliferation and lineage progression. The K+ channel blocker tetraethylammonium also inhibited oligodendrocyte progenitor cell proliferation. These findings indicate that in rat cerebellar tissue slices: (i) glutamate specifically modulates oligodendrocyte but not astrocyte development through selective activation of alpha -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, and (ii) cell depolarization and blockage of voltage-dependent K+ channels is likely to be the triggering mechanism.

Cells of the oligodendrocyte lineage proliferate following cortical stab wounds: an in vitro analysis

We have previously shown that a cortical stab wound induces the proliferation of microglia and astrocytes in situ, but no evidence was obtained for proliferation of cells of the oligodendrocyte lineage (Amat et al., 1996). To study further the properties of cells involved in repair following brain injury, groups of adult rats received either sham operations or bilateral stab wounds. Proliferating cells were labeled in vivo 3 days later with [3H]-thymidine (Thy) and sacrificed the same day. Oligodendrocyte-enriched preparations were isolated, cultured, and analyzed. The fate and antigenic phenotype of the proliferating cells was analyzed using three-color immunofluorescence combined with autoradiography at 1, 2, 3, 5, and 10 days in vitro (DIV). Cells were immunostained for ganglioside GD3 (glial stem cells), O4 antigen (cells of the oligodendrocyte lineage), galactosyl ceramide (GC, differentiated oligodendrocytes), and GFAP (astrocytes). Thymidine-labeled O4+/GC- cells were found only in cultures from wounded animals and most of them differentiated in vitro as mature oligodendrocytes, but no Thy+/O4+/GC+ oligodendrocytes were seen at 1, 2, or 3 DIV. There was also a marked increase in the number of Thy+/GD3+ cells in the experimental cultures. In both experimental and control groups the total number of Thy+ and Thy- GD3+ cells declined with time in culture concomitant with an increase in total number of both Thy+ and Thy- GFAP+ astrocytes, and without any significant change in the Thy+ cell fraction of O4+ oligodendrocytes in the experimental cultures. Therefore most of the GD3+/O4- cells apparently differentiated as GFAP+ astrocytes, not as oligodendrocytes. We conclude that O4+/GC- oligodendrocyte precursor cells, but not differentiated oligodendrocytes, proliferate in response to brain injury. These cells proliferate slowly or not at all in normal adult animals and constitute a phenotypically and kinetically distinct group from the GD3+ glial precursors. This result is consistent with the existence within the adult CNS of a quiescent premyelinating oligodendrocyte. We propose that these immature committed oligodendrocytes are induced to proliferate at the wound site and serve as a source of new oligodendrocytes.

Successive isolation and separation of the major lipid fractions including gangliosides from single biological samples

Currently available techniques concerning extraction and characterization of the different lipids from biological specimens are designed for particular families and do not address consecutive isolation of lipid constituents in their globality. We describe here a simple, nondestructive chromatographic procedure that allows efficient elution and further analysis of the major lipid classes (neutral lipids, phospholipids, nonsialylated sphingolipids, and gangliosides) in their natural states from the same starting material. The procedure describes the use of solvent mixtures adapted to silicic acid column chromatography and permits 90-97% recovery of each of the above lipid groups. We have particularly concentrated on optimizing the efficient recovery of the diverse minor forms of gangliosides, free of other contaminants, from relatively small amounts of neural tissue. As model systems we have used in vivo and in vitro preparations of mammalian retina for which only fragmentary data are available on lipid composition. We show that relative to brain, retina contains, for example, twofold more sphingomyelin and sixfold more GD3 ganglioside. In turn, cultured retinal glial cells contain twofold higher levels of globoside and eightfold higher amounts of GM3 ganglioside with respect to intact retina. Compared to previously published techniques, we obtain improved total ganglioside recovery, with enrichment of poly-sialogangliosides. The technique presented here should be widely applicable to analyze global lipid composition of diverse biological samples.

Normal and reactive NG2+ glial cells are distinct from resting and activated microglia

We have previously used antibodies to the NG2 proteoglycan and the alpha receptor for platelet-derived growth factor (PDGF alpha receptor) to identify oligodendroglial progenitor cells in vivo and in vitro. It has recently become evident that the GD3 antigen, which has been widely used as a marker for oligodendrocyte progenitor cells, is also expressed by microglial cells. In this study we have examined the relationship between the NG2+/PDGF alpha receptor+ glial progenitor cells and microglial cells in normal developing and mature rat brain and in inflammatory lesions in mice with experimental autoimmune encephalomyelitis (EAE). Double-labeling of sections from normal rat brain using anti-NG2 antibodies and lectin from Griffonia simplicifolia (GSA I-B4) or monoclonal antibody 4H1 indicated that there is no overlap between NG2+ glial progenitor cells and microglia in the parenchyma of the central nervous system. In EAE lesions, both NG2+ cells and microglia, identified by antibodies to F4/80 and CD45, displayed reactive changes characterized by increased cell number and staining intensity and shortening and thickening of cell processes. Both cell types were found surrounding perivascular infiltrates of lymphocytes. Double-labeling EAE sections for NG2 and F4/80 or CD45 failed to reveal cells that co-expressed both antigens, suggesting that reactive NG2+ cells are distinct from activated microglia. However, a close spatial relationship between NG2+ cells and microglia was observed in the normal brain and to a greater extent in EAE, where processes of an activated microglial cell were sometimes seen to encircle an NG2+ cell. These observations are indicative of a functional interaction between microglia and the NG2+ glial cells.

Oligodendroglial progenitors labeled with the O4 antibody persist in the adult rat cerebral cortex in vivo

The monoclonal antibody O4 has been used to define a biologically distinct stage of the oligodendroglial lineage in vitro. Furthermore, O4+ oligodendroglial progenitors have been found in cell cultures derived from mature tissue, leading to speculation about the presence of oligodendroglial progenitors in the adult central nervous system (CNS). However, the existence of adult oligodendroglial progenitors has yet to be conclusively demonstrated in the intact animal. We have investigated the expression of O4 immunoreactivity in the developing and mature rat forebrain and the relationship of these cells to cells expressing the early oligodendroglial progenitor markers GD3 ganglioside and NG2 chondroitin sulfate proteoglycan, and to differentiated galactocerebroside expressing oligodendroglia. By the day of birth O4+ cells were already widely distributed throughout the formative corpus callosum and increased in number in the white matter and cortical gray matter over the first 2 postnatal weeks. In contrast to cell culture observations, most O4+ cells seen over this period failed to express GD3, although the majority did express NG2. Beginning at postnatal day 4, NG2+/O4-progenitors in the corpus callosum and cerebral cortical gray matter underwent a wave of differentiation into NG2+/O4+ cells and then into galactocerebroside-positive oligodendroglia. Interestingly, not all cells underwent this progression: a population remained as O4+/NG2+ progenitors. Furthermore, this O4+/NG2+ population persisted into adulthood and failed to express their GD3, galactocerebroside, RIP, or myelin basic protein (MBP). They were also distinguishable from glial fibrillary acidic protein+ and glutamine synthetase+ astrocytes and OX-42+ microglia. We therefore propose that these O4+/NG2+ cells represent adult oligodendroglial progenitors hitherto only described in cell culture.