The tardigrade Hypsibius exemplaris as an emerging model to study the mitochondrial alternative oxidase at animal organismal level

Mitochondrial alternative oxidase (AOX) is present in mitochondria of many invertebrates. Independently of the reason concerning the enzyme occurrence in animal mitochondria, expression of AOX in human mitochondria is regarded as a potential therapeutic strategy. Till now, relevant data were obtained due to heterologous AOX expression in cells and animals without natively expressed AOX. Application of animals natively expressing AOX importantly contribute the research. Thus, we investigated Hypsibius exemplaris as a model for AOX activity analysis. We observed that H. exemplaris tolerance to the blockage of the MRC complexes was diminished in the presence of AOX inhibitor and the inhibitor-sensitive respiration enabled the tardigrade respiration under condition of the blockage. Furthermore, although detection of AOX at protein level and pronounced oxygraphic registration of its activity required the MRC complex blockage, the obtained data indicated that AOX clearly contributed animal functioning. We demonstrated that AOX activity in tardigrades, can be monitored by measurement of intact specimen whole-body respiration. Furthermore, it was also possible to monitor the impact of the MRC complex IV blockage on AOX expression and AOX inhibition in the absence of the blockage on animal functioning. Thus, H. exemplaris is applied as a whole-animal model suitable to study AOX. * AA : antimycin A AOX : mitochondrial alternative oxidase BHAM : benzohydroxamic acid KCN : potassium cyanide MRC : mitochondrial respiratory chain