Molecular cloning and expression analysis of two lipopolysaccharide-induced TNF-α factors (LITAFs) from rock bream, Oplegnathus fasciatus

Lipopolysaccharide-induced TNFα factor (LITAF) promotes inflammatory responses and activates apoptosis in zebrafish Danio rerio

Lipopolysaccharide-induced TNFα factor (LITAF) is an important transcription factor which activates the transcription of TNFα and regulates cell apoptosis and inflammatory response. In the present study, a LITAF gene homologue was identified in zebrafish (Danio rerio) and was shown to be well conserved in the protein sequence, genomic organization and synteny with human LITAF. DrLITAF was constitutively expressed in tissues, with the highest expression detected in the gills. Its expression could be modulated by LPS, poly(I:C), and infection with Edwardsiella tarda, Aeromonus hydrophila and septicemia viremia of carp virus (SVCV). DrLITAF, when overexpressed, was shown to be located on the cellular membrane and nuclear membrane of HEK293T and ZF4 cells and was associated with the endoplasmic reticulum. Stimulation with LPS resulted in rapid translocation of DrLITAF into the nucleus. In addition, DrLITAF was able to induce cell apoptosis and the expression of caspase 3. The results demonstrate that DrLITAF is involved in the immune defence against bacterial and viral infection and plays a role in regulating inflammation and apoptosis.

Identification and Characterization of Lipopolysaccharide Induced TNFα Factor from Blunt Snout Bream, Megalobrama amblycephala

Lipopolysaccharide induced TNFα factor (LITAF) is an important transcription factor responsible for regulation of tumor necrosis factor α. In this study, a novel litaf gene (designated as Malitaf) was identified and characterized from blunt snout bream, Megalobrama amblycephala. The full-length cDNA of Malitaf was of 956 bp, encoding a polypeptide of 161 amino acids with high similarity to other known LITAFs. A phylogenetic tree also showed that Malitaf significantly clustered with those of other teleost, indicating that Malitaf was a new member of fish LITAF family. The putative maLITAF protein possessed a highly conserved LITAF domain with two CXXC motifs. The mRNA transcripts of Malitaf were detected in all examined tissues of healthy M. amblycephala, including kidney, head kidney, muscle, liver, spleen, gill, and heart, and with the highest expression in immune organs: spleen and head kidney. The expression level of Malitaf in spleen was rapidly up-regulated and peaked (1.29-fold, p < 0.05) at 2 h after lipopolysaccharide (LPS) stimulation. Followed the stimulation of Malitaf, Matnfα transcriptional level was also transiently induced to a high level (51.74-fold, p < 0.001) at 4 h after LPS stimulation. Taken together, we have identified a putative fish LITAF ortholog, which was a constitutive and inducible immune response gene involved in M. amblycephala innate immunity during the course of a pathogenic infection.

Immunohistochemical study of inducible nitric oxide synthase and tumour necrosis factor alpha response in turbot (Scophthalmus maximus) experimentally infected with Aeromonas salmonicida subsp. salmonicida

Aeromonas salmonicida subsp. salmonicida represents one of the major threats in aquaculture, especially in salmonid fish and turbot farming. In order to fight bacterial infections, fish have an immune system composed by innate and specific cellular and humoral elements analogous to those present in mammals. However, innate immunity plays a primordial role against bacterial infections in teleost fish. Among these non-specific mechanisms, the production of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) pathway and the tumour necrosis factor-alpha (TNFα) produced by mononuclear phagocytes, are two of the main immune effectors to eliminate bacterial pathogens. In this study, the distribution and kinetic of iNOS and TNFα-producing cells of kidney and spleen of turbot experimentally inoculated with A. salmonicida was assessed by immunohistochemistry. In control and challenged fish, individual iNOS(+) and TNFα(+) cells, showing a similar pattern of distribution, were detected. In challenged fish, the number of immunoreactive cells was significantly increased in the evaluated organs, as well as the melanomacrophage centres showed variable positivity for both antigens. These results indicate that A. salmonicida induced an immune response in challenged turbot, which involved the increase of the activity of iNOS and TNFα in the leukocytic population from kidney and spleen.

Characterization of immune-related genes in the yellow catfish Pelteobagrus fulvidraco in response to LPS challenge

Fish are considered an excellent model for studies in comparative immunology as they are a representative population of lower vertebrates linked to invertebrate evolution. To gain a better understanding of the immune response in fish, we constructed a subtractive cDNA library from the head kidney of lipopolysaccharide-stimulated yellow catfish (Pelteobagrus fulvidraco) using suppression subtractive hybridization (SSH). A total of 300 putative EST clones were identified which contained 95 genes, including 27 immune-related genes, 7 cytoskeleton-related genes, 3 genes involved in the cell cycle and apoptosis, 9 respiration and energy metabolism-related genes, 7 genes related to transport, 24 metabolism-related genes, 10 genes involved in stress responses, seven genes involved in regulation of transcription and translation and 59 unknown genes. Using real-time quantitative reverse transcription PCR, a subset of randomly selected genes involved in the immune response to lipopolysaccharide challenge were investigated to verify the reliability of the SSH data which identified 16 up-regulated genes. The genes identified in this study provide novel insight into the immune response in fish.

CsTNF1, a teleost tumor necrosis factor that promotes antibacterial and antiviral immune defense in a manner that depends on the conserved receptor binding site

Tumor necrosis factor (TNF) is one of the most important cytokines involved in inflammation, apoptosis, cell proliferation, and stimulation of the immune system. The TNF gene has been cloned in teleost fish; however, the in vivo function of fish TNF is essentially unknown. In this study, we report the identification of a TNF homologue, CsTNF1, from tongue sole (Cynoglossus semilaevis) and analysis of its expression and biological effect. CsTNF1 is composed of 242 amino acid residues and possesses a TNF domain and conserved receptor binding sites. Expression of CsTNF1 was detected in a wide range of tissues and up-regulated in a time-dependent manner by experimental challenge with bacterial and viral pathogens. Bacterial infection of peripheral blood leukocytes (PBL) caused extracellular secretion of CsTNF1. Purified recombinant CsTNF1 (rCsTNF1) was able to bind to PBL and stimulate the respiratory burst activity of PBL. In contrast, rCsTNF1M1 and rCsTNF1M2, the mutant CsTNF1 bearing substitutions at the receptor binding site, failed to activate PBL. Fish administered with rCsTNF1, but not with rCsTNF1M1 and rCsTNF1M2, exhibited enhanced expression of IL-1, IL-6, IL-8, IL-27, TLR9 and G3BP in a time-dependent manner and augmented resistance against bacterial and viral infection. These results provide the first evidence that the receptor binding sites are essential to a fish TNF, and that CsTNF1 is involved in the innate immune defense of fish against microbial pathogens.

First description of programmed cell death10 (PDCD10) in rock bream (Oplegnathus fasciatus): Potential relations to the regulation of apoptosis by several pathogens

In this study, we isolated and characterized programmed cell death10 (PDCD10), which is known to be related to apoptosis, from rock bream (Oplegnathus fasciatus). The full-length rock bream PDCD10 (RbPDCD10) cDNA (1459 bp) contains an open reading frame of 633 bp that encodes 210 amino acids. Furthermore, multiple alignments revealed that the six of the α-helix bundles were well conserved among the other PDCD10 sequences tested. RbPDCD10 was significantly expressed in the liver, RBC (red blood cell), gill, intestine, trunk kidney and spleen. RbPDCD10 gene expression was also examined in several tissues, including the kidney, spleen, liver, and gill, under bacterial and viral challenges. Generally, all of the examined tissues from the fish that were infected with Edwardsiella tarda and the red sea bream iridovirus (RSIV) exhibited significant up-regulations of RbPDCD10 expression compared to the controls. However, RbPDCD10 expression exhibited dramatic down-regulations in all of the examined tissues following injections of Streptococcus iniae, which is major bacterial pathogen that is responsible for mass mortality in rock bream. Our results revealed that rock bream PDCD10 may be involved in the apoptotic regulation of rock bream immune responses.

Coagulation factor II from rock bream (Oplegnathus fasciatus): First report on the molecular biological function and expression analysis in the teleost

The rapid haemostasis of fish prevents bleeding or infection that could be caused by physical properties of the aquatic environment. Additionally, the innate immune system is the first line of defence against infection and is responsible for the recognition of pathogen-associated molecular patterns, which are important for the activation of acquired immune responses. Coagulation factor II (CFII) is an important factor in the coagulation system and is involved in recognition and interaction with various bacterial and extracellular proteins. In this study, we identified and characterised the gene encoding CFII in rock bream (Oplegnathus fasciatus) (RbCFII) and analysed its expression in various tissues after a pathogen challenge. The full-length RbCFII cDNA (2079 bp) contained an open reading frame of 1854 bp encoding 617 amino acids. Alignment analysis revealed that a gamma-carboxyglutamic acid-rich domain, two kringle domains, and a trypsin-like serine protease domain of the deduced protein were well conserved. RbCFII was ubiquitously expressed in all tissues examined but, predominantly detected in the liver and skin. RbCFII expression was dramatically up-regulated in the kidney, spleen and liver after infection with Edwardsiella tarda, Streptococcus iniae, or red seabream iridovirus. The recombinant protein RbCFII (rRbCFII) produced using an Escherichia coli expression system was able to bind all examined bacteria. Interestingly, rRbCFII has agglutination activities towards E. coli and E. tarda, while no agglutination was shown toward Vibrio ordalii and S. iniae. These findings indicate that rRbCFII performs an immunological function in the immune response, and might be involved in innate immunity as well as blood coagulation.

First molecular characterisation and expression analysis of a teleost thioredoxin-interacting protein (TXNIP) gene from rock bream (Oplegnathus fasciatus)

Thioredoxin-interacting protein (TXNIP) is an important regulator of glucose metabolism that functions by inhibiting cellular glucose uptake. The full-length rock bream (Oplegnathus fasciatus) TXNIP (RbTXNIP) cDNA (2499 bp) contains an open reading frame of 1188 bp encoding 396 amino acids. Furthermore, multiple alignments showed that the arrestin domain was well conserved among the other TXNIP sequences tested. RbTXNIP was predicted to contain a PxxP and PPxY motif. Phylogenetic analysis indicated that RbTXNIP is most closely related to Fugu rubripes TXNIP. RbTXNIP was expressed significantly in the RBC, intestine, and spleen. RbTXNIP mRNA expression was also examined in several tissues under conditions of bacterial and viral challenge. Generally, all tissues examined from fish infected with Streptococcus iniae, Edwardsiella tarda and red sea bream iridovirus (RSIV) showed significant downregulation in RbTXNIP expression compared to controls. However, RbTXNIP expression showed significant upregulation in the spleen and kidney after injection of recombinant rock bream TRx1 protein. These findings provide a molecular foundation for functional studies and applications in teleosts.

Functional characterisation and expression analysis of recombinant serum amyloid P isoform 1 (RbSAP1) from rock bream (Oplegnathus fasciatus)

Lectins are carbohydrate-binding proteins that play important roles in the recognition and elimination of pathogens via the innate immune system. Pentraxins (PTX) are humoral lectins, which are multifunctional proteins in vertebrates. Pentraxins can be divided into two groups based on their primary structure: short (C-reactive protein and serum amyloid P [SAP]) and long pentraxins (PTX3 and neuronal pentraxins). Previously, SAP was shown to have Ca(2+)-dependent binding specificity for various ligands and to be a major acute phase protein. In this study, we identified and characterised the gene encoding SAP isoform 1 in rock bream (Oplegnathus fasciatus) (RbSAP1) and analysed its expression in various tissues after a pathogen challenge. An alignment analysis conducted based on the deduced amino acid sequence of RbSAP1 (1918 bp full-length cDNA with a 699 bp open reading frame encoding 232 amino acids) and SAPs and PTXs isolated from other organisms, revealed that the pentraxin domain and cysteine residues of the deduced protein are conserved. RbSAP1, which was ubiquitously expressed in all tissues examined, was predominantly detected in head kidney, trunk kidney, peripheral blood leukocytes, and gills. RbSAP1 expression was dramatically up-regulated in the kidney and liver after infection with Edwardsiella tarda, Streptococcus iniae, or red seabream iridovirus. Purified rRbSAP1 was able to bind Gram-negative bacteria, Gram-positive bacteria, and pathogen-associated molecular patterns. Interestingly, rRbSAP1 aggregated Gram-negative bacteria in the presence of Ca(2+). The anti-pathogen activity of rRbSAP1 suggests that SAP functions in innate immunity in the rock bream.