P38 MAPK is involved in enhanced NMDA receptor-dependent excitotoxicity in YAC transgenic mouse model of Huntington disease

High Magnesium Promotes the Recovery of Binocular Vision from Amblyopia via TRPM7

Abnormal visual experience during the critical period can cause deficits in visual function, such as amblyopia. High magnesium (Mg2+) supplementary can restore ocular dominance (OD) plasticity, which promotes the recovery of amblyopic eye acuity in adults. However, it remains unsolved whether Mg2+ could recover binocular vision in amblyopic adults and what the molecular mechanism is for the recovery. We found that in addition to the recovery of OD plasticity, binocular integration can be restored under the treatment of high Mg2+ in amblyopic mice. Behaviorally, Mg2+-treated amblyopic mice showed better depth perception. Moreover, the effect of high Mg2+ can be suppressed with transient receptor potential melastatin-like 7 (TRPM7) knockdown. Collectively, our results demonstrate that high Mg2+ could restore binocular visual functions from amblyopia. TRPM7 is required for the restoration of plasticity in the visual cortex after high Mg2+ treatment, which can provide possible clinical applications for future research and treatment of amblyopia.

Huntington's Disease: Complex Pathogenesis and Therapeutic Strategies

Huntington's disease (HD) arises from the abnormal expansion of CAG repeats in the huntingtin gene (HTT), resulting in the production of the mutant huntingtin protein (mHTT) with a polyglutamine stretch in its N-terminus. The pathogenic mechanisms underlying HD are complex and not yet fully elucidated. However, mHTT forms aggregates and accumulates abnormally in neuronal nuclei and processes, leading to disruptions in multiple cellular functions. Although there is currently no effective curative treatment for HD, significant progress has been made in developing various therapeutic strategies to treat HD. In addition to drugs targeting the neuronal toxicity of mHTT, gene therapy approaches that aim to reduce the expression of the mutant HTT gene hold great promise for effective HD therapy. This review provides an overview of current HD treatments, discusses different therapeutic strategies, and aims to facilitate future therapeutic advancements in the field.

Network Pharmacology and Experimental Verification to Unveil the Mechanism of N-Methyl-D-Aspartic Acid Rescue Humantenirine-Induced Excitotoxicity

Gelsemium is a medicinal plant that has been used to treat various diseases, but it is also well-known for its high toxicity. Complex alkaloids are considered the main poisonous components in Gelsemium. However, the toxic mechanism of Gelsemium remains ambiguous. In this work, network pharmacology and experimental verification were combined to systematically explore the specific mechanism of Gelsemium toxicity. The alkaloid compounds and candidate targets of Gelsemium, as well as related targets of excitotoxicity, were collected from public databases. The crucial targets were determined by constructing a protein-protein interaction (PPI) network. Subsequently, Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to explore the bioprocesses and signaling pathways involved in the excitotoxicity corresponding to alkaloids in Gelsemium. Then, the binding affinity between the main poisonous alkaloids and key targets was verified by molecular docking. Finally, animal experiments were conducted to further evaluate the potential mechanisms of Gelsemium toxicity. A total of 85 alkaloids in Gelsemium associated with 214 excitotoxicity-related targets were predicted by network pharmacology. Functional analysis showed that the toxicity of Gelsemium was mainly related to the protein phosphorylation reaction and plasma membrane function. There were also 164 pathways involved in the toxic mechanism, such as the calcium signaling pathway and MAPK signaling pathway. Molecular docking showed that alkaloids have high affinity with core targets, including MAPK3, SRC, MAPK1, NMDAR_2B and NMDAR_2A. In addition, the difference of binding affinity may be the basis of toxicity differences among different alkaloids. Humantenirine showed significant sex differences, and the LD₅₀ values of female and male mice were 0.071 mg·kg^-1 and 0.149 mg·kg^-1, respectively. Furthermore, we found that N-methyl-D-aspartic acid (NMDA), a specific NMDA receptor agonist, could significantly increase the survival rate of acute humantenirine-poisoned mice. The results also show that humantenirine could upregulate the phosphorylation level of MAPK3/1 and decrease ATP content and mitochondrial membrane potential in hippocampal tissue, while NMDA could rescue humantenirine-induced excitotoxicity by restoring the function of mitochondria. This study revealed the toxic components and potential toxic mechanism of Gelsemium. These findings provide a theoretical basis for further study of the toxic mechanism of Gelsemium and potential therapeutic strategies for Gelsemium poisoning.

Oncogenic Pathways in Neurodegenerative Diseases

Cancer and neurodegenerative diseases are two of the leading causes of premature death in modern societies. Their incidence continues to increase, and in the near future, it is believed that cancer will kill more than 20 million people per year, and neurodegenerative diseases, due to the aging of the world population, will double their prevalence. The onset and the progression of both diseases are defined by dysregulation of the same molecular signaling pathways. However, whereas in cancer, these alterations lead to cell survival and proliferation, neurodegenerative diseases trigger cell death and apoptosis. The study of the mechanisms underlying these opposite final responses to the same molecular trigger is key to providing a better understanding of the diseases and finding more accurate treatments. Here, we review the ten most common signaling pathways altered in cancer and analyze them in the context of different neurodegenerative diseases such as Alzheimer's (AD), Parkinson's (PD), and Huntington's (HD) diseases.

4-Trifluoromethyl-(E)-cinnamoyl]-L-4-F-phenylalanine acid exerts its effects on the prevention, post-therapeutic and prolongation of the thrombolytic window in ischemia-reperfusion rats through multiple mechanisms of action

Ischemic stroke is one of the leading causes of death and disability worldwide. The severe sequelae caused by ischemic thrombolysis and the narrow time window are now the main clinical challenges. Our previous study has reported 4-Trifluoromethyl-(E)-cinnamoyl]-L-4-F-phenylalanine Acid (AE-18) was a promising candidate for Parkinson's Disease. In this study, the preventive and therapeutic effects of AE-18 on focal cerebral ischemia-reperfusion injury and the mechanisms are explored. In oxygen glucose deprivation/reoxygenation (OGD/R)-induced well-differentiated PC12 cells model, AE-18 (10 or 20 μM) can significantly reduce nerve damage when administered before or after molding. In middle cerebral artery occlusion-reperfusion (MCAO/R) rat model, pre-modelling, or post-modelling administration of AE-18 (5 or 10 mg/kg) was effective in reducing neurological damage, decreasing infarct volume and improving motor disturbances. In addition, AE-18 (5 mg/kg) given by intravenous injection immediately after occlusion significantly reduce the infarct volume caused by reperfusion for different durations, indicating that AE-18 could extend the time window of thrombolytic therapy. Further studies demonstrate that AE-18 exerts the effects in the prevention, treatment, and prolongation of the time window of cerebral ischemic injury mainly through inhibiting excitotoxicity and improving BBB permeability, VEGF and BDNF. These results suggest that AE-18 is a good candidate for the treatment of ischemic stroke.

Molecular Mechanism of Tetramethylpyrazine Ameliorating Neuroexcitotoxicity through Activating the PKA/CREB Signaling Pathway

Background

Excitotoxicity plays a key role in nervous system disease and can trigger a critical cascade of reaction which affects cell viability and promotes neuronal death. Tetramethylpyrazine (TMP) reveals its effect in the treatment of neurovascular diseases by antiapoptosis. Recently, there were several studies that demonstrated that the PKA/CREB signaling pathway played a role in neural disease because of excitotoxicity, such as stroke, AD, and Parkinson's disease. In this study, we wanted to focus on the protective effect of tetramethylpyrazine against excitotoxicity through the PKA/CREB signaling pathway.

Methods

In order to verify whether tetramethylpyrazine can attenuate excitotoxicity through the PKA/CREB signaling pathway, we first used molecular docking technology to predict the combinational strength and mode of tetramethylpyrazine with the proteins in the PKA/CREB signaling pathway. Then, we determined the optimal concentration and time according to the model effect of glutamate (Glu) with different concentration gradients and action times in PC12 cells. After the determination of concentration and time of glutamate in the previous step as the model way, tetramethylpyrazine was added to determine its influence on the cell viability under different doses and times. The TUNEL assay and flow cytometry were used to detect apoptosis. RT-PCR was used to detect the expression of Bcl-2, Bax, PKA, and 5CREB genes, and Western blot was used to detect the expression of these factors.

Result

Tetramethylpyrazine had a good docking score (-5.312) with PKA and had a moderately docking score (-3.838) with CREB. The CCK-8 cell activity assay showed that the activity of PC12 cells decreased gradually with the increase in glutamate concentration and time, and PC12 cells were treated with 10 mM/L glutamate (the half of the inhibitory concentration (IC50)) for 12 hours. Then, the cell viability increased gradually following the increased concentration of tetramethylpyrazine. When PC12 cells were treated with 0.1 mM/L tetramethylpyrazine, the cell viability was increased significantly compared with the control group (P < 0.05). The TUNEL assay and flow cytometry also showed that tetramethylpyrazine could decrease the apoptosis induced by glutamate. In the result of RT-PCR, the transcriptional levels of Bcl-2, PKA, and CREB were increased and Bax was decreased. Meanwhile, Western blot showed that expression levels of Bcl-2, PKA, CREB, and p-CREB were increased and Bax was decreased.

Conclusions

This study provided evidence that tetramethylpyrazine can protect against apoptosis caused by neuroexcitotoxicity and the protective mechanism is closely related to the activation of the PKA/CREB signaling pathway.

Protective effects of apigenin on methylmercury-induced behavioral/neurochemical abnormalities and neurotoxicity in rats

Methylmercury (MeHg) is a neurotoxin that induces neurotoxicity and cell death in neurons. MeHg increases oligodendrocyte death, glial cell activation, and motor neuron demyelination in the motor cortex and spinal cord. As a result, MeHg plays an important role in developing neurocomplications similar to amyotrophic lateral sclerosis (ALS). Recent research has implicated c-JNK and p38MAPK overactivation in the pathogenesis of ALS. Apigenin (APG) is a flavonoid having anti-inflammatory, antioxidant, and c-JNK/p38MAPK inhibitory activities. The purpose of this study is to determine whether APG possesses neuroprotective effects in MeHg-induced neurotoxicity in adult rats associated with ALS-like neuropathological alterations. In the current study, the neurotoxin MeHg causes an ALS-like phenotype in Wistar rats after 21 days of oral administration at a dose of 5 mg/kg. Prolonged administration of APG (40 and 80 mg/kg) improved neurobehavioral parameters such as learning memory, cognition, motor coordination, and grip strength. This is mainly associated with the downregulation of c-JNK and p38MAPK signaling as well as the restoration of myelin basic protein within the brain. Furthermore, APG inhibited neuronal apoptotic markers (Bax, Bcl-2, and caspase-3), restored neurotransmitter imbalance, decreased inflammatory markers (TNF- and IL-1), and alleviated oxidative damage. As a result, the current study shows that APG has neuroprotective potential as a c-JNK and p38MAPK signaling inhibitor against MeHg-induced neurotoxicity in adult rats. Based on these promising findings, we suggested that APG could be a potential new therapeutic approach over other conventional therapeutic approaches for MeHg-induced neurotoxicity in neurobehavioral, molecular, and neurochemical abnormalities.

Phytoconstituents from ten natural herbs as potent inhibitors of main protease enzyme of SARS-COV-2: In silico study

BACKGROUND

Lack of treatment of novel Coronavirus disease led to the search of specific antivirals that are capable to inhibit the replication of the virus. The plant kingdom has demonstrated to be an important source of new molecules with antiviral potential.

PURPOSE

The present study aims to utilize various computational tools to identify the most eligible drug candidate that have capabilities to halt the replication of SARS-COV-2 virus by inhibiting Main protease (Mpro) enzyme.

METHODS

We have selected plants whose extracts have inhibitory potential against previously discovered coronaviruses. Their phytoconstituents were surveyed and a library of 100 molecules was prepared. Then, computational tools such as molecular docking, ADMET and molecular dynamic simulations were utilized to screen the compounds and evaluate them against Mpro enzyme.

RESULTS

All the phytoconstituents showed good binding affinities towards Mpro enzyme. Among them laurolitsine possesses the highest binding affinity i.e. -294.1533 kcal/mol. On ADMET analysis of best three ligands were simulated for 1.2 ns, then the stable ligand among them was further simulated for 20 ns. Results revealed that no conformational changes were observed in the laurolitsine w.r.t. protein residues and low RMSD value suggested that the Laurolitsine-protein complex was stable for 20 ns.

CONCLUSION

Laurolitsine, an active constituent of roots of Lindera aggregata, was found to be having good ADMET profile and have capabilities to halt the activity of the enzyme. Therefore, this makes laurolitsine a good drug candidate for the treatment of COVID-19.

Regulation of Phosphorylated State of NMDA Receptor by STEP61 Phosphatase after Mild-Traumatic Brain Injury: Role of Oxidative Stress

Traumatic Brain Injury (TBI) mediates neuronal death through several events involving many molecular pathways, including the glutamate-mediated excitotoxicity for excessive stimulation of N-methyl-D-aspartate receptors (NMDARs), producing activation of death signaling pathways. However, the contribution of NMDARs (distribution and signaling-associated to the distribution) remains incompletely understood. We propose a critical role of STEP₆₁ (Striatal-Enriched protein tyrosine phosphatase) in TBI; this phosphatase regulates the dephosphorylated state of the GluN2B subunit through two pathways: by direct dephosphorylation of tyrosine-1472 and indirectly via dephosphorylation and inactivation of Fyn kinase. We previously demonstrated oxidative stress’s contribution to NMDAR signaling and distribution using SOD2^+/− mice such a model. We performed TBI protocol using a controlled frontal impact device using C57BL/6 mice and SOD2^+/− animals. After TBI, we found alterations in cognitive performance, NMDAR-dependent synaptic function (decreased synaptic form of NMDARs and decreased synaptic current NMDAR-dependent), and increased STEP₆₁ activity. These changes are reduced partially with the STEP₆₁-inhibitor TC-2153 treatment in mice subjected to TBI protocol. This study contributes with evidence about the role of STEP₆₁ in the neuropathological progression after TBI and also the alteration in their activity, such as an early biomarker of synaptic damage in traumatic lesions.

When Good Kinases Go Rogue: GSK3, p38 MAPK and CDKs as Therapeutic Targets for Alzheimer's and Huntington's Disease

Alzheimer's disease (AD) is a mostly sporadic brain disorder characterized by cognitive decline resulting from selective neurodegeneration in the hippocampus and cerebral cortex whereas Huntington's disease (HD) is a monogenic inherited disorder characterized by motor abnormalities and psychiatric disturbances resulting from selective neurodegeneration in the striatum. Although there have been numerous clinical trials for these diseases, they have been unsuccessful. Research conducted over the past three decades by a large number of laboratories has demonstrated that abnormal actions of common kinases play a key role in the pathogenesis of both AD and HD as well as several other neurodegenerative diseases. Prominent among these kinases are glycogen synthase kinase (GSK3), p38 mitogen-activated protein kinase (MAPK) and some of the cyclin-dependent kinases (CDKs). After a brief summary of the molecular and cell biology of AD and HD this review covers what is known about the role of these three groups of kinases in the brain and in the pathogenesis of the two neurodegenerative disorders. The potential of targeting GSK3, p38 MAPK and CDKS as effective therapeutics is also discussed as is a brief discussion on the utilization of recently developed drugs that simultaneously target two or all three of these groups of kinases. Multi-kinase inhibitors either by themselves or in combination with strategies currently being used such as immunotherapy or secretase inhibitors for AD and knockdown for HD could represent a more effective therapeutic approach for these fatal neurodegenerative diseases.

A high-throughput screening to identify small molecules that suppress huntingtin promoter activity or activate huntingtin-antisense promoter activity

Huntington’s disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in exon 1 of huntingtin (HTT). While there are currently no disease-modifying treatments for HD, recent efforts have focused on the development of nucleotide-based therapeutics to lower HTT expression. As an alternative to siRNA or oligonucleotide methods, we hypothesized that suppression of HTT expression might be accomplished by small molecules that either (1) directly decrease HTT expression by suppressing HTT promoter activity or (2) indirectly decrease HTT expression by increasing the promoter activity of HTT-AS, the gene antisense to HTT that appears to inhibit expression of HTT. We developed and employed a high-throughput screen for modifiers of HTT and HTT-AS promoter activity using luminescent reporter HEK293 cells; of the 52,041 compounds tested, we identified 898 replicable hits. We used a rigorous stepwise approach to assess compound toxicity and the capacity of the compounds to specifically lower huntingtin protein in 5 different cell lines, including HEK293 cells, HD lymphoblastoid cells, mouse primary neurons, HD iPSCs differentiated into cortical-like neurons, and HD hESCs. We found no compounds which were able to lower huntingtin without lowering cell viability in all assays, though the potential efficacy of a few compounds at non-toxic doses could not be excluded. Our results suggest that more specific targets may facilitate a small molecule approach to HTT suppression.

Modulation of dopamine D1 receptors via histamine H3 receptors is a novel therapeutic target for Huntington's disease

Early Huntington's disease (HD) include over-activation of dopamine D₁ receptors (D₁R), producing an imbalance in dopaminergic neurotransmission and cell death. To reduce D₁R over-activation, we present a strategy based on targeting complexes of D₁R and histamine H₃ receptors (H₃R). Using an HD mouse striatal cell model and HD mouse organotypic brain slices we found that D₁R-induced cell death signaling and neuronal degeneration, are mitigated by an H₃R antagonist. We demonstrate that the D₁R-H₃R heteromer is expressed in HD mice at early but not late stages of HD, correlating with HD progression. In accordance, we found this target expressed in human control subjects and low-grade HD patients. Finally, treatment of HD mice with an H₃R antagonist prevented cognitive and motor learning deficits and the loss of heteromer expression. Taken together, our results indicate that D₁R - H₃R heteromers play a pivotal role in dopamine signaling and represent novel targets for treating HD.

DARK Classics in Chemical Neuroscience: Kava

Kava (kava kava, Piper methysticum) is a common drug-containing plant in the Pacific islands. Kavalactones, its psychoactive compounds, exert potent central nervous system (CNS) action clinically and in animal models. However, the exact pharmacological profiles and mechanisms of action of kava on the brain and behavior remain poorly understood. Here, we discuss clinical and experimental data on kava psychopharmacology and summarize chemistry and synthesis of kavalactones. We also review its societal impact, drug use and abuse potential, and future perspectives on translational kava research.

Modified Glutamatergic Postsynapse in Neurodegenerative Disorders

The postsynaptic density (PSD) is a complex subcellular domain important for postsynaptic signaling, function, and plasticity. The PSD is present at excitatory synapses and specialized to allow for precise neuron-to-neuron transmission of information. The PSD is localized immediately underneath the postsynaptic membrane forming a major protein network that regulates postsynaptic signaling and synaptic plasticity. Glutamatergic synaptic dysfunction affecting PSD morphology and signaling events have been described in many neurodegenerative disorders, either sporadic or familial forms. Thus, in this review we describe the main protein players forming the PSD and their activity, as well as relevant modifications in key components of the postsynaptic architecture occurring in Huntington's, Parkinson's and Alzheimer's diseases.

HttQ111/+ Huntington's Disease Knock-in Mice Exhibit Brain Region-Specific Morphological Changes and Synaptic Dysfunction

Background:

Successful disease-modifying therapy for Huntington’s disease (HD) will require therapeutic intervention early in the pathogenic process. Achieving this goal requires identifying phenotypes that are proximal to the HTT CAG repeat expansion.

Objective:

To use Htt CAG knock-in mice, precise genetic replicas of the HTT mutation in patients, as models to study proximal disease events.

Methods:

Using cohorts of B6J.Htt^Q111/+ mice from 2 to 18 months of age, we analyzed pathological markers, including immunohistochemistry, brain regional volumes and cortical thickness, CAG instability, electron microscopy of striatal synapses, and acute slice electrophysiology to record glutamatergic transmission at striatal synapses. We also incorporated a diet perturbation paradigm for some of these analyses.

Results:

B6J.Htt^Q111/+ mice did not exhibit significant neurodegeneration or gliosis but revealed decreased striatal DARPP-32 as well as subtle but regional-specific changes in brain volumes and cortical thickness that parallel those in HD patients. Ultrastructural analyses of the striatum showed reduced synapse density, increased postsynaptic density thickness and increased synaptic cleft width. Acute slice electrophysiology showed alterations in spontaneous AMPA receptor-mediated postsynaptic currents, evoked NMDA receptor-mediated excitatory postsynaptic currents, and elevated extrasynaptic NMDA currents. Diet influenced cortical thickness, but did not impact somatic CAG expansion, nor did it show any significant interaction with genotype on immunohistochemical, brain volume or cortical thickness measures.

Conclusions:

These data show that a single Htt^Q111 allele is sufficient to elicit brain region-specific morphological changes and early neuronal dysfunction, highlighting an insidious disease process already apparent in the first few months of life.

SAP97-mediated rescue of NMDA receptor surface distribution in a neuronal model of Huntington's disease

Huntington's disease (HD) is a genetic neurodegenerative disorder caused by an expansion of the CAG repeat tract in the HTT gene, leading to motor, cognitive, and psychiatric symptoms. At the cellular level, NMDA-type glutamate receptors are upregulated at glutamatergic extrasynaptic sites in HD, triggering cell death signaling pathways and driving HD neurodegeneration. Extrasynaptic and synaptic glutamate receptor trafficking and surface distribution are regulated by the α and β N-terminal isoforms of SAP97, a postsynaptic density protein localized at glutamatergic synapses. Here we examined the surface distribution of NMDARs and AMPARs in a cellular model of HD, and whether the manipulation of individual SAP97 isoforms can regulate receptor distribution in diseased neurons. Using dSTORM super-resolution imaging, we reveal that mutant HTT drives the elevation of extrasynaptic NMDAR clusters located 100-500 nm from the postsynaptic density. This was accompanied by a decline in synaptic NMDAR-mediated currents while surface NMDAR-mediated currents remained unchanged. These effects were induced within 3 days of mutant HTT expression in rat hippocampal neurons in vitro, and were specific for NMDARs and not observed with AMPARs. Intriguingly, upregulation of either α- or βSAP97 expression increased synaptic and/or perisynaptic NMDAR localization and prevented the shift of NMDARs to extrasynaptic sites in mutant HTT neurons. This was accompanied by the rescue of normal synaptic NMDAR-mediated currents. Taken together, our high-resolution data reveals plasticity in surface NMDAR localization driven by mutant HTT and identifies the similar but independent roles of SAP97 N-terminal isoforms in maintaining normal synaptic function in pathological states.

Decreased expression of lncRNA Malat1 in rat spinal cord contributes to neuropathic pain by increasing neuron excitability after brachial plexus avulsion

Purpose: Neuropathic pain (NP) is a challenging clinical problem due to its complex pathogenesis. In our previous study using microarray, we found that the levels of lncRNA Malat1 were decreased in the spinal cord of NP rat after brachial plexus avulsion, but its contribution to NP remain unclear. The purpose of this study was to investigate its role in the pathogenesis of NP.

Methods: In the NP model of complete brachial plexus avulsion rat, spinal cords were harvested, and fluorescence in situ hybridization (FISH) was used to test the spatial expression of Malat1 and qRT-PCR was used to confirm the quantitative expression of Malat1. In primary cultured neurons, Malat1 expression interfered with adenovirus. Spontaneous electric activities of neurons were tested using multi-electrode arrays and apoptosis of neurons was tested using TUNEL method. The change of intracellular calcium concentration was analyzed using calcium imaging method.

Results: Decreased Malat1 expression was confirmed using qRT-PCR, and Malat1 was identified in the cytoplasm of neurons in spinal cord, but not in glia. In vitro, the decrease of Malat1 resulted in an increase in the frequency of spontaneous electric activity in neurons but had no effect on neuronal apoptosis. Further analysis indicated during glutamate stimulation, the change of intracellular calcium concentration in neurons with downregulated Malat1 expression was significantly greater than that in normal neurons.

Conclusion: Reduced Malat1 expression may induce NP by increasing neuronal excitability in the spinal cord via regulation of calcium flux.

Altered Regulation of Striatal Neuronal N-Methyl-D-Aspartate Receptor Trafficking by Palmitoylation in Huntington Disease Mouse Model

N-methyl-D-aspartate receptors (NMDARs) play a critical role in synaptic signaling, and alterations in the synaptic/extrasynaptic NMDAR balance affect neuronal survival. Studies have shown enhanced extrasynaptic GluN2B-type NMDAR (2B-NMDAR) activity in striatal neurons in the YAC128 mouse model of Huntington disease (HD), resulting in increased cell death pathway activation contributing to striatal vulnerability to degeneration. However, the mechanism(s) of altered GluN2B trafficking remains unclear. Previous work shows that GluN2B palmitoylation on two C-terminal cysteine clusters regulates 2B-NMDAR trafficking to the surface membrane and synapses in cortical neurons. Notably, two palmitoyl acyltransferases (PATs), zDHHC17 and zDHHC13, also called huntingtin-interacting protein 14 (HIP14) and HIP14-like (HIP14L), directly interact with the huntingtin protein (Htt), and mutant Htt disrupts this interaction. Here, we investigated whether GluN2B palmitoylation is involved in enhanced extrasynaptic surface expression of 2B-NMDARs in YAC128 striatal neurons and whether this process is regulated by HIP14 or HIP14L. We found reduced GluN2B palmitoylation in YAC128 striatum, specifically on cysteine cluster II. Consistent with that finding, the palmitoylation-deficient GluN2B Cysteine cluster II mutant exhibited enhanced, extrasynaptic surface expression in striatal neurons from wild-type mice, mimicking increased extrasynaptic 2B-NMDAR observed in YAC128 cultures. We also found that HIP14L palmitoylated GluN2B cysteine cluster II. Moreover, GluN2B palmitoylation levels were reduced in striatal tissue from HIP14L-deficient mice, and siRNA-mediated HIP14L knockdown in cultured neurons enhanced striatal neuronal GluN2B surface expression and susceptibility to NMDA toxicity. Thus, altered regulation of GluN2B palmitoylation levels by the huntingtin-associated PAT HIP14L may contribute to the cell death-signaling pathways underlying HD.

Higher Levels of Protein Palmitoylation in the Frontal Cortex across Aging Were Associated with Reference Memory and Executive Function Declines

Cognitive decline with aging is often due to altered levels of protein expression. The NMDA receptor (NMDAR) and the complex of proteins surrounding the receptor are susceptible to age-related changes in expression. In the frontal cortex of aged mice, there is a significant loss of expression of the GluN2B subunit of the NMDAR, an increase in Fyn expression, and no change in PSD-95. Studies have also found that, in the frontal cortex, phosphorylation of GluN2B subunits and palmitoylation of GluN2 subunits and NMDAR complex proteins are affected by age. In this study, we examined some of the factors that may lead to the differences in the palmitoylation levels of NMDAR complex proteins in the frontal cortex of aged animals. The Morris water maze was used to test spatial learning in 3- and 24-month-old mice. The acyl–biotinyl exchange method was used to precipitate palmitoylated proteins from the frontal cortices and hippocampi of the mice. Additionally, brain lysates from old and young mice were probed for the expression of fatty acid transporter proteins. An age-related increase of palmitoylated GluN2A, GluN2B, Fyn, PSD-95, and APT1 (acyl protein thioesterase 1) in the frontal cortex was associated with poorer reference memory and/or executive functions. These data suggest that there may be a perturbation in the palmitoylation cycle in the frontal cortex of aged mice that contributes to age-related cognitive declines.

Humanin Attenuates NMDA-Induced Excitotoxicity by Inhibiting ROS-dependent JNK/p38 MAPK Pathway

Humanin (HN) is a novel 24-amino acid peptide that protects neurons against N-methyl-d-aspartate (NMDA)-induced toxicity. However, the contribution of the different mitogen-activated protein kinases (MAPKs) signals to HN neuroprotection against NMDA neurotoxicity remains unclear. The present study was therefore aimed to investigate neuroprotective mechanisms of HN. We analyzed intracellular Ca²⁺ levels, reactive oxygen species (ROS) production, and the MAPKs signal transduction cascade using an in vitro NMDA-mediated excitotoxicity of cortical neurons model. Results showed that: (1) HN attenuated NMDA-induced neuronal insults by increasing cell viability, decreasing lactate dehydrogenase (LDH) release, and increasing cell survival; (2) HN reversed NMDA-induced increase in intracellular calcium; (3) pretreatment by HN or 1,2-bis(2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid (BAPTA-AM), an intracellular calcium chelator, decreased ROS generation after NMDA exposure; (4) administration of HN or N-Acetyl-l-cysteine (NAC), a ROS scavenger, inhibited NMDA-induced JNK and p38 MAPK activation. These results indicated that HN reduced intracellular elevation of Ca²⁺ levels, which, in turn, inhibited ROS generation and subsequent JNK and p38 MAPK activation that are involved in promoting cell survival in NMDA-induced excitotoxicity. Therefore, the present study suggests that inhibition of ROS-dependent JNK/p38 MAPK signaling pathway serves an effective strategy for HN neuroprotection against certain neurological diseases.

Propofol produces preventive analgesia via GluN2B-containing NMDA Receptor/ERK1/2 Signaling Pathway in a rat model of inflammatory pain

Abstract

Propofol, an intravenous anesthetic, has been shown to offer superior analgesic effect clinically. Whether propofol has preventive analgesic property remains unexplored. The present study investigated the antinociceptive effect of propofol and underlying molecular and cellular mechanisms via pre-emptive administration in a formalin-induced inflammatory pain model in rats. Male adult Sprague–Dawley rats were randomly allocated into four groups: naïve (Group Naïve), formalin injection only (Group Formalin), and formalin injection at 30 min (Group P-30 min) or 2 h (Group P-2 h) after intravenous infusion of propofol (0.6 mg kg−1 min−1) for 1 h. Nociceptive responses and protein expression of phosphorylated- or pan-GluN2B, ERK1/2, p38 mitogen-activated protein kinase, and c-Jun N-terminal kinase in the spinal dorsal horn were evaluated. Alteration of intracellular Ca2+ concentration induced by N-methyl-D-aspartate (NMDA) receptor agonists with or without pre-treatment of propofol was measured using fluorometry in SH-SY5Y cells while neuronal activation in the spinal dorsal horn by immunofluorescence. Pre-emptive propofol reduced pain with a delayed response to formalin and a reduction in hypersensitivity that lasted at least for 2 h. The formalin-induced activation of spinal GluN2B and ERK1/2 but not p38 or c-Jun N-terminal kinase was also diminished by propofol treatment. Preconditioning treatment with 3 µM and 10 µM of propofol inhibited Ca2+ influx mediated through NMDA receptors in SH-SY5Y cells. Propofol also reduced the neuronal expression of c-Fos and p-ERK induced by formalin. This study shows that pre-emptive administration of propofol produces preventive analgesic effects on inflammatory pain through regulating neuronal GluN2B-containing NMDA receptor and ERK1/2 pathway in the spinal dorsal horn.

The differences between GluN2A and GluN2B signaling in the brain

The N-methyl-d-aspartate (NMDA) receptor, a typical ionotropic glutamate receptor, is a crucial protein for maintaining brain function. GluN2A and GluN2B are the main types of NMDA receptor subunit in the adult forebrain. Studies have demonstrated that they play different roles in a number of pathophysiological processes. Although the underlying mechanism for this has not been clarified, the most fundamental reason may be the differences between the signaling pathways associated with GluN2A and GluN2B. With the aim of elucidating the reasons behind the diverse roles of these two subunits, we described the signaling differences between GluN2A and GluN2B from the aspects of C-terminus-associated molecules, effects on typical downstream signaling proteins, and metabotropic signaling. Because there are several factors interfering with the determination of subunit-specific signaling, there is still a long way to go toward clarifying the signaling differences between these two subunits. Developing better pharmacology tools, such as highly selective antagonists for triheteromeric GluN2A- and GluN2B-containing NMDA receptors, and establishing new molecular biological methods, for example, engineering photoswitchable NMDA receptors, may be useful for clarifying the signaling differences between GluN2A and GluN2B.

Cognitive dysfunction in Huntington's disease: mechanisms and therapeutic strategies beyond BDNF

One of the main focuses in Huntington's disease (HD) research, as well as in most neurodegenerative diseases, is the development of new therapeutic strategies, as currently there is no treatment to delay or prevent the progression of the disease. Neuronal dysfunction and neuronal death in HD are caused by a combination of interrelated pathogenic processes that lead to motor, cognitive and psychiatric symptoms. Understanding how mutant huntingtin impacts on a plethora of cellular functions could help to identify new molecular targets. Although HD has been classically classified as a neurodegenerative disease affecting voluntary movement, lately cognitive dysfunction is receiving increased attention as it is very invalidating for patients. Thus, an ambitious goal in HD research is to find altered molecular mechanisms that contribute to cognitive decline. In this review, we have focused on those findings related to corticostriatal and hippocampal cognitive dysfunction in HD, as well as on the underlying molecular mechanisms, which constitute potential therapeutic targets. These include alterations in synaptic plasticity, transcriptional machinery and neurotrophic and neurotransmitter signaling.

Inflammation alters AMPA-stimulated calcium responses in dorsal striatal D2 but not D1 spiny projection neurons

Neuroinflammation precedes neuronal loss in striatal neurodegenerative diseases and can be exacerbated by the release of proinflammatory molecules by microglia. These molecules can affect trafficking of AMPARs. The preferential trafficking of calcium-permeable versus impermeable AMPARs can result in disruptions of [Ca2+ ]i and alter cellular functions. In striatal neurodegenerative diseases, changes in [Ca2+ ]i and L-type voltage-gated calcium channels (VGCCs) have been reported. Therefore, this study sought to determine whether a proinflammatory environment alters AMPA-stimulated [Ca2+ ]i through calcium-permeable AMPARs and/or L-type VGCCs in dopamine-2- and dopamine-1-expressing striatal spiny projection neurons (D2 and D1 SPNs) in the dorsal striatum. Mice expressing the calcium indicator protein, GCaMP in D2 or D1 SPNs, were utilized for calcium imaging. Microglial activation was assessed by morphology analyses. To induce inflammation, acute mouse striatal slices were incubated with lipopolysaccharide (LPS). Here we report that LPS treatment potentiated AMPA responses only in D2 SPNs. When a nonspecific VGCC blocker was included, we observed a decrease of AMPA-stimulated calcium fluorescence in D2 but not D1 SPNs. The remaining agonist-induced [Ca2+ ]i was mediated by calcium-permeable AMPARs because the responses were completely blocked by a selective calcium-permeable AMPAR antagonist. We used isradipine, the highly selective L-type VGCC antagonist to determine the role of L-type VGCCs in SPNs treated with LPS. Isradipine decreased AMPA-stimulated responses selectively in D2 SPNs after LPS treatment. Our findings suggest that dorsal striatal D2 SPNs are specifically targeted in proinflammatory conditions and that L-type VGCCs and calcium-permeable AMPARs are important mediators of this effect.

Hypoxia-ischemia modifies postsynaptic GluN2B-containing NMDA receptor complexes in the neonatal mouse brain

The N-methyl-d-aspartate-type glutamate receptor (NMDAR)-associated multiprotein complexes are indispensable for synaptic plasticity and cognitive functions. While purification and proteomic analyses of these signaling complexes have been performed in adult rodent and human brain, much less is known about the protein composition of NMDAR complexes in the developing brain and their modifications by neonatal hypoxic-ischemic (HI) brain injury. In this study, the postsynaptic density proteins were prepared from postnatal day 9 naïve, sham-operated and HI-injured mouse cortex. The GluN2B-containing NMDAR complexes were purified by immunoprecipitation with a mouse GluN2B antibody and subjected to mass spectrometry analysis for determination of the GluN2B binding partners. A total of 71 proteins of different functional categories were identified from the naïve animals as native GluN2B-interacting partners in the developing mouse brain. Neonatal HI reshaped the postsynaptic GluN2B interactome by recruiting new proteins, including multiple kinases, into the complexes; and modifying the existing associations within 1h of reperfusion. The early responses of postsynaptic NMDAR complexes and their related signaling networks may contribute to molecular processes leading to cell survival or death, brain damage and/or neurological disorders in term infants with neonatal encephalopathy.

Animal and model systems for studying cystic fibrosis

The cystic fibrosis (CF) field is the beneficiary of five species of animal models that lack functional cystic fibrosis transmembrane conductance regulator (CFTR) channel. These models are rapidly informing mechanisms of disease pathogenesis and CFTR function regardless of how faithfully a given organ reproduces the human CF phenotype. New approaches of genetic engineering with RNA-guided nucleases are rapidly expanding both the potential types of models available and the approaches to correct the CFTR defect. The application of new CRISPR/Cas9 genome editing techniques are similarly increasing capabilities for in vitro modeling of CFTR functions in cell lines and primary cells using air-liquid interface cultures and organoids. Gene editing of CFTR mutations in somatic stem cells and induced pluripotent stem cells is also transforming gene therapy approaches for CF. This short review evaluates several areas that are key to building animal and cell systems capable of modeling CF disease and testing potential treatments.

Pyk2 modulates hippocampal excitatory synapses and contributes to cognitive deficits in a Huntington's disease model

The structure and function of spines and excitatory synapses are under the dynamic control of multiple signalling networks. Although tyrosine phosphorylation is involved, its regulation and importance are not well understood. Here we study the role of Pyk2, a non-receptor calcium-dependent protein-tyrosine kinase highly expressed in the hippocampus. Hippocampal-related learning and CA1 long-term potentiation are severely impaired in Pyk2-deficient mice and are associated with alterations in NMDA receptors, PSD-95 and dendritic spines. In cultured hippocampal neurons, Pyk2 has autophosphorylation-dependent and -independent roles in determining PSD-95 enrichment and spines density. Pyk2 levels are decreased in the hippocampus of individuals with Huntington and in the R6/1 mouse model of the disease. Normalizing Pyk2 levels in the hippocampus of R6/1 mice rescues memory deficits, spines pathology and PSD-95 localization. Our results reveal a role for Pyk2 in spine structure and synaptic function, and suggest that its deficit contributes to Huntington's disease cognitive impairments.

A small molecule p75NTR ligand normalizes signalling and reduces Huntington's disease phenotypes in R6/2 and BACHD mice

Decreases in the ratio of neurotrophic versus neurodegenerative signalling play a critical role in Huntington’s disease (HD) pathogenesis and recent evidence suggests that the p75 neurotrophin receptor (NTR) contributes significantly to disease progression. p75NTR signalling intermediates substantially overlap with those promoting neuronal survival and synapse integrity and with those affected by the mutant huntingtin (muHtt) protein. MuHtt increases p75NTR-associated deleterious signalling and decreases survival signalling suggesting that p75NTR could be a valuable therapeutic target. This hypothesis was investigated by examining the effects of an orally bioavailable, small molecule p75NTR ligand, LM11A-31, on HD-related neuropathology in HD mouse models (R6/2, BACHD). LM11A-31 restored striatal AKT and other pro-survival signalling while inhibiting c-Jun kinase (JNK) and other degenerative signalling. Normalizing p75NTR signalling with LM11A-31 was accompanied by reduced Htt aggregates and striatal cholinergic interneuron degeneration as well as extended survival in R6/2 mice. The p75NTR ligand also decreased inflammation, increased striatal and hippocampal dendritic spine density, and improved motor performance and cognition in R6/2 and BACHD mice. These results support small molecule modulation of p75NTR as an effective HD therapeutic strategy. LM11A-31 has successfully completed Phase I safety and pharmacokinetic clinical trials and is therefore a viable candidate for clinical studies in HD.

Huntington's disease: Molecular basis of pathology and status of current therapeutic approaches

Huntington's disease (HD) is a frequent and incurable hereditary neurodegenerative disorder that impairs motor and cognitive functions. Mutations in huntingtin (HTT) protein, which is essential for neuronal development, lead to the development of HD. An increase in the number of CAG repeats within the HTT gene, which lead to an expansion of polyglutamine tract in the resulting mutated HTT protein, which is toxic, is the causative factor of HD. Although the molecular basis of HD is known, there is no known cure for this disease other than symptomatic relief treatment approaches. The toxicity of mutHTT appears to be more detrimental to striatal medium spiny neurons, which degenerate in this disease. Therapeutic strategies addressing a reduction in the mutHTT content at the transcriptional level using zinc finger proteins and at the translational level with RNA interference and antisense oligonucleotides or promoting the proteosomal degradation of mutHTT are being studied extensively in preclinical models and also to a limited extent in clinical trials. The post-translational modification of mutHTT is another possibility that is currently being investigated for drug development. In addition to the pharmacological approaches, several lines of evidence suggested the potential therapeutic use of stem cell therapy, in particular using the patient-derived induced pluripotent stem cells, to replace the lost striatal neurons. The multi-pronged clinical investigations currently underway may identify therapies and potentially improve the quality of life for the HD patients in future.

Striatal synaptic dysfunction and altered calcium regulation in Huntington disease

Synaptic dysfunction and altered calcium homeostasis in the brain is common to many neurodegenerative disorders. Among these, Huntington disease (HD), which is inherited in an autosomal dominant fashion, can serve as a model for investigating these mechanisms. HD generally manifests in middle age as a disorder of movement, mood and cognition. An expanded polymorphic CAG repeat in the HTT gene results in progressive neurodegeneration that impacts striatal spiny projection neurons (SPNs) earliest and most severely. Striatal SPNs receive massive glutamatergic input from cortex and thalamus, and these excitatory synapses are a focus for early changes that can trigger aberrant downstream signaling to disrupt synaptic plasticity and lead to later degeneration. Mitochondrial dysfunction and altered intracellular calcium-induced calcium release and sequestration mechanisms add to the impairments in circuit function that may underlie prodromal cognitive and subtle motor deficits. These mechanisms and implications for developing disease-modifying therapy will be reviewed here.

Aquaporin-4 deficiency facilitates fear memory extinction in the hippocampus through excessive activation of extrasynaptic GluN2B-containing NMDA receptors

Aquaporin-4 (AQP-4) is the predominant water channel in the brain and primarily expressed in astrocytes. Astrocytes have been generally believed to play important roles in regulating synaptic plasticity and information processing. A growing number of evidence shows that AQP-4 plays a potential role in the regulation of astrocyte function. However, little is known about the function of AQP-4 for synaptic plasticity in the hippocampus. Therefore, we evaluated long-term depression (LTD) in the hippocampus and the extinction of fear memory of AQP-4 knockout (KO) and wild-type (WT) mice. We found that AQP-4 deficiency facilitated fear memory extinction and NMDA receptors (NMDARs)-dependent LTD in the CA3-CA1 pathway. Furthermore, AQP-4 deficiency selectively increased GluN2B-NMDAR-mediated excitatory postsynaptic currents (EPSCs). The excessive activation of extrasynaptic GluN2B-NMDAR contributed to the facilitation of NMDAR-dependent LTD and enhancement of fear memory extinction in AQP-4 KO mice. Thus, it appears that AQP-4 may be a potential target for intervention in fear memory extinction. This article is part of the Special Issue entitled 'Ionotropic glutamate receptors'.

Preventive effects of imperatorin on perfluorohexanesulfonate-induced neuronal apoptosis via inhibition of intracellular calcium-mediated ERK pathway

Early life neuronal exposure to environmental toxicants has been suggested to be an important etiology of neurodegenerative disease development. Perfluorohexanesulfonate (PFHxS), one of the major perfluoroalkyl compounds, is widely distributed environmental contaminants. We have reported that PFHxS induces neuronal apoptosis via ERK-mediated pathway. Imperatorin is a furanocoumarin found in various edible plants and has a wide range of pharmacological effects including neuroprotection. In this study, the effects of imperatorin on PFHxS-induced neuronal apoptosis and the underlying mechanisms are examined using cerebellar granule cells (CGC). CGC were isolated from seven-day old rats and were grown in culture for seven days. Caspase-3 activity and TUNEL staining were used to determine neuronal apoptosis. PFHxS-induced apoptosis of CGC was significantly reduced by imperatorin and PD98059, an ERK pathway inhibitor. PFHxS induced a persistent increase in intracellular calcium, which was significantly blocked by imperatorin, NMDA receptor antagonist, MK801 and the L-type voltage-dependent calcium channel blockers, diltiazem and nifedipine. The activation of caspase-3 by PFHxS was also inhibited by MK801, diltiazem and nifedipine. PFHxS-increased ERK activation was inhibited by imperatorin, MK801, diltiazem and nifedipine. Taken together, imperatorin protects CGC against PFHxS-induced apoptosis via inhibition of NMDA receptor/intracellular calcium-mediated ERK pathway.

Higher levels of phosphorylated Y1472 on GluN2B subunits in the frontal cortex of aged mice are associated with good spatial reference memory, but not cognitive flexibility

The N-methyl-D-aspartate receptor (NMDAr) is particularly vulnerable to aging. The GluN2B subunit of the NMDAr, compared to other NMDAr subunits, suffers the greatest losses of expression in the aging brain, especially in the frontal cortex. While expression levels of GluN2B mRNA and protein in the aged brain are well documented, there has been little investigation into age-related posttranslational modifications of the subunit. In this study, we explored some of the mechanisms that may promote differences in the NMDAr complex in the frontal cortex of aged animals. Two ages of mice, 3 and 24 months, were behaviorally tested in the Morris water maze. The frontal cortex and hippocampus from each mouse were subjected to differential centrifugation followed by solubilization in Triton X-100. Proteins from Triton-insoluble membranes, Triton-soluble membranes, and intracellular membranes/cytosol were examined by Western blot. Higher levels of GluN2B tyrosine 1472 phosphorylation in frontal cortex synaptic fractions of old mice were associated with better reference learning but poorer cognitive flexibility. Levels of GluN2B phosphotyrosine 1336 remained steady, but there were greater levels of the calpain-induced 115 kDa GluN2B cleavage product on extrasynaptic membranes in these old good learners. There was an age-related increase in calpain activity, but it was not associated with better learning. These data highlight a unique aging change for aged mice with good spatial learning that might be detrimental to cognitive flexibility. This study also suggests that higher levels of truncated GluN2B on extrasynaptic membranes are not deleterious to spatial memory in aged mice.

Research progress in NOS1AP in neurological and psychiatric diseases

Nitric Oxide Synthase 1 Adaptor Protein (NOS1AP, previously named CAPON) was firstly identified in rat brain in 1998. Structurally, NOS1AP consists of a phosphotyrosine-binding (PTB) domain at its N-terminal and a PDZ (PSD-95/discs-large/ZO-1) ligand motif at its C-terminal. The PTB domain of NOS1AP mediates the interactions with Dexras1, scribble, and synapsins. The PDZ ligand motif of NOS1AP binds to the PDZ domain of NOS1, the enzyme responsible for nitric oxide synthesis in the nervous system. NOS1AP is implicated in Dexras1 activation, neuronal nitric oxide production, Hippo pathway signaling, and dendritic development through the association with these important partners. An increasing body of evidence is pointing to the significant roles of NOS1AP in excitotoxic neuronal damage, traumatic nervous system injury, bipolar disorder, and schizophrenia. However, the study progress in NOS1AP in neurological or psychiatric diseases, has not been systematically reviewed. Here we introduce the expression, structure, and isoforms of NOS1AP, then summarize the physiological roles of NOS1AP, and discuss the relationships between NOS1AP alterations and the pathophysiology of some neurological and psychiatric disorders. The review will promote the further investigation of NOS1AP in brain disorders and the development of drugs targeting the NOS1AP PTB domain or PDZ-binding motif in the future.

Compound MQA, a Caffeoylquinic Acid Derivative, Protects Against NMDA-Induced Neurotoxicity and Potential Mechanisms In Vitro

AIMS

Compound MQA (1,5-O-dicaffeoyl-3-O-[4-malic acid methyl ester]-quinic acid) is a natural derivative of caffeoylquinic acid isolated from Arctium lappa L. roots. However, we know little about the effects of MQA on the central nervous system. This study aims to investigate the neuroprotective effects and underlying mechanisms of MQA against the neurotoxicity of N-methyl-d-aspartate (NMDA).

METHODS AND RESULTS

Pretreatment with MQA attenuated the loss of cell viability after SH-SY5Y cells treated with 1 mM NMDA for 30 min by MTT assay. Hoechst 33342 and Annexin V-PI double staining showed that MQA inhibited NMDA-induced apoptosis. In addition to preventing Ca(2+) influx, the potential mechanisms are associated with increases in the Bcl-2/Bax ratio, attenuation of cytochrome c release, caspase-3, caspase-9 activities, and expressions. Also, MQA inhibited NMDA-induced phosphorylation of ERK1/2, p38, and JNK1/2. Furthermore, deactivation of CREB, AKT, and GSK-3β, upregulation of GluN2B-containing NMDA receptors (NMDARs), and downregulation of GluN2A-containing NMDARs were significantly reversed by MQA treatment. Computational docking simulation indicates that MQA possesses a well affinity for NMDARs.

CONCLUSION

The protective effects of MQA against NMDA-induced cell injury may be mediated by blocking NMDARs. The potential mechanisms are related with mitochondrial apoptosis, ERK-CREB, AKT/GSK-3β, p38, and JNK1/2 pathway.

Chronic Glutamate Toxicity in Neurodegenerative Diseases-What is the Evidence?

Together with aspartate, glutamate is the major excitatory neurotransmitter in the brain. Glutamate binds and activates both ligand-gated ion channels (ionotropic glutamate receptors) and a class of G-protein coupled receptors (metabotropic glutamate receptors). Although the intracellular glutamate concentration in the brain is in the millimolar range, the extracellular glutamate concentration is kept in the low micromolar range by the action of excitatory amino acid transporters that import glutamate and aspartate into astrocytes and neurons. Excess extracellular glutamate may lead to excitotoxicity in vitro and in vivo in acute insults like ischemic stroke via the overactivation of ionotropic glutamate receptors. In addition, chronic excitotoxicity has been hypothesized to play a role in numerous neurodegenerative diseases including amyotrophic lateral sclerosis, Alzheimer's disease and Huntington's disease. Based on this hypothesis, a good deal of effort has been devoted to develop and test drugs that either inhibit glutamate receptors or decrease extracellular glutamate. In this review, we provide an overview of the different pathways that are thought to lead to an over-activation of the glutamatergic system and glutamate toxicity in neurodegeneration. In addition, we summarize the available experimental evidence for glutamate toxicity in animal models of neurodegenerative diseases.

Unexpected Heterodivalent Recruitment of NOS1AP to nNOS Reveals Multiple Sites for Pharmacological Intervention in Neuronal Disease Models

The protein NOS1AP/CAPON mediates signaling from a protein complex of NMDA receptor, PSD95 and nNOS. The only stroke trial for neuroprotectants that showed benefit to patients targeted this ternary complex. NOS1AP/nNOS interaction regulates small GTPases, iron transport, p38MAPK-linked excitotoxicity, and anxiety. Moreover, the nos1ap gene is linked to disorders from schizophrenia, post-traumatic stress disorder, and autism to cardiovascular disorders and breast cancer. Understanding protein interactions required for NOS1AP function, therefore, has broad implications for numerous diseases. Here we show that the interaction of NOS1AP with nNOS differs radically from the classical PDZ docking assumed to be responsible. The NOS1AP PDZ motif does not bind nNOS as measured by multiple methods. In contrast, full-length NOS1AP forms an unusually stable interaction with nNOS. We mapped the discrepancy between full-length and C-terminal PDZ motif to a novel internal region we call the ExF motif. The C-terminal PDZ motif, although neither sufficient nor necessary for binding, nevertheless promotes the stability of the complex. It therefore potentially affects signal transduction and suggests that functional interaction of nNOS with NOS1AP might be targetable at two distinct sites. We demonstrate that excitotoxic pathways can be regulated, in cortical neuron and organotypic hippocampal slice cultures from rat, either by the previously described PDZ ligand TAT-GESV or by the ExF motif-bearing region of NOS1AP, even when lacking the critical PDZ residues as long as the ExF motif is intact and not mutated. This previously unrecognized heterodivalent interaction of nNOS with NOS1AP may therefore provide distinct opportunities for pharmacological intervention in NOS1AP-dependent signaling and excitotoxicity.

A novel phosphorylation site of N-methyl-D-aspartate receptor GluN2B at S1284 is regulated by Cdk5 in neuronal ischemia

N-methyl-D-aspartate receptors (NMDARs) are a key player in synaptic and several neurological diseases, such as stroke. Phosphorylation of NMDAR subunits at their cytoplasmic carboxyl termini has been considered to be an important mechanism to regulate the receptor function. Cyclin-dependent kinase 5 (Cdk5) has been demonstrated to be responsible for regulating phosphorylation and function of NMDARs. Besides, it is also suggested that Cdk5 is involved in ischemic insult. In the present study, we showed that GluN2B subunit serine 1284 at its cytoplasmic carboxyl termini was regulated by Cdk5 in neuronal ischemia. Interestingly, both oxygen glucose deprivation (OGD) in cultured hippocampal neurons and transient global ischemia in mice induce dramatic changes in the phosphorylated level of GluN2B at S1284. However, no significant changes in the phosphorylation of this site are found neither in chemical LTP stimulation in cultured hippocampal neurons nor fear conditioning in adult mice. Taken together, our study identified NMDAR GluN2B S1284 as a novel phosphorylation site regulated by Cdk5 with implication in neuronal ischemia.

HD iPSC-derived neural progenitors accumulate in culture and are susceptible to BDNF withdrawal due to glutamate toxicity

Huntington's disease (HD) is a fatal neurodegenerative disease, caused by expansion of polyglutamine repeats in the Huntingtin gene, with longer expansions leading to earlier ages of onset. The HD iPSC Consortium has recently reported a new in vitro model of HD based on the generation of induced pluripotent stem cells (iPSCs) from HD patients and controls. The current study has furthered the disease in a dish model of HD by generating new non-integrating HD and control iPSC lines. Both HD and control iPSC lines can be efficiently differentiated into neurons/glia; however, the HD-derived cells maintained a significantly greater number of nestin-expressing neural progenitor cells compared with control cells. This cell population showed enhanced vulnerability to brain-derived neurotrophic factor (BDNF) withdrawal in the juvenile-onset HD (JHD) lines, which appeared to be CAG repeat-dependent and mediated by the loss of signaling from the TrkB receptor. It was postulated that this increased death following BDNF withdrawal may be due to glutamate toxicity, as the N-methyl-d-aspartate (NMDA) receptor subunit NR2B was up-regulated in the cultures. Indeed, blocking glutamate signaling, not just through the NMDA but also mGlu and AMPA/Kainate receptors, completely reversed the cell death phenotype. This study suggests that the pathogenesis of JHD may involve in part a population of 'persistent' neural progenitors that are selectively vulnerable to BDNF withdrawal. Similar results were seen in adult hippocampal-derived neural progenitors isolated from the BACHD model mouse. Together, these results provide important insight into HD mechanisms at early developmental time points, which may suggest novel approaches to HD therapeutics.

A novel manganese-dependent ATM-p53 signaling pathway is selectively impaired in patient-based neuroprogenitor and murine striatal models of Huntington's disease

The essential micronutrient manganese is enriched in brain, especially in the basal ganglia. We sought to identify neuronal signaling pathways responsive to neurologically relevant manganese levels, as previous data suggested that alterations in striatal manganese handling occur in Huntington's disease (HD) models. We found that p53 phosphorylation at serine 15 is the most responsive cell signaling event to manganese exposure (of 18 tested) in human neuroprogenitors and a mouse striatal cell line. Manganese-dependent activation of p53 was severely diminished in HD cells. Inhibitors of ataxia telangiectasia mutated (ATM) kinase decreased manganese-dependent phosphorylation of p53. Likewise, analysis of ATM autophosphorylation and additional ATM kinase targets, H2AX and CHK2, support a role for ATM in the activation of p53 by manganese and that a defect in this process occurs in HD. Furthermore, the deficit in Mn-dependent activation of ATM kinase in HD neuroprogenitors was highly selective, as DNA damage and oxidative injury, canonical activators of ATM, did not show similar deficits. We assessed cellular manganese handling to test for correlations with the ATM-p53 pathway, and we observed reduced Mn accumulation in HD human neuroprogenitors and HD mouse striatal cells at manganese exposures associated with altered p53 activation. To determine if this phenotype contributes to the deficit in manganese-dependent ATM activation, we used pharmacological manipulation to equalize manganese levels between HD and control mouse striatal cells and rescued the ATM-p53 signaling deficit. Collectively, our data demonstrate selective alterations in manganese biology in cellular models of HD manifest in ATM-p53 signaling.

Targets for future clinical trials in Huntington's disease: what's in the pipeline?

The known genetic cause of Huntington's disease (HD) has fueled considerable progress in understanding its pathobiology and the development of therapeutic approaches aimed at correcting specific changes linked to the causative mutation. Among the most promising is reducing expression of mutant huntingtin protein (mHTT) with RNA interference or antisense oligonucleotides; human trials are now being planned. Zinc-finger transcriptional repression is another innovative method to reduce mHTT expression. Modulation of mHTT phosphorylation, chaperone upregulation, and autophagy enhancement represent attempts to alter cellular homeostasis to favor removal of mHTT. Inhibition of histone deacetylases (HDACs) remains of interest; recent work affirms HDAC4 as a target but questions the assumed centrality of its catalytic activity in HD. Phosphodiesterase inhibition, aimed at restoring synaptic function, has progressed rapidly to human trials. Deranged cellular signaling provides several tractable targets, but specificity and complexity are challenges. Restoring neurotrophic support in HD remains a key potential therapeutic approach. with several approaches being pursued, including brain-derived neurotrophic factor (BDNF) mimesis through tyrosine receptor kinase B (TrkB) agonism and monoclonal antibodies. An increasing understanding of the role of glial cells in HD has led to several new therapeutic avenues, including kynurenine monooxygenase inhibition, immunomodulation by laquinimod, CB2 agonism, and others. The complex metabolic derangements in HD remain under study, but no clear therapeutic strategy has yet emerged. We conclude that many exciting therapeutics are progressing through the development pipeline, and combining a better understanding of HD biology in human patients, with concerted medicinal chemistry efforts, will be crucial for bringing about an era of effective therapies.

NMDA receptor-mediated ERK 1/2 pathway is involved in PFHxS-induced apoptosis of PC12 cells

Perfluorohexanesulfonate (PFHxS) is one of the major perfluoroalkyl compounds (PFCs) found in human blood and its possible neurotoxicity has been suggested. However, the neuronal responses to PFHxS are not much known. Many studies have demonstrated that the early exposure to environmental chemicals increases the risk of neurodegenerative diseases such as Parkinson's disease in later life. In this study, the effects of PFHxS on the neuronal cell death and the underlying mechanisms were examined using PC12 cells as a model of dopaminergic neuron. The treatment with PFHxS reduced cell viability in a dose-dependent manner. PFHxS increased cell apoptosis which was measured by caspase-3 activity and TUNEL staining. MK801, a NMDA receptor antagonist reduced PFHxS-induced apoptosis. PFHxS increased the activations of ERK1/2, JNK and p38 MAPK with different temporal activations. The treatment with PD98059, an ERK inhibitor, significantly reduced apoptosis, whereas SB203580, a p38 MAPK inhibitor, had no effect. JNK inhibition by SP600125 significantly increased apoptosis. PFHxS exposure also increased ROS formation, which was completely blocked by antioxidants, Trolox or N-acetylcysteine (NAC). However, neither Trolox nor NAC reduced PFHxS-increased apoptosis, suggesting that ROS may not be a critical mediator for PFHxS-induced apoptosis of cells. Moreover, ERK activation induced by PFHxS was blocked by MK801 but not antioxidants. Taken together, these results have demonstrated that PFHxS induces the apoptosis of dopaminergic neuronal cells, where NMDA receptor-mediated ERK pathway plays a pro-apoptotic role and JNK plays an anti-apoptotic role. Our results may contribute to understanding cellular mechanisms for PFHxS-induced neurotoxicity.

Expression, pharmacology and functional activity of adenosine A1 receptors in genetic models of Huntington's disease

Adenosine A1 receptor (A1R) stimulation exerts beneficial effects in response to various insults to the brain and, although it was found neuroprotective in a lesional model of Huntington's disease (HD), the features of this receptor in genetic models of HD have never been explored. In the present study we characterized the expression, affinity and functional effects of A1Rs in R6/2 mice (the most widely used transgenic model of HD) and in a cellular model of HD. Binding studies revealed that the density of A1Rs was significantly reduced in the cortex and the striatum of R6/2 mice compared to age-matched wild-type (WT), while receptor affinity was unchanged. The selective A1R agonist cyclopentyladenosine (CPA, 300nM) was significantly more effective in reducing synaptic transmission in corticostriatal slices from symptomatic R6/2 than in age-matched WT mice. Such an effect was due to a stronger inhibition of glutamate release from the pre-synaptic terminal. The different functional activities of A1Rs in HD mice were associated also to a different intracellular signaling pathway involved in the synaptic effect of CPA. In fact, while the PKA pathway was involved in both genotypes, p38 MAPK inhibitor SB203580 partially prevented synaptic effects of CPA in R6/2, but not in WT, mice; moreover, CPA differently modulated the phosphorylation status of p38 in the two genotypes. In vitro studies confirmed a different behavior of A1Rs in HD: CPA (100 nM for 5h) modulated cell viability in STHdh(Q111/Q111) (mhttHD cells), without affecting the viability of STHdh(Q7/Q7) (wthtt cells). This effect was prevented by the application of SB203580. Our results demonstrate that in the presence of the HD mutation A1Rs undergo profound changes in terms of expression, pharmacology and functional activity. These changes have to be taken in due account when considering A1Rs as a potential therapeutic target for this disease.

Ethyl pyruvate ameliorates 3-nitropropionic acid-induced striatal toxicity through anti-neuronal cell death and anti-inflammatory mechanisms

The potential neuroprotective value of ethyl pyruvate (EP) for the treatment of the striatal toxicity is largely unknown. We investigated whether EP promotes the survival of striatal neurons in a 3-nitropropionic acid (3-NP)-induced mouse model of Huntington's disease (HD). EP (5, 10, 20, and 40mg/kg/day, i.p.) was daily injected from 30min before 3-NP intoxication (pretreatment) and from onset/progression/peak point of neurological impairment by 3-NP intoxication. EP produced a neuroprotective effect in dose- and time-dependant manners. EP pretreatment of 40mg/kg/day produced the best neuroprotective effect among other conditions. Pretreatment of EP significantly attenuated neurological impairment and lethality and prevented formation of lesion area and neuronal loss in the striatum after 3-NP intoxication. This neuroprotection afforded by EP was associated with the suppression of succinate dehydrogenase activity, apoptosis, and microglial activation. The suppressive effect of EP corresponded to the down-regulation of mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-κB) signal pathways, and mRNA expression of inflammatory mediators including tumor necrosis factor-alpha, interleukin (IL)-1β, IL-6, inducible nitric oxide synthase, and cyclooxygenase-2 in the striatum after 3-NP intoxication. Interestingly, the intrathecal introduction of inhibitors MAPKs and NF-κB into control mice decreased the lethality after 3-NP intoxication. Our findings indicate that EP may effectively alleviate 3-NP-induced striatal toxicity by inhibition of the MAPKs and NF-κB pathways in the striatum, and that EP has a wide therapeutic window, suggesting that EP may have therapeutic value in the treatment of aspects of HD's disease related to inflammation.