The Biology of Gangliosides

The Human Ganglioside Interactome in Live Cells Revealed Using Clickable Photoaffinity Ganglioside Probes

Gangliosides, sialic acid bearing glycosphingolipids, are components of the outer leaflet of plasma membranes of all vertebrate cells. They contribute to cell regulation by interacting with proteins in their own membranes (cis) or their extracellular milieu (trans). As amphipathic membrane constituents, gangliosides present challenges for identifying their ganglioside protein interactome. To meet these challenges, we synthesized bifunctional clickable photoaffinity gangliosides, delivered them to plasma membranes of cultured cells, then captured and identified their interactomes using proteomic mass spectrometry. Installing probes on ganglioside lipid and glycan moieties, we captured cis and trans ganglioside-protein interactions. Ganglioside interactomes varied with the ganglioside structure, cell type, and site of the probe (lipid or glycan). Gene ontology revealed that gangliosides engage with transmembrane transporters and cell adhesion proteins including integrins, cadherins, and laminins. The approach developed is applicable to other gangliosides and cell types, promising to provide insights into molecular and cellular regulation by gangliosides.

Expanding Clinical Spectrum of Anti-GQ1b Antibody Syndrome: A Review

Importance

The discovery of the anti-GQ1b antibody has expanded the nosology of classic Miller Fisher syndrome to include Bickerstaff brainstem encephalitis, Guillain-Barré syndrome with ophthalmoplegia, and acute ophthalmoplegia without ataxia, which have been brought under the umbrella term anti-GQ1b antibody syndrome. It seems timely to define the phenotypes of anti-GQ1b antibody syndrome for the proper diagnosis of this syndrome with diverse clinical presentations. This review summarizes these syndromes and introduces recently identified subtypes.

Observations

Although ophthalmoplegia is a hallmark of anti-GQ1b antibody syndrome, recent studies have identified this antibody in patients with acute vestibular syndrome, optic neuropathy with disc swelling, and acute sensory ataxic neuropathy of atypical presentation. Ophthalmoplegia associated with anti-GQ1b antibody positivity is complete in more than half of the patients but may be monocular or comitant. The prognosis is mostly favorable; however, approximately 14% of patients experience relapse.

Conclusions and Relevance

Anti-GQ1b antibody syndrome may present diverse neurological manifestations, including ophthalmoplegia, ataxia, areflexia, central or peripheral vestibulopathy, and optic neuropathy. Understanding the wide clinical spectrum may aid in the differentiation and management of immune-mediated neuropathies with multiple presentations.

Analysis of O-acetylated sialic acids by 3-nitrophenylhydrazine derivatization combined with LC-MS/MS

Sialic acids are a family of monosaccharides that share a nine-carbon backbone and a carboxyl group. A recent derivatization method based on 3-nitrophenylhydrazine (3-NPH) provides a mild chemical labeling technique for biomolecules containing carbonyl or carboxyl groups. In this study, we utilized 3-NPH to label sialic acids via a two-step derivatization process. The derivatized species can produce a common reporter ion corresponding to C1-C3 with two labels, and a fragment differentiating between Neu5Ac, Neu5Gc, and KDN. This method is compatible with O-acetylated sialic acids and provides high sensitivity to Neu5Gc and KDN, and since the utilization of dual labeling significantly enhances the hydrophobicity of derivatives, it can effectively mitigate matrix effects when combined with parallel reaction monitoring technology. Negative-ion tandem mass spectrometry (MS/MS) analysis reveals a distinctive fragmentation profile for the 4-O-acetylated species, while the other sialic acids yield similar MS/MS spectra with a high abundance of reporter ions. Using the reporter ion as a transition, this analytical strategy is effective for analyzing complex biological samples. For example, it was successfully employed to quantify sialic acids in the intestinal tissues of several carp species, demonstrating its potential in sialylation research.

Interplay of α-synuclein with Lipid Membranes: Cooperative Adsorption, Membrane Remodeling and Coaggregation

α-Synuclein is a small neuronal protein enriched at presynaptic termini. It is hypothesized to play a role in neurotransmitter release and synaptic vesicle cycling, while the formation of α-synuclein amyloid fibrils is associated with several neurodegenerative diseases, most notably Parkinson's Disease. The molecular mechanisms of both the physiological and pathological functions of α-synuclein remain to be fully understood, but in both cases, interactions with membranes play an important role. In this Perspective, we discuss several aspects of α-synuclein interactions with lipid membranes including cooperative adsorption, membrane remodeling and α-synuclein amyloid fibril formation in the presence of lipid membranes. We highlight the coupling between the different phenomena and their interplay in the context of physiological and pathological functions of α-synuclein.

Trajectories of Human Milk Gangliosides during the First Four Hundred Days and Maternal-to-Offspring Transfer of Gangliosides: Results from a Chinese Cohort Study

BACKGROUND

Gangliosides are crucial for early-life cognition and immunity development. However, limited data exist on gangliosides within the Chinese population, and maternal-to-fetal/infant ganglioside transport remains unclear.

OBJECTIVES

This study aimed to investigate gangliosides concentrations and trajectories in Chinese human milk during the first 400 d of lactation, and seek to understand gangliosides transmission between mother and offspring.

METHODS

This study involved 921 cross-sectional participants providing human milk samples across 0-400 d of lactation and 136 longitudinal participants offering maternal plasma, cord plasma, and human milk samples within the first 45 d postpartum. Ultrahigh-performance liquid chromatography-tandem mass spectrometry was used for the quantification of gangliosides.

RESULTS

Human milk GM3 (Neu5Acα2-3Galβ1-4GlcβCer) concentration increased from 2.29 ± 1.87 to 13.93 ± 4.82 μg/mL, whereas GD3 (Neu5Acα2-8Neu5Acα2-3Galβ1-4GlcβCer) decreased from 17.94 ± 6.41 to 0.30 ± 0.50 μg/mL during the first 400 d postpartum (all P < 0.05). Consistent results were observed in cross-sectional and longitudinal participants. GD3 concentration gradually increased from maternal plasma (1.58 μg/mL) through cord plasma (2.05 μg/mL) to colostrum (21.35 μg/mL). Significant positive correlations were observed between maternal and cord plasma for both GM3 (r = 0.30, P < 0.001) and GD3 (r = 0.35, P < 0.001), and maternal plasma GD3 also correlated positively with colostrum concentrations (r = 0.21, P = 0.015). Additionally, in maternal and cord plasma, gangliosides were mainly linked with 16- and 18-carbon fatty acids. However, human milk GM3 showed a broad spectrum of fatty acid chain lengths, whereas GD3 was primarily tied to very long-chain fatty acids (≥20 carbon).

CONCLUSIONS

We identified an increase in GM3 and a decrease in GD3 concentration in human milk, with GD3 notably more concentrated in cord plasma and colostrum. Importantly, ganglioside concentrations in maternal plasma positively correlated with those in cord plasma and colostrum. Our findings contribute to the existing Chinese data on gangliosides and enhance understanding of their transmission patterns from mother to offspring. This trial was registered at chictr.org.cn as ChiCTR1800015387.

Chemoenzymatic Synthesis of GAA-7 Glycan Analogues and Evaluation of Their Neuritogenic Activities

Ganglioside GAA-7 exhibits higher neurite outgrowth than ganglioside GM1a and most echinodermatous gangliosides (EGs) when tested on neuron-like rat adrenal pheochromocytoma (PC12) cells in the presence of nerve growth factor (NGF). The unique structure of GAA-7 glycan, containing an uncommon sialic acid (8-O-methyl-N-glycolylneuraminic acid) and sialic acid-α-2,3-GalNAc linkage, makes it challenging to synthesize. We recently developed a streamlined method to chemoenzymatically synthesize GAA-7 glycan and employed this modular strategy to efficiently prepare a library of GAA-7 glycan analogues incorporating N-modified or 8-methoxyl sialic acids. Most of these synthetic glycans exhibited moderate efficacy in promoting neuronal differentiation of PC12 cells. Among them, the analogue containing common sialic acid shows greater potential than the GAA-7 glycan itself. This result reveals that methoxy modification is not essential for neurite outgrowth. Consequently, the readily available analogue presents a promising model for further biological investigations.

Comparison of glycosyl donors: a supramer approach

The development of new methods for chemical glycosylation commonly includes comparison of various glycosyl donors. An attempted comparison of chemical properties of two sialic acid-based thioglycoside glycosyl donors, differing only in the substituent at O-9 (trifluoroacetyl vs chloroacetyl), at different concentrations (0.05 and 0.15 mol·L-1) led to mutually excluding conclusions concerning their relative reactivity and selectivity, which prevented us from revealing a possible influence of remote protective groups at O-9 on glycosylation outcome. According to the results of the supramer analysis of the reaction solutions, this issue might be related to the formation of supramers of glycosyl donors differing in structure hence chemical properties. These results seem to imply that comparison of chemical properties of different glycosyl donors may not be as simple and straightforward as it is usually considered.

GM1 ganglioside exerts protective effects against glutamate-excitotoxicity via its oligosaccharide in wild-type and amyotrophic lateral sclerosis motor neurons

Alterations in glycosphingolipid metabolism have been linked to the pathophysiological mechanisms of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease affecting motor neurons. Accordingly, administration of GM1, a sialic acid-containing glycosphingolipid, is protective against neuronal damage and supports neuronal homeostasis, with these effects mediated by its bioactive component, the oligosaccharide head (GM1-OS). Here, we add new evidence to the therapeutic efficacy of GM1 in ALS: Its administration to WT and SOD1G93A motor neurons affected by glutamate-induced excitotoxicity significantly increased neuronal survival and preserved neurite networks, counteracting intracellular protein accumulation and mitochondria impairment. Importantly, the GM1-OS faithfully replicates GM1 activity, emphasizing that even in ALS the protective function of GM1 strictly depends on its pentasaccharide.

T7 phage display reveals NOLC1 as a GM3 binding partner in human breast cancer MCF-7 cells

Ganglioside GM3 is a simple monosialoganglioside (NeuAc-Gal-Glc-ceramide) that modulates cell adhesion, proliferation, and differentiation. Previously, we reported isolation of GM3-binding vascular endothelial growth factor receptor and transforming growth factor-β receptor by the T7 phage display method (Chung et al., 2009; Kim et al., 2013). To further identify novel proteins interacting with GM3, we extended the T7 phage display method in this study. After T7 phage display biopanning combined with immobilized biotin-labeled 3'-sialyllactose prepared on a streptavidin-coated microplate, we isolated 100 candidate sequences from the human lung cDNA library. The most frequently detected clones from the blast analysis were the human nucleolar and coiled-body phosphoprotein 1 (NOLC1) sequences. We initially identified NOLC1 as a molecule that possibly binds to GM3 and confirmed this binding ability using the glutathione S-transferase fusion protein. Herein, we report another GM3-interacting protein, NOLC1, that can be isolated by the T7 phage display method. These results are expected to be helpful for elucidating the functional roles of ganglioside GM3 with NOLC1. When human breast cancer MCF-7 cells were examined for subcellular localization of NOLC1, immunofluorescence of NOLC1 was observed in the intracellular region. In addition, NOLC1 expression was increased in the nucleolus after treatment with the anticancer drug doxorubicin. GM3 and NOLC1 levels in the doxorubicin-treated MCF-7 cells were correlated, indicating possible associations between GM3 and NOLC1. Therefore, direct interactions between carbohydrates and cellular proteins can pave the path for new signaling phenomena in biology.

Influence of ganglioside combined with methylprednisolone sodium succinate on efficacy and neurological function in patients with acute myelitis

BACKGROUND

Acute myelitis (AM) can lead to sudden sensory, motor and autonomic nervous dysfunction, which negatively affects their daily activities and quality of life, so it is necessary to explore optimization from a therapeutic perspective to curb the progression of the disease.

AIM

To investigate the effect of ganglioside (GM) combined with methylprednisolone sodium succinate (MPSS) on the curative effect and neurological function of patients with AM.

METHODS

First, we selected 108 AM patients visited between September 2019 and September 2022 and grouped them based on treatment modality, with 52 patients receiving gamma globulin (GG) + MPSS and 56 patients receiving GM + MPSS, assigned to the control group (Con) and observation group (Obs), respectively. The therapeutic effect, neurological function (sensory and motor function scores), adverse events (AEs), recovery (time to sphincter function recovery, time to limb muscle strength recovery above grade 2, and time to ambulation), inflammatory factors (IFs) [interleukin (IL)-6, C-reactive protein (CRP), and tumor necrosis factor (TNF)-α] and other data of the two groups were collected for evaluation and comparison.

RESULTS

The Obs had: (1) A significantly higher response rate of treatment than the Con; (2) Higher scores of sensory and motor functions after treatment that were higher than the baseline (before treatment) and higher than the Con levels; (3) Lower incidence rates of skin rash, gastrointestinal discomfort, dyslipidemia, osteoporosis and other AEs; (4) Faster posttreatment recovery of sphincter function, limb muscle strength and ambulation; and (5) Markedly lower posttreatment IL-6, CRP and TNF-α levels than the baseline and the Con levels.

CONCLUSION

From the above, it can be seen that GM + MPSS is highly effective in treating AM, with a favorable safety profile comparable to that of GG + MPSS. It can significantly improve patients’ neurological function, speed up their recovery and inhibit serum IFs.

Clinical Features and Neurotologic Findings in Patients With Acute Unilateral Peripheral Vestibulopathy Associated With Antiganglioside Antibody

BACKGROUND AND OBJECTIVES

Anecdotal studies have reported the presence of antiganglioside antibodies in acute unilateral peripheral vestibulopathy (AUPV). This study aimed to determine the prevalence, clinical characteristics, and neurotologic findings of AUPV associated with antiganglioside antibodies.

METHODS

Serum antigangliosides were measured in consecutive patients with AUPV according to the Bárány Society criteria during the acute and recovery phases in a referral-based university hospital in South Korea from September 2019 to January 2023. Clinical characteristics and neurotologic findings were compared between those with and without antiganglioside antibodies. The results of video-oculography, video head impulse and bithermal caloric tests, and other neurotologic evaluations including ocular and cervical vestibular-evoked myogenic potentials and subjective visual vertical were compared between the 2. MRIs dedicated to the inner ear were also conducted when considered necessary.

RESULTS

One hundred five patients (mean age ± SD = 60 ± 13 years, 57 male) were included for analyses. During the acute phase, 12 patients (12/105, 11%) were tested positive for serum antiganglioside antibodies, including anti-GQ1b immunoglobulin (Ig) G (n = 5) or IgM (n = 4), anti-GM1 IgM (n = 3), and anti-GD1a IgG (n = 1, including 1 patient with a positive anti-GQ1b antibody). Patients with antiganglioside antibodies showed lesser intensity of spontaneous nystagmus (median [interquartile range] = 1.8 [1.2-2.1] vs 3.4 [1.5-9.5], p = 0.003) and a lesser degree of canal paresis (30 [17-47] vs 58 [34-79], p = 0.028) and gain asymmetry of the vestibulo-ocular reflex for the horizontal semicircular canal during head impulse tests (0.07 [-0.04 to 0.61] vs 0.36 [0.18-0.47], p = 0.032) than those without antibodies. Negative conversion of antibodies and vestibular recovery were observed in most patients (6/8, 75%). Among 30 patients with AUPV with 4-hour delayed 3D fluid-attenuated inversion recovery dedicated to the inner ear, gadolinium enhancement was observed in 18 (18/30, 60%), either in the vestibule (n = 9), semicircular canal (n = 6), or vestibular nerve (n = 5). The positivity rates based on specific antibodies could not be determined due to limited sample sizes.

DISCUSSION

The association between antiganglioside antibodies and AUPV suggests an immune-mediated mechanism in acute vestibular failure and extends the clinical spectrum of antiganglioside antibody syndrome.

Sugar distributions on gangliosides guide the formation and stability of amyloid-β oligomers

Aggregation of Aβ peptides is a key contributor to the etiology of Alzheimer's disease. Being intrinsically disordered, monomeric Aβ is susceptible to conformational excursions, especially in the presence of important interacting partners such as membrane lipids, to adopt specific aggregation pathways. Furthermore, components such as gangliosides in membranes and lipid rafts are known to play important roles in the adoption of pathways and the generation of discrete neurotoxic oligomers. Yet, what roles do carbohydrates on gangliosides play in this process remains unknown. Here, using GM1, GM3, and GD3 ganglioside micelles as models, we show that the sugar distributions and cationic amino acids within Aβ N-terminal region modulate oligomerization of Aβ temporally, and dictate the stability and maturation of oligomers. These results demonstrate the selectivity of sugar distributions on the membrane surface toward oligomerization of Aβ and thus implicate cell-selective enrichment of oligomers.

Ganglioside GM3 deficiency enhances mast cell sensitivity

Mast cells are a significant source of cytokines and chemokines that play a role in pathological processes. Gangliosides, which are complex lipids with a sugar chain, are present in all eukaryotic cell membranes and comprise lipid rafts. Ganglioside GM3, the first ganglioside in the synthetic pathway, is a common precursor of the specifying derivatives and is well known for its various functions in biosystems. Mast cells contain high levels of gangliosides; however, the involvement of GM3 in mast cell sensitivity is unclear. Therefore, in this study, we elucidated the role of ganglioside GM3 in mast cells and skin inflammation. GM3 synthase (GM3S)-deficient mast cells showed cytosolic granule topological changes and hyperactivation upon IgE-DNP stimulation without affecting proliferation and differentiation. Additionally, inflammatory cytokine levels increased in GM3S-deficient bone marrow-derived mast cells (BMMC). Furthermore, GM3S-KO mice and GM3S-KO BMMC transplantation showed increased skin allergic reactions. Besides mast cell hypersensitivity caused by GM3S deficiency, membrane integrity decreased and GM3 supplementation rescued this loss of membrane integrity. Additionally, GM3S deficiency increased the phosphorylation of p38 mitogen-activated protein kinase. These results suggest that GM3 increases membrane integrity, leading to the suppression of the p38 signalling pathway in BMMC and contributing to skin allergic reaction.

Chemoenzymatic Synthesis of N-Acetyl Analogues of 9-O-Acetylated b-Series Gangliosides

The stable N-acetyl analogues of biologically important 9-O-acetylated b-series gangliosides including 9NAc-GD3, 9NAc-GD2, 9NAc-GD1b, and 9NAc-GT1b were chemoenzymatically synthesized from a GM3 sphingosine. Two chemoenzymatic methods using either 6-azido-6-deoxy-N-acetylmannosamine (ManNAc6N3) as a chemoenzymatic synthon or 6-acetamido-6-deoxy-N-acetylmannosamine (ManNAc6NAc) as an enzymatic precursor for 9-acetamido-9-deoxy-N-acetylneuraminic acid (Neu5Ac9NAc) were developed and compared for the synthesis of 9NAc-GD3. The latter method was found to be more efficient and was used to produce the desired 9-N-acetylated glycosylsphingosines. Furthermore, glycosylsphingosine acylation reaction conditions were improved to obtain target 9-N-acetylated gangliosides in a faster reaction with an easier purification process compared to the previous acylation conditions.

[Exosomes in the life cycle of viruses and the pathogenesis of viral infections]

Exosomes are extracellular vesicles of endosomal origin, with a bilayer membrane, 30160 nm in diameter. Exosomes are released from cells of different origins and are detected in various body fluids. They contain nucleic acids, proteins, lipids, metabolites and can transfer the contents to recipient cells. Exosome biogenesis involves cellular proteins of the Rab GTPase family and the ESCRT system, which regulate budding, vesicle transport, molecule sorting, membrane fusion, formation of multivesicular bodies and exosome secretion. Exosomes are released from cells infected with viruses and may contain viral DNA and RNA, as well as mRNA, microRNA, other types of RNA, proteins and virions. Exosomes are capable of transferring viral components into uninfected cells of various organs and tissues. This review analyzes the impact of exosomes on the life cycle of widespread viruses that cause serious human diseases: human immunodeficiency virus (HIV-1), hepatitis B virus, hepatitis C virus, SARS-CoV-2. Viruses are able to enter cells by endocytosis, use molecular and cellular pathways involving Rab and ESCRT proteins to release exosomes and spread viral infections. It has been shown that exosomes can have multidirectional effects on the pathogenesis of viral infections, suppressing or enhancing the course of diseases. Exosomes can potentially be used in noninvasive diagnostics as biomarkers of the stage of infection, and exosomes loaded with biomolecules and drugs - as therapeutic agents. Genetically modified exosomes are promising candidates for new antiviral vaccines.

Sugar distributions on gangliosides guide the formation and stability of amyloid-β oligomers

Aggregation of Aβ peptides has been known as a key contributor to the etiology of Alzheimer's disease. Being intrinsically disordered, the monomeric Aβ is susceptible to conformational excursions, especially in the presence of key interacting partners such as membrane lipids, to adopt specific aggregation pathways. Furthermore, key components such as gangliosides in membranes and lipid rafts are known to play important roles in the adoption of pathways and the generation of discrete neurotoxic oligomers. Yet, what roles the carbohydrates on gangliosides play in this process remains unknown. Here, using GM1, GM3, and GD3 ganglioside micelles as models, we show that the sugar distributions and cationic amino acids within Aβ N-terminal region modulate oligomerization of Aβ temporally, and dictate the stability and maturation of oligomers.

Recently developed glycosphingolipid probes and their dynamic behavior in cell plasma membranes as revealed by single-molecule imaging

Glycosphingolipids, including gangliosides, are representative lipid raft markers that perform a variety of physiological roles in cell membranes. However, studies aimed at revealing their dynamic behavior in living cells are rare, mostly due to a lack of suitable fluorescent probes. Recently, the ganglio-series, lacto-series, and globo-series glycosphingolipid probes, which mimic the behavior of the parental molecules in terms of partitioning to the raft fraction, were developed by conjugating hydrophilic dyes to the terminal glycans of glycosphingolipids using state-of-art entirely chemical-based synthetic techniques. High-speed, single-molecule observation of these fluorescent probes revealed that gangliosides were scarcely trapped in small domains (100 nm in diameter) for more than 5 ms in steady-state cells, suggesting that rafts including gangliosides were always moving and very small. Furthermore, dual-color, single-molecule observations clearly showed that homodimers and clusters of GPI-anchored proteins were stabilized by transiently recruiting sphingolipids, including gangliosides, to form homodimer rafts and the cluster rafts, respectively. In this review, we briefly summarize recent studies, the development of a variety of glycosphingolipid probes as well as the identification of the raft structures including gangliosides in living cells by single-molecule imaging.

Process Engineering and Glycosyltransferase Improvement for Short Route Chemoenzymatic Total Synthesis of GM1 Gangliosides

Large-scale synthesis of GM1, an important ganglioside in mammalian cells especially those in the nervous system, is needed to explore its therapeutic potential. Biocatalytic production is a promising platform for such a purpose. We report herein the development of process engineering and glycosyltransferase improvement strategies to advance chemoenzymatic total synthesis of GM1. Firstly, a new short route was developed for chemical synthesis of lactosylsphingosine from the commercially available Garner's aldehyde. Secondly, two glycosyltransferases including Campylobacter jejuni β1-4GalNAcT (CjCgtA) and β1-3-galactosyltransferase (CjCgtB) were improved on their soluble expression in E. coli and enzyme stability by fusing with an N-terminal maltose binding protein (MBP). Thirdly, the process for enzymatic synthesis of GM1 sphingosines from lactosylsphingosine was engineered by developing a multistep one-pot multienzyme (MSOPME) strategy without isolating intermediate glycosphingosines and by adding a detergent, sodium cholate, to the later enzymatic glycosylation steps. Installation of a desired fatty acyl chain to GM1 glycosphingosines led to the formation of target GM1 gangliosides. The combination of glycosyltransferase improvement with chemical and enzymatic process engineering represents a significant advance in obtaining GM1 gangliosides containing different sialic acid forms by total chemoenzymatic synthesis in a short route and with high efficiency.

Dietary sialic acids: distribution, structure, and functions

Sialic acids (Sias), a group of over 50 structurally distinct acidic saccharides on the surface of all vertebrate cells, are neuraminic acid derivatives. They serve as glycan chain terminators in extracellular glycolipids and glycoproteins. In particular, Sias have significant implications in cell-to-cell as well as host-to-pathogen interactions and participate in various biological processes, including neurodevelopment, neurodegeneration, fertilization, and tumor migration. However, Sia is also present in some of our daily diets, particularly in conjugated form (sialoglycans), such as those in edible bird's nest, red meats, breast milk, bovine milk, and eggs. Among them, breast milk, especially colostrum, contains a high concentration of sialylated oligosaccharides. Numerous reviews have concentrated on the physiological function of Sia as a cellular component of the body and its relationship with the occurrence of diseases. However, the consumption of Sias through dietary sources exerts significant influence on human health, possibly by modulating the gut microbiota's composition and metabolism. In this review, we summarize the distribution, structure, and biological function of particular Sia-rich diets, including human milk, bovine milk, red meat, and egg.

Therapeutic effects of anti-GM2 CAR-T cells expressing IL-7 and CCL19 for GM2-positive solid cancer in xenograft model

BACKGROUND

While chimeric antigen receptor (CAR)-T cell therapy has demonstrated excellent efficacy in hematopoietic malignancies, its clinical application in solid cancers has yet to be achieved. One of the reasons for such hurdle is a lack of suitable CAR targets in solid cancers.

METHODS

GM2 is one of the gangliosides, a group of glycosphingolipids with sialic acid in the glycan, and overexpressed in various types of solid cancers. In this study, by using interleukin (IL)-7 and chemokine (C-C motif) ligand 19 (CCL19)-producing human CAR-T system which we previously developed, a possibility of GM2 as a solid tumor target for CAR-T cell therapy was explored in a mouse model with human small-cell lung cancer.

RESULTS

Treatment with anti-GM2 IL-7/CCL19-producing CAR-T cells induced complete tumor regression along with an abundant T cell infiltration into the solid tumor tissue and long-term memory responses, without any detectable adverse events. In addition, as measures to control cytokine-release syndrome and neurotoxicity which could occur in association with clinical use of CAR-T cells, we incorporated Herpes simplex virus-thymidine kinase (HSV-TK), a suicide system to trigger apoptosis by administration of ganciclovir (GCV). HSV-TK-expressing anti-GM2 IL-7/CCL19-producing human CAR-T cells were efficiently eliminated by GCV administration in vivo.

CONCLUSIONS

Our study revealed the promising therapeutic efficacy of anti-GM2 IL-7/CCL19-producing human CAR-T cells with an enhanced safety for clinical application in the treatment of patients with GM2-positive solid cancers.

Synthesis and biological activity of ganglioside GM3 analogues with a (S)-CHF-Sialoside linkage and an alkyne tag

The alkyne tag, consisting of only two carbons, is widely used as a bioorthogonal functional group due to its compactness and nonpolar structure, and various probes consisting of lipids bearing an alkyne tag have been developed. Here, we designed and synthesized analogues of ganglioside GM3 bearing an alkyne tag in the fatty acid moiety and evaluated the effect of the alkyne tag on the biological activity. To eliminate the influence of other factors such as degradation of the glycan chain when evaluating biological activity in a cellular environment, we introduced the tag into sialidase-resistant (S)-CHF-linked GM3 analogues developed by our group. The designed analogues were efficiently synthesized by tuning the protecting group of the glucosylsphingosine acceptor. The growth-promoting effect of these analogues on Had-1 cells was dramatically altered depending upon the position of the alkyne tag.

Ganglioside GM3 stimulates lipid-protein co-assembly in α-synuclein amyloid formation

Parkinson's disease is characterized by the aggregation of the presynaptic protein α-synuclein (αSyn), and its co-assembly with lipids and other cellular matter in the brain. Here we investigated lipid-protein co-assembly in a system composed of αSyn and model membranes containing the glycolipid ganglioside GM3. We quantified the uptake of lipids into the co-assembled aggregates and investigated how lipid molecular dynamics is altered by being present in the co-assemblies using solution ¹H- and solid-state ¹³C NMR spectroscopy. Aggregate morphology was studied using cryo-TEM. The overall lipid uptake in the co-assembled aggregates was found to increase with the molar ratio of GM3 in the vesicles. The lipids present in the co-assembled aggregates have reduced acyl chain and headgroup dynamics compared to the protein-free bilayer system. These findings may improve our understanding of how different types of lipids can influence the composition of αSyn aggregates, which may have consequences for amyloid formation in vivo.

Sialyltransferase Activity Assay for Ganglioside GM3 Synthase

GM3 synthase (GM3S) is a sialyltransferase that transfers sialic acid from CMP-sialic acid to lactosylceramide. This reaction results in formation of ganglioside GM3 and is essential for biosynthesis of its downstream derivatives, which include a- and b-series gangliosides. Here, we describe a method for GM3S enzymatic assay using fluorescence-labeled alkyl lactoside as acceptor substrate, followed by HPLC for separation of enzymatic product. The method allows quantitative assay of GM3S sialyltransferase activity in cultured cells and mouse brain tissues.

Neuronal Ganglioside and Glycosphingolipid (GSL) Metabolism and Disease : Cascades of Secondary Metabolic Errors Can Generate Complex Pathologies (in LSDs)

Glycosphingolipids (GSLs) are a diverse group of membrane components occurring mainly on the surfaces of mammalian cells. They and their metabolites have a role in intercellular communication, serving as versatile biochemical signals (Kaltner et al, Biochem J 476(18):2623-2655, 2019) and in many cellular pathways. Anionic GSLs, the sialic acid containing gangliosides (GGs), are essential constituents of neuronal cell surfaces, whereas anionic sulfatides are key components of myelin and myelin forming oligodendrocytes. The stepwise biosynthetic pathways of GSLs occur at and lead along the membranes of organellar surfaces of the secretory pathway. After formation of the hydrophobic ceramide membrane anchor of GSLs at the ER, membrane-spanning glycosyltransferases (GTs) of the Golgi and Trans-Golgi network generate cell type-specific GSL patterns for cellular surfaces. GSLs of the cellular plasma membrane can reach intra-lysosomal, i.e. luminal, vesicles (ILVs) by endocytic pathways for degradation. Soluble glycoproteins, the glycosidases, lipid binding and transfer proteins and acid ceramidase are needed for the lysosomal catabolism of GSLs at ILV-membrane surfaces. Inherited mutations triggering a functional loss of glycosylated lysosomal hydrolases and lipid binding proteins involved in GSL degradation cause a primary lysosomal accumulation of their non-degradable GSL substrates in lysosomal storage diseases (LSDs). Lipid binding proteins, the SAPs, and the various lipids of the ILV-membranes regulate GSL catabolism, but also primary storage compounds such as sphingomyelin (SM), cholesterol (Chol.), or chondroitin sulfate can effectively inhibit catabolic lysosomal pathways of GSLs. This causes cascades of metabolic errors, accumulating secondary lysosomal GSL- and GG- storage that can trigger a complex pathology (Breiden and Sandhoff, Int J Mol Sci 21(7):2566, 2020).

GM3 synthase deficiency increases brain glucose metabolism in mice

GM3 synthase (GM3S) deficiency is a rare neurodevelopmental disorder caused by an inability to synthesize gangliosides, for which there is currently no treatment. Gangliosides are brain-enriched, plasma membrane glycosphingolipids with poorly understood biological functions related to cell adhesion, growth, and receptor-mediated signal transduction. Here, we investigated the effects of GM3S deficiency on metabolism and mitochondrial function in a mouse model. By indirect calorimetry, GM3S knockout mice exhibited increased whole-body respiration and an increased reliance upon carbohydrate as an energy source. 18F-FDG PET confirmed higher brain glucose uptake in knockout mice, and GM3S deficient N41 neuronal cells showed higher glucose utilization in vitro. Brain mitochondria from knockout mice respired at a higher rate on Complex I substrates including pyruvate. This appeared to be due to higher expression of pyruvate dehydrogenase (PDH) and lower phosphorylation of PDH, which would favor pyruvate entry into the mitochondrial TCA cycle. Finally, it was observed that blocking glucose metabolism with the glycolysis inhibitor 2-deoxyglucose reduced seizure intensity in GM3S knockout mice following administration of kainate. In conclusion, GM3S deficiency may be associated with a hypermetabolic phenotype that could promote seizure activity.

Regulation of signal transduction by gangliosides in lipid rafts: focus on GM3-IR and GM1-TrkA interactions

The interactions between gangliosides and proteins belonging to the same or different lipid domains and their influence on physiological and pathological states have been analysed in detail. A well-known factor impacting on lipid-protein interactions and their biological outcomes is the dynamic composition of plasma membrane. This review focuses on GM1 and GM3 gangliosides because they are an integral part of protein-receptor complexes and dysregulation of their concentration shows a direct correlation with the onset of pathological conditions. We first discuss the interaction between GM3 and insulin receptor in relation to insulin responses, with an increase in GM3 correlating with the onset of metabolic dysfunction. Next, we describe the case of the GM1-TrkA interaction, relevant to nerve-cell differentiation and homeostasis as deficiency in plasma-membrane GM1 is known to promote neurodegeneration. These two examples highlight the fact that interactions between gangliosides and receptor proteins within the plasma membrane are crucial in controlling cell signalling and pathophysiological cellular states.

Molecular dynamics simulations and solid-state nuclear magnetic resonance spectroscopy measurements of C-H bond order parameters and effective correlation times in a POPC-GM3 bilayer

Glycolipids such as gangliosides affect the properties of lipid membranes and in extension the interactions between membranes and other biomolecules like proteins. To better understand how the properties of individual lipid molecules can contribute to shape the functional aspects of a membrane, the spatial restriction and dynamics of C-H bond segments can be measured using nuclear magnetic resonance (NMR) spectroscopy. We combine solid-state NMR spectroscopy with all-atom molecular dynamics (MD) simulations to investigate how ganglioside GM3 affects the bilayer structure and dynamics of C-H bond segments. These two methods yield reorientational correlation functions, molecular profiles of C-H bond order parameters |S_CH| and effective correlation times τ_e, which we compare for lipids in POPC bilayers with and without 30 mol% GM3. Our results revealed that all C-H segments of POPC reorient slower in the presence of GM3 and that the defining features of the GM3-POPC bilayer lie in the GM3 headgroup; it gives the bilayer an extended headgroup layer with high order (|S_CH| up to 0.3-0.4) and slow dynamics (τ_e up to 100 ns), a character that may be mechanistically important in ganglioside interactions with other biomolecules.

Identification of ST3GAL5 as a prognostic biomarker correlating with CD8+ T cell exhaustion in clear cell renal cell carcinoma

Aberrant sialylation is frequently observed in tumor development, but which sialyltransferases are involved in this event are not well known. Herein, we performed comprehensive analyses on six ST3GAL family members, the α-2,3 sialyltransferases, in clear cell renal cell carcinoma (ccRCC) from public datasets. Only ST3GAL5 was consistently and significantly overexpressed in ccRCC (n = 791 in total), compared with normal kidney tissues. Its overexpression was positively correlated with tumor stage, grade, and the poor prognosis in ccRCC patients. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses indicated the involvement of ST3GAL5 in tumor immunoregulation. Then we revealed that ST3GAL5 expression showed a positive correlation with CD8⁺ T cell infiltration, using multiple tools on TIMER2.0 web server. Notably, ST3GAL5 overexpression was further identified to be associated with expression signature of CD8⁺ T cell exhaustion in ccRCC samples from three datasets (n = 867 in total; r > 0.3, p < 0.001). In our own ccRCC cohort (n = 45), immunohistochemistry and immunofluorescence staining confirmed that ST3GAL5 overexpression was accompanied by high CD8⁺ T cell infiltration with the increased exhaustion markers. Altogether, ST3GAL5 as a promising prognostic biomarker with CD8⁺ T cell exhaustion in ccRCC is indicated.

Start Me Up: How Can Surrounding Gangliosides Affect Sodium-Potassium ATPase Activity and Steer towards Pathological Ion Imbalance in Neurons?

Gangliosides, amphiphilic glycosphingolipids, tend to associate laterally with other membrane constituents and undergo extensive interactions with membrane proteins in cis or trans configurations. Studies of human diseases resulting from mutations in the ganglioside biosynthesis pathway and research on transgenic mice with the same mutations implicate gangliosides in the pathogenesis of epilepsy. Gangliosides are reported to affect the activity of the Na⁺/K⁺-ATPase, the ubiquitously expressed plasma membrane pump responsible for the stabilization of the resting membrane potential by hyperpolarization, firing up the action potential and ion homeostasis. Impaired Na⁺/K⁺-ATPase activity has also been hypothesized to cause seizures by several mechanisms. In this review we present different epileptic phenotypes that are caused by impaired activity of Na⁺/K⁺-ATPase or changed membrane ganglioside composition. We further discuss how gangliosides may influence Na⁺/K⁺-ATPase activity by acting as lipid sorting machinery providing the optimal stage for Na⁺/K⁺-ATPase function. By establishing a distinct lipid environment, together with other membrane lipids, gangliosides possibly modulate Na⁺/K⁺-ATPase activity and aid in “starting up” and “turning off” this vital pump. Therefore, structural changes of neuronal membranes caused by altered ganglioside composition can be a contributing factor leading to aberrant Na⁺/K⁺-ATPase activity and ion imbalance priming neurons for pathological firing.

Structural characterization and analysis of different epimers of neutral glycosphingolipid LcGg4 by ion mobility spectrometry-mass spectrometry

LcGg4, a neutral glycosphingolipid (GSL) and cancer antigen, its epimers GalNAc-LcGg4 and GlcNAc-LcGg4, and three lipid forms of GalNAc-LcGg4 were studied by mass spectrometry (MS). It was found that different forms of GalNAc-LcGg4 carrying homologous (d16:1/18:0) and (d18:1/18:0) lipids were easily separated and identified using liquid chromatography (LC)-MS. In addition, like gangliosides, homologous lipid forms of GalNAc-LcGg4 showed the same fragmentation pattern, except for a uniform shift of their glycolipid product ions by a certain m/z number determined by the varied lipid structure. It was also disclosed that LcGg4 and its epimers GalNAc-LcGg4 and GlcNAc-LcGg4, which are different only in the C4-configuration of their non-reducing end sugar residues, gave the same MS/MS product ions in similar relative intensities, as well as the same LC retention time, suggesting the challenge to differentiate epimeric GSLs by LC-MS. However, ion mobility spectrometry (IMS)-MS was able to efficiently separate and distinguish these epimers. This study has demonstrated the promise of IMS-MS for isomeric GSL characterization and the IMS-MS and LC-MS/MS combination for natural GSL analysis.

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

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

Ganglioside GM3 Synthase Deficiency in Mouse Models and Human Patients

Gangliosides (glycosphingolipids containing one or more sialic acids) are highly expressed in neural tissues in vertebrates, and four species (GM1a, GD1a, GD1b, GT1b) are predominant in mammalian brains. GM3 is the precursor of each of these four species and is the major ganglioside in many nonneural tissues. GM3 synthase (GM3S), encoded by ST3GAL5 gene in humans, is a sialyltransferase responsible for synthesis of GM3 from its precursor, lactosylceramide. ST3GAL5 mutations cause an autosomal recessive form of severe infantile-onset neurological disease characterized by progressive microcephaly, intellectual disability, dyskinetic movements, blindness, deafness, intractable seizures, and pigment changes. Some of these clinical features are consistently present in patients with ST3GAL5 mutations, whereas others have variable expression. GM3S knockout (KO) mice have deafness and enhanced insulin sensitivity, but otherwise do not display the above-described neurological defects reported in ST3GAL5 patients. The authors present an overview of physiological functions and pathological aspects of gangliosides based on findings from studies of GM3S KO mice and discuss differential phenotypes of GM3S KO mice versus human GM3S-deficiency patients.

Mass Spectrometry-Based Techniques to Elucidate the Sugar Code

Cells encode information in the sequence of biopolymers, such as nucleic acids, proteins, and glycans. Although glycans are essential to all living organisms, surprisingly little is known about the "sugar code" and the biological roles of these molecules. The reason glycobiology lags behind its counterparts dealing with nucleic acids and proteins lies in the complexity of carbohydrate structures, which renders their analysis extremely challenging. Building blocks that may differ only in the configuration of a single stereocenter, combined with the vast possibilities to connect monosaccharide units, lead to an immense variety of isomers, which poses a formidable challenge to conventional mass spectrometry. In recent years, however, a combination of innovative ion activation methods, commercialization of ion mobility-mass spectrometry, progress in gas-phase ion spectroscopy, and advances in computational chemistry have led to a revolution in mass spectrometry-based glycan analysis. The present review focuses on the above techniques that expanded the traditional glycomics toolkit and provided spectacular insight into the structure of these fascinating biomolecules. To emphasize the specific challenges associated with them, major classes of mammalian glycans are discussed in separate sections. By doing so, we aim to put the spotlight on the most important element of glycobiology: the glycans themselves.

SARS-CoV-2 Attacks in the Brain: Focus on the Sialome

The epidemiological observations suggest that respiratory and gastrointestinal symptoms caused by severe acute respiratory coronavirus 2 (SARS-CoV-2) are accompanied by short- and long-term neurological manifestations. There is increasing evidence that the neuroinvasive potential of SARS-CoV-2 is closely related to its capacity to interact with cell membrane sialome. Given the wide expression of sialylated compounds of cell membranes in the brain, the interplay between cell membrane sialoglycans and the virus is crucial for its attachment and cell entry, transport, neuronal damage and brain immunity. Here, we focus on the significance of the brain sialome in the progress of coronavirus disease 2019 (COVID-19) and SARS-CoV-2-induced neuropathology.

Role of GD3 Synthase ST8Sia I in Cancers

Simple Summary

The carbohydrate moiety of cell surface glycolipids is modified in cancers of neuro–ectoderm origin, leading to the expression of more complex structures with two or more sialic acid residues. These alterations result from the upregulation of the ST8SIA1 gene that encodes GD3 synthase, the enzyme controlling the biosynthesis of complex gangliosides, and are usually associated with a more aggressive phenotype and a poor outcome for patients, making GD3 synthase an interesting target for cancer therapy. This review reports our general knowledge of GD3 synthase gene expression and regulation, its role in both epithelial–mesenchymal transition (EMT) and cancer progression, and the different approaches targeting GD3S expression in cancers.

Abstract

GD3 synthase controls the biosynthesis of complex gangliosides, bearing two or more sialic acid residues. Disialylated gangliosides GD3 and GD2 are tumor-associated carbohydrate antigens (TACA) in neuro–ectoderm-derived cancers, and are directly involved in cell malignant properties, i.e., migration, invasion, stemness, and epithelial–mesenchymal transition. Since GD3 and GD2 levels are directly linked to GD3 synthase expression and activity, targeting GD3 synthase appears to be a promising strategy through which to interfere with ganglioside-associated malignant properties. We review here the current knowledge on GD3 synthase expression and regulation in cancers, and the consequences of complex ganglioside expression on cancer cell signaling and properties, highlighting the relationships between GD3 synthase expression and epithelial–mesenchymal transition and stemness. Different strategies were used to modulate GD3 synthase expression in cancer cells in vitro and in animal models, such as inhibitors or siRNA/lncRNA, which efficiently reduced cancer cell malignant properties and the proportion of GD2 positive cancer stem cells, which are associated with high metastatic properties, resistance to therapy, and cancer relapse. These data show the relevance of targeting GD3 synthase in association with conventional therapies, to decrease the number of cancer stem cells in tumors.

COVID-19, Cation Dysmetabolism, Sialic Acid, CD147, ACE2, Viroporins, Hepcidin and Ferroptosis: A Possible Unifying Hypothesis

Background: iron and calcium dysmetabolism, with hyperferritinemia, hypoferremia, hypocalcemia and anemia have been documented in the majority of COVID-19 patients at later/worse stages. Furthermore, complementary to ACE2, both sialic acid (SA) molecules and CD147 proved relevant host receptors for SARS-CoV-2 entry, which explains the viral attack to multiple types of cells, including erythrocytes, endothelium and neural tissue. Several authors advocated that cell ferroptosis may be the core and final cell degenerative mechanism.

Methods: a literature research was performed in several scientific search engines, such as PubMed Central, Cochrane Library, Chemical Abstract Service. More than 500 articles were retrieved until mid-December 2021, to highlight the available evidence about the investigated issues.

Results: based on COVID-19 literature data, we have highlighted a few pathophysiological mechanisms, associated with virus-based cation dysmetabolism, multi-organ attack, mitochondria degeneration and ferroptosis. Our suggested elucidated pathological sequence is: a) spike protein subunit S1 docking with sialylated membrane glycoproteins/receptors (ACE2, CD147), and S2 subunit fusion with the lipid layer; b) cell membrane morpho-functional changes due to the consequent electro-chemical variations and viroporin action, which induce an altered ion channel function and intracellular cation accumulation; c) additional intracellular iron concentration due to a deregulated hepcidin-ferroportin axis, with higher hepcidin levels. Viral invasion may also affect erythrocytes/erythroid precursors, endothelial cells and macrophages, through SA and CD147 receptors, with relative hemoglobin and iron/calcium dysmetabolism. AB0 blood group, hemochromatosis, or environmental elements may represent possible factors which affect individual susceptibility to COVID-19.    

Conclusions: our literature analysis confirms the combined role of SA molecules, ACE2, CD147, viroporins and hepcidin in determining the cation dysmetabolism and final ferroptosis in the cells infected by SARS-CoV-2. The altered ion channels and electrochemical gradients of the cell membrane have a pivotal role in the virus entry and cell dysmetabolism, with subsequent multi-organ immune-inflammatory degeneration and erythrocyte/hemoglobin alterations.

Systemic Lectin-Glycan Interaction of Pathogenic Enteric Bacteria in the Gastrointestinal Tract

Microorganisms, such as bacteria, viruses, and fungi, and host cells, such as plants and animals, have carbohydrate chains and lectins that reciprocally recognize one another. In hosts, the defense system is activated upon non-self-pattern recognition of microbial pathogen-associated molecular patterns. These are present in Gram-negative and Gram-positive bacteria and fungi. Glycan-based PAMPs are bound to a class of lectins that are widely distributed among eukaryotes. The first step of bacterial infection in humans is the adhesion of the pathogen's lectin-like proteins to the outer membrane surfaces of host cells, which are composed of glycans. Microbes and hosts binding to each other specifically is of critical importance. The adhesion factors used between pathogens and hosts remain unknown; therefore, research is needed to identify these factors to prevent intestinal infection or treat it in its early stages. This review aims to present a vision for the prevention and treatment of infectious diseases by identifying the role of the host glycans in the immune response against pathogenic intestinal bacteria through studies on the lectin-glycan interaction.

Ganglioside binding domains in proteins: Physiological and pathological mechanisms

Gangliosides are anionic lipids that form condensed membrane clusters (lipid rafts) and exert major regulatory functions on a wide range of proteins. In this review, we propose a new view of the structural features of gangliosides with special emphasis on emerging properties associated with protein binding modes. We analyze the different possibilities of molecular associations of gangliosides in lipid rafts and the role of cholesterol in this organization. We are particularly interested in amide groups of N-acetylated sugars which make it possible to neutralize the negative charge of the carboxylate group of sialic acids. We refer to this effect as "NH trick" and we demonstrate that it is operative in GM1, GD1a, GD1b and GT1b gangliosides. The NH trick is key to understand the different topologies adopted by gangliosides (chalice-like at the edge of lipid rafts, condensed clusters in central areas) and their impact on protein binding. We define three major types of ganglioside-binding domains (GBDs): α-helical, loop shaped, and large flat surface. We describe the mode of interaction of each GBD with typical reference proteins: synaptotagmin, 5HT1A receptor, cholera and botulinum toxins, HIV-1 surface envelope glycoprotein gp120, SARS-CoV-2 spike protein, cellular prion protein, Alzheimer's β-amyloid peptide and Parkinson's disease associated α-synuclein. We discuss the common mechanisms and peculiarities of protein binding to gangliosides in the light of physiological and pathological conditions. We anticipate that innovative ganglioside-based therapies will soon show an exponential growth for the treatment of cancer, microbial infections, and neurodegenerative diseases.

Mammalian brain glycoproteins exhibit diminished glycan complexity compared to other tissues

Glycosylation is essential to brain development and function, but prior studies have often been limited to a single analytical technique and excluded region- and sex-specific analyses. Here, using several methodologies, we analyze Asn-linked and Ser/Thr/Tyr-linked protein glycosylation between brain regions and sexes in mice. Brain N-glycans are less complex in sequence and variety compared to other tissues, consisting predominantly of high-mannose and fucosylated/bisected structures. Most brain O-glycans are unbranched, sialylated O-GalNAc and O-mannose structures. A consistent pattern is observed between regions, and sex differences are minimal compared to those in plasma. Brain glycans correlate with RNA expression of their synthetic enzymes, and analysis of glycosylation genes in humans show a global downregulation in the brain compared to other tissues. We hypothesize that this restricted repertoire of protein glycans arises from their tight regulation in the brain. These results provide a roadmap for future studies of glycosylation in neurodevelopment and disease.

The Structural Diversity of Natural Glycosphingolipids (GSLs)

Glycosphingolipids (GSLs) are a subclass of glycolipids made of a glycan and a ceramide that, in turn, is composed of a sphingoid base moiety and a fatty acyl group. GSLs represent the vast majority of glycolipids in eukaryotes, and as an essential component of the cell membrane, they play an important role in many biological and pathological processes. Therefore, they are useful targets for the development of novel diagnostic and therapeutic methods for human diseases. Since sphingosine was first described by J. L. Thudichum in 1884, several hundred GSL species, not including their diverse lipid forms that can further amplify the number of individual GSLs by many folds, have been isolated from natural sources and structurally characterized. This review tries to provide a comprehensive survey of the major GSL species, especially those with distinct glycan structures and modification patterns, and the ceramides with unique modifications of the lipid chains, that have been discovered to date. In particular, this review is focused on GSLs from eukaryotic species. This review has listed 251 GSL glycans with different linkages, 127 glycans with unique modifications, 46 sphingoids, and 43 fatty acyl groups. It should be helpful for scientists who are interested in GSLs, from isolation and structural analyses to chemical and enzymatic syntheses, as well as their biological studies and applications.

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.

Studies and Application of Sialylated Milk Components on Regulating Neonatal Gut Microbiota and Health

Breast milk is rich in sialic acids (SA), which are commonly combined with milk oligosaccharides and glycoconjugates. As a functional nutrient component, SA-containing milk components have received increasing attention in recent years. Sialylated human milk oligosaccharides (HMOs) have been demonstrated to promote the growth and metabolism of beneficial gut microbiota in infants, bringing positive outcomes to intestinal health and immune function. They also exhibit antiviral and bacteriostatic activities in the intestinal mucosa of new-borns, thereby inhibiting the adhesion of pathogens to host cells. These properties play a pivotal role in regulating the intestinal microbial ecosystem and preventing the occurrence of neonatal inflammatory diseases. In addition, some recent studies also support the promoting effects of sialylated HMOs on neonatal bone and brain development. In addition to HMOs, sialylated glycoproteins and glycolipids are abundant in milk, and are also critical to neonatal health. This article reviews the current research progress in the regulation of sialylated milk oligosaccharides and glycoconjugates on neonatal gut microbiota and health.

Role of hypothalamic de novo ceramides synthesis in obesity and associated metabolic disorders

Background

Sphingolipid-mediated signalling pathways are described as important players in the normal functioning of neurons and nonneuronal cells in the central nervous system (CNS).

Scope of review

This review aims to show role of de novo ceramide synthesis in the CNS in controling key physiological processes, including food intake, energy expenditure, and thermogenesis. The corollary is a condition that leads to a dysfunction in ceramide metabolism in these central regions that can have major consequences on the physiological regulation of energy balance.

Major conclusions

Excessive hypothalamic de novo ceramide synthesis has been shown to result in the establishment of central insulin resistance, endoplasmic reticulum stress, and inflammation. Additionally, excessive hypothalamic de novo ceramide synthesis has also been associated with changes in the activity of the autonomic nervous system. Such dysregulation of hypothalamic de novo ceramide synthesis forms the key starting point for the initiation of pathophysiological conditions such as obesity – which may or may not be associated with type 2 diabetes.

DNA damage response in vascular endothelial senescence: Implication for radiation-induced cardiovascular diseases

A post-exposure cohort study in Hiroshima and Nagasaki reported that low-dose exposure to radiation heightened the risk of cardiovascular diseases (CVD), such as stroke and myocardial infarction, by 14-18% per Gy. Moreover, the risk of atherosclerosis in the coronary arteries reportedly increases with radiation therapy of the chest, including breast and lung cancer treatment. Cellular senescence of vascular endothelial cells (ECs) is believed to play an important role in radiation-induced CVDs. The molecular mechanism of age-related cellular senescence is believed to involve genomic instability and DNA damage response (DDR); the chronic inflammation associated with senescence causes cardiovascular damage. Therefore, vascular endothelial cell senescence is believed to induce the pathogenesis of CVDs after radiation exposure. The findings of several prior studies have revealed that ionizing radiation (IR) induces cellular senescence as well as cell death in ECs. We have previously reported that DDR activates endothelial nitric oxide (NO) synthase, and NO production promotes endothelial senescence. Endothelial NO synthase (eNOS) is a major isoform expressed in ECs that maintains cardiovascular homeostasis. Therefore, radiation-induced NO production, a component of the DDR in ECs, may be involved in CVDs after radiation exposure. In this article, we describe the pathology of radiation-induced CVD and the unique radio-response to radiation exposure in ECs.

Homeostatic and pathogenic roles of the GM3 ganglioside

Two decades ago, we achieved molecular cloning of ganglioside GM3 synthase (GM3S; ST3GAL5), the enzyme responsible for initiating biosynthesis of complex gangliosides. The efforts of our research group since then have been focused on clarifying the physiological and pathological roles of gangliosides, particularly GM3. This review summarizes our long-term studies on the roles of GM3 in insulin resistance and adipogenesis in adipose tissues, cholesterol uptake in intestine, and leptin resistance in hypothalamus. We hypothesized that GM3 plays a role in innate immune function of macrophages and demonstrated that molecular species of GM3 with differing acyl-chain structures and modifications functioned as pro- and anti-inflammatory endogenous Toll-like receptor 4 (TLR4) modulators in macrophages. Very-long-chain and α-hydroxy GM3 species enhanced TLR4 activation, whereas long-chain and unsaturated GM3 species counteracted this effect. Lipidomic analyses of serum and adipose tissues revealed that imbalances between such pro- and anti-inflammatory GM3 species promoted progression of metabolic disorders. GM3 thus functions as a physiological regulatory factor controlling the balance between homeostatic and pathological states. Ongoing studies based on these findings will clarify the mechanisms underlying ganglioside-dependent control of energy homeostasis and innate immune responses.

Chemoenzymatic Synthesis and Facile Purification of Gangliosides

Gangliosides are biologically important sialic acid-containing glycolipids found commonly in human and other vertebrates. Isolation of pure gangliosides from cells or tissues is difficult, and chemical synthesis of gangliosides usually involves numerous steps with low synthetic yields. We report here a chemoenzymatic synthesis and purification protocol for two ganglioside cancer antigens, GM3 and GD3. One-pot multienzyme glycosylation reactions are used to sequentially prepare GM3 and GD3 sphingosines from chemically synthesized lactosyl sphingosine. A facile C18-cartridge purification procedure after each glycosylation reaction provides the desired pure glycosyl sphingosine product, which is readily acylated to form the target ganglioside. © 2021 Wiley Periodicals LLC. Basic Protocol: Chemoenzymatic synthesis and purification of GM3 and GD3 gangliosides Support Protocol: Monitoring reactions by thin-layer chromatography.