Abstract 15652: Insulin-Like Growth Factor-1 Induces Vascular Smooth Muscle Cell Contractile Phenotype via a PI3K-Mediated Post-Transcriptional Mechanism Dependent on the α5β1 Integrin
In the progression of atherosclerosis, remodeling of the vessel wall occurs in which the extracellular matrix environment is altered and smooth muscle cells (SMCs) undergo a loss of contractile phenotype leading to increased plaque vulnerability and propensity for aneurysm formation. Our earlier studies have shown that insulin-like growth factor-1 (IGF-1)-infusion or SMC-specific IGF-1 overexpression increases contractile SMCs in atherosclerotic plaques of ApoE-/- mice. To investigate signal transduction mechanisms whereby IGF-1 induces contractile protein expression, human aortic SMCs were cultured and treated with 0-100 ng/mL IGF-1 for 0-24 hours in the presence of various inhibitors. IGF-1 induced a dose-dependent increase in expression of SMC contractile proteins, alpha-actin (αSMA) and smooth muscle 22-alpha (SM22α) (~2-fold-increase each with 100 ng/mL, p<0.01, n=10), without affecting mRNA levels. Additionally, IGF-1-upregulation of αSMA and SM22α protein expression was not blocked by actinomycin D, indicating posttranscriptional regulation by IGF-1. A PI3K-inhibitor (LY2940032) prevented the ability of IGF-1 to increase expression of αSMA and SM22α, while an Erk1/2-inhibitor (PD98059) had no effect. Although PI3K has been shown to activate downstream target, mTOR, rapamycin did not inhibit the IGF-1-induced increase in αSMA and SM22α expression, indicating an alternate mechanism by IGF-1. Furthermore, pretreatment with a collagen synthesis inhibitor, EDHB (a prolyl-hydroxylase inhibitor), or a blocking antibody for the α2β1 integrin (receptor for collagen) reduced basal expression of αSMA and SM22α and proliferation marker, PCNA; however, IGF-1 still significantly increased αSMA, SM22α, and PCNA expression. Interestingly, presence of a blocking antibody against the α5β1 integrin (receptor for fibronectin) increased basal PCNA expression and completely inhibited the ability of IGF-1 to increase αSMA and SM22α expression (n=6), indicating that the α5β1 integrin is critical in mediating the IGF-1-induction of contractile SMC phenotype. Overall, our studies provide new insights into integrin-mediated and IGF-1-signaling mechanisms that may play a role in vascular remodeling in atherosclerosis.
Author Disclosures: C. Blackstock: None. Y. Higashi: None. S. Sukhanov: Research Grant; Significant; NHLBIR21 grant, PI. S. Shai: None. P. Delafontaine: None.
- © 2014 by American Heart Association, Inc.