The bone marrow-derived endothelial progenitor cell response is impaired in delayed wound healing from ischemia.

OBJECTIVE: Vasculogenesis relies on the recruitment of bone marrow-derived endothelial progenitor cells (BMD EPCs) and is stimulated by tissue-level ischemia. We hypothesized that the BMD EPC response is impaired in ischemic wounds and studied the relationship between BMD EPCs and wound healing.
METHODS: We used transgenic Tie-2/LacZ mice, which carry the beta-galactosidase (beta-gal) reporter gene under Tie-2 promoter control. Wild-type mice were lethally irradiated and reconstituted with Tie-2/LacZ bone marrow. Four weeks later, the mice underwent unilateral femoral artery ligation/excision and bilateral wounding of the hindlimbs. Ischemia was confirmed and monitored with laser Doppler imaging. A subset of mice received incisional vs excisional nonischemic bilateral hindlimb wounds, without femoral ligation. Excisional wound closure was measured by using daily digital imaging and software-assisted calculation of surface area.
RESULTS: Ischemia resulted in significantly delayed wound healing and differentially affected the number of BMD EPCs recruited to wound granulation tissue and muscle underlying the wounds. At 3 days postwounding, the granulation tissue of the wound base contained significantly fewer numbers of BMD EPCs in ischemic wounds compared with the nonischemic wounds (P < .05). In contrast, significantly more BMD EPCs were present in the muscle underlying the ischemic wounds at this same time point compared with the muscle under the nonischemic wounds (P < .05). In ischemic wounds, eventual wound closure significantly correlated with a delayed rise in BMD EPCs within the wound granulation tissue (Kendall's correlation, -.811, P = .0005) and was significantly associated with a gradual recovery of hindlimb perfusion (P < .0001). By 7 days postwounding, BMD EPCs were incorporated into the neovessels in the granulation tissue. At 14 days and 75 days, BMD EPCs were rarely observed within the wounds.
CONCLUSIONS: Granulation tissue of excisional ischemic wounds showed significantly less BMD EPCs 3 days postwounding, in association with significantly delayed wound closure. However, the number of BMD EPCs were increased in ischemic hindlimb skeletal muscle, consistent with the notion that ischemia is a powerful signal for vasculogenesis. To our knowledge, this is the first report identifying a deficit in BMD EPCs in the granulation tissue of ischemic skin wounds and reporting the key role for these cells in both ischemic and nonischemic wound healing.