FUNCTIONAL AND MORPHOLOGICAL ABNORMALITIES OF MITOCHONDRIA IN HUMAN-CELLS CONTAINING MITOCHONDRIAL-DNA WITH PATHOGENIC POINT MUTATIONS IN TRANSFER-RNA GENES

mtDNA with a point mutation in the tRN(Ile) gene at nucleotide positio n 4269 found in a patient with fatal cardiomyopathy and mtDNA with a p oint mutation in the tRNA(Arg) gene at 10410 found in a patient with A lpers disease were transferred cytoplasmically to rho degrees HeLa cel ls (HeLa cells lacking mtDNA) to determine whether these novel mtDNA m utations in the tRNA genes are responsible for the defects in mitochon drial respiration function observed in these diseases. Cybrid clones ( clones of rho degrees HeLa cells with mtDNA from the patients) were is olated, and respiratory function and morphology of the mitochondria of the cybrid clones containing wild-type mtDNA and mutant mtDNA predomi nantly were compared. The results showed that accumulation of mutant m tDNA at 4269 alone without defects in the nuclear genome was sufficien t to produce a disease phenotype, while mutant mtDNA at 10410 was not related to pathogenesis and reflected one of the rare polymorphic site s of human mtDNA. Moreover, we found that mitochondria in living cells were significantly swollen only when they contained predominantly the pathogenic mutant mtDNA, suggesting that the functional abnormality o f mitochondria induced by pathogenic mtDNA mutations in tRNA genes is always associated with their swollen structure.