Garcia, G. S. | bioRxiv Science

bioRxiv2025

The alternative oxidase reconfigures the larval mitochondrial electron transport system to accelerate growth and development in Drosophila melanogaster

The alternative oxidase (AOX) is naturally present in the mitochondrial electron transfer system (ETS) of many organisms but absent in vertebrates and most insects. AOX oxidizes coenzyme Q and reduces O2 in H2O, partially replacing the ETS cytochrome c segment and alleviating the oxidative stress caused by ETS overload. As successfully demonstrated in animal models, AOX shows potential in mitigating mitochondrial diseases. However, its non-proton-pumping nature may uncouple mitochondria, leading to excessive heat generation and interference with normal metabolism and physiology. Here we show that AOX from the tunicate Ciona intestinalis accelerates development of Drosophila melanogaster, elevating larval biomass accumulation (primarily due to increased fat), mobility and food intake, without increasing body heat production. AOX intensifies Leak respiration and lowers oxidative phosphorylation efficiency through functional interactions with the mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH). This is associated with increased complex I (CI)-driven respiration and supercomplex formation, higher cellular NAD+/NADH ratios, and an enhanced flux through the central carbon metabolism. Chemical uncouplers and rotenone confirm the roles of mitochondrial uncoupling and CI in the development of AOX-expressing larvae. Thus, AOX appears to be promoting increased growth by reinforcing the larval proliferative metabolic program via an intricate mechanism that reconfigures the larval ETS.

biochemistry↗

bioRxiv2021

Systemic impact of the expression of the mitochondrial alternative oxidase on Drosophila development

Despite the beneficial effects of xenotopically expressing the mitochondrial alternative oxidase AOX from Ciona intestinalis in mammalian and insect models, important detrimental outcomes have also been reported, raising concerns regarding its potential deployment as a therapeutic enzyme for human mitochondrial diseases. Because of its non-protonmotive terminal oxidase activity, AOX can bypass the cytochrome segment of the respiratory chain whilst not contributing to mitochondrial ATP synthesis. We have previously shown that pupal lethality occurs when AOX-expressing Drosophila larvae are cultured on a low-nutrient diet, indicating that AOX can perturb normal metabolism during development. Here, combined omics analyses revealed multiple correlates of this diet-dependent lethality, including a general alteration of larval amino acid and lipid metabolism, functional and morphological changes to the larval digestive tract, and a drastic decrease in larval biomass accumulation. Pupae at the pre-lethality stage presented a general downregulation of mitochondrial metabolism and a signature of starvation and deregulated signaling. AOX-induced lethality was partially rescued when the low-nutrient diet was supplemented with tryptophan and/or methionine, but not with proline and/or glutamate, strongly suggesting perturbation of one-carbon metabolism. The developmental dependence on tryptophan and/or methionine, associated with elevated levels of lactate dehydrogenase, 2-hydroxyglutarate, choline-containing metabolites and breakdown products of membrane phospholipids, indicates that AOX expression promotes tissue proliferation and larval growth, but this is ultimately limited by energy dissipation due to partial mitochondrial uncoupling. We speculate that the combination of dietary interventions and AOX expression might, nevertheless, be useful for the metabolic regulation of proliferative tissues, such as tumors.

biochemistry↗