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BackgroundAtrial fibrillation (AF), the most common sustained cardiac arrhythmia, increases thromboembolic stroke risk five-fold. Although atrial hypocontractility contributes to stroke risk in AF, the molecular mechanisms reducing myofilament contractile function remain unknown. We tested the hypothesis that increased expression of PPP1R12C, the PP1 regulatory subunit targeting atrial myosin light chain 2 (MLC2a), causes hypophosphorylation of MLC2a and results in atrial hypocontractility.MethodsRight atrial appendage tissues were isolated from human AF patients versus sinus rhythm (SR) controls. Western blots, co-immunoprecipitation, and phosphorylation studies were performed to examine how the PP1c-PPP1R12C interaction causes MLC2a de-phosphorylation.In vitrostudies of pharmacologic MRCK inhibitor (BDP5290) in atrial HL-1 cells were performed to evaluate PP1 holoenzyme activity on MLC2a. Cardiac-specific lentiviral PPP1R12C overexpression was performed in mice to evaluate atrial remodeling with atrial cell shortening assays, echocardiography, and AF inducibility with EP studies.ResultsIn human patients with AF, PPP1R12C expression was increased two-fold versus SR controls (P=2.0×10−2, n=12,12 in each group) with > 40% reduction in MLC2a phosphorylation (P=1.4×10−6, n=12,12 in each group). PPP1R12C-PP1c binding and PPP1R12C-MLC2a binding were significantly increased in AF (P=2.9×10−2and 6.7×10−3respectively, n=8,8 in each group).In vitrostudies utilizing drug BDP5290, which inhibits T560-PPP1R12C phosphorylation, demonstrated increased PPP1R12C binding with both PP1c and MLC2a, and dephosphorylation of MLC2a. Lenti-12C mice demonstrated a 150% increase in LA size versus controls (P=5.0×10−6, n=12,8,12), with reduced atrial strain and atrial ejection fraction. Pacing-induced AF in Lenti-12C mice was significantly higher than controls (P=1.8×10−2and 4.1×10−2respectively, n= 6,6,5).ConclusionsAF patients exhibit increased levels of PPP1R12C protein compared to controls. PPP1R12C overexpression in mice increases PP1c targeting to MLC2a and causes MLC2a dephosphorylation, which reduces atrial contractility and increases AF inducibility. These findings suggest that PP1 regulation of sarcomere function at MLC2a is a key determinant of atrial contractility in AF.

Background: Plasma proteins are critical mediators of cardiovascular processes and are the targets of many drugs. Previous efforts to characterize the genetic architecture of the plasma proteome have been limited by a focus on individuals of European descent and leveraged genotyping arrays and imputation. Here we describe whole genome sequence analysis of the plasma proteome in individuals with greater African ancestry, increasing our power to identify novel genetic determinants. Methods: Proteomic profiling of 1301 proteins was performed in 1852 Black adults from the Jackson Heart Study using aptamer-based proteomics (SomaScan). Whole genome sequencing association analysis was ascertained for all variants with minor allele count ≥5. Results were validated using an alternative, antibody-based, proteomic platform (Olink) as well as replicated in the Multi-Ethnic Study of Atherosclerosis and the HERITAGE Family Study (Health, Risk Factors, Exercise Training and Genetics). Results: We identify 569 genetic associations between 479 proteins and 438 unique genetic regions at a Bonferroni-adjusted significance level of 3.8×10 -11 . These associations include 114 novel locus-protein relationships and an additional 217 novel sentinel variant-protein relationships. Novel cardiovascular findings include new protein associations at the APOE gene locus including ZAP70 (sentinel single nucleotide polymorphism [SNP] rs7412-T, β=0.61±0.05, P =3.27×10 -30 ) and MMP-3 (β=-0.60±0.05, P =1.67×10 -32 ), as well as a completely novel pleiotropic locus at the HPX gene, associated with 9 proteins. Further, the associations suggest new mechanisms of genetically mediated cardiovascular disease linked to African ancestry; we identify a novel association between variants linked to APOL1-associated chronic kidney and heart disease and the protein CKAP2 (rs73885319-G, β=0.34±0.04, P =1.34×10 -17 ) as well as an association between ATTR amyloidosis and RBP4 levels in community-dwelling individuals without heart failure. Conclusions: Taken together, these results provide evidence for the functional importance of variants in non-European populations, and suggest new biological mechanisms for ancestry-specific determinants of lipids, coagulation, and myocardial function.

Background: Increased free fatty acids (FFA) and FA infiltration, both major hallmarks of obesity can individually modulate changes leading to AF. For example, mass spectrometry on obese mouse heart tissues have shown that saturated FAs (SFA), monounsaturated FAs (MUFA), and polyunsaturated FAs (PUFA) are all significantly increased compared to controls. The highest increase was shown to be in linoleic acid (LA), a PUFA followed by palmitic acid (PA, SFA) and oleic acid (OA, MUFA). Although reports suggest that some FAs induce ventricular arrhythmias in mice, the differential electrophysiological effects of SFAs, MUFAs, and PUFAs on the atria remain unclear. Objective: To determine the individual roles of SFAs, MUFAs, and PUFAs in mediating atrial remodeling in obesity-induced AF using mature human induced pluripotent stem-derived atrial cardiomyocytes (iPSC-aCMs). Methods: We compared iPSC-aCMs and HL-1 cells treated with bovine serum albumin (BSA) with palmitic acid (PA), oleic acid (OA) and LA cells (600 uM each) for 24 hours and 1 week. Ion channel function were assessed using optical voltage mapping and whole-cell patch clamping, and we assessed atrial remodeling using qPCR, and western blotting. Results: iPSC-aCMs treated with PA, OA, and LA displayed higher expression of FABP3 and CPT1A suggesting increased FA metabolism (Figure A-C). In HL1 cells, protein expression of Cpt1a was increased in all groups after FA treatment (Figure D). PA differentially modulated expression of Kv7.1 and NCX1 in HL1 cells (Figure E-F) and ion channel mRNA expression in iPSC-aCMs (Figure G-L). After 1 week PA and LA treatment b-adrenergic signaling was significantly increased in iPSC-aCMs while OA decreased it compared to controls (Figure M-O). Lastly, 24-hour PA, OA, LA treatment differentially modulated the atrial action potential (AP). While PA and LA significantly shorten the action potential, there was no significant changes to the AP after OA treatment. Conclusions: Using mature iPSC-aCMs, we showed for the first time that SFA, MUFA, and PUFA not only increased FA metabolism but differentially affected b-adrenergic signaling and ion channel remodeling leading to differential effects on the atrial AP. Our findings may have important implications for the management of obesity-induced AF in patients.

BackgroundInherited cardiomyopathies can present with broad variation of phenotype. Data are limited regarding genetic screening strategies and outcomes associated with putative pathogenic variants (PuPV) in cardiomyopathy-associated genes in the general population.ObjectiveWe aimed to determine the risk of mortality and cardiomyopathy-related outcomes associated with PuPV in cardiomyopathy-associated genes in UK Biobank.MethodsUsing whole exome sequencing data, variants in dilated, hypertrophic and arrhythmogenic cardiomyopathy-associated genes with at least limited evidence of disease causality according to ClinGen Expert Panel curations, were annotated using REVEL (≥0.65) and ANNOVAR (predicted loss of function) to identify PuPVs. Individuals with PuPV comprised the genotype-positive (G+) and those without PuPV the genotype-negative (G-) cohorts. Group comparisons were made using time-to-event analyses for the primary (all-cause mortality) and secondary outcomes (diagnosis of cardiomyopathy; composite outcome of diagnosis of cardiomyopathy, heart failure, arrhythmia, stroke, and death).ResultsAmong 200,619 participants, 22,401 (11.2%) were found to host ≥1 PuPV in cardiomyopathy-associated genes (G+). After adjusting for age and sex, G+ individuals had increased all-cause mortality [HR 1.07 (95%CI 1.02-1.13; p=0.011)] and increased rates of diagnosis of cardiomyopathy later in life [HR 2.37 (95%CI 1.98-2.85; pConclusionsAdults with PuPV in cardiomyopathy-associated genes have higher all-cause mortality and increased risk of developing cardiomyopathy-associated features and complications, compared to genotype-negative controls.Condensed AbstractLeveraging the UK Biobank prospective cohort, we analyzed whole exome sequencing data in dilated, hypertrophic and arrhythmogenic cardiomyopathy-associated genes using a population screening ‘genotype-first’ approach. Individuals with putative pathogenic variants in genes implicated in cardiomyopathies showed an increased risk of all-cause mortality, higher risk of developing clinical cardiomyopathy later in life, and higher risk of a composite outcome (cardiomyopathy, heart failure, arrhythmia, stroke, and death) compared to genotype-negative controls. These findings highlight the potential role of ‘genotype-first’ approach in elevating personalized medicine into population level precision health in the future.

The prevalence and economic burden of atrial fibrillation (AF) are predicted to more than double over the next few decades. In addition to anticoagulation and treatment of concomitant cardiovascular conditions, early and standardized rhythm control therapy reduces cardiovascular outcomes as compared with a rate control approach, favouring the restoration, and maintenance of sinus rhythm safely. Current therapies for rhythm control of AF include antiarrhythmic drugs (AADs) and catheter ablation (CA). However, response in an individual patient is highly variable with some remaining free of AF for long periods on antiarrhythmic therapy, while others require repeat AF ablation within weeks. The limited success of rhythm control therapy for AF is in part related to incomplete understanding of the pathophysiological mechanisms and our inability to predict responses in individual patients. Thus, a major knowledge gap is predicting which patients with AF are likely to respond to rhythm control approach. Over the last decade, tremendous progress has been made in defining the genetic architecture of AF with the identification of rare mutations in cardiac ion channels, signalling molecules, and myocardial structural proteins associated with familial (early-onset) AF. Conversely, genome-wide association studies have identified common variants at over 100 genetic loci and the development of polygenic risk scores has identified high-risk individuals. Although retrospective studies suggest that response to AADs and CA is modulated in part by common genetic variation, the development of a comprehensive clinical and genetic risk score may enable the translation of genetic data to the bedside care of AF patients. Given the economic impact of the AF epidemic, even small changes in therapeutic efficacy may lead to substantial improvements for patients and health care systems., Graphical Abstract

Summary Mutations in SCN5A, encoding the cardiac sodium channel, are linked with familial atrial fibrillation (AF) but the underlying pathophysiologic mechanisms and implications for therapy remain unclear. To characterize the pathogenesis of AF-linked SCN5A mutations, we generated patient-specific induced pluripotent stem cell-derived atrial cardiomyocytes (iPSC-aCMs) from two kindreds carrying SCN5A mutations (E428K and N470K) and isogenic controls using CRISPR-Cas9 gene editing. We showed that mutant AF iPSC-aCMs exhibited spontaneous arrhythmogenic activity with beat-to-beat irregularity, prolonged action potential duration, and triggered-like beats. Single-cell recording revealed enhanced late sodium currents (INa,L) in AF iPSC-aCMs that were absent in a heterologous expression model. Gene expression profiling of AF iPSC-aCMs showed differential expression of the nitric oxide (NO)-mediated signaling pathway underlying enhanced INa,L. We showed that patient-specific AF iPSC-aCMs exhibited striking in vitro electrophysiological phenotype of AF-linked SCN5A mutations, and transcriptomic analyses supported that the NO signaling pathway modulated the INa,L and triggered AF., Highlights • Mutations in SCN5A, the gene encoding the cardiac sodium channel, have been linked with familial atrial fibrillation (AF) • SCN5A mutant iPSC-derived atrial cardiomyocytes (aCMs) exhibited arrhythmogenic activity with an AF-like phenotype • AF iPSC-aCMs carrying SCN5A mutation exhibited enhanced late sodium currents (INa,L) • Nitric oxide-mediated signaling pathway modulated enhanced INa,L in AF iPSC-aCMs, Hong et al. showed that patient-specific iPSC-aCMs exhibited striking electrophysiological phenotype of an AF-linked mutation that produced minimal changes in heterologous expression system, and discovered a link between enhanced late sodium currents (INa,L), transcriptional regulation of NO signaling, and triggered AF. These findings not only provide insights into underlying cellular mechanisms of AF-linked mutations but also highlight potential mechanism-based therapies for this common arrhythmia.

The Trans-Omics for Precision Medicine (TOPMed) programme seeks to elucidate the genetic architecture and biology of heart, lung, blood and sleep disorders, with the ultimate goal of improving diagnosis, treatment and prevention of these diseases. The initial phases of the programme focused on whole-genome sequencing of individuals with rich phenotypic data and diverse backgrounds. Here we describe the TOPMed goals and design as well as the available resources and early insights obtained from the sequence data. The resources include a variant browser, a genotype imputation server, and genomic and phenotypic data that are available through dbGaP (Database of Genotypes and Phenotypes)1. In the first 53,831 TOPMed samples, we detected more than 400 million single-nucleotide and insertion or deletion variants after alignment with the reference genome. Additional previously undescribed variants were detected through assembly of unmapped reads and customized analysis in highly variable loci. Among the more than 400 million detected variants, 97% have frequencies of less than 1% and 46% are singletons that are present in only one individual (53% among unrelated individuals). These rare variants provide insights into mutational processes and recent human evolutionary history. The extensive catalogue of genetic variation in TOPMed studies provides unique opportunities for exploring the contributions of rare and noncoding sequence variants to phenotypic variation. Furthermore, combining TOPMed haplotypes with modern imputation methods improves the power and reach of genome-wide association studies to include variants down to a frequency of approximately 0.01%., The goals, resources and design of the NHLBI Trans-Omics for Precision Medicine (TOPMed) programme are described, and analyses of rare variants detected in the first 53,831 samples provide insights into mutational processes and recent human evolutionary history.

Background Studies in the general population suggest that atrial fibrillation (AF) is an independent risk factor for decline in cognitive function, but this relationship has not been examined in adults with chronic kidney disease (CKD). We investigated the association between incident AF and changes in cognitive function over time in this population. Methods and Results We studied a subgroup of 3254 adults participating in the Chronic Renal Insufficiency Cohort Study. Incident AF was ascertained by 12-lead electrocardiogram (ECG) obtained at a study visit and/or identification of a hospitalization with AF during follow-up. Cognitive function was assessed biennially using the Modified Mini-Mental State Exam. Linear mixed effects regression was used to evaluate the association between incident AF and longitudinal change in cognitive function. Compared with individuals without incident AF (n = 3158), those with incident AF (n = 96) were older, had a higher prevalence of cardiovascular disease and hypertension, and lower estimated glomerular filtration rate. After median follow-up of 6.8 years, we observed no significant multivariable association between incident AF and change in cognitive function test score. Conclusion In this cohort of adults with CKD, incident AF was not associated with a decline in cognitive function.

Human genetic studies support an inverse causal relationship between leukocyte telomere length (LTL) and coronary artery disease (CAD), but directionally mixed effects for LTL and diverse malignancies. Clonal hematopoiesis of indeterminate potential (CHIP), characterized by expansion of hematopoietic cells bearing leukemogenic mutations, predisposes both hematologic malignancy and CAD. TERT (which encodes telomerase reverse transcriptase) is the most significantly associated germline locus for CHIP in genome-wide association studies. Here, we investigated the relationship between CHIP, LTL, and CAD in the Trans-Omics for Precision Medicine (TOPMed) program ( n = 63,302) and UK Biobank ( n = 47,080). Bidirectional Mendelian randomization studies were consistent with longer genetically imputed LTL increasing propensity to develop CHIP, but CHIP then, in turn, hastens to shorten measured LTL (mLTL). We also demonstrated evidence of modest mediation between CHIP and CAD by mLTL. Our data promote an understanding of potential causal relationships across CHIP and LTL toward prevention of CAD.

The voltage-gated sodium channels play a key role in the generation and propagation of the cardiac action potential. Emerging data indicate that the Nav1.8 channel, encoded by the SCN10A gene, is a modulator of cardiac conduction and variation in the gene has been associated with arrhythmias such as atrial fibrillation (AF) and Brugada syndrome (BrS). The voltage gated sodium channels contain a calmodulin (CaM)-binding IQ domain involved in channel slow inactivation, we here investigated the role of CaM regulation of Nav1.8 channel function, and showed that CaM enhanced slow inactivation of the Nav1.8 channel and hyperpolarized steady-state inactivation curve of sodium currents. The effects of CaM on the channel gating were disrupted in the Nav1.8 channel truncated IQ domain. We studied Nav1.8 IQ domain mutations associated with AF and BrS, and found that a BrS-linked mutation (R1863Q) reduced the CaM-induced hyperpolarization shift, AF-linked mutations (R1869C and R1869G) disrupted CaM-induced enhanced inactivation, and effects of CaM on both development and recovery from slow inactivation were attenuated in all pathogenic mutations. Our findings indicate a role of CaM in the regulation of Nav1.8 channel function in cardiac arrhythmias.

BACKGROUND: Asthma is a common respiratory disorder with a highly heterogeneous nature that remains poorly understood. The objective was to use whole genome sequencing (WGS) data to identify regions of common genetic variation contributing to lung function in individuals with a diagnosis of asthma. METHODS: WGS data were generated for 1,053 individuals from trios and extended pedigrees participating in the family-based Genetic Epidemiology of Asthma in Costa Rica study. Asthma affection status was defined through a physician’s diagnosis of asthma, and most participants with asthma also had airway hyperresponsiveness (AHR) to methacholine. Family-based association tests for single variants were performed to assess the associations with lung function phenotypes. RESULTS: A genome-wide significant association was identified between baseline FEV(1)/FVC ratio and a single-nucleotide polymorphism in the top hit cysteine-rich secretory protein LCCL domain-containing 2 (CRISPLD2) (rs12051168; P = 3.6 × 10(−8) in the unadjusted model) that retained suggestive significance in the covariate-adjusted model (P = 5.6 × 10(−6)). Rs12051168 was also nominally associated with other related phenotypes: baseline FEV(1) (P = 3.3 × 10(−3)), postbronchodilator (PB) FEV(1) (7.3 × 10(−3)), and PB FEV(1)/FVC ratio (P = 2.7 × 10(−3)). The identified baseline FEV(1)/FVC ratio and rs12051168 association was meta-analyzed and replicated in three independent cohorts in which most participants with asthma also had confirmed AHR (combined weighted z-score P = .015) but not in cohorts without information about AHR. CONCLUSIONS: These findings suggest that using specific asthma characteristics, such as AHR, can help identify more genetically homogeneous asthma subgroups with genotype-phenotype associations that may not be observed in all children with asthma. CRISPLD2 also may be important for baseline lung function in individuals with asthma who also may have AHR.

A diverse set of driver genes, such as regulators of DNA methylation, RNA splicing, and chromatin remodeling, have been associated with pre-malignant clonal expansion of hematopoietic stem cells (HSCs). The factors mediating expansion of these mutant clones remain largely unknown, partially due to a paucity of large cohorts with longitudinal blood sampling. To circumvent this limitation, we developed and validated a method to infer clonal expansion rate from single timepoint data called PACER (passenger-approximated clonal expansion rate). Applying PACER to 5,071 persons with clonal hematopoiesis accurately recapitulated the known fitness effects due to different driver mutations. A genome-wide association study of PACER revealed that a common inherited polymorphism in the TCL1A promoter was associated with slower clonal expansion. Those carrying two copies of this protective allele had up to 80% reduced odds of having driver mutations in TET2, ASXL1, SF3B1, SRSF2, and JAK2, but not DNMT3A. TCL1A was not expressed in normal or DNMT3A-mutated HSCs, but the introduction of mutations in TET2 or ASXL1 by CRISPR editing led to aberrant expression of TCL1A and expansion of HSCs in vitro. These effects were abrogated in HSCs from donors carrying the protective TCL1A allele. Our results indicate that the fitness advantage of multiple common driver genes in clonal hematopoiesis is mediated through TCL1A activation. PACER is an approach that can be widely applied to uncover genetic and environmental determinants of pre-malignant clonal expansion in blood and other tissues.

Introduction: Catheter ablation (CA) is now an established therapy for symptomatic atrial fibrillation (AF). Although the procedural success rate is high, the role of race-ethnicity and clinical predictors in preventing recurrence of AF remains unclear. Methods: Patients prospectively enrolled in an AF clinical-DNA biorepository and treated with CA for AF were included in the study. Recurrence of AF was assessed with symptom assessment, ECG, Holter, and event recorder evaluations in all patients during follow-up visits and Holter recordings were done when appropriate. Recurrence of AF was defined as AF detected Results: Of the 238 enrolled, 84 (35.3%) were European American (EAs), 106 (44.5%) were African American (AA) and 48 (20.2%) were Hispanic American (HA). Baseline clinical characteristics were similar across the groups. Eighty-eight (37%) patients had AF recurrence within 12 months of CA. Multivariate analysis showed that compared to EAs, AAs (odds ratio [OR] 0.48, 95% confidence interval [CI]: 0.24-0.96, P+0.048) and HAs (OR 0.42, 95% CI: 0.18 - 0.94, P+0.048) are less likely to experience AF recurrence after CA (Table 1). Other clinical predictors included left atrial dilatation (OR 1.88, 95% 1.04 - 3.44, P+0.036), persistent AF (OR] 1.94, 95% [CI]: 1.04-3.64, P+0.074), valvular heart disease (VHD) (OR 2.66, 95% CI: 1.02-7.20; P=0.046) and history of smoking (OR 2.16, 95% CI: 1.18-3.99; P=0.012). Conclusion: We showed that clinical predictors of recurrence of AF after CA included left atrial dilatation, VHD, persistent AF and a history of smoking. Surprisingly, we found that AAs and HAs were less likely to experience AF recurrence than EAs and reasons for this differential response remains unclear.

Introduction: Although smoking is associated with increased risk of developing atrial fibrillation (AF) and stroke, whether it also predicts response to rhythm control therapy across race-ethnicity remains unclear. Hypothesis: We hypothesize that smokers are less likely to respond to rhythm control therapy for AF than non-smokers. Methods: In this cohort study, patients managed with rhythm control strategy at the time of enrollment to the study were prospectively enrolled in an AF multi-center clinical-DNA biorepository. Rhythm control includes antiarrhythmic drugs (AADs) and\or catheter ablation. Successful response was defined as continuation of the same AAD for at least 6 months and/or successful catheter ablation without recurrence of AF for 12 months. Results: Of the 362 enrolled, 132 (36.4%) were European American, 155 (42.8%) were African- American and 75 (20.7%) were Hispanic American. 125 patients were smokers and 237 patients were non-smokers. Baseline clinical characteristics were similar in both groups (Table 1). Compared to nonsmokers, smokers were less likely to respond to rhythm control strategy (odds ratio [OR] 1.36, 95% confidence interval [CI]: 0.88-2.11, P-value: 0.07). Adjusted for the type of rhythm control, smokers were more likely to have a recurrence of AF catheter ablation as compared with nonsmokers ([OR] 1.38, 95% [CI]: 1.031-2.348, P-value: 0.044). However, there was no significant difference between smokers and non-smokers in terms of response to AADs ([OR] 1.25, 95% [CI]: 0.560-2.809, P-value: 0.292). Conclusions: Patients with a smoking history were less likely to respond rhythm control therapy as compared to nonsmokers. After adjusting for the type of rhythm treatment, smokers were more likely to have a recurrence of AF when compared to non-smokers but there was no difference in response to AADs between the two groups.

Background: Obesity-induced atrial fibrillation (AF) is modulated in part by increased serum free fatty acids (FFA) and FA infiltration of the heart. Mass spectrometry data on obese mice have shown increased saturated FAs (SFA), monounsaturated FAs (MUFA), and polyunsaturated FAs (PUFA) compared to lean controls with the largest increase in the PUFA, linoleic acid (LA). Although reports suggest that some FAs induce ventricular arrhythmias in mice, the differential electrophysiological (EP) effects of SFAs, MUFAs, and PUFAs on the atria remain unclear. Objective: To determine if SFAs, MUFAs, and PUFAs differentially modulate atrial remodeling using mature human induced pluripotent stem-derived atrial cardiomyocytes (iPSC-aCMs) and HL1 cells. . Methods: We compared iPSC-aCMs and HL-1 cells treated with bovine serum albumin (BSA) with palmitic acid (PA), oleic acid (OA) and LA (600 uM each) for 1 week. Ion channel function was assessed using whole-cell patch clamping and we assessed β-oxidation and atrial remodeling with using ELISA, qPCR, and Western blotting. Results: iPSC-aCMs treated with PA, OA, and LA displayed higher expression of FABP3 , ANGPTL4 , and CPT1A suggesting increased FA metabolism and β-oxidation (Figure A-C). In HL1 cells, protein expression of Cpt1a was increased in all groups after FA treatment (Figure D). PA differentially modulated expression of Kv7.1 and NCX1 in HL1 cells (Figure E-F) and ion channel mRNA expression in iPSC-aCMs (Figure G-L). After 1 week PA and LA treatment β-adrenergic signaling was significantly increased in iPSC-aCMs while OA decreased it compared to controls (Figure M-O). Conclusions: Using mature iPSC-aCMs, we showed for the first time that SFA, MUFA, and PUFA not only increased FA metabolism but also differentially modulated ion channel and structural remodeling and β-adrenergic signaling in the atria. Our findings may have important implications for the management of obesity-induced AF in patients.

The QT interval is an electrocardiographic measure representing the sum of ventricular depolarization (QRS duration) and repolarization (JT interval). Abnormalities of the QT interval are associated with potentially fatal ventricular arrhythmia. We conducted genome-wide multi-ancestry analyses in >250,000 individuals and identified 177, 156 and 121 independent loci for QT, JT and QRS, respectively, including a male-specific X-chromosome locus. Using gene-based rare-variant methods, we identified associations with Mendelian disease genes. Enrichments were observed in established pathways for QT and JT, with new genes indicated in insulin-receptor signalling and cardiac energy metabolism. In contrast, connective tissue components and processes for cell growth and extracellular matrix interactions were significantly enriched for QRS. We demonstrate polygenic risk score associations with atrial fibrillation, conduction disease and sudden cardiac death. Prioritization of druggable genes highlighted potential therapeutic targets for arrhythmia. Together, these results substantially advance our understanding of the genetic architecture of ventricular depolarization and repolarization.

Importance Early-onset atrial fibrillation (AF) can be the initial manifestation of a more serious underlying inherited cardiomyopathy or arrhythmia syndrome. Objective To examine the results of genetic testing for early-onset AF. Design, Setting, and Participants This prospective, observational cohort study enrolled participants from an academic medical center who had AF diagnosed before 66 years of age and underwent whole genome sequencing through the National Heart, Lung, and Blood Institute’s Trans-Omics for Precision Medicine program. Participants were enrolled from November 23, 1999, to June 2, 2015. Data analysis was performed from October 24, 2020, to March 11, 2021. Exposures Rare variants identified in a panel of 145 genes that are included on cardiomyopathy and arrhythmia panels used by commercial clinical genetic testing laboratories. Main Outcomes and Measures Sequencing data were analyzed using an automated process followed by manual review by a panel of independent, blinded reviewers. The primary outcome was classification of rare variants using American College of Medical Genetics and Genomics criteria: benign, likely benign, variant of undetermined significance, likely pathogenic, or pathogenic. Disease-associated variants were defined as pathogenic/likely pathogenic variants in genes associated with autosomal dominant or X-linked dominant disorders. Results Among 1293 participants (934 [72.2%] male; median [interquartile range] age at enrollment, 56 [48-61] years; median [interquartile range] age at AF diagnosis, 50 [41-56] years), genetic testing identified 131 participants (10.1%) with a disease-associated variant, 812 (62.8%) with a variant of undetermined significance, 92 (7.1%) as heterozygous carriers for an autosomal recessive disorder, and 258 (20.0%) with no suspicious variant. The likelihood of a disease-associated variant was highest in participants with AF diagnosed before the age of 30 years (20 of 119 [16.8%; 95% CI, 10.0%-23.6%]) and lowest after the age of 60 years (8 of 112 [7.1%; 95% CI, 2.4%-11.9%]). Disease-associated variants were more often associated with inherited cardiomyopathy syndromes compared with inherited arrhythmias. The most common genes wereTTN(n = 38),MYH7(n = 18),MYH6(n = 10),LMNA(n = 9), andKCNQ1(n = 8). Conclusions and Relevance In this cohort study, genetic testing identified a disease-associated variant in 10% of patients with early-onset AF (the percentage was higher if diagnosed before the age of 30 years and lower if diagnosed after the age of 60 years). Most pathogenic/likely pathogenic variants are in genes associated with cardiomyopathy. These results support the use of genetic testing in early-onset AF.

Introduction: Atrial fibrillation (AF), is the most common sustained arrhythmia, with an estimated prevalence in the U.S. of 2.7 million to 6.1 million and is predictive to increase to 12.1 million in 2030. AF increases the chances of a thromboembolic stroke in five-fold. Although atrial hypocontractility contributes to stroke risk in AF, the molecular mechanisms reducing myofilament contractile function in AF remains unknown. Objective: The overexpression of PPP1R12C, causes hypophosphorylation of atrial myosin light chain 2 (MLC2a), decreasing atrial contractility. Methods and Results: Left and right atrial appendage tissues were isolated from AF patients versus sinus rhythm (SR). To evaluated the role of PP1c-PPP1R12C interaction in MLC2a de-phosphorylation we used Western blots, coimmunoprecipitation, and phosphorylation assays. In patients with AF, PPP1R12C expression was increased 3.5-fold versus SR controls with an 88% reduction in MLC2a phosphorylation. PPP1R12C-PP1c binding and PPP1R12C-MLC2a binding were significantly increased in AF. In vitro studies of either pharmacologic (BDP5290) or genetic (T560A) PPP1R12C activation demonstrated increased PPP1R12C binding with both PP1c and MLC2a, and dephosphorylation of MLC2a. Additionally, to evaluate the role of PPP1R12C expression in cardiac function, mice with lentiviral cardiac-specific overexpression of PPP1R12C (Lenti-12C) were evaluated for atrial contractility using echocardiography, versus wild-type and Lenti-controls. Lenti-12C mice demonstrated a 150% increase in left atrium size versus controls, with reduced atrial strain and atrial ejection fraction. Also, programmed electrical stimulation was performed to evaluate AF inducibility in vivo. Pacing-induced AF in Lenti-12C mice was significantly higher than controls. Conclusion: The Overexpression of PPP1R12C increases PP1c targeting to MLC2a and provokes dephosphorylation, that cause a reduction in atrial contractility and increases AF inducibility. All these discoveries advocate that PP1 regulation of sarcomere function at MLC2a is a main regulator of atrial contractility in AF.

Background: Inducible atrial fibrillation (AF) in diet-induced obese (DIO) mice is mediated in part by a combined effect of ion channel remodeling and atrial fibrosis. NADPH oxidase 2 (NOX2), a major source of reactive oxygen species (ROS) production in human atria, is increased in DIO mice. Although a mitochondrial antioxidant (MitoTEMPO) reduced AF burden, and reversed ion channel and structural remodeling, the role of NOX2 in increased ROS production and atrial remodeling in obesity-induced AF remains unclear. Objective: To test the hypothesis that increased NOX2 modulates atrial remodeling in obesity-induced AF, we treated DIO mice with apocynin, NOX2 inhibitor, and fed a 60% high fat diet (HFD) to Nox2 -KO mice. Methods: Weight, BP, plasma glucose, trans-esophageal rapid (TE) pacing and F 2 -isoprostanes were measured in DIO mice and compared to controls. Echocardiography, electrophysiology (EP), immunohistochemistry, Western blotting, cellular patch clamping and optical mapping studies were performed. Results: The average weight of DIO mice treated with apocynin (DIO-A) and vehicle control mice was 38.4 ± 3.8 g versus 44.0 ± 7.5 g versus 31.7 ± 1.19 g respectively (P≤0.0001). Both groups of DIO mice displayed progressive increase in weight over 10 weeks of HFD + drug treatment compared to controls (P≤0.0001). After TE pacing, DIO mice treated with apocynin showed significantly reduced pacing-induced AF burden when compared to DIO mice treated with vehicle. DIO mice treated with apocynin displayed 20.2 ± 26.1 sec versus 162.3 ± 133.7 sec and 18.3 ± 18.1 sec in DIO mice treated with vehicle and control mice respectively (P≤0.0001). Western blotting experiments showed that potassium channels, Kv7.1 and Kv1.5 protein expression is restored in Nox2 -KO HFD mice compared to DIO mice thus indicating restoration of ion channel remodeling upon Nox2 inhibition. Conclusions: We showed that genetic and pharmacological inhibition of NOX2 abrogates ion channel remodeling and reverses obesity-induced AF burden. Our findings may have important implications for the management of obesity-mediated AF in patients.