Molecular characterization of an antimicrobial peptide LEAP-2 in Onychostoma macrolepis: Expression pattern, antimicrobial ability and immunomodulation function.

Antimicrobial peptides (AMPs) as the host's antimicrobial source are promising candidates for the development of novel antibacterial agents. Our study identified and analyzed the LEAP-2 gene from the cavefish - Onychostoma macrolepis (OmLEAP-2), and antimicrobial activity of OmLEAP-2 was assessed through both in vivo and in vitro experiments. The OmLEAP-2 encodes 92 amino acids with a hydrophobic surface (LAMMPWY) and two disulfide bonds. Following A. hydrophila infection, OmLEAP-2 expression was up-regulated in the liver, spleen and intestine in Onychostoma macrolepis. Recombinant OmLEAP-2 protein exhibited dose-dependent antimicrobial activity against both Gram-negative and Gram-positive bacteria, particularly A. hydrophila and A. veronii. OmLEAP-2 overexpression not only reduced bacterial load and increased survival rate, but also suppressed expression of TNF-α and IL-1β in A. hydrophila-infected Onychostoma macrolepis. Furthermore, OmLEAP-2 regulated iron metabolism by increasing liver iron levels, altering serum iron content, and modulating iron-related genes (fpn1 and hepcidin) expression. Collectively, these findings demonstrate that OmLEAP-2 exhibits broad-spectrum antibacterial activity against aquatic pathogens and shows potential as a therapeutic peptide for treating bacterial disease.