Translational responses and oxidative stress of mussels experimentally exposed to Hg, Cu and Cd: one pattern does not fit at all

Copper induces cytotoxicity in freshwater bivalve Anodonta woodiana hemocytes

Hemocytes of freshwater bivalves are an important target model for evaluating copper (Cu) toxicity in vitro, with excess Cu causing adverse responses in these organisms. Despite this, the mechanisms underlying cytotoxicity remain poorly understood. The freshwater bivalve Anodonta woodiana, employed as a model organism in freshwater environments, was utilized in this study. Hemocytes of A. woodiana were exposed to various aqueous Cu treatments (0.001, 0.01, 0.1, 1, and 10 mg/L), and a control group (no Cu added) for 3 h to investigate the cytotoxic mechanisms of Cu. The results showed a significant increase in the production of reactive oxygen species in hemocytes of all Cu exposed groups compared to the control (p < 0.05). Remarkably, Cu treatments disrupted the cellular membrane (p < 0.05) but did not induce significant changes in the stability of the lysosomal membrane. Cu targeted the mitochondria, leading to a reduction in mitochondrial membrane potential. Additionally, all Cu treatments significantly increased the degree of DNA damage (p < 0.05). Cellular damage and a significant decline in cell viability were observed when the Cu exposure concentration reached 0.1, 1, and 10 mg/L (p < 0.05). Our study provides new insights into the cytotoxicity mechanisms triggered by Cu in hemocytes of the freshwater bivalve A. woodiana, even under environmentally relevant conditions of 0.01 mg/L exposure.

Evaluating quaternium-15 effects on Mytilus galloprovincialis: New insights on physiological and cellular responses

Among personal care products, quaternium-15 is prominently featured as a preservative in items such as shampoos, soaps, shaving products, and cosmetics. The widespread use of these products in people's daily routines contributes to quaternium-15 release into aquatic ecosystems. In this context, the primary aim of the study was to assess the physiological and cellular responses of the digestive gland and gills in Mytilus galloprovincialis to quaternium-15 exposure. Cell viability and the ability of digestive gland cells to regulate their volume were evaluated. Additionally, the expression of the genes involved in oxidative stress response was assessed to further substantiate the compound's harmful effects. Results indicated a significant decrease in both the viability of digestive gland cells and their RVD (regulatory volume decrease) capacity when exposed to a hypotonic solution. Furthermore, impairment of digestive gland cell function was corroborated by the modulation of oxidative stress-related gene expression, including SOD, Cat, as well as Hsp70 and CYP4Y1. Similar gene expression alterations were observed in the gills, reflecting impaired functionality in this vital organ as well. In summary, the outcomes of the study provide conclusive evidence of the toxicity of quaternium-15. This underscores the urgent need to further investigate the toxicological effects of this contaminant on aquatic ecosystems and emphasises the necessity of limiting the use of products containing quaternium-15.

Effect of acute cadmium exposure on oxidative stress and antioxidant system of the scallop Aequipecten tehuelchus

This study aimed to assess the impact of acute exposure (96 h) to Cd in gills, digestive gland and muscle of the Tehuelche scallop Aequipecten tehuelchus from San José gulf in Patagonia, Argentina. Scallops were exposed to Cd concentrations of 0, 25, 50, 100, 150, 204, 275, 371, and 500 μg/L, and mortality rates were recorded after 96 h of exposure. Surviving organisms were analyzed for the biochemical response through reactive oxygen and nitrogen species (RONS), activities of catalase (CAT) and glutathione-S-transferase (GST), metallothioneins (MT), lipid peroxidation (LPO) and liposoluble antioxidants α-tocopherol (α-T) and β-carotene (β-C). The mean lethal concentration (LC50) was 155.8 μg Cd/L, a lower value than other scallops' species, showing that A. tehuelchus has a particular sensitivity to Cd. In the three tissues, at all exposure concentrations, there was no significant response in RONS levels, GST activity or LPO. Nevertheless, CAT activity and α-T levels decreased in the gills but increased in the digestive gland, with no significant response in the muscle. Two-way ANOVA revealed a significant interaction between Cd concentration and tissue on MT, which increased significantly in gills, decreased in digestive gland with 100 compared to 50 μg Cd/L; whereas in muscle a significant increase was observed with 25 μg Cd/L compared to control. The results show a significant effect of Cd in scallop's gills on CAT activity and α-T levels, highlighting this tissue as the primary target against relevant concentrations of metal in seawater. The effect on digestive gland and muscle was minimal. The overall results suggest that Cd toxicity is tissue-specific. This study will help reduce the existence knowledge gap regarding potential impacts of acute exposure to Cd in a bivalve species with high ecological and commercial importance, as well as identifying the most responsive biomarkers associated with Cd stress for monitoring assessment.

Oxidative response to accumulation of trace metals in tissue of two bivalves, the Asian green mussel Perna viridis and the blood cockle Tegillarca granosa, living in Pattani Bay, Thailand

OBJECTIVE

Using bivalves to indicate aquatic pollutants was favorable for discerning the negative effects of high levels of metal accumulation in tissue. We investigated the correlation between trace metal accumulation and the tissue oxidative response of two bivalves.

METHODS

The Asian green mussel Perna viridis and the blood cockle Tegillarca granosa were sampled along with seawater and sediments from three locations around Pattani Bay, Thailand. Accumulation of nine trace metals (cadmium, cobalt, copper, chromium, nickel, manganese, iron, zinc, and lead) in seawater, sediments, and tissue and the oxidative tissue response were evaluated. Metal bioaccumulation factor, biota-sediment accumulation factor, and histopathology were also indicated.

RESULT

The present study found that P. viridis and T. granosa were macroconcentrators and bioaccumulative of cadmium, and their tissue accumulation of cadmium was strongly related to lipid peroxidation activation. Perna viridis exhibited a higher oxidative response than T. granosa, as indicated by malondialdehyde, catalase, and reduced glutathione levels.

CONCLUSION

The present study indicated that P. viridis and T. granosa were macroconcentrators and bioaccumulative of cadmium, and their tissue accumulation of cadmium was strongly related to lipid peroxidation activation. Research has shown discernible negative effects of a high level of metal accumulation in tissue, and deformed and damaged tissues were present in the gills, digestive glands, intestines, and feet of P. viridis and T. granosa.

The combined effects of polyethylene microplastics and benzoanthracene on Manila clam Ruditapes philippinarum

Microplastic (MP) toxicity has recently been explored in various marine species. Along with the toxicity of plastics polymer itself, additional substances or pollutants that are absorbed onto it may also be harmful. In the present study, we investigated the combined impacts of polyethylene microplastics (PE MPs) and an organic pollutant (Benzo(a)anthracene, BaA) on Manila clam Ruditapes philippinarum during a one-week exposure. Two PE MPs concentrations (26 μg L^-1 and 260 μg L^-1) and one BaA concentration (3 μg L^-1) were tested. The clams were exposed to BaA and PE MPs either alone or in combination. BaA and PE MPs were incubated before the combined exposure. The biological effects of PE MPs and BaA on the clams were evaluated by considering several assays such as feeding rate, anti-oxidant enzyme activities, and the expression levels of stress-related genes. The feeding rate significantly decreased in individual PE MPs and individual BaA groups while it remained unchanged in combined groups. Superoxide dismutase (SOD) was the most affected among the biochemical parameters. Malondialdehyde (MDA), and glutathione peroxidase (GPx) activities were slightly affected, whereas no changes were observed in glutathione s-transferase (GST) activities. CYP1A1, CYP3A4, and HSP70 gene expressions displayed slightly significant changes. Considering all stressor groups, high PE MPs exposure (260 μg L^-1 PE MPs) more effectively altered the biological parameters in the clams compared to individual low PE MPs and BaA exposure, and their combination. The results also indicated the negligible vector role of PE MPs to transport BaA into the clam tissues.

Meta-analysis reveals the species-, dose- and duration-dependent effects of cadmium toxicities in marine bivalves

Cadmium (Cd) is a typical pollutant in marine environment. Increasing studies have focused on the toxicological effects of Cd in marine bivalves. However, there were many conflicting findings of toxicological effects of Cd in marine bivalves. An integrated analysis performed on the published data of Cd toxicity in marine bivalves is still absent. In this study, a meta-analysis was performed on the toxic endpoints in bivalves exposed to aqueous-phase Cd from 87 studies screened from 1519 papers. Subgroup analyses were conducted according to the categories of species, tissue, exposure dose and duration. The results showed significant species-, duration- and dose-dependent responses in bivalves to aqueous-phase Cd exposure. In details, clams were more sensitive to Cd than oysters, mussels and scallops, indicated by the largest effect size in clams. Gill, hepatopancreas and hemolymph were top three tissues used to indicate Cd-induced toxicity and did not present a significant tissue-specific manner among them. With regard to toxicological effect subgroups, oxidative stress and detoxification were top two subgroups indicating Cd toxicities. Detoxification and genotoxicity subgroups presented higher response magnitudes. What is more, toxicological effect subgroups presented multiple dose- and duration-dependent curves. Oxidative stress and genotoxicity related endpoints presented significant increase trends with Cd exposure dose and were preferable biomarkers to marine Cd pollution. Detoxification and energy metabolism related endpoints showed inverted U-shaped and U-shaped dose-response curves, both of which could be explained by hormesis. The linear decrease in oxidative stress and energy metabolism related endpoints over time suggested their involvement into the adaptive mechanism in bivalves. Overall, this study provided not only a better understanding the responsive mechanisms of marine bivalves to Cd stress, but also a selection reference for biomarkers to aqueous-phase Cd pollution in marine environment.

Detection of superoxide radical in all biological systems by Thin Layer Chromatography

The study presents a new method that detects O₂^•-, via quantification of 2-hydroxyethidium (2-ΟΗ-Ε⁺) as low as ∼30 fmoles by High-Performance Thin Layer Chromatography (HPTLC). The method isolates 2-ΟΗ-Ε⁺ after its extraction by the anionic detergent SDS (at 18-fold higher than its CMC) together with certain organic/inorganic reagents, and its HPTLC-separation from di-ethidium (di-Ε⁺) and ethidium (Ε⁺). Quantification of 2-OH-E⁺ is based on its ex/em maxima at 290/540 nm, and of di-E⁺ and E⁺ at 295/545 nm. The major innovations of the present method are the development of protocols for (i) efficient extraction (by SDS) and (ii) sensitive quantification (by HPTLC) for 2-OH-E⁺ (as well as di-E⁺ and E⁺) from most biological systems (animals, plants, cells, subcellular compartments, fluids). The method extracts 2-ΟΗ-Ε⁺ (by neutralizing the strong binding between its quaternary N⁺ and negatively charged sites on phospholipids, DNA etc) together with free HE, while protects both from biological oxidases, and also extracts/quantifies total proteins (hydrophilic and hydrophobic) for expressing O₂^•- levels per protein quantity. The method also uses SDS (at 80-fold lower than its CMC) to extract/remove/wash 2-ΟΗ-Ε⁺ from cell/organelle exterior membrane sites, for more accurate internal content quantification. The new method is applied on indicative biological systems: (1) artificially stressed (mouse organs and liver mitochondria and nuclei, ±exposed to paraquat, a known O₂^•- generator), and (2) physiologically stressed (cauliflower plant, exposed to light/dark).

The cadmium toxicity in gills of Mytilus coruscus was accentuated by benzo(a)pyrene of higher dose but not lower dose

In natural environment, the existence of interactions of toxic mixtures could induce diverse biochemical pathways and consequently exert different toxicological responses in aquatic organisms. However, little information is available on the effects of combined xenobiotics on lower aquatic invertebrates. Here, we assessed the effects of cadmium (Cd, 0.31 mg/L) as well as the mixture of Cd (0.31 mg/L) and benzo(a)pyrene (Bap, 5 or 50 μg/L) on bioaccumulation, antioxidant, lipid peroxidation (LPO) and metallothionein (MT) responses in gills of thick shell mussel Mytilus coruscus. Upon exposed to single Cd, the metal bioaccumulation, antioxidant enzymes activities, LPO and MT level significantly increased in the gills, suggesting an apparent toxicity to mussels. The interaction of Cd + 5 μg/L Bap did not significantly alter these endpoints compared to single Cd. However, once the dose of Bap elevated to 50 μg/L, the induction of bioaccumulation, antioxidant system and LPO was even more pronounced while the induction of MT was remarkably inhibited, implying an accentuated toxicity. Collectively, the current results demonstrated that 0.31 mg/L Cd exposure resulted in severe toxicity to mussels despite of the induction of MT system to alleviate the metal toxicity. Once the Cd exposure combined with Bap, the lower dose of Bap could not change the Cd toxicity while the higher dose of Bap accentuated the toxicity by inhibiting metallothionein synthesis. These findings might provide some useful clues for elucidation the mechanism of the interaction of combined xenobiotics in molluscs.

Transcriptome analysis provides insights into copper toxicology in piebald naked carp (Gymnocypris eckloni)

Background

Copper was used for many years in aquaculture operations as an effective algaecide or a parasite treatment of fish. It is an essential nutrient with numerous functions in organisms, but is toxic at high concentrations. However, the toxicity of copper to fish remains unclear. In this study, we used the piebald naked carp, Gymnocypris eckloni, as a model. RNA-seq data from different tissues, including gills, kidney, and liver, were used to investigate the underlying mechanism of copper toxicology in G. eckloni.

Results

We compared the transcriptomes from different tissues with different time durations of copper ion treatment. After 72 h copper ion treatment, the number of genes with different expression in gills and liver changed dramatically, but not in kidneys. In KEGG functional enrichment, the pattern of differentially expressed genes (DEGs) was also similar in the gills and liver. The most enriched pathway of DEGs was “Ribosome” in both tissues. Furthermore, we analyzed the expression levels of genes involved in oxidative stress response and protein synthesis using qPCR and RNA-seq data. Our results showed that several genes involved in oxidative stress response were up-regulated both in gills and liver. Up-regulation of these genes indicated that copper treatment caused oxidative stress, which is likely to result in ribosome damage. In addition, our results showed that the expression of Eef1b2, a transcription elongation factor, was decreased in the liver under oxidative stress, and the expression of translation initiation factors Eif4ebp1 and eIF2α, and elongation factor eEF2 was up-regulated. These results supported the idea that oxidative stress inhibits protein synthesis in cells.

Conclusions

Our results indicate that copper exposure caused different responses in different tissues, since the gene expression patterns changed substantially either in the gills or liver, while the effect on the kidney was relatively weak. Furthermore, our results indicated that the expression pattern of the genes involved in the ribosome, which is a complex molecular machine orchestrating protein synthesis in the cell, together with translation initiation factor and elongation factors, were affected by copper exposure both in the gills and liver of piebald naked carp. This result leads us to speculate that the downregulation of global protein synthesis is an acute response strategy of fish to metal-induced oxidative stress. Moreover, we speculate that this strategy not only exists in the selective translation of proteins but also exists in the specific translation of functional proteins in tissues and cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07673-4.

Integrated analysis of physiological, transcriptomics and metabolomics provides insights into detoxication disruption of PFOA exposure in Mytilus edulis

Perfluorooctanoic acid (PFOA), a persistent environmental contaminant, resists environmental degradation and bioaccumulates in food chains. Lots of literatures have proved that PFOA exposure could disrupt detoxifying function in a variety of organisms, however, it still remained poorly known about this in mollusk. Here, we examined physiological, transcriptomic, and metabolomic responses to PFOA in Mytilus edulis, a model organism frequently used in studies of aquatic pollution. We aimed to characterize PFOA-induced stress responses and detoxification mechanisms. PFOA exposure significantly altered antioxidant enzyme activity levels and the abundances of lipid peroxidation products. In addition, transcriptomic analysis indicated that several genes associated with oxidative stress and detoxication were differentially expressed after PFOA exposure. In combination, transcriptomic and metabolomic analyses showed that PFOA exposure disturbed several metabolic processes in M. edulis, including the lipid metabolism, amino acid metabolism, and carbohydrate metabolism etc. Molecular examination and enzymes assay of PFOA-exposed M. edulis after a 7-day depuration period still did not recover to control levels. The Pathway enrichment analysis proved that several pathways related to detoxification, such as c-Jun N-terminal kinase (JNK) and p38-dependent mitogen-activated protein kinase (MAPK) pathway, Peroxisome proliferator-activated receptor γ (PPARγ) pathway etc, were obviously affected. The present work verifies firstly PFOA disruption to molluscan detoxification and identifies the key pathways to understand the molecular mechanisms thereof. This study provides new insights into the detoxication disruption invoked in response to PFOA exposure in M. edulis.

Balancing essential and non-essential metal bioavailability during hatchery rearing of Greenshell mussel (Perna canaliculus) larvae

The use of ethylenediaminetetraacetic acid (EDTA) during bivalve hatchery production is thought to improve larval yields due to the reduced exposure to toxic metals (such as Cu); however, few studies have focused on the bioavailability of metals during the rearing process. Greenshell™ mussels (Perna canaliculus) were reared for 48 h with and without EDTA (12 µM) exposure and larvae were subsequently raised to 21 days post-fertilisation with and without EDTA exposure. Survival, shell length, algal ingestion rate, swimming activity, total metal concentration in water, bioavailable metal concentrations and larval metal accumulation were monitored for the 21 day period. Larval fitness (specifically D-yields) was improved on day 2 in the EDTA treatment, whereas an overall negative effect of EDTA treatment on fitness was observed on day 10 and 21. During the first 48 h, increased survival in the EDTA treatment is believed to be due to the reduction of bioavailable Zn concentrations in the rearing seawater. No other metal (essential or non-essential) displayed a consistent trend when comparing metal bioavailability to any of the fitness parameters measured throughout the experiment. Though the measured metal bioavailability was not clearly linked to fitness, the uptake of Al, P, Cr, Fe, Co, Ni, Zn, As, Cd, and Hg by P. canaliculus was reduced during the first 48 h, suggesting that the biological regulation of these elements is just as important as the bioavailability. Overall, treatment of the rearing seawater with 12 µM EDTA is effective for improving Greenshell™ mussel larval yields by decreasing metal bioavailability during the first two days of development but has minimal benefit between day 2 and 21.

Study on the oxidative stress and transcriptional level in Cr(VI) and Hg(II) reducing strain Acinetobacter indicus yy-1 isolated from chromium-contaminated soil

The bioreduction of Cr(VI) and Hg(II) has become a hot topic in the field of heavy metals bioremediation. However, the mechanism of antioxidant stress in Cr(VI) and Hg(II) reducing bacteria is still not clear. In this work, a novel Cr(VI) and Hg(II) reducing strain Acinetobacter indicus yy-1, was isolated from chromium landfill at a chromate factory, which was used to investigate the mechanism of antioxidant stress during the Cr(VI) and Hg(II) reduction process. The results demonstrated that the removal of Cr(VI) and Hg(II) by A. indicus yy-1 from solution was through reduction rather than biosorption. The reduction rates of Cr(VI) and Hg(II) by resting cells reached 59.71% and 31.73% at 24 h with initial concentration of 10 mg L^-1, respectively. X-ray photoelectron spectroscopy (XPS) analysis further showed that Cr(III) and Hg(0) were mainly the Cr(VI)- and Hg(II)-reduced productions, respectively. Results of physiological assays showed Hg(II) was more toxic to A. indicus yy-1 than Cr(VI), and the activities of antioxidant enzymes (SOD and CAT) were significantly increased in A. indicus yy-1 for relieving the oxidative stress. The transcriptional level of genes related to Cr(VI) and Hg(II) reductases and antioxidant enzymes were up-regulated, indicating that the reductases have participated in the reduction of Cr(VI) and Hg(II), and SOD and CAT served as the vital antioxidant enzymes for defending the oxidative stress. This work provides a deep insight into the mechanism of antioxidant stress in Cr(VI) and Hg(II) reducing bacteria, which helps seek the highly resistant heavy metal reducing bacteria.

Oxidative Damage of Mussels Living in Seawater Enriched with Trace Metals, from the Viewpoint of Proteins Expression and Modification

The impact of metals bioaccumulation in marine organisms is a subject of intense investigation. This study was designed to determine the association between oxidative stress induced by seawater enriched with trace metals and protein synthesis using as a model the mussels Mytilus galloprovincialis. Mussels were exposed to 40 μg/L Cu, 30 μg/L Hg, or 100 μg/L Cd for 5 and 15 days, and the pollution effect was evaluated by measuring established oxidative biomarkers. The results showed damage on the protein synthesis machine integrity and specifically on translation factors and ribosomal proteins expression and modifications. The exposure of mussels to all metals caused oxidative damage that was milder in the cases of Cu and Hg and more pronounced for Cd. However, after prolonged exposure of mussels to Cd (15 days), the effects receded. These changes that perturb protein biosynthesis can serve as a great tool for elucidating the mechanisms of toxicity and could be integrated in biomonitoring programs.

Will temperature rise change the biochemical alterations induced in Mytilus galloprovincialis by cerium oxide nanoparticles and mercury?

It is known that, for marine coastal ecosystems, pollution and global warming are among the most threatening factors. Among emerging pollutants, nanoparticles (NPs) deserve particular attention as their possible adverse effects are significantly influenced by environmental factors such as salinity, pH and temperature, as well as by their ability to interact with other contaminants. In this framework, the present study aimed to evaluate the potential interactions between CeO₂ NPs and the toxic classic metal mercury (Hg), under current and warming conditions. The marine bivalve Mytilus galloprovincialis was used as biological model and exposed to CeO₂ NPs and Hg, either alone or in combination, for 28 day at 17 °C and 22 °C. A suite of biomarkers related to energetic metabolism, oxidative stress/damage, redox balance, and neurotoxicity was applied in exposed and non-exposed (control) mussels. The Hg and Ce accumulation was also assessed. Results showed that the exposure to CeO₂ NPs alone did not induce toxic effects in M. galloprovincialis. On the contrary, Hg exposure determined a significant loss of energetic metabolism and a general impairment in biochemical performances. Hg accumulation in mussels was not modified by the presence of CeO₂ NPs, while the biochemical alterations induced by Hg alone were partially canceled upon co-exposure with CeO₂ NPs. The temperature increase induced loss of metabolic and biochemical functions and the effects of temperature prevailed on mussels exposed to pollutants acting alone or combined.

Effects of waterborne exposure to cadmium on biochemical responses in the freshwater gastropod, Bellamya aeruginosa

The biochemical responses of Bellamya aeruginosa as a dominant and widespread freshwater gastropod throughout China to waterborne cadmium (Cd) were investigated to explore the impacts of exposure concentration and duration in this potential sentinel species. After the 7 days' test of dosage-mortality relationship, gastropods were exposed for either 7 days at the LC₅₀ (1.7 mg/L), the LC₁₀ (0.7 mg/L) and 0.02 mg/L Cd, or 28 days at 0.02 mg/L Cd. A suite of biochemical indicators including metallothionein-like protein (MTLP), reduced glutathione (GSH), catalase (CAT), contents of tissue metal (Cd, Fe, Mn, Cu, Zn), and the compartments of these metals bound to MTLP were examined. The treatment of 0.02 mg/L Cd led to the increase of Cd bound to MTLP (Cd-MTLP) levels, the decrease of GSH content, and the upregulation of CAT activity, but no induction of MTLP, indicating that the intrinsic MTLP and GSH worked together for the detoxification of Cd at the low exposure. When the exposure concentration increased, GSH was depleted severely and synthesis of MTLP was triggered, leading to a strong and significant relationship between MTLP level and Cd accumulation. At the lethal concentrations (1.7 mg/L), both MTLP induction and CAT activity were inhibited while the proportion of Cd-MTLP to total Cd were increased, suggesting more intrinsic MTLP were utilized to sequester free Cd ions. Therefore, the content of Cd-MTLP in digestive glands of B. aeruginosa was recommended as a reliable biomarker for Cd contamination.

Biomarker responses in oysters Crassostrea hongkongensis in relation to metal contamination patterns in the Pearl River Estuary, southern China

The Pearl River Estuary (PRE) is the third largest estuary in China, where estuarine organisms are under metal stress at various biological levels. Based on the metal concentrations measured in oyster Crassostrea hongkongensis, we documented a change in dominance of metal contamination from Cd, Cr, Cu, Ni and Zn to Ag, Cd, Cu and Zn. In general, metal concentrations were higher in upstream stations and displayed a clear up-downstream gradient. Compared to the historical values, we noted the reductions in Cd, Cr and Ni concentrations, and the changing inputs due to evolving industrial activities were responsible for shaping the metal contamination profile in the PRE region. Along with metal concentrations, a suite of biomarkers was analyzed. Among the metals measured in the oyster tissues, Ag, Cd, Cu, Ni and Zn showed the strongest associations with pro-oxidant and oxidative stress responses (superoxide dismutase, lipid peroxidation and lysosomal membrane destabilization) and detoxification responses (glutathione and metallothionein), suggesting that the present metal contamination still exerts significant amount of stress in biota in the PRE. Metal contamination in estuaries in China is still severe compared to other countries, therefore continuous efforts should be taken to monitor the changing metal profiles with necessary control and remediation measures.

Alterations in the properties of sperm protamine-like II protein after exposure of Mytilus galloprovincialis (Lamarck 1819) to sub-toxic doses of cadmium

Protamine-like proteins (PL-II, PL-III and PL-IV) represent the major basic nuclear component of Mytilus galloprovincialis L sperm chromatin. The present study investigates the effects induced on the properties of PL-II protein after exposure of Mytilus galloprovincialis L for 24 h to 1.5 and 5 µM CdCl₂. We found cadmium accumulation in protamine-like proteins with a linear grow up with the exposition dose. In particular, after 5 µM CdCl₂ mussels exposure, the mobility of PL-II band changed in SDS-PAGE, suggesting structural rearrangement in presence of cadmium. Structural analysis using fluorescent probes, indicated that at 5 µM CdCl₂ the complete conformational change of PL-II protein was reached. In the same condition of mussels exposure of 5 µM CdCl₂, PL-II protein changed its DNA binding mode, which determined a closer DNA binding, because higher amount of NaCl were required for PL-II protein release by sperm nuclei. These results supported the hypothesis that mussel exposure to this CdCl₂ dose, although lower to toxic ones, affects the properties of this protein and as a consequence chromatin organization of spermatozoa that is essential for the success of fertilization.

Multiplexing polysome profiling experiments to study translation in Escherichia coli

Polysome profiling is a widely used method to monitor the translation status of mRNAs. Although it is theoretically a simple technique, it is labor intensive. Repetitive polysome fractionation rapidly generates a large number of samples to be handled in the downstream processes of protein elimination, RNA extraction and quantification. Here, we propose a multiplex polysome profiling experiment in which distinct cellular extracts are pooled before loading on the sucrose gradient for fractionation. We used the multiplexing method to study translation in E. coli. Multiplexing polysome profiling experiments provided similar mRNA translation status to that obtained with the non-multiplex method with comparable distribution of mRNA copies between the polysome profiling fractions, similar ribosome occupancy and ribosome density. The multiplexing method was used for parallel characterization of gene translational responses to changing mRNA levels. When the mRNA level of two native genes, cysZ and lacZ was increased by transcription induction, their global translational response was similar, with a higher ribosome load leading to increased ribosome occupancy and ribosome densities. However the pattern and the magnitude of the translational response were gene specific. By reducing the number of polysome profiling experiments, the multiplexing method saved time and effort and reduced cost and technical bias. This method would be useful to study the translational effect of mRNA sequence-dependent parameters that often require testing multiple samples and conditions in parallel.

Effects of low concentrations copper on antioxidant responses, DNA damage and genotoxicity in thick shell mussel Mytilus coruscus

For the aim to study potential detrimental effects induced by Cu exposure at low, environmentally relevant concentrations, the in vivo activities at different levels of biological organisations of thick shell mussel Mytilus coruscus exposed to two levels of copper were assessed. Cu-induced stresses were evaluated through antioxidant responses, DNA damage and genotoxicity. The results revealed significant higher SOD and CAT activities, and MDA concentration in haemocytes of M. coruscus with Cu exposure at 8 μg/L, while only significant accumulation in CAT activity with Cu exposure at 2 μg/L and no significant changes with SOD activity and MDA concentration at this level of Cu exposure. Copper exposure induced DNA damage as induction of OTM value in a time- and concentration-dependent manner. In addition, copper exposure could significantly induced the expressions of MT-10, Hsp70, Hsp90 and C3. The present results deepen the mussels as a suitable model marine invertebrate species to study potential detrimental effects induced by possible toxicants, in combinations at different levels of biological organisations.

BaP-metals co-exposure induced tissue-specific antioxidant defense in marine mussels Mytilus coruscus

Both benzo(α)pyrene (BaP) and metals are frequently found in marine ecosystem and can cause detrimental effects in marine organism, especially the filter feeder-marine mussels. Although the biological responses in mussels have been well-studied upon the single metal or BaP exposure, the information about antioxidant defense, especially in different tissues of mussels, are still limited. Considering the variety of contaminants existing in the actual marine environment, single BaP (56 μg/L) and the co-exposure with Cu, Cd and Pb (50 μg/L, 50 μg/L and 3 mg/L respectively) were applied in a 6 days exposure followed by 6 days depuration experiment. The alterations of superoxide dismutase (SOD), catalase (CAT) activities and total antioxidant capacity (TAC) level were assessed in haemolymph, gills and digestive glands of marine mussels, Mytilus coruscus. An unparalleled change in antioxidant biomarkers was observed in all cells/tissues, with the SOD activity showing higher sensitivity to exposure. A tissue-specific response showing unique alteration in gill was investigated, indicating the different function of tissues during stress responses. Depressed antioxidant effects were induced by BaP-metals co-exposure, indicating the interaction may alter the intact properties of BaP. To our knowledge, this is the first research to explore the antioxidant defense induced by combined exposure of BaP-metals regarding to tissue-specific responses in marine mussels. The results and experimental model will provide valuable information and can be utilized in the investigation of stress response mechanisms, especially in relation to tissue functions in marine organism in the future.

Functional Involvement of Carbonic Anhydrase in the Lysosomal Response to Cadmium Exposure in Mytilus galloprovincialis Digestive Gland

Carbonic anhydrase (CA) is a ubiquitous metalloenzyme, whose functions in animals span from respiration to pH homeostasis, electrolyte transport, calcification, and biosynthetic reactions. CA is sensitive to trace metals in a number of species. In mussels, a previous study demonstrated CA activity and protein expression to be enhanced in digestive gland by cadmium exposure. The aim of the present work was to investigate the functional meaning, if any, of this response. To this end the study addressed the possible involvement of CA in the lysosomal system response of digestive gland cells to metal exposure. The in vivo exposure to acetazolamide, specific CA inhibitor, significantly inhibited the acidification of the lysosomal compartment in the digestive gland cells charged with the acidotropic probe LysoSensor Green D-189, demonstrating in vivo the physiological contribution of CA to the acidification of the lysosomes. Under CdCl₂ exposure, CA activity significantly increased in parallel to the increase of the fluorescence of LysoSensor Green charged cells, which is in turn indicative of proliferation and/or increase in size of lysosomes. Acetazolamide exposure was able to completely inhibit the cadmium induced Lysosensor fluorescence increase in digestive gland cells. In conclusion, our results demonstrated the functional role of CA in the lysosomal acidification of Mytilus galloprovincialis digestive gland and its involvement in the lysosomal activation following cadmium exposure. CA induction could physiologically respond to a prolonged increased requirement of H⁺ for supporting lysosomal acidification during lysosomal activation.

Oxidative damage of 18S and 5S ribosomal RNA in digestive gland of mussels exposed to trace metals

Numerous studies have shown the ability of trace metals to accumulate in marine organisms and cause oxidative stress that leads to perturbations in many important intracellular processes, including protein synthesis. This study is mainly focused on the exploration of structural changes, like base modifications, scissions, and conformational changes, caused in 18S and 5S ribosomal RNA (rRNA) isolated from the mussel Mytilus galloprovincialis exposed to 40μg/L Cu, 30μg/L Hg, or 100μg/L Cd, for 5 or 15days. 18S rRNA and 5S rRNA are components of the small and large ribosomal subunit, respectively, found in complex with ribosomal proteins, translation factors and other auxiliary components (metal ions, toxins etc). 18S rRNA plays crucial roles in all stages of protein synthesis, while 5S rRNA serves as a master signal transducer between several functional regions of 28S rRNA. Therefore, structural changes in these ribosomal constituents could affect the basic functions of ribosomes and hence the normal metabolism of cells. Especially, 18S rRNA along with ribosomal proteins forms the decoding centre that ensures the correct codon-anticodon pairing. As exemplified by ELISA, primer extension analysis and DMS footprinting analysis, each metal caused oxidative damage to rRNA, depending on the nature of metal ion and the duration of exposure. Interestingly, exposure of mussels to Cu or Hg caused structural alterations in 5S rRNA, localized in paired regions and within loops A, B, C, and E, leading to a continuous progressive loss of the 5S RNA structural integrity. In contrast, structural impairments of 5S rRNA in mussels exposed to Cd were accumulating for the initial 5days, and then progressively decreased to almost the normal level by day 15, probably due to the parallel elevation of metallothionein content that depletes the pools of free Cd. Regions of interest in 18S rRNA, such as the decoding centre, sites implicated in the binding of tRNAs (A- and P-sites) or translation factors, and areas related to translation fidelity, were found to undergo significant metal-induced conformational alterations, leading either to loosening of their structure or to more compact folding. These modifications were associated with parallel alterations in the translation process at multiple levels, a fact suggesting that structural perturbations in ribosomes, caused by metals, pose significant hurdles in translational efficiency and fidelity.

Variations of biomarkers response in mussels Mytilus galloprovincialis to low, moderate and high concentrations of organic chemicals and metals

The changes of acetylcholinesterase activity (AChE), metallothioneins content (MTs), catalase activity (CAT) and lipid peroxidation (LPO) were assessed after 4 days exposure of mussels Mytilus galloprovincialis to a wide range of sublethal concentrations of chlorpyrifos (CHP, 0.03-100 μg/L), benzo(a)pyrene (B(a)P, 0.01-100 μg/L), cadmium (Cd, 0.2-200 μg/L) and copper (Cu, 0.2-100 μg/L). The activity of AChE in the gills decreased after exposure to CHP and Cu, whereas no change of activity was detected after exposure to B(a)P and Cd. Both induction and decrease of MTs content in digestive gland occurred after exposure to CHP and B(a)P, while a marked increase was evident at highest exposure concentrations of Cd. The content of MTs progressively decreased of MTs with increasing concentration of Cu. CAT activity and LPO in the gills did not change after exposure to any of the chemicals. The results demonstrate different response profile in relation to the type of chemical compound, and highlight the potential implications for evaluation of biological effect of contaminants in marine environment. Furthermore, the AChE activity in the gills and MTs content in the digestive gland could be modulated by CHP and Cu at environmentally relevant concentrations indicating the potential risks of short-term transient mussels exposure that may occur due to run-off from land or accidental releases.

Early and efficient induction of antioxidant defense system in Mytilus galloprovincialis embryos exposed to metals and heat stress

The present study aims to elucidate the stress response of early life stages of Mytilus galloprovincialis to the combine effects of selected metals and elevated temperature. For this purpose, we investigated the response of a large panel of oxidative stress markers such as catalase (CAT), superoxide dismutase (SOD), glutathione-S-transferase (GST) activities and lipid peroxidation (thiobarbituric acid reactive substrates (TBARS) concentration) and metallothionein accumulation (MT) as well as selected gene transcription level and metal accumulation in mussels larvae exposed to a sub-lethal concentration of Cu (9.54µg/L), Ag (2.55µg/L) and mixture of the two metals (Cu (6.67µg/L)+Ag (1.47µg/L)) along with a temperature gradient (18, 20 and 22°C) for 48h. Cu and Ag applied as single or mixture were differentially accumulated in mussel larvae according to the exposure temperature. Sod, cat, gst and mt-10 gene transcription levels showed an important increase in larvae exposed to Cu, Ag or to the mix compared to the control condition at 18°C. The same pattern but with higher induction levels was recorded in larvae co-exposed to metals at 20°C. At 22°C, a significant decrease in mRNA abundance of cat, gst and sod and a significant up-regulation of mts targets (mt10 and mt20) were observed.

RESULTS

suggest that co-exposure to metals and moderate elevated temperature (20 and 22°C) significantly increased the antioxidant enzyme activities of catalase (CAT), and glutathione-S-transferase (GST) and caused an increase of metal and metallothionein concentrations. In contrast, no significant change in lipid peroxidation products measured as TBARS content was observed indicating a protective response of anti-oxidative system. This study provides first evidences of the early and efficient protective response of antioxidant defense mechanisms in mussel's early life stages facing in multi stressors situations.

How does the metallothionein induction in bivalves meet the criteria for biomarkers of metal exposure?

Metallothionein (MT) concentrations in the whole soft tissue or in a particular tissue of bivalves have widely been used in ecotoxicological studies and biomonitoring programmes. This approach is based on the reported results on the enhancement of MT induction in bivalves in response to metal exposure. The validity of using MT induction as a biomarker is briefly assessed in the present study. The sensitivity of MT induction in these organisms is questionable due to the high basal MT level as well as the high natural variability related to the effects of a number of biotic and abiotic factors, which are not well described yet. Moreover, the relationship between exposure to metals, the toxic effects of that exposure, and the appearance of MT in soft tissue, is not well characterized. A variety of factors may influence the appearance and distribution of MT: 1) the uneven distribution of metals in particular portions of the soft tissue and in particular subcellular compartments; 2) pre-exposure to metals, perhaps at non-toxic levels; 3) metal-metal competition and metal-protein interactions; and 4) tissue-specific induction, functions, and isoforms of MT. Therefore, attention is required when using MT induction in bivalves for assessment of metal exposure or consequent toxic effects. The MT concentration can be a reliable indicator only when it is considered in relation with metal uptake kinetics and subcellular partitioning while specifying the isoform of MT synthesised and considering various confounding factors. The kinetic turnover of MT may provide useful information on metal exposure and biological effects since it covers both the synthesis and breakdown of MT as well as the chemical species of metals accumulated and MT.

Cadmium-containing carbonic anhydrase CDCA1 in marine diatom Thalassiosira weissflogii

The Carbon Concentration Mechanism (CCM) allows phytoplakton species to accumulate the dissolved inorganic carbon (DIC) necessary for an efficient photosynthesis even under carbon dioxide limitation. In this mechanism of primary importance for diatoms, a key role is played by carbonic anhydrase (CA) enzymes which catalyze the reversible hydration of CO2, thus taking part in the acquisition of inorganic carbon for photosynthesis. A novel CA, named CDCA1, has been recently discovered in the marine diatom Thalassiosira weissflogii. CDCA1 is a cambialistic enzyme since it naturally uses Cd2+ as catalytic metal ion, but if necessary can spontaneously exchange Cd2+ to Zn2+. Here, the biochemical and structural features of CDCA1 enzyme will be presented together with its putative biotechnological applications for the detection of metal ions in seawaters.

Perturbations in ROS-related processes of the fish Gambusia holbrooki after acute and chronic exposures to the metals copper and cadmium

Metallic contamination is a widespread phenomena, particularly in areas impacted by human activities, and has become a relevant environmental concern. However, the toxicity of metals on fish requires full characterization in terms of short- and long-term effects. Thus, the purpose of this study was to determine the acute and chronic oxidative stress response in liver and gills of Gambusia holbrooki exposed to copper and cadmium. To assess the effects of these two metals, we adopted a strategy of analyzing the pollution effects caused by salts of the two metallic elements, and we quantified the oxidative stress biomarkers catalase, glutathione reductase, glutathione-S-transferases, and lipid peroxidation after exposure (4 and 28 days) to ecologically relevant concentrations, thus simulating actual conditions of exposure in the wild. Our results showed that copper elicited strong effects in all tested biomarkers for both acute and chronic challenges. Cadmium caused a similar response and was shown to cause significant changes particularly in catalase and glutathione-S-transferases activities. These findings evidence that ecologically relevant concentrations of common anthropogenic contaminants are causative agents of serious imbalances (namely oxidative stress) that are likely to trigger life-threatening events.

Changes of polyamine pattern in digestive glands of mussel Mytilus galloprovincialis under exposure to cadmium

Polyamines, in particular spermidine and spermine, have been identified as important antioxidants, highly induced by oxidative stress in a variety of organisms. However, little is known about changes in polyamine content of metal-stressed marine organisms. In the present study, mussels (Mytilus galloprovincialis) were experimentally exposed to 25 μg/L Cd(2+) or 100 μg/L Cd(2+) for up to 15 days. Cd(2+) was progressively accumulated in mussel tissues, leading to a characteristic oxidative-stress status. Free putrescine (PUT) production was noticeably induced in response to Cd(2+) at day 5 and then declined. In contrast, free spermidine (SPD) content was gradually reduced, whereas the concentration of free spermine (SPM) increased. In combination, these changes led to a 69% or 88% reduction in the ratio of (SPD+SPM)/PUT at day 5, dependent on the Cd(2+) concentration used, which subsequently followed an upward trend in values, albeit not reaching those of controls. Conjugated polyamines constantly increased, in particular conjugated spermidine and spermine, tagging along with metallothionein production. Acetylated polyamines showed a diverse profile of changes, but their content was generally kept at low levels throughout the exposure period. Collectively, our results suggest that certain polyamine compounds could play a significant role in the tolerance of mussels against Cd(2+)-mediated stress, and that the ratio (SPD+SPM)/PUT could be a good indicator of the metal-stress status.

Evaluation of bioaccumulation and toxic effects of copper on hepatocellular structure in mice

The present study was to evaluate the hepatotoxicity effects in mice exposed to copper (Cu) used as dietary supplements for 95 days. Cu-treated mice showed increased body weight, and no toxic symptoms were observed at the beginning, but the tendency gradually changed with progress of experiment. In the liver, beneficial metals [Cu, iron (Fe), zinc (Zn), manganese (Mn), and molybdenum (Mo)] were analyzed by flame atomic absorption spectrometry. The content of Cu maintained at the same level during the experiments, but not resulting in the imbalance of Fe, Zn, Mn, and Mo being distributed. The activities of alkaline phosphatase (AKP) and super oxidation dismutase (SOD) showed significantly improvement during the first 30 days in Cu-supplemented group (P<0.01) but declined rapidly from 30th to 60th days, and later, they stabilized and were not statistically significant compared with control (P>0.05). No statistically significant correlation of ceruloplasmin (CPL) activity was appreciated during the experiment. The histopathological and ultrastructural abnormalities changes were observed in the liver of mice including vacuolar degeneration, necrosis, karyorrhexis, and endolysis. Many hepatocytes showed increased collagenic fibers, appearance of triglyceride droplets, and swollen mitochondria due to oral route of copper, which may lead to lipid peroxidation and free radicals. In conclusion, our study showed that exposure to copper influenced behavioral pattern and body weight, affected several enzymatic activities, and led to the physiological and considerable structural changes in the liver of mice. The public should pay more attention to avoid being exposed to copper.

A novel C1q-domain-containing (C1qDC) protein from Mytilus coruscus with the transcriptional analysis against marine pathogens and heavy metals

The C1q-domain-containing (C1qDC) proteins, which are involved in various processes of vertebrates, are important pattern recognition receptors in innate immunity of invertebrates. In present study, a novel C1qDC was identified from Mytilus coruscus (designated as McC1qDC), which was 917 bp in length encoding 236 amino acids with a typical signal peptide of 19 amino acid residues in N-terminus. Based on its conserved C1q domain and molecular architecture of 10 β-strand jelly-roll folding topology structure, McC1qDC might be classified as a member of the C1q family. The mRNA transcript of McC1qDC was predominantly detectable in the hemocytes, and a less degree in gill, gonad and mantle, but trace in foot, adductor and digestive gland. Upon induction by Vibrio harveyi and Vibrio alginolyticus, McC1qDC expression was significantly up-regulated. Time-dependent mRNA expression of McC1qDC was found during copper and cadmium exposure for its heavy metal-binding domain. These results indicated that McC1qDC was a novel member of the C1qDC protein family as a pattern recognition receptor against pathogens, and might be developed as a potential indicator for monitoring heavy metals pollution.

Differential response of two ferritin subunit genes (VpFer1 and VpFer2) from Venerupis philippinarum following pathogen and heavy metals challenge

As a principal extracellular iron storage molecule, ferritin plays an important role in the iron-withholding strategy of innate immunity and detoxification system. In this study, we cloned and characterized another ferritin from Venerupis philippinarum (designated as VpFer2), in addition to one previously reported (VpFer1). VpFer2 possessed all the conserved features critical for the fundamental structure and function of ferritin H subunit. VpFer1 and VpFer2 mRNA were both found to be most abundantly expressed in hepatopancreas. Vibrio challenge could significantly up-regulate the mRNA expression of VpFers, and VpFer2 showed more sensitive to Vibrio anguillarum infection. For heavy metals exposure, the expression level of VpFer1 was significantly induced by Cd at 48 h, but kept relatively constant after exposure to Cu. With regards to VpFer2, the expression level dropped significantly at 24 h, then began to increase to the peak value at 48 h under Cd exposure, while Cu exposure constantly depressed the expression level of VpFer2 throughout the time course. Similarly, VpFer2 seemed to be more sensitive to heavy metals exposure than VpFer1 as its mRNA level changed by higher magnitudes. All these results suggested that VpFers may be important proteins involved in host immune defense and heavy metals detoxification. The diverse expression patterns of VpFers demonstrated that VpFer2 was an early and sensitive responder to environmental stress in V. philippinarum.

Cadmium versus copper toxicity: insights from an integrated dissection of protein synthesis pathway in the digestive glands of mussel Mytilus galloprovincialis

The main purpose of this study was to investigate the impact of metal-mediated stress on the protein-synthesis pathway in mussels. To this end, mussels (Mytilus galloprovincialis) underwent a 15 days exposure to 100 μg/L Cu(2+) or Cd(2+). Both metals, in particular Cd(2+), accumulated in mussel digestive glands and generated a specific status of oxidative-stress. Exposure of mussels to each metal resulted in 40% decrease of the tRNA-aminoacylation efficiency, at the end of exposure. Cu(2+) also caused a progressive loss in the capability of 40S-ribosomal subunits to form 48S pre-initiation complex, which reached 34% of the control at the end of exposure. Other steps of translation underwent less pronounced, but measurable damages. Mussels exposed to Cd(2+) for 5 days presented a similar pattern of translational dysfunctions in digestive glands, but during the following days of exposure the ribosomal efficiency was gradually restored. Meanwhile, metallothionein levels significantly increased, suggesting that upon Cd(2+)-mediated stress the protein-synthesizing activity was reorganized both quantitatively and qualitatively. Conclusively, Cd(2+) and Cu(2+) affect translation at several levels. However, the pattern of translational responses differs, largely depending on the capability of each metal to affect cytotoxic pathways in the tissues, such as induction of antioxidant defense and specific repair mechanisms.

Biochemical biomarker responses of green-lipped mussel, Perna canaliculus, to acute and subchronic waterborne cadmium toxicity

The biochemical responses of the green-lipped mussel, Perna canaliculus, to waterborne cadmium (Cd) were investigated in order to delineate toxic mechanisms, and the impacts of exposure dose and duration, of this important toxicant in a potential sentinel species. Mussels were exposed for either 96 h (acute: 0, 2000, 4000 μgL(-1) Cd) or for 28 d (subchronic: 0, 200, 2000 μgL(-1) Cd), and the digestive gland, gill and haemolymph were examined for impacts. Biochemical responses measured included those associated with metal detoxification (metallothionein-like protein; MTLP), oxidative stress (catalase, lipid peroxidation), cellular homeostasis (alkaline phosphatase, Na(+), K(+)-ATPase; NKA), and energy utilisation (glycogen, haemolymph protein). Following acute exposure, digestive gland glycogen and gill NKA activity were significantly altered by Cd exposure relative to levels in mussels exposed to Cd-free seawater. Subchronic Cd exposure resulted in a significant increase in MTLP levels in both the gill and the digestive gland. This increase was correlated strongly with the levels of Cd accumulation measured in these tissues (R=0.957 for gill, 0.964 for digestive gland). Catalase activity followed a similar pattern, although the correlation with tissue Cd accumulation was not as strong (R=0.907 for gill, 0.708 for digestive gland) as that for MTLP. Lipid peroxidation increased in the digestive gland at Days 7 and 14 at both subchronic Cd levels tested, but this effect had largely dissipated by Days 21 and 28 (with the exception of the 2,000 μgL(-1) group at Day 28). Alkaline phosphatase activity decreased significantly with Cd exposure in both tissues. This effect was observed at both tested concentrations in the gill, but only at the highest concentration for digestive gland. A decrease in digestive gland glycogen levels was observed in Cd-exposed mussels (Days 14 and 21 at 2,000 μgL(-1)), while haemolymph protein levels increased as a result of subchronic Cd exposure. These findings indicated that biochemical responses in Cd-exposed mussels were tissue-specific, dose- and time-dependent, with duration of exposure being the predominant effect. This study shows that biochemical changes in Cd-exposed green-lipped mussels can be linked to tissue metal accumulation and are consistent with previously reported physiological effects. It also suggests that green-lipped mussels are amenable to a multiple biomarker approach and may be of use as a bioindicator species for monitoring coastal metal pollution.

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.

Dysfunctions of the translational machinery in digestive glands of mussels exposed to mercury ions

Mercury is an element naturally occurring in the biosphere, but is also released into the environment by human activities, such as mining, smelting, and industrial discharge. Mercury is a biologically harmful element and any exposure of living organisms mainly due to contamination, can cause severe or even lethal side effects. In every form detected, elemental, inorganic, or organic, mercury exhibits toxicity associated with induced oxidative stress. Although the genotoxicity of mercury has been well demonstrated in mussels, little is known about its toxic effects on the translational machinery at the molecular level. To investigate possible effects, we exposed the common mussel Mytilus galloprovincialis in seawater supplemented by 30 μg/L Hg²⁺ for 15 days. We observed that Hg²⁺ was significantly accumulated in the digestive glands of mussels, reaching a level around 80 μg/g tissue (dry weight) at the 15th day of exposure. Exposure of mussels to Hg²⁺ resulted in failure of redox homeostasis, as reflected on lipid peroxidation levels and superoxide dismutase activity in glands, and micronucleus frequency in gills. Extracts from digestive glands after 15-day exposure to Hg²⁺ exhibited decreased tRNA aminoacylation ability and, moreover, a 70% reduction in the ability of 40S ribosomal subunits to form the 48S initiation ribosomal complex. A similar reduction was detected in the ability of ribosomes to translocate peptidyl-tRNA from the A-site to the P-site, an observation coinciding with the notion that regulation of protein synthesis by Hg²⁺ mainly occurs at the initiation and elongation stages of translation. A-site binding, peptidyl transferase activity, and termination of peptide chain synthesis underwent less pronounced but measurable reductions, a finding which explains why poly(Phe)-synthesis in ribosomes isolated from exposed mussels is reduced by 70%. In conclusion, Hg²⁺ apart from being a genotoxic ion acts as a modulator of protein synthesis in mussels, an observation probably related with its ability to induce oxidative stress.

DNA damage and transcriptional changes in the gills of mytilus galloprovincialis exposed to nanomolar doses of combined metal salts (Cd, Cu, Hg)

Aiming at an integrated and mechanistic view of the early biological effects of selected metals in the marine sentinel organism Mytilus galloprovincialis, we exposed mussels for 48 hours to 50, 100 and 200 nM solutions of equimolar Cd, Cu and Hg salts and measured cytological and molecular biomarkers in parallel. Focusing on the mussel gills, first target of toxic water contaminants and actively proliferating tissue, we detected significant dose-related increases of cells with micronuclei and other nuclear abnormalities in the treated mussels, with differences in the bioconcentration of the three metals determined in the mussel flesh by atomic absorption spectrometry. Gene expression profiles, determined in the same individual gills in parallel, revealed some transcriptional changes at the 50 nM dose, and substantial increases of differentially expressed genes at the 100 and 200 nM doses, with roughly similar amounts of up- and down-regulated genes. The functional annotation of gill transcripts with consistent expression trends and significantly altered at least in one dose point disclosed the complexity of the induced cell response. The most evident transcriptional changes concerned protein synthesis and turnover, ion homeostasis, cell cycle regulation and apoptosis, and intracellular trafficking (transcript sequences denoting heat shock proteins, metal binding thioneins, sequestosome 1 and proteasome subunits, and GADD45 exemplify up-regulated genes while transcript sequences denoting actin, tubulins and the apoptosis inhibitor 1 exemplify down-regulated genes). Overall, nanomolar doses of co-occurring free metal ions have induced significant structural and functional changes in the mussel gills: the intensity of response to the stimulus measured in laboratory supports the additional validation of molecular markers of metal exposure to be used in Mussel Watch programs.

A common response to common danger? Comparison of animal and plant signaling pathways involved in cadmium sensing

Exposure to cadmium results in disturbances in cell homeostasis in all living organisms. The first response to stress factors, including cadmium, is activation of signal transduction pathways that mobilize cell defense mechanisms. The aim of this review is a comparison between the signaling network triggered by Cd in plants and animals. Despite differences in the structure and physiology of plant and animal cells, their cadmium signal transduction pathways share many common elements. These elements include signaling molecules such as ROS, Ca(2+) and NO, the involvement of phospholipase C, mitogen-activated protein kinase cascades, and activation of transcription factors. Undoubtedly, both animals and plants also possess specific signaling pathways. In case of animals, Wnt/β-catenin, sonic hedgehog and oestorgen signaling are engaged in the transduction of cadmium signal. Plant specific signal transduction pathways include signaling mediated by plant hormones. The role of ethylene and jasmonic, salicylic and abscisic acid in plant response to cadmium is also discussed.