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Aim: In most vertebrates, oxygen deprivation and subsequent re‐oxygenation are associated with mitochondrial impairment and excess production of reactive oxygen species (ROS) like hydrogen peroxide (H2O2). This in turn triggers a cascade of cell‐damaging events in a temperature‐dependent manner. The crucian carp (Carassius carassius) is one of few vertebrates that survives months without oxygen at cold temperatures and overcomes oxidative damage during re‐oxygenation periods. Mitochondria of this anoxia‐tolerant species therefore serve as an excellent model in translational research to study adaptation and resilience to low oxygen conditions and thermal variability. Methods: Here, we used high‐resolution respirometry on isolated mitochondria from hearts of crucian carp and the anoxia‐intolerant mouse (Mus musculus), at 37 and 8°C; two temperatures relevant for transplantation medicine (i.e., graft preservation and subsequent rewarming). Results: We find: (1) a striking difference in H2O2 release between the two species at 37°C despite comparable mitochondrial efficiency and capacity, (2) a massive H2O2 release after inhibition of complex V in mouse at 37°C that is absent in crucian carp, and prevented in mouse by incubation at 8°C or uncoupling with a protonophore at 37°C, and (3) indications that differences in mitochondrial complex I and II capacity and thermal sensitivity influence the release of mitochondrial H2O2 relative to respiration. Conclusion: Our findings provide comparative insights into a spectrum of mitochondrial adaptations in vertebrates and the importance of thermal variability. Furthermore, the species‐ and temperature‐related changes associated with mitochondria highlighted in this study may help identify mitochondria‐based targets for translational medicine. [ABSTRACT FROM AUTHOR]

Background: IL-1β is a highly potent pro-inflammatory cytokine and its secretion is tightly regulated. Inactive pro-IL-1β is transcribed in response to innate immune receptors activating NFκB. If tissue damage occurs, danger signals released from necrotic cells, such as ATP, can activate NLRP3-inflammasomes (multiprotein complexes consisting of NLRP3, ASC, and active caspase-1) which cleaves and activates pro-IL-1β. NLRP3 activation also depends on NEK7 and mitochondrial ROS-production. Thus, IL-1β secretion may be regulated at the level of each involved component. We have previously shown that NLRP3-dependent IL-1β release can be induced in cardiac fibroblasts by pro-inflammatory stimuli. However, anti-inflammatory mechanisms targeting IL-1β release in cardiac cells have not been investigated. mTOR is a key regulator of protein metabolism, including autophagy and proteasome activity. In this study we explored whether autophagy or proteasomal degradation are regulators of NLRP3 inflammasome activation and IL-1β release from cardiac fibroblasts. Methods and Results: Serum starvation selectively reduced LPS/ATP-induced IL-1β secretion from cardiac fibroblasts. However, no other inflammasome components, nor mitochondrial mass, were affected. The mTOR inhibitor rapamycin restored pro-IL-1β protein levels as well as LPS/ATP-induced IL-1β release from serum starved cells. However, neither serum starvation nor rapamycin induced autophagy in cardiac fibroblasts. Conversely, chloroquine and bafilomycin A (inhibitors of autophagy) and betulinic acid (a proteasome activator) effectively reduced LPS-induced pro-IL-1β protein levels. Key findings were reinvestigated in human monocyte-derived macrophages. Conclusion: In cardiac fibroblasts, mTOR inhibition selectively favors pro-IL-1β synthesis while proteasomal degradation and not autophagy is the major catabolic anti-inflammatory mechanism for degradation of this cytokine. [ABSTRACT FROM AUTHOR]