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Abstract: The OPA1 gene, encoding a dynamin-like mitochondrial GTPase, is involved in autosomal dominant optic atrophy (ADOA, OMIM #165500). ADOA, also known as Kjer''s optic atrophy, affects retinal ganglion cells and the axons forming the optic nerve, leading to progressive visual loss. OPA1 gene sequencing in patients with hereditary optic neuropathies indicates that the clinical spectrum of ADOA is larger than previously thought. Specific OPA1 mutations are responsible for several distinct clinical presentations, such as ADOA with deafness (ADOAD), and severe multi-systemic syndromes, the so-called “ADOA plus” disorders, which involve neurological and neuromuscular symptoms similar to those due to mitochondrial oxidative phosphorylation defects or mitochondrial DNA instability. The study of the various clinical presentations of ADOA in conjunction with the investigation of OPA1 mutations in fibroblasts from patients with optic atrophy provides new insights into the pathophysiological mechanisms of the disease while underscoring the multiple physiological roles played by OPA1 in energetic metabolism, mitochondrial structure and maintenance, and cell death. Finally, OPA1 represents an important new paradigm for emerging neurodegenerative diseases affecting mitochondrial structure, plasticity and functions. [Copyright &y& Elsevier]

Complex I (CI) deficiency is the most common respiratory chain defect representing more than 30% of mitochondrial diseases. CI is an L-shaped multi-subunit complex with a peripheral arm protruding into the mitochondrial matrix and a membrane arm. CI sequentially assembled into main assembly intermediates: the P (pumping), Q (Quinone) and N (NADH dehydrogenase) modules. In this study, we analyzed 11 fibroblast cell lines derived from patients with inherited CI deficiency resulting from mutations in the nuclear or mitochondrial DNA and impacting these different modules. In patient cells carrying a mutation located in the matrix arm of CI, blue native-polyacrylamide gel electrophoresis (BN-PAGE) revealed a significant reduction of fully assembled CI enzyme and an accumulation of intermediates of the N module. In these cell lines with an assembly defect, NADH dehydrogenase activity was partly functional, even though CI was not fully assembled. We further demonstrated that this functional N module was responsible for ROS production through the reduced flavin mononucleotide. Due to the assembly defect, the FMN site was not re-oxidized leading to a significant oxidative stress in cell lines with an assembly defect. These findings not only highlight the relationship between CI assembly and oxidative stress, but also show the suitability of BN-PAGE analysis in evaluating the consequences of CI dysfunction. Moreover, these data suggest that the use of antioxidants may be particularly relevant for patients displaying a CI assembly defect. [ABSTRACT FROM AUTHOR]

Abstract: Mitochondria form dynamic tubular networks through processes of fission and fusion. Defect in mitochondrial dynamics lead to various pathologies, including several common and some rare neurodegenerative disorders. OPA1 and MFN2 are two key players in mitochondrial fusion associated with Autosomal Dominant Optic Atrophy and Charcot Marie Tooth neuropathy type 2A respectively. We used micropatterned coverslips to standardize the visualization of mitochondrial distribution in skin fibroblasts. In fibroblasts from affected patients, mutations in the OPA1 and MFN2 genes were found to affect the volume and cellular distribution of mitochondria. In G1/S cell cycle phase, mitochondria emerging from the microtubule organizing centre may be crucial to mitochondrial biogenesis since it appeared to be protected against mitochondrial fragmentation induced by OPA1 mutations. The standardized quantitative analysis of the mitochondrial network and the description of mitochondrial subcellular distribution should lead to better diagnostic criteria for mitochondrial diseases and yield new insights into mitochondrial dysfunction in disease and aging. [Copyright &y& Elsevier]