β-Defensin: An adroit saviour in teleosts

Identification of a Novel β-Defensin Gene in Gilthead Seabream (Sparus aurata)

The excessive use of antibiotics in aquaculture favors the natural selection of multidrug-resistant bacteria, and antimicrobial peptides (AMPs) could be a promising alternative to this problem. The most studied AMPs in teleost fish are piscidins, hepcidins, and β-defensins. In this work, we have found a new gene (defb2) encoding a type 2 β-defensin in the genome of gilthead seabream, a species chosen for its economic interest in aquaculture. Its open reading frame (192 bp) encodes a protein (71 amino acids) that undergoes proteolytic cleavage to obtain the functional mature peptide (42 amino acids). The genetic structure in three exons and two introns and the six characteristic cysteines are conserved as the main signature of this protein family. In the evolutionary analysis, synteny shows a preservation of chromosomal localization and the phylogenetic tree constructed exposes the differences between both types of β-defensin as well as the similarities between seabream and European seabass. In relation to its basal expression, β-defensin 2 is mostly expressed in the intestine, thymus, skin, and gonads of the gilthead seabream (Sparus aurata). In head kidney leucoytes (HKLs), the expression was very low and did not change significantly when stimulated with various immunocompetent agents. However, the expression was significantly down-regulated in the liver, head-kidney, and blood 4 h post-injection with the fish pathogen Vibrio harveyi. When infected with nodavirus, the expression was downregulated in brain at 7 days post-infection. These results denote a possible complementarity between the expression patterns of β-defensins and hepcidins. Further studies are needed to analyze gene duplications and expression patterns of β-defensins and describe their mechanism of action in seabream and other teleost fish.

The antibacterial defence role of β-defensin in the seahorse testis

Seahorses represent the only known group of animals with male pregnancy. Seahorses have small testis that produce a limited quantity of sperm. To date, the response of this immune-privileged organ to pathogenic infections has not been reported. β-defensin (BD) is an important innate immune defence factor against pathogens in vertebrate testis. To elucidate its immunoprotection in seahorse testis, we identified the Hippocampus erectus β-defensin (HeBD) sequence in its genome via phylogenetic tree and protein-sequence structure analysis. Gene-expression analysis showed that HeBD was highly expressed in the seahorse testis and was significantly upregulated after bacterial infection, indicating that HeBD expression was related to testicular immune responses. Furthermore, antibacterial activity testing demonstrated that the mature HeBD peptide exhibited broad-spectrum aggregation activity but only moderate antibacterial activity. We found that the mature HeBD mature significantly neutralised bacterial endotoxin activity. In conclusion, our results imply that HeBD serves an immunoprotective role in seahorse testis.

Rational design of novel peptide-based vaccine against the emerging OZ virus

Oz virus (OZV) belongs to the Orthomyxoviridae family which includes viruses with a negative-sense, single-stranded, and segmented RNA genome. OZV is a zoonotic pathogen, particularly since the virus can cause deadly illness when injected intracerebrally into nursing mice. OZV is an emerging pathogen with the potential to spark a pandemic as there is no preventive and licensed treatment against this virus. The goal of this study was to develop a novel multi-epitope vaccination against OZV proteins utilizing immunoinformatics and immunological simulation analysis. This work evaluated immunological epitopes (B cells, MHC-I, and MHC-II) to identify highly antigenic OZV target proteins. Shortlisted epitopes were joined together by using appropriate linkers and adjuvants to design multi-epitope vaccine constructs (MEVC). The vaccine models were designed, improved, validated, and the globular regions and post-translational modifications (PTMs) were also evaluated in the vaccine's structure. Molecular docking analysis with the Toll-like receptor (TLR4) showed strong interactions and appropriate binding energies. Molecular dynamics (MD) simulation confirmed stable interactions between the vaccines and TLR4. Bioinformatics tools helped optimize codons, resulting in successful cloning into appropriate host vectors. This study showed that the developed vaccines are stable and non-allergenic in the human body and successfully stimulated immunological responses against OZV. Finally, a mechanism of action for the designed vaccine construct was also proposed. Further experimental validations of the designed vaccine construct will pave the way to create a potentially effective vaccine against this emerging pathogen.

A Novel Beta-Defensin Isoform from Malabar Trevally, Carangoides malabaricus (Bloch & Schneider, 1801), an Arsenal Against Fish Bacterial Pathogens: Molecular Characterization, Recombinant Production, and Mechanism of Action

Antimicrobial peptides (AMPs), including beta-defensin from fish, are a crucial class of peptide medicines. The focus of the current study is the molecular and functional attributes of CmDef, a 63-amino acid beta-defensin AMP from Malabar trevally, Carangoides malabaricus. This peptide demonstrated typical characteristics of AMPs, including hydrophobicity, amphipathic nature, and +2.8 net charge. The CmDef was recombinantly expressed and the recombinant peptide, rCmDef displayed a strong antimicrobial activity against bacterial fish pathogens with an MIC of 8 µM for V. proteolyticus and 32 µM for A. hydrophila. The E. tarda and V. harveyi showed an inhibition of 94% and 54%, respectively, at 32 µM concentration. No activity was observed against V. fluvialis and V. alginolyticus. The rCmDef has a multimode of action that exerts an antibacterial effect by membrane depolarization followed by membrane permeabilization and ROS production. rCmDef also exhibited anti-cancer activities in silico without causing hemolysis. The peptide demonstrated stability under various conditions, including different pH levels, temperatures, salts, and metal ions (KCl and CaCl2), and remained stable in the presence of proteases such as trypsin and proteinase K at concentrations up to 0.2 µg/100 µl. The strong antibacterial efficacy and non-cytotoxic nature suggest that rCmDef is a single-edged sword that can contribute significantly to aquaculture disease management.

Antibacterial Efficacy and Mechanisms of Action of a Novel Beta-Defensin from Snakehead Murrel, Channa striata

Beta-defensins, identified from fishes, constitute a crucial category of antimicrobial peptides important in combating bacterial fish pathogens. The present investigation centers on the molecular and functional characterization of CsDef, a 63-amino acid beta-defensin antimicrobial peptide derived from snakehead murrel (Channa striata). The physicochemical attributes of CsDef align with the distinctive characteristics observed in AMPs. CsDef was recombinantly produced, and the recombinant peptide, rCsDef, exhibited notable antibacterial efficacy against bacterial fish pathogens with an MIC of 16 μM for V. proteolyticus. A. hydrophila exhibited 91% inhibition, E. tarda 92%, and V. harveyi 53% at 32 μM of rCsDef. The rCsDef exhibited a multifaceted mechanism of action against bacteria, i.e., through membrane depolarization, membrane permeabilization, and generation of ROS. The rCsDef was non-hemolytic to hRBCs and non-cytotoxic to normal mammalian cell line CHO-K1. However, it exhibited anticancer properties in MCF-7. rCsDef demonstrated notable stability with respect to pH, temperature, salt, metal ions, and proteases. These findings suggest it is a potential candidate molecule for prospective applications in aquaculture.

Decrypting the multi-genome data for chimeric vaccine designing against the antibiotic resistant Yersinia pestis

Yersinia pestis, the causative agent of plague, is a gram-negative bacterium that can be fatal if not treated properly. Three types of plague are currently known: bubonic, septicemic, and pneumonic plague, among which the fatality rate of septicemic and pneumonic plague is very high. Bubonic plague can be treated, but only if antibiotics are used at the initial stage of the infection. But unfortunately, Y. pestis has also shown resistance to certain antibiotics such as kanamycin, minocycline, tetracycline, streptomycin, sulfonamides, spectinomycin, and chloramphenicol. Despite tremendous progress in vaccine development against Y. pestis, there is no proper FDA-approved vaccine available to protect people from its infections. Therefore, effective broad-spectrum vaccine development against Y. pestis is indispensable. In this study, vaccinomics-assisted immunoinformatics techniques were used to find possible vaccine candidates by utilizing the core proteome prepared from 58 complete genomes of Y. pestis. Human non-homologous, pathogen-essential, virulent, and extracellular and membrane proteins are potential vaccine targets. Two antigenic proteins were prioritized for the prediction of lead epitopes by utilizing reverse vaccinology approaches. Four vaccine designs were formulated using the selected B- and T-cell epitopes coupled with appropriate linkers and adjuvant sequences capable of inducing potent immune responses. The HLA allele population coverage of the T-cell epitopes selected for vaccine construction was also analyzed. The V2 constructs were top-ranked and selected for further analysis on the basis of immunological, physicochemical, and immune-receptor docking interactions and scores. Docking and molecular dynamic simulations confirmed the stability of construct V2 interactions with the host immune receptors. Immune simulation analysis anticipated the strong immune profile of the prioritized construct. In silico restriction cloning ensured the feasible cloning ability of the V2 construct in the expression system of E. coli strain K12. It is anticipated that the designed vaccine construct may be safe, effective, and able to elicit strong immune responses against Y. pestis infections and may, therefore, merit investigation using in vitro and in vivo assays.

Identification of antimicrobial peptide genes from transcriptomes in Mandarin fish (Siniperca chuatsi) and their response to infection with Aeromonas hydrophila

Mandarin fish (Siniperca chuatsi) is a valuable freshwater fish species widely cultured in China. Its aquaculture production is challenged by bacterial septicaemia, which is one of the most common bacterial diseases. Antimicrobial peptides (AMPs) play a critical role in the innate immune system of fish, exhibiting defensive and inhibitory effects against a wide range of pathogens. This study aimed to identify the antimicrobial peptide genes in mandarin fish using transcriptomes data obtained from 17 tissue in our laboratory. Through nucleotide sequence alignment and protein structural domain analysis, 15 antimicrobial peptide genes (moronecidin, pleurocidin, lysozyme g, thymosin β12, hepcidin, leap 2, β-defensin, galectin 8, galectin 9, apoB, apoD, apoE, apoF, apoM, and nk-lysin) were identified, of which 9 antimicrobial peptide genes were identified for the first time. In addition, 15 AMPs were subjected to sequence characterization and protein structure analysis. After injection with Aeromonas hydrophila, the number of red blood cells, hemoglobin concentration, and platelet counts in mandarin fish showed a decreasing trend, indicating partial hemolysis. The expression change patterns of 15 AMP genes in the intestine after A. hydrophila infection were examined by using qRT-PCR. The results revealed, marked up-regulation (approximately 116.04) of the hepcidin gene, down-regulation of the piscidin family genes expression. Moreover, most AMP genes were responded in the early stages after A. hydrophila challenge. This study provides fundamental information for investigating the role of the different antimicrobial peptide genes in mandarin fish in defense against A. hydrophila infection.

Quercetin alleviates DEHP exposure-induced pyroptosis and cytokine expression changes in grass carp L8824 cell line by inhibiting ROS/MAPK/NF-κB pathway

Bis(2-ethylhexyl) phthalate (DEHP) is not only a widely used plasticizer but also a common endocrine disruptor that frequently lingers in water, posing a threat to the health of aquatic organisms. Quercetin (Que) is a common flavonol found in the plant kingdom known for its antioxidant, anti-inflammatory, and immunomodulatory effects. However, it is still unclear whether DEHP can cause pyroptosis and affect the expression of cytokines of grass carp L8824 cells and whether Que has antagonistic effect in this process. In our study, grass carp L8824 cells were treated into four groups after 24 h, namely NC group, DEHP group (1000 μM DEHP), Que group (5 μM Que), and DEHP + Que group (1000 μM DEHP + 5 μM Que). Our results indicate a significant increase in the level of ROS in L8824 cells after exposure to DEHP. DEHP upregulated oxidative stress markers (H2O2 and MDA) and downregulated antioxidant markers (CAT, GSH, SOD, and T-AOC). DEHP also upregulated MAPK and NF-κB signal pathway-related proteins and mRNA expressions (p-p38, p-JNK, p-EPK, and p65). As for cell pyroptosis and its related pathways, DEHP upregulated pyroptosis-related protein and mRNA expressions (GSDMD, IL-1β, NLRP3, Caspase-1, LDH, pro-IL-18, IL-18, and ASC). Finally, DEHP can up-regulated cytokines (IL-6 and TNF-α) expression, down-regulated cytokines (IL-2 and IFN-γ) expression, and antimicrobial peptides (β-defensin, LEAP2, and HEPC). The co-treatment of L8824 cells with DEHP and Que inhibited the activation of the ROS/MAPK/NF-κB axis, alleviated pyroptosis, and restored expression of immune-related indicators. Finally, NAC was applied to reverse intervention of oxidative stress. In summary, Que inhibited DEHP-induced pyroptosis and the influence on cytokine and antimicrobial peptide expression in L8824 cells by regulating the ROS/MAPK/NF-κB pathway. Our results demonstrate the threat to fish health from DEHP exposure and confirmed the harm of DEHP to the aquatic ecological environment and the detoxification effect of Que to DEHP, which provides a theoretical basis for environmental toxicology.

Unravelling the Proteomic Profiles of Bovine Colostrum and Mature Milk Derived from the First and Second Lactations

Bovine colostrum (BC) and mature bovine milk are highly nutritious. In addition to being consumed by adults, these dairy products are also used as protein ingredients for infant formula. However, the differences in the nutritional composition of BC and mature milk, especially regarding proteins present in trace amounts, have not been comprehensively studied. Furthermore, the distinct proteomic profiles of mature milk derived from the first lactation (Milk-L1) and the second lactation (Milk-L2) are not fully understood. To address these gaps, this study aims to uncover the subtle differences in protein compositions of BC, Milk-L1, and Milk-L2 by proteomics. Compared with BC, anti-microbial proteins β-defensins and bovine hemoglobin subunit were up-regulated in Milk-L1, while Milk-L2 exhibited higher levels of enteric β-defensin, sterol regulatory element binding transcription factor 1, sydecan-2, and cysteine-rich secretory protein 2. Additionally, immune proteins such as vacuolar protein sorting-associated protein 4B, polymeric immunoglobulin receptor (PIGR), and Ig-like domain-containing protein were found at higher levels in Milk-L1 compared with Milk-L2. The study provides a comprehensive understanding of the distinct proteomic profiles of BC, Milk-L1, and Milk-L2, which contributes to the development of protein ingredients for infant formula.

Effects of diets rich in Agaricus bisporus polysaccharides on the growth, antioxidant, immunity, and resistance to Yersinia ruckeri in channel catfish

To promote the application of Agaricus bisporus polysaccharides (ABPs) in channel catfish (Ictalurus punctatus) culture, we evaluated the effects of ABPs on the growth, immunity, antioxidant, and antibacterial activity of channel catfish. When the amount of ABPs was 250 mg/kg, channel catfish's weight gain and specific growth rates increased significantly while the feed coefficient decreased. We also found that adding ABPs in the feed effectively increased the activities of ACP, MDA, T-SOD, AKP, T-AOC, GSH, and CAT enzymes and immune-related genes such as IL-1β, Hsp70, and IgM in the head kidney of channel catfish. Besides, long-term addition will not cause pathological damage to the head kidney. When the amount of ABPs was over 125 mg/kg, the protection rate of channel catfish was more than 60%. According to the intestinal transcriptome analysis, the addition of ABPs promoted the expression of intestinal immunity genes and growth metabolism-related genes and enriched multiple related KEEG pathways. When challenged by Yersinia ruckeri infection, the immune response of channel catfish fed with ABPs was intenser and quicker. Additionally, the 16S rRNA gene sequencing analysis showed that the composition of the intestinal microbial community of channel catfish treated with ABPs significantly changed, and the abundance of microorganisms beneficial to channel catfish growth, such as Firmicutes and Bacteroidota increased. In conclusion, feeding channel catfish with ABPs promoted growth, enhanced immunity and antioxidant, and improved resistance to bacterial infections. Our current results might promote the use of ABPs in channel catfish and even other aquacultured fish species.

Identification and characterization of two novel antimicrobial peptides from Japanese sea bass (Lateolabrax japonicus) with antimicrobial activity and MO/MФ activation capability

Piscidins participate in the innate immune response of fish, which aims to eliminate recognized foreign microbes and restore the homeostasis of immune system. We characterized two piscidin-like antimicrobial peptides (LjPL-3 and LjPL-2) isolated from Japanese sea bass (Lateolabrax japonicus). LjPL-3 and LjPL-2 showed different expression patterns in tissues. After Vibrio harveyi infection, the mRNA expression of LjPL-3 and LjPL-2 was upregulated in the liver, spleen, head kidney, and trunk kidney. The synthetic mature peptides LjPL-3 and LjPL-2 exhibited different antimicrobial spectra. Furthermore, LjPL-3 and LjPL-2 treatments decreased inflammatory cytokine production while promoting chemotaxis and phagocytosis in monocytes/macrophages (MO/MФ). LjPL-2, but not LjPL-3, displayed bacterial killing capability in MO/MФ. LjPL-3 and LjPL-2 administration increased Japanese sea bass survival after V. harveyi challenge, which was accompanied by a decline in bacterial burden. These data suggested that LjPL-3 and LjPL-2 participate in immune response through direct bacterial killing and MO/MФ activation.

Expression and functional characterization of three β-defensins in grass carp (Ctenopharyngodon idella)

β-defensins (BDs) are a group of cysteine-rich cationic antimicrobial peptides and play important roles in the first line of defense against infection. In this study, the expression and antibacterial activities of three grass carp (Ctenopharyngodon idella) (Ci) β-defensin (BD) peptides were comparatively investigated. Expression analysis reveals that CiBD1-3 were constitutively expressed in tissues, with the highest expression detected in the skin. The CiBD-1 transcripts were more abundant than CiBD-2 and CiBD-3. In the primary head kidney leukocytes, CiBDs were induced by PHA, LPS, poly(I:C) and cytokines such as IL-1β and IFN-γ. In vivo challenge of fish with Aeromonas hydrophila resulted in the up-regulation of CiBDs in the head kidney and hindgut. To determine the biological activities, recombinant CiBD proteins were produced in the HEK293-F cells and purified for the minimum inhibitory concentration assay. It was found that all three recombinant CiBD proteins were effective to inhibit the growth of Gram-negative fish bacterial pathogens including Aeromonas hydrophila, Edwardsiella tarda, Flavobacterium columnare and Klebsiella pneumoniae and Gram-positive Staphylococcus aureus. CiBD-2 and CiBD-3 were more effective than CiBD-1. Our results demonstrate that all the three CiBDs have broad antibacterial activity against fish bacterial pathogens.

Eucalyptol relieves the toxicity of diisobutyl phthalate in Ctenopharyngodon idellus kidney cells through Keap1/Nrf2/HO-1 pathway: Apoptosis-autophagy crosstalk and immunoregulation

Diisobutyl phthalate (DiBP), one of the commonly used plasticizers in industry, is an endocrine disruptor and environmental contaminant that can persist in water and threaten the health of aquatic creatures. Eucalyptol (Euc), a monoterpenoid extracted from plants, has been proved to have anti-inflammatory, antioxidant, and detoxification properties. However, the protective mechanism of Euc against cell injury caused by DiBP exposure and the involvement of apoptosis, autophagy, and immunity remains unknown. In the current investigation, 27.8 μg/mL DiBP or/and 20 μM Euc has been applied to Ctenopharyngodon idellus kidney (CIK) cells for 24 h. The findings showed that exposure to DiBP raised intracellular ROS levels, inducing oxidative stress, and enhanced the rate of apoptosis as well as the expression of the apoptotic markers Bax, Caspase3, Caspase9, and Cytc while decreasing the expression of Bcl-2. Furthermore, DiBP inhibited IL-2, IFN-γ, Hepcidin-1, and β-defensin expression and elevated TNF-α, and IL-1β levels, causing immune dysfunction. DiBP and Euc co-treatment significantly activated the Keap1/Nrf2/HO-1 pathway, restored antioxidant enzyme activity, and elevated autophagy pathway-associated genes ATG5, Beclin1, and LC3B decreased p62 expression, enhanced cell autophagy, reduced apoptosis, and improved immunity. In conclusion, Euc promotes autophagy, alleviates DiBP-induced apoptosis, and improves immunological dysfunction in CIK cells by regulating the Keap1/Nrf2/HO-1 pathway. These results demonstrated the threat of DiBP exposure to fish while providing a theoretical foundation for using Euc in aquaculture.