Circular RNAs in the cardiovascular system

CircHAT1 regulates the proliferation and phenotype switch of vascular smooth muscle cells in lower extremity arteriosclerosis obliterans through targeting SFRS1

This study aimed to decipher the mechanism of circular ribonucleic acids (circRNAs) in lower extremity arteriosclerosis obliterans (LEASO). First, bioinformatics analysis was performed for screening significantly down-regulated cardiac specific circRNA-circHAT1 in LEASO. The expression of circHAT1 in LEASO clinical samples was detected by quantitative real-time polymerase chain reaction (qRT-PCR). The protein expression of splicing factor arginine/serine-rich 1 (SFRS1), α-smooth muscle actin (α-SMA), Calponin (CNN1), cyclin D1 (CNND1) and smooth muscle myosin heavy chain 11 (SMHC) in vascular smooth muscle cells (VSMCs) was detected by Western blotting. Cell Counting Kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU) and Transwell assays were used to evaluate cell proliferation and migration, respectively. RNA immunoprecipitation (RNA-IP) and RNA pulldown verified the interaction between SFRS1 and circHAT1. By reanalyzing the dataset GSE77278, circHAT1 related to VSMC phenotype conversion was screened, and circHAT1 was found to be significantly reduced in peripheral blood mononuclear cells (PBMCs) of LEASO patients compared with healthy controls. Knockdown of circHAT1 significantly promoted the proliferation and migration of VSMC cells and decreased the expression levels of contractile markers. However, overexpression of circHAT1 induced the opposite cell phenotype and promoted the transformation of VSMCs from synthetic to contractile. Besides, overexpression of circHAT1 inhibited platelet-derived growth factor-BB (PDGF-BB)-induced phenotype switch of VSMC cells. Mechanistically, SFRS1 is a direct target of circHAT1 to mediate phenotype switch, proliferation and migration of VSMCs. Overall, circHAT1 regulates SFRS1 to inhibit the cell proliferation, migration and phenotype switch of VSMCs, suggesting that it may be a potential therapeutic target for LEASO.

Epigenetic programing of cancer stemness by transcription factors-non-coding RNAs interactions

Cancer 'stemness' is fundamental to cancer existence. It defines the ability of cancer cells to indefinitely perpetuate as well as differentiate. Cancer stem cell populations within a growing tumor also help evade the inhibitory effects of chemo- as well as radiation-therapies, in addition to playing an important role in cancer metastases. NF-κB and STAT-3 are representative transcription factors (TFs) that have long been associated with cancer stemness, thus presenting as attractive targets for cancer therapy. The growing interest in non-coding RNAs (ncRNAs) in the recent years has provided further insight into the mechanisms by which TFs influence cancer stem cell characteristics. There is evidence for a direct regulation of TFs by ncRNAs, such as, microRNAs (miRNAs), long non-coding RNAs (lncRNAs) as well as circular RNAs (circRNAs), and vice versa. Additionally, the TF-ncRNAs regulations are often indirect, involving ncRNA-target genes or the sponging of other ncRNA species by individual ncRNAs. The information is rapidly evolving and this review provides a comprehensive review of TF-ncRNAs interactions with implications on cancer stemness and in response to therapies. Such knowledge will help uncover the many levels of tight regulations that control cancer stemness, providing novel opportunities and targets for therapy in the process.

Hsa_circ_0008673 Promotes Breast Cancer Progression by MiR-578/GINS4 Axis

BACKGROUND

Circular RNAs (circRNAs) play a crucial role in breast cancer (BC) development. This study aimed to explore the new potential mechanism of hsa_circ_0008673 in BC.

MATERIALS AND METHODS

Hsa_circ_0008673, microRNA-578 (miR-578) and recombinant human GINS complex subunit 4 (GINS4) abundances were measured via quantitative real-time PCR or western blot. Cell proliferation, metastasis, angiogenesis and apoptosis were assessed via EdU assay, transwell assay, tube formation assay, and flow cytometry. The interactions among hsa_circ_0008673, miR-578 and GINS4 were tested via dual-luciferase reporter analysis and RNA pull-down assay. Animal studies were performed to assess the effect of hsa_circ_0008673 on BC tumor growth.

RESULTS

Hsa_circ_0008673 level was increased in BC tissues and cells. Hsa_circ_0008673 silencing repressed BC cell growth, metastasis and angiogenesis, as well as hampered BC tumor growth. Hsa_circ_0008673 acted as miR-578 sponge, and miR-578 targeted GINS4. Furthermore, hsa_circ_0008673 modulated GINS4 expression through sponging miR-578. Additionally, miR-578 inhibitor or GINS4 overexpression could reverse the inhibitory effect of hsa_circ_0008673 silencing on BC cell progression.

CONCLUSION

Hsa_circ_0008673 might promote BC progression via modulating miR-578/GINS4 pathway.

Involvement of circHIPK3 in the pathogenesis of diabetic cardiomyopathy in mice

AIMS/HYPOTHESIS

In a mouse model of diabetic cardiomyopathy (DCM) the expression of the circular RNA circHIPK3 was found to be significantly increased. This study aimed to discover the molecular mechanisms linking circHIPK3 to the pathogenesis of DCM.

METHODS

The diabetic mouse model was established by i.p. injection of streptozotocin, which led to the development of DCM. Echocardiographic measurements were used to evaluate cardiac structure and function, and histological staining was applied to detect myocardial fibrosis in mice. 5-Ethynyl-2'-deoxyuridine incorporation was performed to determine cell proliferation and RNA fluorescent in situ hybridisation was employed to examine circHIPK3 expression in cardiac fibroblasts. RNA immunoprecipitation and luciferase reporter assay were conducted to explore the pathological mechanism of circHIPK3 in myocardial fibrosis.

RESULTS

Knockdown of circHIPK3 was found to attenuate myocardial fibrosis and enhance cardiac function in DCM mice. In addition, silencing of circHIPK3 could suppress proliferation of cardiac fibroblasts treated with angiotensin II. Furthermore, RNA immunoprecipitation and luciferase reporter assay revealed a circHIPK3-miR-29b-3p-Col1a1-Col3a1 regulatory network in the pathogenesis of myocardial fibrosis.

CONCLUSIONS/INTERPRETATION

circHIPK3 contributes to increased myocardial fibrosis during DCM by functioning as a competing endogenous RNA that upregulates Col1a1 and Col3a1 expression through suppressing miR-29b-3p.

Circular RNA RBPMS inhibits bladder cancer progression via miR-330-3p/RAI2 regulation

Bladder cancer is a severe cancer with high mortality because of invasion and metastasis. Growing evidence has revealed that circular RNAs play critical roles in biological function, which is closely connected to proliferation and invasion of bladder cancer. In our study, we employed qRT-PCR, RNA fluorescence in situ hybridization (FISH), 5-ethynyl-2′-deoxyuridine (EdU), CCK-8, Transwell assays, luciferase reporter assays, xenografts, and live imaging to detect the roles of circular RNA binding protein with multiple splicing (circRBPMS) in bladder cancer (BC). Bioinformatics analysis and WB were performed to investigate the regulatory mechanism. Expression profile analysis of circular RNAs (circRNAs) in BC revealed that circRBPMS was significantly downregulated. Low circRBPMS expression correlates with aggressive BC phenotypes, whereas upregulation of circRBPMS suppresses BC cell proliferation and metastasis by directly targeting the miR-330-3p/ retinoic acid induced 2 (RAI2) axis. miR-330-3p upregulation or silencing of RAI2 restored BC cell proliferation, invasion, and migration following overexpression of circRBPMS. RAI2 silencing reversed miR-330-3p-induced cell invasion and migration as well as growth inhibition in vitro. Moreover, through bioinformatic analysis of the downstream target of RAI2 in the TCGA database, we identified and validated the biological role of circRBPMS through the RAI2-mediated ERK and epithelial-mesenchymal transition (EMT) pathways. We summarize the circRBPMS/miR-330-3p/RAI2 axis, where circRBPMS acts as a tumor suppressor, and provide a potential biomarker and therapeutic target for BC.

Circular RNAs as biomarkers and therapeutic targets in cancer

Circular RNAs (circRNAs) are a class of single-stranded closed non-coding RNA molecules (ncRNAs), which are formed as a result of reverse splicing of mRNAs. Despite their relative abundance, an interest in understanding their regulatory importance is rather recent. High stability, abundance and evolutionary conservation among species underline some of their important traits. CircRNAs perform a variety of cellular functions ranging from miRNA and proteins sponges to transcriptional modulation and splicing. Additionally, most circRNAs are expressed aberrantly in pathological conditions suggesting their possible exploitation as diagnostic biomarkers. Their covalent closed cyclic structure resulting in resistance to RNases further makes them suitable as cancer biomarkers. Studies involving human tumors have verified differences in the expression profiles of circRNAs, indicating a regulatory role in cancer pathogenesis and metastasis. As endogenous competitive RNA, circRNAs can regulate tumor proliferation and invasion. Further, some circRNAs located in the nucleus can regulate transcription of genes by binding to RNA polymerase II. In this review, we elaborate the characteristics, functions and mechanisms of action of circRNAs in cancer. We also discuss the possibility of using circRNAs as potential therapeutic targets and biomarkers for cancer.

Hsa_circ_0002060 Knockdown Ameliorates Osteoporosis by Targeting MiR-198-5p

Osteoporosis (OP) is increasingly becoming one of a major health concerns all over the world. However, the limitations of current therapeutic drugs for OP are including considerable side effects and low efficacy. Therefore, it is required to develop new therapeutic drugs for OP. This study aimed to investigate the role of hsa_circ_0002060 in the regulation of osteoporosis. Osteoblast cells (hFOB 1.19) were transfected with hsa_circ_0002060 small interfering RNA (siRNA), following by stimulated with dexamethasone (DEX) to mimic OP in vitro. Cell counting kit-8, apoptosis, and JC-1 mitochondrial membrane potential assays were used to evaluate the cell viability, apoptosis, and mitochondrial membrane potential, respectively. Western blot was conducted to detect the expression of proteins. In addition, the levels of reactive oxygen species, superoxide dismutase, glutathione and malondialdehyde were measured with enzyme-linked immunosorbent assay (ELISA). The putative target of hsa_circ_0002060 was verified by dual luciferase reporter assay and RNA pull down. At last, the role of hsa_circ_0002060 in the progression of OP was investigated with an ovariectomy (OVX)-induced OP mouse model. The results indicated DEX could induce cell viability decline in hFOB 1.19 cells, which was ameliorated by hsa_circ_0002060 knockdown. Consistently, DEX-induced cell apoptosis of hFOB 1.19 was ameliorated by hsa_circ_0002060 knockdown as well. As for the underlying mechanisms study, hsa_circ_0002060 was proved to regulate the viability of hFOB 1.19 cells through targeting miR-198-5p/Bax axis. Additionally, hsa_circ_0002060 knockdown alleviated ovariectomy-induced OP in a mouse model. Taken together, hsa_circ_0002060 knockdown alleviated the progression of OP by targeting miR-198-5p. Hsa_circ_0002060 might possibly be served as a therapeutic target for treating OP.

Cerina: systematic circRNA functional annotation based on integrative analysis of ceRNA interactions

Circular RNAs, a family of covalently circularized RNAs with tissue-specific expression, were recently demonstrated to play important roles in mammalian biology. Regardless of extensive research to predict, quantify, and annotate circRNAs, our understanding of their functions is still in its infancy. In this study, we developed a novel computational tool: Competing Endogenous RNA for INtegrative Annotations (Cerina), to predict biological functions of circRNAs based on the competing endogenous RNA model. Pareto Frontier Analysis was employed to integrate ENCODE mRNA/miRNA data with predicted microRNA response elements to prioritize tissue-specific ceRNA interactions. Using data from several circRNA-disease databases, we demonstrated that Cerina significantly improved the functional relevance of the prioritized ceRNA interactions by several folds, in terms of precision and recall. Proof-of-concept studies on human cancers and cardiovascular diseases further showcased the efficacy of Cerina on predicting potential circRNA functions in human diseases.

The Role of Exosomal Non-Coding RNAs in Coronary Artery Disease

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality worldwide. Atherosclerosis (AS) is a major cause of CVD. Oxidative stress, endothelial dysfunction, and inflammation are key factors involved in the development and progression of AS. Exosomes are nano-sized vesicles secreted into the extracellular space by most types of cells, and are ideal substances for the transmission and integration of signals between cells. Cells can selectively encapsulate biologically active substances, such as lipids, proteins and RNA in exosomes and act through paracrine mechanisms. Non-coding RNAs (ncRNAs) are important for communication between cells. They can reach the recipient cells through exosomes, causing phenotypic changes and playing a molecular regulatory role in cell function. Elucidating their molecular mechanisms can help identify therapeutic targets or strategies for CVD. Coronary artery disease (CAD) is the most important disease in CVD. Here, we review the role and the regulatory mechanism of exosomal ncRNAs in the pathophysiology of CAD, as well as the potential contribution of exosomal ncRNA to diagnosis and treatment of CAD.

Extracellular Vesicle-Mediated Vascular Cell Communications in Hypertension: Mechanism Insights and Therapeutic Potential of ncRNAs

Hypertension, a chronic and progressive disease, is an outstanding public health issue that affects nearly 40% of the adults worldwide. The increasing prevalence of hypertension is one of the leading causes of cardiovascular morbidity and mortality. Despite of the available treatment medications, an increasing number of hypertensive individuals continues to have uncontrolled blood pressure. In the vasculature, endothelial cells, vascular smooth muscle cells (VSMCs), and adventitial fibroblasts play a fundamental role in vascular homeostasis. The aberrant interactions between vascular cells might lead to hypertension and vascular remodeling. Identification of the precise mechanisms of vascular remodeling may be highly required to develop effective therapeutic approaches for hypertension. Recently, extracellular vesicle-mediated transfer of proteins or noncoding RNAs (ncRNAs) between vascular cells holds promise for the treatment of hypertension. Especially, extracellular vesicle-packaging ncRNAs have gained enormous attention of basic and clinical scientists because of their tremendous potential to act as novel clinical biomarkers and therapeutic targets of hypertension. Here we will discuss the current findings focusing on the emerging roles of extracellular vesicle-carrying ncRNAs in the pathologies of hypertension and its associated vascular remodeling. Furthermore, we will highlight the potential of extracellular vesicles and ncRNAs as biomarkers and therapeutic targets for hypertension. The future research directions on the challenges and perspectives of extracellular vesicles and ncRNAs in hypertensive vascular remodeling are also proposed.

Circular RNAs: Regulatory functions in respiratory tract cancers

Circular RNAs (circRNAs) are a class of single-stranded RNAs having a covalently closed loop structure generated from back-splicing of pre-mRNA. These novel RNAs are characterized by high stability, abundance and conservation. Accumulating evidence has revealed that circRNAs are intimately associated with the pathogenesis, development and progression of multiple human diseases, including respiratory tract cancers. CircRNAs may serve as oncogenes or tumor suppressors to influence cell proliferation, differentiation, apoptosis, invasion and metastasis. CircRNAs may act as microRNA (miRNA) sponges, interact with RNA-binding proteins (RBPs), regulate gene transcription and/or translate into mini-peptides or proteins. In this review, we discuss recent progress in understanding the pathologic roles of circRNAs in respiratory tract cancers, such as nasopharyngeal carcinoma, laryngeal squamous cell carcinoma, and especially lung adenocarcinoma. We further discuss the diagnostic, therapeutic and prognostic roles as potential biomarkers in respiratory tract cancers, providing insight into the possibilities of applying circRNAs as therapeutic targets and biomarkers in precision oncology.

Role of Non-coding RNA in Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DCM) is the leading cause of morbidity and mortality in diabetic population worldwide, characteristic by cardiomyocyte hypertrophy, apoptosis and myocardial interstitial fibrosis and eventually developing into heart failure. Non-coding RNAs, such as microRNAs (miRNAs), circular RNAs (circRNAs), long non-coding RNAs (lncRNAs) and other RNAs without the protein encoding function were emerging as a popular regulator in various types of processes during human diseases. The evidences have shown that miRNAs are regulators in diabetic cardiomyopathy, such as insulin resistance, cardiomyocytes apoptosis, and inflammatory, especially their protective effect on heart function. Besides that, the functions of lncRNAs and circRNAs have been gradually confirmed in recent years, and their functions in DCM have become increasingly prominent. We highlighted the nonnegligible roles of non-coding RNAs in the pathological process of DCM and showed the future possibilities of these non-coding RNAs in DCM treatment. In this chapter, we summarized the present advance of the researches in this filed and raised the concern and the prospect in the future.

Critical function of circular RNAs in lung cancer

Lung cancer is one of the main causes of cancer-related death in the world, especially due to its frequency and ineffective therapeutically approaches in the late stages of the disease. Despite the recent advent of promising new targeted therapies, lung cancer diagnostic strategies still have difficulty in identifying the disease at an early stage. Therefore, the characterizations of more sensible and specific cancer biomarkers have become an important goal for clinicians. Circular RNAs (circRNAs), a type of RNA with covalently closed continuous loop structures that display high structural resistance and tissue specificity pointed toward a potential biomarker role. Current investigations have identified that circRNAs have a prominent function in the regulation of oncogenic pathways, by regulating gene expression both at transcriptional and post-transcriptional level. The aim of this review is to provide novel information regarding the implications of circRNAs in lung cancer, with an emphasis on the role in disease development and progression. Initially, we explored the potential utility of circRNAs as biomarkers, focusing on function, mechanisms, and correlation with disease progression in lung cancer. Further, we will describe the interaction between circRNAs and other non-coding species of RNA (particularly microRNA) and their biological significance in lung cancer. Describing the nature of these interactions and their therapeutic potential will provide additional insight regarding the altered molecular landscape of lung cancer and consolidate the potential clinical value of these circular transcripts. This article is categorized under: RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems RNA in Disease and Development > RNA in Disease RNA in Disease and Development > RNA in Development.

A novel circRNA-miRNA-mRNA network identifies circ-YOD1 as a biomarker for coronary artery disease

Circular RNAs (circRNAs) are involved in many physiological functions. Whether circulating circRNAs serve as markers for coronary artery disease (CAD) is unknown. Seven CAD-related microarray datasets were downloaded from the Gene Expression Omnibus (GEO) database and were analyzed using clustering and functional enrichment to identify hub mRNAs and miRNAs. StarBase V3.0 and circinteractome databases were used to predict interactions between circRNAs and miRNAs whereas miRwalk and DIANA TOOLS were used to predict interactions between miRNAs and mRNAs. Altogether, this helped establish a circRNA-miRNA-mRNA triple network for diagnosis of CAD. Five non-coding RNAs (ncRNAs) were identified in our study population with the use of quantitative real-time PCR (RT-PCR). The prognostic values of circYOD1, hsa-miR-21-3p and hsa-miR-296-3p were evaluated using a receiver operating characteristic (ROC) curve. A CAD circRNA-miRNA-mRNA network was established from our analyses containing one circRNA, four miRNAs and thirteen mRNAs. After performing RT-PCR validation between CAD and non-CAD samples, only three ncRNAs of five ncRNAs showed significance for further analysis. The area under ROC curve (AUC) of circ-YOD1 was 0.824, the AUC of hsa-miR-21-3p was 0.731 and hsa-miR-296-3p was 0.776. The pairwise comparison results showed that circ-YOD1 had statistical significance (P_YOD1-21 < 0.01 and P_YOD1-296 < 0.05). The results of functional enrichment analysis of interacting genes and microRNAs showed that the shared circ-YOD1 may act as a new biomarker for CAD. Our investigation of the triple regulatory networks of circRNA-miRNA-mRNA in CAD revealed circ-YOD1 as a potential biomarker for CAD.

[CircRNA_005647 inhibits expressions of fibrosis-related genes in mouse cardiac fibroblasts via sponging miR-27b-3p]

OBJECTIVE

To investigate the effect of circRNA_005647 on fibrotic phenotype of mouse cardiac fibroblasts (CFs) and explore its mechanism.

METHODS

We used an angiotensin Ⅱ (Ang-Ⅱ) capsule pump (daily dose of 1.46 mg/kg for 2 weeks) to establish a mouse model of myocardial fibrosis in C57BL/6 mice. Masson staining was used to detect myocardial fibrosis in the myocardium. The expression of circRNA_005647 in the myocardium of Ang-Ⅱ-infused mice and in Ang-Ⅱ-treated CFs were detected with real-time PCR. Actinomycin D and RNase R exonuclease digestion were used to test the stability of circRNA_005647 in mouse CFs. Over- expression of circRNA_005647 was achieved in the CFs by infecting the cells with a recombinant circRNA_005647 adenovirus (rAd-circRNA_005647), and the expressions of Col1a1, Col3a1 and Acta2 were detected in the cells with real-time PCR and Western blotting. Dual luciferase reporter assay, RNA antisense purification and RNA Pull down assay were performed to identify the interaction between circRNA_005647 and miR-27b-3p.

RESULTS

CircRNA_005647 was up- regulated in the myocardium of Ang-Ⅱ- infused mice and in Ang-Ⅱ-treated mouse CFs (P < 0.01). CircRNA_005647 was more stable than its host gene Myosin IXA (Myo9a) in response to actinomycin D (P < 0.01) and RNase R exonuclease treatment. The expressions of fibrosis-associated genes was down-regulated in the CFs over-expressing circRNA_ 005647 (P < 0.05). Dual luciferase reporter assay, RNA antisense purification and RNA Pull down assay revealed the interaction between miR-27b-3p and circRNA_005647. MiR-27b-3p obviously enhanced the fibrotic phenotype but reversed the inhibitory effect of circRNA_005647 on the expression of fibrosis associated genes in the CFs (P < 0.05).

CONCLUSIONS

CircRNA_005647 is upregulated in cardiac fibrosis and inhibits the expression of fibrosis-related genes through sponging miR-27b-3p in mouse CFs.

Increased circulating circular RNA_103516 is a novel biomarker for inflammatory bowel disease in adult patients

BACKGROUND

Increasing evidence demonstrates that by acting as microRNA sponges modulating gene expression at the transcriptional or post-transcriptional level, circular RNAs (circRNAs) participate in the pathogenesis of a variety of diseases and are considered ideal biomarkers of human disease.

AIM

To examine the expression of circRNA_103516 in inflammatory bowel disease (IBD) and its associations with clinical phenotypes and inflammatory cytokines.

METHODS

Peripheral blood mononuclear cells (PBMCs) were obtained from patients with IBD, healthy controls (HCs), and patient controls (PCs). Expression of circRNA_103516 and hsa-miR-19b-1-5p was assessed by quantitative reverse transcription-polymerase chain reaction. Crohn's disease activity index (CDAI), Mayo score, C-reactive protein (CRP) level, and erythrocyte sedimentation rate (ESR) were measured. To assess the inflammatory cytokines tumour necrosis factor α (TNF-α), interferon-γ (IFN-γ), and interleukin-10 (IL-10), blood samples were analysed by flow cytometry.

RESULTS

Ninety Crohn’s disease (CD) and 90 ulcerative colitis (UC) patients, 80 HCs, and 35 PCs were included in the study. CircRNA_103516 was upregulated in CD and UC patients compared with HCs and PCs (P < 0.05). The area under the curve of circRNA_103516 for diagnosing CD and UC was 0.790 and 0.687, respectively. In addition, circRNA_103516 levels were increased in active CD and UC compared with remittent groups (P = 0.027, P = 0.045). Furthermore, in CD, circRNA_103516 correlated positively with CDAI (P < 0.001), CRP (P < 0.001), ESR (P < 0.001), TNF­α (P < 0.001), and IFN-γ (P < 0.001) and negatively correlated with IL-10 (P = 0.006). In UC patients, circRNA_103516 correlated with Mayo score (P < 0.001), CRP (P < 0.001), ESR (P < 0.001), TNF­α (P < 0.001), IFN-γ (P =0.011), and IL-10 (P = 0.002). Additionally, circRNA_103516 correlated positively with stricturing (P = 0.018) and penetrating (P = 0.031) behaviour. Moreover, hsa-miR-19b-1-5p correlated negatively with circRNA_103516 in CD.

CONCLUSION

CircRNA_103516 levels in PBMCs can be considered an ideal candidate biomarker for diagnosing IBD. Dysregulation of circRNA_103516 may participate in the molecular mechanism of IBD through hsa-miR-19b-1-5p sponging.

Exosomal non-coding RNAs (Exo-ncRNAs) in cardiovascular health

Extracellular vesicles (EVs) play a role in the pathophysiological processes and in different diseases, including cardiovascular disease. Out of several categories of EVs, exosomes (smallest - 30 to 150 nm) are gaining most of the focus as the next generation of biomarkers and in therapeutic strategies. This is because exosomes can be differentiated from other types of EVs based on the expression of tetraspanin molecules on the surface. More importantly, exosomes can be traced back to the cell of origin by identifying the unique cellular marker(s) on the exosomal surface. Recently, several researchs have demonstrated an important and underappreciated mechanism of paracrine cell-cell communication involving exosomal transfer, and its subsequent functional impact on recipient cells. Exosomes are enriched in proteins, mRNAs, miRNAs, and other non-coding RNAs, which can potentially alter myocardial function. Additionally, different stages of tissue damage can also be identified by measuring these bioactive molecules in the circulation. There are several aspects of this new concept still unknown. Therefore, in this review, we have summarized the knowledge we have so far and highlighted the potential of this novel concept of next generation biomarkers and therapeutic intervention.

Circular RNAs as novel regulators, biomarkers and potential therapies in fibrosis

Fibrosis is the excess deposition of extracellular matrix components which ultimately leads to the disruption of organ architecture and loss of function. Circular RNAs (circRNAs) are a newly discovered type of long noncoding RNAs with single-stranded covalently closed loops. It is known that circRNAs are novel regulators of gene expression via various ways, including miRNA sponge, protein sponge, regulation of transcription and post transcription. Recently, a growing body of evidence suggests that circular RNAs are also involved in tissue fibrosis in several organs. In this review, we summarized current studies of circular RNAs in fibrosis and hopefully aid in better understanding the molecular mechanism of fibrosis and provide a basis to explore new therapeutic targets of fibrosis.

Non-coding RNA involvement in the pathogenesis of diabetic cardiomyopathy

In recent years, the incidence of diabetes has been increasing rapidly, which seriously endangers human health. Diabetic cardiomyopathy, an important cardiovascular complication of diabetes, is characterized by myocardial fibrosis, ventricular remodelling and cardiac dysfunction. It has been documented that mitochondrial dysfunction, oxidative stress, inflammatory response, autophagy, apoptosis, diabetic microangiopathy and myocardial fibrosis are implicated in the pathogenesis of diabetic cardiomyopathy. With the development of molecular biology technology, accumulating evidence demonstrates that non‐coding RNAs (ncRNAs) are critically involved in the molecular mechanisms of diabetic cardiomyopathy. In this review, we summarize the pathological roles of three types of ncRNAs (microRNA, long ncRNA and circular RNA) in the progression of diabetic cardiomyopathy, which may provide valuable insights into the pathogenesis of diabetic cardiovascular complications.

CircPCMTD1 Acts as the Sponge of miR-224-5p to Promote Glioma Progression

Glioma is the most common malignant tumor of the central nervous system with high morbidity and mortality. Circular RNAs (circRNAs) are abundant non-coding RNAs, which contribute to tumor progression by competing with other endogenous RNAs such as microRNA (miRNA). MiRNA are a class of small non-coding RNAs, which interrupt the translation of target mRNAs. CircPCMTD1 (hsa-circ-0001801) is a newly discovered circRNA that was found to be significantly upregulated in glioma. However, its function is unclear. In this study, circPCMTD1 upregulation promoted the cell viability, migration and invasion dramatically, while the inhibition of circPCMTD1 led to a significant reduction of tumor growth in vivo. MiRNAs microarray analyses on circPCMTD1 silencing models in U251 and U118MG cells were performed, and the results suggested that circPCMTD1 knockdown could upregulate the expression of miR-224-5p and downregulate the expression of mTOR, one of miR-224-5p targets, in both cell lines. According to the prediction from circular RNA interactome and Targetscan, there was a complementary sequence in circPCMTD1 for miR-224-5p. Dual-luciferase reporter assay demonstrated that circPCMTD1 were targets of miR-224-5p. RIP assay was also performed to further confirm their directly interaction. Overexpression of miR-224-5p inhibited the viability and proliferation, migration, and invasion of U251 and U118MG glioma cells. In conclusion, circPCMTD1 could contribute to the promotion of glioma progression, and it may serve as the sponge of miR-224-5p to exert its function.

Increasing Upstream Chromatin Long-Range Interactions May Favor Induction of Circular RNAs in LysoPC-Activated Human Aortic Endothelial Cells

Circular RNAs (circRNAs) are non-coding RNAs that form covalently closed continuous loops, and act as gene regulators in physiological and disease conditions. To test our hypothesis that proatherogenic lipid lysophosphatidylcholine (LPC) induce a set of circRNAs in human aortic endothelial cell (HAEC) activation, we performed circRNA analysis by searching our RNA-Seq data from LPC-activated HAECs, and found: (1) LPC induces significant modulation of 77 newly characterized cirRNAs, among which 47 circRNAs (61%) are upregulated; (2) 34 (72%) out of 47 upregulated circRNAs are upregulated when the corresponding mRNAs are downregulated, suggesting that the majority of circRNAs are upregulated presumably via LPC-induced “abnormal splicing” when the canonical splicing for generation of corresponding mRNAs is suppressed; (3) Upregulation of 47 circRNAs is temporally associated with mRNAs-mediated LPC-upregulated cholesterol synthesis-SREBP2 pathway and LPC-downregulated TGF-β pathway; (4) Increase in upstream chromatin long-range interaction sites to circRNA related genes is associated with preferred circRNA generation over canonical splicing for mRNAs, suggesting that shifting chromatin long-range interaction sites from downstream to upstream may promote induction of a list of circRNAs in lysoPC-activated HAECs; (5) Six significantly changed circRNAs may have sponge functions for miRNAs; and (6) 74% significantly changed circRNAs contain open reading frames, suggesting that putative short proteins may interfere with the protein interaction-based signaling. Our findings have demonstrated for the first time that a new set of LPC-induced circRNAs may contribute to homeostasis in LPC-induced HAEC activation. These novel insights may lead to identifications of new therapeutic targets for treating metabolic cardiovascular diseases, inflammations, and cancers.

Comprehensive analysis of circular RNAs in pathological states: biogenesis, cellular regulation, and therapeutic relevance

Circular RNAs (circRNAs) are members of the non-coding transcriptome; however, some of them are translated into proteins. These transcripts have important roles in both physiological and pathological mechanisms due to their ability to directly influence cellular signaling pathways. Specifically, circRNAs are regulators of transcription, translation, protein interaction, and signal transduction. An increased knowledge within their area is observed over the last few years, concomitant with the development of next-generation sequencing techniques. circRNAs are mostly tissue and disease specific with the ability of specifically changing the biological behavior of cells. The altered expression profile is currently investigated as novel minimally invasive diagnosis/prognosis tool and also therapeutic target in human disease. The diagnosis approach is based on their level modification within pathological states, especially cancer, where circRNAs' therapies are intensively explored in anti-aging strategies, diabetes, cardiovascular diseases, and malignant pathologies, and are relying on the restoration of homeostatic profiles.

Circular RNAs and their roles in head and neck cancers

Circular RNAs are abundant endogenous non-coding RNA with no 5′ cap and 3′ polyadenylation tail that modify liner mRNAs and have no terminal structures. Our knowledge of the biogenesis of circular RNAs has been expanded, and circular RNAs were shown to be key regulators of various diseases, especially cancers. Head and neck cancers are the sixth most popular cancers worldwide, and the overall survival rates remain unsatisfactory. Recent studies have indicated that circular RNAs are involved in the tumorigenesis, progression, invasion and chemosensitivity of head and neck cancers and that some circular RNAs could serve as diagnostic and prognostic biomarkers. In this study, we summarize research advances in the regulation of circular RNA biogenesis, their characteristics and functions, the involvement of circular RNAs in the pathophysiology of head and neck cancers and their potential clinical utilization, as well as the likely directions of future studies.

Circular RNA Profiling by Illumina Sequencing via Template-Dependent Multiple Displacement Amplification

Circular RNAs (circRNAs) are newly discovered incipient non-coding RNAs with potential roles in disease progression in living organisms. Significant reports, since their inception, highlight the abundance and putative functional roles of circRNAs in every organism checked for, like O. sativa, Arabidopsis, human, and mouse. CircRNA expression is generally less than their linear mRNA counterparts which fairly explains the competitive edge of canonical splicing over non-canonical splicing. However, existing methods may not be sensitive enough for the discovery of low-level expressed circRNAs. By combining template-dependent multiple displacement amplification (tdMDA), Illumina sequencing, and bioinformatics tools, we have developed an experimental protocol that is able to detect 1,875 novel and known circRNAs from O. sativa. The same method also revealed 9,242 putative circRNAs in less than 40 million reads for the first time from the Nicotiana benthamiana whose genome has not been fully annotated. Supported by the PCR-based validation and Sanger sequencing of selective circRNAs, our method represents a valuable tool in profiling circRNAs from the organisms with or without genome annotation.

Role of circular RNAs in cardiovascular diseases

IMPACT STATEMENT

Circular RNAs are important regulators of multiple biological processes such as organogenesis and oncogenesis. Although the bulk of concerning studies focused on revealing their diversified roles in various types of cancers, reports began to accumulate in cardiovascular field these days. We summarize circular RNAs implicated in cardiovascular diseases, aiming to highlight the advances in the knowledge of such diseases and their potential of being promising target for diagnosis and therapy.

Non-coding RNAs and exercise: pathophysiological role and clinical application in the cardiovascular system

There is overwhelming evidence that regular exercise training is protective against cardiovascular disease (CVD), the main cause of death worldwide. Despite the benefits of exercise, the intricacies of their underlying molecular mechanisms remain largely unknown. Non-coding RNAs (ncRNAs) have been recognized as a major regulatory network governing gene expression in several physiological processes and appeared as pivotal modulators in a myriad of cardiovascular processes under physiological and pathological conditions. However, little is known about ncRNA expression and role in response to exercise. Revealing the molecular components and mechanisms of the link between exercise and health outcomes will catalyse discoveries of new biomarkers and therapeutic targets. Here we review the current understanding of the ncRNA role in exercise-induced adaptations focused on the cardiovascular system and address their potential role in clinical applications for CVD. Finally, considerations and perspectives for future studies will be proposed.