Apolipoprotein A-I from striped bass (Morone saxatilis) demonstrates antibacterial activity in vitro

Proteomic profile of epidermal mucus from Labeo rohita reveals differentially abundant proteins after Aeromonas hydrophila infection

We report the proteomic profile of Epidermal Mucus (EM) from Labeo rohita and identified the differentially abundant proteins (DAPs) against Aeromonas hydrophila infection through label-free liquid chromatography-mass spectrometry (LC-MS/MS). Using discovery-based proteomics, a total of 2039 proteins were quantified in nontreated group and 1,328 proteins in the treated group, of which 114 were identified as DAPs in both the groups. Of the 114 DAPs, 68 proteins were upregulated and 46 proteins were downregulated in the treated group compared to nontreated group. Functional annotations of these DAPs shows their association with metabolism, cellular process, molecular process, cytoskeletal, stress, and particularly immune system. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis and Fisher's exact test between the two groups shows that most of the proteins were immune-related, which were significantly associated with the proteasome, phagosome, and Salmonella infection pathways. Overall, this study shows a basic and primary way for further functional research of the involvement of vitellogenin 2, alpha-2-macroglobulin-like protein, toll-like receptors (TLR-13), calpain, keratin-like proteins, and heat shock proteins against bacterial infection. Nonetheless, this first-ever comprehensive report of a proteomic sketch of EM from L. rohita after A. hydrophila infection provides systematic protein information to broadly understand the biological role of fish EM against bacterial infection.

Apolipoprotein A-I (ApoA-I) protects Nile tilapia (Oreochromis niloticus) against bacterial infection

Apolipoprotein A-I (ApoA-I) is a lipoprotein involved in a variety of physiological and pathological processes. However, the immunomodulatory functions of ApoA-I in fish are not well understood. In this study, ApoA-I from Nile tilapia (Oreochromis niloticus) (On-ApoA-I) was identified, and its function in bacterial infection was investigated. The open reading frame of On-ApoA-I is 792 bp, which codes for a protein containing 263 amino acids. On-ApoA-I shared over 60% sequence similarity with other teleost fish and more than 20% with mammalian ApoA-I. On-ApoA-I was found to be highly expressed in the liver and significantly induced during Streptococcus agalactiae infection by qRT‒PCR analysis. Furthermore, in vivo studies revealed that recombinant On-ApoA-I protein could suppress inflammation and apoptosis and improve the likelihood of surviving bacterial infection. Additionally, On-ApoA-I showed in vitro antimicrobial properties against Gram-positive and Gram-negative bacteria. These findings offer a theoretical basis for further investigations into the role of ApoA-I in fish immunology.

Allelically and Differentially Expressed Genes After Infection of Edwardsiella ictaluri in Channel Catfish as Determined by Bulk Segregant RNA-Seq

Identification of genetic markers associated with resistance against enteric septicemia of catfish (ESC) is of great interest for genetic enhancement programs of catfish. In the present study, bulk segregant RNA-Seq analysis was applied to determine differentially expressed genes and alleles after ESC infection. Here we report three genomic regions on LG1, LG12, and LG26, containing significant single-nucleotide polymorphisms (SNPs). These genomic regions aligned well with quantitative trait loci (QTL) previously identified. Within the QTL regions, eleven genes were found to be differentially regulated between phenotypic bulks. Importantly, the QTL on linkage group 1 (LG1) were found to be expressed in the liver, whereas the QTL on LG12 and LG26 were expressed in the intestine, suggesting multiple mechanisms of ESC resistance. It is apparent that apolipoproteins may be important for ESC resistance as the QTL on LG1 included the 14-kDa apolipoprotein genes that are both allelically expressed and differentially expressed between the resistant and susceptible bulks. Traf2 and NCK-interacting protein kinase (TNIK) were found in the QTL on LG12, and it was downregulated in resistant fish, suggesting the importance of NCK downregulation in ESC resistance, as previously reported. In addition, we observed divergent gene expression patterns between the liver and intestine after infection. Immune/inflammatory-related processes were overrepresented from liver DEGs, while those DEGs identified from intestine were enriched for proteolysis and wounding processes. Taken together, the BSR-Seq analysis presented here advanced the knowledge of ESC resistance, providing information of not only positions of QTL but also genes and their differential expression between resistant and susceptible fish, making it one step closer to the identification of the causal genes for ESC resistance.

Plasma Proteome Responses in Salmonid Fish Following Immunization

Vaccination plays a critical role in the protection of humans and other animals from infectious diseases. However, the same vaccine often confers different protection levels among individuals due to variation in genetics and/or immunological histories. While this represents a well-recognized issue in humans, it has received little attention in fish. Here we address this knowledge gap in a proteomic study of rainbow trout (Oncorhynchus mykiss, Walbaum), using non-lethal repeated blood sampling to establish the plasma protein response of individual fish following immunization. Six trout were immunized with adjuvanted hen egg-white lysozyme (HEL) and peripheral blood sampled at ten time points from day 0 to day 84 post-injection. We confirm that an antigen-specific antibody response to HEL was raised, showing differences in timing and magnitude among individuals. Using label-free liquid chromatography-mass spectrometry, we quantified the abundance of 278 plasma proteins across the timecourse. As part of the analysis, we show that this approach can distinguish many (but not all) duplicated plasma proteins encoded by paralogous genes retained from the salmonid-specific whole genome duplication event. Global variation in the plasma proteome was predominantly explained by individual differences among fish. However, sampling day explained a major component of variation in abundance for a statistically defined subset of 41 proteins, representing 15% of those detected. These proteins clustered into five groups showing distinct temporal responses to HEL immunization at the population level, and include classical immune (e.g. complement system members) and acute phase molecules (e.g. apolipoproteins, haptoglobins), several enzymes and other proteins supporting the immune response, in addition to evolutionarily conserved molecules that are as yet uncharacterized. Overall, this study improves our understanding of the fish plasma proteome, provides valuable marker proteins for different phases of the immune response, and has implications for vaccine development and the design of immune challenge experiments.

Effects of octylphenol exposure on the lipid metabolism and microbiome of the intestinal tract of Rana chensinensis tadpole by RNAseq and 16s amplicon sequencing

Octylphenol (OP) is a widely distributed endocrine disrupting chemical (EDC), and can be commonly found in various and diverse environmental media. Previous studies have reported that OP exposure could cause many adverse effects on aquatic animals. However, knowledge concerning the impact of OP on lipid metabolism in amphibians was still limited. In our study, Rana chensinensis tadpoles were exposed to different OP concentrations (0, 10^-8, 10^-7 and 10^-6 mol/L) from the Gosner stage (Gs) 25-38. The RNA-seq analysis of tadpole intestines was explored by RNA-seq, and six differentially expressed genes (DEGs) related to the fat digestion and absorption were validated by RT-qPCR. Moreover, we used 16s amplicon sequencing to evaluate effects of OP on intestinal microbiome in tadpoles, further determining the variations of lipid metabolism. Our results revealed that OP exposure influenced gene expression levels related to fat digestion and absorption and led to alteration of structure and composition of intestinal microbiome. At the phylum level, the Firmicutes/Bacteroidetes ratio was gradually decreased in OP exposure groups, which disrupted lipid metabolism. According to the results of intestinal microbial functional prediction, OP exposure interfered with metabolic function and increased risk of disease. These data provide us with powerful resources to assess the effects of OP on lipid metabolism by integrating RNAseq and 16s amplicon sequencing analysis of intestinal tract and intestinal microbiome.

Proteomic profiling of yellow catfish (Pelteobagrus fulvidraco) skin mucus identifies differentially-expressed proteins in response to Edwardsiella ictaluri infection

Fish mucus acts as a physiological and immunological barrier for maintaining normal fish physiology and conferring defense against pathogens infection. Here we report proteomic profiling of skin mucus of yellow catfish before and after E. ictaluri infection by Label-free LC-MS/MS approach. A total of 918 non-redundant proteins were identified from 54443 spectra referring to yellow catfish genome database. Further annotation via GO and KEGG database revealed complex protein composition of yellow catfish mucus. Besides structural proteins in mucus, a lot of immune-related proteins were retrieved, such as lectins, complement components, antibacterial peptides and immunoglobins. 133 differentially-expressed proteins (DEPs), including 76 up-regulated and 57 down-regulated proteins, were identified, most of which were enriched into 17 pathways centering on "immune system" category with 33 proteins involved. Consistently, significant proliferation of mucus-secreting goblet cells and CYPA-expressing cells were observed along outside of yellow catfish skin after E. ictaluri infection, indicating an enhanced immune response to E. ictaluri infection in yellow catfish skin mucus. The proteomic data provide systematic protein information to comprehensively understand the biological function of yellow catfish skin mucus in response to bacterial infection.

Deimination Protein Profiles in Alligator mississippiensis Reveal Plasma and Extracellular Vesicle-Specific Signatures Relating to Immunity, Metabolic Function, and Gene Regulation

Alligators are crocodilians and among few species that endured the Cretaceous-Paleogene extinction event. With long life spans, low metabolic rates, unusual immunological characteristics, including strong antibacterial and antiviral ability, and cancer resistance, crocodilians may hold information for molecular pathways underlying such physiological traits. Peptidylarginine deiminases (PADs) are a group of calcium-activated enzymes that cause posttranslational protein deimination/citrullination in a range of target proteins contributing to protein moonlighting functions in health and disease. PADs are phylogenetically conserved and are also a key regulator of extracellular vesicle (EV) release, a critical part of cellular communication. As little is known about PAD-mediated mechanisms in reptile immunology, this study was aimed at profiling EVs and protein deimination in Alligator mississippiensis. Alligator plasma EVs were found to be polydispersed in a 50-400-nm size range. Key immune, metabolic, and gene regulatory proteins were identified to be posttranslationally deiminated in plasma and plasma EVs, with some overlapping hits, while some were unique to either plasma or plasma EVs. In whole plasma, 112 target proteins were identified to be deiminated, while 77 proteins were found as deiminated protein hits in plasma EVs, whereof 31 were specific for EVs only, including proteins specific for gene regulatory functions (e.g., histones). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed KEGG pathways specific to deiminated proteins in whole plasma related to adipocytokine signaling, while KEGG pathways of deiminated proteins specific to EVs included ribosome, biosynthesis of amino acids, and glycolysis/gluconeogenesis pathways as well as core histones. This highlights roles for EV-mediated export of deiminated protein cargo with roles in metabolism and gene regulation, also related to cancer. The identification of posttranslational deimination and EV-mediated communication in alligator plasma revealed here contributes to current understanding of protein moonlighting functions and EV-mediated communication in these ancient reptiles, providing novel insight into their unusual immune systems and physiological traits. In addition, our findings may shed light on pathways underlying cancer resistance, antibacterial and antiviral resistance, with translatable value to human pathologies.

Post-Translational Protein Deimination Signatures in Serum and Serum-Extracellular Vesicles of Bos taurus Reveal Immune, Anti-Pathogenic, Anti-Viral, Metabolic and Cancer-Related Pathways for Deimination

The bovine immune system is known for its unusual traits relating to immunoglobulin and antiviral responses. Peptidylarginine deiminases (PADs) are phylogenetically conserved enzymes that cause post-translational deimination, contributing to protein moonlighting in health and disease. PADs also regulate extracellular vesicle (EV) release, forming a critical part of cellular communication. As PAD-mediated mechanisms in bovine immunology and physiology remain to be investigated, this study profiled deimination signatures in serum and serum-EVs in Bos taurus. Bos EVs were poly-dispersed in a 70-500 nm size range and showed differences in deiminated protein cargo, compared with whole sera. Key immune, metabolic and gene regulatory proteins were identified to be post-translationally deiminated with some overlapping hits in sera and EVs (e.g., immunoglobulins), while some were unique to either serum or serum-EVs (e.g., histones). Protein-protein interaction network analysis of deiminated proteins revealed KEGG pathways common for serum and serum-EVs, including complement and coagulation cascades, viral infection (enveloped viruses), viral myocarditis, bacterial and parasitic infections, autoimmune disease, immunodeficiency intestinal IgA production, B-cell receptor signalling, natural killer cell mediated cytotoxicity, platelet activation and hematopoiesis, alongside metabolic pathways including ferroptosis, vitamin digestion and absorption, cholesterol metabolism and mineral absorption. KEGG pathways specific to EVs related to HIF-1 signalling, oestrogen signalling and biosynthesis of amino acids. KEGG pathways specific for serum only, related to Epstein-Barr virus infection, transcription mis-regulation in cancer, bladder cancer, Rap1 signalling pathway, calcium signalling pathway and ECM-receptor interaction. This indicates differences in physiological and pathological pathways for deiminated proteins in serum-EVs, compared with serum. Our findings may shed light on pathways underlying a number of pathological and anti-pathogenic (viral, bacterial, parasitic) pathways, with putative translatable value to human pathologies, zoonotic diseases and development of therapies for infections, including anti-viral therapies.

Analysis of apolipoprotein multigene family in spotted sea bass (Lateolabrax maculatus) and their expression profiles in response to Vibrio harveyi infection

Apolipoproteins (Apos), which are the protein components of plasma lipoproteins, play important roles in lipid transport in vertebrates. It has been demonstrated that in teleosts, several Apos display antimicrobial activity and play crucial roles in innate immunity. Despite their importance, apo genes have not been systematically characterized in many aquaculture fish species. In our study, a complete set of 23 apo genes was identified and annotated from spotted sea bass (Lateolabrax maculatus). Phylogenetic and homology analyses provided evidence for their annotation and evolutionary relationships. To investigate their potential roles in the immune response, the expression patterns of 23 apo genes were determined in the liver and intestine by qRT-PCR after Vibrio harveyi infection. After infection, a total of 20 differentially expressed apo genes were observed, and their expression profiles varied among the genes and tissues. 5 apo genes (apoA1, apoA4a.1, apoC2, apoF and apoO) were dramatically induced or suppressed (log2 fold change >4, P < 0.05), suggesting their involvement in the immune response of spotted sea bass. Our study provides a valuable foundation for future studies aimed at uncovering the specific roles of each apo gene during bacterial infection in spotted sea bass and other teleost species.

Liver Transcriptome and miRNA Analysis of Silver Carp (Hypophthalmichthys molitrix) Intraperitoneally Injected With Microcystin-LR

Next-generation sequencing was used to analyze the effects of toxic microcystin-LR (MC-LR) on silver carp (Hypophthalmichthys molitrix). Silver carps were intraperitoneally injected with MC-LR, and RNA-seq and miRNA-seq in the liver were analyzed at 0.25, 0.5, and 1 h. The expression of glutathione S-transferase (GST), which acts as a marker gene for MC-LR, was tested to determine the earliest time point at which GST transcription was initiated in the liver tissues of the MC-LR-treated silver carps. Hepatic RNA-seq/miRNA-seq analysis and data integration analysis were conducted with reference to the identified time point. Quantitative PCR (qPCR) was performed to detect the expression of the following genes at the three time points: heme oxygenase 1 (HO-1), interleukin-10 receptor 1 (IL-10R1), apolipoprotein A-I (apoA-I), and heme binding protein 2 (HBP2). Results showed that the liver GST expression was remarkably decreased at 0.25 h (P < 0.05). RNA-seq at this time point revealed that the liver tissue contained 97,505 unigenes, including 184 significantly different unigenes and 75 unknown genes. Gene Ontology (GO) term enrichment analysis suggested that 35 of the 145 enriched GO terms were significantly enriched and mainly related to the immune system regulation network. KEGG pathway enrichment analysis showed that 18 of the 189 pathways were significantly enriched, and the most significant was a ribosome pathway containing 77 differentially expressed genes. miRNA-seq analysis indicated that the longest miRNA had 22 nucleotides (nt), followed by 21 and 23 nt. A total of 286 known miRNAs, 332 known miRNA precursor sequences, and 438 new miRNAs were predicted. A total of 1,048,575 mRNA–miRNA interaction sites were obtained, and 21,252 and 21,241 target genes were respectively predicted in known and new miRNAs. qPCR revealed that HO-1, IL-10R1, apoA-I, and HBP2 were significantly differentially expressed and might play important roles in the toxicity and liver detoxification of MC-LR in fish. These results were consistent with those of high-throughput sequencing, thereby verifying the accuracy of our sequencing data. RNA-seq and miRNA-seq analyses of silver carp liver injected with MC-LR provided valuable and new insights into the toxic effects of MC-LR and the antitoxic mechanisms of MC-LR in fish.

The RNA/miRNA data are available from the NCBI database Registration No. : SRP075165.

Physiological responses of reared sea bream (Sparus aurata Linnaeus, 1758) to an Amyloodinium ocellatum outbreak

Amyloodiniosis represents a major bottleneck for semi-intensive aquaculture production in Southern Europe, causing extremely high mortalities. Amyloodinium ocellatum is a parasitic dinoflagellate that can infest almost all fish, crustacean and bivalves that live within its ecological range. Fish mortalities are usually attributed to anoxia, associated with serious gill hyperplasia, inflammation, haemorrhage and necrosis in heavy infestations; or with osmoregulatory impairment and secondary microbial infections due to severe epithelial damage in mild infestation. However, physiological information about the host responses to A. ocellatum infestation is scarce. In this work, we analysed the proteome of gilthead sea bream (Sparus aurata) plasma and relate it with haematological and immunological indicators, in order to enlighten the different physiological responses when exposed to an A. ocellatum outbreak. Using 2D-DIGE, immunological and haematological analysis and in response to the A. ocellatum contamination we have identified several proteins associated with acute-phase response, inflammation, lipid transport, homoeostasis, and osmoregulation, wound healing, neoplasia and iron transport. Overall, this preliminary study revealed that amyloodiniosis affects some fish functional pathways as revealed by the changes in the plasma proteome of S. aurata, and that the innate immunological system is not activated in the presence of the parasite.

Comparative proteome and peptidome analysis of the cephalic fluid secreted by Arapaima gigas (Teleostei: Osteoglossidae) during and outside parental care

Parental investment in Arapaima gigas includes nest building and guarding, followed by a care provision when a cephalic fluid is released from the parents’ head to the offspring. This fluid has presumably important functions for the offspring but so far its composition has not been characterised. In this study the proteome and peptidome of the cephalic secretion was studied in parental and non-parental fish using capillary electrophoresis coupled to mass spectrometry (CE-MS) and GeLC-MS/MS analyses. Multiple comparisons revealed 28 peptides were significantly different between males and parental males (PC-males), 126 between females and parental females (PC-females), 51 between males and females and 9 between PC-males and PC-females. Identification revealed peptides were produced in the inner ear (pcdh15b), eyes (tetraspanin and ppp2r3a), central nervous system (otud4, ribeye a, tjp1b and syn1) among others. A total of 422 proteins were also identified and gene ontology analysis revealed 28 secreted extracellular proteins. From these, 2 hormones (prolactin and stanniocalcin) and 12 proteins associated to immunological processes (serotransferrin, α-1-antitrypsin homolog, apolipoprotein A-I, and others) were identified. This study provides novel biochemical data on the lateral line fluid which will enable future hypotheses-driven experiments to better understand the physiological roles of the lateral line in chemical communication.

Immune relevant molecules identified in the skin mucus of fish using -omics technologies

This review will give an overview of immune relevant molecules in fish skin mucus. The skin of fish is continuously exposed to a water environment, and unlike that of terrestrial vertebrates, it is a mucosal surface with a thin epidermis of live cells covered by a mucus layer. The mucosa plays an important role in maintaining the homeostasis of the fish and preventing the entry of invading pathogens. This review provides an overview of proteins, RNA, DNA, lipids and carbohydrates found in the skin mucus of studied species. Proteins such as actin, histones, lectins, lysozyme, mucin, and transferrin have extracellular immune relevant functions. Complement complement molecules, heat shock molecules and superoxide dismutase present in mucus show differential expression during pathogen challenge in some species, but their functions in mucus, if any, need to be shown. RNA, DNA, lipids, carbohydrates and metabolites in mucus have been studied to a limited extent in fish, the current knowledge is summarized and knowledge gaps are pointed out.

Opacification Domain of Serum Opacity Factor Inhibits Beta-Hemolysis and Contributes to Virulence of Streptococcus pyogenes

Streptococcus pyogenes is a major human pathogen causing more than 700 million infections annually. As a successful pathogen, S. pyogenes produces many virulence factors that facilitate colonization, proliferation, dissemination, and tissue damage. Serum opacity factor (SOF), an extracellular protein, is one of the virulence factors made by S. pyogenes. The underlying mechanism of how SOF contributes to virulence is not fully understood. SOF has two major features: (i) it opacifies host serum by interacting with high-density lipoprotein, and (ii) it inhibits beta-hemolysis on blood agar. In this study, we demonstrate that the domain of SOF essential for opacifying serum is also essential for SOF-mediated beta-hemolysis inhibition and SOF-mediated virulence. Our results shed new light on the molecular mechanisms of SOF-host interaction.

Serum opacity factor (SOF) is a cell surface virulence factor made by the human pathogen Streptococcus pyogenes. We found that S. pyogenes strains with naturally occurring truncation mutations in the sof gene have markedly enhanced beta-hemolysis. Moreover, deletion of the sof gene in a SOF-positive parental strain resulted in significantly increased beta-hemolysis. Together, these observations suggest that SOF is an inhibitor of beta-hemolysis. SOF has two major functional domains, including an opacification domain and a fibronectin-binding domain. Using a SOF-positive serotype M89 S. pyogenes parental strain and a panel of isogenic mutant derivative strains, we evaluated the relative contribution of each SOF functional domain to beta-hemolysis inhibition and bacterial virulence. We found that the opacification domain, rather than the fibronectin-binding domain, is essential for SOF-mediated beta-hemolysis inhibition. The opacification domain, but not the fibronectin-binding domain of SOF, also contributed significantly to virulence in mouse models of bacteremia and necrotizing myositis. Inasmuch as the opacification domain of SOF is known to interact avidly with host high-density lipoprotein (HDL), we speculate that SOF-HDL interaction is an important process underlying SOF-mediated beta-hemolysis inhibition and SOF-mediated virulence.

IMPORTANCEStreptococcus pyogenes is a major human pathogen causing more than 700 million infections annually. As a successful pathogen, S. pyogenes produces many virulence factors that facilitate colonization, proliferation, dissemination, and tissue damage. Serum opacity factor (SOF), an extracellular protein, is one of the virulence factors made by S. pyogenes. The underlying mechanism of how SOF contributes to virulence is not fully understood. SOF has two major features: (i) it opacifies host serum by interacting with high-density lipoprotein, and (ii) it inhibits beta-hemolysis on blood agar. In this study, we demonstrate that the domain of SOF essential for opacifying serum is also essential for SOF-mediated beta-hemolysis inhibition and SOF-mediated virulence. Our results shed new light on the molecular mechanisms of SOF-host interaction.

Analysis of apolipoprotein genes and their involvement in disease response of channel catfish after bacterial infection

Apolipoproteins are protein component of plasma lipoproteins. They exert crucial roles in lipoprotein metabolism and serve as enzyme cofactors, receptor ligands, and lipid transfer carriers in mammals. In teleosts, apolipoproteins are also involved in diverse processes including embryonic and ontogenic development, liver and digestive system organogenesis, and innate immunity. In this study, we identified a set of 19 apolipoprotein genes in channel catfish (Ictalurus punctatus). Phylogenetic analysis and syntenic analysis were conducted to determine their identities and evolutionary relationships. The expression signatures of apolipoproteins in channel catfish were determined in healthy tissues and after infections with two major bacterial pathogens, Edwardsiella ictaluri and Flavobacterium columnare. In healthy channel catfish, most apolipoprotein genes exhibited tissue-specific expression patterns in channel catfish. After ESC and columnaris infections, 5 and 7 apolipoprotein genes were differentially expressed respectively, which presented a pathogen-specific and time-dependent pattern of regulation. After ESC infection, three exchangeable apolipoproteins (apoA-IB, apoC-I, and apoE-B) were suppressed in catfish intestine, while two nonexchangeable apolipoproteins (apoB-A and apoB-B) were slightly up-regulated. After columnaris infection, apoB-B, apoD-B, and apoE-A were significantly down-regulated in catfish gill, while apoF, apoL-IV, apoO-like, and apo-14 kDa showed significantly up-regulation. Taken together, these results suggested that apolipoprotein genes may play significant roles in innate immune responses to bacterial pathogens in channel catfish.

Peptides from American alligator plasma are antimicrobial against multi-drug resistant bacterial pathogens including Acinetobacter baumannii

BACKGROUND

Our group has developed a new process for isolating and identifying novel cationic antimicrobial peptides from small amounts of biological samples. Previously, we identified several active antimicrobial peptides from 100 μl of plasma from Alligator mississippiensis. These peptides were found to have in vitro antimicrobial activity against Pseudomonas aeruginosa and Staphylococcus aureus. In this work, we further characterize three of the novel peptides discovered using this process: Apo5, Apo6, and A1P.

RESULTS

We examined the activity of these peptides against multi-drug resistant strains and clinical isolates of common human pathogens. We investigated their structural characteristics using circular dichroism and tested for membrane disruption and DNA binding. These peptides were found to have strong in vitro activity against multi-drug resistant and clinically isolated strains of S. aureus, Escherichia coli, P. aeruginosa, and Acinetobacter baumannii. Apo5 and Apo6, peptides derived from alligator apolipoprotein C-1, depolarized the bacterial membrane. A1P, a peptide from the serpin proteinase inhibitor, did not permeabilize membranes. Performing circular dichroism analysis, Apo5 and Apo6 were found to be predominantly helical in SDS and TFE buffer, while A1P has significantly different structures in phosphate buffer, SDS, and TFE. None of these peptides were found to be hemolytic to sheep red blood cells or significantly cytotoxic up to 100 μg/ml after 24 h exposure.

CONCLUSIONS

Overall, we suggest that Apo5 and Apo6 have a different mode of action than A1P, and that all three peptides make promising candidates for the treatment of drug-resistant bacteria, such as A. baumannii.

Apolipoprotein A-I in Labeo rohita: Cloning and functional characterisation reveal its broad spectrum antimicrobial property, and indicate significant role during ectoparasitic infection

Apolipoprotein A-I (ApoA-I) is the most abundant and multifunctional high-density lipoprotein (HDL) having a major role in lipid transport and potent antimicrobial activity against a wide range of microbes. In this study, a complete CDS of 771 bp of Labeo rohita (rohu) ApoA-I (LrApoA-I) encoding a protein of 256 amino acids was amplified, cloned and sequenced. Tissue specific transcription analysis of LrApoA-I revealed its expression in a wide range of tissues, with a very high level of expression in liver and spleen. Ontogenic study of LrApoA-I expression showed presence of transcripts in milt and 3 h post-fertilization onwards in the larvae. The expression kinetics of LrApoA-I was studied upon infection with three different types of pathogens to elucidate its functional significance. Its expression was found to be up-regulated in the anterior kidney of L. rohita post-infection with Aeromonas hydrophila. Similarly following poly I:C (poly inosinic:cytidylic) stimulation, the transcript levels increased in both the anterior kidney and liver tissues. Significant up-regulation of LrApoA-I expression was observed in skin, mucous, liver and anterior kidney of the fish challenged with the ectoparasite Argulus siamensis. Immunomodulatory effect of recombinant LrApoA-I (rApoA-I) produced in Escherichia coli was demonstrated against A. hydrophila challenge in vivo. L. rohita administered with rApoA-I at a dose of 100 μg exhibited significantly higher protection (∼55%) upon challenge with A. hydrophila 12 h post-administration of the protein, in comparison to that observed in control group, along with higher level of expression of immune-related genes. The heightened expression of ApoA-I observed post-infection reflected its involvement in immune responses against a wide range of infections including bacterial, viral as well as parasitic pathogens. Our results also suggest the possibility of using rApoA-I as an immunostimulant, particularly rendering protection against A. hydrophila.

Molecular characterization and developmental expression patterns of apolipoprotein A-I in Senegalese sole (Solea senegalensis Kaup)

The apolipoprotein A-I (ApoA-I) is an essential component of the high density lipoproteins (HDL). In this study, the cDNA and genomic sequences of this apolipoprotein were characterized for first time in Solea senegalensis. The predicted polypeptide revealed conserved structural features including ten repeats in the lipid-binding domain and some residues involved in cholesterol interaction and binding. The gene structure analysis identified four exons and three introns. Moreover, the synteny analysis revealed that apoA-I did not localize with other apolipoproteins indicating a divergent evolution with respect to the apoA-IV and apoE cluster. The phylogenetic analyses identified two distinct apoA-I paralogs in Ostariophysi (referred to as Ia and Ib) and only one (Ib) in Acanthopterygii. Whole-mount in situ hybridization located the apoA-I signal mainly in the yolk syncytial layer in lecitotrophic larval stages. Later at mouth opening, the mRNA signals were detected mainly in liver and intestine compatible with its role in the HDL formation. Moreover, a clear signal was detected in some regions of the brain, retina and neural cord suggesting a role in local regulation of cholesterol homeostasis. After metamorphosis, apoA-I was also detected in other tissues such as gills, head kidney and spleen suggesting a putative role in immunity. Expression analyses in larvae fed two diets with different triacylglycerol levels indicated that apoA-I mRNA levels were more associated to larval size and development than dietary lipid levels. Finally, qPCR analyses of immature and mature transcripts revealed distinct expression profiles suggesting a posttranscriptional regulatory mechanism.

Differential proteome profile of skin mucus of gilthead seabream (Sparus aurata) after probiotic intake and/or overcrowding stress

Gilthead seabream (Sparus aurata L.) is the major cultured fish species in the Mediterranean area. High density stocking causes stress and increases the impact of diseases leading to economic losses. Probiotics could represent a solution to prevent diseases through several mechanisms such as improving the immune status and/or mucosal microbiota or competing with pathogens. The probiotic Shewanella putrefaciens, also known as Pdp11, was firstly isolated from the skin of healthy gilthead seabream. Our study focuses on the skin mucus proteome after dietary probiotic Pdp11 intake in fish maintained under normal or overcrowding conditions. 2-DE of skin mucus followed by LC-MS/MS analysis was done for each experimental group and differentially expressed proteins were identified. The results showed differentially expressed proteins especially involved in immune processes, such as lysozyme, complement C3, natural killer cell enhancing factor and nonspecific cytotoxic cell receptor protein 1, whose transcript profiles were studied by qPCR. A consistency between lysozyme protein levels in the mucus and lysozyme mRNA levels in skin was found. Further research is necessary to unravel the implications of skin mucosal immunity on fish welfare and disease.

BIOLOGICAL SIGNIFICANCE

The present work reveals the proteomic changes, which are taking place in the skin mucus of stressed and non-stressed gilthead seabream after Pdp11 probiotic intake. The study contributes to improving the knowledge on skin mucosal immunology of this relevant farmed fish species. Furthermore, the paper shows for the first time how a suitable proteomic methodology, in this case 2-DE followed by LC-MS/MS is useful to perform a comparative study with a non-invasive technique of skin mucus of gilthead seabream.

Skin mucus proteome map of European sea bass (Dicentrarchus labrax)

Skin mucus is the first barrier of fish defence. Proteins from skin mucus of European sea bass (Dicentrarchus labrax) were identified by 2DE followed by LC-MS/MS. From all the identified proteins in the proteome map, we focus on the proteins associated with several immune pathways in fish. Furthermore, the real-time PCR transcript levels in skin are shown. Proteins found include apolipoprotein A1, calmodulin, complement C3, fucose-binding lectin, lysozyme and several caspases. To our knowledge, this is the first skin mucus proteome study and further transcriptional profiling of the identified proteins done on this bony fish species. This not only contributes knowledge on the routes involved in mucosal innate immunity, but also establishes a non-invasive technique based on locating immune markers with a potential use for prevention and/or diagnosis of fish diseases.

Expression of apolipoprotein A-I and A-II in rainbow trout reproductive tract and their possible role in antibacterial defence

Antimicrobial proteins such as apolipoproteins A (ApoA-I and ApoA-II) play an important role in the primary defence barrier in vertebrates including fish. The aims of the present study were to isolate and characterise rainbow trout seminal plasma ApoA-I and ApoA-II, to examine the mRNA expression of each apolipoprotein in testis and spermatic ducts, and to test the antibacterial properties of the apolipoproteins. Using a three-step isolation procedure consisting of ion-exchange chromatography, gel filtration and preparative SDS-PAGE, apolipoproteins were purified and identified as ApoA-I and ApoA-II. Both apolipoproteins were represented by several proteoforms. The expression of ApoA-I and ApoA-II mRNA in the reproductive tract and their antibacterial properties against Escherichia coli suggest that seminal apolipoproteins play an important role in innate immunity in the rainbow trout reproductive tract. The functions of seminal ApoA can be related to protection of sperm and reproductive tissue from microbial attack and to the maintenance of sperm membrane integrity.

Isolation and function analysis of apolipoprotein A-I gene response to virus infection in grouper

Apolipoproteins, synthesized mainly in liver and intestine and bounded to lipids, play important roles in lipid transport and uptake through the circulation system. In this study, an apolipoprotein A-I gene homologue was cloned from orange-spotted grouper Epinephelus coioides (designed as Ec-ApoA-I) by rapid amplification of cDNA ends (RACE) PCR. The full-length cDNA of Ec-ApoA-I was comprised of 1278 bp with a 792 bp open reading frame (ORF) that encodes a putative protein of 264 amino acids. Quantitative real-time PCR (qPCR) analysis revealed that Ec-ApoA-I was abundant in liver and intestine, and the expression in liver was significantly (P < 0.01) up-regulated after the stimulation of LPS, Poly(I:C), Vibrio alginolyticus, and Singapore grouper iridovirus (SGIV). Recombinant Ec-ApoA-I (rEc-ApoA-I) was produced in Escherichia coli BL21 (DE3) expression system exhibited bacteriolyticactivity against Microcococcus lysodeikticus and Aeromonas hydrophila. Intracellular localization revealed that Ec-ApoA-I distributed in both cytoplasm and nucleus, and predominantly in the cytoplasm. Overexpression of Ec-ApoA-I in grouper Brain (GB) cells could inhibit the replication of SGIV. These results together indicated that Ec-ApoA-I perhaps is involved in the responses to bacterial and viral challenge.

Characterization, expression and antibacterial properties of apolipoproteins A from carp (Cyprinus carpio L.) seminal plasma

Apolipoproteins A are multifunctional proteins that, in addition to contributing to lipid metabolism and transport, are associated with the innate immune system in fish. Using a three step isolation procedure consisting of affinity chromatography on Blue-Sepharose, delipidation and reverse phase HPLC we isolated apolipoproteins from carp seminal plasma and identified them as ApoA-I and Apo-14 kDa. Moreover, we provided the full-length cDNA sequence of ApoA-I encoding 257 amino acids including a 18 amino acid signal peptide and a 4 amino acid propeptide. Apolipoproteins corresponded to the most abundant proteins in carp seminal plasma. Both ApoA-I and Apo-14 kDa were represented by several proteoforms that differ both in molecular mass and isoelectric point. The proteoforms of ApoA-I characteristic for seminal plasma were distinguished from those of blood. Carp seminal plasma ApoA-I and Apo-14 kDa showed a high immunologic similarity to their counterparts in carp blood and seminal plasma of other Cyprinid species. The mRNA expression analysis and immunohistochemical study suggest synthesis and secretion of ApoA-I and Apo-14 kDa in the fish reproductive tract and suggest a role in spermatogenesis and the stabilization of sperm membrane. Moreover, ApoA-I displayed bactericidal activity against Escherichia coli and bacteriostatic activity against Aeromonas hydrophila which suggests that ApoA-I is associated with innate immune system of the fish reproductive tract.

Effects of increased CO2 on fish gill and plasma proteome

Ocean acidification and warming are both primarily caused by increased levels of atmospheric CO₂, and marine organisms are exposed to these two stressors simultaneously. Although the effects of temperature on fish have been investigated over the last century, the long-term effects of moderate CO₂ exposure and the combination of both stressors are almost entirely unknown. A proteomics approach was used to assess the adverse physiological and biochemical changes that may occur from the exposure to these two environmental stressors. We analysed gills and blood plasma of Atlantic halibut (Hippoglossus hippoglossus) exposed to temperatures of 12°C (control) and 18°C (impaired growth) in combination with control (400 µatm) or high-CO₂ water (1000 µatm) for 14 weeks. The proteomic analysis was performed using two-dimensional gel electrophoresis (2DE) followed by Nanoflow LC-MS/MS using a LTQ-Orbitrap. The high-CO₂ treatment induced the up-regulation of immune system-related proteins, as indicated by the up-regulation of the plasma proteins complement component C3 and fibrinogen β chain precursor in both temperature treatments. Changes in gill proteome in the high-CO₂ (18°C) group were mostly related to increased energy metabolism proteins (ATP synthase, malate dehydrogenase, malate dehydrogenase thermostable, and fructose-1,6-bisphosphate aldolase), possibly coupled to a higher energy demand. Gills from fish exposed to high-CO₂ at both temperature treatments showed changes in proteins associated with increased cellular turnover and apoptosis signalling (annexin 5, eukaryotic translation elongation factor 1γ, receptor for protein kinase C, and putative ribosomal protein S27). This study indicates that moderate CO₂-driven acidification, alone and combined with high temperature, can elicit biochemical changes that may affect fish health.

Proteomic diversity of high density lipoproteins: our emerging understanding of its importance in lipid transport and beyond

Recent applications of mass spectrometry technology have dramatically increased our understanding of the proteomic diversity of high density lipoproteins (HDL). Depending on the method of HDL isolation, upwards of 85 proteins have been identified, and the list continues to grow. In addition to proteins consistent with traditionally accepted roles in lipid transport, HDL carries surprising constituents, such as members of the complement pathway, protease inhibitors involved in hemostasis, acute-phase response proteins, immune function mediators, and even metal-binding proteins. This compositional diversity fits well with hundreds of studies demonstrating a wide functional pleiotrophy, including roles in lipid transport, oxidation, inflammation, hemostasis, and immunity. This review summarizes the progression of our understanding of HDL proteomic complexity and points out key experimental observations that reinforce the functional diversity of HDL. The possibility of specific HDL subspecies with distinct functions, the evidence supporting this concept, and some of the best examples of experimentally defined HDL subspecies are also discussed. Finally, key challenges facing the field are highlighted, particularly the need to identify and define the function of HDL subspecies to better inform attempts to pharmacologically manipulate HDL for the benefit of cardiovascular disease and possibly other maladies.

Apolipoprotein A1 in channel catfish: transcriptional analysis, antimicrobial activity, and efficacy as plasmid DNA immunostimulant against Aeromonas hydrophila infection

The objectives of this study were to: 1) determine transcriptional profiles of apolipoprotein A1 (ApoA1) in collected channel catfish tissues after infection with Aeromonas hydrophila by bath immersion; 2) investigate whether recombinant channel catfish apolipoprotein A1 produced in Escherichia coli expression system possesses any antimicrobial activity against A. hydrophila; 3) evaulate whether recombinant channel catfish apolipoprotein A1 plasmid DNA could be used as immunostimulant to protect fish against A. hydrophila infection. Quantitative PCR revealed that the transcription levels of ApoA1 in infected catfish were significantly (P < 0.05) more induced in the anterior kidney. Recombinant apoA1 produced in E. coli expression system exhibited lytic activity against Gram-positive Micrococcus lysodeikticus and Gram-negative A. hydrophila. When pcDNA3.2-vectored recombinant apoA1 was transfected in channel catfish gill cells G1B, the over-expression of pcDNA-ApoA1 offered significant (P < 0.05) protection to G1B cells against A. hydrophila infection. When channel catfish were intraperitoneally injected with QCDCR adjuvant formulated pcDNA-ApoA1 and challenged with a highly virulent A. hydrophila strain AL-09-71 at two days post injection, pcDNA-ApoA1 injection offered 100% protection to channel catfish. Macrophages of fish injected with pcDNA-ApoA1 produced significantly (P < 0.05) higher amounts of reactive oxygen species and nitric oxide than that of fish injected with pcDNA vector alone. Our results suggest that pcDNA-ApoA1 could be used as a novel immunostimulant to offer immediate protection to catfish against A. hydrophila infection.

Apolipoprotein A-I binding to anionic vesicles and lipopolysaccharides: role for lysine residues in antimicrobial properties

Human apolipoprotein A-I (apoA-I) is a 28kDa protein and a major component of high-density lipoproteins, mediating several essential metabolic functions related to heart disease. In the present study the potential protective role against bacterial pathogens was explored. ApoA-I suppressed bacterial growth of Escherichia coli and Klebsiella pneumoniae. The protein was able to bind lipopolysaccharides and showed a strong preference for bilayer vesicles made of phosphatidylglycerol over phosphatidylcholine. Lysine side chains of apoA-I were acetylated to evaluate the importance of electrostatic forces in the binding interaction with both membrane components. Electrophoresis properties, dot blot analysis, circular dichroism, and fluorescence spectroscopy to probe for changes in protein structure indicated that the acetylated protein displayed a strongly reduced lipopolysaccharide and phosphatidylglycerol binding. A mutant containing only the N-terminal domain of apoA-I also showed a reduced ability to interact with the membrane components, although to a lesser extent. These results indicate the potential for apoA-I to function as an antimicrobial protein and exerts this function through lysine residues.

HDL functionality

PURPOSE OF REVIEW

HDL cholesterol concentration is inversely correlated with cardiovascular disease and has a wide range of functions involved in many systems. The purpose of this review is to summarize HDL functionality, its relevance to atherosclerosis and factors affecting HDL functions.

RECENT FINDINGS

The contribution of HDL to reverse cholesterol transport may not be as great as first envisaged. However, it still plays an important role in cholesterol efflux from peripheral tissues. The capacity of HDL to promote cellular cholesterol efflux in an ex-vivo model has been reported to correlate more closely with carotid intima-media thickness than HDL cholesterol concentration. Recently, a variety of other functions of HDL have been described including antimicrobial, antioxidant, antiglycation, anti-inflammatory, nitric oxide--inducing, antithrombotic and antiatherogenic activity and immune modulation as well as a potential role in glucose homeostasis, diabetes pathophysiology and complications.

SUMMARY

HDL has a wide range of functions some of which are independent of its cholesterol content. Its cargo of apolipoproteins, various proteins and phospholipids contributes most to its various functions. These functions are affected by a number of genetic, physiological and pathological factors.

Molecular and comparative analyses of type IV antifreeze proteins (AFPIVs) from two Antarctic fishes, Pleuragramma antarcticum and Notothenia coriiceps

Antifreeze protein type IV (AFPIV) cDNAs and genomic DNAs from the Antarctic fishes Pleuragramma antarcticum (Pa) and Notothenia coriiceps (Nc) were cloned and sequenced, respectively. Each cDNA encoded 128 amino acids, with 94% similarity between the two and 83% similarity with AFPIV of the longhorn sculpin, Myoxocephalus octodecemspinosus. The genome structures of both genes consisted of four exons and three introns, and were highly conserved in terms of sequences and positions. In contrast, the third intron of PaAFPIV had additional nucleotides with inverted repeats at each end, which appeared to be a MITE-like transposable element. Comparative analysis revealed that fish AFPIVs were widely distributed across teleost fishes, well conserved in their intron positions, but more variable in intron sequences and sizes. However, the intron sequences of two Antarctic fishes were highly conserved, indicating recent radiation of notothenioids in the evolutionary lineage. The recombinant PaAFPIV and NcAFPIV were expressed in E. coli, and examined antifreeze activity. PaAFPIV and NcAFPIV gave ice crystals with star-shaped morphology, and thermal hysteresis (TH) values were 0.08°C at the concentration of 0.5mg/ml.

High density lipoprotein: it's not just about lipid transport anymore

Plasma levels of high density lipoprotein cholesterol (HDL-C) have long been associated with protection against cardiovascular disease (CVD) in large populations. However, HDL-C has been significantly less useful for predicting CVD risk in individual patients. This has ignited a new debate on the merits of measuring HDL quantity versus quality in terms of protective potential. In addition, numerous recent studies have begun to uncover HDL functions that vary surprisingly from traditional lipid transport roles. In this paper, we review recent findings that point to important functions for HDL that go well beyond lipid transport. These discoveries suggest that HDL might be a platform that mediates protection from a host of disease states ranging from CVD to diabetes to infectious disease.

Effect of ivermectin on the liver of gilthead sea bream Sparus aurata: a proteomic approach

Gilthead sea bream Sparus aurata is the most commercialized Mediterranean aquacultured fish species. Ivermectin has recently (experimentally) started to be used to control ectoparasitic infestations in Mediterranean cultured marine fish. The potential hepatotoxicity of ivermectin was investigated in gilthead sea bream juveniles (35g) following oral administration at the recommended dose of 0.2 mgkg(-1) fish for 10d. Difference Gel Electrophoresis Technology (DIGE) was used to study the effect of this treatment in gilthead sea bream liver protein profile under routine culture conditions. The 2D-DIGE protein maps obtained were analyzed using the DeCyder 6.5 software. The results obtained showed significant changes in the expression of 36 proteins respect to the control group. Among these proteins, six increased in abundance, and 30 decreased. Spot showing differential expression respect to the control were analyzed by mass spectrometry and database search, which resulted in three positive identifications corresponding to hepatic proteins involved in lipid metabolism (apoA-I), oxidative stress responses and energy generation (beta-globin, ATP synthase subunit beta). These proteins have not been previously associated to invermectin effect.

Conventional and unconventional antimicrobials from fish, marine invertebrates and micro-algae

All eukaryotic organisms, single-celled or multi-cellular, produce a diverse array of natural anti-infective agents that, in addition to conventional antimicrobial peptides, also include proteins and other molecules often not regarded as part of the innate defences. Examples range from histones, fatty acids, and other structural components of cells to pigments and regulatory proteins. These probably represent very ancient defence factors that have been re-used in new ways during evolution. This review discusses the nature, biological role in host protection and potential biotechnological uses of some of these compounds, focusing on those from fish, marine invertebrates and marine micro-algae.