Exosomal circRNAs: Novel biomarkers and therapeutic targets for urinary tumors

Exosomal circRNAs have emerged as promising biomarkers and therapeutic targets for urinary tumors. In this review, we explored the intricate role of exosomal circRNAs in urological cancers, focusing on their biological functions, dysregulation in tumors, and potential clinical applications. The review delves into the mechanisms by which exosomal circRNAs contribute to tumor progression and highlights their diagnostic and therapeutic implications. By synthesizing current research findings, we present a compelling case for the significance of exosomal circRNAs in the context of urinary tumors. Furthermore, the review discusses the challenges and opportunities associated with utilizing exosomal circRNAs as diagnostic tools and targeted therapeutic agents. There is a need for further research to elucidate the specific mechanisms of exosomal circRNA secretion and delivery, as well as to enhance the detection methods for clinical translational applications. Overall, this comprehensive review underscores the pivotal role of exosomal circRNAs in urinary tumors and underscores their potential as valuable biomarkers and therapeutic tools in the management of urological cancers.

Fat mass and obesity-associated protein (FTO) mediated m6A modification of circFAM192A promoted gastric cancer proliferation by suppressing SLC7A5 decay

Gastric cancer (GC) is a common malignant tumor worldwide, especially in East Asia, with high incidence and mortality rate. Epigenetic modifications have been reported to participate in the progression of gastric cancer, among which m6A is the most abundant and important chemical modification in RNAs. Fat mass and obesity-associated protein (FTO) is the first identified RNA demethylase but little is known about its role in gastric cancer. In our study, data from TCGA and clinical samples showed that FTO was highly expressed in gastric cancer tissues. Kaplan-Meier plotter suggested that patients with the high level of FTO had a poor prognosis. In vitro and in vivo experiments confirmed the role of FTO in promoting gastric cancer cell proliferation. Mechanistically, we found that FTO bound to circFAM192A at the specific site and removed the m6A modification in circFAM192A, protecting it from degradation. CircFAM192A subsequently interacted with the leucine transporter solute carrier family 7 member 5 (SLC7A5) and enhancing its stability. As a result, an increased amount of SLC7A5 was on the membrane, which facilitated leucine uptake and activated the mTOR signaling pathway. Therefore, our study demonstrated that FTO promoted gastric cancer proliferation through the circFAM192A/SLC7A5 axis in the m6A-dependent manner. Our study shed new light on the role of FTO in gastric cancer progression.

Investigation of Circular RNA Expression Profiles in Ultrasound-guided Incomplete Radiofrequency Ablation Transplanted Tumor Models of Human Liver Cancer

BACKGROUND

Abnormally expressed circular RNAs (circRNAs) are associated with many diseases and have important biological effects on the regulation of gene expression. However, the circRNA expression profile in incomplete radiofrequency ablation (RFA)-treated liver cancer (LC) patients has not been characterized. This study investigated the potential biological effects of differentially expressed (DE) circRNAs in an incomplete RFA-treated transplantation tumor model of human LC.

MATERIAL/METHODS

A circRNA microarray was utilized to analyze changes in the circRNA expression profiles. CircRNA host gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were also conducted using computational biology. Quantitative real-time PCR (qPCR) was also performed on the selected DE-circRNAs to verify the reliability of the microarray. The circRNA/miRNA interactions were predicted by Arraystar software and confirmed by a dual-luciferase assay.

RESULTS

Following RFA incomplete ablation, 76 DE-circRNAs were detected (|fold change |>1.5, P-value < 0.05), 21 of which were upregulated and 55 of which were downregulated. Computational biological analysis revealed that the T-cell receptor signaling pathway was the most significantly enriched pathway of the genes related to altered expression, as indicated by enrichment of LCK, AKT3 and DLG1. PCR results for the upregulated hsa_circRNA_103595 and downregulated hsa_circRNA_001264 indicated that the circRNA microarray sequencing results were reliable. Double luciferase reporter assays confirmed that hsa-miR-185-3p was the target miRNA of hsa_circRNA_103595.

CONCLUSIONS

The current study confirmed the changes in the expression profiles of circRNAs in tumor transplantation models after incomplete ablation, these changes may play a crucial role in the pathophysiological process of residual cancer transplantation tumors. These findings could lead to new directions for investigating the molecular biological mechanisms underlying RFA-treated LC as well as new ideas for treating LC by regulating circRNAs.

Circular RNA hsa_circ_0050386 suppresses non-small cell lung cancer progression via regulating the SRSF3/FN1 axis

BACKGROUND

Lung cancer is the most prevalent cancer worldwide, with non-small cell lung cancer (NSCLC) accounting for 85% of all cases. Circular RNAs(circRNA) play crucial roles in regulating the progression of lung cancer. Despite the identification of a large number of circRNAs, their expression patterns, functions, and mechanisms of action in NSCLC development remain unclear.This study aims to investigate the transcriptional expressions, functions, and potential mechanisms of circRNA hsa_circ_0050386 in NSCLC.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) was utilized for the analysis of hsa_circ_0050386 expression. Cell proliferation was detected using the IncuCyte Live Cell Analysis System and clone formation assays. Migration and invasion of NSCLC cells were evaluated through Transwell assays. Flow cytometry was performed to assay cell cycle and apoptosis. Western blot was used to investigate protein expression. Protein binding analysis was conducted by employing pull-down assays, RNA immunoprecipitation (RIP), and mass spectrometry. The role of hsa_circ_0050386 in vivo was evaluated through the use of a xenograft model.

RESULTS

The study discovered that hsa_circ_0050386 displayed lower expression levels in NSCLC tissues when compared to adjacent normal tissues. Patients exhibiting lower levels of hsa_circ_0050386 expression exhibited an inverse correlation with the Clinical Stage, T-stage, and M-stage of NSCLC. Functionally, hsa_circ_0050386 suppressed the proliferation and invasion of NSCLC cells both in vitro and in vivo. A comprehensive examination exposed the interaction between hsa_circ_0050386 and RNA binding protein Serine and arginine-rich splicing factor 3 (SRSF3), resulting in the down-regulation of Fibronectin 1 (FN1) expression, which inhibits the progression of NSCLC.

CONCLUSIONS

Our study shows that hsa_circ_0050386 suppresses the malignant biological behavior of NSCLC cells by down-regulating the expression of FN1, and may serve as a potential biomarker and therapeutic target for NSCLC treatment.

Characterizing Post-transcriptional Modifications of circRNAs to Investigate Biogenesis and Translation

Recent studies have shown that circular RNAs (circRNAs) are decorated with N6-methyladenosine (m6A), a co-transcriptional modification known to participate in the regulation of many processes governing linear RNA metabolism. Nevertheless, the activity of this mark on circRNAs is still poorly understood. In order to facilitate the study of m6A-dependent regulation of these molecules, we provide protocols that enable circOme-wide detection of m6A as well as the perturbation of several components of the m6A machinery followed by assays useful to evaluate the impact of their depletion on the production and, when applicable, on the translation of circRNAs. Other modifications exist and can be explored following the same principles.

Multiple novel functions of circular RNAs in diabetes mellitus

Circular RNAs (circRNAs), as an emerging group of non-coding RNAs (ncRNAs), have received the attention given evidence indicating that these novel ncRNAs are implicated in various biological processes. Due to the absence of 5' and 3' ends in circ-RNAs, their two ends are covalently bonded together, and they are synthesised from pre-mRNAs in a process called back-splicing, which makes them more stable than linear RNAs. There is accumulating evidence showing that circRNAs play a critical role in the pathogenesis of diabetes mellitus (DM). Moreover, it has been indicated that dysregulation of circRNAs has made them promising diagnostic biomarkers for the detection of DM. Recently, increasing attention has been paid to investigate the mechanisms underlying the DM process. It has been demonstrated that there is a strong correlation between the expression of circRNAs and DM. Hence, our aim is to discuss the crosstalk between circRNAs and DM and its complications.

In silico whole-transcriptome analysis reveals a potential hsa_circ_0000375-miR-424-5p-TPM2/SRPX/SRGAP1 regulatory network related to liver metastasis of colorectal cancer

Liver metastasis is the main lethal cause of colorectal cancer (CRC). The knowledge of role and mechanism of circular RNA (circRNA) in liver metastasis of CRC is still inadequate. In this study, whole-transcriptome analysis was performed using three datasets (GSE147597, GSE147602 and GSE147603). A total of 14 potential circRNAs were identified, after which their structural patterns and binding miRNAs were obtained. Next, 45 differentially expressed miRNAs (DEmiRNAs) between CRC without and with liver metastasis were acquired, consisting 38 upregulated and 7 downregulated miRNAs. After conducting intersection analysis, expression validation and correlation analysis, miR-761 and miR-424-5p were selected as the most potential miRNAs linked to liver metastasis of CRC. Subsequently, the target genes of miR-761 or miR-424-5p were predicted and differentially expressed genes (DEGs) between CRC without and with liver metastasis were obtained. 257 genes that were commonly appeared in predicted genes and DEGs were significantly enriched in "epithelial-to-mesenchymal transition" and "signaling by Robo receptor". Among these enriched genes, only TPM2, SRPX and SRGAP1 were significantly negatively correlated with miR-424-5p and were positively linked to hsa_circ_0000375 in CRC without or with liver metastasis. Collectively, the current findings elucidated a potential hsa_circ_0000375-miR-424-5p-TPM2/SRPX/SRGAP1 network contributing to liver metastasis of CRC.

Comprehensive analysis of circular RNAs in nasopharyngeal cancer

BACKGROUND

Nasopharyngeal cancer (NPC) is a type of epithelial malignancy that is positive for Epstein-Barr virus (EBV) and affects several populations worldwide. Due to the high rates of relapse and metastasis following primary treatment, there is an urgent need to identify new candidates for NPC therapy. Recently, circular RNA (circRNA) has emerged as a promising target for cancer diagnosis and prevention.

OBJECTIVE

This study aimed to study the circRNAs enriched in NPC patients, and further analyze potential signaling pathways involved.

METHODS

A new bioinformatic tool named psirc was used to analyze RNA-sequencing datasets from NPC patients and normal specimens to study the NPC-enriched circRNAs.

RESULTS

We identified and quantified the full-length circRNA in these samples and found the top 10 enriched circRNAs in NPC patients compared to control samples. Furthermore, we selected the most enriched circRNA, circEEF1A1_E8B1, and studied its protein coding ability, microRNA and RNA-binding protein (RBP) binding capacity. We also constructed a protein-protein interaction (PPI) network for its binding proteins and extracted hub genes. Finally, we conducted survival analysis for these hub genes in head and neck cancer patients.

CONCLUSIONS

In summary, our study has revealed the presence of previously unidentified circRNAs that are enriched in NPC patients. Through an analysis of their molecular functions, we have advanced our understanding of the potential role of circRNAs in NPC development.

Circular RNA Tmcc1 improves astrocytic glutamate metabolism and spatial memory via NF-κB and CREB signaling in a bile duct ligation mouse model: transcriptional and cellular analyses

BACKGROUND

Hepatic encephalopathy-induced hyperammonemia alters astrocytic glutamate metabolism in the brain, which is involved in cognitive decline. To identify specific therapeutic strategies for the treatment of hepatic encephalopathy, various molecular signaling studies, such as non-coding RNA functional study, have been conducted. However, despite several reports of circular RNAs (circRNAs) in the brain, few studies of circRNAs in hepatic encephalopathy-induced neuropathophysiological diseases have been conducted.

METHODS

In this study, we performed RNA sequencing to identify whether the candidate circRNA cirTmcc1 is specifically expressed in the brain cortex in a bile duct ligation (BDL) mouse model of hepatic encephalopathy.

RESULTS

Based on transcriptional and cellular analysis, we investigated the circTmcc1-dysregulation-induced changes in the expression of several genes that are associated with intracellular metabolism and astrocyte function. We found that the circTmcc1 binds with the NF-κB p65-CREB transcriptional complex and regulates the expression of the astrocyte transporter EAAT2. Furthermore, circTmcc1 contributed to the secretion of proinflammatory mediators and glutamate metabolism in astrocytes and subsequently modulated an improvement in spatial memory by mediating neuronal synaptic plasticity.

CONCLUSIONS

Thus, circTmcc1 may be a promising circRNA candidate for targeted interventions to prevent and treat the neuropathophysiological complications that occur due to hepatic encephalopathy.

Promising roles of non-exosomal and exosomal non-coding RNAs in the regulatory mechanism and as diagnostic biomarkers in myocardial infarction

Non-exosomal non-coding RNAs (non-exo-ncRNAs) and exosomal ncRNAs (exo-ncRNAs) have been associated with the pathological development of myocardial infarction (MI). Accordingly, this analytical review provides an overview of current MI studies on the role of plasma non-exo/exo-ncRNAs. We summarize the features and crucial roles of ncRNAs and reveal their novel biological correlations via bioinformatics analysis. The following contributions are made: (1) we comprehensively describe the expression profile, competing endogenous RNA (ceRNA) network, and "pre-necrotic" biomarkers of non-exo/exo-ncRNAs for MI; (2) functional enrichment analysis indicates that the target genes of ncRNAs are enriched in the regulation of apoptotic signaling pathway and cellular response to chemical stress, etc.; (3) we propose an updated and comprehensive view on the mechanisms, pathophysiology, and biomarker roles of non-exo/exo-ncRNAs in MI, thereby providing a theoretical basis for the clinical management of MI.

Exosomal circular RNAs: A chief culprit in cancer chemotherapy resistance

Chemotherapy is one of the primary treatments for malignant tumors. However, the acquired drug resistance hinders clinical efficacy and leads to treatment failure in most patients. Exosomes are cell-derived vesicles with a diameter of 30-150 nm carrying and delivering substances such as DNAs, RNAs, lipids, and proteins for cellular communication in tumor development. Circular RNAs (circRNAs) present covalently closed-loop RNA structures, which regulate tumor cell proliferation, apoptosis, and metastasis by controlling different genes and signaling pathways. CircRNAs are abundant and stably expressed in exosomes. Recent studies have shown that they play critical roles in chemotherapy resistance in various cancers. In this review, we summarized the origin of exosomes and discussed the regulation mechanism of exosomal circRNAs in cancer drug resistance.

Circularized RNA as novel therapeutics in cancer

Circular RNAs (CircRNAs) regulate gene expression by functioning as microRNA sponges, regulating protein stability, and gilding proteins for gene transcription and translation. Also, limited circRNAs harbour protein-coding ability through cap-independent pathways. These molecular mechanisms of circRNAs contribute to their importance in several cellular processes. Particularly, the dysregulation of circRNAs also plays a critical role in disease development. Targeting disease-causing circRNAs by restoring their normal expression by gain-of-function or loss-of-function approach and regulating their molecular activities could be potential direction for the development of anti-cancer therapies. Furthermore, due to unique covalently closed circular structure, the superior stability of circRNAs also grants them as novel therapeutic tools replacing the therapeutic small interfering RNAs and messenger RNAs. Here, we will review the functional and molecular mechanisms of circRNAs in pathogenesis, the current methods for targeting the dysregulated circRNAs, and the potential of using synthetic circRNAs in disease treatment and prevention.

The Function and Therapeutic Potential of Circular RNA in Cardiovascular Diseases

Circular RNA (circRNA) has a closed-loop structure, and its 3' and 5' ends are directly covalently connected by reverse splicing, which is more stable than linear RNA. CircRNAs usually possess microRNA (miRNA) binding sites, which can bind miRNAs and inhibit miRNA function. Many studies have shown that circRNAs are involved in the processes of cell senescence, proliferation and apoptosis and a series of signalling pathways, playing an important role in the prevention and treatment of diseases. CircRNAs are potential biological diagnostic markers and therapeutic targets for cardiovascular diseases (CVDs). To identify biomarkers and potential effective therapeutic targets without toxicity for heart disease, we summarize the biogenesis, biology, characterization and functions of circRNAs in CVDs, hoping that this information will shed new light on the prevention and treatment of CVDs.

An in silico study to find potential effective circRNAs in the progression of Huntington's disease

Objectives

Huntington's disease (HD) is identified as a progressive genetic disorder caused by a mutation in the Huntington gene. Although the pathogenesis of this disease has not been fully understood, investigations have demonstrated the role of various genes and non-coding RNAs in the disease progression. In this study, we aimed to discover the potential promising circRNAs which can bind to miRNAs of HD.

Materials and Methods

We used several bioinformatics tools such as ENCORI, Cytoscape, circBase, Knime, and Enrichr to collect possible circRNAs and then evaluate their connections with target miRNAs to reach this goal. We also found the probable relationship between parental genes of these circRNAs and the disease progress.

Results

According to the data collected, more than 370 thousand circRNA-miRNA interactions were found for 57 target miRNAs. Several of circRNAs were spliced out of parental genes involved in the etiology of HD. Some of them need to be further investigated to elucidate their role in this neurodegenerative disease.

Conclusion

This in silico investigation highlights the potential role of circRNAs in the progression of HD and opens up new horizons for drug discovery as well as diagnostic approaches for the disease.

Exosomal circular RNA: a signature for lung cancer progression

Membrane vesicles having a diameter of 30-150 nm are known as exosomes. Several cancer types secrete exosomes, which may contain proteins, circular RNAs (circRNAs), microRNAs, or DNA. CircRNAs are endogenous RNAs that do not code for proteins and can create continuous and covalently closed loops. In cancer pathogenesis, especially metastasis, exosomal circRNAs (exo-circRNAs) have a crucial role mainly due to the frequently aberrant expression levels within tumors. However, neither the activities nor the regulatory mechanisms of exo-circRNAs in advancing lung cancer (LC) are obvious. A better understanding of the regulation and network connections of exo-circRNAs will lead to better treatment for LCs. The main objective of the current review is to highlight the functions and mechanisms of exo-circRNAs in LC and assess the relationships between exo-circRNA dysregulation and LC progression. In addition, underline the possible therapeutic targets based on exo-circRNA modulating.

Bioinformatic analysis of dysregulated circular RNAs in pediatric pulmonary hypertension linked congenital heart disease

BACKGROUND

Circular RNAs (circRNAs) may play important roles in the progression of pulmonary arterial hypertension. However, the potential roles they play in childhood pulmonary arterial hypertension associated congenital heart disease (CHD) progression remains unclear.

METHODS

Thirteen human plasma samples including eight from pulmonary arterial hypertension secondary to CHD patients and five from a control group were analyzed using the Arraystar Human circRNA array. The relative expression levels of five differentially expressed circRNAs in pulmonary arterial hypertension were detected using real-time polymerase chain reaction (PCR) analysis. In parallel, these levels were also taken on control samples from 32 CHD patients. We used miRanda and TargetScan software packages to predict potential microRNA (miRNA)targets, which were then combined into a circRNA-miRNA-messenger RNA (mRNA) network.

RESULTS

Twenty-seven circRNAs (three upregulated and 24 downregulated) were differentially expressed between the pulmonary arterial hypertension and control groups. Compared to control group levels, circ_003416 expression in the pulmonary arterial hypertension group was significantly downregulated, while circ_005372 expression, in contrast, was significantly upregulated. The differential expression of these circRNAs was mainly linked to variation in levels of oxidative phosphorylation and tight junction signaling.

CONCLUSIONS

We identified one overexpressed and one underexpressed circRNA in plasma samples from children with CHD associated pulmonary arterial hypertension. Bioinformatic analysis indicated these dysregulated circRNAs might be associated with the occurrence and regulation of pulmonary arterial hypertension.

Genome-wide identification and functional analysis of circRNAs in Trichophyton rubrum conidial and mycelial stages

Background

Circular RNAs (circRNAs) are a group of noncoding RNAs that participate in gene expression regulation in various pathways. The essential roles of circRNAs have been revealed in many species. However, knowledge of circRNAs in fungi is still not comprehensive.

Results

Trichophyton rubrum (T. rubrum) is considered a model organism of human pathogenic filamentous fungi and dermatophytes. In this study, we performed a genome-wide investigation of circRNAs in T. rubrum based on high-throughput sequencing and ultimately identified 4254 circRNAs. Most of these circRNAs were specific to the conidial or mycelial stage, revealing a developmental stage-specific expression pattern. In addition, 940 circRNAs were significantly differentially expressed between the conidial and mycelial stages. PCR experiments conducted on seven randomly selected differentially expressed (DE-) circRNAs confirmed the circularized structures and relative expression levels of these circRNAs. Based on their genome locations, most circRNAs originated from intergenic regions, unlike those in plants and animals. Furthermore, we constructed circRNA-miRNA-mRNA regulatory networks that included 661 DE-circRNAs targeting 140 miRNAs and further regulating 2753 mRNAs. The relative expression levels of two randomly selected circRNA-miRNA-mRNA axes were investigated by qRT-PCR, and the competing endogenous RNA (ceRNA) network theory was validated. Functional enrichment analysis of the target genes suggested that they were significantly involved in posttranscriptional processes and protein synthesis as well as some small-molecule metabolism processes. CircRNAs are relatively more conserved in closely related dermatophytes but rarely conserved in distantly related species. Tru_circ07138_001 is a highly conserved circRNA that was conserved in all ten dermatophytes analyzed in our study and three distantly related species. Its host gene TERG_07138 was also highly conserved in two of these distantly related species Gallus gallus and Caenorhabditis elegans. The specific role of this circRNA deserves further exploration.

Conclusions

Our study is the first to provide a global profile of circRNAs in T. rubrum as well as dermatophytes. These results could serve as valuable resources for research on circRNA regulatory mechanisms in fungi and reveal new insights for further investigation of the physical characteristics of these significant human fungal pathogens.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08184-y.

Bioinformatic Analysis of CircRNA from RNA-seq Datasets

Circular RNAs (circRNAs) are a vast class of covalently closed, noncoding RNAs expressed in specific tissues and developmental stages. The molecular, cellular, and pathophysiologic roles of circRNAs are not fully known, but their impact on gene expression programs is beginning to emerge, as circRNAs often associate with RNA-binding proteins and nucleic acids. With rising interest in identifying circRNAs associated with disease processes, it has become particularly important to identify circRNAs in RNA sequencing (RNA-seq) datasets, either generated by the investigator or reported in the literature. Here, we present a methodology to identify and analyze circRNAs in RNA-seq datasets, including those archived in repositories. We elaborate on the unique features of circRNAs that require specialized attention in RNA-seq datasets, the software packages designed for circRNA identification, the ongoing efforts to reconstruct the body of circRNAs starting from unique circularizing junctions, and the interacting factors that can be proposed from putative circRNA body sequences. We discuss the advantages and limitations of the current approaches for high-throughput circRNA analysis from RNA-sequencing datasets and identify areas that would benefit from the development of superior bioinformatic tools.

CircRNAs and their regulatory roles in cancers

Circular RNAs (circRNAs), a novel type of non-coding RNAs (ncRNAs), have a covalently closed circular structure resulting from pre-mRNA back splicing via spliceosome and ribozymes. They can be classified differently in accordance with different criteria. As circRNAs are abundant, conserved, and stable, they can be used as diagnostic markers in various diseases and targets to develop new therapies. There are various functions of circRNAs, including sponge for miR/proteins, role of scaffolds, templates for translation, and regulators of mRNA translation and stability. Without m7G cap and poly-A tail, circRNAs can still be degraded in several ways, including RNase L, Ago-dependent, and Ago-independent degradation. Increasing evidence indicates that circRNAs can be modified by N-6 methylation (m6A) in many aspects such as biogenesis, nuclear export, translation, and degradation. In addition, they have been proved to play a regulatory role in the progression of various cancers. Recently, methods of detecting circRNAs with high sensitivity and specificity have also been reported. This review presents a detailed overview of circRNAs regarding biogenesis, biomarker, functions, degradation, and dynamic modification as well as their regulatory roles in various cancers. It’s particularly summarized in detail in the biogenesis of circRNAs, regulation of circRNAs by m6A modification and mechanisms by which circRNAs affect tumor progression respectively. Moreover, existing circRNA detection methods and their characteristics are also mentioned.

A urine extracellular vesicle circRNA classifier for detection of high-grade prostate cancer in patients with prostate-specific antigen 2-10 ng/mL at initial biopsy

The aim of this study was to identify a urine extracellular vesicle circular RNA (circRNA) classifier that could detect high-grade prostate cancer (PCa) of Grade Group (GG) 2 or greater. For this purpose, we used RNA sequencing to identify candidate circRNAs from urinary extracellular vesicles from 11 patients with high-grade PCa and 11 case-matched patients with benign prostatic hyperplasia. Using ddPCR in a training cohort (n = 263), we built a urine extracellular vesicle circRNA classifier (Ccirc, containing circPDLIM5, circSCAF8, circPLXDC2, circSCAMP1, and circCCNT2), which was evaluated in two independent cohorts (n = 497, n = 505). Ccirc showed higher accuracy than two standard of care risk calculators (RCs) (PCPT-RC 2.0 and ERSPC-RC) in both the training cohort and the validation cohorts. In all three cohorts, this novel urine extracellular vesicle circRNA classifier plus RCs was statistically more predictive than RCs alone for predicting ≥ GG2 PCa. This assay, which does not require precollection digital rectal examination nor special handling, is repeatable, noninvasive, and can be easily implemented as part of the basic clinical workflow.

Expression profile of circular RNAs in oral lichen planus

BACKGROUND

This study sought to identify the circular RNAs (circRNAs) differentially expressed in oral lichen planus (OLP) to investigate the possible role of circRNAs in this disease's pathogenesis.

METHODS

Six OLP and six normal oral mucosal tissues were used for circRNA detection and sequencing. 10 selected circRNAs were verified by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). A gene ontology (GO) functional analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed to predict the functions of circRNAs in OLP. TargetScan and miRanda were applied to predict targeted micro (mi)RNAs and messenger (m)RNAs of circRNAs, and competing endogenous (ce)RNA networks were mapped.

RESULTS

One hundred and thirty-five circRNAs were identified differentially expressed in OLP tissues compared to normal control tissues, including 83 upregulated circRNAs, and 52 down-regulated circRNAs. RT-qPCR confirmed that 10 circRNAs were all abnormally expressed in OLP. The GO functional analysis and KEGG pathway analysis showed that differentially expressed circRNAs were involved in 535 GO functional items and 78 signal pathways. A ceRNA network analysis showed that circRNAs might interact with a variety of miRNAs.

CONCLUSIONS

This study mapped the expression profile of abnormally expressed circRNAs in OLP tissues for the first time and showed that circRNAs appear to play an important role in the pathogenesis of OLP.

Role of the epithelial-mesenchymal transition-related circular RNA, circ-10720, in non-small-cell lung cancer

Background

Circular RNAs (circRNAs) are non-coding RNAs with a circular structure that have recently emerged as important regulators of tumorogenesis. Recently, several circRNAS, including circ-10720 have been related to epithelial-mesenchymal transition (EMT) process. In the present study, we have analyzed the role of circ-10720 in non-small-cell lung cancer (NSCLC) and studied its prognostic relevance in resected stage I-IIIa NSCLC patients.

Methods

Circ-10720 expression was analyzed using a custom TaqMan assay in four NSCLC cell lines (HCC44, A549, H23 and H1299) and in the normal immortalized lung cell line BEAS2B. Silencing of circ-10720 was performed using two custom siRNAs which were transfected using lipofectamine 2000. Protein levels were evaluated by Western blot and immunofluorescence. Wound healing and invasion assays were performed to evaluate the impact the circRNA on cell motility. Apoptosis was analyzed by evaluation of Caspase 3-7 activity and proliferation by MTS assay. Moreover, the expression levels of the circRNA were studied in 119 resected NSCLC patients. The expression in tumor tissue was correlated with the main clinicopathological characteristics and with time to relapse (TTR).

Results

Circ-10720 was overexpressed in HCC44 and A549 and underexpressed in H23 and H1299 NSCLC cell lines in comparison to BEAS2B normal immortalized lung cell line. CircRNA knockdown in the two circ-10720 overexpressing cell lines was associated with a decrease of Vimentin (VIM) and an increase of E-cadherin (CDH1) protein levels, loss of mesenchymal phenotype, and a significant reduction of migration and invasion capacity. After silencing circ-10720, the apoptosis rate increased and the proliferation was significantly reduced. Furthermore, circ-10720 was upregulated in tumor vs. normal tissue from 119 resected NSCLC patients. In the group of patients not receiving adjuvant treatment, those with high levels of circ-10720 had a shorter TTR than those with low levels and emerged as an independent prognostic value in the multivariate analysis. In tumor tissue, circ-10720 levels positively correlated with the EMT gene Twist1 levels.

Conclusions

Circ-10720 regulates EMT, apoptosis and proliferation and acts as a biomarker of relapse in NSCLC.

iCDA-CMG: identifying circRNA-disease associations by federating multi-similarity fusion and collective matrix completion

Circular RNAs (circRNAs) are a special class of non-coding RNAs with covalently closed-loop structures. Studies prove that circRNAs perform critical roles in various biological processes, and the aberrant expression of circRNAs is closely related to tumorigenesis. Therefore, identifying potential circRNA-disease associations is beneficial to understand the pathogenesis of complex diseases at the circRNA level and helps biomedical researchers and practitioners to discover diagnostic biomarkers accurately. However, it is tremendously laborious and time-consuming to discover disease-related circRNAs with conventional biological experiments. In this study, we develop an integrative framework, called iCDA-CMG, to predict potential associations between circRNAs and diseases. By incorporating multi-source prior knowledge, including known circRNA-disease associations, disease similarities and circRNA similarities, we adopt a collective matrix completion-based graph learning model to prioritize the most promising disease-related circRNAs for guiding laborious clinical trials. The results show that iCDA-CMG outperforms other state-of-the-art models in terms of cross-validation and independent prediction. Moreover, the case studies for several representative cancers suggest the effectiveness of iCDA-CMG in screening circRNA candidates for human diseases, which will contribute to elucidating the pathogenesis mechanisms and unveiling new opportunities for disease diagnosis and targeted therapy.

A novel circular RNA hsa_circ_0060927 may serve as a potential diagnostic biomarker for human colorectal cancer

CYP24A1 plays a role in strictly regulated vitamin D metabolism pathway and has been nominated as a prognostic biomarker for colorectal cancer (CRC). Increasing evidence suggests that circular RNAs (circRNAs) are involved in cancer initiation and progression; however, their diagnostic values in cancers as the new potential biomarkers are still not fully understood. In the present study, by using quantitative real-time polymerase chain reaction (qRT-PCR), we demonstrated that CYP24A1 and hsa_circ_0060927 were only transcribed in 33 and 25 out of 83 CRC tissues, respectively. In these samples, we demonstrated that CYP24A1 was up-regulated in both linear and circular forms (P < 0.05). Furthermore, we showed that CYP24A1and hsa_circ_0060927 transcription were induced after vitamin D treatment in HCT-116 and HT-29 colon cancer cell lines. Importantly, analysis of the ROC curve in expressed samples indicated that CYP24A1 and hsa_circ_0060927 could serve as the potential diagnostic markers of CRC, but due to the fact that these transcripts are not expressed in many samples, the diagnostic role of these transcripts could be rejected. Taken together, for the first time, the results of our study illustrated the expression levels hsa_circ_0060927 in CRC; however, further studies are required to validate the present results.

Systematic Identification and Analysis of Light-Responsive Circular RNA and Co-expression Networks in Lettuce (Lactuca sativa)

Circular RNA (circRNA) is a covalently-closed single-stranded RNA molecule that plays an important role in transcriptional regulation of gene expression in a variety of species. Light intensity is a pivotal environmental factor affecting plant growth and development. However, little is known regarding photoresponsive plant circRNAs. Here, we aimed to investigate the expression and function of circRNAs in lettuce leaves in response to different light intensity treatments. We performed RNA sequencing (RNA-Seq) on leaves of lettuce (Lactuca sativa) to determine circRNA expression profiles and reverse-transcription polymerase chain reaction (PCR) to validate the candidate circRNA molecules. We then combined bioinformatics approach to explore the function of the parental genes of circRNA, including network, Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes pathway analysis. We identified 1650 circRNAs in lettuce, of which 1508 (86.40%) were derived from exons. Using real-time PCR, we characterized 10 validated differentially expressed circRNAs and their parental genes, all of which showed expression patterns consistent with RNA-Seq data. Interestingly, the expression of circRNA was, in some cases, inversely correlated with the expression of the parental gene. Furthermore, analysis of the circRNA-microRNA-mRNA network suggests that circRNAs may be involved in plant hormone signaling and chlorophyll metabolism during photoreactivity. These findings provide an essential reference basis for studying circRNAs' biological mechanisms in light-treated plants.

Circular RNA circZFR promotes tumorigenic capacity of lung cancer via CCND1

BACKGROUND

To explore the role of circular RNA (circRNA) circZFR in tumorigenic capacity of lung cancer (LC).

METHODS

Thirty primary LC tissues were used to detect circRNAs expression. CircZFR was silenced in two LC cell lines using lentivirus-mediated short hairpins RNAs. Quantitative real time PCR (qRT-PCR), northern blot and in situ hybridization (ISH) assay were used to measure the expression of circRNA.

RESULTS

CircRNA circZFR was highly expressed in LC tumors. CircZFR deficiency significantly abrogated clone formation. CircZFR depletion substantially decreased tumor growth compared to WT control cells. CircZFR overexpression was dramatically increased cell growth in LC cell lines. Consequently, circZFR overexpression substantially promoted tumor propagation. Consistently, circZFR deficiency significantly reduced the expression of CCND1 and major cell cycle genes in LC cell lines. In contrast, circZFR depletion did not alter the expression of ZFR. Consequently, circZFR deficiency dramatically decreased H3K4me3 levels on the CCND1 promoter at -1,100 to -900 bp segment of CCND1 promoter.

CONCLUSIONS

CircZFR was related with LC growth in vitro and in vivo and tumorigenic capacity of LC. The possible mechanism was to regulating expression of CCND1, indicating the circZFR/CCND1 signaling might be a promising therapeutic target for LC treatment.

Comprehensive characterization of circular RNAs in osteosarcoma cell lines

Circular RNA (circRNA) is a looped noncoding RNA with a stable structure and tissue-specific expression and widely reported to regulate cancer initiation and progression. However, the circRNA expression patterns and their roles in osteosarcoma initiation and progression are still poorly understood. In this study, we characterized the landscape of circRNAs in osteosarcoma (OS) cell lines, and calculated the epithelial-mesenchymal transition (EMT) scores for OS cell lines. The differential expression analysis revealed that the EMT-related genes were significantly upregulated in the OS cell lines with higher metastatic potentials, and some inflammation-related pathways and pathways involved in cell-cell communications were enriched by these upregulated genes. Furthermore, we constructed a circRNA-based competing endogenous RNA (ceRNA) network, which consisted of 5 circRNAs, 17 miRNAs, and 73 mRNAs. Particularly, hsa_circ_0085360, which had the highest correlation with TRPS1, were characterized by some cancer-related pathways, and TRPS1 and its target gene FGFR3 were closely associated with both event-free survival and overall survival of OS, indicating that hsa_circ_0085360 might have the potential to predict the OS prognosis. In summary, we profiled the circRNA expression patterns in OS, predicted their functionality, and explored the underlying mechanism and prognostic values, which might provide some evidences for OS-related circRNA researches.

Prognostic role of dysregulated circRNAs in patients with non-small cell lung cancer: a meta-analysis

Background

Lung cancer is the leading cause of cancer incidence and mortality. Non-small cell lung cancer (NSCLC) accounts for the vast majority of lung cancer, which lacks comprehensive prognostic biomarkers to predict the prognosis of patients. This research was performed to assess the potential prognostic role of circular RNAs (circRNAs) in patients with NSCLC.

Methods

We searched the following databases: PubMed, Web of Science, Embase, and Ovid MEDLINE(R) up to May 20, 2019 to identify studies which explored the association between circRNAs and NSCLC. Newcastle-Ottawa Scale (NOS) was applied to assess the quality of the included studies. Pooled hazard ratios (HRs) and the corresponding 95% confidence interval (CI) were calculated to assess the prognostic value of circRNAs in patients with NSCLC. Subgroup analyses were performed to explain heterogeneity among the included studies. Publication bias was estimated using Begg’s funnel plot. Sensitivity analysis was performed to test the stability of pooled results.

Results

A total of 19 eligible studies including 1,650 NSCLC patients were included in this research. Pooled results indicated that the up-regulated expression of circRNAs was significantly associated with worse prognosis of patients with NSCLC (HR =2.08, 95% CI: 1.81–2.40).

Conclusions

Our finding indicated that circRNAs could serve as prognostic biomarkers in patients with NSCLC. However, further large-scale prospective studies about the clinical significance of circRNAs are of great need in order to obtain conclusive results.

A novel protein encoded by a circular RNA circPPP1R12A promotes tumor pathogenesis and metastasis of colon cancer via Hippo-YAP signaling

Background

It has been well established that circular RNAs (circRNAs) play an important regulatory role during tumor progression. Recent studies have indicated that even though circRNAs generally regulate gene expression through miRNA sponges, they may encode small peptides in tumor pathogenesis. However, it remains largely unexplored whether circRNAs are involved in the tumorigenesis of colon cancer (CC).

Methods

The expression profiles of circRNAs in CC tissues were assessed by circRNA microarray. Quantitative real-time PCR, RNase R digestion assay and tissue microarray were used to confirm the existence and expression pattern of circPPP1R12A. The subcellular distribution of circPPP1R12A was analyzed by nuclear mass separation assay and fluorescence in situ hybridization (FISH). SDS-PAGE and LC/MS were employed to evaluate the protein-coding ability of circPPP1R12A. CC cells were stably transfected with lentivirus approach, and cell proliferation, migration and invasion, as well as tumorigenesis and metastasis in nude mice were assessed to clarify the functional roles of circPPP1R12A and its encoded protein circPPP1R12A-73aa. RNA-sequencing and Western blotting analysis were furthered employed to identify the critical signaling pathway regulated by circPPP1R12A-73aa.

Results

We firstly screened the expression profiles of human circRNAs in CC tissues and found that the expression of hsa_circ_0000423 (termed as circPPP1R12A) was significantly increased in CC tissues. We also found that circPPP1R12A was mostly localized in the cytoplasm of CC cells. Kaplan–Meier analysis showed that patients with higher levels of circPPP1R12A had a significantly shorter overall survival. By gain- and loss-of-function approaches, the results suggested that circPPP1R12A played a critical role in proliferation, migration and invasion of CC cells. Furthermore, we showed that circPPP1R12A carried an open reading frame (ORF), which encoded a functional protein (termed as circPPP1R12A-73aa). Next, we found that PPP1R12A-C, not circPPP1R12A, promoted the proliferation, migration and invasion abilities of CC in vitro and in vivo. Finally, we identified that circPPP1R12A-73aa promoted the growth and metastasis of CC via activating Hippo-YAP signaling pathway. In addition, the YAP specific inhibitor Peptide 17 dramatically alleviated the promotive effect of circPPP1R12A-73aa on CC cells.

Conclusions

In the present study, we illustrated the coding-potential of circRNA circPPP1R12A in the progression of CC. Moreover, we identified that circPPP1R12A-73aa promoted the tumor pathogenesis and metastasis of CC via activating Hippo-YAP signaling pathway. Our findings might provide valuable insights into the development of novel potential therapeutic targets for CC.

Electronic supplementary material

The online version of this article (10.1186/s12943-019-1010-6) contains supplementary material, which is available to authorized users.

Systematical Identification of Breast Cancer-Related Circular RNA Modules for Deciphering circRNA Functions Based on the Non-Negative Matrix Factorization Algorithm

Circular RNA (circRNA), a kind of special endogenous RNA, has been shown to be implicated in crucial biological processes of multiple cancers as a gene regulator. However, the functional roles of circRNAs in breast cancer (BC) remain to be poorly explored, and relatively incomplete knowledge of circRNAs handles the identification and prediction of BC-related circRNAs. Towards this end, we developed a systematic approach to identify circRNA modules in the BC context through integrating circRNA, mRNA, miRNA, and pathway data based on a non-negative matrix factorization (NMF) algorithm. Thirteen circRNA modules were uncovered by our approach, containing 4164 nodes (80 circRNAs, 2703 genes, 63 miRNAs and 1318 pathways) and 67,959 edges in total. GO (Gene Ontology) function screening identified nine circRNA functional modules with 44 circRNAs. Within them, 31 circRNAs in eight modules having direct relationships with known BC-related genes, miRNAs or disease-related pathways were selected as BC candidate circRNAs. Functional enrichment results showed that they were closely related with BC-associated pathways, such as ‘KEGG (Kyoto Encyclopedia of Genes and Genomes) PATHWAYS IN CANCER’, ‘REACTOME IMMUNE SYSTEM’ and ‘KEGG MAPK SIGNALING PATHWAY’, ‘KEGG P53 SIGNALING PATHWAY’ or ‘KEGG WNT SIGNALING PATHWAY’, and could sever as potential circRNA biomarkers in BC. Comparison results showed that our approach could identify more BC-related functional circRNA modules in performance. In summary, we proposed a novel systematic approach dependent on the known disease information of mRNA, miRNA and pathway to identify BC-related circRNA modules, which could help identify BC-related circRNAs and benefits treatment and prognosis for BC patients.

Reconstruction of full-length circular RNAs enables isoform-level quantification

Currently, circRNA studies are shifting from the identification of circular transcripts to understanding their biological functions. However, such endeavors have been limited by large-scale determination of their full-length sequences and also by the inability of accurate quantification at the isoform level. Here, we propose a new feature, reverse overlap (RO), for circRNA detection, which outperforms back-splice junction (BSJ)-based methods in identifying low-abundance circRNAs. By combining RO and BSJ features, we present a novel approach for effective reconstruction of full-length circRNAs and isoform-level quantification from the transcriptome. We systematically compared the difference between the BSJ-level and isoform-level differential expression analyses using human liver tumor and normal tissues and highlight the necessity of deepening circRNA studies to the isoform-level resolution. The CIRI-full software can be accessed at https://sourceforge.net/projects/ciri.

Circular RNA profiling provides insights into their subcellular distribution and molecular characteristics in HepG2 cells

Circular RNA (circRNA) is a novel RNA molecule that has become a research focus recently. Although some research indicated that the circRNAs in different subcellular compartments could execute different regulatory functions, a panoramic analysis of the subcellular distribution and the transport mechanism of circRNA is still required. In this study, we comprehensively analyzed the subcellular distribution/characteristics and the transport mechanism, through systemically investigating the circRNA profiles among the subcellular fractions of HepG2 cell (nucleus, cytoplasm, mitochondria, ribosome, cytosol and exosome). CircRNAs were widely distributed among the subcellular fractions except in the mitochondria, with differences in the subcellular distribution/characteristics in terms of classification, length, GC content, alternative circularization and parental gene function. Further analysis indicated this might be due to the selective transportation mediated by the transport-related RNA binding proteins (RBPs). The circRNAs may follow the same transportation mechanism of linear RNAs, in which the RBPs specially recognize/transport the RNAs with the corresponding binding motifs. Interestingly, we found that the exosome could selectively package the circRNAs containing the purine-rich 5'-GMWGVWGRAG-3' motif, with the characteristic of 'garbage dumping' and 'intercellular signaling' functions. Besides, although we observed numerous circRNAs enriched in the ribosome, we did not reliably identify any unique-peptides from circRNAs using 3D-LC-MS/MS strategy. This suggests that circRNAs rarely function as translation templates in vivo like lincRNA. Our findings not only indicates the differential distributions/characteristics among the subcellular fractions, but also reveals the possible transportation mechanism. This provides an improved understanding of the life history and molecular behavior of circRNA in cells.

The circular RNA circ-ITCH suppresses ovarian carcinoma progression through targeting miR-145/RASA1 signaling

As the leading cause of death for gynecological cancers, ovarian cancer (OC) ranks fifth overall for cancer-related death among women. Emerging evidence has indicated that circular RNA (circRNA), recognized as functional non-coding transcripts in eukaryotic cells, may be involved in many physiological or pathological processes. It was reported that circ-ITCH is downregulated in multi cancers and serves as a powerful tumor suppressor among through a competing endogenous RNA (ceRNA) pathway. However, the existence and the role of circ-ITCH in OC was not reported. Here, we found a broad down-regulation of circ-ITCH in OC tissues and cells, which correlates with a worse prognosis in OC patients. Functional studies suggest that circ-ITCH overexpression inhibits the cell viability and motility by CCK8, cell cycle, wound healing assay and invasion assay. It also inhibits the tumorigenesis ability in xenograft NOD mice in vivo. Mechanically, we demonstrated that circ-TCH acts as a ceRNA to sponge miR-145, increases the level of RASA1, and inhibits the malignant progression of OC cells via the circ-ITCH-miR-145-RASA1 axis in vitro and in vivo. Taken together, our findings provide a novel tumor suppressive role regarding circ-ITCH function in the malignant progression of OC.

Circular RNA expression profiles of mouse ovaries during postnatal development and the function of circular RNA epidermal growth factor receptor in granulosa cells

PURPOSE

Circular RNAs (circRNAs) are a class of noncoding RNAs that can regulate gene expression at the post-transcriptional level. The contribution of circRNAs in the regulation of granulosa cells (GCs) functions is not yet clear. The aim of this study was to analyze circRNA expression in adult and neonate ovaries, uncover the biological roles of circ_0002861 (circEGFR) and identify the mechanism by which it modulates follicular development.

BASIC PROCEDURES

The circRNA expression profiles of adult and neonatal mouse ovaries were explored by high-throughput sequencing. The function of circEGFR was measured by RNA fluorescence in situ hybridization, overexpression, knockdown, RNA immunoprecipitation and luciferase reporter assays in GCs.

MAIN FINDINGS

Numerous differentially expressed circRNAs were identified in adult and neonatal ovaries. Through circRNAs expression patterns and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, estrogen signaling was found to be upregulated in adult ovaries compared with neonate ovaries. Further analysis revealed that the expression of circEGFR (circ_0002861, ID: mmu_circ_0002861 in circBase) was increased in adult ovaries compared with neonate ovaries. circEGFR is formed by splicing from exons 14 and 15 of the epidermal growth factor receptor (EGFR) gene to produce a covalently linked 249-nucleotide circRNA. Overexpression of circEGFR increased estradiol (E₂) production and GCs growth, whereas circEGFR knockdown enhanced progesterone production and inhibited (E₂) secretion by GCs. Bioinformatic screening identified several binding sites for miR-125a-3p in the circEGFR sequence. RNA immunoprecipitation and luciferase reporter assays demonstrated that circEGFR may act as a sponge for miR-125a-3p, thus modulating Fyn expression.

PRINCIPAL CONCLUSIONS

These findings illustrate that circEGFR may play a vital role in ovarian GCs by modulating Fyn via competitive binding with miR-125a-3p. Our results suggest potential applications of circEGFR in reproductive and steroid-related disorder therapy.

The Circular RNA Profiles of Colorectal Tumor Metastatic Cells

Circular RNAs (circRNAs) have been reported that can be used as biomarkers for colorectal cancers (CRC) and other types of tumors. However, a limited number of studies have been performed investigating the potential role of circRNAs in tumor metastasis. Here, we examined the circRNAs in two CRC cell lines (a primary tumor cell SW480 and its metastasis cell SW620), and found a large set of circRNA (2,919 ncDECs) with significantly differential expression patterns relative to normal cells (NCM460). In addition, we uncovered a set of 623 pmDECs that differ between the primary CRC cells and its metastasis cells. Both differentially expressed circRNA (DEC) sets contain many previously unknown putative CRC-related circRNAs, thereby providing many new circRNAs as candidate biomarkers for CRC development and metastasis. These studies are the first large-scale identification of metastasis-related circRNAs for CRC and provide valuable candidate biomarkers for diagnostic and a starting point for additional investigations of CRC metastasis.

Detection and Reconstruction of Circular RNAs from Transcriptomic Data

Recent studies have shown that circular RNAs (circRNAs) are a novel class of abundant, stable, and ubiquitous noncoding RNA molecules in eukaryotic organisms. Comprehensive detection and reconstruction of circRNAs from high-throughput transcriptome data is an initial step to study their biogenesis and function. Several tools have been developed to deal with this issue, but they require many steps and are difficult to use. To solve this problem, we provide a protocol for researchers to detect and reconstruct circRNA by employing CIRI2, CIRI-AS, and CIRI-full. This protocol can not only simplify the usage of above tools but also integrate their results.

Altered expression of circular RNAs in Moyamoya disease

Moyamoya disease (MMD) is the most common pediatric cerebrovascular disease in Eastern Asian countries but the etiology is not well understood. Circular RNAs (circRNAs) have been implicated in various biological processes, but their role in the development of MMD remains unclear. To address this issue, we carried out a comparative circRNA microarray analysis of blood samples obtained from patients with MMD and healthy subjects and identified 146 circRNAs that were differentially expressed between the two groups. Of these, 29 were upregulated and 117 were downregulated in patients as compared to controls (fold change ≥2.0 and P<0.05). The microarray results were validated by quantitative reverse-transcription PCR. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses revealed that the differentially expressed circRNAs were primarily involved in angiogenesis, metabolism, and immune responses in MMD. In addition, the mitogen-activated protein kinase signaling pathway was found to be the core regulatory pathway associated with disease pathogenesis. These results indicate that specific circRNAs are aberrantly expressed in MMD and are potential therapeutic targets for its treatment.