Molecular Identification Of Scavenger Receptor Of Teraodon Nigroyiridis And Its Functional Investigation In Inflammation

This article focus on the molecular cloning and identification of scavenger receptor in Tetraodon nigroviridis, Tn-SR and its function in immune response induced by LPS to clarify the biological characterization of scavenger receptor in fish.A novel Tn-SR was predicted and identified as an ortholog of mammalian SCARA5by bioinformatics methods, which has a typical structure of type II membrane receptor containing a short N-terminal cytoplasmic domain, a transmembrane domain and a long C-terminal extracelluar domain. In the extracelluar part of Tn-SR, the coiled-coil structure, collagenous domain and a scavenger receptor cysteine-rich domain (SRCR) are conserved organization of SR class A members in mammals. TRAF2-binding consensus motif at residue10-13and linear YXX? motif in transmembrane domain were found, which implied Tn-SR involving in the process of immune reaction. Expression in HEK293cells confirmed that Tn-SR assembles as a homotrimer and is expressed at the plasma membrane of leukocytes from Tetraodon nigroviridis.The gene expression profile showed that Tn-SR is detected in all tissues including liver, intestine, spleen, kidney, skin, gill, muscle and brain. After stimulated by LPS, expression levels of Tn-SR on spleen, muscle, brain and kidney were significantly up-regulated compared with other tissues.Tn-SR played a dual role in immune response stimulated by LPS. The extracelluar part of Tn-SR was ability to bind LPS detected by ELISA. Tn-SR involved in the LPS recognition and binding/phagocytosis of leukocytes from Tetraodon nigroviridis. Tn-SR was internalized to cytoplasma to ingest or clear LPS to reduce the toxic influence of LPS and inflammation by LPS. Although Tn-SR was not able to directly transduce the singling pathway induced by LPS, it involved in the negative regulation of NF-κB activation. In model of zebrafish embryos, fold induction of NF-κB were decreased remarkably in groups with different expression levels of Tn-SR induced by LPS at different concentrations. Tn-SR was certified to interacting with Tn-TRAF2by CO-IP under normal and LPS conditions.Tn-SR bind with TRAF2to inhibit NF-κB activation in tumor necrosis factor-tumor necrosis factor receptor signaling pathway to weaken the inflammation by LPS.These results suggested that scavenger receptor plays a key role in the resistant to toxic effect of LPS in fish and provided new supports to understanding the scavenger receptor as a pattern recognition receptor in innate immunity.