Characterization of MyD88 in Japanese eel, Anguilla japonica

Effects of TLR2/4 signalling pathway in western mosquitofish (Gambusia affinis) after Edwardsiella tarda infection

Gambusia affinis is regarded as an important animal model. Edwardsiella tarda is one of the most serious pathogens affecting aquaculture. The study explores the effects of TLR2/4 partial signalling pathway in G. affinis of E. tarda infection. The study collected the brain, liver, and intestine after E. tarda LD₅₀ and 0.85% NaCl solution challenge at different times (0 h, 3 h, 9 h, 18 h, 24 h, and 48 h). In these three tissues, the mRNA levels of PI3K, AKT3, IRAK4, TAK1, IKKβ, and IL-1β were substantially enhanced (p < .05) then returned to normal levels. Additionally, Rac1 and MyD88 in liver had different trend with other genes in brain and intestine, which displayed significantly indifference. The overexpression of IKKβ, and IL-1β indicated that E. tarda also caused immune reaction in intestine and liver, which would be consistent with delayed edwardsiellosis, which causes intestinal lesions and liver and kidney necrosis. Additionally, MyD88 plays a smaller role than IRAK4 and TAK1 in this signalling pathways. This study could enrich the understanding of the immune mechanism of the TLR2/4 signalling pathway in fish and might help to prescribe preventive measures against E. tarda to prevent infectious diseases in fish.

Molecular Characterization of MyD88 in Anodonta woodiana and Its Involvement in the Innate Immune Response to Bacterial Infection

Myeloid differentiation factor 88 (MyD88) is a key adapter molecule in Toll-like receptor signal transduction that triggers downstream immune cascades involved in the host defense response to exogenous pathogens. However, the function of MyD88s in mollusks, especially in freshwater shellfish, remains poorly understood. In this study, a novel freshwater shellfish MyD88 (denoted AwMyD88) was characterized from Anodonta woodiana. The present AwMyD88 protein consists of 474 amino acids and contains a conserved a typical death domain (DD) and a conservative Toll/IL-1R (TIR) domain with three typical boxes. Quantitative real-time PCR (qRT-PCR) analysis showed that AwMyD88 was broadly expressed in all the examined tissues, and the highest expression level was observed in hemocytes of A. woodiana. When challenged with Aeromonas hydrophila and lipopolysaccharide (LPS), the mRNA expression levels of AwMyD88 were significantly induced in hemocytes of A. woodiana in vivo and in vitro. In addition, in vivo injection experiments revealed that MyD88 signaling pathway genes showed strong responsiveness to A. hydrophila challenge, and their expression levels were significantly upregulated in hemocytes. Knockdown of AwMyD88 reduced the transcript levels of immune related transcription factors (AwNF-κB and AwAP-1) and effectors (AwTNF, AwLYZ, AwDefense and AwAIF) during A. hydrophila infection. Moreover, subcellular localization analysis indicated that AwMyD88 was mainly localized to the cytoplasm in HEK293T cells. Finally, luciferase reporter assays revealed that AwMyD88 associates with AwTLR to activate the NF-κB and AP-1 signaling pathways in HEK293T cells. These results suggested that AwMyD88 might be involved in the host defense response to bacterial challenge, providing new insight into the immune function of the MyD88 signaling pathway in freshwater shellfish.

Metabolites of Gut Microbiota and Possible Implication in Development of Diabetes Mellitus

Diabetes mellitus is characterized by having a disorder of glucose metabolism. The types of diabetes mellitus include type 1 diabetes mellitus, type 2 diabetes mellitus, gestational diabetes mellitus, and other specific types of diabetes mellitus. Many risk factors contribute to diabetes mellitus mainly including genetics, environment, obesity, and diet. In the recent years, gut microbiota has been shown to be linked to the development of diabetes. It has been reported that the gut microbiota composition of diabetic patients is different from that of healthy people. Although the mechanism behind the abnormality remains to be explored, most hypotheses focus on the inflammation response and leaky gut in relation to the changes in production of endotoxins and metabolites derived from the intestinal flora. Consequently, the above-mentioned abnormalities trigger a series of metabolic changes, gradually leading to development of hyperglycemia, insulin resistance, and diabetes. This review is (i) to summarize the differences in gut microbiota between diabetic patients and healthy people, (ii) to discuss the underlying mechanism(s) by which how lipopolysaccharide, diet, and metabolites of the gut microbiota affect diabetes, and (iii) to provide a new insight in the prevention and treatment of diabetes.

Aeromonas hydrophila infection induces Toll-like receptor 2 (tlr2) and associated downstream signaling in Indian catfish, Clarias magur (Hamilton, 1822)

Motile Aeromonas septicaemia (MAS), caused by Aeromonas hydrophila, is one of the most significant bacterial disease responsible for mortality in Indian catfish, Clarias magur, a potential aquaculture species in the Indian subcontinent. In fish, innate immunity elicited by pathogen recognition receptors (PRRs) plays an important role in providing protection against bacterial infection. Information on PRRs including Toll-like receptors (tlrs) and their response to bacterial pathogens remains unexplored in magur. Toll-like receptor 2 (tlr2), a phylogenetically conserved germ-line encoded PRR recognizes specific microbial structure and trigger MyD88-dependent signaling pathway to induce release of various cytokines responsible for innate immune response. In the present study, tlr2 gene of magur was characterized and downstream signaling was studied following challenge with A. hydrophila. The full-length cDNA of magur tlr2 (mtlr2) comprised of 3,066 bp with a single open reading frame of 2,373 bp encoding 790 amino acids having a theoretical pI value of 6.11 and molecular weight of 90 kDa. Structurally, it comprised of signal peptide (1–42aa), one leucine-rich repeat region (LRR) at N-terminal (LRR1-NT: 50–73 aa) and C-terminal (LRR-CT: 588–608 aa), twenty LRRs in between, one trans-membrane (Tm) domain (609–631aa) followed by cytoplasmic TIR domain (670–783aa). Phylogenetically, mtlr2 is closely related to pangasius and channel catfish. Highest basal expression of mtlr2, myd88 and il-1β in spleen, nf-kb in anterior kidney was observed. Lowest basal expression of mtlr2 in skin and myd88, nf-kb and il-1β in muscle was detected. Significant up-regulation of mtlr2 and downstream expression occurred at 3, 8, 24 h post infection to A. hydrophila in important immune organs such as liver, spleen, intestine and kidney. These findings highlight the vital role of tlr2 in eliciting innate immune defence against A. hydrophila infection.

Fish-specific TLR18 in Nile tilapia (Oreochromis niloticus) recruits MyD88 and TRIF to induce expression of effectors in NF-κB and IFN pathways in melanomacrophages

Toll-like receptors (TLRs) are evolutionarily conserved proteins of pattern recognition receptors (PRRs) and play a crucial role in innate immune systems recognition of conserved pathogen-related molecular samples (PAMPs). We identified and characterized TLR18 from Nile tilapia (Oreochromis niloticus), OnTLR18, to elucidate its role in tissue expression patterns, modulation of gene expression after microbial challenge and TLR ligands, subcellular localization in fish and human cells, and the possible effectors TLR18 induces in a melanomacrophage-like cell line (tilapia head kidney (THK) cells). OnTLR18 expression was detected in all tissues examined, with the highest levels in the intestine and the lowest in the liver. OnTLR18 transcript was up-regulated in immune-related organs after bacterial and polyinosinic-polycytidylic acid (poly I:C) challenges and in the THK cells after lipopolysaccharide (LPS) stimulation. In transfected THK and human embryonic kidney (HEK) 293 cells, OnTLR18 localizes in the intracellular compartment. OnMyD88 and OnTRIF, but not OnTIRAP, were co-immunoprecipitated with OnTLR18, suggesting that the former two molecules are recruited by OnTLR18 as adaptors. The constitutively active form of OnTLR18 induced the production of pro-inflammatory cytokines, type I interferon (IFN), and antimicrobial peptides such as tumor necrosis factor α, interferon (IFN) d2.13, tilapia piscidin (TP)2, TP3, TP4, and hepcidin in THK cells. Our results suggest that OnTLR18 plays an important role in innate immunity through initiating nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and IFN signaling pathways via OnMyD88 and OnTRIF and induces the production of various effectors in melanomacrophages.

Functional characterization of four TIR domain-containing adaptors, MyD88, TRIF, MAL, and SARM in mandarin fish Siniperca chuatsi

Toll/interleukin-1 receptor (TIR) domain-containing adaptors, serve as pivotal signal transduction molecules in Toll-like receptor (TLR) signalling pathway to mediate downstream signalling cascades. In this study, four TIR-domain containing adaptors, MyD88, TRIF, MAL and SARM, were identified in mandarin fish Siniperca chuatsi, and they all contain TIR domains, of which MyD88 and SARM had high sequence homology with their vertebrate homologues. The expression analysis at mRNA level indicated that these genes were ubiquitously distributed in different tissues, being high in immune- and mucosa-related tissues such as head-kidney and intestine. The transcripts of these adaptor genes were up-regulated by poly(I:C) and LPS stimulation in isolated head-kidney lymphocytes (HKLs) of mandarin fish. Fluorescence microscopy revealed that all these molecules were localized in cytoplasm, and further investigations showed that the over-expression of MyD88, TRIF and MAL activated the NF-κB, ISRE or type Ι IFN promoters and inhibited SVCV replication, whereas their antiviral effects were significantly impaired when co-transfected with SARM. It was also confirmed by co-immunoprecipitation (Co-IP) that SARM interacts separately with MyD88, TRIF and MAL, and MAL interacts with MyD88. However, the regulatory mechanisms of these adaptors involved in signalling pathways of different TLRs should be of interest for further research.

Molecular insight, expression profile and subcellular localization of two STAT family members, STAT1a and STAT2, from Japanese eel, Anguilla japonica

Signal transducer and activator of transcription 1 (STAT1) and STAT2 are critical components of type I and type II IFNs signaling. To date, seven STAT family proteins have been identified from mammals. However, the information on STAT genes in teleost fish is still limited. In the present study, two STAT family genes (STAT1a and STAT2) were identified from Japanese eel, Anguilla japonica and designated as AjSTAT1a and AjSTAT2. The open reading frames of AjSTAT1a and AjSTAT2 are 2244 bp and 2421 bp, encoding for polypeptides of 747 aa and 806 aa, respectively. Both AjSTAT1a and AjSTAT2 contain the conserved domains of STAT proteins. Phylogenetic analysis was performed based on the STATs protein sequences, and showed that AjSTAT1a and AjSTAT2 shared the closest relationship with Oncorhynchus mykiss. Quantitative real-time PCR analysis revealed that AjSTAT1a and AjSTAT2 were expressed in most examined tissues, with the highest expression both in blood. Significantly up-regulated transcripts of AjSTAT1a and AjSTAT2 were detected in response to poly I:C stimulation, and Edwardsiella tarda induced increase in the expression of AjSTAT1a and AjSTAT2 genes. Subcellular localization analysis showed that in both IFNγ-stimulated and unstimulated EPC cells AjSTAT1a and AjSTAT2 were mainly distributed in the cytoplasm, but few AjSTAT1a was distributed in the nucleus. All these results suggested that AjSTAT1a and AjSTAT2 may be critical for regulating the host innate immune defense against pathogens invasion.

Expression profile, subcellular localization and signaling pathway analysis of fish-specific TLR25 in Nile tilapia (Oreochromis niloticus)

The Nile tilapia (Oreochromis niloticus) is one of the major food fish species produced in tropical and subtropical regions. However, this industry has been facing significant challenges from microbial infections. Understanding how hosts initiate immune responses against invading microbes is the first requirement for addressing disease outbreak prevention and disease resistance. Toll-like receptors (TLRs) are a family of evolutionarily conserved proteins that can recognize pathogen-associated molecular patterns (PAMPs). They thus play an essential role in innate immunity. TLR25 is a newly identified fish-specific member of the TLR1 subfamily. In this study, we investigate the molecular and functional characteristics of O. niloticus TLR25 (OnTLR25) via tissue expression patterns, gene expression modulation after challenge with bacteria and TLR ligands, subcellular localization in human and fish cells, and the signaling pathways TLR25 may induce. Transcriptional levels of OnTLR25 are high in immune-related organs such as the spleen and head kidney, and are increased following bacterial challenges. In addition, we show that OnTLR25 preferentially localizes to the intracellular compartment in transfected tilapia head kidney (THK) cell line. Furthermore, overexpression of the truncated form of OnTLR25 in THK cell line induced the expression of proinflammatory cytokines, such as tumor necrosis factor α, interleukin (IL)-1β, IL-8, IL-12a, and interferon-d2.13. Combined, our results suggest that TLR25 is likely to play an important role in the antimicrobial responses of the innate immune system of Nile tilapia.

Characterization and expression analysis of rockfish (Sebastes schlegelii) myeloid differentiation factor-88 (SsMyD88) and evaluation of its ability to induce inflammatory cytokines through NF-ĸB

Innate immunity is characterized by nonspecific, prompt reactions toward armada of antigens. Animals funnel down a repertoire of immune stimulants to activate non-selective defense mechanisms rapidly. This study was conducted to characterize the rockfish (Sebastes schlegelii) adaptor protein MyD88 (SsMyD88), which interacts with both toll-like receptors and interleukin receptors. The tissue expression of unchallenged SsMyD88 was evaluated by quantitative real time PCR (qPCR). Fish were intraperitoneally injected with immune stimulants including poly I:C, lipopolysaccharides, and Streptococcus iniae. Then, the temporal expression of SsMyD88 was analyzed. Finally, the inflammatory gene expression and downstream promoter activation were analyzed. Strongest expressions were reported in the liver, gills and spleen in unchallenged conditions. All diverse immune stimulants were found to be capable of significantly altering SsMyD88 transcription during the challenge experiment. Evaluation of downstream promoter biases by SsMyD88 found a predominant activation of NF-ĸB transcription factors when compared with the AP-1, revealing significant and substantial upregulation of major inflammatory mediators such as IL-1-β, IL-6, iNOS, COX-2 and TNF-α. Fluorescent detection confirmed an intense production of NO and the predominant differentiation of macrophages into M1 lineage with the overexpression of SsMyD88 in vitro. These results further corroborate the role of SsMyD88 as a mediatory molecule that bridges distinct immune stimulants to induce drastic immune responses in fish.

Characterization, subcellular localization and function analysis of myeloid differentiation factor 88 (Pt-MyD88) in swimming crab, Portunus trituberculatus

Myeloid differentiation factor 88 (MyD88) is a universal and essential adaptor protein required for the Toll-like receptors (TLRs) pathway activation in invertebrates as well as in vertebrates. Herein, we characterized a MyD88 (Pt-MyD88) cDNA sequence in the swimming crab (Portunus trituberculatus). The Pt-MyD88 ORF is predicted to encode 469 peptides with an N-terminal death domain and a typical C-terminal TIR domain. Real-Time quantitative PCR analysis showed that the Pt-MyD88 transcriptions were constitutively expressed in hemocytes, gill, intestine, heart and muscle in normal crab. The expressions of Pt-MyD88 would be down-regulated by V. alginolyticus or LPS challenge, and be up-regulated by WSSV infection in hemocytes. Intracellular localization showed Pt-MyD88 was distributed mainly in the cytoplasm when it was over-expressed in human cell HEK293T or in Drosophila Schneider 2 (S2). Functionally, over-expression of Pt-MyD88 could either activate the NF-κB in HEK293T cells or activate the promoters of Drosophila antimicrobial peptide genes (AMPs) in S2 cell. In primary cultured hemocytes of swimming crab, after Pt-MyD88 was knocked-down by specific long double strand RNA, the expression of anti-lipopolysaccharide factor1 (ALF1), hyastatin3, crustin1 and crustin3 have been significantly inhibited, while the expression of other AMPs is normal compared to non-specific dsRNA treated cells.

Myeloid differentiation factor 88 (Myd88) is involved in the innate immunity of black carp (Mylopharyngodon piceus) defense against pathogen infection

Myeloid differentiation factor 88 (MyD88) is an important transduction protein in the Toll-like receptor signaling pathway. In this study, we identified the cDNA of the MpMyD88 gene in black carp. We found that MpMyD88 was widely distributed in the tissues tested and showed significant immune responses both in vitro and in vivo after stimulation with bacterial and pathogen-associated molecular patterns. After MpMyD88 overexpression/silencing, proinflame-matory cytokines (TNF-α, IFN-α, IL-6, and IL-8) also showed significant up-regulation/down-regulation. Moreover, we found that the antibacterial ability of cells over-expressing MpMyD88 was significantly stronger than that of control cells, while that of silenced MpMyD88 was significantly lower than that in control cells. Besides, we found that the overexpression of MpMyD88 significantly increased the activity of NF-κB. These results indicate that MpMyD88 plays an important role in the innate immune response.

Northeast Chinese lamprey (Lethenteron morii) MyD88: Identification, expression, and functional characterization

Myeloid differentiation factor 88 (MyD88) is a key adaptor of Toll-like receptors (TLR), an important pattern recognition receptor of the innate immune system. To study the origin and evolution of the vertebrate TLR signaling pathway in innate immune systems, we analyzed the biological characteristics and functions of the MyD88 gene in Northeast Chinese lamprey (Lethenteron morii) using PCR amplification, real-time PCR analysis, dual luciferase reporter gene assay, immunofluorescence assay, and other methods. Bioinformatics analysis showed that LmMyD88 has a modular structure consisting of Toll/IL-1R domain (TIR) and death domain (DD), which is typical of the MyD88 family. A phylogenetic tree showed that the homology of LmMyD88 was consistent with the phylogenetic status of lampreys. Tissue expression analysis indicated that the mRNA expression was expressed in some normal tissues of larval and adult L. morii. Real-time PCR analysis showed that the expression of LmMyD88 in tissues, such as gill and kidney, of the adult increased significantly after infection by Pseudomonas aeruginosa. Subcellular localization results showed that LmMyD88 was expressed in the nucleus, cytoplasm, and other parts. A dual luciferase reporter assay indicated that LmMyD88 activated nuclear factor kappa B downstream of the TLR signaling pathway. This study suggested that LmMyD88 might play an important role in the innate immune signal transduction process of L. morii.

Molecular characterization, expression patterns, and functional analysis of toll-interacting protein (Tollip) in Japanese eel Anguilla japonica

Toll-interacting protein (Tollip) is a key negative regulator of TLR-mediated innate immune responses. The structure and function of Tollip have been well identified in mammals, but the information about Tollip is still limited in teleost fishes. In the present study, the homologue of Tollip was cloned from Japanese eel. It contained an open reading frame encoding a polypeptide of 276 amino acids which shared high identities with other homologues from different species. Multiple alignment of the amino acid sequence showed that the AjTollip protein has the typical conserved domains including an N-terminal Target of Myb1 (Tom1) binding domain (TBD), a central conserved 2 (C2) domain, and a C-terminal coupling of ubiquitin to endoplasmic reticulum degradation (CUE) domain. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis revealed a broad expression for AjTollip in a wide range of tissues, with the highest expression in the liver, a relatively high expression in the spleen, kidney, gills, skin and intestine, and a low expression in the heart and muscle. The AjTollip expressions in the liver and kidney were significantly induced following injection with the bacterial mimic LPS, the viral mimic poly I:C, and Aeromonas hydrophila infection. In vitro, the AjTollip transcripts of Japanese eel liver cells were significantly enhanced by the treatment of LPS, poly I:C, CpG-DNA, and PGN or the stimulation of high concentration of Aeromonas hydrophila (1 × 10⁷ cfu/mL and 1 × 10⁸ cfu/mL). Subcellular localization study showed that AjTollip was mainly distributed in the cytoplasm in a condensed state. When AjTollip was co-transfected with AjMyD88 into HEK293 cells, the luciferase activities of NF-κB were significantly decreased compared with that of AjMyD88 single-transfection groups in natural state or under the stimulation of LPS and poly I:C. These results collectively suggested that AjTollip functions as a negative regulator of MyD88-dependent TLR signaling and plays an important role in fish defense against viral and bacterial infections.

Spotted knifejaw (Oplegnathus punctatus) MyD88: Intracellular localization, signal transduction function and immune responses to bacterial infection

Myeloid differentiation factor 88 (MyD88) links members of the toll-like receptor (TLR) and interleukin-1 receptor (IL-1R) superfamily to the downstream activation of NF-κB as a "bridge" molecular in response to exogenous pathogen, but the function in spotted knifejaw (Oplegnathus. punctatus), a commercial fish in China, is still unknown. We present a functional analysis of spotted knifejaw MyD88 (OppMyD88) with a typical death domain (DD) at the N-terminus and a conservative Toll/IL-1R (TIR) domain at the C-terminus and suggest that MyD88 is important for the activation of TLR-mediated NF-κB with the synergy between domains. Subcellular localization showed that OppMyD88 was distributed in the cytoplasm in a condensed form. Tissues expression profiling analysis showed that OppMyD88 ubiquitously expressed in all tested tissues with the highest expression in the liver, as determined by real-time PCR. The expression of OppMyD88 significantly upregulated in the liver, spleen, kidney and gills within 120 h post Vibrio anguillarum infection. Moreover, we further confirmed that over-expressed OppMyD88 could also induce apoptosis. These results indicate that OppMyD88 might possess important roles in defense against microbial infection and other biological processes in spotted knifejaw similar to those in mammals, which will deepen our understandings in innate immunity of spotted knifejaw.

Molecular cloning and expression analysis of MyD88 and TRAF6 in Qihe crucian carp Carassius auratus

Myeloid differentiation factor 88 (MyD88) and tumor necrosis factor receptor-associated factor 6 (TRAF6) are two critical signal transducers in toll-like receptor (TLR) pathway. In the present study, we identified and characterized the homologues of MyD88 and TRAF6 in Qihe crucian carp Carassius auratus, termed as CaMyD88 and CaTRAF6, respectively, and examined their roles during pathogenic infection. Full-length cDNA of CaMyD88 was 2463 bp, including a 191 bp 5'-untranslated region (UTR), a 1417 bp 3'-UTR, and an 855 bp open reading frame (ORF) encoding for a putative protein with 284 amino acids. Full-length cDNA of CaTRAF6 was identified to be 2555 bp, consisting of a 52 bp 5'-UTR, an 871 bp 3'-UTR, and a 1632 bp ORF encoding a protein of 543 amino acids. Deduced amino acid sequences of CaMyD88 and CaTRAF6 contained the typical domains (CaMyD88: death domain and TIR domain; CaTRAF6: one RING-type zinc finger domain, two TRAF-type zinc finger domains, one coiled-coil region, and one conserved C-terminal meprin and TRAF homology domain) as in other fish. Quantitative Real-Time PCR (qRT-PCR) analysis revealed that both CaMyD88 and CaTRAF6 were ubiquitously expressed throughout the development stages and appeared to be developmentally regulated. In addition, CaMyD88 and CaTRAF6 had a broadly distribution of expression in all examined eleven tissues of healthy fish, although the transcript levels varied among the different tissues. Moreover, it was found that mRNA expressions of CaMyD88 and CaTRAF6 were generally up-regulated after stimulation by polyI:C, flagellin, and Aeromonas hydrophila in spite of the down-regulation appeared at some time points or tissues. These results indicated that CaMyD88 and CaTRAF6 play the critical roles in the immune defense of Qihe crucian carp against pathogenic invasion. The present findings will provide the valuable information for understanding the innate immune responses of Qihe crucian carp and contribute to develop the preventive way against pathogens.