Ganglioside biochemistry

Gangliosides as Therapeutic Targets for Neurodegenerative Diseases

Gangliosides, sialic acid-containing glycosphingolipids, are abundant in cell membranes and primarily involved in controlling cell signaling and cell communication. The altered ganglioside pattern has been demonstrated in several neurodegenerative diseases, characterized during early-onset or infancy, emphasizing the significance of gangliosides in the brain. Enzymes required for the biosynthesis of gangliosides are linked to several devastating neurological disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), hereditary spastic paraplegia (HSP). In this review, we summarized not only the critical roles of biosynthetic enzymes and their inhibitors in ganglioside metabolism but also the efficacy of treatment strategies of ganglioside to address their significance in those diseases.

Amyloid oligomers and their membrane toxicity - A perspective study

Amyloidosis is a condition involving a disparate group of pathologies characterized by the extracellular deposition of insoluble fibrils composed of broken-down proteins. These proteins can accumulate locally, causing peculiar symptoms, or in a widespread way, involving many organs and. causing severe systemic failure. The damage that is created is related not only to the accumulation of. amyloid fibrils but above all to the precursor oligomers of the fibrils that manage to enter the cell in a very particular way. This article analyzes the current state of research related to the entry of these oligomers into the cell membrane and the theories related to their toxicity. The paper proposed here not only aims to review the contents in the literature but also proposes a new vision of amyloid toxicity. that could occur in a multiphase process catalyzed by the cell membrane itself. In this process, the denaturation of the lipid bilayer is followed by the stabilization of a pore through energetically favorable self-assembly processes which are achieved through particular oligomeric structures.

Cinnamic acid, a natural plant compound, exhibits neuroprotection in a mouse model of Sandhoff disease via PPARα

Tay-Sachs disease (TSD) and its severe form Sandhoff disease (SD) are autosomal recessive lysosomal storage metabolic disorders, which often result into excessive GM2 ganglioside accumulation predominantly in lysosomes of nerve cells. Although patients with these diseases appear normal at birth, the progressive accumulation of undegraded GM2 gangliosides in neurons leads to early death accompanied by manifestation of motor difficulties and gradual loss of behavioral skills. Unfortunately, there is still no effective treatment available for TSD/SD. The present study highlights the importance of cinnamic acid (CA), a naturally occurring aromatic fatty acid present in a number of plants, in inhibiting the disease process in a transgenic mouse model of SD. Oral administration of CA significantly attenuated glial activation and inflammation and reduced the accumulation of GM2 gangliosides/glycoconjugates in the cerebral cortex of Sandhoff mice. Besides, oral CA also improved behavioral performance and increased the survival of Sandhoff mice. While assessing the mechanism, we found that oral administration of CA increased the level of peroxisome proliferator-activated receptor α (PPARα) in the brain of Sandhoff mice and that oral CA remained unable to reduce glycoconjugates, improve behavior and increase survival in Sandhoff mice lacking PPARα. Our results indicate a beneficial function of CA that utilizes a PPARα-dependent mechanism to halt the progression of SD and thereby increase the longevity of Sandhoff mice.

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.

Advances in Mass Spectrometry of Gangliosides Expressed in Brain Cancers

Gangliosides are highly abundant in the human brain where they are involved in major biological events. In brain cancers, alterations of ganglioside pattern occur, some of which being correlated with neoplastic transformation, while others with tumor proliferation. Of all techniques, mass spectrometry (MS) has proven to be one of the most effective in gangliosidomics, due to its ability to characterize heterogeneous mixtures and discover species with biomarker value. This review highlights the most significant achievements of MS in the analysis of gangliosides in human brain cancers. The first part presents the latest state of MS development in the discovery of ganglioside markers in primary brain tumors, with a particular emphasis on the ion mobility separation (IMS) MS and its contribution to the elucidation of the gangliosidome associated with aggressive tumors. The second part is focused on MS of gangliosides in brain metastases, highlighting the ability of matrix-assisted laser desorption/ionization (MALDI)-MS, microfluidics-MS and tandem MS to decipher and structurally characterize species involved in the metastatic process. In the end, several conclusions and perspectives are presented, among which the need for development of reliable software and a user-friendly structural database as a search platform in brain tumor diagnostics.

Neurotrophic Natural Products

Neurotrophins (NGF, BDNF, NT3, NT4) can decrease cell death, induce differentiation, as well as sustain the structure and function of neurons, which make them promising therapeutic agents for the treatment of neurodegenerative disorders. However, neurotrophins have not been very effective in clinical trials mostly because they cannot pass through the blood-brain barrier owing to being high-molecular-weight proteins. Thus, neurotrophin-mimic small molecules, which stimulate the synthesis of endogenous neurotrophins or enhance neurotrophic actions, may serve as promising alternatives to neurotrophins. Small-molecular-weight natural products, which have been used in dietary functional foods or in traditional medicines over the course of human history, have a great potential for the development of new therapeutic agents against neurodegenerative diseases such as Alzheimer's disease. In this contribution, a variety of natural products possessing neurotrophic properties such as neurogenesis, neurite outgrowth promotion (neuritogenesis), and neuroprotection are described, and a focus is made on the chemistry and biology of several neurotrophic natural products.

Lipid raft interacting galectin 8 regulates primary ciliogenesis

Primary cilium is a specialized sensory organelle that transmits environmental information into cells. Its length is tightly controlled by various mechanisms such as the frequency or the cargo size of the intraflagellar transport trains which deliver the building materials such as tubulin subunits essential for the growing cilia. Here, we show the sialoglycan interacting galectin 8 regulates the process of primary ciliogenesis. As the epithelia become polarized, there are more galectin 8 being apically secreted and these extracellular galectin 8 molecules apparently bind to a lipid raft enriched domain at the base of the primary cilia through interacting with lipid raft components, such as GD3 ganglioside and scaffold protein caveolin 1. Furthermore, the binding of galectin 8 at this critical region triggers rapid growth of primary cilia by perturbing the barrier function of the transition zone (TZ). Our study also demonstrates the functionality of this barrier depends on intact organization of lipid rafts at the cilia as genetically knockout of Cav1 and pharmacologically inhibition of lipid raft both phenocopy the effect of apical addition of recombinant galectin 8; that is, rapid elongation of primary cilia and redistribution of cilia proteins from TZ to the growing axoneme. Indeed, as cilia elongated, endogenous galectin 8, caveolin 1, and TZ component, TMEM231, also transited from the TZ to the growing axoneme. We also noted that the interaction between caveolin 1 and TMEM231 could be perturbed by exogenous galectin 8. Taken together, we proposed that galectin 8 promoted primary cilia elongation through impeding the barrier function of the TZ by interfering with the interaction between caveolin 1 and TMEM231.

The Ying and Yang of Ganglioside Function in Cancer

The plethora of information about the expression of cancer cell-associated gangliosides, their role(s) in signal transduction, and their potential usefulness in the development of cancer treatments makes this an appropriate time to review these enigmatic glycosphingolipids. Evidence, reflecting the work of many, indicates that (1) expression of specific gangliosides, not generally found in high concentrations in most normal human cells, can be linked to certain types of cancer. (2) Gangliosides can affect the ability of cells to interact either directly or indirectly with growth factor receptors, thereby changing such things as a cell's mobility, rate of proliferation, and metastatic ability. (3) Anti-ganglioside antibodies have been tested, with some success, as potential treatments for certain cancers. (4) Cancer-associated gangliosides shed into the circulation can (a) affect immune cell responsiveness either positively or negatively, (b) be considered as diagnostic markers, and (c) be used to look for recurrence. (5) Cancer registries enable investigators to evaluate data from sufficient numbers of patients to obtain information about potential therapies. Despite advances that have been made, a discussion of possible approaches to identifying additional treatment strategies to inhibit metastasis, responsible for the majority of deaths of cancer patients, as well as for treating therapy-resistant tumors, is included.

Guillain-Barré Syndrome

OBJECTIVE

This article summarizes the clinical features, diagnostic criteria, differential diagnosis, pathogenesis, and prognosis of Guillain-Barré syndrome (GBS), with insights into the current and future diagnostic and therapeutic interventions for this neuromuscular syndrome.

LATEST DEVELOPMENTS

GBS is an acute, inflammatory, immune-mediated polyradiculoneuropathy that encompasses many clinical variants and divergent pathogenic mechanisms that lead to axonal, demyelinating, or mixed findings on electrodiagnostic studies. The type of antecedent infection, the development of pathogenic cross-reactive antibodies via molecular mimicry, and the location of the target gangliosides affect the subtype and severity of the illness. The data from the International GBS Outcome Study have highlighted regional variances, provided new and internationally validated prognosis tools that are beneficial for counseling, and introduced a platform for discussion of GBS-related open questions. New research has been undertaken, including research on novel diagnostic and therapeutic biomarkers, which may lead to new therapies.

ESSENTIAL POINTS

GBS is among the most frequent life-threatening neuromuscular emergencies in the world. At least 20% of patients with GBS have a poor prognosis and significant residual deficits despite receiving available treatments. Research is ongoing to further understand the pathogenesis of the disorder, find new biomarkers, and develop more effective and specific treatments.

Synthetic GM1 improves motor and memory dysfunctions in mice with monoallelic or biallelic disruption of GM3 synthase

This study attempts to answer the question of whether mice with biallelic and monoallelic disruption of the St3gal5 (GM3 synthase) gene might benefit from GM1 replacement therapy. The GM3 produced by this sialyltransferase gives rise to downstream GD3 and the ganglio-series of gangliosides. The latter includes the a-series (GM1 + GD1a), which has proved most essential for neuron survival and function (especially GM1, for which GD1a provides a reserve pool). These biallelic mice serve as a model for children with this relatively rare autosomal recessive condition (ST3GAL5-/-) who suffer rapid neurological decline including motor loss, intellectual disability, visual and hearing loss, failure to thrive, and other severe conditions leading to an early death by 2-5 years of age without supportive care. Here, we studied both these mice, which serve as a model for the parents and close relatives of these children who are likely to suffer long-term disabilities due to partial deficiency of GM1, including Parkinson's disease (PD). We find that the movement and memory disorders manifested by both types of mice can be resolved with GM1 application. This suggests the potential therapeutic value of GM1 for disorders stemming from GM1 deficiency, including GM3 synthase deficiency and PD. It was noteworthy that the GM1 employed in these studies was synthetic rather than animal brain-derived, reaffirming the therapeutic efficacy of the former.

Biology of GD2 ganglioside: implications for cancer immunotherapy

Part of the broader glycosphingolipid family, gangliosides are composed of a ceramide bound to a sialic acid-containing glycan chain, and locate at the plasma membrane. Gangliosides are produced through sequential steps of glycosylation and sialylation. This diversity of composition is reflected in differences in expression patterns and functions of the various gangliosides. Ganglioside GD2 designates different subspecies following a basic structure containing three carbohydrate residues and two sialic acids. GD2 expression, usually restrained to limited tissues, is frequently altered in various neuroectoderm-derived cancers. While GD2 is of evident interest, its glycolipid nature has rendered research challenging. Physiological GD2 expression has been linked to developmental processes. Passing this stage, varying levels of GD2, physiologically expressed mainly in the central nervous system, affect composition and formation of membrane microdomains involved in surface receptor signaling. Overexpressed in cancer, GD2 has been shown to enhance cell survival and invasion. Furthermore, binding of antibodies leads to immune-independent cell death mechanisms. In addition, GD2 contributes to T-cell dysfunction, and functions as an immune checkpoint. Given the cancer-associated functions, GD2 has been a source of interest for immunotherapy. As a potential biomarker, methods are being developed to quantify GD2 from patients' samples. In addition, various therapeutic strategies are tested. Based on initial success with antibodies, derivates such as bispecific antibodies and immunocytokines have been developed, engaging patient immune system. Cytotoxic effectors or payloads may be redirected based on anti-GD2 antibodies. Finally, vaccines can be used to mount an immune response in patients. We review here the pertinent biological information on GD2 which may be of use for optimizing current immunotherapeutic strategies.

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.

A Distinctive Metabolomics Profile and Potential Biomarkers for Very Long Acylcarnitine Dehydrogenase Deficiency (VLCADD) Diagnosis in Newborns

Very long-chain acylcarnitine dehydrogenase deficiency (VLCADD) is a rare inherited metabolic disorder associated with fatty acid β-oxidation and characterized by genetic mutations in the ACADVL gene and accumulations of acylcarnitines. VLCADD, developed in neonates or later adults, can be diagnosed using newborn bloodspot screening (NBS) or genetic sequencing. These techniques have limitations, such as a high false discovery rate and variants of uncertain significance (VUS). As a result, an extra diagnostic tool is needed to deliver improved performance and health outcomes. As VLCADD is linked with metabolic disturbance, we postulated that newborn patients with VLCADD could display a distinct metabolomics pattern compared to healthy newborns and other disorders. Herein, we applied an untargeted metabolomics approach using liquid chromatography-high resolution mass spectrometry (LC-HRMS) to measure the global metabolites in dried blood spot (DBS) cards collected from VLCADD newborns (n = 15) and healthy controls (n = 15). Two hundred and six significantly dysregulated endogenous metabolites were identified in VLCADD, in contrast to healthy newborns. Fifty-eight and one hundred and eight up- and down-regulated endogenous metabolites were involved in several pathways such as tryptophan biosynthesis, aminoacyl-tRNA biosynthesis, amino sugar and nucleotide sugar metabolism, pyrimidine metabolism and pantothenate, and CoA biosynthesis. Furthermore, biomarker analyses identified 3,4-Dihydroxytetradecanoylcarnitine (AUC = 1), PIP (20:1)/PGF1alpha) (AUC = 0.982), and PIP2 (16:0/22:3) (AUC = 0.978) as potential metabolic biomarkers for VLCADD diagnosis. Our findings showed that compared to healthy newborns, VLCAADD newborns exhibit a distinctive metabolic profile, and identified potential biomarkers that can be used for early diagnosis, which improves the identification of the affected patients earlier. This allows for the timely administration of proper treatments, leading to improved health. However, further studies with large independent cohorts of VLCADD patients with different ages and phenotypes need to be studied to validate our potential diagnostic biomarkers and their specificity and accuracy during early life.

Siglec-6 mediates the uptake of extracellular vesicles through a noncanonical glycolipid binding pocket

Immunomodulatory Siglecs are controlled by their glycoprotein and glycolipid ligands. Siglec-glycolipid interactions are often studied outside the context of a lipid bilayer, missing the complex behaviors of glycolipids in a membrane. Through optimizing a liposomal formulation to dissect Siglec-glycolipid interactions, it is shown that Siglec-6 can recognize glycolipids independent of its canonical binding pocket, suggesting that Siglec-6 possesses a secondary binding pocket tailored for recognizing glycolipids in a bilayer. A panel of synthetic neoglycolipids is used to probe the specificity of this glycolipid binding pocket on Siglec-6, leading to the development of a neoglycolipid with higher avidity for Siglec-6 compared to natural glycolipids. This neoglycolipid facilitates the delivery of liposomes to Siglec-6 on human mast cells, memory B-cells and placental syncytiotrophoblasts. A physiological relevance for glycolipid recognition by Siglec-6 is revealed for the binding and internalization of extracellular vesicles. These results demonstrate a unique and physiologically relevant ability of Siglec-6 to recognize glycolipids in a membrane.

Single Cerebral Organoid Mass Spectrometry of Cell-Specific Protein and Glycosphingolipid Traits

Cerebral organoids are a prolific research topic and an emerging model system for neurological diseases in human neurobiology. However, the batch-to-batch reproducibility of current cultivation protocols is challenging and thus requires a high-throughput methodology to comprehensively characterize cerebral organoid cytoarchitecture and neural development. We report a mass spectrometry-based protocol to quantify neural tissue cell markers, cell surface lipids, and housekeeping proteins in a single organoid. Profiled traits probe the development of neural stem cells, radial glial cells, neurons, and astrocytes. We assessed the cell population heterogeneity in individually profiled organoids in the early and late neurogenesis stages. Here, we present a unifying view of cell-type specificity of profiled protein and lipid traits in neural tissue. Our workflow characterizes the cytoarchitecture, differentiation stage, and batch cultivation variation on an individual cerebral organoid level.

Introduction to the Complexity of Cell Surface and Tissue Matrix Glycoconjugates

This chapter provides an overview of structures and functions of complex carbohydrates (commonly called glycans) that are covalently linked to proteins or lipids to form glycoconjugates known as glycoproteins, glycolipids, and proteoglycans. To understand the complexity of the glycan structures, the nature of their monosaccharide building blocks, how the monomeric units are covalently linked to each other, and how the resulting glycans are attached to proteins or lipids are discussed. Then, the classification, nomenclature, structural features, and functions of the glycan moieties of animal glycoconjugates are briefly described. All three classes of glycoconjugates are constituents of plasma membranes of all animal cells, including those of the nervous system. Glycoproteins and proteoglycans are also found abundantly as constituents of tissue matrices. Additionally, glycan-rich mucin glycoproteins are the major constituents of mucus secretions of epithelia of various organs. Furthermore, the chapter draws attention to the incredible structural complexity and diversity of the glycan moieties of cell surface and extracellular glycoconjugates. Finally, the involvement of glycans as informational molecules in a wide range of essential functions in almost all known biological processes, which are crucial for development, differentiation, and normal functioning of animals, is discussed.

Peptide mimotopes to emulate carbohydrates

Glycoconjugates on animal cell surfaces are involved in numerous biological functions and diseases, especially the adhesion/metastasis of cancer cells, infection, and the onset of glycan-related diseases. In addition to glycoantigen detection, the regulation of glycan (carbohydrate)-protein interactions is needed to develop therapeutic strategies for glycan-related diseases. Preparation of a diverse range of glycan derivatives requires a massive effort, but the preparation and identification of alternative glycan-mimetic peptide mimotopes may provide a solution to this issue. Peptide mimotopes are recognized by glycan-binding proteins, such as lectins, enzymes, and antibodies, alternative to glycan ligands. Phage-display technology is the first choice in the selection of "glycan (carbohydrate)-mimetic peptide mimotopes" from a large repertoire of library sequences. This tutorial review describes the advantages of peptide mimotopes in comparison to glycan ligands, as well as their structural and functional mimicry. The detailed library design is followed by a description of the strategy used to improve affinity, and finally, an outline of the vaccine application of glycan-mimetic peptides is provided.

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.

Enterohemorrhagic Escherichia coli and a Fresh View on Shiga Toxin-Binding Glycosphingolipids of Primary Human Kidney and Colon Epithelial Cells and Their Toxin Susceptibility

Enterohemorrhagic Escherichia coli (EHEC) are the human pathogenic subset of Shiga toxin (Stx)-producing E. coli (STEC). EHEC are responsible for severe colon infections associated with life-threatening extraintestinal complications such as the hemolytic-uremic syndrome (HUS) and neurological disturbances. Endothelial cells in various human organs are renowned targets of Stx, whereas the role of epithelial cells of colon and kidneys in the infection process has been and is still a matter of debate. This review shortly addresses the clinical impact of EHEC infections, novel aspects of vesicular package of Stx in the intestine and the blood stream as well as Stx-mediated extraintestinal complications and therapeutic options. Here follows a compilation of the Stx-binding glycosphingolipids (GSLs), globotriaosylceramide (Gb3Cer) and globotetraosylceramide (Gb4Cer) and their various lipoforms present in primary human kidney and colon epithelial cells and their distribution in lipid raft-analog membrane preparations. The last issues are the high and extremely low susceptibility of primary renal and colonic epithelial cells, respectively, suggesting a large resilience of the intestinal epithelium against the human-pathogenic Stx1a- and Stx2a-subtypes due to the low content of the high-affinity Stx-receptor Gb3Cer in colon epithelial cells. The review closes with a brief outlook on future challenges of Stx research.

Sialic acid, the secret gift for the brain

The human brain grows rapidly in early life which requires adequate nutrition. Human milk provides optimal nutrition for the developing brain, and breastfeeding significantly improves the cognition development of infants. These benefits have been largely attributed to human milk oligosaccharides (HMOS), associated with sialic acid (Sia). Subsequently, sialylated HMOS present a vital source of exogenous Sia to infants. Sialic acid is a key molecule essential for proper development of gangliosides, and therefore critical in brain development and function. Recent pre-clinical studies suggest dietary supplementation with Sia or sialylated oligosaccharides enhances intelligence and cognition performance in early and later life. Furthermore, emerging evidence suggests the involvement of Sia in brain homeostasis and disbalance correlates with common pathologies such as Alzheimer's disease (AD). Therefore, this review will discuss early brain health and development and the role of Sia in this process. Additionally, studies associating breastfeeding and specific HMOS to benefits in cognitive development are critically assessed. Furthermore, the review will assess studies implying the potential role of HMOS and microbiota in brain development via the gut-brain axis. Finally, the review will summarize recent advances regarding the role of Sia in neurodegenerative disease in later life and potential roles of dietary Sia sources.

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.

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.

Role of inhibitory B cell co-receptors in B cell self-tolerance to non-protein antigens

Antibodies to non-protein antigens such as nucleic acids, polysaccharides, and glycolipids play important roles in both host defense against microbes and development of autoimmune diseases. Although non-protein antigens are not recognized by T cells, antibody production to non-protein antigens involve T cell-independent mechanisms such as signaling through TLR7 and TLR9 in antibody production to nucleic acids. Although self-reactive B cells are tolerized by various mechanisms including deletion, anergy, and receptor editing, T cell tolerance is also crucial in self-tolerance of B cells to protein self-antigen because self-reactive T cells induce autoantibody production to these self-antigens. However, presence of T cell-independent mechanism suggests that T cell tolerance is not able to maintain B cell tolerance to non-protein self-antigens. Lines of evidence suggest that B cell response to non-protein self-antigens such as nucleic acids and gangliosides, sialic acid-containing glycolipids, are suppressed by inhibitory B cell co-receptors CD72 and Siglec-G, respectively. These inhibitory co-receptors recognize non-protein self-antigens and suppress BCR signaling induced by these antigens, thereby inhibiting B cell response to these self-antigens. Inhibitory B cell co-receptors appear to be involved in B cell self-tolerance to non-protein self-antigens that can activate B cells by T cell-independent mechanisms.

Age-dependent reference intervals in children for the disialoganglioside, GD2, a circulating tumor biomarker for the childhood cancer, neuroblastoma

BACKGROUND

The disialoganglioside G_D2 is a circulating tumor biomarker for the childhood cancer, neuroblastoma. This study establishes reference intervals for G_D2 concentration in children within the age range where neuroblastoma commonly occurs.

METHODS

Leftover plasma samples taken for routine clinical laboratory tests from children without cancer were collected and assayed for the 18-carbon fatty acid chain length lipoform of G_D2 using a validated high-pressure liquid chromatography tandem mass spectrometry method with a lower limit of quantification of 3 nM. Samples were stratified into 5 age cohorts (0-6 months, 6-12 months, 12-36 months, 3-10 years and > 10 years). Non-parametric statistical methods were used to define the upper bound of the reference interval for each age cohort.

RESULTS

G_D2 was measurable in 90% of samples from children < 10 years of age and G_D2 concentration was age-dependent, peaking at 9 months followed by a gradual decline. G_D2 was below the lower limit of quantification in 55% of samples in the > 10 years cohort. Upper bounds of reference intervals were 15.5 nM in 0-6 month cohort, 35.1 nM in 6-12 month cohort, 24.9 nM in 12-36 month cohort, 18.4 in 3-10 year cohort and 10.4 nM in > 10 year cohort.

CONCLUSIONS

Age-dependent reference intervals were defined for circulating G_D2 in children. G_D2 concentration was highest in the 6-12 month age cohort, which is below the age of most children with high-risk neuroblastoma. The peak G_D2 concentration at 9 months may reflect neurodevelopmental events in the brain.

The role of Globo H and SSEA-4 in the development and progression of cancer, and their potential as therapeutic targets

Glycans, chains of sugar molecules found conjugated to cell proteins and lipids, contribute to their growth, movement and differentiation. Aberrant glycosylation is a hallmark of several medical conditions including tumorigenesis. Glycosphingolipids (GSLs), consisting of glycans conjugated to a lipid (ceramide) core, are found in the lipid bilayer of eukaryotic cell membranes. GSLs, play an active role in cell processes. Several GSLs are expressed by human embryonic stem cells and have been found to be overexpressed in several types of cancer. In this review, we discuss the data, hypotheses and perspectives related to the GSLs Globo H and SSEA-4.

Development and validation of capillary electrophoresis method for quantification of gangliosides in brain synaptosomes

Gangliosides are sialic acid containing glycosphingolipids of the plasma membrane with diverse biological functions. They are most abundant in neural tissues where their dysregulation has been suggested to be involved in various pathological conditions. Due to their importance, efficient analytical methods are needed to determine individual gangliosides in biological samples. Here we report a capillary electrophoresis method, optimized and validated for the simultaneous quantification of major neural gangliosides GM1, GD1a, GD1b, GT1b and GQ1b in their underivatized form. The most abundant extraneural monosialogangloside, GM3 can also be separated by this method. Micelles of the highly amphiphilic gangliosides were disrupted with cyclodextrins (CyDs) in the aqueous separation buffer. Among the tested CyDs, the best resolution was observed using 20 mM randomly methylated alpha-CyD in alkaline sodium borate buffer enabling the separation of all studied gangliosides. The method was applied for the quantification of gangliosides in rat cerebral and cerebellar synaptosomes.

GM1 Gangliosidosis-A Mini-Review

GM1 gangliosidosis is a progressive, neurosomatic, lysosomal storage disorder caused by mutations in the GLB1 gene encoding the enzyme β-galactosidase. Absent or reduced β-galactosidase activity leads to the accumulation of β-linked galactose-containing glycoconjugates including the glycosphingolipid (GSL) GM1-ganglioside in neuronal tissue. GM1-gangliosidosis is classified into three forms [Type I (infantile), Type II (late-infantile and juvenile), and Type III (adult)], based on the age of onset of clinical symptoms, although the disorder is really a continuum that correlates only partially with the levels of residual enzyme activity. Severe neurocognitive decline is a feature of Type I and II disease and is associated with premature mortality. Most of the disease-causing β-galactosidase mutations reported in the literature are clustered in exons 2, 6, 15, and 16 of the GLB1 gene. So far 261 pathogenic variants have been described, missense/nonsense mutations being the most prevalent. There are five mouse models of GM1-gangliosidosis reported in the literature generated using different targeting strategies of the Glb1 murine locus. Individual models differ in terms of age of onset of the clinical, biochemical, and pathological signs and symptoms, and overall lifespan. However, they do share the major abnormalities and neurological symptoms that are characteristic of the most severe forms of GM1-gangliosidosis. These mouse models have been used to study pathogenic mechanisms, to identify biomarkers, and to evaluate therapeutic strategies. Three GLB1 gene therapy trials are currently recruiting Type I and Type II patients (NCT04273269, NCT03952637, and NCT04713475) and Type II and Type III patients are being recruited for a trial utilizing the glucosylceramide synthase inhibitor, venglustat (NCT04221451).

Avoiding artifacts in liposome leakage measurements via cuvette- and liposome-surface modifications

The barrier properties of lipid membranes are often determined by investigating their solute permeability with the help of spectroscopic methods and the use of liposome-encapsulated self-quenching fluorescent dyes, for example, Carboxyfluorescein (CF). It was shown previously that liposome-surface interactions, and thus the choice of cuvette material, influence the result of such spectroscopic permeability/leakage experiments. In this work, we explore different methods to minimize the artifacts observed in spontaneous leakage measurements performed with cholesterol-containing liposomes. The spontaneous leakage of CF from liposomes with different composition and surface properties is monitored in cuvettes composed of quartz, polystyrene (PS), and Poly(methyl methacrylate) (PMMA). Our results show that significantly different leakage profiles are recorded for the exact same liposome batch depending on the cuvette material used. Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) experiments indicate that these discrepancies likely arise from side processes occurring at the solution-cuvette interface, mainly, the attaching and spreading of liposomes. Further, we show that in some cases it is possible to minimize liposome-cuvette interactions, and reduce the experimental artifacts, by supplementing the liposomes with polyethylene glycol (PEG)-grafted lipids or gangliosides, and/or by pre-adsorbing free PEG to the cuvette walls. The collected data suggest that quartz cuvettes modified by adsorption of PEG8000 are suitable for spontaneous leakage experiments with POPC:cholesterol-based liposomes, while other cuvette materials perform poorly in the same experiments.

Genome-scale metabolic network reconstruction of model animals as a platform for translational research

Genome-scale metabolic models (GEMs) are used extensively for analysis of mechanisms underlying human diseases and metabolic malfunctions. However, the lack of comprehensive and high-quality GEMs for model organisms restricts translational utilization of omics data accumulating from the use of various disease models. Here we present a unified platform of GEMs that covers five major model animals, including Mouse1 (Mus musculus), Rat1 (Rattus norvegicus), Zebrafish1 (Danio rerio), Fruitfly1 (Drosophila melanogaster), and Worm1 (Caenorhabditis elegans). These GEMs represent the most comprehensive coverage of the metabolic network by considering both orthology-based pathways and species-specific reactions. All GEMs can be interactively queried via the accompanying web portal Metabolic Atlas. Specifically, through integrative analysis of Mouse1 with RNA-sequencing data from brain tissues of transgenic mice we identified a coordinated up-regulation of lysosomal GM2 ganglioside and peptide degradation pathways which appears to be a signature metabolic alteration in Alzheimer's disease (AD) mouse models with a phenotype of amyloid precursor protein overexpression. This metabolic shift was further validated with proteomics data from transgenic mice and cerebrospinal fluid samples from human patients. The elevated lysosomal enzymes thus hold potential to be used as a biomarker for early diagnosis of AD. Taken together, we foresee that this evolving open-source platform will serve as an important resource to facilitate the development of systems medicines and translational biomedical applications.

A pathogenic HEXA missense variant in wild boars with Tay-Sachs disease

Gangliosidoses are inherited lysosomal storage disorders caused by reduced or absent activity of either a lysosomal enzyme involved in ganglioside catabolism, or an activator protein required for the proper activity of a ganglioside hydrolase, which results in the intra-lysosomal accumulation of undegraded metabolites. We hereby describe morphological, ultrastructural, biochemical and genetic features of GM2 gangliosidosis in three captive bred wild boar littermates. The piglets were kept in a partially-free range farm and presented progressive neurological signs, starting at 6 months of age. Animals were euthanized at approximately one year of age due to their poor conditions. Neuropathogens were excluded as a possible cause of the signs. Gross examination showed a reduction of cerebral and cerebellar consistency. Central (CNS) and peripheral (PNS) nervous system neurons were enlarged and foamy, with severe and diffuse cytoplasmic vacuolization. Transmission electron microscopy (TEM) of CNS neurons demonstrated numerous lysosomes, filled by parallel or concentric layers of membranous electron-dense material, defined as membranous cytoplasmic bodies (MCB). Biochemical composition of gangliosides analysis from CNS revealed accumulation of GM2 ganglioside; furthermore, Hex A enzyme activity was less than 1% compared to control animals. These data confirmed the diagnosis of GM2 gangliosidosis. Genetic analysis identified, at a homozygous level, the presence of a missense nucleotide variant c.1495C > T (p Arg499Cys) in the hexosaminidase subunit alpha gene (HEXA), located within the GH20 hexosaminidase superfamily domain of the encoded protein. This specific HEXA variant is known to be pathogenic and associated with Tay-Sachs disease in humans, but has never been identified in other animal species. This is the first report of a HEXA gene associated Tay-Sachs disease in wild boars and provides a comprehensive description of a novel spontaneous animal model for this lysosomal storage disease.

Protective Effect of GM1 Attenuates Hippocampus and Cortex Apoptosis After Ketamine Exposure in Neonatal Rat via PI3K/AKT/GSK3β Pathway

Ketamine is a widely used analgesic and anesthetic in obstetrics and pediatrics. Ketamine is known to promote neuronal death and cognitive dysfunction in the brains of humans and animals during development. Monosialotetrahexosyl ganglioside (GM1), a promoter of brain development, exerts neuroprotective effects in many neurological disease models. Here, we investigated the neuroprotective effect of GM1 and its potential underlying mechanism against ketamine-induced apoptosis of rats. Seven-day-old Sprague Dawley (SD) rats were randomly divided into the following four groups: (1) group C (control group: normal saline was injected intraperitoneally); (2) group K (ketamine); (3) group GM1 (GM1 was given before normal saline injection); and (4) GM1+K group (received GM1 30 min before continuous exposure to ketamine). Each group contained 15 rats, received six doses of ketamine (20 mg/kg), and was injected with saline every 90 min. The Morris water maze (MWM) test, the number of cortical and hippocampal cells, apoptosis, and AKT/GSK3β pathway were analyzed. To determine whether GM1 exerted its effect via the PI3K/AKT/GSK3β pathway, PC12 cells were incubated with LY294002, a PI3K inhibitor. We found that GM1 protected against ketamine-induced apoptosis in the hippocampus and cortex by reducing the expression of Bcl-2 and Caspase-3, and by increasing the expression of Bax. GM1 treatment increased the expression of p-AKT and p-GSK3β. However, the anti-apoptotic effect of GM1 was eliminated after inhibiting the phosphorylation of AKT. We showed that GM1 lessens ketamine-induced apoptosis in the hippocampus and cortex of young rats by regulating the PI3K/AKT/GSK3β pathway. Taken together, GM1 may be a potential preventive treatment for the neurotoxicity caused by continuous exposure to ketamine.

Sphingolipids of Asteroidea and Holothuroidea: Structures and Biological Activities

Sphingolipids are complex lipids widespread in nature as structural components of biomembranes. Commonly, the sphingolipids of marine organisms differ from those of terrestrial animals and plants. The gangliosides are the most complex sphingolipids characteristic of vertebrates that have been found in only the Echinodermata (echinoderms) phylum of invertebrates. Sphingolipids of the representatives of the Asteroidea and Holothuroidea classes are the most studied among all echinoderms. In this review, we have summarized the data on sphingolipids of these two classes of marine invertebrates over the past two decades. Recently established structures, properties, and peculiarities of biogenesis of ceramides, cerebrosides, and gangliosides from starfishes and holothurians are discussed. The purpose of this review is to provide the most complete information on the chemical structures, structural features, and biological activities of sphingolipids of the Asteroidea and Holothuroidea classes.

Innovative and Promising Strategies to Enhance Effectiveness of Immunotherapy for CNS Tumors: Where Are We?

Although there are several immunotherapy approaches for the treatment of Central Nervous System (CNS) tumors under evaluation, currently none of these approaches have received approval from the regulatory agencies. CNS tumors, especially glioblastomas, are tumors characterized by highly immunosuppressive tumor microenvironment, limiting the possibility of effectively eliciting an immune response. Moreover, the peculiar anatomic location of these tumors poses relevant challenges in terms of safety, since uncontrolled hyper inflammation could lead to cerebral edema and cranial hypertension. The most promising strategies of immunotherapy in neuro-oncology consist of the use of autologous T cells redirected against tumor cells through chimeric antigen receptor (CAR) constructs or genetically modified T-cell receptors. Trials based on native or genetically engineered oncolytic viruses and on vaccination with tumor-associated antigen peptides are also under evaluation. Despite some sporadic complete remissions achieved in clinical trials, the outcome of patients with CNS tumors treated with different immunotherapeutic approaches remains poor. Based on the lessons learned from these unsatisfactory experiences, novel immune-therapy approaches aimed at overcoming the profound immunosuppressive microenvironment of these diseases are bringing new hope to reach the cure for CNS tumors.

Ganglioside isomer analysis using ion polarity switching liquid chromatography-tandem mass spectrometry

Gangliosides are ubiquitously present on cell surface. They are more abundantly expressed in nerve cells and tissues and involved in pathology of various diseases. Diversity of molecular structures in the carbohydrate head group, fatty acyl, and long chain base increases the complexity of analyzing gangliosides. In this study, an ultrahigh-performance liquid chromatography-tandem mass spectrometry method is developed for analysis of the co-eluting ganglioside isomers, which uses ion polarity switching to integrate glycan head isomer identification, ceramide isomer differentiation, and quantification of ganglioside into one analysis. The method is facilitated with an extensive ganglioside target list by combining the various glycan head groups, long chain bases, and the experimentally determined fatty acyls. Correlation between the retention time of ganglioside and its ceramide total carbon number is experimentally validated and used to predict retention time of ganglioside target list for scheduling the final multiple reaction monitoring method. This method was validated according to the FDA guidelines: 96.5% of gangliosides with good accuracy (80-120%), precision (< 15%), and linearity R² > 0.99. The authenticated gangliosides were quantified from mouse brain by isotope dilution. Overall, 165 gangliosides were quantified using 10 mg mouse brain tissue, including 100 isomers of GM1, GM2, GM3, GD1a, GD1b, GD2, GD3, and GT1b.

GM1 Gangliosidosis: Mechanisms and Management

The lysosomal storage disorder, GM1 gangliosidosis (GM1), is a neurodegenerative condition resulting from deficiency of the enzyme β-galactosidase (β-gal). Mutation of the GLB1 gene, which codes for β-gal, prevents cleavage of the terminal β-1,4-linked galactose residue from GM1 ganglioside. Subsequent accumulation of GM1 ganglioside and other substrates in the lysosome impairs cell physiology and precipitates dysfunction of the nervous system. Beyond palliative and supportive care, no FDA-approved treatments exist for GM1 patients. Researchers are critically evaluating the efficacy of substrate reduction therapy, pharmacological chaperones, enzyme replacement therapy, stem cell transplantation, and gene therapy for GM1. A Phase I/II clinical trial for GM1 children is ongoing to evaluate the safety and efficacy of adeno-associated virus-mediated GLB1 delivery by intravenous injection, providing patients and families with hope for the future.

Iminosugar glucosidase inhibitors reduce hepatic inflammation in HAV-infected Ifnar1-/- mice

Iminosugar compounds are monosaccharide mimetics with broad but generally weak antiviral activities related to inhibition of enzymes involved in glycobiology. Miglustat (N-butyl-1-deoxynojirimycin), which is approved for treatment of lipid storage diseases in humans, and UV-4 (N-(9-methoxynonyl)-1-deoxynojirimycin), inhibit replication of hepatitis A virus (HAV) in cell culture (IC₅₀ 32.13 μM and 8.05 μM, respectively) by blocking the synthesis of gangliosides essential for HAV cell entry. We used a murine model of hepatitis A and targeted mass spectrometry to assess the capacity of these compounds to deplete hepatic gangliosides and modify the course of HAV infection in vivo Miglustat, given by gavage to Ifnar1^-/- mice (4800 mg/kg/day) depleted hepatic gangliosides by 69-75%, but caused substantial gastrointestinal toxicity and failed to prevent viral infection. UV-4, similarly administered in high doses (400 mg/kg/day), was well tolerated, but depleted hepatic gangliosides by only 20% after 14 days. UV-4 depletion of gangliosides varied by class. Several GM2 species were paradoxically increased, likely due to inhibition of β-glucosidases that degrade gangliosides. Both compounds enhanced, rather than reduced, virus replication. Nonetheless, both iminosugars had surprising anti-inflammatory effects, blocking the accumulation of inflammatory cells within the liver. UV-4 treatment also resulted in a decrease in serum alanine aminotransferase (ALT) elevations associated with acute hepatitis A. These anti-inflammatory effects may result from iminosugar inhibition of cellular α-glucosidases, leading to impaired maturation of glycan moieties of chemokine and cytokine receptors, and point to the potential importance of paracrine signaling in the pathogenesis of acute hepatitis A.IMPORTANCEHepatitis A virus (HAV) is a common cause of viral hepatitis. Iminosugar compounds block its replication in cultured cells by inhibiting synthesis of gangliosides required for HAV cell entry, but have not been tested for their ability to prevent or treat hepatitis A in vivo We show that high doses of the iminosugars miglustat and UV-4 fail to deplete gangliosides sufficiently to block HAV infection in mice lacking a key interferon receptor. These compounds nonetheless have striking anti-inflammatory effects on the HAV-infected liver, reducing the severity of hepatitis despite enhancing chemokine and cytokine expression resulting from hepatocyte-intrinsic antiviral responses. We propose that iminosugar inhibition of cellular α-glucosidases impairs maturation of glycan moieties of chemokine and cytokine receptors required for effective signaling. These data highlight the potential importance of paracrine signaling pathways in the inflammatory response to HAV, and add to our understanding of HAV pathogenesis in mice.

Transient Lipid-Protein Structures and Selective Ganglioside Uptake During α-Synuclein-Lipid Co-aggregation

α-Synuclein is a membrane-interacting protein involved in Parkinson's disease. Here we have investigated the co-association of α-synuclein and lipids from ganglioside-containing model membranes. Our study relies on the reported importance of ganglioside lipids, which are found in high amounts in neurons and exosomes, on cell-to-cell prion-like transmission of misfolded α-synuclein. Samples taken along various stages of the aggregation process were imaged using cryogenic transmission electron microscopy, and the composition of samples corresponding to the final state analyzed using NMR spectroscopy. The combined data shows that α-synuclein co-assembles with lipids from the ganglioside (GM1)-containing model membranes. The lipid-protein samples observed during the aggregation process contain non-vesicular objects not present at the final stage, thus capturing the co-existence of species under non-equilibrium conditions. A range of different lipid-protein co-assemblies are observed during the time course of the reaction and some of these appear to be transient assemblies that evolve into other co-aggregates over time. At the end of the aggregation reaction, the samples become more homogeneous, showing thin fibrillar structures heavily decorated with small vesicles. From the NMR analysis, we conclude that the ratio of GM1 to phosphatidyl choline (PC) in the supernatant of the co-aggregated samples is significantly reduced compared to the GM1/PC ratio of the lipid dispersion from which these samples were derived. Taken together, this indicates a selective uptake of GM1 into the fibrillar aggregates and removal of GM1-rich objects from the solution.

Heterogeneous Ganglioside-Enriched Nanoclusters with Different Densities in Membrane Rafts Detected by a Peptidyl Molecular Probe

The specific features of the lateral distribution of gangliosides play key roles in cell-cell communications and the onset of various diseases related to the plasma membrane. We herein demonstrated that an artificial peptide identified from a phage-displayed library is available as a molecular probe for specific ganglioside nanoclustering sites in caveolae/membrane rafts on the cell surface. Atomic force microscopy studies indicated that the peptide specifically binds to the highly enriched monosialoganglioside GM1 nanodomains of reconstituted lipid bilayers composed of GM1, sphingomyelin, cholesterol, and unsaturated phospholipids. The ganglioside-containing area recognized by the peptide on the surface of PC12 cells was part of the area recognized by the cholera toxin B subunit, which has high affinity for GM1. Furthermore, the peptide bound to the cell surface after a treatment with methyl-β-cyclodextrin (MβCD), which disrupts membrane rafts by removing cholesterol. The present results indicate that there are heterogeneous ganglioside clusters with different ganglioside densities in caveolae/membrane rafts, and the peptidyl probe selectively recognizes the high-density ganglioside nanodomain that resists the MβCD treatment. This peptidyl probe will be useful for obtaining information on the lipid organization of the cell membrane and will help clarify the mechanisms by which the lateral distribution of gangliosides affects biological functions and the onset of diseases.

A Diversity-Oriented Strategy for Chemical Synthesis of Glycosphingolipids: Synthesis of Glycosphingolipid LcGg4 and Its Analogues and Derivatives

A diversity-oriented strategy was developed for the synthesis of glycosphingolipids (GSLs). This strategy was highlighted by using a simple lactoside containing the core structures of GSL glycan and lipid as the universal starting material to obtain different synthetic targets upon stepwise elongation of the glycan via chemical glycosylations and on-site remodeling of the lipid via chemoselective cross-metathesis and N-acylation. The strategy was verified with the synthesis of a lacto-ganglio GSL, LcGg4, which is a biomarker of undifferentiated malignant myeloid cells, and a series of its analogues or derivatives carrying different sugar chains and unique functionalities or molecular labels. This synthetic strategy should be widely applicable and, therefore, be utilized to rapidly access various GSLs and related derivatives by using different donors for glycosylations and different substrates for lipid remodeling following each glycosylation.

Gb3-cSrc complex in glycosphingolipid-enriched microdomains contributes to the expression of p53 mutant protein and cancer drug resistance via β-catenin-activated RNA methylation

Glucosylceramide synthase (GCS) is a key enzyme catalyzing ceramide glycosylation to generate glucosylceramide (GlcCer), which in turn serves as the precursor for cells to produce glycosphingolipids (GSLs). In cell membranes, GSLs serve as essential components of GSL-enriched microdomains (GEMs) and mediate membrane functions and cell behaviors. Previous studies showed that ceramide glycosylation correlates with upregulated expression of p53 hotspot mutant R273H and cancer drug resistance. Yet, the underlying mechanisms remain elusive. We report herewith that globotriaosylceramide (Gb3) is associated with cSrc kinase in GEMs and plays a crucial role in modulating expression of p53 R273H mutant and drug resistance. Colon cancer cell lines, either WiDr homozygous for missense-mutated TP53 (R273H+/+) or SW48/TP53-Dox bearing heterozygous TP53 mutant (R273H/+), display drug resistance with increased ceramide glycosylation. Inhibition of GCS with Genz-161 (GENZ 667161) resensitized cells to apoptosis in these p53 mutant-carrying cancer cells. Genz-161 effectively inhibited GCS activity, and substantially suppressed the elevated Gb3 levels seen in GEMs of p53-mutant cells exposed to doxorubicin. Complex formation between Gb3 and cSrc in GEMs to activate β-catenin was detected in both cultured cells and xenograft tumors. Suppression of ceramide glycosylation significantly decreased Gb3-cSrc in GEMs, β-catenin, and methyltransferase-like 3 for m6A RNA methylation, thus altering pre-mRNA splicing, resulting in upregulated expression of wild-type p53 protein, but not mutants, in cells carrying p53 R273H. Altogether, increased Gb3-cSrc complex in GEMs of membranes in response to anticancer drug induced cell stress promotes expression of p53 mutant proteins and accordant cancer drug resistance.

Gangliosides in the Brain: Physiology, Pathophysiology and Therapeutic Applications

Gangliosides are glycosphingolipids highly abundant in the nervous system, and carry most of the sialic acid residues in the brain. Gangliosides are enriched in cell membrane microdomains ("lipid rafts") and play important roles in the modulation of membrane proteins and ion channels, in cell signaling and in the communication among cells. The importance of gangliosides in the brain is highlighted by the fact that loss of function mutations in ganglioside biosynthetic enzymes result in severe neurodegenerative disorders, often characterized by very early or childhood onset. In addition, changes in the ganglioside profile (i.e., in the relative abundance of specific gangliosides) were reported in healthy aging and in common neurological conditions, including Huntington's disease (HD), Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), stroke, multiple sclerosis and epilepsy. At least in HD, PD and in some forms of epilepsy, experimental evidence strongly suggests a potential role of gangliosides in disease pathogenesis and potential treatment. In this review, we will summarize ganglioside functions that are crucial to maintain brain health, we will review changes in ganglioside levels that occur in major neurological conditions and we will discuss their contribution to cellular dysfunctions and disease pathogenesis. Finally, we will review evidence of the beneficial roles exerted by gangliosides, GM1 in particular, in disease models and in clinical trials.

Recent advances in the mass spectrometric analysis of glycosphingolipidome - A review

Aberrant expression of glycosphingolipids has been implicated in a myriad of diseases, but our understanding of the strucural diversity, spatial distribution, and biological function of this class of biomolecules remains limited. These challenges partly stem from a lack of sensitive tools that can detect, identify, and quantify glycosphingolipids at the molecular level. Mass spectrometry has emerged as a powerful tool poised to address most of these challenges. Here, we review the recent developments in analytical glycosphingolipidomics with an emphasis on sample preparation, mass spectrometry and tandem mass spectrometry-based structural characterization, label-free and labeling-based quantification. We also discuss the nomenclature of glycosphingolipids, and emerging technologies like ion mobility spectrometry in differentiation of glycosphingolipid isomers. The intrinsic advantages and shortcomings of each method are carefully critiqued in line with an individual's research goals. Finally, future perspectives on analytical sphingolipidomics are stated, including a need for novel and more sensive methods in isomer separation, low abundance species detection, and profiling the spatial distribution of glycosphingolipid molecular species in cells and tissues using imaging mass spectrometry.

GM2 Gangliosidoses: Clinical Features, Pathophysiological Aspects, and Current Therapies

GM2 gangliosidoses are a group of pathologies characterized by GM2 ganglioside accumulation into the lysosome due to mutations on the genes encoding for the β-hexosaminidases subunits or the GM2 activator protein. Three GM2 gangliosidoses have been described: Tay-Sachs disease, Sandhoff disease, and the AB variant. Central nervous system dysfunction is the main characteristic of GM2 gangliosidoses patients that include neurodevelopment alterations, neuroinflammation, and neuronal apoptosis. Currently, there is not approved therapy for GM2 gangliosidoses, but different therapeutic strategies have been studied including hematopoietic stem cell transplantation, enzyme replacement therapy, substrate reduction therapy, pharmacological chaperones, and gene therapy. The blood-brain barrier represents a challenge for the development of therapeutic agents for these disorders. In this sense, alternative routes of administration (e.g., intrathecal or intracerebroventricular) have been evaluated, as well as the design of fusion peptides that allow the protein transport from the brain capillaries to the central nervous system. In this review, we outline the current knowledge about clinical and physiopathological findings of GM2 gangliosidoses, as well as the ongoing proposals to overcome some limitations of the traditional alternatives by using novel strategies such as molecular Trojan horses or advanced tools of genome editing.

A Clinician's Guide to Cancer-Derived Exosomes: Immune Interactions and Therapeutic Implications

Understanding of the role of immunity in the regulation of cancer growth continues to rapidly increase. This is fuelled by the impressive results yielded in recent years by immune checkpoint inhibitors, which block regulatory pathways to increase immune-mediated cancer destruction. Exosomes are cell-secreted membranous nanoscale vesicles that play important roles in regulating physiological and pathophysiological processes. Cancer-derived exosomes (CDEXs) and their biologically-active cargos have been proven to have varied effects in malignant progression, including the promotion of angiogenesis, metastasis, and favorable microenvironment modification. More recently, there is an increasing appreciation of their role in immune evasion. In addition to CDEXs, there are immune-derived exosomes that facilitate communication between immune cells in the non-malignant setting. Investigation of cancer-mediated mechanisms behind interruption or modification of these normal exosomal pathways may provide further understanding of how malignant immune evasion is accomplished. Accumulating evidence indicates that immune-active CDEXs also have the potential to impact clinical oncological management. Whilst immune checkpoint inhibitors have well-established pharmacologically-targeted pathways involving the immune system, other widely used treatments such as radiation and cytotoxic chemotherapies do not. Thus, investigating exosomes in immunotherapy is important for the development of next-generation combination therapies. In this article, we review the ways in which CDEXs impact individual immune cell types and how this contributes to the development of immune evasion. We discuss the relevance of lymphocytes and myeloid-lineage cells in the control of malignancy. In addition, we highlight the ways that CDEXs and their immune effects can impact current cancer therapies and the resulting clinical implications.

Influence of glycosphingolipids on cancer cell energy metabolism

A growing number of studies describe a connection between glycosphingolipids (GSLs) and glutamine metabolism, glucose metabolism and mitochondrial dysfunction in cancer cells. Since deregulated cell energy metabolism is one of cancer cells hallmarks, investigating this connection is an important step in the development of anti-cancer therapies. GSL species are often aberrantly regulated in human cancers. They cluster in signaling platforms in the plasma membrane and organelle membranes in so called glycosphingolipid enriched microdomains (GEMs), thereby regulating cell signaling pathways. The most important glutamine transporter for epithelial cells, alanine-serine-cysteine transporter 2 (ASCT2) locates in GEMs and is regulated by GEM composition. The accumulation of glucosylceramide and lactosylceramide in mitochondria associated ER membranes (MAMs) leads to increased oxidative phosphorylation. This increases mitochondrial reactive oxygen species (ROS) levels and influences mitochondrial dynamics. Here, we review current knowledge about deregulated GSL species in cancer, GSL influence on glutamine and glucose metabolism. In addition, the role of GSLs in MAMs, oxidative phosphorylation (OXPHOS) and mitochondrial dynamics with a special focus on mechanistic target of rapamycin (mTOR) signaling is discussed. mTOR seems to play a pivotal role in the connection between GSLs and glutamine metabolism as well as in mitochondrial signaling.