Ly6CHi Blood Monocyte/Macrophage Drive Chronic Inflammation and Impair Wound Healing in Diabetes Mellitus

Objective Wound monocyte-derived macrophage plasticity controls the initiation and resolution of inflammation that is critical for proper healing, however, in diabetes mellitus, the resolution of inflammation fails to occur. In diabetic wounds, the kinetics of blood monocyte recruitment and the mechanisms that control in vivo monocyte/macrophage differentiation remain unknown. Approach and Results Here, we characterized the kinetics and function of Ly6C(Hi) [Lin(-) (CD3(-)CD19(-)NK1.1(-)Ter-119(-)) Ly6G(-)CD11b(+)] and Ly6C(Lo) [Lin(-) (CD3(-)CD19(-)NK1.1(-)Ter-119(-)) Ly6G(-)CD11b(+)] monocyte/macrophage subsets in normal and diabetic wounds. Using flow-sorted tdTomato-labeled Ly6C(Hi) monocyte/macrophages, we show Ly6C(Hi) cells transition to a Ly6C(Lo) phenotype in normal wounds, whereas in diabetic wounds, there is a late, second influx of Ly6C(Hi) cells that fail transition to Ly6C(Lo). The second wave of Ly6C(Hi) cells in diabetic wounds corresponded to a spike in MCP-1 (monocyte chemoattractant protein-1) and selective administration of anti-MCP-1 reversed the second Ly6C(Hi) influx and improved wound healing. To examine the in vivo phenotype of wound monocyte/macrophages, RNA-seq-based transcriptome profiling was performed on flow-sorted Ly6C(Hi) [Lin(-)Ly6G(-)CD11b(+)] and Ly6C(Lo) [Lin(-)Ly6G(-)CD11b(+)] cells from normal and diabetic wounds. Gene transcriptome profiling of diabetic wound Ly6C(Hi) cells demonstrated differences in proinflammatory and profibrotic genes compared with controls. Conclusions Collectively, these data identify kinetic and functional differences in diabetic wound monocyte/macrophages and demonstrate that selective targeting of CD11b(+)Ly6C(Hi) monocyte/macrophages is a viable therapeutic strategy for inflammation in diabetic wounds.