Abstract
BackgroundComplex I (CI or NADH:ubiquinone oxidoreductase) deficiency is the most frequent cause of mitochondrial respiratory chain defect. Successful attempts to rescue CI function by introducing an exogenous NADH dehydrogenase, such as the NDI1 from Saccharomyces cerevisiae (ScNDI1), have been reported although with drawbacks related to competition with CI. In contrast to ScNDI1, which is permanently active in yeast naturally devoid of CI, plant alternative NADH dehydrogenases (NDH-2) support the oxidation of NADH only when the CI is metabolically inactive and conceivably when the concentration of matrix NADH exceeds a certain threshold. We therefore explored the feasibility of CI rescue by NDH-2 from Arabidopsis thaliana (At) in human CI defective fibroblasts.ResultsWe showed that, other than ScNDI1, two different NDH-2 (AtNDA2 and AtNDB4) targeted to the mitochondria were able to rescue CI deficiency and decrease oxidative stress as indicated by a normalization of SOD activity in human CI-defective fibroblasts. We further demonstrated that when expressed in human control fibroblasts, AtNDA2 shows an affinity for NADH oxidation similar to that of CI, thus competing with CI for the oxidation of NADH as opposed to our initial hypothesis. This competition reduced the amount of ATP produced per oxygen atom reduced to water by half in control cells.ConclusionsIn conclusion, despite their promising potential to rescue CI defects, due to a possible competition with remaining CI activity, plant NDH-2 should be regarded with caution as potential therapeutic tools for human mitochondrial diseases.
Highlights
Human NADH:ubiquinone oxidoreductase or complex I (CI) is the largest complex of the respiratory chain, withCI catalyzes the consecutive transfer of two electrons, one per time, to a ubiquinone pool for each molecule of NADH oxidized
We decided to focus our subsequent analysis on three NDH-2: ScNDI1, the internal NDH-2 of Saccharomyces cerevisiae; AtNDB4, an Arabidopsis thaliana NDH-2 localized to the external side of inner mitochondrial membrane (IMM); AtNDA2, another Arabidopsis thaliana NDH-2 localized to the internal side of IMM
In order to examine the rescuing efficiency of plant NDH-2 in more depth, we chose to focus on fibroblasts carrying a pathogenic homozygous mutation in the nuclear gene NDUFS4, as a wellestablished cellular model of complex I deficiency
Summary
Human NADH:ubiquinone oxidoreductase or complex I (CI) is the largest complex of the respiratory chain, withCI catalyzes the consecutive transfer of two electrons, one per time, to a ubiquinone pool for each molecule of NADH oxidized. Human NADH:ubiquinone oxidoreductase or complex I (CI) is the largest complex of the respiratory chain, with. NADH oxidizing activity of CI is tightly controlling intra-mitochondrial metabolism, and electron transfer is coupled to both heat and ATP generation. CI deficiency can result in a combination of abnormalities: impaired oxidation of NADH to NAD+, which alters the NADH/NAD+ ratio and leads to intra-mitochondrial metabolic disequilibrium and to lactic accumulation, release of electrons that are not correctly channeled to the ubiquinone subsequently generating radical oxygen species (ROS), and loss of proton pumping activity, which reduces mitochondrial potential, lowering ATP synthesis. Complex I (CI or NADH:ubiquinone oxidoreductase) deficiency is the most frequent cause of mitochondrial respiratory chain defect. We explored the feasibility of CI rescue by NDH-2 from Arabidopsis thaliana (At) in human CI defective fibroblasts
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