Regulation Of Cellular Type Ⅰ Ifn Production By Infectious Bursal Disease Virus Infection

Infectious bursal disease(IBD)is considered to be the "AIDS" of chickens because of its significant immunosuppressive symptoms.The disease mainly affects the central lymphoid organs,thus results immunosuppression.Once the chickens are infected,it will disturb the vaccine immune effects of other infectious diseases,which will cause heavy losses to the poultry production.Infectious bursal disease virus(IBDV)belongs to the only representative member of the birnaviridae avibirnavirus family,and its pathogenic mechanism remains unclear.This study was the first to use RNAseq technology to analyze the transcriptome of IBDV infection,and further analyzed the protein degradation mechanism of the innate immune factor,which had more significant changes by comparison in gene expression.Our research provide a theoretical basis for the study of IBDV infection inhibiting host innate immune response.First,this study used high-throughput sequencing technology to analyze the transcriptome changes in host cells caused by IBDV infection and screened for significant changes.A total of 3,417 differentially expressed genes were found,of which 1887 were relatively highly expressed in the IBDV-infected group and 1,530 were relatively low-expressed(FC>2 and P≤0.05).The GO annotation and KEGG signaling pathway enrichment analysis of differential genes revealed that IBDV infection can cause significant changes in more than 20 signaling pathways such as Toll-like receptor signaling pathway,RIG-I-like receptor signaling pathway,NOD-like receptor signaling pathway,cytokine-cytokine receptor,apoptosis pathway,etc.Most of these pathways regulate the production of interferon directly or indirectly.A large number of gene expression in RIG-I-like receptor signaling pathway was significantly up-regulated,such as IRF7,IFIH1,TRAF3,TRAF6 and so on.qPCR results showed that the expression levels of CMPK2,EPSTI1,SNX10,IFIH1,TJP2 and other genes were consistent with the transcript analysis,and the up-regulation of IFIH1,encoding MDA5,the key regulator in the type I interferon pathway,was more significant by comparison.However,further studies found that IBDV infection can cause degradation of MDA5,and this process was induced by the genome dsRNA of IBDV.Then poly(I:C),a pattern recognition molecule of MDA5,mimics the viral genome dsRNA and activates the interferon signaling pathway.In this study,we used poly(I:C)to stimulate cells to instead the infection of the IBDV genome and found that poly(I:C)stimulation can significantly cause MDA5 degradation,with the same biological phenomenon as dsRNA.Under the action of autophagy inhibitor Chloroquine(CQ),the half-life of MDA5 was significantly slowed,indicating that the degradation of MDA5 can be regulated by autophagy;in turn,autophagy activation promotes the interaction between MDA5 and p62.Further studies found that the autophagy inhibitor CQ was able to maintain sustained up-regulation of IFN-β under poly(I:C)stimulation.Silencing of endogenous MDA5 by siRNA interference revealed that autophagy inhibitor CQ could not maintain continuous up-regulation of IFN-βunder poly(I:C)stimulation,indicating that MDA5 can undergo autophagy degradation to inhibit IFN-β production.The above results demonstrate that autophagy inhibits the production of IFN-β by degrading MDA5 in the late stage.In summary,although IBDV infection activates cellular immune-related genes transcription,the significant change in MDA5 encoded by IFIH1 is degraded by p62-regulated autophagy,finally caused the inhibition of the interferon in the late stage induced by IBDV infection.