Amyloid-β induced toxicity involves ganglioside expression and is sensitive to GM1 neuroprotective action

Role of SIRT1 in Potentially Toxic Trace Elements (Lead, Fluoride, Aluminum and Cadmium) Associated Neurodevelopmental Toxicity

The formation of the central nervous system is a meticulously planned and intricate process. Any modification to this process has the potential to disrupt the structure and operation of the brain, which could result in deficiencies in neurological growth. When neurotoxic substances are present during the early stages of development, they can be exceptionally dangerous. Prenatally, the immature brain is extremely vulnerable and is therefore at high risk in pregnant women associated with occupational exposures. Lead, fluoride, aluminum, and cadmium are examples of possibly toxic trace elements that have been identified as an environmental concern in the aetiology of a number of neurological and neurodegenerative illnesses. SIRT1, a member of the sirtuin family has received most attention for its potential neuroprotective properties. SIRT1 is an intriguing therapeutic target since it demonstrates important functions to increase neurogenesis and cellular lifespan by modulating multiple pathways. It promotes axonal extension, neurite growth, and dendritic branching during the development of neurons. Additionally, it contributes to neurogenesis, synaptic plasticity, memory development, and neuroprotection. This review summarizes the possible role of SIRT1 signalling pathway in potentially toxic trace elements -induced neurodevelopmental toxicity, highlighting some molecular pathways such as mitochondrial biogenesis, CREB/BDNF and PGC-1α/NRF1/TFAM.

Lipid rafts and human diseases: why we need to target gangliosides

Gangliosides are functional components of membrane lipid rafts that control critical functions in cell communication. Many pathologies involve raft gangliosides, which therefore represent an approach of choice for developing innovative therapeutic strategies. Beginning with a discussion of what a disease is (and is not), this review lists the major human pathologies that involve gangliosides, which includes cancer, diabetes, and infectious and neurodegenerative diseases. In most cases, the problem is due to a protein whose binding to gangliosides either creates a pathological condition or impairs a physiological function. Then, I draw up an inventory of the different molecular mechanisms of protein-ganglioside interactions. I propose to classify the ganglioside-binding domains of proteins into four categories, which I name GBD-1, GBD-2, GBD-3, and GBD-4. This structural and functional classification could help to rationalize the design of innovative molecules capable of disrupting the binding of selected proteins to gangliosides without generating undesirable effects. The biochemical specificities of gangliosides expressed in the human brain must also be taken into account to improve the reliability of animal models (or any animal-free alternative) of Alzheimer's and Parkinson's diseases.

Ganglioside GM1 and the Central Nervous System

GM1 is one of the major glycosphingolipids (GSLs) on the cell surface in the central nervous system (CNS). Its expression level, distribution pattern, and lipid composition are dependent upon cell and tissue type, developmental stage, and disease state, which suggests a potentially broad spectrum of functions of GM1 in various neurological and neuropathological processes. The major focus of this review is the roles that GM1 plays in the development and activities of brains, such as cell differentiation, neuritogenesis, neuroregeneration, signal transducing, memory, and cognition, as well as the molecular basis and mechanisms for these functions. Overall, GM1 is protective for the CNS. Additionally, this review has also examined the relationships between GM1 and neurological disorders, such as Alzheimer's disease, Parkinson's disease, GM1 gangliosidosis, Huntington's disease, epilepsy and seizure, amyotrophic lateral sclerosis, depression, alcohol dependence, etc., and the functional roles and therapeutic applications of GM1 in these disorders. Finally, current obstacles that hinder more in-depth investigations and understanding of GM1 and the future directions in this field are discussed.

Uptake of severe acute respiratory syndrome coronavirus 2 spike protein mediated by angiotensin converting enzyme 2 and ganglioside in human cerebrovascular cells

Introduction

There is clinical evidence of neurological manifestations in coronavirus disease-19 (COVID-19). However, it is unclear whether differences in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)/spike protein (SP) uptake by cells of the cerebrovasculature contribute to significant viral uptake to cause these symptoms.

Methods

Since the initial step in viral invasion is binding/uptake, we used fluorescently labeled wild type and mutant SARS-CoV-2/SP to study this process. Three cerebrovascular cell types were used (endothelial cells, pericytes, and vascular smooth muscle cells), in vitro.

Results

There was differential SARS-CoV-2/SP uptake by these cell types. Endothelial cells had the least uptake, which may limit SARS-CoV-2 uptake into brain from blood. Uptake was time and concentration dependent, and mediated by angiotensin converting enzyme 2 receptor (ACE2), and ganglioside (mono-sialotetrahexasylganglioside, GM1) that is predominantly expressed in the central nervous system and the cerebrovasculature. SARS-CoV-2/SPs with mutation sites, N501Y, E484K, and D614G, as seen in variants of interest, were also differentially taken up by these cell types. There was greater uptake compared to that of the wild type SARS-CoV-2/SP, but neutralization with anti-ACE2 or anti-GM1 antibodies was less effective.

Conclusion

The data suggested that in addition to ACE2, gangliosides are also an important entry point of SARS-CoV-2/SP into these cells. Since SARS-CoV-2/SP binding/uptake is the initial step in the viral penetration into cells, a longer exposure and higher titer are required for significant uptake into the normal brain. Gangliosides, including GM1, could be an additional potential SARS-CoV-2 and therapeutic target at the cerebrovasculature.

Ischemia preconditioning induces an adaptive response that defines a circulating metabolomic signature in ischemic stroke patients

Transient ischemic attacks (TIAs) before an acute ischemic stroke (AIS) could induce ischemic tolerance (IT) phenomena. with an endogenous neuroprotective role (Ischemic preconditioning. IPC). A consecutive prospective cohort of patients with AIS were recruited from 8 different hospitals. Participants were classified by those with non-previous recent TIA vs. previous TIA (within seven days. TIA ≤7d). A total of 541 AIS patients were recruited. 40 (7.4%). of them had previous TIA ≤7d. In line with IPC. patients with TIA ≤7d showed: 1) a significantly less severe stroke at admission by NIHSS score. 2) a better outcome at 7-90 days follow-up and reduced infarct volumes. 3) a specific upregulated metabolomics/lipidomic profile composed of diverse lipid categories. Effectively. IPC activates an additional adaptive response on increasing circulation levels of structural and bioactive lipids to facilitate functional recovery after AIS which may support biochemical machinery for neuronal survival. Furthermore. previous TIA before AIS seems to facilitate the production of anti-inflammatory mediators that contribute to a better immune response. Thus. the IT phenomena contributes to a better adaptation of further ischemia. Our study provides first-time evidence of a metabolomics/lipidomic signature related to the development of stroke tolerance in AIS patients induced by recent TIA.

Glucosylceramide synthase inhibition reduces ganglioside GM3 accumulation, alleviates amyloid neuropathology, and stabilizes remote contextual memory in a mouse model of Alzheimer’s disease

Background

Gangliosides are highly enriched in the brain and are critical for its normal development and function. However, in some rare neurometabolic diseases, a deficiency in lysosomal ganglioside hydrolysis is pathogenic and leads to early-onset neurodegeneration, neuroinflammation, demyelination, and dementia. Increasing evidence also suggests that more subtle ganglioside accumulation contributes to the pathogenesis of more common neurological disorders including Alzheimer’s disease (AD). Notably, ganglioside GM3 levels are elevated in the brains of AD patients and in several mouse models of AD, and plasma GM3 levels positively correlate with disease severity in AD patients.

Methods

Tg2576 AD model mice were fed chow formulated with a small molecule inhibitor of glucosylceramide synthase (GCSi) to determine whether reducing glycosphingolipid synthesis affected aberrant GM3 accumulation, amyloid burden, and disease manifestations in cognitive impairment. GM3 was measured with LC-MS, amyloid burden with ELISA and amyloid red staining, and memory was assessed using the contextual fear chamber test.

Results

GCSi mitigated soluble Aβ42 accumulation in the brains of AD model mice when treatment was started prophylactically. Remarkably, GCSi treatment also reduced soluble Aβ42 levels and amyloid plaque burden in aged (i.e., 70 weeks old) AD mice with preexisting neuropathology. Our analysis of contextual memory in Tg2576 mice showed that impairments in remote (cortical-dependent) memory consolidation preceded deficits in short-term (hippocampal-dependent) contextual memory, which was consistent with soluble Aβ42 accumulation occurring more rapidly in the cortex of AD mice compared to the hippocampus. Notably, GCSi treatment significantly stabilized remote memory consolidation in AD mice—especially in mice with enhanced cognitive training. This finding was consistent with GCSi treatment lowering aberrant GM3 accumulation in the cortex of AD mice.

Conclusions

Collectively, our results indicate that glycosphingolipids regulated by GCS are important modulators of Aβ neuropathology and that glycosphingolipid homeostasis plays a critical role in the consolidation of remote memories.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-00966-0.

Structure and function of glycosphingolipids on small extracellular vesicles

Extracellular vesicles (EVs) are membrane-delineated particles secreted by most types of cells under both normal and pathophysiological conditions. EVs are believed to mediate intercellular communication by serving as carriers of different bioactive ingredients, including proteins, nucleic acids and lipids. Glycoconjugates are complex molecules consisting of covalently linked carbohydrate with proteins or lipids. These glycoconjugates play essential roles in the sorting of vesicular protein and the uptake of small extracellular vesicles (30–100 nm, sEVs) into recipient cells. Glycosphingolipids (GSLs), one subtype of glycolipids, which are ubiquitous membrane components in almost all living organisms, are also commonly distributed on sEVs. However, the study of functional roles of GSLs on sEVs are far behind than other functional cargos. The purpose of this review is to highlight the importance of GSLs on sEVs. Initially, we described classification and structure of GSLs. Then, we briefly introduced the essential functions of GSLs, which are able to interact with functional membrane proteins, such as growth factor receptors, integrins and tetraspanins, to modulate cell growth, adhesion and cell motility. In addition, we discussed analytical methods for studying GSLs on sEVs. Finally, we focused on the function of GSLs on sEVs, including regulating the aggregation of extracellular α-synuclein (α-syn) or extracellular amyloid-β (Aβ) and influencing tumor cell malignancy.

Amyloid-β peptide dimers undergo a random coil to β-sheet transition in the aqueous phase but not at the neuronal membrane

Mounting evidence suggests that the neuronal cell membrane is the main site of oligomer-mediated neuronal toxicity of amyloid-β peptides in Alzheimer's disease. To gain a detailed understanding of the mutual interference of amyloid-β oligomers and the neuronal membrane, we carried out microseconds of all-atom molecular dynamics (MD) simulations on the dimerization of amyloid-β (Aβ)42 in the aqueous phase and in the presence of a lipid bilayer mimicking the in vivo composition of neuronal membranes. The dimerization in solution is characterized by a random coil to β-sheet transition that seems on pathway to amyloid aggregation, while the interactions with the neuronal membrane decrease the order of the Aβ42 dimer by attenuating its propensity to form a β-sheet structure. The main lipid interaction partners of Aβ42 are the surface-exposed sugar groups of the gangliosides GM1. As the neurotoxic activity of amyloid oligomers increases with oligomer order, these results suggest that GM1 is neuroprotective against Aβ-mediated toxicity.

Glycosphingolipids

Glycosphingolipids are amphiphilic plasma membrane components formed by a glycan linked to a specific lipid moiety. In this chapter we report on these compounds, on their role played in our cells to maintain the correct cell biology.In detail, we report on their structure, on their metabolic processes, on their interaction with proteins and from this, their property to modulate positively in health and negatively in disease, the cell signaling and cell biology.

Genistein attenuates amyloid-beta-induced cognitive impairment in rats by modulation of hippocampal synaptotoxicity and hyperphosphorylation of Tau

Alzheimer's disease is a progressive neurodegenerative disorder characterized by extracellular accumulation of amyloid-beta (Aβ) peptide, which induces synaptic dysfunction, alteration of intracellular signaling pathways, hyperphosphorylation of the Tau protein, and cognitive impairment. Genistein, one of the major isoflavones present in soy and soy products, has been shown to modulate some of the pathogenic events associated with the neurodegeneration process. However, its underlying mechanisms remain to be clarified. Therefore, the objectives of the present study were to evaluate the ability of genistein to protect against Aβ_1-42-induced cognitive impairment in rats and to elucidate some of the possible mechanisms involved in its neuroprotective effects in the hippocampus. Male Wistar rats received bilateral intracerebroventricular infusions of Aβ_1-42 (2 nmol) and genistein 10 mg/kg orally for 10 days. The Aβ-infused animals showed significant impairment of memory, which was accompanied by the following neurochemical alterations in the hippocampus: decreased levels of the synaptic proteins synaptophysin and postsynaptic density protein 95 (PSD-95), hyperphosphorylation of Tau with increased activation of glycogen synthase kinase-3β and c-Jun N-terminal kinase, and inactivation of ERK. Treatment with genistein improved Aβ-induced cognitive impairment by attenuation of synaptotoxicity, hyperphosphorylation of Tau, and inactivation of ERK. Furthermore, treatment with this soy isoflavone did not cause systemic toxicity. These findings provide further evidence of the neuroprotective effect of genistein in an in vivo model of Aβ toxicity and, importantly, extend the current knowledge concerning the mechanisms associated with the neuroprotective effects of this compound in the hippocampus.

Neurotrophic effects of GM1 ganglioside, NGF, and FGF2 on canine dorsal root ganglia neurons in vitro

Dogs share many chronic morbidities with humans and thus represent a powerful model for translational research. In comparison to rodents, the canine ganglioside metabolism more closely resembles the human one. Gangliosides are components of the cell plasma membrane playing a role in neuronal development, intercellular communication and cellular differentiation. The present in vitro study aimed to characterize structural and functional changes induced by G_M1 ganglioside (G_M1) in canine dorsal root ganglia (DRG) neurons and interactions of G_M1 with nerve growth factor (NGF) and fibroblast growth factor (FGF2) using immunofluorescence for several cellular proteins including neurofilaments, synaptophysin, and cleaved caspase 3, transmission electron microscopy, and electrophysiology. G_M1 supplementation resulted in increased neurite outgrowth and neuronal survival. This was also observed in DRG neurons challenged with hypoxia mimicking neurodegenerative conditions due to disruptions of energy homeostasis. Immunofluorescence indicated an impact of G_M1 on neurofilament phosphorylation, axonal transport, and synaptogenesis. An increased number of multivesicular bodies in G_M1 treated neurons suggested metabolic changes. Electrophysiological changes induced by G_M1 indicated an increased neuronal excitability. Summarized, G_M1 has neurotrophic and neuroprotective effects on canine DRG neurons and induces functional changes. However, further studies are needed to clarify the therapeutic value of gangliosides in neurodegenerative diseases.

Imaging mass spectrometry allows for neuroanatomic-specific detection of gangliosides in the healthy and diseased brain

Gangliosides have a wide variety of biological functions due to their location on the outer leaflet of plasma membranes. They form a critical component of membrane rafts, or ganglioside-enriched microdomains, where they influence the physical properties of the membrane as well as its function. Gangliosides can change their structure to meet their external and internal environmental demands. This ability to change structure makes gangliosides both fascinating and technologically challenging targets to identify and understand. A full understanding on how gangliosides are regulated within the central nervous system (CNS) is critical, as ganglioside dysregulation is observed in the aging brain as well as in several neurodegenerative injuries and diseases such as stroke, Alzheimer's disease, Parkinson's disease, Huntington's disease and several lysosomal storage disorders diseases, including Tay Sach's disease. Mass spectrometry (MS) has become a useful means to better understand ganglioside composition and function. Imaging mass spectrometry (IMS) provides the added benefit of placing analytical information within an anatomical context. This review article will discuss recent advances in MS-based detection methods, with a focus on IMS-based approaches to help understand the spatial-specific role gangliosides in the healthy brain as in CNS injuries and disease.

Genistein protects against amyloid-beta-induced toxicity in SH-SY5Y cells by regulation of Akt and Tau phosphorylation

Alzheimer's disease is a neurodegenerative disorder characterized by extracellular deposition of amyloid-β (Aβ) peptide and hyperphosphorylation of Tau protein, which ultimately leads to the formation of intracellular neurofibrillary tangles and cell death. Increasing evidence indicates that genistein, a soy isoflavone, has neuroprotective effects against Aβ-induced toxicity. However, the molecular mechanisms involved in its neuroprotection are not well understood. In this study, we have established a neuronal damage model using retinoic-acid differentiated SH-SY5Y cells treated with different concentrations of Aβ_25-35 to investigate the effect of genistein against Aβ-induced cell death and the possible involvement of protein kinase B (PKB, also termed Akt), glycogen synthase kinase 3β (GSK-3β), and Tau as an underlying mechanism to this neuroprotection. Differentiated SH-SY5Y cells were pre-treated for 24 hr with genistein (1 and 10 nM) and exposed to Aβ_25-35 (25 μM), and we found that genistein partially inhibited Aβ induced cell death, primarily apoptosis. Furthermore, the protective effect of genistein was associated with the inhibition of Aβ-induced Akt inactivation and Tau hyperphosphorylation. These findings reinforce the neuroprotective effects of genistein against Aβ toxicity and provide evidence that its mechanism may involve regulation of Akt and Tau proteins.

GM1 Ameliorates Lead-Induced Cognitive Deficits and Brain Damage Through Activating the SIRT1/CREB/BDNF Pathway in the Developing Male Rat Hippocampus

Developmental lead (Pb) exposure involves various serious consequences, especially leading to neurotoxicity. In this study, we examined the possible role of monosialoganglioside (GM1) in lead-induced nervous impairment in the developing rat. Newborn male Sprague-Dawley rat pups were exposed to lead from birth for 30 days and then subjected to GM1 administration (0.4, 2, or 10 mg/kg; i.p.) or 0.9% saline. The results showed that developmental lead exposure significantly impaired spatial learning and memory in the Morris water maze test, reduced GM1 content, induced oxidative stress, and weakened the antioxidative systems in the hippocampus. However, co-treatment with GM1 reversed these effects. Moreover, GM1 counteracted lead-induced apoptosis by decreasing the expression of Bax, cleaved caspase-3, and by increasing the level of Bcl-2 in a dose-dependent manner. Furthermore, we found that GM1 upregulated the expression of SIRT1, CREB phosphorylation, and BDNF, which underlie learning and memory in the lead-treated developing rat hippocampus. In conclusion, our study demonstrated that GM1 exerts a protective effect on lead-induced cognitive deficits via antioxidant activity, preventing apoptosis, and activating SIRT1/CREB/BDNF in the developing rat hippocampus, implying a novel potential assistant therapy for lead poisoning.

Ganglioside GQ1b ameliorates cognitive impairments in an Alzheimer's disease mouse model, and causes reduction of amyloid precursor protein

Brain-derived neurotrophic factor (BDNF) plays crucial roles in memory impairments including Alzheimer’s disease (AD). Previous studies have reported that tetrasialoganglioside GQ1b is involved in long-term potentiation and cognitive functions as well as BDNF expression. However, in vitro and in vivo functions of GQ1b against AD has not investigated yet. Consequently, treatment of oligomeric Aβ followed by GQ1b significantly restores Aβ_1–42-induced cell death through BDNF up-regulation in primary cortical neurons. Bilateral infusion of GQ1b into the hippocampus ameliorates cognitive deficits in the triple-transgenic AD mouse model (3xTg-AD). GQ1b-infused 3xTg-AD mice had substantially increased BDNF levels compared with artificial cerebrospinal fluid (aCSF)-treated 3xTg-AD mice. Interestingly, we also found that GQ1b administration into hippocampus of 3xTg-AD mice reduces Aβ plaque deposition and tau phosphorylation, which correlate with APP protein reduction and phospho-GSK3β level increase, respectively. These findings demonstrate that the tetrasialoganglioside GQ1b may contribute to a potential strategy of AD treatment.

Membrane-lipid homeostasis in a prodromal rat model of Alzheimer's disease: Characteristic profiles in ganglioside distributions during aging detected using MALDI imaging mass spectrometry

BACKGROUND

Accumulation of simple gangliosides GM2 and GM3, and gangliosides with longer long-chain bases (d20:1) have been linked to toxicity and the pathogenesis of Alzheimer's disease (AD). Conversely, complex gangliosides, such as GM1, have been shown to be neuroprotective. Recent evidence using matrix-assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS) has demonstrated that a-series gangliosides are differentially altered during normal aging, yet it remains unclear how simple species are shifting relative to complex gangliosides in the prodromal stages of AD.

METHODS

Ganglioside profiles in wild-type (Wt) and transgenic APP21 Fischer rats were detected and quantified using MALDI-IMS at P0 (birth), 3, 12, and 20 months of age and each species quantified to allow for individual species comparisons.

RESULTS

Tg APP21 rats were found to have a decreased level of complex gangliosides in a number of brain regions as compared to Wt rats and showed higher levels of simple gangliosides. A unique pattern of expression was observed in the white matter as compared to gray matter regions, with an age-dependent decrease in GD1 d18:1 species observed and significantly elevated levels of GM3 in Tg APP21 rats.

CONCLUSIONS

These results are indicative of a pathological shift in ganglioside homeostasis during aging that is exacerbated in Tg APP21 rats.

GENERAL SIGNIFICANCE

Ganglioside dysregulation may occur in the prodromal stages of neurodegenerative diseases like AD.

Gangliosides of the Nervous System

This review begins by attempting to recount some of the pioneering discoveries that first identified the presence of gangliosides in the nervous system, their structures and topography. This is presented as prelude to the current emphasis on physiological function, about which much has been learned but still remains to be elucidated. These areas include ganglioside roles in nervous system development including stem cell biology, membranes and organelles within neurons and glia, ion transport mechanisms, receptor modulation including neurotrophic factor receptors, and importantly the pathophysiological role of ganglioside aberrations in neurodegenerative disorders. This relates to their potential as therapeutic agents, especially in those conditions characterized by deficiency of one or more specific gangliosides. Finally we attempt to speculate on future directions ganglioside research is likely to take so as to capitalize on the impressive progress to date.

Three-Dimensional Models of the Human Brain Development and Diseases

Deciphering the human brain pathophysiology remains one of the greatest challenges of the 21st century. Neurological disorders represent a significant proportion of diseases burden; however, the complexity of the brain physiology makes it challenging to model its diseases. Simple in vitro models have been very useful for precise measurements in controled conditions. However, existing models are limited in their ability to replicate complex interactions between various cells in the brain. Studying human brain requires sophisticated models to reconstitute the tangled architecture and functions of brain cells. Recently, advances in the development of three-dimensional (3D) brain cell culture models have begun to recapitulate various aspects of the human brain physiology in vitro and replicate basic disease processes of Alzheimer's disease, amyotrophic lateral sclerosis, and microcephaly. In this review, we discuss the progress, advantages, limitations, and future directions of 3D cell culture systems for modeling the human brain development and diseases.

Age-dependent and regional heterogeneity in the long-chain base of A-series gangliosides observed in the rat brain using MALDI Imaging

Alterations in the long chain base of the sphingosine moiety of gangliosides have been shown to play a role in neurodevelopment and neurodegeneration. Indeed, the accumulation of d20:1 sphingosine has been referred to as a metabolic marker of aging in the brain, however, this remains to be shown in simple gangliosides GM2 and GM3. In this study, Matrix-assisted laser desorption/ionization Imaging Mass Spectrometry (MALDI IMS) was used to examine the neuroanatomical distribution of A-series gangliosides with either 18 or 20 carbon sphingosine chains (d18:1 or d20:1) in Fisher 344 rats across the lifespan. The ratio of d20:1/d18:1 species was determined across 11 regions of interest in the brain. Interestingly, a decrease in the d20:1/d18:1 ratio for GM2 and GM3 was observed during early development with the exception of the peri-ventricular corpus callosum, where an age-dependent increase was observed for ganglioside GM3. An age-dependent increase in d20:1 species was confirmed for complex gangliosides GM1 and GD1 with the most significant increase during early development and a high degree of anatomical heterogeneity during aging. The unique neuroanatomically-specific responses of d20:1 ganglioside abundance may lead to a better understanding of regional vulnerability to damage in the aging brain.

Impact of GM1 on Membrane-Mediated Aggregation/Oligomerization of β-Amyloid: Unifying View

In this perspective we summarize current knowledge of the effect of monosialoganglioside GM₁ on the membrane-mediated aggregation of the β-amyloid (Aβ) peptide. GM₁ has been suggested to be actively involved in the development of Alzheimer's disease due to its ability to seed the aggregation of Aβ. However, GM₁ is known to be neuroprotective against Aβ-induced toxicity. Here we suggest that the two scenarios are not mutually exclusive but rather complementary, and might depend on the organization of GM₁ in membranes. Improving our understanding of the molecular details behind the role of gangliosides in neurodegenerative amyloidoses might help in developing disease-modifying treatments.

Monosialoganglioside 1 may alleviate neurotoxicity induced by propofol combined with remifentanil in neural stem cells

Monosialoganglioside 1 (GM1) is the main ganglioside subtype and has neuroprotective properties in the central nervous system. In this study, we aimed to determine whether GM1 alleviates neurotoxicity induced by moderate and high concentrations of propofol combined with remifentanil in the immature central nervous system. Hippocampal neural stem cells were isolated from newborn Sprague-Dawley rats and treated with remifentanil (5, 10, 20 ng/mL) and propofol (1.0, 2.5, 5.0 μg/mL), and/or GM1 (12.5, 25, 50 μg/mL). GM1 reversed combined propofol and remifentanil-induced decreases in the percentage of 5-bromodeoxyuridine(+) cells and also reversed the increase in apoptotic cell percentage during neural stem cell proliferation and differentiation. However, GM1 with combined propofol and remifentanil did not affect β-tubulin(+) or glial fibrillary acidic protein(+) cell percentage during neural stem cell differentiation. In conclusion, we show that GM1 alleviates the damaging effects of propofol combined with remifentanil at moderate and high exposure concentrations in neural stem cells in vitro, and exerts protective effects on the immature central nervous system.

New Insights on Non-Enzymatic Oxidation of Ganglioside GM1 Using Mass Spectrometry

Gangliosides are acidic glycosphingolipids that are present in cell membranes and lipid raft domains, being particularly abundant in central nervous systems. They participate in modulating cell membrane properties, cell-cell recognition, cell regulation, and signaling. Disturbance in ganglioside metabolism has been correlated with the development of diseases, such as neurodegenerative diseases, and in inflammation. Both conditions are associated with an increased production of reactive oxidation species (ROS) that can induce changes in the structure of biomolecules, including lipids, leading to the loss or modification of their function. Oxidized phospholipids are usually involved in chronic diseases and inflammation. However, knowledge regarding oxidation of gangliosides is scarce. In order to evaluate the effect of ROS in gangliosides, an in vitro biomimetic model system was used to study the susceptibility of GM1 (Neu5Acα2-3(Galβ1-3GalNAcβ1-4)Galβ1-4Glcβ1Cer) to undergo oxidative modifications. Oxidation of GM1 under Fenton reaction conditions was monitored using high resolution electrospray ionization-mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS). Upon oxidation, GM1 underwent oxidative cleavages in the carbohydrate chain, leading to the formation of other gangliosides GM2 (GalNAcβ1-4Gal(Neu5Acα2-3)1-4Glcβ1Cer), GM3 (Neu5Acα2-3Galβ1-4Glcβ1Cer), asialo-GM1 (Galβ1-3GalNAcβ1-4Galβ1-4Glcβ1Cer), asialo-GM2 (GalNAcβ1-4Galβ1-4Glcβ1Cer), of the small glycolipids lactosylceramide (LacCer), glucosylceramide (GlcCer), and of ceramide (Cer). In addition, oxygenated GM1 and GM2 (as keto and hydroxy derivatives), glycans, oxidized glycans, and oxidized ceramides were also identified. Nonenzymatic oxidation of GM1 under oxidative stress contributes to the generation of other gangliosides that may participate in the imbalance of gangliosides metabolism in vivo, through uncontrolled enzymatic pathways and, consequently, play some role in neurodegenerative processes. Graphical Abstract ᅟ.

GM1 Ganglioside Inhibits β-Amyloid Oligomerization Induced by Sphingomyelin

β-Amyloid (Aβ) oligomers are neurotoxic and implicated in Alzheimer's disease. Neuronal plasma membranes may mediate formation of Aβ oligomers in vivo. Membrane components sphingomyelin and GM1 have been shown to promote aggregation of Aβ; however, these studies were performed under extreme, non-physiological conditions. We demonstrate that physiological levels of GM1 , organized in nanodomains do not seed oligomerization of Aβ40 monomers. We show that sphingomyelin triggers oligomerization of Aβ40 and that GM1 is counteractive thus preventing oligomerization. We propose a molecular explanation that is supported by all-atom molecular dynamics simulations. The preventive role of GM1 in the oligomerization of Aβ40 suggests that decreasing levels of GM1 in the brain, for example, due to aging, could reduce protection against Aβ oligomerization and contribute to the onset of Alzheimer's disease.

Effects of Ganglioside on Working Memory and the Default Mode Network in Individuals with Subjective Cognitive Impairment: A Randomized Controlled Trial

This randomized, double-blind, placebo-controlled trial examined whether the administration of ganglioside, an active ingredient of deer bone extract, can improve working memory performance by increasing gray matter volume and functional connectivity in the default mode network (DMN) in individuals with subjective cognitive impairment. Seventy-five individuals with subjective cognitive impairment were chosen to receive either ganglioside (330[Formula: see text][Formula: see text]g/day or 660[Formula: see text][Formula: see text]g/day) or a placebo for 8 weeks. Changes in working memory performance with treatment of either ganglioside or placebo were assessed as cognitive outcome measures. Using voxel-based morphometry and functional connectivity analyses, changes in gray matter volume and functional connectivity in the DMN were also assessed as brain outcome measures. Improvement in working memory performance was greater in the ganglioside group than in the placebo group. The ganglioside group, relative to the placebo group, showed greater increases in gray matter volume and functional connectivity in the DMN. A significant relationship between increased functional connectivity of the precuneus and improved working memory performance was observed in the ganglioside group. The current findings suggest that ganglioside has cognitive-enhancing effects in individuals with subjective cognitive impairment. Ganglioside-induced increases in gray matter volume and functional connectivity in the DMN may partly be responsible for the potential nootropic effects of ganglioside. The clinical trial was registered with ClinicalTrials.gov (identifier: NCT02379481).

Organotypic brain slice cultures: A review

In vitro cell cultures are an important tool for obtaining insights into cellular processes in an isolated system and a supplement to in vivo animal experiments. While primary dissociated cultures permit a single homogeneous cell population to be studied, there is a clear need to explore the function of brain cells in a three-dimensional system where the main architecture of the cells is preserved. Thus, organotypic brain slice cultures have proven to be very useful in investigating cellular and molecular processes of the brain in vitro. This review summarizes (1) the historical development of organotypic brain slices focusing on the membrane technology, (2) methodological aspects regarding culturing procedures, age of donors or media, (3) whether the cholinergic neurons serve as a model of neurodegeneration in Alzheimer’s disease, (4) or the nigrostriatal dopaminergic neurons as a model of Parkinson’s disease and (5) how the vascular network can be studied, especially with regard to a synthetic blood–brain barrier. This review will also highlight some limits of the model and give an outlook on future applications.

Increased Expression of Simple Ganglioside Species GM2 and GM3 Detected by MALDI Imaging Mass Spectrometry in a Combined Rat Model of Aβ Toxicity and Stroke

The aging brain is often characterized by the presence of multiple comorbidities resulting in synergistic damaging effects in the brain as demonstrated through the interaction of Alzheimer's disease (AD) and stroke. Gangliosides, a family of membrane lipids enriched in the central nervous system, may have a mechanistic role in mediating the brain's response to injury as their expression is altered in a number of disease and injury states. Matrix-Assisted Laser Desorption Ionization (MALDI) Imaging Mass Spectrometry (IMS) was used to study the expression of A-series ganglioside species GD1a, GM1, GM2, and GM3 to determine alteration of their expression profiles in the presence of beta-amyloid (Aβ) toxicity in addition to ischemic injury. To model a stroke, rats received a unilateral striatal injection of endothelin-1 (ET-1) (stroke alone group). To model Aβ toxicity, rats received intracerebralventricular (i.c.v.) injections of the toxic 25-35 fragment of the Aβ peptide (Aβ alone group). To model the combination of Aβ toxicity with stroke, rats received both the unilateral ET-1 injection and the bilateral icv injections of Aβ25-35 (combined Aβ/ET-1 group). By 3 d, a significant increase in the simple ganglioside species GM2 was observed in the ischemic brain region of rats who received a stroke (ET-1), with or without Aβ. By 21 d, GM2 levels only remained elevated in the combined Aβ/ET-1 group. GM3 levels however demonstrated a different pattern of expression. By 3 d GM3 was elevated in the ischemic brain region only in the combined Aβ/ET-1 group. By 21 d, GM3 was elevated in the ischemic brain region in both stroke alone and Aβ/ET-1 groups. Overall, results indicate that the accumulation of simple ganglioside species GM2 and GM3 may be indicative of a mechanism of interaction between AD and stroke.

GM1 and GD1a gangliosides modulate toxic and inflammatory effects of E. coli lipopolysaccharide by preventing TLR4 translocation into lipid rafts

Exogenous gangliosides are known to inhibit the effects of Escherichia coli lipopolysaccharide (LPS) in different cells exhibiting anti-inflammatory and immunosuppressive activities. The mechanisms underlying ganglioside action are not fully understood. Because LPS recognition and receptor complex formation occur in lipid rafts, and gangliosides play a key role in their maintenance, we hypothesize that protective effects of exogenous gangliosides would depend on inhibition of LPS signaling via prevention of TLR4 translocation into lipid rafts. The effect of GM1 and GD1a gangliosides on LPS-induced toxic and inflammatory reactions in PC12 cells, and in epithelial cells isolated from the frog urinary bladder, was studied. In PC12 cells, GD1a and GM1 significantly reduced the effect of LPS on the decrease of cell survival and on stimulation of reactive oxygen species production. In epithelial cells, gangliosides decreased LPS-stimulated iNOS expression, NO, and PGE2 production. Subcellular fractionation, in combination with immunoblotting, showed that pretreatment of cells with GM1, GD1a, or methyl-β-cyclodextrin, completely eliminated the effect of LPS on translocation of TLR4 into lipid rafts. The results are consistent with the hypothesis that ganglioside-induced prevention of TLR4 translocation into lipid rafts could be a mechanism of protection against LPS in various cells.

Gangliosides and glycolipids in neurodegenerative disorders

Glycolipids and gangliosides play important roles in maintaining the functional integrity of the nervous system. However, surprisingly little is known about how glycolipids and gangliosides in particular participate in various neurodegenerative processes. For example, it has been known for a long time that administration of gangliosides and in particular, GM1 ganglioside, can ameliorate damage to the central and peripheral nervous systems and can mitigate effects of a variety of neurodegenerative processes. What is not known is the extent to which dysfunctional biosynthesis or metabolism of gangliosides may be involved in various neurodegenerative disorders and if alterations observed reflect an intrinsic disease-related process or represent the response of the brain to a degenerative process. This chapter briefly reviews recent advances in the study of glycolipids and gangliosides and their potential participation in a variety of neurodegenerative disorders including Parkinson's disease, Alzheimer's disease, Huntington's disease and the potential link between Gaucher disease and Parkinson's disease.

Knockout of Toll-like receptor 2 attenuates Aβ25-35-induced neurotoxicity in organotypic hippocampal slice cultures

Toll-like receptors (TLRs), which have been implicated in various neuroinflammatory responses, are thought to act in defense mechanisms by inhibiting neuronal cell death in Alzheimer's disease. In this study, we evaluated the effects of TLR2 on amyloid beta peptide 25-35 (Aβ25-35)-induced neuronal cell death, synaptic dysfunction, and microglial activation in organotypic hippocampal slice cultures (OHSCs) from wild-type (WT) C57BL/6 mice and TLR2-knockout (KO) mice. In WT mice, Aβ25-35 induced β-amyloid aggregation and surrounding TLR2 expression. And, propidium iodide (PI) uptake, which is a measure of cell death, increased in a dose-dependent manner in slices with Aβ25-35 treatment. In the Aβ25-35-treated TLR2-KO OHSCs, the PI uptake was significantly attenuated to the control level, indicating that the cells were less susceptible to Aβ25-35-induced neuronal toxicity. In the ultrastructural analysis, nuclear shrinkage, slightly swollen mitochondria, and degraded organelles were detected in the Aβ25-35-treated slices from WT mice but not in the Aβ25-35-treated slices from TLR2-KO, suggesting the resistance of TLR2-KO to Aβ25-35-induced neurotoxicity. In Aβ25-35-treated OHSCs of WT mice, the levels of phosphorylated tau were increased and the levels of synaptophysin were decreased in a dose-dependent manner, but they were not changed in OHSCs of TLR2-KO mice. In WT mice, Aβ25-35 increased total protein level and immunoreactivity of Iba-1, which was colocalized with TLR2. However, there were no significant changes in the slices of Aβ25-35-treated TLR2-KO mice. These results suggested that TLR2 may play a role in Aβ25-35-induced neuronal cell loss and synaptic dysfunction through the activation of microglia in OHSCs.

Amyloid precursor protein (APP) mediated regulation of ganglioside homeostasis linking Alzheimer's disease pathology with ganglioside metabolism

Gangliosides are important players for controlling neuronal function and are directly involved in AD pathology. They are among the most potent stimulators of Aβ production, are enriched in amyloid plaques and bind amyloid beta (Aβ). However, the molecular mechanisms linking gangliosides with AD are unknown. Here we identified the previously unknown function of the amyloid precursor protein (APP), specifically its cleavage products Aβ and the APP intracellular domain (AICD), of regulating GD3-synthase (GD3S). Since GD3S is the key enzyme converting a- to b-series gangliosides, it therefore plays a major role in controlling the levels of major brain gangliosides. This regulation occurs by two separate and additive mechanisms. The first mechanism directly targets the enzymatic activity of GD3S: Upon binding of Aβ to the ganglioside GM3, the immediate substrate of the GD3S, enzymatic turnover of GM3 by GD3S was strongly reduced. The second mechanism targets GD3S expression. APP cleavage results, in addition to Aβ release, in the release of AICD, a known candidate for gene transcriptional regulation. AICD strongly down regulated GD3S transcription and knock-in of an AICD deletion mutant of APP in vivo, or knock-down of Fe65 in neuroblastoma cells, was sufficient to abrogate normal GD3S functionality. Equally, knock-out of the presenilin genes, presenilin 1 and presenilin 2, essential for Aβ and AICD production, or of APP itself, increased GD3S activity and expression and consequently resulted in a major shift of a- to b-series gangliosides. In addition to GD3S regulation by APP processing, gangliosides in turn altered APP cleavage. GM3 decreased, whereas the ganglioside GD3, the GD3S product, increased Aβ production, resulting in a regulatory feedback cycle, directly linking ganglioside metabolism with APP processing and Aβ generation. A central aspect of this homeostatic control is the reduction of GD3S activity via an Aβ-GM3 complex and AICD-mediated repression of GD3S transcription.