Abstract 16239: A Novel Ryanodine Receptor Mutation Linked to Human Hypertrophic Cardiomyopathy
Hypertrophic cardiomyopathy (HCM) is one of the most common sudden death predisposing, genetic heart disease. Mutations in Ca2+-handling proteins can contribute to the pathogenesis of HCM. We identified a novel mutation in the cardiac Ca2+ release channel/ryanodine receptor, RyR2-P1124L, in a patient with obstructive HCM and a mid-ventricular septal thickness of 24 mm. The patient has experienced several episodes of ventricular fibrillation and also has a positive family history of HCM. RyR2-P1124L falls outside the canonical domains of RyR2-mediated Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT), and thus, its study may yield unique insights into the mechanisms by which RyR2 dysfunction may lead to HCM. We expressed recombinant mouse cardiac RyR2 carrying the RyR2-P1124L mutation to characterize its molecular phenotype. The P1124L mutation significantly hinders the expression of RyR2 in HEK293 cells (49.4±3.6% vs. WT expression, n=6 transfections, p<0.05), a phenomenon not observed with most CPVT-associated RyR2 mutations. The Ca2+-dependence of [3H]ryanodine binding, an indirect measure of channel activity, was depressed in RyR2-P1124L with respect to WT, yielding a curve that required higher [Ca2+] for activation (ED50 = 0.61 and 0.19 μM, respectively) and with lower plateau (70% of WT). These data support the pathogenic role of RyR2-P1124L and uncovers a different molecular phenotype than CPVT-associated RyR2 mutations, which are mostly indistinguishable from WT in [3H]ryanodine binding assays. We generated a mouse line expressing RyR2-P1124L (RyR2PL) and started the characterization of the cellular mechanisms that lead to HCM. Although the expression and phosphorylation of RyR2 are not altered in RyR2PL mice (n=3 mice/genotype, p>0.05), homozygous mice are more susceptible than WT to develop caffeine/epinephrine-induced arrhythmias (3/5 vs. 0/2 mice, 8-month old), including bidirectional ventricular tachycardia (2/5 vs. 0/2). Furthermore, RyR2PL mice have a tendency for increased LV diastolic (p=0.06) and systolic volume (p=0.07) than WT (n=4 mice/genotype). The RyR2PL mouse may be an invaluable tool to elucidate the molecular mechanisms by which mutations in Ca2+-handling proteins are linked to HCM in humans.
- © 2013 by American Heart Association, Inc.