Porcine reproductive and respiratory syndrome (PRRS) has caused substantial damage to the pig industry. MicroRNAs (miRNAs) were found to play crucial roles in modulating the pathogenesis of PRRS virus (PRRSV). In the present study, we revealed that PRRSV induced let-7f-5p to influence lipid metabolism to regulate PRRSV pathogenesis. A transcriptome analysis of PRRSV-infected PK15^CD163 cells transfected with let-7f-5p mimics or negative control (NC) generated 1718 differentially expressed genes, which were primarily associated with lipid metabolism processes. Furthermore, the master regulator of lipogenesis SREBP2 was found to be directly targeted by let-7f-5p using a dual-luciferase reporter system and Western blotting. The findings demonstrate that let-7f-5p modulates lipogenesis by targeting SREBP2, providing novel insights into miRNA-mediated PRRSV pathogenesis and offering a potential antiviral therapeutic target.

Lipids provide essential membrane components and energy sources for viral replication, playing multiple roles in viral infection. However, the mutual influence between lipid metabolism and PRRSV proliferation remains unclear. Using transcriptomics, lipidomics, BODIPY staining, and Western blot (WB) analysis, our findings revealed that PRRSV infection significantly altered the abundance of lipid-metabolism-associated genes and lipid metabolites in cells. qRT-PCR confirmed that PRRSV infection dose-dependently upregulated SREBP2 expression (p < 0.01), while BODIPY staining demonstrated a significant increase in intracellular lipid droplets post-infection (p < 0.01). Let-7f-5p significantly reduced lipid droplet accumulation and suppressed PRRSV N protein expression. Notably, 15 lipid species that were upregulated during PRRSV infection were downregulated by let-7f-5p overexpression. These lipids were enriched in pathways related to phosphatidylcholines, monounsaturated fatty acids, and C16-C18 fatty acid metabolism. Exogenous palmitic acid (C16:0) treatment reversed the inhibitory effects of let-7f-5p on SREBP2 expression and viral replication, demonstrating that viral proliferation can be regulated by modulating host lipid metabolism. This study reveals that PRRSV hijacks host lipid metabolism to facilitate viral replication, whereas let-7f-5p exerts antiviral effects through dual mechanisms. These findings provide new insights into host-directed antiviral strategies against PRRSV infection.