The cold but not hard fats in ectotherms: consequences of lipid restructuring on susceptibility of biological membranes to peroxidation, a review

The bioenergetics response of the coral Pocillopora damicornis to temperature changes during its reproduction stage

Sexual reproduction of reef-building corals is vital for coral reef ecosystem recovery. Corals allocate limited energy to growth and reproduction, when being under environmental disturbance, which ultimately shapes the community population dynamics. In the present study, energetic and physiological parameters of both parental colonies and larvae of the coral Pocillopora damicornis were measured during their reproduction stage under four temperatures; 28 °C (low-temperature acclimation, LA), 29 °C (control temperature, CT), 31 °C (high-temperature acclimation, HA), and 32 °C (heat stress, HS). The results showed temperature changes altered the larvae release timing and fecundity in P. damicornis. Parental colonies exposed to the LA treatment exhibited reduced investment in reproduction and released fewer larvae, while retaining more energy for their development. However, each larva acquired higher energy and symbiont densities enabling survival through longer planktonic periods before settlement. In contrast, parental colonies exposed to the HA treatment had increased investment for reproduction and larvae output, while per larva gained less energy to mitigate the threat of higher temperature. Furthermore, the energy allocation processes restructured fatty acids concentration and composition in both parental colonies and larvae as indicated by shifts in membrane fluidity under adaptable temperature changes. Notably, parental colonies from the HS treatment expended more energy in response to heat stress, resulting in adverse effects, especially after larval release. Our study expands the current knowledge on the energy allocation strategies of P. damicornis and how it is impacted by temperature. Parental colonies employed different energy allocation strategies under distinct temperature regimes to optimize their development and offspring success, but under heat stress, both were compromised. Lipid metabolism is essential for the success of coral reproduction and further understanding their response to heat stress can improve intervention strategies for coral reef conservation in warmer future oceans.

Oleic acid as modulator of oxidative stress in European sea bass (Dicentrarchus labrax) juveniles fed high dietary lipid levels

Although the benefits of oleic acid (OA) have been established in mammals, its effects on fish remain understudied. The aim of this study was to evaluate the antioxidant potential of OA in the liver, intestine, and muscle of European sea bass juveniles fed diets containing different lipid levels. For that purpose, six diets with 16 or 22% lipids and 0, 1, and 2% OA were formulated and triplicate groups of European sea bass juveniles (21.4 g) were fed with these experimental diets for 9 weeks. Increasing dietary lipid levels or OA supplementation did not affect antioxidant enzyme activity in the liver and muscle. Superoxide dismutase (SOD) activity in the intestine increased with both the dietary lipid and OA levels, while glucose 6 phosphate dehydrogenase (G6PDH) activity increased only with dietary OA supplementation. Reduced glutathione (GSH) and total glutathione (tGSH) content were higher in the liver and intestine of fish fed the low-lipid diets, while in the high-lipid diets it was lower in the muscle than in the liver and intestine. Present findings suggest that OA plays a role in the antioxidant defense mechanisms of European sea bass, particularly at the intestine level, but additional research is required to further assess the potential benefits of incorporating OA into the diets.

Transcriptome and coexpression network analysis reveals properties and candidate genes associated with grape (Vitis vinifera L.) heat tolerance

Temperature is one of the most important environmental factors affecting grape season growth and geographical distribution. With global warming and the increasing occurrence of extreme high-temperature weather, the impact of high temperatures on grape production has intensified. Therefore, identifying the molecular regulatory networks and key genes involved in grape heat tolerance is crucial for improving the resistance of grapes and promoting sustainable development in grape production. In this study, we observed the phenotypes and cellular structures of four grape varieties, namely, Thompson Seedless (TS), Brilliant Seedless (BS), Jumeigui (JMG), and Shine Muscat (SM), in the naturally high-temperature environment of Turpan. Heat tolerance evaluations were conducted. RNA-seq was performed on 36 samples of the four varieties under three temperature conditions (28°C, 35°C, and 42°C). Through differential expression analysis revealed the fewest differentially expressed genes (DEGs) between the heat-tolerant materials BS and JMG, and the DEGs common to 1890 were identified among the four varieties. The number of differentially expressed genes within the materials was similar, with a total of 3767 common DEGs identified among the four varieties. KEGG enrichment analysis revealed that fatty acid metabolism, starch and sucrose metabolism, plant hormone signal transduction, the MAPK signaling pathway, and plant-pathogen interactions were enriched in both between different temperatures of the same material, and between different materials of the same temperature. We also conducted statistical and expression pattern analyses of differentially expressed transcription factors. Based on Weighted correlation network analysis (WGCNA), four specific modules highly correlated with grape heat tolerance were identified by constructing coexpression networks. By calculating the connectivity of genes within the modules and expression analysis, six candidate genes (VIT_04s0044g01430, VIT_17s0000g09190, VIT_01s0011g01350, VIT_01s0011g03330, VIT_04s0008g05610, and VIT_16s0022g00540) related to heat tolerance were discovered. These findings provide a theoretical foundation for further understanding the molecular mechanisms of grape heat tolerance and offer new gene resources for studying heat tolerance in grapes.

The effects of winter cold acclimation on acute and chronic cadmium bioaccumulation and toxicity in the banded killifish (Fundulus diaphanus)

Temperate freshwater fishes can experience large seasonal temperature fluctuations that could affect their exposure and sensitivity to trace metals. Yet, temperature effects are overlooked in ecotoxicology studies, especially for cold temperatures typical of the winter. In the present study, the effects of long-term cold acclimation on Cd bioaccumulation and toxicity were investigated in a freshwater fish, the banded killifish (Fundulus diaphanus). Killifish were acclimated to 14 °C or gradually cooled (2 °C/week) to 4 °C and cold acclimated for 6 weeks. Then, both acclimation groups were exposed to environmentally realistic waterborne Cd concentrations (0, 0.5 or 5 µg Cd L-1) for a further 28 d at their respective acclimation temperatures. Tissue metal bioaccumulation, fish survival, condition, and markers of oxidative and ionoregulation stress, were measured after 0, 2, 5 and 28 days of Cd exposure. Cadmium tissue accumulation increased over the exposure duration and was typically lower in cold-acclimated fish. In agreement with this lower bioaccumulation, fewer Cd toxic effects were observed in cold-acclimated fish. There was little evidence of a difference in intrinsic Cd sensitivity between 4 °C- and 14 °C-acclimated fish, as Cd toxicity appeared to closely follow Cd bioaccumulation. Our study suggests that current environmental water quality guidelines would be protective in the winter for the abundant and ecologically-important banded killifish.

The Relationship between Lifespan of Marine Bivalves and Their Fatty Acids of Mitochondria Lipids

Marine bivalves belonging to the Mytilidae and Pectinidae Families were used in this research. The specific objectives of this study were: to determine the Fatty Acids (FAs) of mitochondrial gill membranes in bivalves with different lifespans, belonging to the same family, and to calculate their peroxidation index; to compare the levels of ROS generation, malondialdehyde (MDA), and protein carbonyls in the mitochondria of gills, in vitro, during the initiation of free-radical oxation; to investigate whether the FAs of mitochondria gill membranes affect the degree of their oxidative damage and the maximum lifespan of species (MLS). The qualitative membrane lipid composition was uniform in the studied marine bivalves, regardless of their MLS. In terms of the quantitative content of individual FAs, the mitochondrial lipids differed significantly. It is shown that lipid matrix membranes of the mitochondria of long-lived species are less sensitive to in vitro-initiated peroxidation compared with the medium and short-lived species. The differences in MLS are related to the peculiarities of FAs of mitochondrial membrane lipids.

Heat induces multiomic and phenotypic stress propagation in zebrafish embryos

Heat alters biology from molecular to ecological levels, but may also have unknown indirect effects. This includes the concept that animals exposed to abiotic stress can induce stress in naive receivers. Here, we provide a comprehensive picture of the molecular signatures of this process, by integrating multiomic and phenotypic data. In individual zebrafish embryos, repeated heat peaks elicited both a molecular response and a burst of accelerated growth followed by a growth slowdown in concert with reduced responses to novel stimuli. Metabolomes of the media of heat treated vs. untreated embryos revealed candidate stress metabolites including sulfur-containing compounds and lipids. These stress metabolites elicited transcriptomic changes in naive receivers related to immune response, extracellular signaling, glycosaminoglycan/keratan sulfate, and lipid metabolism. Consequently, non-heat-exposed receivers (exposed to stress metabolites only) experienced accelerated catch-up growth in concert with reduced swimming performance. The combination of heat and stress metabolites accelerated development the most, mediated by apelin signaling. Our results prove the concept of indirect heat-induced stress propagation toward naive receivers, inducing phenotypes comparable with those resulting from direct heat exposure, but utilizing distinct molecular pathways. Group-exposing a nonlaboratory zebrafish line, we independently confirm that the glycosaminoglycan biosynthesis-related gene chs1 and the mucus glycoprotein gene prg4a, functionally connected to the candidate stress metabolite classes sugars and phosphocholine, are differentially expressed in receivers. This hints at the production of Schreckstoff-like cues in receivers, leading to further stress propagation within groups, which may have ecological and animal welfare implications for aquatic populations in a changing climate.

Ectotherm mitochondrial economy and responses to global warming

Temperature is a key abiotic factor affecting ecology, biogeography, and evolution of species. Alterations of energy metabolism play an important role in adaptations and plastic responses to temperature shifts on different time scales. Mitochondrial metabolism affects cellular bioenergetics and redox balance making these organelles an important determinant of organismal performances such as growth, locomotion, or development. Here I analyze the impacts of environmental temperature on the mitochondrial functions (including oxidative phosphorylation, proton leak, production of reactive oxygen species(ROS), and ATP synthesis) of ectotherms and discuss the mechanisms underlying negative shifts in the mitochondrial energy economy caused by supraoptimal temperatures. Owing to the differences in the thermal sensitivity of different mitochondrial processes, elevated temperatures (beyond the species- and population-specific optimal range) cause reallocation of the electron flux and the protonmotive force (Δp) in a way that decreases ATP synthesis efficiency, elevates the relative cost of the mitochondrial maintenance, causes excessive production of ROS and raises energy cost for antioxidant defense. These shifts in the mitochondrial energy economy might have negative consequences for the organismal fitness traits such as the thermal tolerance or growth. Correlation between the thermal sensitivity indices of the mitochondria and the whole organism indicate that these traits experience similar selective pressures but further investigations are needed to establish whether there is a cause-effect relationship between the mitochondrial failure and loss of organismal performance during temperature change.

Ageing across the great divide: tissue transformation, organismal growth and temperature shape telomere dynamics through the metamorphic transition

Telomere attrition is considered a useful indicator of cellular and whole-organism ageing rate. While approximately 80% of animal species undergo metamorphosis that includes extensive tissue transformations (involving cell division, apoptosis, de-differentiation and de novo formation of stem cells), the effect on telomere dynamics is unknown. We measured telomeres in Xenopus laevis developing from larvae to adults under contrasting environmental temperatures. Telomere dynamics were linked to the degree of tissue transformation during development. Average telomere length in gut tissue increased dramatically during metamorphosis, when the gut shortens by 75% and epithelial cells de-differentiate into stem cells. In the liver (retained from larva) and hindlimb muscle (newly formed before metamorphosis), telomeres gradually shortened until adulthood, likely due to extensive cell division. Tail muscle telomere lengths were constant until tail resorption, and those in heart (retained from larva) showed no change over time. Telomere lengths negatively correlated with larval growth, but for a given growth rate, telomeres were shorter in cooler conditions, suggesting that growing in the cold is more costly. Telomere lengths were not related to post-metamorphic growth rate. Further research is now needed to understand whether telomere dynamics are a good indicator of ageing rate in species undergoing metamorphosis.

Metabolic Regulation Effect and Potential Metabolic Biomarkers of Pre-Treated Delphinidin on Oxidative Damage Induced by Paraquat in A549 Cells

Delphinidin (Del) is an anthocyanin component with high in vitro antioxidant capacity. In this study, based on the screening of a cell model, gas chromatography-time of flight mass spectrometry (GC-TOF/MS) was used to evaluate the effect of Del pre-protection on the metabolite levels of intracellular oxidative stress induced by paraquat (PQ). According to the cytotoxicity and reactive oxygen species (ROS) responses of four lung cell lines to PQ induction, A549 cell was selected and treated with 100 μM PQ for 12 h to develop a cellular oxidative stress model. Compared with the PQ-induced group, the principal components of the Del pretreatment group had significant differences, but not significant with the control group, indicating that the antioxidant activity of Del can be correlated to the maintenance of metabolite levels. Del preconditioning protects lipid-related metabolic pathways from the disturbance induced by PQ. In addition, the levels of amino acid- and energy-related metabolites were significantly recovered. Del may also exert an antioxidant effect by regulating glucose metabolism. The optimal combinations of biomarkers in the PQ-treatment group and Del-pretreatment group were alanine-valine-urea and alanine-galactose-glucose. Cell metabolome data provided characteristic fingerprints associated with the antioxidant activity of Del.

Upregulated galectin-1 in Angiostrongylus cantonensis L5 reduces body fat and increases oxidative stress tolerance

Background

Angiostrongylus cantonensis L5, parasitizing human cerebrospinal fluid, causes eosinophilic meningitis, which is attributed to tissue inflammatory responses caused primarily by the high percentage of eosinophils. Eosinophils are also involved in killing helminths, using the peroxidative oxidation and hydrogen peroxide (H₂O₂) generated by dismutation of superoxide produced during respiratory burst. In contrast, helminthic worms have evolved to attenuate eosinophil-mediated tissue inflammatory responses for their survival. In previous study, we demonstrated the extracellular function of Acan-Gal-1 in inducing the apoptosis of macrophages. Here, the intracellular functions of Acan-Gal-1 were investigated, aiming to further reveal the mechanism involved in A. cantonensis L5 worms surviving inflammatory responses in the human central nervous system.

Methods

In this study, a model organism, Caenorhabditis elegans, was used as a surrogate to investigate the intracellular functions of Acan-Gal-1 in protecting the worm from its host’s immune attacks. First, structural characterization of Acan-Gal-1 was analyzed using bioinformatics; second, qRT-PCR was used to monitor the stage specificity of Acan-gal-1 expression in A. cantonensis. Microinjections were performed to detect the tissue specificity of lec-1 expression, the homolog of Acan-gal-1 in C. elegans. Third, microinjection was performed to develop Acan-gal-1::rfp transgenic worms. Then, oxidative stress assay and Oil Red O fat staining were used to determine the functions of Acan-Gal-1 in C. elegans.

Results

The results of detecting the stage specificity of Acan-gal-1 expression showed that Acan-Gal-1 was upregulated in both L5 and adult worms. Detection of the tissue specificity showed that the homolog of Acan-gal-1 in C. elegans, lec-1 was expressed ubiquitously and mainly localized in cuticle. Investigating the intracellular functions of Acan-Gal-1 in the surrogate C. elegans showed that N2 worms expressing pCe-lec-1::Acan-gal-1::rfp, with lipid deposition reduced, were significantly resistant to oxidative stress; lec-1 mutant worms, where lipid deposition increased, showed susceptible to oxidative stress, and this phenotype could be rescued by expressing pCe-lec-1::Acan-gal-1::rfp. Expressing pCe-lec-1::Acan-gal-1::rfp or lec-1 RNAi in fat-6;fat-7 double-mutant worms, where fat stores were reduced, had no significant effect on the oxidative stress tolerance.

Conclusion

In C. elegans worms, upregulated Acan-Gal-1 plays a defensive role against damage due to oxidative stress for worm survival by reducing fat deposition. This might indicate the mechanism by which A. cantonensis L5 worms, with upregulated Acan-Gal-1, survive the immune attack of eosinophils in the human central nervous system.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05171-4.

Cold and warm waters: energy metabolism and antioxidant defenses of the freshwater fish Astyanax lacustris (Characiformes: Characidae) under thermal stress

Subtropical fish are exposed to seasonal variations in temperature that impose a set of adaptations on their metabolism necessary for the maintenance of homeostasis. In this study, we addressed the effects of temperature variation on the metabolism of Astyanax lacustris, a species of freshwater fish common in the subtropical region of Brazil. Biomarkers of carbohydrate and protein metabolism, antioxidant defense, and oxidative damage were evaluated in the liver of A. lacustris exposed to low (15 °C) and high (31 °C) temperature thermal shock, with controls at 23 °C for 2, 6, 12, 24, 48, 72, and 96 h. A high energy demand was observed during the first 48 h of exposure to 15 °C, which is necessary for metabolic adjustment at low temperatures, with an increase in glycolysis, citric acid cycle, and amino acid catabolism. In addition, at 31 °C, glucose was exported in the first 12 h of exposure, and an increase in the citric acid cycle suggested acetyl-CoA as the pathway substrate, originating from the oxidation of lipids. The antioxidant defenses did not change at 15 °C, as opposed to 31 °C, in which there were changes in several antioxidant defense markers, indicating a response to the production of ROS. However, oxidative stress was observed at both temperatures, with oxidative damage detected by lipid peroxidation at 15 °C and protein carbonylation at 31 °C.

Molecular organization in hydroperoxidized POPC bilayers

Lipid hydroperoxides are the primary reaction products of lipid oxidation, a natural outcome of life under oxygen. While playing a major role in cell metabolism, the microscopic origins of the effects of lipid hydroperoxidation on biomembranes remain elusive. Here we probe the polar structure of partially to fully hydroperoxidized bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) by a combination of environment-sensitive fluorescent probes and coarse-grained Martini numerical simulations. We find that the inserted organic hydroperoxide group -OOH migrates preferentially to the surface for bilayers with small fractions of hydroperoxidized lipids, but populates also significantly the bilayer interior for larger fractions. Our findings suggest that by modifying the intimate polarity of biomembranes, lipid peroxidation will have a significant impact on the activity of transmembrane proteins and on the bio-medical efficiency of membrane active molecules such as cell-penetrating and antimicrobial peptides.

Mammals to membranes: A reductionist story

This is the story of a series of reductionist studies that started with an attempt to explain what underpins the high-level of aerobic metabolism in mammals (i.e. associated with the evolution of endothermy) and almost forty years later had led to investigations into the role of membrane lipids in determining metabolism. Initial studies showed that the increase in aerobic metabolism in mammals was driven by a combination of increases in mitochondrial volume and membrane densities, organ size and changes in the molecular activity of enzymes. The increase in the capacity to produce energy was matched by an increase in energy use, notably driven by increases in H⁺, Na⁺ and K⁺ fluxes. In the case of increased Na⁺ flux, it was found this was matched by increases in Na⁺-dependent metabolism at the tissue level and increases in enzyme activity at a cellular level but not by an increase in the number of sodium pumps. To maintain Na⁺ gradient across cell membranes, increased Na⁺ flux is not controlled by an increase in sodium pump number but rather by an increase in sodium pump molecular activity (i.e. an increase the substrate turnover rate of each sodium pump) in tissues of endotherms. This increase in molecular activity is coupled to an increase in the level of highly unsaturated polyunsaturated fatty acids (PUFA) in membranes, a mechanism similar to that used by ectotherms to ameliorate decreasing activities of metabolic processes in the cold. Determination of how changes in membrane fatty acid composition can change the activities of proteins in membranes will be the next step in this story.

Temperature and hypoxia on oxidative stress responses in pacu Piaractus mesopotamicus

The aim of this study was to verify the effects of the interaction between different temperatures and levels of dissolved oxygen in the oxidative stress parameters of pacu juveniles. A total of 81 pacu juveniles (61.7 ± 9.1 g) were exposed to three temperatures (18, 23, and 28 °C), acclimated for a period of 30 days, and then submitted to three levels of dissolved oxygen: control or normoxia (7 mg L^-1); moderate hypoxia (4 mg L^-1); and severe hypoxia (2 mg L^-1) for 12 h. Glutathione-S-transferase (GST) activity, total antioxidant capacity against peroxyl radicals (ACAP), and protein thiol content (PSH) and LPO (lipid peroxidation) [measured by the TBARS] were measured in gill, liver, muscle and brain. The results indicated that the interaction between different temperatures and dissolved oxygen levels caused alterations in the antioxidant system and induced lipid and protein damage in pacu juveniles. In addition, the effects were organ specific. In conclusion, exposure to moderate and severe hypoxia affect oxidative stress parameters and have been shown to be organ-specific in pacu juveniles. The interaction between 23 °C and hypoxia caused greater disturbances in oxidative stress markers, such as PSH in the gills and liver and LPO in the muscle.

Modeling the influence of time and temperature on the levels of fatty acids in the liver of Antarctic fish Trematomus bernacchii

Antarctic fish (Trematomus bernacchii) are an ideal group for studying the effect of ocean warming on vital physiological and biochemical mechanisms of adaptation, including changes in the fatty acid composition to higher heat tolerance in the sub-zero waters of the Southern Ocean. Despite the awareness of the impact of ocean warming on marine life, bioclimatic models describing the effect of temperature and time on fatty acid levels in marine species have not been considered yet. The objective of the present study was to investigate changes in the concentrations of fatty acids in liver from T. bernacchii in response to an increase in temperature in the Antarctic region. Changes in the concentrations of fatty acids in liver from T. bernacchii were observed after varying simultaneously and systematically the temperature and time. The fatty acid profiles were determined by gas chromatography prior to acclimation (− 1.8 °C) and after acclimation (0.0, 1.0, and 2.0 °C) at different times (1, 5, and 10 days). The observed changes were graphically visualized by expressing the fatty acid concentration in absolute units (mg g−1) as a function of the temperature and time using polynomial models. Major changes in fatty acid composition were observed at day 1 of exposition at all temperatures. At day 5, the fish seem to tolerate the new temperature condition. The concentrations of saturated fatty acids were almost constant throughout the various conditions. The concentrations of monounsaturated fatty acids (in particular 18:1n − 9) decrease at day 1 for all temperatures. In contrast, there was an increase in the concentrations of polyunsaturated fatty acids (in particular 20:5n − 3 and 22:6n − 3) with increasing temperatures after 1, 5, and 10 days of exposure. The proposed models were in agreement with reported studies on polar and temperate fish, indicating possibly similar adaptation mechanisms for teleost to cope with global warming.

Mitochondrial membranes in cardiac muscle from Antarctic notothenioid fishes vary in phospholipid composition and membrane fluidity

Antarctic notothenioid fishes are highly stenothermal, yet their tolerance for warming is species-dependent. Because a body of literature points to the loss of cardiac function as underlying thermal limits in ectothermic animals, we investigated potential relationships among properties of ventricular mitochondrial membranes in notothenioids with known differences in both cardiac mitochondrial metabolism and organismal thermal tolerance. Fluidity of mitochondrial membranes was quantified by fluorescence depolarization for the white-blooded Chaenocephalus aceratus and the red-blooded Notothenia coriiceps. In these same membranes, lipid compositions and products of lipid peroxidation, the latter of which can disrupt membrane order, were analyzed in both species and in a second icefish, Pseudochaenichthys georgianus. Mitochondrial membranes from C. aceratus were significantly more fluid than those of the more thermotolerant species N. coriiceps (P < .0001). Consistent with this, ratios of total phosphatidylethanolamine (PE) to total phosphatidylcholine (PC) were lower in membranes from both species of icefishes, compared to those of N. coriiceps (P < .05). However, membranes of N. coriiceps displayed a greater unsaturation index (P < .0001). No differences among species were found in membrane products of lipid peroxidation. With rising temperatures, greater contents of PC in mitochondrial membranes from ventricles of icefishes are likely to promote membrane hyperfluidization at a lower temperature than for cardiac mitochondrial membranes from the red-blooded notothenioid. We propose that physical and chemical properties of the mitochondrial membranes may contribute to some of the observed differences in thermal sensitivity of physiological function among these species.

Differential plasticity of membrane fatty acids in northern and southern populations of the eastern newt (Notophthalmus viridescens)

Seasonal changes in membrane composition and metabolic activity allow many temperate ectotherms to contend with changes in body temperature, but few studies have investigated whether the plasticity of these traits has diverged within a single species. Therefore, we studied the effects of thermal acclimation on the membrane fatty acid composition and the activities of cytochrome c oxidase (CCO) and citrate synthase (CS) in the skeletal muscle and liver of eastern newts from Maine and Florida. Newts were acclimated to either 6 °C or 28 °C for 12 weeks prior to experiments. Cold acclimation resulted in a lower saturated fatty acid (SFA) content in the muscle membranes of both populations. SFA content in liver was lower in cold compared to warm-acclimated newts from Florida, but acclimation did not affect SFA content in liver membranes of the Maine population. In liver, cold acclimation resulted in a higher monounsaturated fatty acid (MUFA) content in the Florida population and a higher polyunsaturated fatty acid (PUFA) content in the Maine population. Regardless of acclimation conditions, the muscle and liver membranes of the Maine population had higher SFA and PUFA contents compared to those of the Florida population. MUFA content of muscle and liver membranes was higher in the Florida population compared to the Maine population. The effect of acclimation on CCO and CS activity was tissue-specific. In muscle, CCO and CS activities were higher in cold compared to warm-acclimated newts in both populations, and CS and CCO activities were higher in the Maine compared to the Florida population. In liver, CCO and CS activity were unaffected by acclimation in the Florida population, but activity was lower in cold compared to warm-acclimated Maine newts. These results demonstrate that the phenotypic plasticity of these traits in response to seasonal change has diverged between northern and southern populations.

The loss of hemoglobin and myoglobin does not minimize oxidative stress in Antarctic icefishes

The unusual pattern of expression of hemoglobin (Hb) and myoglobin (Mb) among Antarctic notothenioid fishes provides an exceptional model system for assessing the impact of these proteins on oxidative stress. We tested the hypothesis that the lack of oxygen-binding proteins may reduce oxidative stress. Levels and activity of pro-oxidants and small-molecule and enzymatic antioxidants, and levels of oxidized lipids and proteins in the liver, oxidative skeletal muscle and heart ventricle were quantified in five species of notothenioid fishes differing in the expression of Hb and Mb. Levels of ubiquitinated proteins and rates of protein degradation by the 20S proteasome were also quantified. Although levels of oxidized proteins and lipids, ubiquitinated proteins, and antioxidants were higher in red-blooded fishes than in Hb-less icefishes in some tissues, this pattern did not persist across all tissues. Expression of Mb was not associated with oxidative damage in the heart ventricle, whereas the activity of citrate synthase and the contents of heme were positively correlated with oxidative damage in most tissues. Despite some tissue differences in levels of protein carbonyls among species, rates of degradation by the 20S proteasome were not markedly different, suggesting either alternative pathways for eliminating oxidized proteins or that redox tone varies among species. Together, our data indicate that the loss of Hb and Mb does not correspond with a clear pattern of either reduced oxidative defense or oxidative damage.

What modulates animal longevity? Fast and slow aging in bivalves as a model for the study of lifespan

Delineating the physiological and biochemical causes of aging process in the animal kingdom is a highly active area of research not only because of potential benefits for human health but also because aging process is related to life history strategies (growth and reproduction) and to responses of organisms to environmental conditions and stress. In this synthesis, we advocate studying bivalve species as models for revealing the determinants of species divergences in maximal longevity. This taxonomic group includes the longest living metazoan on earth (Arctica islandica), which insures the widest range of maximum life span when shorter living species are also included in the comparative model. This model can also be useful for uncovering factors modulating the pace of aging in given species by taking advantages of the wide disparity of lifespan among different populations of the same species. For example, maximal lifespan in different populations of A islandica range from approximately 36 years to over 500 years. In the last 15 years, research has revealed that either regulation or tolerance to oxidative stress is tightly correlated to longevity in this group which support further investigations on this taxon to unveil putative mechanistic links between Reactive Oxygen Species and aging process.

Biochemical alterations in native and exotic oyster species in Brazil in response to increasing temperature

The increase of temperature in marine coastal ecosystems due to atmospheric greenhouse gas emissions is becoming an increasing threat for biodiversity worldwide, and may affect organisms' biochemical performance, often resulting in biogeographical shifts of species distribution. At the same time, the introduction of non-native species into aquatic systems also threatens biodiversity and ecosystem functions. Oysters are among the most valuable socio economic group of bivalve species in global fishery landings, and also provide numerous ecosystem services. However, the introduction of non-native oyster species, namely Crassostrea gigas for aquaculture purposes may threaten native oyster species, mainly by out competing their native congeners. It is therefore of upmost importance to understand physiological and biochemical responses of native and introduced oyster species in a scenario of global temperature rise, in order to provide knowledge that may allow for better species management. Hence, we compared biochemical alterations of the introduced C. gigas and the native Crassostrea brasiliana, the most important oyster species in Brazil, in response to different thermal regimes for 28days (24, 28 and 32°C). For this, metabolism (ETS), energy content (GLY), antioxidant system (SOD, CAT and GSH/GSSG) and cellular damage (LPO) were assessed in adult and juvenile specimens of both species. Juvenile C. gigas were the most affected by increased temperatures, presenting higher mortality, more pronounced antioxidant response (SOD), whereas adults were more tolerant than juveniles, showing no mortality, no significant changes in antioxidant enzymes activity neither energy expenditure. Native C. brasiliana juveniles presented lower mortality and less pronounced biochemical alterations were noted at higher temperature comparing to non-native C. gigas juveniles. Adult C. brasiliana were the least responsive to tested temperatures. Results obtained in this study bring interesting new insights on different oyster species life stages' physiological and biochemical tolerance towards thermal stress. The native species C. brasiliana showed ability to maintain biochemical performance at higher temperatures, with less pronounced biochemical changes than the non-native species. The introduced (C. gigas) showed to be more sensitive, presenting biochemical alterations to cope with the increase of temperature. Despite the lower observed fitness of the introduced species to temperatures closer to those naturally experienced by the native species, the ability of C. gigas to cope with higher temperatures should still raise concerns towards the native species C. brasiliana management and protection.

Interactions between parental traits, environmental harshness and growth rate in determining telomere length in wild juvenile salmon

A larger body size confers many benefits, such as increased reproductive success, ability to evade predators and increased competitive ability and social status. However, individuals rarely maximize their growth rates, suggesting that this carries costs. One such cost could be faster attrition of the telomeres that cap the ends of eukaryotic chromosomes and play an important role in chromosome protection. A relatively short telomere length is indicative of poor biological state, including poorer tissue and organ performance, reduced potential longevity and increased disease susceptibility. Telomere loss during growth may also be accelerated by environmental factors, but these have rarely been subjected to experimental manipulation in the natural environment. Using a wild system involving experimental manipulations of juvenile Atlantic salmon Salmo salar in Scottish streams, we found that telomere length in juvenile fish was influenced by parental traits and by direct environmental effects. We found that faster‐growing fish had shorter telomeres and there was a greater cost (in terms of reduced telomere length) if the growth occurred in a harsher environment. We also found a positive association between offspring telomere length and the growth history of their fathers (but not mothers), represented by the number of years fathers had spent at sea. This suggests that there may be long‐term consequences of growth conditions and parental life history for individual longevity.

Revisiting the membrane-centric view of diabetes

Fundamental questions remain unresolved in diabetes: What is the actual mechanism of glucose toxicity? Why is there insulin resistance in type 2 diabetes? Why do diets rich in sugars or saturated fatty acids increase the risk of developing diabetes? Studying the C. elegans homologs of the anti-diabetic adiponectin receptors (AdipoR1 and AdipoR2) has led us to exciting new discoveries and to revisit what may be termed “The Membrane Theory of Diabetes”. We hypothesize that excess saturated fatty acids (obtained through a diet rich in saturated fats or through conversion of sugars into saturated fats via lipogenesis) leads to rigid cellular membranes that in turn impair insulin signalling, glucose uptake and blood circulation, thus creating a vicious cycle that contributes to the development of overt type 2 diabetes. This hypothesis is supported by our own studies in C. elegans and by a wealth of literature concerning membrane composition in diabetics. The purpose of this review is to survey this literature in the light of the new results, and to provide an admittedly membrane-centric view of diabetes.

Tocopherols in Seafood and Aquaculture Products

Fish products contain various nutritionally beneficial components, namely, ω3-polyunsaturated fatty acids (ω3-PUFA), minerals, and vitamins. Particularly, tocopherols (α-, β-, γ-, and δ-tocopherol) can be provided by seafood and aquaculture products. Hence, this review shows the various aspects of tocopherols in seafood and aquaculture products. For tocopherol determination in these products, HPLC methods coupled with diode array detection in the UV area of the spectrum or fluorescence detection have been shown as sensitive and accurate. These newest methods have helped in understanding tocopherols fate upon ingestion by seafood organisms. Tocopherols pass through the intestinal mucosa mainly by the same passive diffusion mechanism as fats. After absorption, the transport mechanism is thought to consist of two loops. The first loop is dietary, including chylomicrons and fatty acids bound to carrier protein, transporting lipids mainly to the liver. The other is the transport from the liver to tissues and storage sites. Moreover, tocopherol levels in fish organisms correlate with diet levels, being adjusted in fish body depending on diet concentration. For farmed fish species, insufficient levels of tocopherols in the diet can lead to poor growth performance or to nutritional disease. The tocopherol quantity needed as a feed supplement depends on various factors, such as the vitamer mixture, the lipid level and source, the method of diet preparation, and the feed storage conditions. Other ingredients in diet may be of great importance, it has been proposed that α-tocopherol may behave as a prooxidant synergist at higher concentrations when prooxidants such as transition metals are present. However, the antioxidant action of tocopherols outweighs this prooxidant effect, provided that adequate conditions are used. In fact, muscle-based foods containing higher levels of tocopherol show, for instance, higher lipid stability. Besides, tocopherols are important not only from the nutritional point of view but also from the physiological one, since they are involved in many metabolic processes in the human organism. Moreover, synergistic interactions with selenium and ascorbic acid have been reported. It deserves attention that there is evidence tocopherols taken with food can prevent heart disease, while no such evidence was found for α-tocopherol as supplement. From this perspective, eating fish is advisable, since, for instance, a 100 g serving of salmon may provide nearly 14% of recommended dietary allowance.

Caenorhabditis elegans PAQR-2 and IGLR-2 Protect against Glucose Toxicity by Modulating Membrane Lipid Composition

In spite of the worldwide impact of diabetes on human health, the mechanisms behind glucose toxicity remain elusive. Here we show that C. elegans mutants lacking paqr-2, the worm homolog of the adiponectin receptors AdipoR1/2, or its newly identified functional partner iglr-2, are glucose intolerant and die in the presence of as little as 20 mM glucose. Using FRAP (Fluorescence Recovery After Photobleaching) on living worms, we found that cultivation in the presence of glucose causes a decrease in membrane fluidity in paqr-2 and iglr-2 mutants and that genetic suppressors of this sensitivity act to restore membrane fluidity by promoting fatty acid desaturation. The essential roles of paqr-2 and iglr-2 in the presence of glucose are completely independent from daf-2 and daf-16, the C. elegans homologs of the insulin receptor and its downstream target FoxO, respectively. Using bimolecular fluorescence complementation, we also show that PAQR-2 and IGLR-2 interact on plasma membranes and thus may act together as a fluidity sensor that controls membrane lipid composition.

Effects of cadmium exposure on critical temperatures of aerobic metabolism in eastern oysters Crassostrea virginica (Gmelin, 1791)

Cadmium (Cd) and elevated temperatures are common stressors in estuarine and coastal environments. Elevated temperature can sensitize estuarine organisms to the toxicity of metals such as Cd and vice versa, but the physiological mechanisms of temperature-Cd interactions are not well understood. We tested a hypothesis that interactive effects of elevated temperature and Cd stress involve Cd-induced reduction of the aerobic scope of an organism thereby narrowing the thermal tolerance window of oysters. We determined the effects of prolonged Cd exposure (50 μg Cd l(-1)for 30 days) on the upper critical temperature of aerobic metabolism (assessed by accumulation of anaerobic end products L-alanine, succinate and acetate), cellular energy status (assessed by the tissue levels of adenylates, phosphagen/aphosphagen and glycogen and lipid reserves) and oxidative damage during acute temperature rise (20-36 °C) in the eastern oysters Crassostrea virginica. The upper critical temperature (TcII) was shifted to lower values (from 28 to 24 °C) in Cd-exposed oysters in spring and was lower in both control and Cd-exposed groups in winter (24 and <20 °C, respectively). This indicates a reduction of thermal tolerance of Cd-exposed oysters associated with a decrease of the aerobic scope of the organism and early transition to partial anaerobiosis. Acute warming had no negative effects on tissue energy reserves or parameters of cellular energy status of oysters (except a decrease in adenylate content at the extreme temperature of 36 °C) but led to an increase in oxidative lesions of proteins at extreme temperatures. These data show that transition to partial anaerobiosis (indicated by the accumulation of anaerobic end products) is the most sensitive biomarker of temperature-induced transition to energetically non-sustainable state in oysters, whereas disturbances in the cellular energy status (i.e. decline in adenylate and phosphagen levels) and oxidative stress ensue at considerably higher temperatures, nearing the lethal range. This study indicates that long-term exposure of oysters to environmentally relevant levels of Cd may increase their sensitivity to elevated temperatures during seasonal warming and/or the global climate change in polluted estuaries.

Bioadhesive giant vesicles for monitoring hydroperoxidation in lipid membranes

Osmotic stresses, protein insertion or lipid oxidation lead to area increase of self-assembled lipid membranes. However, methods to measure membrane expansion are scarce. Challenged by recent progress on the control of phospholipid hydroperoxidation, we introduce a method to quantitatively evaluate membrane area increase based on the bio-adhesion of Giant Unilamellar Vesicles.

Polyethylene glycol protects primary hepatocytes during supercooling preservation

Cold storage (at 4°C) offers a compromise between the benefits and disadvantages of cooling. It allows storage of organs or cells for later use that would otherwise quickly succumb to warm ischemia, but comprises cold ischemia that, when not controlled properly, can result in severe damage as well by both similar and unique mechanisms. We hypothesized that polyethylene glycol (PEG) 35 kDa would ameliorate these injury pathways and improve cold primary hepatocyte preservation. We show that reduction of the storage temperature to below zero by means of supercooling, or subzero non-freezing, together with PEG supplementation increases the viable storage time of primary rat hepatocytes in University of Wisconsin (UW) solution from 1 day to 4 days. We find that the addition of 5% PEG 35 kDa to the storage medium prevents cold-induced lipid peroxidation and maintains hepatocyte viability and functionality during storage. These results suggest that PEG supplementation in combination with supercooling may enable a more optimized cell and organ preservation.

Polyethylene glycol protects primary hepatocytes during supercooling preservation

Cold storage (at 4°C) offers a compromise between the benefits and disadvantages of cooling. It allows storage of organs or cells for later use that would otherwise quickly succumb to warm ischemia, but comprises cold ischemia that, when not controlled properly, can result in severe damage as well by both similar and unique mechanisms. We hypothesized that polyethylene glycol (PEG) 35 kDa would ameliorate these injury pathways and improve cold primary hepatocyte preservation. We show that reduction of the storage temperature to below zero by means of supercooling, or subzero non-freezing, together with PEG supplementation increases the viable storage time of primary rat hepatocytes in University of Wisconsin (UW) solution from 1 day to 4 days. We find that the addition of 5% PEG 35 kDa to the storage medium prevents cold-induced lipid peroxidation and maintains hepatocyte viability and functionality during storage. These results suggest that PEG supplementation in combination with supercooling may enable a more optimized cell and organ preservation.

The influence of dietary fat source on liver and skeletal muscle mitochondrial modifications and lifespan changes in calorie-restricted mice

The Membrane Theory of Aging proposes that lifespan is inversely related to the level of unsaturation in membrane phospholipids. Calorie restriction (CR) without malnutrition extends lifespan in many model organisms, which may be related to alterations in membrane phospholipids fatty acids. During the last few years our research focused on studying how altering the predominant fat source affects the outcome of CR in mice. We have established four dietary groups: one control group fed 95 % of a pre-determined ad libitum intake (in order to prevent obesity), and three CR groups fed 40 % less than ad libitum intake. Lipid source for the control and one of the CR groups was soybean oil (high in n-6 PUFA) whereas the two remaining CR groups were fed diets containing fish oil (high in n-3 PUFA), or lard (high in saturated and monounsaturated fatty acids). Dietary intervention periods ranged from 1 to 18 months. We performed a longitudinal lifespan study and a cross-sectional study set up to evaluate several mitochondrial parameters which included fatty acid composition, H(+) leak, activities of electron transport chain enzymes, ROS generation, lipid peroxidation, mitochondrial ultrastructure, and mitochondrial apoptotic signaling in liver and skeletal muscle. These approaches applied to different cohorts of mice have independently indicated that lard as a fat source often maximizes the effects of 40 % CR on mice. These effects could be due to significant increases of monounsaturated fatty acids levels, in accordance with the Membrane Theory of Aging.

Products of lipid peroxidation, but not membrane susceptibility to oxidative damage, are conserved in skeletal muscle following temperature acclimation

Changes in oxidative capacities and phospholipid remodeling accompany temperature acclimation in ectothermic animals. Both responses may alter redox status and membrane susceptibility to lipid peroxidation (LPO). We tested the hypothesis that phospholipid remodeling is sufficient to offset temperature-driven rates of LPO and, thus, membrane susceptibility to LPO is conserved. We also predicted that the content of LPO products is maintained over a range of physiological temperatures. To assess LPO susceptibility, rates of LPO were quantified with the fluorescent probe C11-BODIPY in mitochondria and sarcoplasmic reticulum from oxidative and glycolytic muscle of striped bass (Morone saxatilis) acclimated to 7°C and 25°C. We also measured phospholipid compositions, contents of LPO products [i.e., individual classes of phospholipid hydroperoxides (PLOOH)], and two membrane antioxidants. Despite phospholipid headgroup and acyl chain remodeling, these alterations do not counter the effect of temperature on LPO rates (i.e., LPO rates are generally not different among acclimation groups when normalized to phospholipid content and compared at a common temperature). Although absolute levels of PLOOH are higher in muscles from cold- than warm-acclimated fish, this difference is lost when PLOOH levels are normalized to total phospholipid. Contents of vitamin E and two homologs of ubiquinone are more than four times higher in mitochondria prepared from oxidative muscle of warm- than cold-acclimated fish. Collectively, our data demonstrate that although phospholipid remodeling does not provide a means for offsetting thermal effects on rates of LPO, differences in phospholipid quantity ensure a constant proportion of LPO products with temperature variation.

Histological and enzymatic responses of Japanese flounder (Paralichthys olivaceus) and its hybrids (P. olivaceus ♀ × P. dentatus ♂) to chronic heat stress

This study investigated the effects of long-term heat exposure on Japanese flounder (Paralichthys olivaceus) and its hybrids (P. olivaceus ♀ × summer flounder Paralichthys dentatus ♂). From 24 ± 0.5°C, temperature was increased by 1 ± 0.5°C in a day and was kept at that temperature for 5 days before next rise. Cumulative survival rate (CSR), cumulative survival rate under different temperature (CSR-T), histological alteration, and related enzyme activities were investigated. In P. olivaceus, mass mortality occurred at 29 and 32 °C (the CSR-T dropped to 42.39%), and serious gill damages appeared at 30 and 32°C. Meanwhile, the activities of superoxide dismutase (SOD), catalase (CAT), lysozyme (LZM), and pyruvate kinase (PK) declined around 29 and 32°C (except for CAT). In comparison with P. olivaceus, the CSR of the hybrids was higher, the gill kept a better structural integrity, and the activities of SOD, CAT, LZM, and PK showed tiny fluctuations. The results suggested that during the process of chronic heat stress, P. olivaceus seemed to be more sensitive to 29 and 32°C, and the manifestations in survival, histology, and enzyme activity were generally consistent. For the hybrids, the comparatively insensitivity to high temperature might imply its better heat tolerance.

Lipid oxidation induces structural changes in biomimetic membranes

Oxidation can intimately influence and structurally compromise the levels of biological self-assembly embodied by intracellular and plasma membranes. Lipid peroxidation, a natural metabolic outcome of life with oxygen under light, is also a salient oxidation reaction in photomedicine treatments. However, the effect of peroxidation on the fate of lipid membranes remains elusive. Here we use a new photosensitizer that anchors and disperses in the membrane to achieve spatial control of the oxidizing species. We find, surprisingly, that the integrity of unsaturated unilamellar vesicles is preserved even for fully oxidized membranes. Membrane survival allows for the quantification of the transformations of the peroxidized bilayers, providing key physical and chemical information to understand the effect of lipid oxidation on protein insertion and on other mechanisms of cell function. We anticipate that spatially controlled oxidation will emerge as a new powerful strategy for tuning and evaluating lipid membranes in biomimetic media under oxidative stress.

PAQR-2 regulates fatty acid desaturation during cold adaptation in C. elegans

C. elegans PAQR-2 is homologous to the insulin-sensitizing adiponectin receptors in mammals, and essential for adaptation to growth at 15°C, a low but usually acceptable temperature for this organism. By screening for novel paqr-2 suppressors, we identified mutations in genes involved in phosphatidylcholine synthesis (cept-1, pcyt-1 and sams-1) and fatty acid metabolism (ech-7, hacd-1, mdt-15, nhr-49 and sbp-1). We then show genetic evidence that paqr-2, phosphatidylcholines, sbp-1 and Δ9-desaturases form a cold adaptation pathway that regulates the increase in unsaturated fatty acids necessary to retain membrane fluidity at low temperatures. This model is supported by the observations that the paqr-2 suppressors normalize the levels of saturated fatty acids, and that low concentrations of detergents that increase membrane fluidity can rescue the paqr-2 mutant.

Cold-blooded organisms such as insects, fish or worms must make physiological adjustments when the temperature in their environment decreases. One essential adaptive measure is to increase the fluidity of the cellular membranes that are made of fatty molecules and would tend to harden at low temperatures, just as butter would. In our study we identify genes that are regulated by PAQR-2, a membrane protein that we show to be essential for adjusting the membrane fluidity during cold adaptation in the nematode C. elegans. Interestingly, the genes influenced by PAQR-2 are all involved in fatty acid metabolism. We speculate that the human homologs of PAQR-2, which are receptors for the hormone adiponectin, may have similar functions.

Seasonal changes in minor membrane phospholipid classes, sterols and tocopherols in overwintering insect, Pyrrhocoris apterus

Ectotherm animals including insects are known to undergo seasonal restructuring of the cell membranes in order to keep their functionality and/or protect their structural integrity at low body temperatures. Studies on insects so far focused either on fatty acids or on composition of molecular species in major phospholipid classes. Here we extend the scope of analysis and bring results on seasonal changes in minor phospholipid classes, lysophospholipids (LPLs), free fatty acids, phytosterols and tocopherols in heteropteran insect, Pyrrhocoris apterus. We found that muscle tissue contains unusually high amounts of LPLs. Muscle and fat body tissues also contain high amounts of β-sitosterol and campesterol, two phytosterols derived from plant food, while only small amounts of cholesterol are present. In addition, two isomers (γ and δ) of tocopherol (vitamin E) are present in quantities comparable to, or even higher than phytosterols in both tissues. Distinct seasonal patterns of sterol and tocopherol concentrations were observed showing a minimum in reproductively active bugs in summer and a maximum in diapausing, cold-acclimated bugs in winter. Possible adaptive meanings of such changes are discussed including: preventing the unregulated transition of membrane lipids from functional liquid crystalline phase to non-functional gel phase; decreasing the rates of ion/solute leakage; silencing the activities of membrane bound enzymes and receptors; and counteracting the higher risk of oxidative damage to PUFA in winter membranes.

Lipids in Marine Ecosystems

Lipids provide the densest form of energy in marine ecosystems. They are also a solvent and absorption carrier for organic contaminants and thus can be drivers of pollutant bioaccumulation. Among the lipids, certain essential fatty acids and sterols are considered to be important determinants of ecosystem health and stability. Fatty acids and sterols are also susceptible to oxidative damage leading to cytotoxicity and a decrease in membrane fluidity. The physical characteristics of biological membranes can be defended from the influence of changing temperature, pressure, or lipid peroxidation by altering the fatty acid and sterol composition of the lipid bilayer. Marine lipids are also a valuable tool to measure inputs, cycling, and loss of materials. Their heterogeneous nature makes them versatile biomarkers that are widely used in marine trophic studies, often with the help of multivariate statistics, to delineate carbon cycling and transfer of materials. Principal components analysis has a strong following as it permits data reduction and an objective interpretation of results, but several more sophisticated multivariate analyses which are more quantitative are emerging too. Integrating stable isotope and lipid data can facilitate the interpretation of both data sets and can provide a quantitative estimate of transfer across trophic levels.

Effects of temperature and dietary protein level on hepatic oxidative status of Senegalese sole juveniles (Solea senegalensis)

Effects of 55 and 45% dietary protein levels (55P and 45P diets, respectively) and temperature (12 and 18 °C) on hepatic activity of superoxide dismutase (SOD), catalase, glutathione peroxidase, glutathione reductase (GR), glucose-6-phosphate dehydrogenase and lipid peroxidation (LPO) levels of Solea senegalensis juveniles were studied. Further, effects of acute thermal shocks provoked by a drop (18 °C to 12 °C) or a rise (12 °C to 18 °C) of water temperature on sole oxidative state was also evaluated. Dietary protein reduction increased LPO levels though no major alterations were found on antioxidant enzyme activities between dietary treatments. At 12 °C GR activity was higher and SOD activity was lower than 18 °C but LPO levels were not affected. In both thermal shock cases, LPO levels increased in 55P group, probably due to insufficient antioxidant enzyme activation. In contrast, fish of 45P group under acute exposition to warmer and colder temperature exhibited no substantial changes and a significant decrease on LPO levels, respectively, along with no major changes in antioxidant enzymes. Overall, results suggest that independently of rearing temperatures 45P group was more susceptible to oxidative stress than 55P group. Thermal shock either due to rise or drop of temperature seemed to induce oxidative stress in 55P group.

Exposure to critical thermal maxima increases oxidative stress in hearts of white- but not red-blooded Antarctic notothenioid fishes

Antarctic icefishes have a significantly lower critical thermal maximum (CT(max)) compared with most red-blooded notothenioid fishes. We hypothesized that the lower thermal tolerance of icefishes compared with red-blooded notothenioids may stem from a greater vulnerability to oxidative stress as temperature increases. Oxidative muscles of icefishes have high volume densities of mitochondria, rich in polyunsaturated fatty acids, which can promote the production of reactive oxygen species (ROS). Moreover, icefishes have lower levels of antioxidants compared with red-blooded species. To test our hypothesis, we measured levels of oxidized proteins and lipids, and transcript levels and maximal activities of antioxidants in heart ventricle and oxidative pectoral adductor muscle of icefishes and red-blooded notothenioids held at 0°C and exposed to their CT(max). Levels of oxidized proteins and lipids increased in heart ventricle of some icefishes but not in red-blooded species in response to warming, and not in pectoral adductor muscle of any species. Thus, increases in oxidative damage in heart ventricles may contribute to the reduced thermal tolerance of icefishes. Despite an increase in oxidative damage in hearts of icefishes, neither transcript levels nor activities of antioxidants increased, nor did they increase in any tissue of any species in response to exposure to CT(max). Rather, transcript levels of the enzyme superoxide dismutase (SOD) decreased in hearts of icefishes and the activity of SOD decreased in hearts of the red-blooded species Gobionotothen gibberifrons. These data suggest that notothenioids may have lost the ability to elevate levels of antioxidants in response to heat stress.

Inter-relationship between mitochondrial function and susceptibility to oxidative stress in red- and white-blooded Antarctic notothenioid fishes

It is unknown whether Antarctic fishes can defend themselves against oxidative stress induced by elevations in temperature. We hypothesized that Antarctic icefishes, lacking the oxygen-binding protein hemoglobin, might be more vulnerable to temperature-induced oxidative stress compared with red-blooded notothenioids because of differences in their mitochondrial properties. Mitochondria from icefishes have higher densities of phospholipids per mg of mitochondrial protein compared with red-blooded species, and these phospholipids are rich in polyunsaturated fatty acids (PUFA), which can promote the formation of reactive oxygen species (ROS). Additionally, previous studies have shown that multiple tissues in icefishes have lower levels of antioxidants compared with red-blooded species. We quantified several properties of mitochondria, including proton leak, rates of ROS production, membrane composition and susceptibility to lipid peroxidation (LPO), the activity of superoxide dismutase (SOD) and total antioxidant power (TAOP) in mitochondria isolated from hearts of icefishes and red-blooded notothenioids. Mitochondria from icefishes were more tightly coupled than those of red-blooded fishes at both 2°C and 10°C, which increased the production of ROS when the electron transport chain was disrupted. The activity of SOD and TAOP per mg of mitochondrial protein was equivalent between icefishes and red-blooded species, but TAOP normalized to mitochondrial phospholipid content was significantly lower in icefishes compared with red-blooded fishes. Additionally, membrane susceptibility to peroxidation was only detectable in icefishes at 1°C and not in red-blooded species. Together, our results suggest that the high density of mitochondrial phospholipids in hearts of icefishes may make them particularly vulnerable to oxidative stress as temperatures rise.

Oxidative stress is transient and tissue specific during cold acclimation of threespine stickleback

Linkages between cold acclimation and oxidative stress in fishes are unclear and contradictory results have been published. We sought to determine whether oxidative stress occurs during cold acclimation of threespine stickleback (Gasterosteus aculeatus), and, if so, when it occurs and whether it varies among tissues. Fish were warm (20°C) or cold (8°C) acclimated for 9 weeks, and harvested during acclimation. Oxidative stress was assessed in oxidative and glycolytic muscles and liver by measuring levels of protein carbonyls and glutathione, and the activity and transcript levels of superoxide dismutase (SOD). Protein carbonyl levels increased in liver after 1 week at 8°C and then decreased after week 4, and remained unchanged in glycolytic and oxidative muscle. Glutathione levels increased in liver on day 3 of cold acclimation and may minimize oxidative stress later during acclimation. When measured at a common temperature, the activity of SOD increased in oxidative and glycolytic muscles on day 2 of cold acclimation, and on day 3 in liver, and remained elevated in all tissues compared with warm-acclimated animals. When measured at the acclimation temperature, the activity of SOD was significantly higher only at week 9 in oxidative muscle of cold-acclimated stickleback compared with warm-acclimated fish, and remained constant in glycolytic muscle and liver. Increased SOD activity in oxidative muscle may be required to prevent oxidative stress brought about by increased mitochondrial density. In both muscle and liver, SOD activity increased independently of an increase in transcript level, suggesting post-translational modifications regulate SOD activity.

Diet-independent remodeling of cellular membranes precedes seasonally changing body temperature in a hibernator

Polyunsaturated fatty acids (PUFA) have a multitude of health effects. Their incorporation into membrane phospholipids (PL) is generally believed to depend directly on dietary influx. PL influence transmembrane protein activity and thus can compensate temperature effects; e.g. PL n-6 PUFA are thought to stabilize heart function at low body temperature (T_b), whereas long chain (>C18) n-3 PUFA may boost oxidative capacity. We found substantial remodeling of membranes in free-living alpine marmots which was largely independent of direct dietary supply. Organ PL n-6 PUFA and n-6 to n-3 ratios were highest at onset and end of hibernation after rapid increases during a brief transitional period prior to hibernation. In contrast, longer chain PL n-3 PUFA content was low at end of summer but maximal at end of hibernation. After termination of hibernation in spring, these changes in PL composition were rapidly reversed. Our results demonstrate selective trafficking of PUFA within the body, probably governed by a circannual endogenous rhythm, as hibernating marmots were in winter burrows isolated for seven months from food and external cues signaling the approaching spring. High concentrations of PL n-6 PUFA throughout hibernation are in line with their hypothesized function of boosting SERCA 2a activity at low T_b. Furthermore, we found increasing rate of rewarming from torpor during winter indicating increasing oxidative capacity that could be explained by the accumulation of long-chain PL n-3 PUFA. It may serve to minimize the time necessary for rewarming despite the increasing temperature range to be covered, because rewarming is a period of highest metabolic rate and hence production of reactive oxygen species. Considering the importance of PUFA for health our results may have important biomedical implications, as seasonal changes of T_b and associated remodeling of membranes are not restricted to hibernators but presumably common among endothermic organisms.

Mitochondrial biogenesis in cold-bodied fishes

Mitochondrial biogenesis is induced in response to cold temperature in many organisms. The effect is particularly pronounced in ectotherms such as fishes, where acclimation to cold temperature increases mitochondrial density. Some polar fishes also have exceptionally high densities of mitochondria. The net effect of increasing mitochondrial density is threefold. First, it increases the concentration of aerobic metabolic enzymes per gram of tissue, maintaining ATP production. Second, it elevates the density of mitochondrial membrane phospholipids, enhancing rates of intracellular oxygen diffusion. Third, it reduces the diffusion distance for oxygen and metabolites between capillaries and mitochondria. Although cold-induced mitochondrial biogenesis has been well documented in fishes, little is known about the molecular pathway governing it. In mammals, the co-transcriptional activator peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) is thought to coordinate the three components of mitochondrial biogenesis: the synthesis of mitochondrial proteins, the synthesis of phospholipids and the replication of mitochondrial DNA. Some components of the mitochondrial biogenic pathway are conserved between fishes and mammals, yet the pathway appears more versatile in fishes. In some tissues of cold-acclimated fishes, the synthesis of mitochondrial proteins increases in the absence of an increase in phospholipids, whereas in some polar fishes, densities of mitochondrial phospholipids increase in the absence of an increase in proteins. The ability of cold-bodied fishes to fine-tune the mitochondrial biogenic pathway may allow them to modify mitochondrial characteristics to meet the specific needs of the cell, whether it is to increase ATP production or enhance oxygen diffusion.

Temperature acclimation alters oxidative capacities and composition of membrane lipids without influencing activities of enzymatic antioxidants or susceptibility to lipid peroxidation in fish muscle

Cold acclimation of ectotherms results typically in enhanced oxidative capacities and lipid remodeling, changes that should increase the risk of lipid peroxidation (LPO). It is unclear whether activities of antioxidant enzymes may respond in a manner to mitigate the increased potential for LPO. The current study addresses these questions using killifish (Fundulus heteroclitus macrolepidotus) and bluegill (Lepomis macrochirus) acclimated to 5 and 25 degrees C for 9 days and 2 months, respectively. Because the effects of temperature acclimation on pro- and antioxidant metabolism may be confounded by variable activity levels among temperature groups, one species (killifish) was also subjected to a 9-day exercise acclimation. Oxidative capacity of glycolytic (skeletal) muscle (indicated by the activity of cytochrome c oxidase) was elevated by 1.5-fold in killifish, following cold acclimation, but was unchanged in cardiac muscle and also unaffected by exercise acclimation in either tissue. No changes in citrate synthase activity were detected in either tissue following temperature acclimation. Enzymatic antioxidants (catalase and superoxide dismutase) of either muscle type were unaltered by temperature or exercise acclimation. Mitochondria from glycolytic muscle of cold-acclimated killifish were enriched in highly oxidizable polyunsaturated fatty acids (PUFA), including diacyl phospholipids (total carbons:total double bonds) 40:8 and 44:12. Increased oxidative capacity, coupled with elevated PUFA content in mitochondria from cold-acclimated animals did not, however, impact LPO susceptibility when measured with C11-BODIPY. The apparent mismatch between oxidative capacity and enzymatic antioxidants following temperature acclimation will be addressed in future studies.