Endogenous SNAP-25 regulates native voltage-gated calcium channels in glutamatergic neurons

Genetic Risk Loci and Familial Associations in Migraine: A Genome-Wide Association Study in the Han Chinese Population of Taiwan

BACKGROUND AND PURPOSE

Migraine is a condition that is often observed to run in families, but its complex genetic background remains unclear. This study aimed to identify the genetic factors influencing migraines and their potential association with the family medical history.

METHODS

We performed a comprehensive genome-wide association study of a cohort of 1,561 outpatients with migraine and 473 individuals without migraine in Taiwan, including Han Chinese individuals with or without a family history of migraine. By analyzing the detailed headache history of the patients and their relatives we aimed to isolate potential genetic markers associated with migraine while considering factors such as sex, episodic vs. chronic migraine, and the presence of aura.

RESULTS

We revealed novel genetic risk loci, including rs2287637 in DEAD-Box helicase 1 and long intergenic non-protein coding RNA 1804 and rs12055943 in engulfment and cell motility 1, that were correlated with the family history of migraine. We also found a genetic location downstream of mesoderm posterior BHLH transcription factor 2 associated with episodic migraine, whereas loci within the ubiquitin-specific peptidase 26 exonic region, dual specificity phosphatase 9 and pregnancy-upregulated non-ubiquitous CaM kinase intergenic regions, and poly (ADP-ribose) polymerase 1 and STUM were linked to chronic migraine. We additionally identified genetic regionsassociated with the presence or absence of aura. A locus between LINC02561 and urocortin 3 was predominantly observed in female patients. Moreover, three different single-nucleotide polymorphisms were associated with the family history of migraine in the control group.

CONCLUSIONS

This study has identified new genetic locations associated with migraine and its family history in a Han Chinese population, reinforcing the genetic background of migraine. The findings point to potential candidate genes that should be investigated further.

Minocycline Inhibits Tick-Borne Encephalitis Virus and Protects Infected Cells via Multiple Pathways

Tick-borne Encephalitis (TBE) is a zoonotic disease caused by the Tick-borne Encephalitis virus (TBEV), which affects the central nervous system of both humans and animals. Currently, there is no specific therapy for patients with TBE, with symptomatic treatment being the primary approach. In this study, the effects of minocycline (MIN), which is a kind of tetracycline antibiotic, on TBEV propagation and cellular protection in TBEV-infected cell lines were evaluated. Indirect immunofluorescence, virus titers, and RT-qPCR results showed that 48 h post-treatment with MIN, TBEV replication was significantly inhibited in a dose-dependent manner. In addition, the inhibitory effect of MIN on different TBEV multiplicities of infection (MOIs) in Vero cells was studied. Furthermore, the transcriptomic analysis and RT-qPCR results indicate that after incubation with MIN, the levels of TBEV and CALML4 were decreased, whereas the levels of calcium channel receptors, such as RYR2 and SNAP25, were significantly increased. MIN also regulated MAPK-ERK-related factors, including FGF2, PDGFRA, PLCB2, and p-ERK, and inhibited inflammatory responses. These data indicate that administering MIN to TBEV-infected cells can reduce the TBEV level, regulate calcium signaling pathway-associated proteins, and inhibit the MAPK-ERK signaling pathway and inflammatory responses. This research offers innovative strategies for the advancement of anti-TBEV therapy.

An updated review on animal models to study attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is a neuropsychiatric disorder affecting both children and adolescents. Individuals with ADHD experience heterogeneous problems, such as difficulty in attention, behavioral hyperactivity, and impulsivity. Recent studies have shown that complex genetic factors play a role in attention-deficit hyperactivity disorders. Animal models with clear hereditary traits are crucial for studying the molecular, biological, and brain circuit mechanisms underlying ADHD. Owing to their well-managed genetic origins and the relative simplicity with which the function of neuronal circuits is clearly established, models of mice can help learn the mechanisms involved in ADHD. Therefore, in this review, we highlighting the important genetic animal models that can be used to study ADHD.

The Relationship between SNAP25 and Some Common Human Neurological Syndromes

Over the years, research on the pathogenesis of neurological diseases has progressed slowly worldwide. However, as the incidence rate continues to increase and the disease gradually develops, early diagnosis and treatment have become a top priority. SANP25, a protein present on the presynaptic membrane and involved in neurotransmitter release, is closely related to the loss or abnormal expression of synapses and neurons. SNAP25 deficiency can lead to synaptic disorders and inhibit neurotransmitter release. Therefore, a large amount of literature believes that SNAP25 gene mutation is a risk factor for many neurological diseases. This review used advanced search on PubMed to conduct extensive article searches for relevant literature. The search keywords included SNAP25 and Alzheimer's disease, SNAP25 and Parkinson's disease, and so on. After reading and summarizing the previous papers, the corresponding conclusions were obtained to achieve the purpose of the review. The deficiency or variation of SNAP25 might be related to the onset of schizophrenia, epilepsy, attention deficit/hypoactivity disorder, bipolar disorder effective disorder, and autism. SNAP25 has been found to be used as a neuropathological marker for neurological diseases, which could be the target of diagnosis or treatment of Alzheimer's disease and Parkinson's disease. Cerebrospinal Fluid (CSF) or blood has been found to enable more effective drug development.

Reduction in hippocampal GABAergic transmission in a low birth weight rat model of depression

Prenatal stress is believed to increase the risk of developing neuropsychiatric disorders, including major depression. Adverse genetic and environmental impacts during early development, such as glucocorticoid hyper-exposure, can lead to changes in the foetal brain, linked to mental illnesses developed in later life. Dysfunction in the GABAergic inhibitory system is associated with depressive disorders. However, the pathophysiology of GABAergic signalling is poorly understood in mood disorders. Here, we investigated GABAergic neurotransmission in the low birth weight (LBW) rat model of depression. Pregnant rats, exposed to dexamethasone, a synthetic glucocorticoid, during the last week of gestation, yielded LBW offspring showing anxiety- and depressive-like behaviour in adulthood. Patch-clamp recordings from dentate gyrus granule cells in brain slices were used to examine phasic and tonic GABAA receptor-mediated currents. The transcriptional levels of selected genes associated with synaptic vesicle proteins and GABAergic neurotransmission were investigated. The frequency of spontaneous inhibitory postsynaptic currents (sIPSC) was similar in control and LBW rats. Using a paired-pulse protocol to stimulate GABAergic fibres impinging onto granule cells, we found indications of decreased probability of GABA release in LBW rats. However, tonic GABAergic currents and miniature IPSCs, reflecting quantal vesicle release, appeared normal. Additionally, we found elevated expression levels of two presynaptic proteins, Snap-25 and Scamp2, components of the vesicle release machinery. The results suggest that altered GABA release may be an essential feature in the depressive-like phenotype of LBW rats.

Neuromuscular recovery from botulism involves multiple forms of compensatory plasticity

Introduction

Botulinum neurotoxin (BoNT) causes neuroparalytic disease and death by blocking neuromuscular transmission. There are no specific therapies for clinical botulism and the only treatment option is supportive care until neuromuscular function spontaneously recovers, which can take weeks or months after exposure. The highly specialized neuromuscular junction (NMJ) between phrenic motor neurons and diaphragm muscle fibers is the main clinical target of BoNT. Due to the difficulty in eliciting respiratory paralysis without a high mortality rate, few studies have characterized the neurophysiological mechanisms involved in diaphragm recovery from intoxication. Here, we develop a mouse model of botulism that involves partial paralysis of respiratory muscles with low mortality rates, allowing for longitudinal analysis of recovery.

Methods and results

Mice challenged by systemic administration of 0.7 LD50 BoNT/A developed physiological signs of botulism, such as respiratory depression and reduced voluntary running activity, that persisted for an average of 8-12 d. Studies in isolated hemidiaphragm preparations from intoxicated mice revealed profound reductions in nerve-elicited, tetanic and twitch muscle contraction strengths that recovered to baseline 21 d after intoxication. Despite apparent functional recovery, neurophysiological parameters remained depressed for 28 d, including end plate potential (EPP) amplitude, EPP success rate, quantal content (QC), and miniature EPP (mEPP) frequency. However, QC recovered more quickly than mEPP frequency, which could explain the discrepancy between muscle function studies and neurophysiological recordings. Hypothesizing that differential modulation of voltage-gated calcium channels (VGCC) contributed to the uncoupling of QC from mEPP frequency, pharmacological inhibition studies were used to study the contributions of different VGCCs to neurophysiological function. We found that N-type VGCC and P/Q-type VGCC partially restored QC but not mEPP frequency during recovery from paralysis, potentially explaining the accelerated recovery of evoked release versus spontaneous release. We identified additional changes that presumably compensate for reduced acetylcholine release during recovery, including increased depolarization of muscle fiber resting membrane potential and increased quantal size.

Discussion

In addition to identifying multiple forms of compensatory plasticity that occur in response to reduced NMJ function, it is expected that insights into the molecular mechanisms involved in recovery from neuromuscular paralysis will support new host-targeted treatments for multiple neuromuscular diseases.

Extracellular transglutaminase-2, nude or associated with astrocytic extracellular vesicles, modulates neuronal calcium homeostasis

We have uncovered a novel role for astrocytes-derived extracellular vesicles (EVs) in controlling intraneuronal Ca²⁺ concentration ([Ca²⁺]_i) and identified transglutaminase-2 (TG2) as a surface-cargo of astrocytes-derived EVs. Incubation of hippocampal neurons with primed astrocyte-derived EVs have led to an increase in [Ca²⁺]_i, unlike EVs from TG2-knockout astrocytes. Exposure of neurons or brain slices to extracellular TG2 promoted a [Ca²⁺]_i rise, which was reversible upon TG2 removal and was dependent on Ca²⁺ influx through the plasma membrane. Patch-clamp and calcium imaging recordings revealed TG2-dependent neuronal membrane depolarization and activation of inward currents, due to the Na⁺/Ca²⁺-exchanger (NCX) operating in the reverse mode and indirect activation of L-type VOCCs, as indicated by VOCCs/NCX pharmacological inhibitors. A subunit of Na⁺/K⁺-ATPase was selected by comparative proteomics and identified as being functionally inhibited by extracellular TG2, implicating Na⁺/K⁺-ATPase inhibition in NCX reverse mode-switching leading to Ca²⁺ influx and higher basal [Ca²⁺]_i. These data suggest that reactive astrocytes control intraneuronal [Ca²⁺]_i through release of EVs with TG2 as responsible cargo, which could have a significant impact on synaptic activity in brain inflammation.

Mammalian Brain Ca2+ Channel Activity Transplanted into Xenopus laevis Oocytes

Several mutations on neuronal voltage-gated Ca²⁺ channels (VGCC) have been shown to cause neurological disorders and contribute to the initiation of epileptic seizures, migraines, or cerebellar degeneration. Analysis of the functional consequences of these mutations mainly uses heterologously expressed mutated channels or transgenic mice which mimic these pathologies, since direct electrophysiological approaches on brain samples are not easily feasible. We demonstrate that mammalian voltage-gated Ca²⁺ channels from membrane preparation can be microtransplanted into Xenopus oocytes and can conserve their activity. This method, originally described to study the alteration of GABA receptors in human brain samples, allows the recording of the activity of membrane receptors and channels with their native post-translational processing, membrane environment, and regulatory subunits. The use of hippocampal, cerebellar, or cardiac membrane preparation displayed different efficacy for transplanted Ca²⁺ channel activity. This technique, now extended to the recording of Ca²⁺ channel activity, may therefore be useful in order to analyze the calcium signature of membrane preparations from unfixed human brain samples or normal and transgenic mice.

Invertebrate neurons as a simple model to study the hyperexcitable state of epileptic disorders in single cells, monosynaptic connections, and polysynaptic circuits

Epilepsy is a neurological disorder characterized by a hyperexcitable state in neurons from different brain regions. Much is unknown about epilepsy and seizures development, depicting a growing field of research. Animal models have provided important clues about the underlying mechanisms of seizure-generating neuronal circuits. Mammalian complexity still makes it difficult to define some principles of nervous system function, and non-mammalian models have played pivotal roles depending on the research question at hand. Mollusks and the Helix land snail have been used to study epileptic-like behavior in neurons. Neurons from these organisms confer advantages as single-cell identification, isolation, and culture, either as single cells or as physiological relevant monosynaptic or polysynaptic circuits, together with amenability to different protocols and treatments. This review's purpose consists in presenting relevant papers in order to gain a better understanding of Helix neurons, their characteristics, uses, and capabilities for studying the fundamental mechanisms of epileptic disorders and their treatment, to facilitate their more expansive use in epilepsy research.

PRRT2 modulates presynaptic Ca2+ influx by interacting with P/Q-type channels

Loss-of-function mutations in proline-rich transmembrane protein-2 (PRRT2) cause paroxysmal disorders associated with defective Ca2+ dependence of glutamatergic transmission. We find that either acute or constitutive PRRT2 deletion induces a significant decrease in the amplitude of evoked excitatory postsynaptic currents (eEPSCs) that is insensitive to extracellular Ca2+ and associated with a reduced contribution of P/Q-type Ca2+ channels to the EPSC amplitude. This synaptic phenotype parallels a decrease in somatic P/Q-type Ca2+ currents due to a decreased membrane targeting of the channel with unchanged total expression levels. Co-immunoprecipitation, pull-down assays, and proteomics reveal a specific and direct interaction of PRRT2 with P/Q-type Ca2+ channels. At presynaptic terminals lacking PRRT2, P/Q-type Ca2+ channels reduce their clustering at the active zone, with a corresponding decrease in the P/Q-dependent presynaptic Ca2+ signal. The data highlight the central role of PRRT2 in ensuring the physiological Ca2+ sensitivity of the release machinery at glutamatergic synapses.

Family-based association study identifies SNAP25 as a susceptibility gene for autism in the Han Chinese population

Autism is a neurodevelopmental disorder with high heritability. Synaptosome associated protein 25 (SNAP25) encodes a presynaptic membrane-binding protein. It plays a crucial role in neurotransmission and may be involved in the pathogenesis of autism. However, the association between SNAP25 and autism in the Han Chinese population remains unclear. To investigate whether single nucleotide polymorphisms (SNPs) in SNAP25 contribute to the risk of autism, we performed a family-based association study of 14 tagSNPs in SNAP25 in 640 Han Chinese autism trios. Our results demonstrated that rs363018 in SNAP25 was significantly associated with autism under both additive (A > G, Z = 3.144, P = .0017) and recessive models (A > G, Z = 3.055, P = .0023) after Bonferroni correction (P < .0036). An additional SNP, rs8636, was nominally associated with autism under the recessive model (C > T, Z = 1.972, P = .0487). Haplotype-based association test revealed that haplotypes A-T (Z = 2.038, P = .0415) and G-T (Z = -3.114, P = .0018) of rs363018-rs362582 were significantly associated with autism after the permutation test (P = .0158). These findings suggest that SNAP25 may represent a susceptibility gene for autism in the Han Chinese population.

Exploring the Hereditary Nature of Migraine

Migraine is a common neurological disorder which affects 15-20% of the population; it has a high socioeconomic impact through treatment and loss of productivity. Current forms of diagnosis are primarily clinical and can be difficult owing to comorbidity and symptom overlap with other neurological disorders. As such, there is a need for better diagnostic tools in the form of genetic testing. Migraine is a complex disorder, encompassing various subtypes, and has a large genetic component. Genetic studies conducted on rare monogenic subtypes, including familial hemiplegic migraine, have led to insights into its pathogenesis via identification of causal mutations in three genes (CACNA1A, ATP1A2 and SCN1A) that are involved in transport of ions at synapses and glutamatergic transmission. Study of familial migraine with aura pedigrees has also revealed other causal genes for monogenic forms of migraine. With respect to the more common polygenic form of migraine, large genome-wide association studies have increased our understanding of the genes, pathways and mechanisms involved in susceptibility, which are largely involved in neuronal and vascular functions. Given the preponderance of female migraineurs (3:1), there is evidence to suggest that hormonal or X-linked components can also contribute to migraine, and the role of genetic variants in mitochondrial DNA in migraine has been another avenue of exploration. Epigenetic studies of migraine have shown links between hormonal variation and alterations in DNA methylation and gene expression. While there is an abundance of preliminary studies identifying many potentially causative migraine genes and pathways, more comprehensive genomic and functional analysis to better understand mechanisms may aid in better diagnostic and treatment outcomes.

SNAP23 depletion enables more SNAP25/calcium channel excitosome formation to increase insulin exocytosis in type 2 diabetes

SNAP23 is the ubiquitous SNAP25 isoform that mediates secretion in non-neuronal cells, similar to SNAP25 in neurons. However, some secretory cells like pancreatic islet β cells contain an abundance of both SNAP25 and SNAP23, where SNAP23 is believed to play a redundant role to SNAP25. We show that SNAP23, when depleted in mouse β cells in vivo and human β cells (normal and type 2 diabetes [T2D] patients) in vitro, paradoxically increased biphasic glucose-stimulated insulin secretion corresponding to increased exocytosis of predocked and newcomer insulin granules. Such effects on T2D Goto-Kakizaki rats improved glucose homeostasis that was superior to conventional treatment with sulfonylurea glybenclamide. SNAP23, although fusion competent in slower secretory cells, in the context of β cells acts as a weak partial fusion agonist or inhibitory SNARE. Here, SNAP23 depletion promotes SNAP25 to bind calcium channels more quickly and longer where granule fusion occurs to increase exocytosis efficiency. β Cell SNAP23 antagonism is a strategy to treat diabetes.

Interactions of Rabconnectin-3 with Cav2 calcium channels

This study describes the interaction between Cav2 calcium channels and Rabconnectin-3, a di-subunit protein that is associated with synaptic vesicles. Immunostaining reveals that both Rabconnectin-3α (RB-3α) and Rabconnectin-3β (RB-3β) are colocalized in mouse hippocampal neurons. Co-immunoprecipitations from brain tissue is consistent with the formation of a protein complex between RB-3α and RB-3β and both Cav2.2 and the related Cav2.1 calcium channel. The coexpression of either RB-3α or RB-3β with Cav2.2 calcium channels in tsA-201 cells led to a reduction in Cav2.2 current density without any effects on the voltage-dependence of activation or inactivation. Coexpression of both Rabconnectin-3 subunits did not cause an additive effect on current densities. Finally, the presence of Rabconnectin-3 did not interfere with μ-opioid receptor mediated Gβγ modulation of Cav2.2 channels. Altogether, our findings show that Rabconnectin-3 has the propensity to regulate calcium entry mediated by Cav2.2 channels.

Advances in genetics of migraine

Background

Migraine is a complex neurovascular disorder with a strong genetic component. There are rare monogenic forms of migraine, as well as more common polygenic forms; research into the genes involved in both types has provided insights into the many contributing genetic factors. This review summarises advances that have been made in the knowledge and understanding of the genes and genetic variations implicated in migraine etiology.

Findings

Migraine is characterised into two main types, migraine without aura (MO) and migraine with aura (MA). Hemiplegic migraine is a rare monogenic MA subtype caused by mutations in three main genes - CACNA1A, ATP1A2 and SCN1A - which encode ion channel and transport proteins. Functional studies in cellular and animal models show that, in general, mutations result in impaired glutamatergic neurotransmission and cortical hyperexcitability, which make the brain more susceptible to cortical spreading depression, a phenomenon thought to coincide with aura symptoms. Variants in other genes encoding ion channels and solute carriers, or with roles in regulating neurotransmitters at neuronal synapses, or in vascular function, can also cause monogenic migraine, hemiplegic migraine and related disorders with overlapping symptoms. Next-generation sequencing will accelerate the finding of new potentially causal variants and genes, with high-throughput bioinformatics analysis methods and functional analysis pipelines important in prioritising, confirming and understanding the mechanisms of disease-causing variants.

With respect to common migraine forms, large genome-wide association studies (GWAS) have greatly expanded our knowledge of the genes involved, emphasizing the role of both neuronal and vascular pathways. Dissecting the genetic architecture of migraine leads to greater understanding of what underpins relationships between subtypes and comorbid disorders, and may have utility in diagnosis or tailoring treatments. Further work is required to identify causal polymorphisms and the mechanism of their effect, and studies of gene expression and epigenetic factors will help bridge the genetics with migraine pathophysiology.

Conclusions

The complexity of migraine disorders is mirrored by their genetic complexity. A comprehensive knowledge of the genetic factors underpinning migraine will lead to improved understanding of molecular mechanisms and pathogenesis, to enable better diagnosis and treatments for migraine sufferers.

The Control of Neuronal Calcium Homeostasis by SNAP-25 and its Impact on Neurotransmitter Release

The process of neurotransmitter release is central to the control of cell-to-cell communication in brain. SNAP-25 is a component of the SNARE complex, which, together with syntaxin-1 and synaptobrevin, mediates synaptic vesicle fusion with the plasma membrane. The genetic ablation of the protein or its proteolytic cleavage by botulinum neurotoxins results in a complete block of synaptic transmission. In the last years, several evidences have indicated that SNAP-25 also plays additional modulatory roles in neurotransmission through the control of voltage-gated calcium channels and presynaptic calcium ion concentration. Consistently, reduced levels of the protein affect presynaptic calcium homeostasis and result in pathologically enhanced glutamate exocytosis. The SNAP-25-dependent alterations of synaptic calcium dynamics may have direct impact on the development of neuropsychiatric disorders where the Snap-25 gene has been found to be involved.

Postsynaptic SNARE Proteins: Role in Synaptic Transmission and Plasticity

Soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) proteins mediate membrane fusion events in eukaryotic cells. Traditionally recognized as major players in regulating presynaptic neurotransmitter release, accumulative evidence over recent years has identified several SNARE proteins implicated in important postsynaptic processes such as neurotransmitter receptor trafficking and synaptic plasticity. Here we analyze the emerging data revealing this novel functional dimension for SNAREs with a focus on the molecular specialization of vesicular recycling and fusion in dendrites compared to those at axon terminals and its impact in synaptic transmission and plasticity.

Brain-Specific SNAP-25 Deletion Leads to Elevated Extracellular Glutamate Level and Schizophrenia-Like Behavior in Mice

Several studies have associated reduced expression of synaptosomal-associated protein of 25 kDa (SNAP-25) with schizophrenia, yet little is known about its role in the illness. In this paper, a forebrain glutamatergic neuron-specific SNAP-25 knockout mouse model was constructed and studied to explore the possible pathogenetic role of SNAP-25 in schizophrenia. We showed that SNAP-25 conditional knockout (cKO) mice exhibited typical schizophrenia-like phenotype. A significantly elevated extracellular glutamate level was detected in the cerebral cortex of the mouse model. Compared with Ctrls, SNAP-25 was dramatically reduced by about 60% both in cytoplasm and in membrane fractions of cerebral cortex of cKOs, while the other two core members of SNARE complex: Syntaxin-1 (increased ~80%) and Vamp2 (increased ~96%) were significantly increased in cell membrane part. Riluzole, a glutamate release inhibitor, significantly attenuated the locomotor hyperactivity deficits in cKO mice. Our findings provide in vivo functional evidence showing a critical role of SNAP-25 dysfunction on synaptic transmission, which contributes to the developmental of schizophrenia. It is suggested that a SNAP-25 cKO mouse, a valuable model for schizophrenia, could address questions regarding presynaptic alterations that contribute to the etiopathophysiology of SZ and help to consummate the pre- and postsynaptic glutamatergic pathogenesis of the illness.

Massive transcriptome sequencing of human spinal cord tissues provides new insights into motor neuron degeneration in ALS

ALS is a devastating and debilitating human disease characterized by the progressive death of upper and lower motor neurons. Although much effort has been made to elucidate molecular determinants underlying the onset and progression of the disorder, the causes of ALS remain largely unknown. In the present work, we have deeply sequenced whole transcriptome from spinal cord ventral horns of post-mortem ALS human donors affected by the sporadic form of the disease (which comprises ~90% of the cases but which is less investigated than the inherited form of the disease). We observe 1160 deregulated genes including 18 miRNAs and show that down regulated genes are mainly of neuronal derivation while up regulated genes have glial origin and tend to be involved in neuroinflammation or cell death. Remarkably, we find strong deregulation of SNAP25 and STX1B at both mRNA and protein levels suggesting impaired synaptic function through SNAP25 reduction as a possible cause of calcium elevation and glutamate excitotoxicity. We also note aberrant alternative splicing but not disrupted RNA editing.

Genetics of Migraine: Insights into the Molecular Basis of Migraine Disorders

Migraine is a complex, debilitating neurovascular disorder, typically characterized by recurring, incapacitating attacks of severe headache often accompanied by nausea and neurological disturbances. It has a strong genetic basis demonstrated by rare migraine disorders caused by mutations in single genes (monogenic), as well as familial clustering of common migraine which is associated with polymorphisms in many genes (polygenic). Hemiplegic migraine is a dominantly inherited, severe form of migraine with associated motor weakness. Family studies have found that mutations in three different ion channels genes, CACNA1A, ATP1A2, and SCN1A can be causal. Functional studies of these mutations has shown that they can result in defective regulation of glutamatergic neurotransmission and the excitatory/inhibitory balance in the brain, which lowers the threshold for cortical spreading depression, a wave of cortical depolarization thought to be involved in headache initiation mechanisms. Other putative genes for monogenic migraine include KCKN18, PRRT2, and CSNK1D, which can also be involved with other disorders. There are a number of primarily vascular disorders caused by mutations in single genes, which are often accompanied by migraine symptoms. Mutations in NOTCH3 causes cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a hereditary cerebrovascular disease that leads to ischemic strokes and dementia, but in which migraine is often present, sometimes long before the onset of other symptoms. Mutations in the TREX1 and COL4A1 also cause vascular disorders, but often feature migraine. With respect to common polygenic migraine, genome-wide association studies have now identified single nucleotide polymorphisms at 38 loci significantly associated with migraine risk. Functions assigned to the genes in proximity to these loci suggest that both neuronal and vascular pathways also contribute to the pathophysiology of common migraine. Further studies are required to fully understand these findings and translate them into treatment options for migraine patients.

High frequency stimulation induces sonic hedgehog release from hippocampal neurons

Sonic hedgehog (SHH) as a secreted protein is important for neuronal development in the central nervous system (CNS). However, the mechanism about SHH release remains largely unknown. Here, we showed that SHH was expressed mainly in the synaptic vesicles of hippocampus in both young postnatal and adult rats. High, but not low, frequency stimulation, induces SHH release from the neurons. Moreover, removal of extracellular Ca²⁺, application of tetrodotoxin (TTX), an inhibitor of voltage-dependent sodium channels, or downregulation of soluble n-ethylmaleimide-sensitive fusion protein attachment protein receptors (SNAREs) proteins, all blocked SHH release from the neurons in response to HFS. Our findings suggest a novel mechanism to control SHH release from the hippocampal neurons.

Select putative neurodevelopmental toxins modify SNAP-25 expression in primary cultures of rat cerebellar granule cells

A presynaptic protein SNAP-25 belonging to SNARE complex which is instrumental in intracellular vesicular trafficking and exocytosis, has been implicated in hyperactivity and cognitive abilities in some neuropsychiatric disorders. The unclear etiology of the behavior disrupting neurodevelopmental disabilities in addition to genetic causes most likely involves environmental factors. The aim of this in vitro study was to test if various suspected developmental neurotoxins can alter SNAP-25 mRNA and protein expression in neurons. Real-time PCR and Western blotting analyses were used to assess SNAP-25 mRNA and protein levels in primary cultures of rat cerebellar granule cells (CGCs). The test substances: tetrabromobisphenol-A (TBBPA), thimerosal (TH), silver nanoparticles (NAg), valproic acid (VPA) and thalidomide (THAL), were administered to CGC cultures at subtoxic concentrations for 24h. The results demonstrated that SNAP-25 mRNA levels were increased by 49 and 66% by TBBPA and THAL, respectively, whereas VPA and NAg reduced these levels to 48 and 64% of the control, respectively. The SNAP-25 protein content in CGCs was increased by 79% by TBBPA, 25% by THAL and 21% by NAg; VPA and TH reduced these levels to 73 and 69% of the control, respectively. The variety of changes in SNAP-25 expression on mRNA and protein level suggests the diversity of the mechanism of action of the test substances. This initial study provided no data on concentration-effect relations and on functional changes in CGCs. However it is the first to demonstrate the effect of different compounds that are suspected of causing neurodevelopmental disabilities on SNAP-25 expression. These results suggest that this protein may be a common target for not only inherited but also environmental modifications linked to behavioral deficits in neurodevelopmental disabilities.

Regulation of Ca2+ channels by SNAP-25 via recruitment of syntaxin-1 from plasma membrane clusters

SNAP-25 regulates Ca²⁺ channels in an unknown manner. Endogenous and exogenous SNAP-25 inhibit Ca²⁺ currents indirectly by recruiting syntaxin-1 from clusters on the plasma membrane, thereby making it available for Ca²⁺ current inhibition. Thus the cell can regulate Ca²⁺ influx by expanding or contracting syntaxin-1 clusters.

SNAP-25 regulates Ca²⁺ channels, with potentially important consequences for diseases involving an aberrant SNAP-25 expression level. How this regulation is executed mechanistically remains unknown. We investigated this question in mouse adrenal chromaffin cells and found that SNAP-25 inhibits Ca²⁺ currents, with the B-isoform being more potent than the A-isoform, but not when syntaxin-1 is cleaved by botulinum neurotoxin C. In contrast, syntaxin-1 inhibits Ca²⁺ currents independently of SNAP-25. Further experiments using immunostaining showed that endogenous or exogenous SNAP-25 expression recruits syntaxin-1 from clusters on the plasma membrane, thereby increasing the immunoavailability of syntaxin-1 and leading indirectly to Ca²⁺ current inhibition. Expression of Munc18-1, which recruits syntaxin-1 within the exocytotic pathway, does not modulate Ca²⁺ channels, whereas overexpression of the syntaxin-binding protein Doc2B or ubMunc13-2 increases syntaxin-1 immunoavailability and concomitantly down-regulates Ca²⁺ currents. Similar findings were obtained upon chemical cholesterol depletion, leading directly to syntaxin-1 cluster dispersal and Ca²⁺ current inhibition. We conclude that clustering of syntaxin-1 allows the cell to maintain a high syntaxin-1 expression level without compromising Ca²⁺ influx, and recruitment of syntaxin-1 from clusters by SNAP-25 expression makes it available for regulating Ca²⁺ channels. This mechanism potentially allows the cell to regulate Ca²⁺ influx by expanding or contracting syntaxin-1 clusters.

ApoE and SNAP-25 Polymorphisms Predict the Outcome of Multidimensional Stimulation Therapy Rehabilitation in Alzheimer’s Disease

Background. Alzheimer’s disease (AD) is a highly prevalent neurodegenerative disorder. Rate of decline and functional restoration in AD greatly depend on the capacity for neural plasticity within residual neural tissues; this is at least partially influenced by polymorphisms in genes that determine neural plasticity, including Apolipoprotein E4 ( ApoE4) and synaptosomal-associated protein of 25 kDa ( SNAP-25). Objective. We investigated whether correlations could be detected between polymorphisms of ApoE4 and SNAP-25 and the outcome of a multidimensional rehabilitative approach, based on cognitive stimulation, behavioral, and functional therapy (multidimensional stimulation therapy [MST]). Methods. Fifty-eight individuals with mild-to-moderate AD underwent MST for 10 weeks. Neuro-psychological functional and behavioral evaluations were performed blindly by a neuropsychologist at baseline and after 10 weeks of therapy using Mini-Mental State Examination (MMSE), Functional Living Skill Assessment (FLSA), and Neuropsychiatric Inventory (NPI) scales. Molecular genotyping of ApoE4 and SNAP-25 rs363050, rs363039, rs363043 was performed. Results were correlated with ΔMMSE, ΔNPI and ΔFLSA scores by multinomial logistic regression analysis. Results. Polymorphisms in both genes correlated with the outcome of MST for MMSE and NPI scores. Thus, higher overall MMSE scores after rehabilitation were detected in ApoE4 negative compared to ApoE4 positive patients, whereas the SNAP-25 rs363050(G) and rs363039(A) alleles correlated with significant improvements in behavioural parameters. Conclusions. Polymorphisms in genes known to modulate neural plasticity might predict the outcome of a multistructured rehabilitation protocol in patients with AD. These data, although needing confirmation on larger case studies, could help optimizing the clinical management of individuals with AD, for example defining a more intensive treatment in those subjects with a lower likelihood of success.

LRRK2 Regulates Voltage-Gated Calcium Channel Function

Voltage-gated Ca²⁺ (Ca_V) channels enable Ca²⁺ influx in response to membrane depolarization. Ca_V2.1 channels are localized to the presynaptic membrane of many types of neurons where they are involved in triggering neurotransmitter release. Several signaling proteins have been identified as important Ca_V2.1 regulators including protein kinases, G-proteins and Ca²⁺ binding proteins. Recently, we discovered that leucine rich repeat kinase 2 (LRRK2), a protein associated with inherited Parkinson’s disease, interacts with specific synaptic proteins and influences synaptic transmission. Since synaptic proteins functionally interact with Ca_V2.1 channels and synaptic transmission is triggered by Ca²⁺ entry via Ca_V2.1, we investigated whether LRRK2 could impact Ca_V2.1 channel function. Ca_V2.1 channel properties were measured using whole cell patch clamp electrophysiology in HEK293 cells transfected with Ca_V2.1 subunits and various LRRK2 constructs. Our results demonstrate that both wild type (wt) LRRK2 and the G2019S LRRK2 mutant caused a significant increase in whole cell Ca²⁺ current density compared to cells expressing only the Ca_V2.1 channel complex. In addition, LRRK2 expression caused a significant hyperpolarizing shift in voltage-dependent activation while having no significant effect on inactivation properties. These functional changes in Ca_V2.1 activity are likely due to a direct action of LRRK2 as we detected a physical interaction between LRRK2 and the β3 Ca_V channel subunit via coimmunoprecipitation. Furthermore, effects on Ca_V2.1 channel function are dependent on LRRK2 kinase activity as these could be reversed via treatment with a LRRK2 inhibitor. Interestingly, LRRK2 also augmented endogenous voltage-gated Ca²⁺ channel function in PC12 cells suggesting other Ca_V channels could also be regulated by LRRK2. Overall, our findings support a novel physiological role for LRRK2 in regulating Ca_V2.1 function that could have implications for how mutations in LRRK2 contribute to Parkinson’s disease pathophysiology.

SNAP-25, a Known Presynaptic Protein with Emerging Postsynaptic Functions

A hallmark of synaptic specializations is their dependence on highly organized complexes of proteins that interact with each other. The loss or modification of key synaptic proteins directly affects the properties of such networks, ultimately impacting synaptic function. SNAP-25 is a component of the SNARE complex, which is central to synaptic vesicle exocytosis, and, by directly interacting with different calcium channels subunits, it negatively modulates neuronal voltage-gated calcium channels, thus regulating intracellular calcium dynamics. The SNAP-25 gene has been associated with distinct brain diseases, including Attention Deficit Hyperactivity Disorder (ADHD), schizophrenia and bipolar disorder, indicating that the protein may act as a shared biological substrate among different "synaptopathies". The mechanisms by which alterations in SNAP-25 may concur to these psychiatric diseases are still undefined, although alterations in neurotransmitter release have been indicated as potential causative processes. This review summarizes recent work showing that SNAP-25 not only controls exo/endocytic processes at the presynaptic terminal, but also regulates postsynaptic receptor trafficking, spine morphogenesis, and plasticity, thus opening the possibility that SNAP-25 defects may contribute to psychiatric diseases by impacting not only presynaptic but also postsynaptic functions.

The Association of SNAP25 Gene Polymorphisms in Attention Deficit/Hyperactivity Disorder: a Systematic Review and Meta-Analysis

Attention deficit/hyperactivity disorder (ADHD) is one of the most highly heritable psychiatric disorders in childhood. The risk gene mutation accounts for about 60 to 90 % cases. Synaptosomal-associated protein of 25 kDa (SNAP-25) is a presynaptic plasma membrane protein which is expressed highly and specifically in the neuronal cells. A number of evidences have suggested the role of SNAP-25 in the etiology of ADHD. Notably, the animal model of coloboma mouse mutant bears a ∼2-cM deletion encompassing genes including SNAP25 and displays spontaneous hyperkinetic behavior. Previous investigators have reported association between SNPs in SNAP25 and ADHD, and controversial results were observed. In this study, we analyzed the possible association between six polymorphisms (rs3746544, rs363006, rs1051312, rs8636, rs362549, and rs362998) of SNAP25 and ADHD in a pooled sample of ten family-based studies and four case-control studies by using meta-analysis. The combined analysis results were significant only for rs3746544 (P = 0.010) with mild association (odds ratio (OR) = 1.14). And, the meta-analysis data for rs8636, rs362549, and rs362998 are the first time to be reported; however, no positive association was detected. In conclusion, we report some evidence supporting the association of SNAP25 to ADHD. Future research should emphasize genome-wide association studies in more specific subgroups and larger independent samples.

Knock-down of synapsin alters cell excitability and action potential waveform by potentiating BK and voltage-gated Ca(2+) currents in Helix serotonergic neurons

Synapsins (Syns) are an evolutionarily conserved family of presynaptic proteins crucial for the fine-tuning of synaptic function. A large amount of experimental evidences has shown that Syns are involved in the development of epileptic phenotypes and several mutations in Syn genes have been associated with epilepsy in humans and animal models. Syn mutations induce alterations in circuitry and neurotransmitter release, differentially affecting excitatory and inhibitory synapses, thus causing an excitation/inhibition imbalance in network excitability toward hyperexcitability that may be a determinant with regard to the development of epilepsy. Another approach to investigate epileptogenic mechanisms is to understand how silencing Syn affects the cellular behavior of single neurons and is associated with the hyperexcitable phenotypes observed in epilepsy. Here, we examined the functional effects of antisense-RNA inhibition of Syn expression on individually identified and isolated serotonergic cells of the Helix land snail. We found that Helix synapsin silencing increases cell excitability characterized by a slightly depolarized resting membrane potential, decreases the rheobase, reduces the threshold for action potential (AP) firing and increases the mean and instantaneous firing rates, with respect to control cells. The observed increase of Ca(2+) and BK currents in Syn-silenced cells seems to be related to changes in the shape of the AP waveform. These currents sustain the faster spiking in Syn-deficient cells by increasing the after hyperpolarization and limiting the Na(+) and Ca(2+) channel inactivation during repetitive firing. This in turn speeds up the depolarization phase by reaching the AP threshold faster. Our results provide evidence that Syn silencing increases intrinsic cell excitability associated with increased Ca(2+) and Ca(2+)-dependent BK currents in the absence of excitatory or inhibitory inputs.

Positively charged amino acids at the SNAP-25 C terminus determine fusion rates, fusion pore properties, and energetics of tight SNARE complex zippering

SNAP-25 is a Q-SNARE protein mediating exocytosis of neurosecretory vesicles including chromaffin granules. Previous results with a SNAP-25 construct lacking the nine C terminal residues (SNAP-25Δ9) showed changed fusion pore properties (Fang et al., 2008), suggesting a model for fusion pore mechanics that couple C terminal zipping of the SNARE complex to the opening of the fusion pore. The deleted fragment contains the positively charged residues R198 and K201, adjacent to layers 7 and 8 of the SNARE complex. To determine how fusion pore conductance and dynamics depend on these residues, single exocytotic events in bovine chromaffin cells expressing R198Q, R198E, K201Q, or K201E mutants were investigated by carbon fiber amperometry and cell-attached patch capacitance measurements. Coarse grain molecular dynamics simulations revealed spontaneous transitions between a loose and tightly zippered state at the SNARE complex C terminus. The SNAP-25 K201Q mutant showed no changes compared with SNAP-25 wild-type. However, K201E, R198Q, and R198E displayed reduced release frequencies, slower release kinetics, and prolonged fusion pore duration that were correlated with reduced probability to engage in the tightly zippered state. The results show that the positively charged amino acids at the SNAP-25 C terminus promote tight SNARE complex zippering and are required for high release frequency and rapid release in individual fusion events.

Reduced SNAP-25 increases PSD-95 mobility and impairs spine morphogenesis

Impairment of synaptic function can lead to neuropsychiatric disorders collectively referred to as synaptopathies. The SNARE protein SNAP-25 is implicated in several brain pathologies and, indeed, brain areas of psychiatric patients often display reduced SNAP-25 expression. It has been recently found that acute downregulation of SNAP-25 in brain slices impairs long-term potentiation; however, the processes through which this occurs are still poorly defined. We show that in vivo acute downregulation of SNAP-25 in CA1 hippocampal region affects spine number. Consistently, hippocampal neurons from SNAP-25 heterozygous mice show reduced densities of dendritic spines and defective PSD-95 dynamics. Finally, we show that, in brain, SNAP-25 is part of a molecular complex including PSD-95 and p140Cap, with p140Cap being capable to bind to both SNAP-25 and PSD-95. These data demonstrate an unexpected role of SNAP-25 in controlling PSD-95 clustering and open the possibility that genetic reductions of the protein levels - as occurring in schizophrenia - may contribute to the pathology through an effect on postsynaptic function and plasticity.

SNAP-25 is abundantly expressed in enteric neuronal networks and upregulated by the neurotrophic factor GDNF

Control of intestinal motility requires an intact enteric neurotransmission. Synaptosomal-associated protein 25 (SNAP-25) is an essential component of the synaptic vesicle fusion machinery. The aim of the study was to investigate the localization and expression of SNAP-25 in the human intestine and cultured enteric neurons and to assess its regulation by the neurotrophic factor glial cell line-derived neurotrophic factor (GDNF). SNAP-25 expression and distribution were analyzed in GDNF-stimulated enteric nerve cell cultures, and synaptic vesicles were evaluated by scanning and transmission electron microscopy. Human colonic specimens were processed for site-specific SNAP-25 gene expression analysis and SNAP-25 immunohistochemistry including dual-labeling with the pan-neuronal marker PGP 9.5. Additionally, gene expression levels and distributional patterns of SNAP-25 were analyzed in colonic specimens of patients with diverticular disease (DD). GDNF-treated enteric nerve cell cultures showed abundant expression of SNAP-25 and exhibited granular staining corresponding to synaptic vesicles. SNAP-25 gene expression was detected in all colonic layers and isolated myenteric ganglia. SNAP-25 co-localized with PGP 9.5 in submucosal and myenteric ganglia and intramuscular nerve fibers. In patients with DD, both SNAP-25 mRNA expression and immunoreactive profiles were decreased compared to controls. GDNF-induced growth and differentiation of cultured enteric neurons is paralleled by increased expression of SNAP-25 and formation of synaptic vesicles reflecting enhanced synaptogenesis. The expression of SNAP-25 within the human enteric nervous system and its downregulation in DD suggest an essential role in enteric neurotransmission and render SNAP-25 as a marker for impaired synaptic plasticity in enteric neuropathies underlying intestinal motility disorders.

Association between SNAP-25 gene polymorphisms and cognition in autism: functional consequences and potential therapeutic strategies

Synaptosomal-associated protein of 25 kDa (SNAP-25) is involved in different neuropsychiatric disorders, including schizophrenia and attention-deficit/hyperactivity disorder. Consistently, SNAP-25 polymorphisms in humans are associated with hyperactivity and/or with low cognitive scores. We analysed five SNAP-25 gene polymorphisms (rs363050, rs363039, rs363043, rs3746544 and rs1051312) in 46 autistic children trying to correlate them with Childhood Autism Rating Scale and electroencephalogram (EEG) abnormalities. The functional effects of rs363050 single-nucleotide polymorphism (SNP) on the gene transcriptional activity, by means of the luciferase reporter gene, were evaluated. To investigate the functional consequences that SNAP-25 reduction may have in children, the behaviour and EEG of SNAP-25(+/-) adolescent mice (SNAP-25(+/+)) were studied. Significant association of SNAP-25 polymorphism with decreasing cognitive scores was observed. Analysis of transcriptional activity revealed that SNP rs363050 encompasses a regulatory element, leading to protein expression decrease. Reduction of SNAP-25 levels in adolescent mice was associated with hyperactivity, cognitive and social impairment and an abnormal EEG, characterized by the occurrence of frequent spikes. Both EEG abnormalities and behavioural deficits were rescued by repeated exposure for 21 days to sodium salt valproate (VLP). A partial recovery of SNAP-25 expression content in SNAP-25(+/-) hippocampi was also observed by means of western blotting. A reduced expression of SNAP-25 is responsible for the cognitive deficits in children affected by autism spectrum disorders, as presumably occurring in the presence of rs363050(G) allele, and for behavioural and EEG alterations in adolescent mice. VLP treatment could result in novel therapeutic strategies.

Mechanism underlying unaltered cortical inhibitory synaptic transmission in contrast with enhanced excitatory transmission in CaV2.1 knockin migraine mice

Familial hemiplegic migraine type 1 (FHM1), a monogenic subtype of migraine with aura, is caused by gain-of-function mutations in Ca_V2.1 (P/Q-type) calcium channels. In FHM1 knockin mice, excitatory neurotransmission at cortical pyramidal cell synapses is enhanced, but inhibitory neurotransmission at connected pairs of fast-spiking (FS) interneurons and pyramidal cells is unaltered, despite being initiated by Ca_V2.1 channels. The mechanism underlying the unaltered GABA release at cortical FS interneuron synapses remains unknown. Here, we show that the FHM1 R192Q mutation does not affect inhibitory transmission at autapses of cortical FS and other types of multipolar interneurons in microculture from R192Q knockin mice, and investigate the underlying mechanism. Lowering the extracellular [Ca²⁺] did not reveal gain-of-function of evoked transmission neither in control nor after prolongation of the action potential (AP) with tetraethylammonium, indicating unaltered AP-evoked presynaptic calcium influx at inhibitory autapses in FHM1 KI mice. Neither saturation of the presynaptic calcium sensor nor short duration of the AP can explain the unaltered inhibitory transmission in the mutant mice. Recordings of the P/Q-type calcium current in multipolar interneurons in microculture revealed that the current density and the gating properties of the Ca_V2.1 channels expressed in these interneurons are barely affected by the FHM1 mutation, in contrast with the enhanced current density and left-shifted activation gating of mutant Ca_V2.1 channels in cortical pyramidal cells. Our findings suggest that expression of specific Ca_V2.1 channels differentially sensitive to modulation by FHM1 mutations in inhibitory and excitatory cortical neurons underlies the gain-of-function of excitatory but unaltered inhibitory synaptic transmission and the likely consequent dysregulation of the cortical excitatory–inhibitory balance in FHM1.

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Multipolar interneuron autaptic transmission is unaltered in FHM1 knockin mice.

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This is due to unaltered action potential (AP)-evoked presynaptic Ca influx.

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Unaltered AP-evoked Ca influx is not due to short duration of interneuron APs.

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Ca_V2.1 channels of multipolar interneurons are barely affected by the FHM1 mutation.

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This may explain unaltered inhibitory neurotransmission in FHM1.

SNAP-25 regulates spine formation through postsynaptic binding to p140Cap

Synaptosomal-associated protein of 25 kDa (SNAP-25) is a member of the Soluble N-ethylmaleimide-sensitive-factor attachment protein receptors (SNARE) protein family, required for exocytosis of synaptic vesicles and regulation of diverse ion channels. Here, we show that acute reduction of SNAP-25 expression leads to an immature phenotype of dendritic spines that are, consistently, less functional. Conversely, over-expression of SNAP-25 results in an increase in the density of mature, Postsynaptic Density protein 95 (PSD-95)-positive spines. The regulation of spine morphogenesis by SNAP-25 depends on the protein's ability to bind both the plasma membrane and the adaptor protein p140Cap, a key protein regulating actin cytoskeleton and spine formation. We propose that SNAP-25 allows the organization of the molecular apparatus needed for spine formation by recruiting and stabilizing p140Cap.

The E1015K variant in the synprint region of the CaV2.1 channel alters channel function and is associated with different migraine phenotypes

Mutations in the CACNA1A gene, which encodes the pore-forming α1A subunit of the CaV2.1 voltage-gated calcium channel, cause a number of human neurologic diseases including familial hemiplegic migraine. We have analyzed the functional impact of the E1015K amino acid substitution located in the "synprint" domain of the α1A subunit. This variant was identified in two families with hemiplegic migraine and in one patient with migraine with aura. The wild type (WT) and the E1015K forms of the GFP-tagged α1A subunit were expressed in cultured hippocampal neurons and HEK cells to understand the role of the variant in the transport activity and physiology of CaV2.1. The E1015K variant does not alter CaV2.1 protein expression, and its transport to the cell surface and synaptic terminals is similar to that observed for WT channels. Electrophysiological data demonstrated that E1015K channels have increased current density and significantly altered inactivation properties compared with WT. Furthermore, the SNARE proteins syntaxin 1A and SNAP-25 were unable to modulate voltage-dependent inactivation of E1015K channels. Overall, our findings describe a genetic variant in the synprint site of the CaV2.1 channel which is characterized by a gain-of-function and associated with both hemiplegic migraine and migraine with aura in patients.

Cytotoxicity of botulinum neurotoxins reveals a direct role of syntaxin 1 and SNAP-25 in neuron survival

Botulinum neurotoxins (BoNT/A-G) are well-known to act by blocking synaptic vesicle exocytosis. Whether BoNTs disrupt additional neuronal functions has not been addressed. Here we report that cleavage of syntaxin 1 (Syx 1) by BoNT/C and cleavage of SNAP-25 by BoNT/E both induce degeneration of cultured rodent and human neurons. Furthermore, although SNAP-25 cleaved by BoNT/A can still support neuron survival, it has reduced capacity to tolerate additional mutations and also fails to pair with syntaxin isoforms other than Syx 1. Syx 1 and SNAP-25 are well-known for mediating synaptic vesicle exocytosis, but we found that neuronal death is due to blockage of plasma membrane recycling processes that share Syx 1/SNAP-25 for exocytosis, independent of blockage of synaptic vesicle exocytosis. These findings reveal neuronal cytotoxicity for a subset of BoNTs and directly link Syx 1/SNAP-25 to neuron survival as the prevalent SNARE proteins mediating multiple fusion events on neuronal plasma membranes.

Reduced SNAP-25 alters short-term plasticity at developing glutamatergic synapses

SNAP-25 is a key component of the synaptic-vesicle fusion machinery, involved in several psychiatric diseases including schizophrenia and ADHD. SNAP-25 protein expression is lower in different brain areas of schizophrenic patients and in ADHD mouse models. How the reduced expression of SNAP-25 alters the properties of synaptic transmission, leading to a pathological phenotype, is unknown. We show that, unexpectedly, halved SNAP-25 levels at 13-14 DIV not only fail to impair synaptic transmission but instead enhance evoked glutamatergic neurotransmission. This effect is possibly dependent on presynaptic voltage-gated calcium channel activity and is not accompanied by changes in spontaneous quantal events or in the pool of readily releasable synaptic vesicles. Notably, synapses of 13-14 DIV neurons with reduced SNAP-25 expression show paired-pulse depression as opposed to paired-pulse facilitation occurring in their wild-type counterparts. This phenotype disappears with synapse maturation. As alterations in short-term plasticity represent a new mechanism contributing to cognitive impairments in intellectual disabilities, our data provide mechanistic clues for neuronal circuit alterations in psychiatric diseases characterized by reduced expression of SNAP-25.

Time-Dependent Compensatory Responses to Chronic Neuroinflammation in Hippocampus and Brainstem: The Potential Role of Glutamate Neurotransmission

Chronic neuroinflammation is characteristic of neurodegenerative diseases and is present during very early stages, yet significant pathology and behavioral deficits do not manifest until advanced age. We investigated the consequences of experimentally-induced chronic neuroinflammation within the hippocampus and brainstem of young (4 mo) F-344 rats. Lipopolysaccharide (LPS) was infused continuously into the IV^th ventricle for 2, 4 or 8 weeks. The number of MHC II immunoreactive microglia in the brain continued to increase throughout the infusion period. In contrast, performance in the Morris water maze was impaired after 4 weeks but recovered by 8 weeks. Likewise, a transient loss of tyrosine hydroxylase immunoreactivity in the substantia nigra and locus coeruleus was observed after 2 weeks, but returned to control levels by 4 weeks of continuous LPS infusion. These data suggest that direct activation of microglia is sufficient to drive, but not sustain, spatial memory impairment and a decrease in tyrosine hydroxylase production in young rats. Our previous studies suggest that chronic neuroinflammation elevates extracellular glutamate and that this elevation underlies the spatial memory impairment. In the current study, increased levels of GLT1 and SNAP25 in the hippocampus corresponded with the resolution of performance deficit. Increased expression of SNAP25 is consistent with reduced glutamate release from axonal terminals while increased GLT1 is consistent with enhanced clearance of extracellular glutamate. These data demonstrate the capacity of the brain to compensate for the presence of chronic neuroinflammation, despite continued activation of microglia, through changes in the regulation of the glutamatergic system.

In vivo activation of azipropofol prolongs anesthesia and reveals synaptic targets

General anesthetic photolabels have been instrumental in discovering and confirming protein binding partners and binding sites of these promiscuous ligands. We report the in vivo photoactivation of meta-azipropofol, a potent analog of propofol, in Xenopus laevis tadpoles. Covalent adduction of meta-azipropofol in vivo prolongs the primary pharmacologic effect of general anesthetics in a behavioral phenotype we termed "optoanesthesia." Coupling this behavior with a tritiated probe, we performed unbiased, time-resolved gel proteomics to identify neuronal targets of meta-azipropofol in vivo. We have identified synaptic binding partners, such as synaptosomal-associated protein 25, as well as voltage-dependent anion channels as potential facilitators of the general anesthetic state. Pairing behavioral phenotypes elicited by the activation of efficacious photolabels in vivo with time-resolved proteomics provides a novel approach to investigate molecular mechanisms of general anesthetics.

Mutant PrP suppresses glutamatergic neurotransmission in cerebellar granule neurons by impairing membrane delivery of VGCC α(2)δ-1 Subunit

How mutant prion protein (PrP) leads to neurological dysfunction in genetic prion diseases is unknown. Tg(PG14) mice synthesize a misfolded mutant PrP which is partially retained in the neuronal endoplasmic reticulum (ER). As these mice age, they develop ataxia and massive degeneration of cerebellar granule neurons (CGNs). Here, we report that motor behavioral deficits in Tg(PG14) mice emerge before neurodegeneration and are associated with defective glutamate exocytosis from granule neurons due to impaired calcium dynamics. We found that mutant PrP interacts with the voltage-gated calcium channel α(2)δ-1 subunit, which promotes the anterograde trafficking of the channel. Owing to ER retention of mutant PrP, α(2)δ-1 accumulates intracellularly, impairing delivery of the channel complex to the cell surface. Thus, mutant PrP disrupts cerebellar glutamatergic neurotransmission by reducing the number of functional channels in CGNs. These results link intracellular PrP retention to synaptic dysfunction, indicating new modalities of neurotoxicity and potential therapeutic strategies.

The SNARE complex in neuronal and sensory cells

Transmitter release at synapses ensures faithful chemical coding of information that is transmitted in the sub-second time frame. The brain, the central unit of information processing, depends upon fast communication for decision making. Neuronal and neurosensory cells are equipped with the molecular machinery that responds reliably, and with high fidelity, to external stimuli. However, neuronal cells differ markedly from neurosensory cells in their signal transmission at synapses. The main difference rests in how the synaptic complex is organized, with active zones in neuronal cells and ribbon synapses in sensory cells (such as photoreceptors and hair cells). In exocytosis/neurosecretion, SNAREs (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptors) and associated proteins play a critical role in vesicle docking, priming, fusion and synchronization of neurotransmitter release. Recent studies suggest differences between neuronal and sensory cells with respect to the molecular components of their synaptic complexes. In this review, we will cover current findings on neuronal and sensory-cell SNARE proteins and their modulators. We will also briefly discuss recent investigations on how deficits in the expression of SNARE proteins in humans impair function in brain and sense organs.

Variants in SNAP25 are targets of natural selection and influence verbal performances in women

Descriptions of genes that are adaptively evolving in humans and that carry polymorphisms with an effect on cognitive performances have been virtually absent. SNAP25 encodes a presynaptic protein with a role in regulation of neurotransmitter release. We analysed the intra-specific diversity along SNAP25 and identified a region in intron 1 that shows signatures of balancing selection in humans. The estimated TMRCA (time to the most recent common ancestor) of the SNAP25 haplotype phylogeny amounted to 2.08 million years. The balancing selection signature is not secondary to demographic events or to biased gene conversion, and encompasses rs363039. This SNP has previously been associated to cognitive performances with contrasting results in different populations. We analysed this variant in two Italian cohorts in different age ranges and observed a significant genotype effect for rs363039 on verbal performances in females alone. Post hoc analysis revealed that the effect is driven by differences between heterozygotes and both homozygous genotypes. Thus, heterozygote females for rs363039 display higher verbal performances compared to both homozygotes. This finding was replicated in a cohort of Italian subjects suffering from neuromuscular diseases that do not affect cognition. Heterozygote advantage is one of the possible reasons underlying the maintenance of genetic diversity in natural populations. The observation that heterozygotes for rs363039 display higher verbal abilities compared to homozygotes perfectly fits the underlying balancing selection model. Although caution should be used in inferring selective pressures from observed signatures, SNAP25 might represent the first description of an adaptively evolving gene with a role in cognition.

Native presynaptic metabotropic glutamate receptor 4 (mGluR4) interacts with exocytosis proteins in rat cerebellum

The eight pre- or/and post-synaptic metabotropic glutamatergic receptors (mGluRs) modulate rapid excitatory transmission sustained by ionotropic receptors. They are classified in three families according to their percentage of sequence identity and their pharmacological properties. mGluR4 belongs to group III and is mainly localized presynaptically. Activation of group III mGluRs leads to depression of excitatory transmission, a process that is exclusively provided by mGluR4 at parallel fiber-Purkinje cell synapse in rodent cerebellum. This function relies at least partly on an inhibition of presynaptic calcium influx, which controls glutamate release. To improve the understanding of molecular mechanisms of the mGluR4 depressant effect, we decided to identify the proteins interacting with this receptor. Immunoprecipitations using anti-mGluR4 antibodies were performed with cerebellar extracts. 183 putative partners that co-immunoprecipitated with anti-mGluR4 antibodies were identified and classified according to their cellular functions. It appears that native mGluR4 interacts with several exocytosis proteins such as Munc18-1, synapsins, and syntaxin. In addition, native mGluR4 was retained on a Sepharose column covalently grafted with recombinant Munc18-1, and immunohistochemistry experiments showed that Munc18-1 and mGluR4 colocalized at plasma membrane in HEK293 cells, observations in favor of an interaction between the two proteins. Finally, affinity chromatography experiments using peptides corresponding to the cytoplasmic domains of mGluR4 confirmed the interaction observed between mGluR4 and a selection of exocytosis proteins, including Munc18-1. These results could give indications to explain how mGluR4 can modulate glutamate release at parallel fiber-Purkinje cell synapses in the cerebellum in addition to the inhibition of presynaptic calcium influx.