Increased Reactive Oxygen Species-Mediated Ca²⁺/Calmodulin-Dependent Protein Kinase II 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 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 with wild-type controls, BTHS-induced pluripotent stem cell-derived cardiomyocytes had increased diastolic Ca²⁺ and decreased Ca²⁺ transient amplitude. BTHS-induced pluripotent stem cell-derived cardiomyocytes had higher levels of mitochondrial and cellular reactive oxygen species than wild-type controls, which activated CaMKII (Ca²⁺/calmodulin-dependent protein kinase II). Activated CaMKII phosphorylated the RYR2 (ryanodine receptor 2) on serine 2814, increasing Ca²⁺ leak through RYR2. Inhibition of this reactive oxygen species-CaMKII-RYR2 pathway through pharmacological inhibitors or genome editing normalized aberrant Ca²⁺ handling in BTHS-induced pluripotent stem cell-derived cardiomyocytes and improved their contractile function. Murine Taz knockout cardiomyocytes also exhibited elevated diastolic Ca²⁺ and decreased Ca²⁺ transient amplitude. These abnormalities were ameliorated by Ca²⁺/calmodulin-dependent protein kinase II or reactive oxygen species inhibition.

Conclusions: This study identified a molecular pathway that links TAZ mutation with abnormal Ca²⁺ handling and decreased cardiomyocyte contractility. This pathway may offer therapeutic opportunities to treat BTHS and potentially other diseases with elevated mitochondrial reactive oxygen species production.