031 IGF‐I stimulates VEGF production in endothelial cells by inhibiting poly(ADP‐Ribose)‐polymerase

Abstract

Introduction: Vascular Endothelial Growth Factor (VEGF) mediated angiogenesis plays a key role in wound healing. Insulin‐like Growth Factor I (IGF‐I) has been reported to be angiogenic. However, the mechanism is not known. Recently, a link between transcriptional activity and inhibition of poly(ADP‐Ribose)polymerase (PARP) has been reported. We investigated whether IGF‐I increases VEGF expression and whether this effect is regulated by the inhibition of PARP. Material and methods: Subconfluent monolayers of human umbilical vein cells were cultured and serum starved. Cultures were treated with Long‐R3‐IGF‐I for 20 h. VEGF in the supernatant was measured by ELISA and lactate by a lactate analyser. PARP activity was assessed by measuring the incorporation of 14C‐radiolabeled NAD+. All experiments were performed in triplicate. Results are given as percent change compared to control ± SD; p < 0.05 calculated by Student‘s t‐test was considered significant. Results: IGF‐I increased both VEGF (20 ± 10%, 50 ± 16%(p = 0.01) and 79 ± 13%(p = 0.0003)) and lactate production (12 ± 11%, 20 ± 12% and 48 ± 16%(p = 0.01)) in a dose dependent manner (25, 50 and 100 ng/ml). Blocking glucose utilization by 2‐desoxyglucose, decreased lactate by 70 ± 11%(p = 0.0001), but not VEGF expression. Inhibitors of MAP‐kinase (PD 98059) and Proteinkinase C (Staurosporine) reduced the IGF‐I effect on VEGF expression by 40 ± 6%(p = 0.0003) and 30 ± 7%(p = 0.01). 3‐Aminobenzamide and nicotinamide alone, inhibitors of PARP, stimulated VEGF production by 66 ± 5%(p = 0.0003) and 32 ± 8%(p = 0.002), respectively. IGF‐I inhibited PARP by 44 ± 3%(p = 0.01). Conclusion: IGF‐I enhances VEGF protein expression in endothelial cells. This is mediated through signal transduction and by inhibition of PARP.