Regulation of the SK3 channel by microRNA-499--potential role in atrial fibrillation

Endogenous ether lipids differentially promote tumor aggressiveness by regulating the SK3 channel

SK3 channels are potassium channels found to promote tumor aggressiveness. We have previously demonstrated that SK3 is regulated by synthetic ether lipids, but the role of endogenous ether lipids is unknown. Here, we have studied the role of endogenous alkyl- and alkenyl-ether lipids on SK3 channels and on the biology of cancer cells. Experiments revealed that the suppression of alkylglycerone phosphate synthase or plasmanylethanolamine desaturase 1, which are key enzymes for alkyl- and alkenyl-ether-lipid synthesis, respectively, decreased SK3 expression by increasing micro RNA (miR)-499 and miR-208 expression, leading to a decrease in SK3-dependent calcium entry, cell migration, and matrix metalloproteinase 9-dependent cell adhesion and invasion. We identified several ether lipids that promoted SK3 expression and found a differential role of alkyl- and alkenyl-ether lipids on SK3 activity. The expressions of alkylglycerone phosphate synthase, SK3, and miR were associated in clinical samples emphasizing the clinical consistency of our observations. To our knowledge, this is the first report showing that ether lipids differentially control tumor aggressiveness by regulating an ion channel. This insight provides new possibilities for therapeutic interventions, offering clinicians an opportunity to manipulate ion channel dysfunction by adjusting the composition of ether lipids.

ROS in diabetic atria regulate SK2 degradation by Atrogin-1 through the NF-κB signaling pathway

One of the independent risk factors for atrial fibrillation is diabetes mellitus (DM); however, the underlying mechanisms causing atrial fibrillation in DM are unknown. The underlying mechanism of Atrogin-1-mediated SK2 degradation and associated signaling pathways are unclear. The aim of this study was to elucidate the relationship among reactive oxygen species (ROS), the NF-κB signaling pathway, and Atrogin-1 protein expression in the atrial myocardia of DM mice. We found that SK2 expression was downregulated comitant with increased ROS generation and enhanced NF-κB signaling activation in the atrial cardiomyocytes of DM mice. These observations were mimicked by exogenously applicating H2O2 and by high glucose culture conditions in HL-1 cells. Inhibition of ROS production by diphenyleneiodonium chloride or silencing of NF-κB by siRNA decreased the protein expression of NF-κB and Atrogin-1 and increased that of SK2 in HL-1 cells with high glucose culture. Moreover, chromatin immunoprecipitation assay demonstrated that NF-κB/p65 directly binds to the promoter of the FBXO32 gene (encoding Atrogin-1), regulating the FBXO32 transcription. Finally, we evaluated the therapeutic effects of curcumin, known as a NF-κB inhibitor, on Atrogin-1 and SK2 expression in DM mice and confirmed that oral administration of curcumin for 4 weeks significantly suppressed Atrogin-1 expression and protected SK2 expression against hyperglycemia. In summary, the results from this study indicated that the ROS/NF-κB signaling pathway participates in Atrogin-1-mediated SK2 regulation in the atria of streptozotocin-induced DM mice.

Role of miRNA in Cardiovascular Diseases in Children-Systematic Review

The number of children suffering from cardiovascular diseases (CVDs) is rising globally. Therefore, there is an urgent need to acquire a better understanding of the genetic factors and molecular mechanisms related to the pathogenesis of CVDs in order to develop new prevention and treatment strategies for the future. MicroRNAs (miRNAs) constitute a class of small non-coding RNA fragments that range from 17 to 25 nucleotides in length and play an essential role in regulating gene expression, controlling an abundance of biological aspects of cell life, such as proliferation, differentiation, and apoptosis, thus affecting immune response, stem cell growth, ageing and haematopoiesis. In recent years, the concept of miRNAs as diagnostic markers allowing discrimination between healthy individuals and those affected by CVDs entered the purview of academic debate. In this review, we aimed to systematise available information regarding miRNAs associated with arrhythmias, cardiomyopathies, myocarditis and congenital heart diseases in children. We focused on the targeted genes and metabolic pathways influenced by those particular miRNAs, and finally, tried to determine the future of miRNAs as novel biomarkers of CVD.

MicroRNA-499-5p inhibits transforming growth factor-β1-induced Smad2 signaling pathway and suppresses fibroblast proliferation and collagen synthesis in rat by targeting TGFβ-R1

BACKGROUND

Artial fibrosis has been recognized as a typical pathological change in atrial fibrillation. Although present evidence suggests that microRNA-499-5p (miR-499-5p) plays an important role in the development of atrial fibrosis, the specific mechanism is not fully understood. Therefore, this study attempted to assess the influence of miR-499-5p on atrial fibroblasts and explore the potential molecular mechanism.

METHODS

Atrial fibroblasts from sprague dawley rat were respectively transfected with miR-499-5p mimic, miR-499-5p negative control and miR-499-5p inhibitor, atrial fibroblasts without any treatment were also established. Cell counting kit-8 assay and transwell assay were used to detect the proliferation and migration of atrial fibroblasts in each group. Expressions of miR-499-5p, TGF-β1, smad2, α-SMA, collagen-I and TGFβ-R1 in mRNA and protein level were subsequently detected via quantitative real-time polymerase chain reaction and western blot. Furthermore, the prediction of the binding sites of miR-499-5p and TGFβ-R1 was performed via the bioinformatics online software TargetScan and verified by dual luciferase reporter.

RESULTS

By utilizing miR-499-5p-transfected atrial fibroblasts model, expression of miR-499-5p in the miR-499-5p mimic group was upregulated, while it was downregulated in the miR-499-5p inhibitors group. Upregulated miR-499-5p expression led to to a significant decrease in the proliferative and migratory ability of cultured atrial fibroblasts, while downregulated miR-499-5p expression led to a significant increase in the proliferative and migratory ability of cultured atrial fibroblasts. Additionally, upregulated miR-499-5p expression made a significant rise in TGF-β1-induced mRNA and protein expression of TGF-β1, TGFβ-R1, smad2, α-SMA and collagen-I in atrial fibroblasts. Furthermore, results from the dual luciferase reporter conformed that miR-499-5p may repress TGFβ-R1 by binding the 3'UTR of TGFβ-R1 directly.

CONCLUSIONS

miR-499-5p is able to inhibit the activation of transforming growth factor β-induced Smad2 signaling and eventually suppressed the proliferation, migration and invasion of atrial fibroblasts and collagen synthesis by targeting TGFβ-R1.

Research progress of non-coding RNA in atrial fibrillation

Atrial fibrillation (AF) is a common arrhythmia in clinic, and its incidence is increasing year by year. In today's increasingly prevalent society, ageing poses a huge challenge to global healthcare systems. AF not only affects patients' quality of life, but also causes thrombosis, heart failure and other complications in severe cases. Although there are some measures for the diagnosis and treatment of AF, specific serum markers and targeted therapy are still lacking. In recent years, ncRNAs have become a hot topic in cardiovascular disease research. These ncRNAs are not only involved in the occurrence and development of AF, but also in pathophysiological processes such as myocardial infarction and atherosclerosis, and are potential biomarkers of cardiovascular diseases. We believe that the understanding of the pathophysiological mechanism of AF and the study of diagnosis and treatment targets can form a more systematic diagnosis and treatment framework of AF and provide convenience for individuals with AF and the society.

Clinical Significance of MicroRNAs, Long Non-Coding RNAs, and CircRNAs in Cardiovascular Diseases

Based on recent research, the non-coding genome is essential for controlling genes and genetic programming during development, as well as for health and cardiovascular diseases (CVDs). The microRNAs (miRNAs), lncRNAs (long ncRNAs), and circRNAs (circular RNAs) with significant regulatory and structural roles make up approximately 99% of the human genome, which does not contain proteins. Non-coding RNAs (ncRNA) have been discovered to be essential novel regulators of cardiovascular risk factors and cellular processes, making them significant prospects for advanced diagnostics and prognosis evaluation. Cases of CVDs are rising due to limitations in the current therapeutic approach; most of the treatment options are based on the coding transcripts that encode proteins. Recently, various investigations have shown the role of nc-RNA in the early diagnosis and treatment of CVDs. Furthermore, the development of novel diagnoses and treatments based on miRNAs, lncRNAs, and circRNAs could be more helpful in the clinical management of patients with CVDs. CVDs are classified into various types of heart diseases, including cardiac hypertrophy (CH), heart failure (HF), rheumatic heart disease (RHD), acute coronary syndrome (ACS), myocardial infarction (MI), atherosclerosis (AS), myocardial fibrosis (MF), arrhythmia (ARR), and pulmonary arterial hypertension (PAH). Here, we discuss the biological and clinical importance of miRNAs, lncRNAs, and circRNAs and their expression profiles and manipulation of non-coding transcripts in CVDs, which will deliver an in-depth knowledge of the role of ncRNAs in CVDs for progressing new clinical diagnosis and treatment.

microRNAs as Biomarkers of Endothelial Dysfunction and Therapeutic Target in the Pathogenesis of Atrial Fibrillation

The pathophysiology of atrial fibrillation (AF) may involve atrial fibrosis/remodeling and dysfunctional endothelial activities. Despite the currently available treatment approaches, the progression of AF, its recurrence rate, and the high mortality risk of related complications underlay the need for more advanced prognostic and therapeutic strategies. There is increasing attention on the molecular mechanisms controlling AF onset and progression points to the complex cell to cell interplay that triggers fibroblasts, immune cells and myofibroblasts, enhancing atrial fibrosis. In this scenario, endothelial cell dysfunction (ED) might play an unexpected but significant role. microRNAs (miRNAs) regulate gene expression at the post-transcriptional level. In the cardiovascular compartment, both free circulating and exosomal miRNAs entail the control of plaque formation, lipid metabolism, inflammation and angiogenesis, cardiomyocyte growth and contractility, and even the maintenance of cardiac rhythm. Abnormal miRNAs levels may indicate the activation state of circulating cells, and thus represent a specific read-out of cardiac tissue changes. Although several unresolved questions still limit their clinical use, the ease of accessibility in biofluids and their prognostic and diagnostic properties make them novel and attractive biomarker candidates in AF. This article summarizes the most recent features of AF associated with miRNAs and relates them to potentially underlying mechanisms.

Circulating miR-451a Expression May Predict Recurrence in Atrial Fibrillation Patients after Catheter Pulmonary Vein Ablation

Atrial fibrillation is the most prevalent tachyarrhythmia in clinical practice, with very high cardiovascular morbidity and mortality with a high-cost impact in health systems. Currently, it is one of the main causes of stroke and subsequent heart failure and sudden death. miRNAs mediate in several processes involved in cardiovascular disease, including fibrosis and electrical and structural remodeling. Several studies suggest a key role of miRNAs in the course and maintenance of atrial fibrillation. In our study, we aimed to identify the differential expression of circulating miRNAs and their predictive value as biomarkers of recurrence in atrial fibrillation patients undergoing catheter pulmonary vein ablation. To this effect, 42 atrial fibrillation patients were recruited for catheter ablation. We measured the expression of 84 miRNAs in non-recurrent and recurrent groups (45.2%), both in plasma from peripheral and left atrium blood. Expression analysis showed that miRNA-451a is downregulated in recurrent patients. Receiver operating characteristic curve analysis showed that miR-451a in left atrium plasma could predict atrial fibrillation recurrence after pulmonary vein isolation. In addition, atrial fibrillation recurrence is positively associated with the increment of scar percentage. Our data suggest that miRNA-451a expression plays an important role in AF recurrence by controlling fibrosis and progression.

Circulatory miR-411-5p as a Novel Prognostic Biomarker for Major Adverse Cardiovascular Events in Patients with Atrial Fibrillation

The risk stratification of patients with atrial fibrillation (AF) for subsequent cardiovascular events could help in guiding prevention strategies. In this study, we aimed at investigating circulating microRNAs as prognostic biomarkers for major adverse cardiovascular events (MACE) in AF patients. We conducted a three-stage nested case-control study within the framework of a prospective registry, including 347 AF patients. First, total small RNA-sequencing was performed in 26 patients (13 cases with MACE) and the differential expression of microRNAs was analyzed. Seven candidate microRNAs with promising results in a subgroup analysis on cardiovascular death were selected and measured via using RT-qPCR in 97 patients (42 cases with cardiovascular death). To further validate our findings and investigate broader clinical applicability, we analyzed the same microRNAs in a subsequent nested case-control study of 102 patients (37 cases with early MACE) by using Cox regression. In the microRNA discovery cohort (n = 26), we detected 184 well-expressed microRNAs in circulation without overt differential expression between the cases and controls. A subgroup analysis on cardiovascular death revealed 26 microRNAs that were differentially expressed at a significance level < 0.05 (three of which with an FDR-adjusted p-value <0.05). We, therefore, proceeded with a nested case-control approach (n = 97) focusing on patients with cardiovascular death and selected, in total, seven microRNAs for further RT-qPCR analysis. One microRNA, miR-411-5p, was significantly associated with cardiovascular death (adjusted HR (95% CI): 1.95 (1.04-3.67)). Further validation (n = 102) in patients who developed early MACE showed similar results (adjusted HR (95% CI) 2.35 (1.17-4.73)). In conclusion, circulating miR-411-5p could be a valuable prognostic biomarker for MACE in AF patients.

Non-coding RNAs in human health and disease: potential function as biomarkers and therapeutic targets

Human diseases have been a critical threat from the beginning of human history. Knowing the origin, course of action and treatment of any disease state is essential. A microscopic approach to the molecular field is a more coherent and accurate way to explore the mechanism, progression, and therapy with the introduction and evolution of technology than a macroscopic approach. Non-coding RNAs (ncRNAs) play increasingly important roles in detecting, developing, and treating all abnormalities related to physiology, pathology, genetics, epigenetics, cancer, and developmental diseases. Noncoding RNAs are becoming increasingly crucial as powerful, multipurpose regulators of all biological processes. Parallel to this, a rising amount of scientific information has revealed links between abnormal noncoding RNA expression and human disorders. Numerous non-coding transcripts with unknown functions have been found in addition to advancements in RNA-sequencing methods. Non-coding linear RNAs come in a variety of forms, including circular RNAs with a continuous closed loop (circRNA), long non-coding RNAs (lncRNA), and microRNAs (miRNA). This comprises specific information on their biogenesis, mode of action, physiological function, and significance concerning disease (such as cancer or cardiovascular diseases and others). This study review focuses on non-coding RNA as specific biomarkers and novel therapeutic targets.

Progress in molecular biology and translational science: Epigenetics in cardiovascular health and disease

Conrad Waddington's epigenetics landscape has provided a metaphorical framework for how cells progress from undifferentiated states to one of several discrete, distinct, differentiated cell fates. The understanding of epigenetics has evolved over time, with DNA methylation being the most studied epigenetic modification, followed by histone modifications and non-coding RNA. Cardiovascular diseases (CVD) are leading contributors to death worldwide, with the prevalence of CVDs increasing across the last couple of decades. Significant amount of resources being poured into researching key mechanisms and underpinnings of the various CVDs. These molecular studies looked at the genetics, epigenetics as well as the transcriptomics of various cardiovascular conditions, aiming to provide mechanistic insights. It has paved the way for therapeutics to be developed and in recent years, epi-drugs for the treatment of CVDs. This chapter aims to cover the various roles of epigenetics in the context of cardiovascular health and disease. The following will be examined in detail: the developments in basic experimental techniques used to study epigenetics, the role of epigenetics in various CVDs (hypertension, atrial fibrillation, atherosclerosis, and heart failure), and current advances in epi-therapeutics, providing a holistic view of the current concerted efforts in advancing the field of epigenetics in CVDs.

Pharmacological nNOS inhibition modified small-conductance Ca2+-activated K+ channel without altering Ca2+ dynamics

Atrial fibrillation (AF) is associated with electrical remodeling processes that promote a substrate for the maintenance of AF. Although the small-conductance Ca²⁺-activated K⁺ (SK) channel is a key factor in atrial electrical remodeling, the mechanism of its activation remains unclear. Regional nitric oxide (NO) production by neuronal nitric oxide synthase (nNOS) is involved in atrial electrical remodeling. In this study, atrial tachyarrhythmia (ATA) induction and optical mapping were performed on perfused rat hearts. nNOS is pharmacologically inhibited by S-methylthiocitrulline (SMTC). The influence of the SK channel was examined using a specific channel inhibitor, apamin (APA). Parameters such as action potential duration (APD), conduction velocity, and calcium transient (CaT) were evaluated using voltage and calcium optical mapping. The dominant frequency was examined in the analysis of AF dynamics. SMTC (100 nM) increased the inducibility of ATA and apamin (100 nM) mitigated nNOS inhibition-induced arrhythmogenicity. SMTC caused abbreviations and enhanced the spatial dispersion of APD, which was reversed by apamin. By contrast, conduction velocity and other parameters associated with CaT were not affected by SMTC or apamin administration. Apamin reduced the frequency of SMTC-induced ATA. In summary, nNOS inhibition abbreviates APD by modifying the SK channels. A specific SK channel blocker, apamin, mitigated APD abbreviation without alteration of CaT, implying an underlying mechanism of posttranslational modification of SK channels.NEW & NOTEWORTHY We demonstrated that pharmacological nNOS inhibition increased the atrial arrhythmia inducibility and a specific small-conductance Ca²⁺-activated K⁺ channel blocker, apamin, reversed the enhanced atrial arrhythmia inducibility. Apamin mitigated APD abbreviation without alteration of Ca²⁺ transient, implying an underlying mechanism of posttranslational modification of SK channels.

Emerging Antiarrhythmic Drugs for Atrial Fibrillation

Atrial fibrillation (AF), the most common cardiac arrhythmia worldwide, is driven by complex mechanisms that differ between subgroups of patients. This complexity is apparent from the different forms in which AF presents itself (post-operative, paroxysmal and persistent), each with heterogeneous patterns and variable progression. Our current understanding of the mechanisms responsible for initiation, maintenance and progression of the different forms of AF has increased significantly in recent years. Nevertheless, antiarrhythmic drugs for the management of AF have not been developed based on the underlying arrhythmia mechanisms and none of the currently used drugs were specifically developed to target AF. With the increased knowledge on the mechanisms underlying different forms of AF, new opportunities for developing more effective and safer AF therapies are emerging. In this review, we provide an overview of potential novel antiarrhythmic approaches based on the underlying mechanisms of AF, focusing both on the development of novel antiarrhythmic agents and on the possibility of repurposing already marketed drugs. In addition, we discuss the opportunity of targeting some of the key players involved in the underlying AF mechanisms, such as ryanodine receptor type-2 (RyR2) channels and atrial-selective K⁺-currents (I_K2P and I_SK) for antiarrhythmic therapy. In addition, we highlight the opportunities for targeting components of inflammatory signaling (e.g., the NLRP3-inflammasome) and upstream mechanisms targeting fibroblast function to prevent structural remodeling and progression of AF. Finally, we critically appraise emerging antiarrhythmic drug principles and future directions for antiarrhythmic drug development, as well as their potential for improving AF management.

The Interplay Between Gut Microbiota and miRNAs in Cardiovascular Diseases

The human microbiota contains microorganisms found on the skin, mucosal surfaces and in other tissues. The major component, the gut microbiota, can be influenced by diet, genetics, and environmental factors. Any change in its composition results in pathophysiological changes that can further influence the evolution of different conditions, including cardiovascular diseases (CVDs). The microbiome is a complex ecosystem and can be considered the metagenome of the microbiota. MicroRNAs (miRNAs) are speculated to interact with the intestinal microbiota for modulating gene expressions of the host. miRNAs represent a category of small non-coding RNAs, consisting of approximately 22 nucleotides, which can regulate gene expression at post-transcriptional level, by influencing the degradation of mRNA and modifying protein amounts. miRNAs display a multitude of roles, being able to influence the pathogenesis and progression of various diseases. Circulating miRNAs are stable against degradation, due to their enclosure into extracellular vesicles (EVs). This review aims to assess the current knowledge of the possible interactions between gut microbiota, miRNAs, and CVDs. As more scientific research is conducted, it can be speculated that personalized patient care in the future may include the management of gut microbiota composition and the targeted treatment against certain expression of miRNAs.

Circulatory MicroRNAs in Plasma and Atrial Fibrillation in the General Population: The Rotterdam Study

Background: MicroRNAs (miRNAs), small non-coding RNAs regulating gene expression, have been shown to play an important role in cardiovascular disease. However, limited population-based data regarding the relationship between circulatory miRNAs in plasma and atrial fibrillation (AF) exist. Moreover, it remains unclear if the relationship differs by sex. We therefore aimed to determine the (sex-specific) association between plasma circulatory miRNAs and AF at the population level. Methods: Plasma levels of miRNAs were measured using a targeted next-generation sequencing method in 1999 participants from the population-based Rotterdam Study. Logistic regression and Cox proportional hazards models were used to assess the associations of 591 well-expressed miRNAs with the prevalence and incidence of AF. Models were adjusted for cardiovascular risk factors. We further examined the link between predicted target genes of the identified miRNAs. Results: The mean age was 71.7 years (57.1% women), 98 participants (58 men and 40 women) had prevalent AF at baseline. Moreover, 196 participants (96 men and 100 women) developed AF during a median follow-up of 9.0 years. After adjusting for multiple testing, miR-4798-3p was significantly associated with the odds of prevalent AF among men (odds ratio, 95% confidence interval, 0.39, 0.24–0.66, p-value = 0.000248). No miRNAs were significantly associated with incident AF. MiR-4798-3p could potentially regulate the expression of a number of AF-related genes, including genes involved in calcium and potassium handling in myocytes, protection of cells against oxidative stress, and cardiac fibrosis. Conclusions: Plasma levels of miR-4798-3p were significantly associated with the odds of prevalent AF among men. Several target genes in relation to AF pathophysiology could potentially be regulated by miR-4798-3p that warrant further investigations in future experimental studies.

Exosomes and Exosomal Non-coding RNAs Are Novel Promises for the Mechanism-Based Diagnosis and Treatments of Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia worldwide and has a significant impact on human health and substantial costs. Currently, there is a lack of accurate biomarkers for the diagnosis and prognosis of AF. Moreover, the long-term efficacy of the catheter ablation in the AF is unsatisfactory. Therefore, it is necessary to explore new biomarkers and treatment strategies for the mechanism-based AF. Exosomes are nano-sized biovesicles released by nearly all types of cells. Since the AF would be linked to the changes of the atrial cells and their microenvironment, and the AF would strictly influence the exosomal non-coding RNAs (exo-ncRNAs) expression, which makes them as attractive diagnostic and prognostic biomarkers for the AF. Simultaneously, the exo-ncRNAs have been found to play an important role in the mechanisms of the AF and have potential therapeutic prospects. Although the role of the exo-ncRNAs in the AF is being actively investigated, the evidence is still limited. Furthermore, there is a lack of consensus regarding the most appropriate approach for exosome isolation and characterization. In this article, we reviewed the new methodologies available for exosomes biogenesis, isolation, and characterization, and then discussed the mechanism of the AF and various levels and types of exosomes relevant to the AF, with the special emphasis on the exo-ncRNAs in the diagnosis, prognosis, and treatment of the mechanism-based AF.

Biomarkers in the clinical management of patients with atrial fibrillation and heart failure

Atrial fibrillation (AF) and heart failure (HF) are two cardiovascular diseases with an increasing prevalence worldwide. These conditions share common pathophysiologiesand frequently co-exit. In fact, the occurrence of either condition can 'cause' the development of the other, creating a new patient group that demands different management strategies to that if they occur in isolation. Regardless of the temproral association of the two conditions, their presence is linked with adverse cardiovascular outcomes, increased rate of hospitalizations, and increased economic burden on healthcare systems. The use of low-cost, easily accessible and applicable biomarkers may hasten the correct diagnosis and the effective treatment of AF and HF. Both AF and HF effect multiple physiological pathways and thus a great number of biomarkers can be measured that potentially give the clinician important diagnostic and prognostic information. These will then guide patient centred therapeutic management. The current biomarkers that offer potential for guiding therapy, focus on the physiological pathways of miRNA, myocardial stretch and injury, oxidative stress, inflammation, fibrosis, coagulation and renal impairment. Each of these has different utility in current clinincal practice.

MicroRNA‑499a (rs3746444A/G) gene variant and susceptibility to type 2 diabetes‑associated end‑stage renal disease

Diabetic nephropathy (DN) is a major risk factor for end-stage renal disease (ESRD). MicroRNAs (miRNAs/miRs) and their variants may be implicated in health and disease, including DN. The present study aimed to investigate the association of the miRNA-499a gene (MIR499A) A/G seed region variant (rs3746444) with DN-associated ESRD susceptibility in patients with diabetes mellitus, and to determine whether there was an association between the different genotypes and the patients' laboratory and clinical data. A case-control pilot study was conducted on 180 adult patients with type 2 diabetes mellitus. A total of 90 patients with ESRD on regular hemodialysis were considered as the cases, and 90 age-, sex- and ethnicity-matched diabetic patients with normo-albuminuria were considered as the controls. MIR499A genotyping was performed using a TaqMan Real-Time allele discrimination assay. Results demonstrated that the MIR499A rs3746444*G variant conferred susceptibility to the development of ESRD under co-dominant [(odds ratio (95% confidence interval): 2.49 (1.41-3.89) and 2.41 (1.61-6.68) for heterozygous and homozygous comparison, respectively], dominant [2.30 (1.18-3.90)] and allelic [1.82 (1.17-2.83)] models. Different genotypes of the specified variant did not exhibit significant associations with the clinic-laboratory data of the studied patients or the circulating miR-499a plasma levels. In conclusion, results of the present study suggested that MIR499A rs3746444 may be a susceptibility variant for DN-associated ESRD in the study population. However, larger sample size studies with different ethnicities are warranted to verify these findings.

A narrative review of non-coding RNAs in atrial fibrillation: potential therapeutic targets and molecular mechanisms

Objective

This review summarizes the advances in the study of ncRNAs and atrial remodeling mechanisms to explore potential therapeutic targets and strategies for AF.

Background

Atrial fibrillation (AF) is one of the most common arrhythmias, and its morbidity and mortality rates are gradually increasing. Non-coding ribonucleic acid RNAs (ncRNAs) are transcribed from the genome and do not have the ability to be translated into proteins. A growing body of evidence has shown ncRNAs are extensively involved in the pathophysiological processes underlying AF. However, the precise molecular mechanisms of these associations have not been fully elucidated. Atrial remodeling plays a key role in the occurrence and development of AF, and includes electrical remodeling, structural remodeling, and autonomic nerve remodeling. Research has shown that ncRNA expression is altered in the plasma and tissues of AF patients that mediate cardiac excitation and arrhythmia, and is closely related to atrial remodeling.

Methods

Literatures about ncRNAs and atrial fibrillation were extensively reviewed to discuss and analyze.

Conclusions

The biology of ncRNAs represents a relatively new field of research and is still in an emerging stage. Recent studies have laid a foundation for understanding the molecular mechanisms of AF, future studies aimed at identifying how ncRNAs act on atrial fibrillation to provide potentially promising therapeutic targets for the treatment of atrial fibrillation.

Microrna: the role in the pathophysiology of atrial fibrillation and potential use as a biomarker

The aim of the study was to analyze medical literature on the role of microRNA in the pathophysiology of atrial fibrillation and the possibilities of using microRNAs as biomarkers.The analysis of modern medical literature was carried out using the PubMed – NCBI database.

Atrial fibrillation (AF) is a common and serious cardiovascular disease. The pathophysiological mechanisms underlying the development of atrial fibrillation are not entirely clear. In addition, there are no optimal biomarkers for early detection and assessment of the prognosis for patients with atrial fibrillation. Recently, the attention of researchers has been directed to the molecules of microRNA. There is a lot of evidence that they are involved in the pathogenesis of neurological, oncological, and cardiovascular diseases. This review examines the role of microRNAs in the pathophysiology of atrial fibrillation. The possibility of using microRNA as a biomarker for the diagnosis and prediction of atrial fibrillation is also discussed.MicroRNAs play a crucial role in the pathophysiology of atrial fibrillation, regulating the mechanisms of atrial remodeling, such as electrical remodeling, structural remodeling, remodeling of the autonomic nervous system, and impaired regulation of calcium levels. The stability of microRNAs and the possibility to study them in various biological fluids and tissues, including blood, make these molecules a promising diagnostic biomarker for various cardiovascular diseases. The presented data clearly indicate that AF is associated with changes in the expression level of various microRNAs, which can be quantified using a polymerase chain reaction. Further research is required to assess the role of microRNAs as biomarkers for atrial fibrillation, in particular to establish precise reference limits.

New Strategies for the Treatment of Atrial Fibrillation

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia in the clinical practice. It significantly contributes to the morbidity and mortality of the elderly population. Over the past 25-30 years intense effort in basic research has advanced the understanding of the relationship between the pathophysiology of AF and atrial remodelling. Nowadays it is clear that the various forms of atrial remodelling (electrical, contractile and structural) play crucial role in initiating and maintaining the persistent and permanent types of AF. Unlike in ventricular fibrillation, in AF rapid ectopic firing originating from pulmonary veins and re-entry mechanism may induce and maintain (due to atrial remodelling) this complex cardiac arrhythmia. The present review presents and discusses in detail the latest knowledge on the role of remodelling in AF. Special attention is paid to novel concepts and pharmacological targets presumably relevant to the drug treatment of atrial fibrillation.

Cardiac K+ Channels and Channelopathies

The physiological heart function is controlled by a well-orchestrated interplay of different ion channels conducting Na⁺, Ca²⁺ and K⁺. Cardiac K⁺ channels are key players of cardiac repolarization counteracting depolarizating Na⁺ and Ca²⁺ currents. In contrast to Na⁺ and Ca²⁺, K⁺ is conducted by many different channels that differ in activation/deactivation kinetics as well as in their contribution to different phases of the action potential. Together with modulatory subunits these K⁺ channel α-subunits provide a wide range of repolarizing currents with specific characteristics. Moreover, due to expression differences, K⁺ channels strongly influence the time course of the action potentials in different heart regions. On the other hand, the variety of different K⁺ channels increase the number of possible disease-causing mutations. Up to now, a plethora of gain- as well as loss-of-function mutations in K⁺ channel forming or modulating proteins are known that cause severe congenital cardiac diseases like the long-QT-syndrome, the short-QT-syndrome, the Brugada syndrome and/or different types of atrial tachyarrhythmias. In this chapter we provide a comprehensive overview of different K⁺ channels in cardiac physiology and pathophysiology.

Emerging roles of microRNA-208a in cardiology and reverse cardio-oncology

Cardiovascular diseases (CVDs) and cancer, which are the leading causes of mortality globally, have been viewed as two distinct diseases. However, the fact that cancer and CVDs may coincide has been noted by cardiologists when taking care of patients with CVDs caused by cancer chemotherapy; this entity is designated cardio-oncology. More recently, patients with CVDs have also been found to have increased risk of cancers, termed reverse cardio-oncology. Although reverse cardio-oncology has been highlighted as an important disease state in recent studies, how the diseased heart affects cancer and the potential mediators of the crosstalk between CVDs and cancer are largely unknown. Here, we focus on the roles of cardiac-specific microRNA-208a (miR-208a) in cardiac and cancer biology and explore its essential roles in reverse cardio-oncology. Accumulating evidence has shown that within the heart, increased miR-208a promotes myocardial injury, arrhythmia, cardiac remodeling, and dysfunction and that secreted miR-208a in the circulation may have novel roles in promoting tumor proliferation and invasion. This review, therefore, provides insights into the novel roles of miR-208a in reverse cardio-oncology and strategies to prevent secondary carcinogenesis in patients with early- or late-stage heart failure.

Circular RNA mmu_circ_0005019 inhibits fibrosis of cardiac fibroblasts and reverses electrical remodeling of cardiomyocytes

BACKGROUND

Circular RNA (circRNA) have been reported to play important roles in cardiovascular diseases including myocardial infarction and heart failure. However, the role of circRNA in atrial fibrillation (AF) has rarely been investigated. We recently found a circRNA hsa_circ_0099734 was significantly differentially expressed in the AF patients atrial tissues compared to paired control. We aim to investigate the functional role and molecular mechanisms of mmu_circ_0005019 which is the homologous circRNA in mice of hsa_circ_0099734 in AF.

METHODS

In order to investigate the effect of mmu_circ_0005019 on the proliferation, migration, differentiation into myofibroblasts and expression of collagen of cardiac fibroblasts, and the effect of mmu_circ_0005019 on the apoptosis and expression of Ito, INA and SK3 of cardiomyocytes, gain- and loss-of-function of cell models were established in mice cardiac fibroblasts and HL-1 atrial myocytes. Dual-luciferase reporter assays and RIP were performed to verify the binding effects between mmu_circ_0005019 and its target microRNA (miRNA).

RESULTS

In cardiac fibroblasts, mmu_circ_0005019 showed inhibitory effects on cell proliferation and migration. In cardiomyocytes, overexpression of mmu_circ_0005019 promoted Kcnd1, Scn5a and Kcnn3 expression. Knockdown of mmu_circ_0005019 inhibited the expression of Kcnd1, Kcnd3, Scn5a and Kcnn3. Mechanistically, mmu_circ_0005019 exerted biological functions by acting as a miR-499-5p sponge to regulate the expression of its target gene Kcnn3.

CONCLUSIONS

Our findings highlight mmu_circ_0005019 played a protective role in AF development and might serve as an attractive candidate target for AF treatment.

miR-455-5p regulates atrial fibrillation by targeting suppressor of cytokines signaling 3

Atrial fibrillation (AF) is a condition that heart beats quaveringly or irregularly, which causes blood clots, heart failure, stroke, and other heart-related complications. Therefore, early diagnosis and timely preventions are necessary for AF treatment. Compelling evidence indicated that microRNAs (miRNAs) become emerging biomarkers of AF; thus, we aimed to investigate the possibility of miR-455-5p as an AF marker to provide a new strategy for early diagnosis of AF. A minipump containing angiotensin II was implanted into mice to induce AF, and adeno-associated virus (AAV) carrying anti-miR-negative control (NC) or anti-miR-455-5p was injected into the pericardial space of mice respectively. Next, myocytes isolated from wild-type newborn mice were stimulated with angiotensin II and anti-miR-NC or anti-miR-455-5p mimic. The results showed that the expression of miR-455-5p was positively correlated with the severity of AF, and miR-455-5p mimic accelerated the progression of AF by directly binding to its target gene suppressor of cytokines signaling 3 (SOCS3), leading to the activation of signal transducer and activator of transcription 3 (STAT3) signaling pathway. On the contrary, inhibition of miR-455-5p expression effectively ameliorated AF. In conclusion, miR-455-5p might serve as a biomarker of AF.

Small Conductance Ca2 +-Activated K+ (SK) Channel mRNA Expression in Human Atrial and Ventricular Tissue: Comparison Between Donor, Atrial Fibrillation and Heart Failure Tissue

In search of more efficacious and safe pharmacological treatments for atrial fibrillation (AF), atria-selective antiarrhythmic agents have been promoted that target ion channels principally expressed in the atria. This concept allows one to engage antiarrhythmic effects in atria, but spares the ventricles from potentially proarrhythmic side effects. It has been suggested that cardiac small conductance Ca²⁺-activated K⁺ (SK) channels may represent an atria-selective target in mammals including humans. However, there are conflicting data concerning the expression of SK channels in different stages of AF, and recent findings suggest that SK channels are upregulated in ventricular myocardium when patients develop heart failure. To address this issue, RNA-sequencing was performed to compare expression levels of three SK channels (KCNN1, KCNN2, and KCNN3) in human atrial and ventricular tissue samples from transplant donor hearts (no cardiac disease), and patients with cardiac disease in sinus rhythm or with AF. In addition, for control purposes expression levels of several genes known to be either chamber-selective or differentially expressed in AF and heart failure were determined. In atria, as compared to ventricle from transplant donor hearts, we confirmed higher expression of KCNN1 and KCNA5, and lower expression of KCNJ2, whereas KCNN2 and KCNN3 were statistically not differentially expressed. Overall expression of KCNN1 was low compared to KCNN2 and KCNN3. Comparing atrial tissue from patients with AF to sinus rhythm samples we saw downregulation of KCNN2 in AF, as previously reported. When comparing ventricular tissue from heart failure patients to non-diseased samples, we found significantly increased ventricular expression of KCNN3 in heart failure, as previously published. The other channels showed no significant difference in expression in either disease. Our results add weight to the view that SK channels are not likely to be an atria-selective target, especially in failing human hearts, and modulators of these channels may prove to have less utility in treating AF than hoped. Whether targeting SK1 holds potential remains to be elucidated.

Modulation of SK Channels: Insight Into Therapeutics of Atrial Fibrillation

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia in the world. Although much technological progress in the treatment of AF has been made, there is an urgent need for better treatment of AF due to its high rates of morbidity and mortality. The anti-arrhythmic drugs currently approved for marketing have significant limitations and side effects such as life-threatening ventricular arrhythmias and hypotension. The small conductance Ca²⁺-activated K⁺ channels (SK channels) are dependent on intracellular Ca²⁺ concentrations, which tightly integrate with membrane potential. Given the predominant expression in the atria of many species, including humans, they are now emerging as a therapeutic target for treating AF. This review aimed to illustrate the characteristics and function of SK channels. Moreover, it discussed the regulation of SK channels and their potential as a therapeutic target of AF.

Cardiac small-conductance calcium-activated potassium channels in health and disease

Small-conductance Ca2+-activated K+ (SK, KCa2) channels are encoded by KCNN genes, including KCNN1, 2, and 3. The channels play critical roles in the regulation of cardiac excitability and are gated solely by beat-to-beat changes in intracellular Ca2+. The family of SK channels consists of three members with differential sensitivity to apamin. All three isoforms are expressed in human hearts. Studies over the past two decades have provided evidence to substantiate the pivotal roles of SK channels, not only in healthy heart but also with diseases including atrial fibrillation (AF), ventricular arrhythmia, and heart failure (HF). SK channels are prominently expressed in atrial myocytes and pacemaking cells, compared to ventricular cells. However, the channels are significantly upregulated in ventricular myocytes in HF and pulmonary veins in AF models. Interests in cardiac SK channels are further fueled by recent studies suggesting the possible roles of SK channels in human AF. Therefore, SK channel may represent a novel therapeutic target for atrial arrhythmias. Furthermore, SK channel function is significantly altered by human calmodulin (CaM) mutations, linked to life-threatening arrhythmia syndromes. The current review will summarize recent progress in our understanding of cardiac SK channels and the roles of SK channels in the heart in health and disease.

Inhibiting microRNA-155 attenuates atrial fibrillation by targeting CACNA1C

BACKGROUND

Reduction in L-type Ca²⁺ current (I_Ca,L) density is a hallmark of the electrical remodeling in atrial fibrillation (AF). The expression of miR-155, whose predicted target gene is the α1c subunit of the calcium channel (CACNA1C), was upregulated in atrial cardiomyocytes (aCMs) from patients with paroxysmal AF.The study is to determine miR-155 could target the gene expression of I_Ca,L and contribute to electrical remodeling in AF.

METHODS

The expression of miR-155 and CACNA1C was assessed in aCMs from patients with paroxysmal AF and healthy control. I_Ca,L properties were observed after miR-155 transfection in human induced pluripotent stem cell derived atrial cardiomyocytes (hiPSC-aCMs). Furthermore, an miR-155 transgene (Tg) and knock-out (KO) mouse model was generated to determine whether miR-155 was involved in I_Ca,L-related electrical remodeling in AF by targeting CACNA1C.

RESULTS

The expression level of miR-155 was increased, while the expression level of CACNA1C reduced in the aCMs of patients with AF. miR-155 transfection in hiPSC-aCMs produced changes in I_Ca,L properties qualitatively similar to those produced by AF. miR-155/Tg mice developed a shortened action potential duration and increased vulnerability to AF, which was associated with decreased I_Ca,L and attenuated by an miR-155 inhibitor. Finally, the genetic inhibition of miR-155 prevented AF induction in miR-155/KO mice with no changes in I_Ca,L properties.

CONCLUSIONS

The increased miR-155 expression in aCMs was sufficient for the reduction in the density of I_Ca,L and the underlying electronic remodeling. The inhibition of miR-155 prevented I_Ca,L-related electric remodeling in AF and might constitute a novel anti-AF approach targeting electrical remodeling.

Overexpression of MiR-29b-3p Inhibits Atrial Remodeling in Rats by Targeting PDGF-B Signaling Pathway

Purpose

Studies have found that microRNAs (miRNAs) are closely associated with atrial fibrillation, but their specific mechanism remains unclear. The purpose of this experiment is to explore the function of miR-29b-3p in regulating atrial remodeling by targeting PDGF-B signaling pathway and thereby also explore the potential mechanisms.

Methods

We randomly divided twenty-four rats into four groups. Caudal intravenous injections of angiotensin-II (Ang-II) were administered to establish atrial fibrosis models. Expressions of miR-29b-3p and PDGF-B were then tested via RT-PCR, western blot, and immunohistochemistry. Binding sites were then analyzed via the bioinformatics online software TargetScan and verified by Luciferase Reporter. We used Masson staining to detect the degree of atrial fibrosis, while immunofluorescence and western blot were used to detect the expressions of Collagen-I and a-SMA. We used immunohistochemistry and western blot to detect the expression of connexin 43 (Cx43).

Results

In comparison with the Ang-II group, miR-29b-3p was seen to lower the degree of atrial fibrosis, decrease the expression of fibrosis markers such as Collagen-I and a-SMA, and increase the protein expression of Cx43. MiR-29b-3p can lower the expression of PDGF-B, while the Luciferase Reporter showed that PDGF-B is the verified target gene of miR-29b-3p.

Conclusions

MiR-29b-3p was able to reduce atrial structural and electrical remodeling in the study's rat fibrosis model. This biological function may be expressed through the targeted regulation of the PDGF-B signaling pathway.

The regulation of the small-conductance calcium-activated potassium current and the mechanisms of sex dimorphism in J wave syndrome

Apamin-sensitive small-conductance calcium-activated potassium (SK) current (I_KAS) plays an important role in cardiac repolarization under a variety of physiological and pathological conditions. The regulation of cardiac I_KAS relies on SK channel expression, intracellular Ca²⁺, and interaction between SK channel and intracellular Ca²⁺. I_KAS activation participates in multiple types of arrhythmias, including atrial fibrillation, ventricular tachyarrhythmias, and automaticity and conduction abnormality. Recently, sex dimorphisms in autonomic control have been noticed in I_KAS activation, resulting in sex-differentiated action potential morphology and arrhythmogenesis. This review provides an update on the Ca²⁺-dependent regulation of cardiac I_KAS and the role of I_KAS on arrhythmias, with a special focus on sex differences in I_KAS activation. We propose that sex dimorphism in autonomic control of I_KAS may play a role in J wave syndrome.

HDAC2-dependent remodeling of KCa2.2 (KCNN2) and KCa2.3 (KCNN3) K+ channels in atrial fibrillation with concomitant heart failure

AIMS

Atrial fibrillation (AF) with concomitant heart failure (HF) is associated with prolonged atrial refractoriness. Small-conductance, calcium-activated K⁺ (K_Ca, KCNN) channels promote action potential (AP) repolarization. KCNN2 and KCNN3 variants are associated with AF risk. In addition, histone deacetylase (HDAC)-related epigenetic mechanisms have been implicated in AP regulation. We hypothesized that HDAC2-dependent remodeling of KCNN2 and KCNN3 expression contributes to atrial arrhythmogenesis in AF complicated by HF. The objectives were to assess HDAC2 and KCNN2/3 transcript levels in AF/HF patients and in a pig model, and to investigate cellular epigenetic effects of HDAC2 inactivation on KCNN expression.

MATERIALS AND METHODS

HDAC2 and KCNN2/3 transcript levels were quantified in patients with AF and HF, and in a porcine model of atrial tachypacing-induced AF and reduced left ventricular function. Tachypacing and anti-Hdac2 siRNA treatment were employed in HL-1 atrial myocytes to study effects on KCNN2/3 mRNA and K_Ca protein abundance.

KEY FINDINGS

Atrial KCNN2 and KCNN3 expression was reduced in AF/HF patients and in a corresponding pig model. HDAC2 displayed significant downregulation in humans and a tendency towards reduced expression in right atrial tissue of pigs. Tachypacing recapitulated downregulation of Kcnn2/K_Ca2.2, Kcnn3/K_Ca2.3 and Hdac2/HDAC2, indicating that high atrial rates trigger epigenetic remodeling mechanisms. Finally, knock-down of Hdac2 in vitro reduced Kcnn3/K_Ca2.3 expression.

SIGNIFICANCE

KCNN2/3 and HDAC2 expression is suppressed in AF complicated by HF. Hdac2 directly regulates Kcnn3 mRNA levels in atrial cells. The mechanistic and therapeutic significance of epigenetic electrophysiological effects in AF requires further validation.

Small and Intermediate Calcium Activated Potassium Channels in the Heart: Role and Strategies in the Treatment of Cardiovascular Diseases

Calcium-activated potassium channels are a heterogeneous family of channels that, despite their different biophysical characteristics, structures, and pharmacological signatures, play a role of transducer between the ubiquitous intracellular calcium signaling and the electric variations of the membrane. Although this family of channels was extensively described in various excitable and non-excitable tissues, an increasing amount of evidences shows their functional role in the heart. This review aims to focus on the physiological role and the contribution of the small and intermediate calcium-activated potassium channels in cardiac pathologies.

Revisiting Antiarrhythmic Drug Therapy for Atrial Fibrillation: Reviewing Lessons Learned and Redefining Therapeutic Paradigms

Since the clinical use of digitalis as the first pharmacological therapy for atrial fibrillation (AF) 235 years ago in 1785, antiarrhythmic drug therapy has advanced considerably and become a cornerstone of AF clinical management. Yet, a preventive or curative panacea for sustained AF does not exist despite the rise of AF global prevalence to epidemiological proportions. While multiple elevated risk factors for AF have been established, the natural history and etiology of AF remain incompletely understood. In the present article, the first section selectively highlights some disappointing shortcomings and current efforts in antiarrhythmic drug therapy to uncover reasons why AF is such a clinical challenge. The second section discusses some modern takes on the natural history of AF as a relentless, progressive fibro-inflammatory "atriomyopathy." The final section emphasizes the need to redefine therapeutic strategies on par with new insights of AF pathophysiology.

MicroRNAs: New contributors to mechano-electric coupling and atrial fibrillation

Atrial fibrillation (AF) is a multifactorial disease, which often occurs in the presence of underlying cardiac abnormalities and is supported by electrophysiological and structural alterations, generally referred to as atrial remodeling. Abnormal substrates are commonly encountered in various conditions that predispose to AF, such as hypertension, heart failure, obesity, and sleep apnea, in which atrial stretch plays a key mechanistic role. Emerging evidence suggests a role for microRNAs (small non-coding RNAs) in the pathogenesis of AF, where they can act as post-transcriptional regulators of the genes involved in atrial remodeling. This review summarizes the experimental and clinical evidence that supports the role of microRNAs in the modulation of atrial electrical and structural remodeling with a focus on overload-induced atrial alterations, and discusses the potential contribution of microRNAs to mechano-electrical coupling and AF.

Genetics and Epigenetics of Atrial Fibrillation

Atrial fibrillation (AF) is known to be the most common supraventricular arrhythmia affecting up to 1% of the general population. Its prevalence exponentially increases with age and could reach up to 8% in the elderly population. The management of AF is a complex issue that is addressed by extensive ongoing basic and clinical research. AF centers around different types of disturbances, including ion channel dysfunction, Ca²⁺-handling abnormalities, and structural remodeling. Genome-wide association studies (GWAS) have uncovered over 100 genetic loci associated with AF. Most of these loci point to ion channels, distinct cardiac-enriched transcription factors, as well as to other regulatory genes. Recently, the discovery of post-transcriptional regulatory mechanisms, involving non-coding RNAs (especially microRNAs), DNA methylation, and histone modification, has allowed to decipher how a normal heart develops and which modifications are involved in reshaping the processes leading to arrhythmias. This review aims to provide a current state of the field regarding the identification and functional characterization of AF-related epigenetic regulatory networks

Non-coding RNAs and Atrial Fibrillation

Atrial fibrillation is the most frequent type of cardiac arrhythmia in humans, with an estimate incidence of 1-2% in the general population, rising up to 8-10% in the elderly. Cardiovascular risk factors such as diabetes, obesity, hypertension and hyperthyroidism can increase the occurrence of AF. The onset of AF triggers additional AF episodes, leading to structural and electrical remodeling of the diseased heart. Understanding the molecular bases of atrial fibrillation have greatly advance over the last decade demonstrating a pivotal role of distinct ion channels in AF pathophysiology. A new scenario has opened on the understanding of the molecular mechanisms underlying AF, with the discovery of non-coding RNAs and their wide implication in multiple disease states, including cardiac arrhythmogenic pathologies. microRNAs are small non-coding RNAs of 22-24 nucleotides that are capable of regulating gene expression by interacting with the mRNA transcript 3'UTRs and promoting mRNA degradation and/or protein translation blockage. Long non-coding RNAs are a more diverse group of non-coding RNAs, providing transcriptional and post-transcriptional roles and subclassified according to their functional properties. In this chapter we summarized current state-of-the-art knowledge on the functional of microRNAs and long non-coding RNAs as well as their cross-talk regulatory mechanisms in atrial fibrillation.

Roles of endogenous ether lipids and associated PUFAs in the regulation of ion channels and their relevance for disease

Ether lipids (ELs) are lipids characterized by the presence of either an ether linkage (alkyl lipids) or a vinyl ether linkage [i.e., plasmalogens (Pls)] at the sn1 position of the glycerol backbone, and they are enriched in PUFAs at the sn2 position. In this review, we highlight that ELs have various biological functions, act as a reservoir for second messengers (such as PUFAs) and have roles in many diseases. Some of the biological effects of ELs may be associated with their ability to regulate ion channels that control excitation-contraction/secretion/mobility coupling and therefore cell physiology. These channels are embedded in lipid membranes, and lipids can regulate their activities directly or indirectly as second messengers or by incorporating into membranes. Interestingly, ELs and EL-derived PUFAs have been reported to play a key role in several pathologies, including neurological disorders, cardiovascular diseases, and cancers. Investigations leading to a better understanding of their mechanisms of action in pathologies have opened a new field in cancer research. In summary, newly identified lipid regulators of ion channels, such as ELs and PUFAs, may represent valuable targets to improve disease diagnosis and advance the development of new therapeutic strategies for managing a range of diseases and conditions.

miRBase: from microRNA sequences to function

miRBase catalogs, names and distributes microRNA gene sequences. The latest release of miRBase (v22) contains microRNA sequences from 271 organisms: 38 589 hairpin precursors and 48 860 mature microRNAs. We describe improvements to the database and website to provide more information about the quality of microRNA gene annotations, and the cellular functions of their products. We have collected 1493 small RNA deep sequencing datasets and mapped a total of 5.5 billion reads to microRNA sequences. The read mapping patterns provide strong support for the validity of between 20% and 65% of microRNA annotations in different well-studied animal genomes, and evidence for the removal of >200 sequences from the database. To improve the availability of microRNA functional information, we are disseminating Gene Ontology terms annotated against miRBase sequences. We have also used a text-mining approach to search for microRNA gene names in the full-text of open access articles. Over 500 000 sentences from 18 542 papers contain microRNA names. We score these sentences for functional information and link them with 12 519 microRNA entries. The sentences themselves, and word clouds built from them, provide effective summaries of the functional information about specific microRNAs. miRBase is publicly and freely available at http://mirbase.org/.

A Roadmap for Fixing the Heart: RNA Regulatory Networks in Cardiac Disease

With the continuous development of RNA biology and massive genome-wide transcriptome analysis, more and more RNA molecules and their functions have been explored in the last decade. Increasing evidence has demonstrated that RNA-related regulatory networks play an important role in a variety of human diseases, including cardiovascular diseases. In this review, we focus on RNA regulatory networks in heart disease, most of which are devastating conditions with no known cure. We systemically summarize recent discoveries of important new components of RNA regulatory networks, including microRNAs, long non-coding RNAs, and circular RNAs, as well as multiple regulators that affect the activity of these networks in cardiac physiology and pathology. In addition, this review covers emerging micropeptides, which represent short open reading frames (sORFs) in long non-coding RNA transcripts that may modulate cardiac physiology. Based on the current knowledge of RNA regulatory networks, we think that ongoing discoveries will not only provide us a better understanding of the molecular mechanisms that underlie heart disease, but will also identify novel biomarkers and therapeutic targets for the diagnosis and treatment of cardiac disease.

The Therapeutic Potential of MicroRNAs in Atrial Fibrillation

One of the most globally prevalent supraventricular arrhythmias is atrial fibrillation (AF). Knowledge of the structures and functions of messenger RNA (mRNA) has recently increased. It is no longer viewed as solely an intermediate molecule between DNA and proteins but has come to be seen as a dynamic and modifiable gene regulator. This new perspective on mRNA has led to rising interest in it and its presence in research into new therapeutic schemes. This paper, therefore, focuses on microRNAs (miRNAs), which are small noncoding RNAs that regulate posttranscriptional gene expression and play a vital role in the physiology and normative development of cardiovascular systems. This means they play an equally vital role in the development and progression of cardiovascular diseases. In recent years, multiple studies have pinpointed particular miRNA expression profiles as being associated with varying histological features of AF. These studies have been carried out in both animal models and AF patients. The emergence of miRNAs as biomarkers and their therapeutic potential in AF patients will be discussed in the body of this paper.

Small Molecules with Big Impacts on Cardiovascular Diseases

Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide. Although in recent years there has been a significant progress in the diagnosis, treatment, and prognosis of CVD, but due to their complex pathobiology, developing novel biomarkers and therapeutic interventions are still in need. MicroRNAs (miRNAs) are a fraction of non-coding RNAs that act as micro-regulators of gene expression. Mounting evidences over the last decade confirmed that microRNAs were deregulated in several CVDs and manipulating their expression could affect homeostasis, differentiation, and function of cardiovascular system. Here, we review the current knowledge concerning the roles of miRNAs in cardiovascular diseases with more details on cardiac remodeling, arrhythmias, and atherosclerosis. In addition, we discuss the latest findings on the potential therapeutic applications of miRNAs in cardiovascular diseases.

MicroRNA expression signatures of atrial fibrillation: The critical systematic review and bioinformatics analysis

Association between microRNA (miRNA) expression signatures and atrial fibrillation has been evaluated with inconsistent findings in different studies. This study aims to identify miRNAs that actually play vital role in pathophysiological process of atrial fibrillation and explore miRNA-targeted genes and the involved pathways. Relevant studies were retrieved from the electronic databases of Embase, Medline, and Cochrane Library to determine the miRNA expression profiles between atrial fibrillation subjects and non-atrial fibrillation controls. Robustness of results was assessed using sensitivity analysis. Subgroup analyses were performed based on species, miRNA detection method, sample source, and ethnicity. Quality assessment of studies was independently conducted according to QUADAS-2. Bioinformatics analysis was applied to explore the potential genes and pathways associated with atrial fibrillation, which were targeted by differentially expressed miRNAs. Form of pooled results was shown as log10 odds ratios (logORs) with 95% confidence intervals (CI), and random-effects model was used. In total, 40 articles involving 283 differentially expressed miRNAs were reported. And 51 significantly dysregulated miRNAs were identified in consistent direction, with 22 upregulated and 29 downregulated. Among above-mentioned miRNAs, miR-223-3p (logOR 6.473; P < 0.001) was the most upregulated, while miR-1-5p (logOR 7.290; P < 0.001) was the most downregulated. Subgroup analysis confirmed 53 significantly dysregulated miRNAs (21 upregulated and 32 downregulated) in cardiac tissue, with miRNA-1-5p and miRNA-223-3p being the most upregulated and downregulated miRNAs, respectively. Additionally, miR-328 and miR-1-5p were highly blood-specific, and miR-133 was animal-specific. In the detection method sub-groups, miRNA-29b and miRNA-223-3p were differentially expressed consistently. Four miRNAs, including miRNA-223-3p, miRNA-21, miRNA-328, and miRNA-1-5p, were consistently dysregulated in both Asian and non-Asian. Results of sensitivity analysis showed that 47 out of 51 (92.16%) miRNAs were dysregulated consistently. Totally, 51 consistently dysregulated miRNAs associated with atrial fibrillation were confirmed in this study. Five important miRNAs, including miR-29b, miR-328, miR-1-5p, miR-21, and miR-223-3p may act as potential biomarkers for atrial fibrillation.

Impact statement

Atrial fibrillation (AF) is considered as the most common arrhythmia, and it subsequently causes serious complications including thrombosis and heart failure that increase the social burden. The definite mechanisms underlying AF pathogenesis remain complicated and unclear. Many studies attempted to discover the transcriptomic changes using microarray technologies, and the present studies for this hot topic have assessed individual miRNAs profiles for AF. However, results of different articles are controversial and not each reported miRNA is actually associated with the pathogenesis of AF. The present systematic review and meta-analysis identified that 51 consistently dysregulated miRNAs were associated with AF. Of these miRNAs, five miRNAs (miRNA-1-5p, miRNA-328, miRNA-29b, miRNA-21, and miRNA-223-3p) may act as novel biomarkers for AF. The findings could offer a better description of the biological characteristics of miRNAs, meanwhile might serve as new target for the intervention and monitoring AF in future studies.

MicroRNA expression studies: challenge of selecting reliable reference controls for data normalization

Accurate determination of microRNA expression levels is a prerequisite in using these small non-coding RNA molecules as novel biomarkers in disease diagnosis and prognosis. Quantitative PCR is the method of choice for measuring the expression levels of microRNAs. However, a major obstacle that affects the reliability of results is the lack of validated reference controls for data normalization. Various non-coding RNAs have previously been used as reference controls, but their use may lead to variations and lack of comparability of microRNA data among the studies. Despite the growing number of studies investigating microRNA profiles to discriminate between healthy and disease stages, robust reference controls for data normalization have so far not been established. In the present article, we provide an overview of different reference controls used in various diseases, and highlight the urgent need for the identification of suitable reference controls to produce reliable data. Our analysis shows, among others, that RNU6 is not an ideal normalizer in studies using patient material from different diseases. Finally, our article tries to disclose the challenges to find a reference control which is uniformly and stably expressed across all body tissues, fluids, and diseases.

MicroRNAs: Emerging biomarkers for atrial fibrillation

Atrial fibrillation (AF) causes severe cardiac dysrhythmia among patients with cardiovascular diseases. AF increases the risk of stroke and heart failure and is a growing public health concern. AF is also associated with various disease conditions such as hypertension, coronary artery disease, aging, and diabetes mellitus. The mechanism underlying AF is not completely understood due to its complexity. However, experimental and clinical data have revealed that the prevalence of this disease is associated with atrial arrhythmogenic remodeling. Currently, there are no biomarkers that are available for the early diagnosis of AF. Several studies have proposed microRNAs (miRNAs) as useful biomarkers for the diagnosis of AF due to their stability and easy availability both in atrial tissue and circulating blood. miRNAs play an important role in the development of the heart. The dysregulation of miRNA expression is associated with cardiac remodeling. Genetic factors strongly contribute to the pathogenesis of AF. Recently, single nucleotide polymorphisms (SNPs) in various genes and miRNAs have been reported to be associated with AF. The aim of this review was to discuss the correlation between SNPs in miRNAs and AF, including those miRNAs that are commonly reported as potential biomarkers for AF.

Biomarkers in Atrial Fibrillation and Heart Failure

Atrial fibrillation (AF) is the most common sustained arrhythmia encountered in clinical practice and an important contributor to cardiovascular morbidity and mortality. Although the exact mechanisms behind AF are not completely elucidated, the underlying pathophysiological changes have been well described. Predisposal factors for AF include the older age, the increased left atrial size, the decreased left atrial function, the presence of heart failure and left ventricular systolic dysfunction and the presence of coronary heart disease or pulmonary or mitral valve disease. In addition to these factors, emerging evidence demonstrate that myocardial strain, fibrosis and inflammation, are associated with AF as well as the pathogenesis of the arrhythmia. The natruretic peptide system including Atrial Natriuretic Peptide (ANP), Brain Natriuretic Peptide (BNP) and C-type Natriuretic Peptide (CNP) is indicative of the level of myocardial strain which may predispose to AF. As a result, the aforementioned peptides are increased in AF patients. The levels of myocardial fibrosis biomarkers, such as ST2 and Galectin-3, are elevated suggesting atrial structural abnormalities, while the increased levels of CRP and Interleukin-6 supplement the inflammatory profile of AF patients. Emerging data for the aforementioned biomarkers are discussed in the present review.

Atria-selective antiarrhythmic drugs in need of alliance partners

Atria-selective antiarrhythmic drugs in need of alliance partners. Guideline-based treatment of atrial fibrillation (AF) comprises prevention of thromboembolism and stroke, as well as antiarrhythmic therapy by drugs, electrical rhythm conversion, ablation and surgical procedures. Conventional antiarrhythmic drugs are burdened with unwanted side effects including a propensity of triggering life-threatening ventricular fibrillation. In order to solve this therapeutic dilemma, 'atria-selective' antiarrhythmic drugs have been developed for the treatment of supraventricular arrhythmias. These drugs are designed to aim at atrial targets, taking advantage of differences in atrial and ventricular ion channel expression and function. However it is not clear, whether such drugs are sufficiently antiarrhythmic or whether they are in need of an alliance partner for clinical efficacy. Atria-selective Na⁺ channel blockers display fast dissociation kinetics and high binding affinity to inactivated channels. Compounds targeting atria-selective K⁺ channels include blockers of ultra rapid delayed rectifier (Kv1.5) or acetylcholine-activated inward rectifier K⁺ channels (Kir3.x), inward rectifying K⁺ channels (Kir2.x), Ca²⁺-activated K⁺ channels of small conductance (SK), weakly rectifying two-pore domain K⁺ channels (K_2P), and transient receptor potential channels (TRP). Despite good antiarrhythmic data from in-vitro and animal model experiments, clinical efficacy of atria-selective antiarrhythmic drugs remains to be demonstrated. In the present review we will briefly summarize the novel compounds and their proposed antiarrhythmic action. In addition, we will discuss the evidence for putative improvement of antiarrhythmic efficacy and potency by addressing multiple pathophysiologically relevant targets as possible alliance partners.

F-box protein-32 down-regulates small-conductance calcium-activated potassium channel 2 in diabetic mouse atria

Diabetes mellitus (DM) is an independent risk factor for atrial fibrillation, but the underlying ionic mechanism for this association remains unclear. We recently reported that expression of the small-conductance calcium-activated potassium channel 2 (SK2, encoded by KCCN2) in atria from diabetic mice is significantly down-regulated, resulting in reduced SK currents in atrial myocytes from these mice. We also reported that the level of SK2 mRNA expression is not reduced in DM atria but that the ubiquitin-proteasome system (UPS), a major mechanism of intracellular protein degradation, is activated in vascular smooth muscle cells in DM. This suggests a possible role of the UPS in reduced SK currents. To test this possibility, we examined the role of the UPS in atrial SK2 down-regulation in DM. We found that a muscle-specific E3 ligase, F-box protein 32 (FBXO-32, also called atrogin-1), was significantly up-regulated in diabetic mouse atria. Enhanced FBXO-32 expression in atrial cells significantly reduced SK2 protein expression, and siRNA-mediated FBXO-32 knockdown increased SK2 protein expression. Furthermore, co-transfection of SK2 with FBXO-32 complementary DNA in HEK293 cells significantly reduced SK2 expression, whereas co-transfection with atrogin-1ΔF complementary DNA (a nonfunctional FBXO-32 variant in which the F-box domain is deleted) did not have any effects on SK2. These results indicate that FBXO-32 contributes to SK2 down-regulation and that the F-box domain is essential for FBXO-32 function. In conclusion, DM-induced SK2 channel down-regulation appears to be due to an FBXO-32-dependent increase in UPS-mediated SK2 protein degradation.