Single-cell mRNA analysis of colon tissue during DSS colitis in CX3CR1cre/+EP4fl/fl mice suggests PGE2 signaling via EP4 promotes survival of protective macrophages

Abstract

Abstract Prostaglandin E2 signaling through its receptor EP4 on macrophages (MPs) protects against DSS-induced colitis, however the mechanisms involved are not clear. Here we perform single cell RNA sequencing on the colons of CX3CR1cre/+EP4fl/fl(Cre+) mice and CX3CR1+/+EP4fl/fl(Cre−) littermate controls at days 0, 3 and 7 following DSS treatment. We identified monocyte (MO), MP, DC1, DC2 and pre-DC populations, with MPs clustering into Hes1hi, Mrc1hi Siglec1(CD169)hi, Retnlahi, and Il1r2hiCd80hi populations. With colitis there was a dramatic increase in the proportions of inflammatory MOs and a loss of all mature MPs, along with an increase in cDC2 but not cDC1 in both mouse strains. However, in Cre+ mice, which develop worse disease with universal GI bleeding, the loss of Mrc1hi Siglec1hi MPs was accelerated together with an increased proportion of Il1r2hiCd80hi MPs compared to Cre− littermates. Analysis of DEGs showed the Il1r2hiCd80hi MP cluster expresses high levels of leukocyte chemoattractants, suggesting that PGE2 may prevent leukocyte recruitment during inflammation. Cre+ mice also had fewer Retnlahi macrophages than Cre− mice both at days 0 and 7 post DSS. Genes highly expressed in the Retnlahi cluster are associated with wound healing and maintenance of vascular integrity indicating their loss could account for the enhanced GI bleeding in the inflamed Cre+ mice. This is the first detailed scmRNA analysis of immune cell populations involved in DSS colitis. While additional investigation is necessary, the data suggest a role for PGE2 signaling via EP4 on MPs in preventing excessive inflammatory cell infiltration, decreasing vascular permeability, and contributing to tissue repair by maintaining protective MP populations.