Interactions of copper with temperature and oxygen depletion stress on reactive oxygen species (ROS) homeostasis in heart mitochondria

Isei, Michael O.

Dissertation/Thesis

2021

Kamunde, Collins

Spears, Jonathan
Pichaud, Nicholas
Wang, Yanwen
Kamunde, Collins
van den Heuvel, Michael

Stevens, Don
Greenwood, Spencer
Sweeney-Nixon, Marva
van den Heuvel, Michael

Doctor of Philosophy

Biomedical Sciences

Biomedical Sciences

University of Prince Edward Island

Charlottetown, PE

Mitochondria are a common target of multiple abiotic stressors that alter reactive oxygen species (ROS) metabolism. Thus, assessing the effects of multiple stressors on mitochondrial ROS metabolism can be used to integrate the interactions and effects of combined exposure to stressors in aquatic ectotherms. The overarching aim of this thesis was to probe the interactions of copper (Cu) with temperature rise and oxygen depletion stress on ROS homeostasis in rainbow trout (Oncorhynchus mykiss) Show moreMitochondria are a common target of multiple abiotic stressors that alter reactive oxygen species (ROS) metabolism. Thus, assessing the effects of multiple stressors on mitochondrial ROS metabolism can be used to integrate the interactions and effects of combined exposure to stressors in aquatic ectotherms. The overarching aim of this thesis was to probe the interactions of copper (Cu) with temperature rise and oxygen depletion stress on ROS homeostasis in rainbow trout (Oncorhynchus mykiss) heart mitochondria. First, the interactions of Cu and temperature on mitochondrial ROS (as H2O2) emission were examined and it was found that Cu modulated H2O2 emission differently depending on temperature and substrate type. Notably, the magnitude of the stimulatory and inhibitory effects of Cu varied with temperature (11 > 23 > 4 oC) during succinate oxidation while H2O2 emission in mitochondria oxidizing glutamate-malate was not altered by temperature rise. In addition, the site-specific capacities of H2O2 emission were: complex III outer ubiquinone binding site (site IIIQo) > complex II flavin site (site IIF) ≥ complex I flavin site (site IF). Surprisingly, experiments revealed the absence of succinate-driven ROS production from complex I ubiquinone-binding site (site IQ) by reverse electron transport (RET). Second, effects of thermal stress and Cu on H2O2 scavenging systems and mitochondrial ROS consumption capacity were investigated. Results indicated that the glutathione (GSH)-dependent peroxidase pathway is the predominant H2O2 scavenging system while catalase played negligible role. The effect of thermal stress depended on substrate wherein temperature rise suppressed the rate of H2O2 consumption during oxidation of glutamate-malate or succinate but not palmitoylcarnitine. Notably, Cu intensified the temperature-induced suppression of H2O2 consumption. Third, assessment of how anoxia-reoxygenation and Cu influence mitochondrial H2O2 emission showed that anoxia-reoxygenation suppressed H2O2 emission regardless of the duration of anoxia and substrate type by increasing activities of antioxidant enzymes and suppressing ROS production from QH2/Q isopotential sites. Moreover, anoxia-reoxygenation attenuated or intensified the effect of Cu depending on the redox site and duration of anoxia exposure. Lastly, given that fatty acids are the preferred metabolic substrate in the heart with significant contributions from carbohydrates, the rates of H2O2 emission and effects of Cu in heart mitochondria oxidizing a fatty acid substrate or pyruvate was examined. Results indicated that heart mitochondrial preference of fatty acids to carbohydrates due to high energy yield likely comes with greater propensity for ROS formation and oxidative damage to the heart. The intensity and patterns of Cu effects varying depending on the metabolic fuel being oxidized. Altogether, this research improves our knowledge of the interactions and effects of Cu with thermal stress and anoxia in fish heart and established that changes in mitochondrial ROS metabolism serves as an important marker that can integrate and be used to assess the effects of multiple stressors in aquatic organisms. Show less

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