Regulation of axonal development by plasma membrane gangliosides

Genotoxicity Study of Glycopeptide (G-7%NANA)

Glycomacropeptide (GMP), a whey protein of milk, has functions including differentiation and development of nervous system, and anticancer and antiviral effects. To develop new functions, N-acetylneuraminic acid (NANA) containing 7% sialic acid was separated from GMP to produce G-7%NANA. N-glycolylneuraminic acid (Neu5Gc) is another type of sialic acid separated from GMP, which has been linked to immune disorders and chronic inflammation-mediated diseases. Therefore, safety was a concern in the use of G-7%NANA in functional foods. To ensure safety, in this study, three genetic toxicity tests on G-7%NANA were conducted. In the reverse mutation test using Salmonella typhimurium TA98, TA100, TA1535, TA1537, and Escherichia coli WP2uvrA, and in the chromosome aberration test using CHO-K1 cells, no significant differences from negative control were found at all dose levels. Similarly, no dose-related differences were evident compared to negative control in the micronucleus test using ICR mice. There was no evidence of G-7%NANA-related genetic toxicity.

Repeated dose 90-day oral toxicity test of G-7% NANA in rats: An application of new criterion for toxicity determination to test article-induced changes

G-7% NANA is N-acetylneuraminic acid(NANA) containing 7% sialic acid isolated from glycomacropeptide (GMP), a compound of milk. Since NANA is likely to have immunotoxicity, the need to ensure safety for long-term administration has been raised. In this study, a 90-day repeated oral dose toxicity test was performed in rats using G-7% NANA in the dosages of 0, 1250, 2500 and 5000 mg/kg/day.A toxicity determination criterion based on the significant change caused by the administration of the substancewas developed for estimating NOEL, NOAEL and LOAELapplied to this study. When analyzing the immunological markers, no significant changes were observed, even if other significant changes were observed in the high dose group. In accordance with the toxicity determination criterion developed, the NOEL in male and female has been determined as 2500 mg/kg/day, and the NOAEL in females has been determined as 5000 mg/kg/day. The toxicity determination criterion, applied for the first time in the repeated dose toxicity tests, could provide a basis for distinguishing NOEL and NOAEL more clearly; nevertheless, the toxicity determination criterion needs to be supplemented by adding differentiating adverse effects and non-adverse effects based on more experiences of the repeated dose toxicity tests.

Electroconvulsive therapy enhances endocannabinoids in the cerebrospinal fluid of patients with major depression: a preliminary prospective study

Despite the lack of clinical data about the role of the endocannabinoid system (ECS) in affective disorders, preclinical work suggests that the ECS is relevant in both with regard to the etiology of depression as well as the mediation of antidepressant effects. We measured the intraindividual levels of the endocannabinoids N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) in the cerebrospinal fluid of 12 patients suffering from a major depressive episode before and after the antidepressant treatment by electroconvulsive therapy (ECT). AEA was significantly elevated after ECT as compared to baseline. The AEA increase positively correlated with the number of individually performed ECT sessions. Although the sample size was small and confounders were not rigorously controlled for, our finding corroborates preclinical work and should encourage further exploration of the involvement of the ECS in depressive disorder.

Sweet complementarity: the functional pairing of glycans with lectins

Carbohydrates establish the third alphabet of life. As part of cellular glycoconjugates, the glycans generate a multitude of signals in a minimum of space. The presence of distinct glycotopes and the glycome diversity are mapped by sugar receptors (antibodies and lectins). Endogenous (tissue) lectins can read the sugar-encoded information and translate it into functional aspects of cell sociology. Illustrated by instructive examples, each glycan has its own ligand properties. Lectins with different folds can converge to target the same epitope, while intrafamily diversification enables functional cooperation and antagonism. The emerging evidence for the concept of a network calls for a detailed fingerprinting. Due to the high degree of plasticity and dynamics of the display of genes for lectins the validity of extrapolations between different organisms of the phylogenetic tree yet is inevitably limited.

Cannabinoids and Glucocorticoids in the Basolateral Amygdala Modulate Hippocampal-Accumbens Plasticity After Stress

Acute stress results in release of glucocorticoids, which are potent modulators of learning and plasticity. This process is presumably mediated by the basolateral amygdala (BLA) where cannabinoids CB1 receptors have a key role in regulating the hypothalamic-pituitary-adrenal (HPA) axis. Growing attention has been focused on nucleus accumbens (NAc) plasticity, which regulates mood and motivation. The NAc integrates affective and context-dependent input from the BLA and ventral subiculum (vSub), respectively. As our previous data suggest that the CB1/2 receptor agonist WIN55,212-2 (WIN) and glucocorticoid receptor (GR) antagonist RU-38486 (RU) can prevent the effects of stress on emotional memory, we examined whether intra-BLA WIN and RU can reverse the effects of acute stress on NAc plasticity. Bilateral, ipsilateral, and contralateral BLA administration of RU or WIN reversed the stress-induced impairment in vSub-NAc long-term potentiation (LTP) and the decrease in cAMP response element-binding protein (CREB) activity in the NAc. BLA CB1 receptors were found to mediate the preventing effects of WIN on plasticity, but not the preventing effects of RU, after stress. Inactivating the ipsilateral BLA, but not the contralateral BLA, impaired LTP. The possible mechanisms underlying the effects of BLA on NAc plasticity are discussed; the data suggest that BLA-induced changes in the NAc may be mediated through neural pathways in the brain's stress circuit rather than peripheral pathways. The results suggest that glucocorticoid and cannabinoid systems in the BLA can restore normal function of the NAc and hence may have a central role in the treatment of a variety of stress-related disorders.

Programming of neural cells by (endo)cannabinoids: from physiological rules to emerging therapies

Among the many signalling lipids, endocannabinoids are increasingly recognized for their important roles in neuronal and glial development. Recent experimental evidence suggests that, during neuronal differentiation, endocannabinoid signalling undergoes a fundamental switch from the prenatal determination of cell fate to the homeostatic regulation of synaptic neurotransmission and bioenergetics in the mature nervous system. These studies also offer novel insights into neuropsychiatric disease mechanisms and contribute to the public debate about the benefits and the risks of cannabis use during pregnancy and in adolescence.

Neu3 sialidase-mediated ganglioside conversion is necessary for axon regeneration and is blocked in CNS axons

PNS axons have a high intrinsic regenerative ability, whereas most CNS axons show little regenerative response. We show that activation of Neu3 sialidase, also known as Neuraminidase-3, causing conversion of GD1a and GT1b to GM1 ganglioside, is an essential step in regeneration occurring in PNS (sensory) but not CNS (retinal) axons in adult rat. In PNS axons, axotomy activates Neu3 sialidase, increasing the ratio of GM1/GD1a and GM1/GT1b gangliosides immediately after injury in vitro and in vivo. No change in the GM1/GD1a ratio after axotomy was observed in retinal axons (in vitro and in vivo), despite the presence of Neu3 sialidase. Externally applied sialidase converted GD1a ganglioside to GM1 and rescued axon regeneration in CNS axons and in PNS axons after Neu3 sialidase blockade. Neu3 sialidase activation in DRGs is initiated by an influx of extracellular calcium, activating P38MAPK and then Neu3 sialidase. Ganglioside conversion by Neu3 sialidase further activates the ERK pathway. In CNS axons, P38MAPK and Neu3 sialidase were not activated by axotomy.

Mass Spectrometry of Gangliosides from Human Sensory and Motor Cortex

Sialylated glycosphingolipids, known as gangliosides, are highly expressed in the central nervous system exhibiting region-specific composition in correlation to the specialised functions of particular brain regions. In the present study high resolution tandem mass spectrometry on a quadrupole time-of-flight instrument with nanoelectrospray was optimised and applied for the first comparative assessment of the ganglioside profile in single specimens of adult human motor and somatosensory cortex. In the second stage, the structural analysis performed by collision induced dissociation tandem MS disclosed the presence in motor cortex of a fucose-ganglioside Fuc-GM1 (d18 : 1/20 : 0) isomer exhibiting both N-acetylneuraminic acid and fucose residues linked to the inner galactose.

Profiling and sequencing of gangliosides from human caudate nucleus by chip-nanoelectrospray mass spectrometry

Gangliosides (GGs), sialic acid-containing glycosphingolipids are involved in many brain functions at the cell and molecular level. Compositional and structural elucidation of GGs in mixtures extracted from human brain is essential for correlating their profile with the specialized function of each brain area in health and disease. As a part of our ongoing study on GG expression and structure in different healthy and diseased brain regions, in this work, a preliminary investigation of GGs in a specimen of human caudate nucleus (CN) was carried out using an advanced mass spectrometry (MS) technique. By chip-nanoelectrospray MS performed on a NanoMate robot coupled to a high capacity ion trap instrument, 81 GG components were detected in human CN in only 1.5 min of signal acquisition. Although the native GG mixture from CN was found dominated by mono-, di- and trisialylated GGs with a slight dominance of disialylated forms (GD), four tetrasialylated structures (GQ) and two pentasialylated (GP) species were also identified. Additionally, species with unusually long fatty acid chains, exceeding 30 carbon atoms in their ceramide (Cer) composition, and several glycoforms modified by fucosyl (Fuc), O-acetyl (O-Ac) and/or lactonization were discovered. By tandem MS (MS(2) ) using collision-induced dissociation, two atypical mono and disialylated species with long-chain fatty acids in their Cer could be confirmed and structurally characterized. These results may be a starting point for new GG-based approaches in the study of CN functions and ethiopathogenesis of CN-related neurodegenerative disorders.

Deficiency in endocannabinoid signaling in the nucleus accumbens induced by chronic unpredictable stress

The nucleus accumbens (NAc) is a critical component of the reward circuitry, and dysfunction of the NAc may account for anhedonia and other symptoms of depression. Here, we investigated whether alterations in endocannabinoid (eCB) signaling in the NAc contribute to depression-like behaviors induced by chronic unpredictable stress (CUS) in mice. We compared three types of eCB/CB1 receptor-mediated synaptic plasticity in slices prepared from the NAc core of control and stress-exposed mice: depolarization-induced suppression of excitation, long-term depression, and the depression of field excitatory postsynaptic potentials (fEPSPs) induced by group I metabotropic glutamate receptor agonist DHPG. CUS (5-6-week exposure to stressors), but not sub-CUS (1 week exposure to stressors), induces depression-like behaviors and impairs these forms of eCB/CB1 receptor-mediated plasticity examined in the NAc core. Neither sub-CUS nor CUS altered the tissue contents of the eCBs, anandamide and 2-arachidonoylglycerol in the striatum. However, exposure to CUS, but not to sub-CUS, attenuated the depression of fEPSPs induced by the CB1 receptor agonist WIN 55 212-2. CUS exposure reduced the maximal effect without affecting the EC(50) of WIN 55 212-2 to induce fEPSP depression. Thus, impaired CB1 receptor function could account for CUS-induced deficiency in eCB signaling in the NAc. Both CUS-induced deficiency in eCB signaling and depression-like behaviors were reversed by in vivo administration of antidepressant fluoxetine. These results suggest that downregulation of eCB signaling in the NAc occurs after CUS and contributes to the pathophysiology of depression.

Impaired ganglioside metabolism in Huntington's disease and neuroprotective role of GM1

Huntington's disease (HD) is a neurodegenerative disorder caused by the expansion of a polyglutamine stretch in the protein huntingtin (Htt). HD neurons are dysfunctional at multiple levels and have increased susceptibility to stress and apoptotic stimuli. We have discovered that synthesis of the ganglioside GM1 is reduced in fibroblasts from HD patients and in cell and animal models of HD, and that decreased GM1 levels contribute to heighten HD cell susceptibility to apoptosis. The apoptotic susceptibility is recapitulated through inhibition of ganglioside synthesis in wild-type striatal cells, suggesting that decreased GM1 levels might be one of the key events leading to HD pathogenesis and progression. Administration of GM1 restores ganglioside levels in HD cells and promotes activation of AKT and phosphorylation of mutant Htt, leading to decreased mutant Htt toxicity and increased survival of HD cells. Our data identify GM1 as a potential treatment for HD.

Long-term fluoxetine treatment modulates cannabinoid type 1 receptor-mediated inhibition of adenylyl cyclase in the rat prefrontal cortex through 5-hydroxytryptamine 1A receptor-dependent mechanisms

Increasing data indicate that brain endocannabinoid system plays a role in the effects of antidepressant medications. Here we examined the effect of in vivo exposure to the selective serotonin uptake inhibitor fluoxetine on cannabinoid type 1 (CB(1)) receptor density and functionality in the rat prefrontal cortex (PFC) and cerebellum. Long-term treatment with fluoxetine (10 mg/kg/day) enhanced CB(1) receptor inhibition of adenylyl cyclase (AC) in the PFC and reduced it in the cerebellum without altering receptor density and agonist stimulation of guanosine 5'-O-(3-[(35)S]thio) triphosphate ([(35)S]GTP gamma S) in either area. Analysis of [(35)S]GTP gamma S-labeled G alpha subunits allowed for the detection of up-regulated CB(1) receptor coupling to G alpha(i2), G alpha(i3) in the PFC, and reduced coupling to G alpha(i3) in the cerebellum of fluoxetine-treated rats. Concomitant administration of the 5-HT(1A) receptor antagonist N-[2-[4- (2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide maleate (WAY100635; 0.1 mg/kg/day) reduced fluoxetine-induced modulation of CB(1) receptor coupling to G alpha subunits and AC in the PFC but not in the cerebellum. These results indicate that increased CB(1) receptor signaling at the G alpha(i)-AC transduction level is a long-term adaptation induced by fluoxetine in the PFC and point to a role for 5-HT(1A) receptors in this effect. Basal AC activity, protein kinase A (PKA) catalytic subunit expression, and phospho-cAMP response element-binding protein (pCREB)/CREB ratio were also up-regulated in the PFC of fluoxetine-treated animals, whereas no differences were detected in the cerebellum. It is interesting that long-term Delta(9)-tetrahydrocannabinol treatment did not elicit antidepressant-like effects or modulated behavioral responses of fluoxetine in an animal model of depression (olfactory bulbectomy). These data suggest that altered signal transduction through CB(1) receptors in the PFC may participate in the regulation of the AC-PKA-CREB cascade induced by fluoxetine in this brain area.

Glycosylated SV2 and gangliosides as dual receptors for botulinum neurotoxin serotype F

Botulinum neurotoxin causes rapid flaccid paralysis through the inhibition of acetylcholine release at the neuromuscular junction. The seven BoNT serotypes (A-G) have been proposed to bind motor neurons via ganglioside-protein dual receptors. To date, the structure-function properties of BoNT/F host receptor interactions have not been resolved. Here, we report the crystal structures of the receptor binding domains (HCR) of BoNT/A and BoNT/F and the characterization of the dual receptors for BoNT/F. The overall polypeptide fold of HCR/A is essentially identical to the receptor binding domain of the BoNT/A holotoxin, and the structure of HCR/F is very similar to that of HCR/A, except for two regions implicated in neuronal binding. Solid phase array analysis identified two HCR/F binding glycans: ganglioside GD1a and oligosaccharides containing an N-acetyllactosamine core. Using affinity chromatography, HCR/F bound native synaptic vesicle glycoproteins as part of a protein complex. Deglycosylation of glycoproteins using alpha(1-3,4)-fucosidase, endo-beta-galactosidase, and PNGase F disrupted the interaction with HCR/F, while the binding of HCR/B to its cognate receptor, synaptotagmin I, was unaffected. These data indicate that the HCR/F binds synaptic vesicle glycoproteins through the keratan sulfate moiety of SV2. The interaction of HCR/F with gangliosides was also investigated. HCR/F bound specifically to gangliosides that contain alpha2,3-linked sialic acid on the terminal galactose of a neutral saccharide core (binding order GT1b = GD1a >> GM3; no binding to GD1b and GM1a). Mutations within the putative ganglioside binding pocket of HCR/F decreased binding to gangliosides, synaptic vesicle protein complexes, and primary rat hippocampal neurons. Thus, BoNT/F neuronal discrimination involves the recognition of ganglioside and protein (glycosylated SV2) carbohydrate moieties, providing a structural basis for the high affinity and specificity of BoNT/F for neurons.

Role of endocannabinoid signaling in anxiety and depression

Cannabinoid receptors and their endogenous ligands are located throughout the limbic, or "emotional," brain, where they modulate synaptic neurotransmission. Converging preclinical and clinical data suggest a role for endogenous cannabinoid signaling in the modulation of anxiety and depression. Augmentation of endocannabinoid signaling (ECS) has anxiolytic effects, whereas blockade or genetic deletion of CB₁ receptors has anxiogenic properties. Augmentation of ECS also appears to have anti-depressant actions, and in some assays blockade and genetic deletion of CB₁ receptors produces depressive phenotypes. These data provide evidence that ECS serves in an anxiolytic, and possibly anti-depressant, role. These data suggest novel approaches to treatment of affective disorders which could include enhancement of endogenous cannabinoid signaling, and warrant cautious use of CB₁ receptor antagonists in patients with pre-existing affective disorders.

High-throughput analysis of gangliosides in defined regions of fetal brain by fully automated chip-based nanoelectrospray ionization multi-stage mass spectrometry

Gangliosides (GGs), a large group of sialylated glycosphingolipids, are considered biomarkers of human brain development, aging and certain diseases. Determination of individual GG components in complex mixtures extracted from a human brain represents a fundamental prerequisite for correlating their specificity with the specialized function of each brain area. In the context of modern glycomics, detailed investigation of GG expression and structure in human brain requires a continuous development and application of innovative methods able to improve the quality of data and speed of analysis. In this work, for the first time, a high-throughput mapping and sequencing of gangliosides in human fetal brain was performed by a novel mass spectrometry (MS)-based approach developed recently in our laboratory. Three GG mixtures extracted and purified from different regions of the same fetal brain in the 36th gestational week: frontal neocortex (NEO36), white matter of the frontal lobe (FL36) and white matter of the occipital lobe (OL36) were subjected to comparative high-throughput screening and multi-stage fragmentation by fully automated chip-based nanoelectrospray ionization (nanoESI) high capacity ion trap (HCT) MS. Using this method, in only a few minutes of signal acquisitions, over 100 GG and asialo-GG species were detected and identified in the three mixtures. Obtained data revealed for the first time that differences in GG expression in human fetal brain are dependent on phylogenetic development rather than topographic factors. While a significant variation of GG distribution in NEO36 vs FL36 was observed, no significant differences in GG expression in white matter of frontal vs occipital lobe were detected. Additionally, the largest number of species was identified in NEO36, which correlates with the functional complexity of neocortex as the newest brain region. In the last stage of analysis, using MS(2)-MS(3) molecular ion fragmentation at variable amplitudes, a NEO36-associated GD1b isomer could clearly be discriminated. Present results indicate that the combination of fully automated chipESI with HCT MS(n) is able to provide ultra-fast, sensitive and reliable analyses of complex lipid-linked carbohydrates from which the pattern of their expression and structure in a certain type of bio-matrix can be determined.

High-throughput screening of cell lysates for ganglioside synthesis

A high-throughput screen to detect the synthesis of natural and non-natural gangliosides by cell lysates has been developed and automated. Utilizing the binding specificity of cholera toxin B-subunit for the oligosaccharide moiety of the ganglioside G M1, the synthesis of sugar-sphingolipid glycosidic linkages was detected using a modified enzyme-linked immunosorbent assay (ELISA)/enzyme-linked lectin assay (ELLA). The screen was optimized and validated for high-throughput screening of cell lysates by evaluating different vectors, promoters, substrates and detection strategies. The extent of ganglioside synthesis was found to be proportional to enzyme concentration and length of incubation time. As a test of the finalized screen efficacy, individual colonies from a saturation mutagenesis library of nucleophile mutants of an endoglycoceramidase were screened to identify the most active enzyme for ganglioside synthesis. This screen should find general application in assaying both glycolipid biosynthesis and glycolipid hydrolysis, as it is highly sensitive and can be used with crude cell extracts.