Stage-specific expression of TNFα regulates bad/bid-mediated apoptosis and RIP1/ROS-mediated secondary necrosis in Birnavirus-infected fish cells

Infectious pancreatic necrosis virus (IPNV) is a fish-derived pathogen and possess a bi-segmented, double-stranded RNA genome. By using zebrafish 14K oligo-microarray and quantitative RT-PCR, we identified differential expression of a defined subset of genes involved in apoptosis and immunity at 6-, 12- and 24- hour after IPNV infection. Transcripts divided into 11 functional categories were significantly modulated by IPNV, including immune response, apoptosis, transcription, signal transduction, lipid and cholesterol metabolism, carbohydrate metabolism, oxidative phosphorylation, cell cycle, protein degradation, protein folding and stress response, protein synthesis, nucleoside metabolism and synthesis. Most of pro-apoptotic bcl-2 family members were up-regulated after IPNV infection. Activation of pro-apoptotic members might disrupt potential of mitochondria and leaded to the mitochondria-mediated apoptosis in the late stage of IPNV infection. After treating the IPNV-infected cells with TNFα inhibitor AP126, expression of two bcl-2 family genes Bad and Bid and activation of caspase-8 and -3 had been inhibited significantly in early stage of IPNV infection. Expression of RIP-1 and Bmf-1 these two necroptosis-related genes and production of ROS were diminished in virus-infected cells which pre-treated with AP126. Our study shows the interactions between host cells and IPNV, the molecular mechanisms involved in IPNV-induced pathogenesis, and the variation of transcriptome through TNFα during infection which shows the important component of host defense. TNFα might lead to apoptosis in early stage and necrosis in late stage in ZF4 cells infected by IPNV. TNFα is crucial to apoptosis and ROS-mediated necrosis caused by IPNV in zebrafish cells. Zebrafish ZF4 cell line was derived from 24h post-fertilization zebrafish embryos. Previous studies have been shown that adult zebrafish and zebrafish cell line could be infected with IPNV. In the present study, ZF4 cells were infected with IPNV, and total RNA was isolated from infected and uninfected control cells at 0 h, 6 h, 12 h, 24 h post-infection. Microarray analysis gene expression between IPNV-infected and uninfected cells relative to internal control on slides. The zebrafish 14K oligo microarray we used comprise 1800 zebrafish gene sequences from the NCBI and a database of 12768 putative open reading frames using NCBI zebrafish EST sequence information. Data files were imported into GeneSpring GX 7.3 for further analysis. Expression data sets must pass all the following quality control categories before used for cluster analysis. Clustering analysis allowed us to observe differences in cellular gene expression. A similar expression pattern was seen when comparing differentially expressed host cell genes between 12 and 24 h post-infection. The expression profiles were significantly different between 6 and 12 h post-infection. Therefore, we conclude that the regulation of host gene expression was changed after 12 h post-infection, and progressed into the late stage. To understand the interactions between host cells and IPNV and the molecular mechanisms involved in IPNV-induced pathogenesis, we used zebrafish oligo microarrays to investigate the gene expression profiles of IPNV-infected zebrafish embryonic cells. We also studied expression of specific genes related to immune response and apoptosis which were not present on the microarray we used by real-time quantitative RT-PCR. We used Pathway Studio’s software to analyze the altered genes in cellular pathway for IPNV, TNFα was shown to be crucial to these genes of host response. Our study proved the variation of transcriptome during infection, which shows the activation of important component of host defense, apoptosis and necrosis through TNFα mediate pathway.