Alterations in miRNA Levels in the Dentate Gyrus in Epileptic Rats

Abstract

The aim of this study was to characterize changes in miRNA expression in the epileptic dentate gyrus. Status epilepticus evoked by amygdala stimulation was used to induce epilepsy in rats. The dentate gyri were isolated at 7 d, 14 d, 30 d and 90 d after stimulation (n=5). Sham-operated time-matched controls were prepared for each time point (n=5). The miRNA expression was evaluated using Exiqon microarrays. Additionally, mRNA from the same animals was profiled using Affymetrix microarrays. We detected miRNA expression signatures that differentiate between control and epileptic animals. Significant changes in miRNA expression between stimulated and sham operated animals were observed at 7 and 30 d following stimulation. Moreover, we found that there are ensembles of miRNAs that change expression levels over time. Analysis of the mRNA expression from the same animals revealed that the expression of several mRNAs that are potential targets for miRNA with altered expression level is regulated in the expected direction. The functional characterization of miRNAs and their potential mRNA targets indicate that miRNA can participate in several molecular events that occur in epileptic tissue, including immune response and neuronal plasticity. This is the first report on changes in the expression of miRNA and the potential functional impact of these changes in the dentate gyrus of epileptic animals. Complex changes in the expression of miRNAs suggest an important role for miRNA in the molecular mechanisms of epilepsy.

Epileptogenesis

“…miR-132, a miRNA that influences neuronal morphology by increasing dendritic outgrowth and arborization, and participating in regulation of spine density, is enriched in neurons and consistently up-regulated following epileptogenic stimuli (Jovičić et al 2013). Recently, Bot et al (2013) made an attempt to predict the functional impact of changes in miRNA expression during epileptogenesis by analyzing the expression of their potential mRNA targets. The data revealed that the protein products of miRNA-regulated mRNAs were involved in different types of molecular processes, including the regulation of transcription, second messenger signaling, ion homeostasis, immune response, response to wounding, and regulation of cell death (Bot et al 2013).…”

“…Recently, Bot et al (2013) made an attempt to predict the functional impact of changes in miRNA expression during epileptogenesis by analyzing the expression of their potential mRNA targets. The data revealed that the protein products of miRNA-regulated mRNAs were involved in different types of molecular processes, including the regulation of transcription, second messenger signaling, ion homeostasis, immune response, response to wounding, and regulation of cell death (Bot et al 2013). The significance of these complex changes in the expression of miRNAs during epileptogenesis is still difficult to interpret, and will require gathering more information on the function miRNA expression in the brain tissue and in-depth knowledge on the targets of each miRNA.…”

MicroRNA and epilepsy

“…This includes up-regulation of miR-146a and miR-132, as well as miR-9 and miR-99a [18], miR-27a and miR-203 [19] and miR-135a [21]. From those down-regulated, experimental models also detected miR-30a/b, miR-138, miR-324 and miR-330 [20] and miR-187 [21]. Nevertheless, this represents only ∼20% of the total regulated in human epilepsy.…”

“…Indeed, up- and down-regulated miRNAs may target the same genes in epilepsy [21]; without protein data the outcome is not possible to predict. The recent study by Bot et al offered an improved approach, combining mRNA data with miRNA to support functional targeting [20]. Ago2 pull-down studies can provide critical direct evidence that a miRNA is “functional”.…”

MicroRNAs as biomarkers in molecular diagnosis of refractory epilepsy

“…Researchers suppose that such heterogeneity may be the result of the influence exerted by epilepsyinduced brain tissue damage to miRNA detection, thus choosing to conduct miRNA profiling in brain tissues extracted at least 2 months (chronic stage) after epileptic seizures. Four animal-based studies utilizing gene chips to identify miRNA expression, respectively conducted by Song et al [26] Hu et al [27] Bot et al [28] and Gorter et al [29], together reported about 25 differentially expressed miRNAs. Those mentioned in more than one of the studies include 14 up-regulated miRNAs and 9 down-regulated miRNAs.…”