부산대학교 도서관

Previous studies have indicated that advanced age is associated with impaired angiogenesis in part because of reduced levels of vascular endothelial growth factor (VEGF) expression. To investigate potential mechanisms responsible for this age-dependent defect in VEGF expression, aortic smooth muscle cells isolated from young rabbits (ages 6–8 months) or old rabbits (ages 4–5 years) were exposed to normoxic (21% oxygen) or hypoxic (0.1% oxygen) conditions. Hypoxia-induced VEGF expression was significantly lower in old versusyoung cells. VEGF mRNA stability in hypoxic conditions was similar in both young and old cells. However, transient transfection with a luciferase reporter gene that was transcriptionally regulated by the VEGF promoter revealed a significant defect in VEGF up-regulation following hypoxia in oldversusyoung cells (a 43 versus117% increase in luciferase activity, p< 0.05); this difference was not seen when a deletion construct lacking the hypoxia-inducible 1 (HIF-1) binding site was used. Moreover, although HIF-1α-mRNA expression was shown to be similar in young and old smooth muscle cells, HIF-1α protein and DNA binding activity were significantly reduced in old versusyoung smooth muscle cells that were exposed to hypoxia. We propose that age-dependent reduction in hypoxia-induced VEGF expression results from reduced HIF-1 activity and may explain the previously described age-dependent impairment of angiogenesis in response to ischemia.