Porcine Parvovirus Induces Autophagy In ST Cells And Benefits Its Replication

Porcine parvovirus infection?PPI?is a viral infectious disease caused by porcine parvovirus?PPV?.The main clinical manifestations of the disease are embryonic and fetal infections,such as malformed fetuses,mummified fetuses and even stillbirths.PPV is one of the major causes of sow reproductive disorders,posing a huge threat to the pig industry and causing huge economic losses worldwide.Autophagy is a physiological process of cell self-defense and self-protection.Although many viruses can cause autophagy when they enter and replicate in host cells,the relationship between autophagy and PPV infection has not been reported.Therefore,this study will investigate the effect of PPV infection on the autophagy in swine testicular cells?ST?,and whether the autophagy can promote the replication of PPV.In this paper,Western blot,indirect immunofluorescence and fluorescent quantitative PCR were used to investigate the appearance of autophagy and the interaction mechanism between autophagy and virus replication in PPV-infected ST cells.The results were as follows:Western blot showed that,the conversion of LC3-I to LC3-II increased with the time gone,and the level of p62decreased significantly in the rapamycin-treated and the PPV-infected group compared with that of the control group.Indirect immunofluorescence assay showed that a large number of positive fluorescent spots of GFP-LC3 protein appeared in PPV-infected ST cells,similar to that of the rapamycin-treated group,while the GFP-LC3-positive fluorescence was diffusely distributed in the control group.Transmission electron microscopy revealed the presence of autophagosome-like vesicles in PPV-infected and rapamycin-treated ST cells.The above results indicated that PPV could induce autophagy in ST cells.In the experiment to explore whether autophagy could promote viral replication in ST cells,western blot analysis showed that rapamycin can significantly increase the expression of PPV VP2,and when added autophagy inhibitor wortmannin,VP2 expression was markedly reduced.In the PPV TCID₅₀ assay,the virus titer of the rapamycin-treated group was higher than that of the PPV-infected group.Conversely,the titer of PPV decreased after treatment with wortmannin.The nearly same results were obtained in real-time fluorescence quantitative PCR detection of virus copy number experiments.Furthermore,increase of rapamycin concentration postinoculation of PPV,virus copy number gradually increased.It demonstrated that PPV-induced autophagy in ST cells could be beneficial for virus replication.In conclusions,this study confirms that PPV can induce autophagy in ST cells,and that the occurrence of autophagy reversely promotes the virus replication,which may be one of the mechanisms by which the virus infects host cells.This will help to further elucidate the pathogenesis of PPV infection,and provide theoretical and practical basis for effective prevention and treatment of the disease.