ITRAQ-based comparative proteomic analysis of the Lithobates catesbeianus bullfrog spleen following challenge with Citrobacter freundii

Abstract

As a common aquaculture pathogen, Citrobacter freundii has resulted in inconceivable economic losses in aquaculture. In this study, we investigated the spleen immune response of Lithobates catesbeianus to C. freundii infection at the protein level. A comparative proteomic analysis of spleens from C. freundii-infected L. catesbeianus was performed by using isobaric tags for relative and absolute quantitation (iTRAQ) approaches. A total of 2400 proteins were identified by LC-MS/MS spectra and sequencing data. In addition, 316 differentially expressed proteins (DEPs) were identified, of which 154 were significantly upregulated and 162 were significantly downregulated. Seven DEPs that are immune related including Kelch-like protein 22 (KLHL 22), saxiphilin (Sax), integrin beta-3 (ITGB3), retinoic acid-inducible gene I (RIG-I), laboratory of genetics and physiology 2 (LGP2), E3 ubiquitin-protein ligase TRIM39-like (TRIM39L), and phospholipid scramblase 1 (PLSCR1) were selected for further study. The expression profile of these genes in the spleen at 48 h post-C. freundii-infection showed a similar trend as the iTRAQ data. Altogether, the current study is the first to report the spleen proteome of bullfrogs (L. catesbeianus), providing insight into the immune response to C. freundii infection.