Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0036572 (seizures)
 80,221 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

SV2 proteins are abundant synaptic vesicle proteins expressed in two major (SV2A and SV2B) and one minor isoform (SV2C) that resemble transporter proteins. We now show that SV2B knockout mice are phenotypically normal while SV2A- and SV2A/SV2B double knockout mice exhibit severe seizures and die postnatally. In electrophysiological recordings from cultured hippocampal neurons, SV2A- or SV2B-deficient cells exhibited no detectable abnormalities. Neurons lacking both SV2 isoforms, however, experienced sustained increases in Ca2+-dependent synaptic transmission when two or more action potentials were triggered in succession. These increases could be reversed by EGTA-AM. Our data suggest that without SV2 proteins, presynaptic Ca2+ accumulation during consecutive action potentials causes abnormal increases in neurotransmitter release that destabilize synaptic circuits and induce epilepsy.
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PMID:SV2A and SV2B function as redundant Ca2+ regulators in neurotransmitter release. 1062 62

Here, we show that the synaptic vesicle protein SV2A is the brain binding site of levetiracetam (LEV), a new antiepileptic drug with a unique activity profile in animal models of seizure and epilepsy. The LEV-binding site is enriched in synaptic vesicles, and photoaffinity labeling of purified synaptic vesicles confirms that it has an apparent molecular mass of approximately 90 kDa. Brain membranes and purified synaptic vesicles from mice lacking SV2A do not bind a tritiated LEV derivative, indicating that SV2A is necessary for LEV binding. LEV and related compounds bind to SV2A expressed in fibroblasts, indicating that SV2A is sufficient for LEV binding. No binding was observed to the related isoforms SV2B and SV2C. Furthermore, there is a high degree of correlation between binding affinities of a series of LEV derivatives to SV2A in fibroblasts and to the LEV-binding site in brain. Finally, there is a strong correlation between the affinity of a compound for SV2A and its ability to protect against seizures in an audiogenic mouse animal model of epilepsy. These experimental results suggest that SV2A is the binding site of LEV in the brain and that LEV acts by modulating the function of SV2A, supporting previous indications that LEV possesses a mechanism of action distinct from that of other antiepileptic drugs. Further, these results indicate that proteins involved in vesicle exocytosis, and SV2 in particular, are promising targets for the development of new CNS drug therapies.
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PMID:The synaptic vesicle protein SV2A is the binding site for the antiepileptic drug levetiracetam. 1521 Sep 74

Levetiracetam (LEV), a newer antiepileptic drug (AED) useful for several epilepsy syndromes, binds to SV2A. Identifying genetic variants that influence response to LEV may allow more tailored use of LEV. Obvious candidate genes are SV2A, SV2B and SV2C, which encode the only known binding site, synaptic vesicle protein 2 (SV2), with LEV binding to the SV2A isoform. SV2A is an essential protein as homozygous SV2A knockout mice appear normal at birth but fail to grow, experience severe seizures and die by 3 weeks. We addressed characterising AED response issues in pharmacogenetics and whether variation in these genes associates with response to LEV in two independent cohorts with epilepsy. We also investigated whether variation in these three genes associated with epilepsy predisposition in two larger cohorts of patients with various epilepsy phenotypes. Common genetic variation in SV2A, encoding the actual binding site of LEV, was fully represented in this study whereas SV2B and SV2C were not fully covered. None of the polymorphisms tested in SV2A, SV2B or SV2C influence LEV response or predisposition to epilepsy. We found no association between genetic variation in SV2A, SV2B or SV2C and response to LEV or epilepsy predisposition. We suggest this study design may be used in future pharmacogenetic work examining AED or LEV efficacy. However, different study designs would be needed to examine common variation with minor effect sizes, or rare variation, influencing AED or LEV response or epilepsy predisposition.
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PMID:No major role of common SV2A variation for predisposition or levetiracetam response in epilepsy. 1897 20

LEV (levetiracetam), an antiepileptic drug which possesses a unique profile in animal models of seizure and epilepsy, has as its unique binding site in brain, SV2A (synaptic vesicle protein 2A). Previous studies have used a chimaeric and site-specific mutagenesis approach to identify three residues in the putative tenth transmembrane helix of SV2A that, when mutated, alter binding of LEV and related racetam derivatives to SV2A. In the present paper, we report a combined modelling and mutagenesis study that successfully identifies another 11 residues in SV2A that appear to be involved in ligand binding. Sequence analysis and modelling of SV2A suggested residues equivalent to critical functional residues of other MFS (major facilitator superfamily) transporters. Alanine scanning of these and other SV2A residues resulted in the identification of residues affecting racetam binding, including Ile273 which differentiated between racetam analogues, when mutated to alanine. Integrating mutagenesis results with docking analysis led to the construction of a mutant in which six SV2A residues were replaced with corresponding SV2B residues. This mutant showed racetam ligand-binding affinity intermediate to the affinities observed for SV2A and SV2B.
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PMID:Combining modelling and mutagenesis studies of synaptic vesicle protein 2A to identify a series of residues involved in racetam binding. 2193 12

Synaptic vesicle protein 2 (SV2) is a glycoprotein that exists in three isoforms, SV2A, SV2B, and SV2C. SV2A knockout (KO) mice and SV2A/SV2B double KO (DKO) mice, but not SV2B KO animals, start to experience severe seizures and weight loss 7 days after birth and die at about postnatal day (P)14-P23. Because excitatory and inhibitory inputs play a major role in controlling neuronal excitability in the hippocampus, we examined the effects of SV2A and/or SV2B deletions on glutamatergic and GABA(A) neurotransmission in hippocampal CA1 pyramidal neurons. Spontaneous and miniature excitatory and inhibitory postsynaptic currents (sEPSCs, mEPSCs, sIPSCs, and mIPSCs, respectively) were recorded using the whole-cell patch-clamp technique in slices from P6-P14 mice. The frequency of sEPSCs was increased in SV2A KO and SV2A/SV2B DKO mice, but their amplitude was unchanged. Such changes were not observed in SV2B KOs. On the contrary, the frequency and amplitude of sIPSCs were decreased in SV2A KO and SV2A/SV2B DKO mice but not in SV2B KO animals, as reported previously for the CA3 region. Kinetic parameters of sIPSCs and sEPSCs were unchanged. Importantly, no changes were observed in any genotype when examining mEPSCs and mIPSCs. We conclude that action potential- and Ca(2+) -dependent glutamatergic and GABAergic synaptic transmission are differentially altered in the hippocampus of SV2A-deficient mice, whereas the mechanism of exocytosis itself is not changed. The altered balance between these major excitatory and inhibitory inputs is probably a contributing factor to seizures in SV2A KO and SV2A/SV2B DKO mice.
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PMID:Altered balance between excitatory and inhibitory inputs onto CA1 pyramidal neurons from SV2A-deficient but not SV2B-deficient mice. 2284 29

The synaptic vesicle glycoprotein SV2A belongs to the major facilitator superfamily (MFS) of transporters and is an integral constituent of synaptic vesicle membranes. SV2A has been demonstrated to be involved in vesicle trafficking and exocytosis, processes crucial for neurotransmission. The anti-seizure drug levetiracetam was the first ligand to target SV2A and displays a broad spectrum of anti-seizure activity in various preclinical models. Several lines of preclinical and clinical evidence, including genetics and protein expression changes, support an important role of SV2A in epilepsy pathophysiology. While the functional consequences of SV2A ligand binding are not fully elucidated, studies suggest that subsequent SV2A conformational changes may contribute to seizure protection. Conversely, the recently discovered negative SV2A modulators, such as UCB0255, counteract the anti-seizure effect of levetiracetam and display procognitive properties in preclinical models. More broadly, dysfunction of SV2A may also be involved in Alzheimer's disease and other types of cognitive impairment, suggesting potential novel therapies for levetiracetam and its congeners. Furthermore, emerging data indicate that there may be important roles for two other SV2 isoforms (SV2B and SV2C) in the pathogenesis of epilepsy, as well as other neurodegenerative diseases. Utilization of recently developed SV2A positron emission tomography ligands will strengthen and reinforce the pharmacological evidence that SV2A is a druggable target, and will provide a better understanding of its role in epilepsy and other neurological diseases, aiding in further defining the full therapeutic potential of SV2A modulation.
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PMID:Synaptic Vesicle Glycoprotein 2A Ligands in the Treatment of Epilepsy and Beyond. 2775 44