Cloning, characterization and mRNA expression of interleukin-6 in blunt snout bream (Megalobrama amblycephala)

Manipulated C5aR1 over/down-expression associates with IL-6 expression during bacterial inflammation in half-smooth tongue sole (Cynoglossus semilaevis)

The complement component 5a/complement component 5 receptor 1 (C5a/C5aR1) pathway plays a crucial role in the onset and development of inflammation, but relevant studies in fish are lacking. In this study, we successfully characterized the relationship between half-smooth tongue sole (Cynoglossus semilaevis) C5aR1 (CsC5aR1) and bacterial inflammation. First, we showed that the overexpression of CsC5aR1 significantly increased bacterial pathological damage in the liver and intestine, whereas inhibition attenuated the damage. The in vitro experiments suggested that CsC5aR1 was able to positively regulate the phagocytic activity and respiratory burst of tongue sole macrophages. In terms of both transcriptional and translational levels, overexpression/inhibition of CsC5aR1 was followed by a highly consistent up-regulation/decrease of its downstream canonical inflammatory factor interleukin-6 (CsIL-6). Furthermore, we stimulated macrophages by lipopolysaccharide (LPS) and lipoteichoic acid (LTA) and found a broad-spectrum response to bacterial infections by the C5a/C5aR1 complement pathway together with the downstream inflammatory factor CsIL-6. Subsequently, we directly elucidated that CsIL-6 is an indicator of C5a/C5aR1-mediated inflammation at different infection concentrations, different infectious bacteria (Vibrio anguillarum and Mycobacterium marinum), and different detection levels. These results might provide a new inflammation bio-marker for early warning of bacteria-induced hyperinflammation leading to fish mortality and a promising target for the treatment of bacterial inflammation in teleost.

Molecular Characterization and Expression Analysis of IL-10 and IL-6 in Channel Catfish (Ictalurus punctatus)

IL-10 and IL-6 play important roles in protecting against inflammation and clearing pathogens from the body. In this study, homologous compounds of IL-10 and IL-6 were identified in channel catfish, and their immune responses were analyzed. The CDS sequences of IL-10 and IL-6 were 549 bp and 642 bp, respectively, and showed the highest homology with Ameiurus melas. In addition, the expression of the IL-10 and IL-6 genes was ubiquitous in 10 tissues examined. IL-10 is highly expressed in the liver and slightly expressed in the gill. The high expression of the IL-6 gene was observed in the spleen, heart, and gonad, with the lowest levels in the liver. LPS, Poly(I:C), PHA, and PMA showed a highly significant increase in IL-10 and IL-6 expression 48 h after CCK stimulation (p < 0.01). Otherwise, Yersinia ruckeri, Streptococcus iniae, channel catfish virus, and deltamethrin induced IL-10 and IL-6 expression, varying in intensity between different organs. Our results suggest that IL-10 and IL-6 are involved in the immune response of the host against the pathogen.

Effect of dietary phenylalanine on growth performance and intestinal health of triploid rainbow trout (Oncorhynchus mykiss) in low fishmeal diets

This study aimed to investigate the effects of phenylalanine on the growth, digestive capacity, antioxidant capability, and intestinal health of triploid rainbow trout (Oncorhynchus mykiss) fed a low fish meal diet (15%). Five isonitrogenous and isoenergetic diets with different dietary phenylalanine levels (1.82, 2.03, 2.29, 2.64, and 3.01%) were fed to triplicate groups of 20 fish (initial mean body weight of 36.76 ± 3.13 g). The weight gain rate and specific growth rate were significantly lower (p < 0.05) in the 3.01% group. The trypsin activity in the 2.03% group was significantly higher than that in the control group (p < 0.05). Amylase activity peaked in the 2.64% treatment group. Serum superoxide dismutase, catalase, and lysozyme had the highest values in the 2.03% treatment group. Liver superoxide dismutase and catalase reached their maximum values in the 2.03% treatment group, and lysozyme had the highest value in the 2.29% treatment group. Malondialdehyde levels in both the liver and serum were at their lowest in the 2.29% treatment group. Interleukin factors IL-1β and IL-6 both reached a minimum in the 2.03% group and were significantly lower than in the control group, while IL-10 reached a maximum in the 2.03% group (p < 0.05). The tight junction protein-related genes occludin, claudin-1, and ZO-1 all attained their highest levels in the 2.03% treatment group and were significantly higher compared to the control group (p < 0.05). The intestinal villi length and muscle layer thickness were also improved in the 2.03% group (p < 0.05). In conclusion, dietary phenylalanine effectively improved the growth, digestion, absorption capacity, antioxidant capacity, and intestinal health of O. mykiss. Using a quadratic curve model analysis based on WGR, the dietary phenylalanine requirement of triploid O. mykiss fed a low fish meal diet (15%) was 2.13%.

The effects of blunt snout bream (Megalobrama amblycephala) IL-6 trans-signaling on immunity and iron metabolism via JAK/STAT3 pathway

Interleukin-6 (IL-6) is a pleiotropic inflammatory cytokine, which plays a dual role in mammalian inflammation through both classical signaling (IL-6 binds to IL-6 receptor/IL-6R) and trans-signaling (IL-6 binds to soluble IL-6R). However, the function of IL-6, especially the regulatory mechanism of IL-6 trans-signaling in immunity and iron metabolism remains largely unclear in teleost. Here, L8824 cells (Ctenopharyngodon idella hepatic cells) were stimulated with blunt snout bream (Megalobrama amblycephala) IL-6 combination with sIL-6R protein (rmaIL-6+rmasIL-6R/maIL-6 trans-signaling) or STAT3 inhibitor (c188-9), and RNA-sequencing, global transcriptional analyses. The enrichment analysis of GO and KEGG showed that maIL-6 trans-signaling is mainly involved in stress and inflammation response, and the activation of STAT3 is mainly related to cell proliferation, apoptosis and immune regulation. Furthermore, after treated L8824 cells with JAK2 inhibitors, it was found that the induction of IL-6 trans-signaling on the selected immune-related genes could be inhibited. These results implied that in early stage after rmaIL-6+rmasIL-6R treatment, the maIL-6 trans-signaling played an important role in the immune regulation through the JAK2/STAT3 pathway. By extending the rmaIL-6+rmasIL-6R treatment time, it was found that maIL-6 trans-signaling could promote the expression of iron metabolism related genes (ft, tf, tfr1, hamp and fpn1) in L8824 cells, indicating that maIL-6 trans-signaling may be involved in iron metabolism in the non-acute immune phase. Finally, after treated L8824 cells with JAK2 and STAT3 inhibitors, it was found that only tf and fpn1 were regulated by maIL-6 trans-signaling through the JAK2/STAT3 pathway. These findings provided novel insights into IL-6 trans-signaling regulatory mechanism in teleost, enriching our knowledge of fish immunity and iron metabolism.

Classical Signaling and Trans-Signaling Pathways Stimulated by Megalobrama amblycephala IL-6 and IL-6R

Interleukin-6 (IL-6) is a multipotent cytokine. IL-6 plays a dual role in inflammation through both classical signaling (IL-6 binds membrane IL-6 receptor/IL-6R) and trans-signaling (IL-6 binds soluble IL-6R). However, the regulation of IL-6 activity, especially the regulation of signaling pathways and downstream genes mediated by IL-6 trans-signaling, remains largely unclear in teleost. Grass carp (Ctenopharyngodon idellus) hepatic (L8824) cells, kidney (CIK) cells, and primary hepatocytes were used as test models in this study. First, the biological activity of recombinant blunt snout bream (Megalobrama amblycephala) IL-6 (rmaIL-6) and sIL-6R (rmasIL-6R) was verified by quantitative PCR (qPCR) and western blot. The western blot results showed that rmaIL-6 significantly upregulated signal transducer and activator of transcription 3 (STAT3) phosphorylation in L8824 cells and primary hepatocytes, while rmaIL-6 in combination with rmasIL-6R (rmaIL-6+rmasIL-6R) significantly upregulated STAT3 phosphorylation in all types of cells. Furthermore, maIL-6 and maIL-6+rmasIL-6R could only induce extracellular-signal-regulated kinase 1/2 (ERK1/2) phosphorylation in L8824 cells and CIK cells, respectively. Therefore, IL-6 mainly acts by activating the janus kinase (JAK)/STAT3 pathway rather than the mitogen-activated protein kinase (MEK)/ERK pathway. Finally, the activation of the JAK2/STAT3 pathway was shown to be essential for the generation of socs3a and socs3b induced by IL-6 trans-signaling after treatment by JAK2/STAT3 pathway inhibitors (c188-9 and TG101348). These findings provide functional insights into IL-6 classical signaling and trans-signaling regulatory mechanisms in teleost, enriching our knowledge of fish immunology.

Molecular cloning, expression HSP70 and its response to bacterial challenge and heat stress in Microptenus salmoides

The gene encoding HSP70 was isolated from Microptenus salmoides by homologous cloning and rapid amplification of cDNA ends (RACE). The HSP70 transcripts were 2116 bp long and contained 1953 open reading frames encoding proteins of 650 amino acids with a molecular mass of 71.2 kDa and theoretical isoelectric point of 5.22. The qRT-PCR analysis showed that the HSP70 gene was differentially expressed in various tissues under normal conditions, and the highest HSP70 level was observed in the spleen and the lowest levels in the muscle and heart. The clear time-dependent expression level of HSP70 was observed after bacterial challenge and heat stress. A significant increase in HSP70 expression level was detected and reached a maximum at 3 h and 6 h in liver, spleens and gill tissues after Aeromonas hydrophila infection and heat stress, respectively (P < 0.05). As time progressed, the expression of HSP70 transcript was downregulated and mostly dropped back to the original level at 48 h. The concentration of cortisol, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) increased as the time of stress progressed, with the highest level found on 3 h and later declined rapidly and reached to the control levels at the 48 h. Those results suggested that HSP70 was involved in the immune response to bacterial challenge and heat stress. The cloning and expression analysis of the HSP70 provide theoretical basis to further study the mechanism of anti-adverseness in Microptenus salmoides.

Withania somnifera dietary supplementation improves lipid profile, intestinal histomorphology in healthy Nile tilapia (Oreochromis niloticus), and modulates cytokines response to Streptococcus infection

Despite Withania somnifera (WS), stimulating effects have been investigated on many animal species, its role on lipid profile and intestinal histomorphology in healthy animals, and its modulating role on pro-inflammatory cytokines following infection in fish are yet scarce. In this context, lipid profile, liver, and intestinal histomorphology were measured in Nile tilapia fed with a basal diet or diets containing 2.5 and 5% of supplementary WS for 60 days. Besides, cytokines response was measured at 1, 3,7, and 14 days following Streptococcus iniae (S. iniae) infection after the feeding trial. All lipid profile parameters were nominally lowered, excluding high-density lipoprotein (HDL) that exhibited a significant increase in WS 5% group compared to other groups. Improved gut health integrity was observed, especially in WS 5% group in terms of increased goblet cell numbers, villous height, the width of lamina propria in all parts of the intestine, and a decrease in the diameter of the intestinal lumen of the distal intestine only. A significant down-regulation in the mRNA transcript level of cytokine genes (interleukin 1β/IL-1β, tumor necrosis factor α/TNFα, and interleukin 6/IL-6) was demonstrated in the kidney and spleen of WS-supplemented groups following S. iniae infection compared with the control infected (positive control/PC) group. Our findings give new insights for the potential roles of WS dietary inclusion not only on lipid profile and intestinal health integrity improvement in healthy fish under normal rearing but also as a prophylactic against the infection. Thus, WS can be incorporated as a promising nutraceutical in aquaculture.

A New IL6 Isoform in Chinese Soft-Shelled Turtle (Pelodiscus sinesis) Discovered: Its Regulation during Cold Stress and Infection

The Chinese soft-shelled turtle (Pelodiscus sinesis) is a widely cultured commercial species in East and Southeast Asian countries. The turtles frequently suffer from acute cold stress during farming in China. Stress-induced factor such as Interleukin-6 (IL6) is a multifunctional molecule that plays important roles in innate and adaptive immune response. In the present study, we found that the turtle possessed two IL6 transcripts, where one IL6 transcript contained a signal peptide sequence (psIL6), while the other IL6 transcript (psIL6ns) possessed no such signal peptide gene. To test any differential expression of the two isoforms during temperature and microbial stress, turtles were adapted to optimal environmental water temperature (25 °C), stressed by acute cooling for 24 h, followed with the challenge of Aeromonas hydrophila (1.8 × 10⁸ CFU) or Staphylococcus aureus (5.8 × 10⁸ CFU). Gene characterization revealed that psIL6ns, a splicer without codons encoding a signal peptide and identical to the one predicted from genomic sequence, and psIL6, a splicer with codons encoding a signal peptide, were both present. Inducible expression was documented in primary spleen cells stimulated with ConA and poly I: C. The splenic and intestinal expression of psIL6ns and psIL6 was increased in response to temperature stress and bacterial infection.

Regulation of Il-10 gene expression by Il-6 via Stat3 in grass carp head kidney leucocytes

Interleukin (IL)-10 is a critical anti-inflammatory and late cytokine being produced after the proinflammatory mediators while IL-6 is a promptly synthesized cytokine in response to inflammation in mammals. This chronological expression of interleukin (Il)-6 and Il-10 was also found in grass carp head kidney leucocytes (HKLs) treated by heat-killed Aeromonas hydrophila, supporting the possible interplay between grass carp (gc)Il-6 and gcIl-10 in HKLs. Our further findings were in agreement with this hypothesis that recombinant gcIl-6 (rgcIl-6) promptly and transiently increased gcil10 mRNA levels in grass carp HKLs. Moreover, rgcIl-6 enhanced its own mRNA level and this self-enhancement of gcil6 mRNA level could be partially blocked by rgcIl-10. These results collectively suggest that gcIl-10 production stimulated by gcIl-6 may provide a negative feedback to gcIl-6 production. Interestingly, rgcIl-6 significantly decreased gcil10 mRNA levels in grass carp HKLs after the treatment for 12 and 24 h in contrast to its enhancement of gcil10 levels after the treatment for 3 h. Involvement of Stat3 but not MEK, p38 MAPK or JNK pathway in the increase of gcil10 mRNA levels by rgcIl-6 was revealed by using the signaling pathway inhibitors. This was supported by the fact that rgcIl-6 stimulated Stat3 phosphorylation in grass carp HKLs. Furthermore, rgcIl-6 had no effect on the stability of gcil10 mRNA after the treatment for 3 to 36 h while it increased gcil10 promoter activity after the treatment for 24 h. Taken these data together, gcIl-6 can stimulate Il-10 production at early stage but subsequently inhibit il10 mRNA expression in grass carp HKLs, shedding light on the dynamic regulation of il10 mRNA expression by Il-6 in fish immune cells.

The interleukin-6 regulates the function of monocytes/macrophages (MO/MФ) via the interleukin-6 receptor β in ayu (Plecoglossus altivelis)

Interleukin-6 (IL-6) is one of the most pleiotropic cytokines because of its wide range of effects on cells of the immune and non-immune systems in the body. However, the role of IL-6 in fish monocytes/macrophages (MO/MФ) is poorly understood. In this study, we cloned the cDNA sequence of the IL-6 gene from ayu (Plecoglossus altivelis) and demonstrated using a tissue distribution assay that ayu interleukin-6 (PaIL-6) mRNA is expressed in all tested tissues. Changes in expression were observed in immune tissues as well as in MO/MФ after a Vibrio anguillarum infection; subsequently, PaIL-6 was expressed and purified to prepare anti-PaIL-6 antibodies. Recombinant PaIL-6 protein (rPaIL-6) treatment enhanced pro-inflammatory cytokine expression. Ayu interleukin-6 receptor β (PaIL-6Rβ) knockdown resulted in decreased pro-inflammatory cytokine expression in MO/MФ treated with rPaIL-6, whereas no significant changes were observed after ayu interleukin-6 receptor α (PaIL-6Rα) knockdown in MO/MФ. PaIL-6 and PaIL-6Rβ knockdown in MO/MФ inhibited the phosphorylation of signal transducer and activator of transcription 1. Moreover, PaIL-6Rβ knockdown inhibited the phagocytic and bactericidal ability of ayu MO/MФ treated with rPaIL-6. These data indicate that PaIL-6 may be able to regulate the function of ayu MO/MФ.

Comparative transcriptomic analysis reveals the gene expression profiles in the liver and spleen of Japanese pufferfish (Takifugu rubripes) in response to Vibrio harveyi infection

Japanese pufferfish (Takifugu rubripes) is one of the main marine aquatic fish species cultured in Asia due to its high nutritional value. In recent years, disease caused by Vibrio harveyi infections have led to serious mortality in Japanese pufferfish industry. To understand the complex molecular mechanisms between V. harveyi and Japanese pufferfish, we performed a transcriptome analysis of liver and spleen samples from Japanese pufferfish at 1 and 2 day post-infection. Between-group comparisons revealed 922 genes that were significantly differentially expressed. The altered genes emphasized the function in several immune related pathways including MAPK signaling pathway, JAK-STAT signaling pathway, toll-like receptor signaling pathway, cytokine-cytokine receptor interaction and lysosomal pathway. The data generated in this study provided insight into the responses of Japanese pufferfish against V. harveyi at the transcriptome level, promoting our comprehensive understanding of immune responses for aquatic animal against V. harveyi.

Molecular characterization of p38 MAPK from blunt snout bream (Megalobrama amblycephala) and its expression after ammonia stress, and lipopolysaccharide and bacterial challenge

p38 mitogen-activated protein kinase (MAPK) is an important protein which plays a key role in regulating the innate immunity, so exploring its molecular characterization is helpful in understanding the resistance against microbial infections in cultured fish. Here, a full-length cDNA of p38 MAPK was cloned from liver of blunt snout bream (Megalobrama amblycephala) which covered 2419 bp with an open reading frame of 1086 bp encoding 361 amino acids. p38 MAPK contained the characteristic structures of Thr-Gly-Tyr (TGY) motif and substrate binding site Ala-Thr-Arg-Trp (ATRW), which are conserved in MAPK family. To investigate p38 MAPK functions, two in vivo experiments were carried out to examine its expression following ammonia exposure and bacterial challenge. Also, an in vitro experiment was conducted to assess the role of p38 MAPK in inflammation of primary hepatocytes induced by lipopolysaccharide (LPS). The results showed the ubiquitous expression of p38 MAPK in all the tested tissues with varying levels. p38 MAPK mRNA expression was significantly up-regulated by ammonia stress and Aeromonas hydrophila challenge, and altered in a time-dependent manner. Moreover, the results indicated that the inflammatory response induced by LPS in hepatocytes is p38 MAPK dependent as knockdown of p38 MAPK using siRNA technology depressed the expression of IL-1β and IL-6. The findings in this study showed that p38 MAPK has anti-stress property, and plays key role in protection against bacterial infection and inflammation in blunt snout bream.

Differential effects of β-glucan on oxidative stress, inflammation and copper transport in two intestinal regions of large yellow croaker Larimichthys crocea under acute copper stress

The aim of the present study was to evaluate investigate the effects of β-glucan on oxidative stress, inflammation and copper transport in two intestinal regions of large yellow croaker under acute copper stress. Fish were injected with β-glucan at a dose of 0 or 5 mg kg^-1 body weight on 6, 4 and 2 days before exposed to 0 and 368 μg Cu L^-1 for 48 h. Biochemical indicators (MDA, Cu content, MTs protein levels, Cu/Zn-SOD, CAT and iNOS activities), gene expressions of oxidative stresses (Cu/Zn-SOD, CAT, Nrf2, MTs and MTF-1), inflammatory responses (NF-κB, iNOS, IL-1β, IL-6 and TNF-α) and Cu transporters (ATP7A, ATP7B and CTR1) were determined. In the anterior intestine, β-glucan increased MTs levels, activities of Cu/Zn-SOD, CAT and iNOS, mRNA levels of MTs, CAT, iNOS, ATP7A and ATP7B, and reduced Cu content and CTR1 gene expression to inhibite Cu-induced MDA. But β-glucan had no effect on inflammatory gene expressions. In the mid intestine, β-glucan increased activities of Cu/Zn-SOD and iNOS, mRNA levels of Cu/Zn-SOD, CAT and iNOS to maintain MDA content. However, unlike the anterior intestine, β-glucan had no effect on Cu transporter gene expressions. Furthermore, transcription factors (Nrf2, NF-κB and MTF-1) paralleled with their target genes in the mid intestine, but no correlation was observed between NF-κB and IL-1β and TNF-α gene expressions in the anterior intestine. In conclusion, our results unambiguously showed that β-glucan induced oxidative stress, inflammation and copper transport were varied between the anterior and mid intestines of fish under Cu stress.

Molecular cloning, expression and antibacterial activity of goose-type lysozyme gene in Microptenus salmoides

It is well known that lysozymes are key proteins to teleosts in the innate immune system and possess high bactericidal properties. In the present study, a g-type lysozyme gene was cloned from Microptenus salmoides. The g-type sequence consisted of 582 bp, which translated into a 193 amino acid (AA) protein (GenBank accession no: MH087462). The predicted molecular weight and theoretical isoelectric point were 21.36 kDa and 6.91 respectively and no signal peptide was observed. The qRT-PCR analysis showed that the g-type lysozyme gene was differentially expressed in various tissues under normal conditions and the highest g-type lysozyme level was observed in liver, gill and spleen while there seemed to be low expression in the muscle, heart and head-kidney. The expression of g-type lysozyme was differentially upregulated in the spleen, gill and intestine after stimulation with heat stress and Aeromonas hydrophila (A. hydrophila). Under heat stress and A. hydrophila injection, the g-type lysozyme mRNA levels all in spleens, gill and intestine tissues increased significantly (P < 0.05), with the maximum levels attained at 12 h, 24 h (or 12 h) and 24 h. Thereafter, they all decreased significantly (P < 0.01) and the expression in gill returned to nearly the basal value within 72 h. Those results suggested that g-type lysozyme was involved in the immune response to heat stress and bacterial challenge. The cloning and expression analysis of the g-type lysozyme provide theoretical basis to further study the mechanism of anti-adverseness in Microptenus salmoides. The g-type lysozyme gene perhaps also played an important role in the immune responses against bacterial invasion.

Effects of heat and cadmium exposure on stress-related responses in the liver of female zebrafish: Heat increases cadmium toxicity

In this study, female zebrafish (Danio rerio) were exposed to 26°C or 34°C, 0 or 197μg/L cadmium (Cd), singly or in combination for 7days. Multiple stress-related indicators were evaluated in the liver. Mortality, lipid peroxidation (LPO) and ultrastructural damage increased significantly by Cd exposure alone, and were not affected by heat alone. Interestingly, the combined exposure increased LPO, ultrastructural damage, and mortality compared with Cd exposure alone. The results indicated that elevated temperature increased Cd toxicity, which could be explained by several reasons. Firstly, Cd-exposed fish failed to activate the antioxidant defense system under heat stress. Secondly, expression levels of heat shock protein 70 (HSP70) were not significantly up-regulated by heat in Cd-exposed fish but increased by 117 times in Cd-free fish. Besides, hypermethylation of heat shock factor (HSF) binding motif in HSP70 promoter was observed during the combined exposure, indicating that simultaneous exposure may have partially suppressed the cytoprotective up-regulation of HSP70. Thirdly, heat induced an immunosuppressive effect in Cd-exposed fish, as reflected by the reduced mRNA and activity levels of nitric oxide synthase (iNOS) and interleukin-1β (IL-1β) expression levels. Finally, heat down-regulated Zir-, Irt-like protein 8 (ZIP8) and copper transporter 1 (CTR1) and up-regulated metallothioneins (MTs) in Cd-exposed fish, possibly suggesting Cu and Zn depletion and Cd accumulation. Hence, our data provide evidences that warmer temperatures can potentiate Cd toxicity, involved in the regulation of gene transcription, enzymatic activity, and DNA methylation. We found that heat indicators showed varied sensitivity between normal and Cd-exposed fish, emphasizing that the field metal pollution should be carefully considered when evaluating effects of climate change.

Heat-induced oxidative stress and inflammation involve in cadmium pollution history in the spleen of zebrafish

Zebrafish were exposed to 0, 2.5 and 5 μg/L cadmium (Cd) for 10 weeks, and then each group was exposed to 26 °C(control) and 32 °C (high temperature) for 7 days. 22 indicators were compared between 26 °C and 32 °C in the spleen, including body weight, LPO and NO levels, activity levels of Cu/Zn-SOD, CAT and iNOS, MTs protein levels, and mRNA levels of Nrf2, Cu/Zn-SOD, CAT, HSF1, HSF2, HSP70, MTF-1, MTs, IL-6, IL-10, IL-1β, TNF-α, iNOS and NF-κB. Most indicators were not significantly affected by heat in fish from no Cd pollution. However, almost all of indicators were responsive to heat in fish pre-exposed to Cd. Several indicators were sensitive to heat in fish pre-exposed to 2.5 μg/L Cd such as iNOS activities, and mRNA levels of iNOS and IL-10. Most other indicators were sensitive to heat in fish pre-exposed to 5 μg/L. The mRNA levels of HSP70 and MTF-1 were up-regulated by heat in fish pre-exposed to 0, 2.5 and 5 μg/L Cd. However, the magnitude of increase was the greatest in fish pre-exposed to 5 μg/L Cd. These differences between control and high temperature would serve as biomarkers to distinguish healthy from Cd-polluted group. The findings imply that metal pollution history should be carefully considered when screening heat biomarkers in fish.

Effect of Dietary Acidolysis-Oxidized Konjac Glucomannan Supplementation on Serum Immune Parameters and Intestinal Immune-Related Gene Expression of Schizothorax prenanti

The present study was conducted to investigate the effects of dietary acidolysis-oxidized konjac glucomannan (A-OKGM) (0%, 0.4%, 0.8%, and 1.6%) supplementation on the immunity and expression of immune-related genes in Schizothorax prenanti. After feeding for eight weeks, the serum and guts were used for measurement of biochemical parameters, and immune-related gene expression in the gut were also analyzed by real-time quantitative polymerase chain reaction (RT-qPCR). C-reactive protein and IgM levels were significantly higher in the A-OKGM fed groups than in the control group, regardless of the dosage. The 0.4% and 1.6% A-OKGM groups showed significant up-regulation of tumor necrosis factor α (TNFα) in the anterior gut. The 0.8% and 1.6% A-OKGM groups also showed significantly enhanced TNFα expression in the mid- and distal guts. Interleukin-1β (IL-1β) expression in the anterior gut of fish fed with 0.4% and 1.6% A-OKGM diets was significantly enhanced. The 0.8% and 1.6% A-OKGM diets resulted in significantly increased the expression of IL-1β in the distal gut. Similarly, the interleukin-6 (IL-6) messenger RNA (mRNA) levels in the 0.4% and 1.6% diet groups were significantly higher in the anterior gut. The 0.8% and 1.6% A-OKGM diet groups showed significant induction of IL-6 gene expression in the distal gut. A-OKGM modified from KGM can act as an immunostimulant to enhance the immunity of S. prenanti.

Preheating mitigates cadmium toxicity in zebrafish livers: Evidence from promoter demethylation, gene transcription to biochemical levels

The working hypothesis for this study was that moderate heat stress would alleviate the deleterious effects of subsequent cadmium (Cd) exposure on fish. Thus, zebrafish (Danio rerio) were subjected to water maintained at 26°C and 34°C for 4days, and then exposed to 0 or 200μg/L Cd for 1 week at 26°C. Multiple indicators were measured from livers of zebrafish at different levels, including DNA, RNA, protein and enzymatic activity associated with oxidative stress, inflammation and metal transport. The ameliorative effect of preheatinging on Cd toxicity was demonstrated. In the Cd-exposed groups, preheating decreased mortality and lipid peroxidation, increased activity levels of catalase (CAT) and copper/zinc-superoxide dismutase (Cu/Zn-SOD), and up-regulated mRNA levels of heat shock protein 70 (HSP70) and heat shock factor 2 (HSF2). Preheating also mitigated Cd-induced increases in protein and mRNA levels of metallothioneins (MTs), and mRNA levels of several inflammation-related genes. Furthermore, preheating alone dramatically up-regulated mRNA levels of genes related to antioxidant and immune defenses, zinc and copper transporters, protein folding, and reduced methylation levels in the HSF binding motif of the HSP70 promoter. Overall, preheating-induced accumulation of transcripts via demethylation might support the rapid defense responses at post-transcriptional levels caused by subsequent Cd exposure, indicating an adaptive mechanism for organisms exposed to one mild stressor followed by another.

Immunosuppressive effects and associated compensatory responses in zebrafish after full life-cycle exposure to environmentally relevant concentrations of cadmium

In natural environments, fish survive in polluted water by cadmium (Cd) throughout their whole life cycle. However, little information is available on Cd toxicity considering a life cycle assessment. The present study investigated effects of environmental levels of cadmium (0, 2.5, and 5μg/L) on immune responses in liver and spleen of zebrafish for 15 weeks, from embryos to sexually maturity. Nitric oxide (NO) levels and iNOS activity declined in liver and spleen of zebrafish exposed to 5μg/L Cd, suggesting an immunosuppressive effect. The result was further supported by the decreased transcriptional levels of proinflammatory cytokines by Cd, such as interleukin-6 (IL-6), interleukin-10 (IL-10), interleukin-1β (IL-1β), and tumour necrosis factor-α (TNF-α) in liver. However, a sharp increase in the mRNA levels of these cytokines was observed in spleen of zebrafish exposed to Cd. The increased mRNA expression of these proinflammatory cytokines may be the secondary effect following immunosuppression and just reflect a compensatory mechanism for coping with the decreased immunity, which may explain an increase in mRNA levels and a decrease in iNOS activity in spleen of zebrafish exposed to Cd. In liver, the down-regulated mRNA levels of iNOS paralleled with the decreased iNOS activity, suggesting a synchronous response from a molecular level to a biochemical level. Positive correlations between mRNA expression levels of nuclear transcription factor κB (NF-κB) and proinflammatory cytokines were also observed, suggesting that NF-κB might be required for the protracted induction of inflammatory genes. The corresponding changes in the mRNA levels of the inhibitor of κBα (IκBαa and IκBαb) may form a feedback loop to restore transcriptional activity of NF-κB. Furthermore, splenic ROS levels were increased by 5μg/L Cd, possibly activating NF-κB pathway. Taken together, immunosuppressive effects and tissue-dependent compensatory responses were demonstrated in zebrafish after full life-cycle exposure to environmental levels of Cd, indicating a compromise between survival and immunity.

Effect of ammonia-N and pathogen challenge on complement component 8α and 8β expression in the darkbarbel catfish Pelteobagrus vachellii

The complement components C8α and C8β mediate the formation of the membrane attack complex (MAC) to resist pathogenic bacteria and play important roles in innate immunity. Full-length complement C8α (Pv-C8α) and C8β (Pv-C8β) cDNA were identified in the darkbarbel catfish Pelteobagrus vachellii, and their mRNA expression levels were analyzed after ammonia-N and pathogen treatment. The Pv-C8α gene contained 1983 bp, including a 1794-bp open reading frame (ORF) encoding 598 amino acids. The Pv-C8β gene contained 1952 bp, including a 1761-bp ORF encoding 587 amino acids. Pv-C8α and Pv-C8β had the highest amino acid identity with rainbow trout Oncorhynchus mykiss C8α (62%) and Japanese flounder Paralichthys olivaceus C8β (83%), respectively. Sequence analysis indicated that both Pv-C8α and Pv-C8β contained a thrombospondin type-1 (TSP1) domain, a low-density lipoprotein receptor class A (LDLR-A) domain, a membrane attack complex/perforin (MACPF) domain and an epidermal growth factor-like (EGF-like) domain. In addition, Pv-C8α and Pv-C8β were mainly distributed in the liver, head kidney, spleen, and eggs. Under ammonia-N stress, the Pv-C8α and Pv-C8β mRNA levels significantly decreased (P < 0.05), with minimum levels, respectively, attained at 24 and 48 h in the liver, 48 and 24 h in the head kidney, and 24 and 24 h in the spleen. After Aeromonas hydrophila challenge, the Pv-C8α and Pv-C8β mRNA levels significantly increased (P < 0.05), with maximum levels, respectively, attained at 48 and 24 h in the liver, 24 and 48 h in the head kidney, and 48 and 48 h in the spleen. The present study indicated that Pv-C8α and Pv-C8β exhibited important immune responses to infection and that ammonia-N in water decreased the immune responses of Pv-C8α and Pv-C8β.