Expression and antibacterial analysis of galectin-8 and -9 genes in mandarin fish, Siniperca chuatsi

Galectin-8-like isoform X1 mediates antibacterial, antiviral, and antioxidant responses in red-lip mullet (Planiliza haematocheilus) through positive modulation of pro-inflammatory cytokine, chemokine, and enzymatic antioxidant activity

Galectin 8 belongs to the tandem repeat subclass of the galectin superfamily. It possesses two homologous carbohydrate recognition domains linked by a short peptide and preferentially binds to β-galactoside-containing glycol-conjugates in a calcium-independent manner. This study identified Galectin-8-like isoform X1 (PhGal8X1) from red-lip mullet (Planiliza haematocheilus) and investigated its role in regulating fish immunity. The open reading frame of PhGal8X1 was 918bp, encoding a soluble protein of 305 amino acids. The protein had a theoretical isoelectric (pI) point of 7.7 and an estimated molecular weight of 34.078 kDa. PhGal8X1 was expressed in various tissues of the fish, with prominent levels in the brain, stomach, and intestine. PhGal8X1 expression was significantly (p < 0.05) induced in the blood and spleen upon challenge with different immune stimuli, including polyinosinic:polycytidylic acid, lipopolysaccharide, and Lactococcus garvieae. The recombinant PhGal8X1 protein demonstrated agglutination activity towards various bacterial pathogens at a minimum effective concentration of 50 μg/mL or 100 μg/mL. Subcellular localization observations revealed that PhGal8X1 was primarily localized in the cytoplasm. PhGal8X1 overexpression in fathead minnow cells significantly (p < 0.05) inhibited viral hemorrhagic septicemia virus (VHSV) replication. The expression levels of four proinflammatory cytokines and two chemokines were significantly (p < 0.05) upregulated in PhGal8X1 overexpressing cells in response to VHSV infection. Furthermore, overexpression of PhGal8X1 exhibited protective effects against oxidative stress induced by H2O2 through the upregulation of antioxidant enzymes. Taken together, these findings provide compelling evidence that PhGal8X1 plays a crucial role in enhancing innate immunity and promoting cell survival through effective regulation of antibacterial, antiviral, and antioxidant defense mechanisms in red-lip mullet.

Comparative transcriptome profile reveals insight into the antibacterial immunity mechanism of the loach (Misgurnus anguillicaudatus) fed with soybean fermented broth during lipopolysaccharide (LPS) exposure

Loach (Misgurnus anguillicaudatus) is a common freshwater commercial fish species in China. The meat of this fish is a good source of protein and other nutrients that are needed for human health. Aquaculture challenges such as diseases and pest susceptibility, excessive density, and nutritional deficiency result in low production of loach rather than increased demand. Due to a lack of knowledge about the immune system of loaches, we carried out this study to better understand its antibacterial molecular mechanism. Here, we performed RNA sequencing from liver tissue obtained from soya bean-fermented fed loach after subjecting it to the LPS challenge. The results revealed a total of 18,399 differentially expressed genes (DEGs) in the LPS-treated and control groups. There were 7482 DEGs that were upregulated and 10,917 DEGs were downregulated. The enrichment analysis of DEGs revealed that the majority of DEGs were found to be abundant in the pathways of DNA replication, spliceosome, nucleotide exception repair, cell cycle, and Herpes simplex virus 1 infection. Furthermore, qRT-PCR analysis of 21 selected DEGs demonstrated that the transcriptomic data is extremely reliable. Overall, this study provides insight into the molecular features and control mechanisms of genes that affect loach growth. The availability of this information will also contribute to the enhancement of the breeding and protection of loach resources.

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.

Expression profiling and antibacterial analysis of cd36 in mandarin fish, Siniperca chuatsi

Cd36 is classified as a class B scavenger receptor and has also been identified as a pattern recognition receptor. In this study, we investigated the genomic structure and molecular characteristics of cd36 in mandarin fish (Siniperca chuatsi), examined its tissue distribution, and evaluated its antibacterial activity. Genomic structure analysis showed that Sccd36 consists of 12 exons and 11 introns. Sequencing analysis confirmed that the open reading frame of Sccd36 contains 1410 bp, encoding 469 amino acids. Sccd36 is deeply conserved with other vertebrates in terms of genomic structure, gene loci and molecular evolution, and the feature of two transmembrane was observed in ScCd36 through structural prediction. Sccd36 was constitutively expressed in all tissues tested, with the strongest expression in the intestine, followed by the heart and the kidney. Dramatic changes of Sccd36 mRNA were detected in mucosal tissues, including the intestine, gill and skin, when stimulated by the microbial ligands lipopolysaccharide and lipoteichoic acid. In addition, ScCd36 was identified as having strong binding ability to microbial ligands and antibacterial activity against the gram-negative bacteria Aeromonas hydrophila and the gram-positive bacteria Streptococcus lactis. Furthermore, we verified that the genetic ablation of cd36 impaired the resistance of fish to bacterial challenge by using zebrafish cd36 knockout line. In conclusion, our findings suggest that ScCd36 plays a crucial role in the innate immune response of mandarin fish against bacterial infections. This also sets the stage for further exploration into the antibacterial function of Cd36 in lower vertebrate species.

Systematic analysis of circRNA-related ceRNA networks of black rockfish (Sebastes schlegelii) in response to Aeromonas salmonicides infection

Aeromonas salmonicides is a type of Gram-negative bacteria and has become the main fish pathogen in aquaculture because of its characteristics of worldwide distribution, broad host range and potentially devastating impacts. In the past years, studies have been focused to explore the regulatory roles of circRNA-miRNA-mRNA network in fish diseases. However, there are only few systematic studies linked to the anti-bacterial roles of circRNA-related ceRNA networks in the spleen immune system of black rockfish (Sebastes schlegelii). In this study, the whole-transcriptome sequencing (RNA-seq) was conducted in the black rockfish spleen with A. salmonicida challenging. The differentially expressed (DE) circRNAs were identified comprehensively for the following enrichment analysis. Interactions of miRNA-circRNA pairs and miRNA-mRNA pairs were predicted for the construction of circRNA-related ceRNA regulatory networks. Then, protein-protein interaction (PPI) analysis of mRNAs from these ceRNA networks were conducted. Finally, a total number of 39 circRNAs exhibited significantly differential expressions during A. salmonicida infection in the black rockfish spleen in 4338 identified circRNAs from 12 samples in 4 libraries. Functional enrichment analysis suggested that they were significantly enriched in several immune-related pathways, including Endocytosis, FoxO signaling pathway, Jak-STST signaling pathway, Herpes simplex infection, etc. Subsequently, 290 circRNA-miRNA-mRNA pathways (91 at 2 h, 142 at 12 h and 65 at 24 h) were constructed including 31 circRNAs, 50 miRNAs, and 156 mRNAs. In conclusion, the circRNA-related ceRNA networks were established, which will provide some novel insights in molecular mechanistic investigations of anti-bacterial immune response in teleost. Also, these findings will propose significant predictive values for the development of methods of treatment and prevention in black rockfish after bacterial infection in the future.

An Update of Lectins from Marine Organisms: Characterization, Extraction Methodology, and Potential Biofunctional Applications

Lectins are a unique group of nonimmune carbohydrate-binding proteins or glycoproteins that exhibit specific and reversible carbohydrate-binding activity in a non-catalytic manner. Lectins have diverse sources and are classified according to their origins, such as plant lectins, animal lectins, and fish lectins. Marine organisms including fish, crustaceans, and mollusks produce a myriad of lectins, including rhamnose binding lectins (RBL), fucose-binding lectins (FTL), mannose-binding lectin, galectins, galactose binding lectins, and C-type lectins. The widely used method of extracting lectins from marine samples is a simple two-step process employing a polar salt solution and purification by column chromatography. Lectins exert several immunomodulatory functions, including pathogen recognition, inflammatory reactions, participating in various hemocyte functions (e.g., agglutination), phagocytic reactions, among others. Lectins can also control cell proliferation, protein folding, RNA splicing, and trafficking of molecules. Due to their reported biological and pharmaceutical activities, lectins have attracted the attention of scientists and industries (i.e., food, biomedical, and pharmaceutical industries). Therefore, this review aims to update current information on lectins from marine organisms, their characterization, extraction, and biofunctionalities.

Molecular characterization and antibacterial ability of galectin-3 and galectin-9 in Onychostoma macrolepis

Galectins belong to the β-galactoside binding protein family, which have conserved carbohydrate-recognition domains (CRDs) and participate in innate and acquired immunity in animals. In this study, two galectin genes were cloned from Onychostoma macrolepis, OmGal-3 (galectin-3) and OmGal-9 (galectin-9). The open reading frames (ORFs) of OmGal-3 and OmGal-9 contain 732 and 978 base pairs, encoding 243 and 325 amino acids, respectively. OmGal-3 contains a C-terminal CRD, but OmGal-9 contains an N-terminal CRD and a C-terminal CRD. Two galectins were expressed at varying levels in all tissues examined, with the liver showing the highest expression. The relative gene expression levels of OmGal-3 and OmGal-9 following Aeromonas hydrophila infection were significantly up-regulated in the liver and spleen, and OmGal-9 had a greater increase than OmGal-3. The recombinant OmGal-3 and OmGal-9 proteins (rOmGal-3 and rOmGal-9) were authenticated and verified by SDS-PAGE and western blotting. ROmGal-3 and rOmGal-9 agglutinated all tested bacteria, including 3 g-positive bacteria (Aeromonas hydrophila, Escherichia coli, and Vibrio parahaemolyticus) and 3 g-negative bacteria (Streptococcus agalactiae, Staphylococcus aureus, and Bacillus cereus) in vivo without Ca²⁺. ROmGal-3 showed strong binding both to gram-positive and gram-negative bacteria and OmGal-9 had a stronger binding activity against gram-positive bacteria. Furthermore, rOmGal-3 and rOmGal-9 exhibited dose-dependent binding capability to two classic pathogens associated molecular pattern (LPS and PGN) and two sugars (d-lactose and d-galactose), and rOmGal-3 has better binding activity at lower concentrations in LPS and PGN than rOmGal-3. The integrated analyses indicate that the two galectins probably play an important role in innate immune defense by binding to bacterial cells via the CRD domain against pathogen infection.

Molecular characterization and expression profiling of tandem-repeat galectin-8 from red-spotted grouper (Epinephelus akaara): Potential antibacterial, antiviral, and wound healing activities

Galectin-8 is a typical β-galactoside binding lectin, which primarily functions as a pattern recognition receptor and/or danger receptor that is engaged in pathogen recognition by the host innate immune system. Although several fish galectins have been identified, the role of galectin-8 in teleost immunity is still not fully understood. In this study, molecular, transcriptional, and immune-related functions of galectin-8 (EaGal8) from red-spotted grouper (Epinephelus akaara) were analyzed. The open reading frame of EaGal8 comprised 960 bp encoding 319 amino acids of a ∼35 kDa protein, composed of the N- and C-terminal carbohydrate recognition domains joined by a short hinge peptide. Phylogenetic analysis revealed that EaGal8 was closely related to the Epinephelus lanceolatus galectin-8-like protein. Although EaGal8 showed ubiquitous tissue expression, the highest expression level was observed in the blood. Immunostimulants, including lipopolysaccharide, poly(I:C), and nervous necrosis virus, significantly upregulated the EaGal8 transcription level in a time-dependent manner (p < 0.05). Furthermore, recombinant EaGal8 (rEaGal8) showed a binding affinity toward seven different carbohydrates in a concentration-dependent manner. In addition, rEaGal8 caused strong agglutination of fish red blood cells and several gram-positive and gram-negative bacteria, including Streptococcus iniae, Streptococcus parauberis, Lactococcus garvieae, Escherichia coli, Edwardsiella tarda, Vibrio alginolyticus, Vibrio parahaemolyticus, and Pseudomonas aeruginosa. For the first time in teleosts, we report the wound healing ability of galectin-8 in this study. At low concentrations, rEaGal8 showed potential wound healing responses in FHM cells, in vitro. Thus, this study reinforces the role of EaGal8 in innate immune responses against bacterial and viral infections and wound healing in red-spotted grouper.

Molecular Characterization and Functional Analysis of the Nattectin-like Toxin from the Venomous Fish Thalassophryne maculosa

TmC4-47.2 is a toxin with myotoxic activity found in the venom of Thalassophryne maculosa, a venomous fish commonly found in Latin America whose envenomation produces an injury characterized by delayed neutrophil migration, production of major pro-inflammatory cytokines, and necrosis at the wound site, as well as a specific systemic immune response. However, there are few studies on the protein structure and functions associated with it. Here, the toxin was identified from the crude venom by chromatography and protein purification systems. TmC4-47.2 shows high homology with the Nattectin from Thalassophryne nattereri venom, with 6 cysteines and QPD domain for binding to galactose. We confirm its hemagglutinating and microbicide abilities independent of carbohydrate binding, supporting its classification as a nattectin-like lectin. After performing the characterization of TmC4-47.2, we verified its ability to induce an increase in the rolling and adherence of leukocytes in cremaster post-capillary venules dependent on the α5β1 integrin. Finally, we could observe the inflammatory activity of TmC4-47.2 through the production of IL-6 and eotaxin in the peritoneal cavity with sustained recruitment of eosinophils and neutrophils up to 24 h. Together, our study characterized a nattectin-like protein from T. maculosa, pointing to its role as a molecule involved in the carbohydrate-independent agglutination response and modulation of eosinophilic and neutrophilic inflammation.

The N- and C-terminal carbohydrate recognition domains of galectin-9 from Carassius auratus contribute differently to its immunity functions to Aeromonas hydrophila and Staphylococcus aureus

Galectin-9, an important pathogen recognition receptor (PRR), could recognize and bind pathogen-associated molecular patterns (PAMPs) on the surface of invading microorganisms, initiating the innate immune responses. A galectin-9 was identified from Qihe crucian carp Carassius auratus and designated as CaGal-9. The predicted CaGal-9 protein contained two non-identical carbohydrate recognition domains (CRDs), namely, N-CRD and C-CRD. The recombinant proteins (rCaGal-9, rN-CRD and rC-CRD) were purified from Escherichia coli BL21 (DE3) and exhibited strong agglutinating activity with erythrocytes of rabbit. The haemagglutination was inhibited by D-galactose, α-lactose and N-acetyl-D-galactose. Results of microbial agglutination assay showed that three recombinant proteins agglutinated Gram-negative bacterium Aeromonas hydrophila and Gram-positive bacterium Staphylococcus aureus. With regard to the binding activity, each recombinant protein could bind to LPS, PGN and the examined microorganisms (A. hydrophila and S. aureus) with different binding affinities. The integrated analyses suggested that CaGal-9 with two CRD domains could play an important role in immune defence against pathogenic microorganisms for C. auratus.

A Fish Galectin-8 Possesses Direct Bactericidal Activity

Galectins are a family of animal lectins with high affinity for β-galactosides. Galectins are able to bind to bacteria, and a few mammalian galectins are known to kill the bound bacteria. In fish, no galectins with direct bactericidal effect have been reported. In the present study, we identified and characterized a tandem repeat galectin-8 from tongue sole Cynoglossus semilaevis (designated CsGal-8). CsGal-8 possesses conserved carbohydrate recognition domains (CRDs), as well as the conserved HXNPR and WGXEE motifs that are critical for carbohydrate binding. CsGal-8 was constitutively expressed in nine tissues of tongue sole and up-regulated in kidney, spleen, and blood by bacterial challenge. When expressed in HeLa cells, CsGal-8 protein was detected both in the cytoplasm and in the micro-vesicles secreted from the cells. Recombinant CsGal-8 (rCsGal-8) bound to lactose and other carbohydrates in a dose dependent manner. rCsGal-8 bound to a wide range of gram-positive and gram-negative bacteria and was co-localized with the bound bacteria in animal cells. Lactose, fructose, galactose, and trehalose effectively blocked the interactions between rCsGal-8 and different bacteria. Furthermore, rCsGal-8 exerted potent bactericidal activity against some gram-negative bacterial pathogens by directly damaging the membrane and structure of the pathogens. Taken together, these results indicate that CsGal-8 likely plays an important role in the immune defense against some bacterial pathogens by direct bacterial interaction and killing.