Recognition of MDP and activation of NF-κB by cytosolic sensor NOD2 in Oreochromis niloticus

Abstract The NOD-like receptors (NLRs) are an important part of the innate immune system, capable of recognizing or sensing pathogens or cell homeostasis imbalance, and play an important role in pathogen removal and body protection. NOD2 is one of the important members in NLR family. In present study, NOD2 was cloned and identified from Nile tilapia (Oreochromis niloticus). The Nile tilapia NOD2 ORF was 2961 bp in length encoding a peptide of 986 amino acid residues with a typical structure of CARD-CARD-NACHT-LRRs. Phylogenetic and synteny analysis illustrated that NOD2 was highly conserved between different species. Tissue distribution of NOD2 mRNA showed that it was widely expressed and highly expressed in immune-related tissues (blood, head kidney, liver and spleen). Post Streptococcus agalactiae challenge, NOD2 mRNA expression levels were altered in immune organs or tissues (liver, head kidney, spleen and blood). Subcellular localization of Nile tilapia NOD2 illuminated that it was an intracellular PRR like mammalian counterparts, most of which was co-localized with mitochondria, and a few of which was co-localized with endosome and endoplasmic reticulum. In addition, Nile tilapia NOD2-mediated signaling pathway and ligand recognition were also studied, it illuminated that Nile tilapia NOD2 could recognize MDP intracellularly and activate NF-κB signaling pathway. In conclusion, this study indicated that the Nile tilapia NOD2 was conservative and had a significant role in innate immune defense against bacterial infection.