Cell-Surface MMP-9 Protein Is a Novel Functional Marker to Identify and Separate Proangiogenic Cells from Early Endothelial Progenitor Cells Derived from CD133⁺ Cells

To develop cell therapies for ischemic diseases, endothelial progenitor cells (EPCs) have been expected to play a pivotal role in vascular regeneration. It is desirable to use a molecular marker that is related to the function of the cells. Here, a quantitative polymerase chain reaction array revealed that early EPCs derived from CD133⁺ cells exhibited significant expression of MMP-9. Some populations of early EPCs expressed MMP-9 on the cell surface and others did not. We also attempted to separate the proangiogenic fraction from early EPCs derived from CD133⁺ cells using a functional cell surface marker, and we then analyzed the MMP-9⁺ and MMP-9^- cell fractions. The MMP-9⁺ cells not only revealed higher invasion ability but also produced a high amount of IL-8. Moreover, the stimulative effect of MMP-9⁺ cells on angiogenesis in vitro and in vivo was prohibited by anti-IL-8 antibody. These data indicate that MMP-9 is one of the useful cell surface markers for the separation of angiogenic cells. Our treatment of early EPCs with hyaluronidase caused not only a downregulation of cell-surface MMP-9 but also a decrease in invasion ability, indicating that membrane-bound MMP-9, which is one of the useful markers for early EPCs, plays an important role in angiogenesis.