In many lower organism and plants, alternative oxidases (AOXs) are expressed that bypass the mitochondrial respiratory chain by transferring electrons directly from ubiquinol to oxygen in a non-proton-motive manner. Their main physiological role is to maintain electron flow under conditions when the classical respiratory chain is impaired, limiting excess production of oxygen radicals and supporting redox and metabolic homeostasis. AOXs are absent in mammals.
To study disruptions and impairments in the mitochondrial respiratory chain, AOX from Ciona intestinalis, a marine tunicate with very soft tunic, has been integrated into mammalian cell lines, Drosophila disease models and, recently, in the mouse. These experiments showed that the deleterious consequences of toxic or pathological inhibition of the downstream portion of the mitochondrial respiratory chain, specifically OXPHOS complexes III (cIII) and IV (cIV), which AOX bypasses, were averted.
The scientists around Marten Szibor proposed that the expression of AOX in commonly studied animal models could be used to elucidate the pathophysiology underlying mitochondrial OXPHOS disorders, providing a rational basis for its eventual implementation in therapeutic applications.
Therefore they created a genetically tractable transgenic mouse that ubiquitously expresses a single copy of Ciona AOX at substantial levels, after targeted insertion into the Rosa26 locus, a locus used for constitutive, ubiquitous gene expression in mice. The Rosa26 knock-in gave rise to a functional enzyme, which conferred resistance to respiratory poisons.
Surprisingly, comprehensive phenotyping in the GMC revealed only minor, biologically inconsequential effects of AOX expression in the AOXRosa26 mouse. The authors expect that new model will be a promising tool for elucidating the mechanisms of mitochondrial pathology and charting the way towards future therapies.
Marten Szibor, Praveen K. Dhandapani, Eric Dufour, Kira M. Holmström, Yuan Zhuang, Isabelle Salwig, Ilka Wittig, Juliana Heidler, Zemfira Gizatullina, Timur Gainutdinov, German Mouse Clinic Consortium, Helmut Fuchs, Valérie Gailus-Durner, Martin Hrabě de Angelis, Jatin Nandania, Vidya Velagapudi, Astrid Wietelmann, Pierre Rustin, Frank N. Gellerich, Howard T. Jacobs, and Thomas Braun. Broad AOX expression in a genetically tractable mouse model does not disturb normal physiology. Dis Model Mech. 2017 Feb 1;10(2):163-171. doi: 10.1242/dmm.027839.