Background:
Wound healing in chronic diseases, such as type 2 diabetes (T2D), is impaired due to dysregulated inflammation. Innate immune cells, particularly macrophages, play a significant role in regulated inflammation following tissue injury. After injury, CCR2+ monocytes are recruited to the peripheral wound. This recruitment is mediated in part by the CCR2 ligand, CCL2. Thus, we hypothesized that the CCL2/CCR2 interaction is vital for normal wound healing and appropriate inflammation, and that this signaling cascade is impaired in T2D.
Methods:
CCR2
-/-
mice and littermate controls underwent 4mm hindlimb wounds, and wound closure was compared daily. Wound macrophages (CD3-CD19-NK1.1-CD11b+ cells) were analyzed on day 3 by flow cytometry for intracellular cytokine production. Adoptive transfer was performed using blood CD11b+ cells from WT C57BL/6 or CCR2
-/-
mice isolated by magnetic sorting and transferred into CCR2
-/-
mice via tail vein injection. Mice were then wounded and wound closure was compared between the two groups. C57BL/6 mice were maintained on normal or high fat diet for 12-14 weeks, wounds were created, and CD11b+ cells were isolated from wounds on day 2. ELISA for CCL2 was performed.
Results:
CCR2
-/-
mice showed significantly impaired wound healing on days 2-7 compared with littermate controls. Macrophages isolated on day 3 from wounds of CCR2
-/-
mice expressed significantly less inflammatory cytokines (IL-1β, TNF-α) by qPCR. Flow cytometry analysis revealed less Ly6C hi macrophages in the wounds, as well as macrophages that made significantly less IL-1β, NOS2, and TNF-α. When adoptive transfer was performed, wound healing was restored to normal in the mice that received WT compared to those that received CCR2
-/-
CD11b+ cells (P< 0.01). Since CCR2 is important for normal wound inflammation, and we have previously shown that inflammation is impaired in the diet-induced obese (DIO) mice, we examined CCL2 in DIO wounds. CCL2 was significantly decreased in DIO wound macrophages on day 2.
Conclusion:
Appropriate CCR2/CCL2 interaction plays a crucial role in macrophage recruitment and regulated inflammation in normal wound healing. Impairment in CCR2/CCL2 signaling may be responsible, in part, for delayed early inflammation in T2D.
Murine macrophage chemokine receptor CCR2 plays a crucial role in macrophage recruitment and regulated inflammation in wound healing
