A proteomic analysis of green and white sturgeon larvae exposed to heat stress and selenium

Metabolomics in sturgeon research: a mini-review

Sturgeons are ancient fish, with 27 species distributed in the Northern Hemisphere. This review first touches upon the significance of sturgeons in the context of their biological, ecological, and economic importance, highlighting their status as "living fossils" and the challenges they face in genomic research due to their diverse chromosome numbers. This review then discusses how omics technologies (genomics, transcriptomics, proteomics, and metabolomics) have been used in sturgeon research, which so far has only been done on Acipenser species. It focuses on metabolomics as a way to better understand how sturgeons work and how they react to their environment. Specific studies in sturgeon metabolomics are cited, showing how metabolomics has been used to investigate various aspects of sturgeon biology, such as growth, reproduction, stress responses, and nutrition. These studies demonstrate the potential of metabolomics in improving sturgeon aquaculture practices and conservation efforts. Overall, the review suggests that metabolomics, as a relatively new scientific tool, has the potential to enhance our understanding of sturgeon biology and aid in their conservation and sustainable aquaculture, contributing to global food security efforts.

Cross-species apical microinjected selenomethionine toxicity in embryo-larval fishes

Selenium (Se) is an essential micronutrient that becomes toxic when exposures minimally exceed those that are physiologically required. Studies on Se contaminated aquatic environments have identified that embryo-larval fishes are at particular risk of Se toxicity, primarily due to maternal Se transfer to developing eggs during oogenesis. This study emulated these exposures in embryo-larval fathead minnow (FHM), rainbow trout (RBT), white sucker (WSu), and white sturgeon (WSt) using embryonic selenomethionine (SeMet) microinjections. Adverse Se-outcomes observed across these species included spinal and edematous deformities, total individuals deformed, and reduced survival. Spinal deformity was the most sensitive sublethal endpoint and developed at the lowest concentrations in WSt (10 % effects concentration (EC10) = 12.42 μg (total) Se/g dry weight (d.w.)) followed by WSu (EC10 = 14.49 μg Se/g d.w.) and FHM (EC10 = 18.10 μg Se/g d.w.). High mortality was observed in RBT, but SeMet influences were confounded by the species' innate sensitivity to the microinjections themselves. 5 % hazardous concentrations derived across exposure type data subsets were ∼49 % higher when derived from within-species maternal transfer exclusive data as opposed to all, or within-species microinjection exclusive, data. These results support the current exclusion of SeMet microinjections during regulatory guideline derivation and their inclusion when studying mechanistic Se toxicity across phylogenetically distant fishes.

Innate immune and chronic heat stress responses in sturgeons: Advances and insights from studies on Russian sturgeons

Chronic stress deteriorates the immune function of fish, thereby increasing their vulnerability to infections. However, the molecular and cellular mechanisms underlying stress-mediated immunosuppression and infection susceptibility in fish remain largely unknown. Understanding these mechanisms will contribute to improving fish welfare and their farm production. Herein, we review the challenges of sturgeon aquaculture in subtropical countries, where current climate change has giving rise to significant temperature increments during summer. This leads to the exposure of fish to stressful conditions during these months. Chronic heat stress deserves attention considering the rapid warming rate of the planet. It is already affecting wild fish populations, with disastrous consequences for sturgeons, which are one of the most endangered fish species in the world. In this context, we discuss the most recent advances through the studies on the effects of chronic heat stress on the innate immune components of sturgeons. To this end, we summarise the findings of studies focusing on the aquaculture of Russian sturgeons and observations made on other Acipenser species. Special attention is given to acute-phase proteins, as they might be valuable biomarkers of heat stress and infection, with applicability in monitoring the fish health status in farms.

Integrated biochemical, transcriptomic and metabolomic analyses provide insight into heat stress response in Yangtze sturgeon (Acipenser dabryanus)

Temperature fluctuations caused by climate change and global warming pose a great threat to various species. Most fish are particularly vulnerable to elevated temperatures. Understanding the mechanism of high-temperature tolerance in fish can be beneficial for proposing effective strategies to help fish cope with global warming. In this study, we systematically studied the effects of high temperature on Acipenser dabryanus, an ancient living fossil and flagship species of the Yangtze River, at the histological, biochemical, transcriptomic and metabolomic levels. Intestinal and liver tissues from the control groups (18 °C) and acute heat stress groups (30 °C) of A. dabryanus were sampled for histological observation and liver tissues were assessed for transcriptomic and metabolomic profiling. Histopathological analysis showed that the intestine and liver tissues were damaged after heat stress. The plasma cortisol content and the levels of oxidative stress markers (catalase/glutathione reductase) and two aminotransferases (aspartate aminotransferase/alanine aminotransferase) increased significantly in response to acute heat stress. Transcriptomic and metabolomic methods showed 6707 upregulated and 4189 downregulated genes and 64 upregulated and 78 downregulated metabolites in the heat stress group. Heat shock protein (HSP) genes showed striking changes in expression under heat stress, with 21 genes belonging to the HSP30, HSP40, HSP60, HSP70 and HSP90 families significantly upregulated by short-term heat stress. The majority of genes associated with ubiquitin and various immune-related pathways were also markedly upregulated in the heat stress group. In addition, the combined analysis of metabolites and gene profiles suggested an enhancement of amino acid metabolism and glycometabolism and the suppression of fatty acid metabolism during heat stress, which could be a potential energy conservation strategy for A. dabryanus. To the best of our knowledge, the present study represents the first attempt to reveal the mechanisms of heat stress responses in A. dabryanus, which can provide insights into improved cultivation of fish in response to global warming.

A different transcriptional landscape sheds light on Russian sturgeon (Acipenser gueldenstaedtii) mechanisms to cope with bacterial infection and chronic heat stress

Sturgeons are chondrostean fish of high economic value and critically endangered due to anthropogenic activities, which has led to sturgeon aquaculture development. Russian sturgeon (Acipenser gueldenstaedtii), the second most important species reared for caviar, is successfully farmed in subtropical countries, including Uruguay. However, during the Uruguayan summer, sturgeons face intolerable warmer temperatures that weaken their defences and favour infections by opportunistic pathogens, increasing fish mortality and farm economic losses. Since innate immunity is paramount in fish, for which the liver plays a key role, we used deep RNA sequencing to analyse differentially expressed genes in the liver of Russian sturgeons exposed to chronic heat stress and challenged with Aeromonas hydrophila. We assembled 149.615 unigenes in the Russian sturgeon liver transcriptome and found that metabolism and immune defence pathways are among the top five biological processes taking place in the liver. Chronic heat stress provoked profound effects on liver biological functions, up-regulating genes related to protein folding, heat shock response and lipid and protein metabolism to meet energy demands for coping with heat stress. Besides, long-term exposure to heat stress led to cell damage triggering liver inflammation and diminishing liver ability to mount an innate response to A. hydrophila challenge. Accordingly, the reprogramming of liver metabolism over an extended period had detrimental effects on fish health, resulting in weight loss and mortality, with the latter increasing after A. hydrophila challenge. To our knowledge, this is the first transcriptomic study describing how chronic heat-stressed sturgeons respond to a bacterial challenge, suggesting that liver metabolism alterations have a negative impact on the innate anti-bacterial response.

Heat Stress Weakens the Skin Barrier Function in Sturgeon by Decreasing Mucus Secretion and Disrupting the Mucosal Microbiota

Heat stress induced by global warming has damaged the well-being of aquatic animals. The skin tissue plays a crucial role as a defense barrier to protect organism, however, little is known about the effect of heat stress on fish skin, particularly in cold-water fish species. Here, we investigated the effects of mild heat stress (24°C, MS) and high heat stress (28°C, HS) on Siberian sturgeon skin using RNA-seq, histological observation, and microbial diversity analysis. In RNA-seq, 8,819 differentially expressed genes (DEGs) in MS vs. C group and 12,814 DEGs in HS vs. C group were acquired, of which the MS vs. C and HS vs. C groups shared 3,903 DEGs, but only 1,652 DEGs were successfully annotated. The shared DEGs were significantly enriched in pathways associating with mucins synthesis. Histological observation showed that the heat stresses significantly reduced the number of skin mucous cells and induced the damages of epidermis. The microbial diversity analysis elicited that heat stress markedly disrupted the diversity and abundance of skin microbiota by increasing of potential pathogens (Vibrionimonas, Mesorhizobium, and Phyllobacterium) and decreasing of probiotics (Bradyrhizobium and Methylovirgula). In conclusion, this study reveals that heat stress causes adverse effects on sturgeon skin, reflecting in decreasing the mucus secretion and disordering the mucosal microbiota, which may contribute to develop the preventive strategy for heat stress caused by global warming.

Organochlorine and Metal Contaminants in the Blood Plasma of Green Sturgeon Caught in Washington Coastal Estuaries

Non-invasive monitoring was used to evaluate the concentrations of 40 contaminants in the blood plasma of the North American Green Sturgeon Acipenser medirostris caught and released from three estuaries in Washington State. The highest contaminant concentrations were found in fish caught in the most urbanized sites. Few statistical differences were found when evaluating contaminant levels according to sex, maturation stage, or distinct population segments of Green Sturgeon. The results indicate that recent exposure to legacy contaminants was reflected in Green Sturgeon plasma. Aldrin, 4,4-DDE, α-HCH, copper, and selenium were the most frequently detected contaminants. This study also explored the challenges of assessing toxicity in threatened species using non-lethal approaches. There is currently a lack of environmental contaminant monitoring data in estuaries frequented by Green Sturgeon and limited plasma to tissue toxicity correlations.

Ribosomal Protein SA-Positive Neutrophil Elicits Stronger Phagocytosis and Neutrophil Extracellular Trap Formation and Subdues Pro-Inflammatory Cytokine Secretion Against Streptococcus suis Serotype 2 Infection

Streptococcus suis serotype 2 (SS2), an important zoonotic pathogen that causes septicemia, arthritis, and irreversible meningitis in pigs and humans, can be transmitted to humans from pigs. S. suis causes huge economic losses to the swine industry and poses a serious threat to public health. Previously, we found that the brain tissues of mice with SS2-induced meningitis showed disrupted structural integrity and significantly enhanced polymorphonuclear neutrophil (PMN) infiltration. We showed that the brain tissues of SS2-infected mice had increased ribosomal protein SA (RPSA)-positive PMN counts. However, the inflammatory responses of RPSA⁺ PMNs to SS2 and their effects on the blood-brain barrier (BBB) remain unclear. Therefore, in studying the pathogenesis of SS2-induced meningitis, it is essential that we explore the functions of RPSA⁺ PMNs and their effects on the BBB. Herein, using flow cytometry and immunofluorescence microscopy analyses, we found that RPSA expression enhances PMN-induced phagocytosis and PMN-induced formation of neutrophil extracellular traps (NETs), which facilitate further elimination of bacteria. PMN surface expression of RPSA also alleviates local inflammation and tissue injuries by inhibiting secretion of the pro-inflammatory cytokines, TNF-α and IL-6. Moreover, the single-cell BBB model showed that RPSA disrupts BBB integrity by downregulating expression of tight junction-associated membrane proteins on PMNs. Taken together, our data suggest that PMN-surface expression of RPSA is a double-edged sword. RPSA+ PMN owns a stronger ability of bacterial cleaning and weakens inflammatory cytokines release which are useful to anti-infection, but does hurt BBB. Partly, RPSA+ PMN may be extremely useful to control the infection as a therapeutic cellular population, following novel insights into the special PMN population.

Salmonid gene expression biomarkers indicative of physiological responses to changes in salinity and temperature, but not dissolved oxygen

An organism's ability to respond effectively to environmental change is critical to its survival. Yet, life stage and overall condition can dictate tolerance thresholds to heightened environmental stressors, such that stress may not be equally felt across individuals and at all times. Also, the transcriptional responses induced by environmental changes can reflect both generalized responses as well as others that are highly specific to the type of change being experienced. Thus, if transcriptional biomarkers specific to a stressor, even under multi-stressor conditions, can be identified, the biomarkers could then be applied in natural environments to determine when and where an individual experiences such a stressor. Here, we experimentally challenged juvenile Chinook salmon (Oncorhynchus tshawytscha) to validate candidate gill gene expression biomarkers. A sophisticated experimental design manipulated salinity (freshwater, brackish water and seawater), temperature (10, 14 and 18°C) and dissolved oxygen (normoxia and hypoxia) in all 18 possible combinations for 6 days using separate trials for three smolt statuses (pre-smolt, smolt and de-smolt). In addition, changes in juvenile behaviour, plasma variables, gill Na+/K+-ATPase activity, body size, body morphology and skin pigmentation supplemented the gene expression responses. We identified biomarkers specific to salinity and temperature that transcended the multiple stressors, smolt status and mortality (live, dead and moribund). Similar biomarkers for dissolved oxygen were not identified. This work demonstrates the unique power of gene expression biomarkers to identify a specific stressor even under multi-stressor conditions, and we discuss our next steps for hypoxia biomarkers using an RNA-seq study.

Integrating physiological data with the conservation and management of fishes: a meta-analytical review using the threatened green sturgeon (Acipenser medirostris)

Reversing global declines in the abundance and diversity of fishes is dependent on science-based conservation solutions. A wealth of data exist on the ecophysiological constraints of many fishes, but much of this information is underutilized in recovery plans due to a lack of synthesis. Here, we used the imperiled green sturgeon (Acipenser medirostris) as an example of how a quantitative synthesis of physiological data can inform conservation plans, identify knowledge gaps and direct future research actions. We reviewed and extracted metadata from peer-reviewed papers on green sturgeon. A total of 105 publications were identified, spanning multiple disciplines, with the primary focus being conservation physiology (23.8%). A meta-analytical approach was chosen to summarize the mean effects of prominent stressors (elevated temperatures, salinity, low food availability and contaminants) on several physiological traits (growth, thermal tolerance, swimming performance and heat shock protein expression). All examined stressors significantly impaired green sturgeon growth, and additional stressor-specific costs were documented. These findings were then used to suggest several management actions, such as mitigating salt intrusion in nursery habitats and maintaining water temperatures within optimal ranges during peak spawning periods. Key data gaps were also identified; research efforts have been biased towards juvenile (38.1%) and adult (35.2%) life-history stages, and less data are available for early life-history stages (embryonic, 11.4%; yolk-sac larvae, 12.4%; and post yolk-sac larvae, 16.2%). Similarly, most data were collected from single-stressor studies (91.4%) and there is an urgent need to understand interactions among stressors as anthropogenic change is multi-variate and dynamic. Collectively, these findings provide an example of how meta-analytic reviews are a powerful tool to inform management actions, with the end goal of maximizing conservation gains from research efforts.

Global metabolic responses of the lenok (Brachymystax lenok) to thermal stress

High temperature is a powerful stressor for fish living in natural and artificial environments, especially for cold water species. Understanding the impact of thermal stress on physiological processes of fish is crucial for better cultivation and fisheries management. However, the metabolic mechanism of cold water fish to thermal stress is still not completely clear. In this study, a NMR-based metabonomic strategy in combination with high-throughput RNA-Seq was employed to investigate global metabolic changes of plasma and liver in a typical cold water fish species lenok (Brachymystax lenok) subjected to a sub-lethal high temperature. Our results showed that thermal stress caused multiple dynamic metabolic alterations of the lenok with prolonged stress, including repression of energy metabolism, shifts in lipid metabolism, alterations in amino acid metabolism, changes in choline and nucleotide metabolisms. Specifically, thermal stress induced an activation of glutamate metabolism, indicating that glutamate could be an important biomarker associated with thermal stress. Evidence from Hsp 70 gene expression, blood biochemistry and histology confirmed that high temperature exposure had negative effects on health of the lenok. These findings imply that thermal stress has a severe adverse effect on fish health and demonstrate that the integrated analyses combining NMR-based metabonomics and transcriptome strategy is a powerful approach to enhance our understanding of metabolic mechanisms of fish to thermal stress.

Developing specific molecular biomarkers for thermal stress in salmonids

Background

Pacific salmon (Oncorhynchus spp.) serve as good biological indicators of the breadth of climate warming effects on fish because their anadromous life cycle exposes them to environmental challenges in both marine and freshwater environments. Our study sought to mine the extensive functional genomic studies in fishes to identify robust thermally-responsive biomarkers that could monitor molecular physiological signatures of chronic thermal stress in fish using non-lethal sampling of gill tissue.

Results

Candidate thermal stress biomarkers for gill tissue were identified using comparisons among microarray datasets produced in the Molecular Genetics Laboratory, Pacific Biological Station, Nanaimo, BC, six external, published microarray studies on chronic and acute temperature stress in salmon, and a comparison of significant genes across published studies in multiple fishes using deep literature mining. Eighty-two microarray features related to 39 unique gene IDs were selected as candidate chronic thermal stress biomarkers. Most of these genes were identified both in the meta-analysis of salmon microarray data and in the literature mining for thermal stress markers in salmonids and other fishes. Quantitative reverse transcription PCR (qRT-PCR) assays for 32 unique genes with good efficiencies across salmon species were developed, and their activity in response to thermally challenged sockeye salmon (O. nerka) and Chinook salmon (O. tshawytscha) (cool, 13–14 °C and warm temperatures 18–19 °C) over 5–7 days was assessed. Eight genes, including two transcripts of each SERPINH1 and HSP90AA1, FKBP10, MAP3K14, SFRS2, and EEF2 showed strong and robust chronic temperature stress response consistently in the discovery analysis and both sockeye and Chinook salmon validation studies.

Conclusions

The results of both discovery analysis and gene expression showed that a panel of genes involved in chaperoning and protein rescue, oxidative stress, and protein biosynthesis were differentially activated in gill tissue of Pacific salmon in response to elevated temperatures. While individually, some of these biomarkers may also respond to other stressors or biological processes, when expressed in concert, we argue that a biomarker panel comprised of some or all of these genes could provide a reliable means to specifically detect thermal stress in field-caught salmon.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5108-9) contains supplementary material, which is available to authorized users.

Effect of selenomethionine on cell viability and heat shock protein 70 levels in rainbow trout intestinal epithelial cells at hypo-, normo-, and hyper-thermic temperatures

As global warming and environmental pollution modify aquatic environments, the thermal biology of fish could be affected by interactions between temperature and pollutants, such as selenium (Se). Therefore, selenomethionine (SeMet) was studied for effects on cell viability and on heat shock protein 70 (HSP70) levels in the rainbow trout intestinal epithelial cell, RTgutGC, at hypothermic (4 °C), normothermic (14 and 18 °C) and hyperthermic (26 °C) temperatures. RTgutGC cultures remained viable for at least a week at all temperatures, although energy metabolism as measured with Alamar Blue (resazurin) was appreciably diminished at 4 °C. Over a 7-day incubation, HSP 70 levels in cultures remained steady at 4 °C, declined at 18 °C, and increased slightly at 26 °C. When 125 μM SeMet was present, cultures remained viable and HSP70 levels were neither increased nor decreased relative to control cultures, regardless of the temperature. With 500 and 1000 μM SeMet, cell viability was profoundly impaired after 7 days in cultures at 14, 18 and 26 °C but was unchanged at 4 °C. Overall the results suggest that only hypothermia modulated the response of rainbow trout cells to SeMet.

Influence of maternal age on the effects of seleno-l-methionine in the model organism Daphnia pulex under standard and heat stress conditions

Selenium deficiency and toxicity increase the risk of adverse developmental and reproductive outcomes; however, few multi-stressor studies have evaluated the influence of maternal age on organic selenium dose-response and additional stressors over the life course. While multi-stressor research in mammalian models is time-consuming and expensive, use of alternative models can efficiently produce screening data for prioritizing research in mammalian systems. As a well-known eco-toxicological model, Daphnia pulex, may offer advantages in screening for impacts of multi-stressor exposures. We evaluated the influence of maternal age on the effects of seleno-methionine (SeMet) for lifespan, reproduction, and heat-stress resistance in D. pulex. Our results show effects of SeMet-treatment and maternal age, where the highest SeMet-treatment had reduced lifespan and absence of reproduction, and where Daphnia from late life broods had increased resistance to heat-induced stress. Further analysis suggests an additional interactive effect between maternal age and SeMet treatment on time to first reproduction.

Russian sturgeon cultured in a subtropical climate shows weaken innate defences and a chronic stress response

Russian sturgeon (Acipenser gueldenstaedtii) has been successfully farmed in Uruguay for the past ten years. However, during the Uruguayan summer fish endure high water temperatures and increased bacterial infections that threaten aquaculture. Our understanding of sturgeon's immune system and its interplay with environmental factors like temperature is almost unknown. This study analysed the way in which seasonal variations affect enzymatic blood components of Russian sturgeon's innate defences, including the serum alternative complement pathway (ACP), ceruloplasmin (Cp) and lysozyme activities. Results showed that summertime conditions in the farm altered these defences in different ways, inducing a significant decrease in ACP and Cp, and an increase in lysozyme. In addition, serum levels of total protein and cortisol decreased in summer, suggesting a chronic stress response was induced in parallel. Subsequently, we analysed whether the increase in water river temperature during summer could account for the observed results. To that end, we acclimated juvenile sturgeons to mild (18 °C) or warm (24 °C) temperatures for 37 days. Like in summer, sturgeons exposed to 24 °C showed lower levels of serum ACP, Cp and total proteins, together with a progressive decrease in body weight and increased fish mortality. Administration of an immunostimulant containing Se and Zn slightly reverted the temperature-induced effects on sturgeon's defences. Altogether, our study provides novel data on various physiological parameters of the Russian sturgeon and highlights the impact warm temperature has on stress and innate immunity in this chondrostean fish.

Ocean warming alters cellular metabolism and induces mortality in fish early life stages: A proteomic approach

Climate change has pervasive effects on marine ecosystems, altering biodiversity patterns, abundance and distribution of species, biological interactions, phenology, and organisms' physiology, performance and fitness. Fish early life stages have narrow thermal windows and are thus more vulnerable to further changes in water temperature. The aim of this study was to address the sensitivity and underlying molecular changes of larvae of a key fisheries species, the sea bream Sparus aurata, towards ocean warming. Larvae were exposed to three temperatures: 18°C (control), 24°C (warm) and 30°C (heat wave) for seven days. At the end of the assay, i) survival curves were plotted for each temperature treatment and ii) entire larvae were collected for proteomic analysis via 2D gel electrophoresis, image analysis and mass spectrometry. Survival decreased with increasing temperature, with no larvae surviving at 30°C. Therefore, proteomic analysis was only carried out for 18°C and 24°C. Larvae up-regulated protein folding and degradation, cytoskeletal re-organization, transcriptional regulation and the growth hormone while mostly down-regulating cargo transporting and porphyrin metabolism upon exposure to heat stress. No changes were detected in proteins related to energetic metabolism suggesting that larval fish may not have the energetic plasticity needed to sustain cellular protection in the long-term. These results indicate that despite proteome modulation, S. aurata larvae do not seem able to fully acclimate to higher temperatures as shown by the low survival rates. Consequently, elevated temperatures seem to have bottleneck effects during fish early life stages, and future ocean warming can potentially compromise recruitment's success of key fisheries species.

Changes in Neurotransmitter Profiles during Early Zebrafish (Danio rerio) Development and after Pesticide Exposure

During early development, neurotransmitters are important stimulants for the development of the central nervous system. Although the development of different neuronal cell types during early zebrafish (Danio rerio) development is well-studied, little is known of the levels of neurotransmitters, their precursors and metabolites during development, and how these levels are affected by exposure to environmental contaminants. A method based on hydrophilic interaction liquid chromatography coupled to tandem mass spectrometry has been applied for the first time to zebrafish embryos and larvae to study five neurotransmitter systems in parallel, including the dopaminergic-andrenergic, glutaminergic-GABAnergic, serotoninergic, histaminergic, and cholinergic systems. Our method enables the quantification of neurotransmitters and their precursors and metabolites in whole zebrafish from the period of zygote to free-swimming larvae 6 days postfertilization (dpf). We observed a developmental stage-dependent pattern with clear differences between the first 2 days of development and the following days. Whereas the neurotransmitter levels steadily increased, the precursors showed a peak at 3 dpf. After exposure to several pesticides, significant differences in concentrations of neurotransmitters and precursors were observed. Our study revealed new insights about neurotransmitter systems during early zebrafish development and showed the usefulness of our approach for environmental neurotoxicity studies.

Using molecular biomarkers and traditional morphometric measurements to assess the health of slimy sculpin (Cottus cognatus) from streams with elevated selenium in North-Eastern British Columbia

Canadian fish-based environmental effects monitoring programs use individual and population-level endpoints to assess aquatic health. Impacts of coal mining and selenium (Se) exposure were assessed in slimy sculpin (Cottus cognatus) from reference streams located both inside and outside of a coal zone, and from 1 stream with a history of coal mining, using traditional environmental effects monitoring endpoints. In addition, physical characteristics of the streams and benthic macro-invertebrate communities were assessed. To determine whether the assessment of effects could be improved by including molecular markers, real-time polymerase chain reaction assays were optimized for genes associated with reproduction (vtg, esr1, star, cyp19a1, and gys2), and oxidative and cellular stress (sod1, gpx, gsr, cat, and hsp 90). Water Se levels exceeded guidelines in the stream with historical mining (4 μg/L), but benthic macroinvertebrates did not exceed dietary thresholds (2-3 μg/g dry wt). Whole-body Se levels were above British Columbia's tissue guideline in fish from all streams, but only above the draft US Environmental Protection Agency (USEPA) criterion (7.91 μg/g dry wt) at the reference stream inside the coal zone. Some markers of cellular and oxidative stress were elevated in fish liver at the exposed site (sod1, gpx), but some were lower (cat, sod1, gpx, gsr, hsp90) in the gonads of fish inside the coal zone. Some of the differences in gene expression levels between the reference and impacted sites were sex dependent. Based on benthic macroinvertebrate assessments, the authors hypothesize that traditional and molecular differences in slimy sculpin at impacted sites may be driven by food availability rather than Se exposure. The present study is the first to adapt molecular endpoints in the slimy sculpin for aquatic health assessments.

Impact of nutrition and salinity changes on biological performances of green and white sturgeon

Green and white sturgeon are species of high conservational and economic interest, particularly in the San Francisco Bay Delta (SFBD) for which significant climate change-derived alterations in salinity and nutritional patterns are forecasted. Although there is paucity of information, it is critical to test the network of biological responses underlying the capacity of animals to tolerate current environmental changes. Through nutrition and salinity challenges, climate change will likely have more physiological effect on young sturgeon stages, which in turn may affect growth performance. In this study, the two species were challenged in a multiple-factor experimental setting, first to levels of feeding rate, and then to salinity levels for different time periods. Data analysis included generalized additive models to select predictors of growth performance (measured by condition factor) among the environmental stressors considered and a suite of physiological variables. Using structural equation modeling, a path diagram is proposed to quantify the main linkages among nutrition status, salinity, osmoregulation variables, and growth performances. Three major trends were anticipated for the growth performance of green and white sturgeon in the juvenile stage in the SFBD: (i) a decrease in prey abundance will be highly detrimental for the growth of both species; (ii) an acute increase in salinity within the limits studied can be tolerated by both species but possibly the energy spent in osmoregulation may affect green sturgeon growth within the time window assessed; (iii) the mechanism of synergistic effects of nutrition and salinity changes will be more complex in green sturgeon, with condition factor responding nonlinearly to interactions of salinity and nutrition status or time of salinity exposure. Green sturgeon merits special scientific attention and conservation effort to offset the effects of feed restriction and salinity as key environmental stressors in the SFBD.

Selenium tissue burden compartmentalization in resident white sturgeon (Acipenser transmontanus) of the San Francisco Bay Delta estuary

High selenium (Se) loads in the San Francisco Bay Delta are bioaccumulated and biomagnified in food webs and can impair the reproduction of resident oviparous animals such as white sturgeon. The objective of the present study was to determine the Se tissue burden in San Francisco Bay Delta-resident white sturgeon to assess Se bioaccumulation in different organs, including ovaries and liver where egg yolk precursor proteins are synthesized. The authors obtained 54 San Francisco Bay Delta-resident white sturgeon including 26 female and 28 male subadults with immature gonads, 8 females with vitellogenic eggs, and 13 males with maturing gonads. Length, weight, age, reproductive stage of development, and kidney, liver, gonad, and muscle Se concentrations were determined in all fish. Concentrations of Se in muscle, gonads, and liver significantly increased with fish size, whereas kidney Se was not correlated to body size and was at the highest level compared with other organs. There was no difference between the sexes (p > 0.05) in Se concentrations in kidney (12.83 ± 0.51 µg · g(-1) dry wt), liver (11.85 ± 1.04 µg · g(-1) dry wt), and muscle (7.09 ± 0.52 µg · g(-1) dry wt; mean ± standard error, n = 47); but Se concentration was higher in the ovary than in testis (p = 0.04). Females with vitellogenic eggs had higher Se concentrations in the ovaries (20.77 ± 4.11 µg · g(-1) dry wt vs 5.22 ± 2.50 µg · g(-1) dry wt), liver (21.84 ± 2.07 µg · g(-1) dry wt vs 8.03 ± 1.03 µg · g(-1) dry wt), and muscle (10.18 ± 1.93 µg · g(-1) dry wt vs 5.48 ± 0.64 µg · g(-1) dry wt) compared with less advanced, previtellogenic females (p < 0.05). The elevated Se concentrations in the ovaries and liver of vitellogenic San Francisco Bay Delta white sturgeon were comparable with levels previously shown to cause reproductive toxicity in dietary Se experiments with captive white sturgeon.

Effects of cadmium exposure on the gill proteome of Cottus gobio: modulatory effects of prior thermal acclimation

Temperature and trace metals are common environmental stressors, and their importance is increasing due to global climate change and anthropogenic pollution. The aim of the present study was to investigate whether acclimation to elevated temperature affects the response of the European bullhead (Cottus gobio) to subsequent cadmium (Cd) exposure by using enzymatic and proteomic approaches. Fish acclimated to 15 (standard temperature), 18 or 21 °C for 28 days were exposed to 1mg Cd/L for 4 days at the respective acclimation temperature. First, exposure to Cd significantly decreased the activity of the lactate dehydrogenase (LDH) in gills of fish acclimated to 15 or 18 °C. However, an acclimation to 21 °C suppressed the inhibitory effect of Cd. Second, using a proteomic analysis by 2D-DIGE, we observed that thermal acclimation was the first parameter affecting the protein expression profile in gills of C. gobio, while subsequent Cd exposure seemed to attenuate this temperature effect. Moreover, our results showed opposite effects of these two environmental stressors at protein expression level. From the 52 protein spots displaying significant interaction effects of temperature and Cd exposure, a total of 28 different proteins were identified using nano LC-MS/MS and the Peptide and Protein Prophet algorithms of Scaffold software. The identified differentially expressed proteins can be categorized into diverse functional classes, related to protein turnover, folding and chaperoning, metabolic process, ion transport, cell signaling and cytoskeleton. Within a same functional class, we further reported that several proteins displayed reverse responses following sequential exposure to heat and Cd. This work provides insights into the molecular pathways potentially involved in heat acclimation process and the interactive effects of temperature and Cd stress in ectothermic vertebrates.

Transcriptomic responses to heat stress and nickel in the mussel Mytilus galloprovincialis

The exposure of marine organisms to stressing agents may affect the level and pattern of gene expression. Although many studies have examined the ecological effects of heat stress on mussels, little is known about the physiological mechanisms that maybe affected by co-exposure to heat stress and environmental contaminants such as nickel (Ni). In the present work, we investigated the effects of simultaneous changes in temperature and Ni supply on lysosomal membrane stability (LMS) and malondialdehyde accumulation (MDA) in the digestive gland (DG) of the blue mussel Mytilus galloprovincialis (Lam.). To elucidate how the molecular response to environmental stressors is modulated, we employed a cDNA microarray with 1673 sequences to measure relative transcript abundances in the DG of mussels exposed to Ni along with a temperature increase. A two-way ANOVA revealed that temperature and Ni rendered additive effects on LMS and MDA accumulation, increasing the toxic effects of metal cations. Ni loads in the DG were also affected by co-exposure to 26°C. In animals exposed only to heat stress, functional genomics analysis of the microarray data (171 differentially expressed genes (DEGs)) highlighted seven biological processes, largely dominated by the up-regulation of folding protein-related genes and the down-regulation of genes involved in cell migration and cellular component assembly. Exposure to Ni at 18°C and 26°C yielded 188 and 262 DEGs, respectively, exhibiting distinct patterns in terms of biological processes. In particular, the response of mussels exposed to Ni at 26°C was characterized by the up-regulation of proteolysis, ribosome biogenesis, response to unfolded proteins, and catabolic-related genes, as well as the down-regulation of genes encoding cellular metabolic processes. Our data provide new insights into the transcriptomic response in mussels experiencing temperature increases and Ni exposure; these data should be carefully considered in view of the biological effects of heat stress, particularly in polluted areas.

Transcriptional response of the mussel Mytilus galloprovincialis (Lam.) following exposure to heat stress and copper

Global warming is a major factor that may affect biological organization, especially in marine ecosystems and in coastal areas that are particularly subject to anthropogenic pollution. We evaluated the effects of simultaneous changes in temperature and copper concentrations on lysosomal membrane stability (N-acetyl-hexosaminidase activity) and malondialdehyde accumulation (MDA) in the gill of the blue mussel Mytilus galloprovincialis (Lam.). Temperature and copper exerted additive effects on lysosomal membrane stability, exacerbating the toxic effects of metal cations present in non-physiological concentrations. Mussel lysosomal membrane stability is known to be positively related to scope for growth, indicating possible effects of increasing temperature on mussel populations in metal-polluted areas. To clarify the molecular response to environmental stressors, we used a cDNA microarray with 1,673 sequences to measure the relative transcript abundances in the gills of mussels exposed to copper (40 µg/L) and a temperature gradient (16°C, 20°C, and 24°C). In animals exposed only to heat stress, hierarchical clustering of the microarray data revealed three main clusters, which were largely dominated by down-regulation of translation-related differentially expressed genes, drastic up-regulation of protein folding related genes, and genes involved in chitin metabolism. The response of mussels exposed to copper at 24°C was characterized by an opposite pattern of the genes involved in translation, most of which were up-regulated, as well as the down-regulation of genes encoding heat shock proteins and "microtubule-based movement" proteins. Our data provide novel information on the transcriptomic modulations in mussels facing temperature increases and high copper concentrations; these data highlight the risk of marine life exposed to toxic chemicals in the presence of temperature increases due to climate change.

Identification of differential expressed proteins and characterization their mRNA expression in thermally stressed Apostichopus japonicus

In this study, we present a comparative proteomic analysis of the global protein expression changes in sea cucumber after 7 days exposure at 25°C. Using two-dimensional electrophoresis followed by MALDI-TOF MS/MS, 27 protein spots with significant differences in abundance were identified and characterized. The identified proteins belonged primarily to the following four functional categories: cytoskeletal, material and energy metabolism, calcium homeostasis and extracellular matrix. The mRNA expression levels of 7 differentially expressed proteins were further assessed by qRT-PCR. The expression levels of 6 genes, including collagen, ATP synthase, major yolk protein, ferritin, nectin and protein disulfide isomerase showed significant differences under thermal stress, and among them, only two genes-ATP synthase and major yolk protein-showed consistent levels of protein and mRNA expression. Our results offer insight into the complex changes in protein turnover during higher temperature exposure in sea cucumber.

Increased temperatures affect oxidative stress markers and detoxification response to benzo[a]pyrene exposure in mussel Mytilus galloprovincialis

The present research work was designed to study mussel's (Mytilus galloprovincialis) digestive gland biotransformation and detoxification responses to benzo[a]pyrene (B[a]P) exposure along with heat stress. Mussels were exposed to a sublethal dose of B[a]P [75 nM (19 μg/L/animal)] + temperature gradient (18, 20, 22, 24 and 26 °C) for 7 days. B[a]P hydroxylase (BPH) and glutathione-S-transferase (GST) activities were assessed in digestive gland tissues as phase I and phase II biotransformation parameters. Catalase (CAT) activity and malonedialdehyde (MDA) were measured as potential biomarkers of oxidative stress and lipid peroxidation. The cholinergic system was evaluated using acetylcholinesterase (AChE) activity. DNA damage was assessed using micronuclei (MN) test. BPH and GST activities showed a decreasing trend in B[a]P-exposed animals at 24 and 26 °C. CAT activity showed a bell-shaped response in B[a]P-exposed and in heat-stressed organisms at a maximum temperature of 22 °C. AChE activity was significantly inhibited in response to B[a]P being more pronounced at a temperature of 26 °C. MN in digestive gland cells suggest that B[a]P exposure induced significant DNA alteration with a maximum response in organisms coexposed to B[a]P and a temperature of 26 °C. Biomarker data are further discussed in relation B[a]P accumulation in mussels digestive gland. These data should be carefully considered in view of the biological effects of organic pollutants, particularly in organisms under the challenging effects of extreme temperature fluctuations.

Malachite green toxicity assessed on Asian catfish primary cultures of peripheral blood mononuclear cells by a proteomic analysis

The potential genotoxic and carcinogenic properties reported for malachite green (MG) and the frequent detection of MG residues in fish and fish products, despite the ban of MG, have recently generated great concern. Additional toxicological data are required for a better understanding of the mechanism of action and a more comprehensive risk assessment for the exposure of fish to this fungicide. To date, the use of fish peripheral blood mononuclear cells (PBMCs) has not been exploited as a tool in the assessment of the toxicity of chemicals. However, PBMCs are exposed to toxicants and can be easily collected by blood sampling. The present study aims at better understanding the effects of MG by a proteomic analysis of primary cultured PBMC from the Asian catfish, Pangasianodon hypophthalmus, exposed to MG. The two lowest concentrations of 1 and 10 ppb were selected based on the MTS (water soluble tetrazolium salts) cytotoxicity test. Using a proteomic analysis (2D-DIGE), we showed that 109 proteins displayed significant changes in abundance in PBMC exposed during 48 h to MG. Most of these proteins were successfully identified by nano LC-MS/MS and validated through the Peptide and Protein Prophet of Scaffold™ software, but only 19 different proteins were considered corresponding to a single identification per spot. Our data suggest that low concentrations of MG could affect the mitochondrial metabolic functions, impair some signal transduction cascades and normal cell division, stimulate DNA repair and disorganize the cytoskeleton. Altogether, these results confirm that the mitochondrion is a target of MG toxicity. Further studies on the identified proteins are needed to better understand the mechanisms of MG toxicity in fish produced for human consumption.

Proteomic analysis of blood cells in fish exposed to chemotherapeutics: evidence for long term effects

Proteomics technology are increasingly used in ecotoxicological studies to characterize and monitor biomarkers of exposure. The present study aims at identifying long term effects of malachite green (MG) exposure on the proteome of peripheral blood mononuclear cells (PBMC) from the Asian catfish, Pangasianodon hypophthalmus. A common (0.1 ppm) concentration for therapeutic treatment was applied twice with a 72 h interval. PBMC were collected directly at the end of the second bath of MG (T1) and after 1 month of decontamination (T2). Analytical 2D-DIGE gels were run and a total of 2551±364 spots were matched. Among them, MG induced significant changes in abundance of 116 spots with no recovery after one month of decontamination. Using LC-MS/MS and considering single identification per spot, we could identify 25 different proteins. Additionally, MG residues were measured in muscle and in blood indicating that leuco-MG has almost totally disappeared after one month of decontamination. This work highlights long term effects of MG treatment on the PBMC proteome from fish intended for human consumption.

Ecotoxicoproteomics in gills of the sentinel fish species, Cottus gobio, exposed to perfluorooctane sulfonate (PFOS)

The environmental persistence, bioaccumulative tendency and potential toxicity of perfluorooctane sulfonate (PFOS) have generated great concern. This study aimed at evaluating the toxicity of short-term PFOS exposure in gills of the European bullhead Cottus gobio, a candidate sentinel species, by monitoring the response of some enzymes (citrate synthase CS, cytochrome c oxidase CCO, and lactate dehydrogenase LDH), and by undertaking a proteomic analysis using 2D-DIGE. First, a 96-h exposure to 1mg PFOS/L significantly altered the activity of mitochondrial CS and CCO. Second, 2D-DIGE gels were used to compare gills from the control fish group with tissues from fish exposed for 96h to either 0.1 or 1mg PFOS/L. From the 27 protein spots displaying significant changes in abundance following PFOS exposure, a total of 20 different proteins were identified using nano LC-MS/MS and the Peptide and Protein Prophet of Scaffold software. The differentially expressed proteins that were identified are involved in the general stress response, ubiquitin-proteasome system, energy metabolism, and actin cytoskeleton, which provide clues on the cellular pathways and components mainly affected by PFOS. Moreover, our results showed that most proteins were differentially expressed at the low but not at the high PFOS concentration. This work provides insights into the biochemical and molecular events in PFOS-induced toxicity in gill tissue, and suggests that further studies on the identified proteins could provide crucial information to better understand the mechanisms of PFOS toxicity in fish.