# Effect of Dietary Taurine on the Innate Immune Responses, Digestive Function, and mTOR Signaling in Coho Salmon (Oncorhynchus kisutch)

## TL;DR

This study shows that adding taurine to the diet of coho salmon improves their immune responses, digestion, and intestinal health through the mTOR signaling pathway.

## Contribution

The study reveals a novel role of dietary taurine in modulating innate immunity and intestinal function via mTOR signaling in coho salmon.

## Key findings

- Dietary taurine enhanced antioxidant enzyme activity and reduced ROS in the small intestine of coho salmon.
- Taurine improved intestinal barrier function by upregulating tight junction proteins and inflammatory cytokines.
- mTOR signaling appears to regulate immune and digestive processes, as shown by RAPA's suppression of gene expression.

## Abstract

In this study, the effect of dietary taurine (Tau) on the innate immune responses, digestive function, and mammalian target of rapamycin (RAPA; mTOR) signaling was investigated in coho salmon (Oncorhynchus kisutch). Coho salmon were fed diets supplemented with 0, 0.2, 0.4, and 0.6 g/kg Tau for 8 weeks. The results demonstrated that the activity of antioxidant enzymes was enhanced, while reactive oxygen species (ROS) production was reduced by dietary Tau in the small intestine. Furthermore, Tau supplementation altered the homeostasis of essential nutrients, including Na, K, and Ca. Dietary Tau enhanced intestinal barrier function by upregulating tight junction proteins, including occludin, ZO‐1, and claudin‐18 gene expression. Dietary Tau also upregulated the gene expression of inflammatory cytokines such as IL‐1β, TNFα, and IL‐6, as well as the gene expression related to mTOR signaling pathway. Notably, Tau positively influenced intestinal villus morphology and trypsin activity and increased levels of free amino acids. In addition, the mTOR inhibitor RAPA was used to reveal mTOR’s role in regulating the expression of molecules associated with innate immune responses. The results showed that RAPA treatment suppressed the gene expression related to antioxidant enzymes and intestinal tight junction. In conclusion, Tau could modulate innate immune responses, digestive function, and intestinal barrier integrity, and mTOR may play a role in regulating these physiological processes in the small intestine of coho salmon.