Circular RNA CircFndc3b modulates cardiac repair after myocardial infarction via FUS/VEGF-A axis

CircUCK2 regulates HECTD1-mediated endothelial-mesenchymal transition inhibition by interacting with FUS and protects the blood-brain barrier in ischemic stroke

Ischemic stroke (IS) has become a cerebrovascular disease of widespread concern. Overexpression of circUCK2 alleviates neuronal damage in IS. However, the specific regulatory mechanisms of circUCK2 are not fully understood. In this study, we found that circUCK2 and HECT domain E3 ubiquitin ligase 1 (HECTD1) were downregulated in IS models in vitro and in vivo. Overexpression of circUCK2 or HECTD1 inhibited endothelial-mesenchymal transition (EndoMT) and protected the blood-brain barrier (BBB) in transient middle cerebral artery occlusion mice from damage. It was further discovered that circUCK2 regulated HECTD1 expressions by interacting with fused in sarcoma (FUS). Moreover, FUS overexpression partially restored the effect of circUCK2 on EndoMT, and overexpression of HECTD1 weakened the effect of FUS on EndoMT. Collectively, circUCK2 upregulates the expression of HECTD1 by combining with FUS and inhibits EndoMT to alleviate BBB damage in IS both in vivo and in vitro.

CircZNF367 suppresses osteogenic differentiation of human bone marrow mesenchymal stromal/stem cells via reducing HuR-mediated mRNA stability of LRP5

Osteoporosis is a highly prevalent disease characterized by bone mass loss and structural deterioration. There are evidences that altered differentiation of human bone marrow mesenchymal stromal/stem cells (hBMSCs) is a major cause for osteoporosis. Recent studies suggest that circular RNAs (circRNAs) are dysregulated in osteoporosis patients and involved in the pathogenesis of osteoporosis. In the present study, we are aimed to analyze the circRNA expression profiles in osteoporosis patients and identify potential circRNAs that involved in the differentiation of hBMSCs during osteoporosis. Transcriptome RNA-sequencing was conducted to search for differentially expressed circRNAs. Transwell assay, ARS and ALP staining, and ectopic bone formation model were performed to evaluate osteogenic differentiation of hBMSCs. RNA pull-down assay, RNA immunoprecipitation, western blot, and in vitro binding assay were conducted to evaluate the interaction of circRNAs and RNA-binding protein HuR. We found that hsa_circ_0008842 (designated as circZNF367) was upregulated in osteoporosis patients and decreased in hBMSCs during osteogenic differentiation. CircZNF367 overexpression suppressed migration, invasion and osteogenic differentiation of hBMSCs in vitro and in vivo. In comparison, knockdown of circZNF367 promoted migration, invasion and osteogenic differentiation of hBMSCs. CircZNF367 could interact with the RNA-binding protein HuR, thus reduced the mRNA stability of LRP5. Furthermore, HuR overexpression or LRP5 restoration abrogated the effects of circZNF367 overexpression on osteogenic differentiation of hBMSCs. Our results indicated that circZNF367 played a role in osteogenic differentiation of hBMSCs via reducing HuR-mediated mRNA stability of LRP5.

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

Purpose

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

Methods

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

Results

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

Conclusion

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

N6 -methyladenosine-modified circRNA RERE modulates osteoarthritis by regulating β-catenin ubiquitination and degradation

OBJECTIVES

N⁶ -methyladenosine (m6A) is one of the most abundant internal RNA modifications. We investigated the role of m6A-modified circRERE in osteoarthritis (OA) and its mechanism.

MATERIALS AND METHODS

CircRERE and IRF2BPL were screened by microarrays. The role of m6A-modification in circRERE was examined by methylated RNA precipitation and morpholino oligo (MOs) treatment. The axis of circRERE/miR-195-5p/IRF2BPL/β-catenin was determined using flow cytometry, western blotting and immunofluorescence in human chondrocytes (HCs) and corroborated using a mouse model of destabilization of medial meniscus (DMM) with intra-articular (IA) injection of adeno-associated viruses (AAV).

RESULTS

CircRERE was decreased in OA cartilage and chondrocytes compared with control. CircRERE downregulation was likely attributed to its increased m6A modification prone to endoribonucleolytic cleavage by YTHDF2-HRSP12-RNase P/MRP in OA chondrocytes. MOs transfection targeting HRSP12 binding motifs in circRERE partially reversed decreased circRERE expression and increased apoptosis in HCs treated with IL-1β for 6 h. CircRERE exerted chondroprotective effects by targeting miR-195-5p/IRF2BPL, thus regulating the ubiquitination and degradation of β-catenin. CircRere (mouse homologue) overexpression by IA-injection of AAV-circRere into mice attenuated the severity of DMM-induced OA, whereas AAV-miR-195a-5p or AAV-sh-Irf2bpl reduced the protective effects. The detrimental effects of AAV-sh-Irf2bpl on DMM-induced OA were substantially counteracted by ICG-001, an inhibitor of β-catenin.

CONCLUSIONS

Our study is a proof-of-concept demonstration for targeting m6A-modified circRERE and its target miR-195-5p/IRF2BPL/β-catenin as potential therapeutic strategies for OA treatment.

Dysfunctional network of hub genes in hypertrophic cardiomyopathy patients

BACKGROUND

Considering it is one of the major causes of sudden cardiac arrest, the proper management of hypertrophic cardiomyopathy (HCM) is essential. However, efficient treatment options for this disease are still lacking. The discovery of HCM-associated hub genes may help in diagnosis and offer a reliable tool for developing effective therapeutic strategies.

METHODS

We examined HCM-based gene expression datasets (GSE36961) from the Gene Expression Omnibus (GEO) database for the identification of differentially expressed genes (DEGs), PPI network development, module screening, and shortlisting of hub genes via GEOR2, STRING, and Cytoscape. Moreover, we also used another HCM-based gene expression dataset (GSE32453) for the expression validation of hub genes. Following this, we constructed the lncRNA-cricRNA-miRNA-mRNA regulatory network after retrieving information from the miRTarBase, miRDB, and MiRcode databases. Finally, we used DAVID to perform functional and pathway analysis of the hub genes.

RESULTS

From GSE36961, a total of the 262 most significant DEGs, including 162 down-regulated and 76 up-regulated, were identified between HCM patients and normal individuals. Among these DEGs, a total of 10 significantly down-regulated DEGs, including cluster of differentiation 14 (CD14), beta2 Integrin Gene (ITGB2), C1q subcomponent subunit B (C1QB), Cluster of Differentiation 163 (CD163), Hematopoietic Cell-Specific Lyn Substrate 1 (HCLS1), Arachidonate 5-Lipoxygenase Activating Protein (ALOX5AP), Pleckstrin (PLEK), Complement C1q C Chain (C1QC), Fc fragment Of IgE receptor Ig (FCER1G), and tyrosine kinase binding protein (TYROBP), were shortlisted as the hub genes. Pathway enrichment analysis showed that the identified hub genes were involved in the dysregulation of some diverse pathways in HCM patients. Such as, Pertussis, Complement and coagulation cascade, Legnionellosis, Asthma, Staphylococcus aureus infection, etc. Lastly, we also explored hub genes' regulatory 2 MicroRNAs (miRNAs, has-mir-7-5p and has-mir-27a-3p), one Long non-coding RNAs (lncRNA, OIP5-AS1-201), and one Circular RNA (cricRNA, CDR1as) via lncRNA-cricRNA-miRNA-mRNA regulatory network.

CONCLUSION

Our study revealed that ten hub genes (CD14, ITGB2, C1QB, CD163, HCLS1, ALOX5AP, PLEK, C1QC, FCER1G, and TYROBP) are involved in the development and progression of HCM. These genes can potentially be used as biomarkers and therapeutic targets for HCM patients.

circPLIN2 promotes clear cell renal cell carcinoma progression by binding IGF2BP proteins and miR-199a-3p

Recent evidence has indicated that circular RNAs (circRNAs), a novel type of regulatory RNA, play important roles in the development and progression of various cancers. However, the potential regulatory roles and molecular mechanisms of circRNAs in clear cell renal cell carcinoma (ccRCC) remain largely unclear. Here, we explored circRNA expression profiles in 10 paired samples of RCC (including cancer tissues and surrounding tissues) from the Gene Expression Omnibus (GEO) datasets GSE124453 and GSE108735. We initially identified hsa_circ_0086457, designated circPLIN2, derived from exons 4 to 5 of the PLIN2 gene. We observed that circPLIN2 was preferentially located in the cytoplasm and was more stable than its linear counterpart PLIN2. circPLIN2 was significantly upregulated in ccRCC cells and tissues, and its overexpression was correlated with higher clinical stage and worse prognosis for ccRCC patients. Moreover, gain- and loss-of-function assays indicated that circPLIN2 promoted ccRCC cell proliferation, migration, and invasion in vitro and ccRCC tumor growth and metastasis in vivo. Mechanistically, circPLIN2 not only increased the stability of the c-Myc and MARCKSL1 mRNAs by binding to the KH domains of IGF2BP proteins but also competitively sponged miR-199a-3p to abolish the repressive effect of miR-199a-3p on ZEB1 expression, which ultimately resulted in ccRCC tumorigenesis and progression. Collectively, our results suggest that circPLIN2 may represent a promising diagnostic and prognostic biomarker and a potential therapeutic target for ccRCC patients.

Mechanisms of circular RNA degradation

Circular RNAs (CircRNAs) are a class of noncoding RNAs formed by backsplicing during cotranscriptional and posttranscriptional processes, and they widely exist in various organisms. CircRNAs have multiple biological functions and are associated with the occurrence and development of many diseases. While the biogenesis and biological function of circRNAs have been extensively studied, there are few studies on circRNA degradation and only a few pathways for specific circRNA degradation have been identified. Here we outline basic information about circRNAs, summarize the research on the circRNA degradation mechanisms and discusses where this field might head, hoping to provide some inspiration and guidance for scholars who aim to study the degradation of circRNAs.

Dihydromyricetin Alleviates H9C2 Cell Apoptosis and Autophagy by Regulating CircHIPK3 Expression and PI3K/AKT/mTOR Pathway

OBJECTIVE

To investigate the effect and potential mechanism of dihydromyricetin (Dmy) on H9C2 cell proliferation, apoptosis, and autophagy.

METHODS

H9C2 cells were randomly divided into 7 groups, namely control, model, EV (empty pCDH-CMV-MCS-EF1-CopGFP-T2A-Puro vector), IV (circHIPK3 interference), Dmy (50 µ mol/L), Dmy+IV, and Dmy+EV groups. Cell proliferation and apoptosis were detected by cell counting kit-8 assay and flow cytometry, respectivley. Western blot was used to evaluate the levels of light chain 3 II/I (LC3II/I), phospho-phosphoinositide 3-kinase (p-PI3K), protein kinase B (p-AKT), and phospho-mammalian target of rapamycin (p-mTOR). The level of circHIPK3 was determined using reverse transcriptase polymerase chain reaction. Electron microscopy was used to observe autophagosomes in H9C2 cells.

RESULTS

Compared to H9C2 cells, the expression of circHIPK in H9C2 hypoxia model cells increased significantly (P<0.05). Compared to the control group, the cell apoptosis and autophagosomes increased, cell proliferation rate decreased significantly, and the expression of LC3 II/I significantly increased (all P<0.05). Compared to the model group, the rate of apoptosis and autophagosomes in IV, Dmy, and Dmy+IV group decreased, the cell proliferation rate increased, and the expression of LC3 II/I decreased significantly (all P<0.05). Compared to the control group, the expressions of p-PI3K, p-AKT, and p-mTOR in the model group significantly reduced (P<0.05), whereas after treatment with Dmy and sh-circHIPK3, the above situation was reversed (P<0.05).

CONCLUSION

Dmy plays a protective role in H9C2 cells by inhibiting circHIPK expression and cell apoptosis and autophagy, and the mechanism may be related to PI3K/AKT/mTOR pathway.

CircRNA_45478 promotes ischemic AKI by targeting the miR-190a-5p/PHLPP1 axis

A few studies suggested that circular RNAs were involved in the development of ischemic acute kidney injury (AKI). However, the function and regulation mechanism of circRNA_45478 in ischemic AKI remains unknown. In the present study, ischemic injury induced the expressions of circRNA_45478 in mouse proximal tubule-derived cell lines (BUMPT cells) and kidneys of C57BL/6 mice. Functionally, circRNA_45478 mediated I/R-induced apoptosis in BUMPT cells. Mechanistically, circRNA_45478 upregulated the expression of Pleckstrin homology (PH) domain leucine-rich repeat protein phosphatase 1 (PHLPP1) via sponging of microRNA (miR)-190a-5p. Finally, inhibition of circRNA_45478 significantly alleviated the progression of ischemic AKI through regulation of the miR-190a-5p/PHLPP1 pathway. Taken together, our data showed that circRNA_45478/miR-190a-5p/PHLPP1 axis mediated the progression of ischemic AKI.

CircCLTH promotes skeletal muscle development and regeneration

Buffalo holds an excellent potential for beef production, and circRNA plays an important role in regulating myogenesis. However, the regulatory mechanism of circRNAs during buffalo skeletal muscle development has not been fully explored. In this study, circRNA expression profiles during the proliferation and differentiation stages of buffalo myoblasts were analysed by RNA-seq. Here, a total of 3,142 circRNAs candidates were identified, and 110 of them were found to be differentially expressed in the proliferation and differentiation stages of buffalo myoblast libraries. We focused on a 347 nt circRNA subsequently named circCLTH. It consists of three exons and is expressed specifically in muscle tissues. It is a highly conserved non-coding RNA with about 95% homology to both the human and the mouse circRNAs. The results of cell experiments and RNA pull-down assays indicated that circCLTH may capture PLEC protein, promote the proliferation and differentiation of myoblasts as well as inhibit apoptosis. Overexpression of circCLTH in vivo suggests that circCLTH is involved in the stimulation of skeletal muscle regeneration. In conclusion, we identified a novel noncoding regulator, circCLTH, that promotes proliferation and differentiation of myoblasts and skeletal muscles.

Comparative Analysis of Non-Coding RNA Transcriptomics in Heart Failure

Heart failure constitutes a clinical complex syndrome with different symptomatic characteristics depending on age, sex, race and ethnicity, among others, which has become a major public health issue with an increasing prevalence. One of the most interesting tools seeking to improve prevention, diagnosis, treatment and prognosis of this pathology has focused on finding new molecular biomarkers since heart failure relies on deficient cardiac homeostasis, which is regulated by a strict gene expression. Therefore, currently, analyses of non-coding RNA transcriptomics have been oriented towards human samples. The present review develops a comparative study emphasizing the relevance of microRNAs, long non-coding RNAs and circular RNAs as potential biomarkers in heart failure. Significantly, further studies in this field of research are fundamental to supporting their widespread clinical use. In this sense, the various methodologies used by the authors should be standardized, including larger cohorts, homogeneity of the samples and uniformity of the bioinformatic pipelines used to reach stratification and statistical significance of the results. These basic adjustments could provide promising steps to designing novel strategies for clinical management of patients with heart failure.

Involvement of circRNAs in the Development of Heart Failure

In recent years, interest in non-coding RNAs as important physiological regulators has grown significantly. Their participation in the pathophysiology of cardiovascular diseases is extremely important. Circular RNA (circRNA) has been shown to be important in the development of heart failure. CircRNA is a closed circular structure of non-coding RNA fragments. They are formed in the nucleus, from where they are transported to the cytoplasm in a still unclear mechanism. They are mainly located in the cytoplasm or contained in exosomes. CircRNA expression varies according to the type of tissue. In the brain, almost 12% of genes produce circRNA, while in the heart it is only 9%. Recent studies indicate a key role of circRNA in cardiomyocyte hypertrophy, fibrosis, autophagy and apoptosis. CircRNAs act mainly by interacting with miRNAs through a "sponge effect" mechanism. The involvement of circRNA in the development of heart failure leads to the suggestion that they may be promising biomarkers and useful targets in the treatment of cardiovascular diseases. In this review, we will provide a brief introduction to circRNA and up-to-date understanding of their role in the mechanisms leading to the development of heart failure.

Role of circular RNA cdr1as in modulation of macrophage phenotype

AIMS

Macrophages are crucial for the initiation and resolution of an inflammatory response. Non-coding circular RNAs are ubiquitously expressed in mammalian tissue, highly conserved among species, and recently implicated in the regulation of macrophage activation. We sought to determine whether circRNAs modulate monocyte/macrophage biology and function.

MATERIALS AND METHODS

We performed circRNA microarray analyses to assess transcriptome changes using RNA isolated from bone marrow derived macrophages polarized to a pro-inflammatory phenotype (INFγ + TNFα) or an anti-inflammatory phenotype (IL-10, IL-4, and TGF-β). Among differentially expressed circRNAs, circ-Cdr1as was chosen for further investigation. Additionally, we performed loss or gain of function studies to investigate if circ-Cdr1as is involved in phenotypic switching. For gain of function, we overexpressed circ-Cdr1as using pc3.1 plasmid with laccase2 flanking regions to promote circularization. For loss of function, we used a lentiviral short hairpin RNA targeting the circ-Cdr1as splicing junction.

KEY FINDINGS

Among circRNAs that are highly conserved and differentially expressed in pro- and anti-inflammatory lineages, circ-Cdr1as was one of the most downregulated in pro-inflammatory macrophages and significantly upregulated in anti-inflammatory macrophages in vitro. Overexpression of circ-Cdr1as increased transcription of anti-inflammatory markers and percentage of CD206+ cells in naïve and pro-inflammatory macrophages in vitro. Meanwhile, knockdown decreased transcription of anti-inflammatory markers and increased the percentage of CD86+ cells in naïve and anti-inflammatory macrophages in vitro.

SIGNIFICANCE

This study suggests that circ-Cdr1as plays a key role in regulating anti-inflammatory phenotype of macrophages and may potentially be developed as an anti-inflammatory regulator in tissue inflammation.

Epigenetic regulation in myocardial infarction: Non-coding RNAs and exosomal non-coding RNAs

Myocardial infarction (MI) is one of the leading causes of deaths globally. The early diagnosis of MI lowers the rate of subsequent complications and maximizes the benefits of cardiovascular interventions. Many efforts have been made to explore new therapeutic targets for MI, and the therapeutic potential of non-coding RNAs (ncRNAs) is one good example. NcRNAs are a group of RNAs with many different subgroups, but they are not translated into proteins. MicroRNAs (miRNAs) are the most studied type of ncRNAs, and have been found to regulate several pathological processes in MI, including cardiomyocyte inflammation, apoptosis, angiogenesis, and fibrosis. These processes can also be modulated by circular RNAs and long ncRNAs via different mechanisms. However, the regulatory role of ncRNAs and their underlying mechanisms in MI are underexplored. Exosomes play a crucial role in communication between cells, and can affect both homeostasis and disease conditions. Exosomal ncRNAs have been shown to affect many biological functions. Tissue-specific changes in exosomal ncRNAs contribute to aging, tissue dysfunction, and human diseases. Here we provide a comprehensive review of recent findings on epigenetic changes in cardiovascular diseases as well as the role of ncRNAs and exosomal ncRNAs in MI, focusing on their function, diagnostic and prognostic significance.

Hsa_circ_0008870 suppresses bone formation of growth plate through inhibition of miR-185-3p/ MAPK1 axis in idiopathic short stature

Idiopathic short stature (ISS) is the most common clinical cause of the short stature with an unclear aetiology and a lack of effective treatment. Circular RNAs have been shown to play a significant regulatory role through various signal transduction pathways in a variety of diseases in recent years. However, the role of circular RNAs on ISS is not yet well-understood and requires a special attention. The differentially expressed circular RNAs were screened by microarray chip analysis, and RT-qPCR was used to verify the expression of hsa_circ_0008870 in ISS patients. Subsequently, in vitro and in vivo experiments were conducted to determine the biological functions of hsa_circ_0008870 in ISS. The authors first confirmed that hsa_ circ_0008870 was downregulated in ISS children. Meanwhile, we also observed that the downregulated hsa_circ _0008870 significantly inhibited chondrocyte proliferation and endochondral ossification in vivo and in vitro. Mechanistically, hsa_circ_0008870 regulates MAPK1 expression by sponge miR-185-3p. This mechanism of action was further verified through rescue experiments. Finally, the authors revealed that the silencing of hsa_circ_0008870 induces low expression of MAPK1 by impairing the sponge action of miR-185-3p, thereby inhibiting chondrocyte proliferation, hypertrophy, and endochondral ossification, which results in a short stature phenotype. In addition to these, we also observed an interesting phenomenon that upregulated of miR-185-3p can in turn inhibit the expression of hsa_circ_0008870 in chondrocytes. This suggests that hsa_circ_0008870 could potentially serve as a therapeutic target for the treatment of ISS.

Expression Profiles and Functional Analysis of Plasma Exosomal Circular RNAs in Acute Myocardial Infarction

Acute myocardial infarction (AMI) is a common cardiovascular disease with high rates of morbidity and mortality globally. The dysregulation of circular RNAs (circRNAs) has been shown to be closely related to various pathological aspects of AMI. However, the function of exosomal circRNAs in AMI has yet to be investigated. The purpose of this study was to investigate the expression profiles of plasma exosomal circRNAs in AMI and explore their potential functionality. The expression profiles of plasma exosomal circRNAs in patients with AMI, stable coronary heart atherosclerotic disease (CAD), and healthy controls were obtained from a GEO expression dataset (GSE159657). We also analyzed bioinformatics functionality, potential pathways, and interaction networks related to the microRNAs associated with the differentially expressed circRNAs. A total of 253 exosomal circRNAs (184 up- and 69 down-regulated) and 182 exosomal circRNAs (94 up- and 88 down-regulated) were identified as being differentially expressed between the control group and the AMI and CAD patients, respectively. Compared with the CAD group, 231 different exosomal circRNAs (177 up- and 54 down-regulated) were identified in the AMI group. Functional analysis suggested that the parental genes of exosomal has_circ_0061776 were significantly enriched in the biological process of lysine degradation. Pathway interaction network analysis further indicated that exosomal has_circ_0061776 was associated with has-miR-133a, has-miR-214, has-miR-423, and has-miR-217 and may play a role in the pathogenesis of AMI through the MAPK signaling pathway. This study identified the differential expression and functionality of exosomal circRNAs in AMI and provided further understanding of the potential pathogenesis of an exosomal circRNA-related competing endogenous RNA (ceRNA) network in AMI.

circKMT2E Protect Retina from Early Diabetic Retinopathy through SIRT1 Signaling Pathway via Sponging miR-204-5p

Objective

To explore the changes of circRNAs in the retina of diabetic patients without diabetic retinopathy (DR) to screen latent protective factor.

Methods

The sequencing data of the retina from three diabetic donors that possess no noticeable pathological feature of the retina at ultimate eye inspection and three healthy donative samples were involved in this study. Herein, we carried out bioinformatics analysis to disclose the expression pattern and characteristics of circRNAs on the basis of Gene Ontology as well as KEGG pathway analyses. Then, sequencing data were applied to infer the interaction between selected circRNAs and miR-204-5p. The potential miRNA response elements for the annotated circRNAs and their target gene were speculated using TargetScan as well as miRanda.

Results

RNA sequencing detected 28,978 alternative circRNAs. Thereinto, 1063 were expressed with significant difference. circKMT2E was upregulated more than two folds in alloxan-induced diabetic retinal tissues compared with normal retinal tissues, exhibiting an expression trend opposite to miR-204-5p. Bioinformatics analysis showed that circKMT2E have four seed sequences on hsa-miR-204-5p. Thus, circKMT2E was speculated to have function on the basis of sponging miR-204-5p in order to participate in the pathogenetic process of DR. Besides, miR-204-5p was speculated to be able to bind SIRT1, which can interact with its target proteins, and adjusts various cell functions including cellular inflammatory responses, proliferation, as well as apoptosis.

Conclusion

The upregulation of circKMT2E in the early stage of DR may be involved in its pathogenesis and may activate the SIRT1 signaling pathway to protect the retina by the sponge function to miR-204-5p.

circ_0086296 induced atherosclerotic lesions via the IFIT1/STAT1 feedback loop by sponging miR-576-3p

Extensive inflammation of endothelial cells (ECs) facilitates atherosclerotic lesion formation. Circular RNA (circRNA) participates in atherosclerosis (AS)-related inflammation responses; however, whether and how circ_0086296 regulates atherosclerotic inflammation and lesions have not been investigated. Microarray analysis, quantitative real-time polymerase chain reaction, and fluorescence in situ hybridization assay were performed to detect the expression and location of hsa_circ_0086296 in human carotid artery plaques, aorta of atherosclerotic mice, and human umbilical vein endothelial cells (HUVECs). Sanger sequencing was used to verify the loop structure of circ_0086296. The relationship among circ_0086296, miR-576-3p, IFIT1, STAT1, and EIF4A3 was validated using bioinformatics, luciferase assay, RNA pull-down assay, and RNA immunoprecipitation. The atherosclerosis mouse model was used to evaluate the function of circ_0086296 in vivo. circ_0086296 expression was significantly upregulated in human carotid artery plaques, oxidized low-density lipoprotein (ox-LDL)-treated HUVECs, and the aorta of atherosclerotic mice. Functional analysis indicated that circ_0086296 promotes ECs injury in vitro and atherosclerosis progression in vivo. The mechanism analysis indicated that circ_0086296 sponged miR-576-3p to promote IFIT1–STAT1 expression. Moreover, STAT1 upregulated circ_0086296 expression, forming the circ_0086296/miR-576-3p/IFIT1/STAT1 feedback loop. Notably, inhibition of the circ_0086296/miR-576-3p/IFIT1 axis could block atherosclerotic lesion formation both in vivo and in vitro. Finally, circ_0086296 was overexpressed in exosomes of patients with atherosclerosis and exosomes of ox-LDL-treated ECs. Therefore, the circ_0086296/miR-576-3p/IFIT1/STAT1 feedback loop participates in atherosclerosis progression and contributes to the high circ_0086296 expression observed in the exosomes of serum of patients with atherosclerosis. This study sought to provide a deep understanding of the mechanisms underlying the aberrant EC phenotype in AS.

circANKRD17(has_circ_0007883) confers paclitaxel resistance of ovarian cancer via interacting with FUS to stabilize FOXR2

Emerging numbers of endogenous circular RNAs (circRNAs) have gained much attention to serve as essential regulators in the carcinogenesis of human cancers. Unfortunately, the occurrence of paclitaxel (PTX) resistance to ovarian cancer remains to be responsible for the poor prognosis. Herein, the aim of our study is to reveal a dysregulation of a particular circRNA, circANKRD17 (has_circ_0007883), and its exact role involving in chemoresistance of ovarian cancer. Expression patterns of circANKRD17 in PTX-resistant ovarian cancer tissues and cell lines was examined using quantitative real-time PCR analysis. Role of circANKRD17 on drug resistance and cell viability was evaluated by CCK-8 assay. Colony formation was subjected to measure cell proliferation. Flow cytometry was employed to evaluate cell cycle either or cell apoptosis. Xenograft models were constructed for further in vivo confirmation. The cicrANKRD17/FUS/FOXR2 axis was demonstrated using bioinformatics analysis, RNA pull-down, as well as RNA immunoprecipitation assays. Dramatically high expressed circANKRD17 observed in ovarian cancer tissues and cells was correlated with PTX resistance, which indicated the poor prognosis. Functionally, knockdown of circANKRD17 decreased PTX resistance via inhibiting cell viability and inducing cell apoptosis. Mechanistically, circANKRD17 interacted with the RNA-binding protein, fused in sarcoma (FUS) to stabilize FOXR2. In summary, our study uncovered a novel machinery of circANKRD17/FUS/FOXR2 referring to ovarian cancer drug sensitivity and tumorigenesis, highlighting a potential strategy for circRNAs in chemoresistance.

The emerging roles of circular RNA-mediated autophagy in tumorigenesis and cancer progression

Circular RNA (circRNA) is characterized by a specific covalently closed ring structure. The back-splicing of precursor mRNA is the main way of circRNA generation, and various cis/trans-acting elements are involved in regulating the process. circRNAs exhibit multiple biological functions, including serving as sponges of microRNAs, interacting with proteins to regulate their stabilities and abilities, and acting as templates for protein translation. Autophagy participates in many physiological and pathological processes, especially it plays a vital role in tumorigenesis and carcinoma progression. Increasing numbers of evidences have revealed that circRNAs are implicated in regulating autophagy during tumor development. Until now, the roles of autophagy-associated circRNAs in carcinoma progression and their molecular mechanisms remain unclear. Here, the emerging regulatory roles and mechanisms of circRNAs in autophagy were summarized. Furtherly, the effects of autophagy-associated circRNAs on cancer development were described. We also prospected the potential of autophagy-associated circRNAs as novel therapeutic targets of tumors and as biomarkers for cancer diagnosis and prognosis.

Oxidant stress-sensitive circRNA Mdc1 controls cardiomyocyte chromosome stability and cell cycle re-entry during heart regeneration

Targeting cardiomyocyte plasticity has emerged as a new strategy for promoting heart repair after myocardial infarction. However, the precise mechanistic network underlying heart regeneration is not completely understood. As noncoding RNAs, circular RNAs (circRNAs) play essential roles in regulating cardiac physiology and pathology. The present study aimed to investigate the potential roles of circMdc1 in cardiac repair after injury and elucidate its underlying mechanisms. Here, we identified that circMdc1 levels were upregulated in postnatal mouse hearts but downregulated in the regenerative myocardium. The expression of circMdc1 in cardiomyocytes is sensitive to oxidative stress, which was attenuated by N-acetyl-cysteine. Enforced circMdc1 expression inhibited cardiomyocyte proliferation, while circMdc1 silencing led to cardiomyocyte cell cycle re-entry. In vivo, the cardiac-specific adeno-associated virus-mediated knockdown of circMdc1 promoted cardiac regeneration and heart repair accompanied by improved heart function. Conversely, circMdc1 overexpression blunted the regenerative capacity of neonatal hearts after apex resection. Moreover, circMdc1 was able to block the translation of its host gene Mdc1 specifically by binding to PABP, affecting DNA damage and the chromosome stability of cardiomyocytes. Furthermore, overexpression of Mdc1 caused damaged mouse hearts to regenerate and repair after myocardial infarction in vivo. Oxidative stress-sensitive circMdc1 plays an important role in cardiac regeneration and heart repair after injury by regulating DNA damage and chromosome stability in cardiomyocytes by blocking the translation of the host gene Mdc1.

circHECTD1 attenuates apoptosis of alveolar epithelial cells in acute lung injury

Circular RNAs (circRNAs) play important roles in many lung diseases. This study aimed to investigate the role of circHECTD1 in acute lung injury (ALI). The mouse and cell models of ALI were induced by lipopolysaccharide (LPS). The apoptosis of alveolar epithelial cells (AECs) was detected by flow cytometry. The relationships between circHECTD1, miRNAs, and target genes were assessed by RNA pull-down, luciferase reporter gene, and RNA-FISH assays. circHECTD1 was downregulated in LPS-induced human and mouse AECs (HBE and MLE-12). The knockdown of circHECTD1 increased the apoptotic rates and the expressions of miR-136 and miR-320a, while its overexpression caused opposite effects in LPS-induced HBE and MLE-12 cells. Mechanistically, circHECTD1 bound to miR-320a and miR-136. miR-320a targeted PIK3CA and mediated the effect of circHECTD1 on PIK3CA expression. miR-136 targeted Sirt1 and mediated the effect of circHECTD1 on Sirt1 expression. Silencing PIK3CA and/or Sirt1 reversed the effect of circHECTD1 overexpression on the apoptosis of LPS-induced HBE and MLE-12 cells. In vivo, overexpression of circHECTD1 alleviated the LPS-induced ALI of mice. Our findings suggested that circHECTD1 inhibits the apoptosis of AECs through miR-320a/PIK3CA and miR-136/Sirt1 pathways in LPS-induced ALI.

circEZH2 inhibits opening of mitochondrial permeability transition pore via interacting with PiC and up-regulating RSAD2

Transmissible gastroenteritis virus (TGEV) infection can lead to mitochondrial damage in porcine intestinal epithelial cells-jejunum 2 (IPEC-J2) cell line. The abnormal opening of mitochondrial permeability transition pore (mPTP) is the most important factor for mitochondrial damage. We previously demonstrated that circEZH2 could inhibit the abnormal opening of mPTP by binding miR-22. However, circEZH2 binding to miR-22 cannot completely enable mPTP opening to recover to normal level compared with the control group. So, we assume that circEZH2 also regulates the mPTP opening in other ways. To prove it, we identified the differentially expressed proteins (DEPs) caused by circEZH2 and circEZH2-interacting proteins by liquid chromatography-tandem mass spectrometry (LC-MS/MS). It turns out there are 123 DEPs (0.83 ≤ fold change ≥ 1.2) upon overexpression circEZH2 and 200 proteins interacted with circEZH2. The kyoto encyclopedia of genes and genomes (KEGG) analysis, gene ontology (GO) analysis, subcellular localization analysis, and protein interaction network results show that the DEPs and circEZH2-interacting proteins may involve in the regulation of mPTP opening. RNA immunoprecipitation (RIP) assay and flow cytometry (FCM) results indicate that circEZH2 can inhibit the opening of mPTP by interacting with Pi carrier (PiC, also named SLC25A3). Quantitative real-time polymerase chain reaction (qRT-PCR), western blotting, and FCM results reveal that circEZH2 can inhibit mPTP opening by promoting the expression of radical s-adenosyl methionine domain-containing protein 2 (RSAD2). In addition, PiC can promote RSAD2 expression. The data indicate that circEZH2 inhibits TGEV-induced mPTP opening by interacting with PiC and upregulating RSAD2.

Regulation of Podocyte Injury by CircHIPK3/FUS Complex in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a major microvascular complication of diabetes mellitus and is one of the leading causes of end-stage kidney disease. Circular RNAs (circRNAs) are a class of endogenous non-coding RNAs that play important roles in various diseases, yet their roles in DKD are poorly understood. CircRNA HIPK3 (circHIPK3), a highly conserved circRNA, is closely related to various cellular functions, including cell proliferation and apoptosis. The association between circHIPK3 and diabetic complications has been well demonstrated in multiple previous studies. However, the role of circHIPK3 in podocyte injury in DKD remains unclear. Herein, we discovered that circHIPK3 expression is markedly elevated in cultured podocytes under high-glucose (HG) conditions and glomeruli of diabetic mice, which is closely associated with podocyte injury in DKD. Functionally, lentivirus-mediated knockdown of circHIPK3 dramatically suppresses HG-induced podocyte apoptosis in vitro. Therapeutically, silencing circHIPK3 by adeno-associated virus-mediated RNA interference ameliorates podocyte injury and albuminuria in STZ-induced diabetic mice. Mechanistically, circHIPK3 facilitates the enrichment of fused in sarcoma (FUS) on the ectodysplasin A2 receptor (EDA2R) promoter, resulting in the upregulation of EDA2R expression and activation of apoptotic signaling. Taken together, these results indicate circHIPK3/FUS/EDA2R axis as a therapeutic target for podocyte injury and DKD progression.

Circular RNAs: New Players in Cardiomyopathy

Cardiomyopathies comprise a heterogeneous group of cardiac diseases identified by myocardium disorders and diminished cardiac function. They often lead to heart failure or heart transplantation and constitute one of the principal causes of morbidity and mortality worldwide. Circular RNAs (circRNAs) are a novel type of noncoding RNAs. They are covalently closed and single-stranded and derived from the exons and introns of genes by alternative splicing. This specific structure renders them resistant to exonuclease digestion. Many recent studies have demonstrated that circRNAs are highly abundant and conserved and can play central roles in biological functions such as microRNA (miRNA) sponging, splicing, and transcription regulation. Emerging evidence indicates that circRNAs can play significant roles in cardiovascular diseases, including cardiomyopathies. In this review, we briefly describe the current understanding regarding the classification, nomenclature, characteristics, and function of circRNAs and report recent significant findings concerning the roles of circRNAs in cardiomyopathies. Furthermore, we discuss the clinical application potential of circRNAs as the therapeutic targets and diagnostic biomarkers of cardiomyopathies.

Circular RNA BIRC6 depletion promotes osteogenic differentiation of periodontal ligament stem cells via the miR-543/PTEN/PI3K/AKT/mTOR signaling pathway in the inflammatory microenvironment

BACKGROUND

Periodontal ligament stem cells (PDLSCs) are the ideal seed cells for periodontal tissue regeneration. It is well established that persistent inflammation significantly impairs the osteogenic differentiation capability of PDLSCs. Therefore, maintaining PDLSC osteogenic potential under the inflammatory microenvironment is important for treating bone loss in periodontitis. The aim of our study was to explore the potential role of circular RNA BIRC6 (circBIRC6) in regulating osteogenic differentiation of PDLSCs in the inflammatory conditions.

METHODS

Alkaline phosphatase staining, Alizarin Red staining, quantitative real-time polymerase chain reaction, western blotting and immunofluorescence staining were used to evaluated the effects of circBIRC6 on the osteogenic differentiation of PDLSCs. RNA pull-down and luciferase assays were performed to explore the interaction between circBIRC6 and miR-543. Then, the downstream signaling pathway affected by circBIRC6/miR-543 axis was further investigated.

RESULTS

The expression level of circBIRC6 was higher in PDLSCs exposed to inflammatory stimulus and in periodontitis tissues compared to the respective controls. Downregulation of circBIRC6 enhanced the osteogenic potential of PDLSCs under the inflammatory conditions, and upregulation of circBIRC6 led to opposite findings. Mechanistically, we found that circBIRC6 modulated PDLSC osteogenic differentiation through sponging miR-543. More importantly, we have demonstrated that circBIRC6/miR-543 axis regulated the mineralization capacity of PDLSCs via PTEN/PI3K/AKT/mTOR signaling pathway in the inflammatory microenvironment.

CONCLUSIONS

In summary, the expression of miR-543 is significantly increased following circBIRC6 downregulation, leading to inhibition of PTEN and subsequently activation of PI3K/AKT/mTOR signaling pathway. Therefore, targeting circBIRC6 might represent a potential therapeutic strategy for improving bone loss in periodontitis.

CircWalk: a novel approach to predict CircRNA-disease association based on heterogeneous network representation learning

Background

Several types of RNA in the cell are usually involved in biological processes with multiple functions. Coding RNAs code for proteins while non-coding RNAs regulate gene expression. Some single-strand RNAs can create a circular shape via the back splicing process and convert into a new type called circular RNA (circRNA). circRNAs are among the essential non-coding RNAs in the cell that involve multiple disorders. One of the critical functions of circRNAs is to regulate the expression of other genes through sponging micro RNAs (miRNAs) in diseases. This mechanism, known as the competing endogenous RNA (ceRNA) hypothesis, and additional information obtained from biological datasets can be used by computational approaches to predict novel associations between disease and circRNAs.

Results

We applied multiple classifiers to validate the extracted features from the heterogeneous network and selected the most appropriate one based on some evaluation criteria. Then, the XGBoost is utilized in our pipeline to generate a novel approach, called CircWalk, to predict CircRNA-Disease associations. Our results demonstrate that CircWalk has reasonable accuracy and AUC compared with other state-of-the-art algorithms. We also use CircWalk to predict novel circRNAs associated with lung, gastric, and colorectal cancers as a case study. The results show that our approach can accurately detect novel circRNAs related to these diseases.

Conclusions

Considering the ceRNA hypothesis, we integrate multiple resources to construct a heterogeneous network from circRNAs, mRNAs, miRNAs, and diseases. Next, the DeepWalk algorithm is applied to the network to extract feature vectors for circRNAs and diseases. The extracted features are used to learn a classifier and generate a model to predict novel CircRNA-Disease associations. Our approach uses the concept of the ceRNA hypothesis and the miRNA sponge effect of circRNAs to predict their associations with diseases. Our results show that this outlook could help identify CircRNA-Disease associations more accurately.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-022-04883-9.

Screening differential circular RNAs expression profiles in Vulvar Lichen Sclerosus

Background

Vulvar lichen sclerosus (VLS) is one of the most common clinical manifestations of vulva. Thirteen percent of women have symptomatic vulvar diseases. The aim of this study is to investigate the expression profile of circular RNA (circRNAs) in vulvar lichen sclerosus, and to identify the underlying core genes of VLS.

Methods

We removed rRNA for sequencing, and screened the differentially expressed messenger RNA (mRNAs), long non-coding RNA (lncRNAs) and single-stranded circRNA in 20 groups of VLS tissues and 20 groups of healthy female vulvar skin tissues. Bioinformatics analysis was used to analyze its potential functions.

Results

A total of 2545 differentially expressed mRNAs were assessed in VLS patients, of which 1541 samples were up-regulated and 1004 samples were down-regulated. A total of 1453 differentially expressed lncRNAs were assessed, of which 812 samples were up-regulated and 641 samples were down-regulated. A total of 79 differentially expressed circRNAs were assessed, of which 54 were up-regulated and 25 were down-regulated. The differential expression of circRNAs was closely related to biological processes and molecular functions. The differences in circRNAs were mainly related to the “human T-cell leukemia virus 1 infection” signaling pathway and the “axon guidance” signaling pathway.

Conclusion

The profile of abnormal regulation of circRNA exists in VLS. According to biological informatics analysis, the dysregulation of circRNAs may be related to the pathogenesis and pathological process of VLS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12938-022-01013-7.

The circRNA-miRNA/RBP regulatory network in myocardial infarction

Myocardial infarction (MI) is a serious heart disease that causes high mortality rate worldwide. Noncoding RNAs are widely involved in the pathogenesis of MI. Circular RNAs (circRNAs) are recently validated to be crucial modulators of MI. CircRNAs are circularized RNAs with covalently closed loops, which make them stable under various conditions. CircRNAs can function by different mechanisms, such as serving as sponges of microRNAs (miRNAs) and RNA-binding proteins (RBPs), regulating mRNA transcription, and encoding peptides. Among these mechanisms, sponging miRNAs/RBPs is the main pathway. In this paper, we systematically review the current knowledge on the properties and action modes of circRNAs, elaborate on the roles of the circRNA-miRNA/RBP network in MI, and explore the value of circRNAs in MI diagnosis and clinical therapies. CircRNAs are widely involved in MI. CircRNAs have many advantages, such as stability, specificity, and wide distribution, which imply that circRNAs have a great potential to act as biomarkers for MI diagnosis and prognosis.

Manipulating Cardiomyocyte Plasticity for Heart Regeneration

Pathological heart injuries such as myocardial infarction induce adverse ventricular remodeling and progression to heart failure owing to widespread cardiomyocyte death. The adult mammalian heart is terminally differentiated unlike those of lower vertebrates. Therefore, the proliferative capacity of adult cardiomyocytes is limited and insufficient to restore an injured heart. Although current therapeutic approaches can delay progressive remodeling and heart failure, difficulties with the direct replenishment of lost cardiomyocytes results in a poor long-term prognosis for patients with heart failure. However, it has been revealed that cardiac function can be improved by regulating the cell cycle or changing the cell state of cardiomyocytes by delivering specific genes or small molecules. Therefore, manipulation of cardiomyocyte plasticity can be an effective treatment for heart disease. This review summarizes the recent studies that control heart regeneration by manipulating cardiomyocyte plasticity with various approaches including differentiating pluripotent stem cells into cardiomyocytes, reprogramming cardiac fibroblasts into cardiomyocytes, and reactivating the proliferation of cardiomyocytes.

Circular RNA EIF4G3 suppresses gastric cancer progression through inhibition of β-catenin by promoting δ-catenin ubiquitin degradation and upregulating SIK1

BACKGROUND

Increasing studies suggest that circular RNAs (circRNAs) are critical regulators of cancer development and progression. However, the biological roles and mechanisms of circRNAs in gastric cancer (GC) remain largely unknown.

METHODS

We identified the differentially expressed circRNAs in GC by analyzing Gene Expression Omnibus (GEO) datasets. We explored the biological roles of circRNAs in GC by in vitro functional assays and in vivo animal studies. We performed tagged RNA affinity purification (TRAP), RNA immunoprecipitation (RIP), mass spectrometry (MS), RNA sequencing, luciferase reporter assays, and rescue experiments to investigate the mechanism of circRNAs in GC.

RESULTS

Downregulated expression of circular RNA EIF4G3 (circEIF4G3; hsa_circ_0007991) was found in GC and was associated with poor clinical outcomes. Overexpression of circEIF4G3 suppressed GC growth and metastasis through the inhibition of β-catenin signaling, whereas knockdown of circEIF4G3 showed the opposite effects. Mechanistic studies revealed that circEIF4G3 bound to δ-catenin protein to promote its TRIM25-mediated ubiquitin degradation and interacted with miR-4449 to upregulate SIK1 expression.

CONCLUSION

Our findings uncovered a tumor suppressor function of circEIF4G3 in GC through the regulation of δ-catenin protein stability and miR-4449/SIK1 axis. CircEIF4G3 may act as a promising prognostic biomarker and therapeutic target for GC.

Fabrication and Characterization of pcDNA3.1(+) Location within Chitosan/Nanoparticles Complexes for Enhanced Gene Delivery

BACKGROUND

Chitosan nanoparticles (CSNP) are becoming a popular alternative for delivering nucleic acids to tissues for gene transfer (gene therapy). The size and morphology of these biodegradable nano-carriers are adjustable, and their positive charge allows them to interact strongly with negatively charged nucleic acids.

OBJECTIVE

This study aimed to fabricate and characterize pcDNA3.1 (+) plasmid (pDNA) and CSNP complexes and determine the plasmid location in these vehicles.

MATERIALS AND METHODS

The characteristics of the pDNA/CSNP complex after production were investigated by SEM, XRD, DLS, TGA, and FTIR. The capacity of CSNP to form complexes with pDNA was investigated by labeling free plasmids with the fluorescent intercalating dye OliGreen. The stability of pDNA/CSNP in the presence of chitosanase was evaluated. Surface-Enhanced Raman Spectroscopy (SERS) for pDNA localization was performed, and absorption rate in BALB/c mice was assessed by real-time PCR.

RESULTS

The optimum pDNA/CSNP ratio for plasmid complex formation was established to be 1:2 (w.w) by measuring spectroscopy. At these optimum complex formation ratios, spectroscopy, and gel digest experiments, SERS indicated that a part of the pDNA was present on the complex outer surface. The findings of plasmid absorption in mouse thigh tissue by real-time PCR revealed that the rate of gene uptake was significantly greater at a dose of 1:2 (w.w) of pDNA/CSNP than in other groups (P< 0.001).

CONCLUSIONS

The findings of this study reveal exactly pDNA fits into polymer nanostructured delivery systems, allowing the formulation to be adjusted for selective distribution. This understanding will aid future research into the system's functioning in vitro and in vivo.

Epigenetic regulation in cardiovascular disease: mechanisms and advances in clinical trials

Epigenetics is closely related to cardiovascular diseases. Genome-wide linkage and association analyses and candidate gene approaches illustrate the multigenic complexity of cardiovascular disease. Several epigenetic mechanisms, such as DNA methylation, histone modification, and noncoding RNA, which are of importance for cardiovascular disease development and regression. Targeting epigenetic key enzymes, especially the DNA methyltransferases, histone methyltransferases, histone acetylases, histone deacetylases and their regulated target genes, could represent an attractive new route for the diagnosis and treatment of cardiovascular diseases. Herein, we summarize the knowledge on epigenetic history and essential regulatory mechanisms in cardiovascular diseases. Furthermore, we discuss the preclinical studies and drugs that are targeted these epigenetic key enzymes for cardiovascular diseases therapy. Finally, we conclude the clinical trials that are going to target some of these processes.

Critical Roles of Circular RNA in Tumor Metastasis via Acting as a Sponge of miRNA/isomiR

Circular RNAs (circRNAs), a class of new endogenous non-coding RNAs (ncRNAs), are closely related to the carcinogenic process and play a critical role in tumor metastasis. CircRNAs can lay the foundation for tumor metastasis via promoting tumor angiogenesis, make tumor cells gain the ability of migration and invasion by regulating epithelial-mesenchymal transition (EMT), interact with immune cells, cytokines, chemokines, and other non-cellular components in the tumor microenvironment, damage the normal immune function or escape the immunosuppressive network, and further promote cell survival and metastasis. Herein, based on the characteristics and biological functions of circRNA, we elaborated on the effect of circRNA via circRNA-associated competing endogenous RNA (ceRNA) network by acting as miRNA/isomiR sponges on tumor angiogenesis, cancer cell migration and invasion, and interaction with the tumor microenvironment (TME), then explored the potential interactions across different RNAs, and finally discussed the potential clinical value and application as a promising biomarker. These results provide a theoretical basis for the further application of metastasis-related circRNAs in cancer treatment. In summary, we briefly summarize the diverse roles of a circRNA-associated ceRNA network in cancer metastasis and the potential clinical application, especially the interaction of circRNA and miRNA/isomiR, which may complicate the RNA regulatory network and which will contribute to a novel insight into circRNA in the future.

Reduction of A-to-I RNA editing in the failing human heart regulates formation of circular RNAs

Alterations of RNA editing that affect the secondary structure of RNAs can cause human diseases. We therefore studied RNA editing in failing human hearts. Transcriptome sequencing showed that adenosine-to-inosine (A-to-I) RNA editing was responsible for 80% of the editing events in the myocardium. Failing human hearts were characterized by reduced RNA editing. This was primarily attributable to Alu elements in introns of protein-coding genes. In the failing left ventricle, 166 circRNAs were upregulated and 7 circRNAs were downregulated compared to non-failing controls. Most of the upregulated circRNAs were associated with reduced RNA editing in the host gene. ADAR2, which binds to RNA regions that are edited from A-to-I, was decreased in failing human hearts. In vitro, reduction of ADAR2 increased circRNA levels suggesting a causal effect of reduced ADAR2 levels on increased circRNAs in the failing human heart. To gain mechanistic insight, one of the identified upregulated circRNAs with a high reduction of editing in heart failure, AKAP13, was further characterized. ADAR2 reduced the formation of double-stranded structures in AKAP13 pre-mRNA, thereby reducing the stability of Alu elements and the circularization of the resulting circRNA. Overexpression of circAKAP13 impaired the sarcomere regularity of human induced pluripotent stem cell-derived cardiomyocytes. These data show that ADAR2 mediates A-to-I RNA editing in the human heart. A-to-I RNA editing represses the formation of dsRNA structures of Alu elements favoring canonical linear mRNA splicing and inhibiting the formation of circRNAs. The findings are relevant to diseases with reduced RNA editing and increased circRNA levels and provide insights into the human-specific regulation of circRNA formation.

Small molecules as modulators of regulated cell death against ischemia/reperfusion injury

Ischemia/reperfusion (IR) injury contributes to disability and mortality worldwide. Due to the complicated mechanisms and lack of proper therapeutic targets, few interventions are available that specifically target the pathogenesis of IR injury. Regulated cell death (RCD) of endothelial and parenchymal cells is recognized as the promising intervening target. Recent advances in IR injury suggest that small molecules exhibit beneficial effects on various RCD against IR injury, including apoptosis, necroptosis, autophagy, ferroptosis, pyroptosis, and parthanatos. Here, we describe the mechanisms behind these novel promising therapeutic targets and explain the machinery powering the small molecules. These small molecules exert protection by targeting endothelial or parenchymal cells to alleviate IR injury. Therapies of the ideal combination of small molecules targeting multiple cell types have shown potent synergetic therapeutic effects, laying the foundation for novel strategies to attenuate IR injury.

Mesenchymal stem cells-derived exosomes prevent sepsis-induced myocardial injury by a CircRTN4/miR-497-5p/MG53 pathway

Sepsis is a life-threatening organ function dysfunction featured by stimulated oxidative stress and inflammatory responses, in which about 40%-60% of sepsis patients are accompanied with cardiac dysfunction. Mesenchymal stem cells (MSCs)-derived exosomes exert critical roles in the treatment of multiple diseases through transferring non-coding RNAs. Circular RNA (circRNA) is a novel form of functional RNAs that involves in the progression of multiple cardiac pathological condition. Nevertheless, the function of MSCs-derived exosomal circRTN4 in sepsis-induced myocardial injury is still obscure. Significantly, FISH assay demonstrated the location of circRTN4 in cytoplasm of cardiomyocytes. The expression of circRTN4 was reduced in the cardiac tissues from caecal ligation and puncture (CLP) rats and LPS-treated cardiomyocytes. CircRTN4 could be delivered to cardiomyocytes cells via MSCs-derived exosomes. The cardiac injury and apoptosis were induced in the CLP rats and the treatment of MSCs-derived exosomal circRTN4 relieved the phenotypes. MSCs-derived exosomal circRTN4 notably suppressed the upregulated ROS level in the CLP rats. The activity of SOD and GSH was repressed in CLP rats, in which MSCs-derived exosomal circRTN4 rescued the activity in the rats. The upregulated IL-1β, IL-6, and TNF-α levels in CLP rats were reduced by the treatment of MSCs-derived exosomal circRTN4. MSCs-derived exosomal circRTN4 improved cell survival and suppressed apoptosis of LPS-treated cardiomyocytes. CircRTN4 direct interact with miR-497-5p to upregulate MG53 expression in cardiomyocytes. MSCs-derived exosomal circRTN4 relieves LPS-stimulated cardiomyocyte damage via targeting miR-497-5p/MG53 axis. Therefore, we determine that MSCs-derived exosomes prevent sepsis-induced myocardial injury by a circRTN4/miR-497-5p/MG53 pathway. Our data provides novel insight into the regulatory mechanism by which MSCs-derived exosomal circRTN4 regulates sepsis-induced myocardial injury. MSCs-derived exosomal circRTN4 may be applied as a promising therapeutic approach for sepsis-induced myocardial injury.

Emerging roles of circRNAs in mice kidney with aging

Circular RNA (circRNA) is a novel type of noncoding RNA expressed in different tissues and species. Up to now, little is known of the function and expression of circRNAs in kidney aging. In this research, we used RNA sequencing to identify 11,929 circRNAs in kidney from 3-, 12-, and 24-month-old mice, of which 12 circRNAs were validated by qPCR. Based on the validated circRNAs and their predicted miRNA-mRNA target pairs, a circRNA-miRNA-mRNA interactions network was conducted. Bioinformatics analysis for all the mRNAs in the ceRNA network showed that the most enriched gene ontology (GO) term and one of the most enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were associated with endoplasmic reticulum (ER). The network also identified circNpas2, which was decreased significantly in mice kidney during aging, as a hub gene. Subsequently, we found that the cell cycle was arrested in G1 phase and the expression of P53 and P16 increased significantly in the circNpas2-knockdown cells. Moreover, knockdown of circNpas2 inhibited expression of ER-related proteins, HSPA5 and ERO1L. Taken together, our findings contribute to a better understanding of the role played by circRNA during kidney aging and provide potential therapeutic targets for the prevention of kidney aging.

Role of circular RNA in myocardial ischemia and ageing-related diseases

Circular RNA (circRNA) is a new endogenous transcription product, which has attracted significant attention in RNA biology research.CircRNA comprise exons or introns involved in regulation of various mechanisms.These molecules are stable and species-specific, as well as cell and tissue-specific.Cardiovascular diseases particularly myocardial ischemia and ageing-related diseases, pose a major health care burden and novel treatments and biomarkers should be explored.Recent findings indicate that circRNAs are implicated in biological processes, such as glucose metabolism, fatty acid oxidation, mitochondrial biosynthesis, implying that they are potential targets for myocardial ischemia treatment.In the present review, the functions of circRNAs in the heart are described, with emphasis given on in the relationship with myocardial ischemia and cardiac aging-related diseases.Directions for future research are also summarized.

Circ_0000811 acts as a miR-15b sponge and inhibits Prkar2a-mediated JAK2/STAT1 pathway to attenuate cerebral ischemic vertigo

Circular RNAs (circRNAs) have been noted to express in the brain and thus participate in various diseases related to the central nervous system. However, the potential role of circRNAs in cerebral ischemia (CI)-induced vertigo remains unknown. We initially predicted through bioinformatics analysis the poor expression of circ_0000811 related to CI. A mouse model of CI-induced vertigo was then established, which was validated by measurement of escape latency and medial vestibular nucleus (MVN) blood flow, with NeuN/Annexin counterstaining utilized to detect cell apoptosis in the MVN. An oxygen glucose deprivation (OGD)-exposed neuron-like cell model was further established for in vitro gain- and loss- of function assays, with flow cytometry performed to detect cell apoptosis. The poorly expressed circ_0000811, up-regulated miR-15b expression, and down-regulated Prkar2a expression were observed in both mice with CI-induced vertigo and OGD-exposed cells. Our data then demonstrated that circ_0000811 restoration alleviated CI-induced vertigo in mouse models, and that circ_0000811 acted as a miR-15b sponge to inhibit miR-15b expression. Prkar2a was validated as the target gene of miR-15b. Prkar2a restoration was subsequently revealed to repress OGD-induced neuronal apoptosis through JAK2/STAT1 signaling pathway inactivation. Furthermore, inactivation of the JAK2/STAT1 signaling pathway exerted an anti-apoptotic effect in OGD-induced neurons and an alleviatory effect in mice with CI-induced vertigo with Prkar2a overexpression and circ_0000811 overexpression. Taken together, our work suggests that circ_0000811 is involved in neuronal apoptosis of CI-induced vertigo and may be used as a biomarker for ameliorating CI-induced vertigo.

Role of circRNA circ_0000080 in myocardial hypoxia injury

This study aimed to investigate the potential role of circRNA circ_0000080 in myocardial hypoxia injury and the underlying mechanisms. Patients with myocardial hypoxia injury who were admitted to Xi’an No. 1 Hospital, China, were included in this study. The expression levels of circ_0000080, miR-367-5p, and COX2 were analyzed by real-time quantitative PCR (RT-qPCR); cell viability was measured by cell counting kit-8 (CCK-8) assay; and apoptosis was detected by flow cytometry. In addition, the release of cytokines was determined by Enzyme-linked immunosorbent assay (ELISA), and the binding sites between miR-367-5p and circ_0000080/COX2 were predicted by bioinformatics analysis and confirmed by dual-luciferase reporter and RNA pull-down assays. circ_0000080 was upregulated in patients with MI and in H9c2 cells treated with H₂O₂ and hypoxia/reoxygenation (H/R). Silencing circ_0000080 reduced the H/R-mediated apoptosis of cardiomyocytes and secretion of pro-inflammatory cytokines. Moreover, circ_0000080 functioned as an miR-367-5p sponge to regulate the expression of COX2. Downregulated miR-367-5p or overexpressed COX2 degraded cellular functions of cardiomyocytes. circ_0000080 knockdown alleviated myocardial hypoxia injury through the miR-367-5p/COX2 axis.

Specific Gain and Loss of Co-Expression Modules in Long-Lived Individuals Indicate a Role of circRNAs in Human Longevity

Deep RNA sequencing of 164 blood samples collected from long-lived families was performed to investigate the expression patterns of circular RNAs (circRNAs). Unlike that observed in previous studies, circRNA expression in long-lived elderly individuals (98.3 ± 3.4 year) did not exhibit an age-accumulating pattern. Based on weighted circRNA co-expression network analysis, we found that longevous elders specifically gained eight but lost seven conserved circRNA-circRNA co-expression modules (c-CCMs) compared with normal elder controls (spouses of offspring of long-lived individuals, age = 59.3 ± 5.8 year). Further analysis showed that these modules were associated with healthy aging-related pathways. These results together suggest an important role of circRNAs in regulating human lifespan extension.

HIF-1α-regulated lncRNA-TUG1 promotes mitochondrial dysfunction and pyroptosis by directly binding to FUS in myocardial infarction

Myocardial infarction (MI) is a fatal heart disease that affects millions of lives worldwide each year. This study investigated the roles of HIF-1α/lncRNA-TUG1 in mitochondrial dysfunction and pyroptosis in MI. CCK-8, DHE, lactate dehydrogenase (LDH) assays, and JC-1 staining were performed to measure proliferation, reactive oxygen species (ROS), LDH leakage, and mitochondrial damage in hypoxia/reoxygenation (H/R)-treated cardiomyocytes. Enzyme-linked immunoassay (ELISA) and flow cytometry were used to detect LDH, creatine kinase (CK), and its isoenzyme (CK-MB) levels and caspase-1 activity. Chromatin immunoprecipitation (ChIP), luciferase assay, and RNA-immunoprecipitation (RIP) were used to assess the interaction between HIF-1α, TUG1, and FUS. Quantitative real-time polymerase chain reaction (qRT-PCR), Western blotting, and immunohistochemistry were used to measure HIF-1α, TUG1 and pyroptosis-related molecules. Hematoxylin and eosin (HE), 2,3,5-triphenyltetrazolium chloride (TTC), and terminal deoxynucleotidyl transferase dUTP risk end labelling (TUNEL) staining were employed to examine the morphology, infarction area, and myocardial injury in the MI mouse model. Mitochondrial dysfunction and pyroptosis were induced in H/R-treated cardiomyocytes, accompanied by an increase in the expression of HIF-α and TUG1. HIF-1α promoted TUG1 expression by directly binding to the TUG1 promoter. TUG1 silencing inhibited H/R-induced ROS production, mitochondrial injury and the expression of the pyroptosis-related proteins NLRP3, caspase-1 and GSDMD. Additionally, H/R elevated FUS levels in cardiomyocytes, which were directly inhibited by TUG1 silencing. Fused in sarcoma (FUS) overexpression reversed the effect of TUG1 silencing on mitochondrial damage and caspase-1 activation. However, the ROS inhibitor N-acetylcysteine (NAC) promoted the protective effect of TUG1 knockdown on H/R-induced cardiomyocyte damage. The in vivo MI model showed increased infarction, myocardial injury, ROS levels and pyroptosis, which were inhibited by TUG1 silencing. HIF-1α targeting upregulated TUG1 promotes mitochondrial damage and cardiomyocyte pyroptosis by combining with FUS, thereby promoting the occurrence of MI. HIF-1α/TUG1/FUS may serve as a potential treatment target for MI.

Downregulation of circ-ZNF609 Promotes Heart Repair by Modulating RNA N6-Methyladenosine-Modified Yap Expression

Circular RNAs take crucial roles in several pathophysiological processes. The regulatory role and its underlying mechanisms of circ-ZNF609 in the heart remains largely unknown. Here, we report that circ-ZNF609 is upregulated during myocardial ischemia/reperfusion (I/R) remodeling. Knockdown of circ-ZNF609 protects against acute I/R injury and attenuates left ventricle dysfunction after I/R remodeling in vivo. In vitro, circ-ZNF609 regulates cardiomyocyte survival and proliferation via modulating the crosstalk between Hippo-YAP and Akt signaling. Mechanically, N⁶-methyladenosine-modification is involved in the regulatory role of circ-ZNF609 on YAP. An in-depth study indicates that knockdown of circ-ZNF609 decreases the expression of YTHDF3 and further fine-tuned the accessibility of Yap mRNA to YTHDF1 and YTHDF2 to regulate YAP expression. circ-ZNF609 knockdown represents a promising therapeutic strategy to combat the pathological process of myocardial I/R injury.

Berberine: A Review of its Pharmacokinetics Properties and Therapeutic Potentials in Diverse Vascular Diseases

Traditional Chinese medicine plays a significant role in the treatment of various diseases and has attracted increasing attention for clinical applications. Vascular diseases affecting vasculature in the heart, cerebrovascular disease, atherosclerosis, and diabetic complications have compromised quality of life for affected individuals and increase the burden on health care services. Berberine, a naturally occurring isoquinoline alkaloid form Rhizoma coptidis, is widely used in China as a folk medicine for its antibacterial and anti-inflammatory properties. Promisingly, an increasing number of studies have identified several cellular and molecular targets for berberine, indicating its potential as an alternative therapeutic strategy for vascular diseases, as well as providing novel evidence that supports the therapeutic potential of berberine to combat vascular diseases. The purpose of this review is to comprehensively and systematically describe the evidence for berberine as a therapeutic agent in vascular diseases, including its pharmacological effects, molecular mechanisms, and pharmacokinetics. According to data published so far, berberine shows remarkable anti-inflammatory, antioxidant, antiapoptotic, and antiautophagic activity via the regulation of multiple signaling pathways, including AMP-activated protein kinase (AMPK), nuclear factor κB (NF-κB), mitogen-activated protein kinase silent information regulator 1 (SIRT-1), hypoxia-inducible factor 1α (HIF-1α), vascular endothelial growth factor phosphoinositide 3-kinase (PI3K), protein kinase B (Akt), janus kinase 2 (JAK-2), Ca²⁺ channels, and endoplasmic reticulum stress. Moreover, we discuss the existing limitations of berberine in the treatment of vascular diseases, and give corresponding measures. In addition, we propose some research perspectives and challenges, and provide a solid evidence base from which further studies can excavate novel effective drugs from Chinese medicine monomers.

Circular RNAs in cardiovascular diseases

In eukaryotes, precursor mRNAs (pre-mRNAs) produce a unique class of biologically active molecules namely circular RNAs (circRNAs) with a covalently closed-loop structure via back-splicing. Because of this unconventional circular form, circRNAs exhibit much higher stability than linear RNAs due to the resistance to exonuclease degradation and thereby play exclusive cellular regulatory roles. Recent studies have shown that circRNAs are widely expressed in eukaryotes and display tissue- and disease-specific expression patterns, including in the cardiovascular system. Although numerous circRNAs are discovered by in silico methods, a limited number of circRNAs have been studied. This review intends to summarize the current understanding of the characteristics, biogenesis, and functions of circRNAs and delineate the practical approaches for circRNAs investigation. Moreover, we discuss the emerging roles of circRNAs in cardiovascular diseases.