Intraventricular Sialidase Administration Enhances GM1 Ganglioside Expression and Is Partially Neuroprotective in a Mouse Model of Parkinson's Disease

Mouse brain glycomics - Insights from exploring the Allen Brain Atlas and the implications for the neuroimmune brain

The Allen Institute Mouse Brain Atlas, with visualisation using the Brain Explorer software, offers a 3-dimensional view of region-specific RNA expression of thousands of mouse genes. In this Viewpoint, we focused on the region-specific expression of genes related to cellular glycosylation, and discuss their relevance towards psychoneuroimmunology. Using specific examples, we show that the Atlas validates existing observations reported by others, identifies previously unknown potential region-specific glycan features, and highlights the need to promote collaborations between glycobiology and psychoneuroimmunology researchers.

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.

The endo-lysosomal system in Parkinson's disease: expanding the horizon

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease, and its prevalence is increasing with age. A wealth of genetic evidence indicates that the endo-lysosomal system is a major pathway driving PD pathogenesis with a growing number of genes encoding endo-lysosomal proteins identified as risk factors for PD, making it a promising target for therapeutic intervention. However, detailed knowledge and understanding of the molecular mechanisms linking these genes to the disease are available for only a handful of them (e.g. LRRK2, GBA1, VPS35). Taking on the challenge of studying poorly characterized genes and proteins can be daunting, due to the limited availability of tools and knowledge from previous literature. This review aims at providing a valuable source of molecular and cellular insights into the biology of lesser-studied PD-linked endo-lysosomal genes, to help and encourage researchers in filling the knowledge gap around these less popular genetic players. Specific endo-lysosomal pathways discussed range from endocytosis, sorting, and vesicular trafficking to the regulation of membrane lipids of these membrane-bound organelles and the specific enzymatic activities they contain. We also provide perspectives on future challenges that the community needs to tackle and propose approaches to move forward in our understanding of these poorly studied endo-lysosomal genes. This will help harness their potential in designing innovative and efficient treatments to ultimately re-establish neuronal homeostasis in PD but also other diseases involving endo-lysosomal dysfunction.

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.

Sialic acid: an attractive biomarker with promising biomedical applications

This broad, narrative review highlights the roles of sialic acids as acidic sugars found on cellular membranes. The role of sialic acids in cellular communication and development has been well established. Recently, attention has turned to the fundamental role of sialic acids in many diseases, including viral infections, cardiovascular diseases, neurological disorders, diabetic nephropathy, and malignancies. Sialic acid may be a target for developing new drugs to treat various cancers and inflammatory processes. We recommend the routine measurement of serum sialic acid as a sensitive inflammatory marker in various diseases.

Defect in cytosolic Neu2 sialidase abrogates lipid metabolism and impairs muscle function in vivo

Sialic acid (SA) is present in glycoconjugates and important in cell-cell recognition, cell adhesion, and cell growth and as a receptor. Among the four mammalian sialidases, cytosolic NEU2 has a pivotal role in muscle and neuronal differentiation in vitro. However, its biological functions in vivo remain unclear due to its very low expression in humans. However, the presence of cytoplasmic glycoproteins, gangliosides, and lectins involved in cellular metabolism and glycan recognition has suggested the functional importance of cytosolic Neu2 sialidases. We generated a Neu2 knockout mouse model via CRISPR/Cas9-mediated genome engineering and analyzed the offspring littermates at different ages to investigate the in vivo function of cytosolic Neu2 sialidase. Surprisingly, knocking out the Neu2 gene in vivo abrogated overall lipid metabolism, impairing motor function and leading to diabetes. Consistent with these results, Neu2 knockout led to alterations in sialylated glycoproteins involved in lipid metabolism and muscle function, as shown by glycoproteomics analysis.

Human Neuraminidases: Structures and Stereoselective Inhibitors

This Perspective describes the classification, structures, substrates, mechanisms of action, and implications of human neuraminidases (hNEUs) in various pathologies. Some inhibitors have been developed for each isoform, leading to more precise interactions with hNEUs. Although crystal structure data are available for NEU2, most of the findings are based on NEU1 inhibition, and limited information is available for other hNEUs. Therefore, the synthesis of new compounds would facilitate the enrichment of the arsenal of inhibitors to better understand the roles of hNEUs and their mechanisms of action. Nevertheless, due to the already known inhibitors of human neuraminidase enzymes, a structure-activity relationship is presented along with different approaches to inhibit these enzymes for the development of potent and selective inhibitors. Among the different emerging strategies, one is the inhibition of the dimerization of NEU1 or NEU3, and the second is the inhibition of certain receptors located close to hNEU.

Glycosphingolipid metabolism and its role in ageing and Parkinson's disease

It is well established that lysosomal glucocerebrosidase gene (GBA) variants are a risk factor for Parkinson’s disease (PD), with increasing evidence suggesting a loss of function mechanism. One question raised by this genetic association is whether variants of genes involved in other aspects of sphingolipid metabolism are also associated with PD. Recent studies in sporadic PD have identified variants in multiple genes linked to diseases of glycosphingolipid (GSL) metabolism to be associated with PD. GSL biosynthesis is a complex pathway involving the coordinated action of multiple enzymes in the Golgi apparatus. GSL catabolism takes place in the lysosome and is dependent on the action of multiple acid hydrolases specific for certain substrates and glycan linkages. The finding that variants in multiple GSL catabolic genes are over-represented in PD in a heterozygous state highlights the importance of GSLs in the healthy brain and how lipid imbalances and lysosomal dysfunction are associated with normal ageing and neurodegenerative diseases. In this article we will explore the link between lysosomal storage disorders and PD, the GSL changes seen in both normal ageing, lysosomal storage disorders (LSDs) and PD and the mechanisms by which these changes can affect neurodegeneration.

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.

Innovative treatment targeting gangliosides aimed at blocking the formation of neurotoxic α-synuclein oligomers in Parkinson's disease

Parkinson's disease (PD) is a major neurodegenerative disorder which exhibits many of the characteristics of a pandemic. Current therapeutic strategies are centered on the dopaminergic system, with limited efficacy, so that a treatment that has a direct impact on the underlying disease pathogenesis is urgently needed. Although α-synuclein is a privileged target for such therapies, this protein has been in the past wrongly considered as exclusively intracellular, so that the impact of paracrine neurotoxicity mechanisms in PD have been largely ignored. In this article we review the data showing that lipid rafts act as plasma membrane machineries for the formation of α-synuclein pore-like oligomers which trigger an increase of intracellular Ca²⁺. This Ca²⁺ influx is responsible for a self-sustained cascade of neurotoxic events, including mitochondrial oxidative stress, tau phosphorylation, Ca²⁺ release from the endoplasmic reticulum, Lewy body formation, and extracellular release of α-synuclein in exosomes. The first step of this cascade is the binding of α-synuclein to lipid raft gangliosides, suggesting that PD should be considered as both a proteinopathy and a ganglioside membrane disorder lipidopathy. Accordingly, blocking α-synuclein-ganglioside interactions should annihilate the whole neurotoxic cascade and stop disease progression. A pipeline of anti-oligomer molecules is under development, among which an in-silico designed synthetic peptide AmyP53 which is the first drug targeting gangliosides and thus able to prevent the formation of α-synuclein oligomers and all downstream neurotoxicity. These new therapeutic avenues challenge the current symptomatic approaches by finally targeting the root cause of PD through a long-awaited paradigm shift.

A critical role for GM1 ganglioside in the pathophysiology and potential treatment of Parkinson's disease

Parkinson's disease (PD) is slowly progressing neurodegenerative disorder that affects millions of patients worldwide. While effective symptomatic therapies for PD exist, there is no currently available disease modifying agent to slow or stop the progression of the disease. Many years of research from various laboratories around the world have provided evidence in favor of the potential ability of GM1 ganglioside to be a disease modifying agent for PD. In this paper, information supporting the use of GM1 as a disease modifying therapeutic for PD is reviewed along with information concerning the role that deficiencies in GM1 ganglioside (and potentially other important brain gangliosides) may play in the pathogenesis of PD.

Replication of Influenza A Virus in Secondary Lymphatic Tissue Contributes to Innate Immune Activation

The replication of viruses in secondary lymphoid organs guarantees sufficient amounts of pattern-recognition receptor ligands and antigens to activate the innate and adaptive immune system. Viruses with broad cell tropism usually replicate in lymphoid organs; however, whether a virus with a narrow tropism relies on replication in the secondary lymphoid organs to activate the immune system remains not well studied. In this study, we used the artificial intravenous route of infection to determine whether Influenza A virus (IAV) replication can occur in secondary lymphatic organs (SLO) and whether such replication correlates with innate immune activation. Indeed, we found that IAV replicates in secondary lymphatic tissue. IAV replication was dependent on the expression of Sialic acid residues in antigen-presenting cells and on the expression of the interferon-inhibitor UBP43 (Usp18). The replication of IAV correlated with innate immune activation, resulting in IAV eradication. The genetic deletion of Usp18 curbed IAV replication and limited innate immune activation. In conclusion, we found that IAV replicates in SLO, a mechanism which allows innate immune activation.

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.

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.

GM1 Oligosaccharide Crosses the Human Blood-Brain Barrier In Vitro by a Paracellular Route

Ganglioside GM1 (GM1) has been reported to functionally recover degenerated nervous system in vitro and in vivo, but the possibility to translate GM1′s potential in clinical settings is counteracted by its low ability to overcome the blood–brain barrier (BBB) due to its amphiphilic nature. Interestingly, the soluble and hydrophilic GM1-oligosaccharide (OligoGM1) is able to punctually replace GM1 neurotrophic functions alone, both in vitro and in vivo. In order to take advantage of OligoGM1 properties, which overcome GM1′s pharmacological limitations, here we characterize the OligoGM1 brain transport by using a human in vitro BBB model. OligoGM1 showed a 20-fold higher crossing rate than GM1 and time–concentration-dependent transport. Additionally, OligoGM1 crossed the barrier at 4 °C and in inverse transport experiments, allowing consideration of the passive paracellular route. This was confirmed by the exclusion of a direct interaction with the active ATP-binding cassette (ABC) transporters using the “pump out” system. Finally, after barrier crossing, OligoGM1 remained intact and able to induce Neuro2a cell neuritogenesis by activating the TrkA pathway. Importantly, these in vitro data demonstrated that OligoGM1, lacking the hydrophobic ceramide, can advantageously cross the BBB in comparison with GM1, while maintaining its neuroproperties. This study has improved the knowledge about OligoGM1′s pharmacological potential, offering a tangible therapeutic strategy.

GM1 Ganglioside Is A Key Factor in Maintaining the Mammalian Neuronal Functions Avoiding Neurodegeneration

Many species of ganglioside GM1, differing for the sialic acid and ceramide content, have been characterized and their physico-chemical properties have been studied in detail since 1963. Scientists were immediately attracted to the GM1 molecule and have carried on an ever-increasing number of studies to understand its binding properties and its neurotrophic and neuroprotective role. GM1 displays a well balanced amphiphilic behavior that allows to establish strong both hydrophobic and hydrophilic interactions. The peculiar structure of GM1 reduces the fluidity of the plasma membrane which implies a retention and enrichment of the ganglioside in specific membrane domains called lipid rafts. The dynamism of the GM1 oligosaccharide head allows it to assume different conformations and, in this way, to interact through hydrogen or ionic bonds with a wide range of membrane receptors as well as with extracellular ligands. After more than 60 years of studies, it is a milestone that GM1 is one of the main actors in determining the neuronal functions that allows humans to have an intellectual life. The progressive reduction of its biosynthesis along the lifespan is being considered as one of the causes underlying neuronal loss in aged people and severe neuronal decline in neurodegenerative diseases. In this review, we report on the main knowledge on ganglioside GM1, with an emphasis on the recent discoveries about its bioactive component.

Diversity of sialidases found in the human body - A review

Sialidases are enzymes essential for numerous organisms including humans. Hydrolytic sialidases (EC 3.2.1.18), trans-sialidases and anhydrosialidases (intramolecular trans-sialidases, EC 4.2.2.15) are glycoside hydrolase enzymes that cleave the glycosidic linkage and release sialic acid residues from sialyl substrates. The paper summarizes diverse sialidases present in the human body and their potential impact on development of antiviral compounds - inhibitors of viral neuraminidases. It includes a brief overview of catalytic mechanisms of action of sialidases and describes the origin of sialidases in the human body. This is followed by description of the structure and function of sialidase families with a special focus on the GH33 and GH34 families. Various effects of sialidases on human body are also briefly described. Modulation of sialidase activity may be considered a useful tool for effective treatment of various diseases. In some cases, it is desired to completely suppress the activity of sialidases by suitable inhibitors. Specific sialidase inhibitors are useful for the treatment of influenza, epilepsy, Alzheimer's disease, diabetes, different types of cancer, or heart defects. Challenges and future directions are shortly depicted in the final part of the paper.

Parkinson's disease recovery by GM1 oligosaccharide treatment in the B4galnt1+/- mouse model

Given the recent in vitro discovery that the free soluble oligosaccharide of GM1 is the bioactive portion of GM1 for neurotrophic functions, we investigated its therapeutic potential in the B4galnt1^+/− mice, a model of sporadic Parkinson’s disease. We found that the GM1 oligosaccharide, systemically administered, reaches the brain and completely rescues the physical symptoms, reduces the abnormal nigral α-synuclein content, restores nigral tyrosine hydroxylase expression and striatal neurotransmitter levels, overlapping the wild-type condition. Thus, this study supports the idea that the Parkinson’s phenotype expressed by the B4galnt1^+/− mice is due to a reduced level of neuronal ganglioside content and lack of interactions between the oligosaccharide portion of GM1 with specific membrane proteins. It also points to the therapeutic potential of the GM1 oligosaccharide for treatment of sporadic Parkinson’s disease.

The Neuroprotective Role of the GM1 Oligosaccharide, II3Neu5Ac-Gg4, in Neuroblastoma Cells

Recently, we demonstrated that the GM1 oligosaccharide, II³Neu5Ac-Gg₄ (OligoGM1), administered to cultured murine Neuro2a neuroblastoma cells interacts with the NGF receptor TrkA, leading to the activation of the ERK1/2 downstream pathway and to cell differentiation. To understand how the activation of the TrkA pathway is able to trigger key biochemical signaling, we performed a proteomic analysis on Neuro2a cells treated with 50 μM OligoGM1 for 24 h. Over 3000 proteins were identified. Among these, 324 proteins were exclusively expressed in OligoGM1-treated cells. Interestingly, several proteins expressed only in OligoGM1-treated cells are involved in biochemical mechanisms with a neuroprotective potential, reflecting the GM1 neuroprotective effect. In addition, we found that the exogenous administration of OligoGM1 reduced the cellular oxidative stress in Neuro2a cells and conferred protection against MPTP neurotoxicity. These results confirm and reinforce the idea that the molecular mechanisms underlying the GM1 neurotrophic and neuroprotective effects depend on its oligosaccharide chain, suggesting the activation of a positive signaling starting at plasma membrane level.

GM1 promotes TrkA-mediated neuroblastoma cell differentiation by occupying a plasma membrane domain different from TrkA

Recently, we highlighted that the ganglioside GM1 promotes neuroblastoma cells differentiation by activating the TrkA receptor through the formation of a TrkA-GM1 oligosaccharide complex at the cell surface. To study the TrkA-GM1 interaction, we synthesized two radioactive GM1 derivatives presenting a photoactivable nitrophenylazide group at the end of lipid moiety, 1 or at position 6 of external galactose, 2; and a radioactive oligosaccharide portion of GM1 carrying the nitrophenylazide group at position 1 of glucose, 3. The three compounds were singly administered to cultured neuroblastoma Neuro2a cells under established conditions that allow cell surface interactions. After UV activation of photoactivable compounds, the proteins were analyzed by PAGE separation. The formation of cross-linked TrkA-GM1 derivatives complexes was identified by both radioimaging and immunoblotting. Results indicated that the administration of compounds 2 and 3, carrying the photoactivable group on the oligosaccharide, led to the formation of a radioactive TrkA complex, while the administration of compound 1 did not. This underlines that the TrkA-GM1 interaction directly involves the GM1 oligosaccharide, but not the ceramide. To better understand how GM1 relates to the TrkA, we isolated plasma membrane lipid rafts. As expected, GM1 was found in the rigid detergent-resistant fractions, while TrkA was found as a detergent soluble fraction component. These results suggest that TrkA and GM1 belong to separate membrane domains: probably TrkA interacts by 'flopping' down its extracellular portion onto the membrane, approaching its interplay site to the oligosaccharide portion of GM1.

The Role of Lipids in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disease characterized by a progressive loss of dopaminergic neurons from the nigrostriatal pathway, formation of Lewy bodies, and microgliosis. During the past decades multiple cellular pathways have been associated with PD pathology (i.e., oxidative stress, endosomal-lysosomal dysfunction, endoplasmic reticulum stress, and immune response), yet disease-modifying treatments are not available. We have recently used genetic data from familial and sporadic cases in an unbiased approach to build a molecular landscape for PD, revealing lipids as central players in this disease. Here we extensively review the current knowledge concerning the involvement of various subclasses of fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, and lipoproteins in PD pathogenesis. Our review corroborates a central role for most lipid classes, but the available information is fragmented, not always reproducible, and sometimes differs by sex, age or PD etiology of the patients. This hinders drawing firm conclusions about causal or associative effects of dietary lipids or defects in specific steps of lipid metabolism in PD. Future technological advances in lipidomics and additional systematic studies on lipid species from PD patient material may improve this situation and lead to a better appreciation of the significance of lipids for this devastating disease.

Sialidase activity in human pathologies

Sialic acid residues are frequently located at the terminal positions of glycoconjugate chains of cellular glycocalyx. Sialidases, or neuraminidases, catalyse removal of these residues thereby modulating various normal and pathological cellular activities. Recent studies have revealed the involvement of sialidases in a wide range of human disorders, including neurodegenerative disorders, cancers, infectious diseases and cardiovascular diseases. The accumulating data make sialidases an interesting potential therapeutic target. Modulating the activity of these enzymes may have beneficial effects in several pathologies. Four types of mammalian sialidases have been described: NEU1, NEU2, NEU3 and NEU4. They are encoded by different genes and characterized by different subcellular localization. In this review, we will summarize the current knowledge on the roles of different sialidases in pathological conditions.

Lentiviral-mediated knock-down of GD3 synthase protects against MPTP-induced motor deficits and neurodegeneration

Converging evidence demonstrates an important role for gangliosides in brain function and neurodegenerative diseases. Exogenous GM1 is broadly neuroprotective, including in rodent, feline, and primate models of Parkinson's disease, and has shown positive effects in clinical trials. We and others have shown that inhibition of the ganglioside biosynthetic enzyme GD3 synthase (GD3S) increases endogenous levels GM1 ganglioside. We recently reported that targeted deletion of St8sia1, the gene that codes for GD3S, prevents motor impairments and significantly attenuates neurodegeneration induced by 1-methy-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The current study investigated the effects of GD3S inhibition on the neurotoxicity and parkinsonism induced by MPTP. Mice were injected intrastriatally with a lentiviral-vector-mediated shRNA construct targeting GD3S (shGD3S) or a scrambled-sequence control (scrRNA). An MPTP regimen of 18 mg/kg x 5 days reduced tyrosine-hydroxylase-positive neurons in the substantia nigra pars compacta of scrRNA-treated mice by nearly two-thirds. In mice treated with shGD3S the MPTP-induced lesion was approximately half that size. MPTP induced bradykinesia and deficits in fine motor skills in mice treated with scrRNA. These deficits were absent in shGD3S-treated mice. These results suggest that inhibition of GD3S protects against the nigrostriatal damage, bradykinesia, and fine-motor-skill deficits associated with MPTP administration.

Gangliosides, α-Synuclein, and Parkinson's Disease

This review addresses the role of α-synuclein (αSyn) in the etiopathology of Parkinson's disease (PD), with emphasis on its interaction with GM1 ganglioside. We begin with a brief review of some of the milestone discoveries that helped to elucidate PD neuropathology, including the fibrous inclusions of Lewy that characterize the degenerating dopaminergic neurons of the substantia nigra and the presence of αSyn as a major constituent of these Lewy bodies and neurites. This enabled Braak et al. to define the progressive nature of PD in developing their staging hypothesis which described the topographically predictable sequence of neuropathological changes giving rise to prodromal nonmotor symptoms that precede the classical motor dysfunctions. We recount recent studies demonstrating strong, specific binding of αSyn to GM1 that serves to inhibit fibril formation and the key role of N-acetylation of αSyn in enhancing GM1 binding and specificity. The consequences of insufficient GM1 are illustrated in a newly presented mouse model of PD based on partial deletion of this ganglioside due to heterologous disruption of B4galnt1 (GM2/GD2 synthase), such mice presenting accurate recapitulation of the PD phenotype. A key feature of these mice was marked elevation of αSyn aggregates which accompanied motor impairment, both aggregates and motor dysfunction being corrected by GM1 replacement therapy. Such therapy was achieved with high dosage of GM1 and more effectively with lower doses of LIGA20, a membrane permeable analog of GM1. The accuracy of this mouse model was emphasized by the finding that various central nervous system and noncentral nervous system tissues from PD patients manifested similar GM1 deficiency as the B4galnt1^+/- mouse. A mechanism is proposed whereby the GM1 deficiency detected in PD patients gives rise to αSyn aggregation and facilitation by the latter in blocking glial cell-derived neurotrophic factor neuroprotection.

Sphingomyelin and GM1 Influence Huntingtin Binding to, Disruption of, and Aggregation on Lipid Membranes

Huntington disease (HD) is an inherited neurodegenerative disease caused by the expansion beyond a critical threshold of a polyglutamine (polyQ) tract near the N-terminus of the huntingtin (htt) protein. Expanded polyQ promotes the formation of a variety of oligomeric and fibrillar aggregates of htt that accumulate into the hallmark proteinaceous inclusion bodies associated with HD. htt is also highly associated with numerous cellular and subcellular membranes that contain a variety of lipids. As lipid homeostasis and metabolism abnormalities are observed in HD patients, we investigated how varying both the sphingomyelin (SM) and ganglioside (GM1) contents modifies the interactions between htt and lipid membranes. SM composition is altered in HD, and GM1 has been shown to have protective effects in animal models of HD. A combination of Langmuir trough monolayer techniques, vesicle permeability and binding assays, and in situ atomic force microscopy (AFM) were used to directly monitor the interaction of a model, synthetic htt peptide and a full-length htt-exon1 recombinant protein with model membranes comprised of total brain lipid extract (TBLE) and varying amounts of exogenously added SM or GM1. The addition of either SM or GM1 decreased htt insertion into the lipid monolayers. However, TBLE vesicles with an increased SM content were more susceptible to htt-induced permeabilization, whereas GM1 had no effect on permeablization. Pure TBLE bilayers and TBLE bilayers enriched with GM1 developed regions of roughened, granular morphologies upon exposure to htt-exon1, but plateau-like domains with a smoother appearance formed in bilayers enriched with SM. Oligomeric aggregates were observed on all bilayer systems regardless of induced morphology. Collectively, these observations suggest that the lipid composition and its subsequent effects on membrane material properties strongly influence htt binding and aggregation on lipid membranes.

Current understanding of the molecular mechanisms in Parkinson's disease: Targets for potential treatments

Gradual degeneration and loss of dopaminergic neurons in the substantia nigra, pars compacta and subsequent reduction of dopamine levels in striatum are associated with motor deficits that characterize Parkinson’s disease (PD). In addition, half of the PD patients also exhibit frontostriatal-mediated executive dysfunction, including deficits in attention, short-term working memory, speed of mental processing, and impulsivity. The most commonly used treatments for PD are only partially or transiently effective and are available or applicable to a minority of patients. Because, these therapies neither restore the lost or degenerated dopaminergic neurons, nor prevent or delay the disease progression, the need for more effective therapeutics is critical. In this review, we provide a comprehensive overview of the current understanding of the molecular signaling pathways involved in PD, particularly within the context of how genetic and environmental factors contribute to the initiation and progression of this disease. The involvement of molecular chaperones, autophagy-lysosomal pathways, and proteasome systems in PD are also highlighted. In addition, emerging therapies, including pharmacological manipulations, surgical procedures, stem cell transplantation, gene therapy, as well as complementary, supportive and rehabilitation therapies to prevent or delay the progression of this complex disease are reviewed.

Targeted deletion of GD3 synthase protects against MPTP-induced neurodegeneration

Parkinson's disease is a debilitating neurodegenerative condition for which there is no cure. Converging evidence implicates gangliosides in the pathogenesis of several neurodegenerative diseases, suggesting a potential new class of therapeutic targets. We have shown that interventions that simultaneously increase the neuroprotective GM1 ganglioside and decrease the pro-apoptotic GD3 ganglioside - such as inhibition of GD3 synthase (GD3S) or administration of sialidase - are neuroprotective in vitro and in a number of preclinical models. In this study, we investigated the effects of GD3S deletion on parkinsonism induced by 1-methyl-4phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP was administered to GD3S-/- mice or controls using a subchronic regimen consisting of three series of low-dose injections (11 mg/kg/day × 5 days each, 3 weeks apart), and motor function was assessed after each. The typical battery of tests used to assess parkinsonism failed to detect deficits in MPTP-treated mice. More sensitive measures - such as the force-plate actimeter and treadmill gait parameters - detected subtle effects of MPTP, some of which were absent in mice lacking GD3S. In wild-type mice, MPTP destroyed 53% of the tyrosine-hydroxylase (TH)-positive neurons in the substantia nigra pars compacta (SNc) and reduced striatal dopamine 60.7%. In contrast, lesion size was only 22.5% in GD3S-/- mice and striatal dopamine was reduced by 37.2%. Stereological counts of Nissl-positive SNc neurons that did not express TH suggest that neuroprotection was complete but TH expression was suppressed in some cells. These results show that inhibition of GD3S has neuroprotective properties in the MPTP model and may warrant further investigation as a therapeutic target.

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.