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Microarray profile of seizure damage-refractory hippocampal CA3 in a mouse model of epileptic preconditioning.

ABSTRACT: A neuroprotected state can be acquired by preconditioning brain with a stimulus that is subthreshold for damage (tolerance). Acquisition of tolerance involves coordinate, bi-directional changes to gene expression levels and the re-programmed phenotype is determined by the preconditioning stimulus. While best studied in ischemic brain there is evidence brief seizures can confer tolerance against prolonged seizures (status epilepticus). Presently, we developed a model of epileptic preconditioning in mice and used microarrays to gain insight into the transcriptional phenotype within the target hippocampus at the time tolerance had been acquired. Epileptic tolerance was induced by an episode of non-damaging seizures in adult C57Bl/6 mice using a systemic injection of kainic acid. Neuron and DNA damage-positive cell counts 24 h after status epilepticus induced by intraamygdala microinjection of kainic acid revealed preconditioning given 24 h prior reduced CA3 neuronal death by approximately 45% compared with non-tolerant seizure mice. Microarray analysis of over 39,000 transcripts (Affymetrix 430 2.0 chip) from microdissected CA3 subfields was undertaken at the point at which tolerance was acquired. Results revealed a unique profile of small numbers of equivalently up- and down-regulated genes with biological functions that included transport and localization, ubiquitin metabolism, apoptosis and cell cycle control. Select microarray findings were validated post hoc by real-time polymerase chain reaction and Western blotting. The present study defines a paradigm for inducing epileptic preconditioning in mice and first insight into the global transcriptome of the seizure-damage refractory brain.

SUBMITTER: Hatazaki S

PROVIDER: S-EPMC2268097 | biostudies-literature | 2007 Dec

REPOSITORIES: biostudies-literature

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Microarray profile of seizure damage-refractory hippocampal CA3 in a mouse model of epileptic preconditioning.

Hatazaki S S Bellver-Estelles C C Jimenez-Mateos E M EM Meller R R Bonner C C Murphy N N Matsushima S S Taki W W Prehn J H M JH Simon R P RP Henshall D C DC

Neuroscience 20070914 2

A neuroprotected state can be acquired by preconditioning brain with a stimulus that is subthreshold for damage (tolerance). Acquisition of tolerance involves coordinate, bi-directional changes to gene expression levels and the re-programmed phenotype is determined by the preconditioning stimulus. While best studied in ischemic brain there is evidence brief seizures can confer tolerance against prolonged seizures (status epilepticus). Presently, we developed a model of epileptic preconditioning ...[more]

PMID: 17935890

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Project description:BACKGROUND: Prolonged febrile seizures constitute an initial precipitating injury (IPI) commonly associated with refractory mesial temporal lobe epilepsy (RMTLE). In order to investigate IPI influence on the transcriptional phenotype underlying RMTLE we comparatively analyzed the transcriptomic signatures of CA3 explants surgically obtained from RMTLE patients with (FS) or without (NFS) febrile seizure history. Texture analyses on MRI images of dentate gyrus were conducted in a subset of surgically removed sclerotic hippocampi for identifying IPI-associated histo-radiological alterations. METHODOLOGY/PRINCIPAL FINDINGS: DNA microarray analysis revealed that CA3 global gene expression differed significantly between FS and NFS subgroups. An integrative functional genomics methodology was used for characterizing the relations between GO biological processes themes and constructing transcriptional interaction networks defining the FS and NFS transcriptomic signatures and its major gene-gene links (hubs). Co-expression network analysis showed that: i) CA3 transcriptomic profiles differ according to the IPI; ii) FS distinctive hubs are mostly linked to glutamatergic signalization while NFS hubs predominantly involve GABAergic pathways and neurotransmission modulation. Both networks have relevant hubs related to nervous system development, what is consistent with cell genesis activity in the hippocampus of RMTLE patients. Moreover, two candidate genes for therapeutic targeting came out from this analysis: SSTR1, a relevant common hub in febrile and afebrile transcriptomes, and CHRM3, due to its putative role in epilepsy susceptibility development. MRI texture analysis allowed an overall accuracy of 90% for pixels correctly classified as belonging to FS or NFS groups. Histological examination revealed that granule cell loss was significantly higher in FS hippocampi. CONCLUSIONS/SIGNIFICANCE: CA3 transcriptional signatures and dentate gyrus morphology fairly correlate with IPI in RMTLE, indicating that FS-RMTLE represents a distinct phenotype. These findings may shed light on the molecular mechanisms underlying refractory epilepsy phenotypes and contribute to the discovery of novel specific drug targets for therapeutic interventions.

Project description:BackgroundThe brain extracellular fluid (ECF), composed of secreted neurotransmitters, metabolites, peptides, and proteins, may reflect brain processes. Analysis of brain ECF may provide new potential markers for synaptic activity or brain damage and reveal additional information on pathological alterations. Epileptic seizure induction is an acute and harsh intervention in brain functions, and it can activate extra- and intracellular proteases, which implies an altered brain secretome. Thus, we applied a 4-aminopyridine (4-AP) epilepsy model to study the hippocampal ECF peptidome alterations upon treatment in rats.MethodsWe performed in vivo microdialysis in the hippocampus for 3-3 h of control and 4-AP treatment phase in parallel with electrophysiology measurement. Then, we analyzed the microdialysate peptidome of control and treated samples from the same subject by liquid chromatography-coupled tandem mass spectrometry. We analyzed electrophysiological and peptidomic alterations upon epileptic seizure induction by two-tailed, paired t-test.ResultsWe detected 2540 peptides in microdialysate samples by mass spectrometry analysis; and 866 peptides-derived from 229 proteins-were found in more than half of the samples. In addition, the abundance of 322 peptides significantly altered upon epileptic seizure induction. Several proteins of significantly altered peptides are neuropeptides (Chgb) or have synapse- or brain-related functions such as the regulation of synaptic vesicle cycle (Atp6v1a, Napa), astrocyte morphology (Vim), and glutamate homeostasis (Slc3a2).ConclusionsWe have detected several consequences of epileptic seizures at the peptidomic level, as altered peptide abundances of proteins that regulate epilepsy-related cellular processes. Thus, our results indicate that analyzing brain ECF by in vivo microdialysis and omics techniques is useful for monitoring brain processes, and it can be an alternative method in the discovery and analysis of CNS disease markers besides peripheral fluid analysis.

Project description:Neurodegenerative brain disorders become more common in the aged. Most of these disorders are associated with or caused by selective death of certain neuronal subpopulations. The mechanisms underlying the differential vulnerability of certain neuronal populations are still largely unexplored and few neuroprotective treatments are available to date. Elucidation of these mechanisms may lead to a greater understanding of the pathogenesis and treatment of neurodegenerative diseases. Moreover, preconditioning by a short seizure confers neuroprotection following a subsequent prolonged seizure. Our goal is to identify pathways that confer vulnerability and resistance to neurotoxic conditions by comparing the basal and preconditioned gene expression profiles of three differentially vulnerable hippocampal neuron populations. Hippocampal CA1 and CA3 pyramidal neurons are highly susceptible to seizures and ischemia, whereas dentate gyrus granule cells are relatively resistant. A brief preconditioning seizure confers protection to the pyramidal cells. We will first determine gene expression profiles of untreated rat CA1 and CA3 pyramidal cells, and dentate granule cells, using laser capture microscopy to obtain region-specific neuronal mRNA. We will then determine the effect of a brief preconditioning seizure, which is neuroprotective in CA1 and CA3, on these expression profiles. We hypothesize that common molecular mechanisms exist in neurons that determine their susceptibility to seizure-induced injury. Intrinsic differences in gene expression exist between hippocampal glutamatergic CA1 and CA3 pyramidal neurons, on the one hand, and dentate granule cells on the other, which contribute to the greater susceptibility of pyramidal neurons to degeneration in experimental stroke and epilepsy. We specifically hypothesize that differences in basal energy metabolism genes may confer differential susceptibility to neurodegeneration produced by seizures and ischemia. Anesthetized animals will be sacrificed by decapitation, and frozen 10 micron sections will be lightly stained with cresyl violet to identify cell layers in the hippocampus. Approximately 1000 neurons from each of the three cell layers will be isolated by LCM. Poly-A RNA will be amplified using a modified Eberwine protocol. The quality of our aRNA will be evaluated by quantitative RT-PCR of GluR6 and KA2 mRNA levels before we send the samples to the Center for labeling and hybridization to Affymetrix rat 230A arrays. We will provide a one-round amplification cDNA product to the center for labeling and hybridization. This protocol is identical to a previously approved study by Jim Greene in our laboratory.

Project description:Injury of the CA1 subregion induced by a single injection of kainic acid (1M-CM-^WKA) is attenuated when juvenile animals (P20) have a history of two sustained neonatal seizures on P6 and P9. To identify gene candidates involved in the spatially protective effects produced by early life conditioning seizures, we profiled and compared the transcriptomes of CA1 subregions from control, 1M-CM-^WKA, and 3M-CM-^WKA treated animals. More genes were regulated following 3M-CM-^WKA (9.6%) than after 1M-CM-^WKA (7.1%). Following 1M-CM-^WKA, genes supporting oxidative stress, growth, development, inflammation, and neurotransmission were upregulated (e.g., Cacng1, Nadsyn1, Kcng1, Aven, S100a4, GFAP, Vim, Hrsp12, Grik1). After 3M-CM-^WKA, protective genes were differentially over-expressed (e.g., Cat, Gpx7, GAD1, Hspa12A, Foxn1, adenosine A1 receptor, Ca2+ adaptor and homeostatic proteins, Cacnb4, Atp2b2, anti-apoptotic Bcl-2 gene members, intracellular trafficking protein, Grasp, suppressor of cytokine signaling (Socs3)). Distinct anti-inflammatory interleukins not observed in adult tissues (e.g., IL6 transducer, IL23 and IL33 or their receptors (ILF2)) were also over-expressed. Several transcripts were validated by real-time polymerase chain reaction (QPCR) and immunohistochemistry. QPCR showed that casp 6 was increased after 1M-CM-^WKA but reduced after 3M-CM-^WKA; pro-inflammatory gene cox1 was either upregulated or unchanged after 1M-CM-^WKA but reduced by ~70% after 3M-CM-^WKA. Enhanced GFAP immunostaining following 1M-CM-^WKA was selectively attenuated in the CA1 subregion after 3M-CM-^WKA. The observed differential transcriptional responses may contribute to early life seizure-induced pre-conditioning and neuroprotection by reducing glutamate receptor-mediated Ca2+ permeability of the hippocampus and redirecting inflammatory and apoptotic pathways which could lead to new genetic therapies for epilepsy. The transcriptomes of the hippocampal CA1 region of Sprague Dawley 23-day-old male rats after 1 or 3 seizures induced by kainic acid injection were compared to the corresponding controls (injected with PBS) using Duke 27k oligonucleotide arrays.

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Microarray profile of seizure damage-refractory hippocampal CA3 in a mouse model of epileptic preconditioning.

Publications

Microarray profile of seizure damage-refractory hippocampal CA3 in a mouse model of epileptic preconditioning.

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