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Pitx2 prevents susceptibility to atrial arrhythmias by inhibiting left-sided pacemaker specification.

ABSTRACT: Atrial fibrillation (AF), the most prevalent sustained cardiac arrhythmia, often coexists with the related arrhythmia atrial flutter (AFL). Limitations in effectiveness and safety of current therapies make an understanding of the molecular mechanism underlying AF more urgent. Genome-wide association studies implicated a region of human chromosome 4q25 in familial AF and AFL, approximately 150 kb distal to the Pitx2 homeobox gene, a developmental left-right asymmetry (LRA) gene. To investigate the significance of the 4q25 variants, we used mouse models to investigate Pitx2 in atrial arrhythmogenesis directly. When challenged by programmed stimulation, Pitx2(null+/-) adult mice had atrial arrhythmias, including AFL and atrial tachycardia, indicating that Pitx2 haploinsufficiency predisposes to atrial arrhythmias. Microarray and in situ studies indicated that Pitx2 suppresses sinoatrial node (SAN)-specific gene expression, including Shox2, in the left atrium of embryos and young adults. In vivo ChIP and transfection experiments indicated that Pitx2 directly bound Shox2 in vivo, supporting the notion that Pitx2 directly inhibits the SAN-specific genetic program in left atrium. Our findings implicate Pitx2 and Pitx2-mediated LRA-signaling pathways in prevention of atrial arrhythmias.

SUBMITTER: Wang J

PROVIDER: S-EPMC2906838 | biostudies-other | 2010 May

REPOSITORIES: biostudies-other

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Pitx2 prevents susceptibility to atrial arrhythmias by inhibiting left-sided pacemaker specification.

Wang Jun J Klysik Elzbieta E Sood Subeena S Johnson Randy L RL Wehrens Xander H T XH Martin James F JF

Proceedings of the National Academy of Sciences of the United States of America 20100510 21

Atrial fibrillation (AF), the most prevalent sustained cardiac arrhythmia, often coexists with the related arrhythmia atrial flutter (AFL). Limitations in effectiveness and safety of current therapies make an understanding of the molecular mechanism underlying AF more urgent. Genome-wide association studies implicated a region of human chromosome 4q25 in familial AF and AFL, approximately 150 kb distal to the Pitx2 homeobox gene, a developmental left-right asymmetry (LRA) gene. To investigate th ...[more]

PMID: 20457925

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Project description:BackgroundLeft atrium (LA) physiology is influenced by changes in left ventricular (LV) performance and load.ObjectivesThe purpose of this study was to define the effect of acute changes in LV loading conditions on LA physiology in subacute myocardial infarction (MI).MethodsMI was percutaneously induced in 19 Yorkshire pigs. One to 2 weeks after MI, 14 pigs underwent acute LV unloading using a percutaneous LV assist device, Impella. The remaining 5 pigs underwent acute LV loading by percutaneous induction of aortic regurgitation. A pressure-volume catheter was inserted into the LA using a percutaneous transseptal approach, and LA pressure-volume loops were continuously monitored. Atrial arrhythmia inducibility was examined by burst-pacing of the right atrium. Nicotinamide adenine dinucleotide phosphate oxidase (NOX) levels and ryanodine receptor phosphorylation were examined in LA tissues to study the potential effect of stretch-dependent oxidative stress.ResultsMI resulted in reduced LV ejection fraction and increased LV end-diastolic pressure with concomitant increase in LA pressure and volumes. Acute LV unloading resulted in a reduction of LV end-diastolic pressure, which led to proportional decreases in mean LA pressure and maximum LA volume. LA pressure-volume loops exhibited a pump flow-dependent, left-downward shift. This was associated with reduced LA passive stiffness, suggesting the alleviation of the LA stretch that was present after MI. Prior to acute unloading of the LV, 71% of the pigs were arrhythmia-inducible; LV unloading reduced this to 29% (p = 0.02). Time to spontaneous termination of atrial arrhythmias was decreased from median 55 s (range 5 to 300 s) to 3 s (range 0 to 59 s). In contrast, acute LV loading with aortic regurgitation increased LA pressure without a significant effect on arrhythmogenicity. Molecular analysis of LA tissue revealed that NOX2 expression was increased after MI, whereas acute LV unloading reduced NOX2 levels and diminished ryanodine receptor phosphorylation.ConclusionsAcute LV unloading relieves LA stretch and reduces atrial arrhythmogenicity in subacute MI.

Project description:BackgroundRenin released by ischemia/reperfusion from cardiac mast cells activates a local renin-angiotensin system (RAS). This exacerbates norepinephrine release and reperfusion arrhythmias (ventricular tachycardia and fibrillation), making RAS a new therapeutic target in myocardial ischemia.Methods and resultsWe investigated whether ischemic preconditioning (IPC) prevents cardiac RAS activation in guinea pig hearts ex vivo. When ischemia/reperfusion (20 minutes of ischemia/30 minutes of reperfusion) was preceded by IPC (two 5-minute ischemia/reperfusion cycles), renin and norepinephrine release and ventricular tachycardia and fibrillation duration were markedly decreased, a cardioprotective anti-RAS effect. Activation and blockade of adenosine A(2b)/A(3) receptors and activation and inhibition of protein kinase Cepsilon (PKCepsilon) mimicked and prevented, respectively, the anti-RAS effects of IPC. Moreover, activation of A(2b)/A(3) receptors or activation of PKCepsilon prevented degranulation and renin release elicited by peroxide in cultured mast cells (HMC-1). Activation and inhibition of mitochondrial aldehyde dehydrogenase type-2 (ALDH2) also mimicked and prevented, respectively, the cardioprotective anti-RAS effects of IPC. Furthermore, ALDH2 activation inhibited degranulation and renin release by reactive aldehydes in HMC-1. Notably, PKCepsilon and ALDH2 were both activated by A(2b)/A(3) receptor stimulation in HMC-1, and PKCepsilon inhibition prevented ALDH2 activation.ConclusionsThe results uncover a signaling cascade initiated by A(2b)/A(3) receptors, which triggers PKCepsilon-mediated ALDH2 activation in cardiac mast cells, contributing to IPC-induced cardioprotection by preventing mast cell renin release and the dysfunctional consequences of local RAS activation. Thus, unlike classic IPC in which cardiac myocytes are the main target, cardiac mast cells are the critical site at which the cardioprotective anti-RAS effects of IPC develop.

Project description:ImportanceNew-onset postoperative atrial fibrillation (POAF) is a common complication of cardiac surgery. However, data on the long-term risk of thromboembolism in patients who develop POAF after heart valve surgery are conflicting. In addition, data on stroke prophylaxis in this setting are lacking.ObjectiveTo assess the long-term risk of thromboembolism in patients developing new-onset POAF after isolated left-sided heart valve surgery relative to patients with nonsurgical, nonvalvular atrial fibrillation (NVAF).Design, setting, and participantsThis observational cohort study was conducted from January 1, 2000, through December 31, 2015, using Danish nationwide registries and the Eastern Danish Heart Surgery Database. Patients who developed POAF after isolated left-sided heart valve surgery (bioprosthetic aortic or mitral valve replacement and/or aortic or mitral valve repair) from 2000 through 2015 were included. These patients were matched with patients with nonsurgical NVAF in a 1:3 ratio by age, sex, heart failure, hypertension, diabetes, a history of thromboembolism, ischemic heart disease, and year of diagnosis. Data analyses took place from January to March 2019.Main outcomes and measuresRates of thromboembolism.ResultsOf the 1587 patients who underwent isolated left-sided heart valve surgery, 741 patients (46.7%) developed POAF during admission. Of the 712 patients with POAF who were eligible for matching, 675 patients were matched with 2025 patients with NVAF and made up the study population. In the matched study population, the median age was 71 (interquartile range, 65-77) years, and 1600 (59.3%) were men. Oral anticoagulation therapy was initiated within 30 days postdischarge in 420 patients with POAF (62.9%) and in 1030 patients with NVAF (51.4%). The crude incidence rates of thromboembolism were 21.9 (95% CI, 17.4-27.6) and 17.7 (95% CI, 15.2-20.6) events per 1000 person-years for patients with POAF and patients with NVAF, respectively. In the adjusted analysis, the long-term risk of thromboembolism was similar in patients with POAF and NVAF (hazard ratio, 1.22 [95% CI, 0.88-1.68]). Oral anticoagulation therapy during follow-up was associated with a lower risk of thromboembolic events in patients with POAF (hazard ratio, 0.45 [95% CI, 0.22-0.90]) as well as patients with NVAF (hazard ratio, 0.63 [95% CI, 0.45-0.87]) compared with no anticoagulation therapy.Conclusions and relevanceNew-onset POAF after isolated left-sided heart valve surgery was associated with a similar long-term risk of thromboembolism as NVAF. These data warrant studies addressing the role of anticoagulation therapy in POAF after left-sided heart valve surgery.

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Pitx2 prevents susceptibility to atrial arrhythmias by inhibiting left-sided pacemaker specification.

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Pitx2 prevents susceptibility to atrial arrhythmias by inhibiting left-sided pacemaker specification.

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