Soybean glycinin impaired immune function and caused inflammation associated with PKC-ζ/NF-κb and mTORC1 signaling in the intestine of juvenile grass carp (Ctenopharyngodon idella)

Glycinin is a major protein and antinutritional factor of soybean. However, how dietary glycinin affect intestinal immune function of fish were largely unknown. In this study, we used juvenile grass carp as a model to investigate the impacts of glycinin on intestinal immune function of fish and involved mechanisms. We set three treatments including control, glycinin and glycinin + glutamine in this trial. For immune components, results revealed that compared with control group, glycinin group had lower acid phosphatase activities in the foregut, midgut and hindgut, lower C3 and C4 content, and lower mRNA abundances of IgM, IgZ, hepcidin, LEAP-2A, LEAP-2B and beta-defensin-1 in the midgut and hindgut rather than foregut of grass carp. For pro-inflammatory cytokines and relevant signaling, glycinin elevated mRNA abundances of IL-1 beta, IL-8, IL-12p35, IL-12p40 and IL-17D in the midgut and IL-1 beta, IFN-gamma 2, IL-6, IL-8, IL-12p35, IL-12p40 and IL-17D in the hindgut, and increased protein abundances of PKC-zeta and nuclear NF-kappa B p65 in the midgut and hindgut in comparison to control. For anti-inflammatory cytokines and relevant signaling, glycinin reduced mRNA abundances of TGF-beta 1, TGF-beta 2, IL-4/13B (rather than IL-4/13A), IL-10 and IL-11 in the midgut and hindgut, and reduced p-mTOR (Ser 2448), p-S6K1 (Thr 389) and p-4EBP1 (Thr 37/46) protein abundances in the midgut and hindgut rather than foregut. Co-administration of glutamine with glycinin could partially enhance intestinal function and reduce intestinal inflammation compared with glycinin treatment. Concluded, glycinin decreased intestinal immune components and caused intestinal inflammation associated with PKC-zeta/NF-kappa B and mTORC1 signaling.