Current Trends and Research Challenges Regarding “Preparation for Oxidative Stress”

Abstract

Survival under stress, such as exposure to hypoxia, anoxia, freezing, dehydration, air exposure of water breathing organisms, and estivation, is commonly associated to enhanced endogenous antioxidants, a phenomenon coined “preparation for oxidative stress” (POS). The regulation of free radical metabolism seems to be crucial under these selective pressures, since this response is widespread among animals. A hypothesis of how POS works at the molecular level was recently proposed and relies on two main processes: increased reactive species production under hypoxia, and activation of redox-sensitive transcription factors and signaling pathways, increasing the expression of antioxidants. The present paper brings together the current knowledge on POS and considers its future directions. Data indicate the presence of POS in 83 animal species (71.6% among investigated species), distributed in eight animal phyla. Three main research challenges on POS are presented: (i) to identify the molecular mechanism(s) that mediate/induce POS, (ii) to identify the evolutionary origins of POS in animals, and (iii) to determine the presence of POS in natural environments. We firstly discuss the need of evidence for increased RS production in hypoxic conditions that underlie the POS response. Secondly, we discuss the phylogenetic origins of POS back 700 million years, by identifying POS-positive responses in cnidarians. Finally, we present the first reports of the POS adaptation strategy in the wild. The investigation of these research trends and challenges may prove useful to understand the evolution of animal redox adaptations and how they adapt to increasing stressful environments on Earth.

Physiological performance by growth rate, pigment and protein content of the brown seaweed <em>Sargassum filipendula</em> (Ochrophyta: Fucales) induced by moderate UV radiation exposure in the laboratory

“…For a large group of organisms, a biological phenomenon referred to as preparation for oxidative stress (POS) has been reported (Hermes-Lima and Storey 1998), in which an antioxidant upregulation linked exclusively to low oxygen stress is established. Several laboratory studies have shown increases in activity of the enzymes catalase, superoxide dismutases, and glutathione peroxidases and reduced levels of glutathione under hypoxia conditions (Moreira et al 2017). Although POS has not been reported for conditions other than low oxygen, changes in enzymatic and non-enzymatic antioxidant systems have been widely reported for other stress conditions than hypoxia.…”

Oxidative stress markers and antioxidant defense in hibernating common Asian toads, Duttaphrynus melanostictus

“…Our results showing an increased ascorbic acid content in liver and brain tissues corroborate this. This augmented ascorbic acid content in liver and brain tissues could be a preparatory mechanism to minimize the potential injury of ROS during hibernation and rewarming after hibernation [17,24,53,54]. The rise in ascorbic acid indicates the ability of the common Asian toad to adapt to oxidative stress.…”

Mitochondria, metabolic control and microRNA: Advances in understanding amphibian freeze tolerance

“…), or (c) responses to pollutants, heavy metals, UV radiation or other environmental factors. Where these cycles are predictable (e.g., daily or seasonal), organisms may maintain elevated antioxidant defenses at all times or enhance them in advance (e.g., in response to a seasonal trigger) in a situation termed “preparation for oxidative stress” . Such preparative measures are particularly valuable when organisms are in a hypometabolic state (e.g., frozen solid, oxygen deprived, hibernating, etc.)…”