Transcriptional regulation of vascular smooth muscle cell proliferation, differentiation and senescence: Novel targets for therapy

Vascular smooth muscle cells (SMC) possess a unique cytoplasticity, regulated by transcriptional, translational and phenotypic transformation in response to a diverse range of extrinsic and intrinsic pathogenic factors. The mature, differentiated SMC phenotype is physiologically typified transcriptionally by expression of genes encoding "contractile" proteins, such as SMα-actin (ACTA2), SM-MHC (myosin-11) and SM22α (transgelin). When exposed to various pathological conditions (e.g., pro-atherogenic risk factors, hypertension), SMC undergo phenotypic modulation, a bioprocess enabling SMC to de-differentiate in immature stages or trans-differentiate into other cell phenotypes. As recent studies suggest, the process of SMC phenotypic transformation involves five distinct states characterized by different patterns of cell growth, differentiation, migration, matrix protein expression and declined contractility. These changes are mediated via the action of several transcriptional regulators, including myocardin and serum response factor. Conversely, other factors, including Kruppel-like factor 4 and nuclear factor-κB, can inhibit SMC differentiation and growth arrest, while factors such as yin yang-1, can promote SMC differentiation whilst inhibiting proliferation. This article reviews recent advances in our understanding of regulatory mechanisms governing SMC phenotypic modulation. We propose the concept that transcription factors mediating this switching are important biomarkers and potential pharmacological targets for therapeutic intervention in cardiovascular disease.

WWC3 inhibits intimal proliferation following vascular injury via the Hippo signaling pathway

The Hippo signaling pathway is involved in the formation and development of the cardiovascular system. In the present study, the effects of WWC family member 3 (WWC3) on vascular smooth muscle cells (VSMCs) following injury were investigated, in addition to the associated mechanisms underlying this process. Platelet-derived growth factor BB (PDGF-BB) was used as a cell injury factor, and rats with balloon injuries were used as a model of carotid intimal injury. Furthermore, the expression levels of WWC3 in VSMCs and arteries post-injury were investigated, in addition to the effect of WWC3 on the proliferation and migration of VSMCs. The results demonstrated that following injury, WWC3 expression was suppressed in VSMCs and the rat carotid artery, and the activity of the Hippo signaling pathway was significantly downregulated. In addition, the expression of YY1-associated protein-1 (YAP) and a number of its downstream target genes, including connective tissue growth factor (CTGF), were enhanced, thus enhancing the proliferation and migration of VSMCs. Knockdown of WWC3 suppressed the levels of large tumor suppressor kinase 1 (LATS1) expression and YAP phosphorylation, and the expression of YAP, CTGF and cyclin E was subsequently enhanced, thus promoting cell proliferation and migration. Similar results were obtained following overexpression of WWC3. Treatment with PDGF-BB was revealed to suppress the proliferation and migration of VSMCs transfected with the WWC3 plasmid, compared with VSMCs transfected with an empty vector. The present study demonstrated that WWC3 may interact with LATS1 in order to upregulate the Hippo signaling pathway via co-immunoprecipitation and enhancement of the phosphorylation of LATS1, in addition to the corresponding suppression of the nuclear import of YAP. However, VSMCs transfected with WWC3 plasmid with a deletion of the WW domain fail to exhibit this effect. These results suggested that WWC3 expression is downregulated in VSMCs during neointimal hyperplasia following injury (PDGF-BB stimulation or balloon injury). WWC3 upregulates the activity of the Hippo signaling pathway, and weakens the proliferation and migration of VSMCs. Furthermore, the results of the present study suggested that WWC3 may interact with LATS1 to promote the phosphorylation of YAP and reduce its nuclear translocation, upregulate the activity of the Hippo pathway, and suppress the proliferation and migration of VSMCs following injury.

cAMP attenuates angiotensin-II-induced Egr-1 expression via PKA-dependent signaling pathway in vascular smooth muscle cells

cAMP has been shown to inhibit vascular smooth muscle cell proliferation and exerts a vasculoprotective effect. An upregulation of the early growth response protein-1 (Egr-1) expression has been linked with the development of atherosclerosis and intimal hyperplasia. We have recently demonstrated that angiotensin-II (Ang-II) stimulates Egr-1 expression via Ca²⁺/ERK-mediated cAMP-response element binding protein (CREB) activation. However, whether Ang-II-induced signaling leading to Egr-1 expression is modulated by cAMP remains unexplored. Therefore, in the present studies, we have examined the effect of cAMP on Ang-II-induced expression of Egr-1 and associated signaling pathways. Isoproterenol (ISO) and forskolin (FSK) attenuated Ang-II-induced Egr-1 expression in a dose-dependent fashion. In addition, dibutyryl-cAMP and benzoyl-cAMP, as well as isobutylmethylxanthine, attenuated Ang-II-induced Egr-1 expression. Moreover, inhibition of Ang-II-induced Egr-1 expression was accompanied by an increase in the phosphorylation of the vasodilator-activated phosphoprotein (VASP), and this was associated with a concomitant decrease in ERK phosphorylation. Blockade of PKA using H89 decreased VASP phosphorylation, restored Ang-II-induced ERK phosphorylation, and abolished ISO- and FSK-mediated inhibition of Ang-II-induced Egr-1 expression. In summary, these results suggest that PKA-mediated suppression of Ang-II-induced Egr-1 expression and phosphorylation of ERK may be among the mechanisms by which cAMP exerts its vasculoprotective effects.

Src tyrosine kinase mediates endothelin-1-induced early growth response protein-1 expression via MAP kinase-dependent pathways in vascular smooth muscle cells

We have previously demonstrated that the non-receptor protein tyrosine kinase (NR-PTK) c-Src is an upstream regulator of endothelin-1 (ET-1) and angiotensin II-induced activation of protein kinase B (PKB) signaling in vascular smooth muscle cells (VSMCs). We have also demonstrated that ET-1 potently induces the expression of the early growth response protein-1 (Egr-1), a zinc finger transcription factor that is overexpressed in models of vascular diseases, such as atherosclerosis. However, the involvement of c-Src in ET-1‑induced Egr-1 expression has not yet been investigated and its role in mitogen-activated protein kinase (MAPK) signaling remains controversial. Therefore, the aim of the present study was to examine the role of c-Src in the ET-1-induced phosphorylation of extracellular signal-regulated kinase (ERK)1/2, c-Jun N-terminal kinase (JNK) and p38 MAPK, 3 key members of the MAPK family and in the regulation of Egr-1 expression in rat aortic A10 VSMCs. ET-1 rapidly induced the phosphorylation of MAPKs, as well as the expression of Egr-1; however, treatment of the VSMCs with PP2, a specific pharmacological inhibitor of c-Src, dose-dependently reduced the phosphorylation of the 3 MAPKs and the expression of Egr-1 induced by ET-1. Furthermore, in mouse embryonic fibroblasts (MEFs) deficient in c-Src (SYF), the ET-1-induced Egr-1 expression and MAPK phosphorylation were significantly suppressed, as compared to MEFs expressing normal Src levels. These results suggest that c-Src plays a critical role in mediating ET-1-induced MAPK phosphorylation and Egr-1 expression in VSMCs.

Early growth response-1 in the pathogenesis of cardiovascular disease

This article reviews the regulatory roles of the immediate-early gene product and prototypic zinc finger transcription factor, early growth response-1 in models of cardiovascular pathobiology, focusing on insights using microRNA, DNAzymes, small hairpin RNA, small interfering RNA, oligonucleotide decoy strategies and mice deficient in early growth response-1.