MicroRNAs (miRNAs) are ~22 nucleotides long, noncoding RNAs that control cellular function by either degrading mRNAs or arresting their translation. To understand their functional significance in ischemic pathophysiology, we profiled miRNAs in adult rat brain as a function of reperfusion time after transient middle cerebral artery occlusion. Of the 238 miRNAs evaluated, 8 showed increased and 12 showed decreased expression at least at 4 out of 5 reperfusion time points studied between 3 h and 3 days compared with sham. Of those, 17 showed >5 fold change. Bioinformatics analysis indicated a correlation between miRNAs altered to several mRNAs known to mediate inflammation, transcription, neuroprotection, receptors function, and ionic homeostasis. Antagomir-mediated prevention of mir-145 expression led to an increased protein expression of its downstream target superoxide dismutase-2 in the postischemic brain. In silico analysis showed sequence complementarity of eight miRNAs induced after focal ischemia to 877 promoters indicating the possibility of noncoding RNA-induced activation of gene expression. The mRNA expression of the RNases Drosha and Dicer, cofactor Pasha, and the pre-miRNA transporter exportin-5, which modulate miRNA biogenesis, were not altered after transient middle cerebral artery occlusion. Thus, the present studies indicate a critical role of miRNAs in controlling mRNA transcription and translation in the postischemic brain.

Background and Purpose Long noncoding RNAs (lncRNAs) play a significant role in cellular physiology. We evaluated the effect of focal ischemia on the expression of 8,314 lncRNAs in rat cerebral cortex using microarrays. Methods Ischemia was induced by transient middle cerebral artery occlusion. Genomic and transcriptomic correlates of the stroke-responsive lncRNAs and the transcription factor binding sties in their promoters were evaluated with bioinformatics. Results 359 lncRNAs were upregulated (>2-fold) and 84 were downregulated (<0.5 fold) at 3h to 12h of reperfusion following MCAO compared to sham. 62 stroke-responsive lncRNAs showed >90% sequence homology with exons of protein-coding genes. Promoters of stroke-responsive lncRNA genes and their homologous protein-coding genes showed highly overlapping transcription factor binding sites. Despite presence of ORFs, lncRNAs did not form any product when subjected to in vitro translation. Conclusions Stroke significantly alters cerebral lncRNA expression profiles.

Recent studies showed that stroke extensively alters cerebral microRNA (miRNA) expression profiles and several miRNAs play a role in mediating ischemic pathophysiology. We currently evaluated the significance of miR-29c, a highly expressed miRNA in rodent brain that was significantly down-regulated after focal ischemia in adult rats as well as after oxygen-glucose deprivation in PC12 cells. Bioinformatics indicated that DNA methyltransferase 3a (DNMT3a) is a major target of miR-29c and co-transfection with premiR-29c prevented DNMT3a 3′UTR vector expression. In PC12 cells, treatment with premiR-29c prevented OGD-induced cell death (by 58±6%; p<0.05). Furthermore, treatment with antagomiR-29c resulted in a 46±5% cell death in PC12 cells. When rats were treated with premiR-29c and subjected to transient focal ischemia, post-ischemic miR-29c levels were restored and the infarct volume decreased significantly (by 34±6%; p<0.05) compared to control premiR treated group. DNMT3a siRNA treatment also significantly curtailed the post-OGD cell death in PC12 cells (by 54±6%; p<0.05) and decreased the post-ischemic infarct volume in rats (by 30±5%; p<0.05) compared to respective control siRNA treated groups. The miR-29c gene promoter showed specific binding sites for the transcription factor REST and the miR-29c promoter vector expression was curtailed when cotransfected with a REST expressing plasmid. Furthermore, treatment with REST siRNA prevented the post-ischemic miR-29c down-regulation and DNMT3a induction in PC12 cells and curtailed ischemic cell death (by 64±9%; p<0.05) compared to control siRNA treatment. These studies suggest that miR-29c is a pro-survival miRNA and its down-regulation is a promoter of ischemic brain damage by acting through its target DNMT3a. Furthermore, REST is an upstream transcriptional controller of miR-29c and curtailing REST induction prevents miR-29c down-regulation and ischemic neuronal death.

J. Neurochem. (2010) 113, 1685–1691. Abstract Cerebral gene expression is known to be significantly influenced by a sublethal ischemic event (pre‐conditioning; PC) that induces tolerance to future damaging ischemic events. Small non‐coding RNAs known as microRNAs (miRNAs) were recently shown to control the mRNA translation. We currently profiled cerebral miRNAs in the cerebral cortex of rats subjected to PC. The miRNAome reacted quickly and by 6 h following PC, levels of 51 miRNAs were altered (26 up‐ and 25 down‐regulated; > 1.5‐fold change). Twenty of these stayed at the altered level even at 3 days after PC. At least nine miRNAs showed > 5‐fold change at one or more time points between 6 h to 3 days after PC compared with sham. Bioinformatics analysis showed 2007 common targets of the miRNAs that were up‐regulated and 459 common targets of the miRNAs that were down‐regulated after PC. Pathways analysis showed that MAP‐kinase and Mammalian target of rapamycin (mTOR) signaling are the top two Kyoto Encyclopedia of Genes and Genomes pathways targeted by the up‐regulated miRNAs, and Wnt and GnRH signaling are the top two Kyoto Encyclopedia of Genes and Genomes pathways targeted by the down‐regulated miRNAs after PC. We hypothesize that alterations in miRNAs and their down‐stream mRNAs of signaling pathways might play a role in the induction of ischemic tolerance.

Background and Purpose The piwi-interacting RNA (piRNA) is the most predominant RNA species in eukaryotes. The piRNA are a class of non-coding (nc) RNA that bind and degrade the RNA formed by the transposons to control the transposon -induced gene mutations. The role of piRNA after focal ischemia is not yet evaluated. Methods We profiled 39,727 piRNAs in the cerebral cortex of adult rats subjected to transient focal ischemia using microarrays. The RT targets of stroke-responsive piRNAs were identified with bioinformatics. To understand how piRNA are controlled, we analyzed the transcription factor (TF) binding sites in the putative promoters of 10 representative stroke-responsive piRNAs. Results In the ipsilateral cortex of ischemic rats, 105 piRNAs showed altered expression (54 up- and 51 down-regulated; >2.5 fold) compared to sham. Twenty five of those showed >5-fold change. A bioinformatics search showed that the transposon targets of the highly stroke-responsive piRNAs are distributed among the 20 autosomal chromosomes and there is a redundancy in the targets between the piRNAs. Furthermore, the transposon targets were observed to be highly repetitious for each piRNA across the chromosome length. Of the 159 TFs observed to have binding sites in the piRNA gene promoters, 59% belonged to 20 major families indicating that TFs control stroke-responsive piRNAs in a redundant manner. Conclusions The present study is the first to show that many piRNAs are expressed in adult rodent brain and several of them respond to focal ischemia.

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LncRNAs (long non-coding RNAs) are thought to play a significant role in cellular homeostasis during development and disease by interacting with CMPs (chromatin-modifying proteins). We recently showed that following transient focal ischemia, the expression of many lncRNAs was altered significantly in rat brain. We currently analyzed whether focal ischemia also alters the association of lncRNAs with the CMPs Sin3A and coREST (corepressors of the RE-1 silencing transcription factor). RIP (RNA immunoprecipitation) combined with lncRNA microarray analysis showed that 177 of the 2497 lncRNAs expressed in rat cerebral cortex showed significantly increased binding to either Sin3A or coREST following ischemia compared with sham. Of these, 26 lncRNAs enriched with Sin3A and 11 lncRNAs enriched with coREST were also up-regulated in their expressions after ischemia. A majority of the lncRNAs enriched with these CMPs were intergenic in origin. Evaluation of the expression profiles of corresponding protein-coding genes showed that their expression levels correlate with those of the lncRNAs with which they shared a common locus. This is the first study to show that stroke-induced lncRNAs might associate with CMPs to modulate the post-ischemic epigenetic landscape.

MicroRNAs (miRNAs) are known to repress translation by binding to the 3’UTRs of mRNAs. Using bioinformatics, we recently reported that several miRNAs also have target sites in DNA particularly in the promoters of the protein-coding genes. To understand the functional significance of this phenomenon, we tested the effects of miR-324-3p binding to RelA promoter. In PC12 cells, co-transfection with premiR-324-3p induced a RelA promoter plasmid in a dose-dependent manner and this effect was lost when the miR-324-3p binding site in the promoter was mutated. PremiR-324-3p transfection also significantly induced the endogenous RelA mRNA and protein expression in PC12 cells. Furthermore, transfection with premiR-324-3p increased the levels of cleaved caspase-3 which is a marker of apoptosis. Importantly, the miR-324-3p effects were Ago2 mediated as Ago2 knockdown prevented RelA expression and cleavage of caspase-3. Thus, our studies show that miRNA-mediated transcriptional activation can be seen in PC12 cells which are neural in origin.