Screening circular RNA expression patterns following focal cerebral ischemia in mice

Circ_0000115 Protects Against Cerebral Ischemia Injury by Suppressing Neuronal Apoptosis, Oxidative Stress and Inflammation by miR-1224-5p/Nos3 Axis In Vitro

Cerebral ischemia is a severe neurological disability related to neuronal apoptosis and cellular stress response. Circular RNAs (circRNAs) are emerging regulators of cerebral ischemia. Herein, this study proposed to probe the action of circ_0000115 in cerebral ischemia injury. The mouse neuroblastoma cells N2a and HT22 underwent oxygen-glucose deprivation (OGD) were used as a model of in vitro cerebral ischemia. Levels of genes and proteins were detected by qRT-PCR and western blotting. Cell proliferation and apoptosis were determined by EdU assay and flow cytometry. Western blotting was used to detect the protein level of pro-inflammatory factors. The oxidative stress injury was evaluated by detecting reactive oxygen species (ROS), malondialdehyde (MDA) and superoxide dismutase (SOD) generation. Dual-luciferase reporter and RIP assays were used to confirm the target relationship between miR-1224-5p and circ_0000115 or nitric oxide synthase 3 (NOS3). OGD exposure decreased circ_0000115 and NOS3 expression, and increased miR-1224-5p in N2a and HT22 cells in a time-dependent manner. Circ_0000115 silencing attenuated OGD-induced apoptosis, oxidative stress and inflammation in N2a and HT22 cells. Mechanistically, circ_0000115 directly sponged miR-1224-5p, which targeted NOS3. Furthermore, rescue experiments showed that miR-1224-5p overexpression abolished the neuroprotective effect of circ_0000115 in N2a and HT22 cells under OGD treatment. Besides that, silencing of miR-1224-5p protected N2a and HT22 cells against OGD-evoked injury, which was counteracted by NOS3 knockdown. Circ_0000115 protects N2a and HT22 cells against OGD-evoked neuronal apoptosis, inflammation, and oxidative stress via the miR-1224-5p/NOS3 axis, providing an exciting view of the pathogenesis of cerebral ischemia.

circ_0000018 downregulation peripherally ameliorates neuroprotection against acute ischemic stroke through the miR‑871/BCL2L11 axis

Acute ischemic stroke (AIS) is a common acute cerebrovascular disease. Circular RNAs (circRNAs) have been demonstrated to have critical functions in a wide range of physiological processes and disorders in humans. However, their precise function in ischemic stroke (IS) remains largely unknown. The present study explored the function and potential mechanisms of circ_0000018 in AIS in vivo and in vitro. The cerebral ischemia/reperfusion injury model was established in vivo and in vitro using the oxygen‑glucose deprivation (OGD/R) and transient middle cerebral artery occlusion (tMCAO) methods. Subsequently, the impact of circ_0000018 on cerebral ischemia/reperfusion injury was assessed using various techniques, including TTC staining, quantitative PCR, western blotting, cell counting kit‑8 assay, Annexin V‑FITC Apoptosis Detection Kit, luciferase reporter gene assays, and others. The levels of circ_0000018 were markedly increased in the OGD/R‑treated neuronal cells and in a mouse model of tMCAO. The blocking of microRNA (miR)‑871 by circ_0000018 promoted Bcl‑2‑like protein 11 (BCL2L11) expression to increase neuronal cell damage. Furthermore, circ_0000018 knockdown significantly improved neuronal cell viability and attenuated OGD/R‑treated neuronal cell death. Meanwhile, circ_0000018 knockdown improved brain infarct volume and neuronal apoptosis in tMCAO mice. The present study found that circ_0000018 knockdown relieved cerebral ischemia‑reperfusion injury progression in vitro and in vivo. Mechanistically, circ_0000018 regulated the levels of BCL2L11 by sponging miR‑871.

Are Ischemic Stroke and Alzheimer's Disease Genetically Consecutive Pathologies?

Complex diseases that affect the functioning of the central nervous system pose a major problem for modern society. Among these, ischemic stroke (IS) holds a special place as one of the most common causes of disability and mortality worldwide. Furthermore, Alzheimer's disease (AD) ranks first among neurodegenerative diseases, drastically reducing brain activity and overall life quality and duration. Recent studies have shown that AD and IS share several common risk and pathogenic factors, such as an overlapping genomic architecture and molecular signature. In this review, we will summarize the genomics and RNA biology studies of IS and AD, discussing the interconnected nature of these pathologies. Additionally, we highlight specific genomic points and RNA molecules that can serve as potential tools in predicting the risks of diseases and developing effective therapies in the future.

Association of Circulating Circular RNAs (hg38_circ_0008980, and CircDLGAP4) in Diagnosis, Diseases Severity, and Prognosis of Ischemic Stroke

Background

Fast diagnosing ischemic stroke (IS) is a critical issue in clinical studies, as it allows more effective therapy and stops the progression of IS. The blood level of circular RNAs (CircRNAs) after stroke may be a rapid diagnostic marker.

Methods

In this study, the blood level of circRNAs was evaluated using a real-time polymerase chain reaction (PCR). We used logistic and linear regression analysis to assess the potential of circRNAs levels with the risk of IS.

Results

circRNA DLG associated protein 4 (CircDLGAP4) was decreased in patients compared with controls, and logistic regression showed its expression negatively associated with IS risk. The expression level of human genome version 38_Circular_0008980 (hg38_circ_0008980) was reduced significantly in patients with small vessel disease (SVD), and the linear regression analysis showed a negative relationship between hg38_circ_0008980 expressions with SVD subtype. hg38_circ_0008980 expression relative to controls showed a significant association with IS risk.

Conclusion

Taken together, we found a significant decrease in the level of hg38_circ_0008980 after IS; it may act as a novel circRNA in IS pathophysiology with a positive correlation with stroke severity.

Extracellular Vesicles Derived from Bone Mesenchymal Stem Cells Carrying circ_0000075 Relieves Cerebral Ischemic Injury by Competitively Inhibiting miR-218-5p and Up-regulating E3 Ubiquitin Ligase SMURF2

Extracellular vesicle (EV)-encapsulated circRNAs have the potential role in affecting brain disorders. However, the role of circ_0000075 in cerebral ischemic injury remains unclear. Here, we tried to investigate the mechanism of bone marrow mesenchymal stem cell (BMSC)-derived EVs carrying circ_0000075 in the control of cerebral ischemic injury. Initially, a mouse model with cerebral ischemic injury was induced by middle cerebral artery occlusion (MCAO), followed by the determination of circ_0000075 expression. Then, neurons were isolated and subjected to oxygen-glucose deprivation/reperfusion. BMSCs were isolated for extraction of EVs. The correlation among circ_0000075, microRNA (miR)-218-5p, and Smad ubiquitination regulatory factor 2 (SMURF2) was detected with their roles in cerebral ischemic injury analyzed in vivo and in vitro. circ_0000075 was down-regulated in MCAO mice and engineered RVG-EVs were internalized by neurons to up-regulate circ_0000075 expression. Treatment of RVG-circ_0000075-EVs reduced brain tissue damage, increased neuronal count, and significantly curtailed apoptosis rate, suppressing cerebral ischemic injury in vitro and in vivo. miR-218-5p was targeted by circ_0000075 in neurons, which promoted SMURF2 expression. A negative correlation between SMURF2 and transcriptional regulator Yin Yang 1 (YY1) was identified. In vitro experiments further proved that circ_ 00,000 75 could down-regulate the expression of YY1 through SMURF2, and finally relieving cerebral ischemic injury. Collectively, engineered EVs delivered circ_0000075 into brain tissues and increased circ_0000075 expression, which down-regulated miR-218-5p and up-regulated SMURF2, thus alleviating cerebral ischemic injury.

H2S-mediated inhibition of RhoA/ROCK pathway and noncoding RNAs in ischemic stroke

Ischemic stroke is one of major causes of disability. In the pathological process of ischemic stroke, the up-regulation of Ras homolog gene family, member A (RhoA) and its downstream effector, Ras homolog gene family (Rho)-associated coiled coil-containing kinase (ROCK), contribute to the neuroinflammation, blood-brain barrier (BBB) dysfunction, neuronal apoptosis, axon growth inhibition and astrogliosis. Accumulating evidences have revealed that hydrogen sulphide (H₂S) could reduce brain injury in animal model of ischemic stroke via inhibiting the RhoA/ROCK pathway. Recently, noncoding RNAs (ncRNAs) such as circular RNAs (circRNAs), long noncoding RNAs (lncRNAs) and microRNAs (miRNAs) have attracted much attention because of their essential role in adjusting gene expression both in physiological and pathological conditions. Numerous studies have uncovered the role of RhoA/ROCK pathway and ncRNAs in ischemic stroke. In this review, we focused on the role of H₂S, RhoA/ROCK pathway and ncRNAs in ischemic stroke and aimed to reveal new strategies for preventing and treating this devastating disease.

Non-coding RNAs in stroke pathology, diagnostics, and therapeutics

Ischemic stroke is a leading cause of death and disability worldwide. Methods to alleviate functional deficits after ischemic stroke focus on restoration of cerebral blood flow to the affected area. However, pharmacological or surgical methods such as thrombolysis and thrombectomy have a narrow effective window. Harnessing and manipulating neurochemical processes of recovery may provide an alternative to these methods. Recently, non-coding RNA (ncRNA) have been increasingly investigated for their contributions to the pathology of diseases and potential for diagnostic and therapeutic applications. Here we will review several ncRNA - H19, MALAT1, ANRIL, NEAT1, pseudogenes, small nucleolar RNA, piwi-interacting RNA and circular RNA - and their involvement in stroke pathology. We also examine these ncRNA as potential diagnostic biomarkers, particularly in circulating blood, and as targets for therapeutic interventions. An important aspect of this is a discussion of potential methods of treatment delivery to allow for targeting of interventions past the blood-brain barrier, including lipid nanoparticles, polymer nanoparticles, and viral and non-viral vectors. Overall, several long non-coding RNA (lncRNA) discussed here have strong implications for the development of pathology and functional recovery after ischemic stroke. LncRNAs H19 and ANRIL show potential as diagnostic biomarkers, while H19 and MALAT1 may prove to be effective therapeutics for both minimising damage as well as promoting recovery. Other ncRNA have also been implicated in ischemic stroke but are currently too poorly understood to make inferences for diagnosis or treatment. Whilst the field of ncRNAs is relatively new, significant work has already highlighted that ncRNAs represent a promising novel investigative tool for understanding stroke pathology, could be used as diagnostic biomarkers, and as targets for therapeutic interventions.

Circular RNA circPRDX3 mediates neuronal survival apoptosis in ischemic stroke by targeting miR-641 and NPR3

OBJECTIVE

circPRDX3 is a circular RNA (circRNA) that has received little attention yet. The purpose of this research is to elucidate circPRDX3 expression pattern and its underlying network in ischemic stroke (IS).

METHODS

Oxygen-glucose deprivation on/reoxygenation (OGD/R) and mice model of middle cerebral artery occlusion (MCAO) were used to generate IS model in N2a cells or mice, respectively. Expression levels of circPRDX3, miR-641, Natriuretic Peptide Receptor 3 (NPR3), and members of the mitogen-activated protein kinases (MAPK) pathway were determined using real-time quantitative PCR (qRT-PCR) and western blot. Cell viability was assessed by CCK-8 assay and apoptosis was evaluated using TUNEL staining and flow cytometry. Molecule-molecule interactions were verified by dual luciferase and RNA immunoprecipitation (RIP) assays. The infarcted area was depicted by Triphenyl tetrazolium chloride (TTC) staining and the level of neurological function was measured using National Institute of Health stroke scale (NIHSS).

RESULTS

CircPRDX3 and NPR3 were shown to be considerably downregulated in IS samples, as well as OGD/R cells or MCAO mice, while miR-641 was found to be significantly upregulated. A circPRDX3/miR-641/NPR3 mechinary was verified using luciferase and RIP assays. Overexpression of circPRDX3 dramatically reduced miR-641 expression and increased NPR3 expression, boosting cell survival and lowering apoptosis in an OGD/R model, either with inactivated MAPK signaling pathways. Moreover, overexpression of circPRDX3 lowered infarct volume and enhanced neurobehavioral outcomes in mice after MCAO, and these protective effects were dramatically abrogated by depletion of NPR3.

CONCLUSION

Altogether, circPRDX3 inhibited the development of IS by sponging miR-641, hence increasing NPR3 expression and inactivating MAPK pathway. These results may aid in the search of potential therapy targets for IS.

A crosstalk between circular RNA, microRNA, and messenger RNA in the development of various brain cognitive disorders

Patients with Alzheimer's disease (AD), Parkinson's disease (PD), traumatic brain injury (TBI), stroke, and postoperative neurocognitive disorder (POND) are commonly faced with neurocognitive disorders with limited therapeutic options. Some non-coding ribonucleic acids (ncRNAs) are involved in the development of various brain cognitive disorders. Circular RNAs (circRNAs), a typical group of ncRNAs, can function as competitive endogenous RNAs (ceRNAs) to dysregulate shared microRNAs (miRNAs) at post-transcription level, inhibiting regulation of miRNAs on their targeted messenger RNAs (mRNAs). circRNAs are abundant in central nervous system (CNS) diseases and cause brain disorders, but the exact roles of circRNAs are unclear. The crosstalk between circRNA, miRNA, and mRNA plays an important role in the pathogenesis of these neurocognitive dysfunction diseases and abnormal conditions including AD, PD, stroke, TBI, and POND. In this review, we summarized the participation of circRNA in neuroglial damage and inflammation. Finally, we aimed to highlight the regulatory mechanisms of circRNA–miRNA–mRNA networks in the development of various brain cognitive disorders and provide new insights into the therapeutics of these diseases.

A systematic review of the research progress of non-coding RNA in neuroinflammation and immune regulation in cerebral infarction/ischemia-reperfusion injury

Cerebral infarction/ischemia-reperfusion injury is currently the disease with the highest mortality and disability rate of cardiovascular disease. Current studies have shown that nerve cells die of ischemia several hours after ischemic stroke, which activates the innate immune response in the brain, promotes the production of neurotoxic substances such as inflammatory cytokines, chemokines, reactive oxygen species and − nitrogen oxide, and mediates the destruction of blood-brain barrier and the occurrence of a series of inflammatory cascade reactions. Meanwhile, the expression of adhesion molecules in cerebral vascular endothelial cells increased, and immune inflammatory cells such as polymorphonuclear neutrophils, lymphocytes and mononuclear macrophages passed through vascular endothelial cells and entered the brain tissue. These cells recognize antigens exposed by the central nervous system in the brain, activate adaptive immune responses, and further mediate secondary neuronal damage, aggravating neurological deficits. In order to reduce the above-mentioned damage, the body induces peripheral immunosuppressive responses through negative feedback, which increases the incidence of post-stroke infection. This process is accompanied by changes in the immune status of the ischemic brain tissue in local and systemic systems. A growing number of studies implicate noncoding RNAs (ncRNAs) as novel epigenetic regulatory elements in the dysfunction of various cell subsets in the neurovascular unit after cerebral infarction/ischemia-reperfusion injury. In particular, recent studies have revealed advances in ncRNA biology that greatly expand the understanding of epigenetic regulation of immune responses and inflammation after cerebral infarction/ischemia-reperfusion injury. Identification of aberrant expression patterns and associated biological effects of ncRNAs in patients revealed their potential as novel biomarkers and therapeutic targets for cerebral infarction/ischemia-reperfusion injury. Therefore, this review systematically presents recent studies on the involvement of ncRNAs in cerebral infarction/ischemia-reperfusion injury and neuroimmune inflammatory cascades, and elucidates the functions and mechanisms of cerebral infarction/ischemia-reperfusion-related ncRNAs, providing new opportunities for the discovery of disease biomarkers and targeted therapy. Furthermore, this review introduces clustered regularly interspaced short palindromic repeats (CRISPR)-Display as a possible transformative tool for studying lncRNAs. In the future, ncRNA is expected to be used as a target for diagnosing cerebral infarction/ischemia-reperfusion injury, judging its prognosis and treatment, thereby significantly improving the prognosis of patients.

Pathophysiology of Ischemic Stroke: Noncoding RNA Role in Oxidative Stress

Stroke is a neurological disease that causes significant disability and death worldwide. Ischemic stroke accounts for 75% of all strokes. The pathophysiological processes underlying ischemic stroke include oxidative stress, the toxicity of excitatory amino acids, ion disorder, enhanced apoptosis, and inflammation. Noncoding RNAs (ncRNAs) may have a vital role in regulating the pathophysiological processes of ischemic stroke, as confirmed by the altered expression of ncRNAs in blood samples from acute ischemic stroke patients, animal models, and oxygen-glucose-deprived (OGD) cell models. Due to specific changes in expression, ncRNAs can potentially be biomarkers for the diagnosis, treatment, and prognosis of ischemic stroke. As an important brain cell component, glial cells mediate the occurrence and progression of oxidative stress after ischemic stroke, and ncRNAs are an irreplaceable part of this mechanism. This review highlights the impact of ncRNAs in the oxidative stress process of ischemic stroke. It focuses on specific ncRNAs that underlie the pathophysiology of ischemic stroke and have potential as diagnostic biomarkers and therapeutic targets.

Circ_TLK1 knockdown alleviates oxygen-glucose deprivation/reoxygenation-induced PC12 cell injury by regulating microRNA-136-5p/follistatin like-1 axis

BACKGROUND

Circular RNAs (circRNAs) are aberrantly expressed in the central nervous system (CNS) and are involved in diverse CNS diseases. However, the functions of circRNAs in ischemic stroke (IS) are largely unknown. In this study, we aimed to explore the effect of circ_TLK1 in oxygen-glucose deprivation/reoxygenation (OGD/R)-induced PC12 cell injury.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) was performed for the levels of circ_TLK1, TLK1, microRNA-136-5p (miR-136-5p), and follistatin like-1 (FSTL1). RNase R and Actinomycin D assays were conducted to analyze the features of circ_TLK1. 3-(4, 5-ethynyl-2'-deoxyuridine [EdU] assay and 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT) assay were adopted to analyze cell proliferation capacity. Flow cytometry analysis was applied to determine cell death. Western blot assay was employed to measure protein levels. The release of lactate dehydrogenase (LDH) was measured with specific kits. The interaction between circ_TLK1 and miR-136-5p, as well as miR-136-5p and FSTL1, was verified by Dual-luciferase reporter assay.

RESULTS

Circ_TLK1 was upregulated in OGD/R-injured PC12 cells. OGD/R treatment inhibited cell proliferation, promoted cell death, and increased LDH release in PC12 cells, while circ_TLK1 knockdown partially alleviated OGD/R-induced PC12 cell injury. Circ_TLK1 directly bound to miR-136-5p and miR-136-5p inhibition reversed the effect of circ_TLK1 knockdown on OGD/R-induced PC12 cell damage. Moreover, FSTL1 was targeted by miR-136-5p. MiR-136-5p upregulation inhibited PC12 cell injury induced by OGD/R, while FSTL1 overexpression partially reversed the effect.

CONCLUSION

Circ_TLK1 knockdown ameliorated OGD/R-induced PC12 cell injury by modulating miR-136-5p and FSTL1, which might provide a new understanding of IS treatment.

CircUSP36 attenuates ischemic stroke injury through the miR-139-3p/SMAD3/Bcl2 signal axis

Circular RNAs (circRNAs) play important roles in a variety of physiological and pathological processes. Researches demonstrated that circRNAs provided novel strategies for the prevention and treatment of IS. However, the biological function of hsa_circ_0045932 (circUSP36) has not been revealed yet. Here, we explored the effect of circUSP36 on IS and its mechanism. In this study, we found that circUSP36 expression was significantly decreased in the peripheral blood of IS patients and was negatively correlated with the severity, infarct volume and poor prognosis of IS. Functionally, circUSP36 silencing inhibited cellular activity and proliferation and promoted apoptosis after oxygen-glucose deprivation/reperfusion (OGD/R) treatment, while circUSP36 overexpression reversed these cellular phenotypes in vitro. Adeno-associated virus (AAV)-mediated overexpression of circUSP36 attenuates brain injury and neurological deficit and promotes motor function recovery of transient middle cerebral artery occlusion (tMCAO) mice. Subsequently, the RNA antisense purification (RAP) and luciferase reporter assay confirmed that circUSP36 acts as a sponge to adsorb miR-139-3p, and miR-139-3p could bind and inhibit SMAD3 expression. Further rescue experiments showed that both miR-139-3p overexpression and SMAD3 silencing could abolish the antiapoptotic effect of circUSP36. In summary, we reveal for the first time that circUSP36 attenuates ischemic stroke injury through the miR-139-3p/SMAD3/Bcl2 signal axis, which make circUSP36 a potential therapeutic target for IS.

CircRNA and miRNA expression profiles during remote ischemic postconditioning attenuate brain ischemia/reperfusion injury

Remote ischemic postconditioning (RIPostC) is a protective procedure for brain damage caused by ischemia/reperfusion (IR), yet the mechanism of this treatment remains to be elucidated. Circular RNAs (circRNAs) are endogenous non-coding RNAs that have recently been recognized to play vital roles in ischemic brain injury. The aim of this study was to explore the role of circRNAs in the protective mechanism of RIPostC and to analyze the circRNA-microRNA (miRNA) regulation network in RIPostC. Nine rats were assigned randomly into three groups (three rats per group): sham, IR, and RIPostC. Their brain tissues were extracted for next-generation RNA sequencing and bioinformatics analysis was performed for two comparisons: sham vs. IR and IR vs. RIPostC. The expression patterns of selected circRNAs and miRNAs were validated by quantitative real-time PCR (qPCR). We detected 82 upregulated and 51 downregulated circRNAs and 137 upregulated and 127 downregulated miRNAs in the IR group compared with the sham group, and 41 upregulated and 100 downregulated circRNAs and 45 upregulated and 64 downregulated miRNAs in the RIPostC group compared with the IR group. The proposed competitive endogenous RNA (ceRNA) network, which included 24 circRNAs, 20 miRNAs, and 145 mRNAs, indicated that the dysregulated circRNAs played important roles in brain IR injury. On the basis of the expression patterns of selected circRNAs, miRNAs, and mRNAs obtained by qPCR, we proposed a circRNA_0002286-miR-124-3p-VLCAD pathway. In PC12 cell, the expression level of miR-124-3p was significantly upregulated when the expression of circRNA_0002286 was repressed and the expression level of VLCAD (very-long chain acyl-CoA dehydrogenase) was significantly downregulated, which suggested that circRNA_0002286 may act as a miRNA sponge for miR-124-3p to regulate the expression of VLCAD. We found that upregulation of circRNA_0002286 attenuated IR injury and was associated with downregulation of miR-124-3p and upregulation of VLCAD. This is the first time that circRNAs have been shown to be closely related to brain IR injury and RIPostC and suggests that targeting the circRNA_0002286-miR-124-3p-VLCAD pathway might attenuate brain IR injury.

Impact of CircRNAs on Ischemic Stroke

Circular RNA (circRNA) is a recently discovered class of endogenous non-coding RNA that is generated by cyclization, driven by intron pairing, and regulated by related regulators. An important biological function of CircRNA is acting as a molecular sponge to significantly alter miRNA levels over a short period. Several studies have shown that circRNA is closely related to stroke. Therefore, a better understanding of CircRNA function and regulatory mechanism in ischemic brain will help us for the early detection, early diagnosis, and early treatment of stroke. Here, we summary the biological characteristics, expression of circRNA, and its effect on outcome after ischemic stroke.

Circular RNAs and glioblastoma multiforme: focus on molecular mechanisms

Glioblastoma multiforme (GBM), as a deadly and almost incurable brain cancer, is the most invasive form of CNS tumors that affects both children and adult population. It accounts for approximately half of all primary brain tumors. Despite the remarkable advances in neurosurgery, radiotherapy, and chemotherapeutic approaches, cell heterogeneity and numerous genetic alterations in cell cycle control, cell growth, apoptosis, and cell invasion, result in an undesirable resistance to therapeutic strategies; thereby, the median survival duration for GBM patients is unfortunately still less than two years. Identifying new therapeutics and employing the combination therapies may be considered as wonderful strategies against the GBM. In this regard, circular RNAs (circRNAs), as tumor inhibiting and/or stimulating RNA molecules, can regulate the cancer-developing processes, including cell proliferation, cell apoptosis, invasion, and chemoresistance. Hereupon, these molecules have been introduced as potentially effective therapeutic targets to defeat GBM. The current study aims to investigate the fundamental molecular and cellular mechanisms in association with circRNAs involved in GBM pathogenesis. Among multiple mechanisms, the PI3K/Akt/mTOR, Wnt/β-catenin, and MAPK signaling, angiogenic processes, and metastatic pathways will be thoroughly discussed to provide a comprehensive understanding of the role of circRNAs in pathophysiology of GBM. Video Abstract.

Genome-Wide RNA-Sequencing Reveals Massive Circular RNA Expression Changes of the Neurotransmission Genes in the Rat Brain after Ischemia-Reperfusion

Ischemic brain stroke is one of the most serious and socially significant diseases. In addition to messenger RNAs (mRNAs), encoding protein, the study of regulatory RNAs in ischemic has exceptional importance for the development of new strategies for neuroprotection. Circular RNAs (circRNAs) have a closed structure, predominantly brain-specific expression, and remain highly promising targets of research. They can interact with microRNAs (miRNAs), diminish their activity and thereby inhibit miRNA-mediated repression of mRNA. Genome-wide RNA-Seq analysis of the subcortical structures of the rat brain containing an ischemic damage focus and penumbra area revealed 395 circRNAs changed their expression significantly at 24 h after transient middle cerebral artery occlusion model (tMCAO) conditions. Furthermore, functional annotation revealed their association with neuroactive signaling pathways. It was found that about a third of the differentially expressed circRNAs (DECs) originate from genes whose mRNA levels also changed at 24 h after tMCAO. The other DECs originate from genes encoding non-regulated mRNAs under tMCAO conditions. In addition, bioinformatic analysis predicted a circRNA–miRNA–mRNA network which was associated with the neurotransmission signaling regulation. Our results show that such circRNAs can persist as potential miRNA sponges for the protection of mRNAs of neurotransmitter genes. The results expanded our views about the neurotransmission regulation in the rat brain after ischemia–reperfusion with circRNA action.

Circular RNAs: The Novel Actors in Pathophysiology of Spinal Cord Injury

Spinal Cord Injury (SCI) can elicit a progressive loss of nerve cells promoting disability, morbidity, and even mortality. Despite different triggering mechanisms, a cascade of molecular events involving complex gene alterations and activation of the neuroimmune system influence either cell damage or repair. Effective therapies to avoid secondary mechanisms underlying SCI are still lacking. The recent progression in circular RNAs (circRNAs) research has drawn increasing attention and opened a new insight on SCI pathology. circRNAs differ from traditional linear RNAs and have emerged as the active elements to regulate gene expression as well as to facilitate the immune response involved in pathophysiology-related conditions. In this review, we focus on the impact and possible close relationship of circRNAs with pathophysiological mechanisms following SCI, where circRNAs could be the key transcriptional regulatory molecules to define neuronal death or survival. Advances in circRNAs research provide new insight on potential biomarkers and effective therapeutic targets for SCI patients.

Noncoding RNA crosstalk in brain health and diseases

The mammalian brain expresses several classes of noncoding RNAs (ncRNAs), including long ncRNAs (lncRNAs), circular RNAs (circRNAs), and microRNAs (miRNAs). These ncRNAs play vital roles in regulating cellular processes by RNA/protein scaffolding, sponging and epigenetic modifications during the pathophysiological conditions, thereby controlling transcription and translation. Some of these functions are the result of crosstalk between ncRNAs to form a competitive endogenous RNA network. These intricately organized networks comprise lncRNA/miRNA, circRNA/miRNA, or lncRNA/miRNA/circRNA, leading to crosstalk between coding and ncRNAs through miRNAs. The miRNA response elements predominantly mediate the ncRNA crosstalk to buffer the miRNAs and thereby fine-tune and counterbalance the genomic changes and regulate neuronal plasticity, synaptogenesis and neuronal differentiation. The perturbed levels and interactions of the ncRNAs could lead to pathologic events like apoptosis and inflammation. Although the regulatory landscape of the ncRNA crosstalk is still evolving, some well-known examples such as lncRNA Malat1 sponging miR-145, circRNA CDR1as sponging miR-7, and lncRNA Cyrano and the circRNA CDR1as regulating miR-7, has been shown to affect brain function. The ability to manipulate these networks is crucial in determining the functional outcome of central nervous system (CNS) pathologies. The focus of this review is to highlights the interactions and crosstalk of these networks in regulating pathophysiologic CNS function.

Circular RNA 0025984 Ameliorates Ischemic Stroke Injury and Protects Astrocytes Through miR-143-3p/TET1/ORP150 Pathway

MiR-143-3p is aberrantly expressed in patients with ischemic stroke and associated with ischemic brain injury. However, the underlying mechanisms are largely unknown. Here, we confirmed circ_0025984 and TET1 as a sponge and target of miR-143-3p, respectively, by luciferase reporter assay. In astrocytes, OGD significantly decreased circ_0025984 and TET1 levels but increased miR-143-3p levels, which was also observed in brains of mice with MCAO. Treatment with miR-143-3p inhibitor or circ_0025984 significantly decreased astrocyte apoptosis and autophagy, as well as cerebral injury and neuron loss in mice with MCAO. Notably, TET1 overexpression decreased astrocyte apoptosis and autophagy and induced promoter hypomethylation and expression of ORP150. Our results demonstrated for the first time that circ_0025984 protects astrocytes from ischemia-induced autophagy and apoptosis by targeting the miR-143-3p/TET1 pathway and might inhibit cerebral injury induced by ischemic stroke. Furthermore, our data revealed the important positive regulation of ORP150 by TET1, which could be associated with its neuroprotective role. Graphical abstract Model for signaling pathway of circ_0025984/miR-143-3p/TET1 inastrocytes cultured under OGD. In astrocytes, circ_0025984 acts as a sponge of miR-143-3p, which directly targets TET1 and decreases its expression (A). After translocatinginto the nucleus, TET1 binds to the promoter of ORP150, converts 5mC into 5hmC,leading to DNA demethylation and increased expression of ORP150 (B). In astrocytescultured under OGD, ER stress is induced and eventually leads to apoptosis andautophagy mediated by ATG7, which is regulated by circ_0025984 via ORP150 andGRP78 (C).

The Emerging Role of Circular RNAs in Cerebral Vascular Disorders

BACKGROUND

Circular RNAs (circRNAs) are covalently closed circular noncoding RNAs that are expressed in various life forms. CircRNAs have many characteristics, such as structural stability and tissue-specific expression that contribute to their role as a microRNA (sponge in gene regulation.

SUMMARY

Recent evidence suggests that circRNAs play an important role in the pathogenesis of cerebrovascular diseases (CVDs); however, the exact mechanism remains controversial. CircRNAs that are related to CVDs have great clinical significance. Key Messages: The present review provides an overview of the general biology of circRNAs, their relevant regulatory mechanisms, and their role in the pathophysiology of CVDs.

Recent progress in study of circRNAs and its role in leukemia

Circular RNAs (circRNAs) are a class of newly identified noncoding RNA and are considered as a new feature of eukaryotic gene expression. Hundreds of thousands of endogenous circRNAs have been found in mammalian cells, which we knew little before. CircRNAs are covalently closed, circular RNA molecules that typically comprise exonic sequences and are spliced at canonical splice sites. Researchers with RNA-Seq technology have identified that the expression of circRNAs is developmentally regulated, tissue- and cell-type specific. Like long noncoding RNAs (lncRNAs), circRNAs are becoming a new research hotspot in the RNA field, and aberrant expression of circRNAs could contribute to carcinogenesis. Recent studies have demonstrated that circRNAs play important roles in the development, maintenance, and progression of leukemia. Herein, we describe the biologic characteristics and functions of circRNAs, with a focus on circRNAs that play essential roles in leukemia.

Circular RNA hsa_circ_0096157 contributes to cisplatin resistance by proliferation, cell cycle progression, and suppressing apoptosis of non-small-cell lung carcinoma cells

Circular RNAs (circRNAs) play a major role in cancer development and chemotherapy resistance. This study aimed to characterize circRNA profiles associated with Cisplatin (diamminedichloroplatinum, DDP) resistance of non-small-cell lung carcinoma (NSCLC) cells. The half-maximal inhibitory concentration (IC50) of A549 and A549/DDP cells was determined using CCK-8 assay. Further, circRNA profiles and differentially expressed genes in A549 and A549/DDP cells were characterized by deep sequencing and cell proliferation was measured using MTS assay. Cell cycle progression was analyzed using flow cytometry. Apoptosis experiment was performed by TUNEL assay and flow cytometry. Cell migration and invasion were assessed using the Transwell system. Finally, signalling protein levels related to cell cycle progression and migration were measured by western blot. CCK-8 assay showed that A549/DDP cells obtained strong DDP resistance. Further deep sequencing results showed that 689 circRNAs and 87 circRNAs were significantly upregulated and downregulated in A549/DDP cells compared to A549 cells, respectively. Moreover, the circRNA hsa_circ_0096157 with the highest expression level in A549/DPP cells was further analyzed for its potential mechanism of DDP resistance in A549/DDP. With or without DDP treatment, hsa_circ_0096157 knockdown inhibited proliferation, migration, invasion and cell cycle progression but promoted apoptosis of A549/DDP cells. In addition, the western blot results also showed that hsa_circ_0096157 knockdown in A549/DDP cells increased P21 and E-cadherin but decreased CDK4, Cyclin D1, Bcl-2, N-cadherin, and Vimentin protein expression levels, indicating that cell cycle progression might be inhibited by increased P21 protein level to inhibit the expression of CDK4-cyclin D1 complex and decreased Bcl-2 protein level; and migration and invasion were suppressed by the increased E-cadherin and decreased N-cadherin and Vimentin expression levels. In contrast, hsa_circ_0096157 overexpression in A549 cells caused the opposite cellular and molecular alterations. DDP resistance in NSCLC cells was associated with significant circRNA profile alterations. Moreover, increased hsa_circ_0096157 expression contributed to DDP resistance in NSCLC cells by promoting cell proliferation, migration, invasion and cell cycle progression and inhibiting apoptosis.

Altered circular RNA expression profiles in the non-ischemic thalamus in focal cortical infarction mice

Focal cerebral infarction leads to secondary changes in non-ischemic areas remote from but connected to the infarct site. Circular RNAs (circRNAs) are involved in the pathophysiological processes of many diseases. However, the expression and roles of circRNAs in non-ischemic remote regions after ischemic stroke remain unknown. In this study, adult male C57BL/6J mice were subjected to permanent distal middle cerebral artery occlusion (MCAO) to establish focal cortical infarction. High-throughput sequencing was used to profile the circRNA expression in the mouse ipsilateral thalamus at 7 and 14 d after MCAO. Bioinformatics analyses were conducted to predict the function of the differential expressed circRNAs' host and target genes. Compared with sham group, a total of 2659 circRNAs were significantly altered in the ipsilateral thalamus at 7 or 14 d after MCAO in mice. Among them, 73 circRNAs were significantly altered at both two time points after stroke. GO and KEGG analyses indicated that circRNAs plays important roles in secondary thalamic neurodegeneration and remodeling after focal cortical infarction. This is the first study to profile the circRNA expression in non-ischemic region of ischemic stroke, suggesting that circRNAs may be therapeutic targets for reducing post-stroke secondary remote neurodegeneration.

Silencing of circular RNA ANRIL attenuates oxygen-glucose deprivation and reoxygenation-induced injury in human brain microvascular endothelial cells by sponging miR-622

BACKGROUND

Circular RNA (circRNA) is highly expressed in the brain tissue, but its molecular mechanism in cerebral ischemia-reperfusion remains unclear. Here, we explored the role and underlying mechanisms of circRNA antisense non-coding RNA in the INK4 locus (circ_ANRIL) in oxygen-glucose deprivation and reoxygenation (OGD/R)-induced cell injury.

RESULTS

The expression of circ_ANRIL in OGD/R-induced human brain microvascular endothelial cells (HBMECs) was significantly up-regulated, while that of miR-622 was significantly down-regulated. Overexpression of circ_ANRIL significantly inhibited the proliferation of OGD/R-induced HBMECs and aggravated OGD/R-induced cell apoptosis. Moreover, circ_ANRIL overexpression further increased the secretion of interleukin (IL)-1β, IL-6, tumor necrosis factor-α, and monocyte chemoattractant protein-1 in OGD/R-treated HBMECs. The results of bioinformatics analysis and luciferase reporter assay indicated that circ_ANRIL served as an miR-622 sponge to negatively regulate the expression of miR-622 in OGD/R-treated HBMECs. Additionally, circ_ANRIL silencing exerted anti-apoptotic and anti-inflammatory effects by positively regulating the expression of miR-622. Furthermore, inhibition of OGD/R-induced activation of the nuclear factor (NF)-κB pathway by circ_ANRIL silencing was significantly reversed by treatment with miR-622 inhibitor.

CONCLUSIONS

Knockdown of circ_ANRIL improved OGD/R-induced cell damage, apoptosis, and inflammatory responses by inhibiting the NF-κB pathway through sponging miR-622.

Intracerebral overexpression of miR-669c is protective in mouse ischemic stroke model by targeting MyD88 and inducing alternative microglial/macrophage activation

Background

Ischemic stroke is a devastating disease without a cure. The available treatments for ischemic stroke, thrombolysis by tissue plasminogen activator, and thrombectomy are suitable only to a fraction of patients and thus novel therapeutic approaches are urgently needed. The neuroinflammatory responses elicited secondary to the ischemic attack further aggravate the stroke-induced neuronal damage. It has been demonstrated that these responses are regulated at the level of non-coding RNAs, especially miRNAs.

Methods

We utilized lentiviral vectors to overexpress miR-669c in BV2 microglial cells in order to modulate their polarization. To detect whether the modulation of microglial activation by miR-669c provides protection in a mouse model of transient focal ischemic stroke, miR-669c overexpression was driven by a lentiviral vector injected into the striatum prior to induction of ischemic stroke.

Results

Here, we demonstrate that miR-669c-3p, a member of chromosome 2 miRNA cluster (C2MC), is induced upon hypoxic and excitotoxic conditions in vitro and in two different in vivo models of stroke. Rather than directly regulating the neuronal survival in vitro, miR-669c is capable of attenuating the microglial proinflammatory activation in vitro and inducing the expression of microglial alternative activation markers arginase 1 (Arg1), chitinase-like 3 (Ym1), and peroxisome proliferator-activated receptor gamma (PPAR-γ). Intracerebral overexpression of miR-669c significantly decreased the ischemia-induced cell death and ameliorated the stroke-induced neurological deficits both at 1 and 3 days post injury (dpi). Albeit miR-669c overexpression failed to alter the overall Iba1 protein immunoreactivity, it significantly elevated Arg1 levels in the ischemic brain and increased colocalization of Arg1 and Iba1. Moreover, miR-669c overexpression under cerebral ischemia influenced several morphological characteristics of Iba1 positive cells. We further demonstrate the myeloid differentiation primary response gene 88 (MyD88) transcript as a direct target for miR-669c-3p in vitro and show reduced levels of MyD88 in miR-669c overexpressing ischemic brains in vivo.

Conclusions

Collectively, our data provide the evidence that miR-669c-3p is protective in a mouse model of ischemic stroke through enhancement of the alternative microglial/macrophage activation and inhibition of MyD88 signaling. Our results accentuate the importance of controlling miRNA-regulated responses for the therapeutic benefit in conditions of stroke and neuroinflammation.

Noncoding RNAs and Intracerebral Hemorrhage

BACKGROUND & OBJECTIVE

Intracerebral hemorrhage (ICH) is the most devastating subtype of stroke, for which there are few effective interventions. Computed tomography is accepted as the gold standard for diagnosis, whereas surgical evacuation is the main treatment for ICH. However, in emergency rooms, time is limited and information regarding a patient's clinical status or tolerance is typically not available. Many studies over the last decade have investigated the fundamental mechanisms of ICH and especially hematoma, which not only cause physical damage but also release toxins that have detrimental effects. However, there remain many gaps in our understanding of ICH. Compared to ischemic stroke, there is little known about the ICH pathogenesis and treatment options, and few specific biomarkers are available for monitoring disease progression, which include hematoma enlargement and perihematoma edema. Noncoding RNAs (ncRNAs) are involved in various biological processes and are potential biomarkers and therapeutic tools in central nervous system diseases. Recent studies have examined the role of ncRNAs including microRNAs, long noncoding RNAs, and circular RNAs-the three main subgroups associated with stroke-in ICH models. A deeper understanding of the functions of ncRNAs in different biological processes can provide a basis for developing more effective therapeutic strategies to prevent neuronal damage following ICH. In clinical settings, ncRNAs can serve as biomarkers for predicting the degree of injury resulting from ICH.

CONCLUSION

In this review, we discuss the current state of knowledge of the role of ncRNAs in ICH.

Circular RNA expression profile in blood according to ischemic stroke etiology

Background

The discovery of novel biomarkers of stroke etiology would be most helpful in management of acute ischemic stroke patients. Recently, circular RNAs (circRNAs) have been proposed as candidate biomarkers of neurological conditions due to its high stability. circRNAs function as sponges, sequestering miRNAs and are involved in most relevant biological functions. Our aim was to identify differentially expressed circRNAs in acute ischemic stroke patients according to stroke etiology.

Methods

A comprehensive expression profile of blood circRNAs was conducted by Arraystar Human circRNA arrays (13,617 probes) on a discovery cohort of 30 stroke patients with different stroke etiologies by TOAST classification. Real-time quantitative PCR (RT-qPCR) was used to validate array results in a cohort of 50 stroke patients. Functional in silico analysis was performed to identify potential interactions with microRNAs (miRNAs) and pathways underlying deregulated circRNAs.

Results

A set of 60 circRNAs were found to be upregulated in atherotrombotic versus cardioembolic strokes (fold-change > = 1.5 and p-value ≤ 0.05). Differential expression of hsa_circRNA_102488, originated from UBA52 gene, was replicated in the validation cohort. RNA-binding proteins (RBPs) sites of hsa_circRNA_102488 clustered around AGO2 and FUS proteins. Further functional analysis revealed interactions between deregulated circRNAs and a set of miRNAs involved in stroke-related pathways, such as fatty acid biogenesis or lysine degradation.

Conclusion

Different stroke subtypes show specific profiles of circRNAs expression. circRNAs may serve as a new source of biomarkers of stroke etiology in acute ischemic stroke patients.

Role of circular RNAs in brain development and CNS diseases

In mammals, many classes of noncoding RNAs (ncRNAs) are expressed at a much higher level in the brain than in other organs. Recent studies have identified a new class of ncRNAs called circular RNAs (circRNAs), which are produced by back-splicing and fusion of either exons, introns, or both exon-intron into covalently closed loops. The circRNAs are also highly enriched in the brain and increase continuously from the embryonic to the adult stage. Although the functional significance and mechanism of action of circRNAs are still being actively explored, they are thought to regulate the transcription of their host genes and sequestration of miRNAs and RNA binding proteins. Some circRNAs are also shown to have translation potential to form peptides. The expression and abundance of circRNAs seem to be spatiotemporally maintained in a normal brain. Altered expression of circRNAs is also thought to mediate several disorders, including brain-tumor growth, and acute and chronic neurodegenerative disorders by affecting mechanisms such as angiogenesis, neuronal plasticity, autophagy, apoptosis, and inflammation. This review discusses the involvement of various circRNAs in brain development and CNS diseases. A better understanding of the circRNA function will help to develop novel therapeutic strategies to treat CNS complications.

Inhibition of MiR-122 Decreases Cerebral Ischemia-reperfusion Injury by Upregulating DJ-1-Phosphatase and Tensin Homologue Deleted on Chromosome 10 (PTEN)/Phosphonosinol-3 Kinase (PI3K)/AKT

BACKGROUND Ischemia-reperfusion injury is caused by a blood reperfusion injury in ischemic brain tissue, and usually occurs in the treatment stage of ischemic disease, which can aggravate brain tissue injury. MiR-122 is closely related to ischemia-reperfusion injury in the myocardium, kidney, and liver; however, the role in cerebral ischemia-reperfusion injury has not been established. MATERIAL AND METHODS In this study, cerebral ischemia-reperfusion injury was established in a rat model, and the control group was a sham-operated group. After ischemia-reperfusion injury for 6, 12, and 24 hours, brain tissue specimens were collected and the expression of miR-122 and DJ-1 were determined using quantitative real-time polymerase chain reaction. Flow cytometry was used to determine the reactive oxygen species (ROS) content. The modified Neurological Severity Score (mNSS) scale was used to evaluate the sensory and motor function defects of the rats. The malondialdehyde (MDA), superoxide dismutase (SOD), and enzyme activity were determined. The rats in the cerebral ischemia-reperfusion injury model were divided into 2 groups (antagomir-NC group and antagomir miR-122 group). Brain neuron RN-c cells were divided into the following 4 groups: antagomir-NC, antagomir miR-122, pIRES2-blank, and pIRES2-DJ-1. Seventy-two hours after transfection, ischemia-reperfusion treatment was carried out and conventional cultured RN-c cells were used as the control group. Flow cytometry was used to detect apoptosis and western blot was used to detect the expression of DJ-1, PTEN, AKT, and p-AKT. RESULTS The expression of miR-122 increased significantly in the process of ischemia-reperfusion damage after cerebral infarction, while the expression of DJ-1 decreased significantly. Downregulation of miR-122 significantly increased the expression of DJ-1, enhanced the activity of the PTEN/PI3K/AKT pathway, reduced cell apoptosis, and alleviated cerebral ischemia-reperfusion injury. CONCLUSIONS Inhibition of miR-122 can decrease cerebral ischemia-reperfusion injury by upregulating DJ-1-PTEN/PI3K/AKT pathway.

Identification of Blood Circular RNAs as Potential Biomarkers for Acute Ischemic Stroke

Many hospitals lack facilities for accurate diagnosis of acute ischemic stroke (AIS). Circular RNA (circRNA) is highly expressed in the brain and is closely associated with stroke. In this study, we examined whether the blood-borne circRNAs could be promising candidates as adjunctive diagnostic biomarkers and their pathophysiological roles after stroke. We profiled the blood circRNA expression in mice subjected to experimental focal cerebral ischemia and validated the selected circRNAs in AIS patients. We demonstrated that 128, 198, and 789 circRNAs were significantly altered at 5 min, 3 h, and 24 h after ischemic stroke, respectively. Our bioinformatics analysis revealed that the circRNA-targeted genes were associated with the Hippo signaling pathway, extracellular matrix-receptor interaction, and fatty acid metabolism at 5 min, 3 h and 24 h after ischemic stroke, respectively. We verified that many of these circRNAs existed in the mouse brain. Furthermore, we found that most of the predicted circRNA-miRNA interactions apparently exhibited functional roles in terms of regulation of their target gene expression in the brain. We also verified that many of these mouse circRNAs were conserved in human. Finally, we found that circBBS2 and circPHKA2 were differentially expressed in the blood of AIS patients. These results demonstrate that blood circRNAs may serve as potential biomarkers for AIS diagnosis and reveal the pathophysiological responses in the brain after ischemic stroke.

Remote ischemic conditioning reduced cerebral ischemic injury by modulating inflammatory responses and ERK activity in type 2 diabetic mice

Remote ischemic preconditioning (RIPreC) and postconditioning (RIPostC) have been demonstrated to attenuate brain injury after ischemic stroke in healthy animals. This study investigated whether RIPreC and RIPostC exerted neuroprotection against cerebral ischemic injury in type 2 diabetic mice. RIPreC (24 h before ischemia) and RIPostC (immediately after reperfusion) were performed in an ischemia/reperfusion induced stroke model with type 2 diabetes. Ischemic outcomes, flow cytometry, multiplex cytokine assay, and western blotting were analyzed after 45 min of ischemia followed by 48 h of reperfusion. Our data indicated that RIPreC and RIPostC attenuated cerebral injuries and neurological deficits. RIPreC significantly reduced CD4 T cell and CD8 T cell infiltration and increased B cell infiltration into the ischemic brain. It also upregulated CD4 and CD8 T cell levels in the peripheral blood. However, RIPostC significantly decreased CD8 T cells infiltration and increased B cell infiltration into the ischemic brain. RIPreC inhibited IL-6 level in both the brain and blood, while RIPostC treatment attenuated IL-6 level upregulation in the peripheral blood. In addition, both RIPreC and RIPostC significantly increased p-ERK expression in the ipsilateral hemisphere in diabetic mice. This study indicated that RIPreC and RIPostC neuroprotection is present in type 2 diabetic mice via the modulation of brain ERK activity and inflammatory responses in both the peripheral blood and ischemic brain. However, the benefit was lower in RIPostC.

The role of non-coding RNAs in neuroprotection and angiogenesis following ischemic stroke

Stroke is the leading cause of death and physical disability worldwide. Non-coding RNAs (ncRNAs) are endogenous molecules that play key roles in the pathophysiology and retrieval processes following ischemic stroke. The potential of ncRNAs, especially microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) in neuroprotection and angiogenesis highlights their potential as targets for therapeutic intervention. In this review, we document the miRNAs and lncRNAs that have been reported to exert regulatory actions in neuroprotective and angiogenic processes through different mechanisms involving their interaction with target coding genes. We believe that exploration of the expression profiles and the possible functions of ncRNAs during the recovery processes will help comprehension of the molecular mechanisms responsible for neuroprotection and angiogenesis, and may also contribute to find biomarkers and targets for future stroke intervention.

Remote ischemic preconditioning protects against ischemic stroke in streptozotocin-induced diabetic mice via anti-inflammatory response and anti-apoptosis

OBJECTIVE

It has been shown that remote ischemic preconditioning (RIPreC) attenuates ischemic injury after stroke in healthy rats or mice. The present study aims to examine whether RIPreC offers neuroprotection against ischemic stroke in streptozotocin-induced diabetic mice.

METHODS

Streptozotocin (STZ, 120 mg/kg) was intraperitoneally injected into the mice to induce type 1 diabetic model. The immune and inflammatory changes were analyzed 2 days after reperfusion by flow cytometry and multiplex cytokine assay analysis, respectively.

RESULTS

We found that RIPreC reduced infarct sizes and alleviated neurological impairment in diabetic mice. RIPreC decreased CD8 T cells infiltrated into the brain, and attenuated the decreases of CD8 T cells in the blood, CD4 T cells and CD8 T cells in the spleen. Results from multiplex cytokine assay showed that RIPreC treatment decreased IL-6, IL-1 beta and TNF alpha levels in the cortex, while it inhibited IL-6 level in the hippocampus and striatum, and TNF alpha level in the hippocampus. RIPreC treatment also downregulated IL-6 and IFN gamma level in the blood, which increased after cerebral ischemic injury. In addition, RIPreC reduced pro-apoptotic protein BAX expression in the ischemic brain.

CONCLUSIONS

Our results indicate that RIPreC attenuates cerebral injuries in streptozotocin-induced diabetic mice via anti-inflammatory response and anti-apoptosis in the ischemic brain.

Non-coding RNA and neuroinflammation: implications for the therapy of stroke

Stroke is the major leading cause of death and serious, long-term disability with major economic consequences. At present, the lack of rapid diagnostic, prognostic biomarkers and effective treatment methods are two major challenges facing stroke. Circular RNAs (circRNAs) are potential clinical biomarkers in central nervous system diseases. However, the potential role of circRNAs in neuroinflammation and neuron functional recovery in acute ischaemic stroke (AIS) remains largely unknown. This review aimed to give an overview of the function of circRNAs in AIS and summarise the latest achievements in this field.

Current status and potential role of circular RNAs in neurological disorders

Given the importance of non-coding RNAs in modulating normal brain functions and their implications in the treatment of neurological disorders, non-coding RNA-based diagnostic and therapeutic strategies have shown great clinical potential. Circular RNAs (circRNAs) have emerged as potentially important players in this field. Recent studies have indicated that circRNAs might play vital roles in Alzheimer's disease, Parkinson's disease, ischemic brain injury, and neurotoxicity. However, the mechanisms of action of circRNAs have not been fully characterized. We aimed to review recent advances in circRNA research in the brain to provide new insights on the roles of circRNAs in neurological disorders.

Circular RNA expression profiles in neonatal rats following hypoxic-ischemic brain damage

Circular RNAs (circRNAs) have been studied in a number of diseases. However, the roles of circRNAs in hypoxic‑ischemic brain damage (HIBD) remains unknown. In the present study, high throughput sequencing was used to profile altered circRNAs in HIBD rats. A total of 66 circRNAs were identified to be differentially expressed (fold‑change >2 and P‑value <0.05) in HIBD rats compared with the control group, including 20 upregulated and 46 downregulated circRNAs. Gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that numerous mRNAs transcribed from the host genes of altered circRNAs were involved in brain damage and neural regeneration. The interaction of circRNA/microRNA was predicted based on TargetScan and miRanda. The results of this study demonstrated an altered circRNA expression pattern in HIBD rats and suggests important roles in HIBD physiological and pathological processes. These findings suggest a novel focus for future studies investigating the molecular mechanism underlying HIBD and possibilities for the treatment of HIBD through modulating circRNAs.

Circular RNA Expression Alteration and Bioinformatics Analysis in Rats After Traumatic Spinal Cord Injury

Spinal cord injury (SCI) is mostly caused by trauma. As primary mechanical injury is unavoidable in SCI, a focus on the pathophysiology and underlying molecular mechanisms of SCI-induced secondary injury is necessary to develop promising treatments for SCI patients. Circular RNAs (circRNAs) are associated with various diseases. Nevertheless, studies to date have not yet determined the functional roles of circRNAs in traumatic SCI. We examined circRNA expression profiles in the contused spinal cords of rats using microarray and quantitative reverse transcription-PCR (qRT-PCR) then predict their potential roles in post-SCI pathophysiology with bioinformatics. We found a total of 1676 differentially expressed circRNAs (fold change ≥ 2.0; P < 0.05) in spinal cord 3 days after contusion using circRNA microarray; 1261 circRNAs were significantly downregulated, whereas the remaining 415 were significantly upregulated. Then, five selected circRNAs, namely, rno_circRNA_005342, rno_circRNA_015513, rno_circRNA_002948, rno_circRNA_006096, and rno_circRNA_013017 were all significantly downregulated in the SCI group after verification by qRT-PCR, demonstrating a similar expression pattern in both microarray and PCR data. The next section of the study was concerned with the prediction of circRNA/miRNA/mRNA interactions using bioinformatics analysis. In the final part of the study, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes analyses indicated carbohydrate metabolic process was one of the most significant enrichments and meaningful terms after GO analysis, and the top two signaling pathways affected by the circRNAs-miRNAs axes were the AMP-activated protein kinase signaling pathway and the peroxisome related pathway. In summary, this study showed an altered circRNA expression pattern that may be involved in physiological and pathological processes in rats after traumatic SCI, providing deep insights into numerous possibilities for SCI treatment targets by regulating circRNAs.

Novel circular RNAs expressed in brain microvascular endothelial cells after oxygen-glucose deprivation/recovery

Circular RNAs (circRNAs) are generated by head-to-tail splicing and are ubiquitously expressed in all multicellular organisms. Their important biological functions are increasingly recognized. Cerebral ischemia reperfusion injury-induced brain microvascular endothelial cell dysfunction is an initial stage of blood-brain barrier disruption. The expression profile and potential function of circRNAs in brain microvascular endothelial cells is unknown. Rat brain microvascular endothelial cells were extracted and cultured in glucose-free medium for 4 hours with 5% CO₂ and 95% N₂, and the medium was then replaced with complete growth medium for 6 hours. The RNA in these cells was then extracted. The circRNA was identified by Find_circ and CIRI2 software. Functional and pathway enrichment analysis of genes that were common to differentially expressed mRNAs and circRNA host genes was performed by the Database for Annotation, Visualization and Integrated Discovery Functional Annotation Tool. Miranda software was used to predict microRNAs that were potentially sponged by circRNAs. Furthermore, cytoscape depicted the circR-NA-microRNA interaction network. The results showed that there were 1288 circRNAs in normal and oxygen-glucose deprived/recovered primary brain microvascular endothelial cells. There are 211 upregulated and 326 downregulated differentially expressed circRNAs. The host genes of these differentially expressed circRNAs overlapped with those of differentially expressed mRNAs. The shared genes were further studied by functional enrichment analyses, which revealed that circRNAs may contribute to calcium ion function and the cyclic guanosine 3′,5′-monophosphate (CAMP) dependent protein kinase (PKα) signaling pathway. Next, quantitative reverse transcription polymerase chain reaction assays were performed to detect circRNA levels transcribed from the overlapping host genes. Eight out of the ten circRNAs with the highest fold-change identified by sequencing were successfully verified. Subsequently, the circRNA-microRNA interaction networks of these eight circRNAs were explored by bioinformatic analysis. These results demonstrate that altered circRNAs may be important in the pathogenesis of cerebral ischemia reperfusion injury and consequently may also be potential therapeutic targets for cerebral ischemia diseases. All animal experiments were approved by the Chongqing Medical University Committee on Animal Research, China (approval No. CQMU20180086) on March 22, 2018.

Non-Coding RNAs to Aid in Neurological Prognosis after Cardiac Arrest

Cardiovascular disease in general, and sudden cardiac death in particular, have an enormous socio-economic burden worldwide. Despite significant efforts to improve cardiopulmonary resuscitation, survival rates remain low. Moreover, patients who survive to hospital discharge have a high risk of developing severe physical or neurological symptoms. Being able to predict outcomes after resuscitation from cardiac arrest would make it possible to tailor healthcare approaches, thereby maximising efforts for those who would mostly benefit from aggressive therapy. However, the identification of patients at risk of poor recovery after cardiac arrest is still a challenging task which could be facilitated by novel biomarkers. Recent investigations have recognised the potential of non-coding RNAs to aid in outcome prediction after cardiac arrest. In this review, we summarize recent discoveries and propose a handful of novel perspectives for the use of non-coding RNAs to predict outcome after cardiac arrest, discussing their use for precision medicine.