Mechanism Of PCV2 Replication Promoted By Oxidative Stress-induced Autophagy And Regulation Of Taurine

Porcine circovirus type 2(PCV2)is a pathogen of porcine circovirus-associated disease(PCVAD).However,not all pigs infects with PCV2 will develop PCVAD,PCVAD development has been linked to animal management,presence of concurrent viral infections,nutrition and oxidative stress,suggesting that other trigger factors are associated with the disease.However,to date,the pathogenesis of PCV2 is still unclear.The ROS content is a dynamic process in the organism,which determines the state of oxidative stress Ochratoxin A(OTA)is a worldwide mycotoxin which could cause an increase in ROS levels in animals.Previous research found that oxidative stress and OTA exposure could promote PCV2 replication by inducing autophagy.Apoptosis is an autonomous cell death based on a genetic program.Although autophagy and apoptosis are two completely different cell processes,previous studies suggested that autophagy and apoptosis interact with each other under certain conditions,and this dynamic balance may affect virus replication.However,it is still unknown whether autophagy interacts with apoptosis in the promotion of PCV2 replication induced by oxidative stress.Nutrition supplementation is suggested to be an effective prophylactic protection against viral infectin.Taurine is the most abundant free amino acid in the body.Different functions of taurine include detoxication,antioxidant,and cytoprotective activities.However,whether taurine has effects on PCV2 replication and the underlying mechanism is still unclearThe present study was conducted to investigate the mechanism of PCV2 replication promotion by oxidative stress-induced autophagy and reglation of taurine,which is hepful for the study of pathogenesis of porcine cirovirus disease,and could provide scientific basis for the application of taurine in animal husbandry production.Experiment 1:PCV2 replication promoted by oxidative stress is dependent on the regulation of autophagy on apoptosisThe intracellular redox state casuses effects on the viral replication in host cells.By evaluating cap protein expression,viral DNA copies and the number of infected cells,the present study further confirmed that oxidative stress can promote PCV2 replication.The results showed that oxidative stress induced autophagy in PCV2-infected PK15 cells.Blocking autophagy with inhibitor 3-methladeine or ATG5-specific siRNA significantly inhibited oxidative stress-promoted PCV2 replication.Importantly,autophagy inhibition significantly increased apoptosis in oxidative stress-treated PK15 cells.Suppression of apoptosis by benzyloxycarbonyl-Val-Ala-Asp fluoromethylketone in conditions of autophagy inhibition restored PCV2 replication.Taken together,autophagy protected host cells against potential apoptosis and then contributed to PCV2 replication promotion caused by oxidative stress.Our findings can partly explain the pathogenic mechanism of PCV2 related to the oxidative stress-induced autophagy.Experiment 2:Taurine attenuates OTA-promoted PCV2 replication through blocking ROS-dependent autophagy via inhibiting AMPK/mTOR signaling pathwayPrevious research found that ochratoxin A(OTA)could promote PCV2 replication by inducing autophagy.The aim of this study is to evaluate the effect of dietary amino acid derivative taurine on OTA-promoted PCV2 replication and explore the underlying mechanism.The results showed that taurine could inhibit OTA-promoted PCV2 replication in PK-15 cells.The effect of taurine could be mediated by its ability to attenuate ROS level and block OTA-promoted autophagy.Indeed,induction of autophagy by rapamycin could suppress the inhibitory effect of taurine on OTA-promoted PCV2 replication.Furthermore,taurine supplementation inhibited 5’AMP-activated protein kinase(AMPK)and activated mammalian target of rapamycin(mTOR).Activation of AMPK by acadesine could suppress the effect of taurine.In conclusion,taurine treatment suppresses autophagy by regulating the ROS/AMPK/mTOR signaling axis,thereby inhibiting OTA-promoted PCV2 replication.These findings provide the rationale for the use of taurine as an intervention against PCV2 infection.