Increased ROS-Mediated CaMKII Activation Contributes to Calcium Handling Abnormalities and Impaired Contraction in Barth Syndrome.

Background: Mutations in tafazzin ( TAZ ), a gene required for biogenesis of cardiolipin, the signature phospholipid of the inner mitochondrial membrane, causes Barth syndrome (BTHS). Cardiomyopathy and risk of sudden cardiac death are prominent features of BTHS, but the mechanisms by which impaired cardiolipin biogenesis causes cardiac muscle weakness and arrhythmia are poorly understood. Methods: We performed in vivo electrophysiology to define arrhythmia vulnerability in cardiac specific TAZ knockout mice. Using cardiomyocytes derived from human induced pluripotent stem cells (iPSC-CMs) and cardiac specific TAZ knockout mice as model systems, we investigated the effect of TAZ inactivation on Ca2+ handling. Through genome editing and pharmacology, we defined a molecular link between TAZ mutation and abnormal Ca2+ handling and contractility. Results: A subset of mice with cardiac-specific TAZ inactivation developed arrhythmias including bidirectional ventricular tachycardia, atrial tachycardia, and complete atrioventricular block. Compared to WT, BTHS iPSC-CMs had increased diastolic Ca2+ and decreased Ca2+ transient amplitude. BTHS iPSC-CMs had higher levels of mitochondrial and cellular ROS than WT, which activated Ca2+ /calmodulin-dependent protein kinase II (CaMKII). Activated CaMKII phosphorylated the cardiac ryanodine receptor (RYR2) on serine 2814, increasing Ca2+ leak through RYR2. Inhibition of this ROS-CaMKII-RYR2 pathway through pharmacological inhibitors or genome editing normalized aberrant Ca2+ handling in BTHS iPSC-CMs and improved their contractile function. Murine Taz knockout cardiomyocytes also exhibited elevated diastolic Ca2+ and decreased Ca2+ transient amplitude. These abnormalities were ameliorated by CaMKII or ROS inhibition. Conclusions: This study identified a molecular pathway that links TAZ mutation to abnormal Ca2+ handling and decreased cardiomyocyte contractility. This pathway may offer therapeutic opportunities to treat BTHS and potentially other diseases with elevated mitochondrial ROS production.