Murine epidermal side population possesses unique angiogenic properties

Total epidermal keratinocytes are a heterogeneous population of cells, including undifferentiated stem/progenitor cells (EpSPs) and their more differentiated progeny (Non-SP cells). Our previous in vivo data showed that EpSPs enhanced blood flow restoration when injected into an ischemic limb, whereas Non-SP cells had no significant effect on in vivo blood flow restoration. However, the cellular and molecular mechanisms of this observation remain largely unknown. Therefore, the aim of this study was to investigate the angiogenic properties of different epidermal subpopulations in vitro and the mechanism by which EpSPs enhanced blood flow in vivo. Using migration assay and capillary network formation, we show that EpSPs secrete higher levels of pro-angiogenic molecules compared to Non-SP cells, unsorted keratinocytes and fibroblasts in vitro. Secretion of vascular endothelial growth factor (VEGF) was detected at higher levels in EpSP conditioned medium than the medium conditioned by other epidermal subpopulations and fibroblasts. Also, RT-PCR analyses revealed a unique angiogenic gene profile for EpSPs. Finally, gene array data indicate significant changes in angiogenic gene expression six days after cell injection in murine ischemic limbs. Therefore, we conclude that EpSPs possess unique angiogenic properties and that these cells may be indirectly responsible for the angiogenic response previously observed in our ischemic limb model.