The induction of yes-associated protein expression after arterial injury is crucial for smooth muscle phenotypic modulation and neointima formation.

OBJECTIVE: Abnormal proliferation and migration of vascular smooth muscle cells (SMCs) are the key events in the progression of neointima formation in response to vascular injury. The goal of this study is to investigate the functional role of a potent oncogene yes-associated protein (YAP) in SM phenotypic modulation in vitro and in vivo. METHODS AND RESULTS: In vitro cell culture and in vivo in both mouse and rat arterial injury models YAP expression is significantly induced and correlated with the vascular SMC synthetic phenotype. Overexpression of YAP promotes SMC migration and proliferation while attenuating SM contractile gene expression. Conversely, knocking down endogenous YAP in SMCs upregulates SM gene expression but attenuates SMC proliferation and migration. Consistent with this, knocking down YAP expression in a rat carotid balloon injury model and genetic deletion of YAP, specifically, in vascular SMCs in mouse after carotid artery ligation injury attenuates injury-induced SM phenotypic switch and neointima formation. CONCLUSIONS: YAP plays a novel integrative role in SM phenotypic modulation by inhibiting SM-specific gene expression while promoting SM proliferation and migration in vitro and in vivo. Blocking the induction of YAP would be a potential therapeutic approach for ameliorating vascular occlusive diseases.

Transforming growth factor-ß1-induced transcript 1 protein, a novel marker for smooth muscle contractile phenotype, is regulated by serum response factor/myocardin protein.

Serum response factor (SRF) plays a central role in regulating expression of smooth muscle-specific genes partly by associating with the potent tissue-specific cofactor myocardin. Previous studies have shown that transforming growth factor-ß1-induced transcript 1 (TGFB1I1, also known as Hic-5) is a TGF-ß-responsive gene and is involved in the cellular response to vascular injury, but the regulation of TGFB1I1 expression remains elusive. In this report, we demonstrated that TGFB1I1 is a novel marker for the smooth muscle contractile phenotype and is regulated by SRF/myocardin. We found that TGFB1I1 is specifically expressed in smooth muscle cells (SMCs) and in smooth muscle-rich tissues. Furthermore, TGFB1I1 expression is significantly down-regulated in a variety of models for smooth muscle phenotypic modulation. The TGFB1I1 promoter contains an evolutionarily conserved CArG element, and this element is indispensible for myocardin-induced transactivation of TGFB1I1 promoter. By oligonucleotide pulldown and chromatin immunoprecipitation assays, we found that SRF binds to this CArG element in vitro and in vivo. Ectopic expression of myocardin is sufficient to induce endogenous TGFB1I1 expression in multiple cell lines whereas knocking-down myocardin or SRF significantly attenuated TGFB1I1 expression in SMCs. Furthermore, our data demonstrated that SRF is essential for TGF-ß-mediated induction of TGFB1I1. Finally, silencing of TGFB1I1 expression significantly promotes SMC proliferation. Collectively, this study provides the first evidence that TGFB1I1 is not only an SRF/myocardin-regulated smooth muscle marker but also critical for maintaining smooth muscle contractile phenotype by inhibiting smooth muscle proliferation.