Direct interaction between GluR2 and GAPDH regulates AMPAR-mediated excitotoxicity

Immunoexcitoxicity as the possible major pathophysiology behind multiple sclerosis and other autoimmune disorders

Autoimmune disorders are destructive processes considered to be an attack on "self " antigens by the immune system CD-+4 T-cells that are directed toward antigens, in the case of multiple sclerosis (MS), particularly myelin antigens. Yet, there is growing evidence that the major destructive events in MS, as well as other non-central nervous system (CNS) autoimmune disorders, are much more than an immune attack on the CNS initiated by a misdirected immune system that attacks a "self " antigen or antigens by a process called molecular mimicry. Extensive evidence suggests that inflammation, in turn, initiates excitotoxicity, which is responsible for the majority of pathological findings in all stages of the disease, especially a loss of oligodendroglia (source of myelin) and axon injury in MS. Excitotoxicity also is a better explanation for progressive MS, in which the immune attack has either slowed or is halted; yet, the destructive pathology continues to progress. It also explains the destructive lesions seen in gray matter, which is essentially devoid of inflammation. It has recently been shown that most of the damage to the oligodendrocytes, as well as axonal injury, is secondary to excitotoxicity. While there is a growing appreciation that excitotoxicity plays a major role, there has been little effort to link the immune changes to the excitotoxic process, recently named immunoexcitotoxicity, even though the role of excitotoxicity has been shown to occur in the inflammatory stage in the beginning and throughout the process of the disease, particularly the chronic progressive stage. It is also known that peripheral glutamate receptors exist throughout the body, thus making the process of immunoexcitotoxicity a possible integral part of all or most autoimmune disorders in which the immune system is intimately linked to enhancing the excitotoxic process. This is of special concern now that peripheral glutamate receptors have been isolated in many peripheral tissues and are known to be fully functional.

Novel α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor (AMPAR) potentiator LT-102: A promising therapeutic agent for treating cognitive impairment associated with schizophrenia

AIMS

We aimed to evaluate the potential of a novel selective α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor (AMPAR) potentiator, LT-102, in treating cognitive impairments associated with schizophrenia (CIAS) and elucidating its mechanism of action.

METHODS

The activity of LT-102 was examined by Ca2+ influx assays and patch-clamp in rat primary hippocampal neurons. The structure of the complex was determined by X-ray crystallography. The selectivity of LT-102 was evaluated by hERG tail current recording and kinase-inhibition assays. The electrophysiological characterization of LT-102 was characterized by patch-clamp recording in mouse hippocampal slices. The expression and phosphorylation levels of proteins were examined by Western blotting. Cognitive function was assessed using the Morris water maze and novel object recognition tests.

RESULTS

LT-102 is a novel and selective AMPAR potentiator with little agonistic effect, which binds to the allosteric site formed by the intradimer interface of AMPAR's GluA2 subunit. Treatment with LT-102 facilitated long-term potentiation in mouse hippocampal slices and reversed cognitive deficits in a phencyclidine-induced mouse model. Additionally, LT-102 treatment increased the protein level of brain-derived neurotrophic factor and the phosphorylation of GluA1 in primary neurons and hippocampal tissues.

CONCLUSION

We conclude that LT-102 ameliorates cognitive impairments in a phencyclidine-induced model of schizophrenia by enhancing synaptic function, which could make it a potential therapeutic candidate for CIAS.

Small-molecule targeting AMPA-mediated excitotoxicity has therapeutic effects in mouse models for multiple sclerosis

While most research and treatments for multiple sclerosis (MS) focus on autoimmune reactions causing demyelination, it is possible that neurodegeneration precedes the autoimmune response. Hence, glutamate receptor antagonists preventing excitotoxicity showed promise in MS animal models, though blocking glutamate signaling prevents critical neuronal functions. This study reports the discovery of a small molecule that prevents AMPA-mediated excitotoxicity by targeting an allosteric binding site. A machine learning approach was used to screen for small molecules targeting the AMPA receptor GluA2 subunit. The lead candidate has potent effects in restoring neurological function and myelination while reducing the immune response in experimental autoimmune encephalitis and cuprizone MS mouse models without affecting basal neurotransmission or learning and memory. These findings facilitate development of a treatment for MS with a different mechanism of action than current immune modulatory drugs and avoids important off-target effects of glutamate receptor antagonists. This class of MS therapeutics could be useful as an alternative or complementary treatment to existing therapies.

Synaptotagmin-3 interactions with GluA2 mediate brain damage and impair functional recovery in stroke

Synaptotagmin III (Syt3) is a Ca2+-dependent membrane-traffic protein that is highly concentrated in synaptic plasma membranes and affects synaptic plasticity by regulating post-synaptic receptor endocytosis. Here, we show that Syt3 is upregulated in the penumbra after ischemia/reperfusion (I/R) injury. Knockdown of Syt3 protects against I/R injury, promotes recovery of motor function, and inhibits cognitive decline. Overexpression of Syt3 exerts the opposite effects. Mechanistically, I/R injury augments Syt3-GluA2 interactions, decreases GluA2 surface expression, and promotes the formation of Ca2+-permeable AMPA receptors (CP-AMPARs). Using a CP-AMPAR antagonist or dissociating the Syt3-GluA2 complex via TAT-GluA2-3Y peptide promotes recovery from neurological impairments and improves cognitive function. Furthermore, Syt3 knockout mice are resistant to cerebral ischemia because they show high-level expression of surface GluA2 and low-level expression of CP-AMPARs after I/R. Our results indicate that Syt3-GluA2 interactions, which regulate the formation of CP-AMPARs, may be a therapeutic target for ischemic insults.

Development of a novel peptide to prevent entry of SARS-CoV-2 into lung and olfactory bulb cells of hACE2 expressing mice

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus that has caused a global pandemic Coronavirus Disease 2019 (COVID-19). Currently, there are no effective treatments specifically for COVID-19 infection. The initial step in SARS-CoV-2 infection is attachment to the angiotensin-converting enzyme 2 (ACE2) on the cell surface. We have developed a protein peptide that effectively disrupts the binding between the SARS-CoV-2 spike protein and ACE2. When delivered by nasal spray, our peptide prevents SARS-CoV-2 spike protein from entering lung and olfactory bulb cells of mice expressing human ACE2. Our peptide represents a potential novel treatment and prophylaxis against COVID-19.

Research Progress on Neuroprotection of Insulin-like Growth Factor-1 towards Glutamate-Induced Neurotoxicity

Insulin-like growth factor-1 (IGF-1) and its binding proteins and receptors are widely expressed in the central nervous system (CNS), proposing IGF-1-induced neurotrophic actions in normal growth, development, and maintenance. However, while there is convincing evidence that the IGF-1 system has specific endocrine roles in the CNS, the concept is emerging that IGF-I might be also important in disorders such as ischemic stroke, brain trauma, Alzheimer’s disease, epilepsy, etc., by inducing neuroprotective effects towards glutamate-mediated excitotoxic signaling pathways. Research in rodent models has demonstrated rescue of pathophysiological and behavioral abnormalities when IGF-1 was administered by different routes, and several clinical studies have shown safety and promise of efficacy in neurological disorders of the CNS. Focusing on the relationship between IGF-1-induced neuroprotection and glutamate-induced excitatory neurotoxicity, this review addresses the research progress in the field, intending to provide a rationale for using IGF-I clinically to confer neuroprotective therapy towards neurological diseases with glutamate excitotoxicity as a common pathological pathway.

Constraint-induced movement therapy enhances AMPA receptor-dependent synaptic plasticity in the ipsilateral hemisphere following ischemic stroke

Constraint-induced movement therapy (CIMT) can promote the recovery of motor function in injured upper limbs following stroke, which may be associated with upregulation of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) at synapses in the ipsilateral sensorimotor cortex in our previous study. However, AMPAR distribution is tightly regulated, and only AMPARs on the postsynaptic membrane can mediate synaptic transmission. We speculated that synaptic remodeling induced by movement-associated synaptic activity can promote functional recovery from stroke. To test this hypothesis, we compared AMPAR expression on the postsynaptic membrane surface in a rat model of ischemic stroke induced by middle cerebral artery occlusion (MCAO) with versus without CIMT, which consisted of daily running wheel training for 2 weeks starting on day 7 after MCAO. The results showed that CIMT increased the number of glutamate receptor (GluR)2-containing functional synapses in the ipsilateral sensorimotor cortex, and reduced non-GluR2 AMPARs in the ipsilateral sensorimotor cortex and hippocampal CA3 region. In addition, CIMT enhanced AMPAR expression on the surface of post-synaptic membrane in the ipsilateral sensorimotor cortex and hippocampus. Thus, CIMT promotes the recovery of motor function of injured upper limbs following stroke by enhancing AMPAR-mediated synaptic transmission in the ischemic hemisphere. These findings provide supporting evidence for the clinical value of CIMT for restoring limb movement in stroke patients. All experimental procedures and protocols were approved by the Department of Laboratory Animal Science of Fudan University, China (approval No. 201802173S) on March 3, 2018.

High Pressure Stress Response: Involvement of NMDA Receptor Subtypes and Molecular Markers

Professional divers who are exposed to high pressure (HP) above 1.1 MPa suffer from high pressure neurological syndrome (HPNS), which is characterized by reversible CNS hyperexcitability and cognitive and motor deficits. HPNS remains the final major constraints on deep diving at HP. Prolonged and repetitive exposure to HP during deep sea saturation dives may result in permanent memory and motor impairment. Previous studies revealed that CNS hyperexcitability associated with HPNS is largely induced by N-methyl-D-aspartate receptors (NMDARs). NMDARs that contain the GluN2A subunit are the only ones that show a large (∼60%) current increase at He HP. NMDAR subtypes that contain other GluN2 members show minor decrease or no change of the current. Immunoprecipitation was used in order to test the hypothesis that current augmentation may result from inserting additional NMDARs into the membrane during the 20–25 min compression. The results indicated that there is no increase in surface expression of NMDARs in the oocyte membrane under HP conditions. In contrast, consistent increase in glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and β-actin was discovered. GAPDH and β-actin are cytosolic proteins which involve in various cellular control processes, increase of their expression suggests the presence of a general cellular stress response to HP. Understanding the precise hyperexcitation mechanism(s) of specific NMDAR subtypes and other possible neurotoxic processes during HP exposure could provide the key for eliminating the adverse, yet reversible, short-term effects of HPNS and hopefully the deleterious long-term ones.

Long-term depression induced by endogenous cannabinoids produces neuroprotection via astroglial CB1R after stroke in rodents

Ischemia not only activates cell death pathways but also triggers endogenous protective mechanisms. However, it is largely unknown what is the essence of the endogenous neuroprotective mechanisms induced by preconditioning. In this study we demonstrated that systemic injection of JZL195, a selective inhibitor of eCB clearance enzymes, induces in vivo long-term depression at CA3-CA1 synapses and at PrL-NAc synapses produces neuroprotection. JZL195-elicited long-term depression is blocked by AM281, the antagonist of cannabinoid 1 receptor (CB₁R) and is abolished in mice lacking cannabinoid CB₁ receptor (CB₁R) in astroglial cells, but is conserved in mice lacking CB₁R in glutamatergic or GABAergic neurons. Blocking the glutamate NMDA receptor and the synaptic trafficking of glutamate AMPA receptor abolishes both long-term depression and neuroprotection induced by JZL195. Mice lacking CB₁R in astroglia show decreased neuronal death following cerebral ischemia. Thus, an acute elevation of extracellular eCB following eCB clearance inhibition results in neuroprotection through long-term depression induction after sequential activation of astroglial CB₁R and postsynaptic glutamate receptors.

Glial Cell AMPA Receptors in Nervous System Health, Injury and Disease

Glia form a central component of the nervous system whose varied activities sustain an environment that is optimised for healthy development and neuronal function. Alpha-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA)-type glutamate receptors (AMPAR) are a central mediator of glutamatergic excitatory synaptic transmission, yet they are also expressed in a wide range of glial cells where they influence a variety of important cellular functions. AMPAR enable glial cells to sense the activity of neighbouring axons and synapses, and as such many aspects of glial cell development and function are influenced by the activity of neural circuits. However, these AMPAR also render glia sensitive to elevations of the extracellular concentration of glutamate, which are associated with a broad range of pathological conditions. Excessive activation of AMPAR under these conditions may induce excitotoxic injury in glial cells, and trigger pathophysiological responses threatening other neural cells and amplifying ongoing disease processes. The aim of this review is to gather information on AMPAR function from across the broad diversity of glial cells, identify their contribution to pathophysiological processes, and highlight new areas of research whose progress may increase our understanding of nervous system dysfunction and disease.

Phased Treatment Strategies for Cerebral Ischemia Based on Glutamate Receptors

Extracellular glutamate accumulation following cerebral ischemia leads to overactivation of glutamate receptors, thereby resulting in intracellular Ca²⁺ overload and excitotoxic neuronal injury. Multiple attempts have been made to counteract such effects by reducing glutamate receptor function, but none have been successful. In this minireview, we present the available evidence regarding the role of all types of ionotropic and metabotropic glutamate receptors in cerebral ischemia and propose phased treatment strategies based on glutamate receptors in both the acute and post-acute phases of cerebral ischemia, which may help realize the clinical application of glutamate receptor antagonists.

Disruption of the GluA2/GAPDH complex using TAT-GluA2NT1-3-2 peptide protects against AMPAR-mediated excitotoxicity after epilepsy

Excitotoxicity and neuronal death following epilepsy involve α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). It forms a protein complex with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and co-internalizes upon activation of AMPA receptors after epilepsy. Disruption of the GluA2/GAPDH complex with an interfering peptide, TAT-GluA2NT1-3-2, protects cells against AMPAR-mediated excitotoxicity, which have been identified in in-vitro and in-vivo models of brain ischemia. We postulated that disruption of the GluA2/GAPDH interaction with the TAT-GluA2NT1-3-2 peptide would also protect against AMPAR-induced neuronal injury in an in-vivo model of status epilepticus (SE). In the present study, we divided pilocarpine-induced SE Wistar rats into three main groups: the TAT-GluA2NT1-3-2 peptide group, the TAT-GluA2NT-scram peptide group, and the normal saline group, and injected different doses of peptides stereotaxically into the hippocampus of SE rats to investigate whether the GluA2/GAPDH interaction could be disrupted by our TAT-GluA2NT1-3-2 peptide and determine its most appropriate dose. Then, the dose was administered stereotaxically at different time points after SE to determine the best administration time of neuronal protection. We found that the TAT-GluA2NT1-3-2 peptide can disrupt the GluA2/GAPDH interaction and protects against epilepsy-induced neuronal damage. The GluA2/GAPDH interaction may be a novel therapeutic target for epilepsy.

Monogenic, Polygenic, and MicroRNA Markers for Ischemic Stroke

Ischemic stroke (IS) is a leading disease with high mortality and disability, as well as with limited therapeutic window. Biomarkers for earlier diagnosis of IS have long been pursued. Family and twin studies confirm that genetic variations play an important role in IS pathogenesis. Besides DNA mutations found previously by genetic linkage analysis for monogenic IS (Mendelian inheritance), recent studies using genome-wide associated study (GWAS) and microRNA expression profiling have resulted in a large number of DNA and microRNA biomarkers in polygenic IS (sporadic IS), especially in different IS subtypes and imaging phenotypes. The present review summarizes genetic markers discovered by clinical studies and discusses their pathogenic molecular mechanisms involved in developmental or regenerative anomalies of blood vessel walls, neuronal apoptosis, excitotoxic death, inflammation, neurogenesis, and angiogenesis. The possible impact of environment on genetics is addressed as well. We also include a perspective on further studies and clinical application of these IS biomarkers.

Targeting redox regulation to treat substance use disorder using N‐acetylcysteine

Substance use disorder (SUD) is a chronic relapsing disorder characterized by transitioning from acute drug reward to compulsive drug use. Despite the heavy personal and societal burden of SUDs, current treatments are limited and unsatisfactory. For this reason, a deeper understanding of the mechanisms underlying addiction is required. Altered redox status, primarily due to drug-induced increases in dopamine metabolism, is a unifying feature of abused substances. In recent years, knowledge of the effects of oxidative stress in the nervous system has evolved from strictly neurotoxic to include a more nuanced role in redox-sensitive signaling. More specifically, S-glutathionylation, a redox-sensitive post-translational modification, has been suggested to influence the response to drugs of abuse. In this review we will examine the evidence for redox-mediating drugs as therapeutic tools focusing on N-acetylcysteine as a treatment for cocaine addiction. We will conclude by suggesting future research directions that may further advance this field.

Specific Alterations in Astrocyte Properties via the GluA2-GAPDH Complex Associated with Multiple Sclerosis

There is strong evidence indicating neuroinflammation is an important mediator in multiple sclerosis (MS), with astrogliosis playing a significant role in this process. Surprisingly, astrocytes exert paradoxical roles during disease development, but the mechanisms remain unknown. Previously, we have reported that administering an interfering peptide (GluA2-G-Gpep) which specifically disrupts the GluA2-GAPDH interaction rescued neurological symptoms in the EAE mouse model of MS. In this study, we validated that the GluA2-GAPDH complex was elevated in LPS-induced primary reactive astrocytes, and GluA2-G-Gpep treatment significantly reduced GFAP expression levels in both EAE mice and reactive astrocytes. Further in vivo and in vitro analyses revealed that GluA2-G-Gpep administration normalized EAAT1 and EAAT2 expression, rescued compromised blood-brain barrier integrity via AQP4, promoted actin reorganization and changed mitochondrial dynamics. These alterations may partially be explained by changes in the nuclear GAPDH and p53 transcription pathways. Our findings provide critical implications for understanding the astrocyte properties regulated by GluA2-GAPDH associated with MS, and insights for novel treatment options targeting at astrocytes.

Endophilin A1 mediates seizure activity via regulation of AMPARs in a PTZ-kindled epileptic mouse model

Endophilin A1 is a member of the endophilin A family and is primarily expressed in the central nervous system. Endophilin A1 can mediate neuronal excitability by regulating neuronal synaptic plasticity, which indicates that the protein may be involved in epilepsy. However, to date, its role in epilepsy remains unclear. To explore the role of endophilin A1 in epilepsy, we aimed to investigate the expression patterns of endophilin A1 in patients with temporal lobe epilepsy (TLE) and in a pentylenetetrazole (PTZ)-kindled epileptic mouse model and to conduct behavioral and electrophysiological analyses after lentivirus-mediated knockdown of endophilin A1 in the hippocampus of epileptic mice. This study found that the expression of endophilin A1 was significantly up-regulated in the temporal neocortex of TLE patients and in the hippocampus and adjacent temporal cortex of the PTZ-kindled epileptic mouse model. Behavioral analyses indicated that knockdown of endophilin A1 in the mouse hippocampus increased the latency of the first seizure and reduced the frequency and duration of seizure activity. Whole-cell patch-clamp recordings of pyramidal neurons in the hippocampal CA3 area indicated that knockdown of endophilin A1 in the mouse hippocampus resulted in a reduced frequency of action potentials and decreased amplitudes of miniature excitatory postsynaptic currents (mEPSCs) and evoked AMPA-dependent EPSCs. Moreover, western blotting analysis showed that the surface expression of the AMPAR GluR2 subunit was also decreased after endophilin A1 knockdown, and co-immunoprecipitation indicated an association between endophilin A1 and AMPAR GluR2 in the mouse hippocampus. Further, when AMPARs were activated by CX546, the antiepileptic function of endophilin A1 knockdown was decreased. Based on these results, endophilin A1 plays a critical role in epilepsy, and its suppression in the mouse hippocampus can restrain neuronal excitability and seizure activity via regulating AMPARs.

Elevated sterol regulatory elementary binding protein 1 and GluA2 levels in the hippocampal nuclear fraction of Genetic Absence Epilepsy Rats from Strasbourg

Studies in animal models and human tissues show that nuclear translocation of sterol regulatory element binding protein 1 (SREBP1) and glutamate A2 subunit (GluA2) of cell-surface AMPA receptor (AMPAR) trigger neuronal excitotoxicity-induced apoptosis in stroke. However, it is not known whether a similar type of underlying pathophysiology occurs in absence epilepsy. To explore this issue, we examined the levels of mature SREBP1, GluA2, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), p53, and activated to total caspase 3 ratio in nuclear fractions (NF) of hippocampal homogenate from 8 to 10 week old male Genetic Absence Epilepsy Rats from Strasbourg (GAERS) and non-epileptic control (NEC) strains. Mature SREBP1 and GluA2 levels were elevated approximately two-fold in NFs of GAERS hippocampal homogenates compared to NEC animals. Significant increases in GAPDH (∼15-fold) and total caspase 3 (∼10-fold) levels were also found in NFs of GAERS hippocampal homogenates in comparison to the non-epileptic strain. Data from the current study suggest that absence epilepsy in GAERS is associated with nuclear translocation of mature SREBP1, GluA2 subunit of AMPARs, and recruitment of pro-cell death signaling proteins such as GAPDH and caspase 3. These changes may contribute to hippocampal neuronal/glial cell death in GAERS. Therefore, inhibiting the nuclear accumulation of mature SREBP1 and GluA2 translocation may reduce the pathophysiology of absence epilepsy.

Advances in understanding the role of disease-associated proteins in spinal muscular atrophy

INTRODUCTION

Spinal muscular atrophy (SMA) is a neurodegenerative disorder characterized by alpha motor neuron loss in the spinal cord due to reduced survival motor neuron (SMN) protein level. While the genetic basis of SMA is well described, the specific molecular pathway underlying SMA is still not fully understood. Areas covered: This review discusses the recent advancements in understanding the molecular pathways in SMA using different omics approaches and genetic modifiers identified in both vertebrate and invertebrate systems. The findings that are summarized in this article were deduced from original articles and reviews with a particular focus on the latest advancements in the field. Expert commentary: The identification of genetic modifiers such as PLS3 and NCALD in humans or of SMA modulators such as Elavl4 (HuD), Copa, Uba1, Mapk10 (Jnk3), Nrxn2 and Tmem41b (Stasimon) in various SMA animal models improved our knowledge of impaired cellular pathways in SMA. Inspiration from modifier genes and their functions in motor neuron and neuromuscular junctions may open a new avenue for future SMA combinatorial therapies.

Anti-GAPDH Autoantibodies as a Pathogenic Determinant and Potential Biomarker of Neuropsychiatric Diseases

OBJECTIVE

To investigate the potential role of circulating autoantibodies specific to neuronal cell surface antigens in the pathophysiology of neuropsychiatric disorders.

METHODS

Two different kinds of immunoscreening approaches were used to identify autoantigens associated with neuropsychiatric disorders in the serum of patients with schizophrenia. The presence of autoantibodies specific to the identified autoantigens was then tested in patients with various psychiatric disorders and in patients with systemic lupus erythematosus (SLE) and concomitant neuropsychiatric manifestations. Furthermore, the potential pathogenic role of these autoantibodies was assessed both in vitro and in vivo.

RESULTS

GAPDH was identified as a novel autoantigen associated with neuropsychiatric disorders. Serum anti-GAPDH IgG was detected in the serum of 51% of patients with schizophrenia and 50% of patients with major depression. Moreover, SLE patients with comorbid psychiatric manifestations presented significantly higher serum levels of anti-GAPDH antibodies than did SLE patients without psychiatric manifestations (P = 0.004 by chi-square test). Of note, a significant positive correlation (R = 0.48, P = 0.0049, by Spearman's rank correlation test) was found between the levels of serum anti-GAPDH antibodies and cognitive dysfunction in patients with SLE. In vitro analysis of the effects of purified human anti-GAPDH autoantibodies on SH-SY5Y cells showed an immediate neurite retraction. Finally, in vivo administration of anti-GAPDH autoantibodies in the right cerebral ventricle of C57BL/6J mice resulted in specific behavioral changes associated with a detrimental cognitive and emotional profile.

CONCLUSION

Overall, these data suggest that anti-GAPDH autoantibodies play a role in the pathogenesis of neuropsychiatric disorders, thus representing a potentially promising tool for the screening of individual vulnerability to these disabling conditions.

Disrupting GluA2-GAPDH Interaction Affects Axon and Dendrite Development

GluA2-containing AMPA receptors (AMPARs) play a critical role in various aspects of neurodevelopment. However, the molecular mechanisms underlying these processes are largely unknown. We report here that the interaction between GluA2 and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is necessary for neuron and cortical development. Using an interfering peptide (GluA2-G-Gpep) that specifically disrupts this interaction, we found that primary neuron cultures with peptide treatment displayed growth cone development deficits, impairment of axon formation, less dendritic arborization and lower spine protrusion density. Consistently, in vivo data with mouse brains from pregnant dams injected with GluA2-G-Gpep daily during embryonic day 8 to 19 revealed a reduction of cortical tract axon integrity and neuronal density in post-natal day 1 offspring. Disruption of GluA2-GAPDH interaction also impairs the GluA2-Plexin A4 interaction and reduces p53 acetylation in mice, both of which are possible mechanisms leading to the observed neurodevelopmental abnormalities. Furthermore, electrophysiological experiments indicate altered long-term potentiation (LTP) in hippocampal slices of offspring mice. Our results provide novel evidence that AMPARs, specifically the GluA2 subunit via its interaction with GAPDH, play a critical role in cortical neurodevelopment.

Quantitative proteomics analysis of zebrafish exposed to sub-lethal dosages of β-methyl-amino-L-alanine (BMAA)

The non-protein amino acid β-methylamino-L-alanine (BMAA) is a neurotoxin present in microalgae and shown to accumulate in the food web. BMAA has been linked to the complex neurodegenerative disorder of Guam and to increased incidents sporadic ALS. Two main neurotoxic routes are suggested; an excitotoxic by acting as an agonist towards glutamate receptors and a metabolic by misincorporating into cellular proteins. We have used zebrafish, an increasingly used model for neurodegenerative diseases, to further identify signaling components involved in BMAA-induced toxicity. Zebrafish embryos were exposed to sub-lethal dosages of BMAA and a label-free proteomics analysis was conducted on larvae 4 days post fertilization. The exposed larvae showed no developmental abnormalities, but a reduced heart rate and increased expression of GSK3 isoforms. Search towards a reviewed database containing 2968 entries identified 480 proteins. Only 17 of these were regulated 2-fold or more in the exposed larvae. Seven of these proteins could be associated to glutamate receptor signaling and recycling. The remaining nine have all been linked to disturbance in protein homeostasis, reactive oxygen species (ROS) development or neuronal cell death. We also found that BMAA influenced the endocannabinoid system by up-regulation of fatty acid amide hydrolase (FAAH) and that FAAH inhibitor URB597 reduced the BMAA effect on heart rate and GSK3 expression.

Enzyme Complexes Important for the Glutamate-Glutamine Cycle

Transient multienzyme and/or multiprotein complexes (metabolons) direct substrates toward specific pathways and can significantly influence the metabolism of glutamate and glutamine in the brain. Glutamate is the primary excitatory neurotransmitter in brain. This neurotransmitter has essential roles in normal brain function including learning and memory. Metabolism of glutamate involves the coordinated activity of astrocytes and neurons and high affinity transporter proteins that are selectively distributed on these cells. This chapter describes known and possible metabolons that affect the metabolism of glutamate and related compounds in the brain, as well as some factors that can modulate the association and dissociation of such complexes, including protein modifications by acylation reactions (e.g., acetylation, palmitoylation, succinylation, SUMOylation, etc.) of specific residues. Development of strategies to modulate transient multienzyme and/or enzyme-protein interactions may represent a novel and promising therapeutic approach for treatment of diseases involving dysregulation of glutamate metabolism.

Chemical genetics and its application to moonlighting in glycolytic enzymes

Glycolysis is an ancient biochemical pathway that breaks down glucose into pyruvate to produce ATP. The structural and catalytic properties of glycolytic enzymes are well-characterized. However, there is growing appreciation that these enzymes participate in numerous moonlighting functions that are unrelated to glycolysis. Recently, chemical genetics has been used to discover novel moonlighting functions in glycolytic enzymes. In the present mini-review, we introduce chemical genetics and discuss how it can be applied to the discovery of protein moonlighting. Specifically, we describe the application of chemical genetics to uncover moonlighting in two glycolytic enzymes, enolase and glyceraldehyde dehydrogenase. This led to the discovery of moonlighting roles in glucose homoeostasis, cancer progression and diabetes-related complications. Finally, we also provide a brief overview of the latest progress in unravelling the myriad moonlighting roles for these enzymes.

Blocking GluR2-GAPDH ameliorates experimental autoimmune encephalomyelitis

OBJECTIVE

Multiple sclerosis (MS) is the most common disabling neurological disease of young adults. The pathophysiological mechanism of MS remains largely unknown and no cure is available. Current clinical treatments for MS modulate the immune system, with the rationale that autoimmunity is at the core of MS pathophysiology.

METHODS

Experimental autoimmune encephalitis (EAE) was induced in mice with MOG35-55 and clinical scoring was performed to monitor signs of paralysis. EAE mice were injected intraperitoneally with TAT-fusion peptides daily from day 10 until day 30 after immunization, and their effects were measured at day 17 or day 30.

RESULTS

We report a novel target for the development of MS therapy, which aimed at blocking glutamate-mediated neurotoxicity through targeting the interaction between the AMPA (2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl) propanoic acid) receptor and an interacting protein. We found that protein complex composed of the GluR2 subunit of AMPA receptors and GAPDH (glyceraldehyde-3-phosphate dehydrogenase) was present at significantly higher levels in postmortem tissue from MS patients and in EAE mice, an animal model for MS. Next, we developed a peptide that specifically disrupts the GluR2 -GAPDH complex. This peptide greatly improves neurological function in EAE mice, reduces neuron death, rescues demyelination, increases oligodendrocyte survival, and reduces axonal damage in the spinal cords of EAE mice. More importantly, our peptide has no direct suppressive effect on naive T-cell responses or basal neurotransmission.

INTERPRETATION

The GluR2 -GAPDH complex represents a novel therapeutic target for the development of medications for MS that work through a different mechanism than existing treatments.

Involvement of GluR2 up-regulation in neuroprotection by electroacupuncture pretreatment via cannabinoid CB1 receptor in mice

We investigated whether glutamate receptor subunit 2 (GluR2) is involved in EA pretreatment-induced neuroprotection via cannabinoid CB1 receptors (CB1R) after global cerebral ischemia in mice. Two hours after electric acupuncture (EA) pretreatment, global cerebral ischemia (GCI) was induced by bilateral common carotid artery occlusion (BCCAO) for 20 min. The GluR2 expression was examined in the hippocampus after reperfusion. Cell survival, neuronal apoptosis, the Bax/Bcl-2 ratio and neurological scores were evaluated at 24 h after BCCAO in the presence or absence of the GluR2 inhibitor. Furthermore, the GluR2 was determined in the presence and absence of CB1R inhibitor. Our results showed EA pretreatment enhanced expression of GluR2 in the hippocampus 2 h after reperfusion. Moreover, EA pretreatment improved neurological outcome, promoted cell survival, inhibited neuronal apoptosis, and decreased the Bax/Bcl-2 ratio after reperfusion. GluR2 knockdown by GluR2 siRNA effectively reversed the beneficial effects of EA pretreatment. Furthermore, CB1R siRNA and two CB1R antagonists blocked the elevation of GluR2 expression by EA pretreatment, whereas the two CB1R agonists up-regulated GluR2 expression as EA pretreatment. In conclusion, GluR2 up-regulation is involved in neuroprotection of EA pretreatment against GCI through CB1R, suggesting that GluR2 may be a novel target for stroke intervention.

"Moonlighting" GAPDH Protein Localizes with AMPA Receptor GluA2 and L1 Axonal Cell Adhesion Molecule at Fiber Cell Borders in the Lens

PURPOSE

The canonical role of glyceraldehyde phosphate dehydrogenase (GAPDH) is as an enzyme in glycolysis. GAPDH is also a principal "moonlighting" protein with additional roles at diverse sites in a variety of cells. Surface GAPDH on mammalian, yeast, and bacterial cells acts as a receptor and also mediates cell contacts. In neurons, extracellular GAPDH localizes at synapses. Two GAPDH binding partners at synapses are α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptor (AMPA) GluA2 subunit at dendritic spines and L1 cell adhesion molecule at pre-synaptic membranes, and both proteins are also expressed in lenses. Fiber cell membrane protrusions and dendritic spines have similar size, shape, and spacing, contain F-actin, and express clathrin/AP-2 Adaptor at their surfaces linked with Tyr-phosphatase STEP-regulated endocytosis of AMPA/GluA2 receptors. AMPA receptors work with NMDA (N-methyl-d-aspartate) and GABA (γ-aminobutyric acid) receptors, calcium calmodulin kinase II (CaMKIIα), channel proteins, STEP, and ephrin receptors, which are also expressed in lenses. In neurons, coordinate AMPA/GluA2 receptor endocytosis with GAPDH is linked with disease. GAPDH was previously characterized as a fiber cell membrane protein and shown to decrease substantially in interior fiber cells in human age-related cataract. Here, we examined GAPDH spatial expression in healthy lenses in two vertebrate species.

METHODS

In situ methods were used to examine GAPDH expression in lenses of healthy young adult rabbits and chickens. Immunoblots were used to detect L1 in lenses.

RESULTS

The present study demonstrated that GAPDH is present at fiber cell borders in adult rabbit and chicken lenses with evidence of focal concentrations along the fiber cell perimeter, and overlapped with detection of p-Tyr-GluA2, L1, STEP, actin and clathrin. We observed that L1-140 kDa was the prominent form in lens.

CONCLUSIONS

Our findings indicate investigations into GAPDH "moonlighting" activities similar to its role in cell-cell interactions at neuron surfaces are warranted in the lens.

Ligand-gated ion channel interacting proteins and their role in neuroprotection

Ion channel receptors are a vital component of nervous system signaling, allowing rapid and direct conversion of a chemical neurotransmitter message to an electrical current. In recent decades, it has become apparent that ionotropic receptors are regulated by protein-protein interactions with other ion channels, G-protein coupled receptors and intracellular proteins. These other proteins can also be modulated by these interactions with ion channel receptors. This bidirectional functional cross-talk is important for critical cellular functions such as excitotoxicity in pathological and disease states like stroke, and for the basic dynamics of activity-dependent synaptic plasticity. Protein interactions with ion channel receptors can therefore increase the computational capacity of neuronal signaling cascades and also represent a novel target for therapeutic intervention in neuropsychiatric disease. This review will highlight some examples of ion channel receptor interactions and their potential clinical utility for neuroprotection.

Disruption of the nuclear p53-GAPDH complex protects against ischemia-induced neuronal damage

Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is conventionally considered a critical enzyme that involves in glycolysis for energy production. Recent previous studies have suggested that GAPDH is important in glutamate-induced neuronal excitotoxicity, while accumulated evidence also demonstrated that GAPDH nuclear translocation plays a critical role in cell death. However, the molecular mechanisms underlying this process remain largely unknown. In this study, we showed that GAPDH translocates to the nucleus in a Siah1-dependent manner upon glutamate stimulation. The nuclear GAPDH forms a protein complex with p53 and enhances p53 expression and phosphorylation. Disruption of the GAPDH-p53 interaction with an interfering peptide blocks glutamate-induced cell death and GAPDH-mediated up-regulation of p53 expression and phosphorylation. Furthermore, administration of the interfering peptide in vivo protects against ischemia-induced cell death in rats subjected to tMCAo. Our data suggest that the nuclear p53-GAPDH complex is important in regulating glutamate-mediated neuronal death and could serve as a potential therapeutic target for ischemic stroke treatment.

Ascorbate prevents cell death from prolonged exposure to glutamate in an in vitro model of human dopaminergic neurons

Ascorbate (vitamin C) is a nonenzymatic antioxidant highly concentrated in the brain. In addition to mediating redox balance, ascorbate is linked to glutamate neurotransmission in the striatum, where it renders neuroprotection against excessive glutamate stimulation. Oxidative stress and glutamatergic overactivity are key biochemical features accompanying the loss of dopaminergic neurons in the substantia nigra that characterizes Parkinson's disease (PD). At present, it is not clear whether antiglutamate agents and ascorbate might be neuroprotective agents for PD. Thus, we tested whether ascorbate can prevent cell death from prolonged exposure to glutamate using dopaminergic neurons of human origin. To this purpose, dopamine-like neurons were obtained by differentiation of SH-SY5Y cells and then cultured for 4 days without antioxidant (antiaging) protection to evaluate glutamate toxicity and ascorbate protection as a model system of potential factors contributing to dopaminergic neuron death in PD. Glutamate dose dependently induced toxicity in dopaminergic cells largely by the stimulation of AMPA and metabotropic receptors and to a lesser extent by N-methyl-D-aspartate and kainate receptors. At relatively physiological levels of extracellular concentration, ascorbate protected cells against glutamate excitotoxicity. This neuroprotection apparently relies on the inhibition of oxidative stress, because ascorbate prevented the pro-oxidant action of the scavenging molecule quercetin, which occurred over the course of prolonged exposure, as is also seen with glutamate. Our findings show the relevance of ascorbate as a neuroprotective agent and emphasize an often underappreciated role of oxidative stress in glutamate excitotoxicity. Occurrence of a glutamate-ascorbate link in dopaminergic neurons may explain previous contradictions regarding their putative role in PD.

Disruption of the GluR2/GAPDH complex protects against ischemia-induced neuronal damage

BACKGROUND

Excitotoxicity and neuronal death following ischemia involve AMPA (α-amino-3hydroxy-5-methylisoxazole-4-propionic acid) glutamate receptors. We have recently reported that the GluR2 subunit of AMPA receptors (AMPARs) forms a protein complex with GAPDH (glyceraldehyde-3-phosphate dehydrogenase). The GluR2/GAPDH complex co-internalizes upon activation of AMPA receptors. Disruption of the GluR2/GAPDH interaction with an interfering peptide protects cells against AMPAR-mediated excitotoxicity and protects against damage induced by oxygen-glucose deprivation (OGD), an in vitro model of brain ischemia.

OBJECTIVE

We sought to test the hypothesis that disruption of the GluR2/GAPDH interaction with an interfering peptide would protect against ischemia-induced neuronal damage in vivo.

METHOD

The rat 4-vessel occlusion (4-VO) model was used to investigate whether the GluR2/GAPDH interaction was enhanced in the hippocampus, and if our newly developed interfering peptide could protect against neuronal death in the ischemic brain area. The transient rat middle cerebral artery occlusion (tMCAo) model was used to determine whether our peptide could reduce infarction volume and improve neurological function. Finally, GAPDH lentiviral shRNA was injected into the brain to reduce GAPDH expression one week prior to tMCAo, to confirm the role of GAPDH in the pathophysiology of brain ischemia.

RESULTS

The GluR2/GAPDH interaction is upregulated in the hippocampus of rats subjected to transient global ischemia. Administration of an interfering peptide that is able to disrupt the GluR2/GAPDH interaction in vivo protects against ischemia-induced cell death in rat models of global ischemia and decreases the infarct volume as well as neurological score in a rat model focal ischemia. Consistent with these observations, decreased GAPDH expression also protects against ischemia-induced cell death in an animal model of focal ischemia.

CONCLUSION

Disruption of the GluR2/GAPDH interaction protects against ischemia-induced neuronal damage in vivo. The GluR2/GAPDH interaction may be a novel therapeutic target for development of treatment for ischemic stroke.