Autophagy And Apoptosis Of IBV-Infected CEK Cells And Their Effects On Viral Replication

Avian infectious bronchitis(IB),caused by avian infectious bronchitis virus(IBV),is an acute,highly contactive infectious disease of chicken.The IBV M41 strain is the standard virulent strain of IBV.Chicken embryonic kidney(CEK)cells could simulate the native host environment and are the most sensitive cells to IBV infection.CEK cells have been widely used as a kind of host cell model to study IBV pathogenesis.Autophagy and apoptosis are important biological processes in various organisms.They are both actively involved in the development and the growth of the body.Many researches have been conducted to study the role of autophagy and apoptosis in the process of viral infection.However,for IBV,the occurrence of autophagy and apoptosis and their key roles in the process of viral replication have not been systematically studied in depth yet.In this study,we first studied whether autophagy and apoptosis occurred in IBV-infected CEK cells with Western Blot,real-time quantitative PCR(q RT-PCR)and electron microscopy.The results showed that autophagy and apoptosis occurred within 0-48 h post IBV infection of CEK cells,autophagy first increased and then decreased(30 h was the turning point).Apoptosis began to increase from 30 h,and there might be a certain regularity in the occurrence of autophagy and apoptosis.Western Blot and virus titer test results showed that activation of autophagy within 0-48 hours,viral replication increased firstly and then decreased.Furthermore,inhibition of autophagy could firstly decrease viral replication and then increase.It was concluded that autophagy first promoted and then inhibited viral replication.The studies of the effect of apoptosis on viral replication showed that apoptosis activation within 30-48 hours,viral replication reduced.And inhibition of apoptosis,viral replication increased.This indicated that apoptosis inhibited viral replication.In order to further study whether autophagy and apoptosis interact each other,and further affect viral replication,Western Blot and q RT-PCR were used to conduct related detections.The results showed that 30 h and 36 h post IBV infection,activation of autophagy could increase apoptosis,and inhibition of autophagy decreased apoptosis.While activation or inhibition of apoptosis had no change in autophagy.At 42 h and 48 h,apoptotic activation could reduce autophagy,and autophagy increased in the case of inhibition of apoptosis.While apoptosis did not change in the case of activation or inhibition of autophagy.It was demonstrated that autophagy firstly leaded to promotion of apoptosis and then apoptosis leaded to inhibition of autophagy.At the meantime,autophagy inhibited viral replication more strongly than apoptosis at early stage,and then apoptosis inhibited viral replication more strongly than autophagy at later time.In summary,IBV-infected CEK cells undergo autophagy and apoptosis.Autophagy firstly promotes viral replication and inhibits viral replication afterwards,and apoptosis inhibits viral replication.Autophagy firstly promotes apoptosis with the result of a decline in viral replication,and apoptosis inhibits autophagy with the decreased viral replication too.