Pathway and gene ontology based analysis of gene expression in a rat model of cerebral ischemic tolerance.
ABSTRACT Ischemic tolerance is a phenomenon whereby a sublethal ischemic insult [ischemic preconditioning (IPC)] provides robust protection against subsequent lethal ischemia. Activation of N-methyl-D-aspartate (NMDA) receptors and subsequent new gene transcription are required for tolerance. We utilized the NMDA antagonist, MK801, prior to the IPC stimulus to separate candidate genes from epiphenomenona. Rats were divided into four groups: vehicle/IPC (preconditioned), MK801/IPC (attenuated preconditioning), vehicle/sham (non-preconditioned), and MK801/sham (non-preconditioned). Hippocampi (5/group/time point) were harvested immediately after ischemia as well as 1, 4, and 24 h post-ischemia to profile gene expression patterns using microarray analyses. Extracted mRNAs were pooled and subsequently hybridized to Affymetrix arrays. In addition, groups of rats were sacrificed for Western blot analysis and histological studies. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and gene ontology (GO) analyses were used to identify functionally related groups of genes whose modulation was statistically significant, while hierarchical cluster analysis was used to visualize the fold expression within these groups. Significantly modulated pathways included: MAP kinase signaling pathway, Toll receptor pathway, TGF-beta signaling pathways, and pathways associated with ribosome function and oxidative phosphorylation. Our data suggest that the tolerant brain responds to subsequent ischemic stress by partially downregulating inflammatory and upregulating protein synthesis and energy metabolism pathways.
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ABSTRACT: Despite efforts to reduce mortality caused by stroke and perinatal asphyxia, these are still the 2(nd) largest cause of death worldwide in the age groups they affect. Furthermore, survivors of cerebral hypoxia-ischemia often suffer neurological morbidities. A better understanding of pathophysiological mechanisms in focal and global brain ischemia will contribute to the development of tailored therapeutic strategies. Similarly, insight in molecular pathways involved in preconditioning-induced brain protection will provide possibilities for future treatment. Microarray technology is a great tool for investigating large scale gene expression, and has been used in many experimental studies of cerebral ischemia and preconditioning to unravel molecular (patho-) physiology. However, the amount of data across microarray studies can be daunting and hard to interpret which is why we aim to provide a clear overview of available data in experimental rodent models. Findings for both injurious ischemia and preconditioning are reviewed under separate subtopics such as cellular stress, inflammation, cytoskeleton and cell signaling. Finally, we investigated the transcriptome signature of brain protection across preconditioning studies in search of transcripts that were expressed similarly across studies. Strikingly, when comparing genes discovered by single-gene analysis we observed only 15 genes present in two studies or more. We subjected these 15 transcripts to DAVID Annotation Clustering analysis to derive their shared biological meaning. Interestingly, the MAPK signaling pathway and more specifically the ERK1/2 pathway geared toward cell survival/proliferation was significantly enriched. To conclude, we advocate incorporating pathway analysis into all microarray data analysis in order to improve the detection of similarities between independently derived datasets.Brain research 04/2014; · 2.46 Impact Factor
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ABSTRACT: Ischemic preconditioning is an innate neuroprotective mechanism in which a sub-injurious ischemic exposure increases the brain's ability to withstand a subsequent, normally injurious ischemic insult. Part of ischemic preconditioning neuroprotection stems from an epigenetic reprogramming of the brain to a phenotype of ischemic tolerance, which results in a gene expression profile different from that observed in the non-injured and ischemia-injured brains. Such neuroprotective reprograming, activated by ischemic preconditioning, requires specific changes in DNA accessibility coordinated with activation of transcriptional activator and repressor proteins, which allows for expression of specific neuroprotective proteins despite a general repression of gene expression. In this review we examine the effects of injurious ischemia and ischemic preconditioning on the regulation of DNA methylation, histone post-translational modifications, and non-coding RNA expression. There is increasing interest in the role of epigenetics in disease pathobiology, and whether and how pharmacological manipulation of epigenetic processes may allow for ischemic neuroprotection. Therefore, a better understanding of the epigenomic determinants underlying the modulation of gene expression that lead to ischemic tolerance or cell death offers the promise of novel neuroprotective therapies that target global reprograming of genomic activity versus individual cellular signaling pathways.Journal of the American Society for Experimental NeuroTherapeutics 07/2013; · 5.38 Impact Factor
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ABSTRACT: Fetal asphyctic (FA) preconditioning is effective in attenuating brain damage incurred by a subsequent perinatal asphyctic insult. Unraveling mechanisms of this endogenous neuroprotection, activated by FA preconditioning, is an important step towards new clinical strategies for asphyctic neonates. Genomic reprogramming is thought to be, at least in part, responsible for the protective effect of preconditioning. Therefore we investigated whole genome differential gene expression in the preconditioned rat brain. FA preconditioning was induced on embryonic day 17 by reversibly clamping uterine circulation. Male control and FA offspring were sacrificed 96 h after FA preconditioning. Whole genome transcription was investigated with Affymetrix Gene1.0ST chip. Data were analyzed with the Bioconductor Limma package, which showed 53 down-regulated and 35 up-regulated transcripts in the FA-group. We validated these findings with RT-qPCR for adh1, edn1, leptin, rdh2, and smad6. Moreover, we investigated differences in gene expression across different brain regions. In addition, we performed Gene Set Enrichment Analysis (GSEA) which revealed 19 significantly down-regulated gene sets, mainly involved in neurotransmission and ion transport. 10 Gene sets were significantly up-regulated, these are mainly involved in nucleosomal structure and transcription, including genes such as mecp2. Here we identify for the first time differential gene expression after asphyctic preconditioning in fetal brain tissue, with the majority of differentially expressed transcripts being down-regulated. The observed down-regulation of cellular processes such as neurotransmission and ion transport could represent a restriction in energy turnover which could prevent energy failure and subsequent neuronal damage in an asphyctic event. Up-regulated transcripts seem to exert their function mainly within the cell nucleus, and subsequent Gene Set Enrichment Analysis suggests that epigenetic mechanisms play an important role in preconditioning induced neuroprotection.BMC Neuroscience 06/2013; 14(1):61. · 3.00 Impact Factor