A G/C element mediates repression of the SM22alpha promoter within phenotypically modulated smooth muscle cells in experimental atherosclerosis

Hormonal influence: unraveling the impact of sex hormones on vascular smooth muscle cells

Sex hormones play a pivotal role as endocrine hormones that exert profound effects on the biological characteristics and vascular function of vascular smooth muscle cells (VSMCs). By modulating intracellular signaling pathways, activating nuclear receptors, and regulating gene expression, sex hormones intricately influence the morphology, function, and physiological state of VSMCs, thereby impacting the biological properties of vascular contraction, relaxation, and growth. Increasing evidence suggests that abnormal phenotypic changes in VSMCs contribute to the initiation of vascular diseases, including atherosclerosis. Therefore, understanding the factors governing phenotypic alterations in VSMCs and elucidating the underlying mechanisms can provide crucial insights for refining interventions targeted at vascular diseases. Additionally, the varying levels of different types of sex hormones in the human body, influenced by sex and age, may also affect the phenotypic conversion of VSMCs. This review aims to explore the influence of sex hormones on the phenotypic switching of VSMCs and the development of associated vascular diseases in the human body.

Basal ATP release signals through the P2Y2 receptor to maintain the differentiated phenotype of vascular smooth muscle cells

BACKGROUND AND AIMS

Vascular smooth muscle cell (VSMC) dedifferentiation contributes substantively to vascular disease. VSMCs spontaneously release low levels of ATP that modulate vessel contractility, but it is unclear if autocrine ATP signaling in VSMCs is critical to the maintenance of the VSMC contractile phenotype.

METHODS

We used pharmacological inhibitors to block ATP release in human aortic smooth muscle cells (HASMCs) for studying changes in VSMC differentiation marker gene expression. We employed RNA interference and generated mice with SMC-specific inducible deletion of the P2Y2 receptor (P2Y2R) gene to evaluate resulting phenotypic alterations.

RESULTS

HASMCs constitutively release low levels of ATP that when blocked results in a significant decrease in VSMC differentiation marker gene expression, including smooth muscle actin (SMA), smooth muscle myosin heavy chain (SMMHC), SM-22α and calponin. Basal release of ATP represses transcriptional activation of the Krüppel-Like Factor 4 (KFL4) thereby preventing platelet-derived growth factor-BB (PDGF-BB) from inhibiting expression of SMC contractile phenotype markers. SMC-restricted conditional deletion of P2Y2R evoked dedifferentiation characterized by decreases in aortic contractility and contractile phenotype markers expression. This loss was accompanied by a transition to the synthetic phenotype with the acquisition of extracellular matrix (ECM) proteins characteristic of dedifferentiation, such as osteopontin and vimentin.

CONCLUSIONS

Our data establish the first direct evidence that an autocrine ATP release mechanism maintains SMC cytoskeletal protein expression by inhibiting VSMCs from transitioning to a synthetic phenotype, and further demonstrate that activation of the P2Y2R by basally released ATP is required for maintenance of the differentiated VSMC phenotype.

The mitochondrial protease ClpP is a druggable target that controls VSMC phenotype by a SIRT1-dependent mechanism

Vascular smooth muscle cells (VSMCs), known for their remarkable lifelong phenotypic plasticity, play a pivotal role in vascular pathologies through their ability to transition between different phenotypes. Our group discovered that the deficiency of the mitochondrial protein Poldip2 induces VSMC differentiation both in vivo and in vitro. Further comprehensive biochemical investigations revealed Poldip2's specific interaction with the mitochondrial ATPase caseinolytic protease chaperone subunit X (CLPX), which is the regulatory subunit for the caseinolytic protease proteolytic subunit (ClpP) that forms part of the ClpXP complex - a proteasome-like protease evolutionarily conserved from bacteria to humans. This interaction limits the protease's activity, and reduced Poldip2 levels lead to ClpXP complex activation. This finding prompted the hypothesis that ClpXP complex activity within the mitochondria may regulate the VSMC phenotype. Employing gain-of-function and loss-of-function strategies, we demonstrated that ClpXP activity significantly influences the VSMC phenotype. Notably, both genetic and pharmacological activation of ClpXP inhibits VSMC plasticity and fosters a quiescent, differentiated, and anti-inflammatory VSMC phenotype. The pharmacological activation of ClpP using TIC10, currently in phase III clinical trials for cancer, successfully replicates this phenotype both in vitro and in vivo and markedly reduces aneurysm development in a mouse model of elastase-induced aortic aneurysms. Our mechanistic exploration indicates that ClpP activation regulates the VSMC phenotype by modifying the cellular NAD+/NADH ratio and activating Sirtuin 1. Our findings reveal the crucial role of mitochondrial proteostasis in the regulation of the VSMC phenotype and propose the ClpP protease as a novel, actionable target for manipulating the VSMC phenotype.

Anemoside B4 attenuates abdominal aortic aneurysm by limiting smooth muscle cell transdifferentiation and its mediated inflammation

Abdominal aortic aneurysm (AAA) is a degenerative disease characterized by local abnormal dilation of the aorta accompanied by vascular smooth muscle cell (VSMC) dysfunction and chronic inflammation. VSMC dedifferentiation, transdifferentiation, and increased expression of matrix metalloproteinases (MMPs) are essential causes of AAA formation. Previous studies from us and others have shown that Anemoside B4 (AB4), a saponin from Pulsatilla chinensis, has anti-inflammatory, anti-tumor, and regulatory effects on VSMC dedifferentiation. The current study aimed to investigate whether AB4 inhibits AAA development and its underlying mechanisms. By using an Ang II induced AAA model in vivo and cholesterol loading mediated VSMC to macrophage transdifferentiation model in vitro, our study demonstrated that AB4 could attenuate AAA pathogenesis, prevent VSMC dedifferentiation and transdifferentiation to macrophage-like cells, decrease vascular inflammation, and suppress MMP expression and activity. Furthermore, KLF4 overexpression attenuated the effects of AB4 on VSMC to macrophage-like cell transition and VSMC inflammation in vitro. In conclusion, AB4 protects against AAA formation in mice by inhibiting KLF4 mediated VSMC transdifferentiation and inflammation. Our study provides the first proof of concept of using AB4 for AAA management.

TRIM13 reduces cholesterol efflux and increases oxidized LDL uptake leading to foam cell formation and atherosclerosis

Impaired cholesterol efflux and/or uptake can influence arterial lipid accumulation leading to atherosclerosis. Here, we report that tripartite motif-containing protein 13 (TRIM13), a RING-type E3 ubiquitin ligase, plays a role in arterial lipid accumulation leading to atherosclerosis. Using molecular approaches and KO mouse model, we found that TRIM13 expression was induced both in the aorta and peritoneal macrophages (pMφ) of ApoE-/- mice in response to Western diet (WD) in vivo. Furthermore, proatherogenic cytokine interleukin-1β also induced TRIM13 expression both in pMφ and vascular smooth muscle cells. Furthermore, we found that TRIM13 via ubiquitination and degradation of liver X receptor (LXR)α/β downregulates the expression of their target genes ABCA1/G1 and thereby inhibits cholesterol efflux. In addition, TRIM13 by ubiquitinating and degrading suppressor of cytokine signaling 1/3 (SOCS1/3) mediates signal transducer and activator of transcription 1 (STAT1) activation, CD36 expression, and foam cell formation. In line with these observations, genetic deletion of TRIM13 by rescuing cholesterol efflux and inhibiting foam cell formation protects against diet-induced atherosclerosis. We also found that while TRIM13 and CD36 levels were increased, LXRα/β, ABCA1/G1, and SOCS3 levels were decreased both in Mφ and smooth muscle cells of stenotic human coronary arteries as compared to nonstenotic arteries. More intriguingly, the expression levels of TRIM13 and its downstream signaling molecules were correlated with the severity of stenotic lesions. Together, these observations reveal for the first time that TRIM13 plays a crucial role in diet-induced atherosclerosis, and that it could be a potential drug target against this vascular lesion.

KLF13 promotes VSMCs phenotypic dedifferentiation by directly binding to the SM22α promoter

Krüppel-like factor 13 (KLF13), a zinc finger transcription factor, is considered as a potential regulator of cardiomyocyte differentiation and proliferation during heart morphogenesis. However, its precise role in the dedifferentiation of vascular smooth muscle cells (VSMCs) during atherosclerosis and neointimal formation after injury remains poorly understood. In this study, we investigated the relationship between KLF13 and SM22α expression in normal and atherosclerotic plaques by bioanalysis, and observed a significant increase in KLF13 levels in the atherosclerotic plaques of both human patients and ApoE-/- mice. Knockdown of KLF13 was found to ameliorate intimal hyperplasia following carotid artery injury. Furthermore, we discovered that KLF13 directly binds to the SM22α promoter, leading to the phenotypic dedifferentiation of VSMCs. Remarkably, we observed a significant inhibition of platelet-derived growth factor BB-induced VSMCs dedifferentiation, proliferation, and migration when knocked down KLF13 in VSMCs. This inhibitory effect of KLF13 knockdown on VCMC function was, at least in part, mediated by the inactivation of p-AKT signaling in VSMCs. Overall, our findings shed light on a potential therapeutic target for treating atherosclerotic lesions and restenosis after vascular injury.

Mechanisms of Arsenic Exposure-Induced Hypertension and Atherosclerosis: an Updated Overview

Arsenic is an abundant element in the earth's crust. In the environment and within the human body, this toxic element can be found in both organic and inorganic forms. Chronic exposure to arsenic can predispose humans to cardiovascular diseases including hypertension, stroke, atherosclerosis, and blackfoot disease. Oxidative damage induced by reactive oxygen species is a major player in arsenic-induced toxicity, and it can affect genes expression, inflammatory responses, and/or nitric oxide homeostasis. Exposure to arsenic in drinking water can lead to vascular endothelial dysfunction which is reflected by an imbalance between vascular relaxation and contraction. Arsenic has been shown to inactivate endothelial nitric oxide synthase leading to a reduction of the generation and bioavailability of nitric oxide. Ultimately, these effects increase the risk of vascular diseases such as hypertension and atherosclerosis. The present article reviews how arsenic exposure contributes to hypertension and atherosclerosis development.

Vascular Smooth Muscle Cells Phenotypic Switching in Cardiovascular Diseases

Vascular smooth muscle cells (VSMCs), the major cell type in the arterial vessel wall, have a contractile phenotype that maintains the normal vessel structure and function under physiological conditions. In response to stress or vascular injury, contractile VSMCs can switch to a less differentiated state (synthetic phenotype) to acquire the proliferative, migratory, and synthetic capabilities for tissue reparation. Imbalances in VSMCs phenotypic switching can result in a variety of cardiovascular diseases, including atherosclerosis, in-stent restenosis, aortic aneurysms, and vascular calcification. It is very important to identify the molecular mechanisms regulating VSMCs phenotypic switching to prevent and treat cardiovascular diseases with high morbidity and mortality. However, the key molecular mechanisms and signaling pathways participating in VSMCs phenotypic switching have still not been fully elucidated despite long-term efforts by cardiovascular researchers. In this review, we provide an updated summary of the recent studies and systematic knowledge of VSMCs phenotypic switching in atherosclerosis, in-stent restenosis, aortic aneurysms, and vascular calcification, which may help guide future research and provide novel insights into the prevention and treatment of related diseases.

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).

Myotubularin‐Related Protein14 Prevents Neointima Formation and Vascular Smooth Muscle Cell Proliferation by Inhibiting Polo‐Like Kinase1

Background

Restenosis is one of the main bottlenecks in restricting the further development of cardiovascular interventional therapy. New signaling molecules involved in the progress have continuously been discovered; however, the specific molecular mechanisms remain unclear. MTMR14 (myotubularin‐related protein 14) is a novel phosphoinositide phosphatase that has a variety of biological functions and is involved in diverse biological processes. However, the role of MTMR14 in vascular biology remains unclear. Herein, we addressed the role of MTMR14 in neointima formation and vascular smooth muscle cell (VSMC) proliferation after vessel injury.

Methods and Results

Vessel injury models were established using SMC‐specific conditional MTMR14‐knockout and ‐transgenic mice. Neointima formation was assessed by histopathological methods, and VSMC proliferation and migration were assessed using fluorescence ubiquitination‐based cell cycle indicator, transwell, and scratch wound assay. Neointima formation and the expression of MTMR14 was increased after injury. MTMR14 deficiency accelerated neointima formation and promoted VSMC proliferation after injury, whereas MTMR14 overexpression remarkably attenuated this process. Mechanistically, we demonstrated that MTMR14 suppressed the activation of PLK1 (polo‐like kinase 1) by interacting with it, which further leads to the inhibition of the activation of MEK/ERK/AKT (mitogen‐activated protein kinase kinase/extracellular‐signal‐regulated kinase/protein kinase B), thereby inhibiting the proliferation of VSMC from the medial to the intima and thus preventing neointima formation.

Conclusions

MTMR14 prevents neointima formation and VSMC proliferation by inhibiting PLK1. Our findings reveal that MTMR14 serves as an inhibitor of VSMC proliferation and establish a link between MTMR14 and PLK1 in regulating VSMC proliferation. MTMR14 may become a novel potential therapeutic target in the treatment of restenosis.

Cysteine-Rich LIM-Only Protein 4 (CRP4) Promotes Atherogenesis in the ApoE-/- Mouse Model

Vascular smooth muscle cells (VSMCs) can switch from their contractile state to a synthetic phenotype resulting in high migratory and proliferative capacity and driving atherosclerotic lesion formation. The cysteine-rich LIM-only protein 4 (CRP4) reportedly modulates VSM-like transcriptional signatures, which are perturbed in VSMCs undergoing phenotypic switching. Thus, we hypothesized that CRP4 contributes to adverse VSMC behaviours and thereby to atherogenesis in vivo. The atherogenic properties of CRP4 were investigated in plaque-prone apolipoprotein E (ApoE) and CRP4 double-knockout (dKO) as well as ApoE-deficient CRP4 wildtype mice. dKO mice exhibited lower plaque numbers and lesion areas as well as a reduced content of α-smooth muscle actin positive cells in the lesion area, while lesion-associated cell proliferation was elevated in vessels lacking CRP4. Reduced plaque volumes in dKO correlated with significantly less intra-plaque oxidized low-density lipoprotein (oxLDL), presumably due to upregulation of the antioxidant factor peroxiredoxin-4 (PRDX4). This study identifies CRP4 as a novel pro-atherogenic factor that facilitates plaque oxLDL deposition and identifies the invasion of atherosclerotic lesions by VSMCs as important determinants of plaque vulnerability. Thus, targeting of VSMC CRP4 should be considered in plaque-stabilizing pharmacological strategies.

Assessing serum levels of SM22α as a new biomarker for patients with aortic aneurysm/dissection

Background

Aortic aneurysm/dissection (AAD) is now encountered more often because of the increasing prevalence of atherosclerosis and hypertension in the population. Despite many therapeutic improvements, in particular timely and successful surgery, in-hospital mortality rates are still higher. Timely identification of patients at high risk will help improve the overall prognosis of AAD. Since early clinical and radiological signs are nonspecific, there is an urgent need for accurate biomarkers. Smooth muscle 22α (SM22α) is a potential marker for AAD because of its abundant expression in vascular smooth muscle, which is involved in development of AAD.

Methods

We prepared three different mouse models, including abdominal aortic aneurysm, neointimal hyperplasia and atherosclerosis. SM22α levels were assessed in serum and vascular tissue of the mice. Next, the relationships between serum SM22α level and vascular lesion were studied in mice. Finally, serum from 41 patients with AAD, 107 carotid artery stenosis (CAS) patients and 40 healthy volunteers were tested for SM22α. Serum levels of SM22α were measured using an enzyme-linked immunosorbent assay (ELISA).

Results

Compared with the controls, serum SM22α levels were reduced in the models of aortic aneurysm, neointimal formation and atherosclerosis, and elevated in mice with ruptured aneurysm. Serum SM22α level was negatively correlated with apoptosis rate of vascular smooth muscle cells (VSMC), ratio of intima/ media (I/M) area and plaque size. Patients with AAD had significantly higher serum SM22α levels than patients with only CAS, or normal controls.

Conclusion

Serum SM22α could be a potential predictive marker for AAD, and regulation of VSMC is a possible mechanism for the effects of SM22α.

circ-Sirt1 Decelerates Senescence by Inhibiting p53 Activation in Vascular Smooth Muscle Cells, Ameliorating Neointima Formation

Vascular smooth muscle cell (VSMC) senescence is a major driver of neointimal formation. We have demonstrated that circ-Sirt1 derived from the SIRT1 gene suppressed VSMC inflammation and neointimal formation. However, the effect of circ-Sirt1 inhibiting inflammation on VSMC senescence during neointimal hyperplasia remains to be elucidated. Here, we showed that circ-Sirt1 was highly expressed in young and healthy arteries, which was decreased in aged arteries and neointima of humans and mice. Overexpression of circ-Sirt1 delayed Ang II-induced VSMC senescence in vitro and ameliorated neointimal hyperplasia in vivo. Mechanically, circ-Sirt1 inhibited p53 activity at the levels of transcription and post-translation modulation. In detail, circ-Sirt1, on the one hand, interacted with and held p53 to block its nuclear translocation, and on the other hand, promoted SIRT1-mediated p53 deacetylation and inactivation. In conclusion, our data suggest that circ-Sirt1 is a novel p53 repressor in response senescence-inducing stimuli, and targeting circ-Sirt1 may be a promising approach to ameliorating aging-related vascular disease.

Smooth muscle 22 alpha protein inhibits VSMC foam cell formation by supporting normal LXRα signaling, ameliorating atherosclerosis

Vascular smooth muscle cells (VSMCs) are indispensable components in foam cell formation in atherosclerosis. However, the mechanism behind foam cell formation of VSMCs has not been addressed. We found a potential association between deletion of smooth muscle (SM) 22α and deregulated nuclear receptors liver X receptors (LXRs)/retinoid X receptor (RXR) signaling in mice. Here, we investigated the roles of SM22α in LXRα-modulated cholesterol homeostasis, and explore possible mechanisms underlying this process. We identified that the depletion of SM22α was a primary event driving VSMC cholesterol accumulation and the development of atherosclerosis in mice. Proteomic and lipidomic analysis validated that downregulation of SM22α was correlated with reduced expression of LXRα and ATP-binding cassette transporter (ABCA) 1 and increased cholesteryl ester in phenotypically modulated VSMCs induced by platelets-derived growth factor (PDGF)-BB. Notably, LXRα was mainly distributed in the cytoplasm rather than the nucleus in the neointimal and Sm22α^-/- VSMCs. Loss of SM22α inhibited the nuclear import of LXRα and reduced ABCA1-mediated cholesterol efflux via promoting depolymerization of actin stress fibers. Affinity purification and mass spectrometry (AP-MS) analysis, co-immunoprecipitation and GST pull-down assays, confocal microscopy, and stochastic optical reconstruction microscopy (STORM) revealed that globular-actin (G-actin), monomeric actin, interacted with and retained LXRα in the cytoplasm in PDGF-BB-treated and Sm22α^-/- VSMCs. This interaction blocked LXRα binding to Importin α, a karyopherin that mediates the trafficking of macromolecules across the nuclear envelope, and the resulting reduction of LXRα transcriptional activity. Increasing SM22α expression restored nuclear localization of LXRα and removed cholesterol accumulation via inducing actin polymerization, ameliorating atherosclerosis. Our findings highlight that LXRα is a mechanosensitive nuclear receptor and that the nuclear import of LXRα maintained by the SM22α-actin axis is a potential target for blockade of VSMC foam cell formation and development of anti-atherosclerosis.

Vascular smooth muscle cells in atherosclerosis: time for a re-assessment

Vascular smooth muscle cells (VSMCs) are key participants in both early and late-stage atherosclerosis. VSMCs invade the early atherosclerotic lesion from the media, expanding lesions, but also forming a protective fibrous cap rich in extracellular matrix to cover the 'necrotic' core. Hence, VSMCs have been viewed as plaque-stabilizing, and decreased VSMC plaque content-often measured by expression of contractile markers-associated with increased plaque vulnerability. However, the emergence of lineage-tracing and transcriptomic studies has demonstrated that VSMCs comprise a much larger proportion of atherosclerotic plaques than originally thought, demonstrate multiple different phenotypes in vivo, and have roles that might be detrimental. VSMCs down-regulate contractile markers during atherosclerosis whilst adopting alternative phenotypes, including macrophage-like, foam cell-like, osteochondrogenic-like, myofibroblast-like, and mesenchymal stem cell-like. VSMC phenotypic switching can be studied in tissue culture, but also now in the media, fibrous cap and deep-core region, and markedly affects plaque formation and markers of stability. In this review, we describe the different VSMC plaque phenotypes and their presumed cellular and paracrine functions, the regulatory mechanisms that control VSMC plasticity, and their impact on atherogenesis and plaque stability.

Purine-rich element binding protein B attenuates the coactivator function of myocardin by a novel molecular mechanism of smooth muscle gene repression

Myocardin is a potent transcriptional coactivator protein, which functions as the master regulator of vascular smooth muscle cell differentiation. The cofactor activity of myocardin is mediated by its physical interaction with serum response factor, a ubiquitously expressed transactivator that binds to CArG boxes in genes encoding smooth muscle-restricted proteins. Purine-rich element binding protein B (Purβ) represses the transcription of the smooth muscle α-actin gene (Acta2) in fibroblasts and smooth muscle cells by interacting with single-stranded DNA sequences flanking two 5' CArG boxes in the Acta2 promoter. In this study, the ability of Purβ to modulate the cofactor activity of myocardin was investigated using a combination of cellular and biochemical approaches. Results of smooth muscle gene promoter-reporter assays indicated that Purβ specifically inhibits the coactivator function of myocardin in a manner requiring the presence of all three single-stranded DNA binding domains in the Purβ homodimer. DNA binding analyses demonstrated that Purβ interacts with CArG-containing DNA elements with a much lower affinity compared to other purine-rich target sequences present in the Acta2 promoter. Co-immunoprecipitation and DNA pull-down assays revealed that Purβ associates with myocardin and serum response factor when free or bound to duplex DNA containing one or more CArG boxes. Functional analysis of engineered Purβ point mutants identified several amino acid residues essential for suppression of myocardin activity. Collectively, these findings suggest an inhibitory mechanism involving direct protein-protein interaction between the homodimeric Purβ repressor and the myocardin-serum response factor-CArG complex.

The dynamic change of phenotypic markers of smooth muscle cells in an animal model of cerebral small vessel disease

BACKGROUND

The pathological character of cerebral small vessel disease (CSVD) is the dysfunction of cerebral small arteries caused by risk factors. A switch from the contractile phenotype to the synthetic phenotype of vascular smooth muscle cells (SMCs) can decrease the contractility of arteries. The alteration of the vascular wall extracellular matrix (ECM) is found to regulate the process. We speculated that SMCs phenotype changes may also occur in CSVD induced by hypertension and the alteration of ECM especially fibronectin and laminin may regulate the process.

METHOD

Male spontaneously hypertensive rats (SHR) were used as a CSVD animal model. SMCs phenotypic markers and the ECM expression of the cerebral small arteries of SHR at different ages were evaluated by immunofluorescence. The phenotype changes of primary brain microvascular SMCs cultured on laminin-coating dish or fibronectin-coating dish were evaluated by western blot.

RESULT

A switch from the contractile phenotype to synthetic phenotype in SHR at 10 and 22 weeks of age was observed. Meanwhile, increased expression of fibronectin and a temporary decline of laminin was found in small arteries of SHR at 22 weeks. In vitro experiments also convinced that SMCs cultured on a fibronectin-coating dish failed to maintain contractile phenotype. While at 50 weeks, significant drops of both synthetic and contractile phenotypic markers were witnessed in SHR, with high expressions of four kinds of ECM.

CONCLUSION

SMCs in cerebral small arteries exhibited a switch from the contractile phenotype to synthetic phenotype during the chronic process of hypertension and aging. Moreover, the change of fibronectin and laminin may regulate the process.

Curcumin inhibits proliferation, migration and neointimal formation of vascular smooth muscle via activating miR-22

Context: Curcumin has antitumor, antioxidative, anti-inflammatory, and anti-proliferative properties.Objective: To investigate the role of miR-22 during curcumin-induced changes in vascular smooth muscle cells (VSMC) and neointima formation in balloon-injured rat abdominal aorta.Materials and methods: Sprague-Dawley rats were randomised to the sham-operated (n = 10), operated control (injured, n = 10), and curcumin treatment (n = 10) groups. miR-22 expression was determined by real-time PCR. SP1 was assessed by western blot and real-time PCR. Rat aortic smooth muscle A7r5 cells were used to determine VSMC proliferation and migration, which were measured by the MTS, EdU staining, Transwell, and wound healing assays.Results: miR-22 levels declined following arterial balloon injury in vivo (48% at 3d, p < 0.05) and serum stimulation in vitro (45% at 24 h, p < 0.01). Functional studies revealed that miR-22 negatively regulated the proliferation and migration of VSMCs by directly targeting the SP1 transcription factor in VSMCs. Curcumin increased the expression of miR-22 (81%, p < 0.05) and decreased the protein expression of SP1 in VSMCs (25%, p < 0.05). miR-22 inhibition was found to attenuate the effects of curcumin on VSMC functions. Curcumin increased miR-22 (46%, p < 0.01), decreased the SP1 protein (19%, p < 0.05), and inhibited vascular neointimal area (48%, p < 0.01) in vivo.Discussion: The miR-22/SP1 pathway is involved in the protective role of curcumin during arterial balloon injury, but the mechanisms remain unclear.Conclusion: miR-22 is involved in the inhibitory effects of curcumin on VSMCs' proliferation, migration and neointima hyperplasia after arterial balloon injury in rats. Curcumin could be used to prevent neointimal hyperplasia after angioplasty.

Role of Vascular Smooth Muscle Cell Plasticity and Interactions in Vessel Wall Inflammation

The pathobiology of atherosclerotic disease requires further elucidation to discover new approaches to address its high morbidity and mortality. To date, over 17 million cardiovascular-related deaths have been reported annually, despite a multitude of surgical and nonsurgical interventions and advances in medical therapy. Existing strategies to prevent disease progression mainly focus on management of risk factors, such as hypercholesterolemia. Even with optimum current medical therapy, recurrent cardiovascular events are not uncommon in patients with atherosclerosis, and their incidence can reach 10–15% per year. Although treatments targeting inflammation are under investigation and continue to evolve, clinical breakthroughs are possible only if we deepen our understanding of vessel wall pathobiology. Vascular smooth muscle cells (VSMCs) are one of the most abundant cells in vessel walls and have emerged as key players in disease progression. New technologies, including in situ hybridization proximity ligation assays, in vivo cell fate tracing with the CreER^T2-loxP system and single-cell sequencing technology with spatial resolution, broaden our understanding of the complex biology of these intriguing cells. Our knowledge of contractile and synthetic VSMC phenotype switching has expanded to include macrophage-like and even osteoblast-like VSMC phenotypes. An increasing body of data suggests that VSMCs have remarkable plasticity and play a key role in cell-to-cell crosstalk with endothelial cells and immune cells during the complex process of inflammation. These are cells that sense, interact with and influence the behavior of other cellular components of the vessel wall. It is now more obvious that VSMC plasticity and the ability to perform nonprofessional phagocytic functions are key phenomena maintaining the inflammatory state and senescent condition and actively interacting with different immune competent cells.

Involvement of Myeloid Cells and Noncoding RNA in Abdominal Aortic Aneurysm Disease

Significance: Abdominal aortic aneurysm (AAA) is a potentially fatal condition, featuring the possibility of high-mortality rupture. To date, prophylactic surgery by means of open surgical repair or endovascular aortic repair at specific thresholds is considered standard therapy. Both surgical options hold different risk profiles of short- and long-term morbidity and mortality. Targeting early stages of AAA development to decelerate disease progression is desirable. Recent Advances: Understanding the pathomechanisms that initiate formation, maintain growth, and promote rupture of AAA is crucial to developing new medical therapeutic options. Inflammatory cells, in particular macrophages, have been investigated for their contribution to AAA disease for decades, whereas evidence on lymphocytes, mast cells, and neutrophils is sparse. Recently, there has been increasing interest in noncoding RNAs (ncRNAs) and their involvement in disease development, including AAA. Critical Issues: The current evidence on myeloid cells and ncRNAs in AAA largely originates from small animal models, making clinical extrapolation difficult. Although it is feasible to collect surgical human AAA samples, these tissues reflect end-stage disease, preventing examination of critical mechanisms behind early AAA formation. Future Directions: Gaining more insight into how myeloid cells and ncRNAs contribute to AAA disease, particularly in early stages, might suggest nonsurgical AAA treatment options. The utilization of large animal models might be helpful in this context to help bridge translational results to humans.

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 multilayered scaffold for regeneration of smooth muscle and connective tissue layers

Tissue regeneration often requires recruitment of different cell types and rebuilding of two or more tissue layers to restore function. Here, we describe the creation of a novel multilayered scaffold with distinct fiber organizations-aligned to unaligned and dense to porous-to template common architectures found in adjacent tissue layers. Electrospun scaffolds were fabricated using a biodegradable, tyrosine-derived terpolymer, yielding densely-packed, aligned fibers that transition into randomly-oriented fibers of increasing diameter and porosity. We demonstrate that differently-oriented scaffold fibers direct cell and extracellular matrix (ECM) organization, and that scaffold fibers and ECM protein networks are maintained after decellularization. Smooth muscle and connective tissue layers are frequently adjacent in vivo; we show that within a single scaffold, the architecture supports alignment of contractile smooth muscle cells and deposition by fibroblasts of a meshwork of ECM fibrils. We rolled a flat scaffold into a tubular construct and, after culture, showed cell viability, orientation, and tissue-specific protein expression in the tube were similar to the flat-sheet scaffold. This scaffold design not only has translational potential for reparation of flat and tubular tissue layers but can also be customized for alternative applications by introducing two or more cell types in different combinations.

Molecular signatures of atherosclerotic plaques: An up-dated panel of protein related markers

Atherosclerosis remains the leading cause of ischemic syndromes such as myocardial infarction or brain stroke, mainly promoted by plaque rupture and subsequent arterial blockade. Identification of vulnerable or high-risk plaques constitutes a major challenge, being necessary to identify patients at risk of occlusive events in order to provide them with appropriate therapies. Clinical imaging tools have allowed the identification of certain structural indicators of prone-rupture plaques, including a necrotic lipidic core, intimal and adventitial inflammation, extracellular matrix dysregulation, and smooth muscle cell depletion and micro-calcification. Additionally, alternative approaches focused on identifying molecular biomarkers of atherosclerosis have also been applied. Among them, proteomics has provided numerous protein markers currently investigated in clinical practice. In this regard, it is quite uncertain that a single molecule can describe plaque rupture, due to the complexity of the process itself. Therefore, it should be more accurate to consider a set of markers to define plaques at risk. Herein, we propose a selection of 76 proteins, from classical inflammatory to recently related markers, all of them identified in at least two proteomic studies analyzing unstable atherosclerotic plaques. Such panel could be used as a prognostic signature of plaque instability.

SM22α (Smooth Muscle 22α) Prevents Aortic Aneurysm Formation by Inhibiting Smooth Muscle Cell Phenotypic Switching Through Suppressing Reactive Oxygen Species/NF-κB (Nuclear Factor-κB)

Objective- Vascular smooth muscle cell phenotypic transition plays a critical role in the formation of abdominal aortic aneurysms (AAAs). SM22α (smooth muscle 22α) has a vital role in maintaining the smooth muscle cell phenotype and is downregulated in AAA. However, whether manipulation of the SM22α gene influences the pathogenesis of AAA is unclear. Here, we investigated whether SM22α prevents AAA formation and explored the underlying mechanisms. Approach and Results- In both human and animal AAA tissues, a smooth muscle cell phenotypic switch was confirmed, as manifested by the downregulation of SM22α and α-SMA (α-smooth muscle actin) proteins. The methylation level of the SM22α gene promoter was dramatically higher in mouse AAA tissues than in control tissues. SM22α knockdown in ApoE^-/- (apolipoprotein E-deficient) mice treated with Ang II (angiotensin II) accelerated the formation of AAAs, as evidenced by a larger maximal aortic diameter and more medial elastin degradation than those found in control mice, whereas SM22α overexpression exerted opposite effects. Similar results were obtained in a calcium chloride-induced mouse AAA model. Mechanistically, SM22α deficiency significantly increased reactive oxygen species production and NF-κB (nuclear factor-κB) activation in AAA tissues, whereas SM22α overexpression produced opposite effects. NF-κB antagonist SN50 or antioxidant N-acetyl-L-cysteine partially abrogated the exacerbating effects of SM22α silencing on AAA formation. Conclusions- SM22α reduction in AAAs because of the SM22α promoter hypermethylation accelerates AAA formation through the reactive oxygen species/NF-κB pathway, and therapeutic approaches to increase SM22α expression are potentially beneficial for preventing AAA formation.

Mitochondrial Protein Poldip2 (Polymerase Delta Interacting Protein 2) Controls Vascular Smooth Muscle Differentiated Phenotype by O-Linked GlcNAc (N-Acetylglucosamine) Transferase-Dependent Inhibition of a Ubiquitin Proteasome System

RATIONALE

The mitochondrial Poldip2 (protein polymerase interacting protein 2) is required for the activity of the tricarboxylic acid cycle. As a consequence, Poldip2 deficiency induces metabolic reprograming with repressed mitochondrial respiration and increased glycolytic activity. Though homozygous deletion of Poldip2 is lethal, heterozygous mice are viable and show protection against aneurysm and injury-induced neointimal hyperplasia, diseases linked to loss of vascular smooth muscle differentiation. Thus, we hypothesize that the metabolic reprograming induced by Poldip2 deficiency controls VSMC differentiation.

OBJECTIVE

To determine the role of Poldip2-mediated metabolic reprograming in phenotypic modulation of VSMC.

METHODS AND RESULTS

We show that Poldip2 deficiency in vascular smooth muscle in vitro and in vivo induces the expression of the SRF (serum response factor), myocardin, and MRTFA (myocardin-related transcription factor A) and dramatically represses KLF4 (Krüppel-like factor 4). Consequently, Poldip2-deficient VSMC and mouse aorta express high levels of contractile proteins and, more significantly, these cells do not dedifferentiate nor acquire macrophage-like characteristics when exposed to cholesterol or PDGF (platelet-derived growth factor). Regarding the mechanism, we found that Poldip2 deficiency upregulates the hexosamine biosynthetic pathway and OGT (O-linked N-acetylglucosamine transferase)-mediated protein O-GlcNAcylation. Increased protein glycosylation causes the inhibition of a nuclear ubiquitin proteasome system responsible for SRF stabilization and KLF4 repression and is required for the establishment of the differentiated phenotype in Poldip2-deficient cells.

CONCLUSIONS

Our data show that Poldip2 deficiency induces a highly differentiated phenotype in VSMCs through a mechanism that involves regulation of metabolism and proteostasis. Additionally, our study positions mitochondria-initiated signaling as key element of the VSMC differentiation programs that can be targeted to modulate VSMC phenotype during vascular diseases.

Pharmacological inhibition of Notch signaling regresses pre-established abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is characterized by transmural infiltration of myeloid cells at the vascular injury site. Previously, we reported preventive effects of Notch deficiency on the development of AAA by reduction of infiltrating myeloid cells. In this study, we examined if Notch inhibition attenuates the progression of pre-established AAA and potential implications. Pharmacological Notch inhibitor (N-[N-(3,5-difluorophenacetyl)-L-alanyl]-(S)-phenylglycine t-butyl ester; DAPT) was administered subcutaneously three times a week starting at day 28 of angiotensin II (AngII) infusion. Progressive increase in pulse wave velocity (PWV), maximal intra-luminal diameter (MILD) and maximal external aortic diameter (MEAD) were observed at day 56 of the AngII. DAPT prevented such increase in MILD, PWV and MEAD (P < 0.01). Histologically, the aortae of DAPT-treated Apoe-/- mice had significant reduction in inflammatory response and elastin fragmentation. Naked collagen microfibrils and weaker banded structure observed in the aortae of Apoe-/- mice in response to AngII, were substantially diminished by DAPT. A significant decrease in the proteolytic activity in the aneurysmal tissues and vascular smooth muscle cells (vSMCs) was observed with DAPT (P < 0.01). In human and mouse AAA tissues, increased immunoreactivity of activated Notch signaling correlated strongly with CD38 expression (R2 = 0.61). Collectively, we propose inhibition of Notch signaling as a potential therapeutic target for AAA progression.

PAPP-A and the IGF system in atherosclerosis: what's up, what's down?

Pregnancy-associated plasma protein-A (PAPP-A) is a metalloproteinase with a well-established role in releasing bioactive insulin-like growth factor-1 (IGF-1) from IGF-binding protein-2, -4, and -5 by proteolytic processing of these. The IGF system has repeatedly been suggested to be involved in the pathology of atherosclerosis, and both PAPP-A and IGF-1 are proposed biomarkers and therapeutic targets for this disease. Several experimental approaches based on atherosclerosis mouse models have been undertaken to obtain causative and mechanistic insight to the role of these molecules in atherogenesis. However, reports seem conflicting. The literature suggests that PAPP-A is detrimental, while IGF-1 is beneficial. This raises important questions that need to be addressed. Here we summarize the various studies and discuss potential underlying explanations for this seemingly inconsistency with the objective of better understanding complexities and limitations when manipulating the IGF system in mouse models of atherosclerosis. A debate clarifying what's up and what's down is highly warranted going forward with the ultimate goal of improving atherosclerosis therapy by targeting the IGF system.

Smooth Muscle Cell Phenotypic Diversity

Vascular smooth muscle cells (SMC) play a critical role in controlling blood pressure and blood distribution, as well as maintaining the structural integrity of the blood vessel. SMC also participate in physiological and pathological vascular remodeling due to their remarkable ability to dynamically modulate their phenotype. During the past decade, the development of in vivo fate mapping systems for unbiased identification and tracking of SMC and their progeny has led to major discoveries as well as the reevaluation of well-established concepts about the contribution of vascular SMC in major vascular diseases including atherosclerosis. Lineage tracing studies revealed that SMC undergoes multiple phenotypic transitions characterized by the expression of markers of alternative cell types (eg, macrophage-like and mesenchymal-stem cell-like) and populate injured or diseased vessels by oligoclonal expansion of a limited number of medial SMC. With the development of high-throughput transcriptomics and single-cell RNA sequencing (scRNAseq), the field is moving forward towards in-depth SMC phenotypic characterization. Herein, we review the major observations put forth by lineage and clonality tracing studies and the evidence in support for SMC phenotypic diversity in healthy and diseased vascular tissue. We will also discuss the opportunities and remaining challenges of combining lineage tracing and single-cell transcriptomics technologies, as well as studying the functional relevance of SMC phenotypic transitions and identifying the mechanisms controlling them.

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.

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

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

miRNA Regulation of the Hyperproliferative Phenotype of Vascular Smooth Muscle Cells in Diabetes

Harnessing the mechanisms underlying the exacerbated vascular remodeling in diabetes mellitus (DM) is pivotal to prevent the high toll of vascular diseases in patients with DM. miRNA regulates vascular smooth muscle cell (VSMC) phenotypic switch. However, miRNA modulation of the detrimental diabetic VSMC phenotype is underexplored. Streptozotocin-induced type 1 DM (T1DM) Wistar rats and type 2 DM (T2DM) Zucker rats underwent right carotid artery experimental angioplasty, and global miRNA/mRNA expression profiling was obtained by RNA sequencing (RNA-Seq). Two days after injury, a set of six miRNAs were found to be uniquely downregulated or upregulated in VSMCs both in T1DM and T2DM. Among these miRNAs, miR-29c and miR-204 were the most significantly misregulated in atherosclerotic plaques from patients with DM. miR-29c overexpression and miR-204 inhibition per se attenuated VSMC phenotypic switch in DM. Concomitant miR-29c overexpression and miR-204 inhibition fostered an additive reduction in VSMC proliferation. Epithelial membrane protein 2 (Emp2) and Caveolin-1 (Cav1) mRNAs were identified as direct targets of miR-29c and miR-204, respectively. Importantly, contemporary miR-29c overexpression and miR-204 inhibition in the injured artery robustly reduced arterial stenosis in DM rats. Thus, contemporaneous miR-29c activation and miR-204 inhibition in DM arterial tissues is necessary and sufficient to prevent the exaggerated VSMC growth upon injury.

Salvianolic acid A targeting the transgelin-actin complex to enhance vasoconstriction

BACKGROUND

Salvia miltiorrhiza is used extensively to treat cardiovascular diseases. SAA is a major bioactive component in Salvia miltiorrhiza and mediates myocardial ischemia (MI). However, the industrial production of SAA is limited due to low yields. In addition, the direct targets of SAA are unknown. Here we explore cardioprotective mechanisms and targets of SAA in the cardiovascular system.

METHODS

Transgelin and actin were identified as targets of SAA using a chemical biology method and were validated by Biacore analysis, microscale thermophoresis and single-molecule imaging. Studies of transgelin (-/-) knockout mice further verify the target. Cardioprotective mechanisms and targets of SAA were studied in cultured vascular smooth muscle cells and transgenic mice.

FINDINGS

In WT mice, SAA targeted transgelin and had a protective effect on myocardium but did not have the same protective effect on transgelin (-/-) mice. SAA stabilizes the transgelin-actin complex, modulates the reorganization of the actin cytoskeleton, facilitates F-actin bundling, further enhances the contractility and blood flows of coronary arteries, and improves outcomes of myocardial ischemia. Based on the target, a more active SAA derivative offering myocardial protection, SAA-30, was obtained.

INTERPRETATION

We report on the direct targets of SAA and mechanisms of myocardial ischemia treatment. We also find that transgelin may act as a novel therapeutic target of myocardial ischemia. Furthermore, a more effective derivative of SAA provides the basis for further clinical translational research.

The roles of mechanotransduction, vascular wall cells, and blood cells in atheroma induction

BACKGROUND

This paper describes and analyzes the cellular and molecular mechanisms underlying atherosclerosis development. In particular, the roles of monocytes/macrophages, smooth muscle cells, and vascular endothelium in the formation of stable/unstable atheromatous plaques, and the contributions of some processes to atheroma formation.

METHODS AND RESULTS

In this study we analyzed endothelium: function, dysfunction, and involvement into atherogenesis; cell proteins mediating mechanotransduction; proatherogenic role of monocytes; the role of macrophages in the development of unstable atheromatous plaques and smooth muscle cell origin in atherosclerosis. Smooth muscle cell phenotypic switching; their functioning; the ability to retain cholesterol and lipoproteins as well as secretion of pro- and anti-inflammatory molecules and extracellular matrix proteins, their response to extracellular stimuli secreted by other cells, and the effect of smooth muscle cells on the cells surrounding atheromatous plaques are fundamentally important for the insight into atherosclerosis molecular basis.

CONCLUSION

Atheromatous plaque transcriptome studies will be helpful in the identification of the key genes involved in atheroma transformation and development as well as discovery of the new targets for diagnosis and therapy.

Smooth muscle cell-driven vascular diseases and molecular mechanisms of VSMC plasticity

Vascular smooth muscle cells (VSMCs) are the major cell type in blood vessels. Unlike many other mature cell types in the adult body, VSMC do not terminally differentiate but retain a remarkable plasticity. Fully differentiated medial VSMCs of mature vessels maintain quiescence and express a range of genes and proteins important for contraction/dilation, which allows them to control systemic and local pressure through the regulation of vascular tone. In response to vascular injury or alterations in local environmental cues, differentiated/contractile VSMCs are capable of switching to a dedifferentiated phenotype characterized by increased proliferation, migration and extracellular matrix synthesis in concert with decreased expression of contractile markers. Imbalanced VSMC plasticity results in maladaptive phenotype alterations that ultimately lead to progression of a variety of VSMC-driven vascular diseases. The nature, extent and consequences of dysregulated VSMC phenotype alterations are diverse, reflecting the numerous environmental cues (e.g. biochemical factors, extracellular matrix components, physical) that prompt VSMC phenotype switching. In spite of decades of efforts to understand cues and processes that normally control VSMC differentiation and their disruption in VSMC-driven disease states, the crucial molecular mechanisms and signalling pathways that shape the VSMC phenotype programme have still not yet been precisely elucidated. In this article we introduce the physiological functions of vascular smooth muscle/VSMCs, outline VSMC-driven cardiovascular diseases and the concept of VSMC phenotype switching, and review molecular mechanisms that play crucial roles in the regulation of VSMC phenotypic plasticity.

Mechanisms Underlying Atheroma Induction: The Roles of Mechanotransduction, Vascular Wall Cells, and Blood Cells

BACKGROUND

The objective of this article is to review cellular mechanism of atherosclerosis (AS) development. The pathogenesis of AS comprises a sequence of biological events leading to build up of a dense or loose atheromatous plaque (AP).

METHODS

In this review, we tried to attempt to analyze the cellular mechanisms underlying AS development, including the roles of monocytes/macrophages and smooth muscle cells in the formation of stable/unstable APs.

RESULTS

As a rule, APs are formed in the regions with irregular blood flow; both mechanical perturbations of the vascular wall and several biological events contribute to plaque formation. Blood lipid/lipoprotein deposition, recruitment of monocytes/macrophages, foam cell formation, migration and proliferation of smooth muscle cells, secretion of extracellular matrix, and formation of the connective tissue in plaques are among the latter events.

CONCLUSIONS

The review briefs the contributions of different processes to atheroma formation and describes the molecular mechanisms involved in AS development. AP transcriptome studies will be helpful in the identification of the key genes involved in atheroma transformation and development as well as discovery of the new targets for diagnosis and therapy.

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.

SM22α suppresses cytokine-induced inflammation and the transcription of NF-κB inducing kinase (Nik) by modulating SRF transcriptional activity in vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) phenotypic modulation is characterized by the downregulation of SMC actin cytoskeleton proteins. Our published study shows that depletion of SM22α (aka SM22, Transgelin, an actin cytoskeleton binding protein) promotes inflammation in SMCs by activating NF-κB signal pathways both in cultured VSMCs and in response to vascular injury. The goal of this study is to investigate the underlying molecular mechanisms whereby SM22 suppresses NF-κB signaling pathways under inflammatory condition. NF-κB inducing kinase (Nik, aka MAP3K14, activated by the LTβR) is a key upstream regulator of NF-κB signal pathways. Here, we show that SM22 overexpression suppresses the expression of NIK and its downstream NF-κB canonical and noncanonical signal pathways in a VSMC line treated with a LTβR agonist. SM22 regulates NIK expression at both transcriptional and the proteasome-mediated post-translational levels in VSMCs depending on the culture condition. By qPCR, chromatin immunoprecipitation and luciferase assays, we found that Nik is a transcription target of serum response factor (SRF). Although SM22 is known to be expressed in the cytoplasm, we found that SM22 is also expressed in the nucleus where SM22 interacts with SRF to inhibit the transcription of Nik and prototypical SRF regulated genes including c-fos and Egr3. Moreover, carotid injury increases NIK expression in Sm22-/- mice, which is partially relieved by adenovirally transduced SM22. These findings reveal for the first time that SM22 is expressed in the nucleus in addition to the cytoplasm of VSMCs to regulate the transcription of Nik and its downstream proinflammatory NF-kB signal pathways as a modulator of SRF during vascular inflammation.

Altered Expression of MicroRNA-15a and Kruppel-Like Factor 4 in Cerebrospinal Fluid and Plasma After Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Cerebral vasospasm (CVS) is a major determinant of prognosis in patients with subarachnoid hemorrhage (SAH). Alteration in the vascular phenotype contributes to development of CVS. However, little is known about the role of microRNAs (miRNAs) in the phenotypic alteration after SAH. We investigated the expression profile of miRNAs and the chronologic changes in the expression of microRNA-15a (miR-15a) and Kruppel-like factor 4 (KLF4), a potent regulator of vascular phenotype modulation that modulates the expression of miR-15a, in the plasma and cerebrospinal fluid (CSF) of patients with SAH.

METHODS

Peripheral blood and CSF samples were collected from 8 patients with aneurysmal SAH treated with endovascular obliteration. Samples obtained from 3 patients without SAH were used as controls in the analysis. Exosomal miRNAs were isolated and subjected to microarray analysis with the three-dimensional-gene miRNA microarray kit. The time course of the expression of miR-15a and KLF4 was analyzed using quantitative real-time polymerase chain reaction.

RESULTS

Microarray analysis showed that 12 miRNAs including miR-15a were upregulated or downregulated both in the CSF and in plasma after SAH within 3 days. Quantitative real-time polymerase chain reaction showed that miR-15a expression was significantly increased in both the CSF and plasma, with a peak around 3-5 days after SAH, whereas the expression of KLF4 was significantly decreased around 1-3 days after SAH and remained lower than in controls.

CONCLUSIONS

Our results suggest that an early and persistent decrease in KLF4 followed by an increase in miR-15a may contribute to the altered vascular phenotype, resulting in development of CVS.

Smooth muscle cell-specific Notch1 haploinsufficiency restricts the progression of abdominal aortic aneurysm by modulating CTGF expression

Aims

Infiltration of macrophages and apoptosis of vascular smooth muscle cells (VSMCs) promote the development of abdominal aortic aneurysm (AAA). Previously, we demonstrated that global Notch1 deficiency prevents the formation of AAA in a mouse model. Herein, we sought to explore the cell-specific roles of Notch1 in AAA development.

Methods and results

Cell-specific Notch1 haploinsufficient mice, generated on Apoe^-/- background using Cre-lox technology, were infused with angiotensin II (1000 ng/min/kg) for 28 days. Notch1 haploinsufficiency in myeloid cells (n = 9) prevented the formation of AAA attributed to decreased inflammation. Haploinsufficiency of Notch1 in SMCs (n = 14) per se did not prevent AAA formation, but histoarchitectural traits of AAA including elastin degradation and aortic remodeling, were minimal in SMC-Notch1^+/-;Apoe^-/- mice compared to Apoe^-/- mice (n = 33). Increased immunostaining of the contractile SMC-phenotype markers and concomitant decreased expression of synthetic SMC-phenotype markers were observed in the aortae of SMC-Notch1^+/-;Apoe^-/- mice. Expression of connective tissue growth factor (CTGF), a matrix-associated protein that modulates the synthetic VSMC phenotype, increased in the abdominal aorta of Apoe^-/- mice and in the adventitial region of the abdominal aorta in human AAA. Notch1 haploinsufficiency decreased the expression of Ctgf in the aorta and in vitro cell culture system. In vitro studies on SMCs using the Notch1 intracellular domain (NICD) plasmid, dominant negative mastermind-like (dnMAML), or specific siRNA suggest that Notch1, not Notch3, directly modulates the expression of CTGF.

Conclusions

Our data suggest that lack of Notch1 in SMCs limits dilation of the abdominal aorta by maintaining contractile SMC-phenotype and preventing matrix-remodeling.

miR-125a-5p Modulates Phenotypic Switch of Vascular Smooth Muscle Cells by Targeting ETS-1

MicroRNAs are key regulators of vascular smooth muscle cells (VSMCs) phenotypic switch, one of the main events responsible for bare metal in-stent restenosis after percutaneous coronary intervention. miR-125a-5p is an important modulator of differentiation, proliferation, and migration in different cell types; however, its role in VSMCs is still unknown. The aim of this study was to evaluate the role of miR-125a-5p in VSMCs phenotypic switch. Our results suggest that miR-125a-5p is highly expressed in VSMCs, but it is down-regulated after vascular injury in vivo. Its overexpression is sufficient to reduce VSMCs proliferation and migration, and it is able to promote the expression of selective VSMCs markers such as alpha smooth muscle actin, myosin heavy chain 11, and smooth muscle 22 alpha. Interestingly, miR-125a-5p directly targets ETS-1, a transcription factor implicated in cell proliferation and migration and is crucial in PDGF-BB pathway in VSMCs. Thus, miR-125a-5p in this context inhibits PDGF-BB pathway and is therefore a potential regulator of VSMCs phenotypic switch.

Alisol A 24-Acetate, a Triterpenoid Derived from Alisma orientale, Inhibits Ox-LDL-Induced Phenotypic Transformation and Migration of Rat Vascular Smooth Muscle Cells through Suppressing ERK1/2 Signaling

Alisol A 24-acetate, a triterpenoid extracted from Alisma orientale, has shown antiatherosclerotic actions. The purpose of this study was to evaluate the inhibition of alisol A 24-acetate on oxidized low-density lipoprotein (Ox-LDL)-induced phenotypic transformation and migration of rat vascular smooth muscle cells (VSMCs), and to explore the underlying mechanisms. VSMCs were pretreated with alisol A 24-acetate and a specific extracellular signal-regulated kinase (ERK) inhibitor, U0126, and then stimulated with 50 mg/l Ox-LDL in vitro. The expression of VSMC phenotypic marker SM22α was determined using immunocytochemistry, and the migration of VSMCs was detected using a scratch-wound healing assay. The expression of matrix metalloproteinase (MMP)-9, MMP-2, phosphorylated ERK1/2 (pERK1/2) and total ERK was determined. Ox-LDL treatment caused a reduction in SM22α expression, VSMC transformation to the synthetic phenotype, increased MMP-2 and MMP-9 synthesis, the extension of VSMC migration distance and the upregulation of pERK1/2 expression, while the addition of alisol A 24-acetate or U0126 resulted in the elevation of SM22α expression, VSMC transformation to the contractile phenotype, a reduction in MMP-2 and MMP-9 expression, the shortening of cell migration distance and decreased pERK1/2 expression. The results of this study demonstrate that alisol A 24-acetate effectively reverses the phenotypic transformation and inhibits the migration of VSMCs, which may be associated with the suppression of the ERK1/2 signaling pathway.

Responses of adventitial CD34+ vascular wall-resident stem/progenitor cells and medial smooth muscle cells to carotid injury in rats

Cell culture and carotid injury studies with SD rats were performed to investigate the roles of CD34⁺ vascular wall-resident stem/progenitor cells (VRS/Pcs) and vascular smooth muscle cells (SMCs) in neointimal formation. In vitro, the media-isolated SM MHC⁺ SMCs occupied 93.92±8.62% of total BrdU⁺ cells, whereas the CD34⁺ cells, only 2.61±0.82%, indicating that the cell expansion in SMC culture was attributed to SM MHC⁺ SMCs. The adventitia-isolated CD34⁺ VRS/Pcs responded to PDGF-BB by differentiating into SMC-like cells which expressed SM22α (an early stage SMC marker), but seldom SM MHC (a late stage SMC marker). In carotid injury model, the CD34⁺ VRS/Pcs differentiated SMC-like cells migrated in very few numbers into only the outer layer of the media, and this was further confirmed by a cell tracking analysis. While the neointimal cells were consistently SM MHC⁺ and CD34^- SMCs during whole course of the post-injury remodeling. Thus it is speculated that the adventitial CD34⁺ VRS/Pcs, at least in rat model, do not directly participate in neointimal formation, but function to maintain homeostasis of the media during injury-induced vascular wall remodeling.

Lineage tracing of cells involved in atherosclerosis

BACKGROUND AND AIMS

Despite the clinical importance of atherosclerosis, the origin of cells within atherosclerotic plaques is not fully understood. Due to the lack of a definitive lineage-tracing strategy, previous studies have provided controversial results about the origin of cells expressing smooth muscle and macrophage markers in atherosclerosis. We here aim to identify the origin of vascular smooth muscle (SM) cells and macrophages within atherosclerosis lesions.

METHODS

We combined a genetic fate mapping approach with single cell expression analysis in a murine model of atherosclerosis.

RESULTS

We found that 16% of CD68-positive plaque macrophage-like cells were derived from mature SM cells and not from myeloid sources, whereas 31% of αSMA-positive smooth muscle-like cells in plaques were not SM-derived. Further analysis at the single cell level showed that SM-derived CD68(+) cells expressed higher levels of inflammatory markers such as cyclooxygenase 2 (Ptgs2, p = 0.02), and vascular cell adhesion molecule (Vcam1, p = 0.05), as well as increased mRNA levels of genes related to matrix synthesis such as Col1a2 (p = 0.01) and Fn1 (p = 0.04), than non SM-derived CD68(+) cells.

CONCLUSIONS

These results demonstrate that smooth muscle cells within atherosclerotic lesions can switch to a macrophage-like phenotype characterized by higher expression of inflammatory and synthetic markers genes that may further contribute to plaque progression.

Modulation of cysteine-rich protein 2 expression in vascular injury and atherosclerosis

Vascular smooth muscle cells (VSMCs) of the arterial wall normally display a differentiated and contractile phenotype. In response to arterial injury, VSMCs switch to a synthetic phenotype, contributing to vascular remodeling. Cysteine-rich protein 2 (CRP2) is a cytoskeletal protein expressed in VSMCs and blunts VSMC migration in part by sequestering the scaffolding protein p130Cas at focal adhesions. CRP2 deficiency in mice increases neointima formation following arterial injury. The goal of this study was to use Csrp2 promoter-lacZ transgenic mice to analyze CRP2 expression during VSMC phenotypic modulation. In a neointima formation model after carotid artery cessation of blood flow, lacZ reporter activity and smooth muscle (SM) α-actin expression in the media were rapidly downregulated 4 days after carotid ligation. Fourteen days after ligation, there was a high level expression of both Csrp2 promoter activity and SM α-actin protein expression in neointimal cells. In atherosclerosis prone mice fed an atherogenic diet, Csrp2 promoter activity was detected within complex atherosclerotic lesions. Interestingly, Csrp2 promoter activity was also present in the fibrous caps of complicated atherosclerotic lesions, indicating that CRP2 might contribute to plaque stability. These findings support the concept that CRP2 contributes to the phenotypic modulation of VSMCs during vascular disease. Modulating transcription to increase CRP2 expression during vascular injury might attenuate vascular remodeling. In addition, increased CRP2 expression at the fibrous caps of advanced lesions might also serve to protect atherosclerotic plaques from rupture.

Recent insights into the cellular biology of atherosclerosis

Atherosclerosis occurs in the subendothelial space (intima) of medium-sized arteries at regions of disturbed blood flow and is triggered by an interplay between endothelial dysfunction and subendothelial lipoprotein retention. Over time, this process stimulates a nonresolving inflammatory response that can cause intimal destruction, arterial thrombosis, and end-organ ischemia. Recent advances highlight important cell biological atherogenic processes, including mechanotransduction and inflammatory processes in endothelial cells, origins and contributions of lesional macrophages, and origins and phenotypic switching of lesional smooth muscle cells. These advances illustrate how in-depth mechanistic knowledge of the cellular pathobiology of atherosclerosis can lead to new ideas for therapy.

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.