Hepcidin cDNA evolution in vertebrates

Hepcidin from Onychostoma macrolepis: Response to Aeromonas hydrophila infection by down-regulating expression of inflammatory factor genes and regulating iron homeostasis potentially

Hepcidin, as an antimicrobial peptide, is associated with innate immunity and is considered a potential antibiotic substitute. In the present study, the hepcidin gene from the cavefish - Onychostoma macrolepis was identified and analyzed. The recombinant hepcidin protein (rOmhepc) was obtained by prokaryotic expression, evaluating the inhibitory effect of 5 pathogenic bacteria in vitro. Sixty O. macrolepis injected with 100 μL A. hydrophila (1.5 × 108 CFU/mL) were randomly divided into the therapeutic group and infection group, and therapeutic group was injected with 100 μL rOmhepc (100 μg/mL) at 6 and 18 h. The survival rates of O. macrolepis and bacterial load in liver were measured at 24 h. The liver tissues were collected at 0, 6, 12, and 24 h after A. hydrophila injection for investigating expression levels of immune-related, inflammatory factor genes and FPN1 gene. The results demonstrated that the hepcidin CDS contained 279 bp and encoded 93 aa. Hepcidin protein has a hydrophobic surface formed by multiple hydrophobic residues (CCGCCYC), and the theoretical pI was 7.53. Omhepc gene was expressed at varying levels in tested tissues, with the liver showing the highest expression, followed by the spleen. The expression of hepcidin gene following A. hydrophila infection was up-regulated and then down-regulated in liver, and the highest expression level was found at 12 h with a 10.93-fold. The rOmhepc remarkably inhibited the growth of A. hydrophila, Staphylococcus aureus, and Streptococcus agalactiae, with inhibition rates reaching 69.67 %, 42.97 %, and 65.74 % at 100 μg/mL. The mortality rates of O. macrolepis and bacterial load in liver were significantly decreased in the therapeutic group than that of infection group (p < 0.05). After the rOmhepc therapeutic, interleukin-1β (IL-1β) and interleukin-6 (IL-6) were significantly down-regulated with 14.4-fold and 106.07-fold at 24 h. Furthermore, the expression of immune-related genes (C3, TNF-α, IFN-γ) and Ferroportin gene (FPN1) significantly decreased (p < 0.05). The integrated analyses indicated that the rOmhepc could significantly inhibit the growth of A. hydrophila both in vitro and in vivo, attenuating the over-expression of inflammatory factor, FPN1 and immune-related genes.

Massive gene expansion of hepcidin, a host defense peptide, in gilthead seabream (Sparus aurata)

Host defense peptides (HDP) are among the most ancient immune molecules in animals and clearly reflect an ancestral evolutionary history involving pathogen-host interactions. Hepcidins are a very widespread family of HDPs among vertebrates and are especially diverse in teleosts. We have investigated the identification of new hepcidins in gilthead seabream (Sparus aurata), a fish farmed in the Mediterranean. Targeted gene predictions supported with expressed sequence tags (ESTs) derived from Hidden Markov Models were used to find the hamp genes in the seabream genome. The results revealed a massively clustered hamp duplication on chromosome 17. In fact, the seabream genome contains the largest number of hepcidin copies described in any vertebrate. The evolutionary history of hepcidins in seabream, and vertebrates generally, clearly indicates high adaptation in teleosts and novel subgroups within hepcidin type II. Furthermore, basal hepcidin gene expression analysis indicates specific-tissue expression profiles, while the presence and distribution of transcription factor binding sites (TFBS) in hamp promoters as well as their transcription profile upon bacterial challenge indicates different immune roles depending on the type of hepcidin and tissue. This massive duplication of HDP genes in a bony fish could point to a far more specific and adaptive innate immune system than assumed in the classic concept of immunity in mammals. Hence, a new world of knowledge regarding hepcidins in fish and vertebrates is being initiated.

Hepcidin Gene Co-Option Balancing Paternal Immune Protection and Male Pregnancy

Viviparity has originated independently more than 150 times in vertebrates, while the male pregnancy only emerged in Syngnathidae fishes, such as seahorses. The typical male pregnancy seahorses have closed sophisticated brood pouch that act as both uterus and placenta, representing an excellent model system for studying the evolutionary process of paternal immune protection. Phylogenetic analysis indicated that the hampII gene family has multiple tandem duplicated genes and shows independent lineage-specific expansion in seahorses, and they had the highest ratio of nonsynonymous substitutions to synonymous substitutions (dN/dS) in the seahorse phylogenetic branch. The expression levels of hampIIs in the brood pouch placenta were significantly higher during pregnancy than non-pregnancy. Both LPS stimulation test in vivo and cytotoxicity test in vitro proved the immunological protection function of hampIIs against pathogen infection in seahorse. Besides, seahorse hampII peptides exhibit weaker antibacterial function, but stronger agglutination and free endotoxin inhibition. We assumed that the modified immunological function seemed to be a trade-off between the resistance to microbial attack and offspring protection. In brief, this study suggests that the rapid co-option of hampIIs contributes to the evolutionary adaption to paternal immune care during male pregnancy.

Antimicrobial Peptides and Copper(II) Ions: Novel Therapeutic Opportunities

The emergence of new pathogens and multidrug resistant bacteria is an important public health issue that requires the development of novel classes of antibiotics. Antimicrobial peptides (AMPs) are a promising platform with great potential for the identification of new lead compounds that can combat the aforementioned pathogens due to their broad-spectrum antimicrobial activity and relatively low rate of resistance emergence. AMPs of multicellular organisms made their debut four decades ago thanks to ingenious researchers who asked simple questions about the resistance to bacterial infections of insects. Questions such as "Do fruit flies ever get sick?", combined with pioneering studies, have led to an understanding of AMPs as universal weapons of the immune system. This review focuses on a subclass of AMPs that feature a metal binding motif known as the amino terminal copper and nickel (ATCUN) motif. One of the metal-based strategies of hosts facing a pathogen, it includes wielding the inherent toxicity of copper and deliberately trafficking this metal ion into sites of infection. The sudden increase in the concentration of copper ions in the presence of ATCUN-containing AMPs (ATCUN-AMPs) likely results in a synergistic interaction. Herein, we examine common structural features in ATCUN-AMPs that exist across species, and we highlight unique features that deserve additional attention. We also present the current state of knowledge about the molecular mechanisms behind their antimicrobial activity and the methods available to study this promising class of AMPs.

Hepcidin secretion was not directly proportional to intracellular iron-loading in recombinant-TfR1 HepG2 cells: short communication

Hepcidin is the master regulator of systemic iron homeostasis and its dysregulation is observed in several chronic liver diseases. Unlike the extracellular iron-sensing mechanisms, the intracellular iron-sensing mechanisms in the hepatocytes that lead to hepcidin induction and secretion are incompletely understood. Here, we aimed to understand the direct role of intracellular iron-loading on hepcidin mRNA and peptide secretion using our previously characterised recombinant HepG2 cells that over-express the cell-surface iron-importer protein transferrin receptor-1. Gene expression of hepcidin (HAMP) was determined by real-time PCR. Intracellular iron levels and secreted hepcidin peptide levels were measured by ferrozine assay and immunoassay, respectively. These measurements were compared in the recombinant and wild-type HepG2 cells under basal conditions at 30 min, 2 h, 4 h and 24 h. Data showed that in the recombinant cells, intracellular iron content was higher than wild-type cells at 30 min (3.1-fold, p < 0.01), 2 h (4.6-fold, p < 0.01), 4 h (4.6-fold, p < 0.01) and 24 h (1.9-fold, p < 0.01). Hepcidin (HAMP) mRNA expression was higher than wild-type cells at 30 min (5.9-fold; p = 0.05) and 24 h (6.1-fold; p < 0.03), but at 4 h, the expression was lower than that in wild-type cells (p < 0.05). However, hepcidin secretion levels in the recombinant cells were similar to those in wild-type cells at all time-points, except at 4 h, when the level was lower than wild-type cells (p < 0.01). High intracellular iron in recombinant HepG2 cells did not proportionally increase hepcidin peptide secretion. This suggests a limited role of elevated intracellular iron in hepcidin secretion.

Human Antimicrobial Peptide Hepcidin 25-Induced Apoptosis in Candida albicans

Hepcidin 25 (hep 25) is a cysteine-rich 25-amino acid antimicrobial peptide containing the amino-terminal Cu(II)/Ni(II)-binding (ATCUN) motif. Upon metal binding, the ATCUN motif is known to be involved in the generation of reactive oxygen species (ROS), especially hydrogen peroxide and hydroxyl radicals, which act against different bacterial species. However, the antifungal activity and its correlation to the Cu(II)-ATCUN complex of Hep 25 are still poorly understood. Here, we found that ROS accumulation plays an important role in the fungicidal activity of hep 25 against Candida albicans. In addition, Annexin V-FITC staining and TUNEL assay results provide clues about the apoptosis induced by hep 25. Moreover, hep 25 also increases the generation of ROS, possibly because of copper binding to the ATCUN motif, which is relevant to its activity against C. albicans. Finally, the C. albicans killing action of hep 25 is an energy- and temperature-dependent process that does not involve targeting the membrane. Taken together, our results provide new insights into the mechanisms of hep 25 against C. albicans cells and the potential use of hep 25 and its derivatives as novel antifungal agents.

Transcriptome analysis identifies immune-related genes and antimicrobial peptides in Siamese fighting fish (Betta splendens)

Siamese fighting fish (Betta splendens) is one of the most widely cultivated ornamental fish in global trade. However, transcriptomic data, which can reveal valuable genetic data for disease control and prevention, are extremely limited for this species. In this study, whole-body transcriptome sequencing of juvenile betta fish generated 4.457 GB of clean data and a total of 71,775 unigenes using the Illumina HiSeq4000 platform. These unigenes were functionally classified using 7 functional databases, yielding 45,316 NR (63.14%), 47,287 NT (65.88%), 39,105 Swiss-Prot (54.48%), 16,492 COG (22.98%), 37,694 KEGG (52.52%), 4,506 GO (6.28%), and 35,374 Interpro (49.28%) annotated unigenes. Furthermore, we also detected 13,834 SSRs distributed on 10,636 unigenes and 49,589 predicted CDSs. Based on KEGG analysis, five innate immune pathways (997 unigenes) were reported, including the NOD-like receptor signaling pathway, complement and coagulation cascades, toll-like receptor signaling pathway, RIG-I-like receptor signaling pathway and cytosolic DNA-sensing pathway. Moreover, four antimicrobial peptide (AMP) families (hepcidin, piscidin, LEAP-2, and defensins) from the betta fish transcriptome were also identified. Additionally, cDNA and genomic DNA of two β-defensins was successfully isolated from four betta fish species. RT-PCR analysis showed that BsBD1 transcripts were most abundant in the muscle and kidney and BsBD2 transcripts were most abundant in the gill. The genomic organization showed that the BD1 and BD2 genes consisted of three exons and two introns according to the GT-AG rule. Most importantly, this is the first report of the betta fish whole-body transcriptome obtained by high-throughput sequencing. Our transcriptomic data and the discovery of betta fish AMPs should promote a better understanding of molecular immunology for disease prevention for further ornamental fish aquaculture.