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. 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. 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.
