Circular RNA DLGAP4 Ameliorates Ischemic Stroke Outcomes by Targeting miR-143 to Regulate Endothelial-Mesenchymal Transition Associated with Blood-Brain Barrier Integrity

The Roles of circMTO1 in Cancer

Circular RNAs (circRNAs) are a recently discovered type of covalently-closed circular non-coding RNAs, mainly formed by non-sequential back-splicing of precursor mRNAs (pre-mRNAs). Recent studies have demonstrated that circRNAs can have either oncogenic or tumor-suppressor roles depending on the cellular context. CircRNA mitochondrial tRNA translation optimization 1 (circMTO1), a recently reported circular RNA originating from exons of MTO1 located on chromosome 6q13, was proved to be abnormally expressed in many malignant tumors, such as hepatocellular carcinoma, gastric carcinoma and colorectal cancer, resulting in tumor initiation and progression. However, there are no reviews focusing on the roles of circMTO1 in cancer. Here, we first summarize the main biological characteristics of circMTO1, and then focus on its biological functions and the possible underlying molecular mechanisms. Finally, we summarize the roles of circMTO1 in cancer and discuss future prospects in this area of research.

The biogenesis, function and clinical significance of circular RNAs in breast cancer

Circular RNAs (circRNAs) are noncoding RNAs that form covalently closed loop structures. CircRNAs are dysregulated in cancer and play key roles in tumorigenesis, diagnosis, and tumor therapy. CircRNAs function as competing endogenous RNAs or microRNA sponges that regulate transcription and splicing, binding to proteins, and translation. CircRNAs may serve as novel biomarkers for cancer diagnosis, and they show potential as therapeutic targets in cancers including breast cancer (BC). In women, BC is the most common malignant tumor worldwide and the second leading cause of cancer death. Although evidence indicates that circRNAs play a critical role in BC, the mechanisms regulating the function of circRNAs in BC remain poorly understood. Here, we provide literature review aiming to clarify the role of circRNAs in BC and summarize the latest research. We provide a systematic overview of the biogenesis and biological functions of circRNAs, elaborate on the functional roles of circRNAs in BC, and highlight the value of circRNAs as diagnostic and therapeutic targets in BC.

The functions of fluoxetine and identification of fluoxetine-mediated circular RNAs and messenger RNAs in cerebral ischemic stroke

Fluoxetine is used to improve cognition, exercise ability, depression, and neurological functions in patients with cerebral ischemic stroke. Circular RNAs (circRNAs) play important regulatory roles in multiple diseases. However, studies regarding the fluoxetine-mediated circRNA-microRNA-messenger RNA (mRNA) axis have not been conducted. This study is aim to investigate the functions of fluoxetine and identification of fluoxetine-mediated circRNAs and mRNAs in cerebral ischemic stroke. The middle cerebral artery occlusion (MCAO) rat models were successfully established at fisrt, and then rats were intraperitoneally injected with 10-mg/kg fluoxetine hydrochloride for 14 d. Afterward, the cerebral infarction area was evaluated using triphenyltetrazolium chloride staining. High-throughput sequencing was adopted to screen the differential circRNAs and mRNAs. The candidate circRNAs, mRNAs, and potential microRNAs were verified using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). In addtion, microRNA and circRNA binding was verified using the dual-luciferase reporter assay. Results revealed that fluoxetine markedly diminished the cerebral infarction area in rats after MCAO. The circRNAs and mRNAs were differentially expressed, which includes 879 circRNAs and 815 mRNAs between sham and MCAO groups, respectively, and 958 circRNAs and 838 mRNAs between MCAO and fluoxetine groups, respectively. In which, circMap2k1 and Pidd1 expression was significantly increased in the MCAO group but suppressed after fluoxetine treatment. Moreover, circMap2k1 directly binds with miR-135b-5p. Taken together, we verified that fluoxetine could improve brain injury after cerebral ischemic stroke. Moreover, the circMap2k1/miR-135b-5p/Pidd1 axis is potentially involved in cerebral ischemic stroke.

circSAMD4A participates in the apoptosis and autophagy of dopaminergic neurons via the miR‑29c‑3p‑mediated AMPK/mTOR pathway in Parkinson's disease

Parkinson's disease (PD) can lead to movement injury and cognitive dysfunction. Although advances have been made in attenuating PD, the effect of inhibiting the development of PD remains disappointing. Therefore, the present study aimed at investigating the etiology of Parkinson's disease and developing an alternative therapeutic strategy for patients with PD. A PD mouse model was established using an intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP-HCl; 30 mg/kg/day for 5 days), and a PD cellular model was established by treating SH-SY5Y cells with different concentrations of 1-methyl-4-phenylpyridinium (MPP⁺) for 24 h. The expression levels of circular RNA sterile α motif domain containing 4A (circSAMD4A) and microRNA (miR)-29c-3p in both midbrain tissues and SH-SY5Y cells were detected via reverse transcription-quantitative PCR. The interaction between circSAMD4A and miR-29c-3p was verified using a dual-luciferase reporter experiment. Apoptosis-, autophagy- and 5′AMP-activated protein kinase (AMPK)/mTOR cascade-associated proteins in midbrain tissues and SH-SY5Y cells were detected using western blotting. Furthermore, TUNEL staining and flow cytometry were used to analyze cell apoptosis. It was found that circSAMD4A was upregulated, while miR-29c-3p was downregulated in both PD animal and cellular models. Moreover, circSAMD4A directly targeted and negatively regulated miR-29c-3p. Further studies identified that circSAMD4A knockdown inhibited MPTP- or MPP⁺-induced apoptosis and autophagy; however, these effects were abolished by an miR-29c-3p inhibitor. In addition, circSAMD4A knockdown repressed phosphorylated-AMPK expression and increased mTOR expression in MPTP- or MPP⁺-induced PD models, the effects of which were reversed by a miR-29c-3p inhibitor. Collectively, these results suggested that circSAMD4A participated in the apoptosis and autophagy of dopaminergic neurons by modulating the AMPK/mTOR cascade via miR-29c-3p in PD.

Effect of circular RNA, mmu_circ_0000296, on neuronal apoptosis in chronic cerebral ischaemia via the miR-194-5p/Runx3/Sirt1 axis

Chronic cerebral ischaemia (CCI) is a common pathological disorder, which is associated with various diseases, such as cerebral arteriosclerosis and vascular dementia, resulting in neurological dysfunction. As a type of non-coding RNA, circular RNA is involved in regulating the occurrence and development of diseases, such as ischaemic brain injury. Here, we found that HT22 cells and hippocampus treated with CCI had low expression of circ_0000296, Runx3, Sirt1, but high expression of miR-194-5p. Overexpression of circ_0000296, Runx3, Sirt1, and silenced miR-194-5p significantly inhibited neuronal apoptosis induced by CCI. This study demonstrated that circ_0000296 specifically bound to miR-194-5p; miR-194-5p bound to the 3'UTR region of Runx3 mRNA; Runx3 directly bound to the promoter region of Sirt1, enhancing its transcriptional activity. Overexpression of circ_0000296 by miR-194-5p reduced the negative regulatory effect of miR-194-5p on Runx3, promoted the transcriptional effect of Runx3 on Sirt1, and inhibited neuronal apoptosis induced by CCI. mmu_circ_0000296 plays an important role in regulating neuronal apoptosis induced by CCI through miR-194-5p/Runx3/Sirt1 pathway.

Targeting circular RNAs as a therapeutic approach: current strategies and challenges

Significant progress has been made in circular RNA (circRNA) research in recent years. Increasing evidence suggests that circRNAs play important roles in many cellular processes, and their dysregulation is implicated in the pathogenesis of various diseases. CircRNAs are highly stable and usually expressed in a tissue- or cell type-specific manner. Therefore, they are currently being explored as potential therapeutic targets. Gain-of-function and loss-of-function approaches are typically performed using circRNA expression plasmids and RNA interference-based strategies, respectively. These strategies have limitations that can be mitigated using nanoparticle and exosome delivery systems. Furthermore, recent developments show that the cre-lox system can be used to knockdown circRNAs in a cell-specific manner. While still in the early stages of development, the CRISPR/Cas13 system has shown promise in knocking down circRNAs with high specificity and efficiency. In this review, we describe circRNA properties and functions and highlight their significance in disease. We summarize strategies that can be used to overexpress or knockdown circRNAs as a therapeutic approach. Lastly, we discuss major challenges and propose future directions for the development of circRNA-based therapeutics.

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.

Circular RNAs: Expression, localization, and therapeutic potentials

Circular RNAs (circRNAs) are RNAs with a unique circular structure that is generated from back-splicing processes. These circular molecules were discovered more than 40 years ago but failed to raise scientific interest until lately. Increasing studies have found that these circular RNAs might not just be byproducts of the splicing process but possess important regulatory functions through different cellular events. Most circular RNAs are currently being studied in the field of cancer, and many of them have been confirmed to be involved in the process of tumorigenesis. However, many circular RNAs are implicated in the developmental stages of diseases other than cancer. In this review, we focus on discussing the role of circular RNAs in non-cancer diseases, especially in cardiovascular diseases. Following the summary of the life cycle of circRNAs, we provide input on studying circRNA-protein interactions based on our experience, which modulate protein translocation. Furthermore, we outline the potential of circRNAs to be potent biomarkers, effective therapeutic targets, and potential treatments in cardiovascular diseases as well as other non-cancer fields.

ZC3H4 mediates silica-induced EndoMT via ER stress and autophagy

BACKGROUND

Inflammatory reactions induced by alveolar macrophages and excessive fibroblast activation lead to pulmonary fibrosis in silicosis. The endothelial-mesenchymal transition (EndoMT) is a key source of myofibroblasts. ZC3H4 is a member of the CCCH zinc finger protein family that participates in macrophage activation and epithelial mesenchymal transition (EMT). However, whether ZC3H4 is involved in EndoMT in silicosis has not yet been elucidated. Therefore, we conducted further studies into the role of ZC3H4 in silica-induced EndoMT in pulmonary vessels.

METHODS

Western blotting and immunofluorescence staining were used to detect the regulatory influences of SiO2 on pulmonary fibrosis and EndoMT. ZC3H4 was specifically downregulated using CRISPR/Cas9 to explore whether ZC3H4 regulated EndoMT during silicosis. C57BL/6 J mice were administered with SiO2 via the trachea to establish a silicosis animal model.

RESULTS

1) SiO2 exposure increased ZC3H4 expression in pulmonary vessels. 2) ZC3H4 was involved in EndoMT induced by silica. 3) ZC3H4 mediated EndoMT via endoplasmic reticulum stress (ER stress) and autophagy.

CONCLUSIONS

ZC3H4 greatly affects the progression of SiO2-induced EndoMT via ER stress and autophagy, which provides the possibility that ZC3H4 may become a novel target in pulmonary fibrosis treatment.

Expression and function of circular RNAs in the mammalian brain

Mammalian brain presents extraordinary complexity reflected in the structure, function, and dynamic changes in the biological and physiological processes of development, maturity, and aging. Recent transcriptomic profiles from the brain tissues of distinct species have described a novel class of transcripts with a covalently closed-loop structure, called circular RNAs (circRNAs), which are produced by alternative back-splicing and derived from genes associated with synaptogenesis and neural activities. Brain is a tightly regulated and largely unexplored organ where circRNAs are highly enriched and expressed in the cell type-, spatiotemporal-specific, sex-biased, and age-related manner. Although the biological functions of most of the circRNAs in the brain remain elusive, increased evidence suggests that dynamic changes in circRNA expression are critical for brain function and the maintenance of physiological homeostasis in the brain. Here, we review the latest immense progresses in the understanding of circRNA expression and function in the mammalian brain. We also discuss possibly biological functions of circRNAs in the brain, which may provide new sights of understanding brain development and aging, as well as the pathogenesis of mental diseases.

The role of exosomal non-coding RNAs in aging-related diseases

Aging is a biological process caused by the accumulation of senescent cells with a permanent proliferative arrest. To the influence of aging on human life expectancy, there is essential for new biomarkers which possibly will assistance in recognizing age-associated pathologies. Exosomes, which are cell-secreted nanovesicles, make available a new biomarker detection and therapeutic approach for the transfer of different molecules with high capacity. Recently, non-coding RNAs (ncRNA) which are contained in exosomes have developed as important molecules regulating the complexity of aging and relevant human diseases. The discovery of ncRNA provided perceptions into an innovative regulatory platform that could interfere with cellular senescence. The non-coding transcriptome includes a different of RNA species, spanning from short ncRNAs (<200 nucleotides) to long ncRNAs, that are >200 bp long. Upgraded evidence displays that targeting ncRNAs possibly will influence senescence pathways. In this article, we will address ncRNAs that participated in age-related and cellular senescence diseases. Growing conception of ncRNAs in the aging process possibly will be responsible for new understandings into the improvement of age-related diseases and elongated life span.

Methods to study circRNA-protein interactions

Circular RNAs (circRNAs) have been studied extensively in the last few years, uncovering functional roles in a diverse range of cell types and organisms. As shown for a few cases, these functions may be mediated by trans-acting factors, in particular RNA-binding proteins (RBPs). However, the specific interaction partners for most circRNAs remain unknown. This is mainly due to technical difficulties in their identification and in differentiating between interactors of circRNAs and their linear counterparts. Here we review the currently used methodology to systematically study circRNA-protein complexes (circRNPs), focusing either on a specific RNA or protein, both on the gene-specific or global level, and discuss advantages and challenges of the available approaches.

ΜicroRNA-122 protects against ischemic stroke by targeting Maf1

The protection of brain tissue against damage and the reduction of infarct size is crucial for improving patient prognosis following ischemic stroke. Therefore, the present study aimed to investigate the regulatory effect of microRNA (miR)-122 and its target gene repressor of RNA polymerase III transcription MAF1 homolog (Maf1) on the infarct area in ischemic stroke. Reverse transcription-quantitative PCR (RT-qPCR) was performed to determine miR-122 expression levels in an ischemic stroke [middle cerebral artery occlusion (MCAO)] mouse model. Nissl staining was conducted to measure the infarct area of the MCAO mouse model. Moreover, RT-qPCR was performed to investigate the relationship between the expression of Maf1 and miR-122 in the MCAO mouse model. Dual-luciferase reporter assay in vitro and miR-122 mimic or inhibitor treatment in vivo were conducted to verify that miR-122 targeted and inhibited Maf1 expression. The results suggested that miR-122 was upregulated in the brain tissue of MCAO model mice. miR-122 overexpression effectively reduced the size of the infarct area in comparison with a control and miR-122 knockdown in brain tissue resulted in the opposite effect. Moreover, Maf1 was confirmed to be a direct target of miR-122. The results of a dual-luciferase reporter assay indicated that miR-122 bound to the 3'-untranslated region of Maf1. Maf1 expression decreased after stroke model induction in comparison with that in sham animals, and Maf1 expression was negatively associated with the expression of miR-122. In addition, miR-122 knockdown increased Maf1 expression levels, whereas miR-122 overexpression decreased Maf1 expression levels in comparison with a control. In conclusion, the results suggested that miR-122 improved the outcome of acute ischemic stroke by reducing the expression of Maf1.

Involvement of HECTD1 in LPS-induced astrocyte activation via σ-1R-JNK/p38-FOXJ2 axis

BACKGROUND

Astrocytes participate in innate inflammatory responses within the mammalian central nervous system (CNS). HECT domain E3 ubiquitin protein ligase 1 (HECTD1) functions during microglial activation, suggesting a connection with neuroinflammation. However, the potential role of HECTD1 in astrocytes remains largely unknown.

RESULTS

Here, we demonstrated that HECTD1 was upregulated in primary mouse astrocytes after 100 ng/ml lipopolysaccharide (LPS) treatment. Genetic knockdown of HECTD1 in vitro or astrocyte-specific knockdown of HECTD1 in vivo suppressed LPS-induced astrocyte activation, whereas overexpression of HECTD1 in vitro facilitated LPS-induced astrocyte activation. Mechanistically, we established that LPS activated σ-1R-JNK/p38 pathway, and σ-1R antagonist BD1047, JNK inhibitor SP600125, or p38 inhibitor SB203580 reversed LPS-induced expression of HECTD1, thus restored LPS-induced astrocyte activation. In addition, FOXJ2 functioned as a transcription factor of HECTD1, and pretreatment of primary mouse astrocytes with BD1047, SB203580, and SP600125 significantly inhibited LPS-mediated translocation of FOXJ2 into the nucleus.

CONCLUSIONS

Overall, our present findings suggest that HECTD1 participates in LPS-induced astrocyte activation by activation of σ-1R-JNK/p38-FOXJ2 pathway and provide a potential therapeutic strategy for neuroinflammation induced by LPS or any other neuroinflammatory disorders.

Differential expression profiles of circular RNAs in the rat hippocampus after deep hypothermic circulatory arrest

Neurological dysfunction commonly occurs after cardiac surgery with deep hypothermic circulatory arrest (DHCA). The mechanisms underlying DHCA-associated brain injury remain poorly understood. This study determined the changes in expression profiles of circular RNAs (circRNAs) in the hippocampus in rats that underwent DHCA, with an attempt to explore the potential role of circRNAs in the brain injury associated with DHCA. Adult male Sprague Dawley rats were subjected to cardiopulmonary bypass with DHCA. Brain injury was evaluated by neurological severity scores and histological as well as transmission electron microscope examinations. The expression profiles of circRNAs in the hippocampal tissues were screened by microarray. Quantitative real-time PCR (RT-qPCR) was used to validate the reliability of the microarray results. Bioinformatic algorithms were applied to construct a competing endogenous RNA (ceRNA) network, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to explore the potential biological roles of the circRNAs. Out of 14 145 circRNAs screened, 56 were differentially expressed in the hippocampus between the DHCA and sham-operated rats, including 30 upregulated and 26 downregulated circRNAs. The expression changes of six selected circRNAs (upregulated: rno_circRNA_011190, rno_circRNA_012988, rno_circRNA_000544; downregulated: rno_circRNA_010393, rno_circRNA_012043, rno_circRNA_015149) were further confirmed by RT-qPCR. Bioinformatics analysis showed the enrichment of these confirmed circRNAs and their potential target mRNAs in several KEGG pathways including histidine metabolism, adipocytokine signaling, and cAMP signaling. By revealing the change expression profiles of circRNAs in the brain after DHCA, this study indicates possible involvements of these dysregulated circRNAs in brain injury and suggests a potential of targeting circRNAs for prevention and treatment of neurological dysfunction associated with DHCA.

Exosomal miR-155 from M1-polarized macrophages promotes EndoMT and impairs mitochondrial function via activating NF-κB signaling pathway in vascular endothelial cells after traumatic spinal cord injury

Pathologically, blood-spinal-cord-barrier (BSCB) disruption after spinal cord injury (SCI) leads to infiltration of numerous peripheral macrophages into injured areas and accumulation around newborn vessels. Among the leaked macrophages, M1-polarized macrophages are dominant and play a crucial role throughout the whole SCI process. The aim of our study was to investigate the effects of M1-polarized bone marrow-derived macrophages (M1-BMDMs) on vascular endothelial cells and their underlying mechanism. Microvascular endothelial cell line bEnd.3 cells were treated with conditioned medium or exosomes derived from M1-BMDMs, followed by evaluations of endothelial-to-mesenchymal transition (EndoMT) and mitochondrial function. After administration, we found conditioned medium or exosomes from M1-BMDMs significantly promoted EndoMT of vascular endothelial cells in vitro and in vivo, which aggravated BSCB disruption after SCI. In addition, significant dysfunction of mitochondria and accumulation of reactive oxygen species (ROS) were also detected. Furthermore, bioinformatics analysis demonstrated that miR-155 is upregulated in both M1-polarized macrophages and microglia. Experimentally, exosomal transfer of miR-155 participated in M1-BMDMs-induced EndoMT and mitochondrial ROS generation in bEnd.3 cells, and subsequently activated the NF-κB signaling pathway by targeting downstream suppressor of cytokine signaling 6 (SOCS6), and suppressing SOCS6-mediated p65 ubiquitination and degradation. Finally, a series of rescue assay further verified that exosomal miR155/SOCS6/p65 axis regulated the EndoMT process and mitochondrial function in vascular endothelial cells. In summary, our work revealed a potential mechanism describing the communications between macrophages and vascular endothelial cells after SCI which could benefit for future research and aid in the development of potential therapies for SCI.

Coding and non-coding nucleotides': The future of stroke gene therapeutics

Stroke is the foremost cause of death ranked after heart disease and cancer. It is the fatal life-threatening event that requires immediate medical admissions to overcome following morbidity and mortality. The therapeutic advances in stroke therapy have been manipulated with diverse paths for last 5 years. Recent research and clinical trials have investigated a variety of anti-stroke agents including anti-coagulants, cerebro-protective agents, antiplatelet therapy, stem-cell therapy, and specified gene therapy. In recent advanced studies, genetic therapies including noncoding RNAs (ncRNAs), long non-coding RNAs (LncRNAs), small interfering RNAs (siRNAs), microRNAs (miRNAs), Piwi interacting RNAs (PiWi RNAs) have shown better potential as targeted future therapeutics with a better outcome than conventional stroke therapeutics. The potential of targeted gene therapy is much more advanced in not only the induction of neuroprotection but also safer non-toxic targeted therapeutics. In the current state of the art review, we have focused on the recent advancements made towards the stroke with RNA modifications and targeted gene therapeutics.

Rs41291957 polymorphism in the promoter region of microRNA‑143 serves as a prognostic biomarker for patients with intracranial hemorrhage

The present study aimed to investigate the function of the single nucleotide polymorphism (SNP) rs41291957 in the prognosis of intracerebral hemorrhage (ICH). In addition, the molecular mechanisms underlying the role of microRNA (miR)‑143, Toll‑like receptor 2 (TLR2) and interleukin‑16 (IL‑16) were studied in patients with ICH that carried different alleles in the locus of the rs41291957 SNP. Kaplan‑Meier survival curves were calculated for 182 patients with ICH, genotyped as CC, presenting a cytosine in both chromosome, CT, presenting both variants, and TT, presents a thymine in both chromosomes. In addition, the possible regulatory relationships between miR‑143 and TLR2/IL‑16 were studied using computational analysis, luciferase assays and western blot assay. In addition, the inflammatory profiles of cerebrospinal fluid (CSF) and serum samples collected from the subjects were compared. The patients genotyped as TT presented the lowest survival rate, while patients genotyped as CC presented the highest survival rate. TLR2 mRNA was identified as a potential target of miR‑143, while IL‑16 showed no direct interaction with miR‑143. The above regulatory relationships were further investigated using cells transfected with miR‑143 precursor or TLR2 small interfering RNA. In addition, the expression levels of inflammatory factors, such as tumor necrosis factor α, interferon, IL‑6, IL‑10 and NF‑L‑6, were highest in the CSF/serum samples collected from patients genotyped as TT and lowest in patients genotyped as CC. By contrast, the expression levels of miR‑143 showed an opposite trend in the expression of the above inflammatory factors. The rs41291957 SNP, located in the promoter region of miR‑143, reduced the expression of miR‑143 and upregulated the expression of the pro‑inflammatory factor TLR2, eventually leading to a poorer prognosis in patients with ICH.

Emerging Clues of Regulatory Roles of Circular RNAs through Modulating Oxidative Stress: Focus on Neurological and Vascular Diseases

Circular RNAs (circRNAs) are novel noncoding RNAs that play regulatory roles in gene expression. Dysregulation of circRNAs is associated with the development and progression of several diseases, such as diabetes mellitus, nervous system diseases, cardiovascular diseases, and cancer. CircRNAs functionally participate in cell physiological activities through various molecular mechanisms. However, these molecular mechanisms are unclear. Oxidative stress is an essential factor in the pathogenesis of various diseases, including neurological diseases. Emerging roles of circRNAs have been identified in different systems in response to oxidative stress. In this review, we summarize the current understanding of circRNA biogenesis, properties, expression profiles, and the clues indicating the regulatory roles of circRNAs through oxidative stress in various systems, especially the nervous system.

LncRNA Rian ameliorates sevoflurane anesthesia-induced cognitive dysfunction through regulation of miR-143-3p/LIMK1 axis

Sevoflurane could stimulate neurotoxicity and result in postoperative cognitive dysfunction (POCD). Long non-coding RNAs (lncRNAs) have been implicated in the regulation of nervous system disease. This study was performed to investigate role and mechanism of lncRNA Rian (RNA imprinted and accumulated in nucleus) in sevoflurane anesthesia-induced cognitive dysfunction. Mice post-sevoflurane anesthesia showed cognitive impairments and neuronal damage and apoptosis. However, intracerebroventricularly injection with Adenovirus (Ad) for the over-expression of Rian ameliorated sevoflurane-induced neuronal damage and apoptosis. Cognitive impairments induced by sevoflurane were attenuated by injection with Ad-Rian. Moreover, transfection with Ad-Rian also protected isolated primary hippocampal neurons against sevoflurane-induced decrease of cell viability and increase of lactic acid dehydrogenase (LDH) and apoptosis. Mechanistically, Rian bind to miR-143-3p, and decreased expression of LIMK1 (Lim kinase 1) through negative regulation of miR-143-3p. Knockdown of LIMK1 aggravated sevoflurane-induced decrease of cell viability and increase of LDH and apoptosis in neurons, while over-expression attenuated LIMK1 silence-induced neuronal damage post-sevoflurane anesthesia. In conclusion, Rian demonstrated neuroprotective effects against sevoflurane anesthesia-induced cognitive dysfunction through regulation of miR-143-3p/LIMK1 axis, providing promising target for sevoflurane anesthesia-induced cognitive dysfunction.

Circular RNAs in Sudden Cardiac Death Related Diseases: Novel Biomarker for Clinical and Forensic Diagnosis

The prevention and diagnosis of sudden cardiac death (SCD) are among the most important keystones and challenges in clinical and forensic practice. However, the diagnostic value of the current biomarkers remains unresolved issues. Therefore, novel diagnostic biomarkers are urgently required to identify patients with early-stage cardiovascular diseases (CVD), and to assist in the postmortem diagnosis of SCD cases without typical cardiac damage. An increasing number of studies show that circular RNAs (circRNAs) have stable expressions in myocardial tissue, and their time- and tissue-specific expression levels might reflect the pathophysiological status of the heart, which makes them potential CVD biomarkers. In this article, we briefly introduced the biogenesis and functional characteristics of circRNAs. Moreover, we described the roles of circRNAs in multiple SCD-related diseases, including coronary artery disease (CAD), myocardial ischemia or infarction, arrhythmia, cardiomyopathy, and myocarditis, and discussed the application prospects and challenges of circRNAs as a novel biomarker in the clinical and forensic diagnosis of SCD.

Insights Into the Role of CircRNAs: Biogenesis, Characterization, Functional, and Clinical Impact in Human Malignancies

Circular RNAs (circRNAs) are an evolutionarily conserved novel class of non-coding endogenous RNAs (ncRNAs) found in the eukaryotic transcriptome, originally believed to be aberrant RNA splicing by-products with decreased functionality. However, recent advances in high-throughput genomic technology have allowed circRNAs to be characterized in detail and revealed their role in controlling various biological and molecular processes, the most essential being gene regulation. Because of the structural stability, high expression, availability of microRNA (miRNA) binding sites and tissue-specific expression, circRNAs have become hot topic of research in RNA biology. Compared to the linear RNA, circRNAs are produced differentially by backsplicing exons or lariat introns from a pre-messenger RNA (mRNA) forming a covalently closed loop structure missing 3′ poly-(A) tail or 5′ cap, rendering them immune to exonuclease-mediated degradation. Emerging research has identified multifaceted roles of circRNAs as miRNA and RNA binding protein (RBP) sponges and transcription, translation, and splicing event regulators. CircRNAs have been involved in many human illnesses, including cancer and neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease, due to their aberrant expression in different pathological conditions. The functional versatility exhibited by circRNAs enables them to serve as potential diagnostic or predictive biomarkers for various diseases. This review discusses the properties, characterization, profiling, and the diverse molecular mechanisms of circRNAs and their use as potential therapeutic targets in different human malignancies.

Roles of Non-coding RNAs in Central Nervous System Axon Regeneration

Axons in the central nervous system often fail to regenerate after injury due to the limited intrinsic regeneration ability of the central nervous system (CNS) and complex extracellular inhibitory factors. Therefore, it is of vital importance to have a better understanding of potential methods to promote the regeneration capability of injured nerves. Evidence has shown that non-coding RNAs play an essential role in nerve regeneration, especially long non-coding RNA (lncRNA), microRNA (miRNA), and circular RNA (circRNA). In this review, we profile their separate roles in axon regeneration after CNS injuries, such as spinal cord injury (SCI) and optic nerve injury. In addition, we also reveal the interactive networks among non-coding RNAs.

Tight junctions and their regulation by non-coding RNAs

Tight junction (TJ) is a “zippering up” junction structure located at the uppermost portion of adjacent epithelial/endothelial cells in organs and tissues. TJs maintain the relative stability of intracellular substances and functions by closing or opening intercellular pathways, coordinating the entry and exit of molecules of different sizes and charges, and regulating the permeability of paracellular barrier. TJs also prevent microbial invasion, maintain epithelial/endothelial cell polarity, and regulate cell proliferation. TJs are widely present in the skin and mucosal epithelial barriers, intestinal epithelial barrier, glomerular filtration barrier, bladder epithelial barrier, blood-brain barrier, brain-blood tumor barrier, and blood-testis barrier. TJ dysfunction in different organs can lead to a variety of diseases. In addition to signal pathways, transcription factors, DNA methylation, histone modification, TJ proteins can also be regulated by a variety of non-coding RNAs, such as micro-RNAs, long-noncoding RNAs, and circular RNAs, directly or indirectly. This review summarizes the structure of TJs and introduces the functions and regulatory mechanisms of TJs in different organs and tissues. The roles and mechanisms of non-coding RNAs in the regulation of TJs are also highlighted in this review.

Neuroprotective Effects of Peptides in the Brain: Transcriptome Approach

The importance of studying the action mechanisms of drugs based on natural regulatory peptides is commonly recognized. Particular attention is paid to the peptide drugs that contribute to the restoration of brain functions after acute cerebrovascular accidents (stroke), which for many years continues to be one of the main problems and threats to human health. However, molecular genetic changes in the brain in response to ischemia, as well as the mechanisms of protective effects of peptides, have not been sufficiently studied. This limits the use of neuroprotective peptides and makes it difficult to develop new, more efficient drugs with targeted action on brain functions. Transcriptome analysis is a promising approach for studying the mechanisms of the damaging effects of cerebral ischemia and neuroprotective action of peptide drugs. Beside investigating the role of mRNAs in protein synthesis, the development of new neuroprotection strategies requires studying the involvement of regulatory RNAs in ischemia. Of greatest interest are microRNAs (miRNAs) and circular RNAs (circRNAs), which are expressed predominantly in the brain. CircRNAs can interact with miRNAs and diminish their activity, thereby inhibiting miRNA-mediated repression of mRNAs. It has become apparent that analysis of the circRNA/miRNA/mRNA system is essential for deciphering the mechanisms of brain damage and repair. Here, we present the results of studies on the ischemia-induced changes in the activity of genes and peptide-mediated alterations in the transcriptome profiles in experimental ischemia and formulate the basic principles of peptide regulation in the ischemia-induced damage.

Identification of Circular RNA hsa_circ_0001599 as a Novel Biomarker for Large-Artery Atherosclerotic Stroke

Circular RNAs (circRNAs) are a recently discovered noncoding RNA isoform capable of regulating neurological disease incidence. The present study was designed to characterize the circRNA expression profiles present in large-artery atherosclerosis (LAA)-type acute ischemic stroke patients and to detect biomarkers suitable for LAA-stroke detection. Using a RNA-seq-based approach, we characterized circRNA expression profiles in five LAA-stroke patients and four controls. We confirmed the differential expression of target circRNAs through quantitative real-time polymerase chain reaction (qRT-PCR), and used Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses to explore their functional roles. The diagnostic value of specific circRNAs was evaluated through a receiver operating characteristic (ROC) curve analysis. We identified 182 upregulated and 176 downregulated circRNAs in LAA-stroke patients and confirmed the differential expression of six circRNAs through qRT-PCR. These differentially expressed circRNAs are primarily associated with chromatin modification, autophagy, platelet activation, and neural precursor cell proliferation. The hsa_circRNA_0001599 expression levels were positively correlated with the National Institutes of Health Stroke Scale scores and infarct volumes, with an ROC analysis of hsa_circRNA_0001599 in LAA-stroke, yielding an area under the curve of 0.805 (95% confidence interval: 0.748-0.862; p < 0.001), consistent with sensitivity and specificity values of 64.41% and 89.93%, respectively, for the diagnosis of LAA-stroke. A transcriptome-wide survey of differential circRNA expression in LAA-stroke patients revealed hsa_circRNA_0001599 as a putative circRNA biomarker of LAA-stroke diagnosis.

Circular RNA circPHC3 Promotes Cell Death and Apoptosis in Human BMECs After Oxygen Glucose Deprivation via miR-455-5p/TRAF3 Axis in vitro

OBJECTIVE

Brain microvascular endothelial cells (BMECs) are involved in brain vascular dysfunction in ischemic stroke. Abnormal expression of circular RNAs regulate physiological and pathophysiological processes in the central nervous system. The aim of the present study was to investigate profile circRNAs in human BMECs after oxygen glucose deprivation (OGD), which was an in vitro model of ischemic stroke, and find promising biomarkers in ischemic stroke.

METHODS

RNA sequencing (RNA-seq) technology was conducted to analyze the differential expression of circRNAs between BMECs after OGD and non-OGD treated BMECs. RT-qPCR, cell proliferation, cell apoptosis and dual-luciferase assay, and so on, were used to investigate the functions and molecular mechanisms of hsa_circ_0001360 (named circPHC3 in this study) in ischemic stroke.

RESULTS

CircPHC3 was highly expressed in human BMECs after OGD. Knockdown of circPHC3 inhibited cell death and apoptosis in human BMECs treated with OGD. Mechanistically, circPHC3 acted as miR-455-5p sponge to activate TRAF3 to promote cell death and apoptosis in human BMECs after OGD.

CONCLUSION

In short, circPHC3 promotes cell death and apoptosis in ischemic stroke in vitro model, which might be a novel molecular target for acute cerebrovascular protection.

Retina as a window to cerebral dysfunction following studies with circRNA signature during neurodegeneration

Ischemia-induced cerebral injury is a major cause of dementia or death worldwide. The pre-diagnosis is still challenging due to the retarded symptoms. The retina is regarded as the extension of cerebral tissue. Circular RNAs have emerged as the crucial regulators in gene regulatory network and disease progression. However, it is still unknown whether circRNAs can be used as the common regulators and diagnostic markers for cerebral neurodegeneration and retinal neurodegeneration. Methods: C57BL/6J mice were subjected to transient middle cerebral artery occlusion and circRNA microarray profiling was performed to identify neurodegeneration-related circRNAs. Quantitative reverse-transcription PCR (qRT-PCR) assays were performed to verify circRNA expression pattern. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis was performed to determine the biologic modules and signaling pathway. TTC staining, Nissl's staining, and immunofluorescence staining assays were performed to investigate the role of circRNA in cerebral neurodegeneration and retinal neurodegeneration in vivo. MTT assay, Propidium iodide (PI)/Calcein-AM staining, and Rhodamine 123 assays were performed to investigate the role of circRNA in neuronal injury in vitro. Bioinformatics, RIP, and luciferase activity assays were performed to determine the regulatory mechanism of circRNA in neurodegeneration. Results: 217 differentially expressed circRNAs were identified between ischemic cerebral tissues and normal controls. Among them, cGLIS3 was shown as the common regulator of cerebral neurodegeneration and retinal neurodegeneration. cGLIS3 silencing alleviated ischemia-induced retinal neurodegeneration and MCAO-induced cerebral neurodegeneration in vivo. cGLIS3 silencing protected against OGD/R-induced RGC injury in vitro. The circulating levels of cGLIS3 were significantly increased in the patients with ischemic stroke compared to healthy subjects. cGLIS3 levels were also increased in the aqueous humor of the patients with retinal vein occlusion. cGLIS3 regulated neuronal cell injury by acting as miR-203 sponge and its level was controlled by EIF4A3. Conclusions: This study provides molecular evidence that the retina is window of the brain from circRNA perspective. cGLIS3 is a common regulator and diagnostic marker of cerebral neurodegeneration and retinal neurodegeneration.

A Narrative Review of Circular RNAs in Brain Development and Diseases of Preterm Infants

Circular RNAs (circRNAs) generated by back-splicing are the vital class of non-coding RNAs (ncRNAs). Circular RNAs are highly abundant and stable in eukaryotes, and many of them are evolutionarily conserved. They are blessed with higher expression in mammalian brains and could take part in the regulation of physiological and pathophysiological processes. In addition, premature birth is important in neurodevelopmental diseases. Brain damage in preterm infants may represent the main cause of long-term neurodevelopmental disorders in surviving babies. Until recently, more and more researches have been evidenced that circRNAs are involved in the pathogenesis of encephalopathy of premature. We aim at explaining neuroinflammation promoting the brain damage. In this review, we summarize the current findings of circRNAs properties, expression, and functions, as well as their significances in the neurodevelopmental impairments, white matter damage (WMD) and hypoxic-ischemic encephalopathy (HIE). So we think that circRNAs have a direct impact on neurodevelopment and brain injury, and will be a powerful tool in the repair of the injured immature brain. Even though their exact roles and mechanisms of gene regulation remain elusive, circRNAs have potential applications as diagnostic biomarkers for brain damage and the target for neuroprotective intervention.

Beyond regulations at DNA levels: A review of epigenetic therapeutics targeting cancer stem cells

In the past few years, the paramount role of cancer stem cells (CSCs), in terms of cancer initiation, proliferation, metastasis, invasion and chemoresistance, has been revealed by accumulating studies. However, this level of cellular plasticity cannot be entirely explained by genetic mutations. Research on epigenetic modifications as a complementary explanation for the properties of CSCs has been increasing over the past several years. Notably, therapeutic strategies are currently being developed in an effort to reverse aberrant epigenetic alterations using specific chemical inhibitors. In this review, we summarize the current understanding of CSCs and their role in cancer progression, and provide an overview of epigenetic alterations seen in CSCs. Importantly, we focus on primary cancer therapies that target the epigenetic modification of CSCs by the use of specific chemical inhibitors, such as histone deacetylase (HDAC) inhibitors, DNA methyltransferase (DNMT) inhibitors and microRNA‐based (miRNA‐based) therapeutics.

Circular RNAs: Promising Biomarkers for Age-related Diseases

Aging is a complex biological process closely linked with the occurrence and development of age-related diseases. Despite recent advances in lifestyle management and drug therapy, the late diagnosis of these diseases causes severe complications, usually resulting in death and consequently impacting social economies. Therefore, the identification of reliable biomarkers and the creation of effective treatment alternatives for age-related diseases are needed. Circular RNAs (circRNAs) are a novel class of RNA molecules that form covalently closed loops capable of regulating gene expression at multiple levels. Several studies have reported the emerging functional roles of circRNAs in various conditions, providing new perspectives regarding cellular physiology and disease pathology. Notably, accumulating evidence demonstrates the involvement of circRNAs in the regulation of age-related pathologies, including cardio-cerebrovascular disease, neurodegenerative disease, cancer, diabetes, rheumatoid arthritis, and osteoporosis. Therefore, the association of circRNAs with these age-related pathologies highlights their potential as diagnostic biomarkers and therapeutic targets for better disease management. Here, we review the biogenesis and function of circRNAs, with a special focus on their regulatory roles in aging-related pathologies, as well as discuss their potential as biological biomarkers and therapeutic targets for these diseases.

Novel insights toward human stroke-related epigenetics: circular RNA and its impact in poststroke processes

Aim: Circular RNAs (circRNAs) are dysregulated in complex diseases, so we investigated their global expression profile in stroke. Material & methods: Public RNA-Seq data of human ischemic stroke lesion tissues and controls were used to perform the global expression analysis. Target RNA binding proteins and microRNAs were predicted in silico. Functional enrichment analysis was performed to infer the circRNAs' potential roles. Results: We found that circRNAs are potentially involved in synaptic components and transmission, inflammation and ataxia. An integrative analysis revealed that hsa_circ_0078299 and FXN may be major players in the molecular stroke-context. Conclusion: Our results suggest a broad involvement of circRNAs in some stroke-related processes, indicating their potential as therapeutic targets to allow neuroprotection and brain recovery.

Exosomal circ_DLGAP4 promotes diabetic kidney disease progression by sponging miR-143 and targeting ERBB3/NF-κB/MMP-2 axis

Diabetic kidney disease (DKD) is closely associated with the high risk of cardiovascular disease and mortality. Exosomal circRNAs can exert significant roles in the pathology of various diseases. Nevertheless, the role of exosomal circRNAs in DKD progression remains barely known. Circular RNA DLGAP4 has been reported to be in involved in acute ischemic stroke. In our study, we found exosomal circ_DLGAP4 was increased in the exosomes isolated from HG-treated mesangial cells (MCs), DKD patients, and DKD rat models compared with the corresponding normal subjects. Then, we observed that exo-circ_DLGAP4 significantly promoted proliferation and fibrosis of MCs cells. Moreover, to study the underlying mechanism of circ_DLGAP4 in regulating DKD, bioinformatics method was consulted and miR-143 was predicted as its target. The direct correlation between miR-143 and circ_DLGAP4 was validated in MCs. MCs proliferation and fibrosis were increased by circ_DLGAP4, which could be decreased by mimic-miR-143. Next, elevated expression of Erb-b2 receptor tyrosine kinase 3 (ERBB3) is involved in various diseases. However, the function of ERBB3 in DKD development remains poorly known. Next, ERBB3 was predicted as the downstream target for miR-143. It was displayed that circ_DLGAP4 promoted proliferation and fibrosis of MCs by sponging miR-143 and regulating ERBB3/NF-κB/MMP-2 axis. Meanwhile, the loss of exo-circ_DLGAP4 induced miR-143 and repressed ERBB3/NF-κB/MMP-2 expression in MCs. Subsequently, in vivo assays were performed and it was proved that overexpression of circ_DLGAP4 markedly promoted DKD progression in vivo via modulating miR-143/ERBB3/NF-κB/MMP-2. In conclusion, we indicated that exosomal circ_DLGAP4 could prove a novel insight for DKD development.

Phenotype-genotype network construction and characterization: a case study of cardiovascular diseases and associated non-coding RNAs

The phenotype–genotype relationship is a key for personalized and precision medicine for complex diseases. To unravel the complexity of the clinical phenotype–genotype network, we used cardiovascular diseases (CVDs) and associated non-coding RNAs (ncRNAs) (i.e. miRNAs, long ncRNAs, etc.) as the case for the study of CVDs at a systems or network level. We first integrated a database of CVDs and ncRNAs (CVDncR, http://sysbio.org.cn/cvdncr/) to construct CVD–ncRNA networks and annotate their clinical associations. To characterize the networks, we then separated the miRNAs into two groups, i.e. universal miRNAs associated with at least two types of CVDs and specific miRNAs related only to one type of CVD. Our analyses indicated two interesting patterns in these CVD–ncRNA networks. First, scale-free features were present within both CVD–miRNA and CVD–lncRNA networks; second, universal miRNAs were more likely to be CVDs biomarkers. These results were confirmed by computational functional analyses. The findings offer theoretical guidance for decoding CVD–ncRNA associations and will facilitate the screening of CVD ncRNA biomarkers.

Database URL: http://sysbio.org.cn/cvdncr/

Seeing Is Believing: Visualizing Circular RNAs

Advancement in the RNA sequencing techniques has discovered hundreds of thousands of circular RNAs (circRNAs) in humans. However, the physiological function of most of the identified circRNAs remains unexplored. Recent studies have established that spliceosomal machinery and RNA-binding proteins modulate circRNA biogenesis. Furthermore, circRNAs have been implicated in regulating crucial cellular processes by interacting with various proteins and microRNAs. However, there are several challenges in understanding the mechanism of circRNA biogenesis, transport, and their interaction with cellular factors to regulate cellular events because of their low abundance and sequence similarity with linear RNA. Addressing these challenges requires systematic studies that directly visualize the circRNAs in cells at single-molecule resolution along with the molecular regulators. In this review, we present the design, benefits, and weaknesses of RNA imaging techniques such as single-molecule RNA fluorescence in situ hybridization and BaseScope in fixed cells and fluorescent RNA aptamers in live-cell imaging of circRNAs. Furthermore, we propose the potential use of molecular beacons, multiply labeled tetravalent RNA imaging probes, and Cas-derived systems to visualize circRNAs.

Circular RNAs: Emerging Role in Cancer Diagnostics and Therapeutics

Circular RNAs (circRNAs) are rapidly coming to the fore as major regulators of gene expression and cellular functions. They elicit their influence via a plethora of diverse molecular mechanisms. It is not surprising that aberrant circRNA expression is common in cancers and they have been implicated in multiple aspects of cancer pathophysiology such as apoptosis, invasion, migration, and proliferation. We summarize the emerging role of circRNAs as biomarkers and therapeutic targets in cancer.

Practical guide for circular RNA analysis: Steps, tips, and resources

Recent technological advances in RNA sequencing and analysis have allowed an increasingly thorough investigation of a previously unexplored class of transcripts, circular (circ)RNAs. Accumulating evidence suggests that circRNAs have unique functions which often rely on their association with microRNAs and RNA-binding proteins. Through these interactions, circRNAs have been implicated in major cellular processes and hence in the pathophysiology of a range of diseases. Here, we provide guidelines to consider when developing studies on circRNAs, including detecting and selecting the circRNAs, identifying their binding partners and sites of interaction, modulating circRNA levels, assessing copy numbers and stoichiometry, and addressing other points unique to circRNA analysis. This article is categorized under: Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs.

Circular RNAs are a novel type of non-coding RNAs in ROS regulation, cardiovascular metabolic inflammations and cancers

Circular RNAs (circRNAs) are a novel class of endogenous non-coding RNAs characterized by a covalently closed-loop structure generated through a special type of alternative splicing termed back-splicing. Currently, an increasing body of evidence has demonstrated that 1) majority of circRNAs are evolutionarily conserved across species, stable, and resistant to RNase R degradation, and often exhibit cell-specific, and tissue-specific/developmental-stage-specific expression and can be largely independent of the expression levels of the linear host gene-encoded linear RNAs; 2) the biogenesis of circRNAs via back-splicing is different from the canonical splicing of linear RNAs; 3) circRNA biogenesis is regulated by specific cis-acting elements and trans-acting factors; 4) circRNAs regulate biological and pathological processes by sponging miRNAs, binding to RNA-binding protein (RBP), regulators of splicing and transcription, modifiers of parental gene expression, and regulators of protein translation or being translated into peptides in various diseases; 5) circRNAs have been identified for their enrichment and stability in exosomes and detected in body fluids such as human blood, saliva, and cerebrospinal fluids, suggesting that these exo-circRNAs have potential applications as disease biomarkers and novel therapeutic targets; 6) several circRNAs are regulated by oxidative stress and mediate reactive oxygen species (ROS) production as well as promote ROS-induced cellular death, cell apoptosis, and inflammation; 7) circRNAs have also emerged as important regulators in atherosclerotic cardiovascular disease, metabolic disease, and cancers; 8) the potential mechanisms of several circRNAs have been described in diseases, hinting at their potential applications as novel therapeutic targets. In this highlight, we summarized the current understandings of the biogenesis and functions of circRNAs and their roles in ROS regulation and vascular inflammation-associated with cardiovascular and metabolic disease. (Word count: 272).

Downregulation of circular RNA HECTD1 induces neuroprotection against ischemic stroke through the microRNA-133b/TRAF3 pathway

AIMS

Circular RNAs (circRNAs) have been shown to play crucial roles in various biological processes and human diseases. However, their exact functions in ischemic stroke remain largely unknown. In this study, we explored the functional role of circRNA HECTD1 (circ-HECTD1) and its underlying mechanism in cerebral ischemia/reperfusion injury.

METHODS

Mouse middle cerebral artery occlusion (MCAO) model and oxygen-glucose deprivation (OGD) model in HT22 cells were used to mimic the cerebral ischemia/reperfusion injury. Brain infarct volume, flow cytometry, caspase 3 activity, NF-κB activity, and TUNEL staining were performed to evaluate the function of circ-HECTD1. Luciferase report assay was used to explore the regulatory mechanism.

FINDINGS

The results showed that the expression of circ-HECTD1 and tumor necrosis factor receptor-associated factor 3 (TRAF3) was remarkably up-regulated, while miR-133b was down-regulated in oxygen-glucose deprivation (OGD)-induced HT22 cells and mouse middle cerebral artery occlusion (MCAO) model. circ-HECTD1 knockdown relieved OGD-caused neuronal cell death in vitro. Simultaneously, circ-HECTD1 knockdown improved cerebral infarction volume and neuronal apoptosis in MCAO mice. circ-HECTD1 was able to negatively regulate the expression of miR-133b, and TRAF3 is one of the targets of miR-133b. Upregulation of miR-133b inhibited the expression of TRAF3 in OGD-stimulated cells, whereas circ-HECTD1 upregulation reversed this effect. Furthermore, upregulation of miR-133 was able to inhibit OGD-caused cell apoptosis and NF-κB activation, whereas upregulation of circ-HECTD1 attenuated these effects of miR-133b mimics.

SIGNIFICANCE

Taken together, circ-HECTD1 knockdown inhibited the expression of TRAF3 by targeting miR-133b, thereby attenuating neuronal injury caused by cerebral ischemia.

Regulation of Glycolysis by Non-coding RNAs in Cancer: Switching on the Warburg Effect

The “Warburg effect” describes the reprogramming of glucose metabolism away from oxidative phosphorylation toward aerobic glycolysis, and it is one of the hallmarks of cancer cells. Several factors can be involved in this process, but in this review, the roles of non-coding RNAs (ncRNAs) are highlighted in several types of human cancer. ncRNAs, including microRNAs, long non-coding RNAs, and circular RNAs, can all affect metabolic enzymes and transcription factors to promote glycolysis and modulate glucose metabolism to enhance the progression of tumors. In particular, the 5′-AMP-activated protein kinase (AMPK) and the phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathways are associated with alterations in ncRNAs. A better understanding of the roles of ncRNAs in the Warburg effect could ultimately lead to new therapeutic approaches for suppressing cancer.

Role of circular RNAs in digestive system tumors

Circular RNAs (circRNAs), a class of endogenous closed-loop noncoding RNAs, are expressed widely in all kinds of eukaryotic cells and have the characteristics of stable structure, high conservation, cell specificity, and tissue specificity. Several studies have revealed that circRNAs are closely related to the occurrence and development of cardiovascular system diseases, nervous system diseases, tumors, and other diseases. Recently, more and more studies have indicated that circRNAs have good clinical efficacy in the diagnosis and treatment of digestive system tumors, and they are expected to become biomarkers for early diagnosis and new therapeutic targets for the development of novel anticancer drugs. Therefore, it has become a hot topic of the current and future development direction in clinical research. circRNAs play a dual role in the pathological evolution of digestive system tumors, wherein they acting as miRNA sponges could play significant roles in carcinogenesis and anticarcinogenesis. This paper reviews the biological characteristics of circRNAs, summarizes the research progress of circRNAs in digestive system tumors, and discusses the potential use of circRNAs as targets for prevention, diagnosis, and treatment of digestive system tumors in the future.

circ_2858 Helps Blood-Brain Barrier Disruption by Increasing VEGFA via Sponging miR-93-5p during Escherichia coli Meningitis

Meningitic Escherichia coli invasion of the host brain can lead to increased blood-brain barrier (BBB) permeability. Circular RNAs (circRNAs) are non-coding RNAs, highly abundant in the brain, that are widely involved in the pathological processes of central nervous system (CNS) disorders; however, whether circRNAs participate in the regulation of BBB permeability during E. coli meningitis remains unknown. Here, we identified a novel circRNA, circ_2858, that was significantly upregulated in human brain microvascular endothelial cells (hBMECs) upon meningitic E. coli infection. We also found that circ_2858 regulated BBB permeability in hBMECs by competitively binding miR-93-5p, thereby inducing the upregulation of vascular endothelial growth factor A and finally resulting in downregulation as well as altered distribution of tight junction proteins such as ZO-1, Occludin, and Claudin-5. These findings provide novel insights into the influence of circ_2858 on BBB permeability during the pathogenic process of E. coli meningitis, suggesting potential nucleic acid targets for future prevention and therapy of CNS infection induced by meningitic E. coli.

Exosomes Derived From CircAkap7-Modified Adipose-Derived Mesenchymal Stem Cells Protect Against Cerebral Ischemic Injury

Background

Cerebral ischemic injury is a complicated pathological process. Adipose-derived stromal cells (ADSCs) have been used as a therapeutic strategy, with their therapeutic effects chiefly attributed to paracrine action rather than trans-differentiation. Studies have shown that circAkap7 was found to be downregulated in a mouse model of transient middle cerebral artery occlusion (tMCAO).

Methods

To explore whether exosomes derived from circAkap7-modified ADSCs (exo-circAkap7) have therapeutic effects on cerebral ischemic injury, a mouse model of tMCAO, as well as an in vitro model of oxygen and glucose deprivation-reoxygenation (OGD-R) in primary astrocytes, were used.

Results

Results showed that treatment with exo-circAkap7 protected against tMCAO in mice, and in vitro experiments confirmed that co-culture with exo-circAkap7 attenuated OGD-R-induced cellular injury by absorbing miR-155-5p, promoting ATG12-mediated autophagy, and inhibiting NRF2-mediated oxidative stress.

Conclusion

We demonstrate here that exo-circAkap7 protected against cerebral ischemic injury by promoting autophagy and ameliorating oxidative stress.

miR-103a-3p alleviates oxidative stress, apoptosis, and immune disorder in oxygen-glucose deprivation-treated BV2 microglial cells and rats with cerebral ischemia-reperfusion injury by targeting high mobility group box 1

Background

Cerebral ischemia-reperfusion injury (CI/R) is among the most common diseases affecting the central nervous system. Due to the poor efficacy and adverse side effects of the drugs used to treat CI/R in clinical trials, a new treatment strategy is urgently needed. In this study, we aimed to investigate whether miR-103a-3p alleviates CI/R in vivo and vitro and to explore the relevant mechanisms.

Methods

BV2 microglial cells underwent oxygen-glucose deprivation (OGD) treatment to imitate the pathophysiology of CI/R in vitro. A middle cerebral artery occlusion (MCAO) rat model was established to imitate the pathophysiology of CI/R in vivo. The expression levels of miR-103a-3p and HMGB1 were detected by reverse transcription-polymerase chain reaction (RT-PCR) and western blot. Flow cytometry, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, enzyme-linked immunosorbent assay (ELISA), and hematoxylin and eosin (H&E) and Nissl staining were used to evaluated apoptosis, oxidative stress, inflammatory response, and histopathology, respectively.

Results

OGD-stimulated BV2 microglial cells and brain tissues with CI/R had low expression of miR-103a-3p but high expression of high mobility group box 1 (HMGB1). As expected, miR-103a-3p and HMGB1 had a targeting relationship. Overexpression of HMGB1 enhanced the the levels of interleukin (IL)-1 beta, tumor necrosis factor-alpha (TNF-α) and malondialdehyde (MDA), but reduced the content of superoxide dismutase (SOD), IL-4, and IL-10, in vitro. Moreover, high expression of HMGB1 aggravated the brain injury of the model rats, and increased the secretion of inflammatory factors, exacerbated oxidative stress, and further induced tissue apoptosis in the brain tissue. Importantly, these effects of HMGB1 overexpression were partly reversed by miR-103a-3p overexpression on HMGB1 interference.

Conclusions

HMGB1 is targeted by miR-103a-3p, which may be a new strategy in the treatment of CI/R.

Role of non-coding RNAs in age-related vascular cognitive impairment: An overview on diagnostic/prognostic value in Vascular Dementia and Vascular Parkinsonism

Age is the pivotal risk factor for different common medical conditions such as cardiovascular diseases, cancer and dementia. Among age-related disorders, cardiovascular and cerebrovascular diseases, represent the leading causes of premature mortality strictly related to vascular ageing, a pathological condition characterized by endothelial dysfunction, atherosclerosis, hypertension, heart disease and stroke. These features negatively impact on the brain, owing to altered cerebral blood flow, neurovascular coupling and impaired endothelial permeability leading to cerebrovascular diseases (CVDs) as Vascular Dementia (VD) and Parkinsonism (VP). It is an increasing opinion that neurodegenerative disorders and cerebrovascular diseases are associated from a pathogenetic point of view, and in this review, we discuss how cerebrovascular dysfunctions, due to epigenetic alterations, are linked with neuronal degeneration/dysfunction that lead to cognitive impairment. The relation between neurodegenerative and cerebrovascular diseases are reviewed with a focus on role of ncRNAs in age-related vascular diseases impairing the endothelium in the blood-brain barrier with consequent dysfunction of cerebral blood flow. In this review we dissert about different regulatory mechanisms of gene expression implemented by ncRNAs in the pathogenesis of age-related neurovascular impairment, aiming to highlight the potential use of ncRNAs as biomarkers for diagnostic/prognostic purposes as well as novel therapeutic targets.

Overexpression of circRNA circUCK2 Attenuates Cell Apoptosis in Cerebral Ischemia-Reperfusion Injury via miR-125b-5p/GDF11 Signaling

Circular RNAs (circRNAs) are expressed at high levels in the brain and are involved in various central nervous system diseases. However, the potential role of circRNAs in ischemic stroke-associated neuronal injury remains largely unknown. Herein, we uncovered the function and underlying mechanism of the circRNA UCK2 (circUCK2) in ischemia stroke. The oxygen-glucose deprivation model in HT-22 cells was used to mimic ischemia stroke in vitro. Neuronal viability and apoptosis were determined by Cell Counting Kit-8 (CCK-8) assays and TUNEL (terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick end labeling) staining, respectively. Middle cerebral artery occlusion was conducted to evaluate the function of circUCK2 in mice. The levels of circUCK2 were significantly decreased in brain tissues from a mouse model of focal cerebral ischemia and reperfusion. Upregulated circUCK2 levels significantly decreased infarct volumes, attenuated neuronal injury, and improved neurological deficits. circUCK2 reduced oxygen glucose deprivation (OGD)-induced cell apoptosis by regulating transforming growth factor β (TGF-β)/mothers against decapentaplegic homolog 3 (Smad3) signaling. Furthermore, circUCK2 functioned as an endogenous miR-125b-5p sponge to inhibit miR-125b-5p activity, resulting in an increase in growth differentiation factor 11 (GDF11) expression and a subsequent amelioration of neuronal injury. Consequently, these findings showed that the circUCK2/miR-125b-5p/GDF11 axis is an essential signaling pathway during ischemia stroke. Thus, the circRNA circUCK2 may serve as a potential target for novel treatment in patients with ischemic stroke.

Disease-Associated Circular RNAs: From Biology to Computational Identification

Circular RNAs (circRNAs) are endogenous RNAs with a covalently closed continuous loop, generated through various backsplicing events of pre-mRNA. An accumulating number of studies have shown that circRNAs are potential biomarkers for major human diseases such as cancer and Alzheimer's disease. Thus, identification and prediction of human disease-associated circRNAs are of significant importance. To this end, a computational analysis-assisted strategy is indispensable to detect, verify, and quantify circRNAs for downstream applications. In this review, we briefly introduce the biology of circRNAs, including the biogenesis, characteristics, and biological functions. In addition, we outline about 30 recent bioinformatic analysis tools that are publicly available for circRNA study. Principles for applying these computational strategies and considerations will be briefly discussed. Lastly, we give a complete survey on more than 20 key computational databases that are frequently used. To our knowledge, this is the most complete and updated summary on publicly available circRNA resources. In conclusion, this review summarizes key aspects of circRNA biology and outlines key computational strategies that will facilitate the genome-wide identification and prediction of circRNAs.

Biogenesis of circular RNAs and their role in cellular and molecular phenotypes of neurological disorders

Circular RNA (circRNA) is an unusual class of RNA-like structures composed by exonic and/or intronic sequences that are regulated by the backsplicing mechanism and by the spliceosome-mediated machinery. These circular transcripts tend to accumulate during aging in several human tissues, especially in the mammalian brain, and their expression is correlated with the occurrence of several human pathologies, including a broad spectrum of neurological disorders. Previous findings have also shown that circRNAs are significantly present in the neuronal tissue and are up-regulated during neurogenesis, with a significant number been derived from neural genes, suggesting these circular molecules are involved in the cellular and molecular phenotype of our brain. However, the complete biogenesis, the many types of circRNA molecules, and their involvement with neuronal phenotype and with the occurrence of pathologies are still a challenging avenue for researchers. In this updated review, we discuss the current findings of the biogenesis and the diversity of cirRNAs and their molecular involvement in neurological tissue phenotype. We also discuss how some circRNAs can act as sponge molecules, regulating the activity of microRNA expression over gene translation. Finally, we also show the correlation of altered circRNA expression in neurological disorders.