Programming smooth muscle plasticity with chromatin dynamics

The lysine methyltransferase SMYD2 facilitates neointimal hyperplasia by regulating the HDAC3-SRF axis

Coronary restenosis is an important cause of poor long-term prognosis in patients with coronary heart disease. Here, we show that lysine methyltransferase SMYD2 expression in the nucleus is significantly elevated in serum- and PDGF-BB-induced vascular smooth muscle cells (VSMCs), and in tissues of carotid artery injury-induced neointimal hyperplasia. Smyd2 overexpression in VSMCs (Smyd2-vTg) facilitates, but treatment with its specific inhibitor LLY-507 or SMYD2 knockdown significantly inhibits VSMC phenotypic switching and carotid artery injury-induced neointima formation in mice. Transcriptome sequencing revealed that SMYD2 knockdown represses the expression of serum response factor (SRF) target genes and that SRF overexpression largely reverses the inhibitory effect of SMYD2 knockdown on VSMC proliferation. HDAC3 directly interacts with and deacetylates SRF, which enhances SRF transcriptional activity in VSMCs. Moreover, SMYD2 promotes HDAC3 expression via tri-methylation of H3K36 at its promoter. RGFP966, a specific inhibitor of HDAC3, not only counteracts the pro-proliferation effect of SMYD2 overexpression on VSMCs, but also inhibits carotid artery injury-induced neointima formation in mice. HDAC3 partially abolishes the inhibitory effect of SMYD2 knockdown on VSMC proliferation in a deacetylase activity-dependent manner. Our results reveal that the SMYD2-HDAC3-SRF axis constitutes a novel and critical epigenetic mechanism that regulates VSMC phenotypic switching and neointimal hyperplasia.

SWI/SNF Complex in Vascular Smooth Muscle Cells and Its Implications in Cardiovascular Pathologies

Mature vascular smooth muscle cells (VSMC) exhibit a remarkable degree of plasticity, a characteristic that has intrigued cardiovascular researchers for decades. Recently, it has become increasingly evident that the chromatin remodeler SWItch/Sucrose Non-Fermentable (SWI/SNF) complex plays a pivotal role in orchestrating chromatin conformation, which is critical for gene regulation. In this review, we provide a summary of research related to the involvement of the SWI/SNF complexes in VSMC and cardiovascular diseases (CVD), integrating these discoveries into the current landscape of epigenetic and transcriptional regulation in VSMC. These novel discoveries shed light on our understanding of VSMC biology and pave the way for developing innovative therapeutic strategies in CVD treatment.

Epigenetic regulation of vascular smooth muscle cell phenotypic switch and neointimal formation by PRMT5

AIMS

Phenotypic transition of vascular smooth muscle cells (VSMCs) from a contractile to a synthetic state is involved in the development of cardiovascular diseases, including atherosclerosis, hypertension, and post-angioplasty restenosis. Arginine methylation catalyzed by protein arginine methyltransferases (PRMTs) has been implicated in multiple cellular processes, however, its role in VSMC biology remains undetermined. The objective of this study was to determine the role of PRMTs in VSMC phenotypic switch and vascular remodelling after injury.

METHODS AND RESULTS

Our results show that PRMT5 is the most abundantly expressed PRMT in human aortic SMCs, and its expression is up-regulated in platelet-derived growth factor (PDGF)-stimulated VSMCs, human atherosclerotic lesions, and rat carotid arteries after injury, as determined by western blot and immunohistochemical staining. PRMT5 overexpression inhibits the expression of SMC marker genes and promotes VSMC proliferation and migration, while silencing PRMT5 exerts the opposite effects. Mechanistically, we found that PRMT5 overexpression led to histone di-methylation of H3R8 and H4R3, which in turn attenuates acetylation of H3K9 and H4, thus limiting recruitment of the SRF/myocardin complexes to the CArG boxes of SMC marker genes. Furthermore, both SMC-specific deletion of PRMT5 in mice and local delivery of lentivirus expressing shPRMT5 to rat carotid arteries significantly attenuated neointimal formation after injury. Likewise, pharmacological inhibition of PRMT5 by EPZ015666 markedly inhibited carotid artery ligation-induced neointimal formation in mice.

CONCLUSIONS

Our results identify PRMT5 as a novel regulator in VSMC phenotypic switch and suggest that inhibition of PRMT5 may represent an effective therapeutic strategy for proliferative vascular diseases.

KLF4-PFKFB3-driven glycolysis is essential for phenotypic switching of vascular smooth muscle cells

Vascular smooth muscle cells (VSMCs) within atherosclerotic lesions undergo a phenotypic switching in a KLF4-dependent manner. Glycolysis plays important roles in transdifferentiation of somatic cells, however, it is unclear whether and how KLF4 mediates the link between glycolytic switch and VSMCs phenotypic transitions. Here, we show that KLF4 upregulation accompanies VSMCs phenotypic switching in atherosclerotic lesions. KLF4 enhances the metabolic switch to glycolysis through increasing PFKFB3 expression. Inhibiting glycolysis suppresses KLF4-induced VSMCs phenotypic switching, demonstrating that glycolytic shift is required for VSMCs phenotypic switching. Mechanistically, KLF4 upregulates expression of circCTDP1 and eEF1A2, both of which cooperatively promote PFKFB3 expression. TMAO induces glycolytic shift and VSMCs phenotypic switching by upregulating KLF4. Our study indicates that KLF4 mediates the link between glycolytic switch and VSMCs phenotypic transitions, suggesting that a previously unrecognized KLF4-eEF1A2/circCTDP1-PFKFB3 axis plays crucial roles in VSMCs phenotypic switching.

Chaetocin attenuates atherosclerosis progression and inhibits vascular smooth muscle cell phenotype switching

We aimed to explore the effect of chaetocin on atherosclerosis and its possible mechanism. In vitro, we observed that chaetocin treatment significantly inhibited the proliferation of VSMCs in concentration- and time-dependent manner. We also found that chaetocin suppressed the migration of VSMCs. Moreover, chaetocin treatment induced a contractile phenotype in VSMCs by increasing α-SMA and SM22α expression. In addition, chaetocin treatment attenuated the accumulation of H3K9me3 on VSMCs contractile gene promoters, which promoted the expression of α-SMA and SM22α. In vivo, chaetocin treatment decreased the H3K9me3 expression, diminished atherosclerotic plaque formation, and increased plaque stability by decreasing necrotic core area and lipid accumulation and increasing collagen content and contractile VSMC phenotype. We demonstrated a new function of chaetocin in inhibiting atherosclerosis progression and increasing plaque stability partly by inhibiting pathological phenotypic switching of VSMCs. These newly identified roles of chaetocin might provide a novel therapeutic target in atherosclerosis.

Smooth muscle cell FTO regulates contractile function

The fat mass and obesity gene (FTO) is a N6-methyladenosine RNA demethylase that was initially linked by Genome-wide association studies to increased rates of obesity. Subsequent studies have revealed multiple mass-independent effects of the gene, including cardiac myocyte contractility. We created a mouse with a conditional and inducible smooth muscle cell deletion of Fto (Myh11 Cre+ Ftofl/fl) and did not observe any changes in mouse body mass or mitochondrial metabolism. However, the mice had significantly decreased blood pressure (hypotensive), despite increased heart rate and sodium, and significantly increased plasma renin. Remarkably, the third-order mesenteric arteries from these mice had almost no myogenic tone or capacity to constrict to smooth muscle depolarization or phenylephrine. Microarray analysis from Fto-/--isolated smooth muscle cells demonstrated a significant decrease in serum response factor (Srf) and the downstream effectors Acta2, Myocd, and Tagln; this was confirmed in cultured human coronary arteries with FTO siRNA. We conclude Fto is an important component to the contractility of smooth muscle cells.NEW & NOTEWORTHY We show a key role for the fat mass obesity (FTO) gene in regulating smooth muscle contractility, possibly by methylation of serum response factor (Srf).

Platelet derived growth factor and its receptor in intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a common and highly disabling or fatal neurological disorder in adults. Recent studies have suggested that the platelet derived growth factor (PDGF) signaling pathway plays an important role in the development of ICH. PDGF is involved in vascular remodeling and can be used as a biomarker of cerebral amyloid angiopathy which is one of the major causes of ICH. PDGF and its receptors are involved in the mechanism of the secondary injury after ICH by affecting the integrity of the blood-brain barrier and inflammatory response. PDGF and its receptors may also participate in the mechanism of repair after ICH by promoting angiogenesis. This article reviews the latest research progress on the involvement of PDGF signaling pathway in the pathophysiology of intracerebral hemorrhage, and introduces the relevant antagonists using PDGFR as the therapeutic target, to provide information for the development of therapeutic options for intracerebral hemorrhage.

Activation of AMP-activated protein kinase ablated the formation of aortic dissection by suppressing vascular inflammation and phenotypic switching of vascular smooth muscle cells

BACKGROUND

Aortic dissection (AD) is a fatal vascular disease in absence of effective pharmaceutical therapy. Adenosine monophosphate-activated protein kinase α (AMPKα) plays a critical role in various cardiovascular diseases. Whether AMPKα is involved in the pathogenesis of aortic dissection remains unknown. We aimed to determine whether activation of AMPKα prevents the formation of AD.

METHODS AND RESULTS

Reduced expression of phosphorylated AMPKα (Thr172) and exacerbated phenotypic switching were observed in human aortic tissues from aortic dissection patients compared with those in tissues from controls. In vivo, the formation of aortic dissection in ApoE^-/- mice was successfully induced by continuous infusion of angiotensin II (AngII) for two weeks, characterized by the activation of vascular inflammation, infiltration of macrophages and phenotypic switching of vascular smooth muscle cells (VSMCs). rAAV2-mediated overexpression of constitutively active AMPKα (CA-AMPKα) enhanced the expression of phosphorylated AMPKα (Thr172) and attenuated AngII-induced occurrence of aortic dissection by suppressing the infiltration of macrophages, activation of vascular inflammation and phenotypic switching of VSMCs. The pathogenesis above was conversely exacerbated by rAAV2-mediated overexpression of dominant negative AMPKα2 (DN-AMPKα). In vitro, we demonstrated that the administration of an AMPK agonist (AICAR) or transfection of CA-AMPKα induced the activation of AMPKα and then ameliorated AngII-induced phenotypic switching in the VSMCs and inflammation in the bone marrow-derived macrophages (BMDMs). This could be reversed by the addition of AMPK inhibitor compound C or transfection of DN-AMPKα.

CONCLUSION

Impaired activation of AMPKα may increase the susceptibility to aortic dissection. Our findings verified the protective effects of AMPKα on the formation of aortic dissection and may provide evidence for clinical prevention or treatment.

LSD1 downregulates p21 expression in vascular smooth muscle cells and promotes neointima formation

Neointima formation is characterized by the proliferation of vascular smooth muscle cells (VSMC). Although lysine-specific demethylase 1 (LSD1) has critical functions in several diseases, its role in neointima formation remains to be clarified. In this study, we aimed to explore the crucial role of LSD1 on neointima formation using a carotid artery injury model in mice. We observed that aberrant LSD1 expression was increased in human and mouse stenotic arteries and platelet-derived growth factor-BB (PDGF-BB)-treated VSMC. Furthermore, LSD1 knockdown significantly mitigated neointima formation in vivo and inhibited PDGF-BB-induced VSMC proliferation in vitro. We further uncovered that LSD1 overexpression exhibited opposite phenotypes in vivo and in vitro. Finally, LSD1 knockdown inhibited VSMC proliferation by increasing p21 expression, which is associated with LSD1 mediated di-methylated histone H3 on lysine 4 (H3K4me2) modification. Taken together, our data suggest that LSD1 may be a potential therapeutic target for the treatment of neointima formation.

FAK Activation Promotes SMC Dedifferentiation via Increased DNA Methylation in Contractile Genes

Rationale: Vascular smooth muscle cells (SMCs) exhibit remarkable plasticity and can undergo dedifferentiation upon pathological stimuli associated with disease and interventions. Objective: Although epigenetic changes are critical in SMC phenotype switching, a fundamental regulator that governs the epigenetic machineries regulating the fate of SMC phenotype has not been elucidated. Methods and Results: Using SMCs, mouse models, and human atherosclerosis specimens, we found that focal adhesion kinase (FAK) activation elicits SMC dedifferentiation by stabilizing DNA methyltransferase 3A (DNMT3A). FAK in SMCs is activated in the cytoplasm upon serum stimulation in vitro or vessel injury and active FAK prevents DNMT3A from nuclear FAK-mediated degradation. However, pharmacological or genetic FAK catalytic inhibition forced FAK nuclear localization, which reduced DNMT3A protein via enhanced ubiquitination and proteasomal degradation. Reduced DNMT3A protein led to DNA hypomethylation in contractile gene promoters, which increased SMC contractile protein expression. RNA sequencing identified SMC contractile genes as a foremost upregulated group by FAK inhibition from injured femoral artery samples compared to vehicle group. DNMT3A knockdown in injured arteries reduced DNA methylation and enhanced contractile gene expression supports the notion that nuclear FAK-mediated DNMT3A degradation via E3 ligase TRAF6 drives differentiation of SMCs. Furthermore, we observed that SMCs of human atherosclerotic lesions exhibited decreased nuclear FAK, which was associated with increased DNMT3A levels and decreased contractile gene expression. Conclusions: This study reveals that nuclear FAK induced by FAK catalytic inhibition specifically suppresses DNMT3A expression in injured vessels resulting in maintaining SMC differentiation by promoting the contractile gene expression. Thus, FAK inhibitors may provide a new treatment option to block SMC phenotypic switching during vascular remodeling and atherosclerosis.

Regulation of endothelial cell differentiation in embryonic vascular development and its therapeutic potential in cardiovascular diseases

During vertebrate development, the cardiovascular system begins operating earlier than any other organ in the embryo. Endothelial cell (EC) forms the inner lining of blood vessels, and its extensive proliferation and migration are requisite for vasculogenesis and angiogenesis. Many aspects of cellular biology are involved in vasculogenesis and angiogenesis, including the tip versus stalk cell specification. Recently, epigenetics has attracted growing attention in regulating embryonic vascular development and controlling EC differentiation. Some proteins that regulate chromatin structure have been shown to be directly implicated in human cardiovascular diseases. Additionally, the roles of important EC signaling such as vascular endothelial growth factor and its receptors, angiopoietin-1 and tyrosine kinase containing immunoglobulin and epidermal growth factor homology domain-2, and transforming growth factor-β in EC differentiation during embryonic vasculature development are briefly discussed in this review. Recently, the transplantation of human induced pluripotent stem cell (iPSC)-ECs are promising approaches for the treatment of ischemic cardiovascular disease including myocardial infarction. Patient-specific iPSC-derived EC is a potential new target to study differences in gene expression or response to drugs. However, clinical application of the iPSC-ECs in regenerative medicine is often limited by the challenges of maintaining cell viability and function. Therefore, novel insights into the molecular mechanisms underlying EC differentiation might provide a better understanding of embryonic vascular development and bring out more effective EC-based therapeutic strategies for cardiovascular diseases.

Multiple cell types contribute to the atherosclerotic lesion fibrous cap by PDGFRβ and bioenergetic mechanisms

Stable atherosclerotic plaques are characterized by a thick, extracellular matrix-rich fibrous cap populated by protective ACTA2⁺ myofibroblast (MF)-like cells, assumed to be almost exclusively derived from smooth muscle cells (SMCs). Herein, we show that in murine and human lesions, 20% to 40% of ACTA2⁺ fibrous cap cells, respectively, are derived from non-SMC sources, including endothelial cells (ECs) or macrophages that have undergone an endothelial-to-mesenchymal transition (EndoMT) or a macrophage-to-mesenchymal transition (MMT). In addition, we show that SMC-specific knockout of the Pdgfrb gene, which encodes platelet-derived growth factor receptor beta (PDGFRβ), in Apoe^-/- mice fed a Western diet for 18 weeks resulted in brachiocephalic artery lesions nearly devoid of SMCs but with no changes in lesion size, remodelling or indices of stability, including the percentage of ACTA2⁺ fibrous cap cells. However, prolonged Western diet feeding of SMC Pdgfrb-knockout mice resulted in reduced indices of stability, indicating that EndoMT- and MMT-derived MFs cannot compensate indefinitely for loss of SMC-derived MFs. Using single-cell and bulk RNA-sequencing analyses of the brachiocephalic artery region and in vitro models, we provide evidence that SMC-to-MF transitions are induced by PDGF and transforming growth factor-β and dependent on aerobic glycolysis, while EndoMT is induced by interleukin-1β and transforming growth factor-β. Together, we provide evidence that the ACTA2⁺ fibrous cap originates from a tapestry of cell types, which transition to an MF-like state through distinct signalling pathways that are either dependent on or associated with extensive metabolic reprogramming.

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.

Reactive Oxygen Species: Modulators of Phenotypic Switch of Vascular Smooth Muscle Cells

Reactive oxygen species (ROS) are natural byproducts of oxygen metabolism in the cell. At physiological levels, they play a vital role in cell signaling. However, high ROS levels cause oxidative stress, which is implicated in cardiovascular diseases (CVD) such as atherosclerosis, hypertension, and restenosis after angioplasty. Despite the great amount of research conducted to identify the role of ROS in CVD, the image is still far from being complete. A common event in CVD pathophysiology is the switch of vascular smooth muscle cells (VSMCs) from a contractile to a synthetic phenotype. Interestingly, oxidative stress is a major contributor to this phenotypic switch. In this review, we focus on the effect of ROS on the hallmarks of VSMC phenotypic switch, particularly proliferation and migration. In addition, we speculate on the underlying molecular mechanisms of these cellular events. Along these lines, the impact of ROS on the expression of contractile markers of VSMCs is discussed in depth. We conclude by commenting on the efficiency of antioxidants as CVD therapies.

Role of smooth muscle cells in Cardiovascular Disease

Normally, smooth muscle cells (SMCs) are localized in the tunica media of the vasculature, where they take responsibility for vascular contraction and extracellular matrix (ECM) generation. SMCs also play a significant role in obedience and elastic rebound of the artery in response to the haemodynamic condition. However, under pathological or stressed conditions, phenotype switching from contractile to synthetic state or other cell types will occur in SMCs to positively or negatively contribute to disease progression. Various studies demonstrated that functional changes of SMCs are implicated in several cardiovascular diseases. In this review, we present the function of vascular SMCs (VSMCs) and the involved molecular mechanisms about phenotype switching, and summarize the roles of SMCs in atherosclerosis, hypertension, arterial aneurysms and myocardial infarction, hoping to obtain potential therapeutic targets against cardiovascular disease in the clinical practices.

A novel role of VEPH1 in regulating AoSMC phenotypic switching

Abdominal aortic aneurysm (AAA) is a potentially lethal disease featured by focal dilatation in the aorta. The transition of vascular smooth muscle cells (SMCs) from a contractile/differentiated to a synthetic/dedifferentiated phenotype is considered to contribute to AAA formation and expansion. Our previous gene microarray data showed that Ventricular Zone Expressed PH Domain Containing 1 (VEPH1) expression increased in angiotensin II (Ang II)-infused aortic tissues. This study was thus performed to further explore the role of VEPH1. Herein, we first demonstrate that VEPH1 increases in the SMCs of Ang II-treated abdominal aortas. As in vivo, Ang II also upregulated VEPH1 expression in cultured hAoSMCs. The dedifferentiation of human aortic SMCs (hAoSMCs) was induced by a 24-hr stimulation of Ang II (1 μM)-the expression of contractile SMC markers, MYH11 and α-smooth muscle actin (α-SMA) decreased and that of synthetic markers, proliferating cell nuclear antigen and Vimentin increased. Inhibition of VEPH1 prevented Ang II-induced pathological dedifferentiation of hAoSMCs as indicated by the restored expression of MYH11 and α-SMA. In contrast, the forced overexpression of VEPH1 aggravated Ang II's effects. Furthermore, we demonstrated that VEPH1 and transforming growth factor-β1 (TGF-β1), a key regulator responsible for vascular SMC differentiation, negatively regulated each other's transcription. In contrast to VEPH1 silencing, its overexpression inhibited recombinant TGF-β1-induced increases in MYH11 and α-SMA and suppressed Smad3 phosphorylation and nuclear accumulation. Collectively, our study demonstrates that VEPH1 elevation promotes the synthetic phenotype switching of AoSMCs and suppressed the TGF-β1/Smad3 signaling pathway. Identification of VEPH1 as a pathogenic molecule for AAA formation provides novel insights into this disease.

Aortic Aneurysms and Dissections Series

The aortic wall is composed of highly dynamic cell populations and extracellular matrix. In response to changes in the biomechanical environment, aortic cells and extracellular matrix modulate their structure and functions to increase aortic wall strength and meet the hemodynamic demand. Compromise in the structural and functional integrity of aortic components leads to aortic degeneration, biomechanical failure, and the development of aortic aneurysms and dissections (AAD). A better understanding of the molecular pathogenesis of AAD will facilitate the development of effective medications to treat these conditions. Here, we summarize recent findings on AAD published in ATVB. In this issue, we focus on the dynamics of aortic cells and extracellular matrix in AAD; in the next issue, we will focus on the role of signaling pathways in AAD.

Early Programming of Adult Systemic Essential Hypertension

Cardiovascular diseases are being included in the study of developmental origins of health and disease (DOHaD) and essential systemic hypertension has also been added to this field. Epigenetic modifications are one of the main mechanisms leading to early programming of disease. Different environmental factors occurring during critical windows in the early stages of life may leave epigenetic cues, which may be involved in the programming of hypertension when individuals reach adulthood. Such environmental factors include pre-term birth, low weight at birth, altered programming of different organs such as the blood vessels and the kidney, and living in disadvantageous conditions in the programming of hypertension. Mechanisms behind these factors that impact on the programming include undernutrition, oxidative stress, inflammation, emotional stress, and changes in the microbiota. These factors and their underlying causes acting at the vascular level will be discussed in this paper. We also explore the establishment of epigenetic cues that may lead to hypertension at the vascular level such as DNA methylation, histone modifications (methylation and acetylation), and the role of microRNAs in the endothelial cells and blood vessel smooth muscle which participate in hypertension. Since epigenetic changes are reversible, the knowledge of this type of markers could be useful in the field of prevention, diagnosis or epigenetic drugs as a therapeutic approach to hypertension.

Dynamic transcriptome, accessible genome, and PGR cistrome profiles in the human myometrium

The myometrium undergoes structural and functional remodeling during pregnancy. We hypothesize that myometrial genomic elements alter correspondingly in preparation for parturition. Human myometrial tissues from nonpregnant (NP) and term pregnant (TP) human subjects were examined by RNAseq, ATACseq, and PGR ChIPseq assays to profile transcriptome, assessible genome, and PGR occupancy. NP and TP specimens exhibit 2890 differentially expressed genes, reflecting an increase of metabolic, inflammatory, and PDGF signaling, among others, in adaptation to pregnancy. At the epigenome level, patterns of accessible genome change between NP and TP myometrium, leading to the altered enrichment of binding motifs for hormone and muscle regulators such as the progesterone receptor (PGR), Krüppel-like factors, and MEF2A transcription factors. PGR genome occupancy exhibits a significant difference between the two stages of the myometrium, concomitant with distinct transcriptomic profiles including genes such as ENO1, LHDA, and PLCL1 in the glycolytic and calcium signaling pathways. Over-representation of SRF, MYOD, and STAT binding motifs in PGR occupying sites further suggests interactions between PGR and major muscle regulators for myometrial gene expression. In conclusion, changes in accessible genome and PGR occupancy are part of the myometrial remodeling process and may serve as mechanisms to formulate the state-specific transcriptome profiles.

Ablation of serum response factor in hepatic stellate cells attenuates liver fibrosis

Trans-differentiation, or activation, of hepatic stellate cells (HSCs) is a hallmark event in liver fibrosis although the underlying mechanism is not fully appreciated. Serum response factor (SRF) is a pleiotropic sequence-specific transcription factor with a ubiquitous expression pattern. In the present study, we investigated the effect of HSC-specific ablation of SRF on liver fibrosis in vivo and the underlying mechanism. We report that SRF bound to the promoter regions of pro-fibrogenic genes, including collagen type I (Col1a1/Col1a2) and alpha smooth muscle actin (Acta2), with greater affinity in activated HSCs compared to quiescent HSCs. Ablation of SRF in HSCs in vitro downregulated the expression of fibrogenic genes by dampening the accumulation of active histone marks. SRF also interacted with MRTF-A, a well-documented co-factor involved in liver fibrosis, on the pro-fibrogenic gene promoters during HSC activation. In addition, SRF directly regulated MRTF-A transcription in activated HSCs. More importantly, HSC conditional SRF knockout (CKO) mice developed a less robust pro-fibrogenic response in the liver in response to CCl₄ injection and BDL compared to wild-type littermates. In conclusion, our data demonstrate that SRF may play an essential role in HSC activation and liver fibrosis. KEY MESSAGES: • SRF deficiency decelerates activation of hepatic stellate cells (HSCs) in vitro. • SRF epigenetically activates pro-fibrogenic transcription to promote HSC maturation. • SRF interacts with MRTF-A and contributes to MRTF-A transcription. • Conditional SRF deletion in HSCs attenuates BDL-induced liver fibrosis in mice. • Conditional SRF ablation in HSCs attenuates CCl₄-induced liver fibrosis in mice.

Uterine spiral artery muscle dedifferentiation

STUDY QUESTION

Is vascular smooth muscle cell (VSMC) dedifferentiation a feature of uterine spiral artery (SpA) remodelling in early human pregnancy?

SUMMARY ANSWER

Remodelling of human uterine SpAs is associated with dedifferentiation of VSMCs and can be induced in vitro by uterine natural killer (uNK) cells and extravillous trophoblast cells (EVTs).

WHAT IS KNOWN ALREADY

Uterine SpAs undergo profound morphological changes in normal pregnancy with replacement of the musculoelastic arterial wall structure by fibrinoid containing EVTs. The fate of VSMCs in SpA remodelling is unknown; in guinea pig uterine artery VSMCs dedifferentiate, remain in the vessel wall and differentiate after parturition to restore the arterial wall. There is increasing evidence that uNK cells play a role in SpA remodelling. We hypothesized that SpA remodelling in human pregnancy is associated with VSMC dedifferentiation, initiated by uNK cell-derived growth factors.

STUDY DESIGN, SIZE, DURATION

Formalin fixed, paraffin embedded placental bed biopsies were immunostained for angiogenic growth factor (AGF) receptors and markers of VSMC differentiation. An in vitro model of SpA remodelling using chorionic plate arteries (CPAs) was used to test the effect of different cell types and AGFs on VSMC differentiation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Placental bed biopsies were immunostained for vascular endothelial growth factor receptors 1-3 (VEGF-R1, VEGF-R2, VEGF-R3), transforming growth factor beta 1 receptors I and II (TGF-βRI, TGF-βRII), interferon gamma receptors 1 and 2 (IFN-γR1, IFN-γR2), Tie2, α-smooth muscle actin (α-SMA), H-caldesmon (H-Cal), myosin heavy chain (MyHC), osteopontin and smoothelin. Staining intensity was assessed using a modified quickscore. Expression by VSMCs of the AGF receptors was confirmed by laser capture microdissection and real-time RT-PCR of non-remodelled SpAs, after laser removal of the endothelium. As an in vitro model, VSMC differentiation was assessed in CPAs by immunohistochemistry after culture in uNK cell-conditioned medium (CM), EVT-CM, uNK cell/EVT co-culture CM, Ang-1, Ang-2, IFN-γ, VEGF-A and VEGF-C, and after blocking of both Ang-1 and Ang-2 in uNK-CM.

MAIN RESULTS AND THE ROLE OF CHANCE

SpA VSMC expression of Tie-2 (P = 0.0007), VEGF-R2 (P = 0.005) and osteopontin (P = 0.0001) increased in partially remodelled SpAs compared with non-remodelled SpAs, while expression of contractile VSMC markers was reduced (α-SMA P < 0.0001, H-Cal P = 0.03, MyHC P = 0.03, smoothelin P = 0.0001). In the in vitro CPA model, supernatants from purified uNK cell (H-Cal P < 0.0001, MyHC P = 0.03, α-SMA P = 0.02, osteopontin P = 0.03), EVT (H-Cal P = 0.0006, MyHC P = 0.02, osteopontin P = 0.01) and uNK cell/EVT co-cultures (H-Cal P = 0.001, MyHC P = 0.05, osteopontin P = 0.02) at 12–14 weeks, but not 8–10 weeks, gestational age induced reduced expression of contractile VSMC markers and increased osteopontin expression. Addition of exogenous (10 ng/ml) Ang-1 (P = 0.006) or Ang-2 (P = 0.009) also reduced H-Cal expression in the CPA model. Inhibition of Ang-1 (P = 0.0004) or Ang-2 (P = 0.004) in uNK cell supernatants blocked the ability of uNK cell supernatants to reduce H-Cal expression.

LIMITATIONS, REASONS FOR CAUTION

This is an in vitro study and the role of uNK cells, Ang-1 and Ang-2 in SpA remodelling in vivo has not yet been shown.

WIDER IMPLICATIONS OF THE FINDINGS

VSMC dedifferentiation is a feature of early SpA remodelling and uNK cells and EVT play key roles in this process by secretion of Ang-1 and Ang-2. This is one of the first studies to suggest a direct role for Ang-1 and Ang-2 in VSMC biology.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by a grant from British Biotechnology and Biosciences Research Council (BB/E016790/1). The authors have no competing interests to declare.

Smooth muscle cell fate and plasticity in atherosclerosis

Current knowledge suggests that intimal smooth muscle cells (SMCs) in native atherosclerotic plaque derive mainly from the medial arterial layer. During this process, SMCs undergo complex structural and functional changes giving rise to a broad spectrum of phenotypes. Classically, intimal SMCs are described as dedifferentiated/synthetic SMCs, a phenotype characterized by reduced expression of contractile proteins. Intimal SMCs are considered to have a beneficial role by contributing to the fibrous cap and thereby stabilizing atherosclerotic plaque. However, intimal SMCs can lose their properties to such an extent that they become hard to identify, contribute significantly to the foam cell population, and acquire inflammatory-like cell features. This review highlights mechanisms of SMC plasticity in different stages of native atherosclerotic plaque formation, their potential for monoclonal or oligoclonal expansion, as well as recent findings demonstrating the underestimated deleterious role of SMCs in this disease.

Coronary Intimal Thickening Begins in Fetuses and Progresses in Pediatric Population and Adolescents to Atherosclerosis

The prevalence of coronary intimal thickening (IT) was assessed in fetuses and pediatric population. We studied the coronary arteries of 63 hearts obtained from fetuses, infants, children, and adolescents, deceased from noncardiac disease or trauma. Histomorphometric analysis, planimetry, and immunohistochemical studies were conducted. Intimal thickening consisted of proliferation of smooth muscle cells and scarce monocytes embedded in amorphous deposits within the internal elastic membrane (IEM). Intermingled lesions of intimal hyperplasia and parietal nonstenotic plaques were also observed. Intimal thickening was found in 10% of 20 fetuses, in 33.3% of 18 infants, 73.3% of 15 children, and 100% of 10 adolescents. A significant correlation (r = 0.671, P < 0.001) was found between the extent of IT and age. The IEM was duplicated or interrupted in 43% of patients, showing a positive correlation with the degree of IT (P = 0.01). Intimal thickening was predominantly found near bifurcation sites in the left anterior descending coronary artery (55.6%) and in zones free of bifurcation in the right coronary artery (75%). In conclusion, the prevalence and extension of IT lesions are higher at older ages within a young population. Intimal thickening may be regarded as the first event occurring in coronary preatherosclerosis, preceding lipid deposition.

The phenotype of vascular smooth muscle cells co-cultured with endothelial cells is modulated by PDGFR-β/IQGAP1 signaling in LPS-induced intravascular injury

Background Sepsis, a leading cause of death in intensive care units, is generally associated with vascular dysfunction. However, its pathophysiological process has not been fully clarified, lacking in-depth knowledge of its pathophysiological process may hinder the improvement of diagnosis and therapy for sepsis. Hence, as the key parts of the vascular wall, the interaction between endothelial cells (ECs) and smooth muscle cells (SMCs) under septic situation need to be further studied. Methods ECs and SMCs were co-cultured using Transwell plates. Lipopolysaccharide (LPS) was used to induce sepsis. A scratch-wound assay was used to assess cell migration, and western blotting was used to assess the level of redifferentiation of SMCs as well as the expression of PDGFR-β and IQGAP1. Results Co-culture with ECs reduced the redifferentiation of SMCs induced by LPS (10 μg/ml), which was characterized by increased migration ability and decreased expression of contractile proteins (e.g., SM22 and α-SMA). The production of TNF-α could decrease the level of PDGFR-β in SMCs. Treatment of SMCs with the PDGFR-β inhibitor imatinib (5 μM) was able to counteract LPS-induced SMC redifferentiation and reduce IQGAP1 protein expression, especially when SMCs were co-cultured with ECs. Conclusion The phenotype of vascular SMCs co-cultured with ECs was modulated by IQGAP1 through the PDGFR-β pathway, which may lead to vascular remodeling and homeostasis in LPS-induced intravascular injury. This pathway could be a novel target for the treatment of vascular damage.

UHRF1 epigenetically orchestrates smooth muscle cell plasticity in arterial disease

Adult vascular smooth muscle cells (VSMCs) dedifferentiate in response to extracellular cues such as vascular damage and inflammation. Dedifferentiated VSMCs are proliferative, migratory, less contractile, and can contribute to vascular repair as well as to cardiovascular pathologies such as intimal hyperplasia/restenosis in coronary artery and arterial aneurysm. We here demonstrate the role of ubiquitin-like containing PHD and RING finger domains 1 (UHRF1) as an epigenetic master regulator of VSMC plasticity. UHRF1 expression correlated with the development of vascular pathologies associated with modulation of noncoding RNAs, such as microRNAs. miR-145 - pivotal in regulating VSMC plasticity, which is reduced in vascular diseases - was found to control Uhrf1 mRNA translation. In turn, UHRF1 triggered VSMC proliferation, directly repressing promoters of cell-cycle inhibitor genes (including p21 and p27) and key prodifferentiation genes via the methylation of DNA and histones. Local vascular viral delivery of Uhrf1 shRNAs or Uhrf1 VSMC-specific deletion prevented intimal hyperplasia in mouse carotid artery and decreased vessel damage in a mouse model of aortic aneurysm. Our study demonstrates the fundamental role of Uhrf1 in regulating VSMC phenotype by promoting proliferation and dedifferentiation. UHRF1 targeting may hold therapeutic potential in vascular pathologies.

DNA methylation, through DNMT1, has an essential role in the development of gastrointestinal smooth muscle cells and disease

DNA methylation is a key epigenetic modification that can regulate gene expression. Genomic DNA hypomethylation is commonly found in many gastrointestinal (GI) diseases. Dysregulated gene expression in GI smooth muscle cells (GI-SMCs) can lead to motility disorders. However, the consequences of genomic DNA hypomethylation within GI-SMCs are still elusive. Utilizing a Cre-lox murine model, we have generated SMC-restricted DNA methyltransferase 1 (Dnmt1) knockout (KO) mice and analyzed the effects of Dnmt1 deficiency. Dnmt1-KO pups are born smaller than their wild-type littermates, have shortened GI tracts, and lose peristaltic movement due to loss of the tunica muscularis in their intestine, causing massive intestinal dilation, and death around postnatal day 21. Within smooth muscle tissue, significant CpG hypomethylation occurs across the genome at promoters, introns, and exons. Additionally, there is a marked loss of differentiated SMC markers (Srf, Myh11, miR-133, miR-143/145), an increase in pro-apoptotic markers (Nr4a1, Gadd45g), loss of cellular connectivity, and an accumulation of coated vesicles within SMC. Interestingly, we observed consistent abnormal expression patterns of enzymes involved in DNA methylation between both Dnmt1-KO mice and diseased human GI tissue. These data demonstrate that DNA hypomethylation in embryonic SMC, via congenital Dnmt1 deficiency, contributes to massive dysregulation of gene expression and is lethal to GI-SMC. These results suggest that Dnmt1 has a necessary role in the embryonic, primary development process of SMC with consistent patterns being found in human GI diseased tissue.

Cigarette Smoke Initiates Oxidative Stress-Induced Cellular Phenotypic Modulation Leading to Cerebral Aneurysm Pathogenesis

OBJECTIVE

Cigarette smoke exposure (CSE) is a risk factor for cerebral aneurysm (CA) formation, but the molecular mechanisms are unclear. Although CSE is known to contribute to excess reactive oxygen species generation, the role of oxidative stress on vascular smooth muscle cell (VSMC) phenotypic modulation and pathogenesis of CAs is unknown. The goal of this study was to investigate whether CSE activates a NOX (NADPH oxidase)-dependent pathway leading to VSMC phenotypic modulation and CA formation and rupture.

APPROACH AND RESULTS

In cultured cerebral VSMCs, CSE increased expression of NOX1 and reactive oxygen species which preceded upregulation of proinflammatory/matrix remodeling genes (MCP-1, MMPs [matrix metalloproteinase], TNF-α, IL-1β, NF-κB, KLF4 [Kruppel-like factor 4]) and downregulation of contractile genes (SM-α-actin [smooth muscle α actin], SM-22α [smooth muscle 22α], SM-MHC [smooth muscle myosin heavy chain]) and myocardin. Inhibition of reactive oxygen species production and knockdown of NOX1 with siRNA or antisense decreased CSE-induced upregulation of NOX1 and inflammatory genes and downregulation of VSMC contractile genes and myocardin. p47phox^-/- NOX knockout mice, or pretreatment with the NOX inhibitor, apocynin, significantly decreased CA formation and rupture compared with controls. NOX1 protein and mRNA expression were similar in p47phox^-/- mice and those pretreated with apocynin but were elevated in unruptured and ruptured CAs. CSE increased CA formation and rupture, which was diminished with apocynin pretreatment. Similarly, NOX1 protein and mRNA and reactive oxygen species were elevated by CSE, and in unruptured and ruptured CAs.

CONCLUSIONS

CSE initiates oxidative stress-induced phenotypic modulation of VSMCs and CA formation and rupture. These molecular changes implicate oxidative stress in the pathogenesis of CAs and may provide a potential target for future therapeutic strategies.

Targeting AGGF1 (angiogenic factor with G patch and FHA domains 1) for Blocking Neointimal Formation After Vascular Injury

Background

Despite recent improvements in angioplasty and placement of drug‐eluting stents in treatment of atherosclerosis, restenosis and in‐stent thrombosis impede treatment efficacy and cause numerous deaths. Research efforts are needed to identify new molecular targets for blocking restenosis. We aim to establish angiogenic factor AGGF1 (angiogenic factor with G patch and FHA domains 1) as a novel target for blocking neointimal formation and restenosis after vascular injury.

Methods and Results

AGGF1 shows strong expression in carotid arteries; however, its expression is markedly decreased in arteries after vascular injury. AGGF1^+/− mice show increased neointimal formation accompanied with increased proliferation of vascular smooth muscle cells (VSMCs) in carotid arteries after vascular injury. Importantly, AGGF1 protein therapy blocks neointimal formation after vascular injury by inhibiting the proliferation and promoting phenotypic switching of VSMCs to the contractile phenotype in mice in vivo. In vitro, AGGF1 significantly inhibits VSMCs proliferation and decreases the cell numbers at the S phase. AGGF1 also blocks platelet‐derived growth factor‐BB–induced proliferation, migration of VSMCs, increases expression of cyclin D, and decreases expression of p21 and p27. AGGF1 inhibits phenotypic switching of VSMCs to the synthetic phenotype by countering the inhibitory effect of platelet‐derived growth factor‐BB on SRF expression and the formation of the myocardin/SRF/CArG‐box complex involved in activation of VSMCs markers. Finally, we show that AGGF1 inhibits platelet‐derived growth factor‐BB–induced phosphorylation of MEK1/2, ERK1/2, and Elk phosphorylation involved in the phenotypic switching of VSMCs, and that overexpression of Elk abolishes the effect of AGGF1.

Conclusions

AGGF1 protein therapy is effective in blocking neointimal formation after vascular injury by regulating a novel AGGF1‐MEK1/2‐ERK1/2‐Elk‐myocardin‐SRF/p27 signaling pathway.

Platelet-Derived Growth Factor Receptor-β Regulates Vascular Smooth Muscle Cell Phenotypic Transformation and Neuroinflammation After Intracerebral Hemorrhage in Mice

OBJECTIVE

Platelet-derived growth factor-BB activates platelet-derived growth factor receptor-β and promotes vascular smooth muscle cell phenotypic transformation. Elevated levels of non-muscle myosin IIB (SMemb) are found in secretory smooth muscle cells along with inflammatory mediators, such as intercellular adhesion molecule-1, which can amplify neutrophil infiltration into the brain. In the present study, we investigated the role of platelet-derived growth factor-BB/platelet-derived growth factor receptor-β following intracerebral hemorrhage-induced brain injury in mice, with emphasis on its ability to promote vascular smooth muscle cell phenotypic transformation followed by increased intercellular adhesion molecule-1 expression and elevated neutrophil infiltration in the vicinity of the hematoma. We also determined the extent to which plasmin from the hematoma influences the platelet-derived growth factor-BB/platelet-derived growth factor receptor-β system subsequent to intracerebral hemorrhage.

DESIGN

Controlled in vivo laboratory study.

SETTING

Animal research laboratory.

SUBJECTS

One hundred and fifty six eight-week-old male CD1 mice.

INTERVENTIONS

Brain injury was induced by autologous arterial blood or plasmin injection into mouse brains. Small interfering RNA targeting platelet-derived growth factor receptor-β was administered 24 hours before intracerebral hemorrhage. A platelet-derived growth factor receptor antagonist, Gleevec, was administered following intracerebral hemorrhage. A mitogen-activated protein kinase-activated protein kinase 2 inhibitor (KKKALNRQLGVAA) was delivered with platelet-derived growth factor-BB in naïve animals. Platelet-derived growth factor-BB was injected with a plasmin inhibitor (ε-aminocaproic acid) in intracerebral hemorrhage mice. Plasmin-injected mice were given platelet-derived growth factor receptor-β small interfering RNA 24 hours before the operation. Neurological deficits, brain edema, western blots, and immunofluorescence were evaluated.

MEASUREMENTS AND MAIN RESULTS

Platelet-derived growth factor receptor-β small interfering RNA attenuated SMemb and intercellular adhesion molecule-1 expression and neutrophil infiltration at 24 hours post injury and reduced neurological deficits and brain edema at 24 and 72 hours following intracerebral hemorrhage. The platelet-derived growth factor receptor antagonist, Gleevec, reduced SMemb and intercellular adhesion molecule-1 expression. Platelet-derived growth factor receptor-β activation led to increased expression of intercellular adhesion molecule-1 and was reversed by KKKALNRQLGVAA in naïve mice. Plasmin inhibition suppressed platelet-derived growth factor receptor-β activation and neutrophil infiltration, whereas exogenous platelet-derived growth factor-BB increased platelet-derived growth factor receptor-β activation, regardless of plasmin inhibition. Platelet-derived growth factor receptor-β small interfering RNA decreased the expression of intercellular adhesion molecule-1 by plasmin injection.

CONCLUSION

The platelet-derived growth factor-BB/platelet-derived growth factor receptor-β system contributes to neuroinflammation through vascular smooth muscle cell phenotypic transformation near the hematoma via the p38 mitogen-activated protein kinase/mitogen-activated protein kinase-activated protein kinase 2 pathway following intracerebral hemorrhage. Plasmin is hypothesized to be upstream of the proposed neuroinflammatory system. The therapeutic intervention targeting the platelet-derived growth factor-BB/platelet-derived growth factor receptor-β is a novel strategy to prevent plasmin-induced brain injury following intracerebral hemorrhage.

Mechanisms of Vascular Smooth Muscle Contraction and the Basis for Pharmacologic Treatment of Smooth Muscle Disorders

The smooth muscle cell directly drives the contraction of the vascular wall and hence regulates the size of the blood vessel lumen. We review here the current understanding of the molecular mechanisms by which agonists, therapeutics, and diseases regulate contractility of the vascular smooth muscle cell and we place this within the context of whole body function. We also discuss the implications for personalized medicine and highlight specific potential target molecules that may provide opportunities for the future development of new therapeutics to regulate vascular function.

Physical exercise and epigenetic adaptations of the cardiovascular system

During the last decade, epigenetics became one of the fastest growing research fields in numerous clinical and basic science disciplines. Evidence suggests that chromatin modifications (e.g., histone modifications and DNA methylation) as well as the expression of micro-RNA molecules play a crucial role in the pathogenesis of several cardiovascular diseases. On the one hand, they are involved in the development of general risk factors like chronic inflammation, but on the other hand, epigenetic modifications are conducive to smooth muscle cell, cardiomyocyte, and endothelial progenitor cell proliferation/differentiation as well as to extracellular matrix processing and endothelial function (e.g., endothelial nitric oxide synthase regulation). Therefore, epigenetic medical drugs have gained increased attention and provided the first promising results in the context of cardiovascular malignancies. Beside other lifestyle factors, physical activity and sports essentially contribute to cardiovascular health and regeneration. In this review we focus on recent research proposing physical activity as a potent epigenetic regulator that has the potential to counteract pathophysiological alterations in almost all the aforementioned cardiovascular cells and tissues. As with epigenetic medical drugs, more knowledge about the molecular mechanisms and dose-response relationships of exercise is needed to optimize the outcome of preventive and rehabilitative exercise programs and recommendations.

Epigenetic Control of Smooth Muscle Cell Identity and Lineage Memory

Vascular smooth muscle cells (SMCs), like all cells, acquire a cell-specific epigenetic signature during development that includes acquisition of a unique repertoire of histone and DNA modifications. These changes are postulated to induce an open chromatin state (referred to as euchromatin) on the repertoire of genes that are expressed in differentiated SMC, including SMC-selective marker genes like Acta2 and Myh11, as well as housekeeping genes expressed by most cell types. In contrast, genes that are silenced in differentiated SMC acquire modifications associated with a closed chromatin state (ie, heterochromatin) and transcriptional silencing. Herein, we review mechanisms that regulate epigenetic control of the differentiated state of SMC. In addition, we identify some of the major limitations in the field and future challenges, including development of innovative new tools and approaches, for performing single-cell epigenetic assays and locus-selective editing of the epigenome that will allow direct studies of the functional role of specific epigenetic controls during development, injury repair, and disease, including major cardiovascular diseases, such as atherosclerosis, hypertension, and microvascular disease, associated with diabetes mellitus.

Smooth Muscle Cell Genome Browser: Enabling the Identification of Novel Serum Response Factor Target Genes

Genome-scale expression data on the absolute numbers of gene isoforms offers essential clues in cellular functions and biological processes. Smooth muscle cells (SMCs) perform a unique contractile function through expression of specific genes controlled by serum response factor (SRF), a transcription factor that binds to DNA sites known as the CArG boxes. To identify SRF-regulated genes specifically expressed in SMCs, we isolated SMC populations from mouse small intestine and colon, obtained their transcriptomes, and constructed an interactive SMC genome and CArGome browser. To our knowledge, this is the first online resource that provides a comprehensive library of all genetic transcripts expressed in primary SMCs. The browser also serves as the first genome-wide map of SRF binding sites. The browser analysis revealed novel SMC-specific transcriptional variants and SRF target genes, which provided new and unique insights into the cellular and biological functions of the cells in gastrointestinal (GI) physiology. The SRF target genes in SMCs, which were discovered in silico, were confirmed by proteomic analysis of SMC-specific Srf knockout mice. Our genome browser offers a new perspective into the alternative expression of genes in the context of SRF binding sites in SMCs and provides a valuable reference for future functional studies.

KLF4 mediates the link between TGF-β1-induced gene transcription and H3 acetylation in vascular smooth muscle cells

Transcriptional activation by transcription factors is coupled with histone acetylation and chromatin remodeling. However, the relationship between TGF-β1-induced gene transcription by Krüppel-like factor (KLF)-4 and histone acetylation remains unknown. In our study, KLF4 overexpression or knockdown, respectively increased or decreased H3 acetylation and p300 occupancy, which is concentrated in the region containing TGF-β1 control elements (TCEs) of the genes by TGF-β1 regulation during vascular smooth muscle cell (VSMC) differentiation. Coimmunoprecipitation and glutathione S-transferase pull-down assays showed that phosphatase and tensin homolog (PTEN) formed a complex with KLF4 to inhibit the phosphorylation of the latter in basal conditions. After TGF-β1 signaling activation, PTEN was phosphorylated by p38 MAPK or PI3K/Akt signaling, phosphorylated PTEN lost its ability to dephosphorylate KLF4, and the cofactors interacting with KLF4 switched from PTEN to p300. Then, KLF4-p300 complexes were recruited to KLF4-binding sites of the gene promoter of VSMCs, to acetylate histone H3 and activate transcription. In addition, phosphorylated KLF4 enhanced p300 histone acetyltransferase (HAT) activity via the p38 MAPK pathway, which may be responsible for H3 acetylation. Taken together, the results of our study reveal a novel mechanism whereby KLF4 mediates the link between TGF-β1-induced gene transcription activation and H3 acetylation during VSMC differentiation.

KLF4-dependent phenotypic modulation of smooth muscle cells has a key role in atherosclerotic plaque pathogenesis

Previous studies investigating the role of smooth muscle cells (SMCs) and macrophages in the pathogenesis of atherosclerosis have provided controversial results owing to the use of unreliable methods for clearly identifying each of these cell types. Here, using Myh11-CreER(T2) ROSA floxed STOP eYFP Apoe(-/-) mice to perform SMC lineage tracing, we find that traditional methods for detecting SMCs based on immunostaining for SMC markers fail to detect >80% of SMC-derived cells within advanced atherosclerotic lesions. These unidentified SMC-derived cells exhibit phenotypes of other cell lineages, including macrophages and mesenchymal stem cells (MSCs). SMC-specific conditional knockout of Krüppel-like factor 4 (Klf4) resulted in reduced numbers of SMC-derived MSC- and macrophage-like cells, a marked reduction in lesion size, and increases in multiple indices of plaque stability, including an increase in fibrous cap thickness as compared to wild-type controls. On the basis of in vivo KLF4 chromatin immunoprecipitation-sequencing (ChIP-seq) analyses and studies of cholesterol-treated cultured SMCs, we identified >800 KLF4 target genes, including many that regulate pro-inflammatory responses of SMCs. Our findings indicate that the contribution of SMCs to atherosclerotic plaques has been greatly underestimated, and that KLF4-dependent transitions in SMC phenotype are critical in lesion pathogenesis.

Phosphorylation of GATA-6 is required for vascular smooth muscle cell differentiation after mTORC1 inhibition

Vascular smooth muscle cells (VSMCs) undergo transcriptionally regulated reversible differentiation in growing and injured blood vessels. This dedifferentiation also contributes to VSMC hyperplasia after vascular injury, including that caused by angioplasty and stenting. Stents provide mechanical support and can contain and release rapamycin, an inhibitor of the mechanistic target of rapamycin complex 1 (mTORC1). Rapamycin suppresses VSMC hyperplasia and promotes VSMC differentiation. We report that rapamycin-induced differentiation of VSMCs required the transcription factor GATA-6. Inhibition of mTORC1 stabilized GATA-6 and promoted the nuclear accumulation of GATA-6, its binding to DNA, its transactivation of promoters encoding contractile proteins, and its inhibition of proliferation. These effects were mediated by phosphorylation of GATA-6 at Ser(290), potentially by Akt2, a kinase that is activated in VSMCs when mTORC1 is inhibited. Rapamycin induced phosphorylation of GATA-6 in wild-type mice, but not in Akt2(-/-) mice. Intimal hyperplasia after arterial injury was greater in Akt2(-/-) mice than in wild-type mice, and the exacerbated response in Akt2(-/-) mice was rescued to a greater extent by local overexpression of the wild-type or phosphomimetic (S290D) mutant GATA-6 than by that of the phosphorylation-deficient (S290A) mutant. Our data indicated that GATA-6 and Akt2 are involved in the mTORC1-mediated regulation of VSMC proliferation and differentiation. Identifying the downstream transcriptional targets of mTORC1 may provide cell type-specific drug targets to combat cardiovascular diseases associated with excessive proliferation of VSMCs.

Sodium butyrate promotes the differentiation of rat bone marrow mesenchymal stem cells to smooth muscle cells through histone acetylation

Establishing an effective method to improve stem cell differentiation is crucial in stem cell transplantation. Here we aimed to explore whether and how sodium butyrate (NaB) induces rat bone marrow mesenchymal stem cells (MSCs) to differentiate into bladder smooth muscle cells (SMCs). We found that NaB significantly suppressed MSC proliferation and promoted MSCs differentiation into SMCs, as evidenced by the enhanced expression of SMC specific genes in the MSCs. Co-culturing the MSCs with SMCs in a transwell system promoted the differentiation of MSCs into SMCs. NaB again promoted MSC differentiation in this system. Furthermore, NaB enhanced the acetylation of SMC gene-associated H3K9 and H4, and decreased the expression of HDAC2 and down-regulated the recruitment of HDAC2 to the promoter regions of SMC specific genes. Finally, we found that NaB significantly promoted MSC depolarization and increased the intracellular calcium level of MSCs upon carbachol stimulation. These results demonstrated that NaB effectively promotes MSC differentiation into SMCs, possibly by the marked inhibition of HDAC2 expression and disassociation of HDAC2 recruitment to SMC specific genes in MSCs, which further induces high levels of H3K9ace and H4ace and the enhanced expression of target genes, and this strategy could potentially be applied in clinical tissue engineering and cell transplantation.

Development and pathologies of the arterial wall

Arteries consist of an inner single layer of endothelial cells surrounded by layers of smooth muscle and an outer adventitia. The majority of vascular developmental studies focus on the construction of endothelial networks through the process of angiogenesis. Although many devastating vascular diseases involve abnormalities in components of the smooth muscle and adventitia (i.e., the vascular wall), the morphogenesis of these layers has received relatively less attention. Here, we briefly review key elements underlying endothelial layer formation and then focus on vascular wall development, specifically on smooth muscle cell origins and differentiation, patterning of the vascular wall, and the role of extracellular matrix and adventitial progenitor cells. Finally, we discuss select human diseases characterized by marked vascular wall abnormalities. We propose that continuing to apply approaches from developmental biology to the study of vascular disease will stimulate important advancements in elucidating disease mechanism and devising novel therapeutic strategies.

Synergistic effects of matrix nanotopography and stiffness on vascular smooth muscle cell function

Vascular smooth muscle cells (vSMCs) retain the ability to undergo modulation in their phenotypic continuum, ranging from a mature contractile state to a proliferative, secretory state. vSMC differentiation is modulated by a complex array of microenvironmental cues, which include the biochemical milieu of the cells and the architecture and stiffness of the extracellular matrix. In this study, we demonstrate that by using UV-assisted capillary force lithography (CFL) to engineer a polyurethane substratum of defined nanotopography and stiffness, we can facilitate the differentiation of cultured vSMCs, reduce their inflammatory signature, and potentially promote the optimal functioning of the vSMC contractile and cytoskeletal machinery. Specifically, we found that the combination of medial tissue-like stiffness (11 MPa) and anisotropic nanotopography (ridge width_groove width_ridge height of 800_800_600 nm) resulted in significant upregulation of calponin, desmin, and smoothelin, in addition to the downregulation of intercellular adhesion molecule-1, tissue factor, interleukin-6, and monocyte chemoattractant protein-1. Further, our results allude to the mechanistic role of the RhoA/ROCK pathway and caveolin-1 in altered cellular mechanotransduction pathways via differential matrix nanotopography and stiffness. Notably, the nanopatterning of the stiffer substrata (1.1 GPa) resulted in the significant upregulation of RhoA, ROCK1, and ROCK2. This indicates that nanopatterning an 800_800_600 nm pattern on a stiff substratum may trigger the mechanical plasticity of vSMCs resulting in a hypercontractile vSMC phenotype, as observed in diabetes or hypertension. Given that matrix stiffness is an independent risk factor for cardiovascular disease and that CFL can create different matrix nanotopographic patterns with high pattern fidelity, we are poised to create a combinatorial library of arterial test beds, whether they are healthy, diseased, injured, or aged. Such high-throughput testing environments will pave the way for the evolution of the next generation of vascular scaffolds that can effectively crosstalk with the scaffold microenvironment and result in improved clinical outcomes.

TNF-α induces phenotypic modulation in cerebral vascular smooth muscle cells: implications for cerebral aneurysm pathology

Little is known about vascular smooth muscle cell (SMC) phenotypic modulation in the cerebral circulation or pathogenesis of intracranial aneurysms. Tumor necrosis factor-alpha (TNF-α) has been associated with aneurysms, but potential mechanisms are unclear. Cultured rat cerebral SMCs overexpressing myocardin induced expression of key SMC contractile genes (SM-α-actin, SM-22α, smooth muscle myosin heavy chain), while dominant-negative cells suppressed expression. Tumor necrosis factor-alpha treatment inhibited this contractile phenotype and induced pro-inflammatory/matrix-remodeling genes (monocyte chemoattractant protein-1, matrix metalloproteinase-3, matrix metalloproteinase-9, vascular cell adhesion molecule-1, interleukin-1 beta). Tumor necrosis factor-alpha increased expression of KLF4, a known regulator of SMC differentiation. Kruppel-like transcription factor 4 (KLF4) small interfering RNA abrogated TNF-α activation of inflammatory genes and suppression of contractile genes. These mechanisms were confirmed in vivo after exposure of rat carotid arteries to TNF-α and early on in a model of cerebral aneurysm formation. Treatment with the synthesized TNF-α inhibitor 3,6-dithiothalidomide reversed pathologic vessel wall alterations after induced hypertension and hemodynamic stress. Chromatin immunoprecipitation assays in vivo and in vitro demonstrated that TNF-α promotes epigenetic changes through KLF4-dependent alterations in promoter regions of myocardin, SMCs, and inflammatory genes. In conclusion, TNF-α induces phenotypic modulation of cerebral SMCs through myocardin and KLF4-regulated pathways. These results demonstrate a novel role for TNF-α in promoting a pro-inflammatory/matrix-remodeling phenotype, which has important implications for the mechanisms behind intracranial aneurysm formation.

Modifications of Chromatin Dynamics Control Smad2 Pathway Activation in Aneurysmal Smooth Muscle Cells

Rationale :

The activation of the Smad2 signaling pathway is thought to play an important role in human aneurysmal diseases as described by an important body of research. We previously showed that constitutive Smad2 activation is associated with Smad2 mRNA overexpression in aneurysmal vascular smooth muscle cells (VSMCs), which is dependent on epigenetic regulation of the SMAD2 promoter involving histone modifications. However, the underlying molecular mechanisms controlling Smad2 overexpression are currently unknown.

Objective :

The aim of the present study is to understand the mechanisms regulating the constitutive Smad2 overexpression in VSMCs by identification of the histone-modifying enzymes, transcription factors, and cofactors responsible for Smad2 promoter activation in aneurysmal disease.

Methods and Results :

This study was performed on medial tissue extracts and primary cultures of VSMCs of human thoracic aneurysms (n=17) and normal thoracic aortas (n=10). Here, we demonstrate that the activation of SMAD2 promoter is driven by the recruitment of a multipartner complex, including the transcription factor p53 and histone acetyltransferases. Remarkably, the transcriptional regulatory network of the SMAD2 promoter is dramatically altered in human aneurysmal VSMCs in vitro and in situ with a switch from Myc-dependent repression of SMAD2 in normal vessel to a p53-dependent activation of SMAD2 in aneurysms. Furthermore, histone acetyltransferases p300 and P300/CBP-associated protein play a major role in SMAD2 promoter activation by acting on histone acetylation, p53 recruitment, and acetylation.

Conclusions :

These results provide evidence for a major role of p53 and the complex composed of p300 and p300/CBP-associated protein in Smad2 activation in human aneurysmal VSMCs.

Cigarette smoke modulates vascular smooth muscle phenotype: implications for carotid and cerebrovascular disease

BACKGROUND

The role of smooth muscle cell (SMC) phenotypic modulation in the cerebral circulation and pathogenesis of stroke has not been determined. Cigarette smoke is a major risk factor for atherosclerosis, but potential mechanisms are unclear, and its role in SMC phenotypic modulation has not been established.

METHODS AND RESULTS

In cultured cerebral vascular SMCs, exposure to cigarette smoke extract (CSE) resulted in decreased promoter activity and mRNA expression of key SMC contractile genes (SM-α-actin, SM-22α, SM-MHC) and the transcription factor myocardin in a dose-dependent manner. CSE also induced pro-inflammatory/matrix remodeling genes (MCP-1, MMPs, TNF-α, IL-1β, NF-κB). CSE increased expression of KLF4, a known regulator of SMC differentiation, and siKLF4 inhibited CSE induced suppression of SMC contractile genes and myocardin and activation of inflammatory genes. These mechanisms were confirmed in vivo following exposure of rat carotid arteries to CSE. Chromatin immune-precipitation assays in vivo and in vitro demonstrated that CSE promotes epigenetic changes with binding of KLF4 to the promoter regions of myocardin and SMC marker genes and alterations in promoter acetylation and methylation.

CONCLUSION

CSE exposure results in phenotypic modulation of cerebral SMC through myocardin and KLF4 dependent mechanisms. These results provides a mechanism by which cigarette smoke induces a pro-inflammatory/matrix remodeling phenotype in SMC and an important pathway for cigarette smoke to contribute to atherosclerosis and stroke.

The role of redox signaling in epigenetics and cardiovascular disease

SIGNIFICANCE

The term epigenetics refers to the changes in the phenotype and gene expression that occur without alterations in the DNA sequence. There is a rapidly growing body of evidence that epigenetic modifications are involved in the pathological mechanisms of many cardiovascular diseases (CVDs), which intersect with many of the pathways involved in oxidative stress.

RECENT ADVANCES

Most studies relating epigenetics and human pathologies have focused on cancer. There has been a limited study of epigenetic mechanisms in CVDs. Although CVDs have multiple established genetic and environmental risk factors, these explain only a portion of the total CVD risk. The epigenetic perspective is beginning to shed new light on how the environment influences gene expression and disease susceptibility in CVDs. Known epigenetic changes contributing to CVD include hypomethylation in proliferating vascular smooth muscle cells in atherosclerosis, changes in estrogen receptor-α (ER-α) and ER-β methylation in vascular disease, decreased superoxide dismutase 2 expression in pulmonary hypertension (PH), as well as trimethylation of histones H3K4 and H3K9 in congestive heart failure.

CRITICAL ISSUES

In this review, we discuss the epigenetic modifications in CVDs, including atherosclerosis, congestive heart failure, hypertension, and PH, with a focus on altered redox signaling.

FUTURE DIRECTIONS

As advances in both the methodology and technology accelerate the study of epigenetic modifications, the critical role they play in CVD is beginning to emerge. A fundamental question in the field of epigenetics is to understand the biochemical mechanisms underlying reactive oxygen species-dependent regulation of epigenetic modification.

Microvascular repair: post-angiogenesis vascular dynamics

Vascular compromise and the accompanying perfusion deficits cause or complicate a large array of disease conditions and treatment failures. This has prompted the exploration of therapeutic strategies to repair or regenerate vasculatures, thereby establishing more competent microcirculatory beds. Growing evidence indicates that an increase in vessel numbers within a tissue does not necessarily promote an increase in tissue perfusion. Effective regeneration of a microcirculation entails the integration of new stable microvessel segments into the network via neovascularization. Beginning with angiogenesis, neovascularization entails an integrated series of vascular activities leading to the formation of a new mature microcirculation, and includes vascular guidance and inosculation, vessel maturation, pruning, AV specification, network patterning, structural adaptation, intussusception, and microvascular stabilization. While the generation of new vessel segments is necessary to expand a network, without the concomitant neovessel remodeling and adaptation processes intrinsic to microvascular network formation, these additional vessel segments give rise to a dysfunctional microcirculation. While many of the mechanisms regulating angiogenesis have been detailed, a thorough understanding of the mechanisms driving post-angiogenesis activities specific to neovascularization has yet to be fully realized, but is necessary to develop effective therapeutic strategies for repairing compromised microcirculations as a means to treat disease.

Inactivation of Serum Response Factor Contributes To Decrease Vascular Muscular Tone and Arterial Stiffness in Mice

Rationale:

Vascular smooth muscle (SM) cell phenotypic modulation plays an important role in arterial stiffening associated with aging. Serum response factor (SRF) is a major transcription factor regulating SM genes involved in maintenance of the contractile state of vascular SM cells.

Objective:

We investigated whether SRF and its target genes regulate intrinsic SM tone and thereby arterial stiffness.

Methods and Results:

The SRF gene was inactivated SM-specific knockout of SRF (SRF SMKO ) specifically in vascular SM cells by injection of tamoxifen into adult transgenic mice. Fifteen days later, arterial pressure and carotid thickness were lower in SRF SMKO than in control mice. The carotid distensibility/pressure and elastic modulus/wall stress curves showed a greater arterial elasticity in SRF SMKO without modification in collagen/elastin ratio. In SRF SMKO , vasodilation was decreased in aorta and carotid arteries, whereas a decrease in contractile response was found in mesenteric arteries. By contrast, in mice with inducible SRF overexpression, the in vitro contractile response was significantly increased in all arteries. Without endothelium, the contraction was reduced in SRF SMKO compared with control aortic rings owing to impairment of the NO pathway. Contractile components (SM-actin and myosin light chain), regulators of the contractile response (myosin light chain kinase, myosin phosphatase target subunit 1, and protein kinase C–potentiated myosin phosphatase inhibitor) and integrins were reduced in SRF SMKO .

Conclusions:

SRF controls vasoconstriction in mesenteric arteries via vascular SM cell phenotypic modulation linked to changes in contractile protein gene expression. SRF-related decreases in vasomotor tone and cell-matrix attachment increase arterial elasticity in large arteries.

MicroRNA-31 controls phenotypic modulation of human vascular smooth muscle cells by regulating its target gene cellular repressor of E1A-stimulated genes

Phenotypic modulation of vascular smooth muscle cells (VSMCs) plays a critical role in the pathogenesis of a variety of proliferative vascular diseases. The cellular repressor of E1A-stimulated genes (CREG) has been shown to play an important role in phenotypic modulation of VSMCs. However, the mechanism regulating CREG upstream signaling remains unclear. MicroRNAs (miRNAs) have recently been found to play a critical role in cell differentiation via target-gene regulation. This study aimed to identify a miRNA that binds directly to CREG, and may thus be involved in CREG-mediated VSMC phenotypic modulation. Computational analysis indicated that miR-31 bound to the CREG mRNA 3' untranslated region (3'-UTR). miR-31 was upregulated in quiescent differentiated VSMCs and downregulated in proliferative cells stimulated by platelet-derived growth factor and serum starvation, demonstrating a negative relationship with the VSMC differentiation marker genes, smooth muscle α-actin, calponin and CREG. Using gain-of-function and loss-of-function approaches, CREG and VSMC differentiation marker gene expression levels were shown to be suppressed by a miR-31 mimic, but increased by a miR-31 inhibitor at both protein and mRNA levels. Notably, miR-31 overexpression or inhibition affected luciferase expression driven by the CREG 3'-UTR containing the miR-31 binding site. Furthermore, miR-31-mediated VSMC phenotypic modulation was inhibited in CREG-knockdown human VSMCs. We also determined miR-31 levels in the serum of patients with coronary artery disease (CAD), with or without in stent restenosis and in healthy controls. miR-31 levels were higher in the serum of CAD patients with restenosis compared to CAD patients without restenosis and in healthy controls. In summary, these data demonstrate that miR-31 not only directly binds to its target gene CREG and modulates the VSMC phenotype through this interaction, but also can be an important biomarker in diseases involving VSMC phenotypic modulation. These novel findings may have extensive implications for the diagnosis and therapy of a variety of proliferative vascular diseases.