Abstract 311: Osteogenic Transcription Factor Runx2 Represses Connective Tissue Growth Factor Gene Expression And TGFβ Signaling In Vascular Smooth Muscle Cells
[Objective] Runx2, a key transcription factor in osteoblast differentiation, is expressed in calcified atherosclerotic plaques. We have recently shown that Runx2 represses vascular smooth muscle cells (VSMCs) differentiation and promotes their osteogenic differentiation. Connective tissue growth factor (CTGF) has been implicated in the progression to vulnerable plaque by inducing mononuclear cell chemotaxis and VSMCs apoptosis despite of its potent stimulatory effect on connective tissue cell the proliferation and extracellular matrix synthesis. To assess the role of Runx2 in the process of plaque development, we investigated the molecular mechanism of the CTGF gene expression by Runx2 in VSMCs.
[Methods and Results] RT-PCR analyses showed that adenovirally overexpressed Runx2 significantly repressed the basal expression of the CTGF gene in human aortic SMCs (HASMCs). Consistent with this, knockdown of the Runx2 expression in HASMCs by small interfering RNA (siRNA) increased CTGF mRNA levels. Luciferase assays showed that Runx2 reduced the transcriptional activity of the CTGF promoter. Transfection of a series of 5′-deletion constructs revealed that Runx2 inhibited CTGF expression through the sequence element located at 5′ untranslated region of CTGF mRNA. We next examined the effects of Runx2 on the TGFβ-induced CTGF expression. Runx2 overexpression significantly repressed CTGF expression in HASMCs stimulated with TGFβ, and knockdown of Runx2 by siRNA enhanced the induction of CTGF expression in response to TGFβ. Runx2 repressed TGFβ-induced CTGF promoter activity through the sequence including Smad binding element (SBE). Overexpression of Runx2 significantly reduced TGFβ- and Smad3-mediated luciferase activity of Smad-dependent promoter which contains four copies of SBE. Biotinylated DNA pulldown assay using SBE of CTGF promoter showed that Runx2 formed a complex with Smad3 and Smad4.
[Conclusion] Runx2 repressed basal and TGFβ-induced CTGF gene expression in VSMCs. Thus, in addition to the potential for inducing vascular calcification, Runx2 may affect plaque stability by modulating extracellular matrix synthesis through inhibiting CTGF gene expression and TGFβ signaling.