IDENTIFICATION AND CHARACTERIZATION OF NUCLEAR GENES RESPONSIBLE FOR HUMAN MITOCHONDRIAL DISORDERS

Mitochondrial disorders are due to abnormalities of the mitochondrial energy metabolism, i.e. oxidative phosphorylation (OXPHOS). Because of its dual genetic control, OXPHOS disorders can be due to mutations in mtDNA or nuclear DNA genes. In contrast with the wealth of information on mtDNA mutations gained in the past years, the number of nuclear disease genes associated with mitochondrial syndromes is still rather small, and the genetic basis of many such disorders remains unknown. This is particularly frequent in OXPHOS disorders of infancy and childhood, in which mutations of mtDNA are much less common than in adult cases. The aims of the present projects are: (1) to identify new nuclear disease genes; (2) study their in vivo pathogenesis by means of cellular and mouse disease models. The first aim will be pursued by studying several families and cell lines with OXPHOS defects, by linkage analysis or functional complementation strategies. The identification of the disease locus will be followed by search for mutations in candidate genes. The second aim will be pursued by: (1) producing mouse and fruit-fly knockout models for Surf1, an assembly gene for complex IV, which is frequently mutated in Leigh syndrome; (2) produce mutant mouse and yeast models for ANT1 and POLG1, two disease genes associated with the accumulation of multiple mtDNA deletions in humans; (3) produce additional fruit-fly knockout models for other assembly genes of complex IV and for Twinkle, another gene associated with multiple mtDNA deletions in humans; (4) characterize the expression profiles of OXPHOS-defective cell lines from both human patients and knockout mice. The expected deliverables of this project are (i) to make progress in the understanding of the genetic basis of mitochondrial disease; (ii) to obtain in vivo disease models that recapitulate human OXPHOS disease phenotypes, in order to better understand their pathogenesis; (iii) to obtain tools for rational therapeutic trials.