Abstract 9459: Growth Factor Induced Neointima Formation is Mediated by the p110alpha Isoform of PI 3-kinase
Neointima formation following balloon injury is characterized by an excessive migration and proliferation of vascular smooth muscle cells (VSMC), which are both induced by peptide growth factor mediated activation of receptor tyrosine kinases (RTKs). PI 3-Kinase (PI3K) was identified as the crucial downstream mediator of RTKs in vitro and in vivo, and therefore represents a promising therapeutic target. In VSMCs, RTKs induce the activation of two catalytic class IA PI3Ks isoforms (p110α, and p110β). We hypothesized that gene deletion or inhibition of p110α or p110β significantly reduces proliferation and migration of VSMC and thus diminishes neointima formation following balloon angioplasty in vivo. We investigated the specific function of these isoforms in growth factor induced proliferation (BrdU incorporation assay) and migration (modified Boyden-chamber) of rat and human VSMC using isoform-specific inhibitors (PIK75 and TGX221, for p110α and p110β, respectively) or siRNA. Additionally, we determined the protein expression of PI3K isoforms in balloon injured rat carotid arteries. Finally, we assessed the relevance of p110α signaling for neointima formation in balloon injured carotid arteries from smooth muscle specific p110α deficient mice. Platelet-derived growth factor BB (PDGF, 50 ng/ml), epidermal growth factor (50 ng/ml), or fibroblast growth factor (50 ng/ml) induced proliferation and migration were abrogated by selective inhibition (IC50 = 200 nM) or knockdown (20 nM siRNA) of p110α (p<0.05 vs. control, respectively), but not of p110β. Furthermore, immunohistochemical analysis indicated that p110α protein expression and downstream activation of Akt are markedly elevated in neointimal VSMCs in balloon injured arteries compared to medial VSMCs in uninjured vessels. Consequently, VSMC specific gene deletion of p110α significantly reduced neointima formation in murine carotid arteries following balloon injury. Our results indicate that the catalytical class IA PI3K subunit p110α is crucial for growth factor induced proliferation and migration of VSMCs and represents a promising target for the prevention of restenosis.
- © 2010 by American Heart Association, Inc.