The Connection Between Oxidative Stress and Estivation in Gastropods and Anurans

Noise accelerates embryonic development in a key crab species: Morphological and physiological carryover effects on early life stages

Anthropogenic noise is considered one important global pollutant. The impact of noise on marine invertebrates has been less assessed. The present study evaluated the chronic effect of the motorboat noise obtained from a lagoon's soundscape, the natural habitat of the key crab Neohelice granulata, on its whole embryonic development, considering morphological and physiological carryover effects on embryos and hatched larvae. Results demonstrated that embryonic development was shortened under noise exposure. The effects on advanced embryos, larvae and adult females were: increased heartbeats and non-viable eggs, and decreased fecundity. Biochemical responses showed lipid peroxidation in embryos while antioxidant enzymes were activated in larvae and adults, indicating a counteracting effect related to the life stage. The negative effects on fitness offspring may imply ecological consequences at the population level. Results are discussed in terms of the ecosystem engineer species studied and the habitat, a MAB UNESCO Reserve lagoon, suggesting the urgent need to develop mitigation plans.

Morpho-functional changes of lungfish Protopterus dolloi skin in the shift from freshwater to aestivating conditions

African dipnoi (Protopterus sp.) are obligate air-breathing fish that, during dry season, may experience a period of dormancy named aestivation. Aestivation is characterized by complete reliance on pulmonary breathing, general decrease of metabolism and down-regulation of respiratory and cardiovascular functions. To date, little is known about morpho-functional rearrangements induced by aestivation in the skin of African lungfishes. Our study aims to identify, in the skin of P. dolloi, structural modifications and stress-induced molecules in response to short-term (6 days) and long-term (40 days) aestivation. Light microscopy showed that short-term aestivation induces major reorganization, with narrowing of epidermal layers and decrease of mucous cells; prolonged aestivation is characterized by regenerative processes and re-thickening of epidermal layers. Immunofluorescence reveals that aestivation correlates with an increased oxidative stress and changes of Heat Shock Proteins expression, suggesting a protective role for these chaperons. Our findings revealed that lungfish skin undergoes remarkable morphological and biochemical readjustments in response to stressful conditions associated with aestivation.

Effect of biological and anthropogenic habitat sounds on oxidative stress biomarkers and behavior in a key crab species

Soundscapes are characterized by a combination of natural and anthropogenic sounds. This study evaluated the stress effect of biological and anthropogenic sounds characterizing a Man and Biosphere UNESCO wetland, by assessing the protein content, oxidative biomarkers, and behavior of a key crab species (Neohelice granulata), through a tank-laboratory experiment. Biological sounds corresponded to predators of N. granulata (fish and crustacean stimuli), while anthropogenic ones belonged to motorboat passages (boat stimulus). Biochemical results showed differences depending on the sound stimuli used and the crab tissue analyzed. Protein content was higher in hemolymph when crabs were exposed to fish and boat stimuli, and in gills when exposed to boat stimulus. The enzymatic activity in hemolymph showed a decreased GST (fish stimulus) and CAT (fish and boat stimuli) activity, in hepatopancreas a higher GST (crustacean stimulus) and CAT (crustacean and boat stimuli) activity was found, and in gills a higher CAT activity was also observed (crustacean and boat stimuli). Lipid peroxidation was higher only in hemolymph (fish and crustacean stimuli). Protein oxidation was higher in gills (fish stimulus) and hepatopancreas (crustacean stimulus). Behavioral analysis demonstrated that the crab locomotion activity diminished when exposed to diverse sound stimuli. Thus, both sound sources caused physiological and behavioral stress in this species. The results contribute important data to be used in the development of management plans considering the habitat importance in terms of biodiversity, the ecosystem services provided and the role of the studied species.

Physiological, Diurnal and Stress-Related Variability of Cadmium-Metallothionein Gene Expression in Land Snails

The terrestrial Roman snail Helix pomatia has successfully adapted to strongly fluctuating conditions in its natural soil habitat. Part of the snail’s stress defense strategy is its ability to express Metallothioneins (MTs). These are multifunctional, cysteine-rich proteins that bind and inactivate transition metal ions (Cd²⁺, Zn²⁺, Cu⁺) with high affinity. In Helix pomatia a Cadmium (Cd)-selective, inducible Metallothionein Isoform (CdMT) is mainly involved in detoxification of this harmful metal. In addition, the snail CdMT has been shown to also respond to certain physiological stressors. The aim of the present study was to investigate the physiological and diurnal variability of CdMT gene expression in snails exposed to Cd and non-metallic stressors such as desiccation and oxygen depletion. CdMT gene expression was upregulated by Cd exposure and desiccation, whereas no significant impact on the expression of CdMT was measured due to oxygen depletion. Overall, Cd was clearly more effective as an inducer of the CdMT gene expression compared to the applied non-metallic stressors. In unexposed snails, diurnal rhythmicity of CdMT gene expression was observed with higher mRNA concentrations at night compared to daytime. This rhythmicity was severely disrupted in Cd-exposed snails which exhibited highest CdMT gene transcription rates in the morning. Apart from diurnal rhythmicity, feeding activity also had a strong impact on CdMT gene expression. Although underlying mechanisms are not completely understood, it is clear that factors increasing MT expression variability have to be considered when using MT mRNA quantification as a biomarker for environmental stressors.

Molecular characterization of argininosuccinate synthase and argininosuccinate lyase from the liver of the African lungfish Protopterus annectens, and their mRNA expression levels in the liver, kidney, brain and skeletal muscle during aestivation

Argininosuccinate synthase (Ass) and argininosuccinate lyase (Asl) are involved in arginine synthesis for various purposes. The complete cDNA coding sequences of ass and asl from the liver of Protopterus annectens consisted of 1,296 and 1,398 bp, respectively. Phylogenetic analyses revealed that the deduced Ass and Asl of P. annectens had close relationship with that of the cartilaginous fish Callorhinchus milii. Besides being strongly expressed in the liver, ass and asl expression were detectable in many tissues/organs. In the liver, mRNA expression levels of ass and asl increased significantly during the induction phase of aestivation, probably to increase arginine production to support increased urea synthesis. The increases in ass and asl mRNA expression levels during the prolonged maintenance phase and early arousal phase of aestivation could reflect increased demand on arginine for nitric oxide (NO) production in the liver. In the kidney, there was a significant decrease in ass mRNA expression level after 6 months of aestivation, indicating possible decreases in the synthesis and supply of arginine to other tissues/organs. In the brain, changes in ass and asl mRNA expression levels during the three phases of aestivation could be related to the supply of arginine for NO synthesis in response to conditions that resemble ischaemia and ischaemia-reperfusion during the maintenance and arousal phase of aestivation, respectively. The decrease in ass mRNA expression level, accompanied with decreases in the concentrations of arginine and NO, in the skeletal muscle of aestivating P. annectens might ameliorate the potential of disuse muscle atrophy.

Decreased hydrogen peroxide production and mitochondrial respiration in skeletal muscle but not cardiac muscle of the green-striped burrowing frog, a natural model of muscle disuse

Suppression of disuse-induced muscle atrophy has been associated with altered mitochondrial reactive oxygen species (ROS) production in mammals. However, despite extended hindlimb immobility aestivating animals exhibit little skeletal muscle atrophy compared with artificially-immobilised mammalian models. Therefore, we studied mitochondrial respiration and ROS (H2O2) production in permeabilised muscle fibres of the green-striped burrowing frog, Cyclorana alboguttata. Mitochondrial respiration within saponin-permeabilised skeletal and cardiac muscle fibres was measured concurrently with ROS production using high-resolution respirometry coupled to custom-made fluorometers. After four months of aestivation, C. alboguttata had significantly depressed whole body metabolism by approximately 70% relative to control (active) frogs, and mitochondrial respiration in saponin-permeabilised skeletal muscle fibres decreased by almost 50% both in the absence of ADP and during oxidative phosphorylation. Mitochondrial ROS production showed up to an 88% depression in aestivating skeletal muscle when malate, succinate and pyruvate were present at concentrations likely reflecting those in vivo. The percentage ROS released per O2 molecule consumed was also approximately 94 % less at these concentrations indicating an intrinsic difference in ROS production capacities during aestivation. We also examined mitochondrial respiration and ROS production in permeabilised cardiac muscle fibres and found that aestivating frogs maintained respiratory flux and ROS production at control levels. These results show that aestivating C. alboguttata has the capacity to independently regulate mitochondrial function in skeletal and cardiac muscles. Furthermore, this work indicates that ROS production can be suppressed in the disused skeletal muscle of aestivating frogs, which may in turn protect against potential oxidative damage and preserve skeletal muscle structure during aestivation and following arousal.

Each to their own: skeletal muscles of different function use different biochemical strategies during aestivation at high temperature

Preservation of muscle morphology depends on a continuing regulatory balance between molecules that protect, and molecules that damage, muscle structural integrity. Excessive disruption of the biochemical balance that favours reactive oxygen species (ROS) in disused muscles may lead to oxidative stress; which in turn is associated with increased atrophic or apoptotic signalling and/or oxidative damage to the muscle and thus muscle disuse atrophy. Increases in rate of oxygen consumption likely increase the overall generation of ROS in vivo. Temperature-induced increases in muscle oxygen consumption rate occur in some muscles of ectotherms undergoing prolonged muscular disuse during aestivation. In the green-striped burrowing frog, Cyclorana alboguttata, both large jumping muscles and small non-jumping muscles undergo atrophy seemingly commensurate with their rate of oxygen consumption during aestivation. However, since the extent of atrophy in these muscles is not enhanced at higher temperatures despite a temperature sensitive rate of oxygen consumption in the jumping muscle, we proposed that muscles are protected by biochemical means that when mobilised at higher temperatures inhibit atrophy. We proposed the biochemical response to temperature would be muscle-specific. We examined the effect of temperature on the antioxidant and heat shock protein systems and evidence of oxidative damage to lipids and proteins in two functionally different skeletal muscles, gastrocnemius (jumping muscle) and iliofibularis (non-jumping muscle), by aestivating frogs at 24 and 30oC for six months. We assayed small molecule antioxidant capacity, mitochondrial and cytosolic SOD and Hsp70 to show that protective mechanisms in disused muscles are differentially regulated both with respect to temperature and aestivation. High aestivation temperature results in an antioxidant response in the metabolically temperature-sensitive jumping muscle. We assayed lipid peroxidation and protein oxidation to show that oxidative damage is apparent during aestivation and its pattern is muscle-specific, but unaffected by temperature. Consideration is given to how the complex responses of muscle biochemistry inform of the different strategies muscles may use in regulating their oxidative environment during extended disuse and disuse at high temperature.