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Date of Award
MIRIAM L. GREENBERG
As the signature phospholipid of the mitochondrial membranes, cardiolipin (CL) plays an essential role in mitochondrial bioenergetic functions. Impaired CL metabolism leads to Barth syndrome (BTHS), a severe human genetic disorder resulting from the loss-of-function of the CL transacylase tafazzin. The clinical phenotypes of BTHS including cardio- and skeletal myopathy, exercise intolerance, and lactic acidosis, point to metabolic defects. I utilized both yeast and mouse cells to study the function of CL in metabolic regulation. These studies may contribute to the identification of potential therapeutic strategies for BTHS patients.
Previous studies indicated that CL deficient cells exhibit decreased levels of acetyl-CoA and reduced activities of TCA cycle enzymes, aconitase and succinate dehydrogenase (SDH). To gain insight into how CL deficiency affects the TCA cycle, metabolic flux of C13-glucose was analyzed in tafazzin knockout (TAZ-KO) mouse cells. TAZ-KO cells exhibited decreased flux of C13-glucose to acetyl-CoA and TCA cycle intermediates. These deficiencies were associated with decreased activity of pyruvate dehydrogenase (PDH) and SDH in TAZ-KO cells. Importantly, CL was found to bind to the PDH complex and stimulate PDH activity. These studies suggest that CL is required for the optimal activation of PDH, and that PDH and SDH activities are decreased in BTHS.
As decreased SDH activity may result from decreased Fe-S biosynthesis in yeast crd1Δ cells, my study suggested that iron homeostasis is also impaired in TAZ-KO mouse cells. Iron defects were assayed in TAZ-KO cells, which exhibit reduced mitochondrial Fe-S enzyme activity and elevated sensitivity to iron and H2O2. In addition, this mutant exhibits up-regulated expression of ferroportin (an iron exporter) and down-regulated expression of transferrin receptor (an iron importer) accompanied by elevated mitochondrial iron. The iron chelator deferoxamine alleviated the sensitivity of TAZ-KO cells to H2O2. Both TAZ-KO mouse cells and BTHS lymphoblasts exhibit decreased frataxin, a protein required for Fe-S biogenesis. Decreased frataxin resulted from defects in mitochondrial import or processing. These findings suggest that loss of tafazzin leads to perturbation of Fe-S biogenesis in mammalian as well as yeast cells.
Li, Yiran, "Cardiolipin Deficiency Imposes Metabolic Dysfunction That May Contribute To Barth Syndrome Pathology" (2018). Wayne State University Dissertations. 1942.