脑病相关神经节苷脂研究进展

神经节苷脂是一种糖链结构上包含有唾液酸的酸性鞘糖脂,是动物细胞膜的重要组成成分,并在细胞膜表面上参与各种重要的生物学进程.正常生理情况下,脑内的神经节苷脂在神经细胞的形态稳定和神经信号的传递等生物进程中发挥至关重要的作用,这些生物进程和大脑的生长发育与认知发展密切相关.在一些患者各脑区检测到的神经节苷脂含量与种类的明显改变,提示着不同脑部疾病的发生与发展,例如在一些脱髓鞘疾病患者脑内常常伴随有神经节苷脂减少的现象.此外,定位于胞膜上的神经节苷脂还能极大地影响阿尔茨海默病等神经退行性疾病和胶质瘤等脑部肿瘤的发生和发展.以上所述的种种病症看似发病机制相去甚远,但这些脑病之间却因为神经节苷脂的联系而具有一定的共性和发病模式,例如在数年前流行于南美的寨卡病毒与常见的神经脱髓鞘疾病格林-巴利综合症均是由于自身B细胞产生的抗GQ1b神经节苷脂抗体与脑内神经细胞膜表面GQ1b的结合所引起的.本文就脑内数种疾病涉及神经节苷脂的发病机制进行总结并概括了几种可能的共同发病模式,以期未来在脑内疾病的诊断和治疗中提供一个新的思路.     

Gangliosides play important roles in the nervous system by regulating ion concentrations

Gangliosides are important components of the neuronal cell membrane and play a vital role in the development of neurons and the brain. They participate in neurotransmission and are considered as the structural basis of learning and memory. Gangliosides participate in several and important physiological processes, such as cell differentiation, cell signaling, neuroprotection, nerve regeneration and apoptosis. The stability of ion concentration in excitable cells is particularly important in the maintenance of a steady state of cells and in the regulation of physiological functions. Ion concentration has been found to be related to the ganglioside’s regulation in many neurological diseases, and several studies have found that they can stabilize intracellular ion concentration by regulating ion channels, which highlights their important regulatory role in neuronal excitability and synaptic transmission. Gangliosides can influence some forms of ion transport, by directly binding to ion transporters or through indirect binding and activation of transport proteins via appropriate signaling pathways. Therefore, the important and special role of gangliosides in the homeostasis of ion concentration is becoming a hot topic in the field and a theoretical basis in promoting help gangliosides use as key drugs for the treatment of nervous system diseases.

     

Functional Roles of Gangliosides in Neurodevelopment: An Overview of Recent Advances

Gangliosides are sialic acid-containing glycosphingolipids that are most abundant in the nervous system. They are localized primarily in the outer leaflets of plasma membranes and participated in cell–cell recognition, adhesion, and signal transduction and are integral components of cell surface microdomains or lipid rafts along with proteins, sphingomyelin and cholesterol. Ganglioside-rich lipid rafts play an important role in signaling events affecting neural development and the pathogenesis of certain diseases. Disruption of gangloside synthase genes in mice induces developmental defects and neural degeneration. Targeting ganglioside metabolism may represent a novel therapeutic strategy for intervention in certain diseases. In this review, we focus on recent advances on metabolic and functional studies of gangliosides in normal brain development and in certain neurological disorders.     

Imaging mass spectrometry detection of gangliosides species in the mouse brain following transient focal cerebral ischemia and long-term recovery

Gangliosides, a member of the glycosphingolipid family, are heterogeneously expressed in biological membranes and are particularly enriched within the central nervous system. Gangliosides consist of mono- or poly-sialylated oligosaccharide chains of variable lengths attached to a ceramide unit and are found to be intimately involved in brain disease development. The purpose of this study is to examine the spatial profile of ganglioside species using matrix-assisted laser desorption/ionization (MALDI) imaging (IMS) following middle cerebral artery occlusion (MCAO) reperfusion injury in the mouse. IMS is a powerful method to not only discriminate gangliosides by their oligosaccharide components, but also by their carbon length within their sphingosine base. Mice were subjected to a 30 min unilateral MCAO followed by long-term survival (up to 28 days of reperfusion). Brain sections were sprayed with the matrix 5-Chloro-2-mercaptobenzothiazole, scanned and analyzed for a series of ganglioside molecules using an Applied Biosystems 4800 MALDI TOF/TOF. Traditional histological and immunofluorescence techniques were performed to assess brain tissue damage and verification of the expression of gangliosides of interest. Results revealed a unique anatomical profile of GM1, GD1 and GT1b (d18:1, d20:1 as well as other members of the glycosphingolipid family). There was marked variability in the ratio of expression between ipsilateral and contralateral cortices for the various detected ganglioside species following MCAO-reperfusion injury. Most interestingly, MCAO resulted in the transient induction of both GM2 and GM3 signals within the ipsilateral hemisphere; at the border of the infarcted tissue. Taken together, the data suggest that brain region specific expression of gangliosides, particularly with respect to hydrocarbon length, may play a role in neuronal responses to injury.     

Ganglioside molecular species containing C18- and C20-sphingosine in mammalian nervous tissues and neuronal cell cultures

Gangliosides exist as a very complex mixture of species differing in both the hydrophilic and hydrophobic moieties. They are particularly abundant in the central nervous system (CNS), where they have been associated with development and maturation of the brain, neuritogenesis, synaptic transmission, memory formation and synaptic aging. Today, many data suggest that some of the effects exerted by gangliosides are due to interactions with proteins that participate in the transduction of signals through the membrane in membrane microdomains. A specific characteristic of CNS gangliosides is the structure of their long-chain base (LCB). In fact, considering all the mammalian cell sphingolipids, gangliosides, sulphatides, neutral glycosphingolipids, sphingomyelin and ceramides, it would seem that while the LCB with 18 carbons is the main component of all sphingolipids, only CNS gangliosides contain significant amounts of LCB with 20 carbons. C18-Sphingosine is always present in cell gangliosides; the individual ganglioside species containing C18-sphingosine increase during cell differentiation then remain constant during cell aging. Gangliosides containing C20-sphingosine are absent, or present only in traces, in undifferentiated cells but with the onset of cell differentiation they appear, their content slowly but continuously increasing throughout the life span. In this review we discuss the chemistry, physico-chemistry and metabolism of ganglioside species differing in LCB length and introduce the hypothesis that the varying ratio between C18- and C20-gangliosides during CNS development and aging can be instrumental in modulating membrane domain organisation and cell properties.     

Gangliosides in the nervous system

Gangliosides, sialic acid-containing glycosphingolipids, are embedded in neural plasma membranes to provide cell surface recognition sites with negative charges. Exogenous ligands such as bacterial toxins, hormones, growth factors, antibodies, viruses, and interferons bind to specific gangliosides to induce sequential activations of cellular metabolisms. Predominant expression of some of ganglioside series (A, B, C or hematosides) occurs during cell differentiation and transformation. Gangliosides may regulate cell growth and nerve sprouting, suggesting the potential therapeutic value for some neurological disorders. Current ganglioside research is more rapidly growing largely due to advancing methodologies.     

Dendritic morphology and spine density is not altered in motor cortex and dentate granular cells in mice lacking the ganglioside biosynthetic gene B4galnt1 - A quantitative Golgi cox study

Gangliosides are characteristic plasma membrane constituents of vertebrate brain used as milestones of neuronal development. As neuronal morphology is a good indicator of neuronal differentiation, we analyzed how lack of the ganglioside biosynthetic gene Galgt1 whose product is critical for production of four major adult mammalian brain complex gangliosides (GM1, GD1a, GD1b and GT1b) affects neuronal maturation in vivo. To define maturation of cortical neurons in mice lacking B4galnt1 we performed a morphological analysis of Golgi-Cox impregnated pyramidal neurons in primary motor cortex and granular cells of dentate gyrus in 3, 21 and 150 days old B4galnt1-null and wild type mice. Quantitative analysis of basal dendritic tree on layer III pyramidal neurons in the motor cortex showed very immature dendritic picture in both mice at postnatal day 3. At postnatal day 21 both mice reached adult values in dendritic length, complexity and spine density. No quantitative differences were found between B4galnt1-null and wild type mice in pyramidal cells of motor cortex or granular cells of dentate gyrus at any examined age. In addition, the general structural and neuronal organization of all brain structures, qualitatively observed on Nissl and Golgi-Cox, were similar Our results demonstrate that neurons can develop normal dendritic complexity and length without presence of complex gangliosides in vivo. Therefore, behavioral differences observed in B4galnt1-null mice may be attributed to functional rather than morphological level of dendrites and spines of cortical pyramidal neurons.     

Regional differences in brain gangliosides of a teleost fish following thermal acclimations

The ability of ectothermic vertebrates to adapt to thermal fluctuations in their environment is mainly based upon adaptive changes within the CNS. These changes are thought to be correlated with functional, metabolism changes in the central nervous system, especially in neuronal membranes. Gangliosides, being highly enriched in synaptic membranes (1)show characteristic perculiarities concerning concentration and molecular composition with regard to their sialylation status (2,3,4). In order to get further information concerning the biological function of gangliosides with respect to thermal adaptation, it was of interest to investigate possible correlation between the nervous ganglioside metabolism of different brain regions after various temperature adaptations.     

Imaging mass spectrometry technology and application on ganglioside study; visualization of age-dependent accumulation of C20-ganglioside molecular species in the mouse hippocampus

Gangliosides are particularly abundant in the central nervous system (CNS) and thought to play important roles in memory formation, neuritogenesis, synaptic transmission, and other neural functions. Although several molecular species of gangliosides have been characterized and their individual functions elucidated, their differential distribution in the CNS are not well understood. In particular, whether the different molecular species show different distribution patterns in the brain remains unclear. We report the distinct and characteristic distributions of ganglioside molecular species, as revealed by imaging mass spectrometry (IMS). This technique can discriminate the molecular species, raised from both oligosaccharide and ceramide structure by determining the difference of the mass-to-charge ratio, and structural analysis by tandem mass spectrometry. Gangliosides in the CNS are characterized by the structure of the long-chain base (LCB) in the ceramide moiety. The LCB of the main ganglioside species has either 18 or 20 carbons (i.e., C18- or C20-sphingosine); we found that these 2 types of gangliosides are differentially distributed in the mouse brain. While the C18-species was widely distributed throughout the frontal brain, the C20-species selectively localized along the entorhinal-hippocampus projections, especially in the molecular layer (ML) of the dentate gyrus (DG). We revealed development- and aging-related accumulation of the C-20 species in the ML-DG. Thus it is possible to consider that this brain-region specific regulation of LCB chain length is particularly important for the distinct function in cells of CNS.     

Distribution of major brain gangliosides in olfactory tract of frogs

Gangliosides are major cell-surface determinants in the central nervous system (CNS) of vertebrates, found both in neuronal and glial cell membranes. Together with cholesterol and glycosylphosphatidylinositol (GPI) - anchored proteins, gangliosides are involved in organization of plasma membrane microdomains. Based on biochemical studies, frog brain was previously described as having low quantities of gangliosides and their distribution pattern in specific brain regions was unknown. Using highly specific monoclonal antibodies generated against four major brain gangliosides (GM1, GD1a, GD1b and GT1b), we examined the distribution of these molecules in CNS of four different species of frogs (Rana esculenta, Rana temporaria, Bufo bufo and Bufo viridis). We also studied the distribution of myelin- associated glycoprotein (MAG), an inhibitor of axonal regeneration, which is a ligand for gangliosides GD1a and GT1b. Our results show that ganglioside GDla is expressed in neurons of olfactory bulb in all studied animals. In the brain of Rana sp., GD1a is expressed in the entire olfactory pathway, from olfactory bulbs to amygdala, while in Bufo sp. GD1a is restricted to the main olfactory bulb. Furthermore, we found that most of myelinated pathways in frogs express MAG, but do not express GD1a, which could be one of the reasons for better axon regeneration of neural pathways after CNS injury in amphibians in comparison to mammals.     

Regeneration of functional synaptic connections between widely separated neurons in the adult mammalian central nervous system

The responses to light of retinal ganglion cells with regenerated axons can be recorded from axons teased from peripheral nerve grafts replacing the optic nerve of the adult rat or hamster. These responses resemble those of normal retinal ganglion cells but can no longer be observed several months after grafting, concomitant with ongoing loss of the population of axotomized retinal ganglion cells. Synapses formed with neurons in the superior colliculus by retinal ganglion cell axons regenerated through peripheral nerve grafts mediate both excitatory and inhibitory responses. These experiments demonstrate that when provided with an appropriate milieu for elongation, neurons indigenous to the adult mammalian central nervous system can make functional reconnections with distant targets within the nervous system.     

Life without gangliosides

Gangliosides are sialic acid containing glycosphingolipids that are present on all plasma cell membranes. Although they represent the major sialoconjugates in the central nervous system, their precise functions remain obscure. We have generated a series of knockout mice with gene disruptions in the ganglioside biosynthetic pathway. Individually these mice lack subsets of gangliosides allowing investigations into their specific functions. By breeding mice to contain multiple mutations in the biosynthetic pathway we have now produced mice without neuronal gangliosides. These mice display an extremely severe phenotype and neuronal pathology highlighting the essential function of gangliosides in the central nervous system.     

GM1 Ganglioside is Involved in Epigenetic Activation Loci of Neuronal Cells

Gangliosides are sialic acid-containing glycosphingolipids that are most abundant in the nerve tissues. The quantity and expression pattern of gangliosides in brain change drastically throughout development and are mainly regulated through stage-specific expression of glycosyltransferase (ganglioside synthase) genes. We previously demonstrated that acetylation of histones H3 and H4 on the N-acetylgalactosaminyltransferase I (GalNAcT, GA2/GM2/GD2/GT2-synthase) gene promoter resulted in recruitment of trans-activation factors. In addition, we reported that epigenetic activation of the GalNAcT gene was also detected as accompanied by an apparent induction of neuronal differentiation in neural stem cells responding to an exogenous supplement of ganglioside GM1. Here, we present evidence supporting the concept that nuclear GM1 is associated with gene regulation in neuronal cells. We found that nuclear GM1 binds acetylated histones on the promoters of the GalNAcT and NeuroD1 genes in differentiated neurons. Our study demonstrates for the first time that GM1 interacts with chromatin via acetylated histones at the nuclear periphery of neuronal cells.     

Ganglioside metabolism in a transgenic mouse model of Alzheimer's disease: expression of Chol-1α antigens in the brain

The accumulation of Aβ (amyloid β-protein) is one of the major pathological hallmarks in AD (Alzheimer''s disease). Gangliosides, sialic acid-containing glycosphingolipids enriched in the nervous system and frequently used as biomarkers associated with the biochemical pathology of neurological disorders, have been suggested to be involved in the initial aggregation of Aβ. In the present study, we have examined ganglioside metabolism in the brain of a double-Tg (transgenic) mouse model of AD that co-expresses mouse/human chimaeric APP (amyloid precursor protein) with the Swedish mutation and human presenilin-1 with a deletion of exon 9. Although accumulation of Aβ was confirmed in the double-Tg mouse brains and sera, no statistically significant change was detected in the concentration and composition of major ganglio-N-tetraosyl-series gangliosides in the double-Tg brain. Most interestingly, Chol-1α antigens (cholinergic neuron-specific gangliosides), such as GT1aα and GQ1bα, which are minor species in the brain, were found to be increased in the double-Tg mouse brain. We interpret that the occurrence of these gangliosides may represent evidence for generation of cholinergic neurons in the AD brain, as a result of compensatory neurogenesis activated by the presence of Aβ.     

Localization of ganglioside 9-O-acetyl GD3 in point contacts of neuronal growth cones

Gangliosides are a large group of sialylated glycosphingolipids widely expressed in mammalian tissues. We have shown previously that the expression of 9-O-acetyl GD3 is highly correlated with periods of neurite outgrowth in the developing nervous system, and that the advance of dorsal root ganglia growth cones on laminin was halted in presence of an antibody specific for 9-O-acetyl GD3. In this work, we examined by immunocytochemistry and confocal microscopy whether this ganglioside is localized in point contacts in neuronal growth cones. We identified point contacts by immunoreactions with proteins, such as vinculin and beta1 integrin, known to be associated with these structures in growth cones. Our observations indicate that 9-O-acetyl GD3 is specifically associated with vinculin and beta1 integrin in point contacts of growth cones, suggesting a possible role for this particular ganglioside in the modulation of these contacts during neurite outgrowth.     

Ganglioside GD3 in the serum of tumor patients

Gangliosides of normal human blood serum and of blood serum of tumour hosts were studied. It has been shown the first time that ganglioside (NeuAc)2LacCer is present in the blood serum of different tumour hosts, but is absent in normal blood serum. The reasons for the appearance of this ganglioside in blood serum are discussed.     

The content and composition of gangliosides in brain subcellular fractions of the frog Rana temporaria

Ganglioside distribution in various frog brain subcellular fractions (myelin, microsomes, mitochondria, synaptosomes, plasma membranes of nerve endings and synaptic vesicles) was investigated. The synaptosomes and plasma membranes of nerve endings were found to be the main places of ganglioside localization, ganglioside concentration being 2.42 and 1.79 times higher than that in homogenates. Gangliosides were shown to be present in synaptic vesicles. The characteristic features of gangliosides from frog brain and its subcellular fractions are the predominance of polysialogangliosides with 3-5 sialic acid residues (up to 57.4%), low content of monosialogangliosides (not more than 7%) and the presence of disialogangliosides with short carbohydrate chain. The increase of ganglioside content per one nerve cell during phylogenetic development of vertebrates is discussed.     

Gangliosides of active and inactive neuroblastoma clones.

It is possible to divide neuroblastoma cells into clones able to synthesize neurotransmitters (active clones) or not (inactive clones). The analysis of gangliosides of active and inactive clones shows that their total lipid sialic acids is markedly lower than that of neuron-enriched fractions prepared from brain. The ganglioside pattern of the cultured cells also differs notably from those obtained with neuronal fractions from brain. The absence of tri- and tetrasialogangliosides and the presence of appreciable amounts of the simplest monosialogangliosides are particularly noticeable in the neuroblastoma. Morphological differentiation obtained by serum deprivation, dibutyryl cyclic AMP or bromodeoxyuridine does not restore a true neuronal pattern. Gangliosides could not therefore be used as a marker of neuronal differentiation in this type of cell. No correlations can be found between the ganglioside pattern and the ability of cells to synthesize neurotransmitters.     

Gangliosides of Active and Inactive Neuroblastoma Clones

It is possible to divide neuroblastoma cells into clones able to synthesize neurotransmitters (active clones) or not (inactive clones).
The analysis of gangliosides of active and inactive clones shows that their total lipid sialic acids is markedly lower than that of neuron-enriched fractions prepared from brain. The ganglioside pattern of the cultured cells also differs notably from those obtained with neuronal fractions from brain. The absence of tri- and tetrasialogangliosides and the presence of appreciable amounts of the simplest monosialogangliosides are particularly noticeable in the neuroblastoma. Morphological differentiation obtained by serum deprivation, dibutyryl cyclic AMP or bromodeoxyuridine does not restore a true neuronal pattern. Gangliosides could not therefore be used as a marker of neuronal differentiation in this type of cell. No correlations can be found between the ganglioside pattern and the ability of cells to synthesize neurotransmitters.     

Control of Cell Survival in Adult Mammalian Neurogenesis

The fact that continuous proliferation of stem cells and progenitors, as well as the production of new neurons, occurs in the adult mammalian central nervous system (CNS) raises several basic questions concerning the number of neurons required in a particular system. Can we observe continued growth of brain regions that sustain neurogenesis? Or does an elimination mechanism exist to maintain a constant number of cells? If so, are old neurons replaced, or are the new neurons competing for limited network access among each other? What signals support their survival and integration and what factors are responsible for their elimination? This review will address these and other questions regarding regulatory mechanisms that control cell-death and cell-survival mechanisms during neurogenesis in the intact adult mammalian brain.