CircRNA-Protein Interactions in Muscle Development and Diseases

Candidate circRNAs related to skeletal muscle development in Dazu black goats

Circular RNA (CircRNA), as a classical noncoding RNA, has been proven to regulate skeletal muscle development (SMD). However, the molecular genetic basis of circRNA regulation in muscle cells remains unclear. In this study, the expression patterns of circRNAs in the longissimus dorsi muscle at embryonic day 75 and postnatal day 1 in DBGs were investigated to identify the key circRNAs that play an important role in SMD in goats. A total of 140 significantly and differentially expressed circRNAs (DEcircRNAs) were identified among the groups at different developmental stages. Among the 116 host genes (HGs) of DEcircRNAs, 76 were significantly and differentially expressed, which was confirmed by previous RNA_seq data. Furthermore, the expression pattern of 10 DEcircRNAs with RT-qPCR was verified, which showed 80% concordance rate with that of RNA_seq datasets. Moreover, the authenticity of seven randomly selected DEcircRNAs was verified by PCR Sanger sequencing. Based on the functional annotation results, among the 76 significantly and differentially expressed HGs, 74 were enriched in 845 GO terms, whereas 35 were annotated to 85 KEGG pathways. The results of this study could provide a comprehensive understanding of the genetic basis of circRNAs involved in SMD and muscle growth.

Research trends and hotspots of circular RNA in cardiovascular disease: A bibliometric analysis

From a global perspective, cardiovascular diseases (CVDs), the leading factor accounting for population mortality, and circRNAs, RNA molecules with stable closed-loop structures, have been proven to be closely related. The latent clinical value and the potential role of circRNAs in CVDs have been attracting increasing, active research interest, but bibliometric studies in this field are still lacking. Thus, in this study, we conducted a bibliometric analysis by using software such as VOSviewer, CiteSpace, Microsoft Excel, and the R package to determine the current research progress and hotspots and ultimately provide an overview of the development trends and future frontiers in this field. In our study, based on our search strategy, a total of 1206 publications published before July 31, 2023 were accessed from the WOSCC database. According to our findings, there is a notable increasing trend in global publications in the field of circRNA in CVDs. China was found to be the dominant country in terms of publication number, but a lack of high-quality articles was a significant fault. A cluster analysis on the co-cited references indicated that dilated cardiomyopathy, AMI, and cardiac hypertrophy are the greatest objects of concern. In contrast, a keywords analysis indicated that high importance has been ascribed to MI, abdominal aortic aneurysm, cell proliferation, and coronary artery diseases.

Roles and mechanisms of circular RNA in respiratory system cancers

Circular RNAs (circRNAs) constitute a class of endogenous non-coding RNAs (ncRNAs) that lack a 5'-ended cap and 3'-ended poly (A) tail and form a closed ring structure with covalent bonds. Due to its special structure, circRNA is resistant to Exonuclease R (RNaseR), making its distribution in the cytoplasm quite rich. Advanced high-throughput sequencing and bioinformatics methods have revealed that circRNA is highly conserved, stable, and disease- and tissue-specific. Furthermore, increasing research has confirmed that circRNA, as a driver or suppressor, regulates cancer onset and progression by modulating a series of pathophysiological mechanisms. As a result, circRNA has emerged as a clinical biomarker and therapeutic intervention target. This article reviews the biological functions and regulatory mechanisms of circRNA in the context of respiratory cancer onset and progression.

Characterised intron retention profiles in muscle tissue of idiopathic inflammatory myopathy subtypes

OBJECTIVES

Idiopathic inflammatory myopathies (IIMs) are a group of heterogeneous autoimmune diseases. Intron retention (IR) serves as an important post-transcriptional and translational regulatory mechanism. This study aims to identify changes in IR profiles in IIM subtypes, investigating their influence on proteins and their correlations with clinical features.

METHODS

RNA sequencing and liquid chromatography-tandem mass spectrometry were performed on muscle tissues obtained from 174 patients with IIM and 19 controls, following QC procedures. GTFtools and iREAD software were used for IR identification. An analysis of differentially expressed IRs (DEIs), exons and proteins was carried out using edgeR or DEP. Functional analysis was performed with clusterProfiler, and SPIRON was used to assess splicing factors.

RESULTS

A total of 6783 IRs located in 3111 unique genes were identified in all IIM subtypes compared with controls. IIM subtype-specific DEIs were associated with the pathogenesis of respective IIM subtypes. Splicing factors YBX1 and HSPA2 exhibited the most changes in dermatomyositis and immune-mediated necrotising myopathy. Increased IR was associated with reduced protein expression. Some of the IIM-specific DEIs were correlated with clinical parameters (skin rash, MMT-8 scores and muscle enzymes) and muscle histopathological features (myofiber necrosis, regeneration and inflammation). IRs in IFIH1 and TRIM21 were strongly correlated with anti-MDA5+ antibody, while IRs in SRP14 were associated with anti-SRP+ antibody.

CONCLUSION

This study revealed distinct IRs and specific splicing factors associated with IIM subtypes, which might be contributing to the pathogenesis of IIM. We also emphasised the potential impact of IR on protein expression in IIM muscles.

MeRIP sequencing reveals the regulation of N6-methyladenosine in muscle development between hypertrophic and leaner broilers

Meat production performance is the most important economic trait in broilers, and skeletal muscle, as the largest organ in animals, is directly related to meat production during embryonic and postnatal growth and development. N6-Methyladenosine (m6A) is a chemical modification occurs on RNA adenosine that has been reported to participate in a variety of biological processes in all species. However, there are still few reports on the regulatory role of muscle growth and development in poultry after birth. This study aims to reveal the distribution of m6A modification sites in chicken pectoralis major muscle after birth and find out the regulatory relationship between m6A and muscle development. As representatives of leaner (Xinghua chicken [XH]) and hypertrophic (White Recessive Rock chicken [WRR]) broilers, there are significant differences in body weight, muscle fiber diameter, and muscle fiber cross-sectional area between XH and WRR chickens. RNA sequencing detected a total of 397 differentially expressed genes (DEG) in the pectoralis major muscle of XH and WRR chicken, and these DEGs were mainly enriched in catalytic activity and metabolic pathways. MeRIP sequencing results showed that among all 6,476 differentially modified m6A peaks, about 90% peaks (5,823) were differentially down regulated in XH chickens. The joint analysis of the mRNA and MeRIP sequencing data found 145 DEGs with differential m6A peak, ALKBH5 as a m6A demethylase, was also included. The highly expression of ALKBH5 in the muscle tissue of poultry and differential expression between XH and WRR chickens suggest that ALKBH5 may play a crucial role in regulating muscle development. Our results revealed that there were significant differences in growth rate, body weight, muscle fiber diameter, and fiber cross-section area between WRR and XH chicken, as well as significant differences in m6A methylation level and muscle metabolism level.

Exploring the evolving roles and clinical significance of circRNAs in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) represents the predominant malignancies in the head and neck region, and has limited therapeutic alternatives. Circular RNAs (circRNAs), a substantial category of non-coding RNA molecules, exert influential roles in human disease development and progression, employing various mechanisms such as microRNA sponging, interaction with RNA-binding proteins, and translational capabilities. Accumulating evidence highlights the differential expression of numerous circRNAs in HNSCC, and numerous dysregulated circRNAs underscore their crucial involvement in malignant advancement and resistance to treatment. This review aims to comprehensively outline the characteristics, biogenesis, and mechanisms of circRNAs, elucidating their functional significance in HNSCC. In addition, we delve into the clinical implications of circRNAs, considering their potential as biomarkers or targets for diagnosis, prognosis, and therapeutic applications in HNSCC. The discussion extends to exploring future challenges in the clinical translation of circRNAs, emphasizing the need for further research.

Circular RNA Gtdc1 Protects Against Offspring Osteoarthritis Induced by Prenatal Prednisone Exposure by Regulating SRSF1-Fn1 Signaling

Chondrodysplasia is closely associated with low birth weight and increased susceptibility to osteoarthritis in adulthood. Prenatal prednisone exposure (PPE) can cause low birth weight; however, its effect on offspring cartilage development remains unexplored. Herein, rats are administered clinical doses of prednisone intragastrically on gestational days (GDs) 0-20 and underwent long-distance running during postnatal weeks (PWs) 24-28. Knee cartilage is assayed for quality and related index changes on GD20, PW12, and PW28. In vitro experiments are performed to elucidate the mechanism. PPE decreased cartilage proliferation and matrix synthesis, causing offspring chondrodysplasia. Following long-distance running, the PPE group exhibited more typical osteoarthritis-like changes. Molecular analysis revealed that PPE caused cartilage circRNomics imbalance in which circGtdc1 decreased most significantly and persisted postnatally. Mechanistically, prednisolone reduced circGtdc1 expression and binding with Srsf1 to promote degradation of Srsf1 via K48-linked polyubiquitination. This further inhibited the formation of EDA/B+Fn1 and activation of PI3K/AKT and TGFβ pathways, reducing chondrocyte proliferation and matrix synthesis. Finally, intra-articular injection of offspring with AAV-circGtdc1 ameliorated PPE-induced chondrodysplasia, but this effect is reversed by Srsf1 knockout. Altogether, this study confirms that PPE causes chondrodysplasia and susceptibility to osteoarthritis by altering the circGtdc1-Srsf1-Fn1 axis; in vivo, overexpression of circGtdc1 can represent an effective intervention target for ameliorating PPE-induced chondrodysplasia.

CircRNA-associated ceRNA regulatory networks as emerging mechanisms governing the development and biophysiopathology of epilepsy

The etiology of epilepsy is ascribed to the synchronized aberrant neuronal activity within the brain. Circular RNAs (circRNAs), a class of non-coding RNAs characterized by their circular structures and covalent linkage, exert a substantial influence on this phenomenon. CircRNAs possess stereotyped replication, transience, repetitiveness, and paroxysm. Additionally, MicroRNA (miRNA) plays a crucial role in the regulation of diverse pathological processes, including epilepsy. CircRNA is of particular significance due to its ability to function as a competing endogenous RNA, thereby sequestering or inhibiting miRNA activity through binding to target mRNA. Our review primarily concentrates on elucidating the pathological and functional roles, as well as the underlying mechanisms, of circRNA-miRNA-mRNA networks in epilepsy. Additionally, it explores the potential utility of these networks for early detection and therapeutic intervention.

High expression circRALGPS2 in atretic follicle induces chicken granulosa cell apoptosis and autophagy via encoding a new protein

BACKGROUND

The reproductive performance of chickens mainly depends on the development of follicles. Abnormal follicle development can lead to decreased reproductive performance and even ovarian disease among chickens. Chicken is the only non-human animal with a high incidence of spontaneous ovarian cancer. In recent years, the involvement of circRNAs in follicle development and atresia regulation has been confirmed.

RESULTS

In the present study, we used healthy and atretic chicken follicles for circRNA RNC-seq. The results showed differential expression of circRALGPS2. It was then confirmed that circRALGPS2 can translate into a protein, named circRALGPS2-212aa, which has IRES activity. Next, we found that circRALGPS2-212aa promotes apoptosis and autophagy in chicken granulosa cells by forming a complex with PARP1 and HMGB1.

CONCLUSIONS

Our results revealed that circRALGPS2 can regulate chicken granulosa cell apoptosis and autophagy through the circRALGPS2-212aa/PARP1/HMGB1 axis.

Bovine enhancer-regulated circSGCB acts as a ceRNA to regulate skeletal muscle development via enhancing KLF3 expression

Skeletal muscle growth and development in livestock and poultry play a pivotal role in determining the quality and yield of meat production. However, the mechanisms of myogenesis are remained unclear due to it finely regulated by a complex network of biological macromolecules. In this study, leveraging previous sequencing data, we investigated a differentially expressed circular RNA (circSGCB) present in fetal and adult muscle tissues among various ruminant species, including cattle, goat, and sheep. Our analysis revealed that circSGCB is a single exon circRNA, potentially regulated by an adjacent bovine enhancer. Functional analysis through loss-of-function tests demonstrated that circSGCB exerts inhibitory effects on bovine myoblast proliferation while promoting myocytes generation. Furthermore, we discovered that circSGCB primarily localizes to the cytoplasm, where it functions as a molecular sponge by binding to bta-miR-27a-3p. This interaction releases the mRNAs of KLF3 gene and further activates downstream functional pathways. In vivo, studies provided evidence that up-regulation of KLF3 contributes to muscle regeneration. These findings collectively suggest that circSGCB operates via a competing endogenous RNA (ceRNA) mechanism to regulate KLF3, thereby influencing myogenesis in ruminants and highlights it may as potential molecular targets for enhancing meat production in livestock and poultry industries.

Interactions between circRNA and protein in breast cancer

Circular RNA (circRNA) is a newly discovered endogenous non-coding RNA that plays important roles in the occurrence and development of various cancers. Current research indicates that circRNA can inhibit the function of miRNA by acting as an miRNA sponge, interacting with proteins, and being translated into proteins. Most current research focuses on the circRNA-miRNA interaction; however, few studies have investigated the interaction between circRNAs and RNA binding proteins (RBPs) in breast cancer. In this review, we systematically summarize the potential molecular mechanism of the circRNA-protein interaction in breast cancer. Specifically, we elaborate on the direct interaction between circRNAs and proteins in breast cancer, including the functions of circRNA as protein sponges, decoys, and scaffolds, thereby affecting the progression of breast cancer. We also discuss the indirect interaction between circRNAs and proteins in breast cancer in which RBPs, transcription factors and m6A modifying enzymes could in turn regulate the expression and formation of circRNA. Finally, we discuss the potential application of circRNA-protein interaction for treating breast cancer, providing a reference for further research in this field.

Multi-omics analysis on the mechanism of the effect of Isatis leaf on the growth performance of fattening sheep

Introduction

This study evaluated the effects of Isatis Leaf (ISL) on the growth performance, gastrointestinal tissue morphology, rumen and intestinal microbiota, rumen, serum and urine metabolites, and rumen epithelial tissue transcriptome of fattening sheep.

Methods

Twelve 3.5-month-old healthy fattening sheep were randomly divided into two groups, each with 6 replicates, and fed with basal diet (CON) and basal diet supplemented with 80 g/kg ISL for 2.5 months. Gastrointestinal tract was collected for histological analysis, rumen fluid and feces were subjected to metagenomic analysis, rumen fluid, serum, and urine for metabolomics analysis, and rumen epithelial tissue for transcriptomics analysis.

Results

The results showed that in the ISL group, the average daily gain and average daily feed intake of fattening sheep were significantly lower than those of the CON group (P < 0.05), and the rumen ammonia nitrogen level was significantly higher than that of the CON group (P < 0.01). The thickness of the reticulum and abomasum muscle layer was significantly increased (P < 0.05). At the genus level, the addition of ISL modified the composition of rumen and fecal microorganisms, and the relative abundance of Methanobrevibacter and Centipeda was significantly upregulated in rumen microorganisms, The relative abundance of Butyrivibrio, Saccharofermentans, Mogibacterium, and Pirellula was significantly downregulated (P < 0.05). In fecal microorganisms, the relative abundance of Papillibacter, Pseudoflavonifractor, Butyricicoccus, Anaerovorax, and Methanocorpusculum was significantly upregulated, while the relative abundance of Roseburia, Coprococcus, Clostridium XVIII, Butyrivibrio, Parasutterella, Macellibacteroides, and Porphyromonas was significantly downregulated (P < 0.05). There were 164, 107, and 77 different metabolites in the rumen, serum, and urine between the ISL and CON groups (P < 0.05). The differential metabolic pathways mainly included thiamine metabolism, niacin and nicotinamide metabolism, vitamin B6 metabolism, taurine and taurine metabolism, beta-Alanine metabolism and riboflavin metabolism. These metabolic pathways were mainly involved in the regulation of energy metabolism and immune function in fattening sheep. Transcriptome sequencing showed that differentially expressed genes were mainly enriched in cellular physiological processes, development, and immune regulation.

Conclusion

In summary, the addition of ISL to the diet had the effect of increasing rumen ammonia nitrogen levels, regulating gastrointestinal microbiota, promoting body fat metabolism, and enhancing immunity in fattening sheep.

circUBE3C modulates myoblast development by binding to miR-191 and upregulating the expression of p27

Noncoding RNAs, including miRNAs (microRNAs) and circRNAs (circular RNA), are crucial regulators of myoblast proliferation and differentiation during muscle development. However, the specific roles and molecular mechanisms of circRNAs in muscle development remain poorly understood. Based on the existing circRNA-miRNA-mRNA network, our study focuses on circUBE3C, exploring its differential expression in fetal and adult muscle tissue of the cattle and investigating its impact on myoblast proliferation, apoptosis, and differentiation. The functional analysis of overexpression plasmids and siRNAs (small interfering RNAs) targeting circUBE3C was comprehensively evaluated by employing an array of advanced assays, encompassing CCK-8 (cell counting kit-8), EdU (5-ethynyl-20-deoxyuridine), flow cytometry, western blot analysis, and RT-qPCR. In vivo investigations indicated that overexpression of circUBE3C impedes the process of skeletal muscle regeneration. Mechanistically, we demonstrated that circUBE3C interacts with miR-191 and alleviates the suppression of p27 through cytoplasmic separation, bioinformatics prediction, dual-luciferase reporter assay, and RIP (RNA immunoprecipitation). Our findings indicate that the novel circRNA circUBE3C competitively binds to miR-191, thereby inhibiting proliferation and promoting apoptosis in bovine primary myoblasts and unveiling a regulatory pathway in bovine skeletal muscle development. These findings expand our understanding of circRNA functions in mammals and provide a basis for further exploration of their role in myogenesis and muscle diseases.

Circular RNA and its potential diagnostic and therapeutic values in breast cancer

Breast cancer (BC) is one of the most common malignant tumors in women and still poses a significant threat to women worldwide. Recurrence of BC in situ, metastasis to distant organs, and resistance to chemotherapy are all attached to high mortality in patients with BC. Non-coding RNA (ncRNA) of the type known as "circRNA" links together from one end to another to create a covalently closed, single-stranded circular molecule. With characteristics including plurality, evolutionary conservation, stability, and particularity, they are extensively prevalent in various species and a range of human cells. CircRNAs are new and significant contributors to several kinds of disorders, including cardiovascular disease, multiple organ inflammatory responses and malignancies. Recent studies have shown that circRNAs play crucial roles in the occurrence of breast cancer by interacting with miRNAs to regulate gene expression at the transcriptional or post-transcriptional levels. CircRNAs offer the potential to be therapeutic targets for breast cancer treatment as well as prospective biomarkers for early diagnosis and prognosis of BC. Here, we are about to present an overview of the functions of circRNAs in the proliferation, invasion, migration, and resistance to medicines of breast cancer cells and serve as a promising resource for future investigations on the pathogenesis and therapeutic strategies.

Involvement of circRNA Regulators MBNL1 and QKI in the Progression of Esophageal Squamous Cell Carcinoma

OBJECTIVES

To investigate the role of circRNA regulators MBNL1 and QKI in the progression of esophageal squamous cell carcinoma.

BACKGROUND

MBNL1 and QKI are pivotal regulators of pre-mRNA alternative splicing, crucial for controlling circRNA production - an emerging biomarker and functional regulator of tumor progression. Despite their recognized roles, their involvement in ESCC progression remains unexplored.

METHODS

The expression levels of MBNL1 and QKI were examined in 28 tissue pairs from ESCC and adjacent normal tissues using data from the GEO database. Additionally, a total of 151 ESCC tissue samples, from stage T1 to T4, consisting of 13, 43, 87, and 8 cases per stage, respectively, were utilized for immunohistochemical (IHC) analysis. RNA sequencing was utilized to examine the expression profiles of circRNAs, lncRNAs, and mRNAs across 3 normal tissues, 3 ESCC tissues, and 3 pairs of KYSE150 cells in both wildtype (WT) and those with MBNL1 or QKI knockouts. Transwell, colony formation, and subcutaneous tumorigenesis assays assessed the impact of MBNL1 or QKI knockout on ESCC cell migration, invasion, and proliferation.

RESULTS

ESCC onset significantly altered MBNL1 and QKI expression levels, influencing diverse RNA species. Elevated MBNL1 or QKI expression correlated with patient age or tumor invasion depth, respectively. MBNL1 or QKI knockout markedly enhanced cancer cell migration, invasion, proliferation, and tumor growth. Moreover, the absence of either MBNL1 or QKI modulated the expression profiles of multiple circRNAs, causing extensive downstream alterations in the expression of numerous lncRNAs and mRNAs. While the functions of circRNA and lncRNA among the top 20 differentially expressed genes remain unclear, mRNAs like SLCO4C1, TMPRSS15, and MAGEB2 have reported associations with tumor progression.

CONCLUSIONS

This study underscores the tumor-suppressive roles of MBNL1 and QKI in ESCC, proposing them as potential biomarkers and therapeutic targets for ESCC diagnosis and treatment.

Circular RNA circSMAD4 regulates cardiac fibrosis by targeting miR-671-5p and FGFR2 in cardiac fibroblasts

Heart failure is a leading cause of death and is often accompanied by activation of quiescent cardiac myofibroblasts, which results in cardiac fibrosis. In this study, we aimed to identify novel circular RNAs that regulate cardiac fibrosis. We applied transverse aortic constriction (TAC) for 1, 4, and 8 weeks in mice. RNA sequencing datasets were obtained from cardiac fibroblasts isolated by use of a Langendorff apparatus and then further processed by use of selection criteria such as differential expression and conservation in species. CircSMAD4 was upregulated by TAC in mice or by transforming growth factor (TGF)-β1 in primarily cultured human cardiac fibroblasts. Delivery of si-circSMAD4 attenuated myofibroblast activation and cardiac fibrosis in mice treated with isoproterenol (ISP). si-circSmad4 significantly reduced cardiac fibrosis and remodeling at 8 weeks. Mechanistically, circSMAD4 acted as a sponge against the microRNA miR-671-5p in a sequence-specific manner. miR-671-5p was downregulated during myofibroblast activation and its mimic form attenuated cardiac fibrosis. miR-671-5p mimic destabilized fibroblast growth factor receptor 2 (FGFR2) mRNA in a sequence-specific manner and interfered with the fibrotic action of FGFR2. The circSMAD4-miR-671-5p-FGFR2 pathway is involved in the differentiation of cardiac myofibroblasts and thereby the development of cardiac fibrosis.

NR1H4-mediated circRHOBTB3 modulates the proliferation, metastasis, and Warburg effects of cervical cancer through interacting with IGF2BP3

Globally, cervical cancer (CC) ranks as the fourth most common cancer and the most lethal malignancy among females of reproductive age. The incidence of CC is increasing in low-income countries, with unsatisfactory outcomes and long-term survival for CC patients. Circular RNAs (CircRNAs) are promising therapeutics that target multiple cancers. In this study, we investigated the tumorigenic role of circRHOBTB3 in CC, showing that circRHOBTB3 is highly expressed in CC cells and circRHOBTB3 knockdown also repressed CC proliferation, migration, invasion, and the Warburg effects. CircRHOBTB3 interacted with the RNA-binding protein, IGF2BP3, to stabilize its expression in CC cells and is putatively transcriptionally regulated by NR1H4. In conclusion, this novel NR1H4/circRHOBTB3/IGF2BP3 axis may provide new insights into CC pathogenesis.

The emerging role of circRNAs on skeletal muscle development in economical animals

CircRNAs are a novel type of closed circular molecules formed through a covalent bond lacking a 5'cap and 3' end tail, which mainly arise from mRNA precursor. They are widely distributed in plants and animals and are characterized by stable structure, high conservativeness in cells or tissues, and showed the expression specificity at different stages of development in different tissues. CircRNAs have been gradually attracted wide attention with the development of RNA sequencing, which become a new research hotspot in the field of RNA. CircRNAs play an important role in gene expression regulation. Presently, the related circRNAs research in the regulation of animal muscle development is still at the initial stage. In this review, the formation, properties, biological functions of circRNAs were summarized. The recent research progresses of circRNAs in skeletal muscle growth and development from economic animals including livestock, poultry and fishes were introduced. Finally, we proposed a prospective for further studies of circRNAs in muscle development, and we hope our research could provide new ideas, some theoretical supports and helps for new molecular genetic markers exploitation and animal genetic breeding in future.

CircRRAS2 promotes myogenic differentiation of bovine MuSCs and is a novel regulatory molecule of muscle development

The proliferation and myogenic differentiation of muscle stem cells (MuSCs) are important factors affecting muscle development and beef quality. There is increasing evidence that circRNAs can regulate myogenesis. We found a novel circRNA, named circRRAS2 that is significantly upregulated in the differentiation phase of bovine MuSCs. Here, we aimed to determine its roles in the proliferation and myogenic differentiation of these cells. The results showed that circRRAS2 was expressed in several bovine tissues. CircRRAS2 inhibited MuSCs proliferation and promoted myoblast differentiation. In addition, chromatin isolation by using RNA purification and mass spectrometry in differentiated muscle cells identified 52 RNA-binding proteins that could potentially bind to circRRAS2, in order to regulate their differentiation. The results suggest that circRRAS2 could be a specific regulator of myogenesis in bovine muscle.HighlightsCircRRAS2 expression is higher in DM cells than in GM cells.CircRRAS2 could significantly inhibit the proliferation and apoptosis of bovine MuSCs.CircRRAS2 promotes the differentiation of bovine MuSCs into myotubes.CircRRAS2 may exert regulatory effects through multiple RNA binding proteins.

CircLRRFIP1 promotes the proliferation and differentiation of chicken skeletal muscle satellite cells by sponging the miR-15 family via activating AKT3-mTOR/p70S6K signaling pathway

Skeletal muscle is important for animal meat production, regulating movements, and maintaining homeostasis. Circular RNAs (circRNAs) have been founded to play vital role in myogenesis. However, the effects of the numerous circRNAs on growth and development of the skeletal muscle are yet to be uncovered. Herein, we identified circLRRFIP1, which is a novel circular RNA that is preferentially expressed in the skeletal muscle. To study the role of circLRRFIP1 in the skeletal muscle, the skeletal muscle satellite cells (SMSCs) was used to silenced or overexpressed circLRRFIP1. The results obtained in this study showed that circLRRFIP1 play a positive role in the proliferation and differentiation of SMSCs. The SMSCs were generated with stable knockdown and overexpression of circLRRFIP1, and the results showed that circLRRFIP1 exerts a stimulatory effect on the proliferation and differentiation of SMSCs. We further generated SMSCs with stable knockdown and overexpression of circLRRFIP1, and the results revealed that circLRRFIP1 exerts a stimulatory effect on the proliferation and differentiation of SMSCs. Mechanistically, circLRRFIP1 targets the myogenic inhibitory factor-miR-15 family to release the suppression of the miR-15 family to AKT3. The knockdown of AKT inhibits SMSC differentiation through the mTOR/p70S6K pathway. Taken together, the results obtained in this present study revealed the important role and the regulatory mechanisms of circLRRFIP1 in the development of chicken skeletal muscle. Therefore, this study provides an attractive target for molecular breeding to enhance meat production in the chicken industry.

CircCPSF6 promotes hepatocellular carcinoma cancer progression by regulating MAP4K4 through sponging miR-145-5p

BACKGROUND

Aberrant expression of circRNAs is involved in the progression of hepatocellular carcinoma (HCC). This study aimed at screening the pro-tumorigenic circular RNAs (circRNAs) in HCC and the mechanisms of circCPSF6 expression influencing HCC characteristics.

METHOD

circCPSF6 was identified in HCC tissues using high-throughput sequencing data, and its expression was verified in both HCC tissues and cell lines using quantitative real-time PCR (qRT-PCR). CCK-8 and Transwell assays were used to evaluate the effects of circCPSF6 on HCC proliferation and migration. A xenograft mouse model was used to investigate the effects of circCPSF6 on HCC progression in vivo, and the significance of circCPSF6 in HCC was verified both in vivo and in vitro. circCPSF6-associated miRNAs and mRNAs were identified using bioinformatic analyses. Luciferase reporter, RNA pull-down, Fluorescence in situ hybridization, and RNA immunoprecipitation assays were performed to elucidate the circCPSF6 regulatory axis in HCC.

RESULT

CircCPSF6 expression was increased in HCC cell lines and tissues, and the expression of its parental mRNA was positively correlated with tumor severity and negatively correlated with survival. Mechanistic analyses of HCC cell lines showed that tumorigenesis was inhibited by circCPSF6 knockdown and promoted by its overexpression. Functional analyses revealed that circCPSF6 mediated HCC development by sponging miR-145-5p as a competing endogenous RNA. Furthermore, this sponging upregulated the miR-145-5p target gene MAP4K4, a classical pro-tumorigenic gene.

CONCLUSION

Our findings reveal a regulatory network that includes the circCPSF6-miR-145-5p-MAP4K4 axis. Elements of this axis are potential HCC biomarkers, as well as targets for HCC treatment.

Circ_0001715 accelerated lung adenocarcinoma process by the miR-1322/CANT1 axis

Lung adenocarcinoma (LUAD) is a type of lung cancer, which belongs to non-small cell lung cancer and has seriously endangered the physical and mental health of people. The study of circRNAs (circRNAs) has been increasingly hot in recent years, in which circRNAs also play an important regulatory role in cancer. The aim of this study was to investigate the biological molecular mechanisms of circ_0001715 in the progression of LUAD. The expression of circ_0001715, miR-1322 and calcium-activated nucleotidase 1 (CANT1) in LUAD tissues and cell lines was assessed by quantitative reverse transcription PCR (RT-qPCR) and western bot assay. Clone formation assay, 5-Ethynyl-2'-Deoxyuridine (EDU) assay and wound healing assay were used to verify the proliferation ability of cells. Dual-luciferase reporter assay and RNA pull-down assay were performed to characterize the interactions between the three factors. Finally, a mouse tumor model was constructed to assess the tumorigenicity of circ_0001715. RT-qPCR assay results showed that circ_0001715 expression was significantly increased in LUAD tissues and cell lines. Finally, knockdown of circ_0001715 could inhibit tumor growth in vivo. Circ_0001715 regulated the progression of LUAD through the miR-1322/CANT1 axis. The results of this study provided ideas for understanding the molecular mechanisms of circ_0001715 in LUAD.

The emerging roles of circRNAs in traits associated with livestock breeding

Many indicators can be used to evaluate the productivity and quality of livestock, such as meat and milk production as well as fat deposition. Meat and milk production are measures of livestock performance, while fat deposition affects the taste and flavor of the meat. The circRNAs, are non-coding RNAs, that are involved in the regulation of all these three traits. We review the functions and mechanisms of circRNAs in muscle and fat development as well as lactation to provide a theoretical basis for circRNA research in animal husbandry. Various phenotypic changes presented in livestock may be produced by different circRNAs. Our current concern is how to use the roles played by circRNAs to our advantage to produce the best possible livestock. Hence, we describe the advantages and disadvantages of knockout techniques for circRNAs. In addition, we also put forward our thoughts regarding the mechanism and network of circRNAs to provide researchers with novel ideas of how molecular biology can help us advance our goals in animal farming. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA Interactions with Proteins and Other Molecules > Protein-RNA Recognition RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes.

Myc derived circRNA promotes triple-negative breast cancer progression via reprogramming fatty acid metabolism

Myc is a well-known proto-oncogene that is frequently amplified and activated in breast cancer, especially in triple-negative breast cancer (TNBC). However, the role of circular RNA (circRNA) generated by Myc remains unclear. Herein, we found that circMyc (hsa_circ_0085533) was remarkably upregulated in TNBC tissues and cell lines, which was attributed to gene amplification. Genetic knockdown of circMyc mediated by lentiviral vector significantly inhibited TNBC cell proliferation and invasion. Importantly, circMyc increased cellular triglycerides, cholesterols and lipid droplet contents. CircMyc was detected in both cytoplasm and nucleus, cytoplasmic circMyc could directly bind to HuR protein, facilitating the binding of HuR to SREBP1 mRNA, resulting in increasing SREBP1 mRNA stability. Nuclear circMyc bound to Myc protein, facilitating the occupation of Myc on SREBP1 promoter, leading to increasing SREBP1 transcription. As a result, the elevated SREBP1 increased the expression of its downstream lipogenic enzymes, enhancing lipogenesis and TNBC progression. Moreover, the orthotopic xenograft model showed that depletion of circMyc markedly inhibited lipogenesis and reduced tumor size. Clinically, high circMyc was closely related to larger tumor volume, later clinical stage and lymph node metastasis, functioning as an adverse prognostic factor. Collectively, our findings characterize a novel Myc-derived circRNA controlling TNBC tumorigenesis via regulation of metabolic reprogramming, implying a promising therapeutic target.

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.

circHECTD1 Promotes the Proliferation and Migration of Human Brain Vascular Smooth Muscle Cells via Interacting with KHDRBS3 to Stabilize EZH2 mRNA Expression

Purpose

The objective of this paper is to explore the role of circHECTD1 in vascular smooth muscle cells (VSMCs) and atherosclerosis (AS).

Methods

VSMCs were treated with platelet-derived growth factor-BB (PDGF-BB) in vitro, and the level of circHECTD1 was determined using qRT-PCR. Cell proliferation, migration, and invasion were analyzed using CCK8 and transwell assays. Cell apoptosis and cell cycle were analyzed using flow cytometry. The binding interaction between circHECTD1 and KHDRBS3 or EZH2 was investigated using the RIP, RNA pull-down.

Results

CircHECTD1 was upregulated in PDGF-BB-induced VSMCs with a dose-dependent and time-dependent manner. Knockdown of circHECTD1 suppressed VSMCsproliferation and migration and enhanced cell apoptosis in VSMCs, while circHECTD1 overexpression yielded opposite effects. Mechanistically, circHECTD1 could interact with KHDRBS3, thus enhanced the stability of EZH2 mRNA and increased EZH2 protein level. In addition, silencing EZH2 in VSMCs reversed the proliferation-enhancing effect of circHECTD1 overexpression.

Conclusion

Our findings provided providing a potential prognostic and therapy biomarker for AS.

Regulatory roles of noncoding RNAs in intervertebral disc degeneration as potential therapeutic targets (Review)

Intervertebral disc degeneration (IDD) is the leading cause of lower back pain, which is one of the primary factors that lead to disability and pose a serious economic burden. The key pathological processes involved are extracellular matrix degradation, autophagy, apoptosis, and inflammation of nucleus pulposus cells. Non-coding RNAs (ncRNAs), including microRNAs, long ncRNAs and circular RNAs, are key regulators of the aforementioned processes. ncRNAs are differentially expressed in tissues of the intervertebral disc between healthy individuals and patients and participate in the pathological progression of IDD via a complex pattern of gene regulation. However, the regulatory mechanisms of ncRNAs in IDD remain unclear. The present review summarizes the latest insights into the regulatory role of ncRNAs in IDD and sheds light on potentially novel therapeutic strategies for IDD that may be implemented in the future.

Association prediction of CircRNAs and diseases using multi-homogeneous graphs and variational graph auto-encoder

As a non-coding RNA molecule with closed-loop structure, circular RNA (circRNA) is tissue-specific and cell-specific in expression pattern. It regulates disease development by modulating the expression of disease-related genes. Therefore, exploring the circRNA-disease relationship can reveal the molecular mechanism of disease pathogenesis. Biological experiments for detecting circRNA-disease associations are time-consuming and laborious. Constrained by the sparsity of known circRNA-disease associations, existing algorithms cannot obtain relatively complete structural information to represent features accurately. To this end, this paper proposes a new predictor, VGAERF, combining Variational Graph Auto-Encoder (VGAE) and Random Forest (RF). Firstly, circRNA homogeneous graph structure and disease homogeneous graph structure are constructed by Gaussian interaction profile (GIP) kernel similarity, semantic similarity, and known circRNA-disease associations. VGAEs with the same structure are employed to extract the higher-order features by the encoding and decoding of input graph structures. To further increase the completeness of the network structure information, the deep features acquired from the two VGAEs are summed, and then train the RF with sparse data processing capability to perform the prediction task. On the independent test set, the Area Under ROC Curve (AUC), accuracy, and Area Under PR Curve (AUPR) of the proposed method reach up to 0.9803, 0.9345, and 0.9894, respectively. On the same dataset, the AUC, accuracy, and AUPR of VGAERF are 2.09%, 5.93%, and 1.86% higher than the best-performing method (AEDNN). It is anticipated that VGAERF will provide significant information to decipher the molecular mechanisms of circRNA-disease associations, and promote the diagnosis of circRNA-related diseases.

Functions and clinical significance of circular RNAs in acute myeloid leukemia

Circular RNAs (circRNAs) are a class of covalently closed single-stranded RNA molecules. Four types of circRNAs have been reported in animal cells, and they have typical characteristics in their biogenesis, nuclear export and degradation. Advances in our understanding of the molecular functions of circRNAs in sponging microRNAs, modulating transcription, regulating RNA-binding proteins, as well as encoding proteins have been made very recently. Dysregulated circRNAs are associated with human diseases such as acute myeloid leukemia (AML). In this review, we focus on the recently described mechanisms, role and clinical significance of circRNAs in AML. Although great progress of circRNAs in AML has been achieved, substantial efforts are still required to explore whether circRNAs exert their biological function by other mechanisms such as regulation of gene transcription or serving as translation template in AML. It is also urgent that researchers study the machineries regulating circRNAs fate, the downstream effectors of circRNAs modulatory networks, and the clinical application of circRNAs in AML.

Comprehensive Analysis of Differentially Expressed mRNAs, lncRNAs and circRNAs Related to Intramuscular Fat Deposition in Laiwu Pigs

Long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) are important classes of small noncoding RNAs that can regulate numerous biological processes. To understand the role of message RNA (mRNAs, lncRNAs and circRNAs) in the regulation of intramuscular fat (IMF) deposition, in this study the expression profiles of longissimus dorsi (LD) muscle from six Laiwu pigs (three with extremely high and three with extremely low IMF content) were sequenced based on rRNA-depleted library construction. In total, 323 differentially expressed protein-coding genes (DEGs), 180 lncRNAs (DELs) and 105 circRNAs (DECs) were detected between the high IMF and low IMF groups. Functional analysis indicated that most DEGs, and some target genes of DELs, were enriched into GO terms and pathways related to adipogenesis, suggesting their important roles in regulating IMF deposition. In addition, 12 DELs were observed to exhibit a positive relationship with stearoyl-CoA desaturase (SCD), phosphoenolpyruvate carboxykinase 1 (PCK1), and adiponectin (ADIPOQ), suggesting they are highly likely to be the target genes of DELs. Finally, we constructed a source gene-circRNA-miRNA connective network, and some of miRNA of the network have been reported to affect lipid metabolism or adipogenesis. Overall, this work provides a valuable resource for further research and helps to understand the potential functions of lncRNAs and circRNAs in IMF deposition.

A web server for identifying circRNA-RBP variable-length binding sites based on stacked generalization ensemble deep learning network

Circular RNA (circRNA) can exert biological functions by interacting with RNA-binding protein (RBP), and some deep learning-based methods have been developed to predict RBP binding sites on circRNA. However, most of these methods identify circRNA-RBP binding sites are only based on single data resource and cannot provide exact binding sites, only providing the probability value of a sequence fragment. To solve these problems, we propose a binding sites localization algorithm that fuses binding sites from multiple databases, and further design a stacked generalization ensemble deep learning model named CirRBP to identify RBP binding sites on circRNA. The CirRBP is trained by combining the binding sites from multiple databases and makes predictions by weighted aggregating the predictions of each sub-model. The results show that the CirRBP outperforms any sub-model and existing online prediction model. For better access to our research results, we develop an open-source web application called CRWS (CircRNA-RBP Web Server). Its back-end learning model of the CRWS is a stacked generalization ensemble learning model CirRBP based on different deep learning frameworks. Given a full-length circRNA or fragment sequence and a target RBP, the CRWS can analyze and provide the exact potential binding sites of the target RBP on the given sequence through the binding sites localization algorithm, and visualize it. In addition, the CRWS can discover the most widely distributed motif in each RBP dataset. Up to now, CRWS is the first significant online tool that uses multi-source data to train models and predict exact binding sites. CRWS is now publicly and freely available without login requirement at: http://www.bioinformatics.team.

CircDCLRE1C Regulated Lipopolysaccharide-Induced Inflammatory Response and Apoptosis by Regulating miR-214b-3p/STAT3 Pathway in Macrophages

The immune cell inflammation response is closely related to the occurrence of disease, and much evidence has shown that circular RNAs (circRNAs) play vital roles in the occurrence of disease. However, the biological function and regulatory mechanisms of circRNAs in the immune cell inflammation response remain poorly understood. In this study, we constructed an inflammatory model using lipopolysaccharide (LPS)-stimulated chicken macrophage lines (also known as HD11) to verify the function and mechanism of the novel circDCLRE1C (ID: gga_circ_0001674), which was significantly upregulated in spleen tissues infected by coccidia and the macrophage cells exposed to LPS. The results showed that circDCLRE1C aggravated LPS-induced inflammation and apoptosis in HD11 cells. Systemically, circDCLRE1C acted as a sponge for miR-214b-3p binding sites thereby regulating the expression of STAT3. The overexpression of miR-214b-3p rescued the pro-inflammatory effect of circDCLRE1C in HD11 cells stimulated with LPS, and rescued the high expression of STAT3. In conclusion, our study showed that circDCLRE1C could aggravate LPS-induced inflammation and apoptosis through competitive adsorption of miR-214b-3p, thereby increasing the expression of STAT3.

Fast and slow myofiber-specific expression profiles are affected by noncoding RNAs in Mongolian horses

The heterogeneity and plasticity of muscle fibers are essential for the athletic performance of horses, mainly at the adaption of exercises and the effect on muscle diseases. Skeletal muscle fibers can be generally distinguished by their characteristics of contraction as slow and fast type myofibers. The diversity of contractile properties and metabolism enable skeletal muscles to respond to the variable functional requirements. We investigated the muscle fiber composition and metabolic enzyme activities of splenius muscle and gluteus medius muscle from Mongolian horses. The deep RNA-seq analysis of detecting differentially expressed mRNAs, lncRNAs, circRNAs and their correlation analysis from two muscles were performed. Splenius muscle and gluteus medius muscle from Mongolian horses showed a high divergence of myofiber compositions and metabolic enzyme activities. Corresponding to their phenotypic characteristics, 57 differentially expressed long noncoding RNAs and 12 differentially expressed circle RNAs were found between two muscles. The analysis results indicate multiple binding sites were detected in lncRNAs and circRNAs with myofiber-specific expressed miRNAs. Among which we found significant correlations between the above noncoding RNAs, miRNAs, their target genes, myofiber-specific developmental transcript factors, and sarcomere genes. We suggest that the ceRNA mechanism of differentially expressed noncoding RNAs by acting as miRNA sponges could be fine tuners in regulating skeletal muscle fiber composition and transition in horses, which will operate new protective measures of muscle disease and locomotor adaption for racehorses.

Exosomal RNAs: Novel Potential Biomarkers for Diseases-A Review

Exosomes are a subset of nano-sized extracellular vesicles originating from endosomes. Exosomes mediate cell-to-cell communication with their cargos, which includes mRNAs, miRNAs, lncRNAs, and circRNAs. Exosomal RNAs have cell specificity and reflect the conditions of their donor cells. Notably, their detection in biofluids can be used as a diagnostic marker for various diseases. Exosomal RNAs are ideal biomarkers because their surrounding membranes confer stability and they are detectable in almost all biofluids, which helps to reduce trauma and avoid invasive examinations. However, knowledge of exosomal biomarkers remains scarce. The present review summarizes the biogenesis, secretion, and uptake of exosomes, the current researches exploring exosomal mRNAs, miRNAs, lncRNAs, and circRNAs as potential biomarkers for the diagnosis of human diseases, as well as recent techniques of exosome isolation.

Circular RNA PIP5K1A act as microRNA-552-3p sponge to regulates inflammation, oxidative damage in glucolipotoxicity-induced pancreatic INS-1 β-cells via Janus kinase 1

Elevated level of glucolipotoxicity induces the loss of pancreatic β-cells functions and plays an important role in the development of type 2 diabetes (T2DM). Previous studies have indicated the importance of developing therapies against T2DM, while circular RNA (circRNA) has gained attraction as a modulator of pancreatic β-cell function. In the present study role of circPIP5K1A in dysfunctional β cells and mouse pancreas was comprehensively analyzed. INS-1E, as it has close similarity with naïve pancreatic β-cells, and clinical samples of T2DM patients were used to investigate the effect of circPIP5K1A, miR-552-3p, and Janus kinase 1 (JAK1). While, INS-1E cells were exposed to PAHG conditions (0.5 mM palmitic acid and 28 mM glucose) as studies have suggested that increased level of fatty acid and glucose resulted in autophagy activation of pancreatic β-cells that leads to T2DM. Key player of JAK1-STAT3 pathway and the level of Reactive Oxygen Species, inflammatory factors, and insulin secretion was detected to analyze the of the active association of circPIP5K1A, miR-552-3p with JAK1pathway. Our study has revealed the elevated level ofcircPIP5K1A and JAK1, but reduced level of miR-552-3pin the serum of T2DM patients. Furthermore, we also found that reduced expression ofcircPIP5K1A leads to decreased rate of inflammation, oxidative damage and apoptosisinINS-1E cells induced by glucolipotoxicity. CircPIP5K1A was available to competitively combine with miR-552-3p, while whose direct target was JAK1. In conclusion, our study suggested a novel involvement of circPIP5K1A in a cross talk between miR5523p/JAK1/STAT3 pathways in β-cells as a new therapeutic target for T2DM.  

Evaluation of CircRNA Sequence Assembly Methods Using Long Reads

The functional study on circRNAs has been increasing in the past decade due to its important roles in micro RNA sponge, protein coding, the initiation, and progression of diseases. The study of circRNA functions depends on the full-length sequences of circRNA, and current sequence assembly methods based on short reads face challenges due to the existence of linear transcript. Long reads produced by long-read sequencing techniques such as Nanopore technology can cover full-length sequences of circRNA and therefore can be used to evaluate the correctness and completeness of circRNA full sequences assembled from short reads of the same sample. Using long reads of the same samples, one from human and the other from mouse, we have comprehensively evaluated the performance of several well-known circRNA sequence assembly algorithms based on short reads, including circseq_cup, CIRI_full, and CircAST. Based on the F1 score, the performance of CIRI-full was better in human datasets, whereas in mouse datasets CircAST was better. In general, each algorithm was developed to handle special situations or circumstances. Our results indicated that no single assembly algorithm generated better performance in all cases. Therefore, these assembly algorithms should be used together for reliable full-length circRNA sequence reconstruction. After analyzing the results, we have introduced a screening protocol that selects out exonic circRNAs with full-length sequences consisting of all exons between back splice sites as the final result. After screening, CIRI-full showed better performance for both human and mouse datasets. The average F1 score of CIRI-full over four circRNA identification algorithms increased from 0.4788 to 0.5069 in human datasets, and it increased from 0.2995 to 0.4223 in mouse datasets.

RNA Sequencing Reveals circRNA Expression Profiles in Chicken DF1 Cells Infected with H5N1 Influenza Virus

Simple Summary

H5N1 is a highly pathogenic avian influenza virus that seriously harms the poultry industry and public health worldwide. However, its pathogenesis is still not well understood. In this study, we analyzed the expression profile of circular RNAs (circRNAs) in H5N1-infected chicken embryo fibroblast (DF1) cells and found their expression to change more significantly as the infection was extended. Differentially expressed circRNAs were significantly enriched in terms relating to virus replication and immune response, suggesting that circRNAs play important roles in the pathogenesis of H5N1 infection. Our study provides new insights into the mechanisms underlying H5N1–host interaction.

Abstract

H5N1, a highly pathogenic avian influenza virus that is prevalent in Asia, seriously harms the poultry industry and global public health. However, its pathogenesis is still not well understood. Circular RNAs (circRNAs), a newly identified type of RNA, reportedly play crucial roles in various pathogenic processes. In this study, RNA sequencing was performed to analyze the expression profile of circRNAs in H5N1-infected chicken embryo fibroblast (DF1) cells. A total of 14,586 circRNAs were identified. The expression profiles of infected cells changed more significantly, relative to uninfected cells, as the infection period was extended; namely, 261, 626, and 1103 circRNAs exhibited differential expression in cells infected for 6 h, 12 h, and 20 h, respectively. GO and KEGG enrichment analysis revealed significant enrichment of the parental genes of the differentially expressed circRNAs for viral replication and immune response-related pathways, such as positive regulation of transcription from the RNA polymerase II promoter, positive regulation of I-kappaB kinase/NF-kappaB signaling, innate immune response, and ubiquitin protein ligase activity. In conclusion, we identified the expression profile of circRNAs in H5N1-infected chicken DF1 cells. Bioinformatic analyses of the dysregulated circRNAs suggest that circRNAs might play important roles in the pathogenesis of H5N1 infection, offering new insights into the mechanisms underlying H5N1–host interaction.

Crosstalk between N6-methyladenosine modification and circular RNAs: current understanding and future directions

N⁶-methyladenosine (m⁶A) is a prevalent internal modification in eukaryotic RNAs regulated by the so-called "writers", "erasers", and "readers". m⁶A has been demonstrated to exert critical molecular functions in modulating RNA maturation, localization, translation and metabolism, thus playing an essential role in cellular, developmental, and disease processes. Circular RNAs (circRNAs) are a class of non-coding RNAs with covalently closed single-stranded structures generated by back-splicing. CircRNAs also participate in physiological and pathological processes through unique mechanisms. Despite their discovery several years ago, m⁶A and circRNAs has drawn increased research interest due to advances in molecular biology techniques these years. Recently, several scholars have investigated the crosstalk between m⁶A and circRNAs. In this review, we provide an overview of the current knowledge of m⁶A and circRNAs, as well as summarize the crosstalk between these molecules based on existing research. In addition, we present some suggestions for future research perspectives.

Circular RNA circZFPM2 promotes epithelial-mesenchymal transition in endometriosis by regulating miR-205-5p/ZEB1 signalling pathway

Endometriosis is a debilitating gynecological disease affecting millions of women worldwide, but its exact pathogenesis remains unclear. Circular RNAs (circRNAs) have been demonstrated to be important regulators in multiple diseases. Nonetheless, the potential regulatory mechanism of aberrant circRNA expression in endometriosis has been elusive. The up-regulated circZFPM2 in ectopic endometrial tissues was previously screened by circRNA high-throughput sequencing and was furtherly validated by quantitative real time reverse transcriptase polymerase chain reaction (RT-qPCR). Overexpression of circZFPM2 promoted the proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) in Ishikawa and End1/E6E7 cells, whereas silencing circZFPM2 produced the opposite effect. Luciferase reporter assays validated that circZFPM2 could directly target miR-205-5p and miR-205-5p target ZEB1. RT-qPCR results showed that miR-205-5p was underexpressed while ZEB1 was overexpressed in ectopic endometrial tissues compared with their expression in eutopic endometria and non-endometriosis control endometria. The expression level of miR-205-5p was inversely proportional and that of ZEB1 was directly proportional with the proliferative, migrative, and invasive ability of endometrial cells. Further in vitro investigation indicated that miR-205-5p could inhibit EMT by targeting ZEB1. Subsequent rescue experiments confirmed that circZFPM2 could induce EMT and promote cell proliferation, migration, and invasion cascades through the miR-205-5p /ZEB1 signaling pathway. Conclusively, circZFPM2 may present a promising biomarker in the diagnosis and treatment of endometriosis.