Abstract
Inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is an immunomodulator to inhibit immune-mediated pro-inflammatory response and has been used to treat various immune-related diseases in mammals. However, the immunoregulatory effect of GABA in crustaceans has not been reported. This study evaluates the regulatory effect of dietary GABA supplementation on the innate immune status and immunoregulatory potential in lipopolysaccharide (LPS)-induced immune response in juvenile Eriocheir sinensis. Juvenile crabs were fed with six diets supplemented with graded GABA levels (0, 40, 80, 160, 320 and 640 mg/kg dry matter) for 8 weeks and then 24 h LPS challenge test was carried out. The results showed that dietary GABA supplementation significantly decreased mortality at 4 and 8 weeks. Moreover, the hemocyanin content, acid phosphatase, and alkaline phosphatase activities significantly increased in the crabs fed GABA supplementation compared with the control. On the contrary, the alanine aminotransferase and alanine aminotransferase activities in serum decreased significantly in the GABA supplementation groups compared with the control. Similarly, superoxide dismutase activity, glutathione content, and the transcriptional expression of the antioxidant-related genes and immune-related genes were significantly higher in the GABA supplementation groups than in the control. In addition, the mRNA expressions of anti-lipopolysaccharide factors (ALF 1, ALF 2, ALF 3) and inflammatory signaling pathways related genes (TLR, Myd88, Relish, LITAF, P38-MAPK, ADAM17) were significantly up-regulated in LPS stimulation groups compared with PBS treatment. Meanwhile, pro-apoptosis-related genes' mRNA expressions were significantly up-regulated, and anti-apoptosis-related genes were significantly down-regulated under LPS stimulation compared with PBS treatment. However, GABA pretreatment effectively alleviated LPS-induced immune overresponse and apoptosis. Therefore, this study demonstrates that dietary GABA supplementation could be used as an immunomodulator to improve the non-specific immunity and antioxidant capacity and alleviate the immune-mediated immune overresponse of juvenile E. sinensis.
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