The spleen recruits endothelial progenitor cell via SDF-1/CXCR4 axis in mice

Endothelial progenitor cell (EPC) therapy represents a novel strategy for a variety of diseases. Interestingly, spleen acts an important reservoir during EPC trafficking. Therefore, we investigated the involvement of stromal cell-derived factor-1 (SDF-1)/CXCR4 in EPC settlement in the spleen. EPC were cultured and characterized as previous methods. Then, 1 x 10(6) EPC were labeled with DiI-LDL and intravenously infused into C57/BL6 mice. Immunohistochemical staining showed homing of transplanted EPC in the spleen 24 h later, indicating recruitment of transplanted EPC into the spleen. The distribution of EPC in different organs was evaluated by fluorescence-activated cell sorting of Sca-1/Flk-1(+) cells, which demonstrated settlement of EPC in the spleen. Removal of the splenic niche by splenectomy augmented circulating EPC 12 and 24 h later, indicating an important role of spleen on modulation of EPC-circulating dynamics. Expressions of SDF-1 in the spleen and CXCR4 in EPC were revealed by enzyme-linked immunosorbent assay (ELISA) and reverse transcription polymerase chain reaction (RT-PCR). A modified Boyden chamber assay showed that SDF-1 (10 or 100 ng/mL) induced EPC migration in vitro. Injection of the SDF-1 protein into the spleen increased the number of splenic EPC. In contrast, injection of a SDF-1 antibody or AMD3100 (SDF-1/CXCR4 axis antagonist) attenuated their settlement and did not induce EPC apoptosis. These results indicate that the SDF-1/CXCR4 axis is involved in recruitment of EPC to the spleen, and enhances our understanding of EPC-circulating kinetics.