Comparative transcriptome analysis reveals induction of apoptosis in chicken kidney cells associated with the virulence of nephropathogenic infectious bronchitis virus

Avian infectious bronchitis virus (IBV) that causes respiratory and nephritic diseases in chicken is a major poultry pathogen leading to serious economic loss worldwide. The nephropathogenic IBV strains cause nephritis and kidney lesions intrinsically and the pathogenic mechanism is still unclear. In the present study, SPF chicks were infected with three nephropathogenic IBVs of different virulence and their gene expression profiles in chicken kidney were compared at transcriptome level. As a result, 1279 differentially expressed (DE) genes were found in very virulent SCDY2 inoculated group, 145 in virulent SCK2 group and 74 in non-virulent LDT3-A group when compared to mock infected group. Gene Ontology (GO) and KEGG pathway enrichment analysis on SCDY2 group displayed that the up-regulated DE genes were mainly involved in cell apoptosis, and the down-regulated genes were involved in metabolic processes and DNA replication. Protein-Protein Interaction (PPI) analysis showed that DE genes in SCDY2 group formed a network, and the core of the network was composed by cell apoptosis and immune response proteins. The clustering of gene expression profile among the three virus inoculated groups indicated that the majority of up-regulated DE genes on apoptosis in very virulent SCDY2 group were up-regulated more or less in virulent SCK2 group and those down-regulated on innate immune response in SCDY2 group were also down-regulated differently in SCK2 group. In addition, the number of apoptotic cells detected experimentally in kidney tissue were very different among the three virus inoculated groups and were positively accordant with the viral titer, kidney lesions and viral virulence of each group. Taken all together, the present study revealed that virulent nephropathogenic IBV infection modified a number of gene expression and induction of apoptosis in kidney cells may be a major pathogenic determinant for virulent nephropathogenic IBV.