Let-7f-5p Inhibits PRRSV Replication by Regulating Lipid Metabolic Reprogramming in Infected Cells

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.