Circular RNAs: Novel Regulators of Neuronal Development

Maternal exposure to glyphosate increased the risk of adverse neurodevelopmental outcomes in rodent offspring: A systematic review

The potential neurotoxicity of environmental contaminants, such as pesticides, is implicated in the etiology of neurodevelopmental disorders, particularly given the heightened vulnerability of the developing brain. Among these contaminants, glyphosate, a widely used herbicide, has been linked to alterations in neurodevelopment, though its precise neurotoxic mechanisms are not fully elucidated. In this context, our systematic review evaluates the impact of maternal exposure to glyphosate alone (GLY) or glyphosate-based-herbicide (GBH) on neurodevelopmental and behavioral outcomes in rodent offspring. This assessment encompasses a comprehensive examination of behavioral, biochemical, morphological, and genetic alterations resulting from perinatal glyphosate exposure. The Systematic review protocol was registered in the platform Open Science Framework (OSF) following the guidelines of the Systematic Review Center for Laboratory Animal Experimentation (SYRCLE). Our analysis demonstrate that glyphosate disrupts redox signaling, metabolic pathways, and neurotransmitter systems, thereby affecting brain architecture and function across genders and developmental stages in rodents. The results of this review elucidate the extensive neurochemical and behavioral disruptions attributed to glyphosate, highlighting the critical need for advanced neurodevelopmental risk assessment methodologies. Such refined evaluations are vital to inform targeted prevention and intervention strategies in the context of environmental neurotoxicants.

Circ_0003764 Regulates the Osteogenic Differentiation of Periodontal Ligament Stem Cells

INTRODUCTION AND AIMS

Specific circular RNAs (circRNAs) have been proven to play crucial roles in osteogenesis in vitro and in vivo. This study aims to identify a certain circRNA involved in the osteogenic differentiation of periodontal ligament stem cells (PDLSCs) and explore its regulatory role.

METHODS

The expression of 5 candidate circRNAs (circ_0026344, circ_ACAP2, circ_0003764, circ_0008259, and circ_0060731) was detected by real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) after PDLSCs were cultured in the osteogenic induction medium or medium supplemented with tumour necrosis factor-α (TNF-α, 10 ng/mL) for 3 and 7 days. The circRNA significantly decreased in both 3 and 7 days of osteogenic induction in PDLSCs and markedly increased in TNF-α-induced PDLSCs for 3 and 7 days screened. Identified circRNA was knocked down or overexpressed, and the effect on the osteogenic differentiation of PDLSCs was investigated by qRT-PCR, western blot, alkaline phosphatase (ALP) staining, and alizarin red S (ARS) staining. Cell counting kit-8 (CCK-8) assay and 5-ethynyl-2'-deoxyuridine (EdU) assay were applied to detect the effect of the circRNA on the proliferation of PDLSCs.

RESULTS

qRT-PCR results showed that the expression of circ_0003764 was significantly decreased when PDLSCs were cultured in the osteogenic induction medium for 3 or 7 days, whereas it was dramatically increased in TNF-α-induced PDLSCs. Knockdown of circ_0003764 promoted the expression of the osteogenesis-related genes (RUNX2, ALP, OCN) and proteins (RUNX2, OCN), enhanced the ALP activity, and elevated the mineralization by PDLSCs, as shown by ARS staining. However, with the overexpression of circ_0003764, the osteogenic differentiation capacity of PDLSCs was significantly reduced. The CCK-8 and EdU results indicated that circ_0003764 could inhibit the proliferation of PDLSCs.

CONCLUSION

Circ_0003764 is involved in the osteogenesis process and inhibits the osteogenic differentiation and proliferation of PDLSCs.

CLINICAL RELEVANCE

This study indicates that circ_0003764 can serve as a diagnostic and therapeutic target in bone regeneration-related diseases treated by PDLSCs-based tissue engineering.

A tripartite circRNA/mRNA/miRNA interaction regulates glutamatergic signaling in the mouse brain

Functional studies of circular RNAs (circRNAs) began quite recently, and few data exist on their function in vivo. Here, we have generated a knockout (KO) mouse model to study circDlc1(2), a circRNA highly expressed in the prefrontal cortex and striatum. The loss of circDlc1(2) led to the upregulation of glutamatergic-response-associated genes in the striatal tissue, enhanced excitatory synaptic transmission in neuronal cultures, and hyperactivity and increased stereotypies in mice. Mechanistically, we found that circDlc1(2) physically interacts with some mRNAs, associated with glutamate receptor signaling (gluRNAs), and with miR-130b-5p, a translational regulator of these transcripts. Notably, differently from canonical microRNA (miRNA) "sponges," circDlc1(2) synergizes with miR-130b-5p to repress gluRNA expression. We found that circDlc1(2) is required to spatially control miR-130b-5p localization at synaptic regions where gluRNA is localized, indicating a different layer of regulation where circRNAs ensure robust control of gene expression via the correct subcellular compartmentalization of functionally linked interacting partners.

Systematic identification and analysis of immune-related circRNAs of Pelteobagrus fulvidraco involved in Aeromonas veronii infection

Circular RNA (circRNA) represents a type of newly discovered non-coding RNA, distinguished by its closed loop structure formed through covalent bonds. Recent studies have revealed that circRNAs have crucial influences on host anti-pathogen responses. Yellow catfish (Pelteobagrus fulvidraco), an important aquaculture fish with great economic value, is susceptible to Aeromonas veronii, a common aquatic pathogen that can cause acute death. Here, we reported the first systematic investigation of circRNAs in yellow catfish, especially those associated with A. veronii infection at different time points. A total of 1205 circRNAs were identified, which were generated from 875 parental genes. After infection, 47 circRNAs exhibited differential expression patterns (named DEcirs). The parental genes of these DEcirs were functionally engaged in immune-related processes. Accordingly, seven DEcirs (novel_circ_000226, 278, 401, 522, 736, 843, and 975) and six corresponding parental genes (ADAMTS13, HAMP1, ANG3, APOA1, FGB, and RALGPS1) associated with immunity were obtained, and their expression was confirmed by RT-qPCR. Moreover, we found that these DEcir-gene pairs likely acted through pathways, such as platelet activation, antimicrobial humoral response, and regulation of Ral protein signal transduction, to influence host immune defenses. Additionally, integrated analysis showed that, of the 7 immune-related DEcirs, three targeted 16 miRNAs, which intertwined into circRNA-miRNA networks. These findings revealed that circRNAs, by targeting genes or miRNAs are highly involved in anti-bacterial responses in yellow catfish. Our study comprehensively illustrates the roles of circRNAs in yellow catfish immune defenses. The identified DEcirs and the circRNA-miRNA network will contribute to the further investigations on the molecular mechanisms underlying yellow catfish immune responses.

Circular RNA as a Biomarker for Diagnosis, Prognosis and Therapeutic Target in Acute and Chronic Lymphoid Leukemia

Circular RNAs (circRNAs) are single-stranded RNAs that have received much attention in recent years. CircRNAs lack a 5' head and a 3' poly-A tail. The structure of this type of RNAs make them resistant to digestion by exonucleases. CircRNAs are expressed in different cells and have various functions. The function of circRNAs is done by sponging miRNAs, changing gene expression, and protein production. The expression of circRNAs changes in different types of cancers, which causes changes in cell growth, proliferation, differentiation, and apoptosis. Changes in the expression of circRNAs can cause the invasion and progression of tumors. Studies have shown that changes in the expression of circRNAs can be seen in acute lymphoid leukemia (ALL) and chronic lymphoid leukemia (CLL). The conducted studies aim to identify circRNAs whose expression has changed in these leukemias and their more precise function so that these circRNAs can be identified as biomarkers, prediction of patient prognosis, and treatment targets for ALL and CLL patients. In this study, we review the studies conducted on the role and function of circRNAs in ALL and CLL patients. The results of the studies show that there is a possibility of using circRNAs as biomarkers in the identification and treatment of patients in the future.

Understanding age-related pathologic changes in TDP-43 functions and the consequence on RNA splicing and signalling in health and disease

TAR DNA binding protein-43 (TDP-43) is a key component in RNA splicing which plays a crucial role in the aging process. In neurodegenerative diseases such as amyotrophic lateral sclerosis, frontotemporal dementia and limbic-predominant age-related TDP-43 encephalopathy, TDP-43 can be mutated, mislocalised out of the nucleus of neurons and glial cells and form cytoplasmic inclusions. These TDP-43 alterations can lead to its RNA splicing dysregulation and contribute to mis-splicing of various types of RNA, such as mRNA, microRNA, and circular RNA. These changes can result in the generation of an altered transcriptome and proteome within cells, ultimately changing the diversity and quantity of gene products. In this review, we summarise the findings of novel atypical RNAs resulting from TDP-43 dysfunction and their potential as biomarkers or targets for therapeutic development.

Competing Endogenous RNAs Crosstalk in Hippocampus: A Potential Mechanism for Neuronal Developing Defects in Down Syndrome

Down syndrome (DS) is the most example of aneuploidy, resulting from an additional copy of all or part of chromosome 21. Competing endogenous RNAs (ceRNAs) play important roles in neuronal development and neurological defects. This study aimed to identify hub genes and synergistic crosstalk among ceRNAs in the DS fetal hippocampus as potential targets for the treatment of DS-related neurodegenerative diseases. We profiled differentially expressed long non-coding RNAs (DElncRNAs), differentially expressed circular RNAs (DEcircRNAs), differentially expressed microRNAs (DEmiRNAs), and differentially expressed messenger RNAs (DEmRNAs) in hippocampal samples from patients with or without DS. Functional enrichment analysis and gene set enrichment analysis were performed, and chromosome 21-related ceRNA and protein-protein interaction networks were constructed. Additionally, the correlations between lncRNA-mRNA and miRNA-mRNA expression in the samples and HEK293T cells were validated. Our finding of changes in the expression of some key genes and ncRNAs on chromosome 21 in DS might not fully conform to the gene dosage hypothesis. Moreover, we found that four lncRNAs (MIR99AHG, PLCB4, SNHG14, GIGYF2) and one circRNA (hsa_circ_0061697) may competitively bind with three miRNAs (hsa-miR-548b-5p, miR-730-5p, and hsa-miR-548i) and subsequently regulate five mRNAs (beta-1,3-galactosyltransferase 5 [B3GALT5], helicase lymphoid-specific [HELLS], thrombospondin-2 [THBS2], glycinamide ribonucleotide transformylase [GART], clathrin heavy chain like 1 [CLTCL1]). These RNAs, whether located on chromosome 21 or not, interact with each other and might activate the PI3K/Akt/mTOR and Wnt signaling pathways, which are involved in autophagosome formation and tau hyperphosphorylation, possibly leading to adverse consequences of trisomy 21. These findings provide researchers with a better understanding of the fundamental molecular mechanisms underlying DS-related progressive defects in neuronal development.

Dysregulation of the circRNA_0087207/miR-548c-3p/PLSR1-TGFB2 axis in Leber hereditary optic neuropathy in vitro

BACKGROUND

Leber hereditary optic neuropathy (LHON) is mainly the degeneration of retinal ganglion cells (RGCs) associated with high apoptosis and reactive oxygen species (ROS) levels, which is accepted to be caused by the mutations in the subunits of complex I of the mitochondrial electron transport chain. The treatment is still infant while efforts of correcting genes or using antioxidants do not bring good and consistent results. Unaffected carrier carries LHON mutation but shows normal phenotype, suggesting that the disease's pathogenesis is complex, in which secondary factors exist and cooperate with the primary complex I dysfunction.

METHODS

Using LHON patient-specific induced pluripotent stem cells (iPSCs) as the in vitro disease model, we previously demonstrated that circRNA_0087207 had the most significantly higher expression level in the LHON patient-iPSC-derived RGCs compared with the unaffected carrier-iPSC-derived RGCs. To elaborate the underlying pathologies regulated by circRNA_008720 mechanistically, bioinformatics analysis was conducted and elucidated that circRNA_0087207 could act as a sponge of miR-548c-3p and modulate PLSCR1/TGFB2 levels in ND4 mutation-carrying LHON patient-iPSC-derived RGCs.

RESULTS

Using LHON iPSC-derived RGCs as the disease-based platform, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis on targeted mRNA of miR-548c-3p showed the connection with apoptosis, suggesting downregulation of miR548c-3p contributes to the apoptosis of LHON patient RGCs.

CONCLUSION

We showed that the downregulation of miR548c-3p plays a critical role in modulating cellular dysfunction and the apoptotic program of RGCs in LHON.

Regulatory mechanisms of circular RNAs during human mesenchymal stem cell osteogenic differentiation

Human osteogenic differentiation is a complex and well-orchestrated process which involves a plethora of molecular players and cellular processes. A growing number of studies have underlined that circular RNAs (circRNAs) play an important regulatory role during human osteogenic differentiation. CircRNAs are single-stranded, covalently closed non-coding RNA molecules that are acquiring increased attention as epigenetic regulators of gene expression. Given their intrinsic high conformational stability, abundance, and specificity, circRNAs can undertake various biological activities in order to regulate multiple cellular processes, including osteogenic differentiation. The most recent evidence indicates that circRNAs control human osteogenesis by preventing the inhibitory activity of miRNAs on their downstream target genes, using a competitive endogenous RNA mechanism. The aim of this review is to draw attention to the currently known regulatory mechanisms of circRNAs during human osteogenic differentiation. Specifically, we provide an understanding of recent advances in research conducted on various human mesenchymal stem cell types that underlined the importance of circRNAs in regulating osteogenesis. A comprehensive understanding of the underlying regulatory mechanisms of circRNA in osteogenesis will improve knowledge on the molecular processes of bone growth, resulting in the potential development of novel preclinical and clinical studies and the discovery of novel diagnostic and therapeutic tools for bone disorders.

hsa_circ_0000417 downregulation suppresses androgen receptor expression and apoptotic signals in human foreskin fibroblasts via sponging miR-6756-5p

BACKGROUND

Dysregulated apoptosis of penile mesenchymal cells during male urethragenesis has been previously demonstrated to underly hypospadiac urethral closure failure, and androgen receptor (AR) has been shown to play a central role in regulating penile mesenchyme cell proliferation and survival. However, the regulatory mechanisms upstream and downstream of AR remain poorly understood. Our clinical data and bioinformatics analysis previously indicated that hsa_circ_0000417, a circRNA significantly downregulated in hypospadias preputial specimens, may act as a ceRNA for AR via sequestering hsa_miR-6756-5p, and that the biological functions of hsa_circ_0000417 may significantly involve the PI3K/AKT pathway. In this study, we employed human foreskin fibroblasts (HFF-1) to experimentally validate this putative hsa_circ_0000417/miR-6756-5p/AR axis and its impact on penile mesenchymal cell proliferation and apoptosis.

METHOD AND RESULTS

We showed that hsa_circ_0000417 knockdown significantly promoted proliferation and suppressed apoptosis of HFF-1 cells. Mechanistically, hsa_circ_0000417 functioned as a molecular sponge for miR-6756-5p in HFF-1 cells and relieved the latter's translational repression on AR mRNA, leading to decreased AKT activation and increased expression of pro-apoptotic proteins BAX and cleaved-caspase 9. Conversely, elevated levels of miR-6756-5p resulted in diminished AR expression concomitant with enhanced AKT activation and HFF-1 cell proliferation.

CONCLUSIONS

Collectively, our data describe for the first time a circRNA-mediated post-transcriptional regulatory mechanism of AR and its functional consequences in penile mesenchymal cells in the context of hypospadias. These findings may contribute to advancing our current understanding of the roles of AR and mesenchymal cell fate decisions during penile morphogenesis.

Functional role of circRNAs in osteogenesis: A review

The extracellular matrixes (ECM), as well as the microenvironmental signals, play an essential role in osteogenesis by regulating intercellular pathways. Recently, it has been demonstrated that a newly identified RNA, circular RNA, contributes to the osteogenesis process. Circular RNA (circRNA), the most recently identified RNA, is involved in the regulation of gene expression at transcription to translation levels. The dysregulation of circRNAs has been observed in several tumors and diseases. Also, various studies have shown that circRNAs expression is changed during osteogenic differentiation of progenitor cells. Therefore, understanding the role of circRNAs in osteogenesis might help the diagnosis as well as treatment of bone diseases such as bone defects and osteoporosis. In this review, circRNA functions and the related pathways in osteogenesis have been discussed.

Non-coding RNAs and exosomal non-coding RNAs in pituitary adenoma

Pituitary adenoma (PA) is the third most common primary intracranial tumor in terms of overall disease incidence. Although they are benign tumors, they can have a variety of clinical symptoms, but are mostly asymptomatic, which often leads to diagnosis at an advanced stage when surgical intervention is ineffective. Earlier identification of PA could reduce morbidity and allow better clinical management of the affected patients. Non-coding RNAs (ncRNAs) do not generally code for proteins, but can modulate biological processes at the post-transcriptional level through a variety of molecular mechanisms. An increased number of ncRNA expression profiles have been found in PAs. Therefore, understanding the expression patterns of different ncRNAs could be a promising method for developing non-invasive biomarkers. This review summarizes the expression patterns of dysregulated ncRNAs (microRNAs, long non-coding RNAs, and circular RNAs) involved in PA, which could one day serve as innovative biomarkers or therapeutic targets for the treatment of this neoplasia. We also discuss the potential molecular pathways by which the dysregulated ncRNAs could cause PA and affect its progression.

Recent advances and application value of circRNA in neuroblastoma

Neuroblastoma (NB) is children’s most prevalent solid malignant tumor, accounting for 15% of childhood cancer mortality. Non-coding RNA is important in NB pathogenesis. As a newly identified non-coding RNA, abnormal regulation (abnormal up-regulation or down-regulation) of the circRNAs expression is implicated in the tumorigenesis of various tumors, including NB. CircRNAs primarily regulate the expression of microRNA (miRNA) target genes by microRNA (miRNA) sponge adsorption. Clinical evidence suggests that the expression of certain circRNAs is associated with the prognosis and clinical features of NB and hence may be exploited as a biomarker or therapeutic target. This review examines circRNAs that have been demonstrated to play a function in NB.

Competing endogenous RNA (ceRNA) networks in Parkinson's disease: A systematic review

Parkinson's disease (PD) is a distinctive clinical syndrome with several causes and clinical manifestations. Aside from an infectious cause, PD is a rapidly developing neurological disorder with a global rise in frequency. Notably, improved knowledge of molecular pathways and the developing novel diagnostic methods may result in better therapy for PD patients. In this regard, the amount of research on ceRNA axes is rising, highlighting the importance of these axes in PD. CeRNAs are transcripts that cross-regulate one another via competition for shared microRNAs (miRNAs). These transcripts may be either coding RNAs (mRNAs) or non-coding RNAs (ncRNAs). This research used a systematic review to assess validated loops of ceRNA in PD. The Prisma guideline was used to conduct this systematic review, which entailed systematically examining the articles of seven databases. Out of 309 entries, forty articles met all criteria for inclusion and were summarized in the appropriate table. CeRNA axes have been described through one of the shared vital components of the axes, including lncRNAs such as NEAT1, SNHG family, HOTAIR, MALAT1, XIST, circRNAs, and lincRNAs. Understanding the multiple aspects of this regulatory structure may aid in elucidating the unknown causal causes of PD and providing innovative molecular therapeutic targets and medical fields.

CircRNA and Ageing

Circular RNAs (circRNAs) are closed-loop RNA transcripts formed by a noncanonical back splicing mechanism. circRNAs are expressed in various tissues and cell types in a temporospatially regulated manner and have diverse molecular functions including their ability to act as miRNA sponges, transcriptional and splicing regulators, protein traps, and even templates for polypeptide synthesis. Emerging evidence suggests that circRNAs are themselves dynamically regulated throughout development in various organisms, with a substantial accumulation during ageing. Their regulatory roles in cellular pathways associated with ageing and senescence, as well as their implications in ageing-related diseases, such as neurological disease, cancer, and cardiovascular disease, suggest that circRNAs are key molecular determinants of the ageing process. Their unique structure, expression specificity, and biological functions highlight a potential capacity for use as novel biomarkers for diagnosis, prognosis, and treatment outcomes in a variety of conditions including pathological ageing. CircRNA may also have potential as target for interventions that manipulate ageing and longevity. In this chapter, we discuss the most recent advances in circRNA changes in ageing and ageing-associated disease.

Circular RNAs: typical biomarkers for bone-related diseases

Bone is a connective tissue that has important functions in the human body. Cells and the extracellular matrix (ECM) are key components of bone and are closely related to bone-related diseases. However, the outcomes of conventional treatments for bone-related diseases are not promising, and hence it is necessary to elucidate the exact regulatory mechanisms of bone-related diseases and identify novel biomarkers for diagnosis and therapy. Circular RNAs (circRNAs) are single-stranded RNAs that form closed circular structures without a 5' cap or 3' tail and polycyclic adenylate tails. Due to their high stability, circRNAs have the potential to be typical biomarkers. Accumulating evidence suggests that circRNAs are involved in bone-related diseases, including osteoarthritis, osteoporosis, osteosarcoma, multiple myeloma, intervertebral disc degeneration, and rheumatoid arthritis. Herein, we summarize the recent research progress on the characteristics and functions of circRNAs, and highlight the regulatory mechanism of circRNAs in bone-related diseases.

Brain Metabolic DNA: A Long Story and Some Conclusions

We have previously outlined the main properties of brain metabolic DNA (BMD) and its involvement in circadian oscillations, learning, and post-trial sleep. The presence of BMD in certain subcellular fractions and their behavior in cesium gradients have suggested that BMD originates from cytoplasmic reverse transcription and subsequently acquires a double-stranded configuration. More recently, it has been reported that some DNA sequences of cytoplasmic BMD in learning mice are different from that of the control animals. Furthermore, BMD is located in vicinity of the genes involved in different modifications of synaptic activity, suggesting that BMD may contribute to the brain's response to the changing environment. The present review outlines recent data with a special emphasis on reverse transcription of BMD that may recapitulate the molecular events at the time of the "RNA world" by activating mitochondrial telomerase and generating RNA templates from mitochondrial transcripts. The latter unexpected role of mitochondria is likely to promote a better understanding of mitochondrial contribution to cellular interactions and eukaryotic evolution. An initial step regards the role of human mitochondria in embryonic BMD synthesis, which is exclusively of maternal origin. In addition, mitochondrial transcripts involved in reverse transcription of BMD might possibly reveal unexpected features elucidating mitochondrial involvement in cancer events and neurodegenerative disorders.

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.

Profile of TREM2-Derived circRNA and mRNA Variants in the Entorhinal Cortex of Alzheimer’s Disease Patients

Genetic variants in TREM2, a microglia-related gene, are well-known risk factors for Alzheimer’s disease (AD). Here, we report that TREM2 originates from circular RNAs (circRNAs), a novel class of non-coding RNAs characterized by a covalent and stable closed-loop structure. First, divergent primers were designed to amplify circRNAs by RT-PCR, which were further assessed by Sanger sequencing. Then, additional primer sets were used to confirm back-splicing junctions. In addition, HMC3 cells were used to assess the microglial expression of circTREM2s. Three candidate circTREM2s were identified in control and AD human entorhinal samples. One of the circRNAs, circTREM2_1, was consistently amplified by all divergent primer sets in control and AD entorhinal cortex samples as well as in HMC3 cells. In AD cases, a moderate negative correlation (r = −0.434) was found between the global average area of Aβ deposits in the entorhinal cortex and circTREM2_1 expression level. In addition, by bioinformatics tools, a total of 16 miRNAs were predicted to join with circTREM2s. Finally, TREM2 mRNA corresponding to four isoforms was profiled by RT-qPCR. TREM2 mRNA levels were found elevated in entorhinal samples of AD patients with low or intermediate ABC scores compared to controls. To sum up, a novel circRNA derived from the TREM2 gene, circTREM2_1, has been identified in the human entorhinal cortex and TREM2 mRNA expression has been detected to increase in AD compared to controls. Unraveling the molecular genetics of the TREM2 gene may help to better know the innate immune response in AD.

Prospect of exosomal circular RNAs in breast Cancer: presents and future

Implementing precision oncology for breast cancer (BC) is a critical method for improving patient outcomes, which relies on the use of reliable biomarkers to be effective and safe. exosomes represent a potential alternative for the diagnosis and therapy of BC, As a "liquid biopsy" and a novel source for biomarkers. Exosomes are nanoscale phospholipid bilayer vesicles released by most cells that contain a large payload of various RNA species that can alter recipient cell activity. Circular RNAs (circRNAs) were recently revealed as a looping subclass of competing endogenous noncoding RNAs (ceRNAs) capable of microRNA sponging to regulate gene expression. They provide critical regulatory functions in carcinogenesis, proliferation, invasion, metastasis, and treatment resistance, as well as cancer prognostic. However, there is still a major gap in our understanding of the role of circRNA in the advancement of BC. CircRNAs are abundant in exosomes, according to various studies, and exosomal circRNAs (exo-circRNAs) play a significant role in cancer biology. Exo-circRNAs can be picked up by nearby or distant cells, affecting many features of the target cells' pathophysiological states, thus boosting cell communication and tumor spread. In this review, we have briefly summarized the major properties and functions of exosomes. Then, we have focused on exo-circRNAs, discussing their potential roles in both driving and inhibiting BC, as well as for cancer diagnosis, prognosis, and monitoring.

CircTmeff-1 in the nucleus accumbens regulates the reconsolidation of cocaine-associated memory

Reconsolidation of drug memories is the process of restoring unstable memories after unconditioned (UCS; e.g., drugs) or conditioned stimulus (CS; e.g., drug-paired contexts), and provides promise for prevention of drug relapse. Circular RNAs (circRNAs) have important effects on the transcription and post-transcriptional regulation of gene expression. However, the role of circRNAs in the reconsolidation of drug memories is unclear. Here, we observed that cocaine-induced memory retrieval significantly increased circTmeff-1 level in the nucleus accumbens (NAc) core but not shell. Importantly, the disrupted expression of circTmeff-1 using virus in the NAc core damaged the reconsolidation of cocaine-associated memories. The knockdown of circTmeff-1 in the NAc shell or without UCS retrieval or 9 h after UCS retrieval had no such effects. Mechanistically, using bioinformatic analysis and loss- or gain- of function assays, we revealed that antagomiR-206 reversed the inhibitory effect of circTmeff-1 knockdown on the expression of brain-derived neurotrophic factor (BDNF) during the reconsolidation of cocaine-associated memories. Taken together, these results demonstrate the role of circTmeff-1 in the reconsolidation of cocaine-associated memory and that circTmeff-1 may function as a decoy for miR-206 to regulate the expression of BDNF.

Hsa_circ_0031608: A Potential Modulator of VSMC Phenotype in the Rupture of Intracranial Aneurysms

Background and Purpose

Phenotypic modulation of vascular smooth muscle cells (VSMCs) plays an important role in the development of intracranial aneurysms (IAs). Growing evidence has demonstrated that circular RNAs (circRNAs) may serve as a potential modulator of VSMC phenotype in various vascular diseases. This study aimed to assess the potential function of circRNAs in the rupture of IAs and VSMC phenotypic modulation.

Methods

Using surgically dissected human ruptured (n = 8) and unruptured (n = 8) IA lesions, differentially expressed circRNAs were screened by transcriptomic sequencing and verified using qRT-PCR. Based on the screened circRNA, we predicted and screened the combined miRNA and downstream mRNAs to construct circRNA-miRNA-mRNA networks. Further in vitro experiments were performed to investigate the relationship between the validated circRNA and the phenotypic switching of VSMCs.

Results

We found 1,373 differentially expressed genes in ruptured versus unruptured aneurysms. The top five dysregulated circRNAs were selected for qRT-PCR validation. We found hsa_circ_0031608 was both highly expressed in ruptured IAs and pro-inflammatory transformation of VSMCs. Then, a regulatory circRNA-miRNA-mRNA with one circRNA node, six miRNA nodes, and 84 mRNA nodes was constructed. GO analysis and KEGG pathway enrichment analysis were performed on mRNAs in the network. Then, a PPI network was built based on these mRNAs and five hub genes were identified (FOXO3, DICER1, CCND2, IGF1R, and TNRC6B) by the cytoHubba plugin in Cytoscape software. In vitro, overexpression of hsa_circ_0031608 influenced the expression of VSMC phenotypic markers validated by qPCR and Western blotting. Furthermore, hsa_circ_0031608 promoted the migration and proliferation capacity of VSMCs.

Conclusion

hsa_circ_0031608 regulated the phenotypic modulation of VSMCs and played an important role in the rupture of IAs. The specific mechanism should be further studied and confirmed.

Potential Role of circRNA-HIPK3/microRNA-124a Crosstalk in the Pathogenesis of Rheumatoid Arthritis

BACKGROUND

Circular RNA-HIPK3 (CircHIPK3) has been shown to be aberrantly expressed in a variety of diseases, contributing to disease initiation and progression. The aim of the present study is to investigate the role of the circHIPK3 RNA/microRNA-124a interaction in the pathogenesis of rheumatoid arthritis (RA).

METHODS

This study included 79 RA patients and 30 control individuals. The patients involved were classified according to the disease activity score (DAS28) into mild (24 patients), moderate (24 patients), and severe (31 patients). Serum samples were collected to estimate the relative gene expression of circHIPK3 RNA and its target gene microRNA-124a by quantitative real time-PCR. Moreover, ELISA was used to detect the serum levels of monocyte chemoattractant protein-1 (MCP-1). Routine laboratory estimation of erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and rheumatoid factor (RF) was also done.

RESULTS

In all grades of RA groups, there was a significantly substantial elevation of circHIPK3 RNA gene expression, with subsequent downregulation of miRNA-124a when compared to the control group. CircHIPK3 and microRNA-124a expression have been established to be inversely linked. Also, estimation of serum levels of MCP-1, ESR, CRP, and RF exhibited a significant increase in all grades of RA as compared to the control group.

CONCLUSION

CircHIPK3 and microRNA-124a might be regarded as key players in the pathogenesis of RA. The cross-talk between them appears to be responsible for inducing joint inflammation by increasing MCP-1 production. Targeting circHIPK3 and microRNA-124a, and their downstream adaptor molecules, poses a new challenge for RA therapy.

The circRNA circ-Nbea participates in regulating diabetic encephalopathy

Circular RNAs (circRNAs) play key roles in various pathogenic and biological processes in human disease. However, the effect of circRNAs on the development of diabetic encephalopathy (DE) remains largely unknown. Therefore, the aim of this study was to investigate changes in the expression of circRNAs and their potential mechanism in DE formation. Compared with db/m mice, spatial learning/memory, dendritic spines, and synaptic plasticity were all impaired in the hippocampus of the db/db mice. In addition, the dendritic spine density of neurons was significantly decreased after treatment with advanced glycation end-products (AGEs). We used high-throughput RNA sequencing (RNA-Seq) to detect circRNA expression in DE, and the results revealed that 183 circRNAs were significantly altered in primary hippocampal neurons treated with AGEs. Three circRNAs were chosen for detection using quantitative real-time polymerase chain reaction (qRT-PCR), including circ-Smox (chr2: 131511984-131516443), circ-Nbea (mmu-chr3: 56079859-56091120), and circ-Setbp1 (chr18: 79086551-79087180), and circ-Nbea expression was significantly decreased. According to the bioinformatics prediction and detection using qRT-PCR and double luciferase assays, circ-Nbea sponges miR-128-3p. Based on these results, we speculated that a newly identified circRNA, circ-Nbea, may play an important role in the development of DE, and the mechanism is mediated by sponging miR-128-3p. This study provides new insight into the treatment of DE.

Epigenetic modifications in acute myeloid leukemia: The emerging role of circular RNAs (Review)

Canonical epigenetic modifications, which include histone modification, chromatin remodeling and DNA methylation, play key roles in numerous cellular processes. Epigenetics underlies how cells that posses DNA with similar sequences develop into different cell types with different functions in an organism. Earlier epigenetic research has primarily been focused at the chromatin level. However, the number of studies on epigenetic modifications of RNA, such as N1‑methyladenosine, 2'‑O‑ribosemethylation, inosine, 5‑methylcytidine, N6‑methyladenosine (m6A) and pseudouridine, has seen an increase. Circular RNAs (circRNAs), a type of RNA species that lacks a 5' cap or 3' poly(A) tail, are abundantly expressed in acute myeloid leukemia (AML) and may regulate disease progression. circRNAs possess various functions, including microRNA sponging, gene transcription regulation and RNA‑binding protein interaction. Furthermore, circRNAs are m6A methylated in other types of cancer, such as colorectal and hypopharyngeal squamous cell cancers. Therefore, the critical roles of circRNA epigenetic modifications, particularly m6A, and their possible involvement in AML are discussed in the present review. Epigenetic modification of circRNAs may become a diagnostic and therapeutic target for AML in the future.

Translational Applications of Linear and Circular Long Noncoding RNAs in Endometriosis

Endometriosis is a chronic gynecologic disease that negatively affects the quality of life of many women. Unfortunately, endometriosis does not have a cure. The current medical treatments involve hormonal manipulation with unwanted side effects and high recurrence rates after stopping the medication. Sadly, a definitive diagnosis for endometriosis requires invasive surgical procedures, with the risk of complications, additional surgeries in the future, and a high rate of recurrence. Both improved therapies and noninvasive diagnostic tests are needed. The unique molecular features of endometriosis have been studied at the coding gene level. While the molecular components of endometriosis at the small RNA level have been studied extensively, other noncoding RNAs, such as long intergenic noncoding RNAs and the more recently discovered subset of long noncoding RNAs called circular RNAs, have been studied more limitedly. This review describes the molecular formation of long noncoding and the unique circumstances of the formation of circular long noncoding RNAs, their expression and function in endometriosis, and promising preclinical studies. Continued translational research on long noncoding RNAs, including the more stable circular long noncoding RNAs, may lead to improved therapeutic and diagnostic opportunities.

The emerging role of circular RNAs in spinal cord injury

Spinal cord injury (SCI) is one kind of severe diseases with high mortality and morbidity worldwide, and lacks effective therapeutic interventions currently, which leads to not only permanent neurological impairments but also heavy social and economic burden. Recent studies have proved that circRNAs are highly expressed in neural tissues, regulating the neuronal and synaptic functions. What's more, significantly altered circRNAs expression profiles are closely associated with the pathophysiology of SCI. In this review, we summarize the current advance on the role of circRNAs in SCI, which may provide a better understanding of pathogenesis and therapeutic strategies of SCI.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

The Translational potential of this article is that A further understanding of circRNAs in the pathogenesis of SCI will promote the circRNA-based clinical applications.

The potential roles of circular RNAs as modulators in traumatic spinal cord injury

Spinal cord injury (SCI) may cause long-term physical impairment and bring a substantial burden to both the individual patient and society. Existing therapeutic approaches for SCI have proven inadequate. This is mainly owing to the incomplete understanding of the cellular and molecular events post-injury. Circular RNAs (circRNAs) represent a new class of non-coding RNAs with a covalently closed annular structure that participates in regulating the transcription of certain genes and are linked to various biological processes and diseases. Mounting evidence is indicative that circRNAs are highly expressed in the spinal cord and they play key roles in multiple processes of neurological diseases. Recently, a role for circRNAs as effectors of SCI has emerged, leading to the continuity of relevant research. In this review, we presented current studies with regards to the abnormality of circRNAs mediating SCI by affecting mechanisms of autophagy, apoptosis, inflammation, and neural regeneration. Furthermore, the potential clinical value of circRNAs as therapeutic targets of SCI was also analyzed.

Diabetic neuropathic pain induced by streptozotocin alters the expression profile of non-coding RNAs in the spinal cord of mice as determined by sequencing analysis

Diabetic neuropathic pain (DNP) is one of the most serious complications of diabetes. Patients with DNP always exhibit spontaneous and stimulus-evoked pain. However, the pathogenesis of DNP remains to be fully elucidated. Non-coding RNAs (ncRNAs) serve important roles in several cellular processes and dysregulated expression may result in the development of several diseases, including DNP. Although ncRNAs have been suggested to be involved in the pathogenesis of DNP, their precise roles remain to be determined. In the present study, sequencing analysis was used to investigate the expression patterns of coding genes, microRNAs (miRNAs), long ncRNAs (lncRNAs) and circular RNAs (circRNAs) in the spinal cord of mice with streptozotocin (STZ)-induced DNP. A total of 30 mRNAs, 148 miRNAs, 9 lncRNAs and 135 circRNAs exhibited significantly dysregulated expression 42 days after STZ injection. Functional enrichment analysis indicated that protein digestion and absorption pathways were the most significantly affected pathways of the differentially expressed (DE) mRNAs. The Rap1 signaling pathway, human T-lymphotropic virus-I infection and the MAPK signaling pathway were the three most significant pathways of the DE miRNAs. A total of 2,118 distinct circRNAs were identified and the length of the majority of the circRNAs was <1,000 nucleotides (nt) (1,552 circRNAs were >1,000 nt) with a median length of 620 nt. In the present study, the expression characteristics of coding genes, miRNAs, lncRNAs and circRNAs in DNP mice were determined; it paves the road for further studies on the mechanisms associated with DNP and potentially facilitates the discovery of novel ncRNAs for therapeutic targeting in the management of DNP.

Circular RNA Plek promotes fibrogenic activation by regulating the miR-135b-5p/TGF-βR1 axis after spinal cord injury

Objectives: The spinal cord rarely repairs itself when damaged; however, methods for encouraging nerves to regrow are on the horizon. Although circular RNAs (circRNAs) contribute to various biological processes, including neuronal processes, their functions in the subacute phase of spinal cord injury (SCI) have not been elucidated. In this study, we identified a novel circRNA, named CircPlek, with increased expression in spinal tissues after SCI.

Materials and Methods: We predicted a regulatory relationship between CircPlek and miR-135b-5p, which showed the most obvious decrease in post-SCI expression. We established the CircPlek/miR-135b-5p/transforming growth factor-beta receptor type I (TGF-βR1) axis using a bioinformatics approach and further evaluated the potential function of the interaction network in vitro.

Results: We confirmed that in TGF-β1-induced fibroblasts, the overexpression of miR-135b-5p or/and inhibition of CircPlek inhibited fibrosis activation via the Smad pathway. Inhibitors of miR-135b-5p had antagonistic effects on CircPlek.

Conclusions: the CircPlek/miR-135b-5p/TGF-βR1 axis may exert important functions in SCI and is a potential therapeutic target.

Hsa Circ 001839 Promoted Inflammation in Renal Ischemia-Reperfusion Injury Through NLRP3 by miR-432-3p

BACKGROUND

In recent years, increasing discovery of the extremely important regulatory effects of circular RNAs on biological development, angiogenesis, tumor genesis, and development, as well as stem cell proliferation and differentiation has provided new opportunities for investigating regulation mechanism in angiogenesis.

OBJECTIVES

This study explored the expression of circ 001839 in renal ischemia-reperfusion injury (RI-RI) rats and whether its upstream microRNA-432-3p (miR-432-3p) affects inflammation in both RI-RI rats and NRK52E cells.

METHODS

Rat model of RI-RI was made, and circ 001839 was identified by the gene-chip analysis in RI-RI rats. Expression of circ 001839 and miR-432-3p was measured by reverse transcription-quantitative polymerase chain reaction, protein expression of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, interferon (IFN)-γ, IL-6, and IL-18 in rat serum and cell supernatant was determined by ELISA, and the expression of NOD-like receptor 3 (NLRP3) and other gap-associated proteins in NRK52E cells was evaluated by Western blot analysis. Next, to verify the regulatory relationship between circ 001839 and miR-432-3p, 2 luciferase reporters were constructed.

RESULTS

Circ 001839 expression of RI-RI rats and NRK52E cells was significantly upregulated, compared with the control group. Circ 001839 overexpression significantly increased inflammation through promoting TNF-α, IFN-γ, and IL-6 expression levels in NRK52E cells. Overexpression of miR-432-3p significantly promoted inflammation in NRK52E cells via induction of NLRP3. Moreover, miR-432-3p decreased the effects of circ 001839-induced inflammation in NRK52E cells.

CONCLUSIONS

These findings suggested that circ 001839 promoted inflammation in RI-RI through NLRP3 by miR-432-3p.

CircNFIX promotes progression of pituitary adenoma via CCNB1 by sponging miR-34a -5p

Previous studies have shown that CCNB1 affects the invasiveness of pituitary adenomas, and it is of great significance to find the upstream mechanism of regulating CCNB1.In this study, we explored a significantly overexpressed circRNA in invasive pituitary adenomas. Based on bioinformatics analysis and mechanism experiments, we determined that circNFIX (has-circ_0005660) affects cell invasion, migration and proliferation in pituitary adenomas by sponging miR-34a-5p through CCNB1. In pituitary adenoma tissues, the expression of circNFIX and CCNB1 was upregulated, while miR-34a-5p expression was downregulated. The silencing of circNFIX or overexpression of miR-34a-5p inhibited cell invasion, migration and proliferation. Inhibition of miR-34a-5p expression reversed the inhibitory effect of circNFIX silencing on the progression of pituitary adenoma. In conclusion, CircNFIX affects cell invasion, migration, and proliferation in pituitary adenomas by sponging miR-34a-5p through CCNB1. Therefore, circNFIX is expected to serve as a potential target for the treatment of pituitary adenomas.

Association Between Circular RNAs and Intracranial Aneurysm Rupture Under the Synergistic Effect of Individual Environmental Factors

Introduction: To study the association between specific circular RNAs and rupture of intracranial aneurysm. To explore its clinical diagnostic significance and synergistic effects with individual environmental influencing factors. Methods: Three hundred and forty seven cases and controls were included in this study. Multivariate analysis was used to explore the main individual environmental factors. Intracranial aneurysm rupture related circular RNAs screened based on sequencing was verified in peripheral blood by PCR. ROC curve, logistic regression model and fork analysis were used to study the association, diagnostic values, and synergistic effects of circular RNA with intracranial aneurysms and individual environmental factors. Results: Smoking, hair dyeing, sitting time ≥6 h/day, single animal oil intake and hypertension are the main risk factors for intracranial aneurysm rupture; People with higher education, sleeping time ≥7 h/day, tea drinking, diabetes, higher levels of (hemoglobin, low density lipoprotein, serum calcium, and apolipoprotein-A1) have a low risk of intracranial aneurysm rupture. Hsa_circ_0008433 and hsa_circ_0001946 are closely related to intracranial aneurysm rupture and have certain clinical diagnostic significance (AUC = 0.726; 95% CI: 0.668~0.784). Hsa_circ_0008433 (OR = 0.497, 95% CI: 0.338~0.731), hsa_circ_0001946 (OR = 0.682, 95% CI: 0.509~0.914) were independent epigenetic factors affecting intracranial aneurysm rupture, and have a multiplicative interaction with age (OR = 3.052, 95% CI: 1.006~9.258). Conclusions: Low expressions of hsa_circ_0008433 and hsa_circ_0001946 are risk factors for intracranial aneurysms rupture and have good clinical diagnostic value. There was a multiplicative interaction between epigenetic score and age. The older and the higher the epigenetic score was, the more likely to have intracranial aneurysm rupture.

Long non-coding RNAs in motor neuron development and disease

Long non-coding RNAs (lncRNAs) are RNAs that exceed 200 nucleotides in length and that are not translated into proteins. Thousands of lncRNAs have been identified with functions in processes such as transcription and translation regulation, RNA processing, and RNA and protein sponging. LncRNAs show prominent expression in the nervous system and have been implicated in neural development, function and disease. Recent work has begun to report on the expression and roles of lncRNAs in motor neurons (MNs). The cell bodies of MNs are located in cortex, brainstem or spinal cord and their axons project into the brainstem, spinal cord or towards peripheral muscles, thereby controlling important functions such as movement, breathing and swallowing. Degeneration of MNs is a pathological hallmark of diseases such as amyotrophic lateral sclerosis and spinal muscular atrophy. LncRNAs influence several aspects of MN development and disruptions in these lncRNA-mediated effects are proposed to contribute to the pathogenic mechanisms underlying MN diseases (MNDs). Accumulating evidence suggests that lncRNAs may comprise valuable therapeutic targets for different MNDs. In this review, we discuss the role of lncRNAs (including circular RNAs [circRNAs]) in the development of MNs, discuss how lncRNAs may contribute to MNDs and provide directions for future research.

Role of circular RNAs in visceral organ fibrosis

Circular RNAs (circRNAs) are a novel class of noncoding RNAs produced during pre-mRNA splicing and are emerging as new members of the gene regulatory network. Unlike linear RNAs, circRNAs have a unique structure with a covalently closed loop formed from the ligation of exons, introns, or both. CircRNAs are widely expressed in various organisms in a species-, tissue-, developmental stage- and disease-specific manner; circRNAs have been demonstrated to play a vital role in the pathogenesis and progression of human diseases. Fibrosis is characterized by an abnormal excessive deposition of extracellular matrix (ECM) in the extracellular space and plays important roles in many different pathologies of various organs. CircRNAs function as master regulators of gene expression to "sponge" or sequester other genes and target gene expression, transcription, splicing, etc. Increasing evidence has revealed that circRNAs are tightly associated with fibrotic diseases in various organs, including the lungs, liver, heart and kidneys. Herein, we provide the current understanding of the molecular characteristics of circRNAs and summarize the findings from circRNA studies in which the functions and mechanisms of action of circRNAs in organ fibrosis were proposed.

Review on circular RNAs and new insights into their roles in cancer

Circular RNAs (circRNAs) are a very interesting class of conserved single-stranded RNA molecules derived from exonic or intronic sequences by precursor mRNA back-splicing. Unlike canonical linear RNAs, circRNAs form covalently closed, continuous stable loops without a 5'end cap and 3'end poly(A) tail, and therefore are resistant to exonuclease digestion. The majority of circRNAs are highly abundant, and conserved across different species with a tissue or developmental-stage-specific expression. circRNAs have been shown to play important roles as microRNA sponges, regulators of gene splicing and transcription, RNA-binding protein sponges and protein/peptide translators. Emerging evidence reveals that circRNAs function in various human diseases, particularly cancers, and may function as better predictive biomarkers and therapeutic targets for cancer treatment. In consideration of their potential clinical relevance, circRNAs have become a new research hotspot in the field of tumor pathology. In the present study, the current understanding of the biogenesis, characteristics, databases, research methods, biological functions subcellular distribution, epigenetic regulation, extracellular transport and degradation of circRNAs was discussed. In particular, the multiple databases and methods involved in circRNA research were first summarized, and the recent advances in determining the potential roles of circRNAs in tumor growth, migration and invasion, which render circRNAs better predictive biomarkers, were described. Furthermore, future perspectives for the clinical application of circRNAs in the management of patients with cancer were proposed, which could provide new insights into circRNAs in the future.

Circular RNA expression profile in human primary multiple intracranial aneurysm

Primary multiple intracranial aneurysm (MIA) is a vascular disease that frequently leads to fatal vascular rupture and subarachnoid hemorrhage. However, the epigenetic regulation associated with MIA has remained largely elusive. Circular RNAs (circRNAs) serve important roles in cardiovascular diseases; however, their association with MIA has remained to be investigated. The present study initially aimed to explore novel mechanisms of MIA through examining circRNA expression profiles. Comprehensive circRNA expression profiles were detected by RNA sequencing (RNA-Seq) in human peripheral blood mononuclear cells. The RNA-Seq results were validated by reverse transcription-quantitative PCR. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses suggested the functions of these circRNAs. A competing endogenous RNA network was constructed to reveal the circRNA-microRNA-mRNA relationship. Among the 3,328 differentially expressed circRNAs between the MIA and matched control groups, 60 exhibited significant expression changes (|log2 fold change|≥2; P<0.05). Among these 60 circRNAs, 20 were upregulated, while the other 40 were downregulated. A number of downregulated circRNAs were involved in inflammation. The most significant KEGG pathway was ‘leukocyte transendothelial migration’. The circRNAs Homo sapiens (hsa)_circ_0135895, hsa_circ_0000682 and hsa_circ_0000690, which were also associated with the above-mentioned pathway, were indicated to be able to regulate protein tyrosine kinase 2, protein kinase Cβ and integrin subunit αL, respectively. To the best of our knowledge, the present study was the first to perform a circRNA sequencing analysis of MIA. The results specifically predicted the regulatory role of circRNAs in the pathogenesis of MIA. ‘Leukocyte transendothelial migration’ may be critical for the pathogenesis of MIA.

Aerobic exercise improves VCI through circRIMS2/miR-186/BDNF-mediated neuronal apoptosis

BACKGROUND

Vascular cognitive impairment (VCI) is a common cognitive disorder caused by cerebrovascular disease, ranging from mild cognitive impairment to dementia. Studies have shown that aerobic exercise might alleviate the pathological development of VCI, and our previous study observed that aerobic exercise could alleviate VCI through NF-κB/miR-503/BDNF pathway. However, there are few studies on the mechanism. Therefore, it is of great significance to fill the gaps in the mechanism for the early diagnosis of VCI and the clinical prevention and treatment of vascular dementia.

METHODS

CircRNA microarray analysis and quantitative real-time PCR were used to detect the expression of circRNA regulating synaptic be exocytosis 2 (RIMS2) (circRIMS2). Cell apoptosis was determined by TdT-mediated dUTP nick-end labeling (TUNEL) assay. The dual-luciferase reporter assay was performed to verify the interaction between circRIMS2 and miR-186, as well as miR-186 and BDNF. RNA pull-down assay detected the binding between circRIMS2 and miR-186. A VCI mouse model was established by repeated ligation of bilateral common carotid arteries (2VO). The lentiviral interfering vector was injected into the VCI mice through the lateral ventricle. The mice in the aerobic exercise group performed 30 min (12 m/min) running for 5 days a week. A Morris water maze test was performed after 4 weeks.

RESULTS

The expression of circRIMS2 and BDNF in the serum of VCI patients was significantly reduced, miR-186 expression was increased, and the expression of circRIMS2 was increased in the 2VO group of mice undergoing aerobic exercise. The expression levels of circRIMS2 and BDNF in the oxygen and glucose deprivation-treated (OGD-treated) cells were decreased, the miR-186 expression and cell apoptosis were increased, while the effect was weakened after transfection with the lentiviral vector pLO-ciR-RIMS2. CircRIMS2 could bind to miR-186, and after interference with circRIMS2 in HT22 cells, the expression of miR-186 was increased. Besides, miR-186 could bind to BDNF, and BDNF expression was decreased because of the overexpression of miR-186 in HT22 cells. The expression level of BDNF in the pLO-ciR-RIMS2 group was increased, and apoptosis was decreased, but the miR-186 mimic weakened the effect of pLO-ciR-RIMS2. Aerobic exercise could shorten the average time that mice reached the platform in the Morris water maze, increase the expression level of circRIMS2 and BDNF, reduce miR-186 expression, and inhibit neuronal apoptosis. However, the interference with circRIMS2 weakened this effect.

CONCLUSION

The expression of circRIMS2 was down-regulated in VCI and aerobic exercise reduced neuronal apoptosis, and circRIMS2 improved VCI through the circRIMS2/miR-186/BDNF axis.

Role of circular RNA expression in the pathological progression after spinal cord injury

Differential expression of non-coding RNA after traumatic spinal cord injury (TSCI) is closely related to the pathophysiological process. The purposes of this study were to systematically profile and characterize expression of circular RNA (circRNA) in the lesion epicenter of spinal tissues after TSCI, and predict the structure and potential function of the regulatory circRNA/miRNA network. Forty-eight C57BL/6 mice were randomly and equally assigned to two groups: one subjected to TSCI at T8–10 with an Allen’s drop impactor, and a second subjected to laminectomy without TSCI. Spinal cord samples were stained with hematoxylin and eosin, sequenced, and validated. RNA-Seq, Gene Ontology analysis, Kyoto Encyclopedia of Genes and Genomes analysis, and network analyses (Targetscan and miRanda) were used to predict and annotate the circRNA/miRNA/mRNA network. Luciferase reporter, quantitative reverse transcription polymerase chain reaction, and western blot assays were used to profile expression and regulation patterns of the network in mouse models of TSCI. Hematoxylin-eosin staining revealed severe damage to the blood-spinal cord barrier after TSCI. Differentially expressed circRNA and miRNA profiles were obtained after TSCI; differentially expressed circRNAs, which were abundant in the cytoplasm, were involved in positive regulation of transcription and protein phosphorylation. miR-135b-5p was the most significantly downregulated miRNA after TSCI; circRNAAbca1 and KLF4 were predicted to be its target circRNA and mRNA, respectively. Subsequently, the circAbca1/miR-135b-5P/KLF4 regulatory axis was predicted and constructed, and its targeted binding was verified. After inhibiting circAbca1, GAP43 expression was upregulated. Differential expression of circRNAs might play an important role after TSCI. circAbca1 plays a neuroinhibitory role by targeted binding of the miR-135b-5P/KLF4 axis. The identified circRNA/miRNA/mRNA network could provide the basis for understanding pathophysiological mechanisms underlying TSCI, as well as guide the formulation of related therapeutic strategies. All animal protocols were approved by the Research Ethics Committee of West China Hospital of China (approval No. 2017128) on May 16, 2017.

The differential expression and potential roles of circular RNAs in children with anti-NMDA receptor encephalitis

To explore the role of circular RNAs (circRNAs) in pediatric anti-N-methyl-d-aspartate (NMDA) receptor encephalitis, we assessed the profiles of circRNAs and mRNAs in blood leukocytes from anti-NMDA receptor encephalitis patients and healthy controls using microarray analysis. 1196 circRNAs and 719 mRNAs (change ≥2, p < .05) were dysregulated in anti-NMDA receptor encephalitis patients, relative to healthy controls, based on microarray data. Further bioinformatic analysis demonstrated that the host genes of dysregulated circRNAs are primarily associated with receptor internalization. In conclusion, circRNAs may be implicated in the pathogenesis of pediatric anti-NMDA receptor encephalitis.

Physiological and pharmacological roles of melatonin in the pathophysiological components of cellular injury after ischemic stroke

Apart from its metabolic or physiological functions, melatonin has a potent cytoprotective activity in the physiological and pathological conditions. It is synthetized by the pineal gland and released into the blood circulation but particularly cerebrospinal fluid in a circadian manner. It can also easily diffuse through cellular membranes due its small size and lipophilic structure. Its cytoprotective activity has been linked to its potent free radical scavenger activity with the desirable characteristics of a clinically- reliable antioxidant. Melatonin detoxifies oxygen and nitrogen-based free radicals and oxidizing agents, including the highly toxic hydroxyl-and peroxynitrite radicals, initiating cellular damage. However, the cytoprotective activity of melatonin is complex and cannot be solely limited to its free radical scavenger activity. It regulates cellular signaling pathways through receptor– dependent and independent mechanisms. Most of these downstream molecules, such as PI3K/AKT pathway components, also contribute to the cytoprotective effects of melatonin. In this term, melatonin is a promising molecule for the treatment of neurodegenerative disorders, such as ischemic stroke, which melatonin reduces ischemic brain injury in animal models of ischemic stroke. It regulates also circadian rhythm proteins after ischemic stroke, playing roles in cellular survival. In this context, present article summarizes the possible role of melatonin in the pathophysiological events after ischemic stroke.

Circular RNAs as New Regulators in Gastric Cancer: Diagnosis and Cancer Therapy

Gastric cancer (GC) is one of the most commonly diagnosed cancers that causes high mortality in the world. Although the surgery tools and chemotherapies have significantly improved the overall survival of patients with GC, the early diagnosis of GC remains insufficient and many patients diagnosed with advanced stages of GC are not able to benefit from curative therapy. Circular RNAs (circRNAs), novel members of the non-coding cancer genome, are being explored with regards to various cancer types including GC. CircRNAs could work as miRNA sponges to regulate cell proliferation, cell migration, and cell cycle in GC. In addition, it was found that abnormal expression of circRNAs was associated with pathological characteristics in GC tissues, which could help to act as potential markers of early diagnosis or predictors of prognosis. Although various functional circRNAs have been discovered and characterized, the studies of circRNAs in GC are still at early stages compared with other RNAs. In order to provide a whole view to better understand the circRNAs in the occurrence and development of GC, we review the current knowledge on circRNAs in relation to their expression and regulation in GC as well as their potential to be diagnosis markers, and their role in drug resistance will be mentioned. It is helpful to address their possibility from basic research into practical application.

Circular RNA circ_0007142 regulates cell proliferation, apoptosis, migration and invasion via miR-455-5p/SGK1 axis in colorectal cancer

Colorectal cancer (CRC) is a frequently diagnosed cancer worldwide. Accumulating researches suggested that circular RNA 0007142 (circ_0007142) contributed to the progression and initiation of CRC. However, the molecular mechanism of circ_0007142 in CRC needs further research. Levels of circ_0007142, microRNA-455-5p (miR-455-5p), and serum- and glucocorticoid-induced protein kinase 1 (SGK1) were identified by quantitative real-time PCR. Cell proliferation was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazol-3-ium bromide assay. Flow cytometry assay was used to detect cell apoptosis in SW480 and HCT116 cells. The relative proteins expression was detected by western blot. Cell migration and invasion were evaluated using transwell assay. Moreover, dual-luciferase reporter and RNA immunoprecipitation assays were conducted to determine the relationship between miR-455-5p and circ_0007142 or SGK1. Finally, xenograft tumor model was established to confirm the effect of circ_0007142 on CRC progression in vivo. Circ_0007142 and SGK1 levels were clearly increased, while miR-455-5p level was reduced in CRC tissues and cell lines. Circ_0007142 silencing promoted cell apoptosis and inhibited cell proliferation, migration and invasion, while these effects of circ_0007142 were partially abolished by miR-455-5p inhibitor in CRC cells. Circ_0007142 could sponge miR-455-5p to regulate SGK1 expression. Moreover, the effects of miR-455-5p on cell proliferation, apoptosis, migration and invasion could be partially reversed by SGK1 overexpression. Besides, circ_0007142 knockdown also suppressed the progression of CRC in vivo. Collectively, Circ_0007142/miR-455-5p/SGK1 axis regulated cell proliferation, apoptosis, migration and invasion of CRC cells, providing a probable therapy target for CRC.

Current Status of Research on the Role of Circular RNAs in Hepatocellular Carcinoma and Clinical Implications

The latest statistics show that rates of morbidity and mortality for hepatocellular carcinoma are gradually increasing over time. Accumulating evidence indicates that circular RNAs (circRNAs) participate in the regulation of gene transcription and translation and exert a crucial role in endogenous RNA network. circRNAs are implicated in the pathogenesis of numerous tumors including hepatocellular carcinoma (HCC), gastric carcinoma and bladder cancer. Of note, the effect of circRNAs in HCC has drawn increasing public attention. Previous studies revealed that the function of circRNAs mainly consists of sponges of miRNA and RNA-binding proteins, alternative splicing of pre-mRNAs, transcriptional and translational regulators, and potential to encode proteins. In addition, recent research data indicate that the expression level of circRNAs is closely correlated with metastasis, invasion, and occurrence of HCC in patients. These findings imply that circRNAs may be useful as biomarkers for diagnosis and prediction of prognosis of HCC. In this review, we have systemically summarized current viewpoints regarding the role of circRNAs expression in HCC to provide an important reference illustrating the underlying mechanism of HCC.

The Secret Garden of Neuronal circRNAs

High-throughput transcriptomic profiling approaches have revealed that circular RNAs (circRNAs) are important transcriptional gene products, identified across a broad range of organisms throughout the eukaryotic tree of life. In the nervous system, they are particularly abundant, developmentally regulated, region-specific, and enriched in genes for neuronal proteins and synaptic factors. These features suggested that circRNAs are key components of an important layer of neuronal gene expression regulation, with known and anticipated functions. Here, we review major recognized aspects of circRNA biogenesis, metabolism and biological activities, examining potential new functions in the context of the nervous system.

Identification of the Potential Key Circular RNAs in Elderly Patients With Postoperative Cognitive Dysfunction

Background

Postoperative cognitive dysfunction (POCD) is one of the severe complications after surgery, inducing low life quality and high mortality, especially in elderly patients. However, the underlying molecular mechanism of POCD remains largely unknown, and the ideal biomarker for clinical diagnosis and prognosis is lacking. Circular RNAs (circRNAs), as a unique class of non-coding RNAs, were characterized by its stability and conservativeness, serving as novel biomarkers in various diseases. Nevertheless, the role of circRNAs in the occurrence of POCD remains elusive.

Methods

To investigate the differentially expressed circRNAs in the serum of POCD patients and its potential role in the development of POCD, we performed a circRNA microarray to screen the differentially expressed circRNAs in the serum samples from three patients of the POCD group and three paired patients of the non-POCD group. Subsequently, quantitative real-time polymerase chain reaction analysis (qRT-PCR) was utilized to verify the microarray data with the serum samples from 10 paired patients. Cytoscape software was used to construct the circRNA–miRNA–mRNA network for circRNAs with different expression levels as well as the target genes. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed the biological functions of the differentially expressed circRNAs target genes.

Results

In total, we have analyzed 10,198 circRNAs through the microarray. Compared with the non-POCD patient group, there were 210 differentially expressed circRNAs with 133 upregulated and 77 downregulated in the POCD group (≥2-fold differential expression, P ≤ 0.05). The qRT-PCR confirmed 10 circRNAs with different expressed levels, and the results were consistent with the microarray findings. Among them, hsa_circRNA_001145, hsa_circRNA_101138, and hsa_circRNA_061570 had the highest magnitude of change. The GO analysis showed that the differentially expressed circRNAs were associated with the regulation of the developmental process, cell-to-cell adhesion, and nervous system development. The KEGG analysis showed that the target genes of circRNAs were enriched in the MAPK signaling pathway and RAS signaling pathway. According to the targetscan7.1 and mirdbV5 databases, the circRNA–miRNA–mRNA network was constructed, and these results provided a vital landscape of circRNA expression profile in POCD.

Conclusions

Our study provides an essential perspective for the differential expression of circRNAs in POCD patients. Further studies need to be performed to explore their potential therapeutic roles in the development of POCD.

The Emerging Role and Promise of Circular RNAs in Obesity and Related Metabolic Disorders

Circular RNAs (circRNAs) are genome transcripts that are produced from back-splicing of specific regions of pre-mRNA. These single-stranded RNA molecules are widely expressed across diverse phyla and many of them are stable and evolutionary conserved between species. Growing evidence suggests that many circRNAs function as master regulators of gene expression by influencing both transcription and translation processes. Mechanistically, circRNAs are predicted to act as endogenous microRNA (miRNA) sponges, interact with functional RNA-binding proteins (RBPs), and associate with elements of the transcriptional machinery in the nucleus. Evidence is mounting that dysregulation of circRNAs is closely related to the occurrence of a range of diseases including cancer and metabolic diseases. Indeed, there are several reports implicating circRNAs in cardiovascular diseases (CVD), diabetes, hypertension, and atherosclerosis. However, there is very little research addressing the potential role of these RNA transcripts in the occurrence and development of obesity. Emerging data from in vitro and in vivo studies suggest that circRNAs are novel players in adipogenesis, white adipose browning, obesity, obesity-induced inflammation, and insulin resistance. This study explores the current state of knowledge on circRNAs regulating molecular processes associated with adipogenesis and obesity, highlights some of the challenges encountered while studying circRNAs and suggests some perspectives for future research directions in this exciting field of study.

Circular RNAs in Embryogenesis and Cell Differentiation With a Focus on Cancer Development

In the recent years thousands of non-coding RNAs have been identified, also thanks to highthroughput sequencing technologies. Among them, circular RNAs (circRNAs) are a well-represented class characterized by the high sequence conservation and cell type specific expression in eukaryotes. They are covalently closed loops formed through back-splicing. Recently, circRNAs were shown to regulate a variety of cellular processes functioning as miRNA sponges, RBP binding molecules, transcriptional regulators, scaffold for protein translation, as well as immune regulators. A growing number of studies are showing that deregulated expression of circRNAs plays important and decisive actions during the development of several human diseases, including cancer. The research on their biogenesis and on the various molecular mechanisms in which they are involved is going very fast, however, there are still few studies that address their involvement in embryogenesis and eukaryotic development. This review has the intent to describe the most recent progress in the study of the biogenesis and molecular activities of circRNAs providing insightful information in the field of embryogenesis and cell differentiation. In addition, we describe the latest research on circRNAs as novel promising biomarkers in diverse types of tumors.

Circular RNA circ_0001368 inhibited growth and invasion in renal cell carcinoma by sponging miR-492 and targeting LATS2

Circular RNAs (circRNAs) act as essential regulators in the tumorigenesis of renal cell carcinoma. Our study aims to investigate the underlying function and the molecular mechanisms of circ_0001368 in renal cell carcinoma. The qRT-PCR results indicate that the circ_0001368 expression level was downregulated in the carcinoma cells and tissues of the renal cell. circ_0001368 weakened cell proliferation and invasion in the ACHN and 786-O cells. The luciferase reporter assay showed that circ_0001368 functioned as an endogenous sponge for miR-492. The transwell and CCK8 assays showed that circ_0001368 suppressed cell proliferation and invasion in the ACHN and 786-O cells. Large tumor suppressor kinase 2 (LATS2) was confirmed by Targetscan as a target gene of miR-492. The overexpression of LATS2 repressed the growth and invasion of ACHN and 786-O cells. circ_0001368 upregulated the LATS2 expression and suppressed ACHN and 786-O cell growth and invasion by sponging miR-492. circ_0001368 suppressed the proliferation ability of 786-O in vivo. In conclusion, circ_0001368 was identified in this study as a novel anti-tumor RNA in renal cell carcinoma and can function as a potential therapeutic target for renal cell carcinoma treatment.

Non-coding RNAs in Nervous System Development and Disease

The rapid advance of RNA sequencing technologies contributed to a deep understanding of transcriptome composition and has allowed the discovery of a large number of non-coding RNAs (ncRNAs). The ability of these RNA molecules to be engaged in intricate and dynamic interactions with proteins and nucleic acids led to a great expansion of gene expression regulation mechanisms. By this matter, ncRNAs contribute to the increase in regulatory complexity that becomes highly specific between tissues and cell types. Among the ncRNAs, long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) are especially abundant in nervous system and have been shown to be implicated in its development, plasticity and aging as well as in neurological disorders. This review provides an overview of how these two diverse classes of ncRNAs control cellular processes during nervous system development, physiology, and disease conditions with particular emphasis on neurodegenerative disorders. The use of ncRNAs as biomarkers, tools, or targets for therapeutic intervention in neurodegeneration are also discussed.