Ribonuclease1 contributes to the antibacterial response and immune defense in blunt snout bream (Megalobrama amblycephala)

Ribonuclease 1 (RNase1) is a vertebrate-specific enzyme that mainly performs digestive activity in herbivorous mammals. Here we used bacterial viability assays to explore its antimicrobial activity in blunt snout bream (Megalobrama amblycephala). The results showed that Ma-RNase1 rapidly killed Gram-negative and Gram-positive bacteria at micromolar concentrations. Ma-RNase1 increased the permeability of bacterial outer and inner membranes, thus reducing the integrity of bacterial cell wall and membrane. Moreover, Ma-RNase1 effectively counteracted the tissue damage and apoptosis caused by Aeromonas hydrophila infection. Quantitative real-time PCR and immunoblot analysis indicated that RNase1 mRNA and protein were up-regulated in the kidney and gut during infection. Furthermore, A. hydrophila infection significantly induced Tnf-α and Il-1β mRNA expression in liver, but not in the RNase1 pre-treatment group. In addition, a significant increase in the expression of immune-related genes (Nf-κb and Tlr4) was found in liver, kidney and gut of A. hydrophila-infected fish, while a decrease in Myd88 and Tlr4 levels was found in liver, spleen, kidney and gut in the group pre-treated with RNase1. Collectively, these data suggest that Ma-RNase1 has antimicrobial function both in vitro and in vivo, and contributes to the protective effect and immune defense of blunt snout bream.