Bone marrow–derived endothelial progenitor cells do not contribute significantly to new vessels during incisional wound healing

Objective To assess the contribution of bone marrow (BM)-derived endothelial progenitor cells (EPCs) to the neovascularisation of cutaneous incisional wounds. Methods Lethally irradiated C57Bl/6 mice were transplanted with BM mononuclear cells from Tie2/lacZ mice, which constitutively overexpressed β-galactosidase (β-gal) in endothelial cells (ECs). Chimeras were wounded and the number of X-gal-stained (β-gal+) BM-derived EPCs were calculated in histological wound sections. Results EPCs were measured in skin sections from unwounded BM transplant (BMT) mice, or at day 1 and 3 postwounding, at the level of 0.1 ± 0.1 (mean ± SEM) per skin/wound section. In day-5 to day-14 wounds, the number of EPCs increased gradually (1.3 ± 0.5 at day 5 and 4.8 ± 0.9 at day 10), peaking at day 14, when there was a significant increase in the number of EPCs per wound section (6.5 ± 1.7) when compared to unwounded skin. Between days 14 and 18 postwounding, there was a rapid fall-off in the number of β-gal+ EPCs (0.8 ± 0.5 at day 18) and numbers returned to baseline by day 21 (0.1 ± 0.1). No evidence of vascular structures derived from BM-derived EPCs (“in situ” vasculogenesis) was observed and it was calculated that these cells contributed only 4.4% ± 1.5% to total wound ECs at their peak. Conclusion These findings indicate that the revascularization of dermal incisional wounds primarily occurs through angiogenesis because the low frequency and temporal expression of EPCs suggests that they do not make a significant contribution to the neovascularization process.