Stress-induced catecholamine changes in the hemolymph of the oyster Crassostrea gigas

Molecular evidence for the adaptive evolution in euryhaline bivalves

Marine bivalves inhabiting intertidal and estuarine areas are frequently exposed to salinity stress due to persistent rainfall and drought. Through prolonged adaptive evolution, numerous bivalves have developed eurysalinity, which are capable of tolerating a wide range of salinity fluctuations through the sophisticated regulation of physiological metabolism. Current research has predominantly focused on investigating the physiological responses of bivalves to salinity stress, leaving a significant gap in our understanding of the adaptive evolutionary characteristics in euryhaline bivalves. Here, comparative genomics analyses were performed in two groups of bivalve species, including 7 euryhaline species and 5 stenohaline species. We identified 24 significantly expanded gene families and 659 positively selected genes in euryhaline bivalves. A significant co-expansion of solute carrier family 23 (SLC23) facilitates the transmembrane transport of ascorbic acids in euryhaline bivalves. Positive selection of antioxidant genes, such as GST and TXNRD, augments the capacity of active oxygen species (ROS) scavenging under salinity stress. Additionally, we found that the positively selected genes were significantly enriched in KEGG pathways associated with carbohydrates, lipids and amino acids metabolism (ALDH, ADH, and GLS), as well as GO terms related to transmembrane transport and inorganic anion transport (SLC22, CLCND, and VDCC). Positive selection of MCT might contribute to prevent excessive accumulation of intracellular lactic acids during anaerobic metabolism. Positive selection of PLA2 potentially promote the removal of damaged membranes lipids under salinity stress. Our findings suggest that adaptive evolution has occurred in osmoregulation, ROS scavenging, energy metabolism, and membrane lipids adjustments in euryhaline bivalves. This study enhances our understanding of the molecular mechanisms underlying the remarkable salinity adaption of euryhaline bivalves.

The effects of SLICE®- and ivermectin-contaminated sediment on avoidance behaviour and oxygen consumption in marine benthic invertebrates

Pest management strategies to reduce sea lice infestations in the salmon aquaculture industry include in-feed treatments with ivermectin (IVM) and SLICE® (active ingredient [AI] emamectin benzoate [EMB]), which can result in local contamination of the environment. These compounds partition to sediments, have moderate persistence, and may pose a risk to non-target benthic organisms. The sub-lethal effects of EMB, IVM and a combination of both (EMB/IVM) on the benthic amphipod Eohaustorius estuarius and polychaete Nereis virens at environmentally relevant sediment concentrations were examined in subchronic exposures (28-30-d). E. estuarius avoided sediment containing >50 μg/kg IVM alone and in combination with EMB. N. virens avoided sediment with >50 μg/kg IVM and >0.5 μg/kg EMB/IVM and exhibited impaired burrowing and locomotory behaviour with both treatments. Oxygen consumption was significantly decreased in E. estuarius (up to 50% compared to controls) and increased in N. virens (by ∼ 200%) when exposed to EMB, IVM and EMB/IVM at concentrations <5 μg/kg. IVM, SLICE® and combination exposures at environmentally relevant concentrations caused adverse effects in E. estuarius and N. virens which could significantly alter organism fitness near salmon aquaculture operations.

Role of the Neuroendocrine System of Marine Bivalves in Their Response to Hypoxia

Mollusks comprise one of the largest phylum of marine invertebrates. With their great diversity of species, various degrees of mobility, and specific behavioral strategies, they haveoccupied marine, freshwater, and terrestrial habitats and play key roles in many ecosystems. This success is explained by their exceptional ability to tolerate a wide range of environmental stresses, such as hypoxia. Most marine bivalvemollusksare exposed to frequent short-term variations in oxygen levels in their marine or estuarine habitats. This stressfactor has caused them to develop a wide variety of adaptive strategies during their evolution, enabling to mobilize rapidly a set of behavioral, physiological, biochemical, and molecular defenses that re-establishing oxygen homeostasis. The neuroendocrine system and its related signaling systems play crucial roles in the regulation of various physiological and behavioral processes in mollusks and, hence, can affect hypoxiatolerance. Little effort has been made to identify the neurotransmitters and genes involved in oxygen homeostasis regulation, and the molecular basis of the differences in the regulatory mechanisms of hypoxia resistance in hypoxia-tolerant and hypoxia-sensitive bivalve species. Here, we summarize current knowledge about the involvement of the neuroendocrine system in the hypoxia stress response, and the possible contributions of various signaling molecules to this process. We thusprovide a basis for understanding the molecular mechanisms underlying hypoxic stress in bivalves, also making comparisons with data from related studies on other species.

A Novel Dop2/Invertebrate-Type Dopamine Signaling System Potentially Mediates Stress, Female Reproduction, and Early Development in the Pacific Oyster (Crassostrea gigas)

The dopaminergic signaling pathway is involved in many physiological functions in vertebrates, but poorly documented in protostome species except arthropods. We functionally characterized a novel dopamine receptor in the Pacific oyster (Crassostrea gigas), activated by dopamine and tyramine with different efficacy and potency orders. This receptor - Cragi-DOP2R - belongs to the D₁-like family of receptors and corresponds to the first representative of the Dop2/invertebrate-type dopamine receptor (Dop2/INDR) group ever identified in Lophotrochozoa. Cragi-DOP2R transcripts were expressed in various adult tissues, with higher expression levels in the visceral ganglia and the gills. Following an experiment under acute osmotic conditions, Cragi-DOP2R transcripts significantly increased in the visceral ganglia and decreased in the gills, suggesting a role of dopamine signaling in the mediation of osmotic stress. Furthermore, a role of the Cragi-DOP2R signaling pathway in female gametogenesis and in early oyster development was strongly suggested by the significantly higher levels of receptor transcripts in mature female gonads and in the early embryonic stages.

Evaluation of Norovirus Reduction in Environmentally Contaminated Pacific Oysters During Laboratory Controlled and Commercial Depuration

Norovirus contamination of oysters is the lead cause of non-bacterial gastroenteritis and a significant food safety concern for the oyster industry. Here, norovirus reduction from Pacific oysters (Crassostrea gigas), contaminated in the marine environment, was studied in laboratory depuration trials and in two commercial settings. Norovirus concentrations were measured in oyster digestive tissue before, during and post-depuration using the ISO 15216-1 quantitative real-time RT-PCR method. Results of the laboratory-based studies demonstrate that statistically significant reductions of up to 74% of the initial norovirus GII concentration was achieved after 3 days at 17-21 °C and after 4 days at 11-15 °C, compared to 44% reduction at 7-9 °C. In many trials norovirus GII concentrations were reduced to levels below 100 genome copies per gram (gcg^-1; limit of quantitation; LOQ). Virus reduction was also assessed in commercial depuration systems, routinely used by two Irish oyster producers. Up to 68% reduction was recorded for norovirus GI and up to 90% for norovirus GII reducing the geometric mean virus concentration close to or below the LOQ. In both commercial settings there was a significant difference between the levels of reduction of norovirus GI compared to GII (p < 0.05). Additionally, the ability to reduce the norovirus concentration in oysters to < LOQ differed when contaminated with concentrations below and above 1000 gcg^-1. These results indicate that depuration, carried out at elevated (> 11 °C) water temperatures for at least 3 days, can reduce the concentration of norovirus in oysters and therefore consumer exposure providing a practical risk management tool for the shellfish industry.

Oxidative stress: Noradrenaline as an integrator of responses in the neuroendocrine and immune systems of the ascidian Phallusia nigra

Neurotransmitters play key roles in regulating the homeostasis of organisms in stressful environments. Noradrenaline (NA) is the main neurotransmitter known to modulate immunological parameters, and is important in the crosstalk between the neuroendocrine and immune systems. In this study, using the ascidian Phallusia nigra, we analyzed the level of catecholamines (CA) in the plasma after mechanical stress, and the effect of NA on the oxidative stress (OS) displayed by immune cells. We measured the concentration of reactive oxygen species (ROS), and analyzed whether α- and/or β-adrenoreceptors (ARs) are involved in ROS modulation, lipid peroxidation (LPO), antioxidant capacity against peroxyl radicals (ACAP), and activity of the enzymes catalase (CAT) and glutathione S transferase (GST) in immune cells after incubation with different concentrations of NA, with or without zymosan (ZnA) challenge. The results showed that NA reduced ROS production, even in immune cells challenged with ZnA, and that this modulation occurred through α₁-and β₁-ARs. ACAP levels showed different responses, depending on whether immune cells were challenged or not with ZnA, and also depending on the NA concentration: 1.0 μM NA increased ACAP levels, but 10.0 μM reduced ACAP levels. NA enhanced the activity of CAT and GST in ZnA-challenged and non-challenged immune cells, while 1.0 and 10.0 μM NA effectively reduced LPO. Taken together, these results show that NA can protect cells from ROS damage, decreasing ROS production and LPO, and enhancing ACAP as well as the activity of CAT and GST. The approach used here with this model contributes to understanding the relationship between the neuroendocrine and immune systems, revealing new effects of NA on OS regulation in ascidians.

Control of mussel Mytilus galloprovincialis Lamarck fouling in water-cooling systems using plasma discharge

To prevent marine macrofouling, the anti-fouling effect of liquid discharge on mussels Mytilus galloprovincialis Lamarck was investigated in a simulated water-cooling system. The effects of input energy, mussel distance from discharge center, continuous discharge time, and discharge energy distribution mode on mussel response (death or detachment) were systematically studied. The results showed that excellent anti-fouling effects could be achieved by increasing input energy, but the detachment rate and mortality of mussels decreased sharply when the mussels were farther away from the discharge center. Low frequency discharge for a long, continuous time and multiple stimuli at long intervals improved the anti-fouling effect. Shock waves are the most likely cause of mussel eradication, and the threshold values of peak pressure to prevent mussel settlement and to cause death were 0.02 MPa and 0.05 MPa, respectively.

The transcriptional response of the Pacific oyster Crassostrea gigas under simultaneous bacterial and heat stresses

Bacterial infection and heat stress are considered as two major environmental threats for the aquaculture industry of oyster Crassostrea gigas. In the present study, the expression profiles of mRNA transcripts in the hemocytes of oysters under bacterial challenge and heat stress were examined by next-generation sequencing. There were 21,095, 21,957 and 21,141 transcripts identified in the hemocytes of oysters from three groups, respectively, including control group (designated as Con group), Vibrio splendidus challenge group (Bac group), and bacterial and heat stress combined treatment group (BacHeat group). There were 4610, 5093 and 5149 differentially expressed transcripts (DTs) in the three pairwise comparisons Con/Bac, Con/BacHeat and Bac/BacHeat, respectively. The main enriched GO terms in biological process category of the DTs included the metabolic processes, cellular process, response to stimulus and immune system process. The expression patterns of DTs involved in pattern recognition, immune signal transduction and energy metabolic indicated that the immune response to bacterial challenge was disturbed under acute heat stress, which was also confirmed by quantitative real-time PCR. The neuroendocrine immunomodulation, especially the catecholaminergic regulation, played indispensable roles in stress response. The total energy reserves as well as cellular energy allocation (CEA) in hepatopancreas of oysters decreased remarkably especially in BacHeat group, while the energy consumption generally increased, suggesting that the immune defense against the simultaneous stimulation of pathogen and heat stress imposed greater costs on oyster's energy expenditure than a single stressor. These results above indicated that, the heat stress disturbed the normal expression of genes involved in immune response and energy metabolism, accelerated energy consumption and broke the metabolic balance, leading to a decline in resilience to infection and mass mortality of oyster in summer.

The Neuroendocrine-Immune Regulation in Response to Environmental Stress in Marine Bivalves

Marine bivalves, which include many species worldwide, from intertidal zones to hydrothermal vents and cold seeps, are important components of the ecosystem and biodiversity. In their living habitats, marine bivalves need to cope with a series of harsh environmental stressors, including biotic threats (bacterium, virus, and protozoan) and abiotic threats (temperature, salinity, and pollutants). In order to adapt to these surroundings, marine bivalves have evolved sophisticated stress response mechanisms, in which neuroendocrine regulation plays an important role. The nervous system and hemocyte are pillars of the neuroendocrine system. Various neurotransmitters, hormones, neuropeptides, and cytokines have been also characterized as signal messengers or effectors to regulate humoral and cellular immunity, energy metabolism, shell formation, and larval development in response to a vast array of environmental stressors. In this review substantial consideration will be devoted to outline the vital components of the neuroendocrine system identified in bivalves, as well as its modulation repertoire in response to environmental stressors, thereby illustrating the dramatic adaptation mechanisms of molluscs.

D1 dopamine receptor is involved in shell formation in larvae of Pacific oyster Crassostrea gigas

Dopamine (DA), a significant member of catecholamines, is reported to induce biomineralization of calcium carbonate vaterite microspheres via dopamine receptor (DR) in bivalves, implying the modulation of dopaminergic system on shell formation during larval development. In this research, a homologue of D1 type DR (CgD1DR-1) was identified from oyster Crassostrea gigas, whose full length cDNA was 1197 bp. It was widely expressed in various tissues of C. gigas, with the significantly higher levels in hepatopancreas, mantle, muscle and gill. During developmental stages, the mRNA transcripts of CgD1DR-1 in D-shape larvae were obviously higher (p < 0.05) than those in trochophore and umbo larvae, and CO₂ exposure could inhibit the synthesis of DA and mRNA expression of CgD1DR-1. After cell transfection and DA treatment, intracellular cAMP in cells with the expression of CgD1DR-1 increased significantly (p < 0.05). Furthermore, the incubation with SCH 23390 for the blockage of CgD1DR-1 significantly restrained the expressions of six shell formation-related genes including CgTyrosinase-1, CgTyrosinase-3, CgChitinaseLP, CgAMC, CgBMP and CgBMPR in trochophore and D-shape larvae. These results jointly suggested that DA together with its receptor CgD1DR-1 might be involved in shell formation during oyster larval development from trochophore to D-shape larvae, and CO₂-induced ocean acidification (OA) might influence marine bivalves by inhibiting the DA-D1DR pathway to prohibit their shell formation.

Short-Term Exposure of Mytilus coruscus to Decreased pH and Salinity Change Impacts Immune Parameters of Their Haemocytes

With the release of large amounts of CO₂, ocean acidification is intensifying and affecting aquatic organisms. In addition, salinity also plays an important role for marine organisms and fluctuates greatly in estuarine and coastal ecosystem, where ocean acidification frequently occurs. In present study, flow cytometry was used to investigate immune parameters of haemocytes in the thick shell mussel Mytilus coruscus exposed to different salinities (15, 25, and 35‰) and two pH levels (7.3 and 8.1). A 7-day in vivo and a 5-h in vitro experiments were performed. In both experiments, low pH had significant effects on all tested immune parameters. When exposed to decreased pH, total haemocyte count (THC), phagocytosis (Pha), esterase (Est), and lysosomal content (Lyso) were significantly decreased, whereas haemocyte mortality (HM) and reactive oxygen species (ROS) were increased. High salinity had no significant effects on the immune parameters of haemocytes as compared with low salinity. However, an interaction between pH and salinity was observed in both experiments for most tested haemocyte parameters. This study showed that high salinity, low salinity and low pH have negative and interactive effects on haemocytes of mussels. As a consequence, it can be expected that the combined effect of low pH and changed salinity will have more severe effects on mussel health than predicted by single exposure.

The oyster immunity

Oysters, the common name for a number of different bivalve molluscs, are the worldwide aquaculture species and also play vital roles in the function of ecosystem. As invertebrate, oysters have evolved an integrated, highly complex innate immune system to recognize and eliminate various invaders via an array of orchestrated immune reactions, such as immune recognition, signal transduction, synthesis of antimicrobial peptides, as well as encapsulation and phagocytosis of the circulating haemocytes. The hematopoietic tissue, hematopoiesis, and the circulating haemocytes have been preliminary characterized, and the detailed annotation of the Pacific oyster Crassostrea gigas genome has revealed massive expansion and functional divergence of innate immune genes in this animal. Moreover, immune priming and maternal immune transfer are reported in oysters, suggesting the adaptability of invertebrate immunity. Apoptosis and autophagy are proved to be important immune mechanisms in oysters. This review will summarize the research progresses of immune system and the immunomodulation mechanisms of the primitive catecholaminergic, cholinergic, neuropeptides, GABAergic and nitric oxidase system, which possibly make oysters ideal model for studying the origin and evolution of immune system and the neuroendocrine-immune regulatory network in lower invertebrates.

Differential response to stress in Ostrea lurida as measured by gene expression

Olympia oysters are the only oyster native to the west coast of North America. The population within Puget Sound, WA has been decreasing significantly since the early 1900’s. Current restoration efforts are focused on supplementing local populations with hatchery bred oysters. A recent study by Heare et al. (2017) has shown differences in stress response in oysters from different locations in Puget Sound however, nothing is known about the underlying mechanisms associated with these observed differences. In this study, expression of genes associated with growth, immune function, and gene regulatory activity in oysters from Oyster Bay, Dabob Bay, and Fidalgo Bay were characterized following temperature and mechanical stress. We found that heat stress and mechanical stress significantly changed expression in molecular regulatory activity and immune response, respectively. We also found that oysters from Oyster Bay had the most dramatic response to stress at the gene expression level. These data provide important baseline information on the physiological response of Ostrea lurida to stress and provide clues to underlying performance differences in the three populations examined.

CgA1AR-1 acts as an alpha-1 adrenergic receptor in oyster Crassostrea gigas mediating both cellular and humoral immune response

We have now cloned an alpha-1 adrenergic receptor (A1AR) from the cDNA library of oyster Crassostrea gigas, designating as CgA1AR-1. The full length of CgA1AR-1 was 1149 bp and it encodes a protein of 382 amino acids containing a 7 transmembrane domain, whose putative topology was similar to the A1ARs in higher organisms and shared similarity of 19% with mammalian A1ARs according to the phylogenic analysis. After cell transfection of CgA1AR-1 into HEK293T cells and the incubation with its specific agonist norepinephrine (NE), the concentration of second messenger Ca²⁺ increased significantly (p < 0.05). But, this increasing of Ca²⁺ could be inhibited by adding A1AR antagonist DOX. Tissue distribution assays using qRT-PCR suggested that CgA1AR-1 mRNA was ubiquitously expressed in all the major tissues of oyster. LPS stimulation could induce the up-regulation of CgA1AR-1 mRNA in haemocytes from 12 h to 24 h post stimulation. Moreover, the blocking of CgA1AR-1 by DOX before LPS stimulation affected the mRNA expression of oyster TNF (CGI_10005109 and CGI_10006440) in haemocytes, resulting in the rise of haemocyte phagocytic rate and apoptosis index. In addition to cellular immunity, CgA1AR-1 was also involved in humoral immunity of oyster. Inhibition of CgA1AR-1 with DOX could repress the up-regulation of LZY and SOD activities caused by LPS stimulation. These results suggested that CgA1AR-1 acted as an α-1 adrenergic receptor in cetacholaminergic neuroendocrine-immune network mediating both cellular and humoral immune response.

Ecological relevance of biomarkers in monitoring studies of macro-invertebrates and fish in Mediterranean rivers

Mediterranean rivers are probably one of the most singular and endangered ecosystems worldwide due to the presence of many endemic species and a long history of anthropogenic impacts. Besides a conservation value per se, biodiversity is related to the services that ecosystems provide to society and the ability of these to cope with stressors, including climate change. Using macro-invertebrates and fish as sentinel organisms, this overview presents a synthesis of the state of the art in the application of biomarkers (stress and enzymatic responses, endocrine disruptors, trophic tracers, energy and bile metabolites, genotoxic indicators, histopathological and behavioural alterations, and genetic and cutting edge omic markers) to determine the causes and effects of anthropogenic stressors on the biodiversity of European Mediterranean rivers. We also discuss how a careful selection of sentinel species according to their ecological traits and the food-web structure of Mediterranean rivers could increase the ecological relevance of biomarker responses. Further, we provide suggestions to better harmonise ecological realism with experimental design in biomarker studies, including statistical analyses, which may also deliver a more comprehensible message to managers and policy makers. By keeping on the safe side the health status of populations of multiple-species in a community, we advocate to increase the resilience of fluvial ecosystems to face present and forecasted stressors. In conclusion, this review provides evidence that multi-biomarker approaches detect early signs of impairment in populations, and supports their incorporation in the standardised procedures of the Water Frame Work Directive to better appraise the status of European water bodies.

Catecholaminergic System of Invertebrates: Comparative and Evolutionary Aspects in Comparison With the Octopaminergic System

In this review we examined the catecholaminergic system of invertebrates, starting from protists and getting to chordates. Different techniques used by numerous researchers revealed, in most examined phyla, the presence of catecholamines dopamine, noradrenaline, and adrenaline or of the enzymes involved in their synthesis. The catecholamines are generally linked to the nervous system and they can act as neurotransmitters, neuromodulators, and hormones; moreover they play a very important role as regards the response to a large number of stress situations. Nevertheless, in some invertebrate phyla belonging to Protostoma, the monoamine octopamine is the main biogenic amine. The presence of catecholamines in some protists suggests a role as intracellular or interorganismal signaling molecules and an ancient origin of their synthetic pathways. The catecholamines appear also involved in the regulation of bioluminescence and in the control of larval development and metamorphosis in some marine invertebrate phyla.

Housing temperature influences the pattern of heat shock protein induction in mice following mild whole body hyperthermia

PURPOSE

Researchers studying the murine response to stress generally use mice housed under standard, nationally mandated conditions as controls. Few investigators are concerned whether basic physical aspects of mouse housing could be an additional source of stress, capable of influencing the subsequent impact of an experimentally applied stressor. We have recently become aware of the potential for housing conditions to impact important physiological and immunological properties in mice.

MATERIALS AND METHODS

Here we sought to determine whether housing mice at standard temperature (ST; 22 °C) vs. thermoneutral temperature (TT; 30 °C) influences baseline expression of heat shock proteins (HSPs) and their typical induction following a whole body heating.

RESULTS

There were no significant differences in baseline expression of HSPs at ST and TT. However, in several cases, the induction of Hsp70, Hsp110 and Hsp90 in tissues of mice maintained at ST was greater than at TT following 6 h of heating (which elevated core body temperature to 39.5 °C). This loss of HSP induction was also seen when mice housed at ST were treated with propranolol, a β-adrenergic receptor antagonist, used clinically to treat hypertension and stress.

CONCLUSIONS

Taken together, these data show that housing temperature significantly influences the expression of HSPs in mice after whole body heating and thus should be considered when stress responses are studied in mice.

Toxicity of five antidepressant drugs on embryo-larval development and metamorphosis success in the Pacific oyster, Crassostrea gigas

Unlike conventional pollutants, pharmaceutical residues are continuously discharged at low levels (low to mid ng l(-1) concentrations), which results in the chronic contamination of non-target organisms, but little is known about the effects of these residues. The purpose of this study was to provide the first assessment of the ecotoxicity of five antidepressants (selective serotonin reuptake inhibitors [SSRIs] fluoxetine and sertraline, tricyclic antidepressants [TCAs] clomipramine and amitriptyline, and serotonin norepinephrine reuptake inhibitor [SNRI] duloxetine) at a wide range of concentrations from 0.1 to 100,000 μg l(-1) on two early life stages in the Pacific oyster. The toxicity was quantified in D-shaped larvae after 36 h of exposure, and in 21-day-old pediveliger larvae after 24 h of exposure using the percentage of normal larval development and the metamorphosis rate as endpoints, respectively. The embryotoxicity assays reported that the EC50 values were within the same range of concentrations (67 to 192 μg l(-1)) for all of the tested molecules. The metamorphosis tests revealed that the antidepressants can be ranked along an increasing severity gradient: clomipramine < amitriptyline < duloxetine ~ fluoxetine. Sertraline appeared to be the less toxic molecule on this endpoint; however, a different concentration range was used. The embryotoxicity test was more sensitive than the metamorphosis bioassay for three of the five molecules tested, but the latter test showed more practical benefits. Overall, the obtained toxicity values were at least 10,000-fold higher than the reported environmental concentrations.

Shotgun proteomics reveals physiological response to ocean acidification in Crassostrea gigas

BACKGROUND

Ocean acidification as a result of increased anthropogenic CO2 emissions is occurring in marine and estuarine environments worldwide. The coastal ocean experiences additional daily and seasonal fluctuations in pH that can be lower than projected end-of-century open ocean pH reductions. In order to assess the impact of ocean acidification on marine invertebrates, Pacific oysters (Crassostrea gigas) were exposed to one of four different p CO2 levels for four weeks: 400 μatm (pH 8.0), 800 μatm (pH 7.7), 1000 μatm (pH 7.6), or 2800 μatm (pH 7.3).

RESULTS

At the end of the four week exposure period, oysters in all four p CO2 environments deposited new shell, but growth rate was not different among the treatments. However, micromechanical properties of the new shell were compromised by elevated p CO2. Elevated p CO2 affected neither whole body fatty acid composition, nor glycogen content, nor mortality rate associated with acute heat shock. Shotgun proteomics revealed that several physiological pathways were significantly affected by ocean acidification, including antioxidant response, carbohydrate metabolism, and transcription and translation. Additionally, the proteomic response to a second stress differed with p CO2, with numerous processes significantly affected by mechanical stimulation at high versus low p CO2 (all proteomics data are available in the ProteomeXchange under the identifier PXD000835).

CONCLUSIONS

Oyster physiology is significantly altered by exposure to elevated p CO2, indicating changes in energy resource use. This is especially apparent in the assessment of the effects of p CO2 on the proteomic response to a second stress. The altered stress response illustrates that ocean acidification may impact how oysters respond to other changes in their environment. These data contribute to an integrative view of the effects of ocean acidification on oysters as well as physiological trade-offs during environmental stress.

The modulation of catecholamines on immune response of scallop Chlamys farreri under heat stress

Catecholamines (CAs) play key roles in mediating the physiological responses to various stresses. In the present study, the expression of CA-related genes were examined in the hemocytes of scallop Chlamys farreri under heat stress, and several immune or metabolism-related parameters were investigated after heat stress and adrenoceptor antagonist stimulation. After the scallops were cultured at 28°C, the mRNA expression level of dopa decarboxylase (CfDDC) and α-adrenoceptor (CfαAR) increased significantly (P<0.01), whereas that of monoamine oxidase (CfMAO) was down-regulated in the first 6h (P<0.05), and then up-regulated to the maximum level at 24h (P<0.01). In the hemocytes of scallops injected with adrenoceptor antagonist, the expression levels of peptidoglycan-recognition protein (CfPGRP-S1) and C-type lectin (CfLec-1) began to increase significantly at 2 and 3h post propranolol and high temperature treatment, respectively (P<0.01). While the up-regulation of heat shock protein 70 (CfHSP70) post heat stress was significantly inhibited by prazosin injection (P<0.01), and that of hexokinase (CfHK) was inhibited by both prazosin and propranolol injection (P<0.01). Moreover, the remarkable increase of relative specific activity of SOD in the hemolymph post heat stress (P<0.01) was further up-regulated early after prazosin or propranolol injection (P<0.01), while that of the relative anti-bacterial ability was down-regulated by prazosin or propranolol treatment (P<0.01). These results collectively indicated that the catecholaminergic neuroendocrine system in scallop could be activated by heat stress to release CAs, which subsequently modulated the immune response and energy metabolism via α- and β-adrenoceptors.

Catecholamine levels in groundwater and stream amphipods and their response to temperature stress

Temperature stress in invertebrates is known to be reflected by changes in catecholamine levels. However, the mechanisms of stress response are not fully understood. Groundwater and surface water amphipods are expected to be differently adapted to temperature elevations due to the different temperature regimes in their habitats and consequently, show a different stress response. No data have been published so far regarding the effects of stress on catecholamine patterns in groundwater invertebrates and accordingly, comparisons with surface water fauna are also missing. In this study, we compared the average catecholamine levels in two taxonomically related amphipod species: Niphargus inopinatus, living in groundwater with constant water temperatures throughout the year, and Gammarus pulex, a surface water stream amphipod frequently exposed to diurnal and seasonal temperature fluctuations. Furthermore, we tracked the immediate changes in whole-animal catecholamine levels in response to heat stress in both species. Pronounced differences in the catecholamine levels of the two species became apparent, with the average dopamine (DA) level of N. inopinatus being almost 1000 times higher than that in G. pulex. The noradrenaline (NA) concentrations in N. inopinatus were on average two orders of magnitude higher than in G. pulex, and for adrenaline (A), the difference constituted one order of magnitude. When exposed to short-term heat stress, both species showed a response in terms of catecholamine levels, but the observed patterns were different. In N. inopinatus, temperature stress was reflected by the appearance of adrenaline, while in G. pulex a significant increase in noradrenaline levels occurred in the treatment with the highest temperature elevation.

Scallop phenylalanine hydroxylase implicates in immune response and can be induced by human TNF-α

Phenylalanine hydroxylase (PAH) is an important metabolic enzyme of aromatic amino acids, which is responsible for the irreversible oxidation of phenylalanine to tyrosine. In the present study, the full-length cDNA encoding PAH from Chlamys farreri (designated CfPAH) was cloned by using rapid amplification of cDNA ends (RACE) approaches and expression sequence tag (EST) analysis. The open reading frame of CfPAH encoded a polypeptide of 460 amino acids, and its sequence shared 64.4-74.2% similarity with those of PAHs from other animals. There were an N-terminal regulatory ACT domain and a C-terminal catalytic Biopterin_H domain in the deduced CfPAH protein. The mRNA transcripts of CfPAH could be detected in all the tested tissues, including adductor muscle, mantle, gill, gonad, haemocytes and hepatopancreas. And its expression level in haemocytes was increased significantly during 3-48 h after bacteria Vibrio anguillarum challenge with the highest level (9.1-fold, P < 0.05) at 24 h. Furthermore, the mRNA expression of CfPAH in haemocytes also increased significantly to 2.6-fold (P < 0.05) at 4 h and 3.3-fold (P < 0.05) at 6 h after the stimulation of 50.0 ng mL(-1) human TNF-α. The cDNA fragment encoding the mature peptide of CfPAH was recombined and expressed in the prokaryotic expression system, and 1 mg recombinant CfPAH protein (rCfPAH) could catalyze the conversion of 192.23 ± 32.35 nmol phenylalanine to tyrosine within 1 min (nmol min(-1) mg(-1) protein) in vitro. These results indicated collectively that CfPAH, as a homologue of phenylalanine hydroxylase in scallop C. farreri, could be induced by cytokine and involved in the immunomodulation of scallops by supplying the starting material tyrosine for the synthesis of melanin and catecholamines.

The modulation of catecholamines to the immune response against bacteria Vibrio anguillarum challenge in scallop Chlamys farreri

Catecholamines are pivotal signal molecules in the neuroendocrine-immune regulatory network, and implicated in the modulation of immune response. In the present study, the activities of some immune-related enzymes and the concentration of catecholamines were determined in circulating haemolymph of scallops Chlamys farreri after bacteria Vibrio anguillarum challenge. The activities of superoxide dismutase (SOD), catalase (CAT) and lysozyme (LYZ) increased significantly and reached 610 U mg(-1) at 12 h, 37.6 U mg(-1) at 6 h and 261.5 U mg(-1) at 6 h after bacteria challenge, respectively. The concentration of norepinephrine, epinephrine and dopamine also increased significantly and reached 114.9 ng mL(-1) at 12 h, 86.9 ng mL(-1) at 24 h and 480.4 pg mL(-1) at 12 h after bacteria challenge, respectively. Meanwhile, the activities of these immune-related enzymes in haemolymph were monitored in those scallops which were challenged by bacteria V. anguillarum and stimulated simultaneously with norepinephrine, epinephrine and adrenoceptor antagonist. The injection of norepinephrine and epinephrine repressed significantly the induction of bacteria challenge on the activities of immune-related enzymes, and they were reduced to about half of that in the control groups. The blocking of α and β-adrenoceptor by antagonist only repressed the increase of CAT and LYZ activities significantly, while no significant effect was observed on the increase of SOD activities. The collective results indicated that scallop catecholaminergic neuroendocrine system could be activated by bacteria challenge to release catecholamines after the immune response had been triggered, and the immune response against bacteria challenge could been negatively modulated by norepinephrine, epinephrine, and adrenoceptor antagonist. This information is helpful to further understand the immunomodulation of catecholamines in scallops.

In vitro effects of noradrenaline on Akoya pearl oyster (Pinctada imbricata) haemocytes

Exposure to fluctuating environmental conditions in bivalve molluscs can lead to physiological stress and up-regulated production of stress-associated hormones, such as noradenaline (NA). Since environmental stressors have been found to have an immunosuppressive effect on Pinctada imbricata, we investigated the in vitro affects of NA exposure on their defensive haemocytes, focussing specifically on markers of apoptosis. Terminal dUTP nick-end (TUNEL) labelling was used to detect cells displaying DNA fragmentation within tissue exposed to NA. DNA fragmentation was most significant when haemocytes were exposed to 10.0 ng NA/μg protein relative to non-treated controls. Similarly, Annexin V-FITC staining, a marker of early apoptotic events, was evident in cells exposed to 5.0 and 10.0 ng NA/μg protein after 120 min (p<0.05), and haemocyte adhesion to glass slides declined significantly when cells were exposed to 10.0 ng NA/μg protein (p<0.05). A number of morphological and ultrastructural changes in NA-exposed haemocytes were also identified using transmission and scanning electron microscopy. These alterations included chromatin and cytoplasmic condensation, the formation of apoptotic bodies, vacuolisation and blebbing. In NA-treated cells, polymerisation of F-actin was observed around the periphery of the cytoplasm. All of these data suggest that NA induces apoptosis in P. imbricata haemocytes.

Immune responses to combined effect of hypoxia and high temperature in the green-lipped mussel Perna viridis

Flow cytometry was used to examine immune responses in haemocytes of the green-lipped mussel Perna viridis under six combinations of oxygen level (1.5 mg O2 l(-1), 6.0 mg O2 l(-1)) and temperature (20 °C, 25 °C and 30 °C) at 24 h, 48 h, 96 h and 168 h. The mussels were then transferred to normoxic condition (6.0 mg O2 l(-1)) at 20 °C for further 24 h to study their recovery from the combined hypoxic and temperature stress. Esterase (Est), reactive oxygen species (ROS), lysosome content (Lyso) and phagocytosis (Pha) were reduced at high temperatures, whereas hypoxia resulted in higher haemocyte mortality (HM) and reduced phagocytosis. For HM and Pha, changes were observed after being exposed to the stresses for 96 h, whereas only a 24 h period was required for ROS and Lyso, and a 48 h one for Est. Recovery from the stresses was observed for HM and Pha but not other immune responses.

Expression of HSP70 in Mytilus californianus following exposure to caffeine

Caffeine, a biologically active drug with many known molecular targets, is recognized as a contaminant of marine systems. Although the concentrations of caffeine reported from aquatic systems are low (ng/l-μg/l), harmful ecological effects not detected by traditional toxicity tests could occur as a result of caffeine contamination. We used Hsp70, a molecular biomarker of cellular stress, to investigate the sub-lethal cellular toxicity of environmentally relevant concentrations of caffeine on the mussel Mytilus californianus, a dominant species in the rocky intertidal zone along the Oregon Coast. Hsp70 concentrations in the gill and mantle tissue of mussels exposed to 0.05, 0.2, and 0.5 μg/l of caffeine for 10, 20, and 30 days were compared to basal levels in control mussels. Hsp70 in the gill tissue of M. californianus had an initial attenuation of the stress protein followed by a significant up-regulation relative to controls in all but the 0.5 μg/l treatment. Hsp70 in the mantle tissue of mussels exposed to caffeine did not differ from control mussels. This study provides laboratory evidence that environmentally relevant concentrations of caffeine can exert an effect on M. californianus gill tissue at the molecular-level.

Larval excretory-secretory products from the parasite Schistosoma mansoni modulate HSP70 protein expression in defence cells of its snail host, Biomphalaria glabrata

Synthesis of heat shock proteins (HSPs) following cellular stress is a response shared by many organisms. Amongst the HSP family, the approximately 70 kDa HSPs are the most evolutionarily conserved with intracellular chaperone and extracellular immunoregulatory functions. This study focused on the effects of larval excretory-secretory products (ESPs) from the parasite Schistosoma mansoni on HSP70 protein expression levels in haemocytes (defence cells) from its snail intermediate host Biomphalaria glabrata. S. mansoni larval stage ESPs are known to interfere with haemocyte physiology and behaviour. Haemocytes from two different B. glabrata strains, one which is susceptible to S. mansoni infection and one which is resistant, both showed reduced HSP70 protein levels following 1 h challenge with S. mansoni ESPs when compared to unchallenged controls; however, the reduction observed in the resistant strain was less marked. The decline in intracellular HSP70 protein persisted for at least 5 h in resistant snail haemocytes only. Furthermore, in schistosome-susceptible snails infected by S. mansoni for 35 days, haemocytes possessed approximately 70% less HSP70. The proteasome inhibitor, MG132, partially restored HSP70 protein levels in ESP-challenged haemocytes, demonstrating that the decrease in HSP70 was in part due to intracellular degradation. The extracellular signal-regulated kinase (ERK) signalling pathway appears to regulate HSP70 protein expression in these cells, as the mitogen-activated protein-ERK kinase 1/2 (MEK1/2) inhibitor, U0126, significantly reduced HSP70 protein levels. Disruption of intracellular HSP70 protein expression in B. glabrata haemocytes by S. mansoni ESPs may be a strategy employed by the parasite to manipulate the immune response of the intermediate snail host.

Cyclic AMP signaling in bivalve molluscs: an overview

The cyclic AMP (cAMP)-dependent signaling accounts for the control of cellular cascades involved in many physiological functions, and a wealth of information is available on the cAMP system that operates in mammalian cells. Nevertheless, cAMP has a central role also in nonmammalian vertebrates and invertebrates. The present review aims at examining the information available on bivalve molluscs, from the first studies carried out in the early 1980s to the last progresses made in the present days. The major focus is on the structural and operational characteristics of the main actors of the signaling pathway, i.e., adenylyl cyclase, G proteins, and protein kinase A, and on the role played by the cyclic nucleotide on smooth muscle, heart, gills, gonads, and metabolism regulation. Moreover, recent evidence regarding the cAMP system as a target of environmental stress factors are discussed. It will become clear that cAMP does play a wide and important role in bivalve physiology. Several issues have been sufficiently clarified, although investigated only in a few model species. However, further fundamental aspects remain unknown, mainly regarding molecular features and interactions with other signaling pathways, thus requiring further elucidation.

The effect of different acclimation temperatures on the prophenoloxidase system and other defence parameters in Litopenaeus vannamei

Water temperature changes (higher and lower than 24 degrees C) were shown to have a significant effect on dopamine (DA) concentration, haemocyte count and the proPO system in the white shrimp Litopenaeus vannamei. No significant difference in any of the parameters was observed in the control group. DA concentration in haemolymph in the experimental groups increased to a peak value at 0.5 days; meanwhile serine protease (SP) activity and proteinase inhibitor (PI) activity decreased. Total haemocyte count (THC), differential haemocyte count (DHC) and PO activity were lowest at 1 day. All defence parameters became stable after 1-3 days, while the total haemocyte and large granular cell count stabilized after 6 days. After these stabilized, there was no significant difference in DA concentration and PI activity between the control and experimental groups, as was the case for the THC, DHC, PO and SP activities of shrimp held at higher temperatures. However these latter four parameters in the lower temperature groups were distinctly lower than the control group. alpha(2)-Macroglobulin activity in the experimental groups increased to a peak value after 1 day compared with the control and then stabilized after 6 days when the activity levels in higher temperature groups were higher than the control, while the lower temperature groups had no significant difference from the control. It was therefore concluded that water temperature changes modulated the immune system of L. vannamei.

Reproductive conflicts affect labor and immune defense in the queenless ant Diacamma sp. "nilgiri"

In many species of social Hymenoptera, totipotency of workers induces potential conflicts over reproduction. However, actual conflicts remain rare despite the existence of a high reproductive skew. One of the current hypotheses assumes that conflicts are costly and thus selected against. We studied the costs of conflicts in 20 colonies of the queenless ant Diacamma sp. "nilgiri" by testing the effects of conflicts on labor and worker immunocompetence, two parameters closely linked to the indirect fitness of workers. In this species, the dominant female is the only mated worker (gamergate) and monopolizes reproduction. We experimentally induced conflicts by splitting each colony into two groups, a control group containing the gamergate and an orphaned group displaying aggressions until a new dominant worker arises. Immunocompetence was assessed by the clearance of Escherichia coli bacteria that we injected into the ants. Time budget analysis revealed a lower rate of labor and especially brood care in orphaned groups, supporting the existence of a cost of conflicts on labor. Fifteen days after splitting, a lower immunocompetence was also found in orphaned groups, which concerned workers involved and not involved in conflicts. We propose that this immunosuppression induced by conflicts could stem from stress and not directly from aggression.

Synergistic impacts of heat shock and spawning on the physiology and immune health ofCrassostrea gigas: an explanation for summer mortality in Pacific oysters

Mass mortality is often observed in cultured oysters during the period following spawning in the summer season. To examine the underlying causes leading to this phenomenon, thermotolerance of the Pacific oyster Crassostrea gigas was assessed using pre- and postspawning oysters that were sequentially treated with sublethal (37°C) and lethal heat shocks (44°C). The effects were examined on a range of immune and metabolic parameters in addition to mortality rate. A preventative 37°C significantly reduced oyster mortality after exposure to a second heat shock of 44°C, but in postspawning oysters mortality remained at 80%, compared with < 10% in prespawning oysters. Levels of the 72 kDa and 69 kDa heat shock proteins were low in the gill tissue from postspawning oysters stimulated by heat shock, indicating spawning reduced heat shock protein synthesis. The postspawning oysters had depleted glycogen stores in the mantle tissue and reduced adenylate energy charge after heat shock, indicative of lower energy for metabolic activity. A cumulative effect of spawning and heat shock was observed on the immunocompetence of oysters, demonstrated by reduced hemocyte phagocytosis and hemolymph antimicrobial activity. These results support the hypothesis that the energy expended during reproduction compromises the thermotolerance and immune status of oysters, leaving them easily subject to mortality if heat stress occurs in postspawning stage. This study improves our understanding of oyster summer mortality and has implications for the long-term persistence of mollusks under the influence of global warming.

In hemocytes from Mytilus galloprovincialis Lmk., treatment with corticotropin or growth factors conditions catecholamine release

The cells in charge of the innate immune response in the sea mussel Mytilus galloprovincialis Lmk. are the hemocytes, which have the capacity to release catecholamines when subjected to stressing conditions. Hemocytes were kept in culture before stimulation. That is, their behaviour was not studied immediately after extraction from the mollusc, as happens in most studies. This avoids the interference and variability caused by the conditions in which mussels may be when collected. This work describes the great variability found in the pattern of catecholamine release when the hemocytes are stimulated with either corticotropins or growth factors. Dopamine, adrenaline and noradrenaline release differs with each of the inducers assayed, with stimulation time and with the season of hemocyte collection. One of the results presented is particularly remarkable; such is the great amount of adrenaline and noradrenaline released to the medium when the hemocytes obtained in summer are stimulated with transforming growth factor-beta1 (TGF-beta1) for 60 min.

Anxiety from a phylogenetic perspective: is there a qualitative difference between human and animal anxiety?

A phylogenetic approach to anxiety is proposed. The different facets of human anxiety and their presence at different levels of the phylum are examined. All organisms, including unicellular such as protozoan, can display a specific reaction to danger. The mechanisms enabling the appraisal of harmful stimuli are fully present in insects. In higher invertebrates, fear is associated with a specific physiological response. In mammals, anxiety is accompanied by specific cognitive responses. The expression of emotions diversifies in higher vertebrates, only primates displaying facial expressions. Finally, autonoetic consciousness, a feature essential for human anxiety, appears only in great apes. This evolutive feature parallels the progress in the complexity of the logistic systems supporting it (e.g., the vegetative and central nervous systems). The ability to assess one's coping potential, the diversification of the anxiety responses, and autonoetic consciousness seem relevant markers in a phylogenetic perspective.

The influence of Zn on signaling pathways and attachment of Mytilus galloprovincialis haemocytes to extracellular matrix proteins

The present study investigates the cytotoxic mechanisms induced by zinc (Zn) in haemocytes of mussel Mytilus galloprovincialis. Haemocytes play a key role in the immune defence of mussels. Micromolar concentration of Zn (50 microM) play an important role in the elevation of pHi and increase in Na+ influx in haemocytes. The observed effects were inhibited by the Na+/H+ exchanger (NHE) inhibitor, ethyl-N-isopropyl-amiloride (EIPA). Furthermore, our results showed that Zn caused an increase in O(-)(2) production that was reversed after NHE inhibition. Phorbol ester (PMA) caused a significant rise both in pHi and Na+ influx as well as in O(-)(2) production. These effects were reversed by calphostin C. Our results indicated that Zn also enhanced haemocyte attachment to both BSA and laminin which was reversed by EIPA and calphostin C. The enhancement of haemocytes attachment to both BSA and laminin after Zn suggests that it is likely to play a signal role in cytoskeleton-dependent process of cell growth and migration in mussel M. galloprovincialis haemocytes. We conclude that Zn induces a signaling pathway with the involvement of NHE, PKC, O(-)(2) and alpha1- and beta-adrenergic receptors.

Cadmium effects on ros production and DNA damage via adrenergic receptors stimulation: role of Na+/H+ exchanger and PKC

The objective of the present study was to elucidate the events that are involved in reactive oxygen species (ROS) production and DNA damage after adrenergic receptors stimulation by cadmium, in relation to cAMP, protein kinase C (PKC) and Na+/H+ exchanger (NHE). Cadmium (50 microM) caused increased levels of ROS with a concomitant increase in DNA damage in digestive gland of Mytilus galloprovincialis. Either the use of EIPA, a NHE blocker, or calphostin C, the inhibitor of PKC, reduced cadmium effects. Cells treated with alpha1-, alpha2-, beta- and beta1- adrenergic antagonists together with cadmium reversed cadmium alone effects, while the respective adrenergic agonists, phenylephrine and isoprenaline, mimic cadmium effects. Moreover, cadmium caused an increase in the levels of cAMP in digestive gland cells that were reversed after NHE and PKC inhibition as well as in the presence of each type of adrenergic antagonist. The different sensitivity of alpha1-, alpha2-, beta-, beta1- adrenergic receptors on ROS, cAMP production and DNA damage possibly leads to the induction of two signaling pathways that may be interacting or to the presence of a compensatory pathway that acts in concert with the alpha- and beta- adrenergic receptors. In these signaling pathways PKC and NHE play significant role.

Cytotoxicity of diatom-derived oxylipins in organisms belonging to different phyla

The cytotoxicity of several saturated and unsaturated marine diatom-derived aldehydes and an oxo-acid have been screened in vitro and in vivo against different organisms, such as bacteria, algae, fungi,echinoderms, molluscs and crustaceans. Conjugated unsaturated aldehydes like 2E,4E-decadienal, 2E,4E-octadienal,5E,7E-9-oxo-nonadienoic acid and 2E-decenal were active against bacteria and fungi and showed weak algicidal activity. By contrast, the saturated aldehyde decanal and the non-conjugated aldehyde 4Z-decenal had either low or no significant biological activity. In assays with oyster haemocytes, 2E,4E-decadienal exhibited a dose-dependent inhibition of cytoskeleton organisation, rate of phagocytosis and oxidative burst and a dose-dependent promotion of apoptosis. A maternal diatom diet that was rich in unsaturated aldehydes induced arrest of cell division and apoptotic cell degradation in copepod embryos and larvae,respectively. This wide spectrum of physiological pathologies reflects the potent cell toxicity of diatom-derived oxylipins, in relation to their non-specific chemical reactivity towards nucleophilic biomolecules. The cytotoxic activity is conserved across six phyla, from bacteria to crustaceans. Deregulation of cell homeostasis is supposed to induce the elimination of damaged cells through apoptosis. However, efficient protection mechanisms possibly exist in unicellular organisms. Experiments with a genetically modified yeast species exhibiting elevated membrane and/or cell wall permeability suggest that this protection can be related to the inability of the oxylipin compounds to enter the cell.

Cadmium induces both pyruvate kinase and Na+/H+exchanger activity through protein kinase C mediated signal transduction, in isolated digestive gland cells ofMytilus galloprovincialis(L.)

The present study investigates the transduction pathway mediated by cadmium in isolated digestive gland cells of mussel Mytilus galloprovincialis. The effects of cadmium treatment on a key glycolytic enzyme, pyruvate kinase (PK), and on Na+/H+ exchanger activity were examined. Cadmium (50 μmol l–1) caused a significant elevation of intracellular pH (pHi) and a rise (176%) of Na influx relative to control values. The amiloride analogue, EIPA (20 nmol l–1), a Na+/H+ exchanger blocker,together with cadmium, significantly reduced the effect of treatment by cadmium alone on both Na+ influx and pHi. In addition, PK activity was significantly increased after treatment with cadmium. PK activity was inhibited after treatment of cells with amiloride or EIPA together with cadmium. Moreover, phorbol-ester (PMA), a potent activator of protein kinase C(PKC), caused a significant rise in both pHi and PK activity, while staurosporine or calphostin C reversed both events. Adrenaline, isoprenaline and phenylephrine alone or together with cadmium also significantly increased the pHi and PK activity of isolated digestive gland cells. The latter effectors in combination with cadmium showed a synergistic effect on pHi and PK. These responses seem to be blocked by propranolol, metoprolol and prazosin. Our findings suggest a hormone-like effect of cadmium on digestive gland cells. The signal transduction pathway induced by cadmium involves the stimulation of PK, PKC and Na+/H+ exchanger in isolated digestive gland cells of Mytilus galloprovincialis.

In vitro effects of LPS, IL-2, PDGF and CRF on haemocytes of Mytilus galloprovincialis Lmk

The cells in charge of the innate immune response in the marine mussel Mytilus galloprovincialis Lmk. are the haemocytes. These cells respond in different ways to agents such as lipopolysaccharide (LPS), interleukin-2 (IL-2), platelet-derived growth factor (PDGF) and corticotropin releasing factor (CRF). After stimulation of the haemocytes, the expression of molecules reactive with monoclonal antibodies raised to the alpha chain of the IL-2 receptor, present in their membrane, differed depending on the agent used. The same happened with regard to the levels of dopamine, adrenaline and noradrenaline released to the medium by the haemocytes. It should also be noted that no catecholamine release was detected and the level of expression of IL-2Ralpha showed no significant variation in cultured cells that had not been treated with inducers. These facts would indicate that most haemocytes were in the same starting condition at the moment that the stimulation was performed. Therefore, cultured haemocytes can be a highly reliable model in the study of the innate immune system.

Evidence for a direct link between stress and immunity in the mollusc Haliotis tuberculata

Stress is thought to cause increased disease outbreaks and mortality in a number of invertebrates but currently very little information is available on mechanisms linking physiological states of stress and reduced disease resistance in these organisms. In the present study, we examined the possibility that stress alters immune functions, the principal line of defense against pathogens, in a molluscan model, the abalone Haliotis turbeculata. Immune parameters were investigated in abalones subjected to a 15 min mechanical disturbance which, as indicated by noradrenaline and dopamine hemolymphatic levels, resulted in a transient state of physiological stress. During the application of the stressor, immune parameters such as the number of circulating hemocytes, the migratory activity, the phagocytic capacity and the respiratory burst responses of hemocytes, decreased significantly. All parameters returned to initial values within 15-30 min after the end of the disturbance and a transient period of immunostimulation occurred between 100 and 480 min after the stress for all immune parameters except intracellular superoxide anion production. These results indicate that in the abalone H. tuberculata, as in vertebrates, a link exists between stress and the immune system. This may begin to answer why stress and disease outbreaks are linked in shellfish.

P35-sensitive caspases, MAP kinases and Rho modulate β-adrenergic induction of apoptosis in mollusc immune cells

Apoptosis is an important mechanism for the preservation of a healthy and balanced immune system in vertebrates. Little is known, however, about how apoptotic processes regulate invertebrate immune defenses. In the present study, we show that noradrenaline, a catecholamine produced by the neuroendocrine system and by immune cells in molluscs, is able to induce apoptosis of oyster Crassostrea gigas hemocytes. The apoptosis-inducing effect of noradrenaline was mimicked by isoproterenol and blocked by propranolol, which indicates that noradrenaline triggers apoptosis via a β-adrenergic signaling pathway. Exposure to the pan-caspase inhibitor Z-VAD-FMK or expression of the caspase inhibitor P35 under the transcriptional control of a mollusc hsp70 gene promoter reduced the number of apoptotic cells among noradrenaline-treated hemocytes. These results suggest that P35-sensitive caspases are involved in the apoptotic process triggered by β-adrenergic signaling. Complementary experiments suggest that mitogen-activated protein kinases and Rho, a member of the Ras GTPase family, may be involved in antiapoptotic mechanisms that modulate the apoptotic effect of noradrenaline. Taken together, these results provide a first insight into apoptotic processes in mollusc immune cells.