2009 Southern Regional Meeting Abstracts

Purpose of Study: We have shown that 12/15-lipoxygenase (LOX) mediates important proatherogenic oxidized low density lipoprotein (OxLDL)-induced effects in smooth muscle cells (SMC), namely, cell apoptosis and downregulation of the insulin-like growth factor I (IGF-1) receptor. In addition, LOX mediates macrophage (MΦ) adhesion to atherosclerotic plaque. Recently we reported that infusion of IGF-1 into Apolipoprotein E-deficient (ApoE-/-) mice suppresses MΦ plaque infiltration and atherosclerosis; however, molecular mechanisms mediating these anti-atherogenic effects are unclear. This study was conducted to further explore such mechanisms.
Methods Used: To study the potential role of LOX in IGF-1-induced effects, ApoE-- mice were injected bi-daily with human recombinant IGF-1 (0.7 mg/kg/day) for seven days. LOX aortic gene expression was measured using atherosclerosis-focused PCR arrays, and was confirmed by traditional RT-PCR gene expression analysis. To determine if the IGF-1-induced LOX expression decrease in the atherosclerotic aortas could be attributed to specific cell lineage, endothelial cells, SMC, and THP-1 derived macrophages were exposed to IGF-1 (10 ng/ml, 50 ng/ml, 24h) and LOX gene expression was analyzed. Lastly, to model in vivo conditions, SMC or MΦ were exposed to OxLDL or native LDL (control, 80 ug/ml, 16 h) and 14,15-leukotriene (a product of LOX-specific enzymatic reaction) levels were measured in conditioned media by ELISA.
Summary of Results: IGF-1 decreased LOX aortic gene expression by 64±6%. Similarly, IGF-1 dose-dependently decreased LOX gene expression in macrophages (IGF-1, 10 ng/ml: 0.81; IGF-1, 50 ng/ml: 0.51 vs. control: 1.0, fold changes, RT-PCR). IGF-1 treatment on endothelial and smooth muscle cells showed no significant effects. OxLDL induced a dramatic increase in LOX activity levels in macrophages (20-fold vs. 1.0, control), and a smaller increase in LOX activity in smooth muscle cells (18-fold vs. 1.0, control).
Conclusions: In summary, IGF-1 suppresses vascular LOX expression in ApoE-- mice and also induces cell type-specific LOX downregulation in human macrophages. Our data suggests that the ability of IGF-1 to downregulate LOX plays an important role in its anti-atherogenic effect.