The circulating non-coding RNA landscape for biomarker research: lessons and prospects from cardiovascular diseases

Expression Profiles of Circular RNA in Human Atrial Fibrillation With Valvular Heart Diseases

Circular RNAs (circRNA) are involved in a variety of human heart diseases, however, circRNA expression profiles and circRNA-miRNA-mRNA regulatory network in human atrial fibrillation (AF) especially with valvular heart diseases (VHD) remain poorly understood. A high-throughput RNA sequencing was used to investigate the differentially expressed circRNAs in left atrial appendage from VHD patients with or without persistent AF. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were performed to predict the potential functions of the host genes of differentially expressed circRNA and their downstream targets. CircRNA-miRNA-mRNA regulatory network was constructed to identify mechanisms underlying circRNAs. qRT-PCR and sanger sequencing were further performed to validate the results. Compared with sinus rhythm (SR) patients, there were 3094 upregulated and 4472 downregulated circRNAs in AF patients respectively. The expression of 10 most differentially expressed circRNAs (circ 255-ITGA7, circ 418-KCNN2, circ 13913-MIB1, circ 44670-BARD1, circ 44782-LAMA2, circ 81906-RYR2, circ 35880-ANO5, circ 22249-TNNI3K, circ 3136-TNNI3K, circ 56186-TNNI3K) between SR and persistent AF patients were verified by qRT-PCR. In addition, specific back-splicing sites of these circRNAs was confirmed by sanger sequencing. GO and KEGG pathway analysis indicated that cAMP signal pathway and Wnt signal pathway might play important role in the development of AF in VHD patients, which might be affected by circRNAs. This study provided a preliminary landscape of circRNAs expression profiles which are involved in persistent AF due to VHD, and established the possibility for future related researches in this field.

Emerging Role of Adipocyte Dysfunction in Inducing Heart Failure Among Obese Patients With Prediabetes and Known Diabetes Mellitus

Adipose tissue dysfunction is a predictor for cardiovascular (CV) events and heart failure (HF) in patient population with obesity, metabolic syndrome, and known type 2 diabetes mellitus. Previous preclinical and clinical studies have yielded controversial findings regarding the role of accumulation of adipose tissue various types in CV risk and HF-related clinical outcomes in obese patients. There is evidence for direct impact of infiltration of epicardial adipocytes into the underlying myocardium to induce adverse cardiac remodeling and mediate HF development and atrial fibrillation. Additionally, perivascular adipocytes accumulation is responsible for release of proinflammatory adipocytokines (adiponectin, leptin, resistin), stimulation of oxidative stress, macrophage phenotype switching, and worsening vascular reparation, which all lead to microvascular inflammation, endothelial dysfunction, atherosclerosis acceleration, and finally to increase in CV mortality. However, systemic effects of white and brown adipose tissue can be different, and adipogenesis including browning of adipose tissue and deficiency of anti-inflammatory adipocytokines (visfatin, omentin, zinc-α2-glycoprotein, glypican-4) was frequently associated with adipose triglyceride lipase augmentation, altered glucose homeostasis, resistance to insulin of skeletal muscles, increased cardiomyocyte apoptosis, lowered survival, and weak function of progenitor endothelial cells, which could significantly influence on HF development, as well as end-organ fibrosis and multiple comorbidities. The exact underlying mechanisms for these effects are not fully understood, while they are essential to help develop improved treatment strategies. The aim of the review is to summarize the evidence showing that adipocyte dysfunction may induce the onset of HF and support advance of HF through different biological mechanisms involving inflammation, pericardial, and perivascular adipose tissue accumulation, adverse and electrical cardiac remodeling, and skeletal muscle dysfunction. The unbalancing effects of natriuretic peptides, neprilysin, and components of renin–angiotensin system, as exacerbating cause of altered adipocytokine signaling on myocardium and vasculature, in obesity patients at high risk of HF are disputed. The profile of proinflammatory and anti-inflammatory adipocytokines as promising biomarker for HF risk stratification is discussed in the review.

Identification of aberrantly expressed circular RNAs in hyperlipidemia-induced retinal vascular dysfunction in mice

Hyperlipidemia-induced retinal vascular dysfunction is a complex pathological process. circRNAs are important regulators of biological processes and disease progression. However, the expression pattern of circRNAs in hyperlipidemia-induced retinal vascular dysfunction remains unclear. Herein, we used a murine model of hyperlipidemia and identified 317 differentially expressed circRNAs between hyperlipidemic retinas and normolipidemic retinas by circRNA microarrays. GO analysis indicated that the host genes of dysregulated circRNAs were targeted to cell differentiation (ontology: biological process), cytoplasm (ontology: cellular component), and protein binding (ontology: molecular function). Pathway analysis revealed that circRNAs-mediated network was mostly enriched in focal adhesion signaling. Notably, circLDB1 was significantly up-regulated in the serum of coronary artery disease patients and aqueous humor of age-related macular degeneration patients. circLDB1 regulated endothelial cell viability, proliferation, and apoptosis in vitro. Thus, circRNAs are the promising targets for the prediction and diagnosis of hyperlipidemia-induced vascular diseases.

Blood levels of microRNAs associated with ischemic heart disease differ between Austrians and Japanese: a pilot study

Mortality from ischemic heart disease (IHD) is significantly lower in Japan than in Western countries. The purpose of this study was to investigate differences in circulating microRNA (miRNA) levels related to IHD in Austrians and Japanese. Participants were middle-aged healthy male Austrians (n = 20) and Japanese (n = 20). Total miRNAs in serum from each participant were analyzed using the 3D-Gene miRNA Oligo chip. Twenty-one miRNAs, previously reported as associated with IHD, were compared between Austrians and Japanese. The expression levels of miR-106a-5p, miR-135a-3p, miR-150-3p, miR-16-5p, miR-17-5p. miR-191-5p, miR-320b, miR-451a, miR-486-5p, miR-663b, and miR-92a-3p were significantly higher, while the miR-2861 expression level was significantly lower in Austrians as compared to Japanese. Both in Austrians and Japanese, there were significant positive correlations between serum expression levels of each pair of the above miRNAs except for miR-2861. The expression level of miR-2861 showed significant positive correlations with the expression levels of miR-106a-5p, miR-150-3p, miR-17-5p, miR-486-5p, miR-663b and miR-92a-3p in Austrians but not in Japanese. In pathway analysis, proinflammatory cytokine production in foam cells and collagen synthesis in vascular smooth muscle cells were associated with differentially expressed miRNAs. Difference in miRNA levels may contribute to lower cardiovascular risk in Japan than in Western countries.

Genome-wide analysis of circular RNA expression profiles in patients with atrial fibrillation

Atrial fibrillation (AF) is one of the most common clinical cardiac arrhythmias. This study was done to screen differentially expressed circular RNAs (circRNAs) in human monocytes from patients with AF and healthy controls using microarray, and preliminarily explore the role of circRNAs in the development of AF. The expression of circRNAs in peripheral blood monocytes of 4 AF patients and 4 healthy donors was detected by chip technology and validated by qRT-PCR. Differentially expressed genes were screened out. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to identify the function of differentially expressed genes and related pathways. Potential connections between circRNAs and miRNAs were explored by using Cytoscape. 120 differentially expressed circRNAs (FC≥2, P<0.05) were preliminarily screened by circRNA microarray, of which 65 were up-regulated and 55 down-regulated. All of 4 upregulated circRNAs (circRNA_0031, circRNA_1837, circRNA_5901 and circRNA_7571) and 3 out of 4 downregulated circRNAs (circRNA_5801, circRNA_7386 and circRNA_7577) were randomly confirmed by RT-PCR. GO and KEGG analysis suggested that differentially expressed circRNA-related genes are mainly involved in inflammation, immunity, and signaling transduction. CircRNA_7571, circRNA_4648, circRNA_4631 and circRNA_2875 were the first 4 circRNAs with the most binding nodes in the co-expression network. In addition, hsa-miR-328 was the highest positively correlated miRNA in the networks. Our findings demonstrated that there were differentially expressed circRNAs in human monocytes from AF patients. circRNA_7571, circRNA_4648, circRNA_4631 and circRNA_2875 were the first 4 circRNAs with the most binding nodes in the co-expression network. hsa-miR-328 was the largest node that interacted with circRNAs in the co-expression network. circRNAs-hsa-miR-328 network may play a critical role in the pathophysiology and mechanism of AF.

Noncoding RNAs in Cardiovascular Disease: Current Knowledge, Tools and Technologies for Investigation, and Future Directions: A Scientific Statement From the American Heart Association

BACKGROUND

The discovery that much of the non-protein-coding genome is transcribed and plays a diverse functional role in fundamental cellular processes has led to an explosion in the development of tools and technologies to investigate the role of these noncoding RNAs in cardiovascular health. Furthermore, identifying noncoding RNAs for targeted therapeutics to treat cardiovascular disease is an emerging area of research. The purpose of this statement is to review existing literature, offer guidance on tools and technologies currently available to study noncoding RNAs, and identify areas of unmet need.

METHODS

The writing group used systematic literature reviews (including MEDLINE, Web of Science through 2018), expert opinion/statements, analyses of databases and computational tools/algorithms, and review of current clinical trials to provide a broad consensus on the current state of the art in noncoding RNA in cardiovascular disease.

RESULTS

Significant progress has been made since the initial studies focusing on the role of miRNAs (microRNAs) in cardiovascular development and disease. Notably, recent progress on understanding the role of novel types of noncoding small RNAs such as snoRNAs (small nucleolar RNAs), tRNA (transfer RNA) fragments, and Y-RNAs in cellular processes has revealed a noncanonical function for many of these molecules. Similarly, the identification of long noncoding RNAs that appear to play an important role in cardiovascular disease processes, coupled with the development of tools to characterize their interacting partners, has led to significant mechanistic insight. Finally, recent work has characterized the unique role of extracellular RNAs in mediating intercellular communication and their potential role as biomarkers.

CONCLUSIONS

The rapid expansion of tools and pipelines for isolating, measuring, and annotating these entities suggests that caution in interpreting results is warranted until these methodologies are rigorously validated. Most investigators have focused on investigating the functional role of single RNA entities, but studies suggest complex interaction between different RNA molecules. The use of network approaches and advanced computational tools to understand the interaction of different noncoding RNA species to mediate a particular phenotype may be required to fully comprehend the function of noncoding RNAs in mediating disease phenotypes.

Reduced serum and local LncRNA MALAT1 expressions are linked with disease severity in patients with non-traumatic osteonecrosis of the femoral head

OBJECTIVE

This study was performed to illustrate the potential relationship between reduced serum and local LncRNA MALAT1 expressions with disease severity in patients with non-traumatic osteonecrosis of the femoral head (ONFH).

METHODS

A total of 104 patients with non-traumatic ONFH and 100 healthy controls were consecutively recruited from our hospital. Serum and local LncRNA MALAT1 expressions were detected using real-time polymerase chain reaction (RT-PCR). Radiographic progression was defined by Ficat classification. Clinical severity was evaluated by Visual Analog Scale (VAS) and Harris Hip Score (HHS). Receiver operating characteristic (ROC) curve was carried out to determine the diagnostic value of MALAT1 in the radiographic progression.

RESULTS

Serum LncRNA MALAT1 expressions were significantly lower in non-traumatic ONFH patients than in healthy controls. In addition, local MALAT1 expressions in non-traumatic ONFH tissue were significantly lower in the affected area than in the non-affected area. Ficat grade 4 has significantly lower serum and local LncRNA MALAT1 expressions in comparison with grade 3, and Ficat grade 3 showed markedly decreased serum and local LncRNA MALAT1 expressions compared with grade 2. Serum and local LncRNA MALAT1 expressions were significantly and negatively associated with VAS and positively related to the HHS. Further ROC curve analysis indicated that serum MALAT1 may act as a decent indicator in the diagnosis of non-traumatic ONFH.

CONCLUSIONS

Decreased serum and local MALAT1 expressions may reflect disease severity in non-traumatic ONFH patients.

Circulating miRNAs in Successful and Unsuccessful Aging. A Mini-review

Aging is a multifactorial process that affects the organisms at genetic, molecular and cellular levels. This process modifies several tissues with a negative impact on cells physiology, tissues and organs functionality, altering their regeneration capacity. The chronic low-grade inflammation typical of aging, defined as inflammaging, is a common biological factor responsible for the decline and beginning of the disease in age. A murine parabiosis model that combines the vascular system of old and young animals, suggests that soluble factors released by young individuals may improve the regenerative potential of old tissue. Therefore, circulating factors have a key role in the induction of aging phenotype. Moreover, lifestyle can influence the physiological status of multiple organs, via epigenetic mechanisms. Recently, microRNAs are considered potential sensors of aging.

Epigallocatechin gallate reverses gastric cancer by regulating the long noncoding RNA LINC00511/miR-29b/KDM2A axis

Epigallocatechin gallate (EGCG), as one of the main ingredients of green tea, has been reported to have potential prevention on a variety of solid tumors. However, the system-wide molecular mechanisms targeted to EGCG's anti-tumor effect have not been illustrated. Here, AGS and SGC7901 GC cells were used to investigate the EGCG-mediated change of gene expression. Our data showed that EGCG retarded cell growth and promoted cell death of GC in dose-dependent manner. Analyses based on transcription, translation as well as function were performed to explore the elusive anticancer role of EGCG. Of them, cell cycle was probably implicated key pathway of EGCG. Besides, our data revealed numerous LncRNAs activated after EGCG treatment. In this study, LINC00511 was discovered to be suppressed by EGCG and highly expressed in GC cells and tissues. Knockdown of LINC00511 inhibited cell growth and promoted cell death ratio in GC. Additionally, our data suggested LINC00511 could decrease the expression of miR-29b, followed by inducing GC development. Knockdown of miR-29b recovered the effects of LINC00511 silencing. In addition, we found overexpression of KDM2A, a target of miR-29b, would rescue the level of LINC00511. All the data showed that the LINC00511/miR-29b/KDM2A axis can be used as a diagnostic and therapeutic target for GC.

MicroRNAs (miRNAs) and Long Non-Coding RNAs (lncRNAs) as New Tools for Cancer Therapy: First Steps from Bench to Bedside

Non-coding RNAs represent a significant proportion of the human genome. After having been considered as 'junk' for a long time, non-coding RNAs are now well established as playing important roles in maintaining cellular homeostasis and functions. Some non-coding RNAs show cell- and tissue-specific expression patterns and are specifically deregulated under pathological conditions (e.g. cancer). Therefore, non-coding RNAs have been extensively studied as potential biomarkers in the context of different diseases with a focus on microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) for several years. Since their discovery, miRNAs have attracted more attention than lncRNAs in research studies; however, both families of non-coding RNAs have been established to play an important role in gene expression control, either as transcriptional or post-transcriptional regulators. Both miRNAs and lncRNAs can regulate key genes involved in the development of cancer, thus influencing tumour growth, invasion, and metastasis by increasing the activation of oncogenic pathways and limiting the expression of tumour suppressors. Furthermore, miRNAs and lncRNAs are also emerging as important mediators in drug-sensitivity and drug-resistance mechanisms. In the light of these premises, a number of pre-clinical and early clinical studies are exploring the potential of non-coding RNAs as new therapeutics. The aim of this review is to summarise the latest knowledge of the use of miRNAs and lncRNAs as therapeutic tools for cancer treatment.

Construction of a ceRNA coregulatory network and screening of hub biomarkers for salt-sensitive hypertension

Salt-sensitive hypertension (SSH) is an independent risk factor for cardiovascular disease. The regulation of long non-coding RNAs, mRNAs and competing endogenous RNAs (ceRNAs) in the pathogenesis of SSH is uncertain. An RNA microarray was performed to discover SSH-associated differentially expressed lncRNAs (DElncRNAs) and mRNAs (DEmRNAs), and 296 DElncRNAs and 44 DEmRNAs were identified, and 247 DElncRNAs and 44 DEmRNAs among these RNAs were included in the coexpression network. The coregulatory network included 23 ceRNA loops, and six hub RNAs (lnc-ILK-8:1, lnc-OTX1-7:1, lnc-RCAN1-6:1, GIMAP8, SUV420H1 and PIGV) were identified for further population validation. The ceRNA correlations among lnc-OTX1-7:1, hsa-miR-361-5p and GIMAP8 were confirmed in SSH and SRH patients. A larger-sample validation confirmed that GIMAP8, SUV420H1 and PIGV were differentially expressed between the SSH and SRH groups. In addition, SUV420H1 was included in the SSH screening model, and the area under the curve of the model was 0.720 (95% CI: 0.624-0.816). Our study explored the transcriptome profiles of SSH and constructed a ceRNA network to help elucidate the mechanism of SSH. In addition, SUV420H1 was identified as a hub element that participates in SSH transcriptional regulation and as a potential biomarker for the early diagnosis of SSH.

Cotransplantation of human umbilical cord mesenchymal stem cells and endothelial cells for angiogenesis and pulp regeneration in vivo

AIMS

To explored the potential of human umbilical cord mesenchymal stem cells (hUCMSCs) as seed cells for dental pulp regeneration and the possibility of cotransplantation hUCMSCs and endothelial cells (ECs) for angiogenesis and pulp regeneration in vivo.

MATERIALS AND METHODS

hUCMSCs and human umbilical vein endothelial cells (HUVECs) were cocultured for matrigel angiogenesis assay in vitro and Matrigel plug assay in vivo. Next, we used the transwell coculture system to coculture hUCMSCs and HUVECs in vitro for RNA- sequencing (RNA-seq). Last, encapsulated hUCMSCs and HUVECs in scaffolds were injected into the root segments, and transplanted into immunodeficient mice for dental pulp regeneration.

KEY FINDINGS

In vitro Matrigel angiogenesis assay and in vivo Matrigel plug assay indicated that cocultured hUCMSCs and HUVECs promote vascular formation of HUVECs, especially in 1:5 (hUCMSCs:HUVECs) coculture group. The RNA-seq result indicated that cocultured HUVECs exhibited high Hif-1 signaling pathway activity. We performed the cell transfection assay to knock down HIF1A-AS2 in HUVECs and then coculture with hUCMSCs, and the expression of VEGFA, HIF1A and PECAM1 were reduced. In pulp regeneration assay, Cotransplantation of hUCMSCs and HUVECs (1,5) group showed pulp-like tissue regeneration.

SIGNIFICANCE

Cocultured hUCMSCs and HUVECs can promote vascular formation of HUVECs, and the optimal coculture ration is 1:5 (hUCMSCs:HUVECs). hUCMSCs promote angiogenesis of HUVECs through the long noncoding RNA HIF1A-AS2-activation of the Hif-1 signaling pathway. Cotransplantation of hUCMSCs and HUVECs can regenerate dental pulp-like tissue in vivo.

Molecular Mechanisms, Diagnostic Aspects and Therapeutic Opportunities of Micro Ribonucleic Acids in Atrial Fibrillation

Micro ribonucleic acids (miRNAs) are short non-coding RNA molecules responsible for regulation of gene expression. They are involved in many pathophysiological processes of a wide spectrum of diseases. Recent studies showed their involvement in atrial fibrillation. They seem to become potential screening biomarkers for atrial fibrillation and even treatment targets for this arrhythmia. The aim of this review article was to summarize the latest knowledge about miRNA and their molecular relation to the pathophysiology, diagnosis and treatment of atrial fibrillation.

Dysregulated CD4+ T Cells and microRNAs in Myocarditis

Myocarditis is a polymorphic disease complicated with indeterminate etiology and pathogenesis, and represents one of the most challenging clinical problems lacking specific diagnosis and effective therapy. It is caused by a complex interplay of environmental and genetic factors, and causal links between dysregulated microribonucleic acids (miRNAs) and myocarditis have also been supported by recent epigenetic researches. Both dysregulated CD4+ T cells and miRNAs play critical roles in the pathogenesis of myocarditis, and the classic triphasic model of its pathogenesis consists of the acute infectious, subacute immune, and recovery/chronic myopathic phase. CD4+ T cells are key pathogenic factors underlying the development and progression of myocarditis, and the effector and regulatory subsets, respectively, promote and inhibit autoimmune responses. Furthermore, the reciprocal interplay of these subsets influences the pathogenesis as well. Dysregulated miRNAs along with their mRNA and protein targets have been identified in heart biopsies (intracellular miRNAs) and body fluids (circulating miRNAs) during myocarditis. These miRNAs show phase-dependent changes, and correlate with viral infection, immune status, fibrosis, destruction of cardiomyocytes, arrhythmias, cardiac functions, and outcomes. Thus, miRNAs are promising diagnostic markers and therapeutic targets in myocarditis. In this review, we review myocarditis with an emphasis on its pathogenesis, and present a summary of current knowledge of dysregulated CD4+ T cells and miRNAs in myocarditis.

Noncoding RNAs versus Protein Biomarkers in Cardiovascular Disease

The development of more sensitive protein biomarker assays results in continuous improvements in detectability, extending the range of clinical applications to the detection of subclinical cardiovascular disease (CVD). However, these efforts have not yet led to improvements in risk assessment compared with existing risk scores. Noncoding RNAs (ncRNAs) have been assessed as biomarkers, and miRNAs have attracted most attention. More recently, other ncRNA classes have been identified, including long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs). Here, we compare emerging ncRNA biomarkers in the cardiovascular field with protein biomarkers for their potential in clinical application, focusing on myocardial injury.

Circular RNA-Centered Regulatory Networks in the Physiopathology of Cardiovascular Diseases

Non-coding regulatory RNAs are generated as a core output of the eukaryotic genomes, being essential players in cell biology. At the organism level, they are key functional actors in those tissues and organs with limited proliferation capabilities such as the heart. The role of regulatory networks mediated by non-coding RNAs in the pathophysiology of cardiovascular conditions is starting to be unveiled. However, a deeper knowledge of the functional interactions among the diverse non-coding RNA families and their phenotypic consequences is required. This review presents the current knowledge about the functional crosstalk between circRNAs and other biomolecules in the framework of the cardiovascular diseases.

Bioinformatics Research Methodology of Non-coding RNAs in Cardiovascular Diseases

The transcriptional complexity generated by the human genomic output is within the core of cell and organ physiology, but also could be in the origin of pathologies. In cardiovascular diseases, the role of specific families of RNA transcripts belonging to the group of the non-coding RNAs started to be unveiled in the last two decades. The knowledge of the functional rules and roles of non-coding RNAs in the context of cardiovascular diseases is an important factor to derive new diagnostic methods, but also to design targeted therapeutic strategies. The characterization and analysis of ncRNA function requires a deep knowledge of the regulatory mechanism of these RNA species that often relies on intricated interaction networks. The use of specific bioinformatic tools to interrogate biological data and to derive functional implications is particularly relevant and needs to be extended to the general practice of translational researchers. This chapter briefly summarizes the bioinformatic tools and strategies that could be used for the characterization and functional analysis of non-coding RNAs, with special emphasis in their applications to the cardiovascular field.

Circular RNA_101237 mediates anoxia/reoxygenation injury by targeting let‑7a‑5p/IGF2BP3 in cardiomyocytes

Circular RNAs (circRNAs) serve important roles in cardiovascular diseases, including myocardial infarction. However, the mechanisms underlying the roles of circRNAs in cardiomyocyte death induced by anoxia/reoxygenation (A/R) are not fully understood. In the present study, the roles of circRNA_101237 and let‑7a‑5p in cardiomyocyte death induced by A/R injury were investigated. It was identified that circRNA_101237 was induced by A/R injury in a time‑dependent manner and that circRNA_101237 knockdown protected cardiomyocytes from A/R‑mediated apoptosis. Additional mechanistic studies revealed that circRNA_101237 served as a sponge for let‑7a‑5p, subsequently regulating insulin‑like growth factor 2 mRNA‑binding protein 3 (IGF2BP3)‑dependent autophagy. IGF2BP3 downregulation decreased the levels of apoptosis and inhibited autophagy induced by A/R challenge in primary cardiomyocytes. These results identified circRNA_101237 as a novel circRNA that regulates cardiomyocyte death and autophagy, and demonstrated that the circRNA‑101237/let‑7a‑5p/IGF2BP3 axis, which serves as a regulator of cardiomyocyte death, may be a potential therapeutic target for the management of cardiovascular diseases.

Genome-wide profiling reveals atrial fibrillation-related circular RNAs in atrial appendages

Atrial fibrillation (AF) is an abnormal heart rhythm characterized by rapid and irregular beating of the atria. The non-coding RNAs (ncRNAs) have attracted much attention of AF researchers, as they play a critical role in the transcriptional and post-transcriptional regulation, which could greatly benefit the interpretation of the pathogenesis of AF. However, circRNAs, as a special member of the ncRNAs, and their role in the pathogenesis of AF is less understood. In the present study, we detected a total of 14,215 circRNAs in AF patients and healthy controls. Differential expression analysis of these circRNAs revealed 20 upregulated and 3 downregulated circRNAs, which were differentially expressed in both left and right atrial appendages. The association analysis of the AF-related circRNAs and their parental genes revealed that hsa_circ_0003965 had significantly negative correlation with its parental gene TMEM245 (PCC = -0.51), suggesting that the dysregulation of hsa_circ_0003965 was not regulated by the transcription of its parental gene, but could be associated with glucagon signaling pathway. The competing endogenous RNA (ceRNA) network analysis revealed two upregulated genes, IFNG and GDF7, and one downregulated gene, BMP7, all of which were involved in TGF-beta signaling pathway, which further suggested that these circRNAs, namely hsa_circ_0000075 and hsa_circ_0082096, participated in the AF pathogenesis via TGF-beta signaling pathway. Consistently, TGF-beta signaling pathway was a well-recognized player for its association with atrial fibrosis in AF. In summary, we aimed to discover and provide key circRNAs involved in AF for AF-related researchers, which had the potential to greatly improve our understanding of the underlying mechanism behind circRNAs and AF.

Biomarkers in primary prevention : Meaningful diagnosis based on biomarker scores?

Cardiovascular (CV) risk assessment is based on the utilization of risk scores, enabling clinicians to estimate an individual's risk to develop CV pathologies and events. Such risk scores comprise classic CV risk factors such as smoking, diabetes, hypertension, and blood cholesterol levels. Recently, other CV biomarkers such as cardiac troponins have been suggested and evaluated as alternative biomarkers not only in the acute diagnostic setting of myocardial infarction, but also as markers for risk stratification in the general population. In this review, we summarize the current knowledge on biomarkers in the field of primary prevention in cardiovascular disease (CVD). Furthermore, we present potential alternative biomarker-based strategies for CV risk assessment. In this respect we provide an outlook on the potential use of genomic variation as well as circulating non-coding RNAs to complement current risk assessment strategies so as to further personalize risk stratification in CVD.

The roles of circRFWD2 and circINO80 during NELL-1-induced osteogenesis

Bone defects caused heavy social and economic burdens worldwide. Nel‐like molecule, type 1 (NELL‐1) could enhance the osteogenesis and the repairment of bone defects, while the specific mechanism remains to be elucidated. Circular RNAs (circRNAs) have been found to play critical roles in the tissue development and serve as biomarkers for various diseases. However, it remains unclear that the expression patterns of circRNAs and the roles of them played in recombinant NELL‐1‐induced osteogenesis of human adipose‐derived stem cells (hASCs). In this study, we performed RNA‐sequencing to investigate the expression profiles of circRNAs in recombinant NELL‐1‐induced osteogenic differentiation and identified two key circRNAs, namely circRFWD2 and circINO80. These two circRNAs were confirmed to be up‐regulated during recombinant NELL‐1‐induced osteogenesis, and knockdown of them affected the positive effect of NELL‐1 on osteogenesis. CircRFWD2 and circINO80 could interact with hsa‐miR‐6817‐5p, which could inhibit the osteogenesis. Silencing hsa‐miR‐6817‐5p could partially reverse the negative effect of si‐circRFWD2 and si‐circINO80 on the osteogenesis. Therefore, circRFWD2 and circINO80 could regulate the expression of hsa‐miR‐6817‐5p and influence the recombinant NELL‐1‐induced osteogenic differentiation of hASCs. It opens a new window to better understanding the effects of NELL‐1 on the osteogenic differentiation of hASCs and provides potential molecular targets and novel methods for bone regeneration efficiently and safely.

The Integrative Regulatory Network of circRNA, microRNA, and mRNA in Atrial Fibrillation

Atrial fibrillation (AF) is the most common irregular heart rhythm which influence approximately 1–2% of the general population. As a potential factor for ischemic stroke, AF could also cause heart failure. The mechanisms behind AF pathogenesis is complex and remains elusive. As a new category of non-coding RNAs (ncRNAs), circular RNAs (circRNAs) have been known as the key of developmental processes, regulation of cell function, pathogenesis of heart diseases and pathological responses which could provide novel sight into the pathogenesis of AF. circRNAs function as modulators of microRNAs in cardiac disease. To investigate the regulatory mechanism of circRNA in AF, especially the complex interactions among circRNA, microRNA and mRNA, we collected the heart tissues from three AF patients and three healthy controls and profiled their circRNA expressions with circRNA Microarray. The differentially expressed circRNAs were identified and the biological functions of their interaction microRNAs and mRNAs were analyzed. Our results provided novel insights of the circRNA roles in AF and proposed highly possible interaction mechanisms among circRNAs, microRNAs, and mRNAs.

Biogenesis and Function of Circular RNAs in Health and in Disease

Circular RNAs (circRNAs) are a class of non-coding RNA that were previously thought to be insignificant byproducts of splicing errors. However, recent advances in RNA sequencing confirmed the presence of circRNAs in multiple cell lines and across different species suggesting a functional role of this RNA species. CircRNAs arise from back-splicing events resulting in a circular RNA that is stable, specific and conserved. They can be generated from exons, exon-introns, or introns. CircRNAs have multifaceted functions. They are likely part of the competing endogenous RNA class. They can regulate gene expression by sponging microRNAs, binding proteins or they can be translated into a protein themselves. CircRNAs have been associated with health and disease, some with disease protective effects, some with disease promoting functions. The widespread expression and disease regulatory mechanisms endow circRNAs to be used as functional biomarkers and therapeutic targets for a variety of different disorders. In this concise article we provide an overview of the association of circRNAs with various diseases including cancer, cardiovascular and kidney disease as well as cellular senescence. We conclude with an assessment of the current status and future outlook of this new field of research that carries immense potential with respect to diagnostic and therapeutic approaches of a variety of diseases.

lncRNA HIF1A Antisense RNA 2 Modulates Trophoblast Cell Invasion and Proliferation through Upregulating PHLDA1 Expression

Long noncoding RNAs (lncRNAs) have been reported to be involved in various human diseases, and increasing studies have revealed that lncRNAs can play a vital role in preeclampsia (PE). In our study, lncRNA hypoxia-inducible factor 1 alpha (HIF1A) antisense RNA 2 (HIF1A-AS2) was found to be significantly downregulated in placenta tissues of PE patients by quantitative real-time PCR analysis. Moreover, Cell Counting Kit-8 (CCK-8) assays showed that downregulation of HIF1A-AS2 can impede cell proliferation of HTR-8/SVneo and JAR trophoblasts cells. Ectopic overexpression of HIF1A-AS2 can increase the function of trophoblasts cell migration and invasion in vitro. RNA-sequencing (RNA-seq), RNA immunoprecipitation (RIP), and chromatin immunoprecipitation (ChIP) experiments showed that HIF1A-AS2 can recruit lysine-specific demethylase 1 (LSD1) and epigenetically repress pleckstrin homology-like domain, family A, member 1 (PHLDA1) transcription in human trophoblasts cells. In summary, our findings suggest that downregulated HIF1A-AS2 may play a role in the pathogenesis and progression of PE, and has potential as a novel prognostic marker in PE.

Deregulation of Circular RNAs in Cancer From the Perspectives of Aberrant Biogenesis, Transport and Removal

CircRNAs (circular RNAs) are a class of RNAs generated from circularization with multiple novel functions. Recent studies have revealed the aberrant expression and aberrant functions of circRNAs in various tumors; thus, circRNAs have been recognized as promising cancer biomarkers. However, the underlying mechanisms behind their aberrant expression and functions remain unclear. In this review, we discuss at length the cancer-specific deregulation of circRNAs and the potential underlying aberrant events in circRNA biogenesis, localization and removal in cancer cells.

The long noncoding RNA XIST regulates cardiac hypertrophy by targeting miR-101

Cardiac hypertrophy and its resultant heart failure are among the most common causes of mortality, worldwide. Long noncoding RNAs (lncRNAs) are involved in diverse biological processes, and their vital role in the regulation of cardiac hypertrophy is increasingly being discovered. Nevertheless, the biological roles of lncRNA X-inactive specific transcript (XIST) in cardiac hypertrophy are scarcely reported, and the current study was designed to determine whether cardiac hypertrophy can be regulated by XIST and to elucidate the related mechanism. The animals were randomized to receive either an adeno-associated virus expressing XIST or control plasmid via a single bolus-tail vein injection. Two weeks later, hypertrophy was established by transverse aortic constriction (TAC) surgery. In vitro, H9c2 cells were used to explore the potential molecular mechanism of XIST in the regulation of phenylephrine (PE)-induced cardiomyocyte hypertrophy. A luciferase reporter assay and RNA immunoprecipitation were performed to explore the relationships among XIST, microRNA (miR)-101, and toll-like receptor 2 (TLR2). In this study, we demonstrated that the expression of XIST was significantly upregulated in hypertrophic mouse hearts and PE-treated cardiomyocytes. Then, we observed that knockdown of XIST attenuated PE-induced cardiomyocyte hypertrophy. Conversely, overexpression of XIST aggravated TAC-induced cardiac hypertrophy. Finally, we demonstrated that miR-101 was a direct target of XIST, whereas TLR2 was a target of miR-101. Rescue assays further confirmed that XIST promoted the progression of cardiac hypertrophy through competitively binding with miR-101 to enhance the expression of TLR2. Collectively, these in vivo and in vitro findings identify XIST as a necessary regulator of cardiac hypertrophy due to its regulation of the miR-101/TLR2 axis, suggesting that XIST might act as a therapeutic target for the treatment of cardiac hypertrophy and heart failure.

Genetics of Atrial Fibrilation: In Search of Novel Therapeutic Targets

Atrial fibrillation (AF) is the most frequent arrhythmogenic disease in humans, ranging from 2% in the general population and rising up to 10-12% in 80+ years. Genetic analyses of AF familiar cases have identified a series of point mutations in distinct ion channels, supporting a causative link. However, these genetic defects only explain a minority of AF patients. Genomewide association studies identified single nucleotide polymorphisms (SNPs), close to PITX2 on 4q25 chromosome, that are highly associated to AF. Subsequent GWAS studies have identified several new loci, involving additional transcription and growth factors. Furthermore, these risk 4q25 SNPs serve as surrogate biomarkers to identify AF recurrence in distinct surgical and pharmacological interventions. Experimental studies have demonstrated an intricate signalling pathway supporting a key role of the homeobox transcription factor PITX2 as a transcriptional regulator. Furthermore, cardiovascular risk factors such as hyperthyroidism, hypertension and redox homeostasis have been identified to modulate PITX2 driven gene regulatory networks. We provide herein a state-of-the-art review of the genetic bases of atrial fibrillation, our current understanding of the genetic regulatory networks involved in AF and its plausible usage for searching novel therapeutic targets.

Novel Roles of Non-Coding RNAs in Opioid Signaling and Cardioprotection

Cardiovascular disease (CVD) is a significant cause of morbidity and mortality across the world. A large proportion of CVD deaths are secondary to coronary artery disease (CAD) and myocardial infarction (MI). Even though prevention is the best strategy to reduce risk factors associated with MI, the use of cardioprotective interventions aimed at improving patient outcomes is of great interest. Opioid conditioning has been shown to be effective in reducing myocardial ischemia-reperfusion injury (IRI) and cardiomyocyte death. However, the molecular mechanisms behind these effects are under investigation and could provide the basis for the development of novel therapeutic approaches in the treatment of CVD. Non-coding RNAs (ncRNAs), which are functional RNA molecules that do not translate into proteins, are critical modulators of cardiac gene expression during heart development and disease. Moreover, ncRNAs such as microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) are known to be induced by opioid receptor activation and regulate opioid signaling pathways. Recent advances in experimental and computational tools have accelerated the discovery and functional characterization of ncRNAs. In this study, we review the current understanding of the role of ncRNAs in opioid signaling and opioid-induced cardioprotection.