2009 Southern Regional Meeting Abstracts

Purpose of Study: 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. In human vascular endothelial cells IGF-1 regulates activity of glutathione peroxidase (GPX), which is a crucial anti-oxidant enzyme and hence is atheroprotective. The aim of this study was to characterize mechanisms whereby IGF-1 regulates GPX expression in endothelial cells.
Methods Used: Cultured human aortic endothelial cells (ECs) were treated with human recombinant IGF-1 (0-100 ng/mL) and tested for oxidized low-density lipoprotein (oxLDL) induced reactive oxygen species (ROS) generation. GPX gene and protein expression levels were tested by realtime-PCR analysis and Western blot analsys.
Summary of Results: IGF-1 prevented oxLDL induced ROS generation (67 ± 9 % decrease with 100 ng/mL IGF-1 vs. oxLDL alone at 24 hr, P<0.01) as assessed by 5-carboxy-2',7'-dichlorodihydrofluorescein diacetate staining. 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 (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.
Conclusions: IGF-1 exerts potent anti-oxidant effects on EC, mediated by translational/post-translational increases in GPX expression and activity via a PI3K dependent pathway.