A dual role for CRTH2 in acute lung injury

Abstract

ABSTRACTAcute respiratory distress syndrome (ARDS) is a life-threatening clinical condition defined by rapid onset respiratory failure following acute lung injury (ALI). Its increased incidence due to COVID-19 and high mortality rate (∼40%) make the study of ARDS pathogenesis a crucial research priority. CRTH2 is a G protein-coupled receptor with established roles in type 2 immunity and well-characterized inhibitors. Prior studies have shown it also promotes neutrophilic inflammation, indicating that CRTH2 inhibition may be a potential therapeutic strategy for ARDS. To test this hypothesis, we first examined the expression pattern of CRTH2 on murine neutrophils. We found it is expressed on neutrophils, but only after extravasation into the lung. Next, we showed that extravasated lung neutrophils generate inflammatory responses upon stimulation with the CRTH2-specific agonist DK-PGD2, as demonstrated by reactive oxygen species (ROS) production. This response was abrogated in CRTH2 KO neutrophils. Inhibition of CRTH2 with fevipiprant suppressed baseline ROS production, indicating an autocrine PGD2-CRTH2 signaling loop. We then evaluated the role of CRTH2 in vivo using a murine model of LPS-induced ALI. Despite the pro-inflammatory effects of CRTH2 on neutrophils in vitro, we observed worsening of lung injury in CRTH2-deficient mice in terms of neutrophilic inflammation, vascular leak, and survival. Bulk RNAseq of lung tissue indicated an impairment in type 2 immune signaling; qPCR and ELISA confirmed downregulation of the key type 2 effector cytokine, IL-4. Thus, CRTH2 appears to play a dual role in ALI, directly promoting neutrophil effector responses, but indirectly suppressing lung injury and neutrophilic inflammation through type 2 immunity. These findings reveal a novel protective function for CRTH2 during lung injury and argue against the use of CRTH2 inhibitors in ARDS.