Molecular Characterization of the Liver-Expressed Antimicrobial Peptide 2 (LEAP2) from Amphiprion ocellaris and Its Role in Antibacterial Immunity.

Liver-expressed antimicrobial peptide 2 (LEAP2) is a cationic peptide that is integral to the innate immune system. However, its regulatory function in the immunity of fish against pathogens remains largely unexplored. This study identifies a LEAP2 homolog (AoLEAP2) in clownfish, Amphiprion ocellaris. Our phylogenetic analysis places AoLEAP2 within the fish LEAP2 cluster, closely related to Tachinotus anak LEAP2. AoLEAP2 mRNA is present across various tissues, with the highest expression in the spleen. Following Vibrio harveyi infection, the AoLEAP2 mRNA levels significantly increased in the liver, spleen, gills, and intestine. The chemically synthesized AoLEAP2 mature peptide exhibits broad-spectrum antibacterial activity without displaying toxicity to FHM cells in vitro. The intraperitoneal injection of AoLEAP2 significantly suppresses the mRNA expression of the pro-inflammatory factors IL1β and TNFα induced by V. harveyi infection, demonstrating its anti-inflammatory and immune-regulatory role.