Identification of duplicated suppressor of cytokine signaling 3 (SOCS3) genes in blunt snout bream (Megalobrama amblycephala)

SOCS6, an inhibitory factor in Japanese eel inhibits the type I IFN pathway and the MyD88-mediated NF-kB pathway

SOCS family genes are a class of repressors in various signaling pathways of mammals involved in regulating immunity, growth, and development, but the information remains limited in teleost. The full-length cDNA sequence of the Japanese eel SOCS6 gene, named AjSOCS6, was first cloned and showed to encode 529 amino acids with a conserved SH2 structural domain and a typical structure of a C-terminal SOCS box. AjSOCS6 is evolutionarily close to that of rainbow trout and zebrafish. AjSOCS6 gene expression was observed across all tissues in Japanese eel, with the highest levels found in the intestine. In vivo studies showed that AjSOCS6 was significantly upregulated in the liver following exposure to LPS, poly I:C, and Aeromonas hydrophila infection. In vitro, stimulation with poly I:C, CpG, and A. hydrophila infection increased AjSOCS6 expression in Japanese eel liver cells. Subcellular localization revealed that AjSOCS6 was dispersed in the cytoplasm. Overexpressing AjSOCS6 significantly suppressed the expression of immune-related genes, such as c-Rel and p65 in the NF-κB pathway, IFN1, IFN2, and IFN4 in the type I IFN signaling pathway, and the downstream inflammatory factor IL-6 in Japanese eel liver cells. Conversely, knocking down AjSOCS6 in vitro in liver cells and in vivo in the liver, spleen, and kidney significantly upregulated these gene expressions. Co-transfection of AjSOCS6 with AjMyD88 into HEK293 cells significantly reduced NF-κB luciferase activities compared to AjMyD88 single-transfection groups, in a natural state and under LPS stimulation. These findings suggest that AjSOCS6 negatively regulates MyD88-dependent NF-κB and type I IFN signaling pathways, underscoring its role in the immune defense of fish against viral and bacterial infections.

Functional exploration of SNP mutations in HIF2αb gene correlated with hypoxia tolerance in blunt snout bream (Megalobrama amblycephala)

Blunt snout bream (Megalobrama amblycephala) is sensitive to hypoxia environment. Hypoxia-inducible factor (HIF) is the most critical factor in the HIF pathway, which strictly regulates the hypoxia stress process of fish. In this study, we found six hifα genes in blunt snout bream that demonstrated different expressions under hypoxia conditions. In HEK293T cells, all six hifαs were detected to activate the HRE region by luciferase reporter assay. More importantly, we identified two linkage-disequilibrium SNP sites at exon 203 and 752 of the hif2αb gene in blunt snout bream. Haplotype II (A²⁰³A⁷⁵²) and its homozygous diplotype II (A²⁰³A²⁰³A⁷⁵²A⁷⁵²) appeared frequently in a selected strain of blunt snout bream with hypoxia tolerance. Diplotype II has a lower oxygen tension threshold for loss of equilibrium (LOE_crit) over a similar range of temperatures. Moreover, its erythrocyte number increased significantly (p < 0.05) than those in diplotype I and diplotype III strains at 48 h of hypoxia. The enzymes related with hypoxia tolerant traits, i.e., reduced glutathione, superoxide dismutase, and catalase, were also significantly (p < 0.05) induced in diplotype II than in diplotype I or III. In addition, the expression of epo in the liver of diplotype II was significantly (p < 0.01) higher than that in the diplotype I or III strains at 48 h of hypoxia. Taken together, our results found that the hypoxia-tolerant-related diplotype II of hif2αb has the potential to be used as a molecular marker in future genetic breeding of hypoxia-tolerant strain.

The transcriptomic responses of blunt snout bream (Megalobrama amblycephala) to acute hypoxia stress alone, and in combination with bortezomib

BACKGROUND

Blunt snout bream (Megalobrama amblycephala) is sensitive to hypoxia. A new blunt snout bream strain, "Pujiang No.2", was developed to overcome this shortcoming. As a proteasome inhibitor, bortezomib (PS-341) has been shown to affect the adaptation of cells to a hypoxic environment. In the present study, bortezomib was used to explore the hypoxia adaptation mechanism of "Pujiang No.2". We examined how acute hypoxia alone (hypoxia-treated, HN: 1.0 mg·L^- 1), and in combination with bortezomib (hypoxia-bortezomib-treated, HB: Use 1 mg bortezomib for 1 kg fish), impacted the hepatic ultrastructure and transcriptome expression compared to control fish (normoxia-treated, NN).

RESULTS

Hypoxia tolerance was significantly decreased in the bortezomib-treated group (LOE_crit, loss of equilibrium, 1.11 mg·L^- 1 and 1.32 mg·L^- 1) compared to the control group (LOE_crit, 0.73 mg·L^- 1 and 0.85 mg·L^- 1). The HB group had more severe liver injury than the HN group. Specifically, the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the HB group (52.16 U/gprot, 32 U/gprot) were significantly (p < 0.01) higher than those in the HN group (32.85 U/gprot, 21. 68 U/gprot). In addition, more severe liver damage such as vacuoles, nuclear atrophy, and nuclear lysis were observed in the HB group. RNA-seq was performed on livers from the HN, HB and NN groups. KEGG pathway analysis disclosed that many DEGs (differently expressed genes) were enriched in the HIF-1, FOXO, MAPK, PI3K-Akt and AMPK signaling pathway and their downstream.

CONCLUSION

We explored the adaptation mechanism of "Pujiang No.2" to hypoxia stress by using bortezomib, and combined with transcriptome analysis, accurately captured the genes related to hypoxia tolerance advantage.

TAK1 of blunt snout bream promotes NF-κB activation via interaction with TAB1 in response to pathogenic bacteria

Transforming growth factor-β activated kinase-1 (TAK1) is an important upstream signaling molecules involved in the NF-κB signaling pathway. TAK1 interacts with TAB1 to form the TAK1-TAB1 complex, which elicits NF-κB activation through a series of cascade reactions in mammals. However, the function of TAK1 in blunt snout bream (Megalobrama amblycephala ( maTak1) and the effects of their interaction between TAK1 and TAB1 on the NF-κB activation still remains largely unknown. In the present study, maTak1 was cloned and characterized successfully based on transcriptome data. Its open reading frame is composed of 1626 nucleotides and the predicted maTAK1 protein contains 541 amino acids, which includes an N-terminal Serine/Threonine protein kinases (S/TKc) and a C-terminal coiled-coil region. Phylogenetic analysis showed that maTAK1 were clustered with those of other teleosts. MaTak1 displayed ubiquitous transcriptional expression in all the examined tissues of healthy blunt snout bream but with varied expression levels. And maTrak1 expression was dramatically enhanced in different tissues and MAF cells after LPS stimulation and A. hydrophila challenge. The result from subcellular localization analysis indicated that both maTAK1 and maTAB1 were cytoplasmic protein. The activity of NF-κB promoter could not be induced by overexpression of maTak1 or maTab1 alone, however, it could be enhanced by co-expression of maTak1 and maTab1. Co-immunoprecipitation and subcellular co-localization assay revealed that maTAK1 can combine with maTAB1 directly. The transcriptional expression level of pro-inflammatory cytokines (IL-1β, IL-6 and IL-8) increased distinctly after the overexpression of maTak1 and maTab1. Taken together, the data obtained in this study demonstrated that the direct interaction between maTAK1 and maTAB1 might play a pivotal role in mediating host innate immune response to pathogen invasion by the production of pro-inflammatory cytokines via NF-κB signaling pathway, which might lay a solid foundation for the establishment of novel therapeutic approach to combat bacterial infection in fish.

The time-dependent variations of zebrafish intestine and gill after polyethylene microplastics exposure

Microplastics (MPs) are common environmental contaminants that present a growing health concern due to their increasing presence in aquatic and human systems. However, the mechanisms behind MP effects on organisms are unclear. In this study, zebrafish (Danio rerio) were used as an in vivo model to investigate the potential risks and molecular mechanisms of the toxic effects of polyethylene MPs (45-53 μm). In the zebrafish intestine, 6, 5, and 186 genes showed differential expression after MP treatment for 1, 5, and 10 days, respectively. In the gills, 318, 92, and 484 genes showed differential expression after MP treatment for 1, 5, and 10 days, respectively. In both the intestine and the gills, Gene Ontology (GO) annotation showed that the main enriched terms were biological regulation, cellular process, metabolic process, cellular anatomical entity, and binding. KEGG enrichment analysis on DEGs revealed that the dominant pathways were carbohydrate metabolism and lipid metabolism, which were strongly influenced by MPs in the intestine. The dominant pathways in the gills were immune and lipid metabolism. The respiratory rate of gills, the activity of SOD and GSH in the intestine significantly increased after exposure to MPs compared with the control (p < 0.05), while the activity of SOD did not change in the gills. GSH activity was only significantly increased after MP exposure for 5 days. Also, the MDA content was not changed in the intestine but was significantly decreased in the gills after MP exposure. The activity of AChE significantly decreased only after MPs exposure for 5 days. Overall, these results indicated that MPs pollution significantly induced oxidative stress and neurotoxicity, increased respiratory rate, disturbed energy metabolism and stimulated immune function in fish, displaying an environmental risk of MPs to aquatic ecosystems.

Two transcription factors PU.1a and PU.1b have different functions in the immune system of teleost ayu

Transcription factor PU.1 is a regulator of macrophage function, however, the specific function of PU.1 in teleost monocytes/macrophages (MO/MФ) remains unknown. We determined the cDNA sequence of two PU.1 genes from ayu (Plecoglossus altivelis; PaPU.1a and PaPU.1b). Sequence comparisons showed that PaPU.1 were most closely related to the PU.1 of rainbow smelt (Osmerus mordax). The PU.1 transcripts were mainly expressed in the spleen, and their expression was altered in various tissues upon infection with Vibrio anguillarum. PaPU.1a and PaPU.1b proteins were upregulated in MO/MФ, after infection. RNA interference was employed to knockdown PaPU.1a and PaPU.1b to investigate their function in MO/MФ. The expression of inflammatory cytokines was regulated by PaPU.1a, but not PaPU.1b, in ayu MO/MФ upon V. anguillarum infection. Both PaPU.1a and PaPU.1b knockdown lowered the phagocytic activity of MO/MФ. Furthermore, PaPU.1b knockdown attenuated MO/MФ bacterial killing capability. Our results indicate that two PaPU.1 genes differentially modulate the immune response in ayu MO/MФ against bacterial infection.