Gilthead sea bream liver proteome altered at low temperatures by oxidative stress

Cold temperature blocks thyroid hormone-induced changes in lipid and energy metabolism in the liver of Lithobates catesbeianus tadpoles

BACKGROUND

Exposure of the American bullfrog Lithobates catesbeianus tadpoles to low temperature affects many biological processes including lipid metabolism and the thyroid hormone (TH) signaling pathway, resulting in arrest of TH-induced metamorphosis. To clarify what molecular events occur in this phenomenon, we investigated the glycerophospholipid and fatty acid (FA) compositions, the activities of mitochondrial enzymes and the transcript levels of related genes in the liver of control (26 °C) and cold-treated (4 °C) tadpoles with or without 5 nM 3,3',5-triiodothyronine (T3).

RESULTS

Exposure to T3 decreased the tail height and polyunsaturation of FAs in the glycerophospholipids, and increased plasma glucose levels and transcript levels of primary TH-response genes including TH receptor, and some energy metabolic (cox4, srebp1 and fas) and FA chain elongase genes (elovl3 and elovl5). However, these T3-induced responses were abolished at 4 °C. Exposure to cold temperature enhanced plasma glucose, triglyceride and free FA levels, monounsaturation of FAs, mitochondrial enzymes activities (cytochrome c oxidase and carnitine palmitoyltransferase; U/g liver), with the upregulation of the genes involved in glycogenolysis (pygl), gluconeogenesis (pck1 and g6pc2), FA β-oxidation (acadl), and cholesterol uptake and synthesis (hmgcr, srebp2 and ldlr1), glycerophospholipids synthesis (pcyt1, pcyt2, pemt, and pparg), and FA monounsaturation (scd1) and chain elongation (elovl1 and elovl2). T3 had little effect on the cold-induced changes.

CONCLUSIONS

Our study demonstrated that exposures to T3 and cold temperature exert different effects on lipid metabolism, resulting in changes in the FA composition in glycerophospholipids, and suggests that a cold-induced signal may block TH-signaling pathway around primary TH-response genes.

Proteomic analysis of cardiac response to thermal acclimation in the eurythermal goby fish Gillichthys mirabilis

Cardiac function is thought to play a central role in determining thermal optima and tolerance limits in teleost fishes. Investigating proteomic responses to temperature in cardiac tissues may provide insights into mechanisms supporting the thermal plasticity of cardiac function. Here, we utilized a global proteomic analysis to investigate changes in cardiac protein abundance in response to temperature acclimation (transfer from 13°C to 9, 19 and 26°C) in a eurythermal goby, Gillichthys mirabilis. Proteomic data revealed 122 differentially expressed proteins across acclimation groups, 37 of which were identified using tandem mass-spectrometry. These 37 proteins are involved in energy metabolism, mitochondrial regulation, iron homeostasis, cytoprotection against hypoxia, and cytoskeletal organization. Compared with the 9 and 26°C groups, proteins involved in energy metabolism increased in 19°C-acclimated fish, indicating an overall increase in the capacity for ATP production. Creatine kinase abundance increased in 9°C-acclimated fish, suggesting an important role for the phosphocreatine energy shuttle in cold-acclimated hearts. Both 9 and 26°C fish also increased abundance of hexosaminidase, a protein directly involved in post-hypoxia stress cytoprotection of cardiac tissues. Cytoskeletal restructuring appears to occur in all acclimation groups; however, the most prominent effect was detected in 26°C-acclimated fish, which exhibited significantly increased actin levels. Overall, proteomic analysis of cardiac tissue suggests that the capacity to adjust ATP-generating processes is crucial to the thermal plasticity of cardiac function. Furthermore, G. mirabilis may optimize cellular functions at temperatures near 19°C, which lies within the species' preferred temperature range.

Proteomics and the search for welfare and stress biomarkers in animal production in the one-health context

Stress and welfare are important factors in animal production in the context of growing production optimization and scrutiny by the general public.

Non-additive effects of ocean acidification in combination with warming on the larval proteome of the Pacific oyster, Crassostrea gigas

Increasing atmospheric carbon dioxide results in ocean acidification and warming, significantly impacting marine invertebrate larvae development. We investigated how ocean acidification in combination with warming affected D-veliger larvae of the Pacific oyster Crassostrea gigas. Larvae were reared for 40h under either control (pH8.1, 20 °C), acidified (pH7.9, 20 °C), warm (pH8.1, 22 °C) or warm acidified (pH7.9, 22 °C) conditions. Larvae in acidified conditions were significantly smaller than in the control, but warm acidified conditions mitigated negative effects on size, and increased calcification. A proteomic approach employing two-dimensional electrophoresis (2-DE) was used to quantify proteins and relate their abundance to phenotypic traits. In total 12 differentially abundant spots were identified by nano-liquid chromatography-tandem mass spectrometry. These proteins had roles in metabolism, intra- and extra-cellular matrix formations, stress response, and as molecular chaperones. Seven spots responded to reduced pH, four to increased temperature, and six to acidification and warming. Reduced abundance of proteins such as ATP synthase and GAPDH, and increased abundance of superoxide dismutase, occurred when both pH and temperature changes were imposed, suggesting altered metabolism and enhanced oxidative stress. These results identify key proteins that may be involved in the acclimation of C. gigas larvae to ocean acidification and warming.

SIGNIFICANCE

Increasing atmospheric CO2 raises sea surface temperatures and results in ocean acidification, two climatic variables known to impact marine organisms. Larvae of calcifying species may be particularly at risk to such changing environmental conditions. The Pacific oyster Crassostrea gigas is ecologically and commercially important, and understanding its ability to acclimate to climate change will help to predict how aquaculture of this species is likely to be impacted. Modest, yet realistic changes in pH and/or temperature may be more informative of how populations will respond to contemporary climate change. We showed that concurrent acidification and warming mitigates the negative effects of pH alone on size of larvae, but proteomic analysis reveals altered patterns of metabolism and an increase in oxidative stress suggesting non-additive effects of the interaction between pH and temperature on protein abundance. Thus, even small changes in climate may influence development, with potential consequences later in life.

Differential proteome profile of skin mucus of gilthead seabream (Sparus aurata) after probiotic intake and/or overcrowding stress

Gilthead seabream (Sparus aurata L.) is the major cultured fish species in the Mediterranean area. High density stocking causes stress and increases the impact of diseases leading to economic losses. Probiotics could represent a solution to prevent diseases through several mechanisms such as improving the immune status and/or mucosal microbiota or competing with pathogens. The probiotic Shewanella putrefaciens, also known as Pdp11, was firstly isolated from the skin of healthy gilthead seabream. Our study focuses on the skin mucus proteome after dietary probiotic Pdp11 intake in fish maintained under normal or overcrowding conditions. 2-DE of skin mucus followed by LC-MS/MS analysis was done for each experimental group and differentially expressed proteins were identified. The results showed differentially expressed proteins especially involved in immune processes, such as lysozyme, complement C3, natural killer cell enhancing factor and nonspecific cytotoxic cell receptor protein 1, whose transcript profiles were studied by qPCR. A consistency between lysozyme protein levels in the mucus and lysozyme mRNA levels in skin was found. Further research is necessary to unravel the implications of skin mucosal immunity on fish welfare and disease.

BIOLOGICAL SIGNIFICANCE

The present work reveals the proteomic changes, which are taking place in the skin mucus of stressed and non-stressed gilthead seabream after Pdp11 probiotic intake. The study contributes to improving the knowledge on skin mucosal immunology of this relevant farmed fish species. Furthermore, the paper shows for the first time how a suitable proteomic methodology, in this case 2-DE followed by LC-MS/MS is useful to perform a comparative study with a non-invasive technique of skin mucus of gilthead seabream.

Proteomic analysis of the European flounder Platichthys flesus response to experimental PAH-PCB contamination

Platichthys flesus is often used as a sentinel species to monitor the estuarine water quality. In this study, we carried out an experimental contamination of fish using a PAHs/PCBs mixture, which was designed to mimic the concentrations found in the Seine estuary (C1) and 10 times these concentrations (C2). We used a proteomic approach to understand the molecular mechanisms implied in the response of P. flesus to these xenobiotics. We showed that 54 proteins were differentially accumulated in one or several conditions, which 34 displayed accumulation factors higher than two. 18 of these proteins were identified by MALDI TOF-TOF mass spectrometry. The results indicated the deregulation of oxidative stress- and glutathione metabolism-(GST, GPx) proteins as well as of several proteins belonging to the betaine demethylation pathway and the methionine cycle (BHMT, SHMT, SAHH), suggesting a role for these different pathways in the P. flesus response to chemical contamination.

The environmental genomics of metazoan thermal adaptation

Continued and accelerating change in the thermal environment places an ever-greater priority on understanding how organisms are going to respond. The paradigm of ‘move, adapt or die', regarding ways in which organisms can respond to environmental stressors, stimulates intense efforts to predict the future of biodiversity. Assuming that extinction is an unpalatable outcome, researchers have focussed attention on how organisms can shift in their distribution to stay in the same thermal conditions or can stay in the same place by adapting to a changing thermal environment. How likely these respective outcomes might be depends on the answer to a fundamental evolutionary question, namely what genetic changes underpin adaptation to the thermal environment. The increasing access to and decreasing costs of next-generation sequencing (NGS) technologies, which can be applied to both model and non-model systems, provide a much-needed tool for understanding thermal adaptation. Here we consider broadly what is already known from non-NGS studies about thermal adaptation, then discuss the benefits and challenges of different NGS methodologies to add to this knowledge base. We then review published NGS genomics and transcriptomics studies of thermal adaptation to heat stress in metazoans and compare these results with previous non-NGS patterns. We conclude by summarising emerging patterns of genetic response and discussing future directions using these increasingly common techniques.

Temperature experienced during incubation affects antioxidant capacity but not oxidative damage in hatchling red-eared slider turtles (Trachemys scripta elegans)

Our understanding of how oxidative stress resistance phenotypes are affected by the developmental environment is limited. One component of the developmental environment, which is likely central to early life oxidative stress among ectothermic and oviparous species, is that of temperature. We investigated how incubation temperature manipulations affect oxidative damage and total antioxidant capacity (TAC) in red-eared slider turtle (Trachemys scripta elegans) hatchlings. First, to determine if temperature fluctuations elicit oxidative stress, eggs from clutches were randomly assigned to either a constant (29.5°C) or daily fluctuating temperature incubation (28.7±3°C) treatment. Second, to assess the effect of temperature fluctuation frequency on oxidative stress, eggs were incubated in one of three fluctuating incubation regimes; 28.7±3°C fluctuations every 12 (Hyper), 24 (Normal), or 48 hours (Hypo). Third, we tested the influence of average incubation temperature by incubating eggs in a daily fluctuating incubation temperature regime with a mean temperature of 26.5°C (Low), 27.1°C (Medium), or 27.7°C (High). Although the accumulation of oxidative damage in hatchlings was unaffected by any thermal manipulation, TAC was affected by both temperature fluctuation frequency and average incubation temperature. Individuals incubated with a low frequency of temperature fluctuations had reduced TAC, while incubation at a lower average temperature was associated with enhanced TAC. These results indicate that while sufficient to prevent oxidative damage, TAC is influenced by developmental thermal environments, potentially due to temperature mediated changes in metabolic rate. The observed differences in TAC may have important future consequences for hatchling fitness and overwinter survival.

Metabolic compensations in mitochondria isolated from the heart, liver, kidney, brain and white muscle in the southern catfish (Silurus meridionalis) by seasonal acclimation

In order to examine the effects of seasonal acclimation on mitochondrial metabolic functions and test tissue-specific pattern of the metabolic compensation within individuals of the southern catfish (Silurus meridionalis Chen), rates of mitochondrial respiration and activities of cytochrome c oxidase (COX) in the heart, liver, kidney, brain and white muscle of this fish in the summer-acclimatized group (153.20±1.66 g) and winter-acclimatized group (177.71±3.04 g) were measured at seven assay temperatures (7.5, 12.5, 17.5, 22.5, 27.5, 32.5 and 37.5°C), respectively. The results show that compensatory adjustments in state III respiratory rate and COX activity occur significantly in the heart, kidney and liver, but do not in the brain and white muscle, which suggest that the metabolic compensation of this fish in response to seasonal acclimation exhibits a tissue-specific pattern. The cold acclimation increases mitochondrial oxidative capacities in the heart, kidney and liver concomitantly with reducing their upper thermal limits of mitochondrial functions at acute warming and the thermal tolerance shifts in the same tissue-specific pattern as the metabolic compensation. When combining the effects of seasonal acclimation on mitochondrial oxidative capacity and organ mass, the metabolic compensation demonstrates an organ-specific pattern with four categories: over-compensation in the heart, complete compensation in the kidney, partial compensation in the liver and no compensation in the brain. The organ-specific pattern of metabolic compensation might be a trade-off strategy of the performance adjustments in the seasonal acclimation for this fish to maximize its fitness.

Impact of three commercial feed formulations on farmed gilthead sea bream (Sparus aurata, L.) metabolism as inferred from liver and blood serum proteomics

Background

The zootechnical performance of three different commercial feeds and their impact on liver and serum proteins of gilthead sea bream (Sparus aurata, L.) were assessed in a 12 week feeding trial. The three feeds, named A, B, and C, were subjected to lipid and protein characterization by gas chromatography (GC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS), respectively.

Results

Feed B was higher in fish-derived lipids and proteins, while feeds C and A were higher in vegetable components, although the largest proportion of feed C proteins was represented by pig hemoglobin. According to biometric measurements, the feeds had significantly different impacts on fish growth, producing a higher average weight gain and a lower liver somatic index in feed B over feeds A and C, respectively. 2D DIGE/MS analysis of liver tissue and Ingenuity pathways analysis (IPA) highlighted differential changes in proteins involved in key metabolic pathways of liver, spanning carbohydrate, lipid, protein, and oxidative metabolism. In addition, serum proteomics revealed interesting changes in apolipoproteins, transferrin, warm temperature acclimation-related 65 kDa protein (Wap65), fibrinogen, F-type lectin, and alpha-1-antitrypsin.

Conclusions

This study highlights the contribution of proteomics for understanding and improving the metabolic compatibility of feeds for marine aquaculture, and opens new perspectives for its monitoring with serological tests.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-014-0044-3) contains supplementary material, which is available to authorized users.

Evaluation of guppy (Poecilia reticulata Peters) immunization against Tetrahymena sp. by enzyme-linked immunosorbent assay (ELISA)

Analysis of the effectiveness of guppy (Poecilia reticulata Peters) immunization based on measurements of antibody (Ab) titers suffers from a shortage of reagents that can detect guppy antibodies (Abs). To overcome this problem, we immunized mice with different preparations of guppy immunoglobulins (Igs) and used the mouse antisera to develop a quantitative enzyme-linked immunosorbent assay (ELISA). The most efficient immunogen for mouse immunization was guppy Igs adsorbed on protein A/G beads. Antisera from mice boosted with this immunoglobulin (Ig) preparation were highly specific and contained high Ab titers. They immunoreacted in a Western blot with Ig heavy and light chains from guppy serum, and Ig heavy chain from guppy whole-body homogenate. The mouse anti-guppy Ig was applied in an ELISA aimed at comparing the efficiency of different routes of guppy immunization against Tetrahymena: (i) anal intubation with sonicated Tetrahymena (40,000 Tetrahymena/fish in a total volume of 10 μL) mixed with domperidon, deoxycholic acid and free amino acids (valine, leucine, isoleucine, phenylalanine and tryptophan), or (ii) intraperitoneal (i.p.) injection of sonicated Tetrahymena in complete Freund's adjuvant (15,000 Tetrahymena/fish in total a volume of 20 μL). Negative control fish were anally intubated with the intubation mixture without Tetrahymena, or untreated. ELISA measurement of anti-Tetrahymena Ab titer revealed a significantly higher level of Abs in i.p.-immunized guppies, compared to the anally intubated and control fish. In addition, the efficiency of immunization was tested by monitoring guppy mortality following (i) i.p. challenge with Tetrahymena (900 Tetrahymena/fish) or (ii) cold stress followed by immersion in water containing 10,000 Tetrahymena/mL. Fish mortality on day 14 post-Tetrahymena infection by i.p. injection exceeded 50% in the control and anally intubated fish, compared to 31% in i.p.-immunized fish. Immunization did not protect from pathogen challenge by immersion. The results suggest a direct correlation between the anti-Tetrahymena Ab response and fish resistance to i.p.-injected Tetrahymena, but not to infection by immersion preceded by cold stress.

Liver transcriptome analysis in gilthead sea bream upon exposure to low temperature

BACKGROUND

Water temperature greatly influences the physiology and behaviour of teleost fish as other aquatic organisms. While fish are able to cope with seasonal temperature variations, thermal excursions outside their normal thermal range might exceed their ability to respond leading to severe diseases and death.Profound differences exist in thermal tolerance across fish species living in the same geographical areas, promoting for investigating the molecular mechanisms involved in susceptibility and resistance to low and high temperatures toward a better understanding of adaptation to environmental challenges. The gilthead sea bream, Sparus aurata, is particularly sensitive to cold and the prolonged exposure to low temperatures may lead to the "winter disease", a metabolic disorder that significantly affects the aquaculture productions along the Northern Mediterranean coasts during winter-spring season. While sea bream susceptibility to low temperatures has been extensively investigated, the cascade of molecular events under such stressful condition is not fully elucidated.

RESULTS

In the present study two groups of wild sea bream were exposed for 21 days to two temperature regimes: 16 ± 0.3°C (control group) and 6.8 ± 0.3°C (cold-exposed group) and DNA microarray analysis of liver transcriptome was carried out at different time points during cold exposure.A large set of genes was found to be differentially expressed upon cold-exposure with increasingly relevant effects being observed after three weeks at low temperature. All major known responses to cold (i.e. anti-oxidant response, increased mitochondrial function, membrane compositional changes) were found to be conserved in the gilthead sea bream, while, evidence for a key role of unfolded protein response (UPR) to endoplasmic reticulum (ER) stress, during short- and long-term exposure to cold is reported here for the first time.

CONCLUSIONS

Transcriptome data suggest a scenario where oxidative stress, altered lipid metabolism, ATP depletion and protein denaturation converge to induce ER stress. The resulting UPR activation further promotes conditions for cell damage, and the inability to resolve ER stress leads to severe liver dysfunction and potentially to death.

Metabolic fingerprinting of gilthead seabream (Sparus aurata) liver to track interactions between dietary factors and seasonal temperature variations

Farmed gilthead seabream is sometimes affected by a metabolic syndrome, known as the "winter disease", which has a significant economic impact in the Mediterranean region. It is caused, among other factors, by the thermal variations that occur during colder months and there are signs that an improved nutritional status can mitigate the effects of this thermal stress. For this reason, a trial was undertaken where we assessed the effect of two different diets on gilthead seabream physiology and nutritional state, through metabolic fingerprinting of hepatic tissue. For this trial, four groups of 25 adult gilthead seabream were reared for 8 months, being fed either with a control diet (CTRL, low-cost commercial formulation) or with a diet called "Winter Feed" (WF, high-cost improved formulation). Fish were sampled at two time-points (at the end of winter and at the end of spring), with liver tissue being taken for FT-IR spectroscopy. Results have shown that seasonal temperature variations constitute a metabolic challenge for gilthead seabream, with hepatic carbohydrate stores being consumed over the course of the inter-sampling period. Regarding the WF diet, results point towards a positive effect in terms of performance and improved nutritional status. This diet seems to have a mitigating effect on the deleterious impact of thermal shifts, confirming the hypothesis that nutritional factors can affect the capacity of gilthead seabream to cope with seasonal thermal variations and possibly contribute to prevent the onset of "winter disease".

Proteomics to study adaptations in marine organisms to environmental stress

Comparisons of proteomic responses of closely related congeners and populations have shown which cellular processes are critical to adapt to environmental stress. For example, several proteomic species comparisons showed that increasing abundances of oxidative stress proteins indicate that reactive oxygen species (ROS) represent a ubiquitous signal and possible co-stressor of warm and cold temperature, acute hyposaline and low pH stress, possibly causing a shift from pro-oxidant NADH-producing to anti-oxidant NADPH-producing and -consuming metabolic pathways. Changes in cytoskeletal and actin-binding proteins in response to several stressors, including ROS, suggest that both are important structural and functional elements in responding to stress. Disruption of protein homeostasis, e.g., increased abundance of molecular chaperones, was severe in response to acute heat stress, inducing proteolysis, but was also observed in response to chronic heat and cold stress and was concentrated to the endoplasmic reticulum during hyposaline stress. Small GTPases affecting vesicle formation and transport, Ca(2+)-signaling and ion transport responded to salinity stress in species- and population-specific ways. Aerobic energy metabolism was in general down-regulated in response to temperature, hypoxia, hyposalinity and low pH stress, but other metabolic pathways were activated to respond to increased oxidative stress or to switch metabolic fuels. Thus, comparative proteomics is a powerful approach to identify functionally adaptive variation. This article is part of a Special Issue entitled: Proteomics of non-model organisms.

Analysis of the Dreissena polymorpha gill proteome following exposure to dioxin-like PCBs: mechanism of action and the role of gender

PCBs are a persistent environmental problem due to their high stability and lipophilicity. The non-ortho- and the mono-ortho-substituted PCBs (dioxin-like-PCBs) share a common and well-described toxicity mechanism in vertebrates, initially involving binding to cytosolic AhRs. Invertebrate AhRs, however, show a lack of dioxin binding, and little information is available regarding the mechanism of toxicity of dl-PCBs in invertebrates. In this study, a proteomic approach was applied to analyse the variations in the pattern of the gill proteome of the freshwater mussel Dreissena polymorpha. Mussels were exposed to a mixture of dl-PCBs, and to perform a more in-depth evaluation, we chose to investigate the role of gender in the proteome response by analysing male and female mussels separately. The results revealed significant modulation of the gill tissue proteome: glycolysis and Ca(2+) homeostasis appear to be the main pathways targeted by dl-PCBs. In light of the differences between the male and female gill proteome profiles following exposure to dl-PCBs, further in-depth investigations of the role of gender in the protein expression profiles of a selected biological model are required.

Alterations in the Atlantic cod (Gadus morhua) hepatic thiol-proteome after methylmercury exposure

Proteomic studies in general have demonstrated that the most effective and thorough analysis of biological samples requires subfractionation and/or enrichment prior to downstream processing. In the present study, Atlantic cod (Gadus morhua) liver samples were fractionated using activated thiol sepharose to isolate hepatic proteins containing free/reactive cysteines. This subset of proteins is of special interest when studying the physiological effects attributed to methylmercury (MeHg) exposure. Methylmercury is a persistent environmental contaminant that has a potent affinity toward thiol groups, and can directly bind proteins via available cysteine residues. Further, alterations in the cod thiol-proteome following MeHg exposure (2 mg/kg body weight) were explored with two-dimensional gel electrophoresis combined with downstream mass spectrometry analyses for protein identifications. Thirty-five protein spots were found to respond to MeHg exposure, and 13 of these were identified when searching cod-specific databases with acquired mass spectrometry data. Among the identified thiol-containing proteins, some are known to respond to MeHg treatment, including constituents of the cytoskeleton, and proteins involved in oxidative stress responses, protein synthesis, protein folding, and energy metabolism. Methylmercury also appeared to affect cod heme metabolism/turnover, producing significantly altered levels of hemoglobin and hemopexin in liver following metal exposure. The latter finding suggests that MeHg may also affect the hematological system in Atlantic cod.

Proteomic approach to skin regeneration in a marine teleost: modulation by oestradiol-17β

Skin and scale formation and regeneration in teleosts have mainly been described from a morphological perspective, and few studies of the underlying molecular events exist. The present study evaluates (1) the change in the skin proteome during its regeneration in a marine teleost fish (gilthead sea bream, Sparus aurata) and (2) the impact of oestradiol-17β (Ε2) on regeneration and the involvement of oestrogen receptor (ER) isoforms. Thirty-five candidate proteins were differentially expressed (p < 0.05) between intact and regenerated skin proteome 5 days after scale removal, and 27 proteins were differentially expressed after E2 treatment. Agglomerative hierarchical clustering of the skin proteome revealed that the skin treated with E2 clustered most closely to intact skin, while regenerating untreated skin formed an independent cluster. Gene Ontology classification associated the differentially expressed proteins in E2-treated skin with developmental processes and cellular morphogenesis. The proteins modified during skin regeneration suggest a balance exists between immune response and anatomical repair. Overall, the results indicate that, even after 5 days regeneration, the composition of mature skin is not attained, and endocrine factors, in particular E2, can accelerate wound repair acting possibly via ERβs expressed in the skin-scales. Several candidate proteins probably involved in scale development, osteoglycin, lipocalin2 and lamin A and the transcription factors PHD and grainyhead were identified. Future studies of fish skin regeneration will be required to provide further insight into this multistage process, and the present study indicates it will be useful to explore immune adaptations of epithelia permanently exposed to an aqueous environment.

Comparative proteomic analysis of the hepatic response to heat stress in Muscovy and Pekin ducks: insight into thermal tolerance related to energy metabolism

The Pekin duck, bred from the mallard (Anas platyrhynchos) in china, is one of the most famous meat duck species in the world. However, it is more sensitive to heat stress than Muscovy duck, which is believed to have originated in South America. With temperature raising, mortality, laying performance, and meat quality of the Pekin duck are severely affected. This study aims to uncover the temperature-dependent proteins of two duck species using comparative proteomic approach. Duck was cultured under 39°C ± 0.5°C for 1 h, and then immediately returned to 20°C for a 3 h recovery period, the liver proteins were extracted and electrophoresed in two-dimensional mode. After analysis of gel images, 61 differentially expressed proteins were detected, 54 were clearly identified by MALDI TOF/TOF MS. Of the 54 differentially expressed protein spots identified, 7 were found in both species, whereas 47 were species specific (25 in Muscovy duck and 22 in Pekin duck). As is well known, chaperone proteins, such as heat shock protein (HSP) 70 and HSP10, were abundantly up-regulated in both species in response to heat stress. However, we also found that several proteins, such as α-enolase, and S-adenosylmethionine synthetase, showed different expression patterns in the 2 duck species. The enriched biological processes were grouped into 3 main categories according to gene ontology analysis: cell death and apoptosis (20.93%), amino acid metabolism (13.95%) and oxidation reduction (20.93%). The mRNA levels of several differentially expressed protein were investigated by real-time RT-PCR. To our knowledge, this study is the first to provide insights into the differential expression of proteins following heat stress in ducks and enables better understanding of possible heat stress response mechanisms in animals.

Naturally occurring stable isotopes reflect changes in protein turnover and growth in gilthead sea bream (Sparus aurata) juveniles under different dietary protein levels

Ideal nutritional conditions are crucial to sustainable aquaculture due to economic and environmental issues. Here we apply stable isotope analysis as an indicator of fish growth and feeding balance, to define the optimum diet for efficient growing conditions. Juveniles of gilthead sea bream were fed with six isoenergetic diets differing in protein to lipid proportion (from 41/26 to 57/20). As protein intake increased, δ¹⁵N and Δδ¹⁵N of muscle and Δδ¹⁵N and Δδ¹³C of its protein fraction decreased, indicating lower protein turnover and higher protein deposition in muscle. This is reflected in the inverse relationship found between Δδ¹⁵N and growth rate, although no differences were observed in either parameter beyond the protein/lipid proportion 47/23. Principal component analysis (PCA) also signaled 47/23 diet as the pivotal point with the highest growing efficiency, with isotopic parameters having the highest discrimination load. Thus, muscle isotope composition, especially ¹⁵N, can be used to evaluate nutritional status in farmed fish.

Significant modulation of the hepatic proteome induced by exposure to low temperature in Xenopus laevis

The African clawed frog, Xenopus laevis, is an ectothermic vertebrate that can survive at low environmental temperatures. To gain insight into the molecular events induced by low body temperature, liver proteins were evaluated at the standard laboratory rearing temperature (22°C, control) and a low environmental temperature (5°C, cold exposure). Using nano-flow liquid chromatography coupled with tandem mass spectrometry, we identified 58 proteins that differed in abundance. A subsequent Gene Ontology analysis revealed that the tyrosine and phenylalanine catabolic processes were modulated by cold exposure, which resulted in decreases in hepatic tyrosine and phenylalanine, respectively. Similarly, levels of pyruvate kinase and enolase, which are involved in glycolysis and glycogen synthesis, were also decreased, whereas levels of glycogen phosphorylase, which participates in glycogenolysis, were increased. Therefore, we measured metabolites in the respective pathways and found that levels of hepatic glycogen and glucose were decreased. Although the liver was under oxidative stress because of iron accumulation caused by hepatic erythrocyte destruction, the hepatic NADPH/NADP ratio was not changed. Thus, glycogen is probably utilized mainly for NADPH supply rather than for energy or glucose production. In conclusion, X. laevis responds to low body temperature by modulating its hepatic proteome, which results in altered carbohydrate metabolism.

Quantitative proteomic analysis reveals the mode-of-action for chronic mercury hepatotoxicity to marine medaka (Oryzias melastigma)

Mercury (Hg) is a widespread persistent pollutant in aquatic ecosystems. We investigated the protein profiles of medaka (Oryzias melastigma) liver chronically exposed to different mercuric chloride (HgCl2) concentrations (1 or 10 μg/L) for 60 d using two-dimensional difference gel electrophoresis (2D-DIGE), as well as cell ultrastructure and Hg content analysis of the hepatic tissue. The results showed that Hg exposure significantly increased metal accumulation in the liver, and subsequently damaged liver ultrastructure. Comparison of the 2D-DIGE protein profiles of the exposed and control groups revealed that the abundance of 45 protein spots was remarkably altered in response to Hg treatment. The altered spots were subjected to matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry analysis, with the resultant identification of 33 spots. These proteins were mainly involved in cytoskeleton assembly, oxidative stress, and energy production. Among them, several proteins related to mitochondrial function (e.g. respiratory metabolism) were significantly altered in the treated hepatocytes, implying that this organelle might be the primary target for Hg attack in the cells. This study provided new insights into the molecular mechanisms and/or toxic pathways by which chronic Hg hepatotoxicity affects aquatic organisms, and also provided basic information for screening potential biomarkers for aquatic Hg monitoring.

Starvation and re-feeding affect Hsp expression, MAPK activation and antioxidant enzymes activity of European sea bass (Dicentrarchus labrax)

In the context of food deprivation in fish (wild and farmed), understanding of cellular responses is necessary in order to develop strategies to minimize stress caused by starvation in the aquaculture section. The present study evaluates the effects of long term starvation (1F-3S: one-month feeding-three-month starvation) and starvation/re-feeding (2S-2F: two-month starvation-two-month re-feeding) compared to the control group (4F-0S: four-month feeding-zero month starvation) on cellular stress response and antioxidant defense in organs, like the intestine, the liver, the red and white muscle of European sea bass Dicentrarchus labrax. Molecular responses were addressed through the expression of Hsp70 and Hsp90, the phosphorylation of stress-activated protein kinases and particularly p38 mitogen-activated protein kinase (p38 MAPK) and the extracellular signal-regulated kinases (ERK-1/2). For the determination of the effect of the oxidative stress caused by food deprivation and/or re-feeding, the (maximum) activities of antioxidant enzymes such as glutathione peroxidise (GPx), catalase (CAT) and superoxide dismutase (SOD) as well as the determination of thiobarbituric acid reactive substances (TBARS) were studied. The experimental feeding trials caused a tissue distinct and differential response on the cellular and antioxidant capacity of sea bass not only during the stressful process of starvation but also in re-feeding. Specifically, the intestine phosphorylation of ERKs and antioxidant enzymatic activities increased in the 2S-2F fish group, while in the 1F-3S group an increase was detected in the levels of the same proteins except for GPx. In the liver and the red muscle of 2S-2F fish, decreased Hsp70 and phosphorylated p38 MAPK levels and increased Hsp90 levels were observed. Additionally, SOD activity decreased in the red muscle of 2S-2F and 1F-3S groups. In the liver and red muscle of 1F-3S group Hsp70 levels increased, while the activation of p38 MAPK in the liver decreased. In the white muscle, Hsp90 levels decreased and the phosphorylation of p38 MAPK increased in both feeding regimes compared to control. In the same tissue, GPx and catalase levels were decreased in 2S-2F regime, while SOD levels were decreased in 1F-3S regime.

Interaction of temperature and an environmental stressor: Moina macrocopa responds with increased body size, increased lifespan, and increased offspring numbers slightly above its temperature optimum

For organisms, temperature is one of the most important environmental factors and gains increasing importance due to global warming, since increasing temperatures may pose organisms close to their environmental tolerance limits and, thus, they may become more vulnerable to environmental stressors. We analyzed the temperature-dependence of the water-soluble antioxidant capacity of the cladoceran Moina macrocopa and evaluated its life trait variables with temperature (15, 20, 25, 30°C) and humic substance (HS) concentrations (0, 0.18, 0.36, 0.90, 1.79 mM DOC) as stressors. Temperatures below and above the apparent optimum (20°C) reduced the antioxidative capacity. Additions of HSs increased body length, but decreased mean lifespan at 15 and 20°C. There was no clear HS-effect on offspring numbers at 15, 20, and 30°C. At 25°C with increasing HS-concentration, lifespan was extended and offspring numbers increased tremendously, reaching 250% of the control. Although the applied HS preparation possesses estrogenic and antiandrogenic activities, a xenohormone mechanism does not seem plausible for the reproductive increase, because comparable effects did not occur at other temperatures. A more convincing explanation appears to be the mitohormesis hypothesis which states that a certain increase of reactive oxygen production leads to improved health and longevity and, with Moina, also to increased offspring numbers. Our results suggest that at least with the eurythermic M. macrocopa, a temperature above the optimum can be beneficial for several life trait variables, even when combined with a chemical stressor. Temperatures approximately 10°C above its optimum appear to adversely affect the lifespan and reproduction of M. macrocopa. This indicates that this cladoceran species seems to be able to utilize temperature as an ecological resource in a range slightly above its thermal optimum.

Marine proteomics: a critical assessment of an emerging technology

The application of proteomics to marine sciences has increased in recent years because the proteome represents the interface between genotypic and phenotypic variability and, thus, corresponds to the broadest possible biomarker for eco-physiological responses and adaptations. Likewise, proteomics can provide important functional information regarding biosynthetic pathways, as well as insights into mechanism of action, of novel marine natural products. The goal of this review is to (1) explore the application of proteomics methodologies to marine systems, (2) assess the technical approaches that have been used, and (3) evaluate the pros and cons of this proteomic research, with the intent of providing a critical analysis of its future roles in marine sciences. To date, proteomics techniques have been utilized to investigate marine microbe, plant, invertebrate, and vertebrate physiology, developmental biology, seafood safety, susceptibility to disease, and responses to environmental change. However, marine proteomics studies often suffer from poor experimental design, sample processing/optimization difficulties, and data analysis/interpretation issues. Moreover, a major limitation is the lack of available annotated genomes and proteomes for most marine organisms, including several "model species". Even with these challenges in mind, there is no doubt that marine proteomics is a rapidly expanding and powerful integrative molecular research tool from which our knowledge of the marine environment, and the natural products from this resource, will be significantly expanded.

Environmental proteomics of the mussel Mytilus: implications for tolerance to stress and change in limits of biogeographic ranges in response to climate change

Climate change will affect temperature extremes and averages, and hyposaline conditions in coastal areas due to extreme precipitation events and oceanic pH. How climate change will push species close to, or beyond, their physiological tolerance limits as well as change the limits of their biogeographic ranges can probably be investigated best in species that have already responded to climate change and whose distribution ranges are currently in flux. Blue mussels provide such a study system, with the invading warm-adapted Mediterranean Mytilus galloprovincialis having replaced the native more cold-adapted Mytilus trossulus from the southern part of its range in southern California over the past century, possibly due to climate change. However, freshwater input may prevent the latter species from expanding further north. We used a proteomics approach to characterize the responses of the two congeners to acute heat stress, chronic thermal acclimation, and hyposaline stress. In addition, we investigated the proteomic changes in response to decreasing seawater pH in another bivalve, the eastern oyster Crassostrea virginica. The results suggest that reactive oxygen species (ROS) are a common costressor during environmental stress, including oceanic acidification, and possibly cause modifications of cytoskeletal elements. All stressors disrupted protein homeostasis, indicated by the induction of molecular chaperones and, in the case of acute heat stress, proteasome isoforms, possibly due both to protein denaturation directly by the stressor and to the production of ROS. Acute stress by heat and hyposalinity changed several small G-proteins implicated in cytoskeletal modifications and vesicular transport, respectively. Changes in abundance of proteins involved in energy metabolism and ROS scavenging further suggest a possible trade-off during acute and chronic stress from heat and cold between ROS-generating NADH-producing pathways and ROS-scavenging NADPH-producing pathways, especially through the reaction of NADPH-dependent isocitrate dehydrogenase and the pentose-phosphate pathway. Some of the proteomic changes may not constitute de novo protein synthesis but rather shifts in abundance of isoforms differing in posttranslational modifications, specifically acetylation by a NAD-dependent deacetylase (sirtuin). Interspecific differences suggest that these processes set physiological tolerance limits and thereby contribute to recent biogeographic shifts in range, possibly caused by climate change.

Effects of triclosan in the freshwater mussel Dreissena polymorpha: a proteomic investigation

Triclosan (TCS, 5-chloro-2-(2,4-dichlorophenoxy)phenol) is commonly used in several personal care products, textiles, and children's toys. Because the removal of TCS by wastewater treatment plants is incomplete, its environmental fate is to be discharged into freshwater ecosystems, where its ecotoxicological impact is still largely unexplored. Previously, we began a structured multi-tiered approach in order to evaluate TCS toxicity in the freshwater mussel Dreissena polymorpha. The results of our previous studies, based on in vitro and in vivo experiments, highlighted a pronounced cytogenotoxic effect exerted by TCS, and showed that an increase in oxidative stress was likely to be one of its main toxic mechanisms. In this work, in order to investigate TCS toxicity mechanisms in aquatic non-target species in greater depth, we decided to use a proteomic approach, analysing changes in protein expression profiles in gills of D. polymorpha exposed for seven days to TCS. Moreover, thiobarbituric acid reactive substances (TBARS) were measured to investigate further the role played by TCS in inducing oxidative stress. Finally, TCS bioaccumulation in mussel tissues was also assessed, to ensure an effective accumulation of the toxicant. Our results not only confirmed the role played by TCS in inducing oxidative stress, but furthered knowledge about the mechanism exerted by TCS in inducing toxicity in an aquatic non-target organisms. TCS induced significant alterations in protein expression profiles in gills of D. polymorpha. The wide range of proteins affected suggested that this chemical has marked effects on various biological processes, especially those involved in calcium binding or stress response. We also confirmed that the proteomic analysis, using 2-DE and de novo sequencing, is a reliable and powerful approach to investigate cellular responses to pollutants in a non-model organism with few genomic sequences available in databases.

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.

PROTEOMICS in aquaculture: applications and trends

Over the last forty years global aquaculture presented a growth rate of 6.9% per annum with an amazing production of 52.5 million tonnes in 2008, and a contribution of 43% of aquatic animal food for human consumption. In order to meet the world's health requirements of fish protein, a continuous growth in production is still expected for decades to come. Aquaculture is, though, a very competitive market, and a global awareness regarding the use of scientific knowledge and emerging technologies to obtain a better farmed organism through a sustainable production has enhanced the importance of proteomics in seafood biology research. Proteomics, as a powerful comparative tool, has therefore been increasingly used over the last decade to address different questions in aquaculture, regarding welfare, nutrition, health, quality, and safety. In this paper we will give an overview of these biological questions and the role of proteomics in their investigation, outlining the advantages, disadvantages and future challenges. A brief description of the proteomics technical approaches will be presented. Special focus will be on the latest trends related to the aquaculture production of fish with defined nutritional, health or quality properties for functional foods and the integration of proteomics techniques in addressing this challenging issue.

Proteomic responses of blue mussel (Mytilus) congeners to temperature acclimation

The ability to acclimate to variable environmental conditions affects the biogeographic range of species, their success at colonizing new habitats, and their likelihood of surviving rapid anthropogenic climate change. Here we compared responses to temperature acclimation (4 weeks at 7, 13 and 19°C) in gill tissue of the warm-adapted intertidal blue mussel Mytilus galloprovincialis, an invasive species in the northeastern Pacific, and the cold-adapted M. trossulus, the native congener in the region, to better understand the physiological differences underlying the ongoing competition. Using two-dimensional gel electrophoresis and tandem mass spectrometry, we showed that warm acclimation caused changes in cytoskeletal composition and proteins of energy metabolism in both species, consistent with increasing rates of filtration and respiration due to increased ciliary activity. During cold acclimation, changes in cytoskeletal proteins were accompanied by increasing abundances of oxidative stress proteins and molecular chaperones, possibly because of the increased production of aldehydes as indicated by the upregulation of aldehyde dehydrogenase. The cold-adapted M. trossulus showed increased abundances of molecular chaperones at 19°C, but M. galloprovincialis did not, suggesting that the two species differ in their long-term upper thermal limits. In contrast, the warm-adapted M. galloprovincialis showed a stronger response to cold acclimation than M. trossulus, including changes in abundance in more proteins and differing protein expression profiles between 7 and 13°C, a pattern absent in M. trossulus. In general, increasing levels of oxidative stress proteins inversely correlate with modifications in Krebs cycle and electron transport chain proteins, indicating a trade-off between oxidative stress resistance and energy production. Overall, our results help explain why M. galloprovincialis has replaced M. trossulus in southern California over the last century, but also suggest that M. trossulus may maintain a competitive advantage at colder temperatures. Anthropogenic global warming may reinforce the advantage M. galloprovincialis has over M. trossulus in the warmer parts of the latter’s historical range.

Molecular characterization and expression analysis of six peroxiredoxin paralogous genes in gilthead sea bream (Sparus aurata): insights from fish exposed to dietary, pathogen and confinement stressors

The aim of this work was to underline the physiological role of the antioxidant peroxiredoxin (PRDX) family in gilthead sea bream (Sparus aurata L.), a perciform fish extensively cultured in the Mediterranean area. First, extensive BLAST searches were done on the gilthead sea bream cDNA database of the AQUAMAX European Project (www.sigenae.org/iats), and six contigs were unequivocally identified as PRDX1-6 after sequence completion by RT-PCR. The phylogenetic analysis evidenced three major clades corresponding to PRDX1-4 (true 2-Cyst PRDX subclass), PRDX5 (atypical 2-Cys PRDX subclass) and PRDX6 (1-Cys PRDX subclass) that reflected the present hierarchy of vertebrates. However, the PRDX2 branch of modern fish including gilthead sea bream was related to the monophyletic PRDX1 node rather than to PRDX2 cluster of mammals and primitive fish, which probably denotes the acquisition of novel functions through vertebrate evolution. Transcriptional studies by means of quantitative real-time PCR evidenced a ubiquitous PRDX gene expression that was tissue specific for each PRDX isoform. In a second set of transcriptional studies, liver and head kidney were chosen as target tissues in fish challenged with i) the intestinal parasite Enteromyxum leei, ii) a plant oil (VO) diet with deficiencies in essential fatty acids and iii) prolonged exposure to high-rearing densities. These studies showed that PRDX genes were highly and mostly constitutively expressed in the liver and were not affected by dietary intervention or high density. In contrast, head kidney was highly sensitive to the different experimental challenges: significantly lower values were found for PRDX5 in the three trials, for PRDX6 in parasitized and high density fish and for PRDX1 in parasitized and VO fish. PRDX2, 3 and 5 were decreased only in VO, high density and parasitized animals, respectively. These findings would highlight the role of PRDXs as integrative and highly predictive biomarkers of health and welfare in fish and gilthead sea bream in particular.

The proteomic response of sea squirts (genus Ciona) to acute heat stress: a global perspective on the thermal stability of proteins

Congeners belonging to the genus Ciona have disparate distributions limited by temperature. Ciona intestinalis is more widespread with a cosmopolitan distribution ranging from tropical to sub-arctic zones, while Ciona savignyi is limited to temperate-latitudes of the northern Pacific Ocean. To compare the heat stress response between congeners, we quantified changes in protein expression using proteomics. Animals were exposed to 22°C, 25°C, and 28°C for 6h, then recovered at a control temperature (13°C) for 16h (high heat stress experiment). In a second experiment we exposed animals to lower levels of heat stress at 18°C, 20°C, and 23°C, with a 16°C control. A quantitative analysis, using 2D gel electrophoresis and MALDI-TOF/TOF mass spectrometry (with a 69% and 93% identification rate for Ciona intestinalis and Ciona savignyi, respectively), showed changes in a number of protein functional groups, including molecular chaperones, extracellular matrix proteins, calcium-binding proteins, cytoskeletal proteins and proteins involved in energy metabolism. Our results indicate that C. intestinalis maintains higher constitutive levels of molecular chaperones than C. savignyi, suggesting that it is prepared to respond faster to thermal stress. Systematic discrepancies between estimated versus predicted molecular masses of identified proteins differed between protein families and were more pronounced under high heat conditions, suggesting that thermal sensitivities are lower for cytoskeletal proteins and ATP-synthase than for any other protein group represented on 2D gels.

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.

Influence of acute cadmium exposure on the liver proteome of a teleost fish, ayu (Plecoglossus altivelis)

Cadmium (Cd) is a toxic heavy metal that causes the disruption of a variety of physiological processes. In this study, the effect of Cd on liver proteome of ayu, Plecoglossus altivelis, was investigated by two-dimensional gel electrophoresis (2-DE) and matrix assisted laser desorption ionization time-of-flight tandem mass spectrometry (MALDI-TOF-MS/MS). Twenty-three altered protein spots were successfully identified. They were involved in oxidative stress response, metal metabolism, methylation, and so on. The mRNA expression of 60S acidic ribosomal protein P0, heat shock protein 70, apolipoprotein A-I, betaine-homocysteine S-methyltransferase, parahox cluster neighbor, and transferrin was subsequently determined by real-time PCR. The mRNA expression of these genes was consistent with proteomic results. These findings enrich our knowledge on the influence of Cd toxicity to teleost fish, and may be worthy of further investigation to develop biomarkers.

Differential protein expression in two bivalve species; Mytilus galloprovincialis and Corbicula fluminea; exposed to Cylindrospermopsis raciborskii cells

The cyanobacteria Cylindrospermopsis raciborskii is considered a threat to aquatic organisms due to the production of the toxin cylindrospermopsin (CYN). Despite the numerous reports evidencing the toxic effects of C. raciborskii cells and CYN in different species, not much is known regarding the toxicity mechanisms associated with this toxin and the cyanobacteria. In this work, a proteomics approach based in the two-dimensional gel electrophoresis and mass spectrometry was used to study the effects of the exposure of two bivalve species, Mytilus galloprovincialis and Corbicula fluminea, to CYN producing (CYN+) and non-producing (CYN-) C. raciborskii cells. Additionally the activities of glutathione S-transferase (GST) and glutathione peroxidase (GPx) were determined. Alterations in actin and tubulin isoforms were detected in gills of both bivalve species and digestive gland of M. galloprovincialis when exposed to CYN- and CYN+ cells. Moreover, GST and GPx activities changed in gills and digestive tract of bivalves exposed to both C. raciborskii freeze dried cells, in comparison to control animals exposed to the green alga Chlorella vulgaris. These results suggest the induction of physiological stress and tissue injury in bivalves by C. raciborskii. This condition is supported by the changes observed in GPx and GST activities which indicate alterations in the oxidative stress defense mechanisms. The results also evidence the capacity of CYN non-producing C. raciborskii to induce biochemical responses and therefore its toxicity potential to bivalves. The heat shock protein 60 (HSP60), extrapallial (EP) fluid protein and triosephosphate isomerase homologous proteins from gills of M. galloprovincialis were down-regulated specifically with the presence of CYN+ C. raciborskii cells. The presence of CYN may lead to additional toxic effects in M. galloprovincialis. This work demonstrates that proteomics is a powerful approach to characterize the biochemical effects of C. raciborskii and to investigate the physiological condition of the exposed 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.

Environmental proteomics: changes in the proteome of marine organisms in response to environmental stress, pollutants, infection, symbiosis, and development

Environmental proteomics, the study of changes in the abundance of proteins and their post-translational modifications, has become a powerful tool for generating hypotheses regarding how the environment affects the biology of marine organisms. Proteomics discovers hitherto unknown cellular effects of environmental stressors such as changes in thermal, osmotic, and anaerobic conditions. Proteomic analyses have advanced the characterization of the biological effects of pollutants and identified comprehensive and pollutant-specific sets of biomarkers, especially those highlighting post-translational modifications. Proteomic analyses of infected organisms have highlighted the broader changes occurring during immune responses and how the same pathways are attenuated during the maintenance of symbiotic relationships. Finally, proteomic changes occurring during the early life stages of marine organisms emphasize the importance of signaling events during development in a rapidly changing environment. Changes in proteins functioning in energy metabolism, cytoskeleton, protein stabilization and turnover, oxidative stress, and signaling are common responses to environmental change.

Dietary keto-acid feed-back on pituitary activity in gilthead sea bream: effects of oral doses of AKG. A proteomic approach

The influence of a daily oral dose of alpha-ketoglutarate (AKG, 0.1 g/kg body weight), an intermediate metabolite in the Krebs cycle and a dietary additive, on the pituitary proteome of gilthead sea bream was determined by two-dimensional electrophoresis (2-DE). A high-resolution map of the sea bream pituitary proteome was generated. Proteins with a modified expression between Controls and AKG treated fish were further analysed by MALDI-TOF/TOF-MS and liquid chromatography combined with a nanoelectrospray (LC-MS/MS). The main changes in the proteome induced by AKG treatment were grouped. Metabolic proteins up-regulated with AKG supplementation included fructose-bis-phosphate aldolase, glyceraldehyde-phosphate dehydrogenase and malate dehydrogenase, all related to glucose metabolism (p<0.000). Protein folding related up-regulation with AKG supplementation included two isoforms of heat shock proteins as well as cyclophylin and chaperonin (p<0.000). An unexpected form of apolipoprotein-A-1 with lower molecular weight (15-16 kDa) was evidenced as being highly abundant in the pituitary proteome of Controls, yet it was down-regulated by AKG treatment. Finally, proteins found to be associated with regeneration of neural function namely cofilin and Vat-protein were up-regulated after AKG supplementation. The only hormone to be modified by AKG treatment was somatolactin, which was significantly down-regulated cf. Controls. In summary, these results provide evidence of a potential endocrine/metabolic regulatory loop activated by AKG supplementation.

The molecular basis of aerobic metabolic remodeling differs between oxidative muscle and liver of threespine sticklebacks in response to cold acclimation

We sought to determine the molecular basis of elevations in aerobic metabolic capacity in the oxidative muscle and liver of Gasterosteus aculeatus in response to cold acclimation. Fishes were cold- or warm-acclimated for 9 wk and harvested on days 1, 2, and 3 and weeks 1, 4, and 9 of cold acclimation at 8 degrees C, and on day 1 and week 9 of warm acclimation at 20 degrees C. Mitochondrial volume density was quantified using transmission electron microscopy and stereological techniques in warm- and cold-acclimated fishes harvested after 9 wk at 20 or 8 degrees C. Changes in aerobic metabolic capacity were assessed by measuring the maximal activity of citrate synthase (CS) and cytochrome-c oxidase (COX) in fishes harvested throughout the acclimation period. Transcript levels of the aerobic metabolic genes CS, COXIII, and COXIV, and known regulators of mitochondrial biogenesis, including peroxisome proliferator-activated receptor-gamma coactivators-1alpha and -1beta (PGC-1alpha and PGC-1beta), nuclear respiratory factor-1 (NRF-1), and mitochondrial transcription factor-A were measured in fishes harvested throughout the acclimation period using quantitative real-time PCR. The maximal activities of CS and COX increased in response to cold acclimation in both tissues, but mitochondrial volume density only increased in oxidative muscle (P < 0.05). The time course for changes in aerobic metabolic capacity differed between liver and muscle. The expression of CS increased within 1 wk of cold acclimation in liver and was correlated with an increase in mRNA levels of NRF-1 and PGC-1beta. Transcript levels of aerobic metabolic genes increased later in oxidative muscle, between weeks 4 and 9 of cold acclimation and were correlated with an increase in mRNA levels of NRF-1 and PGC-1alpha. These results show that aerobic metabolic remodeling differs between liver and muscle in response to cold acclimation and may be triggered by different stimuli.