Effects of glucose, insulin, glucagon, LPS and poly (I:C) on adiponectin receptors expression in grass carp (Ctenophcuyngodon idellus)

Abstract Adiponectin plays critical roles in energy metabolism and immunity of mammals by binding to its receptors (AdipoR1 and AdipoR2). However, they have not been fully understood in fish. The present study examined the distribution of adiponectin receptors (AdipoRs) mRNA in grass carp, and the changes of their expressions under glucose load, insulin or glucagon stimulation, lipopolysaccharide (LPS) or polyinosinic:polycytidylic acid [poly (I:C)] challenge. As for glucose load, fish were orally administrated with glucose (1.67 mg/g BW) for 1, 3, 6, 12 h. For insulin or glucagon stimulation, the primary hepatocytes of grass carp were incubated with 0, 10, 100, 1000 nM insulin or glucagon for 1, 3, 6, 12 h. In the immune challenge experiment, grass carp were intraperitoneally injected with LPS or poly (I:C) (5 μg/g BW) for 3, 6, 12, 24, 48 h. Finally, AdipoRs mRNA expression in all experiments was detected by Real-time quantitative PCR. The results showed that AdipoRs mRNA was widely expressed in various tissues of grass carp. The adipoR1a mRNA was highly expressed in the brain regions, and the highest level of adipoR2 mRNA was observed in the adipose tissue. Glucose load up-regulated adipoR1b and adipoR2 mRNA expressions in the liver at 6 h post administration and decreased adipoR1a expression in the muscle at 3 h. Insulin significantly enhanced adipoR1b and adipoR2 mRNA expressions in the hepatocytes at 1–12 h, and promoted adipoR1a mRNA expression at 1, 3 and 12 h, while glucagon had little effect on their expressions. LPS and poly (I:C) stimuli induced AdipoRs expression in the liver at 6 and 12 h, and their expressions in the muscle were decreased slightly or remained unchanged. In addition, LPS promoted AdipoRs expression in the kidney and spleen, whereas poly (I:C) only induced adipoR1a mRNA expression in the kidney, and increased adipoR2 mRNA level in the spleen. These results suggest that AdipoRs may act as one of the targets of insulin and immune response in grass carp, but whether they are direct target remains to be further studied.