UBC Theses and Dissertations
Adaptive variation of mitochondrial function in response to oxygen variability in intertidal sculpins (Cottidae, Actinopterygii) Lau, Gigi Yik Chee
Variation in environmental oxygen (O₂) poses a significant physiological challenge to animals, not only because of the impact on aerobic metabolism, but also because it can lead to generation of potentially harmful reactive oxygen species (ROS). In this thesis, I aimed to investigate the interplay between two aspects of O2 use at the mitochondria, aerobic respiration and ROS metabolism, using species of intertidal sculpins (Cottidae, Actinopterygii) which are distributed along the marine intertidal zone, exposed to varying O2 conditions and vary in their tolerance to low O₂ (hypoxia). I first hypothesized that there would be a relationship between whole animal hypoxia tolerance and mitochondrial and cytochrome c oxidase (COX) O₂-binding affinity, whereby hypoxia tolerant sculpins would have higher mitochondrial and COX O₂-binding affinity than less hypoxia tolerant sculpins. This hypothesis was supported with functional analysis. In silico modelling of the COX catalytic core revealed that the variation in O₂ binding was related to interspecific differences in the interaction between COX3 and membrane phospholipid, cardiolipin, which could impact O₂ diffusion to its binding site. I then investigated whether intact mitochondria from hypoxia tolerant sculpins were able to use O₂ more efficiently such that phosphorylation efficiency was improved and ROS generation was reduced compared to mitochondria from less hypoxia tolerant sculpins. Although there were relationships between hypoxia tolerance and complex I and II dependencies, there were no interspecies differences in phosphorylation or mitochondrial coupling that would indicate differences in aerobic metabolism. Moreover, mitochondria from hypoxia tolerant sculpins generated more ROS under resting conditions and were more perturbed by in vitro redox and anoxia-recovery challenges. Finally, I confirmed consistent responses of mitochondria to in vivo responses with a whole animal study comparing ROS metabolism (redox status, mitochondrial H₂O₂, oxidative damage and scavenging capacity) between two sculpin species with different hypoxia tolerance to hypoxia, hyperoxia, with normoxia-recovery exposures. Taken together, my thesis demonstrates that hypoxia tolerance is associated with improved O₂ binding at the mitochondria and COX. Further, hypoxia tolerance in sculpins is associated with higher ROS generation compared to less tolerant species, suggesting a potentially important role of ROS in mediating hypoxia tolerance.
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