Aims: Circulating endothelial precursor cells (CEPs) are thought to play a role in angiogenesis. We investigated the angiogenic stress of musculoskeletal trauma on CEP kinetics in trauma patients and their bone marrow progenitor populations in a murine model. Methods: Peripheral blood mononuclear cells (PB-MNCs) were isolated from patients (n=12) on consecutive days following closed lower-limb diaphyseal fractures. CEP levels, deþned by the surface expression patterns of VEGFR2, CD34 and AC133 were determined and cytokine analysis of collected serum was performed. Bonemarrow precursors deþned byLy-6A/E and c-Kit expression were harvested following the traumatic insult from the murine model and quantiþed on ßow cytometry. Human and murine progenitor populations were cultured on þbronectin and examined for markers of endothelial cell lineage (Ulexeuropaeus- agglutinin-1 binding and acetylated-LDL uptake) and cell morphology. Statistical analysis was performed using variance analysis. Results: A consistent increase in human CEPs levels was noted within 72 hours of the initial insult, the percentage increase over day 1 reaching 300% (p=0.008) and returning to normal levels by day 10. Murine bone marrow precursors were mobilisd within 24 hrs peaking at 48hrs (900% p=0.035). On culture, morphologically characteristic endotheliallike cells binding UEA-1 and incorporating LDL were identiþed. Serum VEGF levels increased signiþcantly within 24 hrs of the insult, (p=0.018) preceeding the peak in CEP mobilisation. Conclusion: We propose that musculoskeletal trauma through the release of chemokines such as VEGF, promotes rapid mobilisation of CEPs from born marrow, which have the potential to contribute to reparative neovascularisation. Strategies to enhance CEPs kinetics may accelerate this process and offer a therapeutic role in aberrant fracture healing.

Background: Circulating endothelial precursor cells (CEPS) are thought to play a role in postnatal angiogenesis. We investigated the angiogenic stress of musculoskeletal trauma on CEP kinetics in trauma patients and their bone marrow progenitor populations in a murine model.

Methods: Peripheral blood mononuclear cells (PB-MNCs) were isolated from patients (n=12) on consecutive days following closed lower-limb diaphyseal fractures. CEP levels, defined by the surface expression patterns of VEGFR2, CD34 and AC133 were determined and cytokine analysis of collected serum was performed. Bone marrow precursors defined by Ly-6A/E and c-Kit expression were harvested following traumatic insult from the murine model and quantified on flow cytometry. Human and murine progenitor populations were cultured on fibronectin and examined for markers of endothelial cell linage (Ulexeuropaeus- agglutinin- 1 binding and acetylated-LDL uptake) and cell morphology. Statistical analysis was performed using variance analysis.

Results: A consistent increase in human CEPs levels was noted within 72 hours of the initial insult, the percentage increase over day 1 reaching 300%.

Conclusion: We propose that musculoskeletal trauma through the release of chemokines such as VEGF, promotes rapid mobilisation of CEP from born marrow, which have the potential to contribute to reparative neovascularisation. Strategies to enhance CEPs kinetics may accelerate this process and offer a therapeutic role in aberrant fracture healing.