Dantrolene inhibits aberrant Ca2+ release by stabilizing inter-domain interactions within the ryanodine receptor in cardiac troponin T-related familial hypertrophic cardiomyopathy

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Backgrounds: Cardiac troponin T (cTnT) mutations cause Familial Hypertrophic Cardiomyopathy (FHC), which leads to sudden cardiac death in young age. In many of the non-dilated forms of FHC-linked cTnT mutations, Ca2+ sensitivity in myofilaments was increased. However, the underlying mechanism by which the cTnT mutations lead to lethal arrhythmia and the possibility of developing a therapeutic strategy against lethal arrhythmia remains elusive. Here, we hypothesized that aberrant Ca2+ release via the cardiac ryanodine receptor (RyR2) could be altered arrhythmogenesis in FHC. To verify this hypothesis, we investigated the pathogenic role of aberrant Ca2+ release and the therapeutic effects of Dantrolene, which was found to correct the defective inter-domain interaction of RyR2 in catecholaminergic polymorphic ventricular tachycardia and failing hearts (i.e. unzipping to zipping) in transgenic mouse (TG) model with FHC-related cTnT mutation (delta160E). Methods and results: In 6thmonth-old TG, there was no appreciable difference in the structural or functional features of the hearts between non-TG mice and TG. In response to isoproterenol (ISO; 10 nmol/L), the Ca2+ spark frequency was much higher in TG cardiomyocytes than in non-TG {TG (n=7): 7.9±0.6; non-TG (n=6): 3.5±0.5; p<0.01}, whereas it was largely reversed by dantrolene (1 μM) {TG (n=6): 5.2±0.3; p<0.05}. Time from peak to 70% decline of Ca2+ transient was more prolonged in ISO-treated TG than in ISO-treated non-TG, whereas it was attenuated by dantrolene. ISO-treated TG cardiomyocytes (12/18; n=18, but not ISO-treated non-TG; 0/14; n=14) showed spontaneous Ca2+ transient (sCaT) after 5Hz pacing, whereas it was again attenuated by dantrolene (3/10; n=10). Conclusions: In FHC-linked cTnT mutated hearts, aberrant local Ca2+ release through defective (domain-unzipped) RyR2 was induced by beta-adrenergic stimulation and the inhibition of aberrant Ca2+ release by the stabilization of RyR2 may play a role for arrhythmogenesis in FHC.

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