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Background Molecular analysis of neovascularization related genes by time course in response to ischemia has not been described in the context of aging. We aimed to provide a progressively deeper understanding of how aging compromises neovascularization.Methods Young (3-month) and old (18-month) C57BI mice were subjected to left hindlimb ischemia. Necrosis score was evaluated in calf muscles. Calf muscles,peripheral blood,bone marrow were harvested at different time points. The expressions of matrix metalloproteiniase-9 (MMPg),endothelial nitric oxide synthase (eNOS),vascular endothelial growth factor (VEGF),stromal derived growth factor-1 (SDF1),hypoxia inducible factor-1α (HIF1α),VEGF receptor-1(Fit1),VEGF receptor-2 (Flk1),angiopoietin-1 (Ang1),CD133,CD26 were detected by RT-PCR or Western blotting.White blood cells were counted in the peripheral blood. Gene expression data were compared by two-way analysis of variance.Results MMP9,HIF-1α and SDF-1 were more upregulated during acute ischemia in old vs. young mice,reflecting increased ischemia in aging mice. However VEGF and eNOS exhibited lower expression in old vs. young mice,despite greater ischemia intensity. Ang1 and Flk1 showed similar expression in old vs. young mice. MMP9 peaked earlier in peripheral blood in young vs. old mice. Concurrent decreasing CD26 and increasing CD133 expression in aging bonemarrow suggest aging impairs progenitor cell mobilization,Conclusions Our results indicate that a complex array of defects occur with aging that interfere with optimal neovascularization. These include potential impaired mobilization of progenitor cells to ischemic tissue,decreased levels of eNOS and VEGF and delayed responses to ischemia.ZLEr. WANG Jin-song,Division of Vascular Surgery,the First Affiliated Hospital,Sun Yat-sen University,Guangzhou,Guangdong 510080,China (Tel:86-20-87333440.Fax:86-20-87333242. Email:wangjs@mail.sysu.edu.cn)This work was supported by NIH RO1 HL085003-01A2,NNSF30100179.