Threonine deficiency decreased intestinal immunity and aggravated inflammation associated with NF-κB and target of rapamycin signalling pathways in juvenile grass carp (Ctenopharyngodon idella) after infection with Aeromonas hydrophila

Abstract

This study aimed to investigate the impacts of dietary threonine on intestinal immunity and inflammation in juvenile grass carp. Six iso-nitrogenous semi-purified diets containing graded levels of threonine (3·99-21·66 g threonine/kg) were formulated and fed to fishes for 8 weeks, and then challenged with Aeromonas hydrophila for 14 d. Results showed that, compared with optimum threonine supplementation, threonine deficiency (1) decreased the ability of fish against enteritis, intestinal lysozyme activities (except in the distal intestine), acid phosphatase activities, complement 3 (C3) and C4 contents and IgM contents (except in the proximal intestine (PI)), and it down-regulated the transcript abundances of liver-expressed antimicrobial peptide (LEAP)-2A, LEAP-2B, hepcidin, IgZ, IgM and β-defensin1 (except in the PI) (P<0·05); (2) could up-regulate intestinal pro-inflammatory cytokines TNF-α, IL-1β, IL-6, IL-8 and IL-17D mRNA levels partly related to NF-κB signalling; (3) could down-regulate intestinal anti-inflammatory cytokine transforming growth factor (TGF)-β1, TGF-β2, IL-4/13A (not IL-4/13B) and IL-10 mRNA levels partly by target of rapamycin signalling. Finally, on the basis of the specific growth rate, against the enteritis morbidity and IgM contents, the optimum threonine requirements were estimated to be 14·53 g threonine/kg diet (4·48 g threonine/100 g protein), 15.05 g threonine/kg diet (4·64 g threonine/100 g protein) and 15·17 g threonine/kg diet (4·68 g threonine/100 g protein), respectively.

Keywords: 4E-BP1 eIF4E-binding protein 1; ACP acid phosphatase; C complement; DI distal intestine; FE feed efficiency; GOT glutamate-oxaloacetate transaminase; GPT glutamate-puruvate transaminase; IKK IκB kinase; INFγ interferon γ; IκBα inhibitor of κBα; LA lysozyme activities; LEAP liver-expressed antimicrobial peptide; MI mid intestine; PAC plasma ammonia content; PI proximal intestine; PWG percentage weight gain; S6K1 ribosomal protein S6 kinases 1; SGR special growth rate; TGF transforming growth factor; TOR target of rapamycin; Immunity; Inflammation; Intestine; Juvenile grass carp (Ctenopharyngodon idella); NF-κB and target of rapamycin signalling; Threonine deficiency.