Targeting miR-423-5p Reverses Exercise Training-Induced HCN4 Channel Remodeling and Sinus Bradycardia

Does Long-Term Sport Practice Facilitate the Development of Idiopathic Bradycardia Requiring Early Pacemaker Implantation During the Course of Life?

Background: Sinus bradycardia and first-/second-degree atrioventricular (AV) block in athletes are traditionally considered secondary to increased vagal tone and therefore reversible. However, recent studies have suggested that they may persist even after the cessation of physical activity, and combined with the effects of aging, lead to the earlier onset of clinically significant bradyarrhythmias. Methods: We evaluated the correlation between lifetime sport practice and the age of the onset of premature (≤70 years old) idiopathic sinoatrial node or AV node dysfunction requiring pacemaker (PM) implantation. Results: Of the 1316 patients followed up with at our PM clinic in 2024, we included 79 (6%) who received a PM when they were ≤70 years old for bradyarrhythmias in the absence of secondary causes. Nineteen (24%) had engaged in at least 6 h of sports/week for ≥20 years and were classified as former athletes. For comparison, former athletes who received a PM for idiopathic bradycardia at >70 years old were 6% (p < 0.001). In the group ≤70 years old, the average age of PM implantation was 62.8 years in non-athletes versus 57.9 years in former athletes (p = 0.03). The main reason for PM implantation was AV block in both subgroups. Among former athletes, the correlation between the lifetime volume of sports activity and the age of PM implantation reached borderline statistical significance (p = 0.08). Echocardiography at the time of implant did not reveal significant differences between former athletes and non-athletes. Conclusions: In a cohort of patients who received a PM for bradyarrhythmia before the age of 70 years old in the absence of secondary causes, former athletes were implanted on average ≈5 years before non-athletes. This may suggest a contributing role of cumulative sports activity volume in the development of idiopathic sinus/AV node dysfunction.

Exosomal mir-126-3p derived from endothelial cells induces ion channel dysfunction by targeting RGS3 signaling in cardiomyocytes: a novel mechanism in Takotsubo cardiomyopathy

BACKGROUND

Takotsubo cardiomyopathy (TTC) is marked by an acute, transient, and reversible left ventricular systolic dysfunction triggered by stress, with endothelial dysfunction being one of its pathophysiological mechanisms. However, the precise molecular mechanism underlying the interaction between endothelial cells and cardiomyocytes during TTC remains unclear. This study reveals that exosomal miRNAs derived from endothelial cells exposed to catecholamine contribute to ion channel dysfunction in the setting of TTC.

METHODS

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were treated with epinephrine (Epi) or exosomes (Exo) from Epi-treated human cardiac microvascular endothelial cells (HCMECs) or Exo derived from HCMECs transfected with miR-126-3p. The immunofluorescence staining, flow cytometry, qPCR, single-cell contraction, intracellular calcium transients, patch-clamp, dual luciferase reporter assay and western blot were performed for the study.

RESULTS

Modeling TTC with high doses of epinephrine (Epi) treatment in hiPSC-CMs shows suppression of depolarization velocity (Vmax), prolongation of action potential duration (APD), and induction of arrhythmic events. Exo derived from HCMECs treated with Epi (Epi-exo) mimicked or enhanced the effects of Epi. Epi exposure led to elevated levels of miR-126-3p in both HCMECs and their exosomes. Exo enriched with miR-126-3p demonstrated similar effects as Epi-exo, establishing the crucial role of miR-126-3p in the mechanism of Epi-exo. Dual luciferase reporter assay coupled with gene mutation techniques identified that miR-126-3p was found to target the regulator of G-protein signaling 3 (RGS3) gene. Western blot and qPCR analyses confirmed that miR-126-3p-mimic reduced RGS3 expression in both HCMECs and hiPSC-CMs, indicating miR-126-3p inhibits RGS3 signaling. Additionally, miR-126-3p levels were significantly higher in the serum of TTC patients compared to healthy controls and patients who had recovered from TTC.

CONCLUSIONS

Our study is the first to reveal that exosomal miR-126-3p, originating from endothelial cells, contributes to ion channel dysfunction by regulating RGS3 signaling in cardiomyocytes. These findings provide new perspectives on the pathogenesis of TTC and suggest potential therapeutic targets for treatment.

Extracellular Vesicle-Derived Non-Coding RNAs: Key Mediators in Remodelling Heart Failure

Heart failure (HF), a syndrome of persistent development of cardiac insufficiency due to various heart diseases, is a serious and lethal disease for which specific curative therapies are lacking and poses a severe burden on all aspects of global public health. Extracellular vesicles (EVs) are essential mediators of intercellular and interorgan communication, and are enclosed nanoscale vesicles carrying biomolecules such as RNA, DNA, and proteins. Recent studies have showed, among other things, that non-coding RNAs (ncRNAs), especially microRNAs (miRNAs), long ncRNAs (lncRNA), and circular RNAs (circRNAs) can be selectively sorted into EVs and modulate the pathophysiological processes of HF in recipient cells, acting on both healthy and diseased hearts, which makes them promising targets for the diagnosis and therapy of HF. This review aims to explore the mechanism of action of EV-ncRNAs in heart failure, with emphasis on the potential use of differentially expressed miRNAs and circRNAs as biomarkers of cardiovascular disease, and recent research advances in the diagnosis and treatment of heart failure. Finally, we focus on summarising the latest advances and challenges in engineering EVs for HF, providing novel concepts for the diagnosis and treatment of heart failure.

Symptomatic bradyarrhythmias in the athlete-Underlying mechanisms and treatments

Bradyarrhythmias including sinus bradycardia and atrioventricular (AV) block are frequently encountered in endurance athletes especially at night. While these are well tolerated by the young athlete, there is evidence that generally from the fifth decade of life onward, such arrhythmias can degenerate into pathological symptomatic bradycardia requiring pacemaker therapy. For many years, athletic bradycardia and AV block have been attributed to high vagal tone, but work from our group has questioned this widely held assumption and demonstrated a role for intrinsic electrophysiological remodeling of the sinus node and the AV node. In this article, we argue that bradyarrhythmias in the veteran athlete arise from the cumulative effects of exercise training, the circadian rhythm and aging on the electrical activity of the nodes. We consider contemporary strategies for the treatment of symptomatic bradyarrhythmias in athletes and highlight potential therapies resulting from our evolving mechanistic understanding of this phenomenon.

Cardiac conduction diseases: understanding the molecular mechanisms to uncover targets for future treatments

INTRODUCTION

The cardiac conduction system (CCS) is crucial for maintaining adequate cardiac frequency at rest and modulation during exercise. Furthermore, the atrioventricular node and His-Purkinje system are essential for maintaining atrioventricular and interventricular synchrony and consequently maintaining an adequate cardiac output.

AREAS COVERED

In this review article, we examine the anatomy, physiology, and pathophysiology of the CCS. We then discuss in detail the most common genetic mutations and the molecular mechanisms of cardiac conduction disease (CCD) and provide our perspectives on future research and therapeutic opportunities in this field.

EXPERT OPINION

Significant advancement has been made in understanding the molecular mechanisms of CCD, including the recognition of the heterogeneous signaling at the subcellular levels of sinoatrial node, the involvement of inflammatory and autoimmune mechanisms, and the potential impact of epigenetic regulations on CCD. However, the current treatment of CCD manifested as bradycardia still relies primarily on cardiovascular implantable electronic devices (CIEDs). On the other hand, an If specific inhibitor was developed to treat inappropriate sinus tachycardia and sinus tachycardia in heart failure patients with reduced ejection fraction. More work is needed to translate current knowledge into pharmacologic or genetic interventions for the management of CCDs.

Sports activities and cardiovascular system change

Sports activity is generally considered to be beneficial to health. The World Health Organization (WHO) recommends physical activity as part of a healthy lifestyle. Sports activities significantly affect the cardiovascular system. A number of studies show that they significantly reduce the risk of cardiovascular disease as well as decrease cardiovascular mortality. This review discusses changes in various cardiovascular parameters in athletes - vagotonia/bradycardia, hypertrophy of heart, ECG changes, blood pressure, and variability of cardiovascular parameters. Because of its relationship to the cardiovascular system, VO2max, which is widely used as an indicator of cardiorespiratory fitness, is also discussed. The review concludes with a discussion of reactive oxygen species (ROS) and oxidative stress, particularly in relation to changes in the cardiovascular system in athletes. The review appropriately summarizes the above issues and points out some new implications.

miR-423 sponged by lncRNA NORHA inhibits granulosa cell apoptosis

BACKGROUND

Atresia and degeneration, a follicular developmental fate that reduces female fertility and is triggered by granulosa cell (GC) apoptosis, have been induced by dozens of miRNAs. Here, we report a miRNA, miR-423, that inhibits the initiation of follicular atresia (FA), and early apoptosis of GCs.

RESULTS

We showed that miR-423 was down-regulated during sow FA, and its levels in follicles were negatively correlated with the GC density and the P4/E2 ratio in the follicular fluid in vivo. The in vitro gain-of-function experiments revealed that miR-423 suppresses cell apoptosis, especially early apoptosis in GCs. Mechanically speaking, the miR-423 targets and interacts with the 3'-UTR of the porcine SMAD7 gene, which encodes an apoptosis-inducing factor in GCs, and represses its expression and pro-apoptotic function. Interestingly, FA and the GC apoptosis-related lncRNA NORHA was demonstrated as a ceRNA of miR-423. Additionally, we showed that a single base deletion/insertion in the miR-423 promoter is significantly associated with the number of stillbirths (NSB) trait of sows.

CONCLUSION

These results demonstrate that miR-423 is a small molecule for inhibiting FA initiation and GC early apoptosis, suggesting that treating with miR-423 may be a novel approach for inhibiting FA initiation and improving female fertility.

Regulation of Cervical Cancer Development by a Novel Circ_0000212/miR-1236-3p/GREM1 ceRNA Crosstalk

Circular RNAs (circRNAs) possess important functions in cervical carcinogenesis by operating as competing endogenous RNAs (ceRNAs). Our preliminary bioinformatics predicted the potential circ_0000212/microRNA (miR)-1236-3p/gremlin 1 (GREM1) ceRNA crosstalk. Thus, we further elucidated whether the novel ceRNA crosstalk can participate in cervical cancer development. Circ_0000212, miR-1236-3p and GREM1 were quantified by real-time quantitative polymerase chain reaction (qPCR) and immunoblotting. 5-ethynyl-2'-deoxyuridine (EdU) assay, flow cytometry, and tube formation assay were performed to assess cell proliferation, apoptosis and tube formation, respectively. Transwell assay was used to detect cell migration and invasion. Mouse xenografts were established to evaluate the role of circ_0000212 in vivo. Dual-luciferase reporter assay was performed to verify the direct relationship between miR-1236-3p and circ_0000212 or GREM1. Circ_0000212 expression was elevated in human cervical cancer. Silencing of endogenous circ_0000212 hindered cancer cell proliferation, motility and invasion and induced apoptosis, as well as diminished the tube formation of human umbilical vein endothelial cells (HUVECs) in vitro. Circ_0000212 silencing also weakened tumor growth in vivo. Mechanistically, circ_0000212 directly bound to miR-1236-3p, and downregulation of miR-1236-3p reversed these effects of circ_0000212 silencing on cell malignant phenotypes and HUVEC tube formation. GREM1 was a direct miR-1236-3p target, and its expression was regulated by circ_0000212 through miR-1236-3p. Moreover, miR-1236-3p upregulation impeded cancer cell malignant phenotypes and HUVEC tube formation by targeting GREM1. Our findings identify a novel ceRNA regulatory network, circ_0000212/miR-1236-3p/GREM1 axis, in cervical carcinogenesis, and provide potential targets that can be explored for therapeutic interventions.

MicroRNAs: Midfielders of Cardiac Health, Disease and Treatment

MicroRNAs (miRNAs) are a class of small non-coding RNA molecules that play a role in post-transcriptional gene regulation. It is generally accepted that their main mechanism of action is the negative regulation of gene expression, through binding to specific regions in messenger RNA (mRNA) and repressing protein translation. By interrupting protein synthesis, miRNAs can effectively turn genes off and influence many basic processes in the body, such as developmental and apoptotic behaviours of cells and cardiac organogenesis. Their importance is highlighted by inhibiting or overexpressing certain miRNAs, which will be discussed in the context of coronary artery disease, atrial fibrillation, bradycardia, and heart failure. Dysregulated levels of miRNAs in the body can exacerbate or alleviate existing disease, and their omnipresence in the body makes them reliable as quantifiable markers of disease. This review aims to provide a summary of miRNAs as biomarkers and their interactions with targets that affect cardiac health, and intersperse it with current therapeutic knowledge. It intends to succinctly inform on these topics and guide readers toward more comprehensive works if they wish to explore further through a wide-ranging citation list.

Immediate and sustained increases in the activity of vagal preganglionic neurons during exercise and after exercise training

AIMS

The brain controls the heart by dynamic recruitment and withdrawal of cardiac parasympathetic (vagal) and sympathetic activity. Autonomic control is essential for the development of cardiovascular responses during exercise, however, the patterns of changes in the activity of the two autonomic limbs, and their functional interactions in orchestrating physiological responses during exercise, are not fully understood. The aim of this study was to characterize changes in vagal parasympathetic drive in response to exercise and exercise training by directly recording the electrical activity of vagal preganglionic neurons in experimental animals (rats).

METHODS AND RESULTS

Single unit recordings were made using carbon-fibre microelectrodes from the populations of vagal preganglionic neurons of the nucleus ambiguus (NA) and the dorsal vagal motor nucleus of the brainstem. It was found that (i) vagal preganglionic neurons of the NA and the dorsal vagal motor nucleus are strongly activated during bouts of acute exercise, and (ii) exercise training markedly increases the resting activity of both populations of vagal preganglionic neurons and augments the excitatory responses of NA neurons during exercise.

CONCLUSIONS

These data show that central vagal drive increases during exercise and provide the first direct neurophysiological evidence that exercise training increases vagal tone. The data argue against the notion of exercise-induced central vagal withdrawal during exercise. We propose that robust increases in the activity of vagal preganglionic neurons during bouts of exercise underlie activity-dependent plasticity, leading to higher resting vagal tone that confers multiple health benefits associated with regular exercise.

Long-Term Training Increases Atrial Fibrillation Sustainability in Standardbred Racehorses

Atrial fibrillation (AF) is more prevalent in athletes, and currently, the mechanisms are not fully understood. Atrial fibrillation inducibility and stability was investigated in trained and untrained Standardbred racehorses. The horses underwent echocardiography for evaluation of atrial size. High-density mapping during AF was performed, and the presence of structural remodeling, as well as the expression of inflammatory and pro-inflammatory markers in the atria, was studied. Atrial fibrillation sustained significantly longer after tachypacing in the trained horses, whereas no difference in AF inducibility was found. The untrained horses displayed a significant difference in the AF complexity when comparing right and left atria, whereas such difference was not observed in the trained animals. No evidence of increased structural remodeling or inflammation could be identified. Left atrial dimensions were not significantly increased. The increased AF sustainability in trained horses was not related to fibrosis or inflammation as seen in other animal exercise models.

Emerging Signaling Regulation of Sinoatrial Node Dysfunction

PURPOSE OF REVIEW

The sinoatrial node (SAN), the natural pacemaker of the heart, is responsible for generating electrical impulses and initiating each heartbeat. Sinoatrial node dysfunction (SND) causes various arrhythmias such as sinus arrest, SAN block, and tachycardia/bradycardia syndrome. Unraveling the underlying mechanisms of SND is of paramount importance in the pursuit of developing effective therapeutic strategies for patients with SND. This review provides a concise summary of the most recent progress in the signaling regulation of SND.

RECENT FINDINGS

Recent studies indicate that SND can be caused by abnormal intercellular and intracellular signaling, various forms of heart failure (HF), and diabetes. These discoveries provide novel insights into the underlying mechanisms SND, advancing our understanding of its pathogenesis. SND can cause severe cardiac arrhythmias associated with syncope and an increased risk of sudden death. In addition to ion channels, the SAN is susceptible to the influence of various signalings including Hippo, AMP-activated protein kinase (AMPK), mechanical force, and natriuretic peptide receptors. New cellular and molecular mechanisms related to SND are also deciphered in systemic diseases such as HF and diabetes. Progress in these studies contributes to the development of potential therapeutics for SND.

Identification of Circular RNA Circ_0003256 as a Novel Player in Pediatric Acute Myeloid Leukemia

BACKGROUND

Aberrant expression of circular RNAs (circRNAs) is tightly associated with the pathogenesis of human cancers, including pediatric acute myeloid leukemia (AML). In this report, we sought to define the precise action of circ_0003256 in the pathogenesis of pediatric AML.

MATERIALS AND METHODS

Circ_0003256, microRNA (miR)-582-3p, and protein kinase cAMP-activated catalytic subunit beta (PRKACB) were quantified by quantitative real-time polymerase chain reaction and Western blot. Cell proliferation, cycle distribution, and apoptosis were estimated by MTT, 5-ethynyl-2'-deoxyuridine, and flow cytometry assays, respectively. Direct relationships among circ_0003256, miR-582-3p, and PRKACB were verified by a dual-luciferase reporter and RNA pull-down assays.

RESULTS

Our data indicated that circ_0003256 was highly expressed in pediatric AML patients and cells. Suppression of circ_0003256 hindered cell proliferation and promoted apoptosis in THP-1 and MV4-11 cells. Mechanistically, circ_0003256 contained functional binding sites for miR-582-3p, and circ_0003256 suppression influenced cell behaviors by upregulating miR-582-3p. MiR-582-3p directly targeted and inhibited PRKACB and the inhibition of PRKACB phenocopied miR-582-3p overexpression in regulating cell functional behaviors. Moreover, circ_0003256 involved the posttranscriptional regulation of PRKACB through miR-582-3p.

CONCLUSION

Our findings identify that suppression of circ_0003256 impedes the malignant behaviors of pediatric AML cells by regulating PRKACB expression by competing for shared miR-582-3p.

Pacemaker activity and ion channels in the sinoatrial node cells: MicroRNAs and arrhythmia

The primary pacemaking activity of the heart is determined by a spontaneous action potential (AP) within sinoatrial node (SAN) cells. This unique AP generation relies on two mechanisms: membrane clocks and calcium clocks. Nonhomologous arrhythmias are caused by several functional and structural changes in the myocardium. MicroRNAs (miRNAs) are essential regulators of gene expression in cardiomyocytes. These miRNAs play a vital role in regulating the stability of cardiac conduction and in the remodeling process that leads to arrhythmias. Although it remains unclear how miRNAs regulate the expression and function of ion channels in the heart, these regulatory mechanisms may support the development of emerging therapies. This study discusses the spread and generation of AP in the SAN as well as the regulation of miRNAs and individual ion channels. Arrhythmogenicity studies on ion channels will provide a research basis for miRNA modulation as a new therapeutic target.

Micro RNA-411 Expression Improves Cardiac Phenotype Following Myocardial Infarction in Mice

Induction of endogenous regenerative capacity has emerged as one promising approach to repair damaged hearts following myocardial infarction (MI). Re-expression of factors that are exclusively expressed during embryonic development may reactivate the ability of adult cardiomyocytes to regenerate. Here, we identified miR-411 as a potent inducer of cardiomyocyte proliferation. Overexpression of miR-411 in the heart significantly increased cardiomyocyte proliferation and survival in a model MI. We found that miR-411 enhances the activity of YAP, the main downstream effector of the Hippo pathway, in cardiomyocytes. In conclusion, miR-411 induces cardiomyocyte regeneration and improves cardiac function post-MI likely by modulating the Hippo/YAP pathway.

MicroRNA miR-133a-3p Facilitates Adrenergic Proarrhythmic Ectopy in Rat Pulmonary Vein Myocardium by Increasing cAMP Content

Cardiac-specific microRNA miR-133a-3p modulates adrenergic signaling. Adrenergic receptors and their intracellular pathways are the key players in proarrhythmic ectopy derived from the myocardial sleeves of the pulmonary veins. We studied the effect of miR-133a-3p on ectopy induced by norepinephrine in myocardial tissue of rat pulmonary veins. Using microelectrode technique, we revealed facilitation of proarrhythmic pattern of spontaneous bursts of action potentials induced by norepinephrine in tissue preparations of the pulmonary veins isolated from rats in 24 h after injection of a transfection mixture containing miR-133a-3p (1 mg/kg) in vivo. According to ELISA data, the cAMP level in the pulmonary vein myocardium of rats receiving miR-133a-3p was 2-fold higher than in control animals. Bioinformatic analysis showed that mRNA of protein phosphatases and some phosphodiesterases are most probable targets of miR-133a-3p. The proarrhythmic effect of miR-133a-3p can be related to inhibition of the expression of phosphodiesterases accompanied by cAMP accumulation and increased intracellular β-adrenergic signaling.

A case report of profound atrioventricular block in an endurance athlete: how far do you go?

Background

Athletes presenting with 1st-degree atrioventricular block (AVB) on 12-lead electrocardiogram (ECG) may present a diagnostic conundrum, especially when significantly prolonged and associated with higher degrees of block. A pragmatic stepwise approach to the evaluation of these patients is, therefore, crucial.

Case summary

A 19-year-old waterpolo player was referred for assessment of a 1st-degree heart block and one isolated episode of syncope. All other cardiac investigations were within normal limits except for a 24-h ambulatory ECG which showed Mobitz 1 AVB and episodes of 2:1 block occurring in the context of Wenchebach. An electrophysiological study (EPS) was performed which effectively excluded infranodal conductive tissue disease, confirming physiological intranodal block.

Discussion

The increase in vagal tone is one of the physiological adaptations to an increased demand in cardiac output in athletes, which explains the presence of 1st-degree AVB in up to 7.5% of athletes. The presence of 2:1 AVB on 24 h ECG raises doubts whether the 1st-degree AVB on resting ECG is pathological or physiological, especially considering this particular patient had suffered an episode of syncope. When this diagnostic uncertainty persists despite non-invasive investigations, including cardiopulmonary exercise testing, invasive EPS may be required to assess the refractoriness of the AV node and at what level within the cardiac conductive system block occurs. The electrophysiological study can effectively rule out infranodal disease by confirming physiological intranodal block using incremental atrial pacing.

Electrocardiographic characteristics of trained and untrained standardbred racehorses

Background

Long‐term exercise induces cardiac remodeling that potentially influences the electrical properties of the heart.

Hypothesis/objectives

We assessed whether training alters cardiac conduction in Standardbred racehorses.

Animals

Two hundred one trained and 52 untrained Standardbred horses.

Methods

Cross‐sectional study. Resting ECG recordings were analyzed to assess heart rate (HR) along with standard ECG parameters and for identification of atrial and ventricular arrhythmias. An electrophysiological study was performed in 13 horses assessing the effect of training on sinoatrial (SA) and atrioventricular (AV) nodal function by sinus node recovery time (SNRT) and His signal recordings. Age and sex adjustments were implemented in multiple and logistic regression models for comparison.

Results

Resting HR in beats per minute (bpm) was lower in trained vs untrained horses (mean, 30.8 ± 2.6 bpm vs 32.9 ± 4.2 bpm; P = .001). Trained horses more often displayed second‐degree atrioventricular block (2AVB; odds ratio, 2.59; P = .04). No difference in SNRT was found between groups (n = 13). Mean P‐A, A‐H, and H‐V intervals were 71 ± 20, 209 ± 41, and 134 ± 41 ms, respectively (n = 7). We did not detect a training effect on AV‐nodal conduction intervals. His signals were present in 1 horse during 2AVB with varying H‐V interval preceding a blocked beat.

Conclusions and Clinical Importance

We identified decreased HR and increased frequency of 2AVB in trained horses. In 5 of 7 horses, His signal recordings had variable H‐V intervals within each individual horse, providing novel insight into AV conduction in horses.

MicroRNAs in cardiovascular diseases

Cardiovascular diseases (CVDs) are the leading causes of death and disability worldwide, despite the wide diversity of molecular targets identified and the development of therapeutic methods. MicroRNAs (miRNAs) are a class of small (about 22 nucleotides) non-coding RNAs (ncRNAs) that negatively regulate gene expression at the post-transcriptional level in the cytoplasm and play complicated roles in different CVDs. While miRNA overexpression in one type of cell protects against heart disease, it promotes cardiac dysfunction in another type of cardiac cell. Moreover, recent studies have shown that, apart from cytosolic miRNAs, subcellular miRNAs such as mitochondria- and nucleus-localized miRNAs are dysregulated in CVDs. However, the functional properties of cellular- and subcellular-localized miRNAs have not been well characterized. In this review article, by carefully revisiting animal-based miRNA studies in CVDs, we will address the regulation and functional properties of miRNAs in various CVDs. Specifically, the cell-cell crosstalk and subcellular perspective of miRNAs are highlighted. We will provide the background for attractive molecular targets that might be useful in preventing the progression of CVDs and heart failure (HF) as well as insights for future studies.

Circular RNA circ_0002360 regulates the Taxol resistance and malignant behaviors of Taxol-resistant non-small cell lung cancer cells by microRNA-585-3p-dependent modulation of G protein regulated inducer of neurite outgrowth 1

Drug resistance has become the major obstacle for the treatment of non-small cell lung cancer (NSCLC). Circular RNAs (circRNAs) are tightly linked to the development of drug resistance of NSCLC. Herein, we tested the function of circ_0002360 in the Taxol resistance of NSCLC. Circ_0002360, microRNA (miR)-585-3p and G protein regulated inducer of neurite outgrowth 1 (GPRIN1) were quantified by quantitative real-time PCR (qRT-PCR). To identify the circular structure of circ_0002360, RNase R digestion was applied. To detect cell proliferation, colony formation and 5-ethynyl-2’-deoxyuridine (EdU) assays were used. For assessment of cell apoptosis, flow cytometry was adopted. For motility and invasion analyses, transwell assay was employed. Our data showed that circ_0002360 was mainly located in the cytoplasm and was highly expressed in the Taxol-resistant NSCLC. Silencing of circ_0002360 inhibited cell Taxol resistance, proliferation, motility, and invasiveness and induced apoptosis in vitro. MiR-585-3p was underexpressed in Taxol-resistant NSCLC and was targeted by circ_0002360. MiR-585-3p knockdown alleviated the influence of circ_0002360 silence on Taxol-resistant cells. GPRIN1 was directly targeted by miR-585-3p. The influence of miR-585-3p on cell Taxol resistance and functional behaviors was reversed by GPRIN1 overexpression. Moreover, circ_0002360 modulated GPRIN1 through miR-585-3p. Additionally, silencing of circ_0002360 weakened the growth of xenografts in vivo. Our study demonstrated that silencing of circ_0002360 enhanced the Taxol sensitivity and suppressed the malignant behaviors of Taxol-resistant NSCLC cells by miR-585-3p/GPRIN1 axis, providing novel targets for improving the anti-tumor efficacy of Taxol in NSCLC.

Young endurance training starting age in non-elite athletes is associated with higher proximal aortic distensibility

Objective

Decreased proximal aortic distensibility (AD) is known to significantly predict all-cause mortality and cardiovascular events among individuals without overt cardiovascular disease. This cross-sectional study investigated the association of endurance training (ET) parameters, namely, ET starting age, ET years and yearly ET volume with AD in non-elite endurance athletes.

Methods

Healthy, normotensive, male Caucasian participants of a 10-mile race were assessed with a 2D echocardiogram and comprehensive interview. Ascending aortic diameters were measured simultaneously with pulse pressure. Aortic strain, AD and aortic stiffness index were calculated. Predictors of AD were investigated among training parameters by linear regression models corrected for age, resting heart rate, stroke volume index and mean blood pressure.

Results

Ninety-two of 121 athletes (aged 42±8 years) had sufficient echocardiogram quality and were used for analysis. ET starting age (range 6–52 years) and years of ET (range 2–46 years) were highly collinear and used in two separate models for AD. Significant factors for AD were ET starting age, 10-mile race time and resting heart rate in model I, and age, years of ET, 10-mile race time and heart rate in model II (all p<0.01).

Conclusions

In our cohort of healthy, non-elite, middle-aged runners, AD was significantly higher in athletes with younger ET starting age or more years of ET (in the model adjusted for confounders). In the model with years of ET, age had a negative contribution to AD, suggesting that with older age, the benefit of more years of ET on AD decreased. Future studies assessing the effect of exercise training on arterial properties should include training starting age.

Multilayer control of cardiac electrophysiology by microRNAs

The electrophysiological properties of the heart include cardiac automaticity, excitation (i.e., depolarization and repolarization of action potential) of individual cardiomyocytes, and highly coordinated electrical propagation through the whole heart. An abnormality in any of these properties can cause arrhythmias. MicroRNAs (miRs) have been recognized as essential regulators of gene expression through the conventional RNA interference (RNAi) mechanism and are involved in a variety of biological events. Recent evidence has demonstrated that miRs regulate the electrophysiology of the heart through fine regulation by the conventional RNAi mechanism of the expression of ion channels, transporters, intracellular Ca²⁺-handling proteins, and other relevant factors. Recently, a direct interaction between miRs and ion channels has also been reported in the heart, revealing a biophysical modulation by miRs of cardiac electrophysiology. These advanced discoveries suggest that miR controls cardiac electrophysiology through two distinct mechanisms: immediate action through biophysical modulation and long-term conventional RNAi regulation. Here, we review the recent research progress and summarize the current understanding of how miR manipulates the function of ion channels to maintain the homeostasis of cardiac electrophysiology.

Identification of evodiamine as a suppressor of prostate cancer progression by reducing AR transcriptional activity via targeting Src

Evodiamine (EVO) is a bioactive alkaloid that exerts antitumor activity in various cancers, including prostate cancer (PCa). In this paper, we further investigated the molecular mechanisms underlying the anti-PCa effect of evodiamine. In the present study, cell proliferation, colony formation, migration, and invasion were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), colony formation, and transwell assays, respectively. Animal studies were used to evaluate the effect of evodiamine on the tumorigenicity of LNCaP cells in vivo. The expression levels of steroid receptor coactivator (Src), androgene receptor (AR), and prostate-specific antigen (PSA) were detected by western blot, quantitative real-time PCR (qRT-PCR) or ELISA assay. Association between Src and AR was examined by Co-Immunoprecipitation (CoIP). The impact of evodiamine on AR-mediated transcriptional activity was confirmed by dual-luciferase reporter assay. The results showed that evodiamine reduced LNCaP and 22Rv1 cell proliferation, colony formation, migration, and invasion induced by dihydrotestosterone (DHT) in vitro, as well as diminished tumor growth in vivo. Mechanistically, evodiamine directly targeted Src and reduced DHT-induced Src activation. Moreover, the restoration of Src activation abolished evodiamine-mediated suppression of proliferation, migration, and invasion of DHT-treated LNCaP and 22Rv1 cells. Furthermore, evodiamine inhibited DHT-induced AR transcriptional activity through targeting Src. As a conclusion, our findings demonstrate the antitumor property of evodiamine in PCa by blocking AR transcriptional activity through targeting Src and provide a rationale for developing evodiamine as a promising antitumor agent against PCa.

The novel circ_0084904/miR-802/MAL2 axis promotes the development of cervical cancer

Circular RNAs (circRNAs) have been identified as critical regulators in human cancers, including cervical cancer (CC). However, the precise action of circ_0084904 in cervical carcinogenesis remains to be elucidated. The levels of circ_0084904, microRNA (miR)-802, and Mal, T cell differentiation protein 2 (MAL2) were checked by quantitative real-time PCR (qRT-PCR) or western blot. Ribonuclease R (RNase R) and subcellular localization assays were used to detect the stability and localization of circ_0084904, respectively. Cell colony formation ability was assessed by colony formation assay. Cell cycle and apoptosis were detected by flow cytometry. Cell migration and invasion abilities were gauged by transwell assay. Dual-luciferase reporter and RNA immunoprecipitation (RIP) assays were applied to determine the direct relationship between miR-802 and circ_0084904 or MAL2. The xenograft experiments were performed to evaluate the role of circ_0084904 in tumor growth in vivo. Circ_0084904 was markedly up-regulated in CC tissues and cell lines. Silencing endogenous circ_0084904 impeded cell colony formation, cell cycle progression, migration, invasion, epithelial-mesenchymal transition (EMT), and promoted apoptosis in vitro, as well as diminished tumor growth in vivo. Mechanistically, circ_0084904 targeted miR-802, and the effects of circ_0084904 silencing were mediated by miR-802. MAL2 was directly targeted and inhibited by miR-802, and MAL2 was a functional target of miR-802. Moreover, circ_0084904 modulated MAL2 expression via miR-802. Our study identified circ_0084904 as a novel oncogenic driver in CC depending on the modulation of the miR-802/MAL2 axis, establishing the notion that silencing of circ_0084904 might represent a promising targeted therapy for CC.

Recommendations for participation in leisure-time physical activity and competitive sports in patients with arrhythmias and potentially arrhythmogenic conditions: Part 1: Supraventricular arrhythmias. A position statement of the Section of Sports Cardiology and Exercise from the European Association of Preventive Cardiology (EAPC) and the European Heart Rhythm Association (EHRA), both associations of the European Society of Cardiology

Symptoms attributable to arrhythmias are frequently encountered in clinical practice. Cardiologists and sport physicians are required to identify high-risk individuals harbouring such conditions and provide appropriate advice regarding participation in regular exercise programmes and competitive sport. The three aspects that need to be considered are: (a) the risk of life-threatening arrhythmias by participating in sports; (b) control of symptoms due to arrhythmias that are not life-threatening but may hamper performance and/or reduce the quality of life; and (c) the impact of sports on the natural progression of the underlying arrhythmogenic condition. In many cases, there is no unequivocal answer to each aspect and therefore an open discussion with the athlete is necessary, in order to reach a balanced decision. In 2006 the Sports Cardiology and Exercise Section of the European Association of Preventive Cardiology published recommendations for participation in leisure-time physical activity and competitive sport in individuals with arrhythmias and potentially arrhythmogenic conditions. More than a decade on, these recommendations are partly obsolete given the evolving knowledge of the diagnosis, management and treatment of these conditions. The present document presents a combined effort by the Sports Cardiology and Exercise Section of the European Association of Preventive Cardiology and the European Heart Rhythm Association to offer a comprehensive overview of the most updated recommendations for practising cardiologists and sport physicians managing athletes with supraventricular arrhythmias, and provides pragmatic advice for safe participation in recreational physical activities, as well as competitive sport at amateur and professional level. A companion text on recommendations in athletes with ventricular arrhythmias, inherited arrhythmogenic conditions, pacemakers and implantable defibrillators is published as Part 2 in Europace.

Plasma Exosomal Mir-423-5p Is Involved in the Occurrence and Development of Bicuspid Aortopathy via TGF-β/SMAD2 Pathway

OBJECTIVES

Patients with bicuspid aortic valve (BAV) are at increased risk for ascending aortic dilation (AAD). Our study was aimed at systemically analyzing the expression profile and mechanism of circulating plasma exosomal microRNAs (miRNAs) related to BAV and AAD.

METHODS

We isolated plasma exosomes from BAV patients (n=19), BAV patients with AAD (BAVAD, n=26), and healthy tricuspid aortic valve individuals with low cardiovascular risk (TAVnon, n=16). We applied a small RNA sequencing approach to identify the specific plasma exosomal miRNAs associated with BAV (n=8) and BAVAD (n=10) patients compared with healthy TAVnon (n=6) individuals. The candidate differentially expressed (DE) miRNAs were selected and validated by RT-qPCR in the remaining samples. GO and KEGG pathway enrichment analyses were performed to illustrate the functions of target genes. Western blot analysis and luciferase reporter assay were conducted in human aortic vascular smooth muscle cells (VSMCs) to verify the results of target gene prediction in vitro. Results: The expression levels of three up-regulated (miR-151a-3p, miR-423-5p, and miR-361-3p) and two down-regulated (miR-16-5p and miR-15a-5p) exosomal miRNAs were significantly altered in BAV disease. Additionally, miR-423-5p could be functionally involved in the occurrence and development of BAV and its complication BAVAD by regulating TGF-β signaling. miR-423-5p could target to SMAD2 and decreased the protein levels of SMAD2 and P-SMAD2.

CONCLUSION

Plasma exosomal miR-423-5p regulated TGF-β signaling by targeting SMAD2, thus exerting functions in the occurrence and development of BAV disease and its complication bicuspid aortopathy.

Circular RNA circ_ASAP2 regulates drug sensitivity and functional behaviors of cisplatin-resistant gastric cancer cells by the miR-330-3p/NT5E axis

This study aims to explore the biological actions of circular RNA (circRNA) ArfGAP with SH3 domain, ankyrin repeat and PH domain 2 (circ_ASAP2, circ_0006089) in cisplatin (DDP) resistance of gastric cancer. Circ_ASAP2, ecto-5'-nucleotidase (NT5E) and miR-330-3p were quantified by quantitative real-time PCR or western blot. The measurements of the IC50 value and cell proliferation were done using 3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide (MTT) assay. Cell colony formation, cell cycle distribution, apoptosis, migration and invasion were evaluated by the colony formation, flow cytometry and transwell assays. Dual-luciferase reporter assay was performed to confirm the targeted relationship between different molecules. The role of circ_ASAP2 in tumor growth was gauged by in vivo animal studies. Circ_ASAP2 and NT5E were overexpressed in DDP-resistant gastric cancer tissues and cells. Knockdown of circ_ASAP2 promoted DDP sensitivity, apoptosis and repressed proliferation, migration and invasion of DDP-resistant gastric cancer cells in vitro and diminished tumor growth in vivo. Moreover, NT5E was a downstream effector of circ_ASAP2 in regulating cell DDP sensitivity and functional behaviors. Mechanistically, circ_ASAP2 directly bound to miR-330-3p to promote NT5E expression. Furthermore, circ_ASAP2 modulated cell DDP sensitivity and functional behaviors by targeting miR-330-3p. Knockdown of circ_ASAP2 promoted DDP sensitivity and suppressed malignant behaviors of DDP-resistant gastric cancer cells through targeting the miR-330-3p/NT5E axis.

Altered microRNA and mRNA profiles during heart failure in the human sinoatrial node

Heart failure (HF) is frequently accompanied with the sinoatrial node (SAN) dysfunction, which causes tachy-brady arrhythmias and increased mortality. MicroRNA (miR) alterations are associated with HF progression. However, the transcriptome of HF human SAN, and its role in HF-associated remodeling of ion channels, transporters, and receptors responsible for SAN automaticity and conduction impairments is unknown. We conducted comprehensive high-throughput transcriptomic analysis of pure human SAN primary pacemaker tissue and neighboring right atrial tissue from human transplanted HF hearts (n = 10) and non-failing (nHF) donor hearts (n = 9), using next-generation sequencing. Overall, 47 miRs and 832 mRNAs related to multiple signaling pathways, including cardiac diseases, tachy-brady arrhythmias and fibrosis, were significantly altered in HF SAN. Of the altered miRs, 27 are predicted to regulate mRNAs of major ion channels and neurotransmitter receptors which are involved in SAN automaticity (e.g. HCN1, HCN4, SLC8A1) and intranodal conduction (e.g. SCN5A, SCN8A) or both (e.g. KCNJ3, KCNJ5). Luciferase reporter assays were used to validate interactions of miRs with predicted mRNA targets. In conclusion, our study provides a profile of altered miRs in HF human SAN, and a novel transcriptome blueprint to identify molecular targets for SAN dysfunction and arrhythmia treatments in HF.

Continuous cardiorespiratory monitoring is a dominant source of predictive signal in machine learning for risk stratification and clinical decision support. Physiol Meas 2021;42. [PMID: 34580243 DOI: 10.1088/1361-6579/ac2130]

Beaulieu-Jones and coworkers propose a litmus test for the field of predictive analytics-performance improvements must be demonstrated to be the result of non-clinician-initiated data, otherwise, there should be caution in assuming that predictive models could improve clinical decision-making (Beaulieu-Joneset al2021). They demonstrate substantial prognostic information in unsorted physician orders made before the first midnight of hospital admission, and we are persuaded that it is fair to ask-if the physician thought of it first, what exactly is machine learning for in-patient risk stratification learning about? While we want predictive analytics to represent the leading indicators of a patient's illness, does it instead merely reflect the lagging indicators of clinicians' actions? We propose that continuous cardiorespiratory monitoring-'routine telemetry data,' in Beaulieu-Jones' terms-represents the most valuable non-clinician-initiated predictive signal present in patient data, and the value added to patient care justifies the efforts and expense required. Here, we present a clinical and a physiological point of view to support our contention.

Proteomic Analysis of Cardiac Adaptation to Exercise by High Resolution Mass Spectrometry

Regular exercise has many health benefits, among which is a significant reduction of cardiovascular risk. Although many beneficial effects of exercise are well described, the exact mechanisms by which exercise confers cardiovascular benefits are yet to be fully understood. In the current study, we have used high resolution mass spectrometry to determine the proteomic responses of the heart to exercise training in mice. The impact of exercise-induced oxidative stress on modifications of cardiomyocyte proteins with lipid peroxidation biomarker 4-hydroxynonenal (4-HNE) was examined as well. Fourteen male mice were randomized into the control (sedentary) group and the exercise group that was subjected to a swim exercise training program for 5 days a week for 5 months. Proteins were isolated from the left ventricular tissue, fractionated and digested for shotgun proteomics. Peptides were separated by nanoliquid chromatography and analyzed on an Orbitrap Fusion mass spectrometer using high-energy collision–induced dissociation and electron transfer dissociation fragmentation. We identified distinct ventricular protein signatures established in response to exercise training. Comparative proteomics identified 23 proteins that were upregulated and 37 proteins that were downregulated with exercise, in addition to 65 proteins that were identified only in ventricular tissue samples of exercised mice. Most of the proteins specific to exercised mice are involved in respiratory electron transport and/or implicated in glutathione conjugation. Additionally, 10 proteins were found to be modified with 4-HNE. This study provides new data on the effects of exercise on the cardiac proteome and contributes to our understanding of the molecular mechanisms underlying the beneficial effects of exercise on the heart.

Exosomal circ_0004136 enhances the progression of pediatric acute myeloid leukemia depending on the regulation of miR-570-3p/TSPAN3 axis

Circular RNAs (circRNAs) have been implicated in the progression of pediatric acute myeloid leukemia (AML). Although circ_0004136 has been found to play a crucial role in AML, our understanding of its molecular mechanism remains very limited. The levels of circ_0004136, miR-570-3p and tetraspanin 3 (TSPAN3) were determined by quantitative real-time PCR or western blot. Cell viability, migration, invasion, cell cycle and apoptosis were detected using the Cell Counting Kit-8, transwell and flow cytometry assays. Targeted relationships among circ_0004136, miR-570-3p and TSPAN3 were validated by dual-luciferase reporter and RNA immunoprecipitation assays. Our data showed that circ_0004136 could be transmitted by exosomes, and exosomal circ_0004136 was highly expressed in AML serum and cells. Circ_0004136 was unusually stable and mainly localized in the cytoplasm. Circ_0004136 knockdown mediated by exosomes hampered AML cell viability, cell cycle progression, migration and invasion, and promoted cell apoptosis. Moreover, circ_0004136 worked as a sponge of miR-570-3p and TSPAN3 was a functional target of miR-370-3p in AML cells. The suppression of circ_0004136 knockdown mediated by exosomes on AML cell malignant progression was reversed by miR-570-3p downregulation, and the increased miR-570-3p expression hindered the progression of aggressive AML by downregulating TSPAN3. Furthermore, circ_0004136 worked as a miR-570-3p sponge to modulate TSPAN3 expression. Our findings identified a novel regulatory mechanism in which exosome-mediated circ_0004136 knockdown restrained AML cell malignant progression at least partly through targeting the miR-570-3p/TSPAN3 axis, highlighting a novel therapeutic strategy for AML management.

Identification of a novel circ_0018289/miR-183-5p/TMED5 regulatory network in cervical cancer development

Background

Circular RNAs (circRNAs) are increasingly implicated in regulating human carcinogenesis. Previous work showed the oncogenic activity of circ_0018289 in cervical cancer. However, the molecular basis underlying the modulation of circ_0018289 in cervical carcinogenesis is still not fully understood.

Methods

The levels of circ_0018289, microRNA (miR)-183-5p, and transmembrane p24 trafficking protein 5 (TMED5) were measured by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot assay. Ribonuclease (RNase) R and subcellular localization assays were used to characterize circ_0018289. Cell proliferation was detected by the Cell Counting Kit-8 (CCK-8) and 5-ethynyl-2′-deoxyuridine (Edu) assays. Cell apoptosis and tube formation were assessed by flow cytometry and tube formation assays, respectively. A dual-luciferase reporter assay was performed to confirm the direct relationship between miR-183-5p and circ_0018289 or TMED5. The role of circ_0018289 in tumor growth was gauged by mouse xenograft experiments.

Results

Circ_0018289 was overexpressed in cervical cancer tissues and cells. Circ_0018289 silencing impeded cell proliferation, enhanced cell apoptosis, and suppressed angiogenesis in vitro, as well as diminished tumor growth in vivo. Mechanistically, circ_0018289 targeted and regulated miR-183-5p by binding to miR-183-5p, and circ_0018289 regulated cervical cancer development and angiogenesis partially through miR-183-5p. Moreover, TMED5 was directly targeted and inhibited by miR-183-5p through the perfect complementary sites in TMED5 3′UTR, and TMED5 knockdown phenocopied miR-183-5p overexpression in suppressing cervical cancer development and angiogenesis. Furthermore, circ_0018289 induced TMED5 expression by competitively binding to shared miR-183-5p.

Conclusion

Our observations identified the circ_0018289/miR-183-5p/TMED5 regulatory network as a novel molecular basis underlying the modulation of cervical carcinogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12957-021-02350-y.

Bioengineering the Cardiac Conduction System: Advances in Cellular, Gene, and Tissue Engineering for Heart Rhythm Regeneration

Heart rhythm disturbances caused by different etiologies may affect pediatric and adult patients with life-threatening consequences. When pharmacological therapy is ineffective in treating the disturbances, the implantation of electronic devices to control and/or restore normal heart pacing is a unique clinical management option. Although these artificial devices are life-saving, they display many limitations; not least, they do not have any capability to adapt to somatic growth or respond to neuroautonomic physiological changes. A biological pacemaker could offer a new clinical solution for restoring heart rhythms in the conditions of disorder in the cardiac conduction system. Several experimental approaches, such as cell-based, gene-based approaches, and the combination of both, for the generation of biological pacemakers are currently established and widely studied. Pacemaker bioengineering is also emerging as a technology to regenerate nodal tissues. This review analyzes and summarizes the strategies applied so far for the development of biological pacemakers, and discusses current translational challenges toward the first-in-human clinical application.

Downregulated lncRNA RCPCD promotes differentiation of embryonic stem cells into cardiac pacemaker-like cells by suppressing HCN4 promoter methylation

Long non-coding RNA (lncRNA) is receiving increasing attention in embryonic stem cells (ESCs) research. However, the roles of lncRNA in the differentiation of ESCs into pacemaker-like cells are still unclear. Therefore, the present study aims to explore the roles and mechanisms of lncRNA in the differentiation of ESCs into pacemaker-like cells. ESCs were cultured and induced differentiation to pacemaker-like cells. RNA sequencing was used to identify the differential expression lncRNAs during the differentiation of ESCs into pacemaker-like cells. Cell morphology observation, flow cytometry, quantitative real-time polymerase chain reaction, western blot, and immunofluorescence were used to detect the differentiation of ESCs into pacemaker-like cells. LncRNA and genes overexpression or knockdown through transfected adenovirus in the differentiation process. The fluorescence in situ hybridization (FISH) detected the lncRNA location in the differentiated ESCs. Luciferase reporter gene assay, methylation-specific PCR, chromatin immunoprecipitation assay, and RNA immunoprecipitation assay were performed to reveal the mechanism of lncRNA-regulating HCN4 expression. Rescue experiments were used to confirm that lncRNA regulates the differentiation of ESCs into pacemaker-like cells through HCN4. We cultured the ESCs and induced the differentiation of ESCs into pacemaker-like cells successfully. The expression of lncRNA RCPCD was significantly decreased in the differentiation of ESCs into pacemaker-like cells. Overexpression of RCPCD inhibited the differentiation of ESCs into pacemaker-like cells. RCPCD inhibited the expression of HCN4 by increasing HCN4 methylation at the promoter region through DNMT1, DNMT2, and DNMT3. RCPCD inhibited the differentiation of ESCs into pacemaker-like cells by inhibiting the expression of HCN4. Our results confirm the roles and mechanism of lncRNA RCPCD in the differentiation of ESCs into pacemaker-like cells, which could pave the path for the development of a cell-based biological pacemaker.

Non-Coding RNAs in the Cardiac Action Potential and Their Impact on Arrhythmogenic Cardiac Diseases

Cardiac arrhythmias are prevalent among humans across all age ranges, affecting millions of people worldwide. While cardiac arrhythmias vary widely in their clinical presentation, they possess shared complex electrophysiologic properties at cellular level that have not been fully studied. Over the last decade, our current understanding of the functional roles of non-coding RNAs have progressively increased. microRNAs represent the most studied type of small ncRNAs and it has been demonstrated that miRNAs play essential roles in multiple biological contexts, including normal development and diseases. In this review, we provide a comprehensive analysis of the functional contribution of non-coding RNAs, primarily microRNAs, to the normal configuration of the cardiac action potential, as well as their association to distinct types of arrhythmogenic cardiac diseases.

Regulation of sinus node pacemaking and atrioventricular node conduction by HCN channels in health and disease

The funny current, I_f, was first recorded in the heart 40 or more years ago by Dario DiFrancesco and others. Since then, we have learnt that I_f plays an important role in pacemaking in the sinus node, the innate pacemaker of the heart, and more recently evidence has accumulated to show that I_f may play an important role in action potential conduction through the atrioventricular (AV) node. Evidence has also accumulated to show that regulation of the transcription and translation of the underlying Hcn genes plays an important role in the regulation of sinus node pacemaking and AV node conduction under normal physiological conditions - in athletes, during the circadian rhythm, in pregnancy, and during postnatal development - as well as pathological states - ageing, heart failure, pulmonary hypertension, diabetes and atrial fibrillation. There may be yet more pathological conditions involving changes in the expression of the Hcn genes. Here, we review the role of I_f and the underlying HCN channels in physiological and pathological changes of the sinus and AV nodes and we begin to explore the signalling pathways (microRNAs, transcription factors, GIRK4, the autonomic nervous system and inflammation) involved in this regulation. This review is dedicated to Dario DiFrancesco on his retirement.

Intrinsic Electrical Remodeling Underlies Atrioventricular Block in Athletes

[Figure: see text].

No impact of sex and age on beta-adrenoceptor-mediated inotropy in human right atrial trabeculae

AIM

There is an increasing awareness of the impact of age and sex on cardiovascular diseases (CVDs). Differences in physiology are suspected. Beta-adrenoceptors (beta-ARs) are an important drug target in CVD and potential differences might have significant impact on the treatment of many patients. To investigate whether age and sex affects beta-AR function, we analysed a large data set on beta-AR-induced inotropy in human atrial trabeculae.

METHODS

We performed multivariable analysis of individual atrial contractility data from trabeculae obtained during heart surgery of patients in sinus rhythm (535 trabeculae from 165 patients). Noradrenaline or adrenaline were used in the presence of the beta₂ -selective antagonist (ICI 118 551, 50 nmol/L) or the beta₁ -selective antagonist (CGP 20712A, 300 nmol/L) to stimulate beta₁ -AR or beta₂ -AR respectively. Agonist concentration required to achieve half-maximum inotropic effects (EC₅₀ ) was taken as a measure of beta-AR sensitivity.

RESULTS

Impact of clinical variables was modelled using multivariable mixed model regression. As previously reported, chronic treatment with beta-blockers sensitized beta-AR. However, there was no significant interaction between basal force, maximum force and beta-AR sensitivity when age and sex were modelled continuously. In addition, there was no statistically significant effect of body mass index or diabetes on atrial contractility.

CONCLUSION

Our large, multivariable analysis shows that neither age nor sex affects beta-AR-mediated inotropy or catecholamine sensitivity in human atrial trabeculae. These findings may have important clinical implications because beta-ARs, as a common drug target in CVD and heart failure, do not behave differently in women and men across age decades.

RNAseq shows an all-pervasive day-night rhythm in the transcriptome of the pacemaker of the heart

Physiological systems vary in a day-night manner anticipating increased demand at a particular time. Heart is no exception. Cardiac output is primarily determined by heart rate and unsurprisingly this varies in a day-night manner and is higher during the day in the human (anticipating increased day-time demand). Although this is attributed to a day-night rhythm in post-translational ion channel regulation in the heart's pacemaker, the sinus node, by the autonomic nervous system, we investigated whether there is a day-night rhythm in transcription. RNAseq revealed that ~ 44% of the sinus node transcriptome (7134 of 16,387 transcripts) has a significant day-night rhythm. The data revealed the oscillating components of an intrinsic circadian clock. Presumably this clock (or perhaps the master circadian clock in the suprachiasmatic nucleus) is responsible for the rhythm observed in the transcriptional machinery, which in turn is responsible for the rhythm observed in the transcriptome. For example, there is a rhythm in transcripts responsible for the two principal pacemaker mechanisms (membrane and Ca²⁺ clocks), transcripts responsible for receptors and signalling pathways known to control pacemaking, transcripts from genes identified by GWAS as determinants of resting heart rate, and transcripts from genes responsible for familial and acquired sick sinus syndrome.

Genetic Ablation of G Protein-Gated Inwardly Rectifying K+ Channels Prevents Training-Induced Sinus Bradycardia

Background: Endurance athletes are prone to bradyarrhythmias, which in the long-term may underscore the increased incidence of pacemaker implantation reported in this population. Our previous work in rodent models has shown training-induced sinus bradycardia to be due to microRNA (miR)-mediated transcriptional remodeling of the HCN4 channel, leading to a reduction of the "funny" (I _f) current in the sinoatrial node (SAN). Objective: To test if genetic ablation of G-protein-gated inwardly rectifying potassium channel, also known as I _KACh channels prevents sinus bradycardia induced by intensive exercise training in mice. Methods: Control wild-type (WT) and mice lacking GIRK4 (Girk4 ^-/-), an integral subunit of I _KACh were assigned to trained or sedentary groups. Mice in the trained group underwent 1-h exercise swimming twice a day for 28 days, 7 days per week. We performed electrocardiogram recordings and echocardiography in both groups at baseline, during and after the training period. At training cessation, mice were euthanized and SAN tissues were isolated for patch clamp recordings in isolated SAN cells and molecular profiling by quantitative PCR (qPCR) and western blotting. Results: At swimming cessation trained WT mice presented with a significantly lower resting HR that was reversible by acute I _KACh block whereas Girk4 ^-/- mice failed to develop a training-induced sinus bradycardia. In line with HR reduction, action potential rate, density of I _f, as well as of T- and L-type Ca²⁺ currents (I _CaT and I _CaL ) were significantly reduced only in SAN cells obtained from WT-trained mice. I _f reduction in WT mice was concomitant with downregulation of HCN4 transcript and protein, attributable to increased expression of corresponding repressor microRNAs (miRs) whereas reduced I _CaL in WT mice was associated with reduced Ca_v1.3 protein levels. Strikingly, I _KACh ablation suppressed all training-induced molecular remodeling observed in WT mice. Conclusion: Genetic ablation of cardiac I _KACh in mice prevents exercise-induced sinus bradycardia by suppressing training induced remodeling of inward currents I _f, I _CaT and I _CaL due in part to the prevention of miR-mediated transcriptional remodeling of HCN4 and likely post transcriptional remodeling of Ca_v1.3. Strategies targeting cardiac I _KACh may therefore represent an alternative to pacemaker implantation for bradyarrhythmias seen in some veteran athletes.

Pharmacologic Approach to Sinoatrial Node Dysfunction

The spontaneous activity of the sinoatrial node initiates the heartbeat. Sino-atrial node dysfunction (SND) and sick sinoatrial (sick sinus) syndrome are caused by the heart's inability to generate a normal sinoatrial node action potential. In clinical practice, SND is generally considered an age-related pathology, secondary to degenerative fibrosis of the heart pacemaker tissue. However, other forms of SND exist, including idiopathic primary SND, which is genetic, and forms that are secondary to cardiovascular or systemic disease. The incidence of SND in the general population is expected to increase over the next half century, boosting the need to implant electronic pacemakers. During the last two decades, our knowledge of sino-atrial node physiology and of the pathophysiological mechanisms underlying SND has advanced considerably. This review summarizes the current knowledge about SND mechanisms and discusses the possibility of introducing new pharmacologic therapies for treating SND.

PRMT1 Modulates Processing of Asthma-Related Primary MicroRNAs (Pri-miRNAs) into Mature miRNAs in Lung Epithelial Cells

Protein arginine methyltransferase-1 (PRMT1) is an important epigenetic regulator of cell function and contributes to inflammation and remodeling in asthma in a cell type-specific manner. Disease-specific expression patterns of microRNAs (miRNA) are associated with chronic inflammatory lung diseases, including asthma. The de novo synthesis of miRNA depends on the transcription of primary miRNA (pri-miRNA) transcript. This study assessed the role of PRMT1 on pri-miRNA to mature miRNA process in lung epithelial cells. Human airway epithelial cells, BEAS-2B, were transfected with the PRMT1 expression plasmid pcDNA3.1-PRMT1 for 48 h. Expression profiles of miRNA were determined by small RNA deep sequencing. Comparing these miRNAs with datasets of microarrays from five asthma patients (Gene Expression Omnibus dataset), 12 miRNAs were identified that related to PRMT1 overexpression and to asthma. The overexpression or knockdown of PRMT1 modulated the expression of the asthma-related miRNAs and their pri-miRNAs. Coimmunoprecipitation showed that PRMT1 formed a complex with STAT1 or RUNX1 and thus acted as a coactivator, stimulating the transcription of pri-miRNAs. Stimulation with TGF-β1 promoted the interaction of PRMT1 with STAT1 or RUNX1, thereby upregulating the transcription of two miRNAs: let-7i and miR-423. Subsequent chromatin immunoprecipitation assays revealed that the binding of the PRMT1/STAT1 or PRMT1/RUNX1 coactivators to primary let-7i (pri-let-7i) and primary miR (pri-miR) 423 promoter was critical for pri-let-7i and pri-miR-423 transcription. This study describes a novel role of PRMT1 as a coactivator for STAT1 or RUNX1, which is essential for the transcription of pri-let-7i and pri-miR-423 in epithelial cells and might be relevant to epithelium dysfunction in asthma.

Identification of Key Small Non-Coding MicroRNAs Controlling Pacemaker Mechanisms in the Human Sinus Node

Background The sinus node (SN) is the primary pacemaker of the heart. SN myocytes possess distinctive action potential morphology with spontaneous diastolic depolarization because of a unique expression of ion channels and Ca2+-handling proteins. MicroRNAs (miRs) inhibit gene expression. The role of miRs in controlling the expression of genes responsible for human SN pacemaking and conduction has not been explored. The aim of this study was to determine miR expression profile of the human SN as compared with that of non-pacemaker atrial muscle. Methods and Results SN and atrial muscle biopsies were obtained from donor or post-mortem hearts (n=10), histology/immunolabeling were used to characterize the tissues, TaqMan Human MicroRNA Arrays were used to measure 754 miRs, Ingenuity Pathway Analysis was used to identify miRs controlling SN pacemaker gene expression. Eighteen miRs were significantly more and 48 significantly less abundant in the SN than atrial muscle. The most interesting miR was miR-486-3p predicted to inhibit expression of pacemaking channels: HCN1 (hyperpolarization-activated cyclic nucleotide-gated 1), HCN4, voltage-gated calcium channel (Cav)1.3, and Cav3.1. A luciferase reporter gene assay confirmed that miR-486-3p can control HCN4 expression via its 3' untranslated region. In ex vivo SN preparations, transfection with miR-486-3p reduced the beating rate by ≈35±5% (P<0.05) and HCN4 expression (P<0.05). Conclusions The human SN possesses a unique pattern of expression of miRs predicted to target functionally important genes. miR-486-3p has an important role in SN pacemaker activity by targeting HCN4, making it a potential target for therapeutic treatment of SN disease such as sinus tachycardia.

Translating GWAS-identified loci for cardiac rhythm and rate using an in vivo image- and CRISPR/Cas9-based approach

A meta-analysis of genome-wide association studies (GWAS) identified eight loci that are associated with heart rate variability (HRV), but candidate genes in these loci remain uncharacterized. We developed an image- and CRISPR/Cas9-based pipeline to systematically characterize candidate genes for HRV in live zebrafish embryos. Nine zebrafish orthologues of six human candidate genes were targeted simultaneously in eggs from fish that transgenically express GFP on smooth muscle cells (Tg[acta2:GFP]), to visualize the beating heart. An automated analysis of repeated 30 s recordings of beating atria in 381 live, intact zebrafish embryos at 2 and 5 days post-fertilization highlighted genes that influence HRV (hcn4 and si:dkey-65j6.2 [KIAA1755]); heart rate (rgs6 and hcn4); and the risk of sinoatrial pauses and arrests (hcn4). Exposure to 10 or 25 µM ivabradine—an open channel blocker of HCNs—for 24 h resulted in a dose-dependent higher HRV and lower heart rate at 5 days post-fertilization. Hence, our screen confirmed the role of established genes for heart rate and rhythm (RGS6 and HCN4); showed that ivabradine reduces heart rate and increases HRV in zebrafish embryos, as it does in humans; and highlighted a novel gene that plays a role in HRV (KIAA1755).