Molecular identification and expression analysis of a natural killer cell enhancing factor (NKEF) from rock bream Oplegnathus fasciatus and the biological activity of its recombinant protein

Molecular characterization and functional analysis of peroxiredoxin 1 (Prx1) from roughskin sculpin (Trachidermus fasciatus)

Peroxiredoxin1(Prx1), also known as natural killer enhancing factor A (NKEF-A), is a crucial antioxidant involving in various cellular activities and immune response against bacterial and viral infection in fish. In the present study, a full-length Prx1 cDNA sequence (TfPrx1) was firstly cloned from roughskin sculpin (Trachidermus fasciatus), which was composed of 1044 bp nucleotides encoding a peptide of 199 amino acids with a molecular weight of 22.35 kDa and a theoretical pI of 6.42, respectively. The predicted peptide was a typical 2-cys Prx containing two conserved characteristic motifs 43FYPLDFTFVCPTEI56 and 170GEVCPA175 with the two conserved peroxidatic and resolving cysteine residuals forming disulfide bond. Quantitative real-time PCR analysis showed that TfPrx1 was ubiquitously expressed in all tested tissues with the highest expression in the intestine. It could be significantly induced following LPS injection and heavy metal exposure. Recombinant TfPrx1 (rTfPrx1) displayed insulin disulfide reduction and ROS-scavenging activity in a concentration-dependent manner, and further exhibited DNA and cytoprotective effects under oxidative stress. These results suggested that TfPrx1 protein may play an important role in fish immune protection from oxidative damage.

Fish natural killer enhancing factor-A (NKEF-A) enhance cytotoxicity of nonspecific cytotoxic cells against bacterial infection

Natural killer enhancing factor (NKEF)-A/B is a member of Peroxiredoxin (Prxs) family, which is named for the function of enhancing NK cells activity. NKEF also plays essential roles in multiple physiology/pathology processes including inflammation regulation, cancer development and redox reactions. However, the regulatory effects of fish NKEF on immune cells remain largely unknown. In this study, the full-length cDNA of NKEF-A (Accession No. MK584553, designated as On-NKEF-A) was identified from Nile tilapia (Oreochromis niloticus). On-NKEF-A encoded a 198 amino acid peptide with molecular mass of 22.085 kDa. On-NKEF-A protein contained a typical 2-Cys family domain, two active sites (51aa and 172aa) that were conserved in mammals, birds, amphibians and fish. Phylogenetic analysis showed that On-NKEF-A had the closest relationship with Zebra mbuna (Maylandia zebra) NKEF. The On-NKEF-A transcription was present in all examined tissues or organs. And the relative high expression levels of On-NKEF-A was found in head kidney leucocytes and nonspecific cytotoxic cells (NCC). After Streptococcus agalactiae stimulation, On-NKEF-A was significantly up-regulated in head kidney, spleen, gill and skin. Also, On-NKEF-A was markedly induced post S. agalactiae, LPS and poly I:C stimulation in head kidney-derived NCC. Moreover, On-NKEF-A was mainly distributed in cytoplasm of fathead minnow cells (FHM cells). The further in vitro analysis found that the recombinant protein of On-NKEF-A (rOn-NKEF-A) could induce the expression of various molecular markers of B cells, macrophages and NCC, enhanced the cytotoxicity of NCC via increasing the effectors expression. The present data collectively indicate that On-NKEF-A participates in anti-bacterial immune response via regulating NCC activity, which will provide new ideas to further explore the defense mechanism of fish against bacteria.

Recombinant outer membrane protein OmpC induces protective immunity against Aeromonashydrophila infection in Labeorohita

Aeromonashydrophila is an opportunistic pathogen that causes enormous loss to aquaculture industry. The outer membrane proteins of Aeromonas help in bacterium-host interaction, and are considered to be potential vaccine candidates. In the present study, we evaluated immunogenicity and protective efficacy of recombinant OmpC (rOmpC) of A. hydrophila in Indian major carp, Labeorohita. The rOmpC-vaccinated fish produced specific anti-rOmpC antibodies with a significant antibody titer, and the antisera could specifically detect the rOmpC in the cell lysates of Escherichia coli expressing rOmpC and cross-react with different Aeromonas lysates, indicating the suitability of the anti-rOmpC antisera to detect Aeromonas infection. A significant increase was noted in ceruloplasmin level, myeloperoxidase and anti-protease activities in transient and temporal manner the sera of the rOmpC-immunized fish as compared to PBS-control fish. Higher agglutination- and hemolytic activity titers in the anti-rOmpC antisera indicate stimulation of innate immunity. Expression of immune-related genes comprising various acute phase proteins, cytokines and inflammatory response molecules were modulated in the head kidney of rOmpC-immunized L. rohita. While IgM, IL1β, and TLR-22 were significantly up-regulated at early time points (3 h-72 h), the others showed a transient augmentation at both early and later time points (SOD, lysozymes C and G, NKEF-B, C3, CXCa and TNF-α) in the rOmpC-immunized L. rohita in comparison to PBS-injected controls. These data suggest that the rOmpC-induced immune response is temporally regulated to confer immunity. In vivo challenge of the rOmpC-immunized fish with A. hydrophila showed significantly greater survival when compared to PBS-injected control fish. Thus, our results highlight the immunomodulatory role of rOmpC and demonstrate its protective efficacy in L. rohita, along with the use of anti-rOmpC antisera in detecting Aeromonas infections.

Transcriptional modifications and the cytoprotective, DNA protective, and wound healing effects of peroxiredoxin-1 from Sebastes schlegelii

Peroxiredoxins are a group of thiol-specific antioxidant proteins that take six isoforms in vertebrates and allow the innate immune system to sense and detoxify reactive oxygen species. In this study, we identified and characterized the perxiredoxin-1 (SsPrdx1) cDNA sequence from the rockfish, Sebastes schlegelii. In silico analysis revealed that SsPrdx1 contained a 594 bp long open reading frame (ORF) encoding a protein of 198 amino acids, with a predicted molecular weight and theoretical isoelectric point of 21.97 kDa and 6.30, respectively. The SsPrdx1 gene comprised six exons linked by five introns, while peroxiredoxin signature motifs were found in the highly conserved third, fourth, and fifth exons. Phylogenetic analysis and sequence alignment suggested that SsPrdx1 is evolutionarily conserved and that its most closely related counterpart is Salarias fasciatus. Recombinant SsPrdx1 (rSsPrdx1) displayed supercoiled DNA protection and insulin disulfide reduction activities in a concentration-dependent manner, while cells transiently transfected with pcDNA3.1 (+)/SsPrdx1 exhibited significant cytoprotective effects under oxidative stress and wound healing activity. SsPrdx1 transcripts were constitutively expressed under normal physiological conditions, with the highest expression observed in the blood. Moreover, SsPrdx1 expression increased in the blood, spleen, and liver following immune provocation by LPS, poly I:C, and Streptococcus iniae injection. Thus, this study provides insights into the role of SsPrdx1 in rockfish immune protection.

Cloning and functional characterisation of natural killer enhancing factor-B (NKEF-B) gene of Labeo rohita: Anti-oxidant and antimicrobial activities of its recombinant protein

Natural killer enhancing factor (NKEF) of peroxiredoxin family is an important innate immune molecule with having anti-oxidant activity. Although this gene has already been studied in a few fish species, it is yet to be identified and functionally characterised in Indian major carps. In the present study, the complete NKEF-B cDNA of rohu, Labeo rohita was cloned that encoded a putative protein of 197 amino acids. The phylogenetic study showed that L. rohita NKEF-B (LrNKEF-B) is closely related to NKEF-B of Cyprinus carpio and Danio rerio species. Tissue-specific expression of LrNKEF-B gene revealed the highest transcript level in the liver tissue. In the ontogeny study, the highest level of the expression was observed in milt and at 18 h post-development. The expression pattern of this gene was also studied in various pathogen models viz., Gram-negative bacteria (Aeromonas hydrophila), ectoparasite (Argulus siamensis) and a dsRNA viral analogue (poly I:C) in the liver and anterior kidney tissues of L. rohita juveniles. During A. hydrophila infection, the increase in expression of transcripts was observed at 3 h post-infection in both liver (15-fold) and anterior kidney (8-fold). In A. siamensis infection, the expression gradually increased up to 3 d post-infection in the anterior kidney, whereas in liver 3-fold up-regulation was noticed at 12 h post-infection. Similarly, during poly I:C stimulation, up-regulation of NKEF-B transcript was observed in anterior kidney from 1 h to 24 h post-stimulation and down-regulated afterwards whereas, the transcript level increased gradually from 6 h to 15 d post-stimulation in liver tissue. In vitro exposure to concanavalin, A and formalin-killed A. hydrophila upregulated NKEF-B gene expression in anterior kidney and peripheral blood leukocytes of L. rohita, however, down-regulated the same in the splenic leukocytes. A recombinant protein of LrNKEF-B (rLrNKEF-B) of 22 kDa was produced and it showed anti-oxidant activity by protecting supercoiled DNA and reducing insulin disulfide bonds. The minimum bactericidal concentration of this recombinant protein was found to be 4.54 μM against A. hydrophila and Staphylococcus aureus. Interestingly, rLrNKEF-B showed relative percent survival of 72.6 % in A. hydrophila challenged L. rohita, and the survival was found to be associated with a high level of expression of different cytokines, anti-oxidant genes and perforin in the rLrNKEF-B treated L. rohita. An indirect ELISA assay for estimation of NKEF was developed in L. rohita, and the concentrations of NKEF-B increased with time periods post A. hydrophila challenge viz., 0 h (42.56 ng/mL), 12 h (174 ng/mL) and 48 h (370 ng/mL) in rohu serum. Our results suggest a crucial role of LrNKEF-B in innate immunity against biotic stress and oxidative damage and also having antibacterial activity.

Peroxiredoxin 1 from cuttlefish (Sepiella maindroni): Molecular characterization of development and its immune response against Vibrio alginolyticus

The aim of this work was constructive to understand the function of peroxiredoxin (PRDX) family member Peroxiredoxin 1 in Sepiella maindroni (SmPrx1) through molecular mechanisms of reproduction, embryonic development and immune responses to Vibrio alginolyticus. The full-length cDNA of SmPrx1 was of 1062 bp, contains a 5' untranslated region (UTR) of 79bp, a 3' UTR of 359 bp, an open reading frame of 624 bp encoding 207 amino acids. The conserved peroxidase catalytic center "FYPLDFTFVCPTEI" and "GEVCPA" were observed in the sequence of SmPrx1; this indicated that it was a member of 2-Cys Prx. Quantitative real-time (qRT)-PCR assays revealed that SmPrx1 was ubiquitously expressed in all examined tissues, muscle, ink sac, liver, ovary, testis, intestine, gill and totally blood cells, and showed high levels in testis. SmPrx1 mRNA was ubiquitously detected in all tested tissues, and the expression was comparatively high in testis, hemocyte, liver and ovary. Moreover, the SmPrx1 gene transcript was detected at all five stages of embryonic development phases that were respectively the zygote stage, the pre-embryonic stage, the organogenesis stage, the morphological integrity stage, the pre-hatching stage. The general tendency of expression was gradually increased and rapidly decreased. High expressed in progenitive tissues and embryonic development exhibit the proliferation-associated protein characterization like in mammal. The expression levels of SmPrx1 in liver and hemocytes grew swiftly and quickly reached peak value after Vibrio alginolyticus challenge. As hours passed by, the expression level began to reduce and resumed to normal levels after 48 h. The antioxidant activity and peroxidase activity of SmPrx1 were 6.17 U/mg. The results showed that the recombined protein of SmPrx1 had antioxidant activity and was the importance part of the antioxidant system in Sepiella maindroni. This study provides useful information to help further understand the functional mechanism of Prx 1 in marine cephalopod immunity.

Molecular cloning, characterization and mRNA expression of six peroxiredoxins from Black carp Mylopharyngodon piceus in response to lipopolysaccharide challenge or dietary carbohydrate

Peroxiredoxin (Prx) belongs to a cellular antioxidant protein family that plays important roles in innate immune function and anti-oxidative capability. In the present study, six Prxs were cloned from Black carp Mylopharyngodon piceus (MpPrx) by homology cloning and rapid amplification of cDNA ends (RACE) techniques. There were 199, 197, 250, 260, 189 and 222 amino acids in six MpPrxs, respectively. BLAST analysis reveals that MpPrxs shares high identities and similar characteristics with other known Prxs from animals. The phylogenetic analysis evidenced three major subclasses corresponding to one-Cys-Prx (MpPrx6), typical two-Cys-Prx (MpPrx1-4) and atypical 2-Cys-Prx (MpPrx5) that reflected the present hierarchy of vertebrates and invertebrates. Although six MpPrxs are constitutively expressed in all tissues, relatively higher-level mRNA expression levels of six MpPrxs can be detected in liver, eyes, heart and adipose tissues by real-time PCR assays. The transcriptional patterns of six MpPrxs mRNA in liver were detected by real-time PCR in Black carp after lipopolysaccharide (LPS) challenge and treated with graded levels of dietary carbohydrate (CHO) (106.5, 194.3, 288.4 and 379.1 g kg(-1)), respectively. These results showed that stimulation with LPS could induce up-expression of six MpPrxs mRNA, and the variations of MpPrx4 were more sensitive than these of other MpPrxs in the liver of Black carp. Compared with those in group with 106.5 g kg(-1) dietary CHO, the expression levels of MpPrx2, MpPrx3 and MpPrx6 were significantly down-regulated while MpPrx5 were significantly induced in liver of Black carp fed with adequate dietary CHO (194.3 g kg(-1)). In addition, significant up-regulations of MpPrx2, MpPrx3 and MpPrx6 were observed in Black carp fed with excessive dietary CHO (379.1 g kg(-1)). And MpPrx4 could be constantly induced with increasing dietary CHO contents in this study. These results indicated that MpPrxs were constitutive and inducible proteins and might play important roles in innate immune function after LPS challenge and regulating redox homeostasis in the metabolism of dietary CHO.

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.

A novel antimicrobial peptide derived from fish goose type lysozyme disrupts the membrane of Salmonella enterica

In aquaculture, accumulation of antibiotics resulted in development of resistance among bacterial pathogens. Consequently, it became mandatory to find alternative to synthetic antibiotics. Antimicrobial peptides (AMPs) which are described as evolutionary ancient weapons have been considered as promising alternates in recent years. In this study, a novel antimicrobial peptide had been derived from goose type lysozyme (LyzG) which was identified from the cDNA library of freshwater fish Channa striatus (Cs). The identified lysozyme cDNA contains 585 nucleotides which encodes a protein of 194 amino acids. CsLyzG was closely related to Siniperca chuatsi with 92.8% homology. The depicted protein sequence contained a GEWL domain with conserved GLMQ motif, 7 active residues and 2 catalytic residues. Gene expression analysis revealed that CsLyzG was distributed in major immune organs with highest expression in head kidney. Results of temporal expression analysis after bacterial (Aeromonas hydrophila) and fungal (Aphanomyces invadans) challenges indicated a stimulant-dependent expression pattern of CsLyzG. Two antimicrobial peptides IK12 and TS10 were identified from CsLyzG and synthesized. Antibiogram showed that IK12 was active against Salmonella enterica, a major multi-drug resistant (MDR) bacterial pathogen which produces beta lactamase. The IK12 induced loss of cell viability in the bacterial pathogen. Flow cytometry assay revealed that IK12 disrupt the membrane of S. enterica which is confirmed by scanning electron microscope (SEM) analysis that reveals blebs around the bacterial cell membrane. Conclusively, CsLyzG is a potential innate immune component and the identified antimicrobial peptide has great caliber to be used as an ecofriendly antibacterial substance in aquaculture.

Molecular characterisation and biological activity of a novel CXC chemokine gene in rock bream (Oplegnathus fasciatus)

Chemokines are chemoattractant cytokines defined by the presence of four conserved cysteine residues. In mammals, these cytokines can be divided into four subfamilies depending on the arrangement of the first two conserved cysteines in the sequence, and include the CXC(α), CC(β), C(γ), and CX3C(δ) classes. We identified CXC chemokine cDNA, designated RbCXC, isolated using expressed sequence tag analysis of a lipopolysaccharide (LPS)-stimulated rock bream liver cDNA library. The full-length RbCXC cDNA (742 bp) contained an open reading frame of 342 bp encoding 114 amino acids. Results from phylogenetic analysis showed that RbCXC was strictly separated into a distinct clade compared to other known CXC chemokine subgroups. RbCXC was significantly expressed in the trunk kidney, liver, spleen, gill, peripheral blood leukocytes (PBLs), and head kidney. Rock bream PBLs were stimulated with several mitogens, including LPS and polyinosinic-polycytidylic acid (poly I:C), which significantly induced the expression of RbCXC mRNA. RbCXC mRNA expression was examined in several tissues under conditions of bacterial and viral challenge. Experimental challenges revealed that all examined tissues from fish infected with Edwardsiella tarda and red sea bream iridovirus showed significant increases in RbCXC expression compared to the control. In the case of Streptococcus iniae infection, RbCXC mRNA expression was markedly upregulated in the kidney, spleen, and liver. In addition, a maltose binding protein fusion recombinant RbCXC (~53 kDa) was produced in an Escherichia coli expression system and purified. Subsequently, the addition of purified recombinant RbCXC (rRbCXC) to kidney leukocytes was examined to investigate the impact of proliferative and chemotactic activity. The rRbCXC induced significant kidney leukocyte proliferation and attraction at concentrations ranging from 10 to 300 μg/mL, suggesting that it can be utilised as an immune stimulant and/or molecular adjuvant to enhance the immunological effects of vaccines.

Molecular identification and expression analysis of the CC chemokine gene in rock bream (Oplegnathus fasciatus) and the biological activity of the recombinant protein

We identified the CC chemokine cDNA designated as RbCC1 (CC chemokine 1 in rock bream, Oplegnathus fasciatus), which was isolated using expressed sequence tag (EST) analysis of a lipopolysaccharide (LPS)-stimulated rock bream liver cDNA library. The full-length RbCC1 cDNA (850 bp) contained an open reading frame (ORF) of 366 bp encoding 122 amino acids. Results from our phylogenetic analysis demonstrated that the RbCC1 was closest relationship to the orange-spotted grouper and Mi-iyu croaker CC chemokines located within the fish CC chemokine group. RbCC1 was significantly expressed in the intestine, spleen, liver, and PBLs (peripheral blood leukocytes). Rock bream PBLs were stimulated with several mitogens, LPS and Con A/PMA which significantly induced the expression of RbCC1 mRNA in the PBLs. The RbCC1 mRNA expression in several tissues under conditions of bacterial and viral challenge was examined. The experimental challenge revealed that the kidney and spleen of fish infected with Streptococcus iniae showed the most significant increases in RbCC1 expression compared to the control. In the case of RSIV infection, the RbCC1 mRNA expression was markedly up-regulated in the liver. In this study, recombinant RbCC1 (approximately 53 kDa) was produced using an Escherichia coli expression system followed by purification. Subsequently, the addition of purified rRbCC1 was examined to investigate the impact on the proliferative and chemotactic activity on kidney leukocytes from rock bream. The results demonstrated that the rRbCC1 induces significant biological activity on kidney leukocyte proliferation and attraction at concentrations in the range of 10-300 μg/mL and suggests that rRbCC1 could be utilized as an immune-stimulant and/or molecular adjuvant to enhance the immune effects of vaccines.

Molecular characterization, expression, and functional analysis of two thioredoxins in the black rockfish (Sebastes schlegelii)

Thioredoxins (TRxs) are a family of small evolutionarily conserved proteins that are essential for the maintenance of cellular homeostasis. Two TRx homologue cDNAs were isolated from a black rockfish concanavalin A (Con A)/phorbol myristate acetate (PMA)-stimulated leucocyte cDNA library and named BrTPx1-1 and BrTPx1-2. As compared with other known TRx peptide sequences, the most conserved regions of both BrTRx1-1 and BrTRx1-2 peptides were found to be the redox-active site Trp-Cys-X-X-Cys (WCXXC). The TRx present in most species is a TRx1-2 protein with a Cys-Pro-Gly-Cys (CPGC) active site. However, in the larger 13 kDa BrTRx1-1 protein, a Cys-Pro-Pro-Cys (CPPC) active site was identified. Here, we report the identification of a new member of the TRx protein family from the teleost black rockfish, which defines a new subclass of 13-kDa TRx1-1 proteins. Phylogenetic analysis indicated that both BrTRx1-1 and BrTRx1-2 were grouped with other vertebrate TRx1 peptides. BrTRx1-1 expression was strongly induced in peripheral blood leucocytes (PBLs) 12-24 h following Con A/PMA stimulation, with peak expression at 24 h post-stimulation. BrTRx1-2 was induced in PBLs after stimulation with lipopolysaccharide (LPS), Con A/PMA, or poly I:C at 24 h. The BrTRx1-1 gene was predominantly expressed in the liver and gills, while BrTRx1-2 was expressed in PBLs and gills. After treatment with a high concentration (10 μg/mL) of rBrTRx1-1 or rBrTRx1-2, kidney leucocytes exhibited increased cell proliferation and viability under oxidative stress.