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Aberrant sodium influx causes cardiomyopathy and atrial fibrillation in mice.

ABSTRACT: Increased sodium influx via incomplete inactivation of the major cardiac sodium channel Na(V)1.5 is correlated with an increased incidence of atrial fibrillation (AF) in humans. Here, we sought to determine whether increased sodium entry is sufficient to cause the structural and electrophysiological perturbations that are required to initiate and sustain AF. We used mice expressing a human Na(V)1.5 variant with a mutation in the anesthetic-binding site (F1759A-Na(V)1.5) and demonstrated that incomplete Na+ channel inactivation is sufficient to drive structural alterations, including atrial and ventricular enlargement, myofibril disarray, fibrosis and mitochondrial injury, and electrophysiological dysfunctions that together lead to spontaneous and prolonged episodes of AF in these mice. Using this model, we determined that the increase in a persistent sodium current causes heterogeneously prolonged action potential duration and rotors, as well as wave and wavelets in the atria, and thereby mimics mechanistic theories that have been proposed for AF in humans. Acute inhibition of the sodium-calcium exchanger, which targets the downstream effects of enhanced sodium entry, markedly reduced the burden of AF and ventricular arrhythmias in this model, suggesting a potential therapeutic approach for AF. Together, our results indicate that these mice will be important for assessing the cellular mechanisms and potential effectiveness of antiarrhythmic therapies.

SUBMITTER: Wan E

PROVIDER: S-EPMC4701549 | biostudies-literature | 2016 Jan

REPOSITORIES: biostudies-literature

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Aberrant sodium influx causes cardiomyopathy and atrial fibrillation in mice.

Wan Elaine E Abrams Jeffrey J Weinberg Richard L RL Katchman Alexander N AN Bayne Joseph J Zakharov Sergey I SI Yang Lin L Morrow John P JP Garan Hasan H Marx Steven O SO

The Journal of clinical investigation 20151123 1

Increased sodium influx via incomplete inactivation of the major cardiac sodium channel Na(V)1.5 is correlated with an increased incidence of atrial fibrillation (AF) in humans. Here, we sought to determine whether increased sodium entry is sufficient to cause the structural and electrophysiological perturbations that are required to initiate and sustain AF. We used mice expressing a human Na(V)1.5 variant with a mutation in the anesthetic-binding site (F1759A-Na(V)1.5) and demonstrated that inc ...[more]

PMID: 26595809

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Project description:Background. A recent study identified a rare variant in the MRC2 gene in individuals with familial reentrant supraventricular tachycardia, a Wolff-Parkinson-White (WPW) ECG pattern, and structurally normal hearts. WPW syndrome is associated with atrial fibrillation (AF), and MRC2 was recently proposed as a protective gene for AF. Objective. We aimed to determine whether the E990G-heterozygous (het) loss-of-function variant in MRC2 increases AF susceptibility and aberrant atrial cardiofibroblast (ACF) function in mice. Methods. Programmed electrical stimulation (PES) was performed to determine AF susceptibility in E990G-het mice and wild-type (WT) controls. ACFs were isolated from these mice and cultured, and their migration, and collagen deposition were quantified. Finally, transcriptomic profiling by RNA sequencing and secretomic/proteomic profiling by mass spectrometry were performed on ACFs and whole atrial tissue. Results. E990G-het mice exhibited increased susceptibility to pacing-induced AF and had decreased atrioventricular effective refractory periods compared to WT controls. ACFs isolated from E990G-het mice deposited greater amounts of acid-soluble collagen in 2D cultures as quantified by Sirius red staining compared with WT controls. Transcriptomic, secretomic, and proteomic profiling of cultured ACFs and whole-atrial tissue suggest that some fibrotic regulators are differentially expressed or secreted, including decreased ACF expression of matrix metalloproteinase 13 (MMP-13), which degrades collagen types I, II, and III; decreased ACF expression, ACF secretion, and atrial tissue levels of matrix metalloproteinase 12 (MMP-12), which degrades collagen types I, III, IV, elastin, and fibronectin; and increased tissue levels of cellular communication network factor 2/connective tissue growth factor (CCN2/CTGF), a profibrotic regulator. Conclusions. MRC2 E990G-het mice exhibit increased AF susceptibility, altered collagen deposition by ACFs, and differentially regulated fibrotic genes and proteins. Together, these findings suggest that excessive collagen deposition and reduced MMP-mediated collagen removal generate a substrate for the development of AF in the presence of a loss-of-function variant in MRC2.

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Aberrant sodium influx causes cardiomyopathy and atrial fibrillation in mice.

Publications

Aberrant sodium influx causes cardiomyopathy and atrial fibrillation in mice.

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