ATG5 negatively regulates grass carp reovirus-induced immune-inflammatory response by degrading RIG-I and MDA5.

Grass carp reovirus (GCRV) is the most virulent aquareovirus, inducing hemorrhagic disease that results in significant economic losses for the grass carp aquaculture industry in China. It has been reported that the cytokine storm, resulting from the viral-induced acute immune-inflammatory response, is the primary cause of death associated with viral infections. Therefore, exploring the negative regulatory factors of the immune response may provide important targets for virus prevention and control. In this study, we demonstrated that GCRV infection induces an acute immune-inflammatory response in yearling grass carp, while a milder immune response is observed in 3-year-old grass carp by assessing key gene expression at both the mRNA and protein levels. Furthermore, we found that the upregulation of autophagy core gene, autophagy-related gene 5 (ATG5), inhibits GCRV replication and reduces the excessive immune-inflammatory response induced by the virus. Notably, co-immunoprecipitation and bimolecular fluorescence complementation reveal that ATG5 interacts with RIG-I and MDA5, inhibiting the downstream immune response. Mechanistically, ATG5 promotes autophagy and K48-linked polyubiquitination to degrade RIG-I and MDA5. Importantly, ATG5 reduces IRF7 phosphorylation through the degradation of RIG-I and MDA5, which, in turn, leads to a decreased immune response during GCRV infection. Collectively, our findings suggest that ATG5 serves as an important negative regulatory factor of the viral-induced acute immune-inflammatory response, providing a promising target for the prevention and control of GCRV. IMPORTANCE: Grass carp reovirus (GCRV) is a highly virulent pathogen responsible for hemorrhagic disease in grass carp, leading to devastating losses in aquaculture. The study reveals that GCRV triggers an acute immune-inflammatory response in young grass carp, which is linked to high mortality, while a milder immune response occurs in older, resistant fish. Importantly, the autophagy-related gene ATG5 was identified as a critical regulator that suppresses excessive immune-inflammatory responses by promoting the degradation of RIG-I and MDA5, two key viral sensors. ATG5 not only reduces viral replication but also limits IRF7 phosphorylation, a key step in interferon signaling. This research uncovers a novel mechanism by which autophagy moderates viral-induced immune response, suggesting that ATG5 could be a valuable target for therapeutic interventions aimed at controlling GCRV infection and preventing cytokine storms in aquaculture. These findings could have broader implications for managing viral infections in fish farming.