Blood cell characterization and transcriptome analysis reveal distinct immune response and host resistance of different ploidy cyprinid fish following Aeromonas hydrophila infection

The immune defense response and immune-related genes expression in Odontobutis potamophila infected by Aeromonas salmonicida

Aeromonas salmonicida belongs to the Aeromonas family, which could widely infect economic fish, causing diseases and huge economic losses. Recently, A. salmonicida was also detected in diseased Odontobutis potamophila. Transcriptomic model of A. salmonicida-infected O. potamophila was analyzed to reveal immune response. A total of 113,282 unigenes were obtained and annotated in six databases. After 12 h of infection with A. salmonicides, a total of 614 differentially expressed genes (DEGs) (355 up-regulated genes and 259 down-regulated genes) were identified in the head kidney tissues. Following 24 h of infection, a total of 1689 DEGs were detected in the head kidney tissues, including 313 up-regulated genes and 1376 down-regulated genes. GO and KEGG pathway analyses were conducted to provide functional insights and a clearer understanding of the signal transduction pathways associated with the DEGs. Further analysis of the complement and coagulation cascades pathway and PPAR signaling pathway exhibited that the expression of immune genes was widely activated at the beginning of A. salmonicides infection. Additionally, six DEGs were randomly selected and validated using quantitative real-time PCR, showing expression patterns consistent with the high-throughput sequencing data. These results offer important insights that enhance the understanding of immune response in O. potamophila against A. salmonicida infection.

Identification of antimicrobial peptide genes from transcriptomes in Mandarin fish (Siniperca chuatsi) and their response to infection with Aeromonas hydrophila

Mandarin fish (Siniperca chuatsi) is a valuable freshwater fish species widely cultured in China. Its aquaculture production is challenged by bacterial septicaemia, which is one of the most common bacterial diseases. Antimicrobial peptides (AMPs) play a critical role in the innate immune system of fish, exhibiting defensive and inhibitory effects against a wide range of pathogens. This study aimed to identify the antimicrobial peptide genes in mandarin fish using transcriptomes data obtained from 17 tissue in our laboratory. Through nucleotide sequence alignment and protein structural domain analysis, 15 antimicrobial peptide genes (moronecidin, pleurocidin, lysozyme g, thymosin β12, hepcidin, leap 2, β-defensin, galectin 8, galectin 9, apoB, apoD, apoE, apoF, apoM, and nk-lysin) were identified, of which 9 antimicrobial peptide genes were identified for the first time. In addition, 15 AMPs were subjected to sequence characterization and protein structure analysis. After injection with Aeromonas hydrophila, the number of red blood cells, hemoglobin concentration, and platelet counts in mandarin fish showed a decreasing trend, indicating partial hemolysis. The expression change patterns of 15 AMP genes in the intestine after A. hydrophila infection were examined by using qRT-PCR. The results revealed, marked up-regulation (approximately 116.04) of the hepcidin gene, down-regulation of the piscidin family genes expression. Moreover, most AMP genes were responded in the early stages after A. hydrophila challenge. This study provides fundamental information for investigating the role of the different antimicrobial peptide genes in mandarin fish in defense against A. hydrophila infection.

Characterization and Expression Analysis of Genes from Megalobrama amblycephala Encoding Hemoglobins with Extracellular Microbicidal Activity

Hemoglobin (Hb) usually comprises two α and two β subunits, forming a tetramer responsible for oxygen transportation and storage. Few studies have elucidated fish hemoglobin immune functions. Megalobrama amblycephala is a freshwater-cultured fish prevalent in China. We identified two M. amblycephala hemoglobin subunits and analyzed their expression patterns and antibacterial activities. The respective full-length cDNA sequences of the M. amblycephala Hb α (MaHbα) and β (MaHbβ) subunits were 588 and 603 bp, encoding 143 and 148 amino acids. MaHbα and MaHbβ were highly homologous to hemoglobins from other fish, displaying typical globin-like domains, most heme-binding sites, and tetramer interface regions highly conserved in teleosts. In phylogenetic analyses, the hemoglobin genes from M. amblycephala and other cypriniformes clustered into one branch, and those from other fishes and mammals clustered into other branches, revealing fish hemoglobin conservation. These M. amblycephala Hb subunits exhibit different expression patterns in various tissues and during development. MaHbα is mainly expressed in the blood and brain, while MaHbβ gene expression is highest in the muscle. MaHbα expression was detectable and abundant post-fertilization, with levels fluctuating during the developmental stages. MaHbβ expression began at 3 dph and gradually increased. Expression of both M. amblycephala Hb subunits was down-regulated in most examined tissues and time points post-Aeromonas hydrophila infection, which might be due to red blood cell (RBC) and hematopoietic organ damage. Synthetic MaHbα and MaHbβ peptides showed excellent antimicrobial activities, which could inhibit survival and growth in five aquatic pathogens. Two M. amblycephala hemoglobin subunits were identified, and their expression patterns and antibacterial activities were analyzed, thereby providing a basis for the understanding of evolution and functions of fish hemoglobins.

Alteration of synergistic immune response in gut-liver axis of white crucian carp (Carassius cuvieri) after gut infection with Aeromonas hydrophila

Aeromonas hydrophila can pose a great threat to the survival of farmed fish. In current study, we investigated the pathological characteristics and immune response in gut-liver axis of white crucian carp (WCC) upon gut infection. WCC anally intubated with A. hydrophila exerted a tissue deformation in damaged midgut with elevated levels of goblet cells along with a significant decrease in tight junction proteins and villi length-to-width ratios. In addition, immune-related gene expressions and antioxidant properties increased dramatically in gut-liver axis of WCC following gut infection with A. hydrophila. These results highlighted the immune modulation and redox alteration in gut-liver axis of WCC in response to gut infection.

Gut-liver immune and redox response in hybrid fish (Carassius cuvieri ♀ × Carassius auratus red var. ♂) after gut infection with Aeromonas hydrophila

Aeromonas hydrophila can pose a great threat to fish survival. In this study, we investigated the differential immune and redox response in gut-liver axis of hybrid fish (WR) undergoing gut infection. WR anally intubated with A. hydrophila showed severe midgut injury with decreased length-to-width ratios of villi along with GC hyperplasia and enhanced antioxidant activities, but expression profiles of cytokines, chemokines, antibacterial molecules, redox sensors and tight junction proteins decreased dramatically. In contrast, immune-related gene expressions and antioxidant activities increased significantly in liver of WR following gut infection with A. hydrophila. These results highlighted the differential immune regulation and redox balance in gut-liver axis response to bacterial infection.

Comparative transcriptome analysis provides insights into the TDG supersaturation stress response of Schizothorax davidi

In the dam discharge season, the supersaturation of total dissolved gas (TDG) in the downstream channel can seriously affect the survival of aquatic organisms. However, few studies have revealed the mechanism by which TDG supersaturation affects the physiology of fish thus far. The present study was conducted to study the mechanism of the effect of TDG supersaturation on Schizothorax davidi, a species that is very sensitive to gas bubble disease. S. davidi was exposed to 116 % TDG supersaturation stress for 24 h. Serum biochemical tests showed that the aspartate aminotransferase and alanine aminotransferase levels after TDG supersaturation exposure were significantly decreased compared to those in the control group, while superoxide dismutase activity was significantly increased. RNA-Seq of gill tissues identified 1890 differentially expressed genes (DEGs), which consisted of 862 upregulated genes and 1028 downregulated genes, in the TDG supersaturation group vs. the control group. Pathway enrichment analysis revealed that the cell cycle, apoptosis and immune signaling pathways were affected by TDG stress. The results of this study may contribute to our understanding of the underlying molecular mechanism of environmental stress in fish.

Transcriptome analysis and co-expression network reveal the mechanism linking mitochondrial function to immune regulation in red crucian carp (Carassius auratus red var) after Aeromonas hydrophila challenge

Aeromonas hydrophila is a common pathogen of freshwater fish. In this study, A. hydrophila infection was shown to cause tissue damage, trigger physiological changes as well as alter the expression profiles of immune- and metabolic-related genes in immune tissues of red crucian carp (RCC). Transcriptome analysis revealed that acute A. hydrophila infection exerted a profound effect on mitochondrial oxidative phosphorylation linking metabolic regulation to immune response. In addition, we further identified cellular senescence, apoptosis, necrosis and mitogen-activated protein kinase signal pathways as crucial signal pathways in the kidney of RCC subjected to A. hydrophila infection. These findings may have important implications for understanding modulation of immunometabolic response to bacterial infection.

Metabolite features and oxidative response in kidney of red crucian carp (Carassius auratus red var) after Aeromonas hydrophila challenge

Aeromonas hydrophila can threaten the survival of freshwater fish. In this study, A. hydrophila challenge could induce tissue damage, promote antioxidant imbalance as well as alter the transcript levels of oxidative stress indicators, apoptotic genes and metabolic enzyme genes in kidney of red crucian carp (RCC). Metabolomics analysis revealed that A. hydrophila challenge had a profound effect on amino acid metabolism and lipid metabolism. In addition, we further identified dipeptides, fatty acid derivatives, cortisol, choline and tetrahydrocortisone as crucial biomarkers in kidney of RCC subjected to A. hydrophila infection. These results highlighted the importance of metabolic strategy against bacterial infection.