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. Stem Cells 2016;34:1251–1262