NADPH oxidase involved in immune response via regulating the expression of antioxidant genes in Litopenaeus vannamei

Free radicals such as reactive oxygen species (ROS) play a significant role in the innate immune system. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Noxes) are found to be involved in ROS production and played crucial roles in host biological processes of humans, insects, and plants. However, there are relatively few studies on the function of Noxes in crustaceans. In this study, the full-length cDNA of Nox was cloned from Litopenaeus vannamei by rapid amplification of cDNA ends (RACE) to obtain a 3790 base pairs (bp) cDNA sequence. LvNox cDNA comprised a 5'-untranslated region (UTR) of 454 bp, a 3'-UTR of 333 bp, and a putative open reading frame (ORF) of 3006 bp. Structural analysis showed that LvNox had a transmembrane helical segment (THS) at positions 233-255, a flavin adenine dinucleotide (FAD) binding domain (at positions 447-579), and a nicotinamide adenine dinucleotide (NAD) binding domain (at positions 815-990). Tissue distribution analysis revealed that LvNox mRNA was expressed in heart, intestine, muscle, gill, hepatopancreas, stomach, epidermis, hemocyte, and eyestalk. High expression levels of LvNox were observed in epidermis, hemocyte and eyestalk. The expression levels of LvNox were significantly induced after Vibrio alginolyticus injection for 6, 12, 24 and 48 h, and after Cu exposure for 24 and 48 h. Furthermore, the RNA interference of LvNox significantly reduced the production of ROS and the expression levels of copper/zinc superoxide dismutase (Cu-Zn SOD), catalase (CAT) and nitric oxide synthase (NOS). These results indicated that LvNox could be induced by V. alginolyticus infection and Cu exposure, which might be involved in immune response of shrimp via regulating the expression of antioxidant genes. These findings provide a solid foundation for further study of the function of Noxes in crustaceans.