Suppression of reactive oxygen species generation in heart mitochondria from anoxic turtles: the role of complex I S-nitrosation

Abstract

Freshwater turtles () are among the very few vertebrates capable of tolerating severe hypoxia and re-oxygenation without suffering from damage to the heart. As myocardial ischemia and reperfusion causes a burst of mitochondrial reactive oxygen species (ROS) in mammals, the question arises as to whether, and if so how, this ROS burst is prevented in the turtle heart. We find that heart mitochondria isolated from turtles acclimated to anoxia produce less ROS than mitochondria from normoxic turtles when consuming succinate. As succinate accumulates in the hypoxic heart and is oxidized when oxygen returns, this suggests an adaptation to lessen ROS production. Specific -nitrosation of complex I can lower ROS in mammals and here we show that turtle complex I activity and ROS production can also be strongly depressed by -nitrosation. We detect endogenous -nitrosated complex I in turtle heart mitochondria, but these levels are unaffected upon anoxia acclimation. Thus, while heart mitochondria from anoxia-acclimated turtles generate less ROS and have a lower aerobic capacity than those from normoxic turtles, this is not due to decreases in complex I activity or expression levels. Interestingly, in-gel activity staining reveals that most complex I of heart mitochondria from normoxic and anoxic turtles forms stable super-complexes with other respiratory enzymes and, in contrast to mammals, these are not disrupted by dodecyl maltoside. Taken together, these results show that although-nitrosation of complex I is a potent mechanism to prevent ROS formation upon re-oxygenation after anoxia , this is not a major cause of the suppression of ROS production by anoxic turtle heart mitochondria.

Contraction of atrial smooth muscle reduces cardiac output in perfused turtle hearts

“…Baseline flows were established that were similar to previous perfused heart studies (Bundgaard et al, 2018;Farrell et al, 1994;Joyce et al, 2016) and in vivo blood flow measurements Wang and Hicks, 1996) in this species. Under control conditions, there was a significant negative relationship between input pressure and cardiac output (R 2 =0.63, P=0.01; Fig.…”

Cytoprotective Effects of N-Acetylcysteine on Streptozotocin- Induced Oxidative Stress and Apoptosis in RIN-5F Pancreatic β-Cells

“…Complex I may also be inhibited by excess GSH through glutathionylation [53] since NAC treatment results in an increase in GSH levels. Moreover, the suppression of Complex I activity could also be a result of S-nitrosation of Complex I by NO, which is an effective mechanism to prevent ROS formation, thus protecting the cells from oxidative stress [54,55]. We have previously shown that NAC treatment partially protected the oxidative modification of mitochondrial complexes and helped in preserving the mitochondrial function in HepG2 cells [56].…”

Tissue-dependent variations of hydrogen sulfide homeostasis in anoxic freshwater turtles

“…Adult red-eared sliders of both sex (Trachemys scripta elegans) kept in aquaria at the animal care facility at Zoophysiology, Aarhus University, were used for experiments. While fasted, the turtles were progressively acclimated to low temperature (5°C) followed by randomized exposure to either normoxic (N=5, 0.66±0.13 kg) (termed 'cold normoxia') or anoxic conditions (N=4, 0.64±0.07 kg) (termed 'cold anoxia') for 9 days, according to a previously described protocol (Bundgaard et al, 2018;Bundgaard et al, 2019;Jensen et al, 2014). A control group (N=5, 0.61±0.04 kg) of non-fasting turtles taken directly from the aquaria at 25°C was also included in the study (termed 'warm normoxia').…”

“…Turtles were killed as previously described (Bundgaard et al, 2018). In brief, an overdose of pentobarbital (50 mg kg −1 ) was given via the supravertebral venous sinus.…”

“…Thus, we hypothesized that T. scripta elegans endogenous levels of free H 2 S and BSS in various tissues should change more markedly upon cold acclimation and anoxia than found in the brown bears (Revsbech et al, 2014). Furthermore, NO metabolites are known to increase dramatically in the blood (Jacobsen et al, 2012) and tissues of anoxia-acclimated T. scripta elegans and may contribute further to the strong metabolic suppression of this species (Fago and Jensen, 2015), although not necessarily to cytoprotection against oxidative stress at reoxygenation, at least in the heart (Bundgaard et al, 2018).…”