Regulation of Immune-Related Gene Expression by Salinity-Induced HPI Axis in Large Yellow Croaker, Larimichthys crocea

Large yellow croaker is one of the most popular economic fish species in China. There are studies on the effects of salinity on the growth and development of large yellow croaker (<i>Larimichthys crocea</i>), but the effects of the hypothalamic-pituitary-interrenal axis (HPI), HPI axis-related genes, and immune-related gene expression and its mechanisms have not been reported. This study analyzed the comparative transcriptomics of brain tissue in large yellow croaker under different salinity (12, 24, and 36 ppt) treatments for 4 weeks. The results showed that there were 1568 differential expression genes in the high salinity (HB) and normal salinity (NB) groups, including 494 up-regulated and 1074 down-regulated transcripts, and 1720 differential expression genes in the low salinity (LB) and normal salinity (NB) groups, including 486 up-regulated and 1234 down-regulated transcripts. Some pathways were significantly enriched, including the adrenergic signaling pathway of cardiomyocytes, oxidative phosphorylation, aldosterone synthesis and secretion, chemokine signaling pathway, and cyclic adenosine monophosphate (cAMP) signaling pathway. Quantitative Real-time polymerase chain reaction (qPCR) analysis further confirmed changes in the expression levels of HPI axis-related genes (<i>β2-ADR</i>, <i>GH</i>, and <i>PRL</i>) and significant changes in the expression levels of immune-related genes (<i>IL6st</i>, <i>IL6</i>, <i>CXCL12</i>, <i>CD40</i>, <i>IFNAR1</i>, <i>SOCS2</i>, <i>SOCS6</i>, and <i>IRF1</i>). In summary, this experiment demonstrates that salinity stress can activate the HPI axis and influence its immune function in large yellow croaker. Furthermore, the expression of immune factors during the immune response is regulated by the upstream genes of the HPI axis. The findings of this study are significant for understanding the physiological and immune responses of large yellow croaker to salinity stress.