Evidence of the Autophagic Process during the Fish Immune Response of Skeletal Muscle Cells against Piscirickettsia salmonis

Molecular and epigenetic responses to crowding stress in rainbow trout (Oncorhynchus mykiss) skeletal muscle

Background

Chronic stress is a critical challenge in fish aquaculture, adversely affecting growth, health, and overall productivity. Among the most significant chronic stressors in intensive farming is crowding, which triggers the release of cortisol, the primary stress hormone in fish. Cortisol re-allocates energy away from growth-related processes toward stress response mechanisms. Consequently, overcrowded fish often exhibit slower growth rates, and impaired skeletal muscle development. Understanding the mechanisms underlying crowding stress and their long-term effects, including epigenetic changes, is essential for optimizing farming conditions, and enhancing fish welfare.

Objective

This study aims to characterize the physiological, transcriptomic, and epigenomic responses in juvenile rainbow trout (Oncorhynchus mykiss) exposed for 30 days to high stocking densities.

Results

Crowding stress led to decreased weight in the high-density (HD) group. It also resulted in elevated cortisol levels, oxidative DNA damage, and protein carbonylation in skeletal muscle. Using RNA-seq, we identified 4,050 differentially expressed genes (DEGs), and through whole-genome bisulfite sequencing (WGBS), we detected 11,672 differentially methylated genes (DMGs). Integrative analyses revealed 263 genes with a negative correlation between upregulated expression and downregulated methylation, primarily associated with autophagy, mitophagy, and the insulin signaling pathway. Conversely, 299 genes exhibited the reverse trend, mainly linked to ATP-dependent chromatin remodeling.

Conclusion

This study offers the first detailed exploration of the molecular responses in skeletal muscle to crowding stress, integrating RNA-seq and WGBS analysis in rainbow trout, offering valuable information for improving aquaculture practices.

Sexual dimorphism in fish innate immunity: A functional and transcriptional study in yellowtail kingfish

Sexual dimorphism in immunity has been extensively documented across vertebrates, with marked contrasts observed in immune responses between males and females. These variations are mainly attributed to oestrogens conferring enhanced immune responses in females, while males exhibit greater susceptibility to pathogens. However, in the light of the data, consensus is lacking, as different physiological and environmental factors such, as epigenetics, may impact sex-biased immunity. In fish, the regulation of immune responses through sex hormones is primarily determined by the leucocyte function, which contains sex steroid receptors. However, comparative sex-based research in fish immunity is still very limited. This study aimed to evaluate, for the first time, the disparities between males and females yellowtail kingfish (Seriola lalandi) juveniles in several parameters of local humoral innate immunity related to mucosae (skin mucus and foregut homogenates) and reproductive tissue (ovary and testis homogenates), as well as in serum. We investigated the sexual dimorphism in the expression patterns of genes coding for antimicrobial peptides, antiviral markers, and cytokines. Our findings revealed that the yellowtail kingfish males exhibit significantly higher levels of innate immune parameters, both functionally and transcriptionally, compared to females. These results suggest that females may have a higher susceptibility to pathogen infections, potentially leading to latent infections, which deservers further investigations. Understanding these sex-based differences in immunity could guide breeding strategies improvements and disease management in aquaculture facilities.

Molecular characterization, expression and functional analysis of TAK1, TAB1 and TAB2 in Nile tilapia (Oreochromis niloticus)

The MAPK pathway is the common intersection of signal transduction pathways such as inflammation, differentiation and proliferation and plays an important role in the process of antiviral immunity. Streptococcus agalactiae will have a great impact on tilapia aquaculture, so it is necessary to study the immune response mechanism of tilapia to S. agalactiae. In this study, we isolated the cDNA sequences of TAK1, TAB1 and TAB2 from Nile tilapia (Oreochromis niloticus). The TAK1 gene was 3492 bp in length, contained an open reading frame (ORF) of 1809 bp and encoded a polypeptide of 602 amino acids. The cDNA sequence of the TAB1 gene was 4001 bp, and its ORF was 1491 bp, which encoded 497 amino acids. The cDNA sequence of the TAB2 gene was 4792 bp, and its ORF was 2217 bp, encoding 738 amino acids. TAK1 has an S_TKc domain and a coiled coil structure; the TAB1 protein structure contains a PP2C_SIG domain and a conserved PYVDXA/TXF sequence model; and TAB2 contains a CUE domain, a coiled coil domain and a Znf_RBZ domain. Homology analysis showed that TAK1 and TAB1 had the highest homology with Neolamprologus brichardi, and TAB2 had the highest homology with Simochromis diagramma (98.28 %). In the phylogenetic tree, TAK1, TAB1 and TAB2 formed a large branch with other scleractinian fishes. The tissue expression analysis showed that the expression of TAK1, TAB1 and TAB2 was highest in the muscle. The expression of TAK1, TAB1 and TAB2 was significantly induced in most of the tested tissues after stimulation with LPS, Poly I:C and S. agalactiae. The subcellular localization results showed that TAK1 was located in the cytoplasm, and TAB1 and TAB2 had certain distributions in the cytoplasm and nucleus. Coimmunoprecipitation (Co-IP) results showed that TRAF6 did not interact with the TAK1 protein but interacted with TAB2, while TAB1 did not interact with P38γ but interacted with TAK1. There was also an interaction between TAK1 and TAB2.