Abstract 121: Development of Enzyme Replacement Therapy in Mammalian Models of Barth Syndrome

Abstract

Barth Syndrome (BTHS) is caused by a single gene mutation in the mitochondrial transacylase, tafazzin (TAZ), which results in impaired lipid metabolism leading to dysfunction in highly energetic tissues such as the heart and skeletal muscle. TAZ remodels the signature mitochondrial phospholipid, cardiolipin (CL), which is responsible for providing support to the electron transport chain. BTHS patients suffer from growth deficiencies, cardiomyopathy, hypotonia and neutropenia. Currently, treatment for patients with BTHS is supportive, seeking to ameliorate rather than prevent heart problems, skeletal muscle problems and recurring infections. Protein therapy, on the other hand, might treat and even prevent cardiac, skeletal muscle as well as infection-related morbidities. We designed a recombinant TAZ protein containing a cell penetrating peptide in its C-terminus, which enables the recombinant TAZ to penetrate cells and then treated TAZ-deficient cells with it. We tested the permeability of the recombinant protein by direct delivery to H9C2 cardiomyoblasts and found that the protein is successfully taken up by the cells. We have generated a CRISPR-mediated TAZ knock out cardiomyoblast cell line and we found that TAZ knock out cells show a decrease in oxygen consumption as compared to the wild type cells; this is consistent with data from BTHS patient-derived cells. We are using this cell line to assess the enzymatic activity of the delivered protein by conducting mitochondrial respiration measurements. We have also acquired a mouse model of BTHS and are testing the recombinant TAZ in vivo. Preliminary data shows an augmentation in oxygen consumption following treatment with TAZ. These results indicate that the protein is able to reach the mitochondria, where it is enzymatically active and able to enhance respiration. As the protein is able to rescue respiration in cells in which tafazzin was absent, this suggests that our approach should not only be able to prevent onset of symptoms, but also rescue the phenotype in already affected tissues.