Search

Background: The gut microbiota-dependent metabolite phenylacetylgutamine (PAGln) is both associated with atherothrombotic heart disease in humans, and mechanistically linked to cardiovascular disease pathogenesis in animal models via modulation of adrenergic receptor signaling. Methods: Here we examined both clinical and mechanistic relationships between PAGln and heart failure (HF). First, we examined associations among plasma levels of PAGln and HF, left ventricular ejection fraction, and N-terminal pro-B-type natriuretic peptide in 2 independent clinical cohorts of subjects undergoing coronary angiography in tertiary referral centers (an initial discovery US Cohort, n=3256; and a validation European Cohort, n=829). Then, the impact of PAGln on cardiovascular phenotypes relevant to HF in cultured cardiomyoblasts, and in vivo were also examined. Results: Circulating PAGln levels were dose-dependently associated with HF presence and indices of severity (reduced ventricular ejection fraction, elevated N-terminal pro-B-type natriuretic peptide) independent of traditional risk factors and renal function in both cohorts. Beyond these clinical associations, mechanistic studies showed both PAGln and its murine counterpart, phenylacetylglycine, directly fostered HF-relevant phenotypes, including decreased cardiomyocyte sarcomere contraction, and B-type natriuretic peptide gene expression in both cultured cardiomyoblasts and murine atrial tissue. Conclusions: The present study reveals the gut microbial metabolite PAGln is clinically and mechanistically linked to HF presence and severity. Modulating the gut microbiome, in general, and PAGln production, in particular, may represent a potential therapeutic target for modulating HF. Registration: URL: https://clinicaltrials.gov/ ; Unique identifier: NCT00590200 and URL: https://drks.de/drks_web/ ; Unique identifier: DRKS00020915.

While newborns and children with hearing loss are routinely offered genetic testing, adults are rarely clinically tested for a genetic etiology. One clinically actionable result from genetic testing in children is the discovery of variants in syndromic hearing loss genes. EYA4 is a known hearing loss gene which is also involved in important pathways in cardiac tissue. The pleiotropic effects of rare EYA4 variants are poorly understood and their prevalence in a large cohort has not been previously reported. We investigated cardio-auditory phenotypes in 11,451 individuals in a large biobank using a rare variant, genome-first approach to EYA4. We filtered 256 EYA4 variants carried by 6737 participants to 26 rare and predicted deleterious variants carried by 42 heterozygotes. We aggregated predicted deleterious EYA4 gene variants into a combined variable (i.e. “gene burden”) and performed association studies across phenotypes compared to wildtype controls. We validated findings with replication in three independent cohorts and human tissue expression data. EYA4 gene burden was significantly associated with audiometric-proven HL (p = $${5.43\times 10}^{-5})$$ , Mobitz Type II AV block (p = $${2.16\times 10}^{-5}$$ ) and the syndromic presentation of HL and primary cardiomyopathy (p = 0.0194). Analyses on audiogram, echocardiogram, and electrocardiogram data validated these associations. Prior reports have focused on identifying variants in families with severe or syndromic phenotypes. In contrast, we found, using a genotype-first approach, that gene burden in EYA4 is associated with more subtle cardio-auditory phenotypes in an adult medical biobank population, including cardiac conduction disorders which have not been previously reported. We show the value of using a focused approach to uncover human disease related to pleiotropic gene variants and suggest a role for genetic testing in adults presenting with hearing loss.

ObjectiveCreeping fat, the wrapping of mesenteric fat around the bowel wall, is a typical feature of Crohn’s disease, and is associated with stricture formation and bowel obstruction. How creeping fat forms is unknown, and we interrogated potential mechanisms using novel intestinal tissue and cell interaction systems.DesignTissues from normal, UC, non-strictured and strictured Crohn’s disease intestinal specimens were obtained. The muscularis propria matrisome was determined via proteomics. Mesenteric fat explants, primary human preadipocytes and adipocytes were used in multiple ex vivo and in vitro cell migration systems on muscularis propria muscle cell derived or native extracellular matrix. Functional experiments included integrin characterisation via flow cytometry and their inhibition with specific blocking antibodies and chemicals.ResultsCrohn’s disease muscularis propria cells produced an extracellular matrix scaffold which is in direct spatial and functional contact with the immediately overlaid creeping fat. The scaffold contained multiple proteins, but only fibronectin production was singularly upregulated by transforming growth factor-β1. The muscle cell-derived matrix triggered migration of preadipocytes out of mesenteric fat, fibronectin being the dominant factor responsible for their migration. Blockade of α5β1 on the preadipocyte surface inhibited their migration out of mesenteric fat and on 3D decellularised intestinal tissue extracellular matrix.ConclusionCrohn’s disease creeping fat appears to result from the migration of preadipocytes out of mesenteric fat and differentiation into adipocytes in response to an increased production of fibronectin by activated muscularis propria cells. These new mechanistic insights may lead to novel approaches for prevention of creeping fat-associated stricture formation.

Introduction: Ibrutinib is a Bruton kinase inhibitor which treats many hematological malignancies, but also precipitates atrial fibrillation (AF). The precise mechanism(s) remain to be elucidated. Hypothesis: We hypothesized ibrutinib treatment would decrease mitochondrial function and metabolic gene expression in human inducible pluripotent stem cell-derived atrial cardiomyocytes grown as atrial-like engineered heart tissues (aEHTs). Methods: aEHTs were treated with vehicle or 1 μM ibrutinib daily, for 72 hours. Oxidative phosphorylation was assessed (n=5/group) using an Oroboros Oxygraph. Gene expression was evaluated by RNAseq (n=3/group). Results: Oxidative phosphorylation in the presence of complex I and complex II substrates, and maximal oxidative capacity, was decreased in ibrutinib-treated aEHTs compared to vehicle (Panel A). Subunit expression of complex I (NDUFA6, NDUFA9, NDUFS1, NDUFS2, NDUFS4, ND3, ND4, ND5, ND4L), complex II (SDHA, SDHB, SDHD), complex III (UQCR10, UQCRB, UQCRC1, UQCRC2, UQCRFS1), and complex IV (CO2, COX10, COX7A2, CYCS) was decreased. Ingenuity Pathway Analysis of genes differentially expressed identified TCA Cycle and Glycolysis I (Panel B), pathways that provide reducing equivalents to the electron transport chain, as pathways that were decreased by ibrutinib. These changes were accompanied by decreased AMPK Signaling, including key metabolic regulators (PRKAA2, PRKAB2, PRKAG2, SIRT1, and PPARGC1A), and Calcium Signaling. Tumor protein (TP53), nuclear protein 1 (NUPR1), and erb-B2 receptor tyrosine kinase (ERBB2) were identified as top upstream regulators. Conclusions: Ibrutinib treatment decreased oxidative phosphorylation and gene expression of electron transport chain subunits and key modulators of atrial metabolism. Together, these data identify metabolic pathways that are altered by ibrutinib in aEHTs and metabolic regulators that could be targeted for AF therapeutic intervention.

Introduction: Atrial fibrillation (AF) increases energy demand for contractile and electrical activity. Changes in left atrial (LA) protein expression of AF patients are poorly characterized. Hypothesis: Mitochondrial protein expression in patients with AF is altered in an attempt to meet increased energy demand. Methods: LA appendage tissue was obtained from 198 patients undergoing Maze surgery. At the time of surgery, 80 were in sinus rhythm (SR) (50 paroxysmal AF, 30 persistent AF) and 118 in AF (65 persistent AF, 53 permanent AF). Protein content was assessed by mass spectrometry and 2539 proteins were identified. Results: In AF compared to SR, 257 proteins were differentially expressed (q Conclusions: In one of the largest proteomic datasets in human LA to date, we find that expression of proteins in metabolic, myofibrillar, and calcium regulation pathways is altered in patients with AF. Additional metabolic changes were detected with progression to permanent AF. These data identify proteins that are altered in patients with AF providing insight into cellular pathways that may be targeted for AF prevention and therapy.

Background Patients undergoing surgery for thoracic aortic aneurysms receive statin therapy out of proportion to cardiovascular comorbidity. We sought to determine the prevalence of statin use among patients presenting for thoracic aortic aneurysm surgery and investigate its effect on outcomes. Methods From January 1, 2005 to January 1, 2011, 1,839 consecutive patients underwent aortic replacement for degenerative thoracic aortic aneurysm at Cleveland Clinic. Of these, 771 (42%) were on statins preoperatively. Statin users (vs. nonstatin users) were older (65 ± 11 vs. 56 ± 16 years) and had more hypertension (78 vs. 59%). Propensity matching based on 56 preoperative variables other than lipid levels was used to compare outcomes among 570 matched patient pairs (74% of possible pairs). Results Propensity-matched statin and nonstatin users were aged 64 ± 11 years, 394 (69%) versus 387 (68%) were male, and 437 (77%) versus 442 (78%) had ascending aortic aneurysms, respectively. Overall, 25% of patients were followed for more than 8.2 years and 10% for more than 10 years. Perioperative outcomes were similar, including hospital mortality (11 [1.9%] vs. 5 [0.88%]) and stroke (22 [3.9%] vs. 13 [2.3%]), but 16 statin users (2.8%) versus 5 nonstatin users (0.88%) required temporary dialysis after surgery (p = 0.02). At 6 years, 3.7% of statin users versus 5.1% of nonstatin users (p[log-rank] = 0.5) underwent further aortic surgery, and at 10 years, mortality was 25% in both groups (p > 0.5). Conclusion Patients presenting for thoracic aortic aneurysm surgery frequently receive unnecessary statins. Additionally, statin use was associated with more postoperative renal failure, but not less intermediate-term risk for aortic reintervention or all-cause mortality after surgery. Therefore, presence of a thoracic aortic aneurysm should not be considered an indication for statin therapy in the absence of well-established indications.

Atrial fibrillation (AF) is a significant cause of morbidity and mortality, and effective therapeutic interventions are lacking. Here, we harness an integrative, network medicine approach to repurpose FDA-approved drugs for AF. We hypothesize that the use of an unbiased method for prioritizing AF drugs using patient transcriptomics data can help to identify alternative therapeutic strategies and mechanism-of-action for these drugs. To achieve this, we first characterized the molecular networks specific to AF by incorporating transcriptomic data of left atrial tissue. We quantified the network proximity of genes differentially expressed in AF to drug targets to identify putative drugs for repurposing. We identified nine high-confidence drug candidates that were validated using enrichment analysis of drug-gene signatures in human cell lines. We identified metformin for the potential treatment of AF and validated its use in human inducible pluripotent stem cell-derived atrial-like cardiomyocytes. We identified AF-specific dysregulated networks enriched in cardiac metabolism, ion transport, and immune pathways that were improved following metformin treatment. In summary, this study utilized network-based approaches for rapid identification of drugs that may be repurposed for AF treatment and validated metformin as a candidate drug using a robust human atrial cell model.

Atrial fibrillation (AF) risk is heritable. High rate electrical activity in AF requires increased energy. Atrial mitochondrial structure and function are altered in AF patients in an effort to generate adequate ATP through oxidative phosphorylation. Genomic studies have identified putative AF risk genes, but the association of AF risk genes with expression of mitochondrial genes is unclear. We tested the hypothesis that putative AF risk genes are co-expressed with mitochondrial genes that play a role in atrial energy production. RNA-seq was performed on left atrial appendage (LAA) tissues obtained from 251 cardiac surgery patients. RNA coexpression profiles were evaluated for 222 putative AF risk genes. Genes encoding proteins that localize to the mitochondria were identified using MitoCarta 2.0. Changes in metabolic pathways were detected using Ingenuity Pathway Analysis (IPA). Our analysis identified 128 AF risk genes that coexpressed with at least one mitochondrial gene. The highest level of mitochondrial gene coexpression was evident with PCCB, in which 30% (253 of 848) of coexpressed genes were mitochondrial. CASQ2 (24%, 104 of 431) and ASAH1 (20%, 37 of 182) also showed high levels of mitochondrial gene coexpression. The IPA Oxidative Phosphorylation Pathway was significantly altered (p

Effective drugs for atrial fibrillation (AF) are lacking, resulting in significant morbidity and mortality. This study demonstrates that network proximity analysis of differentially expressed genes from atrial tissue to drug targets can help prioritize repurposed drugs for AF. Using enrichment analysis of drug-gene signatures and functional testing in human inducible pluripotent stem cell (iPSC)-derived atrial-like cardiomyocytes, we identify metformin as a top repurposed drug candidate for AF. Using the active compactor, a new design analysis of large-scale longitudinal electronic health record (EHR) data, we determine that metformin use is significantly associated with a reduced risk of AF (odds ratio = 0.48, 95%, confidence interval [CI] 0.36-0.64, p 0.001) compared with standard treatments for diabetes. This study utilizes network medicine methodologies to identify repurposed drugs for AF treatment and identifies metformin as a candidate drug.

There has been sustained focus on the secondary prevention of coronary heart disease and heart failure; yet, apart from stroke prevention, the evidence base for the secondary prevention of atrial fibrillation (AF) recurrence, AF progression, and AF‐related complications is modest. Although there are multiple observational studies, there are few large, robust, randomized trials providing definitive effective approaches for the secondary prevention of AF. Given the increasing incidence and prevalence of AF nationally and internationally, the AF field needs transformative research and a commitment to evidenced‐based secondary prevention strategies. We report on a National Heart, Lung, and Blood Institute virtual workshop directed at identifying knowledge gaps and research opportunities in the secondary prevention of AF. Once AF has been detected, lifestyle changes and novel models of care delivery may contribute to the prevention of AF recurrence, AF progression, and AF‐related complications. Although benefits seen in small subgroups, cohort studies, and selected randomized trials are impressive, the widespread effectiveness of AF secondary prevention strategies remains unknown, calling for development of scalable interventions suitable for diverse populations and for identification of subpopulations who may particularly benefit from intensive management. We identified critical research questions for 6 topics relevant to the secondary prevention of AF: (1) weight loss; (2) alcohol intake, smoking cessation, and diet; (3) cardiac rehabilitation; (4) approaches to sleep disorders; (5) integrated, team‐based care; and (6) nonanticoagulant pharmacotherapy. Our goal is to stimulate innovative research that will accelerate the generation of the evidence to effectively pursue the secondary prevention of AF.

The incidence of inflammatory bowel diseases (IBD) worldwide has resulted in a global public health challenge. Intestinal fibrosis leading to stricture formation and bowel obstruction is a frequent complication in Crohn's disease (CD), and the lack of anti-fibrotic therapies makes elucidation of fibrosis mechanisms a priority. Progress has shown that mesenchymal cells, cytokines, microbial products, and mesenteric adipocytes are jointly implicated in the pathogenesis of intestinal fibrosis. This recent information puts prevention or reversal of intestinal strictures within reach through innovative therapies validated by reliable clinical trial endpoints. Here, we review the role of immune and non-immune components of the pathogenesis of intestinal fibrosis, including new cell clusters, cytokine networks, host-microbiome interactions, creeping fat, and their translation for endpoint development in anti-fibrotic clinical trials.

Background: Elevated intracardiac pressure attributable to heart failure induces electrical and structural remodeling in the left atrium (LA) that begets atrial myopathy and arrhythmias. The underlying molecular pathways that drive atrial remodeling during cardiac pressure overload are poorly defined. The purpose of this study is to characterize the response of the ETV1 (ETS translocation variant 1) signaling axis in the LA during cardiac pressure overload in humans and mouse models and explore the role of ETV1 in atrial electrical and structural remodeling. Methods: We performed gene expression profiling in 265 left atrial samples from patients who underwent cardiac surgery. Comparative gene expression profiling was performed between 2 murine models of cardiac pressure overload, transverse aortic constriction banding and angiotensin II infusion, and a genetic model of Etv1 cardiomyocyte-selective knockout ( Etv1 f/f Mlc2a Cre /+ ). Results: Using the Cleveland Clinic biobank of human LA specimens, we found that ETV1 expression is decreased in patients with reduced ejection fraction. Consistent with its role as an important mediator of the NRG1 (Neuregulin 1) signaling pathway and activator of rapid conduction gene programming, we identified a direct correlation between ETV1 expression level and NRG1 , ERBB4 , SCN5A , and GJA5 levels in human LA samples. In a similar fashion to patients with heart failure, we showed that left atrial ETV1 expression is downregulated at the RNA and protein levels in murine pressure overload models. Comparative analysis of LA RNA sequencing datasets from transverse aortic constriction and angiotensin II–treated mice showed a high Pearson correlation, reflecting a highly ordered process by which the LA undergoes electrical and structural remodeling. Cardiac pressure overload produced a consistent downregulation of ErbB4 , Etv1 , Scn5a , and Gja5 and upregulation of profibrotic gene programming, which includes Tgfbr1/2, Igf1 , and numerous collagen genes. Etv1 f/f Mlc2a Cre /+ mice displayed atrial conduction disease and arrhythmias. Correspondingly, the LA from Etv1 f/f Mlc2a Cre /+ mice showed downregulation of rapid conduction genes and upregulation of profibrotic gene programming, whereas analysis of a gain-of-function ETV1 RNA sequencing dataset from neonatal rat ventricular myocytes transduced with Etv1 showed reciprocal changes. Conclusions: ETV1 is downregulated in the LA during cardiac pressure overload, contributing to both electrical and structural remodeling.

Introduction: SYNE2 encodes a nuclear membrane protein that connects the nucleus with the cytoskeleton. rs1152591 is a common SNP in the SYNE2 gene that is associated with atrial fibrillation (AF) and with reduced expression of SYNE2α1 , a short isoform, in human left atrial appendage tissue. We previously found that SYNE2α1 over expression (OE) acts as a dominant negative for the nuclear phenotype, similar to the SYNE2 knockdown (KD), leading to enlarged nuclear size and decreased nuclear stiffness. Objectives: To determine if GFP- SYNE2α1 (OE) and KD of all SYNE2 isoforms show similar effects on gene expression and cell physiology in human induced pluripotent stem cell-derived cardiomyocytes (iCMs). Methods and Results: RNAseq after SYNE2α1 OE or SYNE2 KD revealed both congruent changes in expression of specific genes, supporting the dominant negative role of SYNE2α1 , but also divergent changes in expression of some genes, showing specific effects of the SYNE2α1 short isoform. We identified both mitochondrial function and sarcoplasmic reticulum (SR) function as differentially expressed pathways comparing OE vs. KD iCMs. Fura-2 photometry was used to study Ca 2+ cycling in beating iCMs, and revealed delayed calcium reuptake in the SYNE2 KD cells (15.9% increase in reuptake time as % of each contraction, pSYNE2α1 OE cells (not significant). Flow cytometry showed significantly lower SERCA2 expression in the SYNE2 KD cells but not in the SYNE2α1 OE cells (12% decrease, p=0.029). Immunofluorescence microscopy revealed that GFP-SYNE2α1 not only localized to the nuclear membrane but also to the SR, stained with anti-SERCA2. Flow cytometry after MitoTracker Orange staining, to monitor the cellular volume of functional mitochondria, was significantly increased in both the SYNE2α1 OE and SYNE2 KD iCMs vs. their respective controls. Thus, despite differential expression of mitochondrial pathway genes, SYNE2α1 mimics the KD of all SYNE2 isoforms in regard to mitochondrial function. Conclusions: SYNE2α1 OE, unlike KD of all SYNE2 isoforms, preserves SR Ca 2+ reuptake activity, and this may contribute to the mechanism by which the AF risk allele in the SYNE2 gene, associated with decreased expression of SYNE2α1, predisposes carriers to AF.

Introduction: Over 135 genetic loci have been linked to atrial fibrillation (AF), yet the biological pathways of AF pathophysiology remain elusive. Weighted gene coexpression network analysis (WGCNA) constructs gene modules within a network based on correlations in gene expression, and identifies mechanisms related to AF risk. Objective: To identify biological pathways of candidate AF risk genes that will advance our understanding of AF mechanisms. Methods: RNA-sequencing was performed on left atrial appendage tissue from 265 patients. RNA-seq data were adjusted for differences in AF rhythm state and other known AF risk factors. Correlations from adjusted data were further adjusted for latent factors then spatial quantile normalized to correct for mean-variance bias. WGCNA was applied to the resulting adjusted and normalized gene-gene correlations to identify gene modules. Ingenuity Pathway Analysis and gene set over representation analysis (GSOR) were applied to each module. Results: WGCNA identified 63 modules from 17,434 genes; 47 of these contained at least one candidate AF risk gene. AF risk genes were overrepresented in 7 modules (Table 1). Notable top pathways of AF overrepresented modules include apelin signaling, heme metabolism, intracellular ion homeostasis, and the unfolded protein response. These are known to be involved in calcium signaling, iron homeostasis, glucose regulation, heat shock response, and protein ubiquitination during states of high energy demand and stress. These pathways coincide with larger cellular processes of myocyte remodeling, apoptosis, and cell survival, which were also prominent. Conclusions: Biological pathways identified through WGCNA and GSOR suggest that sustained increases in energy demand during AF promotes stress-induced cellular remodeling. Changes in calcium signaling, iron homeostasis, the unfolded protein response and glucose regulation are likely primary mechanisms of AF pathophysiology.

Atrial fibrillation (AF) is strongly associated with risk of stroke and heart failure. AF promotes atrial remodeling that increases risk of stroke due to left atrial thrombogenesis, and increases energy demand to support high rate electrical activity and muscle contraction. While many transcriptomic studies have assessed AF-related changes in mRNA abundance, fewer studies have assessed proteomic changes. We performed a proteomic analysis on left atrial appendage (LAA) tissues from 12 patients with a history of AF undergoing elective surgery; atrial rhythm was documented at time of surgery. Proteomic analysis was performed using liquid chromatography with mass spectrometry (LC/MS-MS). Data-dependent analysis identified 3090 unique proteins, with 408 differentially expressed between sinus rhythm and AF. Ingenuity Pathway Analysis of differentially expressed proteins identified mitochondrial dysfunction, oxidative phosphorylation, and sirtuin signaling among the most affected pathways. Increased abundance of electron transport chain (ETC) proteins in AF was accompanied by decreased expression of ETC complex assembly factors, tricarboxylic acid cycle proteins, and other key metabolic modulators. Discordant changes were also evident in the contractile unit with both up- and down-regulation of key components. Similar pathways were affected in a comparison of patients with a history of persistent vs. paroxysmal AF, presenting for surgery in sinus rhythm. Together, these data suggest that while the LAA attempts to meet the energetic demands of AF, an uncoordinated response may reduce ATP availability, contribute to tissue contractile and electrophysiologic heterogeneity, and promote a progression of AF from paroxysmal episodes to development of a substrate amenable to persistent arrhythmia.

Introduction: Atrial fibrillation after cardiac surgery (AFACS) impacts 10-65% of patients, depending on the complexity and trauma associated with the surgery. AFACS is associated with stroke and other systemic embolic manifestations. Methods: Patients at our hospital who underwent valve surgery procedures including aortic valve replacement (AVR), mitral valve replacement (MVR), AVR with coronary artery bypass grafting (CABG), MVR with CABG, or AVR and MVR with/without CABG were included in this study. Results: 346 patients were included in the current analysis, with a mean age of 51.6±16.1 years; 51% of patients were males. Univariate predictors of AF included age, gender, body mass index (BMI), operation type, ejection fraction (EF), left atrial (LA) diameter, previous history of AF, use of aldosterone antagonists > a month before surgery, use of loop diuretics > a month before surgery, length of ICU stay, total length of stay, cross clamp time > 90 minutes, pump time > 120 minutes, postoperative acute kidney injury, left ventricular systolic and diastolic end dimensions. By multivariate analysis, only age (P=0.028, AOR=10.6), male gender (P=0.021, AOR=3.398), type of surgery (P=0.034, AOR=7.12), history of AF (P=0.018, AOR=2.317), BMI (P

Background: Common genetic variants and inflammatory factors are associated with atrial fibrillation (AF) risk. Although the top AF risk locus is near PITX2 (associated with pulmonary vein (PV) development), regional differential expression (DE) of AF risk genes in the left atrium (LA) and PVs is not well studied. While LAA and PV gene expression have been compared, transcriptome mapping of the entire LA has not been done. We tested the hypothesis that there is significant regional DE in LA structures. Methods: RNAseq was performed in 25 regions within the PVs (n=12), LA body (LAB) (n=10), and LA appendage (LAA) (n=3) from a 75 year old male with hypertension and AF who died of a stroke. DE analysis of regional clusters (R 3.6 Limma package) and gene set enrichment analysis (GSEA) (Broad Institute) were performed. Results: In full transcriptome (n=20664) sequencing, 118 genes were significantly (q < 0.05) upregulated in the LAA, including FOSB (fold change [FC] 67.0), IL6 (FC 15.4), TNF (FC 2.4) and NLRP3 (FC 2.4), and 56 downregulated, including developmental genes such as SHOX2 (FC -12.9) and HOXA4 (FC -4.1). LAA GSEA showed enrichment (FDR < 0.05) of inflammatory response genes and TNF-α, IL-2, IL-6, and IgG signaling pathways. 2454 genes were significantly upregulated and 3737 downregulated in the PVs while 4021 genes were upregulated and 2998 were downregulated in the LAB. In an AF implicated gene set (n=190), 28 genes were upregulated in the PVs, including SIRT1 (FC 1.7), and 31 downregulated, including PMNT (FC -2.1) and CGA (FC -3.2). NEURL1 was significantly upregulated in the inferior PV (n=4) compared to the superior PV (n=8) (FC 3.6). In the LAB, 33 genes were upregulated, including MYH7 (FC 2.2) and PMNT (FC 2.1) , and 38 downregulated including SIRT1 (FC -1.9). PITX2 did not show any significant DE in any gene set. Conclusions: This data shows that genes involved in AF pathogenesis can have substantial regional expression difference, particularly when comparing the LA body, PVs, and LAA. Inflammatory activation in the LAA may contribute to increased stroke risk.

Background: Ablation is a widely used therapy for atrial fibrillation (AF); however, arrhythmia recurrence and repeat procedures are common. Studies examining surrogate markers of genetic susceptibility to AF, such as family history and individual AF susceptibility alleles, suggest these may be associated with recurrence outcomes. Accordingly, the aim of this study was to test the association between AF genetic susceptibility and recurrence after ablation using a comprehensive polygenic risk score for AF. Methods: Ten centers from the AF Genetics Consortium identified patients who had undergone de novo AF ablation. AF genetic susceptibility was measured using a previously described polygenic risk score (N=929 single-nucleotide polymorphisms) and tested for an association with clinical characteristics and time-to-recurrence with a 3 month blanking period. Recurrence was defined as >30 seconds of AF, atrial flutter, or atrial tachycardia. Multivariable analysis adjusted for age, sex, height, body mass index, persistent AF, hypertension, coronary disease, left atrial size, left ventricular ejection fraction, and year of ablation. Results: Four thousand two hundred seventy-six patients were eligible for analysis of baseline characteristics and 3259 for recurrence outcomes. The overall arrhythmia recurrence rate between 3 and 12 months was 44% (1443/3259). Patients with higher AF genetic susceptibility were younger ( P P =0.001). Persistent AF (hazard ratio [HR], 1.39 [95% CI, 1.22–1.58]; P P P =0.008) were associated with increased risk of recurrence. In univariate analysis, higher AF genetic susceptibility trended towards a higher risk of recurrence (HR, 1.08 [95% CI, 0.99–1.18]; P =0.07), which became less significant in multivariable analysis (HR, 1.06 [95% CI, 0.98–1.15]; P =0.13). Conclusions: Higher AF genetic susceptibility was associated with younger age and fewer clinical risk factors but not recurrence. Arrhythmia recurrence after AF ablation may represent a genetically different phenotype compared to AF susceptibility.

Atrial fibrillation (AF) is an age-related arrhythmia of enormous socioeconomic significance. In recent years, our understanding of the basic mechanisms that initiate and perpetuate AF has evolved rapidly, catheter ablation of AF has progressed from concept to reality, and recent studies suggest lifestyle modification may help prevent AF recurrence. Emerging developments in genetics, imaging, and informatics also present new opportunities for personalized care. However, considerable challenges remain. These include a paucity of studies examining AF prevention, modest efficacy of existing antiarrhythmic therapies, diverse ablation technologies and practice, and limited evidence to guide management of high-risk patients with multiple comorbidities. Studies examining the long-term effects of AF catheter ablation on morbidity and mortality outcomes are not yet completed. In many ways, further progress in the field is heavily contingent on the feasibility, capacity, and efficiency of clinical trials to incorporate the rapidly evolving knowledge base and to provide substantive evidence for novel AF therapeutic strategies. This review outlines the current state of AF prevention and treatment trials, including the foreseeable challenges, as discussed by a unique forum of clinical trialists, scientists, and regulatory representatives in a session endorsed by the Heart Rhythm Society at the 12th Global CardioVascular Clinical Trialists Forum in Washington, DC, December 3-5, 2015.

A surge of data has reproducibly identified strong associations of OSA with cardiac arrhythmias. As an extension of epidemiologic and clinic-based findings, experimental investigations have made strides in advancing our understanding of the putative OSA and cardiac arrhythmogenesis mechanistic underpinnings. Although most studies have focused on the links between OSA and atrial fibrillation (AF), relationships with ventricular arrhythmias have also been characterized. Key findings implicate OSA-related autonomic nervous system fluctuations typified by enhanced parasympathetic activation during respiratory events and sympathetic surges subsequent to respiratory events, which contribute to augmented arrhythmic propensity. Other more immediate pathophysiologic influences of OSA-enhancing arrhythmogenesis include intermittent hypoxia, intrathoracic pressure swings leading to atrial stretch, and hypercapnia. Intermediate pathways by which OSA may trigger arrhythmia include increased systemic inflammation, oxidative stress, enhanced prothrombotic state, and vascular dysfunction. Long-term OSA-associated sequelae such as hypertension, atrial enlargement and fibrosis, ventricular hypertrophy, and coronary artery disease also predispose to cardiac arrhythmia. These factors can lead to a reduction in atrial effective refractory period, triggered and abnormal automaticity, and promote slowed and heterogeneous conduction; all of these mechanisms increase the persistence of reentrant arrhythmias and prolong the QT interval. Cardiac electrical and structural remodeling observed in OSA animal models can progress the arrhythmogenic substrate to further enhance arrhythmia generation. Future investigations clarifying the contribution of specific OSA-related mechanistic pathways to arrhythmia generation may allow targeted preventative therapies to mitigate OSA-induced arrhythmogenicity. Furthermore, interventional studies are needed to clarify the impact of OSA pathophysiology reversal on cardiac arrhythmogenesis and related adverse outcomes.

RationaleOur prior RNA sequencing study found that FAM13B gene expression in human left atrial appendages was strongly associated with an atrial fibrillation (AF) susceptibility-associated variant on chr. 5q31.ObjectiveTo identify the common genetic variant responsible for regulating FAM13B expression and the effect of FAM13B expression on cardiomyocyte gene expression in order to gain insight into the functional mechanism of the chr. 5q31 AF susceptibility locus.Methods and ResultsBy taking advantage of a smaller linkage disequilibrium block in African descent subjects and available chromatin conformation data, we identified the common single nucleotide polymorphism (SNP) rs17171731 as a candidate genetic variant controlling FAM13B gene expression in the left atrium. Functional analysis demonstrated that the AF risk allele of rs17171731 had less enhancer activity than the protective allele. Gel mobility shift studies determined that the risk allele bound to an additional protein that may function as a transcriptional repressor. Knockdown of FAM13B expression in stem cell-derived human cardiomyocytes (iCM) altered the expression of >1000 genes and modified the sodium current, consistent with increased susceptibility to atrial fibrillation. Transfection of GFP tagged FAM13B into iCMs demonstrated expression on the plasma membrane and at the Z-disk.ConclusionsThe chr. 5q31 AF risk variant was identified as rs17171731, with the risk allele having less enhancer activity, leading to decreased expression of FAM13B, which resides on the plasma membrane and the Z-disk, and appears to play a role in the regulation of cardiomyocyte gene expression and the late sodium current.

RationaleAtrial fibrillation (AF) genome-wide association studies (GWAS) identified significant associations for rs1152591 and linked variants in the SYNE2 gene encoding the nesprin-2 protein that connects the nuclear membrane with the cytoskeletonObjectiveDetermine the effects of the AF-associated rs1152591 and rs1152595, two linked intronic single nucleotide polymorphisms (SNPs), on SYNE2 expression and investigate the mechanisms for their association with AF.Methods and ResultsRNA sequencing of human left atrial appendage (LAA) tissues indicated that rs1152591 and rs1152595 were significantly associated with the expressions of SYNE2α1, a short mRNA isoform, without an effect on the expression of the full-length SYNE2 mRNA. SYNE2α1 mRNA uses an alternative transcription start site and encodes an N-terminal deleted 62 kDa nesprin-2α1 isoform, which can act as a dominant-negative on nuclear-cytoskeleton connectivity. Western blot and qPCR assays confirmed that AF risk alleles of both SNPs were associated with lower expression of nesprin-2α1 in human LAA tissues. Reporter gene transfections demonstrated that the risk vs. reference alleles of rs1152591 and rs1152595 had decreased enhancer activity. SYNE2 siRNA knockdown (KD) or nesprin-2α1 overexpression studies in human stem cell-derived induced cardiomyocytes (iCMs) resulted in ~12.5 % increases in the nuclear area compared to controls (pConclusionsAF-associated SNPs rs1152591 and rs1152595 downregulate the expression of SYNE2α1, increasing nuclear-cytoskeletal connectivity and nuclear stiffness. The resulting increase in mechanical stress may play a role in the development of AF.

Key points Hyperammonaemia occurs in hepatic, cardiac and pulmonary diseases with increased muscle concentration of ammonia. We found that ammonia results in reduced skeletal muscle mitochondrial respiration, electron transport chain complex I dysfunction, as well as lower NAD+/NADH ratio and ATP content. During hyperammonaemia, leak of electrons from complex III results in oxidative modification of proteins and lipids. Tricarboxylic acid cycle intermediates are decreased during hyperammonaemia, and providing a cell-permeable ester of αKG reversed the lower TCA cycle intermediate concentrations and increased ATP content. Our observations have high clinical relevance given the potential for novel approaches to reverse skeletal muscle ammonia toxicity by targeting the TCA cycle intermediates and mitochondrial ROS. Abstract Ammonia is a cytotoxic metabolite that is removed primarily by hepatic ureagenesis in humans. Hyperammonaemia occurs in advanced hepatic, cardiac and pulmonary disease, and in urea cycle enzyme deficiencies. Increased skeletal muscle ammonia uptake and metabolism are the major mechanism of non-hepatic ammonia disposal. Non-hepatic ammonia disposal occurs in the mitochondria via glutamate synthesis from α-ketoglutarate resulting in cataplerosis. We show skeletal muscle mitochondrial dysfunction during hyperammonaemia in a comprehensive array of human, rodent and cellular models. ATP synthesis, oxygen consumption, generation of reactive oxygen species with oxidative stress, and tricarboxylic acid (TCA) cycle intermediates were quantified. ATP content was lower in the skeletal muscle from cirrhotic patients, hyperammonaemic portacaval anastomosis rat, and C2C12 myotubes compared to appropriate controls. Hyperammonaemia in C2C12 myotubes resulted in impaired intact cell respiration, reduced complex I/NADH oxidase activity and electron leak occurring at complex III of the electron transport chain. Consistently, lower NAD+/NADH ratio was observed during hyperammonaemia with reduced TCA cycle intermediates compared to controls. Generation of reactive oxygen species resulted in increased content of skeletal muscle carbonylated proteins and thiobarbituric acid reactive substances during hyperammonaemia. A cell-permeable ester of α-ketoglutarate reversed the low TCA cycle intermediates and ATP content in myotubes during hyperammonaemia. However, the mitochondrial antioxidant MitoTEMPO did not reverse the lower ATP content during hyperammonaemia. We provide for the first time evidence that skeletal muscle hyperammonaemia results in mitochondrial dysfunction and oxidative stress. Use of anaplerotic substrates to reverse ammonia-induced mitochondrial dysfunction is a novel therapeutic approach.