Abstract 16973: A Novel in vivo Model to Study Mutations in Sick Sinus Syndrome
Introduction: Sick-Sinus Syndrome (SSS) is a disorder of impulse generation that causes symptomatic bradycardia requiring pacemaker implantation. Although mutations in HCN4 are a common cause of SSS, <5% of HCN4 variants have been functionally characterized. We hypothesize that perturbation of zebrafish hcn4 will recapitulate the characteristic arrhythmic manifestations of SSS, and this model system can be used in a high-throughput manner to functionally distinguish pathogenic from benign HCN4 variants.
Methods: To test our hypothesis, 1) morpholinos (MO) were used to knock down endogenous hcn4 expression in wild-type (WT) embryos, and cardiac phenotypes were characterized at 36-48 hour-post-fertilization (hpf). 2) Pharmacological hcn4 blockade was performed by bathing WT embryos with ZD-7288 (1mM), and phenotypes were determined at 48 hpf. 3) Finally, effects of ZD-7288 (10uM) on atrial and ventricular action potentials (APs) were measured in explanted hearts.
Results: Hcn4-morphants had significant bradycardia (89 bpm, n=25) compared with controls (164 bpm, n=15, p-value < 0.001) and sinus pauses were seen in 84% of morphants. Likewise, embryos bathed in ZD-7288 showed bradycardia (90 bpm, n=10) compared to controls (150 bpm, n=10, p < 0.001). Cycle length (CL) of atrial (n=4) and ventricular APs (n=4) were also significantly increased in ZD-7288 and action potential duration (APD90) prolonged in a CL-dependent manner (Table 1).
Conclusions: We concluded that genetic and pharmacological inhibition of hcn4 phenocopies SSS with bradycardia and sinus pauses. These results provide the foundation for future work using the zebrafish model organism for high throughput screening of ion channel variants identified by Next Generation Sequencing.
- © 2013 by American Heart Association, Inc.