Antibacterial mechanisms and pathogen-dependent protective effects of the golden pompano LEAP2-derived peptide...

Antimicrobial peptides (AMPs) are essential components of the innate immune system, with liver-expressed antimicrobial peptide 2 (LEAP2) playing a pivotal role in fish immunity. This study investigated the antimicrobial activity and mechanisms of TroLEAP2-21, a 21-amino-acid short peptide from golden pompano (Trachinotus ovatus), against Gram-positive (Lactococcus garvieae, Staphylococcus epidermidis) and Gram-negative (Vibrio alginolyticus, Vibrio harveyi) bacteria. The predicted three-dimensional structure and helical wheel projection of TroLEAP2-21 suggested typical AMP-like physicochemical features. troleap2 expression in the liver and intestine of T. ovatus was significantly upregulated post L. garvieae or V. harveyi infection, suggesting its potential involvement in antibacterial defense. In vitro, TroLEAP2-21 exhibited antibacterial activity against the tested bacterial strains, with membrane disruption, increased membrane permeability, cytoplasmic leakage, and membrane depolarization observed after peptide treatment. Gel retardation assays further indicated species-dependent association of TroLEAP2-21 with bacterial genomic DNA. In vivo, under the tested intraperitoneal injection conditions, TroLEAP2-21 was associated with improved survival and reduced tissue damage in V. harveyi-infected T. ovatus, whereas no significant survival benefit was observed against L. garvieae. Transcriptomic analysis at 48 h post-infection showed transcriptional changes in immune-related DEGs (rsad2, mx1/mx2, il-8) and enrichment of TLR and Jak-STAT signaling pathways at the transcriptional level in peptide-treated fish. FISH showed the tissue localization of tnf-α and nf-κb transcripts and revealed treatment-associated changes in fluorescence signals, and qRT-PCR of eight immune genes supported transcriptomic results in tissues at 48 h post-infection. Collectively, these findings characterize TroLEAP2-21 as a short LEAP2-derived peptide with antibacterial and immunomodulatory activities. Its comparative advantages over other LEAP2-related peptides and its practical application potential remain to be further investigated.