Two NF-κB inhibitor-alpha (IκBα) genes from rock bream (Oplegnathus fasciatus): molecular characterization, genomic organization and mRNA expression analysis after immune stimulation

Lost and Found: The Family of NF-κB Inhibitors Is Larger than Assumed in Salmonid Fish

NF-κB signalling is largely controlled by the family of 'inhibitors of NF-κB' (IκB). The relevant databases indicate that the genome of rainbow trout contains multiple gene copies coding for iκbα (nfkbia), iκbε (nfkbie), iκbδ (nkfbid), iκbζ (nfkbiz), and bcl3, but it lacks iκbβ (nfkbib) and iκbη (ankrd42). Strikingly, three nfkbia paralogs are apparently present in salmonid fish, two of which share a high sequence identity, while the third putative nfkbia gene is significantly less like its two paralogs. This particular nfkbia gene product, iκbα, clusters with the human IκBβ in a phylogenetic analysis, while the other two iκbα proteins from trout associate with their human IκBα counterpart. The transcript concentrations were significantly higher for the structurally more closely related nfkbia paralogs than for the structurally less similar paralog, suggesting that iκbβ probably has not been lost from the salmonid genomes but has been incorrectly designated as iκbα. In the present study, two gene variants coding for iκbα (nfkbia) and iκbε (nfkbie) were prominently expressed in the immune tissues and, particularly, in a cell fraction enriched with granulocytes, monocytes/macrophages, and dendritic cells from the head kidney of rainbow trout. Stimulation of salmonid CHSE-214 cells with zymosan significantly upregulated the iκbα-encoding gene while elevating the copy numbers of the inflammatory markers interleukin-1-beta and interleukin-8. Overexpression of iκbα and iκbε in CHSE-214 cells dose-dependently quenched both the basal and stimulated activity of an NF-κB promoter suggesting their involvement in immune-regulatory processes. This study provides the first functional data on iκbε-versus the well-researched iκbα factor-in a non-mammalian model species.

PurA facilitates Edwardsiella piscicida to escape NF-κB signaling activation

The host NF-κB signaling pathway plays critical role in defensing against bacterial infection. However, bacteria also evolve strategies to escape from host clearance. Edwardsiella piscicida is a threatening pathogen in aquaculture, while the molecular mechanism of E. piscicida in inhibiting NF-κB signaling remains largely unknown. Herein, using E. piscicida transposon insertion mutant library combined with a NF-κB luciferase reporter system, we identified forty-six genes of E. piscicida, which were involved in inhibiting the NF-κB signaling activation in vitro. Moreover, we further explored the top 10 significantly changed mutants through zebrafish larvae infection model and validated that six genes were involved in inhibiting NF-κB activation in vivo. Specifically, we identified the adenylosuccinate synthase mutated strain (ΔpurA) infection exhibited a robust activation of NF-κB signaling, along with higher expression of cxcl8a and cxcl8b to mediate the recruitment of neutrophils in vivo. Taken together, these results identified the key factors of E. piscicida in inhibiting NF-κB activation, which will contribute to better understanding the pathogenesis of this important pathogen.

Identification of IκBα in Japanese eel Anguilla japonica that impairs the IKKα-dependent activation of NF-κB, AP1, and type I IFN signaling pathways

As a member of inhibitory κB family (IκB) family, IκBα is best-characterized and plays a central negative feedback regulator of NF-κB pathway in mammals, but the information about IκBα in the regulation of immune responses is still limited in teleost fishes. In the present study, the full-length cDNA of an IκBα homologue, AjIκBα, was cloned by 5' and 3' SMART RACE from Japanese eel, and its characteristics of expression in response to various PAMPs and A. hydrophila infection were investigated both in vivo and in vitro using quantitative real-time polymerase chain reaction (qRT-PCR). In addition, the subcellular localization of AjIκBα GFP fusion protein and the induction of AjIκBα alone or co-expression with Japanese eel IKKα (AjIKKα) in the activation of NF-κB, type I IFN and AP1 performed using Dual-Glo luciferase assay system were also detected. Sequence comparison analysis revealed that AjIκBα has typical conserved domains, including the N-terminal conserved degradation motif, the ankyrin repeats, and the C-terminal PEST domain. The predicted three-dimensional structure of AjIκBα is similar to that of human IκBα. qRT-PCR analysis revealed a broad expression for AjIκBα in a wide range of tissues, with the highest expression in the spleen, followed by intestine, liver, gills, skin, kidney, and with a lower expression in the heart and muscle. The AjIκBα expressions in the kidney, spleen, and especially in liver were significantly induced following injection with Gram-negative bacterial component LPS, the viral mimic poly I:C and Aeromonas hydrophila infection. In vitro, the AjIκBα transcripts of Japanese eel liver cells were significantly enhanced by the treatment of LPS, poly I:C, or the stimulation of different concentration of Aeromonas hydrophil. Luciferase assays demonstrated that not only could the AjIκBα expression significantly decrease the activation of NF-κB, AP1, and IFNβ-responsive promoters in HEK293 cells and EPC cells, but also robustly inhibited the activity of these three promoters in HEK293 cells or NF-κB and AP1-responsive promoters in EPC cells induced by AjIKKα. Additionally, subcellular localization studies showed that AjIκBα was evenly distributed in the cytoplasm and nucleus both in HEK293 cells and EPC cells under natural state. AjIκBα was found to aggregate into spots in the cytoplasm and nucleus stimulated by LPS or mostly aggregate into nucleus with the treatment of poly I:C in HEK293 cells, whereas the elevated expression of AjIκBα was observed in the cytoplasm of EPC cells upon the stimulation of poly I:C. These results collectively indicated that AjIκBα function as an important negative regulation in innate immunity of host against antibacterial and antiviral infection likely via the inhibition of the activation of NF-κB, AP1, and type I IFN signaling pathways.

Comparative Characterization of Two cxcl8 Homologs in Oplegnathus fasciatus: Genomic, Transcriptional and Functional Analyses

CXCL8 (interleukin-8, IL-8) is a CXC family chemokine that recruits specific target cells and mediates inflammation and wound healing. This study reports the identification and characterization of two cxcl8 homologs from rock bream, Oplegnathus fasciatus. Investigation of molecular signature, homology, phylogeny, and gene structure suggested that they belonged to lineages 1 (L1) and 3 (L3), and designated Ofcxcl8-L1 and Ofcxcl8-L3. While Ofcxcl8-L1 and Ofcxcl8-L3 revealed quadripartite and tripartite organization, in place of the mammalian ELR (Glu-Leu-Arg) motif, their peptides harbored EMH (Glu-Met-His) and NSH (Asn-Ser-His) motifs, respectively. Transcripts of Ofcxcl8s were constitutively detected by Quantitative Real-Time PCR (qPCR) in 11 tissues examined, however, at different levels. Ofcxcl8-L1 transcript robustly responded to treatments with stimulants, such as flagellin, concanavalin A, lipopolysaccharide, and poly(I:C), and pathogens, including Edwardsiella tarda, Streptococcus iniae, and rock bream iridovirus, when compared with Ofcxcl8-L3 mRNA. The differences in the putative promoter features may partly explain the differential transcriptional modulation of Ofcxcl8s. Purified recombinant OfCXCL8 (rOfCXCL8) proteins were used in in vitro chemotaxis and proliferation assays. Despite the lack of ELR motif, both rOfCXCL8s exhibited leukocyte chemotactic and proliferative functions, where the potency of rOfCXCL8-L1 was robust and significant compared to that of rOfCXCL8-L3. The results, taken together, are indicative of the crucial importance of Ofcxcl8s in inflammatory responses and immunoregulatory roles in rock bream immunity.

Tryptanthrin promotes keratinocyte and fibroblast responses in vitro after infection with Trichophyton benhamiae DSM6916

Exceedingly virulent pathogens and growing antimicrobial resistances require new therapeutic approaches. The zoophilic dermatophyte Trichophyton benhamiae causes highly inflammatory, cutaneous fungal infections. Recently, it could be shown that the plant-derived alkaloid tryptanthrin (TRP) exhibits strong anti-microbial activities against yeasts and dermatophytes. The aim of this study was to analyse the bioactivity of TRP under infectious conditions using an in-vitro dermatophytosis model employing fibroblasts and keratinocytes infected with T. benhamiae DSM6916. Analyses comprised determination of cell viability, effects on the innate immune response including expression and secretion of pro-inflammatory cytokines/chemokines as well as expression of various antimicrobial peptides (AMP), toll-like receptor (TLR) 2 and proliferation marker MKI67. T. benhamiae caused severe inflammation in the cutaneous cell models. TRP almost fully prevented T. benhamiae-derived damage of dermal fibroblasts and substantially reduced it in epidermal keratinocytes. A distinct down-regulation of the expression and secretion of pro-inflammatory cytokines was observed. Further, TRP promoted AMP expression, especially of HBD2 and HBD3, in keratinocytes even without fungal presence. This study provides crucial evidence that TRP is not only a strong antifungal agent but also potentially modulates the innate immune response. This makes it interesting as a natural antimycotic drug for adjuvant treatment and prevention of fungal re-infection.

IκBα phosphorylation and associated NF-κB activation are essential events in lymphocyte activation, proliferation, and anti-bacterial adaptive immune response of Nile tilapia

Inhibitory protein IκBα plays a crucial role in the inflammatory process and immune response by regulating the activity of transcription factor NF-κB. In teleost, great progress has been achieved regarding NF-κB signaling for innate immunity, but whether this pathway modulates adaptive immunity, and how, remains largely unclear. In this study, after characterizing the sequence, structure, and phylogeny of Nile tilapia Oreochromis niloticus IκBα (defined as On-IκBα), we investigated the association between IκBα-regulated NF-κB activation and the lymphocyte-mediated adaptive immune response in Nile tilapia. We found that On-IκBα was evolutionarily conserved, and its mRNA was expressed widely in various tissues, with most abundance in the trunk kidney. mRNA expression of On-IκBα was significantly upregulated in spleen at both innate and adaptive immune stages after Aeromonas hydrophila infection. Moreover, phosphorylation of On-IκBα and the downstream On-NF-κB p65 was obviously elevated in spleen leukocytes at 3, 5, or 8 days after A. hydrophila infection, indicating the activation of NF-κB signaling. Correlating with the augmented protein phosphorylation, leukocyte proliferation was enhanced during the same immune stage, suggesting the potential association of IκBα and IκBα-regulated NF-κB signaling in the primary adaptive immune response. Although lymphocyte activation by the T cell-specific mitogen PHA did not alter On-IκBα mRNA expression significantly, lymphocyte activation by the agonist PMA obviously elevated On-IκBα and OnNF-κB p65 phosphorylation in spleen leukocytes. Together, the results suggest that IκBα phosphorylation and its regulated NF-κB activation are essential events associated with lymphocyte activation, proliferation, and anti-bacterial adaptive immune response in Nile tilapia. Our study aids to understand the regulatory mechanism of adaptive immunity in teleost.

Immunomodulatory Effects of Dietary Seaweeds in LPS Challenged Atlantic Salmon Salmo salar as Determined by Deep RNA Sequencing of the Head Kidney Transcriptome

Seaweeds may represent immuno-stimulants that could be used as health-promoting fish feed components. This study was performed to gain insights into the immunomodulatory effects of dietary seaweeds in Atlantic salmon. Specifically tested were 10% inclusion levels of Laminaria digitata (SW1) and a commercial blend of seaweeds (Oceanfeed^®) (SW2) against a fishmeal based control diet (FMC). Differences between groups were assessed in growth, feed conversion ratio and blood parameters hematocrit and hemoglobin. After a LPS challenge of fish representing each of the three groups, RNAseq was performed on the head kidney as major immune organ to determine transcriptomic differences in response to the immune activation. Atlantic salmon fed with dietary seaweeds did not show major differences in performance in comparison with fishmeal fed fish. RNAseq resulted in ∼154 million reads which were mapped against a NCBI Salmo salar reference and against a de novo assembled S. salar reference for analyses of expression of immune genes and ontology of immune processes among the 87,600 cDNA contigs. The dietary seaweeds provoked a more efficient immune response which involved more efficient identification of the infection site, and processing and presentation of antigens. More specifically, chemotaxis and the chemokine-mediated signaling were improved and therewith the defense response to Gram-positive bacterium reduced. Specific Laminaria digitata effects included reduction of the interferon-gamma-mediated signaling. Highly upregulated and specific for this diet was the expression of major histocompatibility complex class I-related gene protein. The commercial blend of seaweeds caused more differential expression than Laminaria digitata and improved immune processes such as receptor-mediated endocytosis and cell adhesion, and increased the expression of genes involved in response to lipopolysaccharide and inflammatory response. Particularly, expression of many important immune receptors was up-regulated illustrating increased responsiveness. NF-kappa-B inhibitor alpha is an important gene that marked the difference between both seaweed diets as Laminaria digitata inhibits the expression for this cytokine while the blend of seaweeds stimulates it. It can be concluded that the inclusion of seaweeds such as Laminaria digitata can have important modulatory effects on the immune capacity of Atlantic salmon resulting in a more efficient immune response.

Under control: The innate immunity of fish from the inhibitors' perspective

The innate immune response involves a concerted network of induced gene products, preformed immune effectors, biochemical signalling cascades and specialised cells. However, the multifaceted activation of these defensive measures can derail or overshoot and, if left unchecked, overwhelm the host. A plenty of regulatory devices therefore mediate the fragile equilibrium between pathogen defence and pathophysiological manifestations. Over the past decade in particular, an almost complete set of teleostean sequences orthologous to mammalian immunoregulatory factors has been identified in various fish species, which prove the remarkable conservation of innate immune-control concepts among vertebrates. This review will present the current knowledge on more than 50 teleostean regulatory factors (plus additional fish-specific paralogs) that are of paramount importance for controlling the clotting cascade, the complement system, pattern-recognition pathways and cytokine-signalling networks. A special focus lies on those immunoregulatory features that have emerged as potential biomarker genes in transcriptome-wide research studies. Moreover, we report on the latest progress in elucidating control elements that act directly with immune-gene-encoding nucleic acids, such as transcription factors, hormone receptors and micro- and long noncoding RNAs. Investigations into the function of teleostean inhibitory factors are still mainly based on gene-expression profiling or overexpression studies. However, in support of structural and in-vitro analyses, evidence from in-vivo trials is also available and revealed many biochemical details on piscine immune regulation. The presence of multiple gene copies in fish adds a degree of complexity, as it is so far hardly understood if they might play distinct roles during inflammation. The present review addresses this and other open questions that should be tackled by fish immunologists in future.

Tryptanthrin Protects Mice against Dextran Sulfate Sodium-Induced Colitis through Inhibition of TNF-α/NF-κB and IL-6/STAT3 Pathways

Inflammatory bowel disease (IBD) is a notable health problem and may considerably affect the quality of human life. Previously, the protective roles of tryptanthrin (TRYP) against dextran sulfate sodium (DSS) induced colitis has been proved, but the concrete mechanism remained elusive. It has been suggested that TRYP could diminish the weight loss and improve the health conditions of mice with DSS induced colitis. Hematoxylin and eosin staining revealed that TRYP could improve the histopathological structure of the colon tissue. Two signaling pathways (TNF-α/NF-κBp65 and IL-6/STAT3) were investigated using immunochemistry and western blot. The detected concentrations of the two cytokines TNF-α and IL-6 showed that their levels decreased after TRYP treatment of the colitis. The protein expression level of NF-κBp65 in cytoplasm increased after TRYP treatment of the induced colitis. However, the protein level of NF-κBp65 in the nucleus decreased after administration of TRYP. The expression level of IκBα, the inhibitory protein of NF-κBp65, was tested and the results suggested that TRYP could inhibit the degradation of IκBα. The phosphorylation level of STAT3 was inhibited by TRYP and the expression level of STAT3 and p-STAT3 decreased after administration of TRYP. We conclude that TRYP improves the health condition of mice with DSS induced colitis by regulating the TNF-α/NF-κBp65 and IL-6/STAT3 signaling pathways via inhibiting the degradation of IκBα and the phosphorylation of STAT3.

Identification of a gene encoding a membrane-anchored toll-like receptor 5 (TLR5M) in Oplegnathus fasciatus that responds to flagellin challenge and activates NF-κB

Toll-like receptor 5 (TLR5) recognizes bacterial flagellin and induces the downstream signaling through the myeloid differentiation primary response gene 88 (MyD88) protein to produce proinflammatory cytokines. In this study, we describe a TLR5 membrane form (OfTLR5M) and its adaptor protein MyD88 (OfMyD88) in rock bream, Oplegnathus fasciatus. Both Oftlr5m (6.7 kb) and Ofmyd88 (3.7 kb) genes displayed a quinquepartite structure with five exons and four introns. Protein structure of OfTLR5M revealed the conventional architecture of TLRs featured by an extracellular domain with 22 leucine rich repeats (LRR), a transmembrane domain and an endodomain with TIR motif. Primary OfTLR5M sequence shared a higher homology with teleost TLR5M. The evolutional analysis confirmed that TLR5 identified in the current study is a membrane receptor and the data further suggested the co-evolution of the membrane-anchored and soluble forms of TLR5 in teleosts. Inter-lineage comparison of gene structures in vertebrates indicated that the tlr5m gene has evolved with extensive rearrangement; whereas, the myd88 gene has maintained a stable structure throughout the evolution. Inspection of 5' flanking region of these genes disclosed the presence of several transcription factor binding sites including NF-κB. Quantitative real-time PCR (qPCR) detected Oftlr5m mRNA in eleven tissues with the highest abundance in liver. In vivo flagellin administration strongly induced the transcripts of both Oftlr5m and Ofmyd88 in gills and head kidney tissues suggesting their ligand-mediated upregulation. In a luciferase assay, HEK293T cells transiently transfected with Oftlr5m and Ofmyd88 demonstrated a higher NF-κB activity than the mock control, and the luciferase activity was intensified when cells were stimulated with flagellin. Collectively, our study represents the genomic, evolutional, expressional and functional insights into a receptor and adaptor molecules of teleost origin that are involved in flagellin sensing.

Identification, origin and evidence for retained functionality of two IκBα paralogs in Megalobrama amblycephala

IκBα plays an essential role in the innate immune response in mammals. We found two functional IκBα paralogs, originating from the teleost-specific genome duplication, in Megalobrama amblycephala: maIκBαa and maIκBαb. Their size (936/933 bp) and structure are highly analogous to known orthologs. mRNA expression was analysed by qPCR in spleen, liver, kidney, intestine and gills. Apart from maIκBαb in gills (<0.001-fold), both paralogs were constitutively expressed in all tissues. Differential expression was observed in gills (high for maIκBαa) and liver: maIκBαa - 2nd lowest (0.47), maIκBαb - 2nd highest (4.25). Both paralogs (mRNA) were upregulated in liver, spleen and kidney after a bacterial (Aeromonas hydrophila) challenge. In spleen, expressions peaked at 12 h post injection (hpi) (maIκBαa = 14.3-fold, maIκBαb = 21.3-fold), but only maIκBαb was highly upregulated at 4, 24 and 120 hpi. In liver, both were upregulated early, but maIκBαa peaked at 4 hpi (15.2-fold) and maIκBαb at 12 hpi (9.8-fold). In kidney, maIκBαa was highly upregulated only at 12 hpi (8.7-fold), and maIκBαb at 4 (peak - 8.2-fold), 12 and 24 hpi. The results indicate that both IκBα paralogs have retained their functionality, that they are structurally and functionally homologous to IκBα orthologs described in other animal species, and that they both play an important role in the innate immune system of M. amblycephala.

Structurally diverse genes encode Tlr2 in rainbow trout: The conserved receptor cannot be stimulated by classical ligands to activate NF-κB in vitro

The mammalian toll-like receptor 2 (TLR2) is a dominant receptor for the recognition of Gram-positive bacteria. Its structure and functional properties were unknown in salmonid fish. In RT-PCR and RACE experiments, we obtained the full-length cDNA sequence encoding Tlr2 from rainbow trout (Oncorhynchus mykiss) as well as a copy of an unspliced nonsense message from a highly segmented gene. The primary structure of the encoded receptor complies with the domain structure and ligand-binding sites known from mammals and other fish species and sorts well into the evolutionary tree of teleostean Tlr2s. We retrieved a gene version encoding the receptor on a single exon (tlr2a) and also a partial sequence of a second gene variant being segmented into multiple exons (tlr2b). Surprisingly, the abundances of both transcript variants accounted only for ∼10% of all Tlr2-encoding transcripts in various tissues and cell types of healthy fish. This suggests the expression of several distinct tlr2 gene variants in rainbow trout. We expressed tlr2a in HEK-293 cells, but were unable to demonstrate its functionality through NF-κB activation. Neither synthetic lipopeptides known to stimulate mammalian TLR2 nor different bacterial challenges induced OmTLR2-mediated NF-κB activation, not in HEK-293 or in salmon CHSE-214 cells. Positive demonstration of TLR2-MYD88 interaction excluded that its functional impairment caused the failure of NF-κB activation. We discuss impaired heterodimerization with a necessary Tlr partner as one from among several alternatives to explain the dysfunction of Tlr2a in the interspecies reconstitution system of TLR signaling.

Molecular, genomic, and expressional delineation of a piscidin from rock bream (Oplegnathus fasciatus) with evidence for the potent antimicrobial activities of Of-Pis1 peptide

The piscidin family comprises a group of antimicrobial peptides (AMPs) that are vital components of teleost innate immunity. Piscidins protect the host from pathogens, through multifaceted roles as immunomodulators and anti-infective peptides. The present study reports the identification, and characterization of a putative piscidin homolog, Of-Pis1, from rock bream (Oplegnathus fasciatus). A combined genomic and transcriptomic approach revealed that the Of-Pis1 gene comprises 1396 nucleotides (nt), four exons, and three introns. The cDNA with the 213 nt open reading frame encoded a 70-amino acid preprotein consisting of a signal peptide, a mature peptide, and a prodomain. Predicted mature Of-Pis1 was assumed to be a membrane-active AMP, based on the prediction of an amphipathic α-helical conformation with a net charge of +4. In addition, Of-Pis1 demonstrated significant similarities with other piscidin family members in terms of gene structure, sequence homology, and evolutionary relationship. Examination by quantitative real-time PCR (qPCR) of basal transcription of Of-Pis1 in the tissues of naïve rock bream, revealed predominant transcript levels in the gills, followed by the spleen, intestine, skin, and head kidney. In gill tissues, the temporally induced mRNA expression of Of-Pis1, upon in vivo injection trials with lipopolysaccharide (LPS); polyinosinic:polycytidylic acid (poly I:C); and pathogens, including Edwardsiella tarda, Streptococcus iniae, and rock bream iridovirus (RBIV), was weak. In contrast, in vivo flagellin administration led to a robust upregulation of Of-Pis1 in different tissues. Antimicrobial potency was determined by employing recombinant (rOf-Pis1), and synthetic (pOf-Pis1) peptides, in in vitro assays. Recombinant overexpression inhibited the growth of bacteria expressing the rOf-Pis1 protein in a growth delay assay. The broad antimicrobial spectrum of pOf-Pis1 was evidenced by its potent activity against an array of microbes, including bacteria, fungi, and parasitic species. In addition, pOf-Pis1 showed no significant hemolytic toxicity against human erythrocytes. Collectively, the data presented in the current study improve our understanding of the piscidin AMP family, and the contribution of Of-Pis1 to the rock bream immunity.

Gene structure, molecular characterization and transcriptional expression of two p38 isoforms (MAPK11 and MAPK14) from rock bream (Oplegnathus fasciatus)

The p38 kinases are one of the four subgroups of mitogen-activated protein kinase (MAPK) superfamily which are involved in the innate immunity. The p38 subfamily that includes four members namely p38α (MAPK14), p38β (MAPK11), p38γ (MAPK12) and p38δ (MAPK13), regulates the activation of several transcription factors. In this study, a p38β (OfMAPK11) homolog and a p38α (OfMAPK14) homolog of Oplegnathus fasciatus were identified at genomic level. Results clearly showed that both MAPK11 and MAPK14 are well-conserved at both genomic structural- and amino acid (aa)-levels. Genomic sequences of OfMAPK11 (∼ 15.6 kb) and OfMAPK14 (∼ 13.4 kb) had 12 exons. A comparison of exon-intron structural arrangement of these genes from different vertebrate lineages indicated that all the exon lengths are highly conserved, except their terminal exons. Full-length cDNAs of OfMAPK11 (3957 bp) and OfMAPK14 (2504 bp) encoded corresponding proteins of 361 aa and 360 aa, respectively. Both OfMAPK proteins harbored a Ser/Thr protein kinases catalytic domain (S_TKc domain) which includes an activation loop with a dual phosphorylation site (TGY motif) and several specific-binding sites for ATP and substrates. Molecular modeling of the activation loop and substrate binding sites of rock bream MAPKs revealed the conservation of crucial residues and their orientation in 3D space. Transcripts of OfMAPKs were ubiquitously detected in eleven tissues examined, however at different levels. The modulation of OfMAPKs' transcription upon pathogen-associated molecular patterns (PAMPs: flagellin, lipopolysaccharide and poly I:C) and pathogens (Edwardsiella tarda, Streptococcus iniae and rock bream iridovirus) was investigated. Among the seven examined tissues, the flagellin-challenge upregulated the mRNA level of both OfMAPKs in the head kidney. Meanwhile, modulation of OfMAPK mRNA expression in the liver upon other immune-challenges varied in a time-dependent manner. Collectively, these results suggest that OfMAPKs are true members of p38 subfamily, which might be induced by different immune stimuli.

ApoM Suppresses TNF-α-Induced Expression of ICAM-1 and VCAM-1 Through Inhibiting the Activity of NF-κB

To explore the anti-inflammatory effect of apolipoprotein M (apoM) on regulation of tumor necrosis factor-α (TNF-α)-induced expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) and further investigate the molecular mechanism of apoM in this process. We found that TNF-α could decrease expression of apoM and inhibitor of NF-κB-α (IκBα) in HepG2 cells. Overexpression of apoM caused a significant decrease of ICAM-1 and VCAM-1 expression, while it caused a significant increase of IκBα expression in HepG2 cells. Furthermore, the treatment with TNF-α could increase ICAM-1 and VCAM-1 expression, decrease IκBα protein expression, and increase nuclear factor-κB (NF-κB) activity, and these effects were markedly enhanced by small interfering RNA (siRNA)-mediated silencing of apoM in HepG2 cells. Our findings demonstrated that apoM suppressed TNF-α-induced expression of ICAM-1 and VCAM-1 through inhibiting the activity of NF-κB.