Prostaglandin E2 signaling via its receptor EP4 on macrophages protects against acute colitis by preserving intestinal barrier function

Abstract

Abstract The inflammatory bowel diseases are increasing in incidence and cause significant morbidity; however, disease pathogenesis is poorly understood. Prostaglandin E2 (PGE2) may protect against intestinal inflammation and its receptor EP4 is highly expressed on colon macrophages, cells essential for immune homeostasis, suggesting PGE2 signaling on macrophages may prevent gut inflammation. To address this, we induced DSS colitis in CX3CR1CRE/+EP4fl/fl (Cre+) mice, which lack EP4 on macrophages, and in their Cre- wildtype littermates. Cre+ mice developed worse colitis than the Cre- based on clinical scores, including increased rectal bleeding that implies major intestinal barrier disruption, a key mechanism of colitis. Cre+ mice have higher intestinal permeability early during inflammation, further supporting intestinal barrier disruption as a mechanism of increased disease severity in Cre+ mice. To address the protective mechanisms of PGE2, we performed scmRNA sequencing on colon cells of the Cre+ and Cre- mice following DSS treatment. We identified monocyte and macrophage populations, with macrophages (MPs) clustering into CD11c+ MPs expressing inflammatory cytokines, and CD169+ MPs associated with inflammation resolution and wound-healing. During colitis there was a progressive increase in the proportions of inflammatory monocytes and a loss of CD169+ MPs that was accelerated in Cre+ mice. Further, the proportion of CD11c+ MPs was increased in Cre+ mice. These data are the first detailed scmRNA analysis of immune cell populations in DSS colitis and suggest that PGE2 signaling through EP4 may protect non-inflammatory macrophage populations during inflammation, contributing to maintenance of the intestinal barrier.