Molecular pathology of mutations in mitochondrial tRNA-Ile

Mutations of mitochondrial DNA (mtDNA) are an important cause of multisystemic as well as tissue specific degenerative diseases. Mitochondrial transfer RNA (tRNA) genes appear to be the major targets of disease causing mutations: more than 50% of the known mutations affect tRNA genes although they make up less than 10% of mtDNAs coding part. In contrast to the clearly defined role of tRNAs in protein biosynthesis, genotype to phenotype relationships of tRNA mutations are complex and poorly understood. Even mutations within the same tRNA gene may cause entirely different clinical presentations, apparently depending on the nature of the mutation. The technology of transmitochondrial cell lines (cybrids) has been increasingly used to study the molecular and cellular pathologies associated with mtDNA mutations in recent years. In this system a patient`s mutant mtDNA is transferred to a stable cell line and thereby isolated from the patient`s nuclear genetic background. We will use cybrids to study 5 pathogenic mutations within the mitochondrial tRNA Ile gene. Though affecting the same tRNA the 5 mutations caused entirely different clinical diseases, like ophthalmoplegia with exercise intolerance, cardiomyopathy, degenerative encephalopathy, or a heterogenous multisystem disorder. By dissecting the exact molecular deficits and studying the cellular consequences associated with each individual mutation, we want to learn if distinct molecular or cellular deficits correlate with a specific clinical outcome. Is there a characteristic pattern, a signature, of molecular and accordingly cellular deficiencies associated with mutations causing, e.g., multisystem disorder versus mutations causing pure encephalopathy? Naturally, establishing the precise pathogenic mechanisms of mutations may have implications for the development of treatment strategies for the associated diseases, an issue particularly important in diseases like those caused by mtDNA mutations, where no treatment options are currently available.

Mutations of mitochondrial DNA (mtDNA) are an important cause of multisystemic as well as tissue specific degenerative diseases. Mitochondrial transfer RNA (tRNA) genes appear to be the major targets of disease causing mutations: more than 50% of the known mutations affect tRNA genes although they make up less than 10% of mtDNAs coding part. In contrast to the clearly defined role of tRNAs in protein biosynthesis, genotype to phenotype relationships of tRNA mutations are complex and poorly understood. Even mutations within the same tRNA gene may cause entirely different clinical presentations, apparently depending on the nature of the mutation. The technology of transmitochondrial cell lines (cybrids) has been increasingly used to study the molecular and cellular pathologies associated with mtDNA mutations in recent years. In this system a patient`s mutant mtDNA is transferred to a stable cell line and thereby isolated from the patient`s nuclear genetic background. We will use cybrids to study 5 pathogenic mutations within the mitochondrial tRNA IIe gene. Though affecting the same tRNA the 5 mutations caused entirely different clinical diseases, like ophthalmoplegia with exercise intolerance, cardiomyopathy, degenerative encephalopathy, or a heterogenous multisystem disorder. By dissecting the exact molecular deficits and studying the cellular consequences associated with each individual mutation, we want to learn if distinct molecular or cellular deficits correlate with a specific clinical outcome. Is there a characteristic pattern, a signature, of molecular and accordingly cellular deficiencies associated with mutations causing, e.g., multisystem disorder versus mutations causing pure encephalopathy? Naturally, establishing the precise pathogenic mechanisms of mutations may have implications for the development of treatment strategies for the associated diseases, an issue particularly important in diseases like those caused by mtDNA mutations, where no treatment options are currently available.