Transcriptome-wide discovery of circular RNAs in Archaea

Hsa_circ_0008085 acts as a miR-146a-5p sponge to suppress influenza a virus replication via modulating of TRAF6

Influenza A virus (IAV) has attracted considerable attention in recent years due to its increase in incidence and threat to human health. Circular RNA (circRNA) is a non-coding RNA with a closed structural pattern, which often acts as a sponge for microRNAs (miRNAs) in the cell. A growing body of evidence supports several crucial roles for circRNAs in viral infection, including regulation of viral replication, evasion of the host immune response and disease pathogenesis. However, due to the wide variety of circRNAs, their potential functions in IAV infection remain to be elucidated. In this study, we determined that the expression of hsa_circ_0008085 was induced by IAV infection. In addition, the JAK/STAT signaling pathway was associated with the induction of hsa_circ_0008085 in the context of IAV infection, as evidenced by the application of ruxolitinib, a compound that inhibits the activation of the JAK/STAT pathway. In A549 cells, enhanced expression of hsa_circ_0008085 was found to repress viral gene expression and diminish the production of infectious progeny. In contrast, when hsa_circ_0008085 was knocked down, a significant boost in IAV replication was observed. Following a pull-down of RNA utilizing biotin and a luciferase reporter assay, we established that hsa_circ_0008085 binds with miR-146a-5p, functioning as an endogenous sponge that suppresses the activity of miR-146a-5p. This interaction leads to an upregulation of TRAF6 expression, which in turn inhibits the replication of IAV. Conclusively, these data demonstrate that hsa_circ_0008085 inhibits viral replication via the miR-146a-5p/TRAF6 axis, highlighting the promising role of circRNAs in antiviral therapies.

Identification of biomarkers of male infertility through the circRNA expression profiling of seminal plasma

Circular RNAs (circRNAs) are key regulators of reproductive biology. However, limited information is available regarding circRNA expression profiles in seminal plasma samples from individuals with male infertility. The present study aimed to identify circRNAs associated with infertility in seminal plasma samples and to clarify their potential as biomarkers, as well as the possible molecular mechanisms underlying their functions. Next-generation RNA sequencing was conducted to analyze circRNA profiles in seminal plasma from healthy controls, oligoasthenospermia (OAZ) patients, and non-obstructive azoospermia (NOA) patients. Bioinformatics analysis revealed that 637 circRNAs were differentially expressed between OAZ and control subjects, as well as 272 circRNAs that were differentially expressed between NOA and control subjects. The expression of key circRNAs ( hsa-SAP130_0002, hsa-TRPC1_0001, hsa-FBRS_0001, hsa-ACACA_0025, hsa-UTRN_0042, and hsa-ZNF532_0023) was then validated by qPCR, and their diagnostic accuracy for infertility was confirmed through ROC curve analysis. Additionally, possible circRNA-miRNA-mRNA regulatory networks were developed for these candidate biomarkers. Collectively, this study identifies a novel set of circRNAs with potential as diagnostic biomarkers for male infertility and provides molecular insights that may facilitate both diagnostic and therapeutic efforts.

The crosstalk between non-coding RNAs and oxidative stress in cancer progression

As living standards elevate, cancers are appearing in growing numbers among younger individuals globally and these risks escalate with advancing years. One of the reasons is that instability in the cancer genome reduces the effectiveness of conventional drug treatments and chemotherapy, compared with more targeted therapies. Previous research has discovered non-coding RNAs' crucial role in shaping genetic networks involved in cancer cell growth and invasion through their influence on messenger RNA production or protein binding. Additionally, the interaction between non-coding RNAs and oxidative stress, a crucial process in cancer advancement, cannot be overlooked. Essentially, oxidative stress results from the negative effects of radicals within the body and ties directly to cancer gene expression and signaling. Therefore, this review focuses on the mechanism between non-coding RNAs and oxidative stress in cancer progression, which is conducive to finding new cancer treatment strategies.

Effects of circPICALM-miR-132-PHKB regulated by METTL3 on proliferation of porcine skeletal muscle satellite cells

Circular RNA (circRNA) is ubiquitously expressed in highly differentiated eukaryotes, playing an extremely vital regulatory role in muscle growth and development. In this study, we identified circPICALM, a novel circRNA which consists of exons 5 to 9 of the PICALM gene, exhibiting differential expression in the longissimus dorsi muscle (LD) of adult (QA) and newborn (QN) Queshan Black pigs. CircPICALM is resistant to RNase R, mainly located in the cytoplasm with potential coding capacities. When circPICALM was over-expressed in porcine skeletal muscle satellite cells (PSMSCs), there was a significant decrease in the expression levels of PCNA, CDK4, CDK1 and CCND1, which consequently inhibited the proliferation of PSMSCs. Conversely, miR-132, a target molecule of circPICALM, was found to promote the proliferation of PSMSCs. In addition, circPICALM can up-regulate the expression of the target gene PHKB by competitively adsorbing miR-132. The circPICALM-ssc-miR-132-PHKB regulatory axis is regulated by METTL3, which increases the m6A level of both PSMSCs and circPICALM, thereby promoting the proliferation of PSMSCs. Overall, this study furnishes a fundamental reference for further in-depth exploration of the specific molecular mechanisms underlying m6A modification and circPICALM in muscle development and progression.

Structural and biochemical characterization of the 3'-5' tRNA splicing ligases

In archaea and metazoa, tRNA exons are ligated by the RNA ligases RtcB and RTCB, respectively. The metazoan RTCB forms a stable complex with four additional subunits, DDX1, FAM98B, CGI99, and ASHWIN. The role and assembly of these four components remain elusive. Furthermore, we lack structural information of how RNA substrates are recognized by 3'-5' tRNA ligases. Here, we use thiol-based chemical crosslinking to confirm the involvement of specific residues of RtcB in RNA binding, and we present a cryo-EM structure of the purified five-subunit Danio rerio tRNA ligase complex. The structure implies that the DDX1 helicase module is mobile and can modulate the activity of RTCB. Taken together, the presented results enhance our mechanistic understanding of RNA binding by 3'-5' tRNA splicing ligases and architecture of the metazoan tRNA ligase complex.

Circular RNA transcriptome across various development periods of Paralichthys olivaceus reveal skeletal muscle-specific circchd6 regulating myogenesis

The Japanese flounder (Paralichthys olivaceus) is greatly influenced in terms of muscle quality and quantity by the development of skeletal muscle. While the mechanisms underlying skeletal muscle development are well-studied, the role of non-coding RNAs, particularly circRNAs, in the skeletal muscle development of Japanese flounder remains unclear. To investigate the expression patterns of circRNAs during different developmental stages (JP1: 7 days, JP2: 90 days, JP3: 24 months (female), JP4: 24 months (male)) in Japanese flounder, we performed transcriptome sequencing analysis. We identified a total of 3523 circRNAs, of which 10.19 % were differentially expressed. These differentially expressed (DE) circRNAs were studied, and their impacts on muscle development were analyzed. The RNA interaction network revealed that skeletal muscle-specific circchd6 targeted novel-miR-508 and further regulated dual specificity tyrosine-phosphorylation regulated kinase 2 (dyrk2). Functional analysis showed that overexpressed circchd6 and dyrk2 promoted myoblast proliferation and differentiation, while novel-miR-508 inhibited both. Our study identified the circchd6-novel-miR-508-dyrk2 axis as a regulatory mechanism and provided new evidence for the use of epigenetic approaches in genetic breeding.

Circular RNAs in neurological conditions - computational identification, functional validation, and potential clinical applications

Non-coding RNAs (ncRNAs) have gained significant attention in recent years due to advancements in biotechnology, particularly high-throughput total RNA sequencing. These developments have led to new understandings of non-coding biology, revealing that approximately 80% of non-coding regions in the genome possesses biochemical functionality. Among ncRNAs, circular RNAs (circRNAs), first identified in 1976, have emerged as a prominent research field. CircRNAs are abundant in most human cell types, evolutionary conserved, highly stable, and formed by back-splicing events which generate covalently closed ends. Notably, circRNAs exhibit high expression levels in neural tissue and perform diverse biochemical functions, including acting as molecular sponges for microRNAs, interacting with RNA-binding proteins to regulate their availability and activity, modulating transcription and splicing, and even translating into functional peptides in some cases. Recent advancements in computational and experimental methods have enhanced our ability to identify and validate circRNAs, providing valuable insights into their biological roles. This review focuses on recent developments in circRNA research as they related to neuropsychiatric and neurodegenerative conditions. We also explore their potential applications in clinical diagnostics, therapeutics, and future research directions. CircRNAs remain a relatively underexplored area of non-coding biology, particularly in the context of neurological disorders. However, emerging evidence supports their role as critical players in the etiology and molecular mechanisms of conditions such as schizophrenia, bipolar disorder, major depressive disorder, Alzheimer's disease, and Parkinson's disease. These findings suggest that circRNAs may provide a novel framework contributing to the molecular dysfunctions underpinning these complex neurological conditions.

CircZmMED16 delays plant flowering by negatively regulating starch content through its binding to ZmAPS1

Circular RNAs (circRNAs), a type of head-to-tail closed RNA molecules, have been implicated in various aspects of plant development and stress responses through transcriptome sequencing; however, the precise functional roles of circRNAs in plants remain poorly understood. In this study, we identified a highly expressed circular RNA, circZmMED16, derived from exon 8 of the mediator complex subunit 16 (ZmMED16) across different maize (Zea mays L.) inbred lines using circRNA-seq analysis. This circRNA is predominantly expressed in maize tassels and functions in the cytoplasm. Overexpression of circZmMED16 resulted in increased expression of ZmMED16/AtMED16 and delayed flowering in both maize and Arabidopsis thaliana, compared with that in wild-type plants. In contrast, overexpression of the parent gene ZmMED16 did not alter the flowering time of transgenic plants in Arabidopsis, suggesting that circZmMED16 plays a specific role in regulating flowering, distinct from that of linear ZmMED16. To further understand the mechanisms underlying the regulation of flowering time by circZmMED16, we performed RNA pull-down, dual-luciferase, RNA interference (RNAi), and ribonuclease protection assays (RPA). These results indicate that circZmMED16 interacts with small subunit 1 of ADP-glucose pyrophosphorylase (APS1) mRNA in both maize and Arabidopsis. The knockdown of circZmMED16 increased the expression of ZmAPS1, whereas the overexpression of circZmMED16 led to the downregulation of ZmAPS1 RNA and protein. By affecting ZmAPS1 expression, circZmMED16 reduced ADP-glucose pyrophosphorylase (AGPase) activity and led to delayed flowering. These results revealed a novel regulatory mechanism for circRNAs in flowering time and shed light on their functional and regulatory roles in plants.

Functions and application of circRNAs in vascular aging and aging-related vascular diseases

Circular RNAs (circRNAs), constituting a novel class of endogenous non-coding RNAs generated through the reverse splicing of mRNA precursors, possess the capacity to regulate gene transcription and translation. Recently, the pivotal role of circRNAs in controlling vascular aging, as well as the pathogenesis and progression of aging-related vascular diseases, has garnered substantial attention. Vascular aging plays a crucial role in the increased morbidity and mortality of the elderly. Endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) are crucial components of the intima and media layers of the vascular wall, respectively, and are closely involved in the mechanisms underlying vascular aging and aging-related vascular diseases. The review aims to provide a comprehensive exploration of the connection between circRNAs and vascular aging, as well as aging-related vascular diseases. Besides, circRNAs, as potential diagnostic markers or therapeutic targets for vascular aging and aging-related vascular diseases, will be discussed thoroughly, along with the challenges and limitations of their clinical application. Investigating the role and molecular mechanisms of circRNAs in vascular aging and aging-related vascular diseases will provide a novel insight into early diagnosis and therapy, and even effective prognosis assessment of these conditions.

Circ_0011446 Regulates Intramuscular Adipocyte Differentiation in Goats via the miR-27a-5p/FAM49B Axis

Intramuscular fat (IMF), or marbling, is a critical indicator of goat meat quality. Non-coding RNAs play a key role in the formation and deposition of IMF in vertebrates by regulating genes involved in its synthesis, degradation, and transport. The competing endogenous RNA (ceRNA) hypothesis identifies circular RNAs (circRNAs) as natural "sponges" for microRNAs (miRNAs). However, the precise mechanisms of circRNAs in goat IMF remain poorly understood. In the current study, we utilized existing sequencing data to construct a ceRNA regulatory network associated with intramuscular adipogenesis and fat deposition in goats. Our goal was to elucidate the post-transcriptional regulatory mechanism of family with sequence similarity 49 member B (FAM49B). Functionally, FAM49B was found to inhibit the differentiation of intramuscular preadipocytes and to directly interact with miR-27a-5p. Mechanistically, dual-luciferase reporter assays and quantitative real-time PCR (qRT-PCR) confirmed the interaction between circ0011446 and miR-27a-5p. Circ0011446 enhanced the expression of FAM49B mRNA and protein through post-transcriptional regulation. As a ceRNA, circ0011446 competitively binds miR-27a-5p, preventing miR-27a-5p from degrading FAM49B. In conclusion, our findings demonstrate that circ0011446 suppresses goat adipogenic differentiation of intramuscular preadipocytes by regulating the expression of the downstream target gene FAM49B through miR-27a-5p sequestration. This study provides a reference for goat meat quality or livestock breeding.

Species-specific circular RNA circDS-1 enhances adaptive evolution in Talaromyces marneffei through regulation of dimorphic transition

Thermal adaptability is a crucial characteristic for mammalian pathogenic fungi that originally inhabit natural ecosystems. Thermally dimorphic fungi have evolved a unique ability to respond to host body temperature by shifting from mycelia to yeast. The high similarity of protein-coding genes between these fungi and their relatives suggests the indispensable but often overlooked roles of non-coding elements in fungal thermal adaptation. Here, we systematically delineated the landscape of full-length circRNAs in both mycelial and yeast conditions of Talaromyces marneffei, a typical thermally dimorphic fungus causing fatal Talaromycosis, by optimizing an integrative pipeline for circRNA detection utilizing next- and third-generation sequencing. We found T. marneffei circRNA demonstrated features such as shorter length, lower abundance, and circularization-biased splicing. We then identified and validated that circDS-1, independent of its parental gene, promotes the hyphae-to-yeast transition, maintains yeast morphology, and is involved in virulence regulation. Further analysis and experiments among Talaromyces confirmed that the generation of circDS-1 is driven by a T. marneffei-specific region in the flanking intron of circDS-1. Together, our findings not only provide fresh insights into the role of circRNA in fungal thermal adaptation but also reveal a novel molecular mechanism for the adaptive evolution of functional circRNAs derived from intronic mutations.

Predicting circRNA-Disease Associations through Multisource Domain-Aware Embeddings and Feature Projection Networks

Recent studies have highlighted the significant role of circular RNAs (circRNAs) in various diseases. Accurately predicting circRNA-disease associations is crucial for understanding their biological functions and disease mechanisms. This work introduces the MNDCDA method, designed to address the challenges posed by the limited number of known circRNA-disease associations and the high cost of biological experiments. MNDCDA integrates multiple biological data sources with neighborhood-aware embedding models and deep feature projection networks to predict potential pathways linking circRNAs to diseases. Initially, comprehensive biometric data are used to construct four similarity networks, forming a diverse circRNA-disease interaction framework. Next, a neighborhood-aware embedding model captures structural information about circRNAs and diseases, while deep feature projection networks learn high-order feature interactions and nonlinear connections. Finally, a bilinear decoder identifies novel associations between circRNAs and diseases. The MNDCDA model achieved an AUC of 0.9070 on a constructed benchmark dataset. In case studies, 25 out of 30 predicted circRNA-disease pairs were validated through wet lab experiments and published literature. These extensive experimental results demonstrate that MNDCDA is a robust computational tool for predicting circRNA-disease associations, providing valuable insights while helping to reduce research costs.

Circular RNA circPFKP suppress gastric cancer progression through targeting miR-346/CAMD3 axis

Studies have demonstrated that circular RNAs (circRNAs) exert an important regulatory function in the pathogenesis of various tumors. However, their role in gastric cancer (GC) is still not completely understood. In our study, the differentially expressed circRNAs in GC tissues and matched adjacent normal tissues were analyzed by utilizing gene chips GSE93541, GSE89143, and GSE78092. The expression of has_circ_0006608 (circPFKP), miR-346, and CAMD3 was analyzed through quantitative real-time polymerase chain reaction (qRT-PCR). The CCK-8 assay and Transwell assay were employed to detect the effect of circPFKP on the proliferation, migration, and invasion of gastric cancer cells. The mice xenograft assay was used to assess the function of circPFKP in vivo. The targeting relationship between circPFKP, miR-346, and CAMD3 was predicted by bioinformatics analysis and confirmed by the dual-luciferase reporter assay and RNA pull-down assay. Our results screened and verified that circPFKP was down-regulated in gastric cancer tissues and cells. Overexpression of circPFKP in GC cells can inhibit cell proliferation, migration, invasion, and tumor growth in vivo. Additionally, circPFKP has been shown to act as a sponge for miR-346 to modulate the expression of CAMD3. Finally, we demonstrated that overexpression of CAMD3 or miR-346 inhibitor significantly reversed the effects of si-circPFKP on the proliferation, migration, and invasion of gastric cancer cells. In conclusion, this study provided that circPFKP inhibits the progression of GC via the miR-346/CAMD3 axis, this may provide a noval biomarker for the diagnosis and treatment of GC.

Transcriptome Analysis of Muscle Growth-Related circRNA in the Pacific Abalone Haliotis discus hanna

(1) Background: Animal growth is a complex process, involving the coordination of a wide variety of genes, non-coding RNAs, and pathways. Circular RNAs (circRNAs) belong to a novel class of functional non-coding RNAs (ncRNAs). They have a distinctive ring structure and are involved in various biological processes, including the proliferation, differentiation, and apoptosis of muscle cells. The Pacific abalone Haliotis discus hannai is an economically valuable mollusk species cultivated in China. However, the modulation of muscle growth by circRNAs in this species is poorly understood. (2) Methods: In this study, we analyzed the muscle transcriptomes of 6 H. discus hannai specimens: three small (S_HD) and three large (L_HD) groups via RNA-seq and bioinformatics technology. (3) Results: The results indicated the presence of 11,744 circRNAs in abalone adductor muscle. Furthermore, the L_HD group had 250 significantly differentially expressed circRNAs (106 upregulated and 144 downregulated) relative to the S_HD group. Moreover, the bioinformatics assessment revealed that circRNAs were related to lipid transporter activity, lipid biosynthetic process, fat digestion and absorption, the single-organism metabolic process, the thyroid hormone signaling pathway, and the hippo signaling pathway, which regulates growth. Seventeen key candidate circRNAs were identified, and a core functional circRNA-miRNA-mRNA network associated with abalone muscle growth was described. Gene expression was verified using qRT-PCR, confirming the accuracy of the RNA-seq data. (4) Conclusion: Overall, this investigation furnishes novel evidence for the potential muscle growth modulatory mechanisms in Pacific abalone. These high-quality circRNA data of abalone muscle provide a reference for functional studies on the abalone genome.

PlantCircRNA: a comprehensive database for plant circular RNAs

Circular RNAs (circRNAs) represent recently discovered novel regulatory non-coding RNAs. While they are present in many eukaryotes, there has been limited research on plant circRNAs. We developed PlantCircRNA (https://plant.deepbiology.cn/PlantCircRNA/) to fill this gap. The two most important features of PlantCircRNA are (i) it incorporates circRNAs from 94 plant species based on 39 245 RNA-sequencing samples and (ii) it imports the original AtCircDB and CropCircDB databases. We manually curated all circRNAs from published articles, and imported them into the database. Furthermore, we added detailed information of tissue as well as abiotic stresses to the database. To help users understand these circRNAs, the database includes a detection score to measure their consistency and a naming system following the guidelines recently proposed for eukaryotes. Finally, we developed a comprehensive platform for users to visualize, analyze, and download data regarding specific circRNAs. This resource will serve as a home for plant circRNAs and provide the community with unprecedented insights into these mysterious molecule.

Hsa_circ_0023179 modulated the processes of proliferation, apoptosis, and EMT in non-small cell lung cancer cells via the miR-615-5p/CDH3 axis

Circular RNA (circRNA) has been widely studied as a competitive endogenous RNA targeting microRNA (miRNA)/messenger RNA to regulate cancer progression. However, the regulatory mechanism of circ_0023179 in non-small cell lung cancer (NSCLC) remains unclear. The expression levels of circ_0023179, miR-615-5p and Cadherin 3 (CDH3) in NSCLC were detected using quantitative real-time polymerase chain reaction. The stability of circ_0023179 was verified using ribonuclease R enzyme, actinomycin D and agarose gel electrophoresis. Colony formation and thymidine analog 5-ethynyl-2'-deoxyuridine assays were performed to examine proliferation changes in NSCLC cells. Western blot was used to assess the levels of CDH3 and epithelial-mesenchymal transition (EMT)-related marker proteins to evaluate EMT. Dual-luciferase reporter, RNA immunoprecipitation (RIP), and RNA pull-down assays were performed to explore the potential mechanisms of circ_0023179 in regulating NSCLC progression. Finally, the effects of circ_0023179 on NSCLC tumour growth in vivo were explored using a nude mouse subcutaneous tumour model. The results showed that the expression of circ_0023179 was remarkably higher in NSCLC tissues and cells, and it had a significant effect on NSCLC cell proliferation. Additionally, the knockdown of circ_0023179 significantly inhibited tumour growth in NSCLC mice. Mechanistically, circ_0023179 alleviated its inhibition of downstream CDH3 through the sponge-like adsorption of miR-615-5p. The downregulation of miR-615-5p and the upregulation of CDH3 mitigated the inhibitory effect of silencing circ_0023179 on NSCLC cell proliferation. In conclusion, silencing circ_0023179 inhibited NSCLC cell proliferation by targeting the miR-615-5p/CDH3 axis involved in NSCLC progression.

RNase W, a conserved ribonuclease family with a novel active site

Ribosome biogenesis is a complex process requiring multiple precursor ribosomal RNA (rRNA) cleavage steps. In archaea, the full set of ribonucleases (RNases) involved in rRNA processing remains to be discovered. A previous study suggested that FAU-1, a conserved protein containing an RNase G/E-like protein domain fused to a domain of unknown function (DUF402), acts as an RNase in archaea. However, the molecular basis of this activity remained so far elusive. Here, we report two X-ray crystallographic structures of RNase G/E-like-DUF402 hybrid proteins from Pyrococcus furiosus and Sulfolobus acidocaldarius, at 2.1 and 2.0 Å, respectively. The structures highlight a structural homology with the 5' RNA recognition domain of Escherichia coli RNase E but no homology with other known catalytic nuclease domains. Surprisingly, we demonstrate that the C-terminal domain of this hybrid protein, annotated as a putative diphosphatase domain, harbors the RNase activity. Our functional analysis also supports a model by which the RNase G/E-like domain acts as a regulatory subunit of the RNase activity. Finally, in vivo experiments in Haloferax volcanii suggest that this RNase participates in the maturation of pre-16S rRNA. Together, our study defines a new RNase family, which we termed the RNase W family, as the first archaea-specific contributor to archaeal ribosome biogenesis.

SGTCDA: Prediction of circRNA-drug sensitivity associations with interpretable graph transformers and effective assessment

CircRNAs are a type of circular non-coding RNA whose associations with drug sensitivities have been demonstrated in recent studies. Due to the high cost of biomedical experiments for detecting the associations between circRNAs and drug sensitivities, several computational methods have been developed. However, these methods were evaluated mainly based on 5- or tenfold cross-validation, which are often over-optimistic. Furthermore, there are technique issues with these models, such as over-smoothing and over-squashing. To address these issues, we propose a strategy to evaluate models based on independent test sets for association prediction-related studies. In the light of this effective assessment, we constructed a model, SGTCDA, by integrating structural deep network embedding (SDNE) and a graph transformer to predict the potential associations of circRNA-drug sensitivity, which can efficiently capture long-range dependencies and local structural information of nodes. Our results on the training sets and the independent test sets indicate that SGTCDA outperforms the other state-of-the-art models, demonstrating its capacity for accurate prediction of circRNA-drug sensitivity. Moreover, we leveraged EdgeSHAPer to explain the performance of the proposed SGTCDA model, which illustrates that the edges between drugs are more important than other edges for the performance of the model. The source code and dataset of SGTCDA are available at: https://github.com/hwxia/SGTCDA .

Expression and drought functional analysis of one circRNA PecircCDPK from moso bamboo (Phyllostachys edulis)

Drought stress can affect the growth of bamboo. Circle RNAs (CircRNAs) have been found to play a role in drought stress in plants, but their function in moso bamboo is not well understood. In previous studies, we observed that under drought stress, the expression of some circRNAs were altered and predicted to be involved in calcium-dependent protein kinase phosphorylation, as indicated by KEGG enrichment analysis. In this study, we cloned a circRNA called PecircCDPK in moso bamboo that is responsive to drought stress. To further investigate its function, we constructed an overexpression vector using flanking intron sequences supplemented by reverse complementary sequences. When this vector was transferred to Arabidopsis plants, we observed that the roots of the transgenic lines were more developed, the water loss rate decreased, the stomata became smaller, and the activity of antioxidant enzymes increased under drought stress. These findings suggest that overexpression of PecircCDPK can enhance the drought resistance of Arabidopsis thaliana, providing valuable insights for the breeding of moso bamboo with improved resistance to drought.

Therapeutic importance and diagnostic function of circRNAs in urological cancers: from metastasis to drug resistance

Circular RNAs (circRNAs) are a member of non-coding RNAs with no ability in encoding proteins and their aberrant dysregulation is observed in cancers. Their closed-loop structure has increased their stability, and they are reliable biomarkers for cancer diagnosis. Urological cancers have been responsible for high mortality and morbidity worldwide, and developing new strategies in their treatment, especially based on gene therapy, is of importance since these malignant diseases do not respond to conventional therapies. In the current review, three important aims are followed. At the first step, the role of circRNAs in increasing or decreasing the progression of urological cancers is discussed, and the double-edged sword function of them is also highlighted. At the second step, the interaction of circRNAs with molecular targets responsible for urological cancer progression is discussed, and their impact on molecular processes such as apoptosis, autophagy, EMT, and MMPs is highlighted. Finally, the use of circRNAs as biomarkers in the diagnosis and prognosis of urological cancer patients is discussed to translate current findings in the clinic for better treatment of patients. Furthermore, since circRNAs can be transferred to tumor via exosomes and the interactions in tumor microenvironment provided by exosomes such as between macrophages and cancer cells is of importance in cancer progression, a separate section has been devoted to the role of exosomal circRNAs in urological tumors.

The role of circular RNA during the urological cancer metastasis: exploring regulatory mechanisms and potential therapeutic targets

Metastasis is a major contributor to treatment failure and death in urological cancers, representing an important biomedical challenge at present. Metastases form as a result of cancer cells leaving the primary site, entering the vasculature and lymphatic vessels, and colonizing clones elsewhere in the body. However, the specific regulatory mechanisms of action underlying the metastatic process of urological cancers remain incompletely elucidated. With the deepening of research, circular RNAs (circRNAs) have been found to not only play a significant role in tumor progression and prognosis but also show aberrant expression in various tumor metastases, consequently impacting tumor metastasis through multiple pathways. Therefore, circRNAs are emerging as potential tumor markers and treatment targets. This review summarizes the research progress on elucidating how circRNAs regulate the urological cancer invasion-metastasis cascade response and related processes, as well as their role in immune microenvironment remodeling and circRNA vaccines. This body of work highlights circRNA regulation as an emerging therapeutic target for urological cancers, which should motivate further specific research in this regard.

Exosomal circZNF800 Derived from Glioma Stem-like Cells Regulates Glioblastoma Tumorigenicity via the PIEZO1/Akt Axis

Exosomes play a crucial role in regulating crosstalk between tumor and tumor stem-like cells through their cargo molecules. Circular RNAs (circRNAs) have recently been demonstrated to be critical factors in tumorigenesis. This study focuses on the molecular mechanism by which circRNAs from glioma stem-like cell (GSLC) exosomes regulate glioblastoma (GBM) tumorigenicity. In this study, we validated that GSLC exosomes accelerated the malignant phenotype of GBM. Subsequently, we found that circZNF800 was highly expressed in GSLC exosomes and was negatively associated with GBM patients. CircZNF800 promoted GBM cell proliferation and migration and inhibited GBM cell apoptosis in vitro. Silencing circZNF800 could improve the GBM xenograft model survival rate. Mechanistic studies revealed that circZNF800 activated the PIEZO1/Akt signaling pathway by sponging miR-139-5p. CircZNF800 derived from GSLC exosomes promoted GBM cell tumorigenicity and predicted poor prognosis in GBM patients. CircZNF800 has the potential to serve as a promising target for further therapeutic exploration.

Emerging Roles of Circular RNA in Macrophage Activation and Inflammatory Lung Responses

Circular RNA (circRNA) is a type of single-stranded RNA that forms a covalently closed continuous loop, unlike linear RNA. The expression of circRNAs in mammals is often conserved across species and shows tissue and cell specificity. Some circRNA serve as gene regulators. However, the biological function of most circRNAs is unclear. CircRNA does not have 5' or 3' ends. The unique structure of circRNAs provides them with a much longer half-life and more resistance to RNase R than linear RNAs. Inflammatory lung responses occur in the pathogenesis and recovery of many lung diseases. Macrophages form the first line of host defense/innate immune responses and initiate/mediate lung inflammation. For example, in bacterial pneumonia, upon pro-inflammatory activation, they release early response cytokines/chemokines that recruit neutrophils, macrophages, and lymphocytes to sites of infection and clear pathogens. The functional effects and mechanisms by which circRNAs exert physiological or pathological roles in macrophage activation and lung inflammation remain poorly understood. In this article, we will review the current understanding and progress of circRNA biogenesis, regulation, secretion, and degradation. Furthermore, we will review the current reports on the role of circRNAs in macrophage activation and polarization, as well as in the process of inflammatory lung responses.

Circular RNAs: Epigenetic regulators of PTEN expression and function in cancer

Epigenetic regulation of gene expression, without altering the DNA sequence, is involved in many normal cellular growth and division events, as well as diseases such as cancer. Epigenetics is no longer limited to DNA methylation, and histone modification, but regulatory non-coding RNAs (ncRNAs) also play an important role in epigenetics. Circular RNAs (circRNAs), single-stranded RNAs without 3' and 5' ends, have recently emerged as a class of ncRNAs that regulate gene expression. CircRNAs regulate phosphatase and tensin homolog (PTEN) expression at various levels of transcription, post-transcription, translation, and post-translation under their own regulation. Given the importance of PTEN as a tumor suppressor in cancer that inhibits one of the most important cancer pathways PI3K/AKT involved in tumor cell proliferation and survival, significant studies have been conducted on the regulatory role of circRNAs in relation to PTEN. These studies will be reviewed in this paper to better understand the function of this protein in cancer and explore new therapeutic approaches.

Computational approaches and challenges in the analysis of circRNA data

Circular RNAs (circRNA) are a class of non-coding RNA, forming a single-stranded covalently closed loop structure generated via back-splicing. Advancements in sequencing methods and technologies in conjunction with algorithmic developments of bioinformatics tools have enabled researchers to characterise the origin and function of circRNAs, with practical applications as a biomarker of diseases becoming increasingly relevant. Computational methods developed for circRNA analysis are predicated on detecting the chimeric back-splice junction of circRNAs whilst mitigating false-positive sequencing artefacts. In this review, we discuss in detail the computational strategies developed for circRNA identification, highlighting a selection of tool strengths, weaknesses and assumptions. In addition to circRNA identification tools, we describe methods for characterising the role of circRNAs within the competing endogenous RNA (ceRNA) network, their interactions with RNA-binding proteins, and publicly available databases for rich circRNA annotation.

CircSSBP2 acts as a MiR-2400 sponge to promote intramuscular preadipocyte proliferation by regulating NDRG1

Intramuscular fat (IMF) is a critical factor in beef quality. IMF is mainly distributed between muscle fibres and its accumulation can affect the marbling and meat quality of beef. IMF formation and deposition is a complex process and in recent years a group of non-coding RNAs (ncRNAs), known as circRNAs, have been discovered to play an important role in regulating intramuscular fat deposition. CircRNAs form a covalent loop structure after reverse splicing of precursor mRNAs. They can act by adsorbing miRNAs, thereby reducing their repressive effects on downstream target genes. Based on high-throughput sequencing of circRNAs in intramuscular fat of Qinchuan and Japanese black cattle, we identified a novel circSSBP2 that is differentially expressed between the two species and associated with adipogenesis. We show that circSSBP2 knockdown promotes bovine intramuscular preadipocyte proliferation, whereas overexpression inhibits bovine intramuscular preadipocyte proliferation. We also show that circSSBP2 can act as a molecular sponge for miR-2400 and that miR-2400 overexpression promotes bovine intramuscular preadipocyte proliferation. Furthermore, N-myc downstream-regulated gene 1 (NDRG1) was identified as a direct target gene of miR-2400, and NDRG1 interference promoted the proliferation of bovine intramuscular preadipocytes. In conclusion, our results suggest that circSSBP2 inhibits the proliferation of bovine intramuscular preadipocytes by regulating the miR-2400/NDRG1 axis.

Potential therapeutic applications of circular RNA in acute kidney injury

Acute kidney injury (AKI) is a common clinical syndrome characterized by a rapid deterioration in renal function, manifested by a significant increase in creatinine and a sharp decrease in urine output. The incidence of morbidity and mortality associated with AKI is on the rise, with most patients progressing to chronic kidney disease or end-stage renal disease. Treatment options for patients with AKI remain limited. Circular RNA (circRNA) is a wide and diverse class of non-coding RNAs that are present in a variety of organisms and are involved in gene expression regulation. Studies have shown that circRNA acts as a competing RNA, is involved in disease occurrence and development, and has potential as a disease diagnostic and prognostic marker. CircRNA is involved in the regulation of important biological processes, including apoptosis, oxidative stress, and inflammation. This study reviews the current status and progress of circRNA research in the context of AKI.

CIRC_0003907 MODULATES SEPSIS-INDUCED MYOCARDIAL INJURY VIA ENHANCING MYD88/NLRP3/NF-ΚB AXIS BY SPONGING MIR-944

ABSTRACT

Background : Sepsis-induced cardiomyopathy ( SIC ) is a common complication of sepsis with high morbidity and mortality but lacks specific therapy. The purpose of this study was to investigate the role of circularRNA_0003907 (circ_0003907) in myocardium injury induced by sepsis. Methods: In this experiment, human AC16 cells were treated with lipopolysaccharide (LPS) to induce an in vitro cardiomyocyte injury model. Expression of circ_0003907, microRNA-944 (miR-944), and MYD88 was detected using quantitative real-time polymerase chain reaction. Cell proliferation and apoptosis were assessed using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, thymidine analog 5-ethynyl-2'-deoxyuridine, and flow cytometry assays. Secretions of proinflammatory cytokines IL-6 and TNF-α were detected using ELISA kits. Superoxide dismutase (SOD) activity and malondialdehyde (MDA) level were detected using special kits. Protein levels of cyclin D1, cleaved caspase-3, MYD88, NLRP3, P65, and IκBα were determined using western blot assay. After being predicted using Circineractome and starBase, the interaction between miR-944 and circ_0003907 or MYD88 was confirmed using dual-luciferase reporter and RNA immunoprecipitation assays. Results: Circ_0003907 expression was increased in serum from SIC patients and in LPS-treated AC16 cells. Circ_0003907 knockdown might abolish LPS-triggered proliferation inhibition, and the promotion of apoptosis, inflammatory response, and oxidative stress in AC16 cells. In mechanism, circ_0003907 acted as a sponge for miR-944 to increase MYD88 expression. Meanwhile, the absence of circ_0003907 induced miR-944 expression and suppressed MYD88/NLRP3/NF-κB levels. Conclusion: Circ_0003907 sponged miR-944 to aggravate LPS-induced AC16 cell dysfunction via activating the MYD88/NLRP3/NF-κB axis during sepsis, which might provide a new direction for the treatment of SIC .

Integrative Analysis of miRNA and circRNA Expression Profiles and Interaction Network in HSV-1-Infected Primary Corneal Epithelial Cells

PURPOSE

Circular RNAs (circRNAs) are products of alternative splicing with roles as competitive endogenous RNAs or microRNA sponges, regulating gene expression and biological processes. However, the involvement of circRNAs in herpes simplex keratitis remains largely unexplored.

METHODS

This study examines circRNA and miRNA expression profiles in primary human corneal epithelial cells infected with HSV-1, compared to uninfected controls, using microarray analysis. Bioinformatic analysis predicted the potential function of the dysregulated circRNAs and microRNA response elements (MREs) in these circRNAs, forming an interaction network between dysregulated circRNAs and miRNAs.

RESULTS

A total of 332 circRNAs and 16 miRNAs were upregulated, while 80 circRNAs and six miRNAs were downregulated (fold change ≥2.0 and p < 0.05). Gene ontology (GO) and KEGG pathway analyses were performed on parental genes of dysregulated circRNAs to uncover potential functions in HSV-1 infection. Notably, miR-181b-5p, miR-338-3p, miR-635, and miR-222-3p emerged as pivotal miRNAs interacting with multiple dysregulated circRNAs.

CONCLUSIONS

This comprehensive study offers insights into differentially expressed circRNAs and miRNAs during HSV-1 infection in corneal epithelial cells, shedding light on circRNA-miRNA interactions' potential role in herpes simplex keratitis pathogenesis.

Plant non-coding RNAs: The new frontier for the regulation of plant development and adaptation to stress

Most plant transcriptomes constitute functional non-coding RNAs (ncRNAs) that lack the ability to encode proteins. In recent years, more research has demonstrated that ncRNAs play important regulatory roles in almost all plant biological processes by modulating gene expression. Thus, it is important to study the biogenesis and function of ncRNAs, particularly in plant growth and development and stress tolerance. In this review, we systematically explore the process of formation and regulatory mechanisms of ncRNAs, particularly those of microRNAs (miRNAs), small interfering RNAs (siRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs). Additionally, we provide a comprehensive overview of the recent advancements in ncRNAs research, including their regulation of plant growth and development (seed germination, root growth, leaf morphogenesis, floral development, and fruit and seed development) and responses to abiotic and biotic stress (drought, heat, cold, salinity, pathogens and insects). We also discuss research challenges and provide recommendations to advance the understanding of the roles of ncRNAs in agronomic applications.

Multiple structural flavors of RNase P in precursor tRNA processing

The precursor transfer RNAs (pre-tRNAs) require extensive processing to generate mature tRNAs possessing proper fold, structural stability, and functionality required to sustain cellular viability. The road to tRNA maturation follows an ordered process: 5'-processing, 3'-processing, modifications at specific sites, if any, and 3'-CCA addition before aminoacylation and recruitment to the cellular protein synthesis machinery. Ribonuclease P (RNase P) is a universally conserved endonuclease in all domains of life, performing the hydrolysis of pre-tRNA sequences at the 5' end by the removal of phosphodiester linkages between nucleotides at position -1 and +1. Except for an archaeal species: Nanoarchaeum equitans where tRNAs are transcribed from leaderless-position +1, RNase P is indispensable for life and displays fundamental variations in terms of enzyme subunit composition, mechanism of substrate recognition and active site architecture, utilizing in all cases a two metal ion-mediated conserved catalytic reaction. While the canonical RNA-based ribonucleoprotein RNase P has been well-known to occur in bacteria, archaea, and eukaryotes, the occurrence of RNA-free protein-only RNase P in eukaryotes and RNA-free homologs of Aquifex RNase P in prokaryotes has been discovered more recently. This review aims to provide a comprehensive overview of structural diversity displayed by various RNA-based and RNA-free RNase P holoenzymes towards harnessing critical RNA-protein and protein-protein interactions in achieving conserved pre-tRNA processing functionality. Furthermore, alternate roles and functional interchangeability of RNase P are discussed in the context of its employability in several clinical and biotechnological applications. This article is categorized under: RNA Processing > tRNA Processing RNA Evolution and Genomics > RNA and Ribonucleoprotein Evolution RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes.

Circular RNAs and cervical cancer: friends or foes? A landscape on circRNA-mediated regulation of key signaling pathways involved in the onset and progression of HPV-related cervical neoplasms

Cervical cancer (CC) is a common gynecologic malignancy, accounting for a significant proportion of women death worldwide. Human papillomavirus (HPV) infection is one of the major etiological causes leading to CC onset; however, genetic, and epigenetic factors are also responsible for disease expansion. Circular RNAs (circRNAs), which are known as a particular subset of non-coding RNA (ncRNA) superfamily, with covalently closed loop structures, have been reported to be involved in the progression of diverse diseases, especially neoplasms. In this framework, abnormally expressed circRNAs are in strong correlation with CC pathogenesis through regulating substantial signaling pathways. Also, these RNA molecules can be considered as promising biomarkers and therapeutic targets for CC diagnosis/prognosis and treatment, respectively. Herein, we first review key molecular mechanisms, including Wnt/β-catenin, MAPK, and PI3K/Akt/mTOR signaling pathways, as well as angiogenesis and metastasis, by which circRNAs interfere with CC development. Then, diagnostic, prognostic, and therapeutic potentials of these ncRNA molecules will be highlighted in depth.

Identification and characterization of circular RNAs involved in the fertility stability of cotton CMS-D2 restorer line under heat stress

BACKGROUND

As a vital type of noncoding RNAs, circular RNAs (circRNAs) play important roles in plant growth and development and stress response. However, little is known about the biological roles of circRNAs in regulating the stability of male fertility restoration for cytoplasmic male sterility (CMS) conditioned by Gossypium harknessii cytoplasm (CMS-D2) cotton under high-temperature (HT) stress.

RESULTS

In this study, RNA-sequencing and bioinformatics analysis were performed on pollen grains of isonuclear alloplasmic near-isogenic restorer lines NH [N(Rf1rf1)] and SH [S(Rf1rf1)] with obvious differences in fertility stability under HT stress at two environments. A total of 967 circRNAs were identified, with 250 differentially expressed under HT stress. We confirmed the back-splicing sites of eight selected circRNAs using divergent primers and Sanger sequencing. Tissue-specific expression patterns of five differentially expressed circRNAs (DECs) were also verified by RT-PCR and qRT-PCR. Functional enrichment and metabolic pathway analysis revealed that the parental genes of DECs were significantly enriched in fertility-related biological processes such as pollen tube guidance and cell wall organization, as well as the Pentose and glucuronate interconversions, Steroid biosynthesis, and N-Glycan biosynthesis pathways. Moreover, we also constructed a putative circRNA-mediated competing endogenous RNA (ceRNA) network consisting of 21 DECs, eight predicted circRNA-binding miRNAs, and their corresponding 22 mRNA targets, especially the two ceRNA modules circRNA346-miR159a-MYB33 and circRNA484-miR319e-MYB33, which might play important biological roles in regulating pollen fertility stability of cotton CMS-D2 restorer line under HT stress.

CONCLUSIONS

Through systematic analysis of the abundance, characteristics and expression patterns of circRNAs, as well as the potential functions of their parent genes, our findings suggested that circRNAs and their mediated ceRNA networks acted vital biological roles in cotton pollen development, and might be also essential regulators for fertility stability of CMS-D2 restorer line under heat stress. This study will open a new door for further unlocking complex regulatory mechanisms underpinning the fertility restoration stability for CMS-D2 in cotton.

In Vivo Tissue-Specific Knockdown of circRNAs Using shRNAs in Drosophila melanogaster

Studying circular RNAs' function in vivo has been challenging due to the lack of generic tools to manipulate their levels without affecting their linear counterparts. This is particularly challenging as the back-splice junction is the only sequence not shared between the linear and circular version. In this chapter, we describe a method to study circRNA function in vivo targeting shRNAs against the desired back-splice junction to achieve knockdown with tissue-specific resolution in flies.

Directed Circularization of a Short RNA

Basic research and functional analyses of circular RNA (circRNA) have been limited by challenges in circRNA formation of desired length and sequence in adequate yields. Nowadays, circular RNA can be obtained using enzymatic, "ribozymatic," or modulated splice events. However, there are few records for the directed circularization of RNA. Here, we present a proof of principle for an affordable and efficient RNA-based system for the controlled synthesis of circRNA with a physiological 3',5'-phosphodiester conjunction. The engineered hairpin ribozyme variant circular ribozyme 3 (CRZ-3) performs self-cleavage poorly. We designed an activator-polyamine complex to complete cleavage as a prerequisite for subsequent circularization. The developed protocol allows synthesizing circRNA without external enzymatic assistance and adds a controllable way of circularization to the existing methods.

Circular RNA: A promising new star of vaccine

Circular RNAs (circRNAs) are a class of single-stranded RNAs with covalently closed structures. Owing to their not having 3' or 5' ends, circRNAs are highly durable and insusceptible to exonuclease-mediated degradation. Moreover, some circRNAs with certain structures are translatable, making them novel vaccines. Vaccines are efficient tools for immunotherapy, such as for the prevention of infectious diseases and cancer treatment. The immune system is activated during immunotherapy to fight against abnormal allies or invaders. CircRNA vaccines represent a potential new avenue in the vaccine era. Recently, several circRNA vaccines have been synthesized and tested in vitro and in vivo. Our review briefly introduces the current understanding of the biology and function of translatable circRNAs, molecular biology, synthetic methods, delivery of circRNA, and current circRNA vaccines. We also discussed the challenges and future directions in the field by summarizing the developments in circRNA vaccines in the past few years.

Circular RNAs: An emerging precise weapon for diabetic nephropathy diagnosis and therapy

Diabetic nephropathy (DN) is a prevalent chronic microvascular complication associated with diabetes mellitus and represents a major cause of chronic kidney disease and renal failure. Current treatment strategies for DN primarily focus on symptom alleviation, lacking effective approaches to halt or reverse DN progression. Circular RNA (circRNA), characterized by a closed-loop structure, has emerged as a novel non-coding RNA regulator of gene expression, attributed to its conservation, stability, specificity, and multifunctionality. Dysregulation of circRNA expression is closely associated with DN progression, whereby circRNA impacts kidney cell injury by modulating cell cycle, differentiation, cell death, as well as influencing the release of inflammatory factors and stromal fibronectin expression. Consequently, circRNA is considered a predictive biomarker and a potential therapeutic target for DN. This review provides an overview of the latest research progress in the classification, functions, monitoring methods, and databases related to circRNA. The paper focuses on elucidating the impact and underlying mechanisms of circRNA on kidney cells under diabetic conditions, aiming to offer novel insights into the prevention, diagnosis, and treatment of DN.

Identification, biogenesis, and function prediction of a novel circRNA_3238 of chicken

With the development of high-throughput sequencing, circular RNA has come into people's vision and attracted more and more attention. Many studies have found that circular RNA plays an important role in a variety of biological processes and the occurrence and development of diseases. According to the previous sequencing results, circRNA_3238 was differentially expressed in ALV-J infected group and the non-infected group was selected for subsequent verification and analysis. We found that circRNA_3238 is a stable, circular transcript, which mainly exists in the cytoplasm. And it is widely expressed in various tissues of chickens, and highly expressed in lung, lymph, and bursa of fabricius. Bioinformatics results show that circRNA_3238 and the predicted target genes enriched MAPK signaling pathway, Notch signaling pathway, and other pathways related to disease or immune, revealing circRNA_3238 may indirectly regulate the process of ALV-J infection by regulating target genes.

Virus-Encoded Circular RNAs: Role and Significance in Viral Infections

Circular RNAs (circRNAs) have been the focus of intense scientific research to understand their biogenesis, mechanisms of action and regulatory functions. CircRNAs are single stranded, covalently closed RNA molecules lacking the 5'-terminal cap and the 3'-terminal polyadenine chain, characteristics that make them very stable and resistant. Synthesised by both cells and viruses, in the past circRNAs were considered to have no precise function. Today, increasing evidence shows that circRNAs are ubiquitous, some of them are tissue- and cell-specific, and critical in multiple regulatory processes (i.e., infections, inflammation, oncogenesis, gene expression). Moreover, circRNAs are emerging as important biomarkers of viral infection and disease progression. In this review, we provided an updated overview of current understanding of virus-encoded and cellular-encoded circRNAs and their involvement in cellular pathways during viral infection.

Circular RNAs: the next level of gene regulation

Gene regulation is a highly complex process involving the presence and participation of many molecules and complexes that regulate gene expression in the genome, which occurs in a precise and coordinated way. Among all these regulatory molecules, the circular RNAs (circRNAs) are the most novel and peculiar family of noncoding RNAs (ncRNAs) as they have a circular structure, are very specific on their expression, highly conserved, and highly resistant to degradation. These molecules have been described in recent years as excellent disease markers and as potential therapeutic targets. In this review, we focused on general characteristics and on the evolution of the circRNAs, as well as on their biological functions, emphasizing on their participation in the formation of brain tumors.

Exosome-derived circ_0001785 delays atherogenesis through the ceRNA network mechanism of miR-513a-5p/TGFBR3

PURPOSE

Endothelial cell dysfunction is a major cause of early atherosclerosis. Although the role of extracellular vesicles in stabilizing atherosclerotic plaques is well established, the effect of circulating exosomes on plaque formation is still unknown. Here, we explored the effect of exosomes on atherosclerosis based on the function that exosomes can act on intercellular communication.

PATIENTS AND METHODS

We extracted serum exosomes from the blood of CHD patients (CHD-Exo) and healthy individuals (Con-Exo). The obtained exosomes were co-cultured with human umbilical vein endothelial cells (HUVECs) in vitro. In addition, we determined that circ_0001785 functions as a competing endogenous RNA (ceRNAs) in coronary artery disease by dual luciferase reporter gene analysis. The protective effect of circ_0001785 against endothelial cell injury was also verified using over-expression lentiviral transfection functional assays. In vivo experiments, we injected over-expressed circ_0001785 lentivirus into the tail vein of mice to observe its therapeutic effect on a mouse model of atherosclerosis.

RESULTS

The vitro co-cultured results showed that the amount of plasma-derived exosomes have an increase in patients with coronary artery disease, and the inflammation and apoptosis of endothelial cells were exacerbated. Over-expression of circ_0001785 reduced endothelial cell injury through the ceRNA network pathway of miR-513a-5p/TGFBR3. Quantitative reverse transcription-polymerase chain reaction identified that the expressed amount of circ_0001785 was reduced in the circulating peripheral blood of CHD patients and increased within human and mouse atherosclerotic plaque tissue. The results of in vivo experiments showed that circ_0001785 reduced aortic endothelial cell injury and the formation of intraplaque neo-vascularization, and enhanced left ventricular diastolic function, thereby delaying the development of atherosclerosis in mice.

CONCLUSION

Our results demonstrated a new biomarker, exosome-derived circ_0001785, for atherogenesis, which can reduce endothelial cell injury and thus delay atherogenesis through the miR-513a-5p/TGFBR3 ceRNA network mechanism, providing an exosome-based intervention strategy for atherosclerosis.

Circular RNAs in vascular diseases

Vascular diseases are the leading cause of morbidity and mortality worldwide and are urgently in need of diagnostic biomarkers and therapeutic strategies. Circular RNAs (circRNAs) represent a unique class of RNAs characterized by a circular loop configuration and have recently been identified to possess a wide variety of biological functions. CircRNAs exhibit exceptional stability, tissue specificity, and are detectable in body fluids, thus holding promise as potential biomarkers. Their encoding function and stable gene expression also position circRNAs as an excellent alternative to gene therapy. Here, we briefly review the biogenesis, degradation, and functions of circRNAs. We summarize circRNAs discovered in major vascular diseases such as atherosclerosis and aneurysms, with a particular focus on molecular mechanisms of circRNAs identified in vascular endothelial cells and smooth muscle cells, in the hope to reveal new directions for mechanism, prognosis and therapeutic targets of vascular diseases.

CeRNA Network Reveals the Circular RNA Characterization in Goat Ear Fibroblasts Reprogramming into Mammary Epithelial Cells

Circular RNAs (circRNAs) are a type of non-coding RNA that play a crucial role in the development and lactation of mammary glands in mammals. A total of 107 differentially expressed circRNAs (DE circRNAs) were found, of which 52 were up-regulated and 55 were down-regulated. We also found that DE circRNA host genes were mainly involved in GO terms related to the development process of mammary epithelial cells and KEGG pathways were mostly related to mammary epithelial cells, lactation, and gland development. Protein network analysis found that DE circRNAs can competitively bind to miRNAs as key circRNAs by constructing a circRNA-miRNA-mRNA network. CircRNAs competitively bind to miRNAs (miR-10b-3p, miR-671-5p, chi-miR-200c, chi-miR-378-3p, and chi-miR-30e-5p) involved in goat mammary gland development, mammary epithelial cells, and lactation, affecting the expression of core genes (CDH2, MAPK1, ITGB1, CAMSAP2, and MAPKAPK5). Here, we generated CiMECs and systematically explored the differences in the transcription profile for the first time using whole-transcriptome sequencing. We also analyzed the interaction among mRNA, miRNA, and cirRNA and predicted that circRNA plays an important role in the maintenance of mammary epithelial cells.

A linear and circular dual-conformation noncoding RNA involved in oxidative stress tolerance in Bacillus altitudinis

Circular RNAs have been extensively studied in eukaryotes, but their presence and/or biological functionality in bacteria are unclear. Here, we show that a regulatory noncoding RNA (DucS) exists in both linear and circular conformation in Bacillus altitudinis. The linear forms promote B. altitudinis tolerance to H2O2 stress, partly through increased translation of a stress-responsive gene, htrA. The 3' end sequences of the linear forms are crucial for RNA circularization, and formation of circular forms can decrease the levels of the regulatory linear cognates. Bioinformatic analysis of available RNA-seq datasets from 30 bacterial species revealed multiple circular RNA candidates, distinct from DucS, for all the examined species. Experiments testing for the presence of selected circular RNA candidates in four species successfully validated 7 out of 9 candidates from B. altitudinis and 4 out of 5 candidates from Bacillus paralicheniformis; However, none of the candidates tested for Bacillus subtilis and Escherichia coli were detected. Our work identifies a dual-conformation regulatory RNA in B. altitutidinis, and indicates that circular RNAs exist in diverse bacteria. However, circularization of specific RNAs does not seem to be conserved across species, and the circularization mechanisms and biological functionality of the circular forms remain unclear.

Comprehensive analysis of ceRNA network composed of circRNA, miRNA, and mRNA in septic acute kidney injury patients based on RNA-seq

Background: Sepsis is a complex, life-threatening clinical syndrome that can cause other related diseases, such as acute kidney injury (AKI). Circular RNA (circRNA) is a type of non-coding RNA with a diverse range of functions, and it plays essential roles in miRNA sponge. CircRNA plays a huge part in the development of various diseases. CircRNA and the competing endogenous RNA (ceRNA) regulatory network are unknown factors in the onset and progression of septic AKI (SAKI). This study aimed to clarify the complex circRNA-associated regulatory mechanism of circRNAs in SAKI. Methods: We collected 40 samples of whole blood of adults, including 20 cases of SAKI and 20 cases of healthy controls. Moreover, five cases were each analyzed by RNA sequencing, and we identified differentially expressed circRNA, miRNA, and mRNA (DEcircRNAs, DEmiRNAs, and DEmRNAs, respectively). All samples were from SAKI patients with intraperitoneal infection. Results: As a result, we screened out 236 DEcircRNAs, 105 DEmiRNAs, and 4065 DEmRNAs. Then, we constructed two co-expression networks based on RNA-RNA interaction, including circRNA-miRNA and miRNA-mRNA co-expression networks. We finally created a circRNA-miRNA-mRNA regulation network by combining the two co-expression networks. Functional and pathway analyses indicated that DEmRNAs in ceRNA were mostly concentrated in T cell activation, neutrophils and their responses, and cytokines. The protein-protein interaction network was established to screen out the key genes participating in the regulatory network of SAKI. The hub genes identified as the top 10 nodes included the following: ZNF727, MDFIC, IFITM2, FOXD4L6, CIITA, KCNE1B, BAGE2, PPIAL4A, USP17L7, and PRSS2. Conclusion: To our knowledge, this research is the first study to describe changes in the expression profiles of circRNAs, miRNAs, and mRNAs in patients with SAKI. These findings provide a new treatment target for SAKI treatment and novel ideas for its pathogenesis.

Circular RNAs: Emerging roles and new insights in human cancers

Circular RNAs (circRNAs) are single-stranded, covalently closed RNA molecules formed by mRNA exon back-splicing. Although the circRNA functions remain largely unknown, their currently known biological activities include: acting as competing endogenous RNA (ceRNA) to adsorb microRNA (miRNA), binding proteins, regulating transcription or splicing, and ability to be translated into proteins or peptides. A growing number of studies have found that many circRNAs are abnormally expressed in various cancers, and their dysregulation is highly correlated with tumor progression. Therefore, diagnosis and treatment using circRNAs as biomarkers and therapeutic targets, respectively, has gradually become an attractive research topic. In this review, we introduced the canonical biogenesis pathways and degradation mechanisms of circRNAs. In addition, we examined the biological functions of circRNAs in vivo. Finally, we discussed the current clinical applications and challenges faced by circRNA, and proposed future directions for this promising research field.

Progress in circRNA-Targeted Therapy in Experimental Parkinson's Disease

Circular RNAs (circRNAs) are single-stranded RNA molecules often circularized by backsplicing. Growing evidence implicates circRNAs in the underlying mechanisms of various diseases, such as Alzheimer's and Parkinson's disease (PD)-the first and second most prevalent neurodegenerative disorders. In this sense, circSNCA, circHIPK2, circHIPK3, and circSLC8A1 are circRNAs that have been related to the neurodegenerative process of PD. Gain-of-function and loss-of-function studies on circRNAs have shed light on their roles in the pathobiology of various diseases. Gain-of-function approaches typically employ viral or non-viral vectors that hyperexpress RNA sequences capable of circularizing to form the specific circRNA under investigation. In contrast, loss-of-function studies utilize CRISPR/Cas systems, antisense oligonucleotides (ASOs), or RNAi techniques to knock down the target circRNA. The role of aberrantly expressed circRNAs in brain pathology has raised a critical question: could circRNAs serve as viable targets for neuroprotective treatments? Translating any oligonucleotide-based therapy, including those targeting circRNAs, involves developing adequate brain delivery systems, minimizing off-target effects, and addressing the high costs of treatment. Nonetheless, RNAi-based FDA-approved drugs have entered the market, and circRNAs have attracted significant attention and investment from major pharmaceutical companies. Spanning from bench to bedside, circRNAs present a vast opportunity in biotechnology for oligonucleotide-based therapies designed to slow or even halt the progression of neurodegenerative diseases.

A review on circular RNAs and bacterial infections

Bacterial infections and related diseases have been a major burden on social public health and economic stability around the world. However, the effective diagnostic methods and therapeutic approaches to treat bacterial infections are still limited. As a group of non-coding RNA, circular RNAs (circRNAs) that were expressed specifically in host cells and played a key regulatory role have the potential to be of diagnostic and therapeutic value. In this review, we systematically summarize the role of circRNAs in common bacterial infections and their potential roles as diagnostic markers and therapeutic targets.

Circular mitochondrial-encoded mRNAs are a distinct subpopulation of mitochondrial mRNA in Trypanosoma brucei

Since the first identification of circular RNA (circRNA) in viral-like systems, reports of circRNAs and their functions in various organisms, cell types, and organelles have greatly expanded. Here, we report the first evidence, to our knowledge, of circular mRNA in the mitochondrion of the eukaryotic parasite, Trypanosoma brucei. While using a circular RT-PCR technique developed to sequence mRNA tails of mitochondrial transcripts, we found that some mRNAs are circularized without an in vitro circularization step normally required to produce PCR products. Starting from total in vitro circularized RNA and in vivo circRNA, we high-throughput sequenced three transcripts from the 3' end of the coding region, through the 3' tail, to the 5' start of the coding region. We found that fewer reads in the circRNA libraries contained tails than in the total RNA libraries. When tails were present on circRNAs, they were shorter and less adenine-rich than the total population of RNA tails of the same transcript. Additionally, using hidden Markov modelling we determined that enzymatic activity during tail addition is different for circRNAs than for total RNA. Lastly, circRNA UTRs tended to be shorter and more variable than those of the same transcript sequenced from total RNA. We propose a revised model of Trypanosome mitochondrial tail addition, in which a fraction of mRNAs is circularized prior to the addition of adenine-rich tails and may act as a new regulatory molecule or in a degradation pathway.

Aal-circRNA-407 regulates ovarian development of Aedes albopictus, a major arbovirus vector, via the miR-9a-5p/Foxl axis

Aedes albopictus shows a rapid global expansion and dramatic vectorial capacity for various arboviruses, thus posing a severe threat to global health. Although many noncoding RNAs have been confirmed to play functional roles in various biological processes in Ae. albopictus, the roles of circRNA remain a mystery. In the present study, we first performed high-throughput circRNA sequencing in Ae. albopictus. Then, we identified a cysteine desulfurase (CsdA) superfamily gene-originated circRNA, named aal-circRNA-407, which was the third most abundant circRNA in adult females and displayed a fat body highly expressed manifestation and blood feeding-dependent onset. SiRNA-mediated knockdown of circRNA-407 resulted in a decrease in the number of developing follicles and a reduction in follicle size post blood meal. Furthermore, we demonstrated that circRNA-407 can act as a sponge of aal-miR-9a-5p to promote the expression of its target gene Foxl and eventually regulate ovarian development. Our study is the first to report a functional circRNA in mosquitoes, expanding our current understanding of important biological roles in mosquitoes and providing an alternative genetic strategy for mosquito control.