Abstract 18781: Novel Ryanodine Receptor Mutation Associated With Hypertrophic Cardiomyopathy Induces Cardiac Remodeling and Arrhythmia in Mice
Introduction: Hypertrophic Cardiomyopathy (HCM) is the most common cardiac genetic disease. We identified a novel mutation in the cardiac Ca2+ release channel/ryanodine receptor, RyR2-P1124L, in a patient with obstructive HCM and positive family history of HCM. The patient showed a mid-ventricular septal thickness of 24 mm, LVOT obstruction and several episodes of ventricular fibrillation. Here, we use a multi-level approach to determine the pathogenic mechanisms associated with RyR2-P1124L, in order to provide new insights into RyR2-mediated HCM.
Results: Using recombinant RyR2-P1124L channels, we determined the Ca2+-dependence of [3H]ryanodine binding, an indirect measure of RyR2 activity. RyR2-P1124L requires higher [Ca2+] for activation (EC50 = 362.9±74.5 vs. 190.6±9.8 nM, p = 0.04) and has lower Bmax than WT (0.44±0.02 vs. 0.60±0.03 pmol/mg of protein, p < 0.01), suggesting P1124L is a loss-of-function mutation. P1124 is part of a flexible loop in the SPRY2 domain, located at the interface with the neighboring SPRY3 domain. X-ray crystallography data suggest that P1124L induces a substantial conformation change that might alter the SPRY2-SPRY3 interaction, potentially affecting protein stability. Remarkably, at 12 months of age, homozygous RyR2-P1124L mice show increased septal and posterior wall thickness compared to WT (0.88±0.02 vs. 0.75±0.03 mm, p = 0.05; and 0.91±0.03 vs. 0.78±0.02 mm, p = 0.01, respectively), recapitulating the human phenotype. At 8 months of age, mice do not display cardiac remodeling but are already more susceptible to epinephrine/caffeine-induced arrhythmias, including bidirectional VT (5/7 vs. 0/7, p < 0.01). Finally, preliminary data suggest that cardiac myocytes isolated from homozygous mice have a tendency for increased sarcoplasmic reticulum Ca2+ load in the presence of isoproterenol (12.5±0.5 vs. 11.1±0.4 ΔF/F0, p = 0.06), which could provide the basis for cellular Ca2+ mishandling.
Conclusions: RyR2-P1124L is a loss-of-function mutation that alters RyR2 structure and function. To our knowledge, it is the first to induce ventricular remodeling together with arrhythmia. Therefore, it represents a new paradigm for the emerging field of RyR2-mediated cardiac remodeling and Ca2+-dependent HCM.
Author Disclosures: F.J. Alvarado: None. C.R. Valdivia: None. Z. Yuchi: None. C.A. Marcou: None. J.M. Bos: None. F. Van Petegem: None. M.J. Ackerman: Consultant/Advisory Board; Modest; Boston Scientific, Gilead Sciences, Medtronic, St Jude Medical. Other; Significant; Transgenomic. H.H. Valdivia: None.
- © 2016 by American Heart Association, Inc.