Abstract 3389: Insulin-Like Growth Factor-1 Regulates Glutathione Peroxidase Expression and Activity in Vascular Endothelial Cells: Implications for Atheroprotective Actions of Insulin-Like Growth Factor- 1
Oxidative stress plays an important permissive role in the genesis of multiple inflammatory diseases, including atherosclerosis. We have shown recently that systemic administration of insulin-like growth factor-1 (IGF-1) in apoE null mice prevents progression of atherosclerosis, possibly via an anti-inflammatory and anti-oxidant effect. Glutathione peroxidase (GPX) is a crucial anti-oxidant enzyme, and its activity is atheroprotective, as indicated by pronounced atherogenesis in GPX- /apoE- double knock-out mice. The aim of this study was to characterize the potential anti-oxidant effects of IGF-1 in vascular endothelial cells (ECs) and to determine a potential effect of IGF-1 on GPX expression and activity in human aortic ECs. ECs were treated with 0 –100 ng/mL IGF-1 for 0 –24 hr prior to exposure to oxidized low-density lipoprotein (oxLDL) and reactive oxygen species (ROS) generation was measured using 5-carboxy-2′,7′-dichlorodihydrofluorescein diacetate. IGF-1 dose-dependently reduced basal- and oxLDL-induced ROS generation (67 ± 9 % decrease with 100 ng/mL IGF-1 vs. oxLDL alone, P<0.01). IGF-1 did not alter superoxide dismutase or catalase activity but markedly increased glutathione peroxidase activity, which was apparent at 6 hr, persisted up to 24 hr (control 24 hr, 4.4 ± 1.2 U/mg protein; IGF-1 24 hr, 21.2 ± 2.1 U/mg protein, P<0.01). IGF-1 (100 ng/mL) increased GPX-1 protein levels by 2.6-fold at 24 hr (Western blot, P<0.01), however IGF-1 did not increase GPX-1 mRNA levels, indicating translational or post-translational regulation. To identify the signaling pathway mediating IGF-1 upregulation of GPX-1 we exposed ECs to IGF-1 in the presence or absence of ERK1/2 (PD98059, 25 μM), p38 MAPK (SB202190, 10 μM), and PI3K (LY294002, 50 μM) inhibitors. LY294002 blocked IGF-1 induced GPX upregulation, indicating involvement of the PI3K pathway. In conclusion, IGF-1 exerts potent anti-oxidant effects on EC, mediated by translational/post-translational increase in GPX expression and activity via a PI3K dependent pathway. This is the first report that IGF-1 exerts anti-oxidant effects on the vasculature, and this finding and the involvement of GPX has major implications for understanding vasculoprotective effects of IGF-1.