The oxidation‐resistant CaMKII‐MM281/282VV mutation does not prevent arrhythmias in CPVT1

Abstract

Catecholaminergic polymorphic ventricular tachycardia type 1 (CPVT1) is an inherited arrhythmogenic disorder caused by missense mutations in the cardiac ryanodine receptors (RyR2), that result in increased β‐adrenoceptor stimulation‐induced diastolic Ca 2+ leak. We have previously shown that exercise training prevents arrhythmias in CPVT1, potentially by reducing the oxidation of Ca 2+ /calmodulin‐dependent protein kinase type II (CaMKII). Therefore, we tested whether an oxidation‐resistant form of CaMKII protects mice carrying the CPVT1‐causative mutation RyR2‐R2474S (RyR2‐RS) against arrhythmias. Antioxidant treatment (N‐acetyl‐L‐cysteine) reduced the frequency of β‐adrenoceptor stimulation‐induced arrhythmogenic Ca 2+ waves in isolated cardiomyocytes from RyR2‐RS mice. To test whether the prevention of CaMKII oxidation exerts an antiarrhythmic effect, mice expressing the oxidation‐resistant CaMKII‐MM281/282VV variant (MMVV) were crossed with RyR2‐RS mice to create a double transgenic model (RyR2‐RS/MMVV). Wild‐type mice served as controls. Telemetric ECG surveillance revealed an increased incidence of ventricular tachycardia and an increased arrhythmia score in both RyR2‐RS and RyR2‐RS/MMVV compared to wild‐type mice, both following a β‐adrenoceptor challenge (isoprenaline i.p.), and following treadmill exercise combined with a β‐adrenoceptor challenge. There were no differences in the incidence of arrhythmias between RyR2‐RS and RyR2‐RS/MMVV mice. Furthermore, no differences were observed in β‐adrenoceptor stimulation‐induced Ca 2+ waves in RyR2‐RS/MMVV compared to RyR2‐RS. In conclusion, antioxidant treatment reduces β‐adrenoceptor stimulation‐induced Ca 2+ waves in RyR2‐RS cardiomyocytes. However, oxidation‐resistant CaMKII‐MM281/282VV does not protect RyR2‐RS mice from β‐adrenoceptor stimulation‐induced Ca 2+ waves or arrhythmias. Hence, alternative oxidation‐sensitive targets need to be considered to explain the beneficial effect of antioxidant treatment on Ca 2+ waves in cardiomyocytes from RyR2‐RS mice.

CaMKII inhibition has dual effects on spontaneous Ca2+ release and Ca2+ alternans in ventricular cardiomyocytes from mice with a gain-of-function RyR2 mutation

“…Ideally, a therapeutic window optimal for Ca 2+ leak reduction while inducing minimal levels of Ca 2+ alternans or other proarrhythmic mechanisms should be identified. Of note, a previous publication from our group demonstrated similar levels of CaMKII Thr 286 phosphorylation in WT and CPVT animals, also following isoprenaline treatment (85). The beneficial effects of CaMKII inhibition observed in article 2 therefore occurs despite no indications of higher CaMKII activity in CPVT mice, compared to healthy animals.…”

“…β-blockers inhibit the signaling pathways that lead to phosphorylation of RyR2, but is insufficient in some patients (84). Another potential target pathway is direct oxidation of RyR2 (85). Oxidation of RyR2 might be especially relevant in CPVT, where increased diastolic Ca 2+ release can alter mitochondrial Ca 2+ handling and lead to an increase in mitochondrial ROS production (86).…”

Myocardial oxidative stress is increased in early reperfusion, but systemic antioxidative therapy does not prevent ischemia-reperfusion arrhythmias in pigs

“…This is in contrast with findings by Dries et al, where NAC did not affect the Ca 2+ spark frequency, nor Ca 2+ load ( 39 ). However, other studies support NAC as protective against arrhythmogenic Ca 2+ release in mice ( 38 , 40 ). Additionally, NAC both reduced the incidence of IRA in rodent Langendorff-perfused hearts ( 15 ), and protected against arrhythmogenic Ca 2+ release in cardiomyocytes exposed to hypoxia and re-oxygenation ( 14 ).…”