Characterization and evaluation of sex-specific expression of suppressors of cytokine signaling (SOCS)-1 and -3 in juvenile yellow perch (Perca flavescens) treated with lipopolysaccharide

Immunostimulant effects of Pituitary Adenylate Cyclase-Activating Polypeptide and double-stranded (ds)RNA in Orconectes propinquus

Disease outbreaks in crustacean aquaculture caused by opportunistic and obligate pathogens cause severe economic losses to the industry. Antibiotics are frequently used as prophylactic treatments worldwide, although its overuse and misuse has led to microbial resistance, which has driven the search for novel molecules with immunostimulant and antibacterial activities. Antimicrobial peptides (AMP) and double-stranded (ds)RNAs constitute promising immunostimulants in the fight against infectious diseases in aquaculture. Scientists have made significant progress in testing these molecules in aquatic organisms as potential candidates for replacing conventional antibiotics. However, most studies have been conducted in teleost fish, thus little is known about the immunostimulatory effects in crustaceans, especially in freshwater crayfishes. Consequently, in the present work, we evaluate the immunomodulatory effects of the AMP Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) and high molecular weight (HMW) Poly (I:C) in the northern clearwater crayfish Orconectes propinquus. Two bioassays were conducted to evaluate the effects of different doses of PACAP and Poly (I:C) HMW, different administration routes, as well as the effects of the combined treatment on the crayfish immune system. Results showed the immunostimulatory role of PACAP and Poly (I:C) HMW with effects depending on the dose, the site of injection and the treatment assessed. These findings offer new insights into the crayfish immune system and contribute to the development of effective broad-spectrum immune therapies in aquaculture.

Sexual dimorphism in NLR transcripts and its downstream signaling protein IL-1ꞵ in teleost Channa punctata (Bloch, 1793)

Nucleotide-binding oligomerization domain-like receptors (NOD-like receptors or NLRs) are a family of intracellular pattern recognition receptors (PRRs) that initiates as well as regulate inflammatory responses. NLRs are characterized by a centrally located nucleotide binding domain and a leucine rich repeat domain at the C-terminal responsible for the recognition of intracellular microbe-associated molecular patterns (MAMPs) and danger-associated molecular patterns (DAMPs). In the present study in adult spotted snakehead we have investigated the sex-dependent tissue distribution of NLRs known to be associated with inflammation in teleost namely NOD1, NOD2, NLRC3, NLRC5, and NLRX1. Further, the sexual dimorphism in the expression of NLR transcript as well as the pro-inflammatory protein IL-1β was explored in fish under normal conditions, and in fish exposed to bacterial lipopolysaccharide (LPS). The NLRs show ubiquitous and constitutive expression in all the tissues. Moreover, a prominent disparity between males and females was observed in the basal expression of these genes in various tissues. The sexual dimorphism in NLR expression was also prominent when fish were exposed to LPS. Similarly, IL-1β exhibited sexual dimorphism in both normal as well as LPS-exposed fish.

Investigating wastewater treatment plant effluent and pharmaceutical exposure on innate cytokine expression of darters (Etheostoma spp.) in the Grand River watershed

Fish live in continuous contact with various stressors and antigenic material present within their environments. The impact of stressors associated with wastewater-exposed environments on fish has become of particular interest in toxicology studies. The objectives of this study were to examine potential effects of wastewater treatment plant (WWTP) effluent-associated stressors on innate cytokine expression within the gills of darter species (Etheostoma spp.), using both field and laboratory approaches. Male and female darters (rainbow, greenside, fantail, and johnny darters) were collected upstream and downstream of the Waterloo WWTP in the Grand River, Ontario. Gill samples were collected from fish in the field and from a second subset of fish brought back to the laboratory. Laboratory fish were acutely exposed (96-h) to an environmentally relevant concentration of venlafaxine (1.0 μg/L), a commonly prescribed antidepressant. To assess the impacts of these stressors on the innate immunity of darters, the expression of key innate cytokines was examined. Minor significant effects on innate cytokine expression were observed between upstream and downstream fish. Moderate effects on cytokine expression were observed in venlafaxine-exposed fish compared to their control counterparts however, changes were not indicative of a biologically significant immune response occurring due to the exposure. Although the results of this study did not display extensive impacts of effluent and pharmaceutical exposure on innate cytokine expression within the gills, they provide a novel avenue of study, illustrating the importance of examining potential impacts that effluent-associated stressors can have on fundamental immune responses of native fish species.

Molecular Analysis and Sex-specific Response of the Hepcidin Gene in Yellow Perch (Perca Flavescens) Following Lipopolysaccharide Challenge

Hepcidin antimicrobial peptide (hamp) is active in teleosts against invading pathogens and plays important roles in the stress and immune responses of finfish. The response of hamp gene was studied in yellow perch (yp) (Perca flavescens) challenged with lipopolysaccharides to understand if this immunity response is sex-specifically different. The cloned hamp gene consists of an open-reading frame of 273 bp and encodes a deduced protein of 90 amino acids (a.a.), which includes a signal peptide of 24 a.a., a pro-domain of 40 a.a. and a mature peptide of 26 a.a. Yp hamp involves 8 cysteine residues with 4 disulfide bonds, and a protein with an internal alpha helix flanked with C- and N-terminal random coils was modeling predicted. RT-qPCR was used to analyze the relative abundances (RAs) of hamp mRNA in the livers of juvenile female and male yellow perch challenged with lipopolysaccharide. The expression levels of hamp were significantly elevated by 3 h (RA = 7.3) and then peaked by 6 h (RA = 29.4) post-treatment in females but the peak was delayed to 12 h (RA = 65.4) post-treatment in males. The peak mRNA level of challenged males was shown 7.6-fold higher than females. The post-treatment responses in both genders decreased to their lowest levels by 24 h and 48 h. Overall, female perch had an earlier but less-sensitive response to the lipopolysaccharide challenge than male.

First Isolation of a Herpesvirus (Family Alloherpesviridae) from Great Lakes Lake Sturgeon (Acipenser fulvescens)

The lake sturgeon (Acipenser fulvescens; LST) is the only native sturgeon species in the Great Lakes (GL), but due to multiple factors, their current populations are estimated to be <1% of historical abundances. Little is known about infectious diseases affecting GL-LST in hatchery and wild settings. Therefore, a two-year disease surveillance study was undertaken, resulting in the detection and first in vitro isolation of a herpesvirus from grossly apparent cutaneous lesions in wild adult LST inhabiting two GL watersheds (Erie and Huron). Histological and ultrastructural examination of lesions revealed proliferative epidermitis associated with herpesvirus-like virions. A virus with identical ultrastructural characteristics was recovered from cells inoculated with lesion tissues. Partial DNA polymerase gene sequencing placed the virus within the Family Alloherpesviridae, with high similarity to a lake sturgeon herpesvirus (LSHV) from Wisconsin, USA. Genomic comparisons revealed ~84% Average Nucleotide Identity between the two isolates, leading to the proposed classification of LSHV-1 (Wisconsin) and LSHV-2 (Michigan) for the two viruses. When naïve juvenile LST were immersion-exposed to LSHV-2, severe disease and ~33% mortality occurred, with virus re-isolated from representative skin lesions, fulfilling Rivers’ postulates. Results collectively show LSHV-2 is associated with epithelial changes in wild adult LST, disease and mortality in juvenile LST, and is a potential threat to GL-LST conservation.

The intersection of stress, sex and immunity in fishes

While sexual dimorphism in immune responses has been documented in other vertebrates, evidence for a similar phenomenon in fish is lacking. Here, we review the relationship between immunity, stress, spawning, and sex hormones in fish to gain a better understanding of sex-based differences in fish immune responses and its consequences for aquaculture. It is well known that there is a strong link between the stress response and immune function in fish. In addition, research to date has demonstrated that sexual dimorphism in the stress response exists in many species; yet, the relationship between the sexual dimorphic stress responses and immune function has rarely been explored together. Aside from stress, spawning is also known to trigger changes in fish immune responses. Estrogens and androgens have been shown to modulate the immune system which could account for differences between the two sexes of fish when spawning; however, evidence regarding the sexual dimorphism of these changes varies between fishes and is likely related to the spawning strategy employed by a given species. Sex hormones are also used in aquaculture practices to produce monosex populations, and exposure to these hormones early in development has been shown to impact the development of immune organs in several fishes. While female fish are generally thought to be more robust than males, aquaculture practices should also consider the role that maternal stress has on the immune function of the offspring and what role this plays in compromising the immune response of farmed fish.

Reliability evaluation of biomarker reference ranges for mesocosm and field conditions: Cellular innate immunomarkers in Gasterosteus aculeatus

Due to their sensitivity to environmental contamination and their link with fish health status, innate immunomarkers are of great interest for environmental risk assessment studies. Nevertheless, the lack of knowledge about the effect of confounding factors can lead to data misinterpretation and false diagnostics. So, the determination of reference values was of huge interest for the integration of biomarkers in biomonitoring programs. Laboratory immunomarker reference ranges (including cellular mortality, leucocyte distribution, phagocytosis activity, respiratory burst and lysosomal presence) that consider three confounding factors (season, sex and body size) were previously developed in three-spined stickleback, Gasterosteus aculeatus, from our husbandry. Usefulness of these reference ranges in biomonitoring programs depends on how they can be transposed to various experimental levels, such as mesocosm (outdoor artificial pond) and field conditions. Immunomarkers were therefore measured every 2 months over 1 year in one mesocosm and in one site assumed to uncontaminated (Houdancourt, field). Differences between immunomarker seasonal variations in mesocosm and field fish on one side and laboratory fish on the other side were quantified: in some cases, seasonal trends were not significant or did not differ between mesocosm and laboratory conditions, but overall, models developed based on data obtained in laboratory conditions were poorly predictive of data obtained in mesocosm or field conditions. To propose valuable field reference ranges, mesocosm and field data were integrated in innate immunomarker modelling in order to strengthen the knowledge on the effect of confounding factors. As in laboratory conditions, sex was overall a confounding factor only for necrotic cell percentage and granulocyte-macrophage distribution and size was a confounding factor only for cellular mortality, leucocyte distribution and phagocytosis activity. Confounding factors explained a large proportion of immunomarker variability in particular for phagocytosis activity and lysosomal presence. Further research is needed to test the field models in a biomonitoring program to compare the sensitivity of immunomarkers to the confounding factors identified in this study and the sensitivity to various levels of pollution.

Comparative transcriptomic analysis reveals the gene expression profiles in the liver and spleen of Japanese pufferfish (Takifugu rubripes) in response to Vibrio harveyi infection

Japanese pufferfish (Takifugu rubripes) is one of the main marine aquatic fish species cultured in Asia due to its high nutritional value. In recent years, disease caused by Vibrio harveyi infections have led to serious mortality in Japanese pufferfish industry. To understand the complex molecular mechanisms between V. harveyi and Japanese pufferfish, we performed a transcriptome analysis of liver and spleen samples from Japanese pufferfish at 1 and 2 day post-infection. Between-group comparisons revealed 922 genes that were significantly differentially expressed. The altered genes emphasized the function in several immune related pathways including MAPK signaling pathway, JAK-STAT signaling pathway, toll-like receptor signaling pathway, cytokine-cytokine receptor interaction and lysosomal pathway. The data generated in this study provided insight into the responses of Japanese pufferfish against V. harveyi at the transcriptome level, promoting our comprehensive understanding of immune responses for aquatic animal against V. harveyi.

Insights into the Evolution of the Suppressors of Cytokine Signaling (SOCS) Gene Family in Vertebrates

The SOCS family are key negative regulators of cytokine and growth factor signaling. Typically, 8-17 SOCS genes are present in vertebrate species with eight known in mammals, classified as type I (SOCS4-7) and type II (CISH and SOCS1-3) SOCS. It was believed that the type II SOCS were expanded through the two rounds of whole genome duplication (1R and 2R WGDs) from a single CISH/SOCS1-3 precursor. Previously, 12 genes were identified in rainbow trout but here we report 15 additional loci are present, and confirm 26 of the genes are expressed, giving rainbow trout the largest SOCS gene repertoire identified to date. The discovery of the additional SOCS genes in trout has led to a novel model of SOCS family evolution, whereby the vertebrate SOCS gene family was derived from CISH/SOCS2, SOCS1/SOCS3, SOCS4/5, SOCS6, and SOCS7 ancestors likely present before the two WGD events. It is also apparent that teleost SOCS2b, SOCS4, and SOCS5b molecules are not true orthologues of mammalian SOCS2, SOCS4, and SOCS5, respectively. The rate of SOCS gene structural changes increased from 2R vertebrates, to 4R rainbow trout, and the genes with structural changes show large differences and low correlation coefficient of expression levels relative to their paralogues, suggesting a role of structural changes in expression and functional diversification. This study has important impacts in the functional prediction and understanding of the SOCS gene family in different vertebrates, and provides a framework for determining how many SOCS genes could be expected in a particular vertebrate species/lineage.

Individual and combined effects of salinity and lipopolysaccharides on the immune response of juvenile Takifugu fasciatus

Lipopolysaccharides (LPS) and salinity are important variables in aquatic environments. High concentration of LPS and large changes in salinity seriously threat the survival of a variety of organisms, including fish. To reveal the effects of salinity and LPS on a fish immune response, we measured the immune-related parameters (total leukocyte count, total serum protein, albumin and globulin concentrations, complement C3 concentration, and lysozyme activity) and genes (the expressions of TNF-α, IL-1β, and SOCS1-3 at the mRNA and protein levels) of juvenile Takifugu fasciatus exposed to phosphate buffered saline (PBS) or LPS (25 μg mL^-1) under different salinities (0, 15, and 30 ppt) for 24 h. Changes in key immunological indicators suggested that the LPS challenge induced considerable damage to T. fasciatus, whereas an increase in salinity mitigated the harmful effects. Moreover, although the immune responses in blood and other selected tissues (gill and kidney) were suppressed with an increase in salinity, the increased response in liver in saltwater enabled T. fasciatus to conquer large salinity variation during migration. The appropriate addition of salts appeared to be a sensible strategy to mitigate LPS-induced toxicity in the aquaculture of T. fasciatus.

Molecular characterization of nine suppressors of cytokine signaling (SOCS) genes from yellow catfish Pelteobagrus fulvidraco and their changes in mRNA expression to dietary carbohydrate levels

Suppressors of cytokine signaling (SOCS) are important molecules that mediates the regulation of glucose homeostasis. Here, we cloned and characterized the full-length cDNA sequences of nine genes of the SOCS family (SOCS1, 2, 3, 3b, 5, 5b, 6, 7 and CISH) from yellow catfish P. fulvidraco, explored their mRNA abundance across the tissues and their mRNA changes to dietary carbohydrate levels. Structural analysis indicated that the nine members shared conserved functional domains to the orthologues of the mammalian SOCS members, such as SRC homology 2 and the SOCS domains. Their mRNAs were constitutively expressed in various tissues but changed among the tissues. Their mRNA expression in response to dietary carbohydrate levels were explored in the liver, muscle, intestine, testis and ovary. Dietary carbohydrate addition showed significant effects on the mRNA levels of the nine SOCS members. Moreover, their mRNA expressions in response to dietary carbohydrate levels were also tissue-dependent. These indicated that SOCS members potentially mediated the utilization of dietary carbohydrate in yellow catfish.

Molecular characterization and expression of suppressor of cytokine signaling (SOCS) 1, 2 and 3 under acute hypoxia and reoxygenation in pufferfish, Takifugu fasciatus

Hypoxia seriously affects the innate immune system of fish. However, the roles of suppressor of cytokine signaling (SOCS), pivotal anti-inflammatory genes, in response to hypoxia/reoxygenation remain largely unexplored. The primary objective of this study was to elucidate the function of SOCS genes under acute hypoxia and reoxygenation in pufferfish (Takifugu fasciatus). In the present study, SOCS1, 2 and 3 were identified in T. fasciatus referred to as TfSOCS1, 2 and 3. Then, qRT-PCR and western blot analysis were employed to assess their expressions at both the mRNA and protein levels. Tissue distribution demonstrated that the three SOCS genes were predominantly distributed in gill, brain and liver. Under hypoxia challenge (1.63 ± 0.2 mg/L DO for 2, 4, 6 and 8 h), the expressions of TfSOCS1 and 3 in brain and liver at the mRNA and protein levels were significantly decreased, while their expressions showed an opposite trend in gill. Different from the expressions of TfSOCS1 and 3, the expression of TfSOCS2 was inhibited in gill, along with its increased expression in brain and liver. After normoxic recovery (7.0 ± 0.3 mg/L of DO for 4 and 12 h), most of TfSOCS genes were significantly altered at R4 (reoxygenation for 4 h) and returned to the normal level at R12 (reoxygenation for 12 h). SOCS genes played vital roles in response to hypoxia/reoxygenation challenge. Our findings greatly strengthened the relation between innate immune and hypoxia stress in T. fasciatus.

Maturation-associated changes in the non-specific immune response against Flavobacterium psychrophilum in Ayu Plecoglossus altivelis

In this study, we investigated maturation-associated changes in non-specific immune responses of ayu against Flavobacterium psychrophilum. The gonadosomatic index was minimum on 16 June, began to increase on 17 July, and reached the maximum value during August. The highest phagocytic rate (16.3%) was observed on 16 June, which decreased significantly to 5.6% on 26 August. The number of viable bacteria after the serum treatment was highest during August, suggesting that bactericidal activity of the serum decreased along with the sexual maturation. Gene expression levels of interleukin-8, and tumor necrosis factor-α in the spleen did not change significantly during this period, whereas the level of suppressor of cytokine signaling (SOCS)3 was significantly higher on 26 August than that on 16 July (p < 0.05). These results suggest that phagocytic activity of trunk kidney leukocytes and serum bactericidal activity against F. psychrophilum decreased with sexual maturation, and that SOCS3 may be related to the decrease in non-specific immune activity in ayu.

Cortisol plays a role in the high environmental ammonia associated suppression of the immune response in zebrafish

Exposure to high environmental ammonia (HEA) levels increases the vulnerability of fishes to parasitic, viral and bacterial diseases. We tested the hypothesis that elevated plasma cortisol levels play a role in the HEA-mediated immunosuppression in fishes. To this end, we tested the effect of exogenous cortisol treatment on the lipopolysaccharide (LPS)-induced immune response in zebrafish (Danio rerio). Also, to test whether glucocorticoid receptor (GR) signaling is involved in HEA-mediated immunosuppression, zebrafish were treated with mifepristone, a GR antagonist, and the LPS-induced immune response assessed after HEA exposure. We evaluated a panel of important immunity-related genes including interleukin 1β (il1b) and suppressor of cytokine signaling (socs-1a, 2, 3) and acute phase response genes [serum amyloid A (saa), transferrin (tfa), leukocyte cell-derived chemotaxin 2-like (lect2l), haptoglobin (hp), hepcidin (=hepatic anti-microbial peptide hamp), and complement component 3b (c3b)] by real-time quantitative PCR. Our results demonstrate that exogenous cortisol administration as well as elevated cortisol levels in response to HEA exposure modulate mRNA transcript levels of key mediators of the innate immune response in zebrafish. Mifepristone treatment reduced whole body cortisol levels and eliminated the HEA-mediated changes in transcript abundance of socs1a, il1b, as well as APR genes. Together, these results suggest that the HEA effect on the innate immune response is in part mediated by cortisol signaling, while the mode of action, including the receptors involved remains to be elucidated.

Behavioral and physiological responses of yellow perch (Perca flavescens) to moderate hypoxia

While severe hypoxia can be lethal and is usually avoided by mobile aquatic organisms, moderate hypoxic conditions are likely more prevalent and may affect organisms, such as fishes, in a variety of systems. However, fishes have the potential to adjust physiologically and behaviorally and thus reduce the negative effects of hypoxia. Quantifying such physiological responses may shed light on the ability of fishes to tolerate reduced oxygen concentrations. This study assessed how two different hatchery populations of yellow perch Perca flavescens, a fish that is likely to encounter moderate hypoxic conditions in a variety of systems, responded to moderate hypoxic exposure through three experiments: 1) a behavioral foraging experiment, 2) an acute exposure experiment, and 3) a chronic exposure experiment. No marked behavioral or physiological adjustments were observed in response to hypoxia (e.g., hemoglobin, feeding rate, movement frequency, gene expression did not change to a significant degree), possibly indicating a high tolerance level in this species. This may allow yellow perch to utilize areas of moderate hypoxia to continue foraging while avoiding predators that may be more sensitive to moderately low oxygen.

Comparative analysis of the expression patterns of eight suppressors of cytokine signaling in tongue sole, Cynoglossus semilaevis

Suppressor of cytokine signaling (SOCS) family members are inhibitors of cytokine signaling pathways and key regulators of immunological homeostasis. They have been extensively studied in mammalian models, but systematic analyses of SOCS in fish are limited. In the current study, a total of eight SOCS genes from tongue sole (Cynoglossus semilaevis) were characterized. All eight CsSOCS exhibit conserved structures of SOCS and were phylogenetically grouped together with the respective SCOS members known in mammalian and teleost species. Under normal physiological conditions, the expressions of the eight CsSOCS genes were detected at varied levels in nine major tissues, with most CsSOCS highly expressed in kidney. Following challenge with intracellular and extracellular bacterial pathogens, the majority of CsSOCS genes exhibited distinctly different expression profiles in a time-, tissue-, and pathogen-dependent manner. In general, intracellular pathogen caused wider and higher levels of CsSOCS expressions than extracellular pathogen. These results suggest that different members of SOCSs in teleost may play different roles in the infection processes of different bacterial pathogens.

Feeding Glycyrrhiza glabra (liquorice) and Astragalus membranaceus (AM) alters innate immune and physiological responses in yellow perch (Perca flavescens)

The current work assessed the potential immunomodulatory and growth-promoting effects of Astragalus membranaceus (AM) and Glycyrrhiza glabra (liquorice) in Yellow perch (Perca flavescens). In this regard, fish with an average weight of 31 ± 1.0 g were divided into five groups, and fed daily with an additive-free basal diet (control); 1, 2, and 3% (w/w) Glycyrrhiza glabra, and the fifth diet was incorporated with a combination of 1% G. glabra-AM for a four-week period. Immunological, biochemical and growth parameters were measured; and sub-groups of fish were exposed to 1-week starvation. The results showed that incorporating AM and liquorice in the diet significantly improved Immunological [superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), Lipid peroxidase (LPx) and lysozyme activities], biochemical [Aspartate Aminotransferase (AST) and Alanine Transaminase (ALT) activities; and glucose and cortisol concentrations] and growth performance parameters [body mass gain (BMG), specific growth rate (SGR), length, condition factor (K) and feed conversion ratio (FCR)]. In addition, markedly up-regulated the expression of related genes [Insulin-Like Growth Factor-1 (IGF-1), Serum amyloid A (SAA), Complement Component C3 (CCC3), Alpha 2 Macroglobulin (A2M), SOD and GPx] in treated fish groups compared to the control. Conclusively, feeding AM and liquorice diets significantly increased (P < 0.05) growth performance, antioxidant and immune response profiles throughout the entire experiment, suggesting their beneficial rule as natural anti-stress agents.

Type II SOCS as a feedback repressor for GH-induced Igf1 expression in carp hepatocytes

Type II suppressor of cytokine signaling (SOCS) serve as feedback repressors for cytokines and are known to inhibit growth hormone (GH) actions. However, direct evidence for SOCS modulation of GH-induced insulin-like growth factor 1 (Igf1) expression is lacking, and the post-receptor signaling for SOCS expression at the hepatic level is still unclear. To shed light on the comparative aspects of SOCS in GH functions, grass carp was used as a model to study the role of type II SOCS in GH-induced Igf1 expression. Structural identity of type II SOCS, Socs1-3 and cytokine-inducible SH2-containing protein (Cish), was established in grass carp by 5'/3'-RACE, and their expression at both transcript and protein levels were confirmed in the liver by RT-PCR and LC/MS/MS respectively. In carp hepatocytes, GH treatment induced rapid phosphorylation of JAK2, STATs, MAPK, PI3K, and protein kinase B (Akt) with parallel rises in socs1-3 and cish mRNA levels, and these stimulatory effects on type II SOCS were shown to occur before the gradual loss of igf1 gene expression caused by prolonged exposure of GH. Furthermore, GH-induced type II SOCS gene expression could be negated by inhibiting JAK2, STATs, MEK1/2, P38 (MAPK), PI3K, and/or Akt respectively. In CHO cells transfected with carp GH receptor, over-expression of these newly cloned type II SOCS not only suppressed JAK2/STAT5 signaling with GH treatment but also inhibited GH-induced grass carp Igf1 promoter activity. These results, taken together, suggest that type II SOCS could be induced by GH in the carp liver via JAK2/STATs, MAPK, and PI3K/Akt cascades and serve as feedback repressors for GH signaling and induction of igf1 gene expression.

Molecular characterization and immune response to lipopolysaccharide (LPS) of the suppressor of cytokine signaling (SOCS)-1, 2 and 3 genes in Nile tilapia (Oreochromis niloticus)

Suppressor of cytokine signaling (SOCS) proteins are inverse feedback regulators of cytokine and hormone signaling mediated by the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway that are involved in immunity, growth and development of organisms. In the present study, three SOCS genes, SOCS-1, SOCS-2 and SOCS-3, were identified in an economically important fish, Nile tilapia (Oreochromis niloticus) referred to as NtSOCS-1, NtSOCS-2 and NtSOCS-3. Multiple alignments showed that, the three SOCS molecules share highly conserved functional domains, including the SRC homology 2 (SH2) domain, the extended SH2 subdomain (ESS) and the SOCS box with others vertebrate counterparts. Phylogenetic analysis indicated that NtSOCS-1, 2 and 3 belong to the SOCS type II subfamily. Whereas NtSOCS-1 and 3 showed close evolutionary relationship with Perciformes, NtSOCS-2 was more related to Salmoniformes. Tissue specific expression results showed that, NtSOCS-1, 2 and 3 were constitutively expressed in all nine tissues examined. NtSOCS-1 and 3 were highly expressed in immune-related tissues, such as gills, foregut and head kidney. However, NtSOCS-2 was superlatively expressed in liver, brain and heart. In vivo, NtSOCS-1 and 3 mRNA levels were up-regulated after lipopolysaccharide (LPS) challenge while NtSOCS-2 was down-regulated. In vitro, LPS stimulation increased NtSOCS-3 mRNA expression, however it inhibited the transcription of NtSOCS-1 and 2. Collectively, our findings suggest that, the NtSOCS-1 and 3 might play significant role(s) in innate immune response, while NtSOCS-2 may be more involved in metabolic regulation.

Stress-Immune-Growth Interactions: Cortisol Modulates Suppressors of Cytokine Signaling and JAK/STAT Pathway in Rainbow Trout Liver

Chronic stress is a major factor in the poor growth and immune performance of salmonids in aquaculture. However, the molecular mechanisms linking stress effects to growth and immune dysfunction is poorly understood. The suppressors of cytokine signaling (SOCS), a family of genes involved in the inhibition of JAK/STAT pathway, negatively regulates growth hormone and cytokine signaling, but their role in fish is unclear. Here we tested the hypothesis that cortisol modulation of SOCS gene expression is a key molecular mechanism leading to growth and immune suppression in response to stress in fish. Exposure of rainbow trout (Oncorhynchus mykiss) liver slices to cortisol, mimicking stress level, upregulated SOCS-1 and SOCS-2 mRNA abundance and this response was abolished by the glucocorticoid receptor antagonist mifepristone. Bioinformatics analysis confirmed the presence of putative glucocorticoid response elements in rainbow trout SOCS-1 and SOCS-2 promoters. Prior cortisol treatment suppressed acute growth hormone (GH)-stimulated IGF-1 mRNA abundance in trout liver and this involved a reduction in STAT5 phosphorylation and lower total JAK2 protein expression. Prior cortisol treatment also suppressed lipopolysaccharide (LPS)-induced IL-6 but not IL-8 transcript levels; the former but not the latter cytokine expression is via JAK/STAT phosphorylation. LPS treatment reduced GH signaling, but this was associated with the downregulation of GH receptors and not due to the upregulation of SOCS transcript levels by this endotoxin. Collectively, our results suggest that upregulation of SOCS-1 and SOCS-2 transcript levels by cortisol, and the associated reduction in JAK/STAT signaling pathway, may be a novel mechanism leading to growth reduction and immune suppression during stress in trout.

Tissue-specific molecular immune response to lipopolysaccharide challenge in emaciated anadromous Arctic charr

Anadromous Arctic charr (Salvelinus alpinus) undergo voluntary winter fasting for months in the Arctic. We tested the hypothesis that extended fasting will compromise the ability of this species to evoke an immune response. Charr were either fed or fasted for 85 days and challenged with lipopolysaccharide (LPS), and the molecular immune response in the liver and spleen assessed at 8 and 96 h post-injection. LPS increased IL-1β, IL-8, and serum amyloid protein A (SAA) mRNA levels in both groups, but the liver IL-1β and IL-8, and spleen IL-8 responses were reduced in the fasted group. Fasting upregulated SOCS-1 and SOCS-2 mRNA abundance, while LPS stimulated SOCS-3 mRNA abundance and this response was higher in the fasted liver. Collectively, extended fasting and emaciation does not curtail the capacity of charr to evoke an immune response, whereas upregulation of SOCS may be a key adaptation to conserve energy by restricting the inflammatory response.

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.