In vitro response of the striped bass natural resistance-associated macrophage protein, Nramp, to LPS and Mycobacterium marinum exposure

Molecular identification and expression analysis of natural resistance-associated macrophage protein (Nramp) gene from yellow catfish Pelteobagrus fulvidraco (Siluriformes: Bagridae)

Natural resistance associated macrophage protein genes (Nramp) is one of the important candidate genes responsible for regulating immune response against pathogen infection. The aim of the present was to quantify expression of Nramp gene in response to pathogen infection. Here, a Nramp was identified and molecularly characterized from Pelteobagrus fulvidraco (PfNramp). The obtained 3134 bp cDNA fragment of PfNramp comprised a 5'-untranslated region (UTR) of 81 bp, a 3'-UTR of 1403 bp and an open reading frame (ORF) of 1650 bp, encoding a polypeptide of 549 amino acids that contained a typical structural features of Nramp domain (Pfam01566). BLAST analysis exhibited that PfNramp shared sequence similarity to other organisms, in particular to Ictalurus furcatus (92%), Danio rerio (82%), and Homo sapiens (77%). Phylogenetic analysis revealed that PfNramp is close to Teleostei. Real-time quantitative reverse transcription-PCR (qRT-PCR) analysis showed that PfNramp was expressed in all examined tissues, with the highest abundance in liver. The mRNA expression of PfNramp was remarkably increased at different time points after lipopolysaccharide (LPS), and polyriboinosinic polyribocytidylic acid (poly I:C) challenge. These results suggest that PfNramp is an inducible protein in the innate immune reactions of P. fulvidraco and probably in other fish species.

Natural Resistance Associated Macrophage Protein Is Involved in Immune Response of Blunt Snout Bream, Megalobrama amblycephala

The natural resistance-associated macrophage protein gene (Nramp), has been identified as one of the significant candidate genes responsible for modulating vertebrate natural resistance to intracellular pathogens. Here, we identified and characterized a new Nramp family member, named as maNramp, in the blunt snout bream. The full-length cDNA of maNramp consists of a 153 bp 5′UTR, a 1635 bp open reading frame encoding a protein with 544 amino acids, and a 1359 bp 3′UTR. The deduced protein (maNRAMP) possesses the typical structural features of NRAMP protein family, including 12 transmembrane domains, three N-linked glycosylation sites, and a conserved transport motif. Phylogenetic analysis revealed that maNRAMP shares the significant sequence consistency with other teleosts, and shows the higher sequence similarity to mammalian Nramp2 than Nramp1. It was found that maNramp expressed ubiquitously in all normal tissues tested, with the highest abundance in the spleen, followed by the head kidney and intestine, and less abundance in the muscle, gill, and kidney. After lipopolysaccharide (LPS) stimulation, the mRNA level of maNramp was rapidly up-regulated, which reached a peak level at 6 h. Altogether, these results indicated that maNramp might be related to fish innate immunity and similar to mammalian Nramp1 in function.

Antimicrobial responses of teleost phagocytes and innate immune evasion strategies of intracellular bacteria

During infection, macrophage lineage cells eliminate infiltrating pathogens through a battery of antimicrobial responses, where the efficacy of these innate immune responses is pivotal to immunological outcomes. Not surprisingly, many intracellular pathogens have evolved mechanisms to overcome macrophage defenses, using these immune cells as residences and dissemination strategies. With pathogenic infections causing increasing detriments to both aquacultural and wild fish populations, it is imperative to garner greater understanding of fish phagocyte antimicrobial responses and the mechanisms by which aquatic pathogens are able to overcome these teleost macrophage barriers. Insights into the regulation of macrophage immunity of bony fish species will lend to the development of more effective aquacultural prophylaxis as well as broadening our understanding of the evolution of these immune processes. Accordingly, this review focuses on recent advances in the understanding of teleost macrophage antimicrobial responses and the strategies by which intracellular fish pathogens are able to avoid being killed by phagocytes, with a focus on Mycobacterium marinum.

Cytochrome P4501A mRNA and protein induction in striped bass (Morone saxatilis)

The striped bass (Morone saxatilis) supports a valuable recreational fishery and is among the most important piscivorous fish of the San Francisco Estuary. This species has suffered a significant decline in numbers over the past decades, and there is indication that contaminants are important contributors. Polycyclic aromatic hydrocarbons (PAHs) and polyhalogenated aromatic hydrocarbons (PHAHs) including PCBs and dioxins are widespread in the estuary, they typically bioaccumulate through trophic levels, reaching highest levels in top predators and are known to affect the fish health and development. The aim of this study was to investigate the dynamics of cytochrome P4501A (Cyp1a) induction simultaneously at different levels of biological organization (RNA transcription and protein synthesis) as a biomarker of exposure to PAHs and PHAHs. We utilized β-naphthoflavone (BNF) as a model PAH to induce Cyp1a responses in juvenile striped bass in both dose-response and time-response assessments and determined Cyp1a mRNA and protein levels. Significant responses were measured in both systems at 10 mg ΒΝF kg⁻¹, a concentration used for time-response studies. Messenger RNA levels peaked at 6 h post-injection, while protein levels increased progressively with time, significantly peaking at 96 h post-injection; both remaining elevated throughout the duration of the test (8 days). Our data suggest that rapid induction of gene transcription following exposure and subsequent cumulative protein synthesis could provide a useful means of identifying temporal variants in exposure to Cyp1a inducers in Morone saxatilis. The potential application of this combined Cyp1a gene and protein biomarker in this species for field studies is discussed.