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Circular RNAs (CircRNAs) are single-stranded, covalently closed RNA molecules that are ubiquitous across species ranging from viruses to mammals. Important advances have been made in the biogenesis, regulation, localization, degradation and modification of circRNAs. CircRNAs exert biological functions by acting as transcriptional regulators, microRNA (miR) sponges and protein templates. Moreover, emerging evidence has revealed that a group of circRNAs can serve as protein decoys, scaffolds and recruiters. However, the existing research on circRNA-protein interactions is quite limited. Hence, in this review, we briefly summarize recent progress in the metabolism and functions of circRNAs and elaborately discuss the patterns of circRNA-protein interactions, including altering interactions between proteins, tethering or sequestering proteins, recruiting proteins to chromatin, forming circRNA-protein-mRNA ternary complexes and translocating or redistributing proteins. Many discoveries have revealed that circRNAs have unique expression signatures and play crucial roles in a variety of diseases, enabling them to potentially act as diagnostic biomarkers and therapeutic targets. This review systematically evaluates the roles and mechanisms of circRNAs, with the hope of advancing translational medicine involving circRNAs.

Abstract This study aimed to investigate the involvement of hsa_(c)irc₀074763 in the activation of HSCs (hepatic stellate cells ) and liver fibrosis. Additionally, it aimed to conduct a preliminary analysis of the molecular mechanism targeting miR-3667-3p/ACSL4 (Long-chain acyl-CoA synthetase 4), thereby providing novel molecular targets for liver fibrosis. The GEO database was utilized to identify differentially expressed hsa_(c)irc₀074763 and determined its subcellular localization in LX-2 cells using fluorescence in situ hybridization. Bioinformatics analysis was employed for result prediction, and the interaction between hsa_(c)irc₀074763 and miR-3667-3P was confirmed using dual-luciferase reporter gene assay. ACSL4 mediated ferroptosis was detected with kit. Hsa_(c)irc₀074763 exhibits high expression levels in the fibrosis model. Validation through dual-luciferase reporter gene assays confirms the interaction between hsa_(c)irc₀074763 and miR-3667-3P. Functional cell experiments demonstrate that overexpression of hsa_(c)irc₀074763 promotes proliferation of LX-2 cells, elevates inflammation levels, and inhibits apoptosis. Additionally, ACSL4 has been identified as a direct target of miR-3667-3P, with overexpression of hsa_(c)irc₀074763 counteracting the inhibitory effect on ACSL4 by suppressing miR-3667-3P. Overexpression of ACSL4 increased the expression levels of ROS (Lipid Oxidation), Iron (Ferro Orange) and MDA (Malondialdehyde), and decreased the expression levels of GPX4 (Glutathione peroxidase 4) and GSH (Glutathione). Our finding suggests that overexpression of hsa_(c)irc₀074763 likely enhances the HSC activation through modulation of the miR-3667-3P/ACSL4 axis. Therefore, hsa_(c)irc₀074763 holds potential as a therapeutic target for liver fibrosis.

Background: Non-obstructive azoospermia (NOA) is a severe cause of male infertility. Testicular sperm extraction has limited success, largely due to the absence of reliable, non-invasive biomarkers to predict outcomes. Emerging evidence highlights the role of non-coding RNAs in spermatogenesis, providing promising targets for biomarker development. Objective: This study investigated the competing endogenous RNA regulatory axis hsa_(c)irc₀070963/miR-223-3p/CCDC96–CCDC112 as a potential biomarker for predicting microsurgical testicular sperm extraction (micro-TESE) outcomes in NOA individuals. Materials and Methods: In this case-control study, 60 men with NOA undergoing micro-TESE and 40 fertile controls were recruited. Testicular histology categorized individuals into Sertoli cell-only syndrome, hypospermatogenesis, or maturation arrest. Individuals were further stratified into NOA⁺ (successful retrieval) and NOA⁻ (failed retrieval). Plasma RNA was extracted, and expression levels of candidate genes were measured by quantitative reverse transcription polymerase chain reaction. Results: Findings demonstrated significant downregulation of CCDC96 and CCDC112 in NOA plasma, particularly in NOA⁻ individuals, while hsa-miR-223-3p was upregulated, with the highest expression in NOA⁻ cases. Conversely, hsa_(c)irc₀070963 was markedly reduced in NOA, especially in NOA⁻ individuals. Dysregulation was more pronounced in hypospermatogenesis and maturation arrest compared to Sertoli cell-only syndrome. Receiver operating characteristic analysis revealed strong predictive accuracy, with hsa_(c)irc₀070963 (area under the receiver operating characteristic curve = 0.983) and hsa-miR-223-3p (area under the curve = 0.970) outperforming CCDC96 and CCDC112. Conclusion: The hsa_(c)irc₀070963/miR-223-3p/CCDC96–CCDC112 axis represents a novel competing endogenous RNAs regulatory network linked to impaired spermatogenesis. Its expression profile provides mechanistic insights and serves as a robust, non-invasive biomarker for predicting micro-TESE outcomes, supporting improved stratification and individualized treatment strategies in male infertility.

N 6 -methyladenosine (m 6 A), the most abundant modification in eukaryotic cells, regulates RNA transcription, processing, splicing, degradation, and translation. Circular RNA (circRNA) is a class of covalently closed RNA molecules characterized by universality, diversity, stability and conservatism of evolution. Accumulating evidence shows that both m 6 A modification and circRNAs participate in the pathogenesis of multiple diseases, such as cancers, neurological diseases, autoimmune diseases, and infertility. Recently, m 6 A modification has been identified for its enrichment and vital biological functions in regulating circRNAs. In this review, we summarize the role of m 6 A modification in the regulation and function of circRNAs. Moreover, we discuss the potential applications and possible future directions in the field.

Exosomes have emerged as critical mediators of intercellular communication, both locally and systemically, by regulating a diverse range of biological processes between cells. Circular RNA (circRNA) is a novel member of endogenous noncoding RNAs with widespread distribution and diverse cellular functions. Recently, circular RNAs have been identified for their enrichment and stability in exosomes. In this review, we outline the origin, biogenesis and function of exosomal circRNAs as well as their roles in various diseases. Although their precise roles and mechanisms of gene regulation remain largely elusive, exosomal circRNAs have potential applications as disease biomarkers and novel therapeutic targets.

Circular RNAs (circRNAs) are regulatory elements that are involved in orchestrating gene expression and protein functions and are implicated in various biological processes including cancer. Notably, breast cancer has a significant mortality rate and is one of the most common malignancies in women. CircRNAs have been demonstrated to contribute to the pathogenesis of breast cancer including its initiation, progression, metastasis, and resistance to drugs. By acting as miRNA sponges, circRNAs can indirectly influence gene expression by disrupting miRNA regulation of their target genes, ultimately altering the course of cancer development and progression. Additionally, circRNAs can interact with proteins and modulate their functions including signaling pathways involved in the initiation and development of cancer. Recently, circRNAs can encode peptides that play a role in the pathophysiology of breast cancer and other diseases and their potential as diagnostic biomarkers and therapeutic targets for various cancers including breast cancer. CircRNAs possess biomarkers that differentiate, such as stability, specificity, and sensitivity, and can be detected in several biological specimens such as blood, saliva, and urine. Moreover, circRNAs play an important role in various cellular processes including cell proliferation, differentiation, and apoptosis, all of which are integral factors in the development and progression of cancer. This review synthesizes the functions of circRNAs in breast cancer, scrutinizing their contributions to the onset and evolution of the disease through their interactions with exosomes and cancer-related intracellular pathways. It also delves into the potential use of circRNA as a biomarker and therapeutic target against breast cancer. It discusses various databases and online tools that offer crucial circRNA information and regulatory networks. Lastly, the challenges and prospects of utilizing circRNAs in clinical settings associated with breast cancer are explored.

The majority of RNAs transcribed from the human genome have no coding capacity and are termed non-coding RNAs (ncRNAs). It is now widely accepted that ncRNAs play key roles in cell regulation and disease. Circular RNAs (circRNAs) are a form of ncRNA, characterised by a closed loop structure with roles as competing endogenous RNAs (ceRNAs), protein interactors and transcriptional regulators. Functioning as key cellular regulators, dysregulated circRNAs have a significant impact on disease progression, particularly in cancer. Evidence is emerging of specific circRNAs having oncogenic or tumour suppressive properties. The multifaceted nature of circRNA function may additionally have merit as a novel therapeutic target, either in treatment or as a novel biomarker, due to their cell-and disease-state specific expression and long-term stability. This review aims to summarise current findings on how circRNAs are dysregulated in cancer, the effects this has on disease progression, and how circRNAs may be targeted or utilised as future potential therapeutic options.

Circular RNA (circRNA) is a unique closed ring structure of noncoding RNA. Although many human diseases have been confirmed to be inextricably linked with circRNAs, whether circRNAs have a potential regulatory function in the osteogenic differentiation of bone marrow mesenchymal stem cells (BMMSCs) remains to be further elucidated. In a previous study by our team, all the differentially expressed circRNAs and messenger RNAs (mRNAs) involved in the osteogenic differentiation of BMMSCs were identified via high-throughput sequencing, and a competing endogenous RNA (ceRNA) regulatory network was constructed via bioinformatics analysis. The circRNA₁809/miR-370-3p/Kitlg axis may be involved in regulating the osteogenic differentiation of BMMSCs. In this study, gene knockdown/overexpression, small interfering RNA (siRNA) transfection and mimic/inhibitor treatment were used to evaluate the regulatory effects of circRNA₁809 on the miR-370-3p/Kitlg pathway and the osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMMSCs) in vitro. The results revealed that circRNA₁809 was upregulated and that miR-370-3p was downregulated during the osteogenic differentiation of rBMMSCs. The low expression of circRNA₁809 significantly downregulated the expression of Kitlg and decreased the protein expression of ALP and RUNX2. The expression of miR-370-3p was negatively correlated with the expression of Kitlg in rBMMSCs and the ability to undergo osteogenic differentiation. In addition, a dual-luciferase assay confirmed the binding of miR-370-3p and circRNA₁809, and si-circRNA₁809 + miR-370-3p inhibitor cotransfection reversed some of the downregulation of Kitlg induced by si-circRNA₁809, whereas si-circRNA₁809 + miR-370-3p mimic increased the downregulation of Kitlg. Therefore, circRNA₁809 may promote the expression of Kitlg by regulating miR-370-3p and subsequently promote the osteogenic differentiation of rBMMSCs.

Proteins produced by cap‐independent translation mediated by an internal ribosome entry site (IRES) in circular RNAs (circRNAs) play important roles in tumour progression. To date, numerous studies have been performed on circRNAs and the proteins they encode. In this review, we summarize the biogenesis of circRNAs and the mechanisms regulating circRNA‐encoded proteins expression. We also describe relevant research methods and their applications to biological processes such as tumour cell proliferation, metastasis, epithelial‐mesenchymal transition (EMT), apoptosis, autophagy and chemoresistance. This paper offers deeper insights into the roles that circRNA‐encoded proteins play in tumours. It also provides a theoretical basis for the use of circRNA‐encoded proteins as biomarkers of tumorigenesis and for the development of new targets for tumour therapy.