Matrix Metalloproteinase-9 Is Essential for Ischemia-Induced Neovascularization by Modulating Bone Marrow–Derived Endothelial Progenitor Cells

Objective— Both matrix metalloproteinases (MMPs) and endothelial progenitor cells (EPCs) have been implicated in the process of neovascularization. Here we show that the impaired neovascularization in mice lacking MMP-9 is related to a defect in EPC functions in vasculogenesis.Methods and Results— Hindlimb ischemia surgery was conducted in MMP-9−/− mice and wild-type (MMP-9+/+ ) mice. Blood flow recovery was markedly impaired in MMP-9−/− mice when compared with that in wild-type mice as determined by laser Doppler imaging. Flow cytometry demonstrated that the number of EPC-like cells (Sca-1+ /Flk-1+ ) in peripheral blood increased in wild-type mice after hindlimb ischemia surgery and exogenous vascular endothelial growth factor stimulation, but not in MMP-9−/− mice. Plasma levels and bone marrow concentrations of soluble Kit-ligand (sKitL) were significantly elevated in wild-type mice in response to tissue ischemia, but not in MMP-9−/− mice. C-kit positive bone marrow cells of MMP-9−/− mice have attenuated adhesion and migration than those isolated from wild-type mice. In in vitro studies, incubation with selective MMP-9 inhibitor suppressed the colony formation, migration, and tube formation capacities of EPC. Transplantation of bone marrow cells from wild-type mice restored collateral flow formation in MMP-9−/− mice.Conclusions— These findings suggest that MMP-9 deficiency impairs ischemia-induced neovascularization, and these effects may occur through a reduction in releasing the stem cell-active cytokine, and EPC mobilization, migration, and vasculogenesis functions.