Features of Stable Plaque Phenotype Are Increased by Macrophage Specific Insulin‐Like Growth Factor 1

Abstract

Insulin‐like growth factor I (IGF‐1) reduces atherosclerosis in Apoe‐null mice and promotes stable plaque phenotype. We reported that deficiency for macrophage (MF)‐specific IGF‐1 receptor upregulated matrix metalloproteinases (MMPs) and promoted atherogenesis. To test whether MF‐specific IGF‐1 will suppress MMPs, decrease atherosclerosis, and change plaque stability, we generated Apoe‐null mice with IGF‐1 overexpression driven by MF‐specific promoter (scavenger receptor A) (SRA12 and SRA17 mice). IGF‐1 level was increased in peritoneal MF isolated from SRA12 (21±4% increase) and from SRA17 mice (52±9% increase) compared to control Apoe‐null mice (both P<0.05). SRA12 and SRA17 mice were fed with a high fat diet for 12 weeks. MF‐specific IGF‐1 overexpression significantly decreased atherosclerotic burden (SRA12, 23±3% decrease, n=20, and SRA17, 28±6% decrease, n=16, vs. control, n=29, en face analysis) and increased plaque collagen levels (11.1±6%, SRA12 and 66.5±11%, n=11, SRA17, Trichrome). Atherosclerotic plaques in both SRA12 and SRA17 mice had reduced necrotic cores suggesting elevated plaque stability. Increased levels of plaque collagen in SRA17 mice correlated with a significant decrease of MMP1, MMP2, MMP8, MMP12, MMP13, and MMP14 protein levels in peritoneal MF (immunoblotting, 30–72% decrease vs. control). To assess monocyte recruitment into the plaque, macrophage‐cleavable fluorescent red beads were injected (IV). Plaques in both SRA12 and SRA17 mice have reduced number of red beads compared to Apoe‐null mice (77±2% decrease, p=0.027, 74±3% decrease, p=0.0592, respectively) suggesting decreased monocyte recruitment. Cutlured human THP‐1 MFs were incubated with IGF‐1 (0, 20, 100ng/mL) for 48 hrs. IGF‐1 (20ng/ml) decreased expression of MMP8 (34±13% decrease, P<0.05) and MMP14 protein (35±17% decrease, P<0.05) (ELISA). To demonstrate that downregulation of MMPs was mediated via IGF1R‐dependent mechanism, we used Picropodophyllin (PPP), a specific IGF1R inhibitor. MF pre‐treatment with PPP (1ug/ml, 2hrs) abolished IGF‐1‐induced MMP8 downregulation in MF. In summary, we show that IGF‐1 reduced MMPs in vitro and MF IGF‐1 decreased MMPs, upregulated collagen and suppressed atherosclerotic burden in vivo. We identified the novel MMP‐dependent mechanism potentially mediating MF IGF‐1 atheroprotective effect by increasing features of stable plaque phenotype.Support or Funding InformationNIH/NHLBI 2R01HL070241‐13A1