Search

Objective: IGF-1 (insulin-like growth factor 1) exerts pleiotropic effects including promotion of cellular growth, differentiation, survival, and anabolism. We have shown that systemic IGF-1 administration reduced atherosclerosis in Apoe −/ − (apolipoprotein E deficient) mice, and this effect was associated with a reduction in lesional macrophages and a decreased number of foam cells in the plaque. Almost all cell types secrete IGF-1, but the effect of macrophage-derived IGF-1 on the pathogenesis of atherosclerosis is poorly understood. We hypothesized that macrophage-derived IGF-1 will reduce atherosclerosis. Approach and Results: We created macrophage-specific IGF-1 overexpressing mice on an Apoe − / − background. Macrophage-specific IGF-1 overexpression reduced plaque macrophages, foam cells, and atherosclerotic burden and promoted features of stable atherosclerotic plaque. Macrophage-specific IGF1 mice had a reduction in monocyte infiltration into plaque, decreased expression of CXCL12 (CXC chemokine ligand 12), and upregulation of ABCA1 (ATP-binding cassette transporter 1), a cholesterol efflux regulator, in atherosclerotic plaque and in peritoneal macrophages. IGF-1 prevented oxidized lipid-induced CXCL12 upregulation and foam cell formation in cultured THP-1 macrophages and increased lipid efflux. We also found an increase in cholesterol efflux in macrophage-specific IGF1–derived peritoneal macrophages. Conclusions: Macrophage IGF-1 overexpression reduced atherosclerotic burden and increased features of plaque stability, likely via a reduction in CXCL12-mediated monocyte recruitment and an increase in ABCA1-dependent macrophage lipid efflux.

Objective— IGF-1 (insulin-like growth factor 1) is a major autocrine/paracrine growth factor, which promotes cell proliferation, migration, and survival. We have shown previously that IGF-1 reduced atherosclerosis and promoted features of stable atherosclerotic plaque in Apoe −/ − mice—an animal model of atherosclerosis. The aim of this study was to assess effects of smooth muscle cell (SMC) IGF-1 signaling on the atherosclerotic plaque. Approach and Results— We generated Apoe −/− mice with IGF1R (IGF-1 receptor) deficiency in SMC and fibroblasts (SM22α [smooth muscle protein 22 α]-CreKI/IGF1R-flox mice). IGF1R was decreased in the aorta and adventitia of SM22α-CreKI/IGF1R-flox mice and also in aortic SMC, embryonic, skin, and lung fibroblasts isolated from SM22α-CreKI/IGF1R-flox mice. IGF1R deficiency downregulated collagen mRNA-binding protein LARP6 (La ribonucleoprotein domain family, member 6) and vascular collagen, and mice exhibited growth retardation. The high-fat diet–fed SM22α-CreKI/IGF1R-flox mice had increased atherosclerotic burden and inflammatory responses. α-SMA (α-smooth muscle actin)–positive plaque cells had reduced proliferation and elevated apoptosis. SMC/fibroblast-targeted decline in IGF-1 signaling decreased atherosclerotic plaque SMC, markedly depleted collagen, reduced plaque fibrous cap, and increased plaque necrotic cores. Aortic SMC isolated from SM22α-CreKI/IGF1R-flox mice had decreased cell proliferation, migration, increased sensitivity to apoptosis, and these effects were associated with disruption of IGF-1–induced Akt signaling. Conclusions— IGF-1 signaling in SMC and in fibroblast is a critical determinant of normal vascular wall development and atheroprotection.

We have shown that IGF-1 infusion into Apoe-null mice suppressed atherosclerosis. To define mechanisms we performed RT-PCR array and found that IGF-1 (0.8 mg/kg, i.p, 7d) reduced aortic 12/15-lipoxygenase (LOX) expression (64±6% decrease vs. saline control, P To further define mechanisms THP-1-derived MΦ were exposed to IGF-1. IGF-1 (50 ng/ml, 16h) reduced LOX mRNA (49±6% decrease, RT-PCR, P0.05). These data indicate that specific LOX downregulation mediates IGF-1-induced suppression of nLDL oxidation and formation of foam cells. In summary, IGF-1 reduced LOX expression in atherosclerotic plaque and this effect correlated with reduction in plaque lipids and in total atherosclerotic burden. IGF-1 downregulated LOX in cultured MΦ via inhibition of STAT6-dependent transcription and IGF-1 decreased lipid oxidation and uptake by MΦ. Taken together these data strongly suggest that MΦ LOX downregulation mediates IGF-1-induced reduction in foam cells and in atherosclerosis.