Rs4968309 in Myosin Light Chain 4 (MYL4) Associated With Atrial Fibrillation Onset and Predicts Clinical Outcomes After Catheter Ablation in Atrial Fibrillation Patients Without Structural Heart Disease

Myosin light-chain 4 gene-transfer attenuates atrial fibrosis while correcting autophagic flux dysregulation

OBJECTIVES

To determine the role of MYL4 regulation of lysosomal function and its disturbance in fibrotic atrial cardiomyopathy.

BACKGROUND

We have previously demonstrated that the atrial-specific essential light chain protein MYL4 is required for atrial contractile, electrical, and structural integrity. MYL4 mutation/dysfunction leads to atrial fibrosis, standstill, and dysrhythmia. However, the underlying pathogenic mechanisms remain unclear.

METHODS AND RESULTS

Rats subjected to knock-in of a pathogenic MYL4 mutant (p.E11K) developed fibrotic atrial cardiomyopathy. Proteome analysis and single-cell RNA sequencing indicate enrichment of autophagy pathways in mutant-MYL4 atrial dysfunction. Immunofluorescence and electron microscopy revealed undegraded autophagic vesicles accumulated in MYL4p.E11K rat atrium. Next, we identified that dysfunctional MYL4 protein impairs autophagy flux in vitro and in vivo. Cardiac lysosome positioning and mobility were regulated by MYL4 in cardiomyocytes, which affected lysosomal acidification and maturation of lysosomal cathepsins. We then examined the effects of MYL4 overexpression via adenoviral gene-transfer on atrial cardiomyopathy induced by MYL4 mutation: MYL4 protein overexpression attenuated atrial structural remodeling and autophagy dysfunction.

CONCLUSIONS

MYL4 regulates autophagic flux in atrial cardiomyocytes via lysosomal mobility. MYL4 overexpression attenuates MYL4 p.E11K induced fibrotic atrial cardiomyopathy, while correcting autophagy and lysosomal function. These results provide a molecular basis for MYL4-mutant induced fibrotic atrial cardiomyopathy and identify a potential biological-therapy approach for the treatment of atrial fibrosis.

Correlation between Serum Myosin Light Chain 4 Levels and Recurrence after Radiofrequency Ablation in Patients with Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia that is harmful to human health. This study aims to explore the relationship between myosin light chain 4 (MYL4) and AF recurrence after radiofrequency ablation (RFA). Patients with AF (n = 85) were enrolled, and healthy subjects (n = 90) with normal sinus rhythm and no previous history of AF were selected as controls. The serum levels of MYL4, transforming growth factor (TGF) -β1, and procollagen type-I C-terminal propeptide (PICP) were determined. The correlation between MYL4 and atrial fibrosis remodeling indicators (TGF-β1/PICP) and left atrial diameter (LAD) was analyzed. The influence of MYL4 on AF recurrence after RFA was evaluated, and the independent correlation between them was assessed. Patients with AF and the controls showed no significant differences in age, gender, body mass index, systolic blood pressure, diastolic blood pressure, left ventricular ejection fraction, triglycerides, total cholesterol, high-density lipoprotein, low-density lipoprotein, white blood cell count, neutrophil/lymphocyte ratio, brain natriuretic peptide, and history of smoking, drinking, hypertension, and diabetes (P > 0.05), but with increased LAD in patients with AF (P < 0.01). Serum MYL4 level was reduced in patients with AF (0.6 ± 0.2) compared with that of controls (0.1 ± 0.6) (P < 0.01), and it was negatively correlated with TGF-β1, PICP, and LAD (r = -0.2389, P < 0.05; r = -0.5174, P < 0.01; r = -0.3191; P < 0.01). Low levels of MYL4 increased the risk of AF recurrence after RFA (χ² = 16.64; P < 0.0001). A low MYL4 level in patients with AF showed a poorer prognosis. Serum MYL4 level and AF type were independent risk factors affecting AF recurrence after RFA.

Relationship between Serum miR-106 and MYL4 Levels and the Prevalence, Risk Stratification, and Prognosis of Atrial Fibrillation

Objective

To analyze the predictive value of serum microRNA-106 (miRNA-106), miR-106, and myosin light chain 4 (MYL4) levels on the prevalence of atrial fibrillation and to explore the relationship between serum miR-106 and MYL4 and the risk stratification and prognosis of atrial fibrillation, thereby providing basis for them to become clinical targets for the treatment of atrial fibrillation in the future.

Methods

300 patients with atrial fibrillation treated in our hospital from May 2017 to March 2019 were selected as the atrial fibrillation group, and 300 healthy people who came to our hospital for physical examination in the same period were selected as the control group. The general data of the subjects in the two groups were collected. The serum miR-106 level of the subjects in the two groups was detected by fluorescence quantitative polymerase chain reaction (PCR), and the level of MYL4 was detected by enzyme-linked immunosorbent assay (ELISA). The expression of miR-106 and MYL4 in the myocardium was observed by immunohistochemistry. The relationship between the levels of serum miR-106 and MYL4 and the prevalence of atrial fibrillation and the score of atrial fibrillation thromboembolism risk stratification scoring system (cha2ds2) was compared between the two groups. The relationship between serum level of miR-106 and prognosis of patients with atrial fibrillation was analyzed.

Results

The systolic blood pressure, diastolic blood pressure, total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), and left anterior descending artery (LAD) in the atrial fibrillation group were significantly higher than those in the control group, while HDL-C and left ventricular ejection fraction (LVEF) were significantly lower than those in the control group (P < 0.01). The level of serum miR-106 in patients with atrial fibrillation was significantly higher than that in the control group, whereas the level of MYL4 was significantly lower than that in the control group (P < 0.01). miR-106 was mainly localized in the cytoplasm, and the positive expression rate of miR-106 was 71.43% (81/115) in patients with atrial fibrillation and 21.74% (25/115) in patients with sinus rhythm. MYL4 was mainly located in the cell membrane and the positive expression rate of MYL4 was 24.35% (28/115) in patients with atrial fibrillation and 64.35% (74/115) in patients with sinus rhythm. With the increase of the severity of atrial fibrillation, the level of serum miR-106 gradually increased and the level of MYL4 gradually decreased, which were statistically significant compared with the control group (P < 0.05). With the increase of miR-106 level and the decrease of MYL4 level, the prevalence of atrial fibrillation gradually increased. With the increase of cha2ds2 score, the level of serum miR-106 increased and the level of MYL4 decreased. The survival rate of patients with miR − 106 ≤ 1.96 was significantly higher than that of patients with miR − 106 > 1.96. The survival rate of patients with MYL4 ≥ 0.24 was significantly higher than that of patients with MYL4 < 0.24. At the same time, TC and LDL-C were included in the analysis. The results showed that the survival rate of patients with TC ≤ 4.5 mmol/L was significantly higher than that of patients with TC > 4.5 mmol/L, and that of patients with LDL-C ≤ 2.6 mmol/L was significantly higher than that of patients with LDL-C > 2.6 mmol/L.

Conclusion

Serum miR-106 and MYL4 levels are closely related to the prevalence of atrial fibrillation, which can reflect the risk of thromboembolism in patients with atrial fibrillation and can be used as a biological indicator to predict the prognosis of patients with atrial fibrillation.

The Atrium in Atrial Fibrillation - A Clinical Review on How to Manage Atrial Fibrotic Substrates

Atrial fibrillation (AF) is the most common sustained arrhythmia in the population and is associated with a significant clinical and economic burden. Rigorous assessment of the presence and degree of an atrial arrhythmic substrate is essential for determining treatment options, predicting long-term success after catheter ablation, and as a substrate critical in the pathophysiology of atrial thrombogenesis. Catheter ablation of AF has developed into an essential rhythm-control strategy. Nowadays is one of the most common cardiac ablation procedures performed worldwide, with its success inversely related to the extent of atrial structural disease. Although atrial substrate evaluation remains complex, several diagnostic resources allow for a more comprehensive assessment and quantification of the extent of left atrial structural remodeling and the presence of atrial fibrosis. In this review, we summarize the current knowledge on the pathophysiology, etiology, and electrophysiological aspects of atrial substrates promoting the development of AF. We also describe the risk factors for its development and how to diagnose its presence using imaging, electrocardiograms, and electroanatomic voltage mapping. Finally, we discuss recent data regarding fibrosis biomarkers that could help diagnose atrial fibrotic substrates.

Genetically Based Atrial Fibrillation: Current Considerations for Diagnosis and Management

Atrial fibrillation (AF) is the most common atrial arrhythmia and is subcategorized into numerous clinical phenotypes. Given its heterogeneity, investigations into the genetic mechanisms underlying AF have been pursued in recent decades, with predominant analyses focusing on early onset or lone AF. Linkage analyses, genome wide association studies (GWAS), and single gene analyses have led to the identification of rare and common genetic variants associated with AF risk. Significant overlap with genetic variants implicated in dilated cardiomyopathy syndromes, including truncating variants of the sarcomere protein titin, have been identified through these analyses, in addition to other genes associated with cardiac structure and function. Despite this, widespread utilization of genetic testing in AF remains hindered by the unclear impact of genetic risk identification on clinical outcomes and the high prevalence of variants of unknown significance (VUS). However, genetic testing is a reasonable option for patients with early onset AF and in those with significant family history of arrhythmia. While many knowledge gaps remain, emerging data support genotyping to inform selection of AF therapeutics. In this review we highlight the current understanding of the complex genetic basis of AF and explore the overlap of AF with inherited cardiomyopathy syndromes. We propose a set of criteria for clinical genetic testing in AF patients and outline future steps for the integration of genetics into AF care. This article is protected by copyright. All rights reserved.

Expression of atrial‑fetal light chains in cultured human cardiomyocytes after chemical ischemia‑reperfusion injury

Atrial light chains (ALC1) are naturally present in adult heart atria, while ventricular light chains (VLC1) are predominant in ventricles. Degradation of VLC1 and re-expression of ALC1 in heart ventricles are associated with heart disorders in response to pressure overload. The aim of the current study was to investigate changes in myosin light chain expression after simulated ischemia and simulated reperfusion (sI/sR). Human cardiomyocytes (HCM) isolated from adult heart ventricles were subjected to chemical ischemia. The control group was maintained under aerobic conditions. Myocyte injury was determined by testing lactate dehydrogenase (LDH) activity. The gene expression of ALC1, VLC1 and MMP-2 were assessed by reverse transcription-quatitive PCR. Additionally, protein synthesis was measured using ELISA kits and MMP-2 activity was measured by zymography. The results revealed that LDH activity was increased in sI/sR cell-conditioned medium (P=0.02), confirming the ischemic damage of HCM. ALC1 gene expression and content in HCM were also increased in the sI/sR group (P=0.03 and P<0.001, respectively), while VLC1 gene expression after sI/sR was decreased (P=0.008). Furthermore, MMP-2 gene expression and synthesis were lower in the sI/sR group when compared with the aerobic control group (P<0.001 and P=0.03, respectively). MMP-2 activity was also increased in sI/sR cell-conditioned medium (P=0.006). In conclusion, sI/sR treatment led to increased ALC1 and decreased VLC1 expression in ventricular cardiomyocytes, which may constitute an adaptive mechanism to altered conditions and contribute to the improvement of heart function.

Atrial Cardiomyopathy: An Unexplored Limb of Virchow's Triad for AF Stroke Prophylaxis

The most dreaded complication of atrial fibrillation is stroke, and 70–80% of patients with AF-related stroke die or become disabled. The mechanisms of thromboembolism in AF are multifactorial, with evidence demonstrating that all three criteria of Virchow's triad are satisfied in AF: abnormal stasis of blood, endothelial damage, and hypercoagulability. Mechanistic insights into the latter two limbs have resulted in effective stroke prophylactic therapies (left atrial appendage occlusion and oral anticoagulants); however, despite these advances, there remains an excess of stroke in the AF population that may be due, in part, to a lack of mechanistic understanding of atrial hypocontractility resulting in abnormal stasis of blood within the atrium. These observations support the emerging concept of atrial cardiomyopathy as a cause of stroke. In this Review, we evaluate molecular, translational, and clinical evidence for atrial cardiomyopathy as a cause for stroke from AF, and present a rationale for further investigation of this largely unaddressed limb of Virchow's triad in AF.