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Summary: Atrial fibrillation (AF) is the most common arrhythmia in the world. Human genetics can provide strong AF therapeutic candidates, but the identification of the causal genes and their functions remains challenging. Here, we applied an AF fine-mapping strategy that leverages results from a previously published cross-ancestry genome-wide association study (GWAS), expression quantitative trait loci (eQTLs) from left atrial appendages (LAAs) obtained from two cohorts with distinct ancestry, and a paired RNA sequencing (RNA-seq) and ATAC sequencing (ATAC-seq) LAA single-nucleus assay (sn-multiome). At nine AF loci, our co-localization and fine-mapping analyses implicated 14 genes. Data integration identified several candidate causal AF variants, including rs7612445 at GNB4 and rs242557 at MAPT. Finally, we showed that the repression of the strongest AF-associated eQTL gene, LINC01629, in human embryonic stem cell-derived cardiomyocytes using CRISPR inhibition results in the dysregulation of pathways linked to genes involved in the development of atrial tissue and the cardiac conduction system.

Background Cardiac surgery triggers sterile innate immune responses leading to postoperative complications. Clonal hematopoiesis (CH) is associated with short‐term inflammation‐mediated outcomes after cardiac surgery. The impact of CH on long‐term postoperative outcomes remains unknown. Methods and Results In this cohort study, patients undergoing elective cardiac surgery were included from January 2017 to September 2019. Patients were screened for CH using a predefined gene panel of 19 genes. Recorded clinical events were all‐cause death, major adverse cardiac and cerebral events including cardiovascular death, myocardial infarction or nonscheduled coronary revascularization, stroke, and hospitalization for acute heart failure. The primary study outcome was time to a composite criterion including all‐cause mortality and major adverse cardiac and cerebral events. Among 314 genotyped patients (median age: 67 years; interquartile range 59–74 years), 139 (44%) presented with CH, based on a variant allelic frequency ≥1%. Carriers of CH had a higher proportion of patients with a history of atrial fibrillation (26% for CH versus 17% for non‐CH carriers, P=0.022). The most frequently mutated genes were DNMT3A, TET2, and ASXL1. After a median follow‐up of 1203 [813–1435] days, the primary outcome occurred in 50 patients. After multivariable adjustment, CH was independently associated with a higher risk for the primary outcome (hazard ratio, 1.88 [95% CI, 1.05–3.41], P=0.035). Most adverse events occurred in patients carrying TET2 variants. Conclusions In patients undergoing cardiac surgery, CH is frequent and associated with a 2‐fold increased long‐term risk for major adverse clinical outcomes. CH is a novel risk factor for long‐term postcardiac surgery complications and might be useful to personalize management decisions. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT03376165.

Almost half of patients recovering from open-chest surgery experience atrial fibrillation (AF) that results principally from inflammation in the pericardial space surrounding the heart. Given that postoperative AF is associated with increased mortality, effective measures to prevent AF after open-chest surgery are highly desirable. In this study, we tested the concept that extracellular vesicles (EVs) isolated from human atrial explant-derived cells can prevent postoperative AF. Middle-aged female and male rats were randomized to undergo sham operation or induction of sterile pericarditis followed by trans-epicardial injection of human EVs or vehicle into the atrial tissue. Pericarditis increased the probability of inducing AF while EV treatment abrogated this effect in a sex-independent manner. EV treatment reduced infiltration of inflammatory cells and production of pro-inflammatory cytokines. Atrial fibrosis and hypertrophy seen after pericarditis were markedly attenuated by EV pretreatment, an effect attributable to suppression of fibroblast proliferation by EVs. Our study demonstrates that injection of EVs at the time of open-chest surgery shows prominent antiinflammatory effects and prevents AF due to sterile pericarditis. Translation of this finding to patients might provide an effective new strategy to prevent postoperative AF by reducing atrial inflammation and fibrosis.

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.

Background and Objective: Renewal theory is a statistical approach to model the formation and destruction of phase singularities (PS), which occur at the pivots of spiral waves. A common issue arising during observation of renewal processes is an inspection paradox, due to oversampling of longer events. The objective of this study was to characterise the effect of a potential inspection paradox on the perception of PS lifetimes in cardiac fibrillation.Methods: A multisystem, multi-modality study was performed, examining computational simulations (Aliev-Panfilov (APV) model, Courtmanche-Nattel model), experimentally acquired optical mapping Atrial and Ventricular Fibrillation (AF/VF) data, and clinically acquired human AF and VF. Distributions of all PS lifetimes across full epochs of AF, VF, or computational simulations, were compared with distributions formed from lifetimes of PS existing at 10,000 simulated commencement timepoints.Results: In all systems, an inspection paradox led towards oversampling of PS with longer lifetimes. In APV computational simulations there was a mean PS lifetime shift of +84.9% (95% CI, ± 0.3%) (p < 0.001 for observed vs overall), in Courtmanche-Nattel simulations of AF +692.9% (95% CI, ±57.7%) (p < 0.001), in optically mapped rat AF +374.6% (95% CI, ± 88.5%) (p = 0.052), in human AF mapped with basket catheters +129.2% (95% CI, ±4.1%) (p < 0.05), human AF-HD grid catheters 150.8% (95% CI, ± 9.0%) (p < 0.001), in optically mapped rat VF +171.3% (95% CI, ±15.6%) (p < 0.001), in human epicardial VF 153.5% (95% CI, ±15.7%) (p < 0.001).Conclusion: Visual inspection of phase movies has the potential to systematically oversample longer lasting PS, due to an inspection paradox. An inspection paradox is minimised by consideration of the overall distribution of PS lifetimes.

Strategies to improve the function of damaged hearts with progenitor cells have stalled. Here, the authors show that gene transfer of a calcium-dependent potassium channel enhances the functional properties and ability of explant-derived cells to improve heart function after a heart attack.

A mutation in Shugoshin-1 causes the Chronic Atrial and Intestinal Dysrhythmia (CAID) Syndrome, but the underlying mechanisms are unknown. Here, the authors show that Shugoshin-1 controls cardiac pacemaker activity by interacting with HCN4 to enhance its cell-surface expression, and that the CAID-Syndrome mutation disrupts cardiac pacemaking by interfering with this important non-canonical interaction.

Long QT syndrome (LQTS) is an inherited cardiac rhythm disorder associated with increased incidence of cardiac arrhythmias and sudden death. LQTS type 5 (LQT5) is caused by dominant mutant variants of KCNE1, a regulatory subunit of the voltage-gated ion channels generating the cardiac potassium current IKs. While mutant LQT5 KCNE1 variants are known to inhibit IKs amplitudes in heterologous expression systems, cardiomyocytes from a transgenic rabbit LQT5 model displayed unchanged IKs amplitudes, pointing towards the critical role of additional factors in the development of the LQT5 phenotype in vivo. In this study, we demonstrate that KCNE3, a candidate regulatory subunit of IKs channels minimizes the inhibitory effects of LQT5 KCNE1 variants on IKs amplitudes, while current deactivation is accelerated. Such changes recapitulate IKs properties observed in LQT5 transgenic rabbits. We show that KCNE3 accomplishes this by displacing the KCNE1 subunit within the IKs ion channel complex, as evidenced by a dedicated biophysical assay. These findings depict KCNE3 as an integral part of the IKs channel complex that regulates IKs function in cardiomyocytes and modifies the development of the LQT5 phenotype.

The pig is commonly used as an experimental model of human heart disease, including for the study of mechanisms of arrhythmia. However, there exist differences between human and porcine cellular electrophysiology: The pig action potential (AP) has a deeper phase-1 notch, a longer duration at 50% repolarization, and higher plateau potentials than human. Ionic differences underlying the AP include larger rapid delayed-rectifier and smaller inward-rectifier K+-currents (IKr and IK1 respectively) in humans. AP steady-state rate-dependence and restitution is steeper in pigs. Porcine Ca2+ transients can have two components, unlike human. Although a reliable computational model for human ventricular myocytes exists, one for pigs is lacking. This hampers translation from results obtained in pigs to human myocardium. Here, we developed a computational model of the pig ventricular cardiomyocyte AP using experimental datasets of the relevant ionic currents, Ca2+-handling, AP shape, AP duration restitution, and inducibility of triggered activity and alternans. To properly capture porcine Ca2+ transients, we introduced a two-step process with a faster release in the t-tubular region, followed by a slower diffusion-induced release from a non t-tubular subcellular region. The pig model behavior was compared with that of a human ventricular cardiomyocyte (O'Hara-Rudy) model. The pig, but not the human model, developed early afterdepolarizations (EADs) under block of IK1, while IKr block led to EADs in the human but not in the pig model. At fast rates (pacing cycle length = 400 ms), the human cell model was more susceptible to spontaneous Ca2+ release-mediated delayed afterdepolarizations (DADs) and triggered activity than pig. Fast pacing led to alternans in human but not pig. Developing species-specific models incorporating electrophysiology and Ca2+-handling provides a tool to aid translating antiarrhythmic and arrhythmogenic assessment from the bench to the clinic.

RationaleA quantitative framework to summarize and explain the quasi-stationary population dynamics of unstable phase singularities (PS) and wavelets in human atrial fibrillation (AF) is at present lacking. Building on recent evidence showing that the formation and destruction of PS and wavelets in AF can be represented as renewal processes, we sought to establish such a quantitative framework, which could also potentially provide insight into the mechanisms of spontaneous AF termination.ObjectivesHere, we hypothesized that the observed number of PS or wavelets in AF could be governed by a common set of renewal rate constants λf (for PS or wavelet formation) and λd (PS or wavelet destruction), with steady-state population dynamics modeled as an M/M/∞ birth–death process. We further hypothesized that changes to the M/M/∞ birth–death matrix would explain spontaneous AF termination.Methods and ResultsAF was studied in in a multimodality, multispecies study in humans, animal experimental models (rats and sheep) and Ramirez-Nattel-Courtemanche model computer simulations. We demonstrated: (i) that λf and λd can be combined in a Markov M/M/∞ process to accurately model the observed average number and population distribution of PS and wavelets in all systems at different scales of mapping; and (ii) that slowing of the rate constants λf and λd is associated with slower mixing rates of the M/M/∞ birth–death matrix, providing an explanation for spontaneous AF termination.ConclusionM/M/∞ birth–death processes provide an accurate quantitative representational architecture to characterize PS and wavelet population dynamics in AF, by providing governing equations to understand the regeneration of PS and wavelets during sustained AF, as well as providing insight into the mechanism of spontaneous AF termination.

Background - Uncontrolled atrial fibrillation (AF) results in complex changes in the cardiomyocyte electrical and contractile functioning that promote atrial remodeling and the continuation of AF. Recently there has been a growing interest in understanding the role of heat shock proteins (HSPs), which are cytoprotective molecular chaperones, in the pathophysiology of AF. Several groups have examined HSP expression in patients with AF but have yielded mixed results. To allow for better consistency and reproducibility between subjects, we utilized canine models to reproduce AF- promoting conditions to better investigate the role of HSPs in the pathophysiology of AF. Methods - AF promoting conditions were simulated in canine models with fifteen adult mongrel dogs (20.6 to 36.0 kg) divided into three groups: (1) Control (n=5), (2) two week ventricular tachypacing (VTP) induced congestive heart failure (CHF) (n=5), and (3) one week atrial tachypacying (ATP) (n=5). Quick frozen right atrial free wall tissue samples were used for protein isolation and were analyzed via Western blotting with data was expressed as a relative ratio and were analyzed using a two-tailed, unpaired t- test and significance was set at p < 0.05. The expression levels of HSP 90, 70, and 25 were studied along with the phosphorylation status of HSP27 at serine-78. Results - We first examined the effects of the ATP and CHF heart models on the expression of a select group of HSPs via Western Blot. We found that there was no significant difference in levels of expression of HSP 90, 70, or 25 when either ATP or CHF models were compared to control canines. The phosphorylation status of HSP27 was significantly decreased in the CHF canine model when compared to control (p < 0.0111) and it tended towards a decrease in the ATP canine model when compared to control (p=0.0923). Conclusion - This study showed that even though the expression levels of HSPs may remain constant, there are protein phosphorylation and dephosphorylation events that occur in AF that may have important consequences in its pathophysiology. It is therefore necessary to investigate the full scale of HSP modifications during AF and AF-promoting conditions.

Background & Aims: A generalized human pacemaking syndrome, chronic atrial and intestinal dysrhythmia (CAID) (OMIM 616201), is caused by a homozygous SGO1 mutation (K23E), leading to chronic intestinal pseudo-obstruction and arrhythmias. Because CAID patients do not show phenotypes consistent with perturbation of known roles of SGO1, we hypothesized that noncanonical roles of SGO1 drive the clinical manifestations observed. Methods: To identify a molecular signature for CAID syndrome, we achieved unbiased screens in cell lines and gut tissues from CAID patients vs wild-type controls. We performed RNA sequencing along with stable isotope labeling with amino acids in cell culture. In addition, we determined the genome-wide DNA methylation and chromatin accessibility signatures using reduced representative bisulfite sequencing and assay for transposase-accessible chromatin with high-throughput sequencing. Functional studies included patch-clamp, quantitation of transforming growth factor-β (TGF-β) signaling, and immunohistochemistry in CAID patient gut biopsy specimens. Results: Proteome and transcriptome studies converge on cell-cycle regulation, cardiac conduction, and smooth muscle regulation as drivers of CAID syndrome. Specifically, the inward rectifier current, an important regulator of cellular function, was disrupted. Immunohistochemistry confirmed overexpression of Budding Uninhibited By Benzimidazoles 1 (BUB1) in patients, implicating the TGF-β pathway in CAID pathogenesis. Canonical TGF-β signaling was up-regulated and uncoupled from noncanonical signaling in CAID patients. Reduced representative bisulfite sequencing and assay for transposase-accessible chromatin with high-throughput sequencing experiments showed significant changes of chromatin states in CAID, pointing to epigenetic regulation as a possible pathologic mechanism. Conclusions: Our findings point to impaired inward rectifier potassium current, dysregulation of canonical TGF-β signaling, and epigenetic regulation as potential drivers of intestinal and cardiac manifestations of CAID syndrome. Transcript profiling and genomics data are as follows: repository URL: https://www.ncbi.nlm.nih.gov/geo; SuperSeries GSE110612 was composed of the following subseries: GSE110309, GSE110576, and GSE110601. Keywords: CAID Syndrome (Chronic Atrial and Intestinal Dysrhythmia), Chronic Intestinal Pseudo-obstruction, TGF-β Signaling, Epigenetics

The data shown in this article are related to the research article entitled “Characterization of Sgo1 expression pattern in developing and adult mouse” (Song et al., 2017) [3]. The article provides novel data on Sgo1 gene expression pattern utilizing Sgo1_LacZ_Knock in mouse line and immunohistochemistry in wild type mice. The data presents Sgo1 expression pattern during development, and in post-developmental proliferative and quiescent tissue. The article describes following tissues: developing heart, neural tube, adult colon, cerebellum, cerebral cortex, liver, and testis. Keywords: Heart development, Intestinal development, Retinal development, SGO1, CAID syndrome, Cohesin

Atrial fibrillation (AF) and heart failure (HF) are common cardiovascular diseases that often co-exist. Animal models have suggested complex AF-promoting atrial structural, electrical, and Ca2+-handling remodeling in the setting of HF, but data in human samples are scarce, particularly regarding Ca2+-handling remodeling. Here, we evaluated atrial remodeling in patients with severe left ventricular (LV) dysfunction (HFrEF), long-standing persistent (‘chronic’) AF (cAF) or both (HFrEF-cAF), and sinus rhythm controls with normal LV function (Ctl) using western blot in right-atrial tissue, sharp-electrode action potential (AP) measurements in atrial trabeculae and voltage-clamp experiments in isolated right-atrial cardiomyocytes. Compared to Ctl, expression of profibrotic markers (collagen-1a, fibronectin, periostin) was higher in HFrEF and HFrEF-cAF patients, indicative of structural remodeling. Connexin-43 expression was reduced in HFrEF patients, but not HFrEF-cAF patients. AP characteristics were unchanged in HFrEF, but showed classical indices of electrical remodeling in cAF and HFrEF-cAF (prolonged AP duration at 20% and shorter AP duration at 50% and 90% repolarization). L-type Ca2+ current (ICa,L) was significantly reduced in HFrEF, cAF and HFrEF-cAF, without changes in voltage-dependence. Potentially proarrhythmic spontaneous transient-inward currents were significantly more frequent in HFrEF and HFrEF-cAF compared to Ctl, likely resulting from increased sarcoplasmic reticulum (SR) Ca2+ load (integrated caffeine-induced current) in HFrEF and increased ryanodine-receptor (RyR2) single-channel open probability in HFrEF and HFrEF-cAF. Although expression and phosphorylation of the SR Ca2+-ATPase type-2a (SERCA2a) regulator phospholamban were unchanged in HFrEF and HFrEF-cAF patients, protein levels of SERCA2a were increased in HFrEF-cAF and sarcolipin expression was decreased in both HFrEF and HFrEF-cAF, likely increasing SR Ca2+ uptake and load. RyR2 protein levels were decreased in HFrEF and HFrEF-cAF patients, but junctin levels were higher in HFrEF and relative Ser2814-RyR2 phosphorylation levels were increased in HFrEF-cAF, both potentially contributing to the greater RyR2 open probability. These novel insights into the molecular substrate for atrial arrhythmias in HF-patients position Ca2+-handling abnormalities as a likely trigger of AF in HF patients, which subsequently produces electrical remodeling that promotes the maintenance of the arrhythmia. Our new findings may have important implications for the development of novel treatment options for AF in the context of HF.

BackgroundThere is increasing interest in the concept of atrial cardiomyopathy, but the underlying molecular and mechanistic determinants remain poorly defined. We identified a family with heritable atrial cardiomyopathy manifesting as progressive atrial‐selective electromechanical dysfunction, tachyarrhythmias, and bradyarrhythmias requiring pacemaker implantation. Myosin light‐chain 4 (MYL4), encoding the atrial‐selective essential myosin light chain, was identified as a candidate gene. We used genetically modified rat models to investigate the role of MYL4 in atrial cardiomyopathy. Methods and ResultsExome sequencing and systematic bioinformatic analyses identified a rare missense variant of MYL4 (c.31G>A [p.E11K]) in a large multiplex atrial cardiomyopathy family pedigree. The mutation cosegregated with atrial standstill (selected as the principal presenting trait) with a logarithm of the odds score of 5.3. The phenotype of rats with MYL4 mutation knock‐in confirmed the causative role of the mutation. MYL4 knockout rats showed a similar atrial cardiomyopathy phenotype, whereas rats with an adjacent 4‐amino‐acid deletion showed no phenotype. Both MYL4 p.E11K knock‐in rats and MYL4 knockout rats showed progressive atrial electrophysiological, contractile, and fibrotic abnormalities, similar to affected patients. Biochemical analyses of MYL4 p.E11K mutation rats showed activation of proapoptotic and profibrotic signaling, along with increased atrial‐cardiomyocyte terminal deoxynucleotidyl transferase dUTP nick end labeling staining, suggesting enhanced apoptotic cell death, findings that were mimicked by in vitro adenoviral transfer of the mutant gene to neonatal‐rat cardiomyocytes. ConclusionsLoss‐of‐function MYL4 gene variants cause progressive atrial cardiomyopathy in humans and rats. Our findings identify MYL4 as a key gene required for atrial contractile, electrical and structural integrity. These results improve our understanding of the molecular basis of atrial cardiomyopathy and introduce new models for further mechanistic analysis.

BackgroundDerailment of proteostasis, the homeostasis of production, function, and breakdown of proteins, contributes importantly to the self‐perpetuating nature of atrial fibrillation (AF), the most common heart rhythm disorder in humans. Autophagy plays an important role in proteostasis by degrading aberrant proteins and organelles. Herein, we investigated the role of autophagy and its activation pathway in experimental and clinical AF. Methods and ResultsTachypacing of HL‐1 atrial cardiomyocytes causes a gradual and significant activation of autophagy, as evidenced by enhanced LC3B‐II expression, autophagic flux and autophagosome formation, and degradation of p62, resulting in reduction of Ca2+ amplitude. Autophagy is activated downstream of endoplasmic reticulum (ER) stress: blocking ER stress by the chemical chaperone 4‐phenyl butyrate, overexpression of the ER chaperone‐protein heat shock protein A5, or overexpression of a phosphorylation‐blocked mutant of eukaryotic initiation factor 2α (eIF2α) prevents autophagy activation and Ca2+‐transient loss in tachypaced HL‐1 cardiomyocytes. Moreover, pharmacological inhibition of ER stress in tachypaced Drosophila confirms its role in derailing cardiomyocyte function. In vivo treatment with sodium salt of phenyl butyrate protected atrial‐tachypaced dog cardiomyocytes from electrical remodeling (action potential duration shortening, L‐type Ca2+‐current reduction), cellular Ca2+‐handling/contractile dysfunction, and ER stress and autophagy; it also attenuated AF progression. Finally, atrial tissue from patients with persistent AF reveals activation of autophagy and induction of ER stress, which correlates with markers of cardiomyocyte damage. ConclusionsThese results identify ER stress–associated autophagy as an important pathway in AF progression and demonstrate the potential therapeutic action of the ER‐stress inhibitor 4‐phenyl butyrate.

BackgroundCardiac fibroblasts play important functional and pathophysiological roles. Intracellular (“intracrine”) angiotensin‐II (Ang‐II) signaling regulates intercellular communication, excitability, and gene expression in cardiomyocytes; however, the existence and role of intracrine Ang‐II signaling in cardiac fibroblasts is unstudied. Here, we evaluated the localization of Ang‐II receptors on atrial fibroblast nuclei and associated intracrine effects of potential functional significance. Methods and ResultsImmunoblots of subcellular protein‐fractions from isolated canine atrial fibroblasts indicated the presence of nuclear Ang‐II type 1 receptors (AT1Rs) and Ang‐II type 2 receptors (AT2Rs). Fluorescein isothiocyanate–Ang‐II binding displaceable by AT1R‐ and AT2R‐blockers was present on isolated fibroblast nuclei. G‐protein subunits, including Gαq/11, Gαi/3, and Gβ, were observed in purified fibroblast nuclear fractions by immunoblotting and intact‐fibroblast nuclei by confocal immunocytofluorescence microscopy. Nuclear AT1Rs and AT2Rs regulated de novo RNA synthesis ([α32P]UTP incorporation) via IP3R‐ and NO‐dependent pathways, respectively. In intact cultured fibroblasts, intracellular Ang‐II release by photolysis of a membrane‐permeable caged Ang‐II analog led to IP3R‐dependent nucleoplasmic Ca2+‐liberation, with IP3R3 being the predominant nuclear isoform. Intracellular Ang‐II regulated fibroblast proliferation ([3H]thymidine incorporation), collagen‐1A1 mRNA‐expression, and collagen secretion. Intracellular Ang‐II and nuclear AT1R protein levels were significantly increased in a heart failure model in which atrial fibrosis underlies atrial fibrillation. ConclusionsFibroblast nuclei possess AT1R and AT2R binding sites that are coupled to intranuclear Ca2+‐mobilization and NO liberation, respectively. Intracellular Ang‐II signaling regulates fibroblast proliferation, collagen gene expression, and collagen secretion. Heart failure upregulates Ang‐II intracrine signaling‐components in atrial fibroblasts. These results show for the first time that nuclear angiotensin‐II receptor activation and intracrine Ang‐II signaling control fibroblast function and may have pathophysiological significance.