Investigating mitochondrial deoxyribonucleotide metabolism and its role in a family of genetic diseases

Abstract

Abnormal regulation of mitochondrial deoxyribonucleoside triphosphate pools can lead to mitochondrial DNA depletion syndromes, a set of genetic diseases associated with depletion of mitochondrial DNA. Besides mitochondrial DNA depletion syndromes, improper maintenance of mitochondrial deoxyribonucleoside triphosphate pools and mitochondrial DNA have also been implicated in a host of other human pathologies. The unifying objective of this dissertation was to enhance our knowledge of the regulation of mitochondrial deoxyribonucleoside triphosphate pools. The first step was to investigate the characteristics of mitochondrial and cytoplasmic deoxyribonucleoside triphosphate levels. I calculated mitochondrial and cytoplasmic deoxyribonucleoside triphosphate concentrations from previously published data. Cytoplasmic and mitochondrial deoxyribonucleoside triphosphates are strongly correlated in normal cells but not in transformed cells. Following up this discovery with analysis of gene expression, I discovered that, consistent with the trends in deoxyribonucleoside triphosphate concentrations in cells, genes coding for enzymes that maintain cytoplasmic and mitochondrial deoxyribonucleoside triphosphates have correlated expression across normal tissues but not across transformed tissues. To further understand the influence of cytoplasmic deoxyribonucleoside triphosphates on mitochondrial deoxyribonucleoside triphosphates, I simulated the metabolism of mitochondrial deoxyribonucleosides with a computational model. Cytoplasmic deoxyribonucleotides have a substantial and indispensable contribution to mitochondrial deoxyribonucleoside triphosphates in most circumstances. My results further show that import from the cytoplasm would need to occur at either deoxyribonucleoside diphosphate or triphosphate levels.