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

Olfactomedin 2 Regulates Smooth Muscle Phenotypic Modulation and Vascular Remodeling Through Mediating Runt-Related Transcription Factor 2 Binding to Serum Response Factor

OBJECTIVE

The objective of this study is to investigate the role and underlying mechanism of Olfactomedin 2 (Olfm2) in smooth muscle cell (SMC) phenotypic modulation and vascular remodeling.

APPROACH AND RESULTS

Platelet-derived growth factor-BB induces Olfm2 expression in primary SMCs while modulating SMC phenotype as shown by the downregulation of SMC marker proteins. Knockdown of Olfm2 blocks platelet-derived growth factor-BB-induced SMC phenotypic modulation, proliferation, and migration. Conversely, Olfm2 overexpression inhibits SMC marker expression. Mechanistically, Olfm2 promotes the interaction of serum response factor with the runt-related transcription factor 2 that is induced by platelet-derived growth factor-BB, leading to a decreased interaction between serum response factor and myocardin, causing a repression of SMC marker gene transcription and consequently SMC phenotypic modulation. Animal studies show that Olfm2 is upregulated in balloon-injured rat carotid arteries. Knockdown of Olfm2 effectively inhibits balloon injury-induced neointima formation. Importantly, knockout of Olfm2 in mice profoundly suppresses wire injury-induced neointimal hyperplasia while restoring SMC contractile protein expression, suggesting that Olfm2 plays a critical role in SMC phenotypic modulation in vivo.

CONCLUSIONS

Olfm2 is a novel factor mediating SMC phenotypic modulation. Thus, Olfm2 may be a potential target for treating injury-induced proliferative vascular diseases.

Down-regulation of Insulin Receptor Substrate 1 during Hyperglycemia Induces Vascular Smooth Muscle Cell Dedifferentiation

Diabetes is a major risk factor for the development of atherosclerosis, but the mechanism by which hyperglycemia accelerates lesion development is not well defined. Insulin and insulin-like growth factor I (IGF-I) signal through the scaffold protein insulin receptor substrate 1 (IRS-1). In diabetes, IRS-1 is down-regulated, and cells become resistant to insulin. Under these conditions, the IGF-I receptor signals through an alternate scaffold protein, SHPS-1, resulting in pathophysiologic stimulation of vascular smooth muscle cell (VSMC) migration and proliferation. These studies were undertaken to determine whether IRS-1 is functioning constitutively to maintain VSMCs in their differentiated state and, thereby, inhibit aberrant signaling. Here we show that deletion of IRS-1 expression in VSMCs in non-diabetic mice results in dedifferentiation, SHPS-1 activation, and aberrant signaling and that these changes parallel those that occur in response to hyperglycemia. The mice showed enhanced sensitivity to IGF-I stimulation of VSMC proliferation and a hyperproliferative response to vascular injury. KLF4, a transcription factor that induces VSMC dedifferentiation, was up-regulated in IRS-1^-/- mice, and the differentiation inducer myocardin was undetectable. Importantly, these changes were replicated in wild-type mice during hyperglycemia. These findings illuminate a new function of IRS-1: that of maintaining cells in their normal, differentiated state. Because IRS-1 is down-regulated in states of insulin resistance that occur in response to metabolic stresses such as obesity and cytokine stimulation, the findings provide a mechanism for understanding how patients with metabolic stress and/or diabetes are predisposed to developing vascular complications.

Regulation of vascular smooth muscle phenotype by cross-regulation of krüppel-like factors

Regulation of vascular smooth muscle cell (VSMC) phenotype plays an essential role in many cardiovascular diseases. In the present study, we provide evidence that krüppel-like factor 8 (KLF8) is essential for tumor necrosis factor α (TNFα)-induced phenotypic conversion of VSMC obtained from thoracic aorta from 4-week-old SD rats. Stimulation of the contractile phenotype of VSMCs with TNFα significantly reduced the VSMC marker gene expression and KLF8. The gene expression of KLF8 was blocked by TNFα stimulation in an ERK-dependent manner. The promoter region of KLF8 contained putative Sp1, KLF4, and NFκB binding sites. Myocardin significantly enhanced the promoter activity of KLF4 and KLF8. The ectopic expression of KLF4 strongly enhanced the promoter activity of KLF8. Moreover, silencing of Akt1 significantly attenuated the promoter activity of KLF8; conversely, the overexpression of Akt1 significantly enhanced the promoter activity of KLF8. The promoter activity of SMA, SM22α, and KLF8 was significantly elevated in the contractile phenotype of VSMCs. The ectopic expression of KLF8 markedly enhanced the expression of SMA and SM22α concomitant with morphological changes. The overexpression of KLF8 stimulated the promoter activity of SMA. Stimulation of VSMCs with TNFα enhanced the expression of KLF5, and the promoter activity of KLF5 was markedly suppressed by KLF8 ectopic expression. Finally, the overexpression of KLF5 suppressed the promoter activity of SMA and SM22α, thereby reduced the contractility in response to the stimulation of angiotensin II. These results suggest that cross-regulation of KLF family of transcription factors plays an essential role in the VSMC phenotype.

Elongation of Long-Chain Fatty Acid Family Member 6 (Elovl6)-Driven Fatty Acid Metabolism Regulates Vascular Smooth Muscle Cell Phenotype Through AMP-Activated Protein Kinase/Krüppel-Like Factor 4 (AMPK/KLF4) Signaling

BACKGROUND

Fatty acids constitute the critical components of cell structure and function, and dysregulation of fatty acid composition may exert diverging vascular effects including proliferation, migration, and differentiation of vascular smooth muscle cells (VSMCs). However, direct evidence for this hypothesis has been lacking. We investigated the role of elongation of long-chain fatty acid member 6 (Elovl6), a rate-limiting enzyme catalyzing the elongation of saturated and monounsaturated long-chain fatty acid, in the regulation of phenotypic switching of VSMC.

METHODS AND RESULTS

Neointima formation following wire injury was markedly inhibited in Elovl6-null (Elovl6-/-) mice, and cultured VSMCs with siRNA-mediated knockdown of Elovl6 was barely responsive to PDGF-BB. Elovl6 inhibition induced cell cycle suppressors p53 and p21 and reduced the mammalian targets of rapamycin (mTOR) phosphorylation and VSMC marker expression. These changes are ascribed to increased palmitate levels and reduced oleate levels, changes that lead to reactive oxygen species (ROS) production and resulting AMP-activated protein kinase (AMPK) activation. Notably, Elovl6 inhibition robustly induced the pluripotency gene Krüppel-like factor 4 (KLF4) expression in VSMC, and KLF4 knockdown significantly attenuated AMPK-induced phenotypic switching of VSMC, indicating that KLF4 is a bona fide target of AMPK.

CONCLUSIONS

We demonstrate for the first time that dysregulation of Elovl6-driven long-chain fatty acid metabolism induces phenotypic switching of VSMC via ROS production and AMPK/KLF4 signaling that leads to growth arrest and downregulation of VSMC marker expression. The modulation of Elovl6-mediated cellular processes may provide an intriguing approach for tackling atherosclerosis and postangioplasty restenosis.

Vascular Cells in Blood Vessel Wall Development and Disease

The vessel wall is composed of distinct cellular layers, yet communication among individual cells within and between layers results in a dynamic and versatile structure. The morphogenesis of the normal vascular wall involves a highly regulated process of cell proliferation, migration, and differentiation. The use of modern developmental biological and genetic approaches has markedly enriched our understanding of the molecular and cellular mechanisms underlying these developmental events. Additionally, the application of similar approaches to study diverse vascular diseases has resulted in paradigm-shifting insights into pathogenesis. Further investigations into the biology of vascular cells in development and disease promise to have major ramifications on therapeutic strategies to combat pathologies of the vasculature.

Vascular smooth muscle cell contractile protein expression is increased through protein kinase G-dependent and -independent pathways by glucose-6-phosphate dehydrogenase inhibition and deficiency

Homeostatic control of vascular smooth muscle cell (VSMC) differentiation is critical for contractile activity and regulation of blood flow. Recently, we reported that precontracted blood vessels are relaxed and the phenotype of VSMC is regulated from a synthetic to contractile state by glucose-6-phosphate dehydrogenase (G6PD) inhibition. In the current study, we investigated whether the increase in the expression of VSMC contractile proteins by inhibition and knockdown of G6PD is mediated through a protein kinase G (PKG)-dependent pathway and whether it regulates blood pressure. We found that the expression of VSMC-restricted contractile proteins, myocardin (MYOCD), and miR-1 and miR-143 are increased by G6PD inhibition or knockdown. Importantly, RNA-sequence analysis of aortic tissue from G6PD-deficient mice revealed uniform increases in VSMC-restricted genes, particularly those regulated by the MYOCD-serum response factor (SRF) switch. Conversely, expression of Krüppel-like factor 4 (KLF4) is decreased by G6PD inhibition. Interestingly, the G6PD inhibition-induced expression of miR-1 and contractile proteins was blocked by Rp-β-phenyl-1,N2-etheno-8-bromo-guanosine-3',5'-cyclic monophosphorothioate, a PKG inhibitor. On the other hand, MYOCD and miR-143 levels are increased by G6PD inhibition through a PKG-independent manner. Furthermore, blood pressure was lower in the G6PD-deficient compared with wild-type mice. Therefore, our results suggest that the expression of VSMC contractile proteins induced by G6PD inhibition occurs via PKG1α-dependent and -independent pathways.

KLF4 Knockdown Attenuates TBI-Induced Neuronal Damage through p53 and JAK-STAT3 Signaling

AIMS

Traumatic brain injury (TBI) is induced by complex primary and secondary mechanisms that give rise to cell death, inflammation, and neurological dysfunction. Understanding the mechanisms that drive neurological damage as well as those that promote repair can guide the development of therapeutic drugs for TBI. Kruppel-like factor 4 (KLF4) has been reported to negatively regulate axon regeneration of injured retinal ganglion cells (RGCs) through inhibition of JAK-STAT3 signaling. However, the role of KLF4 in TBI remains unreported. Reactive oxygen species (ROS)-induced neuronal death is a pathophysiological hallmark of TBI.

METHODS

In this study, we used H₂ O₂ -treated RGCs in vitro and the optic nerve crush model in vivo to simulate neuronal damage in TBI. The function of KLF4 in RGC survival and axon regeneration in these models was investigated. In addition, the effects of KLF4 knockdown on neuronal damage after a brain impact that mimics moderate TBI were studied.

RESULTS

The results show that H₂ O₂ induces p53-dependent apoptosis of RGCs in vitro through upregulation of KLF4. Additionally, KLF4 knockdown in vivo significantly enhances CNTF-induced axon regeneration of RGCs after optic nerve crush, and more importantly, prevents neuronal damage after a moderate brain impact in rats. Our Western blot analysis and immunoprecipitation assay results indicate that these effects of KLF4 knockdown are mediated by the p53 and JAK-STAT3 pathways.

CONCLUSION

These findings provide evidence that KLF4 plays an important role in the pathophysiology of TBI. Blocking KLF4 may be a potential therapeutic strategy for the treatment of TBI, either alone or in combination with agents that target complementary mechanisms.

Assessing the contribution of thrombospondin-4 induction and ATF6α activation to endoplasmic reticulum expansion and phenotypic modulation in bladder outlet obstruction

Phenotypic modulation of smooth muscle cells is a hallmark of disease. The associated expansion of endoplasmic reticulum (ER) volume remains unexplained. Thrombospondin-4 was recently found to promote ATF6α activation leading to ER expansion. Using bladder outlet obstruction as a paradigm for phenotypic modulation, we tested if thrombospondin-4 is induced in association with ATF6α activation and ER expansion. Thrombospondin-4 was induced and ATF6α was activated after outlet obstruction in rodents. Increased abundance of spliced of Xbp1, another ER-stress sensor, and induction of Atf4 and Creb3l2 was also seen. Downstream of ATF6α, Calr, Manf, Sdf2l1 and Pdi increased as did ER size, whereas contractile markers were reduced. Overexpression of ATF6α, but not of thrombospondin-4, increased Calr, Manf, Sdf2l1 and Pdi and caused ER expansion, but the contractile markers were inert. Knockout of thrombospondin-4 neither affected bladder growth nor expression of ATF6α target genes, and repression of contractile markers was the same, even if ATF6α activation was curtailed. Increases of Xbp1s, Atf4 and Creb3l2 were similar. Our findings demonstrate reciprocal regulation of the unfolded protein response, including ATF6α activation and ER expansion, and reduced contractile differentiation in bladder outlet obstruction occurring independently of thrombospondin-4, which however is a sensitive indicator of obstruction.

Smooth muscle cell progenitors are primed to muscularize in pulmonary hypertension

Excess and ectopic smooth muscle cells (SMCs) are central to cardiovascular disease pathogenesis, but underlying mechanisms are poorly defined. For instance, pulmonary hypertension (PH) or elevated pulmonary artery blood pressure is a devastating disease with distal extension of smooth muscle to normally unmuscularized pulmonary arterioles. We identify novel SMC progenitors that are located at the pulmonary arteriole muscular-unmuscular border and express both SMC markers and the undifferentiated mesenchyme marker platelet-derived growth factor receptor-β (PDGFR-β). We term these cells "primed" because in hypoxia-induced PH, they express the pluripotency factor Kruppel-like factor 4 (KLF4), and in each arteriole, one of them migrates distally, dedifferentiates, and clonally expands, giving rise to the distal SMCs. Furthermore, hypoxia-induced expression of the ligand PDGF-B regulates primed cell KLF4 expression, and enhanced PDGF-B and KLF4 levels are required for distal arteriole muscularization and PH. Finally, in PH patients, KLF4 is markedly up-regulated in pulmonary arteriole smooth muscle, especially in proliferating SMCs. In sum, we have identified a pool of SMC progenitors that are critical for the pathogenesis of PH, and perhaps other vascular disorders, and therapeutic strategies targeting this cell type promise to have profound implications.

Set7 mediated interactions regulate transcriptional networks in embryonic stem cells

Histone methylation by lysine methyltransferase enzymes regulate the expression of genes implicated in lineage specificity and cellular differentiation. While it is known that Set7 catalyzes mono-methylation of histone and non-histone proteins, the functional importance of this enzyme in stem cell differentiation remains poorly understood. We show Set7 expression is increased during mouse embryonic stem cell (mESC) differentiation and is regulated by the pluripotency factors, Oct4 and Sox2. Transcriptional network analyses reveal smooth muscle (SM) associated genes are subject to Set7-mediated regulation. Furthermore, pharmacological inhibition of Set7 activity confirms this regulation. We observe Set7-mediated modification of serum response factor (SRF) and mono-methylation of histone H4 lysine 4 (H3K4me1) regulate gene expression. We conclude the broad substrate specificity of Set7 serves to control key transcriptional networks in embryonic stem cells.

Emerging roles of the myocardin family of proteins in lipid and glucose metabolism

Members of the myocardin family bind to the transcription factor serum response factor (SRF) and act as coactivators controlling genes of relevance for myogenic differentiation and motile function. Binding of SRF to DNA is mediated by genetic elements called CArG boxes, found often but not exclusively in muscle and growth controlling genes. Studies aimed at defining the full spectrum of these CArG elements in the genome (i.e. the CArGome) have in recent years, unveiled unexpected roles of the myocardin family proteins in lipid and glucose homeostasis. This coactivator family includes the protein myocardin (MYOCD), the myocardin-related transcription factors A and B (MRTF-A/MKL1 and MRTF-B/MKL2) and MASTR (MAMSTR). Here we discuss growing evidence that SRF-driven transcription is controlled by extracellular glucose through activation of the Rho-kinase pathway and actin polymerization. We also describe data showing that adipogenesis is influenced by MLK activity through actions upstream of peroxisome proliferator-activated receptor γ with consequences for whole body fat mass and insulin sensitivity. The recently demonstrated involvement of myocardin coactivators in the biogenesis of caveolae, Ω-shaped membrane invaginations of importance for lipid and glucose metabolism, is finally discussed. These novel roles of myocardin proteins may open the way for new unexplored strategies to combat metabolic diseases such as diabetes, which, at the current incidence, is expected to reach 333 million people worldwide by 2025. This review highlights newly discovered roles of myocardin-related transcription factors in lipid and glucose metabolism as well as novel insights into their well-established role as mediators of stretch-dependent effects in smooth muscle. As co-factors for serum response factor (SRF), MKLs regulates transcription of genes involved in the contractile function of smooth muscle cells. In addition to mechanical stimuli, this regulation has now been found to be promoted by extracellular glucose levels in smooth muscle. Recent reports also suggest that MKLs can regulate a subset of genes involved in the formation of lipid-rich invaginations in the cell membrane called caveolae. Finally, a potential role of MKLs in non-muscle cells has been discovered as they negatively influence adipocyte differentiation.

Mast cells promote proliferation and migration and inhibit differentiation of mesenchymal stem cells through PDGF

BACKGROUND

Mast cells (MCs) dynamically participate in wound healing after myocardial infarction (MI) by releasing cytokines. Indeed, MC-deficient mice undergo rapid left ventricular dilation post-MI. Mesenchymal stem cells (MSCs) are recruited to the injured region following an MI and have potential for cardiac repair. In the current study, we evaluate the effect of MCs on MSC proliferation and myogenic differentiation.

METHODS AND RESULTS

MCs were cultured from mouse bone marrow and MC granulate (MCG) was extracted from MCs via freeze-thaw cycles followed by filtration. α-SMA (smooth muscle actin) expression was examined as an indicator of myogenic differentiation. MSC/MC co-culture resulted in decreased MSC differentiation indicated by α-SMA suppression in MSCs. MCG also suppressed α-SMA expression and increased MSC migration and proliferation in a dose-dependent manner. Removal of MCG rescued α-SMA expression and MSC differentiation. Platelet derived growth factor (PDGF) receptor blockade using AG1296 also rescued MSC differentiation even after MCG treatment. Real-time PCR and Western blot showed that MCG exerted its effects on MSCs via downregulation of miR-145 and miR-143, downregulation of myocardin, upregulation of Klf4, and increased Erk and Elk1 phosphorylation.

CONCLUSIONS

MCs promote MSC proliferation and migration by suppressing their myogenic differentiation. MCs accomplish this via activation of the PDGF pathway, downregulation of miR-145/143, and modulation of the myocardin-Klf4 axis. These data suggest a potential role for MSC/MC interaction in the infarcted heart where MCs may inhibit MSCs from differentiation and promote their proliferation whereby increased cardiac MSC accumulation promotes eventual cardiac regeneration after MCs cease activity.

LIX1 regulates YAP1 activity and controls the proliferation and differentiation of stomach mesenchymal progenitors

BACKGROUND

Smooth muscle cell (SMC) plasticity maintains the balance between differentiated SMCs and proliferative mesenchymal progenitors, crucial for muscular tissue homeostasis. Studies on the development of mesenchymal progenitors into SMCs have proven useful in identifying molecular mechanisms involved in digestive musculature plasticity in physiological and pathological conditions.

RESULTS

Here, we show that Limb Expression 1 (LIX1) molecularly defines the population of mesenchymal progenitors in the developing stomach. Using in vivo functional approaches in the chick embryo, we demonstrate that LIX1 is a key regulator of stomach SMC development. We show that LIX1 is required for stomach SMC determination to regulate the expression of the pro-proliferative gene YAP1 and mesenchymal cell proliferation. However, as stomach development proceeds, sustained LIX1 expression has a negative impact on further SMC differentiation and this is associated with a decrease in YAP1 activity.

CONCLUSIONS

We demonstrate that expression of LIX1 must be tightly regulated to allow fine-tuning of the transcript levels and state of activation of the pro-proliferative transcriptional coactivator YAP1 to regulate proliferation rates of stomach mesenchymal progenitors and their differentiation. Our data highlight dual roles for LIX1 and YAP1 and provide new insights into the regulation of cell density-dependent proliferation, which is essential for the development and homeostasis of organs.

Noncoding RNAs in smooth muscle cell homeostasis: implications in phenotypic switch and vascular disorders

Vascular smooth muscle cells (SMC) are a highly specialized cell type that exhibit extraordinary plasticity in adult animals in response to a number of environmental cues. Upon vascular injury, SMC undergo phenotypic switch from a contractile-differentiated to a proliferative/migratory-dedifferentiated phenotype. This process plays a major role in vascular lesion formation and during the development of vascular remodeling. Vascular remodeling comprises the accumulation of dedifferentiated SMC in the intima of arteries and is central to a number of vascular diseases such as arteriosclerosis, chronic obstructive pulmonary disease or pulmonary hypertension. Therefore, it is critical to understand the molecular mechanisms that govern SMC phenotype. In the last decade, a number of new classes of noncoding RNAs have been described. These molecules have emerged as key factors controlling tissue homeostasis during physiological and pathological conditions. In this review, we will discuss the role of noncoding RNAs, including microRNAs and long noncoding RNAs, in the regulation of SMC plasticity.

The role of Krüppel-like factor 4 in transforming growth factor-β-induced inflammatory and fibrotic responses in human proximal tubule cells

Krüppel-like factor 4 (KLF4) is known to mitigate inflammation in several cell types. Using human proximal tubule cells, the present study aimed to investigate the role of KLF4 in regulating transforming growth factor (TGF)-β₁ induced inflammatory and fibrotic responses. Human kidney proximal tubular cells were exposed to high glucose, or TGF-β₁ and KLF4 expressions were determined. Cells were then transfected with empty vector or KLF4 and exposed to 2-ng/mL TGF-β₁ for up to 72 h. Inflammatory proteins (macrophage migration inhibitory factor and monocyte chemoattractant protein-1) and pro-fibrotic proteins (fibronectin and collagen IV) were measured after 72 h by enzyme-linked immunosorbent assay and western blot, respectively. To determine the relevance to in vivo models of chronic kidney disease, KLF4 protein expression in streptozotocin-induced diabetic mice was determined. Krüppel-like factor 4 messenger RNA (mRNA) levels were significantly reduced in high glucose-treated human kidney proximal tubular cells. High glucose increased TGF-β₁ mRNA expression, which significantly increased migration inhibitory factor and monocyte chemoattractant protein-1 protein secretion. Transforming growth factor-β₁ significantly increased fibronectin and collagen IV protein expression. The overexpression of KLF4 significantly reduced TGF-β-mediated increases in migration inhibitory factor and monocyte chemoattractant protein-1 but had no effect on TGF-β-mediated fibronectin and collagen IV mRNA and protein expression. The levels of KLF4 mRNA were significantly reduced in the diabetic kidney, and diabetic animals had a significant reduction in renal tubular expression of KLF4 proteins. This data suggest that KLF4 reduces inflammation induced by TGF-β₁, suggesting a therapeutic role for KLF4 in diabetic nephropathy.

Elevated Glucose Levels Promote Contractile and Cytoskeletal Gene Expression in Vascular Smooth Muscle via Rho/Protein Kinase C and Actin Polymerization

Both type 1 and type 2 diabetes are associated with increased risk of cardiovascular disease. This is in part attributed to the effects of hyperglycemia on vascular endothelial and smooth muscle cells, but the underlying mechanisms are not fully understood. In diabetic animal models, hyperglycemia results in hypercontractility of vascular smooth muscle possibly due to increased activation of Rho-kinase. The aim of the present study was to investigate the regulation of contractile smooth muscle markers by glucose and to determine the signaling pathways that are activated by hyperglycemia in smooth muscle cells. Microarray, quantitative PCR, and Western blot analyses revealed that both mRNA and protein expression of contractile smooth muscle markers were increased in isolated smooth muscle cells cultured under high compared with low glucose conditions. This effect was also observed in hyperglycemic Akita mice and in diabetic patients. Elevated glucose activated the protein kinase C and Rho/Rho-kinase signaling pathways and stimulated actin polymerization. Glucose-induced expression of contractile smooth muscle markers in cultured cells could be partially or completely repressed by inhibitors of advanced glycation end products, L-type calcium channels, protein kinase C, Rho-kinase, actin polymerization, and myocardin-related transcription factors. Furthermore, genetic ablation of the miR-143/145 cluster prevented the effects of glucose on smooth muscle marker expression. In conclusion, these data demonstrate a possible link between hyperglycemia and vascular disease states associated with smooth muscle contractility.

A Novel Selectable Islet 1 Positive Progenitor Cell Reprogrammed to Expandable and Functional Smooth Muscle Cells

Disorders affecting smooth muscle structure/function may require technologies that can generate large scale, differentiated and contractile smooth muscle cells (SMC) suitable for cell therapy. To date no clonal precursor population that provides large numbers of differentiated SMC in culture has been identified in a rodent. Identification of such cells may also enhance insight into progenitor cell fate decisions and the relationship between smooth muscle precursors and disease states that implicate differentiated SMC.  In this study, we used classic clonal expansion techniques to identify novel self-renewing Islet 1 (Isl-1) positive primitive progenitor cells (PPC) within rat bone marrow that exhibited canonical stem cell markers and preferential differentiation towards a smooth muscle-like fate. We subsequently used molecular tagging to select Isl-1 positive clonal populations from expanded and de novo marrow cell populations. We refer to these previously undescribed cells as the PPC given its stem cell marker profile, and robust self-renewal capacity. PPC could be directly converted into induced smooth muscle cells (iSMC) using single transcription factor (Kruppel-like factor 4) knockdown or transactivator (myocardin) overexpression in contrast to three control cells (HEK 293, endothelial cells and mesenchymal stem cells) where such induction was not possible. iSMC exhibited immuno- and cytoskeletal-phenotype, calcium signaling profile and contractile responses similar to bona fide SMC. Passaged iSMC could be expanded to a scale sufficient for large scale tissue replacement.  PPC and reprogramed iSMC so derived may offer future opportunities to investigate molecular, structure/function and cell-based replacement therapy approaches to diverse cardiovascular, respiratory, gastrointestinal, and genitourinary diseases that have as their basis smooth muscle cell functional aberrancy or numerical loss. Stem Cells 2016;34:1354-1368.

Endothelial Plasticity: Shifting Phenotypes through Force Feedback

The endothelial lining of the vasculature is exposed to a large variety of biochemical and hemodynamic stimuli with different gradients throughout the vascular network. Adequate adaptation requires endothelial cells to be highly plastic, which is reflected by the remarkable heterogeneity of endothelial cells in tissues and organs. Hemodynamic forces such as fluid shear stress and cyclic strain are strong modulators of the endothelial phenotype and function. Although endothelial plasticity is essential during development and adult physiology, proatherogenic stimuli can induce adverse plasticity which contributes to disease. Endothelial-to-mesenchymal transition (EndMT), the hallmark of endothelial plasticity, was long thought to be restricted to embryonic development but has emerged as a pathologic process in a plethora of diseases. In this perspective we argue how shear stress and cyclic strain can modulate EndMT and discuss how this is reflected in atherosclerosis and pulmonary arterial hypertension.

KLF2 exerts antifibrotic and vasoprotective effects in cirrhotic rat livers: behind the molecular mechanisms of statins

OBJECTIVE

In the liver, the transcription factor, Kruppel-like factor 2 (KLF2), is induced early during progression of cirrhosis to lessen the development of vascular dysfunction; nevertheless, its endogenous expression results insufficient to attenuate establishment of portal hypertension and aggravation of cirrhosis. Herein, we aimed to explore the effects and the underlying mechanisms of hepatic KLF2 overexpression in in vitro and in vivo models of liver cirrhosis.

DESIGN

Activation phenotype was evaluated in human and rat cirrhotic hepatic stellate cells (HSC) treated with the pharmacological inductor of KLF2 simvastatin, with adenovirus codifying for this transcription factor (Ad-KLF2), or vehicle, in presence/absence of inhibitors of KLF2. Possible paracrine interactions between parenchymal and non-parenchymal cells overexpressing KLF2 were studied. Effects of in vivo hepatic KLF2 overexpression on liver fibrosis and systemic and hepatic haemodynamics were assessed in cirrhotic rats.

RESULTS

KLF2 upregulation profoundly ameliorated HSC phenotype (reduced α-smooth muscle actin, procollagen I and oxidative stress) partly via the activation of the nuclear factor (NF)-E2-related factor 2 (Nrf2). Coculture experiments showed that improvement in HSC phenotype paracrinally ameliorated liver sinusoidal endothelial cells probably through a vascular endothelial growth factor-mediated mechanism. No paracrine interactions between hepatocytes and HSC were observed. Cirrhotic rats treated with simvastatin or Ad-KLF2 showed hepatic upregulation in the KLF2-Nrf2 pathway, deactivation of HSC and prominent reduction in liver fibrosis. Hepatic KLF2 overexpression was associated with lower portal pressure (-15%) due to both attenuations in the increased portal blood flow and hepatic vascular resistance, together with a significant improvement in hepatic endothelial dysfunction.

CONCLUSIONS

Exogenous hepatic KLF2 upregulation improves liver fibrosis, endothelial dysfunction and portal hypertension in cirrhosis.

Essential role of krüppel-like factor 5 during tumor necrosis factor α-induced phenotypic conversion of vascular smooth muscle cells

Tumor necrosis factor α (TNFα) plays an essential role in the regulation of vascular smooth muscle cell (VSMC) phenotype. In the present study, we provide evidence that krüppel-like factor 5 (KLF5) plays an essential role in TNFα-induced phenotypic conversion of VSMCs. Ectopic expression of KLF5 completely blocked phenotypic conversion of VSMCs from synthetic to contractile type. In addition, stimulation of VSMCs with TNFα facilitated expression of KLF5, whereas expression of smooth muscle marker genes such as SM22α and smooth muscle actin (SMA) was significantly down-regulated. TNFα significantly enhanced the promoter activity of KLF5 as well as mRNA level, which is significantly suppressed by the inhibition of the MAPK pathway. Silencing of KLF5 suppressed TNFα-induced phenotypic conversion of VSMCs, whereas overexpression of KLF5 stimulated phenotypic conversion of VSMCs and facilitated the loss of angiotensin II (AngII)-dependent contraction. Finally, overexpression of KLF5 significantly attenuated the promoter activity of SM22α and SMA. Therefore, we suggest that TNFα-dependent induction of KLF5 may play an essential role in phenotypic modulation of VSMCs.

Caveolin-3 Promotes a Vascular Smooth Muscle Contractile Phenotype

Epidemiological studies have demonstrated the importance of cardiovascular diseases in Western countries. Among the cell types associated with a dysfunctional vasculature, smooth muscle (SM) cells are believed to play an essential role in the development of these illnesses. Vascular SM cells are key regulators of the vascular tone and also have an important function in the development of atherosclerosis and restenosis. While in the normal vasculature, contractile SM cells are predominant, in atherosclerotic vascular lesions, synthetic cells migrate toward the neointima, proliferate, and synthetize extracellular matrix proteins. In the present study, we have examined the role of caveolin-3 in the regulation of SM cell phenotype. Caveolin-3 is expressed in vivo in normal arterial SM cells, but its expression appears to be lost in cultured SM cells. Our data show that caveolin-3 expression in the A7r5 SM cell line is associated with increased expression of contractility markers such as SM α-actin, SM myosin heavy chain but decreased expression of the synthetic phenotype markers such as p-Elk and Klf4. Moreover, we also show that caveolin-3 expression can reduce proliferation upon treatment with LDL or PDGF. Finally, we show that caveolin-3-expressing SM cells are less sensitive to apoptosis than control cells upon treatment with oxidized LDL. Taken together, our data suggest that caveolin-3 can regulate the phenotypic switch between contractile and synthetic SM cells. A better understanding of the factors regulating caveolin-3 expression and function in this cell type will permit the development of a better comprehension of the factors regulating SM function in atherosclerosis and restenosis.

Kruppel-like factor 4 signals through microRNA-206 to promote tumor initiation and cell survival

Tumor cell heterogeneity poses a major hurdle in the treatment of cancer. Mammary cancer stem-like cells (MaCSCs), or tumor-initiating cells, are highly tumorigenic sub-populations that have the potential to self-renew and to differentiate. These cells are clinically important, as they display therapeutic resistance and may contribute to treatment failure and recurrence, but the signaling axes relevant to the tumorigenic phenotype are poorly defined. The zinc-finger transcription factor Kruppel-like factor 4 (KLF4) is a pluripotency mediator that is enriched in MaCSCs. KLF4 promotes RAS-extracellular signal-regulated kinase pathway activity and tumor cell survival in triple-negative breast cancer (TNBC) cells. In this study, we found that both KLF4 and a downstream effector, microRNA-206 (miR-206), are selectively enriched in the MaCSC fractions of cultured human TNBC cell lines, as well as in the aldehyde dehydrogenase-high MaCSC sub-population of cells derived from xenografted human mammary carcinomas. The suppression of endogenous KLF4 or miR-206 activities abrogated cell survival and in vivo tumor initiation, despite having only subtle effects on MaCSC abundance. Using a combinatorial approach that included in silico as well as loss- and gain-of-function in vitro assays, we identified miR-206-mediated repression of the pro-apoptotic molecules programmed cell death 4 (PDCD4) and connexin 43 (CX43/GJA1). Depletion of either of these two miR-206-regulated transcripts promoted resistance to anoikis, a prominent feature of CSCs, but did not consistently alter MaCSC abundance. Consistent with increased levels of miR-206 in MaCSCs, the expression of both PDCD4 and CX43 was suppressed in these cells relative to control cells. These results identify miR-206 as an effector of KLF4-mediated prosurvival signaling in MaCSCs through repression of PDCD4 and CX43. Consequently, our study suggests that a pluripotency factor exerts prosurvival signaling in MaCSCs, and that antagonism of KLF4-miR-206 signaling may selectively target the MaCSC niche in TNBC.

Disruption of miR-29 Leads to Aberrant Differentiation of Smooth Muscle Cells Selectively Associated with Distal Lung Vasculature

Differentiation of lung vascular smooth muscle cells (vSMCs) is tightly regulated during development or in response to challenges in a vessel specific manner. Aberrant vSMCs specifically associated with distal pulmonary arteries have been implicated in the pathogenesis of respiratory diseases, such as pulmonary arterial hypertension (PAH), a progressive and fatal disease, with no effective treatment. Therefore, it is highly relevant to understand the underlying mechanisms of lung vSMC differentiation. miRNAs are known to play critical roles in vSMC maturation and function of systemic vessels; however, little is known regarding the role of miRNAs in lung vSMCs. Here, we report that miR-29 family members are the most abundant miRNAs in adult mouse lungs. Moreover, high levels of miR-29 expression are selectively associated with vSMCs of distal vessels in both mouse and human lungs. Furthermore, we have shown that disruption of miR-29 in vivo leads to immature/synthetic vSMC phenotype specifically associated with distal lung vasculature, at least partially due to the derepression of KLF4, components of the PDGF pathway and ECM-related genes associated with synthetic phenotype. Moreover, we found that expression of FBXO32 in vSMCs is significantly upregulated in the distal vasculature of miR-29 null lungs. This indicates a potential important role of miR-29 in smooth muscle cell function by regulating FBXO32 and SMC protein degradation. These results are strongly supported by findings of a cell autonomous role of endogenous miR-29 in promoting SMC differentiation in vitro. Together, our findings suggested a vessel specific role of miR-29 in vSMC differentiation and function by targeting several key negative regulators.

The pathogenesis of some vascular diseases, such as PAH is selectively associated with aberrant differentiation and proliferation of vSMCs of distal arteries. While significant progresses have been made in understanding the core mechanism of differentiation and proliferation of vSMCs, little is known regarding vessel specific regulations. By investigating the expression and function of miR-29 in vivo, we found a vessel selective enriched expression and function of miR-29 during mouse lung development. Interestingly, disruption of miR-29 results in defects in vSMCs differentiation of distal vessels, reminiscent of vSMC phenotype observed in the early stage of PAH in which immature/synthetic vSMCs of distal arteries failed to differentiate and were unable to tune down the expression of collagens and other extracellular-related genes. This is the first evidence that miR-29 selectively regulates vSMCs differentiation and vessel wall formation. Future implications are to study the expression and function of miR-29 in human pulmonary vascular diseases, which might lead to establishing miR-29 as a therapeutic target for disease intervention.

c-Kit+ progenitors generate vascular cells for tissue-engineered grafts through modulation of the Wnt/Klf4 pathway

The development of decellularised scaffolds for small diameter vascular grafts is hampered by their limited patency, due to the lack of luminal cell coverage by endothelial cells (EC) and to the low tone of the vessel due to absence of a contractile smooth muscle cells (SMC). In this study, we identify a population of vascular progenitor c-Kit+/Sca-1- cells available in large numbers and derived from immuno-privileged embryonic stem cells (ESCs). We also define an efficient and controlled differentiation protocol yielding fully to differentiated ECs and SMCs in sufficient numbers to allow the repopulation of a tissue engineered vascular graft. When seeded ex vivo on a decellularised vessel, c-Kit+/Sca-1-derived cells recapitulated the native vessel structure and upon in vivo implantation in the mouse, markedly reduced neointima formation and mortality, restoring functional vascularisation. We showed that Krüppel-like transcription factor 4 (Klf4) regulates the choice of differentiation pathway of these cells through β-catenin activation and was itself regulated by the canonical Wnt pathway activator lithium chloride. Our data show that ESC-derived c-Kit+/Sca-1-cells can be differentiated through a Klf4/β-catenin dependent pathway and are a suitable source of vascular progenitors for the creation of superior tissue-engineered vessels from decellularised scaffolds.

Vascular smooth muscle cell in atherosclerosis

Vascular smooth muscle cells (VSMCs) exhibit phenotypic and functional plasticity in order to respond to vascular injury. In case of the vessel damage, VSMCs are able to switch from the quiescent 'contractile' phenotype to the 'proinflammatory' phenotype. This change is accompanied by decrease in expression of smooth muscle (SM)-specific markers responsible for SM contraction and production of proinflammatory mediators that modulate induction of proliferation and chemotaxis. Indeed, activated VSMCs could efficiently proliferate and migrate contributing to the vascular wall repair. However, in chronic inflammation that occurs in atherosclerosis, arterial VSMCs become aberrantly regulated and this leads to increased VSMC dedifferentiation and extracellular matrix formation in plaque areas. Proatherosclerotic switch in VSMC phenotype is a complex and multistep mechanism that may be induced by a variety of proinflammatory stimuli and hemodynamic alterations. Disturbances in hemodynamic forces could initiate the proinflammatory switch in VSMC phenotype even in pre-clinical stages of atherosclerosis. Proinflammatory signals play a crucial role in further dedifferentiation of VSMCs in affected vessels and propagation of pathological vascular remodelling.

Dedicator of cytokinesis 2, a novel regulator for smooth muscle phenotypic modulation and vascular remodeling

RATIONALE

Vascular smooth muscle cell (SMC) phenotypic modulation and vascular remodeling contribute to the development of several vascular disorders such as restenosis after angioplasty, transplant vasculopathy, and atherosclerosis. The mechanisms underlying these processes, however, remain largely unknown.

OBJECTIVE

The objective of this study is to determine the role of dedicator of cytokinesis 2 (DOCK2) in SMC phenotypic modulation and vascular remodeling.

METHODS AND RESULTS

Platelet-derived growth factor-BB induced DOCK2 expression while modulating SMC phenotype. DOCK2 deficiency diminishes platelet-derived growth factor-BB or serum-induced downregulation of SMC markers. Conversely, DOCK2 overexpression inhibits SMC marker expression in primary cultured SMC. Mechanistically, DOCK2 inhibits myocardin expression, blocks serum response factor nuclear location, attenuates myocardin binding to serum response factor, and thus attenuates myocardin-induced smooth muscle marker promoter activity. Moreover, DOCK2 and Kruppel-like factor 4 cooperatively inhibit myocardin-serum response factor interaction. In a rat carotid artery balloon-injury model, DOCK2 is induced in media layer SMC initially and neointima SMC subsequently after vascular injury. Knockdown of DOCK2 dramatically inhibits the neointima formation by 60%. Most importantly, knockout of DOCK2 in mice markedly blocks ligation-induced intimal hyperplasia while restoring SMC contractile protein expression.

CONCLUSIONS

Our studies identified DOCK2 as a novel regulator for SMC phenotypic modulation and vascular lesion formation after vascular injury. Therefore, targeting DOCK2 may be a potential therapeutic strategy for the prevention of vascular remodeling in proliferative vascular diseases.

Cholesterol loading reprograms the microRNA-143/145-myocardin axis to convert aortic smooth muscle cells to a dysfunctional macrophage-like phenotype

OBJECTIVE

We previously showed that cholesterol loading in vitro converts mouse aortic vascular smooth muscle cells (VSMC) from a contractile state to one resembling macrophages. In human and mouse atherosclerotic plaques, it has become appreciated that ≈40% of cells classified as macrophages by histological markers may be of VSMC origin. Therefore, we sought to gain insight into the molecular regulation of this clinically relevant process.

APPROACH AND RESULTS

VSMC of mouse (or human) origin were incubated with cyclodextrin-cholesterol complexes for 72 hours, at which time the expression at the protein and mRNA levels of contractile-related proteins was reduced and of macrophage markers increased. Concurrent was downregulation of miR-143/145, which positively regulate the master VSMC differentiation transcription factor myocardin. Mechanisms were further probed in mouse VSMC. Maintaining the expression of myocardin or miR-143/145 prevented and reversed phenotypic changes caused by cholesterol loading. Reversal was also seen when cholesterol efflux was stimulated after loading. Notably, despite expression of macrophage markers, bioinformatic analyses showed that cholesterol-loaded cells remained closer to the VSMC state, consistent with impairment in classical macrophage functions of phagocytosis and efferocytosis. In apoE-deficient atherosclerotic plaques, cells positive for VSMC and macrophage markers were found lining the cholesterol-rich necrotic core.

CONCLUSIONS

Cholesterol loading of VSMC converts them to a macrophage-appearing state by downregulating the miR-143/145-myocardin axis. Although these cells would be classified by immunohistochemistry as macrophages in human and mouse plaques, their transcriptome and functional properties imply that their contributions to atherogenesis would not be those of classical macrophages.

MicroRNA MiR-199a-5p regulates smooth muscle cell proliferation and morphology by targeting WNT2 signaling pathway

MicroRNA miR-199a-5p impairs tight junction formation, leading to increased urothelial permeability in bladder pain syndrome. Now, using transcriptome analysis in urothelial TEU-2 cells, we implicate it in the regulation of cell cycle, cytoskeleton remodeling, TGF, and WNT signaling pathways. MiR-199a-5p is highly expressed in the smooth muscle layer of the bladder, and we altered its levels in bladder smooth muscle cells (SMCs) to validate the pathway analysis. Inhibition of miR-199a-5p with antimiR increased SMC proliferation, reduced cell size, and up-regulated miR-199a-5p targets, including WNT2. Overexpression of WNT2 protein or treating SMCs with recombinant WNT2 closely mimicked the miR-199a-5p inhibition, whereas down-regulation of WNT2 in antimiR-expressing SMCs with shRNA restored cell phenotype and proliferation rates. Overexpression of miR-199a-5p in the bladder SMCs significantly increased cell size and up-regulated SM22, SM α-actin, and SM myosin heavy chain mRNA and protein levels. These changes as well as increased expression of ACTG2, TGFB1I1, and CDKN1A were mediated by up-regulation of the smooth muscle-specific transcriptional activator myocardin at mRNA and protein levels. Myocardin-related transcription factor A downstream targets Id3 and MYL9 were also induced. Up-regulation of myocardin was accompanied by down-regulation of WNT-dependent inhibitory Krüppel-like transcription factor 4 in miR-199a-5p-overexpressing cells. In contrast, Krüppel-like transcription factor 4 was induced in antimiR-expressing cells following the activation of WNT2 signaling, leading to repression of myocardin-dependent genes. MiR-199a-5p plays a critical role in the WNT2-mediated regulation of proliferative and differentiation processes in the smooth muscle and may behave as a key modulator of smooth muscle hypertrophy, which is relevant for organ remodeling.

MicroRNAs in pulmonary arterial hypertension: pathogenesis, diagnosis and treatment

Pulmonary arterial hypertension (PAH) is a severe and increasingly prevalent disease, manifested by the maladaptation of pulmonary vasculature, which consequently leads to right heart failure and possibly even death. The development of PAH is characterized by specific functional as well as structural changes, primarily associated with the aberrant function of the pulmonary artery endothelial cells, smooth muscle cells, and vascular fibroblasts. MicroRNAs constitute a class of small ≈22-nucleotides-long non-coding RNAs that post-transcriptionally regulate gene expression and that may lead to significant cell proteome changes. While the involvement of miRNAs in the development of various diseases--especially cancer--has been reported, numerous miRNAs have also been associated with PAH onset, progression, or treatment responsiveness. This review focuses on the role of microRNAs in the development of PAH as well as on their potential use as biomarkers and therapeutic tools in both experimental PAH models and in humans. Special attention is given to the roles of miR-21, miR-27a, the miR-17-92 cluster, miR-124, miR-138, the miR-143/145 cluster, miR-150, miR-190, miR-204, miR-206, miR-210, miR-328, and the miR-424/503 cluster, specifically with the objective of providing greater insight into the pervasive roles of miRNAs in the pathogenesis of this deadly condition.

Induction of angiotensin-converting enzyme after miR-143/145 deletion is critical for impaired smooth muscle contractility

MicroRNAs have emerged as regulators of smooth muscle cell phenotype with a role in smooth muscle-related disease. Studies have shown that miR-143 and miR-145 are the most highly expressed microRNAs in smooth muscle cells, controlling differentiation and function. The effect of miR-143/145 knockout has been established in the vasculature but not in smooth muscle from other organs. Using knockout mice we found that maximal contraction induced by either depolarization or phosphatase inhibition was reduced in vascular and airway smooth muscle but maintained in the urinary bladder. Furthermore, a reduction of media thickness and reduced expression of differentiation markers was seen in the aorta but not in the bladder. Supporting the view that phenotype switching depends on a tissue-specific target of miR-143/145, we found induction of angiotensin-converting enzyme in the aorta but not in the bladder where angiotensin-converting enzyme was expressed at a low level. Chronic treatment with angiotensin type-1 receptor antagonist restored contractility in miR-143/145-deficient aorta while leaving bladder contractility unaffected. This shows that tissue-specific targets are critical for the effects of miR-143/145 on smooth muscle differentiation and that angiotensin converting enzyme is one such target.

Kruppel-like factors in muscle health and disease

Kruppel-like factors (KLF) are zinc-finger DNA-binding transcription factors that are critical regulators of tissue homeostasis. Emerging evidence suggests that KLFs are critical regulators of muscle biology in the context of cardiovascular health and disease. The focus of this review is to provide an overview of the current state of knowledge regarding the physiologic and pathologic roles of KLFs in the three lineages of muscle: cardiac, smooth, and skeletal.

MicroRNAs 206 and 21 cooperate to promote RAS-extracellular signal-regulated kinase signaling by suppressing the translation of RASA1 and SPRED1

Despite the low prevalence of activating point mutation of RAS or RAF genes, the RAS-extracellular signal-regulated kinase (ERK) pathway is implicated in breast cancer pathogenesis. Indeed, in triple-negative breast cancer (TNBC), there is recurrent genetic alteration of pathway components. Using short hairpin RNA (shRNA) methods, we observed that the zinc finger transcription factor Krüppel-like factor 4 (KLF4) can promote RAS-ERK signaling in TNBC cells. Endogenous KLF4 bound to the promoter regions and promoted the expression of two microRNAs (miRs), miR-206 and miR-21 (i.e., miR-206/21). Antisense-mediated knockdown (anti-miR) revealed that miR-206/21 coordinately promote RAS-ERK signaling and the corresponding cell phenotypes by inhibiting translation of the pathway suppressors RASA1 and SPRED1. In TNBC cells, including cells with mutation of RAS, the suppression of either RASA1 or SPRED1 increased the levels of GTP-bound, wild-type RAS and activated ERK 1/2. Unlike the control cells, treatment of RASA1- or SPRED1-suppressed cells with anti-miR-206/21 had little or no impact on the level of activated ERK 1/2 or on cell proliferation and failed to suppress tumor initiation. These results identify RASA1 and SPRED1 mRNAs as latent RAS-ERK pathway suppressors that can be upregulated in tumor cells by anti-miR treatment. Consequently, KLF4-regulated miRs are important for the maintenance of RAS-ERK pathway activity in TNBC cells.

Elevated expression levels of miR-143/5 in saphenous vein smooth muscle cells from patients with Type 2 diabetes drive persistent changes in phenotype and function

Type 2 diabetes (T2DM) promotes premature atherosclerosis and inferior prognosis after arterial reconstruction. Vascular smooth muscle cells (SMC) respond to patho/physiological stimuli, switching between quiescent contractile and activated synthetic phenotypes under the control of microRNAs (miRs) that regulate multiple genes critical to SMC plasticity. The importance of miRs to SMC function specifically in T2DM is unknown. This study was performed to evaluate phenotype and function in SMC cultured from non-diabetic and T2DM patients, to explore any aberrancies and investigate underlying mechanisms. Saphenous vein SMC cultured from T2DM patients (T2DM-SMC) exhibited increased spread cell area, disorganised cytoskeleton and impaired proliferation relative to cells from non-diabetic patients (ND-SMC), accompanied by a persistent, selective up-regulation of miR-143 and miR-145. Transfection of premiR-143/145 into ND-SMC induced morphological and functional characteristics similar to native T2DM-SMC; modulating miR-143/145 targets Kruppel-like factor 4, alpha smooth muscle actin and myosin VI. Conversely, transfection of antimiR-143/145 into T2DM-SMC conferred characteristics of the ND phenotype. Exposure of ND-SMC to transforming growth factor beta (TGFβ) induced a diabetes-like phenotype; elevated miR-143/145, increased cell area and reduced proliferation. Furthermore, these effects were dependent on miR-143/145. In conclusion, aberrant expression of miR-143/145 induces a distinct saphenous vein SMC phenotype that may contribute to vascular complications in patients with T2DM, and is potentially amenable to therapeutic manipulation.

Kruppel-like factor 4 protein regulates isoproterenol-induced cardiac hypertrophy by modulating myocardin expression and activity

Kruppel-like factor 4 (KLF4) plays an important role in vascular diseases, including atherosclerosis and vascular injury. Although KLF4 is expressed in the heart in addition to vascular cells, the role of KLF4 in cardiac disease has not been fully determined. The goals of this study were to investigate the role of KLF4 in cardiac hypertrophy and to determine the underlying mechanisms. Cardiomyocyte-specific Klf4 knockout (CM Klf4 KO) mice were generated by the Cre/LoxP technique. Cardiac hypertrophy was induced by chronic infusion of the β-adrenoreceptor agonist isoproterenol (ISO). Results showed that ISO-induced cardiac hypertrophy was enhanced in CM Klf4 KO mice compared with control mice. Accelerated cardiac hypertrophy in CM Klf4 KO mice was accompanied by the augmented cellular enlargement of cardiomyocytes as well as the exaggerated expression of fetal cardiac genes, including atrial natriuretic factor (Nppa). Additionally, induction of myocardin, a transcriptional cofactor regulating fetal cardiac genes, was enhanced in CM Klf4 KO mice. Interestingly, KLF4 regulated Nppa expression by modulating the expression and activity of myocardin, providing a mechanical basis for accelerated cardiac hypertrophy in CM Klf4 KO mice. Moreover, we showed that KLF4 mediated the antihypertrophic effect of trichostatin A, a histone deacetylase inhibitor, because ISO-induced cardiac hypertrophy in CM Klf4 KO mice was attenuated by olmesartan, an angiotensin II type 1 antagonist, but not by trichostatin A. These results provide novel evidence that KLF4 is a regulator of cardiac hypertrophy by modulating the expression and the activity of myocardin.

Epigenetic regulation of smooth muscle cell plasticity

Smooth muscle cells (SMC) are the major cell type in blood vessels. Their principal function in the body is to regulate blood flow and pressure through vessel wall contraction and relaxation. Unlike many other mature cell types in the adult body, SMC do not terminally differentiate but retain a remarkable plasticity. They have the unique ability to toggle between a differentiated and quiescent "contractile" state and a highly proliferative and migratory "synthetic" phenotype in response to environmental stresses. While there have been major advances in our understanding of SMC plasticity through the identification of growth factors and signals that can influence the SMC phenotype, how these regulate SMC plasticity remains unknown. To date, several key transcription factors and regulatory cis elements have been identified that play a role in modulating SMC state. The frontier in understanding the molecular mechanisms underlying SMC plasticity has now advanced to the level of epigenetics. This review will summarize the epigenetic regulation of SMC, highlighting the role of histone modification, DNA methylation, and our most recent identification of a DNA demethylation pathway in SMC that is pivotal in the regulation of the SMC phenotypic state. Many disorders are associated with smooth muscle dysfunction, including atherosclerosis, the major underlying cause of stroke and coronary heart disease, as well as transplant vasculopathy, aneurysm, asthma, hypertension, and cancer. An increased understanding of the major regulators of SMC plasticity will lead to the identification of novel target molecules that may, in turn, lead to novel drug discoveries for the treatment of these diseases. This article is part of a Special Issue entitled: Stress as a fundamental theme in cell plasticity.

Chromatin properties of regulatory DNA probed by manipulation of transcription factors

Transcription factors (TFs) bind to DNA and regulate the transcription of nearby genes. However, only a small fraction of TF binding sites have such regulatory effects. Here we search for the predictors of functional binding sites by carrying out a systematic computational screening of a variety of contextual factors (histone modifications, nuclear lamin-bindings, and cofactor bindings). We used regression analysis to test if contextual factors are associated with upregulation or downregulation of neighboring genes following the induction or knockdown of the 9 TFs in mouse embryonic stem (ES) cells. Functional TF binding sites appeared to be either active (i.e., bound by P300, CHD7, mediator, cohesin, and SWI/SNF) or repressed (i.e., with H3K27me3 histone marks and bound by Polycomb factors). Active binding sites mediated the downregulation of nearby genes upon knocking down the activating TFs or inducing repressors. Repressed TF binding sites mediated the upregulation of nearby genes (e.g., poised developmental regulators) upon inducing TFs. In addition, repressed binding sites mediated repressive effects of TFs, identified by the downregulation of target genes after the induction of TFs or by the upregulation of target genes after the knockdown of TFs. The contextual factors associated with functions of DNA-bound TFs were used to improve the identification of candidate target genes regulated by TFs.

Mechanical stretch suppresses microRNA-145 expression by activating extracellular signal-regulated kinase 1/2 and upregulating angiotensin-converting enzyme to alter vascular smooth muscle cell phenotype

Phenotype modulation of vascular smooth muscle cells (VSMCs) plays an important role in the pathogenesis of various vascular diseases, including hypertension and atherosclerosis. Several microRNAs (miRNAs) were found involved in regulating the VSMC phenotype with platelet-derived growth factor (PDGF) treatment, but the role of miRNAs in the mechanical stretch-altered VSMC phenotype is not clear. Here, we identified miR-145 as a major miRNA contributing to stretch-altered VSMC phenotype by miRNA array, quantitative RT-PCR and gain- and loss-of-function methods. Our data demonstrated that 16% stretch suppressed miR-145 expression, with reduced expression of contractile markers of VSMCs cultured on collagenI; overexpression of miR-145 could partially recover the expression in stretched cells. Serum response factor (SRF), myocardin, and Kruppel-like factor 4 (KLF4) are major regulators of the VSMC phenotype. The effect of stretch on myocardin and KLF4 protein expression was altered by miR-145 mimics, but SRF expression was not affected. In addition, stretch-activated extracellular signal-regulated kinase 1/2 (ERK1/2) and up-regulated angiotensin-converting enzyme (ACE) were confirmed to be responsible for the inhibition of miR-145 expression. Mechanical stretch inhibits miR-145 expression by activating the ERK1/2 signaling pathway and promoting ACE expression, thus modulating the VSMC phenotype.

Role of Krüppel-like factor 4 and its binding proteins in vascular disease

Krüppel-like factor 4(KLF4) is a zinc-finger transcription factor that plays a key role in cellular differentiation and proliferation during normal development and in various diseases, such as cancer. The results of recent studies have revealed that KLF4 is expressed in multiple vascular cell types, including phenotypically modulated smooth muscle cells(SMCs), endothelial cells and monocytes/macrophages and contributes to the progression of vascular diseases by activating or repressing the transcription of multiple genes via its associations with a variety of partner proteins. For example, KLF4 decreases the expression of markers of SMC differentiation by interacting with serum response factor, ELK1 and histone deacetylases. KLF4 also suppresses SMC proliferation by associating with p53. In addition, KLF4 enhances arterial medial calcification in concert with RUNX2. Furthermore, endothelial KLF4 represses arterial inflammation by binding to nuclear factor-κB. This article summarizes the role of KLF4 in vascular disease with a particular focus on in vivo studies and reviews recent progress in our understanding of the regulatory mechanisms involved in KLF4- mediated gene transcription.

Modulation of vascular smooth muscle cell phenotype by STAT-1 and STAT-3

OBJECTIVE

Smooth muscle cell (SMC) de-differentiation is a key step that leads to pathological narrowing of blood vessels. De-differentiation involves a reduction in the expression of the SMC contractile genes that are the hallmark of quiescent SMCs. While there is considerable evidence linking inflammation to vascular diseases, very little is known about the mechanisms by which inflammatory signals lead to SMC de-differentiation. Given that the Signal Transducers and Activators of Transcription (STAT) transcriptional factors are the key signaling molecules activated by many inflammatory cytokines and growth factors, the aim of the present study was to determine if STAT transcriptional factors play a role SMC de-differentiation.

METHODS AND RESULTS

Using shRNA targeted to STAT-1 and STAT-3, we show by real time RT-PCR and Western immunoblots that STAT-1 significantly reduces SMC contractile gene expression. In contrast, STAT-3 promotes expression of SMC contractile genes. Over-expression studies of STAT-1 and STAT-3 confirmed our observation that STAT-1 down-regulates whereas STAT-3 promotes SMC contractile gene expression. Bioinformatics analysis shows that promoters of all SMC contractile genes contain STAT binding sites. Finally, using ChIP analysis, we show that both STAT-1 and STAT-3 associate with the calponin gene.

CONCLUSION

These data indicate that the balance of STAT-1 and STAT-3 influences the differentiation status of SMCs. Increased levels of STAT-1 promote SMC de-differentiation, whereas high levels of STAT-3 drive SMC into a more mature phenotype. Thus, inhibition of STAT-1 may represent a novel target for therapeutic intervention in the control of vascular diseases such as atherosclerosis and restenosis.

Regulation of an inflammatory disease: Krüppel-like factors and atherosclerosis

This invited review summarizes work presented in the Russell Ross lecture delivered at the 2012 proceedings of the American Heart Association. We begin with a brief overview of the structural, cellular, and molecular biology of Krüppel-like factors. We then focus on discoveries during the past decade, implicating Krüppel-like factors as key determinants of vascular cell function in atherosclerotic vascular disease.

Arp5 is a key regulator of myocardin in smooth muscle cells

Arp5 suppresses myocardin activity through both direct binding to myocardin and binding to SRF to prevent transcriptional activation of myogenic genes by the myocardin–SRF complex.

Myocardin (Myocd) and Myocd-related transcription factors (MRTFs) are robust coactivators of serum response factor (SRF). RPEL motifs are monomeric globular actin (G-actin) binding elements that regulate MRTF localization and activity. However, the function of the RPEL motif in Myocd is largely unknown because of its low affinity for G-actin. Here, we demonstrated that the Myocd RPEL motif bound to actin-related protein 5 (Arp5) instead of conventional actin, resulting in a significant suppression of Myocd activity. In addition, Arp5 bound to a DNA binding domain of SRF via its C-terminal sequence and prevented the association of the Myocd–SRF complex with the promoter regions of smooth muscle genes. Well-differentiated smooth muscle cells mainly expressed a specific splicing variant of arp5; therefore, the protein level of Arp5 was markedly reduced by partial messenger RNA decay and translational suppression. In dedifferentiated smooth muscle cells, Arp5 knockdown restored the differentiated phenotype via Myocd activation. Thus, Arp5 is a key regulator of Myocd activity.