High dietary lipid level decreases the immunity and disease resistance of abalone Haliotis discus hannai and affects the perilipin‐2/TLR4, JNK and Keap1/Nrf2 pathways.

A 100‐day feeding trial was conducted to investigate the influences of dietary lipid levels on the immunity and mechanism in abalone Haliotis discus hannai Ino. Abalones (initial weight: 10.98 ± 0.05 g) were fed with graded levels of dietary lipid, which were 15.73, 23.41, 31.72, 38.25, 46.35, 55.63, 61.70 and 67.19 g/kg. Results showed that compared with the treatment with 38.25 g/kg of dietary lipid, 67.19 g/kg of dietary lipid increased the cumulative mortality of abalone after a challenge with Vibrio parahaemolyticus. Meanwhile, 67.19 g/kg of dietary lipid decreased the activities of lysozyme (LZ) and acid phosphatase (ACP) in serum, and the mRNA levels of β‐defensin and mytimacin 6 in hepatopancreas of abalone. The mRNA levels of tumour necrosis factor α (tnfα), activator protein 1 (ap‐1), nuclear factor κB (nf‐κb), interleukin 1 receptor‐associated kinase‐4 (irak4), myeloid differentiation primary response protein MyD88 (myd88), toll‐like receptor 2 (tlr2), tlr4 and perilipin‐2, and the protein level of interleukin‐1β (IL‐1β), TNFα, NF‐κBp65, AP‐1, MyD88 and Perilipin‐2 in hepatopancreas were up‐regulated by 67.19 g/kg of dietary lipid. However, the mRNA levels of arginase and inhibitor of κBα (iκbα) were down‐regulated. Besides, 67.19 g/kg of dietary lipid up‐regulated the mRNA levels of executor apoptosis‐related cysteine peptidase 3 (caspase‐3), caspase‐7 and B‐cell lymphoma protein‐2‐associated X protein (bax), and the protein levels of caspase‐3 and c‐Jun N‐terminal kinases (JNK) in hepatopancreas. Moreover, high dietary lipid level down‐regulated the mRNA levels of copper/zinc superoxide dismutase (cuznsod), manganese superoxide dismutase (mnsod), catalase (cat), glutathione peroxidase (gpx), glutathione‐S‐transferase (gst) and NF‐E2‐related factor 2 (nrf2), while up‐regulated the mRNA and protein levels of Kelch‐like ECH‐associated protein 1 (Keap1) in hepatopancreas. It was concluded that a high level (67.19 g/kg) of dietary lipid decreased the immunity of abalone, which might be related to the aggravated inflammation and apoptosis, and decreased anti‐oxidative capacity under Perilipin‐2/TLRs/MyD88/IRAK4/(NF‐κB or AP‐1), JNK/Bcl‐2/Bax and Keap1/Nrf2 signalling. [ABSTRACT FROM AUTHOR]