Modulation of calcium signaling depends on the oligosaccharide of GM1 in Neuro2a mouse neuroblastoma cells

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.

Sialyltransferase Mutations Alter the Expression of Calcium-Binding Interneurons in Mice Neocortex, Hippocampus and Striatum

Gangliosides are major glycans on vertebrate nerve cells, and their metabolic disruption results in congenital disorders with marked cognitive and motor deficits. The sialyltransferase gene St3gal2 is responsible for terminal sialylation of two prominent brain gangliosides in mammals, GD1a and GT1b. In this study, we analyzed the expression of calcium-binding interneurons in primary sensory (somatic, visual, and auditory) and motor areas of the neocortex, hippocampus, and striatum of St3gal2-null mice as well as St3gal3-null and St3gal2/3-double null. Immunohistochemistry with highly specific primary antibodies for GABA, parvalbumin, calretinin, and calbindin were used for interneuron detection. St3gal2-null mice had decreased expression of all three analyzed types of calcium-binding interneurons in all analyzed regions of the neocortex. These results implicate gangliosides GD1a and GT1b in the process of interneuron migration and maturation.

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.

GM1 oligosaccharide efficacy against α-synuclein aggregation and toxicity in vitro

Fibrillary aggregated α-synuclein represents the neurologic hallmark of Parkinson's disease and is considered to play a causative role in the disease. Although the causes leading to α-synuclein aggregation are not clear, the GM1 ganglioside interaction is recognized to prevent this process. How GM1 exerts these functions is not completely clear, although a primary role of its soluble oligosaccharide (GM1-OS) is emerging. Indeed, we recently identified GM1-OS as the bioactive moiety responsible for GM1 neurotrophic and neuroprotective properties, specifically reverting the parkinsonian phenotype both in in vitro and in vivo models. Here, we report on GM1-OS efficacy against the α-synuclein aggregation and toxicity in vitro. By amyloid seeding aggregation assay and NMR spectroscopy, we demonstrated that GM1-OS was able to prevent both the spontaneous and the prion-like α-synuclein aggregation. Additionally, circular dichroism spectroscopy of recombinant monomeric α-synuclein showed that GM1-OS did not induce any change in α-synuclein secondary structure. Importantly, GM1-OS significantly increased neuronal survival and preserved neurite networks of dopaminergic neurons affected by α-synuclein oligomers, together with a reduction of microglia activation. These data further demonstrate that the ganglioside GM1 acts through its oligosaccharide also in preventing the α-synuclein pathogenic aggregation in Parkinson's disease, opening a perspective window for GM1-OS as drug candidate.

Bacterial toxins and heart function: heat-labile Escherichia coli enterotoxin B promotes changes in cardiac function with possible relevance for sudden cardiac death

Bacterial toxins can cause cardiomyopathy, though it is not its most common cause. Some bacterial toxins can form pores in the membrane of cardiomyocytes, while others can bind to membrane receptors. Enterotoxigenic E. coli can secrete enterotoxins, including heat-resistant (ST) or labile (LT) enterotoxins. LT is an AB5-type toxin that can bind to specific cell receptors and disrupt essential host functions, causing several common conditions, such as certain diarrhea. The pentameric B subunit of LT, without A subunit (LTB), binds specifically to certain plasma membrane ganglioside receptors, found in lipid rafts of cardiomyocytes. Isolated guinea pig hearts and cardiomyocytes were exposed to different concentrations of purified LTB. In isolated hearts, mechanical and electrical alternans and an increment of heart rate variability, with an IC50 of ~0.2 μg/ml LTB, were observed. In isolated cardiomyocytes, LTB promoted significant decreases in the amplitude and the duration of action potentials. Na+ currents were inhibited whereas L-type Ca2+ currents were augmented at their peak and their fast inactivation was promoted. Delayed rectifier K+ currents decreased. Measurements of basal Ca2+ or Ca2+ release events in cells exposed to LTB suggest that LTB impairs Ca2+ homeostasis. Impaired calcium homeostasis is linked to sudden cardiac death. The results are consistent with the recent view that the B subunit is not merely a carrier of the A subunit, having a role explaining sudden cardiac death in children (SIDS) infected with enterotoxigenic E. coli, explaining several epidemiological findings that establish a strong relationship between SIDS and ETEC E. coli.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12551-023-01100-6.

GM1 Oligosaccharide Efficacy in Parkinson's Disease: Protection against MPTP

Past evidence has shown that the exogenous administration of GM1 ganglioside slowed neuronal death in preclinical models of Parkinson's disease, a neurodegenerative disorder characterized by the progressive loss of dopamine-producing neurons: however, the physical and chemical properties of GM1 (i.e., amphiphilicity) limited its clinical application, as the crossing of the blood-brain barrier is denied. Recently, we demonstrated that the GM1 oligosaccharide head group (GM1-OS) is the GM1 bioactive portion that, interacting with the TrkA-NGF complex at the membrane surface, promotes the activation of a multivariate network of intracellular events regulating neuronal differentiation, protection, and reparation. Here, we evaluated the GM1-OS neuroprotective potential against the Parkinson's disease-linked neurotoxin MPTP, which destroys dopaminergic neurons by affecting mitochondrial bioenergetics and causing ROS overproduction. In dopaminergic and glutamatergic primary cultures, GM1-OS administration significantly increased neuronal survival, preserved neurite network, and reduced mitochondrial ROS production enhancing the mTOR/Akt/GSK3β pathway. These data highlight the neuroprotective efficacy of GM1-OS in parkinsonian models through the implementation of mitochondrial function and reduction in oxidative stress.

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.

β-Glucocerebrosidase Deficiency Activates an Aberrant Lysosome-Plasma Membrane Axis Responsible for the Onset of Neurodegeneration

β-glucocerebrosidase is a lysosomal hydrolase involved in the catabolism of the sphingolipid glucosylceramide. Biallelic loss of function mutations in this enzyme are responsible for the onset of Gaucher disease, while monoallelic β-glucocerebrosidase mutations represent the first genetic risk factor for Parkinson’s disease. Despite this evidence, the molecular mechanism linking the impairment in β-glucocerebrosidase activity with the onset of neurodegeneration in still unknown. In this frame, we developed two in vitro neuronal models of β-glucocerebrosidase deficiency, represented by mouse cerebellar granule neurons and human-induced pluripotent stem cells-derived dopaminergic neurons treated with the specific β-glucocerebrosidase inhibitor conduritol B epoxide. Neurons deficient for β-glucocerebrosidase activity showed a lysosomal accumulation of glucosylceramide and the onset of neuronal damage. Moreover, we found that neurons react to the lysosomal impairment by the induction of their biogenesis and exocytosis. This latter event was responsible for glucosylceramide accumulation also at the plasma membrane level, with an alteration in lipid and protein composition of specific signaling microdomains. Collectively, our data suggest that β-glucocerebrosidase loss of function impairs the lysosomal compartment, establishing a lysosome–plasma membrane axis responsible for modifications in the plasma membrane architecture and possible alterations of intracellular signaling pathways, leading to neuronal damage.

Gangliosides and the Treatment of Neurodegenerative Diseases: A Long Italian Tradition

Gangliosides are glycosphingolipids which are particularly abundant in the plasma membrane of mammalian neurons. The knowledge of their presence in the human brain dates back to the end of 19th century, but their structure was determined much later, in the middle of the 1950s. From this time, neurochemical studies suggested that gangliosides, and particularly GM1 ganglioside, display neurotrophic and neuroprotective properties. The involvement of GM1 in modulating neuronal processes has been studied in detail by in vitro experiments, and the results indicated its direct role in modulating the activity of neurotrophin-dependent receptor signaling, the flux of calcium through the plasma membrane, and stabilizing the correct conformation of proteins, such as α-synuclein. Following, in vivo experiments supported the use of ganglioside drugs for the therapy of peripheral neuropathies, obtaining very positive results. However, the clinical use of gangliosides for the treatment of central neurodegeneration has not been followed due to the poor penetrability of these lipids at the central level. This, together with an ambiguous association (later denied) between ganglioside administration and Guillain-Barrè syndrome, led to the suspension of ganglioside drugs. In this critical review, we report on the evolution of research on gangliosides, on the current knowledge on the role played by gangliosides in regulating the biology of neurons, on the past and present use of ganglioside-based drugs used for therapy of peripheral neuropathies or used in human trials for central neurodegenerations, and on the therapeutic potential represented by the oligosaccharide chain of GM1 ganglioside for the treatment of neurodegenerative diseases.

Novel insights on GM1 and Parkinson's disease: A critical review

GM1 is a crucial component of neuronal membrane residing both in the soma and nerve terminals. As reported in Parkinson’s disease patients, the reduction of GM1 determines the failure of fundamental functional processes leading to cumulative cell distress up to neuron death. This review reports on the role of GM1 in the pathogenesis of the disease, illustrating the current data available but also hypotheses on the additional mechanisms in which GM1 could be involved and which require further study. In the manuscript we discuss these points trying to explain the role of diminished content of brain GM1, particularly in the nigro-striatal system, in Parkinson’s disease etiology and progression.

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.

Plasma membrane glycosphingolipid signaling: a turning point

Plasma membrane interaction is highly recognized as an essential step to start the intracellular events in response to extracellular stimuli. The ways in which these interactions take place are less clear and detailed. Over the last decade my research has focused on developing the understanding of the glycosphingolipids-protein interaction that occurs at cell surface. By using chemical synthesis and biochemical approaches we have characterized some fundamental interactions that are key events both in the immune response and in the maintenance of neuronal homeostasis. In particular, for the first time it has been demonstrated that a glycolipid, present on the outer side of the membrane, the long-chain lactosylceramide, is able to directly modulate a cytosolic protein. But the real conceptual change was the demonstration that the GM1 oligosaccharide chain is able, alone, to replicate numerous functions of GM1 ganglioside and to directly interact with plasma membrane receptors by activating specific cellular signaling. In this conceptual shift, the development and application of multidisciplinary techniques in the field of biochemistry, from chemical synthesis to bioinformatic analysis, as well as discussions with several national and international colleagues have played a key role.

Turning the spotlight on the oligosaccharide chain of GM1 ganglioside

It is well over a century that glycosphingolipids are matter of interest in different fields of research. The hydrophilic oligosaccharide and the lipid moiety, the ceramide, both or separately have been considered in different moments as the crucial portion of the molecule, responsible for the role played by the glycosphingolipids associated to the plasma-membranes or to any other subcellular fraction. Glycosphingolipids are a family of compounds characterized by thousands of structures differing in both the oligosaccharide and the ceramide moieties, but among them, the nervous system monosialylated glycosphingolipid GM1, belonging to the group of gangliosides, has gained particular attention by a multitude of Scientists. In recent years, a series of studies have been conducted on the functional roles played by the hydrophilic part of GM1, its oligosaccharide, that we have named “OligoGM1”. These studies allowed to shed new light on the mechanisms underlying the properties of GM1 defining the role of the OligoGM1 in determining precise interactions with membrane proteins instrumental for the neuronal functions, leaving to the ceramide the role of correctly positioning the GM1 in the membrane crucial for the oligosaccharide-protein interactions. In this review we aim to report the recent studies on the cascade of events modulated by OligoGM1, as the bioactive portion of GM1, to support neuronal differentiation and trophism together with preclinical studies on its potential to modify the progression of Parkinson’s disease.