Peritoneal bacterial infection repressed the expression of IL17D in Siberia sturgeon a chondrostean fish in the early immune response

Transcriptomic Analysis Reveals Functional Interaction of mRNA-lncRNA-miRNA in Trachinotus ovatus Infected by Cryptocaryon irritans

The skin of Trachinotus ovatus is a crucial component of the mucosal immune system and serves as the primary site of infection by Cryptocaryon irritans. In order to investigate the significant role of skin in C. irritans infection, a comprehensive transcriptome analysis was conducted on skin tissues from the infection group, infection-adjacent group, and infection group compared with the infection-adjacent group (ATT_vs_PER, ADJ_vs_PER, ATT_vs_ADJ). This study identified differentially expressed long non-coding RNAs (DE lncRNAs), microRNAs (DE miRNAs), and differentially expressed genes (DEGs). The prediction of lncRNA target genes was accomplished by utilizing positional relationship (co-location) and expression correlation (co-expression) with protein-coding genes. Subsequently, functional enrichment analysis was conducted on the target genes of differentially expressed lncRNAs, revealing their involvement in signaling pathways such as tight junction, MAPK, and cell adhesion molecules. This study describes the regulatory network of lncRNA-miRNA-mRNA in T. ovatus skin tissue infected with C. irritans. Functional prediction analysis showed that differentially expressed lncRNA and miRNA may regulate the expression of immune genes such as interleukin-8 (il8) to resist the infection of C. irritans. Conducting additional research on these non-coding RNAs will facilitate a deeper understanding of their immune regulatory function in T. ovatus during C. irritans infection. The study of non-coding RNA in this study laid a foundation for revealing the molecular mechanism of the immune system of T. ovatus to respond to the infection of C. irritans. It provided a choice for the molecular breeding of Trachinotus ovatus against C. irritans.

Identification and Expression Analysis of LncRNAs Reveal the Immune Mechanism of Visceral White-Nodules Disease Resistance in Large Yellow Croaker

Long non-coding RNAs (lncRNAs) have several known functions in fish growth processes and signal transduction, but their possible roles in response to bacterial diseases remain largely unresolved. In this study, we report a comprehensive cold-water bacterial disease-responsive lncRNA expression profile for understanding the transcriptional regulatory mechanisms of visceral white-nodules disease resistance in large yellow croaker. A total of 2534 high-confidence lncRNAs were identified by a rigorous filtering pipeline as a basic sequence set for comparative transcriptional analysis. In addition, a total of 10,200 lncRNA-mRNA pairs with high correlation coefficients were identified by expressions level correlation analysis, including non-redundant 381 DE lncRNAs and 2590 differential expressed genes. MSTRG_11084_1 and MSTRG_20402_1 were linked to a large number of target genes and may be involved in important functions in immune regulation. We further revealed the conserved and idiosyncratic features of the disease response process between the technical control strain (TCS) and the resistant strain (RS). Immune-related pathways were enriched in GO terms and KEGG pathways, among which cytokine-cytokine receptor interaction, MAPK signaling pathway, and NF-kappa B signaling pathway may play a key role in VWND resistance in large yellow croaker. Protein-protein interaction network (PPI) analysis revealed that immune-related target genes such as il-10, met, acta2, myc, cav1, and ntrk1, as well as growth and metabolism-related target genes such as pik3r2, igf1, sc5d, hmgcr, and lss were considered the main hub genes. This study represents the first characterization of lncRNAs involved in VWND resistance in large yellow croaker and provides new clues for elucidating the disease response mechanism of large yellow croaker.

Effect of secondary attack by Aeromonas hydrophila on the expression level of hif genes in common carp (Cyprinus carpio)

Hypoxia-inducible factors (hifs) are involved in infectious diseases inflammatory reactions, and immune regulation. Common carp, a representative allotetraploid species that has undergone genome-wide replication events, has important research value. In this study, common carp were infected twice with Aeromonas hydrophila. Liver tissues of common carp were collected at 4 h, 12 h, 24 h, 48 h, 3 days, 7 days post-first infection and 4 h, 12 h, 24 h post-second infection. The mRNA levels of hif genes were determined at different time points. The hif2a-2, hif3a-2, hif3b-1 and hif3b-2 expression levels in the infected group were upregulated when compared with those in the control group, whereas the expression levels of other genes were downregulated after the second infection. This indicates that the effect of A. hydrophila infection on gene expression pattern is dependent on the host, pathogen, infected tissue and gene. Pressure analysis of the hif gene family revealed that the non-synonymous substitution to synonymous substitution ratio of 12 hif genes was <1, which indicated that they were in a state of purification and selection. Combined with the differences between copy genes, the polyclonal antibodies against Hif1b-1 and Hif1b-2 were successfully prepared in this study. Western blot analysis showed that the protein expression of Hif1b-1 and Hif1b-2 reached to the highest level 48 h after the first infection. After the second A. hydrophila infection, the protein expression levels of Hif1b-1 and Hif1b-2 reached the highest levels at 4 and 48 h, respectively. This may indicate that the Hif1b-1 and Hif1b-2 genes in common carp play an important role in the immune mechanism at the protein level. The findings of this study will lay the foundation for future studies on the immune regulatory function of common carp hif genes, which may aid in devising novel therapeutic strategies for common carp diseases, such as A. hydrophila infection.

Sub-basal increases of GABA enhance the synthesis of TNF-α, TGF-β, and IL-1β in the immune system organs of the Nile tilapia

The cells of the immune and neuronal systems share different receptors for cytokines or neurotransmitters, producing feedback responses between both systems. Cytokines such as IL-1β and TNF-α can induce inflammation; however, the secretion of these molecules can be modulated by anti-inflammatory cytokines, as is the case for TGF-β, as well as by different hormones or neurotransmitters such as the γ-aminobutyric acid (GABA). In this study, we evaluated the secretion of IL-1β, TNF-α, and TGF-β under basal conditions, in the head of the kidney, spleen, thymus, and serum of the Nile tilapia, as well as their release induced by different sub-basal increases of GABA. We found that at the higher dose of GABA these cytokines were synthesised at a higher concentration compared to the control group. These results may suggest that there is feedback between both systems and that GABA plays a role in the modulation of the immune response.

Interleukin-6 in Siberian sturgeon (Acipenser baeri): Molecular characterization and immune functional activity

Interleukin-6 (IL-6) is a pleiotropic cytokine with crucial immunoregulatory functions in both innate and adaptive immune responses. However, the IL-6 sequence and function remain unknown in sturgeon, one chondrostean fish. In the present study, we identified an interleukin-6 homolog from Siberian sturgeon (Acipenser baeri), named AbIL-6. Its open reading frame (ORF) was 657 nucleotides in length, encoding a polypeptide of 218 amino acids, which contains a signal peptide and the IL-6 family domain. Phylogenetic analysis showed that sturgeon IL-6 had close relationship with both teleost and chondrichthyes IL-6s. Abil-6 mRNA was highly expressed in spleen, brain and liver tissues of healthy sturgeon, and significantly up-regulated in the spleen, head kidney and liver by A.hydrophila (A.h) challenge. Heat-killed A.h and LPS effectively stimulated Abil-6 transcripts in primary spleen cells in vitro. In order to understand the bioactivity and influence of AbIL-6 on immune responses, recombinant AbIL-6 (rAbIL-6) was synthesized by prokaryotes and demonstrated to promote the proliferation of spleen cells and head kidney cells in vitro. Additionally, intraperitoneal injection of rAbIL-6 induced significantly higher expression of four immuno-related genes including il-1β, cxcl10, mhcIIβ and igm. rAbIL-6 improved the survival rate and reduced the tissue bacterial load after A.h infection. Taken together, these results suggest that AbIL-6 plays an important role in inflammatory responses and immune defense against bacterial infection of sturgeon.

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 14-3-3β/α gene expression in response to salinity, thermal, and bacterial stresses in Siberian sturgeon (Acipenser baeri)

The 14-3-3 proteins are a family of widely expressed acidic proteins, which are involved in the regulation of many biological processes of animals. However, no research regarding 14-3-3 has been described in sturgeon to date, one of the most primitive Actinopterygii species. Here, we identified the first 14-3-3 gene from Siberian sturgeon (Acipenser baeri), named Ab14-3-3β/α (GenBank Accession No. KY094076.1). The cDNA of Ab14-3-3β/α is 1212 bp in length, containing a 5'-untranslated region (UTR) of 82 bp, a 3'UTR of 392 bp, and an open reading frame (ORF) of 738 bp, encoding a polypeptide of 245 amino acids which contains a 14-3-3 homologs domain (PF00244). Phylogenetic analysis showed that the 14-3-3 gene product from Acipenser baeri is a counterpart of vertebrate 14-3-3β/α. The deduced Ab14-3-3β/α protein shares high identities of 46.5-95.5% with the homologs of other species. Ab14-3-3β/α mRNA was constitutively expressed in all examined tissues, with high expression levels in the blood and gill. Furthermore, the expression level of Ab14-3-3β/α mRNA increased significantly in the gill at 1 h under acute salinity shock by transfer of Siberian sturgeons from fresh water (FW) to 15 ppt. In fish subjected to a high temperature (31 °C), Ab14-3-3β/α showed a significant upregulation in the liver at 3 h compared with the control group (24 °C). A 4.85-fold increase of Ab14-3-3β/α expression in the spleen of Siberian sturgeon was observed at 24 h following Aeromonas hydrophila challenge. Collectively, these results indicated that Ab14-3-3β/α might play a certain role in sturgeon in response to some environmental stresses and bacterial challenge.

Identification and Regulation of Interleukin-17 (IL-17) Family Ligands in the Teleost Fish European Sea Bass

Interleukin-17 (IL-17) cytokine comprises a family of six ligands in mammals with proinflammatory functions, having an important role in autoimmune disorders and against bacterial, viral, and fungal pathogens. While IL-17A and IL-17F ligands are mainly produced by Th cells (Th17 cells), the rest of the ligands are expressed by other immune and non-immune cells and have different functions. The identification of IL-17 ligands in fish has revealed the presence of six members, counterparts to mammalian ones, and a teleost-specific form, the fish IL-17N. However, tissue distribution, the regulation of gene expression, and scarce bioactivity assays point to similar functions compared to mammalian ones, though this yet to be investigated and confirmed. Thus, we have identified seven IL-17 ligands in the teleost European sea bass (Dicentrarchus labrax), for the first time, corresponding to IL-17A/F1, IL-17A/F2, IL-17A/F3, IL-17C1, IL-17C2, IL-17D, and IL-17N, according to the predicted protein sequences and phylogenetic analysis. They are constitutively and widely transcribed in sea bass tissues, with some of them being mainly expressed in the thymus, brain or intestine. Upon in vitro stimulation of head-kidney leucocytes, the mRNA levels of all sea bass IL-17 ligands were up-regulated by phytohemagglutinin treatment, a well-known T cell mitogen, suggesting a major expression in T lymphocytes. By contrast, the infection of sea bass juveniles with nodavirus (NNV), a very pathogenic virus for this fish species, resulted in the up-regulation of the transcription of IL-17C1 in the head-kidney and of IL-17C1 and IL-17D in the brain, the target tissue for NNV replication. By contrast, NNV infection led to a down-regulated transcription of IL-17A/F1, IL-17A/F2, IL-17C1, IL-17C2, and IL-17D in the head-kidney and of IL-17A/F1 and IL-17A/F3 in the brain. The data are discussed accordingly with the IL-17 ligand expression and the immune response under the different situations tested.

Subfunctionalization and evolution of liver-expressed antimicrobial peptide 2 (LEAP2) isoform genes in Siberian sturgeon (Acipenser baerii), a primitive chondrostean fish species

Two liver-expressed antimicrobial peptide 2 (LEAP2) isoforms were characterized in a primitive chondrostean sturgeon species, Acipenser baerii (Acipenseriformes). A. baerii LEAP2 isoforms represented essentially common structures shared by their vertebrate orthologs at both genomic (i.e., tripartite organization) and peptide (two conserved disulfide bonds) levels. A. baerii LEAP2 isoforms (designed LEAP2AB and LEAP2C, respectively) phylogenetically occupy the most basal position in the actinopterygian lineage and represent an intermediate character between teleostean and tetrapodian LEAP2s in the sequence alignment. Molecular phylogenetic analysis including LEAP2s from extant primitive fish species indicated that the evolutionary origin of ancestral LEAP2 in vertebrate groups should date back to earlier than the actinopterygian-sarcopterygian split. Gene expression assays under both basal and stimulated conditions suggested that A. baerii LEAP2 isoforms have undergone substantial subfunctionalization in tissue distribution pattern, developmental/ontogenetic expression, and immune responses. LEAP2AB showed a predominant liver expression, while LEAP2C exhibited the highest level of expression in the intestine. LEAP2C was a more dominantly expressed isoform during embryonic development and prelarval ontogeny. The LEAP2AB isoform is more closely associated with innate immune response to microbial invasion, compared with LEAP2C, as evidenced by results from LPS, poly(I:C) and Aeromonas hydrophila challenges. Synthetic mature peptides of LEAP2AB displayed a more potent antimicrobial activity than did LEAP2C. Data from this study could be useful not only to provide deeper insights into the evolutionary mechanism of LEAP2 in the actinopterygian lineage but also to better understand the innate immunity of this commercially important chondrostean species.

Molecular characterization and biological functioning of interleukin-8 in Siberian sturgeon (Acipenser baeri)

Interleukin-8, otherwise known as CXCL8, is a CXC chemokine that plays a pivotal regulatory role in immune and inflammation responses of animals. Here, we identified an interleukin-8 homologue from Siberian sturgeon (Acipenser baeri), named AbIL-8, which belongs to the lineage 1 group of teleost fish IL-8s. The cDNA of Abil-8 is 1130 bp in length, containing a 5'- untranslated region (UTR) of 50 bp, a 3'- UTR of 783 bp, and an open reading frame (ORF) of 297 bp that encodes a protein consisting of 98 amino acids. The deduced AbIL-8 contained five cysteines, four of which are highly conserved, and an ELR motif typical of known mammalian CXC chemokines was also found preceding the CXC motif. Our phylogenetic analysis showed that AbIL-8 clustered with the CXCL8_L1 sequences from other teleosts, being clearly distinct from those of either birds or mammals. Abil-8 mRNA was constitutively expressed in all tested tissues and significantly up-regulated in the liver and spleen tissues by the bacteria Aernomas hydrophila. The in vitro experiment using primary spleen cells stimulated with heat-killed Aernomas hydrophila or lipopolysaccharide (LPS) revealed a similar expression pattern to that found in vivo, whereas stimulation on spleen cells with β-glucan or polyI:C elicited negligible changes in levels of Abil-8 mRNA. Purified recombinant AbIL-8 not only exhibited chemotactic activity for lymphocytes and monocytes in peripheral blood leukocytes (PBLs) and, to a lesser extent, spleen cells, but also stimulated the proliferation of spleen cells at 10 ng/mLor above. Furthermore, intraperitoneal injection of rAbIL-8 also up-regulated the expression of immuno-related genes (IL-6, IgM and MHCIIβ) at 24 h. Collectively, these results enhance our understanding of how IL-8 functions in the regulation of the immune responses in sturgeon.