FASEB J. 2022 May;36 Suppl 1
Barth syndrome (BTHS) is a rare, X-linked disorder of mitochondrial phospholipid metabolism caused by variants in the gene TAFAZZIN.TAFAZZIN is a transacylase involved in the remodeling of cardiolipin (CL), a dimeric phospholipid localized to the inner mitochondrial membrane. Lack of TAFAZZIN-based remodeling results in irregular cardiolipin content, characterized by increased unremodeled CL, increased monoloysocardiolipin (the CL remodeling intermediate), and a decrease in remodeled CL, which is enriched in polyunsaturated fatty acyl chains that are tissue-specific in composition. BTHS is clinically characterized by cardiomyopathy, neutropenia, and myopathy, with a high morbidity and mortality. There are no approved disease-specific therapies. To investigate the cellular pathology and to identify new areas of potential therapeutic intervention, we developed two CRISPR-edited cell lines: TAFAZZIN-knockout (KO) HEK293 cells and iPSCs with which to perform broad-based discovery experiments and to study tissue-specific disease effects, respectively. A combined multi-omics approach including proteomics, lipidomics, and metabolomics in TAZ-KO HEK293 cells revealed diverse mitochondrial abnormalities, including defects in complex I of the respiratory chain, abnormal PDK2 expression, and dysregulation of proteins involved in mitochondrial quality control including PARL and PGAM5. Importantly, we discovered that molecules that bind to cardiolipin (SS-31) or inhibit nascent cardiolipin deacylation (bromoenol lactone), partially remediate these mitochondrial defects. We next explored cell-type specific dysfunction in iPSC-derived TAZ-KO and wild-type cardiomyocytes and neurons via lipidomics, RNA-seq, and functional studies. We identified disturbances in cellular lipid content including an expected increase in the monolysocardiolipin content and a reduction that exhibited cell-type specificity. RNAseq identified dysregulation in pathways regulated by PARL and PGAM5 including Wnt signaling, apoptosis, and autophagy in the undifferentiated state, with differentiated cell types highlighting pathways such as glucose metabolism and response to cellular stimuli. Oxygen consumption studies show impaired maximal respiratory capacity in TAZ-KO cardiomyocytes and neurons. Ongoing investigations aim to address cell type specific mitochondrial dysfunction by characterizing PARL abundance, PGAM5 cleavage, and mitochondrial morphology in TAZ-KO iPSC derived cell types. Additionally, we are currently targeting cardiolipin metabolism in differentiated TAZ-deficient cells with the goal of remediating cellular lipids, mitochondrial gene expression, and oxygen consumption abnormalities.