Molecular cloning and functional characterization of the hepcidin gene from the convict cichlid (Amatitlania nigrofasciata) and its expression pattern in response to lipopolysaccharide challenge

Molecular cloning of the hepcidin gene from crescent sweetlips (Plectorhinchus cinctus) and characterization of its encoded antimicrobial peptide

Hepcidin has been identified as an important antimicrobial peptide exerting important innate immunomodulatory activities in many fish species. In the present study, reverse transcription PCR coupled with the rapid amplification of cDNA ends was used to obtain the full-length cDNA of the crescent sweetlips hepcidin gene, which is 829 bp in length and includes an 273 bp ORF encoding a peptide with 90 amino acid residues. Sequence alignment showed a typical RXKR motif and eight conserved cysteine residues in the deduced amino acid sequences. Four disulfide bonds were predicted to form between these eight cysteines, which may stabilize the hairpin structure in hepcidin molecule. Furthermore, phylogenetic analysis showed that the deduced amino acid sequences of crescent sweetlips hepcidin had high sequence homology to hepcidins from fish species of Eupercaria. In addition, the crescent sweetlips hepcidin peptide demonstrated a strong antimicrobial activity in vitro against several types of pathogenic bacteria in fish. In conclusion, the obtained results suggested that crescent sweetlips hepcidin possessed the typical structure similar to other fish hepcidins and had strong antibacterial activity, which showed great potential in the prevention of fish diseases in aquaculture.

Genome-Wide Identification of Trachinotus ovatus Antimicrobial Peptides and Their Immune Response against Two Pathogen Challenges

Golden pompano, Trachinotus ovatus, as a highly nutritious commercially valuable marine fish, has become one of the preferred species for many fish farmers due to its rapid growth, wide adaptability, and ease of feeding and management. However, with the expansion of aquaculture scale, bacterial and parasitic diseases have also become major threats to the golden pompano industry. This study, based on comparative genomics, shows the possibility of preferential evolution of freshwater fish over marine fish by analyzing the phylogenetic relationships and divergence times of 14 marine fish and freshwater fish. Furthermore, we identified antimicrobial peptide genes from 14 species at the genomic level and found that the number of putative antimicrobial peptides may be related to species evolution. Subsequently, we classified the 341 identified AMPs from golden pompano into 38 categories based on the classification provided by the APD3. Among them, TCP represented the highest proportion, accounting for 23.2% of the total, followed by scolopendin, lectin, chemokine, BPTI, and histone-derived peptides. At the same time, the distribution of AMPs in chromosomes varied with type, and covariance analysis showed the frequency of its repeat events. Enrichment analysis and PPI indicated that AMP was mainly concentrated in pathways associated with disease immunity. In addition, our transcriptomic data measured the expression of putative AMPs of golden pompano in 12 normal tissues, as well as in the liver, spleen, and kidney infected with Streptococcus agalactiae and skin infected with Cryptocaryon irritans. As the infection with S. agalactiae and C. irritans progressed, we observed tissue specificity in the number and types of responsive AMPs. Positive selection of AMP genes may participate in the immune response through the MAPK signaling pathway. The genome-wide identification of antimicrobial peptides in the golden pompano provided a complete database of potential AMPs that can contribute to further understanding the immune mechanisms in pathogens. AMPs were expected to replace traditional antibiotics and be developed into targeted drugs against specific bacterial and parasitic pathogens for more precise and effective treatment to improve aquaculture production.

Prokaryotic Expression, Purification, and Antibacterial Activity of the Hepcidin Peptide of Crescent Sweetlips (Plectorhinchus cinctus)

The hepcidin peptide of crescent sweetlips (Plectorhinchus cinctus) is a cysteine-rich, cationic antimicrobial peptide that plays a crucial role in the innate immune system's defense against invading microbes. The aim of this study was to identify the optimal parameters for prokaryotic expression and purification of this hepcidin peptide and characterize its antibacterial activity. The recombinant hepcidin peptides were expressed in Escherichia coli strain Arctic Express (DE3), with culture and induction conditions optimized using response surface methodology (RSM). The obtained hepcidin peptides were then purified before tag cleavage, and their antibacterial activity was determined. The obtained results revealed that induction temperature had the most significant impact on the production of soluble recombinant peptides. The optimum induction conditions were determined to be an isopropylthio-β-galactoside (IPTG) concentration of 0.21 mmol/L, induction temperature of 18.81 °C, and an induction time of 16.01 h. Subsequently, the recombinant hepcidin peptide was successfully purified using Ni-IDA affinity chromatography followed by SUMO protease cleavage. The obtained hepcidin peptide (without His-SUMO tag) demonstrated strong antimicrobial activity in vitro against V. parahaemolyticus, E. coli, and S. aureus. The results showed prokaryotic (E. coli) expression is a feasible way to produce the hepcidin peptide of crescent sweetlips in a cost-effective way, which has great potential to be used as an antimicrobial agent in aquaculture.

Identification of Antibacterial Activity of Hepcidin From Antarctic Notothenioid Fish

Hepcidin is a small peptide composed of signal peptide, propeptide, and the bioactive mature peptide from N terminal to C terminal. Mature hepcidin is an antibacterial peptide and iron regulator with eight highly conserved cysteines forming four intramolecular disulfide bonds, giving it a β sheet hairpin-like structure. Hepcidin homologs are found in a variety of vertebrates, especially fish, and their diversity may be associated with different habitats and different levels of pathogens. Dissostichus mawsoni, an Antarctic notothenioid fish that lives in the coldest water unlike most places of the world, with at least two hepcidin variants with eight cysteines. We confirmed the formation process of activated mature hepcidins from D. mawsoni in Chinese hamster ovary (CHO) cell line, obtained recombinant hepcidin protein from prokaryotes, and characterized its binding ability and antibacterial activity against varying bacteria. The expression of hepcidin in CHO cell line showed that the prepropeptide of Dmhep_8cysV1 and Dmhep_8cysV2 cleavage into smaller mature peptide. The antibacterial assay and flow cytometry showed that Dmhep_8cysV1, Dmhep_8cysV2, and Drhep bound to different bacteria and killed them with different minimum inhibitory concentration. These data suggest that hepcidin plays an important role in the innate immunity of D. mawsoni and is of great value in improving resistance to pathogens.

Development of Disease-Resistance-Associated Microsatellite DNA Markers for Selective Breeding of Tilapia (Oreochromis spp.) Farmed in Taiwan

There are numerous means to improve the tilapia aquaculture industry, and one is to develop disease resistance through selective breeding using molecular markers. In this study, 11 disease-resistance-associated microsatellite markers including 3 markers linked to hamp2, 4 linked to hamp1, 1 linked to pgrn2, 2 linked to pgrn1, and 1 linked to piscidin 4 (TP4) genes were established for tilapia strains farmed in Taiwan after challenge with Streptococcus inae. The correlation analysis of genotypes and survival revealed a total of 55 genotypes related to survival by the chi-square and Z-test. Although fewer markers were found in B and N2 strains compared with A strain, they performed well in terms of disease resistance. It suggested that this may be due to the low potency of some genotypes and the combinatorial arrangement between them. Therefore, a predictive model was built by the genotypes of the parental generation and the mortality rate of different combinations was calculated. The results show the same trend of predicted mortality in the offspring of three new disease-resistant strains as in the challenge experiment. The present findings is a nonkilling method without requiring the selection by challenge with bacteria or viruses and might increase the possibility of utilization of selective breeding using SSR markers in farms.

PACAP modulates the transcription of TLR-1/TLR-5/MyD88 pathway genes and boosts antimicrobial defenses in Clarias gariepinus

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional neuropeptide that belongs to the secretin/glucagon/GHRH/VIP superfamily. Some of these molecules have antimicrobial activity and they are capable of stimulating the immune system. The present work studied the antibacterial and immunostimulatory activity of PACAP-38 from African catfish Clarias gariepinus against the Gram-negative bacterium Pseudomonas aeruginosa in an in vivo test. PACAP-38 improved antimicrobial activity of skin mucus molecules against P. aeruginosa. The peptide modulates the gene expression profile of TLR-1, TLR-5, MyD88, IL-1β, TNF-ɑ, IL-8, pardaxin, hepcidin and G/C-type lysozymes in skin, spleen and head kidney. The influenced exerted depended on the time after infection and tissue analyzed. This study provides the first evidence of a link between PACAP and antimicrobial peptides hepcidin and pardaxin. Our results suggest further use of PACAP as antimicrobial agent that could potentially be used to control disease in aquaculture.

Hepcidin-Expressing Fish Eggs as A Novel Food Supplement to Modulate Immunity against Pathogenic Infection in Zebrafish (Danio rerio)

Hepcidin antimicrobial peptides are difficult to produce in prokaryotic expression systems due to their complex structure and antimicrobial activity. Although synthetic hepcidin provides an alternative to solve this issue, its high cost limits its practical application in various industries. The present study used zebrafish eggs as bioreactors to produce convict cichlid (Amatitlania nigrofasciata) hepcidin (AN-hepc) using the oocyte-specific zona pellucida (zp3) promoter. The expression plasmid pT2-ZP3-AN-hepc-ZP3-EGFP, using EGFP as a reporter of AN-hepc expression, was designed to establish the transgenic line Tg(ZP3:AN-hepc:ZP3:EGFP) for the expression of AN-hepc. The AN-hepc peptide was produced successfully in fertilized eggs, as evidenced by RT-PCR and Western blotting. The AN-hepc-expressing eggs exhibited antimicrobial activity against a variety of aquatic pathogens and antibiotic-resistant pathogens, suggesting that the AN-hepc expressed in fish eggs was bioactive. The immunomodulatory effects of AN-hepc-expressing fertilized eggs on zebrafish innate immunity were evaluated by determining the expression of indicator genes after feeding with AN-hepc-expressing fertilized eggs for two months. Zebrafish supplementation with AN-hepc-expressing fertilized eggs significantly increased the expression of innate immunity-related genes, including IL-1β, IL-6, IL-15, TNF-α, NF-κb, complement C3b, lysozyme and TLR-4a. The zebrafish administered AN-hepc-expressing eggs exhibited higher cumulative survival than fish supplemented with wild-type and control eggs after infection with Aeromonas hydrophila and Streptococcus iniae. In conclusion, the present results showed that supplementation with AN-hepc-expressing fish eggs enhanced zebrafish innate immunity against pathogenic infections, suggesting that fertilized eggs containing AN-hepc have the potential to be developed as a food supplement for improving health status in aquaculture.

Cloning and identification of antimicrobial peptide, hepcidin from freshwater carp, Catla catla on pathogen challenge and PAMPs stimulation

Hepcidin, a cationic cysteine-rich antimicrobial peptide (AMP) acts in hormone regulation and iron homeostasis in the host body. However, the biological property of hepcidin in immune reaction remains unexplored. In aquatic milieu, environmental and pathogenic stressors cause detrimental infections, which are defended by various immunological cells and antimicrobial peptides. In this study, hepcidin gene has been cloned from freshwater carp, Catla catla. The partially cloned hepcidin consists of 200 bp nucleotide sequence encoding 66 amino acids. Nucleotide sequence showed 97% and 91% similarity with Labeo rohita and Cyprinus carpio, respectively. Expression profile revealed significant up-regulation (P ≤ 0.0001) in liver as compared to other tissues in different conditions. In Aeromonas hydrophila challenged C. catla, liver showed higher expression level of hepcidin at 72 h as compared to other tissues. In skin, hepcidin expression showed significant upraise during 24 h in Streptococcus uberis infection. In Argulus sp. infected fishes, up-regulation of hepcidin expression was noted in liver, intestine and skin. The inactivated viral antigen-stimulated fishes, a substantial rise in liver was observed implying hepcidin as an important molecule in combating the pathogenic infections in freshwater carp, C. catla. Fishes stimulated with pathogen-associated molecular patterns (PAMPs) triggered the increased expression of hepcidin mRNA in liver, kidney and skin. This study indicates the presence of hepcidin as antimicrobial peptide in neutralizing the pathogenic infection in fishes.

Cloning, characterization and tissue-specific expression of the antimicrobial peptide hepcidin from caspian trout (Salmo caspius) and the antibacterial activity of the synthetic peptide

Antimicrobial peptides have a wide range of antimicrobial activity and widely occur in different organisms including mollusks, crustaceans and vertebrates. Hepcidins are a group of cysteine-rich antimicrobial peptides that are active against a variety of pathogens including gram-positive and gram-negative bacteria, as well as viruses. In this study, the hepcidin gene of Caspian trout (CtHep) was identified and characterized. Our results showed that CtHep cDNA has a 267-bp Open Reading Frame (ORF), which is translated to 88 amino acids. The CtHep was classified in the HAMP1 class of hepcidins. Comparison of DNA and cDNA sequences showed that CtHep has 3 exons and 2 introns. The signal, prodomain and mature part of CtHep have 24, 39 and 25 amino acids, respectively. The mature peptide has a molecular weight of 2881.43 Da and a theoretical isoelectric point of 8.53. The expression of CtHep mRNA was detected in different tissues of healthy and infected fish. CtHep expression in the liver, head kidney, spleen and skin was significantly enhanced after bacterial challenge. Expression of CtHep in different embryonic development stages was also substantial. Antibacterial activity of synthetic CtHep peptides was investigated against a number of Gram-positive and Gram-negative bacteria. CtHep inhibited some pathogenic bacteria such as Streptococcus iniae and Aeromonas hydrophila. In the in vivo experiment, CtHep upregulated the cytokines IL-6 and TNF-α in both kidney and spleen tissues after 24 h of the peptide injection. In conclusion, our study showed that CtHep plays an important role in the immune system of Caspian trout and also in the embryonic stages. Moreover, CtHep peptide has a potential to be used as an antimicrobial therapeutic agent as well as an immunostimulant in aquaculture.

Cardiomyocyte hepcidin: From intracellular iron homeostasis to physiological function

Cellular iron is required for the utilization of oxygen in the cell. Iron in iron-sulfur and heme groups is required for electron transfer and oxygen activation in oxidative phosphorylation, while labile free iron is required for oxygen activation by dioxygenases, and as a catalyst for redox signaling. At the same time, this reactivity with oxygen underpins the production of cell-damaging free radicals in the presence of excess iron. Because the cardiac cell is a major site of oxygen flux, it requires tight control of intracellular iron levels. Until recently, such control was thought to be mediated predominantly by the action of iron regulatory proteins. However, new evidence reveals that cardiomyocyte hepcidin is indispensable for the control of intracellular iron levels, normal metabolism and heart function. This new evidence highlights the need for better understanding of the regulation of cardiomyocyte hepcidin in health and disease.

Mudskipper (Boleophthalmus pectinirostris) Hepcidin-1 and Hepcidin-2 Present Different Gene Expression Profile and Antibacterial Activity and Possess Distinct Protective Effect against Edwardsiella tarda Infection

Hepcidins are small cysteine-rich antimicrobial peptides that play an important role in fish immunity against pathogens. Most fish species have two or more hepcidin homologs that have distinct functions. This study investigated the immune functions of mudskipper (Boleophthalmus pectinirostris) hepcidin-1 (BpHep-1) and hepcidin-2 (BpHep-2) in vitro and in vivo. Upon infection with Edwardsiella tarda, the expression of BpHep-1 and BpHep-2 mRNA in immune tissues was significantly upregulated, but the expression profiles were different. Chemically synthesized BpHep-1 and BpHep-2 mature peptides exhibited selective antibacterial activity against various bacterial species, and BpHep-2 exhibited a stronger antibacterial activity and broader spectrum than BpHep-1. BpHep-1 and BpHep-2 both inhibited the growth of E. tarda in vitro, with the latter being more effective than the former. In addition, both peptides induced hydrolysis of purified bacterial genomic DNA (gDNA) or gDNA in live bacteria. In vivo, an intraperitoneal injection of 1.0 μg/g BpHep-2 significantly improved the survival rate of mudskippers against E. tarda infection compared with 0.1 μg/g BpHep-2 or 0.1 and 1.0 μg/g BpHep-1. Similarly, only BpHep-2 treatment effectively reduced the tissue bacterial load in E. tarda-infected mudskippers. Furthermore, treatment with 1.0 or 10.0 μg/ml BpHep-2 promoted the phagocytic and bactericidal activities of mudskipper monocytes/macrophages (MO/MФ). However, only the highest dose (10.0 μg/ml) of BpHep-1 enhanced phagocytosis, and BpHep-1 exerted no obvious effects on bactericidal activity. In conclusion, BpHep-2 is a stronger bactericide than BpHep-1 in mudskippers, and acts not only by directly killing bacteria but also through an immunomodulatory function on MO/MФ.

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 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.

Molecular Characterisation of a Novel Isoform of Hepatic Antimicrobial Peptide, Hepcidin (Le-Hepc), from Leiognathus equulus and Analysis of Its Functional Properties In Silico

Hepcidin represents a family of cysteine-rich antimicrobial peptides that are mainly expressed in the liver of living organisms. In this study, we have identified and characterised a novel isoform of hepcidin from the common pony fish, Leiognathus equulus (Le-Hepc). A 261-bp fragment cDNA coding for 86 amino acids was obtained. Homologous analysis showed that Le-Hepc belongs to the hepcidin super family and shares sequence identity with other known fish pre-propeptide hepcidin sequences. The ORF encodes for a 24-amino acid (aa) signal peptide coupled to a 36-aa prodomain followed by a 26-aa mature peptide. The mature peptide region has a calculated molecular weight of 2.73 kDa, a net positive charge of +2 and a theoretical pI of 8.23. Phylogenetic analysis of Le-Hepc showed a strong relationship with other fish hepcidin sequences and clustered into HAMP2 group hepcidins. Secondary structural analysis indicated that Le-Hepc mature peptide contains two antiparallel β-sheets strengthened by four disulphide bonds formed by eight conserved cysteine residues. The physicochemical properties of the peptide and its structural parameters are in agreement with characteristic features of an antimicrobial peptide. This is the first report of an antimicrobial peptide from the common pony fish, L. equulus.

Zebrafish and Streptococcal Infections

Streptococcal bacteria are a versatile group of gram-positive bacteria capable of infecting several host organisms, including humans and fish. Streptococcal species are common colonizers of the human respiratory and gastrointestinal tract, but they also cause some of the most common life-threatening, invasive infections in humans and aquaculture. With its unique characteristics and efficient tools for genetic and imaging applications, the zebrafish (Danio rerio) has emerged as a powerful vertebrate model for infectious diseases. Several zebrafish models introduced so far have shown that zebrafish are suitable models for both zoonotic and human-specific infections. Recently, several zebrafish models mimicking human streptococcal infections have also been developed. These models show great potential in providing novel information about the pathogenic mechanisms and host responses associated with human streptococcal infections. Here, we review the zebrafish infection models for the most relevant streptococcal species: the human-specific Streptococcus pneumoniae and Streptococcus pyogenes, and the zoonotic Streptococcus iniae and Streptococcus agalactiae. The recent success and the future potential of these models for the study of host-pathogen interactions in streptococcal infections are also discussed.

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.