Brain gangliosides and memory formation

SA supplementation during lactation promotes learning and memory by reducing H3K27me3 levels

INTRODUCTION

Sialic acid (SA) is an essential nutrient for brain development and cognition. Infants lack the capacity to synthesize sufficient SA independently, requiring reliance on maternal or exogenous sources. For early nutritional supplementation, elucidating how SA affects learning and memory is necessary.

OBJECTIVES

This study aimed to elucidate the critical time window for SA supplementation that best supports cognitive functions and hippocampal neural mechanisms.

METHODS

The MWM experiment was conducted to elucidate the critical time window and dose of SA supplementation. Morphological and electrophysiological studies were used to observe the structural and functional responses of hippocampal neurons that are exposed to SA. RNA sequencing, Western Blot, immunofluorescence, and electrophysiology were used to screen and validate possible neural mechanisms.

RESULTS

Our results show that SA supplementation during, but not after, the lactation period significantly improves learning and memory. SA promotes neurite outgrowth and increases synaptic transmission without affecting the intrinsic membrane properties of hippocampal CA1 neurons. The effect of SA on CA1 neuronal function is independent of the DG-CA3-CA1 loop. Also, long-term effects on synaptic plasticity are primarily due to intracellular epigenetic changes of H3K27me3 rather than direct binding of extracellular SA to membrane proteins. Consequently, our study indicates that decreased H3K27me3 promotes the glutamate-glutamine cycle under SA, thereby contributing to enhanced learning and memory.

CONCLUSION

Consequently, our study finds that decreased H3K27me3 promotes the glutamate-glutamine cycle under the influence of SA, thereby contributing to enhanced learning and memory. The potential implication of our findings is that SA in early life may contribute to the optimization of children's comprehensive cognitive function.

Deciphering mouse brain spatial diversity via glyco-lipidomic mapping

Gangliosides in the brain play a crucial role in modulating the integrity of vertebrate central nervous system in a region-specific manner. However, to date, a comprehensive structural elucidation of complex intact ganglioside isomers has not been achieved, resulting in the elusiveness into related molecular mechanism. Here, we present a glycolipidomic approach for isomer-specific and brain region-specific profiling of the mouse brain. Considerable region-specificity and commonality in specific group of regions are highlighted. Notably, we observe a similarity in the abundance of major isomers, GD1a and GD1b, within certain regions, which provides significant biological implications with interpretation through the lens of a theoretical retrosynthetic state-transition network. Furthermore, A glycocentric-omics approaches using gangliosides and N-glycans reveal a remarkable convergence in spatial dynamics, providing valuable insight into molecular interaction network. Collectively, this study uncovers the spatial dynamics of intact glyco-conjugates in the brain, which are relevant to regional function and accelerates the discovery of potential therapeutic targets for brain diseases.

Comparison and Possible Binding Orientations of SARS-CoV-2 Spike N-Terminal Domain for Gangliosides GM3 and GM1

SARS-CoV-2 spike glycoprotein is anchored by gangliosides. The sialic acid in the ganglioside headgroup is responsible for virus attachment and entry into host cells. We used coarse-grained (CG) molecular dynamics simulations to expand on our previous study of GM1 interaction with two different orientations of the SARS-CoV-2 S1 subunit N-terminal domain (NTD) and to confirm the role of sialic acid receptors in driving the viral receptor; GM3 was used as another ganglioside on the membrane. Because of the smaller headgroup, sialic acid is crucial in GM3 interactions, whereas GM1 interacts with NTD via both the sialic acid and external galactose. In line with our previous findings for NTD orientations in GM1 binding, we identified two orientations, "compact" and "distributed", comprising sugar receptor-interacting residues in GM3-embedded lipid bilayers. Gangliosides in closer proximity to the compact NTD orientation might cause relatively greater restrictions to penetrate the bilayer. However, the attachment of a distributed NTD orientation with more negative interaction energies appears to facilitate GM1/GM3 to move quickly across the membrane. Our findings likely shed some light on the orientations that the NTD receptor acquires during the early phases of interaction with GM1 and GM3 in a membrane environment.

Which Moiety Drives Gangliosides to Form Nanodomains?

Gangliosides are important glycosphingolipids involved in a multitude of physiological functions. From a physicochemical standpoint, this is related to their ability to self-organize into nanoscopic domains, even at molar concentrations of one per 1000 lipid molecules. Despite recent experimental and theoretical efforts suggesting that a hydrogen bonding network is crucial for nanodomain stability, the specific ganglioside moiety decisive for the development of these nanodomains has not yet been identified. Here, we combine an experimental technique achieving nanometer resolution (Förster resonance energy transfer analyzed by Monte Carlo simulations) with atomistic molecular dynamic simulations to demonstrate that the sialic acid (Sia) residue(s) at the oligosaccharide headgroup dominates the hydrogen bonding network between gangliosides, driving the formation of nanodomains even in the absence of cholesterol or sphingomyelin. Consequently, the clustering pattern of asialoGM₁, a Sia-depleted glycosphingolipid bearing three glyco moieties, is more similar to that of structurally distant sphingomyelin than that of the closely related gangliosides GM₁ and GD_1a with one and two Sia groups, respectively.

Sialic acid and anti-ganglioside M1 antibodies are invaluable biomarkers correlated with the severity of autism spectrum disorder

BACKGROUND

Autism spectrum disorders (ASD) are devastating neurodevelopmental disorders that showed global increased prevalence. They are characterized by impairment of social communication and stereotyped patterns.

OBJECTIVE

This study aimed at measuring the levels of total sialic acid (SA) and anti-ganglioside M1 (anti- GM1) IgG antibodies as essential biomarkers in a cohort of children with ASD to identify their diagnostic yield as well as their correlation with the severity of autistic behaviors.

METHODS

The demographic characteristics, anthropometric measurements, and clinical data were recorded. The levels of total plasma SA and serum anti-GM1 IgG antibodies levels were measured in 100 children with ASD and 100 healthy controls. The severity of ASD-related symptoms was assessed by using the Childhood Autism Rating Scale (CARS).

RESULTS

Children with ASD had significantly higher levels of both SA and anti-GM1 antibodies than healthy controls (p < 0.001). SA showed a statistically significant moderate diagnostic performance while anti-GM1 antibody showed a statistically significant high diagnostic in differentiating severe from mild to moderate autism. Moreover, both SA and anti-GM1 antibodies levels were significantly correlated to the severity of ASD symptoms (p < 0.001).

CONCLUSION

The significantly increased levels of SA and anti-GM1 antibodies in children with ASD and their correlation with autism-related symptoms suggest their possible etiopathogenic role in autism as one of the pediatric autoimmune neuropsychiatric disorders. However, further large-scale studies are still needed to explore their possible bidirectional relationship as biomarkers for autism.

Human Breast Milk: The Key Role in the Maturation of Immune, Gastrointestinal and Central Nervous Systems: A Narrative Review

Premature birth is a major cause of mortality and morbidity in the pediatric population. Because their immune, gastrointestinal and nervous systems are not fully developed, preterm infants (<37 weeks of gestation) and especially very preterm infants (VPIs, <32 weeks of gestation) are more prone to infectious diseases, tissue damage and future neurodevelopmental impairment. The aim of this narrative review is to report the immaturity of VPI systems and examine the role of Human Breast Milk (HBM) in their development and protection against infectious diseases, inflammation and tissue damage. For this purpose, we searched and synthesized the data from the existing literature published in the English language. Studies revealed the significance of HBM and indicate HBM as the best dietary choice for VPIs.

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.

Cognitive improvement effect of nervonic acid and essential fatty acids on rats ingesting Acer truncatum Bunge seed oil revealed by lipidomics approach

Acer truncatum Bunge seed oil (ASO) is rich in ω-9 (53.93%) and ω-6 (30.7%) fatty acids (FAs) and characterized by 3-7% nervonic acid (NA, C24:1ω-9). Evidence suggests that ω-9 FAs such as NA participate in processes of cognitive improvement; however, their mechanism remains ambiguous. In this study, we investigated the effect of ASO on rat memory and the change in lipid profiling and underlying metabolism. After ASO was administrated to rats for one, three and seven days, their capacity for learning and memory significantly increased via the MWM test. Lipid profiling showed alterations in a wide range of metabolic features after ASO was administrated to the rats, in which sphingolipids (SP) in the serum and glycerophospholipids (GP) in the brain were regulated significantly. The changes in the fatty acids in the serum and brain showed the synergetic effects of NA, EA, OA and DHA, where NA, EA and OA exhibited similar change trends. The enrichment analysis based on KEGG indicated that ASO supplementation evoked the pathways of neurotrophin signaling, glycerophospholipid metabolism and sphingolipid metabolism, which are related to memory and cognition improvement. Among the metabolites with different molecular forms, the biomarkers with C24:1ω-9 chains exhibited a positive correlation with others both in the serum SP and brain GP. These results suggest the synergistic effects of ω-9 FAs and that their conversion into each other may result in enhanced cognition in rats ingesting Acer truncatum Bunge seed oil.

Gangliosides as Biomarkers of Human Brain Diseases: Trends in Discovery and Characterization by High-Performance Mass Spectrometry

Gangliosides are effective biochemical markers of brain pathologies, being also in the focus of research as potential therapeutic targets. Accurate brain ganglioside mapping is an essential requirement for correlating the specificity of their composition with a certain pathological state and establishing a well-defined set of biomarkers. Among all bioanalytical methods conceived for this purpose, mass spectrometry (MS) has developed into one of the most valuable, due to the wealth and consistency of structural information provided. In this context, the present article reviews the achievements of MS in discovery and structural analysis of gangliosides associated with severe brain pathologies. The first part is dedicated to the contributions of MS in the assessment of ganglioside composition and role in the specific neurodegenerative disorders: Alzheimer’s and Parkinson’s diseases. A large subsequent section is devoted to cephalic disorders (CD), with an emphasis on the MS of gangliosides in anencephaly, the most common and severe disease in the CD spectrum. The last part is focused on the major accomplishments of MS-based methods in the discovery of ganglioside species, which are associated with primary and secondary brain tumors and may either facilitate an early diagnosis or represent target molecules for immunotherapy oriented against brain cancers.

Plasma Membrane Calcium ATPase-Neuroplastin Complexes Are Selectively Stabilized in GM1-Containing Lipid Rafts

The recent identification of plasma membrane (Ca²⁺)-ATPase (PMCA)-Neuroplastin (Np) complexes has renewed attention on cell regulation of cytosolic calcium extrusion, which is of particular relevance in neurons. Here, we tested the hypothesis that PMCA-Neuroplastin complexes exist in specific ganglioside-containing rafts, which could affect calcium homeostasis. We analyzed the abundance of all four PMCA paralogs (PMCA1-4) and Neuroplastin isoforms (Np65 and Np55) in lipid rafts and bulk membrane fractions from GM2/GD2 synthase-deficient mouse brains. In these fractions, we found altered distribution of Np65/Np55 and selected PMCA isoforms, namely PMCA1 and 2. Cell surface staining and confocal microscopy identified GM1 as the main complex ganglioside co-localizing with Neuroplastin in cultured hippocampal neurons. Furthermore, blocking GM1 with a specific antibody resulted in delayed calcium restoration of electrically evoked calcium transients in the soma of hippocampal neurons. The content and composition of all ganglioside species were unchanged in Neuroplastin-deficient mouse brains. Therefore, we conclude that altered composition or disorganization of ganglioside-containing rafts results in changed regulation of calcium signals in neurons. We propose that GM1 could be a key sphingolipid for ensuring proper location of the PMCA-Neuroplastin complexes into rafts in order to participate in the regulation of neuronal calcium homeostasis.

Influence of Dietary Polar Lipid Supplementation on Memory and Longitudinal Brain Development

Polar lipids, which are found in human milk, serve essential functions within biological membranes, hence their importance in brain development and cognition. Therefore, we aimed to evaluate the longitudinal effects on brain macrostructural and microstructural development and recognition memory of early-life polar lipid supplementation using the translational pig model. Twenty-eight intact (i.e., not castrated) male pigs were provided either a control diet (n = 14) or the control diet supplemented with polar lipids (n = 14) from postnatal day 2 until postnatal week 4. After postnatal week 4, all animals were provided the same nutritionally-adequate diets until postnatal week 24. Pigs underwent magnetic resonance imaging at 8 longitudinal time-points to model brain macrostructural and microstructural developmental trajectories. The novel object recognition task was implemented at postnatal weeks 4 and 8 to evaluate recognition memory. Subtle differences were observed between groups in hippocampal absolute brain volumes and fractional anisotropy, and no differences in myelin water fraction developmental patterns were noted. Behavioral outcomes did not differ in recognition memory, and only minimal differences were observed in exploratory behaviors. Our findings suggest that early-life dietary supplementation of polar lipids has limited effect on brain developmental patterns, object recognition memory, and exploratory behaviors.

Sialometabolism in Brain Health and Alzheimer's Disease

Sialic acids refer to a unique family of acidic sugars with a 9-carbon backbone that are mostly found as terminal residues in glycan structures of glycoconjugates including both glycoproteins and glycolipids. The highest levels of sialic acids are expressed in the brain where they regulate neuronal sprouting and plasticity, axon myelination and myelin stability, as well as remodeling of mature neuronal connections. Moreover, sialic acids are the sole ligands for microglial Siglecs (sialic acid-binding immunoglobulin-type lectins), and sialic acid-Siglec interactions have been indicated to play a critical role in the regulation of microglial homeostasis in a healthy brain. The recent discovery of CD33, a microglial Siglec, as a novel genetic risk factor for late-onset Alzheimer's disease (AD), highlights the potential role of sialic acids in the development of microglial dysfunction and neuroinflammation in AD. Apart from microglia, sialic acids have been found to be involved in several other major changes associated with AD. Elevated levels of serum sialic acids have been reported in AD patients. Alterations in ganglioside (major sialic acid carrier) metabolism have been demonstrated as an aggravating factor in the formation of amyloid pathology in AD. Polysialic acids are linear homopolymers of sialic acids and have been implicated to be an important regulator of neurogenesis that contributes to neuronal repair and recovery from neurodegeneration such as in AD. In summary, this article reviews current understanding of neural functions of sialic acids and alterations of sialometabolism in aging and AD brains. Furthermore, we discuss the possibility of looking at sialic acids as a promising novel therapeutic target for AD intervention.

Simulating the enzymes of ganglioside biosynthesis with Glycologue

Gangliosides are an important class of sialylated glycosphingolipids linked to ceramide that are a component of the mammalian cell surface, especially those of the central nervous system, where they function in intercellular recognition and communication. We describe an in silico method for determining the metabolic pathways leading to the most common gangliosides, based on the known enzymes of their biosynthesis. A network of 41 glycolipids is produced by the actions of the 10 enzymes included in the model. The different ganglioside nomenclature systems in common use are compared and a systematic variant of the widely used Svennerholm nomenclature is described. Knockouts of specific enzyme activities are used to simulate congenital defects in ganglioside biosynthesis, and altered ganglioside status in cancer, and the effects on network structure are predicted. The simulator is available at the Glycologue website, https://glycologue.org/.

Current Perspective of Sialylated Milk Oligosaccharides in Mammalian Milk: Implications for Brain and Gut Health of Newborns

Human milk oligosaccharides (HMOs) are the third most abundant solid component after lactose and lipids of breast milk. All mammal milk contains soluble oligosaccharides, including neutral milk oligosaccharides (NMOs) without sialic acid (Sia) moieties and acidic oligosaccharides or sialylated milk oligosaccharides (SMOs) with Sia residues at the end of sugar chains. The structural, biological diversity, and concentration of milk oligosaccharides in mammalian milk are significantly different among species. HMOs have multiple health benefits for newborns, including development of immune system, modification of the intestinal microbiota, anti-adhesive effect against pathogens, and brain development. Most infant formulas lack oligosaccharides which resemble HMOs. Formula-fed infants perform poorly across physical and psychological wellbeing measures and suffer health disadvantages compared to breast-fed infants due to the differences in the nutritional composition of breast milk and infant formula. Of these milk oligosaccharides, SMOs are coming to the forefront of research due to the beneficial nature of Sia. This review aims to critically discuss the current state of knowledge of the biology and role of SMOs in human milk, infant formula milks, and milk from several other species on gut and brain health of human and animal offspring.

Lasting alterations induced in glial cell phenotypes by short exposure to alcohol during embryonic development in zebrafish

Despite the known teratogenic effects of alcohol (ethanol) on the developing human fetus, the prevalence of fetal alcohol spectrum disorder (FASD) is not decreasing. Appropriate treatment for this life-long disease has not been developed, and even diagnostic biomarkers are unavailable. FASD remains a large unmet medical need. Numerous animal models have been developed to mimic FASD and study potential underlying biological mechanisms. However, most of these models focused on neuronal phenotypes. Given that glial cells represent the majority of cells in the vertebrate brain, and given the increasingly appreciated roles they play in a myriad of neuronal functions as well as CNS disorders, we decided to investigate potential embryonic alcohol exposure induced changes in them. Building upon a previously introduced zebrafish model of milder and most prevalent forms of FASD, we investigated the effect of a 2-hour-long exposure to alcohol (1% vol/vol bath concentration) employed at the 24^th hour postfertilization stage of development of zebrafish on a number of glial cell-related phenotypes. We studied oligodendrocyte, astrocyte as well as microglia-related phenotypes using immunohistochemistry, lipid, and enzyme activity analyses. We report significant changes in wide-spread glial cell phenotypes induced by embryonic alcohol exposure in the zebrafish brain and conclude that the zebrafish will advance our understanding of the mechanisms of this devastating disorder.

Rameli MA, Jaoi Edward M, Mohd Hanafi N, Abdul Aziz S, Abu Hassim H, Mohd Noor MH, Ahmad H. The effects of dietary edible bird nest supplementation on learning and memory functions of multigenerational mice

INTRODUCTION

Edible bird nest (EBN) is a natural food product produced from edible nest swiftlet's saliva which consists of glycoproteins as one of its main components; these glycoproteins contain an abundant of sialic acid. The dietary EBN supplementation has been reported to enhance brain functions in mammals and that the bioactivities and nutritional value of EBN are important during periods of rapid brain growth particularly for preterm infant. However, the effects of EBN in maternal on multigeneration learning and memory function still remain unclear. Thus, the present study aimed to determine the effects of maternal EBN supplementation on learning and memory function of their first (F1)- and second (F2)-generation mice.

METHODS

CJ57BL/6 breeder F0 mice were fed with EBN (10 mg/kg) from different sources. After 6 weeks of diet supplementations, the F0 animals were bred to produce F1 and F2 animals. At 6 weeks of age, the F1 and F2 animals were tested for spatial recognition memory using a Y-maze test. The sialic acid content from EBN and brain gene expression were analyzed using HPLC and PCR, respectively.

RESULTS

All EBN samples contained glycoprotein with high level of sialic acid. Dietary EBN supplementation also showed an upregulation of GNE, ST8SiaIV, SLC17A5, and BDNF mRNA associated with an improvement in Y-maze cognitive performance in both generations of animal. Qualitatively, the densities of synaptic vesicles in the presynaptic terminal were higher in the F1 and F2 animals which might derive from maternal EBN supplementation.

CONCLUSION

This study provided a solid foundation toward the growing research on nutritional intervention from dietary EBN supplementation on cognitive and neurological development in the generation of mammals.

Physiology of gangliosides and the role of antiganglioside antibodies in human diseases

Gangliosides are structurally and functionally polymorphic sialic acid containing glycosphingolipids that are widely distributed in the human body. They play important roles in protecting us against immune attacks, yet they can become targets for autoimmunity and act as receptors for microbes, like the influenza viruses, and toxins, such as the cholera toxin. The expression patterns of gangliosides vary in different tissues, during different life periods, as well as in different animals. Antibodies against gangliosides (AGA) can target immune attack e.g., against neuronal cells and neutralize their complement inhibitory activity. AGAs are important especially in acquired demyelinating immune-mediated neuropathies, like Guillain-Barré syndrome (GBS) and its variant, the Miller-Fisher syndrome (MFS). They can emerge in response to different microbial agents and immunological insults. Thereby, they can be involved in a variety of diseases. In addition, antibodies against GM3 were found in the sera of patients vaccinated with Pandemrix®, who developed secondary narcolepsy, strongly supporting the autoimmune etiology of the disease.

Sphingolipid metabolism - an ambiguous regulator of autophagy in the brain

In mammals, the brain exhibits the highest lipid content in the body next to adipose tissue. Complex sphingolipids are characteristic compounds of neuronal membranes. Vital neural functions including information flux and transduction occur along these membranes. It is therefore not surprising that neuronal function and survival is dependent on the metabolism of these lipids. Autophagy is a critical factor for the survival of post-mitotic neurons. On the one hand, it fulfils homeostatic and waste-recycling functions and on the other hand, it constitutes an effective strategy to eliminate harmful proteins that cause neuronal death. A growing number of experimental data indicate that several sphingolipids as well as enzymes catalyzing their metabolic transformations efficiently but very differently affect neuronal autophagy and hence survival. This review attempts to elucidate the roles and mechanisms of sphingolipid metabolism with regard to the regulation of autophagy and its consequences for brain physiology and pathology.

Heme Oxygenase-1 May Affect Cell Signalling via Modulation of Ganglioside Composition

Heme oxygenase 1 (Hmox1), a ubiquitous enzyme degrading heme to carbon monoxide, iron, and biliverdin, is one of the cytoprotective enzymes induced in response to a variety of stimuli, including cellular oxidative stress. Gangliosides, sialic acid-containing glycosphingolipids expressed in all cells, are involved in cell recognition, signalling, and membrane stabilization. Their expression is often altered under many pathological and physiological conditions including cell death, proliferation, and differentiation. The aim of this study was to assess the possible role of Hmox1 in ganglioside metabolism in relation to oxidative stress. The content of liver and brain gangliosides, their cellular distribution, and mRNA as well as protein expression of key glycosyltransferases were determined in Hmox1 knockout mice as well as their wild-type littermates. To elucidate the possible underlying mechanisms between Hmox1 and ganglioside metabolism, hepatoblastoma HepG2 and neuroblastoma SH-SY5Y cell lines were used for in vitro experiments. Mice lacking Hmox1 exhibited a significant increase in concentrations of liver and brain gangliosides and in mRNA expression of the key enzymes of ganglioside metabolism. A marked shift of GM1 ganglioside from the subsinusoidal part of the intracellular compartment into sinusoidal membranes of hepatocytes was shown in Hmox1 knockout mice. Induction of oxidative stress by chenodeoxycholic acid in vitro resulted in a significant increase in GM3, GM2, and GD1a gangliosides in SH-SY5Y cells and GM3 and GM2 in the HepG2 cell line. These changes were abolished with administration of bilirubin, a potent antioxidant agent. These observations were closely related to oxidative stress-mediated changes in sialyltransferase expression regulated at least partially through the protein kinase C pathway. We conclude that oxidative stress is an important factor modulating synthesis and distribution of gangliosides in vivo and in vitro which might affect ganglioside signalling in higher organisms.

MALDI imaging delineates hippocampal glycosphingolipid changes associated with neurotoxin induced proteopathy following neonatal BMAA exposure

The environmental toxin β-N-methylamino-L-alanine (BMAA) has been proposed to contribute to neurodegenerative diseases. We have previously shown that neonatal exposure to BMAA results in dose-dependent cognitive impairments, proteomic alterations and progressive neurodegeneration in the hippocampus of adult rats. A high BMAA dose (460mg/kg) also induced intracellular fibril formation, increased protein ubiquitination and enrichment of proteins important for lipid transport and metabolism. The aim of this study was therefore to elucidate the role of neuronal lipids in BMAA-induced neurodegeneration. By using matrix assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS), we characterized the spatial lipid profile in the hippocampus of six month-old rats that were treated neonatally (postnatal days 9-10) with 460mg/kg BMAA. Multivariate statistical analysis revealed long-term changes in distinct ganglioside species (GM, GD, GT) in the dentate gyrus. These changes could be a consequence of direct effects on ganglioside biosynthesis through the b-series (GM3-GD3-GD2-GD1b-GT1b) and may be linked to astrogliosis. Complementary immunohistochemistry experiments towards GFAP and S100β further verified the role of increased astrocyte activity in BMAA-induced brain damage. This highlights the potential of imaging MS for probing chemical changes associated with neuropathological mechanisms in situ. This article is part of a Special Issue entitled: MALDI Imaging, edited by Dr. Corinna Henkel and Prof. Peter Hoffmann.

Effect of Dietary Complex Lipids on the Biosynthesis of Piglet Brain Gangliosides

Gangliosides, found in mammalian milk, are known for their roles in brain development of the newborn. However, the mechanism involved in the impact of dietary gangliosides on brain metabolism is not fully understood. The impact of diets containing complex lipids rich in milk-derived ganglioside GD3 on the biosynthesis of gangliosides (assessed from the incorporation of deuterium) in the frontal lobe of a piglet model is reported. Higher levels of incorporation of deuterium was observed in the GM1 and GD1a containing stearic acid in samples from piglets fed milk containing 18.2 μg/mL of GD3 compared to that in those fed milk containing 25 μg/mL of GD3. This could suggest that the gangliosides from the diet may be used as a precursor for de novo biosynthesis of brain gangliosides or lead to the reduction of de novo biosynthesis of these gangliosides. This effect was more pronounced in the left compared to that in the right brain hemisphere.

The role of gangliosides in neurodevelopment

Gangliosides are important components of neuronal cell membranes and it is widely accepted that they play a critical role in neuronal and brain development. They are functionally involved in neurotransmission and are thought to support the formation and stabilization of functional synapses and neural circuits required as the structural basis of memory and learning. Available evidence, as reviewed herein, suggests that dietary gangliosides may impact positively on cognitive functions, particularly in the early postnatal period when the brain is still growing. Further, new evidence suggests that the mechanism of action may be through an effect on the neuroplasticity of the brain, mediated through enhanced synaptic plasticity in the hippocampus and nigro-striatal dopaminergic pathway.

Effects of gangliosides on the activity of the plasma membrane Ca2+-ATPase

Control of intracellular calcium concentrations ([Ca(2+)]i) is essential for neuronal function, and the plasma membrane Ca(2+)-ATPase (PMCA) is crucial for the maintenance of low [Ca(2+)]i. We previously reported on loss of PMCA activity in brain synaptic membranes during aging. Gangliosides are known to modulate Ca(2+) homeostasis and signal transduction in neurons. In the present study, we observed age-related changes in the ganglioside composition of synaptic plasma membranes. This led us to hypothesize that alterations in ganglioside species might contribute to the age-associated loss of PMCA activity. To probe the relationship between changes in endogenous ganglioside content or composition and PMCA activity in membranes of cortical neurons, we induced depletion of gangliosides by treating neurons with d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (d-PDMP). This caused a marked decrease in the activity of PMCA, which suggested a direct correlation between ganglioside content and PMCA activity. Neurons treated with neuraminidase exhibited an increase in GM1 content, a loss in poly-sialoganglioside content, and a decrease in PMCA activity that was greater than that produced by d-PDMP treatment. Thus, it appeared that poly-sialogangliosides had a stimulatory effect whereas mono-sialogangliosides had the opposite effect. Our observations add support to previous reports of PMCA regulation by gangliosides by demonstrating that manipulations of endogenous ganglioside content and species affect the activity of PMCA in neuronal membranes. Furthermore, our studies suggest that age-associated loss in PMCA activity may result in part from changes in the lipid environment of this Ca(2+) transporter.

Ganglioside biochemistry

Gangliosides are sialic acid-containing glycosphingolipids. They occur especially on the cellular surfaces of neuronal cells, where they form a complex pattern, but are also found in many other cell types. The paper provides a general overview on their structures, occurrence, and metabolism. Key functional, biochemical, and pathobiochemical aspects are summarized.

Association of complex lipids containing gangliosides with cognitive development of 6-month-old infants

BACKGROUND

Human breastmilk contains gangliosides which may play an important role in infant neurodevelopment.

AIM

A pilot study was conducted to assess the impact of infant formula supplemented with gangliosides from complex milk lipid on cognitive functions of normal healthy infants.

STUDY DESIGN

The study was a double-blind, randomized, controlled, parallel group clinical trial in which infants received the treatment or control product from 2 to 8 weeks of age until 24 weeks of age. The control group (n=30) received standard infant formula and the treatment group (n=29) received the same formula supplemented with complex milk lipid to increase the ganglioside content to approximately 11 to 12 μg/ml. A reference group (n=32) consisted of normal healthy exclusively breast-fed infants.

OUTCOME MEASURES

Cognitive development using the Griffith Scales and serum gangliosides was measured before (2-8 weeks of age) and after intervention (24 weeks of age).

RESULTS

Ganglioside supplementation using complex milk lipids significantly increased ganglioside serum levels (control group vs treatment group, P=0.002) and resulted in increased scores for Hand and Eye coordination IQ (P<0.006), Performance IQ (P<0.001) and General IQ (P=0.041). Cognitive development scores and serum ganglioside levels for the treatment group did not differ from the reference group.

CONCLUSIONS

Supplementation of infant formula with complex milk lipid to enhance ganglioside content appears to have beneficial effects on cognitive development in healthy infants aged 0-6 months, which may be related to increased serum ganglioside levels.

Molecular mechanism underlying sialic acid as an essential nutrient for brain development and cognition

The early stages of neurodevelopment in infants are crucial for establishing neural structures and synaptic connections that influence brain biochemistry well into adulthood. This postnatal period of rapid neural growth is of critical importance for cell migration, neurite outgrowth, synaptic plasticity, and axon fasciculation. These processes thus place an unusually high demand on the intracellular pool of nutrients and biochemical precursors. Sialic acid (Sia), a family of 9-carbon sugar acids, occurs in large amounts in human milk oligosaccharides and is an essential component of brain gangliosides and sialylated glycoproteins, particularly as precursors for the synthesis of the polysialic acid (polySia) glycan that post-translationally modify the cell membrane-associated neural cell adhesion molecules (NCAM). Human milk is noteworthy in containing exceptionally high levels of Sia-glycoconjugates. The predominate form of Sia in human milk is N-acetylneuraminic acid (Neu5Ac). Infant formula, however, contains low levels of Sia consisting of both Neu5Ac and N-glycolyneuraminic acid (Neu5Gc). Current studies implicate Neu5Gc in several human inflammatory diseases. Polysialylated NCAM and neural gangliosides both play critical roles in mediating cell-to-cell interactions important for neuronal outgrowth, synaptic connectivity, and memory formation. A diet rich in Sia also increases the level of Sia in the brains of postnatal piglets, the expression level of 2 learning-related genes, and enhances learning and memory.

Highly sensitive localization analysis of gangliosides and sulfatides including structural isomers in mouse cerebellum sections by combination of laser microdissection and hydrophilic interaction liquid chromatography/electrospray ionization mass spectrometry with theoretically expanded multiple reaction monitoring

Liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) is suitable for analysis of glycosphingolipids such as fragile gangliosides avoiding the use of the sialic acid elimination. However, it was not possible to distinguish the structural isomers such as GD1a and GD1b with reversed-phase LC/ESI-MS by hydrophobic interaction. Here we report an effective method for targeted analysis of theoretically expanded ganglioside molecular species including structural isomers by hydrophilic interaction liquid chromatography (HILIC)/ESI-MS with multiple reaction monitoring (MRM). As a result of MRM analysis of glycosphingolipid mixtures from porcine brain, each of the lipid classes was detected within 25 min in the following order: sulfatides > GM3 > GM2 > GM1 > GD3 > GD1a > GD2 > GD1b > GT1a > GT1b > GQ1b. For the advanced application, localization analysis of postnatal day 15 (P15) mouse cerebellum layered structures was carried out by combination of MRM and laser microdissection (LMD). As a result, GM3, GD1a, GT1b and GQ1b were abundantly detected in the molecular and granular layers, whereas GM1 was widely presented in each layered structure. These gangliosides were mainly composed of d18:1-18:0 and d18:1-20:0, but GM3 was d18:1-16:0 and d18:1-20:0. Meanwhile, sulfatide molecular species were mostly localized in the myelinated fibers and scarcely found in the molecular layer. These results suggested that our method is suitable to detect a variety of ganglioside classes and sulfatides with high sensitivity at the molecular species level and effective for localization analysis of these glycosphingolipids from mouse brain sections.

Elimination of GD3 synthase improves memory and reduces amyloid-beta plaque load in transgenic mice

Gangliosides have been shown to be necessary for beta-amyloid (Abeta) binding and aggregation. GD3 synthase (GD3S) is responsible for biosynthesis of the b- and c-series gangliosides, including two of the four major brain gangliosides. We examined Abeta-ganglioside interactions in neural tissue from mice lacking the gene coding for GD3S (St8sia1), and in a double-transgenic (APP/PSEN1) mouse model of Alzheimer's disease cross-bred with GD3S-/- mice. In primary neurons and astrocytes lacking GD3S, Abeta-induced cell death and Abeta aggregation were inhibited. Like GD3S-/- and APP/PSEN1 double-transgenic mice, APP/PSEN1/GD3S-/- "triple-mutant" mice are indistinguishable from wild-type mice on casual examination. APP/PSEN1 double-transgenics exhibit robust impairments on a number of reference-memory tasks. In contrast, APP/PSEN1/GD3S-/- triple-mutant mice performed as well as wild-type control and GD3S-/- mice. Consistent with the behavioral improvements, both aggregated and unaggregated Abeta and associated neuropathology were almost completely eliminated in triple-mutant mice. These results suggest that GD3 synthase may be a novel therapeutic target to combat the cognitive deficits, amyloid plaque formation, and neurodegeneration that afflict Alzheimer's patients.

Top-down glycolipidomics: fragmentation analysis of ganglioside oligosaccharide core and ceramide moiety by chip-nanoelectrospray collision-induced dissociation MS2-MS6

We developed a straightforward approach for high-throughput top-down glycolipidomics based on fully automated chip-nanoelectrospray (nanoESI) high-capacity ion trap (HCT) multistage mass spectrometry (MSn) by collision-induced dissociation (CID) in the negative ion mode. The method was optimized and tested on a polysialylated ganglioside fraction (GT1b), which was profiled by MS1 and sequenced in tandem MS up to MS6 in the same experiment. Screening of the fraction in the MS1 mode indicated the occurrence of six [M-2H]2- ions which, according to calculation, support 13 GT1 variants differing in their relative molecular mass due to dissimilar ceramide (Cer) constitutions. By stepwise CID MS2-MS5 on the doubly charged ion at m/z 1077.20 corresponding to a ubiquitous GT1b structure, the complete characterization of its oligosaccharide core including the identification of sialylation sites was achieved. Structure of the lipid moiety was further elucidated by CID MS6 analysis carried out using the Y0 fragment ion, detected in MS5, as a precursor. MS6 fragmentation resulted in a pattern supporting a single ceramide form having the less common (d20 : 1/18 : 0) configuration. The entire top-down experiment was performed in a high-throughput regime in less than 3 min of measurement, with an analysis sensitivity situated in the subpicomolar range.

Sialic acid is an essential nutrient for brain development and cognition

The rapid growth of infant brains places an exceptionally high demand on the supply of nutrients from the diet, particularly for preterm infants. Sialic acid (Sia) is an essential component of brain gangliosides and the polysialic acid (polySia) chains that modify neural cell adhesion molecules (NCAM). Sia levels are high in human breast milk, predominately as N-acetylneuraminic acid (Neu5Ac). In contrast, infant formulas contain a low level of Sia consisting of both Neu5Ac and N-glycolylneuraminic acid (Neu5Gc). Neu5Gc is implicated in some human inflammatory diseases. Brain gangliosides and polysialylated NCAM play crucial roles in cell-to-cell interactions, neuronal outgrowth, modifying synaptic connectivity, and memory formation. In piglets, a diet rich in Sia increases the level of brain Sia and the expression of two learning-related genes and enhances learning and memory. The purpose of this review is to summarize the evidence showing the importance of dietary Sia as an essential nutrient for brain development and cognition.

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.

Increase of GQ1b in the hippocampus of mice following kindled-seizures

The ganglioside GQ1b facilitates the influx of Ca2+ in brain synaptosomes and enhances ATP-induced long-term potentiation in hippocampal slices. Anti-GQ1b antibody impairs the function of peripheral neurons, for example, it had pathogenic effects on presynaptic neuronal membranes and perisynaptic Schwann cells in a mouse model of Guillain-Barré syndrome. The present study demonstrated in vivo that the level of endogenous GQ1b was relevant to neural function in the brain, in that it increased following seizures in amygdaloid kindling mice. GQ1b is subject to epileptogenic regulation and may play a role in the development of epilepsy.

GM1 ganglioside induces vasodilation and increases catalase content in the brain

Monosialoganglioside (GM1) is a glycosphingolipid present in most cell membranes that displays antioxidant and neuroprotective properties. GM1 increases catalase activity in cerebral cortices in vivo, but the mechanisms underlying this effect of GM1 are not known. In the current study we investigated the effect of GM1 (50 mg/kg, ip) on the content of hemoglobin and catalase activity of hippocampus, cortex, and striatum of rats. GM1 administration increased catalase activity and hemoglobin content in brain samples after 30 min, but had no effect on blood catalase activity. GM1-induced increase in catalase activity was abolished by brain perfusion with heparinized saline. Brain catalase activity in the absence of blood, estimated by regression analysis of data from perfused and nonperfused animals, was not altered by the systemic injection of GM1. Moreover, the addition of GM1 (30 or 100 microM) did not increase catalase activity in slices of cerebral cortex in situ, further suggesting that blood circulation is required for this effect. The GM1-induced vasodilation was confirmed in vivo, because the systemic injection of GM1 (50 mg/kg, ip) increased (1.2-1.6 times) the width of pial vessels.

Reduction of gangliosides, phospholipids and cholesterol content in cerebral cortex of rats caused by chronic hypermethioninemia

Neurological dysfunction is observed in patients with severe hypermethioninemia, whose physiopathology is still poorly understood. In the current study we investigated the effect of chronic administration of methionine on the content and species of gangliosides and phospholipids, as well as on the concentration of cholesterol in rat cerebral cortex. Wistar rats received subcutaneous injections of methionine (1.34-2.68 micromol/g of body weight), twice a day, from the 6th to the 28th day of age and controls received saline. Animals were killed 12h after the last injection. Results showed that methionine administration significantly decreased the total content of lipids in cerebral cortex of rats. We also observed that this amino acid significantly reduced the absolute quantity of the major brain gangliosides (GM1, GD1a, GD1b and GT1b) and phospholipids (sphingomyelin, phosphatidylcholine and phosphatidylethanolamine). We also showed that Na+,K+-ATPase activity and TBARS were changed in cerebral cortex of rats subjected to hypermethioninemia. If confirmed in human beings, these data could suggest that the alteration in lipid composition, Na+,K+-ATPase activity and TBARS caused by methionine might contribute to the neurophysiopathology observed in hypermethioninemic patients.

Estrogen-induced cholestasis results in a dramatic increase of b-series gangliosides in the rat liver

Hepatic ganglioside composition was investigated in normal and cholestatic Wistar rats. Cholestasis was induced by 17alpha-ethinylestradiol (EE; 5 mg/kg body weight s.c. for 18 days). As compared with controls, the EE administration resulted in severe cholestasis, as indicated by biochemical as well as morphological signs. Gangliosides isolated from the liver tissue were separated by TLC, with resorcinol-HCl detection and densitometric evaluation. As compared with controls, the total hepatic lipid sialic acid content in cholestatic rats was increased almost 2-fold (44.3 +/- 15.2 vs 79.1 +/- 9.0 nmol/g wet weight of liver tissue, p < 0.01). This increase was primarily due to the increase of ganglioside GD1a (3.6 +/- 1.0 vs 11.8 +/- 3.0 nmol/g wet weight of liver tissue, p = 0.001), as well as to the enormous up-regulation of b-series gangliosides GD3 (0.08 +/- 0.03 vs 2.0 +/- 1.2 nmol/g wet weight of liver tissue, p = 0.002), GD1b (0.1 +/- 0.06 vs 5.4 +/- 1.6 nmol/g wet weight of liver tissue, p = 0.002) and GT1b (0.06 +/- 0.03 vs 6.4 +/- 2.6 nmol/g wet weight of liver tissue, p = 0.002). As the majority of gangliosides are concentrated in cell membranes, our findings suggest that dramatic increase of b-series gangliosides might contribute to the protection of hepatocytes against the deleterious effects of cholestasis.

Ovariectomy enhances acetylcholinesterase activity but does not alter ganglioside content in cerebral cortex of female adult rats

In the present work we investigated the effect of ovariectomy on acetylcholinesterase (AChE) activity and ganglioside content in cerebral cortex of female rats. We also studied the activity of butyrylcholinesterase (BuChE) in serum of these animals. Adult Wistar rats were divided into three groups: (1) naive females (control), (2) sham-operated females and (3) castrated females (ovariectomy). Thirty days after ovariectomy, rats were sacrificed by decapitation without anaesthesia. Blood was collected and the serum used for BuChE determination. Cerebral cortex was homogenized to determine AChE activity and extracted with chlorophorm:methanol for ganglioside evaluation. Results showed that rats subjected to ovariectomy presented a significant increase of AChE activity, but did not change the content and the profile of gangliosides in cerebral cortex when compared to sham or naive rats. BuChE activity was decreased in serum of rats ovariectomized. Our findings suggest that the alteration in the activity of brain AChE, as well as serum BuChE activity caused by ovariectomy may contribute to the impaired cognition and/or other neurological dysfunction found in post-menopausal women.

Induction of neuron-like tubes and liposome networks by cooperative effect of gangliosides and phospholipids

Although there is a rather large abundance of gangliosides in neurons, their functional role is still unclear. We focused on a physicochemical role of gangliosides in the formation of tubular structures, such as axons or dendrites in neurons. When a ganglioside, GM3, was added to cell-size liposomes that consisted of dioleoylphosphatidyl-choline, tubular structures were induced and liposome networks connected by the tubes were observed by differential interference microscopy and fluorescence microscopy. The potential for various gangliosides to induce tubes was dependent on the structures of their hydrophilic head group. With a large excess of gangliosides, the tubes are destabilized and small fragments, or micelles, are generated. The phenomenon was suggested by physical model calculation. Gangliosides may play a role as building material in neural unique tubular structures.

Region-specific and epileptogenic-dependent expression of six subtypes of alpha2,3-sialyltransferase in the adult mouse brain

Sialylated glycoconjugates play important roles in various biological functions. The structures are also observed in brains and it has been proposed that sialylation may affect neural plasticity. To clarify the effects of sialylation in the brain, particular neurons that exhibit sialylation should first be determined. Using in situ hybridization, we performed systematic surveys of the localization of mRNAs encoding the six alpha2,3-sialyltransferases (ST3Gal I-VI) in the adult mouse brain with or without physiological stimulation. First, striking region-specific patterns of expression were observed: While ST3Gal II, III, and V mRNAs were in neuronal cells throughout the brain, ST3Gal I, IV, and VI mRNAs were in restricted brain regions. Next, to assess whether the expression of the six mRNAs can be regulated, we examined the effect of kindling epileptogenesis on the six mRNA levels. Of the six subtypes, upregulation in the ST3Gal IV level in the thalamus was most pronounced; the number of ST3Gal IV-expressing neurons in the anterior thalamic nuclei increased from 2% to 21% in a time-dependent manner during epileptogenesis. Western blot analysis evaluated the increase of the end-products in the thalamus. These findings provide a molecular basis to clarify when and where sialylated glycoconjugates function accompanied by neural plasticity.

Glycosyltransferases in different brain regions during chick embryo development

Glycosphingolipids, in particular gangliosides, play a crucial role in neuronal development and are known to change dramatically in total content and distribution in different brain areas during embryogenesis. In the present work we analyzed the activity of enzymes involved in the metabolism of gangliosides, at different periods of functional maturation in different regions of chick embryo brain. Our data demonstrate differences in the enzymatic activities in the examined areas; these differences might be correlated with the functional lateralization occurring in the brain during development. Significative differences were found in glycosphingolipid composition between controlateral cerebral hemispheres and optic lobes; these results together with previous data we found, contribute to reinforce our hypothesis on the occurrence of biochemical lateralization during early brain development.

Ganglioside alterations in the central nervous system of rats chronically injected with methylmalonic and propionic acids

Neurological dysfunction and structural cerebral abnormalities are commonly found in patients with methylmalonic and propionic acidemia. However, the mechanisms underlying the neuropathology of these disorders are poorly understood. We have previously demonstrated that methylmalonic and propionic acids induce a significant reduction of ganglioside N-acetylneuraminic acid in the brain of rats subjected to chronic administration of these metabolites. In the present study, we investigated the in vivo effects of chronic administration of methylmalonic (MMA) and propionic (PA) acids (from the 6th to the 28th day of life) on the distribution and composition of gangliosides in the cerebellum and cerebral cortex of rats. Control rats were treated with the same volumes of saline. It was first verified that MMA and PA treatment did not modify body, cerebellum, or cortical weight, nor the ganglioside concentration in the cerebral cortex of the animals. In contrast, a significant reduction in total ganglioside content in the cerebellum of approximately 20-30% and 50% of control levels occurred in rats injected with MMA and PA, respectively. Moreover, chronic MMA and PA administration did not interfere with the ganglioside pattern in the cerebral cortex, whereas the distribution of individual gangliosides was altered in the cerebellum of MMA- and PA-treated animals. Rats injected with MMA demonstrated a marked decrease in GM1 and GD3, whereas chronic PA treatment provoked a significant reduction of all ganglioside species, with the exception of an increase in GM2. Since gangliosides are closely related to the dendritic surface and other neural membranes, indirectly reflecting synaptogenesis, these ganglioside abnormalities may be associated with the brain damage found in methylmalonic and propionic acidemias.

Regulation of apoptosis during neuronal differentiation by ceramide and b-series complex gangliosides

Lipid analysis of gestational day E14.5 mouse brain revealed elevation of ceramide to a tissue concentration that induced apoptosis when added to the medium of neuroprogenitor cells grown in cell culture. Elevation of ceramide was coincident with the first appearance of b-series complex gangliosides (BCGs). Expression of BCGs by stable transfection of murine neuroblastoma (F-11) cells with sialyltransferase-II (ST2) resulted in a 70% reduction of ceramide-induced apoptosis. This was most likely due to an 80% reduced expression of prostate apoptosis response-4 (PAR-4). PAR-4 expression and apoptosis were restored by preincubation of ST2-transfected cells with N-butyl deoxinojirimycin (NB-DNJ) or PD98059, two inhibitors of ganglioside biosynthesis or p42/44 mitogen-activated protein (MAPK) kinase, respectively. In sections of day E14.5 mouse brain, the intermediate zone showed intensive staining for complex gangliosides, but only low staining for apoptosis (TUNEL) and PAR-4. Apoptosis and PAR-4 expression, however, were elevated in the ventricular zone which only weakly stained for complex gangliosides. Whole cell patch clamping revealed a 2-fold increased calcium influx in ST2-transfected cells, the blocking of which with nifedipine restored apoptosis to the level of untransfected cells. In serum-free culture, supplementation of the medium with IGF-1 was required to maintain MAPK phosphorylation and the anti-apoptotic effect of BCG expression. BCG-enhanced calcium influx and the presence of insulin-like growth factor-1 may thus activate a cell survival mechanism that selectively protects developing neurons against ceramide-induced apoptosis by up-regulation of MAPK and reduction of PAR-4 expression.

Differential expression of mRNAs for sialyltransferase isoenzymes induced in the hippocampus of mouse following kindled seizures

Sialic acids play important roles in various biological functions. In the brain, evidence suggests that sialylation of glycoproteins and glycolipids affects neural plasticity. While the 18 sialyltransferase isoenzymes (STs) identified to date synthesize individual sialyl-oligosaccharide structures, they each exhibit activity toward more than one substrate and can overlap in their specificity. Therefore, the distribution of STs is a secondary factor in the study of specific sialylation. Here, seven STs; ST3Gal I-IV, ST8Sia IV, ST6Gal I and ST6GalNAc II, the expressions of which were identified in the adult hippocampus by RT-PCR, showed diverse localization patterns in the hippocampus on in situ hybridization, suggesting that the individual cells expressed relevant STS: Furthermore, to assay activity-related changes in ST expression, we used amygdaloid-kindling among models of neural plasticity. Differential expression of the STs participating in the kindling, notably, up-regulation of ST3Gal IV and ST6GalNAc II mRNAs, and down-regulation of ST3Gal I and ST8Sia IV mRNAs, were observed in the hippocampus following kindled seizures. These results indicate that ST expressions are regulated by physiological activity and may play a role in neural plasticity.

Excitotoxicity induces changes in rat brain gangliosides

The patterns of major gangliosides in the rat hippocampi and olfactory bulbs was examined in vivo after microinjections of Ibotenic acid and L-BOAA (NMDA and AMPA receptor agonists, respectively) which were given under free-movement conditions. The excitotoxicity induced by injections of Ibotenic acid promoted transient ganglioside changes in olfactory bulbs and permanent changes in hippocampus. Four days after injections, the amount of gangliosides in the hippocampus increased significantly for GQ1b, GT1b and GD1b and decreased in the olfactory bulb for GQ1b, GT1b, GD1b, GD1a and GM1 compared to normal ganglioside levels. The alterations of gangliosides were minimal 1 day after injections. After 5 weeks, the amounts of GQ1b, GT1b and GD1b dramatically decreased in the hippocampus while in the olfactory bulbs gangliosides recovered to normal levels. The results obtained with L-BOAA 4 days after injections strengthen the results observed in the experiments using Ibotenic acid and corroborate our suggestion that gangliosides have an active role in the compensatory mechanism to maintain the number of glutamate receptors during the excitotoxicity.

Chronic postnatal administration of methylmalonic acid provokes a decrease of myelin content and ganglioside N-acetylneuraminic acid concentration in cerebrum of young rats

Levels of methylmalonic acid (MMA) comparable to those of human methylmalonic acidemia were achieved in blood (2-2.5 mmol/l) and brain (1.35 umol/g) of rats by administering buffered MMA, pH 7.4, subcutaneously twice a day from the 5th to the 28th day of life. MMA doses ranged from 0.76 to 1.67 umol/g as a function of animal age. Control rats were treated with saline in the same volumes. The animals were sacrificed by decapitation on the 28th day of age. Blood was taken and the brain was rapidly removed. Medulla, pons, the olfactory lobes and cerebellum were discarded and the rest of the brain ("cerebrum") was isolated. Body and "cerebrum" weight were measured, as well as the cholesterol and triglyceride concentrations in blood and the content of myelin, total lipids, and the concentrations of the lipid fractions (cholesterol, glycerolipids, phospholipids and ganglioside N-acetylneuraminic acid (ganglioside-NANA)) in the "cerebrum". Chronic MMA administration had no effect on body or "cerebrum" weight, suggesting that the metabolites per se neither affect the appetite of the rats nor cause malnutrition. In contrast, MMA caused a significant reduction of plasma triglycerides, but not of plasma cholesterol levels. A significant diminution of myelin content and of ganglioside-NANA concentration was also observed in the "cerebrum". We propose that the reduction of myelin content and ganglioside-NANA caused by MMA may be related to the delayed myelination/cerebral atrophy and neurological dysfunction found in methylmalonic acidemic children.