Therapeutic Target For Atrial Fibrillation Research Articles

Abstract 18342: Development of Fibrotic Substrate for Atrial Fibrillation in Advanced Heart Failure is Driven Not by Inflammation but by Smad2/3 Dependent Replacement Fibrosis

Introduction: Fibrosis is an important contributor to atrial fibrillation (AF) substrate in heart failure, with TGF-β signaling generating atrial fibrosis. Inflammation is also known to contribute to AF. However, it is not known: a) if inflammation underlies the development of atrial fibrosis, b) if TGF-β signaling is involved in the generation of atrial inflammation and c) what is the relative role of canonical SMAD2/3 versus non-canonical TGF-β-activated kinase 1 (TAK) signaling in the creation of atrial inflammation/fibrosis. Methods: 21 dogs underwent transfection in the posterior left atria of either a plasmid expressing a dominant negative TGF-β type II receptor (pUBC-TGFβ-DN-RII) (N=9) or control vector (pUBC-LacZ) (N=12), followed by 3-4 weeks of right ventricular tachypacing (VTP) (240 bpm). After 3-4 weeks of VTP, the following were assessed: AF by open-chest mapping. Atrial tissue was assessed for signaling (pSMAD2/3 and pTAK) by western blot, fibrosis by trichrome staining and iflammation by CD68 staining. Results: The interstitial fibrosis in LacZ atria was replacement in character (Fig 1A). TGFβ-RII-DN dogs had a significant decrease in replacement fibrosis leading to a decrease in duration of inducible AF (LacZ 63.64 ± 12.12 s vs. TGFβ 26.52 ± 3.79 s, p < 0.05). While both groups demonstrated evidence of inflammation (CD68 staining), there was no difference in inflammation between the groups (Fig 1B). TGFβ-RII-DN dogs had a significant decrease in pSMAD2/3 but not pTAK, compared to pUBC-LacZ dogs. Conclusion: The development of fibrotic substrate for AF in advanced HF is driven not by inflammation but primarily by SMAD2/3 mediated myocardial replacement fibrosis. These findings may have important implications for mechanism-guided therapies for AF, with canonical TGF-β signaling appearing to be an attractive therapeutic target in AF.

Vitamin D: A potential important therapeutic target for atrial fibrillation

Vitamin D: A potential important therapeutic target for atrial fibrillation

Novel biomarkers in cardiology: MicroRNAs in atrial fibrillation.

Atrial fibrillation (AF) is the most common sustained chronic cardiac arrhythmia in clinical practice, which increases the risk of stroke and thromboembolism and is an independent predictor of mortality. The underlying mechanisms involved in the development of AF have yet to be fully elucidated. However, once initiated, AF tends to self-perpetuate, owing to structural and electrical remodeling in the atria. MicroRNAs (miRNAs) represent a sizable sub-group of small non-coding RNAs, which degrades or inhibits the translation of their target mRNAs, thus regulating gene expression and playing an important role in a wide range of biologic processes. Clinically, there is increasing evidence of the potential diagnostic role of miRNAs as biomarkers, representing a novel therapeutic target in AF. The aim of this review is to provide an exhaustive overview of the role of miRNAs in AF and to discuss the diagnostic and therapeutic potential of miRNAs in this arrhythmia.

Evaluation of the role of miR-31-dependent reduction in dystrophin and nNOS on atrial-fibrillation-induced electrical remodelling in man

BackgroundThe management of atrial fibrillation remains a challenge. This condition remodels atrial electrical properties, which promote resistance to treatment. Although remodelling has long been a therapeutic target in atrial fibrillation, its causes remain incompletely understood. We aimed to evaluate the role of miR-31-dependent reduction in dystrophin and neuronal nitric oxide synthase (nNOS, also known as NOS1) on atrial electrical properties and atrial fibrillation inducibility. MethodsWe recruited 258 patients (209 patients in sinus rhythm and 49 with permanent atrial fibrillation) from the John Radcliffe Hospital, Oxford, UK; written informed consent was obtained from each participant. We also used a goat model of pacing-induced atrial fibrillation (24 with atrial fibrillation vs 20 controls in normal sinus rythm) and nNos-knock-out mice (n=28 compared with 27 wild-type littermates). Gene expression of miR-31, dystrophin, and nNOS was assessed by quantitative RT-PCR; protein content was measured by immunoblotting; NOS activity was evaluated with high-performance liquid chromatography; action potential duration (APD) and rate dependent adaptation were assessed by single-cell patch-clamping, and atrial fibrillation inducibility was evaluated by transoesophageal atrial burst stimulation. FindingsWe found that atrial-specific upregulation of miR-31 in human atrial fibrillation caused dystrophin (DYS) translational repression and accelerated mRNA degradation of nNOS leading to a profound reduction in atrial DYS and nNOS protein content and in nitric oxide availability. In human atrial myocytes obtained from patients in sinus rhythm, nNOS inhibition was sufficient to recapitulate hallmark features of remodelling induced by atrial fibrillation, such as shortening of APD and loss of APD rate-dependency, but had no effect in patients with atrial fibrillation. In mice, nNos gene deletion or inhibition shortened atrial APD and increased atrial fibrillation inducibility in vivo. Inhibition of miR-31 in human atrial fibrillation recovered DYS and nNOS, and normalised APD and APD rate-dependency. Prevention of miR-31 binding to nNOS 3′UTR recovered both nNOS protein and gene expression but had no effect on the DYS protein or mRNA level (consistent with the mRNA degradation of nNOS by miR-31). Prevention of miR-31 binding to DYS 3′UTR increased DYS protein but not mRNA is consistent with translation repression of DYS by miR-31; recovery of DYS protein increased nNOS protein but not mRNA in keeping with a stabilising effect of DYS on nNOS protein. In goats, a reduction in dystrophin and nNOS protein content was associated with upregulation of miR-31 in the atria but not in the ventricles. InterpretationThe findings suggest that atrial-specific upregulation of miR-31 in human atrial fibrillation is a key mechanism causing atrial loss of dystrophin and nNOS; this loss leads to the electrical phenotype induced by atrial fibrillation. FundingBritish Heart Foundation (BHF) Programme grant (for BC and XL), BHF Centre of Excellence in Oxford (SR), Leducq Foundation (in part for BC and SR), the European Union's seventh Framework Programme Grant Agree.

MicroRNAs and atrial fibrillation: mechanisms and translational potential.

Atrial fibrillation (AF), the most common sustained arrhythmia in clinical practice, is an important contributor to cardiac morbidity and mortality. Pharmacological approaches currently available to treat patients with AF lack sufficient efficacy and are associated with potential adverse effects. Even though ablation is generally more effective than pharmacotherapy, this invasive procedure has considerable potential complications and is limited by long-term recurrences. Novel therapies based on the underlying molecular mechanisms of AF can provide useful alternatives to current treatments. MicroRNAs (miRNAs), endogenous short RNA sequences that regulate gene expression, have been implicated in the control of AF, providing novel insights into the molecular basis of the pathogenesis of AF and suggesting miRNA targeting as a potential approach for the management of this common arrhythmia. In this Review, we provide a comprehensive analysis of the current experimental evidence supporting miRNAs as important factors in AF and discuss their therapeutic implications. We first provide background information on the pathophysiology of AF and the biological determinants of miRNA synthesis and action, followed by experimental evidence for miRNA-mediated regulation of AF, and finally provide a comprehensive overview of miRNAs as potential novel therapeutic targets for AF.

Paired-like homeodomain 2: a novel therapeutic target for atrial fibrillation?

Paired-like homeodomain 2: a novel therapeutic target for atrial fibrillation?

Expanding role of SK channels in cardiac electrophysiology

The small conductance calcium-activated potassium (SK) channels are an important group of potassium-selective ion channels. SK channels display more pronounced expression in the atrium relative to the ventricle. Current evidence relating to the functional role of SK channels in the atria is conflicting and whether these channels contribute to atrial repolarization under physiological circumstances is a matter of debate. Multiple studies have, however, reported that SK channels are important mediators of proarrhythmogenic electrical remodeling in the atria. In keeping with their expression profile, SK channels do not appear to play a prominent role in ventricular repolarization. SK channels represent potentially attractive therapeutic targets for atrial fibrillation. A number of pharmacological modulators of SK channels have been tested in animal models of atrial fibrillation. However, these studies have also demonstrated inconsistent results and have raised important questions regarding the proarrhythmogenic potential of SK channel modulation. These findings have important implications for drug development. This review summarizes the role of SK channels in cardiac electrophysiology and discusses the potential role of these channels as therapeutic targets.

Epicardial adipose tissue and atrial fibrillation

Atrial fibrillation (AF) is the most frequent cardiac arrhythmia in clinical practice. AF is often associated with profound functional and structural alterations of the atrial myocardium that compose its substrate. Recently, a relationship between the thickness of epicardial adipose tissue (EAT) and the incidence and severity of AF has been reported. Adipose tissue is a biologically active organ regulating the metabolism of neighbouring organs. It is also a major source of cytokines. In the heart, EAT is contiguous with the myocardium without fascia boundaries resulting in paracrine effects through the release of adipokines. Indeed, Activin A, which is produced in abundance by EAT during heart failure or diabetes, shows a marked fibrotic effect on the atrial myocardium. The infiltration of adipocytes into the atrial myocardium could also disorganize the depolarization wave front favouring micro re-entry circuits and local conduction block. Finally, EAT contains progenitor cells in abundance and therefore could be a source of myofibroblasts producing extracellular matrix. The study on the role played by adipose tissue in the pathogenesis of AF is just starting and is highly likely to uncover new biomarkers and therapeutic targets for AF.

MicroRNA-1 Accelerates the Shortening of Atrial Effective Refractory Period by Regulating KCNE1 and KCNB2 Expression: An Atrial Tachypacing Rabbit Model

BackgroundThe potential mechanisms of microRNA-1 (miR-1) in the electrical remodeling of atrial fibrillation remain unclear. The purpose of this study was to evaluate the effects of miR-1 on the atrial effective refractory period (AERP) in a right atrial tachypacing model and to elucidate the potential mechanisms.Methods and ResultsQRT-PCR and western blot were used to detect the expression of the miR-1, KCNE1, and KCNB2 genes after 1-week of right atrial tachypacing in New Zealand white rabbits. The AERP was measured using a programmable multichannel stimulator, and atrial fibrillation was induced by burst stimulation in vivo. The slowly activating delayed rectifier potassium current (IKs) and AERP in atrial cells were measured by whole cell patch clamp in vitro. Right atrial tachypacing upregulated miR-1 expression and downregulated KCNE1 and KCNB2 in this study, while the AERP was decreased and the atrial IKs increased. The downregulation of KCNE1 and KCNB2 levels was greater when miR-1 was further upregulated through in vivo lentiviral infection. Electrophysiological tests indicated a shorter AERP, a great increase in the IKs and a higher atrial fibrillation inducibility. In addition, similar results were found when the levels of KCNE1 and KCNB2 were downregulated by small interfering RNA while keeping miR-1 level unaltered. Conversely, knockdown of miR-1 by anti-miR-1 inhibitor oligonucleotides alleviated the downregulation of KCNE1 and KCNB2, the shortening of AERP, and the increase in the IKs. KCNE1 and KCNB2 as the target genes for miR-1 were confirmed by luciferase activity assay.ConclusionsThese results indicate that miR-1 accelerates right atrial tachypacing-induced AERP shortening by targeting potassium channel genes, which further suggests that miR-1 plays an important role in the electrical remodeling of atrial fibrillation and exhibits significant clinical relevance as a potential therapeutic target for atrial fibrillation.

Connexin Remodeling Contributes to Atrial Fibrillation.

Atrial fibrillation significantly contributes to mortality and morbidity through increased risk of stroke, heart failure and myocardial infarction. Investigations of mechanisms responsible for the development and maintenance of atrial fibrillation have highlighted the importance of gap junctional remodeling. Connexins 40 and 43, the major atrial gap junctional proteins, undergo considerable alterations in expression and localization in atrial fibrillation, creating an environment conducive to sustained reentry. Atrial fibrillation is initiated and/or maintained in this reentrant substrate. This review will focus on connexin remodeling in the context of underlying mechanism and possible therapeutic target for atrial fibrillation.

Mutation E169K in Junctophilin-2 Causes Atrial Fibrillation Due to Impaired RyR2 Stabilization

This study sought to study the role of junctophilin-2 (JPH2) in atrial fibrillation (AF). JPH2 is believed to have an important role in sarcoplasmic reticulum (SR) Ca(2+) handling and modulation of ryanodine receptor Ca(2+) channels (RyR2). Whereas defective RyR2-mediated Ca(2+) release contributes to the pathogenesis of AF, nothing is known about the potential role of JPH2 in atrial arrhythmias. Screening 203 unrelated hypertrophic cardiomyopathy patients uncovered a novel JPH2 missense mutation (E169K) in 2 patients with juvenile-onset paroxysmal AF (pAF). Pseudoknock-in (PKI) mouse models were generated to determine the molecular defects underlying the development of AF caused by this JPH2 mutation. PKI mice expressing E169K mutant JPH2 exhibited a higher incidence of inducible AF than wild type (WT)-PKI mice, whereas A399S-PKI mice expressing a hypertrophic cardiomyopathy-linked JPH2 mutation not associated with atrial arrhythmias were not significantly different from WT-PKI. E169K-PKI but not A399A-PKI atrial cardiomyocytes showed an increased incidence of abnormal SR Ca(2+) release events. These changes were attributed to reduced binding of E169K-JPH2 to RyR2. Atrial JPH2 levels in WT-JPH2 transgenic, nontransgenic, and JPH2 knockdown mice correlated negatively with the incidence of pacing-induced AF. Ca(2+) spark frequency in atrial myocytes and the open probability of single RyR2 channels from JPH2 knockdown mice was significantly reduced by a small JPH2-mimicking oligopeptide. Moreover, patients with pAF had reduced atrial JPH2 levels per RyR2 channel compared to sinus rhythm patients and an increased frequency of spontaneous Ca(2+) release events. Our data suggest a novel mechanism by which reduced JPH2-mediated stabilization of RyR2 due to loss-of-function mutation or reduced JPH2/RyR2 ratios can promote SR Ca(2+) leak and atrial arrhythmias, representing a potential novel therapeutic target for AF.

Abstract 284: Disruption of Nrf2 Promotes Atrial Remodeling and Fibrillation on Aging

Background: Heart failure is a leading health problem with over 500,000 new cases and 275,000 deaths annually in the United States. Recent reports indicate that atrial fibrillation (AF) is linked to various forms of ventricular dysfunction (VD). Over 2 million Americans have AF, which is more prevalent in people over 65 years of age. However, the molecular “cause and effect” relationship between AF and VD has not been elucidated. We hypothesize that abrogation of nuclear erythroid-2 like factor-2 (Nrf2), a master antioxidant transcriptional regulator, induces atrial remodeling and fibrillation on aging. Methods: Age and sex matched WT and Nrf2-/- mice were used in this study. Atrial mass, remodeling, antioxidants and molecular redox signaling were studied at 2 and >20 months of age. Echocardiography, immunoblotting, quantitative real-time PCR and immunofluorescence (fibrosis) analyses were performed in the atrial tissue. Results: At 2 months of age, WT and Nrf2-/- mice had comparable levels of ROS in the atrium. On aging, the ROS levels were significantly increased in atria of Nrf2- null when compared to wild-type (WT) mice at 20 months of age. While decreased Nrf2-antioxidant signaling in response to increased ROS generation in atria of Nrf2- null mice was observed, ventricular function appeared to be normal at 20 months of age. However, upon endurance exercise stress (EES), hypertrophy markers including ANF, BNF, PLN and SERCA2A were significantly (p<0.05) altered in Nrf2- null when compared to age-matched WT mice. Further, activation of fibrotic process was evident in the Nrf2- null mouse atrium as indicated by significantly (p<0.05) increased markers of tissue remodeling (i.e. MMP2/9) on aging. These results indicating an early onset of atrial hypertrophy/remodeling due to age-induced oxidative stress, which cause AF in Nrf2- null mice. Age-dependent decline in Nrf2 and sustained progression of AF could lead to ventricular dysfunction and heart failure. Conclusion: Our findings indicate that atria are primary targets to age-associated oxidative stress and exhibit fibrosis, which promotes atrial fibrillation and remodeling. Thus, activation of Nrf2 signaling to prevent oxidative stress could be a potential therapeutic target for AF.

Receptor for advanced glycation end products (RAGE): Novel biomarker and therapeutic target for atrial fibrillation

Atrial fibrillation (AF) is the most common sustained heart rhythm disturbance encountered in clinical practice, associated with great morbidity and mortality in the population. Therapeutic approaches to AF including pharmacological treatment and catheter ablation have limited efficacy and potential adverse effects. Our understanding of AF pathophysiology has advanced significantly over the past few decades. Ectopic firing and reentry can promote and maintain AF, and both were related to atrial electrical and structural remodeling.

Platelet-derived growth factor: A promising therapeutic target for atrial fibrillation

Atrial fibrillation (AF) is the most common type of cardiac arrhythmia and is characterized by substantial electrophysiological and structural changes. AF is associated with an increased risk of stroke, heart failure, and overall mortality.1,2 The risk of developing AF increases with age and with other risk factors such as diabetes and underlying heart disease.1 Currently, the therapeutic options for the treatment of AF have moderate effectiveness, and side effects, including proarrhythmic events, can often be encountered.

To the Editor—Platelet-derived growth factor, a novel potential therapeutic target for atrial fibrillation

To the Editor—Platelet-derived growth factor, a novel potential therapeutic target for atrial fibrillation

English

This study explores the changes in gene and protein expression of tyrosine hydroxylase (TH) and growth-associated protein 43 (GAP43) in aging patients with atrial fibrillation of Xinjiang Uygur and Han nationalities. Real-time polymerase chain reaction (PCR) and Western blot were used to detect the gene and protein expressions of TH and GAP43 in atrial tissues of 54 patients with valvular heart disease. Comparison of the mRNA and the protein expression of GAP43 and TH between the sinus rhythm group and the atrial fibrillation group was statistically significant (P < 0.05); the protein expression of GAP43 and TH in patients of Xinjiang Uygur and Han nationalities in the sinus rhythm group and atrial fibrillation group was statistically significant (P < 0.05); the protein expression of GAP43 and TH in patients of different nationalities in the sinus rhythm group and atrial fibrillation group was not statistically significant (P > 0.05); the protein expression of GAP43 and TH in patients of different nationalities with different ages in the sinus rhythm group and atrial fibrillation group was not statistically significant (P < 0.05); only the protein expression of GAP43 in patients with different ages in the atrial fibrillation group was statistically significant (P < 0.05). The changes in mRNA and protein expression of TH and GAP43 played a vital role in the process of maintaining atrial fibrillation. The increase in the expression of TH and GAP43 may be one of the molecular bases of the left atrial myoelectricity remodeling of aging patients with atrial fibrillation. TH and GAP43 may be the potential therapeutic targets of atrial fibrillation.   Key words: Atrial fibrillation (AF), aging, Xinjiang Uygur, Han nationality, tyrosine hydroxylase (TH), growth associated protein (GAP43)

Expression of tyrosine hydroxylase and growth-associated protein 43 in aging atrial fibrillation patients of Xinjiang Uygur and Han nationality

The aim of this study was to explore the changes in gene and protein expressions of tyrosine hydroxylase (TH) and growth-associated protein 43 (GAP43) in aging atrial fibrillation patients of Xinjiang Uygur and Han nationality, and the significance of the changes. Real-time polymerase chain reaction and Western blot analysis were used to detect gene and protein expressions of TH and GAP43 in atrial tissues of 54 patients with valvular heart disease. mRNA and protein expressions of GAP43 and TH were significantly different between the sinus rhythm and atrial fibrillation groups (P < 0.05). Protein expressions of GAP43 and TH of both nationalities differed significantly between the sinus rhythm group and the atrial fibrillation group (P < 0.05), whereas there was no statistical difference between the two nationalities within each group (P > 0.05). Protein expressions of GAP43 and TH differed significantly among different age groups of different nationalities in the sinus rhythm and atrial fibrillation groups (P < 0.05); only protein expression of GAP43 differed significantly in different age groups in the atrial fibrillation group (P < 0.05). The changes of mRNA and protein expressions of TH and GAP43 played a vital role in the process of maintaining the atrial fibrillation. Therefore, increased expression of TH and GAP43 might be a molecular mechanism for left atrial myoelectricity remodeling of aging atrial fibrillation patients, which might be potential therapeutic targets of atrial fibrillation.

Connexins and Atrial Fibrillation

Atrial fibrillation (AF) is an extremely common arrhythmia with important consequences and presently suboptimal therapeutic options.1 A great deal of research has been performed to understand the detailed mechanisms of AF, with the hope that a better appreciation of the fundamental determinants of arrhythmogenesis will lead to the development of novel, more successful treatment possibilities.2 Article see p 216 One aspect of AF pathophysiology that has elicited great interest has been changes in gap junction/connexin physiology. An important role for altered gap junction function and the potential importance of gap junctions as a therapeutic target for AF were first emphasized by Spach and Starmer over 15 years ago.3 Since that time, our understanding of gap junction physiology, biophysics, and molecular biology has increased enormously,4,5 as have studies on their role in AF pathogenesis and management.2 Gap junctions contain transmembrane ion-channel proteins called connexins (Figure,panel A). Connexons (containing 6 connexin molecules each) in the gap junctions of adjacent cardiomyocytes line up and attach, transferring ions or molecules <1 kDa freely between cells, coupling them electrically (Figure, panel B). Cardiac tissues express a variety of connexins, including connexin (Cx)40, Cx43, Cx45, Cx30.2/31.9, and Cx37,5 with all but Cx37 present in cardiomyocytes and the most important connexins in atrial tissue being Cx40 and Cx43. There is evidence that posttranslational modification, particularly connexin phosphorylation, is important in governing connexin localization and function.6 Figure. A , Connexons contain 6 connexins each, arranged in a circle. Connexins …

Atrial remodeling in atrial fibrillation and association between microRNA network and atrial fibrillation

Atrial fibrillation (AF) remains one of the leading causes of morbidity and mortality in the world which are related to palpitations, fainting, congestive heart failure or stroke. The mechanism for atrial fibrillation has been identified as electrical remodeling, structure remodeling and intracellular calcium handling remodeling. microRNAs (miRNAs) have recently emerged as one of the important factors in regulating gene expression. So far, thousands of miRNA genes have been found in diverse animals with the function of regulating cell death, cell proliferation, haematopoiesis and even participate in the processing of cardiovascular disease. In this review, we summarize the mechanism of AF and the association of microRNAs network with AF. We provide a potential perspective of miRNAs as the therapeutic target for AF.

Abstract 18255: Atrial Fibrillation in RyR2-R2474S Mice

Background: Atrial fibrillation (AF) is one of the most common arrhythmias. Despite a wealth of information on the electrical abnormalities present in the working atrial muscle, a detailed understanding of the cellular events that underlie AF is lacking. Methods: To explore the role of ryanodine receptor (RyR2) in triggering AF, we executed in vivo intra-esophageal burst pacing induced AF and in vitro atrial myocyte SR Ca2+ leak measurements in WT and RyR2-R2474S+/- mice. Results: With the in vivo stimulation protocol, 70% of RyR2-R2474S+/- mice could be stimulated into AF whereas WT mice showed no AF (WT: n = 33, R2474S: n = 10, P &lt; 0.05). Confocal Ca2+ imaging in isolated atrial myocytes from these mice showed that atrial myocytes from RyR2-R2474S+/- mice exhibited a 152% increase in SR Ca2+ leak compared to WT (WT: n = 25, R2474S: n=20, P &lt; 0.01). Further, pretreatment of RyR2-R2474S+/- atrial myocytes for 2 hours with 10 µM S107, a 1,4-benzothiazepine derivative that stabilizes RyR2 by inhibiting depletion of the stabilizing subunit calstabin2 (FKBP12.6) from the RyR2 channel (thereby reducing SR Ca2+ leak), resulted in a 68% decrease in diastolic SR Ca2+ leak AF (n = 23, P &lt; 0.05). Administration of S107 treatment via drinking water (20mg/kg/day) for two weeks in RyR2-R2474S+/- mice prevented burst pacing induced-AF (from 70% to 0%) (n = 10 in both groups, P &lt; 0.05). Conclusions: Thus, SR Ca2+ leak via RyR2 plays a critical role in the pathogenesis of AF and may be a novel therapeutic target for AF in humans.