Plasma elevation of vascular endothelial growth factor leads to the reduction of mouse hematopoietic and mesenchymal stem/progenitor cells in the bone marrow.

Vascular endothelial growth factor (VEGF) is reported to exhibit potent hematopoietic stem/progenitor cell (HSPC) mobilization activity. However, the detailed mechanisms of HSPC mobilization by VEGF have not been examined. In this study, we investigated the effect of VEGF on bone marrow (BM) cell and the BM environment by intravenous injection of VEGF-expressing adenovirus vector (Ad-VEGF) into mice. A colony assay using peripheral blood cells revealed that plasma elevation of VEGF leads to the mobilization of HSPCs into the circulation. Granulocyte colony-stimulating factor (G-CSF) is known to mobilize HSPCs by decreasing CXC chemokine ligand 12 (CXCL12) levels in the BM. However, we found almost no changes in the CXCL12 levels in the BM after Ad-VEGF injection, suggesting that VEGF can alter the BM microenvironment by different mechanisms from G-CSF. Furthermore, flow cytometric analysis and colony forming unit-fibroblast assay showed a reduction in the number of mesenchymal progenitor cells (MPCs), which have been reported to serve as niche cells to support HSPCs, in the BM of Ad-VEGF-injected mice. Adhesion of donor cells to the recipient BM after transplantation was also impaired in mice injected with Ad-VEGF, suggesting a decrease in the niche cell number. We also observed a dose-dependent chemoattractive effect of VEGF on primary BM stromal cells in vitro. These data suggest that VEGF alters the distribution of MPCs in the BM and can also mobilize MPCs to peripheral tissues. Taken together, our results imply that VEGF-elicited egress of HSPCs would be mediated, in part, by changing the number of MPCs in the BM.