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Network analysis of differentially expressed genes in a rat model of neonatal HI encephalopathy +/- antioxidant

ABSTRACT: Neonatal hypoxic-ischemic (HI) encephalopathy can lead to severe brain damage, and is a common cause of neurological handicaps in adulthood. The modified Levine method (Rice model) has been widely used as an animal model of this condition, which can be rescued by the administration of an antioxidant such as 3-methyl-1-phenyl-2-pyrazolin-5-one (MCI-186). In the present study, by using the Rice model, we performed comprehensive gene expression and gene network analyses of neonatal HI brain insult with and without MCI-186 administration via a DNA microarray to help elucidate the molecular events responsible for the selective vulnerability of neurons to an HI insult and the underlying mechanisms of the effect of MCI-186 on the pathophysiological events. A large difference in gene expression was observed between the Rice model and the control. By performing a clustering analysis of the gene expression pattern after the HI brain insult, we found the following 3 clusters: (i) a cluster of strongly upregulated genes mainly consisting of genes related to immune responses; (ii) a cluster of mildly upregulated genes mainly consisting of genes related to cellular movement, growth and proliferation, and cell death; and (iii) a cluster of downregulated genes mainly consisting of genes related to neuronal activity. The effect of MCI-186 administration on gene expression was much less than and contrary to that of the HI brain insult. The genes upregulated and downregulated on MCI-186 administration were closely related to neuronal activity and immune responses, respectively, thereby reflecting the protective effect of MCI-186 on an HI brain insult.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE18356 | GEO | 2010/03/05

SECONDARY ACCESSION(S): PRJNA118109

REPOSITORIES: GEO

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Project description:Hypoxic-ischemic (HI) injury in the developing brain is a common cause of disability in children, and there are no effective treatments at this time. Exposure to sublethal hypoxic conditions (hypoxic preconditioning) 24 hours prior to hypoxic-ischemic insult is protective in the developing rat model. We have observed protective effects on brain histopathology and on long-term sensory-motor behavioral tasks. Changes in gene expression are thought to underlie this protective effect. By comparing gene expression in rats subjected to hypoxic preconditioning or sham conditioning at several time points from 0 to 24 hrs after preconditioning, we should gain insight into the mechanisms underlying these neuroprotective effects and may identify targets for therapeutic intervention. The aim of this study is to determine the effect of hypoxic preconditioning on global gene expression, and, in littermates, to examine the effect of hypoxic preconditioning 24 h prior to hypoxic-ischemic insult on brain histopathology. We hypothesize that changes in gene expression underlie the protective effect of hypoxic preconditioning against subsequent hypoxic-ischemic insult. Gene expression will be examined in two groups, 1) preconditioned and 2) sham controls, at 4 time points. On postnatal day 6, preconditioned animals are exposed to normothermic hypoxia for 3 hrs (8.0% oxygen, 36 degrees C), and sham animals are simultaneouosly exposed to normoxia at 36 degrees C. Animals are then returned to their dams until euthanized at 4 time points (0h, 2h, 8h, and 24h later). Five brains/group/timepoint will be used, with an equal number of males and females in each group. Brains are removed and dissected on ice. Cerebral cortex is dissected from both hemispheres and rapidly frozen on dry ice. Total RNA is isolated using the QIAGEN RNeasy Protect Maxi Kit. Littermates of these animals will be exposed to hypoxic preconditioning or sham preconditioning and subjected to hypoxic-ischemic injury 24 h later. These animals are euthanized at postnatal day 14 for histopathologic evaluation of injury.

Project description:Hypoxic-ischemic (HI) injury in the developing brain is a common cause of disability in children, and there are no effective treatments at this time. Erythropoietin (EPO) has recently gained interest as a neuroprotective drug, and EPO and its receptor are expressed within the central nervous system. We have recently shown that pretreatment with EPO markedly reduced brain injury caused by unilateral hypoxic-ischemic insult in 7 day old mice. EPO did not reduce early signs of neuronal injury at 6 hours, but significantly protected the neonatal brain when assessed 24 hours and 7 days after HI. The mechanism of this delayed protection is unclear, but is thought to involve transcription of neuroprotective genes, possibly subsequent to activation of NFkB. By comparing gene expression in EPO- and vehicle- (VEH) treated mice after HI, we should gain insight into the mechanisms underlying the neuroprotective effects of EPO and may identify additional targets for therapeutic interventions. We will compare gene expression patterns in 7-day old mouse forebrain after 1) VEH pretreatment plus sham surgery, 2) VEH pretreatment plus HI, and 3) EPO pretreatment plus HI. We will thus identify genes induced by HI in the developing brain and characterize changes in gene expression caused by EPO pretreatment. We will use the model of neonatal hypoxic-ischemic injury and EPO treatment parameters that were used in our prior studies demonstrating neuroprotection. Based on the time-course of neuroprotection defined in our prior study and the pharmacokinetic profile of EPO, we will examine gene expression 18 hours after HI. We hypothesize that changes in gene expression after EPO pretreatment underlie the neuroprotective effects of this cytokine after neonatal hypoxic ischemic injury. We will examine gene expression in 3 groups: 1) 1) VEH pretreatment + sham surgery, 2) VEH pretreatment + HI, and 3) EPO pretreatment + HI. EPO (5U/g, i.p.) or VEH was injected in 7 day old mice, drawn from 4 litters, with 3 to 4 pups per treatment group in each litter. One hour later, the right common carotid artery was ligated under isoflurane anesthesia, animals were allowed to recover for 90 min and were then placed in hypoxic chambers (10% oxygen, balance nitrogen) for 50 min. The animals subjected to sham surgery received isoflurane anesthesia for a comparable period, incision and dissection to visualize the common carotid artery, but no ligation and no hypoxia. Eighteen hrs later, animals were anesthetized with isoflurane and the right hemisphere was rapidly dissected and placed in RNA Later (Qiagen) at 4C. Total RNA was isolated using an RNeasy lipid tissue mini kit (QIAzol lysis and RNeasy purification, Qiagen). RNA concentrations were determined spectrophotometrically and an aliquot of each sample was examined by gel electrophoresis to screen for degradation. Samples were stored at -80C. After quality control screening, we selected 5 male and 5 female samples per treatment group (extra samples were reserved). We plan to pool 1 male and 1 female for each microarray sample and we plan to run 5 microarrays from each treatment group, for a total of 15 microarrays. We would like to have Agilent Bioanalyzer quality control assays on the individual samples carried out by the consortium before pooling. We will send 10 micrograms of each sample for Agilent QC and subsequent pooling of equimolar amounts. We would like to use Affymetrix mouse gene chips (please advise which specific chips are available; are you using the GeneChip Mouse Expression array 430A or the GeneChip Mouse Genome 430 2.0 Array?).

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Network analysis of differentially expressed genes in a rat model of neonatal HI encephalopathy +/- antioxidant

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