Abstract 5549: Bone Morphogenetic Protein-2 (BMP-2) and BMP-7 Act as Instructive Factors to Specify Notch Signaling Controlling Smooth Muscle Cell Phenotype

Abstract

Background: Vascular smooth muscle cells (VSMC) exhibit phenotypic plasticity including synthetic, contractive and osteogenic phenotypes in response to environmental cue. Bone morphogetic proteins (BMPs) and Notch signaling are essential determinants of cellular identity, but their mode of action to specify SMC phenotype is poorly defined. Here we investigate the cooperation between BMPs and Notch signaling in cultured VSMC. Methods and Results: We have recently shown that overexpression of Notch1 intracellular domain (N1-ICD) in human aortic SMC (HASMC) induced expression of both SMC and osteoblast marker genes. Interestingly, BMP-2, an osteogenic BMP implicating in vascular calcification, markedly enhanced N1-ICD-induced expression of osteoblast marker genes. Consistently, ALP activity as well as matrix mineralization were also synergistically induced by Notch and BMP-2 signaling. A specific silencing using siRNA confirmed that Msx-2 was responsible for the enhanced osteogenic phenotype induced by Notch and BMP-2. Experiments using site-specific mutation constructs of Msx2 promoter and ChiP assay revealed that the Msx-2 promoter contains functional RBP-Jk-binding site at −3770, and both this site and Smad-binding site are necessary for synergistic activation of the Msx-2 gene expression by Notch and BMP-2. In contrast, BMP-7 markedly augmented N1-ICD-induced expression of SMC marker genes, whereas expression of osteoblast marker genes was unchanged. Of note, BMP-7 failed to enhance N1-ICD-induced SMC marker gene expression in cells deficient of myocardin, indicating myocardin mediates the crosstalk between Notch and BMP-7 signaling. Conclusion: These results suggest that by BMP-2 and BMP-7 play an instructive role in specifying the Notch/RBP-Jk pathway which induces either differentiated phenotype or osteogenic phenotype of SMC Collectively, this study provides, at least in part, a mechanistic basis for the “context dependency” characteristic of Notch signaling.