Two hepcidin-like antimicrobial peptides in Barramundi Lates calcarifer exhibit differing tissue tropism and are induced in response to lipopolysaccharide

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.

β-Defensin from the Asian Sea Bass, Lates calcarifer: Molecular Prediction and Phylogenetic Analysis

Antimicrobial peptides (AMPs) are an important element of the innate immune system of all living organisms and serve as a barrier that safeguards the organisms against a wide range of pathogens. Fishes are proven to be a prospective source of AMPs, and β-defensins form an important family of AMPs with potent antimicrobial, chemotactic and immunomodulatory activities. The present study reports a β-defensin AMP sequence (Lc-BD) from the Asian sea bass, Lates calcarifer, a commercially important fish species in tropical and subtropical regions of Asia and the Pacific. A 202-bp cDNA fragment with an open reading frame encoding 63 amino acids (aa) was obtained from the mRNA of gill tissue by RT-PCR. The deduced aa sequence of Lc-BD possessed a signal and a mature peptide region with 20 and 43 aa residues, respectively. Lc-BD was characterized at the molecular level, and a molecular weight of 5.24 kDa and a net charge of +4.5 was predicted for the mature peptide. The molecular characterization of Lc-BD revealed the presence of three intramolecular disulphide bonds involving the six conserved cysteine residues in the sequence, and the phylogenetic analysis of Lc-BD showed a close relationship with β-defensins from fishes like Siniperca chuatsi, Argyrosomus regius, Trachinotus ovatus and Oplegnathus fasciatus.

Antibacterial and antioxidant activity of clove oil against Streptococcus iniae infection in Nile tilapia (Oreochromis niloticus) and its effect on hepatic hepcidin expression

This study was designed to evaluate the modulating effect dietary clove essential oil (CL) has on the antioxidant and immunological status of Nile tilapia following Streptococcus iniae (Si) infection. Fish were placed on either control or (1.5 and 3%) CL-supplemented diets for 4 weeks. After sampling, the remaining fish in the control group were divided into 2 groups: an unchallenged (negative control) and an Si-challenged positive control. On the other hand, the remaining fish in CL-supplemented groups were challenged with Si, and mortality was checked for two weeks before the final sampling. Serum immunological parameters, tissue antioxidants, and oxidative stress markers were determined. Moreover, hepatic hepcidin expression was also measured in different groups. The obtained results showed improvements in blood phagocytic, bactericidal, lysozyme, and respiratory burst activities in CL-supplemented fish before and after the Si challenge. Si-challenge caused a remarkable increase in tissue malondialdehyde (MDA) levels that was inhibited by CL supplementation. The activities of glutathione peroxidase (GPx) and superoxide dismutase (SOD) in tissues were significantly elevated in a dose-dependent manner in CL-supplemented groups in both pre- and post-challenge experiments; renal SOD did not show any differences. Hepatic nitric oxide (NO) level was significantly decreased in CL-supplemented fish in a dose-dependent manner. In the post-challenge experiment, nitrosative stress was apparent in the liver and kidney; however, CL supplementation was sufficient to reverse it. Interestingly, a remarkable induction of the hepatic hepcidin expression was observed in all CL-supplemented groups in the pre-challenge experiment and Si-challenged fish, underscoring the role of CL as an antibacterial through inducing hepatic hepcidin expression to combat S. iniae infection. CL-supplementation was associated with lower mortality rates after Si-challenge, which was more pronounced in CL-3% supplemented fish. In conclusion, our results demonstrate that CL has a potent antioxidant role via increasing antioxidant enzymes' activities and antagonizing lipid peroxidation. Moreover, CL has an immune-stimulant effect by inducing the hepatic hepcidin expression and immunological markers in response to S. iniae infection.

Immune Regulation, but Not Antibacterial Activity, Is a Crucial Function of Hepcidins in Resistance against Pathogenic Bacteria in Nile Tilapia (Oreochromis niloticus Linn.)

In this study, the functions of a recombinant propeptide (rProOn-Hep1) and the synthetic FITC-labelled mature peptides sMatOn-Hep1 and sMatOn-Hep2 were analyzed. Moreover, sMatOn-Hep1 and sMatOn-Hep2 were mildly detected in the lymphocytes of peripheral blood mononuclear cells (PBMCs) and strongly detected in head kidney macrophages. The in vitro binding and antibacterial activities of these peptides were slightly effective against several pathogenic bacteria. Immune regulation by sMatOn-Hep1 was also analyzed, and only sMatOn-Hep1 significantly enhanced the phagocytic index in vitro (p < 0.05). Interestingly, intraperitoneal injection of sMatOn-Hep1 (10 or 100 µg) significantly elevated the phagocytic activity, phagocytic index, and lysozyme activity and clearly decreased the iron ion levels in the livers of the treated fish (p < 0.05). Additionally, sMatOn-Hep1 enhanced the expression levels of CC and CXC chemokines, transferrin and both On-Hep genes in the liver, spleen and head kidney, for 1–96 h after injection, but did not properly protect the experimental fish from S. agalactiae infection after 7 days of treatment. However, the injection of S. agalactiae and On-Heps indicated that 100 μg of sMatOn-Hep1 was very effective, while 100 μg of rProOn-Hep1 and sMatOn-Hep2 demonstrated moderate protection. Therefore, On-Hep is a crucial iron-regulating molecule and a key immune regulator of disease resistance in Nile tilapia.

Fish and fish side streams are valuable sources of high-value components

The current practice of fish processing generates increasing quantities of side streams and waste, such as skin, heads, frames, viscera, and fillet cut offs. These may account for up to 70% of the fish used in industrial processing. Low-value fish catches, and under-utilized fish species comprise another source of side streams. These side streams have been discarded in the environment leading to environmental problems or they have ended up as low commercial value products, such as feed for fur animals and aquaculture. However, several studies have shown that fish side streams contain valuable bioactive ingredients and fractions, such as fish oils, proteins and peptides, collagen, gelatin, enzymes, chitin, and minerals. These compounds and fractions may provide the opportunity to develop novel applications in health promoting foods, special feeds, nutraceuticals, pharmaceuticals, and cosmetic products. Better utilization of side streams and low-value fish would simultaneously improve both the environmental and ecological sustainability of production. This review summarizes the current knowledge on fish and fish side streams as sources of high-value components such as peptides with antimicrobial, antioxidative, antihypertensive, and antihyperglycemic properties, proteins such as fish collagen and gelatin, fish enzymes, fish oils and fatty acids, polysaccharides like glucosaminoglycans, chitin and chitosan, vitamin D, and minerals. Production technologies for recovering the high-value fractions and potential product applications are discussed. Furthermore, safety aspects related to the raw material, technologies, and fractions are considered.

Molecular characterization of a hepcidin homologue in starry flounder (Platichthys stellatus) and its synergistic interaction with antibiotics

Hepcidins are small cysteine-rich antimicrobial peptides that play an important role in host immunity against pathogenic organisms. Most fish hepcidins exert bactericidal activities against a wide range of pathogens. In this study, we identified a cDNA sequence encoding a hepcidin homologue (PsHepcidin) in the starry flounder Platichthys stellatus. The predicted amino acid sequence of PsHepcidin comprises a signal peptide and a prodomain, which are followed by the mature peptide. Sequence analysis revealed that PsHepcidin belongs to the fish HAMP2 cluster and that it is closely related to mudskipper hepcidin-2. Expression of PsHepcidin mRNA was detected in all examined immune-related tissues, with the highest transcript levels being found in the liver. In response to lipopolysaccharide treatment, PsHepcidin was significantly up-regulated in the liver, kidney, and spleen in a time-dependent manner. Chemically synthesized mature peptides of PsHepcidin were found to exhibit broad antimicrobial activity in vitro. We also investigated the combined effect of PsHepcidin and conventional antibiotics and found that these combinations showed synergistic effects against most of the examined bacterial strains. Collectively, the results of this study indicate that PsHepcidin exhibits potent antibacterial activity both independently and when used in combination with conventional antibiotics.

Molecular characterisation, ontogeny and expression analysis of melanoma differentiation-associated factor 5 (MDA5) from Asian seabass, Lates calcarifer

MDA5 is the pivotal member of the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) and is reported to play a crucial role in type I IFN-mediated responses against pathogen-associated molecular patterns (PAMPs), especially nucleic acids. In this study, we have identified and cloned the full-length cDNA sequence of MDA5, which comprises 3398 nucleotides and encodes for a putative protein of 978 AA length, in Asian seabass, Lates calcarifer. From the putative amino acid sequence of AsMDA5, four different conserved domains could be predicted: two N-terminal CARD domains, a DExDc domain, a HELICc domain and a C-terminal RIG-1_C-RD domain. The mRNA transcript of AsMDA5 could be detected in all the 11 tissues tested in healthy animals with the highest expression in heart followed by gill and skin. The ontogenetic expression profile showed constitutive expression in developmental stages starting from unfertilized eggs, which implies the possibility of maternally acquired immunity of RLRs in offspring. The viral analogue poly I:C could modulate the AsMDA5 expression both in vivo and in vitro. In all the tissues, AsMDA5 expression was found to be highly regulated following injection with poly I:C with the highest expression observed in kidney. The expression level of AsMDA5 was found to be modulated at different time-points following challenge with Gram-negative bacterium, Vibrio alginolyticus, and Gram-positive bacterium, Staphylococcus aureus. Similarly, noticeable change in AsMDA5 expression was detected in SISK cell line induced with either LPS or PGN. The observations made in this study suggest that in euryhaline marine teleosts like Asian seabass, MDA5 gene serves as one of the pivotal receptor for the detection of viral and bacterial PAMP, and might play an important antimicrobial role during early embryonic development.

Molecular characterization and functional analysis of the hepcidin gene from roughskin sculpin (Trachidermus fasciatus)

Hepcidin is a kind of cysteine-rich antimicrobial peptide that plays a vital role in host innate immune activity and iron regulation. Here, we report the molecular characterization and functional analysis of a novel hamp1 hepcidin isoforms Tf-Hep from roughskin sculpin, Trachidermus fasciatus. A cDNA fragment of 988 bp with an ORF of 273 bp was obtained. The coding sequence encodes for a signal peptide of 24 amino acids coupled with a prodomain of 40 amino acids and a mature peptide of 26 amino acids. Tissue distribution analysis indicated that Tf-Hep was most abundant in the liver. It could be significantly induced post lipopolysaccharide (LPS) challenge and heavy metal exposure. The mature peptide was expressed as a 6.061 kDa fusion protein in Pichia pastoris GS115. The active purified recombinant protein (rTf-Hep) exhibited a wide spectrum of potent antimicrobial activity in vitro against 4 Gram-negative bacteria Escherichia coli, Vibrio Anguillarum, Klebsiella pneumoniae, and Pseudomonas aeruginosa and 4 Gram-positive bacteria Staphylococcus aureus, Bacillus subtilis, Bacillus thuringiensis, and Bacillus megaterium with minimum inhibitory concentrations (MICs) of 5-80 μg/ml (0.825-13.2 μM). It also displayed high affinity to polysaccharides on bacteria surface including LPS, lipoteichoic acid (LTA) and peptidoglycan (PGN). We further revealed that rTf-hep was capable of agglutinating 6 of the 8 bacteria. All these results suggest that rTf-hep may be both an antibacterial effector and a pattern recognition molecule in fish immune defense. The in vivo bacterial treatment results demonstrated that rTf-Hep could significantly improve the survival rate of fish infected with V. anguillarum. Taken together, these data indicate an important role for Tf-hep in the innate immunity of Trachidermus fasciatus and suggest its potential application in aquaculture for increasing fish resistance to disease.

Identification, ontogeny and expression analysis of a novel laboratory of genetics and physiology 2 (LGP2) transcript in Asian seabass, Lates calcarifer

LGP2 (laboratory of genetics and physiology 2) is an important member of the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), which plays a significant role in antiviral innate immunity. In this study, we have cloned the full-length cDNA sequence of LGP2 from Asian seabass, Lates calcarifer (AsLGP2). The complete AsLGP2 cDNA sequence consisted of 2586 nucleotides encoding a putative protein of 681 amino acids with a molecular mass of 77.6 kDa. From the AsLGP2 protein, four different conserved domains were predicted: a DExDc (DEAD/DEAH box helicase domain), a bacterial type III restriction enzyme domain (RES III), a HELICc (Helicase superfamily c-terminal domain and a RIG-I_C-RD (RIG-I C-terminal regulatory domain). The transcript of AsLGP2 could be detected in all the 11 tissues tested in healthy animals with high expression noticed in tissues facing external environment such as gill, hindgut and skin. The ontogenic expression profile of AsLGP2 implies a possible maternal transfer of this gene as it has been detected in all early embryonic developmental stages along with unfertilized eggs. Viral analogue, poly I:C, injection resulted in rapid up-regulated expression in different tissues with the highest modulation of expression observed in kidney followed by liver and gill. A rapid response of AsLGP2 expression was also observed in the different tissues of Vibrio alginolyticus-injected L. calcarifer, while significant change in expression was noticed following Staphylococcus aureus infection. Similarly, exposure to different pathogen-mimicking microbial analogues such as poly I:C, LPS and PGN resulted in enhanced expression of AsLGP2 in SISK cell-line. Taking together, these observations suggest that AsLGP2 can act as both antiviral and antibacterial cytosolic receptor and may play a significant role in embryonic and larval development in marine euryhaline teleosts like Asian seabass.

Genomic organization, expression and antimicrobial activity of a hepcidin from taimen (Hucho taimen, Pallas)

Hepcidin, an antimicrobial peptide, plays a crucial role in innate immune system of teleost fish. As a cysteine-rich peptide, hepcidin possesses a dual function including iron regulation and innate immunity. In the present study, a full-length hepcidin cDNA (HtHep) was cloned and characterized by RT-PCR and RACE techniques from taimen (Hucho taimen, Pallas), which is a type of rare, precious and cold-water fish species in China. The cDNA contains an open reading frame (ORF) of 267 bp encoding 88 amino acid (aa), with 170 bp located in the 5(') untranslated region (UTR) and 151 bp in the 3' UTR. The genomic sequences analysis showed that the HtHep gene consisted of three exons and two introns (with the length 94 and 251 bp, respectively). With a predicted molecular mass of 2881.4 Da and a theoretical pI of 8.53, the deduced amino acid encodes a signal peptide of 24 aa, prodomain of 39 aa and mature peptide of 25 aa. The signal peptidase (SA-VP) and the motif RX (K/R)R of propeptide convertase suggested the cleavage site of signal and mature peptide. Eight conserved cysteine residues were also identified and formed four disulfide bonds. Pair-wise alignments showed that HtHep clustered together with two fish species of Salmonidae family (Salmo salar and Oncorhynchus mykiss) in HAMP1 branch. Quantitative RT-PCR analysis indicated that the mRNA levels of HtHep were detected in a wide range of tissues and the highest level was detected in the liver. Its expression was also detected early during embryonic stage and could be up-regulated in the liver when challenged with pathogenic bacteria (Yersinia ruckeri). The recombinant HtHep (rHtHep) had antimicrobial activity against both gram-positive (Micrococcus lysodeikticus and Staphylococcus aureus) and gram-negative bacteria (Escherichia coli). Our results suggested that HtHep might be involved in the innate immune defense against bacterial pathogens in taimen.

Hepcidin-Dependent Regulation of Erythropoiesis during Anemia in a Teleost Fish, Dicentrarchus labrax

Anemia is a common disorder, characterized by abnormally low levels of red blood cells or hemoglobin. The mechanisms of anemia development and response have been thoroughly studied in mammals, but little is known in other vertebrates, particularly teleost fish. In this study, different degrees of anemia were induced in healthy European sea bass specimens (Dicentrarchus labrax) and at pre-determined time points hematological parameters, liver iron content and the expression of genes involved in iron homeostasis and hematopoiesis, with particular attention on hepcidins, were evaluated. The experimental anemia prompted a decrease in hamp1 expression in all tested organs, in accordance to an increased need for iron absorption and mobilization, with slight increases in hamp2 in the kidney and intestine. The liver was clearly the major organ involved in iron homeostasis, decreasing its iron content and showing a gene expression profile consistent with an increased iron release and mobilization. Although both the spleen and head kidney are involved in erythropoiesis, the spleen was found to assume a more preponderant role in the recovery of erythrocyte levels. The intestine was also involved in the response to anemia, through the increase of iron transporting genes. Administration of Hamp1 or Hamp2 mature peptides showed that only Hamp1 affects hematological parameters and liver iron content. In conclusion, the molecular mechanisms of response to anemia present in sea bass are similar to the ones described for mammals, with these results indicating that the two hepcidin types from teleosts assume different roles during anemia.

Antimicrobial Peptides as Mediators of Innate Immunity in Teleosts

Antimicrobial peptides (AMPs) have been identified throughout the metazoa suggesting their evolutionarily conserved nature and their presence in teleosts is no exception. AMPs are short (18–46 amino acids), usually cationic, amphipathic peptides. While AMPs are diverse in amino acid sequence, with no two AMPs being identical, they collectively appear to have conserved functions in the innate immunity of animals towards the pathogens they encounter in their environment. Fish AMPs are upregulated in response to pathogens and appear to have direct broad-spectrum antimicrobial activity towards both human and fish pathogens. However, an emerging role for AMPs as immunomodulatory molecules has become apparent—the ability of AMPs to activate the innate immune system sheds light onto the multifaceted capacity of these small peptides to combat pathogens through direct and indirect means. Herein, this review focuses on the role of teleost AMPs as modulators of the innate immune system and their regulation in response to pathogens or other exogenous molecules. The capacity to regulate AMP expression by exogenous factors may prove useful in modulating AMP expression in fish to prevent disease, particularly in aquaculture settings where crowded conditions and environmental stress pre-dispose these fish to infection.

Molecular characterization, phylogeny and expression of a hepcidin gene in the blotched snakehead Channa maculata

A hepcidin-like gene (cmHep) was cloned and characterized from the liver of the blotched snakehead Channa maculata. The complete cmHep cDNA was 756 bp in length, containing an open reading frame of 270 bp (encoding 89 amino acids), flanked by 210 bp and 276 bp of 5' and 3' untranslated regions, respectively. The deduced peptide of 89 amino acids consisted of 24 aa, 40 aa and 25 aa for signal peptide, prodomain and mature peptide, respectively. The mature peptide had eight cysteines at the identical conserved positions in common with most of other known hepcidins in vertebrates. cmHepc gene displayed a tripartite structure (three exons interrupted by two introns), which organisation was conserved between the blotched snakehead and other fish species. Phylogenetic analysis of hepcidins from C. maculata and other vertebrates showed that major phylogenetic grouping of fish hepcidin coincided with the current euteleosts classification, indicating the multiphyletic evolution of hepcidin in the teleosts. In the Acanthopterygii subclade, there were two distinct additional subclades named as HAMP-Ac1 and HAMP-Ac2. The blotched snakehead hepcidin was in the group HAMP-Ac1, which has the hypothetical iron regulatory sequence [Q-S/I-H-L/I-S/A] motif in N-terminal of mature peptide. The RT-PCR showed cmHep mRNA transcripts were widely distributed in all tissues tested in the blotched snakehead including the liver, gill, intestine, spleen, head kidney and peripheral white blood cell. The most abundant of cmHep mRNA was detected in liver. A significant up-regulation of cmHep expression was detected only in head kidney at 24h post-challenge with Vibrio parahaemolyticus in blotched snakehead adults, no significant differences found in liver, gill, intestine and spleen. The cmHep expression was up-regulated in spleen, head kidney and intestine at 24h post-injection with LPS in blotched snakehead juveniles, liver cmHep expression was not altered. Iron overloading and poly I:C stimulation down-regulated cmHep expression in liver, but did not significantly change cmHep expression in spleen, head kidney and intestine in blotched snakehead juveniles.

Comparative transcriptomics of Atlantic Salmo salar, chum Oncorhynchus keta and pink salmon O. gorbuscha during infections with salmon lice Lepeophtheirus salmonis

Background

Salmon species vary in susceptibility to infections with the salmon louse (Lepeophtheirus salmonis). Comparing mechanisms underlying responses in susceptible and resistant species is important for estimating impacts of infections on wild salmon, selective breeding of farmed salmon, and expanding our knowledge of fish immune responses to ectoparasites. Herein we report three L. salmonis experimental infection trials of co-habited Atlantic Salmo salar, chum Oncorhynchus keta and pink salmon O. gorbuscha, profiling hematocrit, blood cortisol concentrations, and transcriptomic responses of the anterior kidney and skin to the infection.

Results

In all trials, infection densities (lice per host weight (g)) were consistently highest on chum salmon, followed by Atlantic salmon, and lowest in pink salmon. At 43 days post-exposure, all lice had developed to motile stages, and infection density was uniformly low among species. Hematocrit was reduced in infected Atlantic and chum salmon, and cortisol was elevated in infected chum salmon. Systemic transcriptomic responses were profiled in all species and large differences in response functions were identified between Atlantic and Pacific (chum and pink) salmon. Pink and chum salmon up-regulated acute phase response genes, including complement and coagulation components, and down-regulated antiviral immune genes. The pink salmon response involved the largest and most diverse iron sequestration and homeostasis mechanisms. Pattern recognition receptors were up-regulated in all species but the active components were often species-specific. C-type lectin domain family 4 member M and acidic mammalian chitinase were specifically up-regulated in the resistant pink salmon.

Conclusions

Experimental exposures consistently indicated increased susceptibility in chum and Atlantic salmon, and resistance in pink salmon, with differences in infection density occurring within the first three days of infection. Transcriptomic analysis suggested candidate resistance functions including local inflammation with cytokines, specific innate pattern recognition receptors, and iron homeostasis. Suppressed antiviral immunity in both susceptible and resistant species indicates the importance of future work investigating co-infections of viral pathogens and lice.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-200) contains supplementary material, which is available to authorized users.

Antimicrobial peptides from fish

Antimicrobial peptides (AMPs) are found widely distributed through Nature, and participate in the innate host defense of each species. Fish are a great source of these peptides, as they express all of the major classes of AMPs, including defensins, cathelicidins, hepcidins, histone-derived peptides, and a fish-specific class of the cecropin family, called piscidins. As with other species, the fish peptides exhibit broad-spectrum antimicrobial activity, killing both fish and human pathogens. They are also immunomodulatory, and their genes are highly responsive to microbes and innate immuno-stimulatory molecules. Recent research has demonstrated that some of the unique properties of fish peptides, including their ability to act even in very high salt concentrations, make them good potential targets for development as therapeutic antimicrobials. Further, the stimulation of their gene expression by exogenous factors could be useful in preventing pathogenic microbes in aquaculture.

Molecular characterization of hepcidin gene in common carp (Cyprinus carpio L.) and its expression pattern responding to bacterial challenge

Hepcidin is a cysteine-rich cationic antimicrobial peptide (AMP), which plays an important role in host innate immune system and iron regulation. A great many of hepcidin genes have been identified from vertebrates, including various fish species. Here we report the cloning and identification of a hepcidin cDNA from the liver of common carp (Cyprinus carpio L.). The full-length cDNA of the common carp hepcidin was 647 bp, which contained an ORF of 276 bp encoding a prepropeptide of 91 amino acid residues. The predicted preprohepcidin consisted of three domains: a signal peptide of 24 amino acids, a prodomain of 42 amino acids and a mature peptide of 25 amino acids, which containd eight cysteine residues at the identical conserved position. The genomic organization of common carp hepcidin was identified, which contained three exons and two introns, similarly to corresponding genes in mammals and other fish species. Sequence alignment and phylogenetic analysis showed that hepcidins were conserved in different species, and common carp hepcidin was type 1 hepcidin according to the phylogenetic tree, which had the highest identity with mud loach and zebrafish. Real-time PCR assay showed that the hepcidin gene was mostly expressed in liver, and expressed in all the other tested tissues of common carp in different levels. When challenged with pathogenic bacterium, Vibrio anguillarum, the expression level of common carp hepcidin was quickly up-regulated in liver, spleen, head kidney and hindgut, implying that hepcidin may be an important component of the innate immune system of common carp and involved in mucosal immune response against invading pathogens.

Molecular cloning, recombinant expression, and antimicrobial activity of EC-hepcidin3, a new four-cysteine hepcidin isoform from Epinephelus coioides

Hepcidin, a cysteine-rich antimicrobial peptide, is widespread in fish and shows multiple activities, including antimicrobial, antivirus, and antitumor. Here, a new four-cysteine hepcidin isoform gene, EC-hepcidin3, was cloned from the marine-cultured orange-spotted grouper (Epinephelus coioides). The complete cDNA sequence consisted of 603 bases with an open reading frame (ORF) of 270 bases. The genomic DNA sequence was composed of two introns and three exons, and its 312-bp upstream region had multiple putative transcription factor binding sites. Soluble recombinant protein EC-proHep3 containing a His-tag at the C-terminus was obtained from expression plasmid pET-28a/EC-proHep3 in Escherichia coli Rosetta. It was purified by immobilized metal affinity chromatography (IMAC), and it showed antibacterial activity in vitro. Kinetic studies indicated that recombinant EC-proHep3 has strong, rapid activity against Staphylococcus aureus and Pseudomonas stutzeri. The results indicate that EC-hepcidin3 might be an effective component in the innate immune system of groupers.

Identification and characterization of a hepcidin from half-smooth tongue sole Cynoglossus semilaevis

Hepcidin, an antimicrobial peptide, has a dual function including innate immunity and iron regulation. Here, based on the sequence of an EST database, we have isolated and characterized a hepcidin gene (referred to as CsHepcidin) from half-smooth tongue sole (Cynoglossus semilaevis). Analysis of the coding regions indicated CsHepcidin gene comprised 3 exons and 2 introns. The putative CsHepcidin showed a great similarity to other hepcidin orthologues, particularly with respect to its 24 aa signal peptide, typical RX(K/R)R motif and eight conserved cysteine residues in the mature cationic peptide. Phylogenic analysis indicated that CsHepcidin was a hepcidin 1-type peptide of acanthopterygians, with highly homologous with Solea senegalensis hepcidin. In C. semilaevis ontogeny, CsHepcidin mRNA was detected at a low level in unfertilized eggs, increased on 6 d after hatching, and decreased remarkably at metamorphic stage. CsHepcidin transcripts showed a constitutive basal expression in most of the tissues, especially in liver. Challenge with formalin-inactivated Vibrio anguillarum led to significantly up-regulations of CsHepcidin gene in liver, head kidney and spleen in time-dependent manners. Biological activity analysis showed that recombinant CsHEP exhibited direct antimicrobial activity against bacterial pathogens in vitro, particularly showed strong activity against the principal fish pathogens, V. anguillarum and Edwardsiella tarda. All these results suggest that CsHepcidin may be involved in the initial response to invasion of microbial pathogens. Further exploration to elucidate the role of CsHepcidin in iron regulation and embryogenesis in C. semilaevis are needed.

Genomic organization and tissue-specific expression of hepcidin in the pacific mutton hamlet, Alphestes immaculatus (Breder, 1936)

Hepcidin is a cysteine-rich peptide involved in iron metabolism, inflammatory response and as antimicrobial peptide. Despite the fact that hepcidins have been identified in several fish species, only few have been completely characterized. This study, described the identification and complete molecular characterization of the hepcidin antimicrobial peptide 1 (HAMP1) gene of Alphestes immaculatus. Moreover, its specific expression level at both basal and lipopolysaccharide (LPS)-induced conditions in different tissues was also determined by real-time PCR. Results showed that the HAMP1gene consists of three exons and two introns encoding a preprohepcidin composed of 90 aa (24 aa for signal peptide, 40 aa for prodomain and 26 aa for mature peptide). The promoter region analysis revealed a TATA box sequence and several putative transcription factor binding sites. A comparative analysis showed CEBPα, CEBPβ, NF-kB, HNF3, GATA-1 and c-Rel as the most common found in fishes. The mature peptide possesses a pI of 8.34, which is the average among fish hepcidin. In addition, the structural modeling showed a hairpin structure with four putative disulfide bonds. A phylogenetic analysis revealed that this hepcidin gene is a HAMP1 class, and is clustered into the same group with the Serranid fish Epinephelus moara and the Antarctic fish Lycodichthys dearborni. Finally, the relative expression levels showed high basal values in liver and muscle, whereas in LPS-induced fish the relative expression tendency changed, with the highest values in spleen and head kidney tissues. This study describes the completely characterized HAMP1 gene of A. immaculatus and their patterns of expression level at different conditions and in different tissues, showing by first time muscle hepcidin expression could be relevant in the immune response in fish.