Diet-associated modulation of HPI axis gene expression and POMC paralogs in gilthead seabream

The hypothalamic-pituitary-interrenal (HPI) axis mediates stress responses in fish. Previous work showed that dietary supplementation with B vitamins attenuated cortisol response to acute stress, whereas dietary genistein produced high basal levels of cortisol and altered stress responsiveness. In the present study, we investigated the expression of key genes of the HPI axis and selected hepatic targets to better characterize these responses. Cortisol was correlated with nr3c1 expression in the pituitary of control fish. Conversely, B vitamins supplementation was associated with changes in the relationship between plasma cortisol levels and nr3c1 expression across tissues, including higher basal higher basal expression expression in the head kidney. In parallel, lower hepatic oxidative stress following acute stress in this fish was associated with differences in cortisol levels and liver metabolic responses. Dietary genistein was associated with altered pituitary regulation of pomc paralogs, characterized by reduced pomcb and elevated pomca expression after stress. These expression patterns persisted 4.5 months after dietary exposure, with pomca becoming the only gene showing a positive association with plasma cortisol levels. In addition, genistein supplementation was associated with higher basal expression of the ACTH receptor (mc2r) in the head kidney. Stress challenges performed up to one year after the nutritional intervention revealed convergence of cortisol responses among dietary groups. Overall, these results indicate that dietary components can produce short-term changes in the regulation of the HPI axis. Further studies are required to clarify the mechanisms underlying the dietary effects observed in this study.