Role of circular RNAs in brain development and CNS diseases

Upregulation of RasGRF1 ameliorates spatial cognitive dysfunction in mice after chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion (CCH)-mediated cognitive impairment is a serious problem worldwide. However, given its complexity, the underlying mechanisms by which CCH induces cognitive dysfunction remain unclear, resulting in a lack of effective treatments. In this study, we aimed to determine whether changes in the expression of RasGRF1, an important protein associated with cognition and synaptic plasticity, underlie the associated impairments in cognition after CCH. We found that RasGRF1 levels markedly decreased following CCH. Through prediction and validation studies, we observed that miRNA-323-3p was upregulated after CCH and could bind to the 3'-untranslated region of Rasgrf1 mRNA and regulate its expression in vitro. Moreover, the inhibition of miRNA-323-3p upregulated Rasgrf1 expression in the hippocampus after CCH, which was reversed by Rasgrf1 siRNA. This suggests that miRNA-323-3p is an important regulator of Rasgrf1. The Morris water maze and Y maze tests showed that miRNA-323-3p inhibition and Rasgrf1 upregulation improved spatial learning and memory, and electrophysiological measurements revealed deficits in long-term potentiation after CCH that were reversed by Rasgrf1 upregulation. Dendritic spine density and mature mushroom spine density were also improved after miRNA-323-3p inhibition and Rasgrf1 upregulation. Furthermore, Rasgrf1 upregulation by miRNA-323-3p inhibition improved dendritic spine density and mature mushroom spine density and ameliorated the deterioration of synapses and postsynaptic density. Overall, RasGRF1 regulation attenuated cognitive impairment, helped maintain structural and functional synaptic plasticity, and prevented synapse deterioration after CCH. These results suggest that Rasgrf1 downregulation by miRNA-323-3p plays an important role in cognitive impairment after CCH. Thus, RasGRF1 and miRNA-323-3p may represent potential therapeutic targets for cognitive impairment after CCH.

CircLPAR1 Promotes Neuroinflammation and Oxidative Stress in APP/PS1 Mice by Inhibiting SIRT1/Nrf-2/HO-1 Axis Through Destabilizing GDF-15 mRNA

Circular RNA LPAR1 (circLPAR1) was revealed to be elevated in Alzheimer's disease (AD); nevertheless, its role and mechanisms in AD remain unknown. Memory performance of APP/PS1 mice was assessed by Morris water maze test. Expression of circLPAR1 and indicated messenger RNA (mRNA) in mouse brain tissues or/and SH-SY5Y cells were tested by quantitative real-time PCR (qRT-PCR). Protein expression of indicated gene was examined by western blot. Production of proinflammatory cytokines (tumor necrosis factor-α, TNF-α; interleukin-6, IL-6; interleukin-1β, IL-1β; and interleukin-8, IL-8) and oxidative stress-related factors (reactive oxygen species, ROS; malondialdehyde, MDA; superoxide dismutase, SOD; and glutathione, GSH) were assessed by commercial kits. RNA pull down and RNA immunoprecipitation were performed to verify the interplay between up-frameshift protein 1 (UPF1) and circLPAR1 or growth differentiation factor 15 (GDF-15). CircLPAR1 was elevated, while GDF-15 was decreased in both APP/PS1 mice and Aβ-treated SH-SY5Y cells. Knockdown of circLPAR1 and overexpression of GDF-15 protected cells against Aβ-caused inflammation, oxidative stress, and neuronal apoptosis. CircLPAR1 knockdown was also proved to improve AD-related pathological traits and ameliorate cognitive dysfunctions in vivo. In mechanism, we found that circLPAR1 repressed GDF-15 expression by decreasing GDF-15 mRNA stability through UPF1 recruitment. Rescue assays suggested that sirtuin 1 (SIRT1) knockdown reversed GDF-15 overexpression-induced inhibition on Aβ-induced neuronal damage and nuclear factor E2-related factor (Nrf-2)/heme oxygenase-1 (HO-1) pathway inhibition. Moreover, the protective effect of circLPAR1 knockdown against Aβ-induced apoptosis was abolished by GDF-15 knockdown, and SIRT1 overexpression could counteract this effect of GDF-15 knockdown. CircLPAR1 knockdown improved AD-related pathological traits in vitro and in vivo by inhibiting SIRT1/Nrf-2/HO-1 axis through GDF-15.

CircSYNDIG1 ameliorates stress-induced abnormal behaviors by suppressing miR-344-5p in mice

Circular RNA (circRNA) plays an important role in diverse stress-related neuropsychiatric disorders like depression, anxiety and cognitive disorders. Here, using a circRNA microarray, we found that circSYNDIG1, an unreported circRNA, was significantly downregulated in the hippocampus of chronic unpredictable mild stress (CUMS) mice and further validated this finding in corticosterone (CORT) and lipopolysaccharide (LPS) mice by qRT-PCR, and it was negatively correlated with depressive- and anxiety-like behaviors of these three stressed mice. Furthermore, the interaction of miR-344-5p and circSYNDIG1 was confirmed by in situ hybridization (FISH) assay in hippocampus and dual luciferase reporter assay in 293 T cells. And miR-344-5p mimics could simulate the dendritic spine density reduction, depressive- and anxiety-like behaviors and memory impairment induced by CUMS. Overexpression of circSYNDIG1 in hippocampus significantly ameliorated these abnormal changes induced by CUMS or miR-344-5p. It indicated that circSYNDIG1 functions as an miR-344-5p sponge to inhibit miR-344-5p impact, resulting in the increase of dendritic spine density and the subsequent amelioration of the abnormal behaviors. Therefore, the downregulation of circSYNDIG1 in hippocampus participates in CUMS-induced depressive and anxiety-like behavior of mice though miR-344-5p. These findings represent the first evidence for the involvement of circSYNDIG1 and its coupling mechanism in depression and anxiety, suggesting that circSYNDIG1 and miR-344-5p might be new targets for the treatment of stress-related disorder.

CircRNAs and RNA-Binding Proteins Involved in the Pathogenesis of Cancers or Central Nervous System Disorders

Circular RNAs (circRNAs), a newly recognized group of noncoding RNA transcripts, have established widespread attention due to their regulatory role in cell signaling. They are covalently closed noncoding RNAs that form a loop, and are typically generated during the splicing of precursor RNAs. CircRNAs are key post-transcriptional and post-translational regulators of gene expression programs that might influence cellular response and/or function. In particular, circRNAs have been considered to function as sponges of specific miRNA, regulating cellular processes at the post-transcription stage. Accumulating evidence has shown that the aberrant expression of circRNAs could play a key role in the pathogenesis of several diseases. Notably, circRNAs, microRNAs, and several RNA-binding proteins, including the antiproliferative (APRO) family proteins, could be indispensable gene modulators, which might be strongly linked to the occurrence of diseases. In addition, circRNAs have attracted general interest for their stability, abundance in the brain, and their capability to cross the blood–brain barrier. Here, we present the current findings and theragnostic potentials of circRNAs in several diseases. With this, we aim to provide new insights to support the development of novel diagnostic and/or therapeutic strategies for these diseases.

microRNA and circRNA in Parkinson's Disease and atypical parkinsonian syndromes

Multiple System Atrophy (MSA) and Progressive Supranuclear Palsy (PSP) are atypical parkinsonian syndromes (APS) with various clinical phenotypes and considerable clinical overlap with idiopathic Parkinson's disease (iPD). This disease heterogeneity makes ante-mortem diagnosis extremely challenging with up to 24% of patients misdiagnosed. Because diagnosis is predominantly clinical, there is great interest in identifying biomarkers for early diagnosis and differentiation of the different types of parkinsonism. Compared to protein biomarkers, microRNAs (miRNAs) and circularRNAs (circRNAs) are stable tissue-specific molecules that can be accurately measured by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). This chapter critically reviews miRNAs and circRNAs as diagnostic biomarkers and therapeutics to differentiate atypical parkinsonian disorders and their role in disease pathogenesis.

Construction and analysis of circular RNA-associated competing endogenous RNA network in the hippocampus of aged mice for the occurrence of postoperative cognitive dysfunction

Circular RNAs are highly stable single-stranded circular RNAs and enriched in the brain. Previous studies showed that circRNAs, as part of competing endogenous RNAs (ceRNAs) network, play an important role in neurodegenerative and psychiatric diseases. However, the mechanism of circRNA-related ceRNA networks in postoperative cognitive dysfunction (POCD) has not been elucidated yet. POCD usually occurs in elderly patients and is characterized by hippocampal dysfunction. Here, aged C57BL/6 mice were subjected to exploratory laparotomy under sevoflurane anesthesia, and this POCD model was verified by Morris water maze test. Whole-transcriptome sequencing was performed on the hippocampus of control group (Con) and surgery group. One hundred and seventy-seven DEcircRNAs, 221 DEmiRNAs and 2,052 DEmRNAs were identified between two groups. A ceRNA network was established with 92 DEcircRNAs having binding sites with 76 DEmiRNAs and 549 target DEmRNAs. In functional enrichment analysis, a pathological pattern of POCD was highlighted in the ceRNA network: Abnormal metabolic process in neural cells, including oxygen metabolism, could promote apoptosis and then affect the synaptic function, which may undermine the neural plasticity and eventually lead to changes in cognitive function and other behavioral patterns. In conclusion, this specific ceRNA network of circRNAs–miRNAs–mRNAs has provided novel insights into the regulatory mechanisms of POCD and revealed potential therapeutic gene targets.

Identification of Circular RNA Profiles in the Liver of Diet-Induced Obese Mice and Construction of the ceRNA Network

Obesity is a major risk factor for cardiovascular, cerebrovascular, metabolic, and respiratory diseases, and it has become an important social health problem affecting the health of the population. Obesity is affected by both genetic and environmental factors. In this study, we constructed a diet-induced obese C57BL/6J mouse model and performed deep RNA sequencing (RNA-seq) on liner-depleted RNA extracted from the liver tissues of the mice to explore the underlying mechanisms of obesity. A total of 7469 circular RNAs (circRNAs) were detected, and 21 were differentially expressed (DE) in the high-fat diet (HFD) and low-fat diet (LFD) groups. We then constructed a comprehensive circRNA-associated competing endogenous RNA (ceRNA) network. Bioinformatic analysis indicated that DE circRNAs associated with lipid metabolic-related pathways may act as miRNA sponges to modulate target gene expression. CircRNA1709 and circRNA4842 may serve as new candidates to regulate the expression of PTEN. This study provides systematic circRNA-associated ceRNA profiling in HFD mouse liver, and the results can aid early diagnosis and the selection of treatment targets for obesity in the future.

The landscape of m1A modification and its posttranscriptional regulatory functions in primary neurons

Cerebral ischaemia‒reperfusion injury (IRI), during which neurons undergo oxygen-glucose deprivation/reoxygenation (OGD/R), is a notable pathological process in many neurological diseases. N1-methyladenosine (m¹A) is an RNA modification that can affect gene expression and RNA stability. The m¹A landscape and potential functions of m¹A modification in neurons remain poorly understood. We explored RNA (mRNA, lncRNA, and circRNA) m¹A modification in normal and OGD/R-treated mouse neurons and the effect of m¹A on diverse RNAs. We investigated the m¹A landscape in primary neurons, identified m¹A-modified RNAs, and found that OGD/R increased the number of m¹A RNAs. m¹A modification might also affect the regulatory mechanisms of noncoding RNAs, e.g., lncRNA-RNA binding proteins (RBPs) interactions and circRNA translation. We showed that m¹A modification mediates the circRNA/lncRNA‒miRNA-mRNA competing endogenous RNA (ceRNA) mechanism and that 3' untranslated region (3'UTR) modification of mRNAs can hinder miRNA-mRNA binding. Three modification patterns were identified, and genes with different patterns had intrinsic mechanisms with potential m¹A-regulatory specificity. Systematic analysis of the m¹A landscape in normal and OGD/R neurons lays a critical foundation for understanding RNA modification and provides new perspectives and a theoretical basis for treating and developing drugs for OGD/R pathology-related diseases.

Circular RNA hsa_circ_0000690 as a potential biomarker for diagnosis and prognosis of intracranial aneurysm: Closely relating to the volume of hemorrhage

PURPOSE

This study aimed to explore circular RNA (circRNA) hsa_circ_0000690 as a potential biomarker for diagnosis and prognosis of intracranial aneurysm (IA) and its relationship with clinical factors and complications of IA.

MATERIAL/METHODS

216 IA patients admitted to the neurosurgery department of our hospital from January 2019 to December 2020 were selected as the experimental group, and 186 healthy volunteers were selected as the control group. The expression of hsa_circ_0000690 in peripheral blood was detected by quantitative real-time PCR, and its diagnostic value was assessed by receiver operating characteristic curve. Relationship between hsa_circ_0000690 and clinical factors of IA was assessed by chi-square test. Nonparametric test was used in univariate analysis, and regression analysis was used in multivariate analysis. Multivariate Cox proportional hazards regression analysis was used to analyze the survival time.

RESULTS

CircRNA hsa_circ_0000690 of IA patients was relatively lower than that in the control group (p < .001). The AUC of hsa_circ_0000690 was 0.752, the specificity was 0.780, and sensitivity was 0.620, with diagnostic threshold of 0.0449. In addition, hsa_circ_0000690 expression was correlated with Glasgow Coma Scale, the volume of subarachnoid hemorrhage, modified Fisher scale, Hunt-Hess levels and surgical type. For hydrocephalus and delayed cerebral ischemia, hsa_circ_0000690 was significant in univariate analysis, but nonsignificant in multivariate analysis. For prognosis, hsa_circ_0000690 was significantly associated with modified Rankin Scales after surgery for 3 months, but not associated with survival time.

CONCLUSIONS

The expression of hsa_circ_0000690 can act as a diagnostic marker for IA and predict the prognosis of 3 months after operation and is closely related to the volume of hemorrhage.

CircRNA-104718 promotes glioma malignancy through regulation of miR-218-5p/HMGB1 signalling pathway

Increasing number of studies have proven that circular RNAs (circRNAs) play a major role in the biological processes of many different cancers, including glioma, especially as competitive molecular sponges of microRNAs (miRNAs). However, the clear molecular mechanism of the circRNA network in glioma is still not well understood. The expression level of circRNA-104718 and microRNA (miR)-218-5p in glioma tissues and cells were detected by quantitative real-time polymerase chain reaction (qRT-PCR). The target protein's expression level was assessed by western blotting. Bioinformatics systems were used to predict the possible microRNAs and target genes of circRNA-104718, after which dual-luciferase reporter assays were used to confirm the predicted interactions. The proliferation, invasion, migration and apoptosis of glioma cells were detected by CCK, EdU, transwell, wound-healing and flow cytometry assays. CircRNA-104718 was upregulated in human glioma tissues, and a higher level of circRNA-104718 indicated poorer outcomes in glioma patients. In contrast, in glioma tissues, miR-218-5p was downregulated. Knockdown of circRNA-104718 suppressed migration and invasion while boosting the apoptosis rate of glioma cells. In addition, the upregulation of miR-218-5p in glioma cells caused the same suppression. Mechanistically, circRNA-104718 inhibited the protein expression level of high mobility group box-1 (HMGB1) by acting as a molecular sponge for miR-218-5p. CircRNA-104718 is a suppressive factor in glioma cells and might represent a new target for the treatment of glioma patients. CircRNA-104718 modulates glioma cell proliferation through the miR-218-5p/HMGB1 signalling axis. CircRNA-104718 provides a possible mechanism for understanding the pathogenesis of glioma.

Regulation of Glial Function by Noncoding RNA in Central Nervous System Disease

Non-coding RNAs (ncRNAs) are a class of functional RNAs that play critical roles in different diseases. NcRNAs include microRNAs, long ncRNAs, and circular RNAs. They are highly expressed in the brain and are involved in the regulation of physiological and pathophysiological processes of central nervous system (CNS) diseases. Mounting evidence indicates that ncRNAs play key roles in CNS diseases. Further elucidating the mechanisms of ncRNA underlying the process of regulating glial function that may lead to the identification of novel therapeutic targets for CNS diseases.

Circular RNAs: Biogenesis, Biological Functions, and Roles in Myocardial Infarction

Non-coding RNAs have been excavated as important cardiac function modulators and linked to heart diseases. Significant advances have been obtained in illuminating the effects of microRNAs and long non-coding RNAs. Nevertheless, the characteristics of circular RNAs are rarely mined. Circular RNAs (circRNAs) are widely believed to participate in cardiac pathologic processes, especially in myocardial infarction. In this review, we round up the biogenesis of circRNAs, briefly describe their biological functions, and summarize the latest literature on multifarious circRNAs related to new therapies and biomarkers for myocardial infarction.

Circular RNA METTL9 contributes to neuroinflammation following traumatic brain injury by complexing with astrocytic SND1

BACKGROUND

Circular RNAs (circRNAs) are highly enriched in the central nervous system and have been implicated in neurodegenerative diseases. However, whether and how circRNAs contribute to the pathological processes induced by traumatic brain injury (TBI) has not been fully elucidated.

METHODS

We conducted a high-throughput RNA sequencing screen for well-conserved, differentially expressed circRNAs in the cortex of rats subjected to experimental TBI. Circular RNA METTL9 (circMETTL9) was ultimately identified as upregulated post-TBI and further characterized by RT-PCR and agarose gel electrophoresis, Sanger sequencing, and RNase R treatment. To examine potential involvement of circMETTL9 in neurodegeneration and loss of function following TBI, circMETTL9 expression in cortex was knocked-down by microinjection of a shcircMETTL9 adeno-associated virus. Neurological functions were evaluated in control, TBI, and TBI-KD rats using a modified neurological severity score, cognitive function using the Morris water maze test, and nerve cell apoptosis rate by TUNEL staining. Pull-down assays and mass spectrometry were conducted to identify circMETTL9-binding proteins. Co-localization of circMETTL9 and SND1 in astrocytes was examined by fluorescence in situ hybridization and immunofluorescence double staining. Changes in the expression levels of chemokines and SND1 were estimated by quantitative PCR and western blotting.

RESULTS

CircMETTL9 was significantly upregulated and peaked at 7 d in the cerebral cortex of TBI model rats, and it was abundantly expressed in astrocytes. We found that circMETTL9 knockdown significantly attenuated neurological dysfunction, cognitive impairment, and nerve cell apoptosis induced by TBI. CircMETTL9 directly bound to and increased the expression of SND1 in astrocytes, leading to the upregulation of CCL2, CXCL1, CCL3, CXCL3, and CXCL10, and ultimately to enhanced neuroinflammation.

CONCLUSION

Altogether, we are the first to propose that circMETTL9 is a master regulator of neuroinflammation following TBI, and thus a major contributor to neurodegeneration and neurological dysfunction.

Prenatal alcohol exposure results in brain region- and sex-specific changes in circHomer1 expression in adult mouse brain

Circular RNAs (circRNAs) are a novel category of covalently-closed non-coding RNAs mainly derived from the back-splicing of exons or introns of protein-coding genes. In addition to their inherent high overall stability, circRNAs, have been shown to have strong functional effects on gene expression via a multitude of transcriptional and post-transcriptional mechanisms. Furthermore, circRNAs, appear to be particularly enriched in the brain and able to influence both prenatal development and postnatal brain function. However, little is known about the potential involvement of circRNAs in the long term influence of prenatal alcohol exposure (PAE) in the brain and their relevance for Fetal Alcohol Spectrum Disorders (FASD). Using circRNA-specific quantification, we have found that circHomer1, an activity-dependent circRNA derived from Homer protein homolog 1 (Homer1) and enriched in postnatal brain, is significantly down-regulated in the male frontal cortex and hippocampus of mice subjected to modest PAE. Our data further suggest that the expression of H19, an imprinted embryonic brain-enriched long non-coding RNA (lncRNA), is significantly up-regulated in the frontal cortex of male PAE mice. Furthermore, we show opposing changes in the developmental- and brain region specific- expression of circHomer1 and H19. Lastly, we show that knockdown of H19 results in robust increases in circHomer1 but not linear HOMER1 mRNA expression in human glioblastoma cell lines. Taken together, our work uncovers notable sex- and brain region-specific alterations in circRNA and lncRNA expression following PAE and introduces novel mechanistic insights with potential relevance to FASD.

CircRalgapa1 facilitates morphine tolerance via miR-873a-5p/A20 axis in mice

Morphine tolerance (MT) caused by long-term use of morphine is a major medical problem. The underlying molecular mechanisms of morphine tolerance remain unclear. Here, we establish the morphine tolerance model in mice and verify whether a novel circRNA, circRalgapa1 is involved in morphine tolerance and its specific molecular mechanism. We show that the expression of circRalgapa1 in the spinal cord is significantly down-expressed in the spinal cord of morphine-tolerant mice. CircRalgapa1 is mainly located in the neuronal cytoplasm and co-localizes with miR-873a-5p. Mechanically, circRalgapa1 acts as competing endogenous RNAs (ceRNAs) to regulate the inhibitory of miR-873a-5p on A20 (also known as tumor necrosis factor α-induced protein 3, TNFAIP3). Functionally, overexpression of circRalgapa1 by intrathecal injection of adeno-associated virus (AAV- circRalgapa1) attenuated the formation of morphine tolerance and partially reversed the development of morphine tolerance. Moreover, overexpression of miR-873a-5p blocked the effect of AAV-circRalgapa1 on alleviating morphine tolerance in mice. In conclusion, chronic morphine administration-mediated down-regulation of circRalgapa1 in the spinal cord contributes to morphine tolerance via miR-873a-5p/A20 axis in mice. Overexpression of circRalgapa1 may be a promising RNA-based therapy for morphine tolerance.

Circular RNAs: New players involved in the regulation of cognition and cognitive diseases

Circular RNAs (circRNAs), a type of covalently closed endogenous single-stranded RNA, have been regarded as the byproducts of the aberrant splicing of genes without any biological functions. Recently, with the development of high-throughput sequencing and bioinformatics, thousands of circRNAs and their differential biological functions have been identified. Except for the great advances in identifying circRNA roles in tumor progression, diagnosis, and treatment, accumulated evidence shows that circRNAs are enriched in the brain, especially in the synapse, and dynamically change with the development or aging of organisms. Because of the specific roles of synapses in higher-order cognitive functions, circRNAs may not only participate in cognitive functions in normal physiological conditions but also lead to cognition-related diseases after abnormal regulation of their expression or location. Thus, in this review, we summarized the progress of studies looking at the role of circRNA in cognitive function, as well as their involvement in the occurrence, development, prognosis, and treatment of cognitive-related diseases, including autism, depression, and Alzheimer's diseases.

CircRNA SRRM4 affects glucose metabolism by regulating PKM alternative splicing via SRSF3 deubiquitination in epilepsy

OBJECTIVES

Several reports suggest that epigenetic therapy may be a potential method for treating epilepsy, and circular RNAs (circRNAs) play important roles in mediating the epigenetic mechanisms associated with epilepsy; however, currently there are no effective treatment methods to prevent the progression of epileptogenesis. The circRNA serine/arginine repetitive matrix 4 (circSRRM4) was found to exert regulatory effects in temporal lobe epilepsy (TLE); however, the mechanisms involved are still unknown.

MATERIALS AND METHODS

To elucidate the molecular mechanism of circSRRM4, we investigated human epileptic brain tissue, epileptic rats, neuron and astrocyte cell lines using RT-qPCR, western blot, fluorescence in situ hybridisation, immunofluorescence staining, Nissl stain, micro-PET-CT, RNA-pulldown, liquid chromatography-mass spectrometry, and RBP immunoprecipitation techniques. Furthermore, we evaluated the pyruvate kinase M1/2 (PKM) expression patterns in the human and rat models of TLE.

RESULTS

We detected the increased circSRRM4 expression in the hypometabolic lesions of patients with TLE and discovered that circSrrm4 has specific spatiotemporal characteristics in rats with kainic acid-induced epilepsy. The decreased PKM1 expression and increased PKM2 expression were similar to the Warburg effect in tumours. Notably, circSrrm4 silencing reduced the incidence and frequency of epilepsy, improved local hypometabolism, and prevented neuronal loss and astrocyte activation.

CONCLUSION

PKM2 promotes lactic acid production in the astrocytes by inducing glycolysis, thereby contributing to the energy source for epileptic seizures. Notably, circSRRM4 combines with and inhibits serine and arginine rich splicing factor 3 (SRSF3) from joining the ubiquitin-proteasome pathway, improving the SRSF3-regulated alternative splicing of PKM, and consequently stimulating glycolysis in cells.

CircVAPA contributes to hyper-proliferation and inflammation of keratinocytes through miR-125b-5p/sirt6 axis in psoriasis

Psoriasis is an autoimmune skin disease with abnormal keratinocyte hyperproliferation. The important roles of circular RNAs (circRNAs) in various inflammatory diseases have been revealed. The present study aimed to investigate the roles of circVAPA and its molecular mechanisms in psoriasis. Quantitative real-time polymerase chain reaction was performed to measure the RNA expression. Enzyme-linked immunosorbent assays were employed to examine the production of inflammatory factors. Cell-counting kit-8, EDU and flow cytometry assay were conducted to examine the cell viability, proliferation and apoptosis respectively. Dual-luciferase reporter assay and ribonucleoprotein immunoprecipitation (RIP) were conducted to verify the target relationship between miR-125b-5p and circVAPA or Sirt6. Herein our findings showed increased expression of circVAPA and Sirt6 and decreased level of miR-125b-5p in psoriatic lesional tissues and M5-stimulated keratinocytes. Mechanistically, circVAPA knockdown significantly suppressed the promotion of M5 on cell viability, proliferation, and inflammation of HaCaT cells. circVAPA was verified to interact with miR-125b-5p, while inhibition of miR-125b-5p counteracted circVAPA knockdown-mediated effects in M5-stimulated HaCaT cells. Sirt6 was confirmed as a target of miR-125b-5p, and miR-125b-5p overexpression inhibited cell growth and inflammation partly by targeting Sirt6 in M5-stimulated HaCaT cells. Moreover, circVAPA was featured as a competing endogenous RNA by directly sponging miR-125b-5p to up-regulate the expression of Sirt6. CircVAPA participate in the progression of psoriasis through miR-125b-5p/sirt6 axis by regulating proliferation and inflammation of keratinocytes, highlighting a potential therapeutic target for psoriasis.

Genome-wide characterization of circRNA expression profile in overexpression of RIP2 chicken macrophages associated with avian pathogenic E.coli infection

Avian pathogenic E. coli (APEC) can cause localized and systemic diseases in poultry, threatening human health via meat or egg contamination and resulting in considerable economic losses to the poultry industry globally. Increasing evidence shows circRNAs were widely involved in various biological processes. However, the role of circRNAs in the host response against APEC infection, especially correlated with the regulation of RIP2, remains unclear. Herein, the RNAseq technology was used to identify the circRNA expression profiles in the overexpression of RIP2 macrophages with or without APEC infection. A total of 256 and 287 differentially expressed (DE) circRNAs were identified in the overexpression of RIP2 group (oeRIP2) vs. the wild-type group (WT) and oeRIP2 + APEC vs. APEC, respectively, whose parental genes were involved in MAPK signalling pathway, Wnt signalling pathway, focal adhesion, tight junction, and VEGF signalling pathways. Specifically, the key circRNAs, such as 5:814443-825127, 10:18922360-18928461, 2:8746306-8750639, and 2:124177751-124184063 might play a critical role in APEC infection and the regulation of RIP2. As a whole, these findings will facilitate understanding the molecular mechanism underlying circRNAs, especially related to the regulation of the RIP2 gene. Meanwhile, the study may offer new ideas to improve host immune and inflammatory response against APEC infection.

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.

Circular RNA hsa_circ_0075323 promotes glioblastoma cells proliferation and invasion via regulation of autophagy

BACKGROUND

Protein p62 (sequestosome 1) encoded by gene SQSTM1 plays a vital role in mediating protectively selective autophagy in tumor cells under stressed conditions. CircSQSTM1 (hsa_circ_0075323) is a circular transcript generated from gene SQSTM1 (chr5:179260586-179260782) by back-splicing. However, the potential role of hsa_hsa_circ_0075323 in glioblastoma (GBM) remains unclear. Here, we aimed to explore the biological function of hsa_circ_0075323 in GBM and its relationship with autophagy regulation.

RESULTS

Hsa_circ_0075323 is highly expressed in GBM cells and mainly locates in the cytoplasm. Inhibition of hsa_circ_0075323 in U87-MG and T98G cells attenuated proliferation and invasion ability significantly, while upregulation of has_ circ_0075323 enhanced proliferation and migration of U251-MG and A172 cells. Mechanistically, depletion of hsa_circ_0075323 in GBM cells resulted in impaired autophagy, as indicated by increased expression of p62 and decreased expression of LC3B.

CONCLUSIONS

Hsa_circ_0075323 regulates p62-mediated autophagy pathway to promote GBM progression and may serve as a prognostic biomarker potentially.

Recent insights into the roles of circular RNAs in human brain development and neurologic diseases

Circular RNAs (circRNAs) are a novel class of non-coding RNAs. They are single-stranded RNA transcripts characterized with a closed loop structure making them resistant to degrading enzymes. Recently, circRNAs have been suggested with regulatory roles in gene expression involved in controlling various biological processes. Notably, they have demonstrated abundance, dynamic expression, back-splicing events, and spatiotemporally regulation in the human brain. Accordingly, they are expected to be involved in brain functions and related diseases. Studies in animals and human brain have revealed differential expression of circRNAs in brain compartments. Interestingly, contributing roles of circRNAs in the regulation of central nervous system (CNS) development have been demonstrated in a number of studies. It has been proposed that circRNAs play role in substantial neurological functions like neurotransmitter-associated tasks, neural cells maturation, and functions of synapses. Furthermore, 3 main pathways have been identified in association with circRNAs's host genes including axon guidance, Wnt signaling, and transforming growth factor beta (TGF-β) signaling pathways, which are known to be involved in substantial functions like migration and differentiation of neurons and specification of axons, and thus play role in brain development. In this review, we have an overview to the biogenesis, biological functions of circRNAs, and particularly their roles in human brain development and the pathogenesis of neurodegenerative diseases including Alzheimer's diseases, multiple sclerosis, Parkinson's disease and brain tumors.

The U2AF65/circNCAPG/RREB1 feedback loop promotes malignant phenotypes of glioma stem cells through activating the TGF-β pathway

Glioma is the most aggressive and common malignant neoplasms in human brain tumors. Numerous studies have showed that glioma stem cells (GSCs)drive the malignant progression of gliomas. Recent studies have revealed that circRNAs can maintain stemness and promote malignant progression of glioma stem cells. We used bioinformatics analysis to identify circRNAs and potential RNA-binding proteins (RBPs) in glioma. qRT-PCR, western blotting, RNA FISH, RNA pull-down, RNA immunoprecipitation assay, ChIP, immunohistochemistry, and immunofluorescence methods were used to quantified the expression of circNCAPG, U2AF65, RREB1 and TGF-β1, and the underlying mechanisms between them. MTS, EDU, neurosphere formation, limiting dilution neurosphere formation and transwell assays examined the proliferation and invasive capability of GSCs, respectively. We identified a novel circRNA named circNCAPG was overexpressed and indicated the poor prognosis in glioma patients. Upregulating circNCAPG promoted the malignant progression of GSCs. RNA binding protein U2AF65 could stabilize circNCAPG by direct binding. Mechanically, circNCAPG interacted with and stabilized RREB1, as well as stimulated RREB1 nuclear translocation to activate TGF-β1 signaling pathway. Furthermore, RREB1 transcriptionally upregulated U2AF65 expression to improve the stability of circNCAPG in GSCs, which established a feedback loop involving U2AF65, circNCAPG and RREB1. Since circRNA is more stable than mRNA and can execute its function continuously, targeting circNCAPG in glioma may be a novel promising therapeutic.

Exosomal circRNAs as promising liquid biopsy biomarkers for glioma

Liquid biopsy strategies enable the noninvasive detection of changes in the levels of circulating biomarkers in body fluid samples, providing an opportunity to diagnose, dynamically monitor, and treat a range of diseases, including cancers. Glioma is among the most common forms of intracranial malignancy, and affected patients exhibit poor prognostic outcomes. As such, diagnosing and treating this disease in its early stages is critical for optimal patient outcomes. Exosomal circular RNAs (circRNAs) are involved in both the onset and progression of glioma. Both the roles of exosomes and methods for their detection have received much attention in recent years and the detection of exosomal circRNAs by liquid biopsy has significant potential for monitoring dynamic changes in glioma. The present review provides an overview of the circulating liquid biopsy biomarkers associated with this cancer type and the potential application of exosomal circRNAs as tools to guide the diagnosis, treatment, and prognostic evaluation of glioma patients during disease progression.

The landscape of exosomal non-coding RNAs in breast cancer drug resistance, focusing on underlying molecular mechanisms

Breast cancer (BC) is the most common malignancy among women worldwide. Like many other cancers, BC therapy is challenging and sometimes frustrating. In spite of the various therapeutic modalities applied to treat the cancer, drug resistance, also known as, chemoresistance, is very common in almost all BCs. Undesirably, a breast tumor might be resistant to different curative approaches (e.g., chemo- and immunotherapy) at the same period of time. Exosomes, as double membrane-bound extracellular vesicles 1) secreted from different cell species, can considerably transfer cell products and components through the bloodstream. In this context, non-coding RNAs (ncRNAs), including miRNAs, long ncRNAs (lncRNAs), and circular RNAs (circRNAs), are a chief group of exosomal constituents with amazing abilities to regulate the underlying pathogenic mechanisms of BC, such as cell proliferation, angiogenesis, invasion, metastasis, migration, and particularly drug resistance. Thereby, exosomal ncRNAs can be considered potential mediators of BC progression and drug resistance. Moreover, as the corresponding exosomal ncRNAs circulate in the bloodstream and are found in different body fluids, they can serve as foremost prognostic/diagnostic biomarkers. The current study aims to comprehensively review the most recent findings on BC-related molecular mechanisms and signaling pathways affected by exosomal miRNAs, lncRNAs, and circRNAs, with a focus on drug resistance. Also, the potential of the same exosomal ncRNAs in the diagnosis and prognosis of BC will be discussed in detail.

Functional roles, regulatory mechanisms and theranostics applications of ncRNAs in alcohol use disorder

Alcohol use disorder (AUD) is one of the most prevalent neuropsychological disorders worldwide, and its pathogenesis is convoluted and poorly understood. There is considerable evidence demonstrating significant associations between multiple heritable factors and the onset and progression of AUD. In recent years, a substantial body of research conducted by emerging biotechnologies has increasingly highlighted the crucial roles of noncoding RNAs (ncRNAs) in the pathophysiology of mental diseases. As in-depth understanding of ncRNAs and their mechanisms of action, they have emerged as prospective diagnostic indicators and preclinical therapeutic targets for a variety of psychiatric illness, including AUD. Of note, dysregulated expression of ncRNAs such as circRNAs, lncRNAs and miRNAs was routinely found in AUD individuals, and besides, exogenous regulation of partial ncRNAs has also been shown to be effective in ameliorating alcohol preference and excessive alcohol consumption. However, the exact molecular mechanism still remains elusive. Herein, we systematically summarized current knowledge regarding alterations in the expression of certain ncRNAs as well as their-mediated regulatory mechanisms in individuals with AUD. And finally, we detailedly reviewed the potential theranostics applications of gene therapy agents targeting ncRNAs in AUD mice. Overall, a deeper comprehension of functional roles and biological mechanisms of ncRNAs may make significant contributions to the accurate diagnosis and effective treatment of AUD.

Noncoding RNAs: Novel Targets for Opioid Tolerance

As a global health problem, chronic pain is one of the leading causes of disability, and it imposes a huge economic and public health burden on families and society. Opioids represent the cornerstone of analgesic drugs. However, opioid tolerance caused by long-term application of opioids is a major factor leading to drug withdrawal, serious side effects caused by dose increases, and even the death of patients, placing an increasing burden on individuals, medicine, and society. Despite efforts to develop methods to prevent and treat opioid tolerance, no effective treatment has yet been found. Therefore, understanding the mechanism underlying opioid tolerance is crucial for finding new prevention and treatment strategies. Noncoding RNAs (ncRNAs) are important parts of mammalian gene transcriptomes, and there are thousands of unique noncoding RNA sequences in cells. With the rapid development of high-throughput genome technology, research on ncRNAs has become a hot topic in biomedical research. In recent years, studies have shown that ncRNAs mediate physiological and pathological processes, including chromatin remodeling, transcription, posttranscriptional modification and signal transduction, which are key regulators of physiological processes in developmental and disease environments and have become biomarkers and potential therapeutic targets for various diseases. An increasing number of studies have found that ncRNAs are closely related to the development of opioid tolerance. In this review, we have summarized the evidence that ncRNAs play an important role in opioid tolerance and that ncRNAs may be novel targets for opioid tolerance.

Circular RNAs: emerging players in brain aging and neurodegenerative diseases

Brain aging is closely related to neurodegenerative diseases. Circular RNAs (circRNAs) are a type of conserved RNAs with covalently closed continuous loops. Emerging evidence has shown that circRNAs are implicated in the biology of brain aging and the pathology of age-related neurodegenerative diseases. Here, we summarize current studies on circRNAs associated with brain aging and neurodegenerative diseases by discussing their expression features, pathophysiological roles, and mechanisms of action. We also discuss the potential challenges of circRNA-based therapy against brain aging and neurodegenerative diseases, as well as their potential as diagnostic biomarkers of neurodegenerative diseases. The review provides insights into current progress in the functions of circRNAs in the process of brain aging and neurodegenerative diseases. © 2022 The Pathological Society of Great Britain and Ireland.

Regulation of LncRNAs and microRNAs in neuronal development and disease

Non-coding RNAs (ncRNAs) are RNAs that do not encode proteins but play important roles in regulating cellular processes. Multiple studies over the past decade have demonstrated the role of microRNAs (miRNAs) in cancer, in which some miRNAs can act as biomarkers or provide therapy target. Accumulating evidence also points to the importance of long non-coding RNAs (lncRNAs) in regulating miRNA-mRNA networks. An increasing number of ncRNAs have been shown to be involved in the regulation of cellular processes, and dysregulation of ncRNAs often heralds disease. As the population ages, the incidence of neurodegenerative diseases is increasing, placing enormous pressure on global health systems. Given the excellent performance of ncRNAs in early cancer screening and treatment, here we attempted to aggregate and analyze the regulatory functions of ncRNAs in neuronal development and disease. In this review, we summarize current knowledge on ncRNA taxonomy, biogenesis, and function, and discuss current research progress on ncRNAs in relation to neuronal development, differentiation, and neurodegenerative diseases.

Emerging role of interaction between m6A and main ncRNAs in gastrointestinal (GI) cancers

As a prevalent epigenetic modification, the role of m6A has been increasingly highlighted in the alteration of numerous RNAs implicated with multiple biological processes, such as formation, export, translation, and degradation. With further the understanding of m6A, accumulating evidence shows that m6A modification similarly affects metabolic process of non-coding genes. But the specifical interplay of m6A and ncRNAs (non-coding RNAs) in gastrointestinal cancers still lacks complete discussion. Thus, we analyzed and summarized how ncRNAs affect the regulators of m6A and by what means the expression of ncRNAs is altered via m6A in gastrointestinal cancers. We focused on the effect of the interaction of m6A and ncRNAs on the molecular mechanisms of malignant behavior in gastrointestinal cancers, revealing more possibilities of ncRNAs for diagnosis and treatment in term of epigenetic modification.

RNA editing of microtubule-associated protein tau circular RNAs promotes their translation and tau tangle formation

Aggregation of the microtubule-associated protein tau characterizes tauopathies, including Alzheimer's disease and frontotemporal lobar degeneration (FTLD-Tau). Gene expression regulation of tau is complex and incompletely understood. Here we report that the human tau gene (MAPT) generates two circular RNAs (circRNAs) through backsplicing of exon 12 to either exon 7 (12→7 circRNA) or exon 10 (12→10 circRNA). Both circRNAs lack stop codons. The 12→7 circRNA contains one start codon and is translated in a rolling circle, generating a protein consisting of multimers of the microtubule-binding repeats R1-R4. For the 12→10 circRNA, a start codon can be introduced by two FTLD-Tau mutations, generating a protein consisting of multimers of the microtubule-binding repeats R2-R4, suggesting that mutations causing FTLD may act in part through tau circRNAs. Adenosine to inosine RNA editing dramatically increases translation of circRNAs and, in the 12→10 circRNA, RNA editing generates a translational start codon by changing AUA to AUI. Circular tau proteins self-aggregate and promote aggregation of linear tau proteins. Our data indicate that adenosine to inosine RNA editing initiates translation of human circular tau RNAs, which may contribute to tauopathies.

Inhibition of circ_0004381 improves cognitive function via miR-647/PSEN1 axis in an Alzheimer disease mouse model

Circ_0004381 promotes neuronal damage in Parkinson disease, but its role in Alzheimer disease (AD) is unreported. The goal of this study was to investigate the role and potential mechanisms of circ_0004381 effects in AD models. Primary hippocampal neurons were treated with amyloid-β (Aβ1-42) to construct AD cell models. We found that circ_0004381 was upregulated in Aβ1-42-treated hippocampal neurons. Knockdown of circ_0004381 attenuated Aβ1-42-induced apoptosis, oxidative stress, and mitochondrial dysfunction in hippocampal neurons. Next, we induced microglia activation with lipopolysaccharide (LPS). The results of flow cytometry experiments showed that knockdown of circ_0004381 promoted microglial M2-type polarization and knockdown of circ_0004381 inhibited the production of inflammatory factors by microglia. Furthermore, knockdown of circ_0004381 improved cognitive function of male APPswe/PS1dE9 transgenic mice. Mechanistically, circ_0004381 regulated presenilin-1 (PSEN1) expression by absorbing miR-647. MiR-647 inhibition attenuated the effects of circ_0004381 knockdown. In conclusion, knockdown of circ_0004381 attenuated hippocampal neuronal damage and promoted microglia M2-type polarization through the miR-647/PSEN1 axis, ultimately improving cognitive function in AD model mice.

Urinary exosomal hsa_circ_0001250 as a novel diagnostic biomarker of idiopathic membranous nephropathy

AIMS

Idiopathic membranous nephropathy (IMN) is a common cause of adult nephrotic syndrome. Currently, the diagnosis of IMN mainly depends on renal biopsy, which is invasive. What's more, markers already known for the clinical diagnosis of IMN are not sensitive enough. The present study aims to investigate the profiling of urinary exosomal circular RNAs (circRNAs) of IMN, and to look for a potential biomarker for diagnosis of IMN.

METHODS

Urine exosomes were collected from patients with IMN and idiopathic nephrotic syndrome (INS), as well as healthy controls (HCs) by ultracentrifuge. A pairwise comparison between 5 IMN and 5 HC was performed by high-throughput sequencing. Enrichment analysis were performed to explore the potential functions of differentially expressed circRNAs in IMN. Among three differentially expressed circRNAs which may be involved in signaling pathways of pathogenesis of IMN and matched conserved mouse circRNAs, hsa_circ_0001250 was selected as the target circRNA after quantitative polymerase chain reaction among 23 IMN, 19 INS and 23HC. Sanger sequencing and RNase R digestion assay were performed to validated the ring-structure and sequence of hsa_circ_0001250. ROC (Receiver Operating Characteristic) curve correlation analysis was used to further validate the potential utility of hsa_circ_0001250 as a diagnostic biomarker of IMN. A circRNA-miRNA-mRNA network was constructed to reflect the relationship between hsa_circ_0001250 and its target miRNAs and mRNAs.

RESULTS

766 up-regulated and 283 down-regulated circRNAs were identified in IMN patients. Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed signaling pathways of pathogenesis of IMN which the different expressed circRNAs may participate in. The ring-structure and the sequence of hsa_circ_0001250 were confirmed, the expression of hsa_circ_0001250 was validated significantly increased in IMN, relevant with high level of proteinuria. A circRNA-miRNA-mRNA network reflected that hsa_circ_0001250 may play a role in the pathogenesis of IMN by target hsa-miR-639 and hsa-miR-4449.

CONCLUSION

We revealed the expression and functional profile of differentially expressed urinary exosomal circRNAs of IMN patients. Urinary exosomal hsa_circ_0001250 was tested as a potential biomarker of IMN and a predicted circRNA-miRNA-mRNA network was constructed.

Modulating autophagy and mitophagy as a promising therapeutic approach in neurodegenerative disorders

The high prevalence of neurodegenerative diseases has become a major public health challenge and is associated with a tremendous burden on individuals, society and federal governments worldwide. Protein misfolding and aggregation are the major pathological hallmarks of several neurodegenerative disorders. The cells have evolved several regulatory mechanisms to deal with aberrant protein folding, namely the classical ubiquitin pathway, where ubiquitination of protein aggregates marks their degradation via lysosome and the novel autophagy or mitophagy pathways. Autophagy is a catabolic process in eukaryotic cells that allows the lysosome to recycle the cell's own contents, such as organelles and proteins, known as autophagic cargo. Their most significant role is to keep cells alive in distressed situations. Mitophagy is also crucial for reducing abnormal protein aggregation and increasing organelle clearance and partly accounts for maintaining cellular homeostasis. Furthermore, substantial data indicate that any disruption in these homeostatic mechanisms leads to the emergence of several age-associated metabolic and neurodegenerative diseases. So, targeting autophagy and mitophagy might be a potential therapeutic strategy for a variety of health conditions.

CDR1as regulates α-synuclein-mediated ischemic brain damage by controlling miR-7 availability

Transient focal ischemia decreased microRNA-7 (miR-7) levels, leading to derepression of its major target α-synuclein (α-Syn) that promotes secondary brain damage. Circular RNA CDR1as is known to regulate miR-7 abundance and function. Hence, we currently evaluated its functional significance after focal ischemia. Transient middle cerebral artery occlusion (MCAO) in adult mice significantly downregulated both CDR1as and miR-7 levels in the peri-infarct cortex between 3 and 72 h of reperfusion. Interestingly, neither pri-miR-7a nor 7b was altered in the ischemic brain. Intracerebral injection of an AAV9 vector containing a CDR1as gene significantly increased CDR1as levels by 21 days that persisted up to 4 months without inducing any observable toxicity in both sham and MCAO groups. Following transient MCAO, there was a significant increase in miR-7 levels and CDR1as binding to Ago2/miR-7 in the peri-infarct cortex of AAV9-CDR1as cohort compared with AAV9-Control cohort at 1 day of reperfusion. CDR1as overexpression significantly suppressed post-stroke α-Syn protein induction, promoted motor function recovery, decreased infarct size, and curtailed the markers of apoptosis, autophagy mitochondrial fragmentation, and inflammation in the post-stroke brain compared with AAV9-Control-treated cohort. Overall, our findings imply that CDR1as reconstitution is neuroprotective after stroke, probably by protecting miR-7 and preventing α-Syn-mediated neuronal death.

Obese mice induced by high-fat diet have differential expression of circular RNAs involved in endoplasmic reticulum stress and neuronal synaptic plasticity of hippocampus leading to obesity-associated cognitive impairment

Obesity induced by a high-fat diet (HFD) is an important cause of impaired memory and cognitive function, but the underlying mechanisms are not clear. In the present study, we analyzed the levels of circRNAs in the hippocampus of C57BL/6J mice and evaluated the memory and cognition ability of C57BL/6J mice with HFD using Morris water maze and Y-maze approaches to explore the potential mechanisms linking circRNAs in obesity-associated cognitive impairment. Learning performance showed that HFD-induced obesity mice have impaired memory and cognition. The Arraystar analysis of the hippocampus displayed that HFD-induced obesity leads to the differential expression of circRNAs (DE-circRNAs) in mice. In total, 46 circular RNAs with elevated expression and 10 with decreased expression were identified. Among them, mmu_circRNA_004797 was identified to be significantly downregulated and the expression of mmu_circRNA_21040 was significantly upregulated in the HFD-fed mice, compared with control mice by PCR test. Bioinformatics analysis also showed that the upregulated circRNAs were related to the neuronal function and behavior, and material transport process, while downregulated circRNAs participated in the process of cell response to external stimuli, such as cellular response to nutrient levels. Furthermore, the KEGG pathway analysis showed that the upregulated circRNAs are mainly involved in Axon guidance, calcium signaling pathway, and ErbB signaling pathway. Only a single significant pathway, that is, “protein processing in endoplasmic reticulum”, was observed in the downregulated circRNAs. Finally, we examined the deficits of hippocampal synaptic plasticity and detected the expression of ER stress-related protein. The results showed that ER stress was activated in the hippocampus, and hippocampal synaptic plasticity deficits were displayed. Our results demonstrated that circRNAs were most likely implicated in the predisposition to obesity-associated cognitive impairment.

circKMT2E Protect Retina from Early Diabetic Retinopathy through SIRT1 Signaling Pathway via Sponging miR-204-5p

Objective

To explore the changes of circRNAs in the retina of diabetic patients without diabetic retinopathy (DR) to screen latent protective factor.

Methods

The sequencing data of the retina from three diabetic donors that possess no noticeable pathological feature of the retina at ultimate eye inspection and three healthy donative samples were involved in this study. Herein, we carried out bioinformatics analysis to disclose the expression pattern and characteristics of circRNAs on the basis of Gene Ontology as well as KEGG pathway analyses. Then, sequencing data were applied to infer the interaction between selected circRNAs and miR-204-5p. The potential miRNA response elements for the annotated circRNAs and their target gene were speculated using TargetScan as well as miRanda.

Results

RNA sequencing detected 28,978 alternative circRNAs. Thereinto, 1063 were expressed with significant difference. circKMT2E was upregulated more than two folds in alloxan-induced diabetic retinal tissues compared with normal retinal tissues, exhibiting an expression trend opposite to miR-204-5p. Bioinformatics analysis showed that circKMT2E have four seed sequences on hsa-miR-204-5p. Thus, circKMT2E was speculated to have function on the basis of sponging miR-204-5p in order to participate in the pathogenetic process of DR. Besides, miR-204-5p was speculated to be able to bind SIRT1, which can interact with its target proteins, and adjusts various cell functions including cellular inflammatory responses, proliferation, as well as apoptosis.

Conclusion

The upregulation of circKMT2E in the early stage of DR may be involved in its pathogenesis and may activate the SIRT1 signaling pathway to protect the retina by the sponge function to miR-204-5p.

The Emerging Roles and Clinical Potential of circSMARCA5 in Cancer

Circular RNAs (circRNAs) are a type of endogenous non-coding RNA and a critical epigenetic regulation way that have a closed-loop structure and are highly stable, conserved, and tissue-specific, and they play an important role in the development of many diseases, including tumors, neurological diseases, and cardiovascular diseases. CircSMARCA5 is a circRNA formed by its parental gene SMARCA5 via back splicing which is dysregulated in expression in a variety of tumors and is involved in tumor development with dual functions as an oncogene or tumor suppressor. It not only serves as a competing endogenous RNA (ceRNA) by binding to various miRNAs, but it also interacts with RNA binding protein (RBP), regulating downstream gene expression; it also aids in DNA damage repair by regulating the transcription and expression of its parental gene. This review systematically summarized the expression and characteristics, dual biological functions, and molecular regulatory mechanisms of circSMARCA5 involved in carcinogenesis and tumor progression as well as the potential applications in early diagnosis and gene targeting therapy in tumors.

Mechanism underlying circRNA dysregulation in the TME of digestive system cancer

Circular RNAs (circRNAs) are a new series of noncoding RNAs (ncRNAs) that have been reported to be expressed in eukaryotic cells and have a variety of biological functions in the regulation of cancer pathogenesis and progression. The TME, as a microscopic ecological environment, consists of a variety of cells, including tumor cells, immune cells and other normal cells, ECM and a large number of signaling molecules. The crosstalk between circRNAs and the TME plays a complicated role in affecting the malignant behaviors of digestive system cancers. Herein, we summarize the mechanisms underlying aberrant circRNA expression in the TME of the digestive system cancers, including immune surveillance, angiogenesis, EMT, and ECM remodelling. The regulation of the TME by circRNA is expected to be a new therapeutic method.

Potential clinical and biochemical markers for the prediction of drug-resistant epilepsy: A literature review

Drug resistance is a major challenge in the treatment of epilepsy. Drug-resistant epilepsy (DRE) accounts for 30% of all cases of epilepsy and is a matter of great concern because of its uncontrollability and the high burden, mortality rate, and degree of damage. At present, considerable research has focused on the development of predictors to aid in the early identification of DRE in an effort to promote prompt initiation of individualized treatment. While multiple predictors and risk factors have been identified, there are currently no standard predictors that can be used to guide the clinical management of DRE. In this review, we discuss several potential predictors of DRE and related factors that may become predictors in the future and perform evidence rating analysis to identify reliable potential predictors.

Role of Circular RNAs in Pulmonary Fibrosis

Pulmonary fibrosis is a chronic progressive form of interstitial lung disease, characterized by the histopathological pattern of usual interstitial pneumonia. Apart from aberrant alterations of protein-coding genes, dysregulation of non-coding RNAs, including microRNAs, long non-coding RNAs, and circular RNAs (circRNAs), is crucial to the initiation and progression of pulmonary fibrosis. CircRNAs are single-stranded RNAs that form covalently closed loops without 5′ caps and 3′ tails. Different from canonical splicing of mRNA, they are produced from the back-splicing of precursor mRNAs and have unique biological functions, as well as potential biomedical implications. They function as important gene regulators through multiple actions, including sponging microRNAs and proteins, regulating transcription, and splicing, as well as protein-coding and translation in a cap-independent manner. This review comprehensively summarizes the alteration and functional role of circRNAs in pulmonary fibrosis, with a focus on the involvement of the circRNA in the context of cell-specific pathophysiology. In addition, we discuss the diagnostic and therapeutic potential of targeting circRNA and their regulatory pathway mediators, which may facilitate the translation of recent advances from bench to bedside in the future.

Small Extracellular Vesicles of M1-BV2 Microglia Induce Neuronal PC12 Cells Apoptosis via the Competing Endogenous Mechanism of CircRNAs

Polarized microglia play a vital role in neurodegenerative diseases. However, the effects of polarized microglia-derived small extracellular vesicles (SEVs) on neuronal cells and the regulatory mechanisms of circular RNAs (circRNAs) in SEVs remain incompletely defined. In the present study, we carried out high-throughput sequencing and differential expression analysis of circRNAs in the SEVs of M0-phenotype BV2 microglia (M0-BV2) and polarized M1-phenotype BV2 microglia (M1-BV2). Hub circRNAs in the SEVs and their functions were screened using multiple bioinformatics methods. We further validated the effects of SEVs on neuronal PC12 cells by co-culturing M0-BV2 SEVs and M1-BV2 SEVs with neuronal PC12 cells. Among the differentially expressed circRNAs, the target mRNAs of six hub circRNAs (circ_0000705, circ_0001313, circ_0000229, circ_0001123, circ_0000621, and circ_0000735) were enriched in apoptosis-related biological processes. Furthermore, western blot and flow cytometry analysis demonstrated that M0-BV2 SEVs had no distinct effect on apoptosis of neuronal PC12 cells, while M1-BV2 SEVs remarkably increased the apoptosis of neuronal PC12 cells. We then constructed the competing endogenous RNA (ceRNA) networks of the six hub circRNAs. Taken together, the results suggest that polarized M1-BV2 microglia can induce apoptosis of neuronal PC12 cells through secreted SEVs, and this regulatory effect may be achieved by the circRNAs circ_0000705, circ_0001313, circ_0000229, circ_0001123, circ_0000621, and circ_0000735 through ceRNAs regulatory networks. These findings provide new potential targets for the treatment of neurodegenerative diseases.

MStoCIRC: A powerful tool for downstream analysis of MS/MS data to predict translatable circRNAs

CircRNAs are formed by a non-canonical splicing method and appear circular in nature. CircRNAs are widely distributed in organisms and have the features of time- and tissue-specific expressions. CircRNAs have attracted increasing interest from scientists because of their non-negligible effects on the growth and development of organisms. The translation capability of circRNAs is a novel and valuable direction in the functional research of circRNAs. To explore the translation potential of circRNAs, some progress has been made in both experimental identification and computational prediction. For computational prediction, both CircCode and CircPro are ribosome profiling-based software applications for predicting translatable circRNAs, and the online databases riboCIRC and TransCirc analyze as many pieces of evidence as possible and list the predicted translatable circRNAs of high confidence. Simultaneously, mass spectrometry in proteomics is often recognized as an efficient method to support the identification of protein and peptide sequences from diverse complex templates. However, few applications fully utilize mass spectrometry to predict translatable circRNAs. Therefore, this research aims to build up a scientific analysis pipeline with two salient features: 1) it starts with the data analysis of raw tandem mass spectrometry data; and 2) it also incorporates other translation evidence such as IRES. The pipeline has been packaged into an analysis tool called mass spectrometry to translatable circRNAs (MStoCIRC). MStoCIRC is mainly implemented by Python3 language programming and could be downloaded from GitHub (https://github.com/QUMU00/mstocirc-master). The tool contains a main program and several small, independent function modules, making it more multifunctional. MStoCIRC can process data efficiently and has obtained hundreds of translatable circRNAs in humans and Arabidopsis thaliana.

Stem cell-derived exosomal transcriptomes for wound healing

Wound healing is a complex and integrated process of the interaction of various components within the injured tissue. Accumulating evidence suggested that stem cell-derived exosomal transcriptomes could serve as key regulatory molecules in wound healing in stem cell therapy. Stem cell-derived exosomal transcriptomes mainly consist of long noncoding RNAs (lncRNAs), microRNAs (miRNAs), circular RNAs (circRNAs) and messenger RNAs (mRNAs). In this article we presented a brief introduction on the wound repair process and exosomal transcriptomes. Meanwhile, we summarized our current knowledge of the involvement of exosomal transcriptomes in physiological and pathological wound repair process including inflammation, angiogenesis, and scar formation.

Identification and characterization of N6-methyladenosine circular RNAs in the spinal cord of morphine-tolerant rats

Morphine tolerance (MT) is a tricky problem, the mechanism of it is currently unknown. Circular RNAs (circRNAs) serve significant functions in the biological processes (BPs) of the central nervous system. N6-methyladenosine (m⁶A), as a key post-transcriptional modification of RNA, can regulate the metabolism and functions of circRNAs. Here we explore the patterns of m⁶A-methylation of circRNAs in the spinal cord of morphine-tolerant rats. In brief, we constructed a morphine-tolerant rat model, performed m⁶A epitranscriptomic microarray using RNA samples collected from the spinal cords of morphine-tolerant rats and normal saline rats, and implemented the bioinformatics analysis. In the spinal cord of morphine-tolerant rats, 120 circRNAs with different m⁶A modifications were identified, 54 of which were hypermethylated and 66 of which were hypomethylated. Functional analysis of these m⁶A circRNAs found some important pathways involved in the pathogenesis of MT, such as the calcium signaling pathway. In the m⁶A circRNA-miRNA networks, several critical miRNAs that participated in the occurrence and development of MT were discovered to bind to these m⁶A circRNAs, such as miR-873a-5p, miR-103-1-5p, miR-107-5p. M⁶A modification of circRNAs may be involved in the pathogenesis of MT. These findings may lead to new insights into the epigenetic etiology and pathology of MT.

Identification of ceRNA network to explain the mechanism of cognitive dysfunctions induced by PS NPs in mice

Plastics breaking down of larger plastics into smaller ones (microplastics and nanoplastic) as potential threats to the ecosystem. Previous studies demonstrate that the central nervous system (CNS) is a vulnerable target of nanoplastics. However, the potentially epigenetic biomarkers of nanoplastic neurotoxicity in rodent models are still unknown. The present research aimed to determine the role of competing endogenous RNA (ceRNA) in the process of polystyrene nanoplastics (PS NPs) exposure-induced nerve injury. The study was designed to investigate whether 25 nm PS NPs could cause learning dysfunction and to elucidate the underlying mechanisms in mice. A total of 40 mice were divided into 4 groups and were exposed to PS NPs (0, 10, 25, 50 mg/kg). Chronic toxicity was introduced in mice by administration of oral gavage for 6 months. The evaluation included assessment of their behavior, pathological investigation and determination of the levels of reactive oxygen species (ROS) and DNA damage. RNA-Seq was performed to detect the expression levels of circRNAs, miRNAs and mRNAs in PFC samples of mice treated with 0 and 50 mg/kg PS NPs. The results indicated that exposure of mice to PS NPs caused a dose-dependent cognitive decline. ROS levels and DNA damage were increased in the PFC following exposure of the mice to PS NPs. A total of 987 mRNAs, 29 miRNAs and 67 circRNAs demonstrated significant differences between the 0 and 50 mg/kg PS NPs groups. Functional enrichment analyses indicated that PS NPs may induce major injury in the synaptic function. A total of 96 mRNAs, which were associated with synaptic dysfunction were identified. A competing endogenous RNA (ceRNA) network containing 27 circRNAs, 19 miRNAs and 35 synaptic dysfunction-related mRNAs was constructed. The present study provided insight into the molecular events associated with nanoplastic toxicity and induction of cognitive dysfunction.

Construction of circRNA-Mediated Immune-Related ceRNA Network and Identification of Circulating circRNAs as Diagnostic Biomarkers in Acute Ischemic Stroke

Background and Purpose

Accumulating evidence suggests that circular RNAs (circRNAs) are involved in immune and inflammatory processes after acute ischemic stroke (AIS). However, the roles of circRNA-mediated competing endogenous RNA (ceRNA) in modulating immune inflammation of AIS have not yet been determined. This study aimed to construct a circRNA-mediated immune-related ceRNA network and identify novel circRNAs in AIS.

Methods

Microarray data were downloaded from the GEO database and further analysed by R software. Then, we constructed a circRNA-mediated ceRNA network based on interaction information from the bioinformatics database. A topological property analysis of the ceRNA network was conducted to screen novel circRNAs. Finally, we further applied quantitative real-time polymerase chain reaction (qRT-PCR) to two independent sets.

Results

We constructed an AIS immune-related ceRNA (AISIRC) network containing immune-related genes (IRGs), miRNAs, and circRNAs. Additionally, we extracted the subnetwork from the AISIRC network and screened six immune-related circRNAs. After identification and validation, we finally confirmed that plasma levels of circPTP4A2 and circTLK2 were significantly increased in AIS patients compared with both healthy control subjects (HCs) and transient ischemic attack (TIA) patients. Logistic regression and receiver-operating characteristic (ROC) curve analyses demonstrated that these two circRNAs may function as predictive and discriminative biomarkers for AIS. We also confirmed that plasma levels of circPTP4A2 were elevated in TIA patients compared with HCs and might be an independent risk factor for predicting TIA. Longitudinal analysis of circRNA expression up to 90 days after AIS indicated that the ability of circPTP4A2 and circTLK2 to monitor AIS dynamics was highly desirable.

Conclusion

In summary, the circRNA-mediated immune-related ceRNA network was successfully constructed, and two circulating circRNAs (circPTP4A2 and circTLK2) improved sensitivity for the diagnosis of AIS and could be considered diagnostic biomarkers.

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.

CircRNA: An emerging star in the progression of glioma

Circular RNAs (circRNAs), a class of single-stranded noncoding RNAs with a covalently closed loop structure, are recognized as promising biomarkers and targets for diagnosing and treating dozens of diseases, especially cancers. CircRNAs are extremely stable, abundant and conserved and have tissue- or developmental stage-specific expression. Currently, the biogenesis and biological functions of circRNAs have been increasingly revealed with deep sequencing and bioinformatics. Studies have indicated that circRNAs are frequently expressed in brain tissues and that their expression levels change in different stages of neural development, suggesting that circRNAs may play an important role in diseases of the nervous system, such as glioma. However, because the biogenesis and functions of circRNAs do not depend on a single mechanism but are coregulated by multiple factors, it is necessary to further explore the underlying mechanisms. In this review, we summarized the classification, mechanisms of biogenesis and biological functions of circRNAs. Meanwhile, we emphatically expounded on the process of abnormal expression of circRNAs, methods used in circRNA research, and their effects on the malignant biological capabilities of glioma.

Circular RNA hsa_circ_0004381 Promotes Neuronal Injury in Parkinson's Disease Cell Model by miR-185-5p/RAC1 Axis

The study aims to explore the molecular mechanism involved in Parkinson's disease (PD). Hsa_circ_0004381, microRNA-185-5p (miR-185-5p), and Rac family small GTPase 1 (RAC1) level were measured by real-time quantitative polymerase chain reaction (RT-qPCR). Furthermore, cell viability and apoptosis rate were assessed by Cell Counting Kit-8 (CCK-8) and flow cytometry assays, respectively. Protein levels of B cell lymphoma-2 (Bcl-2), Bcl-2-related X protein (Bax), cleaved-caspase 3 (c-caspase 3), and RAC1 were determined by western blot assay. The levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6 were detected by enzyme-linked immunosorbent assay (ELISA). The ROS generation and LDH and SOD activity were detected by the corresponding kits. The binding relationship between miR-185-5p and hsa_circ_0004381 or RAC1 was predicted by Starbase and then verified by a dual-luciferase reporter and RNA Immunoprecipitation (RIP) assays. Hsa_circ_0004381 and RAC1 were increased, and miR-185-5p was decreased in MPP⁺-triggered SK-N-SH cells. Moreover, hsa_circ_0004381 silencing promoted cell viability, and repressed apoptosis, inflammatory response, and oxidative stress in MPP⁺-treated SK-N-SH cells. The mechanical analysis suggested that hsa_circ_0004381 served as a sponge of miR-185-5p to affect RAC1 expression. Hsa_circ_0004381 could contribute to MPP⁺-triggered neuron injury by targeting the miR-185-5p/RAC1 axis, which provided a novel insight into the pathogenesis and treatment of PD.