Accumulation of Lipid Droplets Induced by Listeria monocytogenes in Macrophages: Implications for Survival and Evasion of Innate Immunity.

Listeriosis, caused by Listeria monocytogenes (L.m.), poses a significant public health concern as one of the most severe foodborne diseases. The pathogenesis of L.m. involves critical steps such as phagosome rupture and escape upon internalization. Throughout infection, L.m. influences various host processes, including lipid metabolism pathways, yet the role of lipid droplets (LDs) remains unclear. Here, we reported a rapid, time-dependent increase in LD formation in macrophages induced by L.m. LD biogenesis was found to be dependent on L.m. viability and virulence genes, particularly on the activity of the pore-forming protein listeriolysin O (LLO). The prevention of LD formation by inhibiting diacylglycerol O-acyltransferase 1 (DGAT1) and cytosolic phospholipase A2 (cPLA2) significantly reduced intracellular bacterial survival, impaired prostaglandin E2 (PGE2) synthesis, and decreased IL-10 production. Additionally, inhibiting LD formation led to increased levels of TNF-α and IFN-ß. Collectively, our data suggest a role for LDs in promoting L.m. cell survival and evasion within macrophages.

Lipid droplet accumulation occurs early following Salmonella infection and contributes to intracellular bacterial survival and replication.

Salmonellosis is a public health problem caused by Salmonella sp., a highly adapted facultative intracellular pathogen. After internalization, Salmonella sp. Manipulates several host processes, mainly through the activation of the type III secretion system (T3SS), including modification of host lipid metabolism and lipid droplet (LD) accumulation. LDs are dynamic and complex lipid-rich organelles involved in several cellular processes. The present study investigated the mechanism involved in LD biogenesis in Salmonella-infected macrophages and its role in bacterial pathogenicity. Here, we reported that S. Typhimurium induced a rapid time-dependent increase of LD formation in macrophages. The LD biogenesis was demonstrated to depend on Salmonella's viability and SPI1-related T3SS activity, with the participation of Toll-Like Receptor (TLR) signaling. We also observed that LD accumulation occurs through TLR2-dependent signaling and is counter-regulated by TLR4. Last, the pharmacologic modulation of LD formation by inhibiting diacylglycerol O-acyltransferase 1 (DGAT1) and cytosolic phospholipase A2 (cPLA2) significantly reduced the intracellular bacterial proliferation and impaired the prostaglandin E2 (PGE2 ) synthesis. Collectively, our data suggest the role of LDs on S. typhimurium intracellular survival and replication in macrophages. This data set provides new perspectives for future investigations about LDs in host-pathogen interaction.