Pseudorabies virus gM and its homologous proteins in herpesviruses induce mitochondria-related apoptosis involved in viral pathogenicity

Apoptosis is a critical host antiviral defense mechanism. But many viruses have evolved multiple strategies to manipulate apoptosis and escape host antiviral immune responses. Herpesvirus infection regulated apoptosis; however, the underlying molecular mechanisms have not yet been fully elucidated. Hence, the present study aimed to study the relationship between herpesvirus infection and apoptosis in vitro and in vivo using the pseudorabies virus (PRV) as the model virus. We found that mitochondria-dependent apoptosis was induced by PRV gM, a late protein encoded by PRV UL10, a virulence-related gene involved in enhancing PRV pathogenicity. Mechanistically, gM competitively combines with BCL-XL to disrupt the BCL-XL-BAK complex, resulting in BCL-2-antagonistic killer (BAK) oligomerization and BCL-2-associated X (BAX) activation, which destroys the mitochondrial membrane potential and activates caspase-3/7 to trigger apoptosis. Interestingly, similar apoptotic mechanisms were observed in other herpesviruses (Herpes Simplex Virus-1 [HSV-1], human cytomegalovirus [HCMV], Equine herpesvirus-1 [EHV-1], and varicella-zoster virus [VZV]) driven by PRV gM homologs. Compared with their parental viruses, the pathogenicity of PRV-Delta UL10 or HSV-1-Delta UL10 in mice was reduced with lower apoptosis and viral replication, illustrating that UL10 is a key virulence-related gene in PRV and HSV-1. Consistently, caspase-3 deletion also diminished the replication and pathogenicity of PRV and HSV-1 in vitro and in mice, suggesting that caspase-3-mediated apoptosis is closely related to the replication and pathogenicity of PRV and HSV-1. Overall, our findings firstly reveal the mechanism by which PRV gM and its homologs in several herpesviruses regulate apoptosis to enhance the viral replication and pathogenicity, and the relationship between gM-mediated apoptosis and herpesvirus pathogenicity suggests a promising approach for developing attenuated live vaccines and therapy for herpesvirus-related diseases. Apoptosis plays a crucial role in eliminating virus-infected cells and maintaining tissue homeostasis. Herpesviruses have evolved numerous strategies for manipulating apoptosis. However, the molecular mechanisms by which herpesvirus infection induces apoptosis are not fully unclear. In this study, PRV was used as a model virus to elucidate the relationship between herpesvirus infection and apoptosis. We reported that PRV gM induced mitochondria-dependent apoptosis by competitively binding to the anti-apoptosis protein BCL-XL and activating the apoptosis effectors caspase-3/7/9 to enhance the viral replication and pathogenicity in vitro and in mice. Importantly, we found that the PRV gM homologs of herpesviruses (HSV-1, HCMV, EHV-1, and VZV) shared the same mechanism to promote apoptosis. Additionally, the reduced pathogenicity of PRV and HSV-1 in caspase-3+/- mice suggested that caspase-3-mediated apoptosis driven by gM protein was a key regulator to the replication and pathogenicity of PRV and HSV-1. Our study firstly reveals the molecular mechanism by which PRV gM and its homologs in several herpesviruses regulate apoptosis to enhance the viral replication and pathogenicity. These findings provide novel insights for developing new vaccine candidates and antiviral drugs. Based on these findings, inhibiting apoptosis is a promising therapeutic strategy for treating herpesvirus-related diseases.