De novo lipid droplet formation regulates leukotriene B4 secretion from activated alveolar macrophages 2831

Abstract Description Alveolar macrophages (AMs) are specialized lung-resident immune cells that clear inhaled bacteria and debris to maintain tissue homeostasis. AMs secrete eicosanoid lipid mediators such as prostaglandin E2 (PGE2) maintaining an anti-inflammatory environment, whereas during infection AMs release leukotriene B4 (LTB4) driving neutrophil infiltration. PGE2 and LTB4 are synthesized by cyclooxygenase 2 and 5-lipoxygenase (5LO), respectively. While lipid droplets (LDs) facilitate eicosanoid secretion by storing eicosanoid precursors such as triacylglycerol (TAG) and arachidonic acid (AA), the cellular mechanisms segregating PGE2 and LTB4 biogenesis remain unclear. We investigated these pathways in rat AMs whose eicosanoid profile closely resembles that of the human AM. In ionophore-activated AMs, we observed an early LTB4 spike, in contrast to a delayed bump in basal PGE2 levels. High-throughput microscopy revealed that in rat AMs, 5LO-activating protein (FLAP) mediates de novo LD biogenesis for LTB4 secretion, without affecting PGE2; which we validated in human PBMC-derived AM-like cells. FLAP also interacts with the LD biogenesis protein Perilipin 1 in an AA-dependent manner. We propose that activated AMs use a FLAP-dependent, AA-rich LD biogenesis pathway for LTB4 synthesis, distinct from steady-state TAG-rich LDs driving PGE2 production. This study highlights LDs’ role in AM production of functionally opposing eicosanoids, offering insights into respiratory immune disorders. Funding Sources NIAID 1R01AI152517; NHLBI 5R35HL144979 Topic Categories Mucosal and Regional Immunology (MUC)