Electrotransfer of the tilapia piscidin 3 and tilapia piscidin 4 genes into skeletal muscle enhances the antibacterial and immunomodulatory functions of Oreochromis niloticus

Tilapia piscidin 3 (TP3) and tilapia piscidin 4 (TP4) are antimicrobial peptides recently isolated from Oreochromis niloticus. We previously showed that synthetic TP3 and TP4 possessed antimicrobial activities. Here, we analyzed the bactericidal abilities and immunomodulatory properties of these AMPs following the electroporation of pCMV-GFP-TP3 or pCMV-GFP-TP4 plasmid into tilapia (O. niloticus) muscle and subsequent infection with Vibrio vulnificus or Streptococcus agalactiae. Prior overexpression of TP3 or TP4 in tilapia muscle tissues efficiently reduced bacterial numbers at 24 and 48 h after V. vulnificus infection and reduced bacterial numbers at 24 h after S. agalactiae infection compared to numbers in controls expressing pCMV-GFP (EGFP). Electroporation of pCMV-EGFP-TP3 (TP3) or pCMV-EGFP-TP4 (TP4) significantly increased expression of several immune-related genes in muscle (IL-1β (12 h, TP3), IL-8 (12 h, TP3), TGFβ (3 h, TP4), and IκB (48 h, TP3, TP4)) and decreased the expression of TLR5 (12 h and 24 h, TP3) after V. vulnificus infection. Following S. agalactiae infection, expression of the following genes was significantly decreased in muscle: IL-1β (12 h, TP3), IL-8 (12 h, TP3, TP4), TLR5 (3 h–24 h, TP3, TP4), TGFβ (3 h, TP4; 24 h, TP3, TP4), and IκB (3 h, TP3). These data suggest that TP3 and TP4 exert antimicrobial effects after overexpression in the O. niloticus muscle, and also play important roles in the regulation of immune-related gene expression.