Mechanisms By Which Mumps Virus Infects The Mouse Testis And Impairs Testicular Function

Objectives of the present study:The mumps virus(MuV)is a pathogen that causes epidemic mumps.MuV also has tropism for the testis and frequently induces orchitis,which may result in male infertility.In this study,we focus on mechanisms by which mumps virus infects the mouse testis and impairs testicular function.Materials and methods:Primary testicular cells were isolated from C57BL/6J and gene knockout(Axl-/-,Mer-/-,Axl-/-Mer-/-,Ifnarl-/-,Tnfa-/-,Cxcl10-/-)mice.MuV was amplified and TCID50 was determined in Vero cells.The primary testicular cells were infected with MuV,and the mRNA levels of gene expression were analyzed using real-time qRT-PCR.The protein levels of gene products were detected by Western blot,and the cellur distribution of proteins was determined by immunofluorescence staining.The levels of cytokines and testosterone were determined by ELISA.Blood-testis barrier(BTB)permeability was assessed by TEER value in vitro and biotin tracer assay in vivo.Apoptosis of germ cells was detected by AO/EB staining and flow cytometry.Results:MuV can infect Sertoli and Leydig cells and replicate in cells.Sertoli and Leydig cells abundantly express sialic acid.The sialic acid facilitates MuV internalization into cells,but does not affect MuV binding to Sertoli and Leydig cells.Knockout of Axl(Axl-/-,Mer and both Axl and Mer(Axl-/-Mer-/-)does not affect MuV binding and internalization to Sertoli and Leydig cells.However,MuV replication is significantly reduced in Axl-/-Mer-/-Sertoli and Leydig cells.Axl-/-Mer-/-cells express higher levels of type 1 interferons and antiviral proteins than WT cells after MuV infection.MuV also infects spermatogonia and spermatocytes but does not infect spermatids,which is associated with sialic acid level in different stages of germ cells.However,MuV faintly replicates in male germ cells.MuV infection inhibits the expression of key steroidogenic enzymes(3?-HSD,P450scc)and testosterone synthesis in Leydig cells.In Sertoli cells,MuV infection inhibits the expression of tight junction proteins(Occludin,ZO-1)and disrupts the permeability of blood-testis barriers(BTB).MuV-induced TNF-? play a critical role in disrupting BTB permeability.Moreover,MuV-caused CXCL10 production in Sertoli cells induced germ cell apoptosis through the activation of caspase 3/8 signaling.Conclusions:Sialic acid facilitates MuV internalization into Sertoli,Leydig and germ cells.Axl and Mer inhibit innate antiviral response in Sertoli and Leydig cells,which facilitates MuV replication.MuV infection inhibits testosterone synthesis and impairs BTB permeability.MuV-induced CXCL10 production by Sertoli cells induces apoptosis of male germ cells.These results provide insights into mechanisms behind MuV infection in testicular cells and detrimental effects on testicular function and male fertility,which may aid in the development of preventive and therapeutic strategies for MuV-caused male infertility.