G protein-coupled bile acid receptor 1 reduced hepatic immune response and inhibited NFκB, PI3K/AKT, and PKC/P38 MAPK signaling pathway in hybrid grouper.

ABSTRACT

The mammalian G protein-coupled bile acid receptor 1 (TGR5) is involved in the inflammatory response. However, the functions of TGR5 in the immune response of fish remain unclear. In this study, the full-length sequence of tgr5 from hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) was cloned, and the function of TGR5 in the immune response was explored. The results showed that the ORF of tgr5 gene in hybrid grouper was 1029 bp and encoded 342 amino acids. Activation of TGR5 by INT-777 significantly decreased the activities and mRNA expression of TNFα and IL1ß, whereas inhibition of TGR5 by SBI-115 showed the opposite effect. SBI-115 treatment significantly increased the expression of phosphorylated inhibitor κB α (p-IKBα) protein. After the INT-777 treatment, the concentration of protein kinase C (PKC) and expression of the p38 mitogen-activated protein kinases (p38a), p38b and p38c, were significantly decreased in vivo. INT-777 agonist significantly decreased the expression of phosphorylated phosphoinositide 3-kinase (p-PI3K) protein and the ratio of phosphorylated and nonphosphorylated serine/threonine-protein kinase (p-AKT/AKT). In conclusion, activation of hepatic TGR5 inhibited the PKC/P38 MAPK, PI3K/AKT, NFκB signaling pathway and improved hepatic immune responses of hybrid grouper in vivo and in vitro.

Recent studies have shown that mammalian G protein-coupled bile acid receptor 1 (TGR5) is involved in inflammatory response. However, the functions of TGR5 in immune response of hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) remain unclear. In this study, the full-length sequence of tgr5 from hybrid grouper was cloned and characterized for the first time, and the functions of TGR5 in the immune response was explored by activating/inhibiting hepatic TGR5 in vivo and in vitro. These results showed that activation of hepatic TGR5 inhibited PKC/P38 MAPK and PI3K/AKT signaling, attenuated the NFκB pathway, and improved the hepatic immune responses of hybrid grouper in vivo and in vitro. The inhibition of TGR5 had the opposite effects. Understanding the functions of hepatic TGR5 may help to develop management strategies to reduce the liver inflammation in fish or other animals.