SDF-1 secreted by mesenchymal stem cells promotes the migration of endothelial progenitor cells via PI3K/Akt pathway

Abstract Background: Cell-based therapeutics bring great hope in areas of unmet medical needs. Mesenchymal stem cells (MSCs) has been suggested to facilitate neovascularization mainly by paracrine action, and endothelial progenitor cells (EPCs) can differentiate into mature endothelial cells. Studies have demonstrated that a combination cell therapy that includes MSCs and EPCs has a favorable effect on ischemic limbs. However, the mechanism of combination cell therapy remains unclear. Herein, we investigate whether stromal cell-derived factor (SDF)-1 secreted by MSCs contributes to. Furthermore, we examined whether SDF-1 affects EPC migration via Phosphoinositide 3-Kinases (PI3K)/protein kinase B (termed as Akt) signaling pathway.Methods: First, intramuscular MSC injections were supplemented with intravenous EPC injections in the mouse model of hind limb ischemia. The incorporation of Qdot® 525 labeled-EPC into the vasculature and capillary density was evaluated by CD31 immunohistochemistry and immunofluorescence, respectively. Then, the concentration of SDF-1 secreted by MSCs was detected via quantitative immunoassay. Flow cytometry was performed to quantify CXC chemokine receptor (CXCR) 4-positive EPCs. The effect of MSCs on EPC migration was measured by a transwell system and a tube-like structure formation on Matrigel. The SDF-1 antagonist AMD3100 and the PI3K inhibitor wortmannin were separately used to determine the participation of CXCR4 and PI3K into EPC migration. Finally, western blot assay was performed to detect the effect of SDF-1 secreted by MSCs on Akt phosphorylation in EPCs.Results: The combination delivery of MSCs and EPCs via a “dual-administration” approach enhanced the incorporation of EPCs into the vasculature and increased the capillary density in mouse ischemic hind limb. The SDF-1 concentration secreted by MSCs was 2.61 ng/ml after 48 h. CXCR4-positive EPCs increased after incubation with MSC-conditioned medium (CM). MSCs contributed to EPC migration and tube-like structure formation, both of which were suppressed by AMD3100 and wortmannin. Phospho-Akt induced by MSC-CM was attenuated when EPCs were pretreated with AMD3100 and wortmannin.Conclusions: The paracrine action of MSCs contributes to EPC migration. Furthermore, SDF-1 secreted by MSCs induces EPC migration. The mechanism of this migration is related to the activation of the Akt pathway