Electrotransfer of the epinecidin-1 gene into skeletal muscle enhances the antibacterial and immunomodulatory functions of a marine fish, grouper (Epinephelus coioides)

The effects of four paralogous piscidin antimicrobial peptides on the chemotaxis, macrophage respiratory burst, phagocytosis and expression of immune-related genes in orange-spotted grouper (Epinephelus coicodes)

Antimicrobial peptides (AMPs) are an essential part of the vertebrate innate immune system. Piscidins are a family of AMPs specific in fish. In our previous investigation, we identified four paralogous genes of piscidins in the orange-spotted grouper (Epinephelus coicodes), which exhibited distinct activities against bacteria, fungi, and parasitic ciliated protozoa. Piscidins demonstrated their capability to modulate the expression of diverse immune-related genes; however, their precise immunoregulatory functions remain largely unexplored. In this study, we examined the immunomodulatory properties of putative mature peptides derived from four E. coicodes piscidins (ecPis1S, ecPis2S, ecPis3S, and ecPis4S) in head kidney leukocytes (HKLs) or monocytes/macrophages (MO/MΦ)-like cells isolated from E. coicodes. Our data demonstrate that E. coicodes piscidins exhibit immunomodulatory activities supported by multiple lines of evidence. Firstly, all four piscidins displayed chemotactic activities towards HKLs, with the most potent chemotactic activity observed in ecPis2S. Secondly, stimulation with E. coicodes piscidins enhanced respiratory burst and phagocytic activity in MO/MФ-like cells, with ecPis3S showing the highest efficacy in increasing phagocytosis of MO/MΦ-like cells. Thirdly, mRNA expression levels of chemokine receptors, Toll-like receptors, T cell receptors, and proinflammatory cytokines were modulated to varying extents by the four piscidins in E. coicodes HKLs. Overall, our findings indicate that the immunological activities of these four paralogous piscidins from E. coicodes are exhibited in a paralog-specific and concentration-dependent manner, highlighting their distinct and versatile immunomodulatory properties. This study makes a significant contribution to the field of fish AMPs immunology by elucidating the novel mechanisms through which members of the piscidin family exert their immunomodulatory effects. Moreover, it provides valuable insights for further exploration of fish immunomodulating agents.

NKL-24: A novel antimicrobial peptide derived from zebrafish NK-lysin that inhibits bacterial growth and enhances resistance against Vibrio parahaemolyticus infection in Yesso scallop, Patinopecten yessoensis

The extensive use of antibiotics in aquaculture has resulted in the prevalence of antibiotic-resistant bacteria and, consequently, new antibacterial strategies or drugs with clear modes of action are urgently needed. Antimicrobial peptides (AMPs) are currently widely considered as alternatives to antibiotics in the treatment of infections in aquatic animals. In this study, we aimed to evaluate the effects of NKL-24, a truncated peptide derived from zebrafish NK-lysin, against Yesso scallop (Patinopecten yessoensis) pathogen, Vibrio parahaemolyticus. The results showed that NKL-24 had a potent antibacterial effect against V. parahaemolyticus via a membrane active cell-killing mechanism. The in vitro study showed that sub-lethal levels of NKL-24 obviously reduced bacterial swimming ability and downregulated the transcription of the selected genes associated with V. parahaemolyticus virulence. Studies on NKL-24 biosafety in hemocytes and in Yesso scallop have shown no adverse effects from this peptide. Bacteria challenge test results demonstrated that NKL-24 significantly decreased the mortality and inhibited bacterial growth in the scallop infected with V. parahaemolyticus, while further in vivo examination revealed that NKL-24 could enhance non-specific immune parameters. Moreover, NKL-24 was capable of modulating a series of V. parahaemolyticus-responsive genes in the scallop. These results suggest the protective action of NKL-24 against V. parahaemolyticus and the potential of this peptide as a promising candidate for aquaculture applications.

Epinecidin-1, an Antimicrobial Peptide Derived From Grouper (Epinephelus coioides): Pharmacological Activities and Applications

Epinecidin-1 is an antimicrobial peptide derived from the orange-spotted grouper (Epinephelus coioides). The mature epinecidin-1 peptide is predicted to have an amphipathic α-helical structure and a non-helical hydrophilic domain at the C-terminal RRRH. The majority of work studying the potential pharmacological activities of epinecidin-1, utilize synthesized epinecidin-1 (Epi-1), which is made up of 21 amino acids, from the amino acid sequence of 22-42 residues of Epi-1-GFIFHIIKGLFHAGKMIHGLV. The synthetized Epi-1 peptide has been demonstrated to possess diverse pharmacological activities, including antimicrobial, immunomodulatory, anticancer, and wound healing properties. It has also been utilized in different clinical and agricultural fields, including topical applications in wound healing therapy as well as the enhancement of fish immunity in aquaculture. Hence, the present work aims to consolidate the current knowledge and findings on the characteristics and pharmacological properties of epinecidin-1 and its potential applications.

The putative mature peptide of piscidin-1 modulates global transcriptional profile and proliferation of splenic lymphocytes in orange-spotted grouper (Epinephelus coioides)

Piscidins are important components in protecting microbial infections in teleost. The present study purified and identified a truncated peptide, whose sequence was very close to that of putative mature peptide of epinecidin-1 (piscidin-1) in orange-spotted grouper (Epinephelus coioides), Epi-1 (also named as short form of ecPis-1, ecPis-1S). The immunomodulatory effects of ecPis-1S on splenic lymphocytes of orange-spotted grouper were explored in vitro. The transcriptome study was carried out by De novo transcriptome sequencing (RNA-Seq) in splenic lymphocytes of orange-spotted grouper. Regarding the profiles of gene expressions, 2994 genes were up-regulated and 2679 genes were down-regulated in the splenic lymphocytes stimulated by ecPis-1S. In the case of differential expression genes, 330 genes were involved in immune related pathways. Among them, 34 genes were involved in T cell receptor signaling pathway, 31 genes in natural killer cell mediated cytotoxicity and 23 genes in leukocyte transendothelial migration, respectively. Immune-related genes selected for qRT-PCR verification, such as interleukin-1β (il-1b), tumor necrosis factor α (tnfa), T cell antigen receptor (tcr), major histocompatibility complex class I (mhc I), and mhc II were significantly up-regulated by ecPis-1S (p < 0.05). ecPis-1S could significantly enhance the proliferation of splenic lymphocytes of orange-spotted grouper in vitro (p < 0.05). In addition, the result of qRT-PCR revealed that ecPis-1S also significantly up-regulated cell cycle-related genes, including cyclin A (cyca), cyclin-dependent kinase 2 (cdk2), cdk4, cell division cycle protein 6 (cdc6), and transforming growth factor β (tgfb) (p < 0.05), which suggested that ecPis-1S promoted the proliferation of lymphocytes by activating cell division cycle. In conclusion, the results indicated that the mature peptide of piscidin-1 in orange-spotted grouper could act as immune modulator and play an important role in regulation of the immune response in fish.

Nile tilapia fry fed on antimicrobial peptide Epinecidin-1-expressing Artemia cyst exhibit enhanced immunity against acute bacterial infection

Artemia are often used as a live feed for fry in aquaculture. We have previously demonstrated that supplementing adult zebrafish feed with Artemia, which express an Epinephelus coioides-derived antimicrobial peptide, Epinecidin-1 (Epi-1), protects against bacterial infection. Thus, Artemia may serve as a bioreactor for producing biofunctional molecules. However, the application of Epi-1 transgenic Artemia in larval aquaculture of commercial fish species has not been investigated. Here we used a Tol2-transposon system to generate stable Epi-1 expressing Artemia. Nile tilapia (Oreochromis niloticus) fry were then fed with decapsulated transgenic cysts and acutely challenged with Gram-positive Streptococcus iniae or Gram-negative Vibrio vulnificus (204). Survival analysis revealed that tilapia fry fed with Epi-1 transgenic cysts were resistant to acute bacterial infection. Immune-related gene expression profiling showed that S. iniae and V. vulnificus inoculations produced distinct immunomodulatory effects in the tilapia fry. Upon S. iniae infection, tilapia fry fed on control diet exhibited an immune response dominated by Tlr-7/MyD88, wherein Tnf-α, Il-8 and Cxcl-10 expression were all induced; conversely, the tilapia fry fed with Epi-1 transgenic cysts showed a Tlr-2/Tlr-5-dominant immune response, marked by the induction of Il-1β, Il-8 and Il-12 expression. However, after V. vulnificus (204) infection control fry exhibited a Tlr-2/MyD88/Traf-6-dominant response with activation of Tnf-α and Il-8 expression; meanwhile tilapia fry fed on Epi-1 transgenic cyst showed a dominant Tlr-2/Tlr-5-mediated immune response, including induction of Il-1β, Il-8, Il-12, and Cxcl-10 expression. These findings suggest that feeding larval fish fry with Epi-1 transgenic Artemia cysts confers enhanced immunity toward bacterial challenge. Epi-1 transgenic cysts should therefore be considered as a potential functional feed for larval aquaculture.

Electrotransfer of single-chain LH gene into skeletal muscle induces early ovarian development of orange-spotted grouper (Epinephelus coioides)

Luteinizing hormone (LH) plays important roles in regulating steroidogenesis and reproductive development of vertebrates. In the present paper, we study function of LH on early ovarian development of orange-spotted grouper by electrotransfer of single-chain LH gene into skeletal muscle for the first time. Short-term and long-term injection experiments were performed in this work, respectively. For short-term injection experiments, fish received one electrotransfer with the plasmid in skeletal muscle, then blood and muscle around the injected area were sampled 1, 3, 5 and 7 days after the injection, mRNA expression levels of LH gene relative to 18S were determined by quantitative real-time PCR (RT-PCR) assays and serum 17β-estradiol (E2) levels were quantified by ELISA method. The results showed that levels of mRNA of LH gene in muscle and serum E2 level increased from 1 day to 7 days after the injection. For long-term injection experiments, fish received electrotransfer with the plasmid 4 times at weekly intervals in skeletal muscle. 48 h after the last injection, blood, gonad and hypothalamus samples were collected. Transcripts of cyp19a1a, cyp19a1b and gnrh1 genes and levels of serum E2 were separately analyzed by RT-PCR assays and ELISA method, and ovarian tissues were made of paraffin sections and stained by hematoxylin-eosin by method and observed by optical microscopy. The results suggested that long-term injection of LH gene into muscle upregulated transcripts of cyp19a1a and cyp19a1b and downregulated that of gnrh1, and stimulated E2 production and early-stage oogenesis. Moreover, statistical data showed that 9 of 10 ovaries of injected fish with LH gene began to develop after the long-term experiments. These data suggest that single-chain LH gene introduced into skeletal muscle via electrotransfer can be expressed and induce the early ovarian development of juvenile orange-spotted grouper. This work contributes to solve reproductive dysfunctions associated with low hormone levels of teleosts, further it may represent the demonstration at regulation of LH on early ovarian development of orange-spotted grouper to a certain extent.

Electrotransfer of the tilapia piscidin 3 and tilapia piscidin 4 genes into skeletal muscle enhances the antibacterial and immunomodulatory functions of Oreochromis niloticus

Tilapia piscidin 3 (TP3) and tilapia piscidin 4 (TP4) are antimicrobial peptides recently isolated from Oreochromis niloticus. We previously showed that synthetic TP3 and TP4 possessed antimicrobial activities. Here, we analyzed the bactericidal abilities and immunomodulatory properties of these AMPs following the electroporation of pCMV-GFP-TP3 or pCMV-GFP-TP4 plasmid into tilapia (O. niloticus) muscle and subsequent infection with Vibrio vulnificus or Streptococcus agalactiae. Prior overexpression of TP3 or TP4 in tilapia muscle tissues efficiently reduced bacterial numbers at 24 and 48 h after V. vulnificus infection and reduced bacterial numbers at 24 h after S. agalactiae infection compared to numbers in controls expressing pCMV-GFP (EGFP). Electroporation of pCMV-EGFP-TP3 (TP3) or pCMV-EGFP-TP4 (TP4) significantly increased expression of several immune-related genes in muscle (IL-1β (12 h, TP3), IL-8 (12 h, TP3), TGFβ (3 h, TP4), and IκB (48 h, TP3, TP4)) and decreased the expression of TLR5 (12 h and 24 h, TP3) after V. vulnificus infection. Following S. agalactiae infection, expression of the following genes was significantly decreased in muscle: IL-1β (12 h, TP3), IL-8 (12 h, TP3, TP4), TLR5 (3 h-24 h, TP3, TP4), TGFβ (3 h, TP4; 24 h, TP3, TP4), and IκB (3 h, TP3). These data suggest that TP3 and TP4 exert antimicrobial effects after overexpression in the O. niloticus muscle, and also play important roles in the regulation of immune-related gene expression.

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.

Zebrafish fed on recombinant Artemia expressing epinecidin-1 exhibit increased survival and altered expression of immunomodulatory genes upon Vibrio vulnificus infection

Artemia has been used extensively in aquaculture as fodder for larval fish, shrimp, and shellfish. Epinecidin-1, an antimicrobial peptide, was isolated from grouper (Epinephelus coioides) in 2005. Epinecidin-1 has been previously reported to possess antimicrobial activity against several Gram-positive and Gram-negative bacterial species, including Staphylococcus coagulase, Pseudomonas aeruginosa, Streptococcus pyogenes, and Vibrio vulnificus. In this study, we used electroporation to introduce plasmid DNA encoding a green fluorescent protein (EGFP)-epinecidin-1 fusion protein under the control of the cytomegalovirus (CMV) promoter into decapsulated Artemia cysts. Optimization of various properties (including cyst weight (0.2 g), plasmid concentration (50 μg/100 μl), and pulse voltage (150 V), length (10 ms), and number (2)) resulted in a hatching rate of 41.15%, a transfection efficiency of 49.81%, and a fluorescence intensity (A.U.) of 47.46. The expression of EGFP-epinecidin-1 was first detected by quantitative RT-PCR at 120 h post-electroporation, and protein was identified by Western blot at the same time. Furthermore, the EGFP-epinecidin-1 protein inhibited V. vulnificus (204) growth, as demonstrated by zone of inhibition studies. Zebrafish fed on transgenic Artemia expressing CMV-gfp-epi combined with commercial fodder were more resistant to infection by V. vulnificus (204): survival rate was enhanced by over 70% at 7, 14, and 21 days post-infection, and bacterial numbers in the liver and intestine were reduced. In addition, feeding of transgenic Artemia to zebrafish affected the immunomodulatory response to V. vulnificus (204) infection; expression of immune-responsive genes, including hepcidin and defbl2, was altered, as shown by qPCR. These findings suggest that feeding transgenic Artemia expressing CMV-gfp-epi to larval fish has antimicrobial effects, without the drawbacks of introducing drug residues or inducing bacterial drug resistance.

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.