Cloning of the glucocorticoid receptor (GR) in gilthead seabream (Sparus aurata). Differential expression of GR and immune genes in gilthead seabream after an immune challenge

Immune and endocrine alterations at the early stage of inflammatory assemblage in toads after stimulation with heat-killed bacteria (Aeromonas hydrophila)

The red-leg syndrome in amphibians is a condition commonly associated with the bacteria Aeromonas hydrophila and has led to population declines. However, there is little information concerning the inflammatory assemblage in infected anurans. We evaluated immune and endocrine alterations induced by stimulation with heat-killed A. hydrophila injected in Rhinella diptycha toads. Control animals were not manipulated, while the others were separated into groups that received intraperitoneal injection of 300 μl of saline or heat-killed bacteria: groups A1 (3 × 107 cells), A2 (3 × 108 cells), and A3 (3 × 109 cells). Animals were bled and euthanized six hours post-injection. We evaluated neutrophil: lymphocyte ratio (NLR), plasma bacterial killing ability (BKA), testosterone (T), melatonin (MEL), and corticosterone (CORT) plasma levels. Heat-killed A. hydrophila increased CORT and NLR, and decreased MEL, especially at higher concentrations. There was no effect of treatment on T and BKA. We then selected the saline and A3 groups to conduct mRNA expression of several genes including glucocorticoid receptor (GR), toll-like receptor-4 (TLR-4), interferon-γ (IFN-γ), interleukin (IL)-1β, IL-6, and IL-10. We found higher expression of IL-6, IL-1β, IL-10, and IFN-γ in group A3 compared to the saline group. These results indicate the beginning of an inflammatory assemblage, notably at the two highest concentrations of bacteria, and give a better understanding of how anurans respond to an infection within an integrated perspective, evaluating different physiological aspects. Future studies should investigate later phases of the immune response to elucidate more about the inflammation in amphibians challenged with A. hydrophila.

Peroxisome proliferator-activated receptors alpha and beta mediate the anti-inflammatory effects of the cyclopentenone prostaglandin 15-deoxy-Δ12,14-PGJ2 in fish granulocytes

Prostaglandins (PGs) are highly reactive small lipophilic molecules derived from polyunsaturated fatty acids of the cell membrane and play a key role in the resolution of inflammation processes. 15-deoxy-Δ^12,14-PGJ₂ (15dPGJ₂) is a cyclopentenone PG (CyPG) of the J series with anti-inflammatory, anti-proliferative and pro-apoptotic effects. This CyPG can signal through: (i) the PGD₂ receptor (DP2) and peroxisome proliferator-activated receptor γ (PPARγ) or (ii) by covalent binding to protein nucleophiles, such as, thiols groups of cysteine, lysine or histidine via a Michael addition reaction, modifying its structure and function. In this work we show that acidophilic granulocytes (AGs) of gilthead seabream (Sparus aurata L.), the functional equivalent to mammalian neutrophils, constitutively expressed ppara, pparb and pparg genes, the latter showing the highest expression and up-regulation when stimulated by bacterial DNA. In addition, we tested the ability of 15dPGJ_2, and its biotinylated analog, as well as several PPARγ ligands, to modulate reactive oxygen species (ROS) and/or cytokines production during a Toll like receptor (TLR)-mediated granulocyte response. Thus, 15dPGJ₂ was able to significantly decrease bacterial DNA-induced ROS production and transcript levels of pparg, interleukin-1β (il1b) and prostaglandin-endoperoxide synthase 2 (ptgs2). In contrast, its biotinylated analog was less potent and a higher dose was required to elicit the same effects on ROS production and cytokine expression. In addition, different PPARγ agonists were able to mimic the effects of 15dPGJ₂. Conversely, the PPARγ antagonist T007097 abolished the effect of 15dPGJ₂ on DNA bacterial-induced ROS production. Surprisingly, transactivation assays revealed that both 15dPGJ₂ and its biotinylated analog signaled via Pparα and Pparβ, but not by Pparγ. These results were further confirmed by HPLC/MS analysis, where Pparβ was identified as an interactor of biotin-15dPGJ₂ in naïve and DNA-stimulated leukocytes. Taken together, our data show that 15dPGJ₂ acts both through Ppar activation and covalent binding to proteins in fish granulocytes and identify for the first time in vertebrates a role for Pparα and Pparβ in the resolution of inflammation mediated by 15dPGJ₂.

Characterization of the glucocorticoid receptor of large yellow croaker (Larimichthys crocea) and its expression in response to salinity and immune stressors

Glucocorticoids are steroidal hormones critical to stress responses in vertebrates. To gain further insight into the role of the glucocorticoid receptor (GR) in acute stress responses in teleost fish, the relevant cDNA of large yellow croaker (Larimichthys crocea; LcGR) was cloned using the rapid amplification of cDNA ends (RACE) technique. Multiple alignment of the amino acids (aa) of LcGR and the GR of other teleosts indicated LcGR contained four commonly conserved domains and lacked the 9-aa insert seen in GR1. Phylogenetic analysis of the amino acid sequence revealed that LcGR grouped most closely with the GR2 of other teleosts and can therefore be considered a GR2 subtype. In healthy L. crocea, Lcgr mRNA was found to be expressed at high levels in the gill, brain, and muscle tissue, expressed at intermediate levels in heart and stomach tissue, and expressed at low levels in the kidney, intestine, head kidney, liver, and spleen tissue. The response of L. crocea to acute low-salinity stress was tested, with a significant increase in plasma cortisol concentration after 3 h, peaking after 6 h, and gradually returning to base levels. Regarding changes of Lcgr expression in different body tissues under the stress, there was up-regulation of the Lcgr transcript in the brain, liver, and gill tissues, but not in muscle tissue. Responses to pathogen mimics were also tested. Injection with lipopolysaccharide resulted in Lcgr expression, with an increase-decrease-increase trend in the head kidney. In contrast, a down-regulation of Lcgr expression in the head kidney was observed throughout the experimental period upon injection of polyinosinic:polycytidylic acid, revealing different roles of Lcgr for different types of pathogens. The results offer novel insights about the effects of different stressors on GR gene expression in L. crocea, and can facilitate further investigations into stress responses in other mariculture fish species.

Influence of chronic stress on the mechanism of the cytotoxic system in common carp (Cyprinus carpio)

Aquaculture conditions expose fish to internal and environmental stressors that increase their susceptibility to morbidity and mortality. The brain accumulates stress signals and processes them according to the intensity, frequency duration and type of stress, recruiting several brain functions to activate the autonomic or limbic system. Triggering the autonomic system causes the rapid release of catecholamines, such as adrenaline and noradrenaline, into circulation from chromaffin cells in the head kidney. Catecholamines trigger blood cells to release proinflammatory and regulatory cytokines to cope with acute stress. Activation of the limbic axis stimulates the dorsolateral and dorsomedial pallium to process emotions, memory, behaviour and the activation of preoptic nucleus‐pituitary gland‐interrenal cells in the head kidney, releasing glucocorticoids, such as cortisol to the bloodstream. Glucocorticoids cause downregulation of various immune system functions depending on the duration, intensity and type of chronic stress. As stress persists, most immune functions, with the exception of cytotoxic functions, overcome these effects and return to homeostasis. The deterioration of cytotoxic functions during chronic stress appears to be responsible for increased morbidity and mortality.

Liver transcriptome analysis and cortisol immune-response modulation in lipopolysaccharide-stimulated in channel catfish (Ictalurus punctatus)

Channel catfish (Ictalurus punctatus) is an important aquaculture species in China. In channel catfish, diseases such as haemorrhagic, sepsis and tail-rot disease are all caused by bacteria as general in China. Most of the pathogenic bacteria are Gram-negative bacteria. Liver transcriptome analysis of the co-injection of cortisol and lipopolysaccharide (LPS) was performed in this study. Preliminary evidence from the results suggest that after the emergence of immune stress, cortisol will up-regulate the complement cascade pathway, down-regulate the coagulation cascade pathway, down-regulate the platelet activation pathway, down-regulate antigen presentation pathway, and show complex regulation relationship to inflammatory factors. At 12 h, the number of differential genes regulated by cortisol was about half less than the number of differential genes regulated by LPS. At 24 h, there was no significant difference between the number of differential genes regulated by cortisol and LPS, but the types of differential genes vary widely. KEGG enrichment analysis found that cortisol regulated LPS-stimulated immune responses mainly focus on cytokines, complement and coagulation cascades pathways, antigen presentation pathways, haematopoiesis, and inflammation. It is suggested that there may be some strategic choice in the regulation of immune response by cortisol. These results will help understand the pathogenesis and host defence system in bacterial disease caused by Gram-negative bacteria.

Molecular characterization and expression patterns of glucocorticoid receptor (GR) genes in protandrous hermaphroditic yellowtail clownfish, Amphiprion clarkii

Sexual differentiation and ovotestis development are closely associated with cortisol levels, the principal indicator of stress, via the glucocorticoid receptor (GR) in teleosts. Thus, GR is regarded as a mediator to expound the relationship between social stress and gonad development. In the present study, two gr genes (gr1 and gr2) were cloned and analyzed from a protandrous hermaphroditic teleost, the yellowtail clownfish (Amphiprion clarkii). GR1 was found to display a conserved nine-amino-acid insert, WRARQNTDG, between two zinc finger domains. The phylogenetic tree of GR showed that yellowtail clownfish GR1 and GR2 are clustered to teleost GR1 and teleost GR2 separately, and differ from tetrapod GR. The result of real-time PCR revealed that high-level gr1 was mainly distributed in the cerebellum, hypothalamus and heart. The gr2 gene was abundant in the pituitary and liver of females and nonbreeders, while gr2 was mainly detected in the medulla oblongata and middle kidney of males. Moreover, GRs can be expressed in cultured eukaryotic cells and functionally interact with dexamethasone (exogenous glucocorticoid), thereby triggering downstream signaling pathways of different potentials. GR1 and GR2 can be activated by 10 nM dexamethasone treatment in HEK-293T cells. Notably, real-time PCR analysis among three social status groups demonstrated that gr2 expression was the highest in the hypothalamus of nonbreeders, but gr1 was no difference. We speculate that social stress would increase the expression of gr2 gene expression in the hypothalamus to inhibit sexual development. These data provide evidence of social stress involving reproductive regulation, which may help to elucidate the underlying mechanism of sex differentiation and change.

Modulation of Pituitary Response by Dietary Lipids and Throughout a Temperature Fluctuation Challenge in Gilthead Sea Bream

Low temperatures provoke drastic reductions in gilthead sea bream (Sparus aurata) activity and nourishment, leading to growth arrest and a halt in production. However, scarce data exist concerning the implications of central core control during the cold season. The aim of this work was to study the effects of low temperature and recovery from such exposure on the pituitary activity of sea bream juveniles fed 18% or 14% dietary lipid. A controlled indoor trial was performed to simulate natural temperature fluctuation (22 °C to 14 °C to 22 °C). Meanwhile, we determined the regulatory role of the pituitary by analyzing the gene expression of some pituitary hormones and hormone receptors via qPCR, as well as plasma levels of thyroidal hormones. In response to higher dietary lipids, hormone pituitary expressions were up-regulated. Induced low temperatures and lower ingesta modulated pituitary function up-regulating GH and TSH and thyroid and glucocorticoid receptors. All these findings demonstrate the capacity of the pituitary to recognize both external conditions and to modulate its response accordingly. However, growth, peripheral tissues and metabolism were not linked or connected to pituitary function at low temperatures, which opens an interesting field of study to interpret the hypothalamus–pituitary–target axis during temperature fluctuations in fish.

Down-regulation of corticosteroid receptor in leucocytes of stressed rainbow trout

The relationship between stress and immunosuppression was investigated in peripheral blood leucocytes (PBL) in rainbow trout, with reference to corticosteroid receptor (CR) expression and responses to cortisol- and/or lipopolysaccharide (LPS)-administration. Confinement stress in shallow water resulted in a sustained elevation of plasma cortisol, whereas lysozyme and immunoglobin levels were suppressed. Significant increases in mRNA levels of caspase-6 and insulin-like growth factor (IGF)-I were observed in PBL isolated from stressed fish. Confinement stress also suppressed proinflammatory cytokine, interleukin (IL)-1β, expression in PBL. There were decreasing tendencies for the mRNA levels of CRs in PBL of stressed fish. In-vitro treatment of cortisol and LPS on isolated PBL from unstressed trout increased both IL-1 β and CR mRNA expression. However, in PBL from stressed fish, cortisol and LPS treatment increased IL-1 β but not CR mRNA levels. Proliferative activities estimated as in-vitro incorporation of bromodeoxyuridine (BrdU) were decreased by cortisol in PBL from the unstressed and stressed fish groups; however, LPS-stimulated proliferation was observed only in the unstressed fish. Ratios of apoptotic PBL quantified as cell fragmentation using an automated cell counter were increased by cortisol in both groups; however, LPS-stimulated apoptosis was observed only in the stressed fish. Our study reveals cortisol has immune-suppressive effects in stressed fish, irrespective of CR down-regulation and desensitization. The complexity of immune-endocrine interaction is shown by the stress-induced attenuation of LPS effects.

Long-chain PUFA profiles in parental diets induce long-term effects on growth, fatty acid profiles, expression of fatty acid desaturase 2 and selected immune system-related genes in the offspring of gilthead seabream

The present study investigated the effects of nutritional programming through parental feeding on offspring performance and expression of selected genes related to stress resistance in a marine teleost. Gilthead seabream broodstock were fed diets containing various fish oil (FO)/vegetable oil ratios to determine their effects on offspring performance along embryogenesis, larval development and juvenile on-growing periods. Increased substitution of dietary FO by linseed oil (LO) up to 80 % LO significantly reduced the total number of eggs produced by kg per female per spawn. Moreover, at 30 d after hatching, parental feeding with increasing LO up to 80 % led to up-regulation of the fatty acyl desaturase 2 gene (fads2) that was correlated with the increase in conversion rates of related PUFA. Besides, cyclo-oxygenase 2 (cox2) and TNF-α (tnf-α) gene expression was also up-regulated by the increase in LO in broodstock diets up to 60 or 80 %, respectively. When 4-month-old offspring were challenged with diets having different levels of FO, the lowest growth was found in juveniles from broodstock fed 100 % FO. An increase in LO levels in the broodstock diet up to 60LO raised LC-PUFA levels in the juveniles, regardless of the juvenile's diet. The results showed that it is possible to nutritionally programme gilthead seabream offspring through the modification of the fatty acid profiles of parental diets to improve the growth performance of juveniles fed low FO diets, inducing long-term changes in PUFA metabolism with up-regulation of fads2 expression. The present study provided the first pieces of evidence of the up-regulation of immune system-related genes in the offspring of parents fed increased FO replacement by LO.

Comparative study of stress and immune-related transcript outcomes triggered by Vibrio anguillarum bacterin and air exposure stress in liver and spleen of gilthead seabream (Sparus aurata), zebrafish (Danio rerio) and rainbow trout (Oncorhynchus mykiss)

The stress and immune-related effects of short-term (1, 6 and 24 h) air exposure stress (1 min), bath vaccination with Vibrio anguillarum bacterin, and both stressors combined were evaluated in liver and spleen of Sparus aurata, Danio rerio and Onchorhynchus mykiss. Expression profiles of immune (interleukin 1 beta: il1β; tumor necrosis factor alpha: tnfα; interleukin 10: il10; tumor growth factor beta: tgfβ1; immunoglobulin M: igm; lysozyme: lys; complement protein c3: c3) and stress-related genes (glucocorticoid receptor: gr; heat shock protein 70: hsp70; and enolase) were analysed by RT-qPCR. Cortisol level was assessed by radioimmunoassay. The gene expression patterns in liver and spleen were found to be differentially regulated in a time- and organ-dependent manner among species. In seabream, a higher il1β-driven inflammatory response was recorded. In zebrafish, air exposure stress but not bath vaccination alone modulated most of the changes in liver and spleen immune transcripts. Stressed and vaccinated trout showed an intermediate pattern of gene expression, with a lower upregulation of immune-related genes in liver and the absence of changes in the expression of hsp70 and enolase in spleen (as it was observed in seabream but not in zebrafish). Following air exposure, cortisol levels increased in plasma 1 h post-stress (hps) and then decreased at 6 hps in O. mykiss and D. rerio. By contrast, in S.aurata the cortisol level remained higher at 6 hps suggesting a greater degree of responsiveness to this stressor. When fish were exposed to combined air exposure plus bath vaccination cortisol levels were also augmented at 1 and 6 hps in O. mykiss and S.aurata and restored to basal level at 24 hps, whereas in D. rerio the response was higher in response to the combination of both stressors. In addition, V. anguillarum bacterin vaccination triggered cortisol secretion only in D. rerio, suggesting a greater responsiveness of D. rerio hypothalamic-pituitary-interrenal axis. Overall, comparing the tissue transcription responsiveness, liver was found to be more implicated in the response to handling stress compared to spleen. These results also indicate that a species-specific response accounts for the deviations of stress and immune onset in the liver and spleen in these fish species.

Glucocorticoid receptor in ayu (Plecoglossus altivelis): Genomic and non-genomic effects on monocytes/macrophages function

The glucocorticoid receptor (GR) is an important feedback regulator of the hypothalamic-pituitary-interrenal (HPI) axis. However, there are a limited number of studies focused on host-pathogen interactions in which an association between GR and immune response has been evaluated in monocytes/macrophages (MO/MФ) after being challenged with highly pathogenic bacteria. Here, we cloned the cDNA sequence of the glucocorticoid receptor (PaGR) gene from ayu fish. The PaGR transcript was expressed in all tissues, and changes in expression were observed in immune tissues and MO/MФ after live Vibrio anguillarum infection. Subsequently, PaGR was expressed and purified to prepare anti-PaGR antibodies. We analyzed the subcellular localization of PaGR. PaGR was expressed not only in the intracellular space but also in the plasma membrane. PaGR activation decreased the expression of pro-inflammatory cytokines and increased the expression of anti-inflammatory cytokines. However, PaGR activation suppressed the phagocytosis activity of V. anguillarum-infected ayu MO/MФ via a non-genomic pathway. Interestingly, PaGR activation could enhance MO/MФ bacterial killing capability and apoptosis. Therefore, PaGR may modulate the immune response in ayu MO/MФ by genomic and non-genomic pathways.

What can we learn from glucocorticoid administration in fish? Effects of cortisol and dexamethasone on intermediary metabolism of gilthead seabream (Sparus aurata L.)

In aquaculture facilities fish welfare could be compromised due to stressors. Fish deal with stress, inter alia, through the activation of the hypothalamic-pituitary-interrenal endocrine axis and, as a result, corticosteroids are released into the blood. Recent studies have described that corticosteroids actions depend on the specific affinities to their receptors, and the subsequent differentiated responses. Cortisol is the main corticosteroid hormone in teleost fish, being its actions dependent on the intensity and time of exposure to stressors. Short-term effects of corticosteroids are well described, but long-term effects, including changes in the energy management directly affecting growth and survival, are less understood in fish. Here we show the effects of chronic oral administration of cortisol and the synthetic glucocorticoid dexamethasone (DXM) on the intermediary metabolism of the gilthead seabream (Sparus aurata). We described a higher energy expenditure associated to both corticosteroids resulting in lower growth rates of fish. Moreover, the effects of these compounds were tissue-dependant, with differences between both hormones. Thus, cortisol-fed animals accumulated triglycerides in the liver, while DXM treatment led to glycogen storage. Cortisol and DXM stimulated amino acids catabolism and gluconeogenic pathways in muscle and gills, but the effects were significantly enhanced in DXM-fed fish. The described effects highlighted differentiated mechanisms of action associated to both corticosteroids under chronic stress conditions. Further studies should aim at describing those pathways in detail, with special attention to the functionality of glucocorticoid receptor isoforms. The effects described here for S. aurata juveniles, may serve as a basis to assess long-term stress in future comparative studies with other aquaculture species.

A possible principal function of corticosteroid signaling that is conserved in vertebrate evolution: Lessons from receptor-knockout small fish

Corticosteroid receptors are critical for homeostasis maintenance, but understanding of the principal roles of the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) throughout vertebrates is limited. Lines of constitutive GR-knockout zebrafish and MR-knockout medaka have recently been generated as the first adult-viable corticosteroid receptor-knockout animals, in contrast to the lethality of these receptor knockouts in mice. Here, we describe behavioral and physiological modifications following disruption of corticosteroid receptor function in these animal models. We suggest these data point toward a potentially conserved function of corticosteroid receptors in integrating brain-behavior and visual responses in vertebrates. Finally, we discuss how future work in cartilaginous fishes (Chondrichthyes) will further advance understanding of the unity and diversity of corticosteroid receptor function, since distinct orthologs of GR and MR derived from an ancestral corticoid receptor appear in these basal jawed vertebrates.

Characterization and Expression Dynamics of Key Genes Involved in the Gilthead Sea Bream (Sparus aurata) Cortisol Stress Response during Early Ontogeny

The present study identified and characterized six key genes involved in the hypothalamic-pituitary-interrenal (HPI) axis of gilthead sea bream (Sparus aurata), a commercially important European aquaculture species. The key genes involved in the HPI axis for which gene structure and synteny analysis was carried out, comprised of two functional forms of glucocorticoid receptors (GR), as well as three forms of pro-opiomelanocortin (POMC) genes and one form of mineralocorticoid receptor (MR) gene. To explore their functional roles during development but also in the stress response, the expression profiles of gr1, gr2, mr, pomc_aI, pomc_aII, and pomc_β were examined during early ontogeny and after an acute stress challenge. The acute stress challenge was applied at the stage of full formation of all fins, where whole body cortisol was also measured. Both the cortisol and the molecular data implied that sea bream larvae at the stage of the full formation of all fins at 45 dph are capable of a response to stress of a similar profile as observed in adult fish.

Comparative Immune- and Stress-Related Transcript Response Induced by Air Exposure and Vibrio anguillarum Bacterin in Rainbow Trout (Oncorhynchus mykiss) and Gilthead Seabream (Sparus aurata) Mucosal Surfaces

Fish have to face various environmental challenges that may compromise the efficacy of the immune response in mucosal surfaces. Since the effect of acute stress on mucosal barriers in fish has still not been fully elucidated, we aimed to compare the short-term mucosal stress and immune transcriptomic responses in a freshwater (rainbow trout, Oncorhynchus mykiss) and a marine fish (gilthead seabream, Sparus aurata) to bacterial immersion (Vibrio anguillarum bacterin vaccine) and air exposure stress in skin, gills, and intestine. Air exposure and combined (vaccine + air) stressors exposure were found to be inducers of the cortisol secretion in plasma and skin mucus on both species in a time-dependent manner, while V. anguillarum bacterin exposure induced cortisol release in trout skin mucus only. This was coincident with a marked differential increase in transcriptomic patterns of stress- and immune-related gene expression profiles. Particularly in seabream skin, the expression of cytokines was markedly enhanced, whereas in gills the response was mainly suppressed. In rainbow trout gut, both air exposure and vaccine stimulated the transcriptomic response, whereas in seabream, stress and immune responses were mainly induced by air exposure. Therefore, our comparative survey on the transcriptomic mucosal responses demonstrates that skin and gut were generally more reactive in both species. However, the upregulation of immune transcripts was more pronounced in gills and gut of vaccinated trout, whereas seabream appeared to be more stress-prone and less responsive to V. anguillarum bacterin in gills and gut. When fish were subjected to both treatments no definite pattern was observed. Overall, the results indicate that (1) the immune response was not homogeneous among mucosae (2), it was greatly influenced by the specific traits of each stressor in each surface and (3) was highly species-specific, probably as a result of the adaptive life story of each species to the microbial load and environmental characteristics of their respective natural habitats.

Physiological and proteomic responses to corticosteroid treatments in Eurasian perch, Perca fluviatilis: Investigation of immune-related parameters

The comparative effects of cortisol and 11-deoxycorticosterone (DOC), two major corticosteroids in fish, have yet received little attention in teleosts. We evaluated the proteomic and immune responses of Eurasian perch to chronic corticosteroid treatments. We implanted immature perch with cortisol (80mg/kg) or DOC (4mg/kg) and measured the proportions of blood leucocytes, immune indices in the plasma, spleen and liver (complement and lysozyme activity, total immunoglobulin and immune gene expression in the tissues) and differential proteome expression (corticosteroid versus control) in the liver and the spleen on days 2, 4 and 14 post-treatment. Implantation of cortisol decreased the ratio of blood leucocytes and depressed Ig levels in both organs while DOC modulated the proportion of leucocyte sub-populations (increase in lymphocytes and decrease in granulocytes). In contrast, the innate humoral immunity was not strongly influenced by any of corticosteroid implants. The only immune parameter that was significantly affected was lysozyme, after DOC treatment. A number of proteins were differentially regulated by these hormones and some were identified in the liver (21 for cortisol and 8 for DOC) and in the spleen (10 for cortisol and 10 for DOC). None of the proteins was directly linked to immunity, except the natural killer enhancing factor, which was repressed by cortisol in the spleen. Our results also confirm that the proteins involved in energetic and glucose metabolism are affected by corticosteroids. Furthermore, these corticosteroids differently regulate immune status in Eurasian perch and they primarily impact leucocytes, as opposed to innate immune function.

Neuroendocrine and Immune Responses Undertake Different Fates following Tryptophan or Methionine Dietary Treatment: Tales from a Teleost Model

Methionine and tryptophan appear to be fundamental in specific cellular pathways involved in the immune response mechanisms, including stimulation of T-regulatory cells by tryptophan metabolites or pro-inflammatory effects upon methionine supplementation. Thus, the aim of this study was to evaluate the immunomodulatory effect of these amino acids on the inflammatory and neuroendocrine responses in juveniles of European seabass, Dicentrarchus labrax. To achieve this, goal fish were fed for 14 days methionine and tryptophan-supplemented diets (MET and TRP, respectively, 2× dietary requirement level) or a control diet meeting the amino acids requirement levels (CTRL). Fish were sampled for immune status assessment and the remaining fish were challenged with intraperitoneally injected inactivated Photobacterium damselae subsp. piscicida and sampled either 4 or 24 h post-injection. Respiratory burst activity, brain monoamines, plasma cortisol, and immune-related gene expression showed distinct and sometimes opposite patterns regarding the effects of dietary amino acids. While neuroendocrine intermediates were not affected by any dietary treatment at the end of the feeding trial, both supplemented diets led to increased levels of plasma cortisol after the inflammatory insult, while brain monoamine content was higher in TRP-fed fish. Peripheral blood respiratory burst was higher in TRP-fed fish injected with the bacteria inoculum but only compared to those fed MET. However, no changes were detected in total antioxidant capacity. Complement factor 3 was upregulated in MET-fed fish but methionine seemed to poorly affect other genes expression patterns. In contrast, fish fed MET showed increased immune cells numbers both before and after immune challenge, suggesting a strong enhancing effect of methionine on immune cells proliferation. Differently, tryptophan effects on inflammatory transcripts suggested an inhibitory mode of action. This, together with a high production of brain monoamine and cortisol levels, suggests that tryptophan might mediate regulatory mechanisms of neuroendocrine and immune systems cooperation. Overall, more studies are needed to ascertain the role of methionine and tryptophan in modulating (stimulate or regulate) fish immune and neuroendocrine responses.

In Vivo Effects of Lipopolysaccharide on Peroxisome Proliferator-Activated Receptor Expression in Juvenile Gilthead Seabream (Sparus Aurata)

Fish are constantly exposed to microorganisms in the aquatic environment, many of which are bacterial pathogens. Bacterial pathogens activate the innate immune response in fish involving the production of pro-inflammatory molecules that, in addition to their immune-related role, can affect non-immune tissues. In the present study, we aimed at investigating how inflammatory responses can affect metabolic homeostasis in the gilthead seabream (Sparus aurata), a teleost of considerable economic importance in Southern European countries. Specifically, we mimicked a bacterial infection by in vivo administration of lipopolysaccharide (LPS, 6 mg/kg body weight) and measured metabolic parameters in the blood and, importantly, the mRNA expression levels of the three isotypes of peroxisome proliferator activated receptors (PPARα, β, and γ) in metabolically-relevant tissues in seabream. PPARs are nuclear receptors that are important for lipid and carbohydrate metabolism in mammals and that act as biological sensors of altered lipid metabolism. We show here that LPS-induced inflammatory responses result in the modulation of triglyceride plasma levels that are accompanied most notably by a decrease in the hepatic mRNA expression levels of PPARα, β, and γ and by the up-regulation of PPARγ expression only in adipose tissue and the anterior intestine. In addition, LPS-induced inflammation results in an increase in the hepatic mRNA expression and protein activity levels of members of the mitogen-activated protein kinase (MAPK) family, known in mammals to regulate the transcription and activity of PPARs. Our results provide evidence for the involvement of PPARs in the metabolic response to inflammatory stimuli in seabream and offer insights into the molecular mechanisms underlying the redirection of metabolic activities under inflammatory conditions in vertebrates.

Chronic stress impairs the local immune response during cutaneous repair in gilthead sea bream (Sparus aurata, L.)

Scale removal in fish triggers a damage-repair program to re-establish the lost epidermis and scale and an associated local immune response. In mammals, chronic stress is known to delay wound healing and to modulate the cutaneous stress axis, but this is unstudied in teleost fish the most successful extant vertebrates. The present study was designed to test the hypothesis that chronic stress impairs cutaneous repair in teleost fish as a consequence of suppression of the immune response. The hypothesis was tested by removing the scales and damaging the skin on one side of the body of fish previously exposed for 4 weeks to a chronic crowding stress and then evaluating cutaneous repair for 1 week. Scale removal caused the loss of the epidermis although at 3days it was re-established. At this stage the basement membrane was significantly thicker (p=0.038) and the hypodermis was significantly thinner (p=0.016) in the regenerating skin of stressed fish relative to the control fish. At 3days, stressed fish also had a significantly lower plasma osmolality (p=0.015) than control fish indicative of reduced barrier function. Chronic stress caused a significant down-regulation of the glucocorticoid receptor (gr) in skin before damage (time 0, p=0.005) and of star at 3 and 7days (p<0.05) after regeneration relative to control fish. In regenerating skin key transcripts of cutaneous repair, pcna, colivα1 and mmp9, and the inflammatory response, tgfβ1, csf-1r, mpo and crtac2, were down-regulated (p<0.05) by chronic stress. Irrespective of chronic stress and in contrast to intact skin many hyper pigmented masses, putative melanomacrophages, infiltrated the epidermis of regenerating skin. This study reveals that chronic stress suppresses the local immune response to scale removal and impairs the expression of key transcripts of wound healing. Elements of the stress axis were identified and modulated by chronic stress during cutaneous repair in gilthead seabream skin.

Estrogen-dependent seasonal adaptations in the immune response of fish

Clinical and experimental evidence shows that estrogens affect immunity in mammals. Less is known about this interaction in the evolutionary older, non-mammalian, vertebrates. Fish form an excellent model to identify evolutionary conserved neuroendocrine-immune interactions: i) they are the earliest vertebrates with fully developed innate and adaptive immunity, ii) immune and endocrine parameters vary with season, and iii) physiology is constantly disrupted by increasing contamination of the aquatic environment. Neuro-immuno-endocrine interactions enable adaption to changing internal and external environment and are based on shared signaling molecules and receptors. The presence of specific estrogen receptors on/in fish leukocytes, implies direct estrogen-mediated immunoregulation. Fish leukocytes most probably are also capable to produce estrogens as they express the cyp19a and cyp19b - genes, encoding aromatase cytochrome P450, the enzyme critical for conversion of C19 steroids to estrogens. Immunoregulatory actions of estrogens, vary among animal species, and also with dose, target cell type, or physiological condition (e.g., infected/non-infected, reproductive status). They moreover are multifaceted. Interestingly, season-dependent changes in immune status correlate with changes in the levels of circulating sex hormones. Whereas E2 circulating in the bloodstream is perhaps the most likely candidate to be the physiological mediator of systemic immune-reproductive trade-offs, leukocyte-derived hormones are hypothesized to be mainly involved in local tuning of the immune response. Contamination of the aquatic environment with estrogenic EDCs may violate the delicate and precise allostatic interactions between the endogenous estrogen system and the immune system. This has negative effects on fish health, but will also affect the physiology of its consumers.

DNA damage and differential gene expression associated with physical stress in gilthead seabream (Sparus aurata)

Fish stress may result in inhibition of reproduction, development and growth. Thus, appropriate indices should be developed to accurately define the physiological plasticity of fish, in terms of coping with stress. Sea bream individuals were subjected to physical stress (fasting and confinement). DNA fragmentation of liver cells was assessed, in addition to gene expression of selected genes and plasma cortisol levels determination. Stress response was characterized with significant temporal alterations. Increased DNA fragmentation was observed as an aftereffect of physical stress and consequently gene expression of tp53 was stimulated. The expression pattern of glucocorticoid receptor (nr3c1) was directly correlated with plasma cortisol. Furthermore, glucokinase (gk) gene expression was considerably upregulated under acute stress, depicting putative energetic demands. Finally, igf1 downregulation during stress, reflects the suppression of the GH/IGF axis and the substantial stress effects on growth. To conclude, most of the indices described in the present study could be synergistically used, in order to robustly quantify physical stress in marine teleosts.

Cold-induced changes in stress hormone and steroidogenic transcript levels in cunner (Tautogolabrus adspersus), a fish capable of metabolic depression

The cunner (Tautogolabrus adspersus) is a fish with a wide latitudinal distribution that is capable of going into metabolic depression during the winter months, and thus, represents a unique model to investigate the impacts of cold temperatures on the stress response. In this study, we measured resting (pre-stress) plasma cortisol levels in 10 °C and 0 °C acclimated cunner from Newfoundland, and both catecholamine and cortisol levels after they were given a standardized handling stress (i.e. 1 min air exposure). In addition, we cloned and characterized cDNAs for several key genes of the cortisol-axis [cytochrome P450scc, steroidogenic acute regulatory protein (StAR) and a glucocorticoid receptor (GR) most likely to be an ortholog of the teleost GR2], determined the tissue distribution of their transcripts, and measured their constitutive (i.e. pre-stress) transcript levels in individuals acclimated to both temperatures. In cunner acclimated to 0 °C, post-stress epinephrine and norepinephrine levels were much lower (by approximately 9- and 5-fold, respectively) compared to 10 °C acclimated fish, and these fish had relatively low resting cortisol levels (~15 ngml(-1)) and showed a typical post-stress response. In contrast, those acclimated to 10 °C had quite high resting cortisol levels (~75 ngml(-1)) that actually decreased (to ~20 ngml(-1)) post-stress before returning to pre-stress levels. Finally, fish acclimated to 10 °C had higher P450scc transcript levels in the head kidney and lower levels of GR transcript in both the head kidney and liver. Taken together, these results suggest that: (1) temperature has a profound effect on the stress response of this species; and (2) although the ancestors of this species inhabited warm waters (i.e. they are members of the family Labridae), populations of cunner from colder regions may show signs of stress at temperatures as low as 10 °C.

Neuroendocrine mechanisms for immune system regulation during stress in fish

In the last years, the aquaculture crops have experienced an explosive and intensive growth, because of the high demand for protein. This growth has increased fish susceptibility to diseases and subsequent death. The constant biotic and abiotic changes experienced by fish species in culture are challenges that induce physiological, endocrine and immunological responses. These changes mitigate stress effects at the cellular level to maintain homeostasis. The effects of stress on the immune system have been studied for many years. While acute stress can have beneficial effects, chronic stress inhibits the immune response in mammals and teleost fish. In response to stress, a signaling cascade is triggered by the activation of neural circuits in the central nervous system because the hypothalamus is the central modulator of stress. This leads to the production of catecholamines, corticosteroid-releasing hormone, adrenocorticotropic hormone and glucocorticoids, which are the essential neuroendocrine mediators for this activation. Because stress situations are energetically demanding, the neuroendocrine signals are involved in metabolic support and will suppress the "less important" immune function. Understanding the cellular mechanisms of the neuroendocrine regulation of immunity in fish will allow the development of new pharmaceutical strategies and therapeutics for the prevention and treatment of diseases triggered by stress at all stages of fish cultures for commercial production.

Lipopolysaccharides isolated from Aeromonas salmonicida and Vibrio anguillarum show quantitative but not qualitative differences in inflammatory outcome in Sparus aurata (Gilthead seabream)

In fish, the defence system recognises pathogenic microorganisms via pathogen recognition receptors (PRRs) that sense particular structures of the pathogens; the so-called pathogen associated molecular patterns (PAMPs) such as bacterial lipopolysaccharides (LPSs). The result of the PAMP-PRR interactions leads to complex and orchestrated immune responses. In this study, Sparus aurata (Gilthead seabream) were intraperitoneally injected with purified lipopolysaccharide (LPS) from Aeromonas salmonicida (As)- and Vibrio anguillarum (Va) (1 mg*Kgfish(-1)), both Gram negative bacteria responsible for vibriosis and furunculosis respectively, therefore causing an impact upon marine fish cultures. Head-kidney, intestine, spleen, liver and blood samples were collected at 3, 6, 12 and 24 h post-injection. Plasma levels of cortisol, prostaglandins and lactate were measured and were significantly increased after As-LPS and Va-LPS treatment. Furthermore, tissue-specific differences of the gene regulatory patterns were evident for each LPS. When monocyte/macrophage cell cultures were challenged with As-LPS and Va-LPS, the pro-inflammatory cytokine mRNA abundances present a similar pattern of response. However, As-LPS always triggered a stronger response concerning TNFα, IL1β and cyclooxygenase-2 (COX2) mRNA abundance as well as PGE2 levels in the supernatant. Overall, the results indicate that specific LPSs do not activate different pro-inflammatory responses and that the observed gene expression pattern is tissue and concentration dependent.

The effect of allostatic load on hypothalamic-pituitary-interrenal (HPI) axis before and after secondary vaccination in Atlantic salmon postsmolts (Salmo salar L.)

The experiment consisted of three experimental groups: (1) "vaccine and stress", (2) "stress and vaccine" and (3) control. All groups have previously been vaccinated 6 months prior to the start of the experiment. At the start of the experiment, the "vaccine and stress" group was vaccinated with Pentium Forte Plus for the second time (25.02.2008) and then given a daily stressor (confinement stressor 267 kg m-3 in 15 min) for a period of 4 weeks. The "stress and vaccine" group was given a similar daily stressor for 4 weeks and then vaccinated for the second time. The control group was neither stressed nor vaccinated a second time. The results indicates that fish in the "stress and vaccine" group may have entered an allostatic overload type 2 due to oversensitivity to ACTH, a reduced efficient negative feedback system with elevated baseline levels of plasma cortisol and reduced immune response with pronounced effects on the well-being of the animal. The "vaccine and stress" group may likewise have entered an allostatic overload type 1 response, with oversensitivity to ACTH and transient reduced efficient negative feedback system. This study shows that if plasma cortisol becomes elevated prior to vaccination, it could perhaps instigate an allostatic overload type 2 with dire consequences on animal welfare. To reduce the risk of compromising the animal welfare during commercial vaccination of salmon, one propose to grade the fish minimum a week prior to vaccination or grade simultaneously with vaccination. This could reduce the overall allostatic load during handling and vaccination and secure a healthy fish with intact immune response and improved animal welfare.

In vivo response of some immune and endocrine variables to LPS in Eurasian perch (Perca fluviatilis, L.) and modulation of this response by two corticosteroids, cortisol and 11-deoxycorticosterone

In fish, the endocrine system, especially corticosteroids pathway, strongly interacts with immune system. On the other hand, in vivo co-stimulation of both systems is not well documented. To better understand this interaction, we decided to evaluate the in vivo effects of both stimulation of the immune system and co-stimulation of both systems in Eurasian perch juveniles. Fish were injected either with 10mgkg(-1) LPS, or with a combination of LPS and 0.8mgkg(-1) cortisol or LPS and 0.08mgkg(-1) 11-deoxycorticosterone (DOC) and sampled 1, 3 or 7days after injection. LPS affected the immune system by increasing plasma lysozyme activity and blood neutrophils populations. During the same time-course, LPS decreased the proportion of a mixture of lymphocytes and thrombocytes in blood and TNF-α expression in spleen. Cortisol modulated the LPS-mediated response in TNF-α mRNA expression levels in spleen. Contrary to LPS alone, the association of LPS with DOC modulated the abundance of complement component 3 (C3) mRNA in spleen. On the other hand, LPS altered the corticotropic axis by decreasing mRNA expression levels of all corticosteroid receptors and of 11β-HSD-2 in spleen. Both corticosteroids injected were not able to balance these LPS-induced suppressive effects on corticosteroid receptors and 11β-HSD-2 expression levels in spleen. Contrary to LPS alone, the association of LPS with DOC modulated GR-1b expression in gills. These results indicated that LPS is a strong modulator of the corticosteroid receptors expression in spleen. Furthermore, we report for the first time a LPS-induced decrease of the mineralocorticoid receptor expression. Finally, corticosteroids were able to modulate the LPS-mediated response at the transcriptional level.

Effects of chronic cortisol administration on global expression of GR and the liver transcriptome in Sparus aurata

The present work was designed to assess the effects of artificially increased high plasma cortisol levels induced by slow-release cortisol implants on the mRNA abundance of the glucocorticoid receptor (GR) in different organs of Sparus aurata (Gilthead sea bream), as well as to evaluate global transcriptional changes in the liver, using the Aquagenomics S. aurata oligo-nucleotide microarray technology. For that purpose, groups of fish were intraperitoneally injected with implants containing two different concentrations of cortisol (50 or 200 μg/g body weight). Blood and organs were sampled after 7 and 14 days of cortisol implantation. Only fish with 200 μg/g implants exhibited a significant rise in plasma cortisol. Thus, we evaluated the expression of the GR in different organs in these fish 7 and 14 days post-implantation. GR mRNA abundance was upregulated in head kidney and heart of fish at both sampling times. In liver and muscle, GR mRNA abundance was upregulated after 14 days, whereas in gills, the GR mRNA transcript was upregulated earlier, at day 7. These results suggest that increased plasma cortisol induced by a slow-release implant of cortisol mimics the overall effects of stress and affects the expression of GR mRNA in a time- and organ-specific manner. Data obtained with the Aquagenomics S. aurata oligo-nucleotide microarray allowed the identification of a total of 491 cortisol-responsive transcripts and highlight the strong intensity of transcriptional modulation in liver of fish implanted with cortisol after 7 days, in contrast to that observed at day 14. Transcriptional remodeling highlighted a significant activity in carbohydrate metabolism mainly in the gluconeogenic pathway linked to downregulation of inflammatory and immune response processes in implanted fish.

The role of 'mineralocorticoids' in teleost fish: relative importance of glucocorticoid signaling in the osmoregulation and 'central' actions of mineralocorticoid receptor

It has long been held that cortisol, a glucocorticoid in many vertebrates, performs glucocorticoid and mineralocorticoid actions in the teleost fish since it lacks aldosterone. However, in addition to the counterparts of tetrapod mineralocorticoid receptors (MRs), 11-deoxycorticosterone (DOC) has been recently identified as a specific endogenous ligand for the MRs in teleosts. Here, we point out the minor role of mineralocorticoid signaling (i.e., DOC-MR) in the osmoregulation compared with those of glucocorticoid signaling (i.e., cortisol-glucocorticoid receptor [GR]), and review the current findings on the physiological roles of the DOC-MR in teleosts. Cortisol promotes both freshwater and seawater adaptation via the GRs in the osmoregulatory organs such as gills and gastrointestinal tracts, but the expressions of MR mRNA are abundant in the brains especially in the key components of the stress axis and cerebellums. Together with the behavioral effects of intracerebroventricular injection with DOC, the MR is suggested to play an important role in the brain dependent behaviors. Since the abundant expression of central MRs has been reported also in higher vertebrates and the MR is thought to be ancestral to the GR, the role of MR in fish might reflect the principal and original function of corticosteroid signaling. Functional evolution of corticosteroid systems is summarized and areas in need of research like our on-going experiments with MR-knockout medaka are outlined.

Differential expression patterns and localization of glucocorticoid and mineralocorticoid receptor transcripts in the osmoregulatory organs of tilapia during salinity stress

The glucocorticoid receptor (GR) plays an essential role during seawater (SW) acclimation. However, the regulation of GR isoforms 1 and 2 (GR1 and GR2) and the mineralocorticoid receptor (MR) during SW acclimation is poorly understood. To address this, we localized and examined the GR1, GR2 and MR transcripts in the tilapia gill, kidney and intestine. Our results indicated that the GR1, GR2 and MR levels were increased in the kidney and intestine on day 1 in seawater (SW) fish, which is in agreement with the recognized osmoregulatory role of the corticosteroid receptors. The SW transfer increased the GR2 and MR transcripts in the gill on day 1 and 4, respectively. Surprisingly, no significant difference was obtained for the GR1 mRNA level. Analysis of the plasma parameters in freshwater (FW) and SW tilapia showed that the plasma cortisol levels were significantly increased at day 1 in the SW fish compared to the FW fish. This is the first study that focused on the spatial distribution of GR1, GR2 and MR in the osmoregulatory organs of freshwater (FW)- and SW-acclimated tilapia by in situ hybridization. Consistent with the Q-PCR results, the expression levels of the GR1, GR2 and MR transcripts were increased or decreased in the SW-acclimated tilapia's gill, kidney and intestine compared to the FW fish. We observed that GR1, GR2 and MR were localized in the branchial epithelial cells and chloride cells of the gill, proximal tubules of the kidney and columnar cells of the intestine. Together, these results indicate that the mobilization of corticosteroid receptors is dependent on the target tissue, salinity and exposure time.

Transcriptomic response of skeletal muscle to lipopolysaccharide in the gilthead seabream (Sparus aurata)

The physiological consequences of the activation of the immune system in fish are not well understood. In particular, skeletal muscle, due to its essential role in locomotion and whole-animal energy homeostasis, is a potentially important target of inflammation. In this study, we have evaluated the in vivo effects of lipopolysaccharide (LPS) on the white and red skeletal muscle transcriptome of the gilthead seabream (Sparus aurata) by microarray analysis at 24 and 72 h after injection. In white muscle, the transcriptomic response was characterized by an up-regulation of genes involved in carbohydrate catabolism and protein synthesis at 24 h and a complete reversal of this pattern at 72 h. In red muscle, an up-regulation of genes involved in carbohydrate catabolism and protein synthesis was observed only at 72 h after LPS administration. Interestingly, both white and red muscles showed a similar consistent down-regulation of immune genes at 72 h post-injection. However, genes involved in muscle contraction showed a general up-regulation in response to LPS in both types of muscle. In summary, LPS administration causes muscle type-specific responses regarding the expression of genes involved in carbohydrate and protein metabolism and a common decreased expression of immune genes in skeletal muscle, concomitant with increased expression of genes for contractile elements. Our results evidence a robust and tissue-specific transcriptomic response of the skeletal muscle to an acute inflammatory challenge.

Cortisol modulates the expression of cytokines and suppressors of cytokine signaling (SOCS) in rainbow trout hepatocytes

Although liver is a key target for corticosteroid action, its role in immune function is largely unknown. We tested the hypothesis that stress levels of cortisol down regulate immune-relevant genes in rainbow trout (Oncorhynchus mykiss) liver. Hepatocytes were treated with lipopolysaccharide (LPS) for 24h either in the presence or absence of cortisol. LPS stimulated heat shock protein 70 expression, enhanced glycolytic capacity, and reduced glucose output. LPS stimulated mRNA abundance of cytokines and serum amyloid protein A (SAA), while suppressors of cytokine signaling (SOCS)-3 was reduced. Cortisol increased mRNA abundances of IL-1β, SOCS-1 and SOCS-2, while inhibiting either basal or LPS-stimulated IL-8, TNF α2 and SAA. These cortisol-mediated effects were rescued by Mifepristone, a glucocorticoid receptor antagonist. Altogether, cortisol modulates the molecular immune response in trout hepatocytes. The upregulation of SOCS-1 and SOCS-2 by cortisol may be playing a key role in suppressing cytokine signaling and the associated inflammatory response.

Dexamethasone modulates expression of genes involved in the innate immune system, growth and stress and increases susceptibility to bacterial disease in Senegalese sole (Solea senegalensis Kaup, 1858)

Cortisol, the main glucocorticoid in fish, undertakes pleiotropic biological effects in response to stressors to maintain homeostasis. It can exert several actions on the immune system, growth and cellular metabolism, establishing a fine-tune regulation stress response and cross-talk interactions with other regulatory pathways. In this study, we investigated a causal relationship between high levels of glucocorticoids and susceptibility to pathogens and modification of gene expression profiles in Senegalese sole. For this purpose, we carried out two experiments using post-metamorphic individuals (21 days after hatching) that were exposed to dexamethasone (DXM), a potent glucocorticoid, in order to mimic cortisol effects. We quantified transcript levels of a wide set of genes involved in innate immune system (g-type lysozyme and hepcidin (hamp1)), HPI axis (crf, crfbp, pomcα, pomcβ, gr1 and gr2), HPT axis (tgb), cellular stress defense system (hsp70 and hsp90aa), GH/IGF axis (igf-I and igf-Ir) and the neuropeptide trh. Short-term exposure to 0.1, 1 and 10 ppm DXM provoked a reduction of pomcβ transcripts and an increase of crfbp mRNAs in a dose-dependent manner at 48 and 72 h after treatment. Moreover, g-type lysozyme transcript levels decreased significantly at 72 h whereas hamp1 mRNA levels increased at 48 h after exposure. Long-term DXM treatment (10 ppm DXM) affected negatively weight of soles (~20% lower than controls). Moreover, reduced mRNA levels were observed for pomcβ after 1 week and igf-I and hamp1 after 2 weeks. In contrast, crfbp and crf increased mRNA levels after 2 weeks. hsp70 exhibited a dual response increasing transcript levels at 1 week after treatment and reducing thereafter. No significant changes in gene expression were observed at any time during this study for tgb, trh, hsp90aa, pomcα, gr1 and gr2. Finally, a challenge experiment using the pathogen Photobacterium damselae subsp piscicida confirmed earlier and higher mortalities in DXM-treated animals. Taken together, these data indicate that a prolonged exposure to DXM increases the susceptibility to pathogens and reduces growth. Moreover, DXM can trigger a wide cellular response modulating the expression of genes involved in the innate immune system, HPI and GH/IGF axes as well as cellular stress defense. These results are highly valuable to evaluate responses associated to aquaculture stressful conditions and discriminate specific glucocorticoid-mediated effects.

Stress and immune modulation in fish

Stress is an event that most animals experience and that induces a number of responses involving all three regulatory systems, neural, endocrine and immune. When the stressor is acute and short-term, the response pattern is stimulatory and the fish immune response shows an activating phase that specially enhances innate responses. If the stressor is chronic the immune response shows suppressive effects and therefore the chances of an infection may be enhanced. In addition, coping with the stressor imposes an allostatic cost that may interfere with the needs of the immune response. In this paper the mechanisms behind these immunoregulatory changes are reviewed and the role of the main neuroendocrine mechanisms directly affecting the building of the immune response and their consequences are considered.

Biological effects of marine contaminated sediments on Sparus aurata juveniles

Chemical analysis of the compounds present in sediment, although informative, often is not indicative of the downstream biological effects that these contaminants exert on resident aquatic organisms. More direct molecular methods are needed to determine if marine life is affected by exposure to sediments. In this study, we used an aquatic multi-species microarray and q-PCR to investigate the effects on gene expression in juvenile sea bream (Sparus aurata) of two contaminated sediments defined as sediment 1 and 2, respectively, from marine areas in Northern Italy. Both sediments affected gene expression as evidenced by aquatic multi-species microarray analysis and q-PCR. Exposure of S. aurata juveniles to sediment 1 and sediment 2 altered expression of genes that are biomarkers for endocrine disruption. There were differences between the effects of sediment 1 and sediment 2 on gene expression in S. aurata juveniles indicating that the chemicals in the two sediments had different physiological targets. These results suggest that the classification of sediment solely on the basis of specific chemical profiles is inadequate, and not a true indicator of its potential to cause harmful effects. Our data also indicate that integration of physiochemical analysis and bioassays for monitoring the downstream harmful effects on aquatic organisms are required to gain a complete understanding of the effects of sediment on aquatic life.

Molecular cloning and characterization of European seabass (Dicentrarchus labrax) and Gilthead seabream (Sparus aurata) complement component C3

We present the complete C3 cDNA sequence of Gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax) and its molecular characterization with a descriptive analysis of their structural elements. We obtained one sequence for Gilthead seabream (gsbC3) which encodes a predicted protein of 1656 amino acids, and two sequences for European seabass (esbC3_1 and esbC3_2) which encode two predicted proteins of 1654 and 1587 amino acids respectively. All sequences present the characteristic structural features of C3 but interestingly esbC3_2 lacks the anaphylotoxin domain and the cysteine residue responsible for thiolester bond formation. Moreover, we have detected and quantified (by real-time PCR-based absolute quantification) specific isoform expression in European seabass depending on pathogen and density conditions in vivo. In addition, we have analyzed the tissue distribution pattern of European seabass and Gilthead seabream C3 genes under crowding stress and under pathological challenges in vivo, and we have observed that crowding and infection status provoke changes in expression levels, tissue expression pattern and C3 isoform expression balance.

Neuroendocrine-immune interaction in fish: differential regulation of phagocyte activity by neuroendocrine factors

Coping with physical, chemical and biological disturbances depends on an extensive repertoire of physiological, endocrinological and immunological responses. Fish provide intriguing models to study bi-directional interaction between the neuroendocrine and the immune systems. Macrophages and granulocytes are the main actors in the first and rapid innate immune response. They are resident in different organs and are moreover rapidly recruited and activated upon infection. They act in response to recognition of pathogen-associated molecular patterns (PAMPs) via a repertoire of surface and intracellular receptors by inducing a plethora of defense reactions aiming to eradicate the pathogen. Subsequent production of inflammatory mediators stimulates other leukocytes required to develop an adaptive and specific antibody response. The type of phagocyte reaction will therefore depend on their differentiation state, specific receptor repertoire and their specific location. Apart from these pathogen induced responses, immune reactivity may be modulated by neuroendocrine factors. Over the last years we extensively studied changes in carp stress axis activity and the effect of its end-products on the immune system in an acute stress paradigm. We focus on specific neuroendocrine receptors on leukocytes and their effect on crucial phagocyte activities. We performed identification and functional analyses of different glucocorticoid, opioid and adrenergic receptors on carp phagocytes. Results show that their ligands of neuroendocrine origin may have substantial impact on specific phagocyte functions in a differential way. Inflammatory and microbicidal responses fight pathogens but may be detrimental to the host tissue. Neuroendocrine modulation may regulate inflammation to reach an optimum defense while preventing excessive host cell damage.

Coping strategies in a strongly schooling fish, the common carp Cyprinus carpio

Individual common carp Cyprinus carpio were screened repeatedly for risk taking (rate of exploration of a novel, potentially dangerous environment) and for competitive ability (success in gaining access to a spatially restricted food source). Marked differences in behaviour were evident, and significant consistency in individual responses across trials was found for both risk taking and competitive ability. In addition, there was a significant positive relationship between individual performance in these two contexts, with fish that explored more quickly in the novel environment tending to be among the first to gain access to restricted food. In two follow-up studies, resting metabolic rate, blood lactate and glucose and the expression of the cortisol receptor gene in the head kidney and brain were compared in fish from the two extremes of the risk-taking spectrum. Mass-specific metabolic rate was significantly higher in risk-taking than in risk-avoiding fish, while plasma lactate and glucose concentrations and expression of the cortisol receptor gene were lower. It was concluded that a behavioural syndrome based on boldness and aggression exists in C. carpio, as it does in many other animals, and that this is associated with differences in metabolic and stress physiology (down to the genomic level) similar to those described in animals with different coping strategies.

Effect of dietary probiotics on clownfish: a molecular approach to define how lactic acid bacteria modulate development in a marine fish

We set out to determine whether probiotic addition would improve larval development in the false percula clownfish Amphiprion ocellaris and to determine what molecular responses could be observed in the larvae following probiotic exposure. We supplied the probiotic bacterial strain Lactobacillus rhamnosus IMC 501 to clownfish larvae from the first day posthatch simultaneously by live prey and with addition to rearing water (group 2) and exclusively by live prey (group 3). We observed twofold higher body weight in both clownfish larvae and juveniles when probiotics were supplied via live prey and added to the rearing water. In addition, development was accelerated with metamorphosis occurring 3 days earlier in fingerlings treated with probiotic. Alteration in molecular biomarkers supported the faster growth observation. There was significantly increased gene expression of factors involved in growth and development (insulin-like growth factors I and II, myostatin, peroxisome proliferator-activated receptors alpha and beta, vitamin D receptor alpha, and retinoic acid receptor gamma) when probiotics were delivered via live prey and added to the rearing water. Moreover, probiotic treatment lessened the severity of the general stress response as exhibited by lower levels of glucocorticoid receptor and 70-kDa heat shock protein gene expression. Furthermore, an improvement of skeletal head development was observed, with a 10-20% reduction in deformities for juveniles treated with probiotic. All data suggest a potent effect on development resulting from the administration of lactic acid bacteria to larval clownfish, and this study provides a preliminary molecular entry path into the investigation of mechanisms responsible for probiotic enhancement in fish development.

The immune response differentially regulates Hsp70 and glucocorticoid receptor expression in vitro and in vivo in common carp (Cyprinus carpio L.)

Heat shock or stress proteins and glucocorticoids (cortisol) regulate a sequential pro-inflammatory and anti-inflammatory cytokine expression profile to effectively kill pathogens, whilst minimizing damage to the host. Cortisol elicits its effects through the glucocorticoid receptor (GR) for which Hsp70 and Hsp90 are required as chaperones. In common carp, (Cyprinus carpio) duplicated glucocorticoid receptor genes and splice variants with different cortisol sensitivities exist. We investigated the expression profiles of heat shock proteins Hsp70, Hsc70, Hsp90alpha and Hsp90beta and the three different variants of GR in vitro in and in vivo to define their role in immune modulation. A rapid transient induction of GR1 (a and b) and Hsp70 was seen after LPS treatment in vitro in head kidney phagocytes, whereas cortisol treatment did not affect constitutive or LPS-induced expression of Hsp70 or GR1 expression. In vivo zymosan-induced peritonitis upregulated GR and Hsp70 expression which appears to increase sensitivity for cortisol-induced immune modulation. Indeed, the increased GR and Hsp70 expression correlates with inhibition of both LPS- and zymosan-induced expression of pro-inflammatory cytokines. Infection with the blood parasite T. borreli decreases GR1a expression in thymus, but increases GR2 expression in spleen. Differentially regulated expression of Hsp70 and of glucocorticoid receptor variants with different cortisol sensitivities, underlines their physiological importance in a balanced immune response.

Dynamics of liver GH/IGF axis and selected stress markers in juvenile gilthead sea bream (Sparus aurata) exposed to acute confinement: differential stress response of growth hormone receptors

The time courses of liver GH/IGF axis and selected stress markers were analyzed in juvenile gilthead sea bream (Sparus aurata) sampled at zero time and at fixed intervals (1.5, 3, 6, 24, 72 and 120 h) after acute confinement (120 kg/m(3)). Fish remained unfed throughout the course of the confinement study, and the fasting-induced increases in plasma growth hormone (GH) levels were partially masked by the GH-stress inhibitory tone. Hepatic mRNA levels of growth hormone receptor-I (GHR-I) were not significantly altered by confinement, but a persistent 2-fold decrease in GHR-II transcripts was found at 24 and 120 h. A consistent decrease in circulating levels of insulin-like growth factor-I (IGF-I) was also found through most of the experimental period, and the down-regulated expression of GHR-II was positively correlated with changes in hepatic IGF-I and IGF-II transcripts. This stress-specific response was concurrent with plasma increases in cortisol and glucose levels, reflecting the cortisol peak (60-70 ng/mL), the intensity and duration of the stressor when data found in the literature were compared. Adaptive responses against oxidative damage were also found, and a rapid enhanced expression was reported in the liver tissue for mitochondrial heat-shock proteins (glucose regulated protein 75). At the same time, the down-regulated expression of proinflammatory cytokines (tumour necrosis factor-alpha) and detoxifying enzymes (cytochrome P450 1A1) might dictate the hepatic depletion of potential sources of reactive oxygen species. These results provide suitable evidence for a functional partitioning of hepatic GHRs under states of reduced IGF production and changing cellular environment resulting from acute confinement.