PRRSV Nsp4 induces ATGL protein degradation to promote viral replication and lipid droplet accumulation

Porcine reproductive and respiratory syndrome (PRRS) is a prevalent disease caused by porcine reproductive and respiratory syndrome virus (PRRSV). Various viruses regulate lipid metabolism to promote their replication. In this study, we investigated the regulation of the host lipid metabolism by PRRSV. We observed that PRRSV infection induced an increase in intracellular triglyceride (TG) and the accumulation of lipid droplets (LDs). Notably, inhibiting TG synthesis with specific drugs suppressed both PRRSV replication and LD accumulation, whereas supplementation with oleic acid (OA), which increases lipid content, promoted PRRSV replication. Moreover, Western blotting assay revealed a marked reduction in adipose triglyceride lipase (ATGL) expression upon PRRSV infection. The overexpression of ATGL inhibited the increase in intracellular TG and LD accumulation while also suppressing PRRSV replication. In contrast, the knockdown of ATGL induced an increase in intracellular TG, promoting PRRSV replication and enhancing LD accumulation. Western blotting assay indicated that PRRSV infection downregulates the expression of endogenous ATGL. Immunofluorescence and co-immunoprecipitation experiments confirmed that Nsp4 bound to the patatin-like domain of ATGL and inducing its protein degradation. Finally, we demonstrated that Nsp4 induced an increase in intracellular TG and promoted OA-induced LD accumulation, whereas its co-expression with ATGL reduced intracellular TG. In conclusion, we propose that PRRSV Nsp4 induced an increase in intracellular TG by degrading ATGL, thereby promoting PRRSV replication and LD accumulation. These findings provided new insights into the infection mechanism of PRRSV.