Novel hepcidin genes in gilthead seabream: Implications for immune response and iron metabolism

Antimicrobial peptides (AMPs) are highly conserved small molecules present in various organisms, including fish. In gilthead seabream (Sparus aurata), one hamp1 and 15 hamp2 genes have been identified. This study aimed to characterize two novel hamp2 genes, hamp2.0 and hamp2.15, located on chromosome 17 of the gilthead seabream genome. Evolutionary analysis revealed that orthologs of both genes first appeared in the Clupeocephala clade 229 million years ago. In silico analysis predicted that the mature peptides, Hamp2α and Hamp2Ω, possess antimicrobial properties. Both peptides exhibited bactericidal activity against Vibrio harveyi, with Hamp2α showing concentration-dependent inhibition and Hamp2Ω demonstrating time-dependent inhibition. Neither peptide displayed cytotoxicity against SAF-1 cells; instead, they promoted cell proliferation. Basal expression of both genes was observed in all tissues analyzed, with the highest levels in liver and gonad. In head kidney leucocytes (HKLs), expression of both genes increased upon stimulation with lypopolysaccharide, poly I:C, nodavirus, or V. anguillarum. In vivo, hamp2.0 expression significantly increased in various tissues of V. harveyi-infected fish, while hamp2.15 expression increased in liver, spleen, head kidney, skin, and brain. In nodavirus-infected fish, hamp2.15 expression decreased in head kidney and brain. Finally, both genes showed significantly increased expression in head kidney and liver 72 h post-iron dextran injection. These findings suggest that the two novel hamp2 genes in gilthead seabream play a role in the immune response to bacterial and viral infections and may be involved in iron metabolism regulation.