Extracellular vesicle-bound S100A8/A9 is differentially expressed in septic shock and prompts acute lung injury.

Background: Sepsis is a common indirect insult leading to acute respiratory distress syndrome (ARDS). Circulating extracellular vesicles (EVs) have been reported to participate in the pathogenesis of sepsis. However, the alteration of EV-bound S100A8/A9 during septic shock, along with the role of S100A8/A9 in driving acute lung injury, remains unexplored.

Methods: EVs were isolated from the plasma of patients upon admission with sepsis or septic shock, as well as from healthy controls. Levels of EV S100A8/A9 were assayed via ELISA. To examine the effects and underlying mechanisms of septic shock EVs in acute lung injury, these EVs were administered intratracheally into wild-type C57BL/6 mice or mice with a deficiency of advanced glycation end-products (RAGE). In addition, a mouse model of polymicrobial sepsis was introduced using cecal ligation and puncture (CLP).

Results: Levels of EV S100A8/A9 were significantly elevated in patients with sepsis or septic shock compared to healthy controls. Receiver operating characteristic (ROC) analysis demonstrated that EV S100A8/A9 effectively distinguished between septic shock and sepsis and had predictive potential for the development of ARDS. Notably, the levels of S100A8/A9 in EVs and alveolar macrophages from CLP mice were significantly higher than those in sham mice. Intratracheal administration of septic shock EVs directly induced acute lung injury and M1 macrophage polarization in a lipopolysaccharide-independent manner. Septic shock EVs were efficiently taken up by alveolar macrophages in vivo, leading to a significant increase in S100A8/A9 levels, which was inhibited by preincubating the EVs with an S100A8/A9 neutralizing antibody. Additionally, mice with deficiency in RAGE, a receptor for S100A8/A9, were partially protected from acute lung injury induced by septic shock EVs. In vitro, septic shock EVs prompted a proinflammatory response in bone marrow-derived macrophages. This response was blocked by preincubating the EVs with the S100A8/A9 neutralizing antibody.

Conclusions: Our results suggested that EV S100A8/A9 has potential value in distinguishing septic shock from sepsis and predicting the development of ARDS. Septic shock EVs-induced lung injury is at least partially mediated through S100A8/A9-RAGE pathway, involving the activation of alveolar macrophages.