Smooth muscle alpha-actin CArG elements coordinate formation of a smooth muscle cell-selective, serum response factor-containing activation complex

Epigenetic Alteration of Smooth Muscle Cells Regulates Endothelin-Dependent Blood Pressure and Hypertensive Arterial Remodeling

Long-standing hypertension (HTN) affects multiple organ systems and leads to pathologic arterial remodeling, which is driven largely by smooth muscle cell (SMC) plasticity. Although genome wide association studies (GWAS) have identified numerous variants associated with changes in blood pressure in humans, only a small percentage of these variants actually cause HTN. In order to identify relevant genes important in SMC function in HTN, we screened three separate human GWAS and Mendelian randomization studies to identify SNPs located within non-coding gene regions, focusing on genes encoding epigenetic enzymes, as these have been recently identified to control SMC fate in cardiovascular disease. We identified SNPs rs62059712 and rs74480102 in the promoter of the human JMJD3 gene and show that the minor C allele increases JMJD3 transcription in SMCs via increased SP1 binding to the JMJD3 promoter. Using our novel SMC-specific Jmjd3-deficient murine model ( Jmjd3 flox/flox Myh11 CreERT ), we show that loss of Jmjd3 in SMCs results in HTN, mechanistically, due to decreased EDNRB expression and a compensatory increase in EDNRA expression. As a translational corollary, through single cell RNA-sequencing (scRNA-seq) of human arteries, we found strong correlation between JMJD3 and EDNRB expression in SMCs. Further, we identified that JMJD3 is required for SMC-specific gene expression, and loss of JMJD3 in SMCs in the setting of HTN results in increased arterial remodeling by promoting the SMC synthetic phenotype. Our findings link a HTN-associated human DNA variant with regulation of SMC plasticity, revealing therapeutic targets that may be used in the screening and/or personalized treatment of HTN.

mDia formins form hetero-oligomers and cooperatively maintain murine hematopoiesis

mDia formin proteins regulate the dynamics and organization of the cytoskeleton through their linear actin nucleation and polymerization activities. We previously showed that mDia1 deficiency leads to aberrant innate immune activation and induces myelodysplasia in a mouse model, and mDia2 regulates enucleation and cytokinesis of erythroblasts and the engraftment of hematopoietic stem and progenitor cells (HSPCs). However, whether and how mDia formins interplay and regulate hematopoiesis under physiological and stress conditions remains unknown. Here, we found that both mDia1 and mDia2 are required for HSPC regeneration under stress, such as serial plating, aging, and reconstitution after myeloid ablation. We showed that mDia1 and mDia2 form hetero-oligomers through the interactions between mDia1 GBD-DID and mDia2 DAD domains. Double knockout of mDia1 and mDia2 in hematopoietic cells synergistically impaired the filamentous actin network and serum response factor-involved transcriptional signaling, which led to declined HSPCs, severe anemia, and significant mortality in neonates and newborn mice. Our data demonstrate the potential roles of mDia hetero-oligomerization and their non-rodent functions in the regulation of HSPCs activity and orchestration of hematopoiesis.

Prdm6 drives ductus arteriosus closure by promoting ductus arteriosus smooth muscle cell identity and contractility

Based upon our demonstration that the smooth muscle cell-selective (SMC-selective) putative methyltransferase, Prdm6, interacts with myocardin-related transcription factor-A, we examined Prdm6's role in SMCs in vivo using cell type-specific knockout mouse models. Although SMC-specific depletion of Prdm6 in adult mice was well tolerated, Prdm6 depletion in Wnt1-expressing cells during development resulted in perinatal lethality and a completely penetrant patent ductus arteriosus (DA) phenotype. Lineage tracing experiments in Wnt1Cre2 Prdm6fl/fl ROSA26LacZ mice revealed normal neural crest-derived SMC investment of the outflow tract. In contrast, myography measurements on DA segments isolated from E18.5 embryos indicated that Prdm6 depletion significantly reduced DA tone and contractility. RNA-Seq analyses on DA and ascending aorta samples at E18.5 identified a DA-enriched gene program that included many SMC-selective contractile associated proteins that was downregulated by Prdm6 depletion. Chromatin immunoprecipitation-sequencing experiments in outflow tract SMCs demonstrated that 50% of the genes Prdm6 depletion altered contained Prdm6 binding sites. Finally, using several genome-wide data sets, we identified an SMC-selective enhancer within the Prdm6 third intron that exhibited allele-specific activity, providing evidence that rs17149944 may be the causal SNP for a cardiovascular disease GWAS locus identified within the human PRDM6 gene.

Positive supercoiling favors transcription elongation through lac repressor-mediated DNA loops

Some proteins, like the lac repressor (LacI), mediate long-range loops that alter DNA topology and create torsional barriers. During transcription, RNA polymerase generates supercoiling that may facilitate passage through such barriers. We monitored E. coli RNA polymerase progress along templates in conditions that prevented, or favored, 400 bp LacI-mediated DNA looping. Tethered particle motion measurements revealed that RNA polymerase paused longer at unlooped LacI obstacles or those barring entry to a loop than those barring exit from the loop. Enhanced dissociation of a LacI roadblock by the positive supercoiling generated ahead of a transcribing RNA polymerase within a torsion-constrained DNA loop may be responsible for this reduction in pause time. In support of this idea, RNA polymerase transcribed 6-fold more slowly through looped DNA and paused at LacI obstacles for 66% less time on positively supercoiled compared to relaxed templates, especially under increased tension (torque). Positive supercoiling propagating ahead of polymerase facilitated elongation along topologically complex, protein-coated templates.

Extreme Diversity of the Human Vascular Mesenchymal Cell Landscape

Background Human mesenchymal cells are culprit factors in vascular (patho)physiology and are hallmarked by phenotypic and functional heterogeneity. At present, they are subdivided by classic umbrella terms, such as "fibroblasts," "myofibroblasts," "smooth muscle cells," "fibrocytes," "mesangial cells," and "pericytes." However, a discriminative marker-based subclassification has to date not been established. Methods and Results As a first effort toward a classification scheme, a systematic literature search was performed to identify the most commonly used phenotypical and functional protein markers for characterizing and classifying vascular mesenchymal cell subpopulation(s). We next applied immunohistochemistry and immunofluorescence to inventory the expression pattern of identified markers on human aorta specimens representing early, intermediate, and end stages of human atherosclerotic disease. Included markers comprise markers for mesenchymal lineage (vimentin, FSP-1 [fibroblast-specific protein-1]/S100A4, cluster of differentiation (CD) 90/thymocyte differentiation antigen 1, and FAP [fibroblast activation protein]), contractile/non-contractile phenotype (α-smooth muscle actin, smooth muscle myosin heavy chain, and nonmuscle myosin heavy chain), and auxiliary contractile markers (h1-Calponin, h-Caldesmon, Desmin, SM22α [smooth muscle protein 22α], non-muscle myosin heavy chain, smooth muscle myosin heavy chain, Smoothelin-B, α-Tropomyosin, and Telokin) or adhesion proteins (Paxillin and Vinculin). Vimentin classified as the most inclusive lineage marker. Subset markers did not separate along classic lines of smooth muscle cell, myofibroblast, or fibroblast, but showed clear temporal and spatial diversity. Strong indications were found for presence of stem cells/Endothelial-to-Mesenchymal cell Transition and fibrocytes in specific aspects of the human atherosclerotic process. Conclusions This systematic evaluation shows a highly diverse and dynamic landscape for the human vascular mesenchymal cell population that is not captured by the classic nomenclature. Our observations stress the need for a consensus multiparameter subclass designation along the lines of the cluster of differentiation classification for leucocytes.

GRAF3 serves as a blood volume-sensitive rheostat to control smooth muscle contractility and blood pressure

Vascular resistance is a major determinant of BP and is controlled, in large part, by RhoA-dependent smooth muscle cell (SMC) contraction within small peripheral arterioles and previous studies from our lab indicate that GRAF3 is a critical regulator of RhoA in vascular SMC. The elevated contractile responses we observed in GRAF3 deficient vessels coupled with the hypertensive phenotype provided a mechanistic link for the hypertensive locus recently identified within the GRAF3 gene. On the basis of our previous findings that the RhoA signaling axis also controls SMC contractile gene expression and that GRAF3 expression was itself controlled by this pathway, we postulated that GRAF3 serves as an important counter-regulator of SMC phenotype. Indeed, our new findings presented herein indicate that GRAF3 expression acts as a pressure-sensitive rheostat to control vessel tone by both reducing calcium sensitivity and restraining expression of the SMC-specific contractile proteins that support this function. Collectively, these studies highlight the potential therapeutic value of GRAF3 in the control of human hypertension.

Druggable targets in the Rho pathway and their promise for therapeutic control of blood pressure

The prevalence of high blood pressure (also known as hypertension) has steadily increased over the last few decades. Known as a silent killer, hypertension increases the risk for cardiovascular disease and can lead to stroke, heart attack, kidney failure and associated sequela. While numerous hypertensive therapies are currently available, it is estimated that only half of medicated patients exhibit blood pressure control. This signifies the need for a better understanding of the underlying cause of disease and for more effective therapies. While blood pressure homeostasis is very complex and involves the integrated control of multiple body systems, smooth muscle contractility and arterial resistance are important contributors. Strong evidence from pre-clinical animal models and genome-wide association studies indicate that smooth muscle contraction and BP homeostasis are governed by the small GTPase RhoA and its downstream target, Rho kinase. In this review, we summarize the signaling pathways and regulators that impart tight spatial-temporal control of RhoA activity in smooth muscle cells and discuss current therapeutic strategies to target these RhoA pathway components. We also discuss known allelic variations in the RhoA pathway and consider how these polymorphisms may affect genetic risk for hypertension and its clinical manifestations.

An update on clonality: what smooth muscle cell type makes up the atherosclerotic plaque?

Almost 50 years ago, Earl Benditt and his son John described the clonality of the atherosclerotic plaque. This led Benditt to propose that the atherosclerotic lesion was a smooth muscle neoplasm, similar to the leiomyomata seen in the uterus of most women. Although the observation of clonality has been confirmed many times, interest in the idea that atherosclerosis might be a form of neoplasia waned because of the clinical success of treatments for hyperlipemia and because animal models have made great progress in understanding how lipid accumulates in the plaque and may lead to plaque rupture. Four advances have made it important to reconsider Benditt's observations. First, we now know that clonality is a property of normal tissue development. Second, this is even true in the vessel wall, where we now know that formation of clonal patches in that wall is part of the development of smooth muscle cells that make up the tunica media of arteries. Third, we know that the intima, the "soil" for development of the human atherosclerotic lesion, develops before the fatty lesions appear. Fourth, while the cells comprising this intima have been called "smooth muscle cells", we do not have a clear definition of cell type nor do we know if the initial accumulation is clonal. As a result, Benditt's hypothesis needs to be revisited in terms of changes in how we define smooth muscle cells and the quite distinct developmental origins of the cells that comprise the muscular coats of all arterial walls. Finally, since clonality of the lesions is real, the obvious questions are do these human tumors precede the development of atherosclerosis, how do the clones develop, what cell type gives rise to the clones, and in what ways do the clones provide the soil for development and natural history of atherosclerosis?

Nuclear PTEN functions as an essential regulator of SRF-dependent transcription to control smooth muscle differentiation

Vascular disease progression is associated with marked changes in vascular smooth muscle cell (SMC) phenotype and function. SMC contractile gene expression and, thus differentiation, is under direct transcriptional control by the transcription factor, serum response factor (SRF); however, the mechanisms dynamically regulating SMC phenotype are not fully defined. Here we report that the lipid and protein phosphatase, PTEN, has a novel role in the nucleus by functioning as an indispensible regulator with SRF to maintain the differentiated SM phenotype. PTEN interacts with the N-terminal domain of SRF and PTEN–SRF interaction promotes SRF binding to essential promoter elements in SM-specific genes. Factors inducing phenotypic switching promote loss of nuclear PTEN through nucleo-cytoplasmic translocation resulting in reduced myogenically active SRF, but enhanced SRF activity on target genes involved in proliferation. Overall decreased expression of PTEN was observed in intimal SMCs of human atherosclerotic lesions underlying the potential clinical importance of these findings.

The transcription factor, serum response factor, SRF regulates critical smooth muscle (SM) contractile gene expression but what else controls SM differentiation is unclear. Here, Horita et al. demonstrate that nuclear PTEN acts with SRF at the transcriptional level to maintain the differentiated SM phenotype.

Cellular and Molecular Mechanisms of Phenotypic Switch in Gastrointestinal Smooth Muscle

As a general rule, smooth muscle cells (SMC) are able to switch from a contractile phenotype to a less mature synthetic phenotype. This switch is accompanied by a loss of differentiation with decreased expression of contractile markers, increased proliferation as well as the synthesis and the release of several signaling molecules such as pro-inflammatory cytokines, chemotaxis-associated molecules, and growth factors. This SMC phenotypic plasticity has extensively been investigated in vascular diseases, but interest is also emerging in the field of gastroenterology. It has in fact been postulated that altered microenvironmental conditions, including the composition of microbiota, could trigger the remodeling of the enteric SMC, with phenotype changes and consequent alterations of contraction and impairment of gut motility. Several molecular actors participate in this phenotype remodeling. These include extracellular molecules such as cytokines and extracellular matrix proteins, as well as intracellular proteins, for example, transcription factors. Epigenetic control mechanisms and miRNA have also been suggested to participate. In this review key roles and actors of smooth muscle phenotypic switch, mainly in GI tissue, are described and discussed in the light of literature data available so far. J. Cell. Physiol. 231: 295-302, 2016. © 2015 Wiley Periodicals, Inc.

SMYD1, an SRF-Interacting Partner, Is Involved in Angiogenesis

Previous studies have demonstrated that Smyd1 plays a critical role in cardiomyocyte differentiation, cardiac morphogenesis and myofibril organization. In this study, we uncovered a novel function of Smyd1 in the regulation of endothelial cells (ECs). Our data showed that Smyd1 is expressed in vascular endothelial cells, and knockdown of SMYD1 in endothelial cells impairs EC migration and tube formation. Furthermore, Co-IP and GST pull-down assays demonstrated that SMYD1 is associated with the Serum Response Factor (SRF). EMSA assays further showed that SMYD1 forms a complex with SRF and enhances SRF DNA binding activity. Our studies indicate that SMYD1 serves as an SRF-interacting protein, enhances SRF DNA binding activity, and is required for EC migration and tube formation to regulate angiogenesis.

STAT3 Protein Regulates Vascular Smooth Muscle Cell Phenotypic Switch by Interaction with Myocardin

The JAK-STAT3 signaling pathway is one of the critical pathways regulating cell proliferation, differentiation, and apoptosis. Myocardin is regarded as a key mediator for the change of smooth muscle phenotypes. However, the relationship between STAT3 and myocardin in the vascular smooth muscle cell (VSMC) phenotypic switch has not been investigated. The goal of this study was to investigate the molecular mechanism by which STAT3 affects the myocardin-regulated VSMC phenotypic switch. Data presented in this study demonstrated that STAT3 was rapidly up-regulated after stimulation with VEGF. Inhibition of the STAT3 activation process impaired VSMC proliferation and enhanced the expression of VSMC contractile genes by increasing serum-response factor binding to the CArG-containing regions of VSMC-specific contractile genes. In contrast, the interaction between serum-response factor and its co-activator myocardin was reduced by overexpression of STAT3. In addition, treated VEGF inhibited the transcription activity of myocardin, and overexpression of STAT3 inhibited myocardin-induced up-regulation of VSMC contractile phenotype-specific genes. Although myocardin and STAT3 are negatively correlated, interestingly, both of them can enhance the expression of VEGF, suggesting a feedback loop to regulate the VSMC phenotypic switch. Taken together, these results indicate that the JAK-STAT3 signaling pathway plays a key role in controlling the phenotypic switch of VSMCs through the interactions between STAT3 and myocardin by various coordinated gene regulation pathways and feedback loops.

Modulation of human valve interstitial cell phenotype and function using a fibroblast growth factor 2 formulation

Valve interstitial cells (VICs) are fibroblastic in nature however in culture it is widely accepted that they differentiate into a myofibroblastic phenotype. This study assessed a fibroblast culture media formulation for its ability to maintain the phenotype and function of VICs as in the intact healthy valve. Normal human VICs were cultured separately in standard DMEM and in fibroblast media consisting of FGF2 (10ng/ml), insulin (50ng/ml) and 2% FCS for at least a week. Cell morphology, aspect ratio, size, levels and distribution of protein expression, proliferation, cell cycle, contraction and migration were assessed. Some VICs and some valve endothelial cells expressed FGF2 in valve tissue and this expression was increased in calcified valves. VICs in DMEM exhibited large, spread cells whereas VICs in fibroblast media were smaller, elongated and spindly. Aspect ratio and size were both significantly higher in DMEM (p<0.01). The level of expression of α-SMA was significantly reduced in fibroblast media at day 2 after isolation (p<0.01) and the expression of α-SMA, SM22 and EDA-fibronectin was significantly reduced in fibroblast media at days 7 and 12 post-isolation (p<0.01). Expression of cytoskeletal proteins, bone marker proteins and extracellular matrix proteins was reduced in fibroblast media. Proliferation of VICs in fibroblast media was significantly reduced at weeks 1 (p<0.05) and 2 (p<0.01). Collagen gel contraction was significantly reduced in fibroblast media (p<0.05). VICs were found to have significantly fewer and smaller focal adhesions in fibroblast media (p<0.01) with significantly fewer supermature focal adhesions in fibroblast media (p<0.001). Ultrastructurally, VICs in fibroblast media resembled native VICs from intact valves. VICs in fibroblast media demonstrated a slower migratory ability after wounding at 72 hours (p<0.01). Treatment of human VICs with this fibroblast media formulation has the ability to maintain and to dedifferentiate the VICs back to a fibroblastic phenotype with phenotypic and functional characteristics ascribed to cells in the intact valve. This methodology is fundamental in the study of normal valve biology, pathology and in the field of tissue engineering.

Antifibrotic effects of noscapine through activation of prostaglandin E2 receptors and protein kinase A

Myofibroblast differentiation is a key process in the pathogenesis of fibrotic disease. We have shown previously that differentiation of myofibroblasts is regulated by microtubule polymerization state. In this work, we examined the potential antifibrotic effects of the antitussive drug, noscapine, recently found to bind microtubules and affect microtubule dynamics. Noscapine inhibited TGF-β-induced differentiation of cultured human lung fibroblasts (HLFs). Therapeutic noscapine treatment resulted in a significant attenuation of pulmonary fibrosis in the bleomycin model of the disease. Noscapine did not affect gross microtubule content in HLFs, but inhibited TGF-β-induced stress fiber formation and activation of serum response factor without affecting Smad signaling. Furthermore, noscapine stimulated a rapid and profound activation of protein kinase A (PKA), which mediated the antifibrotic effect of noscapine in HLFs, as assessed with the PKA inhibitor, PKI. In contrast, noscapine did not activate PKA in human bronchial or alveolar epithelial cells. Finally, activation of PKA and the antifibrotic effect of noscapine in HLFs were blocked by the EP2 prostaglandin E2 receptor antagonist, PF-04418948, but not by the antagonists of EP4, prostaglandin D2, or prostacyclin receptors. Together, we demonstrate for the first time the antifibrotic effect of noscapine in vitro and in vivo, and we describe a novel mechanism of noscapine action through EP2 prostaglandin E2 receptor-mediated activation of PKA in pulmonary fibroblasts.

Myofibroblasts: trust your heart and let fate decide

Cardiac fibrosis is a substantial problem in managing multiple forms of heart disease. Fibrosis results from an unrestrained tissue repair process orchestrated predominantly by the myofibroblast. These are highly specialized cells characterized by their ability to secrete extracellular matrix (ECM) components and remodel tissue due to their contractile properties. This contractile activity of the myofibroblast is ascribed, in part, to the expression of smooth muscle α-actin (αSMA) and other tension-associated structural genes. Myofibroblasts are a newly generated cell type derived largely from residing mesenchymal cells in response to both mechanical and neurohumoral stimuli. Several cytokines, chemokines, and growth factors are induced in the injured heart, and in conjunction with elevated wall tension, specific signaling pathways and downstream effectors are mobilized to initiate myofibroblast differentiation. Here we will review the cell fates that contribute to the myofibroblast as well as nodal molecular signaling effectors that promote their differentiation and activity. We will discuss canonical versus non-canonical transforming growth factor-β (TGFβ), angiotensin II (AngII), endothelin-1 (ET-1), serum response factor (SRF), transient receptor potential (TRP) channels, mitogen-activated protein kinases (MAPKs) and mechanical signaling pathways that are required for myofibroblast transformation and fibrotic disease. This article is part of a Special Issue entitled "Myocyte-Fibroblast Signalling in Myocardium ".

Epigenetic regulation of vascular smooth muscle cell function in atherosclerosis

Epigenetics involve heritable and acquired changes in gene transcription that occur independently of the DNA sequence. Epigenetic mechanisms constitute a hierarchic upper-level of transcriptional control through complex modifications of chromosomal components and nuclear structures. These modifications include, for example, DNA methylation or post-translational modifications of core histones; they are mediated by various chromatin-modifying enzymes; and ultimately they define the accessibility of a transcriptional complex to its target DNA. Integrating epigenetic mechanisms into the pathophysiologic concept of complex and multifactorial diseases such as atherosclerosis may significantly enhance our understanding of related mechanisms and provide promising therapeutic approaches. Although still in its infancy, intriguing scientific progress has begun to elucidate the role of epigenetic mechanisms in vascular biology, particularly in the control of smooth muscle cell phenotypes. In this review, we will summarize epigenetic pathways in smooth muscle cells, focusing on mechanisms involved in the regulation of vascular remodeling.

A robust and sensitive synthetic sensor to monitor the transcriptional output of the cytokinin signaling network in planta

Cytokinins are classic plant hormones that orchestrate plant growth, development, and physiology. They affect gene expression in target cells by activating a multistep phosphorelay network. Type-B response regulators, acting as transcriptional activators, mediate the final step in the signaling cascade. Previously, we have introduced a synthetic reporter, Two Component signaling Sensor (TCS)::green fluorescent protein (GFP), which reflects the transcriptional activity of type-B response regulators. TCS::GFP was instrumental in uncovering roles of cytokinin and deepening our understanding of existing functions. However, TCS-mediated expression of reporters is weak in some developmental contexts where cytokinin signaling has a documented role, such as in the shoot apical meristem or in the vasculature of Arabidopsis (Arabidopsis thaliana). We also observed that GFP expression becomes rapidly silenced in TCS::GFP transgenic plants. Here, we present an improved version of the reporter, TCS new (TCSn), which, compared with TCS, is more sensitive to phosphorelay signaling in Arabidopsis and maize (Zea mays) cellular assays while retaining its specificity. Transgenic Arabidopsis TCSn::GFP plants exhibit strong and dynamic GFP expression patterns consistent with known cytokinin functions. In addition, GFP expression has been stable over generations, allowing for crosses with different genetic backgrounds. Thus, TCSn represents a significant improvement to report the transcriptional output profile of phosphorelay signaling networks in Arabidopsis, maize, and likely other plants that display common response regulator DNA-binding specificities.

Characterization and role of SCAI during renal fibrosis and epithelial-to-mesenchymal transition

During progressive tubulointerstitial fibrosis, renal tubular epithelial cells transform into α-smooth muscle actin (SMA)-expressing myofibroblasts via epithelial-to-mesenchymal transition (EMT). SMA expression is regulated by transforming growth factor (TGF)-β1 and cell contact disruption, through signaling events targeting the serum response factor-myocardin-related transcription factor (MRTF) complex. MRTFs are important regulators of fibrosis, tumor cell invasion, and metastasis. Consistent with the role of MRTFs in tumor progression, suppressor of cancer cell invasion (SCAI) was recently identified as a negative regulator of MRTF. Herein, we studied the role of SCAI in a fibrotic EMT model established on LLC-PK1 cells. SCAI overexpression prevented SMA promoter activation induced by TGF-β1. When co-expressed, it inhibited the stimulatory effects of MRTF-A, MRTF-B or the constitutive active forms of RhoA, Rac1, or Cdc42 on the SMA promoter. SCAI interfered with TGF-β1-induced SMA, connective tissue growth factor, and calponin protein expression; it rescued TGF-β1-induced E-cadherin down-regulation. IHC studies on human kidneys showed that SCAI expression is reduced during fibrosis. Kidneys of diabetic rats and mice with unilateral ureteral obstruction depicted significant loss of SCAI expression. In parallel with the decrease of SCAI protein expression, diabetic rat and mouse kidneys with unilateral ureteral obstruction showed SMA expression, as evidenced by using Western blot analysis. Finally, TGF-β1 treatment of LLC-PK1 cells attenuated SCAI protein expression. These data suggest that SCAI is a novel transcriptional cofactor that regulates EMT and renal fibrosis.

Smooth muscle cell phenotypic switching in atherosclerosis

Smooth muscle cells (SMCs) possess remarkable phenotypic plasticity that allows rapid adaptation to fluctuating environmental cues, including during development and progression of vascular diseases such as atherosclerosis. Although much is known regarding factors and mechanisms that control SMC phenotypic plasticity in cultured cells, our knowledge of the mechanisms controlling SMC phenotypic switching in vivo is far from complete. Indeed, the lack of definitive SMC lineage-tracing studies in the context of atherosclerosis, and difficulties in identifying phenotypically modulated SMCs within lesions that have down-regulated typical SMC marker genes, and/or activated expression of markers of alternative cell types including macrophages, raise major questions regarding the contributions of SMCs at all stages of atherogenesis. The goal of this review is to rigorously evaluate the current state of our knowledge regarding possible phenotypes exhibited by SMCs within atherosclerotic lesions and the factors and mechanisms that may control these phenotypic transitions.

Enhancement of mDia2 activity by Rho-kinase-dependent phosphorylation of the diaphanous autoregulatory domain

It is clear that RhoA activates the DRF (diaphanous-related formin) mDia2 by disrupting the molecular interaction between the DAD (diaphanous autoregulatory domain) and the DID (diaphanous inhibitory domain). Previous studies indicate that a basic motif within the DAD contributes to mDia2 auto-inhibition, and results shown in the present study suggest these residues bind a conserved acidic region within the DID. Furthermore, we demonstrate that mDia2 is phosphorylated by ROCK (Rho-kinase) at two conserved residues (Thr(1061) and Ser(1070)) just C-terminal to the DAD basic region. Phosphomimetic mutations to these residues in the context of the full-length molecule enhanced mDia2 activity as measured by increased actin polymerization, SRF (serum response factor)-dependent smooth muscle-specific gene transcription, and nuclear localization of myocardin-related transcription factor B. Biochemical and functional data indicate that the T1061E/S1070E mutation significantly inhibited the ability of DAD to interact with DID and enhanced mDia2 activation by RhoA. Taken together, the results of the present study indicate that ROCK-dependent phosphorylation of the mDia2 DAD is an important determinant of mDia2 activity and that this signalling mechanism affects actin polymerization and smooth muscle cell-specific gene expression.

Epigenetic control of smooth muscle cell differentiation and phenotypic switching in vascular development and disease

The vascular smooth muscle cell (SMC) in adult animals is a highly specialized cell whose principal function is contraction. However, this cell displays remarkable plasticity and can undergo profound changes in phenotype during repair of vascular injury, during remodeling in response to altered blood flow, or in various disease states. There has been extensive progress in recent years in our understanding of the complex mechanisms that control SMC differentiation and phenotypic plasticity, including the demonstration that epigenetic mechanisms play a critical role. In addition, recent evidence indicates that SMC phenotypic switching in adult animals involves the reactivation of embryonic stem cell pluripotency genes and that mesenchymal stem cells may be derived from SMC and/or pericytes. This review summarizes the current state of our knowledge in this field and identifies some of the key unresolved challenges and questions that we feel require further study.

Myocardin-related transcription factors A and B are key regulators of TGF-β1-induced fibroblast to myofibroblast differentiation

Myofibroblasts are contractile, smooth muscle-like cells that are characterized by the de novo expression of smooth muscle α-actin (SMαA) and normally function to assist in wound closure, but have been implicated in pathological contractures. Transforming growth factor β-1 (TGF-β1) helps facilitate the differentiation of fibroblasts into myofibroblasts, but the exact mechanism by which this differentiation occurs, in response to TGF-β1, remains unclear. Myocardin-related transcription factors A and B (MRTFs, MRTF-A/B) are transcriptional co-activators that regulate the expression of smooth muscle-specific cytoskeletal proteins, including SMαA, in smooth muscle cells and fibroblasts. In this study, we demonstrate that TGF-β1 mediates myofibroblast differentiation and the expression of a contractile gene program through the actions of the MRTFs. Transient transfection of a constitutively active MRTF-A induced an increase in the expression of SMαA and other smooth muscle-specific cytoskeletal proteins, and an increase in myofibroblast contractility, even in the absence of TGF-β1. MRTF-A/B knockdown, in TGF-β1-differentiated myofibroblasts, resulted in decreased smooth muscle-specific cytoskeletal protein expression levels and reduced contractile force generation, as well as a decrease in focal adhesion size and number. These results provide direct evidence that the MRTFs are mediators of myofibroblast differentiation in response to TGF-β1.

Weak up-regulation of serum response factor in gastric ulcers in patients with co-morbidities is associated with increased risk of recurrent bleeding

Background

Serum response factor (SRF) is crucial for gastric ulcer healing process. The study determined if gastric ulcer tissues up-regulate SRF and if such up-regulation correlated with co-morbidities and the risk of recurrent bleeding.

Methods

Ulcer and non-ulcer tissues were obtained from 142 patients with active gastric ulcers for SRF expression assessed by immunohistochemistry. Based on the degree of SRF expression between these two tissue types, SRF up-regulation was classified as strong, intermediate, and weak patterns. The patients were followed-up to determine if SRF up-regulation correlated to recurrent bleeding.

Results

Gastric ulcer tissues had higher SRF expression than non-ulcer tissues (p < 0.05). Patients with strong SRF up-regulation had lower rates of stigmata of recent hemorrhage (SRH) on the ulcer base than the others (p < 0.05). Multivariate logistic regression confirmed that co-morbidities and weak SRF up-regulation were two independent factors of recurrent gastric ulcer bleeding (p < 0.05). Combining both factors, there was an 8.29-fold (95% CI, 1.31~52.62; p = 0.03) higher risk of recurrent gastric ulcer bleeding.

Conclusions

SRF expression is higher in gastric ulcer tissues than in non-ulcer tissues. Weak SRF up-regulation, combined with the presence of co-morbidities, increase the risk of the recurrent gastric ulcer bleeding.

Formin homology domain-containing protein 1 regulates smooth muscle cell phenotype

OBJECTIVE

Our goal was to test whether formin homology protein 1 (FHOD1) plays a significant role in the regulation of smooth muscle cell (SMC) differentiation and, if so, whether Rho kinase (ROCK)-dependent phosphorylation in the diaphanous autoinhibitory domain is an important signaling mechanism that controls FHOD1 activity in SMC.

METHODS AND RESULTS

FHOD1 is highly expressed in aortic SMCs and in tissues with a significant SMC component. Exogenous expression of constitutively active FHOD1, but not wild-type, strongly activated SMC-specific gene expression in 10T1/2 cells. Treatment of SMC with the RhoA activator sphingosine-1-phosphate increased FHOD1 phosphorylation at Thr1141, and this effect was completely prevented by inhibition of ROCK with Y-27632. Phosphomimetic mutations to ROCK target residues enhanced FHOD1 activity, suggesting that phosphorylation interferes with FHOD1 autoinhibition. Importantly, knockdown of FHOD1 in SMC strongly inhibited sphingosine-1-phosphate-dependent increases in SMC differentiation marker gene expression and actin polymerization, suggesting that FHOD1 plays a major role in RhoA-dependent signaling in SMC.

CONCLUSIONS

Our results indicate that FHOD1 is a critical regulator of SMC phenotype and is regulated by ROCK-dependent phosphorylation. Thus, additional studies on the role of FHOD1 during development and the progression of cardiovascular disease will be important.

Epigenetics in atherosclerosis and inflammation

Atherosclerosis is a multifactorial disease with a severe burden on western society. Recent insights into the pathogenesis of atherosclerosis underscore the importance of chronic inflammation in both the initiation and progression of vascular remodelling. Expression of immunoregulatory molecules by vascular wall components within the atherosclerotic lesions is accordingly thought to contribute to the ongoing inflammatory process. Besides gene regulatory proteins (transcription factors), epigenetic mechanisms also play an essential and fundamental role in the transcriptional control of gene expression. These epigenetic mechanisms change the accessibility of chromatin by DNA methylation and histone modifications. Epigenetic modulators are thus critically involved in the regulation of vascular, immune and tissue-specific gene expression within the atherosclerotic lesion. Importantly, epigenetic processes are reversible and may provide an excellent therapeutic target. The concept of epigenetic regulation is gradually being recognized as an important factor in the pathogenesis of atherosclerosis. Recent research provides an essential link between inflammation and reprogramming of the epigenome. In this review we therefore discuss the basis of epigenetic regulation – and the contribution thereof in the regulation of inflammatory processes in general and during atherosclerosis in particular. Moreover we highlight potential therapeutic interventions based on epigenetic mechanisms.

SMYD1, the myogenic activator, is a direct target of serum response factor and myogenin

SMYD1 is a heart and muscle specific SET-MYND domain containing protein, which functions as a histone methyltransferase and regulates downstream gene transcription. We demonstrated that the expression of SMYD1 is restricted in the heart and skeletal muscle tissues in human. To reveal the regulatory mechanisms of SMYD1 expression during myogenesis and cardiogenesis, we cloned and characterized the human SMYD1 promoter, which contains highly conserved serum response factor (SRF) and myogenin binding sites. Overexpression of SRF and myogenin significantly increased the endogenous expression level of Smyd1 in C2C12 cells, respectively. Deletion of Srf in the heart of mouse embryos dramatically decreased the expression level of Smyd1 mRNA and the expression of Smyd1 can be rescued by exogenous SRF introduction in SRF null ES cells during differentiation. Furthermore, we demonstrated that SRF binds to the CArG site and myogenin binds to the E-box element on Smyd1 promoter region using EMSA and ChIP assays. Moreover, forced expression of SMYD1 accelerates myoblast differentiation and myotube formation in C2C12 cells. Taken together, these studies demonstrated that SMYD1 is a key regulator of myogenic differentiation and acts as a downstream target of muscle regulatory factors, SRF and myogenin.

Characteristics of the CArG-SRF binding context in mammalian genomes

Serum response factor (SRF), a member of the MADS family, binds a 10-bp cis element known as the CArG box. However, despite our extensive knowledge of SRF and the CArG box, limited information is available on the CArG-SRF binding context or how CArG flanking sequences are defined. We used statistical tests and computer simulation to find characteristics of the CArG-SRF binding context. Based on the combination of published literature and a search of DBTSS, 150 and 136 functional CArG boxes together with 10 bp flanking on each side were found in mouse and human genomes, respectively. By statistical analysis of the 30 positions we found some new conserved positions of interest (P < 0.005) such as -15, -8, and +8, in addition to the ten highly conserved positions of the CArG box. Intriguingly, studies comparing the flanking positions between consensus CArG boxes and CArG-like boxes showed that there are more conserved positions in the latter. Moreover, CpG content within the CArG-SRF binding context is much higher than that within introns. Collectively, these results suggest that there are some special pre-existing features in the flanking sequences of functional CArG boxes probably contributing to SRF selectively recognizing and binding to the functional CArG from millions of functionless CArG boxes in mammalian genomes. This is a significant step toward understanding the mechanism of transcriptional regulation of SRF-dependent genes.

PKA-dependent phosphorylation of serum response factor inhibits smooth muscle-specific gene expression

OBJECTIVE

Our goal was to identify phosphorylation sites that regulate serum response factor (SRF) activity to gain a better understanding of the signaling mechanisms that regulate SRF's involvement in smooth muscle cell (SMC)-specific and early response gene expression.

METHODS AND RESULTS

By screening phosphorylation-deficient and mimetic mutations in SRF(-/-) embryonic stem cells, we identified T159 as a phosphorylation site that significantly inhibits SMC-specific gene expression in an embryonic stem cell model of SMC differentiation. This residue conforms to a highly conserved consensus cAMP-dependent protein kinase (PKA) site, and in vitro and in vivo labeling studies demonstrated that it was phosphorylated by PKA. Results from gel shift and chromatin immunoprecipitation assays demonstrated that T159 phosphorylation inhibited SRF binding to SMC-specific CArG elements. Interestingly, the myocardin factors could at least partially rescue the effects of the T159D mutation under some conditions, but this response was promoter specific. Finally, PKA signaling had much less of an effect on c-fos promoter activity and SRF binding to the c-fos CArG.

CONCLUSIONS

Our results indicate that phosphorylation of SRF by PKA inhibits SMC-specific transcription suggesting a novel signaling mechanism for the control of SMC phenotype.

Targeting myofibroblasts in model systems of fibrosis by an artificial alpha-smooth muscle-actin promoter hybrid

Myofibroblasts are the main cell types producing extracellular matrix proteins in a variety of fibrotic diseases. Therefore, they are useful targets for studies of intracellular communication and gene therapeutical approaches in scarring diseases. An artificial promoter containing the -702 bp regulatory sequence of the alpha-smooth muscle actin (SMA) gene linked to the first intron enhancer sequence of the beta-actin gene and the beta-globin intron-exon junction was constructed and tested for myofibroblast-dependent gene expression using the green fluorescent protein as a reporter. Reporter expression revealed myofibroblast-specific function in hepatic and renal myofibroblasts, in vitro. In addition, differentiation-dependent activation of the SMA-beta-actin promoter hybrid was shown after induction of myofibroblastic features in mesangial cells by stretching treatment. Furthermore, wound healing experiments with SMA-beta-actin promoter reporter mice demonstrated myofibroblast-specific action, in vivo. In conclusion, the -702 bp regulatory region of the SMA promoter linked to enhancing beta-actin and beta-globin sequences benefits from its small size and is suggested as a promising tool to target myofibroblasts as the crucial cell type in various scarring processes.

Inhibition of transforming growth factor beta signaling by halofuginone as a modality for pancreas fibrosis prevention

OBJECTIVES

Chronic pancreatitis is characterized by inflammation and fibrosis. We evaluated the efficacy of halofuginone, an inhibitor of collagen synthesis and myofibroblast activation, in preventing cerulein-induced pancreas fibrosis.

METHODS

Collagen synthesis was evaluated by in situ hybridization and staining. Levels of prolyl 4-hydroxylase beta (P4Hbeta), cytoglobin/stellate cell activation-associated protein (Cygb/STAP), transgelin, tissue inhibitors of metalloproteinases, serum response factor, transforming growth factor beta (TGFbeta), Smad3, and pancreatitis-associated protein 1 (PAP-1) were determined by immunohistochemistry. Metalloproteinase activity was evaluated by zymography.

RESULTS

Halofuginone prevented cerulein-dependent increase in collagen synthesis, collagen cross-linking enzyme P4Hbeta, Cygb/STAP, and tissue inhibitors of metalloproteinase 2. Halofuginone did not affect TGFbeta levels in cerulein-treated mice but inhibited serum response factor synthesis and Smad3 phosphorylation. In culture, halofuginone inhibited pancreatic stellate cell (PSC) proliferation and TGFbeta-dependent increase in Cygb/STAP and transgelin synthesis and metalloproteinase 2 activity. Halofuginone increased c-Jun N-terminal kinase phosphorylation in PSCs derived from cerulein-treated mice. Halofuginone prevented the increase in acinar cell proliferation and further increased the cerulein-dependent PAP-1 synthesis.

CONCLUSIONS

Halofuginone inhibits Smad3 phosphorylation and increases c-Jun N-terminal kinase phosphorylation, leading to the inhibition of PSC activation and consequent prevention of fibrosis. Halofuginone increased the synthesis of PAP-1, which further reduces pancreas fibrosis. Thus, halofuginone might serve as a novel therapy for pancreas fibrosis.

Kruppel-like factor 4, Elk-1, and histone deacetylases cooperatively suppress smooth muscle cell differentiation markers in response to oxidized phospholipids

Phenotypic switching of vascular smooth muscle cells (SMCs), such as increased proliferation, enhanced migration, and downregulation of SMC differentiation marker genes, is known to play a key role in the development of atherosclerosis. However, the factors and mechanisms controlling this process are not fully understood. We recently showed that oxidized phospholipids, including 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC), which accumulate in atherosclerotic lesions, are potent repressors of expression of SMC differentiation marker genes in cultured SMCs as well as in rat carotid arteries in vivo. Here, we examined the molecular mechanisms whereby POVPC induces suppression of SMC differentiation marker genes in cultured SMCs. Results showed that POVPC induced phosphorylation of ERK1/2 and Elk-1. The MEK inhibitors U-0126 and PD-98059 attenuated POVPC-induced suppression of smooth muscle (SM) alpha-actin and SM-myosin heavy chain. POVPC also induced expression of Krüppel-like factor 4 (Klf4). Chromatin immunoprecipitation assays revealed that POVPC caused simultaneous binding of Elk-1 and Klf4 to the promoter region of the SM alpha-actin gene. Moreover, coimmunoprecipitation assays showed a physical interaction between Elk-1 and Klf4. Results in Klf4-null SMCs showed that blockade of both Klf4 induction and Elk-1 phosphorylation completely abolished POVPC-induced suppression of SMC differentiation marker genes. POVPC-induced suppression of SMC differentiation marker genes was also accompanied by hypoacetylation of histone H4 at the SM alpha-actin promoter, which was mediated by the recruitment of histone deacetylases (HDACs), HDAC2 and HDAC5. Coimmunoprecipitation assays showed that Klf4 interacted with HDAC5. Results provide evidence that Klf4, Elk-1, and HDACs coordinately mediate POVPC-induced suppression of SMC differentiation marker genes.

MKL1 mediates TGF-β1-induced α-smooth muscle actin expression in human renal epithelial cells

Transforming growth factor-β1 (TGF-β1) is known to induce epithelial-mesenchymal transition in the kidney, a process involved in tubulointerstitial fibrosis. We hypothesized that a coactivator of the serum response factor (SRF), megakaryoblastic leukemia factor-1 (MKL1), stimulates α-smooth muscle actin (α-SMA) transcription in primary cultures of renal tubular epithelial cells (RTC), which convert into myofibroblasts on treatment with TGF-β1. Herein, we study the effect of MKL1 expression on α-SMA in these cells. We demonstrate that TGF-β1 stimulation of α-SMA transcription is mediated through CC(A/T)6-rich GG elements known to bind to SRF. These elements also mediate the MKL1 effect that dramatically activates α-SMA transcription in serum-free media. MKL1 fused to green fluorescent protein localizes to the nucleus and induces α-SMA expression regardless of treatment with TGF-β1. Using proteasome inhibitors, we also demonstrate that the proteolytic ubiquitin pathway regulates MKL1 expression. These data indicate that MKL1 overexpression is sufficient to induce α-SMA expression. Inhibition of endogenous expression of MKL1 by small interfering RNA abolishes TGF-β1 stimulation of α-SMA expression. Therefore, MKL1 is also absolutely required for TGF-β1 stimulation of α-SMA expression. Western blot and immunofluorescence analysis show that overexpressed and endogenous MKL1 are located in the nucleus in non-stimulated RTC. Chromatin immunoprecipitation assay demonstrates that TGF-β1 induces binding of endogenous SRF and MKL1 to the α-SMA promoter in chromatin. Since MKL1 constitutes a potent factor regulating α-SMA expression, modulation of endogenous MKL1 expression or activity may have a profound effect on myofibroblast formation and function in the kidney.

HeliCis: a DNA motif discovery tool for colocalized motif pairs with periodic spacing

Background

Correct temporal and spatial gene expression during metazoan development relies on combinatorial interactions between different transcription factors. As a consequence, cis-regulatory elements often colocalize in clusters termed cis-regulatory modules. These may have requirements on organizational features such as spacing, order and helical phasing (periodic spacing) between binding sites. Due to the turning of the DNA helix, a small modification of the distance between a pair of sites may sometimes drastically disrupt function, while insertion of a full helical turn of DNA (10–11 bp) between cis elements may cause functionality to be restored. Recently, de novo motif discovery methods which incorporate organizational properties such as colocalization and order preferences have been developed, but there are no tools which incorporate periodic spacing into the model.

Results

We have developed a web based motif discovery tool, HeliCis, which features a flexible model which allows de novo detection of motifs with periodic spacing. Depending on the parameter settings it may also be used for discovering colocalized motifs without periodicity or motifs separated by a fixed gap of known or unknown length. We show on simulated data that it can efficiently capture the synergistic effects of colocalization and periodic spacing to improve detection of weak DNA motifs. It provides a simple to use web interface which interactively visualizes the current settings and thereby makes it easy to understand the parameters and the model structure.

Conclusion

HeliCis provides simple and efficient de novo discovery of colocalized DNA motif pairs, with or without periodic spacing. Our evaluations show that it can detect weak periodic patterns which are not easily discovered using a sequential approach, i.e. first finding the binding sites and second analyzing the properties of their pairwise distances.

Identification of a novel role of ZIC3 in regulating cardiac development

Mutations in ZIC3 cause X-linked heterotaxy, a disorder characterized by abnormal lateralization of normally asymmetric thoracic and abdominal organs. Animal models demonstrate an early role for ZIC3 in embryonic left-right (LR) patterning. ZIC3 mutations have also been described in patients with isolated cardiovascular malformations. We wished to address the hypothesis that ZIC3 has plieotropic effects in development and may regulate cardiac development independent of its role in LR patterning. We observed significantly reduced expression of several markers of cardiac lineage commitment in Zic3(null/y) embryonic stem cells including atrial natriuretic factor (ANF), Nkx2.5 and Tbx5. Likewise, ANF expression-a molecular marker of trabecular myocardium and a direct target of multiple cardiac-specific transcription factors-was severely reduced in E9.5 Zic3 null hearts. Trabecular myocardium was reduced in these embryos. This finding was similar to that observed in embryos with cardiac-specific ablation of serum response factor (SRF), a direct transcriptional regulator of ANF expression. While ZIC3 by itself had no effect on the ANF promoter, it could bind to and inhibit a cardiac alpha-actin promoter through its zinc finger domains. We observed that ZIC3 could function as a coactivator of SRF on both cardiac alpha-actin and ANF promoters. The zinc fingers of ZIC3 and the mcm1, agamous deficiens SRF (MADS) box motif of SRF were found to mediate their physical and functional interactions. These findings reveal a novel role of ZIC3 in regulating cardiac gene expression and may explain, in part, the association of ZIC3 mutation with cardiovascular malformations.

Smooth muscle cell-specific transcription is regulated by nuclear localization of the myocardin-related transcription factors

On the basis of our previous studies on RhoA signaling in smooth muscle cells (SMC), we hypothesized that RhoA-mediated nuclear translocalization of the myocardin-related transcription factors (MRTFs) was important for regulating SMC phenotype. MRTF-A protein and MRTF-B message were detected in aortic SMC and in many adult mouse organs that contain a large SMC component. Both MRTFs upregulated SMC-specific promoter activity as well as endogenous SM22α expression in multipotential 10T1/2 cells, although to a lesser extent than myocardin. We used enhanced green fluorescent protein (EGFP) fusion proteins to demonstrate that the myocardin factors have dramatically different localization patterns and that the stimulation of SMC-specific transcription by certain RhoA-dependent agonists was likely mediated by increased nuclear translocation of the MRTFs. Importantly, a dominant-negative form of MRTF-A (ΔB1/B2) that traps endogenous MRTFs in the cytoplasm inhibited the SM α-actin, SM22α, and SM myosin heavy chain promoters in SMC and attenuated the effects of sphingosine 1-phosphate and transforming growth factor (TGF)-β on SMC-specific transcription. Our data confirmed the importance of the NH2-terminal RPEL domains for regulating MRTF localization, but our analysis of MRTF-A/myocardin chimeras and myocardin RPEL2 mutations indicated that the myocardin B1/B2 region can override this signal. Gel shift assays demonstrated that myocardin factor activity correlated well with ternary complex formation at the SM α-actin CArGs and that MRTF-serum response factor interactions were partially dependent on CArG sequence. Taken together, our results indicate that the MRTFs regulate SMC-specific gene expression in at least some SMC subtypes and that regulation of MRTF nuclear localization may be important for the effects of selected agonists on SMC phenotype.

Cell contact-dependent regulation of epithelial-myofibroblast transition via the rho-rho kinase-phospho-myosin pathway

Epithelial-mesenchymal-myofibroblast transition (EMT), a key feature in organ fibrosis, is regulated by the state of intercellular contacts. Our recent studies have shown that an initial injury of cell-cell junctions is a prerequisite for transforming growth factor-beta1 (TGF-beta1)-induced transdifferentiation of kidney tubular cells into alpha-smooth muscle actin (SMA)-expressing myofibroblasts. Here we analyzed the underlying contact-dependent mechanisms. Ca(2+) removal-induced disruption of intercellular junctions provoked Rho/Rho kinase (ROK)-mediated myosin light chain (MLC) phosphorylation and Rho/ROK-dependent SMA promoter activation. Importantly, myosin-based contractility itself played a causal role, because the myosin ATPase inhibitor blebbistatin or a nonphosphorylatable, dominant negative MLC (DN-MLC) abolished the contact disruption-triggered SMA promoter activation, eliminated the synergy between contact injury and TGF-beta1, and suppressed SMA expression. To explore the responsible mechanisms, we investigated the localization of the main SMA-inducing transcription factors, serum response factor (SRF), and its coactivator myocardin-related transcription factor (MRTF). Contact injury enhanced nuclear accumulation of SRF and MRTF. These processes were inhibited by DN-Rho or DN-MLC. TGF-beta1 strongly facilitated nuclear accumulation of MRTF in cells with reduced contacts but not in intact epithelia. DN-myocardin abrogated the Ca(2+)-removal- +/- TGF-beta1-induced promoter activation. These studies define a new mechanism whereby cell contacts regulate epithelial-myofibroblast transition via Rho-ROK-phospho-MLC-dependent nuclear accumulation of MRTF.

Selective inhibition of vascular smooth muscle cell proliferation by coptisine isolated from Coptis rhizoma, one of the crude drugs composing Kampo medicines Unsei-in

Acceleration of vascular smooth muscle cell (VSMC) proliferation is closely linked to the pathogenesis of vascular diseases. We, therefore, focused on traditional Japanese herbal medicines (Kampo medicines) used to ameliorate the impairment of microcirculation or blood stasis and screened them for their ability to inhibit rat VSMC proliferation. Among them, Unsei-in was found to effectively suppress VSMC proliferation, and Coptis rhizome was the responsible constituent crude drug. The extract of Coptis rhizome inhibited VSMC proliferation with the GI(50) value of 4.4 microg/ml, which was much lower than those against the proliferation of 3Y1, dRLh-84, B16, and HeLa cells. The Coptis rhizome extract inhibited the progression of VSMC arrested at G(0)/G(1) phase from G(0)/G(1) to S phase, but not that of 3Y1 cells. Biological assay-guided fractionation revealed that an alkaloid of Coptis rhizome, coptisine, was the active ingredient in selectively preventing VSMC proliferation with GI(50) of 3.3 microM (1.2 microg/ml). When the structurally-related isoquinoline alkaloids of protoberberine class were studied for their inhibitory activities, berberine decreased the VSMC proliferation with GI(50) of 95.1 microM (35.4 microg/ml), about 30 times higher concentration than coptisine, while palmatine failed to show any activity. This study provides evidence that coptisine, an ingredient of Unsei-in, prevents VSMC proliferation selectively at lower concentrations compared with various cells or other structurally related alkaloids.

Control of SRF binding to CArG box chromatin regulates smooth muscle gene expression in vivo

Precise control of SMC transcription plays a major role in vascular development and pathophysiology. Serum response factor (SRF) controls SMC gene transcription via binding to CArG box DNA sequences found within genes that exhibit SMC-restricted expression. However, the mechanisms that regulate SRF association with CArG box DNA within native chromatin of these genes are unknown. Here we report that SMC-restricted binding of SRF to murine SMC gene CArG box chromatin is associated with patterns of posttranslational histone modifications within this chromatin that are specific to the SMC lineage in culture and in vivo, including methylation and acetylation to histone H3 and H4 residues. We found that the promyogenic SRF coactivator myocardin increased SRF association with methylated histones and CArG box chromatin during activation of SMC gene expression. In contrast, the myogenic repressor Kruppel-like factor 4 recruited histone H4 deacetylase activity to SMC genes and blocked SRF association with methylated histones and CArG box chromatin during repression of SMC gene expression. Finally, we observed deacetylation of histone H4 coupled with loss of SRF binding during suppression of SMC differentiation in response to vascular injury. Taken together, these findings provide novel evidence that SMC-selective epigenetic control of SRF binding to chromatin plays a key role in regulation of SMC gene expression in response to pathophysiological stimuli in vivo.

Organization and developmental expression of an amphibian vascular smooth muscle alpha-actin gene

A gene encoding a putative homologue of the avian and mammalian vascular smooth muscle alpha-actin was isolated from an amphibian, Rana catesbeiana, and characterized in terms of its sequence, organization, and expression pattern. To assess the expression of this gene during amphibian embryonic development, a cDNA encoding the Xenopus homologue of this mRNA was isolated and characterized by in situ hybridization. The expression of this gene was not detected in the enteric smooth muscle cells or, unlike its avian and mammalian homologues, in the somites/skeletal muscle of the Xenopus embryos/tadpoles. Its initial expression coincides with the onset of cardiac muscle differentiation and is coincidental with the expression of the cardiac alpha-actin mRNAs in the heart-forming region of the stage 26/27 embryo. As development proceeds, transcripts from this gene are expressed throughout the developing heart until the formation of the heart chambers is completed and, thereafter, its expression becomes restricted to the outflow tract of the tadpole heart. The subsequent restricted expression of this gene to the vascular system in both of these amphibians identifies it as the amphibian homologue of the avian and mammalian vascular smooth muscle alpha-actin.

Double blockade of cell cycle progression by coptisine in vascular smooth muscle cells

Coptisine, an isoquinoline alkaloid isolated from rhizome of Coptis japonica, inhibits proliferation of vascular smooth muscle cells (VSMCs). The aim of this study was to evaluate the action of coptisine, along with berberine (a structurally similar isoquinoline alkaloid), on progression of the cell cycle in VSMCs. Coptisine displayed antiproliferative action against VSMCs by blocking the cell cycle at G(1) and G(2)/M phases. The G(1) block was shown by inhibition of [(3)H]thymidine incorporation into VSMCs at coptisine concentrations higher than 15 microM. The mechanism underlying the G(1) arrest involved a decrease in cyclin D1 protein, although cyclin E, A, and B were not affected by coptisine treatment. The selective reduction in cyclin D1 protein was mainly attributable to accelerated proteolysis via proteasome-dependent pathway, since it was inhibited by a proteasome inhibitor, N-carbobenzoxy-L-leucinyl-L-leucinyl-L-norleucinal (MG132) and further the mRNA level of cyclin D1, protein synthesis, and mitogen-activated protein kinase (MAPK) activity remained unaltered. The mechanism underlying the G(2)/M arrest involved partial inhibition of tubulin polymerization, which was apparent at coptisine concentration of 3 microM. Berberine arrested the cell cycle at G(1) phase via a mechanism identical with coptisine, but did not cause block at G(2)/M phase. The results demonstrate that a small difference in the structure between isoquinoline alkaloids produces a big difference in activity, and that coptisine has a unique double action in arresting the cell cycle of VSMCs.

PIAS1 activates the expression of smooth muscle cell differentiation marker genes by interacting with serum response factor and class I basic helix-loop-helix proteins

Although a critical component of vascular disease is modulation of the differentiated state of vascular smooth muscle cells (SMC), the mechanisms governing SMC differentiation are relatively poorly understood. We have previously shown that E-boxes and the ubiquitously expressed class I basic helix-loop-helix (bHLH) proteins, including E2-2 and E12, are important in regulation of the SMC differentiation marker gene, the SM alpha-actin gene. The aim of the present study was to identify proteins that bind to class I bHLH proteins in SMC and modulate transcriptional regulation of SMC differentiation marker genes. Herein we report that members of the protein inhibitor of activated STAT (PIAS) family interact with class I bHLH factors as well as serum response factor (SRF). PIAS1 interacted with E2-2 and E12 based on yeast two-hybrid screens, mammalian two-hybrid assays, and/or coimmunoprecipitation assays. Overexpression of PIAS1 significantly activated the SM alpha-actin promoter and mRNA expression, as well as SM myosin heavy chain and SM22alpha, whereas a small interfering RNA for PIAS1 decreased activity of these promoters, as well as endogenous mRNA expression, and SRF binding to SM alpha-actin promoter within intact chromatin in cultured SMC. Of significance, PIAS1 bound to SRF and activated SM alpha-actin promoter expression in wild-type but not SRF(-/-) embryonic stem cells. These results provide novel evidence that PIAS1 modulates transcriptional activation of SMC marker genes through cooperative interactions with both SRF and class I bHLH proteins.

The postnatal rat aorta contains pericyte progenitor cells that form spheroidal colonies in suspension culture

Pericytes play an important role in modulating angiogenesis, but the origin of these cells is poorly understood. To evaluate whether the mature vessel wall contains pericyte progenitor cells, nonendothelial mesenchymal cells isolated from the rat aorta were cultured in a serum-free medium optimized for stem cells. This method led to the isolation of anchorage-independent cells that proliferated slowly in suspension, forming spheroidal colonies. This process required basic fibroblast growth factor (bFGF) in the culture medium, because bFGF withdrawal caused the cells to attach to the culture dish and irreversibly lose their capacity to grow in suspension. Immunocytochemistry and RT-PCR analysis revealed the expression of the precursor cell markers CD34 and Tie-2 and the absence of endothelial cell markers (CD31 and endothelial nitric oxide synthase, eNOS) and smooth muscle cell markers (alpha-smooth muscle actin, alpha-SMA). In addition, spheroid-forming cells were positive for NG2, nestin, PDGF receptor (PDGFR)-alpha, and PDGFR-beta. Upon exposure to serum, these cells lost CD34 expression, acquired alpha-SMA, and attached to the culture dish. Returning these cells to serum-free medium failed to restore their original spheroid phenotype, suggesting terminal differentiation. When embedded in collagen gels, spheroid-forming cells rapidly migrated in response to PDGF-BB and became dendritic. Spheroid-forming cells cocultured in collagen with angiogenic outgrowths of rat aorta or isolated endothelial cells transformed into pericytes. These results demonstrate that the rat aorta contains primitive mesenchymal cells capable of pericyte differentiation. These immature cells may represent an important source of pericytes during angiogenesis in physiological and pathological processes. They may also provide a convenient supply of mural cells for vascular bioengineering applications.

Regulation of alpha-smooth muscle actin expression in granulation tissue myofibroblasts is dependent on the intronic CArG element and the transforming growth factor-beta1 control element

Myofibroblasts are specialized contractile fibroblasts that are critical in wound closure and tissue contracture. Generation of contractile force is correlated with the expression of alpha-smooth muscle actin (alpha-SMA); however, little is known regarding molecular mechanisms that control activation of alpha-SMA in myofibroblasts in granulation tissue. The aims of the present studies were to identify sufficient promoter regions required for alpha-SMA expression in myofibroblasts in vivo and to determine whether activation of alpha-SMA expression in myofibroblasts in vivo is dependent on an intronic CArG [CC(A/T)6GG] and a transforming growth factor-beta1 control element (TCE) that are required for alpha-SMA expression in smooth muscle cells. A Lac Z transgene construct from -2600 through the first intron was expressed in myofibroblasts within granulation tissue of cutaneous wounds in a pattern that closely mimicked endogenous alpha-SMA expression. Mutation of either the intronic CArG element or the TCE completely inhibited transgene expression in myofibroblasts in granulation tissue and responsiveness to transforming growth factor-beta1 in cultured transgenic fibroblasts. These same elements were also critical in regulating alpha-SMA expression during skeletal muscle repair but not during skeletal muscle development. Taken together, these results provide the first in vivo evidence for the importance of the intronic CArG and TCE cis-elements in the regulation of alpha-SMA expression in myofibroblasts in granulation tissue.

Control of smooth muscle development by the myocardin family of transcriptional coactivators

Differentiation of smooth muscle cells (SMCs) is accompanied by the transcriptional activation of an array of muscle-specific genes that confer the unique contractile and physiologic properties of this muscle cell type. The majority of smooth muscle genes are controlled by serum response factor (SRF), a widely expressed transcription factor that also regulates genes involved in cell proliferation. Myocardin and myocardin-related transcription factors (MRTFs) interact with SRF and potently stimulate SRF-dependent transcription. Gain- and loss-of-function experiments have shown myocardin to be sufficient and necessary for SMC differentiation. SMCs are highly plastic and can switch between differentiated and proliferative states in response to extracellular cues. Suppression of SMC differentiation by growth factor signaling is mediated, at least in part, by the displacement of myocardin from SRF by growth factor-dependent ternary complex factors. The association of SRF with myocardin and MRTFs provides a molecular basis for the activation of SMC genes by SRF and the responsiveness of the smooth muscle differentiation program to growth factor signaling.

Recruitment of the androgen receptor via serum response factor facilitates expression of a myogenic gene

Androgen receptor (AR) induced precocious myogenesis in culture and myogenic specified gene activity. Increased levels of AR expression in replicating C2C12 myoblasts stimulated fusion into post-differentiated multinucleated myotubes and the appearance of skeletal alpha-actin transcripts, even in the absence of ligand. Furthermore, AR activated the skeletal alpha-actin promoter, which lacks GRE sites, in co-transfected C2C12 cells. AR co-activation of the skeletal alpha-actin promoter required co-expressed full-length serum response factor (SRF). In vitro, AR associated with SRF and was recruited by SRF to a alpha-actin promoter SRF binding site. Our data suggest that AR is capable of activating myogenic genes devoid of consensus AR binding sites via its recruitment by the myogenic enriched transcription factor, SRF.

Kruppel-like factor 4 abrogates myocardin-induced activation of smooth muscle gene expression

Platelet-derived growth factor BB (PDGF-BB) has been shown to be an extremely potent negative regulator of smooth muscle cell (SMC) differentiation. Moreover, previous studies have demonstrated that the Kruppel-like transcription factor (KLF) 4 potently represses the expression of multiple SMC genes. However, the mechanisms whereby KLF4 suppresses SMC gene expression are not known, nor is it clear whether KLF4 contributes to PDGF-BB-induced down-regulation of SMC genes. The goals of the present studies were to determine the molecular mechanisms by which KLF4 represses expression of SMC genes and whether it contributes to PDGF-BB-induced suppression of these genes. Results demonstrated that KLF4 markedly repressed both myocardin-induced activation of SMC genes and expression of myocardin. KLF4 was rapidly up-regulated in PDGF-BB-treated, cultured SMC, and a small interfering RNA to KLF4 partially blocked PDGF-BB-induced SMC gene repression. Both PDGF-BB and KLF4 markedly reduced serum response factor binding to CArG containing regions within intact chromatin. Finally, KLF4, which is normally not expressed in differentiated SMC in vivo, was rapidly up-regulated in vivo in response to vascular injury. Taken together, results indicate that KLF4 represses SMC genes by both down-regulating myocardin expression and preventing serum response factor/myocardin from associating with SMC gene promoters, and suggest that KLF4 may be a key effector of PDGF-BB and injury-induced phenotypic switching of SMC.

Laser microdissection-based analysis of mRNA expression in human coronary arteries with intimal thickening

Intimal thickening is an early phase of atherosclerosis characterized by differentiation of plaque smooth muscle cells (SMCs) from a contractile to a synthetic phenotype. We used laser microdissection (LMD) plus real-time RT-PCR to quantify mRNAs for calponin-1 and smoothelin, markers of the contractile phenotype, and for serum response factor (SRF), a regulator of SMC differentiation, in intimal and medial SMCs of human coronary arteries with intimal thickening. RNA expression was also analyzed by ISH and protein expression was detected by IHC. LMD plus RT-PCR found similar levels of SRF mRNA in intimal and medial SMCs, while medial mRNA levels for calponin-1 and smoothelin were higher. ISH confirmed that smoothelin mRNA levels in media exceeded those in intima, whereas SRF mRNA levels were similar at both sites. For calponin-1 and smoothelin, protein levels mirrored respective mRNA levels. By contrast, more medial than intimal SRF protein was present. Our results indicate that intimal SMCs exhibit a largely synthetic phenotype, perhaps reflecting lower intimal levels of SRF protein; ISH and LMD plus real-time RT-PCR provide comparable results; as a valuable alternative to ISH, LMD plus RT-PCR allows parallel measurement of several transcripts; and tissue gene expression studies must measure both protein and mRNA levels.