Abstract 16188: Insulin-Like Growth Factor Increases Collagen-1α and Contractile Protein Expression in Vascular Smooth Muscle: Mechanisms of Atherosclerotic Plaque Stabilization
We have shown that IGF-1 infusion in Apoe-/- mice increases features of atherosclerotic plaque stability including increased expression of collagen and alpha-smooth muscle actin (αSMA)-positive cells. To determine mechanisms, human aortic smooth muscle cells (SMC) were exposed to 0-100ng/mL IGF-1 for 0-24hr. IGF-1 induced a dose-dependent increase in expression of procollagen-1α (2.4-fold with 100ng/mL IGF-1, p<0.001, n=10) and contractile proteins, αSMA and SM22α (∼2-fold, p<0.001, n=10). To determine if interaction with the extracellular matrix is necessary for the ability of IGF-1 to induce contractile protein expression, integrin-blocking antibodies were used. Interestingly, blocking the α5β1-integrin (receptor for fibronectin) prevented the IGF-1-induced increase in αSMA and SM22α expression, while blocking the α2β1-integrin (receptor for collagen) did not block the IGF-1 effect, suggesting that binding of fibronectin (not collagen) is important for the IGF-1 upregulation of contractile protein expression. IGF-1 did not alter Col1a1, Col1a2, αSMA, or SM22α mRNA expression or stability (multiple time-points evaluated via real-time RT-PCR) and IGF-1 upregulation of procollagen-1α, αSMA, or SM22α was not blocked by actinomycin D, indicating a posttranscriptional mechanism. Cycloheximide completely abrogated the IGF-1-induced expression of procollagen-1α and αSMA, indicative of a translation-dependent mechanism. LY2940032, a PI3K-inhibitor, prevented the IGF-1-induced expression of procollagen-1α, αSMA, and SM22α, while PD98059, an Erk1/2-inhibitor, and rapamycin, an mTOR (down-stream target of PI3K)-inhibitor, had no effect. Remarkably, IGF-1 rapidly increased the rate of collagen synthesis (3H-proline incorporation, 2.2-fold increase at 2 hours, p<0.0001, n=6), thus demonstrating translational regulation by IGF-1. In summary, IGF-1 induces procollagen-1α, αSMA, and SM22α protein expression via a PI3K-mediated, but mTOR-independent, translational mechanism. Furthermore, IGF-1 induced contractile protein expression is α5β1-integrin dependent. These findings provide new insights into mechanisms whereby IGF-1 increases atherosclerotic plaque stability.
- © 2012 by American Heart Association, Inc.