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Mice Lacking the β2 Adrenergic Receptor Have a Unique Genetic Profile Before and After Focal Brain Ischemia

ABSTRACT: The role of the beta2 adrenergic receptor (β2AR) after stroke is unclear as pharmacological manipulations of the β2AR have produced contradictory results. We previously showed that mice deficient in the β2AR (β2KO) had smaller infarcts compared to wild-type mice (FVB) after middle cerebral artery occlusion (MCAO), a model of stroke. To elucidate mechanisms of this neuroprotection, we evaluated changes in gene expression using microarrays comparing differences before and after MCAO, and differences between genotypes. Genes associated with inflammation and cell death were enriched after MCAO in both genotypes, and we identified several genes not previously shown to increase following ischemia (Ccl9, Gem, and Prg4). In addition to networks that were similar between genotypes, one network with a central node of G protein-coupled receptor and including biological functions carbohydrate metabolism, small molecule biochemistry and inflammation was identified in FVB mice but not in β2KO mice. Analysis of differences between genotypes revealed 11 genes differentially expressed by genotype in all conditions. We demonstrate greater Glo1 protein levels and lower Pmaip/Noxa mRNA levels in β2KO mice. As both genes are implicated in NFκB signaling, we measured p65 activity and tumor necrosis factor alpha (TNFα) levels 24h after MCAO. MCAO-induced p65 activation and post-ischemic TNFα production were both greater in FVB compared to β2KO mice. These results suggest that loss of β2AR signaling results in a neuroprotective phenotype in part due to decreased NFκB signaling, decreased inflammation, and decreased apoptotic signaling in the brain.

ORGANISM(S): Mus musculus

PROVIDER: GSE30655 | GEO | 2014/07/14

SECONDARY ACCESSION(S): PRJNA144603

REPOSITORIES: GEO

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Project description:Astrogliosis is a hallmark of the response to brain ischemia, comprised of changes in gene expression and morphology. Hsp72 protects from cerebral ischemia, and although several mechanisms of protection have been investigated, effects on astrocyte activation are unknown. To identify potential mechanisms of protection, gene expression was assessed in mice subjected to middle cerebral artery (MCAO) or sham surgery, of either wildtype (WT) or Hsp72-overexpressing (Hsp72Tg) mice. After stroke, both genotypes exhibited genes related to cell death, stress response, and immune response. Furthermore, genes indicative of astrocyte activation, including cytoskeletal proteins and cytokines, were upregulated. To measure astrocyte activation after stroke, detailed histological and morphological analyses were performed in the cortical penumbra after stroke using unbiased stereology. Consistent with other reports, we observed a marked and persistent increase in glial fibrillary acidic protein (GFAP ) as soon as 3 hours after MCAO. In contrast, vimentin immunoreactivity appeared 12-24 hours after stroke, peaked at 72 hours, and returned to baseline after 30 days. Surprisingly, no change in overall astrocyte number was observed based on glutamine synthetase (GS) immunoreactivity. To determine if Hsp72Tg mice exhibited altered astrocyte activation compared to WT controls, morphological evaluation by fractal analysis was used. Overexpression of Hsp72 reduced astrocyte cell area, arbor area, and to a lesser extent fractal dimension, 72 hours following stroke. In conclusion, in vivo overexpression of Hsp72 alters gene expression following stroke, including genes involved in astrocyte activation, and decreases astrocyte activation acutely following MCAO. Thus, modulation of astrogliosis may be a neuroprotective mechanism exerted by Hsp72 after ischemia. A total of 10 samples were analyzed, with 5 of each genotype, wildtype (WT) and Hsp72-overexpressing (Hsp72Tg) mice. Of the 5 in each group, 3 received middle cerebral artery occlusion (MCAO) and 2 received a sham surgery. The sham samples serve as the controls for the MCAO samples in each genotype. All samples were taken from the ischemic or control hemisphere 24 hours after surgery.

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Mice Lacking the β2 Adrenergic Receptor Have a Unique Genetic Profile Before and After Focal Brain Ischemia

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