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

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.