Abstract 13449: Insulin-Like Growth Factor I (IGF-1) Downregulates 12/15-lipoxygenase in Apoe-Deficient Mice and in Cultured Macrophages: Potential Mechanism Mediating IGF-1-Induced Atheroprotection
We have shown that Insulin-like growth factor I (IGF-1) infusion into Apoe-deficient mice suppressed atherosclerosis. To define mechanisms we performed RT arrays and found that IGF-1 (0.8 mg/kg, i.p. for 1 week, n=6) markedly reduced aortic 12/15-lipoxygenase (LOX) expression (64±6% decrease vs. saline control, P<0.05). LOX is a major pro-atherogenic oxidase that promotes scavenger receptor-mediated lipid uptake by macrophages (MΦ) by transforming native low density lipoprotein (nLDL) into its oxidized form (OxLDL). IGF-1 infusion into Apoe-deficient mice (1.5 mg/kg/d, 12 weeks on a Western diet, n=12) reduced LOX plaque immunopositivity (74±9% decrease, P<0.05), suppressed plaque oxidative stress (64±7% decrease, immunohistochemistry with 8-oxo-2’-deoxyguanosine antibody, P<0.05), reduced plaque lipids (35%±6 decrease, Oil Red staining, P<0.05) and decreased atherosclerotic lesion cross-sectional area (IGF-1: 0.259 ± 0.018 mm2, saline: 0.356 ± 0.031 mm2; 28±4% decrease, P<0.05). To further define mechanisms THP-1-derived MΦ were exposed to IGF-1. IGF-1 (0-100 ng/ml, 16 h) dose-dependently reduced basal LOX mRNA levels (50 ng/ml: 49±6% decrease, RT-PCR, P<0.05) and this effect correlated with a complete suppression of STAT-6 transcription factor binding to LOX gene promoter region (CHIP assay with STAT-6 antibody). OxLDL (80 ug/ml, 16 h) dramatically increased (more than 18-fold) MΦ LOX activity (14, 15-leukotriene ELISA) and pre-treatment with IGF-1 inhibited this effect (68±6% decrease, P<0.05). IGF-1 markedly suppressed MΦ-mediated oxidation of nLDL (85±6% decrease, MDA assay) and subsequent LDL internalization (45±8% decrease, staining with Oil Red) indicating that IGF-1 blocked conversion of nLDL into OxLDL by MΦ. In summary, IGF-1 reduced LOX expression in atherosclerotic plaque and this effect correlated with reduction in plaque lipid levels and in total atherosclerotic burden. IGF-1 downregulated LOX in cultured MΦ via inhibition of STAT-6-dependent transcription and IGF-1 decreased lipid oxidation and internalization by MΦ. Taken together these data strongly suggest that IGF-1-induced MΦ LOX downregulation plays a major role in IGF-1-induced reduction of plaque foam cell formation and atherosclerosis.
- © 2012 by American Heart Association, Inc.