A review on fish immuno-nutritional response to indispensable amino acids in relation to TOR, NF-κB and Nrf2 signaling pathways: Trends and prospects

Indispensable amino acids (IAAs) are important regulators of key metabolic pathways associated with protein synthesis, tight junction proteins, inflammatory cytokines and immune-antioxidant related signaling molecules. However, the information pertaining to the immune functions of IAAs in relation to molecular approaches for commercially important fish species are scarce and discordant. This review summarizes the dietary requirements for IAAs necessary for improved growth and immune response in variety of fish species, using molecular approaches (nutrigenomics), particularly the interrelationships between IAAs and genes. Briefly, antioxidant status of fish as well as gene transcriptions regulating antioxidant enzymes are profoundly governed by the nutritional factors including a set of IAAs, and these genes expression are often regulated by the nuclear factor erythoid 2-related factor 2 signaling pathway (Nrf2). IAAs level could also attenuate the inflammatory response in fish partly by down-regulating the expression levels of pro-inflammatory cytokines and up-regulating the anti-inflammatory cytokines. The regulation of these cytokines by IAAs could be mediated by the signaling molecules nuclear transcription factor-kappa B (NF-kappa B) and target of rapamycin (TOR). Overall, this review provides clear and recent molecular mechanisms of fish immuno-nutritional interrelation and highlights regulatory pathways underlying dietary IAAs mediated enhancement in the antioxidant, anti-inflammatory, and immune defense capacities, presenting trends and future perspectives.