Translation of CircRNAs

CircATP5C1 promotes triple-negative breast cancer progression by binding IGF2BP2 to modulate CSF-1 secretion

Triple-negative breast cancer (TNBC) is a common malignant disease among females and severely threatens the health of women worldwide. Nowadays, circular RNAs (circRNAs) aroused our interest for their functions in human cancers, including TNBC. However, the mechanism of most circRNAs in the progression of TNBC remains unclear. We found a novel circRNA named circATP5C1, whose function in TNBC remains uncovered. Tissue microarray was used to analyze the association between the expression of circATP5C1 and the prognoses of TNBC patients. Gain-and loss-of-function experiments were performed to validate the biological functions of circATP5C1 in different TNBC cell lines. RNA-seq analyses were conducted to find out the target genes regulated by circATP5C1. RNA pull-down assay and mass spectrometry were used to select the proteins associated with circATP5C1. RNA FISH-immunofluorescence and RNA immunoprecipitation (RIP) were complemented to validate the interaction between circATP5C1 and its binding protein. CircATP5C1 was identified to have predictive function in prognosis of TNBC patients. CircATP5C1 advanced the progression of TNBC cells. Mechanistically, Colony stimulating factor 1 (CSF-1) is a vital downstream gene regulated by circATP5C1. The alteration of CSF-1 expression level was validated due to the interaction between circATP5C1 and insulin-like growth factor 2 mRNA binding protein 2 (IGF2BP2). Rescue experiments demonstrated that circATP5C1 accelerates the progression of TNBC partly via binding with IGF2BP2 to increase the secretion of CSF-1. This study uncovers a novel mechanism of circATP5C1/IGF2BP2/CSF-1 pathway in regulating progression of TNBC.

Expanded insights into the mechanisms of RNA-binding protein regulation of circRNA generation and function in cancer biology and therapy

RNA-binding proteins (RBPs) regulate the generation of circular RNAs (circRNAs) by participating in the reverse splicing of circRNA and thereby influencing circRNA function in cells and diseases, including cancer. Increasing evidence has demonstrated that the circRNA-RBP network plays a complex and multifaceted role in tumor progression. Thus, a better understanding of this network may provide new insights for the discovery of cancer drugs. In this review, we discuss the characteristics of RBPs and circRNAs and how the circRNA-RBP network regulates tumor cell phenotypes such as proliferation, metastasis, apoptosis, metabolism, immunity, drug resistance, and the tumor environment. Moreover, we investigate the factors that influence circRNA-RBP interactions and the regulation of downstream pathways related to tumor development, such as the tumor microenvironment and N6-methyladenosine modification. Furthermore, we discuss new ideas for targeting circRNA-RBP interactions using various RNA technologies.

CircRNA encoded-peptide: Potential stock in the transcriptomics market

The emergence of circRNA-encoded peptides has sparked significant debate in recent years as a novel mode of action for circRNAs. A mounting body of evidence suggests that these peptides play vital roles in cancer development and immune responses. This review initially elucidates the presence of circRNA-encoded peptides and delineates their specific functions across various biological processes and pathological conditions. It goes on to furnish illustrative instances to underscore the pivotal involvement of circRNA-encoded peptides in both innate and adaptive immune responses. The study sheds new light on the biological roles of circRNAs, their potential tumor-promoting and tumor-suppressing functions of circRNA-encoded peptides in specific tumor environment, and their significance in immunological contexts. Meanwhile, the limitations of existing studies on circRNA-encoded peptides are discussed in depth. In particular, circRNA-encoded peptides are critically analyzed as biomarkers and therapeutic targets. Intriguingly, the review concludes with a more organized discussion of future research on circRNA-encoded peptides.

The role of circular RNAs in regulating cytokine signaling in cancer

Dysregulation of cytokine signaling is central to the development and progression of cancer. Cytokines are not only involved in promoting cancer development but also regulate anti-tumor immune responses. Circular RNAs (circRNAs) are single-stranded, covalently closed RNA molecules lacking free ends, which have emerged as critical regulators of cytokine signaling. Transcriptional and post-transcriptional regulation of cytokine signaling by circRNAs contributes to cancer pathogenesis. Here, we discuss the emerging role of circRNAs in modulating cytokine signaling pathways that regulate cancer development. In particular, we examine the role of circRNAs in TGF-β, IL-6, IL-10, TNF-α, VEGF, FGF, PDGF, and chemokine signaling in cancer.

Novel Truncated Peptide Derived From circCDYL Exacerbates Cardiac Hypertrophy

BACKGROUND

Circular RNAs (circRNAs) have been gradually revealed to regulate the progression of heart disease in depth, showing their clinical significance. However, a mass of cardiac circRNAs still has not been functionally characterized. We aimed to explore the potential candidates that are involved in pathological cardiac hypertrophy.

METHODS

Public substantial RNA-sequencing data of cardiac circRNAs were utilized to search the cardiac hypertrophy-related circRNAs. Cardiomyocyte hypertrophy in vitro was induced by Ang II (angiotensin II) treatment. Mice were subjected to Ang II infusion to induce cardiac hypertrophy in vivo. Gain-of-function and loss-of-function assays were conducted to detect the effect of RNAs or proteins in cardiac hypertrophy.

RESULTS

A circRNA derived from the cdyl (chromodomain Y-like) gene was screened out and named circCDYL. Our results showed that the expression of circCDYL in primary rat cardiomyocytes was significantly induced by Ang II. Gain-of-function and loss-of-function assays demonstrated that circCDYL effectively promoted cardiomyocyte hypertrophy in vitro. CircCDYL could encode a ≈100-aa truncated CDYL peptide (tCDYL-100), whose sequence highly overlaps that of full-length CDYL. The translation of tCDYL-100 was activated by N6-methylation of circCDYL under prohypertrophic stimulation. tCDYL-100 fulfilled the prohypertrophic function of circCDYL. Mechanistically, tCDYL-100 competed with CDYL for binding REST (RE1-silencing transcription factor) and further disrupted the formation of REST-CDYL-EHMT2 (euchromatic histone-lysine N-methyltransferase 2) transcriptional repression complex, resulting in transcriptional activation of rhoa and nppb. Silence of circCDYL in mouse hearts could inhibit Ang II-induced cardiac hypertrophy, while forced expression of tCDYL-100 could cause cardiac hypertrophy.

CONCLUSIONS

In summary, our study uncovered an important circRNA-derived peptide and a regulatory mechanism on transcription mediated by N6-methyladenosine-circRNA-histone methylation in pathological cardiac hypertrophy.

Circ_RPPH1 promotes bladder urothelium carcinoma proliferation and EMT by recruiting and binding to EIF4 A3

BACKGROUND

The involvement of circ_RPPH1 in bladder urothelial carcinoma (BUC) remains unclear, as well as the underlying mechanism.

METHODS

Circ_RPPH1 levels in BUC cells and tissues were measured via RT-qPCR. Downregulation of circ_RPPH1 was assessed using colony formation, CCK-8, wound healing, and Transwell assays to evaluate proliferation, migration, and invasion. RIP and RNA pull-down confirmed circ_RPPH1 binding to EIF4A3, while immunoblotting analyzed EIF4A3 and EMT-related proteins.

RESULTS

High circ_RPPH1 levels in BUC correlated with tumor invasion depth. Its knockout suppressed proliferation, invasion, and EMT, while circ_RPPH1 overexpression reduced EIF4A3 binding to N-cadherin and Vimentin mRNA, promoting EMT.

CONCLUSION

Circ_RPPH1 promotes tumor growth and EMT in BUC by inhibiting EIF4A3-mediated mRNA regulation, activating the EIF4A3/N-cadherin/Vimentin pathway.

Biogenesis of circular RNAs in vitro and in vivo from the Drosophila Nk2.1/scarecrow gene

The scarecrow (scro) gene encodes a fly homolog of mammalian Nkx2.1, which is vital for early fly development and for optic lobe development. Previously, scro was reported to produce a circular RNA in addition to traditional mRNAs. In this study, we report 12 different scro circular RNAs, which are either mono or multiexonic forms. The most abundant ones are circScro(2) carrying the second exon (E2) only and bi-exonic circScro(3,4) having both the third (E3) and fourth exon (E4). Levels of circScro(2) show an age-dependent increase in adult heads, supporting a general trend of high accumulation of circular RNAs in aged fly brains. In silico analysis of the introns flanking circular RNA exons predicts 2 pairs of intronic complementary sequences; 1 pair residing in introns 1 and 2 and the other in introns 2 and 4. The first pair was demonstrated to be essential for the circScro(2) production in cell-based assays; furthermore, deletion of the region including intronic complementary sequence components in the intron-2 reduces in vivo production of both circScro(2) and circScro(3,4) by 80%, indicating them to be essential for the biogenesis of the 2 circular RNAs. Besides the intronic complementary sequence, the intron regions immediately abutting exons seem to be responsible for a basal level of circular RNA formation. Moreover, ectopic intronic complementary sequence derived from the laccase2 locus is comparably effective in circScro production, buttressing the importance of the hairpin loop structure formed by intronic complementary sequence for the biogenesis of circular RNA. Last, overexpressed scro alters outcomes of both linear and circular RNAs from the endogenous scro locus, suggesting that Scro plays a direct or indirect role in regulating the expression levels of either or both forms.

Engineering of a palindrome-crosslinked DNA nanoaggregate for rapid detection of circular RNA and precise identification of lung cancer

Circular RNAs (circRNAs) are endogenous covalently closed non-coding RNAs with cell-/developmental-stage-/tissue-specific expression patterns, and they can act as the miRNA sponges and gene transcription regulatory factors to influence numerous biological processes. Herein, we develop a palindrome-crosslinked DNA nanoaggregate system to rapidly detect circRNA and precisely identify lung cancer. We utilize a self-assembled palindromic DNA nanosphere (DS) as the spatial-confinement scaffold to anchor hairpin probes (HP) for the formation of the hybrid assemblies (DSH). The presence of target circSATB2 can hybridize with the hairpin probe to expose the locked palindromic sequence, initiating the cross-linking of the palindromic ends to form a self-catenated structure through intermolecular hybridization. Then the hybridized palindromic ends serve as the self-primers to initiate extension reaction and eventually assemble into the net-like crosslinked DNA nanoaggregates, resulting in the recovery of Cy5 signals. Taking advantage of the excellent antidegradation capability and superior kinetic behavior of DSH nanostructure, high amplification efficiency of Klenow Fragment polymerase (KF)-mediated extension reaction, and signal enhancement induced by the DNA nanoaggregates, this nanosystem enables mix-and-read detection of circSATB2 within 30 min under isothermal conditions (37 °C) with a limit detection of 77.56 fM. Moreover, it is capable of measuring intracellular circSATB2 with single-cell sensitivity, exploring its biological functions, and precisely identifying different stages (I/II/III) and subtypes (IA1/IA2/IA3/IB) of lung cancers, holding great potential in early screening of lung cancers.

CircRNAs in the tumor microenvironment: new frontiers in cancer progression and therapy

The tumor microenvironment (TME), a dynamic ecosystem which including immune cells, cancer-associated fibroblasts (CAFs), endothelial cells, pericytes and acellular components, is orchestrating cancer progression through crosstalk between malignant cells and stromal components and increasingly recognized as a therapeutic frontier. Within this intricate network, circular RNAs (circRNAs) have emerged as pivotal regulators due to their unique covalently closed structures, which confer exceptional stability and multifunctional capabilities. This regulation is mediated through multiple mechanisms, such as acting as microRNA (miRNA) sponges, interacting with proteins, and, in certain instances, encoding functional peptides. The interaction between circRNAs and the TME not only affects cancer growth and metastasis but also influences immune evasion and therapeutic resistance. Elucidating the mechanisms by which circRNAs orchestrate these interactions is essential for identifying novel diagnostic biomarkers and developing effective therapeutic strategies. Such insights are expected to bridge gaps in current cancer biology, offering promising avenues for precision oncology and ultimately improving clinical outcomes for cancer patients.

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.

RNA therapeutics in cardiovascular medicine

PURPOSE OF REVIEW

RNA therapeutics came to global attention when mRNA-based vaccines provided an answer to the SARS-CoV-2 pandemic. The immense significance of this development notwithstanding, it is important to note that almost a decade prior to the pandemic, RNA drugs had made important inroads toward the amelioration of disease. The first class of RNA therapies to be introduced into clinical use were the antisense oligomers and siRNA drugs which generally induce a therapeutic effect by acting to brake or to modulate mRNA expression. RNA therapeutics is quickly becoming the fourth pillar of pharmacotherapy, and will have broad applications, including for the treatment of cardiovascular disease.

RECENT FINDINGS

The United States (US) Food and Drug Administration (FDA) has approved several antisense oligomers (ASOs) and siRNA-based drugs to treat disorders associated with cardiovascular disease. In addition, multiple RNA-based drugs are in clinical trials to assess their safety and efficacy in patients with cardiovascular disorders, such as Zodasiran, a siRNA therapy that targets angiopoietin-like protein 3 (ANGPTL3) to reduce LDL cholesterol.

SUMMARY

Because of limitless sequence choice; speed of design; and relative ease of synthesis, RNA drugs will be rapidly developed, will have broad applications, and will be generated at lower cost than other drug types. This review aims to highlight RNA therapies for cardiovascular diseases that are approved, and those that are under clinical evaluation.

Coding circular RNA in human cancer

circular RNA (circRNA) is a covalently closed single-stranded RNA that lacks 5' and 3' ends and has long been considered a noncoding RNA. With the development of high-throughput sequencing and bioinformatics technology, the understanding of circRNA has become increasingly advanced. Recent studies have shown that some cytoplasmic circRNAs can be effectively translated into detectable proteins, further indicating the importance of circRNA in cellular pathology and physiological functions. Internal ribosome entry site (IRES) and N6-methyladenosine (m6A) mediated cap-independent translation initiation are considered potential mechanisms of circRNA translation. Multiple circRNAs have been shown to play crucial roles in human cancer. This paper provides an overview of the nature and functions of circRNA and describes the possible mechanisms underlying the initiation of circRNA translation. We summarized the emerging functions of circRNA-encoded proteins in human cancer. Finally, we discuss the therapeutic potential of circRNAs and the challenges of research in this field. This review on circRNA translation will reveal a hidden human proteome and enhance our understanding of the importance of circRNAs in human malignant tumors.

The Potential of RNA Therapeutics in Treating Cardiovascular Disease

Despite significant advances in cardiology over the past few decades, cardiovascular diseases (CVDs) remain the leading cause of global mortality and morbidity. This underscores the need for novel therapeutic interventions that go beyond symptom management to address the underlying causal mechanisms of CVDs. RNA-based therapeutics represent a new class of drugs capable of regulating specific genetic and molecular pathways, positioning them as strong candidates for targeting the root causes of a wide range of diseases. Moreover, owing to the vast diversity in RNA form and function, these molecules can be utilized to induce changes at different levels of gene expression regulation, making them suitable for a broad array of medical applications, even within a single disease context. Several RNA-based therapies are currently being investigated for their potential to address various CVD pathologies. These include treatments aimed at promoting cardiac revascularization and regeneration, preventing cardiomyocyte apoptosis, reducing harmful circulating cholesterols and fats, lowering blood pressure, reversing cardiac fibrosis and remodeling, and correcting the genetic basis of inherited CVDs. In this review, we discuss the current landscape of RNA therapeutics for CVDs, with an emphasis on their classifications, modes of action, advancements in delivery strategies and considerations for their implementation, as well as CVD targets with proven therapeutic potential.

NSUN2-mediated m5C modification of circFAM190B promotes lung cancer progression by inhibiting cellular autophagy

5-Methylcytosine (m5C) modification is an important type of RNA methylation. Diverse noncoding RNAs can undergo m5C modification and play important roles in tumour development, but circRNA m5C modifications have not been fully revealed in tumours. Here, circFAM190B, which was significantly overexpressed in lung cancer cells and tissues, was identified by constructing a differential expression profile of m5C-modified circRNAs. circFAM190B was found to be associated with lung cancer stage and prognosis. Moreover, we proposed the novel hypothesis that NSUN2 can mediate circFAM190B m5C modification and enhance circFAM190B stability in an m5C-dependent manner. We also clarified the biological function of circFAM190B in significantly promoting the development of lung cancer. Mechanistically, circFAM190B targets SFN and regulates its ubiquitination, thereby inhibiting cellular autophagy through the SFN/mTOR/ULK1 pathway and ultimately promoting lung cancer development. This study reveals the existence of m5C modification of circRNAs, and circRNAs modified by m5C can play important roles in the development of lung cancer, which provides a new theoretical basis for elucidating the molecular mechanism of lung cancer development.

A versatile toolbox for determining IRES activity in cells and embryonic tissues

Widespread control of gene expression through translation has emerged as a key level of spatiotemporal regulation of protein expression. A prominent mechanism by which ribosomes can confer gene regulation is via internal ribosomal entry sites (IRESes), whose functions have however, remained difficult to rigorously characterize. Here we present a set of technologies in embryos and cells, including IRES-mediated translation of circular RNA (circRNA) reporters, single-molecule messenger (m)RNA isoform imaging, PacBio long-read sequencing, and isoform-sensitive mRNA quantification along polysome profiles as a new toolbox for understanding IRES regulation. Using these techniques, we investigate a broad range of cellular IRES RNA elements including Hox IRESes. We show IRES-dependent translation in circRNAs, as well as the relative expression, localization, and translation of an IRES-containing mRNA isoform in specific embryonic tissues. We thereby provide a new resource of technologies to elucidate the roles of versatile IRES elements in gene regulation and embryonic development.

Comprehensive analysis of non-coding RNAs in the ovaries of high and low egg production hens

Egg production performance a critical economic trait in the poultry industry. The regulatory mechanisms underlying egg production performance mediated by non-coding RNAs remain to be characterized. To systematically investigate ovarian lncRNAs, circRNAs, and miRNAs associated with laying efficiency, we conducted comparative transcriptomic analyses using RNA sequencing (RNA-seq) of ovarian tissues from phenotypically divergent groups - high egg production (HEP) and low egg production (LEP) hens. In our study, we identified 675 lncRNAs, 140 circRNAs, and 10 miRNAs that were significantly differentially expressed (DE) between HEP and LEP. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that target genes of DE lncRNAs, DE miRNAs, and the source genes of DE circRNAs are involved in the MAPK signaling pathway, endocytosis, notch signaling pathway, among others. Furthermore, we identified five miRNA-mRNA interactions related to egg production including gga-miR-449c-3p, and five genes (GLI2, TAC1, EML6, THOC3, MMP9). These findings establish the first comprehensive ncRNA interactome driving ovarian efficiency, offering both biomarkers for breeding selection and mechanistic targets for reproductive enhancement.

The emerging functions and clinical implications of circRNAs in acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a prevalent haematologic malignancy characterized by significant heterogeneity. Despite the application of aggressive therapeutic approaches, AML remains associated with poor prognosis. Circular RNAs (circRNAs) constitute a unique class of single-stranded RNAs featuring covalently closed loop structures that are ubiquitous across species. These molecules perform crucial regulatory functions in the pathogenesis of various diseases through diverse mechanisms, including acting as miRNA sponges, interacting with DNA or proteins, and encoding functional proteins/polypeptides. Recently, numerous circRNAs have been confirmed to have aberrant expression patterns in AML patients. In particular, certain circRNAs are closely associated with specific clinicopathological characteristics and thus have great potential as diagnostic/prognostic biomarkers and therapeutic targets in AML. Herein, we systematically summarize the biogenesis, degradation, and functional mechanisms of circRNAs while highlighting their clinical relevance. We also outline a series of online databases and analytical tools available to facilitate circRNA research. Finally, we discuss the current challenges and future research priorities in this evolving field.

Circular RNAs exhibit exceptional stability in the aging brain and serve as reliable age and experience indicators

Circular RNAs (circRNAs) increase in the brain with age across various animal systems. To elucidate the reasons behind this phenomenon, we profile circRNAs from fly heads at six time points throughout their lifespan. Our results reveal a linear increase in circRNA levels with age, independent of changes in mRNA levels, overall transcription, intron retention, or host gene splicing, demonstrating that the age-related accumulation is due to high stability rather than increased biogenesis. This remarkable stability suggests that circRNAs can serve as markers of environmental experience. Indeed, flies exposed to a 10-day regimen at 29°C exhibit higher levels of specific circRNAs even 6 weeks after returning to standard conditions, indicating that circRNAs can reveal past environmental stimuli. Moreover, half-life measurements show circRNA stability exceeding 20 days, with some displaying virtually no degradation. These findings underscore the remarkable stability of circRNAs in vivo and their potential as markers for stress and life experiences.

Identification and expression profile analysis of circRNAs associated with goat uterus with different fecundity during estrous cycle

BACKGROUND

The Yunshang Black Goat, a distinguished meat goat breed native to China, is renowned for its superior reproductive capabilities. Despite this, there is considerable phenotypic variability within the breed. During the reproductive cycle, the uterus plays a pivotal role, with its functions evolving in line with the different stages of the cycle. This study focuses on the uterine tissues, including both the endometrium and myometrium, of Yunshang Black Goats with high fecundity (HF) and low fecundity (LF) during the proliferative (FP) and secretory (LP) phases of the estrous cycle. By examining these tissues, we aim to elucidate the underlying molecular and physiological mechanisms of the observed differences in reproductive success.

RESULTS

High-throughput sequencing was conducted, followed by bioinformatics analysis to identify the expression profiles of circRNAs. A total of 7,445 circRNAs were identified through the integration of findings from find_circ and CIRI2 software. Comparative analyses between the FPLF vs. FPHF and LPLF vs. LPHF revealed 149 differentially expressed (DE) circRNAs (94 up-regulated and 55 down-regulated) and 276 DE circRNAs (56 up-regulated and 220 down-regulated), respectively. The enrichment analysis indicated that the primary pathways involved were the Sphingolipid signaling pathway, MAPK signaling pathway, and GnRH signaling pathway, all of which are closely associated with cellular growth and development. Additionally, several key candidate genes were identified, such as FGF2 and MBTPS1. We also predicted a total of 281 miRNA-circRNA binding pairs, encompassing 263 circRNAs and 60 miRNAs, and simultaneously, 14 coding circRNAs were anticipated.

CONCLUSION

Based on the analysis, we have established the expression profiles of circRNAs during the follicular and luteal phases, respectively. Furthermore, using various analytical methods and data from high- and low-yield experimental control groups over different periods, we have identified multiple circRNAs that affect the high reproductive capacity of goats. Through enrichment analysis of the host genes of these circRNAs, we have discovered several key candidate genes. These findings provide fundamental data for the study of the molecular mechanisms underlying the fecundity of goats and pave the way for future genetic improvement strategies.

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.

Unlocking the potential of circular RNA vaccines: a bioinformatics and computational biology perspective

Bioinformatics has significantly advanced RNA-based therapeutics, particularly circular RNAs (circRNAs), which outperform mRNA vaccines, by offering superior stability, sustained expression, and enhanced immunogenicity due to their covalently closed structure. This review highlights how bioinformatics and computational biology optimise circRNA vaccine design, elucidates internal ribosome entry sites (IRES) selection, open reading frame (ORF) optimisation, codon usage, RNA secondary structure prediction, and delivery system development. While circRNA vaccines may not always surpass traditional vaccines in stability, their production efficiency and therapeutic efficacy can be enhanced through computational strategies. The discussion also addresses challenges and future prospects, emphasizing the need for innovative solutions to overcome current limitations and advance circRNA vaccine applications.

Noncanonical circRNA biogenesis driven by alpha and gamma herpesviruses

Herpesviruses require the host transcriptional machinery, inducing significant changes in gene expression to prioritize viral transcripts. We examined alpha- and gamma-herpesvirus alterations to a type of alternative splicing, namely circular RNA (circRNA) synthesis. We developed "Circrnas in Host And viRuses anaLysis pIpEline" (CHARLIE) to facilitate viral profiling. This method identified thousands of back-splicing variants, including circRNA common to lytic and latent phases of infection. Ours is the first report of Herpes Simplex Virus-1 circRNAs, including species derived from ICP0 and the latency-associated transcript. We characterized back-splicing cis- and trans-elements, and found viral circRNAs resistant to spliceosome perturbation and lacking canonical splice donor-acceptors. Subsequent loss-of-function studies of host RNA ligases (RTCB, RLIG1) revealed instances of decreased viral back splicing. Using eCLIP and 4sU-Sequencing, we determined that the KSHV RNA-binding protein, ORF57, enhanced synthesis for a subset of viral and host circRNAs. Our work explores unique splicing mechanisms driven by lytic infection, and identifies a class of transcripts with the potential to function in replication, persistence, or tumorigenesis.

A functional screen uncovers circular RNAs regulating excitatory synaptogenesis in hippocampal neurons

Circular RNAs (circRNAs) are an expanding class of largely unexplored RNAs which are prominently enriched in the mammalian brain. Here, we systematically interrogate their role in excitatory synaptogenesis of rat hippocampal neurons using RNA interference. Thereby, we identify seven circRNAs as negative regulators of excitatory synapse formation, many of which contain high-affinity microRNA binding sites. Knockdown of one of these candidates, circRERE, promotes the formation of electrophysiologically silent synapses. Mechanistically, circRERE knockdown results in a preferential upregulation of synaptic mRNAs containing binding sites for miR-128-3p. Overexpression of circRERE stabilizes miR-128-3p and rescues exaggerated synapse formation upon circRERE knockdown in a miR-128-3p binding site-specific manner. Overall, our results uncover circRERE-mediated stabilization of miR-128-3p as a means to restrict the formation of silent excitatory synaptic co-clusters and more generally implicate circRNA-dependent microRNA regulation in the control of synapse development and function.

Circular RNA in liver cancer research: biogenesis, functions, and roles

Liver cancer, characterized by its insidious nature, aggressive invasiveness, and propensity for metastasis, has witnessed a sustained increase in both incidence and mortality rates in recent years, underscoring the urgent need for innovative diagnostic and therapeutic approaches. Emerging research indicates that CircRNAs (circular RNAs) are abundantly and stably present within cells, with their expression levels closely associated with the progression of various malignancies, including hepatocellular carcinoma. In the context of liver cancer progression, circRNAs exhibit promising potential as highly sensitive diagnostic biomarkers, offering novel avenues for early detection, and also function as pivotal regulatory factors within the carcinogenic process. This study endeavors to elucidate the biogenesis, functional roles, and underlying mechanisms of circRNAs in hepatocellular carcinoma, thereby providing a fresh perspective on the pathogenesis of liver cancer and laying a robust foundation for the development of more precise and effective early diagnostic tools and therapeutic strategies.

CircRNAs: a novel potential strategy to treat breast cancer

Breast cancer is among the most prevalent malignant tumors worldwide, with triple-negative breast cancer (TNBC) being the most aggressive subtype and lacking effective treatment options. Circular RNAs (circRNAs) are noncoding RNAs that play crucial roles in the development of tumors, including breast cancer. This article examines the progress of research on circRNAs in breast cancer, focusing on four main areas: 1) breast cancer epidemiology, classification, and treatment; 2) the structure, discovery process, characteristics, formation, and functions of circRNAs; 3) the expression, mechanisms, clinical relevance, and recent advances in the study of circRNAs in breast cancer cells and the immune microenvironment, particularly in TNBC; and 4) the challenges and future prospects of the use of circRNAs in BC research.

The circular RNA circbabo(5,6,7,8S) regulates lipid metabolism and neuronal integrity via TGF-β/ROS/JNK/SREBP signaling axis in Drosophila

BACKGROUND

Lipid droplets (LDs) are dynamic cytoplasmic lipid-storing organelles that play a pivotal role in maintaining cellular energy balance, lipid homeostasis, and metabolic signaling. Dysregulation of lipid metabolism, particularly excessive lipogenesis, contributes to the abnormal accumulation of LDs in the nervous system, which is associated with several neurodegenerative diseases. Circular RNAs (circRNAs) are a new class of non-coding and regulatory RNAs that are widely expressed in eukaryotes. However, only a subset has been functionally characterized. Here, we identified and functionally characterized a new circular RNA circbabo(5,6,7,8S) that regulates lipogenesis and neuronal integrity in Drosophila melanogaster.

RESULTS

circbabo(5,6,7,8S) is derived from the babo locus which encodes the type I receptor for transforming growth factor β (TGF-β). Depletion of circbabo(5,6,7,8S) in flies causes elevated lipid droplet accumulation, progressive photoreceptor cell loss and shortened lifespan, phenotypes that are rescued by restoring circbabo(5,6,7,8S) expression. In addition, RNA-seq and epistasis analyses reveal that these abnormalities are caused by aberrant activation of the SREBP signaling pathway. Furthermore, circbabo(5,6,7,8S)-depleted tissues display enhanced activation of the TGF-β signaling pathway and compromised mitochondrial function, resulting in upregulation of reactive oxygen species (ROS). Moreover, we provide evidence that circbabo(5,6,7,8S) encodes the protein circbabo(5,6,7,8S)-p, which inhibits TGF-β signaling by interfering with the assembly of babo/put receptor heterodimer complex. Lastly, we show that dysregulation of the ROS/JNK/SREBP signaling cascade is responsible for the LD accumulation, neurodegeneration, and shortened lifespan phenotypes elicited by circbabo(5,6,7,8S) depletion.

CONCLUSIONS

Our study demonstrates the physiological role of the protein-coding circRNA circbabo(5,6,7,8S) in regulating lipid metabolism and neuronal integrity.

Engineering Lipid Nanoparticles for mRNA Immunotherapy

Over the last decades, messenger RNA (mRNA) has emerged as a promising therapeutic modality, enabling the delivery of genetic instructions to cells for producing therapeutic proteins or antigens. As such, mRNA-based therapies can be developed for a wide range of conditions, including infections, cancer, metabolic disorders, and genetic diseases. Nevertheless, using mRNA therapeutically requires chemical modifications to reduce immunostimulatory effects and nanotechnology to prevent degradation and ensure intracellular delivery. Lipid nanoparticles (LNPs) have become the most effective delivery platform for mRNA therapeutics, which are primarily employed for vaccine purposes following local administration and hepatic applications following systemic administration. Here, we review the state-of-the-art LNP-mRNA technology and discuss its potential for immunotherapy. We first outline the requirements for mRNA to be used therapeutically, including the role of LNP-mediated delivery. Next, we highlight LNP-mRNA immunotherapy approaches for vaccination, immuno-oncology, and autoimmune disorders. In addition, we discuss challenges that are limiting LNP-mRNA's widespread use, including tunable biodistribution and immunostimulatory effects. Finally, we provide an outlook on how implementing approaches such as library screening and machine learning will guide the development of next-generation mRNA therapeutics.

A Novel Protein NLRP12-119aa that Prevents Rhabdovirus Replication by Disrupting the RNP Complex Formation

The accurate assembly of the ribonucleoprotein (RNP) complex is fundamental for the replication and transcription of rhabdoviruses, which are known for their broad pathogenic impact. A novel 119-amino-acid protein, NLRP12-119aa is identified, encoded by the circular RNA circNLRP12, that effectively disrupts the formation of rhabdovirus RNP complexes through two distinct mechanisms and significantly reduces their replication. NLRP12-119aa exhibits a strong affinity for the conserved 18-nucleotide sequence at the start of the leader RNA of rhabdoviruses VSV, SCRV, and RABV, outcompeting their native N protein interactions, thereby disrupting the assembly of RNP complexes and inhibiting viral replication. NLRP12-119aa exerts anti-rhabdoviral effects by directly binding to the viral N protein, leading to its destabilization and accelerated degradation, and consequently hindering the formation of the viral RNP complex. To assess the therapeutic potential of circNLRP12 against rhabdovirus infections, a zebrafish model of VSV infection is established and noted a substantial reduction in viral load after-treatment with circNLRP12, as well as the recovery of spleen's to a normalized state from its previously enlarged and hemorrhagic state. Collectively, these findings elucidate a novel dual anti-RNP assembly strategy mediated by NLRP12-119aa, offering valuable insights for further exploration and clinical management of rhabdoviral infections.

NGR-Modified CAF-Derived exos Targeting Tumor Vasculature to Induce Ferroptosis and Overcome Chemoresistance in Osteosarcoma

Osteosarcoma (OS) chemoresistance presents a significant clinical challenge. This study aims to investigate the potential of using tumor vascular-targeting peptide NGR-modified cancer-associated fibroblasts (CAFs)-derived exosomes (exos) to deliver circ_0004872-encoded small peptides promoting autophagy-dependent ferroptosis to reverse chemoresistance in OS. Through combined single-cell transcriptome analysis and high-throughput sequencing, it identified circ_0004872 associated with chemoresistance. Subsequent experiments demonstrated that the small peptide encoded by this Circular RNA (circRNA) can effectively reverse chemoresistance by enhancing OS cell sensitivity to chemotherapy via the mechanism of promoting autophagy-dependent ferroptosis. Moreover, in vitro and in vivo results confirmed the efficient delivery of NGR-modified CAFs-derived exo-packaged circ_0004872-109aa to tumor cells, thereby improving targeted therapy efficacy. This study not only offers a novel strategy to overcome chemoresistance in OS but also highlights the potential application value of utilizing exos for drug delivery.

Circular RNA in Pancreatic Cancer: Biogenesis, Mechanism, Function and Clinical Application

Circular RNAs (circRNAs) are a class of novel RNA molecules featured by single-strand covalently closed circular structure, which not only are extensively found in eukaryotes and are highly conserved, but also conduct paramount roles in the occurrence and progression of pancreatic cancer (PC) through diverse mechanisms. As recent studies have demonstrated, circRNAs typically exhibit tissue-specific and cell specific expression patterns, with strong potential as biomarkers for disease diagnosis and prognosis. On the basis of their localization and specific interactions with DNA, RNA, and proteins, circRNAs are considered to possess specific biological functions by acting as microRNA (miRNA) sponges, RNA binding protein (RBP) sponges, transcriptional regulators, molecular scaffolds and translation templates. On that account, further addressing the technical difficulties in the detection and research of circRNAs and filling gaps in their biological knowledge will definitely push ahead this comparatively young research field and bring circRNAs to the forefront of clinical practice. Thus, this review systematically summarizes the biogenesis, function, molecular mechanisms, biomarkers and therapeutic targets of circRNAs in PC.

Coordinating interleukin-2 encoding circRNA with immunomodulatory lipid nanoparticles to potentiate cancer immunotherapy

Interleukin-2 (IL-2) is a cytokine vital for CD8+ T cell activation and proliferation, holding great potential for cancer immunotherapy. Nevertheless, inherent shortcomings of short half-life, activation of regulatory T (Treg) cells, and systemic toxicity limit its application. To tackle these, a circular RNA (cRNA)-based IL-2 therapy using immunomodulatory lipid nanoparticles [ursodeoxycholic acid lipid nanoparticles (ULNPs)] and sustained-release hydrogel was developed. Fusing fragment crystallizable (Fc) region into IL-2 and encoding this fusion protein IL-2-Fc (IL-2F) in cRNA (cRNAIL-2F) greatly extend the half-life. ULNPs containing ursodeoxycholic acid, a transforming growth factor-β1 inhibitor, suppress the function of Treg cells. Consequently, the ULNPs-cRNAIL-2F formulation promotes CD8+ T cells and suppresses Treg cells, increasing the CD8+/Treg ratio for effective immunotherapy. Furthermore, a locally administrated hydrogel loading with ULNPs-cRNAIL-2F sustains the release, enhancing efficacy and reducing toxicity. This innovative approach achieves remarkable tumor inhibition in both melanoma and orthotopic glioma models with or without surgery, offering a promising future for cancer immunotherapy.

Hsa_circ_0002301 inhibits ferroptosis in gastric cancer by encoding the de novo protein HECTD1-463aa

BACKGROUND

CircRNAs are closely related to ferroptosis in gastric cancer cells; however, the mechanism by which circRNAs regulate ferroptosis in gastric carcinogenesis remains unknown. CircRNA-encoded novel peptides are functional products translated from the open reading frames (ORFs) within circular RNAs, demonstrating that circRNAs not only serve as non-coding regulators but also have the capacity to encode biologically active peptides. Compared with noncancerous cells, cancer cells have greater iron requirements, and ferroptosis occurs in response to radiotherapy, chemotherapy, and immunotherapy; therefore, ferroptosis activation may be a potential strategy to overcome the shortcomings of conventional cancer therapy.

METHODS

A mouse model of ferroptosis in gastric cancer was constructed, and a bioinformatics analysis was performed to analyze and characterize the circRNAs involved in ferroptosis in gastric cancer. The inhibitory effect of hsa_circ_0002301 on ferroptosis in tumors was confirmed both in vitro and in vivo. The presence and expression of HECTD1-463aa were verified using mass spectrometry, protein blotting, and immunofluorescence staining. The molecular mechanism of hsa_circ_0002301 was investigated using mass spectrometry and immunoprecipitation.

RESULTS

We designed and synthesized antibodies specific for the small protein HECTD1-463aa encoded by hsa_circ_0002301 to verify its presence and purified HECTD1-463aa by constructing hsa_circ_0002301 overexpression vectors with FLAG tags and used liquid chromatography-tandem mass spectrometry (LC‒MS/MS) to detect the characterized peptides. In addition, HECTD1 binding to HECTD1-463aa was identified by immunoprecipitation (Co-IP) and mass spectrometry. We found that HECTD1-463aa inhibited HECTD1-mediated GPX4 ubiquitination by binding to HECTD1, an important regulator of cell death in ferroptotic cancer cells.

CONCLUSIONS

hsa_circ_0002301 competitively inhibits the degradation of the GPX4 protein by HECTD1 through the encoded proteins HECTD1-463aa and HECTD1 to affect the ferroptosis level in gastric cancer cells.

Structures of a natural circularly permuted group II intron reveal mechanisms of branching and backsplicing

Circularly permuted (CP) group II introns, identified in various bacteria phyla, swap domains D5 and D6 near the 5' end and have reversed splice sites (SSs), leading to backsplicing and circular RNA formation. In this study, we present multiple high-resolution cryo-electron microscopy structures of a natural CP group II intron from Comamonas testosteroni KF-1 (Cte 1), elucidating the molecular mechanisms of branching and backsplicing. During branching, the 5' SS is positioned by an auxiliary sequence (AUX)-enhanced interaction between the exon-binding site and intron-binding site (IBS) and stacks on the branch-site adenosine within D6, allowing the attacking 2'-OH group to coordinate with a metal ion in the active center. In backsplicing, the 3' SS is aligned with the branching step, leaving IBS in the active center, stabilized by base pairing with the AUX, which enables the free 3'-end hydroxyl group to directly attack the scissile phosphate of 3' SS. Furthermore, a groove in Cte 1 may stabilize the circular RNA. These findings highlight a conserved catalytic mechanism for canonical group II introns, albeit facilitated by the versatile AUX, opening avenues for designing potent ribozymes producing circular RNAs.

Exploratory Review and In Silico Insights into circRNA and RNA-Binding Protein Roles in γ-Globin to β-Globin Switching

β-globin gene cluster regulation involves complex mechanisms to ensure proper expression and function in RBCs. During development, switching occurs as γ-globin is replaced by β-globin. Key regulators, like BCL11A and ZBTB7A, repress γ-globin expression to facilitate this transition with other factors, like KLF1, LSD1, and PGC-1α; these regulators ensure an orchestrated transition from γ- to β-globin during development. While these mechanisms have been extensively studied, circRNAs have recently emerged as key contributors to gene regulation, but their role in β-globin gene cluster regulation remains largely unexplored. Although discovered in the 1970s, circRNAs have only recently been recognized for their functional roles, particularly in interactions with RNA-binding proteins. Understanding how circRNAs contribute to switching from γ- to β-globin could lead to new therapeutic strategies for hemoglobinopathies, such as sickle cell disease and β-thalassemia. This review uses the circAtlas 3.0 database to explore circRNA expressions in genes related to switching from γ- to β-globin expression, focusing on blood, bone marrow, liver, and spleen. It emphasizes the exploration of the potential interactions between circRNAs and RNA-binding proteins involved in β-globin gene cluster regulatory mechanisms, further enhancing our understanding of β-globin gene cluster expression.

The Small Non-Coding RNA Profile of Human and Mouse Sperm

Small non-coding RNAs constitute a dynamic epigenetic layer in mature spermatozoa that can exert transgenerational regulatory functions. Here, we review recent advances in the field of small RNAs in spermatozoa, how their profiles change in response to lifestyle or environmental factors, and their impact on offsprings' physiology. The profile of these RNAs changes dramatically during spermatozoa maturation. The majority of intracellular small RNAs during early spermatogenesis are miRNAs and piRNAs, but, in mature spermatozoa, tRNA- and rRNA-derived fragments (tRFs and rRFs, respectively) are the predominant forms, primarily delivered from the epididymis via extracellular vesicles. Diet, exercise, and environmental exposures have a direct effect on small RNA levels in spermatozoa, and this differential abundance can reprogram the development of the embryo. Offsprings of fathers with different lifestyles can have different phenotypes, including altered metabolism or behavior. Therefore, small RNAs in spermatozoa are emerging as an important epigenetic layer in development and transgenerational inheritance.

CircPTK2 as a Valuable Biomarker and Treatment Target in Cancer

Circular RNA (CircRNA)s, a newly discovered type of noncoding RNAs, have been found to play a role in controlling the development and aggressiveness of tumors. Abnormal control of circRNA has been observed in various types of human cancers, including bladder cancer, hepatocellular carcinoma (HCC), breast cancer, and gastric cancer (GC). CircRNAs possess binding sites for microRNAs (miRNAs) and function as miRNA sponges in posttranscriptional regulation. This mechanism has been documented to influence the course of cancer. Significantly, among these putative circRNAs, circular RNA protein tyrosine kinase 2 (circPTK2) exhibited increased expression and displayed a substantial association with adverse clinical characteristics and a negative prognosis. The production of these transcripts occurs via a back-splicing mechanism. The enclosed conformation of circRNAs shields them from destruction and enhances their potential as biomarkers. Gaining insight into the molecular mechanisms involved in these processes would aid in the development of treatment approaches and the discovery of new tumor markers. This article provides a comprehensive assessment of the latest research on the biosynthesis and features of circRNAs. It examines the role of circPTK2 in the diagnosis, treatment, and prognosis evaluation of cancer.

CircBTBD7-420aa Encoded by hsa_circ_0000563 Regulates the Progression of Atherosclerosis and Construction of circBTBD7-420aa Engineered Exosomes

Circular RNAs are associated with cardiovascular disease, including coronary artery disease, but the mechanisms have not been completely elucidated. We found a new protein, circBTBD7-420aa, encoded by hsa_circ_0000563. Our results suggest that circBTBD7-420aa may inhibit the abnormal proliferation and migration of human coronary artery smooth muscle cells by promoting SLC3A2 degradation through the ubiquitin-proteasome pathway. In addition, we constructed engineered exosomes loaded with circBTBD7-420aa that can target vascular smooth muscle cells by modifying peptide fragments targeting osteopontin. This study suggests that circBTBD7-420aa may inhibit the progression of atherosclerosis and serve as a new target for the diagnosis and treatment of coronary artery disease.

Circular RNA-Cacna1d Plays a Critical Role in Sepsis-induced Lung Injury by Sponging microRNA-185-5p

The role of circular RNAs (circRNAs) in sepsis-induced lung injury is not clear. This study investigated the role and molecular mechanism of a novel circRNA in sepsis-induced lung injury and explored its prognostic value in patients with sepsis. In this study, aberrant circRNA expression profiling in lung tissues from mice with sepsis-induced lung injury was analyzed using high-throughput sequencing. circRNA-Cacna1d was verified by qRT-PCR, and its biological function in sepsis-induced lung injury was validated in vitro and in vivo. The interactions among circRNA-Cacna1d, microRNAs (miRNAs), and their downstream genes were verified. Furthermore, the clinical value of circRNA-Cacna1d in peripheral blood from patients with sepsis was also evaluated. We found that circRNA-Cacna1d expression was significantly increased in lung tissues of mice with sepsis and in microvascular endothelial cells after LPS challenge. circRNA-Cacna1d knockdown alleviated inflammatory response and ameliorated the permeability of vascular endothelium, thereby mitigating sepsis-induced lung injury and significantly improving the survival rate of mice with sepsis. Mechanistically, circRNA-Cacna1d directly interacted with miRNA-185-5p and functioned as a miRNA sponge to regulate the RhoA/ROCK1 signaling pathway. The expression level of circRNA-Cacna1d in patients with early sepsis was significantly higher than that in the healthy control subjects. Higher levels of circRNA-Cacna1d in patients with sepsis were associated with increased disease severity and poorer outcomes. In conclusions, circRNA-Cacna1d may play a role in sepsis-induced lung injury by regulating the RhoA/ROCK1 axis by acting as a miRNA-185-5p sponge. circRNA-Cacna1d is a potential therapeutic target for sepsis-induced lung injury and a prognostic biomarker in sepsis.

Finding functional microproteins

Genome-wide translational profiling has uncovered the synthesis in human cells of thousands of microproteins, a class of proteins traditionally overlooked in functional studies. Although an increasing number of these microproteins have been found to play critical roles in cellular processes, the functional relevance of the majority remains poorly understood. Studying these low-abundance, often unstable proteins is further complicated by the challenge of disentangling their functions from the noncoding roles of the associated DNA, RNA, and the act of translation. This review highlights recent advances in functional genomics that have led to the discovery of >1000 human microproteins required for optimal cell proliferation. Ongoing technological innovations will continue to clarify the roles and mechanisms of microproteins in both normal physiology and disease, potentially opening new avenues for therapeutic exploration.

Exploring precision treatments in immune-mediated inflammatory diseases: Harnessing the infinite potential of nucleic acid delivery

Immune-mediated inflammatory diseases (IMIDs) impose an immeasurable burden on individuals and society. While the conventional use of immunosuppressants and disease-modifying drugs has provided partial relief and control, their inevitable side effects and limited efficacy cast a shadow over finding a cure. Promising nucleic acid drugs have shown the potential to exert precise effects at the molecular level, with different classes of nucleic acids having regulatory functions through varying mechanisms. For the better delivery of nucleic acids, safe and effective viral vectors and non-viral delivery systems (including liposomes, polymers, etc.) have been intensively explored. Herein, after describing a range of nucleic acid categories and vectors, we focus on the application of therapeutic nucleic acid delivery in various IMIDs, including rheumatoid arthritis, inflammatory bowel disease, psoriasis, multiple sclerosis, asthma, ankylosing spondylitis, systemic lupus erythematosus, and uveitis. Molecules implicated in inflammation and immune dysregulation are abnormally expressed in a series of IMIDs, and their meticulous modulation through nucleic acid therapy results in varying degrees of remission and improvement of these diseases. By synthesizing findings centered on specific molecular targets, this review delivers a systematic elucidation and perspective towards advancing and utilization of nucleic acid therapeutics for managing IMIDs.

Structural basis of circularly permuted group II intron self-splicing

Circularly permuted group II introns (CP introns) consist of rearranged structural domains separated by two tethered exons, generating branched introns and circular exons via back-splicing. Structural and mechanistic understanding of circular RNA (circRNA) generation by CP introns remains elusive. We resolve cryo-electron microscopy structures of a natural CP intron in different states during back-splicing at a resolution of 2.5-2.9 Å. Domain 6 (D6) undergoes a conformational change of 65° after branching, to facilitate 3'-exon recognition and circularization. Previously unseen tertiary interactions compact the catalytic triad and D6 for splicing without protein, whereas a metal ion, M35, is observed to stabilize the 5'-exon during splicing. While these unique features were not observed in canonical group II introns and spliceosomes, they are common in CP introns, as demonstrated by the cryo-EM structure of another CP intron discovered by comparative genomics analysis. Our results elucidate the mechanism of CP intron back-splicing dynamics, with potential applications in circRNA research and therapeutics.

The role of circular RNAs in autoimmune diseases: Potential diagnostic biomarkers and therapeutic targets

With the emergence of high-quality sequencing technologies, further research on transcriptomes has become possible. Circular RNA (circRNA), a novel type of endogenous RNA molecule with a covalently closed circular structure through "back-splicing," is reported to be widely present in eukaryotic cells and participates mainly in regulating gene and protein expression in various ways. It is becoming a research hotspot in the non-coding RNA field. CircRNA shows close relation to several varieties of autoimmune diseases (AIDs) in both the physiological and pathological level and could potentially be used clinically in terms of diagnosis and treatment. Here, we focus on reviewing the importance of circRNA in various AIDs, with the aim of establishing new biomarkers and providing novel insights into understanding the role and functions of circRNA in AIDs. Specific signaling pathways of how circular RNAs are regulated in AIDs will also be illustrated in this review.

The Role of the Dysregulation of circRNAs Expression in Glioblastoma Multiforme

Primary brain tumors that were the most severe and aggressive were called glioblastoma multiforme (GBM). Cancers are caused in part by aberrant expression of circular RNA. Often referred to as competitive endogenous RNA (ceRNA), circRNA molecules act as "miRNA sponges" in cells by decreasing the inhibitory impact of miRNA on their target genes and hence raising the expression levels of those genes. circRNA molecules are rich in miRNA binding sites. The discovery of more structurally diverse and GBM-related circRNAs has great promise for the use of GMB prognostic biomarkers and therapeutic targets, as well as for comprehending the molecular regulatory mechanisms of GBM. In this work, we present an overview of the circRNA expression patterns associated with GBM and offer a potential integrated electrochemical strategy for detecting circRNA with extreme sensitivity in the diagnosis of glioblastoma.

Translation of circular RNAs

Circular RNAs (circRNAs) are covalently closed RNAs that are present in all eukaryotes tested. Recent RNA sequencing (RNA-seq) analyses indicate that although generally less abundant than messenger RNAs (mRNAs), over 1.8 million circRNA isoforms exist in humans, much more than the number of currently known mRNA isoforms. Most circRNAs are generated through backsplicing that depends on pre-mRNA structures, which are influenced by intronic elements, for example, primate-specific Alu elements, leading to species-specific circRNAs. CircRNAs are mostly cytosolic, stable and some were shown to influence cells by sequestering miRNAs and RNA-binding proteins. We review the increasing evidence that circRNAs are translated into proteins using several cap-independent translational mechanisms, that include internal ribosomal entry sites, N6-methyladenosine RNA modification, adenosine to inosine RNA editing and interaction with the eIF4A3 component of the exon junction complex. CircRNAs are translated under conditions that favor cap-independent translation, notably in cancer and generate proteins that are shorter than mRNA-encoded proteins, which can acquire new functions relevant in diseases.

CICADA: a circRNA effort toward the ghost proteome

Recent studies have confirmed that certain circRNAs encode proteins that are integral to various biological functions. In this study, we present CICADA, an algorithm specifically designed to assess the protein-coding potential and coding products of circRNAs at high throughput, which enables the identification of previously unknown circRNA-encoded proteins. By harnessing the potential of this algorithm, we identified a variety of functional, protein-coding circRNAs in esophageal squamous cell carcinoma and established circRNA translation profiles for diverse types of cancer. This advancement innovatively explores the hidden proteome within the genome, poised to catalyze discoveries in biomarkers and therapies for cancers and complex diseases. CICADA is accessible as a Python module (https://github.com/SunLab-biotool/CICADA).

Recent advances in the regulatory and non-coding RNA biology of osteogenic differentiation: biological functions and significance for bone healing

Injuries associated with contemporary life, such as automobile crashes and sports injuries, can lead to large numbers of traumatic neuromuscular injuries that are intimately associated with bone fractures. Regulatory and non-coding RNAs play essential roles in multiple cellular processes, including osteogenic differentiation and bone healing. In this review, we discuss the most recent advances in our understanding of the regulatory and non-coding RNA biology of osteogenic differentiation in stem, stromal and progenitor cells. We focused on circular RNAs, small nucleolar RNAs and PIWI-interacting RNAs and comprehensively summarized their biological functions as well as discussed their significance for bone healing and tissue regeneration.

Expanding the Potential of Circular RNA (CircRNA) Vaccines: A Promising Therapeutic Approach

In recent years, circular RNAs (circRNAs) have garnered significant attention due to their unique structure and function, positioning them as promising candidates for next-generation vaccines. The circRNA vaccine, as an RNA vaccine, offers significant advantages in preventing infectious diseases by serving as a vector for protein expression through non-canonical translation. Notably, circRNA vaccines have demonstrated enduring antigenic expression and generate a larger percentage of neutralizing antibodies compared to mRNA vaccines administered at the same dosage. Furthermore, circRNA vaccines can elicit robust cellular and humoral immunity, indicating their potential for tumor vaccine development. However, certain challenges must be addressed to facilitate the widespread use of circRNA vaccines in both infectious disease prevention and tumor treatment. These challenges include the low efficiency of linear RNA circularization, the suboptimal targeting of delivery systems, and the assessment of potential side effects. This work aims to describe the characteristics and functions of circRNAs, elucidate the mechanism behind circRNA vaccines, and discuss their applications in the prevention of infectious diseases and the treatment of tumors, along with their potential future applications.