Cellular ATP is synthesized by the mitochondrial oxidative phosphorylation (OXPHOS) system, composed of five enzyme complexes (Complexes I--V), which consist collectively of over 80 subunits. The majority of these subunits are encoded by nuclear genes, and 13 of them, by mitochondrial DNA (mtDNA). OXPHOS deficiencies resulting in mitochondrial disorders can be caused by either nuclear or mitochondrial mutations; however, most pathogenic mutations reported in adults occur in mtDNA. Such mutations often impair mitochondrial translation and are associated with a characteristic muscle pathology consisting of a mosaic pattern of normal fibers interspersed with fibers displaying mitochondrial proliferation and decreased OXPHOS activity. In this thesis, the molecular basis for a severe mitochondrial myopathy in two adult patients was investigated. All patient muscle fibers showed mitochondrial proliferation and barely detectable Complex IV activity (a measure of OXPHOS activity), a pattern never before reported. Biochemical studies demonstrated decreased activities of Complexes I and IV (5% of control) and Complex II+III (41% of control) in patient muscle. Immunoblot analysis of nuclear and mitochondrial subunits of Complexes 1, III and IV showed a greater than 90% decrease in the steady-state level of these subunits in mature muscle, but no change in nuclear-encoded subunits of Complexes II and V. A generalized mitochondrial translation defect was identified by pulse-label experiments in myotubes, but not in myoblasts cultured from both patients. This defect moved with the nucleus in patient cybrid cells. Myoblasts from one patient transplanted into the muscle bed of SCID mice differentiated into mature muscle fibers that displayed a defect similar to that seen in the patient muscle. Mapping of the defective gene in this patient was attempted using a functional complementation approach. Microcell-mediated transfer of mouse chromosomes in patient
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.84321 |
| Date | January 2003 |
| Creators | Sasarman, Florin |
| Contributors | Shoubridge, Eric A. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Neuroscience.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002031987, proquestno: AAINQ98367, Theses scanned by UMI/ProQuest. |
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