Heparin, piscidins, and copper ions are secreted from the fish phagocyte granules as a first-line of immune defense, however the role of heparin and its interactions with these key components had not been investigated before. Other antimicrobial peptides (AMPs) share physicochemical similarities with piscidin and are known to bind heparin and induce immune-cell chemotaxis through formyl peptide receptors (FPRs) associated with innate immunity. Here, we postulated that piscidin 1 (P1) and 3 (P3) interact with heparin and FPRs dependent on the presence of Cu2+. Using surface plasmon resonance, we found that piscidin-heparin interactions are Cu2+-dependent and reduced at the phagosomal pH. Heparin reduces the antimicrobial activity of P3-Cu, however it does not hinder the antimicrobial capability of P1-Cu and piscidin-mediated FPR1 aggregation. Utilizing FPR-transfected cells and neutrophils, we discovered that both piscidins exclusively use FPR1 and FPR2 to induce chemotaxis while Cu2+ reduces this role of piscidins. Lastly, we learned that FPR1 activation capacity of P1 is greater than that of P3 and other known AMP ligands. This interactome study advances our understanding of phagocyte associated immune response of fish involving heparin and may facilitate therapeutic strategies to eradicate infectious pathogens affecting fish populations.

Interactome study of heparin, piscidins, and copper ions from phagocytes involved in innate immunity of fish

2019 Fall National Meeting

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