Downregulation of NF-kB signaling is involved in berberine-mediated protection of crucian carp (Carassius auratus gibelio) from cyprinid herpesvirus 2 infection

An acute cyprinid herpesvirus 2 (CyHV-2) infection of crucian carp (Carassius auratus gibelio) is characterized with hemorrhagic inflammation and high mortality. Berberine is a biologically active plant alkaloid with an anti-inflammation function involving the regulation of transcription factor NF-xB and its downstream inflammation-related genes in mammalian organisms. Our previous study had indicated that BBH (berberine chloride hydrate) inhibited gene expression and replication of CyHV-2, and might serve as a potential small molecular drug for controlling CyHV-2 infection in crucian carp. Here, NF-xB signaling in CyHV-2-infected crucian carp treated with BBH was investigated both in vitro and in vivo. Real-time RT-PCR and ELISA assays revealed that CyHV-2 could activate the NF-xB signaling resulting in up-regulation of its downstream pro-inflammatory gene expression including IL-6, IL-8, IL-113 and TNF-alpha. BBH could attenuate NF-xB signaling and downregulate the expression of its downstream inflammatory cytokines in a dose-dependent manner both in vivo and in vitro. BBH not only dose-dependently inhibits viral load in CyHV-2-susceptible crucian carp cell lines in infection and inhibition assays, but also ameliorates inflammatory injury in CyHV-2-targeted organ in histopathology examinations. Thus, negative regulation of NF-xB by BBH should contribute to BBH-mediated protection of crucian carp from CyHV-2 infection via attenuating viral gene expression and host inflammatory response simultaneously.