Effects of Diet on the Developmental Metabolism of Drosophila Expressing the Ciona intestinalis Alternative Oxidase

Abstract

The expression of the mitochondrial alternative oxidase AOX from Ciona intestinalis (Tunicata: Ascidiacea) has provided clear beneficial effects in a variety of mammalian and insect mitochondrial disease models. Because of its non-proton pumping terminal oxidase activity, AOX can bypass the cytochrome c segment of the respiratory chain (complexes III and IV), and alleviate the possible overload of electrons that occurs upon oxidative phosphorylation dysfunction, not contributing, though, to the proton-motive force needed for mitochondrial ATP synthesis. Significant detrimental outcomes have also been reported upon AOX expression, raising concerns regarding its putative deployment as a therapy enzyme for human diseases. In Drosophila, AOX expression is developmentally advantageous at low temperatures when the flies are cultured on a standard, rich diet, but it dramatically compromises adult eclosion when the flies are cultured on a low-nutrient diet (LN), at 25ºC or above. Here, we applied transcriptomics and metabolomics analyses to show that the interaction between LN and AOX expression causes a general alteration of larval amino acid metabolism, leading to an almost 40% decrease in biomass at the pre-metamorphosis stage. This reduced nutrient storage impairs development at the late pupa stage with a clear signature for starvation and an overall downregulation of mitochondrial metabolism. Interestingly, lactate dehydrogenase, lactate and 2-hydroxyglutarate are elevated in AOX-expressing flies, irrespective of diet. We have also identified that the addition of very low levels of ethanol to LN is sufficient to rescue the lethal phenotype imposed to the flies by the LN-AOX interaction. We are currently exploring how alcohol dehydrogenase and other enzymes in the ethanol catabolic pathway participate in this rescue phenomenon. Nevertheless, our data points to important roles for two key redox-regulating enzymes, lactate dehydrogenase and alcohol dehydrogenase, in adjusting the physiological changes induced by AOX function in larvae. As diet is one of the most important external factors that influence metabolism, our work provides important insights into how AOX expression could be safely accomplished, with minimal impact for higher animals.