Exosomal PGE2 from M2 macrophage inhibits neutrophil recruitment and NET formation through lipid mediator class switching in sepsis

Abstract Excess polymorphonuclear neutrophil (PMN) recruitment or overzealous neutrophil extracellular trap (NET) formation could lead to the development of multiple organ dysfunction during sepsis. M2 macrophage-derived exosomes (M2-Exo) have exhibited anti-inflammatory activities in some inflammatory diseases to mediate organ functional protection. However, whether M2-Exo could modulate PMN abnormal behaviors to prevent potentially deleterious inflammatory effects during sepsis is poorly understood. Here, we report that M2-Exo inhibited PMN migration and NET formation, alleviated lung injury and reduced the mortality without significantly affecting bacterial load in the lungs in cecal ligation and puncture (CLP)-induced sepsis model. In vitro co-culture experiments using PMNs isolated from both healthy volunteers and septic patients further demonstrated that M2-Exo significantly decreased PMN migration and NET formation capacity, leading to lipid mediator class switching from proinflammatory leukotriene B4 (LTB4) to anti-inflammatory lipoxin A4 (LXA4) through upregulating 15-lipoxygenase (15-LO) expression in PMNs. Treatment with LXA4 receptor inhibitor attenuated the function of M2-Exo on PMNs and lung injury. Mechanistically, LXA4 increased by M2-Exo inhibited PMN function through downregulating chemokine (C-X-C motif) receptor 2 (CXCR2) and reactive oxygen species (ROS) expressions in PMNs. In addition, prostaglandin E2 (PGE2) was highly expressed in M2-Exo. By deleting PGE2 in M2-Exo, we found that exosomal PGE2 from M2 macrophage was necessary for 15-LO upregulation and PMN inhibition through functioning on EP4 receptor. Our findings reveal a previously unknown role of M2-Exo in regulating PMN migration and NET formation, thus highlighting the potential application of M2-Exo in controlling PMN-mediated tissue injury in patients with sepsis.