New insight into the biological activity of Salmo salar NK-lysin antimicrobial peptides

Abstract

NK-lysin is a potent antimicrobial peptide (AMP) with antimicrobial activity against bacteria, fungi, viruses, and parasites. NK-lysin is a type of granulysin, a member of the saposin-like proteins family first isolated from a pig's small intestine. In previous work, for the first time, we identified four variants of <i>nk-lysin</i> from Atlantic salmon (<i>Salmo salar</i>) using EST sequences. In the present study, we reported and characterized two additional transcripts of <i>NK-lysin</i> from <i>S. salar</i>. Besides, we evaluated the tissue distribution of three <i>NK-lysins</i> from <i>S. salar</i> and assessed the antimicrobial, hemolytic, and immunomodulatory activities and signaling pathways of three NK-lysin-derived peptides. The synthetic peptides displayed antimicrobial activity against <i>Piscirickettsia salmonis</i> (LF-89) and <i>Flavobacterium psychrophilum</i>. These peptides induced the expression of immune genes related to innate and adaptive immune responses <i>in vitro</i> and <i>in vivo</i>. The immunomodulatory activity of the peptides involves the mitogen-activated protein kinases-mediated signaling pathway, including p38, extracellular signal-regulated kinase 1/2, and/or c-Jun N-terminal kinases. Besides, the peptides modulated the immune response induced by pathogen-associated molecular patterns (PAMPs). Our findings show that NK-lysin could be a highly effective immunostimulant or vaccine adjuvant for use in fish aquaculture.