Age-dependent defect in vascular endothelial growth factor expression is associated with reduced hypoxia-inducible factor 1 activity

Previous studies have indicated that advanced age is associated with impair ed angiogenesis in part because of reduced levels of vascular endothelial g rowth factor (VEGF) expression. To investigate potential mechanisms respons ible 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) co nditions, Hypoxia-induced VEGF expression was significantly lower in old ve rsus young 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 re vealed a significant defect in VEGF up-regulation following hypoxia in old versus young cells (a 43 versus 117% increase in luciferase activity, p < 0 .05); this difference was not seen when a deletion construct lacking the hy poxia-inducible 1 (HIF-1) binding site was used. Moreover, although HIF-1 a lpha-mRNA expression was shown to be similar in young and old smooth muscle cells, HIF-1 alpha protein and DNA binding activity were significantly red uced in old versus young 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 describe d age-dependent impairment of angiogenesis in response to ischemia.