Transcriptome analysis of the Nile tilapia (Oreochromis niloticus) reveals altered expression of immune genes by cadmium.

Nile tilapia (Oreochromis niloticus) is a worldwide farmed fish and has been widely used for the study on comparative immunology in teleosts. It is well known that cadmium (Cd) can cause a variety of adverse effects in fish. However, data on the effects of Cd in fish liver and the defensive mechanisms of these effects using transcriptome approach are relatively scarce to date. In this study, by using an RNA sequencing approach, the gene expression profiling was performed in livers of tilapia exposed to 0 (control), 50, 100, and 200 µg/L of Cd for 2 months. The results showed that exposure to 50 µg/L Cd altered the expressions of 911 genes, while exposure to 100 and 200 µg/L Cd resulted in 4318 and 3737 differentially expressed genes compared to the control. Weighted correlation network analysis (WGCNA) and gene ontology (GO) analysis identified a 14-gene network linked to the immune system development. Further, in a fuzzy analysis, the GO term immune system development was enriched in cluster 3, and gene expression decreased with increasing Cd levels in a concentration-dependent manner. The qPCR and RNA-seq results identified 4 genes, i.e., dnmt3bb.1, sf3b1, SMARCAL1, and zap70, as convenient potential biological indicators for detecting waterborne Cd. The present results help systematically understand the effects of Cd on the hepatic transcriptome in tilapia.

Combined effects of copper and cadmium exposure on ovarian function and structure in Nile Tilapia (Oreochromis niloticus).

With the rapid development of industrialization and urbanization, the issue of copper (Cu) and cadmium (Cd) pollution in aquatic ecosystems has become increasingly severe, posing threats to the ovarian tissue and reproductive capacity of aquatic organisms. However, the combined effects of Cu and Cd on the ovarian development of fish and other aquatic species remain unclear. In this study, female Nile tilapia (Oreochromis niloticus) were individually or co-exposed to Cu and/or Cd in water. Ovarian and serum samples were collected at 15, 30, 60, 90, and 120 days, and the bioaccumulation, ovarian development, and hormone secretion were analyzed. Results showed that both single and combined exposure significantly reduced the gonadosomatic index and serum hormone levels, upregulated estrogen receptor (er) and progesterone receptor (pr) gene transcription levels, and markedly affected ovarian metabolite levels. Combined exposure led to more adverse effects than single exposure. The data demonstrate that the Cu and Cd exposure can impair ovarian function and structure, with more pronounced adverse effects under Cu and Cd co-exposure. The Cu and Cd affect the metabolic pathways of nucleotides and amino acids, leading to ovarian damage. This study highlights the importance of considering combined toxicant exposure in aquatic toxicology research and provides insights into the potential mechanisms underlying heavy metal-induced reproductive toxicity in fish.

Essential oil from Artemisia argyi alleviated liver disease in zebrafish (Danio rerio) via the gut-liver axis.

The popularity of intensive fish farming has led to the emergence of fish diseases characterized by hepatobiliary syndrome. Artemisia argyi (A. argyi) essential oils have anti-inflammatory and anti-oxidant effects. However, their alleviating effects and mechanism on liver disease in fish are still unclear. Thus, adult zebrafish were used to construct an animal model to observe histopathological damages, determine biochemical parameters and expression of inflammatory cytokines and mRNAs in the PPAR-γ/NF-κB pathway, and conduct 16 S sequencing of intestinal microbiota. The results found that after treatment with A. argyi essential oil, the histopathological damage caused by ethanol was relieved; the CAT, SOD, and GSH levels were remarkably elevated, while the MDA level was obviously lowered (P < 0.05); the expression levels of IL-10 and IFN-γ mRNAs were enhanced, but the levels of IL-1ß, IL-6, PPAR-γ, NF-κB, and TNF-α mRNAs were reduced (P < 0.05) relative to the EtOH group. A. argyi essential oil remarkably attenuated the damage to intestinal tissue structure, and elevated the levels of Muc2, ZO-1, Claudin-1, and Occludin mRNA (P < 0.05). Sequencing of the gut flora showed that A. argyi essential oil significantly altered the composition of gut microbes compared with the EtOH group. In addition, KEGG and COG analyses also showed significant (P < 0.05) changes in acetate cycling metabolism in the EtOH group, catechol 2, 3-dioxygenase and nitroreductase were significantly increased (P < 0.001), and lipid metabolism and terpenoid synthesis were significantly elevated (P < 0.001) in A. argyi essential oil group. The results indicate that A. argyi essential oil could effectively relieve ethanol-caused histopathological damage of livers by modulating the composition of gut microbiota, thus inhibiting the level of IL-1ß and mRNAs in the PPAR-γ/NF-κB pathway, increasing the IL-10 level, reducing the oxidative stress. This may offer a rationale for further research on the rationality of A. argyi as a substitute for feed antibiotics in aquaculture.

Transcriptomics integrated with metabolomics reveals the effect of Lycium barbarum polysaccharide on apoptosis in Nile tilapia (Oreochromis niloticus).

Lycium barbarum polysaccharide (LBP) is one of the main active ingredients in the fruit of L. barbarum L. It has been used as herbal medicine for thousands of years in China. In this study, Nile tilapia (Oreochromis niloticus) was taken as the research object. After feeding tilapia with 5 different doses of LBP (0 mg/kg, 500 mg/kg, 1000 mg/kg, 1500 mg/kg, 2000 mg/kg) for 55 d, it was found that LBP could promote the growth of tilapia, and this effect was the strongest at Group 1500 mg/kg. Apoptosis analysis in the liver and spleen showed that dietary supplementation with 1000 mg/kg LBP had the best protective effect on the spleen and liver in tilapia. Combined transcriptomics and metabolomics of the spleen in tilapia at Group 0 mg/kg and 1000 mg/kg showed that the differentially expressed genes (DEGs) such as NT5C2L1, pmm1, FasL and the differentially metabolites such as xanthine, dGMP, guanine and glutamate were mainly concentrated in signaling pathways such as Purine metabolism and FoxO signaling pathway. In conclusion, LBP regulates the metabolic waste levels of tilapia mainly through Purine metabolism and the FoxO signaling pathway, thereby inhibiting cell apoptosis, improving the utilization of nutrients, and promoting the growth of tilapia. This study not only provides a theoretical basis for the application of LBP in aquatic animals but also provides useful information for the healthy development of the aquaculture.

The Requirement and Protective Effects of Dietary Protein against Chronic Ammonia Exposure in Juvenile Genetically Improved Farmed Tilapia (Oreochromis niloticus).

Ammonia is a key risk factor in intensive aquaculture systems. This experiment is aimed at investigating the influence of dietary protein levels on genetically improved farmed tilapia (GIFT, Oreochromis niloticus) under chronic ammonia stress. GIFT juveniles of 4.00 ± 0.55 g were exposed to high ammonia level at 0.88 mg/L and fed with six diets comprising graded protein levels at 22.64%, 27.26%, 31.04%, 35.63%, 38.47%, and 42.66% for 8 weeks. The fish in negative control was fed the diet with 31.04% protein in normal water (0.02 mg ammonia/L water). Our results showed that high ammonia exposure (0.88 mg/L) caused significant decrease in fish growth performance, hematological parameters, liver antioxidant enzymes (catalase and glutathione peroxidase), and gill Na+- and K+-dependent adenosine triphosphatase (Na+/K+-ATP) activity. When fish were under high ammonia exposure, the weight gain rate, special growth rate, feed efficiency, and survival rate elevated significantly with dietary protein supplementation increase to 35.63%, whereas protein efficiency ratio, hepatosomatic index, and viscerosomatic index showed a decreased tendency. Dietary protein administration significantly enhanced crude protein but reduced crude lipid contents in the whole fish. Fish fed diets with 35.63%-42.66% protein had higher red blood cell counts and hematocrit percentage than fish fed 22.64% protein diet. The values of serum biochemical indices (lactate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase), hepatic antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase), and gill Na+/K+-ATP activity were all elevated with the increment of dietary protein. Moreover, histological analysis indicated that dietary protein administration could prevent the ammonia-induced damages in fish gill, kidney, and liver tissues. Based on weight gain rate as a response criterion, the optimal dietary protein requirement for GIFT juveniles under chronic ammonia stress was 37.9%.

Interactive effects of fluoride and seleno-l-methionine at environmental related concentrations on zebrafish (Danio rerio) liver via the gut-liver axis.

Fluoride (F) is a ubiquitous aquatic environmental pollutant and co-exists with other pollutants to form combined pollution. Selenium (Se) is beneficial at low levels yet toxic at high levels and can interact with some metals. However, the interactive effects of F and Se on the liver in fish remains enigmatic. In this study, zebrafish (Danio rerio) were exposed to F (80 mg/L) and dietary seleno-l-methionine (Se-Met, 0.25, 0.5 and 1.0 µg/g dry weight) alone or in combination for 90 d. The results indicated that co-treatment to F and Se-Met attenuated the histopathological damage, oxidative stress, and inflammatory in the liver, compared with the F treatment alone. Meanwhile, dietary Se-Met treatment improved F-induced intestinal barrier dysfunction, increased the transcripts of tight junction proteins (ZO-1, Claudin-1 and Occludin), and restored the homeostasis of intestinal microbiota. Moreover, dietary Se-Met ameliorated F-induced intestinal and liver inflammation by inhibiting lipopolysaccharide (LPS) levels and transcripts of TLR4 and p65 in the intestine and liver. This study manifested that Se-Met alleviates F-induced liver and intestinal injury when both co-occur at specific concentrations, and that the gut-liver axis pathway may serve as a mechanistic base for these alleviative effects.

Alleviating effects of essential oil from Artemisia vulgaris on enteritis in zebrafish via modulating oxidative stress and inflammatory response.

Artemisia vulgaris (A. vulgaris) is a traditional Chinese medicine widely distributed in China and contains many bioactive compounds with pharmacological effects. However, the anti-inflammatory effects and mechanism of essential oil from A. vulgaris on enteritis in fish are still unclear. In this study, in order to elucidate the underlying mechanism of essential oil from A. vulgaris on zebrafish enteritis, zebrafish were used for establishing animal models to observe the histopathological changes of intestines, determine the activities of immune-related enzymes and oxidative stress indicators, and the mRNA expression of genes in MyD88/TRAF6/NF-KB signaling pathways. The results showed that different doses of A. vulgaris essential oil could effectively alleviate zebrafish enteritis in a dose- and time-dependent manner by improving the intestinal histopathological damage, decreasing the intestinal oxidative stress, repairing the intestinal immune ability, changing the expression levels of IL-1ß, IL-10 and genes in MyD88/TRAF6/NF-κB pathway. In addition, co-treatment with oxazolone and MyD88 inhibitor could alleviate the morphological damage, the induction of oxidative stress, and the levels of immune-related enzymes and the mRNA expression of genes in MyD88/TRAF6/NF-κB signaling pathway. Moreover, essential oil from A. vulgaris had more significantly therapeutic effects on enteritis of male zebrafish than that of female zebrafish. This result will clarify the therapeutic effect and anti-inflammatory mechanism of essential oil from A. vulgaris on zebrafish enteritis, and provide a theoretical basis for further research on the rationality of A. vulgaris to replace feed antibiotics.

Genome-Wide DNA Methylation and RNA Analysis Reveal Potential Mechanism of Resistance to Streptococcus agalactiae in GIFT Strain of Nile Tilapia (Oreochromis niloticus ).

Streptococcus agalactiae is an important pathogenic bacterium causing great economic loss in Nile tilapia (Oreochromis niloticus) culture. Resistant and susceptible groups sharing the same genome showed significantly different resistance to S. agalactiae in the genetically improved farmed tilapia strain of Nile tilapia. The resistance mechanism is unclear. We determined genome-wide DNA methylation profiles in spleen of resistant and susceptible O. niloticus at 5 h postinfection with S. agalactiae using whole-genome bisulfite sequencing. The methylation status was higher in the spleen samples from resistant fish than in the susceptible group. A total of 10,177 differentially methylated regions were identified in the two groups, including 3725 differentially methylated genes (DMGs) (3129 hyper-DMGs and 596 hypo-DMGs). The RNA sequencing showed 2374 differentially expressed genes (DEGs), including 1483 upregulated and 891 downregulated. Integrated analysis showed 337 overlapping DEGs and DMGs and 82 overlapping DEGs and differentially methylated region promoters. By integrating promoter DNA methylation with gene expression, we revealed four immune-related genes (Arnt2, Nhr38, Pcdh10, and Ccdc158) as key factors in epigenetic mechanisms contributing to pathogen resistance. Our study provided systematic methylome maps to explore the epigenetic mechanism and reveal the methylation loci of pathogen resistance and identified methylation-regulated genes that are potentially involved in defense against pathogens.

Low expression of miR-19a-5p is associated with high mRNA expression of diacylglycerol O-acyltransferase 2 (DGAT2) in hybrid tilapia.

DGAT2 (acyl CoA:diacylglycerol acyltransferase 2) is a key and rate-limiting enzyme that catalyzes the final step of triglyceride (TG) synthesis. In this study, hybrid tilapia were generated from Nile tilapia (♀) and blue tilapia (♂) crossing. The TG content levels in the liver of these tilapia were measured. The results showed that the TG content was higher in the hybrid tilapia. In addition, protein and mRNA expression levels in the tilapia livers were determined. Higher hepatic mRNA and protein expression of DGAT2 in the hybrid fish was found. A luciferase reporter assay with HEK293T cells revealed that miRNA-19a-5p targeted the 3'UTR of DGAT2, suggesting a direct regulatory mechanism. Using qRT-PCR, we found that DGAT2 mRNA levels had a negative correlation with miRNA-19a-5p expression in Nile tilapia and hybrid. Taken together, these findings provide evidence that miRNA-19a-5p is involved in TG synthesis in the regulation of lipid metabolism in tilapia.

Ghrelin modulates the immune response and increases resistance to Aeromonas hydrophila infection in hybrid tilapia.

Ghrelin is a peptide hormone secreted by gastrointestinal tract which regulates multiple physiological processes such as appetite, metabolism, growth and gonad development in fish. In the present study, the effects of ghrelin on hybrid tilapia infected with Aeromonas hydrophila are elucidated. Juvenile hybrid tilapia fish (20.0 ± 5.0 g) were intraperitoneally injected with 0, 0.1, 1.0, or 10.0 ng/g ghrelin/body weight synthetic ghrelin alone or in combination with A. hydrophila (0.5 × 106 CFU). At 10 days post treatment, the survival rate in the group that received 1.0 ng/g ghrelin/body weight ghrelin in combination with A. hydrophila was higher (66.66%) than that of the Ah group (13.33%) that received A. hydrophila alone. In tilapia that received ghrelin injections, reactive oxygen species (ROS) levels tended to increase at 5 h, while injection of 10.0 ng/g ghrelin/body weight ghrelin resulted in a significant decrease in ROS levels at 10 h. No changes in serum immune or antioxidant-related indicators were observed in fish injected with A. hydrophila compared to controls. However, ghrelin injection decreased Albumin (ALB), glutathione peroxidase (GSH-Px), lysozyme (LZM) and superoxide dismutase (SOD). Histological analysis showed that ghrelin injection alleviated the pathological changes in liver and spleen caused by A. hydrophila infection. Overall, the expression of HSP70, IL-1ß, and TGF-ß in the liver tended to upregulate compared to the control. In the kidney, HSP70, IL-1ß and TGF-ß levels were increased, and TNF-α expression levels were decreased compared to the control. The HSP70 level in the spleen was decreased, and IL-1ß, TGF-ß, and TNF-α were expressed at significantly higher levels in the spleen in the tilapia that received ghrelin injections. Taken together, our results indicate that injection with 1.0 ng/g ghrelin/body weight ghrelin may effectively protect juvenile hybrid tilapia against A. hydrophila infection by improving hematological indicators, maintaining normal histology and regulating cytokine gene expression.

Effects of dietary Cu and Zn on the accumulation, oxidative stress and the expressions of immune-related genes in the livers of Nile tilapia (Oreochromis niloticus).

Excess Cu and Zn can cause many adverse effects in fish. However, few studies have addressed the effects of dietary Cu and Zn on antioxidant physiology and immunity and the underlying mechanisms in fishes. In this study, accumulation of Cu and Zn, effects on the antioxidant enzymes and the transcriptional expressions of immune-related genes were examined in the Oreochromis niloticus fed the Cu and/or Zn enriched duckweed. The results showed that the liver and intestine had the highest accumulation of Cu2+ and Zn2+ while the muscle had the lowest accumulation of these two metals. The activities of SOD, CAT, GPx and the contents of GSH, GSSG in the liver of all treatment groups were significantly decreased compared to the control group. MDA content was significantly elevated in all treatment groups after feeding for 21 days, implying lipid peroxidation in the liver. In the Cu + Zn group, the activities of SOD, GPx and the GSSG content in the liver were significantly decreased. Compared with the Zn group, the LZM activity in the Cu + Zn group was reversed after feeding for 42 days (P < 0.05). The transcriptional expressions of immune-related genes (TNF-α, INF-γ and IL-1ß) in Cu, Zn, Cu + Zn groups were significantly inhibited compared with the control group after treatment for 21 days. Compared with the Cu + Zn group, the level of INF-γ transcripts was significantly reduced in the Cu and Zn group, while the TNF-α expression was elevated after treatment for 42 days. Cu and Zn had synergistic effects on the antioxidant system. Cu has greater effects than Zn on the immunity of O. niloticus. This study demonstrates that dietary Cu and Zn may pose a potential threat to the tilapia populations.

Effects of Lycium barbarum polysaccharides on immunological parameters, apoptosis, and growth performance of Nile tilapia (Oreochromis niloticus).

In this study, the effect of Lycium barbarum polysaccharides (LBP) on immunological parameters, apoptosis, and growth performance of Nile tilapia (Oreochromis niloticus) was investigated. Dietary supplementation with LBP significantly increased complement 3 (C3) activity and promoted interleukin IL-1ß gene expression in spleen tissue, significantly reduced apoptosis in spleen tissue, increased the specific growth rate (SGR), relative length gain (LG), and relative weight gain (WG) of Nile tilapia. However, dietary supplementation with LBP did not have a significant effect on serum alkaline phosphatase (AKP), malondialdehyde (MDA), and superoxide dismutase (SOD), blood constituents, apoptosis, or gene expression of IL-1ß in liver tissue. Overall, the results showed that dietary supplementation with LBP increased the nonspecific immunity of Nile tilapia and reduced the apoptosis rate to promote growth and development. Thus, LBP has potential for use as a new immunostimulant in aquaculture.

Large-scale profiling of the proteome and dual transcriptome in Nile tilapia (Oreochromis niloticus) challenged with low- and high-virulence strains of Streptococcus agalactiae.

Streptococcus agalactiae is a common pathogen in aquatic animals, especially tilapia, that hinders aquaculture development and leads to serious economic losses. Previously, a S. agalactiae strain named HN016 was identified from infected tilapia, and the attenuated strain YM001 was subsequently obtained by continuous passaging in Tryptic Soy Broth (TSB) medium. YM001 has been demonstrated as a safe vaccine for S. agalactiae infection in tilapia. To understand the molecular bases of the virulence of these two strains, we performed proteomic and transcriptomic analysis to reveal the protein and gene expression changes in the liver and intestine during the infection process. HN016 significantly decreased the contents of white blood cells (WBCs), neutrophils (NEUs), red blood cells (RBCs) and hematocrit (HCT) and increased the levels of total protein (TP), albumin (ALB) and globulin (GLO), while no such significant differences were observed when comparing the control with YM001. During the infection process, pathogenic peptidoglycan hydrolase, CSPA and membrane proteins were significantly differentially expressed between YM001 and HN016. Furthermore, both proteome and transcriptome data showed that the complement and coagulation cascades pathway and the antigen processing and presentation pathway were stimulated in the liver and intestine, respectively, by YM001 infection compared to HN016 infection. The interaction network analysis of key virulence genes from pathogens suggested that CSPA, as a key node, affects the expression of DOLPP1, MIPEP, PA2G4, OCIAD1, G3BP1 and CLIC5 with a positive correlation. The present evidence suggests that during the infection process, CSPA was the key genes contributing to low virulence in YM001.

Genome-wide analysis revealed the virulence attenuation mechanism of the fish-derived oral attenuated Streptococcus iniae vaccine strain YM011.

Streptococcus iniae has become one the most serious aquatic pathogens causing invasive diseases in farmed marine and freshwater fish worldwide, and orally attenuated vaccine is still the best option in protecting these invasive diseases. In this study, the safety, stability, immunogenicity of the S. iniae attenuated strain YM011 were evaluated, and comprehensively analyzed its virulence weakening mechanism at whole genome level. The results shown that attenuated S. iniae strain YM011 completely lost its pathogenicity to tilapia and had good immunogenicity with relative percent survival being 93.25% at 15 days and 90.31% at 30 days via IP injection, respectively, and 76.81% at 15 days and 56.69% at 30 days via oral gavage, respectively. Back-passage safety assay indicated that YM011 did not cause diseases or death in tilapia after 100 generations of serial passaging. Comparative genome-wide sequencing shown that YM011 had a 0.4 M large inversion fragment compared with its parental strain virulent strain GX005, which encoded 372 genes including drug resistance genes pbp2A and tet, as well as known virulence factors including hemolysin transport system gene, recA, and mutator family transposase. The attenuated S. iniae strain YM011 is an ideal attenuated oral vaccine candidate with good immunogenicity, safety and stability. Abnormal expression of important drug resistance genes as well as known virulence factors due to inversion of a 0.4 M large fragment is the leading mechanism underlying its attenuated virulence.

Sesamin attenuates histological alterations, oxidative stress and expressions of immune-related genes in liver of zebrafish (Danio rerio) exposed to fluoride.

Sesamin is the main lignan in sesame and is reported to have many benefits and medicinal properties. However, its protective effects against fluoride-induced damage in the liver of zebrafish have not been elucidated. Our previous studies found that fluoride exposure caused damage to the liver of zebrafish. In the study, the effects of sesamin on oxidative stress and immune damage in liver of zebrafish exposed to fluoride were measured. The results indicated that fluoride exposure damaged the microstructures of liver, increased significantly the oxidative stress, decreased remarkably the activities of ACP, AKP, and LZM, and affected obviously the expressions of immune-related genes. Treatment with sesamin remarkably attenuated fluoride-induced liver damage in a dose-dependent manner, indicated by the histopathological observation. Furthermore, sesamin treatment also significantly inhibited the production of ROS and oxidative stress, such as the decrease of lipid peroxidation level and the increase of CAT and SOD activities in liver. Sesamin treatment reversed the activities of immune-related enzymes and the expressions of immune-related genes in liver exposed to fluoride. These findings suggested that sesamin could protect the liver from fluoride-induced immune damage by oxidative stress downstream-mediated changes in reversing the activities of immune-related enzymes and the expressions of immune-related genes. Taken together, sesamin plays an important role in maintaining hepatic health and preventing liver from toxic damage caused by fluoride.

Subchronic effects of dietary selenium yeast and selenite on growth performance and the immune and antioxidant systems in Nile tilapia Oreochromis niloticus.

Selenium is an essential element but toxic at high levels in animals. The effects of Se on growth performance and the immune system in Nile tilapia remain inconclusive. In this study, Nile tilapia Oreochromis niloticus was fed on selenium yeast (Se(Y))- and selenite (Se(IV))-enriched feed at 0, 3, 6, and 12 µg/g (dry wt) for 45 and 90 d. The growth, bioaccumulation, biochemical markers related to antioxidant, immunological, nervous and digestive systems were evaluated in various fish tissues (liver, intestine, kidney, muscle, brain, spleen, gills). The results showed that the accumulation of Se(Y) was 1.3-2 folds of Se(IV) in most tissues. The growth of tilapia was enhanced by both Se(Y) and Se(IV) at 3 µg/g after 90 d, with Se(Y) better than Se(IV) in tilapia feed. After 45 d, the levels of lipid peroxidation, the activity of the antioxidant enzymes, and the transcriptional levels of the immune related genes (IL-1ß, IFN-γ and TNF-α) and stress proteins (HSP70 and MT) were enhanced in all treatments, except that of MT in the 12 µg/g Se(Y) group. In addition, both Se species inhibited the activity of acetylcholinesterase (AChE) in the brain and one digestive enzyme α-glucosidase (α-Glu) in the intestine at 12 µg/g. However, after 90 d, the effects on most biochemical markers were less pronounced, implying a possible acclimation after prolonged duration. The results demonstrate Se is beneficial to O. niloticus at low levels and toxic at elevated levels. The immunostimulation by Se might be greatly weakened after long term feeding Se-enriched feed. This study helps to better understand the effects of Se on the antioxidant and immune systems and to establish the optimal Se levels in the feed and duration for O. niloticus.

The PFOS disturbed immunomodulatory functions via nuclear Factor-κB signaling in liver of zebrafish (Danio rerio).

Excessive perfluorooctane sulfonate (PFOS) in natural water ecosystem has the potential to detrimentally affect immune system, but little is known of such effects or underlying mechanisms in fish. In the present study, we evaluated the effects of PFOS on growth performance, organizational microstructure, activities of immune-related enzymes and expressions of immune-related genes in male zebrafish (Danio rerio) exposed to different concentrations of 0, 0.02, 0.04 and 0.08 mg/L of PFOS for 7, 14, and 21 days or cotreatment with PFOS and PDTC to investigate the effects of PFOS on immune system and the potential toxic mechanisms caused by PFOS. The results indicated that PFOS accumulated in livers after exposure, and remarkably elevations were found in three exposure groups compared with the control group at three stages. The growth of the adult zebrafish in the experiments was significantly inhibited, the microstructures of liver were serious damaged. The ROS levels were remarkably increased. The activities of ACP, AKP, and lysozyme were obviously decreased, while the activities of MPO and NF-κB were significantly increased. The expressions of immune-related mRNA were significantly affected. After co-treatment with PFOS and PDTC, the growth inhibition, the morphological damage, the ROS induction, and the expressions of immune-related mRNA were reversed. Taken together, the results indicated that PFOS can significantly inhibit the growth, disturb the immune system by changing the normal structure of liver, the activities of immune-related enzymes, and a series of gene transcriptions involved in immune regulation in liver of male zebrafish. PFOS-induced pro-inflammatory effect of hepatocytes was observed, and the involvement of NF-κB signaling pathway was participated in its action mechanism. These findings provide further evidence that PFOS interferes with the immune regulation of liver of male zebrafish under in vivo conditions.

Spatiotemporal distribution of Streptococcus agalactiae attenuated vaccine strain YM001 in the intestinal tract of tilapia and its effect on mucosal associated immune cells.

In this study, the tilapia was orally vaccinated by the attenuated Streptococcus agalactiae(S. agalactiae) strain YM001, and the distribution and the pathological effect of strain YM001 in different intestinal segments of tilapia were evaluated by real-time PCR(qPCR), immunohistochemistry(IHC) and histomorphology. The qPCR results showed that the number of bacteria was the highest in the intestinal tracts at 12 h post oral gavage in the YM001 group, then began to decrease sharply and eliminated at 7 d. And the number of bacteria was highest in the foregut, hindgut, and rectum at 12 h, 24 h, and 3 d, respectively. IHC indicated that bacteria mainly distributed in the margin epithelium and the goblet cells at 12 h - 24 h, and in the submucosa and muscle layer in the YM001 group in 3 d post gavage, then almost disappeared at 7 d. Histological examination of intestines post gavage displayed that an inflammation was observed at 7 d in the YM001 group and the intestinal structure was fully recovered at 15 d. and the intestinal structure was fully recovered at 15 d. Conclusion: The attenuated S. agalactiae vaccine strain YM001 could enter the intestinal tissue after oral gavage and had a strong spatial and temporal selectivity in the intestinal tract, which could cause obvious mucosal immune response and mild pathological reaction, but the pathological change could be gradually repaired with the extinction of bacteria in the body.

Characterization and expression of galectin-3 after Streptococcus agalactiae and Aeromonas hydrophila challenge in GIFT strain Nile tilapia (Oreochromis niloticus).

In mammals, Galectin-3 has been revealed to be widely expressed in immune cells and played important role in immune reactions. However, Galectin-3 is frequently less reported in teleost. In the present study, a molecular characterization and expression analysis of galectin-3 were conducted in GIFT strain Nile tilapia. The full-length cDNA is 1034 bp with 690 bp of protein coding sequences. The result of qRT-PCR showed that the mRNA of galectin-3 was widely expressed in various tissues (heart, liver, spleen, gill, kidney, brain, intestine, skin, muscle, and ovary), and the higher expression was observed in immune-related tissues (liver and spleen). The time-course expression analysis revealed that galectin-3 was significantly up-regulated in intestine (5 h, 50 h, and 7 d), liver (5 h, 50 h, and 7 d), spleen (5 and 50 h), head-kidney (5 and 50 h), gill (5 h and 7 d) after Streptococcus agalactiae challenge, and significantly up-regulated in intestine (18, 24, 36, 72, and 96 h), liver (6, 18, 24, 96 h, and 6 d), spleen (18, 24, 36, 72, and 96 h), head-kidney (6, 12, 18, 24, 36, 72, and 96 h), and gill (12, 18, 24, and 36 h) after Aeromonas hydrophila challenge. Taken together, these data suggest that galectin-3 plays a role in immune responses in Nile tilapia after bacterial challenge.

Nonadditive expression of lipid metabolism pathway-related genes in intestine of hybrids of Nile tilapia females (Oreochromis niloticus) and blue tilapia males (Oreochromis aureus).

Nonadditive expression contributes to heterosis in hybrids. In this study, the expression profiles of twelve lipid metabolism pathway-related genes were investigated in the intestine of Nile tilapia (Oreochromis niloticus) ♀ × blue tilapia (Oreochromis aureus) ♂ hybrid. The expression of genes from the hybrid were assigned to nonadditive and additive expression pattern groups and compared with expression patterns from Nile tilapia and blue tilapia. In the intestine of the hybrid, apoA4B was expressed at intermediate levels, but apoB and MTP were assigned to ELD-B and ELD-N categories, respectively. The LPL and LRP1 showed transgressive up-regulation in the hybrid, but LDLR was assigned to the ELD-B category. For fatty acid uptake related genes, only FABP11a was categorized as nonadditive expression with transgressive up-regulation, while CD36 and FABP3 were categorized as additive expression in the intestine of the hybrid. Two genes in triacylglycerol metabolism, namely, FAS and DGAT2, showed transgressive up-regulation in the hybrid. Most of the genes analyzed in the present study showed nonadditive expression (8 in 12), and five genes showed transgressive up-regulation. These results indicated that the stimulation of lipid metabolism in the hybrid compared to that of its parents. The hyperactive expression of these genes in the hybrid may be associated with the growth and lipid usage vigor.