Circular RNAs in hypertension: challenges and clinical promise

Hsa_circ_0001304 promotes vascular neointimal hyperplasia accompanied by autophagy activation

Aberrant autophagy in vascular smooth muscle cells (VSMCs) is associated with the progression of vascular remodeling diseases caused by neointimal hyperplasia. Platelet-derived growth factor-BB (PDGF-BB)-induced vascular remodeling is accompanied by autophagy activation, however, the involvement of circular RNAs (circRNAs) remains unclear. Here, we show the role of PDGF-BB-regulated hsa_circ_0001304 (circ-1304) in neointimal hyperplasia and its potential involvement in VSMC autophagy, while also elucidating the potential mechanisms. Functionally, overexpression of circ-1304 promotes VSMC autophagy in vitro and exacerbates neointimal hyperplasia in vivo, and this exacerbation is accompanied by autophagy activation. Mechanistically, circ-1304 acts as a sponge for miR-636, resulting in increased protein levels of YTHDF2. Subsequently, the YTHDF2 protein promotes the degradation of mTOR mRNA by binding to the latter's m6A modification sites. We demonstrate that PDGF-BB activates VSMC autophagy via circRNA regulation. Therefore, circ-1304 may serve as a potential therapeutic target for vascular remodeling diseases.

Comparative Analysis of Circular RNAs Expression and Function between Aortic and Intracranial Aneurysms

An aneurysm is an abnormal enlargement or bulging of the wall of a blood vessel. Most often, aneurysms occur in large blood vessels - the aorta (Thoracic Aortic Aneurysm (TAA) and Abdominal Aortic Aneurysm (AAA)) and brain vessels (Intracranial Aneurysm (IA)). Despite the presence of significant differences in the pathogenesis of the development and progression of IA and TAA/AAA, there are also similarities. For instance, both have been shown to be strongly influenced by shear stress, inflammatory processes, and enzymatic destruction of the elastic lamellae and extracellular matrix (ECM) proteins of the vascular wall. Moreover, although IA and TAA are predominantly considered arteriopathies with different pathological mechanisms, they share risk factors with AAA, such as hypertension and smoking. However, there is a need for a more in- -depth study of the key elements that may influence the formation and progression of a particular aneurysm to find ways of therapeutic intervention or search for a diagnostic tool. Today, it is known that the disruption of gene expression is one of the main mechanisms that contribute to the development of aneurysms. At the same time, growing evidence suggests that aberrant epigenetic regulation of gene function is strongly related to the genesis of aneurysms. Although much has been studied of the known protein-coding genes, circular RNAs (circRNAs), a relatively new and rapidly evolving large family of transcripts, have recently received much scientific attention. CircRNAs regulate gene expression through the sponging of microRNAs (miRNAs) and can also be used as therapeutic targets and biomarkers. Increasing evidence has implicated circRNAs in the pathogenesis of multiple cardiovascular diseases, including the development of aneurysms. However, the mechanism of dysregulation of certain circRNAs in a particular aneurysm remains to be studied. The discovery of circRNAs has recently advanced our understanding of the latest mode of miRNAs/target genes regulation in the development and progression of IA and TAA/AAA. The aim of this study is to compare the expression profiles of circRNAs to search for similar or different effects of certain circRNAs on the formation and progression of IA and TAA/AAA.

Future treatments in hypertension: Can we meet the unmet needs of patients?

The prevalence of arterial hypertension is approximately 47% in the United States and 55% in Europe. Multiple different medical therapies are used to treat hypertension including diuretics, beta blockers, calcium channel blockers, angiotensin receptor blockers, angiotensin converting enzyme inhibitors, alpha blockers, central acting alpha receptor agonists, neprilysin inhibitors and vasodilators. However, despite the numerous number of medications, the prevalence of hypertension is on the rise, a considerable proportion of the hypertensive population is resistant to these therapeutic modalities and a definitive cure is not possible with the current treatment approaches. Therefore, there is a need for novel therapeutic strategies to provide better treatment and control of hypertension. In this review, our aim is to describe the latest developments in the treatment of hypertension including novel medication classes, gene therapies and RNA-based modalities.

The Function and Therapeutic Potential of Circular RNA in Cardiovascular Diseases

Circular RNA (circRNA) has a closed-loop structure, and its 3' and 5' ends are directly covalently connected by reverse splicing, which is more stable than linear RNA. CircRNAs usually possess microRNA (miRNA) binding sites, which can bind miRNAs and inhibit miRNA function. Many studies have shown that circRNAs are involved in the processes of cell senescence, proliferation and apoptosis and a series of signalling pathways, playing an important role in the prevention and treatment of diseases. CircRNAs are potential biological diagnostic markers and therapeutic targets for cardiovascular diseases (CVDs). To identify biomarkers and potential effective therapeutic targets without toxicity for heart disease, we summarize the biogenesis, biology, characterization and functions of circRNAs in CVDs, hoping that this information will shed new light on the prevention and treatment of CVDs.

Exosomal circular RNAs: Biogenesis, effect, and application in cardiovascular diseases

As natural nanoparticles, exosomes regulate a wide range of biological processes via modulation of its components, including circular RNAs (circRNAs). CircRNAs are a novel class of closed-loop single-stranded RNAs with a wide distribution, and play diverse biological roles. Due to its stability in exosomes, exosomal circRNAs serve as biomarkers, pathogenic regulators and exert therapeutic potentials in some cardiovascular diseases, including atherosclerosis, acute coronary syndrome, ischemia/reperfusion injury, heart failure, and peripheral artery disease. In this review, we detailed the current knowledge on the biogenesis and functions of exosomes, circRNAs, and exosomal circRNAs, as well as their involvement in these cardiovascular diseases, providing novel insights into the diagnosis and treatment of these diseases.

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.

circMBOAT2 serves as the sponge of miR-433-3p to promote the progression of bladder cancer

BACKGROUND

Bladder cancer (Bca) is the most common cancer in urinary system. Recent studies revealed that circular RNAs (circRNAs) play vital roles in the development and progression of cancers. circMBOAT2 serves as an oncogenic gene in various kinds of cancer, promoting cell growth and metastasis. Nevertheless, the biological function of circMBOAT2 in Bca has not been reported.

METHODS

qRT-PCR was used to measure the mRNA, circRNA and miRNA expression levels in Bca tissues and cells. Loss-of function experiments were carried to investigate the effect of circMBOAT2 on cell proliferation and migration. Nuclear mass separation, RNA pull-down and dual-luciferase reporter were performed to the molecular mechanisms underlying the functions of circMBOAT2.

RESULTS

In this research, we identified that circMBOAT2 expression was increased in Bca tissues and positively corelated with unfavorable prognosis. In vitro assay demonstrated that suppression of circMBOAT2 impaired the proliferation and migration of Bca cells. Mechanically, circMBOAT2 was predominantly spread in cytoplasm and it sponged miR-433-3p to strengthen CREB1 expression.

CONCLUSION

Hence, our study suggested that circMBOAT2 may serve as an oncogene in the development and progression of Bca and it will be the novel tumor biomarker and therapeutic target for Bca.

Exosomal noncoding RNAs: key players in glioblastoma drug resistance

Glioma, as one of the most severe human malignancies, is defined as the Central Nervous System's (CNS) tumors. Glioblastoma (GBM) in this regard, is the most malignant type of gliomas. There are multiple therapeutic strategies to cure GBM, for which chemotherapy is often the first-line treatment. Still, various cellular processes, such as uncontrolled proliferation, invasion and metastasis, may disturb the treatment efficacy. Drug resistance is another process in this way, which can also cause undesirable effects. Thereupon, identifying the mechanisms, involved in developing drug resistance and the relevant mechanisms can be very helpful in GBM management. The discovery of exosomal non-coding RNAs (ncRNAs), RNA molecules that can be transferred between the cells and different tissues using the exosomes, was a milestone in this regard. It has been revealed that the key exosomal ncRNAs, including circular RNAs, microRNAs, and long ncRNAs, are able to modulate GBM drug resistance through different signaling pathways or by affecting regulatory proteins and their corresponding genes. Nowadays, researchers are trying to overcome the limitations of chemotherapy by targeting these RNA molecules. Accordingly, this review aims to clarify the substantial roles of exosomal ncRNAs in GBM drug resistance and involved mechanisms.

Role of Circular RNAs in Cardiovascular Disease

Circular RNAs (circRNAs) have recently been identified as a new class of long noncoding RNAs with gene regulatory roles. These covalently closed transcripts are generated when the pre-mRNA splicing machinery back splices to join a downstream 5' splice site to an upstream 3' splice site. CircRNAs are naturally resistant to degradation by exonucleases and have long half-lives compared with their linear counterpart that potentially could serve as biomarkers for disease. Recent evidence highlights that circRNAs may play an essential role in cardiovascular injury and repair. However, our knowledge of circRNA is still in its infancy with limited direct evidence to suggest that circRNA may play critical roles in the mechanism and treatment of cardiac dysfunction. In this review, we focus on our current understanding of circRNA in the cardiovascular system.

Circular RNA profiling identifies circ102049 as a key regulator of colorectal liver metastasis

Circular RNA (circRNA) plays an essential role in the development and progression of various cancers. However, the functions and mechanisms of circRNA in colorectal liver metastasis have not been fully elucidated. We performed circRNA microarray analysis to screen differentially expressed circRNA in the pathology of colorectal liver metastasis. Quantitative real-time PCR was used to detect the expression of hsa_circ_102049 (circ102049) in colorectal cancer (CRC) samples. CRC cells were transfected with circ102049 overexpression vector or small interfering (si)RNA to assess the effects of circ102049 in vitro. Bioinformatics analysis, fluorescence in situ hybridization, RNA immunoprecipitation, RNA pull-down and luciferase reporter assays were conducted to confirm the relationship of circ102049, miR-761, miR-192-3p and FRAS1. The mechanism by which circ102049 recruits and distributes DGCR8 protein in the cytoplasm was also investigated. We found that circ102049 was highly expressed in primary CRC tumors with liver metastasis and closely correlated with the prognosis of patients with CRC. Circ102049 significantly enhanced the adhesion, migration and invasion abilities of CRC cells, and promoted CRC progression via a micro (mi)R-761/miR-192-3p-FRAS1-dependent mechanism. Notably, due to the distribution of DGCR8 protein, circ102049 may also indirectly reduce the levels of mature miR-761 and miR-192-3p in the cytoplasm. In addition, the role of circ102049 in promoting colorectal liver metastasis was confirmed in vivo. Our findings provide new evidence that circ102049 may be a potential prognostic factor in CRC, and that the circ102049-miR-761/miR-192-3p-FRAS1 axis may be an anti-metastatic target for CRC patients.

Roles of circular RNAs in diabetic complications: From molecular mechanisms to therapeutic potential

Diabetes is characterized by changed homeostasis of blood glucose levels, which is associated with various complications, including cardiomyopathy, atherosclerosis, endothelial dysfunction, nephropathy, retinopathy and neuropathy. In recent years, accumulative evidence has demonstrated that circular RNAs are identified as a novel type of noncoding RNAs (ncRNAs) involving in the regulation of various physiological processes and pathologic conditions. Specifically, the emergence of complications response to diabetes is finely controlled by a complex gene regulatory network in which circular RNAs play a critical role. Recently, circular RNAs are emerging as messengers that could influence cellular functions under diabetic conditions. Dysregulation of circular RNAs has been closely linked to the pathophysiology of diabetes-related complications. In this review, we aimed to summarize the current progression and underlying mechanisms of circular RNA in the development of diabetes-related complications. We will also provide an overview of circular RNA-regulated cell communications in different types of cells that have been linked to diabetic complications. We anticipated that the completion of this review will provide potential clues for developing novel circular RNAs-based biomarkers or therapeutic targets for diabetes and its associated complications.

The Emerging Role and Promise of Circular RNAs in Obesity and Related Metabolic Disorders

Circular RNAs (circRNAs) are genome transcripts that are produced from back-splicing of specific regions of pre-mRNA. These single-stranded RNA molecules are widely expressed across diverse phyla and many of them are stable and evolutionary conserved between species. Growing evidence suggests that many circRNAs function as master regulators of gene expression by influencing both transcription and translation processes. Mechanistically, circRNAs are predicted to act as endogenous microRNA (miRNA) sponges, interact with functional RNA-binding proteins (RBPs), and associate with elements of the transcriptional machinery in the nucleus. Evidence is mounting that dysregulation of circRNAs is closely related to the occurrence of a range of diseases including cancer and metabolic diseases. Indeed, there are several reports implicating circRNAs in cardiovascular diseases (CVD), diabetes, hypertension, and atherosclerosis. However, there is very little research addressing the potential role of these RNA transcripts in the occurrence and development of obesity. Emerging data from in vitro and in vivo studies suggest that circRNAs are novel players in adipogenesis, white adipose browning, obesity, obesity-induced inflammation, and insulin resistance. This study explores the current state of knowledge on circRNAs regulating molecular processes associated with adipogenesis and obesity, highlights some of the challenges encountered while studying circRNAs and suggests some perspectives for future research directions in this exciting field of study.

A Guide to the Short, Long and Circular RNAs in Hypertension and Cardiovascular Disease

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in adults in developed countries. CVD encompasses many diseased states, including hypertension, coronary artery disease and atherosclerosis. Studies in animal models and human studies have elucidated the contribution of many genetic factors, including non-coding RNAs. Non-coding RNAs are RNAs not translated into protein, involved in gene expression regulation post-transcriptionally and implicated in CVD. Of these, circular RNAs (circRNAs) and microRNAs are relevant. CircRNAs are created by the back-splicing of pre-messenger RNA and have been underexplored as contributors to CVD. These circRNAs may also act as biomarkers of human disease, as they can be extracted from whole blood, plasma, saliva and seminal fluid. CircRNAs have recently been implicated in various disease processes, including hypertension and other cardiovascular disease. This review article will explore the promising and emerging roles of circRNAs as potential biomarkers and therapeutic targets in CVD, in particular hypertension.

circRNAs Signature as Potential Diagnostic and Prognostic Biomarker for Diabetes Mellitus and Related Cardiovascular Complications

Circular RNAs (circRNAs) belong to the ever-growing class of naturally occurring noncoding RNAs (ncRNAs) molecules. Unlike linear RNA, circRNAs are covalently closed transcripts mostly generated from precursor-mRNA by a non-canonical event called back-splicing. They are highly stable, evolutionarily conserved, and widely distributed in eukaryotes. Some circRNAs are believed to fulfill a variety of functions inside the cell mainly by acting as microRNAs (miRNAs) or RNA-binding proteins (RBPs) sponges. Furthermore, mounting evidence suggests that the misregulation of circRNAs is among the first alterations in various metabolic disorders including obesity, hypertension, and cardiovascular diseases. More recent research has revealed that circRNAs also play a substantial role in the pathogenesis of diabetes mellitus (DM) and related vascular complications. These findings have added a new layer of complexity to our understanding of DM and underscored the need to reexamine the molecular pathways that lead to this disorder in the context of epigenetics and circRNA regulatory mechanisms. Here, I review current knowledge about circRNAs dysregulation in diabetes and describe their potential role as innovative biomarkers to predict diabetes-related cardiovascular (CV) events. Finally, I discuss some of the actual limitations to the promise of these RNA transcripts as emerging therapeutics and provide recommendations for future research on circRNA-based medicine.

Circular RNA circMAN2B2 promotes growth and migration of gastric cancer cells by down-regulation of miR-145

Background

CircMAN2B2 is a newly discovered circRNA that has been found to be an oncogene in lung cancer and glioma. The present study was designed to reveal the role of circMAN2B2 in gastric carcinoma (GC).

Methods

qRT‐PCR method was utilized to examine circMAN2B2 expression in GC tissues and paracancerous tissues. Next, circMAN2B2 expression in SNU‐16 and AGS cells was silenced by transfection. CCK‐8 assay, colony formation assay, flow cytometer, Transwell assay, and Western blot were conducted for testing cell phenotype changes. Further, the downstream genes and signaling were uncovered by qRT‐PCR and Western blot.

Results

As relative to paracancerous tissues, circMAN2B2 was high‐expressed in GC tissues. Silence of circMAN2B2 clearly declined SNU‐16 and AGS cells viability, survival, migration but enhanced apoptosis. Meanwhile, silence of circMAN2B2 induced the cleavage of caspases (−3 and −9), down‐regulation of MMPs (−2 and −9), and up‐regulation of miR‐145. The impacts of circMAN2B2 silence toward SNU‐16 and AGS cells were attenuated by miR‐145 silence. Moreover, circMAN2B2 silence deactivated PI3K, AKT while activated JNK through regulating miR‐145.

Conclusion

This work presented the oncogenic function of circMAN2B2 in GC cells growth and migration. CircMAN2B2 exerted its function possibly through regulating miR‐145 as well as PI3K/AKT and JNK pathways.

Long noncoding RNAs as novel players in the pathogenesis of hypertension

Long noncoding RNAs (lncRNAs) are non-(protein)-coding RNAs longer than ~200 nucleotides and have been reported to be involved in multiple human diseases by regulating gene expression. A growing body of evidence has demonstrated that lncRNAs are also widely implicated in mechanisms of hypertension, including regulation of the proliferation, migration, and apoptosis of VSMCs; the production of iNOS and NO; and the angiogenic function of endothelial cells. Several lncRNAs were also differentially expressed in the renal and cardiac tissues of hypertensive rats and even in placental samples from preeclampsia patients. In particular, several circulating lncRNAs have been identified as novel biomarkers of hypertension. In this review, we summarize the current studies of lncRNAs in the pathogenesis of hypertension in order to aid in better understanding the molecular mechanism of hypertension and provide a basis to explore new therapeutic targets.

Microarray expression profiles and bioinformatics analysis of mRNAs, lncRNAs, and circRNAs in the secondary temozolomide-resistant glioblastoma

Temozolomide is a first line anti-tumor drug used for the treatment of patients with Glioblastoma multiforme (GBM). However, the drug resistance to temozolomide limits its clinical application. Therefore, novel strategies to overcome chemoresistance are desperately needed for improved treatment of human GBM. Here, we simultaneously detected, for the first time, the expression profiles of mRNAs, lncRNAs, and circRNAs in three pairs of secondary temozolomide-resistant glioblastoma (STRG) and matched primary glioblastoma tissues by microarrays. Using these data, we discovered a total of 92 mRNA, 299 lncRNAs and 53 circRNAs were altered in human glioma tissue after chemotherapy with temozolomide. The functions of differentially expressed lncRNAs, circRNAs were annotated by analysis of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). The results showed that the highest enriched GO terms of the upregulated lncRNAs were embryonic forelimb morphogenesis (BP), extracellular space (CC), and serine-type endopeptidase activity (MF). Meanwhile, GO:0035360(BP), PRC1 complex (CC), and ubiquitin-protein transferase activity (MF) were the highest enriched GO terms targeted by downregulated lncRNAs. The NF-kappa B signaling pathway were significantly enriched in the STRG. However, circRNAs highest enriched GO term was viral process, chromosome, and protein transporter activity, respectively. KEGG pathway analysis showed that circRNAs in the network were enriched in ErbB signaling pathway. Furthermore, we also predicted the potential role of these differentially expressed ncRNAs and constructed a network of lncRNAs-mRNAs and circRNAs-miRNAs to show their interactions. After a series of bioinformatics analyses, we found that low expression of NONHSAT163779 and high expression of circ_0043949 are closely related to the chemoresistance of STRG. Our findings revealed the alteration of expression patterns of mRNAs, lncRNAs, and circRNAs in the secondary temozolomide-resistant glioblastoma for the first time. NONHSAT163779 and hsa_circ_0043949 might be potential therapeutic targets and prognostic biomarkers for the treatment of glioblastoma.

Elevated serum circ_0068481 levels as a potential diagnostic and prognostic indicator in idiopathic pulmonary arterial hypertension

Circular RNAs have continuous, stable, and covalently closed circular structures and are not easily degraded by nucleases, thus they are ideal serum biomarkers for detecting diseases. However, research is still lacking on circular RNAs as diagnostic and prognostic markers for idiopathic pulmonary arterial hypertension. This study investigated the potential role of serum circ_0068481 levels in idiopathic pulmonary arterial hypertension diagnosis and prognosis. This prospective cohort study enrolled 82 patients with idiopathic pulmonary arterial hypertension between January 2016 and July 2018 at Guangdong Provincial People's Hospital. Serum circ_0068481 levels were measured using quantitative reverse transcription-polymerase chain reaction. Baseline data, including clinical background, hemodynamic variables, and biochemical variables, were collected. Receiver operating characteristic curves were used to investigate diagnostic effect, the Kaplan-Meier method was used to estimate survival rates, and univariate analysis of prognostic factors was performed with a Cox proportional hazard model. We found that serum circ_0068481 expression levels were significantly higher in patients with idiopathic pulmonary arterial hypertension and had higher sensitivity and specificity for predicting idiopathic pulmonary arterial hypertension. Additionally, we found that circ_0068481 expression correlated significantly with heart function, 6-min walk distance, serum N-terminal pro-B-type natriuretic peptide, serum H2S, the 6th World Symposium on Pulmonary Hypertension risk stratification, right heart failure, and patient death. Moreover, serum circ_0068481 levels were elevated in patients with idiopathic pulmonary arterial hypertension and right heart failure and were able to predict right heart failure. Serum circ_0068481 levels were also elevated in patients who died with idiopathic pulmonary arterial hypertension and were able to predict poorer clinical outcomes. Circ_0068481 is a novel and noninvasive biomarker for diagnosing idiopathic pulmonary arterial hypertension and predicting poor clinical outcome in patients with idiopathic pulmonary arterial hypertension.