title: The protection effect of LEAP-2 on the mudskipper (Boleophthalmus pectinirostris) against Edwardsiella tarda infection is associated with its immunomodulatory activity on monocytes/macrophages.
abstract: Liver-expressed antimicrobial peptide 2 (LEAP-2) is a cationic peptide that plays an important role in the host's innate immune system. However, the mechanism by which LEAP-2 modulates/regulates the host defense against pathogens remains largely unknown. In this study, we identified a cDNA sequence encoding LEAP-2 homolog (BpLEAP-2) in the mudskipper, Boleophthalmus pectinirostris. Sequence analysis revealed that BpLEAP-2 belonged to the fish LEAP-2A cluster and that it was closely related to ayu LEAP-2. BpLEAP-2 mRNA was detected in a wide range of tissues, with the highest level of transcripts found in the liver. Upon infection with Edwardsiella tarda, BpLEAP-2 mRNA expression was significantly increased in the liver, kidney, spleen, and gill, but decreased in the intestine. Chemically synthesized BpLEAP-2 mature peptide did not exhibit antibacterial activity against E. tarda in vitro. Intraperitoneal injection of BpLEAP-2 (1.0 or 10.0 μg/g) resulted in significantly improved survival rate and reduced tissue bacterial load in E. tarda-infected mudskippers. In E. tarda-infected fish, BpLEAP-2 (0.1, 1.0, or 10.0 μg/g) eliminated E. tarda-induced tissue mRNA expression of BpTNF-α and BpIL-1β. In monocytes/macrophages (MO/MФ), BpLEAP-2 (1.0 or 10.0 μg/ml) induced chemotaxis, enhanced respiratory burst, and inhibited E. tarda-induced mRNA expression of BpTNF-α and BpIL-1β. At a concentration of 10.0 μg/ml, BpLEAP-2 also significantly enhanced the bacterial killing efficiency of MO/MФ. No significant effect was seen in the phagocytic activity of MO/MФ upon treatment with BpLEAP-2. Our study provides evidence, for the first time, that LEAP-2 exhibited immunomodulatory effects on immune cells, and protected the host from pathogenic infections independent of direct bacterial killing function.
authors.affiliation: Laboratory of Biochemistry and Molecular Biology, School of Marine Sciences, Ningbo University, Ningbo 315211, China; Collaborative Innovation Center for Zhejiang Marine High-efficiency and Healthy Aquaculture, Ningbo University, Ningbo 315211, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
authors.affiliation: Laboratory of Biochemistry and Molecular Biology, School of Marine Sciences, Ningbo University, Ningbo 315211, China; Collaborative Innovation Center for Zhejiang Marine High-efficiency and Healthy Aquaculture, Ningbo University, Ningbo 315211, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Chen
authors.affiliation: Laboratory of Biochemistry and Molecular Biology, School of Marine Sciences, Ningbo University, Ningbo 315211, China.
authors.forename: Xin-Jiang
authors.initials: XJ
authors.lastname: Lu
authors.affiliation: Laboratory of Biochemistry and Molecular Biology, School of Marine Sciences, Ningbo University, Ningbo 315211, China; Collaborative Innovation Center for Zhejiang Marine High-efficiency and Healthy Aquaculture, Ningbo University, Ningbo 315211, China. Electronic address: jchen1975@163.com.
authors.forename: Jiong
authors.initials: J
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D020609:Edwardsiella tarda / Q000502:physiology; D004756:Enterobacteriaceae Infections / Q000276:immunology / Q000382:microbiology / Q000662:veterinary*; D005393:Fish Diseases / Q000276:immunology* / Q000382:microbiology; D029941:Fish Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D005399:Fishes; D007113:Immunity, Innate / Q000235:genetics; D056747:Immunomodulation; D008264:Macrophages / Q000276:immunology; D009000:Monocytes / Q000276:immunology; D010802:Phylogeny; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment / Q000662:veterinary
chemical_list: D023181:Antimicrobial Cationic Peptides; D018076:DNA, Complementary; D029941:Fish Proteins; D012333:RNA, Messenger
keywords: Antibacterial activity; Bacterial load; Chemotaxis; Edwardsiella tarda infection; LEAP-2; Monocyte/macrophage functions; Mudskipper; Sequence analysis; Survival rate