-Atrial fibrillation (AF) is frequently associated with enhanced inflammatory response. The "NACHT, LRR and PYD domain containing protein 3" (NLRP3)-inflammasome mediates caspase-1 activation and interleukin-1β release in immune cells, but is not known to play a role in cardiomyocytes (CMs). Here, we assessed the role of CM NLRP3-inflammasome in AF. -NLRP3-inflammasome activation was assessed by immunoblot in atrial whole-tissue lysates and CMs from patients with paroxysmal (pAF) or long-standing persistent (chronic) AF (cAF). To determine whether CM-specific activation of NLPR3 is sufficient to promote AF, a CM-specific knock-in mouse model expressing constitutively active NLRP3 (CM-KI) was established. In vivo electrophysiology was used to assess atrial arrhythmia vulnerability. To evaluate the mechanism of AF, electrical activation pattern, Ca spark frequency (CaSF), atrial effective refractory period (AERP), and morphology of atria were evaluated in CM-KI mice and WT littermates. -NLRP3-inflammasome activity was increased in atrial CMs of pAF and cAF patients. CM-KI mice developed spontaneous premature atrial contractions and inducible AF, which was attenuated by a specific NLRP3-inflammasome inhibitor, MCC950. CM-KI mice exhibited ectopic activity, abnormal sarcoplasmic-reticulum Ca-release, AERP shortening and atrial hypertrophy. Adeno-associated virus subtype-9 mediated CM-specific knockdown of suppressed AF development in CM-KI mice. Finally, genetic inhibition of prevented AF development in CREM transgenic mice, a well-characterized mouse model of spontaneous AF. -Our study establishes a novel pathophysiological role for CM NLRP3-inflammasome signaling with a mechanistic link to the pathogenesis of AF, and establishes inhibition of NLRP3 as a potential novel AF-therapy approach.
Highlights d Creation of a mouse conditionally expressing active YAP called YAP5SA d YAP5SA in adult cardiomyocytes (CMs) induces a more primitive transcriptional state d YAP5SA activates developmental enhancers d YAP5SA expression in CMs causes CM hyperplasia and overall heart hypercellularity
Inhibition of reactive oxygen species or ox-CaMKII protects against proarrhythmic intracellular Ca handling and prevents ventricular arrhythmia in a mouse model of Duchenne muscular dystrophy.
Background
The sodium channel, Na
v
1.5, encoded by
SCN
5A
, undergoes developmentally regulated splicing from inclusion of exon 6A in the fetal heart to exon 6B in adults. These mutually exclusive exons differ in 7 amino acids altering the electrophysiological properties of the Na
v
1.5 channel. In myotonic dystrophy type 1,
SCN
5A
is mis‐spliced such that the fetal pattern of exon 6A inclusion is detected in adult hearts. Cardiac manifestations of myotonic dystrophy type 1 include conduction defects and arrhythmias and are the second‐leading cause of death.
Methods and Results
This work aimed to determine the impact of
SCN
5A
mis‐splicing on cardiac function. We used clustered regularly interspaced short palindromic repeat (
CRISPR)
/CRISPR‐associated protein 9 (Cas9) to delete
Scn5a
exon 6B in mice, thereby redirecting splicing toward exon 6A. These mice exhibit prolonged
PR
and
QRS
intervals, slowed conduction velocity, extended action potential duration, and are highly susceptible to arrhythmias.
Conclusions
Our findings highlight a nonmutational pathological mechanism of arrhythmias and conduction defects as a result of mis‐splicing of the predominant cardiac sodium channel. Animals homozygous for the deleted exon express only the fetal isoform and have more‐severe phenotypes than heterozygotes that also express the adult isoform. This observation is directly relevant to myotonic dystrophy type 1, and possibly pathological arrhythmias, in which individuals differ with regard to the ratios of the isoforms expressed.
BACKGROUND:
Spontaneously depolarizing nodal cells comprise the pacemaker of the heart. Intracellular calcium (Ca
2+
) plays a critical role in mediating nodal cell automaticity and understanding this so-called Ca
2+
clock is critical to understanding nodal arrhythmias. We previously demonstrated a role for Jph2 (junctophilin 2) in regulating Ca
2+
-signaling through inhibition of RyR2 (ryanodine receptor 2) Ca
2+
leak in cardiac myocytes; however, its role in pacemaker function and nodal arrhythmias remains unknown. We sought to determine whether nodal Jph2 expression silencing causes increased sinoatrial and atrioventricular nodal cell automaticity due to aberrant RyR2 Ca
2+
leak.
METHODS:
A tamoxifen-inducible, nodal tissue-specific, knockdown mouse of Jph2 was achieved using a Cre-recombinase-triggered short RNA hairpin directed against Jph2 (Hcn4:shJph2). In vivo cardiac rhythm was monitored by surface ECG, implantable cardiac telemetry, and intracardiac electrophysiology studies. Intracellular Ca
2+
imaging was performed using confocal-based line scans of isolated nodal cells loaded with fluorescent Ca
2+
reporter Cal-520. Whole cell patch clamp was conducted on isolated nodal cells to determine action potential kinetics and sodium-calcium exchanger function.
RESULTS:
Hcn4:shJph2 mice demonstrated a 40% reduction in nodal Jph2 expression, resting sinus tachycardia, and impaired heart rate response to pharmacologic stress. In vivo intracardiac electrophysiology studies and ex vivo optical mapping demonstrated accelerated junctional rhythm originating from the atrioventricular node. Hcn4:shJph2 nodal cells demonstrated increased and irregular Ca
2+
transient generation with increased Ca
2+
spark frequency and Ca
2+
leak from the sarcoplasmic reticulum. This was associated with increased nodal cell AP firing rate, faster diastolic repolarization rate, and reduced sodium-calcium exchanger activity during repolarized states compared to control. Phenome-wide association studies of the
JPH2
locus identified an association with sinoatrial nodal disease and atrioventricular nodal block.
CONCLUSIONS:
Nodal-specific Jph2 knockdown causes increased nodal automaticity through increased Ca
2+
leak from intracellular stores. Dysregulated intracellular Ca
2+
underlies nodal arrhythmogenesis in this mouse model.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.