Vibrio parahaemolyticus flagellin induces cytokines expression via toll-like receptor 5 pathway in orange-spotted grouper, Epinephelus coioides

Molecular Characterization and Gene Expression of Pattern Recognition Receptors in Brown-Marbled Grouper (Epinephelus fuscoguttatus) Fingerlings Responding to Vibriosis Infection

The pathogen recognition system involves receptors and genes that play a crucial role in activating innate immune response in brown-marbled grouper (Epinephelus fuscoguttatus) as a control agent against various infections including vibriosis. Here, we report the molecular cloning of partial open reading frames, sequences characterization, and expression profiles of Pattern Recognition Receptors (PRRs) in brown-marbled grouper. The PRRs, namely pglyrp5, tlr5, ctlD, and ctlE in brown-marbled grouper, possess conserved domains and showed shared evolutionary relationships with other fishes, humans, mammals, birds, reptilians, amphibians, and insects. In infection experiments, up to 50% mortality was found in brown-marbled grouper fingerlings infected with Vibrio alginolyticus compared to 27% mortality infected Vibrio parahaemolyticus and 100% survival of control groups. It is also demonstrated that all four PRRs had higher expression in samples infected with V. alginolyticus compared to V. parahaemolyticus. This PRRs gene expression analysis revealed that all four PRRs expressed rapidly at 4-h post-inoculation even though the Vibrio count was only detected earliest at 12-h post-inoculation in samples. The highest expression recorded was from V. alginolyticus inoculated fish spleen with up to 73-fold change for pglyrp5 gene, followed by 14 to 38-fold expression for the same treatment in spleen, head kidney, and blood samples for other PRRs, namely tlr5, ctlD, and ctlE genes. Meanwhile less than a 10% increase in expression of all four genes was detected in spleen, head kidney, and blood samples inoculated with V. parahaemolyticus. These findings indicated that pglyrp5, tlr5, ctlD, and ctlE play important roles in the early immune response to vibriosis infected, brown-marbled grouper fingerlings.

Salmonid Rickettsial Septicemia (SRS) disease dynamics and Atlantic salmon immune response to Piscirickettsia salmonis LF-89 and EM-90 co-infection

In Chile, Piscirickettsia salmonis contains two genetically isolated genogroups, LF-89 and EM-90. However, the impact of a potential co-infection with these two variants on Salmonid Rickettsial Septicemia (SRS) in Atlantic salmon (Salmo salar) remains largely unexplored. In our study, we evaluated the effect of P. salmonis LF-89-like and EM-90-like co-infection on post-smolt Atlantic salmon after an intraperitoneal challenge to compare changes in disease dynamics and host immune response. Co-infected fish had a significantly lower survival rate (24.1%) at 21 days post-challenge (dpc), compared with EM-90-like single-infected fish (40.3%). In contrast, all the LF-89-like single-infected fish survived. In addition, co-infected fish presented a higher presence of clinical lesions than any of the single-infected fish. The gene expression of salmon immune-related biomarkers evaluated in the head kidney, spleen, and liver showed that the EM-90-like isolate and the co-infection induced the up-regulation of cytokines (e.g., il-1β, ifnγ, il8, il10), antimicrobial peptides (hepdicin) and pattern recognition receptors (PRRs), such as TLR5s. Furthermore, in serum samples from EM-90-like and co-infected fish, an increase in the total IgM level was observed. Interestingly, specific IgM against P. salmonis showed greater detection of EM-90-like antigens in LF-89-like infected fish serum (cross-reaction). These data provide evidence that P. salmonis LF-89-like and EM-90-like interactions can modulate SRS disease dynamics in Atlantic salmon, causing a synergistic effect that increases the severity of the disease and the mortality rate of the fish. Overall, this study contributes to achieving a better understanding of P. salmonis population dynamics.

Design and functional characterization of Salmo salar TLR5 agonist peptides derived from high mobility group B1 acidic tail

Toll-like receptor 5 (TLR5) responds to the monomeric form of flagellin and induces the MyD88-depending signaling pathway, activating proinflammatory transcription factors such as NF-κB and the consequent induction of cytokines. On the other hand, HMGB1 is a highly conserved non-histone chromosomal protein shown to interact with and activate TLR5. The present work aimed to design and characterize TLR5 agonist peptides derived from the acidic tail of Salmo salar HMGB1 based on the structural knowledge of the TLR5 surface using global molecular docking platforms. Peptide binding poses complexed on TLR5 ectodomain model from each algorithm were filtrated based on docking scoring functions and predicted theoretical binding affinity of the complex. Circular dichroism spectra were recorded for each peptide selected for synthesis. Only intrinsically disordered peptides (6W, 11W, and SsOri) were selected for experimental functional assay. The functional characterization of the peptides was performed by NF-κB activation assays, RT-qPCR gene expression assays, and Piscirickettsia salmonis challenge in SHK-1 cells. The 6W and 11W peptides increased the nuclear translation of p65 and phosphorylation. In addition, the peptides induced the expression of genes related to the TLR5 pathway activation, pro- and anti-inflammatory response, and differentiation and activation of T lymphocytes towards phenotypes such as TH1, TH17, and TH2. Finally, it was shown that the 11W peptide protects immune cells against infection with P. salmonis bacteria. Overall, the results indicate the usefulness of novel peptides as potential immunostimulants in salmonids.

UNC93B1 facilitates the localization and signaling of TLR5M in Epinephelus coioides

Toll-like receptor 5 (TLR5), serving as a sensor of bacterial flagellin, mediates the innate immune response to actively engage in the host's immune processes against pathogen invasion. However, the mechanism underlying TLR5-mediated immune response in fish remains unclear. Despite the presumed cell surface expression of TLR5 member form (TLR5M), its trafficking dynamics remain elusive. Here, we have identified Epinephelus coioides TLR5M as a crucial mediator of Vibrio flagellin-induced cytokine expression in grouper cells. EcTLR5M facilitated the activation of NF-κB signaling pathway in response to flagellin stimulation and exerted a modest influence on the mitogen-activated protein kinase (MAPK)-extracellular regulated kinase (ERK) signaling. The trafficking chaperone Unc-93 homolog B1 (EcUNC93B1) participated in EcTLR5M-mediated NF-κB signaling activation and downstream cytokine expression. In addition, EcUNC93B1 combined with EcTLR5M to mediate its exit from the endoplasmic reticulum, and also affected its post-translational maturation. Collectively, these findings first discovered that EcTLR5M mediated the flagellin-induced cytokine expression primarily by regulating the NF-κB signaling pathway, and EcUNC93B1 mediated EcTLR5M function through regulating its trafficking and post-translational maturation. This research expanded the understanding of fish innate immunity and provided a novel concept for the advancement of anti-vibrio immunity technology.

Construction of the flagellin F mutant of Vibrio parahaemolyticus and its toxic effects on silver pomfret (Pampus argenteus) cells

Vibrio parahaemolyticus causes diseases in aquatic organisms, leading to substantial financial losses to the aquaculture industry; its flagellin F (flaF) protein triggers severe inflammation in host cells. To enhance the understanding of the function of flaF in V. parahaemolyticus infection, in this study, a flaF-deficient mutant was constructed by employing two-step homologous recombination. The flaF-deficient mutant induced a significantly lower toll-like receptor 5 (TLR5) expression and apoptosis in fish intestinal epithelial cells than the wild-type V. parahaemolyticus. Furthermore, fluorescence labelling and microscopy analysis of TLR5 showed that V. parahaemolyticus and its mutant strain significantly enhanced TLR5 expression. Additionally, the findings suggest that flaF deletion did not significantly affect the expression of myeloid differentiation factor 88 (MyD88) and interleukin-8 (IL-8) induced by V.parahaemolyticus. In summary, V. parahaemolyticus induced a TLR5-dependent inflammatory response and apoptosis through MyD88, which was observed to be influenced by flaF deletion. In this study, we obtained stable mutants of V. parahaemolyticus via target gene deletion-which is a rapid and effective approach-and compared the induction of inflammatory response and apoptosis by V. parahaemolyticus and its mutant strain, providing novel perspectives for functional gene research in V. parahaemolyticus.

TLR5S negatively regulates the TLR5M-mediated NF-κB signaling pathway in Epinephelus coioides

Nuclear factor kappa-B (NF-κB) pathway is a key mediator of inflammation response that plays a role in host defense for pathogen elimination, but excessive activation may lead to tissue damage or pathogen transmission. The negative regulation of NF-κB in lower vertebrates is largely unknown, hindering further understanding of immune signaling evolution. Here, we provided evidence that Epinephelus coioides soluble toll-like receptor 5 (TLR5S), a member of the TLR5 subfamily, has been newly identified as a negative regulator of NF-κB signaling. EcTLR5S was a cytoplasmic protein consisting of 17 leucine-rich repeat domains, which specifically responded to Vibrio flagellin and suppressed flagellin-induced NF-κB signaling activation and cytokine expression. The amino-terminal LRR 1-5 region was necessary for its negative regulatory function. Dual-luciferase reporter assay showed that EcTLR5S significantly inhibited the NF-κB-luc activity induced by inhibitor of NF-κB kinase α (IKKα) and IKKβ. Subsequently, the functional relationship between EcTLR5M and EcTLR5S was analyzed, revealing that the negative regulatory function of EcTLR5S targeted the activation of the NF-κB pathway mediated by EcTLR5M. The above results reveal that EcTLR5S negatively regulates the flagellin-induced EcTLR5M-NF-κB pathway activation, which may prevent over-activation of immune signaling and restore homeostasis.

The role of flagellin F in Vibrio Parahaemolyticus-induced intestinal immunity and functional domain identification

The marine pathogen Vibrio parahaemolyticus has caused huge economic losses to aquaculture. Flagellin is a key bacterial virulence factor that induces an inflammatory response via activation of Toll-like receptor 5 (TLR5) signaling. Herein, to explore the inflammatory activity of V. parahaemolyticus flagellins (flaA, flaB, flaC, flaD, flaE, and flaF), we investigated their ability to induce apoptosis in a fish cell line. All six flagellins induced severe apoptosis. Moreover, treatment with V. parahaemolyticus flagellins increased TLR5 and myeloid differentiation factor 88 (MyD88) expression and the production of TNF-α and IL-8 significantly. This indicated that flagellins might induce a TLR5-meditated immune response via an MyD88-dependent pathway. FlaF exhibited the strongest immunostimulatory effect; therefore, the interaction between TLR5 and flaF was screened using the yeast two-hybrid system. A significant interaction between the two proteins was observed, indicating that flaF binds directly to TLR5. Finally, the amino acids that participate in the TLR5-flaF interaction were identified using molecular simulation, which indicated three binding sites. These results deepen our understanding of the immunogenic properties of flagellins from V. parahaemolyticus, which could be used for vaccine development in the future.

A soluble TLR5 is involved in PBLs activation and antibacterial immunity via TLR5M-MyD88-signaling pathway in tongue sole Cynoglossus semilaevis

In higher vertebrates, there is only a membranal TLR5 (TLR5M), which is crucial for host defense against microbes via MyD88 signaling pathway. In teleost, both TLR5M and soluble TLR5 (TLR5S) are identified, whereas the antibacterial mechanism of TLR5S is largely unknown. In this study, we studied the immune antibacterial mechanism of Cynoglossus semilaevis TLR5S homologue (named CsTLR5S). CsTLR5S, a 71.1 kDa protein, consists of 649 amino acid residues and shares 41.7 %-57.8 % overall sequence identities with teleost TLR5S homologues. CsTLR5S contains a single extracellular domain (ECD) composed of 12 leucine-rich repeats. CsTLR5S expression was constitutively identified and upregulated by bacterial infection in tissues. In vitro recombinant CsTLR5S (rCsTLR5S) could interact with bacteria and tongue sole rTLR5M (rCsTLR5M). Furthermore, rCsTLR5S could bind to the membranal CsTLR5M of peripheral blood leukocytes (PBLs), which led to enhancing the activity and the antibacterial role of PBLs via Myd88-NF-κB pathway. In vivo rCsTLR5S could activate the Myd88-NF-κB pathway, facilitate the release of proinflammatory cytokines, and enhance the host antibacterial response against Vibrio harveyi. Moreover, the knockdown of CsTLR5M or the Myd88 inhibitor could significantly suppress the antibacterial effect of rCsTLR5S. Collectively, our findings added important insights into the TLR5S immune antibacterial property in a TLR5M-MyD88-dependent manner.

Recombinant Vibrio harveyi flagellin A protein and partial deletions of middle variable region and D0 domain induce immune related genes in Epinephelus coioides and Cyprinus carpio

Vibrio harveyi is a Gram-negative bacterium that causes vibriosis in various aquaculture species, including the orange-spotted grouper (Epinephelus coioides). Bacterial flagellin is a potent pathogen-associated molecule that stimulates the innate and adaptive immune systems through toll-like receptor 5 (TLR5) signaling. In this study, we isolated V. harveyi flagellin A (VhFliA) gene from V. harveyi (originated from orange-spotted grouper) and investigated the in vivo activities of recombinant VhFliA protein. Multiple sequence alignment showed that the amino acid sequence of VhFliA has conserved domains of N- and C-terminals (D0 and D1) and a middle variable (MV) region. We produced the VhFliA recombinant protein (wild type (WT)-VhFliA) by Escherichia coli and investigated its in vivo biological activity. Additionally, we prepared the VhFliA recombinant proteins with deletion of domains (ΔMV-VhFliA and ΔD0MV-VhFliA) to identify the domain for biological activity in the orange-spotted grouper. WT and ΔMV-VhFliA induced the expression of inflammatory cytokines (IFNγ, IL-1β, and IL-8) in groupers. However, ΔD0MV-VhFliA did not induce the expression of inflammatory cytokines. Additionally, to demonstrate the applicability of recombinant VhFliA to teleost species, we performed an in vivo assay of the recombinant proteins in koi carp (Cyprinus carpio). WT-VhFliA stimulates the expression of inflammatory cytokines (IL-1β, IL-6, and IL-8) in carp. ΔMV-VhFliA did not upregulate IL-1β and IL-6, whereas ΔD0MV-VhFliA induced expression in carp. These findings showed the potential of VhFliA as an effective immune stimulant adjuvant and comparative studies of flagellin - TLR5 signaling in teleosts.

Non-coding RNAs targeting NF-κB pathways in aquatic animals: A review

Nuclear factor-kappa B (NF-κB) pathways have a close relationship with many diseases, especially in terms of the regulation of inflammation and the immune response. Non-coding RNAs (ncRNAs) are a heterogeneous subset of endogenous RNAs that directly affect cellular function in the absence of proteins or peptide products; these include microRNAs (miRNAs), long noncoding RNAs (lncRNAs), circular RNAs (circRNAs), etc. Studies on the roles of ncRNAs in targeting the NF-κB pathways in aquatic animals are scarce. A few research studies have confirmed detailed regulatory mechanisms among ncRNAs and the NF-κB pathways in aquatic animals. This comprehensive review is presented concerning ncRNAs targeting the NF-κB pathway in aquatic animals and provides new insights into NF-κB pathways regulatory mechanisms of aquatic animals. The review discusses new possibilities for developing non-coding-RNA-based antiviral applications in fisheries.

Astragalus polysaccharides protect against inactivated Vibrio alginolyticus-induced inflammatory injury in macrophages of large yellow croaker

As an effective immunostimulant, Astragalus polysaccharides (APS) have been widely used in fish aquaculture, however, their action mechanisms remain poorly understood. In the present paper, the inflammatory macrophage model of large yellow croaker (Larimichthys crocea) was constructed by using formalin-inactivated Vibrio alginolyticus. Inactivated V. alginolyticus could cause cellular damage of primary head kidney macrophages (PKM) by decreasing cell activity and inducing reactive oxygen species (ROS) production and cell apoptosis. When PKM were pretreated with APS, the depressed cell activity induced by inactivated V. alginolyticus was significantly improved, and ROS overproduction and cell apoptosis were inhibited. Then the protection mechanism of APS was investigated by transcriptome analysis. After treated with inactivated V. alginolyticus, the expression of immune-related genes (TLR5s, TLR13, Clec4e, IKK, IκB, BCL-3, NF-κB2, REL, IL-1β, and IL-6) and pyroptosis-related genes (caspase-1, NLRP3, and NLRC3) in PKM were significantly up-regulated. However, APS pretreatment reversed the up-regulation of most of the above-mentioned genes, where TLR5s, BCL-3, REL, caspase-1, NLRP12, IL-1β, and IL-6 were significantly down-regulated compared with inactivated V. alginolyticus-treated group. These results suggested that APS could protect large yellow croaker PKM against inactivated V. alginolyticus-induced inflammatory injury, and may exert their protection effects by activating NF-κB and pyroptosis signaling pathways. These findings therefore advance our understanding of the immune regulation mechanism of APS in fish, and facilitate the application of APS in prevention and control of fish bacteriosis.

Integrative analyses of mRNA and microRNA expression profiles reveal the innate immune mechanism for the resistance to Vibrio parahaemolyticus infection in Epinephelus coioides

Vibrio parahaemolyticus, as one of the main pathogens of marine vibriosis, has brought huge losses to aquaculture. However, the interaction mechanism between V. parahaemolyticus and Epinephelus coioides remains unclear. Moreover, there is a lack of comprehensive multi-omics analysis of the immune response of grouper spleen to V. parahaemolyticus. Herein, E. coioides was artificially injected with V. parahaemolyticus, and it was found that the mortality was 16.7% in the early stage of infection, and accompanied by obvious histopathological lesions in the spleen. Furthermore, 1586 differentially expressed genes were screened by mRNA-seq. KEGG analysis showed that genes were significantly enriched in immune-related pathways, Acute-phase immune response, Apoptosis, Complement system and Cytokine-cytokine receptor interaction. As for miRNA-seq analysis, a total of 55 significantly different miRNAs were identified. Further functional annotation analysis indicated that the target genes of differentially expressed miRNAs were enriched in three important pathways (Phosphatidylinositol signaling system, Lysosome and Focal adhesions). Through mRNA-miRNA integrated analysis, 1427 significant miRNA–mRNA pairs were obtained and “p53 signaling pathway”, “Intestinal immune network for IgA production” were considered as two crucial pathways. Finally, miR-144-y, miR-497-x, novel-m0459-5p, miR-7133-y, miR-378-y, novel-m0440-5p and novel-m0084-3p may be as key miRNAs to regulate immune signaling pathways via the miRNA-mRNA interaction network. The above results suggest that the mRNA-miRNA integrated analysis not only sheds new light on the molecular mechanisms underlying the interaction between host and V. parahaemolyticus but also provides valuable and new insights into resistance to vibrio infection.

TLR5 recognizes Aeromonas hydrophila flagellin and interacts with MyD88 in Nile tilapia

Toll-like receptor 5 (TLR5) is responsible for bacterial flagellin recognition in vertebrates. In the present study, TLR5M was identified in the Nile tilapia Oreochromis niloticus (OnTLR5), containing a conserved LRR domain, a transmembrane region and a C-terminal TIR domain, similar to that of other fishes and mammals. OnTLR5 was broadly expressed in all the tissues examined, presenting the highest expression levels in the blood and the lowest in the kidney. OnTLR5 was detected from 2 d postfertilization (dpf) to 8 dpf during embryonic development. Moreover, expression levels of OnTLR5 were clearly altered in all five tissues examined in response to Streptococcus agalactiae infection in vivo. Overexpression of OnTLR5 in HEK293T cells revealed that OnTLR5 was distributed in the cytoplasm and significantly increased NF-κB activation. In response to cotransfection with OnMyd88, OnTLR5 significantly upregulated OnMyd88-induced NF-κB activation. Pulldown assays showed that OnTLR5 interacts with OnMyd88 and revealed an interaction between TLR5 and Aeromonas hydrophila flagellin. Taken together, these findings suggest that OnTLR5 plays important roles in TLR/IL-1R signalling pathways and the immune response to pathogen invasion.

Membrane orthologs of TLR5 of tongue sole Cynoglossus semilaevis: Expression patterns, signaling pathway and antibacterial property

Mammalian toll-like receptor 5 (TLR5) is crucial for recognizing bacterial flagellin and initiating the inflammatory signaling cascades via myeloid differentiation factor 88 (MyD88) signaling pathway, which plays vital roles in innate immune against pathogenic bacteria. Herein, we reported the signaling pathway and antibacterial property of tongue sole (Cynoglossus semilaevis) membrane forms of TLR5 (i.e. CsTLR5M1and CsTLR5M2). CsTLR5M1/M2 contain 936 and 885 amino acid residues respectively. CsTLR5M1 shares 86.7% overall sequence identities with CsTLR5M2. CsTLR5M1/M2 possess the same extracellular domain (ECD) and transmembrane domain (TMD), but the different toll-interleukin-1 receptor (TIR) domain. CsTLR5M1/M2 expression occurred constitutively in multiple tissues and regulated by bacterial stimulation. Recombinant CsTLR5M1/M2 (rCsTLR5M) could bind to flagellin and Gram-negative/positive bacteria, which could suppress bacterial growth. Stimulation of the CsTLR5M pathway by flagellin resulted in increased expression of MyD88-dependent signaling molecules and inflammatory cytokines. Blocking rCsTLR5M by antibody markedly reduced the phagocytosis and ROS production of peripheral blood leukocytes (PBLs), which in turn in vivo promoted the dissemination of bacteria. Overall, these observations add new insights into the signaling pathway and immune function of teleost TLR5M.

Genome-wide identification and characterization of Toll-like receptor genes in black rockfish (Sebastes schlegelii) and their response mechanisms following poly (I:C) injection

Toll-like receptors (TLRs) are canonical transmembrane receptors that play an important role in defending against invading pathogens. In this study, we identified a total of 12 TLR genes in black rockfish (Sebastes schlegelii) with an analysis of their sequence characterizations. The phylogenetic analysis suggested that 12 distinct TLRs were grouped into five subfamilies (i.e., TLR1, TLR3, TLR5, TLR7, and TLR11 subfamilies), and each SsTLR gene respectively corresponded to the orthologs genes of other species. The protein domain analysis indicated that TLRs are type I transmembrane proteins, including an extracellular leucine-rich repeat (LRR), a transmembrane region (TM) domain and an intracellular Toll/IL-1 receptor (TIR) domain. The evolutionary ratios indicted that 12 SsTLRs were under purifying selection. qRT-PCR assays exhibited diverse TLRs molecular expression patterns in the heart, brain, head kidney, kidney, liver, intestine, and spleen of 3 black rockfish, and the expression levels were high in some immune tissues (e.g., head kidney, kidney, and spleen). Subsequently, 30 fish were equally divided into 2 groups i.e., poly (I:C)-treated and PBS-Control groups. After poly (I:C) injection, eight SsTLRs, i.e., SsTLR2, SsTLR2-1, SsTLR2-2, SsTLR3, SsTLR5S, SsTLR7, SsTLR8 and SsTLR22, were dramatically increased. Altogether these results contribute to understanding how SsTLRs respond to immune defense after poly (I:C) injection and provide researchers with comprehensive TLR gene family data of black rockfish.

The flagellin of Vibrio parahaemolyticus induces the inflammatory response of Tetraodon nigroviridis through TLR5M

Vibrio parahaemolyticus is an important marine pathogen that cause inflammation even death in teleost. It has brought huge economic losses to aquaculture and serious threats to the sustainable development of marine fisheries. Here, we isolated the DNA, RNA, and total flagellin from V. parahaemolyticus, and obtained the primary spleen and head kidney cells (including leukocytes) from Tetraodon nigroviridis. V. parahaemolyticus DNA, RNA, and total flagellin were used to treat the T. nigroviridis primary cells described above. The results show that the nitric oxide (NO) production and respiratory burst response were significantly induced after stimulation with V. parahaemolyticus total flagellin in T. nigroviridis head kidney and spleen cells. And total flagellin could promote the gene expression and protein production of IL-1β in T. nigroviridis leukocytes. T. nigroviridis TLR5M (TnTLR5M) and TLR5S (TnTLR5S) ORF sequences were obtained as the main recognition receptor for flagellin. Real-time fluorescent quantitative PCR (qRT-PCR) was performed to detect the expression of pattern recognition receptor TnTLR5M and TnTLR5S, the important signal molecule of inflammatory system TnMyD88 and TnTRAF6, and inflammatory cytokines TnIL-1β and TnIFN-γ2. The results show that there were a significant upregulation after challenge with V. parahaemolyticus total flagellin. We further demonstrated that the total flagellin of V. parahaemolyticus could activate the luciferase activity of the NF-κB reporter gene mediated by TnTLR5M. Overall, our results suggest that V. parahaemolyticus total flagellin activated the NO production, respiratory burst response, and inflammatory cytokines expressions, such as TnIL-1β and TnIFN-γ2, through the TnTLR5M-NF-κB signaling pathway in T. nigroviridis.

Transcriptome analysis revealed multiple immune processes and energy metabolism pathways involved in the defense response of the large yellow croaker Larimichthys crocea against Pseudomonas plecoglossicida

The large yellow croaker (Larimichthys crocea) aquaculture industry is suffering substantial financial losses caused by visceral white nodules disease resulting from Pseudomonas plecoglossicida infection. However, how L. crocea responds to P. plecoglossicida infection remains largely unknown. Here, we characterized the changes in the mRNA profile in the spleen of L. crocea upon P. plecoglossicida infection and explored the related defensive strategies. Sample clustering analysis and qRT-PCR indicated that P. plecoglossicida induced profound and reproducible transcriptome remodeling in the L. crocea spleen. Many innate immune-related genes, such as IL-17 signaling molecules, chemokines and chemokine receptors, complement components, TLR5 signaling molecules, and antimicrobial peptide hepcidins (Hamps), were upregulated by P. plecoglossicida and may play important roles in the L. crocea defense against P. plecoglossicida. The antibacterial activity of Hamp2-5 against P. plecoglossicida was further confirmed by using synthetic mature peptide of Hamp2-5. Additionally, significant enrichment of "Glycolysis/Gluconeogenesis", "Citrate cycle" and "Oxidative phosphorylation" pathways and a significant upregulation of all 6 rate-limiting enzyme genes (HK1, PFK, PKM, CS, IDH2, DLST) in the Glycolysis and Citrate cycle pathways in P. plecoglossicida-infected fish suggested that ATP synthesis may be accelerated to ensure energy supply in response to pathogenic infection. Altogether, our results not only identified the key immune-related genes and immune pathways that participated in the defense response of L. crocea against P. plecoglossicida, but also revealed a novel defensive strategy involving ATP synthesis in this species.

The ERβ-CXCL19/CXCR4-NFκB pathway is critical in mediating the E2-induced inflammation response in the orange-spotted grouper (Epinephelus coioides)

The main physiological function of 17β-estradiol (E2) in vertebrates is to regulate sexual development and reproduction. In fish, especially hermaphroditic fish, estrogen is often used to aid reproduction, but it also can trigger an inflammatory response. However, the molecular mechanism for this E2-induced inflammatory reaction is not clear. In this study, we found that the ERβ-CXCL19/CXCR4-NFκB cascade regulated the E2-induced inflammatory response in the orange-spotted grouper (Epinephelus coioides). Strikingly, E2 treatment resulted in significantly high expression of inflammatory cytokines and induced phosphorylation and degradation of IκBα and translocation of NFκB subunit p65 to the nucleus in grouper spleen cells. However, the E2-induced inflammatory response could be prevented by the broad estrogen receptor (ER) ligand ICI 182,780. Moreover, the luciferase assay showed that E2 induced the inflammatory response by activating the promotor of chemokine CXCL19 through ERβ1 and ERβ2. Knockdown of CXCL19 blocked the E2-induced inflammatory response and NFκB nucleus translocation. Additionally, knockdown of chemokines CXCR4a and CXCR4b together, but not alone, blocked the E2-induced inflammatory response. The immunofluorescence assay and co-immunoprecipitation analysis showed that CXCL19 mediated the E2-induced inflammatory response by activating CXCR4a or CXCR4b. Taken together, these results showed that the ERβ-CXCL19/CXCR4-NFκB pathway mediated the E2-induced inflammatory response in grouper. These findings are valuable for future comparative immunological studies and provide a theoretical basis for mitigating the adverse reactions that occur when using E2 to help fish reproduce.

Comparative immunogenicity of outer membrane protein K and whole-cell antigens of Vibrio parahaemolyticus for diagnosis

The immunogenicity of soluble outer membrane protein K (OmpK)- small ubiquitin-like modifier, OmpK inclusion bodies, formalin, and heat-killed Vibrio parahaemolyticus cells were prepared and studied in a mouse model. The results of whole-cell ELISA and Western blot (WB) revealed that the serum against soluble OmpK and OmpK inclusion bodies reacted only with homologous V. parahaemolyticus. Furthermore, recombinant OmpK proteins were not recognized by the serum against whole-cell V. parahaemolyticus antigens. Unexpectedly, the serum against formalin and heat-killed V. parahaemolyticus reacted broadly with homologous (an immunization strain) and heterologous (non-immunization strains) V. parahaemolyticus and Vibrio species. The WB results revealed that the serum against the two V. parahaemolyticus whole-cell antigens primarily reacted with proteins that were approximately 100, 70, 36, 28, and 22 kDa in the cell lysates from different Vibrio strains, rather than the recombinant OmpK. The 70 and 28 kDa proteins exhibited specificity to Vibrio species, while the 22 kDa protein was more specific to V. parahaemolyticus. This study showed the limitation of recombinant OmpK to prepare diagnostic antibodies and revealed several specific Omps of Vibrio sp. and V. parahaemolyticus that were promising in diagnosis and vaccine development.

Mechanisms by Which Fermented Soybean Meal and Soybean Meal Induced Enteritis in Marine Fish Juvenile Pearl Gentian Grouper

Soy meals can cause intestinal inflammation and even injury in animals, especially infants and juvenile individuals. This study investigated the effects of fermented soybean meal (FSBM) on the growth and intestinal homeostasis of juvenile pearl gentian grouper and examined the mechanisms by which FSBM and soybean meal (SBM) induced enteritis in fish, using "3+2" full-length transcriptome sequencing. We randomly assigned 720 female juvenile groupers into three treatment groups: FM control group, 20% FSBM group (FSBM20), and FSBM40 group (n = 4). Three iso-nitrogenous (50% protein) and iso-lipidic (10% lipid) diets were prepared and fed to fish for 10 weeks. The water volume in each barrel was about 1 m3, using natural light and temperature. Results showed that dietary FSBM, at experimental level, significantly affected fish growth and intestinal structure negatively and significantly increased enteritis indices. The degree of intestinal injury and inflammation was determined by the enzyme activities of trypsin and lysozyme, and the contents of IgM, C3, C4, and malondialdehyde, and the expressions of pro-inflammatory genes (IL1β, IL8, IL17, and TNFα) and anti-inflammatory genes (IL4, IL10, and TGFβ1). Full-length transcriptome analysis identified 2,305 and 3,462 differentially expressed genes (DEGs) in SBM40 and FSBM40 groups, respectively. However, only 18.98% (920/5,445) of DEGs had similar expression patterns, indicating that high levels of SBM40 and FSBM40 have different metabolic strategies. KEGG enrichment analysis indicated that among the significant pathways, ~45% were related to immune diseases/systems, infectious diseases, and signal transduction in both SBM and FSBM groups. Based on PacBio SMRT sequencing, nine toll-like receptor (TLR) members, including TLR1, TLR2, TLR3, TLR5, TLR8, TLR9, TLR13, TLR21, and TLR22, were detected in intestinal tissues of pearl gentian grouper. TLR-MyD88-NF-κB signaling pathway played an important role in the development of FSBM- and SBM-induced enteritis in pearl gentian grouper; however, TLR receptors used in SBM and FSBM groups were different. TLR1, TLR8, TLR13, and TLR22 were the main receptors used in FSBM group, while TLR5, TLR8, TLR9, TLR21, and TLR22 were the main receptors used in SBM group. Present study provides valuable theoretical references for further research on soy protein-induced enteritis in fish.

23S rRNA from Vibrio parahaemolyticus regulates the innate immune response via recognition by TLR13 in orange-spotted grouper (Epinephelus coioides)

Toll-like receptors (TLRs) are major pattern recognition receptors (PRRs) that recognize multiple pathogen-associated molecular patterns (PAMPs) through the leucine-rich repeat (LRR) domain and mount effective immune responses. Vibrio parahaemolyticus is the main pathogen that causes vibriosis in aquatic animals, yet the mechanisms of its recognition by innate immune system in teleost fish remain unknown. Here, the results reveal that TLR13 in orange-spotted grouper (Epinephelus coioides) (EcTLR13) recognizes a conserved 23S ribosomal RNA (23S rRNA) sequence in V. parahaemolyticus, and the 13-nucleotide motif near the 23S rRNA ribozyme activation site (VP13) acts as a PAMP. After challenge with RNA and 23S rRNA from V. parahaemolyticus and with the synthetic oligoribonucleotide VP13, the expression of EcTLR13 in grouper spleen cells (GS cells) was significantly increased. EcTLR13-knockdowned GS cells were stimulated with the same stimulants as listed above, the expression of IL-6, IL-12, IL-1β and TNFα was significantly reduced. RNA-protein immunoprecipitation revealed that VP13 could directly bind to EcTLR13. The dual-luciferase reporter assay also showed that EcTLR13 enhanced the fluorescence activity of IFNβ rather than that of NF-κB when the cells were challenged with RNA from V. parahaemolyticus or with synthetic VP13. Our study established the mechanism of fish TLR13-mediated recognition of microbial products during V. parahaemolyticus infection.

Preconditioning mesenchymal stromal cells with flagellin enhances the anti‑inflammatory ability of their secretome against lipopolysaccharide‑induced acute lung injury

Acute lung injury (ALI) is a complex condition frequently encountered in the clinical setting. The aim of the present study was to investigate the effect of conditioned media (CM) from human adipose‑derived mesenchymal stromal cells (MSCs) activated by flagellin (F‑CM), a Toll‑like receptor 5 ligand, on inflammation‑induced lung injury. In the in vitro study, RAW264.7 macrophages treated with F‑CM had a higher proportion of cells with the M2 phenotype, lower expression of pro‑inflammatory factors and stronger expression of anti‑inflammatory genes compared with the CM from normal adipose‑derived MSCs. Furthermore, in vivo experiments were performed in mice with ALI induced by intraperitoneal injection of lipopolysaccharide. F‑CM significantly alleviated the lung exudation, inhibited inflammatory cell recruitment in lung tissues and decreased the concentration of inflammatory factors in the bronchoalveolar lavage fluid. These findings indicated that F‑CM has superior anti‑inflammation ability compared with CM, and that it may represent a promising therapeutic approach to the treatment of inflammation‑induced ALI.

Rheum officinale extract promotes the innate immunity of orange-spotted grouper (Epinephelus coioides) and exerts strong bactericidal activity against six aquatic pathogens

We investigated the antimicrobial properties and the effects of Rheum officinale extract (ROE) on nonspecific immune parameters of orange-spotted grouper (Epinephelus coioides) in vitro and in vivo. The in vitro analysis was conducted by treating grouper primary head kidney leukocytes with various concentrations of ROE. The phagocytic rate of the leukocytes was elevated in a dose-dependent manner from 0.01 to 0.1 mg/ml, but decreased with higher concentrations of ROE (0.5 and 1.0 mg/ml). The production of reactive oxygen species (ROS) was strongly enhanced in a dose-dependent manner by treatment with ROE doses of 0.1-10.0 mg/ml. However, morphological changes (e.g., rounding and shrinkage of cells, chromatin condensation, fragmentation, and appearance of apoptotic bodies) were observed in the leukocytes after incubation with higher concentrations of ROE (1.0 and 10.0 mg/ml). A 28-day feeding trial was performed to assess the impact of dietary administration of ROE on grouper innate immunity parameters. Fish were fed with feed supplemented with 0, 0.1, 1.0, or 5.0 g ROE per kg of feed. The phagocytic activity of the animals' leukocytes was significantly elevated in all ROE-fed groups on day 1 and in groups fed with ROE at 0.1 or 1.0 g/kg on day 14. Production of ROS was substantially increased on day 1 in fish fed with ROE at 1.0 and 5.0 g/kg, but decreased steadily later on. The ability to generate ROS increased steadily until day 7 in fish fed the lowest concentration of ROE (0.1 mg/ml), but decreased thereafter. ROE showed excellent antibacterial activity against six pathogens of aquatic animals: Vibrio parahaemolyticus, V. vulnificus, V. alginolyticus, V. carchariae, Aeromonas hydrophila, and Edwardsiella tarda. The minimum inhibitory and bactericidal concentrations of measured ROE-derived anthraquinones were 10.57-84.53 μg/ml and 10.57-169.05 μg/ml, respectively.

Molecular characterization and functional analysis of IKKα in orange-spotted grouper (Epinephelus coioides)

Inhibitor of nuclear factor kappa-B kinase subunit alpha (IKKα) plays crucial roles in regulating activation of nuclear factor kappa-B (NF-κB) in response to pathogens infections. Here, we cloned and identified IKKα gene of orange-spotted grouper (Epinephelus coioides), named as EcIKKα. The gene transcript contained a 2262 bp open reading frame, which encoded 753 amino acids. The typically conserved IKKα structure, including serine kinase domain (KD), leucine chain (LZ) structure, helix-loop-helix (HLH) motif and IKKβ-NEMO-binding domain, was identified in EcIKKα. Phylogenetic analysis suggested that EcIKKα had the closest relationship with large yellow croaker (Larimichthy crocea) IKKα. Ecikkα was ubiquitously expressed in all tissues tested and the highest expression level was in ovary. After lipopolysaccharide (LPS), flagellin, polyinosinic-polycytidylic acid (poly I:C), polyadenylic-polyuridylic acid (poly A:U), and Vibrio parahaemolyticus stimulation, the expression of Ecikkα increased in grouper spleen (GS) cells. In the luciferase assay, NF-κB-luc activity was significantly up-regulated when human embryonic kidney 293T (HEK 293T) cells were transfected with EcIKKα plasmid. Moreover, overexpression of EcIKKα significantly increased LPS- and flagellin-induced proinflammatory cytokines (interleukin-6 (il-6) and tumor necrosis factor-α (tnf-α)) expression, but did not significantly affect poly I:C- and poly A:U-induced cytokines (il-6 and tnf-α) expression. Overall, these results suggested that EcIKKα functions like that of mammals to activate NF-κB, and it could be involved in host defense against invading pathogens.

β-glucan alleviates the immunosuppressive effects of oxytetracycline on the non-specific immune responses and resistance against Vibrio alginolyticus infection in Epinephelus fuscoguttatus × Epinephelus lanceolatus hybrids

This study was conducted to examine the combinatory effects of β-glucan and oxytetracycline (OTC) on hybrid giant tiger groupers (Epinephelus fuscoguttatus × Epinephelus lanceolatus). In vitro tests, OTC significantly reduced superoxide anion production and phagocytic activity in primary head kidney leukocytes. However, this suppressive effect was alleviated by co-treatment with β-glucan. Subsequently, feeding trials were performed to investigate the potential immunomodulatory effects of dietary β-glucan alone or in combination with OTC on groupers. A total of 210 healthy groupers (368.00 ± 51.03 g) were divided into six groups. Group 1 was the control group, group 2 (BG) received 5 g β-glucan per kg feed weight, groups 3-5 received 5 g/kg β-glucan in combination with 10, 30, or 50 mg OTC/kg fish weight/day (groups M1, M2, and M3, respectively), and group 6 (O) received 50 mg OTC/kg fish weight/day. Fish were sampled to determine the innate immunity parameters and residual OTC levels in the muscle tissue during a 28-day feeding regimen. Residual OTC levels were considerably higher in groups M3 and O compared with the other groups, and peaked on day 14. This was followed by a slight decrease on day 28, despite a continuous supply of OTC. Notably, fish fed with OTC alone had significantly decreased phagocytic rates and superoxide anion production observed in head kidney leukocytes, as well as poorer protection against Vibrio alginolyticus infection. These immunosuppressive effects were not observed in the fish fed with β-glucan in combination with a lower dose of OTC (group M2). Thus, these data suggest that the combination of dietary β-glucan and OTC exerts synergistic immunostimulating effects that protect groupers from bacterial infection.

Edwardsiella tarda induces enteritis in farmed seahorses (Hippocampus erectus): An experimental model and its evaluation

Bacterial enteritis is an important deadly threat to farmed seahorses. However, its pathogenesis is obscure because of the paucity of reproducible experimental intestinal inflammation models. Herein, a strain of Edwardsiella tarda YT1 from farmed seahorse Hippocampus erectus was isolated and identified by morphological, phylogenetic, and biochemical analysis, and confirmed as a pathogen of enteritis for the first time by challenge experiment. Two E. tarda concentrations (1 × 10⁵ and 1 × 10⁷ colony forming units [cfu] ml^-1) were confirmed suitable for an enteritis model by intraperitoneal injection. To develop and evaluate the experimental model, we challenged seahorses with E. tarda and found that (1) the infection inhibited body length increase, significantly decreased body weight (P < 0.05), and induced typical pathological features including anorexia, anal inflammation, and intestinal fluid retention; (2) 19 external (weight, height, anal inflammation, feeding status, and intestinal fluid retention), histological (goblet and inflammatory cell numbers and thickening of lamina propria and muscularis mucosae), and molecular (hepcidin, liver-expressed antimicrobial peptide, lysozyme, piscidin, interleukin [IL]-1β, IL-1β receptor, IL-2, IL-10, interferon1, tumor necrosis factor [TNF]-α, and toll-like receptor 5 [TLR5]) indicators were suitable for model evaluation, as they could sensitively respond and varied similarly throughout the experiment, indicating the high sensitivity of seahorses against pathogen invasion; (3) TLR5 may play an essential role in triggering host immune responses during E. tarda-induced chronic enteritis, and (4) the evaluating system could reflect the pattern and intensity of disease progression. Thus, we developed an experimental model and an evaluating system of bacterial enteritis in farmed seahorses, helping us to reveal the pathogenesis of bacterial enteritis, identify potential therapeutic drugs, and search suitable genetic markers for seahorse molecular breeding.

Immune gene expression in gilthead seabream (Sparus aurata) after Lymphocystis disease virus (LCDV-Sa) challenge resulting in asymptomatic infection

AIMS

To determine the immune gene expression response of gilthead seabream (Sparus aurata) that is experimentally infected with the lymphocystivirus LCDV-Sa.

METHODS AND RESULTS

Viral DNA and transcripts were detected by qPCR in all samples from fish injected with LCDV-Sa, demonstrating that the virus establish a systemic and asymptomatic infection. The expression of 23 immune-related genes was also analysed by RT-qPCR in the head kidney (HK) and intestine at several times post-infection (dpi). In HK, the expression of five type I interferon (IFN)-related genes (ifn, irf3, mx2, mx3 and isg15), il10 and ck10 was upregulated at 1-3 dpi, while genes related to the inflammation process (tnfα, il1ß, il6, casp1) were not differentially expressed or even downregulated. The expression profile in the intestine was different regarding type I INF-related genes. An upregulated c3 and ighm expression was observed in both HK and intestine at 3-8 dpi. Finally, the transcription of nccrp1 and mhcIIα was induced in HK, whereas tcrβ expression was downregulated in both organs.

CONCLUSIONS

LCDV-Sa seems to trigger an immune response in gilthead seabream characterized by a partial activation of type I IFN system and a lack of systemic inflammatory response which may be related to viral persistence.

SIGNIFICANCE AND IMPACT OF THE STUDY

The immune response observed in gilthead seabream infected by LCDV-Sa could be implicated in the establishment of an asymptomatic persistent infection.

MicroRNA-182-3p negatively regulates cytokines expression by targeting TLR5M in orange-spotted grouper, Epinephelus coioides

Toll-like receptors (TLRs) as essential pattern recognition receptors in innate immunity, can recognize pathogens and trigger immune response to eliminate invading pathogens. MicroRNAs regulates multiple biological processes by suppressing mRNA translation or resulting in mRNA degradation. MiR-182 has previously been implicated in DNA repair, disease and cancer aspects. The potential role of miR-182-3p in TLR signaling pathway against pathogens is unclear. In this study, we found that the expression of miR-182-3p was up-regulated after Vibrio parahaemolyticus flagellin stimulation in grouper spleen (GS) cells, and negatively correlated with the expression of orange-spotted grouper (Epinephelus coioides) TLR5M (EcTLR5M). Then we found that miR-182-3p could directly target EcTLR5M by using bioinformatic analysis and dual-luciferase reporter assay. Dual-luciferase reporter assay also showed that miR-182-3p down-regulated the wild-type EcTLR5M 3'UTR in luciferase activity rather than the mutant group in HEK 293T cells. We further verified the effect of miR-182-3p on the activation of Nuclear factor-κB (NF-κB) signaling pathway, and found that miR-182-3p inhibitors significantly augmented flagellin-induced NF-κB phosphorylation. Additionally, we also demonstrated that the increased expression of miR-182-3p significantly suppressed the flagellin-induced EcTLR5M, pro-inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) mRNA expression. And the endogenous miR-182-3p knockdown experiments reversely verified the regulatory effect of miR-182-3p. These results suggested that miR-182-3p post-transcriptionally controls EcTLR5M expression and thereby suppresses the expression of pro-inflammatory cytokines. This study is the first to demonstrate that miR-182-3p suppresses pro-inflammatory cytokines expression by regulating the TLR signaling pathway.