Abstract 113: Recombinant Tafazzin Enzyme Replacement Therapy Rescues Metabolic and Functional Defects in a Mouse Model of Barth Syndrome

Abstract

Barth syndrome (BTHS) is an X-linked recessive disease where patients most commonly die from cardiomyopathy-induced heart failure before middle age. BTHS is caused by mutations in the tafazzin (TAZ) gene, resulting in defective TAZ protein. TAZ is an enzyme that generates mature cardiolipin (CL) from monolysocardiolipin (MLCL) in the mitochondrial membrane, a reaction essential for normal mitochondrial function. Current therapies can only treat the symptoms of BTHS. In this study, we propose an enzyme replacement therapy for BTHS which utilizes recombinant human TAZ fused to a cell penetrating peptide (hTAZ-CTP) to facilitate tissue uptake. The efficacy of this protein was tested in vitro on C2C12 TAZ-knockout (TAZ-KO) skeletal myoblasts and in vivo on a myocardial-specific TAZ conditional knockout mouse, modelling the cardiomyopathy associated with BTHS. In vitro tests of TAZ-KO cells, using oxygen consumption rate as a measure of mitochondrial activity, showed treatment of the cells with hTAZ-CTP effected a partial rescue of the fatty acid oxidation capabilities of the TAZ-KO cells. In vivo tests showed that BTHS mice display increasing septal wall thickness over time, an effect halted upon treatment with hTAZ-CTP. Pressure-volume (PV) loop analysis indicated that heart function, impaired in the vehicle-treated BTHS mouse, was similar between treated mice and normal mice. The ratio of MLCL/CL, a direct measure of TAZ enzymatic activity, was measured in heart mitochondria isolated from BTHS and control mice after treatment. The vehicle treated BTHS mouse showed the high MLCL/CL ratio typical of BTHS patients, whereas the MLCL/CL ratios in protein-treated mice matched the much lower ratio of the control mice. Similarly, oxygen consumption rate measurements of these isolated heart mitochondria demonstrated partial rescue by hTAZ-CTP treatment. Coupled with the lack of toxicity observed in the liver, spleen, kidney, and heart due to hTAZ-CTP injection, these results indicate that TAZ enzyme replacement therapy has great potential as a future treatment for BTHS.