Pestivirus bovine viral diarrhea virus infection triggers lipophagy through the AMPK-PNPLA2/ATGL signaling pathway to promote viral replication

Macroautophagy/autophagy facilitates the catabolic process by degrading lipids within lysosomes, thereby maintaining cellular energy homeostasis. However, the precise mechanism by which bovine viral diarrhea virus (BVDV) induces autophagy to reprogram lipid metabolism remains unclear. In this study, we determined that BVDV infection depletes ATP and simultaneously induces the reprogramming of intracellular lipid metabolism. We also observed that BVDV infection promotes autophagy-dependent processing of lipid droplets and triglycerides, leading to the release of free fatty acids. The ATP content in BVDV-infected cells was reduced, resulting in an increased AMP:ATP ratio and subsequent phosphorylation of AMP-activated protein kinase (AMPK). Mechanistically, BVDV infection activates AMPK, subsequently enhancing lipophagy and facilitating viral replication. Our study further elucidates that PNPLA2/ATGL (patatin like domain 2, triacylglycerol lipase) may function as a downstream effector in the AMPK pathway, promoting lipophagy during BVDV infection. The BVDV nonstructural protein NS5A was found to induce autophagy via an AMPK-PNPLA2 pathway. Immunoprecipitation assays demonstrated that NS5A interacts with BECN1 and PNPLA2. These findings suggest that BVDV infection modulates lipophagy by regulating the AMPK-PNPLA2 pathway, thereby mobilizing energy for its replication. Overall, our data suggest that targeting the AMPK-PNPLA2 pathway could serve as a novel host-directed antiviral strategy, offering significant insights for the development of innovative BVDV vaccines and therapeutic drugs.