Garcia 2019 MiPschool Coimbra
Event: MiPschool Coimbra 2019
Although the alternative oxidase (AOX) is naturally absent in the mitochondria of vertebrates and insects, its xenotopic expression in model organisms can attenuate diverse phenotypes related to mitochondrial diseases, as this creates an extra path for oxygen reduction when the cytochrome c segment of the electron transfer system (ETS) is overloaded. Due to its non-proton-pumping nature, AOX activity in plants is clearly associated with thermogenesis . We have recently reported that AOX-expressing flies develop faster and have higher viability than control flies at low temperatures , indicating that AOX is also thermogenic in Drosophila and/or it can release developmental constraints imposed on the ETS.
To test which of these mechanisms play a role in this AOX-induced cold advantage during development, we measured mitochondrial oxygen consumption on larval homogenates of the wild-type w1118 and the 3XtubAOX line , at 12 and 25°C. Surprisingly, no differences in coupled respiration and state 3/state 4 ratio were detected when substrates to the two main dehydrogenases in flies, complex I (CI) and mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH), were used concomitantly. In addition, AOX inhibition with n-propyl-gallate did not affect respiration in these conditions. However, when measured separately, CI- and mGPDH-driven coupled respiration at 12 and 25°C diverged in AOX flies, the former being ~48% higher and the latter ~33% lower than in w1118 flies. At 12°C, AOX inhibition led to a ~37% decrease in mGPDH-driven coupled respiration, and to a ~30% decrease in mGPDH-driven leak respiration.
Our data suggests that AOX-expressing larvae are producing heat via mGPDH-AOX functional interactions, which uncouple mitochondria. To compensate for ATP not produced by the mGPDH action, these flies increase oxidative phosphorylation through the CI pathway. At low temperatures, this configuration becomes highly functional, especially because mGPDH appears naturally less sensitive to cold . Since mGPDH directly connects cytosolic processes with ETS, we can predict that the cellular redox state of the larvae is altered in the presence of AOX, affecting other metabolic processes at low temperatures. Furthermore, higher CI-driven coupled respiration could be a result of an increase in the tricarboxylic acid cycle reactions, which in turn would accelerate larval growth via increased cataplerosis. In combination, our data supports mGPDH-linked thermogenesis and CI-linked accelerated cataplerosis as explanations for the increase in fitness observed for AOX-expressing flies at low temperatures.
Labels: MiParea: Respiration, Developmental biology
Coupling state: LEAK, OXPHOS Pathway: N, Gp HRR: Oxygraph-2k
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