Early inflammatory phase macrophages predominately derive from infiltrating monocytes and demonstrate increased production of inflammatory cytokines (IL-1β, IL-12, and TNF-α) with enhanced pathogen killing capacity ( 2), while late inflammatory phase macrophages produce IL-10 and other mediators important in the transition to the proliferative phase of wound healing ( 3, 4). The inflammatory phase of healing can be divided into an “early” phase demonstrated by proinflammatory macrophages that promote inflammation and tissue destruction and a “late” phase where antiinflammatory macrophages promote tissue repair and allow for transition to the proliferative phase of healing. During the inflammatory phase, macrophage plasticity is essential for wound remodeling. Wound repair is a complex process that occurs in overlapping stages of coagulation, inflammation, proliferation, and remodeling ( 1). Our results indicate the epigenetically regulated PGE 2 pathway controls wound macrophage function, and cell-targeted manipulation of this pathway is feasible to improve diabetic wound repair.
Inhibition of the COX-2/PGE 2 pathway genetically ( Cox2 fl/fl Lyz2 Cre+) or with a macrophage-specific nanotherapy targeting COX-2 in tissue macrophages reverses the inflammatory macrophage phenotype and improves diabetic tissue repair. Further, we find mixed-lineage leukemia 1 (MLL1) upregulates cPLA 2 expression and drives COX-2/PGE 2. We demonstrate that TGF-β–induced miRNA29b increases COX-2/PGE 2 production via inhibition of DNA methyltransferase 3b–mediated hypermethylation of the Cox-2 promoter. Further, we identify that COX-2/PGE 2 production in wound macrophages requires epigenetic regulation of 2 key enzymes in the cytosolic phospholipase A 2/COX-2/PGE 2 (cPLA 2/COX-2/PGE 2) pathway. Using single-cell RNA sequencing of human wound tissue, we identify increased NF-κB–mediated inflammation in diabetic wounds and show increased COX-2/PGE 2 in diabetic macrophages. Here, we find in human and murine wound macrophages that cyclooxygenase 2/prostaglandin E 2 (COX-2/PGE 2) is elevated in diabetes and regulates downstream macrophage-mediated inflammation and host defense. Evidence suggests that epigenetic alterations play a critical role in establishing macrophage phenotype and function during normal and pathologic wound repair. Macrophages are a primary immune cell involved in inflammation, and their cell plasticity allows for transition from an inflammatory to a reparative phenotype and is critical for normal tissue repair following injury.