Cbx3 inhibits vascular smooth muscle cell proliferation, migration, and neointima formation

To investigate the role of chromobox protein homolog 3 (Cbx3) in vascular smooth muscle cell (VSMC) proliferation, migration, and neointima formation following vascular injury. Overexpression of Cbx3 led to a significant increase in VSMC contractile gene expression and VSMC apoptosis as well as a dramatic decrease in collagen gene expression, VSMC proliferation, and migration. Meanwhile, the opposite was observed following inhibition of endogenous Cbx3. Luciferase activity assays revealed that Notch signalling, but neither beta-catenin nor NF-kappa B signalling, is regulated by Cbx3 in VSMCs, and among the four Notch receptors, Notch3 is selectively down-regulated by Cbx3 through a transcriptional repression mechanism. Notch3 gene activation recapitulates the effects of Cbx3 knockdown on VSMC proliferation and migration. Consequently, the inhibitory effects of Cbx3 over-expression on VSMC proliferation and migration were reversed by Notch3 gene reactivation. In a model of vascular damage by carotid wire injury, we observed that Cbx3 expression was dramatically down-regulated in the injured arteries. Local ectopic over-expression of Cbx3 in the injured arteries significantly inhibited Notch3 expression, thereby reducing VSMCs proliferation and causing an overall decrease in neointima formation. Additionally, injury-induced neointimal SMC hyperplasia was significantly reduced by aortic inhibition of Notch3. Importantly, a decreased expression level of Cbx3, but an increased expression level of Notch3, was observed in human femoral arteries with atherosclerotic lesions. Cbx3 modulates VSMC contractile and collagen gene expression, as well as VSMC proliferation, migration, and apoptosis via a Notch3 pathway, and plays an important role in controlling injury-induced neointima formation.