Mechanisms underlying the impairment of ischemia-induced neovascularization in matrix metalloproteinase 2-deficient mice

Matrix metalloproteinases ( MMPs) have been implicated in the process of neovascularization. However, the exact roles of individual MMPs in vessel formation are poorly understood. To study the putative role of MMP-2 in ischemia-induced neovascularization, a hindlimb ischemia model was applied to MMP-2(+/+) and MMP-2(+/+) mice. Serial laser Doppler blood-flow analysis revealed that the recovery of the ischemic/normal blood-flow ratio in MMP-2(+/+) young and old mice remained impaired throughout the follow-up period. At day 35, microangiography and anti-L-lectin immunohistochemical staining revealed lesser developed collateral vessels and capillary formation in both old and young MMP-2(+/+) mice compared with the age-matched MMP-2(+/+) mice. An aortic-ring culture assay showed a markedly impaired angiogenic response in MMP-2(+/+) mice, which was partially recovered by supplementation of the culture medium with recombinant MMP-2. Aorta-derived endothelial cells or bone marrow - derived endothelial progenitor cell ( EPC)- like c-Kit(+) cells from MMP-2(+/+) showed marked impairment of invasive or/and proliferative abilities. At day 7, plasma and ischemic tissues of vascular endothelial growth factor protein were reduced in MMP-2(+/+). Flow cytometry showed that the numbers of EPC-like CD31(+) c-Kit(+) cells in peripheral blood markedly decreased in MMP-2 - deficient mice. Transplantation of bone marrow - derived mononuclear cells from MMP-2(-/-) mice restored neovascularization in MMP-2(+/+) young mice. These data suggest that MMP-2 deficiency impairs ischemia-induced neovascularization through a reduction of endothelial cell and EPC invasive and/or proliferative activities and EPC mobilization.