The VIP-VIPR2 axis strengthens intestinal barrier integrity and antimicrobial immunity in Ctenopharyngodon idella.

Abstract

Bacterial pathogens like Aeromonas hydrophila threaten aquaculture by compromising fish immune defenses. The intestinal barrier is a critical frontline defense against pathogenic bacteria in fish, yet its regulation by neuroimmune mechanisms remains poorly understood. In this study, we investigated the role of vasoactive intestinal peptide (VIP) in the immune response of grass carp (Ctenopharyngodon idella) following bacterial challenge. The full-length grass carp VIP gene was 462 bp, encoding a 153-amino acid precursor protein with high sequence conservation across vertebrates. VIP expression was highest in the intestinal tract and significantly upregulated upon A. hydrophila infection. Administration of recombinant grass carp VIP protein enhanced intestinal barrier function by increasing the expression of tight junction molecules (ZO-1, Occludin, Claudin-1) and the immunoregulatory cytokine IL-22, while reducing plasma LPS and D-lactate levels. Furthermore, grass carp VIP treatment promoted the expression of the mucosal barrier component MUC2 and antimicrobial peptides (LEAP-2, Lyz1, Hepcidin-1), reduced bacterial load, and significantly improved survival rates. Mechanistic studies confirmed that VIP interacted specifically with the VIP receptor 2 (VIPR2), and knockdown of VIPR2 abolished the protective effects of VIP on barrier integrity and antimicrobial immunity. These findings demonstrate that the VIP-VIPR2 axis plays a crucial role in modulating intestinal immunity in grass carp, offering new insights into neuroimmune regulation in aquatic animals during pathogenic challenge.