Altered Expression of Long Noncoding RNAs in Blood After Ischemic Stroke and Proximity to Putative Stroke Risk Loci

A Functional Polymorphism rs145204276 in the Promoter of Long Noncoding RNA GAS5 Is Associated with an Increased Risk of Ischemic Stroke

Long noncoding RNAs (lncRNAs) play crucial roles in the regulation of pathological process of ischemic stroke (IS) via affecting cell apoptosis, inflammation, cell death, and angiogenesis. LncRNA growth arrest-specific 5 (GAS5) was observed to be up-regulated in IS, acting as a competing endogenous RNA for miR-137 to mediate the Notch1 signaling pathway. In this study, we aimed to whether an insertion/deletion polymorphism (rs145204276) in the promoter of GAS5 was related to the risk of IS. The rs145204276 was genotyped using polymerase chain reaction (PCR)-polyacrylamide gel electrophoresis in 509 patients with IS and 668 healthy controls with frequencies matched to cases regarding age, gender, living area, and ethnicity. The GAS5 expression levels were determined using qPCR and relative luciferase activity was measured using the Dual Luciferase assay system. The presence of del/del genotype and del allele was associated with an increased risk of IS [del/del versus ins/ins: adjusted odds ratio (OR) = 2.06, 95% confidence interval (CI): 1.37-3.11; recessive model: adjusted OR = 2.07, 95% CI: 1.41-3.04; del versus ins: adjusted OR = 1.31, 95% CI: 1.08-1.57]. Results from logistic regression analysis identified risk factors for IS, including hypertension, total cholesterol, triglyceride, low-density lipoprotein cholesterol, and rs145204276 del/del genotype. Furthermore, patients carrying rs145204276 del/del genotype had significantly higher levels of GAS5 and cells transfected with rs145204276 del allele exhibited a larger increase in luciferase activity. These findings indicate that rs145204276 del allele exhibited a significant association with an increased IS susceptibility by elevating the transcriptional activity and subsequently enhancing the expression of lncRNA GAS5.

Differential long noncoding RNA expressions in peripheral blood mononuclear cells for detection of acute ischemic stroke

Long noncoding RNAs (lncRNAs) have been highlighted to be involved in the pathological process of ischemic stroke (IS). The purpose of the present study was to investigate the expression profile of lncRNAs in peripheral blood mononuclear cells (PBMCs) of acute IS patients and to explore their utility as biomarkers of IS. Distinctive expression patterns of PBMC lncRNAs were identified by an lncRNA microarray and individual quantitative real-time PCR (qRT-PCR) in four independent sets for 206 IS, 179 healthy controls (HCs), and 55 patients with transient ischemic attack (TIA). A biomarker panel (lncRNA-based combination index) was established using logistic regression. LncRNA microarray analysis showed 70 up-regulated and 128 down-regulated lncRNAs in IS patients. Individual qRT-PCR validation demonstrated that three lncRNAs (linc-DHFRL1-4, SNHG15, and linc-FAM98A-3) were significantly up-regulated in IS patients compared with HCs and TIA patients. Longitudinal analysis of lncRNA expression up to 90 days after IS showed that linc-FAM98A-3 normalized to control levels by day 7, while SNHG15 remained increased, indicating the ability of lncRNAs to monitor IS dynamics. Receiver-operating characteristic (ROC) curve analysis showed that the lncRNA-based combination index outperformed serum brain-derived neurotrophic factor (BDNF) and neurone-specific enolase (NSE) in distinguishing IS patients from TIA patients and HCs with areas under ROC curve of more than 0.84. Furthermore, the combination index increased significantly after treatment and was correlated with neurological deficit severity of IS. The panel of these altered lncRNAs was associated with acute IS and could serve as a novel diagnostic method.

Altered Long Non-Coding RNA Transcriptomic Profiles in Ischemic Stroke

A previous study described the important regulatory roles of microRNAs (miRNAs) in ischemic stroke. However, the functional significance of long non-coding RNA (lncRNAs) in ischemic stroke was largely unknown. This study aimed to identify lncRNA profiling and elucidate the regulatory mechanisms in the pathophysiology of stroke. RNA sequencing was performed on the blood of three ischemic stroke patients and three normal controls. Differential expression analysis was used to identify differentially expressed lncRNAs (DElncRNAs) and mRNAs (DEmRNAs). After further correlation and co-expression analysis, the corresponding co-expression networks and miRN-lncRNA-mRNA interaction network were then constructed. The expression of DElncRNAs and DEmRNAs was verified in Gene Expression Omnibus. RNA sequencing and subsequent bioinformatics analysis produced a total of 61 DElncRNAs (14 upregulated and 47 downregulated) and 673 DEmRNAs (432 upregulated and 241 downregulated). LOC105372881 and LOC101929707 were the most highly increased and decreased lncRNAs in ischemic stroke. LncRNA-mRNA co-expression networks were constructed according to 3,008 positively co-expressed and 607 negatively co-expressed lncRNA-mRNA pairs. The DElncRNAs may play roles in the pathways of glycolysis/gluconeogenesis, arrhythmogenic right ventricular cardiomyopathy, adherens junction, lysosome, and hematopoietic cell lineage by regulating their co-expressed mRNAs. Combined with previous data, a miRNA-lncRNA-mRNA interaction network for ischemic stroke was constructed. Based on GSE22255, the expression of six DElncRNAs (CEBPA-AS1, LINC00884, HCG27, MATN1-AS1, HCG26, and LINC01184) and 11 DEmRNAs (TREML4, AHSP, PI3, TESC, ANXA3, OAS1, OAS2, IFI6, ISG15, IFI44L, and LY6E) was similar to the current sequencing data. This study is the first to identify blood lncRNAs in human ischemic stroke using RNA sequencing. The findings may be the foundation for understanding the potential role of lncRNAs in ischemic stroke.

Pathophysiology of Long Non-coding RNAs in Ischemic Stroke

Stroke is a neurological disease with high disability and fatality rates, and ischemic stroke accounts for 75% of all stroke cases. The underlying pathophysiologic processes of ischemic stroke include oxidative stress, toxicity of excitatory amino acids, excess calcium ions, increased apoptosis and inflammation. Long non-coding RNAs (lncRNAs) may participate in the regulation of the pathophysiologic processes of ischemic stroke as indicated by altered expression of lncRNAs in blood samples of acute ischemic stroke patients, animal models of focal cerebral ischemia and oxygen-glucose deprivation (OGD) cell models. Because of the potentially important role, lncRNAs might be useful as biomarkers for the diagnosis, treatment and prognosis of ischemic stroke. This article reviews the functions of lncRNAs in different pathophysiology events of ischemic stroke with a focus on specific lncRNAs that may underlie ischemic stroke pathophysiology and that could therefore serve as potential diagnostic biomarkers and therapeutic targets.

Shifts in Leukocyte Counts Drive the Differential Expression of Transcriptional Stroke Biomarkers in Whole Blood

Our group recently identified a panel of ten genes whose RNA expression levels in whole blood have utility for detection of stroke. The purpose of this study was to determine the mechanisms by which these genes become differentially expressed during stroke pathology. First, we assessed the transcriptional distribution of the ten genes across the peripheral immune system by measuring their expression levels on isolated neutrophils, monocytes, B-lymphocytes, CD-4+ T-lymphocytes, CD-8+ T-lymphocytes, and NK-cells generated from the blood of healthy donors (n = 3). Then, we examined the relationship between the whole-blood expression levels of the ten genes and white blood cell counts in a cohort of acute ischemic stroke patients (n = 36) and acute stroke mimics (n = 15) recruited at emergency department admission. All ten genes displayed strong patterns of lineage-specific expression in our analysis of isolated leukocytes, and their whole-blood expression levels were correlated with white blood cell differential across the total patient population, suggesting that many of them are likely differentially expressed in whole blood during stroke as an artifact of stroke-induced shifts in leukocyte counts. Specifically, factor analysis inferred that over 50% of the collective variance in their whole-blood expression levels across the patient population was driven by underlying variance in white blood cell counts alone. However, the cumulative expression levels of the ten genes displayed a superior ability to discriminate between stroke patients and stroke mimics relative to white blood cell differential, suggesting that additional less prominent factors influence their expression levels which add to their diagnostic utility. These findings not only provide insight regarding this particular panel of ten genes, but also into the results of prior stroke transcriptomics studies performed in whole blood.

Long non-coding RNAs in ischemic stroke

Stroke is one of the leading causes of mortality and disability worldwide. Uncovering the cellular and molecular pathophysiological processes in stroke have been a top priority. Long non-coding (lnc) RNAs play critical roles in different kinds of diseases. In recent years, a bulk of aberrantly expressed lncRNAs have been screened out in ischemic stroke patients or ischemia insulted animals using new technologies such as RNA-seq, deep sequencing, and microarrays. Nine specific lncRNAs, antisense non-coding RNA in the INK4 locus (ANRIL), metastasis-associate lung adenocarcinoma transcript 1 (MALAT1), N1LR, maternally expressed gene 3 (MEG3), H19, CaMK2D-associated transcript 1 (C2dat1), Fos downstream transcript (FosDT), small nucleolar RNA host gene 14 (SNHG14), and taurine-upregulated gene 1 (TUG1), were found increased in cerebral ischemic animals and/or oxygen-glucose deprived (OGD) cells. These lncRNAs were suggested to promote cell apoptosis, angiogenesis, inflammation, and cell death. Our Gene Ontology (GO) enrichment analysis predicted that MEG3, H19, and MALAT1 might also be related to functions such as neurogenesis, angiogenesis, and inflammation through mechanisms of gene regulation (DNA transcription, RNA folding, methylation, and gene imprinting). This knowledge may provide a better understanding of the functions and mechanisms of lncRNAs in ischemic stroke. Further elucidating the functions and mechanisms of these lncRNAs in biological systems under normal and pathological conditions may lead to opportunities for identifying biomarkers and novel therapeutic targets of ischemic stroke.

Discovery of novel stroke-responsive lncRNAs in the mouse cortex using genome-wide RNA-seq

Long noncoding RNAs (lncRNAs) play major roles in regulating gene expression in mammals, but are poorly understood in ischemic stroke. Using a mouse model of transient focal ischemia, we applied RNA-seq to evaluate for the first time the unbiased, genome-wide expression of lncRNAs as a function of reperfusion time in the cerebral cortex. Focal ischemia was induced in adult male C57BL/6 mice followed by reperfusion for 6, 12 or 24h. Total RNA from ipsilateral cortices was used for Illumina sequencing and reads were mapped to the mouse reference genome (GRCm38). Annotated and novel transcript isoforms were identified and differential expression between the groups was estimated. We observed that the baseline expression of lncRNAs in the healthy cortex was low, but many were highly altered after stroke. Very few of these altered lncRNAs were previously annotated. A total of 259 lncRNA isoforms at 6h, 378 isoforms at 12h, and 217 isoforms at 24h of reperfusion were differentially expressed versus sham controls. Of these, 213, 322 and 171 isoforms at 6, 12 and 24h of reperfusion, respectively, were novel lncRNAs. Reperfusion time-point-specific analyses revealed that the lncRNAs reached peak expression levels at 6h of reperfusion. Positional analysis of ischemia-responsive lncRNAs with respect to ischemia-responsive protein-coding genes identified potential gene-regulatory relationships. Overall, this work shows that transient focal ischemia induces widespread changes in the expression of lncRNAs in the mouse cortex with distinct reperfusion time-point-dependent expression characteristics that may underlie progression of the ischemic pathophysiology. The detection of hundreds of novel ischemia-responsive lncRNAs marks the discovery of new disease-related genomic regions in the adult cortex and may help identify novel opportunities for therapeutic targeting.

Circular RNA Expression Profiles Alter Significantly in Mouse Brain After Transient Focal Ischemia

BACKGROUND AND PURPOSE

Circular RNAs (circRNAs) are a novel class of noncoding RNAs formed from many protein-coding genes by backsplicing. Although their physiological functions are not yet completely defined, they are thought to control transcription, translation, and microRNA levels. We investigated whether stroke changes the circRNAs expression profile in the mouse brain.

METHODS

Male C57BL/6J mice were subjected to transient middle cerebral artery occlusion, and circRNA expression profile was evaluated in the penumbral cortex at 6, 12, and 24 hours of reperfusion using circRNA microarrays and real-time PCR. Bioinformatics analysis was conducted to identify microRNA binding sites, transcription factor binding, and gene ontology of circRNAs altered after ischemia.

RESULTS

One thousand three-hundred twenty circRNAs were expressed at detectable levels mostly from exonic (1064) regions of the genes in the cerebral cortex of sham animals. Of those, 283 were altered (>2-fold) at least at one of the reperfusion time points, whereas 16 were altered at all 3 time points of reperfusion after transient middle cerebral artery occlusion compared with sham. Postischemic changes in circRNAs identified by microarray analysis were confirmed by real-time PCR. Bioinformatics showed that these 16 circRNAs contain binding sites for many microRNAs. Promoter analysis showed that the circRNAs altered after stroke might be controlled by a set of transcription factors. The major biological and molecular functions controlled by circRNAs altered after transient middle cerebral artery occlusion are biological regulation, metabolic process, cell communication, and binding to proteins, ions, and nucleic acids.

CONCLUSIONS

This is a first study that shows that stroke alters the expression of circRNAs with possible functional implication to poststroke pathophysiology.