[Show abstract][Hide abstract] ABSTRACT: Exposure of the brain to brief, non-harmful seizures can activate protective mechanisms that temporarily generate a damage-refractory state. This process, termed epileptic tolerance, is associated with large-scale down-regulation of gene expression. Polycomb group proteins are master controllers of gene silencing during development that are re-activated by injury to the brain. Here we explored the transcriptional response of genes associated with polycomb repressor complex (PRC) 1 (Ring1A and Ring1B and Bmi1) and PRC2 (Ezh1, Ezh2 and Suz12), as well as additional transcriptional regulators Sirt1, Yy1 and Yy2, in a mouse model of status epilepticus. Findings were contrasted to changes after status epilepticus in mice previously given brief seizures to evoke tolerance. Real-time quantitative PCR showed status epilepticus prompted an early (1 h) increase in expression of several genes in PRC1 and PRC2 in the hippocampus, followed by down-regulation of many of the same genes at later times points (4 , 8 and 24 h). Spatio-temporal differences were found among PRC2 genes in epileptic tolerance, including increased expression of Ezh2, Suz12 and Yy2 relative to the normal injury response to status epilepticus. In contrast, PRC1 complex genes including Ring 1B and Bmi1 displayed differential down-regulation in epileptic tolerance. The present study characterizes polycomb group gene expression following status epilepticus and shows prior seizure exposure produces select changes to PRC1 and PRC2 composition that may influence differential gene expression in epileptic tolerance.
Full-text · Article · Feb 2015 · Frontiers in Neurology
[Show abstract][Hide abstract] ABSTRACT: Temporal lobe epilepsy is associated with large-scale, wide-ranging changes in gene expression in the hippocampus. Epigenetic changes to DNA are attractive mechanisms to explain the sustained hyperexcitability of chronic epilepsy. Here, through methylation analysis of all annotated C-phosphate-G islands and promoter regions in the human genome, we report a pilot study of the methylation profiles of temporal lobe epilepsy with or without hippocampal sclerosis. Furthermore, by comparative analysis of expression and promoter methylation, we identify methylation sensitive non-coding RNA in human temporal lobe epilepsy. A total of 146 protein-coding genes exhibited altered DNA methylation in temporal lobe epilepsy hippocampus (n = 9) when compared to control (n = 5), with 81.5% of the promoters of these genes displaying hypermethylation. Unique methylation profiles were evident in temporal lobe epilepsy with or without hippocampal sclerosis, in addition to a common methylation profile regardless of pathology grade. Gene ontology terms associated with development, neuron remodelling and neuron maturation were over-represented in the methylation profile of Watson Grade 1 samples (mild hippocampal sclerosis). In addition to genes associated with neuronal, neurotransmitter/synaptic transmission and cell death functions, differential hypermethylation of genes associated with transcriptional regulation was evident in temporal lobe epilepsy, but overall few genes previously associated with epilepsy were among the differentially methylated. Finally, a panel of 13, methylation-sensitive microRNA were identified in temporal lobe epilepsy including MIR27A, miR-193a-5p (MIR193A) and miR-876-3p (MIR876), and the differential methylation of long non-coding RNA documented for the first time. The present study therefore reports select, genome-wide DNA methylation changes in human temporal lobe epilepsy that may contribute to the molecular architecture of the epileptic brain.
[Show abstract][Hide abstract] ABSTRACT: Emerging data support roles for microRNA (miRNA) in the pathogenesis of various neurologic disorders including epilepsy. MicroRNA-134 (miR-134) is enriched in dendrites of hippocampal neurons, where it negatively regulates spine volume. Recent work identified upregulation of miR-134 in experimental and human epilepsy. Targeting miR-134 in vivo using antagomirs had potent anticonvulsant effects against kainic acid-induced seizures and was associated with a reduction in dendritic spine number. In the present study, we measured dendritic spine volume in mice injected with miR-134-targeting antagomirs and tested effects of the antagomirs on status epilepticus triggered by the cholinergic agonist pilocarpine. Morphometric analysis of over 6,400 dendritic spines in Lucifer yellow-injected CA3 pyramidal neurons revealed increased spine volume in mice given antagomirs compared to controls that received a scrambled sequence. Treatment of mice with miR-134 antagomirs did not alter performance in a behavioral test (novel object location). Status epilepticus induced by pilocarpine was associated with upregulation of miR-134 within the hippocampus of mice. Pretreatment of mice with miR-134 antagomirs reduced the proportion of animals that developed status epilepticus following pilocarpine and increased animal survival. In antagomir-treated mice that did develop status epilepticus, seizure onset was delayed and total seizure power was reduced. These studies provide in vivo evidence that miR-134 regulates spine volume in the hippocampus and validation of the seizure-suppressive effects of miR-134 antagomirs in a model with a different triggering mechanism, indicating broad conservation of anticonvulsant effects.
Full-text · Article · May 2014 · Brain Structure and Function
[Show abstract][Hide abstract] ABSTRACT: Prolonged seizures (status epilepticus, SE) can cause neuronal death within brain regions such as the hippocampus. This may contribute to impairments in cognitive functioning and trigger or exacerbate epilepsy. Seizure-induced neuronal death is mediated, at least in part, by apoptosis-associated signaling pathways. Indeed, mice lacking certain members of the potently proapoptotic BH3-only subfamily of Bcl-2 proteins are protected against hippocampal damage caused by status epilepticus. The recently identified BH3-only protein Bcl-2-modifying factor (Bmf) normally interacts with the cytoskeleton, but upon certain cellular stresses, such as loss of extracellular matrix adhesion or energy crisis, Bmf relocalizes to mitochondria, where it can promote Bax activation and mitochondrial dysfunction. Although Bmf has been widely reported in the hematopoietic system to exert a proapoptotic effect, no studies have been undertaken in models of neurological disorders. To examine whether Bmf is important for seizure-induced neuronal death, we studied Bmf induction after prolonged seizures induced by intra-amygdala kainic acid (KA) in mice, and examined the effect of Bmf-deficiency on seizures and damage caused by SE. Seizures triggered an early (1-8 h) transcriptional activation and accumulation of Bax in the cell death-susceptible hippocampal CA3 subfield. Bmf mRNA was biphasically upregulated beginning at 1 h after SE and returning to normal by 8 h, while again being found elevated in the hippocampus of epileptic mice. Bmf upregulation was prevented by Compound C, an inhibitor of adenosine monophosphate-activated protein kinase, indicating Bmf expression may be induced in response to bioenergetic stress. Bmf-deficient mice showed normal sensitivity to the convulsant effects of KA, but, surprisingly, displayed significantly more neuronal death in the hippocampal CA1 and CA3 subfields after SE. These are the first studies investigating Bmf in a model of neurologic injury, and suggest that Bmf may protect neurons against seizure-induced neuronal death in vivo.
[Show abstract][Hide abstract] ABSTRACT: 14-3-3 proteins are ubiquitous molecular chaperones that are abundantly expressed in the brain where they regulate cell functions including metabolism, the cell cycle and apoptosis. Brain levels of several 14-3-3 isoforms are altered in diseases of the nervous system, including epilepsy. The 14-3-3 zeta (ζ) isoform has been linked to endoplasmic reticulum (ER) function in neurons, with reduced levels provoking ER stress and increasing vulnerability to excitotoxic injury. Here we report that transgenic overexpression of 14-3-3ζ in mice results in selective changes to the unfolded protein response pathway in the hippocampus, including down-regulation of glucose-regulated proteins 78 and 94, activating transcription factors 4 and 6, and Xbp1 splicing. No differences were found between wild-type mice and transgenic mice for levels of other 14-3-3 isoforms or various other 14-3-3 binding proteins. 14-3-3ζ overexpressing mice were potently protected against cell death caused by intracerebroventricular injection of the ER stressor tunicamycin. 14-3-3ζ overexpressing mice were also potently protected against neuronal death caused by prolonged seizures. These studies demonstrate that increased 14-3-3ζ levels protect against ER stress and seizure-damage despite down-regulation of the unfolded protein response. Delivery of 14-3-3ζ may protect against pathologic changes resulting from prolonged or repeated seizures or where injuries provoke ER stress.
[Show abstract][Hide abstract] ABSTRACT: Brief seizures (epileptic/seizure preconditioning) are capable of activating endogenous protective pathways in the brain which can temporarily generate a damage-refractory state against subsequent and otherwise harmful episodes of prolonged seizures (tolerance). Altered expression of microRNAs, a class of non-coding RNAs that function post-transcriptionally to regulate mRNA translation has recently been implicated in the molecular mechanism of epileptic tolerance. Here we characterized the effect of seizure preconditioning induced by low-dose systemic kainic acid on microRNA expression in the hippocampus of mice. Seizure preconditioning resulted in up-regulation of 25 mature microRNAs in the CA3 subfield of the mouse hippocampus, with the highest levels detected for miR-184. This finding was supported by real time PCR and in situ hybridization showing increased neuronal miR-184 levels and a reduction in protein levels of a miR-184 target. Inhibiting miR-184 expression in vivo resulted in the emergence of neuronal death after preconditioning seizures and increased seizure-induced neuronal death following status epilepticus in previously preconditioned animals, without altered electrographic seizure durations. The present study suggests miRNA up-regulation after preconditioning may contribute to development of epileptic tolerance and identifies miR-184 as a novel contributor to neuronal survival following both mild and severe seizures.
No preview · Article · Jul 2012 · Experimental Neurology
[Show abstract][Hide abstract] ABSTRACT: Temporal lobe epilepsy is a common, chronic neurological disorder characterized by recurrent spontaneous seizures. MicroRNAs (miRNAs) are small, noncoding RNAs that regulate post-transcriptional expression of protein-coding mRNAs, which may have key roles in the pathogenesis of neurological disorders. In experimental models of prolonged, injurious seizures (status epilepticus) and in human epilepsy, we found upregulation of miR-134, a brain-specific, activity-regulated miRNA that has been implicated in the control of dendritic spine morphology. Silencing of miR-134 expression in vivo using antagomirs reduced hippocampal CA3 pyramidal neuron dendrite spine density by 21% and rendered mice refractory to seizures and hippocampal injury caused by status epilepticus. Depletion of miR-134 after status epilepticus in mice reduced the later occurrence of spontaneous seizures by over 90% and mitigated the attendant pathological features of temporal lobe epilepsy. Thus, silencing miR-134 exerts prolonged seizure-suppressant and neuroprotective actions; determining whether these are anticonvulsant effects or are truly antiepileptogenic effects requires additional experimentation.
[Show abstract][Hide abstract] ABSTRACT: Bioinformatic analysis of genes impacted by significantly down-regulated miRNAs in human TLE-HS. Gene ontology analysis showing cellular component, biological process and molecular functions of the predicted mRNA targets of down-regulated miRNAs in human TLE-HS tissue (MS Word).
[Show abstract][Hide abstract] ABSTRACT: Hippocampal sclerosis (HS) is a common pathological finding in patients with temporal lobe epilepsy (TLE) and is associated with altered expression of genes controlling neuronal excitability, glial function, neuroinflammation and cell death. MicroRNAs (miRNAs), a class of small non-coding RNAs, function as post-transcriptional regulators of gene expression and are critical for normal brain development and function. Production of mature miRNAs requires Dicer, an RNAase III, loss of which has been shown to cause neuronal and glial dysfunction, seizures, and neurodegeneration. Here we investigated miRNA biogenesis in hippocampal and neocortical resection specimens from pharmacoresistant TLE patients and autopsy controls. Western blot analysis revealed protein levels of Dicer were significantly lower in certain TLE patients with HS. Dicer levels were also reduced in the hippocampus of mice subject to experimentally-induced epilepsy. To determine if Dicer loss was associated with altered miRNA processing, we profiled levels of 380 mature miRNAs in control and TLE-HS samples. Expression of nearly 200 miRNAs was detected in control human hippocampus. In TLE-HS samples there was a large-scale reduction of miRNA expression, with 51% expressed at lower levels and a further 24% not detectable. Primary transcript (pri-miRNAs) expression levels for several tested miRNAs were not different between control and TLE-HS samples. These findings suggest loss of Dicer and failure of mature miRNA expression may be a feature of the pathophysiology of HS in patients with TLE.
[Show abstract][Hide abstract] ABSTRACT: Dicer immunoreactive bands at 75 kD in human and experimental TLE-HS. Western blots showing the presence of a cleaved band of Dicer in experimental and human epilepsy (MS Word).
[Show abstract][Hide abstract] ABSTRACT: Upregulated miRNAs in human TLE-HS tissue. Graph showing the expression levels of miRNAs in human TLE-HS tissue for which expression was non-significantly higher than in controls (MS Word).
[Show abstract][Hide abstract] ABSTRACT: Top 40 miRNAs expressed in autopsy control human hippocampus. Table listing the 40 mature miRNAs in autopsy control human hippocampus most enriched based on Ct value (MS Word).
[Show abstract][Hide abstract] ABSTRACT: Effects of simulated autopsy delay on hippocampal miRNA levels and miRNA biogenesis components. Results of simulated autopsy delay experiments using mouse brain. RT-PCR analysis of three miRNAs and Western blots showing effects on protein levels of Dicer, Drosha and Ago2 (MS Word).
[Show abstract][Hide abstract] ABSTRACT: When an otherwise harmful insult to the brain is preceded by a brief, noninjurious stimulus, the brain becomes tolerant, and the resulting damage is reduced. Epileptic tolerance develops when brief seizures precede an episode of prolonged seizures (status epilepticus). MicroRNAs (miRNAs) are small, noncoding RNAs that function as post-transcriptional regulators of gene expression. We investigated how prior seizure preconditioning affects the miRNA response to status epilepticus evoked by intra-amygdalar kainic acid in mice. The miRNA was extracted from the ipsilateral CA3 subfield 24 hours after focal-onset status epilepticus in animals that had previously received either seizure preconditioning (tolerance) or no preconditioning (injury), and mature miRNA levels were measured using TaqMan low-density arrays. Expression of 21 miRNAs was increased, relative to control, after status epilepticus alone, and expression of 12 miRNAs was decreased. Increased miR-132 levels were matched with increased binding to Argonaute-2, a constituent of the RNA-induced silencing complex. In tolerant animals, expression responses of >40% of the injury-group-detected miRNAs differed, being either unchanged relative to control or down-regulated, and this included miR-132. In vivo microinjection of locked nucleic acid-modified oligonucleotides (antagomirs) against miR-132 depleted hippocampal miR-132 levels and reduced seizure-induced neuronal death. Thus, our data strongly suggest that miRNAs are important regulators of seizure-induced neuronal death.
Full-text · Article · Sep 2011 · American Journal Of Pathology
[Show abstract][Hide abstract] ABSTRACT: Crosslinking and the resultant changes in mechanical properties have been shown to influence cellular activity within collagen biomaterials. With this in mind, we sought to determine the effects of crosslinking on both the compressive modulus of collagen-glycosaminoglycan scaffolds and the activity of osteoblasts seeded within them. Dehydrothermal, 1-ethyl-3-3-dimethyl aminopropyl carbodiimide and glutaraldehyde crosslinking treatments were first investigated for their effect on the compressive modulus of the scaffolds. After this, the most promising treatments were used to study the effects of crosslinking on cellular attachment, proliferation, and infiltration. Our experiments have demonstrated that a wide range of scaffold compressive moduli can be attained by varying the parameters of the crosslinking treatments. 1-Ethyl-3-3-dimethyl aminopropyl carbodiimide and glutaraldehyde treatments produced the stiffest scaffolds (fourfold increase when compared to dehydrothermal crosslinking). When cells were seeded onto the scaffolds, the stiffest scaffolds also showed increased cell number and enhanced cellular distribution when compared to the other groups. Taken together, these results indicate that crosslinking can be used to produce collagen-glycosaminoglycan scaffolds with a range of compressive moduli, and that increased stiffness enhances cellular activity within the scaffolds.
Full-text · Article · May 2011 · Tissue Engineering Part A