Abstract
Background: Endothelial progenitor cells (EPCs) have been shown to have angiogenic potential contributing to neovascularization. However, the definition of EPC, including surface marker expression of EPCs promoting vasculo-/angiogenesis in ischemic tissue, remains uncertain. We hypothesized that stem/progenitor (c-kit vs. sca-1) and endothelial cell (EC) markers (CD31) may identify cells with enhanced EPC potential. Methods and Results: Mononuclear cells (MNCs) were isolated from mouse bones, and Lin+ cells were depleted by magnetic cell sorting. Lin- cells were further sorted with the following markers (% of total MNCs) by FACS: c-kit+ (1.87%), sca-1+ (0.6%), c-kit+ /CD31+ (1.1%) and sca-1+ /CD31+ (0.28%). Non-sorted MNCs were used as a control. To examine EC phenotype in culture, cells were labeled with DiI and co-cultured with mature ECs (human microvascular endothelial cells: HMVECs). The percent incorporation of DiI labeled cells into HMVEC tube structures 12 hours after co-culture and BS1-lectin positivity/acLDL uptake were: sca-1+ /CD31+ cells (87 ± 2%) > c-kit+ /CD31+ (79 ± 8%) > sca-1+ (62 ± 8%) > c-kit+ (59 ± 5%) > MNC (50 ± 3% ) . Next, we examined homing capacity of these cells to ischemic myocardium using a mouse myocardial infarction (MI) model. DiI-labeled cells (5x10 4 , IV) were injected to splenectomized mice 3 days after MI, and the hearts were excised 24 hours after the cell injection for histological analysis. Interestingly, the number of recruited/retained DiI-labeled-cells in the MI hearts exactly replicated the findings of the in vitro tube formation assay (cells/HPF): sca-1+ /CD31+ (108 ± 26) > c-kit+ /CD31+ (77 ± 16) > sca-1+ (71 ± 14) > c-kit+ (67 ± 1) > MNCs (48 ± 6) , suggesting that sca-1+ /CD31+ cells might have great functional activities as endothelial precursors. Conclusions: Both stem/progenitor marker Sca-1 and EC marker CD31 expressing EPCs exhibited high potential angiogenic capacity with EC phenotypic features compared with c-kit expressing cells. Our data suggest that Sca-1+ /CD31+ cells may represent EPC-rich cell population, and Sca-1/CD31 could be useful markers to enrich for cells with EPC potential. Ongoing studies will determine the in vivo characteristics of these cells for ischemic tissue repair.
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